Leduc
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leduc clear sky chart from 2005-11-06 to 2025-07-21.

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 9% 6% 5% 5% 4 6% 8% 36%	124350
	Night	8% 10% 4 10% 6% 6% 5% 4 6% 8% 33%	123439
Transparency	Day	43% 8% 17% 22% 9% 1	124094
	Night	47% 8% 15% 20% 9% 1	123339
Seeing	Day	13% 7% 24% 31% 19% 6%	16531
	Night	13% 6% 28% 36% 16% 2	25329

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% 11% 4 11% 9% 7% 5% 4 8% 10% 27%	3179
	11th to 20th	Day	4 11% 4 11% 7% 5% 7% 5% 7% 10% 29%	3159
	21st to end	Day	8% 12% 4 10% 6% 5% 4 4 6% 7% 36%	3792
February	1st to 10th	Day	7% 15% 5% 12% 7% 5% 5% 4 8% 9% 24%	1600
	11th to 20th	Day	5% 13% 7% 12% 7% 6% 6% 5% 6% 7% 27%	1703
	21st to end	Day	3 12% 6% 11% 8% 7% 8% 5% 6% 8% 25%	1545
March	1st to 10th	Day	4 9% 5% 11% 7% 6% 5% 4 6% 10% 33%	4518
	11th to 20th	Day	6% 12% 4 9% 5% 5% 4 4 6% 9% 36%	4951
	21st to end	Day	9% 13% 6% 15% 6% 5% 5% 4 6% 8% 24%	5564
April	1st to 10th	Day	7% 13% 4 9% 6% 6% 5% 4 7% 8% 31%	2495
	11th to 20th	Day	10% 12% 4 8% 5% 5% 5% 5% 7% 7% 30%	2570
	21st to end	Day	11% 9% 4 9% 6% 5% 5% 4 7% 8% 32%	2600
May	1st to 10th	Day	11% 7% 3 8% 6% 5% 5% 4 5% 6% 38%	6588
	11th to 20th	Day	13% 11% 4 9% 6% 6% 6% 4 7% 8% 26%	6734
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 4 6% 8% 40%	7405
June	1st to 10th	Day	15% 7% 3 7% 5% 6% 5% 4 7% 8% 32%	3000
	11th to 20th	Day	18% 10% 4 9% 7% 6% 6% 5% 6% 7% 24%	3000
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 8% 11% 37%	3165
July	1st to 10th	Day	9% 5% 2 6% 4 3 4 4 6% 9% 49%	4890
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 7% 8% 47%	4890
	21st to end	Day	12% 6% 2 5% 4 4 5% 5% 6% 7% 45%	5139
August	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 5% 7% 9% 40%	4500
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 4 8% 10% 43%	4145
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 7% 9% 42%	4521
September	1st to 10th	Day	12% 5% 3 6% 5% 5% 5% 4 6% 8% 42%	2412
	11th to 20th	Day	14% 7% 2 6% 4 3 4 3 5% 9% 42%	2090
	21st to end	Day	9% 6% 2 7% 4 5% 5% 4 7% 8% 43%	2090
October	1st to 10th	Day	9% 8% 3 8% 5% 5% 4 4 6% 7% 41%	3302
	11th to 20th	Day	10% 9% 4 9% 5% 5% 5% 4 5% 9% 36%	2886
	21st to end	Day	8% 11% 3 9% 5% 5% 5% 3 6% 7% 38%	3072
November	1st to 10th	Day	8% 15% 6% 10% 6% 6% 5% 4 6% 6% 27%	1568
	11th to 20th	Day	6% 13% 5% 14% 6% 4 5% 4 6% 7% 30%	1447
	21st to end	Day	5% 12% 6% 14% 7% 6% 6% 4 5% 7% 29%	1400
December	1st to 10th	Day	10% 15% 5% 11% 7% 5% 5% 4 6% 7% 23%	2290
	11th to 20th	Day	9% 12% 5% 11% 8% 7% 6% 5% 8% 8% 22%	2642
	21st to end	Day	3 6% 3 8% 7% 6% 5% 4 6% 7% 44%	3498
January	1st to 10th	Night	4 10% 5% 15% 9% 8% 7% 4 6% 7% 26%	6766
	11th to 20th	Night	3 11% 4 11% 7% 7% 5% 5% 6% 6% 35%	6739
	21st to end	Night	7% 14% 5% 11% 6% 5% 4 4 5% 7% 33%	7206
February	1st to 10th	Night	5% 12% 5% 14% 8% 6% 7% 4 5% 7% 27%	2800
