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 2026-08-30.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 39%	148739
	Night	6% 9% 4 9% 5% 5% 5% 4 6% 8% 38%	142200
Transparency	Day	40% 6% 15% 25% 11% 2	148440
	Night	42% 7% 15% 23% 11% 2	142082
Seeing	Day	12% 8% 27% 31% 17% 5%	17775
	Night	11% 6% 30% 37% 15% 2	26727

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 9% 6% 15% 7% 7% 5% 4 6% 8% 30%	4125
	11th to 20th	Day	2 8% 3 10% 6% 5% 5% 5% 6% 8% 42%	4196
	21st to end	Day	3 6% 3 10% 5% 5% 5% 3 6% 9% 45%	5186
February	1st to 10th	Day	4 12% 6% 12% 6% 7% 6% 5% 6% 7% 28%	1680
	11th to 20th	Day	5% 10% 4 11% 7% 6% 6% 6% 7% 8% 29%	1842
	21st to end	Day	4 11% 5% 11% 6% 5% 5% 4 7% 8% 33%	1678
March	1st to 10th	Day	3 10% 4 11% 6% 5% 5% 3 6% 11% 37%	4618
	11th to 20th	Day	5% 11% 4 9% 4 5% 4 5% 7% 8% 39%	5063
	21st to end	Day	8% 20% 6% 14% 5% 5% 5% 4 6% 6% 20%	5681
April	1st to 10th	Day	8% 15% 4 10% 6% 5% 6% 4 6% 9% 28%	2583
	11th to 20th	Day	11% 13% 4 9% 6% 4 5% 5% 6% 8% 29%	2700
	21st to end	Day	10% 12% 4 9% 5% 5% 5% 4 6% 7% 31%	2730
May	1st to 10th	Day	13% 9% 3 7% 4 4 5% 4 6% 7% 37%	8024
	11th to 20th	Day	11% 11% 4 10% 6% 6% 7% 5% 8% 9% 25%	8755
	21st to end	Day	12% 6% 2 8% 5% 6% 6% 5% 7% 8% 35%	9649
June	1st to 10th	Day	16% 7% 3 8% 5% 6% 6% 5% 7% 8% 30%	3150
	11th to 20th	Day	18% 9% 3 7% 5% 5% 6% 5% 7% 8% 27%	3150
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 9% 9% 40%	3150
July	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 7% 10% 49%	8820
	11th to 20th	Day	8% 4 2 4 3 4 5% 4 7% 10% 48%	8820
	21st to end	Day	7% 4 1 4 3 3 4 3 5% 8% 57%	9374
August	1st to 10th	Day	8% 6% 2 6% 4 4 5% 5% 8% 9% 43%	4681
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 4 8% 11% 45%	4324
	21st to end	Day	9% 4 1 4 3 3 4 4 5% 8% 54%	4782
September	1st to 10th	Day	9% 6% 2 6% 4 4 3 3 5% 7% 51%	2483
	11th to 20th	Day	14% 8% 3 5% 4 4 3 3 5% 8% 45%	2200
	21st to end	Day	8% 8% 2 7% 5% 4 4 4 5% 8% 45%	2200
October	1st to 10th	Day	7% 7% 3 8% 4 5% 5% 5% 6% 9% 43%	3445
	11th to 20th	Day	6% 7% 3 6% 4 5% 5% 5% 6% 10% 43%	3012
	21st to end	Day	7% 7% 2 7% 5% 5% 5% 4 6% 7% 45%	3200
November	1st to 10th	Day	8% 15% 5% 8% 5% 5% 4 4 6% 7% 32%	1713
	11th to 20th	Day	6% 12% 3 8% 6% 5% 4 4 6% 7% 39%	1608
	21st to end	Day	4 13% 5% 10% 6% 5% 3 5% 7% 10% 33%	1470
December	1st to 10th	Day	3 12% 6% 12% 7% 5% 5% 4 6% 7% 32%	2360
	11th to 20th	Day	4 9% 5% 12% 8% 7% 6% 5% 5% 8% 29%	2712
	21st to end	Day	3 10% 4 9% 5% 5% 5% 4 6% 8% 41%	3575
January	1st to 10th	Night	4 13% 5% 12% 8% 6% 6% 4 6% 7% 27%	8768
	11th to 20th	Night	2 8% 4 11% 5% 5% 6% 5% 7% 8% 39%	8761
	21st to end	Night	3 8% 4 11% 6% 5% 5% 4 6% 8% 39%	8994
February	1st to 10th	Night	4 10% 4 13% 7% 7% 6% 4 7% 8% 30%	2940
	11th to 20th	Night	5% 12% 4 11% 6% 6% 6% 5% 7% 8% 29%	2664
	21st to end	Night	2 12% 5% 12% 7% 5% 6% 5% 6% 7% 33%	2127
