Berea
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Berea clear sky chart from 2005-11-06 to 2026-08-15.

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	14% 9% 3 7% 5% 5% 5% 4 6% 7% 36%	143254
	Night	14% 9% 3 8% 5% 4 4 4 5% 7% 38%	138661
Transparency	Day	45% 6% 10% 22% 14% 2	146954
	Night	45% 5% 10% 22% 15% 3	143032
Seeing	Day	19% 11% 23% 23% 16% 8%	17092
	Night	19% 9% 24% 29% 17% 2	27096

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	15% 17% 7% 11% 5% 4 4 3 4 5% 25%	5258
	11th to 20th	Day	12% 13% 6% 14% 4 4 3 2 3 3 36%	5280
	21st to end	Day	19% 11% 6% 7% 6% 4 4 3 4 5% 29%	5780
February	1st to 10th	Day	17% 13% 6% 9% 5% 5% 4 3 4 6% 30%	2042
	11th to 20th	Day	20% 11% 5% 8% 5% 5% 3 3 4 6% 31%	2048
	21st to end	Day	19% 12% 4 8% 5% 4 5% 3 5% 4 32%	1730
March	1st to 10th	Day	18% 12% 4 7% 5% 4 3 3 4 5% 35%	4668
	11th to 20th	Day	12% 9% 3 6% 4 4 4 3 5% 7% 43%	5090
	21st to end	Day	14% 9% 2 7% 4 5% 5% 3 6% 7% 37%	5586
April	1st to 10th	Day	13% 8% 3 7% 5% 4 4 4 5% 8% 39%	2435
	11th to 20th	Day	14% 9% 3 7% 4 4 4 3 5% 6% 41%	2532
	21st to end	Day	16% 7% 3 6% 5% 5% 5% 4 6% 7% 37%	2730
May	1st to 10th	Day	16% 9% 3 8% 5% 6% 5% 5% 6% 8% 30%	7616
	11th to 20th	Day	14% 7% 3 8% 5% 5% 6% 4 6% 7% 36%	7626
	21st to end	Day	18% 8% 3 8% 6% 6% 6% 5% 6% 8% 27%	8391
June	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 5% 7% 8% 40%	2730
	11th to 20th	Day	8% 5% 2 6% 4 6% 6% 5% 6% 11% 40%	2730
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 4 7% 12% 40%	2730
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 5% 7% 9% 38%	7680
	11th to 20th	Day	11% 7% 2 7% 5% 5% 6% 5% 8% 10% 34%	7680
	21st to end	Day	13% 7% 3 8% 6% 6% 6% 5% 8% 10% 28%	8340
August	1st to 10th	Day	9% 5% 2 6% 4 6% 6% 4 7% 10% 41%	4364
	11th to 20th	Day	10% 6% 2 6% 5% 5% 7% 5% 8% 10% 37%	4199
	21st to end	Day	6% 4 2 5% 3 4 4 4 6% 8% 55%	4312
September	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 4 5% 8% 41%	2249
	11th to 20th	Day	12% 5% 2 5% 3 5% 4 3 6% 9% 45%	2200
	21st to end	Day	16% 5% 3 6% 4 4 4 4 4 6% 45%	2200
October	1st to 10th	Day	10% 5% 2 5% 4 4 4 3 6% 7% 52%	2200
	11th to 20th	Day	12% 5% 2 6% 3 4 3 3 4 6% 51%	2040
	21st to end	Day	20% 7% 2 4 3 3 3 3 5% 6% 43%	2108
November	1st to 10th	Day	12% 7% 2 5% 4 3 3 4 5% 6% 50%	1852
	11th to 20th	Day	15% 9% 3 7% 4 3 4 3 4 6% 43%	1890
	21st to end	Day	16% 11% 4 6% 5% 3 3 3 5% 5% 39%	1890
December	1st to 10th	Day	16% 12% 3 8% 5% 4 4 3 4 5% 36%	3020
	11th to 20th	Day	18% 15% 5% 9% 5% 4 4 3 5% 5% 28%	3463
	21st to end	Day	17% 14% 4 11% 6% 5% 5% 4 4 6% 23%	4565
January	1st to 10th	Night	15% 15% 6% 13% 5% 4 3 3 4 5% 28%	7635
	11th to 20th	Night	16% 14% 4 10% 5% 4 3 3 4 4 34%	7680
	21st to end	Night	18% 11% 5% 10% 5% 3 3 2 3 4 36%	8401
February	1st to 10th	Night	17% 11% 4 10% 5% 5% 4 4 4 6% 29%	2574
	11th to 20th	Night	20% 11% 4 10% 5% 3 4 3 4 5% 31%	2458
	21st to end	Night	21% 12% 4 9% 5% 4 3 3 3 4 31%	2076
March	1st to 10th	Night	17% 14% 3 7% 4 4 4 3 4 5% 35%	5404
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 5% 6% 48%	5090
	21st to end	Night	12% 10% 3 9% 6% 5% 5% 4 6% 6% 34%	5588
April	1st to 10th	Night	13% 8% 2 6% 4 4 4 4 5% 7% 43%	2202
	11th to 20th	Night	13% 8% 2 5% 4 4 5% 4 5% 6% 44%	2034
	21st to end	Night	16% 7% 2 7% 4 4 4 4 6% 7% 39%	1890
May	1st to 10th	Night	16% 8% 3 9% 6% 6% 5% 5% 6% 8% 29%	5237
	11th to 20th	Night	13% 7% 2 7% 5% 5% 5% 5% 7% 8% 35%	5234
	21st to end	Night	16% 9% 4 8% 5% 5% 5% 4 5% 8% 31%	5761
June	1st to 10th	Night	9% 5% 2 5% 4 4 5% 4 7% 11% 45%	1890
	11th to 20th	Night	6% 4 2 6% 4 5% 6% 5% 8% 11% 44%	1890
	21st to end	Night	8% 4 1 7% 4 5% 6% 4 9% 12% 41%	1890
July	1st to 10th	Night	7% 6% 2 7% 5% 5% 5% 5% 7% 9% 42%	5278
	11th to 20th	Night	10% 6% 2 7% 4 5% 5% 5% 8% 11% 38%	5277
	21st to end	Night	10% 7% 3 9% 6% 5% 6% 5% 7% 10% 31%	5736
August	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 6% 9% 46%	3005
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 5% 6% 9% 43%	2934
	21st to end	Night	4 3 1 4 3 3 3 4 6% 9% 60%	3586
September	1st to 10th	Night	11% 5% 2 6% 4 4 5% 4 6% 7% 48%	2130
	11th to 20th	Night	11% 6% 2 7% 4 4 4 3 6% 7% 47%	2200
	21st to end	Night	11% 6% 3 5% 3 4 3 3 5% 6% 51%	2200
October	1st to 10th	Night	11% 4 2 4 4 3 3 4 5% 6% 54%	2200
	11th to 20th	Night	15% 5% 2 5% 3 4 3 3 4 7% 50%	2360
	21st to end	Night	19% 6% 2 5% 3 3 4 3 4 5% 45%	2730
November	1st to 10th	Night	13% 6% 3 6% 3 3 3 3 5% 5% 50%	2666
	11th to 20th	Night	15% 10% 2 6% 3 3 3 3 4 6% 45%	2730
	21st to end	Night	18% 10% 4 5% 4 4 3 3 4 5% 40%	2730
December	1st to 10th	Night	16% 14% 4 10% 4 3 3 2 3 4 36%	4380
	11th to 20th	Night	19% 12% 5% 9% 4 3 3 2 4 5% 32%	4952
	21st to end	Night	15% 15% 4 11% 6% 6% 6% 4 5% 6% 22%	6633

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 9% 18% 8% 1	5259
	11th to 20th	Day	55% 3 5% 20% 16% 2	5280
	21st to end	Day	57% 3 7% 21% 10% 1	5780
February	1st to 10th	Day	56% 5% 7% 19% 12% 2	2042
	11th to 20th	Day	57% 3 6% 20% 11% 2	2058
	21st to end	Day	55% 4 8% 18% 12% 4	1730
March	1st to 10th	Day	51% 4 6% 15% 18% 6%	4668
	11th to 20th	Day	41% 5% 9% 22% 21% 2	5090
	21st to end	Day	45% 5% 10% 28% 11% 1	5586
April	1st to 10th	Day	44% 5% 12% 24% 13% 3	2435
	11th to 20th	Day	44% 5% 9% 23% 16% 4	2532
	21st to end	Day	46% 6% 10% 25% 12% 2	2730
May	1st to 10th	Day	49% 6% 12% 22% 10% 1	7651
	11th to 20th	Day	47% 6% 12% 22% 13%	7630
	21st to end	Day	52% 8% 12% 15% 12% 2	8405
June	1st to 10th	Day	41% 7% 10% 24% 16% 2	2730
	11th to 20th	Day	38% 8% 14% 22% 17% 2	2730
	21st to end	Day	36% 9% 15% 20% 17% 3	2730
July	1st to 10th	Day	41% 8% 15% 24% 12% 1	7615
	11th to 20th	Day	43% 8% 14% 26% 8% 1	7611
	21st to end	Day	49% 7% 13% 21% 9% 1	8156
August	1st to 10th	Day	36% 8% 14% 29% 12% 1	4351
	11th to 20th	Day	39% 8% 12% 28% 12% 2	4238
	21st to end	Day	26% 7% 12% 38% 16% 2	4311
September	1st to 10th	Day	42% 6% 12% 18% 17% 5%	2249
	11th to 20th	Day	36% 4 11% 24% 22% 3	2200
	21st to end	Day	40% 5% 10% 23% 20% 3	2200
October	1st to 10th	Day	23% 4 7% 24% 40% 3	3590
	11th to 20th	Day	25% 3 10% 27% 31% 4	3306
	21st to end	Day	31% 3 8% 29% 19% 9%	3384
November	1st to 10th	Day	35% 4 8% 25% 23% 4	1852
	11th to 20th	Day	43% 4 7% 23% 19% 4	1890
	21st to end	Day	47% 4 8% 21% 17% 3	1890
December	1st to 10th	Day	51% 4 6% 22% 16% 1	3020
	11th to 20th	Day	58% 4 8% 17% 12% 1	3460
	21st to end	Day	61% 6% 10% 17% 6% 1	4565
January	1st to 10th	Night	59% 4 10% 19% 7% 1	7636
	11th to 20th	Night	55% 3 5% 18% 16% 3	7680
	21st to end	Night	54% 3 7% 20% 14% 2	8401
February	1st to 10th	Night	56% 4 11% 18% 10% 1	2574
	11th to 20th	Night	57% 4 6% 19% 12% 2	2459
	21st to end	Night	58% 4 7% 16% 12% 3	2076
March	1st to 10th	Night	51% 4 7% 21% 13% 4	5404
	11th to 20th	Night	37% 4 8% 27% 19% 4	5090
	21st to end	Night	49% 6% 9% 23% 12% 1	5588
April	1st to 10th	Night	41% 6% 11% 22% 18% 3	2202
	11th to 20th	Night	40% 5% 10% 22% 18% 6%	2034
	21st to end	Night	43% 6% 11% 25% 14% 1	1890
May	1st to 10th	Night	52% 7% 9% 21% 10% 1	5264
	11th to 20th	Night	44% 7% 14% 22% 12%	5235
	21st to end	Night	50% 8% 12% 18% 11% 1	5771
June	1st to 10th	Night	32% 8% 15% 25% 17% 3	1890
	11th to 20th	Night	31% 9% 16% 23% 19% 2	1890
	21st to end	Night	34% 8% 16% 23% 15% 5%	1890
July	1st to 10th	Night	37% 8% 12% 29% 13% 1	5235
	11th to 20th	Night	38% 8% 17% 24% 10% 2	5226
	21st to end	Night	45% 8% 15% 20% 11% 1	5606
August	1st to 10th	Night	35% 6% 13% 29% 16% 1	2994
	11th to 20th	Night	35% 7% 13% 30% 13% 1	2961
	21st to end	Night	20% 6% 14% 34% 22% 3	3586
September	1st to 10th	Night	34% 7% 13% 20% 20% 6%	2130
	11th to 20th	Night	36% 5% 10% 24% 23% 2	2200
	21st to end	Night	34% 6% 9% 23% 25% 3	2200
October	1st to 10th	Night	24% 5% 7% 22% 38% 3	3590
	11th to 20th	Night	25% 3 7% 24% 32% 9%	3833
	21st to end	Night	30% 3 8% 22% 29% 9%	4404
November	1st to 10th	Night	37% 4 7% 25% 23% 5%	2666
	11th to 20th	Night	42% 3 7% 20% 22% 6%	2730
	21st to end	Night	46% 3 7% 25% 16% 2	2730
December	1st to 10th	Night	53% 4 8% 20% 14% 1	4380
	11th to 20th	Night	55% 3 8% 20% 12% 1	4954
	21st to end	Night	61% 7% 10% 15% 7%	6633

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	28% 19% 32% 15% 6% 1	330
	11th to 20th	Day	30% 25% 29% 12% 3	330
	21st to end	Day	28% 20% 36% 14% 3	363
February	1st to 10th	Day	26% 20% 35% 15% 4	330
	11th to 20th	Day	36% 22% 28% 11% 2 1	330
	21st to end	Day	33% 17% 34% 13% 3	273
March	1st to 10th	Day	28% 20% 31% 16% 5%	366
	11th to 20th	Day	24% 20% 32% 18% 4 1	540
	21st to end	Day	25% 20% 30% 19% 6% 1	594
April	1st to 10th	Day	20% 19% 29% 22% 8% 2	540
	11th to 20th	Day	20% 17% 29% 20% 10% 3	532
	21st to end	Day	21% 14% 29% 24% 10% 3	540
