Janesville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Janesville clear sky chart from 2005-11-06 to 2026-04-02.

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 5% 4 6% 7% 37%	131441
	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 38%	130666
Transparency	Day	45% 4 12% 25% 13% 1	134935
	Night	46% 3 11% 23% 14% 2	135247
Seeing	Day	17% 11% 29% 25% 14% 5%	17723
	Night	18% 9% 30% 30% 11% 1	27733

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% 12% 7% 14% 7% 6% 5% 4 5% 5% 24%	4691
	11th to 20th	Day	7% 12% 6% 12% 4 4 5% 7% 7% 6% 30%	4710
	21st to end	Day	9% 12% 7% 11% 5% 4 5% 2 4 5% 36%	5378
February	1st to 10th	Day	12% 13% 5% 9% 6% 4 6% 4 5% 7% 29%	1890
	11th to 20th	Day	13% 12% 3 8% 5% 5% 5% 3 4 5% 37%	2007
	21st to end	Day	12% 13% 5% 11% 5% 5% 4 4 4 6% 31%	1730
March	1st to 10th	Day	14% 8% 3 6% 4 4 3 3 4 6% 44%	4580
	11th to 20th	Day	11% 7% 2 7% 4 4 4 4 5% 8% 43%	4853
	21st to end	Day	20% 11% 5% 10% 5% 5% 4 3 5% 5% 26%	6069
April	1st to 10th	Day	17% 14% 3 8% 6% 4 4 3 5% 6% 30%	2412
	11th to 20th	Day	17% 10% 3 7% 6% 4 4 3 5% 7% 34%	2374
	21st to end	Day	18% 9% 3 9% 5% 4 4 3 6% 6% 32%	2478
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 6% 38%	5969
	11th to 20th	Day	14% 6% 2 6% 5% 4 5% 4 6% 8% 41%	6319
	21st to end	Day	15% 7% 2 6% 4 4 5% 4 7% 9% 38%	6935
June	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 6% 8% 43%	2800
	11th to 20th	Day	12% 5% 2 5% 4 5% 5% 4 7% 9% 42%	2800
	21st to end	Day	12% 5% 3 6% 5% 5% 5% 5% 8% 9% 39%	2800
July	1st to 10th	Day	10% 7% 2 7% 5% 5% 5% 5% 7% 10% 38%	6360
	11th to 20th	Day	8% 6% 2 6% 4 5% 5% 4 7% 8% 46%	6360
	21st to end	Day	9% 7% 2 7% 5% 5% 5% 4 7% 9% 40%	6924
August	1st to 10th	Day	9% 5% 2 6% 5% 4 6% 5% 7% 9% 41%	4513
	11th to 20th	Day	12% 5% 2 5% 3 4 5% 4 6% 9% 45%	3888
	21st to end	Day	9% 6% 3 7% 4 3 4 4 6% 9% 46%	4312
September	1st to 10th	Day	12% 5% 3 5% 3 5% 5% 3 6% 8% 46%	2400
	11th to 20th	Day	11% 4 2 4 3 4 4 3 5% 8% 53%	2317
	21st to end	Day	11% 7% 3 6% 5% 4 4 3 5% 7% 45%	2200
October	1st to 10th	Day	13% 7% 2 5% 4 3 3 3 5% 7% 47%	2071
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 5% 7% 36%	2000
	21st to end	Day	18% 10% 3 7% 4 4 4 3 4 6% 38%	2000
November	1st to 10th	Day	12% 10% 3 6% 5% 4 4 3 4 6% 44%	1852
	11th to 20th	Day	14% 13% 4 9% 5% 4 5% 3 6% 7% 32%	1890
	21st to end	Day	16% 14% 4 10% 4 3 2 2 4 6% 34%	1711
December	1st to 10th	Day	8% 10% 4 9% 5% 6% 4 4 5% 7% 37%	2690
	11th to 20th	Day	12% 15% 6% 12% 6% 5% 5% 3 6% 7% 24%	3088
	21st to end	Day	19% 22% 9% 13% 5% 4 4 3 4 4 13%	4070
January	1st to 10th	Night	10% 13% 7% 14% 6% 4 3 2 4 4 32%	8232
	11th to 20th	Night	9% 14% 7% 15% 6% 5% 6% 5% 6% 4 22%	8280
	21st to end	Night	10% 14% 6% 10% 5% 4 4 3 5% 6% 32%	8818
February	1st to 10th	Night	12% 14% 4 10% 5% 6% 4 3 4 5% 33%	2730
	11th to 20th	Night	12% 10% 4 9% 4 4 5% 3 5% 6% 38%	2497
