Lone Pine Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lone Pine Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	17% 12% 5% 10% 5% 4 4 4 5% 6% 28%	127584
	Night	16% 14% 5% 11% 6% 4 4 3 4 6% 27%	124080
Transparency	Day	55% 6% 11% 18% 10% 1	131177
	Night	58% 6% 10% 16% 9% 1	128573
Seeing	Day	26% 18% 28% 16% 8% 3	16083
	Night	25% 17% 26% 21% 9% 1	25584

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% 19% 11% 22% 7% 3 3 2 2 3 14%	3677
	11th to 20th	Day	8% 23% 11% 23% 8% 5% 2 2 3 3 11%	3968
	21st to end	Day	17% 15% 8% 14% 9% 4 5% 3 4 4 15%	4466
February	1st to 10th	Day	14% 21% 7% 12% 9% 5% 4 3 3 3 18%	1800
	11th to 20th	Day	12% 16% 8% 17% 7% 5% 4 3 4 4 19%	1753
	21st to end	Day	18% 15% 5% 13% 6% 3 4 3 5% 5% 23%	1591
March	1st to 10th	Day	16% 15% 8% 10% 5% 4 2 2 4 4 30%	4918
	11th to 20th	Day	12% 17% 7% 8% 3 3 3 3 4 6% 33%	4980
	21st to end	Day	19% 14% 5% 11% 5% 4 4 3 4 4 27%	5496
April	1st to 10th	Day	17% 17% 4 9% 5% 3 4 3 4 6% 28%	2400
	11th to 20th	Day	18% 15% 3 7% 4 4 4 5% 5% 5% 31%	2374
	21st to end	Day	20% 12% 3 7% 4 4 4 3 4 5% 33%	2543
May	1st to 10th	Day	26% 11% 3 7% 5% 4 4 3 5% 5% 25%	5888
	11th to 20th	Day	23% 11% 3 8% 5% 5% 4 4 5% 7% 26%	6310
	21st to end	Day	21% 8% 3 8% 5% 5% 5% 4 5% 6% 31%	6949
June	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 9% 34%	2800
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 5% 6% 8% 32%	2800
	21st to end	Day	15% 7% 2 6% 5% 5% 5% 5% 6% 8% 35%	2800
July	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 5% 7% 9% 37%	6360
	11th to 20th	Day	12% 7% 3 8% 6% 6% 6% 5% 7% 10% 31%	6360
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 4 6% 7% 41%	6477
August	1st to 10th	Day	19% 7% 3 8% 5% 5% 5% 5% 7% 8% 30%	4234
	11th to 20th	Day	16% 7% 3 8% 6% 6% 6% 6% 8% 9% 24%	4174
	21st to end	Day	15% 7% 2 6% 4 5% 5% 4 6% 9% 35%	4345
September	1st to 10th	Day	17% 7% 3 6% 4 4 5% 4 5% 7% 39%	2400
	11th to 20th	Day	14% 6% 2 6% 5% 4 4 4 5% 7% 42%	2365
	21st to end	Day	21% 8% 3 7% 6% 4 5% 3 6% 7% 30%	2107
October	1st to 10th	Day	18% 9% 3 7% 4 4 4 3 6% 8% 34%	2000
	11th to 20th	Day	20% 12% 3 9% 5% 4 4 3 6% 5% 30%	2000
	21st to end	Day	24% 16% 2 8% 5% 4 4 2 5% 6% 25%	2200
November	1st to 10th	Day	15% 14% 3 9% 5% 4 4 3 5% 6% 32%	1895
	11th to 20th	Day	16% 21% 4 9% 5% 4 4 4 5% 6% 22%	1680
	21st to end	Day	18% 23% 7% 9% 5% 3 4 4 5% 5% 17%	1680
December	1st to 10th	Day	17% 24% 15% 16% 5% 3 3 2 3 3 9%	2680
	11th to 20th	Day	18% 19% 8% 15% 8% 3 3 2 4 4 17%	3066
	21st to end	Day	19% 25% 8% 12% 6% 4 3 2 3 5% 14%	4048
January	1st to 10th	Night	13% 18% 10% 25% 9% 4 3 2 3 4 10%	6489
	11th to 20th	Night	10% 18% 10% 25% 9% 5% 4 3 3 4 10%	6033
	21st to end	Night	16% 17% 8% 17% 9% 6% 5% 2 3 3 13%	6490
February	1st to 10th	Night	14% 19% 6% 14% 9% 5% 4 3 4 4 17%	2600
	11th to 20th	Night	13% 15% 8% 16% 8% 6% 5% 4 4 4 17%	2533
