MAY 2019: Wednesday Storm Complex/Scattered Showers To End May

[tireman4]

000
FXUS64 KHGX 021800
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
100 PM CDT Thu May 2 2019


.AVIATION...
As indicated in the previous discussion. Boundaries over the area
playing havoc with winds and VFR ceiling heights. Main boundary
now appears to be the outflow boundary sagging south into the
CLL/UTS at this time with storms initiating north of the boundary
(elevated) near KBMQ/KAQO with flow favoring eastward development.
Given the short term guidance showing continued development across
that area shifting ESE with time will be carrying a TSRA in the
TAF forecast for CLL in the 23-03z window and then shifting
further SE possibly into the UTS/CXO/IAH area around 01z but
weakening.

In the wake of the storms probably some brief IFR/LIFR ceilings
then slight improvement. SE flow restrengthens as more potent
forcing comes into the region and expect a larger more organized
complex of storms pushes into the region Friday late
morning/afternoon. Timing is still in question for this system but
is likely.
45

&&

.PREV DISCUSSION... /ISSUED 1128 AM CDT Thu May 2 2019/

NEAR TERM [Through Today]...

Recent mesoanalysis shows that there are a plethora of outflow
boundaries and therefore a plethora of forecast issues through
the next 12 to 24 hours. Visible satellite imagery has been the
best tool to use to diagnose the location of these outflow
boundaries and where they are moving. One boundary was located
along the Gulf coast from Sabine Pass inland across Galveston and
stretched back through Columbus. There was another boundary
moving south over central Texas towards the area and this boundary
curved back towards Abilene. Convection has initiated along this
boundary that intersected with a frontal boundary moving down west
Texas. So for now the convection from this morning has stabilized
the boundary layer over much of the area. Storms today will
largely hinge upon recover of the airmass which could happen
fairly quickly. AMDAR soundings from airplanes show a weaker cap
than yesterday but still some resemblance of a cap around 850mb.
Hi- res convective models show trends of convection this evening
across northern areas from Caldwell to Crockett. This seems to be
where the outflow may push back north or where the boundary from
the north stalls. It is hard to pinpoint which since the models
are not handling these features well. We think it will be where
the outflow from the north stalls. Visible satellite shows
clearing over much of SE Texas so heating should be abundant and
help stall the boundary. We will also need to monitor any
convection that forms over the Hill Country and moves into the
area later tonight but those chances look much lower.

Main changes to the forecast were for ongoing trends and
anticipating some heating today with moisture recovering over the
area. PoPs were updated based on latest hi-res models and will
likely be updated again this afternoon. Overall severe threat
looks on the low end with slight risk from SPC to the west of the
area. Main threats will be hail and damaging winds but again more
so for central Texas than SE Texas.

[srainhoutx]

Midday weather Update from Jeff:

Air mass over SE TX is quickly recovering from the morning round of thunderstorms.

Numerous outflow boundaries are in place over the region and it appears some sort of weak disturbance is moving across S TX which is resulting in a few showers/thunderstorm near Matagorda Bay. Another complex of storms near Brownwood, TX is moving SE in this direction and yet additional storms are developing along an old outflow boundary over the TX Hill Country. Recent aircraft ascents out of IAH and HOU show a much weaker and breakable cap is in place over SE TX. As temperatures rise into the mid 80’s thunderstorms may begin to develop along the leftover boundaries over the area. One boundary is laying nearing the coast and the other extends from Austin to near Crockett. Think the northern boundary will have a better shot at development.

Next question is what happens with all the development to our west. HRRR and TX TECH WRF high resolution models bring a complex of storms at SE TX this evening…with the TX TECH model plowing the complex all the way to near I-45/I-10 while the HRRR weakens the line across the Brazos Valley. Given the poor model trends of late I am not inclined to favor either solution especially since so much if being driven by small scale features. What happens this afternoon and tonight will have impacts on the forecast for Friday.

[srainhoutx]

I don't see any change in the Medium or Longer Range that indicates our rain chances will disappear. The latest Update for the Climate Prediction Center suggests a deep trough situated across the Intermountain West into the Plains will keep a wet and somewhat cooler pattern due to clouds and rainfall well into mid May. We have a high latitude blocking regime established over the Artic into Greenland. The SE Ridge looks to remain in place leaving Texas in a general weakness with an active upper trough nearby.

As we head toward mid May, eyes turn toward Central America where we often see a Monsoonal trough set up and that marks the beginning of the Eastern Pacific Hurricane Season with the North Atlantic Hurricane Season commencing June 1st. Tis that time of year once again.

[srainhoutx]

Stay weather aware this evening...

Mesoscale Discussion 0505
NWS Storm Prediction Center Norman OK
0448 PM CDT Thu May 02 2019

Areas affected...central Texas

Concerning...Severe Thunderstorm Watch 120...

Valid 022148Z - 022345Z

The severe weather threat for Severe Thunderstorm Watch 120
continues.

