Tuesday, January 15, 2008

Weather update: Time for a call

This appears to be a minor, perhaps even marginal, event -- of course, when you've gone two years without ANY event, even minor events are worth SOMETHING.

Here's how it looks:

Precip will begin sometime between midnight and 5 a.m. Thursday morning, probably as a brief burst of snow. It will mix with, then transition to sleet rather quickly. At best, the snow and sleet are enough to cover the ground, but there may not even be that much.

Then we transition to freezing rain. We'll see light icing -- on the order of .1 to .2 inches, then it will turn to rain with temps holding between 32 and 35 for the rest of the day.

This is very close to what the NWS forecast which comes out later today will show and falls in the "marginal event" which was tied for my highest percentage probability Monday afternoon.

What can go wrong: 1) The model trend toward warming continues and we end up with all or nearly all rain. 2) Precip is so light that evaporational cooling does not kick in fully and we end up with all rain

What can go right: 1) Models significantly underestimate the strength of the CAD and we see a longer period of snow, giving us 1-2 inches, before a changeover to ice. 2) The NAM is right, precip is heavy and "dynamical cooling" helps keep precip frozen.

We're still about 36 hours for onset -- that is enough time for changes.

Current percentages:
No precip: Less than 1 percent
All rain: 35 percent
Marginal event (dusting of snow/slight ice glaze) 40 percent
Minor event (1-2 inches of snow/minor ice coating) 20 percent
Moderate event (2-4 inches of snow/moderate ice coating) 5 percent
Major event (4 or more inches of snow/major ice coating) less than 1 percent

Also, an important note, the UK model shows ANOTHER system affecting us Friday night into Saturday. The Euro and GFS suppress the system to our south and east -- this would be either snow or nothing (no ice or rain --- too cold). Looks like a long shot, but worth keeping an eye on.

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