AstroGeek's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AstroGeek's Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
27%
14913
18%
46733
8%
14880
39%
14880
20%
30780

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
19%
2506
6%
716
33%
716
16%
1606
January16th to endNight
14%
768
18%
2688
3%
768
34%
768
14%
1756
February1st to 15thNight
15%
704
17%
2166
3%
701
31%
701
17%
1455
February16th to endNight
15%
631
24%
1893
6%
631
35%
631
19%
1246
March1st to 15thNight
18%
720
17%
2145
6%
720
32%
720
18%
1455
March16th to endNight
20%
768
22%
2048
7%
768
32%
768
22%
1399
April1st to 15thNight
20%
718
17%
1796
4%
718
28%
718
23%
1287
April16th to endNight
23%
585
18%
1665
5%
585
33%
585
21%
1142
May1st to 15thNight
23%
540
14%
1620
6%
540
31%
540
17%
1145
May16th to endNight
28%
447
10%
1569
6%
446
34%
446
16%
1081
June1st to 15thNight
34%
360
11%
1440
9%
360
42%
360
14%
968
June16th to endNight
42%
360
11%
1440
12%
360
48%
360
21%
880
July1st to 15thNight
40%
340
12%
1360
14%
340
46%
340
21%
840
July16th to endNight
46%
376
14%
1418
15%
354
51%
354
20%
897
August1st to 15thNight
45%
533
16%
1603
11%
530
48%
530
28%
1010
August16th to endNight
53%
714
21%
1860
13%
714
56%
714
34%
1205
September1st to 15thNight
43%
700
19%
1819
9%
700
48%
700
32%
1187
September16th to endNight
46%
657
24%
1815
15%
657
52%
657
31%
1141
October1st to 15thNight
34%
660
23%
1826
11%
660
44%
660
26%
1208
October16th to endNight
25%
704
16%
2288
6%
704
38%
704
20%
1482
November1st to 15thNight
29%
700
18%
2277
9%
700
42%
700
20%
1483
November16th to endNight
25%
720
20%
2340
8%
720
40%
720
20%
1475
December1st to 15thNight
21%
720
18%
2463
5%
720
35%
720
16%
1617
December16th to endNight
15%
768
20%
2688
5%
768
34%
768
15%
1815

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
17%6%24424447%40%
47895
Night
17%6%25%424446%40%
46904
Cloud CoverDay
17%6%24424447%40%
47905
Night
17%6%25%424446%40%
46909
TransparencyDay
43%5%11%21%14%2
47584
Night
44%5%11%21%15%2
46733
SeeingDay
20%14%32%21%9%2
5927
Night
21%12%33%24%7%
14913

