Tunnel Ridge Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tunnel Ridge Road clear sky chart from 2005-11-06 to 2024-01-14.

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
42%
23819
18%
74586
14%
23764
48%
23764
22%
49816

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%
760
14%
2459
6%
757
27%
757
13%
1822
January11th to 20thNight
19%
735
14%
2386
8%
735
28%
735
12%
1819
January21st to endNight
19%
792
16%
2574
8%
792
29%
792
16%
1831
February1st to 10thNight
20%
720
12%
2250
6%
720
27%
720
14%
1680
February11th to 20thNight
16%
703
14%
2099
7%
700
24%
700
14%
1547
February21st to endNight
16%
592
15%
1776
6%
592
25%
592
12%
1348
March1st to 10thNight
25%
720
19%
2102
9%
720
34%
720
19%
1453
March11th to 20thNight
24%
720
17%
1980
8%
720
31%
720
20%
1414
March21st to endNight
31%
792
14%
2178
7%
792
36%
792
19%
1571
April1st to 10thNight
36%
671
20%
1931
11%
671
44%
671
26%
1237
April11th to 20thNight
39%
533
22%
1710
15%
533
48%
533
24%
1069
April21st to endNight
33%
540
19%
1620
10%
540
42%
540
23%
1088
May1st to 10thNight
38%
540
16%
1620
10%
540
43%
540
21%
1107
May11th to 20thNight
48%
531
15%
1593
11%
531
51%
531
21%
1104
May21st to endNight
61%
583
17%
1744
14%
582
63%
582
28%
1103
June1st to 10thNight
64%
540
17%
1620
15%
540
66%
540
33%
986
June11th to 20thNight
67%
540
17%
1620
15%
540
69%
540
33%
972
June21st to endNight
62%
540
16%
1620
15%
540
64%
540
29%
1035
July1st to 10thNight
64%
525
13%
1575
13%
525
65%
525
26%
1034
July11th to 20thNight
73%
522
18%
1566
16%
522
75%
522
34%
929
July21st to endNight
66%
591
20%
1672
17%
558
68%
558
29%
1053
August1st to 10thNight
70%
537
20%
1600
19%
534
71%
534
32%
966
August11th to 20thNight
69%
534
19%
1598
17%
534
70%
534
30%
996
August21st to endNight
73%
594
23%
1934
24%
594
74%
594
33%
1105
September1st to 10thNight
65%
684
22%
1944
19%
684
67%
684
32%
1199
September11th to 20thNight
64%
720
26%
1980
21%
720
66%
720
34%
1237
September21st to endNight
57%
720
27%
1980
19%
720
62%
720
35%
1208
October1st to 10thNight
58%
720
26%
1980
23%
720
62%
720
37%
1189
October11th to 20thNight
45%
720
25%
2154
21%
720
52%
720
29%
1324
October21st to endNight
39%
792
25%
2420
19%
792
48%
792
24%
1574
November1st to 10thNight
47%
740
27%
2406
24%
740
56%
740
31%
1401
November11th to 20thNight
36%
760
24%
2470
17%
760
47%
760
24%
1546
November21st to endNight
39%
760
22%
2470
16%
760
47%
760
23%
1602
December1st to 10thNight
25%
760
14%
2470
8%
760
32%
760
14%
1814
December11th to 20thNight
28%
759
18%
2982
11%
759
38%
759
14%
2062
December21st to endNight
23%
829
9%
4503
7%
817
32%
817
7%
3391

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
16%8%36%5%35%5%5%7%37%
74889
Night
15%8%36%5%345%5%7%39%
74882
TransparencyDay
46%7%11%21%13%2
74612
Night
44%7%11%21%15%3
74678
SeeingDay
20%12%24%22%15%7%
13700
Night
19%9%24%29%17%2
23828

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
17%13%6%9%7%34445%28%
1706
11th to 20thDay
