Beaver Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beaver Creek clear sky chart from 2005-11-06 to 2026-04-02.

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	9% 10% 5% 12% 8% 7% 7% 6% 8% 8% 21%	134623
	Night	5% 11% 5% 14% 9% 8% 8% 6% 8% 9% 16%	135839
Transparency	Day	54% 10% 16% 13% 5% 1	134255
	Night	54% 9% 14% 14% 7% 1	135787
Seeing	Day	14% 5% 18% 29% 24% 9%	19388
	Night	10% 3 14% 36% 28% 9%	24777

By Month

Percentage Cloud Cover NW (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	5% 6% 17% 10% 9% 12% 8% 11% 13% 10%	2733
	11th to 20th	Day	1 7% 4 11% 8% 9% 11% 7% 10% 14% 17%	2925
	21st to end	Day	2 8% 5% 13% 9% 8% 12% 9% 11% 10% 12%	3508
February	1st to 10th	Day	3 12% 6% 12% 10% 8% 7% 7% 10% 10% 16%	1470
	11th to 20th	Day	1 11% 6% 14% 10% 10% 7% 6% 10% 9% 16%	1536
	21st to end	Day	2 10% 6% 16% 9% 7% 7% 6% 10% 9% 19%	1557
March	1st to 10th	Day	1 8% 6% 18% 11% 6% 7% 5% 7% 7% 24%	4220
	11th to 20th	Day	1 8% 6% 16% 10% 9% 7% 5% 7% 7% 23%	5090
	21st to end	Day	2 11% 4 12% 8% 7% 7% 6% 9% 8% 27%	5767
April	1st to 10th	Day	3 11% 6% 14% 7% 7% 6% 5% 8% 8% 24%	2614
	11th to 20th	Day	4 13% 5% 10% 8% 6% 7% 5% 7% 8% 28%	2656
	21st to end	Day	5% 12% 5% 12% 7% 7% 7% 4 6% 7% 28%	2984
May	1st to 10th	Day	5% 10% 5% 13% 8% 8% 7% 6% 8% 9% 20%	7035
	11th to 20th	Day	9% 12% 5% 13% 8% 7% 7% 5% 7% 7% 22%	7551
	21st to end	Day	13% 10% 4 9% 7% 6% 7% 6% 8% 8% 21%	8540
June	1st to 10th	Day	12% 11% 4 11% 7% 7% 6% 5% 7% 8% 22%	3662
	11th to 20th	Day	14% 9% 4 11% 8% 7% 6% 5% 7% 7% 22%	3800
	21st to end	Day	16% 9% 4 10% 7% 6% 7% 6% 8% 9% 19%	3800
July	1st to 10th	Day	15% 9% 3 10% 7% 7% 7% 6% 8% 9% 19%	8496
	11th to 20th	Day	14% 10% 4 10% 7% 7% 7% 6% 8% 9% 20%	7700
	21st to end	Day	19% 10% 4 9% 6% 6% 6% 5% 6% 9% 21%	8377
August	1st to 10th	Day	10% 7% 3 9% 7% 6% 5% 5% 6% 7% 34%	5035
	11th to 20th	Day	12% 9% 4 9% 6% 6% 6% 5% 8% 8% 29%	4804
	21st to end	Day	17% 11% 4 10% 7% 7% 7% 5% 7% 6% 19%	4893
September	1st to 10th	Day	14% 12% 4 12% 7% 6% 6% 5% 6% 7% 23%	2595
	11th to 20th	Day	10% 10% 5% 10% 7% 7% 7% 5% 7% 7% 25%	2331
	21st to end	Day	11% 17% 5% 12% 6% 5% 5% 5% 6% 7% 21%	2157
October	1st to 10th	Day	8% 12% 5% 12% 7% 7% 7% 6% 7% 8% 21%	3239
	11th to 20th	Day	5% 13% 5% 15% 7% 7% 6% 5% 6% 9% 23%	2802
	21st to end	Day	8% 18% 7% 15% 7% 7% 6% 5% 7% 7% 13%	2815
