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Edmonton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edmonton clear sky chart from 2005-11-06 to 2024-11-06.

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 8% 6% 5% 5% 4 6% 8% 35%	106088
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 8% 33%	101522
Transparency	Day	44% 8% 17% 22% 7%	105832
	Night	46% 8% 16% 20% 8% 1	101424
Seeing	Day	13% 6% 23% 31% 20% 6%	15787
	Night	13% 6% 26% 36% 17% 2	24409

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% 12% 5% 13% 9% 8% 5% 4 6% 8% 25%	2219
	11th to 20th	Day	5% 10% 4 10% 7% 5% 6% 5% 7% 9% 33%	2199
	21st to end	Day	7% 14% 4 9% 6% 4 5% 4 5% 7% 35%	2613
February	1st to 10th	Day	8% 15% 5% 13% 7% 5% 4 4 7% 7% 23%	1520
	11th to 20th	Day	6% 14% 5% 13% 7% 5% 6% 5% 7% 6% 26%	1609
	21st to end	Day	4 14% 6% 11% 8% 6% 6% 5% 7% 8% 25%	1462
March	1st to 10th	Day	4 12% 6% 15% 8% 5% 5% 4 6% 8% 27%	3138
	11th to 20th	Day	5% 11% 3 8% 4 4 4 4 7% 10% 38%	3454
	21st to end	Day	7% 13% 7% 16% 7% 5% 5% 3 5% 7% 25%	3878
April	1st to 10th	Day	8% 12% 4 9% 6% 6% 7% 4 6% 7% 30%	2375
	11th to 20th	Day	11% 13% 3 7% 6% 5% 5% 5% 6% 8% 31%	2440
	21st to end	Day	12% 12% 4 8% 6% 5% 5% 4 7% 7% 31%	2470
May	1st to 10th	Day	16% 9% 3 9% 6% 5% 5% 4 5% 7% 31%	4635
	11th to 20th	Day	13% 10% 3 8% 6% 6% 6% 5% 6% 8% 29%	4694
	21st to end	Day	14% 8% 3 9% 6% 6% 6% 4 6% 8% 30%	5161
June	1st to 10th	Day	16% 9% 3 8% 6% 4 5% 4 7% 7% 31%	2850
	11th to 20th	Day	19% 10% 3 8% 6% 6% 6% 5% 6% 7% 24%	2923
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 5% 8% 9% 37%	3040
July	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 7% 8% 45%	4836
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 6% 8% 47%	4740
	21st to end	Day	13% 6% 2 6% 4 4 4 4 6% 8% 44%	5138
August	1st to 10th	Day	11% 7% 2 6% 4 5% 5% 4 7% 9% 40%	4514
	11th to 20th	Day	8% 6% 2 6% 4 5% 5% 4 8% 10% 43%	4151
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 4 7% 10% 41%	4521
September	1st to 10th	Day	11% 6% 2 7% 4 4 5% 4 6% 8% 43%	2418
	11th to 20th	Day	13% 8% 2 6% 4 4 4 3 7% 8% 41%	2090
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 43%	2090
October	1st to 10th	Day	9% 8% 3 8% 6% 5% 5% 5% 5% 7% 39%	3298
	11th to 20th	Day	11% 10% 4 8% 4 5% 5% 5% 6% 8% 36%	2883
	21st to end	Day	7% 13% 4 9% 4 4 4 4 6% 7% 36%	3051
November	1st to 10th	Day	9% 15% 5% 9% 7% 5% 5% 4 5% 6% 27%	1528
	11th to 20th	Day	7% 13% 5% 12% 6% 4 5% 4 6% 8% 30%	1366
	21st to end	Day	5% 13% 5% 12% 6% 5% 5% 4 7% 6% 30%	1330
December	1st to 10th	Day	5% 13% 4 11% 9% 7% 6% 5% 5% 8% 26%	1330
	11th to 20th	Day	7% 10% 6% 10% 7% 7% 6% 5% 7% 8% 27%	1682
	21st to end	Day	4 8% 3 7% 7% 6% 5% 4 6% 8% 42%	2442
January	1st to 10th	Night	5% 11% 5% 15% 8% 7% 7% 5% 7% 6% 25%	4726
	11th to 20th	Night	4 9% 4 11% 9% 7% 5% 5% 7% 7% 33%	4699
	21st to end	Night	7% 15% 4 10% 6% 5% 4 4 6% 7% 32%	5072
