MUWIC Newsletter - December 2001

(Issued: December 3, 2001)

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

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LEAD STORY: “Major Drought Possible in 2002”

As we begin the last month of 2001, it looks increasingly likely that a major drought is in store for 2002. As of December 3^rd, the Lancaster area is about 18 inches below its normal year-to-date rainfall. With only 21.67 inches of precipitation recorded at the Millersville University Weather Station this year, we are on track for establishing a new record for driest year on record. Currently, 1930 holds this distinction with only 26.01 inches of precipitation falling in Lancaster that year.

Interestingly, our current dry spell has been building since the second half of last year. Fall 2000 featured infrequent rainfall that added up to a six-inch precipitation deficit by year’s end. Therefore, the aggregate precipitation deficit over the last 17 months is a whooping 24 inches. This helps explain why so many wells and streams are at all-time record low levels. As to when this drought might end, we can only hope for a very wet (or white) winter that turns into a soggy spring. Otherwise, the current Drought Warning will continue deep into 2002.

Map of real-time streamflow compared to historical streamflow for the day of the year.

http://water.usgs.gov/cgi-bin/dailyMainW?state=pa&map_type=real

The current drought watch was issued on August 8^th. For the latest drought information visit the DEP web site at: www.dep.state.pa.us/dep/subject/hotopics/drought/default.htm.

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EVENT OF THE MONTH

November ended with an incredible seven-day streak of unseasonably warm weather. The period of November 24 - 30 averaged 14 degrees above normal, making it one of the warmest late-fall warm spells on record.

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STAT OF THE MONTH

Light rainfall on November 20^th ended a period of 34 consecutive days with no measurable precipitation. This is the second longest rain-free period on record. In 1995, we experienced 35 straight days of without precipitation (August 13 – September 16).

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NOVEMBER CLIMATOLOGY (MU Weather Station)

Average High Temp: 61.6 F

Average Low Temp: 36.7 F

Average Monthly Temp: 49.2 F

(Departure from Normal: +6.0 F)

Precipitation: 0.76 inches

(Departure from Normal: -2.39)

Annual Precipitation: 21.67 inches

(Departure from Normal: -18.07)

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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 47/30 on the first of the month to 39/23 on New Year's Eve. The record high of 76F was set on the 29th (1984), and the record low of -7F was recorded on the 18th (1916). Average liquid precipitation (included melted snowfall) is 3.28 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 2:22PM on December 21st.

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WINTER OUTLOOK

Speculating about an upcoming winter’s weather is a favorite activity of meteorologists, weather enthusiasts, and holiday party goers who consume too much eggnog. This meteorologist is one person who especially enjoys the challenge of piecing together a winter outlook (even without the eggnog). Let’s get started!

Unfortunately, this time around there are no solid signals to key on in making an educated guess as to what this winter may have in store for us. The El Nino – La Nina Pacific Ocean oscillation (ENSO) is in a neutral phase. Furthermore, use of analog techniques (comparing this fall/winter season to similar years in the past) provides only weak “signals” in how this winter might pan out. Many people have asked me if the warm and dry weather of recent months provides any solid clues to this winter’s weather. According to my analysis of local weather records, the answer is “not really.” However, a few subtle trends worth mentioning are—a warm Fall is slightly more likely to be followed by a warm Winter, and ENSO-neutral Winters exhibit a slight tendency toward higher than normal snowfall. Still, these signals are weak, and I’m not comfortable hanging my winter outlook on either.

Therefore, this winter outlook is one where a meteorologist has to leverage his experience and intuition to come up with a winter outlook that is anything more than a flip of the coin. Undoubtedly, the best meteorologists possess keen pattern recognition skills and a well-developed sixth sense of “where things are going.” So, in this vane I’m putting on my Swami hat and tapping into my Zen forecasting skills. Here’s what I’m thinking…

The extremely warm weather of the last six weeks will last, at most, two more weeks. While one more record high is possible on December 5^th or 6^th, I do not expect any more record warmth beyond that (this year). Instead, a progressive and gradual turn to colder conditions will begin around December 8^th and continue through mid-month. A dramatic blast of arctic air will drop into the central or eastern US before Christmas, and I expect the Lancaster area will experience a string of several days of below normal before month’s end. Still, with the first week of December coming in around 10 degrees above normal, my sense is the magnitude of the cold will not be enough to erase this positive anomaly. Precipitation-wise, a few storms will be spawned as part of the pattern change, and I expect significant lake effect snows will provide a white Christmas in the mountains of northwestern PA. However, the southeastern counties will need some good luck to produce a snow storm before Christmas. With the cold air building in during mid-month, snow is possible, but as to our realistic chance of a White Christmas here in Lancaster, I would assess it as about “30 percent.”

Beyond that, I expect rather high variability in our weather during January and February. My sense is that a stubborn jet stream ridge in the vicinity of the Bahamas and Cuba will exert itself and occasionally push mild air masses into the mid-Atlantic region. Meanwhile, persistent arctic chill in Eastern Canada will make frequent glancing blows across the Great Lakes and Northeast. That places Lancaster right in the battle zone, and, hence, I believe that we may partially break the dry spell with near-normal precipitation during the winter season. As allows, how much snow we receive depends on the exact track of low pressure systems, but my sense is that a track to our west may be more prevalent than a track to our east. Therefore, snow changing to ice or ice changing to rain may be a common occurrence. Even so, it only takes one big storm to track up the coast to push us above normal for the season (i.e. forecasting winter season snowfall is largely a matter of luck). But any good Swami would at least take a shot at it, so let’s say this winter’s snowfall will be within six inches of normal (between 20 and 32 inches).