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 2025-05-26.

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% 5% 4 6% 8% 43%	118091
	Night	1 4 2 7% 6% 5% 5% 4 6% 9% 51%	120087
Transparency	Day	33% 9% 12% 21% 18% 7%	117838
	Night	24% 10% 15% 26% 20% 6%	119930
Seeing	Day	19% 27% 28% 17% 7% 1	16275
	Night	11% 25% 30% 23% 10% 1	26412

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 4 12% 8% 10% 6% 3 6% 8% 40%	3638
	11th to 20th	Day	2 2 15% 9% 10% 8% 5% 6% 9% 35%	3866
	21st to end	Day	5% 5% 11% 6% 5% 4 3 5% 6% 49%	4510
February	1st to 10th	Day	3 5% 13% 9% 7% 6% 4 8% 8% 37%	1800
	11th to 20th	Day	3 4 12% 8% 7% 5% 5% 5% 6% 44%	1880
	21st to end	Day	4 3 15% 9% 8% 6% 4 5% 6% 42%	1650
March	1st to 10th	Day	5% 4 18% 7% 4 4 2 4 5% 48%	4564
	11th to 20th	Day	1 5% 5% 14% 6% 5% 5% 4 6% 10% 39%	5000
	21st to end	Day	1 7% 6% 14% 8% 6% 6% 4 8% 8% 32%	5744
April	1st to 10th	Day	1 10% 4 9% 7% 6% 5% 4 7% 7% 40%	2400
	11th to 20th	Day	2 14% 6% 14% 7% 6% 4 3 5% 6% 33%	2371
	21st to end	Day	2 14% 6% 13% 6% 6% 5% 4 5% 7% 32%	2400
May	1st to 10th	Day	3 16% 7% 15% 8% 6% 6% 4 5% 5% 25%	4135
	11th to 20th	Day	4 12% 3 8% 6% 5% 6% 5% 7% 8% 35%	4528
	21st to end	Day	3 7% 3 7% 5% 5% 6% 5% 8% 9% 42%	4897
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	3 5% 1 4 3 3 3 2 3 6% 68%	3170
	11th to 20th	Day	3 7% 2 6% 5% 5% 6% 5% 7% 8% 47%	3150
	21st to end	Day	2 6% 3 7% 3 3 3 3 6% 7% 58%	3386
November	1st to 10th	Day	1 5% 2 8% 4 4 4 3 5% 7% 57%	1763
	11th to 20th	Day	1 5% 3 6% 5% 4 4 3 7% 7% 56%	1800
	21st to end	Day	5% 3 8% 6% 5% 4 3 5% 8% 54%	1644
December	1st to 10th	Day	2 1 7% 8% 5% 6% 3 4 7% 57%	2620
	11th to 20th	Day	4 2 6% 5% 4 4 4 6% 10% 54%	3026
	21st to end	Day	5% 3 11% 8% 6% 5% 4 8% 10% 40%	4004
January	1st to 10th	Night	1 2 11% 12% 9% 5% 4 6% 8% 42%	6327
	11th to 20th	Night	1 1 12% 10% 7% 10% 4 6% 9% 41%	6156
	21st to end	Night	2 2 9% 7% 7% 6% 4 6% 7% 49%	6468
February	1st to 10th	Night	2 2 10% 7% 7% 6% 5% 8% 10% 43%	2600
	11th to 20th	Night	2 3 8% 8% 7% 7% 4 7% 10% 45%	2406
	21st to end	Night	3 3 10% 6% 8% 6% 4 7% 7% 46%	1980
March	1st to 10th	Night	4 5% 11% 6% 6% 5% 4 6% 7% 47%	5299
	11th to 20th	Night	4 4 13% 6% 4 3 3 5% 8% 49%	5000
	21st to end	Night	1 5% 3 10% 7% 7% 6% 5% 9% 11% 37%	5219
April	1st to 10th	Night	5% 2 7% 6% 5% 5% 4 6% 8% 51%	2000
	11th to 20th	Night	1 10% 3 9% 6% 5% 5% 4 6% 6% 44%	1977
	21st to end	Night	2 11% 3 8% 5% 5% 4 2 6% 7% 47%	2000
May	1st to 10th	Night	2 10% 3 9% 7% 4 5% 5% 7% 9% 41%	3047
	11th to 20th	Night	3 10% 3 5% 3 4 6% 5% 8% 10% 43%	2597
	21st to end	Night	1 5% 2 7% 5% 4 4 4 6% 8% 54%	2806
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	1 3 1 2 2 3 3 2 4 5% 74%	3800
	11th to 20th	Night	1 3 1 5% 3 4 3 3 6% 8% 63%	3778
	21st to end	Night	1 4 2 5% 3 3 3 3 4 8% 65%	4141
November	1st to 10th	Night	3 2 6% 3 4 5% 3 5% 9% 61%	2535
	11th to 20th	Night	3 2 7% 4 4 4 4 6% 8% 58%	2600
	21st to end	Night	1 3 3 8% 6% 4 3 4 6% 8% 55%	2754
December	1st to 10th	Night	2 1 4 5% 3 4 3 6% 9% 64%	4570
	11th to 20th	Night	2 1 4 4 5% 5% 5% 8% 11% 54%	5181
	21st to end	Night	4 3 12% 9% 6% 6% 5% 8% 10% 38%	6974