21%15%6%9%6%34445%24%
1647
21st to endDay
17%14%6%7%5%34346%30%
1782
February1st to 10thDay
20%12%6%9%5%34445%27%
1706
11th to 20thDay
23%10%5%6%5%34446%30%
1748
21st to endDay
21%13%5%6%5%4444430%
1480
March1st to 10thDay
19%10%36%334446%37%
1858
11th to 20thDay
22%10%36%5%35%46%5%31%
1980
21st to endDay
21%10%27%6%3445%6%32%
2178
April1st to 10thDay
14%8%46%5%345%5%7%39%
2042
11th to 20thDay
17%7%35%5%35%446%40%
2199
21st to endDay
18%6%36%5%45%45%8%35%
2340
May1st to 10thDay
19%7%36%5%35%5%5%8%34%
2340
11th to 20thDay
19%6%36%6%45%5%5%6%34%
2301
21st to endDay
9%6%25%6%47%7%7%10%37%
2531
June1st to 10thDay
12%5%35%5%5%5%5%6%9%39%
2340
11th to 20thDay
8%5%36%6%35%8%6%9%41%
2340
21st to endDay
11%5%26%6%46%6%6%10%39%
2340
July1st to 10thDay
13%6%27%6%45%5%7%9%37%
2340
11th to 20thDay
11%5%36%6%47%7%7%9%36%
2340
21st to endDay
14%5%36%5%47%6%6%9%36%
2547
August1st to 10thDay
12%6%25%6%46%6%6%10%39%
2327
11th to 20thDay
12%7%35%7%46%6%7%10%34%
2303
21st to endDay
9%5%35%5%46%5%7%9%42%
2419
September1st to 10thDay
14%5%35%435%45%8%43%
1998
11th to 20thDay
12%426%5%345%6%9%44%
1980
21st to endDay
18%425%4235%47%46%
1980
October1st to 10thDay
12%5%245%2345%8%50%
1980
11th to 20thDay
15%7%25%424446%48%
1805
21st to endDay
20%8%24424346%42%
1933
November1st to 10thDay
12%5%24433435%53%
1672
11th to 20thDay
16%9%36%434346%42%
1710
21st to endDay
16%9%46%5%245%5%5%39%
1710
December1st to 10thDay
24%13%46%5%34445%28%
1710
11th to 20thDay
17%14%5%6%5%3445%5%32%
2153
21st to endDay
18%16%48%7%45%5%5%7%22%
3124
January1st to 10thNight
17%12%6%8%6%45%445%29%
2459
11th to 20thNight
21%14%5%8%6%34445%25%
2386
21st to endNight
18%11%5%7%6%34445%33%
2574
February1st to 10thNight
20%11%5%8%5%35%45%5%28%
2250
11th to 20thNight
22%11%5%7%5%34345%31%
2098
21st to endNight
23%13%47%6%3345%428%
1776
March1st to 10thNight
18%10%35%5%34435%39%
2102
11th to 20thNight
19%9%36%5%35%446%35%
1980
21st to endNight
16%9%46%6%45%5%5%7%34%
2178
April1st to 10thNight
13%5%36%435%45%8%44%
1931
11th to 20thNight
14%6%35%4345%5%6%45%
1710
21st to endNight
17%7%35%43445%6%41%
1620
May1st to 10thNight
18%7%26%6%35%5%5%7%37%
1620
11th to 20thNight
16%6%35%6%25%6%6%8%37%
1592
21st to endNight
7%5%25%6%46%6%7%11%41%
1744
June1st to 10thNight
7%5%25%435%6%8%11%44%
1620
11th to 20thNight
5%325%5%45%6%8%10%46%
1620
21st to endNight
11%4245%35%7%7%12%40%
1620
July1st to 10thNight
8%5%37%6%46%5%6%10%40%
1620
11th to 20thNight
5%325%445%5%8%11%48%
1620
21st to endNight
10%5%25%5%45%6%6%11%43%
1771
August1st to 10thNight
9%4245%345%7%10%47%
1611
11th to 20thNight
8%5%36%445%6%7%9%44%
1598
21st to endNight
8%3245%345%7%9%51%
1934
September1st to 10thNight
12%4245%345%5%8%48%
1944
11th to 20thNight
10%5%25%5%3445%7%49%
1980
21st to endNight
11%6%25%434447%51%
1980
October1st to 10thNight
11%5%145%24448%52%
1980
11th to 20thNight
15%6%245%23437%47%
2154
21st to endNight
18%8%25%433446%43%
2420
November1st to 10thNight
12%7%35%423446%51%
2406
