May 2017: Memorial Day/End Of May Outlook

General Weather Discussions and Analysis

Re: May 2017 Weather -Active pattern contine?

Postby tireman4 » Wed May 03, 2017 12:35 pm

XUS64 KHGX 031601
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1101 AM CDT Wed May 3 2017

.UPDATE...
Bulk of thunderstorm activity continues to focus east of Southeast
Texas along a warm front stretching along the Louisiana coast
northwest towards Lufkin/Nacogdoches. Upper air soundings from
Corpus Christi and Del Rio showed 700 MB temperatures in excess of
10 degrees F over South Central and Southwest Texas, and with the
persistent southwest flow aloft across most of Southeast Texas
this morning per the KHGX VAD wind profiler... this has allowed
the cap to build farther east into the region this morning.
Interestingly, it appears the cap has built in as far east as the
Houston metro with mid level temperatures (around 750 MB) warming
nearly 4 degrees C between 1230Z and 15Z per aircraft soundings
out of Houston.

Still expect to see scattered to numerous showers develop beneath
the cap today (mainly along and east of Interstate 45),
especially as temperatures rise into the low to mid 80s this
afternoon. Will have to continue to monitor the extreme eastern
counties (Polk, San Jacinto, Liberty, and Chambers) for a possible
isolated flash flood risk should the warm front sag back into the
area this afternoon, but confidence in this occurrence is low as
subsidence associated with the thunderstorms over southern
Louisiana may also suppress more robust convective development
over the region and limit a heavy rain threat. However, a tornado
threat will continue to persist across portions of Liberty and
Chambers Counties as well as Galveston Bay through at least the
remainder of the morning with these locations being very close to
where thunderstorms are regenerating over Louisiana/extreme
southeastern Texas and low level shear is promoting 0-3 km storm
relative helicity values in excess of 300 m2/s2 per SPC
mesoanalysis. Tornado Watch 190 remains in effect for these areas
through 5 PM CDT.

Surface analysis as of 13Z showed the next feature of interest, a
cold front, stretching from near Sanderson to Abilene to Wichita
Falls and this front will continue to sweep across the state
today. Current timing for the front places it into the northern
counties late this afternoon/early evening with the front moving
off the Upper Texas Coast early Thursday morning. Increasing
instability ahead of the front as well as additional lift from a
passing shortwave trough swinging across the Southern Plains may
make another round of severe weather, including large hail and
damaging winds, possible along the cold front. Some uncertainty
exists on how far south and west storms will be able to build
along the front this evening owing to the presence of the
aforementioned cap. However, enough mid-level cooling may be able
to occur with the approach of the shortwave trough to weaken the
cap enough for thunderstorm development across most of Southeast
Texas with the front this evening and tonight.

Huffman
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Re: May 2017 Weather -Active pattern contine?

Postby tireman4 » Wed May 03, 2017 1:28 pm

FXUS64 KHGX 031734
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1234 PM CDT Wed May 3 2017

.AVIATION...
Mainly MVFR ceilings and developing SHRA/TSRA are expected this
afternoon and on into this evening along/ahead of a cold front.
Lower ceilings/visibilities are possible with the storms. SSW/SW
winds (gusty) ahead of the front and will shift to the NW (gusty)
behind the front. Ceilings will eventually lift after the front
moves on through with VFR conditions expected to develop during
the late night hours. Only issue tomorrow will be the gusty NW
winds (around 15 to 20 knots and higher near the coast) that will
last into the mid to late afternoon hours before slowly diminishing.
42
&&
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Re: May 2017 Weather -Active pattern contine?

Postby houstonia » Wed May 03, 2017 1:49 pm

Travel question: My brother and his wife are here in Houston visiting for the week. They had trouble getting here (spent part of the night in the bathroom of their hotel room in Blytheville, Ark) due to storms and I am wondering if they will run into equally bad weather when they leave on Saturday. They will be driving from Houston back up to Grand Rapids, MI.

Thanks for any opinions!
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Re: May 2017 Weather -Active pattern contine?

Postby houstonia » Wed May 03, 2017 1:50 pm

Risk for storms continues this afternoon:

Outlook from Jeff:

Risk for severe thunderstorms remains this afternoon and evening.

Flash flood event currently unfolding from southern Louisiana into extreme E/SE TX where warm front has stalled out allowing intense thunderstorms producing rainfall rates of 3-4 inches per hour to train from Jasper County, TX ESE along I-10 to E of Lake Charles. Storm totals this morning are nearing 8-9 inches north of Beaumont and Lake Charles.

