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 2018-03-11.

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%
15641
18%
49052
8%
15608
39%
15608
20%
32278

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
19%
2716
5%
776
33%
776
17%
1721
January16th to endNight
14%
832
18%
2912
2%
832
33%
832
15%
1893
February1st to 15thNight
15%
764
17%
2350
3%
761
31%
761
17%
1591
February16th to endNight
14%
683
23%
2049
6%
683
34%
683
18%
1374
March1st to 15thNight
17%
764
17%
2276
6%
764
31%
764
17%
1556
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%
720
19%
1875
9%
720
48%
720
32%
1220
September16th to endNight
45%
717
24%
1980
16%
717
51%
717
30%
1259
October1st to 15thNight
35%
720
22%
1992
11%
720
45%
720
26%
1307
October16th to endNight
25%
768
18%
2496
8%
768
39%
768
21%
1605
November1st to 15thNight
29%
760
17%
2472
8%
760
42%
760
20%
1617
November16th to endNight
25%
780
22%
2535
8%
780
42%
780
20%
1573
December1st to 15thNight
21%
780
18%
2668
5%
780
35%
780
16%
1764
December16th to endNight
15%
832
20%
2912
5%
832
34%
832
15%
1944

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%
49576
Night
17%6%25%424446%40%
49223
Cloud CoverDay
17%6%24424447%40%
49586
Night
17%6%25%424446%40%
49228
TransparencyDay
43%5%11%21%14%2
49265
Night
44%5%11%21%15%2
49052
SeeingDay
20%14%32%20%8%2
6483
Night
21%13%33%24%7%
15641

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%34313346%42%
1552
16th to endDay
16%6%34423445%43%
1664
February1st to 15thDay
19%7%25%3345%47%36%
1836
16th to endDay
16%8%24333446%41%
1710
March1st to 15thDay
20%9%24423446%36%
1911
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
13%424424445%47%
2085
16th to endDay
16%423422346%48%
1980
October1st to 15thDay
20%5%15%313335%44%
1963
16th to endDay
15%6%25%32345%6%44%
1728
November1st to 15thDay
22%6%23323335%41%
1716
16th to endDay
16%6%24324446%44%
1755
December1st to 15thDay
19%6%25%434336%40%
1618
16th to endDay
22%8%24434346%35%
1664
January1st to 15thNight
17%6%25%423336%41%
2716
16th to endNight
17%9%35%423445%39%
2912
February1st to 15thNight
16%8%36%43435%5%38%
2349
16th to endNight
17%7%35%5%2443441%
2049
March1st to 15thNight
17%8%345%25%446%36%
2263
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%46%45%
1875
16th to endNight
15%6%24323445%48%
1980
October1st to 15thNight
17%6%24323336%45%
1992
16th to endNight
18%5%245%33446%41%
2496
November1st to 15thNight
18%5%24424345%42%
2472
16th to endNight
17%5%25%32435%6%43%
2535
December1st to 15thNight
20%7%34424345%38%
2668
16th to endNight
19%8%35%42435%6%37%
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
16%9%24323437%42%
1552
16th to endDay
16%6%3442335%5%43%
1664
February1st to 15thDay
19%7%25%3245%37%37%
1836
16th to endDay
16%8%33423446%41%
1710
March1st to 15thDay
21%9%25%424346%35%
1921
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%47%
2085
16th to endDay
18%413423346%48%
1980
October1st to 15thDay
20%5%24322336%44%
1963
16th to endDay
16%5%34413446%44%
1728
November1st to 15thDay
23%6%13324345%41%
1716
16th to endDay
16%6%34324447%43%
1755
December1st to 15thDay
18%7%24434346%40%
1618
16th to endDay
22%9%245%23435%35%
1664
January1st to 15thNight
17%7%35%423336%41%
2716
16th to endNight
17%9%34423345%39%
2912
February1st to 15thNight
16%9%35%424445%38%
2342
16th to endNight
17%7%35%5%2434441%
2049
March1st to 15thNight
18%8%245%3335%6%36%
2276
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%414334447%46%
1875
16th to endNight
14%6%24323445%47%
1980
October1st to 15thNight
18%6%24423335%45%
1992
16th to endNight
17%5%24434446%41%
2496
November1st to 15thNight
18%6%24324446%41%
2472
16th to endNight
17%5%2442345%6%43%
2535
December1st to 15thNight
20%7%25%423335%39%
2668
16th to endNight
19%8%35%42335%6%37%
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
42%5%10%23%13%3
1553
16th to endDay
42%5%10%25%14%1
1664
February1st to 15thDay
46%6%12%19%12%2
1839
16th to endDay
43%411%22%14%2
1710
March1st to 15thDay
49%312%22%8%2
1921
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%21%21%1
2085
16th to endDay
37%5%8%21%25%2
1980
October1st to 15thDay
41%49%25%15%2
1963
16th to endDay
39%411%24%16%2
1728
November1st to 15thDay
45%412%20%14%1
1716
16th to endDay
41%5%10%25%14%2
1755
December1st to 15thDay
46%414%17%16%
1618
16th to endDay
50%413%17%11%1
1664
January1st to 15thNight
44%412%21%14%1
2716
16th to endNight
47%411%19%15%3
2912
February1st to 15thNight
47%412%20%12%2
2350
16th to endNight
46%310%20%16%2
2049
March1st to 15thNight
48%411%19%13%3
2276
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%12%24%18%1
1875
16th to endNight
37%5%7%22%25%1
1980
October1st to 15thNight
41%5%10%23%16%2
1992
16th to endNight
42%5%13%22%14%1
2496
November1st to 15thNight
43%5%11%20%15%2
2472
16th to endNight
41%312%24%15%2
2535
December1st to 15thNight
47%413%20%13%
2668
16th to endNight
48%411%20%13%1
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
17%35%32%13%1
90
16th to endDay
23%21%41%12%
96
February1st to 15thDay
26%21%38%10%2
304
16th to endDay
18%25%37%14%4
291
March1st to 15thDay
27%24%32%12%3
312
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
16%9%27%25%15%4
315
16th to endDay
23%5%26%21%10%11%
314
October1st to 15thDay
23%10%25%24%11%5%
311
16th to endDay
19%15%32%21%9%1
288
November1st to 15thDay
25%13%32%15%9%3
280
16th to endDay
19%20%30%17%10%
285
December1st to 15thDay
19%18%38%17%5%
148
16th to endDay
27%31%35%42
96
January1st to 15thNight
21%20%37%16%3
780
16th to endNight
25%18%36%16%2
832
February1st to 15thNight
22%19%39%17%1
764
16th to endNight
23%18%39%15%2
683
March1st to 15thNight
23%18%36%17%3
764
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%35%12%1
720
16th to endNight
19%423%28%19%3
717
October1st to 15thNight
21%7%29%27%11%1
720
16th to endNight
21%13%36%18%9%
768
November1st to 15thNight
20%13%31%22%10%1
760
16th to endNight
19%18%32%21%6%1
780
December1st to 15thNight
24%16%34%19%4
780
16th to endNight
25%20%34%16%1
832
Page generated at 2018-03-12 13:28:11. Version ac04

Copyright 2018 A. Danko


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