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Western Chester County (Specific) Weather Analysis 1894-Present


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Hey guys,

So I thought I would analyze the last 13 decades back to the 1890's to see if the first quarter winter months (January-March) outside of the Philadelphia heat island in the more rural areas of the Philadelphia suburbs during the peak winter months of January through March have shown any signs of warming or cooling or more or less snowfall. Keep in mind snowfall amounts are not seasonal totals only January through March totals.

Below is a chart with the analysis of the data. Of interest our most recent complete decade from 2010-2019 was the coldest first quarter since the 1980's! I did not expect to see that!!  The warmest Q1 decade was the 1930's with the coldest being the 1970's. The snowiest was the 1890's followed closely by our most recent complete decade of the 2010's. Overall not surprisingly there appears to be no significant Q1 warming evident outside of the urban heat island impact in SE PA...just typical variability and expected cyclical trends. Snowfall appears to have a stronger cyclical signal with a general fall in snowfall totals from the turn of the 20th century...reaching a low point in the 1930-1950 period with a gradual increase in snowfall through our most recent decade of the 2010's. If I am reading the tea leaves correctly based on cyclical weather I suspect we could be entering a period of declining snowfall over the next 5 decades through the 2060's....with snowfall amounts beginning to climb again starting in the 2070's. Our most recent winter season of 2019/20 may be a sign of the seasons to come as our 5.8" of snow in Chester County PA this season was our 3rd lowest total in history. If these historical trends are indeed cyclical....for many on this forum over 30 years old who love snow - you may be in for some tough sledding (meaning relative to our most recent decade little snow) for the rest of your lives....for the younger folks born since the turn of the century you might at least begin to see snowfall increases as you reach your social security (if it still exists) age in the 2070's.

image.png.8c3d7baa811141f61f3170726743aedc.png

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Jan-Mar average temps for SE PA since 1895.  Its warmed almost 4F with most of that in the past 40 years.

1895-1920 mean - 31.2

1995-2020 mean - 34.9

Highest

2012 - 40.5

2020 - 40.3

1998 -  39.9

sepajanmar.png

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3 hours ago, Chubbs said:

Jan-Mar average temps for SE PA since 1895.  Its warmed almost 4F with most of that in the past 40 years.

1895-1920 mean - 31.2

1995-2020 mean - 34.9

Highest

2012 - 40.5

2020 - 40.3

1998 -  39.9

sepajanmar.png

makes sense including the heat island impacts!

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1 hour ago, chescopawxman said:

makes sense including the heat island impacts!

No the many differences between the early Coatesville site and your site explain the difference. Heat island is corrected for in the chart above. Phl is only one of 40+ sites and both Coatesville sites are included. 

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Why do we constantly  have to post these charts that are non representative of anything besides Paul’s backyard. Things are warming, get over it 

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Makes sense totally understand a pooled 40+ data site approach - it does a nice job of smoothing and attempting to clean up the heat island problem that is PHL and possibly other sites in the data. Therefor it provides a nice finding for the relatively broader area that that data is attempting to target. My data of course makes no such attempt. I am strictly addressing the different local climate of Chester County PA alone. One quick question are you sure the above data includes PHL? Isn't PHL situated on the Atlantic Coastal Plain while Chester County lies in the Piedmont Plateau?

Now, while no doubt folks on here would love to see us rehash what we painfully went through last summer LOL!!. I will only briefly clarify again, With my data set I am choosing to be much more targeted in my analysis (not pooled data) with site specific local data for my area. My data set has already been rigorously tested and compared with now over 184,000 daily data points included in my data set since 1894. I ran a detailed and exhaustive data integrity test on this entire data base and was able to conclusively deliver a highly statistical p-value that demonstrated that the data consistency in my data set is not simply by chance (hence it's highly statistical significance). Therefore the data is scientifically valid and the same for the Chester County area it attempts to analyze.  This site specific and unique local non-pooled data allows me to not require any after the fact adjustments,  nor am I required to apply any statistical corrections like was required in the above data you bring to the discussion. As my data has no need to address or adjust for any heat island impacts of PHL and/or any other potential heat island observation sites that are potentially included in the above data. 