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% 14% 13% 23% 15% 5%	3639
	11th to 20th	Day	33% 14% 13% 21% 15% 4	3866
	21st to end	Day	30% 9% 13% 19% 19% 9%	4510
February	1st to 10th	Day	40% 9% 17% 17% 13% 5%	1800
	11th to 20th	Day	35% 8% 15% 21% 16% 5%	1889
	21st to end	Day	38% 6% 11% 21% 17% 6%	1650
March	1st to 10th	Day	33% 8% 6% 22% 21% 11%	4564
	11th to 20th	Day	34% 11% 12% 26% 15% 2	5000
	21st to end	Day	37% 13% 16% 24% 10% 1	5744
April	1st to 10th	Day	39% 7% 13% 21% 15% 5%	2400
	11th to 20th	Day	48% 7% 11% 17% 15% 3	2374
	21st to end	Day	47% 8% 11% 23% 10% 1	2400
May	1st to 10th	Day	45% 12% 11% 18% 13% 1	4135
	11th to 20th	Day	35% 12% 16% 24% 13% 1	4532
	21st to end	Day	28% 10% 12% 26% 19% 4	4897
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	20% 4 6% 23% 35% 12%	3170
	11th to 20th	Day	29% 8% 12% 28% 20% 4	3150
	21st to end	Day	24% 4 10% 31% 28% 4	3386
November	1st to 10th	Day	26% 6% 13% 22% 29% 5%	1763
	11th to 20th	Day	24% 6% 16% 26% 21% 7%	1800
	21st to end	Day	28% 7% 11% 28% 19% 8%	1644
December	1st to 10th	Day	23% 9% 11% 35% 17% 5%	2620
	11th to 20th	Day	20% 9% 15% 33% 20% 2	3024
	21st to end	Day	29% 10% 15% 19% 23% 4	4004
January	1st to 10th	Night	29% 11% 15% 24% 15% 6%	6327
	11th to 20th	Night	27% 15% 13% 25% 15% 6%	6156
	21st to end	Night	23% 12% 15% 21% 19% 10%	6468
February	1st to 10th	Night	31% 10% 19% 21% 16% 4	2600
	11th to 20th	Night	30% 8% 17% 25% 16% 3	2407
	21st to end	Night	31% 7% 16% 20% 18% 7%	1980
March	1st to 10th	Night	28% 9% 10% 20% 24% 10%	5299
	11th to 20th	Night	25% 11% 10% 24% 24% 5%	5000
	21st to end	Night	26% 13% 24% 27% 8% 1	5219
April	1st to 10th	Night	26% 11% 16% 26% 17% 5%	2000
	11th to 20th	Night	34% 10% 15% 23% 16% 3	1977
	21st to end	Night	34% 6% 15% 29% 15% 1	2000
May	1st to 10th	Night	28% 11% 16% 29% 15% 2	3047
	11th to 20th	Night	27% 14% 18% 27% 14%	2598
	21st to end	Night	19% 10% 17% 30% 22% 2	2806
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	14% 5% 8% 28% 36% 10%	3800
	11th to 20th	Night	16% 6% 12% 42% 19% 5%	3778
	21st to end	Night	17% 5% 10% 30% 31% 7%	4141
November	1st to 10th	Night	20% 7% 14% 27% 26% 6%	2535
	11th to 20th	Night	21% 7% 16% 28% 21% 6%	2600
	21st to end	Night	26% 7% 13% 28% 20% 6%	2754
December	1st to 10th	Night	14% 8% 15% 37% 20% 5%	4570
	11th to 20th	Night	17% 11% 15% 29% 25% 3	5182
	21st to end	Night	29% 14% 15% 20% 19% 3	6974

