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West Chester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Chester clear sky chart from 2005-11-06 to 2024-01-15.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
32%
23272
20%
74637
10%
23224
44%
23224
22%
46920

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
16%
760
24%
2649
8%
757
37%
757
19%
1600
January11th to 20thNight
21%
740
21%
2516
7%
740
40%
740
16%
1632
January21st to endNight
17%
792
24%
2574
6%
792
39%
792
20%
1578
February1st to 10thNight
16%
720
17%
2340
5%
720
32%
720
17%
1523
February11th to 20thNight
10%
703
19%
2157
3%
700
31%
700
15%
1409
February21st to endNight
12%
592
25%
1776
7%
592
32%
592
18%
1161
March1st to 10thNight
20%
720
24%
2134
8%
720
39%
720
23%
1299
March11th to 20thNight
19%
720
21%
1980
7%
720
34%
720
21%
1321
March21st to endNight
19%
792
22%
2068
7%
792
32%
792
25%
1390
April1st to 10thNight
18%
720
19%
1800
3%
720
28%
720
22%
1233
April11th to 20thNight
26%
711
20%
1775
6%
711
33%
711
28%
1181
April21st to endNight
26%
720
19%
1800
4%
720
34%
720
25%
1230
May1st to 10thNight
28%
594
15%
1674
7%
594
34%
594
19%
1177
May11th to 20thNight
30%
354
19%
1416
11%
354
42%
354
16%
894
May21st to endNight
47%
388
15%
1551
14%
388
52%
388
20%
956
June1st to 10thNight
40%
360
18%
1440
16%
360
51%
360
21%
856
June11th to 20thNight
48%
360
15%
1440
14%
360
56%
360
22%
878
June21st to endNight
53%
360
17%
1440
18%
360
60%
360
26%
823
July1st to 10thNight
52%
350
14%
1400
16%
350
57%
350
20%
885
July11th to 20thNight
62%
348
17%
1392
20%
348
66%
348
26%
787
July21st to endNight
56%
467
18%
1555
15%
441
62%
441
27%
918
August1st to 10thNight
61%
537
17%
1600
12%
534
64%
534
29%
1011
August11th to 20thNight
55%
671
17%
1735
11%
671
56%
671
28%
1184
August21st to endNight
57%
792
17%
1980
9%
792
59%
792
33%
1301
September1st to 10thNight
47%
720
22%
1800
10%
720
53%
720
32%
1197
September11th to 20thNight
55%
720
30%
1813
19%
720
60%
720
39%
1129
September21st to endNight
43%
720
23%
2000
15%
720
51%
720
27%
1324
October1st to 10thNight
39%
720
17%
2160
12%
720
47%
720
25%
1407
October11th to 20thNight
39%
720
24%
2160
16%
720
50%
720
29%
1292
October21st to endNight
29%
792
26%
2415
13%
792
45%
792
27%
1476
November1st to 10thNight
33%
740
25%
2407
12%
740
51%
740
29%
1351
November11th to 20thNight
28%
760
25%
2470
12%
760
45%
760
22%
1512
November21st to endNight
27%
760
23%
2608
10%
760
44%
760
23%
1523
December1st to 10thNight
20%
760
19%
2660
6%
760
36%
760
17%
1708
December11th to 20thNight
21%
760
20%
3176
7%
759
38%
759
16%
1909
December21st to endNight
20%
829
14%
4776
7%
817
37%
817
11%
2865

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
15%6%25%5%35%5%5%7%41%
74747
Night
16%6%25%5%3445%7%43%
75033
TransparencyDay
41%6%12%23%16%3
74457
Night
41%5%12%23%17%3
74857
SeeingDay
20%16%28%21%11%3
13849
Night
19%13%31%26%10%1
23280

