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 2024-11-25.

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	16% 12% 4 9% 5% 4 4 4 5% 7% 28%	101597
	Night	17% 14% 5% 10% 5% 4 4 3 4 6% 28%	97864
Transparency	Day	54% 6% 11% 19% 9% 1	105201
	Night	56% 6% 11% 17% 9% 1	102348
Seeing	Day	26% 18% 28% 17% 8% 3	14688
	Night	25% 17% 26% 22% 9% 1	24107

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% 24% 13% 12% 5% 3 3 2 3 3 17%	2517
	11th to 20th	Day	9% 23% 10% 20% 8% 3 3 2 3 4 16%	2758
	21st to end	Day	21% 18% 10% 14% 8% 4 3 3 4 4 11%	3124
February	1st to 10th	Day	14% 22% 7% 12% 10% 6% 4 3 3 3 17%	1710
	11th to 20th	Day	12% 17% 8% 17% 7% 5% 5% 3 4 5% 20%	1663
	21st to end	Day	18% 15% 5% 13% 6% 3 4 3 5% 4 24%	1513
March	1st to 10th	Day	19% 15% 6% 9% 4 4 3 2 4 5% 28%	3418
	11th to 20th	Day	10% 22% 7% 10% 4 3 3 3 4 6% 28%	3480
	21st to end	Day	17% 13% 4 12% 6% 4 4 3 5% 5% 28%	3832
April	1st to 10th	Day	16% 17% 4 9% 5% 3 4 3 4 6% 28%	2280
	11th to 20th	Day	18% 14% 3 7% 4 4 4 5% 5% 5% 31%	2254
	21st to end	Day	21% 12% 3 8% 5% 4 4 3 4 5% 32%	2416
May	1st to 10th	Day	25% 10% 3 6% 5% 4 4 3 5% 6% 29%	4108
	11th to 20th	Day	19% 11% 4 9% 6% 6% 4 4 6% 7% 25%	4390
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 5% 7% 40%	4837
June	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 9% 33%	2660
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 5% 6% 9% 33%	2660
	21st to end	Day	15% 7% 2 6% 5% 5% 5% 5% 6% 8% 34%	2660
July	1st to 10th	Day	11% 6% 2 7% 6% 5% 6% 5% 8% 9% 35%	4440
	11th to 20th	Day	12% 7% 3 6% 5% 6% 6% 5% 7% 10% 33%	4440
	21st to end	Day	10% 7% 3 8% 6% 5% 6% 5% 7% 8% 35%	4505
August	1st to 10th	Day	20% 7% 3 8% 5% 5% 5% 5% 7% 8% 29%	4104
	11th to 20th	Day	16% 7% 3 8% 6% 6% 6% 6% 8% 9% 24%	4044
	21st to end	Day	15% 7% 2 6% 4 5% 5% 4 6% 9% 35%	4212
September	1st to 10th	Day	18% 8% 3 6% 4 4 4 4 5% 7% 38%	2280
	11th to 20th	Day	14% 7% 2 6% 5% 4 4 4 5% 7% 41%	2247
	21st to end	Day	21% 8% 3 7% 6% 4 5% 3 6% 6% 31%	2002
October	1st to 10th	Day	19% 9% 3 7% 4 4 4 3 6% 8% 31%	1900
	11th to 20th	Day	21% 12% 3 9% 5% 3 3 3 6% 5% 30%	1900
	21st to end	Day	24% 16% 3 8% 5% 4 4 2 5% 5% 25%	2090
November	1st to 10th	Day	15% 14% 3 9% 5% 4 4 3 5% 6% 33%	1803
	11th to 20th	Day	16% 21% 4 9% 4 4 4 4 5% 6% 22%	1600
	21st to end	Day	19% 23% 6% 8% 6% 3 4 3 5% 5% 18%	1552
December	1st to 10th	Day	17% 24% 9% 14% 6% 4 3 3 4 4 12%	1520
	11th to 20th	Day	16% 19% 7% 16% 5% 3 4 3 5% 5% 16%	1906
	21st to end	Day	21% 26% 8% 12% 5% 4 3 2 3 4 13%	2772
January	1st to 10th	Night	15% 21% 11% 16% 5% 4 3 2 3 5% 13%	4429
	11th to 20th	Night	12% 21% 11% 17% 7% 5% 4 3 3 4 13%	4185
	21st to end	Night	20% 20% 8% 17% 8% 5% 3 2 3 3 12%	4532
