Wednesday, February 11, 2004

WED 2/10 EVENING UPDATE: "SEVEN DAYS, SO MANY WAYS, BUT I CAN'T RUN AWAY."
- Seven, by Sting in Ten Summoners Tales


This may be good news for some, bad news for others, and no news for many. The next seven days will determine for sure if we are safer to rely solely on computer modeling, or to trust our gut and keep a close eye on the computer in case it "misses the big one." I am not running away from my forecast. I will always give you the straight scoop, but it is important to understand that I will, from time to time, back off a forecast some if I think it needs more analysis. This is one of those cases. There are a few monkey wrenches being thrown into the atmospheric setup for a big snowstorm next week, thus delaying the development of this storm. The elements are still present to create a fairly massive storm in a matter of a few days, however those "few days" could be next week, or in two weeks. This time of the year, when big arctic highs charge southeastward and park in the Northeast, it is usually a tell-tale sign that something is rotten in Denmark. History is littered with huge storms that seemingly exploded out of nowhere, and with no accurate computer modeling to back up their formation. My concern is that I (and Accuweather forecasters) see too many mischevious games being played by the upper air systems to warrant an "all clear" signal that next week will be storm-free.

So first, let me review a little history about one such storm that the computer models blew... and when you read, you'll see how similar the setup then is to what's happening now. I'm talking about the President's Day Storm of 1979. Read on...the source is a private forecaster like myself in Virginia. The numbers in parentheses represent how many elements present then will also be present this coming weekend and into next week.

On the evening of February 18, 1979, the National Weather Service issued a forecast of a minor four inches of snow for the D.C. metro area by the following day's end. This forecast, which was largely based off of operational numerical forecast computer models, would later prove to be anything but accurate.

The last few weeks leading up to the President's Day holiday were exceptionally cold. (1) An extreme arctic anticyclone had established itself over the eastern two thirds of the nation. Numerous record low temperatures were established during this period. The anticyclone reached a maximum high pressure of 1050 mb. (2) Cold air began to bank up against the eastern slopes of the Appalachians by early the morning hours of February 18. A critical ingredient for a major East Coast storm was initiating as arctic air filtered down the seaboard. By 1200Z (700 AM EDT) on the morning of February 18, a very weak low formed along the northern extent of an inverted surface trough axis near Kentucky. This was the primary low. As this low, with its (3) apparent lack of respective air advectional features neared the Eastern Seaboard late in the day on the 18th of February, rapid secondary cyclogenesis occurred. The major winter storm formed off the Georgia, Florida coast and tracked northeastward. Exceptionally heavy snow developed from Richmond to New York City. Especially hard hit would be the Mid Atlantic states. The heavy snows would soon be accompanied by high winds and blizzard conditions.

(4) The area of low pressure did not attain an incredibly low central pressure, however its associated winds were enough to produce blizzard conditions overnight on the 19th in the Washington D.C. area. By dawn the next morning, residents were shocked to find well over a foot of snow on the ground with snow periodstill falling and drifts several feet high. Many people were reported to be trapped in their homes as high winds had drifted snow banks into their front doorways.

The National Weather Service missed this one big time. In fact, at the time, it was classified as the "one of the area’s worst forecasting disasters in recent history." Nearly everyone failed to accurately predict the incredible snow accumulations. As a result, this storm has been heavily studied by the nation's top winter weather analysts. The storm rekindled memories of The Knickerbocker Storm of 1922, which deposited 28 inches of snow in the Washington area. The President's Day Storm of 1979 is the last true blizzard the Northern Virginia area has experienced to date. The Superstorm or Storm of the Century of 1993 came very close to producing blizzard conditions in the extreme northern, mountainous regions of Loudoun and Clarke counties, but would prove unsuccessful in terms of meeting the temperature requirements.


A summary of the situations indicated above from the 1979 storm that are in place today:


(1) An extreme arctic anticyclone had established itself over the eastern two thirds of the nation. Numerous record low temperatures were established during this period. This same scenario will be in place this weekend...a very cold arctic high is going to dominate the weather from the Rockies to the East Coast by Sunday morning.

(2) Cold air began to bank up against the eastern slopes of the Appalachians by early the morning hours of February 18. A critical ingredient for a major East Coast storm was initiating as arctic air filtered down the seaboard. This is again forecasted to be the situation come Sunday morning from Maine to Georgia. It will be so cold that snow is expected in Dallas and Houston.

(3) apparent lack of respective air advectional features That is another way of saying the low responsible for the storm was weak and disorganized. Again, identical to what we have today. The computer models have been demonstrating great difficulty in resolving IF there will be storm next week. One day, the models show a monster off the Virginia coast, the next day they show nothing. That continued reversal of the forecast by the computer is highly suspect that something is indeed brewing. The fact that there is no discernable strong low pressure anywhere to speak of IS the reason why the computer keeping flipping back and forth.

(4) The area of low pressure did not attain an incredibly low central pressure This is a classic signal of past snowstorms on the East Coast this time of year.. they usually do not "bomb out" and become these hugely intense low pressures. The 2003 storm was very weak, pressure wise, it simply had a lot of moisture running into cold air.

February 11, 1983, which was 21 years ago Wednesday, is another example of one of the largest East Coast blizzards of the 20th century, where the computer models MISSED the whole thing until about the day before. That was the storm which got me interested in weather. Even three days before this monster which dropped 21.3 inches on Philadelphia... the weather service was calling for flurries. Baltimore had 23 inches, where 5 days prior the call was for partly cloudy skies. So you can see why I am nervous about just saying next week will be no big deal. It's this time of year, it's snow month, it's the middle of February, which has me concerned. This is when big storms blow up out of nowhere. Despite the fact that it is not an El Nino year, we are still at risk for a major winter event. It will just take some time to get all the players back together again... like the song says above: "Seven days, so many ways...."

SO WHAT ARE YOU SAYING THEN ABOUT NEXT WEEK?

I am saying, don't bank on a big storm yet, but don't rule it out. Two of the six major computer models do show a major event brewing for the east coast. But the US model, (the one that missed the 79 and 83 storms) is surprise, surprise, NOT showing a storms for next week... and that's why all your local and internet forecasts, including the weather channel, don't show anything either.

In conclusion... here is Tip #8 for beating winter-related stress:

8. Prolonged watching of Doppler radar has been known to cause cataracts in laboratory rats, the experts say. Just keep that in mind.

No comments: