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 2018-03-21.

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%
15570
18%
49205
7%
15538
38%
15538
19%
31894

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%
780
19%
2716
6%
776
33%
776
13%
1726
January16th to endNight
14%
832
17%
2912
4%
832
31%
832
13%
1876
February1st to 15thNight
11%
764
15%
2414
3%
761
27%
761
13%
1638
February16th to endNight
15%
683
19%
2049
4%
683
33%
683
15%
1365
March1st to 15thNight
17%
780
16%
2340
6%
780
29%
780
14%
1610
March16th to endNight
24%
792
23%
2083
7%
792
37%
792
22%
1362
April1st to 15thNight
20%
718
17%
1796
3%
718
28%
718
20%
1261
April16th to endNight
24%
603
18%
1683
4%
603
33%
603
21%
1133
May1st to 15thNight
24%
530
16%
1610
7%
530
34%
530
16%
1123
May16th to endNight
30%
375
11%
1497
9%
374
39%
374
14%
994
June1st to 15thNight
28%
360
12%
1440
6%
360
41%
360
14%
951
June16th to endNight
37%
360
10%
1440
10%
360
46%
360
19%
907
July1st to 15thNight
46%
340
13%
1360
16%
340
52%
340
24%
790
July16th to endNight
46%
376
16%
1418
16%
354
55%
354
27%
809
August1st to 15thNight
44%
464
16%
1535
11%
462
49%
462
26%
917
August16th to endNight
48%
736
21%
1882
10%
736
51%
736
36%
1166
September1st to 15thNight
37%
720
20%
1842
7%
720
44%
720
34%
1163
September16th to endNight
45%
717
27%
1980
17%
717
53%
717
35%
1175
October1st to 15thNight
34%
720
20%
2034
10%
720
44%
720
23%
1347
October16th to endNight
22%
768
16%
2490
6%
768
36%
768
16%
1650
November1st to 15thNight
26%
760
20%
2472
9%
760
40%
760
19%
1595
November16th to endNight
23%
780
22%
2570
9%
780
39%
780
17%
1602
December1st to 15thNight
16%
780
16%
2730
4%
780
31%
780
13%
1811
December16th to endNight
13%
832
17%
2912
3%
832
30%
832
11%
1923

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%
49655
Night
15%6%25%5%2445%7%39%
49375
Cloud CoverDay
16%6%35%5%35%45%7%36%
49665
Night
15%6%25%42445%7%40%
49380
TransparencyDay
46%412%21%13%1
49343
Night
43%413%23%13%1
49205
SeeingDay
22%17%28%18%9%3
6364
Night
21%17%29%22%7%
15570

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%5%36%7%345%6%8%34%
1552
16th to endDay
13%6%345%3447%9%37%
1664
February1st to 15thDay
14%8%37%6%48%5%5%7%30%
1775
16th to endDay
12%10%37%6%3445%6%34%
1710
March1st to 15thDay
17%9%45%5%445%6%6%30%
1940
16th to endDay
15%7%45%5%33446%39%
2267
April1st to 15thDay
16%7%35%6%35%35%6%36%
2152
16th to endDay
16%7%25%6%245%46%38%
2277
May1st to 15thDay
22%7%37%5%34445%30%
2351
16th to endDay
18%5%35%5%35%447%36%
2618
June1st to 15thDay
23%6%25%5%25%447%31%
2520
16th to endDay
17%6%36%7%35%46%8%31%
2520
July1st to 15thDay
14%6%25%6%35%5%7%8%34%
2520
16th to endDay
13%5%25%6%36%5%6%7%35%
2654
August1st to 15thDay
13%5%25%6%5%5%5%5%8%34%
2403
16th to endDay
10%325%6%445%6%7%42%
2318
September1st to 15thDay
13%5%245%35%46%6%42%
2118
16th to endDay
13%414423335%51%
1980
October1st to 15thDay
19%6%26%5%2443439%
1923
16th to endDay
18%6%35%434448%35%
1734
November1st to 15thDay
15%7%25%424347%41%
1716
16th to endDay
16%7%26%5%23445%41%
1719
December1st to 15thDay
15%8%26%5%35%5%5%6%34%
1560
16th to endDay
18%11%45%5%3445%6%30%
1664
January1st to 15thNight
12%7%25%5%35%5%6%7%38%
2716
16th to endNight
12%8%35%5%35%5%6%7%36%
2912
February1st to 15thNight
12%9%35%5%45%6%5%7%33%
2413
16th to endNight
13%9%35%4246%5%7%36%
2049
March1st to 15thNight
17%9%35%425%45%6%34%
2327
16th to endNight
13%6%2443445%6%43%
2083
April1st to 15thNight
16%7%35%425%45%6%37%
1796
16th to endNight
18%7%15%5%24446%39%
1683
May1st to 15thNight
20%7%25%5%35%446%33%
1610
16th to endNight
18%5%37%6%3445%7%33%
1495
June1st to 15thNight
24%6%245%24238%33%
1440
16th to endNight
16%415%425%45%7%39%
1440
July1st to 15thNight
12%5%235%3446%9%41%
1440
16th to endNight
12%4243236%6%9%43%
1514
August1st to 15thNight
10%5%25%5%3446%8%43%
1545
16th to endNight
13%42332345%9%47%
1882
September1st to 15thNight
14%41431435%6%50%
1842
16th to endNight
12%413324446%52%
1980
October1st to 15thNight
18%6%245%23346%41%
2034
16th to endNight
20%6%244345%6%5%35%
2490
November1st to 15thNight
15%6%25%5%2435%5%41%
2472
16th to endNight
15%5%25%424447%41%
2570
December1st to 15thNight
17%6%35%5%35%45%7%35%
2730
16th to endNight
17%8%35%5%25%45%7%33%
2912

