***Major storm system to impact TX Saturday-Tuesday***
***Significant rainfall, flash flooding, river flooding, severe weather increasingly likely***
Discussion:
Developing upper level storm system currently over the NW Rockies will drift southward into the SW US while increasing in intensity. Sub-tropical jet stream is clearly seen arcing through MX this morning and the position of the upper level system by late Saturday over NM will place much of TX in a highly favorable divergent upper air pattern. Moisture will begin to increase from the Gulf of Mexico today out west and in across SE TX on Saturday. Models are coming into fairly good agreement on a period of sustained lift from late Sunday into much of Monday and even Tuesday as the very slow moving upper level storm drifts across TX. Also starting to see better indications of a stalled surface trough or even frontal boundary in the mix which will really help to focus the rainfall. Moisture levels by late Sunday at near climo maximums for this time of year with PWS pushing 2.0 inches. This combined with the strong dynamics aloft and hour after hour of sustained lift is very concerning for the potential for prolonged cell training of excessive rainfall.
Can’t rule out fast moving S to N showers on Saturday, but think much of the day will be mostly cloudy and breezy as moisture increases. Strong short wave rotating around the upper level system into the Big Bend region Saturday evening and into C TX early Sunday looks like the trigger to set things off to our west that then slowly move into our area on Sunday. Would not be surprised to see this slowed down a little more with such a slow moving storm system
Rainfall:
Starting to feel more confident in widespread big totals across not only SE TX, but much of C and N TX. Will broadbrush amounts of 3-5 inches widespread across nearly all of C, N, and E TX with several locations of isolated totals greater than 6-8 inches. Really hard to attempt to pin point that upper bound with such a favorable set up and prolonged event. Would not at all be surprised for a few isolated locations to see 12 inches or more of rainfall. QPF “bullseye” has shifted more SE into SE TX over the last 24 hrs and this trend is concerning. Where any training establishes is where some really big totals will be likely along with a significant flash flood threat. Think the greatest threat period will be late Sunday afternoon-Tuesday for SE TX.
Hydro:
Widespread prolonged nature of the event with large areas of high QPF is very worrying for area rivers which are still in recovery from the early March rains. Flood control lakes are in the process of evacuating their remaining flood pools, but there is a large amount of above normal water within many of the river systems over eastern TX and most are running well above base flow. Grounds are not soggy, but they are not dry which will only add to the run-off. Think all river basins over SE TX from the Guadalupe to the SW to the Sabine in the east are in play with this event and current forecasted rainfall amounts would bring many likely to or above flood stage. Based on current QPF patterns I am getting very worried about the Brazos and Navasota Basins with nearly 5-7 inches of QPF across almost the entire basins over a 2-4 day period. That is a tremendous amount of water to be forced on those systems.
Severe:
Starting to see a few more parameters for severe weather Sunday-Monday with better instability. Think main threats will be damaging wind gusts with hail and tornadoes secondary. This still does not look like a big severe weather event, but can’t rule out small scale bow echoes or wind damage along any organized convective system coming out of C TX. The flash flood threat continues to be the primary threat.
5-Day QPF (Rainfall)
Persons with outdoor plans this weekend, especially Sunday, should be fully aware of the threat for rapidly changing weather conditions. Persons across C TX should be fully aware of the potential for flash flooding along creeks and rivers and make sure cell phone weather ALERTS are enabled on their phone, especially for anyone planning to be near any of those river basins. One of the biggest lessons learned from the Blanco River/Wimberley Flood last year was that warning were out, but residents in danger were not getting those warnings.