November	1st to 10th	Day	4 18% 9% 15% 8% 7% 6% 5% 8% 7% 13%	1328
	11th to 20th	Day	4 16% 8% 19% 12% 8% 7% 4 6% 5% 10%	1249
	21st to end	Day	4 12% 5% 15% 10% 9% 9% 8% 9% 10% 9%	1003
December	1st to 10th	Day	1 10% 5% 15% 10% 10% 10% 8% 10% 11% 9%	1340
	11th to 20th	Day	2 12% 8% 17% 9% 8% 9% 6% 12% 12% 7%	1469
	21st to end	Day	1 6% 5% 15% 11% 11% 9% 8% 13% 10% 11%	1542
January	1st to 10th	Night	1 8% 5% 14% 9% 9% 9% 9% 15% 15% 8%	10204
	11th to 20th	Night	2 10% 4 13% 9% 8% 9% 7% 10% 11% 16%	9973
	21st to end	Night	2 9% 5% 15% 11% 11% 11% 7% 10% 10% 11%	10672
February	1st to 10th	Night	2 10% 5% 15% 10% 8% 8% 6% 9% 8% 19%	3150
	11th to 20th	Night	1 11% 6% 12% 9% 8% 7% 7% 9% 11% 19%	2970
	21st to end	Night	2 10% 6% 17% 11% 7% 7% 4 7% 7% 22%	2249
March	1st to 10th	Night	1 7% 6% 19% 13% 9% 7% 5% 6% 7% 20%	5856
	11th to 20th	Night	2 13% 8% 21% 10% 7% 7% 5% 6% 6% 16%	5088
	21st to end	Night	2 12% 5% 13% 8% 7% 8% 6% 8% 8% 23%	5396
April	1st to 10th	Night	4 12% 7% 13% 9% 7% 7% 4 7% 7% 24%	1809
	11th to 20th	Night	5% 14% 4 11% 7% 7% 7% 6% 6% 7% 27%	1693
	21st to end	Night	4 11% 4 10% 8% 7% 6% 6% 9% 10% 25%	1415
May	1st to 10th	Night	6% 10% 4 13% 8% 8% 7% 6% 7% 8% 21%	2933
	11th to 20th	Night	9% 17% 5% 11% 7% 6% 7% 4 7% 7% 19%	2342
	21st to end	Night	18% 12% 4 11% 7% 7% 7% 6% 6% 6% 15%	2334
June	1st to 10th	Night	15% 11% 4 10% 9% 6% 10% 6% 6% 6% 16%	735
	11th to 20th	Night	19% 11% 5% 12% 10% 6% 5% 5% 5% 6% 18%	600
	21st to end	Night	17% 10% 5% 11% 9% 7% 6% 6% 8% 8% 14%	600
July	1st to 10th	Night	20% 9% 3 11% 7% 6% 6% 5% 6% 8% 19%	1479
	11th to 20th	Night	17% 12% 5% 13% 8% 6% 5% 4 7% 7% 16%	2260
	21st to end	Night	23% 9% 4 9% 6% 5% 7% 5% 6% 8% 18%	2466
August	1st to 10th	Night	12% 8% 3 9% 6% 6% 5% 3 4 6% 38%	2121
	11th to 20th	Night	15% 10% 3 9% 6% 6% 6% 5% 8% 9% 23%	2254
	21st to end	Night	19% 11% 4 11% 7% 6% 7% 5% 5% 6% 19%	3014
September	1st to 10th	Night	13% 12% 4 11% 6% 6% 7% 6% 7% 7% 20%	1805
	11th to 20th	Night	11% 11% 4 13% 8% 7% 7% 5% 6% 8% 22%	2066
	21st to end	Night	14% 17% 5% 12% 8% 5% 5% 4 6% 5% 18%	2243
October	1st to 10th	Night	9% 12% 4 12% 7% 7% 7% 5% 7% 9% 22%	3948
	11th to 20th	Night	7% 13% 6% 13% 8% 6% 6% 5% 6% 7% 21%	4346
	21st to end	Night	6% 16% 6% 12% 10% 8% 7% 6% 7% 7% 15%	4986
November	1st to 10th	Night	4 16% 7% 16% 10% 8% 8% 6% 6% 6% 13%	3190
