American Horse Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the American Horse Lake clear sky chart from 2005-11-06 to 2025-08-05.

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	8% 5% 2 5% 3 3 4 3 5% 6% 55%	125682
	Night	7% 5% 2 4 3 3 3 3 5% 7% 58%	122681
Transparency	Day	29% 4 9% 25% 24% 8%	129438
	Night	26% 4 9% 25% 26% 10%	126988
Seeing	Day	11% 8% 28% 31% 18% 4	16431
	Night	10% 9% 34% 34% 12% 1	26280

By Month

Percentage Cloud Cover SE (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	9% 6% 3 7% 4 4 3 3 4 6% 50%	4077
	11th to 20th	Day	5% 5% 2 4 2 3 3 2 3 4 66%	4080
	21st to end	Day	11% 10% 3 5% 3 2 2 2 2 5% 54%	4488
February	1st to 10th	Day	10% 10% 3 6% 3 3 3 2 3 4 53%	1960
	11th to 20th	Day	9% 7% 2 6% 4 3 3 2 4 5% 54%	1949
	21st to end	Day	10% 7% 2 4 3 4 3 4 3 4 56%	1650
March	1st to 10th	Day	10% 6% 2 4 3 2 3 2 3 5% 60%	4711
	11th to 20th	Day	6% 6% 2 5% 3 3 3 3 5% 6% 57%	4980
	21st to end	Day	8% 8% 3 7% 4 4 4 3 5% 7% 48%	5462
April	1st to 10th	Day	9% 4 2 5% 3 3 4 3 5% 8% 54%	2200
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 5% 6% 49%	2412
	21st to end	Day	13% 5% 2 5% 4 4 3 3 5% 6% 51%	2600
May	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 5% 6% 42%	5862
	11th to 20th	Day	9% 5% 1 5% 3 3 3 3 5% 7% 57%	5862
	21st to end	Day	11% 6% 2 7% 5% 4 4 3 4 6% 47%	6434
June	1st to 10th	Day	6% 4 2 5% 4 4 4 4 7% 9% 51%	2600
	11th to 20th	Day	5% 5% 1 4 4 4 4 4 5% 7% 57%	2600
	21st to end	Day	5% 3 1 4 3 3 4 4 6% 9% 59%	2600
July	1st to 10th	Day	8% 6% 3 6% 5% 5% 5% 4 7% 8% 43%	5900
	11th to 20th	Day	5% 4 2 4 3 4 4 4 6% 9% 56%	5900
	21st to end	Day	2 2 1 3 3 3 4 3 6% 8% 64%	6422
August	1st to 10th	Day	6% 3 1 6% 4 4 4 3 7% 9% 54%	4157
	11th to 20th	Day	5% 4 1 4 3 4 4 3 6% 8% 57%	4018
	21st to end	Day	3 3 2 4 3 3 3 3 5% 7% 64%	4180
September	1st to 10th	Day	9% 5% 2 5% 3 3 3 2 4 6% 59%	2091
	11th to 20th	Day	9% 5% 2 6% 4 4 4 3 5% 6% 52%	2090
	21st to end	Day	7% 4 2 4 3 3 4 3 5% 6% 60%	2090
October	1st to 10th	Day	8% 4 2 4 3 3 3 2 3 5% 62%	2090
	11th to 20th	Day	9% 3 1 3 2 2 2 2 3 4 69%	1919
	21st to end	Day	10% 5% 2 3 3 3 2 2 4 5% 62%	2090
November	1st to 10th	Day	8% 4 1 3 3 3 3 3 4 6% 63%	1789
	11th to 20th	Day	6% 5% 2 3 2 3 2 2 4 5% 66%	1800
	21st to end	Day	10% 4 2 4 3 2 3 3 4 5% 60%	1800
December	1st to 10th	Day	4 5% 2 5% 3 2 3 3 4 7% 62%	2940
	11th to 20th	Day	6% 4 1 4 3 3 3 3 4 7% 62%	3391
	21st to end	Day	12% 10% 4 7% 4 4 3 3 4 5% 45%	4488
January	1st to 10th	Night	9% 7% 3 7% 3 4 4 3 5% 5% 50%	5888
	11th to 20th	Night	3 3 1 4 3 3 4 3 4 6% 65%	5900
	21st to end	Night	12% 8% 3 5% 3 3 3 2 3 5% 54%	6490
February	1st to 10th	Night	11% 8% 2 6% 4 3 3 2 3 5% 53%	2457
	11th to 20th	Night	10% 7% 2 5% 3 3 3 3 4 7% 53%	2338
	21st to end	Night	8% 6% 2 5% 3 3 3 3 5% 6% 56%	1980
