Beaver Dam
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beaver Dam clear sky chart from 2005-11-06 to 2025-12-03.

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% 9% 3 8% 5% 4 4 4 6% 7% 38%	127221
	Night	13% 10% 4 8% 4 4 4 3 5% 6% 39%	123715
Transparency	Day	43% 6% 12% 25% 13% 1	130693
	Night	44% 6% 11% 23% 14% 2	128304
Seeing	Day	16% 10% 29% 26% 15% 5%	17397
	Night	17% 9% 31% 31% 11% 1	27254

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	8% 10% 5% 16% 8% 6% 5% 3 5% 6% 27%	3617
	11th to 20th	Day	8% 11% 7% 11% 6% 4 7% 7% 7% 7% 26%	3620
	21st to end	Day	12% 13% 7% 10% 5% 4 3 3 4 6% 33%	4056
February	1st to 10th	Day	11% 12% 6% 10% 6% 5% 6% 4 5% 6% 30%	1800
	11th to 20th	Day	12% 12% 3 7% 5% 5% 5% 4 5% 7% 36%	1899
	21st to end	Day	10% 13% 4 10% 6% 5% 5% 4 5% 7% 31%	1650
March	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 6% 6% 45%	4480
	11th to 20th	Day	11% 6% 3 7% 5% 4 4 3 6% 7% 44%	4721
	21st to end	Day	23% 11% 4 11% 4 3 4 3 4 5% 28%	5959
April	1st to 10th	Day	17% 14% 4 7% 5% 4 4 3 6% 7% 30%	2400
	11th to 20th	Day	17% 11% 3 7% 5% 5% 4 4 5% 6% 34%	2374
	21st to end	Day	18% 10% 3 6% 5% 5% 5% 3 6% 7% 32%	2508
May	1st to 10th	Day	14% 7% 3 6% 4 4 4 3 5% 7% 43%	6016
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 3 6% 7% 42%	6319
	21st to end	Day	16% 7% 2 6% 4 4 4 3 6% 9% 39%	6935
June	1st to 10th	Day	9% 6% 2 6% 5% 4 5% 4 6% 8% 44%	2800
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 4 6% 8% 41%	2800
	21st to end	Day	11% 6% 2 6% 3 4 5% 4 7% 10% 42%	2800
July	1st to 10th	Day	10% 6% 3 7% 5% 4 5% 4 7% 10% 39%	6360
	11th to 20th	Day	6% 5% 2 5% 4 5% 5% 4 7% 9% 48%	6360
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 7% 10% 43%	6924
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 42%	4563
	11th to 20th	Day	12% 5% 2 6% 3 4 3 3 5% 8% 48%	3942
	21st to end	Day	10% 6% 2 6% 5% 4 4 4 6% 9% 44%	4312
September	1st to 10th	Day	12% 6% 2 5% 4 5% 5% 4 6% 8% 45%	2400
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 8% 50%	2311
	21st to end	Day	11% 8% 2 7% 4 4 5% 4 6% 7% 43%	2200
October	1st to 10th	Day	13% 7% 3 6% 4 4 4 3 4 6% 46%	2076
	11th to 20th	Day	19% 10% 3 6% 5% 4 4 3 6% 7% 32%	1996
	21st to end	Day	17% 10% 3 8% 5% 4 3 4 4 5% 37%	1980
November	1st to 10th	Day	12% 8% 2 7% 5% 5% 4 3 6% 7% 42%	1852
	11th to 20th	Day	12% 12% 4 10% 6% 5% 4 3 5% 7% 31%	1890
	21st to end	Day	16% 12% 4 10% 6% 3 4 2 5% 5% 32%	1685
December	1st to 10th	Day	7% 11% 5% 10% 6% 6% 5% 3 6% 8% 32%	2626
	11th to 20th	Day	13% 17% 5% 11% 6% 4 4 3 5% 7% 24%	3008
	21st to end	Day	19% 21% 7% 14% 5% 5% 4 3 4 5% 13%	3982
January	1st to 10th	Night	9% 12% 6% 12% 6% 4 4 3 4 5% 34%	6348
	11th to 20th	Night	10% 13% 6% 14% 6% 5% 6% 5% 6% 5% 24%	6360
	21st to end	Night	11% 15% 7% 11% 5% 5% 4 3 5% 5% 30%	6904
February	1st to 10th	Night	10% 15% 5% 9% 5% 5% 4 3 5% 6% 33%	2600
