Chestermere
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chestermere clear sky chart from 2005-11-06 to 2025-04-26.

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	8% 9% 3 8% 5% 5% 5% 4 6% 8% 38%	117079
	Night	6% 10% 4 9% 5% 5% 5% 4 6% 8% 37%	120253
Transparency	Day	41% 7% 15% 24% 11% 2	116824
	Night	43% 7% 15% 22% 11% 2	120154
Seeing	Day	12% 7% 26% 31% 18% 5%	15874
	Night	11% 6% 30% 37% 15% 2	25160

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 10% 6% 16% 8% 6% 5% 4 5% 7% 31%	3179
	11th to 20th	Day	3 10% 3 12% 6% 5% 5% 5% 7% 7% 37%	3222
	21st to end	Day	3 6% 3 8% 5% 5% 5% 4 6% 8% 45%	4004
February	1st to 10th	Day	4 12% 6% 12% 7% 7% 6% 5% 6% 7% 28%	1600
	11th to 20th	Day	6% 10% 4 11% 7% 7% 6% 7% 7% 7% 28%	1752
	21st to end	Day	4 11% 5% 11% 6% 6% 6% 5% 7% 8% 32%	1600
March	1st to 10th	Day	3 10% 4 11% 6% 5% 5% 3 5% 11% 37%	4518
	11th to 20th	Day	5% 11% 4 9% 4 5% 4 4 6% 8% 40%	4954
	21st to end	Day	8% 20% 6% 14% 5% 5% 5% 4 6% 6% 20%	5559
April	1st to 10th	Day	7% 15% 4 10% 6% 5% 6% 4 6% 8% 28%	2460
	11th to 20th	Day	11% 13% 4 9% 6% 4 5% 5% 6% 8% 29%	2570
	21st to end	Day	10% 13% 4 9% 5% 5% 5% 4 6% 7% 31%	2537
May	1st to 10th	Day	19% 13% 4 8% 5% 4 4 4 5% 6% 28%	4337
	11th to 20th	Day	10% 8% 3 9% 6% 5% 6% 5% 8% 9% 30%	4694
	21st to end	Day	17% 9% 3 9% 7% 7% 6% 5% 6% 7% 24%	5161
June	1st to 10th	Day	17% 7% 3 7% 5% 6% 6% 5% 7% 8% 29%	2850
	11th to 20th	Day	19% 9% 3 7% 6% 5% 6% 5% 7% 8% 26%	2850
	21st to end	Day	8% 5% 2 6% 5% 4 5% 5% 8% 9% 41%	2850
July	1st to 10th	Day	7% 4 2 5% 4 4 6% 4 7% 9% 48%	4740
	11th to 20th	Day	6% 3 2 4 4 4 5% 5% 7% 10% 51%	4740
	21st to end	Day	3 3 1 4 3 3 4 4 7% 10% 58%	5027
August	1st to 10th	Day	8% 6% 2 6% 4 4 5% 5% 8% 9% 42%	4401
	11th to 20th	Day	6% 5% 2 6% 4 4 5% 4 8% 11% 45%	4062
	21st to end	Day	10% 4 1 4 3 3 4 4 5% 8% 53%	4521
September	1st to 10th	Day	9% 6% 2 6% 4 4 3 3 5% 7% 50%	2359
	11th to 20th	Day	14% 8% 2 5% 4 4 3 3 5% 9% 43%	2090
	21st to end	Day	9% 8% 2 7% 6% 4 4 3 5% 8% 44%	2090
October	1st to 10th	Day	7% 7% 3 8% 5% 5% 5% 5% 6% 9% 42%	3340
	11th to 20th	Day	6% 7% 2 6% 4 5% 5% 5% 6% 10% 43%	2919
	21st to end	Day	7% 7% 2 7% 5% 5% 5% 4 6% 7% 44%	3101
November	1st to 10th	Day	8% 15% 5% 8% 6% 5% 5% 4 6% 7% 31%	1630
	11th to 20th	Day	7% 11% 3 8% 6% 5% 4 4 6% 7% 39%	1532
	21st to end	Day	4 13% 5% 9% 6% 5% 4 5% 7% 10% 34%	1400
December	1st to 10th	Day	3 12% 6% 11% 7% 5% 5% 4 6% 7% 33%	2290
	11th to 20th	Day	4 10% 5% 12% 8% 8% 6% 5% 5% 7% 30%	2642
	21st to end	Day	3 10% 4 9% 5% 5% 5% 4 6% 8% 41%	3498
January	1st to 10th	Night	4 14% 5% 14% 9% 7% 6% 4 6% 7% 25%	6766
	11th to 20th	Night	3 9% 5% 13% 5% 5% 6% 5% 6% 8% 34%	6721
	21st to end	Night	3 10% 4 9% 5% 5% 4 4 6% 8% 42%	6952
February	1st to 10th	Night	5% 10% 4 13% 7% 7% 6% 4 6% 8% 30%	2800
	11th to 20th	Night	5% 12% 4 11% 6% 6% 6% 5% 7% 8% 29%	2534
