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 2024-01-14.

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% 8% 6% 3 5% 5% 5% 6% 28%	74675
	Night	16% 13% 5% 9% 6% 3 4 4 4 6% 28%	75071
Transparency	Day	56% 6% 10% 17% 9% 1	74390
	Night	57% 6% 11% 16% 9% 1	74890
Seeing	Day	26% 18% 28% 17% 9% 3	13501
	Night	25% 17% 27% 22% 9% 1	23037

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	14% 19% 11% 13% 8% 4 4 4 3 4 17%	1517
	11th to 20th	Day	14% 21% 9% 14% 9% 4 3 3 4 4 16%	1604
	21st to end	Day	10% 17% 11% 15% 12% 4 5% 4 4 5% 13%	1782
February	1st to 10th	Day	15% 20% 9% 10% 11% 4 5% 3 3 3 16%	1620
	11th to 20th	Day	13% 15% 9% 14% 8% 4 5% 4 4 5% 19%	1573
	21st to end	Day	19% 14% 6% 11% 9% 3 4 3 4 5% 23%	1426
March	1st to 10th	Day	16% 14% 7% 11% 7% 4 4 3 4 4 26%	1963
	11th to 20th	Day	15% 16% 8% 9% 5% 2 4 4 5% 5% 27%	1980
	21st to end	Day	20% 12% 6% 7% 7% 3 4 4 4 5% 28%	2182
April	1st to 10th	Day	16% 15% 6% 8% 5% 2 4 4 4 7% 29%	2160
	11th to 20th	Day	19% 13% 4 6% 5% 3 4 6% 5% 6% 31%	2134
	21st to end	Day	21% 12% 3 7% 5% 3 4 4 4 5% 32%	2288
May	1st to 10th	Day	20% 12% 4 7% 6% 3 5% 3 5% 7% 27%	2340
	11th to 20th	Day	21% 9% 3 6% 5% 4 4 4 5% 6% 31%	2470
	21st to end	Day	14% 6% 3 5% 6% 4 5% 5% 6% 8% 38%	2725
June	1st to 10th	Day	18% 7% 3 6% 5% 3 5% 5% 5% 8% 34%	2520
	11th to 20th	Day	16% 7% 3 6% 6% 4 5% 5% 5% 9% 34%	2520
	21st to end	Day	15% 7% 3 5% 6% 4 5% 6% 6% 8% 35%	2520
July	1st to 10th	Day	11% 6% 3 7% 7% 4 6% 6% 7% 8% 36%	2520
	11th to 20th	Day	13% 6% 3 6% 6% 4 6% 6% 7% 9% 33%	2520
	21st to end	Day	13% 6% 4 6% 7% 4 6% 7% 6% 8% 33%	2572
August	1st to 10th	Day	12% 6% 3 6% 6% 5% 5% 7% 8% 9% 35%	2327
	11th to 20th	Day	14% 8% 3 7% 8% 5% 5% 7% 7% 9% 28%	2303
	21st to end	Day	16% 7% 3 7% 6% 5% 6% 5% 6% 8% 31%	2394
September	1st to 10th	Day	18% 7% 3 5% 5% 3 4 5% 5% 7% 37%	2160
	11th to 20th	Day	15% 7% 2 5% 5% 3 4 5% 5% 7% 40%	2129
	21st to end	Day	19% 7% 4 5% 7% 3 5% 5% 6% 6% 32%	1897
October	1st to 10th	Day	20% 9% 3 6% 6% 4 4 4 6% 8% 31%	1800
	11th to 20th	Day	22% 11% 4 8% 6% 3 4 4 6% 5% 29%	1800
	21st to end	Day	25% 16% 3 7% 6% 3 4 3 4 5% 24%	1980
November	1st to 10th	Day	15% 13% 4 8% 5% 3 4 4 5% 6% 33%	1711
	11th to 20th	Day	17% 19% 6% 8% 5% 2 5% 5% 5% 6% 23%	1520
	21st to end	Day	19% 20% 7% 8% 7% 2 4 5% 5% 5% 19%	1520
December	1st to 10th	Day	17% 21% 11% 13% 7% 3 3 4 4 4 13%	1520
	11th to 20th	Day	17% 18% 8% 15% 6% 2 4 4 5% 6% 17%	1906
	21st to end	Day	22% 24% 9% 11% 6% 3 3 3 3 4 13%	2772
January	1st to 10th	Night	15% 18% 10% 15% 8% 4 5% 4 4 5% 15%	2649
	11th to 20th	Night	16% 19% 9% 13% 8% 3 4 4 3 5% 16%	2430
	21st to end	Night	12% 17% 9% 14% 11% 5% 6% 4 4 4 14%	2574
February	1st to 10th	Night	15% 16% 7% 13% 11% 4 5% 4 4 4 17%	2340
	11th to 20th	Night	13% 14% 8% 13% 9% 5% 6% 5% 4 4 18%	2273
	21st to end	Night	17% 14% 8% 12% 9% 3 4 4 4 4 21%	1829
