Denali National Park & Preserve -- Headquarters
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Denali National Park & Preserve -- Headquarters clear sky chart from 2005-11-06 to 2025-07-21.

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	12% 13% 5% 12% 7% 6% 6% 4 6% 7% 22%	124083
	Night	5% 11% 5% 13% 7% 7% 6% 5% 6% 7% 28%	123791
Transparency	Day	56% 9% 14% 14% 5% 1	123759
	Night	50% 9% 13% 16% 8% 4	123759
Seeing	Day	19% 13% 23% 23% 16% 5%	19408
	Night	12% 11% 21% 27% 21% 7%	23436

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	1 8% 5% 12% 6% 6% 6% 4 5% 7% 41%	1819
	11th to 20th	Day	1 4 5% 12% 6% 6% 6% 6% 10% 8% 36%	1808
	21st to end	Day	1 6% 3 12% 10% 11% 8% 6% 9% 8% 26%	2775
February	1st to 10th	Day	10% 4 10% 6% 5% 6% 5% 7% 8% 39%	1250
	11th to 20th	Day	1 9% 4 14% 7% 7% 8% 5% 8% 9% 28%	1503
	21st to end	Day	2 7% 6% 14% 11% 8% 6% 5% 7% 6% 28%	1360
March	1st to 10th	Day	1 7% 6% 18% 11% 8% 7% 5% 7% 7% 24%	4376
	11th to 20th	Day	7% 4 14% 9% 10% 10% 7% 8% 7% 23%	4627
	21st to end	Day	2 11% 5% 16% 7% 6% 6% 4 7% 7% 30%	5969
April	1st to 10th	Day	2 14% 7% 15% 9% 8% 6% 5% 7% 7% 22%	2525
	11th to 20th	Day	2 13% 5% 14% 8% 6% 5% 4 6% 6% 29%	2766
	21st to end	Day	4 11% 4 9% 7% 7% 6% 4 7% 7% 33%	2972
May	1st to 10th	Day	5% 18% 5% 12% 6% 6% 6% 5% 7% 8% 21%	7260
	11th to 20th	Day	7% 18% 5% 9% 5% 5% 5% 4 5% 6% 29%	7687
	21st to end	Day	12% 16% 4 11% 6% 6% 6% 5% 7% 7% 21%	8911
June	1st to 10th	Day	17% 14% 5% 11% 7% 7% 6% 5% 6% 6% 16%	3705
	11th to 20th	Day	19% 13% 4 10% 7% 6% 5% 3 5% 7% 21%	3978
	21st to end	Day	21% 10% 4 10% 7% 6% 6% 5% 6% 7% 18%	4000
July	1st to 10th	Day	31% 14% 4 9% 5% 5% 4 3 5% 5% 15%	6062
	11th to 20th	Day	24% 13% 4 9% 8% 6% 5% 4 5% 6% 15%	5880
	21st to end	Day	25% 13% 3 8% 5% 5% 5% 4 5% 6% 21%	5950
August	1st to 10th	Day	28% 17% 4 10% 6% 5% 5% 3 4 5% 14%	5046
	11th to 20th	Day	25% 17% 6% 11% 6% 5% 5% 4 5% 5% 11%	4680
	21st to end	Day	24% 20% 5% 12% 6% 5% 5% 3 4 4 12%	4884
September	1st to 10th	Day	21% 16% 5% 12% 5% 5% 5% 4 5% 6% 17%	2431
	11th to 20th	Day	19% 18% 4 11% 6% 6% 5% 4 4 5% 18%	2275
	21st to end	Day	14% 20% 7% 10% 5% 5% 4 4 6% 6% 18%	2028
October	1st to 10th	Day	7% 19% 8% 11% 6% 5% 4 3 6% 6% 26%	3053
	11th to 20th	Day	3 11% 5% 20% 8% 5% 5% 4 5% 8% 26%	2748
	21st to end	Day	6% 15% 7% 14% 6% 5% 8% 5% 6% 6% 22%	2539
