Lake MacDonald
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake MacDonald clear sky chart from 2005-11-06 to 2025-11-18.

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	17% 12% 4 9% 5% 5% 4 3 5% 6% 29%	127185
	Night	17% 13% 4 9% 5% 4 4 3 5% 6% 29%	123164
Transparency	Day	54% 6% 11% 19% 9% 1	130616
	Night	55% 5% 11% 18% 9% 1	127820
Seeing	Day	26% 18% 30% 18% 7% 2	15798
	Night	24% 15% 29% 24% 8% 1	24772

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	14% 23% 6% 15% 7% 5% 5% 2 3 4 16%	3597
	11th to 20th	Day	12% 18% 7% 17% 9% 5% 4 3 4 4 19%	3570
	21st to end	Day	9% 17% 9% 15% 6% 5% 5% 4 4 5% 21%	3960
February	1st to 10th	Day	13% 18% 5% 13% 8% 5% 3 3 4 5% 23%	1790
	11th to 20th	Day	13% 17% 7% 11% 7% 4 4 3 4 6% 23%	1808
	21st to end	Day	17% 17% 6% 9% 7% 6% 3 3 5% 4 24%	1650
March	1st to 10th	Day	17% 17% 5% 12% 6% 5% 4 3 4 5% 22%	4476
	11th to 20th	Day	10% 16% 5% 11% 6% 4 4 4 5% 6% 28%	4796
	21st to end	Day	18% 13% 3 8% 5% 4 4 3 4 5% 33%	5893
April	1st to 10th	Day	20% 15% 3 8% 4 4 4 2 4 5% 31%	2400
	11th to 20th	Day	21% 11% 4 7% 4 4 4 2 4 5% 33%	2374
	21st to end	Day	22% 11% 4 8% 5% 4 4 3 4 5% 30%	2553
May	1st to 10th	Day	24% 11% 4 9% 6% 6% 5% 3 5% 6% 22%	6346
	11th to 20th	Day	19% 10% 3 8% 5% 5% 5% 3 5% 8% 30%	6318
	21st to end	Day	21% 11% 3 7% 5% 4 4 3 5% 7% 29%	6949
June	1st to 10th	Day	22% 9% 3 8% 6% 4 5% 4 5% 7% 27%	2800
	11th to 20th	Day	16% 8% 3 6% 5% 6% 5% 4 6% 9% 33%	2800
	21st to end	Day	22% 9% 3 8% 5% 5% 5% 4 6% 7% 27%	2800
July	1st to 10th	Day	15% 8% 3 8% 6% 6% 6% 5% 7% 8% 29%	6360
	11th to 20th	Day	14% 7% 3 7% 4 5% 5% 4 6% 9% 37%	6360
	21st to end	Day	10% 6% 2 5% 4 4 4 4 6% 10% 44%	6926
August	1st to 10th	Day	16% 6% 3 8% 5% 6% 6% 4 6% 9% 32%	4563
	11th to 20th	Day	15% 8% 3 7% 4 5% 4 4 6% 8% 36%	4140
	21st to end	Day	16% 5% 3 7% 4 4 5% 4 7% 9% 36%	4312
September	1st to 10th	Day	16% 7% 2 5% 5% 4 4 3 6% 7% 42%	2400
	11th to 20th	Day	14% 5% 2 6% 3 4 4 3 5% 7% 47%	2350
	21st to end	Day	20% 7% 2 5% 3 3 4 4 6% 6% 40%	2200
October	1st to 10th	Day	21% 8% 3 6% 3 4 4 3 5% 7% 35%	2010
	11th to 20th	Day	23% 11% 4 8% 5% 4 4 4 5% 6% 27%	1990
	21st to end	Day	24% 13% 4 7% 4 4 4 4 5% 5% 25%	1980
November	1st to 10th	Day	16% 14% 4 8% 4 5% 4 4 5% 6% 29%	1851
	11th to 20th	Day	19% 16% 5% 8% 5% 5% 5% 3 5% 6% 23%	1717
	21st to end	Day	23% 15% 5% 8% 6% 5% 4 3 4 5% 20%	1600
December	1st to 10th	Day	19% 23% 9% 10% 5% 4 4 4 5% 5% 13%	2600
	11th to 20th	Day	18% 20% 7% 11% 5% 4 4 2 4 4 23%	2986
	21st to end	Day	20% 18% 5% 10% 5% 4 4 3 4 4 22%	3960
January	1st to 10th	Night	14% 25% 8% 12% 5% 4 4 3 4 4 18%	6349
	11th to 20th	Night	10% 17% 8% 17% 8% 5% 4 3 4 5% 17%	6315
	21st to end	Night	10% 16% 7% 15% 7% 6% 5% 3 5% 6% 20%	6996
February	1st to 10th	Night	13% 16% 6% 12% 7% 5% 5% 3 4 5% 24%	2605
	11th to 20th	Night	13% 15% 6% 12% 7% 6% 3 3 5% 4 26%	2477