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	26% 34% 18% 15% 5% 1	300
	11th to 20th	Day	24% 42% 20% 11% 2 1	300
	21st to end	Day	18% 42% 25% 12% 4	330
February	1st to 10th	Day	35% 39% 19% 5% 1 1	300
	11th to 20th	Day	39% 34% 20% 5% 2	300
	21st to end	Day	35% 43% 16% 6%	249
March	1st to 10th	Day	27% 36% 23% 12% 2	325
	11th to 20th	Day	24% 33% 28% 13% 2	500
	21st to end	Day	25% 42% 23% 8% 1	550
April	1st to 10th	Day	27% 39% 25% 7% 2	500
	11th to 20th	Day	29% 40% 22% 7% 1	492
	21st to end	Day	21% 40% 29% 7% 3	500
May	1st to 10th	Day	23% 34% 28% 12% 3 1	579
	11th to 20th	Day	18% 22% 34% 18% 6% 1	725
	21st to end	Day	16% 23% 30% 21% 8% 1	760
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% 36% 24% 12% 4	330
November	1st to 10th	Day	25% 38% 21% 8% 7%	300
	11th to 20th	Day	29% 35% 24% 8% 4 1	300
	21st to end	Day	21% 36% 31% 10% 1	300
December	1st to 10th	Day	28% 34% 23% 11% 4	300
	11th to 20th	Day	26% 43% 22% 5% 3	300
	21st to end	Day	28% 37% 22% 10% 2 1	330
January	1st to 10th	Night	19% 31% 26% 18% 6% 1	1000
	11th to 20th	Night	19% 35% 27% 13% 5% 1	920
	21st to end	Night	11% 38% 33% 14% 4	880
February	1st to 10th	Night	16% 40% 30% 11% 4	800
	11th to 20th	Night	16% 38% 30% 13% 3	784
	21st to end	Night	15% 40% 32% 12% 1	660
March	1st to 10th	Night	11% 37% 32% 15% 5%	800
	11th to 20th	Night	9% 30% 34% 22% 5% 1	800
	21st to end	Night	10% 37% 33% 16% 4	765
April	1st to 10th	Night	11% 34% 38% 16% 2	600
	11th to 20th	Night	11% 32% 35% 17% 5%	593
	21st to end	Night	12% 25% 38% 19% 6% 1	600
May	1st to 10th	Night	9% 18% 43% 23% 6% 1	600
	11th to 20th	Night	10% 14% 33% 33% 9%	591
	21st to end	Night	9% 16% 32% 31% 11% 2	634
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% 27% 33% 18% 7% 2	845
November	1st to 10th	Night	9% 34% 35% 15% 7% 1	975
	11th to 20th	Night	16% 37% 29% 13% 3 1	1000
	21st to end	Night	12% 30% 35% 20% 3	1000
December	1st to 10th	Night	13% 39% 31% 15% 2	1000
	11th to 20th	Night	16% 38% 29% 14% 3	1000
	21st to end	Night	18% 34% 30% 14% 4 1	1100

Page generated at 2025-05-23 07:20:57. Version ac07

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