Lady Lake Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lady Lake Astronomical Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	20% 15% 5% 11% 6% 4 4 3 4 5% 21%	127129
	Night	20% 15% 6% 12% 6% 5% 4 3 4 5% 20%	123818
Transparency	Day	38% 40% 8% 10% 3	130599
	Night	39% 40% 8% 9% 3	128463
Seeing	Day	27% 20% 30% 17% 5% 1	19648
	Night	28% 19% 30% 18% 5%	26226

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	21% 17% 9% 16% 5% 4 3 3 3 4 15%	3176
	11th to 20th	Day	18% 21% 9% 17% 5% 3 4 3 3 3 15%	3525
	21st to end	Day	11% 15% 8% 19% 8% 5% 6% 3 3 5% 18%	3982
February	1st to 10th	Day	20% 14% 7% 12% 7% 5% 6% 3 4 5% 15%	1734
	11th to 20th	Day	20% 16% 5% 13% 8% 5% 5% 4 5% 5% 14%	1761
	21st to end	Day	14% 16% 6% 15% 8% 6% 6% 4 4 5% 15%	1650
March	1st to 10th	Day	23% 15% 6% 15% 6% 5% 4 3 4 4 16%	4514
	11th to 20th	Day	22% 16% 9% 11% 6% 4 5% 3 4 4 17%	4980
	21st to end	Day	23% 21% 8% 12% 6% 4 3 2 3 4 14%	5467
April	1st to 10th	Day	21% 21% 5% 10% 7% 5% 4 3 4 4 16%	2419
	11th to 20th	Day	24% 17% 4 10% 5% 3 3 4 4 4 22%	2571
	21st to end	Day	25% 18% 5% 10% 5% 4 3 3 4 5% 19%	2600
May	1st to 10th	Day	22% 25% 6% 9% 4 3 3 2 4 5% 17%	5885
	11th to 20th	Day	23% 17% 5% 9% 5% 4 4 3 4 5% 21%	6399
	21st to end	Day	20% 20% 6% 9% 5% 4 4 3 4 5% 19%	7428
June	1st to 10th	Day	28% 17% 5% 9% 5% 4 4 3 4 4 17%	3000
	11th to 20th	Day	23% 14% 4 8% 6% 4 4 4 5% 6% 23%	3000
	21st to end	Day	22% 14% 4 8% 6% 3 4 4 4 6% 24%	3000
July	1st to 10th	Day	22% 13% 4 9% 5% 5% 5% 4 5% 6% 22%	6800
	11th to 20th	Day	14% 10% 4 10% 7% 6% 5% 4 6% 6% 29%	6768
	21st to end	Day	16% 10% 3 8% 5% 5% 5% 4 6% 7% 31%	6927
August	1st to 10th	Day	19% 12% 4 10% 6% 5% 5% 4 5% 6% 23%	4335
	11th to 20th	Day	18% 9% 3 9% 5% 6% 5% 4 6% 7% 28%	4176
	21st to end	Day	17% 11% 4 8% 5% 4 5% 3 5% 7% 31%	4675
September	1st to 10th	Day	19% 10% 3 8% 4 4 5% 3 5% 7% 31%	2395
	11th to 20th	Day	22% 10% 3 8% 4 5% 5% 3 4 7% 29%	2200
	21st to end	Day	18% 10% 4 7% 5% 5% 5% 3 6% 6% 33%	2200
October	1st to 10th	Day	19% 13% 3 8% 3 5% 4 3 5% 6% 28%	2096
	11th to 20th	Day	22% 15% 4 10% 6% 4 5% 3 4 4 23%	1951
	21st to end	Day	22% 15% 4 10% 7% 5% 5% 3 4 6% 19%	1980
November	1st to 10th	Day	21% 15% 4 12% 4 5% 5% 3 4 5% 23%	1813
	11th to 20th	Day	24% 16% 6% 9% 6% 4 4 3 5% 6% 17%	1680
	21st to end	Day	26% 20% 5% 8% 6% 4 4 2 3 5% 16%	1612
December	1st to 10th	Day	17% 14% 5% 9% 6% 6% 4 4 6% 8% 20%	2304
	11th to 20th	Day	23% 14% 6% 10% 6% 4 4 3 4 4 23%	2628
	21st to end	Day	20% 18% 8% 14% 6% 4 4 4 4 4 13%	3498
January	1st to 10th	Night	18% 20% 8% 13% 7% 5% 4 3 4 4 14%	6789
	11th to 20th	Night	16% 18% 9% 18% 6% 4 4 3 4 4 14%	6379
	21st to end	Night	11% 10% 7% 17% 7% 6% 6% 4 5% 6% 21%	6996
February	1st to 10th	Night	20% 15% 7% 14% 8% 6% 4 3 4 5% 16%	2665
	11th to 20th	Night	21% 13% 5% 12% 8% 6% 6% 5% 4 5% 15%	2523
