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 2025-04-11.

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% 11% 4 10% 6% 5% 5% 4 5% 6% 32%	113198
	Night	14% 13% 5% 12% 7% 5% 5% 3 5% 6% 25%	115128
Transparency	Day	52% 6% 11% 19% 10% 1	116775
	Night	60% 6% 10% 15% 8% 1	119716
Seeing	Day	19% 13% 29% 24% 11% 3	15661
	Night	21% 13% 26% 25% 12% 2	25064

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	13% 17% 10% 20% 16% 6% 5% 3 3 2 5%	3158
	11th to 20th	Day	10% 18% 11% 29% 12% 8% 5% 2 2 2 3	3606
	21st to end	Day	13% 16% 7% 20% 10% 8% 5% 4 4 4 8%	4466
February	1st to 10th	Day	13% 18% 6% 17% 11% 6% 5% 3 4 4 13%	1800
	11th to 20th	Day	10% 15% 6% 15% 9% 8% 5% 5% 5% 5% 16%	1753
	21st to end	Day	12% 15% 5% 11% 8% 8% 6% 4 6% 5% 19%	1607
March	1st to 10th	Day	14% 11% 4 10% 6% 6% 4 4 5% 6% 29%	4769
	11th to 20th	Day	9% 13% 6% 13% 7% 6% 6% 4 6% 6% 26%	4980
	21st to end	Day	17% 11% 5% 11% 6% 4 5% 4 5% 6% 28%	5465
April	1st to 10th	Day	17% 11% 3 7% 6% 5% 5% 4 5% 7% 31%	2316
	11th to 20th	Day	18% 9% 3 7% 4 4 4 3 4 6% 39%	2442
	21st to end	Day	18% 9% 3 6% 4 4 4 4 5% 7% 37%	2470
May	1st to 10th	Day	14% 8% 2 7% 4 4 4 4 5% 7% 40%	4108
	11th to 20th	Day	12% 7% 3 6% 4 4 5% 4 6% 8% 41%	4266
	21st to end	Day	12% 5% 2 6% 4 5% 4 3 5% 7% 47%	4837
June	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 5% 6% 8% 41%	2834
	11th to 20th	Day	9% 6% 2 6% 5% 4 5% 4 6% 8% 46%	2850
	21st to end	Day	12% 7% 2 5% 5% 3 4 4 6% 8% 44%	2850
July	1st to 10th	Day	11% 5% 2 7% 6% 5% 5% 4 6% 7% 41%	4760
	11th to 20th	Day	9% 4 1 5% 3 3 4 4 5% 8% 53%	4698
	21st to end	Day	8% 5% 2 5% 4 3 4 3 6% 8% 53%	4503
August	1st to 10th	Day	10% 5% 2 5% 3 3 5% 4 7% 9% 46%	4104
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 9% 42%	4044
	21st to end	Day	9% 5% 2 6% 4 4 4 4 6% 9% 47%	4513
September	1st to 10th	Day	13% 6% 2 7% 5% 3 5% 3 5% 8% 44%	2252
	11th to 20th	Day	12% 5% 2 6% 4 4 4 4 6% 7% 46%	2090
	21st to end	Day	17% 7% 2 7% 5% 5% 4 3 5% 7% 38%	2090
October	1st to 10th	Day	17% 10% 3 6% 5% 4 5% 4 5% 7% 35%	1929
	11th to 20th	Day	21% 13% 4 9% 6% 5% 5% 4 5% 6% 23%	1900
	21st to end	Day	25% 14% 4 9% 6% 5% 5% 4 5% 6% 17%	2001
November	1st to 10th	Day	15% 16% 4 9% 7% 5% 5% 4 6% 5% 23%	1712
	11th to 20th	Day	17% 16% 4 10% 7% 7% 7% 4 5% 6% 17%	1600
	21st to end	Day	18% 24% 6% 14% 7% 6% 4 3 4 4 10%	1600
December	1st to 10th	Day	14% 28% 9% 16% 7% 6% 5% 3 3 3 5%	2600
	11th to 20th	Day	18% 22% 7% 18% 8% 5% 4 3 4 4 8%	2749
	21st to end	Day	25% 20% 6% 19% 6% 7% 4 2 3 3 5%	3476
January	1st to 10th	Night	14% 17% 8% 22% 12% 6% 4 3 3 3 7%	6790
	11th to 20th	Night	11% 18% 9% 26% 12% 7% 4 3 3 3 5%	6294
	21st to end	Night	11% 16% 9% 20% 11% 9% 6% 3 4 3 9%	6490
February	1st to 10th	Night	10% 18% 6% 17% 10% 6% 5% 4 4 5% 15%	2600
	11th to 20th	Night	10% 16% 7% 15% 9% 7% 6% 4 5% 5% 18%	2533
