Robert A. Schommer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert A. Schommer Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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
31%
23424
19%
80597
9%
23328
43%
23328
20%
50834

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 10thNight
17%
753
24%
4339
7%
737
37%
737
12%
2321
January11th to 20thNight
20%
760
23%
4338
6%
740
37%
740
11%
2505
January21st to endNight
17%
832
14%
4537
6%
814
36%
814
11%
2992
February1st to 10thNight
19%
760
18%
2470
6%
760
35%
760
18%
1595
February11th to 20thNight
11%
743
20%
2225
3%
740
31%
740
16%
1465
February21st to endNight
17%
628
24%
1884
8%
628
37%
628
19%
1215
March1st to 10thNight
20%
760
22%
2280
8%
760
38%
760
21%
1445
March11th to 20thNight
20%
752
22%
2125
8%
752
33%
752
21%
1393
March21st to endNight
19%
792
21%
2016
5%
792
31%
792
24%
1385
April1st to 10thNight
20%
720
19%
1800
4%
720
29%
720
21%
1245
April11th to 20thNight
24%
711
19%
1775
5%
711
31%
711
25%
1217
April21st to endNight
26%
720
20%
1800
6%
720
34%
720
26%
1228
May1st to 10thNight
23%
550
15%
1630
7%
550
30%
550
17%
1149
May11th to 20thNight
29%
375
18%
1437
9%
375
41%
375
16%
936
May21st to endNight
45%
388
14%
1551
13%
388
52%
388
18%
968
June1st to 10thNight
41%
360
17%
1440
14%
360
52%
360
20%
875
June11th to 20thNight
44%
360
15%
1440
14%
360
52%
360
20%
878
June21st to endNight
52%
360
14%
1440
14%
360
59%
360
24%
846
July1st to 10thNight
51%
350
14%
1400
15%
350
57%
350
20%
862
July11th to 20thNight
56%
348
16%
1392
18%
348
60%
348
22%
840
July21st to endNight
53%
394
19%
1486
18%
372
62%
372
26%
845
August1st to 10thNight
57%
503
16%
1567
11%
501
60%
501
27%
985
August11th to 20thNight
53%
710
15%
1774
9%
710
54%
710
27%
1252
August21st to endNight
55%
792
17%
1980
8%
792
57%
792
29%
1346
September1st to 10thNight
45%
720
20%
1800
9%
720
49%
720
29%
1238
September11th to 20thNight
50%
720
27%
1861
17%
720
56%
720
37%
1154
September21st to endNight
43%
720
25%
1980
16%
720
51%
720
27%
1316
October1st to 10thNight
37%
720
16%
2101
10%
720
44%
720
25%
1365
October11th to 20thNight
38%
720
23%
2160
14%
720
50%
720
29%
1304
October21st to endNight
27%
792
22%
2490
12%
792
42%
792
23%
1591
November1st to 10thNight
34%
740
25%
2407
13%
740
51%
740
28%
1387
November11th to 20thNight
27%
760
25%
2470
12%
760
44%
760
21%
1520
November21st to endNight
25%
760
22%
2555
8%
760
43%
760
23%
1517
December1st to 10thNight
19%
760
19%
2660
7%
760
35%
760
16%
1716
December11th to 20thNight
19%
760
20%
3186
6%
759
37%
759
16%
1941
December21st to endNight
20%
831
13%
4801
8%
817
36%
817
10%
2997

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
16%6%35%5%35%5%5%7%40%
78585
Night
17%7%35%5%3445%7%42%
81190
TransparencyDay
42%7%12%22%15%2
78290
Night
41%6%12%23%16%3
81019
SeeingDay
20%15%30%23%10%3
14094
Night
20%12%32%27%9%1
23441