March	1st to 10th	Night	3 8% 4 12% 6% 7% 6% 5% 7% 9% 34%	5496
	11th to 20th	Night	4 9% 4 11% 5% 5% 5% 5% 7% 7% 38%	5156
	21st to end	Night	8% 19% 6% 13% 6% 5% 5% 4 6% 7% 21%	5532
April	1st to 10th	Night	9% 14% 4 9% 6% 6% 5% 4 6% 8% 30%	2037
	11th to 20th	Night	10% 12% 5% 10% 6% 5% 6% 4 7% 6% 30%	1871
	21st to end	Night	11% 11% 4 9% 5% 5% 4 4 7% 8% 32%	1890
May	1st to 10th	Night	13% 10% 3 8% 4 5% 4 3 5% 7% 38%	4897
	11th to 20th	Night	12% 9% 4 8% 6% 5% 5% 4 8% 10% 29%	4105
	21st to end	Night	10% 7% 3 8% 5% 6% 7% 5% 7% 8% 34%	4522
June	1st to 10th	Night	14% 9% 4 8% 4 5% 5% 4 7% 8% 32%	1470
	11th to 20th	Night	16% 7% 3 6% 6% 5% 6% 4 7% 9% 30%	1470
	21st to end	Night	9% 4 1 6% 6% 5% 6% 4 8% 9% 41%	1470
July	1st to 10th	Night	5% 5% 2 6% 5% 5% 4 3 6% 7% 51%	4140
	11th to 20th	Night	7% 4 2 5% 3 4 4 4 7% 9% 50%	4140
	21st to end	Night	8% 4 1 4 3 3 3 3 5% 9% 57%	4691
August	1st to 10th	Night	9% 6% 3 7% 4 4 5% 4 8% 9% 41%	2689
	11th to 20th	Night	7% 5% 2 6% 4 5% 6% 5% 8% 10% 42%	2954
	21st to end	Night	7% 4 1 5% 3 4 4 3 7% 10% 53%	3326
September	1st to 10th	Night	9% 6% 2 6% 3 4 4 4 6% 7% 48%	1915
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 4 8% 49%	2200
	21st to end	Night	9% 6% 2 6% 4 3 5% 4 6% 9% 47%	2200
October	1st to 10th	Night	8% 6% 2 6% 4 5% 4 3 6% 8% 49%	3750
	11th to 20th	Night	6% 7% 2 6% 4 5% 5% 4 6% 8% 47%	4120
	21st to end	Night	5% 8% 3 7% 5% 5% 5% 4 7% 7% 44%	4600
November	1st to 10th	Night	8% 14% 4 8% 5% 4 5% 4 6% 7% 35%	2784
	11th to 20th	Night	4 11% 4 9% 6% 5% 5% 5% 7% 8% 37%	3008
	21st to end	Night	5% 12% 3 8% 5% 5% 5% 4 8% 8% 37%	3150
December	1st to 10th	Night	4 12% 4 11% 7% 7% 6% 5% 6% 8% 30%	5040
	11th to 20th	Night	3 12% 5% 13% 8% 6% 6% 5% 7% 9% 28%	5700
	21st to end	Night	3 10% 5% 9% 5% 5% 5% 4 6% 7% 40%	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	51% 5% 12% 19% 11% 2	4125
	11th to 20th	Day	39% 4 16% 20% 18% 3	4217
	21st to end	Day	35% 7% 15% 30% 13% 1	5187
February	1st to 10th	Day	52% 7% 15% 14% 10% 2	1680
	11th to 20th	Day	49% 7% 14% 19% 10% 1	1851
	21st to end	Day	47% 7% 14% 21% 11% 1	1678
March	1st to 10th	Day	41% 5% 15% 22% 16% 1	4618
	11th to 20th	Day	40% 6% 14% 24% 15% 1	5064
	21st to end	Day	62% 6% 13% 13% 5% 1	5681
April	1st to 10th	Day	50% 8% 15% 18% 9% 1	2583
	11th to 20th	Day	50% 7% 13% 20% 9% 1	2700
	21st to end	Day	50% 6% 13% 21% 9% 1	2730
May	1st to 10th	Day	43% 6% 10% 26% 13% 3	8024
	11th to 20th	Day	49% 8% 13% 22% 7% 1	8759
	21st to end	Day	42% 7% 15% 27% 9%	9650
June	1st to 10th	Day	47% 9% 14% 20% 9% 1	3150
	11th to 20th	Day	50% 10% 13% 19% 7% 2	3150
	21st to end	Day	34% 9% 20% 27% 9% 2	3150
July	1st to 10th	Day	28% 7% 18% 31% 14% 2	8746
	11th to 20th	Day	30% 6% 19% 28% 13% 4	8739
	21st to end	Day	25% 5% 15% 28% 20% 7%	9170
August	1st to 10th	Day	35% 7% 16% 34% 7% 1	4664
	11th to 20th	Day	31% 7% 25% 29% 6% 1	4363
