Tuesday, January 22, 2013

Friday's Snow

Snow on Friday looms for a chunk of the region, perhaps for almost all of the Delaware Valley. It's still really early to speculate on amounts and specifics but modeling has been reasonably consistent on suggesting we get a cold enough solution to produce snow for the majority of the region.

One of the things that will determine how much snow ultimately falls is the strength of a spoke of energy that pivots down around the cold trough that's digging into the East now. This spoke of energy is poised to work through Wednesday night into Thursday, producing some snow showers or flurries for portions of the region.

GFS -- yesterday PM's run at the surface

The spoke of energy for Wednesday night has varied in intensity on the GFS but the strength of this spoke is going to determine how strong Friday's system can get and how much snow we get.  The graphics immediately above and below are yesterday's late afternoon GFS run -- surface up top for Friday afternoon, the mid level "energy shot" below for Thursday morning.

GFS -- yesterday PM's run aloft for Thursday AM.

Last night's GFS run at the surface for Friday

This is last night's GFS run (the one that comes out at 11 PM) -- again, surface reflection for Friday evening up top, mid level energy shot for Thursday AM below.  The model is showing, compared to six hours prior, a stronger lead wave on Wednesday night into Thursday, resulting in a bit of a stronger dig in the trough back to the west.  This yields a weaker Friday system in comparison (see the reduced snow amounts on the surface map compared to the one way up top).  This lead wave, provided it isn't too strong and doesn't dig too much, is beneficial since it will help reinforce the chill that's working into the region now.  If this wave weren't there, air would be able to moderate more quickly and instead of a primarily snow event you'd end up with a thud of an event overall as snow changed to rain.   When the wave's too strong, such as in last night's GFS run, the upper levels are bit less favorable for the Friday wave to intensify just enough to produce snow.

The GFS should likely become much more consistent with Friday's event in the next 24 hours as it improves its handling of this upper air feature.  That should in turn give the model a better handle on Friday.

Last night's GFS run aloft for Thursday AM.

The European computer model is a good bit more consistent in the strength of the lead wave but is waffling a bit on the details of the Friday event from a moisture standpoint.  That said, it's snow for the entire region and several inches of snow would fall if it were right.  The Euro has generally suggested between 3-6 or 4-8 for the region in each run, with some spots getting more than that but the general range has been 3-6/4-8.

Euro precip output for Friday's snow.

The GFS' snowier run suggests 4-8/5-10 type amounts, with the less snowy run more along the lines of 2-4 or even 1-3.  Provided the more consistent Euro continues to hold serve, we are in line for the season's largest snowfall of the winter on Friday.  Even if the "dry" GFS run pans out, it's still at least some snow...it may not reach the levels of December 29th north of the city but it would still be better than nothing.