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%9%34313446%42%
1432
16th to endDay
15%6%35%423445%43%
1536
February1st to 15thDay
18%7%25%3345%47%37%
1690
16th to endDay
15%8%25%333445%42%
1580
March1st to 15thDay
20%8%24423446%37%
1805
16th to endDay
17%8%25%423446%42%
2175
April1st to 15thDay
19%7%25%424446%38%
2152
16th to endDay
18%4245%34346%42%
2295
May1st to 15thDay
26%7%25%323346%33%
2332
16th to endDay
17%5%25%4245%38%40%
2554
June1st to 15thDay
25%6%2442445%7%33%
2520
16th to endDay
14%5%245%35%6%5%10%36%
2520
July1st to 15thDay
13%5%25%5%26%6%6%9%35%
2520
16th to endDay
13%425%5%36%5%6%8%37%
2647
August1st to 15thDay
12%5%25%5%445%6%8%38%
2340
16th to endDay
12%5%25%5%3446%7%43%
2339
September1st to 15thDay
14%5%24424446%47%
2029
16th to endDay
15%413422346%49%
1815
October1st to 15thDay
20%5%25%313335%44%
1799
16th to endDay
15%6%25%42345%6%43%
1584
November1st to 15thDay
23%6%13323335%42%
1581
16th to endDay
17%7%24324446%42%
1620
December1st to 15thDay
19%6%24433346%40%
1494
16th to endDay
23%8%24434345%34%
1536
January1st to 15thNight
18%7%35%423336%40%
2506
16th to endNight
17%9%35%42343439%
2688
February1st to 15thNight
15%8%36%43435%5%38%
2165
16th to endNight
16%6%35%5%2443442%
1893
March1st to 15thNight
17%8%345%25%446%37%
2132
16th to endNight
17%7%35%42333443%
2048
April1st to 15thNight
17%8%35%5%3445%5%36%
1796
16th to endNight
21%6%245%34245%40%
1665
May1st to 15thNight
22%8%35%424347%34%
1620
16th to endNight
18%6%26%5%35%45%7%33%
1567
June1st to 15thNight
22%6%345%34446%34%
1440
16th to endNight
16%5%343245%5%8%40%
1440
July1st to 15thNight
12%5%36%5%246%5%10%38%
1440
16th to endNight
12%5%36%6%37%5%6%8%35%
1514
August1st to 15thNight
8%6%26%5%35%5%6%9%41%
1614
16th to endNight
12%4144345%5%7%45%
1860
September1st to 15thNight
14%4243445%5%6%45%
1819
16th to endNight
14%5%24323446%48%
1815
October1st to 15thNight
18%6%24323336%44%
1826
16th to endNight
17%5%245%33446%41%
2288
November1st to 15thNight
19%5%24423345%43%
2277
16th to endNight
17%6%25%42435%7%41%
2340
December1st to 15thNight
20%6%34423345%39%
2463
16th to endNight
19%9%35%42435%6%36%
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
16%9%24323437%41%
1432
16th to endDay
15%6%3443335%5%42%
1536
February1st to 15thDay
18%6%24325%5%48%37%
1690
16th to endDay
15%8%33423446%42%
1580
March1st to 15thDay
20%8%25%32435%6%36%
1815
16th to endDay
16%9%35%414346%41%
2175
April1st to 15thDay
19%6%24424446%38%
2152
16th to endDay
18%5%145%34445%43%
2295
May1st to 15thDay
26%8%24323346%33%
2332
16th to endDay
17%6%24424447%40%
2554
June1st to 15thDay
26%5%24425%35%8%33%
2520
16th to endDay
14%5%24435%5%6%10%37%
2520
July1st to 15thDay
14%6%25%425%5%5%8%37%
2520
16th to endDay
14%425%5%45%6%6%8%37%
2647
August1st to 15thDay
13%5%26%5%345%5%8%39%
2340
16th to endDay
12%6%25%43445%8%43%
2339
September1st to 15thDay
14%5%23423446%46%
2029
16th to endDay
16%413423346%49%
1815
October1st to 15thDay
20%5%24322336%44%
1799
16th to endDay
15%5%3441335%6%44%
1584
November1st to 15thDay
23%6%13324345%41%
1581
16th to endDay
16%6%35%324447%41%
1620
December1st to 15thDay
18%7%24434246%41%
1494
16th to endDay
23%9%245%23435%35%
1536
January1st to 15thNight
18%7%35%423335%41%
2506
16th to endNight
17%9%35%423345%39%
2688
February1st to 15thNight
15%9%35%424445%38%
2158
16th to endNight
16%7%345%2434442%
1893
March1st to 15thNight
18%7%245%3435%5%38%
2145
16th to endNight
17%7%35%42333442%
2047
April1st to 15thNight
17%8%35%43445%5%36%
1796
16th to endNight
21%5%25%5%34345%40%
1665
May1st to 15thNight
22%7%36%423346%34%
1620
16th to endNight
18%7%25%5%35%5%5%8%33%
1567
June1st to 15thNight
21%6%345%35%446%35%
1440
16th to endNight
17%5%24424449%40%
1440
July1st to 15thNight
13%5%35%5%25%5%5%9%38%
1440
16th to endNight
13%5%36%5%46%5%7%7%35%
1514
August1st to 15thNight
9%6%25%5%345%6%8%41%
1614
16th to endNight
12%3245%2445%8%45%
1860
September1st to 15thNight
14%4143345%47%45%
1819
16th to endNight
13%5%24323445%48%
1815
October1st to 15thNight
19%5%24423335%44%
1826
16th to endNight
17%5%25%434346%41%
2288
