Friday, April 25, 2014

April 26-30 Severe Weather Outbreak: Sunday Outlook

This forecast is solely for the severe weather on Sunday, April 27th. For the Sunday, Monday and Tuesday outlooks, please look at the bottom of this post for links.


The Storm Prediction Center has issued a severe weather outlook for Sunday, April 27th, indicating the continuance of Saturday's severe weather. In the graphical representation of the severe weather risk above, we see there is a large 'slight risk' of severe weather covering Nebraska, Kansas, Oklahoma, Texas, Louisiana, Mississippi, Tennessee, Kentucky, Arkansas, Indiana, Iowa and Missouri. We also see a much more alarming 'Moderate risk' of severe weather, covering extreme northeast Texas, southwest Arkansas, northwest Louisiana and southeast Oklahoma. This moderate risk is particularly alarming, as it appears to be only the 9th time in Storm Prediction Center history that a moderate risk has been issued two days away from the predicted event. 


The image above shows the Storm Prediction Center's graphical representation of the percentage chance of severe weather within 25 miles of any given point. We see the 'slight risk' area as defined by the 15% chance swath, with an enhanced severe weather chance in the 30% red region. But it's the 'moderate risk' area that wins the contest, clocking in at a 45% chance of severe weather within 25 miles of any point. Putting that in simpler terms, you could flip a coin, and there's just about a 50/50 chance of severe weather within 25 miles of that purple area. The black hatched area signifies a 10% or greater chance of significant severe weather (i.e. very large hail, very strong winds or strong tornadoes).

The image above shows isobars (contour lines) and wind speeds (colored) at the 500mb level of the atmosphere on Sunday evening. Here, we see our strong trough that we went over in the Saturday Outlook post has now become a closed low, as seen by the closed isobars in Kansas and Nebraska. This indicates that the storm has passed maturity, and is now on the path to weakening. Despite this, a screaming mid-level Pacific jet stream, clocking in at nearly 100 knots, will be feeding this severe weather threat for days to come. We see the closed low wrapping those strong mid-level winds into the warm sector, enhanced right over that meeting point of Texas, Arkansas and Oklahoma, and right over the Moderate Risk outline. These strong winds indicate the enhanced risk of severe weather.

If we look at wind speeds at the 700mb level, just a few thousand feet off the ground, we see wind speeds of close to 60 knots enhanced over our severe weather area, and especially over that Moderate Risk outline of Texas, Arkansas and Oklahoma. Seeing as this 700mb wind component is also known as the lower level jet stream (LLJ), and is a nocturnal jet stream, we can expect these winds to sustain themselves as Sunday wears on, thus continuing the severe weather threat. These high wind speeds combined with the high mid-level winds we just went over make me more and more concerned for Sunday.

According to model guidance, there is every right to be concerned. The image above shows the forecasted supercell composite for Sunday night. In other words, the higher colors on the legend indicate the higher likelihood for a supercell, which is defined as a rotating thunderstorm. Seeing as the supercell composite is enhanced right over that moderate risk area again, it's clear that this focal point of Louisiana, Arkansas, Texas and Oklahoma will be the bullseye for Sunday's severe weather threat.

Interestingly enough, the forecasted significant tornado composite, which is an index that can help determine the likelihood of tornadoes in a given area, goes off the scale right over the Moderate Risk area, but in my opinion, it's best to wait another day or so before jumping on this train of violent tornadoes (though I will agree that strong tornadoes are possible here).

To summarize:
• A potentially significant severe weather event is expected to occur Sunday.
• A Moderate Risk has been issued for Oklahoma, Texas, Louisiana, and Arkansas.
• Those in the Moderate Risk area may want to prepare for potentially strong tornadoes on this day.

Other posts pertaining to the April 26-30 Severe Weather Outbreak:

• Saturday Severe Weather Outlook: Click Here
• Monday Severe Weather Outlook: Click Here
• Tuesday Severe Weather Outlook: Click Here (Coming soon)

Links labeled Coming Soon will be out in the next few hours.

Andrew

1 comment:

Chuck Justice said...

Looks like I'm pretty much in the, "Bulls Eye", for this system. Shreveport, La to be exact!

I'll keep ya updated as to what we get here!