Clear Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clear Lake clear sky chart from 2005-11-05 to 2017-04-01.

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
62%
14750
27%
45405
23%
14713
67%
14713
38%
24789

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%
717
18%
2399
17%
716
58%
716
23%
1502
January16th to endNight
51%
768
26%
2496
24%
768
58%
768
28%
1524
February1st to 15thNight
49%
700
22%
2288
20%
700
56%
700
21%
1494
February16th to endNight
46%
632
23%
1939
17%
632
54%
632
26%
1205
March1st to 15thNight
48%
720
14%
1989
10%
720
51%
720
23%
1378
March16th to endNight
44%
768
20%
2103
13%
768
50%
768
27%
1375
April1st to 15thNight
42%
663
23%
1659
9%
663
50%
663
28%
1086
April16th to endNight
54%
660
25%
1650
11%
660
60%
660
45%
935
May1st to 15thNight
61%
502
31%
1492
20%
502
69%
502
51%
740
May16th to endNight
65%
351
26%
1377
22%
351
75%
351
44%
564
June1st to 15thNight
65%
330
28%
1320
30%
330
75%
330
42%
570
June16th to endNight
75%
330
33%
1320
41%
330
82%
330
60%
466
July1st to 15thNight
88%
330
36%
1260
46%
330
90%
330
75%
403
July16th to endNight
91%
522
39%
1467
35%
489
93%
489
82%
552
August1st to 15thNight
91%
493
42%
1476
35%
490
92%
490
78%
569
August16th to endNight
89%
676
42%
1726
27%
676
90%
676
80%
765
September1st to 15thNight
90%
660
45%
1650
30%
660
93%
660
86%
710
September16th to endNight
81%
656
43%
1814
35%
656
86%
656
70%
793
October1st to 15thNight
70%
660
32%
1980
29%
660
78%
660
48%
979
October16th to endNight
69%
704
32%
2112
32%
704
74%
704
41%
1134
November1st to 15thNight
64%
700
24%
2184
22%
700
69%
700
34%
1235
November16th to endNight
56%
720
22%
2496
21%
720
60%
720
27%
1437
December1st to 15thNight
49%
720
20%
2520
16%
720
56%
720
20%
1623
December16th to endNight
43%
768
20%
2688
17%
768
50%
768
20%
1750

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%313313336%61%
45697
Night
8%413323346%58%
45591
TransparencyDay
26%47%19%24%17%
45383
Night
28%48%18%23%16%
45406
SeeingDay
11%13%25%29%16%4
5312
Night
10%7%15%28%29%8%
14759

