ChescoWx

How does the ChescoWx East Nantmeal forecast stack up against the National Weather Service? After 7 weeks of scoring every forecast against what actually happened, the temperature results are pretty clear! Since August 22 we have verified 50 days and about 2,800 high and low temperature forecasts, each one matched up against the NWS forecast for the same day issued at the same time. ChescoWx was closer on temperatures on 45 of the 50 days. The NWS was closer on 4 and 1 was dead even. The typical ChescoWx miss was about 1.8 degrees. The typical NWS miss was about 3.0 degrees. For tomorrow's forecast the gap is widest... about 1 degree for ChescoWx vs about 2.5 degrees for the NWS. The edge holds out through day 6 and the two are basically even by day 7. About 8 in 10 ChescoWx forecasts landed within 3 degrees of the actual temperature vs about 6 in 10 for the NWS. Much of the NWS gap is a warm lean on daytime highs of about 3 degrees in our backyard. Rainfall is a different story. On the 10 days with measurable rain the NWS did a bit better, and both forecasts badly missed our two biggest rain events (1.66" on September 3 and 2.42" on October 11). Rain is where we are focused on improving next. Fair caveat... 50 days of late summer and early fall is a start, not a final verdict. We will keep scoring every forecast through the winter, and snow will be the real test! The live scorecard is on the Current Weather page here: https://chescowx.com/current-weather/ Let me know if any questions!

How does the ChescoWx East Nantmeal forecast stack up against the National Weather Service? After 7 weeks of scoring every forecast against what actually happened, the temperature results are pretty clear! Since August 22 we have verified 50 days and about 2,800 high and low temperature forecasts, each one matched up against the NWS forecast for the same day issued at the same time. ChescoWx was closer on temperatures on 45 of the 50 days. The NWS was closer on 4 and 1 was dead even. The typical ChescoWx miss was about 1.8 degrees. The typical NWS miss was about 3.0 degrees. For tomorrow's forecast the gap is widest... about 1 degree for ChescoWx vs about 2.5 degrees for the NWS. The edge holds out through day 6 and the two are basically even by day 7. About 8 in 10 ChescoWx forecasts landed within 3 degrees of the actual temperature vs about 6 in 10 for the NWS. Much of the NWS gap is a warm lean on daytime highs of about 3 degrees in our backyard. Rainfall is a different story. On the 10 days with measurable rain the NWS did a bit better, and both forecasts badly missed our two biggest rain events (1.66" on September 3 and 2.42" on October 11). Rain is where we are focused on improving next. Fair caveat... 50 days of late summer and early fall is a start, not a final verdict. We will keep scoring every forecast through the winter, and snow will be the real test! The live scorecard is on the Current Weather page here: https://chescowx.com/current-weather/ Let me know if any questions!

Not much rain this AM

Extended Ensemble outlook (not a forecast) shows a cooler trend than normal for last week of October and into the first couple weeks of November.

Extended Ensemble outlook (not a forecast) shows a cooler trend than normal for last week of October and into the first couple weeks of November.

Of note 141 years ago today back in 1885 Chester County was on the last day of a 3 day storm that left as much as 2.48" of rain at West Chester 2NW. This was the remnants of an unnamed tropical storm which tracked within about 100 miles of the county. Today we should see highs in the upper 70's to low 80's which is about 15 degrees above normal with lows tonight in the low to mid 50's. Temperatures will run 5 to 10 degrees above normal through Friday but by Saturday we drop to 4 to 8 degrees below normal, before we return to near normal by Tuesday. By Sunday morning lows will be in the low to mid 30's with a freeze possible in the colder valleys! Our best chance of rain is Friday with around 0.31" according to the ChescoWx model.

Of note 141 years ago today back in 1885 Chester County was on the last day of a 3 day storm that left as much as 2.48" of rain at West Chester 2NW. This was the remnants of an unnamed tropical storm which tracked within about 100 miles of the county. Today we should see highs in the upper 70's to low 80's which is about 15 degrees above normal with lows tonight in the low to mid 50's. Temperatures will run 5 to 10 degrees above normal through Friday but by Saturday we drop to 4 to 8 degrees below normal, before we return to near normal by Tuesday. By Sunday morning lows will be in the low to mid 30's with a freeze possible in the colder valleys! Our best chance of rain is Friday with around 0.31" according to the ChescoWx model.

Unseasonably warm weather continues for much of the rest of the work week before we turn unseasonably chilly for the weekend before we rebound to normal to above next week. A couple chances of a shower or two both Wednesday and Thursday night with the better shot on Thursday.

