Long Mountain Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Mountain Ranch clear sky chart from 2005-11-06 to 2024-12-24.

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	11% 5% 2 5% 4 4 4 3 5% 7% 51%	101506
	Night	11% 5% 2 4 3 3 3 3 5% 6% 55%	98711
Transparency	Day	31% 6% 10% 21% 22% 10%	105301
	Night	28% 5% 10% 21% 22% 12%	103030
Seeing	Day	12% 7% 22% 30% 23% 7%	15106
	Night	13% 7% 28% 36% 15% 1	25076

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	11% 9% 2 4 2 2 3 3 4 6% 54%	2847
	11th to 20th	Day	15% 5% 1 3 2 2 2 2 5% 6% 57%	2850
	21st to end	Day	17% 7% 2 6% 3 2 3 2 3 5% 48%	3263
February	1st to 10th	Day	17% 6% 2 5% 3 3 2 2 3 5% 51%	1900
	11th to 20th	Day	15% 8% 2 5% 3 3 3 3 4 5% 48%	1849
	21st to end	Day	18% 6% 1 4 3 3 3 2 4 5% 51%	1570
March	1st to 10th	Day	15% 7% 2 7% 5% 3 4 3 5% 5% 44%	3397
	11th to 20th	Day	19% 6% 3 6% 4 5% 4 4 5% 7% 36%	3480
	21st to end	Day	10% 7% 3 7% 4 4 4 3 6% 6% 46%	3814
April	1st to 10th	Day	13% 7% 3 5% 3 4 4 4 5% 6% 46%	2090
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 5% 6% 45%	2075
	21st to end	Day	12% 6% 1 5% 4 4 4 3 5% 5% 50%	2462
May	1st to 10th	Day	19% 8% 3 7% 5% 4 4 3 6% 7% 35%	4082
	11th to 20th	Day	14% 6% 3 6% 4 4 4 3 5% 6% 46%	4082
	21st to end	Day	11% 6% 3 7% 4 5% 6% 5% 8% 9% 35%	4477
June	1st to 10th	Day	5% 4 1 4 4 5% 5% 4 6% 9% 54%	2470
	11th to 20th	Day	5% 4 1 4 4 4 5% 4 6% 10% 53%	2470
	21st to end	Day	6% 4 2 4 5% 4 6% 5% 7% 8% 50%	2470
July	1st to 10th	Day	5% 4 1 5% 4 5% 5% 5% 6% 9% 51%	4120
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 9% 60%	4120
	21st to end	Day	6% 6% 2 6% 5% 5% 6% 5% 7% 10% 43%	4465
August	1st to 10th	Day	1 1 1 2 3 3 3 2 5% 6% 73%	4104
	11th to 20th	Day	4 2 1 3 2 3 4 3 5% 9% 64%	3831
	21st to end	Day	4 3 2 4 4 4 6% 4 7% 10% 54%	4020
September	1st to 10th	Day	10% 5% 2 5% 5% 5% 4 3 5% 7% 50%	2090
	11th to 20th	Day	9% 6% 2 7% 4 4 4 3 5% 6% 49%	2090
	21st to end	Day	7% 3 1 5% 3 4 5% 3 6% 6% 56%	2090
October	1st to 10th	Day	5% 3 1 5% 3 3 3 3 5% 6% 61%	2090
	11th to 20th	Day	11% 4 1 4 3 3 2 3 4 5% 60%	1937
	21st to end	Day	12% 4 1 3 3 2 3 2 3 4 62%	2090
November	1st to 10th	Day	14% 6% 2 5% 3 3 3 3 4 5% 52%	1958
	11th to 20th	Day	8% 4 1 5% 3 3 4 4 4 6% 58%	1840
	21st to end	Day	15% 6% 2 6% 3 3 3 2 3 5% 51%	1800
December	1st to 10th	Day	15% 6% 2 4 3 4 3 3 5% 5% 51%	1800
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 5% 5% 47%	2251
	21st to end	Day	15% 6% 2 4 2 2 3 3 4 5% 56%	3162
January	1st to 10th	Night	16% 5% 2 3 2 2 2 2 4 4 59%	4108
	11th to 20th	Night	13% 5% 1 3 2 2 2 1 2 4 66%	4120
	21st to end	Night	18% 7% 3 6% 3 3 3 2 3 5% 45%	4432
February	1st to 10th	Night	14% 7% 2 6% 4 2 3 2 3 5% 52%	2280
	11th to 20th	Night	17% 5% 2 5% 2 2 3 2 3 6% 52%	2218
	21st to end	Night	18% 5% 2 4 3 3 2 3 4 5% 51%	1884
