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 2025-02-25.

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 4 2 6% 5% 5% 6% 5% 8% 11% 47%	112751
	Night	2 4 2 6% 5% 5% 6% 5% 9% 11% 45%	114795
Transparency	Day	25% 10% 13% 22% 22% 8%	112508
	Night	22% 10% 15% 25% 21% 6%	114629
Seeing	Day	6% 15% 28% 29% 17% 3	15708
	Night	3 6% 26% 41% 21% 2	25977

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 10% 7% 8% 9% 8% 11% 14% 29%	3818
	11th to 20th	Day	2 1 6% 6% 8% 9% 7% 14% 15% 32%	4100
	21st to end	Day	4 3 7% 6% 7% 12% 6% 8% 12% 34%	4510
February	1st to 10th	Day	4 3 7% 4 5% 5% 6% 10% 16% 41%	1800
	11th to 20th	Day	1 4 2 5% 5% 5% 6% 6% 10% 16% 40%	1825
	21st to end	Day	4 2 8% 6% 5% 6% 6% 8% 12% 43%	1610
March	1st to 10th	Day	1 4 2 5% 5% 5% 7% 6% 10% 14% 42%	3370
	11th to 20th	Day	5% 3 7% 6% 6% 9% 6% 10% 13% 34%	3490
	21st to end	Day	1 9% 3 8% 6% 6% 7% 7% 10% 10% 33%	3883
April	1st to 10th	Day	1 5% 2 4 5% 5% 4 4 9% 13% 48%	2280
	11th to 20th	Day	1 4 3 4 4 6% 5% 5% 7% 13% 48%	2251
	21st to end	Day	1 5% 1 5% 4 4 6% 5% 8% 12% 50%	2280
May	1st to 10th	Day	2 7% 2 6% 4 5% 6% 5% 8% 12% 43%	3976
	11th to 20th	Day	2 5% 2 6% 6% 5% 6% 5% 8% 11% 44%	4242
	21st to end	Day	1 3 1 5% 4 5% 5% 4 7% 8% 56%	4825
June	1st to 10th	Day	2 3 2 4 4 3 4 4 6% 9% 60%	2660
	11th to 20th	Day	3 3 1 4 4 4 3 3 5% 7% 63%	2660
	21st to end	Day	2 2 2 4 4 4 5% 4 6% 9% 57%	2660
July	1st to 10th	Day	2 3 1 4 4 4 4 4 5% 6% 63%	4430
	11th to 20th	Day	2 2 1 5% 5% 6% 7% 7% 10% 12% 41%	4238
	21st to end	Day	3 4 1 6% 4 5% 6% 5% 8% 9% 48%	4454
August	1st to 10th	Day	4 4 2 6% 6% 7% 6% 6% 9% 12% 38%	4092
	11th to 20th	Day	4 3 2 5% 5% 5% 6% 5% 8% 9% 46%	3859
	21st to end	Day	3 4 2 7% 6% 5% 6% 5% 8% 9% 45%	4180
September	1st to 10th	Day	4 4 2 6% 5% 4 4 4 6% 7% 53%	2280
	11th to 20th	Day	4 3 2 5% 4 4 5% 3 6% 8% 56%	2280
	21st to end	Day	4 4 1 5% 3 3 2 3 3 6% 64%	2015
October	1st to 10th	Day	2 2 1 2 2 2 2 3 4 6% 72%	3170
	11th to 20th	Day	2 3 2 6% 5% 5% 6% 5% 7% 8% 50%	3150
	21st to end	Day	2 3 1 4 3 3 4 4 6% 7% 63%	3438
November	1st to 10th	Day	1 3 1 4 3 2 4 4 8% 11% 60%	1872
	11th to 20th	Day	1 3 2 3 4 4 4 5% 7% 12% 56%	1800
	21st to end	Day	1 4 2 5% 4 4 5% 5% 7% 14% 49%	1603
December	1st to 10th	Day	3 1 4 4 4 7% 10% 14% 13% 39%	2620
	11th to 20th	Day	4 1 5% 4 4 6% 8% 15% 17% 36%	3026
	21st to end	Day	1 3 2 8% 5% 6% 7% 7% 11% 15% 35%	4004
January	1st to 10th	Night	3 3 11% 8% 9% 10% 7% 11% 12% 26%	6189
	11th to 20th	Night	2 2 8% 6% 7% 9% 8% 12% 15% 31%	5880
	21st to end	Night	1 8% 4 11% 7% 7% 6% 5% 7% 15% 29%	6468
February	1st to 10th	Night	4 2 7% 5% 5% 5% 5% 10% 13% 44%	2600
	11th to 20th	Night	1 5% 2 6% 3 4 6% 5% 10% 10% 47%	2460
	21st to end	Night	1 6% 3 6% 4 4 6% 5% 9% 10% 47%	1938
March	1st to 10th	Night	1 7% 2 7% 5% 6% 5% 5% 8% 10% 44%	3498
