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 2024-12-06.

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	22% 10% 2 6% 4 4 3 3 4 5% 37%	105673
	Night	26% 11% 2 6% 4 3 3 3 4 5% 34%	102726
Transparency	Day	50% 6% 10% 17% 12% 5%	105416
	Night	55% 6% 9% 15% 11% 4	102572
Seeing	Day	25% 12% 23% 26% 12% 2	14689
	Night	29% 9% 17% 28% 16% 2	23693

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	39% 19% 3 7% 5% 4 3 2 3 4 11%	2539
	11th to 20th	Day	39% 15% 2 6% 4 3 3 2 3 3 19%	2540
	21st to end	Day	42% 12% 2 7% 4 4 3 2 4 4 16%	3022
February	1st to 10th	Day	33% 14% 3 6% 4 4 4 3 6% 4 19%	1710
	11th to 20th	Day	31% 16% 4 7% 5% 4 3 2 4 5% 19%	1665
	21st to end	Day	30% 19% 3 8% 3 4 3 2 3 5% 19%	1509
March	1st to 10th	Day	21% 15% 4 9% 5% 6% 5% 3 6% 7% 20%	3252
	11th to 20th	Day	22% 12% 3 5% 4 4 3 2 3 3 38%	3490
	21st to end	Day	30% 17% 3 8% 6% 5% 4 3 4 4 15%	3937
April	1st to 10th	Day	30% 17% 3 9% 5% 4 3 3 4 4 18%	2280
	11th to 20th	Day	27% 15% 3 7% 5% 4 4 3 4 5% 23%	2249
	21st to end	Day	29% 11% 3 7% 5% 4 4 3 5% 5% 24%	2435
May	1st to 10th	Day	26% 13% 3 5% 4 4 3 2 4 4 31%	4384
	11th to 20th	Day	16% 11% 2 6% 4 3 3 3 5% 7% 41%	4377
	21st to end	Day	28% 10% 3 7% 5% 5% 5% 4 5% 6% 24%	4813
June	1st to 10th	Day	27% 9% 2 6% 4 3 4 3 4 6% 31%	2660
	11th to 20th	Day	27% 10% 3 7% 5% 4 5% 4 5% 6% 25%	2660
	21st to end	Day	12% 6% 2 5% 4 4 3 3 4 6% 51%	2660
July	1st to 10th	Day	6% 3 1 3 2 2 2 2 4 5% 69%	4420
	11th to 20th	Day	5% 2 1 2 2 2 2 2 3 4 75%	4420
	21st to end	Day	7% 3 1 3 3 2 3 2 3 5% 69%	4790
August	1st to 10th	Day	4 4 1 4 3 3 3 3 4 5% 65%	4164
	11th to 20th	Day	7% 4 2 4 4 4 4 4 5% 7% 56%	4026
	21st to end	Day	11% 5% 2 4 3 3 4 3 5% 6% 54%	4260
September	1st to 10th	Day	9% 4 1 4 3 2 3 3 3 7% 60%	2280
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 4 7% 43%	2280
	21st to end	Day	18% 6% 2 5% 4 3 4 2 4 7% 45%	2008
October	1st to 10th	Day	19% 6% 2 3 3 2 2 3 4 6% 50%	3180
	11th to 20th	Day	23% 7% 2 6% 4 3 4 4 5% 7% 34%	3161
	21st to end	Day	31% 10% 3 6% 4 4 4 3 5% 6% 24%	3336
November	1st to 10th	Day	34% 10% 4 7% 4 4 4 2 5% 7% 18%	1684
	11th to 20th	Day	36% 10% 3 7% 4 3 3 4 5% 5% 20%	1600
	21st to end	Day	29% 14% 3 7% 4 4 4 3 4 5% 24%	1600
December	1st to 10th	Day	30% 12% 3 6% 4 4 3 3 3 4 28%	1560
	11th to 20th	Day	34% 12% 3 6% 4 4 4 3 6% 5% 20%	1928
	21st to end	Day	34% 15% 4 8% 4 3 4 2 3 4 18%	2794
January	1st to 10th	Night	38% 20% 3 6% 5% 4 4 2 3 3 13%	4406
	11th to 20th	Night	41% 15% 2 6% 3 3 2 2 3 4 18%	4420
	21st to end	Night	40% 13% 3 7% 4 4 3 3 3 4 17%	4638
February	1st to 10th	Night	31% 16% 4 6% 5% 4 3 2 4 5% 19%	2470
	11th to 20th	Night	34% 15% 3 5% 3 4 3 2 4 5% 23%	2402
	21st to end	Night	32% 19% 2 5% 3 4 3 2 4 6% 19%	1944
