Sunday, January 22, 2012

Forecast for Monday, January 23, 2012

Warmer air will surge northward with a warm front tonight. However, we have cold air trapped at the surface thanks to recent snow and ice and an area of high pressure trying to continue to influence our weather with flow from the north…pumping in the Canadian air. The warm air going overtop the cold air will produce light, overrunning precipitation. Therefore, widespread drizzle is expected and areas of fog. The fog will become more pronounced as temperatures warm and mild air rides over the snow pack in place. Removed from the coast, temperatures will be slightly below or around freezing as the drizzle begins. This may allow for the tiny droplets to create hazardous black ice and leave a light glaze of ice. We anticipate the Pocono Mountains and the Lehigh Valley to hold below freezing the longest, perhaps into the Monday Morning commute.

Warm fronts can cause a wide variation in temperature for the area. This time of the year, especially with the snow covered ground, they can also get hung up and fail to move as far north as one would expect. Fog formation is another factor as mild air sits above a snow pack and the low sun angle takes time to burn fog off. Therefore, our forecast for Monday in the temperature department should be viewed as one made with low confidence. Assuming the more reliable models are correct, Philadelphia should make it to the mid 50s. More aggressive numbers have Philadelphia around 60. Should we get well into the warm sector, thunderstorms would be a possibility on Monday Afternoon and Evening with a strong cold front. The colder air lags about a day behind the front.

Another system approaching for Thursday will bring a chance for rain and maybe some sleet pellets. I would be watching this, especially across our northern areas, for possible colder trends which would increase the chance for less liquid and more frozen precipitation types. A secondary system forming to the south around Saturday will be fighting an area of high pressure just to our north. If the system can move northward enough, snow and sleet could break out in the region with the air appearing cold enough.

This forecast period is not one set in stone. Check back with us throughout the week for updates and tomorrow we will have an update on temperature ranges in our Daycast feature.