Severe Weather Today: 6/16/15

The Storm Prediction Center (SPC) has issued several Slight Risk areas for today.

Associated with the Slight Risk over the Northern Great Plains is a 5% Tornado Threat Ring. I may do a separate post on Tropical Storm Bill, but this post will focus on the tornado threat in the High Plains.

I am changing how I do this forecast slightly; I am going to have a data section (What’s so) and then an analysis section (What I’m putting together).

What’s so:

Visible satellite imagery shows a weakening Mesoscale Convective System (MCS) over the Dakotas, stretching into Nebraska.

The water vapor imagery shows a boundary of moisture extending from the Four Corners area into North Dakota.

The 12Z upper air sounding from Rapid City, SD, shows no Convective Available Potential Energy (CAPE). The dewpoint depressions are under five degrees until around 400 mb.

The hodograph from Rapid City, SD, does show enough deep-layer shear to support rotating storms. At 12Z, the deep-layer shear was 40 kts, and the low-level shear was 33 kts, which is enough to support tornadoes.

The SPC Mesoscale Analysis Surface Observations Map shows a wind direction shift near the Wyoming and Nebraska border that extends northward along the border of Montana and the Dakotas. Surface winds east of this boundary are from the south or southeast, and surface winds west of this boundary are from the northwest. Dewpoints are in the upper 50s and low 60s through the 5% Tornado Threat Ring. The MCS can be charted on this map by lower temperatures in central South Dakota and north-central Nebraska.

The SPC Mesoscale Analysis CAPE Map shows that there is some 1000 J/kg CAPE with no capping inversion nosing into the northwestern corner of Nebraska and the Black Hills region of South Dakota. There is also a ring of 2000 J/kg CAPE over northeastern Colorado, expanding northeast.

The RAP has the CAPE increasing such that by 23Z, there is a small ring of 3500 J/kg CAPE over southwestern Nebraska. The 2500 J/kg ring CAPE extends northeast from this ring into Cherry County, NE, in north central Nebraska.

The SPC Mesoscale Analysis Level of Free Convection (LFC) Map shows that the LFC heights are under 800 m in the Black Hills region of South Dakota. They are also under 1200 m in southwestern Nebraska.

The SPC Mesoscale Analysis Effective Bulk Shear (EBS) shows values over 40 kts (enough to support rotating storms) over Wyoming and creeping into western Nebraska and southwestern South Dakota.

The RAP has the EBS increasing such that by 23Z, the deep-layer shear has increased to 55 kts over the Black Hills, and a few pockets of 40 kts EBS develop over southwestern Nebraska.

Putting it all together:

The morning is starting out slow due to the weakening MCS. At 12Z, the temperatures were low and the soundings did not look good for severe thunderstorms. However, as the MCS weakens and moves away, the area will be subject to diurnal heating. The MCS did not scour away any of the moisture, as shown by the high dewpoints (low 60s is high for this area). Given that the dewpoints are high, the approaching shortwave trough (as shown on the water vapor imagery), and the increased shear throughout the day, I would say that chances are better than I originally thought when I began writing this forecast.

I am tempted by the conditions in southwestern Nebraska. The high CAPE and adequate deep-layer shear make that quite tempting.

However, 33 kts of low-level shear farther north is tempting as well. I don’t particularly like trying to chase in the Black Hills, so I may favor somewhere a little farther south into Nebraska.

Also, the weakening MCS may drop a few outflow boundaries that would act as a trigger for developing storms. I don’t think I could get away with hanging out in the middle somewhere (Scottsbluff, NE) and waiting for one area to develop.

Therefore, I will choose two targets: Chadron, NE, and Enders, NE.

Thank you for reading my post.

The Severe Weather Outlook is from the Storm Prediction Center website.
The satellite imagery is from the NOAA Satellite and Information Service.
The surface observation and upper level charts are from Unisys Weather.

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 and tagged , , , , , , . Bookmark the permalink.

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