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 2024-11-06.

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% 12% 4 11% 6% 6% 6% 5% 6% 7% 26%	107088
	Night	8% 13% 5% 12% 7% 6% 5% 4 6% 7% 27%	100584
Transparency	Day	54% 11% 16% 15% 4	106743
	Night	54% 9% 14% 15% 7% 1	100576
Seeing	Day	14% 6% 17% 27% 26% 11%	18738
	Night	13% 4 17% 33% 27% 7%	22792

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 10% 5% 11% 7% 5% 5% 2 4 5% 42%	905
	11th to 20th	Day	3 13% 6% 11% 8% 6% 5% 5% 5% 7% 30%	1258
	21st to end	Day	4 11% 4 11% 7% 8% 7% 6% 8% 8% 26%	1704
February	1st to 10th	Day	2 13% 5% 11% 6% 5% 5% 4 6% 5% 38%	1140
	11th to 20th	Day	3 13% 5% 16% 8% 6% 6% 5% 7% 8% 23%	1399
	21st to end	Day	4 14% 6% 12% 7% 7% 5% 5% 6% 6% 27%	1256
March	1st to 10th	Day	3 18% 8% 18% 7% 5% 4 3 5% 4 25%	3056
	11th to 20th	Day	3 12% 6% 14% 7% 7% 6% 4 5% 7% 29%	3235
	21st to end	Day	6% 13% 4 11% 6% 5% 6% 4 7% 7% 31%	4165
April	1st to 10th	Day	4 16% 5% 11% 7% 6% 6% 5% 7% 7% 26%	2431
	11th to 20th	Day	4 10% 3 9% 6% 5% 5% 4 7% 8% 39%	2626
	21st to end	Day	4 8% 2 8% 6% 7% 6% 5% 7% 8% 39%	2896
May	1st to 10th	Day	7% 13% 6% 13% 8% 7% 7% 6% 7% 6% 21%	5157
	11th to 20th	Day	4 8% 3 10% 7% 7% 7% 6% 7% 8% 33%	5483
	21st to end	Day	12% 10% 3 9% 6% 6% 7% 5% 8% 8% 26%	6380
June	1st to 10th	Day	10% 9% 4 10% 7% 7% 7% 5% 7% 8% 25%	3738
	11th to 20th	Day	10% 8% 3 9% 7% 7% 6% 6% 8% 8% 28%	3800
	21st to end	Day	13% 7% 3 8% 6% 6% 6% 6% 8% 9% 29%	3800
July	1st to 10th	Day	25% 10% 3 8% 6% 5% 6% 5% 6% 7% 19%	6330
	11th to 20th	Day	13% 10% 4 9% 6% 6% 7% 5% 7% 8% 25%	5795
	21st to end	Day	20% 10% 3 8% 5% 5% 5% 4 6% 7% 27%	6156
August	1st to 10th	Day	25% 11% 4 8% 5% 5% 5% 4 5% 6% 21%	5057
	11th to 20th	Day	20% 10% 4 10% 6% 6% 5% 5% 7% 8% 19%	4823
	21st to end	Day	20% 13% 4 11% 6% 5% 6% 4 6% 7% 17%	4884
September	1st to 10th	Day	17% 11% 4 9% 6% 5% 5% 4 6% 7% 24%	2470
	11th to 20th	Day	20% 14% 5% 11% 6% 5% 5% 4 5% 6% 19%	2252
	21st to end	Day	18% 14% 4 12% 6% 4 5% 3 5% 5% 25%	2057
October	1st to 10th	Day	11% 16% 6% 11% 6% 5% 4 4 4 6% 29%	2991
	11th to 20th	Day	8% 17% 8% 14% 8% 5% 5% 4 5% 5% 21%	2751
	21st to end	Day	11% 16% 6% 16% 7% 6% 5% 4 5% 6% 18%	2447
November	1st to 10th	Day	10% 14% 6% 14% 7% 5% 5% 6% 6% 6% 22%	1190
	11th to 20th	Day	8% 12% 6% 14% 10% 6% 4 3 4 5% 27%	950
	21st to end	Day	8% 15% 7% 13% 7% 7% 5% 3 6% 6% 23%	718
December	1st to 10th	Day	9% 18% 6% 9% 5% 5% 4 5% 9% 7% 23%	570
	11th to 20th	Day	3 20% 5% 14% 10% 4 6% 5% 6% 4 23%	514
	21st to end	Day	3 11% 4 11% 6% 8% 7% 6% 9% 8% 27%	704
January	1st to 10th	Night	4 10% 5% 12% 6% 4 4 4 5% 7% 40%	6080
	11th to 20th	Night	4 14% 5% 12% 6% 5% 5% 4 6% 7% 31%	5650
	21st to end	Night	3 9% 4 11% 7% 6% 7% 6% 8% 7% 32%	5964
February	1st to 10th	Night	2 13% 6% 12% 6% 4 4 3 4 7% 39%	3040
	11th to 20th	Night	4 12% 4 11% 7% 7% 7% 6% 7% 8% 29%	2668
