Dome Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dome Creek clear sky chart from 2005-11-06 to 2026-06-01.

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	11% 12% 4 10% 6% 6% 6% 4 6% 7% 28%	135570
	Night	11% 15% 5% 11% 6% 6% 5% 4 6% 6% 25%	136253
Transparency	Day	51% 10% 17% 16% 6% 1	135258
	Night	53% 10% 16% 16% 5%	136144
Seeing	Day	19% 11% 22% 28% 16% 5%	18385
	Night	23% 9% 20% 31% 15% 1	26479

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	7% 20% 6% 15% 9% 8% 6% 4 4 6% 14%	3605
	11th to 20th	Day	7% 15% 4 11% 5% 5% 5% 4 6% 6% 32%	4119
	21st to end	Day	9% 15% 6% 11% 6% 6% 6% 5% 6% 7% 23%	4691
February	1st to 10th	Day	9% 21% 7% 12% 6% 4 5% 3 4 6% 22%	1680
	11th to 20th	Day	8% 19% 7% 14% 7% 6% 5% 3 4 5% 23%	1829
	21st to end	Day	4 19% 6% 15% 7% 6% 4 4 4 6% 24%	1587
March	1st to 10th	Day	4 17% 7% 13% 7% 6% 5% 4 6% 7% 24%	4618
	11th to 20th	Day	3 14% 5% 11% 6% 7% 8% 6% 9% 10% 22%	4975
	21st to end	Day	6% 16% 5% 10% 6% 5% 5% 4 6% 6% 30%	5955
April	1st to 10th	Day	6% 14% 6% 13% 8% 8% 7% 6% 7% 7% 20%	2520
	11th to 20th	Day	8% 14% 4 12% 7% 6% 6% 5% 6% 8% 24%	2650
	21st to end	Day	9% 14% 4 12% 6% 5% 5% 4 7% 6% 27%	2940
May	1st to 10th	Day	7% 11% 4 10% 7% 6% 7% 6% 8% 8% 27%	6460
	11th to 20th	Day	12% 12% 4 11% 7% 8% 7% 5% 7% 7% 19%	6544
	21st to end	Day	15% 12% 4 10% 6% 6% 7% 5% 7% 7% 20%	8083
June	1st to 10th	Day	14% 9% 4 9% 6% 7% 6% 6% 6% 7% 26%	3201
	11th to 20th	Day	20% 11% 4 9% 7% 7% 6% 5% 6% 8% 18%	3200
	21st to end	Day	15% 9% 4 9% 8% 6% 6% 4 6% 7% 27%	3200
July	1st to 10th	Day	13% 5% 2 7% 5% 5% 6% 5% 6% 7% 40%	7240
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	7040
	21st to end	Day	11% 5% 3 7% 6% 5% 6% 5% 7% 9% 37%	7335
August	1st to 10th	Day	7% 5% 2 6% 5% 4 5% 4 6% 8% 50%	4541
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 6% 8% 42%	4470
	21st to end	Day	17% 7% 3 8% 5% 6% 6% 4 5% 8% 31%	4612
September	1st to 10th	Day	15% 7% 3 7% 6% 5% 6% 4 5% 7% 34%	2400
	11th to 20th	Day	13% 10% 3 7% 6% 6% 5% 4 6% 7% 34%	2400
	21st to end	Day	21% 13% 3 9% 5% 6% 5% 4 5% 7% 23%	2130
October	1st to 10th	Day	15% 13% 4 11% 6% 6% 6% 4 6% 7% 22%	3280
	11th to 20th	Day	17% 15% 5% 9% 6% 5% 5% 4 5% 6% 24%	3142
	21st to end	Day	11% 13% 4 8% 8% 7% 7% 4 6% 6% 26%	3072
November	1st to 10th	Day	17% 20% 6% 11% 6% 5% 4 3 5% 6% 17%	1648
	11th to 20th	Day	9% 22% 7% 13% 7% 5% 5% 4 6% 5% 17%	1575
	21st to end	Day	11% 22% 7% 13% 8% 6% 4 4 6% 4 15%	1428
December	1st to 10th	Day	19% 18% 6% 14% 8% 6% 4 4 5% 5% 12%	2020
	11th to 20th	Day	8% 21% 6% 14% 7% 7% 6% 4 4 6% 17%	2322
	21st to end	Day	7% 18% 7% 12% 6% 5% 5% 4 7% 8% 22%	3058
January	1st to 10th	Night	9% 23% 7% 14% 8% 7% 6% 4 5% 6% 11%	9334
	11th to 20th	Night	9% 16% 4 10% 6% 5% 6% 4 5% 5% 30%	8779
	21st to end	Night	12% 18% 6% 12% 6% 5% 5% 4 4 5% 24%	9475
February	1st to 10th	Night	10% 22% 6% 13% 7% 5% 4 4 4 5% 20%	2940
