GMDRC
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the GMDRC clear sky chart from 2005-11-05 to 2017-09-19.

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
71%
16010
39%
46979
31%
15973
79%
15973
60%
21057

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
67%
716
35%
2327
31%
716
76%
716
49%
1079
January16th to endNight
60%
768
39%
2411
30%
768
73%
768
46%
1166
February1st to 15thNight
66%
697
39%
2111
33%
697
76%
697
57%
955
February16th to endNight
60%
632
37%
1895
34%
632
68%
632
47%
928
March1st to 15thNight
60%
720
35%
2117
29%
720
72%
720
51%
1002
March16th to endNight
63%
768
39%
2112
26%
768
75%
768
58%
993
April1st to 15thNight
50%
719
38%
1799
15%
719
64%
719
58%
888
April16th to endNight
59%
669
43%
1749
19%
669
73%
669
67%
766
May1st to 15thNight
66%
540
41%
1619
26%
539
75%
539
68%
644
May16th to endNight
61%
561
39%
1685
24%
561
72%
561
69%
664
June1st to 15thNight
75%
540
34%
1620
27%
540
80%
540
70%
649
June16th to endNight
82%
540
37%
1620
32%
540
85%
540
80%
618
July1st to 15thNight
88%
510
32%
1530
28%
510
89%
510
66%
659
July16th to endNight
82%
564
35%
1593
31%
531
83%
531
54%
766
August1st to 15thNight
88%
639
38%
1713
26%
636
89%
636
70%
789
August16th to endNight
88%
764
43%
1910
30%
764
89%
764
71%
918
September1st to 15thNight
87%
720
38%
1911
30%
720
88%
720
66%
913
September16th to endNight
82%
671
48%
1856
40%
671
88%
671
79%
761
October1st to 15thNight
75%
660
46%
1815
37%
660
82%
660
68%
807
October16th to endNight
77%
704
44%
2135
39%
704
85%
704
67%
875
November1st to 15thNight
73%
700
40%
2275
37%
700
84%
700
62%
932
November16th to endNight
73%
720
43%
2340
42%
720
80%
720
58%
983
December1st to 15thNight
64%
720
37%
2340
33%
720
74%
720
45%
1113
December16th to endNight
60%
768
37%
2496
31%
768
71%
768
43%
1189

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
2212212235%72%
47839
Night
2212212335%72%
47175
TransparencyDay
14%1212%26%41%
47534
Night
14%1213%27%40%
46981
SeeingDay
5%8%23%37%20%4
5745
Night
45%14%31%34%10%
16023

