Hirsch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hirsch Observatory clear sky chart from 2005-11-05 to 2018-10-08.

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
29%
16180
14%
50997
8%
16149
37%
16149
17%
35996

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
11%
2716
5%
776
24%
776
11%
2020
January16th to endNight
16%
832
11%
2876
3%
832
25%
832
11%
2116
February1st to 15thNight
12%
764
10%
2434
2%
761
21%
761
10%
1900
February16th to endNight
17%
683
13%
2049
6%
683
27%
683
13%
1547
March1st to 15thNight
14%
780
12%
2340
5%
780
24%
780
12%
1777
March16th to endNight
22%
832
20%
2160
7%
832
32%
832
18%
1562
April1st to 15thNight
20%
778
14%
1946
3%
778
25%
778
18%
1463
April16th to endNight
24%
706
16%
1862
4%
706
32%
706
21%
1335
May1st to 15thNight
26%
506
16%
1676
8%
506
36%
506
17%
1155
May16th to endNight
40%
406
12%
1625
9%
406
47%
406
16%
1080
June1st to 15thNight
36%
390
12%
1560
11%
390
45%
390
15%
1048
June16th to endNight
50%
390
12%
1560
14%
390
56%
390
24%
928
July1st to 15thNight
51%
370
14%
1480
17%
370
57%
370
23%
880
July16th to endNight
56%
408
16%
1546
18%
386
61%
386
24%
920
August1st to 15thNight
52%
498
15%
1639
11%
496
56%
496
25%
1030
August16th to endNight
53%
828
17%
2070
9%
828
55%
828
31%
1376
September1st to 15thNight
44%
780
18%
1950
9%
780
48%
780
28%
1344
September16th to endNight
48%
777
24%
2142
16%
777
53%
777
33%
1339
October1st to 15thNight
37%
752
17%
2190
12%
752
44%
752
21%
1535
October16th to endNight
25%
768
13%
2433
8%
768
34%
768
16%
1746
November1st to 15thNight
27%
760
16%
2472
9%
760
36%
760
18%
1692
November16th to endNight
26%
780
15%
2629
9%
780
36%
780
14%
1864
December1st to 15thNight
18%
780
10%
2730
3%
780
27%
780
10%
2059
December16th to endNight
15%
832
9%
2912
3%
832
23%
832
8%
2280

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%7%36%5%35%5%5%7%33%
52145
Night
17%8%36%5%3445%6%34%
51167
Cloud CoverDay
16%8%36%5%35%45%7%33%
52154
Night
17%9%36%5%34446%33%
51173
TransparencyDay
48%7%12%18%11%1
51833
Night
50%6%12%18%11%1
50997
SeeingDay
22%13%26%22%11%3
7051
Night
22%13%29%25%8%
16181

