Gneiss Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gneiss Hill Observatory clear sky chart from 2005-11-05 to 2017-04-25.

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
28%
14336
15%
45648
8%
14307
36%
14307
18%
31514

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
13%
720
8%
2506
3%
716
21%
716
7%
1966
January16th to endNight
20%
768
13%
2583
6%
768
29%
768
12%
1907
February1st to 15thNight
16%
702
12%
2287
3%
701
26%
701
13%
1677
February16th to endNight
18%
631
16%
1982
5%
631
31%
631
15%
1411
March1st to 15thNight
18%
720
15%
2049
6%
720
27%
720
17%
1482
March16th to endNight
30%
768
22%
2068
9%
768
39%
768
25%
1371
April1st to 15thNight
21%
718
17%
1796
5%
718
28%
718
21%
1287
April16th to endNight
30%
624
18%
1674
7%
624
37%
624
24%
1139
May1st to 15thNight
39%
347
20%
1337
17%
347
51%
347
21%
816
May16th to endNight
36%
342
15%
1369
11%
342
49%
342
22%
798
June1st to 15thNight
32%
330
11%
1320
7%
330
44%
330
16%
859
June16th to endNight
44%
330
9%
1320
11%
330
51%
330
21%
800
July1st to 15thNight
49%
310
17%
1240
22%
310
56%
310
30%
642
July16th to endNight
52%
348
14%
1306
12%
326
59%
326
30%
706
August1st to 15thNight
50%
466
16%
1447
11%
464
55%
464
31%
859
August16th to endNight
49%
623
21%
1673
9%
623
55%
623
38%
1000
September1st to 15thNight
43%
660
19%
1650
8%
660
48%
660
32%
1094
September16th to endNight
46%
657
22%
1812
14%
657
52%
657
32%
1148
October1st to 15thNight
32%
660
18%
1980
11%
660
41%
660
19%
1373
October16th to endNight
20%
704
11%
2157
4%
704
29%
704
13%
1622
November1st to 15thNight
27%
700
19%
2364
13%
700
36%
700
18%
1604
November16th to endNight
20%
720
12%
2520
8%
720
27%
720
11%
1895
December1st to 15thNight
16%
720
7%
2520
2%
720
21%
720
9%
1944
December16th to endNight
13%
768
9%
2688
3%
768
20%
768
9%
2114

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
17%9%36%6%34446%31%
45994
Night
16%9%36%5%3445%6%33%
45818
Cloud CoverDay
17%9%36%5%34446%32%
46004
Night
17%9%36%5%2445%6%33%
45823
TransparencyDay
52%310%20%10%1
45682
Night
50%312%21%10%1
45648
SeeingDay
22%12%30%21%9%3
4857
Night
22%11%30%24%9%1
14339

