Sheridan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sheridan clear sky chart from 2005-11-05 to 2018-02-13.

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
50%
15274
14%
48669
13%
15247
52%
15247
21%
32958

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
35%
776
8%
2716
8%
776
37%
776
10%
2161
January16th to endNight
39%
832
11%
2769
11%
832
41%
832
14%
2070
February1st to 15thNight
39%
746
7%
2444
7%
746
41%
746
12%
1923
February16th to endNight
35%
632
10%
2020
7%
632
40%
632
15%
1493
March1st to 15thNight
36%
720
7%
2016
5%
720
37%
720
14%
1610
March16th to endNight
34%
768
8%
2099
6%
768
35%
768
13%
1688
April1st to 15thNight
38%
719
8%
1799
5%
719
39%
719
17%
1413
April16th to endNight
50%
582
12%
1662
8%
582
52%
582
21%
1167
May1st to 15thNight
53%
413
15%
1493
15%
413
57%
413
25%
887
May16th to endNight
58%
375
10%
1496
13%
374
62%
374
20%
922
June1st to 15thNight
57%
360
10%
1440
14%
360
60%
360
22%
859
June16th to endNight
60%
360
15%
1317
19%
360
64%
360
31%
722
July1st to 15thNight
80%
340
20%
1324
30%
340
84%
340
55%
511
July16th to endNight
83%
395
28%
1434
38%
372
87%
372
66%
495
August1st to 15thNight
84%
538
27%
1611
25%
535
86%
535
63%
697
August16th to endNight
79%
642
33%
1788
26%
642
80%
642
55%
886
September1st to 15thNight
78%
720
30%
1800
19%
720
79%
720
64%
916
September16th to endNight
69%
716
26%
1985
23%
716
70%
716
40%
1157
October1st to 15thNight
58%
720
19%
2160
19%
720
61%
720
32%
1316
October16th to endNight
48%
768
15%
2306
15%
768
50%
768
21%
1614
November1st to 15thNight
37%
760
8%
2618
8%
760
39%
760
12%
2028
November16th to endNight
40%
780
8%
2730
8%
780
42%
780
13%
2030
December1st to 15thNight
40%
780
11%
2730
11%
780
43%
780
14%
2006
December16th to endNight
28%
832
7%
2912
6%
832
30%
832
8%
2387

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
15%9%47%6%35%446%32%
49364
Night
14%8%47%6%35%45%6%34%
48839
Cloud CoverDay
15%8%37%6%35%446%32%
49364
Night
15%8%36%6%34446%35%
48843
TransparencyDay
51%413%18%10%2
49037
Night
48%314%19%10%2
48670
SeeingDay
18%8%20%26%17%8%
6236
Night
19%415%34%24%2
15285

By Month

Percentage Cloud Cover NW (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
20%14%7%11%8%35%44415%
1552
16th to endDay
21%10%48%8%45%5%45%20%
1805
February1st to 15thDay
22%15%5%10%7%45%445%14%
1685
16th to endDay
20%15%5%10%8%5%5%345%15%
1453
March1st to 15thDay
24%14%5%10%8%45%44412%
1941
16th to endDay
23%14%6%9%9%45%6%35%12%
2124
April1st to 15thDay
19%14%5%9%9%46%5%46%15%
2149
16th to endDay
17%11%5%9%8%46%6%46%20%
2295
May1st to 15thDay
14%10%36%6%3446%8%31%
2455
16th to endDay
16%7%46%6%36%5%6%8%26%
2615
June1st to 15thDay
16%10%47%6%35%5%5%6%28%
2520
16th to endDay
9%6%37%6%45%45%8%38%
2634
July1st to 15thDay
4314323247%61%
2547
16th to endDay
5%313212347%64%
2636
August1st to 15thDay
331341345%7%60%
2340
16th to endDay
4413423348%58%
2414
September1st to 15thDay
341321345%7%61%
2160
16th to endDay
13%7%25%5%34447%42%
1971
October1st to 15thDay
16%7%47%5%45%45%6%32%
1800
16th to endDay
17%10%49%6%35%45%5%26%
1917
November1st to 15thDay
23%11%410%8%45%5%46%14%
1567
16th to endDay
21%11%5%8%7%5%6%5%35%18%
1560
December1st to 15thDay
18%11%49%8%5%5%6%5%6%20%
1560
16th to endDay
25%13%5%10%7%36%5%45%12%
1664
January1st to 15thNight
20%12%5%10%9%345%6%417%
2716
16th to endNight
17%11%5%9%7%35%5%46%24%
2769
February1st to 15thNight
16%12%6%8%8%46%6%6%6%18%
2432
16th to endNight
15%10%5%9%7%45%5%5%6%24%
2020
March1st to 15thNight
18%10%6%9%9%45%435%21%
2016
16th to endNight
19%12%5%9%7%36%5%6%7%16%
2095
April1st to 15thNight
18%9%5%8%8%46%45%5%23%
1799
16th to endNight
11%8%37%6%36%7%6%7%31%
1662
May1st to 15thNight
9%6%35%7%35%5%5%6%40%
1493
16th to endNight
11%5%35%6%45%6%6%9%34%
1496
June1st to 15thNight
12%6%36%6%2445%7%39%
1440
16th to endNight
6%5%36%5%2345%9%46%
1317
July1st to 15thNight
222212336%70%
1404
16th to endNight
21111239%74%
1531
August1st to 15thNight
21211235%8%69%
1620
16th to endNight
4213322247%65%
1788
September1st to 15thNight
312212345%71%
1800
16th to endNight
7%4245%2446%7%49%
1985
October1st to 15thNight
11%5%244345%5%6%45%
2160
16th to endNight
16%6%37%5%36%46%5%32%
2306
November1st to 15thNight
23%10%48%8%36%5%5%6%19%
2618
16th to endNight
19%8%49%7%46%5%6%5%23%
2730
December1st to 15thNight
16%10%48%7%45%5%5%5%26%
2730
16th to endNight
23%11%6%9%8%45%44416%
2912

