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 2017-09-18.

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
29%
14860
14%
46850
8%
14829
36%
14829
17%
33113

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%
720
11%
2506
5%
716
23%
716
11%
1876
January16th to endNight
15%
768
11%
2655
3%
768
25%
768
10%
1959
February1st to 15thNight
12%
704
9%
2243
2%
701
20%
701
10%
1756
February16th to endNight
17%
631
13%
1893
6%
631
27%
631
13%
1432
March1st to 15thNight
14%
720
13%
2160
5%
720
24%
720
12%
1618
March16th to endNight
22%
768
19%
1994
7%
768
32%
768
18%
1444
April1st to 15thNight
20%
718
14%
1796
3%
718
26%
718
18%
1352
April16th to endNight
25%
660
16%
1740
4%
660
32%
660
21%
1238
May1st to 15thNight
25%
467
16%
1547
7%
467
36%
467
17%
1069
May16th to endNight
39%
374
12%
1497
10%
374
47%
374
16%
998
June1st to 15thNight
36%
360
11%
1440
10%
360
45%
360
15%
972
June16th to endNight
50%
360
12%
1440
13%
360
57%
360
24%
861
July1st to 15thNight
48%
340
12%
1360
14%
340
54%
340
21%
827
July16th to endNight
56%
376
15%
1418
18%
354
61%
354
23%
843
August1st to 15thNight
52%
469
16%
1540
12%
467
56%
467
26%
950
August16th to endNight
52%
764
18%
1910
9%
764
54%
764
32%
1264
September1st to 15thNight
45%
720
18%
1800
9%
720
49%
720
29%
1226
September16th to endNight
47%
669
24%
1844
16%
669
52%
669
34%
1145
October1st to 15thNight
36%
660
18%
1925
13%
660
43%
660
20%
1353
October16th to endNight
24%
704
11%
2230
6%
704
32%
704
16%
1613
November1st to 15thNight
27%
700
16%
2277
9%
700
37%
700
19%
1551
November16th to endNight
26%
720
14%
2427
9%
720
34%
720
13%
1745
December1st to 15thNight
18%
720
10%
2520
3%
720
27%
720
10%
1892
December16th to endNight
16%
768
9%
2688
2%
768
24%
768
7%
2129

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%
47950
Night
17%8%36%5%3445%6%34%
47020
Cloud CoverDay
16%8%36%5%35%45%7%33%
47959
Night
17%9%36%5%34446%33%
47026
TransparencyDay
48%7%12%18%11%1
47638
Night
50%6%12%18%11%1
46850
SeeingDay
21%13%26%22%12%4
5716
Night
22%13%29%25%7%
14861

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%47%6%37%6%5%6%25%
1432
16th to endDay
14%11%47%7%37%5%6%7%25%
1568
February1st to 15thDay
15%12%5%8%8%36%6%5%6%21%
1618
16th to endDay
15%12%48%7%35%445%27%
1580
March1st to 15thDay
19%9%5%7%5%25%446%29%
1790
16th to endDay
17%8%36%5%24345%37%
2228
April1st to 15thDay
19%8%46%6%24435%33%
2152
16th to endDay
16%6%35%425%45%7%37%
2217
May1st to 15thDay
20%8%25%5%345%5%6%31%
2415
16th to endDay
16%5%35%5%25%5%6%8%35%
2618
June1st to 15thDay
19%6%36%5%345%6%8%30%
2520
16th to endDay
14%5%36%5%35%6%7%9%32%
2520
July1st to 15thDay
11%5%35%6%35%5%7%8%36%
2520
16th to endDay
12%435%5%45%6%6%9%36%
2654
August1st to 15thDay
11%6%26%6%45%6%7%8%35%
2397
16th to endDay
12%5%13435%5%7%8%41%
2292
September1st to 15thDay
14%5%24435%45%8%40%
2160
16th to endDay
14%424323347%50%
1840
October1st to 15thDay
19%8%37%423345%36%
1702
16th to endDay
22%8%35%5%245%6%6%28%
1640
November1st to 15thDay
16%7%26%4345%5%6%37%
1581
16th to endDay
16%9%26%5%25%45%6%34%
1530
December1st to 15thDay
19%11%6%7%6%24436%26%
1440
16th to endDay
22%14%48%6%24445%21%
1536
January1st to 15thNight
17%14%47%6%34446%26%
2506
16th to endNight
14%13%48%7%45%446%27%
2655
February1st to 15thNight
14%9%7%10%8%45%45%5%23%
2242
16th to endNight
15%12%48%6%35%45%5%28%
1893
March1st to 15thNight
21%9%47%6%3443430%
2147
16th to endNight
17%8%36%6%34345%36%
1994
April1st to 15thNight
19%8%47%435%446%31%
1796
16th to endNight
18%6%35%42445%6%38%
1740
May1st to 15thNight
20%7%36%5%23436%35%
1547
16th to endNight
15%5%35%5%5%5%5%7%7%33%
1495
June1st to 15thNight
20%5%35%435%45%7%34%
1440
16th to endNight
13%3134345%6%9%43%
1440
July1st to 15thNight
10%425%5%45%47%9%38%
1440
16th to endNight
11%4245%35%46%8%43%
1514
August1st to 15thNight
10%5%25%425%45%8%44%
1550
16th to endNight
13%5%2442345%7%44%
1910
September1st to 15thNight
16%6%2442345%7%43%
1800
16th to endNight
12%5%13423446%50%
1844
October1st to 15thNight
18%7%36%5%24345%38%
1925
16th to endNight
22%8%35%43446%7%30%
2230
November1st to 15thNight
15%9%36%42445%5%37%
2277
16th to endNight
17%9%46%5%35%5%5%5%32%
2427
December1st to 15thNight
22%11%46%5%2445%6%26%
2520
16th to endNight
23%13%5%7%5%35%445%21%
2688

