Berthoud Pass Trailhead
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Berthoud Pass Trailhead clear sky chart from 2005-11-06 to 2024-03-08.

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%
24787
22%
80114
9%
24678
44%
24678
25%
45026

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
20%
940
19%
4346
7%
926
33%
926
13%
2431
January11th to 20thNight
16%
874
20%
4221
7%
854
33%
854
11%
2442
January21st to endNight
14%
831
15%
4334
5%
814
33%
814
12%
2346
February1st to 10thNight
10%
760
19%
2470
3%
760
28%
760
14%
1492
February11th to 20thNight
12%
744
20%
2284
3%
740
31%
740
17%
1325
February21st to endNight
9%
628
22%
1884
3%
628
29%
628
15%
1135
March1st to 10thNight
16%
750
23%
2227
4%
750
34%
750
20%
1289
March11th to 20thNight
24%
720
23%
1980
8%
720
36%
720
28%
1161
March21st to endNight
19%
689
19%
2075
4%
689
34%
689
18%
1260
April1st to 10thNight
17%
540
20%
1800
4%
540
37%
540
19%
1000
April11th to 20thNight
20%
533
18%
1777
8%
533
33%
533
18%
1086
April21st to endNight
24%
540
20%
1800
8%
540
42%
540
22%
1056
May1st to 10thNight
26%
540
18%
1679
6%
540
40%
540
25%
1017
May11th to 20thNight
40%
531
15%
1418
9%
531
45%
531
27%
914
May21st to endNight
40%
584
18%
1552
8%
582
50%
582
34%
898
June1st to 10thNight
51%
540
22%
1440
12%
540
59%
540
44%
789
June11th to 20thNight
45%
540
26%
1440
13%
540
55%
540
43%
768
June21st to endNight
60%
540
25%
1440
18%
540
67%
540
50%
759
July1st to 10thNight
65%
525
20%
1400
16%
525
69%
525
39%
830
July11th to 20thNight
70%
522
24%
1392
18%
522
74%
522
45%
764
July21st to endNight
68%
591
16%
1579
13%
558
71%
558
32%
947
August1st to 10thNight
61%
537
15%
1602
12%
534
63%
534
32%
936
August11th to 20thNight
66%
534
25%
1735
21%
534
73%
534
37%
941
August21st to endNight
63%
594
26%
1980
25%
594
70%
594
34%
1090
September1st to 10thNight
57%
540
30%
1800
23%
540
70%
540
39%
923
September11th to 20thNight
52%
540
34%
1800
25%
540
65%
540
40%
899
September21st to endNight
45%
574
30%
2002
20%
574
59%
574
38%
976
October1st to 10thNight
37%
720
27%
2160
12%
720
49%
720
34%
1187
October11th to 20thNight
31%
720
31%
2160
11%
720
46%
720
35%
1050
October21st to endNight
25%
800
29%
2384
8%
800
42%
800
28%
1321
November1st to 10thNight
22%
925
29%
2405
6%
925
37%
925
33%
1299
November11th to 20thNight
16%
950
29%
2470
6%
950
34%
950
25%
1393
November21st to endNight
21%
950
25%
2616
6%
950
36%
950
28%
1510
December1st to 10thNight
15%
950
22%
2660
4%
950
30%
950
20%
1512
December11th to 20thNight
15%
950
22%
3111
4%
949
29%
949
17%
1768
December21st to endNight
13%
1041
13%
4691
4%
1026
26%
1026
11%
2512

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
47%48%8%46%5%6%7%41%
78645
Night
2426%7%45%5%6%9%50%
80983
TransparencyDay
37%9%13%20%16%5%
78354
Night
27%9%17%25%18%5%
80796
SeeingDay
17%26%29%18%8%2
14570
Night
9%25%30%24%10%1
24806

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 10thDay
238%11%11%8%6%6%8%38%
2538
