Big Meadows
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Meadows clear sky chart from 2005-11-06 to 2024-03-23.

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
40%
23876
20%
80326
12%
23777
49%
23777
23%
49732

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
22%
754
24%
4024
8%
737
42%
737
15%
2094
January11th to 20thNight
26%
759
27%
3967
11%
740
42%
740
14%
2159
January21st to endNight
23%
830
15%
4439
10%
814
41%
814
13%
2688
February1st to 10thNight
27%
760
19%
2470
10%
760
40%
760
22%
1559
February11th to 20thNight
14%
740
18%
2405
5%
740
31%
740
17%
1563
February21st to endNight
19%
628
23%
1832
7%
628
34%
628
21%
1196
March1st to 10thNight
25%
760
25%
2090
10%
760
40%
760
26%
1310
March11th to 20thNight
24%
760
21%
2090
10%
760
35%
760
23%
1368
March21st to endNight
24%
801
19%
2201
8%
801
34%
801
22%
1479
April1st to 10thNight
28%
720
19%
1828
5%
720
37%
720
26%
1215
April11th to 20thNight
35%
711
20%
1775
8%
711
41%
711
32%
1153
April21st to endNight
36%
698
21%
1778
8%
698
42%
698
29%
1188
May1st to 10thNight
40%
540
16%
1620
8%
540
46%
540
23%
1073
May11th to 20thNight
43%
531
15%
1592
8%
531
48%
531
24%
1082
May21st to endNight
54%
409
15%
1572
14%
409
58%
409
22%
971
June1st to 10thNight
58%
360
18%
1440
19%
360
63%
360
25%
828
June11th to 20thNight
58%
360
15%
1440
18%
360
62%
360
21%
889
June21st to endNight
63%
360
18%
1440
20%
360
67%
360
25%
837
July1st to 10thNight
61%
403
15%
1453
15%
403
64%
403
23%
922
July11th to 20thNight
71%
522
14%
1566
12%
522
71%
522
33%
961
July21st to endNight
67%
591
16%
1672
13%
558
70%
558
31%
1061
August1st to 10thNight
65%
537
16%
1600
12%
534
66%
534
26%
1073
August11th to 20thNight
59%
552
18%
1616
13%
552
61%
552
26%
1101
August21st to endNight
59%
792
16%
1980
11%
792
60%
792
28%
1381
September1st to 10thNight
60%
720
22%
1800
14%
720
62%
720
33%
1203
September11th to 20thNight
59%
720
27%
1861
20%
720
62%
720
33%
1211
September21st to endNight
44%
720
20%
2046
15%
720
49%
720
25%
1387
October1st to 10thNight
50%
720
20%
2160
19%
720
55%
720
27%
1373
October11th to 20thNight
44%
720
25%
2160
17%
720
56%
720
29%
1320
October21st to endNight
40%
792
27%
2376
18%
792
53%
792
29%
1442
November1st to 10thNight
41%
740
28%
2221
18%
740
53%
740
31%
1318
November11th to 20thNight
36%
760
25%
2530
15%
760
51%
760
26%
1481
November21st to endNight
36%
760
23%
2660
16%
760
49%
760
26%
1535
December1st to 10thNight
28%
760
20%
2660
10%
760
42%
760
19%
1695
December11th to 20thNight
33%
759
22%
3175
13%
758
47%
758
20%
1869
December21st to endNight
32%
827
14%
4787
12%
817
46%
817
13%
2747

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
14%7%36%5%35%5%6%7%39%
78794
Night
14%6%35%5%345%5%7%43%
81089
TransparencyDay
42%7%12%21%15%3
78513
Night
39%6%12%22%17%3
80889
SeeingDay
19%13%26%23%13%5%
14078
Night
17%10%27%31%14%2
23904

