Sheep Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sheep Hill Observatory clear sky chart from 2005-11-06 to 2024-03-28.

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% 6% 3 5% 5% 3 5% 5% 5% 7% 39%	78687
	Night	17% 7% 2 5% 5% 3 4 4 5% 7% 42%	81297
Transparency	Day	43% 5% 12% 23% 15% 2	78392
	Night	42% 5% 12% 23% 15% 2	81126
Seeing	Day	22% 14% 30% 21% 10% 3	14092
	Night	21% 11% 31% 28% 9% 1	23418

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	15% 6% 2 4 4 3 4 4 5% 5% 46%	2517
	11th to 20th	Day	15% 9% 3 6% 8% 4 6% 4 4 6% 35%	2520
	21st to end	Day	21% 10% 5% 6% 5% 3 4 4 4 5% 33%	3037
February	1st to 10th	Day	17% 8% 3 6% 5% 3 4 5% 5% 6% 38%	1710
	11th to 20th	Day	14% 6% 4 6% 5% 3 5% 4 5% 6% 42%	1833
	21st to end	Day	20% 8% 3 6% 5% 3 4 4 4 6% 37%	1570
March	1st to 10th	Day	15% 7% 3 5% 6% 3 4 4 5% 6% 42%	1897
	11th to 20th	Day	14% 7% 3 5% 5% 4 6% 5% 6% 8% 38%	2023
	21st to end	Day	19% 8% 3 5% 4 2 4 4 4 6% 40%	2424
April	1st to 10th	Day	17% 8% 4 5% 5% 3 4 4 5% 6% 40%	2160
	11th to 20th	Day	16% 6% 3 5% 5% 4 4 4 5% 7% 41%	2134
	21st to end	Day	19% 6% 2 5% 5% 3 4 5% 5% 7% 39%	2164
May	1st to 10th	Day	23% 7% 3 6% 4 3 5% 4 5% 7% 34%	2348
	11th to 20th	Day	21% 5% 2 6% 6% 2 5% 5% 6% 7% 36%	2478
	21st to end	Day	15% 6% 3 5% 4 3 5% 4 5% 9% 40%	2725
June	1st to 10th	Day	17% 5% 2 5% 5% 4 5% 6% 6% 10% 36%	2520
	11th to 20th	Day	16% 6% 3 5% 5% 4 6% 5% 7% 9% 33%	2520
	21st to end	Day	13% 6% 2 5% 6% 4 6% 4 6% 9% 39%	2520
July	1st to 10th	Day	12% 5% 3 6% 6% 4 6% 6% 7% 9% 37%	2520
	11th to 20th	Day	11% 4 2 5% 5% 3 5% 6% 7% 10% 39%	2520
	21st to end	Day	12% 6% 3 6% 6% 4 6% 6% 6% 8% 37%	2744
August	1st to 10th	Day	11% 5% 3 6% 6% 4 7% 7% 7% 8% 37%	2370
	11th to 20th	Day	13% 5% 3 6% 6% 4 5% 6% 6% 8% 37%	2126
	21st to end	Day	15% 6% 2 6% 5% 3 5% 5% 6% 7% 41%	2376
September	1st to 10th	Day	16% 5% 3 5% 5% 3 5% 6% 5% 7% 42%	2160
	11th to 20th	Day	14% 5% 2 4 5% 2 3 3 5% 6% 50%	2098
	21st to end	Day	18% 6% 3 6% 5% 3 5% 4 5% 6% 41%	1980
October	1st to 10th	Day	21% 6% 2 4 5% 3 4 5% 5% 6% 40%	1854
	11th to 20th	Day	16% 5% 2 5% 4 3 5% 3 5% 7% 45%	1800
	21st to end	Day	21% 6% 2 4 4 3 5% 4 4 6% 41%	1854
November	1st to 10th	Day	15% 6% 2 4 3 3 3 3 4 5% 52%	1671
	11th to 20th	Day	19% 5% 2 3 4 2 5% 4 5% 6% 46%	1710
	21st to end	Day	15% 6% 3 4 4 2 4 5% 6% 7% 43%	1606
December	1st to 10th	Day	20% 7% 3 6% 5% 3 4 4 5% 7% 38%	1520
	11th to 20th	Day	22% 5% 2 3 3 3 4 4 6% 6% 43%	1906
	21st to end	Day	18% 9% 4 7% 7% 4 5% 5% 5% 8% 29%	2772
January	1st to 10th	Night	16% 6% 2 4 4 3 4 4 5% 6% 46%	4429
	11th to 20th	Night	15% 8% 3 7% 5% 3 4 4 4 6% 41%	4440
	21st to end	Night	24% 10% 3 4 4 2 4 4 4 6% 34%	4614
February	1st to 10th	Night	17% 8% 3 5% 5% 2 4 4 5% 5% 42%	2470
	11th to 20th	Night	16% 7% 3 6% 4 3 4 5% 5% 5% 42%	2233
	21st to end	Night	19% 7% 3 5% 5% 3 4 3 5% 6% 41%	1884
