Stony Plain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stony Plain 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 9% 6% 5% 5% 4 6% 8% 35%	143035
	Night	8% 10% 4 10% 6% 5% 5% 4 6% 8% 33%	138010
Transparency	Day	45% 7% 17% 23% 8% 1	142732
	Night	48% 7% 16% 20% 9% 1	137896
Seeing	Day	13% 7% 25% 31% 18% 6%	18049
	Night	13% 6% 28% 35% 16% 2	26528

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	7% 15% 5% 11% 7% 5% 6% 5% 6% 7% 25%	4125
	11th to 20th	Day	3 7% 3 9% 6% 6% 6% 5% 7% 9% 37%	4119
	21st to end	Day	7% 11% 4 10% 6% 6% 5% 4 6% 8% 35%	4929
February	1st to 10th	Day	9% 13% 5% 11% 6% 6% 6% 4 7% 9% 23%	1680
	11th to 20th	Day	6% 13% 5% 12% 7% 6% 6% 5% 6% 6% 27%	1766
	21st to end	Day	3 14% 7% 11% 8% 7% 6% 5% 7% 8% 25%	1636
March	1st to 10th	Day	5% 11% 4 11% 7% 6% 6% 5% 6% 9% 32%	4618
	11th to 20th	Day	6% 12% 4 11% 5% 4 4 3 6% 10% 35%	5019
	21st to end	Day	9% 14% 6% 16% 6% 5% 5% 4 6% 7% 22%	5736
April	1st to 10th	Day	9% 13% 3 9% 6% 5% 6% 6% 7% 7% 31%	2608
	11th to 20th	Day	11% 11% 4 8% 6% 5% 6% 5% 7% 8% 30%	2700
	21st to end	Day	10% 11% 4 9% 5% 6% 5% 4 6% 8% 32%	2730
May	1st to 10th	Day	10% 7% 2 7% 5% 5% 5% 4 6% 8% 40%	8602
	11th to 20th	Day	12% 10% 4 10% 6% 6% 6% 5% 7% 8% 26%	8755
	21st to end	Day	11% 6% 3 8% 5% 5% 6% 5% 7% 9% 35%	9649
June	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	3150
	11th to 20th	Day	18% 9% 3 8% 6% 7% 6% 5% 7% 8% 23%	3304
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 5% 7% 10% 37%	3360
July	1st to 10th	Day	7% 4 2 6% 4 5% 5% 4 7% 10% 46%	7067
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 6% 8% 42%	6780
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 7% 9% 42%	7376
August	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 7% 9% 40%	4619
	11th to 20th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 10% 42%	4316
	21st to end	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 41%	4664
September	1st to 10th	Day	11% 6% 2 7% 4 4 5% 3 5% 8% 45%	2530
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 9% 43%	2205
	21st to end	Day	9% 7% 2 8% 5% 6% 4 4 7% 9% 42%	2200
October	1st to 10th	Day	9% 8% 3 8% 5% 5% 4 4 5% 8% 40%	3418
	11th to 20th	Day	11% 11% 3 7% 5% 5% 5% 4 6% 8% 35%	2941
	21st to end	Day	6% 13% 4 8% 5% 5% 4 4 6% 8% 37%	3182
November	1st to 10th	Day	10% 16% 5% 10% 6% 6% 5% 3 6% 8% 26%	1648
	11th to 20th	Day	7% 13% 4 12% 6% 5% 4 4 5% 7% 32%	1486
	21st to end	Day	5% 12% 6% 15% 6% 5% 5% 4 6% 8% 28%	1470
December	1st to 10th	Day	10% 16% 7% 11% 6% 6% 5% 5% 6% 7% 22%	2360
	11th to 20th	Day	8% 12% 4 12% 9% 6% 6% 5% 6% 6% 23%	2712
	21st to end	Day	4 7% 3 10% 6% 5% 5% 5% 6% 8% 41%	3575
January	1st to 10th	Night	8% 13% 5% 14% 8% 6% 6% 4 6% 7% 22%	8768
	11th to 20th	Night	3 8% 4 10% 7% 6% 6% 4 6% 7% 40%	8779
	21st to end	Night	7% 13% 4 11% 5% 4 5% 4 6% 8% 33%	9297
February	1st to 10th	Night	6% 12% 6% 13% 8% 8% 6% 4 5% 6% 27%	2940
