Missoula
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Missoula clear sky chart from 2005-11-05 to 2018-03-21.

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
52%
16009
13%
49251
12%
15980
53%
15980
23%
33089

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
40%
870
6%
2809
6%
869
41%
869
12%
2188
January16th to endNight
43%
832
12%
2912
12%
832
46%
832
17%
2057
February1st to 15thNight
36%
763
7%
2532
6%
759
38%
759
13%
1896
February16th to endNight
39%
684
10%
2081
9%
684
42%
684
16%
1561
March1st to 15thNight
46%
780
8%
2278
7%
780
48%
780
19%
1649
March16th to endNight
43%
792
8%
2178
6%
792
45%
792
18%
1639
April1st to 15thNight
48%
659
8%
1739
5%
659
49%
659
21%
1287
April16th to endNight
48%
540
14%
1620
11%
540
50%
540
22%
1101
May1st to 15thNight
52%
539
13%
1620
12%
539
54%
539
26%
1024
May16th to endNight
55%
374
9%
1349
12%
374
56%
374
19%
905
June1st to 15thNight
53%
360
7%
1260
7%
360
54%
360
21%
812
June16th to endNight
66%
360
14%
1260
17%
360
69%
360
35%
664
July1st to 15thNight
83%
340
19%
1204
24%
340
86%
340
53%
505
July16th to endNight
87%
376
28%
1416
42%
354
90%
354
59%
513
August1st to 15thNight
79%
488
26%
1561
27%
486
80%
486
49%
724
August16th to endNight
75%
573
29%
1719
25%
573
76%
573
49%
853
September1st to 15thNight
73%
705
24%
1875
18%
705
75%
705
48%
1023
September16th to endNight
66%
716
24%
1980
20%
716
67%
716
35%
1206
October1st to 15thNight
58%
720
17%
2070
14%
720
60%
720
27%
1360
October16th to endNight
55%
768
16%
2481
15%
768
58%
768
23%
1643
November1st to 15thNight
45%
780
12%
2490
11%
780
48%
780
18%
1788
November16th to endNight
46%
975
8%
2772
6%
975
48%
975
21%
2003
December1st to 15thNight
44%
975
7%
2925
6%
975
45%
975
15%
2238
December16th to endNight
35%
1040
6%
3120
4%
1040
37%
1040
13%
2450

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
7%8%37%6%35%5%5%7%37%
49621
Night
7%9%47%6%35%5%5%7%37%
49411
Cloud CoverDay
10%10%47%5%3445%6%36%
49622
Night
9%11%47%5%3445%6%36%
49414
TransparencyDay
45%5%14%20%11%2
49284
Night
45%5%17%20%8%1
49251
SeeingDay
15%11%24%29%16%3
6378
Night
13%5%18%41%19%1
16016