March	1st to 10th	Night	13% 14% 8% 11% 8% 4 4 4 5% 5% 24%	1980
	11th to 20th	Night	17% 15% 5% 10% 6% 2 4 3 4 5% 28%	1979
	21st to end	Night	15% 15% 6% 8% 6% 3 4 3 4 6% 29%	2172
April	1st to 10th	Night	18% 14% 5% 8% 6% 3 4 4 4 6% 28%	1800
	11th to 20th	Night	19% 13% 3 7% 4 3 3 4 5% 5% 35%	1775
	21st to end	Night	17% 12% 3 7% 5% 3 4 4 4 7% 33%	1688
May	1st to 10th	Night	19% 9% 4 6% 6% 4 5% 5% 4 5% 33%	1620
	11th to 20th	Night	13% 9% 4 7% 6% 3 5% 5% 5% 6% 36%	1420
	21st to end	Night	13% 6% 3 5% 5% 3 5% 4 5% 8% 43%	1550
June	1st to 10th	Night	15% 6% 2 6% 5% 3 5% 5% 6% 9% 37%	1440
	11th to 20th	Night	14% 5% 3 5% 5% 4 4 5% 5% 9% 39%	1440
	21st to end	Night	13% 6% 2 5% 5% 3 4 5% 5% 8% 43%	1440
July	1st to 10th	Night	9% 7% 3 6% 4 4 4 4 5% 8% 44%	1440
	11th to 20th	Night	10% 6% 2 4 5% 3 5% 5% 6% 8% 48%	1440
	21st to end	Night	12% 5% 3 5% 5% 3 5% 6% 6% 9% 40%	1743
August	1st to 10th	Night	9% 6% 2 6% 5% 3 6% 5% 6% 8% 43%	1611
	11th to 20th	Night	14% 7% 3 7% 5% 4 4 5% 6% 9% 38%	1598
	21st to end	Night	13% 6% 3 6% 5% 3 4 6% 6% 8% 41%	1943
September	1st to 10th	Night	17% 6% 2 5% 5% 3 3 5% 5% 7% 43%	1800
	11th to 20th	Night	15% 7% 3 5% 4 3 3 3 6% 7% 46%	1828
	21st to end	Night	18% 7% 3 6% 5% 4 5% 4 5% 7% 37%	2061
October	1st to 10th	Night	17% 10% 2 6% 5% 3 4 4 5% 7% 38%	2160
	11th to 20th	Night	20% 12% 3 5% 6% 3 4 4 4 7% 31%	2160
	21st to end	Night	27% 14% 3 5% 5% 3 4 3 4 6% 25%	2376
November	1st to 10th	Night	13% 15% 3 6% 6% 3 4 4 4 6% 37%	2360
	11th to 20th	Night	17% 18% 5% 8% 5% 3 4 5% 5% 6% 25%	2660
	21st to end	Night	16% 19% 6% 9% 7% 4 5% 4 4 6% 21%	2660
December	1st to 10th	Night	19% 20% 11% 12% 7% 3 4 4 4 4 12%	2660
	11th to 20th	Night	18% 17% 9% 15% 7% 3 4 5% 3 5% 15%	3288
	21st to end	Night	21% 21% 9% 10% 7% 3 4 4 4 5% 11%	4884

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	72% 4 9% 11% 5%	1518
	11th to 20th	Day	74% 5% 7% 8% 6%	1604
	21st to end	Day	73% 4 8% 8% 5% 1	1782
February	1st to 10th	Day	74% 4 9% 8% 4	1620
	11th to 20th	Day	68% 5% 5% 15% 6% 1	1582
	21st to end	Day	65% 4 10% 15% 5% 2	1426
March	1st to 10th	Day	63% 3 11% 16% 6% 1	1966
	11th to 20th	Day	59% 5% 9% 16% 9% 3	1980
	21st to end	Day	60% 5% 6% 17% 11% 2	2182
April	1st to 10th	Day	57% 5% 10% 16% 11% 1	2160
	11th to 20th	Day	52% 7% 10% 17% 12% 2	2134
	21st to end	Day	54% 5% 9% 18% 12% 2	2288
May	1st to 10th	Day	57% 5% 9% 18% 9% 2	2340
	11th to 20th	Day	54% 6% 9% 18% 12% 1	2474
	21st to end	Day	43% 8% 15% 21% 11% 1	2725
June	1st to 10th	Day	48% 6% 11% 20% 13% 1	2520
	11th to 20th	Day	47% 7% 12% 21% 12% 1	2520
	21st to end	Day	45% 7% 13% 23% 12%	2520
July	1st to 10th	Day	44% 8% 10% 24% 12% 1	2450
	11th to 20th	Day	45% 8% 15% 21% 12%	2445
	21st to end	Day	46% 8% 13% 20% 11% 1	2428
August	1st to 10th	Day	43% 9% 14% 24% 10%	2314
