Visual Reconstructions Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Visual Reconstructions 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
37%
16327
15%
49208
10%
16289
42%
16289
21%
34032

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%
971
10%
2716
4%
970
23%
970
13%
2134
January16th to endNight
21%
893
9%
2765
4%
893
26%
893
11%
2163
February1st to 15thNight
18%
761
8%
2470
2%
761
25%
761
11%
1914
February16th to endNight
23%
683
14%
2049
6%
683
31%
683
15%
1512
March1st to 15thNight
28%
780
15%
2236
10%
780
32%
780
18%
1618
March16th to endNight
34%
792
19%
2178
10%
792
41%
792
23%
1520
April1st to 15thNight
32%
608
14%
1815
7%
608
38%
608
20%
1272
April16th to endNight
38%
540
20%
1620
8%
540
47%
540
26%
1058
May1st to 15thNight
40%
540
14%
1620
10%
540
46%
540
23%
1110
May16th to endNight
50%
562
16%
1684
11%
561
56%
561
29%
1061
June1st to 15thNight
54%
381
17%
1305
16%
381
60%
381
27%
790
June16th to endNight
59%
400
19%
1300
19%
400
64%
400
30%
770
July1st to 15thNight
63%
510
16%
1360
14%
510
66%
510
41%
808
July16th to endNight
67%
564
18%
1524
15%
531
70%
531
39%
883
August1st to 15thNight
64%
539
19%
1609
14%
536
68%
536
36%
946
August16th to endNight
64%
573
24%
1719
18%
573
69%
573
35%
999
September1st to 15thNight
58%
681
22%
1935
17%
681
61%
681
33%
1180
September16th to endNight
59%
717
24%
1980
19%
717
63%
717
35%
1209
October1st to 15thNight
45%
720
18%
2084
15%
720
50%
720
27%
1361
October16th to endNight
27%
768
16%
2386
10%
768
36%
768
17%
1679
November1st to 15thNight
36%
760
20%
2471
15%
760
44%
760
22%
1612
November16th to endNight
26%
780
14%
2639
9%
780
33%
780
15%
1862
December1st to 15thNight
17%
780
8%
2730
3%
780
24%
780
10%
2085
December16th to endNight
14%
1024
7%
3013
2%
1024
20%
1024
9%
2486

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
13%8%47%6%35%5%5%7%32%
49618
Night
14%8%36%5%3445%6%36%
49388
Cloud CoverDay
14%8%36%6%35%5%5%7%33%
49628
Night
14%8%36%5%3445%6%36%
49392
TransparencyDay
48%7%12%19%10%1
49317
Night
47%6%12%21%11%1
49208
SeeingDay
16%7%27%24%15%7%
6370
Night
18%7%29%29%12%1
16335

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%14%5%9%9%36%445%19%
1552
16th to endDay
14%16%8%11%7%45%5%45%15%
1809
February1st to 15thDay
15%14%6%10%8%45%45%5%18%
1719
16th to endDay
13%14%5%10%8%34446%22%
1710
March1st to 15thDay
17%10%5%8%7%35%447%25%
2043
16th to endDay
17%10%48%5%35%445%29%
2174
April1st to 15thDay
17%10%5%6%5%335%5%6%31%
2142
16th to endDay
16%8%45%5%24447%36%
2340
May1st to 15thDay
18%7%46%5%35%447%31%
2331
16th to endDay
13%5%25%5%35%5%5%8%39%
2431
June1st to 15thDay
9%5%35%6%35%46%8%39%
2649
16th to endDay
9%436%6%46%7%6%10%34%
2655
July1st to 15thDay
7%425%5%35%6%6%7%44%
2520
16th to endDay
7%5%25%5%46%7%8%10%37%
2537
August1st to 15thDay
8%426%5%46%6%7%9%37%
2340
16th to endDay
11%425%5%35%5%7%8%39%
2483
September1st to 15thDay
12%5%35%435%5%5%8%40%
2010
16th to endDay
12%6%15%4345%6%8%40%
1980
October1st to 15thDay
13%7%26%435%45%7%39%
1875
16th to endDay
19%10%26%5%44445%32%
1836
November1st to 15thDay
14%8%35%5%35%45%6%37%
1717
16th to endDay
16%10%5%8%6%35%446%29%
1649
December1st to 15thDay
15%12%7%10%6%35%346%22%
1560
16th to endDay
20%15%6%9%7%34445%16%
1556
January1st to 15thNight
20%11%48%6%45%44425%
2716
16th to endNight
12%13%7%10%7%345%45%23%
2765
February1st to 15thNight
14%14%5%8%7%35%45%425%
2468
16th to endNight
16%11%48%6%34446%28%
2049
March1st to 15thNight
16%10%36%6%35%35%5%33%
2224
16th to endNight
15%6%36%5%35%5%46%36%
2178
April1st to 15thNight
18%7%35%5%3445%6%34%
1815
16th to endNight
14%7%245%3345%7%40%
1620
May1st to 15thNight
16%6%36%5%245%5%8%35%
1620
16th to endNight
11%425%5%34448%44%
1682
June1st to 15thNight
9%325%5%35%5%5%7%46%
1305
16th to endNight
9%4244345%7%8%45%
1300
July1st to 15thNight
6%41442335%8%52%
1440
16th to endNight
5%323325%5%6%9%52%
1629
August1st to 15thNight
6%3145%35%5%6%9%49%
1620
16th to endNight
9%4135%23346%53%
1719
September1st to 15thNight
10%434324447%50%
1935
16th to endNight
10%415%423348%49%
1980
October1st to 15thNight
15%7%2442345%6%42%
2084
16th to endNight
19%8%35%6%34445%33%
2386
November1st to 15thNight
14%8%35%5%245%5%6%39%
2471
16th to endNight
19%9%36%5%25%45%6%30%
2639
December1st to 15thNight
19%12%5%8%5%24445%25%
2730
16th to endNight
20%14%7%9%6%3444419%
3013

