Big Trout Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Trout 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	13% 11% 4 10% 6% 6% 6% 5% 6% 7% 27%	107975
	Night	11% 13% 5% 13% 7% 7% 7% 5% 6% 5% 20%	110889
Transparency	Day	55% 6% 11% 19% 8%	111333
	Night	64% 5% 10% 16% 6%	115695
Seeing	Day	19% 12% 30% 25% 11% 3	16156
	Night	19% 10% 31% 28% 11% 2	25704

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	5% 11% 6% 17% 11% 10% 10% 5% 7% 8% 10%	2719
	11th to 20th	Day	4 8% 6% 24% 10% 11% 11% 6% 7% 5% 8%	3085
	21st to end	Day	9% 14% 6% 14% 7% 7% 8% 7% 10% 6% 12%	3732
February	1st to 10th	Day	3 11% 4 11% 7% 9% 11% 11% 11% 7% 14%	1600
	11th to 20th	Day	3 9% 4 12% 7% 9% 8% 7% 12% 9% 20%	1719
	21st to end	Day	3 10% 5% 10% 7% 8% 9% 8% 10% 7% 22%	1506
March	1st to 10th	Day	6% 11% 4 13% 8% 6% 6% 5% 5% 7% 29%	3118
	11th to 20th	Day	7% 15% 6% 14% 11% 8% 6% 5% 6% 4 18%	3347
	21st to end	Day	8% 16% 6% 11% 7% 6% 9% 7% 5% 5% 21%	4100
April	1st to 10th	Day	8% 11% 4 11% 6% 6% 6% 4 6% 6% 33%	2280
	11th to 20th	Day	11% 11% 3 11% 7% 6% 5% 4 6% 6% 32%	2386
	21st to end	Day	9% 10% 4 8% 5% 4 6% 4 6% 7% 38%	2660
May	1st to 10th	Day	14% 13% 4 11% 7% 5% 3 4 5% 6% 29%	4428
	11th to 20th	Day	16% 12% 4 10% 6% 4 4 4 6% 7% 29%	4516
	21st to end	Day	20% 9% 3 8% 5% 4 4 3 4 6% 34%	5488
June	1st to 10th	Day	19% 9% 3 7% 5% 6% 5% 4 6% 7% 30%	3040
	11th to 20th	Day	17% 7% 3 7% 5% 5% 5% 4 6% 7% 34%	3040
	21st to end	Day	16% 7% 2 7% 5% 5% 5% 5% 7% 7% 35%	3040
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 5% 7% 8% 36%	5070
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 5% 7% 9% 36%	5020
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 10% 38%	5060
August	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 39%	4423
	11th to 20th	Day	12% 6% 2 5% 4 4 4 3 5% 7% 48%	4356
	21st to end	Day	16% 6% 3 8% 5% 4 5% 4 5% 9% 35%	4495
September	1st to 10th	Day	22% 9% 3 7% 4 5% 4 4 5% 7% 31%	2280
	11th to 20th	Day	25% 11% 3 8% 5% 4 4 3 5% 6% 26%	2266
	21st to end	Day	19% 13% 3 7% 5% 5% 3 3 6% 6% 30%	2033
October	1st to 10th	Day	24% 20% 5% 8% 4 5% 4 4 5% 5% 19%	1900
	11th to 20th	Day	22% 20% 7% 12% 5% 4 5% 3 4 6% 14%	1786
	21st to end	Day	20% 25% 7% 14% 6% 4 3 2 3 4 12%	1843
November	1st to 10th	Day	17% 21% 9% 17% 8% 5% 4 3 4 4 10%	1567
	11th to 20th	Day	17% 19% 7% 16% 10% 8% 5% 3 4 3 9%	1454
	21st to end	Day	11% 23% 8% 18% 8% 8% 5% 4 4 3 7%	1400
December	1st to 10th	Day	6% 16% 6% 15% 10% 9% 7% 7% 8% 6% 10%	1970
	11th to 20th	Day	6% 15% 6% 18% 7% 6% 8% 8% 7% 5% 14%	2256
	21st to end	Day	10% 17% 6% 11% 7% 8% 8% 5% 6% 6% 16%	2992
January	1st to 10th	Night	5% 13% 7% 18% 9% 9% 11% 7% 7% 5% 10%	7247
	11th to 20th	Night	3 9% 7% 25% 12% 10% 9% 5% 8% 3 9%	6817
	21st to end	Night	8% 14% 6% 16% 8% 7% 10% 6% 10% 5% 9%	7244
February	1st to 10th	Night	6% 10% 5% 13% 8% 10% 14% 8% 7% 5% 14%	2800
