Thursday, February 14, 2013

Slower Outcome = Snowier Result Saturday

Wanted to take a moment and explain the differences between last night's GFS run, which had painted one to three inches of snow, and today's midday GFS run that painted a more significant outcome. Please note that the GFS from midday is, as of now, an outlier to almost all other modeling for this weekend's minor event in terms of outcome.

The midday GFS showed a slower arriving trough into the East.  You can see the differences for 5 PM Saturday on the map immediately below from the slower look of midday today (above) and the fast look of last night below.  The trough, as it hits the coast, helps fire up and intensify low pressure in the Atlantic.  The faster movement of this mid level trough keeps the system a bit weaker and scoots the low pressure along more quickly.

Because that run of the GFS is slower in bringing the mid level trough into the region, the low isn't forced to push along as fast.  The result is that the low can develop closer to us, spread more snow across the region, and allow for several inches of accumulation as opposed to a few.

You can also see how farther northeast the snow shield is on the GFS from last night compared to the midday run.  It's a decent spread geographically of a couple of hundred miles.

The dynamics with this system will be similar to what transpired last night -- the low will develop nearby and precipitation will intensify as the low develops.  Coastal regions *may* do better with this event than west of I-95 due to being closer to the low.

As for snowfall projections?  You'll get the pretty map and graphics tomorrow but as of now I'm still holding the line on a general one to three type event for most of the region that could surpass that in spots near the coast.  Some spots, like Wednesday, do worse than others and it'll be another battle of snow bands as this event moves through.