Sulphur Mountain Cosmic Ray Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sulphur Mountain Cosmic Ray Station clear sky chart from 2005-11-06 to 2024-11-30.

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
25%
24254
9%
99820
5%
24023
30%
24023
12%
66789

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
11%
947
5%
4713
2%
926
16%
926
5%
3769
January11th to 20thNight
15%
864
17%
4464
4%
846
21%
846
7%
2975
January21st to endNight
12%
833
7%
4859
4%
814
23%
814
5%
3676
February1st to 10thNight
17%
760
6%
2660
4%
760
21%
760
8%
2075
February11th to 20thNight
17%
743
9%
2450
4%
740
24%
740
12%
1808
February21st to endNight
22%
628
12%
1884
6%
628
29%
628
13%
1399
March1st to 10thNight
22%
760
11%
3656
5%
744
29%
744
9%
2534
March11th to 20thNight
20%
755
9%
3529
5%
740
27%
740
13%
2117
March21st to endNight
24%
826
5%
3574
2%
814
28%
814
8%
2857
April1st to 10thNight
23%
760
8%
1900
2%
760
26%
760
12%
1476
April11th to 20thNight
27%
566
8%
1694
4%
566
31%
566
14%
1238
April21st to endNight
25%
570
8%
1710
4%
570
30%
570
14%
1265
May1st to 10thNight
33%
396
7%
2504
7%
391
37%
391
7%
1810
May11th to 20thNight
48%
373
7%
2209
11%
364
51%
364
12%
1400
May21st to endNight
38%
404
3%
2413
3%
399
40%
399
8%
1663
June1st to 10thNight
31%
380
1%
1330
0%
380
32%
380
14%
954
June11th to 20thNight
29%
380
0%
1330
0%
380
29%
380
12%
977
June21st to endNight
45%
380
1%
1330
0%
380
45%
380
23%
815
July1st to 10thNight
51%
360
1%
1924
0%
360
52%
360
20%
980
July11th to 20thNight
44%
359
4%
1836
3%
359
46%
359
22%
809
July21st to endNight
59%
409
10%
2298
17%
383
65%
383
25%
1000
August1st to 10thNight
57%
371
13%
2389
17%
366
65%
366
15%
1371
August11th to 20thNight
53%
461
12%
2550
17%
454
60%
454
22%
1190
August21st to endNight
45%
618
12%
3017
12%
605
50%
605
22%
1491
September1st to 10thNight
42%
744
17%
1884
9%
744
45%
744
31%
1201
September11th to 20thNight
39%
760
14%
2050
7%
760
42%
760
25%
1382
September21st to endNight
27%
760
17%
2090
7%
760
35%
760
23%
1366
October1st to 10thNight
29%
755
18%
3400
8%
740
36%
740
16%
1883
October11th to 20thNight
24%
751
10%
3863
5%
740
32%
740
12%
2091
October21st to endNight
19%
827
13%
4297
4%
813
28%
813
11%
2345
November1st to 10thNight
12%
812
8%
2567
3%
812
18%
812
10%
1982
November11th to 20thNight
12%
1000
7%
2952
1%
1000
18%
1000
11%
2230
November21st to endNight
16%
1000
8%
3000
3%
1000
21%
1000
12%
2252
December1st to 10thNight
15%
950
10%
2850
4%
950
21%
950
12%
2121
December11th to 20thNight
11%
950
5%
3507
1%
949
16%
949
8%
2803
December21st to endNight
11%
1042
6%
5137
1%
1026
19%
1026
7%
3484

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
6%11%411%7%6%6%5%7%8%30%
105807
Night
38%411%7%6%6%5%8%9%31%
102357
TransparencyDay
46%11%17%17%8%1
105561
Night
41%14%19%17%7%1
102250
SeeingDay
17%22%33%20%8%1
15326
Night
10%20%39%23%8%1
24366

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 10thDay
13320%14%9%7%7%9%10%17%
2219
11th to 20thDay
4314%9%7%8%5%8%9%33%