	11th to 20th	Night	4 15% 8% 18% 12% 9% 7% 6% 7% 6% 9%	3371
	21st to end	Night	4 12% 6% 16% 11% 9% 9% 8% 8% 8% 9%	3596
December	1st to 10th	Night	3 11% 6% 13% 8% 9% 10% 8% 11% 10% 11%	6060
	11th to 20th	Night	1 8% 8% 19% 9% 9% 9% 6% 9% 10% 10%	6941
	21st to end	Night	2 9% 6% 17% 11% 10% 9% 8% 9% 10% 8%	9674

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	50% 8% 10% 14% 18% 1	2733
	11th to 20th	Day	46% 9% 15% 21% 7% 2	2940
	21st to end	Day	49% 9% 17% 14% 8% 2	3509
February	1st to 10th	Day	50% 8% 13% 15% 12% 2	1470
	11th to 20th	Day	54% 10% 12% 13% 10% 1	1543
	21st to end	Day	52% 8% 14% 14% 10% 1	1557
March	1st to 10th	Day	51% 6% 11% 21% 9% 1	4220
	11th to 20th	Day	49% 10% 12% 13% 14% 2	5090
	21st to end	Day	43% 13% 16% 15% 12% 1	5767
April	1st to 10th	Day	52% 12% 20% 11% 4 1	2614
	11th to 20th	Day	51% 13% 14% 14% 7% 1	2656
	21st to end	Day	52% 11% 15% 15% 6%	2984
May	1st to 10th	Day	51% 14% 13% 15% 7% 1	7035
	11th to 20th	Day	56% 11% 14% 13% 6% 1	7554
	21st to end	Day	54% 12% 13% 17% 5%	8541
June	1st to 10th	Day	58% 14% 14% 10% 4	3662
	11th to 20th	Day	59% 12% 14% 12% 2	3800
	21st to end	Day	60% 13% 16% 10% 1	3800
July	1st to 10th	Day	59% 8% 23% 9% 1	8403
	11th to 20th	Day	59% 9% 22% 10% 1	7607
	21st to end	Day	60% 8% 23% 9%	8142
August	1st to 10th	Day	47% 10% 22% 16% 5%	5015
	11th to 20th	Day	52% 9% 18% 17% 4	4849
	21st to end	Day	63% 9% 17% 11% 1	4892
September	1st to 10th	Day	57% 10% 16% 13% 3	2595
	11th to 20th	Day	52% 14% 17% 16% 2	2331
	21st to end	Day	57% 12% 15% 14% 2	2157
October	1st to 10th	Day	56% 9% 15% 18% 3	3239
	11th to 20th	Day	55% 7% 15% 17% 5%	2802
	21st to end	Day	62% 8% 16% 11% 3	2815
November	1st to 10th	Day	60% 10% 13% 14% 3	1328
	11th to 20th	Day	67% 8% 11% 9% 4	1249
	21st to end	Day	55% 8% 17% 15% 6%	1003
December	1st to 10th	Day	54% 8% 19% 14% 4	1340
	11th to 20th	Day	55% 8% 14% 14% 8% 1	1471
	21st to end	Day	44% 11% 19% 12% 13% 1	1542
January	1st to 10th	Night	49% 8% 10% 15% 17% 1	10205
	11th to 20th	Night	47% 8% 17% 15% 10% 2	10020
	21st to end	Night	53% 9% 15% 13% 7% 3	10672
February	1st to 10th	Night	50% 8% 12% 16% 12% 1	3150
	11th to 20th	Night	49% 9% 13% 17% 10% 2	2974
	21st to end	Night	55% 8% 11% 17% 9% 1	2249
March	1st to 10th	Night	55% 7% 10% 17% 10% 1	5856
	11th to 20th	Night	57% 12% 10% 12% 10% 1	5090
	21st to end	Night	42% 12% 17% 20% 8% 1	5396
