Winter Storm Watch

December 3, 2009

The National Weather Service in Lake Charles has issued a winter storm watch for Vernon, Rapides, Avoyelles, Beauregard, Allen, Evangeline, and St. Landry parishes from Friday evening through Friday night. They’re forecasting 2-3 inches of snow in that time frame. This is a big deal. I don’t recall us having a winter storm watch in Rapides parish in my 8 years down here. I know we’ve seen winter weather advisories, but those are reserved for smaller storms. It remains to be seen if this watch will become a warning, or an advisory, but it is time to take notice of this storm. If the morning runs are all in on this event, I’ll have to follow suit with that. What that means is, if you need to take any precautions due to heavy snow, they’ll need to be taken care of. The nice part about this snow is that it should mainly fall after we get the kids home from school, and ourselves home from work. Even if flakes are flying around 3:00-4:00, there shouldn’t be accumulation until after dark.

Now for what I expect. I’m going to use last night’s model runs for this forecast, but temper them down just a touch. The late night models came in slightly drier, but these intermediate runs typically aren’t given as much weight as the one’s run at 6:00 A.M and P.M. That’s a long explanation I really don’t feel like digging into. That being said, it’s not out of the realm of possibility that these models have latched onto something that would decrease our snow amounts. The nice thing is, they both still give us at least some snow. Instead of 2-5 inches, they are spitting out more like 1/2 to 3 inches. Still snow, just not as much.

The best way for me to break this down is by using something called SREF probabilities. These are Short Range Ensemble Forecast probabilities. This essentially incorporates many different runs of the models into one neat little package. Then it gives me probabilities of a certain threshold of precipitation happening. Here are the probabilities of certain snow accumulations per this model for the time period of 3:00 P.M Friday to 3:00 A.M Saturday.

Greater than 1 inch: 60.8%
Greater than 2 inches: 30.5%
Greater than 4 inches: 7.3%
Greater than 6 inches: 4.8%
Greater than 8 inches: 4.8%

These are as high as I’ve ever seen them here, and it’s a good breakdown of our possibilities. I’d say we have a 90% chance of seeing flakes here at this point. If the morning models look like last night’s, I’ll up that to 95%. The accumulation guidance up there looks pretty good to me. I’d go 80% on us seeing 1 inch *if* the ground was colder. Seeing as our ground is well above freezing, it is entirely legitimate to say that our chances of seeing greater than one inch of snow is around 60%.

My overall time scenario is the same. Some light rain will break out after noon, and should change quickly to snow after 4:00 P.M. Snow will intensify to a steady moderate level throughout the evening, and be done around midnight. I’ll officially say 1-3 inches for Alexandria, with the threat for up to 5 inches in isolated spots should we see some heavier bursts. I’ll update this around noon with the new guidance.

Nick

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