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 2025-02-06.

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% 7% 7% 6% 5% 7% 7% 23%	110913
	Night	5% 12% 5% 13% 9% 8% 7% 5% 7% 8% 19%	115953
Transparency	Day	55% 10% 15% 14% 5% 1	110624
	Night	56% 10% 15% 12% 6% 1	115889
Seeing	Day	16% 13% 24% 25% 17% 5%	17378
	Night	13% 10% 24% 31% 19% 3	24752

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 12% 6% 15% 11% 11% 8% 6% 9% 9% 11%	2463
	11th to 20th	Day	2 17% 5% 15% 6% 6% 9% 6% 6% 8% 20%	2702
	21st to end	Day	3 15% 7% 12% 8% 7% 8% 6% 10% 10% 17%	3173
February	1st to 10th	Day	4 12% 5% 13% 8% 7% 7% 6% 8% 7% 21%	1506
	11th to 20th	Day	2 12% 6% 12% 9% 8% 7% 6% 7% 8% 22%	1480
	21st to end	Day	2 10% 6% 15% 8% 9% 7% 6% 8% 6% 23%	1414
March	1st to 10th	Day	2 8% 3 13% 9% 8% 7% 8% 11% 10% 23%	3126
	11th to 20th	Day	2 11% 5% 16% 9% 7% 7% 6% 7% 9% 21%	3352
	21st to end	Day	2 14% 6% 13% 7% 6% 6% 5% 7% 7% 28%	4027
April	1st to 10th	Day	3 15% 9% 16% 9% 7% 7% 5% 7% 6% 17%	2384
	11th to 20th	Day	3 15% 8% 14% 9% 7% 7% 5% 6% 6% 21%	2438
	21st to end	Day	5% 20% 6% 14% 8% 7% 6% 5% 6% 6% 17%	2721
May	1st to 10th	Day	6% 17% 6% 12% 6% 6% 6% 5% 6% 7% 23%	4740
	11th to 20th	Day	7% 19% 5% 13% 7% 7% 6% 5% 6% 5% 19%	4781
	21st to end	Day	11% 14% 4 10% 7% 6% 6% 5% 7% 8% 21%	5726
June	1st to 10th	Day	14% 13% 4 10% 7% 6% 5% 5% 7% 7% 22%	3230
	11th to 20th	Day	14% 12% 4 12% 8% 6% 6% 4 6% 7% 20%	3230
	21st to end	Day	14% 11% 4 12% 7% 7% 6% 5% 7% 7% 20%	3230
July	1st to 10th	Day	8% 6% 3 7% 6% 5% 7% 5% 8% 9% 36%	5380
	11th to 20th	Day	14% 11% 5% 11% 8% 7% 6% 5% 5% 7% 22%	5124
	21st to end	Day	19% 8% 3 9% 6% 6% 5% 4 6% 8% 26%	5441
August	1st to 10th	Day	9% 6% 2 5% 4 4 4 3 5% 6% 53%	4719
	11th to 20th	Day	12% 8% 2 7% 5% 5% 5% 4 6% 8% 39%	4375
	21st to end	Day	18% 13% 4 10% 6% 6% 6% 5% 5% 6% 22%	4620
September	1st to 10th	Day	15% 12% 3 11% 7% 6% 6% 5% 6% 7% 22%	2428
	11th to 20th	Day	13% 11% 4 10% 6% 6% 5% 5% 6% 7% 27%	2157
	21st to end	Day	16% 15% 5% 12% 7% 7% 6% 4 7% 6% 15%	2090
October	1st to 10th	Day	7% 12% 5% 15% 9% 8% 7% 6% 6% 7% 19%	3157
	11th to 20th	Day	7% 16% 6% 15% 8% 7% 7% 5% 6% 6% 18%	2843
	21st to end	Day	5% 13% 4 12% 7% 9% 8% 5% 7% 9% 20%	2937
November	1st to 10th	Day	5% 17% 6% 13% 8% 7% 8% 5% 8% 7% 14%	1372
	11th to 20th	Day	4 17% 6% 16% 9% 10% 7% 6% 6% 5% 14%	1400