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 15thDay
23%14%7%10%8%45%33414%
1552
16th to endDay
22%10%49%7%46%44420%
1805
February1st to 15thDay
24%13%5%10%7%35%5%35%14%
1685
16th to endDay
20%14%5%10%7%45%445%16%
1453
March1st to 15thDay
24%13%6%9%8%47%44413%
1941
16th to endDay
23%13%5%10%8%46%445%12%
2124
April1st to 15thDay
18%12%411%8%46%45%6%16%
2149
16th to endDay
17%10%48%8%46%7%5%5%21%
2295
May1st to 15thDay
13%9%46%6%245%5%8%32%
2455
16th to endDay
15%7%37%6%46%6%6%8%27%
2615
June1st to 15thDay
15%8%48%7%35%5%5%6%27%
2520
16th to endDay
8%6%37%6%35%5%5%7%40%
2634
July1st to 15thDay
4314324445%61%
2547
16th to endDay
5%212212336%66%
2636
August1st to 15thDay
32135%23447%60%
2340
16th to endDay
45%13314348%59%
2414
September1st to 15thDay
3313323446%62%
2160
16th to endDay
13%5%25%5%4445%6%42%
1971
October1st to 15thDay
15%8%36%7%445%5%5%32%
1800
16th to endDay
18%10%48%6%45%445%27%
1917
November1st to 15thDay
23%12%5%9%7%35%5%5%6%13%
1567
16th to endDay
21%12%5%9%8%36%5%3418%
1560
December1st to 15thDay
19%11%410%6%36%5%45%20%
1560
16th to endDay
26%13%410%7%36%44412%
1664
January1st to 15thNight
22%11%5%9%8%35%45%417%
2716
16th to endNight
19%10%5%9%6%35%445%24%
2769
February1st to 15thNight
19%10%5%9%7%36%5%5%6%19%
2432
16th to endNight
16%10%48%8%35%5%45%25%
2020
March1st to 15thNight
19%11%5%9%7%37%445%21%
2016
16th to endNight
21%11%49%8%45%6%5%6%17%
2099
April1st to 15thNight
18%9%49%8%45%446%24%
1799
16th to endNight
12%7%38%6%35%6%6%7%32%
1662
May1st to 15thNight
9%6%37%6%3446%6%42%
1493
16th to endNight
11%5%36%5%26%6%7%9%34%
1496
June1st to 15thNight
11%5%45%6%35%447%41%
1440
16th to endNight
6%6%35%5%24446%50%
1317
July1st to 15thNight
3212212226%73%
1404
16th to endNight
21112135%78%
1531
August1st to 15thNight
221212246%72%
1620
16th to endNight
422322236%67%
1788
September1st to 15thNight
4111223235%72%
1800
16th to endNight
8%5%1343345%7%51%
1985
October1st to 15thNight
12%5%25%42445%6%46%
2160
16th to endNight
18%8%36%5%35%5%46%33%
2306
November1st to 15thNight
24%9%48%7%45%5%5%5%20%
2618
16th to endNight
20%10%47%6%45%5%45%25%
2730
December1st to 15thNight
18%10%48%7%3445%5%26%
2730
16th to endNight
24%12%5%10%8%45%34316%
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
74%27%9%5%
1552
16th to endDay
64%49%12%5%2
1805
February1st to 15thDay
70%5%11%8%3
1685
16th to endDay
68%410%9%6%
1453
March1st to 15thDay
71%212%9%3
1941
16th to endDay
72%312%9%2
2124
April1st to 15thDay
66%5%13%12%2
2149
16th to endDay
60%5%14%13%5%1
2295
May1st to 15thDay
48%315%22%10%
2455
16th to endDay
51%6%18%18%4
2619
June1st to 15thDay
54%417%18%5%
2520
16th to endDay
41%320%23%8%2
2634
July1st to 15thDay
24%314%29%22%6%
2398
16th to endDay
18%212%31%28%7%
2470
August1st to 15thDay
22%317%34%17%5%
2324
16th to endDay
24%313%33%21%4
2414
September1st to 15thDay
21%312%28%23%10%
2160
16th to endDay
41%315%22%13%2
1971
October1st to 15thDay
51%311%19%11%2
1800
16th to endDay
58%312%14%10%1
1917
November1st to 15thDay
68%411%12%2
1567
16th to endDay
68%39%11%7%