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 10thDay
16%7%2443444447%
2517
11th to 20thDay
15%9%36%6%445%5%7%36%
2520
21st to endDay
23%10%46%424435%34%
3070
February1st to 10thDay
17%6%36%6%34446%41%
1710
11th to 20thDay
15%7%36%434445%42%
1842
21st to endDay
20%8%36%5%34445%38%
1570
March1st to 10thDay
15%7%35%5%3345%7%44%
1897
11th to 20thDay
15%7%35%445%5%6%7%40%
1997
21st to endDay
21%7%34434445%40%
2340
April1st to 10thDay
16%8%37%43445%6%40%
2160
11th to 20thDay
16%6%35%5%3445%9%41%
2134
21st to endDay
19%5%25%5%35%46%6%39%
2160
May1st to 10thDay
21%8%35%5%3445%7%35%
2330
11th to 20thDay
20%6%245%35%46%8%36%
2471
21st to endDay
15%6%25%5%35%46%8%40%
2725
June1st to 10thDay
15%5%25%6%45%5%6%11%37%
2520
11th to 20thDay
14%7%26%7%46%5%6%8%37%
2520
21st to endDay
11%6%25%6%47%5%5%8%40%
2520
July1st to 10thDay
10%5%36%6%5%6%6%7%9%37%
2520
11th to 20thDay
10%4246%36%6%8%10%41%
2520
21st to endDay
11%6%37%7%45%6%6%8%36%
2744
August1st to 10thDay
9%5%36%7%46%6%7%10%38%
2337
11th to 20thDay
12%6%25%5%46%7%7%8%39%
2126
21st to endDay
15%6%25%5%345%6%8%41%
2376
September1st to 10thDay
14%6%25%5%345%5%6%44%
2160
11th to 20thDay
13%5%2443445%8%49%
2098
21st to endDay
17%6%345%3445%7%41%
1980
October1st to 10thDay
20%7%24435%5%46%41%
1855
11th to 20thDay
15%7%24435%46%6%46%
1800
21st to endDay
19%6%2443445%6%43%
1864
November1st to 10thDay
15%5%24423346%52%
1671
11th to 20thDay
17%5%2442346%5%47%
1710
21st to endDay
16%5%245%235%5%8%45%
1623
December1st to 10thDay
18%8%3443346%8%38%
1520
11th to 20thDay
20%6%3442445%6%43%
1906
21st to endDay
18%7%35%6%46%5%6%7%34%
2772
January1st to 10thNight
16%7%2442445%6%46%
4429
11th to 20thNight
17%9%35%434446%42%
4440
21st to endNight
24%10%35%424445%35%
4582
February1st to 10thNight
17%9%35%5%2445%6%41%
2470
11th to 20thNight
17%8%45%43445%5%41%
2223
21st to endNight
20%7%34424446%43%
1884
March1st to 10thNight
17%6%34434446%45%
2270
11th to 20thNight
17%7%25%5%24446%44%
2124
21st to endNight
18%7%25%6%34346%42%
2016
April1st to 10thNight
18%6%36%4445%6%7%38%
1800
11th to 20thNight
17%7%35%44445%7%41%
1775
21st to endNight
20%6%2443445%8%42%
1800
May1st to 10thNight
21%7%37%6%34347%36%
1630
11th to 20thNight
19%6%26%5%3445%6%39%
1436
21st to endNight
16%6%25%5%2445%8%41%
1550
June1st to 10thNight
16%5%25%5%25%5%6%9%41%
1440
11th to 20thNight
13%6%35%5%46%5%6%9%39%
1440
21st to endNight
11%435%5%35%5%6%11%42%
1440
July1st to 10thNight
10%5%26%6%36%5%8%9%40%
1440
11th to 20thNight
11%4246%36%7%7%10%40%
1440
21st to endNight
8%5%35%5%35%6%7%10%44%
1574
August1st to 10thNight
9%6%25%6%35%6%6%9%41%
1577
11th to 20thNight
11%5%36%7%46%5%7%8%38%
1774
21st to endNight
14%6%25%5%4446%9%40%
1980
September1st to 10thNight
15%6%26%5%45%45%6%43%
1800
11th to 20thNight
14%6%23423347%52%
1861
21st to endNight
17%6%25%5%33447%44%
1980
October1st to 10thNight
19%6%35%424445%44%
2101
11th to 20thNight
15%424433446%49%
2160
21st to endNight
19%7%35%42335%5%45%
2490
November1st to 10thNight
12%5%24425%445%53%
2407
11th to 20thNight
18%6%25%424345%48%
2470
21st to endNight
15%6%3443445%7%46%
2555
December1st to 10thNight
20%7%35%5%2445%6%40%
2660
11th to 20thNight
19%6%244245%5%6%43%
3288
21st to endNight
19%9%36%6%34446%37%
4884

