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 2024-03-28.

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% 10% 5% 9% 8% 4 6% 6% 7% 8% 28%	76356
	Night	7% 12% 5% 10% 8% 4 6% 6% 6% 7% 29%	83639
Transparency	Day	52% 11% 16% 15% 5% 1	75963
	Night	53% 9% 14% 16% 8% 1	83613
Seeing	Day	14% 5% 17% 27% 26% 11%	17613
	Night	13% 4 17% 33% 27% 7%	22245

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	5% 10% 6% 9% 8% 3 5% 3 4 5% 42%	905
	11th to 20th	Day	4 12% 7% 10% 9% 5% 6% 6% 6% 7% 31%	1258
	21st to end	Day	4 10% 5% 9% 8% 6% 8% 8% 8% 8% 26%	1704
February	1st to 10th	Day	2 11% 6% 10% 6% 3 5% 5% 5% 6% 39%	1140
	11th to 20th	Day	3 12% 6% 13% 11% 5% 5% 7% 7% 8% 23%	1399
	21st to end	Day	4 13% 7% 11% 9% 5% 7% 5% 6% 7% 27%	1256
March	1st to 10th	Day	4 12% 7% 12% 8% 4 5% 4 7% 6% 29%	1853
	11th to 20th	Day	3 9% 5% 8% 7% 6% 6% 5% 5% 7% 38%	1936
	21st to end	Day	5% 8% 5% 10% 7% 4 6% 5% 6% 6% 38%	2461
April	1st to 10th	Day	5% 14% 6% 9% 8% 4 6% 6% 7% 8% 27%	2302
	11th to 20th	Day	4 9% 4 8% 7% 4 6% 5% 6% 8% 39%	2486
	21st to end	Day	5% 8% 3 7% 7% 5% 7% 6% 7% 9% 38%	2743
May	1st to 10th	Day	6% 8% 6% 10% 8% 6% 8% 7% 7% 7% 29%	2928
	11th to 20th	Day	6% 7% 4 8% 8% 4 7% 6% 7% 7% 36%	3093
	21st to end	Day	10% 8% 3 7% 6% 4 7% 7% 8% 10% 30%	3590
June	1st to 10th	Day	11% 8% 4 9% 8% 5% 7% 7% 7% 8% 26%	3541
	11th to 20th	Day	11% 7% 4 8% 8% 4 7% 7% 7% 8% 29%	3600
	21st to end	Day	14% 7% 3 7% 7% 4 6% 7% 7% 10% 29%	3600
July	1st to 10th	Day	12% 6% 3 7% 7% 5% 7% 7% 8% 10% 29%	3600
	11th to 20th	Day	17% 10% 5% 8% 7% 5% 7% 7% 8% 7% 20%	3307
	21st to end	Day	16% 8% 4 8% 7% 4 7% 7% 7% 9% 23%	3516
August	1st to 10th	Day	22% 11% 5% 8% 7% 4 6% 6% 6% 7% 20%	2876
	11th to 20th	Day	20% 9% 4 8% 7% 4 6% 6% 7% 8% 22%	2756
	21st to end	Day	19% 11% 4 10% 8% 4 6% 5% 6% 7% 21%	2772
September	1st to 10th	Day	17% 11% 4 8% 7% 4 5% 6% 6% 7% 24%	2340
	11th to 20th	Day	20% 13% 5% 10% 7% 3 5% 5% 6% 6% 20%	2134
	21st to end	Day	18% 13% 4 11% 7% 3 5% 5% 5% 5% 25%	1949
October	1st to 10th	Day	15% 16% 7% 11% 8% 4 4 6% 5% 7% 19%	1709
	11th to 20th	Day	9% 17% 6% 13% 9% 3 5% 4 5% 5% 24%	1577
	21st to end	Day	10% 13% 4 11% 10% 5% 5% 6% 6% 8% 21%	1414
November	1st to 10th	Day	10% 13% 6% 12% 9% 4 6% 6% 6% 6% 22%	1155
	11th to 20th	Day	8% 11% 7% 13% 11% 5% 5% 4 4 5% 27%	950
	21st to end	Day	8% 14% 7% 11% 9% 6% 5% 5% 6% 6% 23%	718
