Seward
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Seward clear sky chart from 2005-11-06 to 2026-08-30.

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	8% 5% 2 5% 3 3 4 3 5% 7% 55%	152548
	Night	8% 5% 2 5% 3 3 3 3 5% 7% 56%	147125
Transparency	Day	28% 5% 11% 27% 23% 6%	147360
	Night	27% 4 11% 27% 24% 7%	143325
Seeing	Day	11% 9% 31% 31% 15% 3	18125
	Night	10% 9% 36% 35% 9% 1	27905

By Month

Percentage Cloud Cover SW (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	9% 7% 2 7% 4 4 4 3 5% 7% 48%	5287
	11th to 20th	Day	4 7% 2 8% 4 4 4 3 5% 6% 53%	5310
	21st to end	Day	8% 8% 3 8% 3 3 3 3 3 5% 53%	5812
February	1st to 10th	Day	6% 10% 3 7% 4 4 3 3 5% 7% 48%	1990
	11th to 20th	Day	5% 6% 2 7% 4 4 4 3 5% 7% 52%	2049
	21st to end	Day	6% 5% 2 5% 3 2 3 2 6% 8% 58%	1730
March	1st to 10th	Day	7% 6% 2 4 3 3 3 2 4 5% 60%	4730
	11th to 20th	Day	7% 5% 2 4 2 3 3 3 4 6% 61%	5090
	21st to end	Day	7% 5% 2 5% 4 3 4 4 6% 8% 52%	5585
April	1st to 10th	Day	10% 5% 2 4 4 3 3 2 5% 6% 55%	2383
	11th to 20th	Day	10% 6% 2 6% 4 4 4 3 6% 6% 49%	2568
	21st to end	Day	15% 6% 3 6% 4 4 4 3 5% 6% 45%	2730
May	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 5% 6% 47%	7655
	11th to 20th	Day	7% 3 1 4 2 3 4 3 6% 7% 59%	7627
	21st to end	Day	18% 6% 3 6% 4 4 4 3 5% 6% 41%	8404
June	1st to 10th	Day	5% 4 2 5% 3 4 4 4 5% 8% 57%	2730
	11th to 20th	Day	5% 3 1 5% 4 4 4 4 6% 7% 57%	2730
	21st to end	Day	7% 3 1 4 4 4 5% 4 6% 8% 56%	2730
July	1st to 10th	Day	5% 4 1 4 3 4 4 4 6% 9% 56%	7679
	11th to 20th	Day	5% 3 1 4 3 4 4 4 5% 8% 59%	7680
	21st to end	Day	5% 3 2 5% 3 4 4 4 7% 9% 54%	8339
August	1st to 10th	Day	9% 5% 2 5% 3 4 4 4 6% 8% 52%	5931
	11th to 20th	Day	7% 4 2 5% 3 4 5% 3 6% 9% 53%	5951
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 7% 48%	6192
September	1st to 10th	Day	9% 4 1 4 3 4 4 3 4 5% 59%	2250
	11th to 20th	Day	7% 4 2 5% 3 4 3 4 4 6% 59%	2200
	21st to end	Day	8% 5% 2 5% 3 3 3 3 5% 6% 60%	2200
October	1st to 10th	Day	7% 3 1 3 1 2 2 2 3 5% 74%	3590
	11th to 20th	Day	5% 3 1 3 2 2 2 3 4 7% 67%	3247
	21st to end	Day	8% 5% 1 3 2 3 2 2 4 5% 64%	3418
November	1st to 10th	Day	7% 4 1 3 2 2 3 3 5% 5% 65%	1853
	11th to 20th	Day	7% 5% 1 5% 3 3 2 3 5% 7% 61%	1890
