APRIL 2019: Warm & Muggy WX to End The Month

[srainhoutx]

Thursday morning weather briefing from Jeff live from National Tropical Weather Conference 2019:

Active weather pattern through the weekend with multiple chances for thunderstorms.

Overnight shortwave responsible for the scattered strong to at times severe thunderstorms is moving east into LA this morning, while a secondary shortwave is approaching central TX and heading toward SE TX. Lift overnight helped to force surface parcels through the capping inversion where they were able to tap into a pool of elevated instability with the end result being the scattered storms some of which produced severe hail. Approaching shortwave over central TX will once again impart lift across the area starting late this morning into the early afternoon hours. Expect to see an increase in shower and thunderstorm activity as this feature moves across the area. Any storm that is able to break through the capping inversion may become severe with the main threat being large hail. Storms were also able to generate about an inch of rainfall in a few narrow corridors…mainly from central Harris into Liberty County.

Friday will feature small ridge of high pressure over the area ahead of a much more significant upper level storm system which will impact the state over much of the weekend. An upper level trough will begin to dig into TX late Friday with increasing large scale lift. Moisture will continue to increase and pool over the area with PWS increasing to around 1.5 inches by late Saturday. Fairly impressive low level inflow of 35-45kts from the S/SSW will help to feed moisture into developing storms. Increasing speed and directional wind shear will be in place by Saturday along with decent instability suggesting severe thunderstorms with hail and damaging winds will be possible.

Think the main threat over the weekend may end up on the heavy rainfall side of the spectrum. Overall pattern favors some amounts of heavy rainfall somewhere in SE TX. A few red flags include the good low level inflow off the Gulf and potential for cell training into WSW/SW to ENE/NE bands which would be nearly perpendicular to the low level flow and parallel to the steering flow aloft. Additionally, large scale lift will be maintained over the area for a decent period Saturday afternoon into much of Sunday. 1.5 inch PWS is nothing extraordinary by SE TX standards, but that amount of moisture will be capable for some decent 1-2 inch per hour rainfall rates and maybe could push up to 3 inches per hour. Main lacking feature at this point is any sort of focus on a low level boundary, but that may eventually come from thunderstorm outflow boundaries at some point over the weekend.

For now will go with widespread 1-3 inches over much of the region this weekend with higher isolated totals. Will favor areas along and NE of a line from Wharton to Richmond to Galveston, but really without any good surface focus it is nearly impossible at this point to try and determine any favored areas. Should a surface focus start to become more defined then totals near that boundary would likely need to be raised some. This may not become clear until the event is underway.

Area soil moisture is fairly dry after a dry March so at least the first couple of inches will go toward saturating the soil. Rainfall rates and cell training will likely become the key factors on if and where any sort of flood threat may develop.

[Cpv17]

It’s now starting to look like areas south of 10 won’t get much of anything out of this or much of anything for the next couple weeks..the models can’t be trusted outside of 2-3 days. Rain seems to be shifting off more to our north and east now for this weekend.

[tireman4]

850
FXUS64 KHGX 041559
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1059 AM CDT Thu Apr 4 2019

.DISCUSSION...
Looking at best shower and thunderstorm chances to be in/around our
southeast areas today, especially near the Galveston Bay area late
this morning through early this afternoon. Water vapor satellite
imagery shows some drier and more stable air edging toward our area
from the northwest, and this could help to limit development this
afternoon across our northwest locations. Have not made any major
adjustment to the grids on the morning update as things seem to
be covered well. 42
&&

.PREV DISCUSSION... /ISSUED 652 AM CDT Thu Apr 4 2019/

AVIATION [12Z TAF Issuance]...

Shortwave trough on water vapor imagery has moved across the area
overnight supporting a few isolated thunderstorms along the way.
In its wake, there are still some pockets of light rain and
drizzle but ceilings remain LIFR across much of the area with a
few spots of IFR/MVFR ceilings. Ceilings will be slow to improve
but once ceilings do improve it will be a quick transition to VFR
in the afternoon. This could happen as early as 19-20Z or as late
as 23-00Z. TAFS hedge closer to the later timing but look for the
timing to be adjusted with new guidance and monitoring of ongoing
trends. A few showers may also still be possible this afternoon as
winds veer more to the SW. Ceilings should then lower again with
no change in the moist airmass. MVFR to IFR ceilings look like a
reasonable progression after 00Z this evening.

