SPC issues slight risk of severe wx for South/Southeast Tx

[jeff]

Active weather period on tap for the area.



Strong surface cold front was entering N TX this morning with a strong bow echo moving across Arkansas. The local air mass is juicy with surface dewpoints of at least 70 at most locations. Moisture pools across the region today as the surface front moves southward and greatly slows. PWS increase to near 1.8-2.0 inches by this evening or about 150% above normal for late April. Air mass will become very unstable by late afternoon as capping is completely eroded…CAPE of 2500 J/kg and LI’s of -8 to -10. Surface heating and focus along the cold front will initiate developments. Deep layer shear from an increasing mid level jet along with broad 250mb upper level divergence indicates good jet dynamics will be in place to sustain the activity into the overnight.



Severe Threat:



Front really puts on the brakes as it moves into SE TX awaiting short wave energy to cross from W TX. This means slow moving strong to severe thunderstorms lasting most of the night. There is the potential for multiple rounds of storms, although a slow moving MCS is also just as likely. Severe threat should be from late afternoon through late evening with damaging winds and large hail being the main threats. Surface cooling/slight stabilization should gradually reduce the severe threat after midnight.



Heavy Rainfall:



Factors appear to be coming together for a heavy rainfall event including: a slow moving surface focus (front), high PWS (1.8-2.0 in), broad 250mb divergence, decent low level inflow, alignment of thunderstorms parallel to the upper level flow, and a large profile of high RH through the lower and middle air column. Given the potential for slow moving high precipitation cells along with training of cells along a line….the threat for short term excessive rainfall is a possibility. Flash Flood Guidance is running in the 1.1 (1-hr) to 1.8 (6-hr) for Harris County, although rainfall amounts of 2-3 inches would likely be needed to produce significant run-off. Widespread amounts of 1-2 inches are likely with isolated 3-4 inches amounts possible.



We get a break Thursday and early Friday. Next storm system approaches this weekend. Warm front returns northward and looks active. Given the potential for increased shear along the returning warm front in combination with jet stream energy may result in a very active Saturday. The weekend system looks like it could be multi-day increasing the flooding threat with multiple rounds of thunderstorms.

[cctxhurricanewatcher]

Well all of our on air Mets and the NWS are predicting rain for late tonight into Weds morning . When it is coming down, I will believe it and I will not be turning off my sprinkler system in atticipation of it either.

[jasons2k]

Thanks for the update Jeff!

Looks like we may finally get a good soaker

[jasons2k]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1015 AM CDT TUE APR 25 2006

.DISCUSSION...
RADAR IMAGERY PUTS THE FRONTAL BOUNDARY FROM ROUGHLY CORSICANA TO
TEMPLE AND INTO NORTHERN PORTIONS OF THE HILL COUNTRY. FRONT IS
MAKING BETTER/FASTER SOUTHWARD PROGRESS ACROSS CENTRAL PORTIONS OF
THE STATE THAN EASTERN AREAS...HOWEVER OUTFLOWS FROM STORMS IN NRN
LA MAY BECOME A PLAYER LATER THIS AFTN IF THEY MAKE IT INTO NE PARTS
OF THE CWA. EXTENSIVE CLOUD COVER SHOULD LIMIT INSTABILITY ACROSS
EXTREME NORTHERN PARTS...HOWEVER THE CAPPING INVERSION IS QUITE A
BIT LESS ACROSS NORTHERN AREAS VERSUS THE SOUTH WHERE MORNING
SOUNDINGS AT LCH/CRP SHOW A NOTICEABLE WARM LAYER BETWEEN 800-850
MB. INVERSION WILL WEAKEN WITH TIME AND SURFACE HEATING BUT DON'T
THINK IT'LL BE OVERCOME UNTIL LATE AFTERNOON AT THE EARLIEST. STILL
BELIEVE THE BEST POTENTIAL WILL BE ACROSS SOUTHERN HALF TOWARD
EVENING. CURRENT THINKING IS THAT A COMBINATION OF AFTN
HEATING...INCOMING FRONTAL BOUNDARY...AND POSSIBLE SEABREEZE...MORE
FAVORABLE UPPER DIFFLUENCE MAY ALL COMBINE TO PRODUCE A ROUND OF
TSRA. ONGOING FCST PACKAGE LOOKS PRETTY GOOD. WILL SEND OUT AN
UPDATE TO BUMP TEMPS UP ACROSS SW PARTS AND TWEAK CLOUDS BASED ON
LATEST OBS.