	21st to end	Night	2 12% 5% 12% 7% 5% 6% 5% 6% 8% 33%	2029
March	1st to 10th	Night	3 8% 4 12% 6% 7% 6% 5% 7% 9% 33%	5376
	11th to 20th	Night	4 9% 4 11% 5% 5% 5% 4 7% 7% 38%	5045
	21st to end	Night	8% 19% 6% 13% 6% 5% 5% 4 6% 7% 21%	5412
April	1st to 10th	Night	9% 14% 4 9% 6% 6% 5% 4 7% 8% 30%	1940
	11th to 20th	Night	10% 12% 5% 10% 6% 5% 6% 4 7% 6% 30%	1781
	21st to end	Night	11% 11% 4 9% 5% 5% 5% 4 6% 8% 32%	1759
May	1st to 10th	Night	17% 13% 3 9% 4 5% 4 3 5% 6% 30%	2627
	11th to 20th	Night	9% 8% 3 8% 6% 5% 6% 4 8% 10% 34%	2199
	21st to end	Night	14% 9% 4 10% 6% 5% 7% 5% 7% 8% 25%	2414
June	1st to 10th	Night	14% 9% 4 8% 5% 5% 5% 4 7% 7% 32%	1330
	11th to 20th	Night	17% 7% 3 5% 6% 5% 6% 3 7% 9% 30%	1330
	21st to end	Night	8% 4 1 6% 6% 5% 6% 4 8% 9% 42%	1330
July	1st to 10th	Night	5% 6% 2 7% 6% 5% 5% 3 6% 6% 49%	2220
	11th to 20th	Night	5% 4 1 4 3 5% 6% 5% 9% 11% 47%	2220
	21st to end	Night	4 4 1 4 4 4 4 4 5% 8% 59%	2522
August	1st to 10th	Night	9% 6% 3 7% 4 4 5% 4 8% 9% 41%	2529
	11th to 20th	Night	6% 4 2 6% 4 5% 6% 5% 8% 10% 43%	2776
	21st to end	Night	8% 4 1 5% 3 4 4 3 6% 10% 52%	3146
September	1st to 10th	Night	9% 7% 2 6% 3 4 4 4 6% 7% 47%	1819
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 4 8% 48%	2090
	21st to end	Night	9% 6% 2 6% 4 3 5% 4 6% 9% 46%	2090
October	1st to 10th	Night	8% 6% 2 6% 4 4 4 3 6% 8% 49%	3635
	11th to 20th	Night	6% 7% 2 6% 4 5% 5% 4 6% 8% 47%	3993
	21st to end	Night	5% 8% 3 7% 5% 5% 5% 4 7% 7% 44%	4457
November	1st to 10th	Night	8% 14% 4 8% 5% 4 5% 4 6% 7% 35%	2648
	11th to 20th	Night	4 11% 4 9% 6% 5% 6% 5% 7% 8% 37%	2865
	21st to end	Night	4 12% 4 8% 6% 5% 5% 4 7% 8% 37%	3000
December	1st to 10th	Night	4 11% 4 11% 7% 7% 6% 5% 6% 8% 31%	4890
	11th to 20th	Night	3 12% 5% 13% 8% 6% 5% 5% 7% 9% 28%	5550
	21st to end	Night	3 10% 5% 8% 5% 5% 5% 4 6% 7% 40%	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	52% 5% 12% 21% 9% 2	3179
	11th to 20th	Day	44% 5% 13% 17% 19% 3	3243
	21st to end	Day	35% 7% 15% 30% 13% 1	4004
February	1st to 10th	Day	53% 7% 15% 13% 9% 2	1600
	11th to 20th	Day	50% 7% 14% 19% 9% 2	1761
	21st to end	Day	48% 7% 14% 19% 11% 1	1600
March	1st to 10th	Day	42% 5% 15% 22% 16% 1	4518
	11th to 20th	Day	40% 6% 14% 24% 15% 1	4955
	21st to end	Day	62% 6% 13% 13% 5% 1	5559
April	1st to 10th	Day	50% 8% 14% 18% 9% 1	2460
	11th to 20th	Day	50% 7% 13% 20% 10% 1	2570
	21st to end	Day	50% 7% 13% 21% 9% 1	2537
May	1st to 10th	Day	55% 7% 11% 23% 5%	4337
	11th to 20th	Day	42% 10% 16% 23% 9%	4698
	21st to end	Day	53% 9% 14% 17% 6% 1	5162
June	1st to 10th	Day	48% 9% 14% 19% 8% 1	2850
	11th to 20th	Day	51% 10% 14% 17% 7% 2	2850
	21st to end	Day	34% 9% 20% 26% 10% 2	2850
July	1st to 10th	Day	29% 8% 15% 28% 16% 4	4666
	11th to 20th	Day	26% 7% 19% 35% 12% 1	4659
	21st to end	Day	20% 6% 13% 30% 23% 8%	4868
August	1st to 10th	Day	35% 8% 16% 34% 7% 1	4384
