Waltman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waltman Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
52%
23770
23%
74543
18%
23713
58%
23713
30%
44547

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
30%
950
23%
2458
8%
946
40%
946
30%
1602
January11th to 20thNight
30%
920
24%
2392
9%
920
40%
920
27%
1627
January21st to endNight
29%
974
25%
2558
9%
974
39%
974
28%
1716
February1st to 10thNight
32%
720
23%
2160
11%
720
42%
720
25%
1409
February11th to 20thNight
32%
703
21%
2099
10%
700
40%
700
26%
1343
February21st to endNight
22%
592
22%
1776
8%
592
33%
592
21%
1214
March1st to 10thNight
36%
648
24%
2088
14%
648
44%
648
28%
1257
March11th to 20thNight
35%
540
19%
1980
14%
540
44%
540
20%
1246
March21st to endNight
36%
594
24%
2084
15%
594
47%
594
27%
1213
April1st to 10thNight
40%
540
25%
1800
17%
540
52%
540
28%
1069
April11th to 20thNight
42%
533
26%
1775
19%
533
54%
533
29%
1044
April21st to endNight
48%
540
28%
1800
23%
540
59%
540
36%
970
May1st to 10thNight
57%
540
23%
1800
20%
540
65%
540
36%
994
May11th to 20thNight
59%
531
20%
1769
20%
531
63%
531
32%
1008
May21st to endNight
68%
583
20%
1837
21%
582
71%
582
36%
1050
June1st to 10thNight
71%
540
20%
1440
18%
540
73%
540
34%
921
June11th to 20thNight
81%
540
24%
1440
23%
540
82%
540
48%
822
June21st to endNight
75%
540
23%
1481
21%
540
76%
540
39%
880
July1st to 10thNight
77%
525
16%
1575
18%
525
77%
525
34%
940
July11th to 20thNight
78%
522
17%
1566
19%
522
78%
522
33%
934
July21st to endNight
81%
591
18%
1724
21%
558
82%
558
37%
993
August1st to 10thNight
86%
537
16%
1778
21%
534
86%
534
40%
935
August11th to 20thNight
76%
534
19%
1776
23%
534
77%
534
30%
1061
August21st to endNight
73%
594
20%
1980
25%
594
73%
594
29%
1191
September1st to 10thNight
74%
540
25%
1800
28%
540
75%
540
32%
1058
September11th to 20thNight
70%
554
26%
1814
27%
554
71%
554
32%
1057
September21st to endNight
71%
720
31%
1980
26%
720
72%
720
40%
1140
October1st to 10thNight
72%
720
32%
2110
27%
720
74%
720
48%
1082
October11th to 20thNight
57%
720
32%
2160
25%
720
64%
720
37%
1241
October21st to endNight
54%
792
31%
2376
26%
792
59%
792
34%
1376
November1st to 10thNight
59%
740
32%
2220
26%
740
66%
740
40%
1219
November11th to 20thNight
47%
760
29%
2450
23%
760
56%
760
35%
1341
November21st to endNight
45%
760
26%
2470
20%
760
54%
760
29%
1445
December1st to 10thNight
38%
760
25%
2470
16%
760
49%
760
25%
1542
December11th to 20thNight
37%
834
23%
3023
14%
834
45%
834
22%
1873
December21st to endNight
30%
1039
13%
4534
10%
1026
38%
1026
16%
2734

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
11%6%35%5%35%5%6%8%43%
74684
Night
12%5%25%43445%8%48%
75071
TransparencyDay
38%7%12%19%18%6%
74413
Night
34%7%12%19%21%8%
74863
SeeingDay
13%7%20%25%24%12%
13927
Night
13%6%23%32%22%4
23779