1560
December1st to 15thDay
64%410%12%6%
1560
16th to endDay
74%38%8%3
1664
January1st to 15thNight
67%310%10%6%1
2716
16th to endNight
60%311%12%9%3
2769
February1st to 15thNight
62%6%13%12%4
2444
16th to endNight
57%315%14%7%1
2020
March1st to 15thNight
63%412%14%4
2016
16th to endNight
63%5%14%13%3
2099
April1st to 15thNight
59%415%13%6%
1799
16th to endNight
48%6%16%19%7%1
1662
May1st to 15thNight
41%317%27%8%2
1494
16th to endNight
42%5%22%21%5%
1496
June1st to 15thNight
42%320%24%7%
1440
16th to endNight
34%222%29%7%2
1317
July1st to 15thNight
14%216%33%25%7%
1324
16th to endNight
10%112%32%31%11%
1434
August1st to 15thNight
13%217%40%18%8%
1611
16th to endNight
19%213%35%22%6%
1788
September1st to 15thNight
15%214%28%26%12%
1800
16th to endNight
30%316%26%16%6%
1985
October1st to 15thNight
37%312%26%16%3
2160
16th to endNight
50%412%16%13%2
2306
November1st to 15thNight
62%413%14%4
2618
16th to endNight
59%412%11%10%1
2730
December1st to 15thNight
58%411%14%10%
2730
16th to endNight
70%39%11%3
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
27%6%13%24%18%8%
90
16th to endDay
27%8%15%24%17%6%
237
February1st to 15thDay
29%9%17%24%13%4
273
16th to endDay
29%14%20%21%10%3
217
March1st to 15thDay
37%10%26%17%6%1
270
16th to endDay
32%14%21%20%7%2
288
April1st to 15thDay
19%17%22%20%14%6%
269
16th to endDay
24%13%24%21%8%6%
270
May1st to 15thDay
17%14%27%19%14%5%
288
16th to endDay
14%8%19%22%18%16%
330
June1st to 15thDay
15%8%22%26%16%9%
315
16th to endDay
8%8%26%32%18%5%
429
July1st to 15thDay
4415%34%28%12%
332
16th to endDay
3318%35%28%11%
327
August1st to 15thDay
5%213%37%22%18%
315
16th to endDay
5%316%27%29%18%
332
September1st to 15thDay
5%420%29%24%16%
315
16th to endDay
13%6%18%28%26%6%
315
October1st to 15thDay
19%7%21%24%20%6%
315
16th to endDay
28%6%17%26%13%8%
333
November1st to 15thDay
27%10%29%27%5%2
100
16th to endDay
28%8%23%20%7%11%
90
December1st to 15thDay
31%222%21%12%11%
90
16th to endDay
32%221%25%15%3
96
January1st to 15thNight
27%6%15%27%20%2
780
16th to endNight
24%5%14%31%21%3
832
February1st to 15thNight
24%416%31%21%1
752
16th to endNight
22%6%22%30%16%
632
March1st to 15thNight
25%5%21%31%14%1
720
16th to endNight
26%5%19%28%18%
768
April1st to 15thNight
22%7%18%30%19%1
719
16th to endNight
16%415%39%21%1
582
May1st to 15thNight
13%318%43%20%
414
16th to endNight
14%311%43%24%2
375
June1st to 15thNight
14%213%44%24%
360
16th to endNight
7%218%44%26%
360
July1st to 15thNight
5%8%49%36%
340
16th to endNight
310%47%36%1
395
August1st to 15thNight
45%38%46%4
538
16th to endNight
5%7%40%41%3
642
September1st to 15thNight
4110%33%43%5%
720
16th to endNight
11%29%39%31%5%
716
October1st to 15thNight
15%215%37%24%4
720
16th to endNight
22%117%28%23%5%
768
November1st to 15thNight
28%416%36%13%
760
16th to endNight
25%6%17%29%17%3
780
December1st to 15thNight
23%5%16%31%19%3
780
16th to endNight
29%7%19%27%15%1
832
Page generated at 2018-02-13 17:46:01. Version ac04

Copyright 2018 A. Danko


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