Coal Creek Crest
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coal Creek Crest clear sky chart from 2005-11-06 to 2025-03-27.

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	22% 11% 3 8% 5% 4 4 3 5% 6% 30%	113764
	Night	23% 11% 3 7% 4 4 4 3 4 6% 31%	114264
Transparency	Day	53% 7% 11% 15% 11% 2	113525
	Night	54% 7% 12% 17% 8% 2	114149
Seeing	Day	23% 13% 25% 26% 12% 2	15473
	Night	26% 7% 17% 32% 17% 1	24041

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	40% 17% 4 8% 5% 4 4 3 4 4 8%	3639
	11th to 20th	Day	25% 12% 4 8% 5% 4 5% 4 6% 7% 22%	3616
	21st to end	Day	33% 11% 3 7% 4 3 3 2 3 5% 27%	4347
February	1st to 10th	Day	33% 16% 4 8% 5% 4 4 3 5% 6% 13%	1800
	11th to 20th	Day	30% 17% 5% 10% 6% 4 3 3 4 3 16%	1755
	21st to end	Day	31% 18% 3 9% 5% 3 4 3 4 3 16%	1540
March	1st to 10th	Day	23% 19% 5% 11% 6% 4 5% 3 4 5% 14%	3412
	11th to 20th	Day	25% 14% 3 8% 4 3 3 2 3 4 31%	3600
	21st to end	Day	27% 17% 4 11% 6% 5% 6% 3 4 4 13%	3969
April	1st to 10th	Day	30% 15% 4 9% 5% 4 4 3 5% 6% 14%	2280
	11th to 20th	Day	27% 14% 4 9% 5% 5% 4 3 5% 5% 21%	2280
	21st to end	Day	24% 14% 4 9% 6% 5% 4 4 5% 5% 20%	2470
May	1st to 10th	Day	20% 10% 3 7% 5% 4 4 4 5% 5% 33%	4375
	11th to 20th	Day	13% 8% 3 7% 5% 4 6% 5% 8% 8% 33%	4377
	21st to end	Day	23% 11% 4 9% 6% 6% 5% 4 6% 7% 18%	4813
June	1st to 10th	Day	23% 11% 3 8% 5% 5% 4 4 5% 7% 25%	2660
	11th to 20th	Day	21% 10% 4 10% 7% 5% 6% 4 6% 7% 21%	2802
	21st to end	Day	13% 7% 2 7% 5% 5% 5% 4 6% 7% 39%	2850
July	1st to 10th	Day	5% 4 1 5% 3 3 2 2 4 6% 63%	4719
	11th to 20th	Day	5% 3 1 3 3 3 3 2 4 7% 64%	4420
	21st to end	Day	9% 5% 2 4 3 3 3 3 5% 7% 55%	4790
August	1st to 10th	Day	5% 4 2 4 3 3 3 3 5% 8% 61%	4158
	11th to 20th	Day	8% 6% 2 7% 5% 6% 7% 5% 7% 9% 38%	4026
	21st to end	Day	14% 8% 3 6% 3 4 4 3 6% 7% 43%	4343
September	1st to 10th	Day	8% 7% 2 5% 3 3 4 4 6% 8% 49%	2280
	11th to 20th	Day	13% 9% 3 6% 5% 5% 4 3 6% 8% 36%	2269
	21st to end	Day	19% 7% 3 7% 4 4 4 4 5% 7% 37%	2005
October	1st to 10th	Day	19% 7% 2 5% 4 3 4 3 6% 9% 40%	3180
	11th to 20th	Day	25% 9% 3 8% 4 4 5% 4 6% 7% 24%	3161
	21st to end	Day	30% 11% 3 9% 5% 4 5% 4 5% 5% 19%	3363
November	1st to 10th	Day	34% 14% 4 9% 4 6% 5% 4 4 4 13%	1616
	11th to 20th	Day	37% 13% 4 7% 4 3 4 3 5% 5% 15%	1600
	21st to end	Day	32% 13% 3 10% 4 5% 4 3 4 4 18%	1600
December	1st to 10th	Day	24% 10% 3 7% 5% 5% 5% 4 6% 6% 26%	2620
	11th to 20th	Day	39% 15% 4 10% 6% 4 4 3 3 4 9%	3025
	21st to end	Day	38% 18% 4 11% 5% 4 4 3 3 3 7%	4004
January	1st to 10th	Night	37% 17% 4 10% 5% 4 4 2 3 4 10%	6306
	11th to 20th	Night	24% 12% 3 7% 3 3 4 3 5% 8% 28%	6282
	21st to end	Night	34% 11% 3 6% 3 3 2 2 3 4 30%	6622
February	1st to 10th	Night	30% 14% 5% 8% 6% 5% 4 3 4 5% 16%	2600
	11th to 20th	Night	28% 14% 4 9% 5% 4 4 3 3 5% 22%	2532
