Lion's Head Dark Sky Viewing Platform
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lion's Head Dark Sky Viewing Platform 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	13% 10% 4 10% 6% 5% 5% 4 5% 7% 33%	143941
	Night	13% 12% 5% 12% 7% 5% 5% 3 5% 6% 26%	138052
Transparency	Day	51% 5% 11% 21% 11% 1	147475
	Night	59% 5% 9% 17% 9% 1	142608
Seeing	Day	18% 14% 29% 25% 11% 3	17532
	Night	21% 14% 26% 25% 12% 2	26663

By Month

Percentage Cloud Cover NE (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% 9% 21% 14% 6% 5% 3 3 3 6%	4094
	11th to 20th	Day	8% 19% 12% 28% 12% 8% 4 2 2 1 2	4709
	21st to end	Day	10% 14% 7% 20% 12% 10% 7% 4 4 4 7%	5780
February	1st to 10th	Day	13% 17% 6% 17% 11% 6% 5% 3 4 4 14%	1890
	11th to 20th	Day	11% 15% 6% 15% 9% 8% 6% 5% 5% 5% 16%	1843
	21st to end	Day	12% 15% 5% 11% 8% 8% 7% 4 6% 5% 19%	1685
March	1st to 10th	Day	14% 11% 4 10% 6% 6% 4 4 5% 6% 29%	4875
	11th to 20th	Day	9% 13% 6% 12% 7% 6% 6% 4 6% 6% 26%	5090
	21st to end	Day	17% 11% 5% 11% 6% 4 5% 4 5% 6% 27%	5586
April	1st to 10th	Day	17% 10% 3 7% 6% 5% 5% 4 5% 7% 31%	2432
	11th to 20th	Day	17% 9% 3 7% 4 4 4 3 4 6% 39%	2702
	21st to end	Day	18% 9% 3 6% 4 4 4 4 6% 7% 36%	2730
May	1st to 10th	Day	12% 7% 2 6% 4 4 5% 4 6% 8% 41%	7642
	11th to 20th	Day	10% 7% 3 7% 5% 5% 5% 4 6% 8% 41%	7979
	21st to end	Day	15% 7% 2 6% 4 4 4 3 5% 6% 44%	9060
June	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 5% 6% 8% 41%	3132
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 4 6% 8% 45%	3150
	21st to end	Day	12% 6% 2 5% 5% 4 4 4 6% 8% 43%	3150
July	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 4 6% 8% 43%	8879
	11th to 20th	Day	7% 4 2 5% 3 3 4 3 5% 9% 54%	8762
	21st to end	Day	7% 5% 2 6% 4 4 4 3 5% 8% 52%	8405
August	1st to 10th	Day	10% 5% 2 5% 3 3 5% 4 7% 9% 46%	4364
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 6% 9% 43%	4226
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 47%	4655
September	1st to 10th	Day	12% 6% 2 7% 5% 4 5% 3 5% 8% 44%	2370
	11th to 20th	Day	12% 4 2 6% 4 3 4 4 7% 8% 47%	2200
	21st to end	Day	17% 7% 2 7% 5% 5% 4 3 5% 7% 38%	2200
October	1st to 10th	Day	17% 9% 3 6% 5% 4 5% 4 5% 7% 37%	2030
	11th to 20th	Day	21% 13% 4 9% 6% 5% 5% 4 5% 6% 25%	2000
	21st to end	Day	24% 14% 4 10% 6% 5% 5% 4 5% 6% 18%	2106
November	1st to 10th	Day	15% 16% 5% 9% 7% 5% 5% 4 6% 5% 23%	1799
	11th to 20th	Day	16% 16% 4 10% 7% 7% 7% 4 5% 7% 17%	1680
	21st to end	Day	17% 24% 6% 14% 7% 6% 4 3 4 4 10%	1680
December	1st to 10th	Day	14% 28% 9% 16% 7% 6% 5% 3 3 3 5%	2680
	11th to 20th	Day	18% 22% 7% 18% 8% 6% 4 3 4 4 8%	2823
	21st to end	Day	25% 20% 6% 20% 7% 6% 4 2 3 3 5%	3553
January	1st to 10th	Night	14% 17% 8% 22% 12% 6% 4 3 3 4 7%	8813
	11th to 20th	Night	9% 19% 10% 26% 12% 7% 4 2 3 3 5%	8200
	21st to end	Night	9% 14% 8% 21% 13% 9% 7% 4 4 4 8%	8401
February	1st to 10th	Night	10% 18% 6% 16% 9% 6% 5% 4 4 5% 16%	2730
