Lake Hall
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Hall clear sky chart from 2005-11-06 to 2025-01-07.

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	7% 4 2 4 3 3 3 3 5% 6% 60%	109139
	Night	6% 4 1 4 3 3 3 3 5% 7% 61%	108594
Transparency	Day	25% 4 8% 24% 27% 11%	108903
	Night	23% 4 8% 24% 28% 14%	108420
Seeing	Day	9% 6% 24% 33% 23% 6%	15491
	Night	8% 7% 32% 38% 14% 1	25503

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	6% 6% 2 5% 4 3 3 2 4 6% 59%	2901
	11th to 20th	Day	6% 4 1 2 2 2 3 3 4 5% 66%	2850
	21st to end	Day	12% 7% 2 5% 3 2 3 2 4 6% 53%	3294
February	1st to 10th	Day	7% 8% 3 5% 2 3 3 2 4 5% 59%	1900
	11th to 20th	Day	7% 6% 2 5% 3 2 3 3 3 6% 60%	1849
	21st to end	Day	7% 7% 2 4 3 3 2 3 3 5% 60%	1570
March	1st to 10th	Day	9% 5% 2 3 2 2 3 2 4 6% 61%	3155
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 4 6% 58%	3480
	21st to end	Day	8% 8% 3 7% 4 4 4 4 4 6% 48%	3814
April	1st to 10th	Day	7% 4 2 3 3 2 3 3 5% 6% 61%	2204
	11th to 20th	Day	11% 6% 2 5% 2 3 4 2 4 5% 55%	2251
	21st to end	Day	10% 3 2 3 3 3 3 4 4 6% 58%	2408
May	1st to 10th	Day	13% 6% 2 5% 3 3 3 3 4 6% 52%	4120
	11th to 20th	Day	11% 5% 2 5% 3 3 3 2 4 5% 56%	4082
	21st to end	Day	10% 4 2 5% 3 4 4 3 5% 5% 56%	4489
June	1st to 10th	Day	5% 4 1 4 3 4 5% 5% 7% 9% 54%	2470
	11th to 20th	Day	4 3 1 4 3 4 4 3 6% 8% 58%	2470
	21st to end	Day	3 4 1 4 3 3 5% 3 5% 8% 61%	2470
July	1st to 10th	Day	8% 4 2 5% 4 4 5% 4 7% 8% 50%	4120
	11th to 20th	Day	4 2 1 4 3 3 4 3 5% 8% 61%	4120
	21st to end	Day	2 2 1 3 3 3 4 3 6% 9% 63%	4466
August	1st to 10th	Day	4 3 1 4 3 3 3 3 6% 9% 62%	4103
	11th to 20th	Day	4 2 1 4 3 3 4 3 5% 8% 63%	3733
	21st to end	Day	3 2 1 4 3 3 4 3 6% 7% 64%	4180
September	1st to 10th	Day	7% 4 2 5% 4 4 3 3 5% 6% 58%	2161
	11th to 20th	Day	8% 4 2 4 3 4 4 4 6% 7% 53%	2090
	21st to end	Day	8% 2 1 4 3 3 3 3 5% 6% 64%	2090
October	1st to 10th	Day	5% 2 1 2 2 2 2 2 3 4 75%	3480
	11th to 20th	Day	6% 2 1 3 3 3 3 3 4 6% 67%	3317
	21st to end	Day	6% 2 1 2 2 2 3 1 4 5% 71%	3320
November	1st to 10th	Day	7% 4 2 4 2 2 2 2 4 6% 65%	1763
	11th to 20th	Day	6% 4 1 2 2 2 2 2 4 5% 70%	1800
	21st to end	Day	10% 5% 1 4 2 2 2 2 3 5% 64%	1800
December	1st to 10th	Day	5% 4 1 4 3 2 3 3 5% 6% 64%	2940
	11th to 20th	Day	5% 4 1 4 3 3 4 3 4 5% 66%	3391
	21st to end	Day	8% 8% 3 6% 4 4 4 3 4 4 53%	4488
January	1st to 10th	Night	9% 4 2 5% 3 4 3 3 5% 6% 57%	4187
	11th to 20th	Night	4 3 1 4 3 3 3 3 4 5% 66%	4120
	21st to end	Night	11% 10% 2 4 3 2 2 2 4 5% 54%	4403
February	1st to 10th	Night	10% 6% 2 4 2 3 3 3 5% 6% 56%	2280
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 4 6% 59%	2218
	21st to end	Night	7% 5% 2 5% 3 3 4 3 5% 6% 59%	1884
March	1st to 10th	Night	6% 5% 2 5% 4 3 3 3 4 5% 62%	3707
	11th to 20th	Night	7% 4 2 4 3 3 2 2 4 6% 63%	3480
