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 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	12% 10% 4 10% 6% 6% 6% 5% 6% 7% 28%	138334
	Night	10% 13% 5% 13% 7% 7% 7% 5% 6% 5% 21%	134334
Transparency	Day	54% 5% 11% 20% 9% 1	141641
	Night	63% 4 9% 17% 7%	139116
Seeing	Day	19% 11% 29% 26% 12% 3	18065
	Night	19% 9% 31% 28% 11% 2	27380

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	4 11% 7% 17% 11% 10% 11% 5% 7% 7% 10%	3527
	11th to 20th	Day	4 10% 6% 23% 9% 10% 12% 7% 7% 4 7%	4031
	21st to end	Day	7% 11% 5% 14% 10% 9% 9% 7% 9% 7% 12%	4830
February	1st to 10th	Day	4 11% 4 12% 7% 9% 11% 11% 10% 7% 14%	1680
	11th to 20th	Day	3 9% 4 12% 8% 9% 8% 7% 12% 8% 20%	1807
	21st to end	Day	3 10% 5% 10% 7% 8% 10% 8% 10% 8% 21%	1620
March	1st to 10th	Day	5% 11% 5% 15% 9% 7% 7% 5% 6% 6% 24%	4578
	11th to 20th	Day	8% 12% 6% 12% 10% 10% 7% 6% 6% 4 18%	4897
	21st to end	Day	5% 11% 5% 10% 8% 9% 12% 6% 6% 7% 21%	6006
April	1st to 10th	Day	7% 10% 4 11% 6% 5% 6% 4 6% 6% 34%	2520
	11th to 20th	Day	11% 12% 4 11% 7% 6% 4 4 5% 5% 30%	2641
	21st to end	Day	10% 10% 4 8% 5% 5% 6% 4 6% 7% 36%	2940
May	1st to 10th	Day	13% 14% 5% 11% 6% 4 3 3 4 5% 32%	8241
	11th to 20th	Day	18% 12% 4 10% 5% 4 4 4 5% 6% 27%	8437
	21st to end	Day	13% 8% 3 7% 4 4 4 3 5% 7% 42%	10279
June	1st to 10th	Day	18% 8% 2 7% 5% 6% 6% 4 6% 8% 30%	3360
	11th to 20th	Day	18% 7% 3 7% 5% 5% 5% 4 6% 7% 33%	3360
	21st to end	Day	16% 7% 2 6% 5% 5% 5% 5% 7% 7% 36%	3360
July	1st to 10th	Day	10% 5% 2 7% 5% 5% 5% 5% 7% 8% 40%	7260
	11th to 20th	Day	16% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	7196
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 10% 41%	7276
August	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 6% 9% 39%	4563
	11th to 20th	Day	12% 6% 2 5% 4 4 4 3 5% 7% 47%	4496
	21st to end	Day	16% 6% 3 8% 5% 4 5% 4 5% 9% 35%	4637
September	1st to 10th	Day	23% 10% 3 7% 4 5% 4 4 5% 7% 30%	2400
	11th to 20th	Day	24% 11% 3 8% 5% 4 4 3 5% 6% 27%	2385
	21st to end	Day	19% 13% 3 7% 5% 5% 3 3 6% 6% 31%	2140
October	1st to 10th	Day	23% 19% 5% 8% 4 5% 4 4 5% 5% 19%	2000
	11th to 20th	Day	22% 21% 7% 12% 5% 4 4 3 4 5% 14%	1880
	21st to end	Day	20% 24% 7% 13% 6% 4 3 2 3 4 13%	1940
November	1st to 10th	Day	16% 21% 9% 17% 8% 5% 4 3 4 4 11%	1647
	11th to 20th	Day	17% 20% 7% 15% 10% 7% 5% 3 4 3 9%	1526
	21st to end	Day	11% 22% 8% 19% 8% 8% 5% 4 4 3 7%	1470
December	1st to 10th	Day	6% 16% 7% 15% 10% 9% 7% 7% 7% 6% 9%	2030
	11th to 20th	Day	6% 15% 5% 18% 8% 6% 8% 8% 7% 5% 14%	2316
	21st to end	Day	10% 17% 6% 12% 7% 8% 8% 5% 6% 6% 16%	3058
January	1st to 10th	Night	4 12% 7% 19% 10% 10% 11% 7% 7% 4 8%	9398
	11th to 20th	Night	4 11% 7% 23% 11% 10% 9% 6% 8% 3 9%	8881
	21st to end	Night	6% 11% 5% 14% 9% 10% 12% 8% 11% 5% 11%	9382
February	1st to 10th	Night	6% 10% 6% 13% 8% 10% 14% 8% 7% 5% 13%	2940
