Fort McMurray
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort McMurray clear sky chart from 2005-11-06 to 2025-10-19.

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% 7% 35%	130854
	Night	8% 10% 4 11% 6% 6% 5% 4 6% 7% 32%	127489
Transparency	Day	45% 8% 16% 23% 7%	130534
	Night	49% 7% 15% 21% 7%	127389
Seeing	Day	15% 11% 28% 29% 15% 4	17745
	Night	14% 8% 30% 33% 14% 2	25992

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% 10% 5% 16% 11% 7% 7% 5% 5% 5% 22%	2415
	11th to 20th	Day	5% 10% 5% 11% 9% 8% 9% 6% 7% 8% 22%	3092
	21st to end	Day	6% 14% 7% 16% 7% 5% 5% 4 5% 7% 24%	3498
February	1st to 10th	Day	6% 11% 5% 11% 7% 8% 6% 5% 6% 8% 25%	1506
	11th to 20th	Day	5% 10% 4 10% 7% 8% 8% 5% 5% 7% 32%	1689
	21st to end	Day	4 10% 5% 11% 9% 7% 6% 5% 8% 7% 29%	1485
March	1st to 10th	Day	2 10% 4 11% 7% 8% 7% 5% 7% 10% 28%	4401
	11th to 20th	Day	5% 10% 5% 11% 6% 6% 6% 5% 7% 9% 30%	4999
	21st to end	Day	4 12% 5% 10% 5% 4 4 4 6% 6% 39%	5486
April	1st to 10th	Day	9% 13% 4 10% 6% 5% 5% 4 6% 7% 31%	2575
	11th to 20th	Day	9% 12% 4 11% 7% 6% 5% 4 6% 6% 30%	2570
	21st to end	Day	10% 11% 4 9% 6% 6% 6% 4 6% 8% 30%	2738
May	1st to 10th	Day	11% 9% 4 8% 5% 5% 5% 4 6% 7% 36%	6780
	11th to 20th	Day	16% 10% 3 9% 7% 6% 5% 4 5% 6% 29%	6734
	21st to end	Day	11% 7% 3 7% 5% 5% 5% 4 6% 7% 40%	7808
June	1st to 10th	Day	16% 8% 3 8% 6% 5% 5% 5% 7% 7% 30%	3362
	11th to 20th	Day	19% 9% 3 8% 6% 5% 5% 4 6% 7% 28%	3400
	21st to end	Day	13% 8% 2 7% 5% 5% 5% 4 7% 8% 35%	3400
July	1st to 10th	Day	8% 5% 2 7% 5% 6% 6% 6% 8% 11% 35%	7700
	11th to 20th	Day	5% 3 2 4 3 4 4 4 6% 8% 56%	7184
	21st to end	Day	13% 4 2 5% 4 4 5% 4 7% 9% 44%	7376
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 6% 8% 48%	4870
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 8% 37%	4476
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 6% 7% 39%	4664
September	1st to 10th	Day	16% 7% 2 7% 4 4 5% 4 5% 8% 37%	2553
	11th to 20th	Day	13% 9% 2 6% 5% 5% 5% 4 6% 6% 39%	2278
	21st to end	Day	11% 8% 3 8% 5% 5% 5% 4 5% 7% 40%	2195
October	1st to 10th	Day	10% 10% 3 9% 5% 5% 5% 4 7% 9% 33%	3270
	11th to 20th	Day	11% 12% 4 9% 6% 5% 5% 4 6% 7% 32%	3011
	21st to end	Day	10% 15% 5% 12% 5% 4 4 3 5% 6% 32%	2799
November	1st to 10th	Day	11% 14% 6% 13% 7% 4 3 3 4 6% 27%	1553
	11th to 20th	Day	12% 14% 5% 14% 8% 7% 5% 4 5% 4 22%	1389
	21st to end	Day	8% 15% 6% 12% 9% 5% 5% 3 5% 5% 28%	1200
December	1st to 10th	Day	5% 13% 7% 15% 8% 7% 5% 4 5% 6% 24%	1960
	11th to 20th	Day	9% 18% 6% 11% 7% 5% 5% 2 5% 5% 27%	1952
	21st to end	Day	4 11% 6% 12% 6% 5% 5% 3 6% 6% 35%	2486
January	1st to 10th	Night	6% 12% 6% 17% 8% 5% 6% 5% 6% 6% 24%	7530
	11th to 20th	Night	5% 9% 4 11% 7% 7% 9% 7% 7% 6% 27%	6804
	21st to end	Night	4 12% 6% 13% 6% 7% 6% 4 6% 7% 28%	7458
February	1st to 10th	Night	5% 11% 5% 11% 9% 8% 7% 5% 6% 6% 28%	2910