	21st to end	Night	6% 5% 2 6% 4 4 4 3 6% 7% 54%	3817
April	1st to 10th	Night	5% 4 1 3 4 4 4 4 5% 6% 61%	1971
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 6% 7% 55%	1877
	21st to end	Night	9% 3 2 3 3 3 4 3 5% 7% 59%	1771
May	1st to 10th	Night	16% 6% 1 4 3 2 3 3 3 4 55%	2850
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 5% 7% 51%	2823
	21st to end	Night	10% 4 1 4 3 3 3 3 4 6% 60%	3098
June	1st to 10th	Night	4 3 1 4 2 4 4 4 6% 12% 55%	1710
	11th to 20th	Night	3 3 1 4 3 3 4 4 7% 11% 58%	1710
	21st to end	Night	4 4 1 3 3 3 3 3 6% 9% 61%	1710
July	1st to 10th	Night	5% 4 1 5% 4 4 4 4 7% 9% 53%	2850
	11th to 20th	Night	3 2 1 3 2 3 3 4 7% 12% 59%	2850
	21st to end	Night	1 2 1 3 3 3 4 3 5% 9% 66%	3097
August	1st to 10th	Night	2 2 1 3 2 2 3 3 6% 10% 66%	2836
	11th to 20th	Night	3 3 1 4 3 4 4 5% 8% 12% 54%	3103
	21st to end	Night	2 2 1 3 2 3 3 3 6% 10% 64%	3487
September	1st to 10th	Night	7% 4 1 3 3 3 4 3 5% 7% 59%	2019
	11th to 20th	Night	10% 4 3 5% 3 3 4 3 6% 7% 51%	2090
	21st to end	Night	6% 3 1 3 3 3 2 3 5% 6% 65%	2090
October	1st to 10th	Night	4 2 1 2 2 2 2 2 3 4 77%	3480
	11th to 20th	Night	7% 3 1 4 2 2 2 2 4 6% 67%	3555
	21st to end	Night	5% 2 1 2 1 2 2 2 4 7% 73%	4230
November	1st to 10th	Night	7% 3 1 2 2 2 3 2 5% 5% 68%	2535
	11th to 20th	Night	5% 3 1 2 2 2 3 3 4 5% 70%	2600
	21st to end	Night	7% 4 1 4 3 3 3 3 5% 6% 62%	2600
December	1st to 10th	Night	5% 2 1 3 2 2 2 3 4 7% 68%	4250
	11th to 20th	Night	5% 3 1 4 3 3 3 2 5% 6% 65%	4816
	21st to end	Night	8% 7% 2 5% 3 3 3 3 4 5% 56%	6490

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	27% 4 7% 24% 29% 10%	2902
	11th to 20th	Day	21% 3 9% 25% 35% 7%	2850
	21st to end	Day	34% 3 5% 24% 28% 6%	3294
February	1st to 10th	Day	30% 2 7% 24% 27% 10%	1900
	11th to 20th	Day	28% 3 7% 26% 25% 12%	1859
	21st to end	Day	29% 2 6% 17% 29% 17%	1570
March	1st to 10th	Day	26% 3 6% 14% 26% 26%	3155
	11th to 20th	Day	28% 4 7% 23% 29% 9%	3480
	21st to end	Day	35% 4 10% 22% 21% 8%	3814
April	1st to 10th	Day	24% 4 8% 22% 24% 18%	2204
	11th to 20th	Day	33% 4 7% 19% 23% 15%	2254
	21st to end	Day	27% 4 9% 23% 28% 9%	2408
May	1st to 10th	Day	34% 5% 9% 16% 20% 16%	4120
	11th to 20th	Day	30% 5% 9% 26% 20% 9%	4086
	21st to end	Day	29% 7% 9% 19% 20% 17%	4489
June	1st to 10th	Day	24% 7% 16% 28% 16% 8%	2470
	11th to 20th	Day	23% 5% 10% 26% 24% 10%	2470
	21st to end	Day	21% 6% 12% 25% 25% 11%	2470
July	1st to 10th	Day	30% 6% 10% 28% 21% 5%	4056
	11th to 20th	Day	20% 5% 10% 31% 29% 6%	4051
	21st to end	Day	18% 5% 11% 31% 31% 4	4325
August	1st to 10th	Day	19% 5% 11% 23% 32% 11%	4090
	11th to 20th	Day	19% 5% 11% 25% 30% 11%	3769
	21st to end	Day	19% 6% 12% 30% 28% 6%	4179
September	1st to 10th	Day	28% 5% 8% 22% 23% 14%	2161
	11th to 20th	Day	29% 6% 11% 21% 27% 7%	2090