	21st to end	Night	29% 16% 3 8% 5% 4 4 4 3 4 19%	2090
March	1st to 10th	Night	22% 19% 4 9% 6% 4 4 3 4 5% 19%	3679
	11th to 20th	Night	21% 13% 3 6% 4 4 3 3 3 4 36%	3599
	21st to end	Night	30% 17% 5% 9% 5% 4 4 2 4 4 15%	3821
April	1st to 10th	Night	24% 17% 4 8% 7% 5% 4 3 4 5% 20%	1900
	11th to 20th	Night	21% 14% 3 8% 5% 4 4 4 5% 6% 26%	1847
	21st to end	Night	21% 12% 3 8% 5% 5% 4 4 5% 7% 26%	1710
May	1st to 10th	Night	22% 10% 3 5% 3 3 3 3 4 6% 38%	2586
	11th to 20th	Night	10% 8% 2 6% 4 4 4 4 7% 8% 43%	2516
	21st to end	Night	11% 12% 4 9% 6% 6% 5% 4 6% 6% 31%	2762
June	1st to 10th	Night	17% 8% 3 8% 5% 5% 3 4 4 7% 36%	1520
	11th to 20th	Night	17% 9% 2 7% 5% 4 3 4 6% 8% 34%	1372
	21st to end	Night	9% 7% 2 6% 3 4 3 3 5% 6% 52%	1330
July	1st to 10th	Night	3 3 1 3 2 2 3 2 4 6% 70%	2238
	11th to 20th	Night	3 3 1 4 3 3 2 3 4 6% 69%	2540
	21st to end	Night	4 3 2 3 2 2 3 3 4 7% 67%	2762
August	1st to 10th	Night	2 2 1 3 2 3 3 3 5% 7% 70%	2777
	11th to 20th	Night	7% 5% 1 5% 5% 4 5% 4 6% 8% 50%	2812
	21st to end	Night	11% 6% 3 5% 4 3 4 3 4 6% 51%	3329
September	1st to 10th	Night	8% 4 1 4 3 3 4 3 4 8% 59%	1900
	11th to 20th	Night	12% 7% 3 7% 5% 3 4 3 5% 6% 45%	1909
	21st to end	Night	14% 6% 3 5% 4 4 4 3 5% 8% 44%	2175
October	1st to 10th	Night	13% 7% 2 6% 4 3 4 4 6% 9% 44%	3800
	11th to 20th	Night	21% 9% 3 9% 4 4 4 3 5% 7% 31%	3777
	21st to end	Night	29% 10% 3 7% 5% 4 4 3 5% 6% 24%	4201
November	1st to 10th	Night	34% 11% 3 7% 5% 4 4 3 4 5% 20%	2678
	11th to 20th	Night	37% 12% 4 7% 5% 3 3 3 5% 4 18%	2800
	21st to end	Night	28% 13% 4 7% 5% 5% 4 3 3 4 23%	2800
December	1st to 10th	Night	22% 11% 3 6% 4 4 4 4 7% 7% 28%	4560
	11th to 20th	Night	40% 17% 4 9% 4 4 3 2 3 3 11%	5180
	21st to end	Night	39% 19% 5% 10% 5% 4 3 2 3 3 9%	6952

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	81% 6% 5% 5% 3	3639
	11th to 20th	Day	62% 8% 9% 15% 6% 1	3640
	21st to end	Day	61% 6% 6% 14% 11% 2	4347
February	1st to 10th	Day	70% 7% 11% 9% 3	1800
	11th to 20th	Day	73% 6% 7% 8% 6% 1	1764
	21st to end	Day	72% 4 9% 8% 6% 1	1540
March	1st to 10th	Day	68% 8% 13% 8% 4	3412
	11th to 20th	Day	56% 5% 10% 24% 4	3600
	21st to end	Day	71% 9% 11% 8% 2	3969
April	1st to 10th	Day	69% 9% 10% 10% 1	2280
	11th to 20th	Day	65% 7% 10% 10% 8% 1	2280
	21st to end	Day	65% 7% 11% 11% 5%	2470
May	1st to 10th	Day	51% 8% 13% 17% 11%	4375
	11th to 20th	Day	44% 10% 22% 18% 5%	4380
	21st to end	Day	63% 10% 15% 10% 1	4814
June	1st to 10th	Day	59% 7% 16% 13% 6%	2660
	11th to 20th	Day	60% 9% 15% 12% 4	2802
	21st to end	Day	42% 9% 16% 23% 9% 2	2850
July	1st to 10th	Day	25% 5% 8% 18% 21% 23%	4645
	11th to 20th	Day	20% 4 7% 23% 40% 6%	4345
	21st to end	Day	26% 4 12% 29% 26% 3	4639
August	1st to 10th	Day	23% 6% 10% 28% 27% 6%	4141
	11th to 20th	Day	35% 12% 19% 22% 10% 3	4065
	21st to end	Day	40% 6% 11% 23% 17% 3	4342
