YFOS
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the YFOS clear sky chart from 2005-11-05 to 2017-03-21.

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
26%
14317
17%
45243
7%
14285
38%
14285
19%
29313

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
16%
720
19%
2506
6%
716
33%
716
13%
1606
January16th to endNight
13%
768
18%
2688
4%
768
31%
768
13%
1720
February1st to 15thNight
11%
704
14%
2225
2%
701
26%
701
12%
1500
February16th to endNight
15%
631
20%
1893
4%
631
34%
631
15%
1250
March1st to 15thNight
17%
720
17%
2160
6%
720
31%
720
15%
1453
March16th to endNight
25%
728
21%
1915
7%
728
36%
728
22%
1253
April1st to 15thNight
19%
658
18%
1646
3%
658
28%
658
21%
1146
April16th to endNight
25%
553
17%
1543
4%
553
34%
553
21%
1033
May1st to 15thNight
25%
486
17%
1476
8%
486
35%
486
17%
1021
May16th to endNight
30%
343
11%
1369
9%
342
39%
342
15%
898
June1st to 15thNight
28%
330
11%
1320
6%
330
41%
330
13%
891
June16th to endNight
39%
330
10%
1320
10%
330
46%
330
19%
825
July1st to 15thNight
46%
310
14%
1240
17%
310
53%
310
23%
726
July16th to endNight
45%
348
15%
1306
14%
326
54%
326
27%
745
August1st to 15thNight
43%
425
17%
1406
11%
423
49%
423
26%
847
August16th to endNight
47%
674
19%
1724
9%
674
50%
674
35%
1073
September1st to 15thNight
39%
660
21%
1688
8%
660
46%
660
34%
1072
September16th to endNight
45%
657
26%
1815
16%
657
53%
657
36%
1066
October1st to 15thNight
32%
660
21%
1864
10%
660
43%
660
22%
1250
October16th to endNight
22%
704
14%
2282
5%
704
35%
704
16%
1518
November1st to 15thNight
27%
700
20%
2277
10%
700
42%
700
20%
1457
November16th to endNight
24%
720
20%
2372
8%
720
38%
720
17%
1510
December1st to 15thNight
16%
720
16%
2520
4%
720
31%
720
13%
1665
December16th to endNight
13%
768
17%
2688
3%
768
29%
768
11%
1788

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
16%6%35%5%35%45%7%36%
45625
Night
15%6%25%5%2445%7%39%
45413
Cloud CoverDay
15%6%35%5%35%45%7%36%
45635
Night
15%6%25%42445%7%40%
45418
TransparencyDay
46%412%21%13%1
45313
Night
43%413%23%12%1
45243
SeeingDay
21%16%27%20%10%3
5092
Night
21%17%29%22%7%
14317

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
13%6%36%7%345%6%7%34%
1432
16th to endDay
12%7%345%25%47%9%37%
1536
February1st to 15thDay
14%8%36%5%38%5%5%7%30%
1634
16th to endDay
12%10%37%6%3445%6%34%
1580
March1st to 15thDay
16%9%45%5%35%5%6%6%32%
1790
16th to endDay
14%6%45%5%33446%40%
2077
April1st to 15thDay
15%7%45%6%35%35%6%36%
1972
16th to endDay
16%8%25%6%245%46%38%
2087
May1st to 15thDay
22%7%37%5%34446%32%
2154
16th to endDay
17%5%36%5%35%447%36%
2394
June1st to 15thDay
24%6%25%5%25%447%29%
2310
16th to endDay
17%6%36%6%35%46%9%31%
2310
July1st to 15thDay
13%6%25%6%46%5%7%8%33%
2310
16th to endDay
13%5%35%6%36%5%6%8%35%
2458
August1st to 15thDay
13%5%25%6%5%5%5%6%9%34%
2203
16th to endDay
11%425%6%445%6%7%41%
2124
September1st to 15thDay
13%5%245%35%46%6%41%
1942
16th to endDay
13%424423346%51%
1815
October1st to 15thDay
20%6%36%5%2443437%
1763
16th to endDay
18%6%36%434449%33%
1590
November1st to 15thDay
15%7%25%42435%7%40%
1581
16th to endDay
17%7%26%5%23345%41%
1587
December1st to 15thDay
16%8%26%5%35%5%5%6%34%
1440
16th to endDay
18%11%45%5%35%45%6%29%
1536
January1st to 15thNight
12%8%25%5%35%5%6%7%38%
2506
16th to endNight
12%8%35%5%35%5%5%6%37%
2688
February1st to 15thNight
11%9%45%5%45%6%5%7%33%
2224
16th to endNight
13%9%344245%5%7%36%
1893
March1st to 15thNight
16%8%35%425%5%5%6%36%
2147
16th to endNight
14%6%2433446%7%42%
1915
April1st to 15thNight
16%7%245%25%45%6%37%
1646
16th to endNight
18%7%15%5%24346%40%
1543
May1st to 15thNight
19%7%26%6%3445%6%34%
1476
16th to endNight
18%5%36%6%3445%7%34%
1367
June1st to 15thNight
24%7%35%5%25%348%31%
1320
16th to endNight
16%415%425%45%7%40%
1320
July1st to 15thNight
12%4245%35%5%6%9%40%
1320
16th to endNight
11%5%243236%6%10%42%
1402
August1st to 15thNight
10%5%26%5%3446%8%42%
1416
16th to endNight
12%4234235%5%9%45%
1724
September1st to 15thNight
14%41431435%6%49%
1688
16th to endNight
12%412323447%52%
1815
October1st to 15thNight
19%6%245%23346%39%
1864
16th to endNight
20%6%244345%6%5%35%
2282
November1st to 15thNight
15%6%25%5%25%35%5%42%
2277
16th to endNight
15%6%26%5%25%447%39%
2372
December1st to 15thNight
17%6%35%5%35%45%7%35%
2520
16th to endNight
18%8%35%5%25%45%7%32%
2688