Overpeck

PREV DISCUSSION /Issued 427 AM CDT Thu Apr 4 2019/...

DISCUSSION...
Patchy fog has developed along and west of I-45 this morning. Fog
plus showers will continue to lower visibilities through the
morning hours, as the fog layer begins to lift and burn off. A
lull in heavier showers and isolated thunderstorms is anticipated
through shortly after sunrise, before coverage begins to increase
once more. An upper-level trough axis at 330 AM was oriented N-S
draped across N TX and through central TX continuing to swing
eastward. Out ahead of this feature, a smaller scale shortwave
looked to be embedded in the upper level flow, helping to provide
additional lift to break through the 600mb cap that was in place
area wide. This shortwave trough axis at 330AM was oriented N to S
and draped just to the east of I-45, providing additional lift
out the the east of this mesoscale feature. As a result, showers
were able to tap into upper level instability above this cap and
develop into thunderstorms this morning. Some of these storms had
a history of being strong to severe. Storms that were able to
break the cap were able to tap into MU CAPE values of 1500 J/kg
with bulk shear values of 35 knots, and a strong low level jet in
place.

Coverage of showers and isolated thunderstorms should increase as
we move through the late morning hours and begin to wane later
this afternoon. Global guidance shows some discrepancies in
overall rainfall accumulation through the evening hours today. GFS
and NAM12 keep things on the drier side for the remainder of the
day, only placing anywhere from 0.10-0.25 of an inch along the
coastal counties and across our far eastern counties from Houston
to Chambers. The ECMWF and Canadian on the other hand place
rainfall totals of about 1.0-1.5 inches across these same areas
through this evening. Based off radar trends over the last few
hours, would side closer to the ECMWF/Canadian solutions, as rain
gauges across the area this morning have already seen anywhere
from 0.25 to 0.75 of an inch. Isolated areas in Harris County saw
closer to an inch, with Liberty County saw closer to one to two
inches.

This upper level shortwave will push east of the area later this
afternoon and shortwave ridging will build in for most of the day
Friday. Patchy fog will be possible tonight area wide into Friday
morning, as dew point depressions narrow and low level moisture
from today`s precipitation lingers. Otherwise, Friday will be the
driest day precipitation wise through the remainder of this week.
The chance for showers return late Friday into Saturday ahead of
our next storm system anticipated to push through the region this
weekend.

Global guidance has slowed down the timing of this weekend`s weather
maker by approximately 6-12 hours depending on the model.
Precipitation looks to start in our northwestern zones near College
Station as early as Saturday morning 12Z, spreading eastward
across SE TX through the afternoon mainly north of I-10. A break
from the better coverage of showers and thunderstorms looks to
occur early Saturday evening, before the upper-level trough really
digs south and pushes eastward shortly after midnight Sunday and
throughout the day. Global guidance is still struggling to get a
good handle on this system, but run to run consistency has show
the strength of this system to be quite strong. Taking a look at
the forecast soundings, NAM12 and GFS both show a small cap near
850mb Saturday afternoon and throughout the day Sunday, which
looks breakable given convective temperatures should reach into
the upper 70s to low 80s. With high temperatures Saturday and
Sunday are also anticipated to be in the upper 70s to 80s given
ample cloud cover, so convection will be possible. If this cap is
broken there will be plenty of instability to work with, with the
best instability elevated with 3-6km lapse rates near 7.5-8.0 deg C
per km, and MU CAPE roughly 2500-3000 J/kg. Gulf moisture will
continue to pump into SE TX, as the 850mb low level jet during
this time frame will be out of the southwest between 35-45 knots.
Precipitable water values at this time also look to rise to
between 1.4-1.6 inches. Upper level forcing looks favorable with
additional lift provided by the 300mb 60-70kt jet streak that
should be positioned over E TX. All in all, still plenty of
details to be worked out Saturday and Sunday, but the chance for
strong to severe storms is growing in confidence and localized
flooding will be possible this weekend.

A cold front ushers in across the region late Sunday into Monday,
and the beginning of next week looks dry and sunny, with winds out
of the northwest around 10 mph. High temperatures for the first half
of the week will be warm with ample sunshine, rising into the low to
upper 80s across the region. Low level moisture returns by mid week
as winds turn back onshore.

