Elk Creek Visitor's Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elk Creek Visitor's Center clear sky chart from 2005-11-06 to 2026-07-16.

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	2 3 2 5% 4 5% 6% 5% 8% 11% 48%	146881
	Night	2 4 2 6% 5% 5% 6% 5% 9% 11% 46%	143378
Transparency	Day	23% 9% 13% 24% 22% 8%	141789
	Night	22% 11% 15% 26% 21% 6%	139480
Seeing	Day	6% 15% 28% 30% 17% 4	17687
	Night	3 6% 26% 42% 21% 2	27775

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 2 9% 6% 7% 8% 7% 11% 14% 32%	4956
	11th to 20th	Day	1 1 5% 5% 6% 8% 6% 12% 13% 43%	5340
	21st to end	Day	4 3 6% 5% 6% 10% 6% 8% 13% 40%	5844
February	1st to 10th	Day	4 3 7% 4 4 5% 5% 10% 15% 43%	1890
	11th to 20th	Day	1 4 2 5% 5% 5% 7% 7% 11% 16% 39%	1919
	21st to end	Day	4 2 7% 6% 4 6% 6% 9% 12% 44%	1730
March	1st to 10th	Day	4 2 5% 5% 6% 8% 7% 10% 13% 40%	4959
	11th to 20th	Day	4 2 6% 6% 7% 10% 7% 10% 12% 35%	5110
	21st to end	Day	1 7% 2 6% 5% 6% 6% 6% 10% 14% 37%	5693
April	1st to 10th	Day	1 4 2 4 4 5% 4 4 9% 12% 49%	2520
	11th to 20th	Day	1 4 2 4 4 5% 5% 5% 7% 12% 49%	2491
	21st to end	Day	1 5% 1 4 4 4 6% 5% 8% 12% 50%	2520
May	1st to 10th	Day	2 5% 2 5% 4 4 6% 6% 8% 11% 46%	7388
	11th to 20th	Day	2 4 2 6% 5% 5% 5% 5% 7% 9% 50%	7907
	21st to end	Day	1 2 1 4 4 5% 5% 5% 7% 8% 57%	9026
June	1st to 10th	Day	2 3 2 4 4 4 5% 4 6% 9% 59%	2940
	11th to 20th	Day	2 3 1 4 3 4 3 3 5% 7% 65%	2940
	21st to end	Day	2 2 1 4 4 3 5% 4 6% 9% 59%	2940
July	1st to 10th	Day	2 2 1 4 4 4 4 4 5% 6% 65%	6479
	11th to 20th	Day	2 2 1 4 4 7% 8% 7% 10% 12% 43%	6134
	21st to end	Day	3 3 1 6% 5% 6% 7% 6% 9% 10% 43%	6401
August	1st to 10th	Day	3 3 1 5% 5% 5% 5% 5% 8% 11% 47%	5779
	11th to 20th	Day	3 3 2 4 4 5% 6% 5% 7% 8% 53%	5564
	21st to end	Day	4 5% 2 7% 5% 5% 6% 5% 8% 9% 43%	5984
September	1st to 10th	Day	4 4 2 6% 5% 5% 4 4 6% 8% 53%	2400
	11th to 20th	Day	4 3 2 6% 4 4 5% 3 6% 8% 55%	2400
	21st to end	Day	4 4 1 5% 3 3 3 4 3 7% 63%	2121
October	1st to 10th	Day	3 2 1 3 3 2 2 3 4 6% 72%	3270
	11th to 20th	Day	2 3 2 6% 5% 5% 6% 5% 7% 8% 51%	3250
	21st to end	Day	2 3 1 4 3 3 4 4 6% 7% 63%	3548
November	1st to 10th	Day	1 3 1 3 3 2 4 4 8% 11% 60%	1967
	11th to 20th	Day	1 3 2 3 4 4 4 5% 7% 13% 56%	1890
	21st to end	Day	1 4 2 5% 4 4 6% 5% 7% 13% 50%	1683
December	1st to 10th	Day	3 1 4 3 5% 7% 10% 14% 13% 39%	2700
	11th to 20th	Day	4 1 5% 4 4 6% 8% 15% 16% 36%	3106
	21st to end	Day	1 3 2 8% 5% 6% 7% 7% 11% 15% 35%	4092
January	1st to 10th	Night	3 3 11% 7% 9% 11% 7% 10% 11% 26%	8021
	11th to 20th	Night	2 1 6% 5% 6% 8% 7% 14% 17% 34%	7650
	21st to end	Night	1 6% 4 9% 6% 6% 6% 5% 9% 16% 33%	8370
February	1st to 10th	Night	3 2 7% 5% 5% 5% 5% 11% 13% 44%	2730
	11th to 20th	Night	1 5% 2 6% 4 4 6% 5% 10% 10% 45%	2586
	21st to end	Night	1 5% 3 5% 4 4 5% 5% 9% 11% 47%	2076
March	1st to 10th	Night	1 5% 3 8% 5% 6% 6% 5% 11% 12% 39%	5147