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
13%6%35%6%35%5%6%7%42%
1517
11th to 20thDay
14%7%36%7%35%5%46%40%
1546
21st to endDay
15%7%36%5%36%5%47%39%
1782
February1st to 10thDay
16%7%36%6%345%5%8%37%
1620
11th to 20thDay
17%6%36%6%4445%6%40%
1689
21st to endDay
19%10%36%5%34346%37%
1480
March1st to 10thDay
14%5%35%6%35%436%47%
1821
11th to 20thDay
17%6%35%5%36%45%7%39%
1980
21st to endDay
21%7%25%5%3435%6%39%
2286
April1st to 10thDay
14%7%46%5%25%5%47%42%
2160
11th to 20thDay
15%6%345%35%5%5%7%43%
2134
21st to endDay
17%6%25%5%45%5%5%7%39%
2160
May1st to 10thDay
18%7%35%6%35%5%5%6%37%
2301
11th to 20thDay
19%7%35%5%35%5%6%7%36%
2478
21st to endDay
14%7%25%5%35%5%5%9%41%
2725
June1st to 10thDay
13%5%35%5%36%5%7%10%38%
2520
11th to 20thDay
13%6%36%6%45%5%7%8%37%
2520
21st to endDay
11%425%5%35%6%6%10%42%
2520
July1st to 10thDay
10%5%25%5%47%7%7%10%39%
2520
11th to 20thDay
7%325%6%36%6%8%11%43%
2520
21st to endDay
9%5%46%8%46%6%7%9%36%
2668
August1st to 10thDay
10%6%25%6%5%6%7%7%8%39%
2327
11th to 20thDay
11%6%26%6%35%5%7%9%39%
2146
21st to endDay
12%6%246%35%5%6%9%41%
2376
September1st to 10thDay
16%5%35%5%35%5%5%7%43%
2160
11th to 20thDay
13%5%234345%47%51%
2147
21st to endDay
18%6%36%6%35%446%39%
1957
October1st to 10thDay
18%6%25%42445%7%42%
1800
11th to 20thDay
17%5%24423447%47%
1800
21st to endDay
19%6%25%42345%6%44%
1940
November1st to 10thDay
14%7%23423346%53%
1671
11th to 20thDay
16%5%1443446%6%47%
1710
21st to endDay
15%6%34425%36%6%46%
1568
December1st to 10thDay
18%7%35%5%35%447%39%
1520
11th to 20thDay
20%7%2442445%6%42%
1906
21st to endDay
17%6%26%6%46%6%6%6%36%
2772
January1st to 10thNight
15%6%25%434446%46%
2649
11th to 20thNight
19%7%244345%5%7%39%
2516
21st to endNight
14%7%35%5%35%45%6%44%
2574
February1st to 10thNight
17%9%35%435%446%39%
2340
11th to 20thNight
19%6%35%5%35%45%5%41%
2155
21st to endNight
18%8%25%5%24446%41%
1776
March1st to 10thNight
14%5%245%34447%47%
2124
11th to 20thNight
17%6%26%5%2444444%
1979
21st to endNight
17%8%26%5%24446%43%
2068
April1st to 10thNight
16%7%35%5%3446%6%41%
1800
11th to 20thNight
15%6%36%5%3445%7%43%
1775
21st to endNight
19%5%25%43435%8%42%
1800
May1st to 10thNight
19%7%36%6%35%5%5%6%35%
1674
11th to 20thNight
19%5%35%5%45%5%5%7%38%
1415
21st to endNight
15%6%36%43445%9%41%
1550
June1st to 10thNight
15%5%35%5%2435%8%43%
1440
11th to 20thNight
11%6%35%5%45%5%6%10%39%
1440
21st to endNight
10%5%25%436%6%8%11%42%
1440
July1st to 10thNight
10%6%36%6%37%5%7%9%38%
1440
11th to 20thNight
6%425%6%46%6%8%10%43%
1440
21st to endNight
10%5%345%25%6%8%10%42%
1647
August1st to 10thNight
9%6%25%5%36%6%7%9%42%
1611
11th to 20thNight
13%5%36%6%45%5%6%8%39%
1735
21st to endNight
13%425%5%35%5%6%7%44%
1980
September1st to 10thNight
15%7%25%5%2345%6%47%
1800
11th to 20thNight
13%5%23324446%53%
1813
21st to endNight
18%5%25%5%345%5%7%42%
2000
October1st to 10thNight
20%5%35%433446%43%
2160
11th to 20thNight
17%5%2433345%6%49%
2160
21st to endNight
18%7%24323346%48%
2415
November1st to 10thNight
11%6%2443345%6%53%
2407
11th to 20thNight
17%6%24423445%47%
2470
21st to endNight
13%5%245%345%6%7%46%
2608
December1st to 10thNight
19%7%25%4345%5%6%39%
2660
11th to 20thNight
18%5%25%43445%6%43%
3288
21st to endNight
17%7%35%5%35%5%6%7%38%
4884

