Forest Acres Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Forest Acres Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
49%
24333
22%
74382
15%
24280
56%
24280
27%
46738

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
31%
759
23%
2459
11%
757
47%
757
24%
1507
January11th to 20thNight
34%
736
24%
2391
12%
736
49%
736
24%
1465
January21st to endNight
30%
792
27%
2574
16%
792
45%
792
26%
1552
February1st to 10thNight
35%
720
21%
2327
13%
720
47%
720
24%
1445
February11th to 20thNight
28%
702
22%
2098
11%
699
41%
699
24%
1353
February21st to endNight
29%
592
25%
1715
11%
592
43%
592
26%
1097
March1st to 10thNight
38%
720
27%
1980
16%
720
48%
720
32%
1226
March11th to 20thNight
34%
720
22%
1980
12%
720
42%
720
26%
1296
March21st to endNight
35%
792
22%
2178
9%
792
45%
792
28%
1407
April1st to 10thNight
40%
720
24%
1980
12%
720
48%
720
32%
1186
April11th to 20thNight
44%
711
25%
1794
12%
711
51%
711
36%
1124
April21st to endNight
50%
634
29%
1714
16%
634
57%
634
38%
1004
May1st to 10thNight
49%
540
22%
1620
12%
540
55%
540
33%
962
May11th to 20thNight
52%
531
15%
1593
9%
531
56%
531
25%
1055
May21st to endNight
65%
582
20%
1744
16%
582
67%
582
28%
1115
June1st to 10thNight
61%
540
14%
1620
12%
540
63%
540
23%
1096
June11th to 20thNight
65%
540
14%
1620
11%
540
66%
540
27%
1059
June21st to endNight
67%
540
13%
1620
10%
540
68%
540
23%
1105
July1st to 10thNight
68%
525
12%
1575
10%
525
68%
525
24%
1075
July11th to 20thNight
72%
522
11%
1566
10%
522
72%
522
24%
1054
July21st to endNight
70%
591
13%
1672
11%
558
71%
558
24%
1156
August1st to 10thNight
68%
537
11%
1600
10%
534
68%
534
21%
1139
August11th to 20thNight
64%
534
14%
1598
13%
534
64%
534
22%
1123
August21st to endNight
62%
754
14%
1942
10%
754
62%
754
24%
1392
September1st to 10thNight
66%
720
19%
1977
17%
720
67%
720
29%
1299
September11th to 20thNight
61%
720
20%
1980
17%
720
63%
720
26%
1352
September21st to endNight
57%
720
19%
1980
16%
720
60%
720
27%
1327
October1st to 10thNight
56%
720
26%
2081
24%
720
61%
720
33%
1255
October11th to 20thNight
54%
720
30%
2160
27%
720
62%
720
35%
1218
October21st to endNight
54%
792
32%
2376
26%
792
64%
792
36%
1349
November1st to 10thNight
53%
740
29%
2221
23%
740
61%
740
35%
1259
November11th to 20thNight
43%
760
28%
2375
21%
760
54%
760
31%
1384
November21st to endNight
47%
760
26%
2470
22%
760
56%
760
30%
1448
December1st to 10thNight
39%
760
23%
2470
15%
760
51%
760
22%
1602
December11th to 20thNight
43%
759
28%
2922
21%
758
53%
758
24%
1658
December21st to endNight
35%
828
16%
4410
16%
817
45%
817
13%
2594

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
12%5%25%5%35%5%6%8%43%
74936
Night
13%5%25%5%345%5%7%45%
74832
TransparencyDay
38%8%12%20%18%5%
74659
Night
38%7%11%18%19%7%
74628
SeeingDay
15%8%22%24%20%10%
14206
Night
15%6%22%32%21%3
24346

