Wednesday, January 12, 2011

Next Tuesday's Storm System

Our next chance of precipitation will arrive next Tuesday, and although it appears as though it will just be a cold rain, there are a few things worth watching. As always, there will be shifts in the track and timing of the storm system. The air mass this time around will be relatively warm, so things will need to come together just right for us to get a good snow. Based on the location of high pressure over New England early next week, if we get wintry weather on Tuesday, it could be in the form of freezing rain. Computer forecast models don't do a good job of resolving low-level cold air advection, and this is a case where pattern recognition is more valuable in forecasting than anything else. When strong high pressure develops over New England we get an effect in central Virginia called cold air damming, also called a "wedge". Dense cold surface air rotating around the high will funnel down the east side of the Appalachians, creating a shallow layer of cold air at the surface. The GFS is indicating temperatures in the mid to upper 50s early next week, but we won't even get close to that if the high is located where it is suggesting it will be. I've gone mid-40s for highs on Tuesday as somewhat of a middle ground, but if there is more consistency with this pattern, 30s will be more likely, and freezing rain could be a possibility. There's always the chance, of course, that I'll wake up tomorrow morning to see something very different depicted in the models next Tuesday. So goes medium range forecasting. I'll have another update on Friday after getting a few more looks at the data.

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