	11th to 20th	Night	6% 12% 4 11% 7% 6% 6% 6% 7% 6% 28%	2740
	21st to end	Night	5% 12% 5% 10% 8% 7% 5% 4 6% 8% 29%	2170
March	1st to 10th	Night	3 9% 5% 12% 7% 6% 5% 4 7% 9% 31%	5496
	11th to 20th	Night	5% 10% 3 11% 7% 7% 7% 5% 7% 8% 29%	5200
	21st to end	Night	10% 15% 7% 14% 6% 5% 5% 4 6% 6% 23%	5479
April	1st to 10th	Night	8% 11% 3 10% 8% 7% 7% 4 7% 7% 29%	2011
	11th to 20th	Night	9% 12% 3 11% 8% 6% 5% 5% 7% 7% 27%	1871
	21st to end	Night	13% 10% 4 7% 5% 4 5% 5% 5% 9% 34%	1890
May	1st to 10th	Night	13% 8% 3 7% 4 5% 4 4 6% 7% 39%	4312
	11th to 20th	Night	11% 9% 4 11% 7% 7% 7% 5% 7% 7% 25%	4105
	21st to end	Night	11% 8% 3 7% 5% 4 5% 4 7% 9% 37%	4522
June	1st to 10th	Night	16% 10% 4 8% 6% 5% 6% 4 5% 7% 31%	1470
	11th to 20th	Night	16% 8% 4 9% 8% 8% 7% 6% 6% 9% 19%	1311
	21st to end	Night	12% 6% 3 7% 5% 5% 6% 5% 8% 8% 35%	1260
July	1st to 10th	Night	9% 5% 2 6% 4 4 5% 4 6% 8% 46%	2892
	11th to 20th	Night	12% 7% 3 7% 6% 5% 5% 4 7% 10% 34%	3180
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 7% 9% 41%	3467
August	1st to 10th	Night	14% 6% 2 7% 6% 4 5% 4 7% 7% 37%	2528
	11th to 20th	Night	12% 8% 2 8% 5% 4 5% 4 6% 10% 36%	2737
	21st to end	Night	12% 5% 2 6% 4 4 4 4 6% 10% 44%	3245
September	1st to 10th	Night	10% 6% 2 7% 4 4 4 4 5% 8% 45%	1867
	11th to 20th	Night	11% 8% 2 6% 4 4 5% 3 6% 8% 45%	2195
	21st to end	Night	10% 7% 3 7% 5% 4 4 5% 7% 8% 42%	2200
October	1st to 10th	Night	9% 7% 3 8% 5% 5% 5% 4 7% 7% 39%	3775
	11th to 20th	Night	9% 8% 3 7% 5% 5% 5% 4 7% 9% 38%	4206
	21st to end	Night	7% 9% 4 9% 6% 5% 5% 4 6% 8% 36%	4600
November	1st to 10th	Night	13% 15% 5% 11% 6% 5% 5% 3 5% 7% 26%	2855
	11th to 20th	Night	7% 14% 4 12% 6% 6% 5% 4 6% 7% 28%	3129
	21st to end	Night	6% 13% 5% 12% 7% 6% 6% 4 5% 8% 28%	3150
December	1st to 10th	Night	10% 19% 5% 11% 6% 5% 5% 4 5% 7% 23%	5040
	11th to 20th	Night	8% 16% 6% 13% 7% 6% 5% 4 6% 7% 22%	5700
	21st to end	Night	3 8% 4 10% 5% 6% 6% 4 6% 8% 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	56% 6% 11% 15% 11%	4125
	11th to 20th	Day	42% 5% 16% 17% 19% 2	4140
	21st to end	Day	47% 6% 21% 22% 4	4930
February	1st to 10th	Day	55% 7% 15% 14% 8% 1	1680
	11th to 20th	Day	54% 7% 13% 16% 9%	1774
	21st to end	Day	53% 9% 13% 18% 7%	1636
March	1st to 10th	Day	48% 6% 18% 20% 8%	4618
	11th to 20th	Day	44% 7% 15% 24% 10%	5020
	21st to end	Day	58% 7% 10% 18% 7%	5736
April	1st to 10th	Day	48% 9% 17% 19% 7% 1	2608
	11th to 20th	Day	50% 7% 14% 21% 9% 1	2700
	21st to end	Day	48% 8% 13% 22% 7% 1	2730
May	1st to 10th	Day	40% 5% 11% 28% 14% 1	8602
	11th to 20th	Day	52% 7% 11% 24% 6%	8759
	21st to end	Day	41% 9% 20% 23% 6% 1	9650
June	1st to 10th	Day	49% 6% 15% 20% 9% 1	3150
	11th to 20th	Day	57% 9% 14% 15% 5%	3304
	21st to end	Day	39% 9% 21% 24% 6% 1	3360
July	1st to 10th	Day	31% 8% 20% 29% 11% 1	6991
	11th to 20th	Day	38% 7% 17% 28% 9%	6699
	21st to end	Day	38% 7% 22% 24% 9%	7169
