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 2024-10-25.

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	9% 9% 3 8% 5% 5% 5% 4 6% 8% 38%	101814
	Night	7% 9% 4 9% 5% 5% 5% 4 7% 8% 37%	97083
Transparency	Day	41% 7% 15% 24% 10% 2	101559
	Night	42% 8% 15% 22% 11% 2	96984
Seeing	Day	12% 7% 26% 31% 18% 5%	15350
	Night	11% 5% 29% 37% 15% 2	24372

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	3 10% 6% 13% 6% 4 5% 4 6% 8% 35%	2219
	11th to 20th	Day	4 10% 3 12% 6% 6% 6% 6% 8% 7% 32%	2234
	21st to end	Day	5% 7% 3 9% 6% 6% 6% 4 7% 8% 39%	2794
February	1st to 10th	Day	4 13% 6% 11% 7% 7% 6% 5% 6% 7% 28%	1520
	11th to 20th	Day	6% 11% 4 11% 6% 6% 6% 6% 7% 7% 29%	1662
	21st to end	Day	4 12% 5% 12% 7% 6% 6% 5% 6% 8% 30%	1522
March	1st to 10th	Day	2 11% 5% 12% 8% 7% 6% 4 6% 7% 31%	3138
	11th to 20th	Day	6% 10% 2 6% 4 5% 4 4 6% 8% 45%	3457
	21st to end	Day	9% 21% 6% 13% 5% 4 4 3 5% 6% 23%	3872
April	1st to 10th	Day	8% 15% 4 10% 6% 5% 6% 4 6% 9% 27%	2337
	11th to 20th	Day	11% 13% 4 9% 6% 5% 5% 5% 6% 8% 29%	2440
	21st to end	Day	11% 13% 4 9% 5% 5% 5% 4 6% 7% 30%	2470
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	11% 10% 3 7% 4 4 4 4 5% 7% 40%	2005
	11th to 20th	Day	9% 8% 3 8% 5% 5% 5% 4 6% 8% 39%	1763
	21st to end	Day	8% 10% 3 8% 5% 5% 5% 4 6% 8% 37%	1822
November	1st to 10th	Day	9% 15% 5% 8% 6% 5% 4 4 6% 7% 31%	1547
	11th to 20th	Day	7% 11% 3 7% 6% 5% 4 4 6% 7% 39%	1456
	21st to end	Day	4 12% 5% 9% 5% 5% 3 5% 7% 10% 36%	1330
December	1st to 10th	Day	5% 13% 5% 10% 8% 5% 6% 4 5% 6% 34%	1330
	11th to 20th	Day	4 10% 6% 13% 7% 5% 5% 5% 5% 7% 30%	1682
	21st to end	Day	3 9% 3 8% 5% 5% 5% 4 6% 8% 43%	2442
January	1st to 10th	Night	4 12% 5% 12% 8% 6% 7% 5% 7% 8% 26%	4726
	11th to 20th	Night	3 8% 5% 15% 5% 5% 6% 5% 7% 8% 33%	4695
	21st to end	Night	4 11% 4 10% 5% 5% 4 4 6% 8% 37%	4862
February	1st to 10th	Night	5% 11% 4 13% 6% 7% 6% 4 6% 8% 31%	2660
	11th to 20th	Night	6% 13% 4 11% 6% 6% 6% 5% 7% 8% 29%	2404
	21st to end	Night	2 12% 5% 13% 7% 5% 6% 4 6% 8% 32%	1931
March	1st to 10th	Night	3 8% 5% 14% 8% 8% 7% 5% 7% 8% 27%	3736
	11th to 20th	Night	6% 8% 2 6% 4 4 5% 4 7% 9% 44%	3522
	21st to end	Night	9% 21% 7% 14% 6% 5% 5% 3 6% 6% 20%	3777
April	1st to 10th	Night	9% 15% 4 9% 6% 6% 5% 4 7% 8% 29%	1843
	11th to 20th	Night	11% 12% 5% 10% 5% 4 5% 4 7% 6% 30%	1691
	21st to end	Night	11% 11% 4 10% 5% 5% 5% 4 6% 8% 32%	1710
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	10% 9% 3 7% 4 5% 4 3 7% 8% 42%	2175
	11th to 20th	Night	7% 8% 3 7% 5% 5% 5% 4 7% 8% 42%	2413
	21st to end	Night	7% 11% 4 8% 5% 4 5% 4 7% 8% 37%	2639
November	1st to 10th	Night	9% 14% 4 8% 5% 4 5% 4 6% 7% 35%	2512
	11th to 20th	Night	4 11% 4 9% 6% 4 5% 5% 7% 8% 38%	2721
	21st to end	Night	4 12% 3 7% 5% 5% 4 4 8% 8% 38%	2850
December	1st to 10th	Night	5% 12% 4 10% 7% 6% 5% 5% 6% 7% 34%	2850
	11th to 20th	Night	2 9% 4 12% 7% 6% 6% 5% 7% 9% 32%	3510
	21st to end	Night	3 9% 4 8% 6% 6% 5% 4 6% 7% 43%	5214