2361
21st to endDay
8%5%10%7%7%8%7%9%12%26%
2794
February1st to 10thDay
19%5%12%11%9%8%7%8%9%21%
1520
11th to 20thDay
19%5%17%10%8%7%5%7%9%24%
1614
21st to endDay
19%5%17%12%9%7%5%7%8%19%
1570
March1st to 10thDay
6%5%20%11%8%5%46%7%27%
3138
11th to 20thDay
211%6%12%8%6%6%47%8%32%
3360
21st to endDay
120%10%19%8%5%5%45%6%16%
4002
April1st to 10thDay
417%8%19%9%7%5%45%5%16%
2280
11th to 20thDay
319%8%17%8%5%5%46%6%19%
2437
21st to endDay
7%21%8%13%6%6%5%45%7%19%
2470
May1st to 10thDay
11%24%5%10%5%5%5%45%6%21%
4387
11th to 20thDay
8%17%5%11%6%6%5%47%7%23%
4648
21st to endDay
14%21%6%14%7%6%5%35%6%13%
5161
June1st to 10thDay
16%16%410%7%5%5%46%6%20%
2850
11th to 20thDay
20%15%5%11%7%6%6%45%6%15%
2850
21st to endDay
11%10%5%11%7%6%6%5%6%7%27%
2850
July1st to 10thDay
7%6%38%6%5%5%46%6%45%
4740
11th to 20thDay
6%426%5%5%6%5%7%8%46%
4740
21st to endDay
4326%5%6%6%5%8%10%45%
4871
August1st to 10thDay
6%6%39%6%6%6%5%7%8%38%
4401
11th to 20thDay
7%5%27%5%6%6%5%8%10%38%
4176
21st to endDay
8%6%26%5%6%6%5%7%9%41%
4521
September1st to 10thDay
9%9%38%6%5%5%35%7%40%
2294
11th to 20thDay
9%10%310%5%5%435%7%37%
2129
21st to endDay
7%10%310%6%5%6%46%8%36%
2090
October1st to 10thDay
7%8%49%6%5%446%8%39%
3386
11th to 20thDay
37%39%5%6%6%49%12%35%
2842
21st to endDay
39%39%7%8%6%5%7%7%37%
3101
November1st to 10thDay
311%5%11%9%7%6%6%6%10%26%
1710
11th to 20thDay
17%49%7%8%7%7%11%11%29%
1445
21st to endDay
19%410%7%7%7%5%9%12%29%
1396
December1st to 10thDay
16%412%9%5%6%7%9%12%28%
1330
11th to 20thDay
5%5%14%10%9%9%7%8%11%22%
1682
21st to endDay
18%49%7%8%7%6%10%12%29%
2442
January1st to 10thNight
7%6%22%13%9%8%6%9%8%12%
4726
11th to 20thNight
4313%10%8%8%8%8%9%27%
4565
21st to endNight
10%8%12%8%7%8%7%9%10%19%
4862
February1st to 10thNight
28%415%10%9%7%7%9%9%19%
2660
11th to 20thNight
18%6%15%8%7%7%6%8%9%25%
2448
21st to endNight
8%5%15%11%7%8%7%8%7%25%
1884
March1st to 10thNight
5%6%14%9%8%8%6%8%10%26%
3736
11th to 20thNight
29%5%9%6%5%5%48%12%34%
3619
21st to endNight
217%9%17%8%6%5%46%6%18%
3648
April1st to 10thNight
314%5%12%9%7%5%5%8%9%24%
1900
11th to 20thNight
212%6%11%7%5%6%6%8%10%27%
1694
21st to endNight
5%16%6%10%6%6%5%5%6%7%29%
1710
May1st to 10thNight
10%22%5%10%5%4335%6%27%
2572
11th to 20thNight
5%11%49%6%5%6%5%8%10%30%
2245
21st to endNight
11%15%410%6%5%6%47%6%26%
2414
June1st to 10thNight
13%11%39%5%4447%8%32%
1330
11th to 20thNight
15%13%28%5%6%5%45%9%28%
1330
21st to endNight
7%6%25%6%45%5%9%9%42%
1330
July1st to 10thNight
4425%5%5%5%46%8%53%
2220
11th to 20thNight
341433447%8%59%
2220
21st to endNight
2316%44446%7%60%
2665
August1st to 10thNight
8%7%37%6%5%5%46%9%42%
2529
11th to 20thNight
6%414435%5%7%11%50%
2656
21st to endNight
8%5%25%34346%9%50%
3146
September1st to 10thNight
7%6%25%44347%9%49%
1884
11th to 20thNight
8%8%37%446%47%8%41%
2050
21st to endNight
6%8%36%35%45%7%9%44%
2090
October1st to 10thNight
48%29%5%5%5%5%7%9%42%
3588
11th to 20thNight
27%38%5%5%5%5%7%10%43%
4086
21st to endNight
29%49%6%7%6%47%9%37%
