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 2025-02-25.

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%	112704
	Night	8% 10% 4 10% 6% 5% 5% 4 6% 8% 32%	114597
Transparency	Day	45% 8% 17% 22% 8% 1	112445
	Night	48% 7% 16% 20% 9% 1	114502
Seeing	Day	13% 7% 25% 31% 18% 6%	16132
	Night	13% 6% 28% 35% 16% 2	24887

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	5% 13% 5% 11% 8% 6% 6% 5% 6% 8% 27%	3179
	11th to 20th	Day	4 9% 3 10% 7% 6% 6% 6% 7% 9% 31%	3159
	21st to end	Day	8% 13% 3 8% 5% 5% 4 4 6% 8% 36%	3802
February	1st to 10th	Day	9% 14% 5% 11% 6% 6% 6% 4 7% 9% 22%	1600
	11th to 20th	Day	6% 12% 6% 13% 7% 7% 6% 5% 6% 6% 27%	1680
	21st to end	Day	3 13% 6% 11% 8% 7% 6% 5% 7% 8% 25%	1521
March	1st to 10th	Day	4 14% 5% 13% 8% 6% 5% 4 5% 7% 27%	3138
	11th to 20th	Day	6% 11% 2 7% 4 4 4 4 7% 11% 39%	3427
	21st to end	Day	7% 13% 7% 19% 6% 5% 5% 4 5% 7% 21%	3912
April	1st to 10th	Day	9% 13% 3 8% 6% 4 6% 6% 7% 7% 30%	2360
	11th to 20th	Day	11% 11% 4 8% 6% 5% 6% 5% 7% 7% 30%	2440
	21st to end	Day	11% 11% 4 9% 5% 6% 5% 4 7% 8% 31%	2470
May	1st to 10th	Day	16% 10% 3 8% 6% 5% 5% 4 5% 7% 30%	4633
	11th to 20th	Day	11% 10% 3 9% 6% 6% 6% 5% 6% 8% 30%	4694
	21st to end	Day	13% 8% 3 9% 6% 6% 6% 5% 7% 9% 29%	5161
June	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 31%	2850
	11th to 20th	Day	18% 10% 3 8% 6% 7% 6% 5% 7% 8% 23%	2989
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 5% 7% 10% 38%	3040
July	1st to 10th	Day	9% 5% 2 6% 4 4 4 4 6% 8% 48%	4942
	11th to 20th	Day	8% 5% 2 5% 5% 5% 5% 4 6% 8% 47%	4740
	21st to end	Day	12% 5% 2 5% 4 4 5% 3 6% 9% 45%	5138
August	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 7% 9% 40%	4477
	11th to 20th	Day	8% 6% 2 6% 5% 5% 5% 4 7% 10% 42%	4181
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 7% 9% 40%	4521
September	1st to 10th	Day	12% 6% 2 7% 4 3 5% 3 5% 8% 44%	2404
	11th to 20th	Day	14% 6% 2 7% 4 4 4 4 5% 9% 41%	2095
	21st to end	Day	9% 7% 2 8% 5% 6% 4 3 7% 9% 42%	2090
October	1st to 10th	Day	9% 8% 3 8% 5% 5% 4 4 5% 8% 40%	3313
	11th to 20th	Day	11% 11% 3 7% 5% 5% 5% 4 6% 8% 35%	2851
	21st to end	Day	7% 13% 4 8% 5% 5% 4 4 6% 8% 36%	3084
November	1st to 10th	Day	10% 16% 5% 11% 6% 6% 5% 3 6% 8% 25%	1568
	11th to 20th	Day	7% 14% 4 12% 6% 5% 4 4 5% 7% 31%	1415
	21st to end	Day	5% 12% 6% 15% 7% 5% 5% 4 6% 8% 28%	1400
December	1st to 10th	Day	10% 15% 6% 11% 6% 6% 5% 4 6% 7% 22%	2290
	11th to 20th	Day	9% 12% 5% 12% 9% 6% 6% 5% 6% 6% 23%	2642
	21st to end	Day	3 7% 3 10% 6% 5% 5% 5% 6% 8% 42%	3498
January	1st to 10th	Night	5% 11% 5% 15% 9% 6% 6% 4 6% 8% 25%	6766
	11th to 20th	Night	3 9% 4 11% 8% 6% 6% 4 6% 6% 35%	6739
	21st to end	Night	8% 14% 4 10% 5% 4 4 4 5% 7% 34%	7186
February	1st to 10th	Night	6% 12% 6% 14% 8% 8% 6% 4 5% 6% 26%	2800
	11th to 20th	Night	6% 13% 4 11% 7% 6% 6% 6% 7% 6% 28%	2606
