Fairbanks
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fairbanks clear sky chart from 2005-11-06 to 2025-11-03.

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% 11% 4 10% 6% 6% 6% 5% 6% 7% 26%	132081
	Night	7% 13% 5% 12% 7% 6% 5% 4 6% 7% 28%	126753
Transparency	Day	53% 10% 16% 15% 5% 1	131682
	Night	53% 8% 15% 15% 8% 1	126730
Seeing	Day	14% 6% 17% 27% 26% 11%	20108
	Night	13% 4 17% 33% 27% 7%	24096

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	4 11% 5% 11% 6% 4 5% 2 5% 6% 40%	1319
	11th to 20th	Day	3 15% 6% 13% 7% 6% 4 4 5% 6% 31%	1808
	21st to end	Day	5% 11% 4 11% 10% 9% 8% 6% 8% 6% 21%	2458
February	1st to 10th	Day	2 14% 5% 11% 5% 5% 5% 4 6% 5% 38%	1200
	11th to 20th	Day	3 13% 5% 15% 8% 7% 6% 5% 7% 8% 24%	1475
	21st to end	Day	4 14% 6% 12% 8% 7% 6% 5% 6% 6% 26%	1320
March	1st to 10th	Day	2 16% 7% 15% 7% 5% 4 3 5% 5% 29%	4388
	11th to 20th	Day	2 11% 6% 15% 8% 7% 5% 4 5% 8% 29%	4623
	21st to end	Day	5% 13% 5% 11% 6% 5% 5% 4 6% 7% 33%	5969
April	1st to 10th	Day	5% 16% 6% 11% 7% 6% 6% 5% 7% 7% 25%	2559
	11th to 20th	Day	4 10% 4 9% 6% 5% 5% 4 6% 8% 39%	2766
	21st to end	Day	4 8% 2 8% 6% 7% 6% 5% 7% 8% 39%	3049
May	1st to 10th	Day	9% 13% 5% 12% 7% 7% 6% 5% 6% 7% 23%	7386
	11th to 20th	Day	4 7% 3 9% 6% 6% 6% 5% 6% 7% 38%	7873
	21st to end	Day	10% 10% 4 11% 7% 7% 8% 6% 8% 9% 21%	9156
June	1st to 10th	Day	10% 9% 4 10% 7% 7% 7% 6% 7% 7% 25%	3935
	11th to 20th	Day	10% 8% 3 8% 6% 6% 6% 6% 8% 9% 30%	4000
	21st to end	Day	13% 7% 3 7% 6% 6% 6% 6% 8% 10% 29%	4000
July	1st to 10th	Day	22% 9% 3 7% 5% 5% 5% 4 6% 7% 28%	9060
	11th to 20th	Day	11% 9% 3 9% 6% 6% 7% 6% 8% 10% 23%	8297
	21st to end	Day	18% 10% 3 8% 5% 6% 6% 5% 7% 8% 24%	8838
August	1st to 10th	Day	25% 11% 4 8% 5% 5% 5% 4 5% 6% 22%	5217
	11th to 20th	Day	20% 10% 4 10% 6% 6% 6% 5% 7% 8% 18%	4978
	21st to end	Day	21% 13% 4 11% 6% 5% 6% 4 6% 7% 17%	5038
September	1st to 10th	Day	17% 11% 5% 10% 6% 6% 5% 5% 6% 7% 23%	2600
	11th to 20th	Day	20% 14% 5% 11% 6% 5% 5% 4 5% 6% 19%	2370
	21st to end	Day	19% 15% 4 12% 6% 4 5% 3 5% 5% 24%	2165
October	1st to 10th	Day	11% 16% 6% 12% 6% 5% 4 4 4 5% 28%	3086
	11th to 20th	Day	8% 17% 8% 14% 8% 5% 5% 3 5% 5% 21%	2838
	21st to end	Day	11% 17% 6% 16% 7% 6% 5% 4 5% 6% 18%	2525
November	1st to 10th	Day	10% 14% 6% 14% 7% 5% 5% 6% 6% 6% 22%	1231
	11th to 20th	Day	8% 12% 7% 14% 10% 6% 4 4 4 5% 26%	1000
	21st to end	Day	7% 16% 7% 13% 7% 7% 4 3 6% 6% 23%	755
December	1st to 10th	Day	8% 13% 4 8% 6% 5% 5% 4 8% 8% 31%	980
	11th to 20th	Day	3 16% 6% 11% 8% 4 6% 5% 6% 5% 29%	807
	21st to end	Day	2 10% 5% 11% 6% 7% 6% 4 7% 7% 33%	1012
January	1st to 10th	Night	3 10% 4 11% 6% 5% 4 3 5% 6% 44%	8690
	11th to 20th	Night	3 12% 5% 11% 6% 5% 5% 5% 7% 8% 32%	8110
	21st to end	Night	6% 12% 4 12% 9% 7% 7% 5% 7% 6% 26%	8522
February	1st to 10th	Night	2 13% 6% 12% 6% 4 4 3 4 7% 38%	3200
