Sheridan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sheridan clear sky chart from 2005-11-06 to 2024-11-02.

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
55%
25715
21%
94133
17%
25549
60%
25549
30%
52247

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
50%
931
21%
4326
15%
926
54%
926
21%
2425
January11th to 20thNight
42%
944
20%
4378
13%
930
50%
930
19%
2627
January21st to endNight
42%
891
15%
4399
13%
881
51%
881
20%
2349
February1st to 10thNight
40%
760
16%
2470
13%
760
46%
760
21%
1648
February11th to 20thNight
41%
741
15%
2403
12%
740
45%
740
23%
1554
February21st to endNight
47%
628
21%
1921
16%
628
54%
628
29%
1188
March1st to 10thNight
49%
752
29%
3581
15%
744
56%
744
26%
1755
March11th to 20thNight
50%
745
19%
3460
14%
740
56%
740
24%
1805
March21st to endNight
45%
750
10%
3680
12%
738
51%
738
14%
2451
April1st to 10thNight
45%
570
16%
1900
12%
570
53%
570
24%
1186
April11th to 20thNight
42%
563
15%
1877
15%
563
46%
563
23%
1197
April21st to endNight
50%
570
17%
1781
16%
570
54%
570
29%
1105
May1st to 10thNight
55%
565
18%
2443
13%
559
59%
559
20%
1582
May11th to 20thNight
56%
551
16%
2448
14%
541
58%
541
22%
1295
May21st to endNight
55%
605
10%
2738
10%
593
57%
593
21%
1479
June1st to 10thNight
60%
570
14%
1520
10%
570
61%
570
37%
931
June11th to 20thNight
56%
570
14%
1520
9%
570
58%
570
38%
920
June21st to endNight
69%
570
19%
1520
14%
570
71%
570
50%
810
July1st to 10thNight
75%
543
21%
2175
15%
535
78%
535
42%
953
July11th to 20thNight
75%
538
22%
2086
20%
533
78%
533
41%
1029
July21st to endNight
81%
608
22%
2226
25%
569
84%
569
43%
1070
August1st to 10thNight
76%
557
23%
2509
24%
545
79%
545
31%
1300
August11th to 20thNight
79%
548
24%
2540
28%
544
82%
544
35%
1201
August21st to endNight
75%
616
27%
2915
33%
605
79%
605
41%
1118
September1st to 10thNight
73%
570
32%
1900
33%
570
78%
570
49%
876
September11th to 20thNight
71%
570
32%
1900
34%
570
75%
570
44%
930
September21st to endNight
65%
703
30%
2157
26%
703
69%
703
47%
1092
October1st to 10thNight
55%
760
25%
2280
20%
760
59%
760
35%
1344
October11th to 20thNight
53%
760
29%
2280
19%
760
60%
760
37%
1295
October21st to endNight
54%
902
27%
2574
17%
902
61%
902
40%
1439
November1st to 10thNight
53%
935
23%
2465
16%
935
57%
935
36%
1527
November11th to 20thNight
48%
950
26%
2660
17%
950
54%
950
35%
1592
November21st to endNight
52%
950
24%
2660
16%
950
58%
950
38%
1546
December1st to 10thNight
47%
950
20%
2660
13%
950
52%
950
32%
1691
December11th to 20thNight
52%
949
26%
3122
17%
949
57%
949
36%
1659
December21st to endNight
44%
1030
15%
4659
12%
1026
51%
1026
24%
2278

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
6%6%25%445%46%8%50%
101599
Night
6%7%36%44446%8%49%
97629
TransparencyDay
29%7%13%26%19%6%
101342
Night
31%7%14%26%17%5%
97476
SeeingDay
10%8%23%34%20%5%
15895
Night
9%5%23%43%17%2
25910

