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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 2024-01-16.

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% 4 8% 7% 4 5% 5% 6% 8% 33%	74956
	Night	9% 9% 4 8% 7% 4 6% 5% 6% 8% 33%	74833
Transparency	Day	46% 9% 17% 21% 7% 1	74637
	Night	47% 8% 15% 20% 8% 1	74670
Seeing	Day	13% 6% 23% 31% 20% 6%	14600
	Night	13% 5% 26% 36% 17% 2	23467

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	6% 10% 6% 11% 11% 6% 7% 5% 6% 7% 25%	1329
	11th to 20th	Day	7% 12% 5% 11% 9% 4 4 3 6% 8% 31%	1295
	21st to end	Day	7% 16% 6% 11% 8% 4 7% 6% 6% 7% 23%	1487
February	1st to 10th	Day	9% 14% 5% 12% 8% 4 4 5% 7% 8% 24%	1440
	11th to 20th	Day	7% 13% 6% 11% 8% 4 6% 6% 8% 6% 25%	1522
	21st to end	Day	4 12% 7% 10% 9% 4 7% 7% 7% 9% 25%	1378
March	1st to 10th	Day	8% 13% 6% 11% 10% 4 5% 5% 6% 7% 24%	1800
	11th to 20th	Day	9% 10% 5% 8% 6% 4 4 6% 7% 8% 33%	1957
	21st to end	Day	10% 12% 7% 10% 8% 5% 6% 5% 6% 9% 22%	2206
April	1st to 10th	Day	9% 10% 5% 8% 7% 5% 7% 6% 6% 8% 30%	2250
	11th to 20th	Day	12% 12% 4 6% 7% 3 6% 6% 5% 8% 30%	2310
	21st to end	Day	12% 11% 4 7% 7% 4 5% 5% 6% 8% 31%	2340
May	1st to 10th	Day	11% 9% 4 8% 7% 5% 6% 6% 7% 7% 29%	2636
	11th to 20th	Day	9% 6% 3 6% 6% 3 6% 6% 5% 10% 39%	2654
	21st to end	Day	17% 7% 3 7% 6% 3 5% 5% 5% 7% 34%	2917
June	1st to 10th	Day	16% 8% 4 8% 6% 3 5% 5% 7% 8% 30%	2700
	11th to 20th	Day	21% 9% 3 7% 7% 4 7% 7% 6% 7% 23%	2769
	21st to end	Day	11% 5% 2 6% 6% 4 6% 6% 7% 9% 37%	2880
July	1st to 10th	Day	11% 6% 3 7% 6% 4 5% 5% 7% 9% 37%	2754
	11th to 20th	Day	11% 6% 2 5% 7% 4 5% 6% 7% 9% 36%	2700
	21st to end	Day	10% 5% 2 5% 5% 4 5% 5% 7% 8% 45%	2938
August	1st to 10th	Day	10% 6% 2 5% 5% 4 6% 7% 7% 11% 38%	2578
	11th to 20th	Day	8% 5% 2 5% 5% 3 5% 5% 7% 10% 44%	2374
	21st to end	Day	11% 6% 2 6% 5% 3 5% 5% 6% 10% 41%	2574
September	1st to 10th	Day	12% 7% 2 6% 5% 3 4 5% 6% 8% 41%	2292
	11th to 20th	Day	14% 7% 2 5% 5% 2 4 4 6% 8% 42%	1980
	21st to end	Day	10% 6% 3 6% 5% 4 5% 5% 6% 8% 43%	1980
October	1st to 10th	Day	11% 10% 4 8% 7% 4 5% 4 4 5% 37%	1872
	11th to 20th	Day	10% 8% 4 8% 6% 3 5% 6% 5% 7% 37%	1648
	21st to end	Day	10% 12% 5% 9% 6% 4 5% 5% 7% 7% 31%	1758
November	1st to 10th	Day	10% 13% 6% 8% 8% 4 6% 6% 5% 6% 27%	1488
	11th to 20th	Day	7% 12% 6% 11% 8% 4 5% 5% 5% 8% 30%	1366
	21st to end	Day	6% 11% 6% 12% 7% 5% 5% 4 7% 6% 30%	1330
December	1st to 10th	Day	6% 12% 5% 10% 10% 5% 7% 6% 5% 8% 26%	1330
	11th to 20th	Day	7% 10% 6% 10% 8% 5% 6% 6% 7% 8% 27%	1682
	21st to end	Day	4 7% 4 7% 7% 5% 6% 5% 6% 8% 42%	2442
January	1st to 10th	Night	6% 11% 6% 11% 10% 5% 7% 7% 6% 6% 25%	2836
