Fort Frances
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Frances clear sky chart from 2005-11-06 to 2025-10-04.

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% 10% 4 9% 5% 5% 5% 4 6% 7% 33%	127007
	Night	12% 12% 5% 11% 6% 5% 5% 4 5% 6% 30%	122651
Transparency	Day	49% 7% 13% 22% 9% 1	130471
	Night	53% 6% 12% 20% 9% 1	127275
Seeing	Day	18% 12% 31% 25% 11% 3	17511
	Night	18% 9% 32% 29% 11% 1	27330

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	6% 13% 7% 16% 8% 7% 6% 4 6% 5% 22%	3178
	11th to 20th	Day	5% 13% 5% 15% 9% 7% 8% 9% 10% 5% 14%	3152
	21st to end	Day	6% 17% 12% 18% 7% 6% 5% 3 4 5% 17%	4162
February	1st to 10th	Day	8% 13% 5% 13% 8% 5% 10% 6% 6% 7% 21%	1800
	11th to 20th	Day	8% 10% 4 11% 7% 6% 5% 5% 6% 7% 31%	1754
	21st to end	Day	7% 13% 4 13% 7% 5% 5% 3 4 7% 32%	1490
March	1st to 10th	Day	9% 10% 3 8% 4 4 4 3 5% 7% 42%	4746
	11th to 20th	Day	10% 10% 5% 12% 7% 5% 4 4 6% 7% 31%	4980
	21st to end	Day	16% 12% 4 8% 5% 3 4 4 4 6% 33%	5555
April	1st to 10th	Day	15% 10% 3 9% 5% 5% 5% 4 5% 7% 32%	2400
	11th to 20th	Day	16% 11% 3 7% 5% 5% 5% 4 5% 7% 31%	2482
	21st to end	Day	18% 11% 3 7% 5% 5% 4 4 4 6% 33%	2620
May	1st to 10th	Day	15% 7% 2 5% 3 4 4 3 5% 7% 45%	6348
	11th to 20th	Day	14% 8% 3 7% 5% 5% 5% 4 6% 8% 35%	6319
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 7% 44%	7037
June	1st to 10th	Day	14% 6% 2 7% 5% 5% 4 5% 7% 8% 37%	3000
	11th to 20th	Day	16% 6% 3 6% 5% 5% 5% 4 5% 7% 37%	3000
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 8% 33%	3000
July	1st to 10th	Day	8% 5% 2 5% 5% 6% 6% 5% 8% 9% 42%	6799
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 7% 9% 40%	6800
	21st to end	Day	12% 7% 3 6% 4 4 5% 4 6% 9% 38%	7023
August	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4442
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 5% 7% 11% 42%	4171
	21st to end	Day	14% 6% 2 6% 4 5% 5% 3 6% 9% 40%	4581
September	1st to 10th	Day	13% 7% 2 7% 4 4 5% 3 6% 7% 43%	2400
	11th to 20th	Day	15% 7% 3 7% 4 4 4 4 5% 8% 37%	2374
	21st to end	Day	19% 7% 3 7% 3 3 4 3 5% 6% 39%	2103
October	1st to 10th	Day	18% 11% 3 8% 5% 4 3 4 5% 7% 31%	1930
	11th to 20th	Day	18% 14% 4 9% 5% 4 4 4 5% 5% 27%	1900
	21st to end	Day	19% 18% 4 10% 6% 4 4 2 4 5% 25%	1947
November	1st to 10th	Day	15% 16% 5% 11% 6% 4 5% 4 5% 5% 23%	1567
	11th to 20th	Day	14% 18% 8% 15% 6% 5% 3 2 5% 5% 19%	1600
	21st to end	Day	14% 17% 8% 18% 8% 5% 4 3 4 4 16%	1600
December	1st to 10th	Day	12% 16% 5% 23% 11% 5% 5% 4 3 4 10%	2610
	11th to 20th	Day	9% 18% 7% 14% 5% 7% 5% 3 5% 5% 22%	2639
	21st to end	Day	16% 20% 7% 18% 8% 5% 4 2 4 3 11%	3498
January	1st to 10th	Night	4 14% 7% 18% 9% 6% 5% 5% 5% 5% 23%	6787
	11th to 20th	Night	6% 12% 6% 15% 11% 10% 9% 8% 7% 3 13%	6753
	21st to end	Night	8% 19% 11% 15% 7% 5% 5% 4 6% 5% 16%	6809
February	1st to 10th	Night	8% 11% 5% 12% 8% 8% 7% 5% 7% 6% 24%	2600
