Half Moon Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Half Moon Bay clear sky chart from 2005-11-05 to

2017-09-12
.

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
58%
15404
23%
46868
20%
15367
62%
15367
29%
28780

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
58%
717
18%
2357
17%
716
62%
716
26%
1455
January16th to endNight
54%
768
24%
2496
25%
768
57%
768
25%
1574
February1st to 15thNight
51%
700
22%
2288
21%
700
56%
700
23%
1479
February16th to endNight
46%
632
20%
1909
16%
632
53%
632
23%
1269
March1st to 15thNight
50%
720
17%
1986
15%
720
53%
720
25%
1344
March16th to endNight
46%
768
19%
2100
14%
768
51%
768
27%
1387
April1st to 15thNight
44%
719
21%
1799
10%
719
48%
719
28%
1207
April16th to endNight
50%
720
24%
1800
10%
720
55%
720
38%
1092
May1st to 15thNight
57%
599
23%
1679
14%
599
61%
599
38%
971
May16th to endNight
51%
422
19%
1545
15%
422
58%
422
24%
922
June1st to 15thNight
56%
360
20%
1440
19%
360
64%
360
24%
824
June16th to endNight
75%
360
30%
1440
39%
360
78%
360
39%
654
July1st to 15thNight
71%
413
23%
1433
25%
413
74%
413
30%
799
July16th to endNight
62%
564
22%
1593
21%
531
63%
531
22%
1065
August1st to 15thNight
62%
544
20%
1617
17%
541
63%
541
23%
1072
August16th to endNight
68%
764
25%
1910
15%
764
69%
764
32%
1284
September1st to 15thNight
75%
706
32%
1765
22%
706
76%
706
42%
1069
September16th to endNight
71%
656
34%
1809
29%
656
74%
656
46%
979
October1st to 15thNight
65%
660
26%
1980
26%
660
70%
660
38%
1113
October16th to endNight
66%
704
30%
2112
30%
704
69%
704
34%
1240
November1st to 15thNight
62%
700
26%
2160
26%
700
66%
700
34%
1250
November16th to endNight
61%
720
24%
2442
25%
720
65%
720
29%
1399
December1st to 15thNight
52%
720
20%
2520
18%
720
59%
720
22%
1601
December16th to endNight
45%
768
19%
2688
17%
768
51%
768
20%
1731

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%6%2442445%8%47%
47786
Night
8%6%35%5%3445%8%45%
47058
TransparencyDay
34%5%8%18%21%12%
47476
Night
36%5%7%17%19%12%
46869
SeeingDay
10%11%25%32%16%3
6041
Night
10%6%12%27%32%9%
15413

