2/25/09: Winter Storm Update

Issued at 11:01 PM CST, Wednesday, February 25th, 2009

Surface analysis at 04z showed low pressure of 1005 mb centered over Eastern Wyoming…Or west of Rapid City South Dakota. A wide area of weak pressure falls stretched from Southern South Dakota down to North Texas late This Evening, so we should see the area of low pressure pull out into the Plains during the Overnight hours.

Water vapor satellite imagery along with the latest enhanced satellite imagery definately reveals that this system is beginning to take off now as forcing associated with this weather system heads out into South Dakota and Southern North Dakota. The main area of snow was favoring the Central, Northern, and Western part of South Dakota attm with movement toward the E/NE.

No changes have been made to the winter weather headlines that are in effect for various parts of Minnesota through Thursday Evening…Refer to my previous blog posting on this information.

The 00z model run from Tonight is pretty much on track with the 12z model run from earlier Today…Only change was that the newest NAM has shifted things (QPF) slightly more to the north again, kind of similar to last night’s NAM run, before the 12z run This Morning took a shift to the south. So it appears that the NAM is having some issues with this developing storm.

The surface low itself should track from the Northern Kansas-Southern Nebraska area…East-northeast toward Chicago Illinois by Thursday Evening. Usually with this type of storm track, heavier snow would be confined to just Southern Minnesota and the South/East parts of Wisconsin, but this storm has lots of upper level support going for it, plus the tremendous temperature disparity. So this storm while lacking a real deep barometric pressure reading will be off-set by all the upper level support it has going for it.

Heaviest snow still looks to favor Western, Central, and Eastern Minnesota with amounts of 5 to 10 inches expected by Thursday Evening. Snowfall rates of 1 to 2 inches per hour are forecast for parts of these areas on Thursday.

I’m more concerned that Southern Minnesota could see more ice or mixed precipitation and less snow as H8 temps of +2 to +4 degrees C were in place per late Evening RUC model, surface temps though were well below freezing in this area…So, as precipitation overspreads Southern Minnesota early Thursday through midday Thursday we could see more ice versus snow with one tenth inch or more of icing certainly possible, especially if this warm layer stays put… Assuming that ice or mixed precipitation lasts longer down South on Thursday, then total snow amounts will likely fall in the 1 to 4 inch range.

For Duluth proper…Snow should commence between 7 AM and 10 AM Thursday with the heavier snow with rates possibly reaching one half inch to one inch an hour moving into the city during the Afternoon or from around Noon through 7 PM. Snow should be winding down in the city Thursday Evening. In my previous forecast I was calling for 1-3″ of total snowfall for Duluth, but after looking at the last few runs of the SREF model including the 21z model run, and after considering the latest GFS, NGM, and NAM forecasts…I will be raising my predicted snow totals to 2 to 5 inches for the city. It wouldn’t surprise me at all if the National Weather Service in Duluth goes ahead and issues a Winter Weather Advisory for the city for Thursday and Thursday Evening. The other thing will have to keep an eye on is the E-NE wind which should develop Thursday Morning and linger through early Thursday Evening here in the city…This could result in lake enhanced snowfall around Lake Superior. Snow ratios here in the city look to be right around 15:1 while we fall under a favorable zone for snowflake growth for about 4-6 hours on Thursday.

I’ll have more updates on this storm as it continues to develop and heads closer to Minnesota.

Stay tuned

Tim

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