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 10thDay
18%6%25%423446%45%
1707
11th to 20thDay
19%8%35%4245%45%42%
1647
21st to endDay
18%7%345%23346%45%
1796
February1st to 10thDay
17%8%35%435%45%6%41%
1800
11th to 20thDay
19%9%35%5%33435%40%
1748
21st to endDay
19%8%36%5%4445%5%37%
1480
March1st to 10thDay
16%7%35%5%3445%6%42%
1886
11th to 20thDay
15%7%46%5%36%5%6%7%37%
1980
21st to endDay
11%7%36%7%45%5%6%7%41%
2272
April1st to 10thDay
11%5%35%5%35%6%7%8%43%
2160
11th to 20thDay
16%6%35%5%3445%6%43%
2134
21st to endDay
9%5%25%5%35%5%6%8%48%
2160
May1st to 10thDay
11%435%5%25%6%6%8%44%
2160
11th to 20thDay
10%5%25%6%36%46%9%44%
2124
21st to endDay
7%426%5%45%6%7%10%42%
2427
June1st to 10thDay
9%426%6%5%7%7%7%10%38%
2520
11th to 20thDay
4435%7%47%7%6%9%45%
2520
21st to endDay
5%426%6%5%7%7%8%9%41%
2471
July1st to 10thDay
6%446%8%5%8%8%8%11%33%
2340
11th to 20thDay
9%435%5%6%8%7%9%10%34%
2340
21st to endDay
7%5%36%6%48%7%9%12%34%
2488
August1st to 10thDay
5%425%6%5%6%7%8%12%40%
2148
11th to 20thDay
8%5%36%6%5%7%7%8%10%36%
2125
21st to endDay
13%5%145%36%6%7%9%41%
2376
September1st to 10thDay
7%5%26%7%46%6%6%8%43%
2160
11th to 20thDay
11%6%35%5%46%45%7%45%
2125
21st to endDay
11%5%14423447%55%
1980
October1st to 10thDay
6%4245%25%45%7%58%
1846
11th to 20thDay
8%5%245%3345%7%54%
1800
21st to endDay
13%5%24423335%55%
1980
November1st to 10thDay
11%433324346%57%
1858
11th to 20thDay
13%5%24424346%53%
1728
21st to endDay
15%6%35%5%3445%6%46%
1710
December1st to 10thDay
17%7%36%43445%7%40%
1710
11th to 20thDay
14%11%46%424446%41%
2029
21st to endDay
14%6%35%5%2345%7%44%
2949
January1st to 10thNight
18%7%24423335%47%
2458
11th to 20thNight
17%8%36%423445%43%
2392
21st to endNight
17%7%35%5%23445%44%
2558
February1st to 10thNight
17%7%36%43445%6%42%
2160
11th to 20thNight
19%7%34333336%46%
2098
21st to endNight
23%8%345%23345%40%
1776
March1st to 10thNight
13%7%25%5%33447%47%
2088
11th to 20thNight
14%6%36%5%345%6%8%39%
1980
21st to endNight
13%5%245%3446%7%47%
2084
April1st to 10thNight
11%5%35%4345%5%7%49%
1800
11th to 20thNight
14%5%25%43445%7%48%
1775
21st to endNight
7%3245%3446%8%53%
1800
May1st to 10thNight
8%324425%45%9%53%
1800
11th to 20thNight
8%425%5%345%7%11%46%
1769
21st to endNight
5%415%5%35%5%7%11%49%
1837
June1st to 10thNight
6%5%25%5%46%47%11%45%
1440
11th to 20thNight
3323435%6%8%11%54%
1440
21st to endNight
4335%5%345%7%13%49%
1481
July1st to 10thNight
4435%436%5%7%13%45%
1620
11th to 20thNight
6%425%5%36%6%8%10%47%
1620
21st to endNight
4324436%5%8%12%48%
1826
August1st to 10thNight
2213436%6%7%15%51%
1790
11th to 20thNight
6%3146%35%6%9%12%44%
1776
21st to endNight
9%4246%345%7%10%46%
1980
September1st to 10thNight
7%5%25%5%35%6%6%9%48%
1800
11th to 20thNight
8%5%34435%5%6%8%48%
1814
21st to endNight
9%42443445%6%56%
1980
October1st to 10thNight
6%31332445%6%64%
2110
11th to 20thNight
12%42432336%6%55%
2160
21st to endNight
14%5%2442333356%
2376
November1st to 10thNight
12%414323335%60%
2220
11th to 20thNight
13%5%1332345%6%55%
2450
21st to endNight
13%5%25%5%34447%49%
2470
December1st to 10thNight
16%6%345%2445%6%44%
2470
11th to 20thNight
15%7%26%5%34445%46%
3162
21st to endNight
16%10%35%433446%41%
4711

