The Pennsylvania Observer

Transcription

1 The Pennsylvania Observer August 3, 2015 July Pennsylvania Weather Recap By: Arthur Person Although this seventh month of 2015 was fairly normal across Pennsylvania as a whole, the details reveal a different picture. There were cooler and warmer areas as well as wetter and drier areas, all making for a smorgasbord of summer weather suitable for just about any weather connoisseur. This pattern was caused by a series of atmospheric disturbances that shifted a frontal boundary north and south of the state at various times during the month. To start the month, a storm system left the region with clearing skies and cooler drier air, but not before dropping of rainfall in eastern counties with amounts greater than 3 in Carbon, Monroe and Pike counties. A frontal boundary behind this storm stalled south of Pennsylvania allowing a weak disturbance to graze the southeast on the 2 nd. Skies were briefly fair on the 3 rd before yielding to cloudiness and showers in the southwest by evening, and on the 4 th, rain fell across all but the northwest portions of the state. The air was cool and dry during this event which led to some exceptionally cool temperatures the night of the 3 rd (Erie 51 F, 5 th coolest; Warren 43 F, 3 rd coolest) and an exceptionally cool day on the 4 th (State College 68 F, 6 th coolest; Williamsport 70 F, 4 th coolest; Scranton 69 F, 4 th coolest). Fair skies returned for the 5 th but clouds gradually overspread the state by evening as a weak storm system in Kentucky moved northeastward. This storm continued northward on the 6 th bringing a mixture of clouds, showers and sunshine. By the 7 th, warm and muggy air had replaced the cooler, drier air pushing temperatures into the mid and upper 80's, setting the stage for showers and severe thunderstorms in western Pennsylvania along an advancing cold front. The front stalled across Pennsylvania on the 8 th leaving lots of clouds, some sunshine and a few stray showers. Warm and muggy conditions continued on the 9 th supporting several bands of showers and severe thunderstorms that crossed the state, including 3 tornadoes reported in eastern Pennsylvania. The 10 th brought some relief from the heat and humidity as temperatures dropped back to seasonal levels with comfortable humidity and sunshine, except in the southwest where a few late day showers occurred. Sunny, dry and seasonable weather on the 11 th gave way to clouds mixed with sunshine for the 12 th and some late afternoon rain in the southwest as warmer temperatures and higher humidity again spread northward for the 13 th. Warm and muggy weather returned to the state for the 14 th as a cold front approached from the west bringing several waves of showers and severe thunderstorms.

2 This system gradually ushered in cooler and drier air for the 15 th and 16 th. Bradford, Altoona and Scranton all recorded their second-lowest minimum temperature on record for the 16 th with values of 37, 48 and 51 F, respectively. A disturbance in the Great Lakes brought some clouds and a few showers to Pennsylvania as the humidity started ticking upward again for the 17 th. Overnight thunderstorms the morning of the 18 th rocked central and southeast counties producing over 3 of rainfall in isolated sections of Blair, Centre and Huntingdon counties. By the 19 th, warm and humid conditions had returned to Pennsylvania allowing scattered afternoon showers and thunderstorms. Pittsburgh recorded its highest low temperature on record for the 18 th with a low temperature of only 75 F. Evening thunderstorms on the 19 th dropped nearly 3 of rain near Forest, Elk and Jefferson counties and helped to cool off the northwestern part of the state for the 20 th while the southeast remained sultry. A cold front from the west finally pushed through on the 21 st bringing drier and more pleasant weather through the 25 th. By the 26 th, a southwesterly flow ahead of a cold front sparked showers and thunderstorms again, a few severe. Clouds were slow to clear in the southeast on the 27 th as this decaying front stalled just south of the Pennsylvania border, while warmer and more humid weather returned for the 28 th and 29 th. Slippery Rock was a hot spot setting a new high temperature record of 95 F on the 28 th. Another cold front slipped across the state on the 30 th to end the month with much lower humidity levels and temperatures near normal. Overall, temperatures and precipitation across the state were close to normal, but the distribution of actual readings was not. Temperatures were as much as 2 degrees above normal in the vicinity of Clearfield and Jefferson counties while parts of the Susquehenna valley were 1-2 degrees below normal. Areas near western Centre county and eastern Luzerne county experienced rainfall as much as 3 above normal while the rest of the state saw values generally within 1.5 of normal. Approximately 12 fronts or storms crossed the state during the month of July, and the wetness in central Pennsylvania was evident in the number of significant precipitation days in State College where it rained 0.10 or more on 13 days of the month, which ranks 2 nd in 123 years of records for the month of July. Severe weather summary: 100 wind, 3 hail, and 3 tornado reports (2 EF-1, 1 EF-0)