April	1st to 10th	Night	52% 11% 18% 13% 5%	1809
	11th to 20th	Night	51% 12% 13% 13% 10% 1	1693
	21st to end	Night	49% 14% 16% 15% 7%	1415
May	1st to 10th	Night	53% 12% 12% 16% 6% 1	2930
	11th to 20th	Night	54% 14% 12% 13% 7%	2342
	21st to end	Night	62% 11% 11% 12% 4	2334
June	1st to 10th	Night	62% 13% 11% 9% 4	735
	11th to 20th	Night	63% 9% 15% 12% 1	600
	21st to end	Night	65% 12% 13% 9% 1	600
July	1st to 10th	Night	62% 8% 19% 10% 1	1463
	11th to 20th	Night	65% 8% 17% 9% 1	2230
	21st to end	Night	64% 7% 20% 8%	2396
August	1st to 10th	Night	47% 7% 18% 21% 6%	2116
	11th to 20th	Night	54% 11% 13% 18% 4	2275
	21st to end	Night	65% 9% 13% 12% 1	3014
September	1st to 10th	Night	57% 12% 17% 13% 1	1805
	11th to 20th	Night	55% 11% 17% 15% 2	2066
	21st to end	Night	60% 12% 13% 12% 3	2243
October	1st to 10th	Night	57% 7% 14% 18% 4	3948
	11th to 20th	Night	58% 7% 13% 17% 4 1	4346
	21st to end	Night	59% 8% 18% 13% 2	4986
November	1st to 10th	Night	62% 9% 13% 14% 3	3190
	11th to 20th	Night	66% 8% 11% 10% 5%	3371
	21st to end	Night	56% 11% 14% 15% 5%	3596
December	1st to 10th	Night	53% 8% 17% 18% 4	6060
	11th to 20th	Night	55% 8% 16% 12% 7% 2	6938
	21st to end	Night	54% 10% 14% 12% 8% 3	9674

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	4 1 7% 36% 35% 16%	110
	11th to 20th	Day	3 3 7% 41% 25% 21%	110
	21st to end	Day	6% 5% 14% 37% 23% 16%	216
February	1st to 10th	Day	5% 2 14% 37% 28% 14%	430
	11th to 20th	Day	5% 3 23% 37% 24% 9%	425
	21st to end	Day	5% 6% 26% 35% 21% 8%	355
March	1st to 10th	Day	3 4 17% 33% 31% 13%	430
	11th to 20th	Day	2 2 24% 34% 26% 13%	430
	21st to end	Day	4 5% 22% 31% 26% 12%	526
April	1st to 10th	Day	5% 6% 23% 34% 27% 5%	706
	11th to 20th	Day	9% 7% 22% 32% 26% 5%	690
	21st to end	Day	10% 6% 20% 31% 26% 7%	700
May	1st to 10th	Day	12% 9% 26% 29% 19% 6%	703
	11th to 20th	Day	16% 7% 20% 29% 21% 8%	725
	21st to end	Day	17% 8% 21% 29% 19% 6%	843
June	1st to 10th	Day	17% 6% 17% 29% 25% 7%	992
	11th to 20th	Day	18% 5% 18% 23% 26% 9%	1130
	21st to end	Day	19% 5% 17% 24% 26% 10%	1130
July	1st to 10th	Day	19% 4 13% 28% 28% 8%	1066
	11th to 20th	Day	20% 6% 13% 26% 25% 11%	718
	21st to end	Day	21% 4 10% 24% 27% 12%	794
August	1st to 10th	Day	19% 6% 13% 25% 24% 13%	726
	11th to 20th	Day	20% 6% 19% 26% 21% 8%	715
	21st to end	Day	22% 7% 15% 28% 22% 6%	803
