The Geek Shed
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Geek Shed clear sky chart from 2005-11-05 to 2017-09-21.

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
35%
15059
17%
46922
10%
15021
43%
15021
21%
30899

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
19%
718
14%
2479
6%
716
30%
716
13%
1719
January16th to endNight
18%
768
17%
2496
5%
768
32%
768
15%
1659
February1st to 15thNight
15%
704
14%
2287
4%
701
28%
701
14%
1597
February16th to endNight
18%
631
18%
1942
6%
631
33%
631
16%
1320
March1st to 15thNight
24%
720
18%
2019
8%
720
35%
720
18%
1397
March16th to endNight
25%
768
20%
2082
8%
768
35%
768
21%
1417
April1st to 15thNight
22%
718
14%
1796
4%
718
28%
718
19%
1293
April16th to endNight
33%
713
18%
1793
5%
713
41%
713
28%
1214
May1st to 15thNight
36%
469
18%
1549
10%
469
45%
469
19%
1036
May16th to endNight
46%
374
17%
1497
15%
374
54%
374
19%
935
June1st to 15thNight
45%
360
16%
1440
15%
360
54%
360
20%
869
June16th to endNight
54%
360
16%
1440
19%
360
60%
360
26%
812
July1st to 15thNight
50%
340
14%
1360
16%
340
55%
340
21%
838
July16th to endNight
62%
477
16%
1511
15%
447
67%
447
29%
893
August1st to 15thNight
62%
539
18%
1609
13%
536
65%
536
31%
989
August16th to endNight
63%
727
22%
1873
14%
727
64%
727
33%
1208
September1st to 15thNight
50%
720
24%
1800
13%
720
54%
720
34%
1165
September16th to endNight
54%
681
23%
1871
18%
681
58%
681
32%
1202
October1st to 15thNight
43%
660
20%
1980
16%
660
50%
660
26%
1271
October16th to endNight
31%
704
19%
2112
10%
704
42%
704
23%
1368
November1st to 15thNight
38%
700
21%
2258
15%
700
48%
700
24%
1402
November16th to endNight
27%
720
16%
2520
9%
720
37%
720
16%
1668
December1st to 15thNight
22%
720
13%
2520
6%
720
32%
720
13%
1763
December16th to endNight
20%
768
13%
2688
3%
768
32%
768
12%
1864

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%7%36%6%35%5%5%7%34%
47934
Night
14%6%35%5%3445%7%38%
47101
Cloud CoverDay
15%6%36%6%35%45%7%35%
47944
Night
14%6%25%5%3445%7%39%
47106
TransparencyDay
47%5%12%20%12%1
47631
Night
43%5%13%22%13%1
46922
SeeingDay
19%13%24%22%15%5%
5599
Night
19%13%26%27%11%1
15062