	21st to end	Night	13% 14% 6% 13% 7% 7% 7% 4 5% 6% 19%	1980
March	1st to 10th	Night	22% 12% 6% 13% 7% 5% 5% 4 5% 5% 18%	5325
	11th to 20th	Night	17% 16% 9% 15% 7% 6% 4 3 4 4 15%	4979
	21st to end	Night	24% 18% 7% 14% 6% 4 4 3 4 3 13%	5465
April	1st to 10th	Night	25% 18% 6% 9% 5% 4 4 3 3 5% 19%	1977
	11th to 20th	Night	23% 15% 4 10% 4 4 4 3 4 4 23%	1778
	21st to end	Night	24% 21% 5% 10% 5% 4 3 3 3 3 20%	1800
May	1st to 10th	Night	24% 18% 8% 13% 5% 4 4 2 3 5% 16%	4075
	11th to 20th	Night	26% 15% 6% 11% 4 4 4 3 4 4 19%	3509
	21st to end	Night	23% 19% 7% 9% 4 4 4 3 4 5% 18%	3468
June	1st to 10th	Night	25% 18% 3 10% 6% 4 4 4 4 4 19%	1400
	11th to 20th	Night	22% 13% 5% 9% 5% 5% 4 4 5% 7% 22%	1400
	21st to end	Night	21% 16% 5% 9% 5% 4 3 4 5% 7% 22%	1400
July	1st to 10th	Night	29% 13% 4 10% 5% 5% 5% 3 4 6% 16%	3179
	11th to 20th	Night	13% 13% 5% 11% 6% 7% 6% 4 6% 6% 23%	3196
	21st to end	Night	13% 10% 5% 12% 5% 5% 5% 3 5% 6% 31%	3948
August	1st to 10th	Night	16% 11% 4 12% 5% 5% 5% 4 6% 8% 23%	2824
	11th to 20th	Night	25% 9% 2 8% 4 3 4 3 5% 7% 31%	2881
	21st to end	Night	23% 11% 4 7% 4 3 4 3 6% 7% 28%	3234
September	1st to 10th	Night	19% 11% 4 8% 5% 5% 4 3 5% 7% 30%	2001
	11th to 20th	Night	22% 11% 3 8% 5% 4 4 4 5% 6% 27%	2200
	21st to end	Night	19% 11% 4 9% 4 4 3 3 6% 6% 32%	2200
October	1st to 10th	Night	20% 10% 4 9% 6% 4 5% 3 5% 6% 27%	2303
	11th to 20th	Night	22% 15% 3 7% 5% 5% 5% 3 6% 6% 23%	2445
	21st to end	Night	23% 15% 5% 9% 5% 5% 4 3 4 5% 22%	2860
November	1st to 10th	Night	23% 13% 4 10% 6% 5% 5% 4 4 6% 22%	2704
	11th to 20th	Night	25% 16% 5% 9% 5% 5% 4 4 4 5% 19%	2940
	21st to end	Night	21% 16% 5% 10% 5% 5% 5% 4 5% 5% 19%	3003
December	1st to 10th	Night	18% 16% 6% 11% 7% 5% 4 3 4 5% 22%	4931
	11th to 20th	Night	26% 14% 6% 10% 5% 4 4 3 4 5% 18%	5581
	21st to end	Night	20% 16% 6% 13% 7% 5% 5% 4 4 4 17%	7480

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	51% 30% 7% 7% 4 1	3177
	11th to 20th	Day	52% 32% 5% 9% 3	3554
	21st to end	Day	44% 33% 6% 11% 6%	3982
February	1st to 10th	Day	26% 63% 4 4 3	1734
	11th to 20th	Day	27% 63% 4 4 1 1	1768
	21st to end	Day	24% 65% 4 3 4 1	1650
March	1st to 10th	Day	46% 33% 5% 10% 4 1	4519
	11th to 20th	Day	48% 32% 7% 7% 5% 1	4980
	21st to end	Day	51% 32% 6% 8% 3	5467
April	1st to 10th	Day	25% 64% 3 5% 3 1	2419
	11th to 20th	Day	24% 64% 4 5% 3	2571
	21st to end	Day	27% 63% 3 5% 2	2600
May	1st to 10th	Day	50% 33% 6% 8% 4	5897
	11th to 20th	Day	46% 32% 8% 11% 3	6403
	21st to end	Day	48% 33% 6% 11% 2	7428
June	1st to 10th	Day	27% 63% 2 6% 2	3000
	11th to 20th	Day	21% 63% 5% 7% 3	3000
	21st to end	Day	24% 62% 5% 7% 3	3000
July	1st to 10th	Day	47% 28% 12% 11% 2	6725
	11th to 20th	Day	37% 28% 17% 13% 5%	6686
	21st to end	Day	34% 27% 18% 17% 3	6730
