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 2026-10-29.

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	7% 8% 4 9% 6% 6% 6% 5% 7% 8% 35%	156368
	Night	6% 10% 4 12% 8% 7% 6% 5% 7% 8% 28%	144340
Transparency	Day	46% 5% 14% 25% 9% 1	156001
	Night	54% 5% 13% 21% 7%	144291
Seeing	Day	10% 5% 20% 31% 24% 10%	19887
	Night	11% 4 22% 34% 23% 5%	27072

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% 8% 5% 13% 9% 8% 11% 7% 8% 9% 16%	2331
	11th to 20th	Day	5% 9% 5% 12% 6% 7% 8% 8% 11% 9% 21%	2847
	21st to end	Day	6% 14% 5% 13% 7% 7% 6% 5% 8% 8% 22%	3793
February	1st to 10th	Day	3 9% 5% 12% 8% 7% 6% 6% 9% 10% 26%	1371
	11th to 20th	Day	2 10% 5% 12% 8% 8% 8% 6% 9% 7% 24%	1639
	21st to end	Day	2 8% 5% 15% 9% 7% 6% 5% 7% 9% 25%	1469
March	1st to 10th	Day	3 10% 5% 11% 6% 6% 8% 7% 9% 11% 25%	4477
	11th to 20th	Day	4 8% 3 13% 8% 7% 6% 6% 8% 10% 28%	4923
	21st to end	Day	2 7% 4 11% 7% 6% 6% 6% 7% 8% 37%	5890
April	1st to 10th	Day	5% 11% 5% 9% 6% 5% 7% 4 6% 8% 35%	2700
	11th to 20th	Day	5% 9% 3 8% 6% 6% 5% 5% 6% 7% 39%	2790
	21st to end	Day	3 8% 3 9% 7% 7% 5% 5% 7% 8% 37%	3150
May	1st to 10th	Day	6% 10% 4 9% 6% 5% 5% 4 6% 7% 38%	9002
	11th to 20th	Day	5% 8% 4 9% 6% 6% 6% 4 6% 7% 39%	9947
	21st to end	Day	9% 8% 3 7% 5% 5% 5% 4 6% 8% 39%	11014
June	1st to 10th	Day	11% 8% 3 7% 5% 5% 5% 4 7% 8% 37%	3885
	11th to 20th	Day	9% 6% 3 7% 6% 5% 6% 4 7% 9% 38%	3990
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 6% 8% 46%	3990
July	1st to 10th	Day	7% 6% 3 8% 6% 6% 6% 5% 8% 10% 36%	10740
	11th to 20th	Day	5% 5% 2 5% 4 4 5% 4 6% 8% 54%	10380
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 5% 8% 10% 39%	10738
August	1st to 10th	Day	5% 4 2 5% 5% 6% 7% 5% 7% 8% 47%	7266
	11th to 20th	Day	14% 6% 2 6% 3 5% 5% 4 6% 7% 42%	6815
	21st to end	Day	8% 8% 4 10% 7% 7% 7% 5% 6% 10% 29%	6865
September	1st to 10th	Day	13% 10% 4 9% 5% 5% 5% 5% 6% 9% 29%	2730
	11th to 20th	Day	13% 12% 4 9% 6% 5% 4 5% 7% 8% 29%	2423
	21st to end	Day	15% 13% 5% 8% 6% 6% 6% 5% 5% 7% 24%	2310
October	1st to 10th	Day	10% 14% 5% 10% 5% 6% 5% 4 7% 9% 26%	3242
	11th to 20th	Day	11% 14% 5% 12% 7% 5% 6% 5% 6% 7% 22%	3000
	21st to end	Day	11% 15% 6% 14% 7% 6% 6% 4 5% 6% 21%	2718
November	1st to 10th	Day	9% 16% 9% 16% 8% 6% 4 4 6% 6% 15%	1408
	11th to 20th	Day	8% 17% 6% 17% 10% 9% 5% 5% 6% 6% 13%	1145
	21st to end	Day	7% 14% 8% 18% 8% 7% 6% 6% 5% 6% 13%	1050
December	1st to 10th	Day	6% 15% 6% 16% 9% 7% 6% 5% 6% 5% 18%	1462
	11th to 20th	Day	4 14% 4 16% 7% 6% 5% 6% 7% 16% 15%	1146
	21st to end	Day	4 16% 7% 17% 10% 8% 11% 5% 5% 6% 12%	1722
January	1st to 10th	Night	3 8% 5% 18% 11% 9% 9% 7% 7% 7% 17%	10562
	11th to 20th	Night	4 8% 4 10% 8% 8% 9% 6% 9% 10% 25%	10051
	21st to end	Night	4 12% 5% 13% 9% 8% 7% 4 6% 8% 25%	10385
February	1st to 10th	Night	3 8% 4 10% 8% 6% 7% 7% 9% 11% 28%	3248
