Roland's Astro Corral
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roland's Astro Corral clear sky chart from 2005-11-05 to 2017-09-24.

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
53%
15999
26%
46933
17%
15958
61%
15958
38%
26419

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
49%
898
29%
2506
18%
895
58%
895
42%
1379
January16th to endNight
42%
861
30%
2589
18%
861
55%
861
40%
1410
February1st to 15thNight
41%
699
22%
2235
13%
697
52%
697
32%
1300
February16th to endNight
40%
632
28%
1894
15%
632
51%
632
35%
1083
March1st to 15thNight
50%
720
26%
2150
15%
720
59%
720
40%
1188
March16th to endNight
41%
657
23%
2001
13%
657
51%
657
33%
1164
April1st to 15thNight
39%
539
21%
1798
14%
539
50%
539
29%
1024
April16th to endNight
37%
540
20%
1800
14%
540
47%
540
25%
1094
May1st to 15thNight
48%
540
19%
1569
17%
540
53%
540
30%
997
May16th to endNight
49%
561
17%
1498
11%
561
53%
561
31%
968
June1st to 15thNight
61%
540
17%
1440
10%
540
65%
540
43%
832
June16th to endNight
71%
540
25%
1440
19%
540
74%
540
52%
768
July1st to 15thNight
68%
510
16%
1360
14%
510
68%
510
37%
826
July16th to endNight
77%
564
26%
1416
22%
531
77%
531
47%
773
August1st to 15thNight
71%
539
19%
1642
20%
536
73%
536
38%
907
August16th to endNight
73%
573
27%
1910
30%
573
76%
573
39%
988
September1st to 15thNight
64%
540
27%
1800
26%
540
71%
540
37%
956
September16th to endNight
67%
519
35%
1885
32%
519
76%
519
46%
839
October1st to 15thNight
54%
624
29%
1944
21%
624
60%
624
38%
1064
October16th to endNight
58%
768
34%
2176
21%
768
66%
768
48%
1156
November1st to 15thNight
56%
875
30%
2275
17%
875
62%
875
46%
1278
November16th to endNight
55%
900
34%
2397
19%
900
64%
900
46%
1314
December1st to 15thNight
45%
900
23%
2520
12%
900
55%
900
37%
1476
December16th to endNight
46%
960
25%
2688
14%
960
55%
960
34%
1635

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
6%42442445%8%52%
48011
Night
6%5%2442445%7%53%
47105
Cloud CoverDay
6%42442445%8%52%
48009
Night
6%5%2442445%7%53%
47105
TransparencyDay
29%411%27%20%7%
47685
Night
29%312%27%20%6%
46933
SeeingDay
10%5%21%31%22%7%
5937
Night
8%425%43%16%1
16008

