Foymount
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Foymount clear sky chart from 2005-11-05 to 2017-12-04.

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
27%
14968
12%
47854
7%
14938
33%
14938
15%
34645

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
13%
720
6%
2506
2%
716
18%
716
5%
2090
January16th to endNight
20%
768
10%
2592
5%
768
26%
768
10%
2000
February1st to 15thNight
15%
702
8%
2287
3%
701
21%
701
10%
1829
February16th to endNight
18%
631
13%
1992
5%
631
29%
631
12%
1476
March1st to 15thNight
16%
720
12%
2045
5%
720
23%
720
13%
1557
March16th to endNight
28%
768
18%
2071
8%
768
37%
768
20%
1443
April1st to 15thNight
20%
718
14%
1796
4%
718
26%
718
18%
1350
April16th to endNight
30%
621
17%
1701
7%
621
36%
621
22%
1200
May1st to 15thNight
32%
373
16%
1453
14%
373
42%
373
16%
963
May16th to endNight
32%
375
13%
1497
9%
374
45%
374
18%
930
June1st to 15thNight
29%
360
8%
1440
6%
360
39%
360
16%
934
June16th to endNight
37%
360
9%
1440
11%
360
44%
360
19%
912
July1st to 15thNight
45%
340
15%
1360
16%
340
54%
340
26%
752
July16th to endNight
48%
376
14%
1418
14%
354
56%
354
26%
803
August1st to 15thNight
50%
501
13%
1572
10%
499
54%
499
26%
987
August16th to endNight
49%
666
20%
1812
10%
666
56%
666
35%
1122
September1st to 15thNight
40%
720
15%
1800
7%
720
43%
720
27%
1254
September16th to endNight
46%
717
21%
1977
14%
717
51%
717
30%
1273
October1st to 15thNight
30%
720
15%
2160
11%
720
37%
720
19%
1508
October16th to endNight
20%
768
11%
2356
5%
768
28%
768
11%
1845
November1st to 15thNight
25%
760
14%
2587
12%
760
32%
760
13%
1893
November16th to endNight
17%
780
9%
2730
6%
780
22%
780
8%
2168
December1st to 15thNight
14%
736
6%
2574
2%
736
18%
736
6%
2135
December16th to endNight
12%
768
7%
2688
3%
768
18%
768
7%
2221

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%10%47%6%34446%30%
48638
Night
16%10%47%6%34446%31%
48025
TransparencyDay
53%6%11%18%9%1
48326
Night
53%6%11%18%9%
47855
SeeingDay
23%13%30%19%9%3
5641
Night
22%14%31%23%8%
14970

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 15thDay
18%13%5%12%6%4443420%
1432
16th to endDay
13%14%6%11%9%45%345%20%
1630
February1st to 15thDay
10%16%6%14%9%35%436%19%
1575
16th to endDay
16%15%6%8%5%35%5%4423%
1479
March1st to 15thDay
15%13%6%9%7%45%435%24%
1900
16th to endDay
13%9%48%5%24445%37%
2152
April1st to 15thDay
22%13%35%5%3423431%
2152
16th to endDay
21%9%36%422335%37%
2270
May1st to 15thDay
20%9%45%5%24446%32%
2496
16th to endDay
16%7%36%5%36%45%7%33%
2618
June1st to 15thDay
22%8%26%5%2445%5%30%
2520
16th to endDay
17%6%35%6%35%6%5%8%31%
2520
July1st to 15thDay
13%6%35%5%45%5%6%9%35%
2520
16th to endDay
12%5%36%6%35%6%6%9%33%
2654
August1st to 15thDay
14%7%27%6%45%5%5%6%34%
2376
16th to endDay
13%5%26%6%35%5%6%8%34%
2376
September1st to 15thDay
20%5%35%423347%38%
2160
16th to endDay
15%7%25%5%3345%6%41%
1979
October1st to 15thDay
22%9%36%424445%31%
1800
16th to endDay
26%12%47%6%3443422%
1866
November1st to 15thDay
15%12%47%5%24436%32%
1599
16th to endDay
19%14%8%8%6%3444419%
1560
December1st to 15thDay
17%18%7%12%7%45%33413%
1468
16th to endDay
19%18%8%10%5%24345%17%
1536
January1st to 15thNight
15%13%6%12%10%46%5%4416%
2506
16th to endNight
11%15%6%8%9%45%445%23%
2592
February1st to 15thNight
12%15%7%9%9%45%445%21%
2285
16th to endNight
13%13%49%7%35%446%27%
1992
March1st to 15thNight
16%12%5%9%6%3433429%
2034
16th to endNight
13%9%5%6%6%3335%5%39%
2071
April1st to 15thNight
20%11%36%5%2333433%
1796
16th to endNight
18%9%25%423448%35%
1701
May1st to 15thNight
21%8%26%423437%35%
1453
16th to endNight
15%5%25%425%5%5%7%39%
1495
June1st to 15thNight
18%6%26%4235%5%7%36%
1440
16th to endNight
15%5%35%4445%6%8%37%
1440
July1st to 15thNight
9%2145%45%448%48%
1440
16th to endNight
9%425%4245%6%8%45%
1514
August1st to 15thNight
10%5%25%5%235%7%7%43%
1582
16th to endNight
9%5%24424448%49%
1812
September1st to 15thNight
17%5%25%5%3445%5%42%
1800
16th to endNight
15%6%13433346%47%
1977
October1st to 15thNight
19%8%26%423345%37%
2160
16th to endNight
23%13%36%5%33345%25%
2356
November1st to 15thNight
17%11%46%6%3435%5%30%
2587
16th to endNight
19%13%5%9%7%3444422%
2730
December1st to 15thNight
17%17%7%11%7%3433418%
2574
16th to endNight
20%17%6%11%6%3433417%
2688

