Kenai
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kenai clear sky chart from 2005-11-06 to 2025-12-18.

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	19% 13% 4 9% 5% 5% 5% 4 5% 6% 25%	131706
	Night	17% 15% 5% 10% 6% 5% 5% 4 5% 6% 24%	128162
Transparency	Day	59% 7% 14% 14% 5% 1	131356
	Night	60% 6% 12% 13% 7% 2	128092
Seeing	Day	23% 5% 12% 23% 26% 11%	19750
	Night	25% 6% 16% 26% 21% 7%	24064

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	12% 19% 4 12% 7% 7% 5% 4 5% 5% 18%	2141
	11th to 20th	Day	13% 16% 5% 10% 6% 6% 6% 4 4 7% 23%	2419
	21st to end	Day	16% 12% 3 7% 5% 5% 4 4 5% 5% 35%	3099
February	1st to 10th	Day	13% 18% 4 9% 6% 5% 4 6% 5% 6% 25%	1400
	11th to 20th	Day	18% 20% 6% 10% 6% 6% 3 4 4 4 19%	1552
	21st to end	Day	12% 12% 2 9% 5% 6% 6% 4 5% 6% 33%	1485
March	1st to 10th	Day	12% 21% 6% 9% 4 3 3 3 3 4 30%	4335
	11th to 20th	Day	9% 15% 5% 12% 6% 6% 5% 4 5% 7% 25%	4791
	21st to end	Day	15% 17% 5% 10% 6% 5% 4 3 5% 5% 25%	5849
April	1st to 10th	Day	10% 15% 4 9% 6% 5% 5% 4 6% 7% 29%	2455
	11th to 20th	Day	11% 16% 4 9% 6% 4 4 3 4 6% 33%	2738
	21st to end	Day	12% 16% 4 8% 7% 5% 5% 4 6% 6% 28%	2800
May	1st to 10th	Day	17% 18% 5% 11% 7% 6% 5% 4 5% 5% 17%	7119
	11th to 20th	Day	15% 14% 4 10% 6% 5% 5% 3 5% 6% 28%	7213
	21st to end	Day	20% 12% 4 9% 5% 5% 5% 4 6% 7% 23%	8253
June	1st to 10th	Day	18% 12% 3 8% 5% 5% 4 4 6% 8% 26%	3600
	11th to 20th	Day	17% 9% 3 8% 6% 5% 5% 3 6% 8% 30%	3600
	21st to end	Day	20% 9% 3 8% 6% 5% 5% 4 7% 8% 26%	3600
July	1st to 10th	Day	21% 11% 4 9% 5% 5% 6% 4 6% 7% 23%	8076
	11th to 20th	Day	26% 10% 4 8% 5% 5% 4 4 6% 7% 23%	7720
	21st to end	Day	24% 8% 3 7% 4 4 5% 4 5% 7% 29%	7905
August	1st to 10th	Day	29% 7% 3 8% 6% 4 4 3 6% 7% 23%	5048
	11th to 20th	Day	27% 8% 3 7% 4 4 4 3 4 6% 30%	4594
	21st to end	Day	28% 9% 3 7% 4 4 4 4 5% 5% 25%	4987
September	1st to 10th	Day	31% 12% 3 9% 5% 5% 4 4 4 5% 17%	2455
	11th to 20th	Day	33% 10% 3 9% 5% 4 4 4 4 5% 20%	2400
	21st to end	Day	22% 12% 3 9% 4 5% 5% 3 6% 6% 26%	2120
October	1st to 10th	Day	19% 11% 4 10% 7% 6% 6% 4 6% 6% 20%	3260
	11th to 20th	Day	14% 11% 3 8% 5% 4 5% 4 5% 6% 36%	2889
	21st to end	Day	19% 12% 3 7% 4 4 4 3 4 5% 35%	2831
November	1st to 10th	Day	20% 17% 4 10% 5% 5% 5% 3 3 5% 23%	1457
	11th to 20th	Day	16% 9% 4 8% 4 5% 5% 4 7% 5% 33%	1260
	21st to end	Day	17% 17% 4 10% 6% 6% 6% 4 4 4 21%	1223
December	1st to 10th	Day	22% 18% 5% 10% 7% 6% 6% 2 4 3 17%	1485
	11th to 20th	Day	16% 24% 8% 11% 4 4 3 3 4 5% 20%	1545
	21st to end	Day	9% 15% 5% 11% 8% 6% 5% 5% 6% 11% 18%	2002
January	1st to 10th	Night	13% 18% 5% 11% 8% 7% 5% 4 4 4 20%	7825
	11th to 20th	Night	16% 18% 6% 11% 6% 6% 4 3 4 5% 21%	7510
	21st to end	Night	17% 12% 3 6% 4 4 4 3 4 6% 38%	7876
February	1st to 10th	Night	14% 15% 4 8% 6% 5% 4 3 5% 6% 29%	3000
	11th to 20th	Night	20% 20% 5% 11% 6% 5% 4 4 4 4 19%	2732
