High Sierra Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the High Sierra Park clear sky chart from 2005-11-06 to 2025-10-19.

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	7% 5% 1 3 2 2 2 2 3 5% 67%	135058
	Night	9% 6% 1 3 2 2 3 2 4 5% 63%	132087
Transparency	Day	22% 3 6% 18% 27% 24%	130049
	Night	25% 3 7% 19% 25% 21%	128075
Seeing	Day	13% 13% 33% 27% 11% 4	16447
	Night	12% 4 17% 36% 25% 6%	25814

By Month

Percentage Cloud Cover SW (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% 10% 2 4 2 2 3 2 4 5% 53%	3639
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 2 4 56%	3898
	21st to end	Day	14% 9% 2 6% 3 3 3 3 4 5% 47%	4510
February	1st to 10th	Day	18% 10% 2 4 3 2 2 3 4 5% 47%	1820
	11th to 20th	Day	13% 12% 3 4 3 3 4 2 4 6% 47%	1950
	21st to end	Day	18% 12% 4 4 2 3 3 2 3 6% 44%	1650
March	1st to 10th	Day	13% 17% 4 7% 4 4 4 4 6% 6% 33%	4518
	11th to 20th	Day	14% 11% 2 4 3 3 3 2 4 6% 47%	4990
	21st to end	Day	15% 14% 3 6% 4 4 3 3 4 6% 38%	5806
April	1st to 10th	Day	12% 10% 2 4 4 3 3 3 4 7% 48%	2400
	11th to 20th	Day	13% 8% 2 5% 3 3 3 3 5% 6% 52%	2369
	21st to end	Day	11% 6% 1 3 3 3 3 3 4 6% 57%	2400
May	1st to 10th	Day	7% 4 1 3 2 2 2 2 3 4 70%	5569
	11th to 20th	Day	4 3 2 3 2 1 2 2 4 4 72%	6096
	21st to end	Day	4 2 1 2 1 2 2 1 3 4 78%	6902
June	1st to 10th	Day	5% 3 1 3 3 3 3 3 4 6% 65%	2800
	11th to 20th	Day	2 2 1 2 2 1 2 2 3 5% 80%	2800
	21st to end	Day	2 2 1 2 1 2 2 2 2 2 82%	2800
July	1st to 10th	Day	1 1 1 1 2 93%	6319
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 87%	6320
	21st to end	Day	1 1 2 1 1 1 1 2 3 86%	6537
August	1st to 10th	Day	1 1 1 2 1 1 2 1 2 2 87%	5659
	11th to 20th	Day	1 1 1 1 1 2 2 91%	5364
	21st to end	Day	2 2 1 2 2 2 2 2 3 3 80%	5984
September	1st to 10th	Day	2 1 1 2 1 1 1 2 3 86%	2400
	11th to 20th	Day	4 2 1 2 1 2 3 2 3 5% 75%	2375
	21st to end	Day	4 2 1 2 2 2 2 2 3 3 78%	2200
October	1st to 10th	Day	4 3 1 3 2 1 2 2 4 4 74%	3316
	11th to 20th	Day	5% 2 1 2 2 1 2 2 3 3 77%	3242
	21st to end	Day	6% 3 1 4 2 2 3 3 4 7% 66%	3431
November	1st to 10th	Day	10% 6% 1 5% 4 3 3 3 5% 6% 55%	1764
	11th to 20th	Day	10% 5% 1 4 3 3 3 3 5% 6% 57%	1800
	21st to end	Day	11% 7% 1 4 3 3 3 3 4 7% 53%	1778
December	1st to 10th	Day	9% 4 1 4 3 4 4 3 5% 7% 59%	2620
	11th to 20th	Day	23% 9% 2 6% 4 3 3 4 4 6% 37%	3028
	21st to end	Day	18% 9% 2 5% 3 4 5% 4 7% 8% 35%	4004
January	1st to 10th	Night	10% 8% 2 4 3 3 3 3 5% 8% 51%	6306
	11th to 20th	Night	15% 6% 1 4 3 3 3 3 4 4 54%	6056
	21st to end	Night	13% 9% 2 5% 4 3 4 3 4 5% 49%	6468
February	1st to 10th	Night	17% 9% 1 5% 3 2 2 3 4 5% 48%	2578
	11th to 20th	Night	13% 12% 2 4 3 3 2 3 5% 7% 48%	2338
	21st to end	Night	15% 10% 3 4 3 3 2 3 3 6% 49%	1980
March	1st to 10th	Night	14% 17% 3 5% 3 3 3 3 5% 5% 38%	5376
