Bonnyville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bonnyville clear sky chart from 2005-11-06 to 2025-11-18.

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%	130729
	Night	8% 10% 4 10% 6% 6% 6% 4 6% 8% 33%	128298
Transparency	Day	45% 7% 17% 23% 7%	130425
	Night	48% 7% 16% 21% 8% 1	128182
Seeing	Day	13% 6% 23% 30% 20% 7%	16974
	Night	13% 5% 25% 37% 17% 2	25956

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 11% 6% 17% 10% 8% 7% 4 6% 6% 21%	3179
	11th to 20th	Day	5% 8% 4 10% 8% 7% 9% 5% 8% 9% 27%	3159
	21st to end	Day	6% 14% 6% 13% 6% 5% 5% 4 6% 7% 27%	3498
February	1st to 10th	Day	6% 12% 5% 13% 7% 6% 6% 6% 8% 7% 24%	1600
	11th to 20th	Day	6% 11% 4 11% 8% 7% 7% 4 7% 9% 25%	1755
	21st to end	Day	5% 12% 5% 12% 9% 6% 6% 5% 7% 8% 25%	1485
March	1st to 10th	Day	6% 8% 4 8% 6% 6% 7% 7% 8% 10% 32%	4523
	11th to 20th	Day	6% 10% 3 11% 7% 7% 6% 5% 7% 10% 28%	4999
	21st to end	Day	9% 16% 6% 11% 5% 5% 4 4 5% 6% 29%	5486
April	1st to 10th	Day	8% 11% 4 9% 6% 5% 6% 4 6% 8% 33%	2519
	11th to 20th	Day	13% 10% 3 10% 5% 6% 5% 5% 5% 7% 31%	2570
	21st to end	Day	13% 11% 3 9% 5% 4 4 4 6% 8% 33%	2689
May	1st to 10th	Day	12% 8% 3 8% 6% 6% 6% 4 6% 6% 36%	6511
	11th to 20th	Day	19% 10% 3 8% 5% 5% 5% 4 6% 6% 30%	6734
	21st to end	Day	11% 7% 3 7% 5% 5% 5% 4 7% 8% 38%	7405
June	1st to 10th	Day	15% 8% 3 8% 5% 5% 5% 4 7% 8% 31%	3162
	11th to 20th	Day	19% 9% 3 8% 6% 5% 6% 4 6% 8% 25%	3200
	21st to end	Day	12% 9% 3 7% 5% 5% 5% 5% 7% 8% 33%	3200
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 4 7% 10% 43%	6837
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 8% 46%	6780
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 5% 7% 8% 41%	7376
August	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 7% 46%	4870
	11th to 20th	Day	8% 5% 3 7% 4 5% 6% 4 7% 9% 41%	4209
	21st to end	Day	9% 5% 2 6% 4 4 5% 5% 6% 9% 46%	4664
September	1st to 10th	Day	11% 7% 2 6% 5% 4 4 4 7% 8% 43%	2505
	11th to 20th	Day	14% 7% 2 6% 4 4 3 4 6% 8% 41%	2287
	21st to end	Day	10% 5% 3 7% 5% 4 5% 4 6% 8% 43%	2186
October	1st to 10th	Day	9% 9% 3 7% 5% 5% 4 4 7% 9% 38%	3270
	11th to 20th	Day	10% 10% 4 8% 5% 4 5% 3 6% 10% 36%	3138
	21st to end	Day	8% 12% 6% 11% 5% 5% 5% 4 6% 8% 31%	2950
November	1st to 10th	Day	11% 15% 4 10% 8% 6% 5% 4 6% 7% 25%	1648
	11th to 20th	Day	7% 13% 4 13% 7% 6% 6% 4 7% 7% 25%	1575
	21st to end	Day	4 13% 6% 13% 8% 8% 5% 4 5% 8% 27%	1369
December	1st to 10th	Day	6% 13% 5% 13% 9% 7% 6% 6% 6% 8% 21%	1960
	11th to 20th	Day	8% 16% 7% 14% 7% 5% 4 4 6% 6% 23%	2259
	21st to end	Day	3 9% 4 14% 8% 5% 6% 5% 5% 6% 35%	3172
January	1st to 10th	Night	4 9% 5% 17% 11% 9% 8% 4 7% 7% 20%	6766
	11th to 20th	Night	4 9% 4 11% 7% 7% 9% 5% 7% 9% 28%	6739
	21st to end	Night	6% 12% 5% 11% 7% 6% 5% 4 5% 7% 32%	7458
February	1st to 10th	Night	6% 11% 4 12% 9% 7% 5% 6% 6% 7% 26%	2816
	11th to 20th	Night	6% 10% 4 10% 7% 7% 6% 4 7% 8% 31%	2532