	21st to end	Night	14% 15% 6% 10% 6% 4 4 4 4 6% 27%	1980
March	1st to 10th	Night	20% 15% 4 10% 5% 4 4 3 4 4 27%	5364
	11th to 20th	Night	12% 16% 3 8% 5% 5% 5% 4 6% 7% 29%	5145
	21st to end	Night	17% 13% 4 9% 6% 5% 5% 3 4 4 30%	5038
April	1st to 10th	Night	22% 12% 3 7% 5% 4 3 2 4 6% 31%	2000
	11th to 20th	Night	20% 11% 3 7% 5% 4 4 3 5% 5% 34%	1975
	21st to end	Night	21% 10% 3 7% 5% 3 4 4 4 5% 34%	1861
May	1st to 10th	Night	19% 10% 4 9% 6% 5% 5% 4 6% 6% 25%	3594
	11th to 20th	Night	19% 9% 3 7% 4 4 4 3 5% 7% 35%	3575
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 5% 7% 29%	3926
June	1st to 10th	Night	19% 8% 3 7% 5% 5% 5% 4 5% 9% 30%	1600
	11th to 20th	Night	17% 7% 2 8% 4 4 4 3 6% 7% 38%	1600
	21st to end	Night	19% 9% 3 6% 4 4 4 4 5% 6% 36%	1600
July	1st to 10th	Night	15% 7% 2 9% 5% 6% 6% 4 7% 8% 32%	3600
	11th to 20th	Night	16% 7% 2 6% 3 3 4 3 5% 7% 41%	3600
	21st to end	Night	10% 5% 2 6% 4 4 5% 5% 7% 8% 46%	3926
August	1st to 10th	Night	14% 7% 3 8% 5% 4 4 4 6% 8% 39%	2586
	11th to 20th	Night	16% 7% 2 5% 5% 3 4 4 6% 7% 41%	2871
	21st to end	Night	15% 7% 3 7% 4 3 5% 3 5% 7% 41%	3586
September	1st to 10th	Night	13% 7% 2 6% 4 3 4 3 5% 7% 46%	2000
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 5% 7% 49%	2049
	21st to end	Night	19% 7% 2 5% 3 4 4 3 4 7% 43%	2200
October	1st to 10th	Night	18% 8% 3 7% 4 4 4 3 5% 5% 39%	2389
	11th to 20th	Night	21% 9% 4 8% 4 5% 4 3 5% 6% 32%	2410
	21st to end	Night	24% 11% 4 8% 5% 3 4 3 4 6% 28%	2860
November	1st to 10th	Night	21% 12% 4 7% 5% 4 3 3 5% 6% 29%	2667
	11th to 20th	Night	19% 12% 4 10% 5% 4 4 3 5% 5% 28%	2836
	21st to end	Night	20% 18% 5% 9% 6% 4 4 3 4 4 22%	2800
December	1st to 10th	Night	17% 19% 7% 12% 8% 5% 4 3 4 5% 15%	4580
	11th to 20th	Night	23% 17% 5% 11% 5% 4 3 3 3 4 24%	5208
	21st to end	Night	21% 21% 4 9% 5% 3 3 2 3 4 25%	6996

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	72% 6% 7% 12% 4	3598
	11th to 20th	Day	68% 5% 5% 13% 7% 1	3600
	21st to end	Day	65% 5% 7% 11% 11% 1	3960
February	1st to 10th	Day	63% 4 8% 16% 7% 2	1790
	11th to 20th	Day	62% 5% 10% 14% 9% 1	1817
	21st to end	Day	64% 4 7% 14% 10% 2	1650
March	1st to 10th	Day	65% 4 7% 10% 11% 3	4479
	11th to 20th	Day	56% 4 15% 13% 10% 2	4796
	21st to end	Day	55% 3 6% 16% 18% 2	5893
April	1st to 10th	Day	56% 3 9% 16% 12% 3	2400
	11th to 20th	Day	53% 4 8% 20% 13% 2	2374
	21st to end	Day	56% 6% 7% 15% 13% 3	2553
May	1st to 10th	Day	62% 6% 7% 17% 7% 1	6357
	11th to 20th	Day	52% 7% 14% 17% 8% 2	6322
	21st to end	Day	54% 6% 10% 16% 13% 1	6949
June	1st to 10th	Day	54% 7% 9% 17% 12% 1	2800
	11th to 20th	Day	46% 7% 12% 21% 12% 3	2800
	21st to end	Day	55% 7% 11% 18% 9% 1	2800
July	1st to 10th	Day	50% 8% 12% 23% 6%	6290
	11th to 20th	Day	41% 7% 14% 29% 8%	6285
	21st to end	Day	35% 6% 16% 34% 9%	6728
August	1st to 10th	Day	48% 7% 16% 21% 7%	4549