	21st to end	Night	12% 15% 5% 9% 5% 4 4 4 5% 4 31%	2145
March	1st to 10th	Night	11% 20% 6% 11% 5% 5% 5% 3 4 4 25%	5519
	11th to 20th	Night	8% 17% 6% 13% 6% 6% 6% 5% 6% 5% 22%	5166
	21st to end	Night	12% 20% 5% 10% 7% 6% 6% 4 5% 5% 22%	5082
April	1st to 10th	Night	14% 18% 4 10% 6% 4 4 3 4 5% 29%	1944
	11th to 20th	Night	13% 14% 4 8% 6% 4 3 3 4 6% 33%	1611
	21st to end	Night	11% 17% 5% 10% 5% 4 4 5% 6% 7% 29%	1600
May	1st to 10th	Night	17% 17% 5% 11% 7% 5% 6% 4 5% 5% 19%	2859
	11th to 20th	Night	19% 16% 4 9% 4 3 4 4 4 5% 28%	2702
	21st to end	Night	17% 12% 4 10% 6% 5% 4 4 6% 7% 23%	2648
June	1st to 10th	Night	21% 13% 4 6% 6% 6% 5% 3 5% 10% 22%	800
	11th to 20th	Night	14% 10% 3 9% 5% 5% 5% 5% 7% 8% 29%	800
	21st to end	Night	19% 10% 3 7% 5% 5% 5% 7% 9% 8% 23%	800
July	1st to 10th	Night	21% 11% 3 10% 6% 7% 6% 4 5% 6% 22%	1906
	11th to 20th	Night	27% 11% 4 9% 5% 5% 4 3 4 6% 22%	2280
	21st to end	Night	24% 8% 2 8% 5% 5% 4 3 6% 7% 28%	2961
August	1st to 10th	Night	28% 9% 2 7% 5% 4 5% 3 4 6% 26%	2109
	11th to 20th	Night	29% 5% 2 5% 4 3 4 4 5% 6% 34%	2464
	21st to end	Night	28% 9% 3 7% 5% 4 4 3 4 5% 25%	2919
September	1st to 10th	Night	32% 12% 4 10% 5% 6% 4 2 3 4 18%	1945
	11th to 20th	Night	31% 10% 3 8% 4 4 5% 4 4 6% 21%	2000
	21st to end	Night	26% 11% 4 8% 4 4 4 3 4 5% 26%	2280
October	1st to 10th	Night	24% 11% 4 9% 7% 6% 7% 4 4 6% 19%	3920
	11th to 20th	Night	15% 10% 4 9% 5% 4 4 3 4 6% 37%	4255
	21st to end	Night	18% 14% 3 9% 5% 4 3 3 4 5% 33%	4970
November	1st to 10th	Night	20% 16% 5% 10% 5% 5% 4 3 4 4 23%	3058
	11th to 20th	Night	13% 12% 3 8% 5% 5% 5% 5% 7% 6% 31%	3360
	21st to end	Night	16% 17% 5% 10% 7% 5% 5% 3 4 4 24%	3395
December	1st to 10th	Night	22% 18% 6% 11% 6% 5% 4 3 4 5% 16%	5919
	11th to 20th	Night	12% 23% 7% 13% 7% 5% 5% 3 4 5% 16%	6826
	21st to end	Night	10% 17% 5% 13% 8% 6% 6% 4 6% 9% 16%	8976

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	64% 6% 11% 11% 8% 1	2141
	11th to 20th	Day	60% 4 8% 16% 10% 1	2434
	21st to end	Day	50% 4 7% 10% 24% 4	3099
February	1st to 10th	Day	56% 7% 10% 14% 11% 3	1400
	11th to 20th	Day	67% 6% 9% 11% 6% 2	1559
	21st to end	Day	49% 7% 12% 18% 13% 1	1485
March	1st to 10th	Day	57% 4 7% 10% 17% 4	4335
	11th to 20th	Day	55% 6% 11% 13% 14% 1	4791
	21st to end	Day	61% 6% 9% 14% 8% 2	5849
April	1st to 10th	Day	55% 7% 14% 14% 8% 2	2455
	11th to 20th	Day	54% 7% 12% 18% 9%	2738
	21st to end	Day	56% 7% 10% 19% 8%	2800
May	1st to 10th	Day	67% 7% 9% 14% 3	7119
	11th to 20th	Day	58% 7% 11% 18% 6%	7216
	21st to end	Day	58% 8% 15% 17% 2	8254
June	1st to 10th	Day	55% 10% 18% 16% 2	3600
	11th to 20th	Day	53% 10% 17% 17% 3 1	3600
	21st to end	Day	56% 12% 22% 11%	3600
July	1st to 10th	Day	60% 8% 24% 8%	7988
	11th to 20th	Day	63% 8% 22% 7%	7627
	21st to end	Day	55% 7% 24% 13%	7683
August	1st to 10th	Day	62% 9% 19% 10%	5029
	11th to 20th	Day	56% 6% 16% 20% 2	4638
