Enhanced Risk: 4/10/16

The Storm Prediction Center (SPC) has issued an Enhanced Risk for severe weather this afternoon across parts of Texas and Oklahoma.

Associated with the Enhanced Risk is a 5% Tornado Threat Ring.

The SPC is basing this threat on a complex synoptic situation. At the surface, there is a trough developing over Baja in the southernmost jetstream branch. As it treks eastward, it will interact with a surface cold front that extends from a disturbance in the northern jetstream branch. Also, lee-side troughing will lower the pressure across the Great Plains ahead of the “Baja Trough.”

Synoptically speaking, the 300 mb NAM chart (from Unisys) shows the weakening Baja Trough, with one jetstreak making its way around the system to eject (though weaker) into the Enhanced Risk area later today.

The 500 mb NAM chart shows some Positive Vorticity Advection (PVA) into central Oklahoma by this evening. The values aren’t particularly strong, though the winds blow directly across the tight gradient.

The 700 mb NAM chart shows some rapidly-rising air by 18Z just southwest of Childress, TX. This is just outside of the Enhanced Risk area, but it may be a good indication of where storms will initiate.

The 850 mb NAM chart shows some weak Warm Air Advection (WAA) over the threat area by 0Z Monday (tonight). The thermal gradient is weak, so the advection is not strong.

The 12Z upper air sounding from Norman, OK, shows a sharp moisture peak near 850 mb and a slight thermal inversion this morning that will hamper morning convection. There will be some skinny Convective Available Potential Energy (CAPE) later this afternoon as the atmosphere cooks over the next few hours, though there was none present this morning. The 0-3 km average lapse rate was only 4.6 C/km, due in no small part to the thermal inversion.

The deep-layer shear was 48 kts, and the low-level shear was 51 kts. The low-level shear is dominated by directional changes, and the deep-layer shear is dominated by speed changes. Both shear values will support rotating updrafts and tornadoes.

Currently, the surface observations (from the SPC Mesoscale Analysis Map) show clearing skies over the western part of the Enhanced Risk area, with dewpoints in the 50’s. The surface winds are from the southwest, which may dry things out a little and temper the severe threat. There is a dryline over the western Oklahoma, with a surface dewpoint of 43 F in Gage, OK, but a surface dewpoint of
55 F in Elk City, OK.

TwisterData.com shows that the surface dryline will remain mostly in place (according to the RAP) throughout the afternoon, though it bulges forward near the area of rapidly-rising air.

The Supercell Parameter shows that by 21Z, the Supercell Parameter reaches 2 for a small area over the Texas Panhandle.

The visible satellite imagery shows the cloud cover slowly drifting out of the area. A few Kelvin-Helmholtz waves are present over central Oklahoma, indicating some overturning in the atmosphere. These indicate that there is some pockets of rising air and some pockets of falling air in this region. Otherwise, there are clear skies over the Enhanced Risk area, which will maximize the diurnal heating this afternoon.

The water vapor satellite imagery shows that our southwest breezes may not hinder us as they would on a “normal” day. The moisture over New Mexico is much higher than it is over the southwest, such that a southwestern breeze into Oklahoma will advect moisture into the area, rather than dry it out.

Overall, I expect that there will be some severe storms today in the threat area. If I was going to chase today, I would be torn; my initial target would be Childress, as I think storms will initiate on the Texas side of the Red River. However, with limited crossings, it might be better to start in very southeastern Oklahoma and wait for the storms to cross the river.

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 TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC

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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, Satellite Imagery, Severe Weather and tagged , , , , , , , , , . Bookmark the permalink.

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