August	1st to 10th	Day	39% 9% 19% 32% 2	4601
	11th to 20th	Day	35% 8% 22% 28% 7%	4358
	21st to end	Day	37% 7% 25% 25% 5%	4663
September	1st to 10th	Day	37% 8% 20% 26% 7% 2	2530
	11th to 20th	Day	38% 7% 18% 29% 8%	2205
	21st to end	Day	37% 8% 18% 26% 8% 2	2200
October	1st to 10th	Day	42% 5% 24% 23% 5%	3418
	11th to 20th	Day	45% 6% 14% 24% 10%	2941
	21st to end	Day	45% 6% 18% 26% 4	3182
November	1st to 10th	Day	55% 8% 14% 16% 6% 1	1648
	11th to 20th	Day	50% 7% 16% 19% 7%	1486
	21st to end	Day	53% 9% 15% 17% 6% 1	1470
December	1st to 10th	Day	61% 7% 16% 11% 4 1	2360
	11th to 20th	Day	58% 8% 16% 14% 4	2714
	21st to end	Day	38% 7% 13% 28% 13% 1	3575
January	1st to 10th	Night	60% 5% 11% 13% 10% 1	8769
	11th to 20th	Night	42% 5% 16% 17% 17% 2	8820
	21st to end	Night	48% 6% 20% 19% 7%	9297
February	1st to 10th	Night	56% 5% 12% 16% 9% 1	2940
	11th to 20th	Night	52% 7% 13% 15% 12% 1	2742
	21st to end	Night	51% 7% 12% 20% 10% 1	2170
March	1st to 10th	Night	46% 6% 18% 21% 9%	5496
	11th to 20th	Night	48% 7% 15% 19% 10%	5200
	21st to end	Night	59% 8% 9% 17% 7%	5479
April	1st to 10th	Night	50% 9% 13% 18% 11% 1	2011
	11th to 20th	Night	52% 7% 13% 16% 10% 2	1871
	21st to end	Night	46% 7% 13% 21% 12% 1	1890
May	1st to 10th	Night	43% 4 10% 26% 16% 2	4309
	11th to 20th	Night	54% 8% 12% 19% 7%	4105
	21st to end	Night	41% 7% 21% 23% 7% 1	4526
June	1st to 10th	Night	51% 8% 12% 19% 9% 1	1470
	11th to 20th	Night	58% 10% 15% 13% 3	1311
	21st to end	Night	42% 10% 21% 22% 4 1	1260
July	1st to 10th	Night	36% 7% 20% 22% 14% 1	2859
	11th to 20th	Night	43% 8% 14% 28% 6%	3138
	21st to end	Night	39% 7% 22% 25% 7%	3369
August	1st to 10th	Night	43% 8% 19% 28% 2	2521
	11th to 20th	Night	42% 8% 21% 21% 7% 1	2761
	21st to end	Night	36% 7% 22% 28% 7%	3245
September	1st to 10th	Night	36% 7% 19% 26% 11% 2	1867
	11th to 20th	Night	37% 7% 15% 28% 10% 2	2195
	21st to end	Night	37% 8% 15% 25% 12% 2	2200
October	1st to 10th	Night	41% 6% 20% 26% 7%	3775
	11th to 20th	Night	41% 6% 14% 30% 8%	4206
	21st to end	Night	44% 7% 20% 24% 5%	4600
November	1st to 10th	Night	57% 6% 11% 19% 7% 1	2855
	11th to 20th	Night	54% 7% 13% 18% 7% 1	3129
	21st to end	Night	53% 8% 15% 18% 6% 1	3150
December	1st to 10th	Night	61% 6% 14% 13% 5% 1	5040
	11th to 20th	Night	60% 7% 16% 12% 5%	5697
	21st to end	Night	41% 6% 14% 24% 14% 2	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	12% 6% 27% 35% 16% 4	220
	11th to 20th	Day	9% 10% 27% 36% 14% 5%	220
	21st to end	Day	14% 10% 29% 29% 14% 6%	242
February	1st to 10th	Day	14% 6% 31% 32% 12% 5%	220
	11th to 20th	Day	11% 5% 30% 37% 14% 4	288
	21st to end	Day	8% 8% 35% 28% 16% 5%	352
March	1st to 10th	Day	13% 7% 29% 32% 17% 2	540
	11th to 20th	Day	11% 5% 29% 33% 17% 5%	540
	21st to end	Day	15% 6% 29% 27% 21% 2	594
April	1st to 10th	Day	11% 10% 30% 33% 12% 4	540
	11th to 20th	Day	13% 9% 27% 31% 15% 5%	532
	21st to end	Day	14% 10% 26% 28% 16% 5%	540
