Greeley Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greeley Hill Observatory clear sky chart from 2005-11-05 to 2017-03-22.

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
72%
14787
29%
45248
28%
14750
75%
14750
45%
23395

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
20%
2482
22%
716
69%
716
33%
1387
January16th to endNight
64%
768
24%
2496
28%
768
66%
768
30%
1496
February1st to 15thNight
63%
700
25%
2205
27%
697
65%
697
31%
1308
February16th to endNight
59%
632
23%
1895
24%
632
61%
632
30%
1180
March1st to 15thNight
59%
720
18%
2100
19%
720
60%
720
31%
1305
March16th to endNight
63%
732
21%
1936
17%
732
65%
732
38%
1179
April1st to 15thNight
57%
659
22%
1649
13%
659
60%
659
37%
1041
April16th to endNight
64%
660
24%
1650
12%
660
67%
660
49%
938
May1st to 15thNight
68%
577
31%
1567
20%
577
71%
577
59%
758
May16th to endNight
72%
343
28%
1368
30%
342
76%
342
46%
570
June1st to 15thNight
79%
330
31%
1320
37%
330
84%
330
54%
500
June16th to endNight
89%
330
35%
1320
46%
330
92%
330
72%
416
July1st to 15thNight
93%
310
38%
1240
50%
310
94%
310
73%
389
July16th to endNight
88%
443
37%
1391
37%
413
89%
413
63%
553
August1st to 15thNight
92%
579
40%
1562
29%
576
92%
576
81%
652
August16th to endNight
93%
700
43%
1750
28%
700
93%
700
83%
778
September1st to 15thNight
93%
660
45%
1650
33%
660
94%
660
81%
743
September16th to endNight
87%
656
44%
1772
40%
656
89%
656
74%
783
October1st to 15thNight
79%
660
31%
1965
34%
660
81%
660
53%
951
October16th to endNight
80%
704
39%
2112
41%
704
83%
704
56%
982
November1st to 15thNight
77%
700
31%
2269
35%
700
78%
700
47%
1109
November16th to endNight
70%
720
28%
2341
30%
720
73%
720
38%
1256
December1st to 15thNight
64%
720
23%
2520
24%
720
68%
720
28%
1469
December16th to endNight
54%
768
22%
2688
22%
768
59%
768
25%
1652

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
9%312212235%64%
45624
Night
10%312212235%62%
45439
TransparencyDay
23%38%18%25%20%
45305
Night
24%39%19%24%18%
45258
SeeingDay
11%8%28%34%12%3
5149
Night
11%19%36%33%8%
14796