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
41%414%22%15%4
1518
11th to 20thDay
44%7%12%22%13%3
1546
21st to endDay
44%5%9%24%15%3
1782
February1st to 10thDay
45%5%14%23%11%2
1620
11th to 20thDay
45%5%8%26%13%3
1698
21st to endDay
49%39%21%13%4
1480
March1st to 10thDay
40%411%28%15%3
1824
11th to 20thDay
44%5%10%21%15%4
1980
21st to endDay
48%47%20%18%3
2286
April1st to 10thDay
42%5%9%21%17%5%
2160
11th to 20thDay
40%6%10%23%16%5%
2134
21st to endDay
43%6%11%18%17%4
2160
May1st to 10thDay
47%6%9%19%16%4
2301
11th to 20thDay
47%6%11%20%14%2
2482
21st to endDay
41%7%14%23%14%2
2725
June1st to 10thDay
40%7%14%24%14%1
2520
11th to 20thDay
43%6%14%23%12%3
2520
21st to endDay
37%6%15%25%16%1
2520
July1st to 10thDay
39%8%12%23%14%3
2450
11th to 20thDay
32%8%15%28%15%3
2445
21st to endDay
42%8%11%21%17%2
2519
August1st to 10thDay
40%8%14%23%15%1
2314
11th to 20thDay
40%6%14%23%15%2
2146
21st to endDay
39%7%13%21%17%3
2376
September1st to 10thDay
41%5%11%20%20%3
2160
11th to 20thDay
34%5%9%25%23%4
2147
21st to endDay
46%5%8%18%21%2
1957
October1st to 10thDay
42%5%12%23%17%2
1800
11th to 20thDay
37%411%24%21%2
1800
21st to endDay
41%49%26%18%2
1940
November1st to 10thDay
34%413%26%20%4
1671
11th to 20thDay
37%5%10%24%21%2
1710
21st to endDay
38%411%33%12%2
1568
December1st to 10thDay
45%5%14%21%13%1
1520
11th to 20thDay
42%412%28%11%2
1906
21st to endDay
45%7%13%23%12%1
2772
January1st to 10thNight
41%310%25%17%4
2649
11th to 20thNight
45%5%13%22%12%2
2516
21st to endNight
40%410%26%17%3
2574
February1st to 10thNight
45%412%24%12%2
2340
11th to 20thNight
45%49%21%17%4
2157
21st to endNight
45%49%22%16%5%
1776
March1st to 10thNight
37%412%26%18%4
2134
11th to 20thNight
43%5%10%21%17%4
1980
21st to endNight
43%310%19%18%6%
2068
April1st to 10thNight
43%410%20%18%4
1800
11th to 20thNight
40%411%21%20%4
1775
21st to endNight
42%5%10%19%19%5%
1800
May1st to 10thNight
48%6%9%17%16%3
1674
11th to 20thNight
45%6%11%16%18%3
1416
21st to endNight
41%8%16%18%15%2
1551
June1st to 10thNight
40%6%11%22%20%2
1440
11th to 20thNight
39%7%15%23%14%1
1440
21st to endNight
33%9%14%27%15%2
1440
July1st to 10thNight
40%11%15%18%13%3
1400
11th to 20thNight
32%9%17%25%14%2
1392
21st to endNight
34%9%17%24%16%2
1555
August1st to 10thNight
36%9%16%24%15%1
1600
11th to 20thNight
41%7%14%20%17%2
1735
21st to endNight
37%6%15%21%17%3
1980
September1st to 10thNight
39%5%12%21%20%3
1800
11th to 20thNight
32%5%9%23%26%4
1813
21st to endNight
41%6%8%21%22%2
2000
October1st to 10thNight
43%412%23%16%2
2160
11th to 20thNight
35%412%29%17%3
2160
21st to endNight
39%310%27%19%2
2415
November1st to 10thNight
33%412%26%19%5%
2407
11th to 20thNight
40%49%22%20%5%
2470
21st to endNight
37%413%28%17%2
2608
December1st to 10thNight
46%412%23%15%1
2660
11th to 20thNight
41%5%12%22%17%4
3288
21st to endNight
45%5%15%24%11%1
4884

