Mount Tamalpais State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Tamalpais State Park clear sky chart from 2005-11-05 to 2018-02-22.

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
57%
16014
25%
48954
21%
15978
63%
15978
33%
28039

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
56%
776
19%
2564
17%
776
60%
776
26%
1578
January16th to endNight
55%
832
23%
2704
23%
832
60%
832
25%
1673
February1st to 15thNight
54%
760
25%
2483
23%
760
61%
760
26%
1510
February16th to endNight
44%
660
24%
2007
17%
660
54%
660
25%
1263
March1st to 15thNight
49%
720
17%
1983
14%
720
52%
720
26%
1328
March16th to endNight
43%
768
21%
2104
13%
768
49%
768
28%
1332
April1st to 15thNight
41%
719
24%
1799
10%
719
48%
719
31%
1154
April16th to endNight
50%
720
26%
1800
11%
720
56%
720
41%
1037
May1st to 15thNight
55%
581
25%
1661
14%
581
62%
581
45%
884
May16th to endNight
55%
417
24%
1540
18%
417
64%
417
35%
754
June1st to 15thNight
57%
360
22%
1440
20%
360
67%
360
32%
690
June16th to endNight
74%
360
32%
1440
38%
360
80%
360
51%
562
July1st to 15thNight
71%
404
25%
1424
27%
404
74%
404
43%
652
July16th to endNight
62%
564
24%
1593
21%
531
64%
531
31%
943
August1st to 15thNight
65%
538
24%
1611
18%
535
67%
535
35%
909
August16th to endNight
70%
759
29%
1905
17%
759
72%
759
46%
1110
September1st to 15thNight
78%
720
33%
1800
22%
720
79%
720
51%
998
September16th to endNight
71%
716
36%
1976
30%
716
77%
716
51%
1021
October1st to 15thNight
64%
720
28%
2160
26%
720
72%
720
44%
1121
October16th to endNight
67%
768
33%
2304
34%
768
71%
768
41%
1246
November1st to 15thNight
62%
760
26%
2348
24%
760
67%
760
38%
1296
November16th to endNight
57%
780
23%
2666
25%
780
61%
780
29%
1523
December1st to 15thNight
52%
780
21%
2730
19%
780
58%
780
23%
1668
December16th to endNight
46%
832
22%
2912
19%
832
53%
832
22%
1787

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
7%5%2442335%8%51%
49299
Night
9%5%24424448%49%
49143
TransparencyDay
31%48%20%23%12%
48989
Night
32%38%19%21%13%
48955
SeeingDay
9%10%24%31%18%5%
6535
Night
10%5%14%30%31%6%
16024

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
17%7%245%2345%7%40%
1703
16th to endDay
14%5%26%5%34446%41%
1872
February1st to 15thDay
16%415%5%2435%5%44%
1711
16th to endDay
15%7%35%4345%5%8%37%
1613
March1st to 15thDay
16%6%26%5%3445%9%35%
1974
16th to endDay
13%5%26%6%2446%7%39%
2118
April1st to 15thDay
12%6%343345%6%7%42%
2149
16th to endDay
5%424423349%56%
2160
May1st to 15thDay
4414223348%59%
2287
16th to endDay
45%25%314349%53%
2572
June1st to 15thDay
5%5%24323347%56%
2520
16th to endDay
221221335%9%65%
2520
July1st to 15thDay
15%2441345%10%56%
2448
16th to endDay
15%2432336%12%54%
2468
August1st to 15thDay
15%2441346%11%54%
2340
16th to endDay
5%2442335%12%54%
2298
September1st to 15thDay
141332335%11%58%
2160
16th to endDay
3313212337%67%
1980
October1st to 15thDay
7%414323246%59%
1800
16th to endDay
8%5%24423346%55%
1920
November1st to 15thDay
9%5%245%2435%7%50%
1840
16th to endDay
14%7%34423345%46%
1622
December1st to 15thDay
16%9%43424345%42%
1560
16th to endDay
18%7%25%5%2335%6%38%
1664
January1st to 15thNight
16%5%245%2345%7%41%
2564
16th to endNight
15%6%24323446%46%
2704
February1st to 15thNight
14%5%25%324345%46%
2471
16th to endNight
14%5%2442345%6%43%
2007
March1st to 15thNight
15%6%35%434447%40%
1983
16th to endNight
13%5%245%24346%47%
2104
April1st to 15thNight
10%4333345%5%7%48%
1799
16th to endNight
6%324223347%59%
1800
May1st to 15thNight
3324423338%59%
1661
16th to endNight
3425%424448%54%
1539
June1st to 15thNight
2335%43445%9%52%
1440
16th to endNight
133212249%66%
1440
July1st to 15thNight
1326%5%26%45%12%50%
1509
16th to endNight
16%48%8%46%5%6%10%37%
1701
August1st to 15thNight
16%37%6%45%46%11%40%
1620
16th to endNight
15%26%6%35%46%10%48%
1905
September1st to 15thNight
1414325%5%6%10%54%
1800
16th to endNight
2323323347%62%
1976
October1st to 15thNight
5%423313336%62%
2160
16th to endNight
6%42332435%8%55%
2304
November1st to 15thNight
8%424313348%54%
2348
16th to endNight
10%6%24423346%50%
2666
December1st to 15thNight
19%5%23423346%44%
2730
16th to endNight
17%6%24323446%44%
2912

