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Edmonton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edmonton clear sky chart from 2005-11-06 to 2025-11-03.

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	10% 9% 3 9% 6% 5% 5% 4 6% 8% 35%	131680
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 8% 33%	127038
Transparency	Day	44% 8% 17% 23% 8%	131379
	Night	47% 8% 16% 20% 9% 1	126917
Seeing	Day	13% 7% 24% 31% 19% 6%	17112
	Night	13% 6% 27% 36% 16% 2	25677

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% 12% 5% 12% 8% 7% 5% 5% 7% 9% 25%	3179
	11th to 20th	Day	4 11% 3 11% 7% 6% 6% 5% 9% 10% 30%	3159
	21st to end	Day	8% 13% 4 9% 5% 4 5% 3 5% 7% 35%	3753
February	1st to 10th	Day	8% 15% 5% 13% 8% 6% 5% 4 7% 7% 23%	1600
	11th to 20th	Day	6% 13% 5% 13% 7% 5% 6% 5% 7% 6% 27%	1697
	21st to end	Day	4 13% 5% 11% 8% 6% 6% 6% 7% 9% 26%	1537
March	1st to 10th	Day	4 9% 5% 13% 8% 5% 6% 4 7% 9% 31%	4518
	11th to 20th	Day	6% 12% 5% 10% 5% 4 4 4 6% 9% 34%	4951
	21st to end	Day	9% 14% 6% 14% 6% 4 4 3 6% 8% 26%	5565
April	1st to 10th	Day	8% 12% 4 9% 6% 6% 6% 4 6% 7% 31%	2500
	11th to 20th	Day	11% 12% 4 7% 6% 5% 5% 5% 6% 8% 31%	2570
	21st to end	Day	11% 11% 4 9% 6% 5% 4 4 7% 7% 32%	2600
May	1st to 10th	Day	12% 7% 3 8% 6% 5% 5% 4 5% 6% 38%	6634
	11th to 20th	Day	14% 11% 3 8% 6% 6% 6% 5% 6% 9% 26%	6734
	21st to end	Day	11% 7% 2 8% 5% 5% 5% 4 6% 8% 41%	7405
June	1st to 10th	Day	15% 8% 3 8% 5% 4 5% 4 7% 7% 32%	3000
	11th to 20th	Day	19% 10% 3 8% 6% 6% 6% 5% 6% 7% 24%	3077
	21st to end	Day	11% 6% 2 7% 5% 6% 5% 5% 7% 9% 37%	3200
July	1st to 10th	Day	8% 5% 2 5% 4 4 5% 5% 8% 10% 44%	6918
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	6780
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 42%	7376
August	1st to 10th	Day	11% 7% 2 6% 4 5% 5% 4 7% 9% 40%	4658
	11th to 20th	Day	9% 6% 2 6% 4 5% 5% 4 7% 10% 42%	4285
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 4 7% 10% 42%	4664
September	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 6% 8% 44%	2545
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 6% 8% 43%	2200
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 43%	2200
October	1st to 10th	Day	9% 8% 3 8% 6% 5% 5% 5% 5% 7% 39%	3402
	11th to 20th	Day	11% 10% 4 8% 4 5% 4 5% 6% 7% 36%	2974
	21st to end	Day	7% 13% 4 9% 4 4 4 4 6% 7% 37%	3148
November	1st to 10th	Day	10% 14% 5% 9% 7% 5% 5% 4 5% 6% 28%	1584
	11th to 20th	Day	7% 13% 5% 12% 7% 5% 5% 4 6% 8% 29%	1437
	21st to end	Day	6% 13% 6% 13% 7% 5% 6% 4 7% 6% 29%	1400
December	1st to 10th	Day	9% 16% 5% 11% 7% 6% 6% 5% 6% 8% 22%	2290
	11th to 20th	Day	9% 13% 5% 11% 7% 7% 6% 5% 7% 8% 21%	2642
	21st to end	Day	3 7% 3 9% 7% 6% 5% 4 6% 7% 42%	3498
January	1st to 10th	Night	4 10% 4 16% 9% 7% 7% 4 7% 8% 24%	6766
	11th to 20th	Night	4 10% 4 11% 8% 7% 5% 4 6% 7% 36%	6739
	21st to end	Night	8% 15% 5% 9% 5% 4 4 4 6% 7% 34%	7246