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
5%14%6%10%9%46%6%6%7%21%
1469
16th to endDay
6%14%6%9%7%45%5%46%28%
1664
February1st to 15thDay
5%13%5%11%8%5%8%5%6%5%22%
1661
16th to endDay
412%6%10%8%5%7%6%7%7%22%
1678
March1st to 15thDay
6%11%5%9%10%5%7%7%7%7%22%
2011
16th to endDay
8%13%5%10%9%5%6%7%6%6%19%
2172
April1st to 15thDay
8%11%5%11%8%46%5%7%8%21%
2207
16th to endDay
10%12%6%9%6%35%446%30%
2340
May1st to 15thDay
8%7%37%7%45%5%6%7%35%
2331
16th to endDay
15%8%47%8%35%5%6%7%26%
2758
June1st to 15thDay
15%6%36%6%36%5%5%7%32%
2700
16th to endDay
8%425%5%35%5%6%6%46%
2700
July1st to 15thDay
321342446%7%59%
2682
16th to endDay
211222335%5%69%
2657
August1st to 15thDay
3233235%5%8%60%
2391
16th to endDay
5%213313347%62%
2483
September1st to 15thDay
5%413424346%58%
2081
16th to endDay
8%5%36%42435%7%48%
1980
October1st to 15thDay
10%8%36%7%35%5%5%6%36%
1890
16th to endDay
8%8%38%7%5%6%5%5%8%31%
1743
November1st to 15thDay
7%13%5%10%9%5%6%5%5%7%23%
1684
16th to endDay
6%10%5%7%6%36%6%6%7%32%
1518
December1st to 15thDay
6%14%413%8%5%5%45%8%21%
1365
16th to endDay
6%14%5%13%8%5%7%5%6%7%18%
1456
January1st to 15thNight
7%12%6%10%8%47%6%5%6%23%
2809
16th to endNight
6%11%5%8%7%45%5%6%7%31%
2912
February1st to 15thNight
6%14%6%10%8%5%5%46%7%25%
2521
16th to endNight
312%5%9%9%5%7%7%6%7%26%
2081
March1st to 15thNight
5%10%37%7%47%7%7%8%29%
2278
16th to endNight
6%12%48%7%45%7%7%9%25%
2175
April1st to 15thNight
8%10%47%6%47%6%6%9%29%
1739
16th to endNight
10%9%37%5%3446%7%36%
1620
May1st to 15thNight
7%7%35%435%6%6%8%41%
1619
16th to endNight
13%8%36%5%35%5%5%9%32%
1349
June1st to 15thNight
16%445%435%5%5%7%38%
1260
16th to endNight
8%4133236%6%8%51%
1260
July1st to 15thNight
311111245%10%66%
1275
16th to endNight
1112212247%72%
1512
August1st to 15thNight
221322445%8%63%
1569
16th to endNight
322325%446%63%
1719
September1st to 15thNight
5%313423347%60%
1875
16th to endNight
10%424434446%50%
1980
October1st to 15thNight
8%7%26%6%35%45%6%42%
2070
16th to endNight
9%8%36%5%35%5%5%7%39%
2481
November1st to 15thNight
9%10%5%8%5%45%5%5%7%30%
2490
16th to endNight
7%9%39%6%47%5%6%8%30%
2772
December1st to 15thNight
413%6%10%6%5%7%5%6%7%26%
2925
16th to endNight
7%14%6%11%8%46%6%6%6%21%
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%20%7%10%7%2435%8%20%
1469
16th to endDay
9%19%6%11%6%2334428%
1664
February1st to 15thDay
10%20%6%10%6%35%445%21%
1661
16th to endDay
7%17%6%12%9%45%5%46%19%
1678
March1st to 15thDay
10%17%6%9%7%36%45%6%21%
2011
16th to endDay
12%16%6%10%8%45%45%5%19%
2173
April1st to 15thDay
11%15%6%10%6%46%5%5%6%21%
2207
16th to endDay
12%15%5%8%5%24446%29%
2340
May1st to 15thDay
9%9%47%5%46%45%7%35%
2331
16th to endDay
18%10%36%6%35%46%7%27%
2758
June1st to 15thDay
17%7%36%5%35%5%5%7%32%
2700
16th to endDay
9%5%245%245%6%6%46%
2700
July1st to 15thDay
321332445%6%59%
2682
16th to endDay
312222345%69%
2657
August1st to 15thDay
321242345%7%61%
2391
16th to endDay
5%312313447%62%
2483
September1st to 15thDay
6%314423337%58%
2081
16th to endDay
10%7%35%5%2335%6%46%
1980
October1st to 15thDay
13%9%36%6%345%48%35%
1890
16th to endDay
14%11%48%6%3445%8%29%
1743
November1st to 15thDay
14%17%7%9%5%3435%6%22%
1684
16th to endDay
10%15%6%8%6%44346%29%
1518
December1st to 15thDay
9%18%6%11%6%46%5%36%20%
1365
16th to endDay
9%17%8%12%7%45%45%6%16%
1456
January1st to 15thNight
11%18%7%9%6%35%446%21%
2809
16th to endNight
9%15%6%9%5%245%5%6%29%
2912
February1st to 15thNight
12%20%6%8%6%33445%24%
2521
16th to endNight
7%16%6%9%8%5%6%446%24%
2081
March1st to 15thNight
9%14%48%5%35%5%6%8%27%
2278
16th to endNight
10%14%5%8%6%46%5%7%7%24%
2178
April1st to 15thNight
9%11%46%7%46%5%6%8%28%
1739
16th to endNight
12%10%46%5%25%446%36%
1620
May1st to 15thNight
8%7%36%5%35%5%5%7%41%
1619
16th to endNight
13%7%36%6%36%5%6%7%32%
1349
June1st to 15thNight
16%6%346%2445%7%38%
1260
16th to endNight
8%41332446%8%51%
1260
July1st to 15thNight
31121245%8%66%
1275
16th to endNight
112221247%72%
1512
August1st to 15thNight
221221245%9%62%
1569
16th to endNight
4212323448%62%
1719
September1st to 15thNight
7%413313246%61%
1875
16th to endNight
12%41442435%6%49%
1980
