Greeley Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greeley Hill Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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
68%
23716
29%
80123
27%
23629
72%
23629
40%
41969

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
52%
749
18%
4347
17%
736
57%
736
17%
2369
January11th to 20thNight
60%
753
18%
4158
23%
740
65%
740
17%
2651
January21st to endNight
56%
830
16%
4401
25%
814
62%
814
16%
2849
February1st to 10thNight
54%
760
25%
2442
23%
760
60%
760
31%
1440
February11th to 20thNight
59%
718
30%
2151
29%
718
65%
718
37%
1216
February21st to endNight
52%
592
23%
1776
22%
592
57%
592
31%
1093
March1st to 10thNight
49%
720
17%
2160
15%
720
54%
720
26%
1402
March11th to 20thNight
53%
720
22%
1980
18%
720
58%
720
33%
1236
March21st to endNight
55%
792
19%
2052
13%
792
59%
792
37%
1283
April1st to 10thNight
56%
720
24%
1800
13%
720
60%
720
40%
1105
April11th to 20thNight
54%
711
28%
1779
13%
711
60%
711
46%
1036
April21st to endNight
63%
720
28%
1800
14%
720
67%
720
51%
1004
May1st to 10thNight
64%
683
29%
1763
17%
683
68%
683
56%
903
May11th to 20thNight
68%
440
35%
1502
31%
440
72%
440
55%
641
May21st to endNight
71%
389
30%
1552
31%
388
78%
388
48%
627
June1st to 10thNight
76%
360
31%
1440
36%
360
80%
360
51%
556
June11th to 20thNight
81%
360
40%
1440
44%
360
91%
360
77%
429
June21st to endNight
85%
360
38%
1440
46%
360
90%
360
70%
462
July1st to 10thNight
93%
350
40%
1400
50%
350
95%
350
83%
403
July11th to 20thNight
90%
348
40%
1392
50%
348
91%
348
68%
451
July21st to endNight
86%
551
39%
1637
36%
521
87%
521
65%
682
August1st to 10thNight
87%
587
39%
1652
30%
584
89%
584
76%
690
August11th to 20thNight
87%
712
38%
1780
23%
712
88%
712
78%
818
August21st to endNight
92%
792
44%
1980
29%
792
93%
792
84%
876
September1st to 10thNight
90%
720
46%
1800
33%
720
92%
720
85%
789
September11th to 20thNight
86%
720
46%
1818
37%
720
88%
720
77%
837
September21st to endNight
83%
720
44%
1980
39%
720
88%
720
73%
862
October1st to 10thNight
79%
720
34%
2134
35%
720
84%
720
59%
985
October11th to 20thNight
78%
720
39%
2160
40%
720
82%
720
60%
960
October21st to endNight
76%
792
43%
2376
42%
792
83%
792
65%
1030
November1st to 10thNight
70%
740
31%
2396
34%
740
73%
740
44%
1202
November11th to 20thNight
67%
760
31%
2470
29%
760
74%
760
45%
1221
November21st to endNight
64%
760
31%
2472
29%
760
70%
760
40%
1299
December1st to 10thNight
58%
760
24%
2660
23%
760
63%
760
31%
1481
December11th to 20thNight
54%
760
20%
3222
23%
759
58%
759
20%
2115
December21st to endNight
48%
827
14%
4811
21%
817
55%
817
14%
2966

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
9%423323345%63%
78443
Night
11%413323345%60%
80645
TransparencyDay
24%49%18%24%22%
78157
Night
26%5%10%19%22%18%
80453
SeeingDay
10%9%27%34%16%4
14189
Night
11%214%39%28%6%
23753

