Prudhoe Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prudhoe Bay clear sky chart from 2005-11-06 to 2024-01-14.

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
Transparency	Day	66% 8% 13% 10% 3	75845
	Night	69% 7% 10% 10% 5% 1	78562
Seeing	Day	17% 3 12% 28% 28% 12%	18861
	Night	13% 3 15% 29% 29% 12%	21480

By Month

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	21st to end	Day	65% 7% 6% 15% 5% 2	364
	February	1st to 10th	Day	56% 5% 12% 13% 13% 1	755
11th to 20th		Day	59% 8% 12% 15% 6%	1060
21st to end		Day	59% 9% 8% 18% 6%	1149
March	1st to 10th	Day	67% 6% 13% 12% 3	1602
	11th to 20th	Day	49% 6% 20% 21% 4	1834
	21st to end	Day	53% 9% 13% 15% 9% 1	2376
April	1st to 10th	Day	71% 9% 8% 6% 6% 1	2458
	11th to 20th	Day	64% 7% 11% 12% 6% 1	2666
	21st to end	Day	66% 7% 10% 12% 4	2992
May	1st to 10th	Day	79% 5% 8% 6% 2 1	3345
	11th to 20th	Day	71% 7% 10% 10% 2	3852
	21st to end	Day	68% 8% 12% 9% 2	4664
June	1st to 10th	Day	62% 8% 10% 16% 5%	4320
	11th to 20th	Day	46% 10% 19% 22% 3	4320
	21st to end	Day	53% 11% 18% 16% 3	4320
July	1st to 10th	Day	51% 13% 22% 14% 1	4201
	11th to 20th	Day	63% 10% 15% 10% 1	4185
	21st to end	Day	68% 11% 15% 6%	4135
August	1st to 10th	Day	73% 10% 11% 6% 1	3349
	11th to 20th	Day	80% 7% 10% 4	2991
	21st to end	Day	76% 8% 11% 4	3017
September	1st to 10th	Day	78% 6% 11% 4 1	2471
	11th to 20th	Day	77% 7% 10% 6%	2181
	21st to end	Day	78% 5% 9% 7% 1	1910
October	1st to 10th	Day	75% 5% 11% 6% 3	1670
	11th to 20th	Day	75% 7% 13% 5% 1	1373
	21st to end	Day	78% 5% 11% 4 1	1197
November	1st to 10th	Day	74% 7% 12% 4 2	755
	11th to 20th	Day	80% 5% 11% 4	333
January	1st to 10th	Night	65% 6% 9% 10% 8% 2	4545
	11th to 20th	Night	64% 7% 8% 14% 6% 1	4385
	21st to end	Night	65% 7% 8% 13% 5% 2	4009
February	1st to 10th	Night	53% 7% 14% 14% 11% 1	3204
	11th to 20th	Night	60% 8% 11% 15% 6%	2799
	21st to end	Night	64% 7% 8% 17% 4 1	2107
March	1st to 10th	Night	61% 9% 12% 16% 2	2358
	11th to 20th	Night	47% 7% 21% 22% 3	2124
	21st to end	Night	53% 8% 15% 13% 9% 1	1980
April	1st to 10th	Night	72% 8% 8% 6% 6%	1500
	11th to 20th	Night	68% 6% 10% 10% 5% 1	1240
	21st to end	Night	70% 6% 6% 14% 4	966
May	1st to 10th	Night	83% 5% 6% 4 2 1	614
	11th to 20th	Night	77% 7% 10% 4 2	153
July	21st to end	Night	74% 15% 5% 7%	110
	August	1st to 10th	Night	72% 8% 11% 7% 1	564
11th to 20th		Night	79% 6% 9% 5%	907
21st to end		Night	77% 8% 11% 4 1	1339
September	1st to 10th	Night	77% 7% 11% 4 1	1489
	11th to 20th	Night	77% 7% 10% 6% 1	1777
	21st to end	Night	79% 6% 9% 5% 1	2047
October	1st to 10th	Night	73% 6% 10% 8% 2	2290
	11th to 20th	Night	77% 7% 11% 5%	2587
	21st to end	Night	80% 6% 10% 4 1	3158
November	1st to 10th	Night	73% 8% 10% 6% 2 1	3302
	11th to 20th	Night	82% 5% 9% 3 1	3853
	21st to end	Night	77% 5% 7% 7% 4 1	4560
December	1st to 10th	Night	69% 8% 10% 9% 3	4560
	11th to 20th	Night	71% 8% 8% 9% 3	5675
	21st to end	Night	64% 7% 7% 10% 11% 1	8360