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
41%47%19%24%5%
1708
11th to 20thDay
45%47%16%21%7%
1647
21st to endDay
42%35%18%25%7%
1796
February1st to 10thDay
44%5%8%17%16%9%
1800
11th to 20thDay
47%46%17%18%7%
1758
21st to endDay
49%5%6%13%18%9%
1480
March1st to 10thDay
43%6%9%13%20%9%
1886
11th to 20thDay
44%8%10%15%17%6%
1980
21st to endDay
41%6%9%20%20%4
2272
April1st to 10thDay
36%7%10%22%18%6%
2160
11th to 20thDay
41%5%8%16%24%6%
2134
21st to endDay
33%7%10%24%24%2
2160
May1st to 10thDay
36%8%11%19%20%5%
2160
11th to 20thDay
36%8%15%25%15%1
2128
21st to endDay
34%10%18%23%14%1
2427
June1st to 10thDay
39%10%15%23%12%2
2520
11th to 20thDay
34%9%16%23%15%3
2520
21st to endDay
35%10%16%22%14%2
2471
July1st to 10thDay
40%13%19%19%7%2
2276
11th to 20thDay
39%13%22%18%6%2
2271
21st to endDay
38%13%20%20%8%1
2350
August1st to 10thDay
33%12%21%27%7%
2136
11th to 20thDay
40%12%16%19%10%3
2125
21st to endDay
37%10%18%19%11%4
2376
September1st to 10thDay
37%9%14%17%17%6%
2160
11th to 20thDay
39%7%10%16%21%7%
2125
21st to endDay
29%6%12%22%20%11%
1980
October1st to 10thDay
26%6%9%21%26%13%
1846
11th to 20thDay
29%5%8%16%29%12%
1800
21st to endDay
33%45%17%30%12%
1980
November1st to 10thDay
30%48%17%31%11%
1858
11th to 20thDay
34%46%15%27%13%
1728
21st to endDay
39%47%18%22%10%
1710
December1st to 10thDay
43%5%10%16%16%8%
1710
11th to 20thDay
44%5%6%15%24%6%
2026
21st to endDay
37%6%9%19%26%3
2949
January1st to 10thNight
40%48%16%26%7%
2458
11th to 20thNight
43%5%6%18%20%7%
2392
21st to endNight
43%45%15%25%7%
2558
February1st to 10thNight
43%47%16%20%9%
2160
11th to 20thNight
41%47%18%20%10%
2099
21st to endNight
48%5%6%12%18%11%
1776
March1st to 10thNight
37%5%9%16%21%12%
2088
11th to 20thNight
42%7%10%17%16%7%
1980
21st to endNight
35%6%10%19%23%6%
2084
April1st to 10thNight
35%7%11%19%20%9%
1800
11th to 20thNight
35%6%9%19%22%9%
1775
21st to endNight
29%5%11%24%27%5%
1800
May1st to 10thNight
28%7%12%25%22%6%
1800
11th to 20thNight
31%7%17%25%17%2
1770
21st to endNight
25%11%18%27%17%2
1838
June1st to 10thNight
32%10%15%25%16%2
1440
11th to 20thNight
21%8%21%28%17%4
1440
21st to endNight
27%9%19%23%18%3
1481
July1st to 10thNight
28%11%24%25%9%3
1575
11th to 20thNight
28%12%26%24%8%2
1566
21st to endNight
24%12%26%26%11%1
1724
August1st to 10thNight
20%12%29%28%11%
1778
11th to 20thNight
28%13%22%21%13%3
1776
21st to endNight
31%11%20%19%14%5%
1980
September1st to 10thNight
30%10%15%21%18%6%
1800
11th to 20thNight
31%8%15%15%21%9%
1814
21st to endNight
27%7%10%25%20%11%
1980
October1st to 10thNight
21%5%10%23%25%16%
2110
11th to 20thNight
31%5%7%15%28%15%
2160
21st to endNight
33%5%6%15%26%16%
2376
November1st to 10thNight
29%47%18%30%13%
2220
11th to 20thNight
30%48%17%26%15%
2450
21st to endNight
36%48%20%20%12%
2470
December1st to 10thNight
40%6%10%18%19%7%
2470
11th to 20thNight
41%5%7%12%27%8%
3164
21st to endNight
43%5%7%17%24%4
4711