	11th to 20th	Night	10% 15% 7% 15% 8% 7% 6% 4 5% 4 18%	2663
	21st to end	Night	14% 14% 5% 11% 8% 5% 6% 5% 5% 5% 22%	2118
March	1st to 10th	Night	12% 10% 4 10% 7% 7% 6% 4 5% 7% 29%	5183
	11th to 20th	Night	9% 12% 4 10% 6% 5% 5% 4 6% 7% 32%	5089
	21st to end	Night	17% 11% 5% 10% 5% 5% 5% 3 5% 5% 29%	5588
April	1st to 10th	Night	19% 10% 3 7% 5% 4 4 3 4 6% 33%	2205
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 4 5% 6% 37%	1867
	21st to end	Night	19% 9% 3 8% 4 5% 4 5% 6% 5% 33%	1890
May	1st to 10th	Night	12% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	5257
	11th to 20th	Night	14% 6% 2 8% 5% 5% 4 3 6% 7% 41%	4877
	21st to end	Night	16% 6% 2 6% 4 4 4 3 5% 7% 42%	5114
June	1st to 10th	Night	12% 7% 2 7% 6% 5% 3 4 5% 8% 41%	1483
	11th to 20th	Night	10% 6% 2 5% 5% 4 5% 5% 7% 8% 43%	1470
	21st to end	Night	12% 6% 2 6% 5% 5% 6% 4 6% 8% 41%	1470
July	1st to 10th	Night	9% 7% 2 6% 4 4 4 4 6% 9% 45%	4110
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 3 5% 9% 49%	4224
	21st to end	Night	8% 6% 3 6% 4 4 4 4 6% 8% 48%	5672
August	1st to 10th	Night	10% 7% 3 5% 4 4 5% 4 6% 8% 45%	3005
	11th to 20th	Night	13% 6% 2 6% 4 5% 5% 4 6% 8% 41%	2911
	21st to end	Night	9% 7% 2 6% 4 4 5% 3 6% 8% 46%	3223
September	1st to 10th	Night	10% 5% 2 6% 4 4 5% 4 7% 8% 47%	2012
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 5% 7% 49%	2200
	21st to end	Night	17% 8% 3 7% 5% 5% 3 3 5% 7% 37%	2200
October	1st to 10th	Night	19% 7% 3 8% 5% 4 5% 3 6% 6% 35%	2370
	11th to 20th	Night	22% 11% 3 9% 5% 5% 5% 4 6% 7% 23%	2400
	21st to end	Night	24% 14% 4 9% 6% 6% 5% 4 5% 5% 20%	2730
November	1st to 10th	Night	16% 14% 4 9% 7% 6% 5% 4 5% 6% 24%	2716
	11th to 20th	Night	15% 18% 5% 11% 6% 7% 6% 4 4 7% 17%	2940
	21st to end	Night	21% 21% 5% 12% 7% 5% 5% 3 4 5% 11%	2940
December	1st to 10th	Night	15% 23% 7% 19% 9% 6% 5% 3 4 4 6%	4720
	11th to 20th	Night	14% 21% 8% 20% 8% 6% 5% 3 4 4 7%	5594
	21st to end	Night	21% 22% 9% 18% 7% 5% 3 2 3 3 7%	7667

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	86% 3 5% 5% 1	4095
	11th to 20th	Day	93% 3 2 2	4740
	21st to end	Day	82% 5% 6% 6% 2	5780
February	1st to 10th	Day	73% 7% 8% 10% 2	1890
	11th to 20th	Day	70% 7% 9% 9% 5%	1852
	21st to end	Day	63% 7% 9% 16% 4	1685
March	1st to 10th	Day	56% 5% 13% 12% 12% 1	4878
	11th to 20th	Day	57% 6% 11% 18% 6% 1	5090
	21st to end	Day	54% 7% 12% 17% 8% 1	5586
April	1st to 10th	Day	51% 7% 11% 20% 10% 1	2432
	11th to 20th	Day	46% 5% 9% 23% 16% 2	2702
	21st to end	Day	46% 6% 12% 21% 12% 3	2730
May	1st to 10th	Day	40% 4 12% 26% 14% 3	7651
	11th to 20th	Day	40% 6% 11% 24% 18% 1	7983
	21st to end	Day	42% 4 10% 25% 16% 3	9061
June	1st to 10th	Day	38% 8% 11% 25% 16% 1	3132
	11th to 20th	Day	36% 6% 12% 27% 17% 1	3150
	21st to end	Day	38% 7% 13% 27% 13% 2	3150
July	1st to 10th	Day	41% 3 16% 25% 13% 1	8806
