Slight Risk: 5/18/14

The Storm Prediction Center (SPC) has issued a Slight Risk for parts of the Northern Great Plains today.

Associated with the Slight Risk is a 5% Tornado Threat Ring:

SPC says another strong trough will produce lee side cyclogenesis, which may fire a few storms this evening. Storms are expected to be fast moving, high based, and will likely start to form in low CAPE environments (< 500 J/kg)

From the soundings- there isn't much CAPE. Any storms that form today will have to form in low CAPE environments. Rapid City, SD has a forecasted CAPE of 610 J/kg, and that is the most CAPE you will see from the 12Z sounding in the target area.

Visible satellite shows a few cloud streets in eastern South Dakota, and a boundary at the Montana/Saskatchewan border. Otherwise, the skies are clear for daytime heating.

According to the 12Z NAM surface chart, there does appear to be some moisture; a plume extending from the Gulf of Mexico. It is not very strong, bringing dewpoints into the upper 40s.

By 0Z Monday (this evening), the 850 mb NAM chart shows winds approaching from the southeast (bringing some moisture) as well as a small amount of Warm Air Advection (WAA) into western South Dakota. The winds aren’t directly against the temperature gradient, so it is not a strong effect.

The 0Z Monday NAM 700 mb chart shows a few pockets of rising air across Wyoming and Montana.

At the 500 mb level (0Z Monday NAM) we can see a local vorticity maximum pushing into the Dakotas. This Positive Vorticity Advection (PVA) could help strengthen storms, even in a low CAPE environment.

At the 300 mb level, we can see the shallow trough approaching from the west. There is also a long jetstreak that will pass through the target region, which will place an area of divergence aloft over Wyoming, and perhaps help draw storms a little higher throughout the day. As it is, the entire region is in an area of diffluence, so storms will already have some draw upwards.

I had other plans today, and I certainly wouldn’t have driven there for today’s threat alone. I would like to see this area of the country (I’ve never been to North Dakota or Montana- those are two of five states left for me to see), but I am thinking today would not have been the day to do it. Near the end of the storm season, I might have been willing to drop the last bit of my storm chasing money into this chase, but I still have three weeks left.

The road network is terrible across Montana. I expect the cell phone service (data) will be likewise as terrible. Montana would make for a difficult chase. Wyoming and South Dakota are into the Black Hills, and that is also difficult chase country. However, I think the chances are better a little farther west, based on the charts shown above. I think the best position would probably be the very southeast corner of Montana, or the northeast corner of Wyoming, prepared to move south and east as necessary.

I hope you enjoyed my post!

The Storm Prediction Center forecast and soundings are from the The satellite imagery is from and the upper air charts are from Unisys – Weather. The radar imagery is from the National Weather Service.

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.
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