Barrington Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Barrington Hills clear sky chart from 2005-11-06 to 2025-11-18.

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	13% 9% 3 7% 5% 4 5% 4 6% 7% 37%	126922
	Night	14% 10% 4 8% 4 4 4 3 5% 6% 39%	123702
Transparency	Day	45% 6% 11% 24% 13% 2	130445
	Night	46% 5% 10% 23% 15% 2	128253
Seeing	Day	17% 14% 31% 24% 11% 4	17258
	Night	17% 12% 32% 27% 11% 1	27074

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% 8% 13% 6% 5% 5% 4 5% 5% 27%	3617
	11th to 20th	Day	9% 12% 7% 12% 4 4 4 6% 6% 5% 31%	3620
	21st to end	Day	15% 18% 6% 7% 4 3 3 2 4 6% 32%	4092
February	1st to 10th	Day	13% 15% 5% 9% 6% 5% 5% 3 5% 7% 27%	1830
	11th to 20th	Day	13% 12% 4 8% 6% 4 3 3 5% 5% 36%	1948
	21st to end	Day	14% 12% 5% 11% 6% 4 3 3 5% 5% 32%	1650
March	1st to 10th	Day	16% 11% 3 7% 4 3 3 3 4 5% 42%	4480
	11th to 20th	Day	10% 7% 3 6% 4 5% 5% 4 6% 9% 41%	4674
	21st to end	Day	20% 13% 7% 12% 6% 5% 4 3 4 5% 21%	5967
April	1st to 10th	Day	18% 14% 4 8% 5% 4 4 3 5% 6% 31%	2400
	11th to 20th	Day	15% 11% 3 7% 5% 5% 5% 3 6% 6% 35%	2374
	21st to end	Day	19% 10% 3 7% 5% 4 4 4 5% 6% 33%	2511
May	1st to 10th	Day	17% 8% 2 6% 5% 4 5% 4 6% 7% 36%	5862
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 4 6% 7% 41%	6219
	21st to end	Day	15% 7% 2 5% 4 4 5% 4 6% 8% 38%	6935
June	1st to 10th	Day	9% 6% 3 6% 4 4 5% 4 7% 7% 46%	2800
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 7% 10% 44%	2800
	21st to end	Day	11% 6% 2 7% 6% 5% 5% 4 7% 8% 40%	2800
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 10% 35%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 9% 42%	6360
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 7% 9% 40%	6924
August	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 6% 8% 43%	4497
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 7% 8% 42%	3880
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 8% 48%	4312
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 3 5% 8% 48%	2400
	11th to 20th	Day	12% 4 2 3 3 3 3 4 6% 7% 53%	2275
	21st to end	Day	11% 6% 3 6% 5% 4 5% 3 6% 8% 44%	2200
October	1st to 10th	Day	12% 6% 3 6% 5% 3 4 3 6% 5% 47%	2140
	11th to 20th	Day	18% 9% 3 7% 5% 4 4 4 5% 6% 36%	1985
	21st to end	Day	20% 9% 3 6% 4 3 4 3 5% 5% 38%	1980
November	1st to 10th	Day	12% 9% 3 6% 4 4 4 4 5% 7% 43%	1852
	11th to 20th	Day	15% 13% 3 8% 5% 4 4 3 5% 6% 34%	1863
	21st to end	Day	18% 12% 4 8% 5% 4 4 3 4 5% 35%	1715
December	1st to 10th	Day	8% 10% 4 8% 5% 4 4 3 5% 6% 42%	2610
	11th to 20th	Day	11% 15% 6% 11% 5% 5% 6% 4 6% 6% 25%	3008
	21st to end	Day	23% 25% 8% 10% 4 4 3 3 3 4 13%	3982
January	1st to 10th	Night	12% 13% 7% 13% 5% 4 3 3 4 5% 32%	6348
	11th to 20th	Night	13% 14% 7% 13% 6% 5% 4 5% 6% 4 23%	6360
	21st to end	Night	17% 15% 6% 9% 4 3 3 3 4 5% 32%	6886
February	1st to 10th	Night	14% 14% 5% 8% 6% 5% 4 2 4 5% 32%	2570