[southerngale]

Well all of our on air Mets and the NWS are predicting rain for late tonight into Weds morning . When it is coming down, I will believe it and I will not be turning off my sprinkler system in atticipation of it either.

You sound like me. I guess we've been burned too many times.

Jeff's forecast looks promising though.

[jasons2k]

1st Mesoscale Disucssion for our area has been issued from the SPC. Can't remember the last time one of those actually applied to me.

[southerngale]

It's actually raining now. I don't think it will last long as it's just a speck on the radar, but some water is falling from the sky!

[southerngale]

Ok, it's over.

[Johnny]

Yep, popcorn convection is popping up on the east side which I think is just the beginning of things.

[Yankeegirl]

NO rain here, yet, but really really muggy!!! Yuck!!!

[Johnny]

I don't see a severe weather outbreak happening today. Sure, their might be some isolated severe storms pop up today...definately not out of the question but the cloud cover is going to hurt in seeing a widespread severe weather event. We will see some pretty healthy storms with some good rain in them no doubt starting in the next couple of hours and going into the evening with some good solid totals coming out of them. Isolated severe weather with damaging winds and large hail, yes.....widespread severe weather, no.

[Johnny]

Hmmm, I see we have some nice cloud breakage going on over our area.

[jasons2k]

Yep, they have already exceeded the forecasted high in Galveston. Almost there in Houston as well....looks like we're adding some nice fuel to the fire.

[southerngale]

I don't see a severe weather outbreak happening today. Sure, their might be some isolated severe storms pop up today...definately not out of the question but the cloud cover is going to hurt in seeing a widespread severe weather event. We will see some pretty healthy storms with some good rain in them no doubt starting in the next couple of hours and going into the evening with some good solid totals coming out of them. Isolated severe weather with damaging winds and large hail, yes.....widespread severe weather, no.

Isn't that the way it usually is around here, though?

[Johnny]

Isn't that the way it usually is around here, though?

Yes ma'm and that's what I'm basing my forecast on.

[jasons2k]

A 2nd Mesoscale Disucssion has been posted...this time it looks like a WW will be issued late PM.

[Johnny]

Hey jschlitz, can you post up the discussion if you get a minute?

[jasons2k]

Hey jschlitz, can you post up the discussion if you get a minute?

Sure, No problem!

Here is the first one:

MESOSCALE DISCUSSION 0651
NWS STORM PREDICTION CENTER NORMAN OK
1107 AM CDT TUE APR 25 2006

AREAS AFFECTED...SE TX...SRN LA...SRN MS

CONCERNING...SEVERE THUNDERSTORM POTENTIAL

VALID 251607Z - 251730Z

A WW IS NOT ANTICIPATED IN THE NEAR TERM...BUT TRENDS WILL CONTINUE
TO BE MONITORED FOR THE POSSIBILITY OF AN INCREASING SEVERE
POTENTIAL.

