MUWIC Newsletter - June 2003

(Issued: June 2, 2003)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: "Damp, Dreary Spring Means No Drought this Summer"

What a difference a year makes. Last year at this time, twenty Pennsylvania counties were under a Drought Emergency. This year the region has been subject to persistent cloudy, cool, and damp conditions that just might have a few people secretly wishing for a drought!

The unsettled pattern that has dominated this Spring is the result of a semi-permanent jet stream trough over the eastern third of North America. This feature initially appeared in early October and has only loosened its grip on the East for brief periods ever since. Consequently, temperatures the last eight months have averaged normal to below normal from New England to the Carolinas. Portions of this same region have also received as much as 150 percent of normal precipitation during this eight-month period.

Locally, we have received over 28 inches of precipitation (rain and melted snow) since the pattern change occurred last fall. In response to the frequent rain and snow of recent months, ground water and surface water levels have returned to normal from the record low levels set last Summer. Consequently, we are not likely to experience a return of parched conditions in the months ahead. While it will certainly turn warmer and drier as the dog days of summer near, current water supplies are sufficient to last through the brief dry spells that occur during the typical summer.

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EVENT OF THE MONTH

Since there was no single standout event in the Lancaster area, May's "event of the month" is the record tornado outbreak that occurred over the nation's heartland during the first eleven days of the month. The preliminary number of tornados that touched down during this period is 495. This is about half the annual average number of tornados that occur in the US!

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STAT OF THE MONTH

May was far from the wettest on record, but it did end up in second place in terms of the greatest number of days with measurable precipitation. The Lancaster area received 0.01 inch or more of rainfall on 19 different days. That's just a day shy of the record number of rainy May days set in 1968.

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MAY CLIMATOLOGY (MU Weather Station)

Average High Temp: 66.5 F

Average Low Temp: 50.8 F

Average Monthly Temp: 58.6 F

(Departure from Normal: -3.3 F)

Precipitation: 3.01 inches

(Departure from Normal: -0.61)

Annual Precipitation: 14.51 inches

(Departure from Normal: -1.44)

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JUNE NORMALS, RECORDS & FACTS

Normal high/low temperatures range from 80/54 on June 1st to 85/61 by month's end. The record high for June is 103 degrees set on the 20th of 1923 and 29th of 1934. The lowest temperature recorded in June is 33 F set on the 5th of 1921 and the 8th of 1932. Normal liquid precipitation for the month is 3.88 inches. The rainiest June on record (14.14 inches) occurred in 1972 when the remains of Hurricane Agnes moved through the region. The driest June was in 1966 when only 0.54 inches fell. Summer officially begins on June 21st.

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JUNE OUTLOOK

The recent trend of unseasonably cool and stormy weather showed little sign of letting up during May, and the Lion-like start to June does not portent well for the week ahead. Given the longevity of this unsettled pattern in the Northeast, it makes one wonder if the coming summer might end up as one of those rare "summers without a summer." No doubt, if the current pattern holds through the summer we'll have a tough time reaching 90 degrees more than a few times. Consider that in a "normal summer" we would reach that benchmark 24 times.

Although the first five days of May will average below normal, I see fundamental changes in the jet stream pattern that indicate a trend toward more normal temperatures. The upper-level trough that has plagued the East for much of the last eight months appears to be retrograding to a position in the nation's midsection. Meanwhile, a developing jet stream ridge in the western Atlantic will gradually gain the look of the common summer time "Bermuda high." Therefore, I do expect temperatures to make a run into the 80s on numerous occasions as June wears on. However, weak storm systems tracking eastward from the mean trough will bring a few cloudy, damp periods as well. Therefore, I do not expect a full-on switch into a hot and dry pattern. Instead, June may conclude within a couple degrees of normal and with near normal rainfall.

Just how the rest of the summer will pan out is hard to say. My intuition is that a relatively active jet stream may persist through much of the summer--if so, the new pattern established in June may continue into July and August. This would mean a marked reduction in the number of 90-degree days we'd experience this summer. However, I cannot rule out the possibility that the aforementioned Bermuda high takes control along the eastern seaboard. This would lead to a rather typical second half of the summer. Take your pick!