AASO/Ridgemont Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AASO/Ridgemont Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
48%
16460
23%
49063
17%
16415
54%
16415
29%
30486

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
31%
975
20%
2716
10%
970
39%
970
24%
1847
January16th to endNight
31%
1040
22%
2720
10%
1040
39%
1040
29%
1826
February1st to 15thNight
28%
776
18%
2304
9%
773
34%
773
21%
1593
February16th to endNight
27%
683
19%
2049
9%
683
35%
683
21%
1401
March1st to 15thNight
30%
764
17%
2292
9%
764
36%
764
22%
1551
March16th to endNight
41%
593
17%
1998
14%
593
46%
593
21%
1327
April1st to 15thNight
41%
539
24%
1797
16%
539
55%
539
33%
1012
April16th to endNight
47%
540
24%
1800
21%
540
55%
540
29%
1074
May1st to 15thNight
48%
539
18%
1661
13%
539
54%
539
26%
1073
May16th to endNight
65%
562
21%
1605
17%
561
67%
561
31%
1009
June1st to 15thNight
71%
540
23%
1440
17%
540
73%
540
41%
863
June16th to endNight
77%
540
24%
1440
19%
540
79%
540
42%
835
July1st to 15thNight
73%
510
17%
1360
16%
510
73%
510
36%
852
July16th to endNight
77%
564
25%
1454
22%
531
79%
531
45%
815
August1st to 15thNight
78%
539
22%
1788
26%
536
79%
536
38%
944
August16th to endNight
76%
573
25%
1910
30%
573
77%
573
35%
1044
September1st to 15thNight
69%
540
27%
1800
29%
540
71%
540
33%
1022
September16th to endNight
66%
717
30%
1980
24%
717
69%
717
39%
1154
October1st to 15thNight
60%
720
30%
2055
24%
720
65%
720
37%
1184
October16th to endNight
48%
768
30%
2363
23%
768
56%
768
33%
1396
November1st to 15thNight
47%
760
30%
2471
25%
760
57%
760
34%
1378
November16th to endNight
40%
780
27%
2535
21%
780
50%
780
29%
1508
December1st to 15thNight
36%
858
19%
2613
12%
858
43%
858
22%
1745
December16th to endNight
30%
1040
19%
2912
9%
1040
38%
1040
21%
2033

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%6%25%43445%7%42%
49567
Night
13%5%24423446%46%
49243
TransparencyDay
40%5%11%23%15%3
49251
Night
37%5%10%23%18%4
49064
SeeingDay
14%318%25%24%13%
6293
Night
16%5%23%31%19%3
16462

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
22%6%35%323445%38%
1552
16th to endDay
14%6%36%434345%43%
1853
February1st to 15thDay
15%9%45%5%3335%5%39%
1887
16th to endDay
17%8%46%5%34346%35%
1710
March1st to 15thDay
21%8%34423445%37%
1905
16th to endDay
17%7%36%5%26%45%7%34%
2233
April1st to 15thDay
12%6%26%323447%45%
2151
16th to endDay
16%7%26%5%335%46%37%
2160
May1st to 15thDay
17%6%25%5%25%5%5%8%36%
2289
16th to endDay
10%6%36%6%35%5%6%8%38%
2506
June1st to 15thDay
7%414425%6%7%9%46%
2520
16th to endDay
43245%35%7%6%10%46%
2520
July1st to 15thDay
9%425%6%445%6%9%41%
2520
16th to endDay
43145%35%6%8%12%43%
2611
August1st to 15thDay
7%5%245%35%5%6%9%43%
2160
16th to endDay
8%4245%45%5%6%10%42%
2292
September1st to 15thDay
12%5%244346%5%7%43%
2146
16th to endDay
11%425%424446%49%
1980
October1st to 15thDay
12%5%145%23345%51%
1902
16th to endDay
16%31332333452%
1860
November1st to 15thDay
14%5%14323346%49%
1717
16th to endDay
18%6%24313335%46%
1755
December1st to 15thDay
19%8%2432345%5%40%
1674
16th to endDay
20%10%35%423336%35%
1664
January1st to 15thNight
19%6%35%323346%40%
2716
16th to endNight
15%6%35%42345%5%44%
2720
February1st to 15thNight
19%7%36%5%23435%38%
2295
16th to endNight
15%7%37%5%34445%39%
2049
March1st to 15thNight
17%8%34424435%40%
2292
16th to endNight
16%7%35%5%24446%39%
1998
April1st to 15thNight
12%5%2341335%7%50%
1797
16th to endNight
15%42342345%7%46%
1800
May1st to 15thNight
17%5%245%235%47%42%
1660
16th to endNight
7%426%5%346%5%10%43%
1604
June1st to 15thNight
6%32442447%8%52%
1440
16th to endNight
42144345%8%12%50%
1440
July1st to 15thNight
7%324435%6%5%9%47%
1440
16th to endNight
5%31432445%12%53%
1553
August1st to 15thNight
43134245%6%8%55%
1800
16th to endNight
7%4134245%7%9%50%
1910
September1st to 15thNight
8%5%25%32335%6%52%
1800
16th to endNight
10%413424346%55%
1980
October1st to 15thNight
10%423433247%53%
2055
16th to endNight
15%5%1442323452%
2363
November1st to 15thNight
13%5%14312347%52%
2471
16th to endNight
16%5%2432233450%
2535
December1st to 15thNight
19%7%2432335%5%39%
2613
16th to endNight
22%8%24424335%39%
2912