November	1st to 10th	Day	3 14% 7% 13% 7% 9% 5% 4 6% 5% 26%	1281
	11th to 20th	Day	3 13% 6% 13% 8% 10% 7% 5% 5% 4 26%	1046
	21st to end	Day	3 10% 4 11% 9% 7% 9% 6% 8% 8% 24%	881
December	1st to 10th	Day	2 13% 4 11% 6% 5% 7% 5% 7% 8% 31%	1194
	11th to 20th	Day	2 10% 5% 15% 6% 4 6% 5% 8% 9% 29%	1134
	21st to end	Day	1 6% 3 9% 7% 6% 6% 5% 7% 6% 44%	1680
January	1st to 10th	Night	1 6% 3 11% 7% 6% 5% 4 6% 7% 43%	8146
	11th to 20th	Night	1 10% 6% 12% 7% 6% 6% 5% 6% 8% 33%	8110
	21st to end	Night	1 6% 4 12% 10% 10% 9% 7% 7% 7% 28%	8210
February	1st to 10th	Night	1 8% 5% 12% 8% 6% 6% 4 6% 7% 38%	3148
	11th to 20th	Night	1 8% 5% 13% 7% 7% 7% 6% 8% 10% 29%	2784
	21st to end	Night	2 10% 6% 17% 10% 8% 7% 5% 4 5% 26%	2269
March	1st to 10th	Night	1 9% 6% 17% 8% 7% 6% 4 7% 7% 29%	5478
	11th to 20th	Night	1 4 4 15% 11% 11% 10% 7% 7% 8% 22%	5328
	21st to end	Night	2 8% 4 13% 8% 7% 7% 5% 7% 7% 32%	4962
April	1st to 10th	Night	2 14% 6% 15% 8% 6% 6% 5% 6% 8% 24%	1874
	11th to 20th	Night	2 12% 5% 12% 7% 6% 7% 6% 6% 8% 30%	1583
	21st to end	Night	4 8% 4 7% 6% 5% 5% 4 8% 10% 38%	1425
May	1st to 10th	Night	3 13% 5% 13% 7% 6% 7% 6% 8% 9% 22%	2720
	11th to 20th	Night	6% 14% 3 7% 6% 6% 6% 5% 6% 7% 34%	2217
	21st to end	Night	11% 13% 4 10% 6% 5% 6% 5% 8% 7% 24%	1986
June	1st to 10th	Night	16% 10% 5% 13% 7% 6% 6% 4 7% 7% 20%	693
	11th to 20th	Night	19% 10% 3 8% 6% 6% 3 3 6% 6% 28%	420
	21st to end	Night	19% 11% 5% 8% 8% 4 7% 6% 7% 8% 20%	400
July	1st to 10th	Night	24% 12% 4 12% 5% 6% 5% 4 5% 7% 16%	1124
	11th to 20th	Night	22% 13% 5% 10% 7% 5% 4 3 4 6% 22%	1310
	21st to end	Night	27% 13% 3 8% 6% 5% 3 4 5% 7% 20%	1615
August	1st to 10th	Night	24% 15% 4 9% 5% 6% 4 5% 6% 5% 17%	1894
	11th to 20th	Night	22% 20% 3 9% 6% 5% 5% 4 5% 7% 15%	2157
	21st to end	Night	24% 21% 5% 11% 5% 4 4 3 4 4 15%	2783
September	1st to 10th	Night	20% 13% 3 10% 6% 5% 5% 4 6% 7% 20%	1747
	11th to 20th	Night	20% 19% 5% 10% 7% 5% 5% 3 4 6% 17%	1905
	21st to end	Night	14% 21% 7% 11% 6% 5% 5% 4 5% 4 18%	2150
October	1st to 10th	Night	7% 18% 7% 11% 6% 6% 6% 4 7% 8% 22%	3911
	11th to 20th	Night	4 13% 7% 18% 8% 6% 5% 3 6% 7% 22%	4178
	21st to end	Night	5% 15% 6% 17% 7% 6% 5% 4 6% 6% 24%	5020
November	1st to 10th	Night	4 14% 6% 13% 8% 6% 5% 4 5% 6% 28%	3017
	11th to 20th	Night	4 11% 6% 17% 10% 9% 7% 4 5% 5% 22%	3354
	21st to end	Night	2 11% 5% 12% 7% 7% 6% 5% 7% 7% 29%	3516
