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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 2005-11-06 to 2024-01-16.

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
56%
23684
16%
74842
13%
23636
61%
23636
16%
54189

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
49%
756
11%
2517
9%
756
53%
756
11%
1965
January11th to 20thNight
51%
740
16%
2405
12%
740
58%
740
14%
1780
January21st to endNight
54%
792
16%
2574
15%
792
57%
792
13%
1920
February1st to 10thNight
53%
720
18%
2340
16%
720
59%
720
17%
1652
February11th to 20thNight
46%
700
14%
2224
11%
700
52%
700
13%
1649
February21st to endNight
45%
592
16%
1776
11%
592
52%
592
15%
1324
March1st to 10thNight
42%
720
13%
1985
9%
720
47%
720
15%
1534
March11th to 20thNight
47%
720
17%
1980
12%
720
51%
720
14%
1546
March21st to endNight
42%
792
13%
2168
6%
792
48%
792
15%
1653
April1st to 10thNight
44%
720
16%
1800
7%
720
49%
720
18%
1360
April11th to 20thNight
44%
711
21%
1779
9%
711
49%
711
19%
1307
April21st to endNight
49%
720
21%
1800
7%
720
55%
720
25%
1254
May1st to 10thNight
51%
604
20%
1684
9%
604
58%
604
22%
1163
May11th to 20thNight
56%
510
19%
1573
13%
510
61%
510
21%
1079
May21st to endNight
54%
388
19%
1552
14%
388
64%
388
14%
1027
June1st to 10thNight
55%
360
14%
1440
11%
360
63%
360
13%
990
June11th to 20thNight
65%
360
23%
1440
20%
360
75%
360
18%
884
June21st to endNight
69%
360
20%
1440
23%
360
74%
360
19%
896
July1st to 10thNight
71%
363
19%
1413
21%
363
74%
363
21%
874
July11th to 20thNight
72%
522
16%
1566
14%
522
73%
522
18%
1110
July21st to endNight
62%
591
12%
1674
11%
558
62%
558
12%
1302
August1st to 10thNight
63%
537
14%
1602
11%
534
64%
534
17%
1158
August11th to 20thNight
68%
614
18%
1682
11%
614
70%
614
21%
1212
August21st to endNight
70%
792
19%
1980
12%
792
71%
792
25%
1424
September1st to 10thNight
78%
720
25%
1800
17%
720
79%
720
29%
1240
September11th to 20thNight
67%
720
21%
1800
15%
720
70%
720
23%
1326
September21st to endNight
69%
720
21%
2063
19%
720
72%
720
25%
1391
October1st to 10thNight
64%
720
17%
2160
17%
720
68%
720
21%
1493
October11th to 20thNight
64%
720
22%
2160
21%
720
69%
720
20%
1495
October21st to endNight
66%
792
22%
2376
21%
792
70%
792
20%
1654
November1st to 10thNight
60%
740
14%
2224
10%
740
65%
740
15%
1672
November11th to 20thNight
62%
760
17%
2472
15%
760
66%
760
16%
1799
November21st to endNight
59%
760
16%
2660
17%
760
62%
760
17%
1823
December1st to 10thNight
51%
760
14%
2660
12%
760
56%
760
14%
1939
December11th to 20thNight
46%
760
11%
3246
12%
759
49%
759
8%
2651
December21st to endNight
43%
828
5%
4827
5%
817
47%
817
5%
3643

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
8%5%25%42445%9%52%
74704
Night
9%5%25%5%3445%7%50%
75106
TransparencyDay
20%37%7%12%15%9%
74426
Night
23%37%7%12%13%9%
74907
SeeingDay
9%10%24%31%20%6%
14296
Night
10%6%16%33%29%6%
23701

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
19%9%26%6%3446%8%34%
1646