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%13%410%9%36%446%19%
1552
16th to endDay
15%16%8%10%8%36%5%45%15%
1809
February1st to 15thDay
16%14%5%9%8%46%5%5%419%
1719
16th to endDay
14%13%5%10%7%44446%23%
1710
March1st to 15thDay
17%10%5%8%7%34437%26%
2054
16th to endDay
18%10%47%6%35%345%29%
2173
April1st to 15thDay
18%10%46%5%335%5%6%30%
2142
16th to endDay
17%8%36%5%23447%36%
2340
May1st to 15thDay
18%7%36%5%35%446%32%
2331
16th to endDay
13%6%25%5%345%5%7%39%
2431
June1st to 15thDay
10%5%25%6%345%5%9%39%
2649
16th to endDay
9%436%6%36%7%6%10%34%
2655
July1st to 15thDay
7%4246%36%6%6%8%44%
2520
16th to endDay
7%425%5%46%7%7%10%37%
2537
August1st to 15thDay
8%426%6%35%6%7%9%38%
2340
16th to endDay
11%425%5%35%6%6%8%39%
2483
September1st to 15thDay
12%5%35%5%35%45%8%41%
2010
16th to endDay
12%5%25%4245%6%8%41%
1980
October1st to 15thDay
13%7%35%5%35%35%7%39%
1875
16th to endDay
20%9%26%5%34436%32%
1836
November1st to 15thDay
14%9%25%435%45%6%37%
1717
16th to endDay
16%10%47%6%35%446%29%
1649
December1st to 15thDay
16%12%8%9%6%35%446%22%
1560
16th to endDay
21%15%7%8%8%34445%16%
1556
January1st to 15thNight
20%11%5%7%7%35%44425%
2716
16th to endNight
13%14%7%10%7%445%45%23%
2765
February1st to 15thNight
14%14%49%7%35%45%425%
2461
16th to endNight
16%11%48%6%25%446%29%
2049
March1st to 15thNight
17%10%46%435%445%33%
2236
16th to endNight
15%6%36%5%35%5%5%6%36%
2178
April1st to 15thNight
18%7%35%5%3445%6%34%
1815
16th to endNight
15%7%25%5%235%5%7%40%
1620
May1st to 15thNight
17%6%26%5%235%5%8%35%
1619
16th to endNight
11%425%5%3445%7%44%
1682
June1st to 15thNight
9%325%4345%6%7%46%
1305
16th to endNight
9%5%244345%6%8%46%
1300
July1st to 15thNight
7%31442446%8%53%
1440
16th to endNight
4423325%5%6%9%52%
1629
August1st to 15thNight
6%3245%35%5%6%8%49%
1620
16th to endNight
9%4245%2435%6%53%
1719
September1st to 15thNight
10%424423447%51%
1935
16th to endNight
11%32442345%8%49%
1980
October1st to 15thNight
16%6%3442345%7%42%
2084
16th to endNight
20%7%26%6%335%45%34%
2386
November1st to 15thNight
13%8%25%43446%6%39%
2471
16th to endNight
20%9%35%6%345%5%6%30%
2639
December1st to 15thNight
19%12%5%7%6%2445%5%25%
2730
16th to endNight
21%14%7%9%6%4444418%
3013

