Slave Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Slave Lake clear sky chart from 2005-11-06 to 2024-01-15.

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% 8% 4 8% 7% 4 6% 6% 7% 9% 33%	74635
	Night	8% 9% 4 8% 7% 4 6% 6% 6% 8% 32%	75131
Transparency	Day	47% 10% 18% 19% 6%	74304
	Night	48% 9% 16% 19% 7% 1	74980
Seeing	Day	14% 15% 31% 25% 12% 3	15172
	Night	13% 13% 31% 28% 13% 2	23678

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% 10% 4 10% 12% 5% 8% 10% 6% 8% 23%	1139
	11th to 20th	Day	6% 12% 5% 8% 8% 4 7% 6% 7% 9% 27%	1180
	21st to end	Day	5% 12% 6% 12% 7% 5% 7% 6% 6% 8% 25%	1464
February	1st to 10th	Day	5% 10% 6% 10% 9% 5% 8% 8% 8% 9% 24%	1440
	11th to 20th	Day	3 11% 7% 12% 8% 5% 6% 7% 7% 9% 26%	1446
	21st to end	Day	4 12% 5% 12% 10% 6% 8% 6% 7% 7% 25%	1394
March	1st to 10th	Day	5% 9% 6% 7% 9% 6% 7% 8% 8% 9% 25%	1800
	11th to 20th	Day	6% 9% 5% 10% 7% 4 6% 6% 6% 8% 33%	1913
	21st to end	Day	7% 13% 6% 11% 8% 4 5% 6% 7% 8% 25%	2268
April	1st to 10th	Day	7% 11% 6% 9% 7% 3 7% 5% 6% 9% 30%	2232
	11th to 20th	Day	9% 11% 3 8% 8% 4 6% 5% 6% 8% 32%	2310
	21st to end	Day	13% 11% 4 8% 6% 4 6% 6% 6% 7% 29%	2417
May	1st to 10th	Day	11% 8% 3 6% 7% 4 6% 7% 6% 8% 33%	2672
	11th to 20th	Day	10% 7% 2 5% 6% 4 4 5% 7% 9% 40%	2654
	21st to end	Day	15% 7% 3 5% 6% 3 6% 6% 6% 8% 36%	2937
June	1st to 10th	Day	15% 7% 3 7% 6% 4 6% 5% 7% 10% 30%	2880
	11th to 20th	Day	21% 8% 3 5% 7% 4 6% 6% 7% 9% 25%	2880
	21st to end	Day	11% 6% 3 7% 6% 4 6% 6% 7% 9% 35%	2880
July	1st to 10th	Day	14% 6% 2 5% 5% 3 5% 6% 6% 9% 38%	2880
	11th to 20th	Day	13% 6% 2 6% 5% 3 5% 6% 8% 10% 34%	2867
	21st to end	Day	12% 4 2 4 5% 3 5% 5% 7% 9% 43%	2938
August	1st to 10th	Day	11% 6% 3 5% 6% 4 6% 6% 7% 10% 35%	2597
	11th to 20th	Day	9% 6% 3 6% 5% 3 6% 6% 6% 9% 42%	2457
	21st to end	Day	14% 6% 2 6% 7% 4 5% 6% 7% 9% 36%	2574
September	1st to 10th	Day	14% 7% 3 6% 5% 3 4 5% 6% 8% 39%	2269
	11th to 20th	Day	13% 9% 3 6% 5% 3 5% 5% 6% 9% 37%	2020
	21st to end	Day	10% 7% 3 6% 7% 3 5% 6% 6% 8% 41%	1980
October	1st to 10th	Day	11% 9% 5% 9% 6% 3 6% 6% 5% 6% 33%	1855
	11th to 20th	Day	10% 10% 5% 7% 7% 4 5% 5% 6% 9% 33%	1620
	21st to end	Day	10% 14% 5% 12% 6% 4 5% 5% 7% 7% 25%	1756
November	1st to 10th	Day	11% 13% 6% 9% 11% 4 4 5% 4 7% 26%	1408