November1st to 15thNight
18%6%24424446%42%
2277
16th to endNight
17%5%2442345%6%42%
2340
December1st to 15thNight
20%7%25%423335%39%
2463
16th to endNight
19%8%36%42335%6%36%
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
43%5%11%24%12%3
1433
16th to endDay
42%49%26%14%1
1536
February1st to 15thDay
44%6%13%19%13%2
1693
16th to endDay
43%411%23%14%2
1580
March1st to 15thDay
48%313%22%9%3
1815
16th to endDay
44%410%20%15%5%
2175
April1st to 15thDay
47%49%20%16%2
2152
16th to endDay
43%49%21%16%4
2295
May1st to 15thDay
52%48%17%14%2
2332
16th to endDay
42%6%14%21%12%2
2558
June1st to 15thDay
50%6%11%19%10%
2520
16th to endDay
40%7%15%21%14%1
2520
July1st to 15thDay
42%8%11%20%14%2
2371
16th to endDay
40%8%15%20%11%3
2480
August1st to 15thDay
41%7%14%20%14%1
2327
16th to endDay
37%6%11%24%17%2
2339
September1st to 15thDay
37%6%11%22%22%
2029
16th to endDay
35%5%8%22%25%2
1815
October1st to 15thDay
41%410%24%16%3
1799
16th to endDay
39%412%24%15%2
1584
November1st to 15thDay
45%412%20%14%1
1581
16th to endDay
42%5%11%24%14%2
1620
December1st to 15thDay
45%415%18%16%
1494
16th to endDay
51%414%17%10%1
1536
January1st to 15thNight
45%412%21%13%1
2506
16th to endNight
47%410%19%15%3
2688
February1st to 15thNight
46%412%21%12%2
2166
16th to endNight
44%310%20%17%2
1893
March1st to 15thNight
47%411%19%14%3
2145
16th to endNight
45%38%18%19%5%
2048
April1st to 15thNight
46%5%9%18%16%2
1796
16th to endNight
47%48%20%15%4
1665
May1st to 15thNight
50%5%10%16%13%3
1620
16th to endNight
48%8%14%18%8%2
1569
June1st to 15thNight
50%6%12%17%12%
1440
16th to endNight
40%7%12%23%15%1
1440
July1st to 15thNight
41%7%11%25%14%
1360
16th to endNight
43%6%13%24%9%2
1418
August1st to 15thNight
37%6%14%24%14%1
1603
16th to endNight
35%6%11%27%18%
1860
September1st to 15thNight
37%5%13%24%18%
1819
16th to endNight
36%5%6%23%25%1
1815
October1st to 15thNight
42%5%10%22%16%3
1826
16th to endNight
43%5%13%21%14%1
2288
November1st to 15thNight
43%5%11%20%15%2
2277
16th to endNight
42%412%23%14%2
2340
December1st to 15thNight
47%413%21%13%
2463
16th to endNight
49%411%20%12%
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
18%30%36%13%1
60
16th to endDay
18%26%40%14%
64
February1st to 15thDay
26%17%41%12%2
248
16th to endDay
16%26%35%16%5%
239
March1st to 15thDay
24%24%32%12%4
270
16th to endDay
19%23%37%10%7%1
288
April1st to 15thDay
22%17%37%15%5%1
270
16th to endDay
21%16%35%19%43
270
May1st to 15thDay
35%17%24%15%5%1
288
16th to endDay
19%10%37%23%8%
331
June1st to 15thDay
25%13%31%20%8%1
315
16th to endDay
14%13%36%26%6%2
315
July1st to 15thDay
18%7%28%31%11%1
305
16th to endDay
13%7%28%31%15%3
326
August1st to 15thDay
15%6%29%31%14%2
313
16th to endDay
13%6%25%30%17%7%
332
September1st to 15thDay
17%9%26%25%15%4
294
16th to endDay
20%5%29%23%9%12%
254
October1st to 15thDay
23%11%25%23%11%5%
252
16th to endDay
17%16%33%21%10%1
240
November1st to 15thDay
26%12%31%15%9%3
235
16th to endDay
20%17%32%17%10%
240
December1st to 15thDay
18%21%36%19%3
114
16th to endDay
32%25%34%43
64
January1st to 15thNight
22%19%37%16%3
720
16th to endNight
26%18%36%16%2
768
February1st to 15thNight
21%19%39%17%1
704
16th to endNight
22%19%38%16%2
631
March1st to 15thNight
22%18%36%18%3
720
16th to endNight
22%17%35%19%4
768
April1st to 15thNight
21%16%38%20%3
718
16th to endNight
23%14%34%22%5%
585
May1st to 15thNight
26%12%33%21%5%
540
16th to endNight
22%9%34%27%6%
447
June1st to 15thNight
23%7%28%31%8%
360
16th to endNight
18%328%39%8%
360
July1st to 15thNight
16%232%38%10%
340
16th to endNight
13%226%46%10%
376
August1st to 15thNight
12%430%41%10%
533
16th to endNight
14%223%40%16%1
714
September1st to 15thNight
16%331%34%12%1
700
16th to endNight
17%425%29%19%3
657
October1st to 15thNight
22%7%30%28%10%2
660
16th to endNight
22%13%36%20%7%
704
November1st to 15thNight
21%14%30%22%10%1
700
16th to endNight
20%18%31%21%6%1
720
December1st to 15thNight
24%16%34%19%4
720
16th to endNight
25%20%34%16%1
768
Page generated at 2017-09-11 19:35:14. Version ac04

Copyright 2017 A. Danko


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