	11th to 20th	Night	15% 12% 3 5% 3 2 3 2 3 4 49%	5005
	21st to end	Night	18% 12% 2 5% 3 3 3 3 5% 7% 39%	5167
April	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 4 7% 52%	2000
	11th to 20th	Night	10% 6% 1 4 3 3 3 3 4 6% 57%	1979
	21st to end	Night	8% 6% 2 3 3 2 2 3 4 7% 60%	2000
May	1st to 10th	Night	3 4 1 2 1 2 2 2 3 5% 73%	4422
	11th to 20th	Night	2 2 1 2 2 1 2 2 4 6% 76%	3801
	21st to end	Night	2 2 1 2 2 1 2 2 2 3 81%	3972
June	1st to 10th	Night	5% 3 1 3 2 3 2 3 5% 6% 68%	1600
	11th to 20th	Night	1 1 2 1 2 2 3 3 84%	1600
	21st to end	Night	1 2 1 2 2 1 2 2 2 3 84%	1600
July	1st to 10th	Night	1 1 1 1 95%	3640
	11th to 20th	Night	2 2 1 2 1 2 2 1 2 3 83%	3640
	21st to end	Night	2 2 1 2 2 2 2 1 3 4 81%	4325
August	1st to 10th	Night	2 2 1 2 1 1 2 2 2 2 85%	4158
	11th to 20th	Night	1 1 1 1 1 2 2 90%	4506
	21st to end	Night	3 2 1 2 1 1 2 1 2 3 81%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 2 88%	2000
	11th to 20th	Night	3 2 1 2 2 3 2 3 4 78%	2023
	21st to end	Night	2 2 1 2 2 1 2 2 3 4 79%	2200
October	1st to 10th	Night	3 2 1 2 2 2 2 2 3 3 78%	3880
	11th to 20th	Night	3 1 1 2 1 2 1 2 3 4 79%	3873
	21st to end	Night	7% 2 1 3 3 3 2 2 4 5% 68%	4137
November	1st to 10th	Night	11% 5% 1 3 2 2 2 2 4 6% 61%	2535
	11th to 20th	Night	10% 4 1 4 3 2 3 3 5% 7% 58%	2600
	21st to end	Night	12% 6% 1 4 3 3 3 3 4 6% 55%	2619
December	1st to 10th	Night	10% 4 1 3 2 3 3 3 4 5% 62%	4560
	11th to 20th	Night	21% 9% 2 4 3 3 4 4 7% 8% 34%	5176
	21st to end	Night	16% 10% 3 8% 5% 5% 5% 4 5% 6% 34%	6952

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	34% 3 12% 22% 21% 8%	3639
	11th to 20th	Day	35% 3 7% 12% 25% 18%	3898
	21st to end	Day	39% 4 8% 13% 20% 15%	4510
February	1st to 10th	Day	40% 3 7% 22% 17% 12%	1820
	11th to 20th	Day	38% 4 7% 21% 23% 7%	1960
	21st to end	Day	43% 4 7% 20% 20% 7%	1650
March	1st to 10th	Day	49% 6% 8% 14% 17% 5%	4518
	11th to 20th	Day	38% 5% 14% 27% 11% 6%	4990
	21st to end	Day	44% 7% 13% 22% 11% 2	5806
April	1st to 10th	Day	35% 6% 13% 22% 19% 5%	2400
	11th to 20th	Day	32% 5% 12% 26% 19% 6%	2372
	21st to end	Day	28% 4 10% 32% 22% 3	2400
May	1st to 10th	Day	18% 4 6% 31% 31% 10%	5569
	11th to 20th	Day	15% 4 6% 32% 36% 8%	6099
	21st to end	Day	12% 3 4 31% 44% 6%	6904
June	1st to 10th	Day	18% 6% 9% 25% 30% 12%	2800
	11th to 20th	Day	10% 3 5% 21% 37% 24%	2800
	21st to end	Day	9% 2 2 11% 34% 42%	2800
July	1st to 10th	Day	3 1 1 5% 20% 71%	6251
	11th to 20th	Day	6% 2 2 5% 18% 68%	6245
	21st to end	Day	6% 2 2 12% 35% 44%	6348
August	1st to 10th	Day	9% 2 1 7% 29% 51%	4121
	11th to 20th	Day	4 2 2 6% 33% 54%	3880
	21st to end	Day	8% 1 2 6% 41% 41%	4311
September	1st to 10th	Day	7% 1 2 10% 34% 46%	2400
	11th to 20th	Day	13% 3 2 22% 40% 20%	2375