	21st to end	Night	4 8% 5% 11% 7% 7% 7% 5% 7% 7% 31%	2145
March	1st to 10th	Night	4 10% 4 12% 6% 7% 6% 5% 7% 9% 28%	5364
	11th to 20th	Night	5% 12% 4 10% 7% 6% 5% 5% 8% 9% 29%	5000
	21st to end	Night	10% 17% 4 10% 6% 5% 4 4 5% 7% 27%	5489
April	1st to 10th	Night	7% 9% 3 9% 7% 5% 6% 5% 6% 9% 35%	1877
	11th to 20th	Night	10% 10% 3 10% 6% 6% 5% 4 5% 8% 33%	1781
	21st to end	Night	13% 10% 4 8% 4 5% 5% 4 6% 8% 33%	1710
May	1st to 10th	Night	12% 8% 2 7% 5% 4 5% 4 5% 7% 42%	3458
	11th to 20th	Night	17% 9% 3 8% 5% 5% 5% 4 6% 8% 30%	3159
	21st to end	Night	11% 9% 3 8% 5% 5% 5% 5% 7% 8% 35%	3470
June	1st to 10th	Night	15% 7% 3 8% 5% 3 6% 5% 7% 7% 34%	1235
	11th to 20th	Night	16% 11% 3 7% 6% 6% 5% 5% 5% 9% 26%	1200
	21st to end	Night	12% 6% 2 7% 4 4 5% 5% 6% 9% 40%	1200
July	1st to 10th	Night	6% 4 2 4 3 4 5% 5% 9% 11% 47%	3106
	11th to 20th	Night	8% 4 1 6% 5% 4 4 4 7% 9% 48%	3180
	21st to end	Night	14% 5% 3 6% 4 4 4 4 6% 9% 41%	3467
August	1st to 10th	Night	13% 5% 2 6% 5% 5% 4 3 6% 8% 42%	2280
	11th to 20th	Night	8% 5% 2 6% 4 5% 6% 5% 7% 10% 40%	2847
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 7% 8% 46%	3245
September	1st to 10th	Night	12% 6% 2 6% 3 4 4 4 5% 8% 46%	1894
	11th to 20th	Night	11% 5% 2 6% 5% 3 5% 4 6% 9% 45%	2110
	21st to end	Night	9% 5% 2 5% 5% 5% 4 5% 7% 8% 46%	2214
October	1st to 10th	Night	8% 7% 3 6% 4 5% 6% 4 7% 9% 41%	3920
	11th to 20th	Night	10% 8% 3 7% 5% 4 5% 4 7% 8% 40%	4009
	21st to end	Night	10% 11% 5% 10% 5% 5% 5% 5% 7% 8% 29%	4818
November	1st to 10th	Night	12% 16% 5% 9% 6% 6% 6% 4 5% 5% 26%	2870
	11th to 20th	Night	8% 13% 6% 13% 7% 6% 6% 5% 5% 7% 24%	2977
	21st to end	Night	5% 12% 6% 14% 7% 5% 5% 4 5% 7% 28%	3029
December	1st to 10th	Night	9% 15% 5% 15% 7% 6% 5% 4 6% 7% 21%	5220
	11th to 20th	Night	6% 15% 6% 15% 8% 7% 6% 5% 6% 7% 19%	5933
	21st to end	Night	3 9% 5% 14% 9% 6% 5% 4 5% 6% 36%	7780

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	61% 6% 10% 18% 5%	3179
	11th to 20th	Day	51% 7% 17% 15% 10% 1	3180
	21st to end	Day	56% 7% 20% 12% 5%	3498
February	1st to 10th	Day	55% 8% 14% 14% 10%	1600
	11th to 20th	Day	52% 8% 16% 16% 8%	1764
	21st to end	Day	53% 7% 16% 17% 6%	1485
March	1st to 10th	Day	43% 7% 22% 22% 5%	4523
	11th to 20th	Day	47% 8% 18% 22% 5%	5000
	21st to end	Day	54% 7% 11% 19% 9%	5486
April	1st to 10th	Day	47% 8% 17% 19% 9%	2519
	11th to 20th	Day	51% 6% 12% 21% 9% 1	2570
	21st to end	Day	48% 7% 14% 22% 8% 1	2689
May	1st to 10th	Day	47% 6% 11% 21% 14% 2	6511
	11th to 20th	Day	52% 7% 11% 22% 8%	6738
	21st to end	Day	40% 9% 16% 22% 11% 2	7406
June	1st to 10th	Day	47% 8% 15% 20% 10% 1	3162
	11th to 20th	Day	56% 9% 13% 17% 5% 1	3200
	21st to end	Day	44% 10% 17% 22% 6% 1	3200
July	1st to 10th	Day	34% 9% 23% 27% 6%	6763
	11th to 20th	Day	35% 7% 15% 31% 13%	6699
	21st to end	Day	38% 9% 20% 28% 5%	7169
August	1st to 10th	Day	37% 8% 21% 31% 2	4852
