April 2017 - MS 150 Forecast This Weekend

[Katdaddy]

A challenging forecast for SE TX that will be based on the cold pool from last night's Central TX convection and the strength of capping as well as mesoscale outflow boundaries. If storms develop and move into SE TX from mid to late morning; expect some locally heavy rain, small hail and gusty winds.

After today rain and thunderstorm chances decrease to 20% through the rest of the week with partly sunny to sunny skies highs in the low 80s.

[tireman4]

000
FXUS64 KHGX 111141
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
641 AM CDT Tue Apr 11 2017

.AVIATION...
Very low confidence with this TAF forecast package. Model guidance
has performed extremely poorly overnight in regards to convection,
at least locally, so not much to rely on there.

Decent moisture levels remain in place as does a shortwave situated
just to our west. Aircraft soundings around midnight showed a
substantial cap in place across the metro area. But recent
aircraft soundings do show that the cap has weakened a fair
amount. With daytime heating, suspect it can eventually be
overcome allowing some areas of tstms to develop across portions
of se Tx. But overall details (timing, location, etc) would just
be somewhat of a guess. Steering flow will weaken thru the day, so
slower moving/training cells along outflows will be of concern
for localized heavy downpours. Expect amendments... 47

&&

.PREV DISCUSSION... /ISSUED 420 AM CDT Tue Apr 11 2017/
Monitoring a better organized line of storms moving east through
Robertson and Leon County that will pass across Madison ...Houston
..and Trinity Counties within the next hour. Nothing overly
impressive with these storms but they will likely drop an inch or
two of rain...small hail and lay down some gusty winds with their
eastern passage. Much uncertainty remains with today`s forecast as
precipitation chances remain high for a possible cluster of
storms to travel southward across the CWA from around sunrise
through early afternoon. A shortwave disturbance pushing into
south central Texas has been the main impetus in flaring up
convection along a near stationary cold front roughly located
along a Junction to Waco to Tyler line. Today`s PoP/Wx forecast is
strictly based upon the idea that a cold pool will propagate
south(east)ward from convection forming along the Balcones
Escarpment...or between the Hill Country and the Coastal Plain...
within the next few hours. The majority of the higher resolution
models do develop and push a QLCS through the forecast area during
the mid to late morning with a strong cold pool advancement...or
bowing of the line...occurring south and west of the city.
Needless to say....but the capping that has delayed the
southeastern movement of these earlier discrete cells will not be
an issue once these mesoscale outflow boundaries reach
southeastern Texas. Downstream warming within a moist and unstable
air mass will allow any gust front lift to tap into surface based
CAPE of between 1-1.2 k J/kg or near 5 to 6 deg/km lower level
lapse rates. Likely northern 2/3rd CWA PoPs to account for the
above...afternoon moderate 50/50 POPS closer to the coast in an
blind darts throw attempt to peg where any propagating cold
pool/outflow may end up. All and all...prepare for a possibly
active first half of the day with main threats centered around
locally heavy rainfall leading to flash flooding...gusty winds to
over 40 mph and hail to quarter size.

The mid range forecast is fairly benign as Mexico-based upper
ridging noses up into the state and keeps rain chances very low.
Other than local breeze-initiated warmth-of-the-day convection...
rain chances remain below slight to near zero through Easter Sunday.
Partially cloudy late week through weekend days with daily afternoon
temperatures warming into the lower to middle 80s...mild evenings
in the upper 60s to middle 70s leading to sunrises in the average
middle 60s. An uneventful several days through Easter with a change
in the weather pattern originating from a West Coast upper trough
occurring early next work week. This shortwave trough is forecast
to track across the Desert SW through Tuesday and provide a more
diffulent wind pattern over the state going into mid week. Disturbances
moving within this flow will come across Texas Monday and Tuesday
and increase regional (scattered) shower and storm chances. This
will be the first real opportunity for areawide precipitation the
area will likely experience in a week (from today`s forecast
QPF). Despite next week`s more overcast and wet pattern...diurnal
temperatures will not modify very much as mid 60s will still be a
morning theme with afternoons still peaking out in the mean lower
80s under...you guessed it...a breezy onshore wind. 31

MARINE...
Showers and thunderstorms across cntl and ne Tx could sag se and
closer to the coast later today. Any associated outflow boundaries
may produce various wind directions at times. Otherwise, winds and
seas should begin taking a downward trend today as the pressure
gradient relaxes a bit. Should be able to downgrade advsy/caution
flags later this morning. Onshore flow should persist thru the
remainder of the week. 47

