WhistleStop Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the WhistleStop Observatory clear sky chart from 2005-11-06 to 2024-01-22.

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
34%
22794
14%
74918
9%
22752
41%
22752
18%
52146

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%
759
10%
2649
4%
757
23%
757
9%
2024
January11th to 20thNight
17%
760
7%
2615
3%
760
22%
760
8%
2119
January21st to endNight
22%
800
12%
2599
6%
800
30%
800
12%
1952
February1st to 10thNight
14%
720
8%
2340
3%
720
20%
720
10%
1821
February11th to 20thNight
19%
701
13%
2275
4%
700
29%
700
13%
1690
February21st to endNight
19%
592
14%
1846
4%
592
31%
592
16%
1315
March1st to 10thNight
25%
720
17%
2026
8%
720
33%
720
18%
1465
March11th to 20thNight
25%
720
16%
1979
7%
720
35%
720
20%
1403
March21st to endNight
33%
792
21%
2152
9%
792
42%
792
25%
1470
April1st to 10thNight
28%
720
17%
1800
5%
720
35%
720
24%
1304
April11th to 20thNight
32%
711
17%
1775
6%
711
36%
711
24%
1274
April21st to endNight
37%
568
16%
1648
8%
568
43%
568
22%
1141
May1st to 10thNight
42%
464
14%
1544
11%
464
47%
464
21%
1033
May11th to 20thNight
44%
354
22%
1416
19%
354
57%
354
23%
813
May21st to endNight
53%
388
17%
1551
19%
388
61%
388
26%
862
June1st to 10thNight
48%
360
13%
1440
13%
360
58%
360
21%
892
June11th to 20thNight
53%
360
16%
1440
22%
360
60%
360
26%
806
June21st to endNight
52%
360
13%
1440
18%
360
57%
360
22%
870
July1st to 10thNight
64%
350
17%
1400
24%
350
69%
350
31%
724
July11th to 20thNight
61%
348
18%
1392
26%
348
65%
348
27%
766
July21st to endNight
59%
448
17%
1537
18%
423
63%
423
31%
861
August1st to 10thNight
63%
537
17%
1600
15%
534
65%
534
33%
960
August11th to 20thNight
63%
534
20%
1598
15%
534
67%
534
33%
980
August21st to endNight
57%
729
20%
1917
11%
729
61%
729
35%
1212
September1st to 10thNight
54%
720
18%
1800
9%
720
57%
720
34%
1181
September11th to 20thNight
59%
720
27%
1808
16%
720
63%
720
38%
1135
September21st to endNight
49%
720
21%
2074
17%
720
53%
720
27%
1347
October1st to 10thNight
40%
720
16%
2160
13%
720
46%
720
22%
1478
October11th to 20thNight
32%
720
13%
2160
9%
720
39%
720
17%
1568
October21st to endNight
26%
792
14%
2384
8%
792
34%
792
15%
1758
November1st to 10thNight
36%
740
17%
2470
14%
740
43%
740
19%
1619
November11th to 20thNight
25%
760
15%
2660
9%
760
34%
760
15%
1825
November21st to endNight
23%
760
10%
2660
6%
760
29%
760
12%
1986
December1st to 10thNight
16%
760
8%
2660
3%
760
22%
760
9%
2111
December11th to 20thNight
17%
759
8%
3247
3%
759
24%
759
8%
2448
December21st to endNight
11%
828
5%
4856
1%
817
18%
817
4%
3933

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%8%36%6%35%5%6%7%36%
74766
Night
17%9%46%6%35%5%5%7%34%
75163
TransparencyDay
46%8%13%21%11%1
74475
Night
49%7%12%19%11%1
74988
SeeingDay
18%11%28%26%13%4
13376
Night
20%9%29%28%13%2
22807

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
16%14%5%10%7%45%5%5%7%22%
1517
11th to 20thDay
16%18%6%10%8%5%5%5%5%5%19%
1562
