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 2026-09-29.

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 6% 3 9% 6% 6% 6% 4 7% 8% 43%	158069
	Night	1 3 2 7% 5% 5% 5% 4 7% 9% 52%	150950
Transparency	Day	32% 10% 12% 21% 18% 7%	153002
	Night	23% 10% 16% 26% 20% 6%	147026
Seeing	Day	20% 27% 28% 16% 7% 1	18202
	Night	12% 25% 30% 23% 9% 1	28139

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	3 4 13% 9% 9% 6% 3 6% 7% 41%	4720
	11th to 20th	Day	2 1 11% 8% 9% 7% 4 6% 9% 43%	5036
	21st to end	Day	3 4 10% 5% 6% 4 3 5% 10% 49%	5844
February	1st to 10th	Day	3 5% 13% 9% 7% 6% 4 7% 8% 39%	1890
	11th to 20th	Day	3 3 12% 8% 7% 5% 5% 5% 7% 43%	1977
	21st to end	Day	4 3 14% 8% 8% 5% 4 5% 6% 43%	1730
March	1st to 10th	Day	5% 4 18% 6% 4 4 2 4 5% 48%	4665
	11th to 20th	Day	1 5% 5% 13% 6% 5% 5% 4 6% 10% 40%	5110
	21st to end	Day	1 7% 6% 14% 8% 6% 6% 4 8% 8% 33%	5871
April	1st to 10th	Day	1 9% 4 9% 6% 6% 5% 4 7% 8% 40%	2520
	11th to 20th	Day	2 14% 6% 14% 7% 5% 4 3 5% 6% 34%	2491
	21st to end	Day	2 14% 6% 12% 6% 6% 5% 4 5% 7% 32%	2520
May	1st to 10th	Day	2 17% 6% 12% 6% 5% 5% 4 5% 5% 30%	7452
	11th to 20th	Day	4 12% 3 8% 5% 6% 7% 5% 7% 8% 36%	8191
	21st to end	Day	4 7% 3 7% 6% 6% 7% 6% 8% 9% 39%	9026
June	1st to 10th	Day	5% 6% 2 7% 5% 6% 6% 4 8% 8% 43%	2940
	11th to 20th	Day	5% 7% 2 5% 5% 5% 5% 4 6% 7% 49%	2940
	21st to end	Day	4 6% 3 6% 5% 5% 6% 5% 7% 8% 47%	2940
July	1st to 10th	Day	4 5% 2 5% 5% 5% 7% 5% 8% 8% 47%	8249
	11th to 20th	Day	3 3 2 6% 6% 6% 7% 6% 9% 9% 43%	8250
	21st to end	Day	6% 7% 3 8% 7% 6% 7% 5% 7% 8% 36%	8608
August	1st to 10th	Day	4 4 2 5% 4 5% 6% 5% 8% 10% 46%	7549
	11th to 20th	Day	6% 6% 3 8% 6% 6% 6% 5% 8% 9% 39%	7120
	21st to end	Day	6% 6% 3 9% 6% 7% 7% 5% 8% 10% 35%	7751
September	1st to 10th	Day	6% 6% 3 7% 5% 4 5% 4 5% 6% 49%	2520
	11th to 20th	Day	7% 6% 2 7% 5% 5% 6% 3 5% 6% 48%	2520
	21st to end	Day	6% 9% 2 5% 3 3 3 2 5% 6% 54%	2258
October	1st to 10th	Day	3 5% 1 4 2 3 3 2 3 6% 68%	3270
	11th to 20th	Day	3 7% 2 6% 5% 5% 6% 5% 7% 8% 47%	3250
	21st to end	Day	2 6% 3 6% 3 3 3 3 6% 7% 58%	3494
November	1st to 10th	Day	1 4 2 8% 4 4 4 3 5% 7% 57%	1853
	11th to 20th	Day	1 5% 3 6% 5% 4 4 3 7% 8% 56%	1890
	21st to end	Day	5% 3 9% 6% 5% 4 3 5% 8% 53%	1726
December	1st to 10th	Day	2 2 7% 7% 5% 6% 3 4 8% 56%	2700
	11th to 20th	Day	4 2 6% 5% 4 4 4 6% 10% 54%	3106
	21st to end	Day	5% 3 11% 8% 6% 5% 4 7% 10% 41%	4092
January	1st to 10th	Night	1 2 10% 10% 8% 5% 4 7% 9% 44%	8201
	11th to 20th	Night	1 1 11% 9% 7% 8% 4 5% 8% 47%	8010
	21st to end	Night	2 2 7% 6% 7% 6% 5% 7% 9% 49%	8370
February	1st to 10th	Night	2 2 10% 7% 7% 6% 4 8% 9% 45%	2730
	11th to 20th	Night	2 3 8% 8% 6% 7% 4 7% 10% 45%	2529
	21st to end	Night	2 3 10% 6% 7% 6% 4 7% 7% 47%	2076
March	1st to 10th	Night	4 5% 11% 6% 6% 5% 4 6% 8% 47%	5418