	11th to 20th	Day	6% 11% 5% 13% 10% 4 6% 5% 6% 7% 25%	1330
	21st to end	Day	3 10% 5% 12% 9% 4 5% 5% 6% 10% 31%	1330
December	1st to 10th	Day	5% 9% 7% 9% 9% 6% 7% 7% 5% 7% 28%	1316
	11th to 20th	Day	8% 10% 5% 9% 7% 5% 7% 8% 8% 9% 25%	1442
	21st to end	Day	2 6% 3 8% 7% 3 5% 6% 6% 10% 43%	2090
January	1st to 10th	Night	5% 11% 5% 10% 10% 5% 7% 7% 7% 9% 25%	3026
	11th to 20th	Night	5% 11% 5% 10% 9% 6% 8% 7% 7% 9% 24%	2868
	21st to end	Night	6% 11% 7% 11% 9% 4 8% 6% 5% 7% 26%	2907
February	1st to 10th	Night	4 11% 6% 10% 10% 5% 7% 7% 6% 8% 25%	2520
	11th to 20th	Night	6% 11% 5% 8% 9% 6% 7% 8% 6% 7% 28%	2399
	21st to end	Night	4 9% 6% 10% 7% 5% 7% 7% 7% 9% 29%	1858
March	1st to 10th	Night	5% 9% 5% 10% 8% 5% 7% 6% 7% 8% 31%	2160
	11th to 20th	Night	6% 9% 4 9% 8% 4 6% 6% 7% 10% 30%	2045
	21st to end	Night	7% 12% 5% 8% 7% 4 6% 5% 6% 9% 29%	2088
April	1st to 10th	Night	6% 8% 3 7% 7% 4 7% 7% 7% 9% 35%	1728
	11th to 20th	Night	8% 10% 5% 7% 7% 4 7% 7% 8% 7% 30%	1601
	21st to end	Night	13% 13% 4 7% 6% 4 6% 5% 5% 7% 31%	1540
May	1st to 10th	Night	10% 9% 3 8% 7% 4 5% 5% 7% 8% 33%	1288
	11th to 20th	Night	12% 7% 4 6% 5% 2 4 5% 5% 7% 43%	1239
	21st to end	Night	16% 6% 3 7% 6% 3 4 5% 5% 9% 35%	1336
June	1st to 10th	Night	12% 6% 2 7% 9% 5% 7% 7% 7% 8% 31%	1080
	11th to 20th	Night	20% 9% 3 7% 6% 4 7% 6% 5% 8% 27%	1080
	21st to end	Night	9% 4 2 6% 7% 4 8% 6% 8% 9% 37%	1080
July	1st to 10th	Night	12% 5% 2 5% 6% 4 7% 7% 7% 10% 36%	1080
	11th to 20th	Night	12% 6% 2 6% 5% 3 5% 5% 7% 11% 38%	1093
	21st to end	Night	11% 4 2 5% 5% 3 4 6% 6% 9% 45%	1379
August	1st to 10th	Night	10% 5% 2 6% 6% 3 5% 5% 6% 8% 43%	1340
	11th to 20th	Night	8% 6% 2 5% 5% 4 5% 6% 7% 8% 45%	1442
	21st to end	Night	16% 6% 3 4 6% 3 4 5% 6% 8% 39%	1782
September	1st to 10th	Night	12% 6% 3 5% 5% 3 4 4 6% 8% 42%	1687
	11th to 20th	Night	11% 7% 2 7% 5% 3 4 4 7% 8% 41%	1940
	21st to end	Night	9% 7% 2 6% 5% 3 5% 5% 7% 8% 42%	1980
October	1st to 10th	Night	12% 10% 3 7% 6% 3 5% 5% 6% 6% 36%	2101
	11th to 20th	Night	9% 8% 4 8% 5% 3 5% 5% 6% 9% 37%	2340
	21st to end	Night	10% 12% 5% 10% 7% 3 5% 6% 6% 7% 28%	2582
November	1st to 10th	Night	10% 14% 6% 11% 9% 5% 5% 4 5% 6% 26%	2666
	11th to 20th	Night	7% 12% 5% 12% 11% 5% 6% 5% 5% 7% 24%	2850
	21st to end	Night	6% 11% 5% 11% 10% 4 7% 6% 7% 9% 25%	2850
