Big Meadows
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Meadows clear sky chart from 2005-11-06 to 2025-08-05.

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% 7% 3 6% 5% 5% 5% 4 6% 7% 39%	125427
	Night	14% 7% 2 6% 4 4 4 4 6% 7% 43%	122606
Transparency	Day	39% 8% 11% 22% 16% 4	129031
	Night	37% 7% 12% 22% 17% 4	127071
Seeing	Day	20% 14% 26% 22% 13% 4	15931
	Night	17% 11% 27% 30% 13% 2	25600

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	13% 6% 2 6% 4 4 4 3 4 5% 49%	4031
	11th to 20th	Day	10% 10% 3 7% 5% 4 4 3 3 4 48%	4060
	21st to end	Day	13% 8% 3 6% 5% 4 4 3 4 5% 44%	4466
February	1st to 10th	Day	11% 9% 4 8% 5% 4 5% 4 5% 5% 39%	1800
	11th to 20th	Day	16% 9% 3 6% 4 5% 4 4 5% 6% 38%	1753
	21st to end	Day	16% 9% 4 7% 3 4 5% 3 5% 6% 40%	1699
March	1st to 10th	Day	16% 8% 3 7% 4 4 4 4 5% 6% 40%	4935
	11th to 20th	Day	10% 5% 2 5% 4 3 4 4 6% 7% 50%	4980
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 4 5% 5% 38%	5465
April	1st to 10th	Day	11% 7% 2 7% 6% 4 4 3 5% 7% 42%	2370
	11th to 20th	Day	13% 7% 2 6% 3 4 4 3 5% 6% 44%	2374
	21st to end	Day	16% 8% 2 8% 5% 4 4 4 5% 6% 38%	2440
May	1st to 10th	Day	16% 7% 2 8% 6% 6% 6% 5% 7% 8% 29%	5862
	11th to 20th	Day	22% 7% 3 6% 4 5% 5% 4 6% 8% 29%	5861
	21st to end	Day	16% 6% 2 6% 4 5% 5% 4 6% 9% 35%	6880
June	1st to 10th	Day	12% 6% 2 6% 5% 6% 5% 4 6% 9% 40%	2800
	11th to 20th	Day	11% 6% 2 7% 5% 7% 5% 5% 7% 9% 35%	2800
	21st to end	Day	9% 4 2 6% 5% 5% 6% 6% 7% 10% 40%	2800
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	6187
	11th to 20th	Day	10% 7% 3 8% 6% 7% 7% 6% 9% 12% 25%	5900
	21st to end	Day	10% 6% 2 7% 6% 6% 7% 5% 7% 10% 32%	6424
August	1st to 10th	Day	15% 6% 2 7% 6% 7% 7% 5% 7% 10% 28%	4156
	11th to 20th	Day	10% 5% 3 7% 5% 6% 7% 6% 9% 9% 33%	3965
	21st to end	Day	10% 5% 2 6% 4 5% 5% 5% 6% 8% 43%	4180
September	1st to 10th	Day	13% 7% 2 6% 4 5% 4 5% 5% 6% 43%	2280
	11th to 20th	Day	14% 7% 3 5% 4 4 4 4 5% 8% 43%	2212
	21st to end	Day	23% 7% 2 6% 5% 4 4 5% 5% 5% 34%	2019
October	1st to 10th	Day	16% 6% 2 6% 3 4 4 2 5% 6% 44%	1900
	11th to 20th	Day	15% 5% 3 5% 3 3 4 3 4 6% 49%	1900
	21st to end	Day	14% 5% 2 5% 4 3 4 3 4 5% 50%	2090
November	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 5% 6% 53%	1957
	11th to 20th	Day	14% 5% 2 4 3 4 4 3 6% 6% 48%	1731
	21st to end	Day	14% 5% 2 6% 4 4 4 4 4 6% 48%	1600
December	1st to 10th	Day	11% 6% 2 6% 4 4 4 3 5% 6% 50%	2600
	11th to 20th	Day	17% 8% 3 6% 2 3 3 3 5% 6% 43%	2990
	21st to end	Day	18% 9% 3 6% 4 4 4 4 6% 7% 36%	3960
January	1st to 10th	Night	11% 7% 2 4 3 4 3 3 5% 6% 51%	5910
	11th to 20th	Night	11% 8% 2 5% 3 3 4 3 4 5% 52%	5900
	21st to end	Night	14% 8% 3 6% 3 3 3 3 4 4 50%	6490
February	1st to 10th	Night	13% 8% 2 6% 5% 5% 4 4 7% 5% 41%	2600
	11th to 20th	Night	18% 9% 2 6% 4 3 4 4 4 6% 40%	2533
	21st to end	Night	14% 9% 3 6% 4 3 4 4 7% 6% 42%	1925