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
35%35%424447%55%
1432
16th to endDay
25%3442445%7%55%
1644
February1st to 15thDay
36%46%5%345%5%6%47%
1626
16th to endDay
27%35%425%45%5%52%
1580
March1st to 15thDay
35%243245%48%54%
1809
16th to endDay
7%7%2443445%9%45%
2223
April1st to 15thDay
9%6%2332445%7%49%
2150
16th to endDay
12%6%25%42446%7%42%
2160
May1st to 15thDay
13%5%243245%6%8%43%
2379
16th to endDay
10%5%25%4245%5%9%43%
2616
June1st to 15thDay
8%31332446%10%50%
2520
16th to endDay
221232447%8%60%
2520
July1st to 15thDay
7%313425%5%7%8%48%
2520
16th to endDay
3113435%5%7%10%51%
2656
August1st to 15thDay
44135%35%6%8%10%46%
2306
16th to endDay
422325%5%6%8%56%
2292
September1st to 15thDay
7%312323347%59%
2160
16th to endDay
6%22312446%65%
1932
October1st to 15thDay
9%414213347%56%
1684
16th to endDay
7%413213336%63%
1683
November1st to 15thDay
35%2432336%8%55%
1583
16th to endDay
25%24413448%58%
1560
December1st to 15thDay
37%37%42436%7%49%
1440
16th to endDay
5%9%36%5%23347%49%
1536
January1st to 15thNight
35%24423347%56%
2506
16th to endNight
35%25%423345%57%
2589
February1st to 15thNight
37%36%5%2445%7%48%
2225
16th to endNight
38%3441435%6%53%
1894
March1st to 15thNight
3425%42445%7%54%
2150
16th to endNight
7%5%3443445%8%48%
2001
April1st to 15thNight
9%6%25%424438%49%
1798
16th to endNight
15%6%2442445%6%43%
1800
May1st to 15thNight
15%5%134245%5%7%43%
1568
16th to endNight
12%4145%35%5%5%8%43%
1497
June1st to 15thNight
7%312325%47%9%52%
1440
16th to endNight
221432347%8%60%
1440
July1st to 15thNight
7%325%425%5%6%8%48%
1440
16th to endNight
3212335%6%8%9%53%
1512
August1st to 15thNight
3315%5%35%5%7%9%48%
1650
16th to endNight
431442445%7%55%
1910
September1st to 15thNight
8%324324447%54%
1800
16th to endNight
5%2231345%5%64%
1885
October1st to 15thNight
11%324323346%55%
1944
16th to endNight
8%412212346%61%
2176
November1st to 15thNight
442332345%6%59%
2275
16th to endNight
35%2332445%6%59%
2397
December1st to 15thNight
46%35%42445%7%51%
2520
16th to endNight
5%7%35%434446%50%
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
36%25%423446%55%
1432
16th to endDay
35%3432445%7%56%
1644
February1st to 15thDay
36%5%5%5%346%5%6%47%
1626
16th to endDay
27%35%325%45%5%53%
1580
March1st to 15thDay
4434425%448%53%
1809
16th to endDay
7%7%1443445%9%46%
2221
April1st to 15thDay
9%6%2342445%7%48%
2150
16th to endDay
13%6%25%425%5%6%7%42%
2160
May1st to 15thDay
14%5%243245%5%7%43%
2379
16th to endDay
10%5%15%5%245%5%8%43%
2616
June1st to 15thDay
8%3134245%6%10%50%
2520
16th to endDay
221232446%8%60%
2520
July1st to 15thDay
7%313425%5%7%8%49%
2520
16th to endDay
3213435%6%7%9%51%
2656
August1st to 15thDay
5%3135%35%6%8%10%46%
2306
16th to endDay
4212325%5%6%8%56%
2292
September1st to 15thDay
8%31222335%7%59%
2160
16th to endDay
5%212322445%65%
1932
October1st to 15thDay
9%413223347%57%
1684
16th to endDay
7%413212336%63%
1683
November1st to 15thDay
442422436%7%55%
1583
16th to endDay
25%2431435%7%58%
1560
December1st to 15thDay
47%37%5%24447%49%
1440
16th to endDay
5%9%35%423346%49%
1536
January1st to 15thNight
35%23423347%57%
2506
16th to endNight
35%25%423445%57%
2589
February1st to 15thNight
46%36%5%2445%7%48%
2225
16th to endNight
48%345%23346%53%
1894
March1st to 15thNight
3435%42445%6%55%
2150
16th to endNight
7%5%3443435%7%49%
2001
April1st to 15thNight
9%6%26%423447%49%
1798
16th to endNight
15%6%24424446%43%
1800
May1st to 15thNight
15%5%1432445%8%43%
1568
16th to endNight
12%5%14435%45%8%43%
1497
June1st to 15thNight
7%212325%46%10%52%
1440
16th to endNight
221332347%8%59%
1440
July1st to 15thNight
7%325%425%5%6%8%48%
1440
16th to endNight
3213335%5%8%9%53%
1512
August1st to 15thNight
43145%346%6%9%49%
1650
16th to endNight
5%32442445%7%56%
1910
September1st to 15thNight
8%414324447%54%
1800
16th to endNight
5%21231345%465%
1885
October1st to 15thNight
11%414313346%55%
1944
16th to endNight
8%412212346%61%
2176
November1st to 15thNight
5%323323346%59%
2275
16th to endNight
35%2332445%6%59%
2397
