Sundre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sundre clear sky chart from 2005-11-06 to 2026-07-01.

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	9% 9% 3 8% 5% 5% 5% 5% 7% 8% 36%	142225
	Night	7% 9% 4 9% 6% 5% 5% 4 6% 8% 37%	138810
Transparency	Day	44% 6% 15% 23% 10% 2	141929
	Night	44% 6% 15% 22% 11% 2	138689
Seeing	Day	14% 9% 28% 30% 16% 4	17466
	Night	11% 6% 32% 35% 14% 2	26495

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	2 8% 6% 13% 6% 7% 6% 4 7% 9% 32%	4125
	11th to 20th	Day	2 8% 3 10% 6% 6% 6% 4 7% 7% 43%	4197
	21st to end	Day	2 7% 4 10% 5% 4 4 4 6% 11% 42%	5186
February	1st to 10th	Day	4 11% 4 12% 8% 6% 5% 4 6% 9% 30%	1680
	11th to 20th	Day	3 12% 3 13% 7% 7% 6% 5% 7% 7% 30%	1784
	21st to end	Day	2 11% 6% 10% 8% 6% 7% 6% 7% 7% 31%	1699
March	1st to 10th	Day	3 8% 4 11% 6% 4 6% 4 7% 11% 37%	4618
	11th to 20th	Day	4 12% 4 9% 5% 4 5% 4 7% 9% 39%	4991
	21st to end	Day	9% 19% 6% 11% 5% 5% 5% 5% 6% 6% 23%	5777
April	1st to 10th	Day	8% 14% 5% 11% 7% 6% 7% 5% 6% 7% 25%	2562
	11th to 20th	Day	10% 16% 5% 9% 6% 5% 5% 4 6% 8% 27%	2700
	21st to end	Day	11% 13% 4 9% 6% 5% 5% 5% 6% 8% 29%	2730
May	1st to 10th	Day	12% 10% 3 7% 5% 5% 5% 4 6% 7% 36%	8194
	11th to 20th	Day	12% 10% 4 9% 7% 6% 6% 5% 7% 8% 24%	8755
	21st to end	Day	14% 9% 3 8% 6% 5% 5% 5% 7% 8% 31%	9649
June	1st to 10th	Day	18% 8% 3 8% 6% 6% 6% 5% 7% 7% 27%	3150
	11th to 20th	Day	19% 10% 4 8% 6% 5% 6% 5% 7% 6% 24%	3150
	21st to end	Day	12% 6% 3 7% 5% 5% 7% 6% 8% 9% 33%	3150
July	1st to 10th	Day	9% 4 2 6% 4 4 6% 5% 7% 10% 42%	6781
	11th to 20th	Day	12% 4 2 5% 4 4 6% 6% 8% 9% 40%	6780
	21st to end	Day	11% 5% 2 5% 4 4 5% 5% 6% 9% 43%	7205
August	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 9% 41%	4541
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 11% 40%	4279
	21st to end	Day	11% 4 2 5% 4 4 5% 4 6% 8% 48%	4664
September	1st to 10th	Day	13% 6% 1 6% 4 4 3 4 6% 7% 46%	2473
	11th to 20th	Day	14% 9% 3 5% 3 4 4 3 4 5% 46%	2213
	21st to end	Day	9% 8% 3 6% 6% 4 5% 3 6% 8% 43%	2200
October	1st to 10th	Day	8% 6% 3 7% 3 4 5% 4 7% 10% 43%	3480
	11th to 20th	Day	8% 7% 3 7% 5% 5% 6% 5% 9% 9% 37%	2937
	21st to end	Day	6% 7% 3 7% 6% 5% 5% 4 6% 8% 42%	3200
November	1st to 10th	Day	7% 14% 4 10% 6% 6% 5% 4 5% 6% 32%	1725
	11th to 20th	Day	5% 12% 4 9% 6% 4 4 5% 6% 8% 38%	1533
	21st to end	Day	4 13% 4 10% 6% 4 5% 5% 6% 9% 34%	1470
December	1st to 10th	Day	5% 10% 4 10% 7% 8% 8% 6% 7% 8% 28%	2360
	11th to 20th	Day	3 11% 4 10% 6% 6% 6% 5% 6% 9% 34%	2712
	21st to end	Day	3 11% 4 9% 6% 5% 5% 4 7% 8% 39%	3575
January	1st to 10th	Night	3 13% 6% 13% 7% 7% 6% 5% 6% 7% 27%	8768
	11th to 20th	Night	1 7% 4 11% 7% 6% 6% 5% 6% 7% 39%	8745
	21st to end	Night	2 8% 4 11% 6% 6% 5% 4 7% 9% 38%	8994
February	1st to 10th	Night	5% 10% 4 13% 8% 8% 6% 4 7% 7% 28%	2940
	11th to 20th	Night	4 11% 4 12% 7% 7% 7% 4 6% 8% 30%	2722