December	1st to 10th	Night	5% 10% 5% 9% 9% 6% 7% 5% 6% 8% 29%	2860
	11th to 20th	Night	6% 12% 5% 10% 8% 5% 8% 7% 7% 7% 24%	3750
	21st to end	Night	2 7% 3 7% 7% 4 6% 6% 7% 10% 41%	5566

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% 6% 16% 14% 6% 1	1139
	11th to 20th	Day	53% 8% 15% 16% 6% 2	1180
	21st to end	Day	55% 10% 14% 14% 7%	1464
February	1st to 10th	Day	51% 10% 17% 14% 8% 1	1440
	11th to 20th	Day	52% 10% 17% 17% 5%	1454
	21st to end	Day	55% 8% 16% 13% 8%	1394
March	1st to 10th	Day	51% 10% 19% 15% 5%	1800
	11th to 20th	Day	48% 9% 13% 22% 8%	1914
	21st to end	Day	55% 11% 14% 16% 4	2268
April	1st to 10th	Day	50% 10% 15% 17% 8%	2232
	11th to 20th	Day	48% 11% 14% 19% 8%	2310
	21st to end	Day	53% 9% 14% 17% 7% 1	2417
May	1st to 10th	Day	47% 10% 17% 19% 8%	2672
	11th to 20th	Day	39% 9% 13% 26% 12% 1	2658
	21st to end	Day	45% 9% 14% 22% 10% 1	2938
June	1st to 10th	Day	47% 10% 15% 21% 6%	2880
	11th to 20th	Day	54% 12% 14% 15% 5%	2880
	21st to end	Day	42% 12% 20% 20% 6%	2880
July	1st to 10th	Day	41% 11% 20% 22% 5% 1	2801
	11th to 20th	Day	42% 15% 24% 17% 2	2780
	21st to end	Day	35% 12% 26% 24% 4	2775
August	1st to 10th	Day	43% 14% 24% 16% 2	2579
	11th to 20th	Day	36% 11% 26% 21% 5%	2457
	21st to end	Day	43% 11% 22% 20% 4	2574
September	1st to 10th	Day	42% 10% 20% 23% 4 1	2269
	11th to 20th	Day	43% 9% 24% 19% 5%	2020
	21st to end	Day	41% 10% 18% 23% 8%	1980
October	1st to 10th	Day	50% 9% 18% 17% 6%	1855
	11th to 20th	Day	48% 8% 18% 20% 5%	1620
	21st to end	Day	57% 9% 13% 16% 5%	1756
November	1st to 10th	Day	58% 6% 16% 15% 4 1	1408
	11th to 20th	Day	58% 10% 17% 12% 4	1330
	21st to end	Day	50% 8% 21% 17% 3 1	1330
December	1st to 10th	Day	54% 8% 14% 17% 7% 1	1316
	11th to 20th	Day	52% 10% 20% 15% 4	1444
	21st to end	Day	35% 8% 12% 30% 14% 1	2090
January	1st to 10th	Night	53% 8% 17% 14% 6% 1	3026
	11th to 20th	Night	56% 9% 15% 13% 5% 1	2868
	21st to end	Night	56% 10% 14% 12% 8% 1	2907
February	1st to 10th	Night	54% 8% 15% 15% 7% 1	2520
	11th to 20th	Night	52% 10% 16% 16% 6%	2401
	21st to end	Night	48% 10% 16% 18% 8%	1858
March	1st to 10th	Night	47% 9% 15% 21% 7%	2160
	11th to 20th	Night	47% 8% 14% 20% 10% 1	2045
	21st to end	Night	50% 8% 15% 20% 7%	2088
April	1st to 10th	Night	42% 8% 15% 21% 13% 1	1728
	11th to 20th	Night	49% 9% 11% 19% 9% 2	1601
