Shepherd's Rest
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shepherd's Rest clear sky chart from 2005-11-06 to 2025-10-04.

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% 2 6% 4 4 4 4 5% 7% 45%	126057
	Night	13% 7% 2 6% 4 3 4 3 5% 6% 47%	123548
Transparency	Day	37% 5% 11% 25% 18% 4	129663
	Night	36% 4 11% 25% 19% 4	128018
Seeing	Day	17% 11% 26% 25% 17% 4	16785
	Night	17% 10% 29% 29% 14% 1	26508

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	16% 10% 2 5% 4 4 3 3 3 5% 45%	4054
	11th to 20th	Day	10% 7% 2 7% 4 4 3 3 4 6% 50%	4080
	21st to end	Day	22% 6% 3 5% 4 2 3 3 3 4 46%	4488
February	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 5% 5% 38%	1800
	11th to 20th	Day	16% 10% 3 6% 3 3 3 3 4 5% 42%	1853
	21st to end	Day	16% 10% 2 6% 5% 4 4 3 5% 5% 40%	1650
March	1st to 10th	Day	16% 10% 2 5% 3 3 3 3 5% 5% 44%	4936
	11th to 20th	Day	10% 5% 2 4 3 3 3 3 5% 7% 53%	4980
	21st to end	Day	14% 7% 2 8% 5% 5% 5% 4 6% 7% 37%	5507
April	1st to 10th	Day	14% 7% 2 6% 4 4 4 3 4 6% 45%	2400
	11th to 20th	Day	17% 7% 2 6% 4 4 4 3 5% 6% 41%	2374
	21st to end	Day	19% 8% 2 7% 5% 5% 4 4 5% 6% 36%	2400
May	1st to 10th	Day	16% 7% 2 7% 5% 6% 5% 5% 7% 8% 32%	5532
	11th to 20th	Day	14% 7% 3 8% 5% 5% 4 4 6% 7% 37%	5862
	21st to end	Day	20% 6% 2 6% 4 4 4 3 5% 7% 37%	6908
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	2800
	11th to 20th	Day	7% 4 2 5% 4 5% 6% 4 7% 10% 47%	2800
	21st to end	Day	5% 3 1 4 5% 5% 5% 5% 7% 10% 50%	2800
July	1st to 10th	Day	8% 4 2 6% 4 5% 5% 4 7% 9% 45%	6183
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 5% 8% 12% 45%	5900
	21st to end	Day	6% 5% 2 6% 4 4 5% 5% 7% 11% 44%	6422
August	1st to 10th	Day	5% 2 1 4 3 3 4 4 6% 9% 59%	4234
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 45%	3943
	21st to end	Day	5% 4 2 4 4 5% 4 3 5% 8% 54%	4312
September	1st to 10th	Day	11% 5% 1 6% 4 5% 4 3 5% 7% 49%	2400
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 7% 46%	2400
	21st to end	Day	9% 5% 2 4 3 3 4 3 5% 6% 55%	2097
October	1st to 10th	Day	9% 4 2 6% 4 3 3 3 4 5% 57%	1930
	11th to 20th	Day	15% 6% 2 4 2 3 2 2 3 5% 56%	1900
	21st to end	Day	19% 7% 2 5% 3 3 3 3 5% 6% 47%	2090
November	1st to 10th	Day	14% 6% 2 4 3 2 3 3 3 5% 56%	1952
	11th to 20th	Day	14% 6% 2 5% 4 4 3 3 4 5% 51%	1800
	21st to end	Day	20% 9% 2 4 3 2 2 2 4 5% 47%	1670
December	1st to 10th	Day	11% 8% 2 6% 3 3 3 2 4 4 54%	2610
	11th to 20th	Day	15% 9% 3 7% 4 3 3 2 4 5% 45%	3008
	21st to end	Day	19% 19% 4 7% 4 3 4 3 4 4 30%	3982
January	1st to 10th	Night	16% 9% 4 7% 4 4 4 3 4 6% 40%	5906
	11th to 20th	Night	11% 7% 2 8% 4 3 4 3 4 5% 49%	5900
	21st to end	Night	18% 10% 3 6% 3 2 3 2 3 4 45%	6490
February	1st to 10th	Night	17% 9% 3 6% 3 3 3 3 4 6% 42%	2600
	11th to 20th	Night	16% 8% 2 7% 4 3 3 2 5% 5% 45%	2433
	21st to end	Night	16% 8% 2 5% 3 4 3 3 6% 5% 46%	1980