	11th to 20th	Night	4 10% 5% 11% 7% 7% 6% 5% 9% 10% 26%	2887
	21st to end	Night	2 10% 5% 14% 10% 7% 7% 4 7% 8% 26%	2337
March	1st to 10th	Night	2 7% 4 12% 7% 7% 6% 6% 9% 10% 29%	5628
	11th to 20th	Night	3 8% 3 8% 7% 7% 7% 6% 8% 9% 33%	5296
	21st to end	Night	2 4 2 7% 5% 5% 6% 5% 5% 7% 52%	5324
April	1st to 10th	Night	4 10% 4 10% 6% 5% 5% 5% 6% 7% 38%	1920
	11th to 20th	Night	4 7% 3 8% 6% 6% 6% 5% 6% 8% 41%	1779
	21st to end	Night	4 7% 2 8% 7% 5% 4 4 8% 8% 44%	1470
May	1st to 10th	Night	10% 10% 4 10% 5% 5% 6% 4 7% 7% 33%	3915
	11th to 20th	Night	5% 9% 3 10% 5% 5% 5% 5% 6% 9% 38%	2915
	21st to end	Night	9% 8% 4 9% 6% 6% 5% 4 5% 7% 37%	3156
June	1st to 10th	Night	12% 7% 2 6% 5% 4 5% 4 8% 9% 39%	735
	11th to 20th	Night	8% 7% 2 7% 4 4 5% 4 7% 9% 43%	630
	21st to end	Night	5% 5% 2 6% 5% 5% 6% 6% 6% 11% 44%	630
July	1st to 10th	Night	4 4 2 9% 6% 6% 6% 5% 8% 11% 39%	2217
	11th to 20th	Night	6% 4 1 5% 4 4 4 3 6% 10% 52%	2579
	21st to end	Night	8% 4 2 5% 4 5% 5% 4 7% 10% 47%	3328
August	1st to 10th	Night	3 3 2 5% 4 5% 5% 5% 7% 9% 52%	2883
	11th to 20th	Night	11% 6% 2 5% 4 3 4 4 6% 8% 46%	3226
	21st to end	Night	10% 9% 3 9% 6% 6% 5% 5% 6% 9% 33%	4270
September	1st to 10th	Night	10% 9% 3 8% 5% 5% 6% 4 6% 9% 36%	1890
	11th to 20th	Night	11% 8% 3 8% 5% 6% 6% 5% 7% 8% 33%	2193
	21st to end	Night	15% 11% 3 9% 6% 5% 5% 4 6% 7% 29%	2310
October	1st to 10th	Night	10% 12% 4 11% 6% 5% 5% 4 6% 8% 30%	4167
	11th to 20th	Night	9% 14% 5% 14% 7% 7% 6% 5% 5% 6% 22%	4346
	21st to end	Night	9% 15% 6% 14% 8% 7% 6% 4 6% 6% 19%	5241
November	1st to 10th	Night	12% 18% 7% 17% 9% 6% 5% 4 4 5% 13%	3108
	11th to 20th	Night	10% 15% 6% 15% 11% 9% 7% 5% 5% 5% 13%	3472
	21st to end	Night	7% 16% 6% 19% 9% 8% 6% 5% 6% 8% 10%	3570
December	1st to 10th	Night	5% 16% 7% 19% 11% 7% 5% 3 4 5% 17%	5932
	11th to 20th	Night	5% 11% 4 13% 8% 6% 7% 5% 9% 14% 16%	7266
	21st to end	Night	6% 15% 7% 16% 10% 8% 7% 4 5% 5% 16%	9474

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% 4 12% 17% 6%	2331
	11th to 20th	Day	54% 5% 10% 24% 7%	2862
	21st to end	Day	60% 5% 8% 19% 8%	3793
February	1st to 10th	Day	50% 6% 12% 23% 8%	1371
	11th to 20th	Day	52% 6% 15% 19% 7%	1647
	21st to end	Day	52% 6% 11% 22% 8% 1	1469
March	1st to 10th	Day	50% 5% 8% 21% 14% 1	4477
	11th to 20th	Day	50% 4 8% 23% 15% 1	4924
	21st to end	Day	44% 4 10% 26% 17%	5890
April	1st to 10th	Day	46% 6% 13% 24% 10% 1	2700
	11th to 20th	Day	41% 7% 13% 32% 6%	2790
	21st to end	Day	41% 9% 15% 28% 7%	3150
May	1st to 10th	Day	47% 4 14% 25% 10%	9002
	11th to 20th	Day	44% 4 11% 32% 8%	9951
	21st to end	Day	42% 3 11% 26% 15% 2	11015
June	1st to 10th	Day	44% 6% 13% 27% 9% 1	3885
	11th to 20th	Day	40% 8% 14% 26% 11% 1	3990
	21st to end	Day	35% 8% 14% 30% 13% 1	3990
July	1st to 10th	Day	44% 4 14% 24% 11% 3	10651
	11th to 20th	Day	30% 3 10% 42% 13%	10281
	21st to end	Day	40% 4 20% 32% 4	10505