	21st to end	Day	2 15% 8% 13% 10% 8% 8% 5% 6% 9% 16%	1149
December	1st to 10th	Day	5% 16% 7% 16% 10% 11% 8% 6% 8% 5% 8%	1630
	11th to 20th	Day	2 9% 6% 19% 10% 10% 7% 5% 6% 10% 15%	1882
	21st to end	Day	2 14% 7% 17% 11% 11% 9% 5% 8% 8% 8%	2486
January	1st to 10th	Night	2 9% 6% 19% 13% 11% 8% 7% 9% 9% 8%	7525
	11th to 20th	Night	3 12% 6% 14% 8% 8% 7% 4 6% 9% 23%	7196
	21st to end	Night	4 17% 6% 12% 9% 7% 8% 6% 9% 8% 15%	7782
February	1st to 10th	Night	4 14% 6% 13% 9% 7% 7% 5% 7% 8% 21%	2783
	11th to 20th	Night	2 13% 5% 15% 9% 8% 7% 5% 8% 8% 20%	2587
	21st to end	Night	2 11% 5% 13% 9% 9% 6% 4 6% 7% 28%	2037
March	1st to 10th	Night	1 8% 4 12% 9% 8% 8% 5% 9% 10% 25%	3738
	11th to 20th	Night	1 11% 6% 14% 9% 7% 8% 7% 8% 8% 20%	3622
	21st to end	Night	3 12% 5% 11% 7% 7% 7% 8% 8% 9% 22%	3619
April	1st to 10th	Night	3 12% 7% 12% 8% 7% 6% 6% 9% 8% 23%	1796
	11th to 20th	Night	4 10% 5% 10% 10% 8% 7% 5% 8% 8% 25%	1691
	21st to end	Night	4 12% 4 10% 8% 10% 7% 6% 8% 7% 25%	1458
May	1st to 10th	Night	5% 13% 5% 10% 8% 7% 5% 5% 7% 7% 27%	2220
	11th to 20th	Night	5% 11% 4 9% 6% 7% 6% 6% 8% 9% 29%	2113
	21st to end	Night	9% 12% 3 9% 6% 6% 7% 5% 8% 8% 26%	1849
June	1st to 10th	Night	11% 11% 4 9% 7% 5% 5% 5% 6% 10% 28%	950
	11th to 20th	Night	12% 9% 5% 9% 7% 6% 8% 6% 8% 9% 21%	950
	21st to end	Night	14% 8% 3 9% 8% 7% 7% 5% 7% 9% 24%	950
July	1st to 10th	Night	8% 6% 3 8% 6% 5% 6% 5% 7% 8% 39%	1580
	11th to 20th	Night	13% 12% 5% 11% 7% 7% 7% 5% 7% 7% 18%	1833
	21st to end	Night	21% 7% 3 7% 6% 6% 5% 4 5% 7% 28%	2110
August	1st to 10th	Night	8% 5% 2 4 4 4 4 3 7% 7% 52%	2211
	11th to 20th	Night	8% 5% 2 8% 6% 5% 5% 5% 7% 10% 41%	2460
	21st to end	Night	18% 13% 4 10% 7% 5% 5% 4 6% 6% 21%	3046
September	1st to 10th	Night	14% 11% 4 12% 7% 7% 6% 5% 6% 7% 20%	1749
	11th to 20th	Night	12% 11% 4 8% 6% 7% 6% 5% 7% 7% 27%	2023
	21st to end	Night	13% 13% 5% 11% 6% 7% 6% 4 6% 7% 21%	2090
October	1st to 10th	Night	7% 12% 4 12% 9% 8% 7% 6% 8% 8% 19%	3817
	11th to 20th	Night	8% 15% 5% 14% 9% 8% 9% 6% 7% 6% 14%	4085
	21st to end	Night	5% 14% 5% 13% 8% 8% 7% 5% 8% 8% 18%	4601
November	1st to 10th	Night	5% 17% 7% 15% 9% 8% 7% 5% 7% 7% 15%	2926
	11th to 20th	Night	3 16% 7% 16% 9% 9% 7% 6% 8% 6% 13%	3000
	21st to end	Night	3 16% 6% 16% 10% 8% 8% 5% 7% 8% 14%	3226
