Final Storm Forecast : Wednesday 2/7/18

A storm system will approach from the southern Ohio Valley on Wednesday.  With plenty of cold air in place, we’ll see a widespread snow event break out across the Hudson Valley during the morning.  However, instead of seeing the low pressure jump to the coast and redevelop… the low pressure will hug the coast, and actually track just inland.  This will allow a surge of warm air… both at the mid levels of the atmosphere, and at the surface… to push into the Hudson Valley.  As a result, as we move through the afternoon on Wednesday, most of us will watch the snow transition to a mix of sleet and freezing rain… before some of us see it turn to a plain cold rain before ending.  Let’s take a look:

Timing

  • 7am to 10am: Snow begins from west to east across the Hudson Valley
  • 10am to 1pm: Snow falls heaviest across most of the region
  • 12pm to 2pm: Snow mixes with/changes to sleet & freezing rain south of I-84
  • 2pm to 5pm: Snow mixes with/changes to sleet & freezing rain north of I-84 (mix turns to rain south of I-84)
  • 6pm to 9pm:  Rain & Mix tapers of from west to east

Snowfall

  • Catskills (Zone 1 & 2) : 6 to 10 inches
  • Majority of the Hudson Valley (Zone 3, 4, 5, 6 & 7): 3 to 6 inches + tenth of an inch of ice
  • Lower Hudson Valley (Zone 8): 2 to 4 inches + tenth of an inch of ice
  • Extreme Lower HV (Zone 9): 1 to 3 inches + some ice

Discussion

The major change from our preliminary forecast is that the center of low pressure is going to track inland, instead of off the coast.  Without a deepening trough and an upper level low pressure to push the storm off the coast… this system wants to track just inland.

Futurecast Radar : 7am through 9pm Wednesday

At first your eyes will be drawn to the snow and wintry mix on this radar… but if you can, try to spot the red “L” indicating the low pressure that starts out over Kentucky and West Virginia (bottom left of the graphic).  Notice how it pushes up through Pennsylvania, and right over the Hudson Valley, before pushing into Massachusetts.  This tremendously western track, allows copious amounts of warm air to surge right up the coast, and into the Hudson Valley.  So despite tons of cold air in place, and lots of moderate to heavy snow on the map initially… most of us will change over to a wintry mix… and possibly even rain in parts of the area.

Take a look at the 850mb temperatures with this storm.  It shows that there is PLENTY of cold air in place when the snow arrives on Wednesday morning…

This is the temperature profile at cloud level, where the precipitation forms, and falls to the surface.  Where you see white… temperatures are below 0°C, cold enough for that moisture to fall from the cloud in the form of snow.  At 7am… temperatures at the ground will be in the 20s… plenty cold enough for that snow to fall all the way to the surface.  So we expect several hours of steady, moderate snowfall across the region.

But watch what happens as the day progresses, you may notice that red and white box at the bottom left of the image, indicating the strong SW flow that is setting up.  As the low pressure tracks NE, into the Hudson Valley… it’s going to pull all that mild (above freezing) air… right up into the Hudson Valley.  By 4pm… here are the 850mb cloud level temperatures…

Notice that all the cold (below 0°C) air has eroded out of the Hudson Valley.  This means that whatever falls from the cloud at this point, will fall as liquid rain.  Now… if the air is cold enough near the ground, that liquid rain may refreeze into sleet or freezing rain.  Much of the Hudson Valley will see that be the case, as temperatures are expected to hold in the upper 20s to low 30s at the surface.

So we anticipate a several hour period of sleet and freezing rain across the Hudson Valley, once the snow changes over.  So that means on top of the snow… a layer of sleet and freezing rain will accumulate.

So in terms of the forecast… we have lowered the snowfall totals in accordance with the development of this inland storm track.  If the storm were to track just off shore, we’d be talking about widespread 4 to 8, or even 6 to 12 inch snowfall totals.  But you can see on the model simulation, the heaviest snows are pushed out of the Hudson Valley… with the exception of the Catskills…

So as always, we’ll track the storm through the event.  There can… and will be… surprises.  There always are.  So we’ll need to keep an eye out as the storm unfolds, to see if the heavier snow bands can really do their work before the milder air pushes into the Hudson Valley.  Remember… despite the slightly lower snowfall totals… conditions will still be treacherous on Wednesday.  3 to 6 inches of snow, followed by sleet and freezing rain will still make for extremely icy travel.  So use extra caution.

Be safe… and have a nice Wednesday…