	11th to 20th	Night	3 10% 4 12% 9% 10% 10% 9% 9% 6% 18%	2695
	21st to end	Night	4 10% 5% 11% 7% 9% 9% 8% 9% 6% 21%	2186
March	1st to 10th	Night	5% 9% 5% 13% 10% 10% 8% 6% 6% 6% 23%	5482
	11th to 20th	Night	9% 14% 5% 13% 9% 10% 5% 5% 5% 5% 19%	5324
	21st to end	Night	6% 12% 4 10% 7% 10% 13% 6% 6% 7% 20%	5166
April	1st to 10th	Night	9% 10% 5% 11% 7% 6% 5% 4 5% 6% 32%	2100
	11th to 20th	Night	13% 13% 3 9% 7% 5% 3 3 5% 6% 32%	1925
	21st to end	Night	12% 9% 4 7% 5% 4 5% 4 4 7% 39%	1680
May	1st to 10th	Night	15% 15% 6% 11% 5% 4 3 2 3 3 33%	4688
	11th to 20th	Night	23% 12% 4 9% 4 4 3 3 5% 6% 28%	4441
	21st to end	Night	12% 8% 3 6% 3 5% 5% 3 6% 8% 41%	3926
June	1st to 10th	Night	17% 9% 4 7% 5% 5% 4 4 7% 8% 30%	1260
	11th to 20th	Night	17% 9% 3 8% 4 5% 5% 3 5% 8% 33%	1260
	21st to end	Night	16% 7% 3 7% 6% 4 5% 4 5% 9% 35%	1260
July	1st to 10th	Night	10% 5% 2 7% 4 5% 5% 4 6% 8% 43%	2720
	11th to 20th	Night	15% 6% 3 7% 5% 5% 5% 5% 6% 8% 35%	2781
	21st to end	Night	11% 5% 2 6% 5% 4 4 4 7% 8% 44%	3597
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 6% 5% 7% 8% 34%	2597
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 6% 8% 48%	2563
	21st to end	Night	18% 8% 4 7% 4 4 4 3 5% 7% 37%	3252
September	1st to 10th	Night	21% 8% 3 7% 5% 5% 4 4 4 8% 33%	2000
	11th to 20th	Night	20% 12% 3 9% 5% 4 4 3 5% 6% 29%	2000
	21st to end	Night	22% 13% 3 8% 5% 4 3 3 4 5% 30%	2253
October	1st to 10th	Night	27% 17% 4 7% 6% 4 3 2 5% 5% 21%	2400
	11th to 20th	Night	21% 22% 6% 9% 5% 4 4 3 4 5% 16%	2519
	21st to end	Night	20% 26% 7% 13% 5% 4 3 2 4 4 12%	2897
November	1st to 10th	Night	17% 21% 8% 15% 7% 6% 4 3 4 4 11%	2871
	11th to 20th	Night	14% 20% 10% 16% 10% 7% 4 3 2 3 9%	3092
	21st to end	Night	11% 23% 9% 20% 9% 7% 5% 3 3 3 8%	3150
December	1st to 10th	Night	5% 17% 7% 19% 11% 9% 8% 6% 6% 4 8%	5375
	11th to 20th	Night	7% 15% 6% 16% 10% 8% 10% 8% 6% 4 10%	6111
	21st to end	Night	7% 17% 7% 15% 7% 8% 6% 4 6% 4 17%	8162

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	71% 3 8% 11% 7%	3528
	11th to 20th	Day	75% 4 6% 12% 3	4059
	21st to end	Day	67% 3 7% 15% 8%	4830
February	1st to 10th	Day	60% 8% 9% 16% 6%	1680
	11th to 20th	Day	54% 6% 12% 21% 7%	1816
	21st to end	Day	53% 7% 10% 16% 13%	1620
March	1st to 10th	Day	58% 4 8% 16% 13% 1	4580
	11th to 20th	Day	65% 4 8% 14% 8% 1	4897
	21st to end	Day	61% 4 7% 21% 6% 1	6006
April	1st to 10th	Day	50% 5% 12% 21% 11%	2520
	11th to 20th	Day	54% 6% 10% 19% 9% 1	2641
	21st to end	Day	47% 6% 10% 22% 14% 1	2940
May	1st to 10th	Day	55% 3 11% 22% 9%	8250
	11th to 20th	Day	57% 5% 9% 17% 11% 1	8441
	21st to end	Day	41% 4 9% 22% 20% 3	10280
June	1st to 10th	Day	52% 7% 9% 19% 13%	3360
	11th to 20th	Day	48% 7% 10% 21% 12% 1	3360
	21st to end	Day	45% 8% 11% 21% 14% 1	3360
July	1st to 10th	Day	39% 4 16% 32% 9%	7182
	11th to 20th	Day	45% 5% 14% 29% 7%	7109
	21st to end	Day	37% 5% 20% 32% 7%	7066