4457
November1st to 10thNight
212%5%12%8%8%8%7%9%10%20%
2567
11th to 20thNight
16%5%11%9%9%9%6%9%11%24%
2952
21st to endNight
8%5%11%8%8%10%7%9%10%23%
3000
December1st to 10thNight
17%411%10%7%7%7%11%12%23%
2850
11th to 20thNight
5%414%11%11%11%8%10%10%16%
3510
21st to endNight
7%411%9%9%10%7%10%12%22%
5214

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
47%21%19%7%5%1
2219
11th to 20thDay
44%13%14%12%14%4
2384
21st to endDay
37%24%23%11%4
2794
February1st to 10thDay
49%15%19%8%6%3
1520
11th to 20thDay
51%14%16%13%6%1
1622
21st to endDay
56%12%15%10%6%1
1570
March1st to 10thDay
50%13%15%11%11%1
3138
11th to 20thDay
42%13%24%17%4
3361
21st to endDay
62%13%11%8%5%
4002
April1st to 10thDay
66%10%14%8%2
2280
11th to 20thDay
62%9%14%11%4
2437
21st to endDay
62%10%13%13%2
2470
May1st to 10thDay
60%9%14%14%3
4387
11th to 20thDay
51%12%17%16%4
4652
21st to endDay
64%13%14%7%2
5162
June1st to 10thDay
60%10%11%14%41
2850
11th to 20thDay
65%10%11%10%4
2850
21st to endDay
51%11%15%15%7%1
2850
July1st to 10thDay
37%7%10%18%22%6%
4666
11th to 20thDay
31%8%12%26%17%5%
4659
21st to endDay
30%7%12%26%22%4
4717
August1st to 10thDay
38%9%14%27%12%1
4384
11th to 20thDay
36%8%22%26%7%1
4218
21st to endDay
35%8%24%25%8%1
4520
September1st to 10thDay
41%8%16%21%11%2
2294
11th to 20thDay
43%10%15%22%10%1
2129
21st to endDay
43%11%18%19%8%1
2090
October1st to 10thDay
42%8%19%25%7%
3386
11th to 20thDay
35%11%28%20%6%
2842
21st to endDay
37%9%26%23%5%
3101
November1st to 10thDay
48%16%20%11%5%
1710
11th to 20thDay
37%21%24%12%6%
1445
21st to endDay
41%16%23%13%6%1
1396
December1st to 10thDay
42%18%19%14%6%1
1330
11th to 20thDay
44%23%19%9%4
1684
21st to endDay
36%17%18%15%12%2
2442
January1st to 10thNight
54%19%15%7%31
4726
11th to 20thNight
45%14%13%11%11%7%
4604
21st to endNight
45%24%17%8%5%1
4862
February1st to 10thNight
52%17%13%10%6%2
2660
11th to 20thNight
48%14%20%11%7%1
2450
21st to endNight
51%11%15%15%8%1
1884
March1st to 10thNight
41%19%19%12%9%
3736
11th to 20thNight
35%14%26%19%5%
3619
21st to endNight
57%13%14%12%3
3648
April1st to 10thNight
50%13%20%12%5%
1900
11th to 20thNight
46%14%21%13%6%
1694
21st to endNight
51%10%17%16%5%1
1710
May1st to 10thNight
56%8%13%19%4
2572
11th to 20thNight
40%15%19%23%4
2245
21st to endNight
48%14%19%14%4
2414
June1st to 10thNight
48%12%14%20%5%
1330
11th to 20thNight
52%11%15%15%7%
1330
21st to endNight
33%12%21%24%9%1
1330
July1st to 10thNight
27%8%16%23%21%5%
2185
11th to 20thNight
20%7%19%31%17%5%
2178
21st to endNight
22%6%14%31%22%5%
2581
August1st to 10thNight
37%9%15%29%9%1
2521
11th to 20thNight
25%8%33%28%6%
2680
21st to endNight
28%8%32%25%6%
3146
September1st to 10thNight
30%10%21%26%11%1
1884
11th to 20thNight
36%13%19%22%10%1
2050
21st to endNight
33%13%22%23%9%
2090
October1st to 10thNight
34%8%23%25%10%
3588
11th to 20thNight
31%11%26%25%6%
4086
21st to endNight
35%10%26%25%4
4457
November1st to 10thNight
48%18%17%11%5%1
2567
11th to 20thNight
44%19%19%11%6%1
2952
