Dease Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dease Lake clear sky chart from 2005-11-06 to 2026-06-01.

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	8% 12% 5% 12% 8% 7% 7% 5% 7% 8% 22%	135465
	Night	5% 11% 5% 13% 9% 8% 8% 6% 8% 8% 19%	136334
Transparency	Day	54% 10% 15% 15% 5% 1	135129
	Night	55% 11% 15% 13% 6% 1	136250
Seeing	Day	16% 13% 24% 25% 17% 5%	19223
	Night	12% 9% 24% 32% 19% 3	26464

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	2 11% 5% 15% 12% 11% 10% 6% 9% 8% 10%	3203
	11th to 20th	Day	4 14% 4 13% 5% 7% 10% 7% 7% 9% 19%	3522
	21st to end	Day	3 14% 7% 11% 7% 7% 8% 6% 11% 10% 17%	4109
February	1st to 10th	Day	4 12% 5% 13% 9% 8% 7% 6% 8% 7% 21%	1622
	11th to 20th	Day	2 12% 6% 12% 9% 8% 7% 6% 8% 8% 23%	1640
	21st to end	Day	1 10% 6% 15% 9% 9% 7% 6% 8% 6% 23%	1558
March	1st to 10th	Day	1 8% 4 13% 9% 9% 7% 7% 10% 10% 23%	4596
	11th to 20th	Day	1 9% 5% 18% 9% 7% 7% 6% 8% 9% 20%	4912
	21st to end	Day	1 11% 5% 12% 7% 6% 7% 5% 7% 8% 30%	5893
April	1st to 10th	Day	2 15% 9% 16% 9% 7% 7% 5% 7% 6% 17%	2636
	11th to 20th	Day	3 15% 8% 14% 9% 7% 7% 5% 6% 6% 20%	2698
	21st to end	Day	4 19% 6% 14% 8% 7% 7% 5% 6% 6% 18%	3008
May	1st to 10th	Day	6% 15% 6% 13% 7% 6% 7% 6% 7% 7% 21%	6930
	11th to 20th	Day	7% 18% 6% 14% 8% 8% 8% 5% 6% 5% 16%	7015
	21st to end	Day	8% 12% 5% 13% 8% 8% 7% 5% 7% 7% 19%	8405
June	1st to 10th	Day	14% 13% 4 10% 7% 6% 6% 5% 7% 7% 22%	3401
	11th to 20th	Day	15% 12% 4 12% 8% 6% 6% 4 6% 7% 20%	3400
	21st to end	Day	13% 11% 4 12% 8% 7% 6% 5% 7% 8% 20%	3400
July	1st to 10th	Day	9% 7% 3 9% 7% 6% 7% 5% 8% 9% 29%	7700
	11th to 20th	Day	12% 10% 4 10% 7% 7% 6% 5% 6% 8% 25%	7332
	21st to end	Day	15% 7% 3 9% 6% 6% 6% 5% 7% 9% 26%	7817
August	1st to 10th	Day	9% 6% 2 5% 4 4 4 3 5% 6% 52%	4869
	11th to 20th	Day	13% 8% 2 7% 5% 5% 5% 4 6% 8% 38%	4516
	21st to end	Day	18% 12% 3 9% 6% 6% 6% 5% 5% 6% 24%	4766
September	1st to 10th	Day	15% 11% 3 11% 7% 6% 5% 5% 6% 8% 24%	2556
	11th to 20th	Day	13% 11% 4 10% 6% 6% 5% 5% 6% 7% 27%	2270
	21st to end	Day	15% 15% 5% 12% 7% 7% 6% 5% 7% 6% 16%	2200
October	1st to 10th	Day	7% 12% 5% 14% 9% 8% 7% 6% 6% 6% 20%	3256
	11th to 20th	Day	6% 16% 6% 15% 8% 7% 7% 5% 6% 6% 19%	2933
	21st to end	Day	5% 12% 4 12% 8% 9% 8% 6% 7% 9% 20%	3031
November	1st to 10th	Day	5% 17% 7% 13% 8% 7% 8% 5% 8% 7% 14%	1442