December	1st to 10th	Night	6% 16% 6% 15% 11% 10% 8% 6% 6% 6% 9%	5550
	11th to 20th	Night	2 11% 6% 17% 11% 10% 9% 6% 8% 8% 12%	6310
	21st to end	Night	2 11% 7% 16% 11% 10% 10% 7% 9% 8% 11%	8470

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	56% 8% 16% 8% 9% 4	2463
	11th to 20th	Day	55% 9% 12% 8% 8% 8%	2720
	21st to end	Day	54% 13% 17% 10% 5%	3173
February	1st to 10th	Day	56% 9% 9% 13% 12% 1	1506
	11th to 20th	Day	56% 10% 15% 10% 7% 1	1488
	21st to end	Day	56% 7% 16% 14% 7% 1	1414
March	1st to 10th	Day	46% 7% 13% 17% 15% 1	3126
	11th to 20th	Day	53% 10% 15% 17% 5%	3352
	21st to end	Day	49% 12% 17% 16% 5%	4027
April	1st to 10th	Day	65% 9% 13% 10% 3	2384
	11th to 20th	Day	62% 8% 11% 14% 6%	2438
	21st to end	Day	63% 9% 15% 11% 2	2721
May	1st to 10th	Day	52% 10% 16% 18% 5%	4740
	11th to 20th	Day	61% 9% 12% 13% 5%	4784
	21st to end	Day	52% 9% 18% 18% 4	5727
June	1st to 10th	Day	58% 9% 14% 15% 4	3230
	11th to 20th	Day	61% 9% 13% 12% 5%	3230
	21st to end	Day	61% 12% 15% 10% 2	3230
July	1st to 10th	Day	39% 12% 26% 18% 4	5296
	11th to 20th	Day	61% 9% 16% 12% 1	5035
	21st to end	Day	55% 10% 13% 19% 3	5269
August	1st to 10th	Day	33% 8% 12% 25% 19% 4	4701
	11th to 20th	Day	43% 8% 14% 25% 7% 3	4418
	21st to end	Day	63% 9% 13% 14% 1	4619
September	1st to 10th	Day	60% 11% 13% 13% 3	2428
	11th to 20th	Day	56% 10% 13% 17% 3	2157
	21st to end	Day	67% 12% 9% 11% 1	2090
October	1st to 10th	Day	60% 9% 14% 14% 3	3157
	11th to 20th	Day	63% 8% 14% 13% 1	2843
	21st to end	Day	53% 12% 22% 12% 2	2937
November	1st to 10th	Day	64% 11% 12% 10% 3	1372
	11th to 20th	Day	67% 10% 11% 9% 3	1400
	21st to end	Day	61% 10% 14% 9% 6%	1149
December	1st to 10th	Day	64% 13% 15% 7% 2	1630
	11th to 20th	Day	58% 10% 18% 9% 5% 1	1884
	21st to end	Day	61% 14% 13% 6% 4 1	2486
January	1st to 10th	Night	61% 9% 14% 7% 8% 1	7525
	11th to 20th	Night	54% 8% 14% 10% 10% 5%	7240
	21st to end	Night	57% 13% 16% 9% 5%	7782
February	1st to 10th	Night	56% 8% 11% 14% 11% 1	2783
	11th to 20th	Night	59% 9% 15% 9% 7% 1	2590
	21st to end	Night	53% 7% 15% 16% 8% 2	2037
March	1st to 10th	Night	49% 5% 14% 15% 17% 1	3738
	11th to 20th	Night	56% 10% 17% 12% 5%	3623
	21st to end	Night	47% 11% 20% 16% 6%	3619
April	1st to 10th	Night	56% 10% 13% 17% 4	1796
	11th to 20th	Night	51% 12% 13% 14% 9%	1691
