Winfree Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winfree Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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
42%
24282
21%
80233
13%
24180
52%
24180
24%
49321

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
23%
755
27%
3990
9%
737
42%
737
15%
2061
January11th to 20thNight
26%
759
28%
3946
10%
740
43%
740
14%
2165
January21st to endNight
22%
832
17%
4445
11%
814
42%
814
14%
2711
February1st to 10thNight
26%
760
21%
2470
11%
760
40%
760
23%
1493
February11th to 20thNight
17%
741
19%
2403
5%
739
35%
739
19%
1522
February21st to endNight
23%
628
25%
1782
9%
628
40%
628
24%
1152
March1st to 10thNight
29%
760
26%
2090
11%
760
43%
760
30%
1299
March11th to 20thNight
27%
752
21%
2068
9%
752
38%
752
22%
1390
March21st to endNight
31%
792
20%
2178
9%
792
40%
792
25%
1444
April1st to 10thNight
29%
720
21%
1870
7%
720
38%
720
27%
1214
April11th to 20thNight
37%
711
23%
1775
9%
711
45%
711
34%
1117
April21st to endNight
37%
678
22%
1758
9%
678
45%
678
30%
1159
May1st to 10thNight
37%
540
16%
1620
7%
540
44%
540
23%
1071
May11th to 20thNight
44%
531
14%
1592
8%
531
48%
531
22%
1103
May21st to endNight
59%
582
15%
1745
12%
582
61%
582
27%
1140
June1st to 10thNight
66%
401
19%
1481
20%
401
68%
401
28%
850
June11th to 20thNight
60%
360
16%
1440
18%
360
65%
360
23%
855
June21st to endNight
69%
483
17%
1563
16%
483
72%
483
30%
942
July1st to 10thNight
66%
525
14%
1575
12%
525
68%
525
27%
1013
July11th to 20thNight
76%
522
16%
1566
14%
522
77%
522
35%
930
July21st to endNight
72%
591
17%
1672
15%
558
73%
558
30%
1058
August1st to 10thNight
64%
537
16%
1600
12%
534
65%
534
25%
1093
August11th to 20thNight
65%
534
19%
1598
17%
534
66%
534
25%
1074
August21st to endNight
65%
792
16%
1980
12%
792
66%
792
30%
1364
September1st to 10thNight
65%
720
22%
1800
15%
720
67%
720
33%
1192
September11th to 20thNight
62%
720
24%
1930
20%
720
63%
720
31%
1261
September21st to endNight
44%
720
19%
2008
14%
720
50%
720
23%
1412
October1st to 10thNight
51%
720
22%
2160
20%
720
58%
720
31%
1323
October11th to 20thNight
46%
720
27%
2160
21%
720
57%
720
30%
1300
October21st to endNight
45%
792
31%
2376
21%
792
60%
792
34%
1355
November1st to 10thNight
42%
740
29%
2221
19%
740
53%
740
31%
1315
November11th to 20thNight
39%
760
27%
2394
15%
760
54%
760
29%
1379
November21st to endNight
39%
760
25%
2660
18%
760
52%
760
27%
1485
December1st to 10thNight
26%
760
21%
2660
10%
760
43%
760
19%
1683
December11th to 20thNight
31%
759
24%
3170
13%
758
47%
758
21%
1827
December21st to endNight
28%
825
16%
4487
10%
817
43%
817
12%
2569

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
14%5%25%5%35%5%6%8%43%
78705
Night
15%5%25%43445%7%45%
81068
TransparencyDay
38%7%12%22%16%4
78426
Night
38%6%11%22%18%4
80866
SeeingDay
19%11%24%25%15%6%
14173
Night
17%9%26%31%16%2
24308

