Great Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Falls clear sky chart from 2005-11-05 to 2018-08-29.

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
41%
16665
16%
50507
11%
16630
47%
16630
24%
33124

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
27%
974
12%
2910
7%
970
31%
970
18%
2069
January16th to endNight
23%
864
17%
2900
10%
864
32%
864
18%
1962
February1st to 15thNight
24%
762
11%
2483
7%
760
31%
760
15%
1812
February16th to endNight
31%
684
11%
2182
6%
684
37%
684
16%
1558
March1st to 15thNight
37%
780
13%
2210
9%
780
42%
780
22%
1559
March16th to endNight
33%
832
9%
2288
4%
832
37%
832
19%
1702
April1st to 15thNight
37%
636
12%
1902
6%
636
42%
636
18%
1381
April16th to endNight
44%
579
15%
1737
11%
579
47%
579
20%
1199
May1st to 15thNight
54%
584
14%
1666
12%
584
56%
584
27%
1102
May16th to endNight
53%
497
11%
1512
9%
495
55%
495
23%
1030
June1st to 15thNight
52%
390
9%
1365
6%
390
56%
390
24%
848
June16th to endNight
55%
390
11%
1365
9%
390
59%
390
28%
772
July1st to 15thNight
75%
370
17%
1295
18%
370
78%
370
44%
611
July16th to endNight
75%
437
24%
1439
28%
413
81%
413
50%
642
August1st to 15thNight
71%
575
23%
1719
22%
572
73%
572
44%
904
August16th to endNight
68%
615
27%
1845
23%
615
70%
615
40%
1006
September1st to 15thNight
64%
600
23%
1833
20%
600
67%
600
40%
997
September16th to endNight
57%
716
25%
1980
17%
716
62%
716
36%
1209
October1st to 15thNight
45%
720
21%
2138
13%
720
52%
720
27%
1381
October16th to endNight
42%
768
22%
2400
12%
768
51%
768
27%
1498
November1st to 15thNight
30%
902
18%
2612
9%
902
38%
902
25%
1709
November16th to endNight
32%
975
17%
2730
7%
975
41%
975
25%
1811
December1st to 15thNight
28%
975
12%
2876
7%
975
34%
975
17%
2095
December16th to endNight
22%
1040
14%
3120
5%
1040
30%
1040
16%
2267

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%7%35%5%3445%8%42%
51777
Night
9%8%36%5%3445%7%41%
50663
Cloud CoverDay
10%7%25%5%3445%7%43%
51778
Night
10%8%36%5%3445%7%41%
50665
TransparencyDay
39%6%13%23%13%4
51436
Night
41%6%14%21%12%3
50508
SeeingDay
14%7%24%26%20%7%
7209
Night
14%7%28%32%15%1
16669

By Month

Percentage Cloud Cover NW (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
7%12%5%7%6%3345%8%35%
1358
16th to endDay
6%13%48%6%35%45%6%34%
1686
February1st to 15thDay
8%14%48%7%4345%7%30%
1710
16th to endDay
5%12%5%10%6%35%6%5%6%32%
1578
March1st to 15thDay
5%9%37%5%35%6%6%9%35%
2080
16th to endDay
8%11%5%8%7%35%6%6%8%29%
2287
April1st to 15thDay
13%10%46%6%46%5%5%6%29%
2374
16th to endDay
14%9%36%5%34446%36%
2498
May1st to 15thDay
12%6%25%5%3446%8%40%
2614
16th to endDay
19%6%26%5%35%6%6%8%29%
2951
June1st to 15thDay
14%425%5%36%5%7%9%36%
2925
16th to endDay
8%314425%46%9%48%
2925
July1st to 15thDay
5%21331346%9%57%
2925
16th to endDay
411222335%8%64%
2989
August1st to 15thDay
431232346%8%59%
2485
16th to endDay
7%21331345%8%58%
2654
September1st to 15thDay
10%412222346%58%
2124
16th to endDay
12%423323436%52%
1980
October1st to 15thDay
14%8%26%42446%6%40%
1821
16th to endDay
10%5%25%5%345%6%10%39%
1823
November1st to 15thDay
9%8%48%6%3436%7%37%
1564
16th to endDay
8%9%37%5%3445%7%39%
1560
December1st to 15thDay
6%12%410%8%44446%33%
1410
16th to endDay
6%14%410%7%35%446%31%
1456
January1st to 15thNight
9%11%47%6%25%5%6%8%32%
2910
16th to endNight
8%9%47%6%3445%6%38%
2900
February1st to 15thNight
10%14%5%7%5%345%5%6%30%
2472
16th to endNight
6%15%6%7%7%3436%6%32%
2182
March1st to 15thNight
5%9%38%7%45%5%6%8%34%
2210
16th to endNight
10%12%47%5%445%5%7%31%
2285
April1st to 15thNight
13%11%36%6%35%5%5%6%32%
1902
16th to endNight
15%9%35%5%2445%6%35%
1737
May1st to 15thNight
11%7%35%5%25%45%6%41%
1666
16th to endNight
20%5%343245%48%36%
1512
June1st to 15thNight
14%4243345%7%9%40%
1365
16th to endNight
11%31342435%8%49%
1365
July1st to 15thNight
5%1232345%7%62%
1365
16th to endNight
322323347%66%
1530
August1st to 15thNight
5%2432345%7%58%
1728
16th to endNight
6%414324446%56%
1845
September1st to 15thNight
10%423312337%55%
1833
16th to endNight
11%5%23324447%50%
1980
October1st to 15thNight
14%7%24324446%44%
2138
16th to endNight
12%6%2442445%7%45%
2400
November1st to 15thNight
9%7%35%5%3445%7%42%
2612
16th to endNight
7%9%46%5%3446%8%40%
2730
December1st to 15thNight
6%12%5%9%7%34448%33%
2876
16th to endNight
7%14%5%8%7%3445%6%31%
3120

