Tuesday, January 29, 2013

January 29 Severe Weather Event -- Updated 4:00 PM

Moderate risk continues to be in effect for Arkansas, northern Louisiana, northern Mississippi, eastern Tennessee, eastern Kentucky, southern Illinois and southeast Missouri.

As of 4:00 PM CT... strong thunderstorms were ongoing across the Plains into the Midwest, with severe weather warnings beginning to be issued as the storms move into a more favorable environment. Special noontime sounding from southern Missouri shows differing wind speeds at different levels, consistent with observed strong wind shearing in the same areas. Analog comparisons to similar soundings reveal at least one tornado did occur in a similar situation. Surface helicity observed to be quite strong, would expect an increasing tornado threat as the night goes on. However, an already-established linear severe weather event will make it hard for stronger tornadoes to evolve, hence the extreme damaging wind concern. Current lower level wind forecast indicates strong winds of over 50 knots. I anticipate these winds to increase dramatically as the evening wears on in response to the nocturnal lower level jet stream mixing with these thunderstorms and really firing them up. By that time, the damaging wind threat will take center stage, enabling many n the moderate risk area to achieve warning-criteria wind speeds.

Today is indeed a Critical Storm Action Day. All resources are now devoted to the severe weather situation, and no posts unrelated to the severe weather situation will be published.

Next update will be at approx. 5:30 PM CT


Special Morning Update - January 29 Severe Weather Event

Today is the big day. We are seeing the Storm Prediction Center maintain a Moderate Risk call for severe weather through much of Arkansas into extreme southern Missouri, extreme northern Louisiana and a very small portion of northwest Mississippi. A slight risk exists across the Plains, Midwest and Gulf Coast.

On a side note, I am maintaining my Storm Action Day call and will not upgrade to a Critical Storm Action Day unless the environment becomes more favorable for such a call.

A tornado watch has already been issued for much of Oklahoma and a few counties in northern Texas. This comes as a result of thunderstorms firing in Oklahoma, extending back through Texas. I anticipate these storms to continue strengthening along the nocturnal lower level jet stream, already feeding on the tight pressure gradient known as a dryline, which does go right up against these thunderstorms. By the looks of them, the tornado threat is highest right now, as the storms are not yet linear and are more individualized. The threat is lower in southeast Kansas and northern Texas, where there are no watches yet. Oklahoma City could be hit by some individual storm cells in coming hours as this not-yet-linear complex of cells moves east.

My main concern at the moment is extreme damaging winds. The above forecast shows wind speeds for 9 PM Central time, with wind speeds just a few thousand feet above the ground. My worry is that these winds will be provoked to move down towards the surface as the storms begin to take on a more linear shape and evolve into a squall line. When this does happen, the risk of tornadoes drops considerably and the threat for damaging winds skyrockets. Looking at the map, we would be seeing lower level winds above 72 knots in parts of the Moderate Risk area, something that could easily provoke extreme damaging winds.

I will provide updates as often as possible throughout the day, and will do another afternoon update later on in the day.

Heed all National Weather Service watches and warnings, and be prepared to seek shelter if you are in the path of these storms.