Growing (Freeze Free) Season in Chester County PA

[chescowx]

Looking at the models both the EURO and GFS have Chester County reaching 34 next Friday morning. If that were to come to pass that would be 181 days since our last sub-freezing temperature back on April 21st. One of our many local farmers in the Township emailed me to ask if I knew or could calculate what was the length of the growing (freeze free) season in East Nantmeal. I surmised that with our modest increase in elevation we should expect less sub freezing readings than the lower valley locales due to less impact from radiational cooling on clear and calm nights. 

For perspective the latest sub freezing temperature was the 32 degree reading way back on May 28, 1927 and the earliest first freeze observed was on September 20, 1956. That growing season of 1956 was the shortest growing season in the county with the last freeze on May 24th resulting in a season of just 119 days. By contrast back in 2005 we had our longest growing season of 233 days. Which is almost 4 more months freeze free weather.

The COOP data from 1894 to 1983 was observed at 340 feet above sea level (ASL) down in the Chester Valley; while readings from 1984 to Present have been observed at over 660 feet ASL on the north ridge of the valley that runs from SW to NE across the middle of Chester County. The number of average below freezing days was 127 at the lower elevations and has decreased to only 115 on average at the higher locales.  At the lower elevations the growing season averaged 172 days. At the higher elevations it has averaged 188 days.

Of interest for the 89 years from 1894 to 1983 there were only 2 seasons that exceeded 200 growing days (1912 and 1938) since 1984 there have been 13 such seasons...including 11 of the past 14 years and the last 4 years 2014-17. 

[White_Mtn_Wx]

15 minutes ago, chescopawxman said:

Looking at the models both the EURO and GFS have Chester County reaching 34 next Friday morning. If that were to come to pass that would be 181 days since our last sub-freezing temperature back on April 21st. One of our many local farmers in the Township emailed me to ask if I knew or could calculate what was the length of the growing (freeze free) season in East Nantmeal. I surmised that with our modest increase in elevation we should expect less sub freezing readings than the lower valley locales due to less impact from radiational cooling on clear and calm nights. 

For perspective the latest sub freezing temperature was the 32 degree reading way back on May 28, 1927 and the earliest first freeze observed was on September 20, 1956. That growing season of 1956 was the shortest growing season in the county with the last freeze on May 24th resulting in a season of just 119 days. By contrast back in 2005 we had our longest growing season of 233 days. Which is almost 4 more months freeze free weather.

The COOP data from 1894 to 1983 was observed at 340 feet above sea level (ASL) down in the Chester Valley; while readings from 1984 to Present have been observed at over 660 feet ASL on the north ridge of the valley that runs from SW to NE across the middle of Chester County. The number of average below freezing days was 127 at the lower elevations and has decreased to only 115 on average at the higher locales.  At the lower elevations the growing season averaged 172 days. At the higher elevations it has averaged 188 days.

Of interest for the 89 years from 1894 to 1983 there were only 2 seasons that exceeded 200 growing days (1912 and 1938) since 1984 there have been 13 such seasons...including 11 of the past 14 years and the last 4 years 2014-17. 

Fascinating info Paul. Thanks for sharing.

[susqushawn]

Nice share, thank you.  Intriguing for me as I note similar microclimate temperature differences at my location 600' up by Valley Forge Park.  Driving from King of Prussia on the highway, for instance, on a good radiational cooling night, the temperature will often drop 5-7° in the midst of low lying Valley Forge Park, where I'llnote more frosty mornings, then bump pack up 2-3° once I get to my house.   

Opposite is true in typical daytime conditions, we are 2° cooler than the "valley" year round, a portion likely attributable to the abundant woodlands that the homes here are set in.

[Gpd105]

@susqushawn  Have you seen examples where your higher elevation has seen more snow than surrounding lower elevations?

[tombo82685]

1 hour ago, Gpd105 said:

@susqushawn  Have you seen examples where your higher elevation has seen more snow than surrounding lower elevations?

I have countless time at work

[Parsley]

October 29, 2011 was probably the clearest elevation dependant snow event I’ve seen around here. Every 100 feet made a difference. 

https://www.weather.gov/phi/10292011wss

[chescowx]

2 hours ago, Parsley said:

October 29, 2011 was probably the clearest elevation dependant snow event I’ve seen around here. Every 100 feet made difference. 

https://www.weather.gov/phi/10292011wss

Yep - 9" at my place to nada in Sea Isle City NJ with not even one flake of snow - not sure what PHL ended up with...

[Parsley]

46 minutes ago, chescopawxman said:

Yep - 9" at my place to nada in Sea Isle City NJ with not even one flake of snow - not sure what PHL ended up with...

PHL was a few tenths I think. Just in a few mile stretch in my town that goes from spots around 100’ on the Perkiomen Creek to 400’ in the higher “hills” there was a range of from a slushy 1” to as much as 4-5 inches. Pretty cool to witness. 

[tombo82685]

3 hours ago, Parsley said:

PHL was a few tenths I think. Just in a few mile stretch in my town that goes from spots around 100’ on the Perkiomen Creek to 400’ in the higher “hills” there was a range of from a slushy 1” to as much as 4-5 inches. Pretty cool to witness. 

Looks like out my way was 6- 8" per the maps I'm seeing

[colonel_kurtz]

7 hours ago, Parsley said:

October 29, 2011 was probably the clearest elevation dependant snow event I’ve seen around here. Every 100 feet made difference. 

https://www.weather.gov/phi/10292011wss

3" Feasterville / Langhorne Bucks - 200' - 250', unfortunately that was the high water mark off the season

Other elevation storms

Mar-Apr 1997 - less than 4" at 30' in Bristol Twp, 8 miles west & 245' at my old place in Lower Southampton Twp 10"

Feb 1987 - 6.5" at PHL, 19" at 300' in Churchville Bucks

[Parsley]

1 hour ago, tombo82685 said:

Looks like out my way was 6- 8" per the maps I'm seeing

Yeah, that day I drove from my place up to just southeast of Gilbertsville on Swamp Pike and some places were definitely close to 6" at 400-500 feet. Crazy event followed by an AWFUL winter. 