By Month

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 10thDay
17%4243245%47%48%
2836
11th to 20thDay
14%6%25%43445%6%44%
2840
21st to endDay
21%7%35%424445%41%
3124
February1st to 10thDay
13%7%25%6%35%5%6%8%42%
1710
11th to 20thDay
19%5%145%345%5%6%43%
1663
21st to endDay
19%8%35%435%45%6%38%
1668
March1st to 10thDay
14%6%24424346%50%
2090
11th to 20thDay
16%6%36%5%35%47%7%40%
2058
21st to endDay
17%7%36%5%335%5%6%39%
2178
April1st to 10thDay
11%5%145%245%5%6%51%
2088
11th to 20thDay
13%5%3443445%8%48%
2134
21st to endDay
16%5%35%5%345%5%7%42%
2217
May1st to 10thDay
13%6%35%5%35%7%6%9%39%
2340
11th to 20thDay
17%5%26%5%35%5%6%9%37%
2301
21st to endDay
13%5%25%7%45%5%7%9%39%
2531
June1st to 10thDay
10%425%5%35%5%6%10%45%
2470
11th to 20thDay
11%425%5%36%6%8%11%39%
2520
21st to endDay
8%5%25%5%36%6%8%11%42%
2388
July1st to 10thDay
9%5%25%6%47%6%8%9%39%
2340
11th to 20thDay
5%425%6%46%8%8%11%40%
2340
21st to endDay
9%5%36%6%5%7%6%7%11%35%
2547
August1st to 10thDay
12%5%36%6%45%6%7%11%36%
2327
11th to 20thDay
12%6%26%7%46%7%6%9%34%
2284
21st to endDay
11%6%26%6%346%7%11%39%
2376
September1st to 10thDay
12%6%25%43446%7%48%
2160
11th to 20thDay
13%6%35%4345%5%7%45%
2026
21st to endDay
21%6%26%5%3445%7%38%
1950
October1st to 10thDay
16%5%24423346%51%
1800
11th to 20thDay
16%424323446%52%
1800
21st to endDay
13%6%24434345%52%
1980
November1st to 10thDay
13%423334445%56%
1857
11th to 20thDay
15%5%245%24446%50%
1780
21st to endDay
15%5%1432345%8%50%
1520
December1st to 10thDay
17%7%24435%6%6%8%38%
1520
11th to 20thDay
16%5%23423336%54%
1910
21st to endDay
20%5%35%5%35%45%8%38%
3032
January1st to 10thNight
14%6%35%434446%49%
4109
11th to 20thNight
16%6%34423446%48%
4120
21st to endNight
21%7%25%433345%42%
4532
February1st to 10thNight
14%6%25%4245%6%8%44%
2470
11th to 20thNight
19%7%34333445%43%
2403
21st to endNight
16%6%345%345%5%7%43%
1782
March1st to 10thNight
14%425%42446%6%48%
2090
11th to 20thNight
18%4245%45%5%5%7%40%
2068
21st to endNight
16%5%25%5%3445%8%43%
2178
April1st to 10thNight
14%6%2443445%8%45%
1870
11th to 20thNight
12%5%25%42445%8%49%
1775
21st to endNight
15%5%25%5%3445%7%44%
1758
May1st to 10thNight
14%5%25%6%35%5%7%7%41%
1620
11th to 20thNight
17%8%35%5%3446%8%37%
1592
21st to endNight
16%425%5%35%45%8%42%
1744
June1st to 10thNight
9%425%435%5%7%12%43%
1481
11th to 20thNight
10%436%6%35%5%6%8%45%
1440
21st to endNight
8%424436%6%6%11%45%
1563
July1st to 10thNight
9%5%36%5%35%5%6%9%43%
1620
11th to 20thNight
5%424437%5%8%11%47%
1620
21st to endNight
7%5%26%5%47%5%9%10%41%
1771
August1st to 10thNight
11%5%36%6%46%5%6%10%37%
1611
11th to 20thNight
11%7%35%6%35%6%6%9%38%
1598
21st to endNight
11%6%26%6%46%6%6%10%39%
1980
September1st to 10thNight
12%5%25%435%5%5%9%45%
1800
11th to 20thNight
14%6%25%5%45%5%5%7%44%
1930
21st to endNight
22%7%35%433446%38%
2008
October1st to 10thNight
16%5%25%423336%49%
2160
11th to 20thNight
14%5%25%43445%6%50%
2160
21st to endNight
14%314333446%54%
2376
November1st to 10thNight
14%5%35%32333454%
2221
11th to 20thNight
13%5%24424446%52%
2394
21st to endNight
13%3244345%5%7%50%
2660
December1st to 10thNight
18%7%34424445%43%
2660
11th to 20thNight
16%6%245%33347%46%
3285
21st to endNight
17%6%25%5%345%6%8%39%
4619

