The Pennsylvania Observer

Transcription

1 The Pennsylvania Observer August 3, 2009 July Pennsylvania Weather Recap Written by: Dan DePodwin After a cool month of June, some hoped July would bring usual summertime warmth to the state of Pennsylvania. Unfortunately, for the first half of the month, a stubborn upper-level trough situated over southeastern Canada and the Great Lakes brought persistent below average temperatures and rounds of showers and thunderstorms to the Commonwealth. Although warmer weather moved in towards the end of the month, July finished well below average temperature-wise. The month started off on a wet note as an area of low pressure moved from the Great Lakes to southern Quebec. Rainfall was scattered throughout the state with Reading receiving 1.42 (36.07mm) from the 1 st -3 rd while Downington recorded only 0.11 (2.79mm) in the same time span. As the system of low pressure pulled northward, dry and pleasant conditions prevailed for the holiday weekend. The 4 th of July featured a mix of sun and clouds with temperatures in the 70s throughout much of the state. As the next work week began on the 6 th, a weak cold front pushed through Pennsylvania bringing isolated showers to much of the state with the exception of the Pocono Region where 0.66 (16.76mm) fell in Hawley. Behind the front, a large dome of high pressure built into the region for the 8 th -10 th keeping conditions pleasant. High pressure began to creep off the East Coast on the 10 th ahead of an approaching cold front. In advance of the front, temperatures in the western half of the state reached well into the 80s on the 11 th. This Saturday also featured some severe storms across the Commonwealth associated with the aforementioned front. High wind reports were common across the central portion of the state and a tornado even was reported on the ground in Northumberland County. Places in Carbon County received upwards of 2.50 (63.50mm) of rain from the storms. Much cooler air rushed into the state from the 12 th -14 th due to an unseasonably strong Canadian high pressure system. Well below normal temperatures were common with near record nighttime readings in northwest counties. Some cool spots included: 40F (4.4C) in Chandlers Valley on the 14 th and 38F (3.3C) in Oswayo on the 15 th. These low temperatures are usually seen at the end of September, not in the middle of July! However, these cold temperatures would be short-lived. On the 16 th, a warm and humid southerly flow ahead of a cold front allowed some locations in southern Pennsylvania to reach 90F (32.2C) for the first time this summer. The hot spot was Shippensburg where 93 was the high temperature. Rainy weather on Friday, associated with a large area of low pressure, kept temperatures in check for the end of the work week. Rainfall amounts were moderate with Latrobe receiving 1.25 (31.75mm). The wet weather cleared out for the weekend of the 18 th. It was cool however, with a high temperature of only 69F (20.5C) in State College, PA on the 18 th.

2 The work week of the 20 th began with dry weather across the state but muggy conditions were felt for the rest of the week as a strong southerly flow brought scattered showers and storms to the Commonwealth. Rainfall amounts were not evenly distributed. State College received 3.28 (83.31mm) while Latrobe only received 0.60 (15.24mm). Some locations in western Pennsylvania received hail on the 21 st from a line of severe thunderstorms. As a low pressure center moved through the mid-atlantic on the 24 th, more rain and storms occurred throughout the state. Behind this system, clear skies but humid conditions built in for the weekend as a Bermuda High pumped sultry air along the Eastern Seaboard. A cold front entered this warm and humid air-mass on the 26 th, spawning scattered severe storms. A tornado was even reported in Elk County. The final week of the month consisted of more humid weather and scattered showers and storms. Widespread rain occurred on the 29 th with 2.07 (52.58mm) falling in Dingmans Ferry. More severe weather occurred in the eastern third of the state with a tornado being reported in Stroudsburg. Drier weather returned on the 30 th before more showers moved in on the last day of the month. Overall, July 2009 was one of the coldest on record (since 1895) throughout the state of Pennsylvania. Temperatures in Harrisburg reached above 90F (32C) only one time during the month which is well below average (9 days). Rainfall was plentiful for much of the state with the exception of the southwestern part. Erie was extremely wet with 6.89 (175.00mm) while Lancaster only reported 2.69 (68.33mm). In the end, although the calendar said July, the weather on many days (especially during the first half of the month) felt like May. Here are the weather extremes across Pennsylvania (observations taken at 8AM EDT) during July 2008 from the NWS Cooperative & ASOS Networks of which our office receives routine observations. The extremes occurred in the 24-hour period prior to the date listed. Parameter Location Value Date (8 AM EDT) County Highest Temperature Shippensburg 93 F July 17 th Cumberland Lowest Temperature Oswayo 38 F July 14 th Potter Greatest Cumulative Liquid Precipitation Least Cumulative Liquid Precipitation West Hickory 8.36 July 1 st July 31 st Forest Berlin 1.04 July 1st July 31st Somerset