	11th to 20th	Day	4 16% 6% 16% 9% 10% 7% 6% 6% 5% 14%	1470
	21st to end	Day	2 15% 7% 13% 10% 8% 9% 5% 6% 9% 16%	1206
December	1st to 10th	Day	5% 16% 7% 16% 10% 11% 8% 6% 8% 5% 8%	1680
	11th to 20th	Day	2 10% 6% 19% 10% 10% 7% 5% 6% 10% 15%	1932
	21st to end	Day	2 14% 7% 17% 11% 11% 9% 6% 8% 8% 8%	2541
January	1st to 10th	Night	2 8% 5% 19% 13% 11% 9% 7% 9% 9% 7%	9747
	11th to 20th	Night	2 10% 5% 14% 8% 9% 8% 6% 7% 9% 21%	9376
	21st to end	Night	3 16% 6% 12% 8% 7% 8% 7% 10% 9% 14%	10070
February	1st to 10th	Night	4 13% 6% 13% 9% 7% 7% 6% 7% 8% 21%	2995
	11th to 20th	Night	2 12% 6% 15% 9% 8% 7% 5% 8% 8% 20%	2867
	21st to end	Night	2 11% 6% 14% 9% 8% 7% 4 6% 7% 27%	2245
March	1st to 10th	Night	1 8% 4 13% 10% 10% 9% 6% 9% 9% 22%	5498
	11th to 20th	Night	1 9% 6% 16% 9% 8% 9% 7% 9% 8% 18%	5298
	21st to end	Night	2 10% 5% 12% 7% 7% 7% 7% 9% 12% 23%	5297
April	1st to 10th	Night	3 12% 6% 13% 8% 6% 6% 6% 9% 8% 22%	1984
	11th to 20th	Night	4 10% 5% 9% 10% 8% 7% 5% 8% 8% 25%	1871
	21st to end	Night	4 12% 4 10% 8% 10% 7% 6% 8% 7% 25%	1611
May	1st to 10th	Night	4 10% 4 10% 8% 7% 6% 5% 9% 8% 28%	3250
	11th to 20th	Night	6% 13% 5% 13% 8% 7% 7% 6% 7% 8% 22%	3098
	21st to end	Night	7% 11% 5% 12% 7% 6% 8% 5% 8% 8% 25%	2712
June	1st to 10th	Night	11% 10% 4 9% 6% 5% 5% 5% 6% 10% 29%	1000
	11th to 20th	Night	12% 9% 5% 9% 7% 6% 8% 5% 8% 9% 22%	1000
	21st to end	Night	13% 8% 3 10% 8% 7% 7% 5% 7% 9% 23%	1000
July	1st to 10th	Night	11% 8% 4 9% 6% 5% 6% 4 6% 7% 33%	2260
	11th to 20th	Night	11% 10% 4 10% 6% 7% 7% 6% 7% 9% 24%	2625
	21st to end	Night	17% 7% 3 7% 6% 7% 5% 5% 7% 10% 26%	3025
August	1st to 10th	Night	8% 5% 2 5% 4 5% 4 3 7% 7% 50%	2281
	11th to 20th	Night	8% 5% 2 8% 6% 5% 5% 5% 7% 10% 40%	2539
	21st to end	Night	17% 13% 4 10% 7% 5% 5% 4 6% 6% 23%	3142
September	1st to 10th	Night	14% 11% 4 11% 6% 7% 6% 5% 6% 7% 22%	1841
	11th to 20th	Night	12% 12% 4 9% 6% 7% 6% 5% 7% 7% 26%	2130
	21st to end	Night	12% 13% 5% 11% 6% 7% 7% 4 6% 7% 21%	2200
October	1st to 10th	Night	8% 12% 4 12% 8% 8% 7% 5% 9% 8% 19%	3938
	11th to 20th	Night	8% 15% 5% 13% 9% 8% 9% 6% 7% 6% 14%	4215
	21st to end	Night	5% 14% 5% 13% 8% 8% 7% 5% 8% 8% 18%	4749
November	1st to 10th	Night	5% 16% 7% 15% 9% 8% 7% 5% 7% 7% 15%	3076
	11th to 20th	Night	3 16% 7% 16% 9% 9% 8% 6% 8% 6% 13%	3150