	11th to 20th	Night	1 8% 3 8% 5% 6% 7% 6% 8% 9% 40%	3490
	21st to end	Night	1 9% 4 9% 6% 7% 7% 5% 8% 8% 36%	3766
April	1st to 10th	Night	1 6% 2 6% 4 4 4 4 8% 9% 52%	1900
	11th to 20th	Night	2 7% 2 6% 4 4 5% 4 6% 9% 51%	1877
	21st to end	Night	2 5% 2 4 4 4 6% 5% 6% 9% 54%	1900
May	1st to 10th	Night	3 7% 2 5% 4 4 4 3 7% 8% 52%	2989
	11th to 20th	Night	3 7% 2 6% 4 4 5% 3 6% 9% 51%	2659
	21st to end	Night	3 4 2 3 3 3 3 3 4 6% 66%	2762
June	1st to 10th	Night	1 2 1 4 3 2 4 3 6% 8% 66%	1520
	11th to 20th	Night	2 2 1 2 3 3 3 3 6% 6% 69%	1520
	21st to end	Night	2 2 1 2 3 2 4 5% 6% 10% 64%	1520
July	1st to 10th	Night	2 2 1 4 4 4 4 3 5% 6% 65%	2540
	11th to 20th	Night	1 2 1 4 4 4 6% 6% 10% 14% 49%	2727
	21st to end	Night	3 3 1 5% 5% 4 6% 5% 7% 9% 53%	3109
August	1st to 10th	Night	4 5% 2 6% 6% 6% 7% 5% 9% 11% 38%	2847
	11th to 20th	Night	3 4 1 3 4 5% 6% 6% 8% 10% 49%	2965
	21st to end	Night	3 4 2 7% 5% 6% 7% 5% 8% 9% 45%	3487
September	1st to 10th	Night	4 4 2 5% 3 4 5% 4 6% 8% 56%	1900
	11th to 20th	Night	4 4 1 5% 3 3 4 3 6% 7% 59%	1900
	21st to end	Night	2 3 1 4 3 3 3 3 4 6% 67%	2161
October	1st to 10th	Night	2 3 1 3 2 3 2 3 5% 6% 71%	3800
	11th to 20th	Night	2 3 1 5% 5% 4 6% 6% 8% 8% 52%	3778
	21st to end	Night	2 4 1 5% 3 4 5% 8% 10% 8% 50%	4120
November	1st to 10th	Night	1 4 1 3 3 3 3 4 7% 10% 59%	2405
	11th to 20th	Night	3 2 3 3 4 5% 6% 9% 11% 55%	2600
	21st to end	Night	1 5% 3 5% 4 5% 5% 6% 8% 13% 46%	2795
December	1st to 10th	Night	1 2 1 5% 5% 7% 8% 7% 13% 19% 34%	4570
	11th to 20th	Night	4 2 5% 5% 6% 8% 9% 12% 19% 30%	5181
	21st to end	Night	1 4 3 10% 7% 7% 8% 7% 13% 13% 27%	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	29% 12% 19% 25% 15% 1	3819
	11th to 20th	Day	23% 7% 22% 21% 23% 4	4100
	21st to end	Day	21% 11% 13% 27% 26% 2	4510
February	1st to 10th	Day	26% 10% 22% 20% 17% 5%	1800
	11th to 20th	Day	27% 9% 15% 25% 20% 5%	1834
	21st to end	Day	30% 9% 10% 22% 24% 5%	1610
March	1st to 10th	Day	23% 9% 13% 26% 25% 4	3370
	11th to 20th	Day	27% 11% 15% 34% 10% 2	3490
	21st to end	Day	38% 11% 14% 20% 15% 2	3883
April	1st to 10th	Day	27% 9% 13% 23% 20% 7%	2280
	11th to 20th	Day	28% 9% 13% 24% 21% 5%	2254
	21st to end	Day	25% 10% 16% 28% 20% 2	2280
May	1st to 10th	Day	27% 9% 14% 20% 23% 7%	3976
	11th to 20th	Day	24% 10% 14% 26% 21% 5%	4246
	21st to end	Day	20% 10% 12% 19% 33% 6%	4825
June	1st to 10th	Day	20% 8% 11% 22% 27% 11%	2660
	11th to 20th	Day	21% 7% 7% 15% 27% 23%	2660
	21st to end	Day	20% 7% 9% 17% 26% 21%	2660
July	1st to 10th	Day	20% 7% 7% 11% 22% 33%	4361
	11th to 20th	Day	25% 12% 17% 25% 14% 7%	4165
	21st to end	Day	26% 12% 14% 17% 15% 16%	4314
August	1st to 10th	Day	34% 14% 19% 13% 14% 6%	4078
	11th to 20th	Day	30% 12% 14% 13% 23% 9%	3898
	21st to end	Day	30% 13% 12% 18% 20% 8%	4179
September	1st to 10th	Day	28% 9% 10% 15% 25% 14%	2280
