Menlo Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Menlo Park clear sky chart from 2005-11-06 to 2024-03-06.

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
64%
23918
24%
80469
23%
23833
68%
23833
33%
46163

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
52%
748
18%
4169
17%
736
56%
736
15%
2432
January11th to 20thNight
55%
750
13%
4099
17%
740
61%
740
13%
2895
January21st to endNight
55%
830
14%
4448
23%
814
58%
814
12%
3199
February1st to 10thNight
56%
760
24%
2470
23%
760
61%
760
29%
1482
February11th to 20thNight
52%
740
22%
2315
20%
740
58%
740
27%
1430
February21st to endNight
56%
628
22%
1884
20%
628
61%
628
32%
1136
March1st to 10thNight
47%
742
16%
2070
13%
742
51%
742
24%
1423
March11th to 20thNight
52%
720
22%
1980
20%
720
55%
720
28%
1314
March21st to endNight
52%
792
18%
2149
12%
792
57%
792
30%
1379
April1st to 10thNight
53%
720
20%
1800
12%
720
56%
720
33%
1181
April11th to 20thNight
52%
711
25%
1779
12%
711
56%
711
36%
1106
April21st to endNight
61%
720
27%
1800
13%
720
65%
720
48%
1017
May1st to 10thNight
64%
656
25%
1736
16%
656
66%
656
44%
993
May11th to 20thNight
68%
493
23%
1556
19%
493
71%
493
39%
815
May21st to endNight
65%
388
22%
1552
21%
388
71%
388
31%
776
June1st to 10thNight
70%
360
23%
1440
23%
360
78%
360
37%
678
June11th to 20thNight
80%
360
34%
1440
38%
360
85%
360
54%
538
June21st to endNight
82%
360
34%
1440
43%
360
85%
360
54%
546
July1st to 10thNight
85%
350
32%
1400
40%
350
87%
350
62%
492
July11th to 20thNight
86%
522
32%
1566
31%
522
87%
522
61%
689
July21st to endNight
83%
591
32%
1674
30%
558
84%
558
60%
734
August1st to 10thNight
78%
537
29%
1602
25%
534
79%
534
45%
788
August11th to 20thNight
82%
649
35%
1717
25%
649
82%
649
64%
817
August21st to endNight
81%
792
34%
1980
23%
792
81%
792
63%
1001
September1st to 10thNight
82%
720
39%
1800
29%
720
82%
720
66%
897
September11th to 20thNight
73%
720
35%
1800
27%
720
75%
720
54%
982
September21st to endNight
80%
720
37%
2048
35%
720
83%
720
61%
949
October1st to 10thNight
76%
720
28%
2160
29%
720
80%
720
52%
1047
October11th to 20thNight
70%
720
32%
2160
33%
720
74%
720
43%
1144
October21st to endNight
73%
792
34%
2376
36%
792
76%
792
45%
1222
November1st to 10thNight
67%
740
28%
2241
29%
740
70%
740
39%
1243
November11th to 20thNight
66%
760
26%
2470
27%
760
68%
760
33%
1396
November21st to endNight
66%
760
27%
2611
28%
760
71%
760
37%
1373
December1st to 10thNight
56%
760
22%
2660
21%
760
62%
760
26%
1607
December11th to 20thNight
51%
760
17%
3243
20%
759
56%
759
16%
2284
December21st to endNight
45%
827
12%
4834
16%
817
52%
817
12%
3158

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%5%2443345%7%56%
78702
Night
7%6%35%5%3445%7%52%
80860
TransparencyDay
27%6%11%20%22%14%
78423
Night
31%7%12%19%19%13%
80661
SeeingDay
7%9%24%32%21%7%
14476
Night
8%5%15%34%31%7%
23960