	21st to end	Night	16% 16% 6% 15% 8% 5% 3 3 4 4 21%	2038
March	1st to 10th	Night	16% 15% 5% 10% 9% 5% 3 3 4 5% 24%	4918
	11th to 20th	Night	15% 16% 6% 8% 4 3 3 3 4 5% 33%	4979
	21st to end	Night	14% 15% 6% 10% 5% 3 3 3 5% 5% 30%	5434
April	1st to 10th	Night	19% 16% 4 10% 5% 3 4 3 4 6% 27%	2000
	11th to 20th	Night	19% 14% 3 7% 3 3 3 3 5% 5% 34%	1975
	21st to end	Night	16% 12% 3 7% 4 4 4 4 4 7% 34%	1874
May	1st to 10th	Night	28% 11% 3 7% 4 4 4 3 4 5% 27%	4053
	11th to 20th	Night	22% 12% 3 7% 4 4 4 3 5% 5% 32%	3580
	21st to end	Night	21% 11% 2 7% 4 4 4 3 4 7% 33%	3926
June	1st to 10th	Night	15% 8% 2 7% 5% 4 5% 4 5% 9% 36%	1600
	11th to 20th	Night	14% 6% 3 6% 4 4 4 4 6% 10% 38%	1600
	21st to end	Night	13% 7% 2 6% 4 4 4 4 5% 8% 43%	1600
July	1st to 10th	Night	13% 9% 3 7% 4 4 4 4 5% 9% 38%	3600
	11th to 20th	Night	12% 7% 2 7% 4 4 5% 4 7% 9% 38%	3600
	21st to end	Night	12% 6% 2 6% 4 5% 4 3 5% 8% 45%	4372
August	1st to 10th	Night	17% 9% 2 7% 4 5% 5% 4 5% 7% 35%	2915
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 6% 7% 35%	2875
	21st to end	Night	12% 7% 2 7% 4 4 4 4 6% 8% 43%	3519
September	1st to 10th	Night	16% 7% 2 6% 4 4 3 4 4 7% 45%	2000
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 6% 7% 48%	2032
	21st to end	Night	21% 8% 3 6% 4 5% 5% 4 5% 6% 34%	2291
October	1st to 10th	Night	16% 10% 2 6% 4 3 4 3 5% 7% 40%	2400
	11th to 20th	Night	19% 13% 3 6% 5% 4 4 3 4 7% 32%	2400
	21st to end	Night	25% 15% 3 6% 4 4 4 3 5% 5% 27%	2640
November	1st to 10th	Night	13% 16% 3 7% 5% 4 4 3 4 6% 36%	2616
	11th to 20th	Night	16% 20% 4 9% 4 4 4 4 5% 5% 24%	2940
	21st to end	Night	16% 21% 7% 10% 5% 5% 4 3 4 5% 19%	2940
December	1st to 10th	Night	15% 22% 13% 19% 5% 4 4 2 3 3 9%	4720
	11th to 20th	Night	20% 18% 9% 14% 6% 3 4 3 3 4 16%	5348
	21st to end	Night	19% 22% 8% 13% 7% 4 3 3 3 4 14%	7150

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	77% 3 6% 9% 5%	3678
	11th to 20th	Day	80% 3 5% 8% 4	4002
	21st to end	Day	71% 4 9% 11% 4	4466
February	1st to 10th	Day	72% 4 9% 10% 5%	1800
	11th to 20th	Day	69% 5% 6% 14% 6% 1	1762
	21st to end	Day	63% 4 10% 16% 5% 2	1591
March	1st to 10th	Day	59% 3 11% 19% 8%	4921
	11th to 20th	Day	53% 4 17% 16% 7% 2	4980
	21st to end	Day	59% 5% 6% 17% 11% 2	5496
April	1st to 10th	Day	58% 5% 9% 16% 11% 1	2400
	11th to 20th	Day	53% 7% 10% 17% 12% 1	2374
	21st to end	Day	53% 5% 9% 18% 13% 2	2543
May	1st to 10th	Day	59% 6% 8% 17% 9% 2	5897
	11th to 20th	Day	56% 8% 8% 18% 9% 1	6314
	21st to end	Day	51% 7% 11% 19% 10% 1	6949
June	1st to 10th	Day	47% 6% 11% 20% 13% 1	2800
	11th to 20th	Day	48% 8% 12% 20% 11% 1	2800
	21st to end	Day	45% 7% 13% 22% 13%	2800
July	1st to 10th	Day	40% 8% 13% 25% 13% 1	6290
	11th to 20th	Day	42% 9% 15% 20% 14%	6285
	21st to end	Day	40% 8% 11% 26% 15% 1	6291
August	1st to 10th	Day	48% 8% 13% 21% 10%	4221