3 Here are the weather extremes across Pennsylvania (observations taken at 8AM EDT) during July 2015 from the NWS Cooperative, ASOS, and CoCoRaHS 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 Phoenixville 1 Mi. E 99 F July 19 th Chester Lowest Temperature Greatest Cumulative Liquid Precipitation Least Cumulative Liquid Precipitation Oswayo 1 Mi. ENE Saylorsburg 2.7 Mi. ENE Charleroi Lock 4 39 F July 16 th Potter 8.66 July 1 st -31 st Monroe 1.74 July 1 st -31 st Westmoreland Links to Pennsylvania Weather Stories during July, 2015 Berks County school destroyed by tornado Businesses, organizations take wet weather in stride in western PA Pittsburghers-say/stories/ Dry weather rare to come by in central PA this summer Excessive heat leads to activation of heatline in Philly

4 The Pennsylvania Observer FEATURED CLIMATE HIGHLIGHT By: Kyle Imhoff This past June was the hottest on record in the Pacific Northwest. The average temperature across all climate divisions in the region for the month was 65.2 F, a remarkable 8.0 F above the average June temperature computed over the entirety of the 20 th century. This was primarily due to a persistent ridge centered over the western US as shown in the image below of 500mb height anomalies.

5 As a result of the location of this ridge, the northeastern US experienced very wet weather with frequent intrusions of cooler air during the month of June. Based on the excessive warmth and strong ridge over the western US, a question that can be posed is can this anomalous atmospheric pattern provide any insight into what fall conditions will be like in the northeastern US? By looking at analogous years in the past (in this case, the 20 years with the highest average temperatures during June in the Northwest), composite temperature and precipitation anomalies for the following September- November time period are shown below.

6 Based on the analogous years, the fall will be slightly warmer and moderately wetter than normal in Pennsylvania.

7 The Pennsylvania Observer LONG RANGE OUTLOOK By: Kyle Imhoff The month of July 2015 s largest temperature/precipitation departures from normal are dominated by the western United States - hot and dry weather occurred in the state of Washington while it was cool in the southwest and wet in Oklahoma. An analog forecast is produced using the assumption there is some correlation between past extreme patterns of temperature and precipitation and the present pattern. Using the temperature and precipitation extremes described above, analogous years in which these conditions occurred can be found. Climate records are examined for these areas and the 25 most extreme years are ranked in the below table. After identifying common years in the four categories, the years with the most categories in common and highest rank are used as analog years.

8 Hot Dry Cool Wet Washington Washington Southwest Oklahoma Years in rank order of coolest, warmest, driest and wettest years for each region. Yellow entries represent years that occur in two categories, orange three categories, and red all four categories of climate extremes. Composite maps of temperature and precipitation anomalies for the months of August and September using the analogous years in the above table are show below. These forecasts show slightly above normal temperatures for August and September and wetter than normal conditions across the state of Pennsylvania, especially in western areas.

9 August and September forecast using composite temperature and precipitation anomalies for analog years. Using Pennsylvania climate data for the highest ranked years from 1948 or later, forecast temperature and precipitation graphs are created and shown below.

10 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 9/30 Mean Temperature Departure from Normal (deg F) Western Pennsylvania Temperature Forecast August-September Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal 0

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) Central Pennsylvania Temperature Forecast August-September Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal 0

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) Eastern Pennsylvania Temperature Forecast August-September Forecast 5-Day Mean Forecast Verification 5-Day Mean Verification Normal