December	1st to 10th	Night	2 10% 4 11% 6% 6% 7% 5% 8% 9% 32%	5960
	11th to 20th	Night	1 10% 7% 16% 6% 6% 6% 5% 7% 8% 28%	7070
	21st to end	Night	1 6% 4 13% 7% 6% 6% 5% 7% 8% 35%	9327

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	41% 6% 11% 19% 9% 14%	1819
	11th to 20th	Day	35% 11% 19% 23% 8% 5%	1820
	21st to end	Day	46% 8% 9% 13% 15% 9%	2775
February	1st to 10th	Day	39% 7% 9% 20% 15% 9%	1250
	11th to 20th	Day	47% 10% 15% 15% 9% 3	1510
	21st to end	Day	50% 8% 11% 17% 12% 2	1360
March	1st to 10th	Day	53% 8% 9% 16% 12% 2	4376
	11th to 20th	Day	44% 13% 11% 16% 14% 2	4627
	21st to end	Day	46% 10% 12% 14% 15% 4	5969
April	1st to 10th	Day	58% 8% 13% 14% 7%	2525
	11th to 20th	Day	53% 8% 14% 16% 8% 2	2766
	21st to end	Day	46% 7% 15% 23% 9%	2972
May	1st to 10th	Day	55% 9% 15% 17% 4	7260
	11th to 20th	Day	49% 9% 15% 20% 6%	7690
	21st to end	Day	54% 11% 17% 16% 3	8912
June	1st to 10th	Day	65% 9% 13% 11% 2	3705
	11th to 20th	Day	61% 8% 17% 13% 2	3978
	21st to end	Day	63% 10% 18% 10%	4000
July	1st to 10th	Day	69% 10% 14% 6%	5973
	11th to 20th	Day	64% 10% 13% 12%	5781
	21st to end	Day	60% 11% 16% 12% 1	5761
August	1st to 10th	Day	70% 9% 13% 8%	5027
	11th to 20th	Day	69% 12% 12% 7%	4728
	21st to end	Day	71% 11% 12% 6%	4883
September	1st to 10th	Day	69% 8% 13% 9% 1	2431
	11th to 20th	Day	69% 7% 14% 9% 1	2275
	21st to end	Day	67% 7% 11% 13% 2	2028
October	1st to 10th	Day	57% 7% 11% 19% 5%	3053
	11th to 20th	Day	49% 13% 17% 18% 3 1	2748
	21st to end	Day	57% 10% 14% 16% 3 1	2539
November	1st to 10th	Day	57% 7% 13% 14% 6% 3	1281
	11th to 20th	Day	57% 7% 12% 16% 7% 1	1046
	21st to end	Day	50% 10% 15% 13% 11% 1	881
December	1st to 10th	Day	47% 8% 14% 19% 11% 1	1194
	11th to 20th	Day	45% 9% 18% 16% 6% 5%	1136
	21st to end	Day	34% 9% 16% 14% 19% 9%	1680
January	1st to 10th	Night	37% 8% 12% 23% 9% 13%	8146
	11th to 20th	Night	41% 11% 17% 21% 8% 2	8160
	21st to end	Night	46% 9% 9% 12% 14% 11%	8210
February	1st to 10th	Night	43% 6% 8% 18% 15% 10%	3148
	11th to 20th	Night	46% 8% 14% 18% 10% 4	2788
	21st to end	Night	57% 6% 9% 15% 11% 2	2269
March	1st to 10th	Night	49% 6% 9% 17% 15% 4	5478
	11th to 20th	Night	47% 11% 10% 16% 13% 2	5330
	21st to end	Night	43% 11% 13% 17% 12% 4	4962
April	1st to 10th	Night	55% 7% 12% 18% 7% 1	1874
	11th to 20th	Night	48% 9% 15% 18% 7% 2	1583
