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 2024-11-02.

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 Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(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

By Month

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 Forecast	Data Points
Cloud Cover	Day	3 7% 4 10% 6% 6% 5% 4 6% 7% 42%	101351
	Night	1 4 2 8% 6% 5% 5% 4 7% 8% 50%	97862
Transparency	Day	35% 9% 12% 20% 17% 6%	101098
	Night	26% 9% 17% 25% 18% 6%	97705
Seeing	Day	17% 27% 29% 18% 8% 2	15563
	Night	10% 25% 30% 24% 10% 1	25576

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	2 3 9% 10% 13% 8% 4 6% 7% 38%	2538
	11th to 20th	Day	3 2 20% 11% 10% 7% 4 4 6% 33%	2696
	21st to end	Day	6% 6% 13% 7% 5% 4 3 4 6% 45%	3146
February	1st to 10th	Day	3 5% 14% 9% 7% 6% 4 7% 7% 36%	1710
	11th to 20th	Day	3 3 12% 8% 7% 5% 5% 5% 6% 45%	1783
	21st to end	Day	4 4 15% 9% 8% 6% 4 5% 6% 41%	1570
March	1st to 10th	Day	5% 5% 19% 7% 4 4 3 4 5% 43%	3180
	11th to 20th	Day	1 7% 7% 14% 5% 4 5% 4 6% 9% 39%	3490
	21st to end	Day	1 9% 7% 17% 9% 7% 5% 4 5% 6% 29%	4005
April	1st to 10th	Day	1 10% 4 9% 7% 6% 5% 4 7% 7% 40%	2280
	11th to 20th	Day	2 14% 6% 14% 8% 6% 4 3 4 6% 32%	2251
	21st to end	Day	2 15% 6% 13% 6% 6% 5% 4 5% 6% 32%	2280
May	1st to 10th	Day	3 16% 7% 15% 8% 6% 6% 5% 5% 5% 25%	4008
	11th to 20th	Day	4 13% 3 8% 6% 5% 6% 5% 7% 7% 36%	4388
	21st to end	Day	3 7% 3 7% 5% 5% 6% 5% 8% 9% 42%	4825
June	1st to 10th	Day	5% 6% 2 7% 5% 5% 6% 4 8% 8% 44%	2660
	11th to 20th	Day	6% 7% 2 6% 5% 5% 5% 4 6% 7% 47%	2660
	21st to end	Day	4 6% 3 6% 5% 5% 6% 5% 7% 8% 46%	2660
July	1st to 10th	Day	5% 6% 2 6% 4 4 5% 4 6% 6% 52%	4430
	11th to 20th	Day	4 5% 2 6% 6% 6% 7% 6% 9% 9% 40%	4430
	21st to end	Day	6% 7% 2 7% 6% 5% 6% 5% 6% 7% 42%	4621
August	1st to 10th	Day	7% 6% 3 8% 7% 6% 7% 6% 8% 9% 33%	4092
	11th to 20th	Day	6% 6% 3 7% 6% 5% 6% 5% 7% 9% 41%	3791
	21st to end	Day	5% 6% 3 9% 6% 6% 6% 5% 7% 8% 39%	4180
September	1st to 10th	Day	7% 6% 3 7% 5% 4 4 4 5% 6% 49%	2280
	11th to 20th	Day	7% 6% 2 6% 5% 4 5% 3 5% 6% 50%	2280
	21st to end	Day	5% 9% 2 5% 3 3 3 2 5% 6% 56%	2061
October	1st to 10th	Day	5% 8% 2 7% 4 5% 5% 3 4 7% 50%	1900
	11th to 20th	Day	3 7% 2 6% 5% 5% 4 3 4 7% 56%	1900
	21st to end	Day	2 7% 3 8% 4 4 3 3 4 7% 53%	2062
November	1st to 10th	Day	1 4 2 7% 4 4 4 3 5% 7% 59%	1682
	11th to 20th	Day	1 5% 3 6% 5% 4 4 3 7% 7% 55%	1710
	21st to end	Day	5% 3 8% 5% 5% 4 3 5% 8% 53%	1562
December	1st to 10th	Day	3 3 10% 9% 7% 7% 5% 5% 9% 43%	1520
	11th to 20th	Day	6% 2 8% 6% 6% 5% 4 7% 11% 44%	1926
	21st to end	Day	4 3 13% 9% 7% 6% 5% 7% 8% 37%	2794
January	1st to 10th	Night	1 2 12% 13% 9% 5% 4 6% 7% 41%	4417
	11th to 20th	Night	1 1 14% 12% 6% 9% 4 5% 8% 39%	4302
	21st to end	Night	3 3 11% 8% 7% 5% 5% 7% 7% 43%	4521
February	1st to 10th	Night	2 2 11% 7% 7% 7% 5% 8% 10% 42%	2470