	21st to end	Night	2 10% 4 11% 7% 6% 5% 4 6% 7% 36%	2104
March	1st to 10th	Night	2 9% 4 11% 6% 6% 6% 5% 6% 8% 36%	5496
	11th to 20th	Night	5% 10% 4 10% 5% 5% 5% 5% 8% 10% 35%	5214
	21st to end	Night	8% 17% 5% 12% 6% 5% 5% 4 6% 7% 26%	5436
April	1st to 10th	Night	7% 13% 4 9% 7% 6% 5% 4 6% 8% 31%	2058
	11th to 20th	Night	9% 14% 6% 10% 6% 4 5% 4 4 8% 29%	1871
	21st to end	Night	10% 11% 5% 9% 6% 6% 6% 4 7% 8% 30%	1890
May	1st to 10th	Night	15% 12% 3 7% 4 4 4 4 4 6% 37%	4712
	11th to 20th	Night	13% 9% 4 8% 5% 5% 6% 4 8% 9% 30%	4105
	21st to end	Night	10% 7% 2 7% 6% 6% 6% 5% 6% 9% 36%	4522
June	1st to 10th	Night	18% 9% 3 7% 6% 4 5% 4 6% 7% 32%	1470
	11th to 20th	Night	16% 9% 3 10% 6% 7% 5% 5% 6% 7% 27%	1470
	21st to end	Night	10% 6% 2 5% 5% 6% 5% 5% 8% 8% 39%	1470
July	1st to 10th	Night	10% 6% 2 7% 5% 5% 5% 4 6% 7% 43%	3180
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 7% 9% 46%	3180
	21st to end	Night	11% 5% 2 5% 3 4 4 3 6% 9% 48%	3635
August	1st to 10th	Night	12% 6% 2 6% 5% 5% 4 4 5% 8% 44%	2609
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 5% 7% 11% 41%	2774
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 8% 49%	3245
September	1st to 10th	Night	12% 5% 1 7% 4 4 4 3 5% 8% 49%	1925
	11th to 20th	Night	14% 8% 2 6% 3 3 4 3 7% 7% 43%	2186
	21st to end	Night	10% 6% 2 5% 4 4 5% 4 6% 8% 45%	2200
October	1st to 10th	Night	8% 7% 3 7% 4 4 4 4 6% 8% 46%	3715
	11th to 20th	Night	6% 7% 3 6% 5% 5% 5% 4 5% 9% 45%	4207
	21st to end	Night	5% 8% 3 8% 4 5% 5% 4 7% 7% 43%	4600
November	1st to 10th	Night	7% 14% 5% 9% 5% 4 5% 5% 6% 7% 33%	2772
	11th to 20th	Night	4 10% 4 9% 6% 6% 5% 5% 7% 9% 35%	3082
	21st to end	Night	4 11% 4 10% 6% 6% 5% 5% 6% 9% 35%	3150
December	1st to 10th	Night	5% 12% 4 10% 6% 7% 6% 5% 7% 8% 30%	5040
	11th to 20th	Night	4 12% 5% 11% 9% 6% 6% 5% 7% 8% 27%	5700
	21st to end	Night	3 11% 4 10% 5% 5% 4 4 6% 7% 41%	7623

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	47% 4 12% 20% 13% 3	4125
	11th to 20th	Day	39% 5% 14% 20% 18% 4	4218
	21st to end	Day	36% 5% 15% 31% 12% 1	5187
February	1st to 10th	Day	49% 7% 14% 17% 11% 3	1680
	11th to 20th	Day	48% 8% 13% 18% 10% 2	1793
	21st to end	Day	48% 7% 13% 19% 11% 2	1699
March	1st to 10th	Day	40% 7% 14% 23% 15% 1	4618
	11th to 20th	Day	40% 6% 15% 23% 15% 1	4992
	21st to end	Day	59% 7% 11% 15% 7% 1	5777
April	1st to 10th	Day	54% 8% 16% 14% 7%	2562
	11th to 20th	Day	54% 7% 12% 18% 8% 1	2700
	21st to end	Day	51% 9% 14% 18% 7% 1	2730
May	1st to 10th	Day	46% 5% 10% 25% 12% 2	8194
	11th to 20th	Day	52% 7% 12% 21% 7% 1	8759
	21st to end	Day	49% 6% 15% 22% 8%	9650
June	1st to 10th	Day	52% 8% 15% 16% 7% 2	3150
	11th to 20th	Day	57% 8% 14% 14% 6% 1	3150
	21st to end	Day	43% 10% 19% 20% 7% 1	3150
July	1st to 10th	Day	35% 6% 17% 24% 14% 3	6707
	11th to 20th	Day	38% 5% 20% 28% 8% 1	6699
	21st to end	Day	37% 5% 17% 26% 13% 3	7001
August	1st to 10th	Day	39% 6% 18% 29% 7% 1	4524