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%12%48%7%46%5%5%6%24%
1432
16th to endDay
14%12%47%8%37%45%6%25%
1568
February1st to 15thDay
15%12%5%8%7%36%5%5%5%20%
1618
16th to endDay
16%12%49%6%36%25%5%27%
1580
March1st to 15thDay
20%9%5%7%5%25%45%5%27%
1800
16th to endDay
17%9%36%5%2433437%
2227
April1st to 15thDay
20%8%46%5%35%335%33%
2152
16th to endDay
17%7%25%434447%36%
2217
May1st to 15thDay
21%8%35%5%25%5%46%30%
2415
16th to endDay
16%7%345%25%5%5%8%35%
2618
June1st to 15thDay
19%8%26%5%35%5%5%8%29%
2520
16th to endDay
15%6%36%435%6%6%8%32%
2520
July1st to 15thDay
12%5%26%5%36%6%7%9%35%
2520
16th to endDay
12%5%26%5%36%6%6%9%35%
2654
August1st to 15thDay
12%6%26%6%35%6%6%9%34%
2397
16th to endDay
12%5%14435%5%6%8%41%
2292
September1st to 15thDay
15%5%245%3445%7%40%
2160
16th to endDay
14%414223347%50%
1840
October1st to 15thDay
20%8%36%423345%35%
1702
16th to endDay
23%10%36%5%33446%27%
1640
November1st to 15thDay
16%8%36%425%45%6%36%
1581
16th to endDay
17%9%37%425%45%6%33%
1530
December1st to 15thDay
19%12%5%8%5%25%346%27%
1440
16th to endDay
22%15%5%7%6%3443421%
1536
January1st to 15thNight
17%15%48%7%34445%25%
2506
16th to endNight
14%14%5%7%7%45%445%26%
2655
February1st to 15thNight
14%10%6%11%9%45%45%5%22%
2235
16th to endNight
15%12%48%6%35%45%427%
1893
March1st to 15thNight
22%10%47%5%3433430%
2160
16th to endNight
18%8%45%5%33345%35%
1994
April1st to 15thNight
20%10%46%435%345%32%
1796
16th to endNight
18%6%36%3335%46%38%
1740
May1st to 15thNight
20%8%37%5%23336%34%
1547
16th to endNight
14%7%246%45%5%7%8%33%
1495
June1st to 15thNight
20%6%35%425%5%47%34%
1440
16th to endNight
13%413425%46%10%42%
1440
July1st to 15thNight
11%5%35%6%25%46%9%39%
1440
16th to endNight
13%3245%25%46%8%42%
1514
August1st to 15thNight
10%5%25%4245%48%44%
1550
16th to endNight
13%5%2443345%6%44%
1910
September1st to 15thNight
16%6%34423446%43%
1800
16th to endNight
13%424322347%50%
1844
October1st to 15thNight
19%7%36%5%24345%38%
1925
16th to endNight
22%9%25%5%2445%7%29%
2230
November1st to 15thNight
16%10%36%4235%46%36%
2277
16th to endNight
17%9%46%6%35%445%31%
2427
December1st to 15thNight
21%11%5%7%5%2445%6%25%
2520
16th to endNight
24%13%5%8%5%25%445%21%
2688