	11th to 20th	Night	4 11% 4 11% 7% 7% 7% 6% 7% 8% 30%	2812
	21st to end	Night	4 15% 7% 12% 7% 7% 5% 4 5% 7% 26%	2310
March	1st to 10th	Night	3 15% 8% 15% 6% 6% 5% 4 5% 6% 28%	5463
	11th to 20th	Night	5% 10% 5% 14% 9% 7% 6% 4 6% 7% 27%	5335
	21st to end	Night	7% 13% 4 8% 5% 5% 5% 4 6% 8% 34%	4962
April	1st to 10th	Night	5% 14% 6% 11% 7% 6% 6% 5% 6% 8% 26%	1840
	11th to 20th	Night	5% 8% 3 11% 8% 6% 5% 4 7% 7% 35%	1583
	21st to end	Night	6% 8% 3 8% 6% 6% 6% 5% 8% 8% 38%	1348
May	1st to 10th	Night	7% 9% 4 11% 8% 8% 8% 6% 8% 9% 23%	2588
	11th to 20th	Night	7% 7% 2 7% 5% 5% 6% 5% 7% 8% 40%	2030
	21st to end	Night	13% 10% 4 11% 8% 6% 7% 4 7% 7% 22%	1741
June	1st to 10th	Night	8% 9% 3 10% 7% 7% 8% 6% 10% 8% 23%	464
	11th to 20th	Night	10% 11% 2 11% 7% 7% 6% 4 7% 11% 27%	400
	21st to end	Night	12% 8% 2 9% 7% 7% 7% 5% 8% 11% 25%	400
July	1st to 10th	Night	23% 10% 4 8% 6% 4 5% 4 4 6% 25%	920
	11th to 20th	Night	14% 12% 4 9% 7% 6% 5% 5% 8% 7% 24%	1669
	21st to end	Night	18% 10% 3 10% 7% 6% 5% 4 5% 8% 24%	2024
August	1st to 10th	Night	24% 10% 4 9% 7% 6% 5% 3 5% 7% 19%	1940
	11th to 20th	Night	25% 15% 4 10% 5% 5% 5% 3 5% 5% 18%	2078
	21st to end	Night	20% 11% 4 11% 7% 7% 6% 4 6% 6% 19%	2871
September	1st to 10th	Night	15% 12% 4 9% 6% 7% 5% 4 7% 8% 24%	1798
	11th to 20th	Night	17% 13% 5% 12% 7% 7% 5% 3 6% 5% 20%	2030
	21st to end	Night	18% 14% 4 10% 6% 4 5% 5% 4 5% 25%	2234
October	1st to 10th	Night	10% 14% 5% 8% 6% 6% 6% 5% 6% 8% 26%	4100
	11th to 20th	Night	10% 15% 6% 12% 9% 6% 5% 4 6% 7% 20%	4307
	21st to end	Night	9% 18% 7% 17% 8% 5% 4 3 4 5% 20%	5276
November	1st to 10th	Night	9% 16% 6% 13% 7% 5% 5% 4 6% 5% 24%	3111
	11th to 20th	Night	7% 15% 7% 15% 8% 6% 5% 3 5% 6% 24%	3400
	21st to end	Night	8% 16% 5% 13% 7% 6% 5% 4 6% 6% 24%	3625
December	1st to 10th	Night	6% 12% 5% 12% 7% 6% 6% 4 6% 7% 29%	6210
	11th to 20th	Night	4 15% 7% 13% 6% 5% 5% 4 6% 6% 29%	7396
	21st to end	Night	3 12% 5% 12% 7% 6% 6% 5% 7% 7% 31%	9966

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	45% 5% 13% 18% 16% 3	1319
	11th to 20th	Day	51% 8% 16% 16% 6% 3	1820
	21st to end	Day	56% 7% 10% 15% 8% 5%	2458
February	1st to 10th	Day	46% 6% 8% 18% 19% 4	1200
	11th to 20th	Day	55% 9% 13% 14% 9% 1	1482
	21st to end	Day	55% 8% 10% 14% 11% 1	1320
March	1st to 10th	Day	56% 6% 9% 17% 11% 1	4388
	11th to 20th	Day	50% 7% 13% 16% 11% 3	4623
	21st to end	Day	47% 10% 15% 17% 11% 1	5969
April	1st to 10th	Day	55% 8% 14% 16% 6% 1	2559
	11th to 20th	Day	43% 8% 16% 24% 8% 2	2766
	21st to end	Day	39% 9% 15% 29% 9%	3049
May	1st to 10th	Day	55% 10% 11% 18% 5%	7386
	11th to 20th	Day	38% 11% 12% 22% 13% 4	7876
	21st to end	Day	50% 13% 16% 17% 4	9157
June	1st to 10th	Day	52% 12% 16% 18% 3	3935
	11th to 20th	Day	46% 13% 17% 20% 3	4000
	21st to end	Day	46% 14% 21% 18% 2	4000
July	1st to 10th	Day	54% 10% 18% 15% 3	8961
	11th to 20th	Day	50% 13% 23% 14%	8194
