Yellowknife
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yellowknife clear sky chart from 2005-11-06 to 2025-07-06.

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	7% 9% 4 9% 6% 6% 6% 5% 7% 8% 34%	123044
	Night	6% 10% 4 12% 8% 7% 6% 5% 7% 8% 27%	124378
Transparency	Day	47% 6% 13% 24% 9%	122728
	Night	54% 5% 13% 20% 8%	124340
Seeing	Day	10% 5% 20% 31% 24% 10%	17997
	Night	12% 4 21% 34% 23% 5%	25393

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	4 8% 4 12% 9% 8% 13% 8% 8% 8% 17%	1799
	11th to 20th	Day	4 8% 4 10% 6% 6% 7% 7% 12% 10% 25%	2181
	21st to end	Day	7% 15% 5% 14% 7% 7% 6% 5% 8% 8% 19%	2925
February	1st to 10th	Day	3 8% 4 12% 8% 8% 6% 6% 9% 10% 27%	1305
	11th to 20th	Day	2 10% 5% 12% 8% 8% 8% 6% 9% 7% 24%	1559
	21st to end	Day	3 9% 6% 15% 9% 7% 6% 5% 7% 8% 25%	1401
March	1st to 10th	Day	3 10% 5% 12% 6% 6% 7% 7% 9% 11% 25%	4380
	11th to 20th	Day	4 8% 3 13% 8% 7% 6% 6% 8% 10% 28%	4817
	21st to end	Day	2 8% 4 10% 6% 6% 6% 6% 7% 8% 37%	5763
April	1st to 10th	Day	5% 11% 5% 9% 6% 5% 7% 4 6% 8% 34%	2571
	11th to 20th	Day	5% 8% 3 8% 6% 6% 5% 5% 6% 7% 40%	2656
	21st to end	Day	3 8% 4 9% 7% 7% 5% 5% 7% 8% 38%	3000
May	1st to 10th	Day	5% 8% 3 9% 6% 5% 5% 4 6% 7% 44%	6949
	11th to 20th	Day	6% 8% 4 9% 6% 6% 6% 4 6% 8% 38%	7650
	21st to end	Day	10% 7% 3 7% 4 4 5% 4 6% 8% 42%	8448
June	1st to 10th	Day	11% 8% 3 7% 6% 5% 5% 4 7% 8% 37%	3700
	11th to 20th	Day	9% 7% 3 7% 6% 5% 6% 4 7% 9% 38%	3800
	21st to end	Day	8% 5% 2 6% 5% 4 5% 4 7% 8% 45%	3800
July	1st to 10th	Day	7% 7% 3 10% 7% 7% 7% 5% 8% 9% 30%	5857
	11th to 20th	Day	7% 6% 2 5% 4 4 5% 3 5% 7% 51%	5572
	21st to end	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 9% 38%	5755
August	1st to 10th	Day	5% 5% 2 5% 4 5% 6% 4 6% 7% 53%	4957
	11th to 20th	Day	19% 7% 3 5% 3 4 4 3 5% 6% 41%	4628
	21st to end	Day	9% 9% 5% 10% 7% 7% 6% 5% 6% 9% 26%	4722
September	1st to 10th	Day	13% 10% 4 9% 5% 5% 5% 5% 7% 9% 29%	2470
	11th to 20th	Day	13% 12% 4 9% 6% 4 4 4 6% 7% 30%	2193
	21st to end	Day	17% 13% 5% 8% 6% 6% 6% 4 5% 7% 25%	2090
October	1st to 10th	Day	10% 14% 6% 9% 5% 6% 5% 4 7% 9% 26%	3050
	11th to 20th	Day	12% 14% 5% 11% 7% 5% 6% 5% 6% 7% 22%	2821
	21st to end	Day	11% 15% 6% 14% 7% 6% 6% 4 5% 5% 20%	2575
November	1st to 10th	Day	9% 16% 9% 16% 9% 6% 4 4 6% 6% 14%	1340
	11th to 20th	Day	9% 17% 6% 16% 10% 8% 5% 4 7% 6% 13%	1091
	21st to end	Day	7% 15% 8% 18% 8% 7% 6% 6% 5% 6% 14%	1000
December	1st to 10th	Day	6% 15% 6% 16% 9% 7% 6% 5% 6% 6% 17%	1419
	11th to 20th	Day	4 14% 4 16% 7% 6% 5% 6% 6% 16% 15%	1116
	21st to end	Day	4 16% 7% 17% 10% 8% 11% 5% 5% 5% 12%	1684
January	1st to 10th	Night	3 9% 5% 16% 10% 9% 9% 7% 7% 7% 18%	8146
	11th to 20th	Night	3 7% 3 8% 8% 7% 9% 6% 10% 11% 28%	7717
	21st to end	Night	4 12% 5% 14% 9% 7% 6% 4 6% 9% 24%	8028
February	1st to 10th	Night	3 7% 4 10% 8% 6% 7% 7% 10% 11% 29%	3094