August	1st to 10th	Day	40% 6% 16% 33% 5%	4548
	11th to 20th	Day	37% 6% 13% 31% 13%	4538
	21st to end	Day	47% 5% 19% 21% 8%	4636
September	1st to 10th	Day	54% 7% 15% 19% 5%	2400
	11th to 20th	Day	58% 5% 14% 21% 2	2385
	21st to end	Day	54% 7% 16% 18% 5%	2140
October	1st to 10th	Day	64% 4 11% 14% 7%	3260
	11th to 20th	Day	60% 8% 10% 18% 4	3044
	21st to end	Day	74% 5% 7% 13% 1	3118
November	1st to 10th	Day	79% 4 8% 7% 2	1647
	11th to 20th	Day	80% 5% 9% 5% 2	1526
	21st to end	Day	82% 4 7% 5% 2	1470
December	1st to 10th	Day	74% 5% 9% 9% 2	2030
	11th to 20th	Day	69% 3 6% 17% 5%	2316
	21st to end	Day	67% 5% 9% 13% 5%	3058
January	1st to 10th	Night	75% 5% 7% 9% 4 1	9398
	11th to 20th	Night	76% 3 8% 11% 2	8928
	21st to end	Night	69% 3 6% 16% 5%	9382
February	1st to 10th	Night	68% 6% 7% 14% 5%	2940
	11th to 20th	Night	59% 6% 10% 19% 5%	2696
	21st to end	Night	57% 5% 9% 16% 13%	2186
March	1st to 10th	Night	59% 4 7% 17% 10% 3	5493
	11th to 20th	Night	66% 4 7% 12% 11%	5325
	21st to end	Night	61% 5% 5% 19% 9% 1	5166
April	1st to 10th	Night	51% 5% 7% 23% 14% 1	2100
	11th to 20th	Night	54% 4 8% 19% 12% 2	1925
	21st to end	Night	45% 4 9% 21% 19% 1	1680
May	1st to 10th	Night	58% 3 8% 21% 11%	4695
	11th to 20th	Night	56% 5% 10% 16% 12% 1	4442
	21st to end	Night	41% 4 9% 24% 21% 1	3926
June	1st to 10th	Night	50% 5% 12% 19% 13% 1	1260
	11th to 20th	Night	49% 7% 8% 20% 15% 1	1260
	21st to end	Night	45% 7% 11% 23% 13% 2	1260
July	1st to 10th	Night	38% 4 15% 29% 13%	2690
	11th to 20th	Night	47% 4 15% 30% 4	2745
	21st to end	Night	37% 5% 14% 38% 6%	3494
August	1st to 10th	Night	45% 6% 15% 27% 6%	2588
	11th to 20th	Night	34% 6% 16% 32% 12%	2587
	21st to end	Night	48% 4 18% 22% 8%	3252
September	1st to 10th	Night	50% 6% 17% 21% 5% 1	2000
	11th to 20th	Night	56% 7% 17% 19% 1	2000
	21st to end	Night	57% 6% 13% 19% 6%	2253
October	1st to 10th	Night	61% 4 12% 16% 7%	3920
	11th to 20th	Night	60% 4 14% 17% 5%	4094
	21st to end	Night	75% 4 8% 10% 3	4671
November	1st to 10th	Night	78% 5% 8% 7% 2	2871
	11th to 20th	Night	82% 4 7% 6% 1	3092
	21st to end	Night	83% 3 5% 7% 2	3150
December	1st to 10th	Night	78% 6% 6% 8% 2	5375
	11th to 20th	Night	75% 4 9% 10% 2	6110
	21st to end	Night	70% 3 7% 16% 4	8162

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% 11% 37% 31% 8% 1	220
	11th to 20th	Day	10% 10% 34% 30% 12% 3	316
	21st to end	Day	13% 9% 26% 34% 14% 3	363
February	1st to 10th	Day	8% 9% 35% 33% 12% 2	330
	11th to 20th	Day	7% 10% 35% 28% 14% 6%	330
	21st to end	Day	6% 17% 31% 29% 13% 4	273
March	1st to 10th	Day	11% 8% 32% 32% 13% 5%	330
	11th to 20th	Day	9% 13% 40% 26% 10% 2	330
	21st to end	Day	11% 12% 30% 30% 12% 4	551
April	1st to 10th	Day	13% 10% 28% 30% 13% 6%	540
	11th to 20th	Day	19% 11% 30% 26% 12% 2	599
	21st to end	Day	16% 11% 28% 24% 15% 5%	750
May	1st to 10th	Day	21% 11% 29% 26% 11% 3	753