March	1st to 10th	Night	18% 9% 3 6% 4 3 3 2 4 4 43%	4947
	11th to 20th	Night	11% 8% 2 5% 4 4 3 3 5% 5% 51%	4980
	21st to end	Night	14% 7% 3 7% 5% 4 4 3 5% 7% 41%	5407
April	1st to 10th	Night	12% 5% 1 5% 3 3 2 3 5% 7% 52%	2000
	11th to 20th	Night	14% 6% 1 6% 3 3 3 3 5% 8% 48%	1975
	21st to end	Night	19% 6% 3 6% 4 3 4 3 5% 6% 40%	2000
May	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 7% 42%	4366
	11th to 20th	Night	14% 7% 3 6% 4 4 4 3 6% 8% 40%	4053
	21st to end	Night	21% 7% 2 6% 5% 4 3 4 5% 6% 38%	3951
June	1st to 10th	Night	8% 5% 1 5% 3 4 5% 4 6% 8% 53%	1600
	11th to 20th	Night	5% 3 1 4 3 3 4 4 6% 11% 57%	1600
	21st to end	Night	3 2 1 3 4 4 3 4 5% 10% 61%	1600
July	1st to 10th	Night	7% 4 2 6% 5% 4 5% 5% 7% 10% 45%	3790
	11th to 20th	Night	3 3 2 4 4 4 4 4 7% 10% 55%	4077
	21st to end	Night	5% 5% 2 6% 3 4 4 4 7% 12% 47%	4449
August	1st to 10th	Night	3 2 1 3 3 3 4 4 6% 8% 63%	2926
	11th to 20th	Night	8% 4 2 5% 5% 4 4 4 6% 8% 50%	3106
	21st to end	Night	4 3 2 4 3 3 3 3 6% 8% 61%	3586
September	1st to 10th	Night	10% 4 2 4 3 3 4 3 5% 8% 55%	2000
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 5% 8% 50%	2000
	21st to end	Night	8% 5% 1 5% 4 3 3 3 4 6% 57%	2276
October	1st to 10th	Night	7% 3 1 4 3 3 3 3 5% 7% 61%	2317
	11th to 20th	Night	14% 4 2 3 2 3 3 3 4 5% 57%	2280
	21st to end	Night	17% 7% 2 5% 3 3 2 2 4 4 50%	2508
November	1st to 10th	Night	13% 5% 2 4 3 3 3 2 4 5% 56%	2345
	11th to 20th	Night	13% 5% 2 4 3 3 3 3 5% 6% 54%	2600
	21st to end	Night	16% 9% 2 5% 3 2 3 3 4 5% 48%	2725
December	1st to 10th	Night	13% 8% 2 4 3 3 3 2 4 6% 51%	4580
	11th to 20th	Night	19% 8% 2 6% 4 3 3 2 3 4 46%	5199
	21st to end	Night	25% 14% 3 7% 4 4 4 3 4 4 29%	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	43% 3 10% 25% 17% 3	4055
	11th to 20th	Day	35% 3 8% 29% 19% 6%	4080
	21st to end	Day	44% 2 8% 17% 19% 9%	4488
February	1st to 10th	Day	48% 3 11% 23% 12% 2	1800
	11th to 20th	Day	45% 3 10% 21% 17% 4	1862
	21st to end	Day	45% 3 8% 21% 16% 7%	1650
March	1st to 10th	Day	43% 4 6% 23% 13% 12%	4936
	11th to 20th	Day	30% 4 7% 24% 23% 12%	4980
	21st to end	Day	45% 5% 11% 26% 12% 1	5509
April	1st to 10th	Day	40% 5% 11% 23% 20% 2	2400
	11th to 20th	Day	44% 5% 12% 20% 16% 5%	2374
	21st to end	Day	48% 6% 10% 21% 14% 2	2400
May	1st to 10th	Day	47% 8% 14% 19% 12% 1	5567
	11th to 20th	Day	45% 6% 13% 23% 12% 1	5866
	21st to end	Day	45% 7% 9% 23% 15% 1	6922
June	1st to 10th	Day	36% 6% 15% 25% 17% 1	2800
	11th to 20th	Day	31% 7% 14% 29% 17% 2	2800
	21st to end	Day	27% 8% 17% 27% 17% 4	2800
July	1st to 10th	Day	32% 8% 14% 25% 19% 2	6117
	11th to 20th	Day	28% 9% 18% 30% 14% 1	5831
	21st to end	Day	32% 9% 18% 29% 12% 1	6240
August	1st to 10th	Day	22% 6% 18% 31% 22% 1	4220
	11th to 20th	Day	36% 6% 14% 29% 14% 1	3981
