UPDATE: Thu 23 Dec 2010 / 5p.m.
There have been no changes to the forecast reasoning of the past few days: Christmas Eve rain will end in time for a partly cloudy to mostly sunny, windy and cold Christmas Day. Friday's updated Christmas forecast will be handled in the regular weather discussion.
I hope yours is especially blessed this year!
Take Care -- Steve
Wed 22 December 2010 / 5:30p.m.
Our Christmas forecast hinges on the movement of arctic air, and a mid-level trough.
The trough is the same one which helped leave California awash in 5 to 10 inches of rain during the past week. This vigorous system will interact with a deep return of Gulf moisture to generate a large area of rain, and even a few thunderstorms late Thursday into Friday. Amounts will range from 1/2" to over 1". Isolated amounts to 2" (of rain) are possible!
The trough’s movement suggests precipitation will end Christmas Eve; during the afternoon in the west to evening in the east (discussion continues below map).
What about snow? It appears cold air is lacking. The coldest air beneath the core of the trough may be sufficient to generate a little snow, but cloud-level temperatures are expected to be above freezing. This means only a small corridor under the cold core of the low would be in line to receive any at all.
So significant accumulating snow is looking to be a long shot, but for you snow optimists there is a 5% chance of something sticking at least for a little while (don't hold your breath!)
The trough moves away Friday night, leaving Christmas Day with decreasing clouds. It will be windy and quite cold.
A large “blob” of arctic air will filter in through Monday keeping nights very cold and day-times rather cool into early next week.
Here’s Hoping You Have A Wonderful Christmas!
Chief Meteorologist / KXII-TV