11th to 20thDay
2315%16%7%9%5%36%34%
2696
21st to endDay
6%6%12%9%34447%45%
3146
February1st to 10thDay
35%12%10%6%7%5%6%8%36%
1710
11th to 20thDay
3410%10%5%6%5%5%6%45%
1783
21st to endDay
3413%11%6%7%5%46%41%
1570
March1st to 10thDay
18%410%8%45%46%7%43%
1892
11th to 20thDay
28%6%12%7%35%5%48%42%
1980
21st to endDay
29%7%11%9%5%6%46%8%33%
2281
April1st to 10thDay
29%48%7%5%5%5%7%8%40%
2160
11th to 20thDay
313%6%12%10%5%5%446%32%
2131
21st to endDay
313%7%11%8%5%5%45%6%32%
2160
May1st to 10thDay
6%15%6%8%7%46%6%6%6%32%
2273
11th to 20thDay
6%14%5%9%7%46%6%5%7%31%
2478
21st to endDay
6%10%5%7%7%46%6%7%8%34%
2724
June1st to 10thDay
6%6%26%6%37%5%7%9%43%
2520
11th to 20thDay
6%7%35%6%35%5%5%8%47%
2520
21st to endDay
46%35%6%46%6%7%8%46%
2520
July1st to 10thDay
7%7%36%7%46%6%7%8%39%
2520
11th to 20thDay
6%6%37%6%47%7%7%7%39%
2520
21st to endDay
9%8%38%9%5%6%7%7%8%31%
2642
August1st to 10thDay
12%7%48%7%45%6%6%7%32%
2328
11th to 20thDay
9%7%46%6%45%5%5%8%42%
2164
21st to endDay
8%7%38%6%5%6%6%7%7%37%
2376
September1st to 10thDay
7%6%36%6%35%45%6%50%
2160
11th to 20thDay
8%6%26%5%35%446%50%
2160
21st to endDay
5%8%2443335%5%56%
1954
October1st to 10thDay
5%8%36%5%45%447%48%
1800
11th to 20thDay
36%25%5%44347%58%
1800
21st to endDay
37%48%5%44447%52%
1954
November1st to 10thDay
1436%5%3445%7%59%
1673
11th to 20thDay
1446%5%3446%8%55%
1710
21st to endDay
437%6%45%348%54%
1562
December1st to 10thDay
339%9%6%7%7%410%43%
1520
11th to 20thDay
5%37%7%5%6%5%7%12%44%
1926
21st to endDay
4411%12%6%6%5%7%9%37%
2794
January1st to 10thNight
129%15%7%7%5%6%8%41%
4417
11th to 20thNight
1111%16%5%9%5%5%8%39%
4302
21st to endNight
3410%10%5%6%6%6%8%43%
4521
February1st to 10thNight
229%8%5%8%5%7%11%42%
2470
11th to 20thNight
237%9%5%7%6%6%10%46%
2283
21st to endNight
239%8%6%7%5%6%9%45%
1884
March1st to 10thNight
336%6%47%46%10%51%
2227
11th to 20thNight
16%48%6%3345%8%53%
1980
21st to endNight
17%47%7%5%6%5%6%8%46%
2075
April1st to 10thNight
15%25%7%45%5%6%8%52%
1800
11th to 20thNight
18%48%7%46%5%6%7%44%
1777
21st to endNight
49%37%6%4436%8%46%
1800
May1st to 10thNight
38%35%5%45%5%7%10%45%
1679
11th to 20thNight
310%44446%7%6%9%44%
1417
21st to endNight
36%25%5%3347%10%52%
1552
June1st to 10thNight
34233345%8%10%57%
1440
11th to 20thNight
42145%345%5%8%61%
1440
21st to endNight
222334448%9%60%
1440
July1st to 10thNight
4325%5%35%5%6%11%50%
1440
11th to 20thNight
2323436%5%8%9%55%
1440
21st to endNight
5%325%5%47%6%7%11%46%
1672
August1st to 10thNight
5%5%35%5%35%5%7%9%48%
1611
11th to 20thNight
6%424426%6%6%7%53%
1735
21st to endNight
44245%35%5%6%10%52%
1980
September1st to 10thNight
43245%3446%8%57%
1800
11th to 20thNight
441343345%8%61%
1800
21st to endNight
35%2332345%7%61%
2002
October1st to 10thNight
25%23435%5%5%8%59%
2160
11th to 20thNight
131433345%6%66%
2160
21st to endNight
26%35%6%34448%56%
2384
November1st to 10thNight
214435%45%8%62%
2405
11th to 20thNight
336%5%345%6%8%58%
2470
