Fort Chipewyan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Chipewyan 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	8% 8% 4 9% 6% 5% 6% 4 7% 8% 35%	142034
	Night	7% 12% 5% 11% 7% 6% 6% 5% 6% 7% 28%	138913
Transparency	Day	30% 36% 9% 18% 6%	141702
	Night	36% 36% 9% 15% 5%	138830
Seeing	Day	13% 9% 28% 30% 16% 4	18981
	Night	13% 7% 27% 33% 17% 3	27166

By Month

Percentage Cloud Cover NW (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% 20% 12% 8% 8% 5% 5% 4 16%	2929
	11th to 20th	Day	6% 10% 5% 14% 8% 6% 9% 6% 8% 6% 22%	3241
	21st to end	Day	6% 18% 7% 12% 7% 6% 7% 5% 6% 7% 20%	4531
February	1st to 10th	Day	5% 11% 5% 13% 10% 8% 8% 6% 7% 7% 20%	1502
	11th to 20th	Day	5% 11% 5% 10% 8% 5% 6% 6% 7% 8% 27%	1732
	21st to end	Day	3 11% 7% 14% 10% 7% 7% 7% 8% 6% 20%	1557
March	1st to 10th	Day	4 12% 6% 13% 7% 6% 7% 5% 9% 7% 24%	4418
	11th to 20th	Day	3 9% 4 14% 8% 7% 6% 5% 6% 8% 30%	5109
	21st to end	Day	2 7% 5% 10% 6% 5% 5% 4 6% 7% 42%	5651
April	1st to 10th	Day	7% 13% 4 9% 6% 4 4 4 5% 7% 36%	2719
	11th to 20th	Day	7% 10% 3 8% 6% 5% 5% 4 6% 7% 38%	2700
	21st to end	Day	7% 11% 3 9% 7% 6% 5% 5% 7% 8% 32%	3004
May	1st to 10th	Day	7% 8% 3 8% 6% 6% 6% 5% 7% 8% 38%	8793
	11th to 20th	Day	10% 7% 3 8% 5% 6% 5% 4 7% 8% 37%	9052
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 7% 9% 43%	10714
June	1st to 10th	Day	14% 8% 2 7% 5% 6% 6% 5% 7% 7% 34%	3570
	11th to 20th	Day	11% 7% 3 8% 5% 5% 6% 4 7% 8% 36%	3570
	21st to end	Day	7% 5% 2 6% 6% 5% 6% 6% 7% 8% 42%	3570
July	1st to 10th	Day	7% 4 2 6% 6% 6% 7% 5% 9% 12% 37%	7701
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 8% 53%	7700
	21st to end	Day	11% 4 2 5% 4 4 4 4 6% 8% 47%	7595
August	1st to 10th	Day	5% 4 2 6% 4 5% 5% 5% 7% 7% 51%	4870
	11th to 20th	Day	11% 6% 3 7% 5% 4 5% 4 6% 7% 42%	4665
	21st to end	Day	13% 7% 3 8% 5% 5% 6% 4 6% 9% 34%	4664
September	1st to 10th	Day	13% 7% 3 7% 5% 4 4 4 6% 8% 37%	2566
	11th to 20th	Day	14% 8% 3 8% 5% 5% 5% 4 7% 7% 34%	2302
	21st to end	Day	13% 8% 4 8% 6% 5% 5% 4 6% 7% 33%	2180
October	1st to 10th	Day	9% 11% 4 9% 6% 7% 6% 4 5% 5% 34%	3270
	11th to 20th	Day	11% 14% 5% 9% 5% 5% 4 3 5% 7% 33%	2952
	21st to end	Day	9% 12% 5% 12% 6% 6% 6% 5% 5% 8% 25%	2842
November	1st to 10th	Day	13% 16% 6% 12% 6% 4 5% 4 6% 7% 22%	1559
	11th to 20th	Day	10% 17% 5% 15% 9% 7% 5% 4 6% 5% 17%	1318
	21st to end	Day	9% 16% 6% 15% 8% 7% 6% 3 5% 5% 20%	1260
December	1st to 10th	Day	5% 19% 7% 19% 10% 10% 6% 4 4 8% 8%	1758
	11th to 20th	Day	6% 16% 8% 15% 7% 6% 5% 7% 4 8% 19%	1929
	21st to end	Day	5% 15% 5% 13% 6% 7% 7% 4 5% 6% 27%	2541
January	1st to 10th	Night	5% 15% 7% 16% 10% 8% 7% 5% 6% 6% 14%	9964
	11th to 20th	Night	5% 10% 5% 12% 9% 7% 10% 7% 7% 7% 23%	9626
	21st to end	Night	6% 17% 6% 12% 7% 6% 6% 5% 6% 7% 22%	9650
February	1st to 10th	Night	4 9% 6% 12% 9% 9% 9% 6% 6% 7% 23%	3136
