The Rolnick Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Rolnick Observatory clear sky chart from 2005-11-05 to 2017-09-15.

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
33%
14985
19%
46814
9%
14954
43%
14954
20%
30182

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
18%
720
21%
2506
8%
716
34%
716
16%
1558
January16th to endNight
17%
768
20%
2631
7%
768
36%
768
17%
1635
February1st to 15thNight
19%
704
18%
2201
5%
701
34%
701
18%
1436
February16th to endNight
22%
631
25%
1893
9%
631
41%
631
20%
1200
March1st to 15thNight
24%
720
18%
2160
8%
720
38%
720
19%
1422
March16th to endNight
24%
768
24%
1998
7%
768
37%
768
23%
1307
April1st to 15thNight
30%
718
17%
1796
5%
718
35%
718
23%
1258
April16th to endNight
33%
672
17%
1752
4%
672
41%
672
23%
1201
May1st to 15thNight
31%
528
17%
1608
8%
528
38%
528
18%
1113
May16th to endNight
41%
374
15%
1497
13%
374
49%
374
15%
964
June1st to 15thNight
42%
360
15%
1440
16%
360
49%
360
17%
924
June16th to endNight
55%
360
14%
1440
16%
360
61%
360
21%
836
July1st to 15thNight
55%
340
12%
1360
16%
340
57%
340
19%
835
July16th to endNight
57%
376
15%
1418
16%
354
66%
354
21%
845
August1st to 15thNight
55%
533
18%
1604
13%
531
59%
531
27%
981
August16th to endNight
60%
764
17%
1910
9%
764
62%
764
31%
1279
September1st to 15thNight
50%
720
23%
1811
13%
720
54%
720
32%
1193
September16th to endNight
48%
657
24%
1815
15%
657
55%
657
29%
1151
October1st to 15thNight
33%
660
20%
1900
13%
660
41%
660
23%
1246
October16th to endNight
28%
704
19%
2225
8%
704
41%
704
20%
1429
November1st to 15thNight
29%
700
21%
2277
11%
700
43%
700
21%
1430
November16th to endNight
26%
720
20%
2364
10%
720
39%
720
18%
1501
December1st to 15thNight
22%
720
16%
2520
6%
720
35%
720
13%
1651
December16th to endNight
16%
768
19%
2688
5%
768
33%
768
13%
1787

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
16%5%2442445%7%40%
47911
Night
17%6%24424446%42%
46984
Cloud CoverDay
15%5%2442445%7%42%
47921
Night
16%5%24424446%42%
46989
TransparencyDay
39%6%13%22%15%2
47599
Night
41%5%12%22%15%2
46814
SeeingDay
17%12%19%27%18%4
5812
Night
17%19%23%25%11%1
14986

