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 2024-09-29.

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	9% 9% 4 9% 6% 5% 6% 5% 7% 8% 34%	102226
	Night	8% 11% 4 11% 7% 6% 6% 5% 6% 7% 29%	96026
Transparency	Day	24% 48% 8% 15% 4	101939
	Night	27% 49% 7% 12% 4	95960
Seeing	Day	13% 8% 28% 31% 16% 4	16650
	Night	13% 7% 27% 33% 17% 3	24728

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	6% 11% 5% 18% 13% 11% 11% 6% 4 4 11%	1579
	11th to 20th	Day	5% 10% 4 13% 8% 7% 12% 8% 10% 7% 16%	1727
	21st to end	Day	9% 20% 7% 11% 8% 6% 6% 4 6% 6% 17%	2442
February	1st to 10th	Day	5% 10% 5% 13% 10% 8% 9% 6% 6% 7% 21%	1358
	11th to 20th	Day	6% 12% 5% 10% 8% 6% 6% 6% 7% 8% 26%	1562
	21st to end	Day	3 10% 6% 13% 9% 7% 7% 7% 9% 7% 22%	1413
March	1st to 10th	Day	4 12% 6% 11% 7% 6% 8% 5% 9% 7% 26%	3000
	11th to 20th	Day	5% 10% 4 12% 7% 6% 6% 5% 7% 7% 31%	3489
	21st to end	Day	3 7% 5% 10% 6% 4 4 4 6% 7% 44%	3855
April	1st to 10th	Day	7% 14% 4 9% 5% 4 4 4 5% 6% 37%	2460
	11th to 20th	Day	7% 10% 3 8% 6% 6% 5% 4 6% 6% 39%	2440
	21st to end	Day	7% 10% 3 9% 7% 6% 5% 5% 7% 8% 33%	2717
May	1st to 10th	Day	8% 9% 3 8% 6% 6% 6% 4 7% 8% 36%	4740
	11th to 20th	Day	12% 10% 3 8% 5% 5% 5% 4 7% 8% 33%	4851
	21st to end	Day	12% 6% 2 5% 4 4 5% 5% 8% 9% 40%	5722
June	1st to 10th	Day	12% 8% 2 8% 5% 6% 6% 5% 7% 7% 35%	3230
	11th to 20th	Day	12% 8% 3 8% 5% 5% 6% 4 7% 8% 34%	3230
	21st to end	Day	8% 5% 3 6% 6% 5% 6% 6% 7% 8% 41%	3230
July	1st to 10th	Day	6% 4 2 6% 6% 6% 7% 5% 9% 12% 38%	5380
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 7% 8% 49%	5380
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 40%	5287
August	1st to 10th	Day	5% 4 2 6% 4 5% 5% 5% 7% 7% 50%	4720
	11th to 20th	Day	11% 6% 3 8% 5% 4 5% 4 6% 8% 43%	4518
	21st to end	Day	13% 7% 3 8% 5% 5% 6% 4 6% 9% 33%	4521
September	1st to 10th	Day	13% 8% 3 8% 5% 4 4 4 6% 8% 37%	2438
	11th to 20th	Day	15% 9% 3 8% 5% 5% 6% 4 7% 7% 32%	2187
	21st to end	Day	14% 8% 4 8% 6% 5% 5% 4 7% 7% 32%	2051
October	1st to 10th	Day	11% 15% 6% 10% 5% 5% 5% 4 5% 5% 30%	1800
	11th to 20th	Day	9% 15% 5% 11% 7% 4 5% 2 5% 8% 28%	1639
	21st to end	Day	10% 17% 6% 14% 7% 6% 5% 4 5% 8% 18%	1584
November	1st to 10th	Day	14% 17% 6% 13% 6% 4 5% 4 5% 7% 20%	1408
	11th to 20th	Day	10% 17% 5% 16% 9% 7% 5% 4 5% 5% 17%	1193
	21st to end	Day	10% 16% 6% 14% 8% 7% 6% 3 5% 5% 20%	1140
December	1st to 10th	Day	5% 17% 6% 16% 11% 9% 8% 5% 4 7% 11%	998
	11th to 20th	Day	6% 13% 8% 15% 9% 8% 4 4 4 7% 22%	1199
	21st to end	Day	6% 10% 5% 10% 7% 6% 7% 4 6% 6% 33%	1738
January	1st to 10th	Night	5% 15% 6% 15% 11% 10% 9% 6% 6% 4 12%	5366
	11th to 20th	Night	5% 9% 5% 12% 9% 8% 12% 8% 7% 6% 18%	5168
	21st to end	Night	6% 20% 7% 13% 7% 5% 6% 4 5% 5% 21%	5214
February	1st to 10th	Night	3 8% 5% 12% 9% 9% 10% 6% 6% 7% 24%	2838