August	1st to 10th	Day	35% 4 22% 27% 13%	7247
	11th to 20th	Day	41% 5% 19% 29% 6%	6860
	21st to end	Day	52% 6% 26% 15%	6864
September	1st to 10th	Day	52% 10% 22% 15% 1	2730
	11th to 20th	Day	52% 8% 21% 18% 1	2423
	21st to end	Day	59% 8% 17% 14% 2	2310
October	1st to 10th	Day	59% 4 15% 20% 2	3242
	11th to 20th	Day	63% 4 15% 17%	3000
	21st to end	Day	69% 4 11% 15% 1	2718
November	1st to 10th	Day	71% 6% 10% 11% 2	1408
	11th to 20th	Day	73% 7% 11% 7% 1	1145
	21st to end	Day	68% 8% 10% 11% 2	1050
December	1st to 10th	Day	67% 5% 8% 15% 5%	1462
	11th to 20th	Day	58% 4 14% 22% 3	1146
	21st to end	Day	73% 5% 10% 11% 3	1722
January	1st to 10th	Night	63% 4 10% 17% 6%	10563
	11th to 20th	Night	53% 4 13% 25% 5%	10098
	21st to end	Night	59% 3 8% 22% 8%	10385
February	1st to 10th	Night	47% 7% 14% 22% 9% 1	3248
	11th to 20th	Night	50% 7% 15% 20% 8%	2889
	21st to end	Night	54% 5% 12% 19% 10% 1	2337
March	1st to 10th	Night	46% 5% 11% 24% 13% 1	5628
	11th to 20th	Night	45% 5% 10% 23% 17%	5296
	21st to end	Night	32% 4 10% 31% 23%	5324
April	1st to 10th	Night	43% 5% 13% 26% 13%	1920
	11th to 20th	Night	39% 7% 11% 34% 9% 1	1779
	21st to end	Night	35% 6% 13% 33% 12%	1470
May	1st to 10th	Night	49% 4 14% 22% 11%	3915
	11th to 20th	Night	44% 4 14% 31% 7%	2915
	21st to end	Night	44% 3 11% 25% 16% 3	3159
June	1st to 10th	Night	38% 7% 15% 29% 11% 1	735
	11th to 20th	Night	35% 6% 16% 32% 10% 1	630
	21st to end	Night	32% 10% 14% 30% 13%	630
July	1st to 10th	Night	39% 4 17% 25% 13% 3	2197
	11th to 20th	Night	28% 3 11% 44% 13%	2555
	21st to end	Night	33% 3 19% 40% 4	3256
August	1st to 10th	Night	28% 4 27% 26% 15%	2877
	11th to 20th	Night	37% 5% 18% 30% 9%	3247
	21st to end	Night	50% 5% 26% 18% 1	4270
September	1st to 10th	Night	43% 9% 26% 20% 2	1890
	11th to 20th	Night	48% 9% 20% 20% 4	2193
	21st to end	Night	55% 8% 17% 17% 2	2310
October	1st to 10th	Night	56% 5% 17% 20% 2	4167
	11th to 20th	Night	66% 4 16% 13% 1	4346
	21st to end	Night	70% 4 13% 12% 1	5241
November	1st to 10th	Night	75% 6% 8% 10% 2	3108
	11th to 20th	Night	74% 8% 9% 7% 2	3472
	21st to end	Night	71% 6% 11% 10% 2	3570
December	1st to 10th	Night	71% 3 8% 15% 4	5932
	11th to 20th	Night	56% 4 12% 24% 4	7265
	21st to end	Night	70% 5% 12% 11% 3	9474

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% 3 20% 36% 22% 13%	220
	11th to 20th	Day	10% 5% 23% 32% 20% 11%	220
	21st to end	Day	10% 6% 21% 37% 21% 5%	242
February	1st to 10th	Day	5% 4 19% 37% 25% 10%	220
	11th to 20th	Day	3 1 17% 41% 32% 6%	220
	21st to end	Day	4 2 15% 34% 31% 13%	227
March	1st to 10th	Day	5% 4 17% 35% 27% 13%	472
	11th to 20th	Day	9% 5% 20% 38% 20% 9%	540
	21st to end	Day	4 3 23% 32% 24% 13%	594
April	1st to 10th	Day	8% 5% 28% 28% 19% 12%	540
	11th to 20th	Day	7% 5% 15% 33% 29% 11%	536
	21st to end	Day	7% 5% 23% 35% 26% 5%	750
May	1st to 10th	Day	12% 9% 25% 29% 20% 5%	811