March	1st to 10th	Night	20% 17% 4 9% 6% 4 4 3 5% 6% 21%	3618
	11th to 20th	Night	22% 10% 2 5% 3 3 3 3 3 5% 42%	3490
	21st to end	Night	33% 17% 4 8% 5% 4 4 3 4 4 14%	3715
April	1st to 10th	Night	31% 18% 3 6% 5% 4 3 2 3 4 21%	1900
	11th to 20th	Night	27% 14% 3 6% 4 3 3 3 5% 6% 28%	1879
	21st to end	Night	31% 13% 2 6% 3 4 3 2 5% 5% 26%	1743
May	1st to 10th	Night	31% 13% 3 5% 2 2 2 2 3 3 34%	2577
	11th to 20th	Night	18% 9% 2 5% 4 3 3 3 4 5% 44%	2516
	21st to end	Night	30% 10% 2 6% 4 3 4 3 5% 6% 27%	2762
June	1st to 10th	Night	24% 8% 3 6% 3 3 4 3 4 5% 36%	1520
	11th to 20th	Night	26% 12% 3 7% 5% 3 3 3 4 5% 31%	1520
	21st to end	Night	14% 6% 2 5% 3 3 3 3 4 5% 52%	1520
July	1st to 10th	Night	8% 3 1 2 2 2 1 2 2 3 74%	2540
	11th to 20th	Night	4 3 1 3 3 2 2 2 2 3 75%	2540
	21st to end	Night	7% 3 1 2 2 1 1 2 3 5% 73%	2761
August	1st to 10th	Night	5% 2 1 3 2 2 2 3 3 7% 70%	2770
	11th to 20th	Night	12% 6% 2 4 4 3 4 3 4 5% 54%	2812
	21st to end	Night	15% 5% 2 4 3 2 3 2 3 4 58%	3402
September	1st to 10th	Night	10% 3 1 4 2 2 3 2 5% 4 64%	1900
	11th to 20th	Night	17% 6% 1 5% 4 4 4 2 4 5% 48%	1900
	21st to end	Night	17% 6% 2 4 3 3 3 3 4 7% 47%	2170
October	1st to 10th	Night	18% 6% 2 4 2 2 2 2 3 6% 51%	3800
	11th to 20th	Night	19% 8% 3 6% 4 4 4 4 6% 7% 37%	3777
	21st to end	Night	32% 11% 3 7% 4 4 3 3 4 5% 25%	4228
November	1st to 10th	Night	35% 10% 3 7% 5% 4 4 2 4 5% 22%	2612
	11th to 20th	Night	39% 10% 3 6% 4 3 3 3 4 4 21%	2800
	21st to end	Night	30% 12% 2 6% 5% 3 4 2 4 4 28%	2800
December	1st to 10th	Night	31% 10% 3 6% 4 3 3 3 4 5% 28%	2736
	11th to 20th	Night	32% 12% 3 7% 4 4 4 3 4 6% 21%	3276
	21st to end	Night	32% 15% 3 7% 5% 5% 4 3 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	80% 4 5% 7% 3 1	2539
	11th to 20th	Day	72% 5% 5% 11% 3 4	2540
	21st to end	Day	74% 4 5% 9% 6% 2	3022
February	1st to 10th	Day	69% 7% 8% 9% 6% 1	1710
	11th to 20th	Day	71% 5% 6% 11% 4 3	1674
	21st to end	Day	71% 5% 8% 7% 7% 2	1509
March	1st to 10th	Day	65% 6% 8% 15% 5% 1	3252
	11th to 20th	Day	55% 4 4 24% 12%	3490
	21st to end	Day	74% 8% 8% 7% 4	3937
April	1st to 10th	Day	72% 6% 8% 10% 3	2280
	11th to 20th	Day	67% 5% 8% 10% 8% 2	2252
	21st to end	Day	65% 7% 9% 12% 6% 2	2435
May	1st to 10th	Day	58% 7% 9% 15% 11%	4384
	11th to 20th	Day	44% 7% 19% 20% 9%	4380
	21st to end	Day	62% 11% 14% 12% 2	4814
June	1st to 10th	Day	56% 7% 14% 16% 6%	2660
	11th to 20th	Day	61% 7% 14% 12% 6%	2660
	21st to end	Day	36% 6% 16% 26% 12% 4	2660
July	1st to 10th	Day	19% 5% 9% 16% 20% 31%	4351
	11th to 20th	Day	15% 3 6% 18% 35% 22%	4345
	21st to end	Day	19% 4 10% 25% 35% 7%	4639
August	1st to 10th	Day	21% 5% 9% 26% 26% 13%	4148
	11th to 20th	Day	27% 7% 16% 33% 13% 5%	4065