Hathaway

MARINE...
Southerly winds overnight reached caution levels which allowed for
seas to build to 5-6ft in the coastal waters. Winds should decrease
this morning ending the small craft exercise caution. Seas will be
slow to subside as winds decrease tonight into Friday morning. Winds
increase again Friday night into Saturday as another strong storm
system develops. Winds in offhsore areas may increase close to
advisory level early Saturday morning but likely require exercise
caution. On shore winds should continue on Sunday with a second
storm system moving across the area. The next cold front should push
off the coast sometime Monday morning. Offshore winds should then
decrease late Monday into Tuesday.

Gulf moisture has increased along the coast this morning. Gulf and
bay water temperatures remain in the mid 60s which may be cool
enough to support sea fog development. Sea fog may first begin to
develop along the middle Texas Coast and over Matagorda bay late
Thursday. Sea fog may spread north along the coast towards Galveston
Bay by Friday morning. Sea fog may persist over the weekend until
the next cold front Monday.

Overpeck

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 83 65 83 67 79 / 50 10 10 50 90
Houston (IAH) 80 67 82 68 80 / 70 10 10 30 60
Galveston (GLS) 74 68 75 68 74 / 50 20 20 20 40

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

[tireman4]

Pro and Amateur Mets, we have an outdoor swim meet from 9 am to 5 pm both days in the Cy Fair area. Our events are 1-5 pm each day. What are your thoughts about getting the meet in?

[MontgomeryCoWx]

Feels disgusting outside.... I hate this time of year to September.

[jasons2k]

This evening’s baseball game is much more pleasant than it was a few days ago. No jackets and blankets required thank goodness. It’s gorgeous right now.

[djmike]

According to qpf. Rain chances looks to be dwindling for immediate SETX. Beaumont we started at 90%, then Thur down to 70% and now this Friday morning, 50% for this weekend. We shall see...

[stormlover]

100 percent from bostwick, 80 from Vaughn not going down

[srainhoutx]

Friday morning weather briefing from Jeff:

Multiple storm systems will affect the region this weekend with severe weather and heavy rainfall increasingly likely.

Stalled frontal boundary this morning from College Station to Lake Charles with dense sea fog having developed south of this feature as a warm and humid air mass moves northward off the Gulf of Mexico. Once the sea fog lifts today inland not expecting much in the way of shower or thunderstorm chances with weak ridging in place.

Saturday:

Short wave approaches central TX late tonight into Saturday and the air mass over SE TX will destabilize as cooler air overspreads and continued warm surface layer resulting in steep lapse rates and building instability on Saturday. Forecast CAPE of 2000 J/kg by midday would certainly support strong to severe thunderstorms capable of large hail and damaging winds. Backed low level onshore flow early in the day becomes increasingly SE and SSE toward midday and afternoon and think any tornado threat will be early and mainly in the College Station to Lake Livingston area. Track of the short wave on Saturday largely aims most activity north of I-10 and think some sort of squall line or broken line will move across the northern ½ of the region from noon-600pm time frame. Again damaging winds to 60mph and large hail will be the primary threats. Surface outflow boundary may be generated and pushed southward from the northern county activity and help focus storms in the afternoon hours closer to the metro Houston area or even WSW/SW of Houston. SPC has the entire area outlooked for slight severe risk, but thinking the coastal areas and southwest counties may not see much on Saturday. Heavy rainfall will also be possible as PWS rise to 1.5-1.7 inches and low level moisture transport flow increasing off the Gulf. Will cap the Saturday rainfall around 1-2 inches especially north of I-10 and given the dry ground…this rain should be more welcomed than cause any significant issues.

Sunday:

Strong short wave will dig further south and produce another couple of rounds of thunderstorms across much of SE TX. Severe threat looks a little more marginal on Sunday as some of the area may be “worked” over from the Saturday activity. Still looking at plenty of instability especially southern areas that may not see much on Saturday for additional severe storms with large hail and damaging winds once again the main threats. Main focus on Sunday may become heavy rainfall as favorable moisture transport continues off the Gulf of Mexico into slower moving clusters of thunderstorms. Will need to closely monitor for any left over low level boundaries from Saturday as they could help focus training thunderstorms on Sunday. Additionally, grounds will likely saturate some depending on the location and amounts of the Saturday rainfall and those areas would be at a greater risk for flooding on Sunday. Expect another 1-2 inches across much of the area on Sunday, but higher amounts are certainly possible.