	11th to 20th	Day	36% 6% 23% 26% 7% 1	4321
	21st to end	Day	33% 7% 19% 31% 9% 2	4663
September	1st to 10th	Day	35% 7% 19% 24% 11% 3	2473
	11th to 20th	Day	40% 6% 14% 26% 11% 2	2213
	21st to end	Day	38% 7% 17% 24% 12% 3	2200
October	1st to 10th	Day	36% 5% 20% 32% 7% 1	3480
	11th to 20th	Day	40% 6% 18% 21% 12% 3	2937
	21st to end	Day	39% 5% 11% 32% 12% 1	3200
November	1st to 10th	Day	51% 7% 12% 18% 10% 2	1725
	11th to 20th	Day	43% 8% 14% 23% 10% 2	1533
	21st to end	Day	44% 8% 16% 20% 9% 3	1470
December	1st to 10th	Day	52% 6% 12% 20% 8% 2	2360
	11th to 20th	Day	45% 7% 21% 19% 8% 1	2714
	21st to end	Day	41% 6% 9% 22% 19% 4	3575
January	1st to 10th	Night	54% 6% 12% 17% 9% 2	8769
	11th to 20th	Night	43% 4 14% 20% 13% 6%	8786
	21st to end	Night	40% 6% 17% 24% 12% 1	8994
February	1st to 10th	Night	51% 9% 9% 17% 12% 3	2940
	11th to 20th	Night	49% 8% 12% 17% 13% 2	2723
	21st to end	Night	46% 5% 11% 23% 14% 2	2104
March	1st to 10th	Night	41% 8% 16% 21% 13% 2	5496
	11th to 20th	Night	41% 8% 14% 21% 15% 1	5214
	21st to end	Night	55% 8% 11% 15% 10% 1	5436
April	1st to 10th	Night	48% 8% 13% 19% 10% 1	2058
	11th to 20th	Night	52% 7% 13% 18% 9% 1	1871
	21st to end	Night	50% 8% 14% 21% 7% 1	1890
May	1st to 10th	Night	48% 4 10% 24% 14% 2	4709
	11th to 20th	Night	46% 6% 16% 22% 9%	4105
	21st to end	Night	42% 7% 18% 27% 6% 1	4526
June	1st to 10th	Night	49% 8% 14% 19% 10% 1	1470
	11th to 20th	Night	54% 8% 13% 16% 7% 2	1470
	21st to end	Night	39% 10% 19% 24% 6% 2	1470
July	1st to 10th	Night	40% 5% 16% 25% 11% 3	3145
	11th to 20th	Night	34% 5% 22% 28% 7% 3	3138
	21st to end	Night	33% 5% 21% 28% 12% 1	3534
August	1st to 10th	Night	38% 7% 14% 33% 8%	2601
	11th to 20th	Night	36% 6% 27% 25% 6% 1	2798
	21st to end	Night	33% 5% 20% 31% 10% 1	3245
September	1st to 10th	Night	33% 6% 18% 26% 13% 4	1925
	11th to 20th	Night	38% 8% 15% 23% 12% 4	2186
	21st to end	Night	35% 7% 17% 23% 14% 3	2200
October	1st to 10th	Night	36% 5% 17% 26% 14% 1	3715
	11th to 20th	Night	36% 5% 18% 26% 13% 2	4207
	21st to end	Night	39% 5% 12% 30% 13% 1	4600
November	1st to 10th	Night	48% 7% 11% 20% 12% 2	2772
	11th to 20th	Night	43% 9% 15% 20% 12% 2	3082
	21st to end	Night	43% 8% 15% 21% 9% 3	3150
December	1st to 10th	Night	50% 5% 17% 19% 7% 2	5040
	11th to 20th	Night	52% 7% 15% 17% 8% 1	5697
	21st to end	Night	40% 5% 10% 23% 17% 4	7623

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	5% 9% 27% 34% 16% 8%	220
	11th to 20th	Day	8% 9% 35% 30% 15% 5%	220
	21st to end	Day	8% 11% 30% 33% 15% 3	242
February	1st to 10th	Day	10% 9% 34% 31% 11% 5%	220
	11th to 20th	Day	9% 7% 35% 33% 15% 2	298
	21st to end	Day	6% 12% 31% 33% 15% 3	415
March	1st to 10th	Day	8% 13% 36% 27% 12% 4	540
	11th to 20th	Day	9% 13% 35% 28% 11% 4	540
	21st to end	Day	14% 16% 31% 25% 10% 4	594
April	1st to 10th	Day	15% 15% 31% 25% 11% 3	540
	11th to 20th	Day	15% 14% 27% 28% 12% 3	532
