MUWIC Newsletter - October 2003

(Issued: October 2, 2003)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: “Isabel Blows Through Region”

September 2003 ended as the fifth most-rainy month on record with 8.59 inches of total rainfall. Interestingly, the month’s most newsworthy storm produced more in the way of wind than rain. The remnants of Hurricane Isabel, which crossed the county on September 18 and 19^th, produced widespread wind damage with sustained winds up to 38 mph and gusts of 51 mph. Twelve hours of pounding easterly winds dropped hundreds of trees across the county and produced widespread power outages. Fortunately, Isabel’s heaviest rains fell south and west of the region, sparing the Lancaster area of flooding.

North Carolina and Virginia weren’t so lucky. Isabel made landfall near Cape Hatteras with sustained winds of 90 mph and gusts to 120 mph. Since wind damage increases exponentially with increasing wind speed, Isabel’s winds produced more than four times the force at landfall than when crossing the Lancaster area. In addition, 5 to 10 inches of rain fell in parts of eastern North Carolina and the barrier islands received a storm surge up to 7 feet.

In the final analysis, Isabel will be remembered as an impressive storm that produced the greatest power outages ever in the mid-Atlantic region. The region was fortunately spared a major catastrophe as Isabel weakened from a powerful Category 5 storm (five days prior) to a more modest Category 2 hurricane at landfall.

NOAA on Isabel: http://www.noaanews.noaa.gov/stories/s2086.htm

Hatteras Damage Photos: http://www.hatterasonmymind.com/Isabel.html

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EVENT OF THE MONTH

Isabel’s wind was certainly the main event in the Lancaster area, however, two rainy sideshows are worth mentioning. On September 15^th, a nearly stationary rain band formed near the Lancaster-Chester county border. Heavy rainfall (up to 7 inches in a few spots) produced flash flooding in extreme eastern Lancaster county and across much of Chester county. Eight days later—and five days after Isabel—a slow moving cold front dropped another two to three inches of rain over a widespread area. Once again, some flooding was reported, primarily along the Conestoga Creek.

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SEPTEMBER CLIMATOLOGY (MU Weather Station)

Average High Temp: 75.7 F

Average Low Temp: 58.2 F

Average Monthly Temp: 66.9 F

(Departure from Normal: + 1.9 F)

Precipitation: 8.59 inches

(Departure from Normal: +4.97)

Annual Precipitation: 37.42 inches

(Departure from Normal: +5.49)

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OCTOBER NORMALS, RECORDS & FACTS

Normal rainfall for October is 3.00 inches making this the third driest month of the year.

The wettest October on record was in 1932 (8.39 inches); the driest was in 1963 when no

measurable precipitation fell. Normal high and low temperatures for October range from 71/47 (high/low) on the 1st to 61/38 on the 30th. The record high for the month is 95F (set on the 4th in 1941); the record low is 19F (set on several different days and years). Finally, Daylight Savings ends on the 26th of this month.

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OCTOBER OUTLOOK

Below normal conditions will dominate the first seven days of October as a powerful jet stream trough amplifies over the Great Lakes region and Northeast. Low temperatures could approach record levels on the mornings of October 3^rd, 6^th, and 7^th, and there will most certainly be frost on these mornings (even if records are not broken). Daytime highs will be similarly below normal through the period. In aggregate, the first week of October should finish up 8 to 10 degrees below seasonal norms.

I am equally confident that a spell of Indian Summer will follow for the period of October 8 – 15^th. The jet stream will return to a more zonal (west to east) configuration and push Pacific air masses—not Canadian—into the western US. This air will warm up as it descends off the continental divide and moves eastward, so I would not be surprise to see several above normal days (highs in the 70s) as we head into mid-month.

Mainly dry conditions will prevail during the chilly early period of October, but one or two rain events are possible as the zonal pattern prevails into mid October. The late month trend is less certain—does a strong trough return to the East with more below normal conditions or does a more-moderate pattern continue? My sense is to lean toward the latter, warmer scenario for the second half of the month. If my hunch is correct, unseasonable chill (and early-season snow) would be more common in the northern Rockies region than in the Northeast.