	11th to 20th	Night	9% 19% 7% 12% 6% 5% 5% 4 5% 6% 22%	2674
	21st to end	Night	5% 20% 5% 12% 8% 5% 5% 3 6% 6% 25%	2218
March	1st to 10th	Night	5% 15% 5% 13% 8% 7% 6% 5% 6% 7% 22%	5496
	11th to 20th	Night	6% 17% 5% 12% 7% 7% 7% 5% 6% 8% 20%	5244
	21st to end	Night	7% 15% 5% 10% 6% 5% 5% 3 6% 7% 32%	5262
April	1st to 10th	Night	7% 15% 6% 11% 6% 5% 7% 5% 7% 5% 25%	2100
	11th to 20th	Night	9% 13% 3 7% 6% 6% 7% 5% 7% 7% 28%	1918
	21st to end	Night	12% 14% 3 8% 6% 5% 5% 4 6% 7% 30%	1680
May	1st to 10th	Night	10% 10% 4 9% 6% 7% 7% 4 7% 8% 29%	3720
	11th to 20th	Night	14% 11% 4 10% 5% 5% 5% 5% 7% 7% 27%	3554
	21st to end	Night	16% 13% 4 9% 6% 5% 5% 4 6% 7% 26%	3034
June	1st to 10th	Night	11% 9% 3 9% 6% 6% 6% 5% 6% 8% 31%	1200
	11th to 20th	Night	19% 10% 3 10% 5% 6% 5% 4 6% 9% 23%	1200
	21st to end	Night	15% 8% 3 7% 7% 5% 5% 5% 7% 8% 30%	1200
July	1st to 10th	Night	11% 5% 2 7% 5% 5% 6% 4 7% 7% 41%	2720
	11th to 20th	Night	11% 6% 2 7% 5% 5% 5% 3 5% 7% 45%	2904
	21st to end	Night	14% 6% 2 8% 5% 5% 5% 4 7% 8% 36%	3508
August	1st to 10th	Night	7% 5% 2 6% 4 3 5% 3 5% 8% 52%	2609
	11th to 20th	Night	9% 6% 2 7% 5% 5% 5% 4 6% 6% 46%	2577
	21st to end	Night	17% 6% 2 8% 5% 5% 5% 5% 6% 7% 33%	3295
September	1st to 10th	Night	16% 8% 3 7% 5% 4 4 4 6% 7% 35%	2000
	11th to 20th	Night	15% 9% 3 7% 4 4 4 3 5% 7% 40%	2000
	21st to end	Night	22% 11% 3 9% 5% 5% 4 3 5% 5% 28%	2267
October	1st to 10th	Night	16% 13% 4 11% 7% 6% 5% 4 6% 6% 22%	3920
	11th to 20th	Night	16% 10% 3 8% 6% 5% 7% 5% 7% 8% 27%	4011
	21st to end	Night	12% 15% 4 10% 7% 7% 7% 5% 6% 7% 20%	4724
November	1st to 10th	Night	17% 21% 4 11% 6% 6% 4 4 5% 6% 16%	2870
	11th to 20th	Night	12% 21% 7% 13% 7% 5% 5% 4 5% 5% 16%	3022
	21st to end	Night	11% 23% 7% 13% 8% 7% 5% 3 4 4 15%	3188
December	1st to 10th	Night	15% 20% 6% 14% 7% 6% 5% 4 5% 5% 13%	5380
	11th to 20th	Night	9% 25% 7% 12% 7% 6% 6% 4 5% 5% 15%	6090
	21st to end	Night	5% 19% 8% 12% 7% 6% 6% 4 5% 7% 22%	8140

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	62% 10% 15% 9% 4	3605
	11th to 20th	Day	45% 9% 23% 11% 8% 3	4140
	21st to end	Day	52% 14% 20% 13% 1	4692
February	1st to 10th	Day	62% 7% 9% 10% 11% 1	1680
	11th to 20th	Day	63% 8% 12% 10% 6% 1	1838
	21st to end	Day	62% 6% 13% 11% 7% 2	1587
March	1st to 10th	Day	53% 9% 13% 15% 10% 1	4618
	11th to 20th	Day	46% 10% 13% 24% 7%	4975
	21st to end	Day	51% 9% 11% 17% 12%	5955
April	1st to 10th	Day	60% 11% 14% 11% 3	2520
	11th to 20th	Day	56% 8% 16% 16% 4	2650
	21st to end	Day	54% 10% 15% 16% 5%	2940
May	1st to 10th	Day	48% 7% 20% 21% 4	6460
	11th to 20th	Day	56% 11% 17% 12% 4	6547
	21st to end	Day	54% 11% 21% 11% 2	8084
June	1st to 10th	Day	54% 10% 13% 15% 7%	3201
	11th to 20th	Day	62% 11% 13% 12% 2	3200
	21st to end	Day	56% 9% 16% 14% 5%	3200
July	1st to 10th	Day	38% 9% 15% 20% 16% 2	7161
	11th to 20th	Day	40% 8% 15% 27% 8% 1	6953
	21st to end	Day	39% 9% 18% 23% 9% 2	7128
