Saturday, January 12, 2013

Perhaps Some Snow On Tuesday Or Wednesday

There's some rumblings from a few of the computer models that Tuesday's precipitation could fall as snow around Philadelphia or nearby. It's possible.  A wave of energy will track along Monday's cold front and with colder air pushing in from the north and northwest, some of the models suggest that precipitation could fall as a bit of light snow (or sleet) on the northern and northwestern edges of the precipitation shield.

Typically in setups where the cold front that is coming in is pushing in faster than what modeling is catching onto as we approach the event, we see the storm track suppress a bit as we approach the event...and I tend to be suspicious of models that try to push snow up into Allentown and points northwest...models like the Canadian, which has a historical bias of strengthening waves of low pressure, are doing this.  It doesn't mean that it won't snow anywhere with the event...but I think any precipitation that comes into the region on Tuesday will likely be confined to Philly and points southeast.

Question then becomes a matter of timing and amount of available cold.  The GFS (below) shows the lower levels are marginally cold as the magic (850) line is running across an Atlantic City-Dover-Washington line (give or take), which means areas north of there could be cold enough for a little bit of accumulation of snow and/or sleet.  The GFS suggests an inch or two could fall south of the city on Tuesday, with a bit more snow possible down towards Washington, DC.

If the track gets suppressed further, which is possible if the push in the wake of cold continues to be pretty robust, we could see this track nudge farther southeast and bring any accumulations farther south and southeast on Tuesday afternoon and evening.

The GFS is faster with the cold push than the Euro is and the Euro is a bit more northwest with the shield.  However, because of the lack of "push" of cold the Euro doesn't get very aggressive on snowfall suggestion.  The Euro does paint "conversational" snowflakes across Maryland into Lancaster County but because precipitation is modest it isn't a significant event.

The key is "not significant" -- it doesn't look like Tuesday's event would be more than a coating/inch type of an event if it even does fall as snow.  It will be a chilled event as precipitation moves in to an advancing colder airmass but the cold is seasonal in nature, not arctic in the first shot.