	21st to end	Night	14% 13% 5% 11% 8% 5% 6% 5% 5% 5% 22%	2020
March	1st to 10th	Night	12% 10% 4 10% 6% 7% 6% 4 5% 7% 29%	5069
	11th to 20th	Night	9% 11% 4 10% 6% 5% 5% 4 6% 7% 33%	4979
	21st to end	Night	17% 11% 4 10% 5% 6% 5% 3 5% 5% 29%	5467
April	1st to 10th	Night	19% 10% 4 7% 5% 4 4 3 4 6% 33%	2100
	11th to 20th	Night	18% 8% 3 7% 5% 4 3 4 5% 6% 38%	1693
	21st to end	Night	19% 9% 3 8% 4 5% 4 4 5% 6% 33%	1710
May	1st to 10th	Night	14% 7% 3 7% 4 5% 5% 3 5% 8% 38%	2833
	11th to 20th	Night	13% 6% 2 8% 5% 5% 5% 4 7% 7% 39%	2623
	21st to end	Night	10% 6% 3 7% 5% 5% 4 4 6% 7% 45%	2738
June	1st to 10th	Night	12% 8% 2 7% 6% 5% 3 4 5% 8% 39%	1342
	11th to 20th	Night	9% 6% 2 5% 4 4 5% 4 6% 8% 45%	1330
	21st to end	Night	11% 6% 2 6% 5% 5% 6% 4 6% 8% 42%	1330
July	1st to 10th	Night	9% 8% 2 6% 4 4 5% 3 4 8% 46%	2210
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 5% 7% 50%	2268
	21st to end	Night	7% 6% 3 5% 4 4 4 3 6% 8% 50%	3048
August	1st to 10th	Night	10% 7% 3 5% 4 4 5% 4 7% 8% 45%	2825
	11th to 20th	Night	13% 6% 2 6% 4 5% 5% 4 6% 9% 41%	2785
	21st to end	Night	9% 7% 2 6% 4 4 4 3 6% 8% 46%	3124
September	1st to 10th	Night	10% 5% 2 6% 4 4 5% 4 6% 8% 47%	1910
	11th to 20th	Night	12% 5% 2 6% 4 4 4 4 5% 7% 48%	2090
	21st to end	Night	17% 8% 3 7% 5% 5% 3 3 5% 7% 37%	2090
October	1st to 10th	Night	20% 7% 3 9% 5% 4 5% 3 6% 6% 33%	2251
	11th to 20th	Night	22% 11% 3 9% 5% 5% 5% 4 5% 7% 23%	2280
	21st to end	Night	24% 14% 4 9% 6% 6% 5% 4 5% 5% 18%	2593
November	1st to 10th	Night	17% 14% 3 9% 7% 6% 5% 4 5% 6% 24%	2583
	11th to 20th	Night	16% 18% 5% 11% 7% 7% 6% 4 4 6% 17%	2800
	21st to end	Night	21% 20% 5% 12% 7% 5% 5% 4 5% 5% 11%	2800
December	1st to 10th	Night	15% 23% 7% 18% 9% 6% 5% 3 4 4 6%	4580
	11th to 20th	Night	14% 22% 8% 20% 7% 5% 5% 3 4 4 7%	5448
	21st to end	Night	22% 22% 9% 18% 7% 5% 3 2 3 3 7%	7502

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	87% 4 4 4 1	3159
	11th to 20th	Day	92% 3 2 2 1	3637
	21st to end	Day	80% 6% 7% 6% 2	4466
February	1st to 10th	Day	74% 7% 8% 10% 2	1800
	11th to 20th	Day	69% 8% 9% 9% 5%	1762
	21st to end	Day	63% 8% 10% 15% 4	1607
March	1st to 10th	Day	56% 5% 13% 11% 12% 1	4772
	11th to 20th	Day	57% 7% 11% 18% 6% 1	4980
	21st to end	Day	54% 7% 12% 18% 8% 1	5465
April	1st to 10th	Day	51% 7% 11% 19% 11% 1	2316
	11th to 20th	Day	46% 6% 9% 23% 15% 2	2442
	21st to end	Day	46% 7% 12% 20% 12% 3	2470
May	1st to 10th	Day	40% 8% 11% 21% 18% 2	4120
	11th to 20th	Day	36% 10% 15% 26% 13% 1	4270
	21st to end	Day	36% 7% 13% 19% 20% 4	4837
June	1st to 10th	Day	38% 8% 12% 25% 15% 1	2834
	11th to 20th	Day	35% 7% 12% 27% 18% 2	2850
	21st to end	Day	38% 8% 13% 26% 14% 2	2850
July	1st to 10th	Day	41% 4 16% 23% 14% 1	4686
	11th to 20th	Day	30% 5% 14% 37% 13% 1	4617
	21st to end	Day	30% 5% 11% 33% 19% 1	4360
August	1st to 10th	Day	34% 5% 15% 30% 15% 1	4091