	11th to 20th	Night	8% 9% 3 11% 6% 6% 6% 5% 6% 6% 33%	2533
	21st to end	Night	8% 13% 5% 12% 7% 7% 5% 4 5% 6% 28%	2140
March	1st to 10th	Night	11% 9% 4 9% 5% 5% 5% 4 5% 7% 35%	5137
	11th to 20th	Night	7% 12% 5% 13% 9% 8% 6% 4 6% 6% 25%	4979
	21st to end	Night	18% 16% 4 10% 4 3 3 3 4 4 30%	5376
April	1st to 10th	Night	16% 11% 3 9% 5% 3 5% 3 6% 6% 33%	2000
	11th to 20th	Night	16% 11% 4 8% 4 5% 4 3 5% 6% 34%	1866
	21st to end	Night	19% 12% 4 7% 5% 5% 5% 3 4 6% 31%	1780
May	1st to 10th	Night	18% 7% 2 4 3 3 3 2 4 6% 50%	3613
	11th to 20th	Night	16% 7% 3 6% 4 4 4 4 6% 7% 41%	3596
	21st to end	Night	17% 6% 2 6% 3 3 4 4 6% 7% 43%	3845
June	1st to 10th	Night	15% 8% 2 6% 5% 3 4 4 6% 7% 41%	1400
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 6% 7% 45%	1400
	21st to end	Night	15% 6% 2 6% 4 4 4 4 6% 9% 42%	1400
July	1st to 10th	Night	9% 3 1 5% 4 5% 4 4 7% 10% 47%	3180
	11th to 20th	Night	10% 5% 2 6% 4 3 5% 4 5% 9% 48%	3180
	21st to end	Night	11% 6% 2 6% 4 3 4 4 6% 9% 45%	3851
August	1st to 10th	Night	11% 5% 2 6% 4 5% 5% 4 6% 8% 44%	2715
	11th to 20th	Night	12% 5% 2 5% 3 4 4 4 6% 8% 47%	2888
	21st to end	Night	13% 5% 2 6% 4 4 4 3 5% 7% 46%	3324
September	1st to 10th	Night	12% 6% 2 7% 4 4 3 3 5% 6% 47%	2000
	11th to 20th	Night	14% 7% 3 6% 4 3 4 3 4 8% 45%	2023
	21st to end	Night	17% 9% 3 6% 4 3 3 3 5% 6% 42%	2276
October	1st to 10th	Night	16% 12% 4 6% 3 4 5% 3 6% 6% 34%	2317
	11th to 20th	Night	18% 14% 4 7% 3 4 4 3 4 7% 31%	2280
	21st to end	Night	19% 14% 4 10% 5% 5% 4 4 5% 5% 25%	2649
November	1st to 10th	Night	14% 17% 5% 10% 6% 5% 4 3 4 5% 26%	2731
	11th to 20th	Night	15% 18% 6% 14% 7% 6% 4 4 4 6% 17%	2800
	21st to end	Night	14% 16% 6% 15% 8% 6% 6% 3 4 5% 18%	2800
December	1st to 10th	Night	10% 20% 10% 19% 9% 8% 5% 3 4 4 9%	4580
	11th to 20th	Night	10% 13% 6% 16% 8% 7% 6% 5% 5% 5% 18%	5563
	21st to end	Night	18% 18% 7% 17% 7% 5% 5% 3 4 4 13%	7480

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	64% 5% 6% 14% 10% 1	3179
	11th to 20th	Day	67% 7% 6% 18% 3	3180
	21st to end	Day	68% 5% 10% 12% 5%	4162
February	1st to 10th	Day	60% 7% 10% 14% 8% 1	1800
	11th to 20th	Day	53% 5% 11% 21% 9% 1	1763
	21st to end	Day	53% 5% 13% 17% 11%	1490
March	1st to 10th	Day	42% 5% 13% 21% 14% 5%	4748
	11th to 20th	Day	51% 6% 13% 20% 10%	4980
	21st to end	Day	53% 5% 9% 21% 12% 2	5555
April	1st to 10th	Day	52% 5% 8% 18% 15% 1	2400
	11th to 20th	Day	52% 6% 11% 19% 11% 1	2482
	21st to end	Day	53% 6% 8% 22% 11% 1	2620
May	1st to 10th	Day	39% 6% 13% 25% 16% 2	6357
	11th to 20th	Day	45% 8% 10% 20% 15% 3	6323
	21st to end	Day	39% 6% 9% 28% 16% 2	7037
June	1st to 10th	Day	43% 10% 14% 22% 10% 1	3000
	11th to 20th	Day	46% 7% 13% 22% 12%	3000
	21st to end	Day	46% 9% 15% 22% 7% 1	3000
July	1st to 10th	Day	35% 11% 20% 26% 8%	6726
	11th to 20th	Day	39% 8% 18% 30% 6%	6719
	21st to end	Day	41% 8% 16% 27% 7%	6822
