Late March snow? Can it happen? Yes!

UPDATE at 3:02 p.m.: SEE BOTTOM OF POST FOR NEW INFORMATION.

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I can't believe I'm writing this, but our best threat for snow this entire winter may very well be next Monday, THE DAY AFTER EASTER!!!

First, some history. You may think a late-March snowstorm is unprecedented. If so, you didn't live here in 1983. As you can see from the above map, we received a major 8-inch dump on that date -- exactly 25 years ago this Monday.

Now, to the current setup.

The first thing I want to tell you about is something called the NAO -- North Atlantic Oscillation. All winter, the NAO has been in a positive phase. This basically means that there is no "blocking" over Greenland, no high pressure in that region to "lock in" in the cold. This means that areas of cold air are transient, they move in and the high pressure slides off the coast before the next storm makes it end.

Well, the NAO is heading toward a negative state -- just in time for spring!

But before Old Man Winter heads into hibernation, he may have a trick up his sleeve.

I'm going to give you lots of links today, lest you think I've fallen off my rocker.

First, the NWS puts out a medium range forecast multiple times a day.

Here is the top of the latest discussion:

PRELIMINARY EXTENDED FORECAST DISCUSSIONNWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD744 AM EDT WED MAR 19 2008 VALID 12Z SUN MAR 23 2008 - 12Z WED MAR 26 2008 ...POTENTIAL FOR LATE SEASON SNOWSTORM FROM THE MID ATLANTICSTATES TO NEW ENGLAND...MODELS ARE CONVERGING TOWARD EAST COAST/W ATLC CYCLOGENESIS DAY5...WITH THE 00Z GFS AND GEFS MEAN TRENDING STRONGLY TOWARD THEDEVELOPED SOLUTION INDICATED BY THE LAST SEVERAL RUNS OF THE ECMWFAND ECMWF ENSEMBLE MEAN. SEVERAL OF THE 00Z GFS ENSEMBLE MEMBERSARE AS INTENSE AS THE 00Z ECMWF WITH THIS LOW...WITH A SIMILARTRACK FROM SOUTH OF CAPE HATTERAS TO THE ATLANTIC BENCHMARK. TAKEN LITERALLY...THIS GUIDANCE THREATENS A FOOT OF SNOW FROM NEARRICHMOND NORTHEASTWARD TO BOSTON...INCLUDING WASHINGTONDC...PHILADELPHIA...AND NEW YORK CITY. THERE IS PLENTY OFPRECEDENT FOR LATE SEASON HEAVY SNOWFALL...EVEN OVER THE CAROLINASAND SOUTHERN MID ATLANTIC REGION. IN MANY WAYS...MARCH IS ANIDEAL MONTH FOR LARGE STORMS AND IF EVERYTHING COMES TOGETHERRIGHT...THEY CAN BE HISTORIC EVENTS. SOME OF THE YEARS THAT HADDEEP LATE SEASON SNOWS AFFECTING PORTIONS OF THIS REGION IN THISREGION IN LATE MARCH 1942 1958 1964 1971 1974 1983.

Now, on to the very latest run of the computer model called GFS: (if you want to skip to the good part, check out the Wee hours Tuesday morning map)

Sunday evening. You can see high pressure building in as our storm gathers over Texas

Wee hours Monday morning. Still cold, storm on the move.

Monday rush hour. Moisture streaming northward. Check out the three separate high pressures

systems to the north -- they are in perfect position to feed in cold air.

Monday early afternoon. The 850mb freezing line -- very generally a rain-snow line, although less so this time of year because of the higher sun angle -- is on a line from Macon to Augusta to Columbia to Wilmington. We pick up a couple tenths of an inch of precip.

Monday evening. Now, if I saw this map in January, I'd be going nuts. PERFECT! 850 line well to our south. About .5 inches of precip. A gorgeous looking map.

Wee hours Tuesday morning. Another tench of an inch of precip.

TOTAL PRECIP MAP FOR THIS PERIOD. That's about .75 inches. Even if you figure this snow is wet and slushy, we're talking 2-4 inches, perhaps even more.

What about other models?

The UKMET and the Canadian model both show a slightly more suppressed solution -- which is good, since the trend has been to move storms NW (BUT, remember, that's been in a world where the NAO is positive -- this is an entirely different pattern).

The 12z Euro JUST came out and .... KABOOM! A major hit for upstate S.C./all of N.C./and up the coast into Va.

So, what's working against us with this storm?

Well, other than pretty model runs just about everything.

1) Climatology. A good definition is: If it doesn't usually happen, it won't happen. While possible, it is quite rare to see measureable snow here this late in the season.

2) Sun angle. One of the reasons its rare is that the sun is much more potent this time of year. That's why the 850 boundary I mentioned before can't be used as a rain-snow line in March like it can in January -- still, that GFS run shows plenty of room to spare cold-weather wise.

3) This winter's pattern. The trend has been for storms to cut up the Appalachians rather than off the coast, where we need them to go. Of course, this is a totally different pattern.

4) Time. This is still 5-6 days out -- hardly a model "sweet spot." The models will very likely lose this storm, then regain it over the next few days. If the GFS or Euro shows the storm in its Friday runs, it will be time to get serious.

What's working FOR us?

1) This STORM's pattern. While the overall winter pattern has stunk, lots of good pieces are in place for this system.

2) We have some wiggle room. There is plenty of precip and we even have a degree or two of cold air to work with as the models continue to evolve.

3) For at least one run, we've got the Euro in our corner -- by far the superior mid-range model.

3) We’re due! Come on – we haven’t had real snow in eons. I don’t care if Peter Cottontail has already done his deal.

Bottom line: Regardless of what the models show, only a fool would predict snow 5-6 days out in mid-late March. But the truth is, we’ve got a chance, which is more than we’ve been able to say for most of this winter. At the least, the week of Spring Break for school children will be chilly and probably wet, at least at the start.

More to come!

3:02 p.m. WED. UPDATE. Wanted you to see an excerpt from the NWS HPC discussion which was updated just after I posted:

... BEST ONSENSUS AT THIS TIME BASE ON NEWER 12Z MODEL RUNS FOR A SIGNIFICANT LATE WINTER STORM EVENT IS FROM THE SRN APPLCHNSACROSS WRN AND NRN PORTIONS OF NC/MUCH OF VA/MD/DELMARVA ANDCOASTAL NJ. AREA IS UNDER RIGHT REAR UPPER LEVEL JET EXIT PUTTINGMUCH OF THIS AREA UNDER FAVORABLE UPWARD VERTICAL MOTION AND HVYPCPN POTENTIAL.