March	1st to 10th	Night	16% 6% 3 5% 5% 2 3 3 5% 7% 44%	2270
	11th to 20th	Night	17% 6% 2 5% 4 3 4 4 5% 6% 44%	2151
	21st to end	Night	17% 8% 2 4 4 3 4 4 5% 7% 43%	2085
April	1st to 10th	Night	17% 8% 2 5% 5% 3 5% 4 5% 7% 39%	1800
	11th to 20th	Night	18% 6% 2 4 6% 3 5% 4 4 6% 41%	1775
	21st to end	Night	20% 6% 2 5% 4 3 3 4 5% 7% 41%	1796
May	1st to 10th	Night	21% 9% 3 7% 6% 3 4 4 4 5% 35%	1620
	11th to 20th	Night	18% 8% 3 5% 5% 2 4 5% 5% 6% 39%	1421
	21st to end	Night	18% 5% 2 4 5% 3 3 5% 5% 8% 42%	1550
June	1st to 10th	Night	16% 5% 2 4 5% 2 5% 4 4 8% 43%	1440
	11th to 20th	Night	14% 6% 3 5% 4 3 4 5% 6% 9% 41%	1440
	21st to end	Night	11% 4 2 4 4 4 5% 5% 6% 10% 46%	1440
July	1st to 10th	Night	11% 5% 2 7% 6% 3 5% 5% 6% 10% 40%	1440
	11th to 20th	Night	11% 5% 2 6% 6% 3 6% 5% 7% 10% 39%	1440
	21st to end	Night	11% 4 2 5% 5% 3 3 6% 6% 12% 43%	1574
August	1st to 10th	Night	9% 5% 2 4 7% 3 5% 5% 7% 9% 43%	1546
	11th to 20th	Night	12% 6% 3 7% 7% 4 7% 5% 6% 8% 36%	1774
	21st to end	Night	14% 5% 3 5% 6% 3 5% 4 5% 8% 43%	1980
September	1st to 10th	Night	17% 5% 2 6% 5% 3 4 5% 4 6% 44%	1800
	11th to 20th	Night	14% 6% 2 4 4 2 3 3 5% 6% 52%	1862
	21st to end	Night	18% 5% 2 4 4 3 4 3 4 7% 45%	1980
October	1st to 10th	Night	20% 7% 3 5% 4 3 3 3 4 6% 42%	2101
	11th to 20th	Night	17% 6% 2 4 4 1 3 4 4 7% 49%	2160
	21st to end	Night	21% 7% 2 5% 4 2 3 4 4 6% 44%	2502
November	1st to 10th	Night	13% 5% 2 4 4 3 4 4 5% 6% 51%	2407
	11th to 20th	Night	20% 6% 2 3 3 2 3 3 4 5% 48%	2470
	21st to end	Night	15% 4 2 5% 4 3 4 4 5% 7% 46%	2571
December	1st to 10th	Night	18% 7% 3 4 5% 4 4 4 5% 7% 39%	2660
	11th to 20th	Night	19% 7% 2 4 4 3 4 4 5% 7% 42%	3288
	21st to end	Night	19% 9% 3 6% 5% 3 4 4 4 6% 36%	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	38% 4 12% 32% 12% 3	2518
	11th to 20th	Day	49% 5% 11% 22% 11% 2	2520
	21st to end	Day	54% 4 9% 20% 11% 2	3037
February	1st to 10th	Day	46% 4 13% 23% 12% 2	1710
	11th to 20th	Day	42% 5% 9% 24% 17% 3	1842
	21st to end	Day	47% 4 10% 22% 13% 3	1570
March	1st to 10th	Day	42% 4 12% 25% 14% 3	1900
	11th to 20th	Day	43% 5% 11% 24% 15% 2	2023
	21st to end	Day	46% 3 9% 19% 18% 5%	2424
April	1st to 10th	Day	45% 4 10% 20% 16% 5%	2160
	11th to 20th	Day	42% 5% 11% 22% 17% 4	2134
	21st to end	Day	44% 5% 9% 21% 16% 4	2164
May	1st to 10th	Day	51% 4 9% 19% 16% 2	2348
	11th to 20th	Day	46% 5% 11% 21% 15% 3	2482
	21st to end	Day	42% 6% 14% 22% 14% 2	2725
June	1st to 10th	Day	42% 7% 14% 21% 15% 1	2520
	11th to 20th	Day	46% 7% 12% 22% 11% 2	2520
	21st to end	Day	40% 6% 14% 23% 16% 1	2520
July	1st to 10th	Day	42% 8% 11% 23% 15% 2	2450
	11th to 20th	Day	36% 7% 15% 25% 14% 2	2445
	21st to end	Day	42% 8% 12% 19% 17% 3	2591
August	1st to 10th	Day	40% 9% 14% 22% 14% 1	2356
	11th to 20th	Day	41% 7% 14% 24% 13% 1	2126
	21st to end	Day	41% 6% 10% 22% 18% 3	2376