	21st to end	Day	27% 7% 14% 35% 15% 3	4311
September	1st to 10th	Day	33% 6% 11% 26% 16% 7%	2400
	11th to 20th	Day	36% 6% 10% 24% 23% 2	2400
	21st to end	Day	30% 5% 8% 26% 28% 3	2097
October	1st to 10th	Day	18% 3 5% 17% 43% 14%	3190
	11th to 20th	Day	22% 2 5% 20% 39% 11%	3140
	21st to end	Day	29% 4 7% 32% 24% 4	3428
November	1st to 10th	Day	33% 3 9% 26% 23% 6%	1952
	11th to 20th	Day	35% 3 7% 23% 23% 8%	1800
	21st to end	Day	42% 3 8% 23% 22% 2	1670
December	1st to 10th	Day	35% 4 9% 33% 19% 1	2610
	11th to 20th	Day	44% 3 6% 25% 21% 1	3005
	21st to end	Day	59% 3 9% 18% 10% 2	3982
January	1st to 10th	Night	45% 3 10% 25% 14% 2	5906
	11th to 20th	Night	38% 3 9% 26% 22% 2	5900
	21st to end	Night	44% 3 8% 21% 19% 5%	6490
February	1st to 10th	Night	44% 4 10% 24% 16% 2	2600
	11th to 20th	Night	43% 3 10% 22% 19% 3	2434
	21st to end	Night	40% 3 10% 22% 19% 6%	1980
March	1st to 10th	Night	46% 3 7% 18% 17% 9%	4947
	11th to 20th	Night	35% 4 8% 24% 18% 11%	4980
	21st to end	Night	42% 4 11% 27% 15% 1	5407
April	1st to 10th	Night	33% 5% 11% 24% 22% 5%	2000
	11th to 20th	Night	36% 4 11% 25% 18% 6%	1975
	21st to end	Night	43% 6% 11% 23% 15% 2	2000
May	1st to 10th	Night	41% 6% 16% 23% 12% 2	4396
	11th to 20th	Night	42% 6% 13% 24% 12% 4	4054
	21st to end	Night	46% 6% 11% 23% 11% 3	3959
June	1st to 10th	Night	29% 5% 15% 29% 20% 2	1600
	11th to 20th	Night	22% 5% 15% 35% 19% 5%	1600
	21st to end	Night	20% 6% 17% 30% 20% 8%	1600
July	1st to 10th	Night	31% 9% 15% 22% 21% 2	3749
	11th to 20th	Night	22% 9% 17% 35% 15% 2	4026
	21st to end	Night	27% 9% 18% 32% 13% 1	4320
August	1st to 10th	Night	17% 7% 17% 38% 21% 1	2916
	11th to 20th	Night	31% 7% 18% 28% 15% 2	3134
	21st to end	Night	20% 6% 15% 35% 20% 4	3586
September	1st to 10th	Night	28% 5% 10% 30% 20% 7%	2000
	11th to 20th	Night	32% 6% 11% 25% 23% 4	2000
	21st to end	Night	29% 5% 9% 22% 32% 4	2276
October	1st to 10th	Night	15% 3 7% 17% 42% 17%	3837
	11th to 20th	Night	21% 3 5% 19% 34% 18%	3779
	21st to end	Night	30% 3 7% 28% 28% 5%	4120
November	1st to 10th	Night	31% 3 9% 26% 24% 7%	2345
	11th to 20th	Night	33% 3 7% 24% 25% 7%	2600
	21st to end	Night	40% 3 7% 25% 22% 3	2725
December	1st to 10th	Night	36% 3 9% 34% 16% 1	4580
	11th to 20th	Night	44% 2 7% 23% 21% 3	5201
	21st to end	Night	59% 3 10% 19% 7% 2	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	25% 21% 36% 14% 3	300
	11th to 20th	Day	31% 24% 30% 14% 2	300
	21st to end	Day	22% 29% 30% 15% 4	330
February	1st to 10th	Day	29% 21% 38% 9% 3 1	300
	11th to 20th	Day	31% 28% 31% 8% 3 1	300
	21st to end	Day	31% 19% 37% 10% 3	249
March	1st to 10th	Day	27% 21% 35% 14% 3	300
	11th to 20th	Day	30% 22% 34% 12% 2	300
	21st to end	Day	28% 25% 37% 9% 1	350
April	1st to 10th	Day	26% 17% 33% 18% 6% 1	500
	11th to 20th	Day	25% 23% 32% 14% 6% 1	492
	21st to end	Day	22% 16% 36% 20% 4 1	500
