Joe Lundberg

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Dry and Cold to Warm and Wet

November 14, 2013; 10:06 AM

Thursday, 11:30 a.m.

One of the first things I do each morning in my regular routine is to analyze a weather map. I'll first draw the isobars across the U.S. and Canada, then mark the areas where I see high and low pressure, then do my best to fit fronts into the picture. I'll then etch in the areas where precipitation is falling and finally scallop in areas where it is fairly cloudy. The end result gives me a snapshot of what the weather is like at that moment, and by comparing it the day before, I can get a nice read on how the weather is changing.

Today that assignment was relatively easy! I had one large high dominating the weather over the eastern half of the country, with another high based over the interior Northwest. There was a weak low over eastern Colorado, with another storm, over the southeast corner of Hudson Bay, and a weak low in central Saskatchewan.

In terms of precipitation, there was virtually none anywhere in the country! A few sprinkles near the east coast of Florida, a couple of snow showers in the mountains of Colorado and Wyoming, with a couple of rain showers in the lower elevations from northwestern Nebraska into South Dakota. A couple of showers dotted the Olympic Peninsula as well. Aside from that, though, it is dry in most of the country! Dry AND cold! Look at the six-hour precipitation forecast for this afternoon from the 12z Nov. 14 NAM model:

And it isn't just dry, but it remains cold! Temperatures slipped into the 20s once again from parts of Texas to the interior Southeast, including northernmost Florida! Many record lows fell this morning as the strong surface high moved into position to foster clear and calm conditions, ideal for radiational cooling processes to take over.

Over the next 72 hours though, the cold, dry air will beat a fairly hasty retreat, to be replaced by a much milder and increasingly moist air mass. The heights have already rebounded from their depths yesterday morning and are now rising above normal in parts of the East. Look at the 0z Nov. 14 GFS ensemble forecast of heights and anomalies this evening:

Now, there is a weak upper-level disturbance coming out of the eastern Rockies and heading into the southern Plains, and it is pulling a fair amount of high level moisture into Texas into two pieces. One area is tied more closely to the upper-level feature and has more impact areas of northwest Texas into the central Plains:

As you can also see, though, the second area is coming up across Mexico into southern and eastern sections of the state and out over the western and northwestern Gulf. By tomorrow morning, there will be a fair amount of showers and thunderstorms showing up over the central and northern Gulf. Pieces of this moisture will impact areas from the central and eastern Gulf Coast into Florida, as well as across the Southeast toward the mid-Atlantic states tomorrow and tomorrow night.

With more moisture now on the playing field going into the weekend in a warmer air mass, the state will be set for another potent upper-level disturbance to come in from the Northwest, bring showers and some mountain snows through Washington and Oregon into Idaho and western Montana.

Low pressure will form later Saturday in the lee of the Rockies. Here's the NAM forecast Saturday evening:

Some snow will fall in the central and northern Rockies this weekend as the trough passes, and the air turns progressively colder. Meanwhile, with the storm taking shape late Saturday and Saturday night in the central Plains, it will tap into the growing moisture supply to its south and cause an expanding area of rain to affect the Midwest, and that will be well in advance of the actual upper-level trough.

On Sunday, this storm will cut across the Midwest toward the upper Great Lakes - stop me when you think you have heard this scenario before - drawing even milder air into the Tennessee and Ohio valleys as well as the Great Lakes. The East will get in on the act, too, and more so on Sunday. All the while this is happening, the upper-level trough will slide eastward across the Plains and start putting the squeeze on the atmosphere that will be plenty warm and moist by the time we get to Sunday. The various computer models handle this squeezing process differently, but suffice it to say that it will rain across the Ohio and Tennessee valleys up into the Great Lakes Sunday, a rain that will spread over the Appalachians into the East with time later Sunday or Sunday night into Monday morning.

But then, just like that, the front will charge over the Appalachians and whip across the East, sweeping the warmth and moisture right out to see again. That will dry out the atmosphere, and usher a much colder air mass right back across the Plains, then into the South and East early next week, completing the cycle.

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

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About This Blog

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