Glacier Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glacier Point clear sky chart from 2005-11-05 to 2017-08-12.

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
65%
15189
29%
46493
25%
15156
70%
15156
43%
24272

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
54%
716
23%
2506
20%
716
62%
716
33%
1355
January16th to endNight
50%
768
27%
2501
20%
768
60%
768
30%
1448
February1st to 15thNight
53%
700
26%
2177
24%
697
60%
697
31%
1290
February16th to endNight
50%
632
22%
1895
21%
632
55%
632
29%
1194
March1st to 15thNight
51%
720
20%
2130
18%
720
56%
720
30%
1324
March16th to endNight
53%
768
21%
2010
14%
768
58%
768
36%
1243
April1st to 15thNight
53%
719
21%
1799
10%
719
58%
719
35%
1153
April16th to endNight
56%
720
23%
1800
11%
720
60%
720
43%
1054
May1st to 15thNight
66%
605
27%
1685
18%
605
69%
605
50%
866
May16th to endNight
69%
405
26%
1528
28%
405
72%
405
40%
713
June1st to 15thNight
77%
360
28%
1440
33%
360
82%
360
46%
594
June16th to endNight
87%
360
38%
1440
48%
360
92%
360
70%
460
July1st to 15thNight
93%
340
33%
1360
44%
340
94%
340
70%
440
July16th to endNight
86%
444
37%
1479
39%
417
88%
417
58%
593
August1st to 15thNight
87%
644
36%
1694
26%
641
87%
641
72%
776
August16th to endNight
91%
700
42%
1750
27%
700
92%
700
78%
799
September1st to 15thNight
88%
660
44%
1650
31%
660
90%
660
75%
772
September16th to endNight
80%
656
42%
1790
36%
656
84%
656
70%
800
October1st to 15thNight
65%
660
32%
1935
28%
660
72%
660
50%
970
October16th to endNight
72%
704
36%
2131
34%
704
78%
704
54%
1001
November1st to 15thNight
69%
700
31%
2275
32%
700
74%
700
43%
1139
November16th to endNight
59%
720
30%
2340
28%
720
66%
720
39%
1248
December1st to 15thNight
52%
720
22%
2490
17%
720
61%
720
28%
1442
December16th to endNight
42%
768
24%
2688
19%
768
53%
768
25%
1598

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%6%23213335%60%
47485
Night
6%6%23212335%61%
46681
TransparencyDay
27%39%21%24%14%
47163
Night
25%39%22%25%13%
46504
SeeingDay
13%14%36%23%8%3
5673
Night
10%415%32%29%8%
15199