21st to endNight
44%18%19%12%5%2
3000
December1st to 10thNight
42%19%17%13%7%1
2850
11th to 20thNight
48%23%17%8%4
3507
21st to endNight
41%19%18%11%8%2
5214

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
12%23%36%20%7%3
180
11th to 20thDay
8%26%44%16%6%1
180
21st to endDay
11%31%36%14%6%2
198
February1st to 10thDay
24%24%33%12%6%2
180
11th to 20thDay
12%20%41%21%41
257
21st to endDay
16%25%34%19%5%1
382
March1st to 10thDay
15%31%32%16%5%2
460
11th to 20thDay
13%29%35%17%42
460
21st to endDay
16%26%34%17%5%2
506
April1st to 10thDay
19%28%34%15%5%
460
11th to 20thDay
15%26%31%20%7%1
452
21st to endDay
17%26%32%18%6%1
460
May1st to 10thDay
19%19%28%22%10%2
463
11th to 20thDay
18%11%30%27%12%2
642
21st to endDay
24%13%24%26%10%1
734
June1st to 10thDay
23%20%31%19%7%1
680
11th to 20thDay
26%21%28%18%7%1
680
21st to endDay
15%17%32%23%11%2
680
July1st to 10thDay
16%14%29%26%15%2
671
11th to 20thDay
15%18%32%23%10%2
668
21st to endDay
9%17%35%27%10%2
586
August1st to 10thDay
13%17%35%24%9%2
487
11th to 20thDay
11%19%38%23%8%2
477
21st to endDay
16%21%34%20%9%1
539
September1st to 10thDay
18%23%32%16%9%1
490
11th to 20thDay
19%20%37%17%6%1
490
21st to endDay
27%28%26%16%31
490
October1st to 10thDay
24%20%30%18%8%1
464
11th to 20thDay
18%27%27%22%5%1
300
21st to endDay
20%26%36%15%21
330
November1st to 10thDay
14%34%35%13%41
300
11th to 20thDay
15%28%46%8%31
223
21st to endDay
14%26%33%15%9%4
199
December1st to 10thDay
11%26%37%18%6%3
180
11th to 20thDay
7%30%43%14%6%
180
21st to endDay
8%28%38%22%31
198
January1st to 10thNight
9%27%48%14%21
950
11th to 20thNight
7%27%47%15%31
866
21st to endNight
7%30%45%14%4
836
February1st to 10thNight
11%22%40%20%7%1
760
11th to 20thNight
8%21%46%21%5%
744
21st to endNight
8%18%42%23%9%1
628
March1st to 10thNight
6%20%47%21%6%1
760
11th to 20thNight
7%21%46%19%6%1
760
21st to endNight
8%18%39%24%10%1
836
April1st to 10thNight
11%20%35%27%7%1
760
11th to 20thNight
7%17%37%31%7%1
566
21st to endNight
12%18%37%25%8%1
570
May1st to 10thNight
14%11%32%33%10%
399
11th to 20thNight
11%8%27%34%19%1
374
21st to endNight
21%8%26%28%16%1
411
June1st to 10thNight
18%13%32%23%12%1
380
11th to 20thNight
22%11%31%26%10%
380
21st to endNight
10%13%26%32%20%
380
July1st to 10thNight
9%8%25%39%18%
370
11th to 20thNight
10%12%28%33%16%1
368
21st to endNight
6%6%21%49%18%
416
August1st to 10thNight
8%7%19%44%22%1
378
11th to 20thNight
10%10%21%38%19%2
470
21st to endNight
11%11%29%33%15%1
627
September1st to 10thNight
13%13%28%29%14%2
744
11th to 20thNight
13%14%29%28%13%3
760
21st to endNight
14%20%35%21%9%1
760
October1st to 10thNight
15%13%36%27%8%
760
11th to 20thNight
12%19%39%25%5%1
760
21st to endNight
11%22%42%21%4
836
November1st to 10thNight
11%27%45%14%3
812
11th to 20thNight
10%29%46%13%21
1000
21st to endNight
9%25%44%18%41
1000
December1st to 10thNight
7%26%44%17%5%
950
11th to 20thNight
6%27%48%14%5%
950
21st to endNight
6%24%49%16%5%
1045
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