George Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the George Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
57%
15329
23%
46857
19%
15284
61%
15284
31%
28057

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
39%
899
22%
2327
11%
895
44%
895
28%
1571
January16th to endNight
40%
960
23%
2496
11%
960
45%
960
29%
1655
February1st to 15thNight
41%
755
23%
2161
13%
751
48%
751
27%
1388
February16th to endNight
36%
523
24%
1785
13%
523
46%
523
24%
1090
March1st to 15thNight
37%
540
24%
1980
17%
540
48%
540
21%
1233
March16th to endNight
48%
576
23%
2112
19%
576
56%
576
28%
1181
April1st to 15thNight
46%
539
21%
1956
17%
539
55%
539
25%
1171
April16th to endNight
43%
540
22%
1800
18%
540
51%
540
23%
1141
May1st to 15thNight
50%
539
21%
1713
19%
539
55%
539
28%
1032
May16th to endNight
64%
562
24%
1685
25%
561
66%
561
34%
994
June1st to 15thNight
81%
540
20%
1620
23%
540
82%
540
46%
840
June16th to endNight
78%
540
15%
1620
19%
540
79%
540
35%
962
July1st to 15thNight
81%
510
18%
1530
23%
510
81%
510
38%
869
July16th to endNight
84%
564
18%
1594
23%
531
85%
531
39%
891
August1st to 15thNight
91%
539
27%
1610
30%
536
91%
536
55%
771
August16th to endNight
79%
573
17%
1958
21%
573
79%
573
28%
1163
September1st to 15thNight
75%
530
15%
1943
17%
530
76%
530
28%
1125
September16th to endNight
73%
492
26%
1815
30%
492
74%
492
28%
1038
October1st to 15thNight
75%
597
33%
1917
30%
597
77%
597
45%
950
October16th to endNight
67%
704
35%
2112
27%
704
71%
704
44%
1106
November1st to 15thNight
63%
700
27%
2100
23%
700
64%
700
34%
1241
November16th to endNight
56%
747
32%
2187
23%
747
62%
747
37%
1265
December1st to 15thNight
42%
900
23%
2340
14%
900
46%
900
26%
1637
December16th to endNight
38%
960
20%
2496
10%
960
43%
960
24%
1743

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
11%6%36%6%36%5%6%8%36%
47795
Night
10%5%2442445%8%48%
47054
TransparencyDay
43%7%11%17%13%6%
47495
Night
34%6%13%21%16%8%
46859
SeeingDay
11%314%27%26%16%
5329
Night
12%418%32%28%4
15332

By Month

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
19%6%345%34445%39%
1611
16th to endDay
19%7%25%312245%43%
1728
February1st to 15thDay
19%8%26%32333442%
1708
16th to endDay
18%8%44424335%39%
1688
March1st to 15thDay
20%8%35%423435%37%
1980
16th to endDay
14%6%36%42435%6%41%
2110
April1st to 15thDay
13%6%45%5%35%45%6%39%
1992
16th to endDay
13%7%46%5%25%446%38%
2160
May1st to 15thDay
10%7%36%6%36%5%6%8%33%
2235
16th to endDay
8%6%37%6%36%6%8%10%32%
2430
June1st to 15thDay
4326%7%49%7%8%10%34%
2340
16th to endDay
7%437%8%5%10%9%8%10%25%
2340
July1st to 15thDay
9%5%36%7%48%7%8%11%26%
2340
16th to endDay
5%437%9%6%8%8%8%10%25%
2466
August1st to 15thDay
3225%6%6%8%8%9%12%36%
2340
16th to endDay
9%436%8%5%6%7%8%9%28%
2238
September1st to 15thDay
8%5%38%7%5%7%6%8%8%30%
1936
16th to endDay
12%7%36%6%45%5%5%7%34%
1815
October1st to 15thDay
8%5%244345%6%6%47%
1702
16th to endDay
9%323434446%54%
1760
November1st to 15thDay
10%6%36%6%35%47%7%39%
1758
16th to endDay
13%5%35%5%24246%46%
1770
December1st to 15thDay
17%8%46%6%35%437%34%
1620
16th to endDay
16%8%36%425%45%6%35%
1728
January1st to 15thNight
18%6%25%423346%42%
2327
16th to endNight
18%5%25%423345%45%
2496
February1st to 15thNight
16%7%245%23346%44%
2153
16th to endNight
16%6%34433246%45%
1785
March1st to 15thNight
18%7%24413446%42%
1980
16th to endNight
9%5%24424446%50%
2112
April1st to 15thNight
12%5%25%42445%6%45%
1956
16th to endNight
14%5%25%425%45%6%41%
1800
May1st to 15thNight
8%5%245%25%5%6%10%42%
1712
16th to endNight
45%234346%8%10%45%
1683
June1st to 15thNight
321332337%12%55%
1620
16th to endNight
4224425%6%8%10%46%
1620
July1st to 15thNight
4423425%46%11%51%
1620
16th to endNight
3223326%5%6%11%51%
1702
August1st to 15thNight
1112235%5%12%63%
1620
16th to endNight
4425%5%25%5%6%11%45%
1958
September1st to 15thNight
6%425%4345%6%10%46%
1943
16th to endNight
7%4245%345%6%8%47%
1815
October1st to 15thNight
6%31221345%7%61%
1917
16th to endNight
8%31331223463%
2112
November1st to 15thNight
10%4244245%5%7%48%
2100
16th to endNight
11%423323345%54%
2187
December1st to 15thNight
16%7%36%5%24446%38%
2340
16th to endNight
16%8%36%423445%39%
2496