SUMMARY...The threat for large, damaging hail will persist from
southwest Texas across the Rio Grande Valley and toward Hill
Country, with a few strong wind gusts into east-central Texas.

DISCUSSION...An MCS persists over central Texas, with a leading
outflow boundary surging southeastward. Ahead of this eastern
activity, a moist and strongly unstable air mass remains in place.
While shear profiles are weak aloft, these storms will continue to
propagate southeastward, aided by modest southeasterly inflow. Given
the amount of outflow, a few strong to severe wind gusts are
possible. Steep lapse rates aloft will also support marginal hail in
the strongest cores.

To the west, easterly flow toward the Rio Grande Valley and
southwest TX will maintain a deep layer of moisture advection
beneath steep lapse rates aloft. Shear will be marginally favorable
for supercells producing large hail, including the threat of
significant hail.

..Jewell/Grams.. 05/02/2019

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...HGX...FWD...CRP...EWX...SJT...MAF...

[Cpv17]

BCS is about to get dumped on. Very heavy rain headed their way.

[Belmer]

A rather great analysis on a very complicated weather forecast during the next 24-36 hours. Overpeck even slid in some 'humor' in the discussion...

Area Forecast Discussion
National Weather Service Houston/Galveston TX
357 PM CDT Thu May 2 2019


.NEAR TERM [Through Tonight]...

After doing another round of map analysis, the only way to
explain the current mesoscale situation is to say there there are
even more outflow boundaries moving in different directions
initiating new convection. Over the last 30 minutes or so, some of
that has calmed and there is more organized linear convection
over central TX with a quasi-bowing segment NW of Belton. There
seems to be some upscale growth to the line on the southern flank.
It stands to reason that this could possibly continue. This
convection may be more elevated since there is one outflow
boundary well to the south from Austin to College Station. There
is still strong SE boundary layer flow with at least some enhanced
LLJ flow through this corridor of activity. Upper level jet is
still to the south over S TX but there is at least some influence
with WNW flow. With upscale growth of convection on the south
flank, this activity over central TX could very well push towards
the Brazos valley over the next 3 to 6 hours. Not only that, but
there could be additional development of storms in this area along
the outflow boundary. We might be seeing signs of this with
convection forming in Austin County NW to Lee County. This
certainly indicates that the cap has weakened and should there be
enough lift surface base convection could become more scattered
through the evening. Most of this activity should stay NW of
Houston. Thunderstorm chances in the forecast keep higher chances
over the Brazos Valley with some slight chances over Houston.
Confidence in convection tonight is certainly higher over central
TX into Brazos Valley.

Should some of these storms become surface based, lapse rates
above the cap support large hail and likely a straight line wind
threat with more organized linear convection. SPC has a slight
risk that includes the western most counties in the forecast area
and this seems on track with latest analysis. Instability is
highest right along this outflow boundary near Austin to College
Station so hail/wind threat highest over the next few hours for
these areas. The question will be if a storm can initiate.

Overpeck

.SHORT TERM [Friday Through Saturday Night]...

Given the mess of a mesoscale environment expected this afternoon
and tonight, Friday`s forecast still has quite a bit of
uncertainty however convection could become more organized due to
upper level support. Water vapor imagery shows a potent jet streak
and trough approaching the Baja Peninsula. This feature should
move over Mexico tonight and reach the Rio Grande valley Friday
morning. Nose of the jet then pushes towards SE Texas with both
diffluent and divergent flow increasing over the area. Capping
should be minimal if any so expect there to be more widespread
convection developing along whichever outflow boundaries exist.
Environment for Friday looks more favorable for heavy rainfall
than severe weather as there will be precipitable water values
increasing to around 2 inches over the area by the afternoon with
strong moisture transport off the Gulf. There should be enough
flow for storms to move, but the problem will be if storms form
along boundaries and then move along them with new convection
forming and then moving over the same area. Models are still not
in great agreement but think areas north of Houston from Brenham
to Livingston northward have a chance to get 2 inches of rain or
more. Houston areas looking like 1-2 inches with less than an inch
along the coast. There could be areas that don`t get rain and
they will be the ones to say we are always wrong. There will also
be a few spots that could see isolated 4 inches of rain like if
the GFS verifies and the people that get that much rain will
probably say we were wrong. All kidding aside, we do need to be
careful because the areas that could get heavy rainfall tomorrow
have already had an inch of rain from last night`s rain and could
get some more depending upon how storms evolve tonight. We are
not looking to issue a flash flood watch yet, but we are on the
edge of doing so with some of these potentially higher rainfall
amounts that could be possible. Again the areas most at risk will
be the Brazos Valley into east Texas, with a watchful eye on the
Houston metro for anything that should happen to develop farther
south. Right now we are not seeing that in any of the model
trends, but this is May where mesoscale processes will make a
difference in the forecast.