	11th to 20th	Night	1 7% 3 6% 4 5% 6% 6% 9% 12% 40%	5110
	21st to end	Night	1 7% 3 7% 5% 6% 6% 6% 10% 10% 40%	5518
April	1st to 10th	Night	1 6% 2 6% 4 4 4 4 8% 9% 52%	2100
	11th to 20th	Night	2 7% 3 6% 4 5% 5% 4 6% 9% 50%	2077
	21st to end	Night	2 5% 2 4 4 4 5% 5% 6% 8% 55%	2100
May	1st to 10th	Night	3 6% 2 6% 4 4 5% 5% 8% 10% 46%	5554
	11th to 20th	Night	3 4 1 5% 3 4 5% 4 7% 9% 55%	4981
	21st to end	Night	2 3 1 3 2 3 4 3 5% 6% 66%	5181
June	1st to 10th	Night	1 2 1 4 3 2 4 3 6% 8% 66%	1680
	11th to 20th	Night	2 2 1 2 2 3 4 3 5% 6% 70%	1680
	21st to end	Night	1 2 1 2 2 2 4 4 6% 10% 66%	1680
July	1st to 10th	Night	1 2 1 3 3 4 5% 4 6% 7% 64%	3720
	11th to 20th	Night	1 2 1 4 4 4 6% 6% 10% 15% 47%	3952
	21st to end	Night	2 3 1 5% 5% 4 6% 5% 8% 11% 51%	4472
August	1st to 10th	Night	3 3 2 5% 4 5% 5% 5% 8% 10% 51%	4033
	11th to 20th	Night	2 3 1 3 4 4 6% 6% 8% 10% 54%	4270
	21st to end	Night	4 5% 2 8% 6% 6% 7% 6% 8% 9% 38%	4993
September	1st to 10th	Night	4 4 2 5% 3 4 5% 4 6% 8% 56%	2000
	11th to 20th	Night	3 4 1 5% 3 3 4 3 7% 7% 58%	2000
	21st to end	Night	2 4 1 4 3 3 3 3 5% 7% 66%	2275
October	1st to 10th	Night	2 3 1 2 2 3 3 3 5% 6% 71%	3920
	11th to 20th	Night	2 3 2 5% 5% 4 6% 5% 8% 8% 52%	3898
	21st to end	Night	2 4 1 5% 3 4 5% 8% 10% 8% 50%	4252
November	1st to 10th	Night	1 4 1 3 3 3 3 4 8% 10% 60%	2528
	11th to 20th	Night	3 2 3 3 4 5% 6% 10% 10% 54%	2730
	21st to end	Night	1 5% 3 5% 4 5% 5% 6% 8% 12% 45%	2935
December	1st to 10th	Night	1 2 1 5% 5% 7% 8% 7% 13% 18% 34%	4710
	11th to 20th	Night	4 2 5% 5% 6% 9% 9% 12% 18% 30%	5321
	21st to end	Night	1 4 3 10% 7% 7% 8% 7% 13% 13% 28%	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	28% 10% 20% 28% 14% 1	4959
	11th to 20th	Day	18% 8% 22% 25% 24% 4	5340
	21st to end	Day	18% 10% 12% 30% 28% 2	5844
February	1st to 10th	Day	25% 10% 21% 22% 17% 5%	1890
	11th to 20th	Day	27% 9% 15% 24% 20% 5%	1928
	21st to end	Day	28% 9% 11% 23% 23% 5%	1730
March	1st to 10th	Day	23% 9% 12% 24% 28% 5%	4959
	11th to 20th	Day	27% 10% 12% 32% 15% 3	5110
	21st to end	Day	31% 12% 18% 24% 14% 1	5693
April	1st to 10th	Day	26% 9% 13% 25% 21% 7%	2520
	11th to 20th	Day	27% 9% 12% 25% 22% 5%	2494
	21st to end	Day	24% 9% 15% 28% 21% 3	2520
May	1st to 10th	Day	24% 10% 12% 26% 22% 6%	7388
	11th to 20th	Day	23% 8% 11% 26% 24% 7%	7911
	21st to end	Day	18% 10% 12% 26% 30% 5%	9027
June	1st to 10th	Day	20% 8% 11% 23% 27% 10%	2940
	11th to 20th	Day	20% 6% 7% 15% 28% 24%	2940
	21st to end	Day	19% 6% 9% 16% 26% 23%	2940
July	1st to 10th	Day	18% 7% 7% 10% 21% 38%	6411
	11th to 20th	Day	24% 12% 18% 24% 14% 8%	6061
	21st to end	Day	28% 12% 15% 20% 13% 12%	6217
August	1st to 10th	Day	33% 14% 18% 14% 15% 6%	4208
	11th to 20th	Day	29% 12% 13% 13% 23% 9%	4023
	21st to end	Day	30% 12% 12% 18% 20% 7%	4311
