Rogers' Astrophysics Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rogers' Astrophysics Observatory clear sky chart from 2005-11-05 to 2018-03-21.

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
49%
16360
23%
49191
16%
16317
57%
16317
28%
30767

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
32%
780
24%
2522
11%
776
47%
776
23%
1551
January16th to endNight
29%
832
26%
2704
14%
832
45%
832
25%
1639
February1st to 15thNight
34%
764
26%
2319
13%
761
48%
761
26%
1432
February16th to endNight
30%
683
25%
2049
11%
683
44%
683
29%
1247
March1st to 15thNight
35%
780
25%
2184
13%
780
46%
780
31%
1358
March16th to endNight
38%
792
21%
2178
11%
792
46%
792
29%
1399
April1st to 15thNight
44%
715
25%
1973
15%
715
52%
715
35%
1170
April16th to endNight
49%
540
24%
1641
16%
540
56%
540
30%
1005
May1st to 15thNight
49%
540
19%
1620
11%
540
55%
540
27%
1028
May16th to endNight
61%
561
19%
1683
14%
561
64%
561
29%
1053
June1st to 15thNight
68%
540
15%
1620
13%
540
70%
540
29%
1054
June16th to endNight
73%
540
15%
1620
14%
540
73%
540
31%
1021
July1st to 15thNight
65%
510
9%
1530
8%
510
65%
510
23%
1077
July16th to endNight
72%
564
14%
1595
13%
531
74%
531
27%
1049
August1st to 15thNight
67%
539
15%
1609
14%
536
68%
536
23%
1114
August16th to endNight
65%
603
16%
1869
16%
603
65%
603
21%
1295
September1st to 15thNight
65%
720
17%
1980
15%
720
66%
720
27%
1325
September16th to endNight
57%
717
22%
1980
17%
717
61%
717
29%
1308
October1st to 15thNight
55%
720
29%
2043
25%
720
60%
720
34%
1230
October16th to endNight
55%
768
35%
2304
28%
768
68%
768
41%
1253
November1st to 15thNight
55%
760
29%
2394
25%
760
63%
760
36%
1331
November16th to endNight
46%
780
28%
2535
21%
780
57%
780
31%
1452
December1st to 15thNight
41%
780
24%
2535
16%
780
52%
780
25%
1581
December16th to endNight
34%
832
23%
2704
15%
832
44%
832
20%
1795

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
12%42442445%8%43%
49653
Night
13%42442445%7%45%
49391
TransparencyDay
37%6%12%20%18%5%
49354
Night
37%6%10%19%19%6%
49194
SeeingDay
15%5%18%24%22%14%
6106
Night
15%5%22%31%21%3
16362

By Month

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
17%5%24423435%45%
1746
16th to endDay
16%5%24323335%48%
1872
February1st to 15thDay
15%5%1442445%6%45%
1868
16th to endDay
17%6%24413346%45%
1710
March1st to 15thDay
16%413413346%49%
2106
16th to endDay
17%424424446%43%
2173
April1st to 15thDay
11%41343445%7%48%
1984
16th to endDay
10%4244245%5%7%49%
2319
May1st to 15thDay
10%425%435%45%8%44%
2331
16th to endDay
10%413435%6%6%10%42%
2431
June1st to 15thDay
8%3245%46%6%7%12%37%
2340
16th to endDay
42145%47%7%8%12%41%
2340
July1st to 15thDay
8%5%35%6%46%6%7%12%32%
2340
16th to endDay
6%325%5%47%7%9%11%36%
2465
August1st to 15thDay
8%5%26%6%46%7%8%10%33%
2340
16th to endDay
12%5%27%6%46%6%6%10%31%
2316
September1st to 15thDay
10%4146%36%6%6%8%40%
1980
16th to endDay
17%31432345%7%44%
1980
October1st to 15thDay
15%5%13312135%56%
1917
16th to endDay
10%31331223461%
1920
November1st to 15thDay
13%423322446%53%
1793
16th to endDay
14%414413346%50%
1755
December1st to 15thDay
19%5%25%413446%42%
1755
16th to endDay
24%7%2442334439%
1872
January1st to 15thNight
16%5%2442433448%
2522
16th to endNight
17%6%24412345%47%
2704
February1st to 15thNight
16%5%14424335%48%
2312
16th to endNight
16%414424345%48%
2049
March1st to 15thNight
14%414323345%50%
2184
16th to endNight
14%425%42345%6%46%
2178
April1st to 15thNight
13%313424346%52%
1973
16th to endNight
10%5%245%25%446%48%
1641
May1st to 15thNight
11%5%25%6%3446%8%41%
1619
16th to endNight
8%4235%35%7%6%9%42%
1682
June1st to 15thNight
9%4246%36%5%8%12%36%
1620
16th to endNight
6%3245%35%7%8%12%40%
1620
July1st to 15thNight
8%5%26%6%47%7%9%12%29%
1620
16th to endNight
6%325%6%46%7%9%12%34%
1703
August1st to 15thNight
9%5%35%6%35%7%8%12%30%
1620
16th to endNight
10%5%26%7%45%7%7%9%32%
1869
September1st to 15thNight
11%4145%447%7%9%37%
1980
16th to endNight
14%5%25%42445%6%43%
1980
October1st to 15thNight
13%5%23313345%52%
2043
16th to endNight
10%31232333460%
2304
November1st to 15thNight
12%423323235%56%
2394
16th to endNight
14%423323345%52%
2535
December1st to 15thNight
16%5%24423345%45%
2535
16th to endNight
20%6%25%434345%39%
2704

