MUWIC Newsletter - May 2002

(Issued: May 2, 2002)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: "April's Wild Ride!"

On Saturday, April 6th, many Lancastrians awoke to find one to two inches of fresh snowfall. Ten days later, a new record high of 90F was set during a four-day mini heat wave. While some may consider such an occurrence extraordinary, I say, "Welcome to Spring in the Northeast!"

Highly variable weather is, in fact, a hallmark of Northeastern US climate due to our location in the mid-latitudes and positioning on the downwind side of a large continent. Fifty degree temperatures swings are not uncommon, nor is snowfall and above normal warmth occurring in the same month. Furthermore, the high frequency of change goes hand-in-hand with the regularity by which we experience low pressure systems and precipitation. By contrast, regions with less variable weather, like southern California, commonly go months with little or no precipitation.

Given the increased volatility of our weather pattern in recent weeks, one can hope this means that more frequent rainfall will continue throughout the Spring and Summer months. Could April's wild ride be a subtle signal that we have turned the corner on the ongoing drought?

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EVENT OF THE MONTH

Take your pick: the measurable snowfall early on April 6th or the brief heat wave that established two new record highs of 90F (April 16th) and 93F (April 17th).

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STAT OF THE MONTH

Over the last two months the drought-plagued mid-Atlantic region has received near normal rainfall-a big step in the right direction given the current drought emergency. Between 6 to 8 inches of rain has fallen across Lancaster County since March 1st, with the higher amounts occurring in the northern half of the county.

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APRIL CLIMATOLOGY (MU Weather Station)

Average High Temp: 66.4 F

Average Low Temp: 43.5 F

Average Monthly Temp: 54.9 F

(Departure from Normal: +3.0 F)

Snowfall: 1.5 inches

(Departure from Normal: +1.0)

Precipitation: 1.79 inches

(Departure from Normal: -1.68)

Annual Precipitation: 7.57 inches

(Departure from Normal: -4.66)

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MAY NORMALS, RECORDS & FACTS

Normal daily temperatures will shoot up 10 degrees this month. The normal high/low ranges from 67/45 on May 1st to 77/55 by month's end. The record high for May is 98 degrees (on 5/23/25) and the record low is 27 F (on 5/1/78). Normal monthly rainfall is 3.62 inches. The rainiest May on record occurred in 1989 (10.07 inches) while the driest May was in 1939 when just a half-inch fell.

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MAY OUTLOOK

As mentioned earlier, May looks to continue the highly variable ways of April. Through mid-month, I expect a jet stream trough to remain near the west coast, a strong ridge to be anchored in the south-central states, and a broad, unseasonably strong trough across much of Canada. This pattern should produce a broad area of warmth in the Deep South that occasionally tries to expand northeastward into the Midwest and mid-Atlantic states. On these occasions, temperatures will surge into the 80s in our region. However, frequent cold fronts will likely drop into the Great Lakes and Northeast, bringing blasts of brisk April-like conditions from time to time.

Precipitation-wise, such a pattern should yield regular opportunity for showers and thunderstorms. Just how much rain we receive often ends up a matter of luck-one or two "direct hits" by thunderstorms could push May rainfall totals above normal, whereas missing one big storm could leave us a bit below the normal monthly precipitation. One concern I have, for later this month, is that the southern ridge may sharpen up and take bonafide control of our weather pattern. If so, we could launch into a summer-like pattern with highs approaching 90 degrees and a much reduced chance of precipitation--definitely not what we want to see given the current Drought Emergency.