May	1st to 10th	Day	20% 16% 34% 21% 8% 1	552
	11th to 20th	Day	17% 14% 32% 22% 13% 2	725
	21st to end	Day	14% 8% 35% 24% 16% 3	789
June	1st to 10th	Day	11% 5% 23% 30% 24% 6%	730
	11th to 20th	Day	7% 4 18% 39% 27% 4	730
	21st to end	Day	6% 5% 26% 36% 22% 6%	730
July	1st to 10th	Day	10% 1 16% 33% 31% 10%	721
	11th to 20th	Day	7% 2 16% 36% 31% 8%	718
	21st to end	Day	9% 3 13% 31% 33% 12%	794
August	1st to 10th	Day	10% 2 13% 40% 28% 7%	726
	11th to 20th	Day	13% 3 16% 28% 29% 10%	577
	21st to end	Day	9% 1 13% 32% 30% 14%	583
September	1st to 10th	Day	10% 4 12% 38% 29% 8%	530
	11th to 20th	Day	9% 4 16% 32% 28% 11%	530
	21st to end	Day	14% 8% 24% 28% 23% 4	360
October	1st to 10th	Day	9% 10% 28% 33% 16% 5%	309
	11th to 20th	Day	20% 13% 35% 24% 6% 2	300
	21st to end	Day	28% 17% 29% 21% 4	330
November	1st to 10th	Day	21% 11% 32% 27% 7% 2	300
	11th to 20th	Day	22% 16% 37% 14% 10% 1	300
	21st to end	Day	31% 15% 30% 16% 6% 2	300
December	1st to 10th	Day	21% 25% 30% 16% 5% 2	300
	11th to 20th	Day	28% 23% 29% 14% 7%	300
	21st to end	Day	31% 22% 29% 15% 3	330
January	1st to 10th	Night	21% 17% 36% 23% 3	1000
	11th to 20th	Night	23% 17% 38% 18% 4	1000
	21st to end	Night	21% 17% 39% 21% 2	1100
February	1st to 10th	Night	23% 16% 38% 21% 2	1000
	11th to 20th	Night	23% 17% 39% 19% 1	879
	21st to end	Night	22% 20% 37% 18% 2	660
March	1st to 10th	Night	23% 16% 35% 23% 3	615
	11th to 20th	Night	23% 15% 33% 25% 4	600
	21st to end	Night	25% 13% 37% 20% 5%	660
April	1st to 10th	Night	16% 15% 41% 25% 4	600
	11th to 20th	Night	19% 16% 33% 26% 7%	593
	21st to end	Night	21% 9% 39% 23% 8% 1	600
May	1st to 10th	Night	17% 8% 35% 32% 8%	600
	11th to 20th	Night	18% 7% 31% 27% 16% 1	591
	21st to end	Night	14% 5% 26% 35% 17% 3	650
June	1st to 10th	Night	9% 5% 19% 35% 30% 2	600
	11th to 20th	Night	6% 2 20% 45% 25% 2	600
	21st to end	Night	4 2 19% 40% 33% 2	600
July	1st to 10th	Night	6% 2 14% 33% 40% 5%	585
	11th to 20th	Night	3 2 10% 41% 38% 6%	582
	21st to end	Night	6% 11% 39% 37% 6%	657
August	1st to 10th	Night	4 1 14% 43% 34% 4	597
	11th to 20th	Night	7% 1 15% 39% 33% 4	594
	21st to end	Night	8% 1 10% 39% 36% 6%	660
September	1st to 10th	Night	11% 2 14% 38% 31% 4	600
	11th to 20th	Night	12% 1 14% 37% 31% 5%	600
	21st to end	Night	9% 6% 21% 35% 26% 3	711
October	1st to 10th	Night	9% 5% 24% 35% 25% 3	773
	11th to 20th	Night	15% 10% 32% 29% 13% 1	760
	21st to end	Night	22% 12% 30% 27% 9%	836
November	1st to 10th	Night	16% 10% 34% 30% 10% 1	780
	11th to 20th	Night	19% 10% 35% 28% 9%	800
	21st to end	Night	23% 13% 32% 23% 9%	925
December	1st to 10th	Night	23% 13% 33% 26% 5%	1000
	11th to 20th	Night	25% 13% 29% 28% 4	1000
	21st to end	Night	27% 17% 32% 20% 4	1100

Page generated at 2025-10-01 00:39:04. Version ac07

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