Abraham Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Abraham Lake clear sky chart from 2005-11-06 to 2025-05-11.

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	5% 9% 4 10% 7% 6% 6% 5% 8% 9% 31%	118035
	Night	3 7% 4 10% 7% 7% 7% 6% 9% 10% 32%	119580
Transparency	Day	43% 11% 17% 19% 9% 1	117782
	Night	41% 12% 19% 20% 8% 1	119479
Seeing	Day	17% 21% 33% 20% 7% 2	16362
	Night	11% 17% 38% 24% 9% 1	24930

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 2 11% 12% 13% 9% 6% 10% 8% 24%	3179
	11th to 20th	Day	3 3 9% 9% 8% 7% 8% 9% 10% 35%	3369
	21st to end	Day	5% 3 9% 6% 6% 7% 6% 10% 11% 36%	4004
February	1st to 10th	Day	1 6% 4 10% 9% 9% 10% 7% 10% 10% 24%	1600
	11th to 20th	Day	1 8% 3 12% 8% 8% 7% 7% 8% 10% 29%	1659
	21st to end	Day	1 5% 4 12% 11% 9% 10% 7% 9% 10% 23%	1650
March	1st to 10th	Day	1 7% 4 14% 10% 8% 6% 5% 7% 8% 31%	4518
	11th to 20th	Day	2 7% 3 11% 8% 7% 7% 6% 8% 9% 31%	4735
	21st to end	Day	2 14% 7% 20% 7% 6% 6% 5% 8% 7% 18%	5836
April	1st to 10th	Day	3 13% 6% 14% 9% 9% 8% 6% 7% 8% 17%	2400
	11th to 20th	Day	3 14% 6% 15% 10% 6% 7% 5% 7% 8% 20%	2550
	21st to end	Day	5% 15% 6% 14% 7% 6% 6% 5% 6% 8% 21%	2657
May	1st to 10th	Day	7% 22% 5% 10% 6% 5% 5% 3 6% 8% 24%	4560
	11th to 20th	Day	6% 12% 4 10% 7% 6% 7% 5% 8% 9% 26%	4655
	21st to end	Day	11% 17% 5% 13% 7% 6% 6% 5% 5% 7% 17%	5161
June	1st to 10th	Day	15% 12% 3 10% 6% 6% 6% 5% 7% 8% 21%	2855
	11th to 20th	Day	19% 13% 3 9% 6% 5% 6% 4 7% 7% 20%	3040
	21st to end	Day	11% 9% 4 8% 8% 6% 7% 5% 7% 7% 28%	3040
July	1st to 10th	Day	7% 6% 3 6% 5% 4 5% 4 6% 7% 48%	5042
	11th to 20th	Day	6% 3 1 4 4 3 4 4 7% 8% 55%	4740
	21st to end	Day	6% 5% 2 6% 5% 4 5% 5% 7% 9% 45%	4895
August	1st to 10th	Day	11% 8% 3 7% 5% 5% 5% 4 7% 7% 37%	4401
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 6% 9% 11% 37%	4271
	21st to end	Day	10% 7% 3 7% 6% 5% 6% 5% 7% 8% 36%	4500
September	1st to 10th	Day	11% 10% 4 7% 4 4 5% 4 5% 8% 39%	2280
	11th to 20th	Day	8% 11% 3 8% 6% 4 5% 5% 6% 8% 37%	2165
	21st to end	Day	8% 9% 4 9% 6% 7% 5% 5% 6% 7% 33%	2090
October	1st to 10th	Day	4 8% 3 7% 5% 6% 7% 6% 8% 9% 37%	3331
	11th to 20th	Day	4 8% 4 9% 6% 6% 7% 6% 8% 11% 32%	2842
	21st to end	Day	1 8% 4 9% 6% 7% 6% 5% 8% 9% 37%	3101
November	1st to 10th	Day	1 7% 4 12% 8% 7% 8% 6% 9% 11% 27%	1679
	11th to 20th	Day	1 6% 3 9% 7% 7% 8% 6% 11% 11% 31%	1400
	21st to end	Day	1 7% 4 11% 8% 9% 7% 6% 7% 10% 31%	1400
December	1st to 10th	Day	1 3 2 9% 8% 6% 7% 7% 11% 12% 34%	2290
	11th to 20th	Day	5% 3 10% 7% 9% 9% 7% 11% 11% 29%	2642
	21st to end	Day	4 3 9% 7% 7% 7% 7% 12% 11% 35%	3498
January	1st to 10th	Night	3 4 16% 10% 10% 8% 6% 11% 10% 20%	6766
	11th to 20th	Night	3 2 9% 9% 8% 8% 6% 11% 11% 33%	6574
	21st to end	Night	4 3 10% 7% 7% 8% 6% 9% 10% 36%	6952
February	1st to 10th	Night	1 8% 3 11% 10% 10% 9% 7% 10% 10% 23%	2800
	11th to 20th	Night	1 6% 4 12% 6% 8% 8% 5% 10% 11% 28%	2622
