Forest Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Forest Lake clear sky chart from 2005-11-06 to 2026-07-01.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 29%	138085
	Night	16% 11% 4 10% 6% 5% 4 3 5% 6% 30%	134299
Transparency	Day	51% 7% 12% 18% 10% 1	141576
	Night	52% 7% 12% 17% 11% 1	138897
Seeing	Day	28% 19% 27% 16% 7% 2	16910
	Night	27% 18% 25% 21% 8% 1	26073

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	11% 14% 8% 17% 10% 8% 5% 3 4 4 17%	4661
	11th to 20th	Day	14% 13% 6% 17% 9% 6% 5% 4 4 4 18%	4650
	21st to end	Day	15% 13% 6% 9% 6% 6% 4 4 6% 6% 26%	5578
February	1st to 10th	Day	14% 14% 5% 12% 8% 5% 5% 3 5% 5% 23%	1890
	11th to 20th	Day	13% 12% 5% 12% 7% 6% 4 3 4 7% 26%	1980
	21st to end	Day	18% 14% 4 10% 6% 5% 4 3 5% 5% 27%	1730
March	1st to 10th	Day	19% 15% 5% 10% 5% 4 4 3 4 5% 29%	4576
	11th to 20th	Day	13% 12% 5% 10% 4 4 4 3 5% 6% 34%	4990
	21st to end	Day	18% 11% 3 9% 6% 5% 5% 3 5% 5% 30%	5993
April	1st to 10th	Day	18% 15% 4 8% 5% 4 5% 3 4 5% 29%	2520
	11th to 20th	Day	16% 11% 3 7% 5% 5% 4 4 5% 6% 33%	2494
	21st to end	Day	18% 12% 4 9% 5% 4 3 3 4 6% 33%	2533
May	1st to 10th	Day	26% 10% 3 8% 5% 4 4 3 5% 6% 26%	7910
	11th to 20th	Day	17% 9% 3 9% 5% 5% 5% 4 5% 6% 31%	8221
	21st to end	Day	22% 9% 3 7% 5% 5% 6% 5% 7% 7% 25%	9060
June	1st to 10th	Day	16% 7% 2 7% 6% 5% 5% 4 7% 8% 31%	2940
	11th to 20th	Day	18% 7% 3 7% 5% 5% 5% 5% 7% 9% 29%	2940
	21st to end	Day	16% 9% 3 8% 5% 4 4 5% 6% 9% 31%	2940
July	1st to 10th	Day	10% 8% 4 9% 6% 5% 6% 5% 7% 8% 34%	6360
	11th to 20th	Day	12% 7% 3 7% 5% 6% 6% 5% 8% 10% 30%	6360
	21st to end	Day	15% 6% 3 7% 5% 5% 5% 4 7% 9% 36%	6926
August	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 4 5% 7% 29%	4371
	11th to 20th	Day	14% 8% 3 7% 5% 5% 6% 6% 8% 9% 30%	3890
	21st to end	Day	16% 5% 2 6% 4 5% 5% 4 7% 8% 36%	4312
September	1st to 10th	Day	17% 6% 3 7% 5% 4 4 3 5% 8% 38%	2400
	11th to 20th	Day	14% 6% 1 5% 4 4 4 5% 6% 8% 42%	2350
	21st to end	Day	20% 8% 2 8% 4 4 4 4 5% 7% 34%	2200
October	1st to 10th	Day	18% 10% 3 8% 4 4 4 3 5% 6% 34%	2024
	11th to 20th	Day	17% 11% 3 6% 5% 4 5% 4 5% 6% 34%	2000
	21st to end	Day	22% 14% 3 7% 4 5% 4 3 5% 6% 27%	2057
November	1st to 10th	Day	14% 10% 4 7% 4 3 5% 4 5% 6% 38%	1851
	11th to 20th	Day	15% 14% 5% 10% 5% 4 4 3 4 4 32%	1890
	21st to end	Day	18% 15% 4 11% 5% 4 5% 3 4 5% 26%	1694
December	1st to 10th	Day	14% 15% 5% 18% 7% 6% 5% 3 4 4 18%	2680
	11th to 20th	Day	18% 16% 6% 11% 5% 3 4 2 4 4 27%	3066
	21st to end	Day	17% 16% 5% 12% 6% 4 4 3 5% 6% 22%	4048
January	1st to 10th	Night	12% 13% 7% 20% 8% 5% 5% 3 4 5% 18%	8234
	11th to 20th	Night	11% 14% 8% 19% 10% 6% 5% 3 4 4 15%	8235
	21st to end	Night	12% 11% 4 10% 8% 8% 8% 5% 5% 5% 23%	8599
February	1st to 10th	Night	15% 13% 4 10% 7% 5% 6% 4 6% 6% 25%	2730
	11th to 20th	Night	13% 11% 4 13% 8% 7% 4 4 6% 6% 23%	2525