Unseasonably warm weather continues for much of the rest of the work week before we turn unseasonably chilly for the weekend before we rebound to normal to above next week. A couple chances of a shower or two both Wednesday and Thursday night with the better shot on Thursday.

After plenty of rain yesterday with between 1.5" to 3" falling we dry out and warm up through much of this week. Temperatures will run 5 to 10 degrees above normal through Wednesday but by next weekend we will drop to over 10 degrees below normal. In fact, by Saturday many ridge locations will struggle to escape the 40's with temperatures not far from freezing at night.

After plenty of rain yesterday with between 1.5" to 3" falling we dry out and warm up through much of this week. Temperatures will run 5 to 10 degrees above normal through Wednesday but by next weekend we will drop to over 10 degrees below normal. In fact, by Saturday many ridge locations will struggle to escape the 40's with temperatures not far from freezing at night.

Hello all. I have spent the last couple of months digging into one question and would welcome feedback and pushback. The question is not whether raw or adjusted data is more accurate. It is simpler than that... based on the data any of us can access, can we prove that NCEI's adjustments to our local temperature record are necessary, and sized correctly? What the adjustments do here Using every Chester County station, 1895 to 2025, the raw record warms about +0.05°F per decade, which is not statistically significant. NCEI's adjusted county series warms +0.25°F per decade. The gap between the two grows at about +0.2°F per decade and that gap is significant. Most of it comes from cooling the early decades, which NCEI runs 1.4 to 2.0°F below what the thermometers recorded. I also compared the three nearest long-record airports, all outside the county, against their own NCEI adjusted series: PHL (1941 to 2025): raw +0.44, adjusted +0.40. NCEI barely touches it. ABE (1948 to 2025): raw +0.31, adjusted +0.60. NCEI cools the early record by up to about 2.5°F, which roughly doubles Allentown's warming trend. RDG: NCEI only has an adjusted series from 2000 on, and it cuts Reading's trend from +1.36 to +0.77. Over the same 1948 to 2025 window, NCEI's adjustments add roughly +0.2 to +0.3°F per decade of warming both at Allentown (+0.29) and in Chester County (+0.17 against all county stations, +0.33 against our two longest continuous stations, West Chester 2NW and Phoenixville 1E). So Allentown and Chester County get about the same boost. PHL is the one that gets almost none. Against our most rural long-record stations, PHL warms roughly 0.2 to 0.3°F per decade faster since 1948. That looks like urban and airport growth that the adjusted PHL series keeps in, although the uncertainty range on it runs from about zero to +0.5. What we can prove Phoenixville shows a step of almost 2°F in 1987. Raw data has real artifacts in it. What we cannot prove We cannot show the adjustments are the right size, or that every one is needed. Coatesville 1SW is the clearest example. It had a documented move in January 1946 and NCEI lists a 1.4°F step for it, then lowers everything before 1946 to match. I compared Coatesville against every neighbor I could find with data on both sides of 1946... Phoenixville, Ephrata, Holtwood and Lancaster, all between 21 and 28 miles away. Each of those tracks Coatesville closely enough on its own to catch a step of about 0.4 to 0.7°F, roughly a third to a half of the size NCEI applies. Against those stations averaged together the step is only -0.25 to +0.07°F and not significant. So these neighbors were sensitive enough to see a step the size NCEI applies, and none of the ones without their own 1948 changes consistently show it. Phoenixville and Ephrata cooled right along with Coatesville. The only neighbors that show a bigger step are West Chester and Lancaster, and both of those had their own location changes in 1948. Coatesville also carries 12 NCEI breakpoints and only 4 are documented. West Chester carries 15 with 4 documented. NOAA's own station history for observation times conflicts with the reading-time schedules commonly assumed for these stations. To be fair, we also cannot show NCEI got it totally wrong. As NCEI compares against a much wider network of neighbors than we can see. So my conclusion: adjustments are necessary in principle, but from public data we can neither verify nor disprove their size here. What would close the gap NCEI's pairwise log for each station, showing which neighbors, which years and what weights were used for each break. I reached out to NCEI who told me this is not something they publish. The time-of-observation step on its own for each station, separate from the other adjustments. The original observer forms (B-91s) for the years where NOAA's records conflict or are blank. Dated site move and instrument change details, including the MMTS changes in the 1980s and ASOS at the airports in the 1990s. Overlapping readings at the old and new sites when a station moved. The Climate Reference Network only began in the 2000s, so it is too short to help with the early record. A re-run of NCEI's published code on the same inputs, to see whether we get the same breaks. Reading's adjusted series before 2000. Let me know if any questions or if you see anything that does not hold up!

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!