February	1st to 10th	Night	6% 13% 5% 14% 8% 6% 6% 5% 5% 6% 26%	2800
	11th to 20th	Night	6% 12% 4 11% 7% 6% 7% 5% 6% 7% 29%	2589
	21st to end	Night	5% 11% 4 10% 7% 6% 6% 5% 6% 8% 31%	2090
March	1st to 10th	Night	4 9% 5% 11% 6% 6% 6% 5% 8% 10% 31%	5376
	11th to 20th	Night	5% 9% 4 11% 6% 6% 6% 5% 7% 9% 31%	5047
	21st to end	Night	11% 14% 7% 14% 6% 6% 5% 4 6% 6% 23%	5407
April	1st to 10th	Night	8% 9% 3 10% 7% 5% 6% 5% 7% 7% 32%	1900
	11th to 20th	Night	9% 12% 4 11% 7% 7% 6% 4 6% 6% 29%	1781
	21st to end	Night	12% 10% 3 8% 5% 5% 4 4 7% 7% 35%	1800
May	1st to 10th	Night	17% 7% 2 8% 4 4 5% 4 5% 6% 39%	3327
	11th to 20th	Night	15% 9% 3 9% 7% 6% 6% 4 6% 7% 27%	3159
	21st to end	Night	13% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	3470
June	1st to 10th	Night	15% 8% 2 8% 5% 6% 5% 5% 7% 7% 30%	1400
	11th to 20th	Night	17% 9% 3 9% 7% 8% 6% 5% 8% 7% 21%	1315
	21st to end	Night	9% 8% 3 7% 6% 5% 5% 4 7% 9% 37%	1200
July	1st to 10th	Night	9% 6% 2 7% 5% 4 4 4 6% 9% 44%	3037
	11th to 20th	Night	12% 6% 2 7% 5% 5% 5% 4 7% 10% 35%	3180
	21st to end	Night	12% 6% 2 6% 4 5% 4 4 7% 9% 41%	3467
August	1st to 10th	Night	14% 6% 2 6% 5% 5% 6% 3 6% 8% 40%	2477
	11th to 20th	Night	12% 7% 3 7% 4 4 5% 4 6% 8% 38%	2768
	21st to end	Night	12% 4 2 6% 4 4 5% 4 6% 9% 43%	3245
September	1st to 10th	Night	12% 4 3 7% 4 4 4 3 5% 8% 46%	1853
	11th to 20th	Night	11% 7% 2 5% 4 4 4 4 5% 8% 46%	2200
	21st to end	Night	9% 7% 2 6% 5% 4 5% 4 6% 8% 44%	2200
October	1st to 10th	Night	8% 7% 3 9% 5% 5% 5% 4 7% 7% 40%	3792
	11th to 20th	Night	10% 8% 3 6% 4 5% 5% 4 7% 9% 40%	4171
	21st to end	Night	7% 9% 3 10% 6% 5% 5% 5% 7% 9% 36%	4619
November	1st to 10th	Night	13% 15% 5% 10% 6% 5% 5% 4 6% 6% 27%	2759
	11th to 20th	Night	8% 15% 6% 11% 6% 6% 6% 4 6% 7% 27%	2960
	21st to end	Night	7% 12% 5% 12% 8% 6% 5% 4 6% 7% 28%	3000
December	1st to 10th	Night	11% 17% 5% 12% 7% 6% 4 3 5% 6% 22%	4890
	11th to 20th	Night	8% 15% 6% 13% 7% 6% 6% 5% 7% 8% 20%	5550
	21st to end	Night	3 7% 4 11% 6% 5% 5% 4 6% 8% 41%	7458

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	53% 8% 12% 18% 8%	3179
	11th to 20th	Day	47% 6% 13% 14% 19% 1	3180
	21st to end	Day	46% 8% 21% 20% 5%	3753
February	1st to 10th	Day	57% 6% 15% 13% 8%	1600
	11th to 20th	Day	53% 8% 14% 16% 8%	1706
	21st to end	Day	51% 7% 13% 20% 8%	1537
March	1st to 10th	Day	48% 6% 19% 20% 8%	4518
	11th to 20th	Day	45% 8% 15% 23% 9%	4952
	21st to end	Day	56% 7% 11% 21% 6%	5565
April	1st to 10th	Day	49% 8% 15% 19% 8% 1	2500
	11th to 20th	Day	48% 7% 14% 22% 9%	2570
	21st to end	Day	48% 8% 15% 21% 7% 1	2600
May	1st to 10th	Day	44% 6% 10% 24% 15% 1	6634
	11th to 20th	Day	50% 8% 13% 23% 6%	6738
	21st to end	Day	38% 9% 21% 23% 9% 1	7406
June	1st to 10th	Day	47% 8% 15% 20% 9% 1	3000
	11th to 20th	Day	56% 10% 15% 15% 4	3077
	21st to end	Day	39% 11% 21% 22% 6% 1	3200
July	1st to 10th	Day	32% 8% 22% 28% 10%	6844
	11th to 20th	Day	37% 8% 17% 27% 10%	6699