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
15%11%36%6%37%6%5%6%25%
1552
16th to endDay
14%10%47%7%36%5%6%7%25%
1699
February1st to 15thDay
16%12%5%8%8%36%6%46%20%
1757
16th to endDay
16%12%48%7%35%5%45%27%
1710
March1st to 15thDay
19%10%47%5%25%446%28%
1940
16th to endDay
16%9%46%5%34345%36%
2414
April1st to 15thDay
19%8%46%6%24446%32%
2332
16th to endDay
18%6%35%425%346%37%
2370
May1st to 15thDay
20%7%25%5%345%5%6%32%
2617
16th to endDay
16%5%35%425%5%6%8%36%
2842
June1st to 15thDay
18%6%36%5%35%5%6%8%30%
2730
16th to endDay
14%5%36%5%35%6%7%9%33%
2730
July1st to 15thDay
10%435%6%35%5%7%8%39%
2730
16th to endDay
12%435%5%45%6%6%9%35%
2878
August1st to 15thDay
11%6%26%6%45%6%7%8%35%
2550
16th to endDay
12%5%14435%5%7%8%41%
2484
September1st to 15thDay
15%6%24435%45%8%39%
2340
16th to endDay
13%424423347%49%
2147
October1st to 15thDay
19%8%37%423345%36%
1937
16th to endDay
22%8%35%5%245%5%6%29%
1789
November1st to 15thDay
16%7%36%4345%46%36%
1716
16th to endDay
16%9%26%6%25%45%6%35%
1657
December1st to 15thDay
19%11%6%7%6%24436%26%
1560
16th to endDay
22%13%48%6%3444422%
1664
January1st to 15thNight
16%13%47%6%34446%26%
2716
16th to endNight
14%13%47%6%45%446%27%
2876
February1st to 15thNight
15%9%7%10%8%4445%5%23%
2433
16th to endNight
15%12%48%6%35%445%28%
2049
March1st to 15thNight
21%11%47%5%3433429%
2327
16th to endNight
17%8%36%6%34346%36%
2160
April1st to 15thNight
19%9%47%435%446%31%
1946
16th to endNight
20%6%35%42445%5%37%
1862
May1st to 15thNight
19%7%36%5%23436%36%
1676
16th to endNight
14%5%35%5%5%5%5%7%7%34%
1623
June1st to 15thNight
19%5%35%435%5%5%7%34%
1560
16th to endNight
12%3134345%6%9%43%
1560
July1st to 15thNight
10%425%5%35%46%8%41%
1560
16th to endNight
11%4245%35%45%8%43%
1642
August1st to 15thNight
11%5%25%425%46%8%43%
1649
16th to endNight
13%5%25%42445%7%43%
2070
September1st to 15thNight
16%6%2442345%7%41%
1950
16th to endNight
12%5%23423446%49%
2142
October1st to 15thNight
18%7%25%5%34445%38%
2190
16th to endNight
21%7%35%43446%7%31%
2433
November1st to 15thNight
15%9%36%42445%5%36%
2472
16th to endNight
17%8%35%5%35%445%33%
2629
December1st to 15thNight
22%11%46%5%24446%26%
2730
16th to endNight
23%12%5%7%5%34445%23%
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
15%11%37%7%46%5%5%6%25%
1552
16th to endDay
14%11%47%8%36%45%6%25%
1699
February1st to 15thDay
17%12%5%8%7%36%5%5%6%20%
1757
16th to endDay
16%12%49%6%36%35%5%27%
1710
March1st to 15thDay
21%10%5%7%5%25%445%26%
1950
16th to endDay
17%10%46%5%34335%36%
2413
April1st to 15thDay
20%9%46%5%35%345%32%
2332
16th to endDay
19%7%25%434446%36%
2370
May1st to 15thDay
21%8%35%5%25%5%47%31%
2617
16th to endDay
17%7%345%25%5%5%7%36%
2842
June1st to 15thDay
19%7%26%5%35%5%5%8%29%
2730
16th to endDay
15%6%36%435%6%6%8%33%
2730
July1st to 15thDay
11%5%25%5%35%5%6%8%38%
2730
16th to endDay
12%5%26%5%46%6%6%8%35%
2878
August1st to 15thDay
12%6%26%6%35%6%6%9%34%
2550
16th to endDay
12%5%14435%5%6%8%41%
2484
September1st to 15thDay
16%5%245%3445%7%39%
2340
16th to endDay
14%414333347%49%
2147
October1st to 15thDay
20%8%36%423345%36%
1937
16th to endDay
22%10%36%433446%29%
1789
November1st to 15thDay
16%8%36%425%45%6%36%
1716
16th to endDay
17%9%26%425%45%5%34%
1657
December1st to 15thDay
18%12%5%9%5%25%346%27%
1560
16th to endDay
22%15%5%7%6%3443422%
1664
January1st to 15thNight
16%14%48%7%34445%25%
2716
16th to endNight
14%14%5%7%7%45%445%26%
2876
February1st to 15thNight
15%10%6%10%9%45%45%5%22%
2426
16th to endNight
16%12%48%6%25%45%5%27%
2049
March1st to 15thNight
22%11%47%5%3433429%
2340
16th to endNight
17%8%45%5%33445%36%
2160
April1st to 15thNight
20%10%46%435%35%5%32%
1946
16th to endNight
20%6%35%333445%37%
1862
May1st to 15thNight
19%8%37%5%23346%35%
1676
16th to endNight
14%7%25%6%35%5%6%8%33%
1623
June1st to 15thNight
20%6%35%435%5%47%34%
1560
16th to endNight
13%413425%46%10%42%
1560
July1st to 15thNight
10%435%6%25%46%9%41%
1560
16th to endNight
13%4245%25%46%8%43%
1642
August1st to 15thNight
11%5%26%4245%5%8%42%
1649
16th to endNight
13%5%25%43345%7%43%
2070
September1st to 15thNight
17%6%34423446%42%
1950
16th to endNight
12%5%24323346%50%
2142
October1st to 15thNight