February	1st to 10th	Night	6% 13% 5% 14% 8% 6% 5% 5% 5% 6% 26%	2660
	11th to 20th	Night	6% 13% 4 10% 7% 5% 6% 5% 6% 7% 29%	2457
	21st to end	Night	5% 11% 4 11% 7% 6% 5% 5% 6% 8% 31%	1989
March	1st to 10th	Night	4 10% 6% 13% 6% 6% 6% 5% 7% 9% 28%	3736
	11th to 20th	Night	5% 8% 3 9% 6% 6% 6% 4 7% 8% 38%	3524
	21st to end	Night	7% 13% 8% 16% 6% 6% 6% 4 6% 7% 22%	3772
April	1st to 10th	Night	9% 9% 3 10% 7% 5% 7% 5% 8% 7% 31%	1805
	11th to 20th	Night	9% 12% 4 10% 7% 7% 6% 4 6% 6% 29%	1691
	21st to end	Night	12% 10% 3 8% 5% 5% 4 4 7% 7% 34%	1710
May	1st to 10th	Night	24% 9% 3 9% 5% 4 4 3 4 5% 30%	2325
	11th to 20th	Night	14% 10% 3 8% 7% 5% 5% 4 7% 8% 29%	2199
	21st to end	Night	15% 9% 3 9% 6% 6% 6% 4 7% 7% 28%	2414
June	1st to 10th	Night	16% 8% 2 9% 5% 6% 5% 5% 7% 7% 30%	1330
	11th to 20th	Night	16% 9% 3 9% 7% 8% 6% 5% 7% 7% 22%	1249
	21st to end	Night	9% 7% 3 7% 6% 5% 5% 4 7% 9% 37%	1140
July	1st to 10th	Night	11% 6% 2 7% 5% 4 4 4 6% 8% 45%	2119
	11th to 20th	Night	9% 5% 2 7% 5% 6% 5% 5% 9% 11% 38%	2220
	21st to end	Night	14% 6% 2 5% 3 4 4 4 6% 10% 41%	2414
August	1st to 10th	Night	14% 6% 2 6% 5% 5% 6% 3 6% 7% 40%	2401
	11th to 20th	Night	12% 7% 3 7% 4 4 5% 4 6% 8% 39%	2682
	21st to end	Night	12% 4 2 6% 4 4 5% 4 6% 9% 42%	3146
September	1st to 10th	Night	13% 5% 3 7% 4 4 4 3 5% 8% 44%	1760
	11th to 20th	Night	12% 7% 2 5% 4 4 4 4 5% 8% 45%	2090
	21st to end	Night	9% 8% 2 6% 5% 4 5% 4 6% 7% 44%	2090
October	1st to 10th	Night	8% 7% 3 8% 5% 5% 5% 4 7% 7% 39%	3676
	11th to 20th	Night	10% 8% 3 7% 4 5% 5% 4 7% 9% 39%	4042
	21st to end	Night	7% 9% 3 10% 6% 5% 5% 4 7% 8% 36%	4475
November	1st to 10th	Night	13% 15% 5% 10% 6% 5% 5% 4 6% 6% 26%	2673
	11th to 20th	Night	8% 15% 6% 10% 6% 5% 5% 4 6% 7% 28%	2812
	21st to end	Night	6% 12% 5% 12% 8% 6% 5% 4 6% 8% 29%	2850
December	1st to 10th	Night	9% 13% 4 11% 8% 5% 4 4 6% 6% 29%	2850
	11th to 20th	Night	7% 13% 6% 12% 6% 5% 5% 5% 7% 8% 25%	3510
	21st to end	Night	3 8% 3 9% 6% 5% 5% 4 6% 9% 42%	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	54% 9% 12% 19% 5%	2219
	11th to 20th	Day	46% 6% 14% 15% 18% 2	2220
	21st to end	Day	47% 8% 20% 20% 5%	2613
February	1st to 10th	Day	57% 6% 15% 14% 8%	1520
	11th to 20th	Day	54% 8% 15% 16% 8%	1618
	21st to end	Day	52% 7% 13% 20% 7%	1462
March	1st to 10th	Day	53% 5% 16% 20% 6%	3138
	11th to 20th	Day	38% 10% 20% 23% 9%	3455
	21st to end	Day	57% 8% 12% 20% 3	3878
April	1st to 10th	Day	50% 9% 16% 18% 7% 1	2375
	11th to 20th	Day	49% 7% 14% 22% 8%	2440
	21st to end	Day	48% 9% 15% 20% 7% 1	2470
May	1st to 10th	Day	50% 7% 11% 24% 7%	4635
	11th to 20th	Day	46% 9% 13% 24% 8%	4698
	21st to end	Day	45% 11% 18% 17% 8%	5162
June	1st to 10th	Day	49% 8% 15% 20% 8%	2850
	11th to 20th	Day	56% 10% 16% 15% 5%	2923
	21st to end	Day	39% 11% 21% 22% 6% 1	3040
July	1st to 10th	Day	34% 8% 16% 29% 13% 1	4762
	11th to 20th	Day	33% 9% 17% 28% 13%	4659
	21st to end	Day	37% 8% 21% 23% 10%	4976
