Tuesday, May 24, 2011

Dangerous situation unfolding across Kansas, Oklahoma, and northern Texas

HIGH RISK OF SEVERE WEATHER FROM SOUTHERN KANSAS, THROUGH OKLAHOMA, AND INTO NORTHERN TEXAS. SEVERAL STRONG, LONG TRACKED TORNADOES POSSIBLE TODAY, ALONG WITH VERY LARGE HAIL AND DAMAGING WINDS.

15z surface analysis shows a low pressure system in the panhandle of Oklahoma, with a stationary front extending northeast across central Kansas, through Iowa and into northern Illinois. A cold front is extending down from the low, and bending around through the panhandle of Texas. A dryline extends south of the low, out in front of the cold front, and will be the focus of today's storms.



The combination of surface heating, high dewpoints, and strong wind shear will lead to an outbreak of supercells capable of producing very large hail, damaging winds, and several large tracked tornadoes, with the area within the high risk the most likely to see these tornadoes. Below are the list of risks, issued by the SPC at 1630z.

RISK

TORNADO RISK

HAIL RISK

WIND RISK

Here's a peak at the first tornado watch of the day, covering the higher risk area for today, with the probability of seeing several strong tornadoes being quite high.



Taking a look at current meso analysis shows significant tornado probabilities climbing quite high, and are expected to continue to increase as the day wears on. 0-6km bulk shear is also climbing rapidly across western Oklahoma, and will continue to move east, and increase as the low level jet strengthens later this afternoon. SPC is forecasting explosive development of cells, with very large hail being the initial threat. As that LLJ continues to strengthen, the tornadic threat will also increase.

Enhanced Tornado Index

0-6 Shear

850mb GFS forecast

People across these risk areas need to pay attention to the changing weather conditions, as several more watches will likely be issued as the day wears on. Any cell that forms will become supercellular rapidly, and has the potential to become tornadic.

Severe weather outbreak possible across parts of the south

POTENTIALLY DANGEROUS SITUATION EVOLVING ACROSS OKLAHOMA AND KANSAS.

Today's greatest focus for severe weather will be from south central Kansas into parts of central and eastern Oklahoma, per the SPC's 06z outlook, which is shown below.



The 06z surface analysis across the south shows a low pressure system in southeast Colorado with a cold front extending down through the Oklahoma and Texas panhandles, and a warm front stretched through central Kansas. A very potent dryline also extends down in front of the cold front into Texas, and will be the focus of today's severe weather. Note on the analysis map below the extreme difference in dewpoints, pre (dewpoints in the upper 60's) and post (dewpoints in the teens and low 20's) dryline.



As the day goes on, the low pressure system will deepen and move slowly to the northeast across central Kansas, while swinging dryline across southern Kansas, Oklahoma, and Texas. 24/00z GFS 30mb dewpoints (see below) clearly show the contrast in dewpoints, and the focal point for thunderstorm development. By 7pm CDT, the low pressure area should be in west central Kansas, with a warm front extending from central Kansas, and off to the northeast across northern Missouri, with the cold front bending back into the Texas panhandle, and dryline extending south of the low through southern Kansas, Oklahoma, and Texas, also seen in the image below.





GFS's 500mb 18z forecast map (see image below) shows a negatively tilted trough with two vort maxes moving with the trough. These vort maxes will assist in the triggering of severe thunderstorms throughout the afternoon and evening hours.



GFS's 700mb 18z forecast map (see image below) shows moderate wind speeds of around 25 knots in the area of concern, increasing to 35-45 knots as the day goes on. These winds are expected to generally be out of the south/southwest. These winds, combined with winds out the southeast at the surface, should provide enough turning in the atmosphere to create supercells capable of dropping large hail, and potentially long tracked tornadoes. The SPC (also posted below) has, therefore, issued a 30% risk for tornadoes, with a hatched risk showing the potential for significant (greater than EF-2) tornadoes.





A quick peek at the GFS's 850mb 18z forecast map shows weak to moderate winds, in the range of 20-30 knots across northern TX, eastern Oklahoma, and southern Kansas, but increasing to 35 to 45 knots by 25/00z. (See images below) These winds will be out of the south, which will help to draw up a significant amount of moisture (see 30mb dewpoint map above) This moisture will add a lot of fuel to the fire, and will also lead to some serious flooding concerns, as these storms will be going over areas that have already been hit hard by severe weather over the past few days.

18z forecast map

00z forecast map

Something else to note is the amount of CAPE (convective available potential energy) this system will have to work with. By 00z Wed, the GFS is showing an band of MLCAPE between 3500 and 4000 J/kg, with CINH (Convective Inhibition) rapidly erroding. These high CAPE numbers, along with little CINH will allow for rapid, explosive development of supercells, and fairly low freezing levels will allow for very large hail to develop. The SPC has highlighted this threat as well with a 45% risk for hail, and have hatched that risk to signify the potential for significant hail.

CAPE

CINH



As the evening and night wears on, the SPC is forecasting for the cells across Texas and along the dryline to begin to diminish as capping takes over, however a continued wind threat may be seen as storms further north continue to press off to the east. SPC has a 30% risk for wind highlighted to cover the initial wind threat, and lessening the threat as it moves east. (See graphic below)



People need to be aware of what is going on through the day if they live in these higher threat areas. It has already been a very active year across the south, and is proof that these storms, even with all the current technology, can be deadly if a person isn't prepared. Keep those NOAA weather radios on, and make sure they have good batteries in them.