	11th to 20th	Day	50% 11% 14% 19% 6%	4213
	21st to end	Day	42% 8% 11% 29% 9% 1	4345
September	1st to 10th	Day	44% 7% 9% 25% 13% 2	2400
	11th to 20th	Day	41% 5% 11% 26% 16% 1	2365
	21st to end	Day	52% 6% 10% 19% 12% 1	2107
October	1st to 10th	Day	42% 8% 12% 21% 17% 1	3260
	11th to 20th	Day	48% 5% 13% 15% 15% 4	3240
	21st to end	Day	48% 5% 14% 22% 10% 1	3538
November	1st to 10th	Day	52% 5% 12% 18% 11% 2	1895
	11th to 20th	Day	62% 5% 10% 15% 6% 2	1680
	21st to end	Day	68% 6% 9% 12% 4 1	1680
December	1st to 10th	Day	80% 4 7% 7% 2	2680
	11th to 20th	Day	71% 5% 10% 11% 3	3066
	21st to end	Day	74% 4 9% 8% 4	4048
January	1st to 10th	Night	79% 4 6% 8% 4	6489
	11th to 20th	Night	78% 5% 8% 7% 2	6074
	21st to end	Night	75% 4 6% 8% 5% 1	6490
February	1st to 10th	Night	71% 4 9% 11% 5%	2600
	11th to 20th	Night	69% 6% 9% 11% 5%	2535
	21st to end	Night	67% 4 8% 12% 7% 1	2038
March	1st to 10th	Night	62% 5% 13% 15% 5%	4928
	11th to 20th	Night	54% 5% 15% 17% 5% 3	4980
	21st to end	Night	54% 5% 9% 15% 14% 2	5434
April	1st to 10th	Night	59% 4 11% 15% 10% 1	2000
	11th to 20th	Night	52% 5% 12% 17% 12% 1	1975
	21st to end	Night	50% 6% 10% 20% 13% 2	1874
May	1st to 10th	Night	60% 5% 7% 16% 8% 3	4060
	11th to 20th	Night	53% 7% 12% 19% 9% 1	3581
	21st to end	Night	50% 7% 10% 19% 11% 3	3927
June	1st to 10th	Night	44% 7% 12% 23% 14% 1	1600
	11th to 20th	Night	42% 8% 15% 23% 12% 1	1600
	21st to end	Night	38% 10% 13% 25% 14% 1	1600
July	1st to 10th	Night	43% 7% 13% 23% 13% 1	3560
	11th to 20th	Night	38% 9% 15% 26% 12% 1	3552
	21st to end	Night	36% 6% 12% 25% 19% 1	4243
August	1st to 10th	Night	47% 9% 13% 23% 8% 1	2904
	11th to 20th	Night	45% 9% 14% 25% 8%	2902
	21st to end	Night	38% 8% 14% 31% 9% 1	3519
September	1st to 10th	Night	39% 6% 12% 27% 13% 3	2000
	11th to 20th	Night	36% 5% 14% 28% 16% 1	2032
	21st to end	Night	49% 6% 13% 18% 12% 1	2291
October	1st to 10th	Night	46% 6% 10% 22% 17% 1	3920
	11th to 20th	Night	46% 5% 12% 17% 14% 5%	3899
	21st to end	Night	45% 5% 15% 24% 10% 1	4252
November	1st to 10th	Night	50% 6% 12% 19% 12% 2	2616
	11th to 20th	Night	61% 5% 11% 15% 7% 2	2940
	21st to end	Night	67% 5% 11% 14% 3 1	2940
December	1st to 10th	Night	78% 7% 8% 6% 2	4720
	11th to 20th	Night	72% 4 8% 11% 5%	5348
	21st to end	Night	74% 6% 7% 9% 4	7150

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	34% 28% 28% 7% 3	220
	11th to 20th	Day	38% 29% 25% 5% 2	293
	21st to end	Day	32% 28% 31% 6% 3	330
February	1st to 10th	Day	42% 28% 24% 5%	300
	11th to 20th	Day	37% 30% 31% 1 1	300
	21st to end	Day	43% 28% 23% 6% 1	355
March	1st to 10th	Day	37% 23% 26% 11% 2	500
	11th to 20th	Day	32% 26% 28% 10% 4 1	500
	21st to end	Day	36% 22% 27% 11% 4 1	550
April	1st to 10th	Day	34% 23% 25% 12% 5% 1	500
	11th to 20th	Day	32% 24% 24% 11% 7% 2	492