	11th to 20th	Night	4 10% 4 11% 9% 10% 10% 9% 9% 6% 18%	2564
	21st to end	Night	5% 9% 5% 11% 7% 9% 9% 8% 8% 7% 22%	2043
March	1st to 10th	Night	7% 10% 4 12% 9% 7% 7% 5% 6% 7% 25%	3722
	11th to 20th	Night	9% 17% 6% 14% 10% 10% 5% 3 4 4 18%	3639
	21st to end	Night	8% 15% 5% 11% 6% 9% 10% 7% 5% 4 20%	3530
April	1st to 10th	Night	10% 10% 5% 10% 7% 5% 4 4 4 6% 33%	1900
	11th to 20th	Night	13% 12% 3 8% 7% 5% 3 3 5% 6% 35%	1740
	21st to end	Night	10% 9% 4 6% 5% 4 4 4 4 7% 40%	1520
May	1st to 10th	Night	18% 13% 5% 11% 6% 4 4 2 3 4 30%	2523
	11th to 20th	Night	23% 12% 3 7% 4 4 4 3 5% 5% 31%	2389
	21st to end	Night	20% 11% 4 9% 4 5% 6% 4 5% 6% 28%	2096
June	1st to 10th	Night	18% 9% 4 7% 5% 5% 4 4 7% 7% 30%	1140
	11th to 20th	Night	16% 9% 3 8% 4 5% 5% 3 5% 8% 34%	1140
	21st to end	Night	16% 7% 3 7% 6% 4 5% 4 5% 9% 35%	1140
July	1st to 10th	Night	14% 6% 2 8% 5% 5% 4 4 5% 8% 39%	1900
	11th to 20th	Night	14% 6% 2 6% 5% 5% 4 5% 6% 9% 38%	1947
	21st to end	Night	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	2503
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 6% 5% 8% 8% 34%	2517
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 6% 8% 49%	2483
	21st to end	Night	18% 8% 4 7% 4 4 4 3 5% 7% 37%	3152
September	1st to 10th	Night	20% 8% 3 7% 5% 5% 4 4 4 8% 34%	1900
	11th to 20th	Night	20% 12% 4 9% 5% 5% 4 3 4 6% 27%	1900
	21st to end	Night	23% 13% 3 8% 5% 4 3 3 4 5% 29%	2140
October	1st to 10th	Night	27% 17% 4 7% 6% 4 3 2 5% 5% 21%	2280
	11th to 20th	Night	21% 22% 5% 10% 5% 4 4 3 5% 5% 16%	2393
	21st to end	Night	20% 26% 7% 13% 5% 4 3 3 4 3 11%	2752
November	1st to 10th	Night	18% 21% 8% 14% 7% 6% 4 3 4 4 11%	2731
	11th to 20th	Night	14% 20% 9% 16% 10% 7% 5% 3 3 3 9%	2945
	21st to end	Night	12% 23% 9% 20% 8% 7% 5% 3 3 3 8%	3000
December	1st to 10th	Night	5% 18% 7% 18% 11% 9% 8% 6% 6% 4 7%	5215
	11th to 20th	Night	7% 15% 6% 16% 10% 8% 10% 8% 6% 4 10%	5951
	21st to end	Night	7% 17% 8% 15% 7% 8% 6% 4 5% 4 17%	7986

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	70% 4 8% 10% 8%	2720
	11th to 20th	Day	75% 5% 7% 11% 2	3113
	21st to end	Day	67% 4 6% 14% 10%	3732
February	1st to 10th	Day	59% 9% 10% 16% 7%	1600
	11th to 20th	Day	53% 7% 12% 21% 7%	1728
	21st to end	Day	53% 7% 10% 16% 13%	1506
March	1st to 10th	Day	55% 6% 11% 17% 10%	3120
	11th to 20th	Day	66% 5% 10% 13% 5%	3347
	21st to end	Day	64% 5% 8% 16% 6% 1	4100
April	1st to 10th	Day	51% 6% 12% 19% 11%	2280
	11th to 20th	Day	53% 6% 10% 20% 10% 1	2386
	21st to end	Day	45% 6% 10% 22% 15% 1	2660
May	1st to 10th	Day	56% 5% 14% 20% 5%	4440
	11th to 20th	Day	53% 8% 7% 16% 14% 2	4520
	21st to end	Day	50% 7% 8% 19% 15% 1	5488
June	1st to 10th	Day	53% 7% 8% 19% 12%	3040
	11th to 20th	Day	47% 7% 10% 21% 13% 2	3040
	21st to end	Day	45% 8% 11% 20% 13% 1	3040
July	1st to 10th	Day	44% 5% 18% 24% 9%	4991
	11th to 20th	Day	43% 6% 15% 30% 6% 1	4933
