MUWIC Newsletter - August 2004

(Issued: August 3, 2004)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: “Stormy Pattern Continues”

Drenching, gusty showers defined July’s weather as between 5 and 10 inches of rain fell across much of Lancaster county. The unstable jet stream pattern that produced the wettest June since 1986 continued for most of July as slow-moving showers produced isolated flooding on several occasions. Hardest hit by gutter-gushing downpours where neighborhoods across the northern and eastern parts of the county. These are some of the same locations that received the heaviest rain in June, so the saturated ground more easily led to localized flooding.

Even more dramatic was the devastating F3 tornado that touched down in Campbelltown (Lebanon county) on July 14^th. Two weaker F1 tornados also developed in Lancaster county—one in the County Park on July 1^st and another just south of Refton on July 27^th. Wind speeds for an F1 tornado range between 73 and 112 mph, whereas an F3 tornado produces winds 158 and 206 mph. See the “Events of the Month” for links to maps and photos for these tornados.

July Rainfall

Holtwood - 4.83”

Millersville University - 5.64”

Lancaster Water Works - 7.15”

Lancaster Airport - 7.69”

New Holland - 8.50”

Ephrata - 9.62”

Harrisburg - 7.90”

York - 5.36”

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EVENTS OF THE MONTH

Severe thunderstorms produced three tornados in our region over the last month. The strongest was a rare F3 tornado in Lebanon county on July 14^th. Two F1 tornados effected parts of Lancaster county on July 1^st and July 27^th.

Link to map of Campbelltown tornado:

http://www.erh.noaa.gov/ctp/features/July14/images/PathMap.gif

Link to photos of Campbelltown post-storm photos:

http://www.erh.noaa.gov/er/ctp/features/July14/damage.shtml

Link to map of Refton tornado path:

http://www.erh.noaa.gov/ctp/features/July27/images/pathmap.gif

Link to WGAL-TV video discussing Refton Tornado

http://www.thewgalchannel.com/video/3588929/detail.html

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STAT OF THE MONTH

Temperatures this summer have only hit the 90-degree mark on three occasions—May 23^rd (90), June 9^th (91), and July 5^th (92). Through the end of July there are normally about fifteen 90-degree days.

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JULY CLIMATOLOGY (MU Weather Station)

Average High Temp: 83.6 F

Average Low Temp: 65.7 F

Average Monthly Temp: 74.7 F

(Departure from Normal: 0 F)

Precipitation: 5.64 inches

(Departure from Normal: +1.13)

Annual Precipitation: 25.24 inches

(Departure from Normal: -0.10)

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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.

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AUGUST OUTLOOK

July produced no extreme heat, largely due to the lack of a Bermuda high, as well as the unusually soggy ground conditions. The big question of this Outlook is whether the July pattern will continue, or will it finally given way to a more typical summertime set-up?

Interestingly, July ended with just a hint of the Bermuda High trying to develop along the eastern seaboard. Temperatures hit 89F on July 31^st--the warmest reading since the high of 92F on July 5^th—and highs are approaching 90F here to begin August. However, the unusually fast jet stream flow, that’s been the hallmark of this summer’s weather, shows no signs of weakening in the coming weeks. Therefore, we may see an interesting battle setting up between a building Bermuda high and the fast westerly flow across the Great Lakes. The bottom line: this setup likely represents “status quo” in terms of our local weather.

Brief bouts of near 90-degree temps will likely occur on several occasions this month as the Bermuda High pulses from time to time. Still, the active jet to our north will continue to send cold fronts our way every few days. So, I do not foresee an extended period over above-90F conditions, at least not during the first half of the month. What we will see is a continuation of showers and thunderstorms—some could be severe with gusty winds and heavy downpours. It’s likely we’ll experience our third consecutive month of above normal rainfall.