Sky Retreat at Westwater
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sky Retreat at Westwater clear sky chart from 2005-11-06 to 2026-03-18.

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	3 4 2 4 3 3 4 4 6% 8% 60%	140053
	Night	3 5% 2 5% 4 4 4 4 6% 8% 56%	138976
Transparency	Day	20% 6% 12% 21% 24% 17%	134897
	Night	24% 7% 12% 23% 21% 13%	135137
Seeing	Day	5% 7% 21% 34% 26% 7%	17035
	Night	6% 3 18% 44% 26% 3	27368

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	3 6% 3 8% 5% 5% 5% 5% 8% 10% 42%	5318
	11th to 20th	Day	2 3 1 5% 4 3 3 4 6% 10% 58%	5340
	21st to end	Day	4 6% 2 6% 3 3 3 3 5% 6% 58%	5844
February	1st to 10th	Day	2 6% 3 7% 4 4 5% 4 8% 11% 46%	1890
	11th to 20th	Day	4 8% 2 7% 5% 4 5% 5% 6% 10% 44%	1845
	21st to end	Day	4 6% 3 6% 5% 3 4 4 5% 8% 51%	1755
March	1st to 10th	Day	2 6% 2 7% 5% 4 5% 3 5% 7% 54%	5064
	11th to 20th	Day	3 7% 3 9% 5% 5% 5% 5% 7% 8% 44%	5078
	21st to end	Day	4 5% 2 6% 5% 6% 6% 6% 7% 8% 45%	5486
April	1st to 10th	Day	4 6% 2 5% 4 3 3 3 5% 8% 57%	2340
	11th to 20th	Day	3 4 2 5% 4 4 5% 4 6% 9% 55%	2371
	21st to end	Day	2 4 1 5% 4 4 4 4 6% 9% 57%	2500
May	1st to 10th	Day	4 4 2 5% 4 4 5% 4 6% 8% 55%	5880
	11th to 20th	Day	2 2 1 5% 4 4 4 4 7% 8% 59%	5841
	21st to end	Day	2 3 1 3 2 3 4 3 5% 7% 65%	6761
June	1st to 10th	Day	2 3 1 3 2 3 3 3 6% 8% 66%	2800
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 6% 73%	2800
	21st to end	Day	1 2 1 3 2 2 2 2 5% 7% 73%	2800
July	1st to 10th	Day	1 1 1 3 2 2 2 3 4 5% 75%	6068
	11th to 20th	Day	1 2 1 3 2 3 4 4 8% 12% 59%	5880
	21st to end	Day	1 1 1 2 2 3 4 4 6% 8% 67%	6401
August	1st to 10th	Day	1 1 1 3 3 3 4 4 7% 11% 61%	5779
	11th to 20th	Day	1 2 1 3 2 3 3 3 5% 9% 69%	5798
	21st to end	Day	4 3 1 4 3 3 4 4 6% 9% 57%	6038
September	1st to 10th	Day	4 2 1 3 2 2 3 3 5% 6% 69%	2400
	11th to 20th	Day	2 3 1 3 3 3 3 3 5% 6% 69%	2265
	21st to end	Day	3 2 2 3 2 2 3 2 3 5% 73%	2179
October	1st to 10th	Day	3 2 1 2 1 2 2 2 3 3 78%	3270
	11th to 20th	Day	3 3 1 3 3 3 4 4 7% 10% 59%	3250
	21st to end	Day	3 3 1 3 2 2 3 3 6% 5% 68%	3548
November	1st to 10th	Day	3 4 1 4 2 3 2 3 5% 7% 66%	2059
	11th to 20th	Day	3 5% 1 4 3 3 3 3 5% 6% 65%	1780
	21st to end	Day	4 4 1 5% 4 3 3 3 6% 7% 59%	1680
December	1st to 10th	Day	2 4 2 4 2 2 3 3 5% 13% 58%	2700
	11th to 20th	Day	3 4 2 5% 5% 3 5% 4 7% 12% 51%	3106
	21st to end	Day	5% 9% 3 6% 4 5% 5% 4 6% 10% 43%	4139
January	1st to 10th	Night	2 8% 3 9% 5% 5% 5% 4 6% 7% 45%	7605
	11th to 20th	Night	3 4 2 5% 3 3 3 3 5% 8% 61%	7650
	21st to end	Night	4 8% 3 6% 3 3 4 3 4 6% 56%	8370
February	1st to 10th	Night	3 6% 3 5% 5% 4 5% 5% 7% 10% 48%	2730
	11th to 20th	Night	5% 8% 3 7% 5% 5% 5% 4 6% 6% 45%	2662
	21st to end	Night	4 7% 3 6% 4 4 4 3 6% 9% 50%	2045
March	1st to 10th	Night	4 7% 2 7% 5% 4 5% 3 4 6% 52%	5050