March	1st to 10th	Night	15% 7% 2 6% 3 3 4 3 4 6% 47%	4918
	11th to 20th	Night	10% 4 2 5% 4 3 4 3 6% 7% 52%	4980
	21st to end	Night	12% 7% 2 7% 5% 4 4 3 5% 6% 45%	5467
April	1st to 10th	Night	14% 8% 2 5% 4 5% 5% 5% 5% 7% 42%	2030
	11th to 20th	Night	12% 7% 2 5% 4 3 4 3 6% 8% 44%	1975
	21st to end	Night	14% 6% 3 5% 4 4 5% 4 5% 7% 42%	1975
May	1st to 10th	Night	19% 8% 3 7% 5% 4 5% 3 5% 8% 32%	4033
	11th to 20th	Night	24% 6% 2 7% 4 4 4 3 7% 8% 31%	4032
	21st to end	Night	15% 7% 3 7% 5% 4 4 4 7% 8% 36%	3969
June	1st to 10th	Night	11% 6% 3 5% 5% 3 5% 4 7% 9% 44%	1600
	11th to 20th	Night	12% 6% 3 5% 5% 5% 5% 4 6% 10% 40%	1600
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 5% 6% 10% 43%	1600
July	1st to 10th	Night	9% 6% 2 6% 4 5% 5% 5% 7% 9% 41%	3752
	11th to 20th	Night	10% 8% 4 9% 6% 6% 6% 6% 8% 9% 29%	4057
	21st to end	Night	8% 7% 2 7% 6% 5% 5% 5% 8% 10% 38%	4427
August	1st to 10th	Night	16% 6% 3 6% 5% 5% 4 4 7% 10% 34%	2861
	11th to 20th	Night	12% 7% 3 9% 5% 5% 5% 4 6% 8% 36%	2817
	21st to end	Night	12% 5% 2 6% 4 3 4 4 5% 8% 47%	3476
September	1st to 10th	Night	14% 6% 2 5% 4 4 3 4 5% 8% 45%	1900
	11th to 20th	Night	14% 6% 2 5% 4 3 4 4 5% 6% 47%	1965
	21st to end	Night	24% 7% 2 5% 4 3 3 3 4 5% 40%	2160
October	1st to 10th	Night	18% 6% 3 5% 4 4 4 2 4 6% 45%	2280
	11th to 20th	Night	13% 6% 2 5% 3 4 4 3 4 7% 50%	2280
	21st to end	Night	14% 5% 1 5% 3 4 4 3 4 6% 52%	2508
November	1st to 10th	Night	11% 8% 2 6% 3 3 4 3 5% 6% 50%	2341
	11th to 20th	Night	13% 6% 2 4 4 4 4 3 5% 6% 48%	2664
	21st to end	Night	13% 6% 2 5% 4 4 4 3 6% 7% 47%	2800
December	1st to 10th	Night	9% 6% 2 5% 3 3 3 3 5% 7% 53%	4580
	11th to 20th	Night	17% 9% 2 5% 4 4 3 3 5% 5% 42%	5205
	21st to end	Night	16% 5% 2 7% 4 4 5% 4 6% 7% 39%	6996

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	37% 5% 6% 21% 23% 7%	4032
	11th to 20th	Day	39% 5% 6% 18% 20% 11%	4060
	21st to end	Day	40% 6% 7% 24% 19% 4	4466
February	1st to 10th	Day	45% 6% 10% 22% 14% 3	1800
	11th to 20th	Day	44% 6% 9% 20% 18% 3	1762
	21st to end	Day	45% 6% 11% 17% 16% 5%	1699
March	1st to 10th	Day	41% 7% 8% 18% 17% 9%	4935
	11th to 20th	Day	31% 6% 8% 27% 21% 6%	4980
	21st to end	Day	44% 7% 9% 16% 18% 6%	5465
April	1st to 10th	Day	40% 7% 11% 19% 17% 7%	2370
	11th to 20th	Day	37% 7% 11% 19% 21% 5%	2374
	21st to end	Day	44% 6% 10% 21% 14% 4	2440
May	1st to 10th	Day	47% 10% 13% 19% 10% 2	5897
	11th to 20th	Day	49% 9% 11% 22% 8% 1	5865
	21st to end	Day	40% 10% 13% 19% 15% 2	6895
June	1st to 10th	Day	39% 8% 13% 23% 16% 1	2800
	11th to 20th	Day	41% 10% 14% 21% 13% 2	2800
	21st to end	Day	35% 10% 16% 24% 14% 1	2800
July	1st to 10th	Day	35% 13% 17% 20% 12% 4	6120
	11th to 20th	Day	44% 14% 17% 19% 6% 1	5831
	21st to end	Day	40% 11% 11% 24% 13% 1	6240
August	1st to 10th	Day	45% 12% 17% 21% 6%	4143
	11th to 20th	Day	38% 13% 12% 25% 11% 1	4004
