Menlo Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Menlo Park clear sky chart from 2005-11-05 to 2017-09-18.

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
67%
15421
25%
46928
23%
15385
70%
15385
37%
26287

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
62%
716
18%
2372
18%
716
64%
716
28%
1441
January16th to endNight
59%
768
24%
2496
25%
768
62%
768
25%
1570
February1st to 15thNight
57%
700
22%
2288
22%
700
61%
700
25%
1438
February16th to endNight
53%
632
21%
1898
18%
632
59%
632
26%
1233
March1st to 15thNight
55%
720
18%
2000
16%
720
58%
720
28%
1325
March16th to endNight
53%
768
19%
2092
14%
768
57%
768
29%
1373
April1st to 15thNight
52%
719
20%
1799
11%
719
55%
719
32%
1191
April16th to endNight
60%
720
24%
1800
12%
720
64%
720
45%
1049
May1st to 15thNight
71%
615
25%
1695
17%
615
73%
615
48%
908
May16th to endNight
68%
405
23%
1528
20%
405
74%
405
35%
758
June1st to 15thNight
73%
360
24%
1440
26%
360
80%
360
39%
660
June16th to endNight
86%
360
35%
1440
45%
360
89%
360
61%
506
July1st to 15thNight
89%
395
32%
1415
37%
395
90%
395
64%
531
July16th to endNight
84%
564
33%
1593
31%
531
85%
531
57%
714
August1st to 15thNight
83%
556
31%
1629
26%
553
83%
553
52%
770
August16th to endNight
84%
764
36%
1910
24%
764
84%
764
63%
966
September1st to 15thNight
84%
720
37%
1800
27%
720
85%
720
65%
894
September16th to endNight
81%
667
37%
1831
34%
667
82%
667
58%
901
October1st to 15thNight
73%
660
27%
1980
28%
660
77%
660
44%
1041
October16th to endNight
71%
704
30%
2112
32%
704
74%
704
41%
1144
November1st to 15thNight
69%
700
26%
2173
28%
700
71%
700
38%
1211
November16th to endNight
65%
720
23%
2429
25%
720
68%
720
33%
1365
December1st to 15thNight
56%
720
21%
2520
19%
720
62%
720
23%
1571
December16th to endNight
48%
768
19%
2688
16%
768
54%
768
22%
1727

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%423323347%58%
47868
Night
7%424423347%55%
47117
TransparencyDay
26%5%10%19%23%14%
47557
Night
28%6%11%19%21%13%
46929
SeeingDay
7%8%23%34%19%6%
6041
Night
8%313%32%33%8%
15431

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 15thDay
12%6%2443345%7%46%
1565
16th to endDay
13%6%245%3335%6%45%
1728
February1st to 15thDay
13%7%35%43246%6%41%
1576
16th to endDay
15%7%345%3435%7%39%
1576
March1st to 15thDay
11%6%35%5%35%46%9%38%
1959
16th to endDay
9%6%246%35%5%5%7%43%
2130
April1st to 15thDay
12%7%3432345%7%45%
2149
16th to endDay
6%423323337%59%
2160
May1st to 15thDay
3313213247%65%
2253
16th to endDay
6%6%14312247%58%
2581
June1st to 15thDay
5%412212347%62%
2520
16th to endDay
211211135%77%
2520
July1st to 15thDay
1212112236%74%
2457
16th to endDay
1112212336%74%
2468
August1st to 15thDay
1313212335%72%
2322
16th to endDay
213212237%72%
2292
September1st to 15thDay
1212212225%73%
2160
16th to endDay
321322235%71%
1852
October1st to 15thDay
5%413322237%61%
1650
16th to endDay
6%423323346%57%
1760
November1st to 15thDay
7%5%2332345%8%51%
1684
16th to endDay
9%7%36%324345%48%
1530
December1st to 15thDay
11%7%37%7%2345%5%41%
1440
16th to endDay
14%7%46%5%2435%7%40%
1536
January1st to 15thNight
12%6%2442445%9%43%
2372
16th to endNight
14%5%24423447%46%
2496
February1st to 15thNight
9%6%36%5%35%446%43%
2276
16th to endNight
12%6%35%5%235%5%8%42%
1898
March1st to 15thNight
12%5%36%5%3435%6%44%
2000
16th to endNight
9%7%35%324346%47%
2092
April1st to 15thNight
8%4245%2447%8%46%
1799
16th to endNight
6%313323347%61%
1800
May1st to 15thNight
132331325%9%61%
1695
16th to endNight
35%14423347%59%
1527
June1st to 15thNight
2323312248%64%
1440
16th to endNight
111211225%78%
1440
July1st to 15thNight
1121125%8%73%
1500
16th to endNight
21331246%11%61%
1701
August1st to 15thNight
12134233411%61%
1638
16th to endNight
2133123412%64%
1910
September1st to 15thNight
222312249%69%
1800
16th to endNight
1312212345%69%
1831
October1st to 15thNight
5%323213447%61%
1980
16th to endNight
5%42431335%6%57%
2112
November1st to 15thNight
7%5%24323347%56%
2173
16th to endNight
7%5%23434447%52%
2429
December1st to 15thNight
11%6%25%424447%45%
2520
16th to endNight
15%6%34423346%44%
2688