December	1st to 10th	Day	10% 16% 6% 9% 6% 4 5% 5% 8% 8% 23%	570
	11th to 20th	Day	3 19% 6% 12% 13% 3 7% 5% 6% 4 23%	514
	21st to end	Day	3 10% 5% 9% 8% 6% 9% 7% 8% 8% 27%	704
January	1st to 10th	Night	4 9% 5% 10% 8% 3 4 5% 5% 7% 40%	6080
	11th to 20th	Night	4 13% 6% 10% 8% 4 5% 5% 6% 8% 31%	5650
	21st to end	Night	3 8% 4 10% 9% 4 7% 8% 8% 7% 32%	5964
February	1st to 10th	Night	2 12% 6% 11% 7% 3 4 4 4 7% 39%	3040
	11th to 20th	Night	4 11% 5% 9% 8% 5% 7% 7% 7% 8% 29%	2668
	21st to end	Night	4 14% 7% 11% 8% 5% 6% 5% 5% 7% 26%	2198
March	1st to 10th	Night	4 14% 7% 11% 9% 5% 6% 5% 4 6% 30%	2324
	11th to 20th	Night	4 9% 4 9% 8% 4 6% 5% 5% 7% 40%	2242
	21st to end	Night	6% 9% 5% 8% 6% 5% 5% 6% 5% 6% 40%	2050
April	1st to 10th	Night	5% 12% 7% 9% 8% 5% 7% 6% 6% 8% 27%	1657
	11th to 20th	Night	5% 7% 3 9% 9% 5% 5% 6% 7% 7% 37%	1423
	21st to end	Night	7% 7% 3 7% 6% 4 6% 6% 7% 9% 38%	1214
May	1st to 10th	Night	6% 8% 3 8% 8% 5% 9% 8% 7% 9% 28%	1032
	11th to 20th	Night	5% 8% 2 6% 7% 5% 6% 7% 6% 10% 38%	800
	21st to end	Night	11% 7% 4 7% 7% 4 6% 7% 6% 9% 32%	685
June	1st to 10th	Night	8% 10% 3 9% 8% 4 9% 8% 9% 10% 23%	418
	11th to 20th	Night	11% 10% 2 11% 9% 4 6% 5% 4 11% 26%	360
	21st to end	Night	13% 8% 3 8% 7% 5% 8% 6% 8% 11% 24%	360
July	1st to 10th	Night	11% 6% 5% 7% 6% 2 7% 8% 8% 12% 29%	360
	11th to 20th	Night	20% 12% 4 7% 8% 4 4 7% 8% 7% 19%	653
	21st to end	Night	15% 7% 4 8% 8% 3 7% 8% 6% 9% 23%	801
August	1st to 10th	Night	22% 10% 4 9% 9% 6% 6% 5% 5% 6% 18%	1060
	11th to 20th	Night	20% 11% 4 9% 7% 5% 7% 5% 6% 7% 20%	1142
	21st to end	Night	23% 10% 4 7% 7% 4 5% 5% 5% 5% 24%	1584
September	1st to 10th	Night	15% 10% 4 8% 7% 5% 6% 5% 6% 8% 25%	1618
	11th to 20th	Night	16% 11% 5% 10% 8% 5% 6% 5% 6% 6% 22%	1826
	21st to end	Night	16% 13% 5% 9% 7% 3 5% 7% 4 5% 26%	2010
October	1st to 10th	Night	15% 16% 5% 9% 8% 4 6% 6% 6% 6% 19%	2251
	11th to 20th	Night	10% 12% 6% 10% 9% 4 4 5% 7% 7% 26%	2380
	21st to end	Night	9% 15% 6% 12% 8% 4 5% 5% 6% 6% 24%	2942
November	1st to 10th	Night	9% 16% 6% 11% 8% 4 6% 6% 5% 5% 24%	2922
	11th to 20th	Night	8% 14% 7% 13% 9% 4 5% 4 5% 6% 25%	3230
	21st to end	Night	8% 13% 6% 12% 9% 4 6% 5% 6% 6% 24%	3443
December	1st to 10th	Night	8% 13% 7% 11% 8% 4 6% 5% 6% 7% 25%	3610
	11th to 20th	Night	5% 17% 8% 15% 9% 5% 7% 5% 5% 6% 18%	4679