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 76 63 81 62 82 / 60 10 20 10 20
Houston (IAH) 78 65 81 64 82 / 60 10 20 10 10
Galveston (GLS) 75 70 75 69 79 / 50 20 20 10 10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flash Flood Watch until 7 AM CDT this morning for the following
zones: Brazos...Burleson...Grimes...Houston...Madison...
Trinity...Walker...Washington.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 10 AM CDT this morning
for the following zones: Waters from Freeport to the
Matagorda Ship Channel from 20 to 60 NM...Waters from High
Island to Freeport from 20 to 60 NM.

&&

$$

[Ounce]

So what has to happen for the instability to occur and cause the rain to pop later this morning? Certainly the atmosphere is moist enough and the more is being provided from the Gulf.

Is it just the cooler air eventually making it down here? Thanks.

[srainhoutx]

Tuesday morning briefing from Jeff:

Mesoscale models have performed horribly overnight with respect to convective evolution over C into SE TX which yields almost no confidence moving forward today. High resolution guidance continues to suggest convective activity which has been anchored over C into E TX overnight will eventually grow upscale into a SE moving MCS…but this has yet to happen. Overnight aircraft ascents out of IAH indicated a stout mid level capping inversion has remained in place which continues to limit the southward extent of the C TX convection. Additionally, activity has remained somewhat disorganized which has prevented a solid formation of a surface cold pool and thus kept the trigger for surface convergence NW of the area.

Recent aircraft data out of Houston indicates the capping inversion is weakening and eroding likely due to lift from an incoming shortwave just to our west. Modest heating this morning will also help to weaken the cap further and likely the feature will be at a breakable level by late morning. Surface heating will also help to tighten the temperature gradient between a warming SE TX air mass and the rain cooled C TX air mass which will help to increase the cold pool generation and likely help to force surface outflow boundaries deeper into the area or in other words bringing a surface trigger into the area.

With the air mass becoming increasingly unstable through the morning into the afternoon hours expect scattered showers and thunderstorms to develop, but where and how organized these storms become remains in question. High resolution guidance continues to support a thunderstorm complex (MCS) moving across the region, but I have my doubts if this will actually transpire. Will go with a more broken line of storms to scattered clusters and have to watch radar trends.

Some factors remain in place for heavy rainfall…and overnight rainfall has been excessive in the areas between Dallas and Austin (around Waco) where up to 8 inches has fallen. Overall steering flow will weaken today which will promote slower cell motions and moisture levels remain high so a quick 1-3 inches of rainfall will be possible. Think the severe threat is generally low with the main dynamics well N of the region, but can’t rule out an isolated large hail or strong gust of wind.

[srainhoutx]

It appears the cold pool across the Brazos Valley into E Texas that is firing storms is getting strong enough to push an outflow boundary SE. Will need to monitor the Western flank of the ongoing convection for potential storm development today as the shortwave approaches from West Texas.

[DoctorMu]

Absolute bust so far as the meso lurked just north last night Leon Country drenched, while CLL remained dry. There is still some hope for outflow boundaries and daytime heating, instability to give us a taste of rain. There's some sagging of the MCS on the radar.

[tireman4]

000
FXUS64 KHGX 111537
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1037 AM CDT Tue Apr 11 2017

.UPDATE...
Radar data this morning is continuing to show showers and
thunderstorms beginning to migrate east southeastward across the
northern counties of our CWA. The cold front that was slowly
propagating into the counties of Brazos, Madison, and Houston has
begun to stall out becoming a stationary front. The chance for
precipitation late this morning and into the evening hours will be
mainly mesoscale driven. The region currently between the main line
of precipitation and I-10, will see most of the shower and
thunderstorm development early this morning, as a cold pool has
pushed out ahead of the main stationary front. The 500 mb pressure
field along with the experimental GOES-R water vapor imagery,
shows a shortwave aloft which should help to provide lift as this
system pushes east southeastward. The cold pool along with the
shortwave overhead, are acting as forcing mechanisms aiding in the
parcels ascent to saturation. During the later hours of the
afternoon and into the early evening, showers should push south of
I-10 and begin to dissipate, leaving behind only a stray shower
or two in the northern zones and scattered showers and
thunderstorms along the coast. Visible imagery shows decent cloud
cover across much of the forecast area today, and the upper levels
are fairly saturated. As a result, there is less instability to
work with as the cold pool pushes southward, which should result
in shallow convection.