By Month

Percentage Cloud Cover SW (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
18%8%24423435%45%
2539
11th to 20thDay
19%6%37%7%5%5%35%6%35%
2746
21st to endDay
20%8%36%5%345%6%7%34%
3146
February1st to 10thDay
19%7%24313445%49%
1735
11th to 20thDay
15%6%23324447%50%
1791
21st to endDay
20%7%33424336%45%
1480
March1st to 10thDay
18%11%345%345%5%8%35%
1800
11th to 20thDay
18%7%35%4335%5%7%40%
1975
21st to endDay
16%6%24425%36%7%46%
2303
April1st to 10thDay
14%5%243335%46%52%
2160
11th to 20thDay
13%424324347%55%
2129
21st to endDay
10%423312346%61%
2160
May1st to 10thDay
6%42332335%6%64%
2196
11th to 20thDay
6%213323346%67%
2387
21st to endDay
8%313324445%62%
2723
June1st to 10thDay
4313222346%70%
2520
11th to 20thDay
111221122483%
2520
21st to endDay
221111213284%
2520
July1st to 10thDay
1111213387%
2520
11th to 20thDay
111111233383%
2520
21st to endDay
11221233381%
2580
August1st to 10thDay
22111122285%
2275
11th to 20thDay
1111123486%
2122
21st to endDay
11111222387%
2376
September1st to 10thDay
21111112288%
2160
11th to 20thDay
311211233480%
2140
21st to endDay
221211222481%
1980
October1st to 10thDay
5%31221233473%
1822
11th to 20thDay
5%211313345%72%
1800
21st to endDay
7%212312345%70%
1980
November1st to 10thDay
9%423424446%56%
1680
11th to 20thDay
10%31341345%5%61%
1710
21st to endDay
11%5%2333335%7%55%
1706
December1st to 10thDay
16%5%14333336%53%
1520
11th to 20thDay
26%8%36%5%23346%35%
1928
21st to endDay
14%7%36%5%45%5%5%8%38%
2794
January1st to 10thNight
16%8%25%42335%6%46%
4406
11th to 20thNight
21%8%25%43445%7%36%
4203
21st to endNight
21%7%25%5%345%5%6%37%
4521
February1st to 10thNight
17%6%24323335%50%
2442
11th to 20thNight
15%5%2432335%7%53%
2151
21st to endNight
18%8%24323335%49%
1776
March1st to 10thNight
20%8%14423345%44%
2160
11th to 20thNight
18%6%14434447%45%
1980
21st to endNight
17%6%23313346%51%
2052
April1st to 10thNight
14%42332435%7%54%
1800
11th to 20thNight
11%423323345%61%
1779
21st to endNight
8%323323436%64%
1800
May1st to 10thNight
7%312213346%68%
1763
11th to 20thNight
6%212212338%70%
1502
21st to endNight
6%213313345%69%
1552
June1st to 10thNight
5%311322346%72%
1440
11th to 20thNight
111133485%
1440
21st to endNight
12111212385%
1440
July1st to 10thNight
111212290%
1440
11th to 20thNight
211221212383%
1440
21st to endNight
311222234476%
1733
August1st to 10thNight
221211123383%
1661
11th to 20thNight
111221223481%
1780
21st to endNight
11121222387%
1980
September1st to 10thNight
1111121290%
1800
11th to 20thNight
31122123383%
1818
21st to endNight
22221223481%
1980
October1st to 10thNight
421232223473%
2134
11th to 20thNight
5%211222245%75%
2160
21st to endNight
6%212212235%76%
2376
November1st to 10thNight
11%423212246%62%
2396
11th to 20thNight
9%31322345%6%60%
2470
21st to endNight
12%323324336%59%
2472
December1st to 10thNight
16%423323445%53%
2660
11th to 20thNight
24%7%35%42445%6%37%
3276
21st to endNight
16%6%36%6%46%5%5%6%37%
4862

