Lake Arrowhead State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Arrowhead State Park clear sky chart from 2005-11-06 to 2025-09-19.

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	9% 4 2 4 3 3 3 3 5% 6% 57%	126192
	Night	8% 4 2 4 3 3 3 3 5% 7% 60%	123179
Transparency	Day	28% 3 8% 24% 26% 11%	129948
	Night	25% 3 8% 23% 28% 13%	127486
Seeing	Day	10% 5% 22% 30% 24% 9%	16432
	Night	10% 6% 31% 38% 15% 1	26249

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	10% 6% 2 5% 4 3 3 3 4 5% 56%	4077
	11th to 20th	Day	6% 4 1 2 2 2 2 2 3 6% 69%	4080
	21st to end	Day	16% 7% 2 4 3 2 3 3 4 5% 52%	4531
February	1st to 10th	Day	11% 5% 3 5% 3 2 3 2 4 7% 56%	2000
	11th to 20th	Day	12% 6% 2 6% 3 3 3 3 4 5% 52%	1949
	21st to end	Day	15% 9% 2 3 2 1 2 2 2 5% 57%	1650
March	1st to 10th	Day	13% 4 1 4 3 3 3 3 4 6% 57%	4759
	11th to 20th	Day	8% 4 1 4 3 3 3 3 5% 5% 60%	4980
	21st to end	Day	7% 6% 2 5% 3 4 4 3 6% 7% 53%	5462
April	1st to 10th	Day	11% 4 1 3 3 3 4 3 5% 6% 57%	2200
	11th to 20th	Day	11% 5% 2 5% 4 3 4 3 5% 5% 55%	2327
	21st to end	Day	11% 5% 2 4 4 3 3 4 5% 6% 54%	2600
May	1st to 10th	Day	15% 6% 2 5% 4 4 4 3 4 7% 46%	5862
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 4 6% 53%	5862
	21st to end	Day	10% 6% 2 7% 4 5% 4 4 6% 7% 45%	6434
June	1st to 10th	Day	6% 4 2 4 3 4 5% 4 7% 8% 53%	2600
	11th to 20th	Day	5% 3 1 4 3 3 4 3 6% 8% 60%	2600
	21st to end	Day	5% 3 1 3 3 2 3 3 6% 7% 63%	2600
July	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 5% 8% 46%	5900
	11th to 20th	Day	4 2 1 4 4 3 4 4 5% 8% 60%	5900
	21st to end	Day	2 2 1 3 2 3 4 3 5% 8% 68%	6422
August	1st to 10th	Day	2 2 1 4 2 3 3 3 5% 8% 67%	4234
	11th to 20th	Day	3 2 1 4 2 3 3 3 6% 10% 61%	4049
	21st to end	Day	4 2 1 3 3 3 4 3 5% 7% 64%	4256
September	1st to 10th	Day	11% 4 1 4 2 3 3 3 4 6% 59%	2200
	11th to 20th	Day	10% 5% 2 6% 4 4 4 3 5% 6% 50%	2178
	21st to end	Day	8% 3 1 3 3 4 4 4 4 6% 61%	2090
October	1st to 10th	Day	5% 3 1 4 3 3 3 3 4 6% 63%	2090
	11th to 20th	Day	9% 3 2 2 2 2 2 2 3 5% 68%	1933
	21st to end	Day	11% 4 1 3 2 2 3 2 2 4 65%	2090
November	1st to 10th	Day	9% 3 2 4 3 3 2 3 4 6% 62%	1858
	11th to 20th	Day	6% 3 1 3 3 2 2 3 3 7% 68%	1800
	21st to end	Day	11% 4 1 4 2 3 3 2 4 5% 59%	1800
December	1st to 10th	Day	9% 6% 2 7% 3 3 3 2 4 6% 56%	2940
	11th to 20th	Day	9% 4 2 5% 4 3 4 3 4 5% 58%	3391
	21st to end	Day	11% 7% 2 6% 4 3 3 2 3 5% 54%	4488
January	1st to 10th	Night	13% 5% 2 4 3 4 3 2 4 6% 55%	5888
	11th to 20th	Night	4 4 1 2 2 1 2 2 3 6% 71%	5900
	21st to end	Night	15% 8% 2 4 3 2 3 2 3 5% 54%	6490
February	1st to 10th	Night	11% 5% 2 5% 2 2 3 3 4 5% 57%	2400
	11th to 20th	Night	13% 5% 2 4 3 3 4 2 4 7% 54%	2338
	21st to end	Night	10% 6% 2 4 3 2 3 2 4 5% 58%	1980
March	1st to 10th	Night	10% 6% 2 4 3 3 3 3 4 6% 57%	5102
