2014 SE TX/ SW LA Weather
Posted: Sat Feb 15, 2014 2:39 pm
It's definitely not winter out today! What a pleasant break from the cold we've had this winter.
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SPC has issued a Severe Thunderstorm Watch effective until 200pm for the northern ½ of SE TX.
Slow moving upper level trough over New Mexico is spreading increasing lift across both a surface warm front over the middle and upper TX coastal waters and a 850mb front located from near Austin to Liberty. Elevated severe thunderstorms producing large hail have developed in the last hour from north of Huntsville ESE to San Jacinto County. Surface low pressure will be re-developing ESE from the Big Bend region toward the middle TX coast by early this afternoon and helping to surge the low level warm front northward to along a line from Victoria to Tomball to Livingston. Air mass south of this front is very moist with dewpoints in the lower 70’s.
For the next 3-6 hours expect elevated thunderstorms above the near surface cool layer to continue to develop mainly along and north of HWY 105 and move northward and northeast out of the area. Think the best severe threat for large hail will be north of HWY 105 and really north of a line from Madisonville to Lake Livingston. South of this line scattered showers, light rain, drizzle, and sea fog will spread northward from the Gulf. Offshore platforms indicate sea fog bank has once again formed as low 70 degree dewpoints spread across mid to upper 60 degree water temperatures. Winds are fairly gusty over the Gulf waters and should only increase today as the surface low develops east of Corpus Christi, so not overly confident that sea fog will be widespread.
This afternoon:
Surface warm front moving northward will bring a warm sector moist and increasingly unstable air mass into the southeastern ½ of the region. Low clouds and some fog will likely prevent much surface heating of the warm sector and jet dynamics aloft look only marginally favorable for good lift. SE TX lies near the eastern edge of warm mid level temperatures being advecting eastward from the higher terrain of NE MX (capping). Looking at both the HRRR and TX TECH meso modeling really does not show much development in the warm sector this afternoon as the surface low moves nearly directly over the area. Appears surface temperatures will need to warm into the mid to upper 70’s to break the capping inversion and this is likely a bit of a stretch given the overcast and light rain/drizzle that will be found in the warm sector. SPC forecasters are a little more aggressive with the threat for surface based severe weather in the warm sector this afternoon…but some many events recently have seen similar set ups with no convective results.
The concern is that if the cap does break favorable low level shear and moderate amounts of instability would support all severe threats south of the warm front (large hail, damaging winds, and tornadoes). Low level shear will be maximized along the warm frontal boundary and such boundaries are notorious for producing supercells with tornadoes. Will have to watch trends and the warm front very closely this afternoon for convective development.
Heavy Rainfall:
Moisture levels will rapidly increase today, but best forcing and training cells look to be focused over far east TX into LA and MS where 3-7 inches will be common. Most of SE TX will be at the far SW edge of a more significant flood/flash flood threat over LA today and this threat has shifted more northward and northeast overnight. Would not be surprised to see some 1-2 inch totals quickly in the stronger storms and the best area for this will be across those northern counties this morning where elevated convection is showing some signs of banding and brief training.
Impressive cold front will cross the area Monday bringing near record low temperatures.
This afternoon:
Warm air advection continues to pump low level moisture into the area from the Gulf of Mexico this morning. Surface dewpoints have risen into the upper 60’s to near 70 over much of the region along with a thick deck of low clouds and some fog. Short wave currently over the Big Bend region will move across N TX this afternoon. SW flow in the mid levels of the atmosphere has advected a warm capping later eastward from the higher terrain of northern MX across much of SE TX this morning and this is confirmed on the CRP and DRT soundings showing a large warn nose in the 850-700mb layer. Main thrust of lift with the incoming short wave will be aimed north of SE TX and suspect this will be another event where the capping wins out and any storms that develop will be up north mainly along and north of a College Station to Lake Livingston line. Would not be surprised to see a few showers across a larger portion of the area…but rainfall amounts will be light.
