Shepherds Lair Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shepherds Lair Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	24% 9% 3 5% 5% 3 4 4 4 5% 35%	74771
	Night	26% 10% 3 5% 4 3 3 3 4 5% 33%	75042
Transparency	Day	53% 6% 10% 16% 11% 3	74474
	Night	56% 5% 9% 15% 11% 4	74860
Seeing	Day	25% 12% 23% 26% 12% 2	13505
	Night	29% 9% 17% 27% 16% 2	22608

By Month

Percentage Cloud Cover SW (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	40% 13% 3 7% 6% 3 3 3 4 4 14%	1519
	11th to 20th	Day	36% 12% 2 5% 5% 3 3 4 4 4 23%	1480
	21st to end	Day	30% 11% 2 5% 5% 3 4 3 5% 5% 26%	1714
February	1st to 10th	Day	34% 13% 3 5% 5% 3 4 4 5% 4 20%	1620
	11th to 20th	Day	31% 15% 5% 7% 5% 3 3 3 3 5% 20%	1575
	21st to end	Day	31% 18% 4 7% 4 3 3 4 3 5% 20%	1422
March	1st to 10th	Day	30% 13% 4 7% 6% 4 5% 3 5% 6% 18%	1862
	11th to 20th	Day	32% 13% 4 6% 6% 3 4 4 4 5% 20%	1980
	21st to end	Day	33% 15% 4 7% 6% 3 5% 4 4 4 14%	2239
April	1st to 10th	Day	31% 15% 4 7% 6% 3 4 4 4 4 18%	2160
	11th to 20th	Day	29% 13% 5% 6% 6% 3 4 4 4 5% 22%	2129
	21st to end	Day	29% 10% 3 7% 5% 3 4 4 5% 6% 24%	2306
May	1st to 10th	Day	24% 11% 3 5% 4 3 4 3 4 4 34%	2497
	11th to 20th	Day	25% 9% 3 7% 5% 3 4 5% 5% 7% 29%	2477
	21st to end	Day	32% 8% 3 5% 4 3 4 4 5% 6% 26%	2723
June	1st to 10th	Day	28% 8% 3 6% 4 3 4 4 4 6% 30%	2520
	11th to 20th	Day	28% 9% 3 6% 6% 4 5% 4 5% 6% 25%	2520
	21st to end	Day	12% 5% 2 5% 4 2 4 4 4 5% 51%	2520
July	1st to 10th	Day	9% 4 1 4 4 2 4 4 5% 6% 58%	2520
	11th to 20th	Day	9% 3 1 3 3 2 3 3 4 6% 62%	2520
	21st to end	Day	7% 3 1 2 2 1 2 2 3 4 71%	2741
August	1st to 10th	Day	7% 4 2 3 4 2 3 3 3 6% 62%	2375
	11th to 20th	Day	6% 3 2 3 3 2 2 4 4 5% 67%	2298
	21st to end	Day	10% 4 2 4 3 2 4 4 5% 6% 55%	2430
September	1st to 10th	Day	10% 4 1 3 4 1 3 4 3 7% 61%	2160
	11th to 20th	Day	15% 7% 2 6% 4 3 4 4 4 7% 44%	2160
	21st to end	Day	19% 6% 2 5% 5% 3 4 3 4 6% 44%	1903
October	1st to 10th	Day	23% 8% 2 4 5% 2 3 5% 4 6% 40%	1800
	11th to 20th	Day	24% 7% 3 5% 5% 2 4 4 4 7% 36%	1800
	21st to end	Day	32% 8% 3 5% 5% 3 3 3 3 4 31%	1921
November	1st to 10th	Day	34% 10% 4 7% 5% 4 3 3 5% 7% 19%	1598
	11th to 20th	Day	36% 8% 4 6% 5% 3 3 5% 5% 5% 21%	1520
	21st to end	Day	30% 12% 4 6% 5% 3 4 5% 4 4 24%	1520
December	1st to 10th	Day	31% 12% 3 6% 5% 3 3 4 3 4 27%	1520
	11th to 20th	Day	34% 11% 3 4 5% 3 4 4 6% 5% 20%	1928
	21st to end	Day	34% 15% 4 7% 6% 2 4 3 3 4 18%	2794
January	1st to 10th	Night	38% 14% 3 6% 5% 3 4 3 3 4 18%	2646
	11th to 20th	Night	36% 13% 3 5% 4 3 3 4 4 5% 21%	2590
	21st to end	Night	31% 11% 3 6% 5% 3 4 4 4 4 26%	2639
February	1st to 10th	Night	32% 15% 4 6% 5% 3 4 3 3 5% 20%	2340
	11th to 20th	Night	33% 14% 3 5% 4 3 3 3 3 5% 24%	2272
	21st to end	Night	32% 18% 3 5% 4 4 3 3 4 6% 20%	1833