11th to 20thNight
15%8%45%433445%45%
2470
21st to endNight
18%10%25%424445%42%
2470
December1st to 10thNight
21%12%5%7%5%33445%30%
2470
11th to 20thNight
18%11%5%9%5%34446%33%
3042
21st to endNight
18%15%48%8%46%5%5%6%20%
4532

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
57%6%8%17%10%1
1707
11th to 20thDay
63%49%16%8%1
1647
21st to endDay
55%49%22%9%1
1782
February1st to 10thDay
59%5%7%19%9%1
1706
11th to 20thDay
56%39%20%9%2
1758
21st to endDay
58%48%16%10%3
1480
March1st to 10thDay
49%410%21%15%2
1858
11th to 20thDay
54%6%9%18%11%3
1980
21st to endDay
53%6%9%21%9%2
2178
April1st to 10thDay
43%6%11%23%14%3
2042
11th to 20thDay
45%5%8%21%17%5%
2199
21st to endDay
47%7%11%22%11%2
2340
May1st to 10thDay
48%7%12%23%9%2
2340
11th to 20thDay
50%8%12%19%10%1
2305
21st to endDay
40%10%15%21%13%1
2531
June1st to 10thDay
39%9%11%24%15%1
2340
11th to 20thDay
36%11%14%20%17%2
2340
21st to endDay
39%10%14%18%16%3
2340
July1st to 10thDay
42%9%15%18%15%1
2275
11th to 20thDay
41%11%14%19%12%3
2271
21st to endDay
41%10%14%22%11%2
2405
August1st to 10thDay
39%10%16%23%12%1
2314
11th to 20thDay
43%10%13%22%12%1
2303
21st to endDay
36%9%16%22%14%3
2419
September1st to 10thDay
39%7%12%21%16%5%
1998
11th to 20thDay
37%7%12%22%19%3
1980
21st to endDay
38%6%10%23%21%2
1980
October1st to 10thDay
33%6%12%23%23%3
1980
11th to 20thDay
38%5%9%23%22%3
1805
21st to endDay
43%48%25%16%3
1933
November1st to 10thDay
35%5%7%26%23%4
1672
11th to 20thDay
44%38%22%19%4
1710
21st to endDay
46%5%8%21%17%3
1710
December1st to 10thDay
57%5%9%20%7%1
1710
11th to 20thDay
52%6%10%17%15%1
2150
21st to endDay
60%7%11%17%5%1
3124
January1st to 10thNight
58%5%8%17%11%2
2459
11th to 20thNight
61%49%16%9%1
2386
21st to endNight
55%310%22%9%2
2574
February1st to 10thNight
58%411%18%7%1
2250
11th to 20thNight
56%48%19%11%2
2099
21st to endNight
59%5%9%13%10%3
1776
March1st to 10thNight
49%47%19%18%3
2102
11th to 20thNight
50%5%10%22%12%2
1980
21st to endNight
49%7%11%20%11%2
2178
April1st to 10thNight
38%6%12%23%18%2
1931
11th to 20thNight
38%7%10%20%18%7%
1710
21st to endNight
44%6%11%22%14%2
1620
May1st to 10thNight
46%7%11%22%11%3
1620
11th to 20thNight
44%10%13%20%12%2
1593
21st to endNight
35%10%16%22%14%2
1745
June1st to 10thNight
31%10%17%23%17%3
1620
11th to 20thNight
29%10%18%22%18%3
1620
21st to endNight
34%11%14%21%15%5%
1620
July1st to 10thNight
38%10%14%19%16%3
1575
11th to 20thNight
28%10%18%21%18%5%
1566
21st to endNight
34%10%13%28%13%1
1672
August1st to 10thNight
31%10%17%24%16%2
1600
11th to 20thNight
34%9%17%25%13%2
1598
21st to endNight
29%9%14%26%18%4
1934
September1st to 10thNight
33%8%13%21%18%7%
1944
11th to 20thNight
34%7%11%22%23%3
1980
21st to endNight
34%5%10%23%26%3
1980
October1st to 10thNight
31%6%12%23%23%5%
1980
11th to 20thNight
38%5%9%23%22%4
2154
21st to endNight
42%5%7%22%19%4
2420
November1st to 10thNight
35%48%25%23%5%
2406
11th to 20thNight
41%48%18%22%5%
2470
21st to endNight
45%49%25%16%2
