May 2017: Memorial Day/End Of May Outlook

General Weather Discussions and Analysis

Re: May 2017:Weekend Showers/Storms Possible

Postby don » Sat May 20, 2017 8:17 am

The European Model also shows widespread rainfall amounts of 3-6 inches :shock: across the southern half of Southeast Texas fwiw
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Re: May 2017:Weekend Showers/Storms Possible

Postby srainhoutx » Sat May 20, 2017 8:18 am

Looking at the 13Z HRRR, the best chance of showers and storms arriving later this afternoon into the early evening hours. It is also noted via MIMIM that a strong surge of deep rich tropical moisture from the NW Caribbean is moving NW into the Gulf of Mexico suggesting more tropical juice of our Region that may coincide with the arrival of the secondary strong front on Monday into early Tuesday.

05202017 13Z hrrr_ref_frzn_scus_8.png


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Re: May 2017:Weekend Showers/Storms Possible

Postby Katdaddy » Sat May 20, 2017 9:54 am

Strong to severe thunderstorms could move into portions of SE TX later this afternoon and evening from storms over S Central and STX. A Severe Thunderstorm Watch was issued a little earlier for much of that region.

The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
South Central Texas
* Effective this Saturday morning and afternoon from 1010 AM until 500 PM CDT.
* Primary threats include...
Scattered large hail and isolated very large hail events to 2.5 inches in diameter possible
Scattered damaging wind gusts to 70 mph possible
A tornado or two possible
SUMMARY...Strong/severe storms currently west of San Antonio are
expected to develop eastward and southeastward along an outflow
boundary into a very warm and moist air mass. The stronger storms
will be capable of producing large hail and damaging wind gusts.
The severe thunderstorm watch area is approximately along and 60
statute miles either side of a line from 90 miles west northwest of
Cotulla TX to 20 miles east northeast of Victoria TX.
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Re: May 2017:Weekend Showers/Storms Possible

Postby DoctorMu » Sat May 20, 2017 12:04 pm

Today was off to a good start in CLL.

The secret was to run the sprinkler system last night as a "prime the pump" strategy...and sure enough, a couple of hours later and before 6am the heavens opened as the outflow boundary/meso held together.

1.2 in IMBY and the first significant rainfall in weeks.

The meso SW of San Antonio has potential later today as it eases NE along the boundary. The cap in the HOU might break in mid-afternoon. Stay tuned.
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Re: May 2017:Weekend Showers/Storms Possible

Postby DoctorMu » Sat May 20, 2017 12:10 pm

Cap battling triggering mechanisms for showers across outflow boundaries.

The cold front has the potential to stall though before disturbances from Mexico move across the region.


Potential for Feast or Famine! - sounds like an iconic Texas forecast


Area Forecast Discussion
National Weather Service Houston/Galveston TX
1239 PM CDT Sat May 20 2017

.AVIATION...
Daytime heating could bring increasing SHRA/TSRA coverage for area TAF
sites this afternoon, so 18Z TAFs are carrying VCSH/VCTS through around
21/01Z. Hard to time disturbances moving across the state in combination
with any mesoscale boundaries are expected to bring periods of SHRA/TSRA
to the area tonight and tomorrow.
Mainly MVFR ceilings are anticipated
during the overnight hours, with VFR conditions anticipated during
the day outside of the storms. We`ll also be dealing with a cold front
and associated wind shift to the north and northeast later tonight
and tomorrow. 42
&&

.PREV DISCUSSION... /ISSUED 1101 AM CDT Sat May 20 2017/

UPDATE...
The line of showers and thunderstorms that moved across the
northeastern counties earlier this morning along an outflow
boundary have cleared
the region, but radar imagery shows isolated
cells developing across the northern half of the forecast area in
its wake. Visible satellite imagery shows an outflow boundary
associated with this line stretching from roughly Brenham to
Cleveland, with surface analysis revealing another outflow
boundary northwest of the region stretching from San Antonio to
Ft. Hood. Expect both of these features to serve as focusing
mechanisms for additional shower (and possibly thunderstorm
development) today as temperatures continue to rise into the 80s.


The environment across Southeast Texas today is capable of
producing thunderstorms today, but have low confidence in overall
coverage
. Stabilization behind this morning`s thunderstorms may
limit development along the northwestern outflow boundary for the
next few hours as it sags across the Brazos Valley, with anvil
debris from ongoing convection near San Antonio`s area also
inhibiting better destabilization across the northern counties as
it advects to the northeast. Additional development is expected
along the southern outflow boundary, but aircraft soundings out of
Houston continue to show mid-level temperatures ranging from 10-12
degrees C and provide enough of a cap to also limit thunderstorm
development.
However, morning upper air analysis showed strong
divergence across the region in response to the upper low lifting
across the Central Plains and this may be enough to overcome the
aforementioned factors. Cannot rule out a strong or severe
thunderstorm producing large hail or damaging winds given mid-
level lapse rates around 7 C/km per SPC mesoanalysis, but this is
all contingent on thunderstorm development. Brief heavy rain will
also be capable in stronger activity.