	11th to 20th	Day	29% 3 12% 41% 15% 1	8681
	21st to end	Day	32% 3 13% 35% 16% 1	8220
August	1st to 10th	Day	34% 4 15% 30% 15% 1	4351
	11th to 20th	Day	38% 5% 17% 28% 11%	4265
	21st to end	Day	33% 5% 15% 35% 11% 1	4655
September	1st to 10th	Day	38% 7% 15% 27% 12% 1	2370
	11th to 20th	Day	34% 8% 15% 31% 12%	2200
	21st to end	Day	46% 8% 14% 23% 9%	2200
October	1st to 10th	Day	42% 4 13% 26% 15%	3303
	11th to 20th	Day	54% 4 12% 22% 8%	3240
	21st to end	Day	61% 5% 12% 17% 5%	3382
November	1st to 10th	Day	63% 7% 10% 15% 5%	1799
	11th to 20th	Day	68% 8% 11% 9% 4	1680
	21st to end	Day	77% 7% 9% 6% 1	1680
December	1st to 10th	Day	87% 4 6% 3 1	2680
	11th to 20th	Day	81% 5% 7% 5% 2	2823
	21st to end	Day	87% 5% 4 4	3553
January	1st to 10th	Night	85% 3 5% 5% 2	8813
	11th to 20th	Night	89% 4 3 3 1	8244
	21st to end	Night	81% 5% 5% 6% 3	8401
February	1st to 10th	Night	71% 6% 9% 11% 3	2730
	11th to 20th	Night	68% 6% 8% 13% 5%	2665
	21st to end	Night	62% 8% 11% 13% 6%	2118
March	1st to 10th	Night	55% 5% 13% 15% 10% 2	5193
	11th to 20th	Night	51% 5% 16% 19% 8% 1	5090
	21st to end	Night	55% 6% 8% 18% 11% 2	5588
April	1st to 10th	Night	52% 5% 10% 21% 11% 1	2205
	11th to 20th	Night	47% 5% 8% 22% 17% 1	1867
	21st to end	Night	51% 5% 10% 16% 15% 3	1890
May	1st to 10th	Night	44% 4 8% 23% 16% 4	5264
	11th to 20th	Night	43% 5% 8% 22% 20% 2	4878
	21st to end	Night	42% 4 8% 26% 17% 3	5115
June	1st to 10th	Night	41% 6% 9% 21% 20% 3	1483
	11th to 20th	Night	37% 5% 12% 26% 18% 1	1470
	21st to end	Night	40% 7% 13% 26% 13% 2	1470
July	1st to 10th	Night	38% 2 15% 27% 15% 2	4075
	11th to 20th	Night	34% 3 9% 38% 16% 1	4182
	21st to end	Night	36% 3 9% 31% 19% 1	5543
August	1st to 10th	Night	37% 4 14% 27% 16% 1	2994
	11th to 20th	Night	41% 5% 18% 22% 13% 1	2938
	21st to end	Night	36% 5% 12% 33% 13% 1	3223
September	1st to 10th	Night	34% 8% 14% 29% 14% 1	2012
	11th to 20th	Night	34% 8% 15% 30% 13%	2200
	21st to end	Night	47% 6% 14% 23% 10%	2200
October	1st to 10th	Night	41% 4 8% 30% 16%	3877
	11th to 20th	Night	53% 5% 13% 21% 8%	3899
	21st to end	Night	58% 5% 14% 18% 5%	4404
November	1st to 10th	Night	60% 7% 11% 17% 4	2716
	11th to 20th	Night	68% 7% 13% 7% 3 1	2940
	21st to end	Night	77% 7% 9% 6% 1	2940
December	1st to 10th	Night	85% 4 6% 4 1	4720
	11th to 20th	Night	82% 4 6% 4 3	5594
	21st to end	Night	86% 4 6% 3 1	7667

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	17% 26% 37% 14% 5% 1	220
	11th to 20th	Day	22% 25% 33% 15% 5%	330
	21st to end	Day	24% 18% 34% 20% 5%	363
February	1st to 10th	Day	22% 27% 33% 15% 2	330
	11th to 20th	Day	22% 27% 34% 15% 2	330
	21st to end	Day	24% 29% 35% 12% 1	273
March	1st to 10th	Day	20% 22% 35% 18% 4	459
	11th to 20th	Day	22% 20% 33% 19% 4 1	540
	21st to end	Day	27% 16% 31% 21% 4 1	594
April	1st to 10th	Day	23% 16% 34% 19% 8% 1	540
	11th to 20th	Day	26% 17% 27% 15% 10% 4	532