August	1st to 10th	Day	30% 10% 17% 32% 11%	4524
	11th to 20th	Day	37% 10% 21% 24% 8%	4512
	21st to end	Day	48% 9% 22% 16% 4 1	4611
September	1st to 10th	Day	48% 10% 18% 16% 7% 1	2400
	11th to 20th	Day	49% 9% 18% 18% 6%	2400
	21st to end	Day	60% 10% 13% 12% 5% 1	2130
October	1st to 10th	Day	55% 11% 19% 11% 3	3280
	11th to 20th	Day	56% 9% 19% 15% 1	3142
	21st to end	Day	51% 9% 26% 11% 1	3072
November	1st to 10th	Day	66% 9% 10% 12% 3 1	1648
	11th to 20th	Day	64% 11% 12% 9% 4 1	1575
	21st to end	Day	68% 10% 9% 7% 5% 1	1428
December	1st to 10th	Day	68% 13% 10% 7% 2	2020
	11th to 20th	Day	63% 9% 13% 11% 4	2324
	21st to end	Day	52% 10% 21% 14% 3	3058
January	1st to 10th	Night	64% 10% 13% 10% 3	9335
	11th to 20th	Night	51% 7% 20% 12% 6% 3	8820
	21st to end	Night	55% 12% 18% 13% 2	9475
February	1st to 10th	Night	65% 7% 9% 11% 8%	2940
	11th to 20th	Night	61% 8% 14% 13% 5%	2676
	21st to end	Night	58% 7% 13% 14% 7% 1	2218
March	1st to 10th	Night	52% 12% 12% 17% 7%	5496
	11th to 20th	Night	53% 8% 12% 19% 7%	5245
	21st to end	Night	46% 8% 15% 21% 10%	5262
April	1st to 10th	Night	55% 11% 13% 15% 5%	2100
	11th to 20th	Night	51% 10% 15% 19% 6%	1918
	21st to end	Night	53% 8% 12% 21% 6%	1680
May	1st to 10th	Night	47% 9% 17% 21% 6%	3717
	11th to 20th	Night	48% 10% 22% 16% 4	3554
	21st to end	Night	52% 11% 18% 15% 3	3034
June	1st to 10th	Night	47% 11% 15% 17% 8% 1	1200
	11th to 20th	Night	57% 12% 13% 16% 2	1200
	21st to end	Night	48% 12% 19% 18% 3	1200
July	1st to 10th	Night	36% 9% 18% 21% 12% 3	2690
	11th to 20th	Night	37% 7% 16% 34% 5%	2868
	21st to end	Night	38% 8% 22% 24% 7%	3410
August	1st to 10th	Night	29% 7% 20% 36% 8%	2601
	11th to 20th	Night	35% 10% 17% 33% 5%	2601
	21st to end	Night	45% 11% 25% 14% 4 1	3295
September	1st to 10th	Night	47% 10% 16% 21% 5% 2	2000
	11th to 20th	Night	43% 8% 17% 25% 7%	2000
	21st to end	Night	55% 11% 13% 14% 7%	2267
October	1st to 10th	Night	53% 12% 18% 13% 3	3920
	11th to 20th	Night	46% 10% 22% 20% 2	4011
	21st to end	Night	52% 12% 22% 11% 3	4724
November	1st to 10th	Night	66% 10% 10% 10% 4	2870
	11th to 20th	Night	66% 11% 10% 8% 4	3022
	21st to end	Night	69% 9% 9% 8% 4 1	3188
December	1st to 10th	Night	63% 16% 12% 7% 3	5380
	11th to 20th	Night	65% 11% 13% 9% 2	6087
	21st to end	Night	54% 11% 18% 15% 2	8140

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	18% 11% 17% 34% 15% 4	220
	11th to 20th	Day	20% 10% 25% 23% 19% 3	220
	21st to end	Day	22% 10% 18% 32% 14% 3	242
February	1st to 10th	Day	24% 15% 18% 28% 13% 2	220
	11th to 20th	Day	18% 13% 22% 28% 14% 4	409
	21st to end	Day	17% 16% 31% 22% 10% 3	372
March	1st to 10th	Day	15% 15% 26% 26% 16% 2	540
	11th to 20th	Day	15% 16% 28% 25% 12% 4	540
	21st to end	Day	20% 16% 23% 24% 12% 5%	594
April	1st to 10th	Day	15% 14% 32% 25% 11% 3	540
	11th to 20th	Day	14% 16% 27% 27% 11% 5%	532
	21st to end	Day	16% 13% 26% 26% 14% 6%	540
May	1st to 10th	Day	16% 10% 28% 27% 17% 3	543
