Wever
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wever 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	12% 8% 3 8% 5% 4 5% 4 6% 7% 40%	144460
	Night	12% 9% 3 8% 4 4 4 3 5% 7% 42%	138119
Transparency	Day	29% 33% 8% 17% 11% 1	148027
	Night	29% 34% 8% 16% 11% 1	142632
Seeing	Day	16% 9% 28% 27% 15% 5%	18314
	Night	17% 8% 30% 31% 13% 1	28052

By Month

Percentage Cloud Cover SE (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	11% 11% 5% 14% 6% 6% 5% 3 5% 7% 27%	4691
	11th to 20th	Day	7% 8% 4 10% 8% 6% 7% 4 6% 6% 33%	4968
	21st to end	Day	11% 14% 6% 12% 6% 5% 4 3 4 4 31%	5812
February	1st to 10th	Day	13% 12% 5% 10% 7% 4 4 4 5% 7% 30%	1890
	11th to 20th	Day	13% 11% 3 8% 5% 4 5% 4 5% 6% 36%	1926
	21st to end	Day	12% 12% 3 9% 5% 4 3 3 4 6% 37%	1730
March	1st to 10th	Day	18% 10% 3 5% 3 3 3 2 3 5% 45%	4754
	11th to 20th	Day	8% 6% 3 6% 4 4 5% 4 6% 9% 46%	5090
	21st to end	Day	18% 11% 3 9% 5% 4 5% 3 6% 7% 30%	5812
April	1st to 10th	Day	16% 12% 3 6% 5% 3 4 3 4 7% 36%	2520
	11th to 20th	Day	15% 9% 2 7% 5% 4 4 3 5% 6% 39%	2494
	21st to end	Day	19% 8% 3 7% 5% 4 4 3 6% 6% 34%	2520
May	1st to 10th	Day	13% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	7649
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 7% 44%	8222
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 4 6% 7% 37%	9047
June	1st to 10th	Day	7% 5% 3 6% 5% 4 5% 4 7% 8% 46%	2940
	11th to 20th	Day	7% 6% 2 7% 5% 5% 5% 4 6% 8% 47%	2940
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 9% 41%	2940
July	1st to 10th	Day	7% 6% 2 6% 4 5% 5% 5% 7% 10% 43%	8280
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 47%	8280
	21st to end	Day	10% 6% 3 7% 5% 5% 5% 4 7% 11% 38%	8693
August	1st to 10th	Day	7% 4 2 6% 4 4 6% 5% 8% 10% 45%	4364
	11th to 20th	Day	10% 6% 2 8% 5% 5% 4 4 7% 9% 40%	4132
	21st to end	Day	6% 5% 2 6% 4 4 4 4 5% 9% 51%	4420
September	1st to 10th	Day	10% 4 2 5% 4 3 4 4 6% 7% 51%	2400
	11th to 20th	Day	9% 4 1 4 3 4 3 4 6% 8% 52%	2400
	21st to end	Day	9% 6% 2 5% 4 4 4 5% 5% 7% 50%	2134
October	1st to 10th	Day	13% 6% 2 5% 3 3 4 3 4 5% 51%	2000
	11th to 20th	Day	15% 8% 2 6% 3 3 4 2 4 6% 46%	2000
	21st to end	Day	18% 8% 3 6% 3 3 4 3 4 6% 42%	2174
November	1st to 10th	Day	12% 7% 2 6% 4 3 4 4 5% 8% 47%	1852
	11th to 20th	Day	16% 10% 3 7% 4 3 4 3 5% 6% 40%	1858
	21st to end	Day	16% 12% 3 8% 5% 3 3 3 4 7% 37%	1680
December	1st to 10th	Day	8% 8% 3 8% 4 4 3 2 5% 6% 48%	2690
	11th to 20th	Day	15% 11% 4 14% 5% 4 5% 3 5% 6% 29%	3088
	21st to end	Day	23% 21% 7% 12% 4 4 3 2 3 4 16%	4070
January	1st to 10th	Night	12% 12% 7% 11% 5% 4 4 3 4 5% 32%	8232
	11th to 20th	Night	9% 11% 4 12% 7% 6% 6% 4 6% 5% 31%	8006
	21st to end	Night	12% 13% 4 11% 5% 4 4 3 4 6% 34%	8402
February	1st to 10th	Night	13% 12% 4 8% 6% 4 4 3 4 6% 36%	2730
	11th to 20th	Night	13% 11% 4 7% 4 4 4 4 5% 7% 38%	2579
