Greenhawk Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenhawk Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
67%
15800
28%
48095
25%
15764
71%
15764
41%
25717

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
60%
716
20%
2374
20%
716
63%
716
29%
1403
January16th to endNight
60%
768
25%
2496
26%
768
63%
768
27%
1540
February1st to 15thNight
58%
700
24%
2284
24%
700
63%
700
27%
1387
February16th to endNight
51%
632
23%
1895
18%
632
58%
632
28%
1190
March1st to 15thNight
56%
720
20%
2007
18%
720
59%
720
30%
1292
March16th to endNight
52%
768
20%
2088
14%
768
57%
768
31%
1339
April1st to 15thNight
49%
719
22%
1799
11%
719
54%
719
34%
1158
April16th to endNight
57%
720
26%
1800
12%
720
62%
720
45%
1030
May1st to 15thNight
65%
626
28%
1706
18%
626
69%
626
55%
857
May16th to endNight
68%
400
28%
1523
24%
400
75%
400
43%
669
June1st to 15thNight
71%
360
29%
1440
30%
360
81%
360
48%
580
June16th to endNight
85%
360
37%
1440
47%
360
88%
360
66%
479
July1st to 15thNight
92%
390
35%
1410
39%
390
94%
390
75%
470
July16th to endNight
87%
564
38%
1593
35%
531
88%
531
66%
676
August1st to 15thNight
85%
562
35%
1635
27%
559
86%
559
61%
731
August16th to endNight
85%
764
41%
1910
27%
764
86%
764
71%
909
September1st to 15thNight
87%
720
42%
1800
30%
720
88%
720
72%
852
September16th to endNight
80%
716
42%
1962
38%
716
83%
716
65%
913
October1st to 15thNight
76%
720
30%
2160
31%
720
81%
720
51%
1043
October16th to endNight
73%
768
36%
2304
37%
768
77%
768
45%
1192
November1st to 15thNight
67%
760
28%
2365
28%
760
71%
760
40%
1277
November16th to endNight
66%
780
26%
2620
28%
780
69%
780
33%
1447
December1st to 15thNight
60%
780
23%
2730
22%
780
66%
780
28%
1571
December16th to endNight
50%
787
21%
2754
18%
787
57%
787
22%
1712

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
6%413323346%60%
48738
Night
6%424323347%56%
48283
TransparencyDay
26%27%20%25%17%
48426
Night
27%38%20%23%17%
48096
SeeingDay
7%11%25%32%18%5%
6339
Night
7%412%34%32%8%
15810

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
11%5%2442445%7%47%
1561
16th to endDay
14%6%24334346%44%
1728
February1st to 15thDay
12%7%35%5%35%446%42%
1579
16th to endDay
14%6%35%6%2435%7%39%
1579
March1st to 15thDay
10%6%35%6%35%5%6%9%38%
1952
16th to endDay
9%5%35%6%35%5%6%7%41%
2136
April1st to 15thDay
11%7%25%42345%8%43%
2149
16th to endDay
7%413313347%59%
2160
May1st to 15thDay
3313212348%65%
2241
16th to endDay
6%423312236%61%
2587
June1st to 15thDay
5%412213347%64%
2520
16th to endDay
111112125%80%
2520
July1st to 15thDay
11111235%80%
2463
16th to endDay
111111235%79%
2468
August1st to 15thDay
212112236%76%
2313
16th to endDay
11112237%77%
2292
September1st to 15thDay
11112225%78%
2160
16th to endDay
322211235%72%
1994
October1st to 15thDay
4312313337%64%
1800
16th to endDay
441232445%6%59%
1920
November1st to 15thDay
7%434325%447%51%
1821
16th to endDay
8%5%25%5%2445%7%48%
1667
December1st to 15thDay
9%5%26%6%345%47%43%
1560
16th to endDay
13%7%36%6%2345%6%40%
1568
January1st to 15thNight
10%6%345%2435%8%44%
2374
16th to endNight
12%5%245%23447%45%
2496
February1st to 15thNight
8%6%35%4345%5%7%44%
2272
16th to endNight
13%7%24424448%42%
1895
March1st to 15thNight
11%5%35%43345%7%44%
2007
16th to endNight
9%5%25%5%25%346%47%
2088
April1st to 15thNight
9%5%2443446%8%45%
1799
16th to endNight
6%2133235%48%59%
1800
May1st to 15thNight
232321335%9%63%
1706
16th to endNight
2413423349%60%
1522
June1st to 15thNight
2213222249%66%
1440
16th to endNight
1112225%80%
1440
July1st to 15thNight
112227%79%
1494
16th to endNight
112222249%69%
1701
August1st to 15thNight
1211313249%68%
1644
16th to endNight
21221225%9%70%
1910
September1st to 15thNight
1111112239%74%
1800
16th to endNight
2212212236%72%
1962
October1st to 15thNight
4212322347%65%
2160
16th to endNight
4324324447%59%
2304
November1st to 15thNight
6%5%25%31335%8%55%
2365
16th to endNight
7%424434348%52%
2620
December1st to 15thNight
8%5%25%4245%5%7%47%
2730
16th to endNight
13%6%36%42345%5%44%
2754