	21st to end	Day	37% 8% 22% 24% 8%	7169
August	1st to 10th	Day	37% 10% 20% 30% 2	4640
	11th to 20th	Day	34% 8% 24% 26% 7%	4327
	21st to end	Day	36% 8% 27% 24% 5%	4663
September	1st to 10th	Day	37% 9% 19% 27% 7% 2	2545
	11th to 20th	Day	38% 8% 20% 27% 8%	2200
	21st to end	Day	37% 8% 19% 27% 8% 2	2200
October	1st to 10th	Day	43% 6% 22% 23% 5%	3402
	11th to 20th	Day	45% 5% 16% 25% 9%	2974
	21st to end	Day	45% 6% 19% 27% 4	3148
November	1st to 10th	Day	55% 8% 14% 15% 6% 1	1584
	11th to 20th	Day	52% 6% 18% 18% 5%	1437
	21st to end	Day	53% 9% 16% 17% 5% 1	1400
December	1st to 10th	Day	60% 7% 17% 12% 4 1	2290
	11th to 20th	Day	58% 8% 17% 13% 4	2644
	21st to end	Day	39% 6% 14% 28% 11% 1	3498
January	1st to 10th	Night	56% 7% 13% 14% 9% 1	6766
	11th to 20th	Night	46% 6% 14% 16% 18% 1	6780
	21st to end	Night	48% 7% 20% 19% 6%	7246
February	1st to 10th	Night	56% 6% 12% 17% 8% 1	2800
	11th to 20th	Night	50% 8% 14% 16% 11% 1	2590
	21st to end	Night	48% 8% 14% 20% 10% 1	2090
March	1st to 10th	Night	45% 7% 19% 22% 8%	5376
	11th to 20th	Night	46% 8% 17% 19% 10% 1	5047
	21st to end	Night	58% 8% 10% 17% 8%	5407
April	1st to 10th	Night	46% 9% 14% 19% 12%	1900
	11th to 20th	Night	52% 7% 12% 17% 11% 2	1781
	21st to end	Night	45% 8% 12% 22% 13% 1	1800
May	1st to 10th	Night	44% 6% 9% 22% 17% 3	3325
	11th to 20th	Night	53% 9% 14% 17% 7% 1	3159
	21st to end	Night	43% 10% 16% 21% 9% 1	3470
June	1st to 10th	Night	47% 9% 14% 20% 9% 1	1400
	11th to 20th	Night	56% 10% 16% 13% 4	1315
	21st to end	Night	41% 10% 23% 21% 5% 1	1200
July	1st to 10th	Night	34% 9% 20% 22% 14% 1	3002
	11th to 20th	Night	42% 8% 14% 29% 7%	3138
	21st to end	Night	37% 9% 22% 26% 7%	3369
August	1st to 10th	Night	41% 8% 21% 28% 2	2470
	11th to 20th	Night	41% 9% 20% 22% 7% 1	2792
	21st to end	Night	35% 8% 23% 27% 6%	3245
September	1st to 10th	Night	36% 7% 18% 28% 10% 2	1853
	11th to 20th	Night	35% 8% 16% 28% 10% 2	2200
	21st to end	Night	37% 8% 15% 26% 12% 2	2200
October	1st to 10th	Night	40% 6% 21% 25% 7%	3792
	11th to 20th	Night	40% 6% 15% 31% 8%	4171
	21st to end	Night	42% 7% 22% 24% 5%	4619
November	1st to 10th	Night	56% 7% 11% 19% 6% 1	2759
	11th to 20th	Night	54% 9% 13% 17% 6% 1	2960
	21st to end	Night	53% 9% 15% 18% 5% 1	3000
December	1st to 10th	Night	61% 7% 14% 12% 5% 1	4890
	11th to 20th	Night	59% 8% 17% 11% 5%	5547
	21st to end	Night	40% 7% 15% 24% 14% 1	7458

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	9% 7% 24% 36% 23% 3	200
	11th to 20th	Day	14% 7% 25% 36% 14% 7%	200
	21st to end	Day	14% 9% 31% 28% 13% 6%	220
February	1st to 10th	Day	12% 8% 29% 31% 17% 5%	200
	11th to 20th	Day	10% 8% 25% 34% 18% 6%	271
	21st to end	Day	7% 7% 28% 33% 19% 7%	301
March	1st to 10th	Day	10% 6% 27% 35% 18% 4	500
	11th to 20th	Day	11% 3 23% 36% 20% 6%	500
	21st to end	Day	15% 5% 22% 30% 24% 3	550
April	1st to 10th	Day	10% 8% 26% 36% 17% 4	500
	11th to 20th	Day	16% 8% 23% 30% 17% 6%	492