	11th to 20th	Night	7% 11% 5% 10% 9% 4 5% 5% 6% 9% 31%	2776
	21st to end	Night	8% 15% 6% 11% 7% 5% 5% 5% 6% 7% 26%	2884
February	1st to 10th	Night	6% 11% 5% 13% 10% 5% 6% 6% 5% 6% 27%	2520
	11th to 20th	Night	7% 12% 5% 9% 9% 4 6% 6% 6% 8% 28%	2324
	21st to end	Night	6% 10% 5% 9% 8% 4 6% 7% 6% 8% 31%	1875
March	1st to 10th	Night	7% 10% 5% 11% 7% 5% 6% 6% 6% 8% 28%	2160
	11th to 20th	Night	9% 8% 5% 8% 7% 5% 7% 6% 7% 8% 29%	2001
	21st to end	Night	9% 12% 6% 9% 7% 4 5% 6% 7% 8% 27%	2147
April	1st to 10th	Night	9% 8% 4 8% 8% 4 7% 7% 7% 8% 31%	1710
	11th to 20th	Night	10% 11% 5% 9% 8% 5% 6% 5% 6% 6% 30%	1601
	21st to end	Night	13% 9% 3 7% 6% 3 4 5% 7% 7% 35%	1620
May	1st to 10th	Night	13% 8% 5% 9% 7% 4 6% 6% 6% 7% 30%	1323
	11th to 20th	Night	10% 7% 3 6% 7% 4 5% 5% 7% 9% 37%	1239
	21st to end	Night	19% 8% 3 5% 6% 3 6% 4 6% 7% 32%	1358
June	1st to 10th	Night	16% 8% 2 7% 6% 3 6% 6% 7% 8% 30%	1260
	11th to 20th	Night	17% 9% 3 8% 8% 6% 7% 6% 7% 7% 22%	1184
	21st to end	Night	9% 6% 4 6% 7% 4 6% 6% 7% 9% 38%	1080
July	1st to 10th	Night	13% 5% 2 6% 6% 3 4 5% 7% 10% 38%	1201
	11th to 20th	Night	10% 5% 2 6% 6% 5% 5% 6% 9% 12% 34%	1260
	21st to end	Night	10% 4 3 5% 4 4 6% 5% 6% 11% 43%	1379
August	1st to 10th	Night	12% 4 2 5% 5% 4 7% 5% 7% 9% 41%	1360
	11th to 20th	Night	11% 6% 2 5% 4 3 6% 5% 6% 8% 44%	1525
	21st to end	Night	11% 5% 3 6% 6% 4 5% 6% 6% 9% 39%	1782
September	1st to 10th	Night	14% 5% 3 6% 5% 3 4 5% 5% 8% 43%	1666
	11th to 20th	Night	12% 7% 2 4 5% 3 4 5% 5% 8% 46%	1980
	21st to end	Night	9% 7% 3 6% 5% 3 4 4 6% 7% 45%	1980
October	1st to 10th	Night	12% 8% 3 8% 6% 3 4 4 6% 6% 39%	2088
	11th to 20th	Night	9% 8% 5% 6% 6% 3 5% 5% 7% 7% 39%	2309
	21st to end	Night	9% 9% 3 9% 8% 4 5% 6% 6% 7% 32%	2579
November	1st to 10th	Night	13% 14% 5% 9% 7% 4 5% 5% 6% 6% 26%	2590
	11th to 20th	Night	8% 13% 7% 9% 7% 4 5% 5% 6% 7% 28%	2812
	21st to end	Night	6% 10% 6% 11% 9% 4 6% 6% 6% 8% 29%	2850
December	1st to 10th	Night	9% 12% 5% 10% 9% 5% 5% 5% 6% 7% 29%	2850
	11th to 20th	Night	7% 12% 6% 11% 8% 4 6% 6% 7% 8% 26%	3510
	21st to end	Night	4 7% 3 8% 7% 4 6% 6% 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	57% 8% 11% 17% 7% 1	1329
	11th to 20th	Day	50% 8% 14% 17% 10% 2	1295
	21st to end	Day	58% 8% 12% 16% 6%	1487
February	1st to 10th	Day	56% 6% 16% 14% 7%	1440
	11th to 20th	Day	55% 8% 15% 15% 6%	1531
	21st to end	Day	52% 7% 14% 20% 7%	1378
March	1st to 10th	Day	58% 6% 16% 16% 4	1800
	11th to 20th	Day	46% 8% 15% 21% 9%	1958
	21st to end	Day	58% 9% 14% 15% 4	2206
April	1st to 10th	Day	51% 9% 16% 18% 7% 1	2250
	11th to 20th	Day	49% 7% 14% 21% 8%	2310
	21st to end	Day	47% 8% 15% 20% 7% 2	2340