	11th to 20th	Night	4 10% 5% 11% 7% 7% 6% 6% 9% 10% 26%	2746
	21st to end	Night	2 10% 6% 14% 10% 7% 7% 4 8% 8% 25%	2229
March	1st to 10th	Night	2 7% 4 12% 7% 7% 6% 6% 9% 10% 29%	5505
	11th to 20th	Night	3 8% 3 8% 7% 7% 7% 5% 8% 9% 33%	5182
	21st to end	Night	2 5% 2 7% 5% 5% 5% 5% 5% 7% 52%	5209
April	1st to 10th	Night	4 11% 4 10% 6% 5% 5% 5% 6% 7% 38%	1829
	11th to 20th	Night	5% 7% 2 7% 6% 6% 5% 5% 6% 8% 42%	1693
	21st to end	Night	4 7% 2 8% 7% 5% 4 4 8% 7% 44%	1400
May	1st to 10th	Night	7% 7% 3 8% 5% 5% 6% 4 8% 8% 39%	3009
	11th to 20th	Night	6% 9% 3 9% 5% 6% 6% 5% 6% 8% 36%	2245
	21st to end	Night	9% 8% 3 8% 6% 5% 5% 4 5% 7% 40%	2425
June	1st to 10th	Night	12% 6% 2 6% 5% 4 4 4 8% 9% 40%	700
	11th to 20th	Night	8% 7% 2 7% 4 4 5% 4 7% 9% 43%	600
	21st to end	Night	6% 5% 2 6% 5% 6% 6% 6% 6% 11% 42%	600
July	1st to 10th	Night	5% 4 2 10% 7% 7% 6% 5% 7% 11% 35%	1211
	11th to 20th	Night	7% 4 1 5% 4 4 4 4 5% 8% 53%	1387
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 4 7% 11% 44%	1795
August	1st to 10th	Night	4 3 2 4 4 4 4 4 6% 8% 58%	1973
	11th to 20th	Night	16% 7% 2 5% 4 3 4 3 5% 6% 45%	2196
	21st to end	Night	11% 9% 3 9% 5% 6% 5% 5% 6% 9% 31%	2939
September	1st to 10th	Night	10% 9% 3 8% 5% 5% 6% 4 6% 9% 36%	1710
	11th to 20th	Night	11% 8% 3 9% 5% 6% 6% 5% 7% 8% 33%	1984
	21st to end	Night	15% 11% 3 9% 6% 5% 6% 4 6% 7% 28%	2090
October	1st to 10th	Night	10% 12% 4 11% 6% 5% 5% 4 6% 8% 29%	3919
	11th to 20th	Night	9% 14% 5% 14% 7% 7% 6% 5% 5% 6% 22%	4086
	21st to end	Night	9% 15% 6% 15% 8% 7% 6% 4 6% 6% 19%	4967
November	1st to 10th	Night	12% 18% 6% 17% 9% 6% 5% 4 4 5% 13%	2956
	11th to 20th	Night	10% 15% 6% 15% 10% 9% 8% 5% 5% 5% 13%	3306
	21st to end	Night	7% 17% 6% 18% 9% 8% 6% 5% 7% 8% 10%	3400
December	1st to 10th	Night	5% 17% 7% 19% 11% 7% 5% 3 4 5% 17%	5756
	11th to 20th	Night	5% 12% 4 14% 8% 6% 7% 5% 9% 14% 16%	7076
	21st to end	Night	6% 16% 7% 17% 10% 8% 7% 4 5% 5% 16%	9270

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	60% 6% 14% 15% 5%	1799
	11th to 20th	Day	48% 7% 11% 27% 8%	2196
	21st to end	Day	63% 7% 6% 16% 8%	2925
February	1st to 10th	Day	49% 6% 11% 24% 9%	1305
	11th to 20th	Day	52% 7% 16% 19% 6%	1567
	21st to end	Day	53% 6% 11% 21% 8% 1	1401
March	1st to 10th	Day	51% 5% 8% 20% 15% 1	4380
	11th to 20th	Day	50% 4 8% 22% 15% 1	4818
	21st to end	Day	43% 4 9% 26% 17%	5763
April	1st to 10th	Day	47% 6% 14% 22% 9% 1	2571
	11th to 20th	Day	41% 8% 14% 32% 6%	2656
	21st to end	Day	41% 9% 15% 28% 7%	3000
May	1st to 10th	Day	39% 5% 13% 29% 13%	6949
	11th to 20th	Day	44% 5% 11% 30% 9%	7654
	21st to end	Day	39% 4 10% 27% 17% 3	8449
June	1st to 10th	Day	44% 7% 13% 27% 9%	3700
	11th to 20th	Day	40% 8% 14% 27% 10% 1	3800
	21st to end	Day	36% 8% 14% 29% 12% 1	3800
July	1st to 10th	Day	49% 6% 16% 24% 4	5768
	11th to 20th	Day	31% 7% 15% 37% 11%	5473
	21st to end	Day	38% 7% 19% 31% 5%	5573