	11th to 20th	Night	4 7% 3 7% 4 4 4 4 6% 9% 47%	5077
	21st to end	Night	6% 8% 3 7% 5% 5% 5% 4 6% 7% 44%	5489
April	1st to 10th	Night	5% 6% 2 6% 4 4 5% 4 6% 6% 53%	2060
	11th to 20th	Night	5% 6% 2 5% 4 5% 5% 4 6% 7% 52%	1977
	21st to end	Night	6% 6% 2 6% 5% 4 3 4 6% 8% 51%	1895
May	1st to 10th	Night	6% 6% 2 6% 4 5% 4 4 6% 8% 48%	4100
	11th to 20th	Night	3 4 2 5% 4 5% 4 4 7% 7% 54%	4074
	21st to end	Night	5% 3 2 3 3 3 3 3 6% 8% 61%	4118
June	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 8% 62%	1600
	11th to 20th	Night	4 3 1 4 3 3 3 3 5% 6% 65%	1600
	21st to end	Night	2 2 1 4 3 3 4 4 4 7% 69%	1600
July	1st to 10th	Night	1 2 1 3 3 3 5% 4 5% 7% 66%	3905
	11th to 20th	Night	1 2 1 5% 4 5% 6% 6% 9% 12% 49%	4100
	21st to end	Night	1 2 1 3 3 4 5% 4 6% 10% 61%	4472
August	1st to 10th	Night	2 2 1 5% 3 5% 5% 5% 9% 11% 52%	4033
	11th to 20th	Night	2 3 1 4 3 4 4 4 6% 7% 63%	4051
	21st to end	Night	3 3 2 6% 4 5% 6% 5% 7% 7% 52%	4939
September	1st to 10th	Night	4 2 1 4 3 2 3 3 5% 8% 65%	2000
	11th to 20th	Night	3 2 1 3 3 4 3 4 5% 6% 68%	2130
	21st to end	Night	3 3 1 3 3 2 3 3 4 5% 71%	2220
October	1st to 10th	Night	3 2 1 3 2 1 2 2 4 5% 75%	3920
	11th to 20th	Night	3 3 1 4 3 3 4 3 6% 8% 60%	3898
	21st to end	Night	4 5% 2 4 3 3 3 2 3 5% 66%	4252
November	1st to 10th	Night	3 3 1 4 2 3 3 3 5% 6% 68%	2460
	11th to 20th	Night	3 4 1 4 2 3 3 3 4 6% 66%	2813
	21st to end	Night	5% 6% 2 4 4 3 3 4 4 7% 58%	2940
December	1st to 10th	Night	3 4 1 4 2 2 3 3 4 9% 63%	4710
	11th to 20th	Night	3 5% 2 5% 4 4 4 4 6% 9% 54%	5321
	21st to end	Night	5% 8% 3 7% 4 4 5% 4 7% 7% 46%	7110

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	33% 11% 23% 23% 9% 1	5321
	11th to 20th	Day	18% 10% 20% 30% 17% 4	5340
	21st to end	Day	26% 8% 16% 28% 18% 4	5844
February	1st to 10th	Day	29% 8% 22% 25% 12% 3	1890
	11th to 20th	Day	34% 8% 16% 26% 14% 3	1854
	21st to end	Day	28% 7% 12% 28% 20% 4	1755
March	1st to 10th	Day	26% 7% 10% 23% 27% 7%	5064
	11th to 20th	Day	32% 8% 14% 25% 18% 3	5078
	21st to end	Day	31% 10% 13% 27% 17% 3	5486
April	1st to 10th	Day	24% 5% 11% 24% 24% 11%	2340
	11th to 20th	Day	23% 6% 13% 23% 24% 11%	2374
	21st to end	Day	20% 7% 11% 23% 30% 9%	2500
May	1st to 10th	Day	22% 7% 12% 18% 30% 11%	5880
	11th to 20th	Day	17% 6% 8% 21% 32% 15%	5844
	21st to end	Day	14% 5% 7% 16% 41% 17%	6762
June	1st to 10th	Day	14% 4 7% 18% 32% 25%	2800
	11th to 20th	Day	12% 3 6% 10% 24% 45%	2800
	21st to end	Day	11% 3 5% 11% 23% 47%	2800
July	1st to 10th	Day	11% 3 5% 8% 13% 60%	6005
	11th to 20th	Day	14% 4 7% 15% 29% 31%	5811
	21st to end	Day	12% 5% 7% 15% 26% 35%	6217
August	1st to 10th	Day	17% 6% 11% 23% 20% 21%	4208
	11th to 20th	Day	17% 5% 11% 19% 24% 24%	4197
	21st to end	Day	19% 5% 8% 20% 25% 23%	4353
September	1st to 10th	Day	16% 4 8% 15% 25% 33%	2400
