Another round of severe weather and heavy rainfall will move across SE TX Wednesday evening into Thursday morning.
A weak disturbance in the SW flow aloft will likely produce a few showers over the area this morning before moving east of the region by early afternoon.
An upper level trough over the SW US will move east across TX tomorrow while a slow moving cool front sags southward over NC TX and into SE TX Wednesday evening. Low level moisture is already returning with dewpoints well into the 60s over much of the region this morning. Moisture will continue to increase over the next 24-36 hours with PWS peaking near 1.9 inches Wednesday evening. Air mass on Wednesday will become increasingly unstable with modest surface heating, but capping in the mid levels should preclude much in the way of thunderstorms. Will likely see a few scattered warm air advection type showers move from the Gulf northward across the area.
Main event comes Wednesday night as a strong upper level disturbance combined with good dynamics aloft, high moisture levels, and a surface front move across the region. Expect a cluster or line of strong to severe thunderstorms to develop Wednesday afternoon over SC TX and move into SE TX Wednesday evening. Main threats will be damaging straight line winds and large hail. SPC has the western and southwestern portions of our area in the Day 2 slight risk.
Other threat will be heavy rainfall with a slow moving line of thunderstorms into Wednesday morning. Widespread rainfall amounts of 1-2 inches appear likely with isolated totals of 3-4 inches where any cell training occurs. Grounds are starting to become wet across the region…especially north of I-10 from the recent rainfall and the middle Trinity and Navasota Rivers are in minor flood, so additional widespread rainfall will likely cause additional rises on area rivers.
SPC Day 2 (Wednesday) Severe Weather Outlook:
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After looking at the morning model runs, not surprised the SPC has decided to expand the 'Slight Risk' further to the east to include SETX. Discussion is below...
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1224 PM CDT Tue Apr 23 2019
Valid 241200Z - 251200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
SOUTHERN AND CENTRAL TEXAS INTO FAR SOUTHWEST LOUISIANA...
...SUMMARY...
Thunderstorms associated with large hail, wind damage and a tornado
threat are expected to develop across parts of southern and
southeast Texas into far southwest Louisiana on Wednesday and
Wednesday night.
...TX and LA Vicinity...
Convection will likely be ongoing Wednesday morning from western
into north-central TX on the cool side of surface cold front. This
activity is not likely to be severe during the morning hours. By
afternoon, additional thunderstorm development is expected in the
warm sector across parts of the central TX when stronger ascent
associated with the eastward advancing upper low overspreads the
region. Southeasterly low level flow will maintain Gulf moisture
ahead of the surface boundary, and dewpoints in the mid 60s to low
70s F are already in place. While cloud cover may inhibit
development through the morning hours, by afternoon, temperatures
warming into the upper 70s and low 80s beneath steepening midlevel
lapse rates should result in 1000-2000 J/kg MLCAPE from the Rio
Grande Valley toward the Upper Texas Coast. Semi-discrete supercells
may develop initially, posing a threat for large hail and damaging
wind gusts. A tornado threat is also possible, given backed low
level flow and maximized SRH in the vicinity of the frontal boundary
and weak surface low.
Convection is expected to grow upscale during the late
afternoon/evening across central TX and track eastward toward
southern portions of the Sabine River Valley/southeast LA overnight.
Latest model guidance suggests a 35-45kt southerly low level jet
will develop ahead of the bowing segment, with deep layer shear,
adequate instability and abundant boundary layer moisture more than
capable of maintaining eastward progression of the line. Thus, an
attendant threat for damaging wind gusts and possibly a QLCS tornado
will extend into southeast TX and far southwest LA overnight.
Time to be weather aware again. An active weather day and night ahead across a large portion of TX. Strong to severe thunderstorms with heavy rain and flash flooding have been moving across the Hill Country, NW TX, N Central and N TX overnight. The strong to severe thunderstorms with heavy rain will move across Central and S Central TX this morning through the afternoon which will then progress across SE and E TX tonight through early Thursday morning.
The Weather Prediction Center has issued a Slight Risk for Excessive Rainfall for today. Areas along and North of the I-10 Corridor appear to appear to have the best chances of seeing some heavy rainfall this afternoon into the overnight hours.
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Area Forecast Discussion
National Weather Service Houston/Galveston TX
539 AM CDT Wed Apr 24 2019
.DISCUSSION...