May	1st to 10th	Day	50% 8% 15% 17% 9%	2636
	11th to 20th	Day	38% 8% 14% 29% 11% 1	2658
	21st to end	Day	47% 8% 13% 21% 10%	2918
June	1st to 10th	Day	50% 7% 15% 20% 7%	2700
	11th to 20th	Day	57% 10% 16% 13% 4	2769
	21st to end	Day	39% 11% 21% 22% 5% 1	2880
July	1st to 10th	Day	40% 10% 20% 24% 5% 1	2680
	11th to 20th	Day	41% 12% 25% 20% 2	2619
	21st to end	Day	34% 10% 27% 25% 3	2775
August	1st to 10th	Day	37% 13% 28% 19% 3	2560
	11th to 20th	Day	32% 9% 27% 24% 6%	2374
	21st to end	Day	36% 10% 21% 26% 7% 1	2574
September	1st to 10th	Day	39% 9% 19% 24% 7% 2	2292
	11th to 20th	Day	39% 8% 20% 26% 7%	1980
	21st to end	Day	37% 8% 20% 26% 8% 2	1980
October	1st to 10th	Day	48% 6% 17% 20% 8%	1872
	11th to 20th	Day	44% 7% 19% 22% 8%	1648
	21st to end	Day	50% 7% 13% 23% 6%	1758
November	1st to 10th	Day	56% 8% 14% 16% 6% 1	1488
	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	56% 8% 14% 14% 6% 1	2836
	11th to 20th	Night	49% 8% 17% 16% 8% 2	2776
	21st to end	Night	56% 7% 14% 15% 8% 1	2884
February	1st to 10th	Night	56% 6% 13% 17% 8% 1	2520
	11th to 20th	Night	52% 8% 15% 16% 9%	2325
	21st to end	Night	48% 8% 14% 19% 9% 1	1875
March	1st to 10th	Night	51% 8% 15% 19% 7% 1	2160
	11th to 20th	Night	49% 7% 14% 19% 10% 1	2001
	21st to end	Night	51% 8% 15% 18% 7% 1	2147
April	1st to 10th	Night	46% 9% 15% 19% 10% 1	1710
	11th to 20th	Night	52% 6% 12% 18% 10% 2	1601
	21st to end	Night	44% 8% 13% 22% 13% 1	1620
May	1st to 10th	Night	50% 10% 10% 20% 9% 1	1323
	11th to 20th	Night	42% 8% 12% 22% 14% 1	1239
	21st to end	Night	50% 6% 13% 19% 10% 2	1358
June	1st to 10th	Night	49% 9% 15% 20% 7% 1	1260
	11th to 20th	Night	57% 11% 15% 13% 4	1184
	21st to end	Night	40% 10% 24% 21% 4 1	1080
July	1st to 10th	Night	39% 12% 19% 23% 7% 1	1166
	11th to 20th	Night	40% 14% 21% 21% 3	1218
	21st to end	Night	33% 12% 23% 28% 4	1302
August	1st to 10th	Night	37% 11% 26% 24% 3	1353
	11th to 20th	Night	36% 10% 22% 25% 6% 1	1525
	21st to end	Night	39% 10% 18% 25% 8% 1	1782
September	1st to 10th	Night	38% 7% 19% 25% 9% 2	1666
	11th to 20th	Night	36% 8% 17% 28% 9% 2	1980
	21st to end	Night	36% 8% 15% 26% 13% 2	1980
October	1st to 10th	Night	44% 7% 15% 24% 10%	2088
	11th to 20th	Night	42% 7% 16% 25% 9% 1	2309
	21st to end	Night	47% 9% 15% 21% 7%	2579
November	1st to 10th	Night	57% 7% 11% 18% 6%	2590
	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% 5% 24% 36% 14% 8%	170
	21st to end	Day	13% 9% 28% 30% 14% 7%	176
February	1st to 10th	Day	13% 6% 29% 31% 16% 4	160
	11th to 20th	Day	13% 8% 25% 33% 18% 4	216
	21st to end	Day	8% 5% 23% 33% 22% 9%	244
March	1st to 10th	Day	11% 6% 27% 34% 18% 4	420