September	1st to 10th	Day	28% 9% 10% 16% 24% 13%	2400
	11th to 20th	Day	25% 9% 11% 17% 26% 12%	2400
	21st to end	Day	22% 7% 8% 21% 33% 10%	2121
October	1st to 10th	Day	14% 5% 7% 21% 35% 18%	3270
	11th to 20th	Day	27% 7% 10% 26% 24% 6%	3250
	21st to end	Day	16% 8% 8% 34% 29% 4	3548
November	1st to 10th	Day	14% 6% 14% 28% 33% 6%	1967
	11th to 20th	Day	17% 6% 11% 35% 25% 5%	1890
	21st to end	Day	23% 6% 14% 28% 22% 7%	1683
December	1st to 10th	Day	19% 15% 17% 34% 14% 2	2700
	11th to 20th	Day	19% 9% 21% 32% 18% 1	3104
	21st to end	Day	25% 10% 18% 22% 21% 5%	4092
January	1st to 10th	Night	32% 15% 16% 26% 11% 1	8022
	11th to 20th	Night	18% 15% 21% 25% 19% 3	7650
	21st to end	Night	23% 8% 13% 27% 24% 4	8370
February	1st to 10th	Night	24% 9% 19% 26% 18% 4	2730
	11th to 20th	Night	26% 8% 17% 25% 20% 4	2587
	21st to end	Night	24% 7% 12% 27% 25% 5%	2076
March	1st to 10th	Night	25% 8% 13% 24% 29% 2	5147
	11th to 20th	Night	22% 9% 17% 32% 19% 2	5110
	21st to end	Night	27% 14% 17% 30% 11% 1	5518
April	1st to 10th	Night	23% 8% 15% 25% 23% 5%	2100
	11th to 20th	Night	25% 8% 13% 25% 23% 5%	2077
	21st to end	Night	22% 8% 14% 31% 23% 2	2100
May	1st to 10th	Night	25% 11% 14% 28% 20% 2	5552
	11th to 20th	Night	18% 8% 13% 31% 26% 4	4982
	21st to end	Night	14% 7% 13% 26% 32% 7%	5182
June	1st to 10th	Night	14% 7% 12% 24% 30% 13%	1680
	11th to 20th	Night	14% 5% 9% 17% 27% 28%	1680
	21st to end	Night	13% 6% 10% 20% 26% 24%	1680
July	1st to 10th	Night	17% 7% 11% 12% 17% 37%	3680
	11th to 20th	Night	18% 12% 28% 24% 10% 8%	3903
	21st to end	Night	23% 11% 21% 24% 10% 11%	4344
August	1st to 10th	Night	31% 16% 19% 14% 12% 9%	2928
	11th to 20th	Night	22% 15% 19% 12% 23% 9%	3087
	21st to end	Night	30% 12% 15% 21% 17% 6%	3597
September	1st to 10th	Night	22% 9% 13% 20% 22% 14%	2000
	11th to 20th	Night	19% 8% 15% 18% 28% 13%	2000
	21st to end	Night	16% 7% 7% 26% 37% 8%	2275
October	1st to 10th	Night	12% 6% 8% 23% 38% 12%	3920
	11th to 20th	Night	20% 12% 11% 28% 23% 6%	3898
	21st to end	Night	16% 15% 10% 33% 23% 4	4252
November	1st to 10th	Night	16% 6% 13% 31% 29% 6%	2528
	11th to 20th	Night	15% 8% 12% 35% 26% 4	2730
	21st to end	Night	24% 6% 12% 27% 26% 5%	2935
December	1st to 10th	Night	15% 20% 15% 32% 15% 2	4710
	11th to 20th	Night	19% 14% 15% 35% 16% 1	5322
	21st to end	Night	27% 14% 16% 21% 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	7% 12% 26% 38% 15% 2	330
	11th to 20th	Day	6% 15% 27% 37% 12% 2	330
	21st to end	Day	2 9% 30% 43% 14% 2	363
February	1st to 10th	Day	3 20% 36% 34% 5% 2	330
	11th to 20th	Day	8% 25% 31% 29% 7% 1	330
	21st to end	Day	9% 22% 32% 28% 8% 1	273
March	1st to 10th	Day	7% 25% 31% 26% 10% 2	483
	11th to 20th	Day	6% 23% 33% 27% 9% 1	540
	21st to end	Day	9% 29% 34% 19% 8% 1	594
April	1st to 10th	Day	11% 27% 30% 21% 9% 2	540
	11th to 20th	Day	12% 33% 30% 17% 7% 1	532