	21st to end	Night	13% 10% 3 8% 5% 3 3 2 4 5% 43%	2076
March	1st to 10th	Night	18% 10% 3 6% 4 3 4 2 3 5% 42%	5363
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 4 7% 51%	5090
	21st to end	Night	15% 12% 5% 9% 5% 4 4 4 5% 6% 31%	5359
April	1st to 10th	Night	15% 9% 3 6% 5% 4 3 4 5% 7% 40%	2100
	11th to 20th	Night	15% 8% 2 7% 3 3 3 4 5% 7% 42%	2075
	21st to end	Night	17% 7% 2 7% 5% 5% 4 4 4 7% 39%	2100
May	1st to 10th	Night	15% 7% 2 7% 4 4 4 4 6% 7% 40%	5220
	11th to 20th	Night	11% 5% 2 6% 3 4 5% 4 7% 9% 44%	4670
	21st to end	Night	14% 7% 3 6% 4 4 4 3 6% 7% 40%	5139
June	1st to 10th	Night	8% 4 1 5% 4 4 4 4 6% 8% 51%	1680
	11th to 20th	Night	8% 6% 2 4 3 4 3 4 7% 10% 49%	1680
	21st to end	Night	8% 5% 2 6% 4 4 4 4 6% 9% 47%	1680
July	1st to 10th	Night	8% 4 2 5% 4 4 4 4 8% 10% 47%	4708
	11th to 20th	Night	6% 5% 2 6% 3 4 4 4 6% 8% 52%	4707
	21st to end	Night	9% 6% 3 6% 4 4 4 4 6% 9% 46%	5410
August	1st to 10th	Night	5% 3 1 4 3 4 4 4 6% 9% 57%	3016
	11th to 20th	Night	7% 5% 1 5% 4 4 4 3 5% 7% 54%	3141
	21st to end	Night	4 4 1 5% 4 4 4 4 6% 9% 56%	3676
September	1st to 10th	Night	10% 4 2 4 2 3 3 3 5% 7% 58%	2000
	11th to 20th	Night	8% 4 1 6% 3 4 5% 3 4 7% 53%	2000
	21st to end	Night	8% 4 2 6% 4 4 4 4 5% 8% 52%	2243
October	1st to 10th	Night	10% 5% 2 5% 3 4 3 2 5% 6% 55%	2400
	11th to 20th	Night	14% 5% 2 6% 3 3 3 2 5% 6% 51%	2400
	21st to end	Night	16% 8% 3 7% 4 4 3 3 5% 5% 42%	2665
November	1st to 10th	Night	12% 6% 2 5% 2 3 4 3 4 6% 54%	2666
	11th to 20th	Night	13% 9% 3 6% 3 3 4 4 6% 7% 42%	2757
	21st to end	Night	16% 10% 3 8% 4 4 4 3 4 5% 39%	2940
December	1st to 10th	Night	8% 9% 4 8% 4 4 4 3 5% 6% 47%	4720
	11th to 20th	Night	15% 9% 4 11% 5% 4 4 3 5% 6% 34%	5339
	21st to end	Night	22% 18% 7% 10% 5% 4 4 3 4 4 19%	7150

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	47% 22% 12% 13% 6% 1	4692
	11th to 20th	Day	39% 21% 6% 18% 14% 3	4968
	21st to end	Day	46% 22% 7% 19% 5% 1	5812
February	1st to 10th	Day	23% 58% 7% 8% 4	1890
	11th to 20th	Day	22% 58% 4 10% 5% 1	1935
	21st to end	Day	18% 59% 4 11% 7% 1	1730
March	1st to 10th	Day	32% 28% 5% 18% 15% 2	4754
	11th to 20th	Day	21% 29% 7% 27% 16% 1	5090
	21st to end	Day	39% 29% 12% 16% 4	5814
April	1st to 10th	Day	24% 59% 5% 8% 4	2520
	11th to 20th	Day	19% 59% 6% 9% 6% 1	2494
	21st to end	Day	21% 59% 5% 9% 6% 1	2520
May	1st to 10th	Day	35% 23% 7% 17% 16% 1	7685
	11th to 20th	Day	31% 22% 10% 23% 11% 3	8226
	21st to end	Day	37% 22% 7% 19% 14% 1	9061
June	1st to 10th	Day	12% 59% 6% 12% 9% 2	2940
	11th to 20th	Day	16% 59% 5% 11% 8% 1	2940
	21st to end	Day	16% 59% 8% 12% 5%	2940
July	1st to 10th	Day	32% 20% 12% 23% 13% 1	8211
	11th to 20th	Day	29% 20% 12% 24% 14% 1	8205
	21st to end	Day	34% 20% 17% 23% 6%	8503
August	1st to 10th	Day	22% 35% 12% 23% 8%	4350
	11th to 20th	Day	29% 35% 9% 20% 7%	4171
