York County Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the York County Star Party clear sky chart from 2005-11-05 to 2017-09-17.

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
38%
15126
20%
46885
11%
15086
47%
15086
25%
29683

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 15thNight
24%
718
18%
2461
9%
716
37%
716
18%
1593
January16th to endNight
20%
768
21%
2496
7%
768
38%
768
21%
1576
February1st to 15thNight
21%
704
18%
2287
6%
701
36%
701
19%
1456
February16th to endNight
18%
631
22%
1925
6%
631
37%
631
20%
1240
March1st to 15thNight
24%
720
20%
2020
8%
720
36%
720
24%
1348
March16th to endNight
24%
768
21%
2079
9%
768
34%
768
25%
1373
April1st to 15thNight
25%
718
18%
1796
6%
718
32%
718
26%
1232
April16th to endNight
38%
720
18%
1800
6%
720
43%
720
31%
1205
May1st to 15thNight
39%
505
17%
1585
10%
505
46%
505
23%
1056
May16th to endNight
50%
374
17%
1497
15%
374
57%
374
21%
892
June1st to 15thNight
53%
360
17%
1440
18%
360
61%
360
24%
825
June16th to endNight
56%
360
17%
1440
19%
360
62%
360
27%
810
July1st to 15thNight
55%
340
13%
1360
15%
340
58%
340
19%
846
July16th to endNight
70%
497
17%
1529
15%
465
73%
465
33%
874
August1st to 15thNight
66%
539
20%
1609
16%
536
67%
536
34%
978
August16th to endNight
66%
747
22%
1893
13%
747
67%
747
37%
1198
September1st to 15thNight
55%
720
25%
1800
13%
720
59%
720
36%
1157
September16th to endNight
56%
665
23%
1828
19%
665
59%
665
30%
1196
October1st to 15thNight
45%
660
23%
1980
19%
660
52%
660
27%
1254
October16th to endNight
35%
704
26%
2112
13%
704
50%
704
30%
1271
November1st to 15thNight
38%
700
23%
2250
15%
700
50%
700
27%
1363
November16th to endNight
30%
720
20%
2490
12%
720
43%
720
21%
1525
December1st to 15thNight
25%
720
15%
2520
6%
720
37%
720
17%
1683
December16th to endNight
21%
768
18%
2688
4%
768
38%
768
19%
1732

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
14%5%25%5%3445%7%39%
47889
Night
14%5%25%42445%7%42%
47066
Cloud CoverDay
14%5%25%5%35%45%7%39%
47899
Night
14%5%25%42445%7%42%
47070
TransparencyDay
42%5%12%22%14%2
47588
Night
40%412%23%15%2
46885
SeeingDay
18%8%23%24%17%7%
5637
Night
17%8%29%30%12%1
15129

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 15thDay
15%6%26%5%25%5%6%6%36%
1475
16th to endDay
13%8%46%5%35%446%36%
1728
February1st to 15thDay
15%7%35%6%26%5%45%36%
1575
16th to endDay
15%6%37%5%33445%38%
1548
March1st to 15thDay
15%6%25%5%35%446%40%
1927
16th to endDay
17%7%35%434347%37%
2145
April1st to 15thDay
16%7%35%5%24446%39%
2152
16th to endDay
18%5%24324436%43%
2160
May1st to 15thDay
18%5%35%5%3445%7%35%
2376
16th to endDay
16%5%25%6%25%5%5%7%36%
2618
June1st to 15thDay
13%5%24435%5%6%10%38%
2520
16th to endDay
11%4145%35%5%6%11%40%
2520
July1st to 15thDay
9%5%25%6%46%6%6%9%38%
2520
16th to endDay
7%425%6%46%7%6%10%37%
2531
August1st to 15thDay
11%5%15%5%36%6%7%9%36%
2340
16th to endDay
13%4145%345%5%8%43%
2297
September1st to 15thDay
15%42442445%6%45%
2160
16th to endDay
16%5%24424447%43%
1836
October1st to 15thDay
18%424433248%43%
1650
16th to endDay
15%6%245%2345%6%41%
1760
November1st to 15thDay
15%6%23323447%46%
1606
16th to endDay
19%6%35%5%24445%39%
1469
December1st to 15thDay
17%8%35%5%35%45%6%34%
1440
16th to endDay
17%7%25%6%34448%34%
1536
January1st to 15thNight
16%7%36%43445%7%36%
2461
16th to endNight
15%7%35%42435%8%39%
2496
February1st to 15thNight
15%7%345%2345%7%39%
2285
16th to endNight
13%6%36%5%345%46%41%
1925
March1st to 15thNight
16%6%25%5%3435%5%41%
2008
16th to endNight
17%6%2442435%6%41%
2079
April1st to 15thNight
15%6%35%4345%5%7%37%
1796
16th to endNight
17%42442445%7%44%
1800
May1st to 15thNight
18%6%25%424447%39%
1585
16th to endNight
12%5%35%5%25%448%41%
1495
June1st to 15thNight
13%324325%46%7%45%
1440
16th to endNight
10%3145%25%5%6%10%44%
1440
July1st to 15thNight
9%435%6%35%6%5%9%40%
1440
16th to endNight
7%324335%5%6%11%45%
1635
August1st to 15thNight
8%425%5%25%5%6%8%45%
1620
16th to endNight
10%4235%35%447%48%
1893
September1st to 15thNight
12%42443335%7%47%
1800
16th to endNight
15%5%24434446%44%
1828
October1st to 15thNight
19%5%23414335%45%
1980
16th to endNight
16%423424448%45%
2112
November1st to 15thNight
12%6%25%423345%48%
2250
16th to endNight
16%5%23435%45%7%40%
2490
December1st to 15thNight
18%6%36%5%345%5%6%35%
2520
16th to endNight
16%6%35%425%45%8%36%
2688