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
37%311%21%15%10%
1561
16th to endDay
41%47%14%19%13%
1728
February1st to 15thDay
43%27%19%20%5%
1579
16th to endDay
45%38%24%14%3
1579
March1st to 15thDay
44%39%21%14%5%
1952
16th to endDay
42%412%19%16%2
2136
April1st to 15thDay
39%312%21%19%2
2149
16th to endDay
27%213%26%23%7%
2160
May1st to 15thDay
19%28%30%31%7%
2241
16th to endDay
26%210%29%25%6%
2591
June1st to 15thDay
22%210%23%25%16%
2520
16th to endDay
9%1417%36%30%
2520
July1st to 15thDay
8%1110%26%50%
2318
16th to endDay
8%2311%31%42%
2313
August1st to 15thDay
11%1114%33%36%
2297
16th to endDay
8%1118%40%30%
2292
September1st to 15thDay
10%1216%34%33%
2160
16th to endDay
16%1326%33%19%
1994
October1st to 15thDay
21%28%20%24%22%
1800
16th to endDay
24%29%22%24%15%
1920
November1st to 15thDay
32%49%26%20%6%
1821
16th to endDay
35%48%19%26%5%
1667
December1st to 15thDay
41%310%16%17%10%
1560
16th to endDay
45%312%16%17%5%
1568
January1st to 15thNight
37%311%21%17%8%
2374
16th to endNight
38%5%7%14%17%16%
2496
February1st to 15thNight
40%28%21%19%7%
2284
16th to endNight
41%311%26%14%3
1895
March1st to 15thNight
40%311%21%15%6%
2007
16th to endNight
38%5%12%20%18%5%
2088
April1st to 15thNight
36%314%24%17%3
1799
16th to endNight
24%413%26%22%9%
1800
May1st to 15thNight
18%29%25%30%12%
1707
16th to endNight
21%213%29%26%6%
1523
June1st to 15thNight
16%39%25%24%20%
1440
16th to endNight
9%1316%32%36%
1440
July1st to 15thNight
7%18%28%54%
1410
16th to endNight
11%2212%28%41%
1593
August1st to 15thNight
15%1112%31%37%
1635
16th to endNight
11%2112%37%35%
1910
September1st to 15thNight
10%2214%30%39%
1800
16th to endNight
14%1422%32%24%
1962
October1st to 15thNight
20%18%22%21%24%
2160
16th to endNight
24%35%22%25%18%
2304
November1st to 15thNight
29%211%26%21%7%
2365
16th to endNight
32%39%24%21%9%
2620
December1st to 15thNight
35%410%16%20%12%
2730
16th to endNight
42%411%16%18%6%
2754

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%13%28%24%14%1
189
16th to endDay
14%12%31%24%13%3
256
February1st to 15thDay
12%16%32%25%10%2
237
16th to endDay
18%15%31%21%10%1
238
March1st to 15thDay
13%20%30%20%11%3
270
16th to endDay
10%20%33%27%7%1
288
April1st to 15thDay
14%23%31%20%7%1
269
16th to endDay
8%28%29%24%7%1
270
May1st to 15thDay
8%16%32%29%10%2
288
16th to endDay
7%13%25%29%18%5%
330
June1st to 15thDay
5%13%31%32%13%3
315
16th to endDay
426%42%19%7%
315
July1st to 15thDay
1115%47%26%7%
305
16th to endDay
14%46%28%8%
327
August1st to 15thDay
21%37%29%9%
315
16th to endDay
115%46%23%12%
332
September1st to 15thDay
1217%42%26%9%
315
16th to endDay
5%7%21%32%25%7%
315
October1st to 15thDay
5%11%25%34%19%4
315
16th to endDay
6%8%24%34%19%7%
336
November1st to 15thDay
9%7%19%28%26%8%
237
16th to endDay
411%28%29%23%2
115
December1st to 15thDay
6%14%21%26%22%8%
90
16th to endDay
8%18%18%23%22%9%
72
January1st to 15thNight
13%5%10%34%28%8%
720
16th to endNight
15%410%33%23%11%
768
February1st to 15thNight
10%7%12%35%25%7%
704
16th to endNight
16%7%16%34%20%5%
632
March1st to 15thNight
12%7%14%31%27%5%
720
16th to endNight
11%7%19%35%23%3
768
April1st to 15thNight
13%10%19%32%21%3
719
16th to endNight
6%8%21%32%23%7%
720
May1st to 15thNight
2320%36%30%6%
627
16th to endNight
2414%36%35%5%
401
June1st to 15thNight
3216%44%30%2
360
16th to endNight
18%48%38%2
360
July1st to 15thNight
332%55%7%
390
16th to endNight
1126%58%12%
564
August1st to 15thNight
2432%53%7%
562
16th to endNight
15%33%49%9%
764
September1st to 15thNight
25%33%46%12%
720
16th to endNight
318%34%39%11%
716
October1st to 15thNight
438%36%35%11%
720
16th to endNight
5%47%29%35%16%
768
November1st to 15thNight
6%211%36%33%9%
760
16th to endNight
9%412%36%28%9%
780
December1st to 15thNight
10%5%12%36%27%7%
780
16th to endNight
14%8%17%33%21%4
787
Page generated at 2017-12-21 04:04:42. Version ac04

Copyright 2017 A. Danko


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