	21st to end	Day	12% 2 5% 17% 37% 27%	2200
October	1st to 10th	Day	14% 3 3 11% 30% 39%	3316
	11th to 20th	Day	14% 2 3 18% 41% 21%	3242
	21st to end	Day	20% 3 5% 18% 38% 16%	3431
November	1st to 10th	Day	30% 4 7% 22% 21% 16%	1764
	11th to 20th	Day	28% 4 7% 20% 27% 13%	1800
	21st to end	Day	31% 4 6% 17% 28% 14%	1778
December	1st to 10th	Day	27% 3 7% 21% 26% 17%	2620
	11th to 20th	Day	49% 3 7% 13% 18% 9%	3028
	21st to end	Day	45% 6% 13% 17% 13% 6%	4004
January	1st to 10th	Night	31% 4 14% 24% 17% 10%	6306
	11th to 20th	Night	34% 3 6% 13% 27% 17%	6056
	21st to end	Night	37% 4 8% 13% 19% 19%	6468
February	1st to 10th	Night	40% 3 6% 20% 19% 12%	2578
	11th to 20th	Night	35% 4 7% 24% 20% 9%	2339
	21st to end	Night	38% 3 10% 21% 20% 8%	1980
March	1st to 10th	Night	47% 5% 6% 17% 16% 9%	5376
	11th to 20th	Night	40% 3 10% 25% 14% 8%	5005
	21st to end	Night	43% 6% 14% 20% 14% 3	5167
April	1st to 10th	Night	33% 4 15% 22% 20% 6%	2000
	11th to 20th	Night	28% 6% 12% 27% 19% 8%	1979
	21st to end	Night	24% 6% 11% 35% 20% 4	2000
May	1st to 10th	Night	15% 3 8% 35% 28% 11%	4419
	11th to 20th	Night	11% 3 9% 32% 35% 10%	3801
	21st to end	Night	11% 2 6% 34% 41% 6%	3972
June	1st to 10th	Night	16% 5% 11% 26% 30% 12%	1600
	11th to 20th	Night	6% 3 6% 23% 37% 25%	1600
	21st to end	Night	8% 2 3 11% 35% 41%	1600
July	1st to 10th	Night	2 1 1 4 21% 72%	3600
	11th to 20th	Night	10% 2 2 4 20% 62%	3592
	21st to end	Night	9% 2 2 11% 31% 44%	4202
August	1st to 10th	Night	11% 2 1 8% 26% 51%	3016
	11th to 20th	Night	5% 1 2 7% 27% 57%	3256
	21st to end	Night	8% 1 1 10% 36% 44%	3608
September	1st to 10th	Night	5% 2 3 9% 35% 46%	2000
	11th to 20th	Night	11% 3 3 20% 39% 24%	2023
	21st to end	Night	11% 2 4 20% 37% 26%	2200
October	1st to 10th	Night	12% 3 3 11% 28% 43%	3880
	11th to 20th	Night	11% 2 3 21% 39% 23%	3873
	21st to end	Night	20% 3 3 20% 36% 19%	4137
November	1st to 10th	Night	25% 3 8% 23% 25% 17%	2535
	11th to 20th	Night	25% 4 7% 22% 28% 14%	2600
	21st to end	Night	30% 3 7% 19% 27% 14%	2619
December	1st to 10th	Night	25% 3 5% 22% 25% 20%	4560
	11th to 20th	Night	47% 4 7% 14% 21% 7%	5176
	21st to end	Night	49% 5% 10% 18% 12% 6%	6952

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	32% 9% 28% 20% 10% 2	200
	11th to 20th	Day	22% 9% 23% 31% 10% 4	315
	21st to end	Day	22% 9% 26% 25% 16% 3	440
February	1st to 10th	Day	30% 13% 22% 21% 10% 4	410
	11th to 20th	Day	21% 14% 34% 20% 8% 2	495
	21st to end	Day	21% 16% 34% 20% 7% 1	414
March	1st to 10th	Day	29% 17% 30% 17% 6% 1	500
	11th to 20th	Day	27% 16% 27% 20% 8% 2	500
	21st to end	Day	24% 18% 33% 18% 7% 1	550
April	1st to 10th	Day	20% 19% 33% 20% 8% 1	500
	11th to 20th	Day	22% 20% 28% 23% 5% 2	492
	21st to end	Day	14% 19% 31% 24% 9% 3	500
May	1st to 10th	Day	15% 22% 33% 20% 7% 4	503
