Joe Lundberg

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Weekend Storm And Beyond

December 11, 2010; 10:16 AM

Saturday, 11 A.M.

Low pressure continues to deepen in central Iowa at this hour, and it is producing a wild snow storm from eastern South Dakota and northeastern Nebraska into northwest Iowa, southern Minnesota, and northern and central Wisconsin. The Minneapolis area has already picked up more than six inches of snow, and it's still coming down hard from there on east into Wisconsin. As the storm rolls slowly eastward and deepens more, not only will the snow persist, but the wind will increase to point where blizzard conditions will prevail for a time this afternoon and tonight.

Even after the snow is over, it will be brutal across the Midwest with temperatures in the single digits and winds gusting to 40 and even 50 mph, making travel all but impossible for a time until the winds can abate from west to east later tomorrow and tomorrow night into Monday.

For all that is going on here, this storm will be much more of a yawner, if you will, for most places across the Ohio Valley on east. Yes, there will be some snow behind the cold front in and especially west of the Appalachians out to Missouri as the arctic air pours in from the north and west. But the snow amounts, in and of themselves, won't be all that impressive, as you can see from our latest snowfall forecast below:

The danger in these areas will be from the rapid drop in temperatures tonight and tomorrow from the eastern Plains and middle Mississippi Valley eastward across the Ohio Valley into the mountains, and southward into the northern Gulf Coast states. The rain that will fall in these areas may not have enough time to completely evaporate off roads surfaces, driveways and sidewalks before temperatures drop quickly below freezing, creating a 'flash freeze' that might even cause some car doors to freeze shut!

Farther east from Georgia and the Carolinas up into eastern New York state and central and southern New England, the main form of precipitation will be rain. There will be some pockets of either icing or mixed precipitation once you get into portions of eastern Pennsylvania and northwestern New Jersey into upstate New York and interior New England, but even in these places most of the storm will feature rain.

With a secondary area of low pressure forming along the cold front tomorrow, then charging northward into the Hudson Valley tomorrow evening, there will be a corridor along the coastal plain up into eastern New York state and points east that will get a wind-driven heavy rain for a time late tomorrow into tomorrow night, and this may trigger flash flooding. Here's a look at the most recent 12z NAM 48-hour precipitation forecast:

By late Monday, the net effect off these two storms joining into one larger storm over southern Quebec will be to develop a cold upper level vortex over Pennsylvania and New York:

A few other things will follow from this point:

1) The cold is driven off the Gulf Coast through Florida, and off the Southeast Coast

2) The impact of the arctic air being driven over the Lakes will cause significant Lake Effect snows, with 2-3 feet expected in the hardest areas, if not more

3) Sub-freezing temperatures will occur, not just TO the Gulf Coast, but IN to Florida, with a freeze on the table Monday night and especially Tuesday night into central parts of the state.

4) Largest temperature anomalies will be from the Ohio Valley to the Southeast. After the warm ip in the East and into New England, the cold will be shoved underneath the Northeast, so that northern and eastern New England will miss most of the severe cold.

5) Extensive wrap-around snows into the mountains of upstate New York and northern New England into Tuesday, lingering even into Wednesday.

6) Sub-zero cold in the Midwest tonight (even where it doesn't clear and there is wind, it is that cold), Sunday night, Monday night, and perhaps even Tuesday night. Once the wind shuts down and the sky clears, with that fresh snow pack, arctic air, and 15 hours of darkness, many places could be 10 to 20 below over the eastern Dakotas and Minnesota into Wisconsin one or two nights.

I am at odds with the GFS, which seems to be underplaying the extent of the cold in its most recent run. The 850mb temperatures are lower on pretty much all other models, as are projected surface temperatures, and with deeper longwave troughs over the East. I'm not sure why the GFS is doing this, but I have a real hard time seeing it above freezing in New York and Philly Tuesday and Wednesday.

After this, the flow WILL become flatter across the country. It's not that there won't be amplification in the pattern! Quite the contrary, actually. Instead, there will a massive block extending from Greenland westward into the central and northern Canada, with another area of strong ridging over the Bering Straits:

This will literally force the jet stream south across the country. With another upper level vortex building over the North Pacific, it will enhance the southward thrust of the jet stream coming into the West. And since we can't get rid of the downstream block, even though the heights will clearly rise over the South and Southeast during the second half of next week, there will still be an upper level low over New England.

And that should raise some red flags for some sort of suppressed storm track, one with the potential to pull cold air farther south on a more consistent basis as well as lay down some snow farther south than we have seen to this point. With regard to the cold, I don't think it means the same type of bitter arctic air that is sending temperatures to record lows with 20 to 25 degree below normal temperature anomalies for a couple of days, but enough that the potential record warmth across the southern Plains and southern/eastern Rockies through the first half of next week will finally get turned back in a more meaningful fashion, with the potential for it to be colder than than the GFS ensembles would lead you to believe late next week and next weekend.

As far as the snow potential is concerned, there will be plenty of cold air around from the central Plains to the East Coast. With the trough evolving off the West Coast, there will undoubtedly be some pieces spit out of the base of that feature into the West and across the Rockies. Chances are they will take a southern track, but unlike the system that got buried earlier this week across the Gulf of Mexico, there's a much better chance of one or two of these systems late next week and beyond trying to attack the cold with some warmth and moisture. Only this time the cold has nowhere to go, so it should put up a pretty decent fight, leading me to believe snow and ice chances are real.

Notes and Asides:

Today, being December 11, would have been my mothers' 87th birthday. May she rest in peace. I'll keep her holiday tradition going this afternoon when I assemble the holiday fruitcake. And I'll also keep my promise to some of the ladies in our church choir and bake another one of her recipes for orange cookies. Miss you, mom.

Last weekend I had the honor of attending the 11th Southern New England Weather Conference at the College of the Holy Cross in Worcester, Massachusetts. I heard from a number of awesome speakers, including our very own Elliot Abrams. And it was a real treat and honor to meet the great Joe D'Aleo for the first time. His work speaks for itself and needs no introduction! I hope to get to more of these in the future.

While I was away, I also attended the Christmas party hosted by the Pequot Cyclists last Monday, and that was a really nice time, too! I only get to ride with them a handful of times during the year, but I was able to strike up a conversation with a couple I'd never met before, making me feel right at home! And it also helped get me excited about the 2011 cycling season despite the current state of cold weather affairs!

And whilst in Connecticut, I got to spend some time with my dad, who is in good health at 83. He's itching to get out and play golf again, which really warms the cockles of my heart! Unfortunately, he's got the same problem I do with cycling right now - the weather is not on our side! In time, dad, in time! I even got to visit one of my brothers, and spend some time with a couple of high school classmates as well.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Joe Lundberg
Joe Lundberg, a veteran AccuWeather.com forecaster and meteorologist, covers both short and long-term U.S. weather on this blog.