Foymount
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Foymount clear sky chart from 2005-11-06 to 2024-02-20.

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
26%
22709
12%
80671
7%
22624
33%
22624
13%
59139

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
12%
752
6%
4418
2%
737
18%
737
3%
3597
January11th to 20thNight
16%
756
6%
4422
4%
740
22%
740
4%
3489
January21st to endNight
20%
829
7%
4625
7%
814
27%
814
6%
3793
February1st to 10thNight
13%
760
8%
2470
3%
760
21%
760
9%
1967
February11th to 20thNight
14%
740
13%
2399
3%
739
26%
739
12%
1801
February21st to endNight
18%
592
14%
1835
5%
592
30%
592
12%
1366
March1st to 10thNight
17%
720
14%
2080
7%
720
24%
720
14%
1557
March11th to 20thNight
19%
720
15%
1979
6%
720
29%
720
16%
1456
March21st to endNight
24%
792
18%
2118
7%
792
33%
792
19%
1503
April1st to 10thNight
18%
720
14%
1800
5%
720
23%
720
17%
1366
April11th to 20thNight
23%
711
17%
1775
6%
711
30%
711
21%
1291
April21st to endNight
28%
572
15%
1652
7%
572
34%
572
17%
1209
May1st to 10thNight
33%
381
17%
1461
13%
381
43%
381
16%
961
May11th to 20thNight
31%
354
21%
1416
15%
354
46%
354
19%
873
May21st to endNight
34%
389
14%
1551
11%
388
47%
388
22%
900
June1st to 10thNight
30%
360
9%
1440
8%
360
39%
360
16%
929
June11th to 20thNight
35%
360
13%
1440
15%
360
43%
360
20%
870
June21st to endNight
36%
360
10%
1440
10%
360
44%
360
18%
930
July1st to 10thNight
44%
350
14%
1400
14%
350
55%
350
24%
803
July11th to 20thNight
45%
348
15%
1392
18%
348
52%
348
23%
805
July21st to endNight
44%
394
15%
1486
13%
372
52%
372
25%
859
August1st to 10thNight
48%
480
14%
1544
11%
478
53%
478
25%
968
August11th to 20thNight
54%
534
17%
1598
11%
534
59%
534
31%
995
August21st to endNight
43%
734
18%
1922
8%
734
49%
734
30%
1259
September1st to 10thNight
41%
720
16%
1800
6%
720
45%
720
31%
1202
September11th to 20thNight
46%
720
21%
1800
11%
720
49%
720
34%
1188
September21st to endNight
42%
720
19%
2065
15%
720
46%
720
24%
1383
October1st to 10thNight
31%
720
17%
2160
11%
720
39%
720
20%
1487
October11th to 20thNight
21%
720
11%
2160
6%
720
28%
720
14%
1629
October21st to endNight
20%
792
12%
2453
6%
792
28%
792
11%
1921
November1st to 10thNight
23%
740
13%
2481
9%
740
31%
740
15%
1753
November11th to 20thNight
19%
760
12%
2660
8%
760
26%
760
10%
2022
November21st to endNight
18%
760
8%
2660
4%
760
23%
760
8%
2121
December1st to 10thNight
13%
760
7%
2660
3%
760
18%
760
6%
2238
December11th to 20thNight
15%
760
9%
3256
4%
759
21%
759
6%
2542
December21st to endNight
11%
829
4%
4853
1%
817
16%
817
3%
4106

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
17%11%48%6%35%45%6%30%
78242
Night
16%12%5%9%7%4445%6%30%
80938
TransparencyDay
53%7%11%18%10%1
77947
Night
54%7%12%17%9%1
80767
SeeingDay
23%17%31%18%8%2
13380
Night
21%15%32%23%8%1
22737

By Month

Percentage Cloud Cover NE (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
15%15%6%13%9%45%5%4420%
2517
11th to 20thDay