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
16%6%2442345%6%46%
1706
11th to 20thDay
15%7%245%345%4446%
1647
21st to endDay
16%6%25%434335%48%
1782
February1st to 10thDay
16%6%36%5%35%45%8%41%
1629
11th to 20thDay
19%6%245%23346%45%
1748
21st to endDay
19%5%36%344346%43%
1539
March1st to 10thDay
13%5%24423446%53%
1980
11th to 20thDay
15%6%35%5%35%46%6%43%
1980
21st to endDay
15%6%25%5%345%6%7%42%
2178
April1st to 10thDay
10%3244345%6%7%52%
1980
11th to 20thDay
11%5%25%4245%6%8%48%
2112
21st to endDay
8%42443446%9%52%
2259
May1st to 10thDay
8%4245%35%5%6%8%50%
2340
11th to 20thDay
12%5%26%5%35%5%6%8%42%
2301
21st to endDay
10%5%26%6%46%5%7%9%38%
2531
June1st to 10thDay
10%6%27%6%36%7%7%11%37%
2340
11th to 20thDay
8%4245%46%6%7%11%43%
2340
21st to endDay
5%435%7%46%7%8%12%39%
2340
July1st to 10thDay
7%5%26%7%48%8%7%12%33%
2340
11th to 20thDay
7%5%36%7%47%7%9%12%33%
2340
21st to endDay
6%426%7%47%8%10%12%33%
2547
August1st to 10thDay
9%5%27%7%5%7%8%9%10%31%
2327
11th to 20thDay
12%6%36%7%5%6%8%8%9%30%
2303
21st to endDay
12%6%36%6%5%6%6%9%11%30%
2393
September1st to 10thDay
8%426%7%46%6%7%9%42%
1980
11th to 20thDay
12%6%35%5%36%5%6%8%41%
1980
21st to endDay
17%6%25%5%345%47%43%
1980
October1st to 10thDay
14%6%25%433446%49%
1877
11th to 20thDay
11%4245%33345%57%
1800
21st to endDay
12%42442333458%
1980
November1st to 10thDay
12%6%13434445%55%
1857
11th to 20thDay
14%5%33423346%53%
1803
21st to endDay
14%5%35%5%23447%49%
1710
December1st to 10thDay
18%7%26%5%3445%6%39%
1710
11th to 20thDay
16%414423446%51%
2153
21st to endDay
19%7%25%32335%6%44%
3124
January1st to 10thNight
16%7%36%333445%47%
2459
11th to 20thNight
14%6%345%34446%46%
2391
21st to endNight
16%6%345%23445%48%
2574
February1st to 10thNight
17%6%25%43445%7%43%
2327
11th to 20thNight
18%6%35%434345%45%
2098
21st to endNight
15%6%35%43445%6%44%
1715
March1st to 10thNight
13%6%25%424446%50%
1980
11th to 20thNight
15%425%5%4446%6%44%
1980
21st to endNight
12%5%35%6%345%5%8%44%
2178
April1st to 10thNight
11%424425%45%8%52%
1980
11th to 20thNight
12%425%43345%6%53%
1794
21st to endNight
10%325%424448%54%
1714
May1st to 10thNight
7%5%25%5%35%46%9%50%
1620
11th to 20thNight
10%426%6%46%6%6%10%39%
1592
21st to endNight
10%425%6%45%7%6%10%43%
1744
June1st to 10thNight
12%5%26%6%45%7%8%10%35%
1620
11th to 20thNight
8%5%25%7%47%5%8%10%39%
1620
21st to endNight
6%5%26%6%48%7%10%13%33%
1620
July1st to 10thNight
8%6%36%7%46%7%8%11%34%
1620
11th to 20thNight
8%5%25%6%46%7%9%12%35%
1620
21st to endNight
6%437%8%46%7%9%12%34%
1771
August1st to 10thNight
9%5%27%7%5%7%8%9%11%31%
1611
11th to 20thNight
10%7%36%6%5%6%7%7%10%33%
1598
21st to endNight
11%6%36%7%45%7%7%11%33%
1942
September1st to 10thNight
8%5%36%6%46%5%7%10%40%
1977
11th to 20thNight
11%6%37%6%45%5%6%6%42%
1980
21st to endNight
16%6%25%5%25%5%5%6%42%
1980
October1st to 10thNight
14%6%25%324346%52%
2081
11th to 20thNight
13%5%2442345%6%54%
2160
21st to endNight
11%42442445%6%55%
2376
November1st to 10thNight
12%5%24313445%56%
2221
11th to 20thNight
14%6%24333346%53%
2375
21st to endNight
14%5%25%43446%7%48%
2470
December1st to 10thNight
17%6%346%24446%42%
2470
11th to 20thNight
17%5%24323335%52%
3042
21st to endNight
19%7%35%4345%46%40%
4532

