The Pennsylvania Observer

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1 The Pennsylvania Observer April 2, 2009 March 2009 Pennsylvania Weather Recap Prepared by Curt Harpster For the month of March the saying, In like a lion and out like a lamb really fit the pattern quite well. The month began with a Nor Easter and then gradually made the transition from wintry precipitation and cooler temperatures to dry and warmer temperatures. Temperatures for the month of March averaged about 1-3 degrees warmer than normal in most of the state. Places in northern and western Pennsylvania hit 3-5 degrees above normal, and places in the extreme southeast were 1-2 degrees below normal. Precipitation throughout the state was one-sided with most of the state receiving 1-2 inches less than normal. Williamsport was 2.13 inches below their typical average for the month. The extreme northwestern portion of the state near Lake Erie was the only location receiving more than the normal amount of precipitation, on the order of 1-2 inches above. The eastern portion of the Commonwealth saw its first snow of the month and in some places the heaviest of the winter as a Nor Easter slid up the coast on the 1 st and 2 nd. Stations in eastern and southeastern Pennsylvania reported average snowfall totals ranging from 4-7 inches, with isolated areas northeast of Philadelphia near Norristown receiving 8-12 inches. In the wake of the storm, brisk winds carried cold air from Canada into the region bringing lake effect snow showers to much of the Commonwealth from the 3 rd to the 5 th, and drove overnight lows into the low teens and single digits. Laurel Summit recorded a low temperature of -2 F during the early morning hours on the 3 rd. After the passage of a warm front on the 6 th, temperatures started to increase, signaling the beginning of a more spring like pattern. A stalled front over the Commonwealth caused some rain in western and northern Pennsylvania. On the 7 th much of the region saw highs reach the 60 s in the north and into the lower 70 s farther south. State College (KUNV) reported a new record high temperature of 70 F on the 7th. A steady stream of storm systems continued to pass to the northwest of the region through the 11 th keeping temperatures mild and producing little precipitation across the southeast half of the Commonwealth. Pleasant, yet dry weather and slightly above normal temperatures prevailed throughout the region from the 12 th through the 15 th. Light rain moved into central and southern portions of the state on the 16 th, but pleasant weather again followed. A cold front passed through the Commonwealth on the evening of the 18 th bringing light rain and snow showers to the region. Rainfall amounts averaged between a trace and 0.25 inches and snowfall accumulations were less than an inch in northern Pennsylvania. Before the cold front passed through on the 18 th, State College (KUNV) reported a new record high temperature of 73 F. High pressure dominated the region from the 20 th through the morning of the 25 th once again bringing dry, pleasant weather to Pennsylvania. During this period temperatures were cool on the 20 th, but then returned to normal or slightly above normal for March. Rain associated with an approaching cold front moved into the Commonwealth during the night on the 25 th. This began a four day span from the 26 th to the 29 th where at least some part of Pennsylvania received precipitation each day. The precipitation was associated with three separate low pressure systems. Total precipitation for this period averaged inches in western PA, inches in central PA, and inches in eastern PA. During these few days, high temperatures generally remained in the 50 s and low 60 s throughout the Commonwealth. During the evening of the 29 th, convection developed in southeastern Pennsylvania prompting 22

2 hail reports and 6 high wind reports as shown in the Storm Prediction Center s records. There was a large amount of golf ball sized hail reported and the National Weather Service confirmed that an EF0 tornado did occur in Lancaster County associated with one of the storm cells. The Commonwealth finished out its last two days of the month with relatively breezy days helping to dry out from the recent rain. Here are the weather extremes across Pennsylvania (observations taken at 8AM EDT) during March 2009 from the NWS Cooperative & ASOS Networks. The extremes occurred in the 24-hour period prior to the date listed. Parameter Location Value Date (8 AM County EDT) Highest Point Marion 76 F March 8 th Greene Temperature Lock Lowest Laurel Summit -2 F March 3 rd Somerset Temperature Greatest Slippery Rock Butler Cumulative Liquid Precipitation Greatest Daily Snowfall Safe Harbor Dam 11 - Lancaster Weather Stories Strong to Severe Storms Across Parts of the Delaware Valley Across-Parts-of-the-Delaware-Valley National Weather Service Confirms Pa. Tornado First Two Months of 2009 Set Record for Driest Start to Year Unusually Dry Winter May Mean Summer Drought not_flooding the_delaware_valley_spring_ worry.html Central PA Winter Wrap-Up 09/03/central_pa_winter_ _wrapup.asp