	11th to 20th	Day	49% 10% 13% 20% 8%	2303
	21st to end	Day	49% 7% 11% 20% 11% 1	2394
September	1st to 10th	Day	46% 7% 9% 23% 13% 2	2160
	11th to 20th	Day	44% 5% 11% 24% 15% 1	2129
	21st to end	Day	50% 6% 10% 21% 12% 1	1897
October	1st to 10th	Day	50% 7% 12% 17% 13% 1	1800
	11th to 20th	Day	56% 6% 12% 17% 8% 1	1800
	21st to end	Day	64% 5% 8% 14% 7% 2	1980
November	1st to 10th	Day	52% 5% 12% 17% 12% 3	1711
	11th to 20th	Day	61% 5% 11% 15% 6% 2	1520
	21st to end	Day	67% 6% 9% 13% 4 1	1520
December	1st to 10th	Day	76% 4 9% 8% 3	1520
	11th to 20th	Day	70% 5% 12% 10% 3	1906
	21st to end	Day	77% 5% 8% 9% 1	2772
January	1st to 10th	Night	74% 4 8% 8% 6%	2649
	11th to 20th	Night	72% 5% 10% 9% 3 1	2430
	21st to end	Night	73% 5% 8% 9% 5% 1	2574
February	1st to 10th	Night	72% 4 10% 9% 5%	2340
	11th to 20th	Night	69% 6% 9% 11% 5%	2275
	21st to end	Night	67% 4 8% 12% 7% 1	1829
March	1st to 10th	Night	62% 5% 9% 18% 5% 1	1990
	11th to 20th	Night	60% 5% 10% 15% 9% 1	1980
	21st to end	Night	58% 5% 9% 14% 12% 3	2172
April	1st to 10th	Night	58% 5% 11% 15% 11%	1800
	11th to 20th	Night	52% 5% 12% 17% 13% 2	1775
	21st to end	Night	52% 5% 9% 19% 13% 2	1688
May	1st to 10th	Night	52% 7% 8% 20% 10% 2	1620
	11th to 20th	Night	48% 7% 11% 21% 12% 1	1421
	21st to end	Night	39% 8% 13% 24% 13% 2	1551
June	1st to 10th	Night	42% 8% 12% 24% 13%	1440
	11th to 20th	Night	41% 8% 15% 22% 13% 2	1440
	21st to end	Night	38% 10% 12% 26% 13% 1	1440
July	1st to 10th	Night	38% 7% 12% 24% 17% 1	1400
	11th to 20th	Night	34% 8% 13% 27% 16% 1	1392
	21st to end	Night	39% 8% 15% 22% 15% 1	1646
August	1st to 10th	Night	37% 9% 15% 28% 10% 1	1600
	11th to 20th	Night	41% 10% 14% 27% 9%	1598
	21st to end	Night	40% 8% 14% 24% 13% 1	1943
September	1st to 10th	Night	41% 6% 12% 26% 12% 3	1800
	11th to 20th	Night	38% 5% 14% 26% 16% 2	1828
	21st to end	Night	46% 7% 14% 20% 13% 1	2061
October	1st to 10th	Night	47% 6% 12% 20% 14% 1	2160
	11th to 20th	Night	53% 5% 13% 17% 10% 1	2160
	21st to end	Night	61% 5% 11% 15% 7% 1	2376
November	1st to 10th	Night	49% 6% 12% 19% 11% 3	2360
	11th to 20th	Night	60% 5% 11% 15% 7% 2	2660
	21st to end	Night	65% 5% 11% 14% 4 1	2660
December	1st to 10th	Night	76% 5% 8% 8% 3	2660
	11th to 20th	Night	74% 4 9% 10% 2	3288
	21st to end	Night	76% 6% 8% 8% 1	4884

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% 26% 29% 8% 4	180
	11th to 20th	Day	35% 29% 27% 5% 3	228
	21st to end	Day	28% 31% 31% 7% 4	264
February	1st to 10th	Day	42% 31% 24% 4	240
	11th to 20th	Day	37% 32% 30% 1	240
	21st to end	Day	43% 28% 22% 6% 1	292
March	1st to 10th	Day	36% 26% 24% 11% 3	420
	11th to 20th	Day	30% 26% 28% 10% 4 1	420
	21st to end	Day	35% 23% 26% 12% 4 1	462
April	1st to 10th	Day	32% 23% 25% 13% 5% 1	420
	11th to 20th	Day	29% 23% 25% 13% 8% 3	412
	21st to end	Day	31% 22% 27% 14% 5% 1	420