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 15thDay
9%12%47%6%2345%8%34%
1358
16th to endDay
6%13%48%5%35%5%5%7%33%
1686
February1st to 15thDay
9%13%47%7%44446%31%
1710
16th to endDay
414%5%9%6%25%5%5%6%33%
1578
March1st to 15thDay
7%8%47%6%345%7%8%36%
2080
16th to endDay
8%10%48%7%35%6%5%9%29%
2288
April1st to 15thDay
14%10%36%6%35%5%5%6%30%
2374
16th to endDay
14%9%45%5%3445%6%37%
2498
May1st to 15thDay
11%6%2444446%7%41%
2614
16th to endDay
20%6%25%5%345%6%8%30%
2951
June1st to 15thDay
15%4245%35%5%7%8%37%
2925
16th to endDay
9%313435%45%9%49%
2925
July1st to 15thDay
5%21232345%8%59%
2925
16th to endDay
311232335%7%65%
2989
August1st to 15thDay
42232346%7%61%
2485
16th to endDay
7%21332335%7%58%
2654
September1st to 15thDay
11%312313345%58%
2124
16th to endDay
12%413423446%53%
1980
October1st to 15thDay
14%8%245%335%46%40%
1821
16th to endDay
10%5%25%5%345%7%9%40%
1823
November1st to 15thDay
10%9%47%6%3335%7%38%
1564
16th to endDay
8%9%46%5%35%45%7%39%
1560
December1st to 15thDay
7%12%5%9%7%35%45%6%33%
1410
16th to endDay
7%13%49%8%35%5%46%31%
1456
January1st to 15thNight
10%11%37%6%345%6%8%33%
2910
16th to endNight
8%10%46%6%3445%6%37%
2900
February1st to 15thNight
11%14%48%5%2445%6%30%
2472
16th to endNight
6%14%6%8%6%35%45%6%31%
2182
March1st to 15thNight
6%9%37%7%35%5%6%9%33%
2210
16th to endNight
10%12%46%5%35%5%6%8%30%
2288
April1st to 15thNight
13%11%36%5%35%46%7%31%
1902
16th to endNight
16%8%35%5%35%346%38%
1737
May1st to 15thNight
12%7%35%5%25%446%42%
1666
16th to endNight
19%6%15%43446%8%36%
1511
June1st to 15thNight
14%3244245%6%9%41%
1365
16th to endNight
10%32442435%8%49%
1365
July1st to 15thNight
5%11222345%7%62%
1365
16th to endNight
3212232246%67%
1530
August1st to 15thNight
5%21242445%7%58%
1728
16th to endNight
7%313423446%56%
1845
September1st to 15thNight
10%413322346%56%
1833
16th to endNight
12%314314446%50%
1980
October1st to 15thNight
14%6%25%423447%43%
2138
16th to endNight
12%6%25%42345%7%44%
2400
November1st to 15thNight
10%8%25%43435%7%43%
2612
16th to endNight
7%8%36%4345%6%7%40%
2730
December1st to 15thNight
7%12%5%8%7%3435%6%33%
2876
16th to endNight
8%14%5%7%7%34446%31%
3120