August	1st to 10th	Day	37% 10% 20% 30% 2	4496
	11th to 20th	Day	33% 8% 24% 27% 7%	4193
	21st to end	Day	37% 8% 28% 24% 4	4520
September	1st to 10th	Day	37% 9% 19% 26% 7% 2	2418
	11th to 20th	Day	40% 8% 20% 26% 7%	2090
	21st to end	Day	37% 8% 19% 26% 8% 2	2090
October	1st to 10th	Day	44% 6% 22% 22% 5%	3298
	11th to 20th	Day	46% 5% 16% 25% 9%	2883
	21st to end	Day	46% 6% 19% 26% 4	3051
November	1st to 10th	Day	56% 8% 14% 16% 6% 1	1528
	11th to 20th	Day	51% 6% 18% 19% 5%	1366
	21st to end	Day	50% 9% 16% 18% 6% 1	1330
December	1st to 10th	Day	56% 8% 12% 17% 7% 1	1330
	11th to 20th	Day	52% 9% 17% 16% 6%	1684
	21st to end	Day	38% 7% 12% 27% 14% 2	2442
January	1st to 10th	Night	55% 9% 13% 16% 6% 1	4726
	11th to 20th	Night	47% 7% 14% 16% 15% 1	4740
	21st to end	Night	49% 8% 18% 17% 7%	5072
February	1st to 10th	Night	56% 7% 12% 17% 7% 1	2660
	11th to 20th	Night	50% 8% 15% 16% 10% 1	2458
	21st to end	Night	49% 8% 14% 20% 9% 1	1989
March	1st to 10th	Night	49% 7% 17% 20% 7%	3736
	11th to 20th	Night	40% 9% 21% 19% 11% 1	3524
	21st to end	Night	56% 9% 12% 17% 5%	3772
April	1st to 10th	Night	47% 9% 14% 19% 10%	1805
	11th to 20th	Night	52% 7% 12% 17% 10% 2	1691
	21st to end	Night	44% 8% 12% 21% 13% 1	1710
May	1st to 10th	Night	55% 7% 8% 20% 10% 1	2325
	11th to 20th	Night	47% 10% 12% 20% 10% 1	2199
	21st to end	Night	49% 13% 14% 15% 9% 1	2414
June	1st to 10th	Night	48% 9% 14% 20% 8% 1	1330
	11th to 20th	Night	56% 11% 15% 14% 5%	1249
	21st to end	Night	41% 10% 23% 20% 5% 1	1140
July	1st to 10th	Night	36% 9% 15% 22% 16% 1	2084
	11th to 20th	Night	36% 10% 16% 28% 9% 1	2178
	21st to end	Night	36% 9% 20% 27% 8%	2337
August	1st to 10th	Night	40% 8% 21% 29% 2	2394
	11th to 20th	Night	41% 9% 20% 22% 8% 1	2706
	21st to end	Night	36% 8% 24% 27% 5%	3146
September	1st to 10th	Night	37% 7% 18% 26% 10% 2	1760
	11th to 20th	Night	36% 8% 17% 28% 9% 2	2090
	21st to end	Night	37% 8% 14% 26% 13% 2	2090
October	1st to 10th	Night	41% 6% 21% 25% 6%	3676
	11th to 20th	Night	40% 6% 15% 32% 7%	4042
	21st to end	Night	42% 7% 23% 23% 5%	4475
November	1st to 10th	Night	57% 7% 12% 18% 6%	2673
	11th to 20th	Night	54% 9% 13% 17% 6% 1	2812
	21st to end	Night	52% 9% 15% 18% 5% 1	2850
December	1st to 10th	Night	54% 6% 13% 17% 9% 1	2850
	11th to 20th	Night	53% 9% 17% 15% 6%	3507
	21st to end	Night	38% 7% 17% 21% 15% 2	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	9% 5% 23% 37% 23% 3	180
	11th to 20th	Day	13% 6% 23% 37% 13% 7%	180
	21st to end	Day	12% 9% 28% 31% 14% 7%	198
February	1st to 10th	Day	13% 7% 29% 31% 16% 5%	180
	11th to 20th	Day	12% 7% 23% 33% 19% 6%	243
	21st to end	Day	7% 5% 26% 34% 20% 8%	274
March	1st to 10th	Day	10% 6% 27% 34% 18% 4	460
	11th to 20th	Day	12% 3 22% 37% 20% 7%	460
	21st to end	Day	16% 4 22% 30% 25% 4	506
April	1st to 10th	Day	11% 8% 26% 35% 15% 4	460
	11th to 20th	Day	15% 6% 22% 31% 19% 6%	452
	21st to end	Day	16% 10% 23% 30% 16% 5%	460