12%12%8%18%9%5%5%446%18%
2520
21st to endDay
15%21%9%14%7%4433317%
3026
February1st to 10thDay
11%15%6%13%10%45%5%45%20%
1710
11th to 20thDay
11%15%7%12%7%35%5%45%26%
1654
21st to endDay
17%15%6%8%7%46%5%45%23%
1419
March1st to 10thDay
14%13%6%11%7%45%436%27%
1873
11th to 20thDay
13%13%6%11%8%45%445%27%
1980
21st to endDay
17%11%48%5%23435%36%
2237
April1st to 10thDay
20%14%46%6%35%346%28%
2160
11th to 20thDay
21%11%36%5%4333437%
2134
21st to endDay
22%11%47%5%24345%32%
2324
May1st to 10thDay
19%9%36%5%34446%35%
2497
11th to 20thDay
18%9%46%5%35%45%7%35%
2478
21st to endDay
15%7%36%6%35%5%5%7%38%
2725
June1st to 10thDay
22%8%37%6%35%45%6%31%
2520
11th to 20thDay
17%6%35%6%35%5%6%8%37%
2520
21st to endDay
16%7%35%6%36%6%6%8%33%
2520
July1st to 10thDay
12%7%35%5%46%5%6%10%38%
2520
11th to 20thDay
13%6%35%6%46%5%7%9%37%
2520
21st to endDay
13%6%35%6%45%6%7%9%37%
2744
August1st to 10thDay
12%7%37%7%46%5%6%7%35%
2381
11th to 20thDay
14%7%26%6%46%5%6%8%36%
2303
21st to endDay
15%6%36%6%36%6%7%9%34%
2415
September1st to 10thDay
17%6%35%435%5%5%7%40%
2160
11th to 20thDay
15%6%25%6%3435%7%43%
2160
21st to endDay
18%8%37%6%345%6%7%35%
1890
October1st to 10thDay
21%10%36%5%34446%33%
1800
11th to 20thDay
22%13%5%7%6%345%45%25%
1800
21st to endDay
27%12%48%6%35%5%45%21%
1902
November1st to 10thDay
14%12%5%7%6%36%5%46%34%
1595
11th to 20thDay
16%14%7%9%7%3345%7%26%
1520
21st to endDay
19%17%7%10%8%445%45%18%
1520
December1st to 10thDay
18%20%7%12%9%45%335%14%
1520
11th to 20thDay
18%16%7%10%7%35%45%422%
1906
21st to endDay
23%19%7%13%7%3322417%
2772
January1st to 10thNight
14%17%9%12%9%45%5%45%16%
4429
11th to 20thNight
10%13%5%13%11%7%6%5%5%6%19%
4440
21st to endNight
14%18%8%11%8%5%6%44418%
4628
February1st to 10thNight
12%15%7%10%9%5%6%5%5%6%21%
2470
11th to 20thNight
12%13%6%10%8%4445%6%28%
2397
21st to endNight
13%14%5%10%7%45%446%27%
1835
March1st to 10thNight
15%13%6%10%7%44345%30%
2070
11th to 20thNight
13%13%5%8%7%4445%6%32%
1979
21st to endNight
13%9%5%8%6%3445%6%37%
2118
April1st to 10thNight
20%12%38%6%33446%31%
1800
11th to 20thNight
19%9%46%434436%37%
1775
21st to endNight
20%11%37%5%345%46%31%
1652
May1st to 10thNight
19%9%26%5%245%5%6%37%
1461
11th to 20thNight
18%6%25%4345%47%40%
1415
21st to endNight
13%5%245%345%6%8%44%
1550
June1st to 10thNight
17%6%37%5%346%6%9%34%
1440
11th to 20thNight
15%6%35%5%345%48%43%
1440
21st to endNight
16%6%36%5%45%46%8%37%
1440
July1st to 10thNight
10%4245%47%5%5%8%46%
1440
11th to 20thNight
12%5%345%445%6%8%44%
1440
21st to endNight
9%5%35%5%35%6%6%9%44%
1574
August1st to 10thNight
10%5%26%6%446%6%8%43%
1554
11th to 20thNight
10%6%35%5%3447%8%46%
1598
21st to endNight
11%6%25%435%5%6%8%44%
1922
September1st to 10thNight
13%6%25%5%3446%6%46%
1800
11th to 20thNight
15%5%2443335%6%49%
1800
21st to endNight
16%8%245%335%5%6%42%
2065
October1st to 10thNight
20%8%37%433447%38%
2160
11th to 20thNight
20%12%37%7%35%45%430%
2160
21st to endNight
22%15%47%6%34446%25%