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
15%5%34423348%44%
1578
16th to endDay
15%5%35%4345%46%43%
1728
February1st to 15thDay
16%7%25%425%345%40%
1576
16th to endDay
15%9%35%5%3345%7%36%
1565
March1st to 15thDay
13%8%36%5%3346%9%35%
1971
16th to endDay
11%8%35%6%35%5%47%39%
2122
April1st to 15thDay
12%6%345%245%47%41%
2149
16th to endDay
7%5%24423349%52%
2160
May1st to 15thDay
45%2442445%9%50%
2268
16th to endDay
9%9%35%333448%44%
2565
June1st to 15thDay
6%6%245%35%5%47%48%
2520
16th to endDay
34132233410%60%
2520
July1st to 15thDay
15%24435%5%5%10%50%
2437
16th to endDay
15%144345%5%12%49%
2468
August1st to 15thDay
26%25%5%36%5%6%11%45%
2334
16th to endDay
15%2443446%13%49%
2292
September1st to 15thDay
25%23324349%56%
2114
16th to endDay
3422213349%61%
1820
October1st to 15thDay
7%413323347%56%
1650
16th to endDay
8%5%245%23346%52%
1760
November1st to 15thDay
7%5%144345%5%8%48%
1698
16th to endDay
11%8%35%5%23345%46%
1515
December1st to 15thDay
15%9%45%5%23446%38%
1440
16th to endDay
18%7%35%423247%39%
1536
January1st to 15thNight
14%7%2443445%7%41%
2357
16th to endNight
15%6%36%423246%44%
2496
February1st to 15thNight
12%8%36%43435%6%40%
2276
16th to endNight
13%8%35%5%35%45%9%36%
1909
March1st to 15thNight
14%6%45%42445%7%39%
1986
16th to endNight
12%9%25%5%3335%7%42%
2100
April1st to 15thNight
10%6%35%435%5%6%8%41%
1799
16th to endNight
7%414425%338%54%
1800
May1st to 15thNight
25%36%33435%7%53%
1679
16th to endNight
6%7%45%5%44447%46%
1544
June1st to 15thNight
36%25%5%35%5%5%8%45%
1440
16th to endNight
142442345%7%60%
1440
July1st to 15thNight
15%245%47%6%7%12%41%
1519
16th to endNight
17%410%8%48%5%6%9%32%
1701
August1st to 15thNight
27%5%9%7%5%6%5%5%11%32%
1626
16th to endNight
5%38%8%5%6%5%7%10%38%
1910
September1st to 15thNight
2325%6%5%5%45%10%48%
1765
16th to endNight
2424422348%59%
1809
October1st to 15thNight
5%5%25%5%23347%55%
1980
16th to endNight
6%5%25%42445%6%51%
2112
November1st to 15thNight
8%5%24414347%52%
2160
16th to endNight
8%5%35%5%23347%50%
2442
December1st to 15thNight
15%7%35%5%24346%40%
2520
16th to endNight
17%7%25%423345%42%
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
39%412%18%15%9%
1578
16th to endDay
41%5%9%12%18%12%
1728
February1st to 15thDay
45%48%18%18%4
1576
16th to endDay
46%5%8%24%11%4
1565
March1st to 15thDay
44%5%12%19%12%5%
1971
16th to endDay
44%5%13%19%13%2
2122
April1st to 15thDay
42%413%21%15%2
2149
16th to endDay
30%415%24%19%5%
2160
May1st to 15thDay
29%5%7%25%24%6%
2268
16th to endDay
38%5%10%20%19%4
2569
June1st to 15thDay
34%6%8%18%20%11%
2520
16th to endDay
21%4316%33%19%
2520
July1st to 15thDay
26%7%28%21%32%
2294
16th to endDay
27%6%310%27%25%
2313
August1st to 15thDay
32%6%110%30%18%
2318
16th to endDay
25%6%216%30%18%
2292
September1st to 15thDay
24%4214%28%25%
2114
16th to endDay
22%3424%27%17%
1820
October1st to 15thDay
26%48%21%24%14%
1650
16th to endDay
33%210%23%18%10%
1760
November1st to 15thDay
34%5%11%26%15%7%
1698
16th to endDay
39%5%9%17%24%4
1515
December1st to 15thDay
47%311%15%18%4
1440
16th to endDay
45%412%16%16%4
1536
January1st to 15thNight
40%411%19%14%8%
2357
16th to endNight
42%48%12%16%15%
2496
February1st to 15thNight
43%47%18%17%7%
2288
16th to endNight
44%5%10%24%11%2
1909
March1st to 15thNight
44%411%20%13%5%
1986
16th to endNight
42%412%18%16%5%
2100
April1st to 15thNight
40%5%14%21%16%2
1799
16th to endNight
29%5%11%25%19%8%
1800
May1st to 15thNight
29%5%7%21%26%10%
1680
16th to endNight
36%7%10%20%18%6%
1545
June1st to 15thNight
32%10%8%16%20%12%
1440
16th to endNight
22%4213%30%25%
1440
July1st to 15thNight
27%11%16%19%33%
1433
16th to endNight
43%8%2414%25%
1593
August1st to 15thNight
41%8%18%20%20%
1617
16th to endNight
36%9%19%20%23%
1910
September1st to 15thNight
27%6%28%23%30%
1765
16th to endNight
24%3320%25%21%
1809
October1st to 15thNight
29%47%19%22%17%
1980
16th to endNight
33%45%21%20%14%
2112
November1st to 15thNight
31%6%12%25%17%7%
2160
16th to endNight
35%38%23%20%8%
2442
December1st to 15thNight
43%5%8%16%20%6%
2520
16th to endNight
44%5%10%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
24%9%21%25%14%3
207
16th to endDay
18%11%22%25%17%3
256
February1st to 15thDay
22%12%23%23%15%1
236
16th to endDay
19%16%27%22%12%1
235
March1st to 15thDay
18%18%23%22%14%2
270
16th to endDay
13%19%35%23%5%1
288
April1st to 15thDay
16%21%33%19%7%1
269
16th to endDay
10%24%31%24%5%2
270
May1st to 15thDay
6%18%33%30%9%1
288
16th to endDay
16%16%21%30%12%3
330
June1st to 15thDay
7%14%35%32%8%1
315
16th to endDay
15%24%43%20%3
315
July1st to 15thDay
2321%45%22%2
305
16th to endDay
1120%48%19%7%
327
August1st to 15thDay
2422%42%24%3
315
16th to endDay
1121%45%24%6%
332
September1st to 15thDay
4420%39%22%9%
300
16th to endDay
38%21%32%25%8%
255
October1st to 15thDay
7%7%25%35%17%5%
255
16th to endDay
12%9%29%25%21%2
272
November1st to 15thDay
10%7%19%23%29%8%
204
16th to endDay
419%23%36%16%
73
December1st to 15thDay
21%13%25%26%13%
60
16th to endDay
15%18%15%20%23%6%
64
January1st to 15thNight
17%6%8%30%29%7%
720
16th to endNight
17%7%9%28%28%8%
768
February1st to 15thNight
16%8%13%28%28%5%
704
16th to endNight
17%10%17%27%21%6%
632
March1st to 15thNight
16%9%12%25%29%5%
720
16th to endNight
16%9%18%29%20%4
768
April1st to 15thNight
13%12%20%29%19%4
719
16th to endNight
9%11%21%25%24%7%
720
May1st to 15thNight
5%421%31%29%6%
600
16th to endNight
10%8%16%29%26%8%
423
June1st to 15thNight
5%7%20%35%27%5%
360
16th to endNight
149%35%43%5%
360
July1st to 15thNight
425%25%47%14%
413
16th to endNight
33322%48%18%
564
August1st to 15thNight
5%3422%50%13%
544
16th to endNight
226%25%50%12%
764
September1st to 15thNight
315%24%48%16%
706
16th to endNight
338%26%43%14%
656
October1st to 15thNight
8%49%26%38%12%
660
16th to endNight
9%5%8%27%32%16%
704
November1st to 15thNight
10%412%27%35%11%
700
16th to endNight
10%6%11%31%30%9%
720
December1st to 15thNight
16%7%13%28%25%7%
720
16th to endNight
21%8%17%28%20%3
768
Page generated at 2017-09-13 04:39:21. Version ac04

Copyright 2017 A. Danko


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