December1st to 15thNight
47%345%2345%7%50%
2520
16th to endNight
5%7%3443345%6%50%
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
29%313%34%16%3
1433
16th to endDay
27%311%32%20%4
1644
February1st to 15thDay
35%413%33%10%3
1627
16th to endDay
30%39%32%19%4
1580
March1st to 15thDay
28%311%27%22%5%
1809
16th to endDay
34%314%26%15%5%
2223
April1st to 15thDay
33%312%27%16%7%
2150
16th to endDay
39%412%24%16%3
2160
May1st to 15thDay
37%411%29%15%2
2379
16th to endDay
36%5%15%23%14%4
2620
June1st to 15thDay
27%5%15%23%20%7%
2520
16th to endDay
19%48%26%27%13%
2520
July1st to 15thDay
29%5%11%22%18%12%
2371
16th to endDay
25%5%10%28%21%9%
2489
August1st to 15thDay
28%5%13%23%16%11%
2290
16th to endDay
22%5%7%26%27%10%
2292
September1st to 15thDay
24%37%25%23%15%
2160
16th to endDay
21%26%27%34%7%
1932
October1st to 15thDay
28%311%23%26%7%
1684
16th to endDay
22%29%32%23%9%
1683
November1st to 15thDay
26%312%26%21%10%
1583
16th to endDay
24%19%29%27%7%
1560
December1st to 15thDay
33%313%32%13%2
1440
16th to endDay
35%314%27%16%3
1536
January1st to 15thNight
27%213%30%22%3
2506
16th to endNight
29%210%29%23%4
2589
February1st to 15thNight
34%313%30%14%3
2235
16th to endNight
32%38%29%20%6%
1894
March1st to 15thNight
28%210%27%24%5%
2150
16th to endNight
33%313%25%20%3
2001
April1st to 15thNight
35%311%28%16%5%
1798
16th to endNight
40%410%24%17%3
1800
May1st to 15thNight
37%5%14%24%15%1
1569
16th to endNight
36%7%18%20%10%5%
1498
June1st to 15thNight
27%420%25%13%8%
1440
16th to endNight
20%412%28%25%8%
1440
July1st to 15thNight
32%5%12%25%14%9%
1360
16th to endNight
23%5%14%29%18%8%
1416
August1st to 15thNight
29%418%23%15%8%
1642
16th to endNight
26%49%26%23%9%
1910
September1st to 15thNight
29%310%22%21%12%
1800
16th to endNight
19%36%30%30%8%
1885
October1st to 15thNight
29%312%22%23%8%
1944
16th to endNight
24%29%30%24%8%
2176
November1st to 15thNight
25%39%24%25%11%
2275
16th to endNight
24%37%31%26%6%
2397
December1st to 15thNight
32%313%31%16%3
2520
16th to endNight
34%413%30%15%2
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
7%321%37%20%10%
90
16th to endDay
9%337%37%5%7%
96
February1st to 15thDay
5%8%27%48%8%
90
16th to endDay
7%6%30%30%20%3
81
March1st to 15thDay
7%12%29%31%16%4
99
16th to endDay
11%12%34%31%8%
288
April1st to 15thDay
14%15%34%24%7%3
269
16th to endDay
22%16%30%18%11%1
270
May1st to 15thDay
17%7%22%29%17%5%
468
16th to endDay
17%5%20%30%20%6%
517
June1st to 15thDay
9%421%30%23%10%
495
16th to endDay
3322%36%28%6%
495
July1st to 15thDay
10%211%30%36%8%
475
16th to endDay
4111%30%39%12%
515
August1st to 15thDay
6%219%35%25%10%
348
16th to endDay
4319%34%28%9%
332
September1st to 15thDay
8%221%32%22%11%
315
16th to endDay
7%222%25%27%14%
142
October1st to 15thDay
11%13%38%21%15%
90
16th to endDay
10%320%23%29%12%
96
November1st to 15thDay
3411%33%25%22%
90
16th to endDay
20%6%26%26%16%3
90
December1st to 15thDay
8%6%28%44%11%
90
16th to endDay
8%7%22%46%13%1
96
January1st to 15thNight
6%7%29%40%13%1
900
16th to endNight
7%438%38%9%
861
February1st to 15thNight
7%435%42%8%
704
16th to endNight
9%7%36%41%6%
632
March1st to 15thNight
5%6%32%43%12%
720
16th to endNight
9%7%35%38%8%
657
April1st to 15thNight
11%6%36%36%7%
539
16th to endNight
17%7%30%32%11%
540
May1st to 15thNight
18%5%21%39%14%1
540
16th to endNight
14%225%38%18%1
563
June1st to 15thNight
9%223%44%19%1
540
16th to endNight
4117%56%20%
540
July1st to 15thNight
8%210%44%32%1
510
16th to endNight
5%18%44%37%1
564
August1st to 15thNight
5%19%53%28%1
539
16th to endNight
7%19%47%32%1
573
September1st to 15thNight
10%216%41%25%3
540
16th to endNight
6%219%44%24%2
519
October1st to 15thNight
13%5%22%37%19%1
624
16th to endNight
11%420%43%17%2
768
November1st to 15thNight
7%5%23%47%14%1
875
16th to endNight
6%5%26%47%12%
900
December1st to 15thNight
8%5%31%46%6%1
900
16th to endNight
8%6%27%47%10%
960
Page generated at 2017-09-25 07:02:17. Version ac04

Copyright 2017 A. Danko


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