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 2024-11-04.

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	13% 13% 5% 11% 7% 6% 6% 4 6% 6% 22%	107254
	Night	6% 11% 5% 13% 7% 7% 6% 5% 6% 7% 27%	100379
Transparency	Day	58% 9% 14% 13% 4 1	106930
	Night	51% 9% 13% 16% 7% 3	100350
Seeing	Day	19% 13% 22% 23% 17% 5%	18478
	Night	12% 11% 21% 27% 22% 7%	22480

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% 4 12% 6% 7% 6% 5% 6% 9% 38%	1269
	11th to 20th	Day	1 5% 6% 11% 5% 5% 5% 6% 11% 8% 36%	1258
	21st to end	Day	1 6% 3 12% 9% 9% 6% 5% 9% 8% 31%	1925
February	1st to 10th	Day	9% 4 10% 6% 5% 6% 6% 7% 8% 39%	1187
	11th to 20th	Day	1 10% 5% 14% 7% 7% 8% 4 7% 9% 27%	1425
	21st to end	Day	2 7% 6% 15% 10% 8% 6% 5% 6% 6% 28%	1294
March	1st to 10th	Day	1 7% 6% 18% 12% 8% 7% 5% 6% 6% 25%	3044
	11th to 20th	Day	1 9% 5% 13% 8% 8% 10% 8% 8% 7% 22%	3239
	21st to end	Day	2 12% 6% 15% 8% 7% 7% 4 6% 6% 24%	4165
April	1st to 10th	Day	2 13% 7% 14% 9% 9% 6% 5% 7% 7% 22%	2399
	11th to 20th	Day	2 12% 5% 14% 9% 7% 5% 4 7% 6% 30%	2626
	21st to end	Day	4 10% 4 9% 7% 7% 6% 4 7% 8% 34%	2823
May	1st to 10th	Day	6% 15% 4 11% 6% 7% 7% 6% 9% 9% 20%	5070
	11th to 20th	Day	5% 13% 4 10% 6% 6% 6% 5% 6% 8% 32%	5351
	21st to end	Day	12% 15% 4 10% 6% 5% 6% 4 6% 7% 26%	6205
June	1st to 10th	Day	18% 13% 5% 11% 7% 7% 6% 5% 7% 6% 15%	3520
	11th to 20th	Day	19% 13% 4 10% 7% 6% 5% 3 5% 6% 20%	3779
	21st to end	Day	21% 10% 4 10% 7% 6% 6% 5% 6% 7% 18%	3800
July	1st to 10th	Day	32% 14% 4 9% 5% 5% 4 3 5% 5% 14%	5876
	11th to 20th	Day	25% 13% 4 9% 8% 6% 5% 4 5% 6% 15%	5700
	21st to end	Day	25% 13% 3 8% 5% 5% 5% 4 5% 6% 21%	5949
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% 5% 6% 5% 26%	1238
	11th to 20th	Day	4 13% 6% 12% 9% 10% 7% 4 5% 5% 27%	994
	21st to end	Day	3 10% 4 11% 9% 7% 9% 6% 8% 8% 24%	837
December	1st to 10th	Day	2 14% 4 12% 7% 7% 8% 6% 8% 9% 23%	700
	11th to 20th	Day	2 10% 5% 17% 9% 5% 6% 6% 7% 10% 25%	724
	21st to end	Day	1 5% 3 8% 7% 7% 6% 6% 8% 7% 42%	1173
January	1st to 10th	Night	1 6% 4 12% 7% 7% 6% 4 6% 8% 39%	5686
	11th to 20th	Night	1 9% 5% 11% 7% 7% 5% 4 6% 9% 36%	5650
	21st to end	Night	1 6% 4 11% 9% 8% 7% 6% 8% 8% 32%	5745
February	1st to 10th	Night	1 8% 4 12% 8% 7% 6% 4 6% 7% 38%	2991
	11th to 20th	Night	1 8% 5% 13% 7% 8% 7% 5% 8% 10% 27%	2642
	21st to end	Night	2 10% 6% 17% 10% 7% 7% 5% 4 5% 26%	2159
March	1st to 10th	Night	1 9% 6% 18% 9% 7% 6% 5% 7% 6% 26%	3810
	11th to 20th	Night	1 6% 4 15% 9% 10% 10% 9% 7% 7% 22%	3716
	21st to end	Night	2 9% 5% 11% 8% 8% 7% 5% 8% 8% 29%	3466
April	1st to 10th	Night	2 14% 6% 15% 8% 7% 6% 5% 7% 8% 24%	1781
	11th to 20th	Night	2 11% 5% 11% 8% 6% 7% 6% 6% 8% 31%	1503
	21st to end	Night	4 8% 4 7% 6% 5% 5% 4 9% 10% 38%	1354
May	1st to 10th	Night	4 13% 6% 13% 8% 7% 8% 6% 8% 8% 20%	1900
	11th to 20th	Night	5% 12% 3 7% 7% 6% 7% 6% 7% 7% 33%	1548
	21st to end	Night	12% 12% 4 9% 6% 4 6% 5% 6% 6% 29%	1381
June	1st to 10th	Night	17% 9% 5% 12% 7% 7% 6% 4 7% 7% 19%	659
	11th to 20th	Night	20% 10% 4 9% 7% 6% 4 4 6% 5% 27%	399
	21st to end	Night	19% 10% 6% 8% 8% 4 7% 5% 6% 7% 20%	380
July	1st to 10th	Night	25% 13% 4 12% 5% 6% 5% 5% 4 7% 15%	1090
	11th to 20th	Night	22% 13% 5% 10% 7% 5% 4 3 4 6% 22%	1270
	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 15% 6% 13% 8% 6% 5% 4 5% 6% 28%	2912
	11th to 20th	Night	4 11% 6% 16% 10% 9% 7% 4 5% 5% 22%	3186
	21st to end	Night	2 10% 5% 12% 7% 7% 6% 5% 7% 8% 30%	3340
December	1st to 10th	Night	3 12% 5% 12% 7% 6% 7% 5% 7% 8% 28%	3458
	11th to 20th	Night	1 10% 6% 16% 7% 7% 7% 5% 7% 7% 26%	4470
	21st to end	Night	1 7% 4 13% 8% 7% 7% 5% 7% 8% 34%	6523

