Arvada
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arvada clear sky chart from 2005-11-06 to 2025-05-11.

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	4 5% 2 5% 4 4 4 4 6% 8% 55%	117811
	Night	4 6% 2 5% 3 3 3 3 5% 7% 59%	120026
Transparency	Day	25% 6% 10% 23% 24% 11%	117555
	Night	24% 6% 10% 24% 26% 10%	119872
Seeing	Day	8% 8% 27% 33% 19% 6%	16222
	Night	7% 4 31% 41% 15% 1	26370

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	1 7% 2 5% 3 3 2 3 6% 7% 60%	3638
	11th to 20th	Day	1 4 2 7% 5% 5% 3 3 5% 8% 57%	3752
	21st to end	Day	1 4 3 6% 3 3 3 3 5% 7% 62%	4510
February	1st to 10th	Day	2 6% 4 7% 3 3 4 4 6% 6% 54%	1800
	11th to 20th	Day	1 4 2 7% 5% 5% 4 3 5% 9% 55%	1922
	21st to end	Day	2 7% 3 7% 3 3 4 3 4 6% 59%	1650
March	1st to 10th	Day	3 10% 3 5% 3 3 3 3 4 6% 58%	4500
	11th to 20th	Day	5% 8% 2 6% 4 4 4 4 6% 9% 48%	4944
	21st to end	Day	4 7% 3 5% 3 4 4 4 7% 8% 52%	5826
April	1st to 10th	Day	6% 6% 1 5% 3 3 4 3 6% 8% 55%	2400
	11th to 20th	Day	9% 8% 3 5% 4 3 4 3 6% 7% 49%	2371
	21st to end	Day	9% 7% 1 5% 3 3 4 5% 6% 8% 47%	2400
May	1st to 10th	Day	9% 7% 2 6% 5% 5% 5% 5% 7% 8% 40%	4136
	11th to 20th	Day	10% 6% 2 5% 4 5% 5% 5% 8% 9% 41%	4385
	21st to end	Day	5% 4 1 4 4 4 5% 6% 8% 9% 50%	4825
June	1st to 10th	Day	5% 3 2 4 4 5% 5% 5% 8% 10% 50%	2660
	11th to 20th	Day	5% 3 1 4 4 4 5% 6% 8% 9% 51%	2660
	21st to end	Day	4 3 1 4 4 5% 6% 6% 8% 10% 49%	2660
July	1st to 10th	Day	5% 3 2 4 3 4 4 4 6% 8% 56%	4430
	11th to 20th	Day	3 3 1 4 4 5% 7% 6% 10% 12% 47%	4430
	21st to end	Day	4 3 2 5% 4 4 5% 4 6% 8% 55%	4719
August	1st to 10th	Day	9% 5% 2 6% 5% 6% 6% 5% 9% 10% 37%	4092
	11th to 20th	Day	3 3 1 4 4 5% 6% 5% 8% 10% 50%	3731
	21st to end	Day	3 4 2 5% 4 4 6% 5% 7% 9% 51%	4180
September	1st to 10th	Day	5% 3 1 4 3 4 4 3 5% 7% 61%	2280
	11th to 20th	Day	5% 4 1 4 3 3 4 4 5% 8% 60%	2259
	21st to end	Day	5% 4 1 4 2 2 3 3 4 6% 65%	2090
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 5% 75%	3184
	11th to 20th	Day	4 4 2 4 3 3 3 3 5% 7% 61%	3150
	21st to end	Day	5% 6% 2 3 2 2 2 2 4 6% 66%	3319
November	1st to 10th	Day	3 5% 2 3 2 2 3 3 6% 7% 65%	1763
	11th to 20th	Day	2 5% 1 3 3 3 3 3 6% 8% 64%	1800
	21st to end	Day	3 6% 2 6% 2 2 2 4 6% 7% 60%	1695
December	1st to 10th	Day	1 4 1 4 3 3 2 2 4 6% 70%	2620
	11th to 20th	Day	1 4 1 3 2 2 2 2 5% 7% 70%	3026
	21st to end	Day	2 6% 3 7% 4 4 4 3 6% 7% 54%	4004
January	1st to 10th	Night	1 8% 3 7% 4 3 3 3 4 7% 57%	6327
	11th to 20th	Night	1 4 2 6% 4 3 4 3 5% 7% 61%	6271
	21st to end	Night	2 6% 3 7% 3 3 3 3 4 5% 60%	6468
February	1st to 10th	Night	2 8% 3 6% 4 3 4 3 4 7% 56%	2600
	11th to 20th	Night	2 8% 3 7% 4 4 4 3 5% 6% 54%	2363
	21st to end	Night	3 8% 2 6% 3 3 3 3 4 6% 59%	1980
March	1st to 10th	Night	4 10% 3 6% 4 3 3 3 5% 5% 56%	5374
