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Still a lot can change between now and Tuesday.
Moderator: S2k Moderators
Slow moving significant storm system to impact TX much of this week.
Severe weather and flooding rainfall over multiple days will be possible.
Discussion:
Powerful upper level storm system arriving into CA this morning will move SE into the SW US on Monday and then into MX on Tuesday where it slows and deepens. SE winds are already underway over TX helping to transport moisture into the region from the Gulf of Mexico, but this current moisture advection is shallow and trapped beneath a strong 800mb inversion (cap). This capping will maintain itself into Monday afternoon, before much more significant moisture arrives late Monday into early Tuesday. Moisture values climb from 1.0 in of PW to nearly 1.8 inches of PW by Tuesday afternoon which would be near record values for early March. Additionally, dry layer above 800mb rapidly moistens on Tuesday with the air column becoming nearly saturated by Tuesday afternoon. Upper level forcing will spread out of MX and across TX Tuesday-Thursday with several surface low formations and rounds of thunderstorms. Capping in the mid levels will be eroded by Tuesday afternoon from incoming cold air aloft along with several upper air disturbances and jet streaks. Upper winds become strong divergent early Wednesday morning and think this is when a very active period is going to transpire.
Monday night/Tuesday:
Short wave will eject out of the incoming large scale trough and develop thunderstorms over NE MX and SW TX. Some of these storms will become severe and this activity will move eastward, but likely weaken early Tuesday morning over C TX. Will need to watch for any boundary trying to move into SE TX early Tuesday that would help to focus development Tuesday afternoon.
Tuesday afternoon-Wednesday midday:
Significant short wave disturbance will likely result in widespread thunderstorms, heavy rainfall, and flash flooding.
Departing short wave Tuesday morning will give way to strong SE onshore flow by midday with significant moisture advection on a 50-60kt low level jet across coastal TX. Air mass will become increasingly unstable with current forecast sounding showing CAPE of over 2000 J/kg and LI’s down in the -4 area. Breaks in the overcast will only lead to more destabilization. Strong lift will spread across SW TX by early Tuesday afternoon and expect vigorous thunderstorm formation in NE MX/SW TX which will then move eastward Tuesday night. Severe parameters are maintained all night with a dramatic increase in the low level shear profiles Tuesday night favoring a threat for tornadoes and wind damage. Not sure how much development will occur over the warm sector ahead of what will by this time become a very well defined MCS over the TX coast bend into C TX where severe and excessive rainfall will be ongoing. Certainly could be cells developing in the warm sector with a tornado threat Tuesday evening and all night over SE TX. Severe probabilities upgrade may be required in additional outlooks if the tornado threat looks higher. All severe modes will be possible at this time with wind and tornadoes the greatest.
Other significant concern is going to be excessive rainfall and flash flooding. Well defined MCS will move slowly eastward into highly moist air mass being fed by 50-60kt low level jet Tuesday night/Wednesday morning. Forecast models want to slow down this MCS over coastal TX/SE TX Wednesday morning where favored wind field become parallel to the mean upper level flow…the result will likely be a period of prolonged cell training and cell mergers. Saturated air column in this setup is concerning for high hourly rainfall rates of 1-3 inches per hour and rapid onset flash flood event. HPC has already outlooked much of the region for slight to moderate risk for flash flooding and excessive rainfall.
Widespread rainfall amounts of 3-5 inches appear likely with isolated totals of 6-8 inches especially east of I-45 where cell training appears the greatest threat. 24-hour storm total from 600am Tuesday to 600am Wednesday are very impressive over the region with a solid 2-4 inches likely. Models have been trending southward and southwest with the axis of maximum rainfall the last few days from around Little Rock now toward Toledo Bend…which is concerning as values around the Sabine River in that same 24 hour period could be 6-9 inches.
Rainfall of this magnitude will cause significant rises on area creeks, bayous, and rivers. I am really worried about the Trinity and San Jacinto Basins given basin wide amounts of 3-5 inches is looking likely. However rises on all basins is almost certain given the widespread nature of the event. Urban flash flooding will also be a concern with higher hourly rainfall rates.
Wednesday afternoon-Thursday:
Hopefully the area will get into a break by Wednesday afternoon and Wednesday evening before another strong short wave rotates around the parent upper level storm which by this time will be located over NE MX/SW TX. Strong height falls will force surface low pressure over S TX which will move NE along or offshore of the TX coast. Current track of this feature is just offshore of SE TX coast and then inland over far E TX/W LA on Thursday. The track of this feature will be very important on additional rainfall on Thursday as another significant round of excessive rainfall will focus on the north and eastern side of this feature Thursday. Think our eastern counties could get clipped by this with the majority of the excessive rainfall over the Sabine River valley where another 6 inches could fall on top of the 6-9 inches on Wednesday. If this surface low tracks more across SE TX, then Thursday will be a very bad day across the region with excessive rainfall and flash flooding almost certain.
Friday:
Not done yet! Main upper level low will eject across TX during the day Friday into possibly Saturday. Very cold air aloft will result in an unstable air mass over the region by late morning with showers and thunderstorms developing. Cold air favors a hail threat with these storms. Think moisture will somewhat limited by Friday, but by that time any additional rainfall will likely lead to problems. Should see the main storm system exit to the east by late Friday, but the latest ECMWF is slower once again and lingers the system over the area in Saturday which would keep rain chances going another day.
Tides:
Strong onshore flow will develop later today and continue for the next 48 hours. SE winds of 25-35mph will raise tide levels along the coast and likely result in tidal run-up and minor coastal flooding at high tide on Monday with better potential on Tuesday as wave run-up is maximized. Total water levels may be up around 2.5-3.5 ft by Tuesday afternoon which could cause issues on Bolivar, near Surfside, and on the western side of Galveston Bay at Shoreacres.
Tireman4 wrote:Houston soundings?
TeamPlayersBlue wrote:Looking at the nino 1-2 region and how it has warmed up, is this likely the reason why late Feb and March is so warm too? The return of my pesky 5H east of Hawaii?
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