	21st to end	Day	30% 22% 28% 14% 4 1	500
May	1st to 10th	Day	32% 18% 26% 14% 6% 3	503
	11th to 20th	Day	28% 17% 28% 17% 8% 3	527
	21st to end	Day	20% 16% 27% 23% 10% 4	573
June	1st to 10th	Day	24% 18% 28% 19% 9% 2	530
	11th to 20th	Day	20% 12% 32% 22% 12% 3	530
	21st to end	Day	18% 16% 35% 21% 7% 2	530
July	1st to 10th	Day	14% 10% 31% 26% 15% 4	525
	11th to 20th	Day	14% 10% 28% 30% 13% 5%	524
	21st to end	Day	14% 8% 36% 26% 11% 5%	576
August	1st to 10th	Day	13% 8% 29% 25% 18% 7%	526
	11th to 20th	Day	16% 9% 28% 26% 14% 8%	519
	21st to end	Day	16% 11% 32% 20% 13% 8%	583
September	1st to 10th	Day	20% 11% 25% 21% 14% 9%	530
	11th to 20th	Day	13% 7% 24% 23% 22% 11%	530
	21st to end	Day	24% 15% 27% 18% 12% 4	530
October	1st to 10th	Day	21% 16% 27% 19% 13% 5%	530
	11th to 20th	Day	29% 22% 27% 13% 7% 2	530
	21st to end	Day	36% 18% 27% 17% 2	583
November	1st to 10th	Day	26% 23% 27% 14% 7% 2	442
	11th to 20th	Day	36% 23% 28% 10% 2 1	220
	21st to end	Day	39% 24% 31% 6%	220
December	1st to 10th	Day	39% 29% 24% 5% 2 1	220
	11th to 20th	Day	40% 27% 26% 5% 2	220
	21st to end	Day	40% 25% 29% 6%	242
January	1st to 10th	Night	31% 26% 28% 12% 3	840
	11th to 20th	Night	30% 27% 28% 12% 2	825
	21st to end	Night	28% 28% 27% 15% 2	880
February	1st to 10th	Night	29% 27% 29% 15% 1	800
	11th to 20th	Night	30% 28% 30% 11% 1	783
	21st to end	Night	34% 25% 26% 13% 2	660
March	1st to 10th	Night	27% 26% 30% 15% 3	800
	11th to 20th	Night	31% 22% 25% 18% 3 1	800
	21st to end	Night	26% 22% 30% 16% 4 1	880
April	1st to 10th	Night	29% 21% 29% 18% 3	800
	11th to 20th	Night	30% 17% 26% 19% 7% 1	791
	21st to end	Night	24% 13% 29% 27% 7%	674
May	1st to 10th	Night	24% 12% 23% 31% 10%	600
	11th to 20th	Night	18% 13% 28% 31% 10% 1	399
	21st to end	Night	16% 10% 27% 31% 15% 1	433
June	1st to 10th	Night	18% 8% 31% 30% 13% 1	400
	11th to 20th	Night	17% 11% 24% 35% 14%	400
	21st to end	Night	13% 7% 30% 35% 15%	400
July	1st to 10th	Night	12% 5% 21% 44% 16% 2	390
	11th to 20th	Night	9% 6% 25% 38% 22% 1	388
	21st to end	Night	14% 4 21% 38% 22% 1	627
August	1st to 10th	Night	14% 4 20% 36% 23% 3	597
	11th to 20th	Night	16% 4 19% 32% 27% 2	594
	21st to end	Night	16% 6% 21% 33% 22% 3	839
September	1st to 10th	Night	19% 6% 24% 31% 18% 2	800
	11th to 20th	Night	16% 6% 18% 27% 29% 4	800
	21st to end	Night	24% 10% 20% 25% 18% 3	800
October	1st to 10th	Night	22% 10% 26% 23% 17% 2	800
	11th to 20th	Night	27% 16% 30% 20% 7% 1	800
	21st to end	Night	34% 15% 28% 19% 4	880
November	1st to 10th	Night	23% 18% 30% 21% 7%	820
	11th to 20th	Night	31% 20% 28% 15% 6% 1	840
	21st to end	Night	31% 23% 27% 14% 4	840
December	1st to 10th	Night	35% 25% 26% 10% 4	840
	11th to 20th	Night	31% 27% 28% 13% 2	840
	21st to end	Night	31% 26% 28% 13% 2	924

Page generated at 2026-01-14 01:14:30. Version ac07

Copyright © 2026 Attilla Danko.