	11th to 20th	Night	7% 10% 2 5% 3 3 3 3 4 6% 54%	5049
	21st to end	Night	7% 9% 2 5% 3 3 3 3 5% 8% 51%	5132
April	1st to 10th	Night	6% 7% 2 4 3 3 3 3 5% 6% 57%	2000
	11th to 20th	Night	10% 8% 2 5% 3 3 3 4 5% 6% 52%	1977
	21st to end	Night	13% 7% 2 5% 3 4 3 4 5% 6% 49%	2000
May	1st to 10th	Night	10% 7% 2 6% 4 4 4 4 5% 8% 46%	3051
	11th to 20th	Night	10% 5% 2 6% 3 4 4 4 5% 9% 48%	2522
	21st to end	Night	7% 5% 2 4 3 3 4 3 5% 7% 57%	2762
June	1st to 10th	Night	5% 4 1 2 3 3 3 4 5% 11% 59%	1520
	11th to 20th	Night	5% 3 1 3 3 3 3 3 6% 8% 63%	1520
	21st to end	Night	5% 2 1 3 3 4 4 5% 6% 9% 59%	1520
July	1st to 10th	Night	4 2 1 3 3 3 5% 4 5% 7% 62%	2540
	11th to 20th	Night	2 2 1 4 4 4 4 5% 7% 10% 57%	2540
	21st to end	Night	3 2 1 4 3 3 5% 4 7% 8% 58%	2840
August	1st to 10th	Night	8% 5% 2 5% 4 4 6% 5% 8% 10% 44%	2847
	11th to 20th	Night	3 2 1 3 3 4 5% 5% 9% 11% 55%	3108
	21st to end	Night	3 2 1 5% 4 4 5% 5% 8% 10% 53%	3487
September	1st to 10th	Night	6% 3 1 4 4 2 4 3 5% 7% 60%	1900
	11th to 20th	Night	6% 3 1 3 2 2 3 3 5% 8% 65%	1920
	21st to end	Night	7% 3 1 3 3 3 3 2 4 5% 65%	2090
October	1st to 10th	Night	5% 3 1 2 2 2 2 2 4 4 75%	3768
	11th to 20th	Night	6% 4 2 4 3 2 3 2 4 7% 64%	3778
	21st to end	Night	6% 6% 2 3 2 2 2 2 3 6% 66%	4208
November	1st to 10th	Night	3 4 1 4 2 3 3 3 5% 7% 66%	2535
	11th to 20th	Night	3 6% 1 4 2 2 3 3 4 5% 66%	2600
	21st to end	Night	4 7% 2 4 2 2 3 3 5% 6% 62%	2704
December	1st to 10th	Night	1 4 2 3 3 2 2 2 3 5% 73%	4570
	11th to 20th	Night	1 4 2 4 3 2 2 2 5% 8% 67%	5181
	21st to end	Night	4 8% 3 6% 4 4 4 3 5% 6% 53%	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	23% 5% 9% 34% 21% 9%	3639
	11th to 20th	Day	25% 6% 10% 23% 26% 10%	3752
	21st to end	Day	23% 4 10% 26% 25% 11%	4510
February	1st to 10th	Day	29% 5% 12% 26% 22% 8%	1800
	11th to 20th	Day	26% 6% 9% 28% 26% 6%	1932
	21st to end	Day	25% 5% 8% 21% 28% 12%	1650
March	1st to 10th	Day	27% 4 7% 18% 29% 16%	4500
	11th to 20th	Day	30% 8% 11% 21% 26% 5%	4944
	21st to end	Day	26% 7% 13% 35% 17% 3	5826
April	1st to 10th	Day	26% 6% 12% 25% 22% 9%	2400
	11th to 20th	Day	33% 7% 11% 21% 19% 9%	2374
	21st to end	Day	31% 7% 13% 24% 21% 2	2400
May	1st to 10th	Day	35% 9% 13% 22% 15% 6%	4136
	11th to 20th	Day	33% 12% 14% 22% 17% 3	4389
	21st to end	Day	24% 10% 15% 23% 21% 7%	4825
June	1st to 10th	Day	26% 10% 15% 24% 17% 9%	2660
	11th to 20th	Day	24% 8% 12% 19% 23% 14%	2660
	21st to end	Day	25% 7% 12% 21% 23% 12%	2660
July	1st to 10th	Day	24% 6% 8% 16% 29% 17%	4361
	11th to 20th	Day	24% 9% 11% 21% 23% 12%	4355
	21st to end	Day	25% 6% 11% 18% 21% 19%	4570
August	1st to 10th	Day	36% 9% 14% 21% 15% 6%	4078
	11th to 20th	Day	26% 7% 14% 17% 21% 15%	3767
	21st to end	Day	26% 5% 11% 19% 25% 14%	4179
September	1st to 10th	Day	23% 5% 8% 20% 25% 19%	2280