	11th to 20th	Day	30% 8% 25% 29% 7% 1	4101
	21st to end	Day	29% 6% 19% 33% 12% 1	4520
September	1st to 10th	Day	33% 6% 15% 26% 14% 5%	2359
	11th to 20th	Day	39% 6% 14% 26% 12% 2	2090
	21st to end	Day	37% 6% 14% 28% 12% 3	2090
October	1st to 10th	Day	38% 6% 17% 31% 7% 1	3340
	11th to 20th	Day	34% 7% 19% 24% 13% 3	2919
	21st to end	Day	38% 6% 10% 33% 12% 1	3101
November	1st to 10th	Day	51% 7% 11% 20% 10% 1	1630
	11th to 20th	Day	44% 7% 15% 23% 10% 1	1532
	21st to end	Day	44% 8% 16% 22% 8% 2	1400
December	1st to 10th	Day	50% 6% 13% 22% 7% 2	2290
	11th to 20th	Day	51% 7% 16% 19% 6% 1	2644
	21st to end	Day	38% 7% 11% 24% 17% 3	3498
January	1st to 10th	Night	56% 8% 10% 19% 5% 1	6766
	11th to 20th	Night	47% 5% 13% 17% 14% 4	6762
	21st to end	Night	39% 6% 15% 26% 13% 1	6952
February	1st to 10th	Night	50% 6% 13% 18% 11% 2	2800
	11th to 20th	Night	49% 7% 13% 19% 10% 1	2535
	21st to end	Night	46% 6% 13% 21% 12% 2	2029
March	1st to 10th	Night	43% 7% 18% 20% 10% 2	5376
	11th to 20th	Night	42% 7% 15% 22% 13% 1	5045
	21st to end	Night	61% 7% 11% 12% 8% 1	5412
April	1st to 10th	Night	50% 7% 13% 19% 11% 1	1940
	11th to 20th	Night	52% 6% 12% 20% 9% 1	1781
	21st to end	Night	47% 8% 14% 21% 8% 2	1759
May	1st to 10th	Night	53% 8% 11% 22% 6%	2627
	11th to 20th	Night	40% 10% 13% 28% 8% 1	2199
	21st to end	Night	50% 11% 16% 17% 6% 1	2414
June	1st to 10th	Night	48% 9% 13% 19% 10% 1	1330
	11th to 20th	Night	48% 9% 16% 18% 8% 2	1330
	21st to end	Night	34% 9% 21% 25% 10% 1	1330
July	1st to 10th	Night	33% 8% 16% 24% 18% 2	2185
	11th to 20th	Night	26% 9% 19% 34% 9% 4	2178
	21st to end	Night	23% 5% 12% 32% 21% 6%	2442
August	1st to 10th	Night	36% 7% 14% 29% 13% 1	2521
	11th to 20th	Night	32% 9% 24% 26% 9% 1	2803
	21st to end	Night	27% 5% 21% 32% 12% 2	3146
September	1st to 10th	Night	33% 7% 14% 25% 15% 6%	1819
	11th to 20th	Night	35% 7% 15% 27% 12% 4	2090
	21st to end	Night	32% 7% 18% 26% 14% 4	2090
October	1st to 10th	Night	33% 5% 17% 27% 18% 2	3635
	11th to 20th	Night	34% 7% 18% 24% 16% 2	3993
	21st to end	Night	37% 6% 11% 32% 13%	4457
November	1st to 10th	Night	47% 7% 13% 19% 11% 2	2648
	11th to 20th	Night	43% 8% 17% 19% 13% 1	2865
	21st to end	Night	43% 7% 18% 20% 9% 3	3000
December	1st to 10th	Night	50% 7% 16% 19% 6% 2	4890
	11th to 20th	Night	51% 8% 19% 17% 6%	5547
	21st to end	Night	40% 6% 10% 25% 16% 3	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	6% 7% 26% 37% 14% 11%	200
	11th to 20th	Day	7% 7% 35% 30% 16% 6%	200
	21st to end	Day	6% 10% 25% 40% 17% 3	220
February	1st to 10th	Day	14% 7% 27% 38% 11% 5%	200
	11th to 20th	Day	7% 6% 33% 37% 14% 2	299
	21st to end	Day	7% 7% 34% 33% 16% 3	364
March	1st to 10th	Day	8% 11% 33% 30% 14% 5%	500
	11th to 20th	Day	8% 10% 32% 32% 14% 4	500
	21st to end	Day	14% 13% 30% 26% 11% 5%	550
April	1st to 10th	Day	12% 13% 33% 27% 13% 2	500
	11th to 20th	Day	14% 12% 27% 31% 12% 4	492