	21st to end	Night	16% 12% 3 8% 4 3 3 4 5% 6% 36%	2076
March	1st to 10th	Night	16% 8% 3 7% 4 4 4 3 3 5% 43%	5493
	11th to 20th	Night	10% 7% 2 6% 4 4 4 3 6% 8% 47%	5372
	21st to end	Night	21% 13% 5% 9% 4 4 4 3 4 5% 28%	5101
April	1st to 10th	Night	17% 9% 2 6% 5% 5% 3 4 5% 6% 37%	2010
	11th to 20th	Night	18% 10% 4 7% 4 3 4 3 4 6% 39%	1975
	21st to end	Night	17% 7% 3 7% 5% 4 4 3 6% 6% 38%	1920
May	1st to 10th	Night	17% 7% 2 6% 5% 4 4 4 5% 8% 39%	3915
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 7% 7% 44%	3596
	21st to end	Night	15% 8% 3 7% 5% 4 4 4 6% 7% 39%	3942
June	1st to 10th	Night	8% 4 2 5% 5% 4 5% 4 7% 8% 48%	1600
	11th to 20th	Night	11% 5% 1 6% 3 4 4 3 6% 10% 46%	1600
	21st to end	Night	11% 7% 2 5% 4 3 4 4 5% 9% 47%	1600
July	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 6% 9% 43%	3618
	11th to 20th	Night	6% 5% 2 5% 3 4 4 4 6% 8% 53%	3617
	21st to end	Night	7% 6% 2 6% 4 4 5% 4 7% 8% 48%	3947
August	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 8% 52%	2643
	11th to 20th	Night	9% 7% 2 5% 4 4 4 3 6% 8% 49%	3161
	21st to end	Night	9% 5% 2 5% 4 4 4 4 5% 8% 50%	3586
September	1st to 10th	Night	8% 4 2 6% 4 3 4 4 4 7% 54%	2000
	11th to 20th	Night	11% 4 1 4 3 4 4 4 5% 8% 53%	2062
	21st to end	Night	11% 5% 2 6% 5% 4 4 3 4 7% 49%	2200
October	1st to 10th	Night	11% 6% 2 5% 4 3 4 2 4 7% 51%	2325
	11th to 20th	Night	17% 9% 3 6% 3 3 3 3 4 5% 44%	2400
	21st to end	Night	19% 9% 3 6% 4 4 4 3 5% 7% 37%	2839
November	1st to 10th	Night	12% 9% 3 6% 4 3 3 3 5% 6% 47%	2666
	11th to 20th	Night	14% 12% 4 9% 5% 4 4 3 5% 6% 36%	2730
	21st to end	Night	16% 12% 4 8% 5% 4 3 3 4 5% 35%	2906
December	1st to 10th	Night	10% 9% 3 7% 5% 5% 5% 4 5% 6% 41%	4720
	11th to 20th	Night	16% 17% 4 10% 5% 4 3 3 4 5% 27%	5339
	21st to end	Night	20% 20% 7% 11% 5% 4 4 3 4 4 17%	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	62% 3 14% 15% 5%	4692
	11th to 20th	Day	53% 3 10% 17% 16% 1	4710
	21st to end	Day	52% 2 12% 23% 10%	5378
February	1st to 10th	Day	56% 3 11% 19% 10% 1	1890
	11th to 20th	Day	50% 3 10% 25% 10% 2	2017
	21st to end	Day	55% 3 10% 21% 10% 2	1730
March	1st to 10th	Day	43% 2 12% 29% 11% 4	4580
	11th to 20th	Day	41% 2 12% 31% 13% 1	4853
	21st to end	Day	61% 4 12% 15% 8% 1	6071
April	1st to 10th	Day	55% 4 10% 21% 10%	2412
	11th to 20th	Day	51% 3 10% 22% 11% 2	2374
	21st to end	Day	52% 4 11% 19% 12% 1	2478
May	1st to 10th	Day	46% 3 9% 23% 18% 1	6004
	11th to 20th	Day	41% 5% 11% 27% 16% 1	6323
	21st to end	Day	42% 4 10% 28% 13% 2	6949
June	1st to 10th	Day	37% 5% 13% 28% 16% 1	2800
	11th to 20th	Day	37% 5% 14% 26% 17% 2	2800
	21st to end	Day	40% 5% 14% 24% 15% 2	2800
July	1st to 10th	Day	39% 6% 14% 29% 10% 1	6291
	11th to 20th	Day	34% 6% 14% 31% 14% 1	6285
	21st to end	Day	39% 7% 15% 21% 17% 2	6728
August	1st to 10th	Day	37% 6% 14% 29% 12% 1	4498