	21st to end	Night	5% 4 10% 12% 8% 8% 7% 9% 10% 27%	1980
March	1st to 10th	Night	1 7% 5% 12% 8% 8% 9% 6% 8% 9% 26%	5376
	11th to 20th	Night	2 6% 3 11% 7% 6% 8% 7% 9% 10% 31%	5251
	21st to end	Night	1 13% 8% 17% 7% 5% 6% 5% 8% 9% 21%	5125
April	1st to 10th	Night	2 11% 5% 12% 9% 7% 6% 6% 9% 9% 25%	2000
	11th to 20th	Night	3 11% 5% 13% 7% 4 5% 5% 8% 8% 30%	1801
	21st to end	Night	3 12% 4 11% 6% 5% 5% 5% 6% 7% 34%	1740
May	1st to 10th	Night	5% 22% 6% 12% 5% 4 5% 3 5% 6% 27%	2620
	11th to 20th	Night	6% 13% 4 10% 5% 6% 5% 6% 7% 9% 30%	2244
	21st to end	Night	9% 12% 4 10% 7% 7% 6% 5% 9% 8% 24%	2414
June	1st to 10th	Night	14% 11% 3 7% 4 6% 5% 4 6% 8% 33%	1321
	11th to 20th	Night	15% 11% 4 9% 6% 6% 6% 4 6% 7% 25%	1140
	21st to end	Night	7% 6% 1 6% 5% 4 4 5% 7% 11% 43%	1140
July	1st to 10th	Night	6% 5% 2 5% 5% 4 4 4 6% 8% 51%	1900
	11th to 20th	Night	5% 4 1 3 3 3 4 3 5% 7% 62%	2220
	21st to end	Night	4 4 2 4 4 4 5% 5% 8% 10% 51%	2654
August	1st to 10th	Night	11% 10% 3 6% 3 3 4 4 6% 9% 40%	2529
	11th to 20th	Night	7% 6% 2 5% 4 3 5% 4 8% 11% 44%	2557
	21st to end	Night	8% 7% 2 6% 4 5% 4 4 6% 9% 43%	3166
September	1st to 10th	Night	8% 8% 2 5% 4 4 6% 4 6% 8% 45%	1900
	11th to 20th	Night	8% 10% 4 8% 5% 4 5% 3 6% 7% 40%	2014
	21st to end	Night	5% 8% 3 8% 4 5% 5% 6% 7% 9% 40%	2090
October	1st to 10th	Night	4 7% 4 8% 4 5% 5% 5% 8% 12% 38%	3645
	11th to 20th	Night	3 8% 3 9% 5% 6% 7% 5% 8% 10% 37%	4086
	21st to end	Night	2 7% 4 11% 7% 7% 6% 5% 7% 8% 35%	4457
November	1st to 10th	Night	1 9% 5% 11% 9% 8% 8% 6% 9% 9% 25%	2598
	11th to 20th	Night	1 5% 3 10% 8% 8% 10% 7% 9% 11% 28%	3000
	21st to end	Night	1 7% 4 11% 9% 7% 8% 6% 9% 9% 28%	3000
December	1st to 10th	Night	1 5% 2 9% 6% 6% 8% 8% 14% 11% 30%	4890
	11th to 20th	Night	4 4 13% 8% 9% 9% 8% 12% 12% 23%	5550
	21st to end	Night	1 5% 3 10% 8% 8% 8% 7% 11% 12% 28%	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	46% 11% 16% 18% 8% 1	3179
	11th to 20th	Day	39% 12% 15% 17% 13% 4	3391
	21st to end	Day	29% 14% 27% 21% 7%	4004
February	1st to 10th	Day	44% 12% 17% 13% 11% 3	1600
	11th to 20th	Day	45% 12% 14% 20% 9% 1	1667
	21st to end	Day	49% 13% 13% 16% 8% 1	1650
March	1st to 10th	Day	40% 13% 17% 16% 14%	4518
	11th to 20th	Day	36% 14% 19% 21% 10%	4736
	21st to end	Day	58% 10% 12% 12% 8%	5836
April	1st to 10th	Day	55% 15% 15% 11% 3	2400
	11th to 20th	Day	57% 11% 13% 15% 4	2550
	21st to end	Day	59% 10% 12% 15% 4	2657
May	1st to 10th	Day	58% 8% 15% 17% 3	4560
	11th to 20th	Day	50% 11% 15% 19% 6%	4659
	21st to end	Day	57% 16% 13% 10% 4	5162
June	1st to 10th	Day	56% 10% 13% 14% 5% 1	2855
	11th to 20th	Day	60% 9% 12% 13% 6%	3040
	21st to end	Day	50% 9% 17% 16% 8% 1	3040
July	1st to 10th	Day	34% 7% 11% 22% 21% 5%	4963
	11th to 20th	Day	27% 6% 13% 31% 21% 3	4659
	21st to end	Day	32% 8% 16% 26% 17% 1	4740
August	1st to 10th	Day	40% 9% 13% 30% 7%	4384