September	1st to 10th	Day	33% 7% 14% 23% 17% 6%	2280
	11th to 20th	Day	45% 8% 13% 15% 16% 4	2269
	21st to end	Day	45% 7% 15% 16% 14% 3	2005
October	1st to 10th	Day	41% 6% 9% 29% 13% 1	3180
	11th to 20th	Day	56% 8% 13% 13% 10%	3161
	21st to end	Day	63% 7% 9% 13% 8%	3363
November	1st to 10th	Day	72% 7% 8% 10% 3	1616
	11th to 20th	Day	70% 7% 9% 7% 5% 2	1600
	21st to end	Day	69% 6% 7% 7% 11%	1600
December	1st to 10th	Day	58% 6% 8% 14% 14% 1	2620
	11th to 20th	Day	77% 8% 7% 8% 1	3028
	21st to end	Day	79% 7% 7% 4 2	4004
January	1st to 10th	Night	79% 7% 7% 5% 3 1	6306
	11th to 20th	Night	55% 10% 10% 19% 5% 1	6320
	21st to end	Night	59% 5% 8% 18% 9% 1	6622
February	1st to 10th	Night	71% 7% 8% 11% 2 1	2600
	11th to 20th	Night	65% 7% 10% 9% 7% 2	2534
	21st to end	Night	68% 7% 11% 8% 6%	2090
March	1st to 10th	Night	66% 8% 11% 12% 3	3679
	11th to 20th	Night	51% 9% 14% 21% 6%	3600
	21st to end	Night	73% 7% 10% 8% 1	3821
April	1st to 10th	Night	67% 6% 13% 10% 3	1900
	11th to 20th	Night	57% 9% 11% 13% 8% 2	1847
	21st to end	Night	57% 8% 14% 15% 5% 1	1710
May	1st to 10th	Night	46% 8% 15% 20% 9% 1	2586
	11th to 20th	Night	35% 8% 25% 22% 10% 1	2516
	21st to end	Night	50% 15% 20% 11% 3	2762
June	1st to 10th	Night	49% 6% 18% 21% 5%	1520
	11th to 20th	Night	46% 10% 21% 19% 3	1372
	21st to end	Night	31% 7% 22% 29% 8% 3	1330
July	1st to 10th	Night	15% 4 11% 27% 19% 24%	2203
	11th to 20th	Night	17% 3 8% 27% 39% 6%	2492
	21st to end	Night	16% 5% 14% 35% 25% 5%	2674
August	1st to 10th	Night	14% 5% 12% 36% 29% 4	2769
	11th to 20th	Night	28% 9% 26% 25% 9% 4	2839
	21st to end	Night	33% 6% 15% 27% 17% 2	3329
September	1st to 10th	Night	26% 6% 14% 28% 18% 8%	1900
	11th to 20th	Night	41% 7% 12% 20% 13% 6%	1909
	21st to end	Night	37% 7% 17% 20% 16% 3	2175
October	1st to 10th	Night	37% 7% 11% 33% 11% 1	3800
	11th to 20th	Night	52% 7% 14% 18% 8% 1	3777
	21st to end	Night	60% 6% 10% 16% 8%	4201
November	1st to 10th	Night	66% 7% 10% 11% 5%	2678
	11th to 20th	Night	69% 7% 8% 8% 5% 3	2800
	21st to end	Night	65% 7% 8% 9% 11% 1	2800
December	1st to 10th	Night	54% 9% 14% 15% 8%	4560
	11th to 20th	Night	77% 7% 7% 7% 3	5176
	21st to end	Night	79% 8% 7% 5% 1	6952

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	41% 15% 21% 15% 6% 3	200
	11th to 20th	Day	33% 14% 26% 16% 9% 4	200
	21st to end	Day	35% 12% 17% 24% 10% 3	368
February	1st to 10th	Day	41% 13% 19% 15% 11% 2	400
	11th to 20th	Day	40% 15% 23% 16% 5% 1	395
	21st to end	Day	38% 17% 21% 17% 7%	359
March	1st to 10th	Day	30% 18% 27% 17% 7% 1	500
	11th to 20th	Day	30% 15% 24% 20% 9% 2	500
	21st to end	Day	34% 18% 24% 16% 8% 1	531
April	1st to 10th	Day	30% 17% 22% 20% 8% 3	460
	11th to 20th	Day	28% 23% 25% 16% 6% 2	452
	21st to end	Day	27% 16% 30% 20% 6% 2	460
May	1st to 10th	Day	19% 16% 27% 25% 10% 2	463