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 10thDay
12%8%36%6%345%6%8%37%
2733
11th to 20thDay
12%8%49%8%5%5%5%46%34%
2860
21st to endDay
16%11%46%7%45%5%5%7%30%
3146
February1st to 10thDay
12%6%35%5%345%6%7%45%
1710
11th to 20thDay
11%7%36%5%3446%7%44%
1754
21st to endDay
10%5%35%5%4445%7%47%
1570
March1st to 10thDay
11%7%36%6%45%6%6%9%37%
2004
11th to 20thDay
10%7%36%6%45%6%7%8%39%
1980
21st to endDay
9%6%25%5%35%5%5%8%46%
2205
April1st to 10thDay
10%7%345%245%6%7%46%
2160
11th to 20thDay
9%5%24423447%57%
2129
21st to endDay
5%433324449%60%
2160
May1st to 10thDay
342442336%8%62%
2221
11th to 20thDay
4414423348%64%
2335
21st to endDay
5%5%2442335%8%59%
2723
June1st to 10thDay
5%42332345%8%62%
2520
11th to 20thDay
1212212347%76%
2520
21st to endDay
2212322235%75%
2520
July1st to 10thDay
1213212237%75%
2516
11th to 20thDay
1212323347%72%
2340
21st to endDay
1212212337%76%
2546
August1st to 10thDay
2313423346%69%
2328
11th to 20thDay
212322346%75%
2183
21st to endDay
1313323337%72%
2376
September1st to 10thDay
1213222225%77%
2160
11th to 20thDay
2423423447%65%
2160
21st to endDay
2213222245%76%
1908
October1st to 10thDay
4313422337%68%
1800
11th to 20thDay
5%32342335%7%63%
1800
21st to endDay
5%5%2442335%7%60%
1980
November1st to 10thDay
6%4345%3346%8%54%
1836
11th to 20thDay
7%6%35%445%5%47%50%
1710
21st to endDay
8%5%35%4235%5%8%53%
1567
December1st to 10thDay
8%5%38%7%445%6%7%44%
1520
11th to 20thDay
14%10%49%7%445%7%6%31%
1928
21st to endDay
12%10%47%6%36%5%6%8%33%
2794
January1st to 10thNight
11%8%36%5%35%5%6%8%40%
4216
11th to 20thNight
14%10%5%9%7%45%5%5%6%30%
4110
21st to endNight
16%12%48%7%35%5%46%30%
4521
February1st to 10thNight
11%6%35%5%34446%49%
2470
11th to 20thNight
8%6%35%6%35%6%5%8%44%
2313
21st to endNight
9%5%25%5%3445%7%50%
1884
March1st to 10thNight
13%7%36%6%35%5%6%6%40%
2070
11th to 20thNight
11%7%36%5%4445%8%43%
1980
21st to endNight
10%7%35%434446%51%
2149
April1st to 10thNight
8%7%25%6%3438%9%46%
1800
11th to 20thNight
7%5%25%5%23447%56%
1779
21st to endNight
431332345%9%62%
1800
May1st to 10thNight
35%245%2435%8%60%
1736
11th to 20thNight
35%2442445%10%57%
1555
21st to endNight
35%25%5%3345%7%59%
1552
June1st to 10thNight
442443335%8%61%
1440
11th to 20thNight
1112212347%76%
1440
21st to endNight
1323322335%74%
1440
July1st to 10thNight
41221135%7%73%
1440
11th to 20thNight
111242335%8%71%
1620
21st to endNight
2234246%7%10%60%
1773
August1st to 10thNight
24244244410%59%
1611
11th to 20thNight
21442345%10%64%
1717
21st to endNight
121442335%10%65%
1980
September1st to 10thNight
2213412347%72%
1800
11th to 20thNight
35%2442345%7%62%
1800
21st to endNight
1222322345%74%
2048
October1st to 10thNight
4323423346%66%
2160
11th to 20thNight
5%425%423346%61%
2160
21st to endNight
45%34423446%62%
2376
November1st to 10thNight
6%6%2442445%7%56%
2241
11th to 20thNight
7%6%35%5%3345%8%51%
2470
21st to endNight
7%42343445%7%57%
2611
December1st to 10thNight
9%7%36%5%345%5%7%46%
2660
11th to 20thNight
18%11%47%5%35%45%8%31%
3276
21st to endNight
12%8%37%7%46%6%7%7%34%
4862

