San Mateo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Mateo clear sky chart from 2005-11-06 to 2024-02-25.

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
60%
23868
15%
80367
13%
23780
63%
23780
15%
58529

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
51%
749
15%
4162
10%
736
53%
736
8%
2736
January11th to 20thNight
52%
750
12%
4100
13%
740
58%
740
7%
3163
January21st to endNight
52%
830
9%
4451
14%
814
56%
814
7%
3607
February1st to 10thNight
53%
760
16%
2470
14%
760
58%
760
16%
1769
February11th to 20thNight
48%
740
14%
2325
12%
740
53%
740
13%
1764
February21st to endNight
50%
610
15%
1829
13%
610
53%
610
16%
1366
March1st to 10thNight
45%
720
12%
2001
9%
720
49%
720
14%
1567
March11th to 20thNight
50%
720
16%
1980
13%
720
52%
720
13%
1573
March21st to endNight
48%
792
12%
2156
7%
792
51%
792
14%
1691
April1st to 10thNight
48%
720
14%
1800
7%
720
51%
720
16%
1408
April11th to 20thNight
48%
711
18%
1779
8%
711
52%
711
18%
1353
April21st to endNight
56%
720
18%
1800
9%
720
60%
720
24%
1296
May1st to 10thNight
61%
640
19%
1720
11%
640
64%
640
23%
1214
May11th to 20thNight
63%
501
16%
1564
13%
501
65%
501
18%
1117
May21st to endNight
55%
388
17%
1552
14%
388
62%
388
14%
1066
June1st to 10thNight
63%
360
13%
1440
13%
360
68%
360
14%
1005
June11th to 20thNight
73%
360
22%
1440
23%
360
79%
360
20%
895
June21st to endNight
73%
360
20%
1440
24%
360
77%
360
18%
918
July1st to 10thNight
76%
357
18%
1407
21%
357
78%
357
22%
855
July11th to 20thNight
79%
522
17%
1566
16%
522
79%
522
23%
1039
July21st to endNight
68%
591
13%
1674
11%
558
70%
558
19%
1165
August1st to 10thNight
64%
537
13%
1602
10%
534
65%
534
18%
1127
August11th to 20thNight
72%
637
19%
1705
13%
637
73%
637
25%
1176
August21st to endNight
75%
792
17%
1980
11%
792
75%
792
27%
1397
September1st to 10thNight
77%
720
25%
1800
18%
720
78%
720
30%
1221
September11th to 20thNight
67%
720
18%
1800
14%
720
68%
720
21%
1363
September21st to endNight
74%
720
21%
2051
21%
720
76%
720
27%
1353
October1st to 10thNight
70%
720
16%
2160
17%
720
73%
720
20%
1517
October11th to 20thNight
68%
720
21%
2160
21%
720
72%
720
19%
1532
October21st to endNight
68%
792
21%
2376
21%
792
71%
792
20%
1673
November1st to 10thNight
63%
740
13%
2234
11%
740
66%
740
16%
1686
November11th to 20thNight
64%
760
17%
2470
17%
760
66%
760
16%
1790
November21st to endNight
66%
760
16%
2626
18%
760
68%
760
17%
1800
December1st to 10thNight
54%
760
14%
2660
13%
760
57%
760
14%
1965
December11th to 20thNight
48%
760
10%
3250
12%
759
50%
759
7%
2668
December21st to endNight
43%
829
5%
4837
6%
817
47%
817
5%
3694

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%35%43445%8%52%
78584
Night
9%6%35%5%3445%8%47%
80743
TransparencyDay
21%37%8%11%14%9%
78305
Night
25%36%9%11%12%8%
80544
SeeingDay
9%11%27%33%16%4
14435
Night
11%5%16%33%28%6%
23907

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
15%6%36%6%4446%8%38%
2740
11th to 20thDay