	21st to end	Day	17% 13% 27% 27% 13% 3	540
May	1st to 10th	Day	18% 13% 26% 25% 15% 2	585
	11th to 20th	Day	16% 9% 22% 32% 17% 5%	775
	21st to end	Day	19% 7% 20% 29% 21% 4	844
June	1st to 10th	Day	17% 10% 26% 31% 12% 3	780
	11th to 20th	Day	23% 9% 24% 28% 13% 4	780
	21st to end	Day	15% 6% 23% 31% 19% 7%	780
July	1st to 10th	Day	14% 5% 21% 31% 24% 5%	722
	11th to 20th	Day	16% 4 23% 32% 21% 4	718
	21st to end	Day	10% 6% 25% 33% 20% 6%	724
August	1st to 10th	Day	13% 5% 27% 31% 17% 8%	527
	11th to 20th	Day	10% 5% 27% 33% 20% 4	517
	21st to end	Day	11% 6% 28% 29% 20% 7%	583
September	1st to 10th	Day	15% 6% 27% 28% 16% 7%	530
	11th to 20th	Day	19% 7% 20% 32% 18% 5%	530
	21st to end	Day	14% 11% 31% 29% 11% 3	530
October	1st to 10th	Day	15% 10% 26% 26% 17% 6%	462
	11th to 20th	Day	13% 9% 35% 25% 14% 3	330
	21st to end	Day	14% 13% 35% 25% 11% 2	363
November	1st to 10th	Day	16% 10% 30% 31% 11% 2	330
	11th to 20th	Day	13% 12% 29% 33% 11% 1	253
	21st to end	Day	6% 8% 36% 29% 14% 6%	220
December	1st to 10th	Day	6% 8% 36% 31% 14% 4	220
	11th to 20th	Day	7% 10% 43% 28% 8% 5%	220
	21st to end	Day	5% 7% 29% 34% 18% 7%	242
January	1st to 10th	Night	8% 9% 37% 33% 12% 1	1050
	11th to 20th	Night	8% 9% 39% 34% 9% 1	1042
	21st to end	Night	9% 9% 38% 32% 10% 1	924
February	1st to 10th	Night	9% 9% 31% 35% 13% 4	840
	11th to 20th	Night	8% 7% 34% 36% 13% 1	824
	21st to end	Night	6% 5% 34% 35% 18% 3	692
March	1st to 10th	Night	8% 4 36% 36% 13% 3	840
	11th to 20th	Night	9% 6% 38% 34% 12% 2	840
	21st to end	Night	12% 7% 34% 31% 14% 2	924
April	1st to 10th	Night	12% 7% 33% 32% 14% 1	798
	11th to 20th	Night	14% 9% 34% 33% 9%	623
	21st to end	Night	15% 11% 27% 35% 12%	630
May	1st to 10th	Night	21% 7% 24% 35% 13%	463
	11th to 20th	Night	13% 4 26% 40% 15% 2	414
	21st to end	Night	19% 5% 18% 38% 19% 1	455
June	1st to 10th	Night	20% 7% 22% 36% 13% 1	420
	11th to 20th	Night	20% 5% 23% 36% 15% 1	420
	21st to end	Night	11% 3 22% 37% 25% 2	420
July	1st to 10th	Night	15% 2 14% 45% 23% 1	390
	11th to 20th	Night	15% 2 20% 40% 20% 2	388
	21st to end	Night	11% 2 16% 43% 26% 2	438
August	1st to 10th	Night	13% 3 12% 36% 33% 3	398
	11th to 20th	Night	11% 3 15% 44% 25% 2	515
	21st to end	Night	10% 3 20% 45% 21% 1	660
September	1st to 10th	Night	15% 3 20% 40% 20% 3	725
	11th to 20th	Night	17% 4 17% 37% 22% 3	800
	21st to end	Night	13% 5% 31% 37% 13% 2	800
October	1st to 10th	Night	16% 4 28% 35% 15% 2	800
	11th to 20th	Night	12% 5% 36% 33% 12% 2	800
	21st to end	Night	11% 9% 34% 36% 10% 1	880
November	1st to 10th	Night	13% 9% 37% 29% 10% 1	927
	11th to 20th	Night	8% 10% 44% 28% 8% 1	1050
	21st to end	Night	8% 6% 38% 37% 9% 2	1050
December	1st to 10th	Night	10% 7% 40% 32% 10% 1	1050
	11th to 20th	Night	7% 7% 39% 35% 10% 1	1050
	21st to end	Night	9% 6% 38% 33% 12% 3	1155

Page generated at 2026-06-28 00:10:43. Version ac07

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