	21st to end	Night	3 15% 6% 16% 10% 8% 8% 5% 7% 8% 14%	3387
December	1st to 10th	Night	6% 17% 6% 16% 11% 10% 8% 6% 6% 6% 9%	5720
	11th to 20th	Night	2 11% 6% 17% 11% 10% 9% 6% 7% 8% 13%	6480
	21st to end	Night	2 11% 7% 16% 10% 10% 10% 7% 9% 8% 11%	8657

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% 7% 15% 10% 8% 3	3203
	11th to 20th	Day	50% 12% 15% 9% 8% 6%	3540
	21st to end	Day	50% 12% 18% 13% 6%	4110
February	1st to 10th	Day	55% 9% 9% 14% 12% 1	1622
	11th to 20th	Day	54% 10% 16% 12% 8% 1	1648
	21st to end	Day	56% 6% 15% 14% 8% 1	1558
March	1st to 10th	Day	46% 8% 16% 18% 13% 1	4596
	11th to 20th	Day	52% 8% 14% 15% 11%	4912
	21st to end	Day	44% 10% 17% 23% 6%	5893
April	1st to 10th	Day	64% 10% 13% 10% 3	2636
	11th to 20th	Day	61% 8% 11% 14% 6%	2698
	21st to end	Day	61% 9% 16% 12% 2	3008
May	1st to 10th	Day	52% 9% 15% 18% 6%	6930
	11th to 20th	Day	62% 9% 13% 12% 4	7018
	21st to end	Day	54% 8% 15% 19% 4	8406
June	1st to 10th	Day	57% 9% 15% 15% 4	3401
	11th to 20th	Day	60% 9% 13% 12% 5%	3400
	21st to end	Day	61% 12% 15% 11% 2	3400
July	1st to 10th	Day	45% 11% 22% 17% 4	7616
	11th to 20th	Day	54% 9% 20% 16% 1	7243
	21st to end	Day	50% 13% 19% 17% 2	7597
August	1st to 10th	Day	33% 8% 13% 24% 19% 3	4851
	11th to 20th	Day	43% 8% 15% 25% 7% 3	4559
	21st to end	Day	61% 9% 13% 15% 2	4765
September	1st to 10th	Day	58% 11% 14% 14% 4	2556
	11th to 20th	Day	56% 10% 13% 17% 3	2270
	21st to end	Day	66% 12% 10% 11% 1	2200
October	1st to 10th	Day	60% 9% 15% 14% 3	3256
	11th to 20th	Day	63% 8% 15% 13% 1	2933
	21st to end	Day	53% 12% 22% 12% 2	3031
November	1st to 10th	Day	64% 11% 12% 10% 3	1442
	11th to 20th	Day	67% 10% 11% 10% 3	1470
	21st to end	Day	60% 11% 14% 9% 6%	1206
December	1st to 10th	Day	64% 12% 15% 7% 2	1680
	11th to 20th	Day	57% 10% 17% 9% 6% 1	1934
	21st to end	Day	61% 14% 13% 6% 5% 1	2541
January	1st to 10th	Night	61% 9% 14% 8% 8% 1	9748
	11th to 20th	Night	50% 11% 15% 11% 9% 4	9420
	21st to end	Night	54% 13% 16% 12% 5%	10070
February	1st to 10th	Night	55% 7% 11% 14% 11% 1	2995
	11th to 20th	Night	58% 8% 15% 10% 8% 1	2870
	21st to end	Night	54% 6% 14% 16% 8% 2	2245
March	1st to 10th	Night	48% 7% 15% 13% 15% 1	5498
	11th to 20th	Night	53% 10% 17% 11% 9%	5299
	21st to end	Night	43% 11% 17% 22% 7%	5297
April	1st to 10th	Night	55% 10% 14% 17% 4	1984
