Monday, November 25, 2013

Nor-Easter Developing: Heavy Snow Imminent

WINTER STORM WARNING FOR ASHTABULA, GEAUGA, TRUMBULL, PORTAGE, STARK, MAHONING AND TUSCARAWAS COUNTIES FROM 12PM TUESDAY TO 4AM THURSDAY. First, some clarification on winter watch/warning definitions: A WINTER STORM WATCH means there may be hazardous winter weather due to heavy snow. Heavy snow means 7 INCHES OR MORE of accumulation in 24 hours or less. A "WATCH" is a long range prediction. They are issued at least 12 hours before the hazardous winter weather is expected to begin. When the storm becomes imminent (inside 12 hours or occurring) or has a high probability of occurring, watches are upgraded to a "WARNING"

The active pattern continues in the month of November. We've already had a little over 3 inches of snow at Hopkins (more in the snowbelt), the most since 2008 through the 25th of November. Our high temperature Sunday of 26 was the coldest daytime high AFTER the 20th since 2005 when we only hit 24 on the 25th. Prior to that, you have to go way back to 1976 to find a colder high temperature during the last 10 days of November.

Updates on my twitter page: SCOTT SABOL, TWITTER


Now for the setup this week: The 500 mB steering currents show a trough digging across the east. Notice that the clipper low is starting to phase with the panhandle low to the south. So that by Wednesday afternoon, both lows are completely absorbed into the mean somewhat negatively tilted trough. In conditions like this, the low can amplify (get stronger) very fast due to the sharp variations in conditions to either side of the trough.  Higher levels of instability can develop which can create bursts of heavy snow. Fortunately, I think that this will occur in western PA and upstate NY.

The US radar is already showing the merging of the two systems...

The snow from the clipper will be the first wave of light snow tonight. Accumulations will be small, perhaps an inch in spots by early Tuesday morning.

The future radar loop (high resolution NAM 4 km) shows distinctly the clipper snow coming in from the northwest, a break, followed by the panhandle snow/rain from the southwest. Here is the youtube clip. Watch the time clock at the top of the video. 

Heaviest snowfall amounts still seem to reside in the eastern counties closest to PA. The latest bring back some of the heavier snow west. Here is our updated snowfall forecast. The NWS forecast is lining up very well with our forecast so I'll go with their numbers. Remember, this is just guidance as snowfall will vary a bit from place to place.

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