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
13%7%38%8%46%5%46%30%
1458
16th to endDay
11%11%6%9%9%5%5%447%24%
1728
February1st to 15thDay
14%14%5%7%6%4345%7%27%
1575
16th to endDay
13%9%49%7%35%5%36%30%
1530
March1st to 15thDay
16%8%36%6%3447%6%32%
1929
16th to endDay
16%9%36%6%24346%35%
2141
April1st to 15thDay
17%8%36%5%3435%5%35%
2152
16th to endDay
16%7%36%5%2435%6%38%
2178
May1st to 15thDay
20%6%36%6%345%46%33%
2400
16th to endDay
16%6%26%6%35%5%6%7%34%
2618
June1st to 15thDay
13%6%36%5%35%5%5%8%35%
2520
16th to endDay
13%5%35%5%35%5%6%10%35%
2520
July1st to 15thDay
10%5%25%6%46%6%6%9%35%
2520
16th to endDay
9%436%6%46%6%7%10%33%
2550
August1st to 15thDay
12%6%26%7%45%6%7%7%33%
2340
16th to endDay
13%5%25%5%445%6%8%36%
2315
September1st to 15thDay
17%5%246%24347%40%
2160
16th to endDay
16%5%25%433436%44%
1878
October1st to 15thDay
18%6%245%23447%39%
1650
16th to endDay
17%6%26%6%345%46%35%
1760
November1st to 15thDay
12%7%25%5%2446%7%41%
1596
16th to endDay
20%6%35%436%45%5%34%
1440
December1st to 15thDay
16%10%5%8%7%35%447%26%
1440
16th to endDay
17%8%47%7%35%5%47%25%
1536
January1st to 15thNight
14%7%36%7%35%5%6%8%30%
2479
16th to endNight
12%8%36%5%35%5%5%8%35%
2496
February1st to 15thNight
13%8%5%5%6%35%46%7%32%
2285
16th to endNight
12%7%36%6%46%5%5%6%36%
1942
March1st to 15thNight
17%6%35%5%2445%6%37%
2007
16th to endNight
14%7%36%42345%7%39%
2082
April1st to 15thNight
17%7%46%5%25%447%34%
1796
16th to endNight
16%425%42345%7%43%
1793
May1st to 15thNight
17%7%35%4245%46%38%
1549
16th to endNight
13%7%15%5%345%5%6%41%
1495
June1st to 15thNight
15%5%35%5%2435%8%42%
1440
16th to endNight
11%3245%245%6%10%43%
1440
July1st to 15thNight
10%425%5%35%45%8%43%
1440
16th to endNight
8%4244245%6%10%44%
1615
August1st to 15thNight
9%425%43346%8%45%
1620
16th to endNight
12%4244345%48%46%
1873
September1st to 15thNight
15%42432335%6%46%
1800
16th to endNight
14%434424446%46%
1871
October1st to 15thNight
19%5%14323347%43%
1980
16th to endNight
17%6%25%42445%7%40%
2112
November1st to 15thNight
12%7%345%24346%45%
2258
16th to endNight
18%7%35%5%2446%7%34%
2520
December1st to 15thNight
17%8%36%5%35%45%8%30%
2520
16th to endNight
17%7%37%5%35%5%5%8%30%
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
13%7%37%8%46%5%5%5%31%
1458
16th to endDay
12%9%6%10%8%45%446%26%
1728
February1st to 15thDay
14%13%5%8%6%35%35%6%28%
1575
16th to endDay
13%9%5%7%7%5%4437%31%
1530
March1st to 15thDay
16%7%46%6%35%5%6%6%33%
1940
16th to endDay
16%8%36%5%34346%36%
2140
April1st to 15thDay
18%7%35%5%35%446%36%
2152
16th to endDay
16%6%26%5%23446%38%
2178
May1st to 15thDay
21%6%26%6%35%445%34%
2400
16th to endDay
17%5%35%435%5%6%7%35%
2618
June1st to 15thDay
13%6%26%5%36%5%5%8%36%
2520
16th to endDay
13%5%245%35%5%6%10%37%
2520
July1st to 15thDay
10%6%35%6%47%5%6%9%35%
2520
16th to endDay
10%5%246%47%6%7%10%35%
2550
August1st to 15thDay
14%426%7%35%6%6%8%34%
2340
16th to endDay
14%5%246%35%5%6%8%37%
2315
September1st to 15thDay
17%5%24434447%42%
2160
16th to endDay
16%5%24424345%44%
1878
October1st to 15thDay
19%5%2442445%5%40%
1650
16th to endDay
17%5%35%7%345%5%6%35%
1760
November1st to 15thDay
12%6%25%5%3435%7%42%
1596
16th to endDay
20%6%345%35%6%5%6%33%
1440
December1st to 15thDay
16%10%48%6%46%45%5%28%
1440
16th to endDay
17%8%37%7%35%5%5%7%26%
1536
January1st to 15thNight
14%7%36%6%45%5%6%7%32%
2479
16th to endNight
12%8%36%6%35%5%5%7%36%
2496
February1st to 15thNight
13%8%47%6%345%6%7%33%
2278
16th to endNight
12%6%36%6%45%5%5%6%37%
1942
March1st to 15thNight
17%6%35%5%34447%38%
2019
16th to endNight
14%7%35%43445%7%40%
2082
April1st to 15thNight
17%7%45%5%3445%7%34%
1796
16th to endNight
16%42442435%6%44%
1793
May1st to 15thNight
19%6%25%423446%39%
1549
16th to endNight
13%6%25%5%3446%7%41%
1495
June1st to 15thNight
15%4345%25%25%7%43%
1440
16th to endNight
11%315%435%46%10%43%
1440
July1st to 15thNight
10%425%5%35%45%8%43%
1440
16th to endNight
8%414435%5%6%10%44%
1615
August1st to 15thNight
9%5%26%43446%7%46%
1620
16th to endNight
12%424433448%46%
1873
September1st to 15thNight
15%5%13323347%47%
1800
16th to endNight
14%5%2442445%7%46%
1871
October1st to 15thNight
19%5%24323446%43%