	21st to end	Day	15% 10% 25% 29% 16% 4	500
May	1st to 10th	Day	15% 9% 23% 31% 18% 4	663
	11th to 20th	Day	11% 6% 24% 33% 20% 6%	725
	21st to end	Day	15% 6% 21% 31% 19% 9%	789
June	1st to 10th	Day	19% 9% 23% 30% 16% 3	730
	11th to 20th	Day	20% 8% 20% 26% 21% 6%	807
	21st to end	Day	12% 6% 20% 30% 24% 9%	930
July	1st to 10th	Day	12% 5% 18% 33% 25% 7%	781
	11th to 20th	Day	11% 5% 22% 29% 24% 9%	718
	21st to end	Day	11% 4 17% 32% 26% 8%	794
August	1st to 10th	Day	12% 4 20% 30% 22% 12%	605
	11th to 20th	Day	11% 6% 25% 29% 24% 5%	517
	21st to end	Day	13% 8% 17% 29% 23% 10%	583
September	1st to 10th	Day	14% 8% 26% 25% 19% 7%	530
	11th to 20th	Day	17% 6% 22% 31% 19% 5%	530
	21st to end	Day	11% 12% 34% 24% 16% 3	530
October	1st to 10th	Day	15% 8% 27% 30% 15% 5%	410
	11th to 20th	Day	15% 11% 28% 30% 14% 3	330
	21st to end	Day	15% 14% 36% 23% 10% 2	363
November	1st to 10th	Day	17% 8% 25% 34% 14% 2	306
	11th to 20th	Day	11% 6% 35% 35% 12% 2	217
	21st to end	Day	8% 4 30% 42% 11% 6%	200
December	1st to 10th	Day	9% 7% 29% 37% 15% 5%	200
	11th to 20th	Day	12% 7% 27% 40% 12% 4	200
	21st to end	Day	7% 4 20% 39% 25% 5%	220
January	1st to 10th	Night	11% 6% 30% 37% 14% 2	1000
	11th to 20th	Night	11% 8% 31% 34% 14% 2	1000
	21st to end	Night	16% 10% 31% 30% 11% 2	1005
February	1st to 10th	Night	10% 7% 24% 37% 19% 3	800
	11th to 20th	Night	11% 5% 32% 36% 16% 1	784
	21st to end	Night	9% 6% 27% 35% 19% 5%	660
March	1st to 10th	Night	9% 5% 27% 40% 17% 3	800
	11th to 20th	Night	13% 5% 26% 38% 15% 3	800
	21st to end	Night	13% 5% 24% 38% 17% 3	880
April	1st to 10th	Night	11% 7% 24% 37% 19% 2	700
	11th to 20th	Night	12% 7% 28% 36% 15% 1	593
	21st to end	Night	16% 7% 27% 34% 15% 1	600
May	1st to 10th	Night	16% 6% 24% 38% 15% 1	429
	11th to 20th	Night	12% 7% 22% 40% 18% 2	394
	21st to end	Night	21% 5% 19% 35% 19% 1	433
June	1st to 10th	Night	19% 8% 23% 36% 12% 2	400
	11th to 20th	Night	20% 6% 20% 30% 22% 2	400
	21st to end	Night	12% 4 18% 37% 27% 3	400
July	1st to 10th	Night	14% 4 16% 42% 23% 1	390
	11th to 20th	Night	12% 3 21% 43% 21% 2	388
	21st to end	Night	11% 4 18% 39% 26% 3	438
August	1st to 10th	Night	12% 3 17% 32% 30% 6%	398
	11th to 20th	Night	11% 6% 17% 39% 25% 2	509
	21st to end	Night	11% 4 20% 41% 23% 1	660
September	1st to 10th	Night	12% 3 20% 41% 22% 2	643
	11th to 20th	Night	13% 4 19% 44% 19% 1	800
	21st to end	Night	13% 5% 29% 38% 14% 1	800
October	1st to 10th	Night	16% 5% 27% 39% 13% 1	800
	11th to 20th	Night	14% 5% 32% 33% 13% 2	800
	21st to end	Night	14% 7% 33% 32% 13%	887
November	1st to 10th	Night	19% 8% 30% 32% 10% 1	986
	11th to 20th	Night	15% 6% 34% 32% 11% 2	1000
	21st to end	Night	10% 6% 34% 36% 12% 2	1000
December	1st to 10th	Night	14% 9% 30% 29% 15% 3	1000
	11th to 20th	Night	11% 7% 30% 36% 15% 2	1000
	21st to end	Night	10% 4 29% 38% 17% 3	1100

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