MUWIC Newsletter - August 2007 (Issued: August 7, 2007) Millersville University Weather Information Center (MUWIC) Eric J. Horst, Director ************************************************************************ LEAD STORY: “Coolest July in 6 Years” A cool July 4th holiday was a harbinger of the climate trend for what is normally Summer’s hottest month. High temperatures in July averaged 2.4 degrees below normal, and the month’s aggregate anomaly was a statistically significant 0.6 degrees below normal. Most noticeable were the lack of 90-degree days. On average, high temperatures reach the 90s on ten July days—this benchmark was achieved just five times in July 2007. Precipitation-wise, showers were rather sparse across the Commonweath in July. Fortunately, cold frontal passages each week did trigger isolated showers, with some of the heaviest downpours developing over southeastern PA. With nearly an inch of rain falling on July 5th and almost two inches on July 29th, local rainfall was not far below normal. ************************************************************************ STAT OF THE MONTH On twenty-two July days, the temperature failed to reach the normal high temperature for the date. ************************************************************************ JULY CLIMATOLOGY (MU Weather Station) Average High Temp: 84.0 F Average Low Temp: 64.2 F Average Monthly Temp: 74.1 F (Departure from Normal: -0.6 F) Precipitation: 3.87 inches (Departure from Normal: -0.64) Annual Precipitation: 22.31 inches (Departure from Normal: -2.03) ************************************************************************ AUGUST NORMALS, RECORDS & FACTS Normal high/low temperatures decrease from 86/63 on August 1st to 83/59 by month’s end. The record high for August is 107 degrees set on the 7th of 1918, while the record low is 35 F set on the 29th in 1982. Normal liquid precipitation for the month is 3.97 inches. The rainiest August on record (13.94 inches) occurred in 1933. The driest August was in 1957 when only 0.51 inches fell. ************************************************************************ AUGUST OUTLOOK For the first time this summer, the jet stream ridge position has made a definitive move from the Plains toward the East coast. As a result, the first extended heat wave of the season has developed for the beginning of August. This pattern looks to hold through August 10th with temperatures and dew points both peaking at the highest levels of the season. A jet stream trough will then redevelop along in the East beginning on August 11th. This feature will bring an end to the extreme heat (for the time being), however, periods of high humidity are likely to continue. Another multi-day surge of above-normal warmth may develop around August 17th. Thus, August will most likely conclude with above normal temperatures and a greater-than-normal number of 90-degree days. More uncertain is the precipitation trend for the month ahead. On August 6th, a Drought Watch was issued for most of central and western Pennsylvania—counties where year-to-date rainfall deficits have grown to between 4 and 8 inches. Frequent showers over southeastern Pennsylvania have maintained water levels in the normal range, so Lancaster (and eight other southeastern counties) are not included in the Drought Watch. Rainfall in the month ahead will vary widely from county to county as muggy August conditions produce heavy downpours in some neighborhoods, while many others are missed. Therefore, the Drought Watch will likely continue into the Fall season. COPYRIGHT 2007 Millersville University Published monthly by the Millersville University Weather Information Center. Subscribe on our homepage at www.atmos.millersville.edu/~wic ******************************************************************** *** Bookmark our web site at: www.atmos.millersville.edu/~wic *** ********************************************************************