	11th to 20th	Day	38% 6% 17% 28% 12%	4083
	21st to end	Day	33% 6% 14% 35% 11% 1	4513
September	1st to 10th	Day	38% 8% 14% 27% 12% 1	2252
	11th to 20th	Day	35% 8% 15% 29% 12%	2090
	21st to end	Day	45% 9% 14% 23% 8%	2090
October	1st to 10th	Day	43% 4 12% 25% 15%	3202
	11th to 20th	Day	55% 4 12% 21% 8%	3140
	21st to end	Day	61% 5% 12% 17% 4	3277
November	1st to 10th	Day	62% 8% 10% 15% 5%	1712
	11th to 20th	Day	68% 8% 11% 9% 4	1600
	21st to end	Day	77% 7% 9% 6% 1	1600
December	1st to 10th	Day	87% 4 6% 3 1	2600
	11th to 20th	Day	81% 5% 7% 5% 2	2749
	21st to end	Day	87% 5% 4 4	3476
January	1st to 10th	Night	85% 4 5% 5% 1	6790
	11th to 20th	Night	87% 5% 4 2 1	6338
	21st to end	Night	79% 7% 5% 5% 3	6490
February	1st to 10th	Night	72% 6% 9% 10% 3	2600
	11th to 20th	Night	68% 6% 8% 13% 5%	2535
	21st to end	Night	61% 8% 11% 13% 6%	2020
March	1st to 10th	Night	55% 5% 13% 14% 10% 2	5079
	11th to 20th	Night	50% 5% 16% 19% 8% 1	4980
	21st to end	Night	55% 6% 8% 18% 11% 2	5467
April	1st to 10th	Night	52% 5% 10% 21% 11% 1	2100
	11th to 20th	Night	46% 5% 8% 22% 18% 2	1693
	21st to end	Night	51% 6% 10% 15% 15% 3	1710
May	1st to 10th	Night	42% 8% 12% 20% 17% 2	2840
	11th to 20th	Night	40% 8% 11% 21% 18% 3	2624
	21st to end	Night	37% 7% 12% 22% 18% 4	2739
June	1st to 10th	Night	43% 7% 9% 20% 18% 3	1342
	11th to 20th	Night	34% 6% 13% 26% 19% 1	1330
	21st to end	Night	39% 7% 12% 26% 13% 2	1330
July	1st to 10th	Night	37% 3 14% 24% 17% 5%	2175
	11th to 20th	Night	34% 5% 8% 37% 15% 1	2226
	21st to end	Night	33% 5% 11% 26% 24% 2	2951
August	1st to 10th	Night	37% 5% 14% 27% 15% 1	2814
	11th to 20th	Night	41% 5% 18% 21% 14% 1	2812
	21st to end	Night	36% 5% 12% 33% 13% 1	3124
September	1st to 10th	Night	33% 9% 14% 28% 15% 1	1910
	11th to 20th	Night	35% 8% 15% 28% 13%	2090
	21st to end	Night	47% 6% 14% 23% 9%	2090
October	1st to 10th	Night	42% 4 8% 30% 16%	3758
	11th to 20th	Night	53% 5% 13% 21% 8%	3779
	21st to end	Night	58% 5% 14% 18% 5%	4267
November	1st to 10th	Night	60% 7% 11% 17% 4	2583
	11th to 20th	Night	68% 8% 13% 7% 3 1	2800
	21st to end	Night	76% 8% 10% 6% 1	2800
December	1st to 10th	Night	85% 4 6% 3 1	4580
	11th to 20th	Night	83% 4 6% 4 3	5448
	21st to end	Night	85% 4 6% 3 1	7502

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% 25% 37% 15% 5% 2	200
	11th to 20th	Day	23% 21% 34% 16% 5%	300
	21st to end	Day	25% 16% 35% 18% 5%	330
February	1st to 10th	Day	24% 28% 31% 15% 2	300
	11th to 20th	Day	22% 28% 35% 15% 1	300
	21st to end	Day	25% 29% 34% 10% 1	249
March	1st to 10th	Day	21% 20% 35% 19% 5%	423
	11th to 20th	Day	21% 19% 34% 21% 5% 1	500
	21st to end	Day	27% 14% 31% 22% 5% 1	550
April	1st to 10th	Day	23% 14% 35% 19% 8% 1	500
	11th to 20th	Day	28% 16% 27% 15% 9% 5%	452
	21st to end	Day	27% 12% 34% 18% 8% 2	460
May	1st to 10th	Day	21% 10% 34% 23% 10% 2	463