March	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 5% 47%	3456
	11th to 20th	Night	17% 6% 2 6% 5% 3 4 5% 6% 7% 39%	3480
	21st to end	Night	10% 7% 2 6% 4 4 3 3 5% 6% 48%	3817
April	1st to 10th	Night	9% 5% 2 6% 4 3 4 3 5% 7% 52%	2090
	11th to 20th	Night	14% 6% 2 6% 4 3 4 3 5% 6% 48%	2049
	21st to end	Night	13% 6% 2 4 4 3 3 2 5% 6% 52%	1715
May	1st to 10th	Night	23% 7% 2 4 2 3 3 3 6% 6% 41%	2823
	11th to 20th	Night	10% 6% 2 6% 4 4 3 4 5% 8% 49%	2823
	21st to end	Night	12% 5% 2 5% 4 4 4 4 6% 8% 46%	3090
June	1st to 10th	Night	3 3 1 3 3 3 3 4 5% 10% 61%	1710
	11th to 20th	Night	4 2 1 3 3 3 3 2 7% 10% 62%	1710
	21st to end	Night	4 4 2 4 3 3 4 4 5% 9% 57%	1710
July	1st to 10th	Night	4 2 1 4 3 3 3 3 6% 8% 63%	2850
	11th to 20th	Night	2 2 1 3 2 2 3 3 6% 10% 65%	2850
	21st to end	Night	3 7% 2 6% 4 4 4 5% 7% 9% 50%	3098
August	1st to 10th	Night	1 1 1 1 1 2 2 4 6% 80%	2836
	11th to 20th	Night	3 2 1 3 2 3 2 3 6% 10% 64%	2990
	21st to end	Night	3 2 1 3 3 3 3 4 7% 10% 60%	3642
September	1st to 10th	Night	8% 4 2 4 4 4 5% 4 6% 8% 53%	2090
	11th to 20th	Night	10% 5% 2 5% 3 3 4 4 6% 7% 49%	2090
	21st to end	Night	8% 3 1 4 3 3 3 3 5% 7% 61%	2090
October	1st to 10th	Night	5% 3 1 2 3 2 3 3 4 6% 67%	2090
	11th to 20th	Night	11% 3 1 3 2 3 3 3 5% 5% 61%	2223
	21st to end	Night	13% 4 1 4 2 2 2 2 4 4 62%	2508
November	1st to 10th	Night	12% 5% 2 4 2 3 3 2 4 6% 57%	2340
	11th to 20th	Night	7% 5% 2 5% 3 3 3 2 4 6% 60%	2555
	21st to end	Night	15% 6% 2 4 3 2 3 3 4 6% 51%	2600
December	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 53%	2600
	11th to 20th	Night	14% 8% 2 6% 3 3 3 3 4 5% 49%	3166
	21st to end	Night	16% 6% 2 4 2 2 2 2 3 4 57%	4578

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	32% 5% 5% 17% 27% 14%	2848
	11th to 20th	Day	29% 3 7% 16% 30% 14%	2850
	21st to end	Day	40% 4 5% 13% 26% 12%	3263
February	1st to 10th	Day	39% 3 7% 14% 22% 16%	1900
	11th to 20th	Day	38% 4 6% 18% 21% 13%	1859
	21st to end	Day	38% 3 5% 15% 22% 17%	1570
March	1st to 10th	Day	40% 6% 6% 14% 22% 13%	3397
	11th to 20th	Day	45% 8% 12% 10% 16% 8%	3480
	21st to end	Day	36% 7% 12% 15% 23% 8%	3814
April	1st to 10th	Day	39% 5% 7% 18% 16% 14%	2090
	11th to 20th	Day	39% 6% 9% 15% 19% 11%	2075
	21st to end	Day	35% 6% 8% 20% 23% 8%	2462
May	1st to 10th	Day	46% 7% 11% 16% 14% 5%	4120
	11th to 20th	Day	38% 6% 9% 17% 26% 4	4086
	21st to end	Day	39% 11% 14% 21% 11% 4	4489
June	1st to 10th	Day	25% 8% 14% 28% 21% 4	2470
	11th to 20th	Day	26% 7% 14% 28% 18% 7%	2470
	21st to end	Day	29% 8% 13% 23% 22% 5%	2470
July	1st to 10th	Day	27% 9% 18% 36% 10% 1	4056
	11th to 20th	Day	19% 7% 14% 37% 19% 4	4051
	21st to end	Day	32% 8% 16% 30% 13% 1	4325
August	1st to 10th	Day	12% 4 12% 33% 38% 1	4090
	11th to 20th	Day	17% 5% 19% 38% 18% 2	3870
	21st to end	Day	22% 10% 20% 26% 19% 2	4019
