Strong to severe thunderstorms are possible across portions of southcentral Texas and the Hill Country later tonight or early Tuesday morning. Even better yet, some of the storms will also produce locally heavy rainfall...
As mentioned in the update to the weekly outlook yesterday, an upper-level weather disturbance over Mexico had slown its Northeastward progress late in the weekend, and will now impact the Lone Star State tonight into the first half of Tuesday. This delay was a good thing, as it has allowed for low-level moisture to increase out of the Gulf of Mexico across the region, as you can see on the latest analysis of the surface dew point (below):
As mentioned in the update to the weekly outlook yesterday, an upper-level weather disturbance over Mexico had slown its Northeastward progress late in the weekend, and will now impact the Lone Star State tonight into the first half of Tuesday. This delay was a good thing, as it has allowed for low-level moisture to increase out of the Gulf of Mexico across the region, as you can see on the latest analysis of the surface dew point (below):
Dew points are already well into the 60s and even approaching the lower 70s across southcentral and southeast Texas (brighter green shaded areas along the Gulf Coast), and the atmosphere will continue to moisten through tonight. This means that there will be plenty of "fuel" for shower and thunderstorm activity as the disturbance moves out into the region later tonight.
Meanwhile, the disturbance in question is currently located over northwestern Mexico, as indicated by the red circled area on the latest water vapor satellite image below:
Stronger winds in the middle and upper levels of the atmosphere are already spreading out across Texas ahead of the system, as shown by the red arrows on the same image.
Computer forecast models are currently suggesting that the main body of the disturbance, which will kick-off shower and thunderstorm activity across the region, will move to near the Rio Grande by about 3am Tuesday morning, and then across the Hill Country and into the Austin-San Antonio corridor toward or just after dawn.
Some of the thunderstorms that develop could become severe, with large hail and damaging wind gusts the primary threats. An isolated tornado or two also cannot be ruled out due to the strength of the winds in the middle and upper atmosphere and how the wind direction will change with height from the surface level on upward. The primary threat of severe weather is expected to take place within the yellow shaded area on the image below (which includes the Austin and San Antonio areas):
Depending upon the exact coverage and speed of movement of the activity late tonight and early Tuesday, it could make for a rough commute in the Austin-San Antonio areas on Tuesday morning, but I know that no one will be complaining about the rain!
Speaking of rain, some of it could be locally heavy. Rainfall amounts of around 1 inch will be widespread, and localized amounts of 2-3 inches are possible in some of the areas that experience repeat thunderstorm activity, especially within the brighter blue shaded area on the image below:
Since the threat of severe weather will take place during the nighttime or early morning hours in most areas, it would be a good idea to have a NOAA Weather Radio with battery back-up on hand. You can actually program newer units to only alert you to severe weather that is threatening your specific area. These units are available at RadioShack and most other major retail stores.
I'll make an updated post later this afternoon or early this evening, and will attempt to be even more specific with regard to the expected time of arrival of the activity later tonight.
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