Saturday, December 24, 2011

Merry Christmas! Forecast for Christmas Day 2011

The big story during the next seven days should be a developing low pressure system to our south and west which will eventually move up the Eastern Seaboard Tuesday Night and especially on Wednesday. The low could deepen to about 996 MB when it moves over us or just offshore. Warm air ahead of the system and warm air brought in by the eventual storm track will ensure mild temperatures and a column that is just too warm to support frozen precipitation. There is one exception and that could be in Mount Pocono where cold air might try to slip in as the system departs. But, periods of soaking rain and strong gusts of wind will be possible. 3 hour pressure rises could be decent. In addition, there may be another surge of mild air ahead of the cold front followed by a low-topped squall line of thunderstorms (with little lightning). We will be placing the finishing touches on the wettest year at Philadelphia International Airport and at many observation stations. One to two inches of rain may fall from this system if the forecasted strength and track hold.

Tuesday’s high may very well be late in the evening in the warm sector. Wednesday’s high could come early in the day prior to the cold front. This is all assuming there is a strong southerly influx ahead of the low and in the warm sector. Right now, I am holding it at around 54 degrees. This past week…lower sixties occurred late at night…and this may once again be a possibility.

Initially, as a warm front moves through our region Monday Night, the Poconos and Lehigh Valley area could deal with a bit of sleet or wet snow. But even in these areas, the search for a white holiday week is going to be continuing past midweek.

There is a hint of a secondary piece of coastal energy around Friday of this week on the GFS. The air behind our first coastal storm could be more supportive of some sort of mix of frozen precipitation. However, this secondary system would have to be a lot stronger than the 12z GFS indicates for it to supply us with enough cold air and precipitation for big issues. This is a possibility and something we will follow through the week, without getting prematurely excited about it. Overall, looking at the 12z guidance, I am still observing signs that La Nina is holding firm with the 540 line unable to stay to our south for any extended period of time. As you know, if you just hit the brief shot of cold air at the right time, you end up with a winter storm. We do get a shot of cold air in the first week of January (at least a portion of the week). It is these shots of cold air that will come and go and we will be waiting for energy to coincide with it. It is like playing blackjack in Atlantic City until you hit the jackpot. But here again, while we may eventually see a piece of energy take hold, we will not be getting excited about it this far out as the computer modeling has been having difficulties handling this entire pattern since the fall. Overall, snow lovers may still be waiting by this time next week. We will soon find out for sure.