	21st to end	Night	4 15% 7% 12% 7% 7% 5% 4 5% 7% 26%	2198
March	1st to 10th	Night	3 18% 8% 17% 6% 6% 4 3 3 5% 27%	3795
	11th to 20th	Night	6% 11% 5% 14% 8% 7% 6% 4 5% 6% 28%	3723
	21st to end	Night	6% 12% 3 8% 5% 5% 5% 5% 7% 9% 34%	3466
April	1st to 10th	Night	5% 14% 6% 11% 7% 6% 6% 5% 6% 8% 27%	1748
	11th to 20th	Night	4 8% 3 10% 8% 6% 6% 4 7% 7% 37%	1503
	21st to end	Night	6% 7% 3 8% 6% 6% 6% 4 8% 8% 39%	1281
May	1st to 10th	Night	6% 10% 4 12% 9% 9% 8% 6% 7% 9% 20%	1810
	11th to 20th	Night	5% 8% 2 8% 7% 6% 7% 5% 8% 9% 34%	1415
	21st to end	Night	16% 10% 4 9% 7% 5% 6% 4 6% 6% 28%	1206
June	1st to 10th	Night	7% 10% 3 9% 7% 7% 8% 7% 10% 9% 23%	441
	11th to 20th	Night	11% 11% 2 12% 7% 7% 6% 3 6% 9% 26%	380
	21st to end	Night	12% 8% 2 9% 7% 7% 7% 5% 8% 11% 25%	380
July	1st to 10th	Night	25% 12% 4 10% 6% 4 6% 5% 5% 6% 17%	640
	11th to 20th	Night	16% 11% 3 9% 6% 5% 4 5% 7% 5% 28%	1161
	21st to end	Night	19% 10% 3 9% 6% 5% 5% 5% 6% 8% 25%	1406
August	1st to 10th	Night	25% 9% 4 9% 7% 6% 5% 3 5% 7% 18%	1880
	11th to 20th	Night	25% 14% 4 10% 5% 5% 5% 3 5% 5% 18%	2013
	21st to end	Night	20% 11% 4 11% 7% 7% 6% 4 6% 6% 19%	2783
September	1st to 10th	Night	14% 11% 4 9% 6% 7% 5% 4 7% 7% 25%	1708
	11th to 20th	Night	17% 13% 5% 11% 7% 6% 5% 3 6% 5% 21%	1928
	21st to end	Night	17% 14% 4 10% 6% 4 5% 5% 4 5% 26%	2122
October	1st to 10th	Night	10% 14% 5% 8% 6% 6% 6% 5% 6% 8% 27%	3975
	11th to 20th	Night	10% 15% 6% 11% 9% 6% 5% 4 6% 7% 20%	4174
	21st to end	Night	9% 18% 7% 17% 8% 5% 3 3 4 5% 20%	5112
November	1st to 10th	Night	9% 17% 5% 13% 7% 5% 5% 4 6% 5% 24%	3009
	11th to 20th	Night	8% 15% 7% 15% 8% 6% 5% 3 5% 6% 24%	3230
	21st to end	Night	8% 15% 5% 13% 7% 6% 6% 4 6% 6% 24%	3443
December	1st to 10th	Night	8% 14% 6% 12% 7% 6% 6% 4 6% 7% 25%	3610
	11th to 20th	Night	5% 18% 8% 17% 7% 6% 6% 4 5% 5% 18%	4679
	21st to end	Night	3 12% 5% 12% 7% 7% 6% 5% 7% 7% 28%	6963

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% 22% 14% 1	905
	11th to 20th	Day	50% 10% 16% 14% 6% 4	1270
	21st to end	Day	50% 6% 12% 14% 11% 7%	1704
February	1st to 10th	Day	45% 7% 8% 18% 19% 4	1140
	11th to 20th	Day	56% 9% 13% 14% 8%	1406
	21st to end	Day	55% 8% 11% 14% 11% 1	1256
March	1st to 10th	Day	62% 6% 8% 11% 12% 1	3056
	11th to 20th	Day	50% 8% 16% 17% 8% 1	3235
	21st to end	Day	48% 12% 19% 13% 8% 1	4165
April	1st to 10th	Day	54% 8% 14% 17% 6% 1	2431
	11th to 20th	Day	42% 8% 16% 24% 8% 2	2626
	21st to end	Day	39% 9% 14% 28% 9%	2896
May	1st to 10th	Day	56% 12% 12% 16% 4	5157
	11th to 20th	Day	40% 12% 15% 27% 5%	5486
	21st to end	Day	47% 13% 15% 19% 6%	6381
June	1st to 10th	Day	52% 12% 16% 17% 3	3738
	11th to 20th	Day	49% 13% 17% 18% 3	3800
	21st to end	Day	47% 14% 21% 18% 2	3800
July	1st to 10th	Day	61% 12% 17% 8% 1	6231
	11th to 20th	Day	52% 12% 18% 18%	5692
	21st to end	Day	53% 11% 18% 14% 3	5961
August	1st to 10th	Day	61% 10% 19% 9% 2	5037