	11th to 20th	Day	15% 6% 9% 17% 26% 27%	2265
	21st to end	Day	16% 3 7% 15% 36% 24%	2179
October	1st to 10th	Day	12% 3 6% 14% 32% 33%	3270
	11th to 20th	Day	19% 5% 8% 27% 33% 9%	3250
	21st to end	Day	16% 5% 12% 31% 30% 6%	3548
November	1st to 10th	Day	18% 4 11% 29% 31% 6%	2059
	11th to 20th	Day	19% 4 13% 36% 24% 3	1780
	21st to end	Day	25% 4 17% 33% 19% 2	1680
December	1st to 10th	Day	19% 10% 23% 34% 13% 1	2700
	11th to 20th	Day	25% 9% 28% 31% 7%	3104
	21st to end	Day	34% 11% 18% 20% 16% 1	4139
January	1st to 10th	Night	35% 8% 22% 24% 9% 2	7605
	11th to 20th	Night	20% 11% 15% 34% 18% 2	7650
	21st to end	Night	29% 6% 17% 24% 20% 4	8370
February	1st to 10th	Night	28% 11% 20% 26% 12% 3	2730
	11th to 20th	Night	34% 9% 14% 24% 16% 3	2663
	21st to end	Night	29% 7% 13% 27% 19% 4	2045
March	1st to 10th	Night	30% 6% 8% 22% 26% 7%	5050
	11th to 20th	Night	29% 8% 12% 26% 20% 5%	5077
	21st to end	Night	33% 9% 11% 26% 19% 2	5489
April	1st to 10th	Night	28% 6% 9% 21% 24% 11%	2060
	11th to 20th	Night	27% 6% 10% 21% 23% 13%	1977
	21st to end	Night	27% 6% 10% 20% 27% 9%	1895
May	1st to 10th	Night	27% 9% 11% 15% 28% 10%	4097
	11th to 20th	Night	22% 7% 9% 21% 30% 11%	4075
	21st to end	Night	17% 5% 6% 17% 38% 16%	4118
June	1st to 10th	Night	17% 5% 8% 15% 29% 26%	1600
	11th to 20th	Night	17% 6% 8% 9% 17% 42%	1600
	21st to end	Night	14% 4 5% 11% 20% 45%	1600
July	1st to 10th	Night	16% 4 6% 7% 11% 55%	3860
	11th to 20th	Night	21% 7% 7% 14% 24% 28%	4046
	21st to end	Night	15% 6% 8% 13% 23% 35%	4344
August	1st to 10th	Night	25% 9% 11% 19% 15% 21%	2928
	11th to 20th	Night	23% 7% 12% 14% 19% 26%	2928
	21st to end	Night	22% 7% 9% 16% 21% 25%	3555
September	1st to 10th	Night	17% 4 9% 15% 19% 36%	2000
	11th to 20th	Night	17% 5% 9% 18% 22% 30%	2130
	21st to end	Night	17% 4 6% 13% 30% 31%	2220
October	1st to 10th	Night	12% 3 5% 13% 28% 38%	3920
	11th to 20th	Night	21% 5% 8% 19% 35% 11%	3898
	21st to end	Night	21% 4 6% 33% 30% 6%	4252
November	1st to 10th	Night	18% 4 9% 26% 33% 10%	2460
	11th to 20th	Night	18% 5% 10% 35% 29% 4	2813
	21st to end	Night	25% 6% 11% 28% 24% 5%	2940
December	1st to 10th	Night	19% 7% 20% 36% 16% 1	4710
	11th to 20th	Night	25% 8% 22% 36% 7%	5322
	21st to end	Night	32% 11% 17% 25% 14% 1	7110

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	9% 4 22% 39% 19% 6%	330
	11th to 20th	Day	6% 4 23% 40% 22% 5%	330
	21st to end	Day	7% 1 15% 47% 25% 6%	363
February	1st to 10th	Day	6% 5% 26% 43% 16% 5%	330
	11th to 20th	Day	9% 6% 27% 41% 15% 2	330
	21st to end	Day	5% 10% 27% 38% 17% 4	362
March	1st to 10th	Day	8% 9% 25% 35% 19% 3	540
	11th to 20th	Day	7% 13% 25% 33% 19% 3	529
	21st to end	Day	8% 12% 34% 31% 13% 2	550
April	1st to 10th	Day	7% 13% 25% 34% 15% 6%	500
	11th to 20th	Day	9% 16% 31% 29% 12% 2	492