September	1st to 10th	Day	41% 6% 10% 22% 18% 3	2160
	11th to 20th	Day	35% 4 11% 23% 25% 3	2098
	21st to end	Day	43% 5% 10% 19% 19% 4	1980
October	1st to 10th	Day	43% 5% 10% 22% 16% 2	1854
	11th to 20th	Day	38% 5% 12% 26% 19% 2	1800
	21st to end	Day	44% 5% 9% 23% 16% 2	1854
November	1st to 10th	Day	36% 3 11% 25% 22% 3	1671
	11th to 20th	Day	39% 4 11% 24% 19% 4	1710
	21st to end	Day	40% 3 14% 29% 12% 2	1606
December	1st to 10th	Day	46% 4 15% 20% 14% 1	1520
	11th to 20th	Day	42% 4 17% 23% 12% 2	1906
	21st to end	Day	52% 6% 11% 23% 8%	2772
January	1st to 10th	Night	38% 4 12% 30% 12% 4	4429
	11th to 20th	Night	44% 5% 13% 24% 12% 2	4440
	21st to end	Night	51% 4 9% 22% 12% 2	4614
February	1st to 10th	Night	44% 4 13% 24% 13% 2	2470
	11th to 20th	Night	43% 5% 10% 20% 17% 5%	2235
	21st to end	Night	45% 3 6% 25% 17% 3	1884
March	1st to 10th	Night	41% 5% 12% 24% 14% 4	2280
	11th to 20th	Night	42% 5% 11% 22% 17% 3	2152
	21st to end	Night	41% 5% 10% 18% 19% 6%	2085
April	1st to 10th	Night	44% 5% 11% 21% 15% 4	1800
	11th to 20th	Night	43% 5% 9% 21% 19% 2	1775
	21st to end	Night	44% 5% 9% 21% 17% 4	1796
May	1st to 10th	Night	51% 5% 9% 18% 15% 2	1620
	11th to 20th	Night	46% 5% 10% 17% 19% 3	1422
	21st to end	Night	40% 8% 15% 21% 12% 3	1551
June	1st to 10th	Night	41% 5% 12% 22% 19% 2	1440
	11th to 20th	Night	40% 7% 15% 25% 12% 1	1440
	21st to end	Night	33% 9% 15% 26% 16% 1	1440
July	1st to 10th	Night	40% 8% 14% 21% 16% 2	1400
	11th to 20th	Night	39% 8% 13% 26% 12% 2	1392
	21st to end	Night	32% 9% 18% 22% 16% 3	1486
August	1st to 10th	Night	36% 9% 15% 23% 15% 2	1536
	11th to 20th	Night	43% 9% 13% 23% 11% 1	1774
	21st to end	Night	40% 7% 12% 18% 20% 2	1980
September	1st to 10th	Night	42% 5% 10% 25% 17% 1	1800
	11th to 20th	Night	34% 4 11% 22% 25% 3	1862
	21st to end	Night	40% 4 9% 23% 23% 2	1980
October	1st to 10th	Night	44% 5% 10% 24% 14% 2	2101
	11th to 20th	Night	37% 5% 12% 28% 16% 2	2160
	21st to end	Night	43% 4 11% 25% 16% 1	2502
November	1st to 10th	Night	35% 4 11% 24% 22% 4	2407
	11th to 20th	Night	40% 3 9% 24% 19% 5%	2470
	21st to end	Night	37% 5% 14% 29% 14% 2	2571
December	1st to 10th	Night	44% 5% 13% 24% 13% 1	2660
	11th to 20th	Night	43% 5% 13% 20% 16% 4	3288
	21st to end	Night	48% 7% 12% 21% 11%	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	24% 26% 32% 16% 3	180
	11th to 20th	Day	31% 26% 33% 8% 2	180
	21st to end	Day	23% 22% 36% 13% 4 1	274
February	1st to 10th	Day	31% 21% 36% 10% 2	270
	11th to 20th	Day	27% 20% 37% 15% 2	441
	21st to end	Day	29% 18% 34% 15% 3	382
March	1st to 10th	Day	27% 22% 30% 18% 4	460
	11th to 20th	Day	24% 23% 33% 15% 4 1	460
	21st to end	Day	30% 20% 29% 16% 5% 1	490
April	1st to 10th	Day	27% 20% 32% 14% 5% 2	420
	11th to 20th	Day	23% 19% 34% 15% 7% 2	412
	21st to end	Day	33% 17% 31% 15% 3 1	420