	21st to end	Day	54% 12% 21% 11% 2	8589
August	1st to 10th	Day	61% 10% 19% 9% 1	5197
	11th to 20th	Day	58% 14% 20% 8%	5026
	21st to end	Day	64% 11% 16% 7% 1	5037
September	1st to 10th	Day	58% 12% 19% 10% 1	2600
	11th to 20th	Day	65% 10% 15% 10%	2370
	21st to end	Day	63% 9% 12% 13% 3	2165
October	1st to 10th	Day	57% 7% 12% 19% 4	3086
	11th to 20th	Day	63% 9% 13% 13% 2	2838
	21st to end	Day	66% 8% 13% 11% 3	2525
November	1st to 10th	Day	60% 9% 16% 12% 4	1231
	11th to 20th	Day	59% 8% 12% 17% 3	1000
	21st to end	Day	61% 8% 12% 13% 6%	755
December	1st to 10th	Day	49% 9% 17% 19% 5% 1	980
	11th to 20th	Day	54% 7% 18% 12% 3 6%	809
	21st to end	Day	45% 9% 19% 14% 13% 1	1012
January	1st to 10th	Night	41% 6% 14% 21% 13% 5%	8690
	11th to 20th	Night	45% 9% 20% 17% 9% 1	8160
	21st to end	Night	53% 6% 11% 13% 12% 5%	8522
February	1st to 10th	Night	47% 4 9% 17% 20% 4	3200
	11th to 20th	Night	48% 9% 13% 19% 10%	2816
	21st to end	Night	57% 6% 13% 15% 8% 1	2310
March	1st to 10th	Night	56% 5% 8% 20% 9% 1	5463
	11th to 20th	Night	52% 7% 13% 15% 11% 2	5337
	21st to end	Night	44% 10% 17% 15% 12% 1	4962
April	1st to 10th	Night	54% 8% 15% 17% 6% 1	1840
	11th to 20th	Night	44% 10% 17% 21% 7% 1	1583
	21st to end	Night	40% 8% 15% 28% 9%	1348
May	1st to 10th	Night	49% 12% 15% 21% 3	2585
	11th to 20th	Night	36% 10% 14% 25% 13% 2	2030
	21st to end	Night	53% 12% 13% 16% 6%	1741
June	1st to 10th	Night	50% 13% 18% 16% 3	464
	11th to 20th	Night	50% 10% 16% 20% 4	400
	21st to end	Night	48% 14% 22% 16% 1	400
July	1st to 10th	Night	58% 10% 13% 13% 5%	910
	11th to 20th	Night	55% 9% 20% 14% 2	1649
	21st to end	Night	55% 11% 18% 12% 4	1968
August	1st to 10th	Night	65% 8% 18% 8% 1	1935
	11th to 20th	Night	67% 9% 17% 7%	2096
	21st to end	Night	63% 12% 16% 8% 1	2871
September	1st to 10th	Night	56% 11% 21% 11% 1	1798
	11th to 20th	Night	64% 9% 14% 12% 1	2030
	21st to end	Night	61% 10% 12% 14% 3	2234
October	1st to 10th	Night	54% 9% 14% 19% 4	4100
	11th to 20th	Night	60% 9% 18% 11% 2	4307
	21st to end	Night	66% 7% 12% 13% 1	5276
November	1st to 10th	Night	60% 8% 14% 15% 4	3111
	11th to 20th	Night	61% 7% 14% 15% 3	3400
	21st to end	Night	59% 7% 11% 17% 6%	3625
December	1st to 10th	Night	51% 9% 16% 17% 6% 1	6210
	11th to 20th	Night	54% 7% 18% 13% 5% 4	7393
	21st to end	Night	48% 9% 17% 12% 13% 1	9966

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	6% 3 12% 50% 23% 6%	100
	11th to 20th	Day	7% 5% 18% 36% 29% 5%	100
	21st to end	Day	8% 4 13% 39% 24% 12%	225
February	1st to 10th	Day	6% 7% 12% 29% 29% 17%	300
	11th to 20th	Day	8% 7% 22% 30% 24% 10%	362
	21st to end	Day	9% 9% 22% 31% 24% 6%	331
March	1st to 10th	Day	6% 5% 22% 39% 21% 7%	400
	11th to 20th	Day	7% 6% 20% 30% 26% 11%	405
	21st to end	Day	8% 6% 20% 29% 29% 8%	660
April	1st to 10th	Day	11% 10% 20% 32% 22% 5%	663
	11th to 20th	Day	8% 6% 24% 30% 26% 7%	690
	21st to end	Day	6% 4 15% 33% 32% 10%	700