March	1st to 10th	Night	6% 5% 2 5% 3 3 3 3 4 6% 61%	5151
	11th to 20th	Night	7% 3 1 3 2 3 3 2 4 5% 67%	4980
	21st to end	Night	6% 6% 2 6% 4 4 4 4 6% 8% 50%	5467
April	1st to 10th	Night	9% 5% 1 3 3 2 4 3 4 7% 59%	2200
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 53%	1933
	21st to end	Night	13% 5% 1 4 3 3 4 2 5% 6% 53%	1800
May	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 6% 48%	4053
	11th to 20th	Night	8% 4 1 4 4 3 4 3 6% 8% 55%	4053
	21st to end	Night	10% 5% 1 4 3 3 3 3 5% 7% 55%	4443
June	1st to 10th	Night	4 3 2 4 3 3 4 4 6% 11% 55%	1800
	11th to 20th	Night	5% 4 1 2 3 3 4 3 5% 10% 60%	1800
	21st to end	Night	4 2 1 3 2 3 3 3 6% 9% 64%	1800
July	1st to 10th	Night	5% 4 2 5% 4 4 6% 4 8% 10% 48%	4078
	11th to 20th	Night	4 2 1 3 3 3 4 4 6% 12% 57%	4077
	21st to end	Night	2 2 1 3 3 3 4 3 6% 10% 62%	4449
August	1st to 10th	Night	2 2 1 3 3 3 4 4 6% 10% 62%	2872
	11th to 20th	Night	5% 3 1 4 3 4 4 4 7% 11% 53%	2817
	21st to end	Night	2 2 1 3 3 3 4 3 6% 9% 65%	3487
September	1st to 10th	Night	7% 5% 2 4 3 2 3 3 5% 6% 61%	2086
	11th to 20th	Night	10% 5% 2 5% 4 4 3 3 4 7% 53%	2090
	21st to end	Night	6% 4 1 4 3 3 4 3 6% 6% 60%	2090
October	1st to 10th	Night	7% 3 2 4 2 2 4 3 5% 7% 61%	2090
	11th to 20th	Night	8% 4 2 3 3 2 3 2 3 4 67%	2242
	21st to end	Night	9% 4 2 4 3 3 2 2 4 4 65%	2508
November	1st to 10th	Night	8% 4 2 3 2 3 2 2 3 6% 65%	2506
	11th to 20th	Night	6% 4 2 4 3 3 3 2 3 6% 66%	2600
	21st to end	Night	9% 5% 1 3 3 3 3 3 4 6% 61%	2600
December	1st to 10th	Night	5% 4 1 4 2 3 2 2 4 6% 66%	4250
	11th to 20th	Night	5% 5% 2 5% 3 3 3 2 3 5% 63%	4816
	21st to end	Night	13% 9% 2 5% 3 3 3 2 3 5% 51%	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	36% 4 10% 26% 21% 4	4078
	11th to 20th	Day	23% 3 8% 20% 36% 10%	4080
	21st to end	Day	37% 2 4 20% 30% 7%	4488
February	1st to 10th	Day	36% 2 8% 24% 23% 7%	1960
	11th to 20th	Day	34% 3 7% 24% 24% 7%	1959
	21st to end	Day	33% 3 5% 20% 27% 12%	1650
March	1st to 10th	Day	29% 3 6% 15% 22% 25%	4711
	11th to 20th	Day	28% 4 7% 18% 27% 17%	4980
	21st to end	Day	35% 5% 10% 29% 18% 3	5464
April	1st to 10th	Day	29% 5% 11% 26% 21% 9%	2200
	11th to 20th	Day	36% 4 9% 22% 21% 9%	2412
	21st to end	Day	34% 4 11% 27% 21% 3	2600
May	1st to 10th	Day	43% 5% 11% 18% 18% 5%	5900
	11th to 20th	Day	28% 5% 9% 25% 21% 12%	5866
	21st to end	Day	37% 6% 9% 21% 17% 9%	6447
June	1st to 10th	Day	27% 8% 16% 29% 15% 5%	2600
	11th to 20th	Day	25% 5% 13% 27% 24% 6%	2600
	21st to end	Day	21% 6% 15% 25% 26% 7%	2600
July	1st to 10th	Day	37% 6% 12% 20% 20% 5%	5836
	11th to 20th	Day	24% 5% 11% 31% 24% 5%	5831
	21st to end	Day	17% 4 16% 37% 23% 3	6240
August	1st to 10th	Day	26% 4 10% 25% 27% 8%	4143
	11th to 20th	Day	24% 5% 12% 31% 23% 4	4057
	21st to end	Day	19% 5% 12% 38% 21% 4	4179
September	1st to 10th	Day	28% 4 8% 23% 24% 12%	2091