August	1st to 10th	Day	31% 6% 17% 30% 16%	4938
	11th to 20th	Day	44% 6% 13% 27% 9%	4673
	21st to end	Day	55% 9% 22% 14%	4721
September	1st to 10th	Day	51% 11% 22% 15% 1	2470
	11th to 20th	Day	52% 9% 19% 19% 1	2193
	21st to end	Day	59% 9% 18% 12% 3	2090
October	1st to 10th	Day	58% 5% 15% 20% 2	3050
	11th to 20th	Day	62% 5% 15% 17%	2821
	21st to end	Day	70% 5% 11% 14% 1	2575
November	1st to 10th	Day	71% 6% 10% 9% 2	1340
	11th to 20th	Day	72% 8% 11% 8% 2	1091
	21st to end	Day	67% 9% 11% 11% 3	1000
December	1st to 10th	Day	67% 5% 8% 14% 5%	1419
	11th to 20th	Day	58% 4 13% 22% 3	1116
	21st to end	Day	73% 5% 10% 10% 2	1684
January	1st to 10th	Night	61% 5% 11% 17% 6%	8146
	11th to 20th	Night	47% 5% 14% 27% 6%	7764
	21st to end	Night	59% 4 7% 20% 10%	8028
February	1st to 10th	Night	45% 8% 15% 23% 10% 1	3094
	11th to 20th	Night	49% 7% 16% 21% 7%	2748
	21st to end	Night	55% 6% 12% 17% 10% 1	2229
March	1st to 10th	Night	47% 5% 10% 24% 13% 1	5505
	11th to 20th	Night	44% 5% 10% 23% 17%	5182
	21st to end	Night	32% 4 9% 31% 23%	5209
April	1st to 10th	Night	43% 5% 14% 24% 13%	1829
	11th to 20th	Night	37% 7% 11% 34% 9% 1	1693
	21st to end	Night	35% 7% 13% 33% 12%	1400
May	1st to 10th	Night	39% 6% 15% 26% 15%	3009
	11th to 20th	Night	45% 5% 13% 31% 7%	2245
	21st to end	Night	41% 4 10% 24% 18% 3	2425
June	1st to 10th	Night	37% 7% 15% 29% 11%	700
	11th to 20th	Night	35% 7% 17% 32% 9%	600
	21st to end	Night	33% 11% 14% 30% 11% 1	600
July	1st to 10th	Night	43% 6% 22% 24% 5%	1191
	11th to 20th	Night	28% 6% 14% 39% 13%	1363
	21st to end	Night	33% 6% 17% 38% 6%	1738
August	1st to 10th	Night	23% 6% 21% 30% 19%	1967
	11th to 20th	Night	41% 7% 13% 27% 12%	2217
	21st to end	Night	50% 6% 25% 17%	2939
September	1st to 10th	Night	42% 10% 26% 20% 2	1710
	11th to 20th	Night	47% 10% 20% 20% 3	1984
	21st to end	Night	56% 9% 18% 16% 2	2090
October	1st to 10th	Night	56% 5% 16% 21% 2	3919
	11th to 20th	Night	66% 4 16% 13% 1	4086
	21st to end	Night	71% 4 13% 12% 1	4967
November	1st to 10th	Night	75% 6% 9% 9% 2	2956
	11th to 20th	Night	74% 8% 9% 6% 2	3306
	21st to end	Night	71% 7% 11% 10% 2	3400
December	1st to 10th	Night	71% 3 8% 14% 4	5756
	11th to 20th	Night	56% 4 12% 24% 5%	7075
	21st to end	Night	70% 5% 11% 11% 3	9270

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	6% 4 22% 37% 22% 11%	200
	11th to 20th	Day	10% 4 22% 33% 21% 12%	200
	21st to end	Day	11% 6% 18% 37% 22% 5%	220
February	1st to 10th	Day	4 2 18% 38% 27% 12%	200
	11th to 20th	Day	3 1 18% 40% 32% 7%	200
	21st to end	Day	5% 2 16% 34% 30% 13%	207
March	1st to 10th	Day	5% 4 16% 34% 28% 14%	435
	11th to 20th	Day	10% 4 20% 39% 19% 8%	500
	21st to end	Day	5% 4 23% 33% 23% 13%	550
April	1st to 10th	Day	8% 6% 29% 28% 18% 11%	500
	11th to 20th	Day	7% 5% 14% 32% 30% 11%	496
	21st to end	Day	7% 4 23% 35% 25% 6%	700
May	1st to 10th	Day	11% 8% 25% 30% 20% 5%	758