	21st to end	Night	52% 7% 10% 21% 10% 1	1540
May	1st to 10th	Night	47% 6% 15% 20% 11%	1288
	11th to 20th	Night	40% 8% 10% 26% 15% 2	1239
	21st to end	Night	46% 7% 12% 24% 11% 1	1336
June	1st to 10th	Night	47% 11% 15% 18% 9%	1080
	11th to 20th	Night	55% 8% 15% 16% 6%	1080
	21st to end	Night	39% 12% 19% 24% 7%	1080
July	1st to 10th	Night	40% 12% 20% 19% 8% 1	1050
	11th to 20th	Night	40% 11% 25% 22% 3	1057
	21st to end	Night	35% 10% 27% 26% 3	1302
August	1st to 10th	Night	37% 11% 24% 25% 2	1333
	11th to 20th	Night	34% 11% 24% 24% 6%	1442
	21st to end	Night	42% 8% 20% 24% 6%	1782
September	1st to 10th	Night	38% 10% 20% 25% 6% 2	1687
	11th to 20th	Night	40% 8% 21% 24% 7%	1940
	21st to end	Night	38% 10% 16% 26% 10% 1	1980
October	1st to 10th	Night	46% 8% 14% 25% 7%	2101
	11th to 20th	Night	44% 9% 18% 23% 6%	2340
	21st to end	Night	54% 9% 15% 17% 5%	2582
November	1st to 10th	Night	59% 5% 14% 18% 4	2666
	11th to 20th	Night	60% 8% 14% 14% 4	2850
	21st to end	Night	55% 9% 18% 14% 3 1	2850
December	1st to 10th	Night	52% 8% 13% 17% 9% 1	2860
	11th to 20th	Night	56% 9% 16% 14% 5%	3747
	21st to end	Night	36% 7% 17% 26% 12% 1	5566

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	7% 17% 34% 26% 12% 4	180
	11th to 20th	Day	11% 22% 31% 24% 10% 2	168
	21st to end	Day	15% 25% 31% 19% 8% 2	176
February	1st to 10th	Day	15% 24% 36% 18% 7%	160
	11th to 20th	Day	8% 20% 44% 20% 6% 2	181
	21st to end	Day	7% 23% 34% 27% 5% 4	260
March	1st to 10th	Day	7% 24% 33% 29% 7%	420
	11th to 20th	Day	9% 19% 39% 21% 10% 2	420
	21st to end	Day	16% 19% 32% 24% 8% 1	462
April	1st to 10th	Day	13% 18% 38% 23% 7% 2	420
	11th to 20th	Day	16% 17% 29% 25% 9% 4	412
	21st to end	Day	17% 19% 38% 19% 6% 1	420
May	1st to 10th	Day	13% 16% 30% 26% 11% 3	575
	11th to 20th	Day	12% 12% 30% 28% 14% 3	625
	21st to end	Day	16% 10% 26% 29% 14% 4	699
June	1st to 10th	Day	16% 12% 33% 25% 12% 2	810
	11th to 20th	Day	23% 10% 25% 25% 15% 3	810
	21st to end	Day	11% 9% 26% 29% 20% 4	810
July	1st to 10th	Day	14% 7% 26% 32% 17% 4	796
	11th to 20th	Day	14% 11% 26% 29% 15% 5%	779
	21st to end	Day	11% 7% 29% 29% 16% 8%	684
August	1st to 10th	Day	17% 7% 27% 24% 19% 6%	537
	11th to 20th	Day	12% 18% 34% 24% 10% 3	437
	21st to end	Day	13% 13% 33% 26% 13% 2	495
September	1st to 10th	Day	19% 18% 31% 20% 10% 3	450