	21st to end	Day	61% 7% 14% 15% 3	4986
September	1st to 10th	Day	71% 6% 12% 9% 2	2455
	11th to 20th	Day	67% 7% 11% 12% 2	2400
	21st to end	Day	60% 7% 12% 17% 3	2120
October	1st to 10th	Day	63% 6% 13% 16% 2	3260
	11th to 20th	Day	49% 6% 15% 20% 11%	2889
	21st to end	Day	51% 7% 9% 27% 5%	2831
November	1st to 10th	Day	64% 8% 11% 11% 6% 1	1457
	11th to 20th	Day	50% 7% 12% 23% 8%	1260
	21st to end	Day	64% 5% 8% 12% 10% 1	1223
December	1st to 10th	Day	70% 6% 6% 12% 5% 1	1485
	11th to 20th	Day	66% 5% 13% 10% 5% 1	1548
	21st to end	Day	56% 6% 15% 12% 9% 3	2002
January	1st to 10th	Night	63% 7% 10% 9% 9% 2	7825
	11th to 20th	Night	64% 4 7% 14% 9% 2	7558
	21st to end	Night	48% 4 7% 13% 22% 7%	7876
February	1st to 10th	Night	56% 5% 9% 14% 13% 3	3000
	11th to 20th	Night	68% 6% 9% 10% 6% 1	2736
	21st to end	Night	54% 6% 10% 19% 10% 2	2145
March	1st to 10th	Night	60% 4 8% 11% 11% 6%	5519
	11th to 20th	Night	58% 7% 11% 12% 11% 1	5168
	21st to end	Night	62% 8% 8% 15% 6% 1	5082
April	1st to 10th	Night	58% 5% 11% 17% 7% 2	1944
	11th to 20th	Night	52% 7% 12% 19% 11%	1611
	21st to end	Night	53% 7% 13% 18% 9%	1600
May	1st to 10th	Night	64% 8% 8% 17% 3	2856
	11th to 20th	Night	59% 7% 10% 17% 7%	2703
	21st to end	Night	55% 8% 17% 17% 3	2648
June	1st to 10th	Night	59% 8% 19% 14% 1	800
	11th to 20th	Night	50% 10% 21% 17% 2 1	800
	21st to end	Night	55% 13% 24% 8%	800
July	1st to 10th	Night	61% 9% 22% 8%	1885
	11th to 20th	Night	65% 7% 21% 6%	2250
	21st to end	Night	56% 5% 26% 12% 1	2878
August	1st to 10th	Night	60% 7% 21% 12% 1	2103
	11th to 20th	Night	51% 6% 20% 21% 2	2486
	21st to end	Night	61% 6% 12% 17% 3	2919
September	1st to 10th	Night	70% 8% 11% 9% 2	1945
	11th to 20th	Night	64% 9% 13% 13% 2	2000
	21st to end	Night	60% 7% 13% 15% 4	2280
October	1st to 10th	Night	65% 7% 11% 16% 2	3920
	11th to 20th	Night	50% 6% 16% 18% 10%	4255
	21st to end	Night	55% 5% 9% 23% 8% 1	4970
November	1st to 10th	Night	64% 6% 11% 12% 6% 1	3058
	11th to 20th	Night	50% 7% 13% 20% 10%	3360
	21st to end	Night	62% 5% 9% 12% 10% 2	3395
December	1st to 10th	Night	70% 4 9% 10% 6%	5919
	11th to 20th	Night	70% 5% 11% 8% 5% 1	6822
	21st to end	Night	63% 5% 12% 11% 6% 4	8976

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	16% 6% 13% 36% 19% 10%	240
	11th to 20th	Day	24% 6% 18% 30% 15% 7%	300
	21st to end	Day	29% 6% 14% 31% 15% 5%	330
February	1st to 10th	Day	21% 5% 15% 30% 18% 11%	300
	11th to 20th	Day	27% 10% 16% 28% 14% 6%	388
	21st to end	Day	16% 7% 16% 38% 15% 8%	331
March	1st to 10th	Day	20% 5% 16% 29% 20% 11%	400
	11th to 20th	Day	13% 5% 11% 33% 27% 11%	515
	21st to end	Day	15% 5% 15% 28% 26% 11%	660
April	1st to 10th	Day	18% 6% 13% 31% 22% 10%	600
	11th to 20th	Day	18% 5% 9% 21% 30% 16%	677
	21st to end	Day	18% 5% 12% 21% 28% 17%	700
May	1st to 10th	Day	19% 6% 13% 24% 28% 10%	703