	11th to 20th	Day	7% 5% 24% 33% 23% 7%	922
	21st to end	Day	10% 6% 22% 33% 23% 6%	1006
June	1st to 10th	Day	14% 5% 21% 29% 24% 7%	930
	11th to 20th	Day	13% 2 21% 31% 24% 9%	930
	21st to end	Day	8% 4 16% 29% 29% 14%	930
July	1st to 10th	Day	9% 5% 18% 30% 28% 10%	887
	11th to 20th	Day	10% 3 15% 27% 29% 15%	852
	21st to end	Day	10% 3 14% 26% 31% 17%	947
August	1st to 10th	Day	9% 3 12% 27% 33% 17%	823
	11th to 20th	Day	19% 4 16% 27% 25% 9%	661
	21st to end	Day	12% 4 16% 27% 28% 13%	539
September	1st to 10th	Day	16% 5% 21% 28% 17% 12%	490
	11th to 20th	Day	17% 6% 19% 27% 20% 11%	490
	21st to end	Day	17% 7% 26% 32% 14% 4	490
October	1st to 10th	Day	17% 8% 25% 25% 17% 8%	340
	11th to 20th	Day	20% 9% 21% 28% 15% 7%	300
	21st to end	Day	15% 5% 24% 34% 18% 4	274
November	1st to 10th	Day	10% 6% 26% 30% 22% 7%	200
	11th to 20th	Day	9% 10% 24% 29% 23% 7%	200
	21st to end	Day	10% 6% 26% 32% 18% 9%	200
December	1st to 10th	Day	10% 6% 26% 28% 23% 7%	163
	11th to 20th	Day	9% 5% 12% 40% 29% 5%	100
	21st to end	Day	4 5% 20% 33% 27% 11%	157
January	1st to 10th	Night	10% 3 21% 34% 23% 9%	1100
	11th to 20th	Night	11% 4 21% 36% 21% 6%	1100
	21st to end	Night	10% 4 27% 37% 17% 6%	1210
February	1st to 10th	Night	4 4 22% 38% 24% 8%	1046
	11th to 20th	Night	6% 3 23% 37% 26% 4	804
	21st to end	Night	5% 2 24% 39% 25% 5%	660
March	1st to 10th	Night	4 2 19% 37% 26% 10%	800
	11th to 20th	Night	6% 5% 21% 39% 23% 5%	800
	21st to end	Night	6% 2 20% 41% 26% 5%	880
April	1st to 10th	Night	7% 5% 26% 36% 21% 6%	629
	11th to 20th	Night	9% 3 19% 39% 28% 3	509
	21st to end	Night	5% 4 23% 44% 23% 1	400
May	1st to 10th	Night	9% 8% 27% 37% 18% 2	400
	11th to 20th	Night	9% 5% 28% 37% 19% 2	394
	21st to end	Night	9% 5% 22% 40% 23%	433
June	1st to 10th	Night	14% 4 21% 36% 23% 2	300
	11th to 20th	Night	12% 4 17% 37% 31% 1	200
	21st to end	Night	7% 2 16% 38% 36% 2	200
July	1st to 10th	Night	8% 3 16% 36% 33% 4	337
	11th to 20th	Night	11% 2 13% 39% 31% 5%	368
	21st to end	Night	7% 3 13% 31% 39% 6%	416
August	1st to 10th	Night	10% 1 10% 33% 39% 7%	378
	11th to 20th	Night	19% 2 13% 35% 25% 6%	376
	21st to end	Night	17% 3 14% 29% 32% 5%	498
September	1st to 10th	Night	14% 4 18% 32% 27% 5%	570
	11th to 20th	Night	14% 5% 20% 33% 23% 5%	731
	21st to end	Night	23% 4 27% 29% 14% 4	760
October	1st to 10th	Night	19% 4 22% 34% 17% 4	760
	11th to 20th	Night	20% 6% 22% 30% 17% 4	760
	21st to end	Night	18% 6% 24% 28% 21% 4	1035
November	1st to 10th	Night	18% 5% 20% 30% 22% 5%	975
	11th to 20th	Night	16% 6% 24% 29% 19% 6%	1054
	21st to end	Night	14% 6% 23% 29% 22% 7%	1100
December	1st to 10th	Night	13% 5% 24% 32% 20% 6%	1100
	11th to 20th	Night	11% 4 21% 37% 21% 6%	1100
	21st to end	Night	10% 3 20% 29% 28% 9%	1210

Page generated at 2025-07-02 23:30:17. Version ac07

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