21st to endDay
12%13%6%10%10%5%7%6%5%6%21%
1791
February1st to 10thDay
13%14%5%12%8%5%6%5%6%5%20%
1620
11th to 20thDay
15%9%5%13%9%35%5%5%6%26%
1573
21st to endDay
20%11%5%8%6%45%447%25%
1409
March1st to 10thDay
14%9%48%7%5%5%5%6%6%29%
1927
11th to 20thDay
14%11%47%6%345%46%35%
1980
21st to endDay
19%9%36%5%33446%37%
2203
April1st to 10thDay
17%8%38%6%35%5%47%33%
2160
11th to 20thDay
19%6%36%5%34446%40%
2134
21st to endDay
19%7%37%6%35%5%6%6%35%
2326
May1st to 10thDay
14%7%47%6%35%5%6%7%37%
2416
11th to 20thDay
13%6%35%425%5%5%8%43%
2478
21st to endDay
11%5%246%35%5%7%8%44%
2725
June1st to 10thDay
16%5%25%5%346%6%9%38%
2520
11th to 20thDay
12%5%25%5%345%6%10%44%
2520
21st to endDay
13%5%25%5%345%6%8%44%
2520
July1st to 10thDay
7%424435%5%6%10%51%
2520
11th to 20thDay
10%4245%45%6%7%9%45%
2520
21st to endDay
8%425%5%35%6%8%10%43%
2686
August1st to 10thDay
8%5%25%5%36%6%7%9%46%
2327
11th to 20thDay
9%5%25%435%6%7%10%45%
2303
21st to endDay
10%5%245%246%6%10%45%
2420
September1st to 10thDay
12%6%245%345%6%8%46%
2160
11th to 20thDay
11%5%2443347%8%51%
2148
21st to endDay
13%6%35%5%45%6%5%7%43%
1886
October1st to 10thDay
17%8%37%6%45%5%47%35%
1800
11th to 20thDay
19%8%46%6%35%5%6%8%32%
1800
21st to endDay
25%10%37%5%4446%6%27%
1972
November1st to 10thDay
14%7%37%6%445%5%9%36%
1605
11th to 20thDay
15%11%47%7%45%6%6%8%29%
1520
21st to endDay
21%11%48%7%4445%7%26%
1520
December1st to 10thDay
18%15%6%8%8%36%6%46%20%
1520
11th to 20thDay
18%14%5%9%5%35%46%6%25%
1906
21st to endDay
29%15%49%6%45%5%35%16%
2772
January1st to 10thNight
19%14%5%9%8%44446%22%
2649
11th to 20thNight
19%15%6%9%8%46%5%5%5%18%
2615
21st to endNight
13%14%5%10%7%46%6%45%26%
2599
February1st to 10thNight
16%15%6%10%7%45%5%5%6%21%
2340
11th to 20thNight
15%12%7%7%7%45%5%5%6%27%
2273
21st to endNight
17%10%37%8%45%6%5%6%30%
1846
March1st to 10thNight
15%10%48%7%45%5%45%34%
2016
11th to 20thNight
17%10%46%6%3345%6%37%
1979
21st to endNight
17%7%37%5%34446%41%
2152
April1st to 10thNight
20%7%35%6%35%5%5%7%34%
1800
11th to 20thNight
17%7%35%7%3445%6%38%
1775
21st to endNight
19%8%26%4345%6%7%35%
1648
May1st to 10thNight
18%7%36%5%445%7%6%36%
1544
11th to 20thNight
13%5%25%5%46%5%47%44%
1415
21st to endNight
11%5%26%5%2445%8%47%
1550
June1st to 10thNight
13%6%35%7%35%5%6%8%39%
1440
11th to 20thNight
10%5%36%5%45%5%7%8%44%
1440
21st to endNight
12%6%26%6%3445%7%44%
1440
July1st to 10thNight
5%425%5%445%5%8%54%
1440
11th to 20thNight
9%5%245%45%5%6%9%47%
1440
21st to endNight
8%6%25%4245%6%9%48%
1628
August1st to 10thNight
8%425%5%345%6%9%48%
1611
11th to 20thNight
8%5%35%5%35%46%8%48%
1598
21st to endNight
10%5%16%425%5%5%8%48%
1917
September1st to 10thNight
12%5%25%6%345%5%9%45%
1800
11th to 20thNight
12%4245%2445%7%52%
1808
21st to endNight
16%5%26%5%34336%46%
2074
October1st to 10thNight
16%7%36%6%44447%37%
2160
11th to 20thNight
20%8%37%6%36%46%7%31%
2160
21st to endNight
22%8%36%5%35%6%6%6%29%
2384
November1st to 10thNight
19%7%345%35%5%5%6%38%
2470
