The Storm Prediction Center upgraded the thunderstorm outlook this morning and there’s now a moderate risk from the Oklahoma City Metro down into northern Texas (this includes much of Texoma). This needs to be taken seriously since several major metro areas are included within the risk areas; more than 28 million people have the chance to see severe thunderstorms today.
Today’s Severe Thunderstorm Outlook (SPC)
Zoomed-In Severe Thunderstorm Outlook (KXII)
A moderate risk is considered a category 4 risk on a scale of 1-5 (with five being the most significant). By SPC definition, a category 4 risk means this area has a likely chance of widespread severe weather with several tornadoes and/or numerous severe thunderstorms.
Severe Thunderstorm Risk Categories (SPC)
Taking a look at the soundings across central and southern Texas, deep and rich moisture has returned to the region and is rapidly being transported northward into northern Texas and Oklahoma. The quality of moisture was questioned initially, but current observations show moisture should not be an issue. The latest short-range numerical guidance shows surface dewpoints in the 60s across the Southern Plains just ahead of the dryline. The current visible satellite imagery indicates sunshine, coupled with the eventual low-level moisture, will allow CAPE values (ML) to exceed 1000-2000 J/kg. This means there will be adequate “food” for the storms.
2m Dewpoint HRRR Forecast This Afternoon (Pivotal Weather)
Mixed Layer CAPE HRRR Forecast This Afternoon (Pivotal Weather)
Thunderstorms should erupt along the dryline around 4:00PM to 5:00PM once surface heating and the arrival of lift aloft erode the cap. The dryline at this time will be about 50 miles west of I-35, so this is the best location for initial thunderstorm development. Once storms initiate, they should move off towards the east-northeast. Looking at the forecast 500mb maps, they indicate storms will develop and remain discrete towards I-35–likely exhibiting supercell characteristics due to southwesterlies of 50-60kts from Oklahoma City down towards Dallas. The Storm Relative Helicity in this area should exceed 100-250m^2/s^2, which indicates if a tornado develops it has the chance to become strong within the first couple of hours of storm initiation from OKC down to Denton. Recent literature shows SRH values, which is basically a measure of potential rotation, larger than 100m^2/s^2 increases the tornado threat.
HRRR Forecast Radar This Afternoon (Pivotal Weather)
HRRR Forecast 500mb Wind This Afternoon (Pivotal Weather)
HRRR Forecast 0-1km SRH This Afternoon (Pivotal Weather)
All modes of severe weather are possible this afternoon. This includes very large hail, tornadoes, and wind. Initially, between 4:00PM and 8:00PM, very large hail (tennis ball to baseball size) and tornadoes are most likely for the I-35 corridor. Then, from about 8:00PM to Midnight, the threat should transition to an isolated tornado and hail threat with more on an emphasis on wind damage for the Red River Valley.
SPC Tornado Probability Map (Pivotal Weather)
SPC Hail Probability Map (Pivotal Weather)
SPC Wind Probability Map (Pivotal Weather)
This forecast is not intended to create hype or worry you. I am simply implying the severe threat is real today if all the parameters come together as the short-range numerical guidance is indicating. Do not panic, just have a plan in place. Tune in to your local television station so you’re notified of warnings, call your elderly neighbors to make sure they have a plan, and know where you will shelter in case a warning is issued for you area. This is nothing unusual for this time of the year in the Southern Plains.