	21st to end	Day	40% 6% 19% 27% 7%	4900
August	1st to 10th	Day	40% 6% 16% 33% 5%	4408
	11th to 20th	Day	35% 6% 13% 32% 14%	4398
	21st to end	Day	47% 5% 19% 20% 8%	4494
September	1st to 10th	Day	53% 8% 15% 19% 6%	2280
	11th to 20th	Day	60% 5% 13% 20% 2	2266
	21st to end	Day	54% 7% 15% 18% 5%	2033
October	1st to 10th	Day	64% 4 10% 14% 7%	3160
	11th to 20th	Day	59% 8% 11% 18% 4	2950
	21st to end	Day	75% 5% 7% 12% 1	3021
November	1st to 10th	Day	80% 4 8% 6% 1	1567
	11th to 20th	Day	80% 5% 8% 5% 1	1454
	21st to end	Day	81% 4 7% 6% 2	1400
December	1st to 10th	Day	74% 5% 10% 9% 2	1970
	11th to 20th	Day	68% 3 6% 17% 5%	2256
	21st to end	Day	67% 5% 9% 13% 6%	2992
January	1st to 10th	Night	73% 5% 8% 9% 4 1	7247
	11th to 20th	Night	75% 3 9% 10% 2	6864
	21st to end	Night	71% 4 4 14% 7%	7244
February	1st to 10th	Night	67% 6% 7% 14% 6%	2800
	11th to 20th	Night	58% 7% 11% 19% 5%	2565
	21st to end	Night	56% 5% 10% 16% 13%	2043
March	1st to 10th	Night	56% 5% 9% 20% 8% 1	3733
	11th to 20th	Night	69% 4 7% 14% 4	3640
	21st to end	Night	65% 6% 6% 14% 8% 1	3530
April	1st to 10th	Night	51% 5% 8% 22% 14% 1	1900
	11th to 20th	Night	51% 4 8% 21% 13% 2	1740
	21st to end	Night	43% 5% 9% 21% 20% 1	1520
May	1st to 10th	Night	59% 4 11% 19% 7%	2530
	11th to 20th	Night	52% 7% 7% 14% 17% 3	2390
	21st to end	Night	56% 6% 9% 17% 12%	2096
June	1st to 10th	Night	51% 6% 11% 18% 13% 1	1140
	11th to 20th	Night	48% 7% 8% 20% 15% 1	1140
	21st to end	Night	46% 7% 12% 22% 12% 1	1140
July	1st to 10th	Night	43% 5% 19% 22% 11%	1870
	11th to 20th	Night	42% 6% 16% 31% 4 1	1911
	21st to end	Night	38% 6% 17% 33% 6%	2424
August	1st to 10th	Night	45% 7% 15% 27% 6%	2508
	11th to 20th	Night	33% 6% 15% 33% 13%	2507
	21st to end	Night	48% 5% 18% 21% 8%	3152
September	1st to 10th	Night	49% 7% 18% 21% 5% 1	1900
	11th to 20th	Night	58% 8% 16% 17% 1	1900
	21st to end	Night	58% 6% 13% 18% 6%	2140
October	1st to 10th	Night	61% 4 12% 16% 8%	3800
	11th to 20th	Night	60% 4 14% 17% 5%	3968
	21st to end	Night	76% 4 7% 10% 3	4526
November	1st to 10th	Night	78% 5% 9% 6% 2	2731
	11th to 20th	Night	82% 4 7% 6% 1	2945
	21st to end	Night	82% 3 6% 7% 2	3000
December	1st to 10th	Night	78% 6% 6% 8% 1	5215
	11th to 20th	Night	74% 4 9% 10% 2	5950
	21st to end	Night	70% 3 7% 16% 4	7986

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	11% 12% 39% 32% 7% 1	200
	11th to 20th	Day	9% 11% 33% 30% 13% 3	287
	21st to end	Day	15% 9% 27% 35% 12% 2	330
February	1st to 10th	Day	7% 9% 36% 35% 11% 2	300
	11th to 20th	Day	8% 11% 36% 27% 13% 5%	300
	21st to end	Day	6% 19% 33% 27% 12% 3	237
March	1st to 10th	Day	11% 10% 31% 29% 13% 6%	270
	11th to 20th	Day	9% 16% 45% 20% 8% 2	270
	21st to end	Day	13% 15% 33% 25% 10% 4	467
April	1st to 10th	Day	15% 11% 31% 28% 10% 5%	460
	11th to 20th	Day	19% 13% 30% 25% 12% 3	512
	21st to end	Day	15% 13% 30% 25% 14% 4	650
