ChescoWx

Hello all. Announcing something new on chescowx.com...ChescoWx Studies! This is an ongoing series looking at what makes Chester County's climate unique, this will include deep analysis of climate patterns and cycles, weather monitoring equipment and tools and past storm write ups and details. Each study takes one question, tests it against our station records and gives you the answer with the numbers behind it. I would welcome any feedback or pushback on the methods or the results. The series lives here and will grow as new studies are finished: https://chescowx.com/chescowx-studies/ Study 1 - Equipment & Siting. Three stations at my place in East Nantmeal. A ground-level fan-aspirated Davis, a rooftop Tempest and a ground-level Ambient with a passive shield. The Tempest highs ran about +3°F in July through September and +3.3°F on sunny, calm days, with 45 days of 90°F vs 8 for the Davis. To separate the roof from the shield, I looked at the Ambient. From 2021 to 2023 its summer highs matched the Davis within a few tenths while the Tempest was +2.8°F...so it is the roof, not the shield. Once the Ambient shield was damaged, though, it ran almost 7°F warm on sunny days. Location first, then upkeep. Study 2 - Elevation & Terrain. Most of our hilltop stations came along decades after the valley ones, and the weather varies from one decade to the next, so I compared them over the same years (2012 to 2025) using USGS 3DEP elevations. 19 stations with at least 8 complete years, by band: 100 to 300 ft (4 stations): high 64.4, low 43.6, 90 degree days 19, freezing nights 111, growing season 182 days 300 to 600 ft (8 stations): high 63.3, low 44.5, 90 degree days 11, freezing nights 101, growing season 192 days 600 ft and up (7 stations): high 62.3, low 45.3, 90 degree days 9, freezing nights 94, growing season 204 days Days follow elevation and nights follow terrain position. Highs drop about 1.7°F for every 300 ft, but lows track how far a station sits above its immediate surroundings, which is why they actually rise as you go up. For snow I used a same-storm comparison (521 storms, 60+ human-observed sites) so a snowy decade at one station does not skew it. Overall the hills get about 8% more snow for every 300 ft (29% per 1,000 ft), but the time of season matters a lot: Oct-Nov (24 storms) about 25% per 300 ft Dec-Jan (251 storms) about 6% Feb (151 storms) about 5% Mar-Apr (95 storms) about 18% March 2004 is a good example: East Nantmeal 11.0, Coatesville 2W 8.8 vs Exton 3.0, Chadds Ford 3.4, West Chester 2.2. There are always a few sites that do not fit, and the southern uplands around West Grove and New London run less than their elevation would suggest. The north also gets a bit more than the south, while the western part of the county gets more only because it is higher. Precipitation showed no elevation effect at all. Let me know if any questions, if you see anything that does not hold up, or if there is a question you would like to see tested next!

Hello all. Announcing something new on chescowx.com...ChescoWx Studies! This is an ongoing series looking at what makes Chester County's climate unique, this will include deep analysis of climate patterns and cycles, weather monitoring equipment and tools and past storm write ups and details. Each study takes one question, tests it against our station records and gives you the answer with the numbers behind it. I would welcome any feedback or pushback on the methods or the results. The series lives here and will grow as new studies are finished: https://chescowx.com/chescowx-studies/ Study 1 - Equipment & Siting. Three stations at my place in East Nantmeal. A ground-level fan-aspirated Davis, a rooftop Tempest and a ground-level Ambient with a passive shield. The Tempest highs ran about +3°F in July through September and +3.3°F on sunny, calm days, with 45 days of 90°F vs 8 for the Davis. To separate the roof from the shield, I looked at the Ambient. From 2021 to 2023 its summer highs matched the Davis within a few tenths while the Tempest was +2.8°F...so it is the roof, not the shield. Once the Ambient shield was damaged, though, it ran almost 7°F warm on sunny days. Location first, then upkeep. Study 2 - Elevation & Terrain. Most of our hilltop stations came along decades after the valley ones, and the weather varies from one decade to the next, so I compared them over the same years (2012 to 2025) using USGS 3DEP elevations. 19 stations with at least 8 complete years, by band: 100 to 300 ft (4 stations): high 64.4, low 43.6, 90 degree days 19, freezing nights 111, growing season 182 days 300 to 600 ft (8 stations): high 63.3, low 44.5, 90 degree days 11, freezing nights 101, growing season 192 days 600 ft and up (7 stations): high 62.3, low 45.3, 90 degree days 9, freezing nights 94, growing season 204 days Days follow elevation and nights follow terrain position. Highs drop about 1.7°F for every 300 ft, but lows track how far a station sits above its immediate surroundings, which is why they actually rise as you go up. For snow I used a same-storm comparison (521 storms, 60+ human-observed sites) so a snowy decade at one station does not skew it. Overall the hills get about 8% more snow for every 300 ft (29% per 1,000 ft), but the time of season matters a lot: Oct-Nov (24 storms) about 25% per 300 ft Dec-Jan (251 storms) about 6% Feb (151 storms) about 5% Mar-Apr (95 storms) about 18% March 2004 is a good example: East Nantmeal 11.0, Coatesville 2W 8.8 vs Exton 3.0, Chadds Ford 3.4, West Chester 2.2. There are always a few sites that do not fit, and the southern uplands around West Grove and New London run less than their elevation would suggest. The north also gets a bit more than the south, while the western part of the county gets more only because it is higher. Precipitation showed no elevation effect at all. Let me know if any questions, if you see anything that does not hold up, or if there is a question you would like to see tested next!

