MUWIC Newsletter - December 2002

(Issued: December 3, 2002)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: “Two-Year Drought Finally Coming to an End”

In the December 2001 issue of the MUWIC Newsletter I conjectured that “as we begin the last month of 2001, it looks increasingly likely that a major drought is in store for 2002.” Now twelve months later I am happy to suggest that the upcoming winter may finally close the door on the mid-Atlantic region’s pesky two-year drought.

A pronounced shift in the jet stream in September resulted in a remarkably stormy pattern that produced nearly double the normal amount of precipitation from mid-September through mid-November. Although the year-to-date rainfall in our region remains a few inches below normal, recent rains have erased deficits in soil moisture and stream flows. Groundwater levels (i.e. well depths) remain somewhat below normal.

On November 7th the Governor downgraded the Drought Emergency to a Drought Warning for Lancaster and 15 other counties. Three counties remain in a Drought Emergency (view map of drought status). A further downgrade of our Drought Status may come this winter, given the near-normal precipitation I am expecting from December through February. You can read my entire Winter Outlook below.

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EVENT OF THE MONTH

A brief period of wet snow fell early on November 27^th accumulating one to two inches on the grass. Two-inch amounts occurred primarily in the northeastern part of the county.

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STAT OF THE MONTH

From mid-September through mid-November there were five storms that produced more than one inch of total rainfall. During the prior twelve months, however, there were just two storms that dropped an inch or more of rainfall.

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NOVEMBER CLIMATOLOGY (MU Weather Station)

Average High Temp: 50.9 F

Average Low Temp: 34.0 F

Average Monthly Temp: 42.4 F

(Departure from Normal: -0.8 F)

Precipitation: 3.08 inches

(Departure from Normal: -0.07)

Annual Precipitation: 29.62 inches

(Departure from Normal: -8.46)

Snowfall: 1.5 inches

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DECEMBER NORMALS, RECORDS & FACTS

December is the third coldest month of the year with an average monthly temperature of 34F. Normal high/low temperatures drop from 46/28 on the first of the month to 39/23 on New Year's Eve. The record high of 78F was set on the 5th (2001), and the record low of -7F was recorded on the 18th (1916). Average liquid precipitation (included melted snowfall) is 2.98 inches. Normal snowfall is about 2 inches with two out of three December's featuring at least a half-inch of snowfall. Winter officially arrives at 8:15PM on December 21st.

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WINTER OUTLOOK

Before we look ahead, let’s look back to last winter—a season that featured very little winter weather. In fact, December 2001 through February 2002 was the second warmest such period on record here in Lancaster with temperatures averaging almost 6 degrees above normal (a remarkable anomaly for a three-month stretch). Furthermore, only 9 inches of snow fell in the Lancaster area, which is but a third of the long-term average seasonal snowfall. Total precipitation (rain and melted snow/ice) was similarly scant—less than 3 inches for the entire three-month period—and helped propel us into severe drought by the middle of this year.

A lot has changed since last winter and, thus, I do not expect any kind of a repeat of last winter’s persistent warm and dry conditions. More likely, this winter will average out to be, well, very average!

One thing I can forecast with absolute certainty is that there will be many stories in the media this winter about El Nino and its effects on the weather in the United States. Chances are that most any event (or non event) will be somehow tied to El Nino. With that said, I promise not to pound the El Nino drum as I’m not convinced that it’s going to be a major player in our winter weather here in Pennsylvania. Currently, the El Nino (warming in the central and eastern Pacific) is in its formative stage and nowhere near the magnitude of the remarkable El Nino that occurred in during the winter of 1997-1998 (the warmest winter on record across much of the nation). Given the building El Nino, however, some forecasters are calling for warmer-than-normal conditions across much of the country, including Pennsylvania. I don’t completely buy into this idea.

Instead, I expect El Nino will have little impact in our region during the first half of the winter. In fact, given the current jet stream configuration we might have a bias towards colder-than-normal weather through at least December. By early next year El Nino might be peaking in the Pacific (as a “moderate” magnitude event), so enhanced flow off the Pacific might limit intrusions of Canadian air masses. Hence, the winter may conclude with a warm bias. In aggregate, the temperature anomaly for this winter could very well turn out as a near “wash”—let’s say somewhere within 2 degrees of normal.

As for total precipitation, I do not expect a continuation of the extremely stormy pattern that produced nearly 200 percent of normal precipitation this fall. Instead, I expect a “normal amount” of storminess, which should total around 9 inches in liquid equivalent (rain and melted snow/ice). Of course, snowfall forecasts hinge largely on luck, since a few degrees difference (warmer or cooler) during a few key storms can turn a “35-inch winter” into a “15-inch winter.” But given my temperature and precipitation forecast, it might be wise to speculate “near-average snowfall” for this winter—let’s say somewhere between 20 to 30 inches. The long-term seasonal average snowfall in Lancaster is about 25 inches.