	11th to 20th	Day	37% 8% 23% 26% 6%	4249
	21st to end	Day	34% 7% 27% 28% 3	4663
September	1st to 10th	Day	38% 8% 20% 26% 7% 1	2505
	11th to 20th	Day	40% 7% 20% 27% 6%	2287
	21st to end	Day	39% 7% 18% 26% 10% 1	2186
October	1st to 10th	Day	42% 5% 21% 28% 3	3270
	11th to 20th	Day	44% 5% 17% 29% 6%	3138
	21st to end	Day	51% 6% 20% 20% 3	2950
November	1st to 10th	Day	58% 8% 13% 16% 5%	1648
	11th to 20th	Day	57% 8% 15% 16% 4	1575
	21st to end	Day	54% 9% 16% 17% 4	1369
December	1st to 10th	Day	59% 9% 12% 16% 4	1960
	11th to 20th	Day	61% 6% 16% 14% 3	2260
	21st to end	Day	48% 6% 13% 25% 7% 1	3172
January	1st to 10th	Night	60% 6% 13% 13% 7%	6766
	11th to 20th	Night	49% 6% 14% 19% 11% 1	6780
	21st to end	Night	51% 6% 22% 16% 4	7458
February	1st to 10th	Night	54% 7% 12% 18% 9%	2816
	11th to 20th	Night	48% 8% 14% 20% 10%	2533
	21st to end	Night	48% 8% 14% 19% 10% 1	2145
March	1st to 10th	Night	49% 6% 19% 18% 7%	5364
	11th to 20th	Night	48% 7% 15% 24% 5%	5000
	21st to end	Night	54% 7% 9% 17% 12%	5489
April	1st to 10th	Night	43% 7% 17% 20% 12% 1	1877
	11th to 20th	Night	47% 6% 13% 20% 11% 3	1781
	21st to end	Night	47% 6% 12% 22% 10% 3	1710
May	1st to 10th	Night	41% 5% 9% 24% 19% 2	3458
	11th to 20th	Night	50% 7% 11% 23% 9% 1	3159
	21st to end	Night	42% 10% 18% 20% 9% 1	3470
June	1st to 10th	Night	46% 8% 13% 22% 10% 1	1235
	11th to 20th	Night	54% 10% 15% 15% 7% 1	1200
	21st to end	Night	38% 10% 20% 23% 8% 1	1200
July	1st to 10th	Night	27% 9% 27% 27% 9%	3071
	11th to 20th	Night	32% 5% 14% 37% 11%	3138
	21st to end	Night	38% 8% 22% 26% 6%	3369
August	1st to 10th	Night	39% 7% 19% 32% 2	2273
	11th to 20th	Night	36% 9% 28% 21% 7%	2873
	21st to end	Night	34% 7% 24% 31% 5%	3245
September	1st to 10th	Night	36% 7% 19% 28% 7% 3	1894
	11th to 20th	Night	36% 7% 20% 28% 9%	2110
	21st to end	Night	33% 8% 16% 30% 11% 2	2214
October	1st to 10th	Night	38% 6% 22% 27% 7%	3920
	11th to 20th	Night	40% 5% 16% 32% 7%	4009
	21st to end	Night	51% 6% 18% 20% 4	4818
November	1st to 10th	Night	58% 7% 11% 17% 6%	2870
	11th to 20th	Night	58% 8% 15% 14% 5%	2977
	21st to end	Night	54% 9% 16% 17% 4	3029
December	1st to 10th	Night	62% 6% 15% 12% 5% 1	5220
	11th to 20th	Night	63% 7% 15% 11% 3	5931
	21st to end	Night	48% 6% 13% 21% 11% 1	7780

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% 3 21% 33% 28% 7%	200
	11th to 20th	Day	15% 7% 21% 29% 24% 6%	200
	21st to end	Day	11% 5% 27% 37% 16% 4	220
February	1st to 10th	Day	6% 5% 30% 36% 18% 5%	215
	11th to 20th	Day	7% 3 27% 31% 27% 6%	300
	21st to end	Day	6% 6% 27% 33% 19% 8%	249
March	1st to 10th	Day	9% 5% 26% 38% 19% 3	430
	11th to 20th	Day	11% 4 28% 35% 17% 5%	500
	21st to end	Day	16% 4 26% 31% 19% 5%	550
April	1st to 10th	Day	11% 6% 27% 35% 16% 5%	500
	11th to 20th	Day	17% 9% 24% 27% 17% 6%	492
	21st to end	Day	18% 6% 26% 33% 11% 5%	589
