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 2025-02-25.

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%	108654
	Night	16% 11% 4 10% 6% 4 4 3 5% 6% 30%	110023
Transparency	Day	51% 7% 12% 19% 10% 1	112191
	Night	51% 6% 12% 17% 11% 1	114650
Seeing	Day	27% 18% 27% 16% 8% 3	15122
	Night	26% 18% 25% 22% 8% 1	24423

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	10% 14% 8% 19% 8% 7% 5% 3 4 5% 18%	3597
	11th to 20th	Day	14% 14% 7% 18% 9% 6% 5% 3 4 4 16%	3570
	21st to end	Day	17% 14% 7% 10% 5% 4 4 4 4 4 27%	4306
February	1st to 10th	Day	15% 14% 5% 12% 9% 5% 5% 3 5% 5% 22%	1800
	11th to 20th	Day	13% 12% 4 12% 7% 6% 4 3 5% 7% 27%	1883
	21st to end	Day	18% 13% 3 10% 6% 5% 4 3 5% 5% 27%	1610
March	1st to 10th	Day	21% 16% 4 9% 5% 4 3 2 3 5% 28%	3116
	11th to 20th	Day	10% 14% 7% 12% 5% 5% 5% 4 5% 6% 28%	3410
	21st to end	Day	20% 12% 3 8% 5% 4 4 2 4 5% 32%	4088
April	1st to 10th	Day	18% 15% 4 8% 5% 4 4 3 4 5% 30%	2280
	11th to 20th	Day	17% 11% 3 7% 5% 5% 3 4 5% 5% 33%	2254
	21st to end	Day	18% 12% 3 9% 5% 5% 4 3 4 5% 32%	2291
May	1st to 10th	Day	27% 10% 3 7% 4 3 3 3 4 6% 30%	4253
	11th to 20th	Day	20% 9% 3 9% 6% 5% 6% 5% 5% 7% 25%	4398
	21st to end	Day	14% 6% 2 6% 4 5% 5% 4 7% 8% 37%	4837
June	1st to 10th	Day	17% 7% 3 8% 6% 6% 5% 4 7% 8% 30%	2660
	11th to 20th	Day	18% 7% 3 7% 5% 6% 5% 5% 7% 9% 29%	2660
	21st to end	Day	16% 8% 3 8% 5% 4 4 5% 6% 9% 31%	2660
July	1st to 10th	Day	11% 7% 3 8% 6% 5% 5% 5% 8% 9% 33%	4440
	11th to 20th	Day	11% 6% 3 7% 5% 5% 6% 5% 9% 11% 32%	4440
	21st to end	Day	15% 8% 3 8% 6% 6% 5% 5% 7% 8% 29%	4814
August	1st to 10th	Day	21% 8% 3 8% 5% 5% 5% 4 5% 7% 28%	4237
	11th to 20th	Day	14% 8% 3 7% 5% 5% 6% 6% 8% 9% 30%	3769
	21st to end	Day	17% 5% 2 6% 4 5% 5% 4 7% 8% 36%	4180
September	1st to 10th	Day	18% 6% 3 7% 5% 4 4 3 5% 8% 37%	2280
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 8% 42%	2233
	21st to end	Day	20% 8% 2 7% 4 4 4 4 5% 6% 35%	2090
October	1st to 10th	Day	19% 10% 3 8% 4 4 4 3 5% 6% 32%	1923
	11th to 20th	Day	17% 11% 3 6% 5% 4 5% 4 5% 6% 35%	1900
	21st to end	Day	23% 13% 3 6% 5% 5% 4 3 5% 6% 27%	1954
November	1st to 10th	Day	14% 10% 4 7% 4 3 5% 4 4 6% 39%	1761
	11th to 20th	Day	16% 13% 4 10% 5% 4 4 3 4 5% 33%	1800
	21st to end	Day	18% 13% 4 10% 6% 4 5% 3 4 5% 27%	1614
December	1st to 10th	Day	14% 16% 6% 19% 7% 6% 5% 3 4 4 17%	2600
	11th to 20th	Day	19% 16% 6% 10% 5% 3 4 2 4 4 27%	2986
	21st to end	Day	17% 17% 5% 12% 6% 4 4 3 5% 6% 22%	3960
January	1st to 10th	Night	12% 11% 6% 20% 8% 5% 5% 3 4 5% 20%	6349
	11th to 20th	Night	11% 14% 8% 18% 10% 6% 4 3 4 4 17%	6315
	21st to end	Night	15% 12% 4 11% 7% 5% 5% 4 6% 6% 24%	6646
February	1st to 10th	Night	15% 13% 4 10% 7% 5% 6% 4 6% 5% 25%	2600
	11th to 20th	Night	13% 11% 4 13% 8% 7% 4 4 6% 6% 24%	2402
	21st to end	Night	17% 11% 4 11% 6% 4 3 4 5% 6% 28%	1939