March	1st to 10th	Night	28% 14% 4 6% 5% 3 4 4 4 5% 24%	2094
	11th to 20th	Night	30% 10% 3 6% 4 3 5% 5% 4 6% 24%	1980
	21st to end	Night	34% 15% 5% 6% 5% 3 4 4 4 5% 16%	2116
April	1st to 10th	Night	31% 16% 3 6% 6% 3 4 3 3 5% 20%	1800
	11th to 20th	Night	27% 13% 3 6% 4 2 3 3 5% 6% 27%	1779
	21st to end	Night	31% 12% 3 5% 4 2 4 3 4 6% 26%	1652
May	1st to 10th	Night	26% 9% 3 5% 3 2 3 3 4 6% 35%	1463
	11th to 20th	Night	25% 7% 2 6% 6% 3 4 5% 5% 7% 29%	1416
	21st to end	Night	27% 8% 2 6% 5% 2 4 4 5% 7% 28%	1552
June	1st to 10th	Night	24% 7% 3 6% 3 2 4 4 5% 5% 36%	1440
	11th to 20th	Night	26% 11% 4 6% 5% 2 3 3 4 5% 30%	1440
	21st to end	Night	13% 6% 2 4 3 3 3 4 4 5% 53%	1440
July	1st to 10th	Night	11% 4 2 3 3 3 2 3 3 5% 62%	1440
	11th to 20th	Night	7% 3 2 3 4 2 3 3 4 4 66%	1440
	21st to end	Night	4 3 1 2 2 1 2 2 3 5% 75%	1576
August	1st to 10th	Night	7% 2 2 3 3 2 2 3 4 8% 64%	1561
	11th to 20th	Night	5% 3 2 2 4 2 3 3 3 5% 68%	1602
	21st to end	Night	8% 5% 1 3 3 2 2 3 4 6% 62%	1926
September	1st to 10th	Night	10% 3 1 3 3 1 3 3 5% 4 65%	1800
	11th to 20th	Night	16% 5% 2 5% 4 3 4 3 4 5% 49%	1800
	21st to end	Night	17% 6% 2 4 4 2 3 4 4 7% 46%	2055
October	1st to 10th	Night	23% 7% 3 4 4 2 3 2 3 5% 45%	2160
	11th to 20th	Night	23% 7% 3 5% 3 2 3 5% 5% 5% 39%	2160
	21st to end	Night	29% 8% 2 5% 5% 3 3 4 3 4 35%	2434
November	1st to 10th	Night	35% 10% 3 6% 5% 3 4 3 4 5% 22%	2478
	11th to 20th	Night	38% 9% 3 5% 5% 2 4 4 3 4 22%	2660
	21st to end	Night	31% 11% 3 4 5% 2 4 3 4 4 29%	2660
December	1st to 10th	Night	32% 9% 3 5% 5% 3 4 3 4 5% 27%	2660
	11th to 20th	Night	32% 12% 3 6% 5% 3 4 4 4 6% 21%	3276
	21st to end	Night	33% 15% 4 6% 6% 3 4 4 3 4 19%	4862

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	75% 5% 6% 8% 5% 1	1519
	11th to 20th	Day	68% 4 7% 9% 5% 7%	1480
	21st to end	Day	62% 5% 7% 12% 10% 3	1714
February	1st to 10th	Day	69% 7% 8% 9% 6% 1	1620
	11th to 20th	Day	71% 5% 7% 11% 4 3	1584
	21st to end	Day	71% 5% 7% 7% 8% 2	1422
March	1st to 10th	Day	70% 6% 8% 11% 5% 1	1862
	11th to 20th	Day	69% 5% 7% 12% 6% 1	1980
	21st to end	Day	76% 7% 8% 8% 1	2239
April	1st to 10th	Day	73% 6% 8% 10% 4	2160
	11th to 20th	Day	68% 5% 8% 10% 7% 2	2132
	21st to end	Day	64% 7% 9% 11% 6% 2	2306
May	1st to 10th	Day	56% 5% 13% 17% 8%	2497
	11th to 20th	Day	58% 7% 12% 17% 6% 1	2480
	21st to end	Day	61% 8% 12% 16% 3	2724
June	1st to 10th	Day	57% 7% 15% 16% 5%	2520
	11th to 20th	Day	62% 7% 15% 11% 5%	2520
	21st to end	Day	37% 5% 16% 26% 11% 4	2520
July	1st to 10th	Day	29% 7% 14% 23% 21% 7%	2451
	11th to 20th	Day	24% 5% 11% 25% 29% 7%	2445
	21st to end	Day	18% 3 7% 29% 36% 7%	2589
August	1st to 10th	Day	24% 6% 13% 31% 18% 7%	2358
	11th to 20th	Day	20% 5% 14% 32% 22% 8%	2298
	21st to end	Day	30% 6% 10% 28% 22% 5%	2430
September	1st to 10th	Day	26% 4 10% 26% 20% 14%	2160