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
39%5%9%19%22%6%
1707
11th to 20thDay
41%5%8%17%22%7%
1647
21st to endDay
40%4419%25%8%
1782
February1st to 10thDay
42%5%10%19%18%6%
1629
11th to 20thDay
42%45%19%25%6%
1758
21st to endDay
44%5%8%15%20%9%
1539
March1st to 10thDay
35%48%21%22%10%
1980
11th to 20thDay
42%6%11%18%17%7%
1980
21st to endDay
41%6%10%18%20%5%
2178
April1st to 10thDay
31%6%10%20%26%7%
1980
11th to 20thDay
34%6%10%19%21%10%
2112
21st to endDay
29%7%11%26%23%4
2259
May1st to 10thDay
32%7%13%23%21%4
2340
11th to 20thDay
39%9%14%19%17%2
2305
21st to endDay
40%9%12%23%15%1
2531
June1st to 10thDay
39%10%15%23%11%2
2340
11th to 20thDay
33%9%18%26%12%2
2340
21st to endDay
35%11%18%22%13%2
2340
July1st to 10thDay
39%14%18%17%10%3
2275
11th to 20thDay
39%15%21%17%7%1
2271
21st to endDay
37%13%21%21%8%1
2405
August1st to 10thDay
43%12%17%19%7%1
2314
11th to 20thDay
45%13%16%17%8%1
2303
21st to endDay
44%13%16%17%8%2
2393
September1st to 10thDay
36%10%13%18%18%4
1980
11th to 20thDay
40%9%11%16%21%3
1980
21st to endDay
41%7%8%20%17%7%
1980
October1st to 10thDay
36%48%21%24%7%
1877
11th to 20thDay
29%49%24%26%8%
1800
21st to endDay
31%46%17%30%12%
1980
November1st to 10thDay
32%46%17%27%12%
1857
11th to 20thDay
33%47%20%24%11%
1803
21st to endDay
37%48%19%22%10%
1710
December1st to 10thDay
44%6%9%19%17%6%
1710
11th to 20thDay
35%46%21%24%10%
2150
21st to endDay
42%47%21%23%3
3124
January1st to 10thNight
40%47%17%24%7%
2459
11th to 20thNight
40%5%9%17%22%8%
2391
21st to endNight
39%45%19%24%9%
2574
February1st to 10thNight
41%49%18%19%9%
2327
11th to 20thNight
42%46%19%21%8%
2099
21st to endNight
39%5%9%18%18%11%
1715
March1st to 10thNight
36%48%16%23%12%
1980
11th to 20thNight
40%7%11%16%20%7%
1980
21st to endNight
38%6%11%20%19%6%
2178
April1st to 10thNight
32%6%11%19%23%9%
1980
11th to 20thNight
32%5%9%21%21%11%
1794
21st to endNight
29%6%11%25%24%5%
1714
May1st to 10thNight
31%8%13%24%20%5%
1620
11th to 20thNight
40%9%15%18%16%1
1593
21st to endNight
35%10%12%25%15%3
1745
June1st to 10thNight
40%11%16%20%11%1
1620
11th to 20thNight
38%10%17%23%9%3
1620
21st to endNight
38%14%18%18%10%2
1620
July1st to 10thNight
39%12%21%14%10%4
1575
11th to 20thNight
37%13%24%17%7%2
1566
21st to endNight
39%13%22%17%8%1
1672
August1st to 10thNight
41%15%20%18%6%1
1600
11th to 20thNight
43%11%21%16%8%1
1598
21st to endNight
41%13%17%18%9%2
1942
September1st to 10thNight
37%9%16%19%14%5%
1977
11th to 20thNight
41%9%11%16%19%3
1980
21st to endNight
41%7%12%17%18%5%
1980
October1st to 10thNight
34%5%9%18%28%6%
2081
11th to 20thNight
32%410%21%23%11%
2160
21st to endNight
30%5%6%18%27%13%
2376
November1st to 10thNight
31%5%8%15%27%15%
2221
11th to 20thNight
34%5%6%17%25%13%
2375
21st to endNight
36%48%18%24%10%
2470
December1st to 10thNight
43%7%8%17%19%7%
2470
11th to 20thNight
36%36%18%26%10%
3044
21st to endNight
45%47%20%20%4
4532

