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TX SVR WX JAN 7-9 2013
01-06-2013, 06:12 PM
Post: #1
TX SVR WX JAN 7-9 2013
Happy new year! From Jeff Linder:

Quote:MAJOR STORM SYSTEM
Increasing potential for widespread heavy rainfall and severe weather Tues-Thurs.

A powerful upper level storm system currently of the California coast will bring high impact weather to much of the state of TX this week.

Discussion:

The potent upper level system will dig SE into N MX over the next 24 hours resulting in the activation of the cold frontal boundary over the western Gulf of Mexico. This front will begin to return northward as a warm front, while above the surface strong moisture advection brings clouds and developing rainfall rapidly northward off the western Gulf by late Monday night. This is in response to deepen moisture profiles and increasing large scale lift. The powerful upper level storm moves into and across TX from the Big Bend area toward NC TX on Tues-Thurs. Surface low pressure will form somewhere over the lower Rio Grande plains and track ENE to NE across SC into EC TX Tues-Wed bringing a warm front northward over nearly all of SE TX. Widespread heavy rainfall is likely with this set up along with sporadic severe weather.

Heavy Rainfall/Flood Threat:

Models and HPC QPF guidance is really pegging the area with some large totals. Moisture level do increase significantly late Monday into Tuesday with PWS approaching 1.6-1.8 inches on Tuesday….which is above +2SD of normal for early January and at or above maximum expected values. This alone raises a warning flag for excessive rainfall, but combine those moisture levels with sustained lift and surface boundaries such as a warm front or slow moving cold front and the potential for flooding rainfall increases. Forecast soundings show a nearly saturated air column by Tuesday afternoon suggesting efficient rainfall processes…or high rainfall rates. Model guidance has been fairly consistent on the placement of amounts of rainfall with this event.

Expect widespread 2-4 inches across much of the area with isolated totals of 4-6 inches possible. Given already moist to wet grounds much of this rainfall is going to run-off. Additionally hourly rainfall rates under the stronger storms may average 1-3 inches suggesting a higher urban flooding threat. With the upper level system slowing as it moves into TX, the threat for training thunderstorms will be increasing and be prolonged from late Tuesday into Wednesday evening. Significant rises on area watersheds appears likely with the amount of rainfall forecasted.

A Flash Flood Watch will likely be required if forecasted rainfall amounts continue to look likely.

Severe Weather:

This system will be highly dynamic with a well defined warm sector spreading inland over the TX coastal plains overspread by strong winds aloft. Track of the surface low will be important for defining where the greatest severe weather threat will reside…best determination at this time is for the surface low to track from near Laredo toward College Station and then toward NW LA with the warm front moving inland across all of SE TX. Elevated instability above the retreating cold dome on Monday night into Tuesday morning will support a threat for strong to severe thunderstorms near the warm front or from north of Corpus Christi to Matagorda Bay. Low level wind shear will increase on Tuesday as ESE to SE surface winds veer to SW mid level flow and increase with height producing strong low level wind shear. Thunderstorms that develop along the warm front or in the warm sector will have very favorable low level turning in place for updraft rotation. Low level helicity values increase to 300-500 m^2/s^2 on Tuesday supporting tornado production in supercell type thunderstorms. Only limiting factor may be a lack of good instability with forecasted CAPE values of 400-800 J/Kg. The setup is similar to the 1-9-12 tornado outbreak over SE TX, only this event will be much longer in duration and wind fields slightly stronger.

Main severe threat will be damaging winds and tornadoes. Some sort of squall line or MCS feature may eventually develop over the coastal bend into C TX Wed-Wed PM and spread toward the coast ahead of a Pacific cold front/dry line. Area may very well be in for a prolonged (12-24 hour) period of severe weather threat from Tuesday PM to Wed PM.

SPC has already outlooked the SW parts of the area for severe weather on Tuesday and much of the area on Wednesday.
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01-06-2013, 11:53 PM
Post: #2
TX SVR WX JAN 7-9 2013
Local (Houston) mets are saying 2+ inches of rain Tuesday and another 2+ inches of rain Wednesday. Mentioning the potential for some severe, but saying the rain fall in the biggest concern.
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