May	1st to 10th	Day	12% 10% 23% 30% 19% 6%	703
	11th to 20th	Day	14% 6% 23% 29% 19% 9%	725
	21st to end	Day	18% 6% 20% 27% 23% 7%	789
June	1st to 10th	Day	18% 10% 25% 26% 16% 4	730
	11th to 20th	Day	22% 7% 20% 27% 17% 7%	730
	21st to end	Day	13% 6% 19% 28% 24% 11%	730
July	1st to 10th	Day	11% 5% 18% 30% 26% 10%	721
	11th to 20th	Day	12% 5% 19% 30% 25% 9%	718
	21st to end	Day	10% 4 21% 29% 26% 10%	794
August	1st to 10th	Day	14% 5% 14% 27% 28% 12%	726
	11th to 20th	Day	9% 7% 22% 31% 23% 8%	551
	21st to end	Day	10% 7% 19% 31% 22% 11%	583
September	1st to 10th	Day	13% 8% 25% 26% 21% 6%	530
	11th to 20th	Day	19% 5% 21% 30% 20% 5%	530
	21st to end	Day	11% 10% 31% 28% 15% 5%	516
October	1st to 10th	Day	10% 9% 27% 28% 21% 5%	330
	11th to 20th	Day	17% 8% 27% 29% 15% 3	330
	21st to end	Day	17% 9% 29% 28% 12% 5%	363
November	1st to 10th	Day	19% 5% 26% 30% 17% 3	330
	11th to 20th	Day	15% 10% 30% 33% 9% 4	280
	21st to end	Day	7% 8% 26% 39% 15% 7%	200
December	1st to 10th	Day	7% 5% 25% 41% 17% 7%	200
	11th to 20th	Day	12% 4 34% 32% 16% 3	200
	21st to end	Day	9% 4 20% 32% 26% 9%	220
January	1st to 10th	Night	12% 5% 28% 38% 17% 2	1000
	11th to 20th	Night	12% 6% 27% 39% 14% 3	1000
	21st to end	Night	15% 7% 31% 34% 11% 2	1100
February	1st to 10th	Night	10% 6% 23% 40% 18% 3	845
	11th to 20th	Night	11% 3 26% 39% 18% 3	784
	21st to end	Night	6% 4 23% 41% 22% 4	660
March	1st to 10th	Night	9% 5% 26% 42% 16% 2	800
	11th to 20th	Night	12% 5% 26% 40% 15% 2	800
	21st to end	Night	15% 5% 23% 36% 18% 3	880
April	1st to 10th	Night	11% 4 27% 39% 18% 1	601
	11th to 20th	Night	15% 4 29% 35% 17% 2	593
	21st to end	Night	17% 5% 23% 37% 16% 2	600
May	1st to 10th	Night	14% 7% 27% 35% 16% 2	522
	11th to 20th	Night	15% 5% 21% 37% 19% 3	394
	21st to end	Night	15% 6% 19% 35% 22% 3	433
June	1st to 10th	Night	19% 6% 21% 34% 18% 2	400
	11th to 20th	Night	22% 6% 17% 30% 24% 2	400
	21st to end	Night	14% 3 15% 35% 30% 4	400
July	1st to 10th	Night	12% 3 16% 39% 28% 1	390
	11th to 20th	Night	12% 2 16% 43% 26% 1	388
	21st to end	Night	8% 4 16% 40% 26% 5%	438
August	1st to 10th	Night	13% 2 12% 37% 31% 6%	398
	11th to 20th	Night	10% 2 20% 41% 25% 2	589
	21st to end	Night	10% 4 18% 42% 23% 2	660
September	1st to 10th	Night	16% 4 21% 36% 22% 1	600
	11th to 20th	Night	15% 3 18% 45% 18% 1	710
	21st to end	Night	11% 4 28% 39% 16% 1	800
October	1st to 10th	Night	15% 4 28% 38% 13% 2	800
	11th to 20th	Night	14% 4 28% 36% 15% 2	800
	21st to end	Night	17% 7% 30% 32% 12% 1	1010
November	1st to 10th	Night	18% 5% 26% 36% 12% 2	1025
	11th to 20th	Night	15% 5% 30% 33% 13% 4	1036
	21st to end	Night	11% 5% 34% 37% 11% 2	1000
December	1st to 10th	Night	13% 5% 29% 33% 16% 4	1000
	11th to 20th	Night	13% 6% 28% 37% 14% 2	1000
	21st to end	Night	10% 3 25% 38% 20% 4	1100

Page generated at 2025-11-14 22:55:57. Version ac07

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