[tombo82685]

32 minutes ago, Parsley said:

Yeah, that day I drove from my place up to just southeast of Gilbertsville on Swamp Pike and some places were definitely close to 6" at 400-500 feet. Crazy event followed by an AWFUL winter. 

yea like 2 miles past waltz's turf farm on swamp pike it jumps to 500'

[Parsley]

3 minutes ago, tombo82685 said:

yea like 2 miles past waltz's turf farm on swamp pike it jumps to 500'

Yup, I'm looking at some homes up in Fagleysville area off Swamp Pike (near Bella Vista Golf Course). If the right home hits the market early next year I could be your new, nearby neighbor. 

[Gpd105]

Does anyone have a good topographic map of the area they can share with me?  I'm always interested in knowing what the elevations are in the surrounding counties of Philadelphia and where the low and high points are.  

[Parsley]

19 minutes ago, Gpd105 said:

Does anyone have a good topographic map of the area they can share with me?  I'm always interested in knowing what the elevations are in the surrounding counties of Philadelphia and where the low and high points are.  

 

 

[susqushawn]

21 hours ago, tombo82685 said:

I have countless time at work

Tom documents it well, his golf course is 500' close by.  I see a particular difference in marginal late season events, and ice storms.

For topo maps:

- Google maps, choose the Terrain map type/filter, can only zoom in so far 

- https://www.topozone.com/pennsylvania/ Excellent detail and ability to zoom.  You can purchase specific topo maps, well if you're as nerdy as I am you can.  Below is a screenshot from that site of Tom's course as an example

 

[tombo82685]

13 hours ago, Parsley said:

Yup, I'm looking at some homes up in Fagleysville area off Swamp Pike (near Bella Vista Golf Course). If the right home hits the market early next year I could be your new, nearby neighbor. 

Yea that’s like 3 or 4 miles from me. We can hit up all stars for some brewskis 

[Chubbs]

1 hour ago, susqushawn said:

Tom documents it well, his golf course is 500' close by.  I see a particular difference in marginal late season events, and ice storms.

Same here, hilltops around here have more snow in marginal events, particularly in late spring. One other elevation effect: the valleys retain snow longer due to cold air pooling at night and shading. Our back yard in a little creek valley often has a lingering snow/ice pack when the hilltops are bare.

[chescowx]

Looking at data...while folks find it hard to believe that a few hundred feet can make a difference regarding the lack of 90+ days above 650 ft ASL....it is equally as clear that above 650ft you have many less freezing days....if you are a winter enthusiast...what do you want less freezing days or more snow? Certainly at higher elevations like mine you can average seasonal snowfall that is the same as Chicago IL...but you should also expect less freezing days etc......what do you want??

[tombo82685]

1 hour ago, chescopawxman said:

Looking at data...while folks find it hard to believe that a few hundred feet can make a difference regarding the lack of 90+ days above 650 ft ASL....it is equally as clear that above 650ft you have many less freezing days....if you are a winter enthusiast...what do you want less freezing days or more snow? Certainly at higher elevations like mine you can average seasonal snowfall that is the same as Chicago IL...but you should also expect less freezing days etc......what do you want??

Your 650’ is not why you have less 90 days it’s because of your area all the trees and lack of asphalt around. 

[Chubbs]

8 minutes ago, tombo82685 said:

Your 650’ is not why you have less 90 days it’s because of your area all the trees and lack of asphalt around. 

Yes. I am at 300' and semi-wooded and don't top 90 that frequently either. Elevation is only one of the differences between Coatesville and East Nantmeal. Below is Lukens Steel, Coatesville  around 1900. At the time the largest steel mill in the US.

[Gpd105]

I would think elevation alone at 650' would account for 2-3 degrees less than near sea level at philly airport.  Probably another couple degrees for your secluded location.  So I think it's fair to say its a combination of your elevation and location for less 90 degree days. 

[tombo82685]

10 hours ago, Gpd105 said:

I would think elevation alone at 650' would account for 2-3 degrees less than near sea level at philly airport.  Probably another couple degrees for your secluded location.  So I think it's fair to say its a combination of your elevation and location for less 90 degree days. 

It helps I’m not denying that, but the main reason is because of his micro climate with trees. Altoona PA elev at 1400 ‘ had over 10 90 days this summer. Scranton has more 90 days than him. Binghamton has 1 less than him. Places in Vt had more 90 days than him with higher elev. so saying elev is the reason why isn’t true imo. It’s because of his micro climate. 650’ is not that high. That should maybe shave 2-3 degrees off his high. If that’s the case he should of had way more 90 days then the 4 he had. Paul is 160' higher than wayne, he had 15 days less of 90 degree days than here. 160 ft  would not make a huge difference at all, it's his local surroundings.

[tombo82685]

9 hours ago, Chubbs said:

Yes. I am at 300' and semi-wooded and don't top 90 that frequently either. Elevation is only one of the differences between Coatesville and East Nantmeal. Below is Lukens Steel, Coatesville  around 1900. At the time the largest steel mill in the US.

Exactly!!

[chescowx]

15 hours ago, tombo82685 said:

Your 650’ is not why you have less 90 days it’s because of your area all the trees and lack of asphalt around. 

No doubt it is a combination of factors that allow the "microclimate" observed at both here and KMQS in Coatesville (also in a pretty wooded spot) to struggle to get to 90+ days