West Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Valley Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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
33%
24071
17%
96871
10%
23824
44%
23824
17%
61124

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
21%
4344
7%
737
35%
737
11%
2451
January11th to 20thNight
22%
760
20%
4278
6%
740
38%
740
9%
2597
January21st to endNight
20%
830
13%
4483
7%
814
37%
814
11%
2960
February1st to 10thNight
20%
760
19%
2470
8%
760
34%
760
17%
1606
February11th to 20thNight
12%
743
18%
2299
3%
740
32%
740
15%
1519
February21st to endNight
16%
628
22%
1884
6%
628
36%
628
18%
1241
March1st to 10thNight
22%
757
18%
3639
9%
744
38%
744
12%
2413
March11th to 20thNight
21%
756
22%
3459
8%
740
35%
740
16%
1802
March21st to endNight
21%
832
13%
3502
6%
814
33%
814
15%
2119
April1st to 10thNight
21%
760
17%
1900
3%
760
30%
760
21%
1320
April11th to 20thNight
26%
751
17%
1875
5%
751
32%
751
25%
1298
April21st to endNight
28%
760
17%
1900
5%
760
34%
760
27%
1275
May1st to 10thNight
30%
573
15%
2756
8%
569
35%
569
12%
1933
May11th to 20thNight
32%
369
10%
2491
11%
364
43%
364
9%
1751
May21st to endNight
47%
405
11%
2722
14%
399
53%
399
12%
1529
June1st to 10thNight
44%
380
19%
1520
18%
380
54%
380
22%
915
June11th to 20thNight
50%
380
14%
1520
14%
380
57%
380
22%
905
June21st to endNight
53%
380
15%
1520
16%
380
59%
380
24%
875
July1st to 10thNight
53%
364
14%
2368
17%
360
57%
360
13%
1407
July11th to 20thNight
58%
360
12%
2240
21%
358
62%
358
14%
1323
July21st to endNight
55%
458
11%
2512
15%
429
60%
429
15%
1580
August1st to 10thNight
60%
555
11%
2722
12%
545
63%
545
15%
1852
August11th to 20thNight
53%
675
15%
2721
10%
668
54%
668
17%
1784
August21st to endNight
53%
817
14%
3098
8%
814
56%
814
23%
1842
September1st to 10thNight
47%
760
23%
1900
10%
760
53%
760
33%
1260
September11th to 20thNight
55%
760
28%
1909
18%
760
59%
760
36%
1201
September21st to endNight
44%
760
23%
2121
16%
760
52%
760
26%
1420
October1st to 10thNight
40%
760
12%
3023
13%
740
47%
740
16%
2152
October11th to 20thNight
40%
760
18%
2525
14%
740
51%
740
24%
1629
October21st to endNight
33%
836
20%
2917
14%
814
46%
814
22%
1759
November1st to 10thNight
35%
760
24%
2470
13%
760
51%
760
28%
1431
November11th to 20thNight
31%
760
24%
2470
13%
760
45%
760
21%
1528
November21st to endNight
28%
760
20%
2643
9%
760
44%
760
21%
1601
December1st to 10thNight
21%
760
16%
2660
6%
760
33%
760
14%
1786
December11th to 20thNight
23%
760
17%
3210
7%
759
37%
759
14%
2014
December21st to endNight
24%
829
11%
4800
7%
817
37%
817
10%
3046

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%7%26%445%46%8%38%
101368
Night
17%7%26%44435%7%41%
97675
TransparencyDay
42%7%13%22%14%2
104928
Night
41%6%12%23%15%2
102203
SeeingDay
21%16%27%21%11%3
14921
Night
20%12%29%28%10%1
24185

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
14%7%36%34445%6%43%
2517
11th to 20thDay
14%10%410%6%5%445%7%30%
2593