	11th to 20th	Day	36% 10% 21% 27% 6% 1	4313
	21st to end	Day	39% 9% 22% 21% 7% 1	4499
September	1st to 10th	Day	41% 8% 18% 23% 9% 1	2280
	11th to 20th	Day	42% 9% 14% 25% 9% 1	2165
	21st to end	Day	43% 11% 16% 19% 9% 1	2090
October	1st to 10th	Day	38% 9% 24% 22% 6%	3331
	11th to 20th	Day	40% 10% 22% 23% 6%	2842
	21st to end	Day	36% 11% 25% 23% 5%	3101
November	1st to 10th	Day	44% 15% 19% 15% 6% 1	1679
	11th to 20th	Day	36% 13% 27% 17% 7%	1400
	21st to end	Day	40% 13% 20% 19% 5% 3	1400
December	1st to 10th	Day	38% 19% 25% 11% 6%	2290
	11th to 20th	Day	39% 13% 23% 19% 5% 1	2644
	21st to end	Day	33% 13% 19% 23% 12% 1	3498
January	1st to 10th	Night	49% 15% 16% 14% 5% 1	6766
	11th to 20th	Night	39% 15% 15% 13% 14% 4	6614
	21st to end	Night	34% 13% 28% 19% 6% 1	6952
February	1st to 10th	Night	48% 12% 13% 14% 10% 2	2800
	11th to 20th	Night	43% 12% 16% 18% 10%	2624
	21st to end	Night	44% 11% 14% 21% 9% 1	1980
March	1st to 10th	Night	43% 13% 17% 17% 11%	5376
	11th to 20th	Night	36% 14% 19% 22% 9%	5251
	21st to end	Night	53% 9% 12% 17% 8%	5125
April	1st to 10th	Night	46% 15% 16% 17% 6%	2000
	11th to 20th	Night	47% 9% 19% 17% 8%	1801
	21st to end	Night	46% 11% 17% 20% 5% 1	1740
May	1st to 10th	Night	56% 6% 16% 19% 3	2620
	11th to 20th	Night	43% 15% 15% 22% 6%	2244
	21st to end	Night	45% 18% 16% 16% 5%	2414
June	1st to 10th	Night	47% 8% 16% 21% 7% 1	1321
	11th to 20th	Night	53% 10% 16% 16% 5%	1140
	21st to end	Night	32% 8% 26% 26% 7% 1	1140
July	1st to 10th	Night	30% 7% 14% 29% 20% 1	1870
	11th to 20th	Night	21% 6% 17% 36% 18% 1	2178
	21st to end	Night	26% 7% 21% 32% 14% 1	2570
August	1st to 10th	Night	37% 7% 18% 33% 4	2521
	11th to 20th	Night	31% 9% 28% 26% 6%	2581
	21st to end	Night	34% 10% 26% 24% 6%	3166
September	1st to 10th	Night	34% 9% 20% 26% 9% 1	1900
	11th to 20th	Night	40% 9% 18% 23% 10% 1	2014
	21st to end	Night	35% 12% 21% 23% 9%	2090
October	1st to 10th	Night	36% 10% 24% 21% 8%	3645
	11th to 20th	Night	38% 10% 23% 23% 6%	4086
	21st to end	Night	40% 11% 21% 23% 5%	4457
November	1st to 10th	Night	48% 15% 14% 14% 7% 1	2598
	11th to 20th	Night	39% 17% 20% 16% 8% 1	3000
	21st to end	Night	43% 14% 17% 16% 6% 3	3000
December	1st to 10th	Night	44% 16% 19% 14% 7% 1	4890
	11th to 20th	Night	45% 15% 20% 14% 6%	5547
	21st to end	Night	39% 12% 21% 20% 7% 1	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	12% 19% 36% 24% 10% 2	200
	11th to 20th	Day	14% 16% 44% 20% 5% 2	200
	21st to end	Day	10% 31% 40% 11% 5% 1	220
February	1st to 10th	Day	18% 22% 38% 16% 5% 2	200
	11th to 20th	Day	12% 19% 39% 24% 6%	270
	21st to end	Day	17% 23% 37% 16% 6% 1	414
March	1st to 10th	Day	16% 26% 32% 17% 7% 2	500
	11th to 20th	Day	14% 26% 34% 20% 4 1	500
	21st to end	Day	17% 25% 32% 19% 5% 2	550
April	1st to 10th	Day	20% 25% 32% 16% 5% 1	500
	11th to 20th	Day	13% 27% 34% 17% 7% 2	492
	21st to end	Day	19% 23% 28% 20% 8% 1	500