21st to endNight
1337%7%245%5%9%54%
2616
December1st to 10thNight
325%8%445%7%10%52%
2660
11th to 20thNight
226%6%5%6%6%9%12%45%
3271
21st to endNight
339%9%5%7%5%6%10%43%
4873

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
30%17%14%20%16%3
2539
11th to 20thDay
37%16%17%18%9%2
2696
21st to endDay
35%9%17%20%14%5%
3146
February1st to 10thDay
42%8%17%17%12%4
1710
11th to 20thDay
35%8%15%21%16%5%
1792
21st to endDay
40%7%11%21%16%5%
1570
March1st to 10thDay
37%8%10%26%17%1
1892
11th to 20thDay
39%7%15%22%13%4
1980
21st to endDay
47%7%12%21%10%2
2281
April1st to 10thDay
40%6%14%19%15%5%
2160
11th to 20thDay
50%6%12%17%13%2
2134
21st to endDay
49%7%11%22%9%1
2160
May1st to 10thDay
48%9%11%19%13%1
2273
11th to 20thDay
49%9%13%20%8%1
2482
21st to endDay
44%10%11%19%13%3
2724
June1st to 10thDay
34%9%14%21%16%6%
2520
11th to 20thDay
33%7%10%16%22%12%
2520
21st to endDay
31%9%10%20%20%10%
2520
July1st to 10thDay
39%9%11%16%18%7%
2451
11th to 20thDay
37%10%13%19%13%7%
2445
21st to endDay
46%12%14%15%11%3
2495
August1st to 10thDay
46%11%12%15%12%4
2313
11th to 20thDay
39%6%11%19%18%7%
2164
21st to endDay
41%9%9%19%16%6%
2376
September1st to 10thDay
33%6%8%16%24%12%
2160
11th to 20thDay
32%7%11%19%23%8%
2160
21st to endDay
29%410%25%26%6%
1954
October1st to 10thDay
34%7%10%21%22%6%
1800
11th to 20thDay
26%410%28%25%7%
1800
21st to endDay
31%5%12%27%19%6%
1954
November1st to 10thDay
24%6%13%22%29%5%
1673
11th to 20thDay
24%6%17%27%20%6%
1710
21st to endDay
29%7%12%28%17%8%
1562
December1st to 10thDay
32%11%17%24%12%4
1520
11th to 20thDay
28%10%15%28%17%2
1924
21st to endDay
32%11%15%18%20%5%
2794
January1st to 10thNight
31%10%19%23%13%3
4417
11th to 20thNight
30%15%17%24%11%4
4302
21st to endNight
29%12%18%23%13%5%
4521
February1st to 10thNight
33%10%19%21%15%3
2470
11th to 20thNight
30%7%17%25%17%3
2284
21st to endNight
32%8%17%21%17%6%
1884
March1st to 10thNight
27%8%15%25%22%2
2227
11th to 20thNight
27%7%16%29%15%5%
1980
21st to endNight
32%8%19%27%11%2
2075
April1st to 10thNight
27%10%16%25%17%5%
1800
11th to 20thNight
34%10%16%23%15%2
1777
21st to endNight
35%6%16%28%15%1
1800
May1st to 10thNight
32%10%17%26%13%2
1679
11th to 20thNight
33%12%19%25%11%1
1418
21st to endNight
26%9%20%23%19%4
1552
June1st to 10thNight
20%8%21%28%16%6%
1440
11th to 20thNight
19%7%14%21%26%13%
1440
21st to endNight
18%7%14%24%24%13%
1440
July1st to 10thNight
27%9%15%22%19%8%
1400
11th to 20thNight
21%8%18%27%18%7%
1392
21st to endNight
27%13%24%21%11%3
1579
August1st to 10thNight
30%9%21%21%14%5%
1602
11th to 20thNight
25%8%16%20%24%7%
1735
21st to endNight
26%9%15%25%20%5%
1980
September1st to 10thNight
23%7%13%21%26%10%
1800
11th to 20thNight
20%8%14%25%21%11%
1800
21st to endNight
21%6%11%31%24%6%
2002
October1st to 10thNight
23%8%13%26%21%8%
2160
11th to 20thNight
16%6%13%31%26%8%
2160
21st to endNight
26%6%15%27%20%5%
2384
November1st to 10thNight
19%7%14%27%26%6%
2405
11th to 20thNight
22%7%16%29%20%6%
2470