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
35%48%30%17%6%
2837
11th to 20thDay
39%5%8%20%23%5%
2840
21st to endDay
46%5%7%22%17%3
3124
February1st to 10thDay
39%5%12%24%16%3
1710
11th to 20thDay
41%5%10%22%19%5%
1672
21st to endDay
46%6%11%15%17%5%
1668
March1st to 10thDay
35%5%10%23%21%6%
2090
11th to 20thDay
42%7%10%18%17%7%
2058
21st to endDay
45%6%11%20%15%4
2178
April1st to 10thDay
32%5%12%24%19%8%
2088
11th to 20thDay
36%5%11%22%20%6%
2134
21st to endDay
42%7%11%22%14%5%
2217
May1st to 10thDay
39%9%16%20%12%3
2340
11th to 20thDay
43%9%14%22%10%2
2305
21st to endDay
40%9%16%24%11%
2531
June1st to 10thDay
34%9%17%26%14%1
2470
11th to 20thDay
36%11%17%20%15%2
2520
21st to endDay
34%10%18%23%14%2
2388
July1st to 10thDay
38%11%16%19%14%3
2275
11th to 20thDay
33%11%20%20%15%1
2271
21st to endDay
40%10%15%22%13%1
2405
August1st to 10thDay
41%9%17%24%9%1
2314
11th to 20thDay
43%10%16%20%10%1
2284
21st to endDay
37%9%18%21%13%2
2376
September1st to 10thDay
35%9%13%20%19%4
2160
11th to 20thDay
37%7%10%24%19%3
2026
21st to endDay
47%6%9%17%18%2
1950
October1st to 10thDay
36%410%26%20%4
1800
11th to 20thDay
34%5%10%26%21%5%
1800
21st to endDay
36%48%26%20%7%
1980
November1st to 10thDay
31%49%24%26%5%
1857
11th to 20thDay
35%49%22%21%8%
1780
21st to endDay
34%410%23%24%4
1520
December1st to 10thDay
43%6%12%20%16%4
1520
11th to 20thDay
34%39%25%21%7%
1906
21st to endDay
42%5%12%26%13%2
3032
January1st to 10thNight
36%48%25%22%5%
4109
11th to 20thNight
38%5%8%20%24%5%
4120
21st to endNight
45%46%24%15%6%
4532
February1st to 10thNight
37%6%12%24%19%3
2470
11th to 20thNight
42%48%20%19%7%
2405
21st to endNight
41%5%11%23%15%6%
1782
March1st to 10thNight
35%5%11%24%21%5%
2090
11th to 20thNight
41%7%9%18%20%4
2068
21st to endNight
40%7%11%20%17%5%
2178
April1st to 10thNight
37%6%11%19%21%6%
1870
11th to 20thNight
34%5%12%21%22%6%
1775
21st to endNight
38%7%11%23%17%4
1758
May1st to 10thNight
39%9%13%20%14%4
1620
11th to 20thNight
45%8%13%21%11%2
1593
21st to endNight
39%8%16%24%11%1
1745
June1st to 10thNight
33%8%16%28%15%1
1481
11th to 20thNight
37%8%17%20%15%2
1440
21st to endNight
30%11%17%21%17%4
1563
July1st to 10thNight
36%10%17%18%15%5%
1575
11th to 20thNight
29%10%22%24%13%2
1566
21st to endNight
35%10%17%25%13%
1672
August1st to 10thNight
41%10%16%20%12%1
1600
11th to 20thNight
41%9%15%22%12%1
1598
21st to endNight
39%9%17%22%10%3
1980
September1st to 10thNight
36%8%15%19%17%5%
1800
11th to 20thNight
37%8%11%23%19%2
1930
21st to endNight
48%5%8%19%17%3
2008
October1st to 10thNight
38%410%25%20%3
2160
11th to 20thNight
36%5%8%25%21%5%
2160
21st to endNight
32%48%23%26%7%
2376
November1st to 10thNight
35%5%8%20%25%8%
2221
11th to 20thNight
33%5%9%21%24%8%
2394
21st to endNight
34%5%8%25%22%6%
2660
December1st to 10thNight
44%5%8%24%16%4
2660
11th to 20thNight
38%49%21%21%7%
3288
21st to endNight
40%6%11%23%18%2
4619