February	1st to 10th	Night	14% 18% 6% 14% 10% 5% 4 3 4 4 18%	2470
	11th to 20th	Night	12% 15% 8% 15% 8% 6% 5% 4 4 4 18%	2403
	21st to end	Night	16% 16% 6% 15% 7% 5% 3 3 4 4 22%	1940
March	1st to 10th	Night	18% 16% 5% 9% 6% 4 3 3 4 5% 27%	3418
	11th to 20th	Night	16% 20% 8% 10% 4 4 3 3 4 5% 24%	3479
	21st to end	Night	14% 14% 4 10% 5% 3 3 3 5% 6% 33%	3798
April	1st to 10th	Night	18% 16% 4 9% 5% 3 4 3 4 6% 28%	1900
	11th to 20th	Night	19% 14% 3 8% 3 3 3 3 5% 5% 35%	1875
	21st to end	Night	17% 12% 3 7% 4 4 4 4 4 7% 34%	1781
May	1st to 10th	Night	25% 10% 3 6% 4 4 4 3 4 5% 31%	2833
	11th to 20th	Night	18% 12% 4 7% 4 4 4 4 5% 6% 32%	2500
	21st to end	Night	14% 7% 2 7% 4 4 4 3 5% 9% 41%	2738
June	1st to 10th	Night	14% 7% 2 7% 5% 4 5% 4 6% 9% 36%	1520
	11th to 20th	Night	13% 6% 3 6% 5% 4 4 4 6% 9% 39%	1520
	21st to end	Night	13% 7% 2 6% 4 5% 4 4 5% 8% 41%	1520
July	1st to 10th	Night	13% 9% 3 7% 4 4 4 4 5% 7% 38%	2520
	11th to 20th	Night	11% 7% 2 6% 4 4 4 4 7% 9% 42%	2520
	21st to end	Night	13% 6% 3 6% 4 5% 4 4 6% 8% 41%	3045
August	1st to 10th	Night	18% 9% 2 7% 4 5% 4 4 5% 7% 35%	2825
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 6% 7% 35%	2785
	21st to end	Night	12% 6% 2 7% 4 4 4 4 6% 8% 43%	3411
September	1st to 10th	Night	16% 7% 2 6% 4 3 3 4 4 7% 43%	1900
	11th to 20th	Night	14% 7% 2 5% 3 3 3 2 6% 7% 46%	1930
	21st to end	Night	20% 8% 2 6% 5% 5% 5% 4 4 6% 35%	2176
October	1st to 10th	Night	17% 10% 2 7% 4 4 4 3 5% 7% 38%	2280
	11th to 20th	Night	20% 13% 2 6% 5% 4 4 3 4 7% 32%	2280
	21st to end	Night	25% 15% 3 6% 4 4 4 3 5% 6% 26%	2508
November	1st to 10th	Night	13% 15% 3 7% 5% 4 4 3 4 6% 36%	2488
	11th to 20th	Night	17% 20% 4 9% 4 4 4 4 5% 6% 24%	2800
	21st to end	Night	16% 21% 6% 10% 6% 5% 4 3 4 6% 20%	2723
December	1st to 10th	Night	19% 23% 9% 13% 6% 4 4 3 4 4 12%	2660
	11th to 20th	Night	18% 18% 8% 16% 6% 4 4 4 3 4 15%	3288
	21st to end	Night	21% 22% 9% 11% 6% 4 4 3 4 4 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	73% 3 7% 11% 4 1	2518
	11th to 20th	Day	74% 3 6% 11% 5%	2758
	21st to end	Day	77% 5% 8% 6% 3 1	3124
February	1st to 10th	Day	72% 4 9% 9% 5%	1710
	11th to 20th	Day	68% 5% 6% 15% 7% 1	1672
	21st to end	Day	63% 4 10% 16% 5% 2	1513
March	1st to 10th	Day	60% 3 9% 22% 5%	3421
	11th to 20th	Day	57% 4 15% 15% 7% 1	3480
	21st to end	Day	58% 5% 7% 20% 9% 1	3832
April	1st to 10th	Day	57% 5% 10% 16% 11% 1	2280
	11th to 20th	Day	53% 7% 10% 17% 12% 1	2254
	21st to end	Day	54% 5% 8% 18% 13% 1	2416
May	1st to 10th	Day	55% 5% 8% 21% 9% 2	4120
	11th to 20th	Day	56% 8% 11% 17% 7% 1	4394
	21st to end	Day	41% 7% 12% 24% 14% 1	4837
June	1st to 10th	Day	48% 6% 11% 20% 13% 1	2660