	21st to end	Day	27% 6% 18% 34% 14% 1	4781
September	1st to 10th	Day	32% 6% 15% 28% 14% 5%	2483
	11th to 20th	Day	38% 6% 14% 27% 13% 2	2200
	21st to end	Day	36% 6% 14% 29% 12% 3	2200
October	1st to 10th	Day	37% 6% 17% 32% 7% 1	3445
	11th to 20th	Day	34% 7% 19% 24% 13% 3	3012
	21st to end	Day	38% 6% 10% 32% 12% 1	3200
November	1st to 10th	Day	50% 7% 12% 20% 10% 2	1713
	11th to 20th	Day	44% 6% 16% 23% 9% 1	1608
	21st to end	Day	45% 7% 15% 22% 8% 2	1470
December	1st to 10th	Day	50% 6% 13% 22% 7% 2	2360
	11th to 20th	Day	51% 7% 16% 19% 6% 1	2714
	21st to end	Day	37% 7% 11% 24% 17% 3	3575
January	1st to 10th	Night	53% 7% 11% 18% 9% 2	8769
	11th to 20th	Night	42% 5% 16% 19% 12% 4	8802
	21st to end	Night	40% 6% 17% 25% 11% 1	8994
February	1st to 10th	Night	50% 6% 13% 17% 12% 2	2940
	11th to 20th	Night	49% 7% 12% 19% 11% 2	2665
	21st to end	Night	46% 6% 12% 22% 12% 2	2127
March	1st to 10th	Night	43% 7% 17% 20% 11% 2	5496
	11th to 20th	Night	42% 7% 15% 22% 13% 1	5156
	21st to end	Night	61% 7% 11% 13% 8% 1	5532
April	1st to 10th	Night	50% 7% 13% 19% 11%	2037
	11th to 20th	Night	51% 6% 13% 20% 9% 1	1871
	21st to end	Night	47% 7% 14% 21% 9% 2	1890
May	1st to 10th	Night	45% 6% 10% 24% 14% 1	4894
	11th to 20th	Night	45% 8% 13% 25% 8% 1	4105
	21st to end	Night	43% 8% 17% 25% 6% 1	4526
June	1st to 10th	Night	48% 9% 13% 20% 10% 1	1470
	11th to 20th	Night	47% 9% 15% 19% 8% 2	1470
	21st to end	Night	35% 9% 21% 25% 9% 1	1470
July	1st to 10th	Night	30% 7% 18% 29% 16% 1	4105
	11th to 20th	Night	29% 7% 18% 31% 11% 4	4098
	21st to end	Night	26% 4 16% 30% 19% 6%	4590
August	1st to 10th	Night	36% 7% 15% 28% 13% 1	2681
	11th to 20th	Night	33% 9% 24% 26% 8% 1	2981
	21st to end	Night	27% 5% 21% 33% 12% 2	3326
September	1st to 10th	Night	32% 7% 14% 26% 14% 6%	1915
	11th to 20th	Night	34% 7% 15% 28% 12% 4	2200
	21st to end	Night	32% 7% 17% 26% 14% 4	2200
October	1st to 10th	Night	33% 5% 17% 27% 17% 1	3750
	11th to 20th	Night	34% 6% 18% 24% 17% 2	4120
	21st to end	Night	37% 6% 11% 33% 13% 1	4600
November	1st to 10th	Night	47% 7% 13% 19% 11% 2	2784
	11th to 20th	Night	42% 8% 17% 20% 13% 1	3008
	21st to end	Night	42% 7% 18% 21% 9% 3	3150
December	1st to 10th	Night	50% 7% 15% 19% 6% 2	5040
	11th to 20th	Night	51% 7% 18% 17% 6%	5697
	21st to end	Night	40% 6% 10% 25% 15% 3	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% 7% 29% 35% 13% 10%	220
	11th to 20th	Day	8% 9% 35% 28% 15% 5%	220
	21st to end	Day	5% 10% 28% 38% 16% 3	242
February	1st to 10th	Day	13% 6% 28% 36% 12% 4	220
	11th to 20th	Day	7% 6% 33% 39% 13% 2	329
	21st to end	Day	8% 7% 35% 32% 16% 3	394
March	1st to 10th	Day	8% 12% 35% 28% 13% 4	540
	11th to 20th	Day	8% 11% 34% 31% 13% 3	540
	21st to end	Day	14% 13% 31% 26% 11% 5%	594
April	1st to 10th	Day	12% 12% 31% 27% 14% 3	540
	11th to 20th	Day	14% 11% 27% 31% 13% 4	532
	21st to end	Day	17% 13% 27% 28% 12% 3	540