	11th to 20th	Night	51% 11% 14% 14% 9%	1871
	21st to end	Night	54% 11% 18% 15% 2	1611
May	1st to 10th	Night	45% 11% 14% 21% 9%	3247
	11th to 20th	Night	54% 11% 15% 14% 5%	3098
	21st to end	Night	52% 8% 13% 22% 5%	2712
June	1st to 10th	Night	50% 10% 13% 20% 7%	1000
	11th to 20th	Night	54% 9% 16% 16% 4	1000
	21st to end	Night	55% 11% 18% 12% 2 1	1000
July	1st to 10th	Night	46% 10% 22% 17% 5%	2235
	11th to 20th	Night	52% 10% 23% 15%	2592
	21st to end	Night	48% 12% 24% 14% 2	2940
August	1st to 10th	Night	31% 7% 15% 26% 18% 2	2274
	11th to 20th	Night	37% 10% 17% 25% 11% 1	2562
	21st to end	Night	62% 8% 16% 12% 3	3142
September	1st to 10th	Night	58% 10% 15% 12% 4	1841
	11th to 20th	Night	53% 11% 15% 17% 4	2130
	21st to end	Night	61% 10% 12% 14% 3	2200
October	1st to 10th	Night	57% 11% 14% 16% 3	3938
	11th to 20th	Night	64% 11% 13% 10% 2	4215
	21st to end	Night	56% 11% 19% 12% 2	4749
November	1st to 10th	Night	62% 10% 13% 12% 3	3076
	11th to 20th	Night	64% 10% 13% 10% 3	3150
	21st to end	Night	62% 10% 13% 10% 4 1	3387
December	1st to 10th	Night	66% 12% 11% 8% 3	5720
	11th to 20th	Night	60% 11% 15% 10% 3 1	6477
	21st to end	Night	57% 15% 13% 8% 6% 1	8657

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	10% 8% 23% 29% 23% 7%	220
	11th to 20th	Day	10% 14% 24% 32% 15% 6%	220
	21st to end	Day	8% 15% 22% 30% 20% 4	242
February	1st to 10th	Day	12% 11% 26% 32% 14% 5%	372
	11th to 20th	Day	10% 13% 24% 30% 17% 6%	425
	21st to end	Day	9% 10% 34% 26% 17% 4	355
March	1st to 10th	Day	8% 14% 33% 19% 18% 8%	430
	11th to 20th	Day	10% 14% 28% 27% 17% 4	492
	21st to end	Day	7% 14% 25% 25% 22% 7%	594
April	1st to 10th	Day	11% 14% 29% 29% 14% 2	540
	11th to 20th	Day	11% 14% 26% 27% 17% 5%	532
	21st to end	Day	14% 18% 28% 24% 13% 3	745
May	1st to 10th	Day	16% 19% 28% 23% 12% 2	753
	11th to 20th	Day	15% 14% 25% 28% 13% 6%	775
	21st to end	Day	15% 15% 23% 25% 16% 6%	985
June	1st to 10th	Day	20% 11% 23% 25% 16% 5%	931
	11th to 20th	Day	19% 8% 24% 24% 20% 5%	930
	21st to end	Day	17% 9% 18% 24% 22% 9%	930
July	1st to 10th	Day	15% 9% 18% 28% 25% 6%	916
	11th to 20th	Day	21% 10% 24% 22% 20% 4	756
	21st to end	Day	19% 8% 23% 20% 22% 8%	794
August	1st to 10th	Day	16% 11% 22% 23% 19% 9%	726
	11th to 20th	Day	24% 17% 25% 18% 13% 3	715
	21st to end	Day	25% 12% 19% 21% 16% 6%	646
September	1st to 10th	Day	21% 14% 24% 22% 14% 5%	530