11th to 20thNight
18%8%46%6%35%5%6%8%31%
2660
21st to endNight
22%10%46%6%45%6%5%7%26%
2660
December1st to 10thNight
20%14%48%7%5%5%5%5%6%20%
2660
11th to 20thNight
18%15%5%7%6%35%5%5%6%25%
3288
21st to endNight
31%15%47%5%345%5%6%16%
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
58%8%13%15%6%
1518
11th to 20thDay
65%8%10%9%8%
1562
21st to endDay
62%7%10%14%6%1
1791
February1st to 10thDay
62%9%11%14%31
1620
11th to 20thDay
59%6%10%14%10%1
1582
21st to endDay
59%6%10%16%8%
1409
March1st to 10thDay
52%7%16%15%10%1
1930
11th to 20thDay
51%6%10%20%12%2
1980
21st to endDay
50%5%7%19%15%4
2203
April1st to 10thDay
51%5%10%20%11%2
2160
11th to 20thDay
46%410%23%16%2
2134
21st to endDay
50%6%9%19%13%3
2326
May1st to 10thDay
46%7%11%19%15%3
2416
11th to 20thDay
39%8%10%25%16%2
2482
21st to endDay
37%8%16%23%14%2
2725
June1st to 10thDay
43%8%13%21%15%1
2520
11th to 20thDay
36%7%14%27%14%1
2520
21st to endDay
38%8%15%23%15%1
2520
July1st to 10thDay
29%9%13%31%17%2
2450
11th to 20thDay
34%9%15%31%11%
2445
21st to endDay
35%10%16%26%12%1
2536
August1st to 10thDay
33%10%17%26%12%1
2314
11th to 20thDay
33%10%17%27%13%
2303
21st to endDay
33%10%14%30%12%1
2420
September1st to 10thDay
36%8%14%29%12%1
2160
11th to 20thDay
31%7%15%32%15%1
2148
21st to endDay
40%8%14%28%9%
1886
October1st to 10thDay
48%8%13%20%11%1
1800
11th to 20thDay
51%8%14%19%7%1
1800
21st to endDay
57%7%13%14%8%1
1972
November1st to 10thDay
46%7%15%20%11%1
1605
11th to 20thDay
50%7%17%16%9%1
1520
21st to endDay
58%8%13%15%6%
1520
December1st to 10thDay
61%10%12%13%4
1520
11th to 20thDay
58%9%13%12%7%
1906
21st to endDay
67%9%11%10%4
2772
January1st to 10thNight
61%7%11%15%6%
2649
11th to 20thNight
65%8%10%10%5%1
2615
21st to endNight
58%6%11%15%9%1
2599
February1st to 10thNight
62%6%13%14%41
2340
11th to 20thNight
56%7%10%17%9%1
2275
21st to endNight
52%6%13%20%8%1
1846
March1st to 10thNight
51%5%11%19%11%2
2026
11th to 20thNight
48%6%10%22%12%1
1980
21st to endNight
45%5%9%21%16%4
2152
April1st to 10thNight
48%5%10%20%14%2
1800
11th to 20thNight
47%6%9%19%18%2
1775
21st to endNight
46%7%12%17%15%3
1648
May1st to 10thNight
46%6%10%18%17%3
1544
11th to 20thNight
37%6%11%25%17%4
1416
21st to endNight
34%6%14%23%18%4
1551
June1st to 10thNight
41%8%12%23%14%3
1440
11th to 20thNight
35%5%14%20%22%3
1440
21st to endNight
40%7%13%23%16%2
1440
July1st to 10thNight
27%8%12%26%25%2
1400
11th to 20thNight
33%7%12%29%18%1
1392
21st to endNight
32%6%14%31%14%2
1537
August1st to 10thNight
31%8%17%28%14%1
1600
11th to 20thNight
33%8%16%29%14%2
1598
21st to endNight
32%8%14%29%15%1
1917
September1st to 10thNight
36%7%15%26%14%2
1800
11th to 20thNight
32%6%13%31%17%1
1808
21st to endNight
41%5%11%29%13%1
2074
October1st to 10thNight
46%6%11%20%15%1
2160
11th to 20thNight
51%8%14%20%8%
2160
21st to endNight
53%7%14%14%11%1
2384
November1st to 10thNight
44%7%14%20%13%1
2470
11th to 20thNight
49%7%15%17%11%1
2660
21st to endNight
54%10%16%14%5%1
2660
December1st to 10thNight