May	1st to 10th	Day	10% 7% 20% 30% 27% 7%	703
	11th to 20th	Day	8% 6% 21% 32% 25% 8%	818
	21st to end	Day	13% 7% 18% 28% 25% 9%	1108
June	1st to 10th	Day	10% 5% 19% 27% 27% 12%	1130
	11th to 20th	Day	10% 4 15% 23% 33% 16%	1130
	21st to end	Day	12% 3 11% 23% 33% 17%	1130
July	1st to 10th	Day	14% 5% 12% 25% 35% 10%	1111
	11th to 20th	Day	18% 3 14% 25% 26% 15%	968
	21st to end	Day	15% 5% 13% 23% 26% 18%	998
August	1st to 10th	Day	23% 6% 17% 21% 24% 10%	726
	11th to 20th	Day	22% 6% 17% 23% 25% 6%	715
	21st to end	Day	24% 7% 18% 21% 20% 11%	803
September	1st to 10th	Day	19% 8% 16% 23% 22% 12%	708
	11th to 20th	Day	26% 8% 15% 25% 16% 9%	590
	21st to end	Day	24% 7% 16% 18% 20% 14%	420
October	1st to 10th	Day	21% 9% 22% 19% 19% 10%	420
	11th to 20th	Day	14% 6% 21% 21% 25% 12%	420
	21st to end	Day	17% 5% 14% 22% 29% 13%	462
November	1st to 10th	Day	15% 7% 12% 29% 27% 11%	302
	11th to 20th	Day	10% 4 15% 26% 25% 20%	100
	21st to end	Day	13% 3 15% 29% 33% 7%	100
December	1st to 10th	Day	17% 6% 19% 35% 18% 5%	100
	11th to 20th	Day	11% 4 28% 31% 22% 4	100
	21st to end	Day	5% 11% 21% 37% 21% 5%	110
January	1st to 10th	Night	7% 3 16% 37% 27% 10%	1155
	11th to 20th	Night	9% 4 20% 40% 22% 5%	1000
	21st to end	Night	9% 4 17% 42% 23% 6%	1055
February	1st to 10th	Night	7% 4 17% 36% 27% 9%	900
	11th to 20th	Night	7% 4 21% 39% 25% 4	884
	21st to end	Night	9% 6% 19% 39% 25% 2	743
March	1st to 10th	Night	9% 3 19% 42% 24% 3	711
	11th to 20th	Night	8% 3 18% 39% 26% 5%	682
	21st to end	Night	10% 3 21% 33% 25% 8%	660
April	1st to 10th	Night	9% 5% 22% 37% 24% 3	600
	11th to 20th	Night	7% 4 20% 37% 28% 4	593
	21st to end	Night	8% 3 11% 35% 37% 6%	542
May	1st to 10th	Night	8% 5% 16% 29% 37% 5%	346
	11th to 20th	Night	7% 5% 21% 41% 25% 2	197
	21st to end	Night	15% 6% 11% 33% 28% 6%	217
June	1st to 10th	Night	10% 3 18% 29% 34% 7%	200
	11th to 20th	Night	12% 4 14% 25% 39% 7%	200
	21st to end	Night	15% 2 7% 28% 42% 7%	200
July	1st to 10th	Night	13% 4 12% 30% 36% 5%	195
	11th to 20th	Night	21% 5% 13% 23% 32% 6%	194
	21st to end	Night	16% 5% 11% 27% 34% 7%	219
August	1st to 10th	Night	25% 3 12% 25% 31% 4	384
	11th to 20th	Night	24% 7% 11% 24% 28% 6%	467
	21st to end	Night	26% 5% 11% 21% 27% 10%	660
September	1st to 10th	Night	20% 5% 14% 24% 29% 9%	600
	11th to 20th	Night	21% 6% 14% 28% 27% 5%	600
	21st to end	Night	23% 5% 17% 25% 26% 5%	619
October	1st to 10th	Night	21% 7% 20% 25% 25% 3	812
	11th to 20th	Night	15% 4 18% 29% 26% 8%	910
	21st to end	Night	14% 4 15% 33% 28% 6%	1001
November	1st to 10th	Night	16% 4 17% 33% 26% 5%	890
	11th to 20th	Night	14% 3 14% 31% 27% 11%	900
	21st to end	Night	14% 3 16% 30% 28% 10%	1040
December	1st to 10th	Night	13% 4 19% 34% 21% 8%	1200
	11th to 20th	Night	10% 5% 20% 32% 27% 6%	1200
	21st to end	Night	8% 4 17% 36% 26% 9%	1320

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