	21st to end	Night	55% 11% 17% 16% 2	1458
May	1st to 10th	Night	50% 12% 13% 20% 6%	2220
	11th to 20th	Night	47% 13% 16% 17% 7% 1	2113
	21st to end	Night	50% 10% 14% 21% 4	1849
June	1st to 10th	Night	51% 10% 12% 20% 7%	950
	11th to 20th	Night	54% 9% 16% 17% 5%	950
	21st to end	Night	55% 11% 18% 13% 2 1	950
July	1st to 10th	Night	39% 10% 24% 20% 6%	1555
	11th to 20th	Night	60% 11% 20% 9%	1800
	21st to end	Night	53% 10% 15% 19% 3	2043
August	1st to 10th	Night	31% 7% 15% 27% 19% 2	2204
	11th to 20th	Night	36% 10% 17% 25% 11% 1	2483
	21st to end	Night	63% 8% 16% 11% 1	3046
September	1st to 10th	Night	61% 10% 14% 11% 3	1749
	11th to 20th	Night	53% 11% 15% 18% 3	2023
	21st to end	Night	62% 10% 12% 13% 3	2090
October	1st to 10th	Night	57% 11% 14% 15% 3	3817
	11th to 20th	Night	64% 11% 13% 10% 1	4085
	21st to end	Night	56% 11% 19% 11% 2	4601
November	1st to 10th	Night	63% 10% 12% 11% 3	2926
	11th to 20th	Night	65% 10% 13% 9% 3	3000
	21st to end	Night	62% 10% 13% 10% 4 1	3226
December	1st to 10th	Night	65% 12% 11% 8% 3	5550
	11th to 20th	Night	61% 11% 15% 10% 3	6307
	21st to end	Night	57% 15% 13% 7% 6% 1	8470

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% 25% 28% 23% 7%	200
	11th to 20th	Day	9% 13% 25% 31% 16% 7%	200
	21st to end	Day	8% 16% 21% 30% 19% 5%	220
February	1st to 10th	Day	13% 12% 26% 31% 15% 4	331
	11th to 20th	Day	11% 13% 25% 31% 16% 5%	365
	21st to end	Day	9% 10% 36% 23% 18% 5%	307
March	1st to 10th	Day	8% 13% 34% 19% 17% 8%	370
	11th to 20th	Day	9% 15% 30% 29% 15% 3	420
	21st to end	Day	9% 15% 25% 23% 23% 6%	506
April	1st to 10th	Day	12% 14% 30% 28% 13% 2	460
	11th to 20th	Day	12% 12% 26% 29% 17% 5%	452
	21st to end	Day	14% 18% 28% 24% 13% 3	645
May	1st to 10th	Day	17% 18% 28% 23% 13% 1	653
	11th to 20th	Day	14% 13% 25% 29% 13% 6%	675
	21st to end	Day	15% 13% 23% 26% 17% 6%	861
June	1st to 10th	Day	20% 10% 23% 26% 17% 5%	870
	11th to 20th	Day	19% 8% 24% 24% 20% 5%	870
	21st to end	Day	18% 9% 19% 24% 22% 8%	870
July	1st to 10th	Day	15% 8% 17% 28% 25% 7%	856
	11th to 20th	Day	21% 10% 23% 22% 20% 3	704
	21st to end	Day	20% 8% 23% 20% 21% 8%	739
August	1st to 10th	Day	15% 11% 21% 24% 20% 9%	676
	11th to 20th	Day	24% 17% 26% 18% 12% 3	665
	21st to end	Day	27% 13% 20% 21% 14% 5%	599
September	1st to 10th	Day	22% 15% 25% 23% 12% 3	490