	21st to end	Day	9% 6% 1 3 2 2 3 2 3 4 63%	1890
December	1st to 10th	Day	4 3 1 4 2 2 2 3 4 6% 68%	3030
	11th to 20th	Day	4 5% 2 4 3 2 2 2 3 6% 65%	3481
	21st to end	Day	10% 11% 4 7% 4 3 4 3 5% 7% 42%	4587
January	1st to 10th	Night	10% 7% 2 8% 5% 4 4 3 4 6% 47%	7634
	11th to 20th	Night	3 5% 2 5% 4 4 4 3 4 5% 61%	7680
	21st to end	Night	10% 8% 3 7% 3 3 3 3 4 5% 52%	8402
February	1st to 10th	Night	8% 8% 4 7% 4 4 4 3 4 5% 50%	2647
	11th to 20th	Night	8% 7% 3 7% 5% 4 3 4 6% 6% 49%	2458
	21st to end	Night	7% 5% 3 6% 3 2 3 2 4 6% 59%	2076
March	1st to 10th	Night	6% 4 1 4 3 3 3 3 4 5% 65%	5357
	11th to 20th	Night	6% 4 1 4 3 3 4 4 5% 6% 60%	5090
	21st to end	Night	7% 7% 2 6% 4 3 4 3 4 6% 54%	5588
April	1st to 10th	Night	9% 5% 1 4 4 3 3 4 5% 8% 53%	2233
	11th to 20th	Night	11% 4 2 5% 3 4 4 3 5% 7% 52%	2000
	21st to end	Night	14% 7% 2 5% 3 3 3 3 5% 7% 49%	1890
May	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 7% 47%	5292
	11th to 20th	Night	7% 3 1 3 3 3 4 4 6% 7% 59%	5265
	21st to end	Night	19% 5% 1 4 3 2 4 3 5% 7% 46%	5803
June	1st to 10th	Night	7% 2 2 3 4 4 3 3 8% 9% 56%	1890
	11th to 20th	Night	5% 3 1 4 3 4 4 3 7% 10% 56%	1890
	21st to end	Night	5% 4 1 4 3 3 4 3 7% 9% 58%	1890
July	1st to 10th	Night	4 3 2 5% 4 4 5% 4 7% 10% 52%	5310
	11th to 20th	Night	5% 3 2 4 3 3 3 3 6% 10% 57%	5310
	21st to end	Night	5% 3 2 5% 4 4 4 4 6% 10% 52%	5770
August	1st to 10th	Night	5% 3 2 5% 4 4 4 4 6% 10% 53%	4101
	11th to 20th	Night	6% 4 2 4 4 4 4 4 6% 9% 53%	4118
	21st to end	Night	11% 5% 2 5% 3 3 3 3 5% 8% 51%	4979
September	1st to 10th	Night	8% 4 1 4 3 3 3 3 4 7% 61%	2150
	11th to 20th	Night	7% 3 2 5% 2 3 3 3 4 7% 60%	2200
	21st to end	Night	7% 4 1 4 3 3 3 3 5% 6% 61%	2200
October	1st to 10th	Night	6% 2 1 3 2 2 2 2 3 4 73%	3590
	11th to 20th	Night	5% 2 1 2 2 2 3 2 4 6% 72%	3857
	21st to end	Night	6% 3 1 3 2 2 2 2 4 6% 68%	4371
November	1st to 10th	Night	7% 4 1 3 2 2 2 3 4 5% 66%	2665
	11th to 20th	Night	6% 4 1 4 3 3 2 3 5% 6% 64%	2730
	21st to end	Night	10% 6% 2 4 3 3 3 3 5% 6% 58%	2730
December	1st to 10th	Night	4 5% 2 4 3 2 3 2 3 5% 67%	4380
	11th to 20th	Night	6% 4 2 4 3 3 3 3 5% 6% 63%	4946
	21st to end	Night	12% 10% 4 7% 3 3 3 2 4 5% 46%	6633