	11th to 20th	Day	22% 12% 31% 23% 9% 3	775
	21st to end	Day	21% 13% 28% 26% 9% 2	844
June	1st to 10th	Day	24% 12% 27% 23% 11% 3	780
	11th to 20th	Day	21% 13% 25% 25% 14% 2	780
	21st to end	Day	19% 8% 25% 25% 17% 6%	780
July	1st to 10th	Day	14% 11% 28% 31% 15% 3	722
	11th to 20th	Day	20% 9% 26% 27% 15% 4	718
	21st to end	Day	16% 6% 27% 27% 18% 5%	794
August	1st to 10th	Day	18% 10% 25% 28% 16% 3	726
	11th to 20th	Day	19% 11% 24% 24% 16% 6%	715
	21st to end	Day	25% 8% 24% 27% 12% 4	713
September	1st to 10th	Day	29% 12% 28% 21% 8% 2	530
	11th to 20th	Day	26% 10% 25% 23% 14% 2	530
	21st to end	Day	24% 11% 31% 23% 9% 3	470
October	1st to 10th	Day	29% 13% 31% 18% 8% 1	330
	11th to 20th	Day	28% 11% 25% 24% 12% 2	330
	21st to end	Day	29% 15% 28% 18% 8% 2	363
November	1st to 10th	Day	23% 14% 36% 18% 7% 1	330
	11th to 20th	Day	27% 12% 32% 21% 6% 1	248
	21st to end	Day	24% 15% 31% 21% 7% 1	220
December	1st to 10th	Day	15% 13% 30% 31% 10% 1	220
	11th to 20th	Day	15% 9% 36% 30% 9%	220
	21st to end	Day	14% 11% 29% 31% 12% 4	242
January	1st to 10th	Night	13% 8% 37% 30% 10% 2	1050
	11th to 20th	Night	14% 11% 31% 33% 10% 1	1050
	21st to end	Night	12% 7% 31% 35% 14% 1	1155
February	1st to 10th	Night	10% 9% 36% 33% 11% 1	1050
	11th to 20th	Night	9% 8% 34% 30% 16% 4	1029
	21st to end	Night	10% 7% 32% 32% 15% 4	802
March	1st to 10th	Night	10% 8% 32% 31% 18% 2	840
	11th to 20th	Night	15% 11% 35% 27% 11% 1	735
	21st to end	Night	14% 10% 29% 31% 13% 3	693
April	1st to 10th	Night	13% 8% 32% 35% 10% 2	630
	11th to 20th	Night	20% 7% 29% 31% 11% 2	623
	21st to end	Night	15% 8% 32% 30% 14% 1	630
May	1st to 10th	Night	22% 9% 31% 29% 8%	630
	11th to 20th	Night	26% 9% 28% 27% 9% 1	548
	21st to end	Night	23% 10% 29% 28% 10%	455
June	1st to 10th	Night	19% 9% 32% 27% 11% 2	420
	11th to 20th	Night	19% 8% 29% 31% 13% 1	420
	21st to end	Night	18% 8% 28% 31% 15% 1	420
July	1st to 10th	Night	16% 5% 29% 34% 14% 1	390
	11th to 20th	Night	18% 7% 27% 34% 15%	410
	21st to end	Night	15% 5% 25% 33% 19% 3	657
August	1st to 10th	Night	21% 6% 22% 35% 15% 1	597
	11th to 20th	Night	20% 5% 26% 29% 18% 3	594
	21st to end	Night	25% 7% 23% 30% 12% 2	660
September	1st to 10th	Night	25% 7% 33% 28% 7% 1	600
	11th to 20th	Night	27% 8% 25% 28% 12% 1	600
	21st to end	Night	29% 9% 29% 23% 9% 1	795
October	1st to 10th	Night	36% 11% 25% 22% 4 1	800
	11th to 20th	Night	31% 11% 24% 22% 10% 2	800
	21st to end	Night	34% 11% 29% 18% 7% 1	917
November	1st to 10th	Night	28% 13% 29% 21% 8% 1	1025
	11th to 20th	Night	24% 10% 37% 20% 7% 2	1050
	21st to end	Night	24% 15% 33% 21% 5% 3	1050
December	1st to 10th	Night	14% 12% 38% 28% 7% 1	1050
	11th to 20th	Night	14% 10% 34% 29% 12% 1	1050
	21st to end	Night	14% 9% 34% 28% 11% 3	1155

Page generated at 2026-06-28 01:10:47. Version ac07

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