May	1st to 10th	Day	14% 10% 24% 33% 15% 3	688
	11th to 20th	Day	13% 6% 24% 33% 18% 6%	775
	21st to end	Day	16% 5% 22% 32% 17% 7%	844
June	1st to 10th	Day	21% 9% 24% 30% 13% 4	780
	11th to 20th	Day	20% 6% 23% 27% 19% 5%	934
	21st to end	Day	13% 4 19% 32% 24% 8%	990
July	1st to 10th	Day	11% 5% 19% 34% 22% 8%	850
	11th to 20th	Day	11% 3 22% 32% 24% 8%	718
	21st to end	Day	11% 4 17% 34% 26% 9%	794
August	1st to 10th	Day	11% 6% 16% 31% 23% 13%	579
	11th to 20th	Day	9% 4 28% 30% 24% 5%	517
	21st to end	Day	14% 7% 17% 28% 24% 10%	583
September	1st to 10th	Day	14% 8% 27% 23% 20% 8%	530
	11th to 20th	Day	16% 5% 22% 31% 19% 6%	530
	21st to end	Day	11% 12% 33% 26% 14% 4	530
October	1st to 10th	Day	13% 8% 26% 31% 18% 4	426
	11th to 20th	Day	13% 9% 32% 28% 15% 3	330
	21st to end	Day	14% 12% 37% 25% 9% 2	363
November	1st to 10th	Day	17% 6% 36% 28% 11% 2	330
	11th to 20th	Day	11% 6% 40% 29% 12% 2	228
	21st to end	Day	9% 5% 33% 35% 10% 7%	220
December	1st to 10th	Day	11% 7% 31% 35% 11% 5%	220
	11th to 20th	Day	12% 7% 32% 34% 12% 3	220
	21st to end	Day	11% 4 21% 37% 23% 5%	242
January	1st to 10th	Night	12% 7% 32% 34% 14% 2	1050
	11th to 20th	Night	12% 8% 33% 34% 12% 1	1050
	21st to end	Night	14% 10% 34% 30% 11% 1	1033
February	1st to 10th	Night	11% 7% 25% 37% 17% 3	840
	11th to 20th	Night	12% 5% 32% 36% 15% 1	824
	21st to end	Night	9% 5% 29% 35% 17% 4	692
March	1st to 10th	Night	11% 4 30% 37% 16% 2	840
	11th to 20th	Night	12% 3 31% 37% 16% 1	840
	21st to end	Night	15% 5% 26% 37% 15% 2	924
April	1st to 10th	Night	12% 6% 27% 38% 16% 2	751
	11th to 20th	Night	13% 6% 32% 32% 16% 1	623
	21st to end	Night	16% 7% 27% 37% 13%	630
May	1st to 10th	Night	15% 6% 26% 38% 15% 1	425
	11th to 20th	Night	10% 5% 27% 38% 18% 2	414
	21st to end	Night	20% 7% 21% 34% 16% 2	455
June	1st to 10th	Night	17% 9% 26% 34% 13% 1	420
	11th to 20th	Night	19% 5% 20% 32% 21% 2	420
	21st to end	Night	12% 4 17% 39% 25% 3	420
July	1st to 10th	Night	13% 2 18% 44% 23% 1	390
	11th to 20th	Night	12% 4 19% 40% 23% 2	388
	21st to end	Night	12% 3 16% 39% 28% 2	438
August	1st to 10th	Night	13% 4 15% 33% 30% 5%	398
	11th to 20th	Night	11% 5% 19% 37% 26% 2	491
	21st to end	Night	13% 2 20% 40% 24% 1	660
September	1st to 10th	Night	13% 3 19% 42% 22% 2	667
	11th to 20th	Night	13% 3 20% 42% 21% 2	800
	21st to end	Night	13% 4 32% 35% 15% 2	800
October	1st to 10th	Night	15% 4 27% 39% 15%	800
	11th to 20th	Night	13% 5% 33% 33% 14% 2	800
	21st to end	Night	13% 8% 34% 31% 12% 1	880
November	1st to 10th	Night	20% 7% 30% 32% 10% 1	1010
	11th to 20th	Night	13% 8% 35% 30% 11% 3	1050
	21st to end	Night	11% 6% 36% 35% 11% 2	1050
December	1st to 10th	Night	14% 8% 33% 30% 13% 3	1050
	11th to 20th	Night	12% 7% 32% 35% 13% 1	1050
	21st to end	Night	11% 4 30% 36% 16% 3	1155

Page generated at 2026-06-28 00:10:48. Version ac07

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