	21st to end	Day	22% 4 7% 24% 33% 11%	2090
October	1st to 10th	Day	16% 3 6% 14% 37% 24%	3480
	11th to 20th	Day	19% 3 6% 25% 28% 19%	3317
	21st to end	Day	17% 2 5% 28% 36% 12%	3320
November	1st to 10th	Day	22% 3 6% 23% 30% 17%	1763
	11th to 20th	Day	18% 2 6% 25% 35% 14%	1800
	21st to end	Day	26% 2 5% 20% 34% 14%	1800
December	1st to 10th	Day	22% 3 6% 36% 25% 8%	2940
	11th to 20th	Day	23% 3 6% 18% 36% 15%	3389
	21st to end	Day	34% 3 7% 23% 24% 9%	4488
January	1st to 10th	Night	27% 4 7% 28% 27% 7%	4187
	11th to 20th	Night	20% 4 13% 21% 31% 10%	4120
	21st to end	Night	34% 3 7% 19% 26% 10%	4403
February	1st to 10th	Night	29% 4 8% 21% 26% 12%	2280
	11th to 20th	Night	28% 3 6% 23% 25% 15%	2218
	21st to end	Night	26% 4 5% 19% 26% 21%	1884
March	1st to 10th	Night	25% 3 5% 16% 23% 28%	3707
	11th to 20th	Night	24% 3 7% 27% 23% 16%	3480
	21st to end	Night	28% 5% 9% 25% 20% 12%	3817
April	1st to 10th	Night	22% 5% 9% 18% 26% 20%	1971
	11th to 20th	Night	28% 5% 9% 20% 23% 15%	1877
	21st to end	Night	25% 5% 11% 24% 24% 10%	1771
May	1st to 10th	Night	33% 5% 8% 17% 19% 19%	2850
	11th to 20th	Night	32% 6% 11% 22% 20% 9%	2824
	21st to end	Night	26% 5% 9% 17% 17% 25%	3099
June	1st to 10th	Night	20% 8% 16% 31% 18% 7%	1710
	11th to 20th	Night	19% 6% 15% 26% 24% 10%	1710
	21st to end	Night	21% 5% 12% 26% 23% 14%	1710
July	1st to 10th	Night	25% 6% 13% 33% 19% 4	2805
	11th to 20th	Night	16% 4 11% 29% 33% 8%	2796
	21st to end	Night	15% 4 12% 26% 36% 7%	2999
August	1st to 10th	Night	14% 4 10% 25% 31% 15%	2826
	11th to 20th	Night	22% 6% 10% 26% 26% 9%	3133
	21st to end	Night	16% 6% 13% 32% 27% 6%	3487
September	1st to 10th	Night	24% 6% 9% 22% 25% 14%	2019
	11th to 20th	Night	31% 6% 10% 18% 27% 8%	2090
	21st to end	Night	21% 4 7% 23% 31% 14%	2090
October	1st to 10th	Night	14% 3 6% 15% 37% 26%	3480
	11th to 20th	Night	21% 2 6% 20% 34% 17%	3555
	21st to end	Night	14% 2 4 25% 38% 16%	4230
November	1st to 10th	Night	19% 2 7% 23% 30% 19%	2535
	11th to 20th	Night	17% 3 5% 25% 33% 16%	2600
	21st to end	Night	24% 3 5% 19% 33% 16%	2600
December	1st to 10th	Night	18% 2 6% 33% 32% 9%	4250
	11th to 20th	Night	22% 2 4 22% 35% 16%	4817
	21st to end	Night	30% 4 7% 26% 24% 10%	6490

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	10% 10% 35% 32% 13% 1	288
	11th to 20th	Day	13% 10% 31% 31% 13% 1	270
	21st to end	Day	8% 12% 36% 31% 12%	297
February	1st to 10th	Day	14% 11% 35% 32% 7% 1	270
	11th to 20th	Day	11% 8% 44% 26% 10% 1	270
	21st to end	Day	12% 17% 40% 23% 8%	225
March	1st to 10th	Day	12% 12% 37% 31% 7%	270
	11th to 20th	Day	16% 13% 35% 25% 10% 1	270
	21st to end	Day	14% 14% 39% 24% 9% 1	297
April	1st to 10th	Day	11% 18% 40% 20% 10%	384
	11th to 20th	Day	13% 17% 45% 21% 4	452
	21st to end	Day	13% 14% 37% 27% 8% 2	588