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%5%36%5%36%5%6%7%36%
1552
16th to endDay
13%6%24435%47%8%39%
1664
February1st to 15thDay
14%7%26%6%38%5%6%7%30%
1775
16th to endDay
13%8%47%5%35%45%6%35%
1710
March1st to 15thDay
18%9%45%5%4446%7%30%
1950
16th to endDay
15%6%36%5%23445%41%
2267
April1st to 15thDay
15%7%36%5%35%446%36%
2152
16th to endDay
17%6%26%5%24445%39%
2277
May1st to 15thDay
22%6%36%6%35%445%31%
2351
16th to endDay
18%5%35%5%35%448%36%
2618
June1st to 15thDay
23%6%25%435%45%8%30%
2520
16th to endDay
16%6%26%6%36%5%5%8%31%
2520
July1st to 15thDay
13%5%26%6%45%6%6%8%34%
2520
16th to endDay
13%426%6%36%6%5%9%35%
2654
August1st to 15thDay
11%5%35%6%46%5%7%8%35%
2403
16th to endDay
10%3246%345%6%8%43%
2318
September1st to 15thDay
13%425%5%45%45%7%41%
2118
16th to endDay
13%5%23422336%51%
1980
October1st to 15thDay
19%6%26%425%34440%
1923
16th to endDay
17%6%26%43435%7%37%
1734
November1st to 15thDay
15%7%25%5%23347%41%
1716
16th to endDay
17%6%35%424335%42%
1719
December1st to 15thDay
15%8%36%5%35%5%46%36%
1560
16th to endDay
18%9%5%5%5%3435%6%31%
1664
January1st to 15thNight
12%7%245%35%45%7%40%
2716
16th to endNight
12%8%36%5%245%5%7%37%
2912
February1st to 15thNight
12%8%35%5%36%5%6%7%35%
2406
16th to endNight
13%10%344345%5%7%37%
2049
March1st to 15thNight
17%9%35%5%35%445%35%
2340
16th to endNight
13%5%24434447%43%
2082
April1st to 15thNight
16%8%245%3445%6%38%
1796
16th to endNight
18%7%25%5%23445%40%
1683
May1st to 15thNight
19%8%25%5%3444435%
1610
16th to endNight
19%436%5%35%45%7%33%
1495
June1st to 15thNight
24%6%24425%446%34%
1440
16th to endNight
16%5%25%426%5%47%39%
1440
July1st to 15thNight
12%4245%25%5%6%7%42%
1440
16th to endNight
12%414425%46%9%43%
1514
August1st to 15thNight
10%5%25%5%2446%8%43%
1545
16th to endNight
13%41332346%8%47%
1882
September1st to 15thNight
14%424312446%50%
1842
16th to endNight
12%413414446%52%
1980
October1st to 15thNight
18%5%25%5%2325%7%42%
2034
16th to endNight
20%6%2442446%6%36%
2490
November1st to 15thNight
15%6%35%434345%42%
2472
16th to endNight
14%6%25%424447%41%
2570
December1st to 15thNight
17%7%36%5%34446%36%
2730
16th to endNight
16%9%25%42445%7%35%
2912