	11th to 20th	Day	26% 12% 26% 22% 11% 3	488
	21st to end	Day	21% 12% 26% 28% 10% 2	529
June	1st to 10th	Day	24% 10% 24% 29% 11% 2	490
	11th to 20th	Day	18% 18% 33% 23% 6% 1	632
	21st to end	Day	10% 13% 31% 31% 14% 2	680
July	1st to 10th	Day	10% 7% 30% 37% 14% 2	663
	11th to 20th	Day	8% 9% 24% 38% 18% 3	484
	21st to end	Day	6% 4 25% 41% 21% 2	531
August	1st to 10th	Day	9% 5% 22% 43% 17% 5%	487
	11th to 20th	Day	4 4 22% 41% 24% 6%	477
	21st to end	Day	10% 8% 30% 34% 14% 4	539
September	1st to 10th	Day	9% 8% 28% 37% 15% 2	490
	11th to 20th	Day	14% 9% 24% 35% 15% 3	490
	21st to end	Day	18% 14% 23% 29% 14% 1	490
October	1st to 10th	Day	23% 11% 24% 26% 13% 2	490
	11th to 20th	Day	25% 11% 22% 24% 16% 3	490
	21st to end	Day	31% 12% 26% 18% 11% 2	490
November	1st to 10th	Day	29% 16% 27% 19% 7% 2	225
	11th to 20th	Day	41% 11% 17% 21% 9% 2	200
	21st to end	Day	29% 19% 21% 15% 15% 2	200
December	1st to 10th	Day	32% 11% 22% 17% 16% 3	200
	11th to 20th	Day	38% 19% 25% 12% 7% 1	200
	21st to end	Day	42% 14% 21% 16% 7%	220
January	1st to 10th	Night	42% 9% 17% 19% 12% 2	800
	11th to 20th	Night	37% 9% 14% 24% 15% 1	800
	21st to end	Night	32% 7% 14% 28% 17% 2	880
February	1st to 10th	Night	34% 9% 15% 29% 12% 1	800
	11th to 20th	Night	31% 9% 17% 30% 13% 1	784
	21st to end	Night	33% 11% 16% 29% 11%	660
March	1st to 10th	Night	30% 10% 21% 25% 14% 1	800
	11th to 20th	Night	32% 10% 17% 29% 13% 1	800
	21st to end	Night	35% 10% 17% 26% 11% 1	862
April	1st to 10th	Night	30% 9% 20% 24% 15% 1	760
	11th to 20th	Night	24% 9% 22% 30% 13% 2	719
	21st to end	Night	26% 6% 17% 35% 14% 1	570
May	1st to 10th	Night	20% 7% 22% 32% 18%	413
	11th to 20th	Night	17% 5% 17% 37% 22% 2	374
	21st to end	Night	15% 6% 17% 38% 23% 1	411
June	1st to 10th	Night	19% 3 19% 41% 18%	380
	11th to 20th	Night	17% 6% 21% 42% 13% 1	380
	21st to end	Night	10% 2 22% 48% 18%	380
July	1st to 10th	Night	5% 2 18% 52% 23%	370
	11th to 20th	Night	5% 2 18% 55% 20% 1	368
	21st to end	Night	3 2 12% 58% 24% 1	416
August	1st to 10th	Night	5% 2 10% 48% 32% 3	522
	11th to 20th	Night	6% 2 9% 44% 36% 3	564
	21st to end	Night	11% 3 16% 43% 24% 2	732
September	1st to 10th	Night	10% 3 18% 42% 26% 2	760
	11th to 20th	Night	14% 4 15% 34% 30% 3	760
	21st to end	Night	15% 6% 18% 39% 21% 2	760
October	1st to 10th	Night	21% 4 16% 36% 21% 3	760
	11th to 20th	Night	24% 5% 15% 30% 23% 3	760
	21st to end	Night	29% 7% 18% 27% 18% 1	836
November	1st to 10th	Night	33% 8% 18% 30% 10%	780
	11th to 20th	Night	40% 9% 16% 22% 13% 1	800
	21st to end	Night	32% 8% 18% 25% 16% 2	800
December	1st to 10th	Night	30% 7% 16% 27% 17% 2	800
	11th to 20th	Night	38% 8% 18% 24% 10% 1	800
	21st to end	Night	43% 11% 19% 19% 7% 1	880

Page generated at 2025-03-24 06:04:31. Version ac07

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