	21st to end	Day	21% 35% 12% 22% 8% 1	4419
September	1st to 10th	Day	12% 58% 6% 13% 11% 1	2400
	11th to 20th	Day	12% 57% 6% 14% 8% 3	2400
	21st to end	Day	16% 58% 5% 13% 9% 1	2134
October	1st to 10th	Day	14% 35% 2 9% 39% 2	3260
	11th to 20th	Day	12% 35% 6% 15% 26% 6%	3240
	21st to end	Day	26% 35% 5% 19% 14% 2	3488
November	1st to 10th	Day	18% 54% 8% 11% 8% 1	1852
	11th to 20th	Day	20% 53% 4 12% 9% 1	1858
	21st to end	Day	25% 53% 6% 11% 4	1680
December	1st to 10th	Day	21% 34% 11% 25% 9%	2690
	11th to 20th	Day	40% 30% 8% 14% 8% 1	3085
	21st to end	Day	60% 26% 7% 5% 2	4070
January	1st to 10th	Night	45% 21% 14% 16% 4	8233
	11th to 20th	Night	45% 20% 7% 13% 13% 2	8006
	21st to end	Night	42% 21% 9% 17% 10% 1	8402
February	1st to 10th	Night	20% 59% 6% 10% 5%	2730
	11th to 20th	Night	20% 58% 4 11% 6%	2580
	21st to end	Night	17% 59% 3 10% 9% 1	2076
March	1st to 10th	Night	36% 29% 3 18% 13% 2	5363
	11th to 20th	Night	23% 28% 5% 25% 16% 5%	5090
	21st to end	Night	38% 30% 11% 14% 6% 1	5359
April	1st to 10th	Night	20% 59% 4 11% 4 1	2100
	11th to 20th	Night	16% 60% 7% 10% 7% 1	2075
	21st to end	Night	19% 59% 5% 8% 7% 2	2100
May	1st to 10th	Night	34% 23% 7% 19% 15% 2	5249
	11th to 20th	Night	28% 23% 14% 20% 12% 4	4671
	21st to end	Night	34% 22% 7% 17% 18% 1	5149
June	1st to 10th	Night	12% 59% 6% 12% 9% 2	1680
	11th to 20th	Night	14% 59% 4 12% 9% 1	1680
	21st to end	Night	13% 59% 7% 13% 7% 1	1680
July	1st to 10th	Night	28% 19% 14% 22% 15% 1	4670
	11th to 20th	Night	27% 20% 10% 24% 18% 1	4662
	21st to end	Night	31% 19% 16% 24% 9% 1	5290
August	1st to 10th	Night	16% 35% 14% 22% 13% 1	3006
	11th to 20th	Night	21% 35% 11% 23% 10% 1	3168
	21st to end	Night	19% 35% 12% 23% 9% 1	3676
September	1st to 10th	Night	10% 57% 6% 14% 12% 2	2000
	11th to 20th	Night	12% 58% 5% 13% 9% 4	2000
	21st to end	Night	15% 57% 5% 11% 11% 1	2243
October	1st to 10th	Night	14% 35% 2 14% 32% 2	3920
	11th to 20th	Night	12% 35% 6% 15% 28% 4	3899
	21st to end	Night	29% 35% 4 14% 15% 3	4301
November	1st to 10th	Night	18% 53% 5% 13% 9% 2	2666
	11th to 20th	Night	19% 54% 5% 11% 10% 1	2757
	21st to end	Night	24% 54% 5% 11% 6%	2940
December	1st to 10th	Night	24% 34% 7% 26% 9%	4720
	11th to 20th	Night	36% 31% 8% 17% 8% 1	5341
	21st to end	Night	56% 25% 7% 8% 3	7150

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	21% 13% 34% 23% 8%	330
	11th to 20th	Day	20% 22% 40% 17% 2	330
	21st to end	Day	22% 15% 37% 21% 4	363
February	1st to 10th	Day	21% 14% 39% 22% 4	330
	11th to 20th	Day	25% 18% 31% 19% 6% 1	330
	21st to end	Day	21% 15% 45% 17% 3	273
March	1st to 10th	Day	20% 18% 40% 19% 3	330
	11th to 20th	Day	23% 17% 32% 22% 5% 1	330
	21st to end	Day	33% 14% 32% 16% 3 1	463
April	1st to 10th	Day	23% 16% 35% 19% 6% 1	540
	11th to 20th	Day	20% 16% 34% 18% 10% 1	532
	21st to end	Day	24% 10% 33% 22% 9% 1	540
