Great Falls Observatory Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Falls Observatory Park clear sky chart from 2005-11-06 to 2024-03-23.

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%
23725
14%
80371
7%
23628
45%
23628
12%
58896

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
18%
754
19%
4237
4%
737
33%
737
7%
2657
January11th to 20thNight
24%
758
21%
3955
5%
740
34%
740
8%
2509
January21st to endNight
20%
830
11%
4449
5%
814
33%
814
7%
3019
February1st to 10thNight
24%
760
15%
2470
5%
760
36%
760
12%
1826
February11th to 20thNight
14%
740
12%
2358
2%
740
27%
740
10%
1784
February21st to endNight
18%
628
16%
1884
4%
628
33%
628
11%
1440
March1st to 10thNight
22%
760
17%
2119
5%
760
34%
760
16%
1536
March11th to 20thNight
23%
760
15%
2090
6%
760
32%
760
13%
1585
March21st to endNight
22%
801
14%
2173
5%
801
30%
801
13%
1696
April1st to 10thNight
23%
720
12%
1800
2%
720
29%
720
13%
1415
April11th to 20thNight
33%
711
16%
1775
6%
711
38%
711
17%
1360
April21st to endNight
35%
720
15%
1800
5%
720
39%
720
17%
1396
May1st to 10thNight
38%
589
13%
1669
6%
589
43%
589
13%
1306
May11th to 20thNight
42%
427
13%
1488
9%
427
47%
427
11%
1151
May21st to endNight
56%
388
11%
1551
11%
388
59%
388
12%
1129
June1st to 10thNight
55%
360
14%
1440
15%
360
59%
360
13%
1019
June11th to 20thNight
51%
360
12%
1440
12%
360
58%
360
12%
1065
June21st to endNight
58%
360
12%
1440
13%
360
63%
360
13%
1028
July1st to 10thNight
60%
350
10%
1400
13%
350
62%
350
11%
1047
July11th to 20thNight
69%
428
10%
1472
10%
428
70%
428
14%
1101
July21st to endNight
66%
591
11%
1672
8%
558
69%
558
17%
1222
August1st to 10thNight
63%
537
11%
1600
8%
534
65%
534
15%
1243
August11th to 20thNight
62%
603
12%
1667
7%
603
63%
603
14%
1317
August21st to endNight
64%
792
9%
1980
6%
792
65%
792
16%
1599
September1st to 10thNight
55%
720
16%
1800
8%
720
58%
720
18%
1401
September11th to 20thNight
62%
720
21%
1800
15%
720
65%
720
21%
1360
September21st to endNight
45%
720
12%
2064
8%
720
49%
720
14%
1606
October1st to 10thNight
48%
720
14%
2160
11%
720
52%
720
16%
1623
October11th to 20thNight
41%
720
17%
2160
12%
720
49%
720
15%
1605
October21st to endNight
36%
792
17%
2376
10%
792
44%
792
15%
1787
November1st to 10thNight
39%
740
18%
2309
11%
740
49%
740
16%
1662
November11th to 20thNight
33%
760
16%
2493
9%
760
43%
760
13%
1867
November21st to endNight
34%
760
13%
2660
8%
760
42%
760
11%
1982
December1st to 10thNight
26%
760
14%
2660
5%
760
38%
760
10%
1999
December11th to 20thNight
26%
760
15%
3166
6%
759
36%
759
9%
2267
December21st to endNight
29%
826
9%
4794
4%
817
39%
817
6%
3287

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%6%25%5%35%5%6%8%42%
78753
Night
15%6%25%5%345%5%7%44%
81119
TransparencyDay
27%36%8%16%11%2
78463
Night
27%35%8%16%11%2
80928
SeeingDay
19%10%26%25%15%6%
14080
Night
18%10%29%30%13%1
23753