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	21st to end	Day	9% 2 18% 38% 29% 5%	66
	February	1st to 10th	Day	3 1 16% 41% 34% 6%	115
11th to 20th		Day	7% 4 13% 33% 31% 13%	255
21st to end		Day	8% 3 15% 32% 29% 12%	265
March	1st to 10th	Day	5% 2 15% 34% 27% 17%	340
	11th to 20th	Day	4 4 15% 25% 25% 27%	356
	21st to end	Day	6% 4 19% 22% 31% 18%	572
April	1st to 10th	Day	4 3 15% 33% 31% 14%	594
	11th to 20th	Day	7% 4 13% 31% 28% 18%	590
	21st to end	Day	7% 1 10% 24% 32% 25%	622
May	1st to 10th	Day	11% 3 9% 23% 34% 19%	865
	11th to 20th	Day	13% 4 14% 26% 29% 15%	1032
	21st to end	Day	16% 4 11% 26% 31% 12%	1263
June	1st to 10th	Day	15% 4 15% 31% 24% 11%	1170
	11th to 20th	Day	11% 2 12% 33% 32% 10%	1170
	21st to end	Day	14% 3 10% 36% 28% 9%	1170
July	1st to 10th	Day	12% 3 9% 34% 33% 9%	1146
	11th to 20th	Day	20% 4 9% 30% 28% 10%	1140
	21st to end	Day	27% 3 8% 27% 26% 8%	1167
August	1st to 10th	Day	29% 4 15% 23% 22% 7%	879
	11th to 20th	Day	41% 5% 11% 22% 15% 7%	690
	21st to end	Day	36% 4 13% 17% 22% 8%	693
September	1st to 10th	Day	35% 3 9% 16% 26% 10%	630
	11th to 20th	Day	30% 5% 13% 22% 23% 7%	550
	21st to end	Day	27% 4 14% 20% 22% 14%	360
October	1st to 10th	Day	21% 5% 16% 25% 21% 13%	360
	11th to 20th	Day	17% 5% 14% 28% 25% 11%	360
	21st to end	Day	13% 6% 15% 26% 26% 14%	270
November	1st to 10th	Day	12% 1 19% 32% 30% 6%	90
	11th to 20th	Day	5% 2 14% 32% 33% 14%	81
January	1st to 10th	Night	6% 4 18% 30% 29% 13%	1220
	11th to 20th	Night	6% 4 18% 33% 28% 12%	1163
	21st to end	Night	5% 3 17% 31% 32% 14%	1139
February	1st to 10th	Night	3 1 14% 38% 32% 12%	880
	11th to 20th	Night	8% 2 15% 33% 31% 11%	784
	21st to end	Night	6% 4 18% 33% 27% 11%	658
March	1st to 10th	Night	6% 2 11% 33% 33% 15%	706
	11th to 20th	Night	4 2 12% 28% 35% 19%	612
	21st to end	Night	5% 4 18% 24% 33% 17%	594
April	1st to 10th	Night	9% 3 17% 29% 31% 12%	540
	11th to 20th	Night	8% 2 14% 32% 31% 13%	469
	21st to end	Night	10% 1 11% 27% 34% 16%	270
May	1st to 10th	Night	13% 4 9% 28% 29% 17%	180
	11th to 20th	Night	19% 8% 9% 31% 26% 8%	93
July	21st to end	Night	33% 9% 31% 26% 2	58
	August	1st to 10th	Night	32% 4 10% 28% 21% 3	179
11th to 20th		Night	41% 2 10% 25% 16% 6%	270
21st to end		Night	34% 3 8% 20% 26% 8%	489
September	1st to 10th	Night	32% 3 11% 21% 24% 9%	540
	11th to 20th	Night	36% 3 14% 21% 22% 4	540
	21st to end	Night	27% 3 12% 28% 22% 8%	573
October	1st to 10th	Night	23% 3 16% 25% 23% 10%	760
	11th to 20th	Night	23% 2 13% 27% 27% 9%	810
	21st to end	Night	19% 3 15% 26% 26% 11%	891
November	1st to 10th	Night	15% 3 16% 31% 25% 9%	928
	11th to 20th	Night	11% 3 13% 29% 30% 14%	1132
	21st to end	Night	12% 3 12% 26% 30% 17%	1220
December	1st to 10th	Night	12% 4 17% 33% 26% 9%	1220
	11th to 20th	Night	8% 3 16% 27% 34% 13%	1220
	21st to end	Night	6% 5% 15% 30% 29% 16%	1342

Page generated at 2024-01-11 00:22:40. Version ac07

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