Rainfall Totals:

Overall weekend storm totals of 2-3 inches look likely north of I-10 with isolated higher amounts…potentially up to 5 inches. Rainfall amounts south of I-10 will likely be in the 1-2 inch range. Rainfall rates on both Saturday and Sunday could reach 1-2 inches per hour which may cause rapid street flooding. As mentioned, dry ground should help negate some run-off at least on Saturday. Will need to monitor closely for any sustained training of cells especially Sunday that could quickly add up rainfall amounts.

SPC (Saturday) Severe Weather Outlook

SPC (Sunday) Severe Weather Outlook:

[/i]

[tireman4]

000
FXUS64 KHGX 051120
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
620 AM CDT Fri Apr 5 2019

.AVIATION [12Z TAF Issuance]...

Begin the period in LIFR across the area with fog and low stratus.
Should see this improve mid to late morning (15Zish), and improve
to VFR for the afternoon. As we go into the evening, look for
degradation to MVFR, and most/all terminals could fall into IFR
very late tonight. Only go to IFR explicitly at GLS for now, but
may need to introduce sub-1000` ceilings towards sunrise in the
next cycle or two if confidence increases.

&&

.PREV DISCUSSION /Issued 445 AM CDT Fri Apr 5 2019/...

.NEAR TERM [Through Today]...

As of 3am a stalled frontal boundary stretched from Beaumont to
College Station. South of the boundary the warm sector airmass has
dewpoints in the upper 60s with light southerly winds if any.
This has allowed for stupid fog to return to the area with sea fog
forming along the Gulf coast and through Galveston/Matagorda
bays. Dense fog advisory is essentially in effect for areas south
of the boundary where visibility is down to a quarter mile or
less. There will be some fluctuations in visibility from hour to
hour but in general, one can expect dense fog across much of the
area including Houston metro. The morning commute may take more
time given the dense fog. Dense fog advisory is in effect until
9am for the inland areas and until noon for the marine areas.

After the fog dissipates later this morning, really there should
not be much in the way of precipitation other than a few showers
along the coast if anything. Upper level analysis shows one
departing wave from yesterday now across the S.E. U.S. with weak
ridging aloft expected over much of Texas for today. This is in
response to an upstream trough over southern Cali and the Baja
peninsula. This system is expected to move across Mexico tonight
and into Texas by Saturday morning. A much stronger jet streak in
the Pacific will then split with a second upper level trough
developing over Texas Saturday night into Sunday. The weekend
forecast hinges on solid model initialization of these features
which right now may be hard to do since these systems are still in
the data void Pacific but hopefully GOES 17 can offer useful
data.


.SHORT TERM [Saturday Through Sunday]...

As with so many severe weather and heavy rainfall events, the
devil will be in the details which hinge greatly on mesoscale
processes that the models will have a terrible time resolving even
2 to 3 days away. WRF model runs are providing some help in the
48hr range, but still so much uncertainty given a shift in
location by even 50 to 100 miles makes a huge impact on the
forecast. Synopticly, we are not seeing too many model
differences between the NAM/GFS/ECMWF in the 00Z data. The first
trough should move across west/central Texas Saturday morning.
Large scale lift looks strongest over central Texas and most
models are focusing convection over this area and then moving into
the Brazos Valley/east Texas later in the day Saturday. Forecast
has focused higher rain chances to north of a Columbus to
Livingston line. Houston very well could be just south of the main
track for thunderstorm activity but it would not take much for
that to change. HREF (mainly NSSL WRF, WRF-ARW and NAMnest
members) highlight this area the most and this agrees favorably
with the synoptic models. Synoptic models may have best chances
for convection a little farther north.