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 10thDay
38%6%11%28%13%3
2518
11th to 20thDay
46%6%11%21%14%2
2520
21st to endDay
53%6%9%21%10%2
3070
February1st to 10thDay
45%5%13%23%12%2
1710
11th to 20thDay
45%5%9%23%16%3
1851
21st to endDay
48%5%10%21%13%4
1570
March1st to 10thDay
41%5%12%25%14%3
1900
11th to 20thDay
42%5%12%23%15%4
1997
21st to endDay
46%6%8%19%16%5%
2340
April1st to 10thDay
44%6%9%20%16%5%
2160
11th to 20thDay
39%6%12%22%17%4
2134
21st to endDay
44%7%10%18%17%4
2160
May1st to 10thDay
49%6%9%17%16%3
2330
11th to 20thDay
46%7%11%19%15%2
2475
21st to endDay
41%8%14%20%14%2
2725
June1st to 10thDay
41%9%14%21%14%2
2520
11th to 20thDay
43%9%13%21%12%3
2520
21st to endDay
40%9%13%22%15%1
2520
July1st to 10thDay
40%10%13%19%16%2
2450
11th to 20thDay
35%10%15%23%15%2
2445
21st to endDay
41%9%12%19%16%3
2591
August1st to 10thDay
38%10%15%22%14%1
2323
11th to 20thDay
41%8%14%22%14%1
2126
21st to endDay
39%8%12%20%18%3
2376
September1st to 10thDay
39%8%12%20%19%3
2160
11th to 20thDay
34%6%11%23%23%3
2098
21st to endDay
43%7%9%17%20%3
1980
October1st to 10thDay
42%7%12%20%17%2
1855
11th to 20thDay
37%6%10%24%21%2
1800
21st to endDay
41%5%11%23%18%2
1864
November1st to 10thDay
35%412%25%21%2
1671
11th to 20thDay
38%5%9%23%22%3
1710
21st to endDay
38%413%30%12%3
1623
December1st to 10thDay
45%5%15%21%13%1
1520
11th to 20thDay
42%7%13%25%12%2
1906
21st to endDay
47%7%12%24%10%1
2772
January1st to 10thNight
39%5%11%30%12%4
4429
11th to 20thNight
44%412%25%12%3
4440
21st to endNight
50%6%9%22%12%2
4582
February1st to 10thNight
43%6%13%24%13%2
2470
11th to 20thNight
44%410%19%18%5%
2225
21st to endNight
43%49%23%17%4
1884
March1st to 10thNight
40%412%24%16%5%
2280
11th to 20thNight
41%6%10%22%18%3
2125
21st to endNight
44%5%9%17%19%6%
2016
April1st to 10thNight
43%6%10%20%17%4
1800
11th to 20thNight
43%6%10%19%21%2
1775
21st to endNight
41%6%10%20%18%5%
1800
May1st to 10thNight
49%6%10%16%17%2
1630
11th to 20thNight
44%9%11%16%18%3
1437
21st to endNight
41%9%16%19%13%2
1551
June1st to 10thNight
40%7%12%21%18%2
1440
11th to 20thNight
40%8%16%23%12%1
1440
21st to endNight
35%9%16%24%15%2
1440
July1st to 10thNight
39%10%14%21%14%2
1400
11th to 20thNight
36%10%13%25%14%2
1392
21st to endNight
32%10%17%23%15%3
1486
August1st to 10thNight
36%9%17%21%14%2
1567
11th to 20thNight
40%10%14%21%13%1
1774
21st to endNight
39%8%13%19%19%2
1980
September1st to 10thNight
41%7%11%21%18%2
1800
11th to 20thNight
33%5%11%23%24%4
1861
21st to endNight
40%7%7%22%22%2
1980
October1st to 10thNight
42%6%12%23%15%2
2101
11th to 20thNight
36%5%13%27%17%2
2160
21st to endNight
42%5%10%23%18%1
2490
November1st to 10thNight
34%5%11%23%23%4
2407
11th to 20thNight
40%5%8%24%19%5%
2470
21st to endNight
38%414%27%16%1
2555
December1st to 10thNight
45%5%12%23%13%2
2660
11th to 20thNight
41%7%12%21%17%4
3288
21st to endNight
47%6%12%23%11%
4884