	11th to 20th	Day	44% 7% 15% 27% 6%	4182
	21st to end	Day	43% 6% 15% 22% 12% 1	4312
September	1st to 10th	Day	41% 6% 14% 28% 12%	2400
	11th to 20th	Day	36% 6% 14% 31% 13% 1	2350
	21st to end	Day	44% 6% 14% 25% 11% 1	2200
October	1st to 10th	Day	47% 5% 12% 27% 8%	3270
	11th to 20th	Day	49% 7% 14% 23% 8% 1	3218
	21st to end	Day	51% 6% 20% 16% 7% 1	3180
November	1st to 10th	Day	54% 7% 13% 19% 7% 1	1851
	11th to 20th	Day	61% 6% 11% 12% 9% 1	1717
	21st to end	Day	65% 7% 12% 12% 3 1	1600
December	1st to 10th	Day	73% 5% 9% 11% 3	2600
	11th to 20th	Day	66% 5% 8% 15% 7%	2986
	21st to end	Day	65% 4 8% 15% 8%	3960
January	1st to 10th	Night	70% 5% 11% 11% 3	6349
	11th to 20th	Night	68% 6% 9% 11% 5%	6360
	21st to end	Night	65% 5% 9% 8% 12% 1	6996
February	1st to 10th	Night	61% 5% 9% 17% 7% 1	2605
	11th to 20th	Night	61% 4 10% 17% 8% 1	2479
	21st to end	Night	58% 5% 9% 16% 10% 2	1980
March	1st to 10th	Night	61% 3 8% 12% 12% 3	5374
	11th to 20th	Night	51% 6% 14% 16% 9% 3	5146
	21st to end	Night	56% 3 7% 19% 11% 2	5038
April	1st to 10th	Night	55% 4 9% 17% 13% 2	2000
	11th to 20th	Night	50% 5% 9% 20% 14% 1	1975
	21st to end	Night	52% 5% 9% 19% 13% 3	1861
May	1st to 10th	Night	57% 7% 9% 18% 7% 2	3600
	11th to 20th	Night	48% 8% 12% 19% 11% 2	3576
	21st to end	Night	54% 6% 10% 17% 12% 1	3927
June	1st to 10th	Night	49% 7% 11% 22% 11%	1600
	11th to 20th	Night	44% 6% 12% 22% 14% 2	1600
	21st to end	Night	49% 8% 10% 19% 13% 1	1600
July	1st to 10th	Night	48% 7% 17% 20% 8%	3560
	11th to 20th	Night	42% 6% 16% 30% 6%	3552
	21st to end	Night	34% 7% 16% 31% 12%	3809
August	1st to 10th	Night	43% 7% 15% 27% 7%	2576
	11th to 20th	Night	42% 6% 18% 27% 8%	2895
	21st to end	Night	41% 6% 16% 24% 11% 2	3586
September	1st to 10th	Night	38% 6% 13% 28% 14% 1	2000
	11th to 20th	Night	35% 6% 14% 34% 11% 1	2049
	21st to end	Night	41% 6% 12% 28% 13%	2200
October	1st to 10th	Night	44% 6% 14% 25% 11% 1	3909
	11th to 20th	Night	47% 7% 13% 24% 9%	3921
	21st to end	Night	50% 5% 18% 16% 10% 1	4610
November	1st to 10th	Night	54% 6% 13% 19% 6% 1	2667
	11th to 20th	Night	57% 5% 12% 16% 8% 2	2836
	21st to end	Night	63% 7% 11% 14% 5%	2800
December	1st to 10th	Night	69% 6% 11% 11% 3	4580
	11th to 20th	Night	66% 3 6% 14% 10% 1	5208
	21st to end	Night	65% 3 6% 12% 13% 1	6996

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	27% 25% 32% 15% 3	200
	11th to 20th	Day	27% 25% 36% 8% 5% 1	200
	21st to end	Day	25% 21% 36% 15% 3	220
February	1st to 10th	Day	36% 28% 29% 5% 1	295
	11th to 20th	Day	26% 34% 33% 7%	355
	21st to end	Day	30% 25% 30% 12% 2	414
March	1st to 10th	Day	28% 22% 32% 14% 2	500
	11th to 20th	Day	30% 25% 28% 13% 3 1	500
	21st to end	Day	31% 23% 24% 15% 5% 1	550
April	1st to 10th	Day	32% 22% 29% 12% 4	500
	11th to 20th	Day	36% 20% 23% 14% 6% 1	492
	21st to end	Day	32% 20% 33% 10% 3 1	500