13%9%5%9%8%5%5%5%46%32%
2860
21st to endDay
19%9%37%7%445%6%7%28%
3146
February1st to 10thDay
13%6%35%5%345%46%44%
1710
11th to 20thDay
11%7%46%5%3446%9%41%
1741
21st to endDay
11%6%35%5%245%47%48%
1521
March1st to 10thDay
12%7%46%435%5%6%10%37%
1956
11th to 20thDay
11%8%37%7%446%5%8%37%
1980
21st to endDay
10%6%25%6%345%5%8%46%
2200
April1st to 10thDay
11%6%35%5%345%6%8%44%
2160
11th to 20thDay
8%425%42345%7%55%
2129
21st to endDay
45%2432446%10%57%
2160
May1st to 10thDay
4435%33445%8%58%
2236
11th to 20thDay
5%6%2432335%10%56%
2325
21st to endDay
5%7%35%42445%9%52%
2723
June1st to 10thDay
5%5%2332445%10%56%
2520
11th to 20thDay
231331335%8%69%
2520
21st to endDay
34133235%5%8%64%
2520
July1st to 10thDay
15%2432345%9%64%
2508
11th to 20thDay
132442346%11%58%
2340
21st to endDay
132332345%10%64%
2546
August1st to 10thDay
25%25%4245%5%11%55%
2328
11th to 20thDay
142432335%10%63%
2193
21st to endDay
143432335%10%62%
2376
September1st to 10thDay
2323322338%69%
2160
11th to 20thDay
35%2443346%11%56%
2160
21st to endDay
3213222338%71%
1902
October1st to 10thDay
4324323337%66%
1800
11th to 20thDay
5%424434448%58%
1800
21st to endDay
7%5%25%433447%58%
1980
November1st to 10thDay
7%5%24435%45%9%53%
1842
11th to 20thDay
7%7%26%5%35%45%7%47%
1710
21st to endDay
10%4345%2335%8%53%
1550
December1st to 10thDay
10%5%47%5%35%5%6%8%43%
1520
11th to 20thDay
19%9%47%6%3446%7%30%
1928
21st to endDay
15%9%47%6%345%5%8%33%
2794
January1st to 10thNight
13%8%36%5%345%6%8%39%
4208
11th to 20thNight
16%10%48%7%45%5%5%5%31%
4110
21st to endNight
19%12%48%6%35%446%29%
4521
February1st to 10thNight
13%6%35%435%35%7%47%
2470
11th to 20thNight
10%6%36%5%45%5%5%8%43%
2323
21st to endNight
11%5%25%5%3446%7%48%
1829
March1st to 10thNight
14%7%45%5%346%6%8%39%
2001
11th to 20thNight
12%8%35%435%46%8%40%
1980
21st to endNight
11%7%35%434436%49%
2156
April1st to 10thNight
8%6%47%6%3447%8%45%
1800
11th to 20thNight
8%5%2442345%8%54%
1779
21st to endNight
3324425%45%9%59%
1800
May1st to 10thNight
3415%5%3336%9%57%
1720
11th to 20thNight
35%26%435%5%5%9%53%
1563
21st to endNight
5%6%25%5%35%5%7%8%49%
1552
June1st to 10thNight
4435%43446%10%53%
1440
11th to 20thNight
121333336%10%65%
1440
21st to endNight
142443335%8%62%
1440
July1st to 10thNight
14244343411%59%
1447
11th to 20thNight
14244345%8%13%53%
1620
21st to endNight
15%46%6%46%7%7%13%42%
1773
August1st to 10thNight
36%36%6%35%5%7%13%42%
1611
11th to 20thNight
4146%47%6%7%14%47%
1705
21st to endNight
1325%435%5%7%14%51%
1980
September1st to 10thNight
121442446%10%63%
1800
11th to 20thNight
35%345%3446%10%53%
1800
21st to endNight
2224423337%68%
2051
October1st to 10thNight
45%24423447%62%
2160
11th to 20thNight
5%4245%3445%7%57%
2160
21st to endNight
6%425%434447%58%
2376
November1st to 10thNight
7%5%2443445%8%53%
2234
11th to 20thNight
8%6%35%5%345%5%8%48%
2470
21st to endNight
8%5%144345%5%9%54%
2626
December1st to 10thNight
12%6%46%5%245%5%8%44%
2660
11th to 20thNight