21st to endNight
27%7%13%28%19%7%
2616
December1st to 10thNight
23%11%22%25%14%5%
2660
11th to 20thNight
25%11%18%22%20%3
3272
21st to endNight
29%11%16%19%20%5%
4873

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
23%33%20%17%6%1
270
11th to 20thDay
23%41%21%12%21
270
21st to endDay
14%44%26%13%4
297
February1st to 10thDay
28%44%21%6%11
270
11th to 20thDay
34%36%22%5%2
270
21st to endDay
34%43%16%7%
225
March1st to 10thDay
26%38%24%10%2
283
11th to 20thDay
22%35%28%13%2
420
21st to endDay
22%45%24%8%1
462
April1st to 10thDay
25%39%26%8%2
420
11th to 20thDay
28%40%23%7%1
412
21st to endDay
20%42%26%7%3
420
May1st to 10thDay
20%34%29%13%41
491
11th to 20thDay
18%21%32%20%7%1
625
21st to endDay
16%21%31%22%8%2
679
June1st to 10thDay
10%18%30%25%14%3
630
11th to 20thDay
11%23%33%23%8%2
630
21st to endDay
7%17%35%24%15%2
630
July1st to 10thDay
8%7%33%30%19%3
621
11th to 20thDay
9%7%31%30%19%4
618
21st to endDay
10%7%30%30%18%5%
584
August1st to 10thDay
15%12%33%28%10%2
447
11th to 20thDay
11%12%34%27%14%3
437
21st to endDay
11%14%33%28%11%3
495
September1st to 10thDay
12%18%30%24%12%4
450
11th to 20thDay
10%17%40%23%8%1
450
21st to endDay
15%18%31%20%13%3
280
October1st to 10thDay
14%27%20%23%11%3
270
11th to 20thDay
20%31%28%13%6%1
270
21st to endDay
23%35%25%13%5%
297
November1st to 10thDay
24%39%20%9%8%
270
11th to 20thDay
23%38%25%9%41
270
21st to endDay
14%38%34%11%1
270
December1st to 10thDay
27%36%21%12%4
270
11th to 20thDay
20%47%24%6%4
270
21st to endDay
24%39%23%11%21
297
January1st to 10thNight
16%31%27%19%6%1
950
11th to 20thNight
17%36%27%14%5%1
874
21st to endNight
9%38%33%14%5%
836
February1st to 10thNight
11%42%32%11%4
760
11th to 20thNight
12%40%31%14%3
744
21st to endNight
13%40%32%12%1
628
March1st to 10thNight
10%38%32%16%5%
750
11th to 20thNight
6%31%36%22%5%1
720
21st to endNight
8%37%32%18%4
689
April1st to 10thNight
10%32%40%17%1
540
11th to 20thNight
10%32%35%18%6%
533
21st to endNight
11%25%36%20%7%1
540
May1st to 10thNight
7%18%44%23%7%1
540
11th to 20thNight
10%12%32%35%10%
531
21st to endNight
9%14%31%33%12%2
584
June1st to 10thNight
6%8%30%37%17%2
540
11th to 20thNight
6%12%33%37%11%1
540
21st to endNight
36%27%40%23%1
540
July1st to 10thNight
6%217%43%29%2
525
11th to 20thNight
3217%41%34%3
522
21st to endNight
5%312%41%36%3
591
August1st to 10thNight
8%316%46%26%1
537
11th to 20thNight
6%417%47%23%3
534
21st to endNight
5%419%41%27%4
594
September1st to 10thNight
5%5%24%40%21%4
540
11th to 20thNight
7%7%29%35%19%3
540
21st to endNight
6%12%33%30%16%3
574
October1st to 10thNight
6%22%33%26%12%3
720
11th to 20thNight
8%30%29%23%8%2
720
21st to endNight
11%27%34%19%7%2
800
November1st to 10thNight
7%34%35%16%7%1
925
11th to 20thNight
15%37%30%14%41
950
21st to endNight
10%29%36%21%3
950
December1st to 10thNight
12%40%31%15%2
950
11th to 20thNight
12%40%30%15%3
950
21st to endNight
15%35%31%14%41
1045
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