	11th to 20th	Day	18% 16% 31% 25% 8% 2	450
	21st to end	Day	14% 19% 34% 20% 12% 1	450
October	1st to 10th	Day	18% 19% 27% 25% 11% 1	369
	11th to 20th	Day	14% 19% 36% 23% 6% 2	270
	21st to end	Day	24% 20% 27% 23% 6% 1	297
November	1st to 10th	Day	16% 19% 36% 21% 6% 2	232
	11th to 20th	Day	15% 20% 38% 16% 9% 2	180
	21st to end	Day	9% 26% 37% 21% 5% 2	180
December	1st to 10th	Day	11% 17% 42% 19% 7% 4	180
	11th to 20th	Day	12% 23% 34% 24% 4 2	180
	21st to end	Day	5% 16% 30% 33% 11% 5%	198
January	1st to 10th	Night	10% 18% 34% 28% 8% 1	1040
	11th to 20th	Night	11% 17% 36% 28% 8% 1	970
	21st to end	Night	15% 20% 33% 24% 7% 2	927
February	1st to 10th	Night	12% 14% 32% 27% 14% 1	720
	11th to 20th	Night	13% 13% 36% 26% 11% 1	704
	21st to end	Night	6% 10% 35% 32% 15% 2	592
March	1st to 10th	Night	9% 13% 35% 28% 13% 2	720
	11th to 20th	Night	10% 12% 33% 33% 11% 2	720
	21st to end	Night	13% 11% 30% 31% 14% 2	792
April	1st to 10th	Night	10% 10% 31% 33% 15% 2	648
	11th to 20th	Night	13% 11% 30% 30% 13% 3	533
	21st to end	Night	20% 11% 28% 29% 12% 1	460
May	1st to 10th	Night	13% 8% 26% 33% 18% 2	360
	11th to 20th	Night	13% 9% 29% 31% 16% 2	354
	21st to end	Night	16% 7% 24% 31% 18% 3	389
June	1st to 10th	Night	14% 8% 30% 29% 18% 2	360
	11th to 20th	Night	23% 7% 22% 21% 24% 3	360
	21st to end	Night	8% 6% 22% 35% 25% 4	360
July	1st to 10th	Night	14% 5% 23% 36% 22% 1	350
	11th to 20th	Night	12% 7% 23% 34% 20% 4	348
	21st to end	Night	13% 5% 22% 30% 26% 5%	394
August	1st to 10th	Night	11% 6% 18% 34% 23% 8%	358
	11th to 20th	Night	9% 8% 24% 33% 24% 2	374
	21st to end	Night	17% 7% 23% 31% 20% 1	594
September	1st to 10th	Night	15% 8% 26% 28% 20% 3	607
	11th to 20th	Night	13% 12% 23% 36% 16% 2	720
	21st to end	Night	12% 16% 28% 28% 15% 2	720
October	1st to 10th	Night	18% 12% 29% 30% 10% 1	720
	11th to 20th	Night	13% 14% 31% 30% 11%	720
	21st to end	Night	17% 19% 30% 25% 8%	800
November	1st to 10th	Night	17% 15% 35% 24% 8% 1	925
	11th to 20th	Night	15% 19% 33% 24% 7% 2	950
	21st to end	Night	12% 21% 39% 21% 7% 1	950
December	1st to 10th	Night	12% 17% 35% 24% 10% 2	955
	11th to 20th	Night	12% 19% 34% 28% 6% 1	1040
	21st to end	Night	8% 15% 33% 29% 12% 3	1144

Page generated at 2024-01-11 20:33:48. Version ac07

Copyright 2024 Attilla Danko