	11th to 20th	Day	35% 5% 13% 33% 13% 1	3924
	21st to end	Day	34% 4 13% 29% 17% 1	4311
September	1st to 10th	Day	37% 4 11% 28% 19% 2	2400
	11th to 20th	Day	31% 4 11% 35% 18% 2	2317
	21st to end	Day	39% 4 9% 30% 17% 1	2200
October	1st to 10th	Day	25% 2 6% 40% 25% 1	3370
	11th to 20th	Day	35% 4 9% 29% 22% 1	3240
	21st to end	Day	43% 3 8% 29% 14% 3	3212
November	1st to 10th	Day	42% 3 14% 25% 15% 2	1852
	11th to 20th	Day	52% 3 13% 21% 9% 1	1890
	21st to end	Day	53% 3 13% 24% 6%	1711
December	1st to 10th	Day	46% 4 21% 23% 6% 1	2690
	11th to 20th	Day	59% 3 12% 18% 6% 2	3085
	21st to end	Day	76% 3 6% 9% 6%	4070
January	1st to 10th	Night	58% 2 10% 21% 9%	8233
	11th to 20th	Night	63% 3 9% 11% 13% 1	8280
	21st to end	Night	54% 3 11% 21% 10%	8818
February	1st to 10th	Night	54% 3 10% 20% 12% 1	2730
	11th to 20th	Night	48% 3 11% 24% 14% 1	2498
	21st to end	Night	49% 3 11% 21% 11% 3	2076
March	1st to 10th	Night	46% 2 12% 23% 10% 6%	5493
	11th to 20th	Night	36% 3 11% 34% 13% 3	5372
	21st to end	Night	60% 2 9% 18% 10% 1	5101
April	1st to 10th	Night	48% 3 10% 22% 15% 2	2010
	11th to 20th	Night	49% 3 6% 21% 18% 3	1975
	21st to end	Night	47% 3 11% 24% 13% 2	1920
May	1st to 10th	Night	45% 3 12% 20% 19% 2	3942
	11th to 20th	Night	39% 4 14% 24% 16% 3	3597
	21st to end	Night	45% 4 10% 23% 15% 3	3950
June	1st to 10th	Night	33% 5% 13% 29% 20% 1	1600
	11th to 20th	Night	35% 5% 10% 24% 24% 3	1600
	21st to end	Night	35% 5% 15% 23% 19% 3	1600
July	1st to 10th	Night	38% 5% 13% 28% 13% 2	3580
	11th to 20th	Night	29% 7% 14% 31% 19% 1	3572
	21st to end	Night	32% 6% 15% 24% 20% 2	3832
August	1st to 10th	Night	30% 5% 14% 30% 19% 2	2634
	11th to 20th	Night	32% 6% 13% 32% 17% 1	3191
	21st to end	Night	31% 5% 13% 30% 18% 3	3586
September	1st to 10th	Night	31% 4 12% 27% 24% 3	2000
	11th to 20th	Night	30% 4 10% 35% 19% 2	2062
	21st to end	Night	36% 3 9% 32% 19% 1	2200
October	1st to 10th	Night	26% 3 6% 37% 28% 1	3806
	11th to 20th	Night	36% 3 9% 26% 23% 3	3899
	21st to end	Night	42% 3 9% 27% 16% 2	4577
November	1st to 10th	Night	39% 3 10% 28% 17% 2	2666
	11th to 20th	Night	50% 4 12% 23% 11% 1	2730
	21st to end	Night	52% 3 12% 22% 10% 1	2906
December	1st to 10th	Night	43% 4 16% 26% 9% 2	4720
	11th to 20th	Night	61% 3 11% 15% 9% 1	5341
	21st to end	Night	71% 3 7% 13% 5%	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	18% 13% 33% 28% 8% 1	330
	11th to 20th	Day	18% 18% 36% 24% 4 1	330
	21st to end	Day	19% 17% 35% 24% 4 1	363
February	1st to 10th	Day	16% 18% 42% 19% 5% 1	330
	11th to 20th	Day	18% 19% 38% 20% 4 1	330
	21st to end	Day	22% 18% 42% 15% 2	273
March	1st to 10th	Day	16% 23% 40% 15% 5%	330
	11th to 20th	Day	24% 20% 33% 16% 6% 1	330
	21st to end	Day	25% 15% 32% 19% 5% 2	577
April	1st to 10th	Day	25% 15% 34% 21% 4	504
	11th to 20th	Day	23% 20% 26% 19% 10% 2	492
	21st to end	Day	25% 13% 30% 21% 10% 2	500