	11th to 20th	Day	23% 15% 22% 21% 16% 4	530
	21st to end	Day	28% 17% 25% 21% 6% 3	530
October	1st to 10th	Day	19% 16% 23% 26% 16% 1	477
	11th to 20th	Day	18% 17% 30% 24% 9% 2	420
	21st to end	Day	13% 14% 28% 26% 15% 4	370
November	1st to 10th	Day	14% 14% 33% 20% 15% 4	220
	11th to 20th	Day	8% 10% 30% 24% 21% 6%	220
	21st to end	Day	10% 12% 24% 30% 21% 3	220
December	1st to 10th	Day	5% 13% 29% 29% 21% 4	220
	11th to 20th	Day	7% 10% 20% 35% 20% 8%	220
	21st to end	Day	6% 8% 20% 34% 22% 10%	242
January	1st to 10th	Night	8% 8% 26% 36% 18% 4	1086
	11th to 20th	Night	12% 12% 29% 32% 13% 2	950
	21st to end	Night	11% 13% 26% 31% 17% 3	1045
February	1st to 10th	Night	12% 8% 27% 33% 17% 3	950
	11th to 20th	Night	7% 10% 28% 35% 17% 4	934
	21st to end	Night	7% 8% 26% 37% 19% 4	703
March	1st to 10th	Night	6% 12% 27% 31% 18% 5%	840
	11th to 20th	Night	6% 11% 28% 35% 17% 4	840
	21st to end	Night	6% 8% 21% 30% 28% 6%	792
April	1st to 10th	Night	8% 8% 22% 31% 25% 5%	630
	11th to 20th	Night	6% 8% 23% 35% 25% 4	623
	21st to end	Night	7% 7% 23% 37% 21% 4	557
May	1st to 10th	Night	12% 10% 23% 33% 19% 4	420
	11th to 20th	Night	9% 6% 19% 34% 30% 3	414
	21st to end	Night	11% 6% 20% 32% 26% 5%	455
June	1st to 10th	Night	16% 8% 22% 28% 23% 4	400
	11th to 20th	Night	17% 6% 20% 28% 27% 3	400
	21st to end	Night	14% 7% 21% 28% 29% 2	400
July	1st to 10th	Night	15% 5% 15% 35% 26% 4	390
	11th to 20th	Night	17% 7% 15% 32% 26% 3	388
	21st to end	Night	15% 5% 20% 25% 29% 6%	438
August	1st to 10th	Night	16% 6% 17% 26% 30% 5%	398
	11th to 20th	Night	16% 8% 20% 29% 23% 5%	567
	21st to end	Night	23% 7% 17% 22% 26% 4	660
September	1st to 10th	Night	22% 9% 19% 29% 18% 3	600
	11th to 20th	Night	19% 10% 19% 27% 21% 3	730
	21st to end	Night	23% 14% 27% 23% 13% 2	800
October	1st to 10th	Night	19% 12% 20% 31% 17% 2	800
	11th to 20th	Night	17% 14% 27% 27% 13% 2	800
	21st to end	Night	16% 12% 23% 32% 13% 3	880
November	1st to 10th	Night	15% 10% 27% 31% 15% 3	930
	11th to 20th	Night	12% 8% 25% 34% 17% 4	950
	21st to end	Night	12% 12% 26% 33% 16% 2	1098
December	1st to 10th	Night	13% 11% 25% 36% 15% 2	1160
	11th to 20th	Night	9% 8% 22% 38% 20% 4	1160
	21st to end	Night	7% 11% 24% 32% 21% 5%	1276

Page generated at 2026-05-28 22:53:31. Version ac07

Copyright © 2026 Attilla Danko.