	11th to 20th	Night	2 3 8% 8% 7% 7% 4 7% 10% 46%	2283
	21st to end	Night	3 3 10% 6% 8% 6% 4 7% 7% 45%	1884
March	1st to 10th	Night	3 5% 11% 6% 5% 6% 4 6% 7% 48%	3685
	11th to 20th	Night	1 5% 5% 14% 6% 3 3 3 4 7% 48%	3490
	21st to end	Night	5% 4 11% 7% 7% 6% 5% 7% 8% 39%	3642
April	1st to 10th	Night	5% 2 7% 6% 5% 5% 4 7% 8% 51%	1900
	11th to 20th	Night	1 10% 3 9% 6% 5% 5% 4 6% 6% 44%	1877
	21st to end	Night	2 11% 3 8% 5% 5% 4 2 6% 7% 46%	1900
May	1st to 10th	Night	2 9% 3 9% 7% 4 5% 5% 7% 9% 41%	2954
	11th to 20th	Night	3 10% 3 5% 3 4 6% 5% 8% 10% 43%	2517
	21st to end	Night	1 5% 2 7% 5% 4 4 4 6% 8% 54%	2762
June	1st to 10th	Night	3 4 2 4 3 3 4 4 8% 10% 57%	1520
	11th to 20th	Night	3 2 1 4 4 4 3 4 5% 8% 61%	1520
	21st to end	Night	2 3 2 3 3 5% 3 4 8% 8% 59%	1520
July	1st to 10th	Night	2 3 1 5% 4 4 4 3 5% 9% 60%	2540
	11th to 20th	Night	1 2 1 3 3 5% 6% 5% 9% 11% 54%	2540
	21st to end	Night	2 3 1 4 4 4 5% 4 7% 9% 56%	2938
August	1st to 10th	Night	3 4 2 5% 4 5% 6% 5% 10% 11% 46%	2847
	11th to 20th	Night	3 3 1 4 3 4 6% 5% 8% 10% 53%	3046
	21st to end	Night	2 3 1 6% 5% 5% 6% 5% 7% 9% 50%	3487
September	1st to 10th	Night	4 3 1 4 4 4 4 4 6% 8% 58%	1900
	11th to 20th	Night	4 4 1 3 3 4 3 3 5% 7% 62%	1900
	21st to end	Night	3 5% 2 4 3 3 3 3 5% 7% 61%	2114
October	1st to 10th	Night	2 5% 2 4 4 4 4 4 5% 8% 60%	2280
	11th to 20th	Night	1 3 1 4 3 4 3 3 6% 6% 66%	2280
	21st to end	Night	2 6% 3 6% 4 3 3 3 4 8% 57%	2517
November	1st to 10th	Night	2 1 5% 3 4 5% 3 5% 8% 62%	2419
	11th to 20th	Night	3 2 7% 4 4 4 4 6% 8% 57%	2470
	21st to end	Night	1 3 3 8% 7% 4 3 4 6% 8% 54%	2616
December	1st to 10th	Night	3 2 6% 7% 5% 5% 4 8% 9% 52%	2660
	11th to 20th	Night	3 2 7% 5% 6% 6% 5% 10% 11% 45%	3271
	21st to end	Night	4 3 10% 7% 7% 6% 4 7% 9% 43%	4873

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	30% 17% 14% 20% 16% 3	2539
	11th to 20th	Day	37% 16% 17% 18% 9% 2	2696
	21st to end	Day	35% 9% 17% 20% 14% 5%	3146
February	1st to 10th	Day	42% 8% 17% 17% 12% 4	1710
	11th to 20th	Day	35% 8% 15% 21% 16% 5%	1792
	21st to end	Day	40% 7% 11% 21% 16% 5%	1570
March	1st to 10th	Day	35% 9% 8% 25% 17% 6%	3180
	11th to 20th	Day	36% 12% 14% 26% 9% 2	3490
	21st to end	Day	44% 10% 13% 22% 9% 1	4005
April	1st to 10th	Day	39% 7% 14% 20% 15% 5%	2280
	11th to 20th	Day	49% 7% 12% 17% 13% 2	2254
	21st to end	Day	48% 8% 11% 22% 10% 1	2280
May	1st to 10th	Day	45% 12% 11% 18% 13% 1	4008
	11th to 20th	Day	36% 12% 16% 23% 13% 1	4392
	21st to end	Day	28% 10% 12% 26% 19% 4	4825
June	1st to 10th	Day	33% 10% 13% 22% 16% 6%	2660
	11th to 20th	Day	33% 7% 11% 16% 22% 11%	2660
	21st to end	Day	31% 9% 10% 20% 20% 10%	2660
July	1st to 10th	Day	28% 7% 8% 13% 23% 21%	4361
	11th to 20th	Day	31% 11% 12% 19% 18% 10%	4355
	21st to end	Day	34% 10% 11% 15% 14% 16%	4475
August	1st to 10th	Day	40% 12% 16% 16% 12% 5%	4078