The HRRR/RAP show any activity developing today sweeping from
northwest to southeast as a cold front stretching from Presidio to
south of the D/FW Metroplex overtakes both outflow boundaries
this afternoon and evening. However, RAP VAD wind profilers show
mid level flow becoming increasingly weak/light during the
afternoon hours and consistent with the previous forecast am
concerned that this may result in the front slowing down or
stalling across the region.
This would result in possibly another
round of rain this evening or tonight as subtle disturbances lift
out of Mexico.
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Re: May 2017:Weekend Showers/Storms Possible

Postby Cromagnum » Sat May 20, 2017 2:36 pm

Gonna go ahead and call bust. Really hope I'm wrong.
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Re: May 2017:Weekend Showers/Storms Possible

Postby mckinne63 » Sat May 20, 2017 3:17 pm

Bust that cap! Just cloudy muggy and humid. :(
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Re: May 2017:Weekend Showers/Storms Possible

Postby DoctorMu » Sat May 20, 2017 8:55 pm

A few scattered showers emerging along the outflow boundary this evening.

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Re: May 2017:Weekend Showers/Storms Possible

Postby Katdaddy » Sun May 21, 2017 7:23 am

.30" early this morning of well needed rain and more on the way. SE TX is in a Moderate Risk for flash flooding tomorrow and expect a Flash Flood Watch to be issued later today. Its been awhile since the windows have condensated from deep tropical moisture.
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Re: May 2017:Weekend Showers/Storms Possible

Postby Katdaddy » Sun May 21, 2017 7:34 am

Latest from Jeff Linder....
Heavy Rainfall Event becoming likely tonight-Monday night.

Flash flooding possible over the region…flash flood watch may be required later today.

Surface front is currently stalling near the coast this morning after an active night of severe thunderstorms producing large hail along and N of I-10. Area is currently in a break between upper level impulses aloft with the next disturbance currently crossing SW TX and will be arriving later this morning across the area. Expect showers and thunderstorms to develop near the stalled frontal boundary across our coastal counties from Matagorda Bay to TX/LA state line and move very slowly this afternoon. This will promote a short fused flash flood threat due to slow cell motions and high rainfall rates. Should see activity weaken and dissipate by early evening.

Tonight-Monday:

Big concern is this period as a very strong short wave trough ejects out of NE MX and across SE TX late tonight and on Monday. Stalled front will remain across the region and PWS climb to extremely high values of 1.9-2.2 inches during this period which is concerning. Upper level winds become strongly divergent (split) aloft helping to vent convection. Parameters are pointing toward an increasing flash flood threat on Monday. Main question will be the exact location of the surface frontal boundary as this will determine where the maximum rainfall occurs. Models are keying in on the US 59 corridor to just offshore for this boundary and this area will likely be at the most threat which also happens to be where storms may develop today and wet the grounds. Should storms develop near the coast or offshore most of the inland locations would be robbed on moisture and rainfall amounts would be fairly low.
With PWS getting up and even above 2.0 inches on Monday the threat for intense short duration rainfall rates of 2-4 inches per hour is threat. Slow storm motions and potential for cell training or cell anchoring will be increasing which will increase help to promote areas where training occurs under intense rainfall rates at a flash flood risk. Patterns like this in the past have certainly produced flooding over the region and some impressive rainfall totals (ie Danbury in April with nearly 11 inches in about 3 hrs).

While grounds remain generally dry across the region, expected rainfall intensities will likely exceed short duration flash flood guidance resulting in run-off which is why WPC has increased the flash flood threat to moderate through Monday night.

Widespread rainfall amounts of 2-3 inches appear likely with much higher totals (8+inches) under any cell training or anchoring. The spatial coverage of the maximum amounts should be small which will help to mitigate the flooding concerns to just those areas.

Tuesday:

Area should get a break at some point Monday night, but a couple of short waves dropping SE in the NW flow aloft on Tuesday will likely spark a thunderstorms complex over NW TX Monday evening which may arrive in some fashion across SE TX on Tuesday. This could bring additional heavy rainfall to the region along with potential severe weather if in fact it makes it this far SE.
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