	21st to end	Night	16% 12% 5% 12% 6% 4 3 4 5% 6% 28%	2076
March	1st to 10th	Night	17% 13% 4 9% 6% 5% 4 3 5% 5% 29%	5484
	11th to 20th	Night	13% 11% 6% 9% 6% 4 4 3 5% 6% 34%	5187
	21st to end	Night	16% 13% 4 10% 6% 5% 4 3 4 4 31%	5180
April	1st to 10th	Night	17% 15% 4 10% 5% 5% 4 4 5% 6% 26%	2100
	11th to 20th	Night	18% 11% 4 8% 5% 4 4 3 4 6% 34%	2075
	21st to end	Night	19% 10% 4 8% 4 4 3 3 5% 5% 35%	2084
May	1st to 10th	Night	26% 10% 3 7% 5% 4 4 3 4 6% 28%	5044
	11th to 20th	Night	18% 11% 4 8% 4 4 4 3 5% 8% 31%	4639
	21st to end	Night	22% 12% 3 8% 5% 4 4 3 5% 7% 28%	5114
June	1st to 10th	Night	16% 7% 3 6% 5% 4 4 3 6% 7% 39%	1680
	11th to 20th	Night	17% 9% 3 5% 4 4 4 3 6% 8% 38%	1680
	21st to end	Night	13% 5% 2 5% 5% 4 5% 4 7% 10% 40%	1680
July	1st to 10th	Night	13% 8% 3 8% 5% 4 5% 4 6% 8% 38%	3600
	11th to 20th	Night	17% 10% 3 7% 4 4 4 4 6% 7% 33%	3600
	21st to end	Night	14% 6% 2 6% 5% 4 4 4 5% 6% 44%	3926
August	1st to 10th	Night	23% 8% 3 8% 4 4 4 4 5% 6% 32%	2774
	11th to 20th	Night	17% 9% 2 7% 5% 3 4 3 5% 6% 39%	3124
	21st to end	Night	13% 6% 2 5% 4 5% 5% 4 5% 6% 44%	3586
September	1st to 10th	Night	16% 8% 2 5% 4 3 4 3 6% 7% 43%	2000
	11th to 20th	Night	14% 6% 2 5% 4 3 3 2 4 7% 50%	2050
	21st to end	Night	18% 8% 3 7% 5% 4 4 3 4 7% 38%	2200
October	1st to 10th	Night	20% 9% 4 6% 3 4 4 3 4 5% 38%	2373
	11th to 20th	Night	19% 10% 3 6% 4 4 3 3 4 6% 39%	2400
	21st to end	Night	20% 14% 3 7% 4 4 3 3 5% 6% 30%	2781
November	1st to 10th	Night	14% 9% 3 7% 4 4 4 4 5% 5% 40%	2667
	11th to 20th	Night	19% 11% 4 8% 5% 4 4 4 5% 6% 31%	2730
	21st to end	Night	15% 12% 5% 10% 6% 5% 5% 4 6% 6% 27%	2924
December	1st to 10th	Night	14% 16% 6% 15% 6% 5% 5% 4 4 5% 20%	4720
	11th to 20th	Night	23% 13% 5% 10% 5% 3 3 2 3 4 28%	5348
	21st to end	Night	19% 16% 5% 11% 6% 5% 4 3 4 4 23%	7150

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	65% 6% 11% 14% 4 1	4662
	11th to 20th	Day	65% 6% 9% 11% 7% 2	4680
	21st to end	Day	54% 7% 11% 19% 9% 1	5578
February	1st to 10th	Day	60% 5% 11% 15% 9%	1890
	11th to 20th	Day	57% 4 10% 17% 10% 1	1989
	21st to end	Day	57% 5% 11% 17% 8% 1	1730
March	1st to 10th	Day	56% 5% 12% 13% 11% 3	4579
	11th to 20th	Day	48% 6% 15% 21% 6% 4	4990
	21st to end	Day	54% 5% 8% 11% 18% 4	5993
April	1st to 10th	Day	56% 5% 8% 18% 10% 3	2520
	11th to 20th	Day	50% 6% 11% 19% 12% 2	2494
	21st to end	Day	53% 5% 9% 18% 12% 3	2533
May	1st to 10th	Day	57% 7% 10% 15% 10% 1	7922
	11th to 20th	Day	51% 8% 10% 21% 10% 1	8225
	21st to end	Day	53% 8% 13% 16% 9% 1	9061
June	1st to 10th	Day	47% 8% 13% 19% 13%	2940
	11th to 20th	Day	49% 9% 13% 19% 9% 1	2940
	21st to end	Day	48% 7% 13% 23% 9%	2940
July	1st to 10th	Day	45% 9% 13% 22% 10% 1	6290
	11th to 20th	Day	43% 10% 15% 22% 10%	6285
	21st to end	Day	42% 8% 12% 24% 13% 1	6728
August	1st to 10th	Day	52% 7% 14% 18% 9% 1	4357