	11th to 20th	Night	4 11% 4 12% 8% 7% 7% 6% 7% 7% 28%	2773
	21st to end	Night	3 11% 5% 14% 10% 7% 8% 6% 6% 7% 25%	2249
March	1st to 10th	Night	3 12% 7% 13% 8% 7% 6% 6% 6% 7% 26%	5684
	11th to 20th	Night	3 8% 4 13% 8% 6% 6% 5% 7% 8% 31%	5110
	21st to end	Night	2 7% 4 13% 7% 5% 5% 5% 6% 7% 39%	5564
April	1st to 10th	Night	8% 11% 4 10% 6% 6% 6% 5% 6% 7% 31%	1898
	11th to 20th	Night	7% 9% 3 8% 6% 5% 6% 4 7% 7% 38%	1871
	21st to end	Night	8% 10% 4 10% 6% 5% 5% 5% 5% 8% 34%	1613
May	1st to 10th	Night	9% 8% 3 8% 6% 5% 6% 5% 7% 9% 35%	4126
	11th to 20th	Night	10% 9% 3 8% 5% 5% 6% 5% 8% 9% 33%	3808
	21st to end	Night	8% 6% 3 7% 6% 6% 6% 4 6% 10% 36%	3456
June	1st to 10th	Night	14% 8% 3 8% 6% 5% 4 5% 8% 7% 33%	1050
	11th to 20th	Night	15% 7% 2 7% 5% 5% 5% 6% 6% 8% 35%	1050
	21st to end	Night	6% 5% 2 6% 6% 5% 5% 5% 9% 8% 42%	1050
July	1st to 10th	Night	9% 6% 2 7% 6% 6% 7% 5% 8% 10% 33%	2260
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 7% 9% 50%	2260
	21st to end	Night	14% 3 1 5% 4 4 4 4 7% 9% 45%	3232
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 6% 7% 52%	2280
	11th to 20th	Night	10% 4 2 5% 4 5% 6% 4 7% 8% 45%	2368
	21st to end	Night	14% 5% 3 8% 6% 5% 6% 5% 7% 8% 32%	3245
September	1st to 10th	Night	11% 7% 3 7% 6% 4 6% 4 6% 8% 39%	1834
	11th to 20th	Night	15% 7% 3 5% 4 4 4 4 6% 8% 40%	2095
	21st to end	Night	11% 8% 4 10% 6% 6% 5% 3 6% 7% 34%	2220
October	1st to 10th	Night	9% 12% 3 8% 5% 5% 5% 4 5% 8% 36%	3920
	11th to 20th	Night	13% 13% 4 8% 5% 4 5% 4 5% 7% 32%	4166
	21st to end	Night	14% 17% 5% 12% 7% 6% 6% 4 5% 5% 18%	4953
November	1st to 10th	Night	11% 16% 6% 12% 7% 6% 5% 4 5% 5% 22%	2959
	11th to 20th	Night	9% 16% 6% 16% 9% 6% 5% 4 6% 5% 18%	3302
	21st to end	Night	9% 16% 7% 15% 9% 6% 5% 4 5% 6% 18%	3360
December	1st to 10th	Night	7% 18% 7% 15% 9% 9% 8% 4 5% 7% 11%	5641
	11th to 20th	Night	6% 16% 6% 13% 9% 8% 7% 5% 6% 7% 19%	6483
	21st to end	Night	4 15% 5% 11% 6% 5% 5% 4 6% 7% 32%	8657

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	59% 21% 5% 11% 4	2929
	11th to 20th	Day	47% 21% 10% 18% 4	3258
	21st to end	Day	51% 24% 9% 12% 4	4531
February	1st to 10th	Day	26% 61% 4 6% 2	1502
	11th to 20th	Day	24% 59% 5% 10% 2	1740
	21st to end	Day	26% 59% 4 7% 4	1557
March	1st to 10th	Day	43% 29% 7% 15% 6%	4418
	11th to 20th	Day	38% 28% 7% 20% 7%	5110
	21st to end	Day	29% 29% 6% 19% 17%	5651
April	1st to 10th	Day	17% 60% 6% 12% 6%	2719
	11th to 20th	Day	19% 59% 4 12% 6%	2700
	21st to end	Day	19% 60% 5% 13% 3	3004
May	1st to 10th	Day	35% 24% 11% 17% 12% 1	8793
	11th to 20th	Day	35% 23% 9% 24% 8%	9056
	21st to end	Day	29% 24% 14% 25% 6% 1	10715
June	1st to 10th	Day	24% 59% 6% 7% 4	3570
	11th to 20th	Day	18% 60% 5% 12% 5%	3570
	21st to end	Day	13% 60% 8% 11% 7% 1	3570
July	1st to 10th	Day	27% 31% 19% 19% 4	7617
	11th to 20th	Day	18% 28% 10% 36% 7% 1	7607
	21st to end	Day	23% 28% 12% 35% 1	7382