	11th to 20th	Night	6% 11% 4 12% 8% 7% 6% 5% 5% 6% 29%	2597
	21st to end	Night	3 9% 5% 13% 7% 7% 6% 5% 8% 8% 29%	2145
March	1st to 10th	Night	3 11% 6% 13% 7% 7% 6% 4 7% 8% 30%	5470
	11th to 20th	Night	5% 11% 6% 13% 7% 6% 6% 4 6% 7% 30%	5000
	21st to end	Night	7% 9% 5% 11% 5% 5% 4 3 5% 7% 38%	5489
April	1st to 10th	Night	9% 13% 3 11% 6% 5% 5% 4 5% 6% 32%	1821
	11th to 20th	Night	8% 10% 4 8% 6% 6% 7% 6% 6% 7% 32%	1781
	21st to end	Night	10% 12% 5% 10% 7% 6% 5% 4 4 6% 31%	1660
May	1st to 10th	Night	12% 9% 3 8% 5% 4 5% 4 6% 8% 35%	3180
	11th to 20th	Night	17% 9% 3 8% 4 5% 5% 4 7% 8% 30%	3159
	21st to end	Night	11% 7% 3 7% 6% 5% 5% 4 7% 7% 37%	3065
June	1st to 10th	Night	17% 7% 2 8% 4 5% 3 3 7% 9% 34%	1035
	11th to 20th	Night	15% 9% 3 8% 7% 7% 5% 4 7% 8% 29%	1000
	21st to end	Night	11% 5% 2 7% 7% 4 5% 5% 7% 9% 39%	1000
July	1st to 10th	Night	8% 4 2 7% 5% 6% 6% 6% 8% 12% 36%	2260
	11th to 20th	Night	5% 3 1 3 3 3 3 4 6% 9% 60%	2773
	21st to end	Night	11% 4 2 4 3 4 4 3 7% 9% 48%	3467
August	1st to 10th	Night	7% 5% 2 6% 4 5% 6% 4 7% 9% 46%	2280
	11th to 20th	Night	12% 7% 2 7% 4 4 5% 4 7% 7% 41%	2573
	21st to end	Night	12% 6% 2 6% 4 5% 4 3 6% 8% 44%	3245
September	1st to 10th	Night	14% 6% 3 8% 4 4 4 4 6% 7% 39%	1847
	11th to 20th	Night	11% 7% 3 7% 5% 4 4 4 6% 8% 39%	2120
	21st to end	Night	11% 8% 2 6% 5% 4 5% 4 7% 7% 40%	2205
October	1st to 10th	Night	13% 10% 3 7% 4 4 4 3 4 6% 42%	3920
	11th to 20th	Night	11% 10% 4 8% 4 5% 5% 4 6% 7% 36%	4089
	21st to end	Night	12% 15% 4 11% 6% 6% 5% 4 5% 5% 25%	4728
November	1st to 10th	Night	13% 14% 5% 10% 7% 5% 4 4 5% 5% 28%	2741
	11th to 20th	Night	11% 13% 5% 14% 8% 6% 4 4 5% 5% 25%	3010
	21st to end	Night	7% 15% 6% 14% 7% 5% 5% 4 6% 6% 25%	3200
December	1st to 10th	Night	8% 13% 5% 16% 8% 7% 7% 4 5% 6% 20%	5220
	11th to 20th	Night	6% 14% 6% 16% 8% 7% 7% 4 5% 7% 20%	6237
	21st to end	Night	4 11% 4 13% 8% 6% 5% 4 5% 6% 33%	8470

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% 8% 12% 14% 5%	2415
	11th to 20th	Day	55% 8% 12% 18% 7%	3113
	21st to end	Day	58% 10% 16% 12% 4	3498
February	1st to 10th	Day	54% 9% 12% 17% 8%	1506
	11th to 20th	Day	50% 9% 15% 19% 7%	1697
	21st to end	Day	51% 6% 16% 20% 6%	1485
March	1st to 10th	Day	48% 7% 16% 24% 4	4401
	11th to 20th	Day	47% 9% 14% 22% 8%	5000
	21st to end	Day	43% 6% 9% 25% 15% 2	5486
April	1st to 10th	Day	51% 7% 13% 18% 10% 1	2575
	11th to 20th	Day	52% 7% 10% 20% 11% 1	2570
	21st to end	Day	50% 7% 12% 23% 7%	2738
May	1st to 10th	Day	45% 6% 12% 23% 12% 1	6780
	11th to 20th	Day	52% 7% 11% 20% 9%	6738
	21st to end	Day	40% 10% 13% 24% 11% 2	7809
June	1st to 10th	Day	50% 8% 12% 21% 9%	3362
	11th to 20th	Day	53% 9% 12% 20% 6%	3400
	21st to end	Day	45% 9% 18% 20% 8% 1	3400
July	1st to 10th	Day	39% 9% 25% 20% 6% 1	7616
	11th to 20th	Day	24% 7% 15% 41% 13%	7093
	21st to end	Day	35% 7% 19% 35% 3	7169