May	1st to 10th	Day	20% 18% 36% 19% 6% 1	503
	11th to 20th	Day	16% 11% 30% 28% 13% 2	647
	21st to end	Day	24% 14% 28% 22% 10% 2	734
June	1st to 10th	Day	21% 22% 31% 20% 5% 1	685
	11th to 20th	Day	26% 20% 30% 17% 7% 1	870
	21st to end	Day	17% 16% 30% 24% 10% 3	870
July	1st to 10th	Day	14% 16% 33% 26% 9% 2	851
	11th to 20th	Day	16% 12% 36% 23% 12% 1	668
	21st to end	Day	11% 17% 35% 23% 11% 3	597
August	1st to 10th	Day	14% 14% 33% 25% 11% 2	487
	11th to 20th	Day	11% 21% 38% 21% 8% 2	477
	21st to end	Day	17% 22% 34% 20% 6% 1	539
September	1st to 10th	Day	19% 25% 29% 21% 5% 1	490
	11th to 20th	Day	20% 19% 36% 19% 5% 1	490
	21st to end	Day	21% 28% 30% 14% 5% 1	490
October	1st to 10th	Day	21% 24% 29% 18% 6% 2	485
	11th to 20th	Day	19% 23% 33% 19% 5%	300
	21st to end	Day	18% 23% 39% 15% 4 1	330
November	1st to 10th	Day	15% 27% 40% 13% 5% 1	283
	11th to 20th	Day	20% 25% 40% 10% 6% 1	200
	21st to end	Day	15% 27% 30% 17% 6% 6%	200
December	1st to 10th	Day	11% 26% 37% 18% 6% 4	200
	11th to 20th	Day	11% 25% 41% 20% 4 1	200
	21st to end	Day	11% 15% 45% 20% 7% 1	220
January	1st to 10th	Night	9% 21% 49% 16% 4	1000
	11th to 20th	Night	8% 26% 45% 17% 4 1	925
	21st to end	Night	7% 29% 43% 15% 5%	880
February	1st to 10th	Night	10% 21% 38% 22% 8% 1	800
	11th to 20th	Night	7% 18% 44% 24% 6%	784
	21st to end	Night	8% 14% 41% 23% 12% 1	660
March	1st to 10th	Night	6% 20% 41% 23% 9% 1	800
	11th to 20th	Night	6% 19% 45% 22% 7% 1	800
	21st to end	Night	8% 16% 37% 28% 10% 1	880
April	1st to 10th	Night	9% 15% 36% 28% 11% 1	800
	11th to 20th	Night	10% 13% 43% 24% 10%	613
	21st to end	Night	12% 13% 37% 30% 8% 1	540
May	1st to 10th	Night	13% 9% 31% 34% 12% 1	400
	11th to 20th	Night	13% 4 28% 38% 17% 1	375
	21st to end	Night	20% 9% 25% 32% 13%	411
June	1st to 10th	Night	19% 8% 34% 28% 10% 1	380
	11th to 20th	Night	21% 10% 31% 27% 10%	380
	21st to end	Night	12% 9% 29% 31% 18% 1	380
July	1st to 10th	Night	12% 5% 32% 34% 15%	370
	11th to 20th	Night	13% 8% 29% 38% 13%	368
	21st to end	Night	6% 6% 25% 44% 18% 1	416
August	1st to 10th	Night	13% 4 19% 37% 25% 2	378
	11th to 20th	Night	12% 6% 25% 36% 20% 1	410
	21st to end	Night	13% 11% 31% 34% 11% 1	634
September	1st to 10th	Night	14% 12% 30% 31% 11% 2	760
	11th to 20th	Night	14% 9% 31% 30% 13% 2	760
	21st to end	Night	17% 19% 31% 21% 10% 1	760
October	1st to 10th	Night	13% 15% 36% 27% 10%	760
	11th to 20th	Night	16% 16% 41% 21% 6%	760
	21st to end	Night	12% 20% 42% 21% 4	836
November	1st to 10th	Night	10% 25% 44% 15% 5%	810
	11th to 20th	Night	13% 24% 46% 13% 3	1000
	21st to end	Night	10% 24% 42% 17% 6% 1	1000
December	1st to 10th	Night	8% 26% 39% 20% 7%	1000
	11th to 20th	Night	8% 23% 45% 17% 6% 1	1000
	21st to end	Night	5% 22% 47% 19% 6% 1	1100

Page generated at 2025-05-08 07:33:57. Version ac07

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