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33 minutes ago, tombo82685 said:

Why do we constantly  have to post these charts that are non representative of anything besides Paul’s backyard. Things are warming, get over it 

Sorry Tom I thought the chart is clear it is ONLY for 1 analyzed area of Chester County - this does not of course refute the warming theory that some folks see. See my latest post it is indeed validated and accurate for ONLY Western Chester County PA - very site specific and the fact that this area is only showing cyclical warming as far as the data shows us....does of course NOT mean there is NOT warming or cooling taking place - only that for the area of analysis in Chester County we do not yet see a solid signal. All that said I of course believe in climate change....that is fact - It is and always will be changing....now is it warming.....cooling....

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6 hours ago, chescopawxman said:

Makes sense totally understand a pooled 40+ data site approach - it does a nice job of smoothing and attempting to clean up the heat island problem that is PHL and possibly other sites in the data. Therefor it provides a nice finding for the relatively broader area that that data is attempting to target. My data of course makes no such attempt. I am strictly addressing the different local climate of Chester County PA alone. One quick question are you sure the above data includes PHL? Isn't PHL situated on the Atlantic Coastal Plain while Chester County lies in the Piedmont Plateau?

Now, while no doubt folks on here would love to see us rehash what we painfully went through last summer LOL!!. I will only briefly clarify again, With my data set I am choosing to be much more targeted in my analysis (not pooled data) with site specific local data for my area. My data set has already been rigorously tested and compared with now over 184,000 daily data points included in my data set since 1894. I ran a detailed and exhaustive data integrity test on this entire data base and was able to conclusively deliver a highly statistical p-value that demonstrated that the data consistency in my data set is not simply by chance (hence it's highly statistical significance). Therefore the data is scientifically valid and the same for the Chester County area it attempts to analyze.  This site specific and unique local non-pooled data allows me to not require any after the fact adjustments,  nor am I required to apply any statistical corrections like was required in the above data you bring to the discussion. As my data has no need to address or adjust for any heat island impacts of PHL and/or any other potential heat island observation sites that are potentially included in the above data. 

meh - E Nantmeal and the airport are fine and can be combined. How do we know that - we compared them for the same time period. Can't do that for the early Coatesville data. I have looked at that data and it is very warm relative to other data collected at the same time. The early Coatesville data also received large adjustments in the NASA/NOAA database for instrumentation/siting changes. Much different instrumentation/site vs yours or the airport.

Below is map of Pa zones

pennsylvania.gif

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Here are annual average temperatures for SE Pa Piedmont  and for the KQMS/ENantmeal combo. KQMS/ENant follow the regional temperatures very closely both on a year-to-year basis and for the longer term. There is no reason for Western Chester County to suddenly deviate from the rest of the region in the period before the KQMS/ENant data.

sepaenant.png

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3 hours ago, Chubbs said:

Here are annual average temperatures for SE Pa Piedmont  and for the KQMS/ENantmeal combo. KQMS/ENant follow the regional temperatures very closely both on a year-to-year basis and for the longer term. There is no reason for Western Chester County to suddenly deviate from the rest of the region in the period before the KQMS/ENant data.

sepaenant.png

No clue what you are talking about....there is no "sudden deviation" in my carefully analyzed and verified 127 years of daily data for Western Chester County...the temps have remained very consistent with only very minor average temperature variation in 13 decades....now if you wish to look at snow - indeed some significant cyclical trends are potentially indicated

 

4 hours ago, Chubbs said:

meh - E Nantmeal and the airport are fine and can be combined. How do we know that - we compared them for the same time period. Can't do that for the early Coatesville data. I have looked at that data and it is very warm relative to other data collected at the same time. The early Coatesville data also received large adjustments in the NASA/NOAA database for instrumentation/siting changes. Much different instrumentation/site vs yours or the airport.

Below is map of Pa zones

pennsylvania.gif

Yikes! adjustments...that is indeed a problem - no adjustments required for our carefully analyzed data for Western Chester County PA- we have no heat island adjustments to input. If you need to adjust your data....have at it!

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4 hours ago, Chubbs said:

meh - E Nantmeal and the airport are fine and can be combined. How do we know that - we compared them for the same time period. Can't do that for the early Coatesville data. I have looked at that data and it is very warm relative to other data collected at the same time. The early Coatesville data also received large adjustments in the NASA/NOAA database for instrumentation/siting changes. Much different instrumentation/site vs yours or the airport.