Percentage Cloud Cover SE (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 15thDay
15%6%35%5%25%5%5%6%37%
1475
16th to endDay
13%8%46%5%35%446%37%
1728
February1st to 15thDay
14%8%25%7%25%6%5%5%36%
1575
16th to endDay
15%6%27%6%2445%439%
1548
March1st to 15thDay
14%6%25%5%36%447%40%
1938
16th to endDay
17%6%35%5%34347%37%
2144
April1st to 15thDay
16%6%25%5%34446%39%
2152
16th to endDay
18%5%25%323446%43%
2160
May1st to 15thDay
18%5%26%435%45%8%35%
2376
16th to endDay
16%5%25%5%25%45%7%37%
2618
June1st to 15thDay
13%424435%5%7%10%38%
2520
16th to endDay
10%4235%35%5%6%10%41%
2520
July1st to 15thDay
9%426%6%36%5%7%9%38%
2520
16th to endDay
8%4247%36%7%6%10%38%
2531
August1st to 15thDay
11%5%25%5%35%6%7%8%37%
2340
16th to endDay
12%4245%3445%7%44%
2297
September1st to 15thDay
15%42432436%6%45%
2160
16th to endDay
16%5%34424347%43%
1836
October1st to 15thDay
18%424323347%44%
1650
16th to endDay
15%6%3442445%6%42%
1760
November1st to 15thDay
15%5%3421335%7%46%
1606
16th to endDay
18%6%36%42345%5%39%
1469
December1st to 15thDay
17%7%26%5%4445%6%35%
1440
16th to endDay
17%6%346%345%47%36%
1536
January1st to 15thNight
16%6%35%5%345%5%7%36%
2461
16th to endNight
15%7%35%424348%40%
2496
February1st to 15thNight
15%7%25%5%3345%7%40%
2278
16th to endNight
13%6%45%5%345%46%41%
1925
March1st to 15thNight
15%6%25%435%35%6%41%
2020
16th to endNight
16%6%245%2335%6%42%
2079
April1st to 15thNight
15%6%36%4245%5%7%37%
1796
16th to endNight
17%5%14314447%44%
1800
May1st to 15thNight
19%5%25%4235%46%38%
1584
16th to endNight
12%5%26%43445%8%42%
1495
June1st to 15thNight
12%3244246%5%7%45%
1440
16th to endNight
10%314425%47%10%44%
1440
July1st to 15thNight
9%425%5%36%5%6%9%40%
1440
16th to endNight
7%414435%5%5%11%45%
1635
August1st to 15thNight
8%5%25%43447%8%45%
1620
16th to endNight
10%424434447%49%
1893
September1st to 15thNight
12%5%24433346%48%
1800
16th to endNight
15%4245%34345%45%
1828
October1st to 15thNight
18%6%24423345%45%
1980
16th to endNight
16%423323447%46%
2112
November1st to 15thNight
12%7%25%42334448%
2250
16th to endNight
16%5%24435%45%8%40%
2490
December1st to 15thNight
17%6%36%6%345%5%5%35%
2520
16th to endNight
16%6%25%435%45%8%37%
2688