By Month

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 10thDay
18%4235%2345%6%46%
2595
11th to 20thDay
15%10%46%5%44445%40%
2840
21st to endDay
18%8%37%6%34445%37%
3124
February1st to 10thDay
14%6%27%6%445%6%7%39%
1710
11th to 20thDay
18%7%35%5%245%6%6%40%
1708
21st to endDay
18%8%36%5%34345%40%
1570
March1st to 10thDay
15%5%3443445%7%47%
2060
11th to 20thDay
16%7%35%5%35%446%42%
2090
21st to endDay
17%6%36%5%35%46%6%38%
2226
April1st to 10thDay
12%7%35%435%45%8%44%
2160
11th to 20thDay
14%5%25%5%2445%7%46%
2134
21st to endDay
19%6%25%43445%7%41%
2160
May1st to 10thDay
15%7%346%45%5%6%8%38%
2307
11th to 20thDay
19%6%35%435%5%6%8%35%
2401
21st to endDay
14%5%25%5%346%6%8%41%
2725
June1st to 10thDay
11%5%26%435%6%6%9%44%
2520
11th to 20thDay
11%5%36%5%36%5%6%10%40%
2520
21st to endDay
9%4245%36%6%7%11%44%
2520
July1st to 10thDay
9%425%6%46%5%6%10%42%
2520
11th to 20thDay
6%4245%46%7%8%10%44%
2436
21st to endDay
10%5%25%5%47%6%7%10%37%
2547
August1st to 10thDay
10%5%26%6%5%6%7%7%9%37%
2327
11th to 20thDay
12%5%36%5%46%7%7%8%39%
2215
21st to endDay
11%436%5%346%7%10%42%
2376
September1st to 10thDay
14%5%25%5%435%5%8%44%
2160
11th to 20thDay
13%5%2442445%8%48%
2160
21st to endDay
19%6%36%4346%48%39%
1891
October1st to 10thDay
18%6%24424447%46%
1800
11th to 20thDay
19%42432345%6%48%
1800
21st to endDay
14%5%25%4345%46%48%
1980
November1st to 10thDay
12%5%23424447%51%
1767
11th to 20thDay
16%42332446%5%50%
1682
21st to endDay
16%6%234245%5%5%48%
1520
December1st to 10thDay
15%6%35%5%35%6%5%7%40%
1520
11th to 20thDay
16%6%25%43445%7%45%
1910
21st to endDay
17%7%26%5%345%6%8%35%
2772
January1st to 10thNight
15%7%25%43445%7%45%
4333
11th to 20thNight
18%7%24433346%45%
4120
21st to endNight
20%9%35%423346%41%
4532
February1st to 10thNight
15%6%36%5%35%5%5%6%41%
2470
11th to 20thNight
19%7%25%433445%43%
2356
21st to endNight
18%7%35%43345%6%42%
1884
March1st to 10thNight
15%4344345%5%6%48%
2119
11th to 20thNight
16%6%25%42346%8%43%
2090
21st to endNight
15%6%36%5%3445%6%41%
2173
April1st to 10thNight
15%6%35%5%35%5%5%6%41%
1800
11th to 20thNight
14%425%5%245%5%6%46%
1775
21st to endNight
17%5%24435%5%5%7%43%
1800
May1st to 10thNight
16%6%25%5%25%5%5%9%39%
1669
11th to 20thNight
18%6%345%35%5%6%7%38%
1488
21st to endNight
13%425%5%35%5%7%10%41%
1550
June1st to 10thNight
11%4245%36%6%6%9%46%
1440
11th to 20thNight
12%5%26%5%35%6%6%9%41%
1440
21st to endNight
8%5%26%5%35%6%7%10%43%
1440
July1st to 10thNight
9%5%26%7%46%6%6%9%40%
1440
11th to 20thNight
6%436%5%36%6%7%11%45%
1520
21st to endNight
8%5%25%5%35%6%8%12%41%
1771
August1st to 10thNight
8%5%27%7%47%7%7%9%39%
1611
11th to 20thNight
11%5%26%6%46%6%6%9%40%
1667
21st to endNight
10%5%25%445%6%6%9%44%
1980
September1st to 10thNight
15%6%25%5%345%5%7%45%
1800
11th to 20thNight
10%5%345%34447%51%
1800
21st to endNight
17%7%36%5%3345%7%41%
2064
October1st to 10thNight
20%5%2443345%6%45%
2160
11th to 20thNight
16%4245%33346%51%
2160
21st to endNight
15%5%25%42445%6%48%
2376
November1st to 10thNight