18%7%25%5%24445%38%
2190
16th to endNight
22%9%25%5%3445%7%30%
2433
November1st to 15thNight
16%9%36%5%245%46%36%
2472
16th to endNight
17%9%46%6%35%445%33%
2629
December1st to 15thNight
21%11%5%7%5%24446%25%
2730
16th to endNight
24%12%5%8%5%34445%22%
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
55%7%11%15%8%1
1553
16th to endDay
56%6%15%14%6%
1699
February1st to 15thDay
61%7%9%13%6%
1760
16th to endDay
57%6%10%14%10%
1710
March1st to 15thDay
56%6%12%14%7%1
1950
16th to endDay
49%5%9%16%15%3
2414
April1st to 15thDay
54%5%9%18%11%1
2332
16th to endDay
47%6%8%18%15%3
2370
May1st to 15thDay
51%7%8%18%11%1
2617
16th to endDay
45%9%12%20%10%1
2846
June1st to 15thDay
50%9%12%18%8%
2730
16th to endDay
45%9%14%18%11%
2730
July1st to 15thDay
40%9%12%22%13%1
2581
16th to endDay
41%10%15%19%12%
2711
August1st to 15thDay
43%10%14%20%9%1
2536
16th to endDay
36%9%14%25%13%
2484
September1st to 15thDay
42%7%12%20%15%1
2340
16th to endDay
35%6%10%27%19%1
2147
October1st to 15thDay
50%6%9%21%10%1
1937
16th to endDay
53%6%13%16%8%1
1789
November1st to 15thDay
47%7%12%19%11%1
1716
16th to endDay
49%6%14%18%10%
1657
December1st to 15thDay
58%6%13%14%6%
1560
16th to endDay
63%6%11%12%6%
1664
January1st to 15thNight
58%5%12%12%9%
2716
16th to endNight
57%5%12%15%7%1
2876
February1st to 15thNight
61%7%11%13%6%
2434
16th to endNight
56%6%12%14%8%1
2049
March1st to 15thNight
58%5%10%16%8%1
2340
16th to endNight
48%6%9%17%13%4
2160
April1st to 15thNight
52%5%10%18%11%1
1946
16th to endNight
46%7%8%18%16%3
1862
May1st to 15thNight
49%5%9%17%14%2
1676
16th to endNight
46%8%13%18%11%1
1625
June1st to 15thNight
48%7%12%20%10%
1560
16th to endNight
36%8%16%25%12%
1560
July1st to 15thNight
36%8%12%25%14%1
1480
16th to endNight
37%7%14%26%12%1
1546
August1st to 15thNight
36%10%15%25%10%1
1639
16th to endNight
37%7%13%27%13%
2070
September1st to 15thNight
41%6%11%22%15%1
1950
16th to endNight
35%5%10%26%20%
2142
October1st to 15thNight
47%6%11%18%14%1
2190
16th to endNight
51%6%14%18%8%
2433
November1st to 15thNight
47%6%12%17%14%2
2472
16th to endNight
52%6%13%18%9%1
2629
December1st to 15thNight
58%7%13%14%6%
2730
16th to endNight
63%6%11%11%7%
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%28%28%11%6%1
90
16th to endDay
34%22%25%16%1
104
February1st to 15thDay
34%25%29%6%3
183
16th to endDay
26%24%30%16%2
291
March1st to 15thDay
30%19%29%18%3
330
16th to endDay
22%22%27%17%8%1
352
April1st to 15thDay
32%19%24%16%6%
330
16th to endDay
22%19%27%19%7%4
319
May1st to 15thDay
27%17%27%15%9%3
348
16th to endDay
22%9%28%26%10%2
395
June1st to 15thDay
18%11%30%24%13%1
375
16th to endDay
16%12%30%25%14%1
375
July1st to 15thDay
12%6%26%32%16%5%
365
16th to endDay
14%427%31%17%4
390
August1st to 15thDay
17%5%25%26%18%6%
358
16th to endDay
13%6%20%27%21%9%
396
September1st to 15thDay
21%7%19%23%18%10%
375
16th to endDay
17%6%21%23%14%15%
374
October1st to 15thDay
24%9%20%23%17%4
345
16th to endDay
26%16%28%21%7%
303
November1st to 15thDay
26%10%25%22%12%1
280
16th to endDay
22%19%30%19%6%1
187
December1st to 15thDay
20%21%40%11%6%1
90
16th to endDay
28%32%32%7%
96
January1st to 15thNight
22%19%36%18%3
780
16th to endNight
23%19%34%20%1
832
February1st to 15thNight
22%19%37%18%1
764
16th to endNight
25%18%33%19%2
683
March1st to 15thNight
30%20%31%15%1
780
16th to endNight
22%19%29%21%5%
832
April1st to 15thNight
26%17%30%21%2
778
16th to endNight
23%17%31%19%7%
706
May1st to 15thNight
22%14%32%23%6%
506
16th to endNight
14%9%30%34%9%1
407
June1st to 15thNight
21%7%28%30%11%
390
16th to endNight
13%327%42%12%
390
July1st to 15thNight
12%227%39%17%
370
16th to endNight
12%320%45%15%1
408
August1st to 15thNight
13%324%40%15%2
498
16th to endNight
15%419%35%21%3
828
September1st to 15thNight
20%5%24%31%16%1
780
16th to endNight
15%5%25%29%18%5%
777
October1st to 15thNight
22%8%24%30%12%1
752
16th to endNight
27%12%29%24%4
768
November1st to 15thNight
22%13%31%23%8%
760
16th to endNight
22%17%29%22%7%
780
December1st to 15thNight
27%17%32%18%3
780
16th to endNight
30%17%31%18%1
832
Page generated at 2018-10-09 10:39:16. Version ac04

Copyright 2018 A. Danko


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