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 2024-10-24.

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	21% 11% 3 8% 5% 4 4 3 5% 6% 31%	102113
	Night	23% 11% 3 7% 4 4 4 3 4 5% 32%	96752
Transparency	Day	53% 7% 11% 15% 11% 3	101874
	Night	54% 7% 12% 16% 9% 2	96637
Seeing	Day	22% 13% 25% 26% 12% 2	15059
	Night	26% 7% 17% 32% 17% 1	23423

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% 19% 4 8% 4 4 4 2 3 4 8%	2539
	11th to 20th	Day	36% 14% 4 7% 3 3 3 3 3 5% 18%	2516
	21st to end	Day	43% 14% 4 9% 4 4 3 2 3 3 11%	3025
February	1st to 10th	Day	34% 16% 4 8% 5% 4 4 3 4 6% 13%	1710
	11th to 20th	Day	30% 17% 5% 10% 6% 4 3 3 4 3 16%	1665
	21st to end	Day	31% 19% 3 9% 5% 3 4 2 4 3 16%	1465
March	1st to 10th	Day	24% 19% 5% 11% 6% 4 5% 3 4 5% 14%	3307
	11th to 20th	Day	25% 14% 3 7% 4 3 3 2 3 4 32%	3490
	21st to end	Day	27% 17% 4 11% 6% 5% 6% 3 4 4 13%	3901
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	24% 9% 2 7% 4 3 4 3 4 5% 34%	1900
	11th to 20th	Day	25% 7% 3 7% 4 4 4 5% 7% 7% 26%	1900
	21st to end	Day	33% 10% 3 8% 5% 4 3 3 4 4 24%	1965
November	1st to 10th	Day	35% 14% 4 9% 4 6% 4 4 4 3 13%	1534
	11th to 20th	Day	37% 13% 3 7% 4 3 4 3 5% 5% 15%	1520
	21st to end	Day	32% 13% 3 10% 4 5% 4 3 4 4 19%	1520
December	1st to 10th	Day	31% 14% 4 8% 5% 5% 3 3 4 4 19%	1520
	11th to 20th	Day	36% 14% 4 9% 6% 4 4 3 5% 5% 11%	1925
	21st to end	Day	34% 18% 4 11% 6% 4 4 3 3 3 9%	2794
January	1st to 10th	Night	36% 18% 4 11% 6% 4 4 2 3 4 10%	4406
	11th to 20th	Night	34% 14% 4 8% 4 3 4 3 3 5% 19%	4382
	21st to end	Night	45% 14% 3 7% 3 3 3 2 3 4 13%	4636
February	1st to 10th	Night	31% 14% 5% 8% 5% 5% 4 2 4 5% 16%	2470
	11th to 20th	Night	28% 14% 4 9% 5% 4 4 2 3 5% 22%	2402
	21st to end	Night	28% 17% 4 8% 5% 4 4 4 4 4 19%	1989
March	1st to 10th	Night	23% 19% 4 9% 6% 5% 4 3 4 5% 19%	3564
	11th to 20th	Night	21% 13% 3 6% 4 4 3 3 3 4 37%	3489
	21st to end	Night	30% 18% 5% 9% 5% 4 4 2 4 3 15%	3751
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	19% 8% 3 5% 4 3 3 3 5% 7% 41%	2280
	11th to 20th	Night	22% 7% 3 7% 4 4 4 3 5% 6% 35%	2280
	21st to end	Night	28% 8% 3 7% 4 3 3 2 5% 5% 32%	2456
November	1st to 10th	Night	35% 11% 3 7% 5% 4 4 3 4 5% 20%	2540
	11th to 20th	Night	36% 11% 4 7% 5% 3 3 3 5% 4 19%	2660
	21st to end	Night	28% 13% 3 7% 5% 5% 4 3 4 5% 24%	2660
December	1st to 10th	Night	30% 13% 4 7% 5% 4 4 3 4 4 22%	2660
	11th to 20th	Night	33% 15% 4 9% 5% 4 4 3 4 4 16%	3280
	21st to end	Night	33% 18% 5% 10% 6% 5% 3 2 3 3 11%	4862