	11th to 20th	Day	36% 8% 13% 15% 18% 10%	3828
	21st to end	Day	37% 9% 9% 16% 20% 9%	4179
September	1st to 10th	Day	33% 6% 8% 17% 24% 12%	2280
	11th to 20th	Day	32% 7% 11% 19% 24% 8%	2280
	21st to end	Day	28% 4 10% 24% 28% 6%	2061
October	1st to 10th	Day	32% 6% 10% 22% 23% 7%	1900
	11th to 20th	Day	27% 5% 10% 28% 24% 6%	1900
	21st to end	Day	30% 5% 11% 28% 20% 6%	2062
November	1st to 10th	Day	24% 6% 13% 22% 29% 5%	1682
	11th to 20th	Day	24% 6% 17% 27% 20% 6%	1710
	21st to end	Day	29% 7% 12% 28% 17% 8%	1562
December	1st to 10th	Day	32% 11% 17% 24% 12% 4	1520
	11th to 20th	Day	28% 10% 15% 28% 17% 2	1924
	21st to end	Day	32% 11% 15% 18% 20% 5%	2794
January	1st to 10th	Night	31% 10% 19% 23% 13% 3	4417
	11th to 20th	Night	30% 15% 17% 24% 11% 4	4302
	21st to end	Night	29% 12% 18% 23% 13% 5%	4521
February	1st to 10th	Night	33% 10% 19% 21% 15% 3	2470
	11th to 20th	Night	30% 7% 17% 25% 17% 3	2284
	21st to end	Night	32% 8% 17% 21% 17% 6%	1884
March	1st to 10th	Night	28% 8% 12% 23% 22% 6%	3685
	11th to 20th	Night	28% 11% 14% 30% 14% 3	3490
	21st to end	Night	27% 12% 24% 27% 9% 1	3642
April	1st to 10th	Night	26% 11% 17% 25% 17% 5%	1900
	11th to 20th	Night	34% 10% 15% 23% 15% 3	1877
	21st to end	Night	35% 6% 16% 28% 15% 1	1900
May	1st to 10th	Night	28% 11% 16% 29% 14% 2	2954
	11th to 20th	Night	27% 15% 18% 26% 14%	2518
	21st to end	Night	19% 10% 17% 30% 21% 2	2762
June	1st to 10th	Night	19% 9% 21% 29% 17% 6%	1520
	11th to 20th	Night	18% 7% 14% 22% 26% 13%	1520
	21st to end	Night	19% 7% 14% 24% 24% 12%	1520
July	1st to 10th	Night	21% 7% 10% 20% 20% 21%	2500
	11th to 20th	Night	18% 9% 18% 31% 18% 7%	2492
	21st to end	Night	20% 10% 17% 26% 11% 16%	2846
August	1st to 10th	Night	27% 10% 24% 20% 17% 3	2838
	11th to 20th	Night	23% 9% 25% 16% 19% 9%	3075
	21st to end	Night	27% 9% 15% 21% 24% 4	3487
September	1st to 10th	Night	23% 7% 13% 22% 26% 9%	1900
	11th to 20th	Night	20% 8% 14% 25% 23% 11%	1900
	21st to end	Night	21% 6% 11% 30% 26% 6%	2114
October	1st to 10th	Night	22% 8% 13% 26% 23% 9%	2280
	11th to 20th	Night	16% 6% 13% 32% 25% 8%	2280
	21st to end	Night	25% 6% 14% 28% 21% 6%	2517
November	1st to 10th	Night	19% 7% 14% 28% 26% 6%	2419
	11th to 20th	Night	22% 7% 16% 29% 20% 6%	2470
	21st to end	Night	27% 7% 13% 28% 19% 7%	2616
December	1st to 10th	Night	23% 11% 22% 25% 14% 5%	2660
	11th to 20th	Night	25% 11% 18% 22% 20% 3	3272
	21st to end	Night	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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	23% 33% 20% 17% 6% 1	270
	11th to 20th	Day	23% 41% 21% 12% 2 1	270
	21st to end	Day	14% 44% 26% 13% 4	297
February	1st to 10th	Day	28% 44% 21% 6% 1 1	270
	11th to 20th	Day	34% 36% 22% 5% 2	270
	21st to end	Day	34% 43% 16% 7%	225
March	1st to 10th	Day	25% 37% 23% 13% 2	294
	11th to 20th	Day	21% 33% 29% 14% 2	460
	21st to end	Day	23% 43% 24% 9% 1	506