	11th to 20th	Day	41% 6% 10% 18% 16% 9%	2160
	21st to end	Day	43% 6% 10% 19% 15% 8%	1903
October	1st to 10th	Day	47% 6% 8% 20% 15% 5%	1800
	11th to 20th	Day	51% 5% 10% 15% 15% 4	1800
	21st to end	Day	58% 6% 5% 14% 16% 1	1921
November	1st to 10th	Day	68% 5% 9% 11% 6% 1	1598
	11th to 20th	Day	67% 6% 8% 10% 6% 2	1520
	21st to end	Day	65% 5% 6% 6% 16% 2	1520
December	1st to 10th	Day	63% 5% 8% 10% 11% 3	1520
	11th to 20th	Day	67% 4 10% 11% 8%	1928
	21st to end	Day	72% 5% 7% 13% 2 1	2794
January	1st to 10th	Night	73% 4 7% 8% 6% 2	2646
	11th to 20th	Night	67% 4 7% 10% 7% 5%	2590
	21st to end	Night	64% 3 7% 12% 10% 4	2639
February	1st to 10th	Night	70% 5% 8% 9% 6% 2	2340
	11th to 20th	Night	66% 5% 8% 11% 6% 3	2274
	21st to end	Night	70% 4 7% 9% 8% 2	1833
March	1st to 10th	Night	65% 6% 8% 15% 5% 1	2094
	11th to 20th	Night	63% 6% 9% 14% 5% 2	1980
	21st to end	Night	73% 6% 8% 10% 2	2116
April	1st to 10th	Night	70% 5% 10% 10% 4	1800
	11th to 20th	Night	62% 7% 11% 11% 6% 3	1779
	21st to end	Night	63% 5% 12% 11% 6% 3	1652
May	1st to 10th	Night	55% 5% 11% 19% 9% 2	1463
	11th to 20th	Night	57% 7% 12% 16% 5% 3	1416
	21st to end	Night	57% 11% 12% 16% 4	1552
June	1st to 10th	Night	54% 7% 16% 18% 6%	1440
	11th to 20th	Night	60% 5% 16% 15% 4 1	1440
	21st to end	Night	37% 5% 16% 26% 10% 5%	1440
July	1st to 10th	Night	28% 6% 11% 26% 22% 7%	1400
	11th to 20th	Night	25% 4 10% 24% 28% 8%	1392
	21st to end	Night	14% 4 7% 32% 33% 11%	1488
August	1st to 10th	Night	21% 5% 13% 35% 19% 7%	1553
	11th to 20th	Night	22% 5% 12% 31% 20% 10%	1602
	21st to end	Night	26% 5% 10% 32% 20% 7%	1926
September	1st to 10th	Night	25% 6% 12% 26% 19% 13%	1800
	11th to 20th	Night	41% 5% 9% 20% 12% 13%	1800
	21st to end	Night	39% 7% 12% 16% 16% 10%	2055
October	1st to 10th	Night	46% 4 7% 19% 19% 6%	2160
	11th to 20th	Night	48% 6% 8% 14% 19% 5%	2160
	21st to end	Night	56% 5% 6% 13% 16% 5%	2434
November	1st to 10th	Night	67% 5% 6% 11% 9% 1	2478
	11th to 20th	Night	67% 6% 7% 9% 8% 3	2660
	21st to end	Night	61% 5% 6% 10% 14% 4	2660
December	1st to 10th	Night	61% 5% 9% 12% 11% 2	2660
	11th to 20th	Night	66% 6% 10% 9% 8% 1	3276
	21st to end	Night	70% 6% 9% 10% 4 1	4862

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	47% 17% 15% 16% 6%	180
	11th to 20th	Day	42% 11% 30% 9% 6% 1	170
	21st to end	Day	39% 11% 19% 22% 9% 1	306
February	1st to 10th	Day	43% 14% 16% 21% 6%	340
	11th to 20th	Day	37% 16% 27% 17% 3 1	335
	21st to end	Day	39% 16% 23% 18% 3	320
March	1st to 10th	Day	35% 17% 28% 15% 6%	420
	11th to 20th	Day	34% 17% 22% 20% 6%	420
	21st to end	Day	38% 18% 21% 17% 5%	462
April	1st to 10th	Day	40% 15% 19% 18% 6% 1	420
	11th to 20th	Day	33% 18% 27% 14% 5% 2	412
	21st to end	Day	28% 16% 28% 19% 7% 1	420
May	1st to 10th	Day	23% 16% 26% 23% 8% 3	423