	21st to end	Day	35% 9% 15% 29% 11% 1	4180
September	1st to 10th	Day	39% 8% 13% 16% 19% 4	2280
	11th to 20th	Day	39% 5% 8% 26% 18% 3	2212
	21st to end	Day	49% 6% 9% 17% 16% 2	2019
October	1st to 10th	Day	36% 5% 6% 19% 28% 6%	3160
	11th to 20th	Day	25% 5% 8% 26% 22% 13%	3140
	21st to end	Day	22% 4 10% 30% 24% 11%	3428
November	1st to 10th	Day	33% 4 10% 25% 24% 4	1957
	11th to 20th	Day	35% 6% 11% 20% 22% 6%	1731
	21st to end	Day	37% 5% 9% 25% 22% 2	1600
December	1st to 10th	Day	33% 6% 11% 23% 21% 5%	2600
	11th to 20th	Day	39% 6% 14% 24% 13% 4	2986
	21st to end	Day	44% 7% 13% 21% 15% 1	3960
January	1st to 10th	Night	31% 6% 9% 22% 26% 6%	5910
	11th to 20th	Night	33% 4 8% 23% 23% 10%	5900
	21st to end	Night	37% 4 8% 25% 22% 3	6490
February	1st to 10th	Night	41% 6% 12% 23% 16% 2	2600
	11th to 20th	Night	44% 6% 9% 20% 16% 6%	2535
	21st to end	Night	41% 5% 12% 20% 16% 6%	1925
March	1st to 10th	Night	37% 6% 8% 23% 19% 8%	4918
	11th to 20th	Night	31% 5% 11% 24% 24% 6%	4980
	21st to end	Night	37% 8% 11% 19% 19% 5%	5467
April	1st to 10th	Night	40% 7% 12% 19% 19% 4	2030
	11th to 20th	Night	36% 7% 13% 20% 19% 5%	1975
	21st to end	Night	38% 6% 12% 26% 14% 4	1975
May	1st to 10th	Night	49% 9% 14% 17% 8% 3	4060
	11th to 20th	Night	48% 8% 12% 23% 9% 1	4033
	21st to end	Night	40% 11% 16% 23% 7% 2	3976
June	1st to 10th	Night	35% 8% 14% 27% 14% 1	1600
	11th to 20th	Night	38% 10% 16% 23% 12% 1	1600
	21st to end	Night	34% 9% 17% 19% 18% 2	1600
July	1st to 10th	Night	36% 13% 19% 18% 13% 2	3711
	11th to 20th	Night	46% 13% 19% 17% 5% 1	4006
	21st to end	Night	35% 11% 16% 25% 12%	4297
August	1st to 10th	Night	44% 8% 18% 23% 6% 1	2850
	11th to 20th	Night	41% 11% 13% 23% 12% 1	2844
	21st to end	Night	34% 7% 17% 31% 10% 1	3476
September	1st to 10th	Night	36% 8% 14% 20% 17% 5%	1900
	11th to 20th	Night	36% 7% 10% 26% 19% 2	1965
	21st to end	Night	47% 5% 10% 19% 17% 2	2160
October	1st to 10th	Night	40% 6% 8% 19% 22% 5%	3800
	11th to 20th	Night	24% 7% 10% 20% 26% 13%	3779
	21st to end	Night	22% 5% 10% 30% 22% 11%	4120
November	1st to 10th	Night	34% 5% 10% 23% 23% 6%	2341
	11th to 20th	Night	36% 6% 8% 22% 23% 6%	2664
	21st to end	Night	35% 5% 11% 24% 21% 4	2800
December	1st to 10th	Night	30% 5% 11% 29% 23% 2	4580
	11th to 20th	Night	43% 5% 11% 18% 17% 5%	5208
	21st to end	Night	39% 8% 15% 21% 16% 1	6996

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	33% 24% 29% 11% 3	295
	11th to 20th	Day	31% 29% 26% 10% 3	300
	21st to end	Day	26% 29% 33% 9% 2 1	330
February	1st to 10th	Day	27% 34% 27% 11% 2	300
	11th to 20th	Day	43% 25% 27% 5% 1	300
	21st to end	Day	31% 22% 29% 15% 2	403
March	1st to 10th	Day	27% 22% 28% 18% 4	500
	11th to 20th	Day	24% 23% 29% 17% 6% 1	500
	21st to end	Day	27% 20% 33% 14% 6% 1	550
April	1st to 10th	Day	25% 26% 25% 17% 6% 1	500
	11th to 20th	Day	23% 20% 26% 19% 10% 2	492