	11th to 20th	Night	11% 10% 3 9% 5% 5% 4 4 5% 5% 39%	2386
	21st to end	Night	16% 13% 4 7% 4 4 5% 3 4 5% 35%	1980
March	1st to 10th	Night	15% 8% 2 6% 4 4 4 3 4 5% 44%	5373
	11th to 20th	Night	10% 7% 2 5% 4 3 4 4 6% 9% 46%	5269
	21st to end	Night	20% 12% 4 9% 4 4 4 3 4 5% 31%	4969
April	1st to 10th	Night	18% 11% 3 6% 4 4 4 3 5% 5% 37%	2000
	11th to 20th	Night	19% 9% 3 6% 4 5% 4 3 5% 6% 37%	1975
	21st to end	Night	17% 8% 3 7% 4 4 3 4 5% 7% 39%	1890
May	1st to 10th	Night	16% 8% 3 6% 4 3 4 3 6% 8% 40%	3871
	11th to 20th	Night	10% 5% 2 6% 5% 5% 5% 4 6% 8% 44%	3596
	21st to end	Night	17% 7% 2 6% 4 5% 5% 4 5% 7% 38%	3942
June	1st to 10th	Night	9% 5% 2 5% 4 5% 4 4 7% 8% 47%	1600
	11th to 20th	Night	11% 5% 3 6% 4 4 4 4 5% 10% 45%	1600
	21st to end	Night	10% 5% 2 6% 4 3 4 4 6% 8% 48%	1600
July	1st to 10th	Night	11% 7% 2 6% 3 4 4 4 6% 8% 45%	3618
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 3 5% 8% 54%	3617
	21st to end	Night	6% 4 2 6% 4 4 5% 4 6% 8% 50%	3947
August	1st to 10th	Night	11% 5% 2 5% 4 4 3 4 6% 8% 49%	2597
	11th to 20th	Night	10% 6% 3 7% 3 4 4 4 5% 8% 46%	3104
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 9% 49%	3586
September	1st to 10th	Night	9% 5% 2 5% 3 3 4 4 5% 6% 55%	2000
	11th to 20th	Night	12% 4 2 5% 3 4 4 3 5% 6% 51%	2068
	21st to end	Night	11% 6% 2 6% 3 3 4 4 6% 7% 49%	2200
October	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 5% 6% 49%	2320
	11th to 20th	Night	18% 8% 2 6% 4 3 4 3 5% 6% 40%	2403
	21st to end	Night	19% 10% 2 7% 4 4 4 3 5% 6% 36%	2860
November	1st to 10th	Night	13% 8% 2 7% 4 4 4 3 5% 6% 44%	2666
	11th to 20th	Night	14% 12% 4 8% 6% 4 4 3 5% 6% 33%	2730
	21st to end	Night	15% 12% 3 8% 5% 4 4 3 5% 5% 35%	2932
December	1st to 10th	Night	8% 10% 3 8% 5% 5% 4 4 5% 8% 40%	4609
	11th to 20th	Night	15% 18% 6% 10% 5% 4 4 3 4 4 27%	5199
	21st to end	Night	20% 19% 6% 11% 5% 4 4 3 4 5% 18%	6996

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	57% 6% 13% 17% 6%	3618
	11th to 20th	Day	53% 6% 11% 14% 15% 1	3620
	21st to end	Day	53% 4 11% 20% 12%	4056
February	1st to 10th	Day	54% 5% 13% 18% 9% 1	1800
	11th to 20th	Day	47% 6% 11% 23% 9% 2	1909
	21st to end	Day	53% 6% 11% 18% 10% 2	1650
March	1st to 10th	Day	39% 5% 13% 26% 13% 4	4480
	11th to 20th	Day	39% 5% 13% 28% 14% 1	4721
	21st to end	Day	58% 5% 10% 16% 10% 1	5961
April	1st to 10th	Day	52% 7% 12% 19% 10%	2400
	11th to 20th	Day	49% 7% 11% 20% 12% 2	2374
	21st to end	Day	49% 8% 12% 20% 10% 1	2508
May	1st to 10th	Day	40% 6% 11% 25% 16% 2	6051
	11th to 20th	Day	40% 7% 11% 26% 16% 1	6323
	21st to end	Day	40% 6% 10% 27% 15% 2	6949
June	1st to 10th	Day	36% 8% 13% 27% 15% 1	2800
	11th to 20th	Day	39% 6% 13% 24% 16% 1	2800
	21st to end	Day	36% 9% 15% 24% 14% 2	2800
July	1st to 10th	Day	38% 7% 13% 31% 9% 1	6291
	11th to 20th	Day	31% 7% 14% 33% 15% 1	6285
	21st to end	Day	35% 8% 15% 23% 18% 2	6728