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
45%5%11%23%11%2
1553
16th to endDay
41%5%16%24%11%1
1664
February1st to 15thDay
51%5%13%19%8%
1778
16th to endDay
49%311%19%13%2
1710
March1st to 15thDay
51%413%15%12%2
1950
16th to endDay
44%310%19%16%4
2267
April1st to 15thDay
48%39%21%13%3
2152
16th to endDay
46%39%20%16%2
2277
May1st to 15thDay
54%28%19%12%2
2351
16th to endDay
47%5%12%19%12%1
2622
June1st to 15thDay
51%5%12%19%9%
2520
16th to endDay
49%6%13%18%12%1
2520
July1st to 15thDay
44%5%13%20%13%1
2371
16th to endDay
42%5%14%24%12%1
2487
August1st to 15thDay
45%6%13%23%10%1
2389
16th to endDay
37%413%26%15%1
2318
September1st to 15thDay
39%5%11%23%18%1
2118
16th to endDay
35%38%27%23%2
1980
October1st to 15thDay
48%39%25%12%2
1923
16th to endDay
46%313%24%9%1
1734
November1st to 15thDay
42%5%14%23%12%1
1716
16th to endDay
44%313%22%14%1
1719
December1st to 15thDay
48%415%19%11%
1560
16th to endDay
54%313%17%10%
1664
January1st to 15thNight
42%5%13%23%12%2
2716
16th to endNight
45%413%21%13%2
2912
February1st to 15thNight
47%5%15%19%11%
2414
16th to endNight
45%413%23%10%3
2049
March1st to 15thNight
49%312%21%10%2
2340
16th to endNight
39%412%19%19%5%
2083
April1st to 15thNight
46%311%20%17%1
1796
16th to endNight
45%311%20%16%3
1683
May1st to 15thNight
50%48%18%15%2
1610
16th to endNight
48%6%13%19%10%1
1497
June1st to 15thNight
50%413%21%8%
1440
16th to endNight
42%7%13%22%12%
1440
July1st to 15thNight
37%6%15%28%12%
1360
16th to endNight
34%7%16%28%12%1
1418
August1st to 15thNight
36%5%16%25%13%1
1535
16th to endNight
33%414%30%15%
1882
September1st to 15thNight
34%5%13%26%19%
1842
16th to endNight
31%49%31%21%1
1980
October1st to 15thNight
43%311%24%13%2
2034
16th to endNight
46%414%24%9%
2490
November1st to 15thNight
44%411%23%14%1
2472
16th to endNight
41%415%25%11%2
2570
December1st to 15thNight
48%415%22%9%
2730
16th to endNight
47%415%21%10%
2912

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
23%26%33%10%6%
90
16th to endDay
25%23%37%12%1
96
February1st to 15thDay
29%27%27%13%3
233
16th to endDay
20%28%28%19%2
291
March1st to 15thDay
31%20%31%13%3
330
16th to endDay
23%27%27%12%7%2
311
April1st to 15thDay
25%21%30%11%7%2
270
16th to endDay
24%18%29%15%9%3
270
May1st to 15thDay
31%19%24%13%8%2
288
16th to endDay
19%15%34%21%7%
331
June1st to 15thDay
26%13%31%19%7%1
315
16th to endDay
19%14%31%25%6%2
315
July1st to 15thDay
18%9%32%26%11%1
305
16th to endDay
14%8%31%29%11%3
326
August1st to 15thDay
14%11%31%24%12%6%
313
16th to endDay
12%9%28%21%19%7%
332
September1st to 15thDay
16%13%27%20%14%7%
315
16th to endDay
18%11%23%16%14%14%
314
October1st to 15thDay
22%12%23%22%14%5%
315
16th to endDay
28%16%27%19%8%
289
November1st to 15thDay
23%18%26%19%11%1
280
16th to endDay
26%23%21%18%8%1
249
December1st to 15thDay
23%32%23%13%6%1
90
16th to endDay
39%27%25%6%2
96
January1st to 15thNight
22%25%32%18%2
780
16th to endNight
22%24%31%18%2
832
February1st to 15thNight
20%25%35%16%1
764
16th to endNight
24%25%30%16%2
683
March1st to 15thNight
29%19%30%17%3
780
16th to endNight
21%22%27%21%6%
792
April1st to 15thNight
22%21%30%21%4
718
16th to endNight
24%19%26%22%5%
603
May1st to 15thNight
23%17%30%22%6%
530
16th to endNight
21%9%31%27%8%1
375
June1st to 15thNight
26%10%28%26%7%
360
16th to endNight
18%7%31%32%9%
360
July1st to 15thNight
14%5%29%38%10%1
340
16th to endNight
12%331%36%15%
376
August1st to 15thNight
12%6%26%38%13%1
464
16th to endNight
15%5%24%33%19%2
736
September1st to 15thNight
15%9%30%26%16%1
720
16th to endNight
15%7%26%28%18%4
717
October1st to 15thNight
23%13%23%25%12%2
720
16th to endNight
24%22%26%20%7%
768
November1st to 15thNight
20%19%26%23%8%1
760
16th to endNight
22%21%27%19%8%1
780
December1st to 15thNight
25%22%31%16%3
780
16th to endNight
26%25%28%16%2
832
Page generated at 2018-03-22 11:34:26. Version ac04

Copyright 2018 A. Danko


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