	11th to 20th	Night	7% 3 1 3 2 3 3 2 4 6% 65%	4980
	21st to end	Night	6% 5% 2 6% 3 3 4 3 6% 7% 54%	5467
April	1st to 10th	Night	9% 5% 2 4 3 3 2 3 5% 7% 58%	2200
	11th to 20th	Night	10% 4 1 4 3 3 3 3 5% 7% 58%	2015
	21st to end	Night	10% 3 2 5% 3 3 3 3 6% 6% 57%	1800
May	1st to 10th	Night	13% 5% 2 5% 3 3 4 3 5% 6% 51%	4053
	11th to 20th	Night	8% 4 1 5% 3 4 4 4 6% 7% 55%	4053
	21st to end	Night	8% 5% 2 5% 4 4 4 3 5% 8% 53%	4443
June	1st to 10th	Night	4 3 1 3 3 2 4 4 7% 12% 57%	1800
	11th to 20th	Night	2 3 2 4 3 3 4 3 5% 12% 60%	1800
	21st to end	Night	3 3 1 3 3 2 3 3 6% 8% 66%	1800
July	1st to 10th	Night	8% 5% 2 6% 5% 5% 4 3 6% 8% 46%	4078
	11th to 20th	Night	2 2 1 2 2 2 3 3 5% 11% 67%	4077
	21st to end	Night	2 2 1 3 2 2 3 3 5% 8% 69%	4449
August	1st to 10th	Night	1 1 2 2 3 3 3 5% 7% 71%	2926
	11th to 20th	Night	3 2 1 3 2 3 2 3 5% 10% 66%	3005
	21st to end	Night	3 2 1 2 2 3 3 3 6% 9% 65%	3651
September	1st to 10th	Night	9% 3 2 5% 3 3 3 3 4 7% 59%	2200
	11th to 20th	Night	8% 6% 2 5% 4 4 4 4 4 5% 53%	2178
	21st to end	Night	7% 3 1 4 2 3 4 3 4 6% 63%	2090
October	1st to 10th	Night	7% 3 1 3 2 3 3 3 5% 6% 65%	2090
	11th to 20th	Night	8% 4 2 3 2 2 2 3 3 4 68%	2227
	21st to end	Night	11% 4 2 3 2 2 3 2 3 4 66%	2508
November	1st to 10th	Night	10% 3 1 4 2 2 3 2 4 4 66%	2435
	11th to 20th	Night	5% 3 1 3 3 2 3 3 5% 6% 66%	2600
	21st to end	Night	11% 5% 1 3 3 2 3 3 4 6% 59%	2600
December	1st to 10th	Night	9% 4 1 4 2 3 3 2 4 6% 61%	4250
	11th to 20th	Night	9% 5% 2 5% 3 3 3 2 4 5% 59%	4816
	21st to end	Night	11% 6% 2 5% 3 3 3 3 4 5% 56%	6490

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	32% 2 5% 30% 25% 6%	4078
	11th to 20th	Day	21% 1 5% 23% 42% 8%	4080
	21st to end	Day	37% 2 5% 19% 23% 14%	4531
February	1st to 10th	Day	31% 3 6% 23% 28% 10%	2000
	11th to 20th	Day	36% 3 6% 21% 24% 10%	1959
	21st to end	Day	34% 1 3 15% 30% 17%	1650
March	1st to 10th	Day	30% 3 5% 13% 23% 26%	4759
	11th to 20th	Day	28% 2 7% 18% 24% 22%	4980
	21st to end	Day	30% 4 8% 25% 24% 9%	5464
April	1st to 10th	Day	28% 3 9% 25% 22% 13%	2200
	11th to 20th	Day	32% 3 7% 20% 23% 14%	2327
	21st to end	Day	31% 3 9% 26% 24% 7%	2600
May	1st to 10th	Day	39% 4 10% 23% 15% 10%	5900
	11th to 20th	Day	33% 3 8% 20% 27% 9%	5866
	21st to end	Day	37% 4 10% 25% 13% 10%	6447
June	1st to 10th	Day	27% 6% 15% 29% 19% 4	2600
	11th to 20th	Day	22% 4 12% 28% 27% 7%	2600
	21st to end	Day	21% 4 12% 28% 27% 8%	2600
July	1st to 10th	Day	37% 5% 10% 26% 18% 4	5836
	11th to 20th	Day	23% 4 12% 29% 28% 5%	5831
	21st to end	Day	15% 4 12% 33% 32% 4	6240
August	1st to 10th	Day	17% 3 9% 25% 32% 13%	4220
	11th to 20th	Day	19% 4 11% 34% 26% 6%	4088
	21st to end	Day	19% 5% 13% 33% 25% 5%	4255
September	1st to 10th	Day	28% 4 7% 22% 27% 13%	2200