August	1st to 10th	Day	37% 37% 11% 11% 3	4321
	11th to 20th	Day	28% 38% 14% 17% 2	4215
	21st to end	Day	31% 37% 12% 18% 2	4675
September	1st to 10th	Day	20% 59% 4 12% 4	2395
	11th to 20th	Day	25% 58% 7% 7% 3	2200
	21st to end	Day	23% 59% 7% 7% 4	2200
October	1st to 10th	Day	38% 40% 8% 11% 2	3414
	11th to 20th	Day	28% 38% 10% 16% 7%	3164
	21st to end	Day	36% 40% 10% 11% 4	3191
November	1st to 10th	Day	28% 55% 7% 6% 3	1813
	11th to 20th	Day	32% 57% 5% 4 2	1680
	21st to end	Day	34% 56% 3 4 2	1612
December	1st to 10th	Day	34% 39% 11% 12% 4	2304
	11th to 20th	Day	39% 33% 13% 9% 6%	2627
	21st to end	Day	55% 29% 6% 8% 2	3498
January	1st to 10th	Night	53% 30% 7% 6% 4 1	6789
	11th to 20th	Night	50% 34% 8% 7% 1	6425
	21st to end	Night	40% 35% 7% 11% 6% 1	6996
February	1st to 10th	Night	26% 63% 3 4 3 1	2665
	11th to 20th	Night	25% 64% 5% 5% 1 1	2527
	21st to end	Night	23% 64% 4 6% 3	1980
March	1st to 10th	Night	44% 33% 8% 10% 5% 1	5333
	11th to 20th	Night	50% 34% 6% 5% 4 1	4980
	21st to end	Night	49% 32% 7% 10% 2	5465
April	1st to 10th	Night	25% 63% 3 5% 4 1	1977
	11th to 20th	Night	24% 64% 3 6% 3 1	1778
	21st to end	Night	28% 63% 3 4 2	1800
May	1st to 10th	Night	50% 33% 6% 11% 1	4080
	11th to 20th	Night	50% 30% 6% 9% 5%	3510
	21st to end	Night	49% 32% 7% 9% 3	3469
June	1st to 10th	Night	25% 63% 5% 6% 1	1400
	11th to 20th	Night	20% 64% 7% 6% 2	1400
	21st to end	Night	23% 63% 5% 7% 2	1400
July	1st to 10th	Night	51% 28% 10% 9% 2	3146
	11th to 20th	Night	37% 30% 16% 16% 1	3154
	21st to end	Night	32% 27% 18% 21% 2	3831
August	1st to 10th	Night	30% 40% 16% 12% 2	2813
	11th to 20th	Night	29% 37% 15% 18% 1	2908
	21st to end	Night	34% 38% 9% 16% 3	3233
September	1st to 10th	Night	21% 59% 5% 9% 5% 1	2001
	11th to 20th	Night	28% 59% 6% 5% 2	2200
	21st to end	Night	22% 59% 7% 8% 4	2200
October	1st to 10th	Night	40% 38% 11% 9% 2	3771
	11th to 20th	Night	27% 39% 12% 15% 6%	3981
	21st to end	Night	33% 39% 10% 14% 4	4610
November	1st to 10th	Night	29% 55% 6% 7% 2	2704
	11th to 20th	Night	32% 57% 5% 4 2	2940
	21st to end	Night	30% 57% 5% 5% 2	3003
December	1st to 10th	Night	36% 39% 7% 13% 6%	4931
	11th to 20th	Night	43% 35% 12% 7% 2	5583
	21st to end	Night	50% 32% 7% 8% 3	7480

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	34% 24% 27% 12% 3 1	400
	11th to 20th	Day	28% 27% 29% 12% 4 1	400
	21st to end	Day	27% 28% 32% 10% 3	440
February	1st to 10th	Day	27% 28% 29% 14% 3	400
	11th to 20th	Day	29% 33% 27% 8% 3	396
	21st to end	Day	24% 31% 29% 14% 2	331
March	1st to 10th	Day	30% 29% 30% 9% 2	400
	11th to 20th	Day	27% 22% 31% 16% 3 2	400
	21st to end	Day	29% 25% 31% 11% 4 1	440
April	1st to 10th	Day	32% 26% 26% 13% 3	529
	11th to 20th	Day	31% 20% 30% 13% 5%	689
	21st to end	Day	31% 23% 27% 15% 4	700