2453
November1st to 10thNight
16%12%47%6%35%45%6%32%
2481
11th to 20thNight
17%13%6%8%7%45%45%5%26%
2660
21st to endNight
18%16%5%10%8%35%45%5%21%
2660
December1st to 10thNight
18%18%8%12%8%35%445%16%
2660
11th to 20thNight
16%18%6%11%7%3443423%
3288
21st to endNight
24%18%6%14%8%3333414%
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
66%10%10%8%6%
2518
11th to 20thDay
66%8%9%10%6%1
2520
21st to endDay
72%5%7%9%5%1
3026
February1st to 10thDay
65%7%8%14%5%1
1710
11th to 20thDay
58%7%12%13%9%1
1663
21st to endDay
62%6%8%12%10%1
1419
March1st to 10thDay
59%5%10%15%9%2
1876
11th to 20thDay
59%6%10%15%9%2
1980
21st to endDay
51%48%18%13%6%
2237
April1st to 10thDay
57%48%17%11%3
2160
11th to 20thDay
51%47%21%14%2
2134
21st to endDay
53%5%8%15%15%3
2324
May1st to 10thDay
50%6%9%18%13%4
2497
11th to 20thDay
48%5%10%19%15%3
2482
21st to endDay
45%7%12%19%13%3
2725
June1st to 10thDay
52%7%11%18%11%1
2520
11th to 20thDay
43%8%11%22%14%2
2520
21st to endDay
46%9%13%19%12%1
2520
July1st to 10thDay
39%8%13%25%13%1
2450
11th to 20thDay
39%9%16%23%12%
2445
21st to endDay
41%10%14%26%9%
2591
August1st to 10thDay
45%8%15%21%10%1
2367
11th to 20thDay
43%10%16%23%8%1
2303
21st to endDay
42%10%15%23%9%1
2415
September1st to 10thDay
41%8%14%25%11%1
2160
11th to 20thDay
40%7%11%29%12%
2160
21st to endDay
48%8%12%23%9%
1890
October1st to 10thDay
52%7%10%19%11%1
1800
11th to 20thDay
60%8%12%14%5%1
1800
21st to endDay
63%7%11%12%6%1
1902
November1st to 10thDay
49%8%15%20%7%
1595
11th to 20thDay
58%8%12%13%8%1
1520
21st to endDay
68%8%10%9%5%1
1520
December1st to 10thDay
73%6%8%9%3
1520
11th to 20thDay
63%9%10%11%6%
1906
21st to endDay
74%46%14%3
2772
January1st to 10thNight
68%9%11%9%2
4429
11th to 20thNight
62%12%12%9%41
4440
21st to endNight
70%6%9%9%6%
4628
February1st to 10thNight
64%7%10%13%6%1
2470
11th to 20thNight
57%7%11%18%7%1
2399
21st to endNight
56%6%10%17%10%1
1835
March1st to 10thNight
57%5%10%16%10%2
2080
11th to 20thNight
53%6%11%18%11%1
1980
21st to endNight
48%6%9%20%14%3
2118
April1st to 10thNight
54%6%7%19%12%2
1800
11th to 20thNight
49%6%8%22%14%2
1775
21st to endNight
53%6%7%16%15%2
1652
May1st to 10thNight
47%7%8%18%16%4
1461
11th to 20thNight
43%6%9%24%16%2
1416
21st to endNight
36%9%15%20%17%3
1551
June1st to 10thNight
43%9%15%21%11%1
1440
11th to 20thNight
38%9%12%25%15%2
1440
21st to endNight
44%8%15%20%12%1
1440
July1st to 10thNight
33%10%13%23%19%2
1400
11th to 20thNight
36%7%15%29%13%
1392
21st to endNight
34%9%18%27%11%1
1486
August1st to 10thNight
36%10%18%23%12%1
1544
11th to 20thNight
34%9%18%27%11%1
1598
21st to endNight
36%8%16%28%10%1
1922
September1st to 10thNight
37%8%14%27%13%1
1800
11th to 20thNight
36%7%15%32%10%
1800
21st to endNight
42%8%13%29%8%
2065
October1st to 10thNight
47%6%12%20%14%
2160
11th to 20thNight
55%8%13%16%7%
2160
21st to endNight
60%7%11%14%7%
2453
November1st to 10thNight
51%7%16%18%8%
2481
11th to 20thNight
58%9%11%14%7%1
2660
