MUWIC Newsletter - July 2006

(Issued: July 5, 2006)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: “Dirt to Mud, Drought to Flood”

The three-month, statewide Drought Watch has come to an end thanks to copious late-June rainfall that produced flooding in some locations. A seven-day rainy period yielded more than a month’s worth of rain--and in some places three-months worth!—as a rare confluence of weather systems took aim on the mid-Atlantic region. The main ingredients were a cold front that stalled over the state on June 23^rd, a large jet stream ridge parked in the western Atlantic, a stationary trough in the Mississippi valley, and a persistent plume of deep tropical moisture flowing northward from near the Bahamas. The result was rainfall that rivaled some of the great tropical rain events of the past such as Floyd in 1999 and Agnus in 1972.

The Drought Watch was issued on April 11^th after a record-dry March produced only 0.65” of precipitation. Hit-and-miss showers in April and May provided enough rainfall for a good start to the growing season, however, ground water improved little during the Spring. Not until June did enough rainfall occur to percolate and benefit the wells. The Drought Watch was lifted on June 30^th.

2006 Rainfall by Month (departure form normal)

January - 3.66 (+0.65)

February - 2.30 (-0.17)

March - 0.65 (-2.73)

April – 4.36 (+0.89)

May – 2.33 (-1.29)

June – 13.34 (+9.46)

TOTAL: 26.64 (+6.81)

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EVENT OF THE MONTH

One of the greatest rain events in Lancaster, save the remnants of Agnus in 1972, dumped 8 to 12 inches of rain across the county from June 22 – 28. Record daily rainfall was recorded at the MU Weather Center on both June 26 (3.43) and June 27 (4.80).

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STAT OF THE MONTH

Official June rainfall totaled 13.34 at the MU Weather Information Center. This exceeds the aggregate rainfall of 13.30 inches over the five previous months!

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JUNE CLIMATOLOGY (MU Weather Center)

Average High Temp: 80.6 F

Average Low Temp: 61.8 F

Average Monthly Temp: 71.2 F

(Departure from Normal: +0.9F)

Precipitation: 13.34 inches

(Departure from Normal: +9.46)

Annual Precipitation: 26.64 inches

(Departure from Normal: +6.81)

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JULY NORMALS, RECORDS & FACTS

Climatologically the warmest month of the year, daily average temperatures peak on July

18th and 19th with a normal high/low of 88/63. The record high for July is 104 degrees set on three different occasions (July 3, 1966, July 10, 1936, and July 21, 1930) and the

record low is 42 set on Independence Day in 1918. Normal precipitation for the month is

4.51 inches. The rainiest July on record occurred in 1941 when 9.48 inches fell. The

driest July was in 1955 when only 0.60 inches fell.

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JULY OUTLOOK

With the exception of the flooding rains of late June, the summer appears to be shaping up as rather average and unremarkable. Through July 5^th, temperatures have reached the 90-degree benchmark only five times (normal is 7 times by this date). Furthermore, the jet stream continues to favor weak trough positions along the northwest US coast and the Canadian Maritimes, with a mean ridge position near the Rockies. The ridge position will occasionally expand eastward, however, I don’t see a fundamental shift of the pattern in the next couple of weeks. Therefore, any warm spell will likely be limited to a few days as backdoor cold fronts occasionally limp in from the north to blunt the heat.

Of course, July is climatologically the warmest month with an average high temperature of 86 degrees and a long-term average of ten days that warm into 90s. This year, I do not see us exceeding these values, and I do not expect any extended periods of extreme heat (five or more consecutive days above 90 degrees). Instead, the hottest weather will likely remain over the Plains and only occasionally pulse eastward. Therefore, warm spells will likely occur two or three days at a time, punctuated with a cold front passage and a round of storms. In the end, temperatures for the month should average within a degree or two of normal.