	11th to 20th	Day	20% 4 11% 23% 31% 11%	725
	21st to end	Day	22% 4 10% 22% 31% 11%	879
June	1st to 10th	Day	18% 5% 10% 19% 31% 17%	930
	11th to 20th	Day	15% 3 7% 22% 38% 15%	930
	21st to end	Day	20% 3 5% 19% 34% 18%	930
July	1st to 10th	Day	22% 2 8% 20% 31% 16%	916
	11th to 20th	Day	23% 4 7% 23% 31% 12%	912
	21st to end	Day	27% 3 7% 24% 26% 14%	800
August	1st to 10th	Day	29% 5% 8% 20% 28% 10%	726
	11th to 20th	Day	25% 4 14% 22% 26% 9%	715
	21st to end	Day	30% 5% 10% 19% 23% 12%	789
September	1st to 10th	Day	33% 7% 12% 18% 22% 9%	620
	11th to 20th	Day	37% 6% 7% 15% 24% 11%	620
	21st to end	Day	25% 4 15% 17% 24% 15%	465
October	1st to 10th	Day	33% 4 13% 23% 19% 8%	420
	11th to 20th	Day	26% 7% 15% 25% 18% 8%	420
	21st to end	Day	27% 7% 14% 25% 18% 9%	462
November	1st to 10th	Day	27% 8% 20% 24% 17% 3	417
	11th to 20th	Day	20% 7% 23% 28% 20% 2	320
	21st to end	Day	24% 8% 22% 22% 20% 3	283
December	1st to 10th	Day	29% 10% 13% 28% 20%	110
	11th to 20th	Day	31% 11% 17% 31% 8% 2	107
	21st to end	Day	24% 12% 21% 26% 13% 5%	110
January	1st to 10th	Night	18% 7% 17% 33% 21% 5%	1000
	11th to 20th	Night	26% 6% 21% 26% 16% 4	964
	21st to end	Night	27% 5% 18% 30% 17% 3	990
February	1st to 10th	Night	20% 6% 18% 32% 19% 5%	900
	11th to 20th	Night	31% 6% 16% 29% 15% 3	872
	21st to end	Night	20% 7% 18% 31% 18% 7%	578
March	1st to 10th	Night	21% 6% 21% 28% 19% 5%	700
	11th to 20th	Night	14% 5% 16% 31% 23% 10%	700
	21st to end	Night	17% 5% 15% 30% 22% 11%	687
April	1st to 10th	Night	21% 7% 13% 27% 23% 9%	600
	11th to 20th	Night	20% 4 11% 23% 29% 12%	593
	21st to end	Night	16% 5% 14% 21% 30% 13%	600
May	1st to 10th	Night	22% 8% 11% 21% 30% 7%	420
	11th to 20th	Night	23% 4 9% 27% 29% 8%	394
	21st to end	Night	21% 5% 10% 26% 30% 9%	388
June	1st to 10th	Night	26% 3 5% 20% 37% 11%	200
	11th to 20th	Night	16% 3 6% 29% 41% 7%	200
	21st to end	Night	22% 2 9% 20% 37% 11%	200
July	1st to 10th	Night	25% 2 7% 23% 33% 10%	228
	11th to 20th	Night	25% 3 7% 23% 32% 10%	388
	21st to end	Night	30% 3 6% 21% 27% 13%	438
August	1st to 10th	Night	31% 4 12% 22% 25% 7%	398
	11th to 20th	Night	31% 3 11% 24% 24% 6%	526
	21st to end	Night	32% 4 11% 20% 23% 10%	660
September	1st to 10th	Night	37% 4 13% 22% 19% 6%	600
	11th to 20th	Night	35% 5% 10% 18% 22% 11%	600
	21st to end	Night	30% 5% 12% 20% 22% 10%	669
October	1st to 10th	Night	37% 6% 11% 25% 15% 7%	710
	11th to 20th	Night	28% 6% 15% 23% 19% 9%	875
	21st to end	Night	28% 6% 17% 23% 20% 6%	1001
November	1st to 10th	Night	29% 7% 19% 22% 18% 4	930
	11th to 20th	Night	20% 7% 22% 31% 18% 2	950
	21st to end	Night	26% 7% 21% 26% 18% 3	950
December	1st to 10th	Night	30% 9% 19% 25% 13% 3	1013
	11th to 20th	Night	26% 9% 19% 29% 14% 3	1042
	21st to end	Night	26% 7% 22% 26% 15% 5%	1100

Page generated at 2025-12-14 21:13:54. Version ac07

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