Models are slow to move activity out overnight into Saturday
morning so there could be multiple rounds of rainfall with some
rounds producing more rainfall than others. These details are
still hard to pinpoint especially since latest performance of CAMs
has been dreadful the last few days. Activity should be ending
Saturday afternoon with a break in convection on Sunday.

Overpeck

.LONG TERM [Sunday Through Thursday]...

Next week will be active again with the potential for severe
weather and heavy rainfall. It looks like another trough will move
across Monday into Tuesday and again Wednesday into Thursday as a
front may move into the region before stalling. Overall there was
not much change in the forecast during this time frame but keeping
an eye on severe weather and heavy rainfall parameters. Overall
confidence is decent enough to include some higher rain chances
but still low when it comes to details as the mesoscale again will
be a large factor for evolution.

Overpeck

[unome]

A rather great analysis on a very complicated weather forecast during the next 24-36 hours. Overpeck even slid in some 'humor' in the discussion...

I do love his write-ups

[jasons2k]

A rather great analysis on a very complicated weather forecast during the next 24-36 hours. Overpeck even slid in some 'humor' in the discussion...

I do love his write-ups

Indeed. We are fortunate to have one of the finest NWS offices in the country, but they all do a fantastic job!

[Cpv17]

Same areas that got rain this morning are getting more rain again this evening. We’ve had some sprinkles here in Wharton, but that’s it.

[MontgomeryCoWx]

I’m at 2 inches today with another heavy round over me. I might hit 2.5-2.75 when this one is done.

[Cpv17]

The Euro is crazy wet for southeast Texas. It has the bulk of the rain over the next 10 days over us while the GFS has it way north of here. Which one will win out?

[Katdaddy]

Another active weather day across a large portion of TX. Ongoing strong to severe thunderstorms across Central and STX this morning. The SPC has a Slight Risk area for STX and most of TX in a Marginal Risk area. Strong to severe thunderstorms and locally heavy rain will be possible across SE TX this afternoon, overnight, and into Saturday morning. Clearing skies tomorrow afternoon and a mostly sunny Sunday on the way.

[srainhoutx]

Active 24 to 36 hours ahead in the weather department. Still a very difficult and challenging forecast ahead regarding our sensible weather through at least midday on Saturday when we get a brief break from the rain and storms.

For today, the Weather Prediction Center has outlined a large Slight Risk for Excessive Rainfall for most of us. Some of the models suggest someone could get up to 5 inches of possibly training heavy rainfall this afternoon into the overnight hours. With so many boundaries around and mesoscale features that cannot be determined beyond 6 hours, it's almost impossible to make a call on the exact location that may get the heaviest of the rain.

Rounds of rain, some of it heavy, return on Monday and increase in areal coverage as the new work week begins. Another round of heavy rainfall may be possible on Tuesday into Wednesday with a continued chance of rain as we finish of the first full week of May!

[Cpv17]

The latest GFS now agrees with the Euro for significant rain totals across SETX. Looks like 6-12” as of right now for most of us over the next couple weeks.

[unome]

a busy day ahead

https://twitter.com/NWStornado

https://twitter.com/NWSSevereTstorm

[srainhoutx]

Will need to monitor trends just to our West. NWS San Antonio/Austin have issued 3 Tornado Warnings for radar indicated rotation (possible tornadoes) in the past 10 to 15 minutes.

[srainhoutx]

05032019 mcd0512.gif (11.19 KiB) Viewed 3815 times

Mesoscale Discussion 0512
NWS Storm Prediction Center Norman OK
0739 AM CDT Fri May 03 2019

Areas affected...middle coastal plain of TX

Concerning...Severe potential...Watch unlikely

Valid 031239Z - 031345Z

Probability of Watch Issuance...20 percent

SUMMARY...A couple of supercells have recently developed within a
moist airmass immediately east of an eastward-moving MCV. A weak
tornado is possible in addition to a localized severe gust. The
localized nature of the expected threat will probably preclude a
watch issuance.

DISCUSSION...Radar imagery shows an MCV near San Antonio moving east
and a couple of supercells have developed. The CRP 12z raob showed
a very moist boundary layer (16 g/kg lowest 100mb mean mixing ratio)
with moderate buoyancy. Despite somewhat modest flow in the lowest
6km, the strongly veering profile has contributed to around 40kt
0-6km shear---supporting storm organization. Current expectation is
for the supercell risk to persist for another hour or two before
gradually diminishing. Nonetheless, a weak/brief tornado is
possible along with a locally damaging gust in the vicinity of a
mesocyclone.

..Smith/Edwards.. 05/03/2019

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...HGX...CRP...EWX...

[tireman4]

NOAA Satellite May 3, 2019

[tireman4]

NWS Houston Forecast 05 03 19

[srainhoutx]

Great blog post regarding the MCS/ MCV down in S Texas early this morning and gravity waves...

https://satelliteliaisonblog.com/2019/0 ... rning-mcs/