23%9%46%6%335%6%7%29%
3276
21st to endNight
15%8%37%7%45%6%7%7%32%
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
31%28%11%22%6%1
2740
11th to 20thDay
41%28%7%10%9%5%
2860
21st to endDay
47%26%6%10%9%3
3146
February1st to 10thDay
24%35%5%14%14%7%
1710
11th to 20thDay
27%38%7%11%12%4
1750
21st to endDay
27%36%6%14%13%4
1521
March1st to 10thDay
27%38%8%15%10%3
1956
11th to 20thDay
30%39%8%13%8%2
1980
21st to endDay
26%40%9%13%10%2
2200
April1st to 10thDay
24%40%9%11%13%3
2160
11th to 20thDay
21%38%10%14%13%4
2132
21st to endDay
17%40%7%19%15%3
2160
May1st to 10thDay
15%40%6%13%20%5%
2236
11th to 20thDay
13%42%6%18%16%5%
2328
21st to endDay
17%43%9%16%15%1
2724
June1st to 10thDay
19%42%9%15%14%2
2520
11th to 20thDay
11%39%7%11%22%9%
2520
21st to endDay
12%37%9%6%19%17%
2520
July1st to 10thDay
9%38%10%312%27%
2439
11th to 20thDay
12%38%11%412%24%
2271
21st to endDay
10%37%11%415%23%
2405
August1st to 10thDay
14%39%11%416%16%
2312
11th to 20thDay
11%35%6%6%20%22%
2193
21st to endDay
11%36%10%5%17%21%
2376
September1st to 10thDay
9%35%6%417%28%
2160
11th to 20thDay
17%38%8%11%16%9%
2160
21st to endDay
9%36%414%20%16%
1902
October1st to 10thDay
16%37%6%12%18%12%
1800
11th to 20thDay
16%37%6%12%16%13%
1800
21st to endDay
17%39%6%14%14%12%
1980
November1st to 10thDay
22%43%7%12%10%6%
1842
11th to 20thDay
23%41%5%12%14%5%
1710
21st to endDay
18%39%6%11%17%8%
1550
December1st to 10thDay
21%41%8%12%13%5%
1520
11th to 20thDay
41%33%8%9%8%2
1928
21st to endDay
41%29%9%13%6%1
2794
January1st to 10thNight
30%29%15%18%5%2
4208
11th to 20thNight
42%28%9%8%7%5%
4110
21st to endNight
49%25%6%8%8%4
4521
February1st to 10thNight
23%35%7%13%13%8%
2470
11th to 20thNight
27%37%7%10%14%4
2325
21st to endNight
25%37%8%17%10%2
1829
March1st to 10thNight
27%39%9%12%10%3
2001
11th to 20thNight
30%38%6%15%9%3
1980
21st to endNight
27%38%8%13%10%3
2156
April1st to 10thNight
25%39%9%13%11%3
1800
11th to 20thNight
22%38%8%14%13%5%
1779
21st to endNight
16%37%8%20%14%5%
1800
May1st to 10thNight
17%37%6%15%18%7%
1720
11th to 20thNight
18%40%7%13%18%4
1564
21st to endNight
18%40%10%15%15%1
1552
June1st to 10thNight
19%41%9%14%15%2
1440
11th to 20thNight
11%38%7%10%21%12%
1440
21st to endNight
15%37%8%9%16%15%
1440
July1st to 10thNight
11%36%8%415%25%
1407
11th to 20thNight
13%37%12%6%7%24%
1566
21st to endNight
19%38%15%39%17%
1674
August1st to 10thNight
20%38%11%5%11%15%
1602
11th to 20thNight
15%37%11%413%19%
1705
21st to endNight
15%36%10%415%19%
1980
September1st to 10thNight
11%36%6%5%13%29%
1800
11th to 20thNight
21%38%10%9%14%9%
1800
21st to endNight
12%36%6%11%19%16%
2051
October1st to 10thNight
17%38%8%11%13%13%
2160
11th to 20thNight
19%38%5%11%13%15%
2160
21st to endNight
17%39%5%12%15%12%
2376
November1st to 10thNight
22%41%10%11%10%6%
2234
11th to 20thNight
20%40%8%14%12%5%
2470
21st to endNight
16%40%7%12%15%10%
2626
December1st to 10thNight
23%40%6%10%14%7%
2660
11th to 20thNight
41%34%6%9%8%2
3276