By Month

Percentage Cloud Cover SE (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%25%5%3445%6%45%
2811
11th to 20thDay
11%11%46%7%35%44438%
2840
21st to endDay
15%9%46%6%35%5%45%37%
3124
February1st to 10thDay
11%9%47%6%35%5%5%6%39%
1710
11th to 20thDay
15%8%35%5%35%45%7%39%
1663
21st to endDay
17%9%46%425%45%6%38%
1616
March1st to 10thDay
13%7%35%424446%47%
2090
11th to 20thDay
14%8%36%6%345%5%6%39%
2090
21st to endDay
17%8%37%7%35%5%5%436%
2200
April1st to 10thDay
10%6%36%6%35%45%7%44%
2132
11th to 20thDay
14%6%35%435%45%7%45%
2134
21st to endDay
17%7%27%6%445%5%6%38%
2196
May1st to 10thDay
15%7%36%6%46%5%6%8%34%
2340
11th to 20thDay
19%7%45%5%35%5%6%7%33%
2301
21st to endDay
15%6%35%6%35%5%6%9%36%
2699
June1st to 10thDay
12%5%25%6%46%6%6%9%40%
2520
11th to 20thDay
12%6%36%6%5%6%6%6%10%34%
2520
21st to endDay
10%436%5%46%7%7%10%39%
2520
July1st to 10thDay
11%6%36%6%46%7%6%10%36%
2459
11th to 20thDay
6%436%6%5%8%7%8%12%34%
2340
21st to endDay
11%7%36%7%47%7%7%9%31%
2547
August1st to 10thDay
10%7%37%7%6%8%7%7%9%29%
2327
11th to 20thDay
14%5%36%7%5%7%6%8%8%31%
2266
21st to endDay
12%6%37%5%46%6%7%9%35%
2376
September1st to 10thDay
14%7%25%5%45%6%5%7%42%
2160
11th to 20thDay
14%6%35%43445%8%43%
2096
21st to endDay
20%7%25%6%445%5%5%35%
1913
October1st to 10thDay
16%7%26%43445%6%43%
1800
11th to 20thDay
16%5%3443435%6%47%
1800
21st to endDay
14%5%25%5%34445%49%
1980
November1st to 10thDay
12%6%24433346%53%
1857
11th to 20thDay
14%424435%45%6%49%
1645
21st to endDay
14%5%25%434446%48%
1520
December1st to 10thDay
15%8%36%5%35%46%7%38%
1520
11th to 20thDay
14%6%25%423447%49%
1910
21st to endDay
18%8%35%5%346%7%7%35%
2772
January1st to 10thNight
12%7%244345%5%7%47%
4130
11th to 20thNight
15%9%34334446%45%
4120
21st to endNight
19%8%35%424445%42%
4532
February1st to 10thNight
13%8%35%5%35%5%7%5%42%
2470
11th to 20thNight
19%8%35%5%245%45%40%
2403
21st to endNight
15%8%36%42446%6%41%
1832
March1st to 10thNight
13%5%25%425%5%5%5%48%
2090
11th to 20thNight
16%7%35%5%2445%7%42%
2090
21st to endNight
15%7%36%5%3445%6%42%
2201
April1st to 10thNight
13%7%25%435%6%5%7%43%
1828
11th to 20thNight
11%7%35%43446%8%46%
1775
21st to endNight
16%6%34435%5%5%7%42%
1778
May1st to 10thNight
15%6%35%6%35%5%5%8%39%
1620
11th to 20thNight
17%6%37%5%3436%7%39%
1592
21st to endNight
14%5%26%5%345%5%9%41%
1571
June1st to 10thNight
11%5%35%5%245%7%10%44%
1440
11th to 20thNight
12%5%346%446%5%9%40%
1440
21st to endNight
10%435%6%36%6%6%10%43%
1440
July1st to 10thNight
11%6%36%435%6%6%8%42%
1496
11th to 20thNight
5%4245%45%7%8%10%45%
1620
21st to endNight
8%5%247%45%6%9%11%39%
1771
August1st to 10thNight
9%5%36%8%46%5%7%9%38%
1611
11th to 20thNight
11%7%36%6%35%6%5%8%39%
1616
21st to endNight
11%6%27%7%45%6%7%10%36%
1980
September1st to 10thNight
15%6%2443345%8%45%
1800
11th to 20thNight
13%6%25%5%235%5%6%48%
1861
21st to endNight
22%7%345%24345%41%
2046
October1st to 10thNight
18%5%345%34446%45%
2160
11th to 20thNight
14%6%34434446%49%
2160
21st to endNight
15%5%14434446%50%
2376
November1st to 10thNight
12%7%35%334346%50%
2221
11th to 20thNight
13%6%3443445%6%49%
2530
21st to endNight
14%5%3443445%7%47%
2660
December1st to 10thNight
15%7%46%435%5%46%41%
2660
11th to 20thNight
15%7%345%3445%6%45%
3285
21st to endNight
16%6%25%5%35%6%6%7%38%
4884