	11th to 20th	Night	13% 11% 3 9% 6% 4 4 3 5% 6% 36%	2338
	21st to end	Night	17% 13% 3 9% 4 3 3 2 4 5% 37%	1980
March	1st to 10th	Night	16% 10% 4 7% 3 3 3 3 4 4 42%	5373
	11th to 20th	Night	10% 7% 2 6% 4 4 4 3 5% 7% 48%	5315
	21st to end	Night	19% 13% 5% 10% 5% 4 5% 3 4 5% 28%	4962
April	1st to 10th	Night	17% 8% 3 6% 4 5% 5% 4 4 5% 38%	2000
	11th to 20th	Night	19% 9% 2 6% 5% 4 4 3 5% 6% 38%	1975
	21st to end	Night	18% 7% 2 6% 4 4 5% 3 5% 6% 39%	1887
May	1st to 10th	Night	19% 7% 2 7% 4 4 4 4 5% 7% 37%	4033
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 6% 9% 43%	3689
	21st to end	Night	18% 7% 3 7% 4 3 4 3 4 6% 41%	3942
June	1st to 10th	Night	10% 5% 2 5% 4 4 5% 4 6% 7% 48%	1600
	11th to 20th	Night	10% 5% 2 6% 5% 4 5% 3 6% 8% 47%	1600
	21st to end	Night	9% 6% 2 6% 4 5% 5% 5% 6% 9% 43%	1600
July	1st to 10th	Night	10% 6% 3 7% 4 5% 6% 4 8% 8% 40%	3618
	11th to 20th	Night	7% 5% 2 5% 4 4 4 3 7% 8% 51%	3617
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 7% 8% 45%	3947
August	1st to 10th	Night	7% 5% 2 5% 5% 4 5% 4 7% 9% 49%	2660
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 5% 7% 51%	3165
	21st to end	Night	8% 5% 1 5% 3 4 4 4 5% 9% 53%	3586
September	1st to 10th	Night	11% 4 2 6% 3 4 3 2 4 7% 53%	2000
	11th to 20th	Night	10% 4 2 5% 3 3 3 3 5% 7% 56%	2104
	21st to end	Night	12% 6% 2 5% 4 4 4 4 5% 7% 47%	2200
October	1st to 10th	Night	11% 5% 2 6% 4 3 4 3 4 5% 53%	2257
	11th to 20th	Night	17% 8% 2 5% 3 4 4 3 4 6% 44%	2415
	21st to end	Night	20% 9% 2 5% 4 3 4 3 5% 5% 38%	2860
November	1st to 10th	Night	12% 9% 3 6% 4 3 4 3 4 5% 47%	2666
	11th to 20th	Night	13% 11% 4 8% 4 4 4 3 5% 6% 38%	2692
	21st to end	Night	16% 11% 4 8% 4 4 4 3 5% 4 37%	2682
December	1st to 10th	Night	11% 9% 3 8% 4 4 4 3 5% 6% 42%	4580
	11th to 20th	Night	16% 16% 5% 8% 5% 4 4 3 5% 6% 29%	5199
	21st to end	Night	23% 19% 6% 9% 4 4 4 3 4 4 17%	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	59% 3 11% 18% 8%	3618
	11th to 20th	Day	53% 5% 10% 12% 15% 4	3620
	21st to end	Day	55% 3 11% 21% 10%	4092
February	1st to 10th	Day	58% 4 11% 15% 10% 1	1830
	11th to 20th	Day	51% 5% 10% 23% 10% 2	1958
	21st to end	Day	54% 6% 10% 18% 11% 2	1650
March	1st to 10th	Day	46% 4 9% 25% 12% 4	4480
	11th to 20th	Day	40% 5% 12% 31% 11% 1	4674
	21st to end	Day	65% 5% 10% 11% 7% 1	5969
April	1st to 10th	Day	56% 4 9% 19% 11%	2400
	11th to 20th	Day	49% 6% 9% 21% 12% 3	2374
	21st to end	Day	50% 6% 12% 18% 12% 1	2511
May	1st to 10th	Day	46% 6% 10% 23% 13% 2	5897
	11th to 20th	Day	40% 7% 10% 26% 15% 1	6223
	21st to end	Day	42% 5% 11% 25% 14% 3	6949
June	1st to 10th	Day	36% 6% 12% 26% 18% 2	2800
	11th to 20th	Day	35% 8% 12% 23% 19% 3	2800
	21st to end	Day	40% 7% 13% 23% 15% 2	2800
July	1st to 10th	Day	41% 7% 12% 25% 13% 2	6291
	11th to 20th	Day	36% 7% 14% 27% 15% 1	6285
	21st to end	Day	39% 7% 15% 21% 16% 2	6728