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
66%6%8%11%6%1
1433
16th to endDay
65%5%9%11%7%1
1630
February1st to 15thDay
65%5%9%13%4
1577
16th to endDay
61%5%9%12%10%1
1479
March1st to 15thDay
61%410%15%6%1
1911
16th to endDay
48%48%19%14%4
2152
April1st to 15thDay
56%37%17%11%2
2152
16th to endDay
49%37%19%16%2
2270
May1st to 15thDay
52%410%16%13%2
2496
16th to endDay
48%6%12%18%11%2
2622
June1st to 15thDay
54%6%10%18%9%
2520
16th to endDay
48%7%11%19%12%1
2520
July1st to 15thDay
41%7%13%23%12%
2371
16th to endDay
44%9%14%22%8%
2487
August1st to 15thDay
48%7%14%20%9%
2362
16th to endDay
42%8%16%23%7%
2376
September1st to 15thDay
45%5%13%24%10%
2160
16th to endDay
43%6%11%29%9%
1979
October1st to 15thDay
54%6%10%17%10%
1800
16th to endDay
65%6%10%12%4
1866
November1st to 15thDay
52%8%14%16%8%
1599
16th to endDay
66%6%9%11%41
1560
December1st to 15thDay
74%6%8%8%2
1468
16th to endDay
69%5%9%10%4
1536
January1st to 15thNight
69%7%9%8%4
2506
16th to endNight
60%6%9%15%7%
2592
February1st to 15thNight
64%6%10%13%4
2287
16th to endNight
56%5%10%17%8%
1992
March1st to 15thNight
58%410%18%7%
2046
16th to endNight
47%5%9%19%15%2
2071
April1st to 15thNight
54%47%18%12%1
1796
16th to endNight
47%5%8%20%15%2
1701
May1st to 15thNight
49%5%7%18%16%2
1453
16th to endNight
41%8%13%21%13%2
1497
June1st to 15thNight
45%7%14%20%10%
1440
16th to endNight
43%7%13%22%12%
1440
July1st to 15thNight
32%7%12%28%17%
1360
16th to endNight
34%6%17%28%12%
1418
August1st to 15thNight
35%10%18%23%11%
1572
16th to endNight
32%7%17%31%10%
1812
September1st to 15thNight
41%7%13%25%10%
1800
16th to endNight
38%5%13%34%8%
1977
October1st to 15thNight
49%5%11%21%12%
2160
16th to endNight
60%6%12%15%5%
2356
November1st to 15thNight
54%6%12%16%8%
2587
16th to endNight
64%6%11%13%3
2730
December1st to 15thNight
69%6%10%11%2
2574
16th to endNight
70%5%9%9%5%
2688

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
31%11%35%16%5%
60
16th to endDay
36%18%30%12%2
80
February1st to 15thDay
30%23%40%411
90
16th to endDay
32%24%28%13%1
138
March1st to 15thDay
27%17%32%18%4
270
16th to endDay
23%19%30%16%8%1
288
April1st to 15thDay
27%21%28%14%6%
270
16th to endDay
26%21%25%13%9%3
270
May1st to 15thDay
32%11%26%17%8%4
288
16th to endDay
23%14%34%16%9%1
331
June1st to 15thDay
28%11%30%18%10%
315
16th to endDay
16%12%33%25%9%2
315
July1st to 15thDay
14%7%33%31%9%3
305
16th to endDay
12%7%36%26%13%3
326
August1st to 15thDay
17%428%30%12%6%
313
16th to endDay
15%7%26%28%12%9%
332
September1st to 15thDay
21%7%25%18%15%11%
315
16th to endDay
17%7%27%22%17%7%
314
October1st to 15thDay
24%15%27%20%9%2
315
16th to endDay
33%16%29%15%4
322
November1st to 15thDay
25%14%32%18%8%1
163
16th to endDay
28%25%34%7%21
90
December1st to 15thDay
23%17%38%14%4
67
16th to endDay
39%31%23%6%
64
January1st to 15thNight
22%21%33%17%4
720
16th to endNight
20%15%36%21%5%
768
February1st to 15thNight
19%18%40%17%4
704
16th to endNight
20%19%36%19%3
631
March1st to 15thNight
24%20%32%19%3
720
16th to endNight
18%19%30%22%8%1
768
April1st to 15thNight
26%16%31%20%4
718
16th to endNight
23%15%28%21%10%
621
May1st to 15thNight
25%8%29%27%8%
373
16th to endNight
17%7%38%25%10%
375
June1st to 15thNight
22%9%32%27%6%
360
16th to endNight
17%8%31%31%10%
360
July1st to 15thNight
10%5%34%35%14%
340
16th to endNight
7%434%38%13%
376
August1st to 15thNight
11%425%38%17%2
501
16th to endNight
10%5%29%35%17%1
666
September1st to 15thNight
20%5%29%24%16%2
720
16th to endNight
19%6%23%28%19%2
717
October1st to 15thNight
22%12%31%22%10%1
720
16th to endNight
32%15%26%18%6%
768
November1st to 15thNight
25%15%28%20%9%1
760
16th to endNight
30%19%25%18%5%
780
December1st to 15thNight
26%22%31%16%2
736
16th to endNight
31%15%32%16%2
768
Page generated at 2017-12-05 10:19:00. Version ac04

Copyright 2017 A. Danko


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