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
20%15%6%9%5%3433423%
1432
16th to endDay
15%15%7%10%8%4433422%
1638
February1st to 15thDay
14%14%5%11%8%35%445%22%
1575
16th to endDay
17%15%5%7%6%23435%27%
1491
March1st to 15thDay
16%13%48%8%45%43327%
1897
16th to endDay
14%10%36%5%24345%39%
2155
April1st to 15thDay
22%10%36%5%34335%32%
2152
16th to endDay
19%8%35%5%2325%5%37%
2184
May1st to 15thDay
17%7%37%5%25%5%46%34%
2284
16th to endDay
14%6%26%5%345%5%6%38%
2394
June1st to 15thDay
21%7%36%5%36%5%5%7%28%
2310
16th to endDay
15%6%36%6%45%5%6%7%33%
2310
July1st to 15thDay
12%6%35%5%26%5%6%8%36%
2310
16th to endDay
10%6%35%6%46%5%7%9%34%
2458
August1st to 15thDay
12%8%26%6%25%5%5%8%35%
2170
16th to endDay
14%6%25%6%45%5%6%7%35%
2165
September1st to 15thDay
16%5%35%5%3435%7%39%
1980
16th to endDay
16%6%245%23346%42%
1818
October1st to 15thDay
22%8%26%5%3345%6%31%
1650
16th to endDay
27%11%36%7%33345%24%
1713
November1st to 15thDay
16%7%37%6%4445%6%33%
1492
16th to endDay
23%13%5%7%5%34345%23%
1440
December1st to 15thDay
20%16%6%8%8%24435%17%
1440
16th to endDay
22%17%6%8%6%23335%19%
1536
January1st to 15thNight
19%14%5%9%8%4443419%
2506
16th to endNight
13%15%5%8%7%34446%25%
2583
February1st to 15thNight
12%14%5%8%6%35%5%6%6%24%
2285
16th to endNight
14%12%46%6%25%5%5%6%29%
1982
March1st to 15thNight
17%11%5%7%5%33445%32%
2037
16th to endNight
15%6%445%23346%42%
2068
April1st to 15thNight
20%9%45%423345%35%
1796
16th to endNight
16%7%25%6%23447%39%
1674
May1st to 15thNight
18%5%25%42346%6%40%
1337
16th to endNight
13%5%25%425%447%43%
1367
June1st to 15thNight
18%5%37%5%25%45%7%34%
1320
16th to endNight
12%5%35%5%346%5%8%40%
1320
July1st to 15thNight
7%3245%35%45%6%50%
1320
16th to endNight
8%413425%46%9%48%
1402
August1st to 15thNight
8%5%245%235%5%8%45%
1457
16th to endNight
9%42442335%7%50%
1673
September1st to 15thNight
14%4245%3445%8%42%
1650
16th to endNight
16%5%25%312345%48%
1812
October1st to 15thNight
21%7%25%5%24446%35%
1980
16th to endNight
24%10%46%5%24446%25%
2157
November1st to 15thNight
17%9%35%5%25%5%5%6%34%
2364
16th to endNight
23%10%46%5%345%45%25%
2520
December1st to 15thNight
21%15%5%8%424447%21%
2520
16th to endNight
22%16%5%8%5%3434420%
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
20%15%6%8%433435%23%
1432
16th to endDay
15%15%7%10%7%4424422%
1638
February1st to 15thDay
14%15%5%11%8%35%445%22%
1575
16th to endDay
17%16%47%6%24335%27%
1491
March1st to 15thDay
17%12%5%8%7%45%44327%
1908
16th to endDay
14%10%35%424345%41%
2154
April1st to 15thDay
22%9%35%424335%33%
2152
16th to endDay
20%8%25%423345%37%
2184
May1st to 15thDay
17%7%46%4245%5%6%35%
2284
16th to endDay
14%5%25%5%35%45%6%38%
2394
June1st to 15thDay
22%6%36%6%25%5%47%28%
2310
16th to endDay
16%5%36%5%35%45%8%33%
2310
July1st to 15thDay
13%5%25%6%35%5%6%8%36%
2310
16th to endDay
11%5%35%6%36%47%9%35%
2458
August1st to 15thDay
12%8%27%5%25%5%5%7%35%
2170
16th to endDay
15%5%15%6%35%5%6%6%37%
2165
September1st to 15thDay
17%5%25%5%3435%7%39%
1980
16th to endDay
17%6%345%24446%41%
1818
October1st to 15thDay
22%8%35%5%3345%6%31%
1650
16th to endDay
28%10%37%7%33345%24%
1713
November1st to 15thDay
16%7%36%6%3445%6%34%
1492
16th to endDay
23%13%5%6%5%35%345%23%
1440
December1st to 15thDay
21%15%5%10%7%345%3417%
1440
16th to endDay
21%17%6%8%5%34335%19%
1536
January1st to 15thNight
19%14%5%10%7%44435%20%
2506
16th to endNight
13%14%5%8%7%34446%25%
2583
February1st to 15thNight
13%14%5%8%6%36%5%6%5%24%
2278
16th to endNight
14%13%46%6%3445%6%29%
1982
March1st to 15thNight
18%11%46%5%34345%32%
2049
16th to endNight
15%6%45%5%24345%43%
2068
April1st to 15thNight
21%8%45%41435%5%36%
1796
16th to endNight
16%7%25%6%23447%39%
1674
May1st to 15thNight
18%5%35%32345%7%40%
1337
16th to endNight
13%5%35%425%447%43%
1367
June1st to 15thNight
18%5%27%5%35%36%7%34%
1320
16th to endNight
12%6%35%5%246%5%8%39%
1320
July1st to 15thNight
8%325%5%25%46%7%50%
1320
16th to endNight
8%31343447%9%47%
1402
August1st to 15thNight
9%5%25%5%2447%7%46%
1457
16th to endNight
9%425%423347%51%
1673
September1st to 15thNight
14%42443445%8%43%
1650
16th to endNight
16%5%24322346%48%
1812
