MUWIC Newsletter - September 2003

(Issued: September 2, 2003)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

************************************************************************

LEAD STORY: “Wet Summer Produces Little Heat”

Summer 2003 will be remembered for its persistent clouds, showers and lack of extreme heat. After a cooler-than-normal start, July and August featured increasing warmth but no long-term heat waves. Ninety-degree days is one popular benchmark for extreme heat, and this summer featured just nine such days with highs in the 90s. By stark contrast, last summer produced 45 days in the 90s (24 days is the long-term average).

Oddly, the summer concluded almost 1 degree above normal. This was due to unusually warm overnight lows for most of July and August. The high frequency of clouds and persistently high dew points (humidity) prevented temperatures from falling to normal levels on many nights. August was particularly notable with an average overnight low 7.2 degrees above normal, while the daytime high was very close to normal (+0.3 above norm).

The wet Labor Day weekend underscores the most remarkable trend of Summer 2003—copious rainfall. Above-normal rainfall precluded any talk of drought this season, whereas last summer was defined by a record drought and a year-to-date rainfall deficit of over 10 inches. This year we begin September with a three-inch surplus of rainfall…and the hopes for a drier Fall!

Temperature Statistics (MU Weather Station):

2003 Temp. 2002 Temp. 2003 Precip. 2002 Precip.

Anomaly Anomaly Total Total

June - 1.6 + 2.3 5.35 3.63

July + 0.5 + 3.4 3.81 0.74

August + 3.8 + 5.5 5.08 2.16

Total +0.9 +3.7 14.24 6.53

************************************************************************

EVENT OF THE MONTH

This month’s event was eleven days long—that is, the first eleven days of August were unusually cloudy and damp as measurable precipitation was recorded on eight out of the eleven days. By comparison, there were only eight days with measurable precipitation during the entire month of August 2002.

************************************************************************

AUGUST CLIMATOLOGY (MU Weather Station)

Average High Temp: 84.5 F

Average Low Temp: 68.0 F

Average Monthly Temp: 76.3 F

(Departure from Normal: +3.8 F)

Precipitation: 5.08 inches

(Departure from Normal: +1.11)

Annual Precipitation: 28.73 inches

(Departure from Normal: +0.42)

************************************************************************

SEPTEMBER NORMALS, RECORDS & FACTS

Fall officially arrives at 6:47 a.m. on the 23rd (autumnal equinox). Normal rainfall for September is 3.62 inches, and normal high and low temperatures range from 82/59 (high/low) on the 1st to 71/47 on the 30th. On average, there are eight days with measurable precipitation (third lowest monthly average) and two days with a high temperature of 90F or above. The record high for September is 99F (9/3/53) and the record low is 27F (9/26/22).

************************************************************************

SEPTEMBER OUTLOOK

Heavy showers on September 1^st produced more than half-a-month’s worth of rain in a single day with about two inches falling across much of the county. Additional rainfall is on tap the next couple of days, so I suspect we’ll have received the normal monthly rainfall by the end of this week! Interestingly, a pattern change may be developing in the long range…let’s break things down.

The persistent jet stream pattern of this year has featured a large ridge over western North American and a mean trough position over the eastern third of the continent. While this pattern has broken down for a few days at a time, it has constantly reformed and repeated the tendency of unsettled weather in the East. With Fall approaching, however, there’s a chance we may see an extended break in this set-up and a shift towards drier weather, at least for a week or two. Right now, I foresee the mean trough axis shifting to a position just off the East coast by early next week. This will direct northwest flow across our region and help build a series of Canadian high pressure systems into the Northeast. Therefore, I will forecast below-normal precipitation for the 10-day period of September 5 – 14^th. One caveat is that no tropical storms come into play during this time frame.

The second half of September is more uncertain—does a “dry” pattern continue or will the jet stream revert to a more-stormy configuration as it has done repeatedly all year? Climatology would favor the former choice, whereas recent experience would lead you to forecast a return to unsettled weather. I honestly do not have a strong opinion here, so I will go with the optimistic middle-of-the-road forecast of a near-normal second half of September (i.e. five dry days per week).