March	1st to 10th	Night	19% 16% 4 8% 4 4 4 3 5% 4 28%	3724
	11th to 20th	Night	10% 13% 8% 11% 7% 5% 4 3 5% 5% 29%	3547
	21st to end	Night	13% 13% 4 10% 6% 5% 4 3 4 4 34%	3543
April	1st to 10th	Night	16% 14% 4 10% 5% 5% 4 4 5% 6% 27%	1900
	11th to 20th	Night	18% 11% 4 7% 5% 4 4 3 4 6% 35%	1875
	21st to end	Night	19% 10% 4 8% 4 3 3 3 5% 5% 35%	1886
May	1st to 10th	Night	26% 9% 3 7% 4 3 4 3 4 6% 31%	2716
	11th to 20th	Night	20% 11% 4 8% 4 4 4 4 6% 7% 30%	2495
	21st to end	Night	15% 10% 2 7% 4 4 5% 4 6% 8% 36%	2738
June	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 7% 8% 38%	1520
	11th to 20th	Night	16% 8% 3 4 4 4 4 4 6% 9% 39%	1520
	21st to end	Night	13% 5% 2 5% 5% 4 5% 4 7% 10% 41%	1520
July	1st to 10th	Night	13% 6% 3 7% 6% 5% 5% 4 6% 8% 37%	2520
	11th to 20th	Night	15% 9% 2 6% 4 4 4 4 7% 9% 38%	2520
	21st to end	Night	18% 7% 3 6% 5% 5% 4 4 6% 6% 37%	2739
August	1st to 10th	Night	23% 9% 3 8% 4 4 4 4 5% 6% 31%	2688
	11th to 20th	Night	17% 9% 2 7% 5% 3 4 3 5% 6% 38%	3026
	21st to end	Night	13% 6% 2 5% 4 5% 5% 4 5% 6% 44%	3476
September	1st to 10th	Night	16% 8% 2 6% 4 3 4 3 6% 7% 42%	1900
	11th to 20th	Night	15% 6% 2 5% 4 3 3 3 4 7% 49%	1947
	21st to end	Night	18% 8% 3 7% 5% 4 4 3 4 7% 38%	2090
October	1st to 10th	Night	20% 9% 4 7% 3 4 4 3 5% 5% 36%	2254
	11th to 20th	Night	19% 10% 3 6% 4 4 3 3 4 6% 39%	2280
	21st to end	Night	21% 14% 4 7% 4 4 3 3 5% 6% 29%	2642
November	1st to 10th	Night	13% 9% 3 7% 4 4 4 4 5% 5% 40%	2537
	11th to 20th	Night	19% 11% 4 8% 5% 4 4 4 5% 6% 32%	2600
	21st to end	Night	15% 12% 4 9% 6% 5% 5% 4 6% 6% 28%	2785
December	1st to 10th	Night	14% 16% 6% 15% 6% 5% 5% 4 4 5% 19%	4580
	11th to 20th	Night	24% 13% 5% 10% 5% 3 3 2 3 4 28%	5208
	21st to end	Night	19% 16% 5% 11% 6% 5% 4 3 4 4 23%	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	62% 5% 12% 15% 4 1	3598
	11th to 20th	Day	69% 6% 8% 10% 5% 2	3600
	21st to end	Day	57% 5% 10% 19% 8% 1	4306
February	1st to 10th	Day	61% 5% 12% 14% 8%	1800
	11th to 20th	Day	56% 4 10% 18% 11% 1	1892
	21st to end	Day	57% 5% 11% 17% 8% 1	1610
March	1st to 10th	Day	59% 4 13% 14% 9% 1	3119
	11th to 20th	Day	52% 7% 13% 20% 8% 1	3410
	21st to end	Day	55% 3 8% 13% 17% 4	4088
April	1st to 10th	Day	56% 5% 8% 19% 10% 3	2280
	11th to 20th	Day	50% 5% 11% 19% 13% 2	2254
	21st to end	Day	54% 5% 9% 18% 11% 3	2291
May	1st to 10th	Day	55% 6% 9% 18% 10% 2	4267
	11th to 20th	Day	55% 10% 10% 18% 7% 1	4402
	21st to end	Day	40% 9% 13% 24% 13% 1	4837
June	1st to 10th	Day	48% 8% 13% 18% 12%	2660
	11th to 20th	Day	49% 9% 13% 19% 9% 1	2660
	21st to end	Day	48% 7% 13% 23% 9%	2660
July	1st to 10th	Day	44% 10% 13% 23% 10% 1	4370
	11th to 20th	Day	41% 10% 17% 21% 11%	4365
	21st to end	Day	49% 9% 13% 18% 11% 1	4661
August	1st to 10th	Day	53% 7% 14% 18% 8%	4223
	11th to 20th	Day	44% 10% 16% 24% 5%	3806