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
56%7%11%16%7%
1433
16th to endDay
56%6%14%14%6%
1568
February1st to 15thDay
61%7%10%13%6%
1621
16th to endDay
57%6%10%14%10%
1580
March1st to 15thDay
55%6%13%15%8%1
1800
16th to endDay
49%5%9%17%15%3
2228
April1st to 15thDay
53%49%19%11%1
2152
16th to endDay
46%6%8%19%15%3
2217
May1st to 15thDay
51%7%8%18%11%2
2415
16th to endDay
45%9%13%19%11%1
2622
June1st to 15thDay
50%9%12%18%8%
2520
16th to endDay
45%10%14%17%11%
2520
July1st to 15thDay
42%9%13%21%11%1
2371
16th to endDay
41%10%16%19%11%
2487
August1st to 15thDay
43%10%13%21%9%1
2383
16th to endDay
36%9%14%25%13%
2292
September1st to 15thDay
41%7%12%21%15%1
2160
16th to endDay
34%6%10%28%19%1
1840
October1st to 15thDay
50%6%10%21%10%2
1702
16th to endDay
54%7%13%14%8%1
1640
November1st to 15thDay
46%7%13%19%11%1
1581
16th to endDay
50%6%13%18%10%1
1530
December1st to 15thDay
58%6%13%14%6%
1440
16th to endDay
64%6%11%12%5%
1536
January1st to 15thNight
58%5%13%12%9%
2506
16th to endNight
57%5%11%15%8%1
2655
February1st to 15thNight
61%7%11%12%6%1
2243
16th to endNight
56%6%11%15%9%1
1893
March1st to 15thNight
57%411%16%8%1
2160
16th to endNight
49%6%9%17%13%4
1994
April1st to 15thNight
52%5%10%18%11%1
1796
16th to endNight
45%7%8%18%16%3
1740
May1st to 15thNight
50%5%9%18%14%2
1547
16th to endNight
46%8%13%18%10%1
1497
June1st to 15thNight
48%7%12%20%10%
1440
16th to endNight
36%8%17%25%12%
1440
July1st to 15thNight
38%9%12%25%12%1
1360
16th to endNight
37%7%15%26%11%1
1418
August1st to 15thNight
35%9%15%26%11%1
1540
16th to endNight
37%6%13%27%13%
1910
September1st to 15thNight
40%6%11%23%16%1
1800
16th to endNight
34%5%10%26%22%
1844
October1st to 15thNight
48%6%10%17%15%1
1925
16th to endNight
52%6%14%17%7%
2230
November1st to 15thNight
47%6%12%17%14%2
2277
16th to endNight
53%6%12%17%8%1
2427
December1st to 15thNight
57%7%13%14%6%
2520
16th to endNight
64%6%11%11%6%
2688

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
21%33%23%13%6%1
60
16th to endDay
39%21%21%14%2
69
February1st to 15thDay
29%28%29%7%4
134
16th to endDay
23%24%30%17%3
239
March1st to 15thDay
27%21%27%20%3
270
16th to endDay
23%22%25%17%9%1
288
April1st to 15thDay
30%18%23%18%7%1
270
16th to endDay
18%20%29%19%7%4
270
May1st to 15thDay
29%16%25%16%9%3
288
16th to endDay
20%11%29%23%11%3
331
June1st to 15thDay
20%10%28%24%13%1
315
16th to endDay
16%11%29%26%14%2
315
July1st to 15thDay
14%6%29%30%15%3
305
16th to endDay
13%427%31%19%3
326
August1st to 15thDay
16%6%26%26%17%6%
313
16th to endDay
13%6%18%27%22%10%
332
September1st to 15thDay
17%9%20%24%18%9%
315
16th to endDay
18%422%22%14%17%
262
October1st to 15thDay
23%9%19%21%19%5%
255
16th to endDay
28%16%28%21%5%
250
November1st to 15thDay
25%10%24%24%13%1
235
16th to endDay
22%16%30%20%8%2
150
December1st to 15thDay
18%25%36%11%6%1
60
16th to endDay
31%31%28%9%
64
January1st to 15thNight
22%19%35%18%3
720
16th to endNight
23%20%33%20%1
768
February1st to 15thNight
21%19%38%18%1
704
16th to endNight
25%19%33%19%2
631
March1st to 15thNight
29%21%30%16%1
720
16th to endNight
22%20%29%21%5%
768
April1st to 15thNight
26%17%31%21%3
718
16th to endNight
22%18%32%18%7%
660
May1st to 15thNight
23%14%32%22%6%
467
16th to endNight
14%9%30%34%9%1
375
June1st to 15thNight
21%7%28%30%11%
360
16th to endNight
13%328%40%12%
360
July1st to 15thNight
13%228%39%15%
340
16th to endNight
12%320%46%16%1
376
August1st to 15thNight
13%324%41%15%1
469
16th to endNight
15%419%35%21%3
764
September1st to 15thNight
20%5%25%31%16%1
720
16th to endNight
15%5%27%28%17%5%
669
October1st to 15thNight
22%8%25%29%11%1
660
16th to endNight
28%12%28%25%3
704
November1st to 15thNight
22%13%32%23%7%
700
16th to endNight
22%17%29%23%7%
720
December1st to 15thNight
28%17%31%18%4
720
16th to endNight
31%17%30%18%2
768
Page generated at 2017-09-19 07:32:31. Version ac04

Copyright 2017 A. Danko


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