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%10%13%25%8%3
2733
11th to 20thDay
49%9%11%12%10%7%
2860
21st to endDay
51%9%9%14%13%5%
3146
February1st to 10thDay
38%6%9%19%18%9%
1710
11th to 20thDay
39%6%11%17%20%7%
1763
21st to endDay
37%6%10%23%18%6%
1570
March1st to 10thDay
44%8%12%19%13%4
2004
11th to 20thDay
43%8%11%19%16%4
1980
21st to endDay
37%8%14%21%17%3
2205
April1st to 10thDay
37%7%14%19%18%4
2160
11th to 20thDay
29%7%15%24%21%5%
2132
21st to endDay
23%7%14%29%22%5%
2160
May1st to 10thDay
22%7%12%25%28%6%
2221
11th to 20thDay
20%6%15%27%25%8%
2338
21st to endDay
25%8%18%25%21%3
2724
June1st to 10thDay
22%8%14%25%23%8%
2520
11th to 20thDay
10%5%12%24%34%15%
2520
21st to endDay
11%48%17%33%27%
2520
July1st to 10thDay
9%49%15%25%38%
2447
11th to 20thDay
11%410%16%24%35%
2271
21st to endDay
8%37%15%32%35%
2405
August1st to 10thDay
15%5%9%18%30%24%
2312
11th to 20thDay
9%48%17%32%31%
2183
21st to endDay
10%5%7%19%33%26%
2376
September1st to 10thDay
10%35%14%29%39%
2160
11th to 20thDay
18%5%10%23%26%17%
2160
21st to endDay
11%48%22%33%22%
1908
October1st to 10thDay
19%48%18%28%23%
1800
11th to 20thDay
21%5%11%18%22%23%
1800
21st to endDay
23%5%10%19%23%19%
1980
November1st to 10thDay
30%6%11%22%20%12%
1836
11th to 20thDay
32%7%10%22%21%7%
1710
21st to endDay
30%5%11%17%28%9%
1567
December1st to 10thDay
37%8%12%18%16%10%
1520
11th to 20thDay
52%6%12%12%13%5%
1928
21st to endDay
47%9%12%18%12%3
2794
January1st to 10thNight
39%9%18%22%9%3
4216
11th to 20thNight
52%9%13%10%9%7%
4110
21st to endNight
54%7%9%11%11%7%
4521
February1st to 10thNight
37%6%10%18%19%11%
2470
11th to 20thNight
37%7%11%18%21%7%
2315
21st to endNight
33%7%12%29%15%4
1884
March1st to 10thNight
44%7%14%17%14%4
2070
11th to 20thNight
40%8%9%21%18%5%
1980
21st to endNight
36%8%14%20%17%5%
2149
April1st to 10thNight
35%8%17%21%16%4
1800
11th to 20thNight
30%8%13%24%19%7%
1779
21st to endNight
19%9%14%32%20%6%
1800
May1st to 10thNight
24%8%10%25%24%10%
1736
11th to 20thNight
21%10%15%24%23%7%
1556
21st to endNight
23%10%19%24%20%3
1552
June1st to 10thNight
21%8%14%25%25%8%
1440
11th to 20thNight
10%7%10%23%31%19%
1440
21st to endNight
13%47%17%33%25%
1440
July1st to 10thNight
9%48%15%28%36%
1400
11th to 20thNight
10%7%10%17%23%33%
1566
21st to endNight
12%5%12%16%26%28%
1674
August1st to 10thNight
20%7%9%18%24%22%
1602
11th to 20thNight
12%5%9%18%27%29%
1717
21st to endNight
12%6%10%20%27%25%
1980
September1st to 10thNight
11%5%7%13%25%39%
1800
11th to 20thNight
19%6%11%22%27%15%
1800
21st to endNight
12%5%8%21%29%25%
2048
October1st to 10thNight
18%5%11%17%25%24%
2160
11th to 20thNight
23%6%9%19%20%23%
2160
21st to endNight
22%5%10%20%24%20%
2376
November1st to 10thNight
27%7%12%24%18%13%
2241
11th to 20thNight
30%7%12%23%19%8%
2470
21st to endNight
27%6%12%21%22%13%
2611
December1st to 10thNight
37%8%10%17%17%12%
2660
11th to 20thNight
52%6%10%13%15%3
3276
21st to endNight
46%11%14%15%11%4
4862