	11th to 20th	Day	23% 14% 21% 22% 16% 4	490
	21st to end	Day	29% 16% 25% 20% 6% 3	490
October	1st to 10th	Day	19% 16% 23% 26% 15% 1	442
	11th to 20th	Day	19% 18% 30% 23% 9% 2	390
	21st to end	Day	13% 12% 28% 27% 16% 3	342
November	1st to 10th	Day	14% 13% 33% 21% 16% 4	200
	11th to 20th	Day	9% 11% 29% 25% 22% 6%	200
	21st to end	Day	11% 13% 24% 30% 22% 2	200
December	1st to 10th	Day	5% 12% 29% 29% 22% 4	200
	11th to 20th	Day	8% 10% 22% 34% 20% 7%	200
	21st to end	Day	6% 8% 20% 35% 23% 9%	220
January	1st to 10th	Night	8% 8% 26% 36% 18% 3	1030
	11th to 20th	Night	12% 11% 29% 32% 14% 2	900
	21st to end	Night	12% 14% 26% 30% 16% 3	990
February	1st to 10th	Night	13% 8% 28% 32% 17% 2	875
	11th to 20th	Night	8% 9% 28% 35% 15% 3	834
	21st to end	Night	7% 8% 24% 36% 21% 4	637
March	1st to 10th	Night	7% 12% 26% 31% 18% 5%	760
	11th to 20th	Night	6% 12% 29% 36% 15% 2	760
	21st to end	Night	7% 9% 22% 30% 26% 7%	717
April	1st to 10th	Night	8% 9% 22% 30% 25% 5%	570
	11th to 20th	Night	6% 8% 23% 34% 25% 4	563
	21st to end	Night	8% 7% 23% 36% 22% 4	504
May	1st to 10th	Night	13% 10% 21% 32% 19% 4	380
	11th to 20th	Night	9% 6% 18% 33% 31% 3	374
	21st to end	Night	11% 6% 17% 33% 28% 5%	411
June	1st to 10th	Night	15% 8% 21% 28% 24% 4	380
	11th to 20th	Night	17% 6% 19% 28% 27% 3	380
	21st to end	Night	14% 7% 21% 27% 28% 2	380
July	1st to 10th	Night	15% 5% 15% 35% 26% 4	370
	11th to 20th	Night	17% 7% 16% 32% 26% 2	368
	21st to end	Night	16% 5% 20% 25% 29% 5%	416
August	1st to 10th	Night	16% 6% 18% 24% 31% 5%	378
	11th to 20th	Night	16% 8% 20% 29% 22% 4	538
	21st to end	Night	25% 8% 18% 21% 25% 4	627
September	1st to 10th	Night	23% 9% 20% 28% 17% 3	570
	11th to 20th	Night	20% 10% 18% 27% 22% 4	693
	21st to end	Night	23% 13% 26% 22% 13% 2	760
October	1st to 10th	Night	18% 12% 20% 31% 17% 2	760
	11th to 20th	Night	18% 14% 26% 26% 14% 2	760
	21st to end	Night	17% 12% 23% 33% 13% 3	836
November	1st to 10th	Night	15% 9% 28% 30% 15% 3	880
	11th to 20th	Night	12% 8% 26% 33% 17% 4	900
	21st to end	Night	12% 12% 27% 32% 15% 2	1041
December	1st to 10th	Night	12% 10% 23% 37% 16% 2	1100
	11th to 20th	Night	9% 8% 23% 38% 19% 3	1100
	21st to end	Night	7% 10% 24% 33% 21% 5%	1210

Page generated at 2025-02-03 00:05:51. Version ac07

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