May	1st to 10th	Day	20% 9% 34% 26% 9% 2	675
	11th to 20th	Day	19% 12% 29% 25% 13% 2	775
	21st to end	Day	16% 7% 29% 29% 14% 6%	844
June	1st to 10th	Day	9% 5% 25% 31% 22% 7%	780
	11th to 20th	Day	9% 4 29% 34% 20% 4	780
	21st to end	Day	12% 8% 30% 32% 14% 4	780
July	1st to 10th	Day	11% 2 16% 32% 27% 12%	771
	11th to 20th	Day	10% 3 20% 34% 25% 8%	768
	21st to end	Day	9% 2 17% 38% 27% 7%	849
August	1st to 10th	Day	9% 2 18% 36% 24% 10%	776
	11th to 20th	Day	10% 4 15% 32% 29% 10%	661
	21st to end	Day	7% 2 16% 32% 32% 11%	619
September	1st to 10th	Day	12% 4 17% 31% 27% 9%	530
	11th to 20th	Day	9% 2 15% 38% 26% 10%	530
	21st to end	Day	12% 7% 25% 24% 24% 9%	449
October	1st to 10th	Day	18% 4 26% 30% 14% 8%	330
	11th to 20th	Day	17% 18% 31% 23% 10% 1	330
	21st to end	Day	29% 13% 33% 20% 5% 1	363
November	1st to 10th	Day	15% 10% 39% 25% 8% 3	330
	11th to 20th	Day	22% 13% 35% 21% 8% 2	330
	21st to end	Day	26% 10% 34% 23% 5%	330
December	1st to 10th	Day	17% 12% 40% 23% 6% 2	330
	11th to 20th	Day	22% 13% 38% 21% 7%	330
	21st to end	Day	28% 17% 36% 15% 3	363
January	1st to 10th	Night	17% 12% 39% 25% 6%	1050
	11th to 20th	Night	18% 14% 40% 22% 6%	1050
	21st to end	Night	19% 14% 36% 26% 4	1155
February	1st to 10th	Night	21% 11% 39% 25% 4	1050
	11th to 20th	Night	19% 14% 36% 28% 3	945
	21st to end	Night	19% 14% 41% 23% 3	692
March	1st to 10th	Night	20% 12% 38% 25% 5%	788
	11th to 20th	Night	20% 10% 35% 28% 7%	630
	21st to end	Night	23% 12% 34% 25% 5%	693
April	1st to 10th	Night	21% 12% 38% 24% 5%	630
	11th to 20th	Night	19% 11% 34% 29% 7%	623
	21st to end	Night	21% 9% 33% 30% 7%	630
May	1st to 10th	Night	18% 6% 39% 29% 8% 1	630
	11th to 20th	Night	17% 7% 26% 37% 12%	621
	21st to end	Night	14% 4 26% 36% 18% 1	683
June	1st to 10th	Night	10% 2 22% 45% 19% 2	630
	11th to 20th	Night	9% 3 25% 42% 20%	630
	21st to end	Night	11% 3 27% 40% 19% 1	630
July	1st to 10th	Night	9% 1 12% 41% 33% 3	615
	11th to 20th	Night	6% 2 16% 45% 29% 3	612
	21st to end	Night	9% 2 12% 45% 31% 1	690
August	1st to 10th	Night	8% 2 12% 43% 31% 4	627
	11th to 20th	Night	8% 3 11% 40% 34% 4	624
	21st to end	Night	7% 1 12% 42% 35% 2	687
September	1st to 10th	Night	13% 2 17% 38% 28% 3	600
	11th to 20th	Night	11% 2 18% 35% 31% 4	600
	21st to end	Night	9% 5% 24% 33% 25% 3	765
October	1st to 10th	Night	12% 6% 26% 33% 21% 2	800
	11th to 20th	Night	17% 9% 32% 32% 11%	800
	21st to end	Night	21% 10% 35% 28% 6%	880
November	1st to 10th	Night	14% 9% 39% 29% 8% 1	820
	11th to 20th	Night	19% 12% 38% 25% 6% 1	867
	21st to end	Night	22% 10% 35% 25% 7%	1050
December	1st to 10th	Night	19% 11% 39% 26% 4 1	1050
	11th to 20th	Night	23% 9% 34% 27% 6%	1050
	21st to end	Night	29% 13% 32% 24% 3	1155

Page generated at 2026-08-27 03:07:10. Version ac07

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