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
39%6%17%22%12%2
2539
11th to 20thDay
48%8%11%13%12%7%
2746
21st to endDay
46%8%14%18%11%3
3146
February1st to 10thDay
38%49%26%16%8%
1735
11th to 20thDay
33%411%22%24%6%
1801
21st to endDay
40%5%9%23%20%2
1480
March1st to 10thDay
44%7%11%19%17%3
1800
11th to 20thDay
40%6%10%22%17%4
1975
21st to endDay
35%7%18%22%15%3
2303
April1st to 10thDay
33%5%13%23%19%8%
2160
11th to 20thDay
29%5%11%27%20%7%
2132
21st to endDay
24%5%11%29%28%4
2160
May1st to 10thDay
20%411%25%31%9%
2196
11th to 20thDay
19%48%25%32%12%
2390
21st to endDay
21%6%11%28%27%8%
2724
June1st to 10thDay
15%5%9%21%32%17%
2520
11th to 20thDay
8%26%18%35%30%
2520
21st to endDay
8%139%31%48%
2520
July1st to 10thDay
5%127%23%62%
2451
11th to 20thDay
8%239%24%55%
2445
21st to endDay
9%248%24%53%
2437
August1st to 10thDay
8%139%25%53%
2259
11th to 20thDay
5%229%30%52%
2122
21st to endDay
6%128%35%49%
2376
September1st to 10thDay
6%137%26%56%
2160
11th to 20thDay
9%3420%38%27%
2140
21st to endDay
10%1317%38%30%
1980
October1st to 10thDay
16%36%17%27%30%
1822
11th to 20thDay
15%37%20%25%30%
1800
21st to endDay
17%37%20%31%23%
1980
November1st to 10thDay
27%6%9%22%22%14%
1680
11th to 20thDay
25%411%22%27%10%
1710
21st to endDay
29%411%19%25%13%
1706
December1st to 10thDay
34%5%12%21%18%11%
1520
11th to 20thDay
53%48%15%14%7%
1928
21st to endDay
40%9%15%23%9%4
2794
January1st to 10thNight
36%8%16%25%12%2
4406
11th to 20thNight
46%7%13%16%11%7%
4203
21st to endNight
45%8%11%20%13%4
4521
February1st to 10thNight
36%49%21%19%9%
2442
11th to 20thNight
30%5%10%26%22%7%
2152
21st to endNight
38%411%24%19%4
1776
March1st to 10thNight
41%6%12%18%19%4
2160
11th to 20thNight
37%412%21%19%6%
1980
21st to endNight
33%6%16%24%16%5%
2052
April1st to 10thNight
30%5%16%22%20%7%
1800
11th to 20thNight
25%5%13%27%22%8%
1779
21st to endNight
21%6%13%31%25%5%
1800
May1st to 10thNight
16%5%12%25%33%10%
1763
11th to 20thNight
15%310%28%32%11%
1502
21st to endNight
16%411%32%29%8%
1552
June1st to 10thNight
15%413%20%31%17%
1440
11th to 20thNight
5%27%21%36%29%
1440
21st to endNight
7%339%31%47%
1440
July1st to 10thNight
4126%27%61%
1400
11th to 20thNight
9%138%21%57%
1392
21st to endNight
12%248%20%54%
1637
August1st to 10thNight
9%1311%24%52%
1652
11th to 20thNight
8%2310%28%49%
1780
21st to endNight
6%128%31%52%
1980
September1st to 10thNight
5%126%27%58%
1800
11th to 20thNight
8%25%17%40%28%
1818
21st to endNight
10%2316%40%30%
1980
October1st to 10thNight
15%37%17%28%30%
2134
11th to 20thNight
13%46%18%28%30%
2160
21st to endNight
13%25%23%32%25%
2376
November1st to 10thNight
24%49%23%22%19%
2396
11th to 20thNight
23%410%25%25%13%
2470
21st to endNight
28%48%21%29%10%
2472
December1st to 10thNight
33%5%9%22%18%12%
2660
11th to 20thNight
47%5%11%15%17%6%
3276
21st to endNight
42%10%15%19%9%5%
4862