	11th to 20th	Day	22% 6% 7% 20% 28% 17%	2259
	21st to end	Day	21% 4 7% 19% 36% 13%	2090
October	1st to 10th	Day	14% 3 6% 15% 37% 26%	3184
	11th to 20th	Day	23% 4 8% 26% 30% 9%	3150
	21st to end	Day	21% 3 5% 23% 37% 11%	3319
November	1st to 10th	Day	19% 3 9% 25% 28% 15%	1763
	11th to 20th	Day	19% 5% 7% 26% 34% 10%	1800
	21st to end	Day	24% 3 7% 23% 30% 13%	1695
December	1st to 10th	Day	18% 3 7% 33% 28% 10%	2620
	11th to 20th	Day	15% 5% 6% 31% 34% 9%	3024
	21st to end	Day	26% 6% 7% 25% 26% 9%	4004
January	1st to 10th	Night	27% 5% 7% 30% 24% 7%	6327
	11th to 20th	Night	21% 7% 10% 25% 24% 14%	6271
	21st to end	Night	26% 5% 10% 23% 25% 11%	6468
February	1st to 10th	Night	27% 5% 9% 28% 24% 6%	2600
	11th to 20th	Night	31% 6% 7% 28% 22% 6%	2363
	21st to end	Night	26% 4 5% 23% 27% 14%	1980
March	1st to 10th	Night	29% 4 6% 17% 33% 10%	5374
	11th to 20th	Night	30% 6% 9% 15% 28% 13%	5049
	21st to end	Night	31% 6% 9% 34% 18% 2	5132
April	1st to 10th	Night	27% 6% 10% 24% 23% 10%	2000
	11th to 20th	Night	32% 7% 10% 23% 20% 8%	1977
	21st to end	Night	34% 7% 10% 25% 20% 4	2000
May	1st to 10th	Night	32% 11% 12% 22% 15% 9%	3051
	11th to 20th	Night	31% 10% 18% 23% 15% 4	2523
	21st to end	Night	22% 11% 20% 22% 19% 6%	2762
June	1st to 10th	Night	20% 7% 20% 31% 14% 9%	1520
	11th to 20th	Night	20% 5% 15% 20% 24% 16%	1520
	21st to end	Night	20% 7% 12% 23% 28% 10%	1520
July	1st to 10th	Night	20% 6% 12% 19% 32% 11%	2500
	11th to 20th	Night	21% 7% 14% 26% 23% 9%	2492
	21st to end	Night	20% 6% 14% 25% 20% 15%	2751
August	1st to 10th	Night	34% 7% 15% 23% 17% 4	2838
	11th to 20th	Night	20% 9% 20% 20% 20% 11%	3138
	21st to end	Night	24% 6% 14% 22% 27% 6%	3487
September	1st to 10th	Night	23% 6% 9% 22% 23% 17%	1900
	11th to 20th	Night	18% 5% 10% 23% 28% 16%	1920
	21st to end	Night	22% 4 8% 21% 33% 12%	2090
October	1st to 10th	Night	15% 4 6% 19% 32% 24%	3768
	11th to 20th	Night	21% 3 9% 26% 30% 10%	3778
	21st to end	Night	23% 3 5% 23% 34% 13%	4208
November	1st to 10th	Night	19% 5% 8% 25% 28% 15%	2535
	11th to 20th	Night	20% 4 7% 26% 34% 9%	2600
	21st to end	Night	24% 4 8% 22% 32% 10%	2704
December	1st to 10th	Night	16% 3 7% 33% 33% 8%	4570
	11th to 20th	Night	18% 4 6% 33% 34% 5%	5182
	21st to end	Night	29% 7% 8% 22% 26% 8%	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	5% 10% 28% 43% 11% 4	300
	11th to 20th	Day	7% 8% 37% 35% 13% 1	300
	21st to end	Day	4 8% 41% 32% 13% 2	330
February	1st to 10th	Day	5% 15% 43% 29% 6% 2	300
	11th to 20th	Day	4 7% 46% 35% 8% 1	300
	21st to end	Day	6% 13% 39% 35% 7%	249
March	1st to 10th	Day	5% 10% 34% 38% 12% 2	300
	11th to 20th	Day	13% 15% 30% 29% 12% 2	470
	21st to end	Day	13% 20% 31% 28% 7% 2	550
April	1st to 10th	Day	12% 17% 31% 29% 10% 2	500
	11th to 20th	Day	15% 19% 34% 23% 7% 2	492
	21st to end	Day	15% 14% 31% 28% 12% 1	500