August	1st to 10th	Day	36% 8% 14% 28% 12% 1	4548
	11th to 20th	Day	34% 6% 12% 36% 12% 1	3980
	21st to end	Day	36% 6% 14% 28% 15% 1	4311
September	1st to 10th	Day	37% 8% 12% 25% 17% 1	2400
	11th to 20th	Day	33% 6% 14% 31% 15% 1	2311
	21st to end	Day	39% 5% 11% 30% 14% 1	2200
October	1st to 10th	Day	25% 4 6% 39% 26% 2	3375
	11th to 20th	Day	38% 5% 9% 27% 20% 1	3224
	21st to end	Day	42% 4 11% 28% 13% 1	3180
November	1st to 10th	Day	42% 5% 15% 22% 14% 2	1852
	11th to 20th	Day	52% 6% 12% 20% 9% 1	1890
	21st to end	Day	54% 4 14% 21% 7%	1685
December	1st to 10th	Day	50% 6% 18% 20% 5%	2626
	11th to 20th	Day	59% 5% 10% 18% 7% 1	3005
	21st to end	Day	74% 4 6% 9% 7%	3982
January	1st to 10th	Night	52% 4 8% 24% 11%	6348
	11th to 20th	Night	60% 5% 8% 10% 16% 1	6360
	21st to end	Night	55% 5% 12% 16% 12%	6904
February	1st to 10th	Night	52% 5% 11% 19% 12% 2	2600
	11th to 20th	Night	47% 5% 11% 22% 14% 1	2387
	21st to end	Night	49% 6% 11% 20% 12% 2	1980
March	1st to 10th	Night	42% 4 13% 23% 13% 4	5373
	11th to 20th	Night	34% 5% 13% 30% 14% 4	5269
	21st to end	Night	56% 5% 9% 16% 12% 1	4969
April	1st to 10th	Night	48% 7% 9% 20% 16% 1	2000
	11th to 20th	Night	48% 4 9% 20% 17% 2	1975
	21st to end	Night	44% 7% 12% 22% 13% 2	1890
May	1st to 10th	Night	41% 6% 13% 18% 20% 2	3898
	11th to 20th	Night	35% 9% 16% 21% 17% 2	3597
	21st to end	Night	45% 7% 9% 23% 13% 4	3950
June	1st to 10th	Night	32% 8% 14% 27% 19% 1	1600
	11th to 20th	Night	35% 7% 11% 27% 18% 2	1600
	21st to end	Night	33% 8% 16% 23% 18% 3	1600
July	1st to 10th	Night	36% 6% 13% 31% 10% 3	3580
	11th to 20th	Night	29% 6% 13% 32% 19% 2	3572
	21st to end	Night	30% 8% 15% 23% 22% 2	3832
August	1st to 10th	Night	33% 6% 15% 24% 20% 1	2588
	11th to 20th	Night	35% 7% 12% 31% 14%	3132
	21st to end	Night	31% 6% 14% 27% 19% 3	3586
September	1st to 10th	Night	29% 8% 11% 28% 23% 2	2000
	11th to 20th	Night	33% 6% 10% 31% 18% 1	2068
	21st to end	Night	34% 6% 11% 31% 17% 2	2200
October	1st to 10th	Night	26% 4 6% 38% 25% 2	3788
	11th to 20th	Night	34% 4 11% 29% 19% 2	3914
	21st to end	Night	44% 4 9% 27% 16% 1	4610
November	1st to 10th	Night	41% 6% 11% 26% 15% 2	2666
	11th to 20th	Night	50% 6% 12% 19% 11% 2	2730
	21st to end	Night	51% 6% 12% 22% 9% 1	2932
December	1st to 10th	Night	42% 6% 17% 25% 7% 3	4609
	11th to 20th	Night	62% 4 8% 14% 10% 1	5201
	21st to end	Night	69% 5% 8% 13% 6%	6996

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	14% 13% 34% 30% 8% 1	300
	11th to 20th	Day	14% 14% 36% 27% 8% 1	300
	21st to end	Day	20% 12% 35% 27% 5% 1	330
February	1st to 10th	Day	15% 14% 41% 22% 6% 1	300
	11th to 20th	Day	17% 18% 35% 22% 7%	300
	21st to end	Day	17% 18% 41% 22% 2	249
March	1st to 10th	Day	16% 15% 42% 22% 3 1	300
	11th to 20th	Day	20% 15% 31% 23% 7% 3	300
	21st to end	Day	25% 11% 32% 23% 7% 1	542
April	1st to 10th	Day	26% 12% 33% 24% 5%	500
	11th to 20th	Day	25% 16% 28% 18% 10% 2	492