	11th to 20th	Night	4 4 13% 6% 4 3 3 5% 8% 49%	5110
	21st to end	Night	1 5% 3 10% 7% 7% 6% 5% 9% 11% 38%	5334
April	1st to 10th	Night	5% 2 7% 6% 5% 5% 4 7% 9% 50%	2100
	11th to 20th	Night	1 9% 3 9% 6% 5% 5% 4 6% 6% 45%	2077
	21st to end	Night	2 11% 3 8% 5% 4 4 2 6% 7% 47%	2100
May	1st to 10th	Night	2 12% 3 8% 5% 4 5% 5% 7% 9% 41%	5487
	11th to 20th	Night	2 8% 2 6% 4 4 5% 4 8% 10% 48%	4701
	21st to end	Night	2 4 2 7% 4 4 4 4 7% 9% 54%	5181
June	1st to 10th	Night	3 4 2 4 3 3 3 4 8% 10% 57%	1680
	11th to 20th	Night	3 2 1 4 4 3 3 4 5% 8% 63%	1680
	21st to end	Night	2 3 2 3 3 5% 3 4 7% 8% 60%	1680
July	1st to 10th	Night	2 2 1 4 3 3 4 4 6% 9% 63%	4740
	11th to 20th	Night	1 1 1 2 3 4 5% 5% 8% 10% 60%	4740
	21st to end	Night	2 2 1 4 4 5% 6% 6% 9% 13% 49%	5483
August	1st to 10th	Night	2 2 1 4 3 4 5% 4 8% 10% 57%	5273
	11th to 20th	Night	2 2 1 3 3 3 5% 4 8% 11% 57%	5734
	21st to end	Night	3 3 2 6% 5% 6% 6% 6% 10% 11% 43%	6465
September	1st to 10th	Night	4 3 1 4 4 4 4 4 6% 8% 58%	2100
	11th to 20th	Night	4 4 1 3 4 4 4 3 6% 7% 60%	2100
	21st to end	Night	3 6% 2 4 3 3 3 3 5% 7% 60%	2313
October	1st to 10th	Night	1 3 1 2 3 3 3 2 4 5% 73%	3920
	11th to 20th	Night	1 3 1 5% 3 4 3 3 6% 8% 63%	3898
	21st to end	Night	1 4 2 4 3 3 3 3 4 8% 65%	4274
November	1st to 10th	Night	3 2 5% 3 4 5% 3 5% 8% 62%	2665
	11th to 20th	Night	3 2 6% 4 4 4 4 6% 8% 58%	2730
	21st to end	Night	1 3 3 8% 6% 4 3 4 7% 8% 54%	2892
December	1st to 10th	Night	2 1 4 5% 4 4 3 6% 10% 63%	4710
	11th to 20th	Night	2 1 4 4 5% 5% 5% 8% 11% 55%	5321
	21st to end	Night	4 3 11% 8% 6% 6% 5% 8% 10% 39%	7128

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	31% 13% 12% 25% 15% 4	4723
	11th to 20th	Day	26% 13% 15% 26% 13% 7%	5036
	21st to end	Day	28% 9% 14% 20% 20% 9%	5844
February	1st to 10th	Day	39% 8% 16% 19% 13% 5%	1890
	11th to 20th	Day	35% 9% 14% 22% 16% 5%	1986
	21st to end	Day	37% 6% 11% 21% 19% 6%	1730
March	1st to 10th	Day	33% 8% 6% 22% 21% 11%	4665
	11th to 20th	Day	33% 11% 12% 26% 16% 3	5110
	21st to end	Day	36% 13% 16% 24% 10% 1	5871
April	1st to 10th	Day	38% 7% 13% 21% 16% 5%	2520
	11th to 20th	Day	46% 7% 11% 17% 16% 3	2494
	21st to end	Day	47% 8% 11% 22% 10% 2	2520
May	1st to 10th	Day	43% 11% 10% 20% 15% 1	7452
	11th to 20th	Day	34% 12% 12% 23% 17% 3	8195
	21st to end	Day	31% 11% 12% 25% 17% 4	9027
June	1st to 10th	Day	33% 10% 13% 21% 17% 5%	2940
	11th to 20th	Day	31% 7% 10% 16% 23% 13%	2940
	21st to end	Day	30% 9% 10% 20% 21% 11%	2940
July	1st to 10th	Day	24% 9% 8% 14% 24% 21%	8181
	11th to 20th	Day	27% 11% 12% 20% 17% 13%	8175
	21st to end	Day	39% 12% 15% 13% 13% 9%	8417
August	1st to 10th	Day	30% 10% 13% 16% 17% 13%	5978
	11th to 20th	Day	36% 11% 17% 16% 13% 7%	5613
	21st to end	Day	36% 11% 16% 17% 14% 6%	6078
September	1st to 10th	Day	32% 7% 9% 18% 23% 11%	2520