By Month

Percentage Cloud Cover SW (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
38%38%5%5%6%5%7%7%43%
2538
11th to 20thDay
36%37%46%6%5%7%9%45%
2540
21st to endDay
25%25%44445%8%57%
3054
February1st to 10thDay
413%6%9%6%5%445%7%37%
1710
11th to 20thDay
312%5%9%45%5%36%8%40%
1665
21st to endDay
38%49%5%5%448%9%40%
1532
March1st to 10thDay
37%36%45%446%9%50%
3220
11th to 20thDay
5%8%36%34446%8%50%
3490
21st to endDay
10%14%48%45%5%47%10%28%
3948
April1st to 10thDay
9%11%36%4445%6%7%41%
2280
11th to 20thDay
10%10%37%45%5%47%9%36%
2251
21st to endDay
14%8%36%445%5%6%8%38%
2398
May1st to 10thDay
18%9%37%5%45%46%6%34%
4394
11th to 20thDay
9%5%26%445%46%8%47%
4388
21st to endDay
12%6%25%436%5%7%9%41%
4825
June1st to 10thDay
8%41445%5%6%8%10%44%
2660
11th to 20thDay
6%425%45%5%5%9%9%46%
2660
21st to endDay
43143446%7%8%58%
2660
July1st to 10thDay
4213345%5%8%8%58%
4430
11th to 20thDay
1112335%6%8%9%61%
4430
21st to endDay
2214345%47%9%60%
4802
August1st to 10thDay
7%425%445%5%7%9%47%
4168
11th to 20thDay
3315%345%5%7%8%56%
4028
21st to endDay
321423336%8%65%
4222
September1st to 10thDay
6%31323435%6%64%
2280
11th to 20thDay
7%31323335%6%63%
2280
21st to endDay
10%41323335%5%62%
2018
October1st to 10thDay
10%8%25%243345%54%
1900
11th to 20thDay
10%6%25%43435%6%54%
1900
21st to endDay
6%9%36%44435%7%49%
2004
November1st to 10thDay
5%8%37%435%45%8%48%
1644
11th to 20thDay
5%7%345%45%47%7%50%
1520
21st to endDay
6%7%25%44346%8%51%
1520
December1st to 10thDay
37%27%5%6%5%47%8%46%
1520
11th to 20thDay
25%25%43446%8%57%
1926
21st to endDay
37%34445%46%9%50%
2794
January1st to 10thNight
39%5%9%445%46%8%43%
4417
11th to 20thNight
38%311%8%6%5%46%6%40%
4430
21st to endNight
48%38%445%45%7%47%
4640
February1st to 10thNight
311%5%12%6%6%5%5%5%6%36%
2470
11th to 20thNight
412%5%9%6%5%5%46%6%39%
2402
21st to endNight
28%410%6%5%446%8%43%
1921
March1st to 10thNight
28%37%5%4447%9%46%
3645
11th to 20thNight
6%8%26%44445%7%49%
3490
21st to endNight
8%13%49%5%4446%8%33%
3701
April1st to 10thNight
10%11%25%44446%8%42%
1900
11th to 20thNight
10%8%37%5%46%46%9%37%
1877
21st to endNight
13%7%36%44436%9%43%
1781
May1st to 10thNight
17%9%35%44445%6%39%
2573
11th to 20thNight
12%5%2444446%8%46%
2517
21st to endNight
13%6%25%4445%6%9%42%
2762
June1st to 10thNight
9%6%25%33447%9%48%
1520
11th to 20thNight
8%415%3345%7%7%52%
1520
21st to endNight
5%41432447%7%60%
1520
July1st to 10thNight
321323447%9%63%
2540
11th to 20thNight
2213345%6%8%10%56%
2540
21st to endNight
2214345%47%10%58%
2761
August1st to 10thNight
7%4244445%6%9%51%
2768
11th to 20thNight
4214345%49%10%53%
2811
21st to endNight
221332335%8%68%
3443
September1st to 10thNight
5%313333347%65%
1900
11th to 20thNight
7%31433335%8%61%
1900
21st to endNight
9%413223247%63%
2157
October1st to 10thNight
13%9%24333346%51%
2280
11th to 20thNight
11%6%24332246%55%
2280
21st to endNight
6%7%25%33346%7%55%
2574
November1st to 10thNight
6%8%36%44436%8%48%
2465
11th to 20thNight
5%9%36%44435%8%49%
2660
21st to endNight
49%25%34435%7%52%
2660
December1st to 10thNight
48%48%6%5%5%5%6%8%42%
2660
11th to 20thNight
27%26%44446%8%53%
3271
21st to endNight
48%26%34446%8%50%
4873

