Wednesday, November 24, 2010

Unfortunate Timing: 1-3" of Icy Snow Later Today

Doppler Update: 8:35 am. Radar shows snow (mostly aloft) - evaporating before reaching the ground. Snow should reach the ground over western MN later this morning, reaching the metro area after 1 or 2 pm, getting heavier/steadier as the afternoon goes on. Strong upward motion overhead may spark a period of freezing drizzle by midday. With surface temperatures below freezing some secondary roads/bridges may become very icy between 11 am and 2 pm.

How Much? This seems like a reasonable solution: most of the metro area in the 1-3" range (more north/east metro, less south of the cities). As much as 6-10" will accumulate along the North Shore of Lake Superior. South of the metro this will be more of an icing event, a period of freezing rain/sleet likely this afternoon. With ice in the mix travel may actually be worse SOUTH of MSP than north (where precipitation will fall as all-snow).

Latest NAM Output. Hot off the wire - the latest amounts are less than the computer runs last night (which were predicting closer to .40 to .50" liquid). The latest model is printing out .23" of liquid. With a 10:1 ratio in place (temperatures in the lowest mile of the atmosphere just below freezing) that should translate into 2, possibly 3" of snow. Far northern/eastern suburbs may pick up closer to 4", less than 1" from Mankato to Red Wing (where more ice will mix in, keeping final snowfall totals down).

Reasonable Continuity. Our blood pressure drops (a bit) when all the models converge on a single solution, when all models are reasonably close in their snowfall outlook. Not sure how we see less than 1-2" across most of the metro, a few spots may pick up 3 or 4", especially from Anoka and Ham Lake to Hugo,  White Bear Lake and Taylors Falls. Yes, it still looks (barely) "plowable". It's not so much the amount - it's the TIMING of the snow & ice.

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