U.S. Severe Weather Blog

April 9, 2009 Severe Weather Potential

A quick briefing about today’s unfolding potential for severe weather across KS, OK and the Ozark Plateau. As always, please see SPC for the latest outlooks and watches. This post also includes an example of some of the experimental model information being used by researchers at the National Severe Storms Lab and the Storm Prediction Center.

A composite chart valid for 9 am CDT:

Composite Chart at 9 a.m. Thu. 2009-04-09

A potent mid level jet will aid deepening surface cyclone across OK/KS through this afternoon. The strong ascent and wind fields/dynamics with this system will be tapping returning low level moisture to contribute to thunderstorm development later this afternoon across KS and OK. Eventually, these storms will spread east into MO/AR. The situation bears watching and SPC has issued a  MDT risk with high probability for significant hail and perhaps a few strong tornadoes if moisture can increase sufficiently in the low levels.

One of the really neat aspects of working in Norman at the National Weather Center where various government, academic, and private entities peruse the latest in forecast technology is that we are always trying out new ideas. Below I have placed a couple of images derived from numerical model data valid for 7 p.m. CDT this evening.

Model forecasts valid at 7 p.m. CDT 2009-04-09

The image above is a combination of the North American Mesoscale (NAM-WRF) Model and the higher resolution WRF-ARW run at the National Severe Storms Laboratory here in Norman. We are looking at a simulated infrared satellite (IR) image for this evening derived from the NAM-WRF. The forecast surface pressure, temperatures (F), and dewpoint values (brown and green values in (F)) are also from the 12h forecast valid for this evening.

Model forecasts valid at 7 p.m. CDT 2009-04-09

In this image, valid at the same time, I’ve removed the pressure, temps, and dewpoints to better reveal the fields from the higher-resolution WRF-ARW run at NSSL. The unique thing about the contours shown on the image is that these are based on maximum values occurring over the past hour valid at this forecast time. We are looking for areas in the model, generally near the surface, that meet certain thresholds. We can see where higher simulated reflectivity in the model indicates thunderstorms. And, where these simulated thunderstorms are particularly intense as far as organized updrafts. While not quite at the scale small enough to depict an individual supercell thunderstorm, this data is getting close to showing us “surrogate severe storms” based on the parameter thresholds that we have chosen.

It is interesting to juxtapose the coarser resolution simulated IR with the higher resolution of the WRF-ARW model reflectivity in this case. This is essentially what we do operationally with these observed data sources where IR satellite imagery is about 4km in resolution and radar data is about 1km or less.

Later today we will see how the models compare with reality.

Greg Carbin is the warning coordination meteorologist at the NOAA Storm Prediction Center in Norman, Oklahoma.

This blog is intended to facilitate communication about the impacts of selected severe weather events, particularly major tornadoes, in the United States. We hope it will allow us to assist interested parties to understand what we at the NOAA Weather Partners in Norman, Oklahoma have been able to gather about the events. It is not intended to provide critical weather forecast information, nor is it intended to provide information on a broad range of research topics associated with severe weather.

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