Percentage Cloud Cover SE (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
13%6%36%6%36%5%6%7%35%
1432
16th to endDay
13%6%25%5%35%47%8%39%
1536
February1st to 15thDay
14%7%26%5%38%5%6%8%30%
1634
16th to endDay
13%9%47%5%35%45%6%35%
1580
March1st to 15thDay
17%8%45%5%4446%7%32%
1800
16th to endDay
15%6%36%5%23445%42%
2077
April1st to 15thDay
15%7%36%5%35%346%37%
1972
16th to endDay
16%6%26%5%24445%40%
2087
May1st to 15thDay
22%6%36%5%34445%33%
2154
16th to endDay
17%5%35%5%35%448%36%
2394
June1st to 15thDay
24%7%25%435%45%8%28%
2310
16th to endDay
17%6%26%6%35%5%5%8%31%
2310
July1st to 15thDay
13%5%26%6%46%6%6%9%34%
2310
16th to endDay
12%436%6%36%6%5%9%34%
2458
August1st to 15thDay
12%5%35%6%46%5%7%8%35%
2203
16th to endDay
10%4246%45%5%6%8%41%
2124
September1st to 15thDay
13%425%5%45%45%7%41%
1942
16th to endDay
13%5%24423336%51%
1815
October1st to 15thDay
20%6%26%435%34438%
1763
16th to endDay
17%6%26%43445%7%36%
1590
November1st to 15thDay
15%7%35%41335%7%41%
1581
16th to endDay
17%6%35%424335%42%
1587
December1st to 15thDay
15%8%36%5%35%445%36%
1440
16th to endDay
18%10%5%5%5%35%35%7%30%
1536
January1st to 15thNight
12%8%345%25%45%7%39%
2506
16th to endNight
13%8%46%5%245%5%7%38%
2688
February1st to 15thNight
12%8%35%5%36%5%6%7%35%
2217
16th to endNight
14%9%343345%5%7%37%
1893
March1st to 15thNight
16%8%35%5%35%445%37%
2160
16th to endNight
13%5%3433445%7%43%
1914
April1st to 15thNight
16%7%245%3445%6%38%
1646
16th to endNight
18%7%25%5%23445%41%
1543
May1st to 15thNight
18%8%25%5%3445%436%
1476
16th to endNight
18%436%5%3445%7%34%
1367
June1st to 15thNight
24%6%25%425%446%32%
1320
16th to endNight
15%5%25%425%5%48%40%
1320
July1st to 15thNight
12%425%5%26%6%6%7%41%
1320
16th to endNight
11%414425%5%6%9%43%
1402
August1st to 15thNight
10%5%26%5%2445%8%43%
1416
16th to endNight
13%41343346%8%46%
1724
September1st to 15thNight
14%424312446%49%
1688
16th to endNight
12%41241345%7%52%
1815
October1st to 15thNight
19%5%25%42325%7%41%
1864
16th to endNight
19%6%25%42446%6%36%
2282
November1st to 15thNight
15%6%25%434345%43%
2277
16th to endNight
15%6%25%4245%47%40%
2372
December1st to 15thNight
17%7%35%434447%37%
2520
16th to endNight
17%9%25%425%45%7%34%
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
46%5%12%23%10%2
1433
16th to endDay
41%416%24%11%1
1536
February1st to 15thDay
51%5%14%19%9%
1637
16th to endDay
49%311%19%13%2
1580
March1st to 15thDay
49%413%16%12%2
1800
16th to endDay
44%311%20%16%4
2077
April1st to 15thDay
47%39%20%14%3
1972
16th to endDay
46%39%21%16%3
2087
May1st to 15thDay
52%28%20%13%2
2154
16th to endDay
47%5%12%19%12%1
2398
June1st to 15thDay
53%5%12%19%8%
2310
16th to endDay
48%6%13%18%12%1
2310
July1st to 15thDay
44%5%13%21%13%1
2161
16th to endDay
42%5%14%23%12%1
2291
August1st to 15thDay
45%6%13%22%11%1
2189
16th to endDay
39%413%26%14%1
2124
September1st to 15thDay
40%411%24%18%
1942
16th to endDay
35%38%27%22%2
1815
October1st to 15thDay
50%39%24%11%2
1763
16th to endDay
46%414%23%9%1
1590
November1st to 15thDay
42%5%14%23%12%2
1581
16th to endDay