	11th to 20th	Day	33% 7% 11% 19% 23% 7%	2520
	21st to end	Day	29% 5% 9% 24% 27% 6%	2258
October	1st to 10th	Day	20% 4 6% 22% 35% 12%	3270
	11th to 20th	Day	28% 8% 12% 28% 20% 5%	3250
	21st to end	Day	23% 4 9% 31% 29% 4	3494
November	1st to 10th	Day	25% 6% 13% 23% 29% 5%	1853
	11th to 20th	Day	23% 6% 16% 28% 20% 7%	1890
	21st to end	Day	28% 7% 11% 28% 18% 7%	1726
December	1st to 10th	Day	23% 9% 12% 35% 17% 5%	2700
	11th to 20th	Day	20% 9% 15% 34% 20% 2	3104
	21st to end	Day	28% 10% 15% 19% 23% 4	4092
January	1st to 10th	Night	26% 11% 15% 28% 15% 5%	8202
	11th to 20th	Night	25% 14% 12% 27% 16% 7%	8010
	21st to end	Night	20% 14% 14% 21% 21% 11%	8370
February	1st to 10th	Night	30% 10% 18% 21% 17% 4	2730
	11th to 20th	Night	29% 8% 17% 26% 16% 4	2530
	21st to end	Night	30% 8% 16% 21% 20% 7%	2076
March	1st to 10th	Night	28% 9% 10% 20% 25% 10%	5418
	11th to 20th	Night	25% 11% 10% 25% 24% 5%	5110
	21st to end	Night	25% 13% 24% 27% 9% 1	5334
April	1st to 10th	Night	25% 11% 16% 27% 17% 4	2100
	11th to 20th	Night	33% 10% 14% 24% 17% 3	2077
	21st to end	Night	33% 6% 15% 29% 16% 1	2100
May	1st to 10th	Night	30% 11% 16% 29% 13% 1	5485
	11th to 20th	Night	23% 12% 14% 33% 16% 1	4702
	21st to end	Night	21% 9% 18% 30% 21% 1	5182
June	1st to 10th	Night	19% 9% 20% 29% 17% 5%	1680
	11th to 20th	Night	17% 7% 13% 22% 27% 14%	1680
	21st to end	Night	19% 6% 13% 23% 25% 14%	1680
July	1st to 10th	Night	16% 6% 8% 17% 32% 21%	4700
	11th to 20th	Night	13% 9% 17% 31% 22% 8%	4692
	21st to end	Night	21% 11% 27% 20% 11% 9%	5362
August	1st to 10th	Night	21% 9% 20% 19% 23% 9%	4168
	11th to 20th	Night	21% 11% 28% 20% 14% 6%	4517
	21st to end	Night	28% 11% 24% 17% 17% 3	5069
September	1st to 10th	Night	22% 7% 13% 24% 25% 9%	2100
	11th to 20th	Night	21% 8% 13% 26% 22% 10%	2100
	21st to end	Night	22% 6% 10% 30% 25% 6%	2313
October	1st to 10th	Night	14% 5% 8% 28% 35% 10%	3920
	11th to 20th	Night	16% 6% 12% 41% 20% 4	3898
	21st to end	Night	17% 5% 10% 30% 31% 7%	4274
November	1st to 10th	Night	19% 7% 14% 27% 27% 6%	2665
	11th to 20th	Night	21% 7% 16% 30% 21% 6%	2730
	21st to end	Night	26% 7% 13% 28% 20% 6%	2892
December	1st to 10th	Night	15% 8% 15% 37% 20% 5%	4710
	11th to 20th	Night	17% 11% 15% 29% 25% 3	5322
	21st to end	Night	28% 13% 15% 20% 20% 3	7128

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	31% 33% 17% 14% 5% 1	330
	11th to 20th	Day	29% 39% 19% 10% 2 1	330
	21st to end	Day	25% 39% 23% 10% 3	363
February	1st to 10th	Day	38% 37% 18% 5% 1 1	330
	11th to 20th	Day	42% 33% 19% 4 2	330
	21st to end	Day	39% 40% 15% 5%	273
March	1st to 10th	Day	29% 37% 21% 11% 1	356
	11th to 20th	Day	29% 31% 26% 12% 2	540
	21st to end	Day	26% 43% 22% 7% 1	594
April	1st to 10th	Day	28% 39% 24% 7% 2	540
	11th to 20th	Day	30% 41% 21% 6% 1	532
	21st to end	Day	23% 40% 28% 6% 3	540