3 Links to Pennsylvania Weather Stories during July, 2009 A dozen tornadoes in Monroe since records are kept Violent Tornado Rips Through Pennsylvania Towns in Pocono Mountains Late tomato blight reported in central Pennsylvania Weather History - July 30: Record Heat, Tropics, Severe Storms, Tornadoes, Hail and Flooding Record-Heat-Tropics-Severe-Storms-Tornadoes-Hail-and-Flooding Weather kills gypsy moths

4 The Pennsylvania Observer FEATURED CLIMATE HIGHLIGHT By: Steve Travis This month s climate highlight selects years in which both temperatures were considerably below average (that is, greater than one standard deviation below the mean) AND precipitation totals were considerably above average (that is, greater than one standard deviation above the mean) for June and July in Massachusetts. These anomalous years were then used to output and compare nationwide temperature and precipitation anomalies for the month of September.

5 The summer has gotten off to a cool and wet start for the state of Massachusetts. The months of June and July are shaping up to be among the coolest and wettest for the two month period with June numbers both greater than one standard deviation away from the mean and July numbers appear to be following the same path. This month s climate highlight attempts to put these numbers into perspective for the Commonwealth of Pennsylvania. Years in which both temperatures were considerably below average (that is, greater than one standard deviation below the mean) AND precipitation totals were considerably above average (that is, greater than one standard deviation above the mean) for June and July were compiled (Table 1) and compared with nationwide temperature and precipitation anomalies for the month of September using these anomalous years (Figures 1 and 2). Year Precipitation (inches) Temperature (F) Table 1: Years in which both an unseasonably wet June/July Precipitation and unseasonably cool June/July mean temperatures existed along with their values. It should be noted that mean values for these variables are 7.12 inches and degrees Fahrenheit, respectively. Figure 1: Nationwide precipitation anomalies using the anomalous years above. Orange and yellow colors correspond to below average precipitation while blue corresponds to above average precipitation amounts.

6 Figure 2: Nationwide temperature anomalies using the anomalous years above. Orange and yellow colors correspond to above average temperatures while blue colors correspond to below average temperatures. Figure 1 would appear to indicate that, as a result of a wet and cool June and July in Massachusetts, the entire Commonwealth of Pennsylvania is in store for below average rainfall in September. Figure 2 is a little less conclusive. It indicates that below average temperatures are likely for the eastern third of Pennsylvania while temperatures well above average seem likely for the northwestern portion of the state. Climatology indicates that other locations across the state should see temperatures near to slightly above average for September. Overall, based on climatology, the majority of Pennsylvania will likely be in for a warm, dry September. This may not be the best news for farmers across the state hoping for better crop yield before the end of growing season but good news for those thousands of children headed back to school and outside recess come Labor Day.

7 The Pennsylvania Observer Outlook The outstanding feature of the July temperatures has been the persistent upper-air pattern that brought higher temperatures to those cities west of the Rocky Mountains and lower temperatures to the Great Lakes.

8 July s rainfall totals were fairly close to normal across the country. Wet exceptions were in ArkLaTex and Rhode Island, which saw rainfall totals greater than six inches above normal. In contrast, portions of Wisconsin, Minnesota and southeastern Georgia experienced a drier than normal month. When the previous conditions were compared with previous July s on a climate division level, the following years were selected as close analogs: 1906, 1910, 1916, 1936, 1939, 1946, 1960, 1967, 1975, Below are the conditions nationwide during the August-September that followed:

9 The map suggests that temperatures will be below normal during the next two months in southern Texas and the Southeastern portion of the United States. Meanwhile, the rest of the nation could see above average temperatures, especially in the Pacific Northwest, the Great Lakes and the Northeast.

10 This long range forecast suggests drier than normal conditions in northern Minnesota and western Wyoming. Very dry conditions are also forecasted for the Pacific Northwest. Contrarily, southern California, southern Texas and much of Alabama should see above average rainfall for the two month period.

11 8/1 8/3 8/5 8/7 8/9 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 8/27 8/29 8/31 9/2 9/4 9/6 9/8 9/10 9/12 9/14 9/16 9/18 9/20 9/22 9/24 9/26 9/28 Mean Temperature Departure from Normal (deg F) Applying those same analog years produced the following daily departures from normal for three regions of Pennsylvania for the period from August September. Western Pennsylvania Temperature Forecast August-September Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal

12 8/1 8/3 8/5 8/7 8/9 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 8/27 8/29 8/31 9/2 9/4 9/6 9/8 9/10 9/12 9/14 9/16 9/18 9/20 9/22 9/24 9/26 9/28 Mean Temperature Departure from Normal (deg F) Central Pennsylvania Temperature Forecast August-September Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal

13 8/1 8/3 8/5 8/7 8/9 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 8/27 8/29 8/31 9/2 9/4 9/6 9/8 9/10 9/12 9/14 9/16 9/18 9/20 9/22 9/24 9/26 9/28 Mean Temperature Departure from Normal (deg F) Eastern Pennsylvania Temperature Forecast August-September Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal