Berry Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Berry Lake clear sky chart from 2005-11-06 to 2026-02-16.

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% 11% 5% 11% 6% 5% 5% 4 5% 7% 31%	130017
	Night	12% 12% 5% 11% 7% 5% 5% 4 5% 6% 29%	131054
Transparency	Day	52% 6% 10% 20% 12% 1	133516
	Night	54% 6% 11% 18% 10% 1	135616
Seeing	Day	18% 14% 30% 23% 11% 4	17420
	Night	18% 11% 31% 29% 11% 1	27600

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	12% 17% 10% 24% 11% 6% 4 2 3 3 8%	4691
	11th to 20th	Day	9% 15% 7% 24% 14% 10% 8% 2 3 3 6%	4710
	21st to end	Day	10% 13% 8% 16% 9% 10% 6% 5% 5% 5% 14%	5156
February	1st to 10th	Day	9% 16% 6% 13% 14% 7% 6% 4 4 5% 15%	1838
	11th to 20th	Day	9% 14% 7% 17% 12% 8% 5% 3 5% 5% 16%	1998
	21st to end	Day	9% 18% 5% 14% 9% 6% 6% 4 4 5% 20%	1650
March	1st to 10th	Day	10% 10% 5% 10% 8% 6% 5% 4 5% 6% 30%	4480
	11th to 20th	Day	11% 9% 5% 13% 6% 5% 5% 5% 6% 7% 29%	4860
	21st to end	Day	20% 12% 6% 15% 6% 5% 4 3 4 4 22%	5641
April	1st to 10th	Day	15% 16% 5% 10% 5% 5% 3 3 5% 6% 28%	2400
	11th to 20th	Day	17% 13% 4 7% 5% 4 3 3 4 6% 34%	2469
	21st to end	Day	14% 11% 4 9% 5% 5% 5% 4 5% 7% 31%	2600
May	1st to 10th	Day	16% 10% 3 6% 4 4 4 3 5% 7% 38%	5862
	11th to 20th	Day	10% 9% 3 7% 5% 5% 5% 4 5% 7% 39%	5989
	21st to end	Day	12% 9% 3 7% 4 4 5% 4 6% 7% 40%	6935
June	1st to 10th	Day	11% 6% 3 7% 6% 4 4 4 7% 7% 42%	2800
	11th to 20th	Day	12% 7% 2 7% 4 5% 4 4 6% 9% 39%	2800
	21st to end	Day	12% 7% 3 7% 6% 4 5% 5% 6% 7% 39%	2800
July	1st to 10th	Day	11% 7% 3 7% 5% 4 5% 4 7% 9% 39%	6360
	11th to 20th	Day	7% 6% 3 6% 4 5% 5% 4 6% 9% 46%	6360
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 4 6% 10% 44%	6924
August	1st to 10th	Day	9% 5% 3 6% 5% 5% 6% 5% 8% 9% 38%	4334
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 5% 7% 44%	4174
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 7% 7% 41%	4457
September	1st to 10th	Day	11% 6% 2 6% 5% 6% 5% 5% 6% 7% 40%	2365
	11th to 20th	Day	11% 5% 3 6% 4 4 4 4 5% 8% 47%	2200
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 3 5% 8% 38%	2200
October	1st to 10th	Day	16% 8% 3 7% 4 4 4 3 5% 6% 41%	2200
	11th to 20th	Day	18% 14% 4 9% 6% 5% 5% 4 5% 5% 24%	1913
	21st to end	Day	18% 13% 4 11% 7% 5% 6% 4 5% 5% 22%	1980
November	1st to 10th	Day	13% 14% 4 8% 5% 5% 5% 4 5% 7% 30%	1852
	11th to 20th	Day	13% 17% 8% 11% 8% 5% 5% 3 5% 6% 19%	1890
	21st to end	Day	16% 20% 8% 15% 6% 4 4 3 4 5% 16%	1885
December	1st to 10th	Day	11% 20% 11% 20% 7% 5% 5% 4 4 4 9%	2356
	11th to 20th	Day	11% 20% 12% 18% 8% 6% 4 3 4 4 11%	2818
	21st to end	Day	20% 23% 8% 16% 6% 5% 4 2 3 3 9%	4070
January	1st to 10th	Night	12% 15% 8% 23% 10% 6% 4 3 3 3 12%	8232
	11th to 20th	Night	8% 16% 8% 20% 12% 12% 8% 3 4 3 6%	8280
	21st to end	Night	8% 14% 7% 20% 10% 8% 7% 4 5% 5% 12%	9058
February	1st to 10th	Night	9% 13% 6% 15% 12% 7% 6% 4 5% 5% 17%	2777
	11th to 20th	Night	10% 12% 5% 14% 9% 6% 6% 5% 6% 6% 20%	2399
	21st to end	Night	12% 12% 4 11% 9% 6% 6% 4 5% 6% 24%	1980
March	1st to 10th	Night	14% 8% 3 9% 6% 5% 4 4 5% 6% 35%	5373
	11th to 20th	Night	10% 9% 4 8% 5% 5% 5% 4 6% 9% 35%	5099
	21st to end	Night	15% 13% 5% 10% 6% 5% 4 3 5% 6% 29%	5330
April	1st to 10th	Night	14% 12% 6% 8% 5% 4 5% 4 5% 6% 32%	2000
	11th to 20th	Night	19% 10% 3 7% 5% 4 4 3 5% 6% 36%	1879
	21st to end	Night	15% 9% 3 8% 5% 4 3 3 5% 6% 38%	1800
May	1st to 10th	Night	14% 9% 2 7% 5% 4 4 4 5% 8% 39%	4033
	11th to 20th	Night	12% 9% 3 7% 5% 4 4 4 5% 7% 38%	3909
	21st to end	Night	18% 6% 2 5% 3 3 3 3 6% 6% 45%	3942
June	1st to 10th	Night	13% 6% 3 6% 4 4 4 4 7% 8% 43%	1600
	11th to 20th	Night	10% 6% 2 7% 5% 4 5% 4 7% 10% 41%	1600
	21st to end	Night	9% 7% 2 7% 4 4 4 4 6% 8% 45%	1600
July	1st to 10th	Night	9% 7% 3 6% 4 5% 5% 4 7% 8% 43%	3618
	11th to 20th	Night	7% 6% 2 4 3 4 5% 4 6% 8% 52%	3617
	21st to end	Night	6% 5% 2 6% 4 4 4 4 6% 8% 51%	3947
August	1st to 10th	Night	10% 5% 2 5% 5% 4 5% 5% 7% 8% 45%	2815
	11th to 20th	Night	11% 6% 2 5% 3 4 4 3 5% 7% 51%	2875
	21st to end	Night	8% 6% 2 6% 4 4 5% 3 6% 7% 48%	3438
September	1st to 10th	Night	9% 5% 2 5% 4 3 4 4 5% 7% 52%	2015
	11th to 20th	Night	10% 5% 2 5% 3 4 4 4 6% 7% 51%	2200
	21st to end	Night	13% 8% 3 8% 4 3 4 3 6% 7% 40%	2200
October	1st to 10th	Night	15% 7% 3 6% 4 3 3 3 4 6% 45%	2200
	11th to 20th	Night	16% 12% 4 8% 5% 5% 4 4 5% 7% 31%	2483
	21st to end	Night	19% 13% 4 8% 5% 4 4 4 5% 6% 28%	2860
November	1st to 10th	Night	10% 13% 4 9% 6% 4 5% 3 5% 7% 32%	2666
	11th to 20th	Night	12% 14% 6% 13% 7% 6% 5% 4 5% 6% 21%	2730
	21st to end	Night	14% 19% 6% 12% 6% 5% 5% 3 4 6% 19%	2730
December	1st to 10th	Night	10% 15% 8% 17% 8% 7% 5% 4 5% 6% 15%	5045
	11th to 20th	Night	11% 21% 8% 17% 9% 6% 5% 3 4 4 11%	5574
	21st to end	Night	20% 23% 7% 14% 6% 5% 4 2 3 4 11%	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	80% 6% 6% 6% 2	4692
	11th to 20th	Day	85% 4 4 5% 2	4710
	21st to end	Day	71% 5% 8% 11% 4	5156
February	1st to 10th	Day	71% 5% 6% 13% 3	1838
	11th to 20th	Day	70% 5% 9% 11% 5%	2008
	21st to end	Day	65% 6% 10% 14% 5% 1	1650
March	1st to 10th	Day	53% 5% 14% 16% 10% 2	4480
	11th to 20th	Day	52% 5% 15% 16% 9% 1	4860
	21st to end	Day	64% 5% 9% 15% 7% 1	5643
April	1st to 10th	Day	58% 4 10% 17% 11%	2400
	11th to 20th	Day	52% 5% 9% 19% 14% 1	2469
	21st to end	Day	51% 6% 12% 15% 14% 2	2600
May	1st to 10th	Day	45% 5% 10% 20% 17% 3	5897
	11th to 20th	Day	43% 7% 10% 23% 16% 2	5993
	21st to end	Day	42% 6% 9% 21% 19% 3	6949
June	1st to 10th	Day	39% 7% 10% 26% 16% 2	2800
	11th to 20th	Day	40% 7% 12% 22% 18% 1	2800
	21st to end	Day	42% 7% 13% 23% 14% 1	2800
July	1st to 10th	Day	40% 6% 11% 26% 16% 1	6291
	11th to 20th	Day	33% 6% 11% 31% 16% 1	6285
	21st to end	Day	33% 7% 13% 29% 17% 1	6728
August	1st to 10th	Day	38% 8% 12% 27% 14% 1	4319
	11th to 20th	Day	38% 7% 12% 27% 16% 1	4213
	21st to end	Day	39% 8% 12% 27% 14% 1	4456
September	1st to 10th	Day	41% 7% 12% 24% 14% 1	2365
	11th to 20th	Day	35% 7% 13% 29% 15% 1	2200
	21st to end	Day	44% 6% 13% 26% 12%	2200
October	1st to 10th	Day	31% 5% 8% 35% 20% 2	3590
	11th to 20th	Day	51% 5% 9% 20% 14%	3077
	21st to end	Day	59% 6% 13% 17% 6%	3180
November	1st to 10th	Day	52% 8% 10% 20% 9%	1852
	11th to 20th	Day	65% 7% 12% 13% 4	1890
	21st to end	Day	72% 4 11% 10% 3	1885
December	1st to 10th	Day	77% 7% 8% 7% 1	2356
	11th to 20th	Day	79% 5% 7% 8% 1	2814
	21st to end	Day	81% 3 5% 7% 3	4070
January	1st to 10th	Night	76% 5% 9% 8% 3	8233
	11th to 20th	Night	82% 4 6% 5% 2	8280
	21st to end	Night	72% 5% 8% 11% 5%	9058
February	1st to 10th	Night	67% 7% 7% 14% 5% 1	2777
	11th to 20th	Night	62% 8% 9% 15% 5%	2400
	21st to end	Night	60% 6% 12% 15% 6% 1	1980
March	1st to 10th	Night	48% 5% 16% 20% 10% 1	5373
	11th to 20th	Night	44% 7% 20% 20% 9% 1	5099
	21st to end	Night	55% 6% 10% 19% 9% 1	5330
April	1st to 10th	Night	51% 8% 8% 20% 13% 1	2000
	11th to 20th	Night	49% 5% 8% 21% 15% 2	1879
	21st to end	Night	47% 6% 11% 19% 15% 2	1800
May	1st to 10th	Night	43% 6% 12% 17% 18% 4	4060
	11th to 20th	Night	43% 6% 9% 27% 14% 1	3910
	21st to end	Night	40% 6% 9% 24% 17% 5%	3950
June	1st to 10th	Night	38% 7% 11% 26% 17% 1	1600
	11th to 20th	Night	38% 7% 13% 22% 19% 1	1600
	21st to end	Night	37% 7% 13% 27% 15% 2	1600
July	1st to 10th	Night	37% 6% 12% 26% 15% 4	3580
	11th to 20th	Night	29% 6% 13% 32% 19% 1	3572
	21st to end	Night	31% 6% 16% 28% 18% 1	3832
August	1st to 10th	Night	33% 8% 16% 28% 14% 1	2806
	11th to 20th	Night	33% 5% 15% 31% 16%	2902
	21st to end	Night	33% 8% 13% 27% 18% 1	3438
September	1st to 10th	Night	30% 7% 14% 30% 18% 2	2015
	11th to 20th	Night	30% 7% 14% 34% 14% 1	2200
	21st to end	Night	42% 7% 13% 27% 10% 1	2200
October	1st to 10th	Night	32% 4 11% 37% 16% 1	3590
	11th to 20th	Night	44% 6% 10% 25% 15% 1	4045
	21st to end	Night	49% 5% 12% 26% 8%	4610
November	1st to 10th	Night	51% 6% 12% 20% 10% 1	2666
	11th to 20th	Night	60% 8% 12% 13% 6% 1	2730
	21st to end	Night	66% 6% 13% 12% 3 1	2730
December	1st to 10th	Night	68% 9% 12% 9% 2	5045
	11th to 20th	Night	76% 6% 8% 8% 2	5576
	21st to end	Night	77% 5% 8% 6% 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	22% 21% 33% 19% 6%	330
	11th to 20th	Day	25% 22% 38% 14% 2	330
	21st to end	Day	23% 17% 37% 17% 5%	363
February	1st to 10th	Day	18% 28% 34% 14% 4 2	330
	11th to 20th	Day	22% 25% 39% 13% 2	315
	21st to end	Day	23% 33% 35% 8% 1	249
March	1st to 10th	Day	21% 28% 38% 12% 2	300
	11th to 20th	Day	26% 15% 30% 20% 9% 1	445
	21st to end	Day	28% 16% 28% 20% 6% 1	550
April	1st to 10th	Day	24% 17% 37% 16% 4 1	500
	11th to 20th	Day	29% 16% 31% 14% 7% 3	492
	21st to end	Day	24% 15% 28% 24% 8% 2	500
