Monday, December 21, 2020

Christmas Snow is Coming...How Much and Where?

Warm Christmas 1982

It's not every year that we receive snow or have snow on the ground on Christmas Day. The chances historically are around 40% which isn't great. 

Back on December 8th in my post HERE I went into detail on the many forecast elements. Most were showing an active storm track with period of milder air. There was ONE we were watching closely as a driver toward a COLDER and snowy solution:  The GREENLAND BLOCK!

Here is the pattern showing the Greenland Block back on December 11th.  See the warmer colors near Greenland and the North Atlantic? 

Along with the Greenland Block, the trough in the western US was promoting the development of a potent storm system. Watch the blue colors across the west...

Here is the Tuesday December 23rd frame from December 8th...

As of this writing, the radar (Monday morning) is now showing that storm system. It's currently off the west coast.

What type of temperatures are we looking at before and after the front goes through? Wednesday will be "mild"

Christmas Eve morning temperatures will be in the 40s.  Watch how FAST the temperatures drop.

The question isn't whether lake effect snow will develop, the question is WHERE and HOW MUCH Christmas Eve night into Christmas Day.

General snow will develop Christmas Eve impacting much of the state of Ohio after morning rain.

Now the Lake Effect:

The 850 mB temperatures (5000 feet) will be around -18C.

Lake Erie temperatures are in the lower 40s.  For comparison, the water is a bit warmer than at this point in 2019.  No ice on the lake anywhere.

All except ONE lake effect parameter is checked:  Wind Direction

A shift from a westerly wind to a more WNW or NW wind can make a HUGE different in snow movement, amounts and locations.

Preliminarily this is what a west wind lake effect snow event could potential look like. A band paralleling the shoreline with a sharp cutoff in snow amounts north to south.
National Weather Service Bufkit is showing a brief period of EXTREME instability Christmas during the day.

It is way too early to post specific snowfall forecast numbers. But given the conditions as we see them now (Monday morning) I think they'll be snow amounts in the Lake County, northern Geauga and Ashtabula snowbelt areas that could exceed 20"+ from late Christmas Eve through Christmas day!