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	35% 4 9% 27% 21% 4	5290
	11th to 20th	Day	30% 5% 9% 27% 22% 7%	5310
	21st to end	Day	35% 3 9% 24% 26% 3	5812
February	1st to 10th	Day	36% 4 13% 26% 15% 6%	1990
	11th to 20th	Day	31% 5% 15% 26% 17% 7%	2059
	21st to end	Day	25% 3 10% 26% 27% 9%	1730
March	1st to 10th	Day	27% 3 8% 17% 29% 16%	4730
	11th to 20th	Day	24% 4 8% 18% 32% 14%	5090
	21st to end	Day	29% 6% 13% 37% 13% 2	5585
April	1st to 10th	Day	30% 4 10% 25% 22% 7%	2383
	11th to 20th	Day	34% 6% 9% 26% 18% 7%	2571
	21st to end	Day	39% 5% 10% 27% 17% 2	2730
May	1st to 10th	Day	37% 6% 10% 22% 19% 5%	7655
	11th to 20th	Day	23% 6% 11% 26% 25% 9%	7631
	21st to end	Day	43% 6% 10% 20% 17% 3	8405
June	1st to 10th	Day	26% 6% 17% 31% 16% 4	2730
	11th to 20th	Day	25% 7% 13% 27% 23% 6%	2730
	21st to end	Day	24% 7% 12% 25% 25% 7%	2730
July	1st to 10th	Day	24% 6% 12% 26% 29% 3	7616
	11th to 20th	Day	22% 6% 13% 28% 22% 9%	7611
	21st to end	Day	25% 6% 12% 34% 21% 3	8155
August	1st to 10th	Day	30% 6% 15% 25% 21% 4	4350
	11th to 20th	Day	29% 6% 14% 28% 20% 4	4340
	21st to end	Day	23% 6% 12% 31% 22% 6%	4493
September	1st to 10th	Day	28% 5% 8% 26% 22% 11%	2250
	11th to 20th	Day	26% 5% 9% 28% 27% 5%	2200
	21st to end	Day	26% 5% 10% 26% 25% 8%	2200
October	1st to 10th	Day	17% 3 5% 21% 42% 12%	3590
	11th to 20th	Day	18% 3 10% 30% 28% 10%	3247
	21st to end	Day	23% 3 8% 24% 34% 10%	3418
November	1st to 10th	Day	22% 3 9% 29% 29% 7%	1853
	11th to 20th	Day	25% 3 9% 28% 28% 8%	1890
	21st to end	Day	27% 3 8% 28% 27% 6%	1890
December	1st to 10th	Day	18% 3 8% 39% 27% 4	3030
	11th to 20th	Day	22% 3 7% 38% 27% 3	3479
	21st to end	Day	41% 5% 8% 29% 15% 3	4587
January	1st to 10th	Night	38% 4 9% 24% 20% 4	7635
	11th to 20th	Night	25% 4 10% 26% 26% 8%	7680
	21st to end	Night	36% 3 9% 23% 23% 6%	8402
February	1st to 10th	Night	37% 4 11% 24% 17% 7%	2647
	11th to 20th	Night	35% 5% 12% 24% 19% 6%	2458
	21st to end	Night	27% 3 8% 22% 28% 13%	2076
March	1st to 10th	Night	22% 3 6% 22% 29% 17%	5357
	11th to 20th	Night	23% 5% 8% 18% 29% 17%	5090
	21st to end	Night	31% 5% 16% 34% 13% 2	5588
April	1st to 10th	Night	28% 5% 12% 22% 26% 6%	2233
	11th to 20th	Night	31% 5% 12% 25% 20% 7%	2000
	21st to end	Night	34% 5% 13% 24% 20% 3	1890
May	1st to 10th	Night	35% 6% 12% 23% 18% 6%	5293
	11th to 20th	Night	23% 6% 11% 27% 23% 10%	5266
	21st to end	Night	37% 6% 14% 23% 16% 4	5805
June	1st to 10th	Night	22% 7% 19% 30% 18% 4	1890
	11th to 20th	Night	22% 6% 15% 31% 21% 5%	1890
	21st to end	Night	22% 6% 13% 27% 24% 8%	1890
July	1st to 10th	Night	25% 6% 18% 26% 23% 2	5265
	11th to 20th	Night	21% 5% 13% 30% 22% 9%	5256
	21st to end	Night	26% 6% 11% 34% 21% 2	5641
August	1st to 10th	Night	26% 5% 13% 28% 23% 5%	3006
	11th to 20th	Night	29% 7% 14% 26% 21% 3	3005
	21st to end	Night	21% 4 14% 36% 19% 5%	3609
September	1st to 10th	Night	25% 5% 12% 23% 25% 11%	2150
	11th to 20th	Night	25% 5% 10% 24% 29% 6%	2200
	21st to end	Night	24% 5% 9% 23% 29% 10%	2200
October	1st to 10th	Night	17% 3 6% 17% 47% 11%	3590
	11th to 20th	Night	15% 3 9% 27% 32% 14%	3857
	21st to end	Night	19% 2 7% 26% 36% 10%	4371
November	1st to 10th	Night	21% 3 9% 27% 28% 11%	2665
	11th to 20th	Night	22% 3 8% 28% 30% 9%	2730
	21st to end	Night	28% 4 8% 28% 23% 9%	2730
December	1st to 10th	Night	22% 3 9% 40% 23% 4	4380
	11th to 20th	Night	24% 3 7% 35% 25% 7%	4947
	21st to end	Night	39% 4 9% 29% 14% 4	6633