	21st to end	Night	6% 12% 4 9% 8% 7% 5% 5% 6% 8% 30%	2027
March	1st to 10th	Night	3 10% 6% 15% 8% 6% 5% 4 7% 9% 27%	3736
	11th to 20th	Night	5% 9% 3 8% 6% 6% 6% 5% 7% 8% 36%	3552
	21st to end	Night	7% 14% 8% 16% 6% 5% 6% 5% 7% 6% 21%	3739
April	1st to 10th	Night	8% 11% 3 9% 8% 7% 7% 5% 7% 7% 29%	1819
	11th to 20th	Night	9% 13% 3 11% 8% 6% 5% 4 7% 7% 27%	1691
	21st to end	Night	13% 10% 4 7% 5% 4 5% 5% 5% 9% 33%	1710
May	1st to 10th	Night	21% 11% 4 9% 5% 5% 4 3 4 5% 29%	2322
	11th to 20th	Night	11% 10% 4 9% 6% 6% 6% 4 7% 8% 29%	2199
	21st to end	Night	14% 10% 3 8% 7% 5% 6% 5% 8% 7% 27%	2414
June	1st to 10th	Night	15% 9% 4 8% 6% 5% 6% 4 5% 7% 32%	1330
	11th to 20th	Night	16% 8% 4 8% 8% 8% 7% 6% 6% 9% 20%	1187
	21st to end	Night	11% 6% 3 7% 5% 6% 6% 5% 8% 9% 34%	1140
July	1st to 10th	Night	10% 5% 2 6% 4 4 5% 4 6% 7% 47%	2016
	11th to 20th	Night	9% 5% 2 7% 6% 5% 5% 5% 7% 12% 36%	2220
	21st to end	Night	14% 6% 2 5% 4 4 4 4 7% 9% 41%	2414
August	1st to 10th	Night	14% 6% 2 7% 6% 4 5% 4 7% 7% 38%	2451
	11th to 20th	Night	12% 8% 2 8% 5% 4 5% 4 6% 10% 36%	2652
	21st to end	Night	12% 5% 2 6% 4 4 4 4 6% 10% 43%	3146
September	1st to 10th	Night	11% 6% 2 7% 4 4 4 4 5% 8% 44%	1773
	11th to 20th	Night	11% 8% 2 6% 4 4 5% 3 6% 8% 44%	2085
	21st to end	Night	10% 7% 2 7% 5% 4 4 4 7% 8% 42%	2090
October	1st to 10th	Night	9% 7% 3 8% 5% 5% 5% 4 7% 7% 39%	3660
	11th to 20th	Night	9% 8% 3 7% 5% 5% 6% 4 7% 9% 37%	4076
	21st to end	Night	7% 9% 4 9% 6% 5% 5% 5% 6% 8% 36%	4457
November	1st to 10th	Night	13% 15% 5% 11% 6% 5% 5% 3 5% 7% 25%	2716
	11th to 20th	Night	7% 15% 4 12% 6% 6% 5% 4 6% 7% 28%	2980
	21st to end	Night	7% 13% 5% 12% 7% 6% 6% 4 5% 8% 28%	3000
December	1st to 10th	Night	10% 18% 5% 11% 6% 5% 5% 4 5% 7% 23%	4890
	11th to 20th	Night	8% 16% 6% 13% 7% 6% 5% 4 6% 7% 22%	5550
	21st to end	Night	2 8% 4 10% 5% 6% 6% 4 6% 8% 42%	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% 7% 13% 17% 9% 1	3179
	11th to 20th	Day	47% 6% 12% 13% 20% 2	3180
	21st to end	Day	45% 6% 22% 21% 6%	3802
February	1st to 10th	Day	56% 7% 15% 14% 8% 1	1600
	11th to 20th	Day	54% 8% 13% 16% 8%	1688
	21st to end	Day	52% 9% 13% 18% 7%	1521
March	1st to 10th	Day	55% 6% 14% 18% 6%	3138
	11th to 20th	Day	36% 9% 20% 22% 12%	3428
	21st to end	Day	58% 9% 11% 17% 4	3912
April	1st to 10th	Day	48% 9% 17% 19% 7% 1	2360
	11th to 20th	Day	50% 7% 14% 21% 8%	2440
	21st to end	Day	48% 9% 14% 21% 7% 2	2470
May	1st to 10th	Day	51% 7% 11% 23% 8%	4633
	11th to 20th	Day	47% 9% 13% 23% 8%	4698
	21st to end	Day	46% 11% 17% 17% 9%	5162
June	1st to 10th	Day	50% 7% 15% 20% 8% 1	2850
	11th to 20th	Day	56% 9% 15% 15% 5%	2989
	21st to end	Day	38% 10% 22% 23% 6% 1	3040
July	1st to 10th	Day	32% 8% 15% 31% 13% 1	4866
	11th to 20th	Day	33% 8% 18% 29% 13%	4659
	21st to end	Day	36% 7% 21% 23% 12%	4976
August	1st to 10th	Day	38% 9% 19% 32% 2	4459
	11th to 20th	Day	35% 8% 22% 28% 7%	4223
