Friday, December 12, 2008

Next Week

You can click on this image to make it larger. It's the BUFKIT program that we use, showing the GFS model. I plotted some simple things like temperature, dewpoint, clouds, precip, and CAPE (severe wx potential). The timestamp goes from right to left.

You can clearly see there are two storms to track. The first one starts bringing in some light showers on Sunday, with most of the action holding off until Monday. Monday is when things get interesting. As temperattures drop, wintry mix may start. More on the "precip type" in a moment.

The next storm comes in on Wednesday. If you notice, the GFS has us greatly warming prior to the storm arriving. The GFS started to hint at this yesterday and it's becoming more likely. That storm could be a severe weather event and need to be watched, BUT let's take one storm at a time.

Look at the image below. It's a forecast sounding for Monday evening.... You can click to make it larger...

A skew T forecast sounding can be used for several factors, but I want to focus on the "precip type" forecast. People have often asked how we determine if the wintry weather will be snow, sleet, or freezing rain. I'll begin by saying it is very difficult and is easy to miss. lol

The first thing I want you to find on the image is the 0°Celsius line. Find the 0°C and follow the dotted line up diagonally. That's the critical freezing line. The red line is the temperture as you go up through the atmosphere and the green line is the dewpoint. If you notice, there is an area of the atmosphere where the tempertures are above freezing (red line to the right of the 0° line). The precip is liquid water there. No snow crystalization is possible now, so snow is eliminated. Now I have to wonder if sleet will fall or if it will be the glazing mess of freezing rain. Notice "under" the area of above 0°C, there is some air well below freezing. The big question is... is there time for the liquid to freeze as it falls and what is the temperature at the suface. I'm looking for about 1100' of atmosphere for the liquidto freeze. In this column of air, sleet should fall. The above sounding shows about 1300' of freezing air. While the above forecast sounding shows a little warmup at the surface, I don't buy it. Even if it is 33°-35°, the sleet will fall briefly.

We'll see what happens! We'll chat about the severe potential for next week later on...


1 comment:

Jason said...

Looks like a crazy week ahead.....just the way I like it, well I could do without the freezing rain.