	11th to 20th	Day	24% 9% 11% 17% 26% 12%	2280
	21st to end	Day	22% 7% 8% 20% 33% 10%	2015
October	1st to 10th	Day	14% 5% 7% 21% 35% 18%	3170
	11th to 20th	Day	27% 7% 10% 26% 24% 6%	3150
	21st to end	Day	17% 8% 8% 35% 29% 4	3438
November	1st to 10th	Day	14% 6% 14% 26% 34% 6%	1872
	11th to 20th	Day	17% 6% 11% 35% 26% 5%	1800
	21st to end	Day	23% 6% 13% 28% 23% 8%	1603
December	1st to 10th	Day	19% 15% 16% 34% 14% 2	2620
	11th to 20th	Day	20% 9% 21% 32% 18% 1	3024
	21st to end	Day	25% 10% 18% 21% 20% 5%	4004
January	1st to 10th	Night	33% 12% 16% 25% 13% 1	6189
	11th to 20th	Night	23% 11% 22% 22% 20% 2	5880
	21st to end	Night	27% 9% 14% 26% 22% 3	6468
February	1st to 10th	Night	25% 7% 20% 25% 19% 5%	2600
	11th to 20th	Night	26% 7% 17% 26% 20% 4	2461
	21st to end	Night	25% 7% 11% 27% 25% 5%	1938
March	1st to 10th	Night	23% 6% 12% 28% 28% 3	3498
	11th to 20th	Night	25% 9% 20% 33% 12% 2	3490
	21st to end	Night	34% 10% 16% 26% 13% 1	3766
April	1st to 10th	Night	24% 8% 16% 24% 23% 5%	1900
	11th to 20th	Night	26% 8% 14% 25% 22% 5%	1877
	21st to end	Night	23% 8% 15% 30% 22% 2	1900
May	1st to 10th	Night	23% 7% 12% 26% 29% 4	2989
	11th to 20th	Night	19% 9% 16% 30% 22% 4	2660
	21st to end	Night	14% 6% 11% 23% 35% 12%	2762
June	1st to 10th	Night	14% 7% 12% 23% 30% 14%	1520
	11th to 20th	Night	14% 5% 9% 18% 26% 27%	1520
	21st to end	Night	13% 6% 11% 22% 26% 22%	1520
July	1st to 10th	Night	18% 6% 9% 14% 19% 33%	2500
	11th to 20th	Night	16% 12% 28% 24% 12% 8%	2678
	21st to end	Night	23% 12% 19% 23% 9% 15%	3011
August	1st to 10th	Night	31% 16% 19% 13% 11% 8%	2838
	11th to 20th	Night	23% 15% 19% 12% 22% 9%	2992
	21st to end	Night	29% 12% 14% 21% 17% 6%	3487
September	1st to 10th	Night	22% 9% 13% 19% 22% 15%	1900
	11th to 20th	Night	19% 7% 15% 17% 29% 13%	1900
	21st to end	Night	16% 6% 7% 25% 38% 8%	2161
October	1st to 10th	Night	12% 6% 8% 23% 38% 13%	3800
	11th to 20th	Night	20% 12% 11% 28% 23% 6%	3778
	21st to end	Night	16% 15% 10% 33% 23% 4	4120
November	1st to 10th	Night	16% 5% 14% 29% 29% 6%	2405
	11th to 20th	Night	15% 7% 12% 35% 28% 4	2600
	21st to end	Night	24% 5% 12% 27% 27% 5%	2795
December	1st to 10th	Night	15% 20% 15% 32% 15% 2	4570
	11th to 20th	Night	20% 13% 15% 36% 16% 1	5182
	21st to end	Night	27% 13% 16% 21% 20% 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	7% 13% 25% 36% 17% 2	300
	11th to 20th	Day	7% 16% 29% 35% 12% 1	300
	21st to end	Day	2 9% 32% 41% 15% 2	330
February	1st to 10th	Day	3 22% 38% 32% 4 1	300
	11th to 20th	Day	7% 26% 33% 27% 7% 1	300
	21st to end	Day	8% 24% 35% 26% 5% 1	237
March	1st to 10th	Day	8% 26% 32% 24% 9% 1	408
	11th to 20th	Day	5% 23% 35% 26% 10% 1	460
	21st to end	Day	10% 31% 36% 18% 5%	506
April	1st to 10th	Day	12% 30% 31% 20% 7% 1	460
	11th to 20th	Day	11% 35% 31% 16% 6% 1	452