September	1st to 10th	Day	33% 7% 11% 20% 18% 10%	2090
	11th to 20th	Day	35% 8% 11% 19% 21% 6%	2090
	21st to end	Day	27% 6% 9% 21% 22% 15%	2090
October	1st to 10th	Day	14% 3 6% 13% 26% 38%	3480
	11th to 20th	Day	18% 3 7% 17% 33% 22%	3190
	21st to end	Day	23% 3 4 19% 39% 13%	3428
November	1st to 10th	Day	35% 4 8% 19% 23% 11%	1958
	11th to 20th	Day	29% 5% 9% 17% 24% 17%	1840
	21st to end	Day	37% 5% 5% 19% 21% 14%	1800
December	1st to 10th	Day	35% 5% 8% 21% 22% 10%	1800
	11th to 20th	Day	38% 6% 8% 12% 23% 13%	2249
	21st to end	Day	33% 3 6% 15% 28% 15%	3162
January	1st to 10th	Night	30% 3 5% 17% 28% 17%	4108
	11th to 20th	Night	26% 2 5% 16% 28% 23%	4120
	21st to end	Night	41% 5% 5% 13% 23% 13%	4432
February	1st to 10th	Night	37% 4 6% 13% 22% 18%	2280
	11th to 20th	Night	36% 3 7% 17% 23% 15%	2218
	21st to end	Night	36% 4 6% 15% 20% 19%	1884
March	1st to 10th	Night	36% 7% 9% 13% 24% 12%	3456
	11th to 20th	Night	41% 8% 12% 15% 15% 9%	3480
	21st to end	Night	35% 7% 10% 18% 22% 8%	3817
April	1st to 10th	Night	32% 6% 10% 20% 18% 16%	2090
	11th to 20th	Night	37% 6% 10% 14% 19% 15%	2049
	21st to end	Night	33% 6% 10% 19% 23% 9%	1715
May	1st to 10th	Night	42% 7% 10% 19% 15% 7%	2850
	11th to 20th	Night	31% 8% 13% 22% 20% 7%	2824
	21st to end	Night	34% 9% 13% 29% 10% 5%	3099
June	1st to 10th	Night	18% 8% 18% 31% 22% 4	1710
	11th to 20th	Night	19% 6% 15% 31% 21% 7%	1710
	21st to end	Night	23% 9% 12% 29% 22% 5%	1710
July	1st to 10th	Night	20% 7% 21% 43% 9% 1	2805
	11th to 20th	Night	14% 6% 18% 41% 19% 2	2796
	21st to end	Night	28% 7% 20% 33% 10% 1	2999
August	1st to 10th	Night	8% 4 13% 37% 36% 2	2826
	11th to 20th	Night	17% 5% 23% 35% 17% 3	3017
	21st to end	Night	18% 10% 21% 31% 17% 3	3642
September	1st to 10th	Night	28% 7% 13% 22% 18% 11%	2090
	11th to 20th	Night	32% 7% 14% 21% 18% 7%	2090
	21st to end	Night	22% 5% 13% 25% 20% 15%	2090
October	1st to 10th	Night	12% 3 7% 15% 22% 42%	3480
	11th to 20th	Night	17% 3 8% 17% 31% 24%	3683
	21st to end	Night	22% 3 5% 20% 35% 16%	4120
November	1st to 10th	Night	30% 4 8% 19% 25% 14%	2340
	11th to 20th	Night	26% 5% 8% 19% 24% 18%	2555
	21st to end	Night	35% 5% 7% 17% 21% 15%	2600
December	1st to 10th	Night	32% 5% 8% 21% 22% 12%	2600
	11th to 20th	Night	38% 4 6% 11% 24% 17%	3167
	21st to end	Night	34% 3 4 14% 28% 17%	4578

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	19% 12% 36% 26% 6% 1	270
	11th to 20th	Day	23% 13% 34% 21% 8% 1	270
	21st to end	Day	17% 15% 37% 23% 8%	297
February	1st to 10th	Day	25% 15% 32% 22% 6%	270
	11th to 20th	Day	22% 16% 40% 19% 3	270
	21st to end	Day	24% 19% 38% 17% 2	225
March	1st to 10th	Day	20% 18% 37% 21% 3	270
	11th to 20th	Day	18% 19% 36% 20% 6%	270
	21st to end	Day	16% 16% 40% 21% 6%	297
April	1st to 10th	Day	20% 18% 42% 17% 3	270
	11th to 20th	Day	19% 13% 39% 22% 6% 1	273