45%313%21%14%1
1587
December1st to 15thDay
48%5%16%19%10%
1440
16th to endDay
55%314%17%9%
1536
January1st to 15thNight
43%5%13%22%11%2
2506
16th to endNight
45%312%21%13%2
2688
February1st to 15thNight
46%5%16%19%10%1
2225
16th to endNight
44%413%24%10%3
1893
March1st to 15thNight
47%312%22%11%2
2160
16th to endNight
39%412%19%19%4
1915
April1st to 15thNight
45%311%20%17%1
1646
16th to endNight
45%211%20%16%3
1543
May1st to 15thNight
49%48%18%15%2
1476
16th to endNight
47%7%13%19%10%1
1369
June1st to 15thNight
52%414%20%7%
1320
16th to endNight
42%6%14%22%12%
1320
July1st to 15thNight
37%6%15%28%11%
1240
16th to endNight
34%7%16%28%10%1
1306
August1st to 15thNight
37%5%15%26%13%1
1406
16th to endNight
34%5%15%29%15%
1724
September1st to 15thNight
34%5%14%27%17%
1688
16th to endNight
30%49%31%21%1
1815
October1st to 15thNight
45%311%23%13%3
1864
16th to endNight
46%414%24%9%
2282
November1st to 15thNight
43%312%23%14%1
2277
16th to endNight
43%314%24%10%2
2372
December1st to 15thNight
47%415%23%8%
2520
16th to endNight
48%415%21%8%
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
25%25%30%11%8%
60
16th to endDay
26%23%31%17%1
64
February1st to 15thDay
30%23%28%14%3
182
16th to endDay
18%26%30%21%3
239
March1st to 15thDay
30%21%30%14%4
270
16th to endDay
17%28%27%15%8%2
245
April1st to 15thDay
25%22%27%12%7%3
210
16th to endDay
21%19%29%14%10%4
210
May1st to 15thDay
31%17%23%15%8%3
228
16th to endDay
17%14%33%23%8%1
267
June1st to 15thDay
28%14%27%18%8%2
255
16th to endDay
18%10%30%29%8%2
255
July1st to 15thDay
17%6%32%27%13%2
245
16th to endDay
13%10%32%30%11%2
270
August1st to 15thDay
13%11%31%25%11%6%
253
16th to endDay
13%7%25%23%22%8%
268
September1st to 15thDay
16%10%23%23%16%9%
255
16th to endDay
19%11%25%17%11%14%
254
October1st to 15thDay
23%14%20%21%14%5%
255
16th to endDay
26%18%26%19%8%
241
November1st to 15thDay
22%17%25%20%12%1
235
16th to endDay
27%22%20%18%9%1
207
December1st to 15thDay
25%31%23%16%11
60
16th to endDay
37%20%31%7%3
64
January1st to 15thNight
22%24%32%17%2
720
16th to endNight
22%24%31%17%2
768
February1st to 15thNight
19%25%35%16%2
704
16th to endNight
24%25%29%16%2
631
March1st to 15thNight
28%20%29%17%3
720
16th to endNight
21%21%27%21%7%
728
April1st to 15thNight
21%22%31%20%3
658
16th to endNight
24%18%26%23%6%
553
May1st to 15thNight
22%17%30%23%6%
486
16th to endNight
20%9%32%26%9%1
343
June1st to 15thNight
26%10%27%26%7%
330
16th to endNight
18%6%30%33%10%
330
July1st to 15thNight
14%5%28%38%11%1
310
16th to endNight
12%332%36%14%
348
August1st to 15thNight
12%7%27%39%12%
425
16th to endNight
15%5%25%32%18%2
674
September1st to 15thNight
15%9%29%27%17%1
660
16th to endNight
15%7%27%28%17%4
657
October1st to 15thNight
24%14%22%24%11%1
660
16th to endNight
24%21%26%21%5%
704
November1st to 15thNight
19%18%27%24%8%1
700
16th to endNight
23%20%26%19%8%1
720
December1st to 15thNight
25%23%31%15%4
720
16th to endNight
27%24%29%15%2
768
Page generated at 2017-03-22 02:42:24. Version ac04

Copyright 2017 A. Danko


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