If/Then/Else

Finally starting to see a consensus evolve, at least with the first two parts of the storm.  However, this remains and “If… Then… Else…” forecast.

IF we stay all snow on Thursday, THEN we’re looking at 8 to 16″, perhaps as much as 20″… ELSE, if rain or sleet enters the equation per warm air aloft, then we’re looking at 4 to 8″, perhaps as much as 10″.

Last night’s model data didn’t do a whole lot to my thought process regarding this, but some clarification on the three parts of the storm:

1) The first part of the storm – Weds night into early Thrs – will feature some pretty heavy snow.  This seems like as close to a slam dunk as you can get, without jinxing the whole thing.  Snow will arrive between 7 and 10 pm, perhaps a bit later in the far north.

2) The second part of the storm – Thrs mid-morning and early afternoon – is still the most uncertain… as warm air gets pulled into the storm aloft (~5,000 ft up).  It will remain plenty cold at the ground for snow, but if the warm air aloft works overhead, then bye bye snow… and hello sleet, freezing rain, and rain.  The overnight model guidance shows this line setting up somewhere between the Bay and the Blue Ridge.  The NAM, UKMET, and Navy Models keep the warm layer (temps about freezing aloft) to our east, and are mostly all snow.  And lots of it.  The European and Canadian pull the warm air aloft almost to the Blue Ridge, so sleet and rain cut into snowfall totals across much of the Piedmont and I-95 corridor.

3) Part three is courtesy of the parent upper-air low… the feature at the jet stream level that helped spawn this whole thing.  It comes thru Thrs afternoon and evening, and will be good for a bonus round of light to moderate snow in the afternoon/evening on Thursday.  Now we’ve got some models showing this feature spawning a new coastal low just east of the Delmarva, which certainly could complicate things.  Something we’ll have to monitor.


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