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%6%35%6%23335%43%
1537
16th to endDay
15%6%25%414347%43%
1728
February1st to 15thDay
15%7%24424447%41%
1576
16th to endDay
17%7%2342436%8%38%
1535
March1st to 15thDay
15%9%37%425%446%34%
1968
16th to endDay
14%5%27%5%25%447%39%
2119
April1st to 15thDay
11%7%345%2435%7%42%
1974
16th to endDay
4323423447%60%
1980
May1st to 15thDay
431221345%8%64%
2125
16th to endDay
5%21332335%7%60%
2381
June1st to 15thDay
3323322346%65%
2310
16th to endDay
2112112481%
2310
July1st to 15thDay
111112386%
2285
16th to endDay
1111387%
2286
August1st to 15thDay
1112386%
2145
16th to endDay
11389%
2124
September1st to 15thDay
11122485%
1980
16th to endDay
2111236%77%
1813
October1st to 15thDay
6%312212345%65%
1650
16th to endDay
9%413323336%59%
1760
November1st to 15thDay
8%3143245%5%7%53%
1672
16th to endDay
11%6%245%24345%48%
1463
December1st to 15thDay
15%8%37%423425%42%
1440
16th to endDay
19%7%26%42345%6%37%
1536
January1st to 15thNight
14%5%2443445%7%42%
2399
16th to endNight
15%6%24223336%48%
2496
February1st to 15thNight
12%6%25%5%35%5%6%6%40%
2276
16th to endNight
13%5%2442445%8%43%
1939
March1st to 15thNight
13%6%36%435%5%5%7%38%
1989
16th to endNight
12%7%34424346%46%
2103
April1st to 15thNight
8%5%245%2445%8%47%
1659
16th to endNight
4213314348%62%
1650
May1st to 15thNight
2213322346%67%
1492
16th to endNight
2112213447%68%
1377
June1st to 15thNight
4212113436%67%
1320
16th to endNight
1111122281%
1320
July1st to 15thNight
1111287%
1341
16th to endNight
12487%
1575
August1st to 15thNight
111111288%
1485
16th to endNight
1213385%
1726
September1st to 15thNight
112487%
1650
16th to endNight
11111247%77%
1814
October1st to 15thNight
5%212312245%67%
1980
16th to endNight
7%213223447%59%
2112
November1st to 15thNight
7%31332447%8%50%
2184
16th to endNight
9%5%24423347%49%
2496
December1st to 15thNight
16%6%35%5%23347%40%
2520
16th to endNight
18%6%24424446%40%
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
44%49%16%14%10%
1537
16th to endDay
42%47%13%19%12%
1728
February1st to 15thDay
43%47%17%21%5%
1576
16th to endDay
43%6%10%22%12%4
1535
March1st to 15thDay
50%5%9%15%12%7%
1968
16th to endDay
45%6%11%17%15%3
2119
April1st to 15thDay
42%5%12%20%16%2
1974
16th to endDay
24%5%12%27%21%7%
1980
May1st to 15thDay
19%49%28%29%8%
2125
16th to endDay
23%5%12%32%19%7%
2385
June1st to 15thDay
21%410%22%25%15%
2310
16th to endDay
10%1418%39%25%
2310
July1st to 15thDay
6%2212%34%41%
2138
16th to endDay
6%2310%29%46%
2131
August1st to 15thDay
6%1217%34%37%
2129
16th to endDay
42315%39%35%
2124
September1st to 15thDay
6%2313%37%37%
1980
16th to endDay
11%35%22%34%23%
1813
October1st to 15thDay
22%37%22%27%17%
1650
16th to endDay
27%47%21%26%12%
1760
November1st to 15thDay
30%6%11%28%14%9%
1672
16th to endDay
39%5%8%19%18%8%
1463
December1st to 15thDay
46%5%6%15%20%5%
1440
16th to endDay
47%48%14%16%8%
1536
January1st to 15thNight
41%5%10%17%16%9%
2399
16th to endNight
39%37%15%18%14%
2496
February1st to 15thNight
43%6%7%16%18%7%
2288
16th to endNight
38%5%12%24%16%3
1939
March1st to 15thNight
43%7%12%14%14%6%
1989
16th to endNight
40%5%11%19%17%5%
2103
April1st to 15thNight
36%6%14%21%16%4
1659
16th to endNight
22%411%30%23%6%
1650
May1st to 15thNight
19%37%23%34%11%
1493
16th to endNight
15%5%15%33%22%7%
1377
June1st to 15thNight
18%5%10%21%25%18%
1320
16th to endNight
10%2417%36%28%
1320
July1st to 15thNight
6%128%36%44%
1260
16th to endNight
5%1411%21%55%
1467
August1st to 15thNight
6%1212%31%45%
1476
16th to endNight
6%2312%36%38%
1726
September1st to 15thNight
41311%35%44%
1650
16th to endNight
9%2422%32%28%
1814
October1st to 15thNight
20%37%20%28%18%
1980
16th to endNight
24%5%7%21%23%17%
2112
November1st to 15thNight
29%6%15%24%14%9%
2184
16th to endNight
35%49%19%21%9%
2496
December1st to 15thNight
44%5%7%14%20%6%
2520
16th to endNight
45%48%15%18%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
31%15%24%12%15%
165
16th to endDay
17%17%25%21%14%3
256
February1st to 15thDay
22%17%23%21%13%2
236
16th to endDay
20%19%22%23%11%
231
March1st to 15thDay
26%21%21%16%10%3
270
16th to endDay
16%23%31%19%7%
288
April1st to 15thDay
19%27%22%17%9%2
211
16th to endDay
11%27%27%21%10%
210
May1st to 15thDay
10%21%35%21%7%2
228
16th to endDay
8%17%24%27%15%6%
266
June1st to 15thDay
6%16%31%34%8%3
255
16th to endDay
39%35%32%12%5%
255
July1st to 15thDay
2222%44%22%4
245
16th to endDay
115%52%21%9%
271
August1st to 15thDay
1125%44%19%7%
255
16th to endDay
1224%37%23%8%
268
September1st to 15thDay
218%44%26%7%
255
16th to endDay
46%21%34%24%8%
255
October1st to 15thDay
9%12%23%30%16%8%
255
16th to endDay
12%13%23%27%20%1
272
November1st to 15thDay
8%12%17%25%28%6%
178
16th to endDay
14%19%34%15%14%1
63
December1st to 15thDay
33%16%33%11%31
60
16th to endDay
15%21%20%18%18%4
64
January1st to 15thNight
16%8%12%31%23%7%
720
16th to endNight
20%7%16%28%20%7%
768
February1st to 15thNight
16%9%17%30%22%3
704
16th to endNight
17%11%19%27%19%4
632
March1st to 15thNight
17%10%17%27%22%4
720
16th to endNight
15%13%22%26%18%4
768
April1st to 15thNight
11%16%25%24%18%4
663
16th to endNight
6%14%21%27%23%6%
660
May1st to 15thNight
35%26%29%28%6%
503
16th to endNight
37%21%30%33%4
352
June1st to 15thNight
46%20%31%33%3
330
16th to endNight
2317%39%33%3
330
July1st to 15thNight
18%27%52%9%
330
16th to endNight
1422%53%17%
522
August1st to 15thNight
15%30%45%17%
493
16th to endNight
8%26%51%12%
676
September1st to 15thNight
15%26%49%15%
660
16th to endNight
2310%28%37%16%
656
October1st to 15thNight
6%5%12%29%33%12%
660
16th to endNight
8%5%13%25%32%13%
704
November1st to 15thNight
9%6%14%30%29%8%
700
16th to endNight
11%10%14%30%24%8%
720
December1st to 15thNight
20%10%13%28%18%7%
720
16th to endNight
20%12%17%28%18%2
768
Page generated at 2017-04-02 04:39:04. Version ac04

Copyright 2017 A. Danko


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