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
41%49%26%16%4
2812
11th to 20thDay
46%6%8%18%15%6%
2840
21st to endDay
47%6%9%21%15%2
3124
February1st to 10thDay
45%5%11%22%14%3
1710
11th to 20thDay
44%6%9%21%18%3
1672
21st to endDay
46%6%11%16%16%5%
1616
March1st to 10thDay
38%5%10%22%21%3
2090
11th to 20thDay
44%6%9%18%18%5%
2090
21st to endDay
48%6%10%18%14%5%
2200
April1st to 10thDay
38%7%11%19%18%7%
2132
11th to 20thDay
38%6%11%19%21%6%
2134
21st to endDay
46%6%11%20%14%4
2196
May1st to 10thDay
45%8%14%17%14%2
2340
11th to 20thDay
48%8%13%19%10%2
2305
21st to endDay
42%9%15%23%10%1
2699
June1st to 10thDay
40%8%13%23%15%1
2520
11th to 20thDay
42%10%14%19%13%2
2520
21st to endDay
36%10%15%24%14%1
2520
July1st to 10thDay
41%11%12%20%15%3
2392
11th to 20thDay
37%11%16%22%12%1
2271
21st to endDay
44%9%12%19%14%1
2405
August1st to 10thDay
45%11%15%20%9%
2314
11th to 20thDay
44%10%15%19%11%1
2266
21st to endDay
42%9%15%21%11%2
2376
September1st to 10thDay
40%8%13%17%18%4
2160
11th to 20thDay
39%5%9%25%18%4
2096
21st to endDay
48%6%10%18%17%2
1913
October1st to 10thDay
40%5%9%25%17%4
1800
11th to 20thDay
38%5%10%23%21%4
1800
21st to endDay
37%49%24%22%5%
1980
November1st to 10thDay
33%49%25%24%5%
1857
11th to 20thDay
35%5%11%21%22%6%
1645
21st to endDay
37%410%25%22%3
1520
December1st to 10thDay
44%7%11%23%13%4
1520
11th to 20thDay
36%411%30%14%5%
1906
21st to endDay
44%8%14%23%11%1
2772
January1st to 10thNight
35%5%12%23%20%4
4130
11th to 20thNight
39%5%12%22%18%5%
4120
21st to endNight
45%5%9%23%18%1
4532
February1st to 10thNight
41%6%12%23%16%2
2470
11th to 20thNight
44%6%9%20%16%6%
2405
21st to endNight
42%6%12%20%15%5%
1832
March1st to 10thNight
36%5%10%26%19%3
2090
11th to 20thNight
41%5%11%21%19%4
2090
21st to endNight
42%7%11%19%16%5%
2201
April1st to 10thNight
39%7%12%20%19%4
1828
11th to 20thNight
36%6%14%20%20%5%
1775
21st to endNight
39%6%12%26%13%4
1778
May1st to 10thNight
42%8%14%20%12%4
1620
11th to 20thNight
45%6%13%21%13%1
1593
21st to endNight
39%9%18%22%11%1
1572
June1st to 10thNight
34%9%15%28%13%1
1440
11th to 20thNight
38%10%15%22%13%1
1440
21st to endNight
35%8%18%18%18%3
1440
July1st to 10thNight
37%11%16%18%14%3
1453
11th to 20thNight
30%11%21%24%12%2
1566
21st to endNight
33%10%19%23%13%1
1672
August1st to 10thNight
39%10%16%23%11%1
1600
11th to 20thNight
41%9%13%24%12%1
1616
21st to endNight
40%10%16%22%9%2
1980
September1st to 10thNight
36%9%15%20%16%4
1800
11th to 20thNight
36%7%10%26%19%2
1861
21st to endNight
45%5%10%20%17%2
2046
October1st to 10thNight
40%5%10%24%17%3
2160
11th to 20thNight
36%6%8%26%21%3
2160
21st to endNight
35%6%9%23%23%4
2376
November1st to 10thNight
35%410%22%23%6%
2221
11th to 20thNight
36%5%8%22%23%6%
2530
21st to endNight
35%5%11%24%21%4
2660
December1st to 10thNight
43%6%10%23%14%3
2660
11th to 20thNight
39%5%10%23%19%4
3288
21st to endNight
41%7%16%21%14%1
4884