	21st to end	Night	3 11% 6% 11% 8% 5% 7% 6% 7% 8% 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	53% 8% 13% 16% 8% 2	1853
	11th to 20th	Day	43% 7% 12% 24% 13% 2	1936
	21st to end	Day	44% 9% 18% 13% 14% 2	2461
April	1st to 10th	Day	53% 9% 14% 17% 7% 1	2302
	11th to 20th	Day	42% 8% 16% 24% 8% 1	2486
	21st to end	Day	40% 9% 15% 27% 9%	2743
May	1st to 10th	Day	50% 11% 13% 20% 6%	2928
	11th to 20th	Day	43% 9% 14% 25% 8%	3096
	21st to end	Day	44% 11% 17% 20% 7%	3591
June	1st to 10th	Day	52% 12% 16% 17% 3	3541
	11th to 20th	Day	49% 13% 17% 18% 3	3600
	21st to end	Day	48% 14% 20% 17% 1	3600
July	1st to 10th	Day	47% 14% 22% 15% 2	3501
	11th to 20th	Day	58% 15% 17% 10%	3204
	21st to end	Day	53% 16% 23% 8%	3320
August	1st to 10th	Day	62% 12% 19% 7%	2856
	11th to 20th	Day	56% 15% 20% 9%	2756
	21st to end	Day	60% 13% 18% 8% 1	2772
September	1st to 10th	Day	57% 12% 19% 10% 1	2340
	11th to 20th	Day	63% 10% 16% 11%	2134
	21st to end	Day	61% 9% 13% 14% 3	1949
October	1st to 10th	Day	65% 9% 14% 9% 3	1709
	11th to 20th	Day	61% 9% 16% 10% 3	1577
	21st to end	Day	59% 10% 17% 13% 1	1414
November	1st to 10th	Day	58% 9% 16% 12% 4	1155
	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	55% 6% 10% 17% 9% 3	2324
	11th to 20th	Night	43% 6% 13% 24% 13% 2	2244
	21st to end	Night	43% 8% 16% 15% 16% 2	2050
April	1st to 10th	Night	52% 8% 15% 18% 6% 1	1657
	11th to 20th	Night	43% 10% 19% 22% 7%	1423
	21st to end	Night	40% 7% 15% 28% 10%	1214
May	1st to 10th	Night	46% 12% 15% 22% 4 1	1032
	11th to 20th	Night	39% 9% 19% 26% 7%	800
	21st to end	Night	47% 9% 13% 21% 9%	685
June	1st to 10th	Night	50% 13% 18% 16% 3	418
	11th to 20th	Night	53% 10% 14% 19% 4	360
	21st to end	Night	50% 14% 21% 15% 1	360
July	1st to 10th	Night	43% 17% 21% 16% 3	350
	11th to 20th	Night	60% 13% 18% 8% 1	633
	21st to end	Night	51% 16% 20% 12%	757
August	1st to 10th	Night	65% 11% 16% 8%	1055
	11th to 20th	Night	62% 13% 14% 12%	1142
	21st to end	Night	60% 12% 19% 8% 1	1584
September	1st to 10th	Night	55% 11% 21% 11% 1	1618
	11th to 20th	Night	62% 10% 14% 13% 1	1826
	21st to end	Night	58% 11% 12% 15% 3	2010
October	1st to 10th	Night	63% 11% 15% 8% 3	2251
	11th to 20th	Night	55% 10% 20% 12% 3	2380
	21st to end	Night	59% 10% 17% 12% 3	2942
November	1st to 10th	Night	60% 8% 14% 15% 4	2922
