Saturday, January 23, 2010

Risk of Storms Tonight

The Storm Prediction Center includes parts of southeast Missouri, western Kentucky, northwest Tennessee, and northeast Arkansas in a "Slight Risk" of seeing severe weather in their 10:30am CT severe weather outlook.

In their discussion, SPC points at damaging wind being the main threat from any storms that develop later this evening in southeast Missouri, western Kentucky, northwest Tennessee.

Here is a look at this morning 6am CT run of the NAM computer forecast model for Paducah, Kentucky.

A couple of things to note.
  1. Look at the temperature. If the NAM is correct, temperatures will run in the upper 50's this afternoon.
  2. Look at the dew point. Dew points are forecast to be up to around 50° this afternoon. Remember, the dew point is basically the measure of the moisture in the atmosphere.
  3. Look at the wind. These are indicated by the multi-colored lines covering the screen. Each line indicates a specific wind speed (in knots) at a specific height. Use the legend in white text on the right of the screen to see the altitude in 1,000's of feet. Winds will be strong and gusty this afternoon. The model indicates sustained winds of 25 knots (approximate 29 mph) by afternoon. Go up a few thousand feet later this evening and you will see the winds increase to 60-70 knots (69-80 mph).
  4. Look at the precipitation. By the NAM's indications, rain will begin to fall around 9pm-10pm CT and will last until early Sunday morning.
For cool-season severe weather in this area numbers 1, 2, and 3 from above are important. Often times, numbers 2 and 3 are most important. As I mentioned earlier, a local NWS study showed that the risk of severe weather greatly increases around this region when dew points climb above 48°. When you combine that with strong winds a few thousand feet above the surface, it wouldn't take much for a thunderstorm to force some of that wind down to the ground.

I agree with the Storm Prediction Center's assessment that the main threat from storms tonight will be damaging wind.

All of this being said, the instability isn't horribly impressive. Typically, we don't need a lot of instability for cool-season thunderstorms to become severe, but you do need some instability to get the thunderstorms started. This becomes one of the big questions, "Can we get thunderstorms to initialize?"

Right now it appears that the best chance for strong to severe thunderstorms will be later this evening. Perhaps as early as 9pm CT (Saturday) through 2am CT (Sunday).

As far as rainfall amounts, the NAM is putting down 1.9" of rain for Paducah, 1.75" for Cape Girardeau, Missouri, and 0.82" for Farmington, Missouri. I don't think we'll see any flash flooding, but look at the 3-hour Flash Flood Guidance put out by the National Weather Service.

We could be up on the edge of the amounts shown in the map so we'll have to keep a close eye on it.

Stay tuned...

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