	21st to end	Day	16% 14% 40% 22% 7% 1	642
May	1st to 10th	Day	13% 11% 37% 29% 9%	653
	11th to 20th	Day	15% 7% 31% 32% 13% 2	675
	21st to end	Day	14% 7% 26% 34% 16% 3	734
June	1st to 10th	Day	5% 2 17% 41% 28% 7%	680
	11th to 20th	Day	6% 1 18% 47% 24% 4	680
	21st to end	Day	6% 2 13% 36% 33% 10%	680
July	1st to 10th	Day	7% 2 8% 35% 35% 13%	671
	11th to 20th	Day	2 4 37% 45% 11%	668
	21st to end	Day	3 1 6% 34% 43% 13%	739
August	1st to 10th	Day	2 5% 32% 46% 14%	676
	11th to 20th	Day	5% 2 4 34% 40% 15%	546
	21st to end	Day	4 1 5% 25% 41% 24%	444
September	1st to 10th	Day	9% 1 5% 25% 38% 23%	300
	11th to 20th	Day	6% 1 6% 23% 45% 19%	300
	21st to end	Day	12% 2 5% 29% 38% 14%	300
October	1st to 10th	Day	4 1 12% 35% 36% 11%	300
	11th to 20th	Day	10% 4 27% 31% 24% 4	300
	21st to end	Day	22% 10% 22% 22% 21% 3	330
November	1st to 10th	Day	21% 7% 30% 27% 12% 4	300
	11th to 20th	Day	14% 11% 27% 30% 15% 3	300
	21st to end	Day	18% 15% 34% 20% 11% 2	300
December	1st to 10th	Day	20% 6% 31% 26% 11% 4	300
	11th to 20th	Day	18% 13% 40% 21% 8% 1	300
	21st to end	Day	21% 10% 37% 21% 9% 2	306
January	1st to 10th	Night	17% 8% 36% 30% 7% 1	950
	11th to 20th	Night	19% 10% 32% 31% 7%	950
	21st to end	Night	17% 11% 35% 30% 7%	984
February	1st to 10th	Night	19% 13% 35% 28% 5%	760
	11th to 20th	Night	21% 13% 39% 26% 3	744
	21st to end	Night	23% 11% 43% 21% 2	628
March	1st to 10th	Night	17% 13% 38% 29% 3	596
	11th to 20th	Night	16% 10% 38% 31% 5%	570
	21st to end	Night	11% 12% 44% 30% 3	627
April	1st to 10th	Night	11% 9% 49% 28% 3	570
	11th to 20th	Night	15% 10% 43% 27% 4	563
	21st to end	Night	14% 9% 44% 25% 8%	570
May	1st to 10th	Night	13% 10% 42% 30% 5%	570
	11th to 20th	Night	12% 5% 37% 33% 12% 1	561
	21st to end	Night	11% 5% 33% 37% 14%	617
June	1st to 10th	Night	3 2 23% 47% 23% 2	570
	11th to 20th	Night	4 2 27% 50% 16% 1	570
	21st to end	Night	4 1 16% 49% 26% 3	570
July	1st to 10th	Night	5% 1 11% 51% 29% 3	555
	11th to 20th	Night	3 1 9% 53% 32% 3	552
	21st to end	Night	3 8% 51% 35% 3	624
August	1st to 10th	Night	1 5% 54% 36% 4	567
	11th to 20th	Night	6% 1 5% 51% 33% 4	564
	21st to end	Night	5% 4 44% 41% 6%	627
September	1st to 10th	Night	9% 2 8% 42% 34% 5%	570
	11th to 20th	Night	12% 1 7% 41% 36% 3	570
	21st to end	Night	9% 1 11% 39% 37% 3	570
October	1st to 10th	Night	7% 1 12% 48% 28% 4	570
	11th to 20th	Night	12% 4 25% 40% 18% 1	703
	21st to end	Night	14% 7% 28% 32% 17% 1	836
November	1st to 10th	Night	14% 3 27% 40% 14% 1	780
	11th to 20th	Night	9% 8% 31% 37% 15% 1	955
	21st to end	Night	18% 9% 30% 31% 11%	1000
December	1st to 10th	Night	15% 8% 30% 36% 10%	1000
	11th to 20th	Night	21% 9% 30% 34% 7%	1000
	21st to end	Night	18% 9% 33% 32% 7%	1063

Page generated at 2024-12-21 03:13:47. Version ac07

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