Below is map of Pa zones

pennsylvania.gif

 

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6 hours ago, chescopawxman said:

No clue what you are talking about....there is no "sudden deviation" in my carefully analyzed and verified 127 years of daily data for Western Chester County...the temps have remained very consistent with only very minor average temperature variation in 13 decades....now if you wish to look at snow - indeed some significant cyclical trends are potentially indicated

 

Yikes! adjustments...that is indeed a problem - no adjustments required for our carefully analyzed data for Western Chester County PA- we have no heat island adjustments to input. If you need to adjust your data....have at it!

Yes, I am going to stick with the regional analysis, almost 4F of warming in 100 years. If you want to maintain your own little "cool island", have at it!

grid-ranks-tavg-202001-202003.png

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That PHL heat island red on that map sure sticks out....I notice it does not seem to cover Western Chester County.....interesting

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1 hour ago, Chubbs said:

Yes, I am going to stick with the regional analysis, almost 4F of warming in 100 years. If you want to maintain your own little "cool island", have at it!

grid-ranks-tavg-202001-202003.png

Interesting that this 4 degree warming seems to be the same difference between PHL and Chesco...of those 40+ sites included in the pooled data can you find the exact sites? I wonder how many represent stations on the coastal plain like PHL vs stations on the piedmont plateau? 

  image.png.13107447f3608035b01c21f8b4232c62.png

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Hey guys, I also changed the Topic title to hopefully clarify so folks understand this is NOT about their backyard only Western Chester County PA

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10 hours ago, chescopawxman said:

Interesting that this 4 degree warming seems to be the same difference between PHL and Chesco...of those 40+ sites included in the pooled data can you find the exact sites? I wonder how many represent stations on the coastal plain like PHL vs stations on the piedmont plateau?

Per the chart I posted above the average temperature for SE PA climate zone is within a few tenths of ENant.

Stations.png

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Nice map - thanks!! Plenty of data sites (did you say there are 40?) to average and adjust as required.

I will continue to note on all future analytics that my data is only for Western Chester County and will choose to keep it distinct and not combined or adjusted post observation

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  • 3 weeks later...

So how unusual is this cold May in Western Chester County PA? very! On top of the potential of snow in the air on Friday and Saturday in May - an extremely rare event in the climate change era....or heck any era climate change or not! We are well on the way to the latest 80+ degree reading in at least the last 38 years here in Chester County. Already through today this is the 5th latest 80+ degree reading so late into May. In looking at the longer range models it looks increasingly possible that we will set a record for the latest 80+ day in County history. Below are the latest such readings 

#1 - 5/22/1988 / #2 - 5/20/1984 / #3 - 5/19/1997 - 5/19/1992 - 5/19/2019 / #4 - 5/10/1987 - #5 - TBD here in 2020

 

 

 

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  • 5 weeks later...

A little late but below is the Climate Summary for May 2020 for Western Chester County PA along with some interesting weather factoids

  • Average Temperature 58.6 (0.7 degrees below normal) ( Avg High 67.4 / Avg. Low 49.8)
  • This was our 2nd consecutive below normal month following the April 49.4 avg (0.5 below normal)
  • The 2 month average of April and May mark the 24th coldest first 2 months of Spring in the Chester County history (1894-Present) and coldest since April/May 2008
  • Rainfall = 2.88" (1.40" below normal)
  • YTD Rainfall stands at 21.29" (2.02" above normal)
  • Highest Temperature was the 81.3 on the 15th - this was our 1st 80 degree day of the year and represents the 7th latest initial 80+ day since records began in 1894. The latest was on 5/27/37
  • Lowest Temperature was the 31.3 reading on the 9th - our last 32 degree reading of the season occurred on the 10th - this was only our 78th sub freezing low in the 2019/20 winter season normal is 115 days
  • The 46.5 maximum recorded on the 9th was the 6th lowest May max daily reading in the historical climate data set

 

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  • 4 weeks later...