August	1st to 10th	Day	16% 38% 9% 31% 5%	4852
	11th to 20th	Day	24% 39% 9% 19% 9% 1	4710
	21st to end	Day	29% 40% 16% 14% 1	4663
September	1st to 10th	Day	20% 59% 11% 9% 2	2566
	11th to 20th	Day	19% 58% 7% 13% 2	2302
	21st to end	Day	20% 58% 8% 10% 3	2180
October	1st to 10th	Day	32% 37% 12% 16% 3	3270
	11th to 20th	Day	33% 37% 9% 17% 4	2952
	21st to end	Day	35% 40% 13% 11% 1	2842
November	1st to 10th	Day	27% 55% 8% 9% 1	1559
	11th to 20th	Day	30% 57% 6% 7% 1	1318
	21st to end	Day	32% 56% 3 6% 2	1260
December	1st to 10th	Day	52% 36% 4 6% 1	1758
	11th to 20th	Day	46% 31% 6% 12% 5%	1930
	21st to end	Day	42% 27% 12% 17% 3	2541
January	1st to 10th	Night	57% 21% 8% 11% 2	9965
	11th to 20th	Night	45% 22% 9% 20% 4	9671
	21st to end	Night	49% 24% 10% 13% 4	9650
February	1st to 10th	Night	25% 62% 5% 7% 2	3136
	11th to 20th	Night	23% 59% 7% 10% 2	2775
	21st to end	Night	24% 60% 4 6% 5%	2249
March	1st to 10th	Night	44% 28% 10% 13% 5%	5684
	11th to 20th	Night	33% 29% 7% 22% 9%	5110
	21st to end	Night	31% 28% 5% 18% 18%	5564
April	1st to 10th	Night	19% 60% 5% 11% 6%	1898
	11th to 20th	Night	18% 59% 2 10% 9%	1871
	21st to end	Night	18% 60% 3 14% 5%	1613
May	1st to 10th	Night	35% 25% 11% 21% 8%	4126
	11th to 20th	Night	37% 24% 10% 20% 9%	3808
	21st to end	Night	35% 24% 11% 24% 6%	3459
June	1st to 10th	Night	23% 61% 5% 9% 3	1050
	11th to 20th	Night	15% 60% 4 12% 9%	1050
	21st to end	Night	13% 60% 7% 12% 7%	1050
July	1st to 10th	Night	33% 30% 17% 17% 3	2235
	11th to 20th	Night	20% 28% 10% 32% 10% 1	2230
	21st to end	Night	25% 28% 12% 33% 2	3141
August	1st to 10th	Night	19% 37% 7% 30% 8%	2273
	11th to 20th	Night	20% 39% 13% 18% 8% 2	2389
	21st to end	Night	29% 39% 18% 12% 2	3245
September	1st to 10th	Night	20% 58% 10% 9% 3	1834
	11th to 20th	Night	14% 58% 8% 17% 3	2095
	21st to end	Night	20% 57% 7% 11% 5%	2220
October	1st to 10th	Night	29% 38% 9% 22% 2	3920
	11th to 20th	Night	34% 37% 11% 16% 2	4166
	21st to end	Night	44% 38% 7% 10% 1	4953
November	1st to 10th	Night	28% 55% 7% 9% 1	2959
	11th to 20th	Night	30% 56% 5% 7% 1	3302
	21st to end	Night	30% 56% 6% 6% 2	3360
December	1st to 10th	Night	50% 37% 6% 5% 2	5641
	11th to 20th	Night	45% 32% 8% 12% 3	6481
	21st to end	Night	36% 26% 15% 18% 5%	8657

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	12% 5% 30% 35% 15% 2	220
	11th to 20th	Day	15% 10% 33% 29% 11% 2	220
	21st to end	Day	13% 16% 32% 31% 6% 2	242
February	1st to 10th	Day	10% 8% 38% 27% 11% 6%	220
	11th to 20th	Day	7% 7% 34% 30% 16% 6%	270
	21st to end	Day	8% 9% 28% 32% 19% 4	273
March	1st to 10th	Day	7% 10% 36% 27% 17% 3	422
	11th to 20th	Day	9% 13% 35% 28% 14% 1	540
	21st to end	Day	8% 9% 33% 33% 13% 4	594
April	1st to 10th	Day	13% 13% 36% 24% 10% 4	540
	11th to 20th	Day	13% 12% 33% 27% 13% 2	532
	21st to end	Day	13% 9% 29% 33% 14% 2	744
May	1st to 10th	Day	14% 10% 29% 30% 15% 2	753
