Moderate Risk: 4/26/16

The Storm Prediction Center (SPC) has issued a Moderate Risk for severe weather today across much of the Central Great Plains.

Associated with the Moderate Risk is a 10% Hatched Tornado Threat Ring.

The SPC is basing this threat on an incredibly complicated synoptic situation that will unfold today. We have several low pressure systems aloft, the most threatening for the Great Plains will move from western Colorado to Wyoming by this evening. As it does, an area of strong vorticity will move northeast from Arizona towards the Moderate Risk area, ejecting into the High Plains and Panhandles Region. As this happens, a new low pressure system will develop over Kansas. At the surface, there were two low pressure systems and an outflow boundary/warm front. Timing, and how storms develop this afternoon will determine the full threat of this system.

Synoptically speaking, the 300 mb NAM chart (from Unisys) shows the trough, which encompasses an elongated low on the east side of the Rocky Mountains by this afternoon. A moderately-weak jetstreak is expected to wrap around the low and eject along the US-83 corridor.

The 500 mb NAM chart shows that there will be Positive Vorticity Advection (PVA) throughout this region by 18Z as well. The winds do not blow directly across the gradient, but they do cross it, and that will enhance convection in this region.

The 700 mb NAM chart shows that by 0Z, there will be quite a few pockets of rapidly-rising air over Kansas, Colorado, Nebraska and Oklahoma.

The 850 mb NAM chart shows that the strongest Warm Air Advection (WAA) will be occurring near the Kansas and Nebraska border by 0Z this evening.

The 12Z upper air sounding from Norman, OK, highlights the severity of this situation. The morning sounding shows 3998 J/kg of fat Convective Available Potential Energy (CAPE) present. There was a strong thermal capping inversion in place, but it was not so strong that it cannot be broken. If the cap does break, there is plenty of energy available for storm development.

The deep-layer shear was 20 kts, and the low-level shear was 27 kts. The deep-layer shear is not enough to support rotating storms, but this deep-layer shear will increase throughout the day. The low-level shear is more than enough to support tornadoes, provided the deep-layer shear becomes more organized.

The 12Z upper air sounding from Topeka, KS is also quite scary. While the CAPE was only 1247 J/kg this morning, the capping inversion is not quite as strong. The sounding also shows a supercell parameter of 25!

The deep-layer shear was 44 kts, and the low-level shear was 21 kts. The shear over Topeka will support rotating storms and tornadoes. shows that by 21 Z, CAPE will not be a limiting factor anywhere in the Moderate Risk area. Even though Topeka shows lower CAPE this morning, it will be over 3000 J/kg by this afternoon. shows that by 21 Z, the surface to 500 mb bulk shear will be adequate along the US-283 corridor, with the maxima near the Kansas/Nebraska border.

Currently, the surface observations (from the SPC Mesoscale Analysis Map) shows a distinct dryline running along the US-183 corridor. Notice in the eastern part of the Texas Panhandle, around Perryton, the dewpoint was 42 F. Cross the line into Oklahoma, and the dewpoint jumps to 57 F. The same is true in Kansas; 42 F at Dodge City, but then 57 F a little ways east.

The Supercell Parameter shows several rings of 12 ahead of the dryline. I expect this coverage and intensity to increase throughout the afternoon.

The visible satellite imagery shows that skies are clearing over western Oklahoma and Kansas, with some ongoing morning convection over northern Kansas and Nebraska. The outflow boundaries from this mess will be a focus for severe weather this afternoon. There are also some very distinct cloud streets over northern Texas and southern Oklahoma, indicating an overturning; rising and sinking air in this area.

The enhanced infrared satellite imagery shows two Mesoscale Convective Systems (MCS) over the Northern Great Plains. These are producing outflow boundaries that may interact with the warm front and be a focal point for severe weather this afternoon.

The water vapor satellite imagery shows the MCSs over the Northern Plains as well. There is also a shortwave trough that runs through Colorado; there is some moisture bunched up in front of this trough.

I debated cancelling class and going for a drive today, but I have too many things happening at school over the next few days. I expect today will be a very busy day in the Great Plains today. If I could target anywhere, I would probably pick somewhere like Concordia, KS, but I’d really watch for an outflow boundary to appear on radar. I haven’t seen one yet, but I will look off and on throughout the day.

Thank you for reading my forecast.

The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC


About highplainschasing

This blog is about my tales in storm chasing. My name is Seth Price and I am an instrumentation instructor at New Mexico Tech. My amateur radio call sign is N3MRA.
This entry was posted in Practicing Concepts, Predictions, Radar Imagery, Satellite Imagery, Severe Weather and tagged , , , , , , , , , , , , , , , . Bookmark the permalink.

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