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 2017-04-09.

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%
15501
26%
45447
17%
15460
61%
15460
38%
25633

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
41%
861
31%
2589
18%
861
54%
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%
521
22%
1738
14%
521
50%
521
29%
1000
April16th to endNight
38%
495
20%
1650
15%
495
47%
495
25%
998
May1st to 15thNight
48%
495
20%
1438
18%
495
53%
495
29%
922
May16th to endNight
50%
513
16%
1370
10%
513
55%
513
31%
882
June1st to 15thNight
58%
495
18%
1320
10%
495
62%
495
40%
783
June16th to endNight
72%
495
24%
1320
18%
495
74%
495
53%
696
July1st to 15thNight
67%
465
17%
1240
14%
465
68%
465
36%
765
July16th to endNight
78%
522
26%
1304
22%
489
77%
489
48%
709
August1st to 15thNight
71%
494
20%
1504
20%
491
72%
491
38%
836
August16th to endNight
71%
525
25%
1750
27%
525
75%
525
38%
921
September1st to 15thNight
61%
495
29%
1650
27%
495
69%
495
35%
892
September16th to endNight
70%
492
35%
1788
33%
492
78%
492
48%
782
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
57%
875
30%
2275
17%
875
63%
875
46%
1278
November16th to endNight
55%
900
35%
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
26%
2688
14%
960
56%
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%
45850
Night
6%5%2442445%7%53%
45619
Cloud CoverDay
6%42442445%8%52%
45848
Night
6%5%2442445%7%53%
45619
TransparencyDay
29%411%27%20%7%
45524
Night
29%312%27%20%6%
45447
SeeingDay
10%5%22%31%22%6%
5189
Night
8%425%43%15%1
15510

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%23425%45%7%48%
2073
16th to endDay
12%6%25%32446%6%43%
1980
May1st to 15thDay
13%6%243245%5%7%43%
2180
16th to endDay
9%5%25%4345%5%9%43%
2392
June1st to 15thDay
8%31332446%10%49%
2310
16th to endDay
221231447%8%60%
2310
July1st to 15thDay
7%313425%5%7%8%49%
2310
16th to endDay
3113435%6%7%10%51%
2460
August1st to 15thDay
34135%35%6%8%10%47%
2114
16th to endDay
422325%5%6%8%56%
2100
September1st to 15thDay
8%313323347%58%
1980
16th to endDay
5%22312446%65%
1841
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%48%
1738
16th to endNight
14%6%2442345%6%44%
1650
May1st to 15thNight
15%5%134245%5%7%42%
1437
16th to endNight
11%4145%35%5%6%8%43%
1369
June1st to 15thNight
7%313325%5%7%10%49%
1320
16th to endNight
211432347%8%60%
1320
July1st to 15thNight
7%325%425%5%6%7%47%
1320
16th to endNight
3212335%5%8%9%53%
1400
August1st to 15thNight
4415%5%35%5%7%9%49%
1512
16th to endNight
5%31442445%7%55%
1750
September1st to 15thNight
8%424324447%53%
1650
16th to endNight
42231345%5%65%
1788
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%7%2342445%7%47%
2073
16th to endDay
13%6%25%425%5%6%7%42%
1980
May1st to 15thDay
14%5%243245%5%7%43%
2180
16th to endDay
10%5%15%5%245%5%9%44%
2392
June1st to 15thDay
9%3134245%6%10%49%
2310
16th to endDay
221232446%8%61%
2310
July1st to 15thDay
7%313425%5%7%8%49%
2310
16th to endDay
3213435%6%8%9%51%
2460
August1st to 15thDay
4313435%6%7%10%47%
2114
16th to endDay
5%212325%5%6%8%56%
2100
September1st to 15thDay
8%31222235%7%59%
1980
16th to endDay
5%212322445%65%
1841
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%48%
1738
16th to endNight
15%6%2342345%6%44%
1650
May1st to 15thNight
15%5%143245%5%8%42%
1437
16th to endNight
12%5%14435%45%8%43%
1369
June1st to 15thNight
8%212336%5%6%10%49%
1320
16th to endNight
211332347%9%60%
1320
July1st to 15thNight
8%325%425%5%6%7%47%
1320
16th to endNight
3213235%5%7%9%54%
1400
August1st to 15thNight
43145%346%6%9%49%
1512
16th to endNight
5%32442445%7%55%
1750
September1st to 15thNight
8%414334447%53%
1650
16th to endNight
5%21221345%465%
1788
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
34%312%27%14%7%
2073
16th to endDay
38%412%24%16%3
1980
May1st to 15thDay
38%411%29%15%1
2180
16th to endDay
36%5%15%22%14%5%
2396
June1st to 15thDay
28%5%15%23%19%7%
2310
16th to endDay
18%49%25%27%14%
2310
July1st to 15thDay
29%5%12%22%17%12%
2161
16th to endDay
24%5%10%28%21%9%
2293
August1st to 15thDay
28%5%13%23%16%12%
2098
16th to endDay
23%5%8%26%26%11%
2100
September1st to 15thDay
25%37%24%23%15%
1980
16th to endDay
20%26%27%35%7%
1841
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
36%311%27%16%4
1738
16th to endNight
40%410%24%17%3
1650
May1st to 15thNight
38%6%15%23%15%2
1438
16th to endNight
36%7%19%19%10%5%
1370
June1st to 15thNight
29%5%20%24%13%7%
1320
16th to endNight
19%412%28%25%9%
1320
July1st to 15thNight
33%5%13%25%13%9%
1240
16th to endNight
22%5%14%30%18%8%
1304
August1st to 15thNight
29%418%22%16%9%
1504
16th to endNight
27%49%26%22%9%
1750
September1st to 15thNight
30%310%21%21%12%
1650
16th to endNight
18%36%31%30%8%
1788
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
15%16%34%22%6%4
244
16th to endDay
25%16%30%16%9%2
210
May1st to 15thDay
18%8%20%32%16%4
393
16th to endDay
16%6%19%29%21%5%
437
June1st to 15thDay
11%5%22%30%22%7%
420
16th to endDay
3323%35%27%7%
420
July1st to 15thDay
10%213%32%34%6%
400
16th to endDay
3113%31%39%11%
445
August1st to 15thDay
6%321%34%24%9%
285
16th to endDay
4321%34%27%8%
268
September1st to 15thDay
9%325%33%21%5%
255
16th to endDay
6%218%25%29%18%
116
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
12%6%36%36%7%
521
16th to endNight
17%8%29%32%12%
495
May1st to 15thNight
18%6%21%38%14%1
495
16th to endNight
14%225%38%18%1
515
June1st to 15thNight
10%224%45%16%
495
16th to endNight
3117%56%21%
495
July1st to 15thNight
9%311%44%30%1
465
16th to endNight
5%18%46%36%1
522
August1st to 15thNight
5%29%52%29%1
494
16th to endNight
7%19%46%32%1
525
September1st to 15thNight
10%217%43%23%2
495
16th to endNight
6%118%45%25%2
492
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 2017-04-10 07:00:42. Version ac04

Copyright 2017 A. Danko


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