12%5%25%423335%54%
2309
11th to 20thNight
14%6%2432435%6%50%
2493
21st to endNight
14%4244345%5%7%48%
2660
December1st to 10thNight
17%7%36%5%345%5%6%41%
2660
11th to 20thNight
17%5%25%5%345%47%43%
3285
21st to endNight
17%6%25%5%35%6%6%8%37%
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
28%26%6%28%11%2
2596
11th to 20thDay
37%26%7%15%11%4
2840
21st to endDay
41%23%10%18%9%1
3124
February1st to 10thDay
28%35%7%19%10%1
1710
11th to 20thDay
28%35%7%17%11%2
1717
21st to endDay
31%34%9%13%10%3
1570
March1st to 10thDay
24%35%8%19%13%1
2060
11th to 20thDay
28%35%7%13%13%4
2090
21st to endDay
32%37%6%14%9%2
2226
April1st to 10thDay
24%37%9%14%12%4
2160
11th to 20thDay
25%36%6%14%14%5%
2134
21st to endDay
28%37%6%15%11%3
2160
May1st to 10thDay
26%38%9%14%11%2
2307
11th to 20thDay
30%39%8%11%10%2
2405
21st to endDay
26%39%9%17%9%1
2725
June1st to 10thDay
22%39%11%17%11%1
2520
11th to 20thDay
26%39%9%16%8%2
2520
21st to endDay
22%39%10%17%10%2
2520
July1st to 10thDay
25%39%10%13%10%2
2450
11th to 20thDay
22%39%10%18%10%2
2361
21st to endDay
25%42%9%12%10%1
2405
August1st to 10thDay
28%38%10%16%8%
2314
11th to 20thDay
28%38%8%12%12%1
2215
21st to endDay
27%39%10%14%8%3
2376
September1st to 10thDay
25%37%7%12%15%4
2160
11th to 20thDay
21%37%6%18%14%3
2160
21st to endDay
29%37%7%11%15%1
1891
October1st to 10thDay
25%36%6%16%14%2
1800
11th to 20thDay
26%36%7%17%13%1
1800
21st to endDay
26%37%417%14%1
1980
November1st to 10thDay
18%40%6%20%13%2
1767
11th to 20thDay
23%40%8%14%12%3
1682
21st to endDay
25%40%7%16%11%1
1520
December1st to 10thDay
26%40%9%17%8%1
1520
11th to 20thDay
27%33%6%23%8%2
1906
21st to endDay
34%28%12%19%7%
2772
January1st to 10thNight
30%25%8%23%12%1
4333
11th to 20thNight
30%25%8%19%15%3
4120
21st to endNight
37%23%8%22%10%1
4532
February1st to 10thNight
27%35%7%18%12%1
2470
11th to 20thNight
30%35%7%16%10%3
2358
21st to endNight
30%34%7%15%11%3
1884
March1st to 10thNight
23%34%8%20%12%2
2119
11th to 20thNight
27%35%8%15%12%3
2090
21st to endNight
28%36%7%15%9%4
2173
April1st to 10thNight
28%37%7%12%13%4
1800
11th to 20thNight
25%36%7%13%15%5%
1775
21st to endNight
24%39%8%16%9%4
1800
May1st to 10thNight
27%39%8%14%9%3
1669
11th to 20thNight
29%39%7%12%11%2
1489
21st to endNight
23%40%13%13%10%1
1551
June1st to 10thNight
22%39%9%18%11%2
1440
11th to 20thNight
26%38%9%15%10%2
1440
21st to endNight
24%37%10%15%12%2
1440
July1st to 10thNight
26%40%11%13%7%3
1400
11th to 20thNight
21%43%10%14%10%2
1472
21st to endNight
19%41%12%17%10%1
1672
August1st to 10thNight
27%39%10%16%9%
1600
11th to 20thNight
29%38%7%15%8%2
1667
21st to endNight
28%39%10%13%7%3
1980
September1st to 10thNight
26%37%5%13%14%5%
1800
11th to 20thNight
22%37%5%18%15%3
1800
21st to endNight
29%37%7%11%13%3
2064
October1st to 10thNight
26%37%6%16%13%2
2160
11th to 20thNight
24%37%7%18%12%2
2160
21st to endNight
25%38%5%16%14%2
2376
November1st to 10thNight
19%40%418%16%3
2309
11th to 20thNight
24%40%6%16%12%3
2493
21st to endNight
24%40%7%14%13%2
2660
December1st to 10thNight