	11th to 20th	Day	32% 5% 8% 24% 25% 6%	2090
	21st to end	Day	25% 4 7% 25% 30% 8%	2090
October	1st to 10th	Day	16% 3 6% 15% 43% 17%	3480
	11th to 20th	Day	17% 3 8% 22% 32% 18%	3172
	21st to end	Day	22% 3 6% 27% 33% 10%	3428
November	1st to 10th	Day	24% 3 7% 25% 30% 12%	1789
	11th to 20th	Day	22% 2 6% 29% 29% 12%	1800
	21st to end	Day	28% 3 5% 27% 27% 11%	1800
December	1st to 10th	Day	24% 3 6% 38% 25% 3	2940
	11th to 20th	Day	24% 2 7% 23% 34% 9%	3389
	21st to end	Day	42% 3 6% 24% 19% 6%	4488
January	1st to 10th	Night	36% 4 8% 28% 21% 4	5888
	11th to 20th	Night	20% 4 10% 21% 33% 12%	5900
	21st to end	Night	36% 2 5% 17% 32% 8%	6490
February	1st to 10th	Night	35% 3 6% 22% 25% 9%	2457
	11th to 20th	Night	32% 4 8% 23% 23% 9%	2338
	21st to end	Night	30% 4 5% 20% 27% 15%	1980
March	1st to 10th	Night	25% 3 5% 16% 25% 25%	5151
	11th to 20th	Night	21% 3 6% 21% 25% 25%	4980
	21st to end	Night	31% 5% 11% 26% 23% 4	5467
April	1st to 10th	Night	26% 4 10% 22% 25% 13%	2200
	11th to 20th	Night	32% 4 8% 26% 20% 10%	1933
	21st to end	Night	32% 5% 11% 26% 21% 5%	1800
May	1st to 10th	Night	40% 4 13% 16% 21% 7%	4080
	11th to 20th	Night	26% 6% 10% 22% 25% 12%	4054
	21st to end	Night	29% 6% 14% 20% 18% 13%	4452
June	1st to 10th	Night	23% 7% 17% 31% 18% 4	1800
	11th to 20th	Night	21% 4 15% 30% 24% 6%	1800
	21st to end	Night	17% 5% 14% 31% 24% 10%	1800
July	1st to 10th	Night	29% 7% 18% 27% 16% 3	4035
	11th to 20th	Night	19% 4 13% 33% 25% 6%	4026
	21st to end	Night	18% 4 14% 34% 27% 2	4320
August	1st to 10th	Night	15% 5% 13% 29% 30% 8%	2862
	11th to 20th	Night	23% 5% 11% 31% 25% 5%	2844
	21st to end	Night	17% 5% 14% 37% 23% 5%	3487
September	1st to 10th	Night	24% 5% 9% 25% 25% 12%	2086
	11th to 20th	Night	32% 5% 9% 20% 25% 9%	2090
	21st to end	Night	23% 4 7% 24% 31% 11%	2090
October	1st to 10th	Night	17% 3 8% 15% 36% 22%	3480
	11th to 20th	Night	16% 3 5% 21% 36% 19%	3715
	21st to end	Night	18% 2 5% 27% 37% 11%	4120
November	1st to 10th	Night	23% 3 8% 23% 30% 14%	2506
	11th to 20th	Night	22% 3 6% 26% 31% 12%	2600
	21st to end	Night	27% 4 6% 22% 29% 13%	2600
December	1st to 10th	Night	21% 2 6% 40% 26% 5%	4250
	11th to 20th	Night	27% 2 4 23% 34% 10%	4817
	21st to end	Night	37% 4 6% 24% 24% 6%	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	12% 13% 40% 27% 6% 1	300
	11th to 20th	Day	14% 18% 38% 23% 6%	300
	21st to end	Day	12% 14% 44% 24% 6%	330
February	1st to 10th	Day	14% 14% 42% 25% 5%	300
	11th to 20th	Day	13% 21% 45% 16% 4 1	300
	21st to end	Day	16% 19% 40% 19% 6%	249
March	1st to 10th	Day	14% 19% 39% 24% 5%	300
	11th to 20th	Day	20% 15% 38% 21% 4 1	300
	21st to end	Day	18% 14% 42% 21% 5%	330
April	1st to 10th	Day	18% 16% 38% 19% 9%	300
	11th to 20th	Day	14% 19% 45% 18% 4	530
	21st to end	Day	16% 15% 38% 24% 6% 2	700