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 15thDay
45%314%22%11%2
1476
16th to endDay
46%314%22%10%2
1728
February1st to 15thDay
47%5%12%22%10%2
1577
16th to endDay
46%312%24%10%1
1548
March1st to 15thDay
44%314%23%12%1
1938
16th to endDay
46%411%20%15%2
2145
April1st to 15thDay
45%410%20%15%3
2152
16th to endDay
41%47%22%18%5%
2160
May1st to 15thDay
46%5%10%21%14%1
2376
16th to endDay
44%6%13%20%12%1
2622
June1st to 15thDay
39%6%14%24%14%
2520
16th to endDay
37%6%15%24%14%1
2520
July1st to 15thDay
39%7%12%20%16%2
2371
16th to endDay
36%8%14%23%14%1
2374
August1st to 15thDay
39%8%13%21%14%1
2327
16th to endDay
36%6%10%26%16%2
2297
September1st to 15thDay
37%5%11%21%20%3
2160
16th to endDay
41%47%20%22%2
1836
October1st to 15thDay
39%312%25%15%2
1650
16th to endDay
41%311%27%15%
1760
November1st to 15thDay
36%5%13%22%17%5%
1606
16th to endDay
46%39%27%12%1
1469
December1st to 15thDay
47%417%19%9%
1440
16th to endDay
47%414%22%9%
1536
January1st to 15thNight
45%413%20%11%3
2461
16th to endNight
43%313%27%11%1
2496
February1st to 15thNight
43%314%23%12%1
2287
16th to endNight
42%410%24%16%1
1925
March1st to 15thNight
43%411%25%13%1
2020
16th to endNight
42%411%22%16%2
2079
April1st to 15thNight
43%411%21%16%3
1796
16th to endNight
39%5%11%19%18%5%
1800
May1st to 15thNight
45%5%10%20%15%2
1585
16th to endNight
39%6%15%20%14%3
1497
June1st to 15thNight
35%7%13%25%17%
1440
16th to endNight
33%7%14%25%17%1
1440
July1st to 15thNight
40%9%11%21%13%3
1360
16th to endNight
30%7%18%23%17%2
1529
August1st to 15thNight
34%5%14%25%18%1
1609
16th to endNight
34%5%12%25%20%3
1893
September1st to 15thNight
35%411%21%24%2
1800
16th to endNight
40%47%22%21%3
1828
October1st to 15thNight
41%49%25%17%1
1980
16th to endNight
36%39%31%17%1
2112
November1st to 15thNight
39%39%24%16%6%
2250
16th to endNight
41%311%25%15%2
2490
December1st to 15thNight
48%413%21%10%
2520
16th to endNight
44%5%16%22%9%
2688

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 15thDay
22%32%32%7%21
67
16th to endDay
25%21%31%18%3
96
February1st to 15thDay
22%30%36%11%
90
16th to endDay
21%18%39%18%1
207
March1st to 15thDay
18%15%31%27%6%
270
16th to endDay
22%13%36%18%7%2
288
April1st to 15thDay
21%13%31%18%12%2
270
16th to endDay
22%7%25%21%16%7%
270
May1st to 15thDay
25%13%24%17%12%5%
288
16th to endDay
21%317%28%20%8%
331
June1st to 15thDay
16%7%22%23%22%7%
315
16th to endDay
13%7%23%32%16%6%
315
July1st to 15thDay
14%319%28%24%9%
305
16th to endDay
9%113%32%27%15%
326
August1st to 15thDay
15%211%28%28%13%
313
16th to endDay
10%29%28%29%18%
332
September1st to 15thDay
17%416%20%25%15%
315
16th to endDay
20%315%28%15%16%
259
October1st to 15thDay
21%5%14%28%23%6%
255
16th to endDay
16%9%32%28%12%1
272
November1st to 15thDay
20%7%25%24%20%1
240
16th to endDay
21%15%30%16%13%2
89
December1st to 15thDay
15%28%28%11%11%5%
60
16th to endDay
29%12%37%17%3
64
January1st to 15thNight
19%14%36%25%3
720
16th to endNight
19%13%42%22%1
768
February1st to 15thNight
20%15%35%27%1
704
16th to endNight
17%18%41%19%2
631
March1st to 15thNight
20%12%38%24%4
720
16th to endNight
20%11%37%23%7%
768
April1st to 15thNight
19%13%38%23%5%
718
16th to endNight
18%6%30%31%11%
720
May1st to 15thNight
20%5%28%32%12%
505
16th to endNight
15%322%40%17%1
375
June1st to 15thNight
14%24%37%21%
360
16th to endNight
10%122%48%16%
360
July1st to 15thNight
13%216%43%22%1
340
16th to endNight
9%111%47%28%1
497
August1st to 15thNight
11%112%45%27%2
539
16th to endNight
12%110%39%31%3
747
September1st to 15thNight
14%219%34%27%1
720
16th to endNight
16%315%29%30%4
665
October1st to 15thNight
21%423%28%19%2
660
16th to endNight
19%8%34%29%8%
704
November1st to 15thNight
16%7%32%29%11%1
700
16th to endNight
19%14%31%25%9%
720
December1st to 15thNight
21%10%35%24%6%
720
16th to endNight
19%12%39%25%2
768
Page generated at 2017-09-18 08:38:22. Version ac04

Copyright 2017 A. Danko


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