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	11% 11% 39% 28% 11% 1	330
	11th to 20th	Day	12% 15% 42% 23% 6% 1	330
	21st to end	Day	10% 11% 50% 24% 6%	363
February	1st to 10th	Day	13% 17% 45% 21% 4 1	330
	11th to 20th	Day	13% 14% 43% 22% 7% 1	330
	21st to end	Day	11% 14% 50% 22% 3	273
March	1st to 10th	Day	13% 15% 41% 24% 6%	330
	11th to 20th	Day	16% 16% 38% 22% 8% 1	330
	21st to end	Day	16% 14% 45% 20% 4 1	363
April	1st to 10th	Day	14% 18% 37% 26% 5%	403
	11th to 20th	Day	13% 18% 42% 24% 3	609
	21st to end	Day	19% 15% 38% 19% 7% 2	750
May	1st to 10th	Day	14% 9% 37% 30% 9% 1	753
	11th to 20th	Day	15% 9% 31% 25% 16% 3	775
	21st to end	Day	16% 8% 32% 28% 13% 3	844
June	1st to 10th	Day	6% 5% 29% 35% 18% 7%	780
	11th to 20th	Day	6% 7% 32% 37% 17% 2	780
	21st to end	Day	8% 6% 30% 42% 13% 2	780
July	1st to 10th	Day	7% 2 19% 39% 27% 6%	771
	11th to 20th	Day	5% 2 14% 42% 29% 8%	768
	21st to end	Day	7% 2 14% 42% 28% 7%	849
August	1st to 10th	Day	8% 2 20% 42% 24% 5%	776
	11th to 20th	Day	7% 3 17% 44% 26% 4	765
	21st to end	Day	8% 3 16% 42% 24% 7%	667
September	1st to 10th	Day	11% 3 16% 39% 27% 4	380
	11th to 20th	Day	4 3 26% 41% 18% 9%	330
	21st to end	Day	12% 5% 28% 24% 24% 6%	330
October	1st to 10th	Day	14% 7% 30% 25% 18% 5%	330
	11th to 20th	Day	6% 10% 42% 26% 12% 3	330
	21st to end	Day	19% 14% 33% 22% 12% 1	363
November	1st to 10th	Day	12% 15% 33% 28% 10% 2	330
	11th to 20th	Day	13% 12% 38% 25% 10% 2	330
	21st to end	Day	16% 12% 34% 26% 9% 3	330
December	1st to 10th	Day	7% 10% 41% 28% 11% 2	330
	11th to 20th	Day	11% 11% 43% 27% 8% 1	330
	21st to end	Day	16% 14% 41% 23% 6%	363
January	1st to 10th	Night	10% 9% 40% 34% 6%	1050
	11th to 20th	Night	9% 12% 40% 31% 7% 1	1050
	21st to end	Night	9% 9% 46% 31% 4	1155
February	1st to 10th	Night	12% 9% 43% 31% 4	967
	11th to 20th	Night	11% 13% 43% 30% 3	824
	21st to end	Night	9% 13% 45% 29% 4	692
March	1st to 10th	Night	9% 16% 42% 29% 4	781
	11th to 20th	Night	14% 12% 38% 28% 7%	630
	21st to end	Night	17% 13% 42% 24% 4	693
April	1st to 10th	Night	13% 13% 43% 26% 5%	630
	11th to 20th	Night	13% 16% 42% 25% 4	623
	21st to end	Night	18% 12% 37% 26% 6%	630
May	1st to 10th	Night	15% 10% 38% 31% 6%	630
	11th to 20th	Night	12% 9% 33% 34% 11% 1	621
	21st to end	Night	14% 9% 31% 33% 12% 1	683
June	1st to 10th	Night	7% 6% 30% 42% 15% 1	630
	11th to 20th	Night	4 7% 39% 40% 10%	630
	21st to end	Night	7% 4 35% 45% 9%	630
July	1st to 10th	Night	6% 3 23% 48% 19% 1	615
	11th to 20th	Night	3 1 25% 49% 21% 1	612
	21st to end	Night	7% 2 22% 47% 21% 1	690
August	1st to 10th	Night	4 2 22% 52% 19% 1	627
	11th to 20th	Night	8% 2 21% 51% 18%	624
	21st to end	Night	5% 2 21% 47% 24% 1	687
September	1st to 10th	Night	10% 3 24% 46% 16% 2	600
	11th to 20th	Night	9% 3 34% 40% 14% 1	600
	21st to end	Night	8% 6% 30% 40% 15% 1	600
October	1st to 10th	Night	10% 6% 32% 36% 14% 1	600
	11th to 20th	Night	10% 8% 41% 34% 7%	771
	21st to end	Night	13% 9% 35% 31% 11% 1	950
November	1st to 10th	Night	10% 9% 36% 35% 10%	1025
	11th to 20th	Night	8% 10% 42% 32% 8%	1050
	21st to end	Night	13% 10% 34% 33% 10%	1050
December	1st to 10th	Night	9% 10% 39% 36% 7%	1050
	11th to 20th	Night	12% 12% 42% 30% 5%	1050
	21st to end	Night	13% 11% 38% 32% 6%	1155

Page generated at 2026-08-27 03:07:14. Version ac07

Copyright © 2026 Attilla Danko.