Below is the Climate Summary for June 2020 for Western Chester County PA along with some interesting weather factoids

  • Average Temperature 70.0 (+2.5 degrees below normal) ( Avg High 79.0 / Avg. Low 61.0)
  • This was our 1st above normal month since March
  • The average temperature during Q2 2020 was 59.4 - this marks the 31st coldest 2nd quarter in Chester County history (1894-Present) and coldest Q2 since 2003 (58.5)
  • June Rainfall = 3.94" (0.10" below normal)
  • YTD Rainfall stands at 25.23" (1.92" above normal)
  • Highest Temperature was the 86.3 on the 10th
  • Lowest Temperature was the 44.1 reading on the 1st of the month
  • The last 90 degree reading was last July 21st when we reached 92.5 degrees - that was the 2nd and last 90 degree reading of the summer of 2019
  • We average 11 days that exceed 90 degrees during the summer (1983 to Present) at the relative higher elevation of Chester County PA
  • However 3 of the last 10 years have seen no days exceeded the 90 degree mark
  • 23 of the last 37 years have seen less than 10 days exceed 90 degrees
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  • 2 weeks later...

Below is my climate summary article for the local newsletter which had been delayed....

Hello again from Paul at the East Nantmeal PA Weather Station (www.chescowx.com). Be sure to follow me on twitter at chescopawxman where  I am tweeting daily climate reports, forecast updates and weather and drone photos of our beautiful Township.

When I wrote my last article, in mid-February the world was a bit different, I trust all of you are staying healthy! Weather wise we would not see any additional accumulating snow, with our last snow on January 18th. The snowless February and March were only the 3rd time in 127 years of local history that we failed to see any accumulating snow in East Nantmeal. Those years being 1950 and 1973 (the only season with no measurable snow in Chester County). February was also continuing the trend begun in January (9th warmest on record) with February average temperature of 38.4 ending as the 4th warmest on record behind only 2017 (41.2) / 1998 (40.0) and 1909 (39.5). Precipitation was near normal at 3.25” while with no snowfall we were 11.8” below our normal snow for the month. March would continue the top 10 warmth for winter months with an average temperature of 46.2 – this was the 9th warmest March on record, with our warmest March on record being way back in 1921 with a 51.5-degree average temperature. Not surprisingly the first quarter of 2020 was the 2nd warmest Q1 on record, with an average temperature of 40.4,  only the first 3 months of 1998 (40.9 avg.) were warmer.

Now before you begin to worry too much about any potential global warming…I decided to run an  analysis of the last 13 decades back to the 1890's to see if the January to March winter months, outside of the Philadelphia heat island in the rural areas of Chester County have indicated any clear signals of either significant warming/cooling or variations in snowfall totals. Keep in mind snowfall amounts are not seasonal totals only January through March totals. Below is a chart with the analysis of the data. Of interest our most recent complete decade from 2010-2019 was the coldest first quarter since the 1980's.  The warmest Q1 decade was the 1930's with the coldest being the 1970's. The snowiest was the 1890's followed closely by our most recent complete decade of the 2010's. Overall the data supports no significant Q1 warming evident outside of the urban heat island impact of Philadelphia...just typical variability and expected cyclical trends. The analysis also shows that colder does not always equal more snow.

image.png.0f423d8ae5e8f3474f4f0d54d9d27b37.png

With the 1st full month of Spring in April we began a cooler than normal pattern that would last well into May. During April, the average temperature was 49.4 (0.5 degrees below normal) ( Avg High 60.3 / Avg. Low 39.6). We did record our last sub-freezing reading of the season on April 17th at 30.3 degrees. We had plenty of rainfall in April with 6.31”falling including a record 2.40” on the 13th of the month. Our normal April rainfall totals 3.91”. The April rainfall was the 10th greatest in Chester County history with the all-time wettest April occurring just 6 years ago with the 10.33” falling in 2014. Highest Temperature was the 72.0 on the 8th. The lowest temperature and only sub-freezing day of the month was the 30.3 reading on the 17th. This however would not be our last sub-freezing day with a couple of rare late season freezes ahead during May. Although we would see some snow in the air and even sleet late in the month, we would finish the 2019/20 winter season with just 5.8” of snow this is almost 31” below our normal seasonal snow total of 36.7”. This was the 3rd lowest snow total behind the only snowless winter in Chester County history in 1972/73 and the 2.4” that fell in the winter of 1949/50.