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
47%36%13%19%8%
1612
16th to endDay
44%35%17%16%12%
1728
February1st to 15thDay
46%45%15%16%11%
1709
16th to endDay
47%37%14%18%7%
1688
March1st to 15thDay
48%5%8%13%17%6%
1980
16th to endDay
42%49%13%22%6%
2112
April1st to 15thDay
42%5%9%17%15%8%
1992
16th to endDay
46%5%8%18%14%7%
2160
May1st to 15thDay
46%7%10%15%12%7%
2235
16th to endDay
41%8%13%19%14%2
2434
June1st to 15thDay
37%10%15%19%15%1
2340
16th to endDay
46%11%16%18%7%
2340
July1st to 15thDay
43%10%19%20%5%
2201
16th to endDay
44%14%19%19%1
2311
August1st to 15thDay
32%12%21%27%5%
2326
16th to endDay
47%13%16%15%6%1
2238
September1st to 15thDay
47%10%15%15%8%3
1936
16th to endDay
46%6%11%14%17%4
1815
October1st to 15thDay
35%48%21%15%14%
1702
16th to endDay
30%46%15%26%16%
1760
November1st to 15thDay
40%411%17%17%8%
1758
16th to endDay
40%45%13%19%17%
1770
December1st to 15thDay
50%48%16%13%7%
1620
16th to endDay
48%6%7%15%14%7%
1728
January1st to 15thNight
43%36%15%19%11%
2327
16th to endNight
41%36%15%18%13%
2496
February1st to 15thNight
40%48%12%18%14%
2163
16th to endNight
41%36%15%21%11%
1785
March1st to 15thNight
43%48%15%17%10%
1980
16th to endNight
34%5%13%16%21%9%
2112
April1st to 15thNight
38%5%9%19%16%10%
1956
16th to endNight
42%5%11%17%14%9%
1800
May1st to 15thNight
35%7%13%20%13%9%
1713
16th to endNight
29%8%17%26%14%2
1685
June1st to 15thNight
21%6%20%28%21%1
1620
16th to endNight
29%9%24%27%9%
1620
July1st to 15thNight
26%8%29%29%6%
1530
16th to endNight
23%9%32%30%3
1594
August1st to 15thNight
14%6%28%42%7%
1610
16th to endNight
31%11%25%25%5%1
1958
September1st to 15thNight
30%10%22%21%11%3
1943
16th to endNight
33%7%13%21%18%5%
1815
October1st to 15thNight
21%5%11%28%19%13%
1917
16th to endNight
25%26%18%27%19%
2112
November1st to 15thNight
32%5%12%23%18%8%
2100
16th to endNight
30%48%17%21%16%
2187
December1st to 15thNight
44%6%9%18%13%7%
2340
16th to endNight
46%47%15%14%10%
2496

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
28%6%22%33%8%
90
16th to endDay
18%11%33%26%9%1
96
February1st to 15thDay
8%10%34%33%12%1
90
16th to endDay
13%6%40%32%7%
81
March1st to 15thDay
34%8%32%14%8%1
90
16th to endDay
15%10%30%28%11%4
96
April1st to 15thDay
11%11%26%29%20%
111
16th to endDay
18%5%26%27%20%2
270
May1st to 15thDay
15%7%28%32%15%1
372
16th to endDay
13%223%36%19%4
517
June1st to 15thDay
6%18%33%38%11%
495
16th to endDay
8%18%28%31%20%
495
July1st to 15thDay
7%429%32%25%
475
16th to endDay
7%1423%33%31%
515
August1st to 15thDay
4219%37%34%
493
16th to endDay
14%139%33%37%
278
September1st to 15thDay
48%26%34%25%
123
16th to endDay
7%410%42%35%
90
October1st to 15thDay
35%42%35%13%
90
16th to endDay
17%113%30%26%11%
96
November1st to 15thDay
16%326%27%20%5%
90
16th to endDay
21%328%30%8%7%
90
December1st to 15thDay
25%325%26%10%8%
90
16th to endDay
23%9%37%20%6%2
96
January1st to 15thNight
20%7%26%34%11%
900
16th to endNight
20%8%26%34%10%
960
February1st to 15thNight
20%7%25%36%9%
755
16th to endNight
18%9%32%33%6%
523
March1st to 15thNight
22%7%27%34%7%
540
16th to endNight
11%7%27%38%14%1
576
April1st to 15thNight
12%7%27%41%10%
539
16th to endNight
17%6%25%35%13%
540
May1st to 15thNight
12%229%44%11%
540
16th to endNight
7%219%45%24%1
563
June1st to 15thNight
3442%45%2
540
16th to endNight
5%5%27%52%9%
540
July1st to 15thNight
5%218%61%11%
510
16th to endNight
3117%58%17%
564
August1st to 15thNight
111%72%13%
539
16th to endNight
7%216%57%16%
573
September1st to 15thNight
7%15%15%55%16%
530
16th to endNight
8%15%22%50%11%
492
October1st to 15thNight
6%111%30%43%7%
597
16th to endNight
8%314%37%32%3
704
November1st to 15thNight
10%217%38%29%3
700
16th to endNight
13%421%37%21%1
747
December1st to 15thNight
20%5%24%32%16%
900
16th to endNight
21%6%26%31%11%1
960
Page generated at 2017-09-13 06:39:10. Version ac04

Copyright 2017 A. Danko


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