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
64%7%11%9%5%
1553
16th to endDay
69%6%10%9%4
1809
February1st to 15thDay
65%6%8%14%5%
1721
16th to endDay
61%5%10%16%5%
1710
March1st to 15thDay
58%6%11%16%6%
2054
16th to endDay
55%5%9%21%6%1
2174
April1st to 15thDay
53%5%10%19%11%
2142
16th to endDay
47%413%17%14%2
2340
May1st to 15thDay
51%6%9%18%11%2
2331
16th to endDay
41%7%12%23%13%1
2435
June1st to 15thDay
39%7%13%24%13%1
2649
16th to endDay
40%9%14%19%14%1
2655
July1st to 15thDay
35%7%11%25%18%2
2371
16th to endDay
36%9%16%21%13%2
2380
August1st to 15thDay
37%10%13%24%12%1
2327
16th to endDay
38%7%12%23%14%2
2483
September1st to 15thDay
38%7%14%26%12%
2010
16th to endDay
37%7%12%29%12%
1980
October1st to 15thDay
42%6%13%22%12%1
1875
16th to endDay
52%5%14%18%7%
1836
November1st to 15thDay
45%6%12%23%10%1
1717
16th to endDay
55%6%13%17%6%
1649
December1st to 15thDay
62%5%12%13%5%
1560
16th to endDay
69%5%12%9%3
1556
January1st to 15thNight
61%5%11%13%7%
2716
16th to endNight
61%6%13%13%4
2765
February1st to 15thNight
59%7%10%14%6%
2470
16th to endNight
56%5%11%18%7%
2049
March1st to 15thNight
52%5%10%19%11%1
2236
16th to endNight
47%5%11%23%10%1
2178
April1st to 15thNight
48%5%11%20%13%
1815
16th to endNight
41%6%11%19%17%4
1620
May1st to 15thNight
45%6%12%20%13%2
1620
16th to endNight
38%6%12%23%16%3
1684
June1st to 15thNight
34%8%11%28%15%1
1305
16th to endNight
33%7%13%24%19%1
1300
July1st to 15thNight
28%6%11%30%21%2
1360
16th to endNight
26%8%17%24%18%3
1524
August1st to 15thNight
30%7%14%30%14%2
1609
16th to endNight
30%6%12%30%17%2
1719
September1st to 15thNight
33%6%12%28%17%1
1935
16th to endNight
33%5%12%32%15%
1980
October1st to 15thNight
41%5%12%21%17%1
2084
16th to endNight
50%5%12%22%7%
2386
November1st to 15thNight
43%6%13%24%11%1
2471
16th to endNight
52%5%14%20%6%
2639
December1st to 15thNight
60%6%13%13%6%
2730
16th to endNight
67%5%10%11%4
3013

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
21%14%41%14%5%1
135
16th to endDay
30%10%43%11%4
144
February1st to 15thDay
23%14%43%17%
135
16th to endDay
20%16%44%14%4
120
March1st to 15thDay
25%14%30%20%8%
239
16th to endDay
23%8%28%29%9%1
311
April1st to 15thDay
20%10%31%22%11%3
270
16th to endDay
22%7%30%19%12%8%
270
May1st to 15thDay
22%6%28%24%13%4
288
16th to endDay
15%7%25%26%17%7%
331
June1st to 15thDay
12%5%29%33%16%3
468
16th to endDay
10%5%34%27%16%5%
495
July1st to 15thDay
9%324%32%20%9%
475
16th to endDay
8%322%31%23%12%
397
August1st to 15thDay
7%118%30%22%18%
313
16th to endDay
15%315%23%24%17%
332
September1st to 15thDay
11%319%22%28%14%
315
16th to endDay
15%413%22%28%14%
314
October1st to 15thDay
17%6%26%21%20%8%
315
16th to endDay
22%14%32%25%41
252
November1st to 15thDay
17%13%27%26%13%2
135
16th to endDay
20%20%39%16%3
110
December1st to 15thDay
20%24%34%14%6%
90
16th to endDay
25%23%39%9%1
116
January1st to 15thNight
26%12%34%21%4
975
16th to endNight
19%11%36%28%5%
893
February1st to 15thNight
22%10%39%23%3
764
16th to endNight
22%10%35%27%4
683
March1st to 15thNight
22%8%35%27%5%
780
16th to endNight
17%8%32%29%10%1
792
April1st to 15thNight
20%12%29%31%5%
608
16th to endNight
17%6%33%30%10%1
540
May1st to 15thNight
19%5%26%35%11%1
540
16th to endNight
13%224%37%19%2
563
June1st to 15thNight
9%227%45%15%
381
16th to endNight
11%219%47%19%
400
July1st to 15thNight
8%117%40%28%3
510
16th to endNight
5%117%47%24%3
564
August1st to 15thNight
7%116%38%31%4
539
16th to endNight
9%216%34%32%4
573
September1st to 15thNight
12%417%32%25%6%
681
16th to endNight
13%316%31%27%6%
717
October1st to 15thNight
18%5%23%29%18%3
720
16th to endNight
25%9%33%25%5%
768
November1st to 15thNight
19%8%30%26%13%1
760
16th to endNight
22%15%30%22%7%
780
December1st to 15thNight
26%12%35%19%5%
780
16th to endNight
27%10%38%20%3
1024
Page generated at 2018-03-22 11:34:27. Version ac04

Copyright 2018 A. Danko


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