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
16%20%44%16%4
270
11th to 20thDay
20%17%37%18%7%
249
21st to endDay
20%24%36%16%3
264
February1st to 10thDay
20%22%33%20%5%
240
11th to 20thDay
33%14%38%13%2
240
21st to endDay
25%14%37%18%5%
257
March1st to 10thDay
18%16%31%27%8%
420
11th to 20thDay
18%15%39%20%8%
420
21st to endDay
19%13%32%23%11%1
462
April1st to 10thDay
16%15%29%26%13%1
420
11th to 20thDay
13%14%29%22%18%4
412
21st to endDay
13%10%27%26%17%8%
420
May1st to 10thDay
10%11%32%22%20%5%
423
11th to 20thDay
15%5%18%26%24%11%
447
21st to endDay
14%5%12%24%25%20%
485
June1st to 10thDay
11%312%29%32%13%
450
11th to 20thDay
11%415%23%28%19%
450
21st to endDay
8%213%31%28%18%
450
July1st to 10thDay
10%18%22%30%29%
445
11th to 20thDay
10%29%20%35%23%
444
21st to endDay
6%110%29%32%22%
488
August1st to 10thDay
13%313%23%27%20%
446
11th to 20thDay
16%29%22%28%22%
439
21st to endDay
13%111%21%32%22%
495
September1st to 10thDay
10%29%28%33%18%
450
11th to 20thDay
15%313%22%32%15%
450
21st to endDay
20%116%25%27%11%
450
October1st to 10thDay
17%319%30%21%9%
450
11th to 20thDay
11%6%23%26%23%10%
450
21st to endDay
14%5%26%29%19%6%
495
November1st to 10thDay
16%6%28%25%19%5%
455
11th to 20thDay
20%10%29%28%10%2
363
21st to endDay
13%13%31%27%14%1
270
December1st to 10thDay
25%13%34%20%6%1
270
11th to 20thDay
21%11%36%20%10%1
270
21st to endDay
25%15%31%19%7%3
297
January1st to 10thNight
22%11%30%29%8%
760
11th to 20thNight
19%10%32%32%7%
736
21st to endNight
20%10%35%32%3
792
February1st to 10thNight
20%12%29%34%5%
720
11th to 20thNight
22%12%33%31%3
703
21st to endNight
19%13%33%29%7%
592
March1st to 10thNight
16%10%32%37%5%
720
11th to 20thNight
18%9%35%30%8%
720
21st to endNight
16%11%33%30%10%
792
April1st to 10thNight
14%12%31%31%11%
720
11th to 20thNight
12%11%28%32%15%
711
21st to endNight
13%6%27%39%15%
634
May1st to 10thNight
11%7%28%37%17%
540
11th to 20thNight
12%225%38%20%3
531
21st to endNight
10%213%36%35%4
584
June1st to 10thNight
13%212%39%29%5%
540
11th to 20thNight
10%212%33%33%11%
540
21st to endNight
9%111%37%34%7%
540
July1st to 10thNight
9%19%33%39%9%
525
11th to 20thNight
10%15%30%47%7%
522
21st to endNight
7%28%32%45%6%
591
August1st to 10thNight
11%18%27%44%9%
537
11th to 20thNight
14%16%30%41%7%
534
21st to endNight
13%112%25%41%8%
754
September1st to 10thNight
10%29%28%44%7%
720
11th to 20thNight
15%113%27%39%5%
720
21st to endNight
19%213%32%30%4
720
October1st to 10thNight
15%318%29%29%5%
720
11th to 20thNight
15%5%21%32%25%3
720
21st to endNight
12%6%24%32%24%2
792
November1st to 10thNight
14%6%23%34%19%3
740
11th to 20thNight
16%9%27%32%14%1
760
21st to endNight
15%7%24%35%18%1
760
December1st to 10thNight
19%9%26%35%10%1
760
11th to 20thNight
19%7%25%36%11%1
760
21st to endNight
24%10%24%31%10%
836
Page generated at 2024-01-11 13:31:59. Version ac07

Copyright 2024 Attilla Danko


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