SPC has a slight risk for severe weather Saturday for a large
area of Texas but as mentioned before, HREF seems to be pointing
to areas north of Houston that have the highest probabilities of
severe weather. Areas from College Station to Huntsville look to
be in this swath of modeled deep convection. Capping could be an
issue but the large scale lift will be strong so leaning towards
the cap eroding for deep convection. NAM and GFS both develop CAPE
of over 2000 J/kg so certainly enough buoyancy for severe
convection due to steep lapse rates more than anything. Deep layer
shear will be enough for organized storms but still hard to say
what kind of storm structures there will be since there will be a
broad area of large scale ascent. Low level shear will be within
thresholds that updrafts could rotate but that shear may be more
directed from the SW and decrease through the day. This means any
tornado potential will be highest in the morning hours. The other
severe weather threats of damaging winds and hail could be in play
as well given the steep lapse rates. If linear storm modes
develop then there will be a threat for damaging wind and some of
the CAMs show that kind of structure. And for good measure,
locally heavy rainfall will be possible given a robust LLJ off the
gulf, PWAT increasing to around 1.5 to 1.7 inches over the area,
and strong forcing. Should an outflow boundary move south from any
of this convection, new storms could form and be a threat for
heavy rainfall as these new storms can take advantage of strong
moisture transport. NAEFS ensemble data certainly provides support
for quick recovery of any stabilized airmass as moisture
transport and high moisture will be in place. WPC is carrying a
marginal risk of excessive rainfall and the only reasons for it
not being a slight risk are the fact that most of the grounds are
dry and uncertainty in overall placement of higher rainfall
amounts.

Sunday a second stronger trough digs into Texas with a stronger
upper level jet and more large scale lift. This will continue to
enhance and support a strong LLJ off the Gulf. SE Texas will
certainly be under the gun for another round of potential severe
weather. SPC has a slight risk of severe weather on the day 3
outlook. Again the main question will be how much the atmosphere
gets worked over by convection on Saturday and whether the
atmosphere can recover to destabilize again on Sunday. Given the
continued moisture transport from the Gulf, we lean more on the
side of the atmosphere re-charging so to speak and kept higher
precipitation chances in the forecast. Again mesoscale processes
will more than likely dictate how the forecast evolves and we are
just not at the point with mesoscale modeling to get those kinds
of details beyond day 2. So we are stuck in a wait see mode on
Sunday but the synoptic pattern will be very supportive of
thunderstorm activity if the atmosphere can recover its buoyancy
from being worked over on Saturday. CAPE could be back above 2000
J/kg on Sunday as well. Deep layer shear will be stronger above 50
knots but low level shear will be weaker. The tornado threat on
Sunday looks lower but still a threat for hail and damaging winds.
The potential for heavy rainfall also looks better on Sunday. The
ECMWF and Canadian really hint at heavy rainfall over northern
portions of SE Texas as well as back to the SW of Houston. Again
these pockets of heavy rainfall amounts will very well shift from
model run to model run so we don`t want to latch on to any one
solution.

We really do not want to pin down rainfall amounts right now, but
to help with messaging of heavy rainfall and flood potential we
are at that point. Saturday there could be a very tight gradient
of rainfall. As mentioned before, the areas along and north of
Columbus to Livingston could get more rainfall than south of that
line...potentially 1 to 3 inches with an inch or less south of
that line which would include Houston. By Sunday rainfall amounts
look to be more 1 to 2 inches area wide. We have not addressed
rainfall rates but given the forcing and moisture - 1 inch in an
hour looks very reasonable in stronger storms. We are not to the
point of needed a flood watch since most of the area has not had
much in the way of rainfall for the last several weeks. Saturday
could be a priming day depending upon rainfall amounts. This means
Sunday could have a higher flood threat with more saturated
grounds from any rain on Saturday.


.LONG TERM [Monday Through Friday]...

The second trough does move east Monday and allows a weak cold
front to push through the area. This should allow for northerly
winds on Monday with weak high pressure over the area on Sunday
allowing for light winds. Upper level ridging builds over Texas
Tuesday and Wednesday and should keep rain chances out of the
forecast for a couple of days.

Overpeck


.MARINE...
Obs, satellite, and webcams show things are pretty socked in along
virtually the entire coast with sea fog, while we see generally
light onshore winds. That should continue today, and though winds
will generally be onshore, they may be somewhat variable through the
day. We will also begin the day with areas of dense sea fog that
have developed overnight. Expect enough mixing to allow visibility
to modestly improve in the afternoon, but the environment will
remain favorable for dense fog to return with a vengeance Friday
night.