Morning soundings from Del Rio and Corpus Christie show the formation of a capping inversion across SC TX which continues to limit the western extent of the training convection over extreme east TX into Louisiana. Mid level temperatures from aircraft ascents out of KIAH have increased 3-4 degrees since this morning. With that said, a strong cold front is advancing through N TX and will be entering SE TX later this afternoon. Visible satellite images show the low level cloud deck scattering out ahead of this boundary with strong heating taking place. Additionally another shortwave nearing the TX Big Bend will be approaching the area this afternoon likely leading to cooling of the mid levels. Air mass is extremely unstable with latest SPC meso analysis showing some extreme values of instability (4500 J/kg) across the western counties of SE TX and 3500-4000 J/kg elsewhere. Forcing along the front combined with the cooling of the mid levels will likely result in the breaking of the cap and release of “extreme” surface instability vertically along steepening lapse rates. End result will likely be a developing squall line along the front capable of damaging winds and large hail that sweeps across SE TX late this afternoon and evening. Given the instability in place some of these storms could be fairly intense.

Also starting to see development along a pre-frontal trough from east of College Station toward Lufkin and some of these storms may also become fairly strong over the next several hours.

Main question is just how far SW the line will build as SW mid level flow will continue to build the capping off the higher terrain of NE MX while mid level cooling and surface heating over SE TX work to attempt to weaken the capping. Think areas NE of a line from Austin to Columbus to Freeport stand the best chances for strong to severe thunderstorms later this afternoon.

Severe thunderstorm watch will likely be needed west of Tornado Watch 190 and south of Severe Thunderstorm Watch 191 or across much of SE TX later this afternoon if trends continue to suggest mid level capping will be broken.
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Re: May 2017 Weather -Active pattern contine?

Postby Cromagnum » Wed May 03, 2017 2:08 pm

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Re: May 2017 Weather -Active pattern contine?

Postby Ounce » Wed May 03, 2017 2:41 pm

houstonia wrote:Travel question: My brother and his wife are here in Houston visiting for the week. They had trouble getting here (spent part of the night in the bathroom of their hotel room in Blytheville, Ark) due to storms and I am wondering if they will run into equally bad weather when they leave on Saturday. They will be driving from Houston back up to Grand Rapids, MI.

Thanks for any opinions!

Weather here on Saturday will be fine. You could check the various weather websites to see how the weather looks for their journey along the way.
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Re: May 2017 Weather -Active pattern contine?

Postby TexasBreeze » Wed May 03, 2017 4:20 pm

That front is rushing southeast and not doing a whole lot so far. It looks similar to the Saturday one. Lawn watering is in full effect...
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Re: May 2017 Weather -Active pattern contine?

Postby jasons » Wed May 03, 2017 5:04 pm

Looking at the satellite, you can see where the cap starts. Pretty stark contrast, or feast vs. famine (as usual).

It's going to be close. I'm glad to see people watering their lawns...maybe that will bribe Murphy into making it rain :-)
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Re: May 2017 Weather -Active pattern contine?

Postby jasons » Wed May 03, 2017 5:16 pm

New Severe Thunderstorm watch hoisted for us...

http://www.spc.noaa.gov/products/watch/ww0192.html
Last edited by jasons on Wed May 03, 2017 5:17 pm, edited 1 time in total.
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Re: May 2017 Weather -Active pattern contine?

Postby srainhoutx » Wed May 03, 2017 5:17 pm

Wednesday evening update from Jeff:

SPC has issued a Severe Thunderstorm Watch for a large part of SE TX until midnight.

Surface cold front is advancing into the northern portions of SE TX while air mass ahead of the boundary has become extremely unstable with surface temperatures reaching the low 90’s from Austin to Huntsville pushing instability values well of 4000 J/kg. At the same time SSW/SW winds off the surface have capped off the air mass with recent 19Z special sounding released from U of H showing a significant cap in place.

Main question is will the cooling mid level temperatures associated with an incoming short wave from NW TX combined with frontal lift be enough to bust the cap allowing pent up extreme surface energy to be released vertically. General thinking is that the cap will be shattered over the next few hours allowing explosive thunderstorm development SW down the surface frontal boundary. Severe storms currently moving into Houston and Trinity Counties along the front have had a history of producing dime to golfball sized hail. Given the very high values of instability over the area…any storms that develop will likely go quickly severe with large hail and damaging winds to 60mph being the main threats. If the cap cannot be overcome, then storms will fail to develop. A quick look a visible satellite images show towering cumulus clouds attempting to punch through the capping inversion along the front between Austin and College Station, but thus far they have been unsuccessful.

Current frontal timing has the boundary passing College Station within the next hour, approaching US 59 800-1000pm and off the coast around midnight. A squall line should gradually fill in along the front over the next few hours.

Severe Thunderstorm Watch Outline:
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