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	42% 7% 14% 23% 9% 5%	1269
	11th to 20th	Day	38% 7% 17% 23% 9% 6%	1270
	21st to end	Day	43% 6% 10% 12% 18% 13%	1925
February	1st to 10th	Day	40% 7% 9% 20% 16% 9%	1187
	11th to 20th	Day	48% 10% 16% 15% 8% 3	1432
	21st to end	Day	50% 7% 11% 17% 12% 2	1294
March	1st to 10th	Day	57% 6% 9% 11% 13% 3	3044
	11th to 20th	Day	46% 13% 12% 15% 11% 2	3239
	21st to end	Day	53% 10% 15% 12% 7% 3	4165
April	1st to 10th	Day	58% 8% 13% 15% 7%	2399
	11th to 20th	Day	52% 8% 14% 15% 8% 2	2626
	21st to end	Day	46% 6% 15% 23% 10%	2823
May	1st to 10th	Day	54% 9% 19% 16% 2	5070
	11th to 20th	Day	46% 9% 18% 24% 4	5354
	21st to end	Day	54% 8% 17% 17% 4	6206
June	1st to 10th	Day	66% 9% 13% 10% 1	3520
	11th to 20th	Day	63% 8% 15% 12% 2	3779
	21st to end	Day	64% 9% 17% 10%	3800
July	1st to 10th	Day	70% 10% 13% 6%	5787
	11th to 20th	Day	64% 10% 12% 13%	5601
	21st to end	Day	60% 11% 16% 12% 1	5760
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% 13% 6% 3	1238
	11th to 20th	Day	57% 6% 12% 16% 7% 1	994
	21st to end	Day	50% 10% 16% 13% 11% 1	837
December	1st to 10th	Day	52% 10% 11% 15% 10% 2	700
	11th to 20th	Day	50% 10% 16% 17% 6% 2	726
	21st to end	Day	34% 8% 13% 18% 16% 10%	1173
January	1st to 10th	Night	39% 8% 13% 28% 6% 5%	5686
	11th to 20th	Night	39% 10% 17% 23% 8% 3	5700
	21st to end	Night	42% 8% 9% 11% 15% 15%	5745
February	1st to 10th	Night	44% 6% 8% 17% 15% 10%	2991
	11th to 20th	Night	47% 8% 14% 17% 10% 3	2646
	21st to end	Night	57% 6% 9% 15% 11% 2	2159
March	1st to 10th	Night	55% 5% 9% 10% 16% 6%	3810
	11th to 20th	Night	47% 12% 12% 17% 10% 3	3718
	21st to end	Night	45% 10% 17% 18% 7% 3	3466
April	1st to 10th	Night	54% 7% 12% 19% 7% 1	1781
	11th to 20th	Night	47% 9% 16% 19% 7% 2	1503
	21st to end	Night	37% 7% 16% 29% 10%	1354
May	1st to 10th	Night	56% 9% 17% 17% 2	1900
	11th to 20th	Night	43% 9% 17% 25% 6%	1548
	21st to end	Night	48% 10% 17% 20% 5%	1381
June	1st to 10th	Night	61% 9% 17% 13% 2	659
	11th to 20th	Night	57% 10% 17% 15% 2	399
	21st to end	Night	61% 9% 20% 10%	380
July	1st to 10th	Night	65% 11% 17% 7%	1070
	11th to 20th	Night	61% 9% 13% 17%	1246
	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	56% 7% 12% 17% 6% 2	2912
	11th to 20th	Night	60% 8% 11% 14% 6%	3186
	21st to end	Night	49% 7% 15% 17% 10% 2	3340
December	1st to 10th	Night	50% 10% 12% 16% 10% 2	3458
	11th to 20th	Night	53% 7% 13% 17% 8% 2	4467
	21st to end	Night	42% 9% 12% 17% 12% 8%	6523