Tonight-Monday:
Strong late season cold front will cross the region between 600am and noon Monday. Short term models show the capping inversion weakening as a secondary short wave brings lift and mid level cooling to the region near the time the surface cold front arrives. This should help weaken the capping inversion enough to allow at least a line of showers and thunderstorms along the front. Short term meso models agree with this and show showers/thunderstorms developing early Monday morning either along or just behind the frontal boundary as it crosses the region. Instability looks to be enough to include a slight risk of severe weather for hail and wind damage, but think this threat is on the low side given the time of day that the system will be crossing the region.
Strong north winds will develop behind the front and temperatures will quickly fall into the 50’s and even the 40’s by late Monday afternoon. It will definitely feel much colder Monday afternoon/evening compared to the last few days.
Tuesday-Wednesday:
850mb 0C line pushes close to our northern counties by Tuesday morning. Think winds will stay up enough to keep temperatures in the mid to upper 30’s on Tuesday morning, but those usual cold spots could drop into the low to mid 30’s if winds weaken just before sunrise. Tuesday will be chilly by mid April standards with highs only in the low to mid 60’s. Clear skies and calm winds Tuesday night will result in a cold Wednesday morning. Guidance currently showing upper 30’s north of I-10, but we could get into the mid 30’s with some frost potential given the near clam winds. Could see a few of the colder location drop to or below freezing on Wednesday morning. Will have to keep a close watch on the temperature trends as a freeze this time of year would be fairly significant for this region.
Late week-next weekend:
GFS shows a potent looking system moving into the plain on Thursday and the ECMWF model has started to trend in that direction some over the past few runs. Not sure moisture will have returned by Thursday, but may need to add low rain chances on Thursday. Weak front looks to push into the area with this storm system and linger into next weekend. GFS has a fairly active pattern over TX for next weekend, but I have seen this time and time again this spring only to have the capping inversion squash any “real” chances of significant rainfall.
Period of prolonged high rain chances appear in the offering over the next several days and possibly beyond.
Upper air pattern supportive of past majoring flooding events in TX appears to be shaping up for most of this week across the state. 500-300mb ridging has been unable to gain a strong foothold over the state as in the past several summers and will weaken/break down even more over the next 48 hours. Upper level weakness (trough of low pressure) between an upper level high over the SW US and a second upper level high over the SW Atlantic Ocean will result in a favorable atmospheric profile for widespread showers and thunderstorms Tuesday into next weekend. Tropical tap of mid and high level moisture is seen streaming NNE across MX from the eastern Pacific while a pool of deep tropical moisture over the central Caribbean Sea (PWS at or above 2.0 inches) is moving WNW and will landfall on the TX coast by Tuesday afternoon.
Global models are in fair enough agreement suggesting a trough or shear axis will actually become increasingly better defined along and east of I-35 during the week and begin to interact with the surging Caribbean moisture. Forecasted profiles show the atmosphere becoming saturated with time as the air mass takes on strong tropical characteristics.
First will see an increase in seabreeze generated convection Tuesday as the moisture surges inland and the lack of capping from upper level ridging allows low trigger temperatures (mid 80’s). Extremely tropical air mass will be in place by mid week and threat will then focus on potential overnight/early morning speed convergence near/along the coast to enhance thunderstorms. Rainfall rates will be fairly high in such an air mass and there appears to be little change in the pattern through next weekend so daily shots of heavy rainfall appear at least possible.
Patterns such as this in the past (July 2012 and July 2002) have resulted in significant rainfall amounts and major flooding across portions of TX as weak vort centers tend to focus much like dying tropical systems in such a tropical like air mass and storm motions tend to be on the very slow side. The CMC model was hinting at such a feature developing over SE TX in the Wed-Thurs time period and lifting north into N TX by late week, but it is the only global model showing such a well defined feature at the moment and is likely on the extreme end of the spectrum.
Regardless additional rainfall appears likely helping to reduce drought conditions and hopefully generate some run-off into area lakes.