	11th to 20th	Night	5% 12% 4 11% 7% 7% 6% 6% 6% 7% 29%	2583
	21st to end	Night	5% 12% 4 10% 8% 6% 6% 5% 5% 7% 32%	2084
March	1st to 10th	Night	3 9% 5% 11% 6% 6% 6% 4 7% 11% 32%	5376
	11th to 20th	Night	4 11% 4 9% 7% 7% 6% 5% 8% 8% 31%	5047
	21st to end	Night	10% 14% 7% 14% 6% 6% 5% 4 5% 6% 23%	5407
April	1st to 10th	Night	6% 10% 2 9% 7% 7% 6% 5% 7% 7% 32%	1904
	11th to 20th	Night	10% 12% 4 10% 7% 7% 6% 4 6% 8% 27%	1781
	21st to end	Night	11% 9% 4 8% 5% 4 5% 5% 7% 8% 33%	1800
May	1st to 10th	Night	16% 8% 3 7% 4 4 4 4 5% 6% 38%	3359
	11th to 20th	Night	13% 10% 4 11% 7% 6% 6% 5% 6% 7% 25%	3159
	21st to end	Night	12% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	3470
June	1st to 10th	Night	14% 7% 5% 8% 5% 5% 5% 5% 6% 8% 31%	1400
	11th to 20th	Night	17% 9% 4 10% 7% 7% 6% 6% 7% 8% 21%	1397
	21st to end	Night	11% 8% 3 7% 5% 5% 6% 5% 7% 8% 35%	1214
July	1st to 10th	Night	10% 7% 3 6% 5% 5% 5% 4 6% 8% 42%	2290
	11th to 20th	Night	8% 6% 3 7% 5% 6% 6% 5% 7% 10% 38%	2290
	21st to end	Night	14% 6% 2 4 4 4 4 4 7% 10% 42%	2414
August	1st to 10th	Night	14% 7% 2 6% 5% 4 4 4 7% 7% 39%	2427
	11th to 20th	Night	11% 8% 3 7% 4 5% 5% 5% 6% 9% 38%	2689
	21st to end	Night	11% 5% 2 7% 5% 5% 5% 4 7% 10% 40%	3146
September	1st to 10th	Night	12% 5% 3 7% 5% 4 4 4 6% 7% 44%	1766
	11th to 20th	Night	12% 7% 2 6% 5% 3 4 3 6% 8% 44%	2090
	21st to end	Night	9% 7% 2 7% 4 5% 4 4 6% 8% 42%	2090
October	1st to 10th	Night	9% 7% 3 8% 4 6% 5% 4 7% 8% 40%	3672
	11th to 20th	Night	9% 8% 3 7% 4 6% 5% 4 7% 9% 39%	4041
	21st to end	Night	6% 9% 4 9% 6% 5% 6% 4 6% 8% 36%	4457
November	1st to 10th	Night	11% 15% 6% 9% 6% 4 5% 3 6% 7% 27%	2727
	11th to 20th	Night	6% 15% 5% 10% 7% 6% 6% 4 6% 7% 28%	2950
	21st to end	Night	6% 13% 5% 12% 8% 6% 6% 4 6% 8% 28%	3000
December	1st to 10th	Night	12% 18% 5% 10% 7% 5% 4 3 5% 6% 23%	4890
	11th to 20th	Night	7% 15% 6% 13% 7% 5% 6% 5% 6% 8% 21%	5550
	21st to end	Night	2 7% 3 10% 6% 5% 6% 4 6% 8% 42%	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	50% 8% 13% 19% 9% 1	3179
	11th to 20th	Day	47% 7% 11% 13% 21% 2	3180
	21st to end	Day	47% 7% 19% 22% 5%	3792
February	1st to 10th	Day	55% 5% 15% 16% 8% 1	1600
	11th to 20th	Day	54% 7% 13% 16% 9%	1712
	21st to end	Day	52% 8% 14% 18% 8% 1	1545
March	1st to 10th	Day	44% 7% 19% 19% 10%	4518
	11th to 20th	Day	44% 8% 14% 23% 10%	4952
	21st to end	Day	55% 7% 10% 20% 7%	5564
April	1st to 10th	Day	47% 10% 15% 20% 8% 1	2495
	11th to 20th	Day	49% 8% 13% 21% 9%	2570
	21st to end	Day	47% 9% 15% 21% 7% 2	2600
May	1st to 10th	Day	44% 7% 10% 24% 15% 1	6588
	11th to 20th	Day	51% 9% 14% 21% 6%	6738
	21st to end	Day	38% 9% 20% 23% 9% 1	7406
June	1st to 10th	Day	47% 7% 16% 21% 9% 1	3000
	11th to 20th	Day	55% 9% 15% 16% 4	3000
	21st to end	Day	38% 11% 22% 23% 6% 1	3165
July	1st to 10th	Day	30% 9% 17% 29% 14% 1	4816
	11th to 20th	Day	32% 9% 18% 29% 12%	4809
	21st to end	Day	35% 9% 20% 24% 12% 1	4977