11th to 20thDay
14%5%25%5%445%5%6%44%
1666
21st to endDay
12%6%37%5%45%6%5%7%40%
1782
February1st to 10thDay
17%5%25%5%2445%6%45%
1620
11th to 20thDay
11%6%26%6%35%47%9%42%
1625
21st to endDay
12%7%35%424447%48%
1480
March1st to 10thDay
15%7%36%6%45%45%9%36%
1970
11th to 20thDay
16%7%25%5%35%46%9%37%
1980
21st to endDay
12%435%5%245%7%9%44%
2187
April1st to 10thDay
12%7%35%5%345%6%7%42%
2160
11th to 20thDay
7%5%244345%48%54%
2129
21st to endDay
442432446%11%56%
2160
May1st to 10thDay
5%5%25%423448%59%
2273
11th to 20thDay
5%425%3243410%58%
2320
21st to endDay
36%35%5%2446%9%53%
2723
June1st to 10thDay
5%5%2442346%9%56%
2520
11th to 20thDay
132332335%10%66%
2520
21st to endDay
222432345%9%63%
2520
July1st to 10thDay
1425%42346%11%58%
2502
11th to 20thDay
15%345%245%5%10%55%
2340
21st to endDay
142442447%12%56%
2546
August1st to 10thDay
15%35%5%2347%12%52%
2328
11th to 20thDay
42432446%12%59%
2219
21st to endDay
15%35%6%3445%11%52%
2376
September1st to 10thDay
131422325%11%65%
2160
11th to 20thDay
35%244245%5%9%57%
2160
21st to endDay
2323222347%70%
1891
October1st to 10thDay
4413423347%64%
1800
11th to 20thDay
7%5%25%42445%6%57%
1800
21st to endDay
9%42442435%7%56%
1980
November1st to 10thDay
9%4245%2445%8%53%
1853
11th to 20thDay
10%8%36%5%3445%6%46%
1706
21st to endDay
11%5%2343335%8%52%
1520
December1st to 10thDay
15%7%35%43445%7%43%
1520
11th to 20thDay
28%10%35%6%33445%29%
1928
21st to endDay
23%7%25%6%3346%8%33%
2794
January1st to 10thNight
17%6%35%6%345%6%7%38%
2517
11th to 20thNight
14%6%36%5%345%5%7%43%
2405
21st to endNight
14%6%25%4245%5%7%46%
2574
February1st to 10thNight
16%5%2443445%5%48%
2340
11th to 20thNight
10%6%36%4345%5%8%46%
2222
21st to endNight
12%5%23435%45%6%51%
1776
March1st to 10thNight
16%7%46%5%35%5%46%38%
1985
11th to 20thNight
14%6%345%35%46%7%42%
1980
21st to endNight
13%6%245%23446%52%
2168
April1st to 10thNight
9%5%25%435%5%6%8%49%
1800
11th to 20thNight
8%435%323447%58%
1779
21st to endNight
432332446%10%59%
1800
May1st to 10thNight
4325%6%24449%57%
1684
11th to 20thNight
3425%5%35%449%57%
1572
21st to endNight
4435%5%4445%8%55%
1552
June1st to 10thNight
45%25%5%345%6%8%53%
1440
11th to 20thNight
122433445%8%64%
1440
21st to endNight
2415%5%2335%8%62%
1440
July1st to 10thNight
1236%7%2445%10%57%
1453
11th to 20thNight
25%26%5%36%5%5%10%50%
1620
21st to endNight
16%5%9%8%47%5%7%9%39%
1773
August1st to 10thNight
28%47%6%45%47%9%44%
1611
11th to 20thNight
437%7%5%6%6%6%10%46%
1682
21st to endNight
15%36%6%35%45%8%53%
1980
September1st to 10thNight
131442445%10%63%
1800
11th to 20thNight
35%26%435%45%9%55%
1800
21st to endNight
2424433347%64%
2063
October1st to 10thNight
4424422446%63%
2160
11th to 20thNight
45%25%424347%58%
2160
21st to endNight
7%42442445%7%58%
2376
November1st to 10thNight
8%435%42335%8%54%
2224
11th to 20thNight
10%6%25%42445%7%51%
2472
21st to endNight
8%5%245%3435%7%55%
2660
December1st to 10thNight
17%6%25%5%33446%45%
2660
11th to 20thNight