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
32%8%23%25%12%1
180
11th to 20thDay
19%7%23%32%13%6%
308
21st to endDay
20%7%20%31%18%3
407
February1st to 10thDay
25%10%21%25%15%3
383
11th to 20thDay
19%10%28%29%12%1
432
21st to endDay
20%14%29%27%10%1
346
March1st to 10thDay
24%14%29%25%7%1
420
11th to 20thDay
23%15%26%20%13%2
420
21st to endDay
22%13%33%24%9%
462
April1st to 10thDay
19%18%30%22%10%1
420
11th to 20thDay
18%18%30%26%7%1
412
21st to endDay
10%16%32%27%13%3
420
May1st to 10thDay
10%18%34%26%10%3
423
11th to 20thDay
10%15%31%29%11%3
448
21st to endDay
11%13%25%34%13%4
485
June1st to 10thDay
413%30%35%12%6%
450
11th to 20thDay
313%32%36%10%5%
450
21st to endDay
38%30%35%18%6%
450
July1st to 10thDay
227%48%16%7%
446
11th to 20thDay
120%51%18%9%
444
21st to endDay
1122%49%18%9%
487
August1st to 10thDay
35%25%44%15%7%
447
11th to 20thDay
1327%44%17%8%
437
21st to endDay
1224%48%18%7%
495
September1st to 10thDay
2424%46%19%5%
450
11th to 20thDay
39%32%34%21%1
450
21st to endDay
37%26%43%19%2
450
October1st to 10thDay
411%28%34%21%3
450
11th to 20thDay
7%7%25%34%23%4
450
21st to endDay
7%7%25%35%22%4
495
November1st to 10thDay
9%8%24%27%28%5%
276
11th to 20thDay
10%5%24%32%24%6%
270
21st to endDay
11%425%31%24%4
268
December1st to 10thDay
17%6%25%29%18%6%
180
11th to 20thDay
21%7%21%28%19%4
180
21st to endDay
22%8%24%25%17%4
198
January1st to 10thNight
22%217%31%20%8%
760
11th to 20thNight
15%416%39%21%5%
760
21st to endNight
20%215%36%21%6%
836
February1st to 10thNight
20%217%37%20%4
760
11th to 20thNight
16%416%34%22%7%
722
21st to endNight
20%5%17%40%15%3
592
March1st to 10thNight
21%418%35%18%3
720
11th to 20thNight
18%5%17%30%22%7%
720
21st to endNight
17%419%38%21%1
792
April1st to 10thNight
14%419%39%22%2
720
11th to 20thNight
11%6%23%35%20%5%
711
21st to endNight
7%419%41%24%4
720
May1st to 10thNight
8%420%40%23%5%
683
11th to 20thNight
6%318%42%28%2
440
21st to endNight
6%216%41%34%2
389
June1st to 10thNight
6%212%42%34%3
360
11th to 20thNight
1115%42%39%2
360
21st to endNight
111%43%42%3
360
July1st to 10thNight
1447%45%3
350
11th to 20thNight
2345%45%5%
348
21st to endNight
25%32%52%9%
551
August1st to 10thNight
216%41%41%9%
587
11th to 20thNight
7%45%42%6%
712
21st to endNight
2341%47%7%
792
September1st to 10thNight
116%41%43%8%
720
11th to 20thNight
219%43%38%8%
720
21st to endNight
3110%39%39%8%
720
October1st to 10thNight
5%111%46%32%6%
720
11th to 20thNight
6%211%41%32%9%
720
21st to endNight
6%114%35%29%15%
792
November1st to 10thNight
13%210%36%29%10%
740
11th to 20thNight
11%216%39%26%7%
760
21st to endNight
13%116%39%24%7%
760
December1st to 10thNight
18%313%41%18%6%
760
11th to 20thNight
23%214%37%20%4
760
21st to endNight
21%419%35%17%3
836
Page generated at 2024-02-12 03:35:34. Version ac07

Copyright 2024 Attilla Danko


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