Happy Friday everyone! Next storm system on track for Saturday and brings with it the threat for severe weather and flash flooding.
It sure turned into a great Friday after a stormy night last night! Look at the rainfall totals since midnight from the Oklahoma Mesonet. The sweet spot in terms of heavy rain came right over my place in far NW OKC! While you're at it check out the rainfall totals for the last 60 days. I had to double take, Did this really happen? Yes, it did! The latest drought monitor reflects the well above average rainfall in the southern plains this Spring. FYI, the drought monitor doesn't count the rain from last night either!
Any plans this evening look just fine. I'm expecting thunderstorms to develop way out west in the western high plains of New Mexico and the Panhandles tonight then move east into western Oklahoma by Saturday morning. Here's the risk for severe weather tonight from the Severe Storms Prediction Center. The best chance for tornadoes this evening seems to be in northeast Colorado.
So don't worry about this evening as any rain should hold off until tomorrow morning. However, all bets off on Saturday as a pretty impressive storm system heads this way. Here's the upper level wind pattern predicted for Saturday evening. This is what we call a negative tilt upper storm system.
Let me explain positive and negative tilt troughs.
Above I posted a pic of a positive tilt trough and then a negative tilt trough. As you can see the trough coming in tomorrow is a strong negative tilt trough! A negative tilt trough is much more likely to produce significant weather as compared to a positive tilt trough. This is because the atmospheric conditions ahead of a negative tilt trough are much more favorable for low pressure to develop with increasing wind shear and rising motion which supports the formation of thunderstorms and possible severe weather outbreaks. This is why I am somewhat concerned with what could happen Saturday evening.
Here's the surface pattern Saturday evening.
Notice the surface low forming in western Kansas and the dry line extending south along the western Oklahoma / Texas Panhandle border. This forecast model predicts morning thunderstorms and rain gradually falling apart and then additional thunderstorms along the dry line by 6pm tomorrow. These are the ones we must watch closely for all modes of severe weather. They will be developing in an area favorable for severe weather including tornadoes and then moving northeast toward central Oklahoma Saturday evening.
The official severe weather risk for Saturday shows a large region of Slight Risk with an Enhanced Risk area just east of the surface low in Nebraska and Kansas then south across western and central Oklahoma into north Texas ahead of the dry line. This is the area of greatest concern for significant severe weather! This area could be upgraded tomorrow.
However, there are complicating factors. One of which is the possibility that rain / thunder that forms later tonight lingers well into the afternoon Saturday before moving off to the east. It's possible that rain cooled air and cloud cover from morning thunderstorms could limit the over all instability in the atmosphere and thus limit the severe weather potential Saturday evening.
But to be honest, we don't know the exact details of the situation yet and even if the atmosphere is cooled due to morning rainfall there still might be enough time to recover by Saturday evening for significant severe weather.
Either way I think there is going to be severe weather in Oklahoma on Saturday. The question is how widespread? High end severe or low end severe? We simply won't know the details until Saturday afternoon when we see the system actually playing out in real time.
This is why it is very important to monitor the weather closely tomorrow afternoon /evening! So heads up for Saturday. Keep an eye to the sky and make sure you have your severe weather safety plan ready to go long before severe weather develops. The key is to be prepared and not scared. Prepare for the worst and hope for the best.
The threat for severe weather and flash flooding will shift east by Sunday. However, we remain in an active severe weather pattern with a long wave trough of low pressure in the upper atmosphere to our west. As long as this pattern persists more chances for severe weather will develop down the road.
Be safe, Jon