UPDATE ON POTENT WINTER STORM...
The latest data from Sunday's morning's models continue to point at a major winter storm for the majority of my area, especially for the area near and south of HWY 20. The storm is expected to materialize mid-day Monday and last into much of Tuesday. As I pointed out in my last post Saturday afternoon , I felt winter storm watches should be out all the way north to Dubuque and east to Chicago and the NWS has now come around to that conclusion. At some point today the NWS will finally upgrade much of the watch area to winter storm warnings as the NWS in Des Moines has already done.
Below you can see the winter storm severity index from the Weather Prediction Center shows major impacts from the storm over much of southern Iowa where the heaviest snowfall is anticipated.
WPC also shows these odds for an inch or more of snow
The indicate these odds for 4 or more inches.
The official NWS forecast for now shows accumulations that look like this
That would be on top of these totals which occurred Saturday night. The highest amounts were concentrated within a triangle from Iowa City to Waterloo and on to Dubuque with 2" plus reports.
THE LATEST MODELS AND THINKING ON MY PART
So what's new to discuss with the latest trends? To me it is clearly what the EURO has been indicating since last night. It has picked up on the idea that the storm is going to reach peak intensity over SC Iowa and then begin weakening as it shears stretches and elongates. The forcing is not as focused and snowfall not as intense as the storm heads east into eastern Iowa and Illinois. With less total QPF (total precip) the amounts begin to decline as the storm drifts off to the east. For example, over the last 3 runs of the EURO which occur every 6 hours, totals in Cedar Rapids have gone from 13.5" to 9.9" and in Davenport from 14.7" to 11.6". The overall track has changed little, just the amounts. This is now what the EURO is showing using the Kuchera method which takes into accounts snow ratios over the traditional 10:1 average.
The high-res 12K and 3k NAM are trending this way too.
The 3k NAM
The 12k NAM
The GFS and Canadian GEM have not gone down that road yet and are still throwing the kitchen sink with accumulations that are several inches higher, ones that would represent top 10 all-time snowfalls in spots. They eventually do show the weakening trend but it happens further east which makes a notable difference. Here's what they show for comparison, again using the Kuchera method.
The Canadian GEM
SO WHAT TO MAKE OF THIS DEVELOPMENT
Needless to say I can't be sure what will happen but the EURO "the Dude" and at this time frame it's usually leading the pack and I hate to bet against it and the idea of an earlier decrease in totals as the storm advances east across my area. For that reason I would use the EURO above as the template as to how this turns out. It is still a significant storm for my region but not the elite one it would be if it were intensifying as opposed to weakening.
Data will be coming in all day and I will be throwing out new models and tidbits on an occasional basis. The new GFS, 3k, and 12k NAM will be on here around 4:00PM so look for that update. We should have warnings out by then which will also be interesting. Meantime it looks like my entire area has a high chance of seeing snowfall of 5-10", maybe a touch more in a few spots. However, if the weakening is even more pronounced the numbers could go down a bit. I'm very anxious to see if the GFS jumps on the back of the EURO. It usually does. See you soon and roll weather...TS
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