	21st to end	Day	38% 7% 26% 24% 4	4520
September	1st to 10th	Day	38% 8% 20% 24% 7% 2	2404
	11th to 20th	Day	40% 7% 18% 28% 7%	2095
	21st to end	Day	37% 9% 18% 26% 8% 2	2090
October	1st to 10th	Day	42% 5% 24% 23% 5%	3313
	11th to 20th	Day	45% 6% 15% 25% 9%	2851
	21st to end	Day	46% 6% 18% 26% 4	3084
November	1st to 10th	Day	56% 8% 15% 15% 5% 1	1568
	11th to 20th	Day	52% 7% 16% 19% 7%	1415
	21st to end	Day	53% 9% 16% 16% 6% 1	1400
December	1st to 10th	Day	60% 7% 16% 12% 4 1	2290
	11th to 20th	Day	58% 8% 16% 14% 4	2644
	21st to end	Day	38% 7% 13% 28% 14% 1	3498
January	1st to 10th	Night	56% 6% 13% 15% 9% 1	6766
	11th to 20th	Night	47% 5% 14% 14% 18% 1	6780
	21st to end	Night	49% 6% 19% 19% 6%	7186
February	1st to 10th	Night	57% 5% 12% 16% 9% 1	2800
	11th to 20th	Night	53% 8% 13% 15% 11% 1	2608
	21st to end	Night	50% 8% 12% 20% 10% 1	2027
March	1st to 10th	Night	50% 8% 16% 19% 8%	3736
	11th to 20th	Night	40% 8% 20% 19% 12% 1	3552
	21st to end	Night	57% 11% 12% 15% 5%	3739
April	1st to 10th	Night	50% 9% 13% 18% 10% 1	1819
	11th to 20th	Night	53% 7% 12% 17% 9% 2	1691
	21st to end	Night	46% 7% 14% 20% 12% 1	1710
May	1st to 10th	Night	57% 5% 8% 19% 11% 1	2322
	11th to 20th	Night	48% 10% 12% 20% 9% 1	2199
	21st to end	Night	50% 11% 14% 14% 10% 1	2414
June	1st to 10th	Night	50% 9% 13% 19% 8% 1	1330
	11th to 20th	Night	57% 11% 15% 13% 4	1187
	21st to end	Night	42% 11% 22% 20% 5% 1	1140
July	1st to 10th	Night	36% 8% 15% 24% 16% 1	1983
	11th to 20th	Night	39% 9% 17% 27% 8%	2178
	21st to end	Night	38% 8% 20% 25% 9%	2337
August	1st to 10th	Night	43% 9% 19% 28% 2	2444
	11th to 20th	Night	42% 8% 21% 21% 8% 1	2676
	21st to end	Night	37% 7% 23% 27% 5%	3146
September	1st to 10th	Night	37% 8% 19% 24% 10% 2	1773
	11th to 20th	Night	38% 7% 16% 28% 9% 2	2085
	21st to end	Night	37% 8% 15% 25% 13% 2	2090
October	1st to 10th	Night	41% 6% 20% 26% 7%	3660
	11th to 20th	Night	41% 6% 14% 30% 7%	4076
	21st to end	Night	44% 7% 21% 23% 5%	4457
November	1st to 10th	Night	57% 7% 11% 19% 6%	2716
	11th to 20th	Night	55% 7% 13% 18% 6% 1	2980
	21st to end	Night	54% 8% 15% 17% 5% 1	3000
December	1st to 10th	Night	61% 6% 14% 13% 5% 1	4890
	11th to 20th	Night	61% 7% 16% 12% 5%	5547
	21st to end	Night	40% 6% 14% 25% 14% 2	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	10% 7% 25% 37% 18% 4	200
	11th to 20th	Day	9% 8% 26% 38% 15% 6%	200
	21st to end	Day	15% 10% 30% 28% 11% 6%	220
February	1st to 10th	Day	14% 7% 31% 32% 12% 5%	200
	11th to 20th	Day	11% 4 31% 38% 13% 5%	262
	21st to end	Day	7% 7% 35% 29% 16% 6%	309
March	1st to 10th	Day	12% 8% 28% 33% 17% 2	460
	11th to 20th	Day	11% 5% 28% 33% 17% 5%	460
	21st to end	Day	14% 6% 29% 27% 21% 3	506
April	1st to 10th	Day	10% 11% 32% 34% 10% 3	460
	11th to 20th	Day	13% 7% 25% 32% 16% 6%	452
	21st to end	Day	14% 11% 27% 29% 15% 4	460
May	1st to 10th	Day	15% 9% 24% 32% 16% 3	594