	21st to end	Day	32% 6% 10% 22% 19% 11%	4259
September	1st to 10th	Day	26% 4 10% 27% 20% 14%	2280
	11th to 20th	Day	41% 6% 11% 17% 15% 9%	2280
	21st to end	Day	41% 6% 11% 20% 15% 8%	2008
October	1st to 10th	Day	37% 5% 7% 22% 23% 6%	3180
	11th to 20th	Day	50% 6% 13% 17% 12% 2	3161
	21st to end	Day	60% 7% 7% 16% 10% 1	3336
November	1st to 10th	Day	68% 5% 9% 11% 5% 1	1684
	11th to 20th	Day	68% 6% 7% 10% 6% 2	1600
	21st to end	Day	64% 6% 6% 7% 15% 2	1600
December	1st to 10th	Day	62% 5% 8% 11% 12% 3	1560
	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	79% 4 5% 7% 4 1	4406
	11th to 20th	Night	71% 5% 6% 11% 4 3	4420
	21st to end	Night	74% 4 6% 8% 6% 2	4638
February	1st to 10th	Night	70% 5% 8% 9% 6% 2	2470
	11th to 20th	Night	67% 5% 8% 11% 7% 3	2404
	21st to end	Night	70% 4 7% 10% 8% 2	1944
March	1st to 10th	Night	66% 6% 8% 14% 4 1	3618
	11th to 20th	Night	50% 5% 9% 22% 13% 1	3490
	21st to end	Night	76% 6% 8% 8% 2	3715
April	1st to 10th	Night	70% 6% 11% 10% 4	1900
	11th to 20th	Night	61% 7% 11% 11% 6% 3	1879
	21st to end	Night	64% 5% 11% 12% 6% 2	1743
May	1st to 10th	Night	58% 7% 7% 17% 10% 1	2577
	11th to 20th	Night	42% 12% 16% 23% 6% 2	2516
	21st to end	Night	58% 13% 18% 9% 2	2762
June	1st to 10th	Night	54% 6% 15% 18% 6% 1	1520
	11th to 20th	Night	59% 5% 15% 16% 5% 1	1520
	21st to end	Night	37% 6% 16% 26% 10% 5%	1520
July	1st to 10th	Night	18% 4 6% 20% 26% 25%	2500
	11th to 20th	Night	18% 3 6% 19% 33% 21%	2492
	21st to end	Night	16% 4 12% 26% 36% 8%	2674
August	1st to 10th	Night	17% 4 9% 31% 26% 12%	2762
	11th to 20th	Night	32% 7% 19% 25% 12% 5%	2839
	21st to end	Night	32% 5% 9% 25% 15% 13%	3402
September	1st to 10th	Night	25% 6% 12% 25% 19% 13%	1900
	11th to 20th	Night	42% 6% 10% 19% 11% 12%	1900
	21st to end	Night	38% 7% 13% 18% 15% 10%	2170
October	1st to 10th	Night	37% 4 6% 23% 26% 4	3800
	11th to 20th	Night	47% 7% 12% 18% 13% 3	3777
	21st to end	Night	62% 6% 7% 13% 10% 3	4228
November	1st to 10th	Night	67% 5% 6% 11% 9% 1	2612
	11th to 20th	Night	69% 6% 7% 9% 8% 3	2800
	21st to end	Night	61% 5% 6% 10% 14% 4	2800
December	1st to 10th	Night	60% 5% 9% 12% 13% 2	2736
	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	41% 11% 31% 9% 6% 1	180
	21st to end	Day	40% 12% 19% 20% 8% 1	335
February	1st to 10th	Day	41% 15% 17% 20% 6% 1	370
	11th to 20th	Day	37% 18% 25% 17% 3 1	365
	21st to end	Day	40% 16% 23% 18% 4	353
March	1st to 10th	Day	34% 18% 27% 16% 5%	460
	11th to 20th	Day	32% 17% 23% 20% 7% 2	460
	21st to end	Day	36% 20% 22% 17% 4	506
April	1st to 10th	Day	38% 17% 19% 18% 6% 1	460
	11th to 20th	Day	31% 20% 28% 14% 5% 2	452
	21st to end	Day	29% 16% 28% 20% 7% 1	460
May	1st to 10th	Day	24% 17% 26% 23% 8% 3	463