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	44% 7% 15% 23% 9% 2	2219
	11th to 20th	Day	46% 6% 11% 16% 17% 4	2255
	21st to end	Day	38% 9% 15% 29% 8% 1	2794
February	1st to 10th	Day	53% 7% 16% 14% 9% 2	1520
	11th to 20th	Day	49% 7% 14% 19% 9% 2	1671
	21st to end	Day	50% 7% 13% 19% 11% 1	1522
March	1st to 10th	Day	49% 6% 15% 16% 13% 1	3138
	11th to 20th	Day	35% 7% 18% 27% 12% 1	3458
	21st to end	Day	60% 6% 13% 16% 4	3872
April	1st to 10th	Day	51% 8% 15% 17% 8% 1	2337
	11th to 20th	Day	49% 7% 13% 20% 10% 1	2440
	21st to end	Day	51% 7% 13% 20% 9% 1	2470
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	43% 7% 15% 24% 9% 2	2005
	11th to 20th	Day	40% 8% 14% 25% 10% 3	1763
	21st to end	Day	44% 7% 13% 24% 11% 1	1822
November	1st to 10th	Day	51% 7% 12% 19% 10% 1	1547
	11th to 20th	Day	43% 7% 16% 23% 9% 1	1456
	21st to end	Day	42% 8% 17% 23% 9% 2	1330
December	1st to 10th	Day	50% 7% 12% 16% 12% 3	1330
	11th to 20th	Day	49% 8% 15% 20% 7% 1	1684
	21st to end	Day	34% 8% 11% 24% 18% 5%	2442
January	1st to 10th	Night	50% 10% 12% 20% 6% 2	4726
	11th to 20th	Night	48% 7% 11% 16% 14% 4	4736
	21st to end	Night	41% 8% 15% 24% 11% 1	4862
February	1st to 10th	Night	50% 6% 13% 18% 11% 2	2660
	11th to 20th	Night	49% 7% 13% 19% 11% 1	2405
	21st to end	Night	47% 6% 12% 21% 12% 2	1931
March	1st to 10th	Night	50% 9% 12% 21% 8% 1	3736
	11th to 20th	Night	34% 8% 20% 22% 14% 1	3522
	21st to end	Night	64% 7% 11% 13% 5%	3777
April	1st to 10th	Night	50% 7% 13% 18% 11% 1	1843
	11th to 20th	Night	52% 6% 12% 20% 9% 1	1691
	21st to end	Night	47% 8% 15% 20% 8% 2	1710
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	39% 7% 14% 24% 14% 1	2175
	11th to 20th	Night	38% 8% 16% 23% 13% 3	2413
	21st to end	Night	42% 8% 14% 24% 11% 1	2639
November	1st to 10th	Night	47% 7% 13% 19% 11% 2	2512
	11th to 20th	Night	42% 8% 17% 19% 13% 1	2721
	21st to end	Night	41% 7% 19% 21% 10% 3	2850
December	1st to 10th	Night	48% 7% 12% 20% 9% 3	2850
	11th to 20th	Night	45% 10% 18% 21% 6% 1	3507
	21st to end	Night	38% 7% 12% 25% 14% 4	5214

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% 6% 25% 37% 14% 12%	180
	11th to 20th	Day	7% 8% 29% 32% 17% 6%	180
	21st to end	Day	6% 7% 23% 42% 19% 4	198
February	1st to 10th	Day	15% 7% 26% 37% 11% 5%	180
	11th to 20th	Day	8% 7% 32% 37% 14% 3	269
	21st to end	Day	7% 5% 33% 36% 17% 3	334
March	1st to 10th	Day	8% 10% 34% 30% 13% 5%	460
	11th to 20th	Day	8% 10% 30% 32% 15% 4	460
	21st to end	Day	13% 13% 30% 27% 12% 6%	506
April	1st to 10th	Day	12% 12% 35% 26% 13% 2	460
	11th to 20th	Day	14% 10% 27% 32% 13% 4	452
	21st to end	Day	17% 13% 27% 27% 12% 3	460
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% 12% 3	311
November	1st to 10th	Day	17% 9% 29% 30% 11% 3	270
	11th to 20th	Day	15% 7% 35% 33% 8% 2	239
	21st to end	Day	6% 6% 37% 24% 19% 8%	180
December	1st to 10th	Day	5% 6% 36% 34% 14% 5%	180
	11th to 20th	Day	6% 8% 34% 36% 13% 3	180
	21st to end	Day	9% 5% 23% 35% 23% 5%	198
January	1st to 10th	Night	9% 8% 32% 38% 11% 2	950
	11th to 20th	Night	10% 6% 35% 36% 12% 1	946
	21st to end	Night	11% 8% 32% 36% 11% 2	836
February	1st to 10th	Night	8% 8% 30% 34% 17% 4	760
	11th to 20th	Night	12% 5% 30% 39% 13% 1	744
	21st to end	Night	7% 4 29% 35% 21% 4	628
March	1st to 10th	Night	8% 5% 30% 38% 15% 4	760
	11th to 20th	Night	9% 6% 33% 38% 12% 2	760
	21st to end	Night	12% 5% 31% 37% 14% 3	836
April	1st to 10th	Night	12% 8% 31% 33% 15% 1	703
	11th to 20th	Night	17% 7% 31% 33% 12%	563
	21st to end	Night	16% 8% 30% 35% 11%	570
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	812
November	1st to 10th	Night	15% 7% 36% 31% 10% 1	847
	11th to 20th	Night	10% 8% 40% 31% 9% 1	950
	21st to end	Night	9% 5% 37% 36% 10% 2	950
December	1st to 10th	Night	10% 5% 33% 35% 14% 2	950
	11th to 20th	Night	7% 4 38% 40% 10% 1	950
	21st to end	Night	11% 4 32% 38% 12% 3	1045

Page generated at 2024-10-22 18:21:02. Version ac07

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