Wednesday, February 27, 2008

Weather update: Major storm looming?

As you probably know by now, the mountains got hammered with a nice snow today. A few stray flurries and snow showers even made it down to our neck of the woods.

Looming, however, is a potentially MAJOR storm. While it is not likely to impact us with snow (although not impossible) it could be a HUGE snow producer for the mountains of N.C./SW Va./Eastern Tenn./extreme NE Ga.

The main feature of this storm is a "cutoff" area of low pressure. These types of lows can be tremendous precip producers and come with a sort of "built in" cold air mechanism.

The big surprise snowstorm that hammered Charlotte and Rock Hill a few years back was from a cutoff low.

Here is a map showing the cutoff low at the upper levels (12z GFS run -- afternoon of March 5).
Obviously, there is tight temperature gradient.
Now, 6 hours later, the evening of March 5.

Now, here is the precip that has fallen, according to the 12z GFS during that span.

Amazingly, the European model shows a similar solution.

Now, a few points:

1) This would be an historic storms and historic storms that are projected on models 7 days out rarely verify.
2) We also are working against climatology -- March storms are rare -- not unprecedented, but rare.
3) It IS interesting that both the Euro and GFS are on to the same type of solution.

Bottom line: Way too early to even get excited about this a little bit, but definitely something to track. Whoever ends up just west of the path of this cutoff low -- if the low even materializes -- would potentially get hammered with many inches of snow. And if the low forms, wherever it tracks, drought-stricken areas of the southeast would likely see beneficial rains.

Stay tuned -- winter ain't over yet!!!!

Wednesday, February 13, 2008

Quick update: No ice Sunday; cold shot early week

Models quickly and strongly backed off the idea of any sort of ice situation Sunday -- now we should just look for a chilly rain.

In the wake of that system a brief, but strong cold shot -- highs in the 40s, lows in the 20s type of thing.

Then another warmup.

Prospect for snow before month's end -- very low.

And as you know, once we cross into March, every day that goes by dramatically reduces our snow chances -- certainly possible (see:1993) but increasingly unlikely.

Monday, February 11, 2008

Good news: A shot at winter weather; bad news .... would be ice if we get it.

An interesting setup being depicted by the last two runs of the GFS model -- this is what is a called a "Miller B' system -- low pressure forms over the western Gulf coast or southern Mississippi valley, tracks northeast toward or even west of the Appalachians, then the low "jumps" east and reforms off the N.C. coast.

As you can see by the following three maps of the 18z run of the GFS, a cold-air damming situation occurs late Saturday into Sunday.

Here is the wee hours Sunday morning. You can see precip moving in. Note the strong (1033 mb) high pressure system parked over New England, pumping in cold, dry air.
Now for dawn on Sunday. The high is still over Maine (although slightly weaker at 1030 mb) and precip is flooding the area, even as the shallow layer of cold air is pumped in from the north.
And early Sunday afternoon. You can still see the CAD "signature" although it has retreated to the north.

Still, computer models are notorious for UNDERforecasting the strength of cold air damming events, so we'll have to see.

Bottom line -- still in the 5-6 day range -- far too soon to even attach probabilities to this. And to be sure, ice storms are events to root AGAINST, not for. But mainly, this is a reminder that we are still well within the window of time when winter events are possible.

Another note -- a few more frames ahead and you would see the low jump off the coast, then a big shot of arctic air will plunge southeast early next week. There are some hints we might see a system during that time, but that's all we have are hints right now.

Stay tuned.