August	1st to 10th	Day	36% 8% 14% 28% 12% 1	4482
	11th to 20th	Day	36% 5% 12% 31% 15% 1	3917
	21st to end	Day	33% 6% 12% 26% 20% 2	4311
September	1st to 10th	Day	35% 6% 11% 27% 18% 3	2400
	11th to 20th	Day	29% 5% 10% 32% 20% 3	2275
	21st to end	Day	39% 5% 9% 28% 18% 1	2200
October	1st to 10th	Day	25% 4 6% 38% 25% 1	3491
	11th to 20th	Day	35% 4 11% 28% 22% 1	3213
	21st to end	Day	43% 3 8% 29% 13% 3	3180
November	1st to 10th	Day	41% 4 12% 24% 17% 2	1852
	11th to 20th	Day	51% 4 11% 22% 10% 1	1863
	21st to end	Day	53% 4 11% 23% 9%	1715
December	1st to 10th	Day	44% 3 17% 28% 7%	2610
	11th to 20th	Day	59% 5% 11% 17% 7% 1	3005
	21st to end	Day	76% 4 5% 10% 5%	3982
January	1st to 10th	Night	57% 3 8% 21% 11% 1	6348
	11th to 20th	Night	63% 4 9% 9% 14% 1	6360
	21st to end	Night	57% 3 13% 16% 11% 1	6886
February	1st to 10th	Night	56% 3 10% 17% 13% 2	2570
	11th to 20th	Night	49% 5% 10% 21% 14% 1	2339
	21st to end	Night	51% 3 10% 21% 10% 4	1980
March	1st to 10th	Night	47% 4 11% 24% 11% 4	5373
	11th to 20th	Night	36% 5% 12% 31% 14% 3	5315
	21st to end	Night	59% 4 8% 18% 10% 1	4962
April	1st to 10th	Night	47% 5% 11% 22% 14% 1	2000
	11th to 20th	Night	48% 5% 8% 20% 16% 4	1975
	21st to end	Night	46% 5% 10% 23% 14% 2	1887
May	1st to 10th	Night	47% 5% 12% 17% 16% 3	4060
	11th to 20th	Night	37% 7% 15% 24% 14% 3	3690
	21st to end	Night	45% 4 9% 22% 16% 4	3950
June	1st to 10th	Night	32% 7% 11% 27% 19% 3	1600
	11th to 20th	Night	36% 5% 10% 25% 22% 2	1600
	21st to end	Night	37% 7% 15% 22% 18% 2	1600
July	1st to 10th	Night	39% 7% 13% 26% 12% 3	3580
	11th to 20th	Night	30% 6% 13% 30% 18% 2	3572
	21st to end	Night	35% 7% 13% 23% 19% 3	3832
August	1st to 10th	Night	31% 8% 14% 28% 18% 1	2651
	11th to 20th	Night	31% 7% 13% 30% 18% 1	3194
	21st to end	Night	29% 5% 12% 33% 17% 4	3586
September	1st to 10th	Night	32% 5% 9% 27% 23% 2	2000
	11th to 20th	Night	29% 4 7% 34% 25% 2	2104
	21st to end	Night	36% 5% 10% 29% 18% 2	2200
October	1st to 10th	Night	23% 3 7% 38% 27% 2	3686
	11th to 20th	Night	37% 3 7% 24% 27% 2	3926
	21st to end	Night	41% 4 9% 26% 18% 3	4610
November	1st to 10th	Night	40% 4 8% 26% 18% 3	2666
	11th to 20th	Night	47% 4 11% 24% 12% 2	2692
	21st to end	Night	50% 4 12% 22% 11%	2682
December	1st to 10th	Night	44% 3 14% 27% 10% 2	4580
	11th to 20th	Night	58% 4 11% 15% 11% 1	5201
	21st to end	Night	70% 4 7% 12% 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	20% 17% 39% 20% 2 1	300
	11th to 20th	Day	22% 22% 38% 15% 2 1	300
	21st to end	Day	25% 22% 35% 14% 4	330
February	1st to 10th	Day	23% 21% 40% 13% 3	300
	11th to 20th	Day	28% 23% 32% 15% 2	300
	21st to end	Day	27% 23% 37% 9% 4	249
March	1st to 10th	Day	22% 29% 36% 12% 1	300
	11th to 20th	Day	28% 20% 34% 13% 5%	323
	21st to end	Day	28% 17% 31% 18% 5% 1	550
April	1st to 10th	Day	27% 19% 29% 21% 4	500
	11th to 20th	Day	25% 23% 23% 20% 8% 2	492
