This page made possible by the sponsorship of: Fremont Peak Observatory Association.

Fremont Peak
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fremont Peak clear sky chart from 2005-11-05 to 2017-09-10.

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
66%
15457
25%
46847
24%
15421
68%
15421
36%
26726

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
64%
716
19%
2381
20%
716
67%
716
30%
1404
January16th to endNight
61%
768
24%
2496
27%
768
63%
768
28%
1534
February1st to 15thNight
61%
700
23%
2256
24%
700
64%
700
26%
1413
February16th to endNight
55%
632
22%
1895
20%
632
59%
632
28%
1202
March1st to 15thNight
57%
720
18%
2028
17%
720
59%
720
29%
1314
March16th to endNight
56%
768
20%
2073
16%
768
59%
768
30%
1365
April1st to 15thNight
53%
719
22%
1799
14%
719
55%
719
32%
1201
April16th to endNight
60%
720
24%
1800
12%
720
63%
720
43%
1072
May1st to 15thNight
66%
673
22%
1753
15%
673
67%
673
41%
1041
May16th to endNight
63%
388
22%
1511
21%
388
67%
388
27%
819
June1st to 15thNight
67%
360
23%
1440
26%
360
71%
360
30%
743
June16th to endNight
81%
360
31%
1440
40%
360
83%
360
52%
560
July1st to 15thNight
82%
382
27%
1402
32%
382
82%
382
48%
604
July16th to endNight
73%
564
28%
1593
25%
531
74%
531
45%
806
August1st to 15thNight
71%
595
25%
1668
19%
592
71%
592
44%
901
August16th to endNight
80%
764
32%
1910
21%
764
80%
764
59%
1016
September1st to 15thNight
83%
700
37%
1750
27%
700
83%
700
62%
903
September16th to endNight
78%
656
38%
1784
35%
656
79%
656
54%
916
October1st to 15thNight
74%
660
29%
1980
31%
660
76%
660
44%
1053
October16th to endNight
71%
704
32%
2112
35%
704
73%
704
41%
1158
November1st to 15thNight
69%
700
30%
2192
32%
700
71%
700
39%
1186
November16th to endNight
67%
720
25%
2376
27%
720
70%
720
35%
1290
December1st to 15thNight
61%
720
23%
2520
24%
720
64%
720
26%
1546
December16th to endNight
53%
768
21%
2688
20%
768
58%
768
23%
1679

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%24323347%56%
47782
Night
8%5%24423447%51%
47035
TransparencyDay
27%48%18%23%17%
47470
Night
31%49%17%21%15%
46848
SeeingDay
9%8%27%34%15%4
5998
Night
9%311%30%33%11%
15467