May	1st to 10th	Day	11% 9% 37% 31% 10% 1	653
	11th to 20th	Day	12% 7% 27% 32% 18% 4	675
	21st to end	Day	10% 7% 26% 36% 17% 4	734
June	1st to 10th	Day	6% 3 19% 41% 25% 5%	680
	11th to 20th	Day	5% 3 23% 44% 23% 3	680
	21st to end	Day	4 2 14% 45% 27% 8%	680
July	1st to 10th	Day	6% 1 8% 34% 39% 13%	671
	11th to 20th	Day	3 1 8% 34% 43% 12%	668
	21st to end	Day	2 1 4 32% 45% 15%	739
August	1st to 10th	Day	5% 1 8% 34% 44% 7%	676
	11th to 20th	Day	5% 2 9% 36% 36% 11%	484
	21st to end	Day	5% 1 8% 32% 39% 16%	539
September	1st to 10th	Day	6% 2 9% 29% 40% 15%	371
	11th to 20th	Day	7% 1 12% 37% 32% 11%	300
	21st to end	Day	10% 3 11% 28% 34% 14%	300
October	1st to 10th	Day	7% 1 20% 39% 23% 9%	300
	11th to 20th	Day	7% 7% 26% 34% 23% 4	300
	21st to end	Day	16% 5% 29% 29% 18% 4	330
November	1st to 10th	Day	12% 7% 28% 32% 18% 3	300
	11th to 20th	Day	11% 10% 27% 29% 18% 4	300
	21st to end	Day	17% 9% 29% 26% 15% 4	300
December	1st to 10th	Day	7% 7% 39% 31% 14% 1	300
	11th to 20th	Day	9% 8% 32% 36% 13% 1	300
	21st to end	Day	16% 12% 38% 25% 8% 1	330
January	1st to 10th	Night	8% 8% 36% 37% 10%	981
	11th to 20th	Night	8% 9% 32% 40% 9% 1	950
	21st to end	Night	9% 7% 34% 40% 9%	968
February	1st to 10th	Night	13% 9% 40% 32% 6% 1	760
	11th to 20th	Night	12% 8% 42% 32% 6%	744
	21st to end	Night	10% 14% 42% 31% 3	628
March	1st to 10th	Night	9% 10% 42% 34% 4	746
	11th to 20th	Night	13% 12% 37% 32% 6%	570
	21st to end	Night	9% 14% 44% 29% 4	627
April	1st to 10th	Night	7% 13% 48% 28% 4	570
	11th to 20th	Night	13% 12% 50% 23% 2	563
	21st to end	Night	11% 10% 43% 30% 6% 1	570
May	1st to 10th	Night	13% 9% 43% 31% 4	570
	11th to 20th	Night	10% 7% 36% 32% 12% 1	561
	21st to end	Night	7% 6% 36% 38% 12%	617
June	1st to 10th	Night	5% 4 28% 48% 15% 1	570
	11th to 20th	Night	4 3 40% 44% 10%	570
	21st to end	Night	5% 2 27% 45% 21%	570
July	1st to 10th	Night	5% 1 15% 45% 31% 3	555
	11th to 20th	Night	5% 1 9% 51% 33% 2	552
	21st to end	Night	2 6% 53% 36% 3	624
August	1st to 10th	Night	2 1 8% 50% 38% 1	567
	11th to 20th	Night	6% 2 13% 46% 32% 1	564
	21st to end	Night	4 10% 43% 42% 2	627
September	1st to 10th	Night	8% 1 13% 46% 31% 1	570
	11th to 20th	Night	11% 2 20% 40% 26% 1	570
	21st to end	Night	7% 2 20% 45% 24% 1	570
October	1st to 10th	Night	8% 4 24% 42% 21% 1	570
	11th to 20th	Night	10% 6% 30% 41% 13%	627
	21st to end	Night	9% 7% 32% 35% 16%	897
November	1st to 10th	Night	8% 5% 32% 41% 13% 1	975
	11th to 20th	Night	7% 7% 36% 39% 11% 1	1000
	21st to end	Night	9% 8% 33% 36% 13% 1	1000
December	1st to 10th	Night	8% 8% 34% 39% 11%	1000
	11th to 20th	Night	11% 8% 37% 36% 8% 1	1000
	21st to end	Night	11% 7% 38% 35% 8%	1100

Page generated at 2025-01-04 02:23:58. Version ac07

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