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	82% 6% 6% 4 3	2539
	11th to 20th	Day	69% 6% 9% 10% 4 2	2540
	21st to end	Day	78% 5% 6% 7% 4	3025
February	1st to 10th	Day	71% 7% 11% 8% 3	1710
	11th to 20th	Day	73% 6% 8% 9% 5% 1	1674
	21st to end	Day	72% 4 9% 8% 5% 1	1465
March	1st to 10th	Day	69% 8% 12% 7% 4	3307
	11th to 20th	Day	55% 5% 10% 25% 4	3490
	21st to end	Day	71% 9% 11% 8% 2	3901
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	53% 6% 8% 21% 11% 2	1900
	11th to 20th	Day	55% 7% 14% 13% 10% 1	1900
	21st to end	Day	63% 5% 8% 14% 10%	1965
November	1st to 10th	Day	72% 7% 7% 10% 3	1534
	11th to 20th	Day	69% 6% 10% 7% 5% 2	1520
	21st to end	Day	69% 5% 6% 8% 12%	1520
December	1st to 10th	Day	70% 5% 6% 10% 8% 1	1520
	11th to 20th	Day	72% 9% 8% 9% 2	1928
	21st to end	Day	77% 7% 8% 5% 3	2794
January	1st to 10th	Night	79% 7% 7% 4 2 1	4406
	11th to 20th	Night	67% 7% 8% 13% 3 2	4420
	21st to end	Night	76% 5% 7% 7% 4 1	4636
February	1st to 10th	Night	71% 7% 8% 11% 2 1	2470
	11th to 20th	Night	65% 7% 11% 9% 6% 2	2404
	21st to end	Night	69% 6% 10% 8% 6%	1989
March	1st to 10th	Night	66% 8% 11% 12% 3	3564
	11th to 20th	Night	49% 9% 14% 21% 6%	3490
	21st to end	Night	73% 7% 10% 9% 1	3751
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	43% 6% 11% 25% 13% 1	2280
	11th to 20th	Night	50% 6% 13% 19% 11% 1	2280
	21st to end	Night	56% 5% 11% 16% 12%	2456
November	1st to 10th	Night	66% 7% 10% 12% 5%	2540
	11th to 20th	Night	68% 7% 8% 9% 5% 3	2660
	21st to end	Night	64% 7% 8% 9% 11% 1	2660
December	1st to 10th	Night	65% 7% 7% 12% 7% 1	2660
	11th to 20th	Night	71% 7% 8% 9% 4	3276
	21st to end	Night	76% 8% 8% 6% 2	4862

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% 14% 21% 14% 7% 3	180
	11th to 20th	Day	36% 14% 26% 14% 8% 2	180
	21st to end	Day	37% 12% 17% 24% 9% 2	338
February	1st to 10th	Day	42% 12% 19% 16% 11% 1	370
	11th to 20th	Day	40% 15% 23% 16% 5% 1	365
	21st to end	Day	37% 17% 22% 16% 7%	332
March	1st to 10th	Day	32% 18% 27% 17% 6% 1	460
	11th to 20th	Day	28% 15% 25% 20% 9% 3	460
	21st to end	Day	33% 18% 24% 16% 8% 1	506
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	30% 13% 25% 17% 12% 2	462
November	1st to 10th	Day	28% 18% 27% 19% 7% 1	203
	11th to 20th	Day	38% 11% 18% 22% 10% 2	180
	21st to end	Day	29% 20% 21% 14% 15% 1	180
December	1st to 10th	Day	34% 12% 23% 16% 13% 2	180
	11th to 20th	Day	37% 19% 23% 13% 8% 1	180
	21st to end	Day	40% 14% 21% 18% 7% 1	198
January	1st to 10th	Night	42% 9% 16% 19% 12% 2	760
	11th to 20th	Night	38% 9% 14% 23% 15% 1	760
	21st to end	Night	34% 7% 14% 27% 16% 2	836
February	1st to 10th	Night	35% 8% 15% 29% 13% 1	760
	11th to 20th	Night	30% 9% 17% 30% 14% 1	744
	21st to end	Night	33% 11% 16% 28% 12%	628
March	1st to 10th	Night	30% 10% 20% 24% 14% 1	760
	11th to 20th	Night	30% 10% 18% 29% 13% 1	760
	21st to end	Night	34% 10% 17% 26% 11% 1	836
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% 19% 27% 18% 1	804
November	1st to 10th	Night	33% 9% 18% 29% 10%	740
	11th to 20th	Night	38% 9% 16% 22% 13% 1	760
	21st to end	Night	32% 8% 18% 25% 16% 2	760
December	1st to 10th	Night	31% 7% 17% 27% 15% 2	760
	11th to 20th	Night	37% 8% 18% 24% 11% 1	760
	21st to end	Night	42% 11% 19% 19% 7% 1	836

Page generated at 2024-10-20 23:20:01. Version ac07

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