May	1st to 10th	Day	23% 19% 31% 18% 7% 2	503
	11th to 20th	Day	17% 12% 31% 25% 11% 4	577
	21st to end	Day	15% 12% 30% 28% 13% 3	789
June	1st to 10th	Day	11% 15% 36% 24% 11% 3	730
	11th to 20th	Day	16% 12% 32% 26% 10% 3	730
	21st to end	Day	15% 10% 33% 28% 11% 3	730
July	1st to 10th	Day	8% 7% 29% 31% 19% 6%	721
	11th to 20th	Day	10% 8% 27% 32% 17% 7%	718
	21st to end	Day	8% 7% 31% 31% 16% 7%	794
August	1st to 10th	Day	10% 6% 24% 27% 23% 10%	588
	11th to 20th	Day	11% 5% 20% 31% 19% 13%	519
	21st to end	Day	12% 8% 22% 32% 18% 8%	583
September	1st to 10th	Day	14% 10% 23% 27% 16% 10%	530
	11th to 20th	Day	9% 7% 21% 28% 22% 13%	530
	21st to end	Day	19% 10% 20% 27% 18% 6%	530
October	1st to 10th	Day	20% 12% 27% 22% 16% 2	530
	11th to 20th	Day	25% 16% 32% 23% 4	425
	21st to end	Day	25% 20% 34% 16% 4 1	363
November	1st to 10th	Day	25% 17% 36% 13% 8%	330
	11th to 20th	Day	26% 22% 34% 13% 4	330
	21st to end	Day	26% 24% 33% 14% 2 1	330
December	1st to 10th	Day	28% 19% 33% 13% 5% 2	223
	11th to 20th	Day	26% 24% 36% 12% 2	250
	21st to end	Day	30% 22% 34% 12% 1 1	363
January	1st to 10th	Night	19% 15% 36% 22% 7% 1	1050
	11th to 20th	Night	21% 16% 35% 22% 6%	1050
	21st to end	Night	17% 10% 39% 26% 6%	1155
February	1st to 10th	Night	17% 15% 38% 25% 4	902
	11th to 20th	Night	18% 15% 37% 25% 6%	804
	21st to end	Night	21% 17% 38% 20% 4	660
March	1st to 10th	Night	17% 14% 35% 24% 9% 1	800
	11th to 20th	Night	18% 12% 37% 26% 7%	800
	21st to end	Night	21% 10% 35% 27% 6% 1	820
April	1st to 10th	Night	19% 12% 37% 26% 5% 1	600
	11th to 20th	Night	24% 13% 31% 24% 8%	593
	21st to end	Night	20% 11% 31% 30% 8% 1	600
May	1st to 10th	Night	15% 9% 35% 32% 9%	600
	11th to 20th	Night	18% 8% 31% 32% 11% 1	591
	21st to end	Night	15% 5% 31% 34% 14% 1	650
June	1st to 10th	Night	14% 7% 31% 35% 12% 1	600
	11th to 20th	Night	12% 6% 30% 36% 16% 1	600
	21st to end	Night	13% 7% 26% 38% 16% 1	600
July	1st to 10th	Night	8% 2 22% 44% 22% 2	585
	11th to 20th	Night	7% 4 22% 40% 23% 4	582
	21st to end	Night	9% 2 23% 41% 23% 1	657
August	1st to 10th	Night	8% 2 21% 46% 21% 2	597
	11th to 20th	Night	8% 5% 18% 38% 27% 5%	594
	21st to end	Night	10% 5% 22% 35% 27% 1	660
September	1st to 10th	Night	12% 4 22% 36% 22% 5%	615
	11th to 20th	Night	11% 5% 21% 35% 25% 4	800
	21st to end	Night	17% 9% 24% 32% 16% 3	800
October	1st to 10th	Night	19% 8% 27% 31% 15% 1	800
	11th to 20th	Night	22% 12% 30% 28% 8% 1	800
	21st to end	Night	27% 12% 28% 25% 8%	880
November	1st to 10th	Night	18% 15% 32% 27% 7% 1	820
	11th to 20th	Night	21% 17% 33% 23% 5%	840
	21st to end	Night	23% 15% 35% 23% 3	840
December	1st to 10th	Night	21% 16% 34% 24% 4	1050
	11th to 20th	Night	21% 16% 40% 19% 4 1	1050
	21st to end	Night	28% 15% 32% 23% 2	1155

Page generated at 2026-02-13 01:42:12. Version ac07

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