A tightening pressure gradient will also force winds to become more
southeasterly Friday night, and increase in speed to be more
moderate. At some point tomorrow, parts of the Gulf may exceed the
SCEC threshold and require caution flags. Additionally, look for
rain and thunderstorm chances to increase significantly through
Saturday evening into Sunday.

A Monday cold frontal passage will veer winds to northwesterly, and
though wind speeds are likely to go slack as the front approaches
and pick up in its wake, no advisory-level winds are anticipated at
this time. Southerly winds - moderate to gusty -should return as
early as Tuesday night, and dominate the mid-week.

Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL) 84 67 79 66 79 / 10 30 80 60 60
Houston (IAH) 83 67 80 68 79 / 10 20 40 60 70
Galveston (GLS) 76 67 74 68 75 / 20 20 30 50 70

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...Dense Fog Advisory until 9 AM CDT this morning for the following
zones: Austin...Brazoria Islands...Chambers...Coastal
Brazoria...Coastal Galveston...Coastal Harris...Coastal
Jackson...Coastal Matagorda...Colorado...Fort
Bend...Galveston Island and Bolivar Peninsula...Inland
Brazoria...Inland Galveston...Inland Harris...Inland
Jackson...Inland Matagorda...Matagorda
Islands...Montgomery...Northern Liberty...Southern
Liberty...Waller...Wharton.

GM...Dense Fog Advisory until noon CDT today for the following zones:
Coastal waters from Freeport to Matagorda Ship Channel TX
out 20 NM...Coastal waters from High Island to Freeport TX
out 20 NM...Galveston Bay...Matagorda Bay.


&&

$$

NEAR TERM...Overpeck
SHORT TERM...Overpeck
LONG TERM...Overpeck
AVIATION...Luchs
MARINE...Luchs

[djmike]

100 percent from bostwick, 80 from Vaughn not going down

According to NWS LC and qpf it has dwindled a bit. Even bostwick mentioned heaviest will now possibly be NW of us lastnight which corresponds with what qpf is showing right bow also. Bostwicks rainfall map showed over 4” two days ago for BMT and lastnight his map showed 0.36” for us thru Sunday. We shall see. Could be bumped back up later today but going off of the lastest data.

[stormlover]

I don’t even look at nws lake Charles lol they struggle, look at nws Galveston they broke it down well, Sunday looks wet for Beaumont

[tireman4]

NWS SPC

[srainhoutx]

The afternoon Updated Day 2 Storm Prediction Center Outlook for Saturday shifts the severe thunderstorm potential a bit N of Metro Houston. The SPC did add an Enhanced Risk to our N and E.

The 12Z Global guidance do suggest a bit deeper shortwave/upper air disturbance and a dip in the jet stream (upper trough) crossing the Rio Grande River near Mc Allen Saturday night into Sunday morning. That is a bit further S than previously expected. That change could enhance our rainfall and storm chances late Saturday into Sunday across our Region.

[stormlover]

Yep, that’s why I don’t jump on model runs so quick they struggle should have a good sense tonight

[tireman4]

FYI from HGX Skywarn....

[djmike]

Hmmmm...

[Cpv17]

The models are so confusing. They’re back to giving areas south of 10 a bunch of rain again. What the heck lol

[Belmer]

As is often the case with deep shortwave troughs that come from the Pacific crossing Mexico, models struggle with initialization due to poor feedback and little upper-air data. As we've done in the past, many times we have to "now-cast" on disturbances like these. For example, below (first image) is the current radar image. Notice how the storms that developed last night moved NE into SW Oklahoma and a new complex of storms formed out in west TX and is currently producing a pretty potent MCS. Models did show another round of storms forming this morning, though many of the high-res models quickly weakened this current complex by this time (11z).

Below the current radar image are the HRRR, NAM 3km and NAM 06z model runs for 11z (right now) respectively. Notice how none of them are really grasping onto the current complex of storms out in west/central TX. This will give the local NWS offices across the state the fits as these systems are so dynamic but models do horribly in showing just how strong the setup is over the area.

What this means for our weather? Think right now it is a little early (relatively speaking to right now compared to later this afternoon) to say what kind of storms we see or how much rainfall we accumulate. Models have been consistent in showing storms firing off in northern Mexico tonight as the deep trough moving onto the West coast begins to slide this way. While tomorrow may be a wash out... it also may not as whatever forms in Mexico could slide more south and mainly be a Gulf/coastal threat. A lot will depend just how deep the trough digs and/or how fast it moves across the State. While I'm not trying to dismiss or discourage looking at the high-res models, I would take them with an understanding of what could evolve over the region, but not necessarily what the intensity of the storms will be over a certain area. Central and north TX is a good example right now as models did not pick up on the intense activity up there this morning.