21st to endNight
40%31%11%10%5%2
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
27%10%26%21%15%1
303
11th to 20thDay
16%11%24%31%14%3
370
21st to endDay
14%11%26%29%17%3
407
February1st to 10thDay
15%15%25%25%18%2
370
11th to 20thDay
16%17%31%25%11%1
401
21st to endDay
13%16%30%27%13%1
363
March1st to 10thDay
18%19%32%21%9%2
420
11th to 20thDay
18%15%29%21%13%4
420
21st to endDay
12%19%32%27%7%2
462
April1st to 10thDay
15%18%33%23%10%1
420
11th to 20thDay
12%21%34%24%7%3
412
21st to endDay
5%21%31%28%10%5%
420
May1st to 10thDay
8%18%34%27%11%2
423
11th to 20thDay
9%16%36%27%10%2
448
21st to endDay
8%16%33%28%11%3
485
June1st to 10thDay
7%12%33%32%13%3
450
11th to 20thDay
311%33%39%11%3
450
21st to endDay
37%31%40%15%4
450
July1st to 10thDay
5%426%49%15%1
446
11th to 20thDay
2222%52%20%2
444
21st to endDay
3124%49%18%6%
487
August1st to 10thDay
5%426%45%16%4
447
11th to 20thDay
3224%43%22%5%
437
21st to endDay
3322%46%22%4
495
September1st to 10thDay
4417%44%22%8%
450
11th to 20thDay
410%25%37%17%6%
450
21st to endDay
39%23%34%26%6%
450
October1st to 10thDay
38%29%32%20%9%
450
11th to 20thDay
6%10%21%29%26%8%
450
21st to endDay
10%8%23%30%22%7%
495
November1st to 10thDay
8%11%22%26%26%7%
438
11th to 20thDay
7%9%17%33%26%8%
270
21st to endDay
9%7%24%31%27%2
194
December1st to 10thDay
13%17%20%23%21%6%
180
11th to 20thDay
14%14%21%29%18%4
180
21st to endDay
19%10%30%26%14%1
198
January1st to 10thNight
19%6%16%31%22%5%
760
11th to 20thNight
15%7%15%32%25%6%
760
21st to endNight
18%6%15%34%24%4
836
February1st to 10thNight
17%7%16%33%23%4
760
11th to 20thNight
13%10%19%33%21%5%
744
21st to endNight
13%11%20%33%20%3
610
March1st to 10thNight
17%9%23%27%22%3
720
11th to 20thNight
17%8%16%31%23%4
720
21st to endNight
16%9%22%33%18%2
792
April1st to 10thNight
12%8%24%34%19%3
720
11th to 20thNight
12%12%23%30%18%5%
711
21st to endNight
7%8%26%33%22%5%
720
May1st to 10thNight
6%5%22%38%23%5%
640
11th to 20thNight
8%417%36%30%4
501
21st to endNight
9%9%22%36%20%4
389
June1st to 10thNight
6%420%41%27%3
360
11th to 20thNight
1418%48%28%3
360
21st to endNight
4414%37%38%3
360
July1st to 10thNight
4212%34%43%4
357
11th to 20thNight
317%38%40%10%
522
21st to endNight
5%29%34%41%9%
591
August1st to 10thNight
9%412%34%34%7%
537
11th to 20thNight
5%211%38%36%7%
637
21st to endNight
4112%36%38%8%
792
September1st to 10thNight
3111%33%40%12%
720
11th to 20thNight
8%314%35%33%7%
720
21st to endNight
3314%31%39%11%
720
October1st to 10thNight
7%313%34%34%10%
720
11th to 20thNight
7%412%29%38%10%
720
21st to endNight
8%412%30%34%13%
792
November1st to 10thNight
9%416%28%34%9%
740
11th to 20thNight
11%312%35%32%7%
760
21st to endNight
11%413%38%28%6%
760
December1st to 10thNight
16%7%15%33%24%5%
760
11th to 20thNight
23%6%16%31%20%3
760
21st to endNight
20%9%21%29%19%2
836
Page generated at 2024-02-22 03:05:43. Version ac07

Copyright 2024 Attilla Danko


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