August	1st to 10th	Day	37% 10% 18% 32% 2	4482
	11th to 20th	Day	33% 9% 23% 29% 7%	4187
	21st to end	Day	35% 8% 29% 23% 4	4520
September	1st to 10th	Day	38% 8% 20% 25% 7% 2	2412
	11th to 20th	Day	38% 8% 19% 29% 7%	2090
	21st to end	Day	36% 10% 19% 26% 8% 2	2090
October	1st to 10th	Day	41% 6% 23% 24% 5%	3302
	11th to 20th	Day	44% 7% 15% 24% 10%	2886
	21st to end	Day	44% 7% 18% 27% 4	3072
November	1st to 10th	Day	55% 9% 14% 15% 6% 1	1568
	11th to 20th	Day	52% 8% 16% 18% 6%	1447
	21st to end	Day	52% 9% 15% 17% 5% 1	1400
December	1st to 10th	Day	58% 8% 17% 12% 4 1	2290
	11th to 20th	Day	56% 9% 17% 14% 4	2644
	21st to end	Day	37% 7% 12% 27% 15% 2	3498
January	1st to 10th	Night	54% 7% 14% 15% 8% 1	6766
	11th to 20th	Night	47% 6% 13% 16% 17% 1	6780
	21st to end	Night	48% 7% 18% 20% 6%	7206
February	1st to 10th	Night	54% 6% 12% 18% 9% 1	2800
	11th to 20th	Night	51% 8% 13% 17% 11% 1	2584
	21st to end	Night	48% 8% 12% 20% 11% 1	2084
March	1st to 10th	Night	44% 7% 18% 22% 9%	5376
	11th to 20th	Night	45% 9% 17% 19% 10%	5047
	21st to end	Night	58% 8% 9% 17% 8%	5407
April	1st to 10th	Night	45% 9% 13% 19% 12% 1	1904
	11th to 20th	Night	53% 7% 11% 18% 9% 2	1781
	21st to end	Night	45% 9% 13% 20% 12% 1	1800
May	1st to 10th	Night	44% 6% 9% 22% 16% 3	3357
	11th to 20th	Night	52% 10% 14% 17% 6% 1	3159
	21st to end	Night	43% 10% 17% 20% 9% 1	3470
June	1st to 10th	Night	49% 10% 13% 20% 9% 1	1400
	11th to 20th	Night	58% 10% 15% 13% 4	1397
	21st to end	Night	42% 11% 21% 21% 4 1	1214
July	1st to 10th	Night	37% 8% 17% 21% 15% 1	2255
	11th to 20th	Night	37% 11% 17% 26% 9% 1	2248
	21st to end	Night	35% 9% 20% 27% 9%	2337
August	1st to 10th	Night	40% 10% 18% 29% 2	2420
	11th to 20th	Night	39% 10% 21% 22% 7%	2713
	21st to end	Night	37% 9% 22% 27% 5%	3146
September	1st to 10th	Night	38% 8% 17% 24% 12% 2	1766
	11th to 20th	Night	38% 8% 16% 28% 8% 2	2090
	21st to end	Night	37% 8% 14% 24% 13% 2	2090
October	1st to 10th	Night	39% 7% 21% 26% 7%	3672
	11th to 20th	Night	39% 7% 15% 31% 7%	4041
	21st to end	Night	43% 8% 20% 24% 5%	4457
November	1st to 10th	Night	55% 7% 11% 19% 7%	2727
	11th to 20th	Night	53% 8% 13% 17% 7% 1	2950
	21st to end	Night	53% 8% 16% 17% 6% 1	3000
December	1st to 10th	Night	61% 6% 14% 12% 5% 1	4890
	11th to 20th	Night	58% 8% 17% 11% 5%	5547
	21st to end	Night	38% 7% 14% 23% 16% 2	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	8% 6% 27% 33% 22% 5%	200
	11th to 20th	Day	8% 11% 27% 36% 15% 5%	200
	21st to end	Day	13% 8% 30% 30% 13% 6%	220
February	1st to 10th	Day	10% 12% 25% 34% 16% 5%	200
	11th to 20th	Day	11% 2 29% 36% 17% 4	275
	21st to end	Day	7% 5% 29% 34% 18% 7%	309
March	1st to 10th	Day	11% 7% 26% 35% 18% 4	500
	11th to 20th	Day	10% 4 26% 35% 18% 7%	500
	21st to end	Day	14% 6% 24% 33% 19% 3	550
April	1st to 10th	Day	10% 12% 27% 34% 13% 4	500
	11th to 20th	Day	14% 9% 24% 30% 18% 5%	492
	21st to end	Day	16% 10% 24% 29% 16% 5%	500