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
17%6%235%35%45%5%41%
1432
16th to endDay
15%6%25%424447%41%
1590
February1st to 15thDay
16%5%25%4345%5%6%40%
1658
16th to endDay
16%6%14425%446%41%
1580
March1st to 15thDay
17%6%25%43445%7%37%
1790
16th to endDay
18%6%24424336%41%
2223
April1st to 15thDay
19%6%3432335%6%40%
2152
16th to endDay
16%5%24424436%44%
2205
May1st to 15thDay
22%7%244145%5%6%35%
2352
16th to endDay
17%425%5%335%6%7%38%
2618
June1st to 15thDay
22%5%25%42446%7%34%
2520
16th to endDay
13%5%245%346%5%9%38%
2520
July1st to 15thDay
12%5%25%5%25%6%6%8%38%
2520
16th to endDay
11%5%25%5%346%7%9%39%
2654
August1st to 15thDay
12%4245%35%6%5%8%41%
2329
16th to endDay
11%42443446%8%45%
2292
September1st to 15thDay
12%4244345%5%8%44%
2138
16th to endDay
15%314435%446%46%
1815
October1st to 15thDay
18%5%25%324346%43%
1727
16th to endDay
17%4145%3445%6%42%
1646
November1st to 15thDay
19%6%23223345%45%
1581
16th to endDay
17%5%2432445%6%44%
1593
December1st to 15thDay
17%6%24424448%38%
1440
16th to endDay
21%8%24324345%38%
1536
January1st to 15thNight
19%5%24413346%44%
2506
16th to endNight
16%8%24323346%43%
2631
February1st to 15thNight
15%7%35%5%34346%41%
2200
16th to endNight
17%6%24423345%45%
1893
March1st to 15thNight
20%5%13424446%42%
2147
16th to endNight
15%7%24323345%46%
1998
April1st to 15thNight
18%6%2442345%6%40%
1796
16th to endNight
19%5%35%423345%43%
1752
May1st to 15thNight
21%6%345%33437%36%
1608
16th to endNight
19%6%2442445%8%37%
1495
June1st to 15thNight
20%6%24424346%39%
1440
16th to endNight
11%425%42445%9%45%
1440
July1st to 15thNight
13%425%5%25%5%6%10%38%
1440
16th to endNight
10%5%24436%6%7%8%39%
1514
August1st to 15thNight
10%4245%25%5%6%7%45%
1614
16th to endNight
13%3235%445%5%8%43%
1910
September1st to 15thNight
14%41442445%6%47%
1811
16th to endNight
15%5%24323335%50%
1815
October1st to 15thNight
16%7%35%423345%44%
1900
16th to endNight
18%5%24433446%42%
2225
November1st to 15thNight
16%6%33323346%45%
2277
16th to endNight
18%5%34324347%41%
2364
December1st to 15thNight
20%6%2442435%7%38%
2520
16th to endNight
20%6%2442435%6%38%
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
16%5%24435%45%5%42%
1432
16th to endDay
15%6%34424447%41%
1590
February1st to 15thDay
16%5%25%433446%41%
1658
16th to endDay
15%5%24434447%42%
1580
March1st to 15thDay
17%7%245%25%45%7%38%
1800
16th to endDay
18%6%23424345%43%
2223
April1st to 15thDay
19%5%24324446%42%
2152
16th to endDay
16%5%14423447%45%
2205
May1st to 15thDay
20%6%2442345%6%37%
2352
16th to endDay
16%5%145%2445%8%40%
2618
June1st to 15thDay
20%5%1442345%8%37%
2520
16th to endDay
11%415%43446%10%42%
2520
July1st to 15thDay
10%425%426%5%6%9%41%
2520
16th to endDay
11%5%245%35%5%7%8%42%
2654
August1st to 15thDay
11%4245%35%45%9%43%
2329
16th to endDay
11%41442445%7%48%
2292
September1st to 15thDay
12%3234245%5%7%46%
2138
16th to endDay
14%41342445%6%47%
1815
October1st to 15thDay
18%5%24323447%43%
1727
16th to endDay
17%4145%3435%6%44%
1646
November1st to 15thDay
19%424324435%45%
1581
16th to endDay
16%5%23414347%45%
1593
December1st to 15thDay
16%5%25%33445%8%39%
1440
16th to endDay
22%7%24324446%38%
1536
January1st to 15thNight
18%5%24423446%44%
2506
16th to endNight
16%7%33423347%42%
2631
February1st to 15thNight
14%8%345%34346%41%
2193
16th to endNight
17%5%24423345%44%
1893
March1st to 15thNight
19%6%2432345%5%42%
2160
16th to endNight
16%6%34324336%45%
1997
April1st to 15thNight
18%6%24433346%41%
1796
16th to endNight
19%5%34423445%42%
1752
May1st to 15thNight
21%6%246%33446%36%
1608
16th to endNight
19%5%2442445%7%38%
1495
June1st to 15thNight
20%5%24433448%38%
1440
16th to endNight
10%5%235%3347%7%45%
1440
July1st to 15thNight
12%5%245%26%47%9%38%
1440
16th to endNight
10%434446%5%7%9%40%
1514
August1st to 15thNight
10%415%4246%5%8%45%
1614
16th to endNight
13%415%5%245%5%7%44%
1910
September1st to 15thNight
15%3135%245%5%5%47%
1811
16th to endNight
14%5%25%413335%49%
1815
October1st to 15thNight
17%6%245%2334444%
1900
16th to endNight
18%5%24424446%42%
2225
November1st to 15thNight
17%6%24313445%46%
2277