August	1st to 10th	Day	41% 8% 16% 23% 11% 1	4427
	11th to 20th	Day	35% 9% 24% 25% 6%	4210
	21st to end	Day	40% 7% 19% 27% 6%	4580
September	1st to 10th	Day	39% 7% 14% 30% 9%	2400
	11th to 20th	Day	44% 8% 21% 22% 5%	2374
	21st to end	Day	46% 6% 13% 27% 7%	2103
October	1st to 10th	Day	41% 5% 17% 27% 10%	3190
	11th to 20th	Day	48% 6% 13% 21% 12%	3140
	21st to end	Day	57% 6% 15% 19% 3	3189
November	1st to 10th	Day	61% 7% 12% 14% 5% 1	1567
	11th to 20th	Day	69% 6% 8% 13% 4	1600
	21st to end	Day	71% 6% 10% 9% 3	1600
December	1st to 10th	Day	78% 6% 8% 7% 1	2610
	11th to 20th	Day	65% 5% 8% 13% 9%	2640
	21st to end	Day	77% 3 6% 10% 3	3498
January	1st to 10th	Night	64% 4 9% 12% 10%	6787
	11th to 20th	Night	70% 6% 7% 13% 4	6800
	21st to end	Night	70% 4 9% 13% 4	6809
February	1st to 10th	Night	57% 5% 13% 14% 9% 1	2600
	11th to 20th	Night	51% 5% 14% 20% 10% 1	2534
	21st to end	Night	56% 5% 10% 20% 8% 1	2140
March	1st to 10th	Night	47% 7% 13% 16% 14% 4	5148
	11th to 20th	Night	59% 6% 12% 15% 8% 1	4980
	21st to end	Night	58% 4 7% 17% 13% 1	5376
April	1st to 10th	Night	51% 6% 9% 17% 16% 1	2000
	11th to 20th	Night	51% 5% 9% 20% 13% 2	1866
	21st to end	Night	54% 5% 7% 20% 13% 1	1780
May	1st to 10th	Night	37% 5% 10% 30% 18% 1	3620
	11th to 20th	Night	40% 7% 13% 21% 17% 2	3597
	21st to end	Night	39% 7% 9% 27% 15% 2	3846
June	1st to 10th	Night	40% 8% 16% 22% 14% 1	1400
	11th to 20th	Night	36% 8% 13% 26% 15% 1	1400
	21st to end	Night	39% 7% 19% 25% 9% 1	1400
July	1st to 10th	Night	30% 8% 22% 31% 9% 1	3145
	11th to 20th	Night	31% 7% 19% 32% 11%	3138
	21st to end	Night	35% 7% 18% 31% 8% 1	3738
August	1st to 10th	Night	36% 8% 16% 29% 11% 1	2706
	11th to 20th	Night	33% 8% 20% 33% 6%	2915
	21st to end	Night	37% 7% 21% 27% 8%	3324
September	1st to 10th	Night	37% 6% 17% 29% 11%	2000
	11th to 20th	Night	38% 9% 19% 27% 8%	2023
	21st to end	Night	44% 6% 15% 29% 7%	2276
October	1st to 10th	Night	38% 6% 13% 34% 10% 1	3837
	11th to 20th	Night	48% 5% 14% 25% 8%	3779
	21st to end	Night	56% 6% 11% 23% 5%	4359
November	1st to 10th	Night	59% 5% 12% 17% 6% 1	2731
	11th to 20th	Night	69% 7% 10% 10% 4	2800
	21st to end	Night	67% 7% 12% 10% 4	2800
December	1st to 10th	Night	80% 6% 7% 7% 1	4580
	11th to 20th	Night	67% 4 9% 11% 8%	5561
	21st to end	Night	75% 5% 6% 12% 3	7480

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	13% 12% 39% 24% 11% 1	300
	11th to 20th	Day	17% 10% 33% 33% 6% 1	300
	21st to end	Day	18% 12% 34% 22% 12% 1	330
February	1st to 10th	Day	16% 12% 43% 22% 6%	300
	11th to 20th	Day	14% 17% 38% 19% 8% 4	300
	21st to end	Day	20% 18% 39% 18% 3 1	249
March	1st to 10th	Day	17% 13% 37% 23% 9% 2	300
	11th to 20th	Day	16% 15% 36% 20% 10% 4	300
	21st to end	Day	19% 17% 32% 21% 9% 2	370
April	1st to 10th	Day	21% 13% 33% 22% 11%	500
	11th to 20th	Day	22% 16% 30% 23% 8% 1	600