	11th to 20th	Day	16% 10% 29% 29% 13% 4	487
	21st to end	Day	14% 7% 30% 30% 15% 5%	529
June	1st to 10th	Day	13% 7% 31% 33% 13% 2	664
	11th to 20th	Day	11% 8% 31% 34% 13% 3	680
	21st to end	Day	17% 6% 28% 33% 12% 3	680
July	1st to 10th	Day	9% 6% 27% 33% 22% 3	671
	11th to 20th	Day	12% 5% 26% 33% 17% 6%	668
	21st to end	Day	10% 5% 27% 34% 18% 5%	556
August	1st to 10th	Day	13% 5% 22% 32% 21% 6%	486
	11th to 20th	Day	12% 5% 18% 36% 19% 9%	479
	21st to end	Day	12% 9% 27% 27% 19% 5%	539
September	1st to 10th	Day	16% 10% 22% 27% 18% 6%	490
	11th to 20th	Day	11% 7% 25% 25% 24% 8%	490
	21st to end	Day	18% 12% 22% 27% 17% 4	490
October	1st to 10th	Day	22% 16% 24% 22% 12% 3	490
	11th to 20th	Day	22% 22% 30% 20% 6% 1	490
	21st to end	Day	30% 21% 28% 18% 2 1	450
November	1st to 10th	Day	27% 23% 31% 16% 4	275
	11th to 20th	Day	22% 26% 33% 15% 4 1	200
	21st to end	Day	27% 26% 32% 14% 2	200
December	1st to 10th	Day	28% 25% 30% 12% 6%	200
	11th to 20th	Day	30% 26% 30% 12% 3	200
	21st to end	Day	31% 26% 31% 8% 2	220
January	1st to 10th	Night	24% 20% 33% 19% 4 1	1000
	11th to 20th	Night	27% 21% 27% 19% 5% 1	991
	21st to end	Night	20% 16% 30% 24% 8% 1	880
February	1st to 10th	Night	21% 22% 33% 20% 5%	800
	11th to 20th	Night	20% 17% 35% 21% 8%	783
	21st to end	Night	21% 18% 35% 22% 4	660
March	1st to 10th	Night	17% 17% 34% 24% 7% 1	800
	11th to 20th	Night	18% 18% 34% 22% 8% 1	800
	21st to end	Night	20% 13% 28% 28% 10%	880
April	1st to 10th	Night	25% 14% 29% 26% 5% 1	795
	11th to 20th	Night	22% 13% 27% 24% 12% 2	565
	21st to end	Night	25% 10% 24% 26% 14% 1	570
May	1st to 10th	Night	17% 5% 25% 34% 16% 2	570
	11th to 20th	Night	16% 6% 22% 35% 19% 2	450
	21st to end	Night	15% 3 24% 37% 18% 2	411
June	1st to 10th	Night	17% 6% 27% 35% 14% 2	380
	11th to 20th	Night	12% 6% 23% 40% 19% 1	380
	21st to end	Night	13% 5% 22% 36% 23% 1	380
July	1st to 10th	Night	9% 4 14% 50% 21% 2	370
	11th to 20th	Night	10% 3 23% 35% 25% 4	400
	21st to end	Night	9% 4 17% 42% 25% 3	624
August	1st to 10th	Night	11% 3 18% 38% 26% 3	567
	11th to 20th	Night	11% 6% 15% 31% 30% 7%	564
	21st to end	Night	14% 4 22% 30% 26% 4	627
September	1st to 10th	Night	12% 7% 21% 32% 21% 6%	746
	11th to 20th	Night	13% 6% 19% 31% 23% 7%	760
	21st to end	Night	19% 9% 20% 27% 19% 6%	760
October	1st to 10th	Night	23% 10% 25% 24% 17% 2	760
	11th to 20th	Night	28% 15% 23% 23% 9% 1	760
	21st to end	Night	32% 14% 28% 21% 4 1	836
November	1st to 10th	Night	28% 16% 25% 23% 7% 1	780
	11th to 20th	Night	25% 22% 25% 19% 8% 1	800
	21st to end	Night	32% 19% 27% 18% 4	800
December	1st to 10th	Night	32% 21% 28% 13% 6%	800
	11th to 20th	Night	28% 22% 32% 15% 4	915
	21st to end	Night	34% 17% 29% 15% 4	1100

Page generated at 2025-04-08 09:17:29. Version ac07

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