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
11%7%25%423347%47%
1555
16th to endDay
15%7%35%313435%45%
1728
February1st to 15thDay
15%7%24423445%45%
1607
16th to endDay
16%8%36%5%15%45%6%38%
1579
March1st to 15thDay
12%5%35%435%5%6%9%38%
1931
16th to endDay
11%7%35%6%245%47%41%
2151
April1st to 15thDay
11%7%45%433447%43%
2149
16th to endDay
8%5%24323346%54%
2160
May1st to 15thDay
4423223448%59%
2195
16th to endDay
6%7%2442435%8%50%
2599
June1st to 15thDay
45%24323347%57%
2520
16th to endDay
1212212236%72%
2520
July1st to 15thDay
212323237%69%
2472
16th to endDay
1212312237%69%
2468
August1st to 15thDay
1424413238%64%
2283
16th to endDay
212213348%69%
2292
September1st to 15thDay
1311112237%73%
2097
16th to endDay
3312212335%69%
1843
October1st to 15thDay
5%313323436%62%
1650
16th to endDay
5%414413245%61%
1760
November1st to 15thDay
9%5%25%423336%54%
1666
16th to endDay
10%5%2332335%6%52%
1581
December1st to 15thDay
15%8%26%41444441%
1440
16th to endDay
15%7%24423446%43%
1536
January1st to 15thNight
10%6%2442345%7%47%
2381
16th to endNight
13%5%25%423345%47%
2496
February1st to 15thNight
12%6%24435%45%6%43%
2245
16th to endNight
14%6%3443335%7%43%
1895
March1st to 15thNight
11%7%36%423447%44%
2028
16th to endNight
10%8%35%4235%47%44%
2073
April1st to 15thNight
11%5%345%2445%6%45%
1799
16th to endNight
7%5%23313348%57%
1800
May1st to 15thNight
35%25%5%34447%53%
1753
16th to endNight
47%46%423446%51%
1510
June1st to 15thNight
46%36%3345%5%7%50%
1440
16th to endNight
1224322336%65%
1440
July1st to 15thNight
132443435%8%58%
1485
16th to endNight
16%27%5%345%5%9%49%
1701
August1st to 15thNight
6%37%7%35%447%48%
1677
16th to endNight
425%43445%8%56%
1910
September1st to 15thNight
2313312346%66%
1750
16th to endNight
25%12412236%66%
1784
October1st to 15thNight
7%413323347%58%
1980
16th to endNight
6%5%15%32335%5%58%
2112
November1st to 15thNight
7%5%34323336%57%
2192
16th to endNight
8%5%33323348%52%
2376
December1st to 15thNight
13%7%24424445%46%
2520
16th to endNight
17%6%24423446%44%
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
37%49%21%16%10%
1555
16th to endDay
42%5%7%12%20%12%
1728
February1st to 15thDay
40%48%18%20%6%
1607
16th to endDay
47%5%8%22%13%2
1579
March1st to 15thDay
40%8%11%17%16%5%
1931
16th to endDay
41%6%14%17%16%2
2151
April1st to 15thDay
41%5%10%23%16%2
2149
16th to endDay
29%6%12%24%20%6%
2160
May1st to 15thDay
21%5%10%27%27%6%
2195
16th to endDay
30%6%10%24%22%5%
2603
June1st to 15thDay
25%5%10%19%24%15%
2520
16th to endDay
11%27%16%30%31%
2520
July1st to 15thDay
13%25%7%22%48%
2327
16th to endDay
11%35%10%25%42%
2313
August1st to 15thDay
15%2412%26%38%
2267
16th to endDay
10%25%14%33%33%
2292
September1st to 15thDay
11%3413%31%36%
2097
16th to endDay
16%2422%34%19%
1843
October1st to 15thDay
22%5%8%21%25%17%
1650
16th to endDay
24%47%22%23%17%
1760
November1st to 15thDay
32%49%19%25%7%
1666
16th to endDay
33%39%18%27%7%
1581
December1st to 15thDay
44%410%13%19%7%
1440
16th to endDay
42%5%12%16%16%6%
1536
January1st to 15thNight
35%5%11%19%19%8%
2381
16th to endNight
39%49%13%18%14%
2496
February1st to 15thNight
39%5%8%17%18%8%
2256
16th to endNight
40%411%25%14%3
1895
March1st to 15thNight
39%5%13%17%16%7%
2028
16th to endNight
39%6%12%18%16%6%
2073
April1st to 15thNight
38%6%12%24%15%3
1799
16th to endNight
27%5%13%24%21%7%
1800
May1st to 15thNight
28%5%9%19%26%10%
1754
16th to endNight
33%5%11%19%24%5%
1511
June1st to 15thNight
28%7%11%14%20%17%
1440
16th to endNight
16%26%12%28%33%
1440
July1st to 15thNight
18%45%8%19%43%
1402
16th to endNight
23%38%11%17%35%
1593
August1st to 15thNight
26%36%13%18%31%
1668
16th to endNight
17%37%12%25%31%
1910
September1st to 15thNight
16%2411%26%38%
1750
16th to endNight
19%3317%33%23%
1784
October1st to 15thNight
25%49%21%21%18%
1980
16th to endNight
27%46%20%23%17%
2112
November1st to 15thNight
29%310%20%27%8%
2192
16th to endNight
30%411%18%25%9%
2376
December1st to 15thNight
38%6%9%16%21%8%
2520
16th to endNight
41%5%11%16%16%7%
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
21%7%27%26%15%
183
16th to endDay
19%7%25%27%17%1
256
February1st to 15thDay
17%9%26%23%21%1
242
16th to endDay
19%13%27%28%7%2
238
March1st to 15thDay
17%15%27%23%13%2
270
16th to endDay
14%17%36%22%7%1
288
April1st to 15thDay
17%21%31%21%8%
269
16th to endDay
11%19%36%24%6%2
270
May1st to 15thDay
9%14%38%29%5%2
288
16th to endDay
11%13%30%28%11%4
330
June1st to 15thDay
6%7%41%29%9%5%
315
16th to endDay
1327%40%20%5%
315
July1st to 15thDay
120%48%20%7%
305
16th to endDay
1117%52%18%9%
327
August1st to 15thDay
2321%47%18%6%
315
16th to endDay
118%48%20%10%
332
September1st to 15thDay
3222%42%19%9%
294
16th to endDay
6%6%20%36%23%7%
255
October1st to 15thDay
6%12%29%34%14%3
255
16th to endDay
10%7%29%34%14%2
272
November1st to 15thDay
8%6%18%27%27%10%
172
16th to endDay
12%6%19%38%22%1
83
December1st to 15thDay
23%6%28%33%8%
60
16th to endDay
17%9%12%32%25%3
64
January1st to 15thNight
13%49%34%28%10%
720
16th to endNight
15%410%30%27%10%
768
February1st to 15thNight
15%411%31%28%8%
704
16th to endNight
17%5%12%35%22%6%
632
March1st to 15thNight
13%413%33%26%8%
720
16th to endNight
13%5%16%35%25%4
768
April1st to 15thNight
12%5%18%36%23%3
719
16th to endNight
8%6%19%30%26%8%
720
May1st to 15thNight
4216%38%28%9%
674
16th to endNight
7%5%14%31%31%8%
389
June1st to 15thNight
7%314%35%32%7%
360
16th to endNight
36%34%46%7%
360
July1st to 15thNight
26%18%55%16%
382
16th to endNight
210%13%49%23%
564
August1st to 15thNight
329%22%50%13%
595
16th to endNight
27%22%52%15%
764
September1st to 15thNight
415%20%52%16%
700
16th to endNight
5%16%26%40%18%
656
October1st to 15thNight
8%28%33%32%14%
660
16th to endNight
8%29%27%31%20%
704
November1st to 15thNight
9%210%32%30%14%
700
16th to endNight
10%111%33%32%10%
720
December1st to 15thNight
14%5%10%36%26%7%
720
16th to endNight
19%5%13%34%22%5%
768
Page generated at 2017-09-11 16:35:30. Version ac04

Copyright 2017 A. Danko


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