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
40%38%17%24%4
1747
16th to endDay
38%26%20%22%8%
1872
February1st to 15thDay
38%49%20%21%5%
1870
16th to endDay
40%47%21%19%6%
1710
March1st to 15thDay
36%47%20%20%9%
2106
16th to endDay
40%5%11%22%17%3
2174
April1st to 15thDay
34%5%10%20%22%5%
1984
16th to endDay
33%6%9%22%21%6%
2319
May1st to 15thDay
36%6%14%20%18%3
2331
16th to endDay
35%8%16%24%14%1
2435
June1st to 15thDay
36%9%21%22%8%1
2340
16th to endDay
31%10%18%22%13%3
2340
July1st to 15thDay
39%11%18%20%7%2
2201
16th to endDay
35%13%19%19%9%2
2310
August1st to 15thDay
42%11%15%19%9%1
2327
16th to endDay
45%12%15%14%10%1
2316
September1st to 15thDay
38%10%12%17%17%3
1980
16th to endDay
38%5%11%20%18%5%
1980
October1st to 15thDay
32%39%20%26%7%
1917
16th to endDay
28%35%20%31%12%
1920
November1st to 15thDay
31%48%17%27%10%
1793
16th to endDay
36%36%19%26%7%
1755
December1st to 15thDay
42%48%19%18%7%
1755
16th to endDay
49%36%19%14%6%
1872
January1st to 15thNight
40%36%15%25%7%
2522
16th to endNight
40%25%19%23%9%
2704
February1st to 15thNight
39%35%20%23%7%
2321
16th to endNight
37%38%22%20%6%
2049
March1st to 15thNight
36%48%17%23%9%
2184
16th to endNight
37%5%11%18%21%5%
2178
April1st to 15thNight
32%38%23%23%7%
1973
16th to endNight
35%6%8%21%19%8%
1641
May1st to 15thNight
38%6%12%20%18%2
1620
16th to endNight
35%8%14%26%12%2
1684
June1st to 15thNight
36%9%19%23%9%1
1620
16th to endNight
32%11%17%21%13%3
1620
July1st to 15thNight
40%13%20%16%6%1
1530
16th to endNight
34%13%22%18%8%2
1595
August1st to 15thNight
41%11%16%20%9%1
1609
16th to endNight
42%11%17%15%11%1
1869
September1st to 15thNight
37%11%16%18%13%3
1980
16th to endNight
39%6%12%18%16%5%
1980
October1st to 15thNight
34%49%18%25%7%
2043
16th to endNight
27%35%18%30%13%
2304
November1st to 15thNight
31%36%17%29%11%
2394
16th to endNight
34%36%17%27%10%
2535
December1st to 15thNight
41%47%19%19%7%
2535
16th to endNight
47%38%15%18%6%
2704

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
22%8%32%31%5%
135
16th to endDay
17%22%31%19%6%2
144
February1st to 15thDay
19%11%45%23%
135
16th to endDay
25%10%34%25%5%
120
March1st to 15thDay
17%14%28%30%8%
291
16th to endDay
19%7%32%22%16%1
311
April1st to 15thDay
15%10%21%24%23%3
270
16th to endDay
12%222%30%20%10%
270
May1st to 15thDay
10%8%28%22%16%13%
288
16th to endDay
15%413%20%23%22%
331
June1st to 15thDay
11%28%24%26%26%
315
16th to endDay
9%10%24%24%30%
315
July1st to 15thDay
10%9%22%29%26%
305
16th to endDay
6%1420%38%27%
326
August1st to 15thDay
17%6%20%30%23%
313
16th to endDay
13%8%23%28%25%
332
September1st to 15thDay
14%210%20%29%23%
315
16th to endDay
19%112%23%27%14%
314
October1st to 15thDay
20%314%31%23%6%
315
16th to endDay
11%5%19%28%28%6%
336
November1st to 15thDay
23%6%19%23%20%7%
211
16th to endDay
8%5%21%36%20%7%
135
December1st to 15thDay
28%10%24%27%8%
135
16th to endDay
33%15%28%16%6%
144
January1st to 15thNight
20%11%30%29%8%
780
16th to endNight
20%11%34%29%4
832
February1st to 15thNight
18%10%31%35%4
764
16th to endNight
17%9%39%29%4
683
March1st to 15thNight
17%8%33%32%6%
780
16th to endNight
15%8%30%29%15%
792
April1st to 15thNight
13%10%28%32%15%
715
16th to endNight
13%425%33%21%1
540
May1st to 15thNight
13%323%37%19%2
540
16th to endNight
11%115%31%34%5%
563
June1st to 15thNight
11%11%30%34%10%
540
16th to endNight
7%10%30%37%12%
540
July1st to 15thNight
10%17%29%41%9%
510
16th to endNight
7%7%26%46%11%
564
August1st to 15thNight
12%15%27%43%9%
539
16th to endNight
14%7%26%42%8%
603
September1st to 15thNight
14%9%26%40%9%
720
16th to endNight
18%113%31%30%5%
717
October1st to 15thNight
15%319%29%26%5%
720
16th to endNight
11%323%33%24%2
768
November1st to 15thNight
14%323%34%22%3
760
16th to endNight
16%7%25%32%17%1
780
December1st to 15thNight
19%7%24%35%11%
780
16th to endNight
22%7%29%31%7%
832
Page generated at 2018-03-22 11:34:21. Version ac04

Copyright 2018 A. Danko


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