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
48%47%26%11%2
1553
16th to endDay
43%412%26%12%1
1853
February1st to 15thDay
48%310%24%11%2
1889
16th to endDay
49%412%20%10%2
1710
March1st to 15thDay
49%49%20%12%4
1905
16th to endDay
49%5%13%22%9%
2235
April1st to 15thDay
38%410%23%19%2
2151
16th to endDay
46%5%9%24%12%1
2160
May1st to 15thDay
45%8%11%19%13%
2289
16th to endDay
41%8%15%19%12%2
2510
June1st to 15thDay
31%8%14%25%18%2
2520
16th to endDay
30%8%14%23%19%3
2520
July1st to 15thDay
38%7%13%22%13%4
2371
16th to endDay
30%8%18%27%14%1
2447
August1st to 15thDay
34%8%14%24%16%2
2148
16th to endDay
33%7%14%23%16%4
2292
September1st to 15thDay
37%6%10%23%18%3
2146
16th to endDay
35%48%22%23%5%
1980
October1st to 15thDay
35%410%22%20%5%
1902
16th to endDay
35%35%29%21%5%
1860
November1st to 15thDay
36%47%20%23%7%
1717
16th to endDay
40%27%26%18%3
1755
December1st to 15thDay
45%411%21%13%2
1674
16th to endDay
50%313%19%10%2
1664
January1st to 15thNight
46%38%22%17%1
2716
16th to endNight
41%410%24%16%1
2720
February1st to 15thNight
49%48%22%13%1
2304
16th to endNight
47%5%10%20%14%2
2049
March1st to 15thNight
46%49%18%15%6%
2292
16th to endNight
45%5%11%22%13%1
1998
April1st to 15thNight
32%412%26%19%5%
1797
16th to endNight
36%48%25%20%3
1800
May1st to 15thNight
40%6%11%22%17%1
1661
16th to endNight
34%8%13%23%15%3
1606
June1st to 15thNight
27%7%14%25%22%2
1440
16th to endNight
24%8%15%24%19%6%
1440
July1st to 15thNight
31%7%14%24%15%6%
1360
16th to endNight
23%6%17%32%17%1
1454
August1st to 15thNight
24%7%15%26%23%2
1788
16th to endNight
28%6%14%25%19%5%
1910
September1st to 15thNight
32%5%8%28%18%6%
1800
16th to endNight
30%49%24%22%7%
1980
October1st to 15thNight
31%49%21%27%6%
2055
16th to endNight
35%35%22%25%6%
2363
November1st to 15thNight
32%37%23%24%8%
2471
16th to endNight
38%27%24%23%3
2535
December1st to 15thNight
45%5%10%20%15%3
2613
16th to endNight
49%311%20%12%2
2912

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
36%334%15%8%1
135
16th to endDay
14%9%45%21%8%
144
February1st to 15thDay
22%11%37%22%4
135
16th to endDay
30%5%38%19%5%
120
March1st to 15thDay
25%441%22%4
121
16th to endDay
19%10%29%28%12%1
225
April1st to 15thDay
13%11%29%28%14%1
270
16th to endDay
19%5%24%29%15%5%
270
May1st to 15thDay
19%7%23%27%14%7%
288
16th to endDay
14%219%26%22%13%
406
June1st to 15thDay
9%114%26%28%20%
495
16th to endDay
7%14%34%29%13%
495
July1st to 15thDay
11%310%27%31%16%
475
16th to endDay
46%21%38%28%
510
August1st to 15thDay
9%6%19%37%26%
313
16th to endDay
13%422%37%21%
332
September1st to 15thDay
12%16%19%34%26%
315
16th to endDay
13%19%20%32%23%
314
October1st to 15thDay
14%313%33%24%10%
237
16th to endDay
15%425%31%17%6%
144
November1st to 15thDay
20%321%27%14%13%
135
16th to endDay
22%5%26%27%16%1
135
December1st to 15thDay
14%9%34%24%13%3
135
16th to endDay
30%11%39%13%4
144
January1st to 15thNight
23%11%29%29%5%
975
16th to endNight
18%8%37%31%4
1040
February1st to 15thNight
23%9%35%28%3
776
16th to endNight
19%12%37%27%2
683
March1st to 15thNight
21%9%33%31%4
764
16th to endNight
18%7%25%34%12%
593
April1st to 15thNight
13%8%33%31%11%1
539
16th to endNight
17%326%35%16%1
540
May1st to 15thNight
17%422%38%15%2
540
16th to endNight
7%115%40%31%3
563
June1st to 15thNight
8%112%37%36%3
540
16th to endNight
419%42%38%4
540
July1st to 15thNight
8%7%32%43%6%
510
16th to endNight
6%6%25%46%14%
564
August1st to 15thNight
7%6%27%47%10%
539
16th to endNight
9%432%46%6%
573
September1st to 15thNight
10%19%30%38%8%
540
16th to endNight
11%212%30%35%8%
717
October1st to 15thNight
11%218%31%29%6%
720
16th to endNight
19%324%33%16%2
768
November1st to 15thNight
14%6%25%33%18%
760
16th to endNight
19%7%28%29%13%1
780
December1st to 15thNight
24%7%27%29%9%
858
16th to endNight
25%7%31%29%4
1040
Page generated at 2018-03-12 12:28:15. Version ac04

Copyright 2018 A. Danko


AASO/Ridgemont Observatory Clear Sky Chart |Charts Home