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	4 10% 24% 30% 20% 11%	90
	11th to 20th	Day	4 8% 32% 33% 18% 4	90
	21st to end	Day	5% 11% 23% 34% 22% 5%	302
February	1st to 10th	Day	5% 10% 22% 28% 22% 13%	280
	11th to 20th	Day	11% 19% 26% 22% 15% 7%	340
	21st to end	Day	8% 17% 32% 22% 15% 5%	307
March	1st to 10th	Day	6% 12% 32% 29% 15% 6%	370
	11th to 20th	Day	6% 12% 30% 28% 20% 5%	405
	21st to end	Day	9% 17% 25% 27% 17% 5%	616
April	1st to 10th	Day	7% 17% 31% 27% 15% 4	596
	11th to 20th	Day	9% 12% 25% 28% 21% 6%	640
	21st to end	Day	8% 9% 21% 31% 26% 6%	650
May	1st to 10th	Day	11% 13% 25% 29% 18% 5%	653
	11th to 20th	Day	12% 13% 25% 27% 17% 6%	720
	21st to end	Day	17% 16% 22% 23% 16% 5%	940
June	1st to 10th	Day	20% 10% 22% 23% 19% 6%	970
	11th to 20th	Day	19% 13% 19% 23% 22% 6%	1060
	21st to end	Day	21% 8% 18% 22% 23% 7%	1060
July	1st to 10th	Day	27% 11% 23% 19% 17% 4	909
	11th to 20th	Day	33% 10% 19% 19% 14% 4	852
	21st to end	Day	27% 12% 22% 20% 14% 5%	894
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	9% 9% 23% 31% 18% 10%	335
	11th to 20th	Day	9% 13% 22% 21% 28% 7%	134
	21st to end	Day	9% 16% 21% 24% 22% 8%	90
December	1st to 10th	Day	9% 18% 17% 33% 19% 4	90
	11th to 20th	Day	13% 11% 20% 32% 19% 4	90
	21st to end	Day	8% 18% 24% 30% 12% 7%	99
January	1st to 10th	Night	5% 9% 21% 30% 25% 10%	940
	11th to 20th	Night	6% 9% 28% 32% 19% 6%	940
	21st to end	Night	5% 11% 25% 33% 22% 5%	976
February	1st to 10th	Night	4 9% 24% 31% 22% 10%	850
	11th to 20th	Night	8% 16% 28% 30% 15% 4	834
	21st to end	Night	8% 15% 25% 27% 21% 4	664
March	1st to 10th	Night	5% 11% 23% 38% 19% 4	660
	11th to 20th	Night	3 6% 19% 33% 30% 8%	657
	21st to end	Night	8% 13% 18% 21% 27% 13%	627
April	1st to 10th	Night	5% 11% 25% 28% 23% 8%	570
	11th to 20th	Night	7% 10% 18% 25% 30% 10%	563
	21st to end	Night	8% 5% 15% 32% 32% 9%	527
May	1st to 10th	Night	12% 8% 18% 27% 26% 9%	380
	11th to 20th	Night	11% 13% 14% 27% 28% 6%	226
	21st to end	Night	15% 12% 18% 27% 25% 4	206
June	1st to 10th	Night	17% 10% 20% 25% 24% 4	190
	11th to 20th	Night	22% 6% 12% 28% 28% 4	190
	21st to end	Night	21% 7% 11% 20% 33% 8%	190
July	1st to 10th	Night	27% 8% 16% 19% 25% 4	185
	11th to 20th	Night	31% 8% 15% 18% 25% 3	184
	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%	847
	11th to 20th	Night	9% 9% 22% 29% 22% 9%	850
	21st to end	Night	9% 12% 22% 26% 24% 8%	902
December	1st to 10th	Night	11% 14% 22% 25% 20% 8%	978
	11th to 20th	Night	7% 10% 24% 30% 20% 9%	1130
	21st to end	Night	8% 11% 22% 30% 20% 8%	1183

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