21st to endDay
20%10%38%5%5%4445%32%
3124
February1st to 10thDay
16%7%26%5%45%46%7%36%
1710
11th to 20thDay
14%8%36%45%446%8%38%
1768
21st to endDay
19%10%26%5%45%45%6%35%
1570
March1st to 10thDay
25%7%26%444446%34%
3169
11th to 20thDay
10%5%26%6%5%6%36%7%44%
3480
21st to endDay
21%8%25%333346%42%
4006
April1st to 10thDay
16%8%36%5%45%46%8%36%
2280
11th to 20thDay
16%7%26%45%435%7%40%
2254
21st to endDay
17%5%26%5%445%6%7%39%
2280
May1st to 10thDay
28%7%26%44445%7%30%
4127
11th to 20thDay
24%8%38%5%45%36%7%27%
4398
21st to endDay
13%5%2444446%9%44%
4837
June1st to 10thDay
13%6%26%5%5%5%5%7%9%38%
2660
11th to 20thDay
14%6%25%5%5%5%5%8%9%37%
2660
21st to endDay
12%5%25%45%5%5%7%9%40%
2660
July1st to 10thDay
7%5%27%6%6%7%6%8%11%36%
4440
11th to 20thDay
9%6%26%45%6%5%7%10%41%
4440
21st to endDay
12%9%38%5%5%6%46%8%35%
4722
August1st to 10thDay
20%6%27%45%5%47%8%32%
4104
11th to 20thDay
14%5%26%46%5%5%5%9%40%
3795
21st to endDay
15%6%2434446%8%46%
4180
September1st to 10thDay
16%5%26%44435%6%44%
2280
11th to 20thDay
14%42433435%8%49%
2271
21st to endDay
21%7%36%44435%5%39%
2055
October1st to 10thDay
18%7%2444445%7%42%
1900
11th to 20thDay
17%5%15%35%445%8%44%
1900
21st to endDay
19%6%25%33346%7%41%
2037
November1st to 10thDay
14%6%34333247%52%
1708
11th to 20thDay
17%6%1434346%6%45%
1710
21st to endDay
17%5%3444447%7%41%
1535
December1st to 10thDay
18%9%36%5%5%346%7%33%
1520
11th to 20thDay
20%7%25%44446%6%38%
1906
21st to endDay
19%8%38%5%6%5%47%6%29%
2772
January1st to 10thNight
16%7%26%44435%8%42%
4429
11th to 20thNight
16%9%27%445%45%6%38%
4362
21st to endNight
24%9%35%434345%35%
4532
February1st to 10thNight
16%9%35%434447%40%
2470
11th to 20thNight
16%7%36%5%4445%6%39%
2297
21st to endNight
19%8%25%444346%40%
1884
March1st to 10thNight
22%10%36%434345%36%
3669
11th to 20thNight
11%6%25%44445%6%48%
3479
21st to endNight
16%9%36%433245%45%
3626
April1st to 10thNight
16%8%35%5%45%45%7%38%
1900
11th to 20thNight
15%6%27%5%4445%7%41%
1875
21st to endNight
20%425%43435%6%44%
1900
May1st to 10thNight
26%9%26%44445%6%31%
2827
11th to 20thNight
24%10%37%5%4435%6%29%
2495
21st to endNight
13%7%26%445%36%9%41%
2738
June1st to 10thNight
16%6%26%5%3336%8%42%
1520
11th to 20thNight
13%7%15%445%5%7%8%42%
1520
21st to endNight
11%5%16%45%5%37%9%44%
1520
July1st to 10thNight
9%5%28%6%6%6%5%7%9%39%
2520
11th to 20thNight
10%5%27%5%5%6%5%8%10%39%
2520
21st to endNight
15%7%26%44447%8%38%
2826
August1st to 10thNight
20%6%28%5%45%46%8%33%
2825
11th to 20thNight
16%6%26%5%4445%6%41%
3000
21st to endNight
13%5%24345%45%8%48%
3476
September1st to 10thNight
14%6%26%443346%47%
1900
11th to 20thNight
13%5%25%44325%6%52%
1909
21st to endNight
20%6%26%434347%42%
2121
October1st to 10thNight
21%6%25%34335%6%43%
2280
11th to 20thNight
17%5%2434335%6%48%
2280
21st to endNight
20%6%1433335%5%47%
2560
November1st to 10thNight
12%5%25%44335%5%51%
2470
11th to 20thNight
17%7%25%433247%45%
2470
21st to endNight
15%5%26%44445%8%43%