	21st to end	Night	37% 7% 16% 30% 10%	1425
May	1st to 10th	Night	52% 9% 14% 21% 3	2717
	11th to 20th	Night	43% 9% 17% 24% 7%	2217
	21st to end	Night	47% 13% 17% 19% 4	1986
June	1st to 10th	Night	60% 9% 16% 13% 2	693
	11th to 20th	Night	54% 9% 18% 17% 2	420
	21st to end	Night	61% 9% 21% 10%	400
July	1st to 10th	Night	65% 11% 17% 7%	1104
	11th to 20th	Night	61% 9% 14% 17%	1286
	21st to end	Night	61% 10% 17% 10% 1	1565
August	1st to 10th	Night	64% 10% 21% 4 1	1888
	11th to 20th	Night	67% 13% 14% 5%	2175
	21st to end	Night	71% 9% 14% 6%	2783
September	1st to 10th	Night	63% 10% 17% 9% 1	1747
	11th to 20th	Night	68% 7% 14% 10% 1	1905
	21st to end	Night	69% 7% 10% 12% 2	2150
October	1st to 10th	Night	57% 7% 14% 16% 5% 1	3911
	11th to 20th	Night	54% 11% 12% 20% 3 1	4178
	21st to end	Night	53% 10% 13% 18% 5% 1	5020
November	1st to 10th	Night	55% 7% 13% 17% 6% 2	3017
	11th to 20th	Night	60% 8% 11% 14% 7%	3354
	21st to end	Night	49% 8% 15% 16% 10% 2	3516
December	1st to 10th	Night	44% 10% 14% 20% 11% 1	5960
	11th to 20th	Night	49% 8% 15% 17% 6% 4	7067
	21st to end	Night	40% 9% 16% 14% 13% 9%	9327

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	5% 12% 25% 29% 19% 10%	100
	11th to 20th	Day	8% 9% 31% 32% 16% 4	100
	21st to end	Day	7% 12% 23% 32% 21% 5%	324
February	1st to 10th	Day	4 10% 23% 30% 22% 12%	300
	11th to 20th	Day	10% 18% 27% 22% 15% 7%	368
	21st to end	Day	8% 17% 32% 23% 16% 5%	331
March	1st to 10th	Day	7% 13% 33% 29% 14% 6%	400
	11th to 20th	Day	6% 12% 29% 28% 21% 5%	437
	21st to end	Day	8% 17% 25% 28% 17% 6%	660
April	1st to 10th	Day	9% 18% 30% 25% 14% 3	640
	11th to 20th	Day	10% 13% 25% 27% 19% 6%	690
	21st to end	Day	9% 10% 21% 30% 25% 6%	700
May	1st to 10th	Day	13% 14% 24% 28% 17% 4	703
	11th to 20th	Day	12% 14% 25% 27% 16% 6%	773
	21st to end	Day	17% 16% 23% 23% 16% 5%	1006
June	1st to 10th	Day	21% 11% 22% 22% 18% 6%	1035
	11th to 20th	Day	18% 12% 19% 24% 22% 6%	1130
	21st to end	Day	21% 9% 18% 22% 23% 7%	1130
July	1st to 10th	Day	25% 12% 24% 19% 16% 4	972
	11th to 20th	Day	32% 10% 19% 20% 14% 4	912
	21st to end	Day	27% 12% 22% 20% 14% 5%	895
August	1st to 10th	Day	36% 13% 24% 15% 10% 4	676
	11th to 20th	Day	38% 15% 17% 18% 10% 2	665
	21st to end	Day	38% 13% 20% 18% 9% 1	748
September	1st to 10th	Day	31% 16% 24% 17% 9% 3	633