	21st to end	Day	23% 18% 31% 19% 9% 1	500
May	1st to 10th	Day	20% 16% 33% 21% 7% 2	503
	11th to 20th	Day	20% 14% 31% 24% 8% 3	677
	21st to end	Day	16% 14% 32% 22% 13% 4	789
June	1st to 10th	Day	10% 13% 34% 27% 13% 4	730
	11th to 20th	Day	11% 11% 35% 28% 12% 3	730
	21st to end	Day	11% 12% 32% 29% 12% 3	730
July	1st to 10th	Day	8% 6% 26% 31% 18% 11%	721
	11th to 20th	Day	10% 7% 31% 31% 14% 7%	718
	21st to end	Day	6% 7% 30% 35% 15% 6%	794
August	1st to 10th	Day	9% 5% 25% 33% 19% 8%	686
	11th to 20th	Day	10% 6% 23% 31% 21% 10%	519
	21st to end	Day	8% 5% 23% 33% 21% 9%	583
September	1st to 10th	Day	15% 7% 24% 28% 20% 6%	530
	11th to 20th	Day	8% 5% 20% 32% 24% 10%	530
	21st to end	Day	13% 14% 25% 26% 16% 6%	530
October	1st to 10th	Day	14% 14% 28% 27% 14% 3	470
	11th to 20th	Day	22% 24% 31% 19% 5%	330
	21st to end	Day	29% 18% 35% 13% 4	363
November	1st to 10th	Day	18% 20% 36% 18% 7% 2	330
	11th to 20th	Day	24% 24% 33% 13% 6%	321
	21st to end	Day	23% 17% 40% 17% 2	300
December	1st to 10th	Day	17% 24% 41% 14% 4	300
	11th to 20th	Day	20% 24% 37% 15% 4	300
	21st to end	Day	27% 25% 33% 13% 2	330
January	1st to 10th	Night	19% 18% 38% 21% 4	1000
	11th to 20th	Night	21% 19% 36% 19% 4 1	1000
	21st to end	Night	22% 14% 37% 23% 3	1100
February	1st to 10th	Night	22% 16% 36% 21% 4	970
	11th to 20th	Night	21% 17% 35% 23% 3	783
	21st to end	Night	24% 17% 38% 18% 3	660
March	1st to 10th	Night	21% 15% 37% 21% 6%	800
	11th to 20th	Night	18% 12% 41% 22% 7%	777
	21st to end	Night	24% 14% 31% 24% 7% 1	660
April	1st to 10th	Night	21% 14% 35% 24% 5%	600
	11th to 20th	Night	22% 17% 31% 23% 7% 1	593
	21st to end	Night	23% 13% 30% 28% 7% 1	600
May	1st to 10th	Night	18% 10% 35% 30% 7% 1	600
	11th to 20th	Night	17% 8% 30% 32% 13%	591
	21st to end	Night	14% 7% 28% 33% 16% 1	650
June	1st to 10th	Night	10% 7% 28% 39% 16% 1	600
	11th to 20th	Night	11% 5% 33% 37% 13% 1	600
	21st to end	Night	10% 6% 33% 34% 17% 1	600
July	1st to 10th	Night	7% 3 22% 38% 28% 3	585
	11th to 20th	Night	7% 4 26% 38% 22% 2	582
	21st to end	Night	6% 1 23% 44% 24% 2	657
August	1st to 10th	Night	5% 2 18% 46% 26% 3	597
	11th to 20th	Night	8% 3 16% 39% 30% 3	594
	21st to end	Night	7% 3 20% 39% 28% 2	660
September	1st to 10th	Night	11% 6% 22% 32% 26% 4	600
	11th to 20th	Night	10% 4 21% 32% 29% 4	704
	21st to end	Night	12% 10% 25% 29% 21% 3	800
October	1st to 10th	Night	14% 7% 26% 33% 19% 2	800
	11th to 20th	Night	21% 14% 32% 25% 9%	800
	21st to end	Night	25% 13% 31% 23% 8%	880
November	1st to 10th	Night	18% 14% 37% 22% 8% 1	820
	11th to 20th	Night	20% 19% 35% 21% 5%	829
	21st to end	Night	21% 16% 38% 20% 6%	882
December	1st to 10th	Night	21% 17% 37% 21% 4	1000
	11th to 20th	Night	23% 16% 36% 23% 4	1000
	21st to end	Night	29% 16% 34% 18% 2	1100

Page generated at 2025-11-14 23:55:57. Version ac07

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