	21st to end	Day	10% 29% 33% 21% 7% 1	540
May	1st to 10th	Day	10% 27% 33% 19% 9% 2	543
	11th to 20th	Day	7% 16% 31% 29% 16% 2	671
	21st to end	Day	6% 17% 27% 30% 18% 2	844
June	1st to 10th	Day	4 12% 26% 30% 25% 3	780
	11th to 20th	Day	4 12% 31% 31% 19% 3	780
	21st to end	Day	4 10% 28% 34% 21% 4	780
July	1st to 10th	Day	3 5% 18% 35% 33% 6%	771
	11th to 20th	Day	4 4 18% 32% 32% 10%	625
	21st to end	Day	6% 4 21% 36% 28% 6%	575
August	1st to 10th	Day	7% 7% 25% 30% 25% 6%	527
	11th to 20th	Day	3 4 28% 35% 23% 7%	517
	21st to end	Day	5% 4 26% 37% 22% 6%	583
September	1st to 10th	Day	6% 6% 27% 29% 23% 8%	530
	11th to 20th	Day	5% 11% 32% 32% 17% 4	530
	21st to end	Day	3 14% 27% 25% 21% 9%	410
October	1st to 10th	Day	10% 11% 17% 28% 22% 13%	330
	11th to 20th	Day	8% 18% 28% 24% 18% 5%	330
	21st to end	Day	8% 17% 23% 30% 19% 3	363
November	1st to 10th	Day	5% 17% 30% 27% 18% 3	330
	11th to 20th	Day	5% 14% 25% 35% 20% 2	330
	21st to end	Day	4 13% 30% 34% 18% 1	330
December	1st to 10th	Day	5% 15% 30% 30% 16% 4	330
	11th to 20th	Day	2 16% 26% 38% 15% 4	330
	21st to end	Day	7% 15% 30% 34% 12% 1	363
January	1st to 10th	Night	2 9% 29% 43% 16% 2	987
	11th to 20th	Night	3 9% 29% 43% 15% 2	840
	21st to end	Night	2 5% 30% 48% 12% 2	924
February	1st to 10th	Night	2 8% 37% 42% 10% 1	840
	11th to 20th	Night	2 9% 40% 40% 9%	824
	21st to end	Night	2 8% 42% 41% 6%	692
March	1st to 10th	Night	3 7% 38% 42% 9% 1	840
	11th to 20th	Night	3 6% 31% 45% 15% 1	840
	21st to end	Night	3 10% 33% 43% 11%	883
April	1st to 10th	Night	4 9% 41% 37% 9%	630
	11th to 20th	Night	5% 9% 35% 40% 10%	623
	21st to end	Night	4 10% 32% 40% 14% 1	630
May	1st to 10th	Night	5% 7% 30% 44% 14%	630
	11th to 20th	Night	5% 4 21% 47% 21% 2	621
	21st to end	Night	5% 8% 24% 40% 21% 2	683
June	1st to 10th	Night	2 2 21% 43% 31% 1	630
	11th to 20th	Night	2 3 21% 51% 20% 2	630
	21st to end	Night	1 2 15% 46% 34% 2	630
July	1st to 10th	Night	3 9% 41% 44% 3	615
	11th to 20th	Night	2 1 6% 33% 52% 6%	597
	21st to end	Night	4 1 7% 30% 53% 5%	657
August	1st to 10th	Night	7% 2 9% 34% 45% 4	597
	11th to 20th	Night	4 1 7% 40% 44% 4	594
	21st to end	Night	5% 1 8% 39% 42% 5%	660
September	1st to 10th	Night	5% 1 11% 43% 38% 3	600
	11th to 20th	Night	4 3 14% 46% 31% 2	600
	21st to end	Night	3 3 15% 40% 34% 5%	755
October	1st to 10th	Night	3 6% 21% 42% 26% 3	800
	11th to 20th	Night	2 5% 26% 45% 20% 3	800
	21st to end	Night	4 6% 25% 42% 21% 2	880
November	1st to 10th	Night	3 6% 28% 42% 19% 2	888
	11th to 20th	Night	3 9% 27% 47% 13% 2	1050
	21st to end	Night	3 10% 27% 41% 17% 1	1050
December	1st to 10th	Night	3 10% 31% 43% 12% 1	1050
	11th to 20th	Night	2 11% 30% 41% 15% 1	1050
	21st to end	Night	4 10% 33% 44% 9% 1	1155

Page generated at 2026-07-13 01:14:47. Version ac07

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