2643
December1st to 10thNight
19%7%37%4445%5%6%36%
2660
11th to 20thNight
19%6%26%44446%6%38%
3288
21st to endNight
19%8%37%44435%6%36%
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
39%7%16%25%10%2
2518
11th to 20thDay
51%8%13%16%11%1
2593
21st to endDay
52%8%12%19%8%1
3124
February1st to 10thDay
45%8%14%20%12%1
1710
11th to 20thDay
43%7%12%23%13%2
1777
21st to endDay
49%6%12%21%10%3
1570
March1st to 10thDay
47%8%11%25%8%2
3172
11th to 20thDay
34%10%14%27%13%3
3480
21st to endDay
44%5%11%17%20%3
4006
April1st to 10thDay
44%7%10%21%13%5%
2280
11th to 20thDay
41%7%11%22%14%4
2254
21st to endDay
41%7%12%20%15%5%
2280
May1st to 10thDay
52%7%12%18%9%2
4139
11th to 20thDay
55%9%12%15%8%1
4402
21st to endDay
33%9%14%26%16%2
4837
June1st to 10thDay
40%9%14%22%13%2
2660
11th to 20thDay
40%9%16%22%10%2
2660
21st to endDay
37%10%14%24%14%1
2660
July1st to 10thDay
39%9%15%22%13%1
4370
11th to 20thDay
37%7%17%25%13%1
4365
21st to endDay
47%7%11%18%16%1
4571
August1st to 10thDay
49%7%14%20%10%
4091
11th to 20thDay
39%6%13%29%12%1
3833
21st to endDay
35%6%12%30%16%2
4180
September1st to 10thDay
40%7%11%20%19%3
2280
11th to 20thDay
33%6%11%24%24%3
2271
21st to endDay
47%5%10%17%20%2
2055
October1st to 10thDay
39%49%20%23%5%
3160
11th to 20thDay
29%411%28%23%5%
3140
21st to endDay
27%415%25%26%3
3339
November1st to 10thDay
34%414%25%19%3
1708
11th to 20thDay
39%6%11%24%18%2
1710
21st to endDay
39%8%13%29%9%2
1535
December1st to 10thDay
49%6%16%18%10%1
1520
11th to 20thDay
45%6%17%23%8%1
1906
21st to endDay
50%9%14%19%7%
2772
January1st to 10thNight
40%6%15%26%11%2
4429
11th to 20thNight
44%7%14%22%10%2
4362
21st to endNight
49%6%11%23%9%1
4532
February1st to 10thNight
44%5%14%25%10%2
2470
11th to 20thNight
45%5%11%19%16%3
2299
21st to endNight
44%5%10%21%16%4
1884
March1st to 10thNight
48%7%9%23%11%2
3679
11th to 20thNight
33%8%14%28%15%2
3480
21st to endNight
43%48%17%22%6%
3626
April1st to 10thNight
43%7%12%22%14%3
1900
11th to 20thNight
41%8%10%20%19%2
1875
21st to endNight
39%7%12%21%17%4
1900
May1st to 10thNight
52%7%10%20%9%2
2834
11th to 20thNight
54%9%13%13%10%1
2496
21st to endNight
37%11%13%22%13%3
2739
June1st to 10thNight
39%7%12%23%18%2
1520
11th to 20thNight
36%9%15%24%14%1
1520
21st to endNight
35%9%15%28%13%1
1520
July1st to 10thNight
41%8%16%17%15%3
2480
11th to 20thNight
39%6%16%24%13%1
2472
21st to endNight
42%7%15%18%17%1
2736
August1st to 10thNight
49%7%17%18%9%1
2814
11th to 20thNight
43%6%13%23%15%1
3028
21st to endNight
34%6%10%29%18%1
3476
September1st to 10thNight
37%6%11%22%20%3
1900
11th to 20thNight
33%6%10%23%26%3
1909
21st to endNight
42%6%9%21%21%2
2121
October1st to 10thNight
43%410%21%21%2
3800
11th to 20thNight
28%49%30%25%4
3779
21st to endNight
28%313%31%22%3
4208
November1st to 10thNight
34%5%14%24%19%4
2470
11th to 20thNight
40%410%24%17%4
2470
21st to endNight
39%6%13%28%13%2
2643
December1st to 10thNight
47%7%13%20%12%1
2660
11th to 20thNight
44%6%15%21%13%2