	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% 27% 8%	601
April	1st to 10th	Day	10% 10% 21% 32% 22% 6%	570
	11th to 20th	Day	8% 6% 22% 29% 28% 7%	590
	21st to end	Day	7% 5% 15% 32% 31% 10%	600
May	1st to 10th	Day	9% 6% 21% 29% 28% 7%	603
	11th to 20th	Day	8% 7% 21% 31% 25% 8%	708
	21st to end	Day	13% 7% 18% 29% 25% 8%	965
June	1st to 10th	Day	11% 4 18% 27% 28% 13%	990
	11th to 20th	Day	10% 4 16% 24% 32% 14%	990
	21st to end	Day	13% 3 12% 24% 32% 15%	990
July	1st to 10th	Day	12% 4 11% 26% 36% 11%	971
	11th to 20th	Day	19% 3 14% 24% 25% 15%	843
	21st to end	Day	16% 4 13% 23% 27% 18%	868
August	1st to 10th	Day	23% 5% 17% 21% 24% 10%	626
	11th to 20th	Day	22% 5% 15% 25% 26% 7%	615
	21st to end	Day	23% 6% 15% 22% 22% 12%	693
September	1st to 10th	Day	20% 7% 15% 23% 22% 13%	612
	11th to 20th	Day	26% 7% 15% 25% 17% 10%	514
	21st to end	Day	23% 6% 17% 21% 20% 14%	360
October	1st to 10th	Day	21% 8% 22% 19% 21% 9%	360
	11th to 20th	Day	14% 5% 21% 20% 27% 13%	360
	21st to end	Day	16% 5% 13% 23% 30% 13%	396
November	1st to 10th	Day	15% 7% 12% 29% 27% 9%	274
	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% 2 21% 33% 25% 8%	615
April	1st to 10th	Night	9% 5% 21% 37% 25% 3	540
	11th to 20th	Night	7% 4 19% 36% 30% 4	533
	21st to end	Night	8% 2 12% 32% 39% 7%	488
May	1st to 10th	Night	9% 4 14% 29% 39% 6%	312
	11th to 20th	Night	7% 5% 21% 40% 26% 2	177
	21st to end	Night	16% 6% 10% 35% 28% 6%	195
June	1st to 10th	Night	11% 2 17% 26% 36% 8%	180
	11th to 20th	Night	13% 3 14% 26% 36% 7%	180
	21st to end	Night	16% 2 7% 30% 38% 8%	180
July	1st to 10th	Night	13% 2 11% 31% 38% 6%	175
	11th to 20th	Night	22% 5% 12% 24% 30% 6%	174
	21st to end	Night	16% 5% 12% 26% 34% 7%	197
August	1st to 10th	Night	26% 3 11% 25% 31% 5%	344
	11th to 20th	Night	24% 5% 11% 25% 28% 6%	419
	21st to end	Night	26% 4 10% 21% 28% 11%	594
September	1st to 10th	Night	20% 4 13% 24% 29% 9%	540
	11th to 20th	Night	20% 4 15% 29% 28% 5%	540
	21st to end	Night	22% 4 18% 25% 27% 4	555
October	1st to 10th	Night	21% 7% 19% 24% 25% 3	721
	11th to 20th	Night	14% 4 18% 30% 26% 8%	810
	21st to end	Night	14% 3 14% 34% 29% 6%	891
November	1st to 10th	Night	17% 4 18% 33% 24% 5%	830
	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 2024-03-24 19:37:05. Version ac07

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