	11th to 20th	Day	44% 10% 16% 25% 5%	3927
	21st to end	Day	41% 7% 13% 29% 9% 1	4312
September	1st to 10th	Day	45% 6% 12% 23% 14% 1	2400
	11th to 20th	Day	38% 6% 11% 23% 20% 1	2350
	21st to end	Day	48% 6% 11% 19% 14% 2	2200
October	1st to 10th	Day	47% 7% 9% 20% 15% 2	3297
	11th to 20th	Day	42% 6% 9% 21% 15% 7%	3240
	21st to end	Day	40% 6% 15% 23% 13% 2	3295
November	1st to 10th	Day	46% 6% 14% 18% 15% 2	1851
	11th to 20th	Day	55% 4 10% 16% 12% 2	1890
	21st to end	Day	60% 4 13% 17% 5% 1	1694
December	1st to 10th	Day	68% 6% 10% 11% 5% 1	2680
	11th to 20th	Day	61% 4 11% 14% 10% 1	3066
	21st to end	Day	62% 5% 9% 12% 10% 3	4048
January	1st to 10th	Night	64% 5% 11% 13% 6% 1	8234
	11th to 20th	Night	67% 8% 9% 9% 6% 1	8280
	21st to end	Night	57% 8% 11% 12% 11% 1	8599
February	1st to 10th	Night	56% 6% 14% 14% 9% 1	2730
	11th to 20th	Night	57% 5% 13% 16% 8% 1	2527
	21st to end	Night	54% 5% 13% 18% 9% 2	2076
March	1st to 10th	Night	52% 7% 13% 15% 10% 2	5494
	11th to 20th	Night	48% 6% 19% 16% 7% 3	5188
	21st to end	Night	53% 5% 8% 15% 17% 2	5180
April	1st to 10th	Night	57% 6% 10% 16% 10% 2	2100
	11th to 20th	Night	51% 6% 11% 17% 15%	2075
	21st to end	Night	49% 5% 9% 19% 15% 3	2084
May	1st to 10th	Night	56% 7% 11% 14% 10% 2	5050
	11th to 20th	Night	49% 9% 12% 20% 8% 1	4640
	21st to end	Night	54% 7% 12% 18% 9%	5115
June	1st to 10th	Night	42% 7% 12% 24% 14% 1	1680
	11th to 20th	Night	43% 8% 15% 24% 10%	1680
	21st to end	Night	36% 9% 18% 24% 13%	1680
July	1st to 10th	Night	43% 8% 15% 19% 14% 1	3560
	11th to 20th	Night	47% 9% 12% 20% 11% 1	3552
	21st to end	Night	36% 8% 13% 28% 13% 1	3809
August	1st to 10th	Night	52% 7% 14% 20% 7% 1	2764
	11th to 20th	Night	44% 7% 16% 25% 8%	3153
	21st to end	Night	35% 10% 13% 31% 11% 1	3586
September	1st to 10th	Night	39% 8% 12% 26% 15% 1	2000
	11th to 20th	Night	35% 6% 10% 26% 22% 1	2050
	21st to end	Night	45% 6% 11% 20% 17% 1	2200
October	1st to 10th	Night	48% 9% 9% 20% 13% 1	3880
	11th to 20th	Night	40% 6% 14% 18% 16% 7%	3899
	21st to end	Night	41% 6% 16% 22% 13% 1	4493
November	1st to 10th	Night	44% 6% 11% 20% 16% 2	2667
	11th to 20th	Night	52% 4 12% 17% 11% 3	2730
	21st to end	Night	54% 5% 16% 19% 6%	2924
December	1st to 10th	Night	63% 7% 11% 15% 3	4720
	11th to 20th	Night	59% 4 12% 12% 12%	5348
	21st to end	Night	62% 5% 10% 10% 10% 3	7150

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	35% 27% 27% 10% 1	220
	11th to 20th	Day	47% 25% 20% 6% 2	220
	21st to end	Day	38% 25% 27% 7% 3	326
February	1st to 10th	Day	37% 33% 24% 6%	330
	11th to 20th	Day	41% 29% 22% 6% 1	468
	21st to end	Day	36% 28% 27% 7% 2	446
March	1st to 10th	Day	35% 22% 28% 12% 2	540
	11th to 20th	Day	38% 23% 26% 10% 2	540
	21st to end	Day	38% 27% 22% 8% 4 1	594
April	1st to 10th	Day	41% 23% 22% 9% 4 1	540
	11th to 20th	Day	34% 25% 23% 11% 5% 2	532
	21st to end	Day	32% 21% 31% 9% 5% 2	540