30%8%3442345%6%31%
3276
21st to endNight
21%7%26%5%35%5%5%6%35%
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
29%40%9%12%7%2
1646
11th to 20thDay
20%42%5%11%14%8%
1666
21st to endDay
28%39%6%8%13%5%
1782
February1st to 10thDay
23%37%5%14%14%7%
1620
11th to 20thDay
24%38%8%14%12%4
1634
21st to endDay
26%37%6%15%12%5%
1480
March1st to 10thDay
26%38%10%14%10%2
1970
11th to 20thDay
30%39%9%14%7%2
1980
21st to endDay
25%39%9%14%11%2
2187
April1st to 10thDay
24%38%10%12%13%3
2160
11th to 20thDay
20%38%9%15%14%4
2132
21st to endDay
15%37%9%22%15%3
2160
May1st to 10thDay
15%37%7%16%20%5%
2273
11th to 20thDay
13%38%6%21%15%6%
2323
21st to endDay
16%40%10%17%16%1
2724
June1st to 10thDay
18%38%9%17%15%3
2520
11th to 20thDay
11%38%7%12%23%10%
2520
21st to endDay
13%36%6%9%22%14%
2520
July1st to 10thDay
12%36%6%419%23%
2434
11th to 20thDay
18%37%7%415%20%
2271
21st to endDay
18%36%6%416%20%
2405
August1st to 10thDay
16%36%7%7%18%15%
2312
11th to 20thDay
14%34%47%22%19%
2219
21st to endDay
17%35%5%6%21%16%
2376
September1st to 10thDay
11%35%4419%26%
2160
11th to 20thDay
17%37%5%14%20%7%
2160
21st to endDay
10%35%416%20%15%
1891
October1st to 10thDay
17%36%6%10%21%10%
1800
11th to 20thDay
19%35%6%13%15%11%
1800
21st to endDay
19%36%6%14%14%10%
1980
November1st to 10thDay
22%41%7%14%9%6%
1853
11th to 20thDay
25%40%6%12%11%5%
1706
21st to endDay
18%39%8%13%14%8%
1520
December1st to 10thDay
23%40%7%13%13%4
1520
11th to 20thDay
43%32%8%8%8%2
1928
21st to endDay
41%28%13%12%5%1
2794
January1st to 10thNight
27%41%8%15%6%3
2517
11th to 20thNight
21%42%6%12%10%9%
2405
21st to endNight
25%38%8%8%14%7%
2574
February1st to 10thNight
21%36%5%15%14%8%
2340
11th to 20thNight
25%37%7%12%14%4
2224
21st to endNight
25%37%8%15%13%3
1776
March1st to 10thNight
27%37%9%14%11%3
1985
11th to 20thNight
29%37%6%16%10%3
1980
21st to endNight
25%38%9%14%11%4
2168
April1st to 10thNight
21%38%9%15%13%3
1800
11th to 20thNight
18%37%8%16%15%6%
1779
21st to endNight
14%36%7%21%17%5%
1800
May1st to 10thNight
16%36%5%14%21%8%
1684
11th to 20thNight
16%38%6%16%20%5%
1573
21st to endNight
16%38%9%17%18%2
1552
June1st to 10thNight
21%38%7%13%18%3
1440
11th to 20thNight
11%38%6%10%22%13%
1440
21st to endNight
15%35%8%8%17%16%
1440
July1st to 10thNight
13%36%5%317%26%
1413
11th to 20thNight
21%37%5%5%9%23%
1566
21st to endNight
32%36%6%28%17%
1674
August1st to 10thNight
25%35%6%7%11%17%
1602
11th to 20thNight
22%34%7%5%12%19%
1682
21st to endNight
18%36%5%5%16%21%
1980
September1st to 10thNight
13%35%5%5%15%27%
1800
11th to 20thNight
20%36%7%11%17%9%
1800
21st to endNight
15%35%412%20%14%
2063
October1st to 10thNight
17%37%8%11%15%12%
2160
11th to 20thNight
18%36%5%12%15%14%
2160
21st to endNight
18%37%5%13%16%11%
2376
November1st to 10thNight
20%43%7%13%10%7%
2224
11th to 20thNight
21%40%7%16%10%6%
2472
21st to endNight
16%40%8%12%16%8%
2660
December1st to 10thNight
22%40%5%12%14%7%
2660
11th to 20thNight
41%33%7%9%9%1
3276
21st to endNight