April	1st to 10th	Day	25% 40% 25% 8% 2	460
	11th to 20th	Day	28% 40% 23% 8% 1	452
	21st to end	Day	20% 42% 28% 7% 3	460
May	1st to 10th	Day	22% 34% 27% 12% 4 1	535
	11th to 20th	Day	17% 22% 34% 19% 7% 1	675
	21st to end	Day	16% 22% 31% 22% 8% 1	734
June	1st to 10th	Day	10% 19% 30% 25% 13% 3	680
	11th to 20th	Day	12% 24% 33% 21% 8% 2	680
	21st to end	Day	9% 19% 34% 22% 14% 2	680
July	1st to 10th	Day	9% 9% 33% 28% 17% 3	671
	11th to 20th	Day	9% 9% 32% 28% 18% 4	668
	21st to end	Day	10% 9% 30% 30% 16% 4	633
August	1st to 10th	Day	15% 14% 34% 26% 9% 2	487
	11th to 20th	Day	12% 15% 33% 25% 12% 3	477
	21st to end	Day	12% 16% 33% 26% 11% 2	539
September	1st to 10th	Day	12% 17% 31% 25% 11% 4	490
	11th to 20th	Day	12% 19% 39% 22% 8% 1	490
	21st to end	Day	15% 20% 31% 19% 13% 3	310
October	1st to 10th	Day	14% 29% 22% 22% 11% 3	300
	11th to 20th	Day	20% 31% 28% 13% 6% 1	300
	21st to end	Day	24% 37% 23% 12% 4	330
November	1st to 10th	Day	24% 39% 21% 9% 8%	273
	11th to 20th	Day	23% 38% 25% 9% 4 1	270
	21st to end	Day	14% 38% 34% 11% 1	270
December	1st to 10th	Day	27% 36% 21% 12% 4	270
	11th to 20th	Day	20% 47% 24% 6% 4	270
	21st to end	Day	24% 39% 23% 11% 2 1	297
January	1st to 10th	Night	16% 31% 27% 19% 6% 1	950
	11th to 20th	Night	17% 36% 27% 14% 5% 1	874
	21st to end	Night	9% 38% 33% 14% 5%	836
February	1st to 10th	Night	11% 42% 32% 11% 4	760
	11th to 20th	Night	12% 40% 31% 14% 3	744
	21st to end	Night	13% 40% 32% 12% 1	628
March	1st to 10th	Night	9% 37% 32% 16% 5%	760
	11th to 20th	Night	6% 30% 36% 23% 5% 1	760
	21st to end	Night	8% 37% 33% 17% 4	727
April	1st to 10th	Night	10% 33% 39% 17% 2	570
	11th to 20th	Night	10% 32% 35% 17% 5%	563
	21st to end	Night	12% 25% 37% 19% 6% 1	570
May	1st to 10th	Night	9% 18% 44% 22% 6% 1	570
	11th to 20th	Night	9% 13% 34% 34% 9%	561
	21st to end	Night	8% 16% 31% 32% 11% 2	617
June	1st to 10th	Night	6% 9% 31% 36% 16% 2	570
	11th to 20th	Night	6% 14% 34% 35% 10% 1	570
	21st to end	Night	4 7% 28% 39% 22% 1	570
July	1st to 10th	Night	6% 4 18% 42% 28% 2	555
	11th to 20th	Night	3 2 19% 41% 32% 3	552
	21st to end	Night	5% 3 14% 41% 34% 3	624
August	1st to 10th	Night	8% 3 18% 45% 25% 1	567
	11th to 20th	Night	6% 5% 19% 45% 21% 3	564
	21st to end	Night	5% 5% 19% 41% 26% 4	627
September	1st to 10th	Night	5% 5% 25% 41% 20% 4	570
	11th to 20th	Night	7% 8% 30% 34% 18% 3	570
	21st to end	Night	7% 12% 33% 30% 16% 3	606
October	1st to 10th	Night	5% 21% 35% 25% 11% 2	760
	11th to 20th	Night	8% 30% 30% 23% 8% 2	760
	21st to end	Night	13% 28% 33% 18% 7% 2	845
November	1st to 10th	Night	8% 34% 35% 16% 7% 1	931
	11th to 20th	Night	15% 37% 30% 14% 4 1	950
	21st to end	Night	10% 29% 36% 21% 3	950
December	1st to 10th	Night	12% 40% 31% 15% 2	950
	11th to 20th	Night	12% 40% 30% 15% 3	950
	21st to end	Night	15% 35% 31% 14% 4 1	1045

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