	11th to 20th	Day	12% 9% 26% 31% 19% 3	775
	21st to end	Day	12% 7% 28% 34% 14% 3	980
June	1st to 10th	Day	19% 11% 26% 27% 13% 3	990
	11th to 20th	Day	16% 8% 27% 31% 15% 3	990
	21st to end	Day	8% 6% 23% 36% 22% 5%	990
July	1st to 10th	Day	12% 6% 20% 38% 20% 4	917
	11th to 20th	Day	11% 5% 19% 37% 22% 6%	912
	21st to end	Day	12% 5% 20% 29% 26% 8%	858
August	1st to 10th	Day	9% 5% 21% 31% 24% 11%	726
	11th to 20th	Day	16% 6% 27% 31% 16% 4	692
	21st to end	Day	16% 6% 27% 29% 17% 5%	583
September	1st to 10th	Day	16% 9% 30% 29% 13% 3	530
	11th to 20th	Day	15% 8% 28% 29% 17% 4	530
	21st to end	Day	17% 13% 30% 25% 12% 3	510
October	1st to 10th	Day	19% 10% 33% 23% 9% 5%	330
	11th to 20th	Day	22% 9% 40% 21% 6% 2	330
	21st to end	Day	16% 13% 37% 21% 12% 1	363
November	1st to 10th	Day	15% 11% 36% 28% 10%	283
	11th to 20th	Day	18% 16% 34% 22% 8% 2	220
	21st to end	Day	16% 8% 35% 30% 10% 1	220
December	1st to 10th	Day	11% 8% 34% 31% 13% 3	220
	11th to 20th	Day	15% 6% 30% 29% 18% 3	220
	21st to end	Day	10% 6% 23% 38% 19% 4	242
January	1st to 10th	Night	13% 8% 30% 31% 15% 3	1160
	11th to 20th	Night	14% 8% 34% 31% 11% 2	1159
	21st to end	Night	15% 8% 31% 32% 12% 2	1155
February	1st to 10th	Night	8% 7% 31% 33% 17% 5%	1036
	11th to 20th	Night	9% 6% 30% 37% 16% 1	824
	21st to end	Night	7% 7% 30% 32% 21% 2	692
March	1st to 10th	Night	8% 8% 25% 33% 25% 3	840
	11th to 20th	Night	10% 6% 33% 35% 15% 1	840
	21st to end	Night	7% 6% 27% 38% 19% 4	903
April	1st to 10th	Night	12% 8% 29% 32% 17% 3	630
	11th to 20th	Night	12% 10% 23% 36% 17% 2	623
	21st to end	Night	12% 7% 28% 37% 15% 1	557
May	1st to 10th	Night	14% 8% 25% 35% 15% 3	420
	11th to 20th	Night	12% 7% 25% 34% 19% 2	414
	21st to end	Night	11% 5% 25% 35% 21% 3	455
June	1st to 10th	Night	16% 5% 21% 35% 18% 5%	420
	11th to 20th	Night	17% 5% 18% 35% 21% 3	420
	21st to end	Night	7% 3 18% 36% 33% 4	420
July	1st to 10th	Night	12% 4 19% 37% 23% 5%	390
	11th to 20th	Night	11% 3 14% 40% 27% 5%	388
	21st to end	Night	11% 3 14% 32% 33% 7%	438
August	1st to 10th	Night	11% 3 15% 33% 30% 8%	398
	11th to 20th	Night	12% 4 23% 39% 19% 3	440
	21st to end	Night	15% 4 21% 35% 22% 3	660
September	1st to 10th	Night	13% 6% 26% 33% 19% 3	600
	11th to 20th	Night	19% 5% 20% 35% 19% 2	695
	21st to end	Night	15% 9% 29% 33% 14% 1	800
October	1st to 10th	Night	17% 11% 30% 26% 13% 3	800
	11th to 20th	Night	18% 7% 31% 29% 12% 2	800
	21st to end	Night	19% 11% 28% 28% 11% 2	1095
November	1st to 10th	Night	18% 8% 28% 30% 13% 2	1025
	11th to 20th	Night	18% 9% 31% 28% 13% 2	1050
	21st to end	Night	16% 10% 32% 28% 11% 2	1050
December	1st to 10th	Night	14% 7% 30% 32% 15% 2	1133
	11th to 20th	Night	13% 7% 31% 34% 12% 3	1160
	21st to end	Night	12% 5% 25% 35% 18% 4	1276

Page generated at 2026-06-28 00:10:45. Version ac07

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