October1st to 15thNight
10%7%36%5%35%5%5%5%40%
2070
16th to endNight
13%9%37%5%2445%6%38%
2481
November1st to 15thNight
15%14%47%6%33446%29%
2490
16th to endNight
10%13%5%8%6%3445%6%28%
2772
December1st to 15thNight
8%17%7%8%7%35%447%24%
2925
16th to endNight
11%19%8%11%7%345%5%5%18%
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
60%7%19%11%1
1469
16th to endDay
55%5%16%15%41
1664
February1st to 15thDay
62%5%16%11%2
1661
16th to endDay
60%414%16%3
1678
March1st to 15thDay
58%5%18%12%4
2011
16th to endDay
62%7%15%12%2
2173
April1st to 15thDay
59%6%15%15%3
2207
16th to endDay
55%413%21%4
2340
May1st to 15thDay
45%417%23%8%
2331
16th to endDay
55%5%17%15%5%
2762
June1st to 15thDay
49%6%14%19%8%1
2700
16th to endDay
35%312%29%15%2
2700
July1st to 15thDay
24%310%25%27%8%
2524
16th to endDay
14%46%20%34%20%
2490
August1st to 15thDay
19%5%10%30%26%8%
2374
16th to endDay
21%310%30%26%6%
2483
September1st to 15thDay
26%310%31%20%6%
2081
16th to endDay
37%317%27%13%1
1980
October1st to 15thDay
46%5%18%23%5%
1890
16th to endDay
50%416%21%6%
1743
November1st to 15thDay
59%6%15%13%4
1684
16th to endDay
49%6%24%16%2
1518
December1st to 15thDay
62%6%17%11%2
1365
16th to endDay
64%5%17%11%1
1456
January1st to 15thNight
60%7%18%11%2
2809
16th to endNight
52%5%18%17%41
2912
February1st to 15thNight
59%419%13%2
2532
16th to endNight
57%5%16%17%3
2081
March1st to 15thNight
50%7%21%16%4
2278
16th to endNight
53%8%19%16%2
2178
April1st to 15thNight
49%7%19%18%4
1739
16th to endNight
46%417%24%5%
1620
May1st to 15thNight
40%5%16%29%8%
1620
16th to endNight
46%7%20%17%7%
1349
June1st to 15thNight
44%5%16%23%8%1
1260
16th to endNight
28%5%15%32%15%2
1260
July1st to 15thNight
15%310%33%26%9%
1204
16th to endNight
12%27%28%31%17%
1416
August1st to 15thNight
18%5%10%32%25%9%
1561
16th to endNight
20%411%27%29%7%
1719
September1st to 15thNight
25%211%29%24%7%
1875
16th to endNight
33%5%15%26%16%2
1980
October1st to 15thNight
41%5%18%26%7%
2070
16th to endNight
44%5%18%22%8%
2481
November1st to 15thNight
52%5%18%18%4
2490
16th to endNight
51%5%23%16%2
2772
December1st to 15thNight
56%7%18%14%2
2925
16th to endNight
62%419%10%2
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
8%115%34%26%13%
90
16th to endDay
13%9%12%43%14%6%
96
February1st to 15thDay
20%9%19%37%8%4
124
16th to endDay
18%15%20%28%15%
259
March1st to 15thDay
22%15%27%22%10%1
330
16th to endDay
22%16%30%24%6%
311
April1st to 15thDay
20%17%30%23%7%
269
16th to endDay
25%16%25%22%8%1
270
May1st to 15thDay
13%20%32%20%10%2
288
16th to endDay
21%9%18%27%16%5%
474
June1st to 15thDay
19%10%22%26%17%3
495
16th to endDay
12%10%24%29%20%2
495
July1st to 15thDay
6%8%22%29%28%3
458
16th to endDay
316%34%27%13%3
327
August1st to 15thDay
410%24%30%20%8%
315
16th to endDay
6%8%23%33%21%7%
332
September1st to 15thDay
10%10%26%23%20%7%
315
16th to endDay
13%9%20%30%20%6%
315
October1st to 15thDay
20%8%15%39%15%1
225
16th to endDay
15%222%36%18%4
144
November1st to 15thDay
16%115%43%20%2
135
16th to endDay
14%420%48%12%
125
December1st to 15thDay
24%316%30%18%6%
90
16th to endDay
17%428%34%14%1
96
January1st to 15thNight
17%7%20%37%15%1
874
16th to endNight
14%6%24%37%15%1
832
February1st to 15thNight
17%8%25%36%10%1
764
16th to endNight
12%7%24%39%13%1
684
March1st to 15thNight
12%6%25%42%11%1
780
16th to endNight
16%6%22%42%12%
792
April1st to 15thNight
11%9%21%39%16%1
659
16th to endNight
16%6%19%42%15%
540
May1st to 15thNight
10%11%19%34%22%1
540
16th to endNight
17%213%30%33%2
375
June1st to 15thNight
17%415%38%22%3
360
16th to endNight
11%412%42%27%1
360
July1st to 15thNight
316%47%40%
340
16th to endNight
25%57%31%1
376
August1st to 15thNight
419%46%37%1
488
16th to endNight
5%411%41%35%1
573
September1st to 15thNight
8%19%40%34%4
705
16th to endNight
14%29%39%28%5%
716
October1st to 15thNight
12%416%45%20%1
720
16th to endNight
16%415%44%18%1
768
November1st to 15thNight
19%6%18%43%10%
780
16th to endNight
15%5%23%44%10%
975
December1st to 15thNight
14%6%22%41%14%
975
16th to endNight
16%7%24%40%10%
1040
Page generated at 2018-03-22 09:34:25. Version ac04

Copyright 2018 A. Danko


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