May	1st to 10th	Day	15% 10% 29% 31% 13% 2	628
	11th to 20th	Day	18% 7% 22% 30% 17% 5%	676
	21st to end	Day	9% 9% 25% 31% 20% 6%	734
June	1st to 10th	Day	6% 5% 20% 33% 26% 10%	680
	11th to 20th	Day	6% 8% 26% 35% 19% 6%	680
	21st to end	Day	6% 5% 25% 34% 24% 7%	680
July	1st to 10th	Day	8% 3 16% 30% 33% 10%	671
	11th to 20th	Day	5% 3 15% 31% 37% 10%	668
	21st to end	Day	5% 3 15% 28% 38% 11%	692
August	1st to 10th	Day	7% 4 23% 29% 25% 12%	487
	11th to 20th	Day	4 4 23% 32% 27% 10%	477
	21st to end	Day	7% 3 19% 38% 24% 8%	539
September	1st to 10th	Day	5% 3 20% 35% 27% 10%	490
	11th to 20th	Day	5% 5% 22% 36% 23% 8%	469
	21st to end	Day	6% 6% 22% 34% 22% 9%	300
October	1st to 10th	Day	9% 5% 22% 30% 25% 10%	300
	11th to 20th	Day	4 8% 27% 39% 17% 5%	300
	21st to end	Day	12% 10% 26% 34% 15% 2	330
November	1st to 10th	Day	6% 7% 32% 36% 14% 5%	300
	11th to 20th	Day	8% 9% 29% 39% 12% 3	300
	21st to end	Day	7% 8% 31% 38% 14% 2	300
December	1st to 10th	Day	7% 9% 31% 35% 15% 3	300
	11th to 20th	Day	5% 8% 39% 41% 6% 1	300
	21st to end	Day	7% 9% 38% 37% 7% 2	330
January	1st to 10th	Night	4 5% 41% 39% 10% 2	1000
	11th to 20th	Night	4 6% 48% 33% 8% 1	970
	21st to end	Night	5% 4 42% 40% 8% 1	880
February	1st to 10th	Night	6% 4 50% 35% 6%	800
	11th to 20th	Night	4 5% 46% 38% 6%	784
	21st to end	Night	7% 7% 45% 38% 3	660
March	1st to 10th	Night	4 5% 43% 39% 9%	800
	11th to 20th	Night	10% 5% 33% 42% 11%	800
	21st to end	Night	9% 8% 39% 38% 6%	730
April	1st to 10th	Night	10% 9% 39% 38% 5%	600
	11th to 20th	Night	13% 8% 33% 37% 9%	593
	21st to end	Night	15% 8% 30% 36% 11% 1	600
May	1st to 10th	Night	14% 7% 23% 42% 14% 1	600
	11th to 20th	Night	16% 4 16% 45% 16% 2	563
	21st to end	Night	9% 5% 23% 39% 23% 1	617
June	1st to 10th	Night	5% 4 16% 46% 27% 3	570
	11th to 20th	Night	6% 2 23% 51% 17% 1	570
	21st to end	Night	5% 2 15% 47% 29% 2	570
July	1st to 10th	Night	6% 3 13% 40% 36% 2	555
	11th to 20th	Night	3 1 10% 46% 38% 3	552
	21st to end	Night	5% 2 6% 44% 40% 3	624
August	1st to 10th	Night	7% 2 9% 44% 37% 2	567
	11th to 20th	Night	4 2 14% 47% 32% 2	564
	21st to end	Night	4 1 11% 47% 33% 3	627
September	1st to 10th	Night	6% 3 12% 46% 27% 5%	570
	11th to 20th	Night	6% 2 14% 50% 24% 4	570
	21st to end	Night	7% 2 21% 46% 22% 3	570
October	1st to 10th	Night	11% 4 22% 42% 19% 3	741
	11th to 20th	Night	6% 2 29% 46% 15% 1	760
	21st to end	Night	10% 5% 30% 41% 13% 2	888
November	1st to 10th	Night	5% 4 35% 44% 12% 2	975
	11th to 20th	Night	6% 6% 38% 44% 7% 1	1000
	21st to end	Night	7% 4 35% 44% 10% 1	1000
December	1st to 10th	Night	4 5% 40% 42% 9%	1000
	11th to 20th	Night	5% 6% 44% 38% 7% 1	1000
	21st to end	Night	7% 6% 42% 37% 7% 1	1100

Page generated at 2025-05-08 07:33:57. Version ac07

Copyright © 2025 Attilla Danko.