May would continue the chillier trend with an average temperature of 58.6 (0.7 degrees below normal) ( Avg High 67.4 / Avg. Low 49.8). This was our 2nd consecutive below normal month. The 2-month average of April and May mark the 24th coldest first 2 months of Spring in Chester County history (1894-Present) and the coldest spring arrival since April/May 2008. Rainfall was 2.88" (1.40" below normal). The highest temperature was the 81.3 on the 15th - this was our 1st 80-degree day of the year and represents the 7th latest initial 80+ day since records began in 1894. The latest was on 5/27/37.  Our lowest temperature was the 31.3 reading on the 9th this was the coldest for the date since the 34-degree reading in 1984. The all-time low for the day was 25 set back in 1947. The next day the 10th we recorded our last 32 degree reading of the season - this was only our 78th sub-freezing low in the 2019/20 winter season normal is 115 days.   That late freezing temperature was the 15th latest freeze in 127 years of records back to 1894. Also, our latest May freeze in 24 years with the 30-degree reading on May 14, 1996. The average final freeze in Chester County is April 18th. The latest freeze in County history was the 32-degree reading on May 28, 1927. The 46.5 maximum recorded on the 9th was the 6th lowest May max daily reading in the historical climate data set.

June would begin a warming trend that well into July. The average Temperature 70.0 (+2.5 degrees above normal) ( Avg High 79.0 / Avg. Low 61.0) This was our 1st above normal month since March. The average temperature during Q2 2020 was 59.4 - this marks the 31st coldest 2nd quarter in Chester County history (1894-Present) and coldest Q2 since 2003 (58.5). June Rainfall was 3.94" (0.10" below normal) our highest temperature was the 86.3 on the 10th. The lowest temperature was the 44.1 reading on the 1st of the month. As I write this on July 12th we are in the middle of warmer and wetter than normal month. We even recorded our 1st two 90-degree day’s although here in the relative high spots of East Nantmeal we needed to round it up to actually record a 90 so with the 89.6 on the 3rd and 89.8 on the 6th. . The last 90-degree reading was last July 21st when we reached 92.5 degrees - that was the 2nd and last 90 degree reading of the summer of 2019. Here in Chester County we average 11 days that exceed 90 degrees during the summer (1983 to Present). However, in 3 of the last 10 years have seen no days exceeded the 90-degree mark and 23 of the last 37 years have seen less than 10 days exceed 90 degrees during the summer. We have also just finished up a very wet 1st 12 days of the month with 3.98” of rain so far including 2.49” of rain on the 10th from Tropical Storm Fay. YTD rainfall now stands at 29.02” which is exactly 4.00” above normal through the 12th – great news for our Township farmers! Now, for those of you that dislike the summer heat… the good news is our hottest day on average is coming up on July 18th with an average high/low temperature of 83.6/64.1. Average temperatures begin to fall from that point right on through January 18th. So, enjoy the remaining days of summer and I look forward to speaking about our weather again in the fall. Stay safe and healthy! All the best - Paul   

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My NWS forecast has a forecast heat wave for Western Chester County. If this verifies it will be our 1st heat wave since July 1-3, 2018. We average a heat wave about every other year here in Chesco. Although, we have only had 2 heat waves in the last 8 years. Below are the last 10 heat waves.

July 1- 3, 2018 /July 5-7, 2012 / July 21-24, 2011 / July 4-7, 2010 / July 18-20, 2008 / June 7-10, 2008 / August 1-3, 2006 / August 12-14, 2005 / June 24-26, 2003 / August 1-5, 2002

Now we have a little battle between the WXSIM and the NWS forecast for my area with the WXSIM only getting us 1 "cheap" rounded 90 (which would be our 3rd cheap 90 this season) while the NWS gives us 4 straight 90+ days -  below are the forecast comparison - who will prevail?

Today - NWS 90 -  WXSIM 84.7 / Sunday - NWS 93 - WXSIM 89.4 / Monday NWS 94 - WXSIM 89.7 / Tuesday NWS 92 - WXSIM 86.4

 

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