MUWIC Newsletter - March 2003

(Issued: March 4, 2003)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: "A Winter To Remember"

It was billed by some forecasters to be a warmer- and drier-than-normal winter in the Northeastern US. It turned out to be one of the coldest and snowiest on record.

Locally, the period of December through February concluded as the 6th coldest and 3rd snowiest on record. Only the winters of 1995-1996 (72 inches) and 1960-1961 (63 inches) brought more snow to the Lancaster area. And, of course, we may very well add to the seasonal snowfall total before we close the books on the current winter season. Definitely do not put your shovel away just yet!

So, what happened to the well-advertised El Nino (warming of the Equatorial Pacific) that was supposed to exert a moderating influence on our winter weather? It simply failed to develop to the magnitude and extent forecast by the National Weather Service. While this event did develop into a moderate El Nino by late Fall 2002, it peaked in early December (see link to 12-month plot below) and then failed to push warmer-than-normal water eastward to the South American coast (note near-normal temps in El Nino regions 1 & 2).

Almost half a world away, the North Atlantic Oscillation (NAO) became the wild card in this winter season. The lesser-known NAO relates to oscillations in atmospheric pressure over the northern Atlantic Ocean. For most of the last three months, the NAO has been in a "negative" phase--during the winter months, a negative NAO signals jet stream blocking over the northern Atlantic and a better-than-normal chance of displacing arctic air southward into Eastern Canada and the Northeast US.

As I write this newsletter, the NAO remains in a negative phase--so it's likely that arctic air will make a few more visits in the coming weeks. In the final analysis, the NAO may be heralded as playing a greater role than the over-billed El Nino in directing the very memorable winter of 2002-2003.

Link to 12-month plots of El Nino in four Pacific regions:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/ssta_c.gif

Link to map showing four regions of interest:

http://iri.columbia.edu/climate/ENSO/background/images/NINO_Regions.jpg

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STAT OF THE MONTH

What a difference a year makes. February 2002 was 4.7 degrees above normal, with less than an inch of snowfall and only 0.27 total precipitation. February 2003 concluded 6.0 degrees below normal with about 36 inches of snow and 4.65 inches of liquid-equivalent precipitation (rain and melted snow/ice).

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EVENT OF THE MONTH

Well, that would be the Blizzard of 2003. Approximately 24 inches of snow fell in the Lancaster area on February 16th and 17th, making it the second biggest snowstorm on record. The largest - in central Lancaster county - is the Blizzard of 1996 (30 inches), while the Blizzard of 1983 (24 inches) ties for second place.

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FEBRUARY CLIMATOLOGY (MU Weather Station)

Average High Temp: 34.1 F

Average Low Temp: 19.3F

Average Monthly Temp: 26.7 F

(Departure from Normal: -6.0 F)

Snowfall: 36.0 inches

(Departure from Normal: +28.5)

Total Precipitation (liquid equivalent): 4.65 inches

(Departure from Normal: +2.18)

Annual Precipitation: 6.36 inches

(Departure from Normal: +0.88)

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MARCH NORMALS, RECORDS & FACTS

Normal high/low temperatures increase rapidly from 46/26 on March 1st to 59/36 on the 31st. The record high for March is 88 degrees (1921, 1945) and the record low is -1 F (1984). Normal liquid precipitation (rain and melted snow) is 3.38 inches. Average snowfall for the month is 3.7 inches.

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MARCH OUTLOOK

March is beginning with a period of de-amplified jet stream flow across the United States. As a result, seasonable to above normal conditions have returned too much of the country, while a large mass of bitterly cold air is now temporarily bottled-up in Canada. A series of weak disturbances tracking across the country will produce a couple brief warm-ups that tease folks in many snow-weary cities. This basic pattern should prevail through March 8th, so local conditions should average out only a few degrees below normal for the first week of the month.

However, high-latitude blocking and the return of a large ridge over Alaska and the Yukon will inevitably result in a renewed push of late-winter weather across the northern third of the county. The arctic boundary should surge southward into the Northern Plains and Upper Midwest on March 8th, then expand eastward into the Great Lakes and Northeastern states on March 9th and 10th. This has the potential to be a major arctic outbreak (by March standards) and I would not be surprised to see some records fall during the period of March 9 - 15th. Beyond this cold snap, I suspect a more zonal (west-to-east) jet stream pattern will return, and the second half of March may feature below normal temperatures across the northern tier states, while unseasonable warmth springs forth south of the 40th parallel. Consequently, Lancaster (about 40 N latitude) will likely experience a rollercoaster ride of changing temperatures. Overall, March should average out a few degrees below normal.

Precipitation-wise, I don't see any large storms through March 8th as a fast moving split flow sends a series of weak disturbances across the country. The mid-month period, however, holds tremendous potential for a large storm somewhere east of the Rockies. At this time, near record cold air gripping the northland will increasingly contrast the springtime warmth building across the south. The best chance of a significant storm is during the onset of the arctic air and, again, when the arctic air begins its retreat (midmonth). Given this setup, it makes you wonder if the memorable winter of 2002-2003 might have some sort of a memorable conclusion?