	21st to end	Day	23% 12% 30% 23% 12% 1	700
May	1st to 10th	Day	22% 16% 32% 19% 9% 2	703
	11th to 20th	Day	22% 12% 29% 24% 11% 2	725
	21st to end	Day	22% 9% 26% 31% 9% 2	789
June	1st to 10th	Day	16% 12% 29% 27% 12% 3	730
	11th to 20th	Day	17% 14% 34% 23% 10% 2	730
	21st to end	Day	18% 8% 27% 28% 13% 4	730
July	1st to 10th	Day	11% 7% 29% 30% 17% 7%	721
	11th to 20th	Day	16% 10% 27% 26% 16% 5%	718
	21st to end	Day	11% 9% 28% 29% 16% 7%	794
August	1st to 10th	Day	9% 10% 27% 33% 16% 4	726
	11th to 20th	Day	13% 8% 25% 29% 17% 8%	715
	21st to end	Day	15% 10% 29% 26% 17% 3	748
September	1st to 10th	Day	15% 11% 28% 28% 15% 2	530
	11th to 20th	Day	18% 10% 32% 28% 11% 2	504
	21st to end	Day	25% 11% 32% 22% 9% 2	330
October	1st to 10th	Day	23% 13% 28% 24% 8% 3	309
	11th to 20th	Day	21% 18% 33% 23% 4	300
	21st to end	Day	32% 17% 32% 15% 4 1	330
November	1st to 10th	Day	21% 16% 34% 21% 7% 1	300
	11th to 20th	Day	26% 17% 32% 18% 6%	300
	21st to end	Day	26% 18% 32% 20% 4 1	300
December	1st to 10th	Day	20% 13% 33% 27% 7%	300
	11th to 20th	Day	18% 15% 43% 20% 4	300
	21st to end	Day	20% 12% 36% 22% 8% 2	330
January	1st to 10th	Night	13% 12% 37% 26% 10% 2	1000
	11th to 20th	Night	17% 9% 38% 26% 9% 1	1000
	21st to end	Night	19% 10% 36% 28% 7%	1100
February	1st to 10th	Night	14% 11% 35% 30% 10% 1	1000
	11th to 20th	Night	13% 9% 37% 28% 10% 3	979
	21st to end	Night	14% 10% 36% 28% 10% 3	820
March	1st to 10th	Night	16% 10% 34% 29% 10% 1	705
	11th to 20th	Night	14% 13% 36% 30% 6% 1	600
	21st to end	Night	21% 12% 30% 24% 11% 3	660
April	1st to 10th	Night	20% 11% 33% 27% 9% 1	600
	11th to 20th	Night	21% 10% 32% 26% 10% 1	593
	21st to end	Night	23% 9% 25% 33% 10%	600
May	1st to 10th	Night	21% 8% 32% 31% 8% 1	600
	11th to 20th	Night	21% 8% 31% 31% 7% 2	591
	21st to end	Night	19% 7% 27% 37% 10%	650
June	1st to 10th	Night	17% 9% 28% 32% 13% 1	600
	11th to 20th	Night	13% 8% 31% 34% 14%	600
	21st to end	Night	15% 5% 29% 33% 18% 1	600
July	1st to 10th	Night	8% 3 26% 39% 23% 1	585
	11th to 20th	Night	10% 4 27% 39% 18% 1	582
	21st to end	Night	9% 4 26% 36% 22% 2	657
August	1st to 10th	Night	9% 3 27% 41% 19% 2	597
	11th to 20th	Night	14% 6% 20% 35% 23% 3	594
	21st to end	Night	13% 7% 26% 34% 18% 1	660
September	1st to 10th	Night	16% 6% 25% 36% 16% 2	600
	11th to 20th	Night	17% 6% 32% 29% 15% 1	600
	21st to end	Night	21% 11% 30% 26% 11% 1	676
October	1st to 10th	Night	24% 11% 31% 27% 8%	773
	11th to 20th	Night	24% 13% 31% 26% 6% 1	760
	21st to end	Night	26% 10% 36% 22% 5% 1	873
November	1st to 10th	Night	23% 10% 33% 28% 6% 1	975
	11th to 20th	Night	25% 12% 32% 25% 5% 1	1000
	21st to end	Night	21% 16% 38% 21% 4	1000
December	1st to 10th	Night	17% 12% 36% 26% 8% 1	1000
	11th to 20th	Night	19% 12% 37% 24% 7% 1	1000
	21st to end	Night	23% 10% 31% 26% 10% 2	1100

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