1980
16th to endNight
17%5%2442445%7%41%
2112
November1st to 15thNight
12%7%25%5%24346%46%
2258
16th to endNight
18%6%35%5%3446%7%34%
2520
December1st to 15thNight
17%7%36%6%35%5%5%7%31%
2520
16th to endNight
16%8%27%6%345%6%7%31%
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
51%5%15%18%8%1
1459
16th to endDay
58%411%17%6%
1728
February1st to 15thDay
56%5%10%19%6%
1577
16th to endDay
53%413%19%7%
1530
March1st to 15thDay
50%5%12%21%8%1
1940
16th to endDay
50%49%20%12%1
2141
April1st to 15thDay
48%49%21%13%2
2152
16th to endDay
45%5%8%19%16%5%
2178
May1st to 15thDay
50%410%19%13%1
2400
16th to endDay
46%6%13%18%12%2
2622
June1st to 15thDay
44%7%12%21%12%1
2520
16th to endDay
41%7%14%23%11%1
2520
July1st to 15thDay
43%7%12%20%14%1
2371
16th to endDay
39%8%15%21%14%
2391
August1st to 15thDay
44%7%11%22%13%
2327
16th to endDay
41%5%10%23%15%2
2315
September1st to 15thDay
42%5%10%21%19%1
2160
16th to endDay
41%38%22%20%2
1878
October1st to 15thDay
44%5%12%22%14%1
1650
16th to endDay
47%5%13%23%9%
1760
November1st to 15thDay
40%414%22%13%4
1596
16th to endDay
48%6%12%22%9%
1440
December1st to 15thDay
55%6%16%15%5%
1440
16th to endDay
54%6%16%16%5%
1536
January1st to 15thNight
50%6%14%17%9%1
2479
16th to endNight
46%5%15%21%10%
2496
February1st to 15thNight
49%6%14%20%7%
2287
16th to endNight
46%5%12%21%13%
1942
March1st to 15thNight
46%5%12%22%12%
2019
16th to endNight
43%5%12%21%14%1
2082
April1st to 15thNight
48%5%9%18%15%1
1796
16th to endNight
39%6%10%22%16%4
1793
May1st to 15thNight
45%6%9%22%14%1
1549
16th to endNight
40%8%13%19%15%3
1497
June1st to 15thNight
39%7%12%24%15%
1440
16th to endNight
34%6%14%26%16%1
1440
July1st to 15thNight
40%7%11%23%14%3
1360
16th to endNight
32%9%14%25%16%2
1511
August1st to 15thNight
35%6%14%22%19%
1609
16th to endNight
36%6%10%25%19%2
1873
September1st to 15thNight
37%411%24%19%2
1800
16th to endNight
37%5%9%24%20%2
1871
October1st to 15thNight
41%412%23%15%1
1980
16th to endNight
41%5%14%25%12%
2112
November1st to 15thNight
40%412%22%15%4
2258
16th to endNight
47%412%21%11%1
2520
December1st to 15thNight
51%6%15%18%8%
2520
16th to endNight
50%6%16%19%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
23%35%21%12%6%1
65
16th to endDay
22%36%22%16%1
96
February1st to 15thDay
22%33%37%6%
90
16th to endDay
21%22%33%20%2
189
March1st to 15thDay
23%20%27%22%6%
270
16th to endDay
22%20%27%19%7%2
288
April1st to 15thDay
21%24%22%20%8%1
270
16th to endDay
20%15%27%14%16%6%
270
May1st to 15thDay
31%20%20%11%11%4
288
16th to endDay
18%13%25%20%16%6%
331
June1st to 15thDay
13%13%27%23%17%3
315
16th to endDay
19%8%31%23%12%3
315
July1st to 15thDay
13%6%29%27%18%5%
305
16th to endDay
10%5%21%29%23%8%
326
August1st to 15thDay
15%419%27%23%8%
313
16th to endDay
14%315%27%22%16%
332
September1st to 15thDay
17%8%18%20%22%12%
315
16th to endDay
20%5%16%22%23%12%
275
October1st to 15thDay
24%6%17%25%21%4
255
16th to endDay
20%12%31%26%8%
272
November1st to 15thDay
16%14%23%27%15%1
235
16th to endDay
21%16%36%15%10%
60
December1st to 15thDay
20%40%15%11%11%1
60
16th to endDay
31%20%39%9%
64
January1st to 15thNight
19%20%34%21%3
720
16th to endNight
17%20%36%23%1
768
February1st to 15thNight
22%20%34%21%
704
16th to endNight
18%23%35%19%3
631
March1st to 15thNight
23%19%30%23%3
720
16th to endNight
20%17%32%22%7%
768
April1st to 15thNight
21%19%33%20%5%
718
16th to endNight
19%13%29%27%9%
713
May1st to 15thNight
24%7%26%28%13%
469
16th to endNight
17%6%22%32%19%1
375
June1st to 15thNight
15%6%23%37%18%
360
16th to endNight
13%324%42%16%
360
July1st to 15thNight
12%324%40%18%
340
16th to endNight
11%215%44%23%1
477
August1st to 15thNight
13%213%43%25%2
539
16th to endNight
14%312%34%32%3
727
September1st to 15thNight
18%419%31%23%2
720
16th to endNight
17%417%26%29%5%
681
October1st to 15thNight
22%9%19%27%18%2
660
16th to endNight
21%12%29%30%6%
704
November1st to 15thNight
17%12%27%31%11%
700
16th to endNight
23%20%23%24%6%1
720
December1st to 15thNight
22%18%31%21%5%
720
16th to endNight
22%18%32%23%2
768
Page generated at 2017-09-22 07:35:38. Version ac04

Copyright 2017 A. Danko


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