	11th to 20th	Night	4 12% 5% 13% 7% 7% 6% 6% 6% 7% 27%	2503
	21st to end	Night	3 10% 4 12% 10% 7% 8% 6% 6% 7% 27%	2041
March	1st to 10th	Night	3 10% 6% 11% 8% 7% 6% 6% 6% 7% 30%	3867
	11th to 20th	Night	4 9% 4 12% 7% 5% 6% 5% 7% 8% 33%	3490
	21st to end	Night	3 8% 5% 12% 6% 5% 5% 5% 6% 6% 40%	3797
April	1st to 10th	Night	9% 11% 5% 10% 6% 6% 6% 5% 6% 7% 30%	1718
	11th to 20th	Night	7% 9% 3 8% 5% 5% 6% 4 7% 8% 39%	1691
	21st to end	Night	7% 10% 4 10% 6% 5% 5% 5% 5% 8% 35%	1460
May	1st to 10th	Night	9% 10% 4 8% 6% 4 5% 5% 6% 8% 36%	2220
	11th to 20th	Night	11% 9% 3 8% 5% 5% 5% 4 8% 9% 33%	2042
	21st to end	Night	11% 7% 3 6% 5% 5% 5% 4 7% 9% 38%	1851
June	1st to 10th	Night	12% 8% 3 8% 6% 5% 4 5% 8% 7% 34%	950
	11th to 20th	Night	15% 8% 2 7% 6% 5% 5% 6% 6% 8% 33%	950
	21st to end	Night	7% 5% 3 6% 6% 5% 4 5% 8% 8% 41%	950
July	1st to 10th	Night	6% 4 2 6% 5% 7% 7% 6% 9% 12% 37%	1580
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 8% 10% 45%	1580
	21st to end	Night	15% 4 2 6% 4 5% 5% 5% 8% 10% 37%	2249
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 6% 7% 52%	2210
	11th to 20th	Night	10% 4 2 5% 4 6% 6% 4 7% 8% 45%	2295
	21st to end	Night	15% 5% 3 8% 6% 5% 6% 5% 7% 8% 31%	3146
September	1st to 10th	Night	12% 7% 3 8% 6% 4 5% 4 6% 7% 39%	1742
	11th to 20th	Night	15% 7% 3 5% 4 4 4 4 6% 8% 39%	1990
	21st to end	Night	11% 8% 4 9% 6% 6% 5% 3 6% 7% 35%	2097
October	1st to 10th	Night	13% 12% 3 9% 5% 5% 5% 4 5% 7% 33%	2160
	11th to 20th	Night	11% 13% 5% 10% 6% 4 6% 4 5% 7% 29%	2305
	21st to end	Night	12% 17% 5% 13% 7% 5% 5% 4 6% 6% 20%	2767
November	1st to 10th	Night	11% 17% 6% 12% 7% 6% 5% 3 5% 5% 22%	2670
	11th to 20th	Night	9% 17% 6% 16% 9% 6% 5% 4 6% 5% 18%	2987
	21st to end	Night	9% 17% 7% 14% 8% 6% 5% 4 6% 6% 18%	3040
December	1st to 10th	Night	7% 14% 6% 14% 9% 8% 7% 5% 7% 7% 15%	3181
	11th to 20th	Night	6% 16% 6% 12% 10% 9% 7% 4 6% 6% 18%	3993
	21st to end	Night	4 10% 4 11% 7% 6% 6% 4 6% 8% 35%	5918

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	54% 36% 2 5% 2	1579
	11th to 20th	Day	38% 37% 8% 14% 3	1744
	21st to end	Day	45% 38% 9% 7% 1	2442
February	1st to 10th	Day	23% 66% 3 5% 2	1358
	11th to 20th	Day	21% 65% 5% 8% 1	1570
	21st to end	Day	21% 65% 4 7% 4	1413
March	1st to 10th	Day	35% 40% 7% 17% 1	3000
	11th to 20th	Day	30% 39% 8% 18% 4	3490
	21st to end	Day	23% 39% 3 21% 13%	3855
April	1st to 10th	Day	14% 65% 5% 10% 6%	2460
	11th to 20th	Day	15% 65% 3 10% 7%	2440
	21st to end	Day	15% 65% 4 12% 3	2717
May	1st to 10th	Day	30% 40% 8% 11% 11% 1	4740
	11th to 20th	Day	32% 38% 6% 16% 7%	4855
	21st to end	Day	26% 39% 8% 20% 6%	5723
June	1st to 10th	Day	20% 65% 5% 6% 3	3230
	11th to 20th	Day	16% 66% 4 9% 4	3230
	21st to end	Day	12% 66% 7% 9% 5%	3230
July	1st to 10th	Day	23% 41% 15% 18% 4	5296
	11th to 20th	Day	16% 38% 10% 31% 5% 1	5287