August	1st to 10th	Day	32% 8% 21% 35% 4	4852
	11th to 20th	Day	43% 9% 21% 20% 6% 1	4521
	21st to end	Day	42% 8% 24% 23% 2	4663
September	1st to 10th	Day	44% 9% 20% 22% 5%	2553
	11th to 20th	Day	44% 7% 21% 22% 5%	2278
	21st to end	Day	42% 9% 17% 24% 8% 1	2195
October	1st to 10th	Day	46% 7% 17% 27% 3	3270
	11th to 20th	Day	50% 6% 16% 24% 3	3011
	21st to end	Day	53% 7% 19% 19% 2	2799
November	1st to 10th	Day	59% 7% 15% 16% 3	1553
	11th to 20th	Day	64% 9% 12% 13% 2	1389
	21st to end	Day	58% 8% 16% 16% 3 1	1200
December	1st to 10th	Day	60% 10% 12% 17% 3	1960
	11th to 20th	Day	59% 5% 13% 21% 2	1953
	21st to end	Day	49% 6% 18% 21% 5% 1	2486
January	1st to 10th	Night	58% 7% 14% 17% 4	7530
	11th to 20th	Night	51% 9% 13% 18% 9%	6845
	21st to end	Night	53% 9% 20% 13% 5%	7458
February	1st to 10th	Night	53% 8% 15% 18% 7%	2910
	11th to 20th	Night	54% 7% 14% 18% 7%	2599
	21st to end	Night	50% 7% 17% 18% 8%	2145
March	1st to 10th	Night	50% 7% 15% 24% 4	5470
	11th to 20th	Night	50% 8% 13% 23% 5%	5000
	21st to end	Night	43% 6% 12% 22% 16% 1	5489
April	1st to 10th	Night	50% 7% 12% 18% 12% 1	1821
	11th to 20th	Night	46% 8% 12% 17% 14% 2	1781
	21st to end	Night	51% 8% 9% 22% 9% 1	1660
May	1st to 10th	Night	44% 7% 10% 24% 13% 2	3180
	11th to 20th	Night	49% 7% 12% 23% 8% 1	3159
	21st to end	Night	42% 9% 11% 25% 11% 1	3065
June	1st to 10th	Night	46% 7% 14% 21% 12%	1035
	11th to 20th	Night	51% 9% 11% 22% 7% 1	1000
	21st to end	Night	41% 9% 18% 21% 11% 1	1000
July	1st to 10th	Night	37% 9% 25% 23% 4	2235
	11th to 20th	Night	20% 6% 14% 45% 14% 1	2741
	21st to end	Night	31% 7% 21% 37% 5%	3369
August	1st to 10th	Night	32% 7% 18% 39% 3	2273
	11th to 20th	Night	39% 9% 22% 23% 7%	2594
	21st to end	Night	38% 7% 28% 24% 3	3245
September	1st to 10th	Night	41% 9% 22% 21% 6%	1847
	11th to 20th	Night	41% 9% 17% 25% 8%	2120
	21st to end	Night	40% 9% 19% 23% 9% 1	2205
October	1st to 10th	Night	44% 5% 13% 28% 9%	3920
	11th to 20th	Night	47% 6% 16% 27% 4	4089
	21st to end	Night	60% 7% 15% 14% 3	4728
November	1st to 10th	Night	57% 7% 14% 17% 4	2741
	11th to 20th	Night	60% 10% 15% 13% 2	3010
	21st to end	Night	59% 9% 14% 15% 3	3200
December	1st to 10th	Night	64% 7% 13% 13% 4	5220
	11th to 20th	Night	63% 7% 16% 13% 2	6235
	21st to end	Night	50% 7% 14% 22% 7% 1	8470

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	10% 7% 28% 38% 14% 3	200
	11th to 20th	Day	11% 12% 29% 37% 11% 2	200
	21st to end	Day	10% 11% 36% 30% 10% 2	220
February	1st to 10th	Day	12% 8% 38% 26% 15% 4	200
	11th to 20th	Day	7% 10% 31% 32% 14% 5%	267
	21st to end	Day	10% 12% 38% 27% 10% 3	249
March	1st to 10th	Day	8% 11% 36% 29% 14% 2	420
	11th to 20th	Day	9% 15% 32% 29% 13% 1	500
	21st to end	Day	10% 13% 32% 31% 12% 2	550
April	1st to 10th	Day	17% 14% 34% 25% 8% 3	500
	11th to 20th	Day	17% 15% 25% 29% 11% 2	492
	21st to end	Day	17% 13% 31% 25% 12% 2	635