May	1st to 10th	Day	25% 34% 26% 12% 3	623
	11th to 20th	Day	19% 23% 33% 17% 6% 1	775
	21st to end	Day	17% 24% 31% 20% 7% 1	844
June	1st to 10th	Day	12% 21% 31% 22% 12% 2	780
	11th to 20th	Day	14% 26% 32% 19% 7% 2	780
	21st to end	Day	11% 21% 33% 21% 12% 2	780
July	1st to 10th	Day	9% 12% 35% 27% 16% 3	771
	11th to 20th	Day	8% 11% 32% 29% 17% 4	768
	21st to end	Day	10% 10% 32% 29% 15% 4	731
August	1st to 10th	Day	15% 19% 33% 23% 8% 2	567
	11th to 20th	Day	11% 17% 33% 24% 12% 2	557
	21st to end	Day	12% 18% 33% 25% 10% 2	627
September	1st to 10th	Day	12% 20% 33% 22% 10% 3	570
	11th to 20th	Day	14% 22% 38% 19% 6% 1	570
	21st to end	Day	17% 20% 32% 17% 11% 2	365
October	1st to 10th	Day	15% 29% 23% 20% 10% 2	330
	11th to 20th	Day	25% 31% 26% 12% 5% 1	330
	21st to end	Day	27% 36% 22% 11% 4	363
November	1st to 10th	Day	28% 38% 20% 8% 6%	330
	11th to 20th	Day	29% 36% 23% 8% 3 1	330
	21st to end	Day	23% 37% 29% 10% 1	330
December	1st to 10th	Day	35% 31% 21% 10% 4	330
	11th to 20th	Day	31% 40% 21% 5% 3	330
	21st to end	Day	33% 35% 21% 9% 2 1	363
January	1st to 10th	Night	21% 30% 25% 17% 6% 1	1050
	11th to 20th	Night	21% 35% 26% 13% 5% 1	966
	21st to end	Night	14% 37% 31% 13% 4	924
February	1st to 10th	Night	17% 40% 29% 10% 4	840
	11th to 20th	Night	18% 38% 29% 13% 3	824
	21st to end	Night	18% 39% 30% 12% 1	692
March	1st to 10th	Night	12% 37% 31% 15% 5%	840
	11th to 20th	Night	13% 28% 33% 21% 4	840
	21st to end	Night	11% 37% 32% 16% 3	803
April	1st to 10th	Night	12% 33% 37% 17% 1	630
	11th to 20th	Night	13% 31% 35% 16% 5%	623
	21st to end	Night	13% 25% 38% 18% 6% 1	630
May	1st to 10th	Night	10% 18% 44% 22% 6% 1	630
	11th to 20th	Night	11% 14% 34% 32% 9%	621
	21st to end	Night	8% 17% 32% 31% 10% 1	683
June	1st to 10th	Night	7% 10% 32% 35% 15% 1	630
	11th to 20th	Night	7% 15% 36% 33% 9% 1	630
	21st to end	Night	5% 9% 29% 36% 20% 1	630
July	1st to 10th	Night	6% 5% 21% 41% 25% 2	615
	11th to 20th	Night	3 2 21% 42% 29% 3	612
	21st to end	Night	5% 2 17% 43% 31% 3	690
August	1st to 10th	Night	7% 5% 22% 42% 22% 1	627
	11th to 20th	Night	6% 4 22% 45% 20% 3	624
	21st to end	Night	5% 5% 22% 40% 24% 4	693
September	1st to 10th	Night	5% 6% 27% 40% 18% 4	630
	11th to 20th	Night	8% 9% 32% 32% 16% 3	630
	21st to end	Night	7% 12% 35% 29% 14% 3	662
October	1st to 10th	Night	6% 22% 35% 24% 11% 2	800
	11th to 20th	Night	10% 30% 30% 22% 8% 2	800
	21st to end	Night	14% 27% 33% 18% 7% 1	890
November	1st to 10th	Night	12% 33% 33% 15% 6% 1	1025
	11th to 20th	Night	17% 38% 29% 12% 3 1	1050
	21st to end	Night	14% 30% 34% 19% 3	1050
December	1st to 10th	Night	16% 38% 30% 14% 2	1050
	11th to 20th	Night	18% 38% 27% 13% 3	1050
	21st to end	Night	21% 33% 29% 13% 3 1	1155

Page generated at 2026-09-26 02:18:40. Version ac07

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