	11th to 20th	Day	15% 6% 23% 31% 20% 5%	616
	21st to end	Day	17% 9% 21% 32% 18% 3	1072
June	1st to 10th	Day	18% 10% 27% 30% 14% 1	931
	11th to 20th	Day	24% 9% 20% 28% 16% 3	930
	21st to end	Day	20% 8% 21% 26% 21% 5%	930
July	1st to 10th	Day	17% 8% 18% 32% 21% 3	916
	11th to 20th	Day	18% 8% 19% 29% 22% 4	829
	21st to end	Day	13% 8% 21% 31% 20% 7%	779
August	1st to 10th	Day	11% 8% 19% 30% 24% 8%	527
	11th to 20th	Day	15% 9% 26% 27% 17% 5%	517
	21st to end	Day	17% 8% 23% 25% 16% 11%	583
September	1st to 10th	Day	17% 9% 18% 25% 21% 9%	530
	11th to 20th	Day	20% 6% 17% 32% 18% 7%	530
	21st to end	Day	30% 13% 23% 20% 11% 3	530
October	1st to 10th	Day	25% 12% 18% 22% 18% 5%	530
	11th to 20th	Day	28% 11% 22% 22% 13% 4	462
	21st to end	Day	28% 12% 20% 27% 10% 4	319
November	1st to 10th	Day	30% 20% 18% 20% 9% 3	220
	11th to 20th	Day	21% 10% 19% 32% 12% 5%	220
	21st to end	Day	26% 13% 20% 25% 10% 6%	220
December	1st to 10th	Day	20% 12% 17% 29% 19% 4	220
	11th to 20th	Day	21% 10% 19% 28% 20% 3	220
	21st to end	Day	19% 10% 19% 33% 14% 5%	242
January	1st to 10th	Night	27% 11% 24% 27% 9% 1	1154
	11th to 20th	Night	26% 13% 23% 29% 9% 1	950
	21st to end	Night	29% 10% 22% 29% 10% 1	1014
February	1st to 10th	Night	26% 11% 20% 27% 14% 1	840
	11th to 20th	Night	22% 9% 22% 33% 13% 1	824
	21st to end	Night	18% 10% 27% 29% 14% 1	692
March	1st to 10th	Night	19% 10% 27% 30% 13%	840
	11th to 20th	Night	16% 11% 28% 34% 11% 1	840
	21st to end	Night	16% 12% 22% 30% 18% 2	924
April	1st to 10th	Night	19% 8% 17% 37% 16% 2	840
	11th to 20th	Night	15% 10% 24% 33% 17%	670
	21st to end	Night	20% 7% 23% 33% 16% 1	420
May	1st to 10th	Night	18% 8% 18% 39% 17% 1	420
	11th to 20th	Night	17% 4 20% 38% 21% 1	414
	21st to end	Night	16% 5% 24% 34% 19% 2	455
June	1st to 10th	Night	16% 7% 20% 40% 16% 1	400
	11th to 20th	Night	26% 5% 15% 35% 17% 2	400
	21st to end	Night	20% 5% 17% 35% 22% 2	400
July	1st to 10th	Night	15% 5% 14% 39% 25% 1	390
	11th to 20th	Night	17% 6% 13% 32% 30% 2	388
	21st to end	Night	14% 7% 10% 37% 29% 3	438
August	1st to 10th	Night	12% 6% 9% 33% 38% 3	398
	11th to 20th	Night	11% 5% 10% 42% 30% 2	396
	21st to end	Night	23% 6% 10% 35% 25% 1	684
September	1st to 10th	Night	24% 5% 10% 35% 25% 1	800
	11th to 20th	Night	20% 4 10% 36% 27% 3	800
	21st to end	Night	30% 11% 17% 28% 13% 1	800
October	1st to 10th	Night	25% 7% 20% 32% 15% 1	800
	11th to 20th	Night	26% 9% 21% 30% 14% 1	800
	21st to end	Night	30% 10% 22% 29% 9% 1	880
November	1st to 10th	Night	34% 13% 22% 22% 9%	820
	11th to 20th	Night	27% 14% 25% 25% 8% 1	922
	21st to end	Night	29% 13% 21% 28% 9% 1	1070
December	1st to 10th	Night	23% 12% 21% 33% 11% 1	1160
	11th to 20th	Night	26% 12% 24% 27% 10% 1	1160
	21st to end	Night	20% 12% 28% 27% 11% 1	1276

Page generated at 2026-05-28 22:53:25. Version ac07

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