OUTFLOW BOUNDARY GENERATED BY OVERNIGHT CONVECTION IS ADVANCING
SLOWLY SOUTHWARD THROUGH THE LOWER MISSISSIPPI VALLEY. THIS FEATURE
HAS YET TO BECOME FOCUS FOR VIGOROUS NEW CONVECTIVE
DEVELOPMENT...BUT BROAD LOW-LEVEL WARM ADVECTION REGIME NORTH AND
SOUTH OF THE BOUNDARY IS PROVIDING SUPPORT FOR INCREASING CONVECTIVE
DEVELOPMENT. MOST VIGOROUS STORMS THROUGH 17-18Z SEEM LIKELY TO
EVOLVE TO THE SOUTH OF THE OUTFLOW...WITH ADDITIONAL ACTIVITY
EVENTUALLY DEVELOPING ALONG THE BOUNDARY ITSELF. AS CONVECTIVE
TEMPERATURES ARE APPROACHED...CONVECTION WILL BECOME ROOTED IN MIXED
BOUNDARY LAYER WITH CAPE IN EXCESS OF 2000 J/KG. LOW-LEVEL WIND
FIELDS ARE RATHER WEAK...BUT MID/UPPER FLOW APPEARS STRONG ENOUGH
FOR DEEP LAYER SHEAR FAVORABLE FOR AT LEAST BRIEF MID-LEVEL UPDRAFT
ROTATION...WHICH WILL ENHANCE POTENTIAL FOR HAIL IN STRONGER CELLS.
LOCALIZED DOWNBURSTS ARE ALSO POSSIBLE.

..KERR.. 04/25/2006


ATTN...WFO...JAN...LIX...LCH...SHV...HGX...FWD...

Graphic here:
http://www.spc.noaa.gov/products/md/md0651.html

Here is the 2nd one:

MESOSCALE DISCUSSION 0652
NWS STORM PREDICTION CENTER NORMAN OK
0135 PM CDT TUE APR 25 2006

AREAS AFFECTED...S-CNTRL TX

CONCERNING...SEVERE THUNDERSTORM POTENTIAL

VALID 251835Z - 252030Z

THUNDERSTORM INITIATION APPEARS MOST PROBABLE BETWEEN 21-23Z. A WW
WILL LIKELY BE NEEDED LATER THIS AFTERNOON.

18Z SURFACE ANALYSIS AND MODIFIED RUC SOUNDINGS SHOW A WEAKENING CAP
ACROSS S-CNTRL TX ALONG A SYNOPTIC COLD FRONT FROM NEAR DRT NEWD TO
SAT AND CLL. VISIBLE SATELLITE HAS SHOWN AGITATED CUMULUS ALONG THE
FRONT OVER THE PAST FEW HOURS. LOW-LEVEL CONVERGENCE ALONG THE FRONT
IS WEAK AND IS EXPECTED TO REMAIN SO...WITH A WEAK MESO HIGH JUST N
OF IAH. HOWEVER...AS TEMPERATURES CONTINUE TO WARM...THE FRONT
SHOULD PROVIDE ENOUGH LIFT TO INITIATE THUNDERSTORMS IN THE LATE
AFTERNOON NEAR THE MEXICO BORDER REGION AND THEN NEWD WITH TIME.
STRONG INSTABILITY WILL EXIST WITH MLCAPES OF 3000 TO 4000
J/KG...ALTHOUGH SHEAR THROUGHOUT THE LOW AND MOST OF THE MID-LEVELS
IS FAIRLY WEAK. MODEST WLY FLOW FROM 500 MB AND ABOVE WILL SUPPORT
STORM ORGANIZATION GIVEN THE HIGH CAPE VALUES. ISOLATED SUPERCELLS
PRODUCING LARGE HAIL APPEARS TO BE THE MAIN SEVERE THREAT.

..GRAMS.. 04/25/2006


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

Graphic here: http://www.spc.noaa.gov/products/md/md0652.html

[Extremeweatherguy]

wow...it is up to 88F at IAH, and 87F at Tomball. These current numbers exceed the forecasted highs by 2-3F. Also...dewpoints remain the upper 60s under variably changing skies. We are certaintly primed for severe weather today!

[cctxhurricanewatcher]

It's 90 here in Corpus with a DP at 73 as of 2PM. I haven't felt it like that in a looooongggg time. Something is getting ready to go down.