	11th to 20th	Day	34% 5% 8% 19% 24% 10%	2178
	21st to end	Day	25% 4 6% 23% 28% 14%	2090
October	1st to 10th	Day	14% 2 6% 14% 37% 28%	3480
	11th to 20th	Day	16% 2 7% 19% 39% 17%	3186
	21st to end	Day	19% 2 4 29% 34% 11%	3428
November	1st to 10th	Day	25% 3 8% 23% 27% 14%	1858
	11th to 20th	Day	20% 2 7% 25% 31% 15%	1800
	21st to end	Day	29% 3 4 23% 29% 12%	1800
December	1st to 10th	Day	32% 2 4 33% 23% 5%	2940
	11th to 20th	Day	30% 2 6% 16% 33% 13%	3389
	21st to end	Day	35% 2 5% 27% 23% 8%	4488
January	1st to 10th	Night	32% 3 5% 29% 25% 6%	5888
	11th to 20th	Night	17% 1 8% 18% 40% 15%	5900
	21st to end	Night	36% 1 5% 18% 27% 13%	6490
February	1st to 10th	Night	31% 3 6% 20% 27% 13%	2400
	11th to 20th	Night	32% 3 7% 21% 24% 14%	2338
	21st to end	Night	31% 2 4 17% 24% 22%	1980
March	1st to 10th	Night	30% 3 3 14% 25% 26%	5102
	11th to 20th	Night	22% 2 6% 20% 19% 31%	4980
	21st to end	Night	29% 4 7% 22% 31% 8%	5467
April	1st to 10th	Night	28% 3 9% 21% 23% 16%	2200
	11th to 20th	Night	27% 3 12% 18% 25% 16%	2015
	21st to end	Night	27% 4 10% 24% 28% 7%	1800
May	1st to 10th	Night	35% 4 11% 21% 21% 8%	4080
	11th to 20th	Night	27% 4 9% 21% 26% 12%	4054
	21st to end	Night	30% 5% 13% 24% 18% 11%	4452
June	1st to 10th	Night	20% 4 16% 35% 19% 5%	1800
	11th to 20th	Night	19% 4 13% 29% 27% 8%	1800
	21st to end	Night	19% 3 11% 26% 31% 11%	1800
July	1st to 10th	Night	35% 5% 11% 29% 17% 3	4035
	11th to 20th	Night	15% 3 11% 34% 32% 7%	4026
	21st to end	Night	14% 3 11% 37% 31% 4	4320
August	1st to 10th	Night	13% 3 7% 27% 37% 13%	2916
	11th to 20th	Night	16% 3 11% 34% 28% 9%	3032
	21st to end	Night	16% 4 15% 35% 25% 6%	3651
September	1st to 10th	Night	26% 3 9% 22% 28% 12%	2200
	11th to 20th	Night	33% 3 7% 23% 23% 11%	2178
	21st to end	Night	22% 3 5% 21% 29% 19%	2090
October	1st to 10th	Night	13% 2 5% 14% 32% 32%	3480
	11th to 20th	Night	17% 2 7% 17% 33% 23%	3700
	21st to end	Night	19% 2 4 27% 34% 13%	4120
November	1st to 10th	Night	23% 2 6% 21% 28% 19%	2435
	11th to 20th	Night	20% 3 6% 22% 32% 17%	2600
	21st to end	Night	28% 3 6% 19% 31% 14%	2600
December	1st to 10th	Night	27% 2 4 29% 29% 9%	4250
	11th to 20th	Night	29% 2 6% 18% 29% 16%	4817
	21st to end	Night	32% 3 5% 23% 27% 9%	6490

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	13% 10% 36% 32% 9% 1	300
	11th to 20th	Day	13% 12% 32% 32% 8% 2	300
	21st to end	Day	13% 7% 40% 28% 10% 2	330
February	1st to 10th	Day	16% 6% 41% 29% 9%	300
	11th to 20th	Day	15% 11% 42% 29% 4	300
	21st to end	Day	21% 8% 40% 22% 8%	249
March	1st to 10th	Day	17% 10% 36% 27% 9%	300
	11th to 20th	Day	16% 13% 40% 24% 6% 1	300
	21st to end	Day	11% 10% 46% 23% 8% 2	330
April	1st to 10th	Day	15% 9% 40% 22% 13% 2	300
	11th to 20th	Day	16% 12% 43% 23% 6%	445
	21st to end	Day	13% 10% 39% 28% 7% 2	700