	11th to 20th	Day	12% 3 23% 36% 20% 7%	420
	21st to end	Day	16% 4 21% 29% 26% 3	462
April	1st to 10th	Day	11% 8% 25% 36% 16% 5%	420
	11th to 20th	Day	17% 5% 20% 32% 19% 7%	412
	21st to end	Day	16% 9% 24% 30% 16% 5%	420
May	1st to 10th	Day	14% 8% 23% 31% 19% 5%	567
	11th to 20th	Day	11% 5% 23% 33% 21% 6%	625
	21st to end	Day	17% 5% 19% 32% 19% 9%	679
June	1st to 10th	Day	19% 7% 23% 30% 17% 3	630
	11th to 20th	Day	20% 7% 19% 26% 22% 6%	699
	21st to end	Day	12% 5% 18% 30% 25% 10%	810
July	1st to 10th	Day	13% 5% 17% 32% 26% 8%	675
	11th to 20th	Day	11% 4 22% 30% 25% 8%	618
	21st to end	Day	10% 4 17% 33% 27% 9%	684
August	1st to 10th	Day	13% 4 19% 30% 22% 13%	518
	11th to 20th	Day	9% 5% 24% 30% 26% 6%	437
	21st to end	Day	13% 7% 17% 29% 24% 10%	495
September	1st to 10th	Day	15% 8% 28% 25% 18% 6%	450
	11th to 20th	Day	18% 6% 23% 30% 19% 4	450
	21st to end	Day	11% 11% 31% 25% 18% 4	450
October	1st to 10th	Day	16% 8% 24% 31% 16% 6%	342
	11th to 20th	Day	13% 10% 26% 33% 16% 3	270
	21st to end	Day	13% 13% 34% 25% 11% 2	297
November	1st to 10th	Day	19% 7% 22% 35% 15% 2	270
	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	12% 7% 30% 34% 15% 2	926
	21st to end	Night	15% 10% 29% 31% 12% 2	904
February	1st to 10th	Night	11% 7% 24% 36% 20% 3	720
	11th to 20th	Night	12% 5% 32% 34% 15% 1	704
	21st to end	Night	10% 4 25% 36% 20% 5%	592
March	1st to 10th	Night	10% 4 26% 39% 18% 3	720
	11th to 20th	Night	14% 4 26% 38% 15% 3	720
	21st to end	Night	13% 4 24% 38% 18% 3	792
April	1st to 10th	Night	12% 6% 23% 36% 21% 2	630
	11th to 20th	Night	13% 5% 27% 37% 16% 1	533
	21st to end	Night	16% 6% 26% 34% 16% 1	540
May	1st to 10th	Night	16% 5% 23% 39% 16% 2	387
	11th to 20th	Night	12% 6% 21% 42% 18% 2	354
	21st to end	Night	22% 5% 18% 34% 20% 2	389
June	1st to 10th	Night	19% 7% 20% 39% 13% 2	360
	11th to 20th	Night	21% 4 20% 31% 22% 3	360
	21st to end	Night	11% 4 16% 38% 28% 3	360
July	1st to 10th	Night	14% 3 14% 44% 24% 1	350
	11th to 20th	Night	11% 3 21% 42% 21% 2	348
	21st to end	Night	11% 4 18% 39% 26% 3	394
August	1st to 10th	Night	11% 3 17% 31% 32% 6%	358
	11th to 20th	Night	11% 5% 17% 39% 26% 2	457
	21st to end	Night	11% 4 19% 42% 24% 1	594
September	1st to 10th	Night	13% 2 21% 40% 21% 2	578
	11th to 20th	Night	13% 4 20% 43% 19% 2	720
	21st to end	Night	12% 4 25% 41% 15% 1	720
October	1st to 10th	Night	17% 3 26% 39% 14% 1	720
	11th to 20th	Night	14% 4 31% 34% 14% 2	720
	21st to end	Night	14% 7% 32% 33% 14%	797
November	1st to 10th	Night	20% 7% 29% 33% 10% 1	925
	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 2024-01-12 23:38:09. Version ac07

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