May	1st to 10th	Day	15% 8% 23% 31% 19% 4	615
	11th to 20th	Day	11% 6% 23% 33% 20% 6%	675
	21st to end	Day	16% 6% 19% 32% 19% 9%	734
June	1st to 10th	Day	19% 8% 23% 30% 17% 3	680
	11th to 20th	Day	20% 8% 20% 26% 21% 6%	753
	21st to end	Day	12% 5% 19% 31% 24% 10%	870
July	1st to 10th	Day	12% 4 17% 33% 26% 8%	728
	11th to 20th	Day	11% 4 22% 29% 25% 9%	668
	21st to end	Day	12% 4 17% 32% 26% 9%	739
August	1st to 10th	Day	13% 4 19% 30% 22% 12%	561
	11th to 20th	Day	9% 5% 25% 30% 25% 6%	477
	21st to end	Day	14% 8% 18% 29% 22% 9%	539
September	1st to 10th	Day	15% 8% 27% 25% 19% 7%	490
	11th to 20th	Day	18% 7% 23% 30% 18% 4	490
	21st to end	Day	12% 12% 32% 24% 17% 3	490
October	1st to 10th	Day	16% 8% 26% 30% 15% 5%	376
	11th to 20th	Day	14% 10% 27% 31% 15% 3	300
	21st to end	Day	14% 13% 35% 24% 11% 3	330
November	1st to 10th	Day	19% 7% 22% 35% 15% 2	285
	11th to 20th	Day	12% 6% 32% 37% 12% 2	196
	21st to end	Day	7% 4 33% 39% 11% 6%	180
December	1st to 10th	Day	8% 6% 28% 37% 16% 5%	180
	11th to 20th	Day	12% 6% 27% 39% 13% 3	180
	21st to end	Day	8% 3 19% 40% 25% 6%	198
January	1st to 10th	Night	11% 6% 30% 37% 14% 2	950
	11th to 20th	Night	11% 7% 31% 35% 15% 2	950
	21st to end	Night	15% 10% 29% 32% 12% 2	955
February	1st to 10th	Night	11% 7% 23% 37% 19% 3	760
	11th to 20th	Night	12% 5% 31% 35% 16% 1	744
	21st to end	Night	9% 5% 25% 36% 20% 5%	628
March	1st to 10th	Night	9% 5% 27% 39% 17% 3	760
	11th to 20th	Night	13% 4 27% 37% 15% 3	760
	21st to end	Night	13% 5% 24% 38% 17% 3	836
April	1st to 10th	Night	12% 6% 24% 36% 20% 2	665
	11th to 20th	Night	13% 6% 26% 38% 16% 1	563
	21st to end	Night	16% 7% 26% 34% 16% 1	570
May	1st to 10th	Night	17% 5% 24% 38% 16% 1	408
	11th to 20th	Night	12% 6% 21% 41% 18% 2	374
	21st to end	Night	21% 5% 18% 35% 20% 1	411
June	1st to 10th	Night	19% 7% 22% 37% 13% 2	380
	11th to 20th	Night	20% 5% 21% 30% 22% 2	380
	21st to end	Night	12% 4 17% 38% 27% 3	380
July	1st to 10th	Night	14% 4 15% 43% 24% 1	370
	11th to 20th	Night	11% 3 21% 42% 21% 2	368
	21st to end	Night	12% 4 18% 39% 25% 3	416
August	1st to 10th	Night	11% 3 18% 31% 31% 6%	378
	11th to 20th	Night	11% 5% 17% 39% 26% 2	483
	21st to end	Night	11% 4 20% 41% 23% 1	627
September	1st to 10th	Night	13% 3 20% 41% 21% 2	611
	11th to 20th	Night	13% 4 19% 43% 19% 1	760
	21st to end	Night	13% 5% 27% 39% 14% 1	760
October	1st to 10th	Night	16% 4 27% 39% 14% 1	760
	11th to 20th	Night	14% 5% 32% 34% 14% 2	760
	21st to end	Night	14% 7% 32% 33% 14%	842
November	1st to 10th	Night	20% 7% 29% 33% 10% 1	955
	11th to 20th	Night	15% 6% 33% 31% 12% 2	950
	21st to end	Night	9% 6% 35% 37% 11% 2	950
December	1st to 10th	Night	14% 8% 30% 30% 15% 3	950
	11th to 20th	Night	10% 7% 31% 36% 15% 2	950
	21st to end	Night	10% 4 29% 37% 17% 3	1045

Page generated at 2024-11-03 11:19:04. Version ac07

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