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
24%29%31%13%12
180
11th to 20thDay
22%41%27%9%2
200
21st to endDay
22%36%27%12%3
264
February1st to 10thDay
29%29%31%8%3
240
11th to 20thDay
30%23%38%8%1
357
21st to endDay
32%23%31%12%3
346
March1st to 10thDay
24%26%30%16%4
420
11th to 20thDay
24%29%30%14%22
420
21st to endDay
28%26%28%12%5%1
462
April1st to 10thDay
21%28%33%12%41
420
11th to 20thDay
23%22%30%16%8%2
412
21st to endDay
27%22%32%15%41
420
May1st to 10thDay
29%20%29%13%7%2
423
11th to 20thDay
21%16%33%21%7%2
447
21st to endDay
20%9%25%25%18%3
485
June1st to 10thDay
16%11%32%26%12%3
450
11th to 20thDay
15%11%31%28%12%3
450
21st to endDay
13%10%28%31%13%5%
450
July1st to 10thDay
15%421%30%23%7%
445
11th to 20thDay
8%323%36%25%5%
444
21st to endDay
13%7%24%34%18%5%
488
August1st to 10thDay
13%326%28%21%8%
446
11th to 20thDay
14%318%37%19%8%
439
21st to endDay
13%6%23%28%20%9%
495
September1st to 10thDay
19%11%19%26%16%9%
450
11th to 20thDay
16%6%27%27%15%10%
450
21st to endDay
24%13%20%27%13%4
450
October1st to 10thDay
24%8%26%22%13%6%
450
11th to 20thDay
17%16%30%23%13%2
450
21st to endDay
23%15%34%17%9%3
475
November1st to 10thDay
18%14%34%19%11%3
365
11th to 20thDay
19%20%34%21%6%
370
21st to endDay
19%23%35%17%5%1
228
December1st to 10thDay
25%29%29%11%6%
180
11th to 20thDay
32%26%27%11%4
180
21st to endDay
26%25%29%13%7%1
198
January1st to 10thNight
19%22%38%17%3
760
11th to 20thNight
25%17%32%23%3
740
21st to endNight
18%22%38%20%2
792
February1st to 10thNight
21%19%39%19%2
720
11th to 20thNight
24%25%36%13%1
703
21st to endNight
25%21%38%14%2
592
March1st to 10thNight
20%22%34%21%3
720
11th to 20thNight
23%20%35%17%5%1
720
21st to endNight
20%16%40%18%5%
792
April1st to 10thNight
22%20%37%17%4
720
11th to 20thNight
20%13%37%24%6%
711
21st to endNight
22%15%33%25%6%
720
May1st to 10thNight
25%11%31%26%7%
594
11th to 20thNight
19%9%37%29%6%
354
21st to endNight
18%5%22%39%15%1
389
June1st to 10thNight
18%428%36%12%1
360
11th to 20thNight
12%6%29%39%14%
360
21st to endNight
8%427%47%13%
360
July1st to 10thNight
13%323%39%21%2
350
11th to 20thNight
6%319%44%26%1
348
21st to endNight
11%421%41%21%2
467
August1st to 10thNight
11%317%44%22%3
537
11th to 20thNight
14%416%38%25%3
671
21st to endNight
14%318%40%23%2
792
September1st to 10thNight
17%5%22%35%18%2
720
11th to 20thNight
15%421%33%23%4
720
21st to endNight
20%5%25%31%17%1
720
October1st to 10thNight
23%7%25%26%15%4
720
11th to 20thNight
19%10%28%31%12%
720
21st to endNight
22%13%34%24%8%
792
November1st to 10thNight
16%11%36%26%11%1
740
11th to 20thNight
21%18%28%25%7%1
760
21st to endNight
17%17%34%24%7%1
760
December1st to 10thNight
25%17%34%17%6%1
760
11th to 20thNight
19%18%37%22%5%
760
21st to endNight
21%18%36%24%2
836
Page generated at 2024-01-12 16:17:47. Version ac07

Copyright 2024 Attilla Danko


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