May	1st to 10th	Day	23% 14% 29% 20% 11% 4	543
	11th to 20th	Day	20% 11% 22% 27% 15% 7%	567
	21st to end	Day	18% 7% 20% 24% 20% 11%	617
June	1st to 10th	Day	13% 5% 21% 28% 20% 12%	570
	11th to 20th	Day	10% 5% 22% 29% 22% 11%	570
	21st to end	Day	12% 4 18% 31% 21% 13%	570
July	1st to 10th	Day	13% 4 13% 24% 23% 24%	565
	11th to 20th	Day	10% 4 16% 26% 27% 17%	564
	21st to end	Day	16% 3 12% 27% 27% 15%	620
August	1st to 10th	Day	14% 2 14% 27% 27% 16%	566
	11th to 20th	Day	11% 3 16% 30% 28% 12%	535
	21st to end	Day	11% 1 10% 26% 32% 19%	583
September	1st to 10th	Day	15% 4 13% 22% 29% 16%	530
	11th to 20th	Day	13% 4 11% 22% 32% 19%	530
	21st to end	Day	18% 6% 17% 26% 25% 8%	530
October	1st to 10th	Day	12% 4 17% 31% 26% 10%	530
	11th to 20th	Day	12% 11% 28% 27% 16% 6%	530
	21st to end	Day	25% 11% 26% 25% 12% 1	491
November	1st to 10th	Day	20% 9% 32% 22% 14% 3	330
	11th to 20th	Day	22% 16% 30% 24% 7% 2	330
	21st to end	Day	25% 13% 32% 23% 6% 1	330
December	1st to 10th	Day	25% 21% 29% 20% 5% 1	330
	11th to 20th	Day	24% 15% 36% 17% 7% 1	330
	21st to end	Day	26% 19% 34% 17% 3 1	363
January	1st to 10th	Night	25% 17% 33% 20% 5%	840
	11th to 20th	Night	31% 16% 30% 20% 3	840
	21st to end	Night	25% 14% 36% 23% 2	924
February	1st to 10th	Night	24% 14% 36% 23% 2	840
	11th to 20th	Night	29% 15% 35% 19% 2	823
	21st to end	Night	29% 15% 37% 17% 2	692
March	1st to 10th	Night	23% 15% 30% 28% 5%	840
	11th to 20th	Night	24% 13% 34% 23% 7%	840
	21st to end	Night	21% 12% 31% 29% 7%	924
April	1st to 10th	Night	18% 11% 33% 29% 8%	732
	11th to 20th	Night	16% 11% 31% 30% 10% 1	623
	21st to end	Night	18% 7% 34% 30% 9% 1	630
May	1st to 10th	Night	19% 7% 28% 30% 13% 3	630
	11th to 20th	Night	17% 5% 21% 36% 19% 2	621
	21st to end	Night	11% 3 17% 37% 27% 5%	683
June	1st to 10th	Night	10% 3 17% 42% 26% 3	630
	11th to 20th	Night	7% 2 18% 38% 31% 3	630
	21st to end	Night	9% 3 15% 41% 29% 4	630
July	1st to 10th	Night	11% 1 9% 31% 36% 11%	615
	11th to 20th	Night	6% 3 9% 34% 42% 6%	612
	21st to end	Night	13% 2 9% 33% 36% 6%	690
August	1st to 10th	Night	11% 3 10% 32% 38% 7%	627
	11th to 20th	Night	8% 2 12% 34% 37% 7%	606
	21st to end	Night	7% 2 8% 37% 38% 8%	660
September	1st to 10th	Night	13% 2 10% 31% 38% 6%	730
	11th to 20th	Night	13% 3 12% 28% 39% 6%	800
	21st to end	Night	15% 3 17% 33% 29% 3	800
October	1st to 10th	Night	12% 4 18% 33% 29% 5%	800
	11th to 20th	Night	18% 5% 26% 31% 18% 2	800
	21st to end	Night	22% 8% 26% 29% 13% 1	880
November	1st to 10th	Night	16% 7% 26% 32% 16% 2	820
	11th to 20th	Night	21% 11% 30% 29% 8% 1	840
	21st to end	Night	24% 11% 25% 30% 9% 1	840
December	1st to 10th	Night	29% 11% 28% 27% 5%	840
	11th to 20th	Night	25% 11% 32% 25% 6% 1	840
	21st to end	Night	27% 16% 28% 25% 3	924

Page generated at 2026-08-12 03:37:16. Version ac07

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