	11th to 20th	Day	12% 6% 25% 34% 17% 6%	675
	21st to end	Day	17% 5% 21% 31% 18% 8%	734
June	1st to 10th	Day	20% 8% 25% 31% 13% 4	680
	11th to 20th	Day	19% 6% 23% 27% 20% 6%	819
	21st to end	Day	12% 4 19% 32% 25% 8%	870
July	1st to 10th	Day	11% 5% 18% 35% 22% 9%	793
	11th to 20th	Day	10% 3 22% 33% 25% 7%	668
	21st to end	Day	11% 4 17% 34% 25% 9%	739
August	1st to 10th	Day	10% 6% 16% 32% 22% 13%	537
	11th to 20th	Day	8% 4 27% 31% 24% 6%	477
	21st to end	Day	15% 7% 18% 29% 22% 9%	539
September	1st to 10th	Day	15% 9% 28% 22% 20% 7%	490
	11th to 20th	Day	18% 6% 24% 30% 17% 6%	490
	21st to end	Day	11% 12% 31% 26% 15% 5%	490
October	1st to 10th	Day	14% 8% 25% 32% 17% 4	391
	11th to 20th	Day	13% 9% 31% 28% 15% 4	300
	21st to end	Day	14% 12% 36% 25% 10% 3	330
November	1st to 10th	Day	17% 6% 34% 29% 12% 2	300
	11th to 20th	Day	12% 5% 40% 29% 13% 2	207
	21st to end	Day	9% 6% 34% 35% 11% 6%	200
December	1st to 10th	Day	9% 8% 31% 36% 13% 5%	200
	11th to 20th	Day	12% 8% 30% 36% 13% 3	200
	21st to end	Day	8% 3 21% 38% 25% 5%	220
January	1st to 10th	Night	11% 7% 32% 34% 14% 2	1000
	11th to 20th	Night	12% 8% 31% 35% 12% 1	1000
	21st to end	Night	14% 11% 34% 30% 11% 1	984
February	1st to 10th	Night	11% 8% 25% 37% 17% 3	800
	11th to 20th	Night	11% 5% 32% 36% 15% 1	784
	21st to end	Night	9% 5% 28% 36% 18% 4	646
March	1st to 10th	Night	10% 4 29% 37% 17% 2	760
	11th to 20th	Night	12% 3 30% 37% 17% 1	760
	21st to end	Night	13% 5% 26% 38% 16% 3	836
April	1st to 10th	Night	11% 7% 27% 37% 16% 2	679
	11th to 20th	Night	13% 6% 31% 33% 16% 1	563
	21st to end	Night	16% 6% 28% 35% 14% 1	570
May	1st to 10th	Night	16% 6% 24% 37% 16% 1	385
	11th to 20th	Night	11% 5% 27% 39% 18% 1	374
	21st to end	Night	21% 6% 21% 34% 16% 2	411
June	1st to 10th	Night	17% 8% 25% 36% 13% 2	380
	11th to 20th	Night	19% 6% 21% 31% 21% 2	380
	21st to end	Night	12% 4 17% 38% 26% 3	380
July	1st to 10th	Night	13% 1 17% 44% 24% 1	370
	11th to 20th	Night	12% 4 20% 40% 23% 2	368
	21st to end	Night	13% 4 16% 38% 27% 2	416
August	1st to 10th	Night	13% 4 15% 33% 31% 5%	378
	11th to 20th	Night	11% 5% 18% 36% 28% 2	466
	21st to end	Night	13% 2 21% 39% 23% 1	627
September	1st to 10th	Night	14% 3 19% 42% 21% 1	633
	11th to 20th	Night	14% 4 21% 41% 20% 2	760
	21st to end	Night	13% 4 31% 35% 15% 2	760
October	1st to 10th	Night	15% 4 27% 39% 15%	760
	11th to 20th	Night	14% 5% 32% 33% 14% 2	760
	21st to end	Night	13% 8% 33% 32% 13% 1	836
November	1st to 10th	Night	20% 6% 30% 33% 11% 1	961
	11th to 20th	Night	13% 9% 35% 31% 10% 3	1000
	21st to end	Night	11% 6% 36% 35% 10% 2	1000
December	1st to 10th	Night	14% 8% 32% 31% 13% 3	1000
	11th to 20th	Night	12% 7% 31% 35% 14% 1	1000
	21st to end	Night	10% 4 29% 36% 17% 3	1100

Page generated at 2025-02-22 04:51:36. Version ac07

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