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%8%14%29%13%1
2539
11th to 20thDay
30%9%20%25%13%3
2540
21st to endDay
24%5%16%36%18%2
3054
February1st to 10thDay
45%6%14%23%10%2
1710
11th to 20thDay
40%7%13%23%12%4
1674
21st to endDay
37%6%13%25%15%5%
1532
March1st to 10thDay
27%6%11%25%27%4
3220
11th to 20thDay
29%8%19%31%11%2
3490
21st to endDay
47%11%17%20%4
3948
April1st to 10thDay
38%7%16%24%13%2
2280
11th to 20thDay
42%7%16%22%12%1
2254
21st to endDay
41%8%15%22%12%1
2398
May1st to 10thDay
47%8%10%24%8%2
4394
11th to 20thDay
31%9%14%30%13%2
4392
21st to endDay
33%10%18%32%6%
4825
June1st to 10thDay
29%12%22%23%13%2
2660
11th to 20thDay
29%9%18%25%16%3
2660
21st to endDay
20%8%13%26%24%9%
2660
July1st to 10thDay
20%7%10%29%24%10%
4361
11th to 20thDay
14%6%9%23%30%17%
4355
21st to endDay
17%6%9%21%32%16%
4651
August1st to 10thDay
29%6%10%20%22%12%
4153
11th to 20thDay
22%6%9%26%30%7%
4067
21st to endDay
16%5%10%22%35%11%
4221
September1st to 10thDay
21%47%23%30%15%
2280
11th to 20thDay
21%5%11%28%27%8%
2280
21st to endDay
24%49%29%26%7%
2018
October1st to 10thDay
32%6%13%22%21%7%
1900
11th to 20thDay
30%5%12%29%19%5%
1900
21st to endDay
33%5%15%27%15%5%
2004
November1st to 10thDay
32%7%12%23%21%5%
1644
11th to 20thDay
29%7%15%27%19%3
1520
21st to endDay
30%5%14%30%18%4
1520
December1st to 10thDay
32%7%16%26%16%4
1520
11th to 20thDay
24%5%20%35%14%2
1924
21st to endDay
29%413%31%17%6%
2794
January1st to 10thNight
35%8%13%31%12%2
4417
11th to 20thNight
42%5%17%19%13%4
4430
21st to endNight
33%7%17%28%13%2
4640
February1st to 10thNight
45%6%15%21%9%3
2470
11th to 20thNight
43%6%14%22%13%3
2403
21st to endNight
37%6%12%24%15%6%
1921
March1st to 10thNight
28%7%13%24%23%5%
3645
11th to 20thNight
30%9%20%25%14%2
3490
21st to endNight
43%13%20%17%6%1
3701
April1st to 10thNight
38%9%16%21%12%3
1900
11th to 20thNight
40%8%14%27%10%1
1877
21st to endNight
37%7%15%27%14%1
1781
May1st to 10thNight
41%8%11%24%15%2
2573
11th to 20thNight
31%9%15%32%11%2
2518
21st to endNight
33%9%20%30%8%1
2762
June1st to 10thNight
30%8%21%24%14%2
1520
11th to 20thNight
28%8%19%23%17%5%
1520
21st to endNight
20%6%14%29%26%6%
1520
July1st to 10thNight
16%6%14%34%22%8%
2500
11th to 20thNight
17%7%10%27%29%11%
2492
21st to endNight
16%7%10%23%29%15%
2674
August1st to 10thNight
27%6%13%23%20%11%
2760
11th to 20thNight
21%6%11%32%21%8%
2838
21st to endNight
15%410%25%32%15%
3443
September1st to 10thNight
19%48%24%30%16%
1900
11th to 20thNight
22%5%11%25%27%10%
1900
21st to endNight
23%39%27%29%8%
2157
October1st to 10thNight
34%412%22%21%6%
2280
11th to 20thNight
31%410%29%20%7%
2280
21st to endNight
27%5%16%30%16%5%
2574
November1st to 10thNight
33%6%14%24%18%5%
2465
11th to 20thNight
33%5%12%30%17%3
2660
21st to endNight
30%5%15%27%17%6%
2660
December1st to 10thNight
37%6%15%22%16%4
2660
11th to 20thNight
26%6%17%36%14%2
3272
21st to endNight
30%5%13%29%16%7%
4873