	11th to 20th	Day	47% 8% 13% 21% 12% 1	2660
	21st to end	Day	45% 7% 13% 23% 12%	2660
July	1st to 10th	Day	41% 8% 13% 24% 12% 1	4370
	11th to 20th	Day	40% 9% 15% 21% 15%	4365
	21st to end	Day	43% 9% 13% 22% 13% 1	4361
August	1st to 10th	Day	49% 8% 13% 21% 9%	4091
	11th to 20th	Day	50% 11% 14% 19% 5%	4083
	21st to end	Day	43% 7% 11% 28% 9% 1	4212
September	1st to 10th	Day	45% 7% 9% 24% 13% 2	2280
	11th to 20th	Day	42% 5% 11% 25% 16% 1	2247
	21st to end	Day	52% 6% 10% 20% 12%	2002
October	1st to 10th	Day	43% 9% 12% 20% 16% 1	3160
	11th to 20th	Day	47% 5% 13% 15% 14% 4	3140
	21st to end	Day	48% 5% 14% 23% 10% 1	3428
November	1st to 10th	Day	52% 5% 12% 18% 12% 3	1803
	11th to 20th	Day	61% 5% 11% 15% 6% 2	1600
	21st to end	Day	67% 6% 9% 12% 4 1	1552
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	75% 4 8% 9% 4	4429
	11th to 20th	Night	75% 5% 9% 9% 2 1	4185
	21st to end	Night	80% 3 5% 8% 3	4532
February	1st to 10th	Night	70% 4 10% 11% 5%	2470
	11th to 20th	Night	68% 6% 9% 11% 5%	2405
	21st to end	Night	67% 4 8% 13% 7% 1	1940
March	1st to 10th	Night	61% 5% 10% 19% 5%	3428
	11th to 20th	Night	63% 4 11% 15% 5%	3480
	21st to end	Night	50% 4 11% 19% 13% 2	3798
April	1st to 10th	Night	58% 4 11% 15% 11%	1900
	11th to 20th	Night	52% 5% 12% 18% 12% 2	1875
	21st to end	Night	50% 6% 10% 20% 13% 2	1781
May	1st to 10th	Night	55% 6% 8% 21% 8% 2	2840
	11th to 20th	Night	52% 7% 14% 19% 7% 1	2501
	21st to end	Night	40% 8% 11% 22% 15% 4	2739
June	1st to 10th	Night	43% 8% 12% 23% 13% 1	1520
	11th to 20th	Night	40% 7% 15% 23% 13% 1	1520
	21st to end	Night	39% 10% 12% 25% 13% 1	1520
July	1st to 10th	Night	45% 7% 12% 20% 15% 1	2480
	11th to 20th	Night	35% 9% 16% 27% 13% 1	2472
	21st to end	Night	41% 7% 12% 23% 16% 1	2948
August	1st to 10th	Night	47% 9% 13% 23% 7% 1	2814
	11th to 20th	Night	45% 9% 14% 25% 7%	2812
	21st to end	Night	38% 8% 14% 30% 9% 1	3411
September	1st to 10th	Night	40% 6% 12% 26% 13% 3	1900
	11th to 20th	Night	37% 5% 14% 25% 17% 2	1930
	21st to end	Night	48% 7% 13% 19% 12% 1	2176
October	1st to 10th	Night	47% 6% 10% 21% 16%	3800
	11th to 20th	Night	46% 5% 12% 17% 14% 6%	3779
	21st to end	Night	45% 5% 16% 24% 10% 1	4120
November	1st to 10th	Night	49% 6% 12% 19% 12% 2	2488
	11th to 20th	Night	60% 5% 11% 15% 7% 2	2800
	21st to end	Night	65% 5% 11% 14% 3 1	2723
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	34% 30% 27% 6% 3	249
	21st to end	Day	29% 30% 31% 7% 3	297
February	1st to 10th	Day	40% 29% 25% 6%	270
	11th to 20th	Day	35% 31% 32% 1 1	270
	21st to end	Day	43% 27% 23% 6% 1	325
March	1st to 10th	Day	36% 24% 26% 12% 3	460
	11th to 20th	Day	31% 26% 27% 10% 4 1	460
	21st to end	Day	36% 22% 27% 11% 4 1	506