October1st to 15thNight
21%6%36%5%23446%35%
1980
16th to endNight
25%9%36%5%24446%25%
2157
November1st to 15thNight
17%9%35%5%35%5%5%6%34%
2364
16th to endNight
23%11%36%5%34446%25%
2520
December1st to 15thNight
21%15%5%7%5%24446%21%
2520
16th to endNight
22%15%5%9%5%3344420%
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
63%39%15%6%
1433
16th to endDay
65%37%12%10%1
1638
February1st to 15thDay
64%310%16%5%
1577
16th to endDay
60%29%14%11%1
1491
March1st to 15thDay
61%311%15%6%1
1908
16th to endDay
47%27%21%15%5%
2155
April1st to 15thDay
54%36%18%14%2
2152
16th to endDay
48%27%20%17%3
2184
May1st to 15thDay
48%410%18%15%2
2284
16th to endDay
44%412%22%13%2
2398
June1st to 15thDay
53%5%10%19%10%
2310
16th to endDay
48%312%21%13%1
2310
July1st to 15thDay
41%412%28%11%
2161
16th to endDay
45%5%13%24%10%
2291
August1st to 15thDay
46%5%14%22%11%
2156
16th to endDay
44%5%13%25%10%
2165
September1st to 15thDay
44%312%27%12%
1980
16th to endDay
43%310%30%11%
1818
October1st to 15thDay
53%310%20%10%1
1650
16th to endDay
63%310%16%5%
1713
November1st to 15thDay
50%414%18%10%
1492
16th to endDay
62%410%13%7%1
1440
December1st to 15thDay
70%311%11%3
1440
16th to endDay
67%310%12%6%
1536
January1st to 15thNight
67%39%13%5%
2506
16th to endNight
59%39%18%8%
2583
February1st to 15thNight
58%313%18%5%
2287
16th to endNight
53%310%20%10%
1982
March1st to 15thNight
54%211%21%9%
2049
16th to endNight
44%29%23%17%2
2068
April1st to 15thNight
50%28%21%15%2
1796
16th to endNight
45%38%20%18%2
1674
May1st to 15thNight
43%310%22%16%4
1337
16th to endNight
39%412%22%16%2
1369
June1st to 15thNight
49%313%20%12%
1320
16th to endNight
42%415%22%14%
1320
July1st to 15thNight
31%413%31%18%1
1240
16th to endNight
31%5%18%28%14%
1306
August1st to 15thNight
35%417%27%13%1
1447
16th to endNight
32%315%33%13%
1673
September1st to 15thNight
40%414%29%11%
1650
16th to endNight
38%311%35%10%
1812
October1st to 15thNight
50%310%21%13%
1980
16th to endNight
59%313%15%7%
2157
November1st to 15thNight
50%313%19%11%1
2364
16th to endNight
60%410%18%5%
2520
December1st to 15thNight
62%414%14%3
2520
16th to endNight
66%310%12%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
30%28%16%18%6%
60
16th to endDay
44%13%30%8%2
81
February1st to 15thDay
37%24%31%5%1
90
16th to endDay
38%17%30%12%2
150
March1st to 15thDay
26%16%30%21%5%
270
16th to endDay
26%14%34%12%10%1
288
April1st to 15thDay
29%18%28%14%8%
270
16th to endDay
22%18%28%14%10%4
250
May1st to 15thDay
22%11%29%22%7%6%
228
16th to endDay
15%13%35%22%10%2
267
June1st to 15thDay
24%10%31%22%9%1
255
16th to endDay
12%10%32%29%12%2
255
July1st to 15thDay
13%6%29%29%17%4
245
16th to endDay
14%7%36%24%12%4
270
August1st to 15thDay
15%326%32%13%7%
253
16th to endDay
14%228%28%14%11%
268
September1st to 15thDay
17%7%25%20%17%11%
255
16th to endDay
20%7%27%24%10%9%
254
October1st to 15thDay
25%13%25%19%12%3
255
16th to endDay
33%15%27%20%2
263
November1st to 15thDay
19%10%34%25%8%2
146
16th to endDay
31%11%33%13%8%1
60
December1st to 15thDay
25%26%28%18%1
60
16th to endDay
39%26%32%1
64
January1st to 15thNight
30%16%31%17%4
720
16th to endNight
23%14%34%21%5%
768
February1st to 15thNight
22%17%38%17%3
704
16th to endNight
20%18%37%19%4
631
March1st to 15thNight
25%15%34%22%1
720
16th to endNight
19%13%31%23%9%2
768
April1st to 15thNight
26%15%31%21%4
718
16th to endNight
22%13%29%23%9%1
624
May1st to 15thNight
21%7%27%32%9%2
347
16th to endNight
14%6%37%27%12%
343
June1st to 15thNight
18%10%28%31%9%
330
16th to endNight
15%6%26%38%12%
330
July1st to 15thNight
7%428%36%21%
310
16th to endNight
9%130%41%15%1
348
August1st to 15thNight
12%227%33%20%3
466
16th to endNight
10%428%33%20%2
623
September1st to 15thNight
17%428%26%20%2
660
16th to endNight
20%7%22%27%19%3
657
October1st to 15thNight
25%11%26%23%11%1
660
16th to endNight
30%13%28%21%6%
704
November1st to 15thNight
23%11%32%21%10%1
700
16th to endNight
33%15%24%18%7%
720
December1st to 15thNight
30%17%29%18%4
720
16th to endNight
32%13%32%17%2
768
Page generated at 2017-04-26 17:21:33. Version ac04

Copyright 2017 A. Danko


Gneiss Hill Observatory Clear Sky Chart | Charts Home