16th to endNight
18%5%25%323346%42%
2364
December1st to 15thNight
20%6%24325%347%38%
2520
16th to endNight
20%6%24414446%38%
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
42%6%13%22%12%2
1433
16th to endDay
42%5%11%24%13%2
1590
February1st to 15thDay
42%5%13%21%14%2
1661
16th to endDay
40%5%11%26%14%1
1580
March1st to 15thDay
44%5%15%22%10%2
1800
16th to endDay
42%410%19%19%3
2223
April1st to 15thDay
42%5%10%21%16%3
2152
16th to endDay
39%411%21%20%3
2205
May1st to 15thDay
44%6%11%20%15%2
2352
16th to endDay
39%9%15%20%13%1
2622
June1st to 15thDay
44%7%13%21%12%1
2520
16th to endDay
36%8%15%24%13%1
2520
July1st to 15thDay
35%8%14%22%16%1
2371
16th to endDay
35%8%15%22%13%2
2487
August1st to 15thDay
35%8%16%23%15%
2315
16th to endDay
32%7%11%25%19%2
2292
September1st to 15thDay
34%7%13%21%21%1
2138
16th to endDay
35%6%9%21%23%2
1815
October1st to 15thDay
41%6%11%21%17%2
1727
16th to endDay
39%5%12%23%16%2
1646
November1st to 15thDay
42%412%19%18%2
1581
16th to endDay
39%412%25%15%2
1593
December1st to 15thDay
42%6%16%19%13%
1440
16th to endDay
47%5%14%19%11%
1536
January1st to 15thNight
41%5%12%23%13%2
2506
16th to endNight
41%411%24%15%2
2631
February1st to 15thNight
44%5%13%21%12%2
2201
16th to endNight
41%39%24%18%2
1893
March1st to 15thNight
43%413%21%13%3
2160
16th to endNight
40%410%22%17%4
1998
April1st to 15thNight
44%5%10%19%16%2
1796
16th to endNight
43%5%9%17%21%3
1752
May1st to 15thNight
47%6%10%17%15%2
1608
16th to endNight
44%7%14%18%13%1
1497
June1st to 15thNight
46%5%11%20%14%1
1440
16th to endNight
35%7%14%26%15%1
1440
July1st to 15thNight
38%9%14%21%14%1
1360
16th to endNight
35%9%15%23%12%2
1418
August1st to 15thNight
33%8%13%25%16%1
1604
16th to endNight
37%7%13%22%17%1
1910
September1st to 15thNight
36%6%10%26%18%1
1811
16th to endNight
37%5%7%21%25%2
1815
October1st to 15thNight
43%411%22%15%3
1900
16th to endNight
42%5%14%21%15%
2225
November1st to 15thNight
40%5%10%20%18%3
2277
16th to endNight
43%411%25%12%2
2364
December1st to 15thNight
45%6%13%20%13%
2520
16th to endNight
46%5%12%20%13%1
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
13%11%38%31%5%
60
16th to endDay
23%5%30%35%5%
73
February1st to 15thDay
21%17%35%23%2
174
16th to endDay
15%17%32%25%8%
239
March1st to 15thDay
20%17%31%23%7%
270
16th to endDay
19%17%34%20%7%2
288
April1st to 15thDay
22%15%21%26%14%
270
16th to endDay
19%14%17%30%16%1
270
May1st to 15thDay
27%13%22%23%12%1
288
16th to endDay
18%10%11%30%23%5%
331
June1st to 15thDay
20%12%11%26%23%6%
315
16th to endDay
14%9%10%39%22%2
315
July1st to 15thDay
12%8%6%37%29%6%
305
16th to endDay
12%11%6%30%31%6%
326
August1st to 15thDay
14%6%5%35%30%8%
313
16th to endDay
12%5%7%29%31%14%
332
September1st to 15thDay
11%8%18%27%21%12%
311
16th to endDay
18%6%15%27%20%11%
254
October1st to 15thDay
22%9%18%23%20%6%
255
16th to endDay
17%14%29%23%14%
251
November1st to 15thDay
20%16%25%21%14%2
235
16th to endDay
15%22%30%20%11%
213
December1st to 15thDay
18%13%38%18%10%1
60
16th to endDay
37%9%34%18%
64
January1st to 15thNight
16%28%32%18%4
720
16th to endNight
18%26%33%19%1
768
February1st to 15thNight
16%23%34%24%1
704
16th to endNight
18%24%30%22%3
631
March1st to 15thNight
21%22%27%22%5%
720
16th to endNight
18%21%31%20%7%
768
April1st to 15thNight
18%20%25%27%6%
718
16th to endNight
17%18%23%29%9%1
672
May1st to 15thNight
20%18%23%25%11%1
528
16th to endNight
20%18%10%33%16%
375
June1st to 15thNight
16%19%13%30%19%1
360
16th to endNight
11%16%8%43%17%1
360
July1st to 15thNight
12%12%10%37%24%2
340
16th to endNight
10%17%8%37%23%2
376
August1st to 15thNight
13%9%11%36%26%2
533
16th to endNight
12%9%8%31%32%5%
764
September1st to 15thNight
16%9%17%32%19%4
720
16th to endNight
17%10%15%28%21%6%
657
October1st to 15thNight
20%15%23%23%14%1
660
16th to endNight
18%17%31%25%6%
704
November1st to 15thNight
16%22%26%22%9%2
700
16th to endNight
16%26%25%21%9%
720
December1st to 15thNight
23%25%24%19%6%
720
16th to endNight
22%27%30%17%2
768
Page generated at 2017-09-16 00:58:30. Version ac04

Copyright 2017 A. Danko


The Rolnick Observatory Clear Sky Chart | Charts Home