	11th to 20th	Day	58% 14% 20% 8%	4871
	21st to end	Day	64% 12% 16% 8% 1	4883
September	1st to 10th	Day	58% 12% 19% 11% 1	2470
	11th to 20th	Day	64% 10% 15% 10%	2252
	21st to end	Day	61% 9% 13% 14% 3	2057
October	1st to 10th	Day	57% 8% 12% 19% 4	2991
	11th to 20th	Day	63% 10% 13% 13% 2	2751
	21st to end	Day	65% 8% 13% 11% 3	2447
November	1st to 10th	Day	59% 8% 16% 12% 4	1190
	11th to 20th	Day	59% 9% 12% 17% 3	950
	21st to end	Day	60% 8% 13% 13% 6%	718
December	1st to 10th	Day	56% 11% 13% 13% 6% 2	570
	11th to 20th	Day	62% 7% 12% 15% 4	516
	21st to end	Day	46% 12% 16% 16% 10% 1	704
January	1st to 10th	Night	43% 8% 16% 26% 6% 2	6080
	11th to 20th	Night	49% 9% 18% 15% 9% 1	5700
	21st to end	Night	45% 6% 11% 14% 17% 6%	5964
February	1st to 10th	Night	46% 4 9% 17% 20% 4	3040
	11th to 20th	Night	49% 9% 12% 20% 9%	2672
	21st to end	Night	57% 7% 13% 15% 8% 1	2198
March	1st to 10th	Night	60% 5% 7% 14% 12% 2	3795
	11th to 20th	Night	52% 7% 15% 16% 8% 1	3725
	21st to end	Night	42% 12% 22% 13% 10% 1	3466
April	1st to 10th	Night	53% 8% 14% 17% 6% 1	1748
	11th to 20th	Night	42% 10% 18% 22% 7% 1	1503
	21st to end	Night	38% 8% 15% 29% 10%	1281
May	1st to 10th	Night	53% 13% 14% 17% 2	1810
	11th to 20th	Night	38% 12% 18% 29% 4	1415
	21st to end	Night	50% 11% 13% 18% 9%	1206
June	1st to 10th	Night	49% 13% 19% 16% 3	441
	11th to 20th	Night	53% 10% 15% 19% 4	380
	21st to end	Night	48% 13% 22% 16% 1	380
July	1st to 10th	Night	65% 12% 12% 9% 2	630
	11th to 20th	Night	54% 9% 17% 18% 2	1141
	21st to end	Night	53% 11% 15% 16% 5%	1362
August	1st to 10th	Night	65% 9% 18% 7% 1	1875
	11th to 20th	Night	66% 10% 17% 7%	2031
	21st to end	Night	62% 12% 17% 9% 1	2783
September	1st to 10th	Night	55% 11% 21% 12% 1	1708
	11th to 20th	Night	63% 9% 14% 13% 1	1928
	21st to end	Night	59% 11% 12% 15% 3	2122
October	1st to 10th	Night	53% 9% 14% 19% 4	3975
	11th to 20th	Night	60% 10% 18% 11% 2	4174
	21st to end	Night	66% 8% 12% 13% 2	5112
November	1st to 10th	Night	60% 8% 14% 14% 4	3009
	11th to 20th	Night	61% 7% 14% 15% 3	3230
	21st to end	Night	59% 8% 11% 16% 6%	3443
December	1st to 10th	Night	57% 9% 13% 13% 6% 1	3610
	11th to 20th	Night	65% 8% 10% 12% 4	4676
	21st to end	Night	49% 9% 14% 14% 12% 1	6963

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%	90
	11th to 20th	Day	7% 3 18% 34% 32% 6%	90
	21st to end	Day	7% 4 10% 40% 25% 13%	208
February	1st to 10th	Day	6% 7% 13% 29% 28% 17%	280
	11th to 20th	Day	8% 7% 22% 31% 22% 10%	335
	21st to end	Day	8% 9% 23% 31% 22% 6%	307
March	1st to 10th	Day	6% 4 22% 39% 21% 8%	370
	11th to 20th	Day	7% 7% 21% 30% 25% 10%	375
	21st to end	Day	8% 6% 21% 30% 28% 7%	616
April	1st to 10th	Day	10% 10% 20% 32% 23% 6%	617
	11th to 20th	Day	8% 6% 23% 30% 27% 7%	640
	21st to end	Day	6% 4 14% 32% 32% 10%	650
May	1st to 10th	Day	9% 7% 21% 30% 27% 7%	653