41%30%12%11%5%1
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
28%8%30%18%14%3
307
11th to 20thDay
16%13%23%28%15%4
356
21st to endDay
13%9%26%30%19%3
374
February1st to 10thDay
17%11%21%25%21%5%
340
11th to 20thDay
15%17%26%23%15%4
357
21st to endDay
13%17%27%25%16%2
346
March1st to 10thDay
20%14%29%24%11%2
420
11th to 20thDay
20%10%30%22%12%6%
420
21st to endDay
14%18%32%24%11%2
462
April1st to 10thDay
16%14%30%24%13%2
420
11th to 20thDay
11%18%31%22%12%5%
412
21st to endDay
7%18%28%27%13%6%
420
May1st to 10thDay
7%17%29%29%16%3
423
11th to 20thDay
8%16%30%26%15%5%
448
21st to endDay
7%12%28%28%21%5%
485
June1st to 10thDay
6%14%26%32%16%6%
450
11th to 20thDay
212%31%39%12%4
450
21st to endDay
15%27%41%22%4
450
July1st to 10thDay
2321%49%23%2
446
11th to 20thDay
117%44%31%6%
444
21st to endDay
2114%53%24%6%
487
August1st to 10thDay
3322%46%23%4
447
11th to 20thDay
2122%40%26%8%
437
21st to endDay
1118%44%27%9%
495
September1st to 10thDay
1417%39%28%11%
450
11th to 20thDay
38%20%35%25%8%
450
21st to endDay
27%22%32%30%7%
450
October1st to 10thDay
5%6%24%28%24%13%
450
11th to 20thDay
6%8%19%22%30%14%
450
21st to endDay
10%7%21%25%26%11%
495
November1st to 10thDay
10%8%19%22%30%10%
449
11th to 20thDay
11%8%15%31%27%8%
268
21st to endDay
10%9%24%32%21%3
180
December1st to 10thDay
19%12%19%27%16%7%
180
11th to 20thDay
21%14%20%26%17%3
180
21st to endDay
21%15%21%28%14%1
198
January1st to 10thNight
21%8%11%30%25%6%
760
11th to 20thNight
17%6%14%33%24%5%
740
21st to endNight
17%6%14%32%27%5%
792
February1st to 10thNight
17%6%15%33%26%4
720
11th to 20thNight
14%9%19%31%21%6%
704
21st to endNight
15%12%20%30%20%3
592
March1st to 10thNight
20%9%18%28%21%3
720
11th to 20thNight
17%7%18%30%24%4
720
21st to endNight
14%10%26%31%18%2
792
April1st to 10thNight
12%9%26%31%18%3
720
11th to 20thNight
10%14%24%26%21%5%
711
21st to endNight
6%13%26%27%25%4
720
May1st to 10thNight
6%6%27%29%26%5%
604
11th to 20thNight
5%422%33%31%4
510
21st to endNight
6%9%20%36%27%3
389
June1st to 10thNight
45%22%40%27%2
360
11th to 20thNight
26%18%49%23%3
360
21st to endNight
3115%48%31%2
360
July1st to 10thNight
2111%42%41%3
363
11th to 20thNight
315%39%44%10%
522
21st to endNight
315%42%42%7%
591
August1st to 10thNight
418%40%40%6%
537
11th to 20thNight
211%41%38%7%
614
21st to endNight
319%35%45%9%
792
September1st to 10thNight
218%38%42%10%
720
11th to 20thNight
5%213%36%37%7%
720
21st to endNight
3313%33%38%9%
720
October1st to 10thNight
6%415%32%33%10%
720
11th to 20thNight
7%414%31%35%9%
720
21st to endNight
10%410%30%35%13%
792
November1st to 10thNight
9%416%27%34%10%
740
11th to 20thNight
12%312%33%32%8%
760
21st to endNight
10%6%15%36%27%6%
760
December1st to 10thNight
19%5%14%31%26%6%
760
11th to 20thNight
23%7%14%31%22%4
760
21st to endNight
20%9%19%29%21%2
836
Page generated at 2024-01-12 22:38:11. Version ac07

Copyright 2024 Attilla Danko


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