25%40%6%18%10%1
2660
11th to 20thNight
28%33%7%15%14%3
3288
21st to endNight
33%29%12%17%8%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
25%22%33%17%31
204
11th to 20thDay
30%19%29%19%3
270
21st to endDay
22%22%36%13%6%1
297
February1st to 10thDay
23%22%37%14%4
270
11th to 20thDay
34%20%34%10%2
315
21st to endDay
28%16%34%19%3
382
March1st to 10thDay
24%18%32%21%4
460
11th to 20thDay
23%19%33%17%6%1
460
21st to endDay
22%17%32%20%8%1
470
April1st to 10thDay
21%17%33%21%7%1
420
11th to 20thDay
16%15%30%22%14%4
412
21st to endDay
26%12%29%22%9%2
420
May1st to 10thDay
23%12%28%20%13%4
423
11th to 20thDay
20%7%31%23%14%4
447
21st to endDay
19%420%28%21%7%
485
June1st to 10thDay
14%326%29%21%8%
450
11th to 20thDay
14%7%23%31%16%9%
450
21st to endDay
9%427%33%19%8%
450
July1st to 10thDay
13%315%30%25%15%
445
11th to 20thDay
5%217%31%34%11%
444
21st to endDay
13%219%30%28%9%
488
August1st to 10thDay
12%315%28%30%13%
446
11th to 20thDay
11%412%31%30%12%
439
21st to endDay
9%117%32%21%19%
495
September1st to 10thDay
18%5%17%21%23%16%
450
11th to 20thDay
15%416%29%22%14%
450
21st to endDay
24%6%23%29%12%6%
450
October1st to 10thDay
22%6%18%26%22%7%
450
11th to 20thDay
17%12%26%27%16%3
450
21st to endDay
19%8%33%26%10%3
495
November1st to 10thDay
17%9%30%28%12%3
413
11th to 20thDay
19%11%32%24%12%2
342
21st to endDay
20%18%29%22%9%2
180
December1st to 10thDay
19%12%41%21%5%2
180
11th to 20thDay
27%13%31%20%9%
180
21st to endDay
24%11%34%23%7%1
198
January1st to 10thNight
21%16%40%19%4
760
11th to 20thNight
24%13%33%26%4
760
21st to endNight
20%15%39%24%2
836
February1st to 10thNight
19%14%38%26%3
760
11th to 20thNight
25%19%37%17%1
743
21st to endNight
25%16%35%21%3
628
March1st to 10thNight
20%15%39%23%3
760
11th to 20thNight
22%16%34%22%41
760
21st to endNight
19%14%39%23%41
801
April1st to 10thNight
19%18%36%23%4
720
11th to 20thNight
16%11%35%28%9%1
711
21st to endNight
21%9%31%32%7%
720
May1st to 10thNight
19%8%29%31%12%1
589
11th to 20thNight
21%5%26%36%11%1
427
21st to endNight
15%320%40%21%1
389
June1st to 10thNight
10%226%40%22%1
360
11th to 20thNight
14%422%37%21%1
360
21st to endNight
8%221%50%18%1
360
July1st to 10thNight
10%216%43%25%4
350
11th to 20thNight
6%213%39%35%4
428
21st to endNight
9%213%43%30%3
591
August1st to 10thNight
11%113%41%32%3
537
11th to 20thNight
11%310%44%29%3
603
21st to endNight
12%313%39%28%4
792
September1st to 10thNight
18%315%31%29%5%
720
11th to 20thNight
12%313%36%32%3
720
21st to endNight
20%422%33%21%1
720
October1st to 10thNight
23%418%30%20%4
720
11th to 20thNight
17%9%27%31%16%
720
21st to endNight
18%10%32%27%13%
792
November1st to 10thNight
14%9%31%33%12%1
740
11th to 20thNight
17%12%32%29%8%1
760
21st to endNight
16%14%32%30%8%1
760
December1st to 10thNight
22%12%34%25%7%
760
11th to 20thNight
18%10%40%26%6%
760
21st to endNight
20%11%35%30%3
836
Page generated at 2024-03-19 23:31:05. Version ac07

Copyright © 2024 Attilla Danko.


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