April	1st to 10th	Day	32% 22% 26% 13% 5% 1	460
	11th to 20th	Day	31% 23% 24% 12% 7% 2	452
	21st to end	Day	30% 22% 28% 15% 5% 1	460
May	1st to 10th	Day	30% 19% 26% 15% 7% 3	463
	11th to 20th	Day	26% 17% 28% 17% 9% 3	487
	21st to end	Day	18% 14% 28% 24% 11% 5%	529
June	1st to 10th	Day	24% 16% 28% 20% 10% 2	490
	11th to 20th	Day	18% 12% 31% 23% 12% 3	490
	21st to end	Day	19% 16% 35% 21% 7% 3	490
July	1st to 10th	Day	14% 10% 31% 25% 15% 4	485
	11th to 20th	Day	14% 10% 27% 30% 13% 5%	484
	21st to end	Day	15% 8% 36% 25% 11% 5%	532
August	1st to 10th	Day	14% 8% 29% 24% 17% 7%	486
	11th to 20th	Day	16% 9% 28% 24% 14% 8%	479
	21st to end	Day	17% 11% 31% 21% 13% 8%	539
September	1st to 10th	Day	21% 11% 26% 20% 14% 9%	490
	11th to 20th	Day	14% 8% 25% 23% 21% 10%	490
	21st to end	Day	25% 15% 26% 18% 12% 4	490
October	1st to 10th	Day	22% 16% 27% 18% 13% 4	490
	11th to 20th	Day	28% 22% 27% 14% 8% 2	490
	21st to end	Day	36% 19% 27% 17% 2	539
November	1st to 10th	Day	25% 21% 28% 15% 8% 2	410
	11th to 20th	Day	35% 24% 28% 10% 2 1	200
	21st to end	Day	37% 23% 32% 6% 1	188
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	760
	21st to end	Night	26% 29% 28% 15% 2	836
February	1st to 10th	Night	28% 26% 30% 15% 1	760
	11th to 20th	Night	29% 29% 31% 11% 1	743
	21st to end	Night	35% 24% 25% 14% 2	628
March	1st to 10th	Night	26% 25% 30% 16% 3	760
	11th to 20th	Night	32% 22% 24% 18% 4 1	760
	21st to end	Night	26% 22% 30% 16% 4 1	836
April	1st to 10th	Night	27% 21% 29% 19% 3	760
	11th to 20th	Night	30% 16% 27% 19% 7% 1	751
	21st to end	Night	24% 12% 29% 27% 7%	641
May	1st to 10th	Night	23% 11% 23% 32% 11%	570
	11th to 20th	Night	17% 12% 29% 31% 10% 1	379
	21st to end	Night	15% 9% 26% 33% 16% 1	411
June	1st to 10th	Night	18% 8% 30% 29% 14% 1	380
	11th to 20th	Night	16% 10% 23% 36% 15%	380
	21st to end	Night	14% 7% 31% 34% 14%	380
July	1st to 10th	Night	12% 4 21% 44% 17% 2	370
	11th to 20th	Night	9% 5% 26% 37% 22% 1	368
	21st to end	Night	14% 4 21% 38% 22% 1	595
August	1st to 10th	Night	15% 4 20% 35% 23% 2	567
	11th to 20th	Night	16% 4 20% 31% 27% 2	564
	21st to end	Night	16% 5% 21% 32% 23% 3	797
September	1st to 10th	Night	19% 6% 24% 30% 18% 2	760
	11th to 20th	Night	16% 6% 19% 26% 28% 4	760
	21st to end	Night	24% 10% 20% 25% 18% 3	760
October	1st to 10th	Night	23% 10% 26% 22% 17% 2	760
	11th to 20th	Night	27% 16% 28% 20% 7% 1	760
	21st to end	Night	35% 15% 28% 19% 4	836
November	1st to 10th	Night	22% 19% 29% 22% 8%	780
	11th to 20th	Night	31% 19% 29% 14% 6% 1	800
	21st to end	Night	30% 22% 28% 15% 5%	779
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 2024-11-22 08:02:28. Version ac07

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