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
7%6%18%40%23%7%
270
11th to 20thDay
12%6%21%36%18%7%
270
21st to endDay
9%12%28%32%14%4
297
February1st to 10thDay
10%11%34%36%9%1
270
11th to 20thDay
10%11%25%40%12%2
270
21st to endDay
5%13%24%41%15%2
225
March1st to 10thDay
8%11%29%37%12%2
321
11th to 20thDay
11%14%30%30%11%5%
460
21st to endDay
18%11%27%28%12%3
506
April1st to 10thDay
18%13%31%27%8%2
460
11th to 20thDay
18%20%29%25%8%
452
21st to endDay
18%12%27%26%15%2
460
May1st to 10thDay
15%11%22%30%18%4
630
11th to 20thDay
17%7%22%29%20%5%
675
21st to endDay
16%7%21%27%22%6%
734
June1st to 10thDay
7%5%20%33%27%8%
680
11th to 20thDay
9%10%24%37%17%4
680
21st to endDay
6%424%38%23%5%
680
July1st to 10thDay
4218%38%31%7%
671
11th to 20thDay
1422%40%30%4
668
21st to endDay
4320%34%34%6%
739
August1st to 10thDay
7%325%38%23%6%
537
11th to 20thDay
5%420%38%24%8%
477
21st to endDay
45%21%37%23%10%
539
September1st to 10thDay
7%6%20%36%24%8%
490
11th to 20thDay
10%5%18%36%23%8%
490
21st to endDay
13%7%18%30%21%10%
364
October1st to 10thDay
12%8%20%26%22%12%
300
11th to 20thDay
14%11%20%29%19%7%
300
21st to endDay
13%10%25%32%15%5%
330
November1st to 10thDay
10%8%27%31%16%8%
273
11th to 20thDay
9%11%24%33%19%4
270
21st to endDay
10%7%19%43%19%2
270
December1st to 10thDay
8%7%20%46%16%3
270
11th to 20thDay
9%10%24%43%13%1
270
21st to endDay
7%9%27%39%14%4
297
January1st to 10thNight
7%7%26%41%17%2
950
11th to 20thNight
8%10%33%33%13%3
950
21st to endNight
9%10%30%37%13%2
903
February1st to 10thNight
7%7%33%40%12%2
760
11th to 20thNight
9%8%30%40%12%1
744
21st to endNight
6%8%29%43%12%3
628
March1st to 10thNight
8%430%43%13%2
760
11th to 20thNight
9%5%27%42%14%3
760
21st to endNight
15%6%26%35%17%2
760
April1st to 10thNight
14%7%28%41%10%1
570
11th to 20thNight
13%7%28%41%10%
563
21st to endNight
15%5%22%42%14%1
570
May1st to 10thNight
14%420%41%19%1
570
11th to 20thNight
17%415%40%23%1
561
21st to endNight
18%5%16%41%21%1
617
June1st to 10thNight
11%420%43%21%2
570
11th to 20thNight
10%5%23%46%15%1
570
21st to endNight
6%316%51%23%1
570
July1st to 10thNight
4114%49%30%2
555
11th to 20thNight
3116%57%23%
552
21st to endNight
2112%54%30%1
624
August1st to 10thNight
4211%57%25%1
567
11th to 20thNight
5%210%50%31%2
564
21st to endNight
3214%50%29%2
627
September1st to 10thNight
6%213%49%27%3
570
11th to 20thNight
7%214%47%25%4
570
21st to endNight
11%317%41%22%6%
703
October1st to 10thNight
17%417%37%20%4
760
11th to 20thNight
13%6%23%36%21%1
760
21st to endNight
10%8%23%42%15%3
902
November1st to 10thNight
10%5%25%44%14%2
935
11th to 20thNight
8%10%29%40%13%1
950
21st to endNight
10%6%27%44%12%1
950
December1st to 10thNight
6%7%30%43%11%1
950
11th to 20thNight
8%5%28%45%13%1
950
21st to endNight
10%7%27%41%13%2
1045
Page generated at 2024-10-30 11:19:23. Version ac07

Copyright © 2024 Attilla Danko.


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