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
17%413212346%52%
1453
16th to endDay
19%6%13423335%46%
1728
February1st to 15thDay
18%5%24313345%48%
1646
16th to endDay
22%6%32324236%40%
1579
March1st to 15thDay
16%7%234245%5%7%39%
1857
16th to endDay
16%5%23324347%44%
2084
April1st to 15thDay
16%5%14322436%48%
1969
16th to endDay
10%413312345%58%
1980
May1st to 15thDay
6%32212235%67%
2048
16th to endDay
8%213324345%59%
2391
June1st to 15thDay
3213212335%70%
2310
16th to endDay
11112285%
2310
July1st to 15thDay
11113384%
2310
16th to endDay
11121222281%
2363
August1st to 15thDay
1112288%
2057
16th to endDay
111122385%
2100
September1st to 15thDay
111112385%
1980
16th to endDay
21111222479%
1856
October1st to 15thDay
6%211212345%67%
1663
16th to endDay
8%212312335%65%
1760
November1st to 15thDay
10%312313345%59%
1587
16th to endDay
13%41332435%6%51%
1617
December1st to 15thDay
18%6%24313235%48%
1440
16th to endDay
21%7%23323346%41%
1536
January1st to 15thNight
15%41321335%7%50%
2482
16th to endNight
17%5%13323345%49%
2496
February1st to 15thNight
16%5%24323346%48%
2203
16th to endNight
21%5%14313335%46%
1895
March1st to 15thNight
19%413323335%48%
2100
16th to endNight
16%31222335%7%50%
1936
April1st to 15thNight
14%423314346%51%
1649
16th to endNight
8%31221243464%
1650
May1st to 15thNight
6%2212236%70%
1567
16th to endNight
6%213312237%66%
1368
June1st to 15thNight
421112235%73%
1320
16th to endNight
1111111286%
1320
July1st to 15thNight
111211384%
1320
16th to endNight
311111122279%
1495
August1st to 15thNight
111112385%
1571
16th to endNight
11122384%
1750
September1st to 15thNight
1111111287%
1650
16th to endNight
11211112381%
1772
October1st to 15thNight
5%21232224468%
1965
16th to endNight
6%11212235%69%
2112
November1st to 15thNight
10%212213245%64%
2269
16th to endNight
11%313224345%57%
2341
December1st to 15thNight
16%423314446%49%
2520
16th to endNight
21%5%23223246%44%
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
33%413%20%20%7%
1453
16th to endDay
41%5%9%16%16%10%
1728
February1st to 15thDay
37%311%25%17%4
1646
16th to endDay
43%410%24%16%
1579
March1st to 15thDay
40%6%11%19%17%5%
1857
16th to endDay
36%6%15%21%17%2
2084
April1st to 15thDay
36%411%22%18%5%
1969
16th to endDay
26%5%11%27%23%6%
1980
May1st to 15thDay
19%28%24%34%10%
2048
16th to endDay
22%6%10%26%26%7%
2395
June1st to 15thDay
16%39%19%26%23%
2310
16th to endDay
7%312%34%41%
2310
July1st to 15thDay
7%127%24%57%
2161
16th to endDay
10%249%22%51%
2205
August1st to 15thDay
429%28%53%
2041
16th to endDay
6%127%36%45%
2100
September1st to 15thDay
7%129%33%45%
1980
16th to endDay
10%1421%37%25%
1856
October1st to 15thDay
18%37%22%26%21%
1663
16th to endDay
20%27%22%29%16%
1760
November1st to 15thDay
26%411%24%24%8%
1587
16th to endDay
32%411%21%25%5%
1617
December1st to 15thDay
40%410%21%17%5%
1440
16th to endDay
42%5%11%19%15%5%
1536
January1st to 15thNight
32%5%13%21%20%7%
2482
16th to endNight
37%410%15%19%12%
2496
February1st to 15thNight
35%410%25%16%7%
2214
16th to endNight
39%312%25%15%3
1895
March1st to 15thNight
37%413%19%19%4
2100
16th to endNight
31%5%14%22%19%5%
1936
April1st to 15thNight
33%6%15%23%18%4
1649
16th to endNight
22%5%14%23%25%7%
1650
May1st to 15thNight
15%38%26%33%12%
1568
16th to endNight
18%310%30%26%9%
1368
June1st to 15thNight
14%312%18%25%25%
1320
16th to endNight
7%1310%34%42%
1320
July1st to 15thNight
7%126%26%55%
1240
16th to endNight
12%137%19%55%
1391
August1st to 15thNight
7%211%27%51%
1562
16th to endNight
6%128%34%47%
1750
September1st to 15thNight
6%137%32%47%
1650
16th to endNight
10%1319%41%25%
1772
October1st to 15thNight
18%48%22%27%18%
1965
16th to endNight
17%36%24%30%18%
2112
November1st to 15thNight
22%311%26%23%13%
2269
16th to endNight
28%48%24%26%7%
2341
December1st to 15thNight
36%410%23%17%6%
2520
16th to endNight
41%412%18%16%7%
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
40%322%22%8%2
81
16th to endDay
25%5%17%29%17%3
256
February1st to 15thDay
24%7%20%24%18%4
249
16th to endDay
25%12%25%23%13%
238
March1st to 15thDay
20%12%27%21%13%3
270
16th to endDay
16%12%33%23%13%
250
April1st to 15thDay
24%17%33%17%5%1
209
16th to endDay
14%17%34%25%7%
210
May1st to 15thDay
14%14%36%27%42
228
16th to endDay
9%17%24%34%8%5%
266
June1st to 15thDay
315%40%31%5%1
255
16th to endDay
27%32%42%9%6%
255
July1st to 15thDay
127%51%11%6%
245
16th to endDay
225%52%9%8%
271
August1st to 15thDay
1433%45%7%7%
255
16th to endDay
1227%50%10%7%
268
September1st to 15thDay
1329%46%14%3
255
16th to endDay
48%29%36%18%2
255
October1st to 15thDay
7%10%34%29%14%3
255
16th to endDay
12%6%26%34%18%1
272
November1st to 15thDay
8%210%21%44%12%
93
16th to endDay
11%7%24%33%21%1
89
December1st to 15thDay
31%5%26%26%10%
60
16th to endDay
26%312%29%23%4
64
January1st to 15thNight
16%19%35%26%10%
720
16th to endNight
21%17%35%25%9%
768
February1st to 15thNight
17%110%35%27%7%
704
16th to endNight
21%310%35%22%6%
632
March1st to 15thNight
17%312%33%26%6%
720
16th to endNight
16%212%36%26%4
732
April1st to 15thNight
14%415%35%25%3
659
16th to endNight
7%417%37%26%6%
660
May1st to 15thNight
6%317%39%27%5%
578
16th to endNight
6%213%36%37%2
343
June1st to 15thNight
6%9%42%37%3
330
16th to endNight
16%42%46%2
330
July1st to 15thNight
1135%58%3
310
16th to endNight
2227%55%11%
443
August1st to 15thNight
337%46%11%
579
16th to endNight
332%56%7%
700
September1st to 15thNight
331%50%12%
660
16th to endNight
26%34%44%12%
656
October1st to 15thNight
6%18%39%34%10%
660
16th to endNight
8%7%32%33%17%
704
November1st to 15thNight
11%5%37%33%11%
700
16th to endNight
12%10%37%28%10%
720
December1st to 15thNight
18%17%42%22%7%
720
16th to endNight
23%111%36%21%4
768
Page generated at 2017-03-23 04:36:12. Version ac04

Copyright 2017 A. Danko


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