	11th to 20th	Day	7% 5% 24% 32% 24% 7%	982
	21st to end	Day	10% 7% 23% 33% 22% 6%	1072
June	1st to 10th	Day	15% 5% 22% 29% 24% 6%	990
	11th to 20th	Day	12% 2 21% 32% 25% 9%	990
	21st to end	Day	8% 3 15% 29% 30% 15%	990
July	1st to 10th	Day	9% 5% 19% 30% 26% 10%	976
	11th to 20th	Day	9% 3 15% 29% 29% 15%	972
	21st to end	Day	9% 3 15% 27% 30% 16%	1079
August	1st to 10th	Day	9% 3 13% 27% 32% 16%	938
	11th to 20th	Day	17% 4 15% 28% 26% 9%	761
	21st to end	Day	11% 5% 18% 27% 27% 11%	627
September	1st to 10th	Day	15% 6% 22% 29% 16% 11%	570
	11th to 20th	Day	16% 7% 21% 27% 18% 10%	570
	21st to end	Day	16% 8% 27% 31% 14% 4	570
October	1st to 10th	Day	16% 8% 25% 26% 16% 8%	404
	11th to 20th	Day	19% 11% 21% 30% 13% 6%	360
	21st to end	Day	15% 7% 26% 33% 17% 3	322
November	1st to 10th	Day	10% 6% 28% 29% 21% 6%	220
	11th to 20th	Day	8% 10% 25% 29% 23% 6%	220
	21st to end	Day	9% 5% 25% 30% 20% 11%	220
December	1st to 10th	Day	11% 6% 25% 28% 22% 7%	179
	11th to 20th	Day	8% 5% 12% 42% 28% 5%	110
	21st to end	Day	4 6% 21% 31% 26% 12%	173
January	1st to 10th	Night	9% 3 20% 34% 24% 9%	1160
	11th to 20th	Night	11% 5% 22% 36% 20% 6%	1160
	21st to end	Night	10% 4 27% 37% 17% 5%	1276
February	1st to 10th	Night	5% 5% 22% 38% 22% 8%	1100
	11th to 20th	Night	6% 3 23% 38% 26% 4	845
	21st to end	Night	5% 2 23% 38% 26% 5%	692
March	1st to 10th	Night	4 3 19% 38% 26% 10%	840
	11th to 20th	Night	6% 5% 20% 38% 25% 5%	840
	21st to end	Night	6% 2 19% 41% 28% 5%	924
April	1st to 10th	Night	7% 5% 25% 35% 23% 5%	660
	11th to 20th	Night	8% 3 20% 38% 28% 3	535
	21st to end	Night	5% 3 23% 44% 24% 1	420
May	1st to 10th	Night	11% 8% 26% 37% 17% 2	420
	11th to 20th	Night	9% 5% 27% 38% 19% 2	414
	21st to end	Night	9% 6% 24% 39% 22%	455
June	1st to 10th	Night	13% 5% 21% 37% 22% 2	315
	11th to 20th	Night	11% 4 17% 37% 30%	210
	21st to end	Night	7% 2 15% 38% 38% 1	210
July	1st to 10th	Night	7% 3 18% 36% 32% 4	365
	11th to 20th	Night	10% 2 13% 39% 31% 5%	408
	21st to end	Night	7% 3 14% 30% 39% 7%	460
August	1st to 10th	Night	9% 2 11% 34% 38% 7%	418
	11th to 20th	Night	17% 1 15% 34% 27% 6%	416
	21st to end	Night	16% 3 15% 30% 31% 5%	550
September	1st to 10th	Night	13% 5% 20% 32% 25% 5%	630
	11th to 20th	Night	14% 5% 22% 33% 22% 4	808
	21st to end	Night	22% 4 26% 29% 15% 4	840
October	1st to 10th	Night	19% 4 22% 34% 17% 4	840
	11th to 20th	Night	20% 7% 22% 31% 16% 4	840
	21st to end	Night	17% 6% 25% 28% 20% 4	1130
November	1st to 10th	Night	19% 5% 21% 29% 21% 5%	1025
	11th to 20th	Night	15% 6% 23% 30% 20% 6%	1110
	21st to end	Night	13% 5% 22% 29% 23% 7%	1160
December	1st to 10th	Night	13% 5% 24% 33% 20% 5%	1160
	11th to 20th	Night	11% 4 21% 37% 22% 6%	1160
	21st to end	Night	10% 4 21% 29% 28% 8%	1276

Page generated at 2026-10-26 02:37:45. Version ac07

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