May	1st to 10th	Day	14% 9% 42% 27% 8% 1	703
	11th to 20th	Day	16% 8% 31% 28% 14% 2	725
	21st to end	Day	13% 7% 32% 29% 15% 3	789
June	1st to 10th	Day	8% 4 23% 39% 21% 4	730
	11th to 20th	Day	7% 3 30% 40% 17% 3	730
	21st to end	Day	5% 2 24% 42% 22% 5%	730
July	1st to 10th	Day	7% 1 13% 34% 33% 11%	721
	11th to 20th	Day	3 2 11% 43% 33% 7%	718
	21st to end	Day	5% 1 6% 40% 37% 11%	794
August	1st to 10th	Day	6% 1 11% 45% 32% 5%	697
	11th to 20th	Day	8% 1 11% 39% 34% 6%	655
	21st to end	Day	4 1 9% 36% 37% 12%	539
September	1st to 10th	Day	7% 7% 41% 35% 10%	301
	11th to 20th	Day	6% 3 16% 42% 28% 5%	300
	21st to end	Day	12% 3 21% 33% 23% 9%	300
October	1st to 10th	Day	8% 5% 30% 30% 20% 6%	300
	11th to 20th	Day	9% 10% 35% 33% 12% 1	300
	21st to end	Day	18% 11% 33% 24% 12% 3	330
November	1st to 10th	Day	12% 8% 35% 33% 9% 3	300
	11th to 20th	Day	14% 11% 38% 23% 12% 2	300
	21st to end	Day	15% 14% 37% 23% 9% 1	300
December	1st to 10th	Day	8% 11% 46% 23% 10% 2	300
	11th to 20th	Day	14% 11% 42% 24% 9%	300
	21st to end	Day	17% 17% 38% 23% 5%	330
January	1st to 10th	Night	9% 13% 39% 33% 6%	1000
	11th to 20th	Night	11% 13% 37% 33% 5%	1000
	21st to end	Night	11% 11% 40% 32% 7%	1100
February	1st to 10th	Night	16% 10% 42% 27% 4	857
	11th to 20th	Night	14% 15% 41% 25% 4	784
	21st to end	Night	14% 13% 46% 24% 3	660
March	1st to 10th	Night	8% 15% 41% 30% 5%	707
	11th to 20th	Night	17% 13% 38% 27% 6%	600
	21st to end	Night	10% 17% 45% 24% 4	660
April	1st to 10th	Night	11% 14% 44% 24% 7%	600
	11th to 20th	Night	14% 16% 44% 24% 3	593
	21st to end	Night	17% 11% 41% 25% 6%	600
May	1st to 10th	Night	14% 11% 42% 29% 4 1	600
	11th to 20th	Night	10% 8% 35% 34% 13%	591
	21st to end	Night	9% 5% 36% 35% 12% 2	650
June	1st to 10th	Night	7% 3 27% 43% 18% 2	600
	11th to 20th	Night	6% 4 34% 44% 12%	600
	21st to end	Night	3 2 30% 48% 16% 1	600
July	1st to 10th	Night	5% 2 15% 46% 29% 3	585
	11th to 20th	Night	4 1 15% 52% 27% 2	582
	21st to end	Night	3 1 8% 56% 30% 3	657
August	1st to 10th	Night	3 16% 49% 30% 2	579
	11th to 20th	Night	7% 1 14% 50% 26% 2	564
	21st to end	Night	4 13% 44% 36% 3	627
September	1st to 10th	Night	7% 2 19% 44% 25% 3	570
	11th to 20th	Night	13% 1 23% 36% 25% 2	570
	21st to end	Night	8% 4 26% 40% 19% 3	570
October	1st to 10th	Night	9% 4 29% 37% 20% 1	570
	11th to 20th	Night	10% 6% 39% 35% 9%	722
	21st to end	Night	11% 10% 36% 30% 12% 1	836
November	1st to 10th	Night	10% 7% 38% 34% 10% 1	946
	11th to 20th	Night	8% 10% 41% 33% 8% 1	1000
	21st to end	Night	13% 12% 33% 31% 10%	1000
December	1st to 10th	Night	11% 9% 39% 32% 9% 1	1000
	11th to 20th	Night	13% 12% 40% 29% 7%	1000
	21st to end	Night	13% 12% 38% 31% 6%	1100

Page generated at 2025-08-02 00:32:23. Version ac07

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