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
37%5%13%18%15%9%
1565
16th to endDay
40%7%8%12%18%12%
1728
February1st to 15thDay
42%5%9%17%20%4
1576
16th to endDay
45%5%9%22%12%3
1576
March1st to 15thDay
43%7%11%18%13%5%
1959
16th to endDay
40%8%13%19%15%2
2130
April1st to 15thDay
39%6%15%18%17%2
2149
16th to endDay
26%6%13%26%21%6%
2160
May1st to 15thDay
19%6%12%26%26%7%
2253
16th to endDay
27%6%15%25%21%5%
2585
June1st to 15thDay
22%7%12%21%21%13%
2520
16th to endDay
10%37%18%35%24%
2520
July1st to 15thDay
10%47%14%22%41%
2313
16th to endDay
10%37%13%29%35%
2313
August1st to 15thDay
13%47%15%31%27%
2306
16th to endDay
10%46%19%35%23%
2292
September1st to 15thDay
12%37%18%28%29%
2160
16th to endDay
15%36%25%28%19%
1852
October1st to 15thDay
24%410%19%24%16%
1650
16th to endDay
26%5%10%22%21%12%
1760
November1st to 15thDay
33%5%11%25%16%7%
1684
16th to endDay
37%6%9%16%25%4
1530
December1st to 15thDay
44%5%12%15%18%4
1440
16th to endDay
44%6%13%15%16%4
1536
January1st to 15thNight
37%413%18%15%8%
2372
16th to endNight
40%6%9%12%16%15%
2496
February1st to 15thNight
39%6%10%18%18%7%
2288
16th to endNight
41%6%12%25%11%2
1898
March1st to 15thNight
41%6%13%19%14%5%
2000
16th to endNight
38%7%13%18%17%5%
2092
April1st to 15thNight
35%7%16%20%16%2
1799
16th to endNight
23%7%14%26%20%8%
1800
May1st to 15thNight
19%7%11%24%25%10%
1696
16th to endNight
23%7%16%26%19%5%
1528
June1st to 15thNight
18%8%13%22%22%14%
1440
16th to endNight
10%26%16%35%27%
1440
July1st to 15thNight
8%45%13%28%38%
1415
16th to endNight
12%5%10%16%24%30%
1593
August1st to 15thNight
16%5%7%17%28%24%
1629
16th to endNight
12%5%8%19%29%25%
1910
September1st to 15thNight
12%48%16%26%32%
1800
16th to endNight
15%46%22%28%21%
1831
October1st to 15thNight
23%5%10%20%22%17%
1980
16th to endNight
26%410%21%23%13%
2112
November1st to 15thNight
28%5%14%26%17%7%
2173
16th to endNight
31%5%11%22%20%8%
2429
December1st to 15thNight
39%7%9%15%19%7%
2520
16th to endNight
43%5%12%15%16%6%
2688

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
18%8%21%33%12%5%
193
16th to endDay
13%8%24%27%20%5%
256
February1st to 15thDay
15%12%23%25%17%4
236
16th to endDay
18%12%25%27%14%1
237
March1st to 15thDay
17%14%25%23%15%3
270
16th to endDay
10%15%38%25%7%2
288
April1st to 15thDay
15%19%33%21%8%2
269
16th to endDay
7%21%31%26%10%2
270
May1st to 15thDay
5%13%36%31%10%2
288
16th to endDay
10%12%24%32%14%5%
330
June1st to 15thDay
411%30%35%14%3
315
16th to endDay
1319%45%23%7%
315
July1st to 15thDay
2113%51%25%6%
305
16th to endDay
115%41%31%9%
327
August1st to 15thDay
120%42%25%9%
315
16th to endDay
114%43%29%10%
332
September1st to 15thDay
214%41%29%10%
315
16th to endDay
35%18%35%26%10%
264
October1st to 15thDay
5%8%20%37%21%6%
255
16th to endDay
9%7%25%31%20%5%
272
November1st to 15thDay
7%324%23%27%13%
190
16th to endDay
5%13%24%29%26%1
75
December1st to 15thDay
10%13%31%28%16%
60
16th to endDay
12%12%15%26%26%6%
64
January1st to 15thNight
15%310%33%29%7%
720
16th to endNight
16%412%31%25%9%
768
February1st to 15thNight
11%7%15%34%25%6%
704
16th to endNight
15%6%17%34%21%5%
632
March1st to 15thNight
14%6%15%29%29%4
720
16th to endNight
11%6%21%34%22%3
768
April1st to 15thNight
10%7%22%35%20%3
719
16th to endNight
6%5%22%34%24%6%
720
May1st to 15thNight
3218%39%30%6%
616
16th to endNight
3417%34%33%6%
406
June1st to 15thNight
2214%44%33%2
360
16th to endNight
9%41%45%2
360
July1st to 15thNight
430%55%8%
395
16th to endNight
15%23%53%15%
564
August1st to 15thNight
215%27%52%10%
556
16th to endNight
16%32%48%10%
764
September1st to 15thNight
36%27%49%12%
720
16th to endNight
319%27%43%13%
667
October1st to 15thNight
6%210%32%36%10%
660
16th to endNight
7%39%30%33%14%
704
November1st to 15thNight
8%13%34%33%9%
700
16th to endNight
9%312%35%29%9%
720
December1st to 15thNight
13%417%33%23%7%
720
16th to endNight
17%6%19%32%20%3
768
Page generated at 2017-09-19 04:32:22. Version ac04

Copyright 2017 A. Danko


Menlo Park Clear Sky Chart | Charts Home