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
23%17%39%15%5%1
270
11th to 20thDay
27%16%31%18%8%1
249
21st to endDay
25%20%32%18%4
264
February1st to 10thDay
21%18%38%17%5%2
240
11th to 20thDay
33%12%38%15%3
240
21st to endDay
28%18%36%15%2
198
March1st to 10thDay
23%15%37%20%5%
240
11th to 20thDay
23%17%35%21%4
240
21st to endDay
17%17%31%25%10%
358
April1st to 10thDay
14%13%34%26%12%1
420
11th to 20thDay
22%11%28%25%12%2
412
21st to endDay
14%9%26%33%17%1
420
May1st to 10thDay
13%8%27%32%16%4
423
11th to 20thDay
12%322%29%24%10%
447
21st to endDay
8%316%31%27%14%
491
June1st to 10thDay
10%410%31%30%15%
630
11th to 20thDay
5%211%31%36%14%
630
21st to endDay
7%110%29%34%18%
630
July1st to 10thDay
5%29%26%37%21%
621
11th to 20thDay
7%1419%40%28%
618
21st to endDay
7%16%21%40%24%
626
August1st to 10thDay
6%16%18%37%31%
446
11th to 20thDay
7%1419%43%26%
439
21st to endDay
15%17%16%33%29%
495
September1st to 10thDay
6%27%27%38%20%
450
11th to 20thDay
11%210%20%35%23%
450
21st to endDay
14%29%29%34%12%
450
October1st to 10thDay
8%221%35%24%10%
316
11th to 20thDay
9%6%24%34%22%5%
270
21st to endDay
20%10%24%25%14%6%
297
November1st to 10thDay
16%6%23%34%17%4
270
11th to 20thDay
14%13%36%24%11%2
270
21st to endDay
16%14%35%20%11%3
270
December1st to 10thDay
21%16%34%20%7%1
270
11th to 20thDay
20%12%37%21%9%1
270
21st to endDay
20%15%38%20%6%1
297
January1st to 10thNight
21%11%33%29%5%
950
11th to 20thNight
19%13%32%29%7%
920
21st to endNight
20%12%36%29%3
974
February1st to 10thNight
19%11%34%30%5%
720
11th to 20thNight
22%13%31%29%5%
703
21st to endNight
25%13%36%24%1
592
March1st to 10thNight
17%12%32%33%6%
648
11th to 20thNight
16%9%36%32%7%1
540
21st to endNight
16%8%36%30%9%
594
April1st to 10thNight
13%8%36%32%11%1
540
11th to 20thNight
14%8%32%32%13%1
533
21st to endNight
7%437%36%15%
540
May1st to 10thNight
9%5%26%43%16%2
540
11th to 20thNight
9%221%41%23%3
531
21st to endNight
6%216%36%34%7%
584
June1st to 10thNight
7%110%38%38%6%
540
11th to 20thNight
326%31%49%9%
540
21st to endNight
5%18%29%45%12%
540
July1st to 10thNight
5%16%29%50%10%
525
11th to 20thNight
5%1325%48%17%
522
21st to endNight
41428%51%13%
591
August1st to 10thNight
3425%50%18%
537
11th to 20thNight
6%15%23%52%14%
534
21st to endNight
10%26%24%42%16%
594
September1st to 10thNight
8%26%32%45%7%
540
11th to 20thNight
9%29%29%44%7%
554
21st to endNight
11%29%36%38%5%
720
October1st to 10thNight
8%214%37%33%6%
720
11th to 20thNight
13%5%21%36%23%2
720
21st to endNight
16%5%21%35%20%3
792
November1st to 10thNight
13%420%39%20%3
740
11th to 20thNight
14%7%28%37%14%1
760
21st to endNight
15%6%29%34%13%2
760
December1st to 10thNight
19%8%32%32%10%
760
11th to 20thNight
20%7%31%33%9%
836
21st to endNight
23%11%30%30%6%
1045
Page generated at 2024-01-11 12:32:04. Version ac07

Copyright 2024 Attilla Danko


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