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 10thDay
22%24%33%16%31
180
11th to 20thDay
26%34%26%12%1
180
21st to endDay
22%25%33%14%41
284
February1st to 10thDay
27%24%36%10%2
270
11th to 20thDay
25%24%39%11%2
450
21st to endDay
28%22%29%18%3
382
March1st to 10thDay
23%26%31%17%3
460
11th to 20thDay
22%26%33%14%41
449
21st to endDay
27%22%32%14%5%1
462
April1st to 10thDay
25%23%32%13%7%1
420
11th to 20thDay
20%21%33%14%9%2
412
21st to endDay
28%21%31%15%32
420
May1st to 10thDay
29%18%30%15%5%2
423
11th to 20thDay
21%14%35%22%7%1
447
21st to endDay
21%8%23%28%17%3
485
June1st to 10thDay
16%9%33%28%12%2
450
11th to 20thDay
17%12%30%28%11%2
450
21st to endDay
14%7%34%29%14%2
450
July1st to 10thDay
12%5%25%31%22%6%
445
11th to 20thDay
9%5%24%35%22%6%
444
21st to endDay
12%7%27%34%17%3
488
August1st to 10thDay
10%6%21%39%18%7%
446
11th to 20thDay
13%321%35%23%4
439
21st to endDay
13%6%26%30%16%8%
495
September1st to 10thDay
16%8%27%23%18%8%
450
11th to 20thDay
15%7%27%28%14%9%
450
21st to endDay
21%11%26%26%11%5%
450
October1st to 10thDay
26%6%24%23%15%6%
450
11th to 20thDay
18%13%30%26%12%2
450
21st to endDay
23%15%32%20%8%2
437
November1st to 10thDay
15%16%32%22%13%2
365
11th to 20thDay
23%19%31%20%6%1
370
21st to endDay
18%19%35%18%8%1
283
December1st to 10thDay
23%28%30%11%7%1
180
11th to 20thDay
33%21%29%12%4
180
21st to endDay
25%19%34%15%6%1
198
January1st to 10thNight
20%20%39%18%3
760
11th to 20thNight
25%17%35%20%3
760
21st to endNight
19%20%39%21%1
836
February1st to 10thNight
22%17%36%23%1
760
11th to 20thNight
25%22%38%14%1
743
21st to endNight
26%20%34%18%2
628
March1st to 10thNight
24%18%34%20%4
760
11th to 20thNight
24%20%34%18%4
752
21st to endNight
22%14%41%19%5%
792
April1st to 10thNight
22%20%35%19%5%
720
11th to 20thNight
20%14%38%23%5%
711
21st to endNight
21%13%36%25%41
720
May1st to 10thNight
25%13%33%23%6%
550
11th to 20thNight
22%9%35%28%6%
375
21st to endNight
17%7%24%38%12%2
389
June1st to 10thNight
17%6%29%36%11%1
360
11th to 20thNight
14%6%29%39%13%
360
21st to endNight
8%329%48%12%1
360
July1st to 10thNight
11%425%41%17%2
350
11th to 20thNight
11%321%43%20%1
348
21st to endNight
9%228%44%17%
394
August1st to 10thNight
12%219%45%19%2
503
11th to 20thNight
14%319%39%23%2
710
21st to endNight
16%417%41%20%2
792
September1st to 10thNight
16%326%35%18%2
720
11th to 20thNight
15%5%23%32%20%4
720
21st to endNight
20%6%23%33%15%2
720
October1st to 10thNight
23%8%26%26%14%3
720
11th to 20thNight
17%12%29%33%10%
720
21st to endNight
24%12%32%24%7%1
792
November1st to 10thNight
15%11%35%27%11%1
740
11th to 20thNight
21%16%32%24%7%
760
21st to endNight
17%17%36%23%6%1
760
December1st to 10thNight
27%16%32%18%6%1
760
11th to 20thNight
22%15%38%22%4
760
21st to endNight
24%15%36%23%2
836
Page generated at 2024-03-15 14:01:42. Version ac07

Copyright © 2024 Attilla Danko.


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