61%10%13%12%4
2660
11th to 20thNight
58%8%13%14%6%1
3288
21st to endNight
68%8%11%9%3
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
23%18%33%17%7%2
180
11th to 20thDay
23%25%30%18%41
200
21st to endDay
20%22%30%22%41
267
February1st to 10thDay
25%26%35%11%2
240
11th to 20thDay
21%23%39%15%2
240
21st to endDay
31%22%32%13%2
275
March1st to 10thDay
20%16%38%20%5%
420
11th to 20thDay
23%16%32%24%41
420
21st to endDay
28%10%35%18%9%
462
April1st to 10thDay
20%15%34%22%8%1
420
11th to 20thDay
23%12%31%20%10%4
412
21st to endDay
23%10%35%22%8%2
420
May1st to 10thDay
23%8%28%27%10%5%
423
11th to 20thDay
16%7%27%32%13%5%
447
21st to endDay
13%425%32%21%5%
485
June1st to 10thDay
18%7%26%31%16%2
450
11th to 20thDay
11%6%27%33%19%4
450
21st to endDay
18%5%24%32%17%4
450
July1st to 10thDay
9%318%36%29%5%
445
11th to 20thDay
13%421%34%20%9%
444
21st to endDay
9%424%43%14%6%
488
August1st to 10thDay
9%421%34%24%9%
446
11th to 20thDay
11%418%33%26%8%
439
21st to endDay
11%6%22%35%19%8%
495
September1st to 10thDay
12%5%24%30%22%8%
450
11th to 20thDay
11%420%31%22%12%
450
21st to endDay
14%7%27%28%19%5%
450
October1st to 10thDay
21%11%27%18%18%5%
450
11th to 20thDay
21%12%32%25%9%1
450
21st to endDay
28%15%27%22%7%
491
November1st to 10thDay
22%17%25%24%10%1
299
11th to 20thDay
20%20%33%21%41
180
21st to endDay
23%17%33%19%7%1
180
December1st to 10thDay
24%19%29%19%8%
180
11th to 20thDay
26%27%31%13%31
180
21st to endDay
32%21%32%14%1
198
January1st to 10thNight
26%16%34%18%6%
760
11th to 20thNight
27%15%30%23%5%
760
21st to endNight
19%14%33%27%6%1
800
February1st to 10thNight
23%15%40%19%3
720
11th to 20thNight
22%14%38%22%4
703
21st to endNight
23%15%38%21%3
592
March1st to 10thNight
20%14%34%28%41
720
11th to 20thNight
22%13%34%25%5%1
720
21st to endNight
20%7%34%29%9%1
792
April1st to 10thNight
21%8%35%28%7%
720
11th to 20thNight
20%9%33%25%11%1
711
21st to endNight
20%8%28%30%13%1
568
May1st to 10thNight
21%324%32%16%3
464
11th to 20thNight
15%327%39%16%
354
21st to endNight
11%426%34%23%2
389
June1st to 10thNight
12%229%39%17%1
360
11th to 20thNight
10%423%38%23%2
360
21st to endNight
12%420%43%21%1
360
July1st to 10thNight
5%121%45%25%3
350
11th to 20thNight
12%218%39%27%3
348
21st to endNight
8%220%46%21%2
448
August1st to 10thNight
11%114%39%31%4
537
11th to 20thNight
8%317%35%32%5%
534
21st to endNight
11%419%37%28%2
729
September1st to 10thNight
14%321%33%25%4
720
11th to 20thNight
14%416%31%28%7%
720
21st to endNight
15%7%22%28%23%5%
720
October1st to 10thNight
19%6%28%24%20%3
720
11th to 20thNight
23%10%28%29%9%1
720
21st to endNight
25%11%31%27%6%
792
November1st to 10thNight
22%11%24%30%12%1
740
11th to 20thNight
21%15%31%24%6%1
760
21st to endNight
24%12%32%24%7%
760
December1st to 10thNight
27%17%33%18%4
760
11th to 20thNight
24%14%38%19%5%
760
21st to endNight
31%14%34%17%4
836
Page generated at 2024-01-19 09:28:35. Version ac07

Copyright 2024 Attilla Danko


WhistleStop Observatory Clear Sky Chart |Charts Home