May	1st to 10th	Day	30% 19% 25% 15% 7% 3	423
	11th to 20th	Day	28% 18% 26% 17% 8% 3	447
	21st to end	Day	18% 15% 28% 24% 11% 5%	485
June	1st to 10th	Day	24% 15% 29% 20% 10% 2	450
	11th to 20th	Day	19% 12% 30% 22% 13% 3	450
	21st to end	Day	18% 14% 36% 22% 8% 3	450
July	1st to 10th	Day	14% 9% 29% 26% 16% 5%	445
	11th to 20th	Day	14% 9% 27% 31% 14% 6%	444
	21st to end	Day	16% 8% 36% 25% 11% 5%	488
August	1st to 10th	Day	12% 7% 30% 25% 19% 7%	446
	11th to 20th	Day	16% 8% 29% 25% 14% 8%	439
	21st to end	Day	17% 10% 31% 21% 12% 9%	495
September	1st to 10th	Day	21% 10% 26% 20% 14% 9%	450
	11th to 20th	Day	15% 8% 26% 22% 20% 9%	450
	21st to end	Day	21% 15% 27% 19% 13% 4	450
October	1st to 10th	Day	22% 15% 27% 17% 13% 5%	450
	11th to 20th	Day	28% 22% 27% 14% 7% 1	450
	21st to end	Day	38% 18% 25% 17% 2	495
November	1st to 10th	Day	26% 20% 28% 16% 8% 2	378
	11th to 20th	Day	38% 23% 24% 11% 2 1	180
	21st to end	Day	36% 24% 33% 7% 1	180
December	1st to 10th	Day	38% 28% 23% 7% 3 2	180
	11th to 20th	Day	38% 26% 28% 6% 2	180
	21st to end	Day	40% 24% 31% 5%	198
January	1st to 10th	Night	31% 25% 28% 12% 4	760
	11th to 20th	Night	30% 25% 29% 13% 2	736
	21st to end	Night	25% 29% 28% 15% 2	792
February	1st to 10th	Night	29% 27% 30% 14% 1	720
	11th to 20th	Night	29% 28% 31% 11% 1	703
	21st to end	Night	35% 25% 26% 13% 2	592
March	1st to 10th	Night	26% 26% 30% 16% 3	720
	11th to 20th	Night	31% 22% 25% 18% 4 1	720
	21st to end	Night	25% 21% 31% 17% 5% 2	792
April	1st to 10th	Night	27% 21% 30% 19% 3	720
	11th to 20th	Night	30% 15% 27% 20% 7% 1	711
	21st to end	Night	25% 12% 30% 27% 7%	608
May	1st to 10th	Night	24% 11% 23% 31% 11%	540
	11th to 20th	Night	17% 12% 30% 31% 10%	359
	21st to end	Night	15% 9% 27% 32% 16% 1	389
June	1st to 10th	Night	18% 7% 30% 29% 14% 1	360
	11th to 20th	Night	17% 11% 23% 35% 14%	360
	21st to end	Night	12% 6% 32% 35% 14%	360
July	1st to 10th	Night	12% 3 21% 44% 17% 3	350
	11th to 20th	Night	9% 5% 25% 37% 22% 1	348
	21st to end	Night	14% 4 22% 38% 22% 1	563
August	1st to 10th	Night	14% 4 20% 36% 23% 2	537
	11th to 20th	Night	16% 3 19% 32% 28% 2	534
	21st to end	Night	16% 5% 21% 33% 22% 3	755
September	1st to 10th	Night	19% 6% 24% 31% 18% 2	720
	11th to 20th	Night	17% 7% 20% 26% 26% 4	720
	21st to end	Night	22% 10% 21% 26% 18% 3	720
October	1st to 10th	Night	23% 10% 26% 23% 16% 2	720
	11th to 20th	Night	28% 16% 29% 20% 6%	720
	21st to end	Night	36% 15% 28% 18% 3	792
November	1st to 10th	Night	22% 18% 29% 22% 8%	740
	11th to 20th	Night	31% 19% 29% 14% 6% 1	760
	21st to end	Night	30% 22% 28% 15% 5%	760
December	1st to 10th	Night	36% 24% 26% 11% 3	760
	11th to 20th	Night	30% 26% 28% 13% 3	760
	21st to end	Night	31% 26% 28% 13% 2	836

Page generated at 2024-01-11 13:32:04. Version ac07

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