	21st to end	Day	5% 15% 31% 27% 20% 1	500
May	1st to 10th	Day	6% 13% 32% 29% 17% 4	503
	11th to 20th	Day	5% 11% 25% 33% 20% 6%	528
	21st to end	Day	4 11% 22% 31% 27% 6%	716
June	1st to 10th	Day	3 6% 18% 38% 30% 6%	730
	11th to 20th	Day	3 7% 25% 34% 26% 4	730
	21st to end	Day	3 6% 20% 37% 30% 4	730
July	1st to 10th	Day	1 3 16% 33% 39% 8%	611
	11th to 20th	Day	3 1 14% 31% 37% 13%	524
	21st to end	Day	3 2 10% 35% 39% 11%	575
August	1st to 10th	Day	2 3 16% 35% 34% 9%	527
	11th to 20th	Day	3 2 13% 33% 36% 13%	517
	21st to end	Day	3 2 16% 34% 34% 11%	583
September	1st to 10th	Day	4 2 17% 30% 33% 15%	530
	11th to 20th	Day	3 6% 23% 33% 28% 7%	530
	21st to end	Day	4 8% 18% 28% 32% 10%	509
October	1st to 10th	Day	7% 7% 17% 26% 26% 17%	330
	11th to 20th	Day	4 8% 20% 31% 28% 9%	330
	21st to end	Day	5% 6% 20% 33% 29% 6%	363
November	1st to 10th	Day	4 11% 24% 31% 25% 6%	330
	11th to 20th	Day	2 4 19% 44% 22% 9%	330
	21st to end	Day	6% 5% 22% 35% 26% 7%	330
December	1st to 10th	Day	4 5% 19% 44% 18% 9%	330
	11th to 20th	Day	6% 2 19% 40% 27% 6%	330
	21st to end	Day	10% 10% 19% 42% 16% 4	363
January	1st to 10th	Night	6% 3 17% 45% 25% 4	840
	11th to 20th	Night	5% 4 17% 46% 25% 3	840
	21st to end	Night	7% 3 19% 47% 21% 3	924
February	1st to 10th	Night	6% 3 24% 45% 19% 3	840
	11th to 20th	Night	7% 4 24% 47% 16% 2	824
	21st to end	Night	7% 6% 25% 48% 14% 1	692
March	1st to 10th	Night	7% 6% 23% 46% 17% 1	840
	11th to 20th	Night	5% 5% 21% 46% 21% 2	828
	21st to end	Night	6% 5% 26% 45% 17% 1	880
April	1st to 10th	Night	8% 6% 28% 46% 13% 1	660
	11th to 20th	Night	6% 7% 27% 44% 15% 1	593
	21st to end	Night	8% 7% 28% 34% 21% 2	600
May	1st to 10th	Night	8% 5% 24% 44% 18% 1	600
	11th to 20th	Night	4 4 19% 45% 24% 3	591
	21st to end	Night	5% 6% 21% 38% 27% 3	650
June	1st to 10th	Night	4 2 19% 42% 32% 2	600
	11th to 20th	Night	3 4 24% 45% 22% 2	600
	21st to end	Night	2 3 15% 46% 34% 1	600
July	1st to 10th	Night	2 2 12% 38% 43% 3	585
	11th to 20th	Night	2 1 6% 38% 48% 4	582
	21st to end	Night	2 8% 34% 51% 4	657
August	1st to 10th	Night	5% 2 6% 40% 45% 3	597
	11th to 20th	Night	4 1 10% 42% 41% 3	594
	21st to end	Night	4 1 7% 39% 44% 5%	660
September	1st to 10th	Night	4 1 10% 42% 38% 5%	600
	11th to 20th	Night	3 1 13% 44% 36% 3	730
	21st to end	Night	5% 2 15% 34% 37% 8%	800
October	1st to 10th	Night	6% 3 17% 43% 27% 4	800
	11th to 20th	Night	4 3 18% 43% 29% 4	800
	21st to end	Night	6% 3 19% 42% 28% 3	880
November	1st to 10th	Night	4 3 18% 45% 27% 3	820
	11th to 20th	Night	4 2 21% 49% 21% 4	961
	21st to end	Night	6% 5% 19% 42% 25% 3	1050
December	1st to 10th	Night	7% 3 17% 50% 21% 2	1050
	11th to 20th	Night	9% 2 20% 44% 23% 2	1050
	21st to end	Night	10% 5% 21% 47% 16% 2	1150

Page generated at 2026-03-15 00:23:53. Version ac07

Copyright © 2026 Attilla Danko.