	11th to 20th	Day	30% 13% 21% 23% 11% 2	488
	21st to end	Day	28% 10% 23% 24% 12% 2	529
June	1st to 10th	Day	26% 11% 20% 27% 13% 3	490
	11th to 20th	Day	24% 15% 27% 23% 9% 1	490
	21st to end	Day	11% 7% 27% 35% 16% 4	490
July	1st to 10th	Day	8% 5% 24% 43% 17% 3	486
	11th to 20th	Day	4 8% 26% 40% 19% 3	484
	21st to end	Day	6% 3 21% 45% 20% 6%	531
August	1st to 10th	Day	5% 6% 16% 49% 17% 7%	487
	11th to 20th	Day	5% 5% 21% 37% 26% 6%	477
	21st to end	Day	9% 8% 27% 35% 16% 5%	539
September	1st to 10th	Day	10% 7% 26% 35% 18% 3	490
	11th to 20th	Day	16% 8% 22% 33% 18% 2	490
	21st to end	Day	19% 10% 26% 31% 14% 2	490
October	1st to 10th	Day	22% 11% 22% 26% 16% 2	490
	11th to 20th	Day	26% 11% 21% 27% 15% 1	490
	21st to end	Day	34% 13% 21% 21% 10% 2	476
November	1st to 10th	Day	35% 17% 17% 23% 7% 2	260
	11th to 20th	Day	38% 14% 25% 15% 8% 2	200
	21st to end	Day	32% 16% 20% 22% 11% 1	200
December	1st to 10th	Day	36% 14% 19% 17% 10% 4	190
	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% 22% 19% 8%	760
	21st to end	Night	36% 10% 23% 23% 7% 1	836
February	1st to 10th	Night	37% 11% 20% 26% 5% 1	760
	11th to 20th	Night	39% 12% 17% 24% 8%	744
	21st to end	Night	41% 13% 19% 21% 6%	628
March	1st to 10th	Night	33% 13% 19% 24% 10% 1	760
	11th to 20th	Night	32% 11% 20% 27% 10% 1	760
	21st to end	Night	38% 13% 17% 21% 9% 1	836
April	1st to 10th	Night	38% 11% 17% 23% 11% 1	760
	11th to 20th	Night	31% 10% 19% 24% 13% 2	751
	21st to end	Night	35% 11% 12% 29% 11% 1	603
May	1st to 10th	Night	27% 10% 14% 31% 15% 2	404
	11th to 20th	Night	24% 7% 13% 30% 24% 1	374
	21st to end	Night	28% 6% 16% 28% 20% 2	411
June	1st to 10th	Night	28% 5% 15% 30% 21% 1	380
	11th to 20th	Night	28% 9% 17% 31% 16% 1	380
	21st to end	Night	14% 5% 14% 39% 26% 1	380
July	1st to 10th	Night	9% 3 9% 41% 37% 1	370
	11th to 20th	Night	6% 2 14% 46% 31% 1	368
	21st to end	Night	4 2 7% 44% 40% 3	416
August	1st to 10th	Night	6% 2 7% 33% 46% 6%	515
	11th to 20th	Night	6% 1 9% 32% 44% 7%	564
	21st to end	Night	9% 4 13% 40% 30% 4	779
September	1st to 10th	Night	11% 3 16% 36% 32% 2	760
	11th to 20th	Night	15% 5% 12% 34% 30% 5%	760
	21st to end	Night	18% 5% 15% 33% 25% 3	760
October	1st to 10th	Night	24% 5% 15% 34% 20% 3	760
	11th to 20th	Night	24% 8% 14% 34% 19% 2	760
	21st to end	Night	31% 10% 21% 25% 11% 3	836
November	1st to 10th	Night	39% 10% 18% 26% 7%	780
	11th to 20th	Night	42% 11% 21% 20% 5%	800
	21st to end	Night	32% 11% 22% 28% 7%	800
December	1st to 10th	Night	34% 11% 22% 24% 7% 1	782
	11th to 20th	Night	41% 12% 21% 20% 6%	760
	21st to end	Night	44% 13% 22% 16% 4 1	836

Page generated at 2024-12-03 03:45:12. Version ac07

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