	11th to 20th	Day	16% 18% 28% 23% 11% 4	528
	21st to end	Day	14% 15% 30% 24% 11% 7%	573
June	1st to 10th	Day	9% 13% 35% 26% 10% 6%	530
	11th to 20th	Day	6% 18% 38% 25% 8% 6%	530
	21st to end	Day	5% 11% 36% 30% 11% 7%	530
July	1st to 10th	Day	2 10% 41% 29% 11% 6%	526
	11th to 20th	Day	2 5% 38% 36% 12% 8%	524
	21st to end	Day	1 6% 37% 36% 10% 9%	575
August	1st to 10th	Day	3 11% 38% 30% 13% 5%	527
	11th to 20th	Day	2 8% 40% 31% 13% 6%	517
	21st to end	Day	2 7% 39% 33% 14% 5%	583
September	1st to 10th	Day	3 8% 43% 29% 15% 2	530
	11th to 20th	Day	8% 11% 36% 32% 12% 2	530
	21st to end	Day	5% 12% 34% 37% 9% 2	530
October	1st to 10th	Day	7% 12% 32% 32% 14% 3	530
	11th to 20th	Day	7% 10% 33% 33% 13% 4	523
	21st to end	Day	9% 10% 30% 32% 15% 3	534
November	1st to 10th	Day	15% 9% 25% 27% 17% 7%	300
	11th to 20th	Day	14% 7% 27% 29% 16% 8%	300
	21st to end	Day	17% 10% 24% 30% 16% 4	288
December	1st to 10th	Day	20% 7% 20% 24% 21% 9%	200
	11th to 20th	Day	21% 11% 26% 20% 18% 6%	200
	21st to end	Day	24% 7% 29% 23% 13% 4	220
January	1st to 10th	Night	21% 4 25% 27% 16% 7%	800
	11th to 20th	Night	16% 6% 23% 34% 16% 5%	800
	21st to end	Night	20% 4 24% 29% 19% 5%	880
February	1st to 10th	Night	21% 5% 22% 30% 17% 5%	800
	11th to 20th	Night	19% 7% 21% 30% 17% 7%	784
	21st to end	Night	21% 5% 21% 37% 13% 3	660
March	1st to 10th	Night	25% 8% 17% 32% 14% 4	800
	11th to 20th	Night	23% 5% 16% 31% 19% 6%	800
	21st to end	Night	22% 5% 21% 33% 18% 2	880
April	1st to 10th	Night	17% 6% 19% 37% 20% 3	800
	11th to 20th	Night	13% 7% 21% 35% 19% 6%	791
	21st to end	Night	11% 4 18% 38% 23% 6%	800
May	1st to 10th	Night	9% 5% 21% 36% 22% 6%	740
	11th to 20th	Night	6% 4 18% 40% 30% 3	475
	21st to end	Night	7% 3 14% 38% 32% 5%	433
June	1st to 10th	Night	6% 2 9% 45% 32% 6%	400
	11th to 20th	Night	1 1 14% 46% 35% 4	400
	21st to end	Night	2 1 11% 45% 38% 5%	400
July	1st to 10th	Night	1 8% 42% 45% 5%	390
	11th to 20th	Night	2 1 8% 43% 41% 6%	388
	21st to end	Night	3 2 9% 29% 44% 14%	588
August	1st to 10th	Night	3 1 11% 38% 38% 9%	645
	11th to 20th	Night	1 10% 42% 39% 8%	792
	21st to end	Night	2 1 7% 42% 42% 6%	880
September	1st to 10th	Night	2 1 9% 42% 38% 8%	800
	11th to 20th	Night	4 11% 39% 37% 10%	800
	21st to end	Night	3 2 13% 41% 31% 10%	800
October	1st to 10th	Night	6% 2 15% 46% 23% 8%	800
	11th to 20th	Night	6% 2 17% 37% 30% 7%	792
	21st to end	Night	7% 3 17% 34% 26% 13%	836
November	1st to 10th	Night	14% 2 13% 36% 26% 9%	780
	11th to 20th	Night	14% 2 22% 36% 20% 7%	800
	21st to end	Night	15% 5% 21% 33% 20% 6%	800
December	1st to 10th	Night	19% 4 19% 35% 16% 6%	800
	11th to 20th	Night	25% 4 22% 29% 17% 4	800
	21st to end	Night	23% 8% 22% 29% 15% 3	880

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