Hello all. Announcing something new on chescowx.com...ChescoWx Studies! This is an ongoing series looking at what makes Chester County's climate unique, this will include deep analysis of climate patterns and cycles, weather monitoring equipment and tools and past storm write ups and details. Each study takes one question, tests it against our station records and gives you the answer with the numbers behind it. I would welcome any feedback or pushback on the methods or the results. The series lives here and will grow as new studies are finished: https://chescowx.com/chescowx-studies/ Study 1 - Equipment & Siting. Three stations at my place in East Nantmeal. A ground-level fan-aspirated Davis, a rooftop Tempest and a ground-level Ambient with a passive shield. The Tempest highs ran about +3°F in July through September and +3.3°F on sunny, calm days, with 45 days of 90°F vs 8 for the Davis. To separate the roof from the shield, I looked at the Ambient. From 2021 to 2023 its summer highs matched the Davis within a few tenths while the Tempest was +2.8°F...so it is the roof, not the shield. Once the Ambient shield was damaged, though, it ran almost 7°F warm on sunny days. Location first, then upkeep. Study 2 - Elevation & Terrain. Most of our hilltop stations came along decades after the valley ones, and the weather varies from one decade to the next, so I compared them over the same years (2012 to 2025) using USGS 3DEP elevations. 19 stations with at least 8 complete years, by band: 100 to 300 ft (4 stations): high 64.4, low 43.6, 90 degree days 19, freezing nights 111, growing season 182 days 300 to 600 ft (8 stations): high 63.3, low 44.5, 90 degree days 11, freezing nights 101, growing season 192 days 600 ft and up (7 stations): high 62.3, low 45.3, 90 degree days 9, freezing nights 94, growing season 204 days Days follow elevation and nights follow terrain position. Highs drop about 1.7°F for every 300 ft, but lows track how far a station sits above its immediate surroundings, which is why they actually rise as you go up. For snow I used a same-storm comparison (521 storms, 60+ human-observed sites) so a snowy decade at one station does not skew it. Overall the hills get about 8% more snow for every 300 ft (29% per 1,000 ft), but the time of season matters a lot: Oct-Nov (24 storms) about 25% per 300 ft Dec-Jan (251 storms) about 6% Feb (151 storms) about 5% Mar-Apr (95 storms) about 18% March 2004 is a good example: East Nantmeal 11.0, Coatesville 2W 8.8 vs Exton 3.0, Chadds Ford 3.4, West Chester 2.2. There are always a few sites that do not fit, and the southern uplands around West Grove and New London run less than their elevation would suggest. The north also gets a bit more than the south, while the western part of the county gets more only because it is higher. Precipitation showed no elevation effect at all. Let me know if any questions, if you see anything that does not hold up, or if there is a question you would like to see tested next!

Of interest the NWS COOP site Phoenixville 1E recorded a low of 32 degrees on Tuesday morning the 6th this is the 20th earliest freeze since records began in 1890. Their average 1st freeze is October 23rd. We should see a beautiful fall day today with highs a few degrees above normal near 70. We turn a bit cooler for the weekend with rain holding off till later Sunday afternoon with the remnants of the Hurricane in the Gulf. We look to turn much chillier again by the middle of next week.

Of interest the NWS COOP site Phoenixville 1E recorded a low of 32 degrees on Tuesday morning the 6th this is the 20th earliest freeze since records began in 1890. Their average 1st freeze is October 23rd. We should see a beautiful fall day today with highs a few degrees above normal near 70. We turn a bit cooler for the weekend with rain holding off till later Sunday afternoon with the remnants of the Hurricane in the Gulf. We look to turn much chillier again by the middle of next week.

Our great stretch of autumnal weather continues through Saturday. Temperatures will stay below normal today before rising to near to slightly above normal tomorrow and Saturday. Rain chances ramp up with the tropical storm remnants by Sunday into Monday. We look to turn sharply cooler around the middle of the month.

Our great stretch of autumnal weather continues through Saturday. Temperatures will stay below normal today before rising to near to slightly above normal tomorrow and Saturday. Rain chances ramp up with the tropical storm remnants by Sunday into Monday. We look to turn sharply cooler around the middle of the month.

This morning was the coldest morning across the area since last spring. Below are the low temperatures and the date we were last this chilly.

This morning was the coldest morning across the area since last spring. Below are the low temperatures and the date we were last this chilly.

The GFS ensemble thinks a below normal temperature month for October is underway...

My ChescoWx forecast has beaten the NWS point and click in 36 of the last 40 days!

My ChescoWx forecast has beaten the NWS point and click in 36 of the last 40 days!

Some light rain and below normal temperatures today before we clear out for most of the rest of the week. We start the week with below normal temperatures with some lower valley locations likely to see some 30's for the first time this year by Tuesday or Wednesday morning. We start a slow warming trend through the week before we turn a bit cooler by next weekend.

Some light rain and below normal temperatures today before we clear out for most of the rest of the week. We start the week with below normal temperatures with some lower valley locations likely to see some 30's for the first time this year by Tuesday or Wednesday morning. We start a slow warming trend through the week before we turn a bit cooler by next weekend.