[unome]

I always appreciate Overpeck's analysis, thorough & detailed, but you don't have to be a meteorologist to understand terminology - thank you Scott, if you read this (& the rest of the crew as well)

Area Forecast Discussion
National Weather Service Houston/Galveston TX
457 AM CDT Sat Apr 6 2019

.DISCUSSION...

Severe weather and heavy rainfall are possible this weekend. While
the weekend will not be a complete washout, people need to be
diligent to monitor weather forecasts for updates, watches and
warnings.

.NEAR TERM [Through Today]...

Mesoanalysis will be essential through out the day as severe
weather and heavy rainfall begins to unfold. Starting out with the
surface, low pressure has developed over west TX in response to
the first jet streak and short wave trough to move into the
plains. This has allowed for winds to back to the ESE over much of
the area. Water vapor imagery is key to the analysis aloft today
as there are many subtle features that if go unanalyzed, could
make an impact on the forecast. Right now water vapor imagery
shows the beginnings of a jet streak coming into south Texas and
we see large scale lift increasing due to resulting shower
activity over the region. This feature may not have initialized
well in the models and could allow for a weakening of the cap more
so than the models indicate. AMDAR airplane soundings over the
area show a fairly strong cap in place with the EML around
800-700mb. Divergence from the left exit region of this southern
jet will act to enhance the LLJ today and a continuing eroding of
any capping. The focus for convection today looks to be centered
along the main jet axis with this first short wave trough pushing
into the southern Plains as a second jet streak comes into Mexico
this afternoon. This jet axis should be oriented across central
Texas towards the Arklatex. At 09Z water vapor imagery already
started to show some enhanced cloud cover over the Hill Country
into central Texas as evidence for stronger lift over the region.
The second jet streak is currently back over California and
western Arizona. There will be no lacking moisture or instability
today as AMDAR soundings also show steep lapse rates above the
EML. PWAT values this morning are 1.5 to 1.6 inches of the lower
Texas Coast. PWAT values are expected to increase through Sunday
and expand across the region.

There is a lot of analysis to digest but SPC and WPC have put
together some solid synthesis of the data. Severe weather risk of
slight to enhanced looks on track for the northern most counties.
Last few runs of the HRRR along with several WRF/HREF runs
continue to highlight an area north of College Station to Crockett
for primarily a wind/hail threat. But there is also a 5% tornado
probability. This area should have the most convergence for storms
but also where moisture/instability/shear combine for convection
capable of severe weather. Most likely the thunderstorm activity
will remain just north of this line more into the NWS Fort Worth
warning area but mesoscale processes with outflow boundaries could
shift this activity south. Our forecast leans on the higher side
of rain chances for this reason but there will be a tight gradient
in precip chances and it could shift. Storm modes look to be more
linear hence the wind/hail threat but a rotating updraft could
also be possible given the shear parameters for a low end tornado
threat. This will be especially true for the enhanced/slight risk
areas of the outlook.

WPC also has a slight risk of excessive rainfall for parts of the
northern counties from College Station to Crockett. This is due to
the possibility of storms training along the same area. Recent
runs of the HRRR and the Texas Tech WRF support this idea with
convection initiating around 15Z and going until 00Z Sunday.
These areas of training storms line up well with the lift from the
jet axis mentioned before. Due to the training, rainfall amounts
could stack up quickly and present a localized flood threat. Again
this axis of higher rainfall should be from say a Temple to
Palestine line but with mesoscale processes we will need to see if
this shifts farther south towards the Brazos valley into east
Texas. NAEFS also highlights this area for higher than normal PWAT
and moisture transport. The flood threat only complicates the
weather message when added to the severe weather threats.

.SHORT TERM [Sunday Through Monday]...

