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 2024-11-12.

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	67% 7% 13% 10% 2	111455
	Night	66% 7% 9% 10% 7% 2	102729
Seeing	Day	17% 4 12% 28% 27% 12%	20277
	Night	12% 3 15% 29% 29% 12%	22338

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	63% 5% 8% 14% 9% 1	630
	February	1st to 10th	Day	58% 5% 12% 12% 12% 1	797
11th to 20th		Day	60% 8% 12% 14% 6%	1120
21st to end		Day	59% 9% 8% 18% 6%	1219
March	1st to 10th	Day	54% 6% 12% 15% 13%	2790
	11th to 20th	Day	52% 7% 14% 18% 9%	3222
	21st to end	Day	64% 8% 11% 11% 5% 1	4165
April	1st to 10th	Day	71% 8% 8% 7% 5% 1	2596
	11th to 20th	Day	64% 7% 11% 11% 6% 1	2817
	21st to end	Day	67% 7% 10% 12% 4	3159
May	1st to 10th	Day	83% 5% 6% 5% 1	5901
	11th to 20th	Day	74% 6% 10% 9% 1	6829
	21st to end	Day	78% 5% 9% 6% 1	8272
June	1st to 10th	Day	63% 8% 10% 15% 5%	4560
	11th to 20th	Day	46% 9% 19% 22% 3	4560
	21st to end	Day	51% 10% 19% 16% 2	4560
July	1st to 10th	Day	59% 9% 18% 13% 1	7481
	11th to 20th	Day	55% 10% 26% 9% 1	7465
	21st to end	Day	67% 7% 15% 10%	7409
August	1st to 10th	Day	70% 8% 13% 9% 1	5907
	11th to 20th	Day	77% 6% 12% 6%	5282
	21st to end	Day	75% 6% 14% 4	5289
September	1st to 10th	Day	78% 6% 11% 4 1	2608
	11th to 20th	Day	77% 7% 10% 6%	2302
	21st to end	Day	78% 5% 9% 7% 1	2016
October	1st to 10th	Day	70% 5% 10% 12% 2	2926
	11th to 20th	Day	80% 5% 10% 4	2385
	21st to end	Day	78% 5% 8% 8% 2	2057
November	1st to 10th	Day	75% 7% 12% 4 2	795
	11th to 20th	Day	80% 5% 10% 4	336
January	1st to 10th	Night	41% 5% 7% 9% 24% 14%	7585
	11th to 20th	Night	53% 7% 7% 11% 13% 10%	7586
	21st to end	Night	60% 7% 9% 16% 7% 1	7065
February	1st to 10th	Night	55% 7% 13% 14% 10% 1	3382
	11th to 20th	Night	61% 8% 10% 15% 5%	2959
	21st to end	Night	64% 7% 8% 17% 4 1	2235
March	1st to 10th	Night	55% 9% 9% 14% 13%	4068
	11th to 20th	Night	48% 8% 15% 17% 13%	3736
	21st to end	Night	65% 7% 12% 10% 5% 1	3466
April	1st to 10th	Night	72% 7% 8% 7% 6%	1582
	11th to 20th	Night	67% 7% 10% 10% 5% 1	1309
	21st to end	Night	72% 6% 6% 13% 4	1019
May	1st to 10th	Night	87% 4 5% 2 1 1	1068
	11th to 20th	Night	87% 4 6% 2 1	265
July	21st to end	Night	84% 9% 3 4	216
	August	1st to 10th	Night	67% 6% 14% 11% 3	1006
11th to 20th		Night	79% 6% 10% 5%	1619
21st to end		Night	74% 6% 15% 4 1	2377
September	1st to 10th	Night	77% 7% 12% 4 1	1572
	11th to 20th	Night	78% 7% 10% 6%	1876
	21st to end	Night	78% 5% 9% 6% 1	2161
October	1st to 10th	Night	69% 6% 11% 12% 2	4042
	11th to 20th	Night	78% 6% 9% 7%	4543
	21st to end	Night	78% 6% 8% 7% 1	5483
November	1st to 10th	Night	74% 7% 10% 7% 2 1	3481
	11th to 20th	Night	82% 5% 9% 3 1	3873
	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	11% 1 19% 36% 27% 5%	74