We have been keeping a close eye on the line of storms over NCTX
through the overnight hours, and have noted its much slower push
to the S/SE. However, there is a weak outflow associated with it
and it appears to be moving into steadily toward our NW counties
at present. This feature may be a concern for later today as the
other ingredients come together for strong/severe storms by late
this afternoon/evening. SE TX is now in the Slight Risk category
for severe weather for later this afternoon through tonight.
We should start the day here fairly quiet/warm/humid with onshore
winds picking up later this morning. As per some of the near-term
models an initial round of storms will be possible along the out-
flow boundary across the Brazos Valley by the afternoon. WV loops
are hinting at a vort max/shortwave (currently about to cross the
Rio Grande) that fits the time frame for this. These rains should
set the stage for potential flooding problems for areas in/around
the Brazos Valley as we head into this evening. A second round of
storms remains possible as the main upper low moves eastward into
our CWA. Progged dynamics continue to look strong and with a very
favorable upper jet pattern/shear profile, the severe threat will
likely remain in place even as the line of storms move into SE TX
during the evening/night time hours. Did add the mention of heavy
rain and possible severe thunderstorms for generally the northern
half of the CWFA this evening. Hail and damaging winds look to be
the primary threats but isolated tornadoes cannot be ruled out at
this time.
As this upper trof and its associated cold front moves out to the
east, we should see rapidly improving conditions across the area.
Clearing skies with much drier air moving in from the north could
make for favorable insolation for Thurs/Fri. Did lean more toward
the warmer side of MOS numbers for this time frame. Otherwise, no
real change in the extended as the warm temps persist through the
weekend and into the start of next week. Our next best chances of
rain look to be next Tues with the passage of the next upper trof.
41
&&
.MARINE...
Fetch has led to moderate seas of 4 to 6 feet across the UTCW this
morning. As the low over the Big Bend slides off to the ENE
today/tonight will see the SE flow of 10 to 18 knots continue so
will be extending the SCEC into Thursday morning for the 20-60nm
waters.
The cold front should push out into the Gulf Thursday morning
accompanied by showers and thunderstorms. Given the abundant
instability tonight over the waters would rule out strong storms
with gusty winds. The front lags the outflow boundary but should be
off the coast 8-11 am Thursday. Weak Pacific high noses into and
across SETX and out into the waters before weakening further
followed by a more continental airmass maintaining the offshore flow.
Saturday return flow gets underway and should persist through
Thursday morning. The gradient Tuesday-Thursday is impressive and
could be looking at an extended period of large swells.
45
&&
.AVIATION...
Again this morning a mix of IFR (north)-VFR (middle)-MVFR (south)
with winds having backed to the east near the coast and just inland.
Spotty light rain moving out of the eastern Hill Country and into
the CLL area with an outflow boundary pushing into KGRK area.
Expecting the line of storms to the northwest of the area to weaken
but impressive WAA should fuel the development of showers so will be
looking to add VCSH a little sooner to the CLL taf. Throughout the
day expect mix of MVFR/VFR conditions before the upper jet intrudes
and enhances the synoptic scale lift dramatically increasing the
chances for showers/thunderstorms over the CLL area gradually
shifting east and southeast tonight. Significant aviation impacts to
area with a large band of showers and thunderstorms reducing
ceilings/visibility streaming SW to NE through the region. The rains
should taper off and ceilings improve at least briefly after 09z but
some MVFR ceilings could redevelop with frontal
inversion...confidence on persistence of these is low.
45
.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION through this afternoon for
the following zones: Waters from Freeport to Matagorda Ship
Channel TX from 20 to 60 NM...Waters from High Island to
Freeport TX from 20 to 60 NM.
Mesoscale Precipitation Discussion 0157
NWS Weather Prediction Center College Park MD
926 AM EDT Wed Apr 24 2019
Areas affected...west-central to east-central TX
Concerning...Heavy rainfall...Flash flooding possible
Valid 241321Z - 241900Z
Summary...Rounds of heavy rain with repeating cell motions at
times will pose a flash flood threat into early afternoon from
west-central to east-central Texas. While not expected to be
widespread, flash flooding may occur with regions that pick up 3-5
inches in a 3 hour time frame.