May	1st to 10th	Day	22% 12% 31% 24% 9% 1	653
	11th to 20th	Day	21% 14% 33% 22% 8% 2	675
	21st to end	Day	24% 15% 31% 23% 6% 1	734
June	1st to 10th	Day	26% 14% 30% 19% 8% 3	680
	11th to 20th	Day	20% 15% 27% 24% 12% 2	680
	21st to end	Day	20% 9% 27% 26% 16% 2	680
July	1st to 10th	Day	15% 11% 28% 31% 13% 2	671
	11th to 20th	Day	19% 9% 28% 25% 15% 4	668
	21st to end	Day	17% 7% 27% 25% 18% 5%	739
August	1st to 10th	Day	18% 10% 26% 29% 14% 2	676
	11th to 20th	Day	18% 12% 24% 25% 16% 6%	665
	21st to end	Day	25% 9% 25% 27% 11% 3	663
September	1st to 10th	Day	28% 13% 29% 21% 7% 1	490
	11th to 20th	Day	27% 11% 27% 23% 11% 1	490
	21st to end	Day	24% 12% 33% 22% 7% 2	433
October	1st to 10th	Day	30% 14% 32% 15% 7% 1	300
	11th to 20th	Day	27% 12% 23% 25% 12% 2	300
	21st to end	Day	29% 16% 29% 18% 7% 1	330
November	1st to 10th	Day	23% 15% 35% 18% 7% 1	300
	11th to 20th	Day	27% 12% 32% 22% 6% 1	226
	21st to end	Day	26% 17% 31% 20% 6% 2	200
December	1st to 10th	Day	17% 14% 30% 29% 9% 2	200
	11th to 20th	Day	17% 10% 37% 28% 9% 1	200
	21st to end	Day	15% 11% 27% 30% 11% 4	220
January	1st to 10th	Night	13% 8% 37% 29% 10% 2	1000
	11th to 20th	Night	14% 12% 31% 32% 10% 1	1000
	21st to end	Night	12% 7% 31% 35% 13% 1	1100
February	1st to 10th	Night	10% 9% 37% 33% 10% 1	1000
	11th to 20th	Night	8% 8% 34% 30% 16% 4	979
	21st to end	Night	9% 8% 33% 31% 15% 4	751
March	1st to 10th	Night	10% 8% 32% 29% 18% 2	760
	11th to 20th	Night	15% 12% 37% 24% 10% 1	665
	21st to end	Night	15% 11% 30% 29% 13% 3	627
April	1st to 10th	Night	14% 9% 34% 33% 9% 2	570
	11th to 20th	Night	19% 8% 29% 31% 12% 2	563
	21st to end	Night	13% 9% 33% 30% 13% 1	570
May	1st to 10th	Night	22% 9% 34% 28% 7%	570
	11th to 20th	Night	26% 9% 30% 26% 8% 1	496
	21st to end	Night	25% 11% 31% 27% 7%	411
June	1st to 10th	Night	20% 10% 34% 26% 9% 2	380
	11th to 20th	Night	18% 8% 31% 31% 12% 1	380
	21st to end	Night	18% 8% 30% 32% 11% 1	380
July	1st to 10th	Night	16% 6% 30% 34% 14% 1	370
	11th to 20th	Night	18% 7% 27% 33% 15%	389
	21st to end	Night	15% 6% 25% 33% 19% 3	624
August	1st to 10th	Night	21% 6% 22% 36% 13% 1	567
	11th to 20th	Night	18% 5% 26% 30% 18% 3	564
	21st to end	Night	26% 7% 24% 29% 12% 2	627
September	1st to 10th	Night	24% 7% 34% 28% 7% 1	570
	11th to 20th	Night	28% 8% 26% 27% 10% 1	570
	21st to end	Night	30% 9% 29% 24% 8% 1	755
October	1st to 10th	Night	36% 12% 25% 22% 5% 1	760
	11th to 20th	Night	30% 12% 24% 22% 9% 2	760
	21st to end	Night	34% 11% 30% 17% 7% 1	871
November	1st to 10th	Night	29% 13% 28% 22% 8% 1	975
	11th to 20th	Night	24% 10% 37% 20% 8% 2	1000
	21st to end	Night	24% 15% 33% 20% 5% 3	1000
December	1st to 10th	Night	15% 12% 38% 28% 7% 1	1000
	11th to 20th	Night	14% 11% 34% 29% 12% 2	1000
	21st to end	Night	14% 9% 34% 28% 12% 3	1100

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