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
47%6%16%21%6%
1358
16th to endDay
48%8%14%17%8%2
1686
February1st to 15thDay
52%7%15%18%6%
1710
16th to endDay
49%8%14%19%7%1
1578
March1st to 15thDay
42%7%19%23%6%
2080
16th to endDay
49%8%15%20%5%
2288
April1st to 15thDay
52%6%14%16%7%
2374
16th to endDay
47%5%10%24%10%1
2498
May1st to 15thDay
40%7%13%26%11%1
2614
16th to endDay
50%9%16%18%5%
2955
June1st to 15thDay
41%8%16%20%12%1
2925
16th to endDay
30%6%12%28%19%2
2925
July1st to 15thDay
22%5%9%30%23%9%
2766
16th to endDay
17%38%23%27%19%
2817
August1st to 15thDay
20%5%10%27%25%9%
2470
16th to endDay
23%49%26%23%12%
2654
September1st to 15thDay
27%39%25%24%9%
2124
16th to endDay
31%5%11%25%18%7%
1980
October1st to 15thDay
43%6%15%22%10%1
1821
16th to endDay
38%7%16%25%9%2
1823
November1st to 15thDay
44%6%14%20%10%2
1564
16th to endDay
43%6%17%22%8%1
1560
December1st to 15thDay
52%5%14%20%6%
1410
16th to endDay
53%8%14%17%5%
1456
January1st to 15thNight
47%8%16%17%7%1
2910
16th to endNight
46%7%13%18%10%2
2900
February1st to 15thNight
54%6%13%17%7%
2483
16th to endNight
52%6%14%18%7%1
2182
March1st to 15thNight
45%8%17%22%6%
2210
16th to endNight
50%8%16%18%41
2288
April1st to 15thNight
51%7%13%20%7%
1902
16th to endNight
48%5%11%23%10%
1737
May1st to 15thNight
41%6%12%26%12%1
1667
16th to endNight
45%6%18%20%9%
1512
June1st to 15thNight
38%7%17%22%11%2
1365
16th to endNight
32%6%11%27%20%1
1365
July1st to 15thNight
19%6%8%28%27%9%
1295
16th to endNight
17%47%21%31%17%
1439
August1st to 15thNight
24%410%27%23%9%
1719
16th to endNight
27%5%8%22%22%14%
1845
September1st to 15thNight
28%38%24%23%11%
1833
16th to endNight
32%6%12%24%17%6%
1980
October1st to 15thNight
39%6%14%25%11%2
2138
16th to endNight
37%6%17%23%14%1
2400
November1st to 15thNight
40%7%17%20%12%3
2612
16th to endNight
40%6%19%23%8%1
2730
December1st to 15thNight
51%7%15%18%6%1
2876
16th to endNight
52%6%16%18%5%
3120

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
11%422%20%30%12%
90
16th to endDay
6%8%46%28%45%
106
February1st to 15thDay
20%15%27%27%7%2
135
16th to endDay
9%15%34%24%12%3
159
March1st to 15thDay
14%14%38%23%7%2
330
16th to endDay
15%16%27%28%10%1
352
April1st to 15thDay
19%11%33%24%10%1
329
16th to endDay
26%5%19%23%17%7%
318
May1st to 15thDay
16%6%20%26%20%8%
436
16th to endDay
21%415%22%24%11%
597
June1st to 15thDay
15%9%21%26%21%6%
570
16th to endDay
13%7%19%28%26%5%
570
July1st to 15thDay
7%220%29%30%8%
550
16th to endDay
3223%33%29%8%
527
August1st to 15thDay
5%323%27%27%13%
359
16th to endDay
7%321%26%27%12%
385
September1st to 15thDay
15%5%22%24%23%8%
315
16th to endDay
14%5%24%22%23%8%
315
October1st to 15thDay
27%5%26%22%14%3
156
16th to endDay
16%9%22%26%15%9%
144
November1st to 15thDay
18%6%32%20%22%
135
16th to endDay
13%17%34%28%7%
135
December1st to 15thDay
12%10%36%26%12%4
100
16th to endDay
20%15%27%21%9%5%
96
January1st to 15thNight
16%13%36%21%10%1
975
16th to endNight
14%12%42%24%6%1
864
February1st to 15thNight
18%9%35%23%9%3
764
16th to endNight
14%9%33%26%13%2
684
March1st to 15thNight
9%5%38%31%13%1
780
16th to endNight
17%5%33%31%11%
832
April1st to 15thNight
19%5%27%33%12%
636
16th to endNight
19%5%24%31%17%1
579
May1st to 15thNight
15%5%18%36%22%1
585
16th to endNight
21%214%32%24%3
497
June1st to 15thNight
16%321%36%20%1
390
16th to endNight
12%322%40%22%
390
July1st to 15thNight
6%112%52%26%
370
16th to endNight
4113%54%24%
437
August1st to 15thNight
7%113%48%27%2
575
16th to endNight
8%114%44%28%3
615
September1st to 15thNight
13%114%39%27%4
600
16th to endNight
12%121%36%22%4
716
October1st to 15thNight
19%6%22%34%16%2
720
16th to endNight
15%7%29%30%15%1
768
November1st to 15thNight
14%11%37%27%8%1
902
16th to endNight
10%10%39%32%6%
975
December1st to 15thNight
14%10%35%26%11%1
975
16th to endNight
14%12%37%23%10%
1040
Page generated at 2018-08-30 03:34:25. Version ac04

Copyright 2018 A. Danko


Great Falls Clear Sky Chart |Charts Home