MUWIC Newsletter - April 2005

(Issued: April 1, 2005)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: “Coldest March in a Decade”

March came in like a Lion, and it maintained lion-like characteristics for much of the month. Twenty-six days featured below normal temperatures, and the average departure from normal for the month was -4.6 degrees. This makes March the coldest since 1996.

The cause of the persistent chill was significant jet stream blocking over eastern Canada and the north Atlantic. A massive area of high pressure formed over Greenland, while low pressure and below normal conditions dominated along the east coast of North America and over parts of western Europe. This pressure pattern is termed a “negative NAO”, the phase of the North Atlantic Oscillation that favors cold and stormy weather in the eastern US. Interestingly, this -NAO episode ranks among the five strongest on record.

An upshot of this historic NAO event is that the jet stream was suppressed far south of its normal position. The mean storm track remained well south of Pennsylvania during the first three weeks of the month, limiting precipitation to only an inch of snow and less than a half-inch of liquid equivalent. Fortunately, the blocking pattern dissipated during the final days of the month and two significant storms brought the monthly rainfall to near normal levels.

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EVENT OF THE MONTH

March 7^th featured spectacular warmth with a 68-degree high temperature that was 20 degrees above normal. But the spring-like warmth did not last. A powerful cold front moved through at 3:00 a.m. on March 8^th sending temperatures on a dramatic 51-degree slide (low temp on March 8^th was 17 degrees!) and yielding an inch of snowfall.

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MARCH CLIMATOLOGY

Average High Temp: 45.8 F

Average Low Temp: 27.9 F

Average Monthly Temp: 36.9 F

(Departure from Normal: -4.6 F)

Snowfall: 1.0 inches

(Departure from Normal: -3.4 in.)

Precipitation: 3.01 inches

(Departure from Normal: -0.37)

Annual Precipitation: 8.86 inches

(Departure from Normal: -0.02)

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APRIL NORMALS, RECORDS & FACTS

Normal high/low temperatures range from 59/37 on April 1st to 70/44 by month's end. The record high for April is 95 degrees (on 4/18/76) and the record low is 11 F (on 4/1/23). Normal liquid precipitation (rain and melted snow) is 3.47 inches. Measurable snow falls in April on an average of once every five years. The rainiest April on record occurred in 1983 (9.14 inches) while the driest April was just two years later (0.39 inches in 1985).

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APRIL OUTLOOK

April is beginning with a chaotic, transitional pattern the will produce frequent storms and wild swings in temperatures. This weekend’s weather exemplifies what to expect over the next week or two, as a sunny warm day gives way to a cold rain and mountain snows. This unsettled pattern could continue for much of the month (I hope not!), or a more stable, mild pattern could develop in the coming weeks. Unfortunately, such a pattern provides few clues as to how long it might persist and, thus, I don’t have a strong opinion about long-term trends. Temperatures may average near normal with an equal number of above and below normal days. One thing that seems likely, however, is a continuation of the recent above normal precipitation trend.