	11th to 20th	Day	33% 21% 22% 14% 9% 2	575
	21st to end	Day	27% 12% 21% 23% 12% 6%	390
October	1st to 10th	Day	26% 19% 22% 18% 11% 5%	390
	11th to 20th	Day	12% 11% 22% 24% 21% 11%	390
	21st to end	Day	14% 14% 18% 23% 24% 8%	429
November	1st to 10th	Day	10% 9% 22% 31% 18% 11%	350
	11th to 20th	Day	8% 13% 21% 23% 29% 6%	146
	21st to end	Day	8% 15% 22% 25% 23% 7%	100
December	1st to 10th	Day	10% 20% 16% 31% 19% 4	100
	11th to 20th	Day	12% 14% 21% 31% 18% 4	100
	21st to end	Day	7% 18% 25% 30% 12% 8%	110
January	1st to 10th	Night	6% 10% 21% 30% 25% 9%	1000
	11th to 20th	Night	8% 9% 27% 31% 18% 6%	1000
	21st to end	Night	8% 11% 25% 31% 21% 4	1035
February	1st to 10th	Night	4 9% 25% 32% 21% 9%	900
	11th to 20th	Night	7% 16% 29% 29% 15% 4	884
	21st to end	Night	8% 14% 25% 28% 21% 4	702
March	1st to 10th	Night	5% 12% 24% 37% 18% 4	700
	11th to 20th	Night	3 6% 18% 33% 30% 8%	697
	21st to end	Night	7% 12% 18% 22% 27% 13%	660
April	1st to 10th	Night	6% 13% 26% 27% 22% 7%	600
	11th to 20th	Night	8% 10% 19% 25% 28% 10%	593
	21st to end	Night	7% 5% 15% 33% 31% 8%	555
May	1st to 10th	Night	12% 9% 18% 27% 25% 9%	400
	11th to 20th	Night	11% 14% 15% 26% 28% 6%	238
	21st to end	Night	14% 12% 19% 27% 24% 4	217
June	1st to 10th	Night	17% 13% 19% 25% 23% 4	200
	11th to 20th	Night	21% 6% 13% 30% 28% 4	200
	21st to end	Night	20% 9% 12% 20% 31% 9%	200
July	1st to 10th	Night	26% 8% 17% 20% 25% 4	195
	11th to 20th	Night	30% 8% 15% 19% 25% 3	194
	21st to end	Night	23% 11% 18% 22% 21% 5%	294
August	1st to 10th	Night	32% 11% 16% 22% 14% 5%	378
	11th to 20th	Night	31% 11% 18% 20% 17% 4	454
	21st to end	Night	32% 13% 11% 19% 19% 6%	627
September	1st to 10th	Night	28% 14% 19% 18% 16% 6%	570
	11th to 20th	Night	31% 16% 16% 18% 13% 6%	570
	21st to end	Night	24% 9% 16% 23% 22% 6%	603
October	1st to 10th	Night	22% 17% 18% 20% 17% 6%	729
	11th to 20th	Night	13% 11% 19% 26% 24% 8%	860
	21st to end	Night	13% 10% 19% 29% 22% 7%	946
November	1st to 10th	Night	9% 10% 22% 30% 22% 7%	880
	11th to 20th	Night	8% 9% 23% 30% 22% 8%	900
	21st to end	Night	9% 11% 23% 27% 23% 7%	958
December	1st to 10th	Night	11% 14% 22% 25% 20% 7%	1041
	11th to 20th	Night	7% 11% 25% 30% 20% 8%	1200
	21st to end	Night	7% 12% 22% 31% 20% 8%	1256

Page generated at 2025-07-17 21:10:02. Version ac07

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