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
21%13%24%25%14%3
296
11th to 20thDay
14%9%22%32%18%5%
370
21st to endDay
13%9%26%28%20%5%
407
February1st to 10thDay
14%15%25%24%17%6%
370
11th to 20thDay
15%17%28%25%13%2
407
21st to endDay
11%15%29%30%14%2
382
March1st to 10thDay
16%17%30%25%10%1
441
11th to 20thDay
16%15%26%25%14%5%
420
21st to endDay
11%17%35%26%10%2
462
April1st to 10thDay
12%15%34%25%12%3
420
11th to 20thDay
11%17%31%25%11%4
412
21st to endDay
5%17%30%29%13%6%
420
May1st to 10thDay
414%34%30%13%5%
423
11th to 20thDay
8%13%33%29%13%4
448
21st to endDay
7%12%28%31%15%7%
485
June1st to 10thDay
410%27%31%20%6%
450
11th to 20thDay
29%29%37%19%5%
450
21st to endDay
15%22%40%24%8%
450
July1st to 10thDay
2416%46%27%5%
446
11th to 20thDay
114%42%32%10%
444
21st to endDay
115%41%33%10%
487
August1st to 10thDay
2322%40%24%9%
447
11th to 20thDay
1119%41%26%12%
437
21st to endDay
218%39%31%9%
495
September1st to 10thDay
1413%40%30%11%
450
11th to 20thDay
26%24%36%24%9%
450
21st to endDay
28%18%34%28%9%
450
October1st to 10thDay
27%23%35%21%12%
450
11th to 20thDay
5%8%17%31%26%13%
450
21st to endDay
7%5%24%30%24%9%
495
November1st to 10thDay
7%9%23%26%25%9%
432
11th to 20thDay
48%17%30%27%14%
270
21st to endDay
7%5%22%28%31%6%
202
December1st to 10thDay
8%13%18%28%25%8%
180
11th to 20thDay
11%12%20%24%23%9%
180
21st to endDay
16%15%22%27%18%3
198
January1st to 10thNight
17%7%17%32%22%5%
760
11th to 20thNight
13%6%15%35%24%7%
760
21st to endNight
17%5%14%36%23%5%
836
February1st to 10thNight
12%7%17%38%22%4
760
11th to 20thNight
12%7%20%34%22%5%
744
21st to endNight
11%8%20%39%19%3
628
March1st to 10thNight
15%10%20%31%23%3
742
11th to 20thNight
14%8%17%33%24%4
720
21st to endNight
11%9%22%37%19%2
792
April1st to 10thNight
10%7%21%38%21%3
720
11th to 20thNight
8%12%21%33%20%5%
711
21st to endNight
5%5%25%35%24%6%
720
May1st to 10thNight
5%420%39%27%5%
656
11th to 20thNight
4417%36%33%6%
493
21st to endNight
5%7%19%35%30%5%
389
June1st to 10thNight
4416%42%32%3
360
11th to 20thNight
1314%47%35%1
360
21st to endNight
149%38%44%3
360
July1st to 10thNight
137%31%55%3
350
11th to 20thNight
1330%50%15%
522
21st to endNight
116%24%57%12%
591
August1st to 10thNight
5%46%29%47%9%
537
11th to 20thNight
129%33%47%8%
649
21st to endNight
118%31%46%11%
792
September1st to 10thNight
2210%31%44%11%
720
11th to 20thNight
5%412%32%39%8%
720
21st to endNight
2211%30%43%12%
720
October1st to 10thNight
4311%36%36%10%
720
11th to 20thNight
6%411%29%39%11%
720
21st to endNight
5%5%9%34%33%13%
792
November1st to 10thNight
7%415%31%34%9%
740
11th to 20thNight
9%312%37%32%7%
760
21st to endNight
8%414%40%27%6%
760
December1st to 10thNight
11%6%17%35%25%6%
760
11th to 20thNight
17%6%18%35%19%4
760
21st to endNight
16%9%22%32%19%2
836
Page generated at 2024-03-03 03:28:58. Version ac07

Copyright © 2024 Attilla Danko.


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