May	1st to 10th	Day	34% 16% 29% 13% 6% 2	423
	11th to 20th	Day	23% 16% 33% 19% 8% 1	447
	21st to end	Day	21% 8% 25% 30% 14% 3	485
June	1st to 10th	Day	18% 10% 33% 24% 12% 3	450
	11th to 20th	Day	21% 12% 32% 24% 10% 1	450
	21st to end	Day	14% 11% 32% 26% 14% 2	450
July	1st to 10th	Day	15% 4 26% 31% 18% 5%	445
	11th to 20th	Day	11% 5% 27% 34% 20% 3	444
	21st to end	Day	14% 7% 30% 32% 14% 2	488
August	1st to 10th	Day	13% 4 26% 34% 15% 8%	446
	11th to 20th	Day	16% 5% 22% 33% 20% 5%	439
	21st to end	Day	14% 7% 30% 27% 15% 7%	495
September	1st to 10th	Day	19% 10% 24% 24% 15% 7%	450
	11th to 20th	Day	16% 6% 29% 24% 12% 12%	450
	21st to end	Day	21% 10% 31% 22% 11% 5%	450
October	1st to 10th	Day	28% 7% 28% 20% 12% 4	450
	11th to 20th	Day	19% 16% 30% 22% 12% 1	450
	21st to end	Day	28% 14% 31% 17% 10% 1	432
November	1st to 10th	Day	21% 12% 30% 24% 10% 4	365
	11th to 20th	Day	27% 16% 31% 21% 4 1	370
	21st to end	Day	20% 20% 36% 18% 4 2	266
December	1st to 10th	Day	26% 24% 29% 14% 7%	180
	11th to 20th	Day	33% 18% 34% 12% 3	180
	21st to end	Day	30% 15% 37% 14% 4 1	198
January	1st to 10th	Night	21% 16% 39% 20% 3	760
	11th to 20th	Night	25% 15% 33% 23% 3	760
	21st to end	Night	21% 17% 38% 22% 2	836
February	1st to 10th	Night	23% 13% 38% 24% 2	760
	11th to 20th	Night	23% 17% 41% 18% 1	743
	21st to end	Night	26% 16% 35% 19% 4	628
March	1st to 10th	Night	24% 16% 36% 20% 4	760
	11th to 20th	Night	23% 17% 36% 21% 3 1	760
	21st to end	Night	22% 16% 36% 20% 5% 1	821
April	1st to 10th	Night	23% 18% 34% 20% 5%	720
	11th to 20th	Night	22% 15% 34% 24% 5%	711
	21st to end	Night	24% 13% 33% 24% 5%	716
May	1st to 10th	Night	25% 12% 35% 21% 7%	540
	11th to 20th	Night	22% 12% 31% 29% 6%	360
	21st to end	Night	20% 6% 21% 38% 14% 1	389
June	1st to 10th	Night	20% 5% 29% 33% 13% 1	360
	11th to 20th	Night	14% 5% 30% 37% 14%	360
	21st to end	Night	11% 4 26% 48% 11%	360
July	1st to 10th	Night	12% 5% 25% 37% 20% 1	350
	11th to 20th	Night	14% 3 20% 43% 19% 1	348
	21st to end	Night	13% 3 22% 44% 15% 2	394
August	1st to 10th	Night	11% 2 21% 42% 22% 2	472
	11th to 20th	Night	14% 4 17% 40% 23% 2	710
	21st to end	Night	16% 5% 17% 40% 20% 2	792
September	1st to 10th	Night	18% 4 24% 35% 18% 2	720
	11th to 20th	Night	18% 5% 20% 33% 20% 3	720
	21st to end	Night	20% 5% 25% 33% 15% 2	720
October	1st to 10th	Night	25% 7% 26% 24% 15% 3	720
	11th to 20th	Night	21% 11% 27% 32% 10%	720
	21st to end	Night	26% 10% 35% 22% 7% 1	792
November	1st to 10th	Night	17% 11% 31% 28% 12% 1	740
	11th to 20th	Night	24% 11% 32% 24% 7% 1	760
	21st to end	Night	18% 16% 33% 27% 6% 1	760
December	1st to 10th	Night	25% 14% 32% 24% 4 1	760
	11th to 20th	Night	23% 13% 34% 27% 3	760
	21st to end	Night	24% 14% 34% 25% 2	836

Page generated at 2024-03-24 23:36:58. Version ac07

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