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    Not a Stormy Pattern, But Fascinating Just the Same

    1/18/2013, 7:31:00 AM

    Friday, 11:30 a.m.

    The storm that dumped a lot of snow on parts of the South in the past 24 hours has come and gone, but boy! Did it leave its mark! Look at the visible satellite image:

    That's a very large area extending from northeastern Tennessee and southeastern Kentucky into parts of North Carolina and Virginia. Some places picked up a foot of snow in western Virginia and southern West Virginia. However, that storm is now well off the coast, skies have cleared, and it's a sunny but chilly day.

    We've also seen an arctic cold front come through the Northeast into the mid-Atlantic overnight. As arctic air masses go, it is clearly strongest across New York and New England, with areas to the south barely getting ankle deep into the cold air. It's best seen in the surface dew points:

    Those are single-digit dew point temperatures across New Jersey and much of Pennsylvania on north. It's not much below normal when you get right down to it in the mid-Atlantic, but it's still a piece of the arctic air mass flying by to the north.

    Just upstream, though, another surge of mild air is already moving into the Midwest from the Plains. As low pressure zips by the Great Lakes tomorrow, it will drag that milder air right back across the Ohio Valley into the mid-Atlantic and into New England. Here's the latest NAM surface map forecast for late tomorrow:

    That will translate into the 40s for Chicago and Detroit and pushing 50 from New York to Philadelphia, and probably in the 50s around Washington, D.C. Don't get used to it!

    If you study that image above, way up in northern Saskatchewan, you might note a local 'dip' in the thickness values. That's actually the signature of another upper-level disturbance that will turn what is a bitterly cold air mass moving into the northern Plains and Midwest tomorrow and make it even colder late Sunday into Monday. In fact, as the leading push of arctic air flows through the Great Lakes into the Northeast and mid-Atlantic states on Sunday, it will lose some of its intensity. I actually think Sunday will be another pretty balmy day by Jamuary standards across southern and eastern New England down into the mid-Atlantic. There won't be a temperature inversion, so the wind that picks up will combine with the sunshine to promote a well-mixed boundary layer. That means despite the falling 850mb temperatures in the afternoon, temperatures at the surface will still be in the 40s, if not 50 or higher in the the mid-Atlantic. Look at the projected surface temperatures Sunday afternoon off the latest NAM model run:

    Then there is that trailing disturbance. Look again at the NAM surface forecast for Sunday afternoon:

    There's a little snow with that disturbance streaking across the Dakotas into the Midwest. It won't be much, but it is a feature that's real. As is the cold that will follow behind it. I'm pretty much convinced Minneapolis gets at least one calendar day with temperatures staying below zero (Monday) and maybe two if Sunday makes it. Chicago may not get that cold, but single digits seem likely for a high Monday, and maybe even Tuesday.

    The cold does go to the Southeast Tuesday and Wednesday, though in studying the 500mb heights through next week, they never drop below about 576dm in central Florida. Period. That tells me the cold isn't as penetrating there as it is farther north and should minimize the threat of a freeze in the citrus groves this time around.

    As this trailing disturbance gets off the East Coast, a surface storm will finally blow up, and it's likely to only graze southern and eastern New England but pull the cold air in from the West more forcefully.

    While all of this is going on, the upper-level ridge that strengthens along the West Coast will promote warmth, especially in California and higher elevations of the Northwest and central and southern Rockies. In the valleys of the interior Northwest and into the central Rockies, there will continue to be a steep temperature inversion that will keep temperatures below normal in places like Pendleton, Boise and Salt Lake City.

    The warmth in the West won't stay there next week. It will come east, moving easily onto the Plains, then running into more and more resistance as it moves across the Ohio Valley into the Great Lakes and Northeast. Still, it will mean an easing of the cold with time Thursday and Friday in these areas ahead of another storm.

    Another fascinating aspect of this pattern is that I can easily see that storm developing off the Northeast coast Tuesday and Tuesday night ends up blowing up and rolling into northeast Canada later in the week. Here's what I can see happening then. It wipes out the downstream block and makes room for the storm late in the week to move through the Great Lakes into New England. You wouldn't expect that given how cold it will be, yet that could easily happen. Again, the warming underneath that storm will run into some pretty stiff resistance as it comes into the Great Lakes and New England, and it could mean those areas get some snow and ice despite the warming aloft. However, once to New York City and points south and west, wouldn't it be ironic to see all these storms go around you to the north and south, go into a very cold pattern, only for a storm to come along and bring rain, not snow in the end? Maybe I'm the only one who sees that!

    And what's really interesting is that it will turn cold again behind that storm next weekend, only for this process to be played out again going into the following week. Several days of cold, then a warmup and rain. That would be too cruel for the snow geese to handle, but I can see it in the mid-Atlantic and Ohio Valley, perhaps even into the lower Great Lakes and parts of southern New England.

    Maybe the cold air will hang on more strongly, and the block won't get wiped out that fast. However, given how the snow has found ways to elude places like Chicago and Washington, D.C., and New York City, would it be that big of a shock, really? Me thinks not.

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


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