3 The Pennsylvania Observer April Climate Highlight: The April Climate Highlight shows the last dates in which at least an inch of snow has fallen in State College. The central and western counties of the Commonwealth have seen an unusually early end to the snow season this year. During 2009, the last inch of snow fell on February 19 (the second earliest ever) in State College.

4 With most of Pennsylvania only receiving 40-70% of normal precipitation so far this year, it is not surprising that the snowfall has been below to well below average in many areas. In addition, the mild, dry March has seen an unusually early end to the snow season for the central and western counties of the Commonwealth. Using the State College cooperative station reports since 1893, the graph below shows the distribution of last dates of an inch of snowfall which varies from the earliest, February 17 (Julian date = 48) to the latest, April 30 (Julian date = 120). Last Date of 1" snowfall at STCP1 140 Julian Days (45=Feb 14) Years ( ) In 2009, the last inch of snow fell on February 19 (the second earliest ever). Listed below are the composite April temperature and precipitation anomalies on the years when the snow ended early in State College. Overall, the April that followed was milder than normal and it was moist in the eastern half of the nation.

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6 The Pennsylvania Observer Outlook Experimental Long Range Outlook for Pennsylvania: April May 2009 The basis of this analog prediction scheme uses the notable temperature and precipitation anomaly from the last 30 days (or so) and in a fuzzy way that is setting all anomalies to +/- 0.5 standard deviations from the long-term mean and matches these patterns to the climate division anomalies from present. The best matched years are selected (using a dozen or less) and these are used to produce the composite anomalies for the next two months and the years are used to create a composite daily anomaly for three regions of Pennsylvania. Here are the anomalies for March, 2009: Notable anomalies during the month of March include unseasonable warmth throughout the Ohio River Valley and the Southwestern states and much below average temperatures in the Dakotas.

7 The Southwest experienced a very dry March, but a late season blizzard kept precipitation in the Dakotas and Minnesota above normal. Also notable are the dry conditions that dominated most of Pennsylvania during the period. The following years were matched: 1900, 1919, 1929, 1941, 1945, 1951, 1968, 1970, 2004, 2007 Below are the composite departures for those years for April and May.

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10 Western Pennsylvania Temperature Forecast April-May Mean Temperature Departure from Normal (deg F) /1 4/3 4/5 4/7 4/9 4/11 4/13 4/15 4/17 4/19 4/21 4/23 4/25 4/27 4/29 5/1 5/3 5/5 5/7 5/9 5/11 5/13 5/15 5/17 5/19 5/21 5/23 5/25 5/27 5/29 Date Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal

11 Central Pennsylvania Temperature Forecast April-May Mean Temperature Departure from Normal (deg F) /1 4/3 4/5 4/7 4/9 4/11 4/13 4/15 4/17 4/19 4/21 4/23 4/25 4/27 4/29 5/1 5/3 5/5 5/7 5/9 5/11 5/13 5/15 5/17 5/19 5/21 5/23 5/25 5/27 5/29 Date Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal

12 Eastern Pennsylvania Temperature Forecast April-May Mean Temperature Departure from Normal (deg F) /1 4/3 4/5 4/7 4/9 4/11 4/13 4/15 4/17 4/19 4/21 4/23 4/25 4/27 4/29 5/1 5/3 5/5 5/7 5/9 5/11 5/13 5/15 5/17 5/19 5/21 5/23 5/25 5/27 5/29 Date Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal