Summit Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Summit Lake clear sky chart from 2005-11-06 to 2024-02-15.

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
30%
24990
15%
80484
8%
24894
38%
24894
18%
55987

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
18%
943
12%
4387
4%
926
28%
926
9%
3260
January11th to 20thNight
18%
946
10%
4382
5%
930
25%
930
8%
3363
January21st to endNight
17%
1032
8%
4843
3%
1023
25%
1023
8%
3728
February1st to 10thNight
20%
950
16%
2480
4%
950
28%
950
19%
1798
February11th to 20thNight
20%
825
21%
2256
5%
821
31%
821
17%
1578
February21st to endNight
17%
592
16%
1776
4%
592
28%
592
14%
1292
March1st to 10thNight
28%
720
18%
2160
9%
720
35%
720
20%
1437
March11th to 20thNight
25%
644
20%
2084
10%
644
36%
644
21%
1355
March21st to endNight
29%
594
19%
1998
13%
594
39%
594
19%
1353
April1st to 10thNight
24%
540
14%
1800
8%
540
35%
540
16%
1257
April11th to 20thNight
28%
533
18%
1775
12%
533
38%
533
19%
1197
April21st to endNight
33%
540
16%
1678
9%
540
39%
540
20%
1165
May1st to 10thNight
25%
540
13%
1470
5%
540
31%
540
19%
1069
May11th to 20thNight
32%
531
17%
1416
8%
531
39%
531
24%
994
May21st to endNight
44%
583
11%
1552
5%
582
48%
582
29%
1021
June1st to 10thNight
44%
540
13%
1440
5%
540
49%
540
32%
903
June11th to 20thNight
39%
540
12%
1440
5%
540
43%
540
28%
964
June21st to endNight
50%
540
15%
1440
6%
540
54%
540
34%
896
July1st to 10thNight
58%
525
17%
1400
8%
525
62%
525
44%
797
July11th to 20thNight
49%
522
16%
1392
8%
522
53%
522
38%
845
July21st to endNight
57%
591
22%
1487
11%
558
62%
558
47%
846
August1st to 10thNight
57%
537
21%
1423
14%
534
61%
534
37%
868
August11th to 20thNight
57%
534
20%
1614
15%
534
64%
534
30%
985
August21st to endNight
50%
594
19%
1980
19%
594
55%
594
30%
1173
September1st to 10thNight
49%
540
23%
1800
20%
540
57%
540
31%
1026
September11th to 20thNight
46%
580
25%
1840
20%
580
53%
580
32%
1071
September21st to endNight
36%
720
18%
1980
10%
720
42%
720
27%
1308
October1st to 10thNight
36%
720
21%
2124
12%
720
43%
720
26%
1331
October11th to 20thNight
25%
720
17%
2178
7%
720
35%
720
18%
1513
October21st to endNight
26%
792
13%
2574
6%
792
35%
792
15%
1845
November1st to 10thNight
23%
740
20%
2406
10%
740
37%
740
20%
1571
November11th to 20thNight
17%
855
15%
2565
5%
855
28%
855
14%
1865
November21st to endNight
19%
950
14%
2660
6%
950
26%
950
15%
2004
December1st to 10thNight
17%
950
11%
2660
3%
950
25%
950
14%
2005
December11th to 20thNight
17%
948
12%
3220
3%
948
24%
948
10%
2439
December21st to endNight
12%
1039
8%
4804
2%
1026
22%
1026
6%
3865

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
13%10%48%6%45%5%5%7%32%
78192
Night
13%10%5%8%6%35%5%5%7%33%
80946
TransparencyDay
51%412%22%10%1
77892
Night
51%411%23%11%1
80766
SeeingDay
19%13%32%22%10%3
14944
Night
18%11%33%27%10%1
25023

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
12%14%6%16%8%45%446%21%
2527
11th to 20thDay
9%14%5%12%11%6%8%7%6%6%16%
2530
21st to endDay
12%17%9%14%7%34446%19%
2783
February1st to 10thDay
8%11%5%9%7%37%6%5%7%31%
1698
11th to 20thDay
8%13%5%9%6%45%5%6%8%30%
1686
21st to endDay
13%13%6%10%8%45%5%5%6%26%
1480
March1st to 10thDay
12%11%5%9%6%45%447%32%
1800
11th to 20thDay
11%10%5%9%6%45%5%5%6%35%
1890
21st to endDay
15%11%5%8%8%45%5%5%8%27%
2357
April1st to 10thDay
15%12%5%8%8%445%5%7%29%
2160
11th to 20thDay
21%11%47%6%35%445%29%
2134
21st to endDay
17%11%46%6%5%5%5%5%6%30%
2281
May1st to 10thDay
17%9%37%6%35%5%5%7%32%
2488
11th to 20thDay
15%9%38%6%45%5%5%6%35%
2479
21st to endDay
13%6%37%7%45%5%6%8%35%
2725
June1st to 10thDay
11%6%35%6%35%5%6%9%41%
2520
11th to 20thDay
13%7%26%6%45%5%6%8%38%
2520
21st to endDay
10%6%36%5%45%6%8%10%37%
2520
July1st to 10thDay
7%4246%46%5%8%11%45%
2520
11th to 20thDay
8%5%36%7%45%6%7%9%42%
2520
21st to endDay
8%435%6%35%6%6%9%45%
2743
August1st to 10thDay
9%5%26%7%45%6%6%10%40%
2507
11th to 20thDay
14%6%26%6%3446%7%42%
2282
21st to endDay
13%6%35%5%35%45%8%43%
2376
September1st to 10thDay
13%6%36%434448%43%
2160
11th to 20thDay
13%6%36%5%35%5%6%8%41%
2102
21st to endDay
14%9%26%6%46%5%6%7%34%
1980
October1st to 10thDay
16%8%36%5%346%5%8%36%
1832
11th to 20thDay
18%13%48%7%44447%26%
1782
21st to endDay
20%14%5%8%5%23347%29%
1782
November1st to 10thDay
14%10%47%5%35%5%7%7%34%
1672
11th to 20thDay
14%12%7%13%7%3446%6%24%
1615
21st to endDay
13%11%6%8%8%45%5%5%8%25%
1520
December1st to 10thDay
12%12%6%11%9%47%6%5%6%23%
1520
11th to 20thDay
13%15%7%10%10%46%6%5%5%19%
1918
21st to endDay
20%24%7%9%5%34345%16%
2783
January1st to 10thNight
12%14%6%12%8%4445%7%23%
4428
11th to 20thNight
9%13%6%12%10%5%7%7%7%7%17%
4440
21st to endNight
10%17%9%15%7%3445%6%20%
4884
February1st to 10thNight
8%11%5%10%8%46%5%5%7%31%
2480
11th to 20thNight
8%10%5%8%7%46%6%6%7%33%
2255
21st to endNight
14%12%5%9%7%45%5%5%6%29%
1776
March1st to 10thNight
12%9%47%5%4446%7%37%
2160
11th to 20thNight
12%9%46%6%45%45%6%40%
2084
21st to endNight
16%9%47%5%25%447%36%
1998
April1st to 10thNight
19%9%48%5%3445%6%32%
1800
11th to 20thNight
22%8%36%5%3435%6%36%
1775
21st to endNight
16%9%47%7%36%5%5%6%33%
1678
May1st to 10thNight
18%9%37%7%45%5%6%6%30%
1470
11th to 20thNight
16%8%45%5%35%46%7%37%
1416
21st to endNight
13%6%35%5%36%5%7%8%40%
1551
June1st to 10thNight
10%6%45%5%446%5%8%45%
1440
11th to 20thNight
12%6%38%5%45%6%5%8%39%
1440
21st to endNight
10%425%5%35%6%5%10%46%
1440
July1st to 10thNight
7%32432445%9%55%
1440
11th to 20thNight
8%424445%6%5%10%48%
1440
21st to endNight
5%5%243245%6%9%55%
1575
August1st to 10thNight
8%325%6%45%6%7%9%46%
1432
11th to 20thNight
10%5%35%5%45%5%5%6%47%
1614
21st to endNight
11%7%36%426%45%6%48%
1980
September1st to 10thNight
11%6%245%3445%7%50%
1800
11th to 20thNight
11%6%24435%5%6%7%48%
1840
21st to endNight
13%8%36%435%5%6%7%41%
1980
October1st to 10thNight
15%6%26%436%46%7%43%
2124
11th to 20thNight
15%12%47%5%44448%33%
2178
21st to endNight
17%12%38%6%45%447%29%
2574
November1st to 10thNight
14%9%46%6%3345%7%37%
2406
11th to 20thNight
13%13%6%9%7%35%347%29%
2565
21st to endNight
13%11%5%11%7%46%45%7%27%
2660
December1st to 10thNight
11%14%5%10%8%45%5%5%7%26%
2660
11th to 20thNight
11%13%7%11%8%45%5%5%6%23%
3279
21st to endNight
22%20%6%9%6%3334419%
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
65%35%19%6%1
2528
11th to 20thDay
67%39%13%6%1
2530
21st to endDay
68%212%14%5%
2783
February1st to 10thDay
52%410%19%14%1
1698
11th to 20thDay
51%5%10%23%9%2
1695
21st to endDay
58%48%18%10%1
1480
March1st to 10thDay
53%311%19%12%2
1800
11th to 20thDay
50%413%20%11%2
1890
21st to endDay
56%411%19%10%1
2357
April1st to 10thDay
56%410%17%12%1
2160
11th to 20thDay
57%47%20%11%1
2134
21st to endDay
55%48%19%12%1
2281
May1st to 10thDay
51%5%12%22%10%1
2488
11th to 20thDay
50%310%23%12%1
2483
21st to endDay
46%5%11%25%11%1
2725
June1st to 10thDay
40%414%29%11%1
2520
11th to 20thDay
44%415%23%14%
2520
21st to endDay
40%6%17%26%11%1
2520
July1st to 10thDay
32%5%16%32%15%1
2451
11th to 20thDay
37%413%29%15%3
2445
21st to endDay
34%5%15%28%17%1
2591
August1st to 10thDay
39%415%29%10%2
2492
11th to 20thDay
41%414%28%12%
2282
21st to endDay
40%413%26%16%1
2376
September1st to 10thDay
41%313%28%14%1
2160
11th to 20thDay
41%417%29%9%1
2102
21st to endDay
48%413%26%9%
1980
October1st to 10thDay
46%412%30%8%
1832
11th to 20thDay
58%5%10%18%9%1
1782
21st to endDay
57%312%20%7%
1782
November1st to 10thDay
48%411%24%12%1
1672
11th to 20thDay
60%49%18%8%1
1615
21st to endDay
57%5%14%19%41
1520
December1st to 10thDay
61%48%21%6%
1520
11th to 20thDay
66%311%13%7%1
1915
21st to endDay
72%36%12%7%
2783
January1st to 10thNight
58%6%8%19%7%1
4428
11th to 20thNight
64%410%16%5%
4440
21st to endNight
66%37%18%6%
4884
February1st to 10thNight
53%37%22%13%2
2480
11th to 20thNight
48%5%9%23%12%3
2256
21st to endNight
56%411%19%9%1
1776
March1st to 10thNight
46%411%26%12%2
2160
11th to 20thNight
46%412%22%15%2
2084
21st to endNight
50%410%22%13%2
1998
April1st to 10thNight
52%48%18%17%1
1800
11th to 20thNight
50%39%22%12%3
1775
21st to endNight
51%49%20%15%1
1678
May1st to 10thNight
53%412%19%11%1
1470
11th to 20thNight
47%5%10%25%12%2
1417
21st to endNight
41%417%23%13%1
1552
June1st to 10thNight
37%415%30%13%1
1440
11th to 20thNight
43%414%22%16%1
1440
21st to endNight
33%6%17%32%11%1
1440
July1st to 10thNight
27%416%34%19%1
1400
11th to 20thNight
32%5%17%29%14%3
1392
21st to endNight
26%417%34%15%3
1487
August1st to 10thNight
34%416%30%14%2
1423
11th to 20thNight
37%5%13%28%15%2
1614
21st to endNight
37%413%26%17%3
1980
September1st to 10thNight
35%311%33%16%1
1800
11th to 20thNight
35%415%36%10%
1840
21st to endNight
42%5%13%28%11%
1980
October1st to 10thNight
41%412%31%12%1
2124
11th to 20thNight
51%412%23%10%1
2178
21st to endNight
55%411%19%10%
2574
November1st to 10thNight
47%311%25%14%1
2406
11th to 20thNight
56%312%17%12%
2565
21st to endNight
57%412%20%6%1
