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 2017-04-30.

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
26%
14306
12%
45681
7%
14276
33%
14276
15%
33180

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%
618
17%
1693
7%
618
36%
618
21%
1196
May1st to 15thNight
33%
342
18%
1332
15%
342
44%
342
17%
861
May16th to endNight
33%
343
14%
1369
10%
342
46%
342
19%
837
June1st to 15thNight
27%
330
9%
1320
6%
330
38%
330
15%
873
June16th to endNight
39%
330
9%
1320
11%
330
45%
330
20%
828
July1st to 15thNight
46%
310
16%
1240
17%
310
55%
310
27%
675
July16th to endNight
47%
348
13%
1306
11%
326
55%
326
26%
739
August1st to 15thNight
49%
459
14%
1440
10%
457
54%
457
27%
903
August16th to endNight
48%
610
18%
1660
9%
610
54%
610
34%
1036
September1st to 15thNight
38%
660
15%
1650
7%
660
42%
660
27%
1155
September16th to endNight
43%
657
19%
1812
12%
657
48%
657
29%
1174
October1st to 15thNight
29%
660
16%
1980
11%
660
37%
660
17%
1410
October16th to endNight
20%
704
10%
2159
5%
704
27%
704
11%
1707
November1st to 15thNight
25%
700
15%
2383
12%
700
33%
700
14%
1733
November16th to endNight
17%
720
9%
2520
6%
720
22%
720
8%
2000
December1st to 15thNight
14%
720
6%
2520
2%
720
19%
720
6%
2087
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%
46045
Night
16%10%47%6%34446%31%
45852
TransparencyDay
54%6%11%17%9%1
45733
Night
53%6%11%18%9%
45682
SeeingDay
23%13%30%19%9%3
4841
Night
22%14%31%22%8%
14308

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%423335%38%
2257
May1st to 15thDay
18%9%46%5%24446%34%
2287
16th to endDay
15%7%36%5%35%45%7%34%
2394
June1st to 15thDay
22%8%26%5%25%45%6%29%
2310
16th to endDay
16%6%346%35%6%5%8%32%
2310
July1st to 15thDay
13%6%35%5%45%5%6%9%35%
2310
16th to endDay
12%5%36%6%36%6%6%9%33%
2458
August1st to 15thDay
14%6%27%6%45%5%5%7%34%
2178
16th to endDay
14%5%26%6%35%6%6%8%34%
2177
September1st to 15thDay
21%6%35%42335%7%36%
1980
16th to endDay
16%7%25%5%2335%6%40%
1814
October1st to 15thDay
22%9%46%424345%30%
1650
16th to endDay
27%12%47%6%2443422%
1711
November1st to 15thDay
15%11%47%5%25%437%33%
1473
16th to endDay
19%14%8%9%6%2444419%
1440
December1st to 15thDay
17%18%7%12%7%46%33413%
1440
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%433448%35%
1693
May1st to 15thNight
19%8%25%5%23437%37%
1332
16th to endNight
15%5%144245%5%7%40%
1367
June1st to 15thNight
19%6%36%4235%5%7%35%
1320
16th to endNight
15%435%435%5%6%8%38%
1320
July1st to 15thNight
9%2135%46%448%48%
1320
16th to endNight
8%425%4345%5%8%46%
1402
August1st to 15thNight
10%5%26%4235%7%7%43%
1450
16th to endNight
9%5%25%424447%49%
1660
September1st to 15thNight
17%5%245%24446%41%
1650
16th to endNight
16%6%13433346%47%
1812
October1st to 15thNight
20%9%27%423345%35%
1980
16th to endNight
24%14%36%5%33345%24%
2159
November1st to 15thNight
16%11%46%6%3435%5%31%
2383
16th to endNight
20%13%5%9%7%3444422%
2520
December1st to 15thNight
17%17%7%11%7%3433418%
2520
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
2257
May1st to 15thDay
49%5%10%17%14%3
2287
16th to endDay
47%6%11%18%12%2
2398
June1st to 15thDay
55%6%10%17%10%
2310
16th to endDay
47%7%11%19%12%1
2310
July1st to 15thDay
41%7%13%23%12%
2161
16th to endDay
45%9%14%21%8%
2291
August1st to 15thDay
47%6%14%20%9%
2164
16th to endDay
43%8%15%23%8%
2177
September1st to 15thDay
46%5%13%23%9%
1980
16th to endDay
44%6%11%28%9%
1814
October1st to 15thDay
54%6%10%17%10%
1650
16th to endDay
66%5%9%12%4
1711
November1st to 15thDay
51%8%14%16%9%
1473
16th to endDay
66%5%10%11%41
1440
December1st to 15thDay
73%6%8%8%2
1440
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
1693
May1st to 15thNight
46%5%7%19%17%3
1332
16th to endNight
39%8%12%21%14%2
1369
June1st to 15thNight
47%7%14%19%10%1
1320
16th to endNight
42%6%13%22%13%
1320
July1st to 15thNight
31%7%13%29%17%1
1240
16th to endNight
34%7%17%27%13%
1306
August1st to 15thNight
35%9%17%23%12%
1440
16th to endNight
33%7%18%30%10%
1660
September1st to 15thNight
42%7%13%26%9%
1650
16th to endNight
39%5%13%33%7%
1812
October1st to 15thNight
51%5%10%20%12%
1980
16th to endNight
61%6%11%14%5%
2159
November1st to 15thNight
54%6%12%16%9%
2383
16th to endNight
65%6%11%13%3
2520
December1st to 15thNight
69%6%10%11%2
2520
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
25%21%25%13%9%3
266
May1st to 15thDay
26%12%27%19%9%5%
228
16th to endDay
19%14%34%19%10%1
267
June1st to 15thDay
28%10%30%18%10%1
255
16th to endDay
14%8%34%28%10%3
255
July1st to 15thDay
13%6%33%32%10%4
245
16th to endDay
11%8%37%25%12%4
270
August1st to 15thDay
17%5%27%30%11%7%
253
16th to endDay
15%7%27%29%10%10%
268
September1st to 15thDay
22%7%26%16%16%10%
255
16th to endDay
19%7%31%20%14%6%
254
October1st to 15thDay
25%14%27%20%9%2
255
16th to endDay
35%14%30%14%4
263
November1st to 15thDay
18%16%33%20%10%1
127
16th to endDay
31%20%31%11%31
60
December1st to 15thDay
25%18%38%13%5%
60
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%11%
618
May1st to 15thNight
23%9%30%26%9%
342
16th to endNight
17%6%39%25%10%
343
June1st to 15thNight
23%10%32%26%6%
330
16th to endNight
19%8%29%31%11%
330
July1st to 15thNight
9%5%34%34%14%
310
16th to endNight
6%5%36%37%13%
348
August1st to 15thNight
11%426%38%16%2
459
16th to endNight
10%5%30%36%15%1
610
September1st to 15thNight
21%6%29%24%16%2
660
16th to endNight
20%7%24%28%16%2
657
October1st to 15thNight
23%13%30%21%10%
660
16th to endNight
33%15%25%18%6%
704
November1st to 15thNight
24%15%28%20%9%1
700
16th to endNight
30%18%25%19%5%
720
December1st to 15thNight
26%23%31%15%3
720
16th to endNight
31%15%32%16%2
768
Page generated at 2017-04-30 20:40:05. Version ac04

Copyright 2017 A. Danko


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