	21st to end	Day	23% 18% 31% 17% 9% 2	500
May	1st to 10th	Day	22% 20% 28% 16% 11% 2	503
	11th to 20th	Day	23% 15% 28% 20% 10% 3	527
	21st to end	Day	23% 7% 25% 25% 15% 6%	573
June	1st to 10th	Day	15% 10% 29% 26% 16% 5%	530
	11th to 20th	Day	16% 9% 28% 28% 14% 5%	530
	21st to end	Day	10% 7% 30% 31% 18% 4	530
July	1st to 10th	Day	14% 4 21% 30% 23% 8%	525
	11th to 20th	Day	5% 5% 21% 34% 25% 10%	524
	21st to end	Day	12% 4 23% 31% 21% 9%	576
August	1st to 10th	Day	13% 5% 22% 25% 24% 10%	502
	11th to 20th	Day	13% 6% 20% 28% 22% 11%	479
	21st to end	Day	10% 4 18% 33% 20% 15%	539
September	1st to 10th	Day	16% 5% 20% 26% 19% 14%	490
	11th to 20th	Day	17% 4 19% 27% 23% 10%	490
	21st to end	Day	30% 9% 20% 23% 13% 4	490
October	1st to 10th	Day	20% 7% 22% 30% 16% 6%	490
	11th to 20th	Day	16% 16% 26% 25% 15% 2	490
	21st to end	Day	17% 15% 33% 23% 10% 2	539
November	1st to 10th	Day	16% 14% 30% 26% 10% 3	495
	11th to 20th	Day	20% 15% 32% 22% 10% 1	319
	21st to end	Day	25% 18% 35% 18% 5%	200
December	1st to 10th	Day	21% 27% 35% 13% 5% 1	200
	11th to 20th	Day	23% 20% 35% 17% 6% 1	200
	21st to end	Day	24% 21% 33% 16% 6%	220
January	1st to 10th	Night	20% 20% 35% 22% 4	800
	11th to 20th	Night	22% 16% 32% 26% 4	800
	21st to end	Night	18% 16% 39% 25% 1	880
February	1st to 10th	Night	17% 17% 36% 28% 2	800
	11th to 20th	Night	26% 21% 36% 17% 1	783
	21st to end	Night	20% 19% 39% 19% 3	660
March	1st to 10th	Night	18% 18% 36% 24% 4	800
	11th to 20th	Night	22% 18% 32% 21% 6% 1	800
	21st to end	Night	18% 19% 36% 22% 5% 1	880
April	1st to 10th	Night	18% 19% 33% 24% 5%	800
	11th to 20th	Night	17% 15% 31% 27% 9% 1	791
	21st to end	Night	18% 11% 32% 31% 7%	775
May	1st to 10th	Night	19% 11% 26% 27% 16% 1	600
	11th to 20th	Night	20% 6% 24% 35% 15% 1	591
	21st to end	Night	15% 4 20% 37% 22% 2	457
June	1st to 10th	Night	11% 4 21% 44% 20% 2	400
	11th to 20th	Night	13% 6% 15% 43% 23% 1	400
	21st to end	Night	9% 3 19% 46% 22% 2	400
July	1st to 10th	Night	13% 2 17% 35% 29% 4	450
	11th to 20th	Night	6% 3 14% 33% 39% 5%	582
	21st to end	Night	7% 3 14% 40% 31% 5%	657
August	1st to 10th	Night	11% 2 12% 42% 30% 3	579
	11th to 20th	Night	12% 3 14% 37% 30% 3	583
	21st to end	Night	13% 2 15% 35% 32% 4	836
September	1st to 10th	Night	16% 3 14% 33% 28% 6%	760
	11th to 20th	Night	15% 3 14% 35% 29% 4	760
	21st to end	Night	27% 3 19% 30% 19% 2	760
October	1st to 10th	Night	19% 8% 19% 29% 20% 4	760
	11th to 20th	Night	16% 9% 28% 31% 16% 1	760
	21st to end	Night	17% 10% 29% 31% 11% 2	836
November	1st to 10th	Night	15% 10% 29% 33% 11% 2	780
	11th to 20th	Night	17% 13% 30% 31% 8% 1	800
	21st to end	Night	17% 14% 31% 29% 10% 1	800
December	1st to 10th	Night	20% 13% 34% 26% 7%	800
	11th to 20th	Night	18% 10% 33% 35% 5%	800
	21st to end	Night	18% 13% 30% 36% 3	880

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