May	1st to 10th	Day	27% 22% 32% 15% 4 1	503
	11th to 20th	Day	24% 21% 29% 19% 6% 1	527
	21st to end	Day	26% 18% 31% 19% 5% 1	573
June	1st to 10th	Day	26% 16% 35% 16% 7%	530
	11th to 20th	Day	19% 19% 32% 20% 9% 1	530
	21st to end	Day	28% 15% 34% 16% 6% 2	530
July	1st to 10th	Day	16% 14% 35% 24% 10% 2	525
	11th to 20th	Day	17% 12% 38% 23% 9% 1	524
	21st to end	Day	16% 13% 35% 27% 8% 1	576
August	1st to 10th	Day	17% 10% 30% 31% 10% 2	526
	11th to 20th	Day	16% 8% 28% 30% 12% 5%	519
	21st to end	Day	20% 14% 28% 21% 13% 5%	583
September	1st to 10th	Day	20% 11% 31% 22% 11% 4	530
	11th to 20th	Day	13% 12% 25% 25% 18% 8%	530
	21st to end	Day	22% 16% 25% 22% 10% 5%	530
October	1st to 10th	Day	26% 15% 25% 19% 12% 2	530
	11th to 20th	Day	28% 21% 28% 16% 6% 1	524
	21st to end	Day	34% 15% 31% 17% 3	462
November	1st to 10th	Day	35% 18% 26% 15% 5%	425
	11th to 20th	Day	29% 23% 31% 12% 5%	275
	21st to end	Day	31% 26% 32% 11% 1	200
December	1st to 10th	Day	34% 18% 32% 14% 4 1	200
	11th to 20th	Day	33% 27% 28% 11% 1 1	200
	21st to end	Day	34% 20% 30% 11% 4 1	220
January	1st to 10th	Night	28% 17% 34% 18% 3	800
	11th to 20th	Night	28% 21% 29% 17% 5%	800
	21st to end	Night	19% 18% 36% 20% 5% 1	880
February	1st to 10th	Night	22% 22% 33% 19% 4	800
	11th to 20th	Night	23% 23% 35% 16% 3	783
	21st to end	Night	24% 19% 33% 22% 3	660
March	1st to 10th	Night	25% 19% 34% 19% 3	800
	11th to 20th	Night	25% 22% 31% 18% 4 1	800
	21st to end	Night	26% 17% 30% 22% 5%	880
April	1st to 10th	Night	30% 17% 28% 22% 4	800
	11th to 20th	Night	27% 16% 31% 20% 6%	791
	21st to end	Night	29% 16% 30% 19% 7%	661
May	1st to 10th	Night	24% 14% 33% 22% 6% 2	400
	11th to 20th	Night	22% 11% 30% 28% 8% 1	394
	21st to end	Night	19% 12% 35% 25% 9%	433
June	1st to 10th	Night	22% 8% 32% 30% 8%	400
	11th to 20th	Night	22% 8% 30% 29% 11% 1	400
	21st to end	Night	23% 7% 26% 32% 13% 1	400
July	1st to 10th	Night	14% 7% 26% 37% 15% 1	390
	11th to 20th	Night	14% 4 26% 39% 16% 1	388
	21st to end	Night	13% 5% 27% 40% 13% 1	438
August	1st to 10th	Night	14% 3 19% 44% 18% 1	398
	11th to 20th	Night	14% 5% 23% 34% 24% 1	587
	21st to end	Night	18% 6% 25% 34% 16% 2	880
September	1st to 10th	Night	16% 7% 29% 33% 15% 1	800
	11th to 20th	Night	18% 7% 20% 32% 21% 2	800
	21st to end	Night	21% 10% 25% 27% 16% 2	800
October	1st to 10th	Night	22% 14% 25% 27% 12% 1	800
	11th to 20th	Night	26% 14% 29% 25% 6% 1	800
	21st to end	Night	31% 13% 29% 23% 5%	880
November	1st to 10th	Night	30% 16% 26% 23% 5% 1	820
	11th to 20th	Night	27% 18% 31% 16% 8%	829
	21st to end	Night	32% 19% 27% 17% 5%	800
December	1st to 10th	Night	31% 19% 29% 17% 4	800
	11th to 20th	Night	30% 21% 27% 17% 4 1	800
	21st to end	Night	35% 18% 28% 16% 3	880

Page generated at 2025-11-15 00:55:59. Version ac07

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