May	1st to 10th	Day	39% 20% 25% 9% 4 2	543
	11th to 20th	Day	24% 21% 32% 16% 5% 2	567
	21st to end	Day	25% 12% 31% 20% 10% 3	617
June	1st to 10th	Day	22% 17% 30% 20% 9% 2	570
	11th to 20th	Day	23% 16% 29% 22% 8% 1	570
	21st to end	Day	21% 17% 33% 19% 8% 2	570
July	1st to 10th	Day	14% 12% 32% 26% 14% 3	525
	11th to 20th	Day	13% 11% 32% 29% 12% 3	524
	21st to end	Day	16% 13% 36% 21% 11% 3	576
August	1st to 10th	Day	14% 14% 27% 23% 16% 6%	526
	11th to 20th	Day	18% 10% 26% 26% 14% 6%	519
	21st to end	Day	17% 11% 30% 21% 13% 7%	583
September	1st to 10th	Day	23% 12% 23% 22% 14% 6%	530
	11th to 20th	Day	14% 12% 25% 23% 14% 12%	530
	21st to end	Day	26% 13% 25% 20% 11% 5%	530
October	1st to 10th	Day	28% 12% 24% 18% 13% 4	530
	11th to 20th	Day	27% 19% 26% 20% 7% 1	530
	21st to end	Day	33% 19% 27% 17% 5%	503
November	1st to 10th	Day	30% 22% 22% 18% 7% 2	425
	11th to 20th	Day	31% 25% 25% 13% 4 1	430
	21st to end	Day	36% 25% 28% 9% 1	234
December	1st to 10th	Day	37% 27% 24% 9% 3	220
	11th to 20th	Day	42% 25% 25% 7% 1	220
	21st to end	Day	38% 26% 25% 8% 2	242
January	1st to 10th	Night	30% 28% 29% 11% 2	840
	11th to 20th	Night	34% 22% 26% 16% 3	840
	21st to end	Night	26% 27% 31% 14% 2	924
February	1st to 10th	Night	32% 22% 30% 14% 1	840
	11th to 20th	Night	31% 27% 29% 12% 1	823
	21st to end	Night	35% 24% 25% 14% 2	692
March	1st to 10th	Night	33% 21% 29% 14% 2	840
	11th to 20th	Night	30% 26% 25% 17% 2	840
	21st to end	Night	28% 25% 28% 13% 5%	924
April	1st to 10th	Night	30% 23% 28% 15% 4	840
	11th to 20th	Night	27% 21% 28% 18% 6%	831
	21st to end	Night	27% 20% 26% 20% 7%	824
May	1st to 10th	Night	32% 16% 24% 22% 6% 1	557
	11th to 20th	Night	23% 13% 28% 30% 7%	414
	21st to end	Night	23% 9% 23% 30% 14% 1	455
June	1st to 10th	Night	21% 7% 27% 30% 14%	420
	11th to 20th	Night	22% 8% 22% 34% 13%	420
	21st to end	Night	14% 6% 25% 41% 13% 1	420
July	1st to 10th	Night	16% 8% 18% 38% 17% 2	390
	11th to 20th	Night	17% 4 21% 40% 17% 2	388
	21st to end	Night	15% 6% 21% 41% 16% 1	438
August	1st to 10th	Night	15% 4 22% 33% 23% 2	508
	11th to 20th	Night	18% 5% 16% 37% 20% 4	741
	21st to end	Night	19% 8% 16% 32% 23% 1	880
September	1st to 10th	Night	21% 7% 24% 26% 19% 3	800
	11th to 20th	Night	18% 8% 20% 27% 21% 7%	800
	21st to end	Night	22% 11% 21% 29% 14% 3	800
October	1st to 10th	Night	27% 15% 19% 21% 17% 2	800
	11th to 20th	Night	27% 14% 25% 26% 7%	800
	21st to end	Night	31% 20% 25% 19% 5%	880
November	1st to 10th	Night	24% 20% 26% 23% 7%	820
	11th to 20th	Night	32% 21% 22% 18% 6% 1	840
	21st to end	Night	27% 23% 27% 17% 4 1	840
December	1st to 10th	Night	34% 24% 25% 13% 4	840
	11th to 20th	Night	35% 22% 25% 16% 2	840
	21st to end	Night	33% 26% 24% 15% 2	924

Page generated at 2026-06-28 02:10:47. Version ac07

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