	21st to end	Day	41% 7% 13% 28% 9% 1	4180
September	1st to 10th	Day	45% 6% 12% 23% 13% 1	2280
	11th to 20th	Day	39% 5% 11% 23% 20% 1	2233
	21st to end	Day	48% 6% 11% 19% 14% 2	2090
October	1st to 10th	Day	48% 8% 9% 19% 15% 1	3196
	11th to 20th	Day	42% 6% 9% 21% 15% 7%	3140
	21st to end	Day	40% 6% 15% 24% 13% 2	3192
November	1st to 10th	Day	45% 6% 14% 18% 15% 2	1761
	11th to 20th	Day	54% 4 11% 17% 12% 3	1800
	21st to end	Day	58% 4 14% 18% 5% 1	1614
December	1st to 10th	Day	69% 6% 10% 10% 4 1	2600
	11th to 20th	Day	61% 4 11% 13% 10% 1	2986
	21st to end	Day	61% 5% 9% 12% 10% 3	3960
January	1st to 10th	Night	61% 5% 12% 14% 7% 1	6349
	11th to 20th	Night	65% 8% 11% 10% 6% 1	6360
	21st to end	Night	55% 6% 13% 11% 13% 1	6646
February	1st to 10th	Night	56% 6% 14% 14% 8% 1	2600
	11th to 20th	Night	57% 5% 13% 16% 9% 1	2404
	21st to end	Night	53% 4 13% 18% 9% 2	1939
March	1st to 10th	Night	56% 5% 12% 17% 8% 2	3734
	11th to 20th	Night	52% 6% 15% 18% 7% 1	3548
	21st to end	Night	51% 4 10% 16% 17% 3	3543
April	1st to 10th	Night	55% 6% 10% 17% 10% 2	1900
	11th to 20th	Night	49% 6% 11% 18% 15%	1875
	21st to end	Night	49% 5% 10% 20% 14% 3	1886
May	1st to 10th	Night	54% 6% 9% 19% 9% 3	2722
	11th to 20th	Night	52% 9% 11% 19% 8% 1	2496
	21st to end	Night	43% 9% 14% 20% 13% 1	2739
June	1st to 10th	Night	42% 7% 12% 24% 13% 1	1520
	11th to 20th	Night	41% 8% 17% 24% 11%	1520
	21st to end	Night	36% 9% 17% 25% 13%	1520
July	1st to 10th	Night	42% 9% 16% 18% 14% 1	2480
	11th to 20th	Night	41% 9% 14% 24% 11%	2472
	21st to end	Night	44% 8% 13% 21% 13% 1	2651
August	1st to 10th	Night	52% 7% 14% 19% 7% 1	2678
	11th to 20th	Night	44% 7% 16% 25% 8%	3055
	21st to end	Night	35% 10% 13% 31% 11%	3476
September	1st to 10th	Night	40% 8% 12% 25% 14% 1	1900
	11th to 20th	Night	36% 6% 10% 24% 22% 1	1947
	21st to end	Night	45% 6% 10% 20% 17% 1	2090
October	1st to 10th	Night	49% 9% 10% 19% 13% 1	3761
	11th to 20th	Night	40% 6% 14% 17% 16% 7%	3779
	21st to end	Night	41% 6% 16% 23% 12% 2	4354
November	1st to 10th	Night	44% 6% 12% 20% 17% 2	2537
	11th to 20th	Night	51% 4 12% 18% 12% 3	2600
	21st to end	Night	52% 5% 16% 19% 6%	2785
December	1st to 10th	Night	63% 7% 11% 15% 3	4580
	11th to 20th	Night	59% 4 12% 12% 12%	5208
	21st to end	Night	62% 5% 10% 10% 10% 3	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	35% 27% 27% 11% 1 1	200
	11th to 20th	Day	46% 24% 22% 7% 2	200
	21st to end	Day	34% 26% 29% 7% 3	296
February	1st to 10th	Day	38% 33% 23% 5%	300
	11th to 20th	Day	42% 30% 20% 6% 1	431
	21st to end	Day	37% 24% 29% 8% 2	398
March	1st to 10th	Day	34% 22% 28% 13% 3	460
	11th to 20th	Day	37% 24% 25% 11% 3	460
	21st to end	Day	36% 26% 23% 9% 5% 1	506
April	1st to 10th	Day	37% 24% 24% 10% 4 1	460
	11th to 20th	Day	34% 23% 23% 12% 6% 3	452
	21st to end	Day	31% 21% 32% 9% 5% 2	460