By Month

Percentage Cloud Cover SW (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
3323312247%65%
1611
16th to endDay
5%313423335%63%
1812
February1st to 15thDay
324312246%67%
1751
16th to endDay
5%313424445%61%
1579
March1st to 15thDay
2111213347%70%
1842
16th to endDay
211221235%6%69%
2112
April1st to 15thDay
3212222236%69%
2146
16th to endDay
111111235%78%
2211
May1st to 15thDay
11212335%77%
2331
16th to endDay
111111235%78%
2429
June1st to 15thDay
121122482%
2340
16th to endDay
11111111286%
2340
July1st to 15thDay
321312345%70%
2340
16th to endDay
3212324348%62%
2467
August1st to 15thDay
22211333474%
2235
16th to endDay
31221333472%
2292
September1st to 15thDay
211212345%74%
2049
16th to endDay
1111112384%
1849
October1st to 15thDay
211231213475%
1815
16th to endDay
111111235%78%
1736
November1st to 15thDay
122222222473%
1584
16th to endDay
322113246%71%
1620
December1st to 15thDay
432331345%8%58%
1620
16th to endDay
6%434313336%59%
1728
January1st to 15thNight
3313322346%65%
2327
16th to endNight
5%31232333465%
2411
February1st to 15thNight
3312212236%69%
2101
16th to endNight
6%31332235%7%61%
1895
March1st to 15thNight
2222213445%67%
2117
16th to endNight
1113223338%68%
2112
April1st to 15thNight
311221224473%
1799
16th to endNight
11111236%78%
1749
May1st to 15thNight
1112335%78%
1619
16th to endNight
11111124479%
1684
June1st to 15thNight
1111112480%
1620
16th to endNight
112187%
1620
July1st to 15thNight
21122334474%
1620
16th to endNight
32123235%5%7%62%
1701
August1st to 15thNight
11112223476%
1722
16th to endNight
21121234475%
1910
September1st to 15thNight
112213245%73%
1911
16th to endNight
11111287%
1856
October1st to 15thNight
21111223477%
1815
16th to endNight
11221222379%
2135
November1st to 15thNight
121221222476%
2275
16th to endNight
3211212235%73%
2340
December1st to 15thNight
4214423446%61%
2340
16th to endNight
6%313213346%62%
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
18%1417%33%23%
1612
16th to endDay
22%15%16%31%23%
1812
February1st to 15thDay
17%1317%29%30%
1751
16th to endDay
23%2217%32%21%
1579
March1st to 15thDay
12%1317%30%33%
1842
16th to endDay
14%1219%37%24%
2112
April1st to 15thDay
16%1114%32%32%
2146
16th to endDay
8%1213%32%41%
2211
May1st to 15thDay
9%1112%30%45%
2331
16th to endDay
10%19%30%47%
2432
June1st to 15thDay
7%7%16%66%
2340
16th to endDay
7%38%79%
2340
July1st to 15thDay
15%218%19%53%
2201
16th to endDay
18%2415%23%35%
2312
August1st to 15thDay
13%218%25%47%
2220
16th to endDay
15%219%25%45%
2292
September1st to 15thDay
11%3311%21%49%
2049
16th to endDay
8%16%23%60%
1849
October1st to 15thDay
13%129%29%44%
1815
16th to endDay
10%1211%27%46%
1736
November1st to 15thDay
14%1213%30%37%
1584
16th to endDay
13%2414%30%35%
1620
December1st to 15thDay
21%25%20%24%24%
1620
16th to endDay
25%26%21%28%16%
1728
January1st to 15thNight
19%2314%29%29%
2327
16th to endNight
21%1318%24%29%
2411
February1st to 15thNight
16%15%18%27%30%
2112
16th to endNight
22%1317%32%22%
1895
March1st to 15thNight
16%2315%32%29%
2117
16th to endNight
13%2319%33%27%
2112
April1st to 15thNight
14%1314%35%30%
1799
16th to endNight
8%1115%29%42%
1749
May1st to 15thNight
8%1213%31%42%
1620
16th to endNight
7%1112%34%42%
1685
June1st to 15thNight
9%18%15%64%
1620
16th to endNight
6%410%77%
1620
July1st to 15thNight
12%118%18%56%
1530
16th to endNight
19%2312%25%36%
1593
August1st to 15thNight
11%219%24%51%
1713
16th to endNight
11%219%25%50%
1910
September1st to 15thNight
13%2210%24%46%
1911
16th to endNight
6%16%23%62%
1856
October1st to 15thNight
11%118%32%44%
1815
16th to endNight
10%139%22%52%
2135
November1st to 15thNight
12%2111%33%38%
2275
16th to endNight
13%2215%26%39%
2340
December1st to 15thNight
21%2416%27%26%
2340
16th to endNight
22%26%18%30%19%
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
17%5%26%36%13%
90
16th to endDay
8%13%20%36%17%3
180
February1st to 15thDay
6%7%30%36%16%3
266
16th to endDay
11%13%34%28%10%
238
March1st to 15thDay
9%10%27%32%18%1
270
16th to endDay
9%14%27%32%14%1
288
April1st to 15thDay
13%16%31%20%15%3
269
16th to endDay
6%26%30%24%8%2
270
May1st to 15thDay
5%10%29%34%14%5%
288
16th to endDay
39%33%37%11%3
330
June1st to 15thDay
27%31%39%15%3
315
16th to endDay
1218%45%25%6%
315
July1st to 15thDay
116%43%27%9%
305
16th to endDay
319%46%28%10%
327
August1st to 15thDay
2115%49%21%8%
315
16th to endDay
413%41%30%9%
332
September1st to 15thDay
3120%45%23%4
315
16th to endDay
3420%42%24%4
268
October1st to 15thDay
5%10%25%40%16%1
255
16th to endDay
6%8%11%37%32%3
143
November1st to 15thDay
18%15%30%34%10%
90
16th to endDay
7%8%30%34%16%2
90
December1st to 15thDay
211%20%38%27%
90
16th to endDay
14%11%16%31%25%1
96
January1st to 15thNight
4413%40%26%10%
720
16th to endNight
7%6%17%32%27%8%
768
February1st to 15thNight
45%17%36%26%9%
704
16th to endNight
8%6%17%39%21%5%
632
March1st to 15thNight
49%19%33%25%7%
720
16th to endNight
310%18%34%25%7%
768
April1st to 15thNight
5%11%27%28%21%6%
719
16th to endNight
212%23%30%23%7%
669
May1st to 15thNight
37%20%35%27%5%
540
16th to endNight
19%24%28%31%5%
563
June1st to 15thNight
2414%39%36%3
540
16th to endNight
1112%36%42%6%
540
July1st to 15thNight
1430%53%9%
510
16th to endNight
5%1318%60%11%
564
August1st to 15thNight
1421%59%12%
639
16th to endNight
3317%53%21%
764
September1st to 15thNight
1429%47%16%
720
16th to endNight
129%25%39%20%
671
October1st to 15thNight
3412%37%31%10%
660
16th to endNight
1412%31%33%17%
704
November1st to 15thNight
1314%33%33%13%
700
16th to endNight
4412%31%33%13%
720
December1st to 15thNight
6%413%36%30%8%
720
16th to endNight
10%8%13%36%25%6%
768
Page generated at 2017-09-20 01:49:44. Version ac04

Copyright 2017 A. Danko


GMDRC Clear Sky Chart | Charts Home