2470
December1st to 10thNight
56%6%9%18%10%1
2470
11th to 20thNight
53%48%21%13%1
3044
21st to endNight
60%8%10%14%7%
4532

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
30%22%30%14%41
270
11th to 20thDay
37%20%29%12%2
249
21st to endDay
33%25%28%13%2
264
February1st to 10thDay
33%25%29%8%5%
240
11th to 20thDay
45%22%26%7%
240
21st to endDay
37%23%31%8%1
198
March1st to 10thDay
31%21%34%11%4
298
11th to 20thDay
27%23%28%17%4
420
21st to endDay
32%18%26%17%6%
462
April1st to 10thDay
23%18%28%20%10%1
420
11th to 20thDay
24%15%30%17%11%2
412
21st to endDay
24%16%30%19%8%3
420
May1st to 10thDay
26%13%30%16%10%4
423
11th to 20thDay
18%12%26%26%13%6%
447
21st to endDay
15%6%24%25%18%12%
485
June1st to 10thDay
15%5%22%28%20%11%
450
11th to 20thDay
11%7%21%32%21%8%
450
21st to endDay
11%6%26%27%19%11%
450
July1st to 10thDay
16%416%22%23%20%
445
11th to 20thDay
10%5%16%31%23%15%
444
21st to endDay
14%416%28%24%13%
488
August1st to 10thDay
15%316%27%25%15%
446
11th to 20thDay
15%5%16%27%24%13%
439
21st to endDay
10%5%12%30%26%18%
495
September1st to 10thDay
14%415%21%32%13%
450
11th to 20thDay
13%5%11%27%30%14%
450
21st to endDay
18%9%18%25%23%7%
450
October1st to 10thDay
12%6%21%30%22%8%
450
11th to 20thDay
16%13%28%25%14%4
450
21st to endDay
25%11%30%23%9%1
448
November1st to 10thDay
17%12%32%26%9%3
270
11th to 20thDay
24%16%32%21%6%1
270
21st to endDay
23%15%37%19%6%1
270
December1st to 10thDay
29%21%28%17%4
270
11th to 20thDay
23%22%34%13%8%
270
21st to endDay
30%22%35%9%4
297
January1st to 10thNight
25%19%31%21%4
760
11th to 20thNight
32%14%30%20%4
735
21st to endNight
23%18%34%22%2
792
February1st to 10thNight
28%14%33%23%3
720
11th to 20thNight
30%17%34%18%1
703
21st to endNight
32%15%34%18%2
592
March1st to 10thNight
25%15%31%25%5%
720
11th to 20thNight
26%15%30%22%7%
720
21st to endNight
21%14%31%27%8%
792
April1st to 10thNight
16%15%29%31%9%
671
11th to 20thNight
17%13%27%29%12%1
533
21st to endNight
21%8%35%27%10%1
540
May1st to 10thNight
20%8%27%28%15%2
540
11th to 20thNight
17%7%21%34%18%2
531
21st to endNight
9%417%35%30%5%
584
June1st to 10thNight
8%319%39%27%3
540
11th to 20thNight
6%215%40%31%5%
540
21st to endNight
11%318%36%30%3
540
July1st to 10thNight
11%211%30%36%10%
525
11th to 20thNight
7%111%33%44%5%
522
21st to endNight
10%310%32%40%5%
591
August1st to 10thNight
10%29%34%39%7%
537
11th to 20thNight
9%38%35%36%9%
534
21st to endNight
8%38%33%41%8%
594
September1st to 10thNight
12%210%32%39%5%
684
11th to 20thNight
10%313%28%40%5%
720
21st to endNight
15%418%32%28%3
720
October1st to 10thNight
13%5%18%30%29%4
720
11th to 20thNight
18%8%24%31%16%2
720
21st to endNight
21%11%26%28%13%1
792
November1st to 10thNight
16%7%25%33%17%2
740
11th to 20thNight
20%13%26%31%9%1
760
21st to endNight
23%11%24%32%10%1
760
December1st to 10thNight
29%14%27%26%4
760
11th to 20thNight
23%13%30%27%6%1
760
21st to endNight
30%13%28%25%3
836
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