Updated 130pm CDT Thursday / 10 May 2012
…. Strong Low Pressure Disturbance to Pass Overhead over the Next 36 Hours ….
…. Beneficial Rainfall Upwards of 2 to 4 Inches …. Some Flooding Possible ….
On this Thursday… a weakening cold front extends from over the northwestern Gulf of Mexico to around Brownsville and into Mexico then northwestward to southwest of the Texas Big Bend. A surface high pressure area.. centered over northern Arkansas and southern Missouri.. is moving eastward out of our area. As a result, an east southeasterly surface wind is blowing across our area.
In the upper levels of the atmosphere, a dynamic upper level low pressure area is located over northern Mexico south and southwest of El Paso. As a result of the upper air wind flow, the upper level winds are moderate southwesterly over our area.
The strong upper air low pressure disturbance over northern Mexico will move slowly east northeastward from northern Mexico and across Texas over the next two days.
Rain is already underway across our area in advance of the system. With its slow movement, several waves of rain showers and thunderstorms are likely with precipitation tapering off by late tomorrow night into early Saturday morning. I am a little more concerned today with the flooding potential than I was yesterday at this time simply because of the slow movement of the system. Periods of heavy rain are possible.. with storm total rainfall of 2 to 4 inches with isolated heavier totals mainly to our south.. as the upper air disturbance weakens and moves east northeast of our area. As mentioned yesterday, localized flooding (urban, small creek and stream as well as low water crossings) is likely with this event. At this point, our soils are more than able to handle several inches of rain but where the rain comes very quickly, flood problems are more likely. It’s a good time to remember.. Turn Around, Don’t Drown.. the NWS slogan for flash flood safety. Here is a link to an animated 1-3 day loop (6 hour increments) of rainfall forecast from the NWS…
http://www.hpc.ncep.noaa.gov/qpf/qpfloop.html
The severe weather threat has become more of a factor than I thought it would at this time yesterday. Marginally severe hail (1 inch or larger in diameter) along with possible strong straightline thunderstorm winds will be the primary threat with the associated tornado threat mainly to our south. A reminder that you can monitor the latest day one severe weather outlook from the NWS Storm Prediction Center (SPC)…
http://www.spc.noaa.gov/products/outlook/day1otlk.html
In addition, here is a link to all current Mesoscale Discussions issued by the SPC…
http://www.spc.noaa.gov/products/md/
After this upper air system weakens and departs to the northeast of the area.. upper level winds are forecast to shift more northwesterly which will support a cold front passing southeastward through the area by late Saturday night into the predawn hours Sunday. A dry and more stable weather pattern will build into the area for late in the weekend into early next week even though clouds may tend to thicken again late Monday into Tuesday with another upper air system affecting the area. Afternoon high temperatures will also warm a bit as some sunshine returns.
My forecast confidence continues medium to high this week (timing of precipitation is always an issue along with exact rainfall amounts) and then high to very high confidence once the system passes on Saturday and continuing into early next week.
For Austin and south central Texas… tonight will see rain showers and thunderstorms.. heavy rain possible. Lows in the 60s. Southeasterly wind. For tomorrow, rain shower and thunderstorm activity will continue.. heavy rain still possible. Highs in the 70s with an easterly wind.
Have a good Thursday night and Friday…
Meteorologist Troy Kimmel