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
10%9%13223346%51%
1432
16th to endDay
10%11%44212346%46%
1722
February1st to 15thDay
8%10%34213446%49%
1676
16th to endDay
10%14%6%5%32332442%
1579
March1st to 15thDay
7%13%5%6%32436%7%39%
1827
16th to endDay
9%13%5%5%423346%41%
2214
April1st to 15thDay
9%13%44323445%43%
2149
16th to endDay
9%10%13313346%51%
2160
May1st to 15thDay
6%7%13213337%58%
2265
16th to endDay
8%9%23323446%51%
2583
June1st to 15thDay
6%413413335%62%
2520
16th to endDay
1112112381%
2520
July1st to 15thDay
11212345%76%
2520
16th to endDay
211221223475%
2586
August1st to 15thDay
11121122380%
2171
16th to endDay
11111222380%
2100
September1st to 15thDay
11221223377%
1980
16th to endDay
211231245%471%
1840
October1st to 15thDay
7%41221235%5%62%
1693
16th to endDay
6%41232233464%
1741
November1st to 15thDay
7%423324435%58%
1584
16th to endDay
8%7%23324345%54%
1620
December1st to 15thDay
14%7%34423345%46%
1467
16th to endDay
13%9%45%313447%43%
1536
January1st to 15thNight
8%8%23313446%53%
2506
16th to endNight
8%9%33323446%50%
2501
February1st to 15thNight
10%8%3431435%7%47%
2176
16th to endNight
9%11%5%4323347%44%
1895
March1st to 15thNight
8%10%44423345%48%
2130
16th to endNight
7%10%43223247%50%
2010
April1st to 15thNight
6%11%34433347%48%
1799
16th to endNight
6%6%23313335%59%
1800
May1st to 15thNight
3412113346%67%
1685
16th to endNight
46%12212346%63%
1527
June1st to 15thNight
4212213336%68%
1440
16th to endNight
11111385%
1440
July1st to 15thNight
221123480%
1440
16th to endNight
321121123474%
1580
August1st to 15thNight
11121112380%
1703
16th to endNight
11111212384%
1750
September1st to 15thNight
11121111283%
1650
16th to endNight
21121212379%
1790
October1st to 15thNight
5%412212235%67%
1935
16th to endNight
5%21222235%70%
2131
November1st to 15thNight
7%5%12212248%61%
2275
16th to endNight
5%7%2332335%5%57%
2340
December1st to 15thNight
11%8%23324346%49%
2490
16th to endNight
14%10%34312346%46%
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
34%310%21%20%8%
1432
16th to endDay
39%5%9%17%15%12%
1722
February1st to 15thDay
36%49%25%15%9%
1676
16th to endDay
46%47%23%15%2
1579
March1st to 15thDay
44%412%15%15%6%
1827
16th to endDay
44%5%15%19%13%2
2214
April1st to 15thDay
42%5%13%21%15%2
2149
16th to endDay
34%5%13%27%15%3
2160
May1st to 15thDay
26%313%33%20%3
2265
16th to endDay
33%413%27%18%3
2587
June1st to 15thDay
24%410%24%25%10%
2520
16th to endDay
10%1319%42%22%
2520
July1st to 15thDay
10%2411%31%39%
2371
16th to endDay
13%27%13%24%38%
2425
August1st to 15thDay
10%1315%31%37%
2155
16th to endDay
10%1414%41%27%
2100
September1st to 15thDay
11%2417%37%26%
1980
16th to endDay
14%37%27%31%15%
1840
October1st to 15thDay
23%38%22%30%10%
1693
16th to endDay
23%36%26%27%12%
1741
November1st to 15thDay
29%310%26%20%9%
1584
16th to endDay
31%5%8%19%29%6%
1620
December1st to 15thDay
40%49%20%17%6%
1467
16th to endDay
41%49%17%15%11%
1536
January1st to 15thNight
31%48%22%23%9%
2506
16th to endNight
33%5%7%18%18%15%
2501
February1st to 15thNight
34%47%25%17%9%
2187
16th to endNight
40%311%21%18%3
1895
March1st to 15thNight
37%410%19%18%8%
2130
16th to endNight
34%416%23%18%3
2010
April1st to 15thNight
35%5%14%25%15%4
1799
16th to endNight
27%414%30%18%3
1800
May1st to 15thNight
19%5%12%34%24%4
1686
16th to endNight
22%413%30%23%5%
1528
June1st to 15thNight
17%312%24%31%9%
1440
16th to endNight
7%2318%44%23%
1440
July1st to 15thNight
7%15%12%32%39%
1360
16th to endNight
14%2413%26%38%
1479
August1st to 15thNight
11%1316%28%38%
1694
16th to endNight
8%1217%45%24%
1750
September1st to 15thNight
10%1315%44%25%
1650
16th to endNight
11%15%32%32%16%
1790
October1st to 15thNight
20%37%27%30%9%
1935
16th to endNight
17%38%23%35%12%
2131
November1st to 15thNight
23%39%26%24%12%
2275
16th to endNight
28%39%21%27%8%
2340
December1st to 15thNight
36%411%21%19%7%
2490
16th to endNight
39%39%16%17%13%
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
45%11%21%15%33
60
16th to endDay
21%13%27%23%10%3
250
February1st to 15thDay
21%16%27%20%11%2
253
16th to endDay
26%19%29%19%41
238
March1st to 15thDay
18%22%28%16%11%1
270
16th to endDay
18%25%31%17%6%
288
April1st to 15thDay
24%20%31%18%4
269
16th to endDay
20%22%35%18%2
270
May1st to 15thDay
21%17%35%18%5%2
288
16th to endDay
22%16%23%25%7%4
330
June1st to 15thDay
11%18%42%16%7%4
315
16th to endDay
312%37%30%9%6%
315
July1st to 15thDay
3246%32%9%5%
305
16th to endDay
38%42%32%6%6%
327
August1st to 15thDay
213%54%17%8%4
300
16th to endDay
27%48%27%7%5%
268
September1st to 15thDay
49%49%26%9%2
255
16th to endDay
8%12%40%28%8%1
255
October1st to 15thDay
11%20%33%26%6%1
255
16th to endDay
12%13%36%31%4
253
November1st to 15thDay
8%7%13%24%34%11%
90
16th to endDay
15%14%26%27%13%2
90
December1st to 15thDay
20%9%38%21%9%1
65
16th to endDay
18%6%29%23%17%4
64
January1st to 15thNight
13%421%29%21%9%
720
16th to endNight
15%8%21%27%18%7%
768
February1st to 15thNight
14%5%19%32%19%7%
704
16th to endNight
18%7%19%28%20%5%
632
March1st to 15thNight
15%8%18%30%20%6%
720
16th to endNight
14%8%17%30%23%4
768
April1st to 15thNight
12%7%20%34%20%5%
719
16th to endNight
11%5%20%30%23%8%
720
May1st to 15thNight
5%419%37%26%6%
606
16th to endNight
9%213%31%35%7%
406
June1st to 15thNight
6%39%33%42%5%
360
16th to endNight
27%41%43%4
360
July1st to 15thNight
232%60%4
340
16th to endNight
3326%53%13%
444
August1st to 15thNight
16%37%43%9%
644
16th to endNight
1433%52%8%
700
September1st to 15thNight
2433%45%13%
660
16th to endNight
2112%31%37%14%
656
October1st to 15thNight
7%418%27%30%11%
660
16th to endNight
8%313%31%29%14%
704
November1st to 15thNight
9%5%12%36%27%9%
700
16th to endNight
10%420%34%22%7%
720
December1st to 15thNight
18%418%35%16%6%
720
16th to endNight
21%8%21%28%16%3
768
Page generated at 2017-08-13 11:16:28. Version ac04

Copyright 2017 A. Danko


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