Discussion...12Z surface analysis placed an outflow boundary from
near JDD, southwestward to BAZ and west to DRT. As mid-level
height falls/CVA begin to advance into western Texas ahead of an
eastward advancing closed low in northern Mexico, convection has
picked up to the north of the outflow boundary over the past hour.
850 mb flow was fairly weak at 12Z, with area VAD wind plots and
RAOB data showing roughly 15-20 kt from the south across
south-central Texas. Another low level convergence axis, centered
near 850 mb, was located from near the Big Bend region to just
east of the DFW metroplex. Locations just north of this
convergence axis were co-located with heavy rain from overnight
with roughly 2-4 inches falling. Lastly, a 110 kt upper level jet
streak was approximated via RAP analyses to be over northern
Mexico with strong diffluence and divergence aloft located over
the Trans Pecos region to western portions of the Edwards Plateau.
As the closed low over northern Mexico continues to advance east
over the next 3-6 hours, 850 mb flow is expected to strengthen to
near 30 kt as far north as roughly the I-10 corridor, east of San
Antonio while a somewhat weaker branch of the 850 mb jet curls
northwestward toward the Trans Pecos region. Low level convergence
along the surface outflow should be located with increasing MLCAPE
of near 1000-1500 J/kg per recent RAP/HRRR forecasts and
increasing upper level divergence/diffluence out ahead of the
advancing northern Mexico jet streak. Periods of rain with
rainfall rates of 1.5-2.5 in/hr and 3-hourly rates of 3-5 inches
will be possible in the vicinity of southern portions of the
outflow boundary through 19Z. Farther north near the 850 mb
convergence axis, there will be less available instability but
increasing forcing for ascent ahead of the upper low such that
repeating rounds of heavy rain with potential for 2-4 inches on a
localized basis will exist from near FST eastward to roughly ACT
in connection with the slow moving 850 mb axis of convergence.
Otto
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Severe threat with all modes increasing for Central and SE TX. Could be interesting being S and SE of the outflow boundary this afternoon and evening if discrete cells develop.
Mesoscale Discussion 0432
NWS Storm Prediction Center Norman OK
1011 AM CDT Wed Apr 24 2019
Areas affected...central into southeastern Texas
Concerning...Severe potential...Watch possible
Valid 241511Z - 241715Z
Probability of Watch Issuance...40 percent
SUMMARY...A WW issuance may be needed in portions of the discussion
area - most likely from 16Z onward.
DISCUSSION...Mostly sub-severe convection continues currently amidst
a complicated surface pattern, with a remnant outflow extending from
near CLL to 40 S SAT to near DRT. Surface-based convection persists
near the outflow, with one dominant cell over western Gonzales
county exhibiting signs of mid-level rotation. Though low-level
wind fields remain weak, any favorable interaction between updrafts
associated with this convection along the remnant outflow may result
in a brief tornado.
Over time, strengthening low-level wind fields associated with
low-level cyclogenesis and approach of a mid-level wave centered
over northern Mexico will probably result in 1) stalling and/or slow
northward retreat of the outflow and 2) gradually increased
organization of convection. Any storms near/south of this outflow
will be surface-based owing to near 70F dewpoints, while steepening
mid-level lapse rates will increase buoyancy and result in an
increased threat for all modes of severe. North of the boundary, a
gradually organizing linear complex near SJT and other scattered
convection near HDO/SAT/AUS may pose a threat for marginally severe
hail and perhaps an isolated damaging wind gust. Convective trends
continue to be monitored, and a WW issuance may be needed at some
point after 16Z or so.
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 98
NWS Storm Prediction Center Norman OK
1150 AM CDT Wed Apr 24 2019
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Parts of south central Texas and the Hill Country
* Effective this Wednesday morning and evening from 1150 AM until
700 PM CDT.
* Primary threats include...
Scattered large hail events to 1.5 inches in diameter likely
Isolated damaging wind gusts to 70 mph possible
A tornado or two possible
SUMMARY...Mainly elevated thunderstorms are expected to continue
developing through the afternoon, with large hail the main threat.
Isolated damaging gusts, and perhaps a tornado, will be possible
with storms closer to the outflow boundary that will sag southward
near the southern edge of the watch area.
The severe thunderstorm watch area is approximately along and 60
statute miles north and south of a line from 80 miles west northwest
of Cotulla TX to 50 miles east southeast of Austin TX. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU8).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.