2660
December1st to 10thNight
58%312%21%5%
2660
11th to 20thNight
61%310%18%7%1
3281
21st to endNight
70%26%16%6%
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
21%17%30%23%7%1
270
11th to 20thDay
22%17%36%20%41
270
21st to endDay
24%14%39%21%2
297
February1st to 10thDay
17%22%41%14%41
270
11th to 20thDay
19%31%35%12%4
252
21st to endDay
23%24%41%11%1
198
March1st to 10thDay
22%23%38%14%3
240
11th to 20thDay
23%20%32%17%6%3
240
21st to endDay
25%17%31%18%7%2
443
April1st to 10thDay
24%16%36%19%41
420
11th to 20thDay
32%14%28%17%7%2
412
21st to endDay
27%13%25%24%9%2
420
May1st to 10thDay
22%18%32%20%6%2
571
11th to 20thDay
21%15%32%20%8%3
625
21st to endDay
19%12%29%26%11%4
679
June1st to 10thDay
12%12%35%25%12%4
630
11th to 20thDay
20%10%31%25%11%3
630
21st to endDay
13%8%32%27%14%5%
630
July1st to 10thDay
10%5%29%30%19%7%
621
11th to 20thDay
11%9%33%27%14%7%
618
21st to endDay
9%5%32%31%17%6%
684
August1st to 10thDay
11%6%27%30%19%6%
626
11th to 20thDay
17%422%30%20%7%
537
21st to endDay
20%8%25%24%17%6%
495
September1st to 10thDay
17%8%25%28%17%5%
450
11th to 20thDay
17%6%31%30%13%4
450
21st to endDay
22%11%30%22%12%2
450
October1st to 10thDay
23%13%26%24%13%2
302
11th to 20thDay
22%24%36%16%2
270
21st to endDay
31%21%35%12%1
297
November1st to 10thDay
21%16%39%19%41
270
11th to 20thDay
22%24%38%11%31
270
21st to endDay
20%25%38%13%4
270
December1st to 10thDay
20%18%43%14%41
270
11th to 20thDay
25%22%38%11%4
270
21st to endDay
29%21%35%11%3
297
January1st to 10thNight
17%15%40%22%5%
950
11th to 20thNight
20%14%38%21%7%1
950
21st to endNight
19%11%38%25%6%
1045
February1st to 10thNight
14%15%39%24%7%1
950
11th to 20thNight
15%18%38%23%5%
825
21st to endNight
22%15%36%23%4
592
March1st to 10thNight
19%14%34%24%9%1
720
11th to 20thNight
19%14%38%22%6%1
644
21st to endNight
22%10%31%25%10%1
594
April1st to 10thNight
24%13%32%24%5%1
540
11th to 20thNight
27%8%32%27%6%
533
21st to endNight
22%9%31%30%6%1
540
May1st to 10thNight
24%9%34%25%7%1
540
11th to 20thNight
22%7%33%29%8%1
531
21st to endNight
17%6%27%38%11%1
584
June1st to 10thNight
12%6%30%38%13%1
540
11th to 20thNight
17%6%29%36%11%1
540
21st to endNight
12%5%26%39%18%1
540
July1st to 10thNight
10%321%41%23%2
525
11th to 20thNight
10%430%34%20%1
522
21st to endNight
8%226%40%21%2
591
August1st to 10thNight
10%222%41%23%2
537
11th to 20thNight
13%320%34%26%4
534
21st to endNight
14%5%26%33%21%2
594
September1st to 10thNight
15%425%35%18%4
540
11th to 20thNight
14%431%34%16%2
580
21st to endNight
17%8%31%28%14%1
720
October1st to 10thNight
19%9%30%27%14%1
720
11th to 20thNight
23%15%29%26%6%
720
21st to endNight
25%10%32%23%10%1
792
November1st to 10thNight
20%11%39%23%6%1
740
11th to 20thNight
21%18%35%20%5%
855
21st to endNight
21%18%35%22%5%
950
December1st to 10thNight
20%17%36%21%6%1
950
11th to 20thNight
19%15%36%23%6%1
950
21st to endNight
28%16%32%20%4
1045
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