May	1st to 10th	Day	14% 10% 23% 33% 16% 4	651
	11th to 20th	Day	12% 6% 21% 36% 19% 6%	725
	21st to end	Day	15% 7% 20% 31% 19% 8%	789
June	1st to 10th	Day	17% 9% 25% 31% 15% 3	730
	11th to 20th	Day	19% 8% 21% 26% 19% 7%	730
	21st to end	Day	12% 5% 20% 30% 24% 8%	895
July	1st to 10th	Day	12% 4 16% 35% 24% 9%	721
	11th to 20th	Day	11% 4 21% 29% 25% 9%	718
	21st to end	Day	10% 5% 17% 31% 25% 11%	740
August	1st to 10th	Day	11% 4 19% 31% 23% 13%	547
	11th to 20th	Day	9% 5% 20% 33% 26% 7%	477
	21st to end	Day	13% 6% 19% 28% 26% 9%	539
September	1st to 10th	Day	14% 7% 26% 25% 20% 8%	490
	11th to 20th	Day	19% 6% 23% 29% 18% 5%	490
	21st to end	Day	12% 12% 29% 28% 15% 4	490
October	1st to 10th	Day	16% 6% 28% 28% 17% 5%	380
	11th to 20th	Day	13% 8% 32% 30% 14% 4	300
	21st to end	Day	15% 14% 31% 26% 12% 3	330
November	1st to 10th	Day	16% 5% 27% 33% 16% 2	300
	11th to 20th	Day	13% 6% 32% 33% 13% 3	223
	21st to end	Day	6% 5% 33% 40% 12% 5%	200
December	1st to 10th	Day	9% 7% 28% 34% 19% 4	200
	11th to 20th	Day	13% 7% 28% 31% 17% 5%	200
	21st to end	Day	8% 4 19% 41% 24% 5%	220
January	1st to 10th	Night	9% 8% 32% 35% 15% 2	1000
	11th to 20th	Night	11% 8% 33% 34% 12% 2	1000
	21st to end	Night	14% 11% 33% 29% 11% 2	991
February	1st to 10th	Night	9% 7% 24% 39% 19% 2	800
	11th to 20th	Night	10% 6% 32% 37% 15% 1	784
	21st to end	Night	9% 5% 27% 35% 20% 4	660
March	1st to 10th	Night	10% 5% 27% 40% 16% 3	800
	11th to 20th	Night	11% 4 29% 38% 15% 3	800
	21st to end	Night	14% 5% 26% 36% 16% 3	880
April	1st to 10th	Night	12% 5% 29% 33% 19% 2	704
	11th to 20th	Night	14% 7% 28% 35% 14% 1	593
	21st to end	Night	15% 7% 28% 34% 15% 1	600
May	1st to 10th	Night	16% 8% 25% 37% 13% 1	437
	11th to 20th	Night	11% 7% 26% 37% 17% 2	394
	21st to end	Night	19% 6% 22% 34% 18% 2	433
June	1st to 10th	Night	18% 7% 27% 34% 12% 2	400
	11th to 20th	Night	19% 5% 25% 32% 18% 2	400
	21st to end	Night	12% 6% 17% 36% 28% 2	400
July	1st to 10th	Night	15% 2 16% 44% 23%	390
	11th to 20th	Night	11% 4 20% 43% 20% 2	388
	21st to end	Night	13% 4 15% 41% 24% 3	416
August	1st to 10th	Night	13% 4 16% 33% 29% 4	378
	11th to 20th	Night	15% 2 17% 38% 25% 2	490
	21st to end	Night	13% 2 20% 41% 23% 1	627
September	1st to 10th	Night	14% 3 18% 42% 21% 2	616
	11th to 20th	Night	14% 3 21% 42% 20% 1	760
	21st to end	Night	11% 5% 30% 39% 14% 1	760
October	1st to 10th	Night	15% 5% 27% 38% 14% 1	760
	11th to 20th	Night	14% 4 33% 33% 13% 2	760
	21st to end	Night	12% 7% 32% 34% 14%	836
November	1st to 10th	Night	19% 6% 30% 34% 9% 1	972
	11th to 20th	Night	13% 8% 33% 32% 11% 2	1000
	21st to end	Night	10% 5% 36% 37% 11% 2	1000
December	1st to 10th	Night	16% 7% 31% 30% 14% 3	1000
	11th to 20th	Night	11% 6% 32% 35% 14% 2	1000
	21st to end	Night	9% 5% 30% 36% 17% 3	1100

Page generated at 2025-07-17 23:10:01. Version ac07

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