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
26%27%26%17%41
270
11th to 20thDay
30%21%34%14%1
270
21st to endDay
29%22%33%13%3
297
February1st to 10thDay
23%22%37%12%5%
270
11th to 20thDay
40%22%29%6%3
270
21st to endDay
32%19%30%16%4
347
March1st to 10thDay
26%17%30%21%5%
460
11th to 20thDay
20%23%32%19%5%
449
21st to endDay
23%17%33%21%5%1
462
April1st to 10thDay
22%20%28%22%8%1
420
11th to 20thDay
19%15%29%21%12%3
412
21st to endDay
24%11%31%22%11%1
420
May1st to 10thDay
21%13%32%22%10%3
423
11th to 20thDay
19%10%25%27%15%4
447
21st to endDay
20%320%30%20%8%
485
June1st to 10thDay
12%425%31%21%6%
450
11th to 20thDay
11%7%21%32%18%10%
450
21st to endDay
10%424%33%22%6%
450
July1st to 10thDay
10%415%28%30%13%
445
11th to 20thDay
5%114%36%30%13%
444
21st to endDay
10%218%31%28%11%
488
August1st to 10thDay
14%6%16%26%26%13%
446
11th to 20thDay
12%315%28%28%14%
439
21st to endDay
12%313%27%27%19%
495
September1st to 10thDay
14%413%25%25%19%
450
11th to 20thDay
15%413%30%26%12%
450
21st to endDay
26%8%18%25%18%5%
450
October1st to 10thDay
22%6%17%31%18%6%
450
11th to 20thDay
16%12%22%28%19%3
450
21st to endDay
17%11%29%30%10%3
495
November1st to 10thDay
18%7%30%27%13%3
455
11th to 20thDay
19%15%27%25%12%2
352
21st to endDay
19%19%26%24%8%3
180
December1st to 10thDay
25%15%34%18%7%1
180
11th to 20thDay
24%13%31%25%6%2
180
21st to endDay
27%14%33%18%6%2
272
January1st to 10thNight
20%16%36%25%4
760
11th to 20thNight
18%18%32%30%3
760
21st to endNight
18%14%41%24%3
836
February1st to 10thNight
16%15%38%27%3
760
11th to 20thNight
25%17%37%20%1
743
21st to endNight
21%14%38%24%3
628
March1st to 10thNight
17%15%36%28%4
760
11th to 20thNight
23%13%33%25%6%1
752
21st to endNight
19%12%35%29%6%
792
April1st to 10thNight
18%15%34%25%7%
720
11th to 20thNight
14%13%32%29%12%
711
21st to endNight
18%6%31%36%8%
678
May1st to 10thNight
16%9%30%30%14%1
540
11th to 20thNight
20%6%22%34%17%1
531
21st to endNight
18%113%33%31%4
584
June1st to 10thNight
9%116%43%29%2
401
11th to 20thNight
12%216%40%27%3
360
21st to endNight
8%212%45%30%3
483
July1st to 10thNight
11%210%37%36%5%
525
11th to 20thNight
6%9%32%47%5%
522
21st to endNight
8%18%43%35%4
591
August1st to 10thNight
13%28%39%32%6%
537
11th to 20thNight
14%26%39%34%4
534
21st to endNight
13%210%35%35%5%
792
September1st to 10thNight
15%28%32%36%7%
720
11th to 20thNight
16%311%34%32%5%
720
21st to endNight
25%5%18%30%22%1
720
October1st to 10thNight
19%419%28%25%5%
720
11th to 20thNight
16%8%23%34%17%2
720
21st to endNight
16%7%27%35%13%1
792
November1st to 10thNight
17%6%29%34%13%2
740
11th to 20thNight
16%11%30%30%12%1
760
21st to endNight
14%11%31%33%10%1
760
December1st to 10thNight
23%10%34%27%6%1
760
11th to 20thNight
17%10%35%32%5%
760
21st to endNight
21%12%33%31%4
836
Page generated at 2024-03-15 14:01:39. Version ac07

Copyright © 2024 Attilla Danko.


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