Forecast Thoughts (Post 1) April 26th, 2016

It’s been a while since I have taken the time to post a forecast blog, so I figured why not? Tomorrow certainly holds the potential to be a big day across the central and southern plains but there are some things left to be desired and ironed out. Here’s the SPC Day 2 outlook issued in the early AM on 4/25/16.

As I always like to do, let’s take a look at CURRENT data.

Currently:

Writing this blog about 930 AM on 4/25. The first thing to note is the location of the trough that will be responsible for the chaos tomorrow across the southern plains. It’s currently just moving onshore across the southwestern US and will dig slowly before ejecting out onto the plains tomorrow.

 

Next, looking at observations and soundings toward the gulf, I see that there is some deeper moisture working north. As noted yesterday, some models were some 5-10 degrees too low with dewpoint temperatures as they likely were unable to capture the recent rainfals and associated greening properly. Moisture did not mix out nearly to the extent that some models had forecast. So again, looking south, there is some pretty decent moisture in CRP, that is fairly decent. We can see good moisture off the warm gulf with good onshore flow, so I really am not too concerned with moisture being our limiting factor tomorrow…

 

 

 

Reaffirming that moisture transport has been ongoing, we see decent 24 hr dewpoint changes, although much of this occured yesterday afternoon, and deeper moisture advection will begin this afternoon/evening as low level response increases as ascent increases ahead of the upper level energy.

 

Forecast:

There is quite a large forecast target area for tomorrow, as evidenced by the large moderate risk area drawn by SPC above. Looking at a simple map of forecast CAPE it’s easy to see the NAM’s progged location of warm front/dryline/low center and to see in general how large and relatively moist/unstable the warm sector will likely be.

But these images don’t tell all the story, most likely. Each “target” will face some of its own potential “fly in the ointment” scenarios which could impact the larger severe weather threat. I am going to try and briefly dissect those and evaluate, here.

There should be a rather substantial vort max moving out into the central plains tomorrow across northern KS into NE and potentially a secondary wave more embedded in the flow that will glance further south central/southern OK into Texas. This COULD mean there could be a lack of convection in between these areas across south central KS into north central Oklahoma, but that is far from a certainty. But regardless, for my purposes, that has me already thinking about a “north and south” target.

The North Target:

The north target features a dryline bulge, and also a decent warm front. A storm that develops off the dryline or near triple point will be in the vicinity of the warm front, where enhanced low level shear could certainly support tornadoes, some strong. My issue with the north target is two fold.

1. Will the slightly east of north storm motion at 30ish MPH allow storms to stay on the warm front, or will they cross over?
2. Upper level flow is better to the south across OK/TX which could allow for better venting of updrafts and less HP structures..

 

 

The South Target:

The south target across S OK into TX should also be able to initiate convection tomorrow evening, as the wave energy ejects out. Favorable vertical wind shear will certainly support supercells with very large hail. The issue with the south target is

1. “Veer back veer” wind profiles can disrupt the supercell process and lead to storms that struggle to organize properly.
2.  The same VBV winds are also putting a severe damper on low level storm relative helicity
   1. However, if a storm can turn right, effective SRH in the low levels could be dramatically higher
   2. Also, the numbers in the soundings below certainly do not suggest no tornadoes, it simply is just not as supportive as strong/long track tornadoes.

Summary:

Tomorrow has the potential to be a significant day with numerous strong supercells and potentially strong tornadoes, but enough questions remain that picking a target is not easy yet. Hopefully 00z data helps decide that better! If you’re not a chaser and are reading this and live in any of the areas outlined in the first picture in this post, please stay alert to local NWS and other media!Severe