	21st to end	Day	22% 12% 30% 23% 11% 2	500
May	1st to 10th	Day	19% 10% 34% 25% 10% 2	566
	11th to 20th	Day	20% 9% 28% 26% 14% 3	725
	21st to end	Day	17% 10% 27% 26% 14% 6%	789
June	1st to 10th	Day	11% 7% 28% 32% 17% 4	730
	11th to 20th	Day	15% 7% 31% 28% 15% 5%	730
	21st to end	Day	15% 7% 27% 30% 17% 3	730
July	1st to 10th	Day	8% 4 18% 32% 26% 12%	721
	11th to 20th	Day	9% 5% 24% 34% 22% 8%	718
	21st to end	Day	7% 3 25% 34% 23% 7%	794
August	1st to 10th	Day	8% 4 20% 33% 24% 11%	726
	11th to 20th	Day	15% 4 15% 27% 25% 14%	557
	21st to end	Day	11% 7% 18% 30% 23% 11%	583
September	1st to 10th	Day	14% 6% 22% 26% 23% 9%	530
	11th to 20th	Day	11% 4 19% 30% 25% 11%	530
	21st to end	Day	15% 9% 24% 25% 19% 7%	530
October	1st to 10th	Day	17% 11% 23% 27% 17% 4	406
	11th to 20th	Day	23% 14% 32% 21% 9% 1	330
	21st to end	Day	22% 14% 34% 23% 6% 1	363
November	1st to 10th	Day	14% 18% 38% 21% 8% 1	330
	11th to 20th	Day	17% 19% 36% 18% 10%	330
	21st to end	Day	23% 14% 40% 18% 5%	330
December	1st to 10th	Day	17% 15% 44% 17% 7% 1	306
	11th to 20th	Day	21% 14% 35% 19% 10% 1	300
	21st to end	Day	27% 15% 35% 18% 5% 1	330
January	1st to 10th	Night	16% 16% 35% 26% 7% 1	1000
	11th to 20th	Night	19% 13% 36% 26% 6% 1	1000
	21st to end	Night	18% 11% 37% 28% 5% 1	1100
February	1st to 10th	Night	17% 12% 37% 27% 7% 1	1000
	11th to 20th	Night	17% 14% 36% 28% 6%	831
	21st to end	Night	22% 13% 37% 23% 4 1	660
March	1st to 10th	Night	19% 10% 35% 28% 7% 1	800
	11th to 20th	Night	17% 11% 35% 29% 7% 1	733
	21st to end	Night	22% 8% 29% 31% 9% 1	660
April	1st to 10th	Night	22% 13% 36% 25% 5%	600
	11th to 20th	Night	22% 11% 32% 27% 7%	593
	21st to end	Night	22% 9% 31% 29% 9% 1	600
May	1st to 10th	Night	18% 9% 34% 31% 8%	600
	11th to 20th	Night	17% 8% 33% 31% 11% 1	591
	21st to end	Night	13% 5% 28% 37% 16% 1	650
June	1st to 10th	Night	10% 5% 26% 44% 15% 1	600
	11th to 20th	Night	13% 5% 30% 39% 13% 1	600
	21st to end	Night	12% 5% 26% 42% 15%	600
July	1st to 10th	Night	9% 2 17% 39% 31% 3	585
	11th to 20th	Night	7% 4 18% 46% 23% 3	582
	21st to end	Night	6% 2 16% 51% 24% 2	657
August	1st to 10th	Night	9% 2 14% 47% 25% 3	597
	11th to 20th	Night	10% 3 15% 40% 28% 4	594
	21st to end	Night	11% 2 18% 43% 24% 3	660
September	1st to 10th	Night	10% 3 23% 37% 21% 6%	600
	11th to 20th	Night	12% 4 21% 34% 25% 4	668
	21st to end	Night	11% 8% 28% 30% 21% 2	800
October	1st to 10th	Night	14% 6% 29% 33% 17% 1	800
	11th to 20th	Night	21% 11% 33% 27% 9%	800
	21st to end	Night	24% 9% 31% 28% 8% 1	880
November	1st to 10th	Night	18% 10% 37% 25% 9% 1	820
	11th to 20th	Night	20% 14% 37% 23% 6%	840
	21st to end	Night	22% 13% 34% 24% 7%	1042
December	1st to 10th	Night	20% 13% 40% 22% 5%	1011
	11th to 20th	Night	23% 13% 35% 23% 6% 1	1000
	21st to end	Night	29% 12% 33% 23% 4	1100

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