	21st to end	Day	17% 13% 28% 28% 11% 3	481
May	1st to 10th	Day	18% 10% 23% 25% 18% 6%	510
	11th to 20th	Day	14% 5% 25% 30% 20% 5%	675
	21st to end	Day	17% 6% 21% 27% 22% 7%	734
June	1st to 10th	Day	16% 7% 23% 34% 16% 4	680
	11th to 20th	Day	19% 9% 27% 28% 15% 3	680
	21st to end	Day	10% 5% 24% 33% 22% 6%	680
July	1st to 10th	Day	10% 4 19% 35% 25% 8%	671
	11th to 20th	Day	11% 3 21% 35% 25% 6%	668
	21st to end	Day	6% 4 23% 35% 24% 8%	677
August	1st to 10th	Day	10% 6% 22% 31% 23% 8%	487
	11th to 20th	Day	7% 3 21% 34% 27% 7%	477
	21st to end	Day	11% 5% 21% 31% 21% 11%	539
September	1st to 10th	Day	11% 6% 26% 30% 20% 6%	490
	11th to 20th	Day	19% 6% 22% 28% 18% 7%	490
	21st to end	Day	13% 12% 29% 30% 12% 4	490
October	1st to 10th	Day	15% 8% 26% 28% 18% 5%	405
	11th to 20th	Day	11% 8% 32% 29% 16% 4	300
	21st to end	Day	15% 11% 33% 26% 11% 4	330
November	1st to 10th	Day	16% 9% 29% 31% 11% 3	300
	11th to 20th	Day	15% 7% 35% 33% 8% 2	265
	21st to end	Day	8% 7% 34% 25% 19% 9%	200
December	1st to 10th	Day	6% 5% 37% 34% 14% 5%	200
	11th to 20th	Day	7% 9% 34% 36% 14% 3	200
	21st to end	Day	10% 5% 25% 35% 22% 5%	220
January	1st to 10th	Night	9% 8% 33% 37% 12% 2	1000
	11th to 20th	Night	10% 7% 35% 35% 12% 1	995
	21st to end	Night	10% 9% 34% 34% 11% 1	880
February	1st to 10th	Night	8% 7% 30% 35% 16% 3	800
	11th to 20th	Night	11% 4 31% 39% 13% 1	784
	21st to end	Night	7% 4 31% 34% 20% 4	660
March	1st to 10th	Night	8% 6% 30% 37% 15% 4	800
	11th to 20th	Night	8% 6% 34% 39% 12% 2	800
	21st to end	Night	12% 5% 32% 36% 13% 3	880
April	1st to 10th	Night	12% 8% 31% 33% 14% 1	740
	11th to 20th	Night	16% 7% 32% 33% 12%	593
	21st to end	Night	16% 7% 30% 36% 11%	587
May	1st to 10th	Night	15% 7% 27% 33% 17%	488
	11th to 20th	Night	12% 7% 25% 38% 18%	374
	21st to end	Night	20% 4 21% 33% 20% 1	411
June	1st to 10th	Night	18% 7% 24% 35% 15% 1	380
	11th to 20th	Night	17% 4 27% 37% 14% 1	380
	21st to end	Night	11% 4 21% 40% 23% 1	380
July	1st to 10th	Night	8% 3 16% 45% 27% 1	370
	11th to 20th	Night	8% 2 21% 45% 21% 3	368
	21st to end	Night	5% 3 20% 46% 24% 2	416
August	1st to 10th	Night	12% 2 13% 43% 28% 2	378
	11th to 20th	Night	8% 2 17% 47% 23% 1	541
	21st to end	Night	11% 4 20% 41% 24%	627
September	1st to 10th	Night	12% 3 23% 39% 20% 2	659
	11th to 20th	Night	16% 4 18% 38% 22% 2	760
	21st to end	Night	11% 6% 30% 36% 16% 2	760
October	1st to 10th	Night	15% 4 26% 37% 16% 2	760
	11th to 20th	Night	12% 5% 31% 34% 15% 3	760
	21st to end	Night	11% 7% 34% 35% 12% 1	836
November	1st to 10th	Night	15% 7% 36% 31% 10% 1	893
	11th to 20th	Night	10% 9% 40% 31% 9% 1	1000
	21st to end	Night	9% 5% 37% 37% 10% 2	1000
December	1st to 10th	Night	10% 6% 34% 35% 13% 2	1000
	11th to 20th	Night	8% 4 37% 40% 10% 1	1000
	21st to end	Night	10% 4 33% 38% 12% 3	1100

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