May	1st to 10th	Day	21% 13% 30% 25% 9% 2	545
	11th to 20th	Day	22% 10% 29% 25% 12% 4	725
	21st to end	Day	17% 10% 28% 25% 15% 6%	789
June	1st to 10th	Day	10% 8% 29% 31% 16% 5%	730
	11th to 20th	Day	12% 7% 31% 29% 16% 5%	730
	21st to end	Day	14% 7% 29% 30% 16% 4	730
July	1st to 10th	Day	8% 6% 18% 32% 24% 13%	721
	11th to 20th	Day	10% 6% 25% 30% 21% 9%	718
	21st to end	Day	9% 4 23% 35% 21% 9%	794
August	1st to 10th	Day	8% 4 19% 34% 24% 11%	726
	11th to 20th	Day	14% 4 17% 27% 25% 14%	546
	21st to end	Day	10% 5% 18% 34% 25% 9%	583
September	1st to 10th	Day	13% 7% 23% 27% 22% 8%	530
	11th to 20th	Day	11% 3 18% 31% 25% 12%	530
	21st to end	Day	13% 10% 27% 24% 18% 8%	530
October	1st to 10th	Day	15% 8% 27% 26% 18% 4	401
	11th to 20th	Day	25% 17% 30% 21% 7% 1	330
	21st to end	Day	28% 13% 31% 21% 6% 1	363
November	1st to 10th	Day	18% 17% 35% 19% 9% 1	330
	11th to 20th	Day	22% 17% 35% 18% 8%	330
	21st to end	Day	28% 11% 38% 19% 5%	330
December	1st to 10th	Day	16% 18% 39% 17% 8% 2	330
	11th to 20th	Day	17% 14% 42% 19% 7% 1	330
	21st to end	Day	26% 16% 38% 17% 2	363
January	1st to 10th	Night	17% 13% 36% 28% 6%	1050
	11th to 20th	Night	21% 13% 37% 22% 5% 1	1050
	21st to end	Night	18% 12% 36% 28% 5%	1155
February	1st to 10th	Night	20% 10% 38% 25% 6%	1050
	11th to 20th	Night	19% 13% 35% 28% 5%	862
	21st to end	Night	23% 13% 38% 22% 4	692
March	1st to 10th	Night	21% 10% 36% 25% 6%	840
	11th to 20th	Night	18% 13% 33% 29% 7%	756
	21st to end	Night	23% 12% 31% 27% 7% 1	693
April	1st to 10th	Night	22% 12% 37% 24% 4	603
	11th to 20th	Night	23% 11% 33% 27% 6%	593
	21st to end	Night	22% 9% 32% 28% 8% 1	600
May	1st to 10th	Night	19% 10% 33% 31% 7% 1	600
	11th to 20th	Night	19% 7% 28% 35% 11%	591
	21st to end	Night	15% 6% 25% 39% 15% 1	650
June	1st to 10th	Night	9% 4 26% 47% 13% 1	600
	11th to 20th	Night	13% 4 31% 41% 11% 1	600
	21st to end	Night	12% 5% 27% 41% 16%	600
July	1st to 10th	Night	9% 3 14% 43% 29% 2	585
	11th to 20th	Night	9% 3 19% 43% 24% 3	582
	21st to end	Night	6% 3 17% 50% 23% 1	657
August	1st to 10th	Night	6% 3 13% 49% 25% 4	597
	11th to 20th	Night	10% 2 13% 39% 31% 5%	594
	21st to end	Night	10% 2 15% 44% 25% 3	660
September	1st to 10th	Night	10% 3 20% 37% 24% 5%	600
	11th to 20th	Night	12% 3 20% 35% 27% 3	662
	21st to end	Night	12% 7% 26% 32% 21% 2	800
October	1st to 10th	Night	13% 7% 31% 32% 15% 2	800
	11th to 20th	Night	22% 12% 28% 30% 8% 1	800
	21st to end	Night	24% 11% 31% 26% 8%	880
November	1st to 10th	Night	17% 11% 37% 25% 10%	820
	11th to 20th	Night	21% 15% 35% 23% 6%	840
	21st to end	Night	22% 13% 34% 24% 6%	1016
December	1st to 10th	Night	22% 13% 37% 22% 6%	1050
	11th to 20th	Night	23% 12% 35% 23% 6% 1	1050
	21st to end	Night	30% 11% 34% 22% 3	1155

Page generated at 2026-03-30 01:18:44. Version ac07

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