Convection allowing short term guidance is still having a hard time
initializing the showers and thunderstorms this morning. Therefore,
currently have low confidence in the HRRR, RAP, and SREF solutions,
which are still showing heavy precip clearing the coast by late this evening.
For the most part, kept with what we already had in the forecast
for PoPs, but did lower them a tad to account for the current
radar trends.

Temperatures also appear to be on track, so only
ingested current observations into the forecast. High
temperatures today will struggle to reach into the 80s. Expecting
temperatures to max out this afternoon in the mid-upper 70s.

Hathaway

[DoctorMu]

One cue, the outflow boundary crushes CLL. Feast or famine. The cell over us now is taking aim down 6 and 290 toward NW Harris Co.

[Cromagnum]

Absolute bust so far as the meso lurked just north last night Leon Country drenched, while CLL remained dry. There is still some hope for outflow boundaries and daytime heating, instability to give us a taste of rain. There's some sagging of the MCS on the radar.

Surprise surprise. Always a dart game with this stuff.

[DoctorMu]

Absolute bust so far as the meso lurked just north last night Leon Country drenched, while CLL remained dry. There is still some hope for outflow boundaries and daytime heating, instability to give us a taste of rain. There's some sagging of the MCS on the radar.

Surprise surprise. Always a dart game with this stuff.

That board is falling toward Harris Co right now...

[unome]

https://mesonet.agron.iastate.edu/lsr/# ... 20459/0101

Time: 2017-04-11T16:30:00Z UTC
Event: TSTM WND DMG
Source: BROADCAST MEDIA
Remark: TWO SMALL TREES SNAPPED ON THE CAMPUS OF TEXAS A AND M.

[srainhoutx]

The Weather Prediction Center shifts a Slight Risk for Excessive Rainfall a bit NE to now include Metro Houston.

[mcheer23]

Storms finally starting to push a little faster toward Houston.

[jabcwb2]

Power is out in Greenspoint. High winds

[jasons2k]

Yeah, moving pretty fast now. I may not even get an inch of rain. Sitting at .60" for now.

[srainhoutx]

Midday Tuesday briefing from Jeff:

Serious flash flood event unfolding over C TX along I-35…major flooding forecasted along the Navasota River.

Within the last 2 hours excessive rainfall of 4-6 inches has occurred along I-35 over the City of San Marcos which is leading to very rapid rises on area creeks throughout the city. Additionally, overnight and this morning rainfall of 10-12 inches has fallen between Austin and Waco along and west of I-35 which has resulted in serious flooding along I-35. Run-off into the middle Brazos River and Navasota River will result in rapid rises over the next 24-72 hours. Significant inflows are currently expected into Lake Limestone on the upper Navasota basin requiring flood gate operations. Major flooding is forecast at all locations below Lake Limestone and the current forecasts are within 1-2 feet of record crests.

Significant rises on the middle Brazos basin will occur with the forecast for Bryan to crest just below flood stage.

Additional heavy rainfall over much of the area this afternoon will only complicate the current forecasts.

[tireman4]

Here it comes...

US64 KHGX 111725
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1225 PM CDT Tue Apr 11 2017

.AVIATION...
Overnight convection that was just north of the CWA is continuing
to sag south into the rest of the region at this time. Have added
the mention of TSRA in the TAFS based on current trends. Clearing
skies expected overnight and along with lighter winds/wet grounds
have kept with the mention of patchy fog toward sunrise tomorrow.
Going with SCT/BKN CU tomorrow afternoon, but likely VFR. 41

&&

.PREV DISCUSSION... /ISSUED 1203 PM CDT Tue Apr 11 2017/

UPDATE...
Storms are continuing to track further south. Adjusted the
forecast to account for the radar trends as precip continues to
fill in just north of I-10. Bumped up PoPs to account for the
shower and thunderstorm development.

Hathaway

[BlueJay]

We have received nearly an inch since about 11:30'ish this morning. Lovely. I won't need to water for a while.

[mcheer23]

Rain has reached US-59. Glad to FINALLY see rain across the area.

[txflagwaver]

Temperature has dropped I know 20°. Wind blew all the pine cones off the tree. Now pouring like crazy! Will no doubt have street flooding in the Space Center Blvd / Bay Area/ El Camino/ El Dorado area.