	21st to end	Day	25% 12% 35% 19% 8% 1	540
May	1st to 10th	Day	18% 11% 36% 24% 9% 2	543
	11th to 20th	Day	14% 10% 31% 28% 12% 4	567
	21st to end	Day	16% 7% 31% 29% 14% 4	617
June	1st to 10th	Day	12% 7% 31% 34% 12% 2	762
	11th to 20th	Day	12% 9% 32% 33% 12% 2	780
	21st to end	Day	17% 6% 29% 34% 12% 3	780
July	1st to 10th	Day	9% 5% 28% 33% 22% 2	771
	11th to 20th	Day	11% 6% 27% 33% 17% 5%	768
	21st to end	Day	9% 6% 28% 36% 17% 5%	646
August	1st to 10th	Day	13% 5% 22% 34% 21% 6%	566
	11th to 20th	Day	13% 6% 19% 35% 19% 8%	535
	21st to end	Day	12% 9% 26% 28% 20% 5%	583
September	1st to 10th	Day	15% 11% 22% 27% 18% 6%	530
	11th to 20th	Day	10% 6% 23% 26% 25% 9%	530
	21st to end	Day	19% 12% 21% 28% 16% 4	530
October	1st to 10th	Day	21% 15% 24% 24% 13% 3	530
	11th to 20th	Day	22% 21% 31% 20% 5% 1	530
	21st to end	Day	28% 20% 30% 19% 2 1	489
November	1st to 10th	Day	28% 23% 29% 15% 4	302
	11th to 20th	Day	22% 27% 33% 15% 3	220
	21st to end	Day	29% 25% 31% 14% 1	220
December	1st to 10th	Day	29% 25% 29% 12% 5%	220
	11th to 20th	Day	30% 27% 29% 12% 2	220
	21st to end	Day	31% 26% 31% 8% 2	242
January	1st to 10th	Night	24% 20% 33% 19% 4 1	1050
	11th to 20th	Night	26% 21% 28% 19% 5% 1	1040
	21st to end	Night	20% 17% 30% 24% 7% 1	924
February	1st to 10th	Night	21% 21% 32% 21% 5%	840
	11th to 20th	Night	19% 17% 35% 21% 8%	823
	21st to end	Night	21% 18% 35% 21% 4	692
March	1st to 10th	Night	17% 17% 34% 24% 7% 1	840
	11th to 20th	Night	19% 19% 33% 22% 8% 1	840
	21st to end	Night	20% 14% 28% 28% 10%	924
April	1st to 10th	Night	24% 15% 29% 25% 5% 1	835
	11th to 20th	Night	21% 13% 27% 25% 12% 2	623
	21st to end	Night	24% 11% 24% 26% 13% 1	630
May	1st to 10th	Night	16% 7% 26% 34% 15% 2	630
	11th to 20th	Night	16% 7% 23% 34% 18% 1	498
	21st to end	Night	16% 4 25% 36% 17% 2	455
June	1st to 10th	Night	17% 5% 28% 35% 14% 2	420
	11th to 20th	Night	12% 7% 23% 39% 17% 1	420
	21st to end	Night	13% 6% 23% 36% 21% 1	420
July	1st to 10th	Night	9% 4 16% 50% 20% 2	410
	11th to 20th	Night	10% 4 23% 36% 24% 3	444
	21st to end	Night	9% 4 19% 42% 24% 3	690
August	1st to 10th	Night	11% 3 19% 38% 26% 3	627
	11th to 20th	Night	12% 6% 15% 32% 28% 6%	606
	21st to end	Night	13% 5% 21% 31% 26% 3	660
September	1st to 10th	Night	12% 8% 20% 32% 21% 6%	786
	11th to 20th	Night	12% 6% 19% 31% 24% 7%	800
	21st to end	Night	19% 9% 20% 27% 20% 6%	800
October	1st to 10th	Night	22% 9% 25% 25% 17% 2	800
	11th to 20th	Night	28% 15% 24% 24% 9% 1	800
	21st to end	Night	32% 13% 28% 22% 4 1	880
November	1st to 10th	Night	28% 16% 25% 22% 7% 1	820
	11th to 20th	Night	25% 23% 25% 19% 8% 1	840
	21st to end	Night	33% 19% 27% 17% 4	840
December	1st to 10th	Night	31% 22% 28% 13% 6%	840
	11th to 20th	Night	27% 22% 32% 14% 4	961
	21st to end	Night	34% 18% 29% 15% 4	1155

Page generated at 2026-08-12 03:37:14. Version ac07

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