	21st to end	Day	10% 29% 34% 21% 5% 1	460
May	1st to 10th	Day	11% 29% 34% 18% 7% 1	463
	11th to 20th	Day	6% 16% 31% 29% 16% 2	581
	21st to end	Day	6% 18% 27% 30% 17% 2	734
June	1st to 10th	Day	4 12% 27% 30% 25% 3	680
	11th to 20th	Day	4 12% 31% 32% 18% 3	680
	21st to end	Day	3 10% 28% 34% 21% 4	680
July	1st to 10th	Day	3 5% 17% 36% 33% 5%	671
	11th to 20th	Day	5% 4 18% 33% 32% 9%	556
	21st to end	Day	6% 3 21% 36% 28% 6%	531
August	1st to 10th	Day	8% 6% 25% 30% 25% 6%	487
	11th to 20th	Day	4 4 29% 35% 21% 6%	477
	21st to end	Day	4 4 27% 36% 23% 6%	539
September	1st to 10th	Day	7% 6% 28% 29% 22% 9%	490
	11th to 20th	Day	5% 11% 32% 31% 18% 4	490
	21st to end	Day	3 15% 28% 24% 22% 8%	376
October	1st to 10th	Day	10% 12% 16% 26% 22% 13%	300
	11th to 20th	Day	7% 17% 26% 24% 20% 6%	300
	21st to end	Day	8% 18% 24% 28% 18% 3	330
November	1st to 10th	Day	6% 17% 32% 26% 18% 2	300
	11th to 20th	Day	4 15% 27% 35% 18% 1	300
	21st to end	Day	3 13% 32% 31% 19% 1	300
December	1st to 10th	Day	5% 16% 30% 28% 17% 4	300
	11th to 20th	Day	2 17% 26% 39% 13% 3	300
	21st to end	Day	8% 16% 31% 33% 11% 1	330
January	1st to 10th	Night	2 9% 28% 42% 16% 2	940
	11th to 20th	Night	3 9% 29% 42% 15% 2	800
	21st to end	Night	3 6% 30% 47% 13% 2	880
February	1st to 10th	Night	2 9% 39% 41% 10% 1	800
	11th to 20th	Night	2 9% 40% 39% 9%	784
	21st to end	Night	3 9% 42% 41% 5%	646
March	1st to 10th	Night	3 7% 40% 39% 9% 1	760
	11th to 20th	Night	3 6% 31% 44% 16% 1	760
	21st to end	Night	3 11% 34% 42% 9% 1	799
April	1st to 10th	Night	4 9% 42% 36% 8%	570
	11th to 20th	Night	5% 10% 36% 39% 10%	563
	21st to end	Night	4 10% 34% 38% 13% 1	570
May	1st to 10th	Night	6% 7% 31% 42% 14%	570
	11th to 20th	Night	6% 4 19% 48% 21% 2	561
	21st to end	Night	5% 8% 25% 38% 21% 2	617
June	1st to 10th	Night	2 2 21% 43% 31% 1	570
	11th to 20th	Night	2 3 22% 50% 20% 2	570
	21st to end	Night	1 2 15% 45% 35% 2	570
July	1st to 10th	Night	3 9% 40% 45% 3	555
	11th to 20th	Night	3 1 6% 32% 52% 6%	552
	21st to end	Night	4 1 6% 30% 53% 5%	624
August	1st to 10th	Night	7% 1 8% 33% 47% 4	567
	11th to 20th	Night	4 1 7% 41% 43% 4	564
	21st to end	Night	5% 1 8% 39% 42% 6%	627
September	1st to 10th	Night	5% 1 11% 42% 39% 3	570
	11th to 20th	Night	4 2 13% 46% 32% 2	570
	21st to end	Night	3 3 16% 40% 34% 5%	717
October	1st to 10th	Night	3 6% 22% 40% 26% 3	760
	11th to 20th	Night	1 4 26% 45% 21% 3	760
	21st to end	Night	3 6% 26% 41% 22% 2	836
November	1st to 10th	Night	3 6% 28% 42% 19% 2	845
	11th to 20th	Night	3 9% 28% 45% 14% 2	1000
	21st to end	Night	3 11% 27% 40% 18% 1	1000
December	1st to 10th	Night	3 10% 31% 42% 13% 2	1000
	11th to 20th	Night	2 11% 31% 41% 15% 1	1000
	21st to end	Night	4 10% 33% 43% 9% 1	1100

Page generated at 2025-02-22 04:51:38. Version ac07

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