By Sunday morning the pattern becomes even more conducive for a
heavy rainfall threat but we do not want to forget about the
severe weather threat. SPC still has the area in a slight risk. By
Sunday morning the upper level trough should be over the Rio
Grande Valley with a strong area of PVA from Del Rio to Laredo.
This vorticity along with a jet streak should move over SE Texas
by 18Z Sunday with a slight negative tilt. This quickly erodes any
capping and brings more enhancement to the LLJ over the area.
PWAT increase to 1.7 to 2.0 inches depending upon the model. The
point here is that these values will be well above the 90th
percentile of climo and nearing record values for the day. NAEFS
also shows higher than 90th percentile of moisture transport
during this time so between the lift and high moisture there is a
growing concern for a heavy rainfall threat. QPF output from the
models varies quite a bit but looking at an area wide of 2 inches
possible on Sunday and likely have some bands of higher amounts.
Hi-res models are showing some signs of these enhanced bands but
again QPF output does not seem to line up well with the overall
synoptic pattern and expected moisture. The other aspect that is
relatively unknown at this point will be any interaction of the
trough with outflow boundaries for focused ascent. WRF runs seem
to be trying to key on these boundaries for higher rainfall
amounts but hard to know the exact evolution of these outflow
boundaries. This is another area where ongoing mesoanalysis will
be key to better pinpoint these details. Another question that
remains will be just how far south this second trough will drop
over Mexico and how the trough moves east or northeast across the
area. If it drops a little more south, the system could be slower
to move over the area and possible produce higher rainfall. This
all remains to be seen but alternate scenarios that deserve
attention.

We are really close to looking at possibly issuing a flash flood
watch for Sunday but this may depend upon how much rainfall falls
today. Grounds are still on the dry side but some areas have had
some rainfall. WPC slight risk of excessive rainfall looks to be a
good outline to follow for a watch area. For now we think we can
wait for the 12Z model runs to help define a watch area.

Overpeck

.LONG TERM [Monday Night Through Saturday]...

Overall we are expecting a dry forecast with rain chances not
possible until the end of the week. Temperatures should be above
normal by a good 5 degrees or more.

&&

.MARINE...

Light easterly flow is in place across the waters very early this
morning, but should become moderate and veer slightly more
southeasterly through the day today. The offshore waters may be
marginal for caution-level winds. Though there will be a chance of
showers and storms today, most of the action today will be well
inland, over North and Central Texas. The better chance for storms
near the waters will be Sunday, as a coastal trough sets up,
possibly enhanced by outflow from yesterday's storm activity. A weak
coastal low may even form along the trough and move across coastal
Southeast Texas through Sunday night. This may tighten the pressure
gradient over the outflow waters to the SCEC threshold, but for the
moment the forecast stays just below it.

A Monday cold frontal passage will veer relatively weak winds
northwest through late Tuesday night. Return flow is expected by
sunrise Wednesday. The strongest winds of the week are forecast from
Wednesday afternoon through Thursday morning, with another cold
front arriving later on Thursday to shift winds northwesterly
again.

Luchs

&&


.HYDROLOGY...

Main impacts from any heavy rainfall this weekend should be rises
on area rivers and bayous. We will have to monitor closely for
bayous rising out of banks and this will largely depend upon rain
rates of the storms and how quickly a bayou responds. Street
flooding will be the greatest impact in urban areas especially on
Sunday. Based on RFC QPF ensemble most rivers/bayous should stay
in banks with only a few gages reaching action stage or even minor
flooding.

Overpeck

&&

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL) 80 67 75 60 80 / 60 60 80 30 10
Houston (IAH) 82 69 75 62 81 / 30 60 80 40 20
Galveston (GLS) 74 67 73 65 76 / 20 50 90 50 20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...Dense Fog Advisory until 11 AM CDT this morning for the
following zones: Coastal Brazoria...Coastal
Galveston...Coastal Jackson...Coastal Matagorda...Galveston
Island and Bolivar Peninsula...Matagorda Islands.

GM...Dense Fog Advisory until 11 AM CDT this morning for the
following zones: Coastal waters from Freeport to Matagorda
Ship Channel TX out 20 NM...Coastal waters from High Island
to Freeport TX out 20 NM...Galveston Bay...Matagorda Bay.


&&

$$

DISCUSSION...Overpeck
NEAR TERM...Overpeck
SHORT TERM...Overpeck
LONG TERM...Overpeck
AVIATION...Luchs
MARINE...Luchs
FIRE WEATHER...Luchs
HYDROLOGY...Overpeck