September	1st to 10th	Day	16% 8% 18% 25% 23% 10%	725
	11th to 20th	Day	13% 7% 19% 28% 27% 6%	491
	21st to end	Day	15% 5% 26% 25% 21% 9%	420
October	1st to 10th	Day	15% 8% 23% 26% 19% 9%	420
	11th to 20th	Day	15% 6% 19% 26% 21% 13%	420
	21st to end	Day	11% 3 16% 33% 26% 11%	462
November	1st to 10th	Day	11% 3 14% 37% 24% 11%	312
	11th to 20th	Day	9% 1 16% 32% 24% 18%	214
	21st to end	Day	5% 2 13% 37% 22% 21%	110
December	1st to 10th	Day	6% 1 12% 36% 32% 13%	110
	11th to 20th	Day	4 2 11% 37% 27% 19%	110
	21st to end	Day	2 3 14% 34% 21% 26%	121
January	1st to 10th	Night	3 1 8% 38% 38% 12%	1036
	11th to 20th	Night	6% 2 15% 44% 25% 7%	950
	21st to end	Night	5% 2 15% 43% 24% 10%	1045
February	1st to 10th	Night	4 2 13% 42% 32% 8%	950
	11th to 20th	Night	4 4 17% 43% 24% 8%	934
	21st to end	Night	4 1 15% 44% 27% 8%	783
March	1st to 10th	Night	3 2 16% 35% 34% 11%	907
	11th to 20th	Night	4 1 11% 36% 33% 15%	630
	21st to end	Night	4 2 16% 29% 38% 10%	693
April	1st to 10th	Night	8% 3 18% 34% 30% 8%	603
	11th to 20th	Night	10% 4 17% 34% 27% 7%	593
	21st to end	Night	7% 3 14% 32% 38% 7%	600
May	1st to 10th	Night	13% 5% 17% 35% 25% 4	496
	11th to 20th	Night	17% 7% 19% 33% 21% 4	242
	21st to end	Night	16% 6% 20% 29% 26% 2	217
June	1st to 10th	Night	20% 4 15% 34% 26% 2	200
	11th to 20th	Night	24% 5% 16% 29% 26% 2	200
	21st to end	Night	19% 8% 14% 26% 32% 3	200
July	1st to 10th	Night	27% 4 9% 33% 26% 2	195
	11th to 20th	Night	24% 5% 12% 29% 27% 2	194
	21st to end	Night	23% 4 12% 29% 30% 2	219
August	1st to 10th	Night	21% 3 16% 27% 28% 6%	487
	11th to 20th	Night	22% 5% 14% 29% 26% 4	594
	21st to end	Night	23% 4 12% 32% 25% 4	660
September	1st to 10th	Night	17% 4 19% 33% 24% 4	600
	11th to 20th	Night	15% 5% 20% 27% 28% 5%	600
	21st to end	Night	18% 4 16% 32% 22% 8%	643
October	1st to 10th	Night	19% 5% 18% 32% 21% 5%	808
	11th to 20th	Night	17% 5% 13% 33% 24% 8%	910
	21st to end	Night	11% 3 13% 35% 30% 8%	1001
November	1st to 10th	Night	9% 2 13% 36% 30% 9%	930
	11th to 20th	Night	8% 2 13% 37% 29% 11%	950
	21st to end	Night	8% 2 14% 38% 25% 14%	976
December	1st to 10th	Night	7% 2 13% 41% 28% 9%	1160
	11th to 20th	Night	5% 2 12% 40% 30% 10%	1177
	21st to end	Night	4 3 12% 36% 29% 17%	1394

Page generated at 2026-03-29 22:18:39. Version ac07

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