	11th to 20th	Day	32% 13% 20% 23% 10% 2	448
	21st to end	Day	28% 9% 23% 25% 12% 2	485
June	1st to 10th	Day	26% 11% 20% 27% 14% 3	450
	11th to 20th	Day	25% 15% 27% 23% 9% 1	450
	21st to end	Day	11% 6% 27% 36% 16% 3	450
July	1st to 10th	Day	8% 5% 24% 43% 17% 3	446
	11th to 20th	Day	5% 8% 27% 40% 18% 3	444
	21st to end	Day	6% 3 20% 46% 20% 6%	487
August	1st to 10th	Day	6% 5% 16% 49% 17% 7%	447
	11th to 20th	Day	4 5% 21% 38% 27% 6%	437
	21st to end	Day	8% 8% 27% 37% 16% 4	495
September	1st to 10th	Day	10% 8% 28% 34% 18% 3	450
	11th to 20th	Day	16% 9% 21% 33% 19% 2	450
	21st to end	Day	20% 10% 25% 31% 13% 1	450
October	1st to 10th	Day	23% 12% 22% 26% 16% 2	450
	11th to 20th	Day	26% 11% 20% 26% 15% 1	450
	21st to end	Day	34% 13% 20% 20% 11% 2	436
November	1st to 10th	Day	35% 17% 18% 24% 6% 1	234
	11th to 20th	Day	33% 14% 27% 16% 9% 2	180
	21st to end	Day	32% 16% 21% 21% 11%	180
December	1st to 10th	Day	37% 15% 20% 18% 9% 1	180
	11th to 20th	Day	47% 13% 22% 12% 6%	180
	21st to end	Day	46% 14% 18% 14% 8%	198
January	1st to 10th	Night	44% 14% 20% 16% 6% 1	760
	11th to 20th	Night	40% 11% 21% 19% 9%	740
	21st to end	Night	35% 9% 23% 24% 7% 1	792
February	1st to 10th	Night	38% 11% 19% 26% 5% 1	720
	11th to 20th	Night	39% 11% 17% 24% 8%	704
	21st to end	Night	41% 13% 18% 22% 5%	592
March	1st to 10th	Night	34% 13% 19% 24% 10% 1	720
	11th to 20th	Night	33% 11% 20% 27% 9%	720
	21st to end	Night	39% 12% 16% 22% 10% 1	792
April	1st to 10th	Night	38% 9% 17% 23% 11% 1	720
	11th to 20th	Night	32% 9% 18% 24% 14% 2	711
	21st to end	Night	35% 10% 12% 30% 12% 1	572
May	1st to 10th	Night	27% 10% 14% 32% 16% 2	383
	11th to 20th	Night	25% 7% 13% 30% 25% 1	354
	21st to end	Night	29% 5% 17% 27% 20% 2	389
June	1st to 10th	Night	28% 5% 16% 29% 21% 1	360
	11th to 20th	Night	28% 9% 16% 31% 16% 1	360
	21st to end	Night	14% 5% 14% 40% 26% 1	360
July	1st to 10th	Night	9% 3 9% 40% 39% 1	350
	11th to 20th	Night	7% 1 14% 47% 30% 1	348
	21st to end	Night	4 2 7% 45% 39% 3	394
August	1st to 10th	Night	7% 2 7% 33% 45% 6%	487
	11th to 20th	Night	6% 1 8% 31% 46% 8%	534
	21st to end	Night	9% 4 14% 40% 30% 4	738
September	1st to 10th	Night	11% 3 16% 36% 31% 2	720
	11th to 20th	Night	14% 5% 12% 33% 31% 5%	720
	21st to end	Night	19% 5% 15% 33% 26% 3	720
October	1st to 10th	Night	25% 5% 15% 33% 20% 3	720
	11th to 20th	Night	24% 8% 14% 33% 19% 2	720
	21st to end	Night	31% 10% 21% 25% 11% 3	792
November	1st to 10th	Night	39% 10% 18% 27% 6%	740
	11th to 20th	Night	41% 11% 22% 21% 6%	760
	21st to end	Night	33% 11% 22% 28% 6%	760
December	1st to 10th	Night	35% 11% 23% 24% 6% 1	760
	11th to 20th	Night	41% 12% 21% 20% 6%	760
	21st to end	Night	44% 13% 22% 16% 4 1	836

Page generated at 2024-01-12 22:38:15. Version ac07

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