3288
21st to endNight
47%7%15%22%9%
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
26%31%24%15%31
180
11th to 20thDay
36%25%27%10%2
202
21st to endDay
23%28%31%13%31
297
February1st to 10thDay
24%31%31%11%21
270
11th to 20thDay
28%26%35%9%1
376
21st to endDay
32%21%28%16%3
382
March1st to 10thDay
27%22%29%18%3
460
11th to 20thDay
25%28%30%12%32
460
21st to endDay
29%23%29%12%6%1
506
April1st to 10thDay
26%25%28%15%5%1
460
11th to 20thDay
22%26%27%15%7%2
452
21st to endDay
27%19%31%15%43
460
May1st to 10thDay
29%20%25%15%6%3
463
11th to 20thDay
23%17%30%21%8%2
487
21st to endDay
19%9%27%24%16%4
529
June1st to 10thDay
16%16%29%22%15%3
490
11th to 20thDay
19%13%27%23%15%3
490
21st to endDay
14%11%33%24%14%4
490
July1st to 10thDay
11%6%24%29%22%7%
485
11th to 20thDay
8%6%25%33%24%4
484
21st to endDay
13%7%29%32%14%5%
532
August1st to 10thDay
12%6%22%33%20%7%
486
11th to 20thDay
14%6%22%32%21%6%
479
21st to endDay
15%6%25%26%17%10%
539
September1st to 10thDay
19%9%20%24%20%7%
490
11th to 20thDay
14%5%25%26%19%11%
490
21st to endDay
26%14%21%21%14%5%
490
October1st to 10thDay
25%8%25%22%14%6%
490
11th to 20thDay
19%16%28%24%12%2
490
21st to endDay
21%17%31%19%11%1
511
November1st to 10thDay
17%16%27%25%12%3
378
11th to 20thDay
22%21%29%21%5%1
370
21st to endDay
24%21%35%13%6%1
195
December1st to 10thDay
29%26%28%11%6%
180
11th to 20thDay
33%27%25%12%4
180
21st to endDay
27%23%30%14%42
198
January1st to 10thNight
20%20%37%20%3
760
11th to 20thNight
25%18%31%23%3
760
21st to endNight
18%19%37%23%2
836
February1st to 10thNight
23%17%36%23%2
760
11th to 20thNight
24%22%37%15%1
743
21st to endNight
25%19%36%18%2
628
March1st to 10thNight
22%21%31%23%4
760
11th to 20thNight
24%19%33%19%5%1
760
21st to endNight
22%16%37%20%4
836
April1st to 10thNight
21%21%34%20%4
760
11th to 20thNight
19%15%36%24%7%
751
21st to endNight
23%13%33%24%7%
760
May1st to 10thNight
25%11%30%26%8%1
577
11th to 20thNight
19%8%34%30%9%
374
21st to endNight
17%7%21%42%12%1
411
June1st to 10thNight
17%5%26%35%17%
380
11th to 20thNight
14%7%24%42%12%1
380
21st to endNight
10%428%45%13%
380
July1st to 10thNight
11%420%41%22%2
370
11th to 20thNight
9%421%40%25%2
368
21st to endNight
12%419%42%21%1
467
August1st to 10thNight
13%315%43%25%2
567
11th to 20thNight
16%415%36%27%2
689
21st to endNight
16%418%36%25%2
836
September1st to 10thNight
17%424%34%19%2
760
11th to 20thNight
15%5%18%35%23%5%
760
21st to endNight
23%5%21%30%19%1
760
October1st to 10thNight
22%8%24%26%18%3
760
11th to 20thNight
18%11%28%32%11%1
760
21st to endNight
23%11%28%28%9%
836
November1st to 10thNight
15%11%34%28%12%1
760
11th to 20thNight
20%17%27%28%8%1
760
21st to endNight
18%17%33%26%7%
760
December1st to 10thNight
24%17%32%22%5%1
760
11th to 20thNight
21%16%33%25%5%
760
21st to endNight
22%16%33%27%2
836
Page generated at 2024-11-03 02:11:18. Version ac07

Copyright © 2024 Attilla Danko.


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