May	1st to 10th	Day	29% 22% 29% 14% 5% 1	703
	11th to 20th	Day	24% 16% 34% 18% 6% 1	724
	21st to end	Day	27% 18% 31% 20% 4 1	790
June	1st to 10th	Day	35% 17% 27% 16% 6%	730
	11th to 20th	Day	28% 14% 30% 18% 8% 1	730
	21st to end	Day	25% 12% 33% 23% 5% 2	730
July	1st to 10th	Day	25% 13% 34% 19% 7% 1	720
	11th to 20th	Day	19% 12% 35% 25% 8% 1	718
	21st to end	Day	22% 13% 32% 25% 8% 1	795
August	1st to 10th	Day	23% 10% 31% 24% 10% 2	725
	11th to 20th	Day	21% 13% 27% 29% 8% 2	717
	21st to end	Day	21% 14% 31% 24% 8% 1	803
September	1st to 10th	Day	19% 13% 29% 26% 10% 2	565
	11th to 20th	Day	27% 19% 28% 20% 5% 1	420
	21st to end	Day	22% 21% 32% 18% 6%	420
October	1st to 10th	Day	23% 18% 32% 21% 6%	420
	11th to 20th	Day	30% 18% 31% 15% 5% 1	420
	21st to end	Day	28% 27% 24% 15% 4 2	462
November	1st to 10th	Day	28% 27% 28% 14% 3	425
	11th to 20th	Day	34% 23% 25% 14% 4	430
	21st to end	Day	35% 28% 25% 10% 3	430
December	1st to 10th	Day	28% 24% 31% 13% 5%	406
	11th to 20th	Day	31% 29% 27% 11% 2	400
	21st to end	Day	25% 25% 30% 15% 4 1	440
January	1st to 10th	Night	29% 25% 30% 12% 4	900
	11th to 20th	Night	28% 24% 30% 12% 5% 1	900
	21st to end	Night	26% 26% 31% 15% 2	990
February	1st to 10th	Night	27% 29% 31% 11% 2	900
	11th to 20th	Night	30% 28% 30% 10% 2	878
	21st to end	Night	23% 25% 32% 16% 5%	660
March	1st to 10th	Night	24% 28% 32% 13% 3	784
	11th to 20th	Night	23% 20% 28% 25% 5%	600
	21st to end	Night	32% 21% 29% 15% 3	660
April	1st to 10th	Night	31% 21% 29% 15% 4 1	600
	11th to 20th	Night	29% 20% 31% 16% 4	594
	21st to end	Night	32% 19% 27% 18% 4 1	600
May	1st to 10th	Night	30% 15% 31% 19% 5% 1	600
	11th to 20th	Night	29% 12% 29% 22% 7%	592
	21st to end	Night	29% 15% 31% 20% 4	649
June	1st to 10th	Night	32% 14% 28% 20% 6%	600
	11th to 20th	Night	28% 11% 29% 24% 7%	600
	21st to end	Night	25% 10% 36% 22% 6% 1	600
July	1st to 10th	Night	23% 11% 36% 23% 5% 1	586
	11th to 20th	Night	23% 9% 38% 25% 5%	582
	21st to end	Night	23% 10% 36% 23% 7%	656
August	1st to 10th	Night	27% 7% 29% 28% 8% 1	598
	11th to 20th	Night	23% 10% 29% 30% 7%	592
	21st to end	Night	23% 11% 34% 25% 7%	660
September	1st to 10th	Night	22% 12% 30% 29% 8%	600
	11th to 20th	Night	27% 14% 31% 22% 6%	600
	21st to end	Night	25% 17% 31% 22% 6%	600
October	1st to 10th	Night	25% 16% 32% 21% 6%	658
	11th to 20th	Night	30% 20% 27% 18% 5% 1	755
	21st to end	Night	31% 21% 24% 19% 4 1	1001
November	1st to 10th	Night	30% 24% 28% 15% 3	930
	11th to 20th	Night	34% 20% 25% 17% 4	950
	21st to end	Night	29% 25% 30% 12% 4	950
December	1st to 10th	Night	28% 23% 29% 15% 4	911
	11th to 20th	Night	35% 27% 26% 10% 2	900
	21st to end	Night	26% 24% 29% 16% 4 1	990

Page generated at 2025-11-30 02:00:53. Version ac07

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