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
28%25%32%12%4
265
11th to 20thDay
29%30%27%11%4
270
21st to endDay
25%28%35%10%21
297
February1st to 10thDay
23%34%29%12%2
270
11th to 20thDay
38%27%29%5%1
270
21st to endDay
31%21%29%16%2
371
March1st to 10thDay
25%22%28%20%5%
460
11th to 20thDay
24%23%29%17%6%1
460
21st to endDay
25%19%34%14%7%1
470
April1st to 10thDay
21%25%26%19%7%1
420
11th to 20thDay
20%18%26%21%11%3
412
21st to endDay
25%16%30%17%10%2
420
May1st to 10thDay
21%20%29%16%12%2
423
11th to 20thDay
21%14%30%21%11%3
447
21st to endDay
21%5%25%26%17%7%
485
June1st to 10thDay
16%6%28%27%18%4
450
11th to 20thDay
16%9%26%28%14%6%
450
21st to endDay
10%6%29%31%19%4
450
July1st to 10thDay
15%420%27%25%9%
445
11th to 20thDay
5%219%35%27%11%
444
21st to endDay
13%321%31%23%9%
488
August1st to 10thDay
12%5%19%27%26%12%
446
11th to 20thDay
14%5%17%28%24%12%
439
21st to endDay
10%318%32%21%16%
495
September1st to 10thDay
17%5%18%26%20%15%
450
11th to 20thDay
16%418%28%23%10%
450
21st to endDay
27%8%21%24%15%5%
450
October1st to 10thDay
19%6%21%30%17%6%
450
11th to 20thDay
16%15%27%24%16%2
450
21st to endDay
19%15%32%22%9%2
495
November1st to 10thDay
16%13%29%28%10%3
455
11th to 20thDay
19%14%31%24%11%1
293
21st to endDay
21%17%37%20%5%
180
December1st to 10thDay
19%25%36%14%6%1
180
11th to 20thDay
23%16%37%17%7%1
180
21st to endDay
22%21%33%17%7%
198
January1st to 10thNight
18%18%36%23%4
760
11th to 20thNight
21%15%32%28%4
760
21st to endNight
18%14%39%26%2
836
February1st to 10thNight
17%15%37%29%2
760
11th to 20thNight
25%20%36%18%1
743
21st to endNight
20%18%39%19%3
628
March1st to 10thNight
17%18%36%24%4
760
11th to 20thNight
22%18%32%21%5%1
760
21st to endNight
17%17%36%23%6%1
801
April1st to 10thNight
17%18%33%26%6%
720
11th to 20thNight
16%13%31%28%10%1
711
21st to endNight
19%9%31%33%7%
698
May1st to 10thNight
18%10%26%28%16%1
540
11th to 20thNight
19%425%35%16%1
531
21st to endNight
14%318%39%23%2
411
June1st to 10thNight
11%219%44%22%2
360
11th to 20thNight
13%5%14%43%25%1
360
21st to endNight
9%217%49%22%2
360
July1st to 10thNight
14%215%33%32%4
403
11th to 20thNight
7%212%33%42%5%
522
21st to endNight
7%213%41%32%5%
591
August1st to 10thNight
9%212%43%31%3
537
11th to 20thNight
13%313%37%32%3
552
21st to endNight
13%215%34%32%4
792
September1st to 10thNight
16%213%33%29%6%
720
11th to 20thNight
14%314%34%30%5%
720
21st to endNight
24%319%31%20%2
720
October1st to 10thNight
19%7%18%31%21%5%
720
11th to 20thNight
16%8%27%32%16%1
720
21st to endNight
17%10%29%31%11%2
792
November1st to 10thNight
16%9%29%33%12%2
740
11th to 20thNight
17%12%30%32%8%1
760
21st to endNight
16%12%31%30%10%1
760
December1st to 10thNight
20%12%33%27%7%
760
11th to 20thNight
16%10%34%35%5%
760
21st to endNight
18%12%30%36%3
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