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
43%411%17%15%6%
1703
16th to endDay
43%6%8%13%16%10%
1872
February1st to 15thDay
40%48%21%19%6%
1711
16th to endDay
43%6%8%24%13%3
1613
March1st to 15thDay
44%6%12%18%13%4
1974
16th to endDay
41%7%12%20%14%2
2118
April1st to 15thDay
38%5%13%21%17%2
2149
16th to endDay
25%5%14%26%22%5%
2160
May1st to 15thDay
23%38%30%26%7%
2287
16th to endDay
27%413%26%22%5%
2576
June1st to 15thDay
26%410%23%23%11%
2520
16th to endDay
16%35%18%36%20%
2520
July1st to 15thDay
22%2410%28%32%
2305
16th to endDay
25%25%11%28%27%
2313
August1st to 15thDay
25%1414%31%22%
2324
16th to endDay
24%2318%32%17%
2298
September1st to 15thDay
21%3416%30%23%
2160
16th to endDay
18%25%26%30%16%
1980
October1st to 15thDay
27%27%18%25%18%
1800
16th to endDay
31%29%23%21%11%
1920
November1st to 15thDay
33%5%12%30%12%6%
1840
16th to endDay
40%310%20%19%5%
1622
December1st to 15thDay
44%410%16%18%6%
1560
16th to endDay
45%5%10%16%15%5%
1664
January1st to 15thNight
40%412%20%14%7%
2564
16th to endNight
39%5%10%13%17%13%
2704
February1st to 15thNight
38%47%20%19%9%
2483
16th to endNight
38%5%11%24%16%2
2007
March1st to 15thNight
43%411%19%15%5%
1983
16th to endNight
38%411%21%18%4
2104
April1st to 15thNight
34%5%12%22%19%4
1799
16th to endNight
24%412%27%22%9%
1800
May1st to 15thNight
23%48%23%29%10%
1662
16th to endNight
25%412%28%22%7%
1540
June1st to 15thNight
25%5%9%19%26%13%
1440
16th to endNight
16%25%14%35%27%
1440
July1st to 15thNight
24%129%26%35%
1424
16th to endNight
38%25%8%16%28%
1593
August1st to 15thNight
34%1313%22%23%
1611
16th to endNight
28%2414%25%24%
1905
September1st to 15thNight
24%25%11%27%28%
1800
16th to endNight
21%15%23%27%19%
1976
October1st to 15thNight
23%46%19%23%22%
2160
16th to endNight
28%28%21%22%15%
2304
November1st to 15thNight
29%412%31%15%6%
2348
16th to endNight
35%39%23%20%7%
2666
December1st to 15thNight
41%38%16%19%9%
2730
16th to endNight
40%5%10%18%17%7%
2912

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
24%6%23%23%16%4
242
16th to endDay
14%10%23%28%17%4
304
February1st to 15thDay
16%8%25%26%18%5%
281
16th to endDay
16%15%24%23%15%3
257
March1st to 15thDay
21%12%28%18%13%5%
270
16th to endDay
15%19%32%20%9%3
288
April1st to 15thDay
15%21%29%23%7%2
269
16th to endDay
11%22%30%22%9%3
270
May1st to 15thDay
5%21%29%29%12%1
288
16th to endDay
9%10%25%27%21%4
330
June1st to 15thDay
6%16%31%33%9%1
315
16th to endDay
430%41%18%4
315
July1st to 15thDay
1217%48%26%2
305
16th to endDay
118%49%22%7%
327
August1st to 15thDay
2324%43%21%4
315
16th to endDay
119%43%26%8%
332
September1st to 15thDay
3318%39%25%9%
315
16th to endDay
37%22%32%26%8%
315
October1st to 15thDay
6%7%25%31%18%9%
315
16th to endDay
10%8%22%24%23%10%
336
November1st to 15thDay
12%6%18%27%24%10%
256
16th to endDay
14%8%26%29%17%2
104
December1st to 15thDay
16%17%16%21%23%4
90
16th to endDay
13%17%10%35%20%2
96
January1st to 15thNight
19%49%31%29%6%
780
16th to endNight
18%5%12%28%28%7%
832
February1st to 15thNight
16%5%12%31%28%5%
764
16th to endNight
16%9%18%28%20%6%
660
March1st to 15thNight
18%7%15%27%26%4
720
16th to endNight
14%9%23%29%20%2
768
April1st to 15thNight
12%13%25%26%18%4
719
16th to endNight
7%14%20%26%25%4
720
May1st to 15thNight
3425%30%30%5%
582
16th to endNight
5%7%20%34%27%3
418
June1st to 15thNight
25%20%41%27%1
360
16th to endNight
2213%47%30%3
360
July1st to 15thNight
18%35%48%5%
404
16th to endNight
35%35%43%12%
564
August1st to 15thNight
36%35%45%7%
538
16th to endNight
38%34%43%9%
759
September1st to 15thNight
215%32%46%11%
720
16th to endNight
3212%31%39%10%
716
October1st to 15thNight
7%315%29%35%9%
720
16th to endNight
8%310%27%35%14%
768
November1st to 15thNight
9%215%30%34%8%
760
16th to endNight
14%5%12%28%29%8%
780
December1st to 15thNight
20%5%11%28%26%6%
780
16th to endNight
19%9%16%29%23%2
832
Page generated at 2018-02-23 08:21:40. Version ac04

Copyright 2018 A. Danko


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