21st to endNight
64%7%13%13%3
2660
December1st to 10thNight
70%8%9%10%3
2660
11th to 20thNight
64%6%9%13%7%1
3288
21st to endNight
75%5%7%10%3
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
21%23%36%17%31
180
11th to 20thDay
28%17%37%14%41
180
21st to endDay
22%24%32%18%4
270
February1st to 10thDay
26%27%35%8%31
270
11th to 20thDay
25%30%39%6%
267
21st to endDay
35%22%31%12%
285
March1st to 10thDay
23%26%33%16%3
420
11th to 20thDay
28%19%33%16%4
420
21st to endDay
31%22%30%12%5%1
462
April1st to 10thDay
29%21%30%13%7%
420
11th to 20thDay
32%20%22%15%8%2
412
21st to endDay
30%20%31%12%5%1
420
May1st to 10thDay
25%19%29%16%8%2
423
11th to 20thDay
22%17%31%19%7%3
447
21st to endDay
19%17%34%18%10%2
485
June1st to 10thDay
25%13%35%20%7%
450
11th to 20thDay
18%16%30%22%10%4
450
21st to endDay
18%14%33%22%11%2
450
July1st to 10thDay
11%8%32%35%11%2
445
11th to 20thDay
13%12%34%25%13%3
444
21st to endDay
13%11%36%26%10%3
488
August1st to 10thDay
15%7%34%27%12%4
446
11th to 20thDay
15%8%28%27%17%6%
439
21st to endDay
16%13%31%25%10%6%
495
September1st to 10thDay
16%13%30%20%15%6%
450
11th to 20thDay
16%12%25%24%15%9%
450
21st to endDay
19%14%30%20%12%5%
450
October1st to 10thDay
27%16%24%17%12%4
450
11th to 20thDay
30%22%27%15%6%1
450
21st to endDay
31%19%28%17%4
455
November1st to 10thDay
25%19%33%16%6%1
289
11th to 20thDay
31%22%32%9%41
180
21st to endDay
27%30%31%8%22
180
December1st to 10thDay
28%17%42%9%3
180
11th to 20thDay
31%31%25%11%11
180
21st to endDay
32%21%31%13%31
198
January1st to 10thNight
24%20%35%17%4
760
11th to 20thNight
24%20%30%20%5%
760
21st to endNight
16%16%38%24%6%
836
February1st to 10thNight
19%21%39%18%3
760
11th to 20thNight
20%19%42%16%3
742
21st to endNight
22%22%33%21%3
592
March1st to 10thNight
23%20%34%20%3
720
11th to 20thNight
23%21%32%19%5%1
720
21st to endNight
19%19%33%21%7%1
792
April1st to 10thNight
28%16%32%21%3
720
11th to 20thNight
24%19%31%17%8%
711
21st to endNight
25%15%27%23%10%1
572
May1st to 10thNight
23%9%30%28%9%1
381
11th to 20thNight
21%10%34%27%7%
354
21st to endNight
15%8%39%27%11%
389
June1st to 10thNight
19%8%38%29%5%1
360
11th to 20thNight
18%9%34%29%11%
360
21st to endNight
19%10%31%28%13%
360
July1st to 10thNight
9%7%37%34%12%1
350
11th to 20thNight
12%7%30%37%14%
348
21st to endNight
7%6%36%39%11%1
394
August1st to 10thNight
10%5%27%38%20%1
480
11th to 20thNight
11%423%40%19%3
534
21st to endNight
12%9%31%30%17%2
734
September1st to 10thNight
15%8%31%27%17%1
720
11th to 20thNight
20%7%24%29%17%3
720
21st to endNight
19%12%23%27%18%2
720
October1st to 10thNight
25%11%29%22%12%2
720
11th to 20thNight
25%17%32%18%8%1
720
21st to endNight
31%17%27%20%5%
792
November1st to 10thNight
25%17%30%21%6%1
740
11th to 20thNight
23%21%30%17%9%1
760
21st to endNight
30%18%26%22%4
760
December1st to 10thNight
27%20%33%16%3
760
11th to 20thNight
26%21%31%19%31
760
21st to endNight
31%18%31%17%3
836
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