May	1st to 10th	Day	38% 18% 26% 11% 5% 3	463
	11th to 20th	Day	24% 20% 31% 17% 5% 3	487
	21st to end	Day	22% 10% 31% 22% 11% 3	529
June	1st to 10th	Day	22% 16% 32% 19% 9% 2	490
	11th to 20th	Day	20% 15% 29% 25% 10% 1	490
	21st to end	Day	21% 16% 33% 19% 9% 1	490
July	1st to 10th	Day	14% 11% 32% 26% 14% 3	485
	11th to 20th	Day	13% 10% 33% 30% 13% 2	484
	21st to end	Day	16% 14% 35% 21% 11% 3	532
August	1st to 10th	Day	15% 14% 26% 23% 16% 5%	486
	11th to 20th	Day	18% 10% 27% 24% 14% 6%	479
	21st to end	Day	18% 11% 29% 21% 14% 7%	539
September	1st to 10th	Day	24% 12% 23% 21% 14% 6%	490
	11th to 20th	Day	15% 13% 25% 22% 14% 11%	490
	21st to end	Day	26% 13% 26% 19% 11% 5%	490
October	1st to 10th	Day	30% 13% 24% 17% 12% 3	490
	11th to 20th	Day	26% 18% 27% 21% 7% 1	490
	21st to end	Day	33% 18% 27% 17% 5%	466
November	1st to 10th	Day	29% 22% 21% 19% 8% 2	395
	11th to 20th	Day	31% 24% 26% 14% 5% 1	400
	21st to end	Day	35% 24% 30% 10% 1	214
December	1st to 10th	Day	36% 27% 25% 10% 3 1	200
	11th to 20th	Day	42% 24% 25% 8% 2	200
	21st to end	Day	36% 27% 25% 9% 2	220
January	1st to 10th	Night	30% 28% 29% 11% 2	800
	11th to 20th	Night	33% 22% 26% 17% 3	800
	21st to end	Night	25% 26% 32% 15% 3	880
February	1st to 10th	Night	32% 22% 31% 14% 1	800
	11th to 20th	Night	32% 28% 28% 11% 1	783
	21st to end	Night	36% 23% 25% 14% 2	647
March	1st to 10th	Night	32% 21% 30% 14% 3	760
	11th to 20th	Night	28% 27% 26% 17% 3	760
	21st to end	Night	28% 24% 28% 14% 5%	836
April	1st to 10th	Night	29% 22% 29% 16% 4	760
	11th to 20th	Night	26% 21% 28% 19% 7%	751
	21st to end	Night	27% 19% 26% 20% 7%	746
May	1st to 10th	Night	31% 15% 22% 24% 6% 1	504
	11th to 20th	Night	22% 12% 29% 30% 6%	374
	21st to end	Night	21% 9% 22% 32% 15% 1	411
June	1st to 10th	Night	21% 8% 27% 30% 14%	380
	11th to 20th	Night	19% 8% 22% 36% 14% 1	380
	21st to end	Night	13% 6% 25% 41% 14% 1	380
July	1st to 10th	Night	16% 8% 19% 38% 17% 2	370
	11th to 20th	Night	17% 2 22% 40% 17% 2	368
	21st to end	Night	15% 6% 20% 40% 17% 1	416
August	1st to 10th	Night	15% 5% 23% 33% 23% 2	482
	11th to 20th	Night	19% 5% 16% 37% 19% 4	703
	21st to end	Night	19% 8% 16% 33% 23% 2	836
September	1st to 10th	Night	21% 7% 25% 26% 18% 3	760
	11th to 20th	Night	19% 8% 21% 26% 20% 7%	760
	21st to end	Night	23% 11% 21% 29% 14% 3	760
October	1st to 10th	Night	28% 15% 19% 21% 15% 2	760
	11th to 20th	Night	26% 14% 26% 27% 8%	760
	21st to end	Night	31% 19% 26% 19% 5%	836
November	1st to 10th	Night	22% 21% 26% 23% 8% 1	780
	11th to 20th	Night	31% 21% 23% 18% 6% 1	800
	21st to end	Night	26% 24% 28% 17% 5% 1	800
December	1st to 10th	Night	34% 24% 24% 13% 4	800
	11th to 20th	Night	34% 22% 25% 17% 2	800
	21st to end	Night	32% 26% 24% 15% 3	880

Page generated at 2025-02-22 06:51:37. Version ac07

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