SUMMARY...Merging streams of moisture/training repeat cells
through saturated ground conditions pose likely flash flooding
across Northern Texas. Highly efficient but faster moving storms
along front may lead to more scattered possible flash flooding
through 00z over Hill county/South Central Texas
DISCUSSION...Dynamic environmental setup with sufficient to
localized above average moisture in place across Texas. GOES-16
WV suite depicts a deep closed low is tracking across N Chihuahua
with an elongated extension of height-falls associated with a
smaller scale shortwave currently crossing out of the N Coahuila N
of the northern bend of the Rio Grande. An associated 100kt 3H
jet is oriented to favorably enhance divergence near the northeast
edge of the shortwave spurring surface deepening an low level flow
response, while providing excellent upper level outflow for strong
updrafts and deep rainfall production layer. At the surface,
last evening's cold pool remains shallow but in place from COT to
NW of VCT to 3T5, limiting surface instability across much of the
area of concern. Yet increasing LLJ from 850-7H of 30-40kts is
saturating the low level environment, with the leading
edge/moisture convergence leading to broken convective line
lifting north which will act as a pivoting deformation zone later
this evening into early overnight.
A surface low is analyzed near MKN with a cold front dropping
south-southwest just passing JCT to DRT. Strengthening NW surface
flow and deepening surface wave is starting to press the cold
front eastward, faster at the southern end with the surface low
acting as a pivot point. The strong moisture convergence is
supporting deep convection with cooling tops in 10um EIR and
increased lightning indicative of increased hail/rainfall
production. WBZ/Freezing level spread is minor and around 9-10K
supporting more efficient rainfall production given TPW of
1.5-1.7" loaded mainly below 7H/10K. This will support rates of
1.5"/hr given modest elevated instability, especially further
south. Further north, while instability is reduced, the duration
is increased as the pivot point is setting up near the surface low
and I-35. North of which was affected last evening lowering FFG
values below 1.5"/3hrs.
Hi-Res CAMs are much too slow with the eastward advancement of the
cold front, but also depict increased low level flow with the
retrograde of the old stationary outflow boundary from PSN to 3T5
will allow for increased moisture confluence as well as warmer
more unstable air...it is expected that the convergence of the
cold front and the warmer air will occur between I-35 and I-45
south of DFW likely closer to I-35 around 22-23z...this will lead
to a significant increase in rainfall rates up to 2-2.5"/hr with
slow eastward motions, leading to 3-4" totals likely north of GTU.
Given lowered FFG values due to recent and longer-term (2 week
positive anomalies per AHPS)...flash flooding is considered likely
in that 22-00z time frame.
South of the GTU, the speed of the cold front will be faster
though with greater moisture (up to 1.8" TPW), leading to reduced
totals relative to north, but faster rates like 3-4"/hr but
lasting 20-30 minutes while passing. Higher FFG values in further
south should also reduced the likelihood for flash flooding
conditions from 22-00z to possible.
Further east, the outflow boundary that stalled from 3T5 to PSN,
warm unstable air SE of the boundary is characterized by low to
mid-70s Temps and upper 60s/low 70s TDs with ideal perpendicular
flow to the boundary. As such convection has been active and
rather efficient with rates over 2.5"/hr occasionally given the
moisture flux convergence. Mean cell motions are generally
parallel or slightly east of the dying outflow boundary supporting
short-term training/repeating. Stronger height-falls and eroding
cold pool should allow for this boundary to retrograde west over
the next few hours and with high FFG values in the
region/relatively dry longer-term conditions, Flash flooding is
only considered possible for the next hour or so for Lavaca to
Madison county.
Gallina
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Area Forecast Discussion
National Weather Service Houston/Galveston TX
1225 PM CDT Wed Apr 24 2019
.AVIATION...
Some convection moving into the KCLL area and will carry a
prevailing thunder group to start the TAF period. Further south,
convective potential is a bit more iffy as capping will limit
potential through the early evening. Better jet dynamics and an
approaching front will give rain chances a boost tonight and
leaned toward a blend of guidance for timing. Convection should
reach the Houston terminals between 04-08z. Fcst soundings show
low level moisture hanging around for part of the morning and will
maintain a mix of IFR/MVFR ceilings before they scatter out after
15z. 43
watching The Weather Channel, saying it should come through here in the middle of the night, so maybe not as severe, but that always makes me worry when we expect bad weather at night
