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    Joe Lundberg

    A Major Winter Storm and an Arctic Outbreak, but Then...

    1/29/2010, 6:56:44 AM

    Friday, 11:30 A.M.

    It's the weekend, baby! I'm so thankful to have two days outside of the office, pretty much not working, though I'll have to keep a constant tab on the maps to track the storm and follow the wayward changes of the models.

    Three things are a lock over the next week. One, the big storm dumping the big snow from parts of Oklahoma and southern Kansas to Virginia and North Carolina into tomorrow night. Two, the Big Chill across the eastern two-thirds of the country through the weekend. And three, the Big Warm-Up next week. Well, okay, it may not be a BIG warm-up, but the arctic chill will disappears from the northern Rockies and northern Plains by Wednesday, and from the Midwest and Great Lakes by Thursday. It will also moderate toward normal or beyond in much of the Northeast, while the chill simply eases across the southern tier of states. Bottom line, the next five days will clearly be colder than the following five.

    With regard to the storm, not much else needs to be said. It's a Southern special, with all of the snow south of the Mason-Dixon Line in an east-west fashion all the way out to northern Missouri and northern Kansas. South of there, a gradual gradation of snow, with some of the big winners easily over a foot of snow, with some places likely to be over 20 inches. I haven't changed my thinking since yesterday on where those lollipops might be.

    I will throw in a greater area for icing with the storm in a belt from the Red River Valley and southeastern Oklahoma all the way to central and southern North Carolina into parts of upstate South Carolina. Out in the Plains, it hasn't been the really cold arctic air mass that is centering itself on the Great Lakes and Northeast this afternoon, but cold enough in the low levels to drive temperatures below freezing, while there's still a wedge of warm air aloft.

    The threat of flooding is ongoing from central Texas eastward throughout the Deep South, as most areas will pick up an inch or two of rain. There is still a risk of severe thunderstorms, albeit a low one, across the Gulf Coast this afternoon into tonight, and perhaps down the Florida Peninsula tomorrow.

    With regard to the cold air, that's already in place, and it will drive temperature departures to 20 below normal this weekend into Monday, particularly in areas that get buried by snow in the next 36 hours. But even where it doesn't snow, it will be a solid 8 to 15 degrees below normal, and northern New England will get another surge of arctic air to open up next week.

    As next week wears on, it won't get any colder. The question is how much will it warm? That's a fascinating question! As some of you have pointed out, some of the teleconnection indexes are really banging the cymbals for cold. For example, the Arctic Oscillation:

    http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.sprd2.gif

    Note that as it went into negative territory in December, we gradually went into the tank across the nation, with the core of the cold centered on the Plains. As the AO started to ascend, the cold eased heading into the second week of January. Now it's trending downward, and we have more cold, and a good snowstorm to boot.

    The North Atlantic Oscillation, or NAO, isn't quite as convincing:

    http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/new.nao_index_ensm.html

    Trending negative, but not in any extraordinary way. However, if you compare that version of the NAO to the NCEP and ESRL/PSD versions, you'll note it much more negative:

    http://www.esrl.noaa.gov/psd/forecasts/teleconn/images/compare.pn.png

    Taking a closer look at the PNA forecast by the same outfits, you'll note it largely positive, with the one exception coming during the middle of next week. Of course, that could well correspond to the next BIG storm likely to come across the country.

    Again, the CPC version of the PNA forecast looks less compelling:

    http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/pna.sprd2.gif

    Perhaps the biggest difference I find is the forecast for the EPO:

    http://www.esrl.noaa.gov/psd/forecasts/teleconn/images/compare.we.png

    If the ESRL/PSD version is more accurate, I would think there's not much chance of a strong Pacific jet crashing onto the West Coast and flooding the country with warm air as we have seen at times in many recent winters!

    But then you take a look at the GFS temperature ensembles:

    http://www.meteo.psu.edu/~gadomski/ENSTDEP2_0z/tloop.html

    What do you see? A flood of warmth! It originates in the northern Rockies and northern Plains during the middle of next week, but spreads out to the east and south late in the week and into next weekend, and it doesn't really retreat much going into the following week!

    Huh?

    It is a head-scratcher, to be simple. The strongly negative (and growing more so, if the modeling is to be believed) suggests the cold air is there to be delivered. The negative NAO would imply blocking, and the positive PNA would imply Western ridging and Eastern troughing, yet the cold allegedly just disappears into thin air!

    To be fair, the Canadian NAEFS product has not been calling for much cold, either:

    http://www.weatheroffice.gc.ca/ensemble/naefs/semaine2_combinee_e.html

    I can't show you the latest European Weekly Climate Forecasts, but the first week of February would appear more in line with what you would expect, with not much warmth. In fact, its largest cold anomalies are over New England (probably owing to the early week arctic outbreak directly aimed at them), then over the Southeast and Tennessee Valley (probably a hangover effect from the snow cover laid down by the current storm), then the Southwest (maybe paying homage to the next storm?), and lastly over the northern Rockies and northern Plains, a complete contrast to what the GFS ensembles are portraying.

    I'm not sure what to make of it, quite honestly. Again, I'm certain it won't be AS COLD as it will be today through Tuesday, but Wednesday through Sunday may not be as warm as the GFS ensembles would lead you to believe. This opens up another can of worms, too. Which idea is right? Another significant warming? While I'd welcome it with open arms, I'm very hesitant to jump on the bandwagon, as my eyes are suggesting something not quite so warm.

    Perhaps what the models are having trouble handling is a redeveloping split in the jet stream. My guess is the various models are interpreting this split in different ways. The GFS and perhaps the Canadian to a lesser extent may be pushing the northern branch farther north that the European, and therefore keeping the arctic highs at high latitudes and not allowing the deep chill to come very far south, while at the same time the very active southern branch keeps the storm train rolling across the southern half of the country to promote the cooler, wetter pattern.

    Indeed, if you examine the Week 2, 3, and 4 European Weeklies, it looks like massive blocking ensues through the entire month of February. The maps are painted blood red across Canada, with warm anomalies across the northern tier of the U.S., and low heights and below-normal temperatures throughout the southern tier of states. And I bet it would be quite wet, too!

    This reeks of a very stormy period. Maybe the severe cold is gone after the early part of next week, and it doesn't get as cold again for the rest of the winter season. I'm not ready to marry myself to that statement. But I have to believe the remainder of winter will hardly be a bore for those of us who are really into weather forecasting! The bust potential is high, but so are the rewards in a high risk pattern.

    Let's see. 15 degrees and partly sunny with a wind chill of 1. Bare ground, nary a flake to be seen this weekend. Yeah, what's not to love about that?

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

    Joe Lundberg