May	1st to 10th	Day	14% 14% 27% 28% 13% 4	703
	11th to 20th	Day	14% 12% 26% 29% 18% 2	725
	21st to end	Day	13% 12% 23% 33% 14% 4	789
June	1st to 10th	Day	20% 15% 26% 25% 12% 2	892
	11th to 20th	Day	21% 9% 25% 28% 14% 3	930
	21st to end	Day	13% 6% 24% 30% 21% 5%	930
July	1st to 10th	Day	12% 8% 23% 34% 19% 4	916
	11th to 20th	Day	12% 7% 21% 30% 23% 8%	827
	21st to end	Day	14% 7% 23% 27% 21% 8%	794
August	1st to 10th	Day	14% 8% 17% 30% 23% 8%	726
	11th to 20th	Day	15% 10% 30% 28% 15% 3	615
	21st to end	Day	16% 6% 25% 29% 19% 4	583
September	1st to 10th	Day	20% 11% 27% 25% 14% 3	530
	11th to 20th	Day	17% 10% 25% 33% 14% 2	530
	21st to end	Day	17% 15% 30% 24% 12% 2	525
October	1st to 10th	Day	16% 18% 26% 28% 9% 3	330
	11th to 20th	Day	16% 16% 39% 22% 6% 1	324
	21st to end	Day	22% 12% 33% 22% 8% 2	330
November	1st to 10th	Day	16% 12% 33% 25% 13% 2	293
	11th to 20th	Day	18% 11% 38% 24% 8% 2	200
	21st to end	Day	17% 11% 36% 24% 10% 3	200
December	1st to 10th	Day	9% 14% 29% 36% 12% 2	200
	11th to 20th	Day	15% 11% 35% 28% 10% 2	200
	21st to end	Day	8% 4 29% 36% 20% 4	220
January	1st to 10th	Night	12% 8% 33% 31% 14% 1	1100
	11th to 20th	Night	12% 8% 33% 35% 10% 2	1013
	21st to end	Night	13% 11% 33% 32% 9% 1	1100
February	1st to 10th	Night	10% 8% 30% 33% 16% 3	910
	11th to 20th	Night	12% 7% 34% 34% 11% 2	784
	21st to end	Night	7% 6% 32% 39% 16% 1	660
March	1st to 10th	Night	8% 10% 34% 34% 12% 2	800
	11th to 20th	Night	14% 9% 33% 32% 13%	800
	21st to end	Night	12% 9% 30% 35% 12% 2	880
April	1st to 10th	Night	13% 9% 33% 33% 11% 1	601
	11th to 20th	Night	12% 9% 31% 33% 13% 2	593
	21st to end	Night	13% 9% 30% 33% 13% 2	595
May	1st to 10th	Night	16% 11% 25% 32% 15% 2	400
	11th to 20th	Night	13% 9% 29% 33% 13% 2	394
	21st to end	Night	14% 7% 25% 39% 12% 3	433
June	1st to 10th	Night	21% 6% 25% 35% 13% 1	400
	11th to 20th	Night	18% 7% 23% 32% 20% 2	400
	21st to end	Night	13% 4 19% 35% 26% 4	400
July	1st to 10th	Night	10% 6% 21% 38% 23% 1	390
	11th to 20th	Night	11% 4 21% 35% 23% 6%	388
	21st to end	Night	14% 3 14% 38% 24% 7%	438
August	1st to 10th	Night	12% 4 16% 33% 31% 5%	398
	11th to 20th	Night	10% 5% 28% 35% 21% 1	490
	21st to end	Night	17% 3 24% 35% 19% 1	660
September	1st to 10th	Night	17% 6% 25% 30% 19% 3	600
	11th to 20th	Night	15% 5% 22% 39% 18% 1	720
	21st to end	Night	15% 10% 31% 33% 11% 1	800
October	1st to 10th	Night	21% 10% 33% 25% 10% 2	800
	11th to 20th	Night	17% 9% 33% 29% 10% 2	792
	21st to end	Night	22% 11% 30% 27% 9% 1	993
November	1st to 10th	Night	18% 8% 32% 29% 11% 1	975
	11th to 20th	Night	19% 8% 35% 28% 8% 2	1000
	21st to end	Night	13% 12% 37% 28% 9% 2	1000
December	1st to 10th	Night	13% 9% 32% 31% 13% 1	1000
	11th to 20th	Night	14% 8% 32% 35% 10% 1	1075
	21st to end	Night	10% 6% 29% 34% 19% 2	1210

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