	11th to 20th	Day	8% 6% 20% 32% 25% 8%	763
	21st to end	Day	14% 7% 17% 28% 25% 8%	1037
June	1st to 10th	Day	10% 4 18% 27% 28% 13%	1060
	11th to 20th	Day	10% 4 16% 24% 32% 15%	1060
	21st to end	Day	13% 3 11% 23% 33% 17%	1060
July	1st to 10th	Day	14% 5% 11% 25% 34% 10%	1041
	11th to 20th	Day	18% 3 14% 25% 25% 14%	905
	21st to end	Day	16% 4 13% 22% 27% 18%	933
August	1st to 10th	Day	24% 5% 17% 21% 23% 10%	676
	11th to 20th	Day	22% 6% 17% 24% 25% 6%	665
	21st to end	Day	22% 7% 16% 21% 21% 12%	748
September	1st to 10th	Day	20% 7% 15% 22% 23% 13%	660
	11th to 20th	Day	26% 9% 16% 25% 16% 9%	552
	21st to end	Day	23% 7% 16% 19% 20% 15%	390
October	1st to 10th	Day	20% 8% 22% 19% 21% 11%	390
	11th to 20th	Day	14% 6% 20% 21% 26% 13%	390
	21st to end	Day	17% 5% 14% 23% 29% 13%	429
November	1st to 10th	Day	15% 7% 12% 28% 28% 10%	289
	11th to 20th	Day	11% 2 17% 27% 27% 17%	90
	21st to end	Day	13% 2 17% 29% 32% 7%	90
December	1st to 10th	Day	17% 7% 19% 34% 18% 6%	90
	11th to 20th	Day	11% 3 29% 30% 22% 4	90
	21st to end	Day	5% 11% 22% 35% 21% 5%	99
January	1st to 10th	Night	7% 2 16% 36% 28% 11%	1088
	11th to 20th	Night	10% 4 18% 40% 23% 5%	940
	21st to end	Night	8% 3 16% 43% 24% 6%	994
February	1st to 10th	Night	6% 4 17% 36% 27% 9%	850
	11th to 20th	Night	7% 5% 21% 39% 25% 4	834
	21st to end	Night	9% 6% 19% 39% 25% 2	703
March	1st to 10th	Night	8% 4 19% 42% 24% 3	671
	11th to 20th	Night	8% 3 18% 39% 26% 6%	644
	21st to end	Night	10% 3 21% 33% 25% 8%	627
April	1st to 10th	Night	9% 5% 22% 36% 25% 3	570
	11th to 20th	Night	7% 4 20% 37% 29% 4	563
	21st to end	Night	8% 2 11% 34% 38% 7%	515
May	1st to 10th	Night	8% 4 15% 29% 38% 6%	329
	11th to 20th	Night	6% 4 21% 42% 25% 2	187
	21st to end	Night	16% 6% 11% 34% 27% 6%	206
June	1st to 10th	Night	11% 2 17% 28% 35% 7%	190
	11th to 20th	Night	13% 4 15% 26% 36% 7%	190
	21st to end	Night	15% 2 7% 29% 40% 7%	190
July	1st to 10th	Night	14% 3 12% 29% 37% 5%	185
	11th to 20th	Night	22% 5% 13% 24% 30% 6%	184
	21st to end	Night	16% 5% 11% 27% 34% 6%	208
August	1st to 10th	Night	26% 3 12% 25% 30% 5%	364
	11th to 20th	Night	24% 6% 11% 24% 28% 6%	443
	21st to end	Night	26% 4 10% 22% 28% 10%	627
September	1st to 10th	Night	19% 5% 13% 24% 30% 9%	570
	11th to 20th	Night	20% 6% 14% 28% 27% 4	570
	21st to end	Night	22% 4 17% 25% 27% 5%	587
October	1st to 10th	Night	20% 7% 19% 25% 26% 4	767
	11th to 20th	Night	14% 4 18% 29% 27% 8%	860
	21st to end	Night	14% 3 14% 34% 28% 6%	946
November	1st to 10th	Night	16% 4 18% 32% 24% 5%	859
	11th to 20th	Night	15% 3 14% 31% 26% 11%	850
	21st to end	Night	14% 2 17% 30% 27% 10%	978
December	1st to 10th	Night	14% 4 19% 34% 21% 8%	1130
	11th to 20th	Night	10% 4 20% 31% 28% 7%	1130
	21st to end	Night	9% 4 17% 35% 25% 10%	1243

Page generated at 2024-11-03 09:19:06. Version ac07

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