May	1st to 10th	Day	18% 10% 25% 26% 17% 5%	595
	11th to 20th	Day	15% 6% 26% 28% 19% 6%	775
	21st to end	Day	16% 6% 22% 29% 21% 7%	844
June	1st to 10th	Day	16% 8% 23% 33% 15% 4	780
	11th to 20th	Day	17% 9% 27% 29% 15% 2	780
	21st to end	Day	11% 6% 22% 33% 22% 6%	780
July	1st to 10th	Day	10% 4 20% 35% 24% 7%	771
	11th to 20th	Day	11% 4 23% 35% 22% 5%	768
	21st to end	Day	7% 4 24% 35% 23% 8%	781
August	1st to 10th	Day	10% 6% 23% 31% 23% 7%	567
	11th to 20th	Day	9% 3 21% 34% 27% 6%	557
	21st to end	Day	10% 5% 20% 32% 22% 11%	620
September	1st to 10th	Day	11% 6% 25% 30% 22% 7%	530
	11th to 20th	Day	18% 6% 21% 28% 21% 7%	530
	21st to end	Day	12% 12% 31% 30% 12% 4	530
October	1st to 10th	Day	15% 7% 25% 30% 18% 5%	440
	11th to 20th	Day	11% 8% 34% 28% 15% 4	330
	21st to end	Day	14% 13% 33% 26% 10% 3	363
November	1st to 10th	Day	17% 9% 30% 30% 11% 3	330
	11th to 20th	Day	15% 8% 35% 32% 9% 2	291
	21st to end	Day	8% 7% 35% 24% 18% 8%	220
December	1st to 10th	Day	5% 6% 40% 32% 13% 4	220
	11th to 20th	Day	6% 10% 36% 33% 12% 2	220
	21st to end	Day	9% 5% 26% 35% 20% 4	242
January	1st to 10th	Night	9% 8% 33% 36% 11% 2	1050
	11th to 20th	Night	10% 7% 36% 34% 11% 1	1045
	21st to end	Night	10% 9% 35% 34% 10% 1	924
February	1st to 10th	Night	8% 8% 31% 35% 16% 3	840
	11th to 20th	Night	11% 5% 32% 39% 12% 1	824
	21st to end	Night	7% 5% 32% 34% 19% 3	692
March	1st to 10th	Night	8% 5% 32% 37% 14% 4	840
	11th to 20th	Night	8% 7% 35% 37% 11% 2	840
	21st to end	Night	12% 5% 33% 35% 13% 2	924
April	1st to 10th	Night	13% 8% 31% 33% 14% 1	777
	11th to 20th	Night	16% 7% 32% 33% 12%	623
	21st to end	Night	16% 8% 29% 35% 11%	630
May	1st to 10th	Night	15% 8% 27% 33% 16%	539
	11th to 20th	Night	13% 7% 26% 36% 18%	414
	21st to end	Night	19% 4 21% 34% 21% 1	455
June	1st to 10th	Night	18% 7% 25% 35% 14% 1	420
	11th to 20th	Night	15% 5% 28% 38% 14% 1	420
	21st to end	Night	11% 5% 20% 40% 22% 1	420
July	1st to 10th	Night	8% 3 16% 46% 25% 1	410
	11th to 20th	Night	9% 2 22% 45% 19% 2	408
	21st to end	Night	6% 2 21% 46% 23% 2	460
August	1st to 10th	Night	12% 2 14% 42% 27% 2	418
	11th to 20th	Night	9% 2 17% 47% 23% 1	599
	21st to end	Night	10% 4 20% 43% 23%	687
September	1st to 10th	Night	12% 3 23% 39% 21% 3	694
	11th to 20th	Night	16% 4 18% 38% 23% 2	800
	21st to end	Night	11% 6% 30% 37% 15% 2	800
October	1st to 10th	Night	14% 5% 26% 37% 16% 2	800
	11th to 20th	Night	12% 5% 32% 34% 14% 3	800
	21st to end	Night	10% 8% 35% 34% 12% 1	880
November	1st to 10th	Night	14% 8% 37% 31% 9% 1	939
	11th to 20th	Night	10% 9% 39% 32% 9% 1	1050
	21st to end	Night	9% 5% 37% 37% 10% 2	1050
December	1st to 10th	Night	10% 7% 35% 34% 13% 2	1050
	11th to 20th	Night	7% 5% 38% 39% 10% 1	1050
	21st to end	Night	10% 5% 34% 38% 11% 3	1155

Page generated at 2026-08-27 02:07:14. Version ac07

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