	February	1st to 10th	Day	2 1 17% 38% 34% 8%	127
11th to 20th		Day	7% 5% 13% 33% 29% 12%	275
21st to end		Day	8% 3 14% 33% 30% 12%	290
March	1st to 10th	Day	5% 2 15% 33% 28% 18%	370
	11th to 20th	Day	4 4 15% 25% 26% 27%	387
	21st to end	Day	7% 4 18% 24% 30% 18%	616
April	1st to 10th	Day	4 3 15% 32% 30% 16%	644
	11th to 20th	Day	6% 4 14% 32% 28% 16%	640
	21st to end	Day	7% 2 10% 26% 31% 24%	674
May	1st to 10th	Day	11% 3 9% 23% 34% 19%	930
	11th to 20th	Day	12% 4 14% 27% 29% 14%	1105
	21st to end	Day	15% 4 11% 27% 30% 13%	1351
June	1st to 10th	Day	14% 5% 15% 30% 25% 11%	1250
	11th to 20th	Day	10% 2 12% 34% 32% 11%	1250
	21st to end	Day	14% 3 10% 34% 29% 10%	1250
July	1st to 10th	Day	14% 3 9% 34% 32% 8%	1226
	11th to 20th	Day	19% 3 9% 30% 28% 9%	1220
	21st to end	Day	29% 3 9% 26% 26% 8%	1249
August	1st to 10th	Day	29% 4 15% 24% 21% 7%	943
	11th to 20th	Day	40% 5% 12% 22% 14% 6%	744
	21st to end	Day	35% 4 13% 17% 22% 8%	748
September	1st to 10th	Day	34% 3 9% 16% 26% 11%	680
	11th to 20th	Day	30% 5% 12% 21% 25% 8%	591
	21st to end	Day	27% 3 14% 21% 22% 13%	390
October	1st to 10th	Day	20% 4 15% 24% 23% 14%	390
	11th to 20th	Day	16% 6% 14% 28% 25% 11%	390
	21st to end	Day	12% 7% 15% 28% 25% 13%	291
November	1st to 10th	Day	12% 2 18% 33% 30% 5%	100
	11th to 20th	Day	5% 2 13% 32% 34% 13%	82
January	1st to 10th	Night	6% 4 18% 30% 29% 13%	1220
	11th to 20th	Night	6% 4 20% 32% 27% 11%	1216
	21st to end	Night	5% 2 17% 31% 31% 13%	1215
February	1st to 10th	Night	3 2 15% 38% 32% 11%	940
	11th to 20th	Night	8% 3 16% 33% 30% 10%	834
	21st to end	Night	6% 4 17% 33% 28% 10%	703
March	1st to 10th	Night	5% 3 12% 33% 33% 14%	750
	11th to 20th	Night	4 2 13% 28% 35% 19%	651
	21st to end	Night	5% 4 18% 24% 32% 17%	627
April	1st to 10th	Night	8% 3 16% 29% 31% 13%	570
	11th to 20th	Night	7% 3 15% 33% 30% 12%	495
	21st to end	Night	11% 1 11% 29% 33% 15%	285
May	1st to 10th	Night	13% 4 9% 28% 30% 16%	190
	11th to 20th	Night	18% 7% 8% 30% 30% 7%	98
July	21st to end	Night	35% 8% 29% 26% 2	62
	August	1st to 10th	Night	33% 4 11% 29% 20% 3	189
11th to 20th		Night	41% 2 11% 24% 16% 6%	286
21st to end		Night	33% 3 8% 21% 26% 8%	517
September	1st to 10th	Night	32% 3 10% 21% 26% 9%	570
	11th to 20th	Night	36% 2 13% 21% 23% 5%	570
	21st to end	Night	27% 3 12% 28% 22% 8%	607
October	1st to 10th	Night	22% 3 15% 25% 24% 11%	808
	11th to 20th	Night	22% 3 13% 27% 27% 8%	860
	21st to end	Night	19% 3 15% 27% 25% 10%	946
November	1st to 10th	Night	15% 3 16% 33% 25% 9%	987
	11th to 20th	Night	11% 3 13% 29% 30% 14%	1140
	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 2024-11-08 18:45:38. Version ac07

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