May	1st to 10th	Day	12% 6% 34% 35% 13% 1	703
	11th to 20th	Day	12% 6% 31% 32% 15% 3	725
	21st to end	Day	10% 4 30% 34% 16% 6%	789
June	1st to 10th	Day	6% 2 14% 41% 30% 7%	730
	11th to 20th	Day	5% 2 15% 42% 28% 8%	730
	21st to end	Day	5% 1 8% 37% 38% 11%	730
July	1st to 10th	Day	6% 1 6% 31% 38% 19%	721
	11th to 20th	Day	3 1 6% 30% 44% 16%	718
	21st to end	Day	2 1 3 27% 44% 23%	794
August	1st to 10th	Day	3 2 4 27% 47% 17%	726
	11th to 20th	Day	5% 2 5% 30% 41% 16%	645
	21st to end	Day	5% 1 4 26% 38% 26%	553
September	1st to 10th	Day	10% 3 21% 39% 27%	330
	11th to 20th	Day	5% 1 7% 22% 41% 24%	324
	21st to end	Day	12% 1 7% 25% 35% 20%	300
October	1st to 10th	Day	3 1 15% 34% 30% 17%	300
	11th to 20th	Day	9% 5% 25% 36% 20% 4	300
	21st to end	Day	18% 6% 25% 28% 20% 3	330
November	1st to 10th	Day	14% 6% 28% 28% 21% 3	300
	11th to 20th	Day	11% 9% 26% 34% 16% 4	300
	21st to end	Day	15% 8% 34% 28% 11% 3	300
December	1st to 10th	Day	13% 5% 37% 28% 14% 2	300
	11th to 20th	Day	11% 7% 35% 32% 14% 1	300
	21st to end	Day	17% 7% 36% 30% 10%	330
January	1st to 10th	Night	11% 8% 39% 36% 7%	1000
	11th to 20th	Night	11% 10% 37% 36% 6%	1000
	21st to end	Night	13% 8% 35% 38% 6%	1100
February	1st to 10th	Night	13% 9% 42% 31% 5%	800
	11th to 20th	Night	16% 10% 39% 30% 4	784
	21st to end	Night	13% 13% 46% 27% 2	660
March	1st to 10th	Night	13% 12% 41% 31% 4	684
	11th to 20th	Night	14% 11% 40% 29% 6%	600
	21st to end	Night	7% 12% 47% 30% 5%	660
April	1st to 10th	Night	10% 11% 49% 26% 4	600
	11th to 20th	Night	10% 10% 49% 27% 3	593
	21st to end	Night	12% 9% 43% 30% 7%	600
May	1st to 10th	Night	11% 6% 45% 31% 7%	600
	11th to 20th	Night	9% 5% 37% 34% 13% 1	591
	21st to end	Night	5% 5% 35% 39% 13% 2	650
June	1st to 10th	Night	6% 2 24% 45% 23% 1	600
	11th to 20th	Night	3 1 27% 56% 13%	600
	21st to end	Night	3 1 17% 51% 26% 2	600
July	1st to 10th	Night	5% 1 10% 45% 35% 4	585
	11th to 20th	Night	2 1 9% 53% 34% 2	582
	21st to end	Night	2 5% 48% 43% 2	657
August	1st to 10th	Night	2 1 6% 54% 36% 1	597
	11th to 20th	Night	5% 1 8% 47% 37% 3	594
	21st to end	Night	4 1 5% 45% 42% 4	660
September	1st to 10th	Night	9% 1 10% 45% 31% 4	600
	11th to 20th	Night	10% 2 13% 43% 31% 1	594
	21st to end	Night	9% 1 16% 47% 26% 2	570
October	1st to 10th	Night	6% 2 22% 44% 24% 1	570
	11th to 20th	Night	10% 4 32% 40% 14% 1	707
	21st to end	Night	12% 6% 32% 36% 14% 1	836
November	1st to 10th	Night	11% 4 32% 39% 13% 1	875
	11th to 20th	Night	6% 9% 36% 37% 11% 1	1000
	21st to end	Night	14% 7% 38% 31% 10% 1	1000
December	1st to 10th	Night	13% 7% 34% 39% 7%	1000
	11th to 20th	Night	14% 7% 37% 37% 5%	1000
	21st to end	Night	12% 8% 40% 33% 7%	1100

Page generated at 2025-09-16 00:49:10. Version ac07

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