	21st to end	Day	25% 38% 12% 24% 1	5119
August	1st to 10th	Day	16% 39% 9% 31% 5%	4702
	11th to 20th	Day	23% 40% 9% 19% 9% 1	4563
	21st to end	Day	29% 41% 16% 13% 1	4520
September	1st to 10th	Day	20% 62% 9% 8% 2	2438
	11th to 20th	Day	18% 61% 7% 12% 2	2187
	21st to end	Day	19% 62% 8% 8% 3	2051
October	1st to 10th	Day	21% 64% 6% 8%	1800
	11th to 20th	Day	23% 64% 4 7% 1	1639
	21st to end	Day	27% 64% 4 5% 1	1584
November	1st to 10th	Day	26% 60% 7% 7%	1408
	11th to 20th	Day	28% 62% 5% 5% 1	1193
	21st to end	Day	27% 61% 4 7% 2	1140
December	1st to 10th	Day	30% 62% 3 4 2	998
	11th to 20th	Day	32% 48% 4 14% 3	1200
	21st to end	Day	27% 37% 9% 23% 4	1738
January	1st to 10th	Night	51% 36% 3 7% 2	5366
	11th to 20th	Night	40% 37% 8% 12% 4	5213
	21st to end	Night	41% 39% 9% 10% 1	5214
February	1st to 10th	Night	21% 68% 4 5% 2	2838
	11th to 20th	Night	20% 65% 6% 8% 1	2505
	21st to end	Night	18% 66% 4 6% 5%	2041
March	1st to 10th	Night	32% 40% 11% 15% 3	3867
	11th to 20th	Night	26% 40% 8% 21% 5%	3490
	21st to end	Night	27% 39% 2 17% 15%	3797
April	1st to 10th	Night	16% 66% 5% 8% 5%	1718
	11th to 20th	Night	13% 65% 2 10% 10%	1691
	21st to end	Night	14% 65% 2 13% 5%	1460
May	1st to 10th	Night	29% 39% 6% 16% 8%	2220
	11th to 20th	Night	32% 38% 6% 15% 8%	2042
	21st to end	Night	27% 39% 6% 19% 8%	1851
June	1st to 10th	Night	18% 67% 5% 9% 2	950
	11th to 20th	Night	14% 66% 3 10% 7%	950
	21st to end	Night	13% 65% 7% 10% 5%	950
July	1st to 10th	Night	22% 40% 14% 19% 4	1555
	11th to 20th	Night	18% 38% 8% 28% 7% 1	1550
	21st to end	Night	26% 39% 13% 20% 1	2179
August	1st to 10th	Night	18% 38% 6% 30% 8%	2203
	11th to 20th	Night	20% 40% 12% 17% 8% 2	2316
	21st to end	Night	29% 40% 18% 11% 1	3146
September	1st to 10th	Night	19% 61% 8% 9% 3	1742
	11th to 20th	Night	13% 61% 8% 15% 2	1990
	21st to end	Night	18% 61% 7% 10% 4	2097
October	1st to 10th	Night	20% 64% 5% 10% 1	2160
	11th to 20th	Night	23% 64% 5% 7%	2305
	21st to end	Night	24% 64% 5% 6% 1	2767
November	1st to 10th	Night	25% 60% 6% 8% 1	2670
	11th to 20th	Night	27% 62% 5% 6% 1	2987
	21st to end	Night	26% 61% 6% 6% 1	3040
December	1st to 10th	Night	27% 61% 7% 3 2	3181
	11th to 20th	Night	35% 49% 7% 6% 3	3991
	21st to end	Night	23% 36% 14% 20% 7%	5918

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% 4 29% 36% 17% 2	180
	11th to 20th	Day	14% 6% 32% 32% 14% 3	180
	21st to end	Day	15% 14% 30% 32% 7% 3	198
February	1st to 10th	Day	8% 8% 37% 29% 11% 7%	180
	11th to 20th	Day	8% 7% 33% 31% 14% 7%	220
	21st to end	Day	6% 9% 29% 34% 18% 4	225
March	1st to 10th	Day	7% 10% 35% 28% 17% 3	353
	11th to 20th	Day	9% 14% 37% 28% 11% 1	460
	21st to end	Day	9% 9% 34% 31% 13% 3	506
April	1st to 10th	Day	13% 13% 36% 24% 10% 4	460
	11th to 20th	Day	11% 12% 33% 28% 13% 2	452
	21st to end	Day	12% 10% 29% 34% 13% 2	644
