Enhanced Risk of Severe Weather

Good Sunday Morning everybody...a very dynamic weather pattern has already begun to set up across south central Texas as evidenced by the elevated thunderstorm activity ongoing across the area now (elevated meaning that the storms developed on top of the capping inversion over the area now)...a strong upper level trough, or line, of low pressure digging south into northern Mexico has helped to create the development of surface low pressure over extreme southeastern Colorado and the Oklahoma Panhandle...that drop in surface pressure in those areas forces winds to turn southerly across a good majority of the state; those southerly winds ultimately allow Gulf moisture to come flooding back north into Texas...another feature that has my attention is the west Texas dry line, which actually pushed well east of IH-35 corridor yesterday and gave us our hottest day of 2015, so far (I'm sure you all noticed how dry it felt yesterday)...we officially topped out at 93ºF here in Austin yesterday...however, around 7 pm Saturday evening that dry line retrograded back west over the IH-35 corridor and is now located well to the west of I-35 now over west Texas as evidenced by latest surface analysis...the dry line is simply a boundary that sets up during the Spring, Summer, and Fall months in west Texas that separates dry, desert air from northern Mexico and the southwestern U.S. from the humid, Gulf air that presides east of it...when conditions are ripe, as they are looking to become this afternoon, the dry line serves as a focus for the development of showers and thunderstorms...storms that develop along the dry line today as it begins its push back east into central Texas, may quickly become severe producing large hail, damaging wind gusts, and even a tornado or two...with that being said, the latest high resolution forecast models indicate that the majority of the storms this afternoon will form just north of our area, however, I'm NOT going to buy into it just yet...I think we have just as good a chance as north central Texas for some potentially mean storms later this afternoon/evening. There is the potential for several rounds of storms today, morning showers and storms are beginning to move out to the northeast...scattered thunderstorms form this afternoon, some of which are likely to become severe with large hail, damaging winds, and possibly a tornado or two...followed by a possible strong line of storms that would move through the area late evening into the early morning hours...with all that being said, today is definitely a day to be weather aware and keep an eye on the sky and the forecast.

Upper Level Trough enhancing severe weather risk today...as it approaches air is forced to rise on a large scale, known as large scale ascent, or lift in the weather world...that rising air is a key to thunderstorm development, hence the risk for severe weather later today given that moisture and instability are both in place and will continue to increase into the afternoon ***Water Vapor Imagery with 500 mb (around 18,500 feet) heights plotted on top*** Check out that spin over Arizona and New Mexico...this is water vapor imagery, you are looking at mid/upper level moisture content in the atmosphere...NOT CLOUDS OR RADAR

***Main points...we are under the gun for possible severe weather this afternoon/evening...a couple of rounds of storms possible with scattered afternoon severe storms giving way to a potential line of storms later this evening***

***STORM THREATS...LARGE HAIL, DAMAGING WIND GUSTS, AND A TORNADO OR TWO POSSIBLE TODAY/TONIGHT ACROSS NORTH CENTRAL, AND SOUTH CENTRAL TEXAS***

With all of that being said, the Storm Prediction Center (SPC) out of Norman, Oklahoma has placed ALL of south central Texas under the ENHANCED RISK AREA for severe weather today:

***WEATHER UPDATE/STORM THREAT***

Forecast Discussion:

Now that early morning showers and thunderstorms have pushed well east of the area…my attention is going to be focused out to the west later this afternoon/evening. The Storm Prediction Center (SPC) has placed south central Texas under the SLIGHT RISK CATEGORY for severe weather today/tonight with an ENHANCED RISK for severe weather for north central and north Texas, including Waco and DFW. The atmosphere was temporarily stabilized after this morning’s activity, however, as of the latest composite mesoanalysis issued by the Storm Prediction Center for the southern plains, it shows that instability has now increased once again across the area…simply, the juice for strong/severe storms has returned, however, at the same time, there is a large area of convective (thunderstorm) inhibition across the western Hill Country and west Texas where a strong cap, or lid, is in place. That lid, simply a layer of warmer air aloft, effectively works to inhibit storm development because it does not allow for air to continue to rise high into the atmosphere. Another inhibiting factor to thunderstorm development this afternoon is the thick cloud cover across the area along and west of the I-35 corridor. If we can get some breaks in that cloud cover out west, which I think is possible, those sun breaks will help to destabilize the surface environment further and would in turn increase our risk for storms. Surface heating is one of the ways in which the cap can be eroded.

High Resolution forecast models continue to show a line of strong, potentially severe storms moving through the area later this evening…now it is just a watch and waiting game. The main threats form the storms that develop this afternoon/evening would be large hail and damaging winds, however, an isolated tornado can never be ruled out.

Current Visible Satellite Imagery over south central Texas: (This is a black and white image of what Texas looks like from space right now):

Today’s Severe Weather Risk Areas:

Major Weather Geek Stuff Here, but this is the SPC’s latest mesoanalysis…see that shaded area of blue west of the Hill Country that is where the strongest cap is in place right now…the red lines represent CAPE values (Convective Available Potential Energy)…anytime CAPE values exceed 1500 joules per kilogram ALONG WITH the other factors necessary for storm development (moisture and lift)…severe weather becomes more likely…CAPE values currently running 1500 to 2500 across the area which tells me that storms, if they are able to get going, they have a good chance of becoming severe. As of the latest forecast model guidance, CAPE values look to continue to go up through the afternoon:

FYI: A thunderstorm is considered severe if it produces thunderstorm winds of 58 mph or greater, and/or one inch diameter hail or larger, and/or a tornado is present…lightning/heavy rain are not considered in the official decision to issue a severe thunderstorm/tornado warning…because those two things are always found with thunderstorms.

Plus, remember a WATCH means conditions are favorable…be on the lookout…it’s a head’s up

A WARNING means the type of severe weather warning issued is occurring or imminent and is likely to pose a risk to property and life