May	1st to 10th	Day	14% 8% 27% 32% 16% 2	653
	11th to 20th	Day	12% 9% 24% 31% 20% 4	675
	21st to end	Day	13% 6% 25% 36% 16% 4	856
June	1st to 10th	Day	17% 10% 26% 29% 14% 4	870
	11th to 20th	Day	17% 9% 26% 30% 16% 3	870
	21st to end	Day	9% 6% 23% 36% 22% 5%	870
July	1st to 10th	Day	12% 6% 20% 38% 20% 5%	856
	11th to 20th	Day	11% 6% 19% 37% 21% 6%	852
	21st to end	Day	12% 5% 20% 30% 25% 9%	800
August	1st to 10th	Day	9% 5% 20% 31% 24% 11%	676
	11th to 20th	Day	15% 6% 27% 31% 16% 5%	643
	21st to end	Day	17% 6% 27% 29% 16% 5%	539
September	1st to 10th	Day	17% 9% 30% 27% 14% 3	490
	11th to 20th	Day	16% 8% 28% 28% 16% 4	490
	21st to end	Day	16% 14% 29% 26% 12% 3	465
October	1st to 10th	Day	20% 10% 31% 24% 11% 5%	270
	11th to 20th	Day	23% 7% 41% 21% 6% 2	270
	21st to end	Day	16% 11% 34% 23% 14% 1	297
November	1st to 10th	Day	16% 9% 34% 30% 10%	232
	11th to 20th	Day	18% 14% 33% 22% 9% 3	180
	21st to end	Day	18% 8% 38% 27% 8% 1	180
December	1st to 10th	Day	11% 6% 33% 32% 14% 4	180
	11th to 20th	Day	14% 6% 31% 28% 17% 3	180
	21st to end	Day	10% 4 21% 40% 21% 5%	198
January	1st to 10th	Night	13% 7% 30% 32% 15% 3	1040
	11th to 20th	Night	14% 8% 32% 32% 12% 2	1040
	21st to end	Night	15% 8% 30% 33% 12% 2	1045
February	1st to 10th	Night	7% 7% 30% 33% 18% 5%	938
	11th to 20th	Night	10% 6% 30% 38% 16% 1	744
	21st to end	Night	7% 7% 30% 33% 21% 2	628
March	1st to 10th	Night	8% 8% 24% 33% 26% 3	760
	11th to 20th	Night	11% 7% 33% 35% 13% 1	760
	21st to end	Night	7% 6% 26% 38% 18% 4	817
April	1st to 10th	Night	12% 8% 29% 31% 17% 3	570
	11th to 20th	Night	10% 9% 23% 38% 18% 2	563
	21st to end	Night	12% 6% 27% 38% 16% 2	504
May	1st to 10th	Night	14% 8% 23% 36% 16% 3	380
	11th to 20th	Night	12% 7% 25% 33% 20% 3	374
	21st to end	Night	12% 4 24% 35% 22% 3	411
June	1st to 10th	Night	14% 5% 22% 36% 19% 5%	380
	11th to 20th	Night	18% 4 18% 36% 20% 3	380
	21st to end	Night	8% 3 19% 34% 33% 4	380
July	1st to 10th	Night	11% 4 18% 38% 24% 5%	370
	11th to 20th	Night	11% 4 15% 40% 26% 5%	368
	21st to end	Night	11% 3 14% 32% 33% 7%	416
August	1st to 10th	Night	11% 3 15% 33% 30% 8%	378
	11th to 20th	Night	11% 4 23% 39% 19% 3	418
	21st to end	Night	15% 4 22% 35% 21% 3	627
September	1st to 10th	Night	13% 6% 25% 33% 19% 3	570
	11th to 20th	Night	19% 5% 20% 36% 18% 3	660
	21st to end	Night	15% 8% 28% 33% 14% 1	756
October	1st to 10th	Night	18% 9% 30% 27% 13% 3	720
	11th to 20th	Night	18% 6% 30% 30% 13% 3	720
	21st to end	Night	19% 10% 29% 28% 11% 3	985
November	1st to 10th	Night	19% 7% 28% 30% 13% 3	925
	11th to 20th	Night	18% 8% 31% 28% 13% 2	950
	21st to end	Night	17% 10% 33% 27% 9% 2	950
December	1st to 10th	Night	14% 6% 30% 33% 16% 2	1017
	11th to 20th	Night	13% 7% 30% 35% 12% 3	1040
	21st to end	Night	13% 5% 24% 35% 19% 5%	1144

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