Glennifer Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glennifer Lake clear sky chart from 2005-11-06 to 2025-10-04.

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 8% 5% 5% 5% 4 6% 8% 36%	130907
	Night	7% 10% 4 10% 6% 5% 5% 4 6% 8% 35%	127177
Transparency	Day	42% 9% 16% 23% 9% 1	130607
	Night	44% 8% 15% 21% 9% 1	127054
Seeing	Day	12% 6% 24% 32% 19% 6%	16600
	Night	12% 5% 29% 38% 15% 2	25509

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% 7% 13% 8% 6% 5% 4 6% 7% 31%	3179
	11th to 20th	Day	3 10% 5% 10% 6% 7% 7% 4 6% 8% 34%	3159
	21st to end	Day	3 9% 3 8% 5% 6% 5% 4 7% 8% 41%	3986
February	1st to 10th	Day	6% 13% 5% 12% 6% 7% 6% 4 6% 8% 28%	1600
	11th to 20th	Day	5% 13% 4 13% 7% 6% 7% 6% 6% 8% 26%	1705
	21st to end	Day	3 11% 6% 12% 8% 6% 6% 6% 7% 7% 29%	1600
March	1st to 10th	Day	3 9% 4 12% 7% 5% 5% 4 5% 9% 38%	4518
	11th to 20th	Day	5% 11% 5% 9% 5% 4 5% 4 7% 8% 37%	4909
	21st to end	Day	10% 21% 6% 10% 5% 5% 6% 4 6% 6% 22%	5612
April	1st to 10th	Day	8% 13% 4 9% 8% 5% 5% 5% 7% 8% 29%	2456
	11th to 20th	Day	12% 14% 4 10% 6% 5% 5% 4 6% 7% 28%	2570
	21st to end	Day	11% 11% 4 8% 6% 5% 4 4 6% 8% 32%	2600
May	1st to 10th	Day	13% 10% 3 7% 5% 5% 5% 4 6% 7% 37%	6392
	11th to 20th	Day	11% 12% 4 10% 6% 6% 6% 5% 7% 8% 25%	6734
	21st to end	Day	13% 8% 3 8% 5% 4 5% 4 6% 7% 36%	7405
June	1st to 10th	Day	16% 7% 3 7% 5% 6% 6% 6% 7% 7% 30%	3000
	11th to 20th	Day	18% 9% 4 8% 6% 6% 5% 5% 6% 7% 25%	3000
	21st to end	Day	10% 6% 3 7% 5% 5% 6% 6% 8% 10% 35%	3000
July	1st to 10th	Day	8% 5% 2 5% 3 4 4 5% 7% 9% 48%	6780
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 5% 8% 10% 42%	6780
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 44%	7290
August	1st to 10th	Day	9% 6% 2 7% 4 4 5% 4 7% 10% 41%	4541
	11th to 20th	Day	7% 5% 2 6% 4 5% 6% 5% 10% 11% 40%	4260
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 8% 48%	4664
September	1st to 10th	Day	12% 5% 2 6% 3 4 4 4 6% 7% 46%	2495
	11th to 20th	Day	15% 8% 2 5% 3 3 4 3 4 7% 45%	2202
	21st to end	Day	9% 7% 3 7% 4 5% 5% 4 6% 8% 43%	2200
October	1st to 10th	Day	7% 6% 3 7% 4 5% 5% 5% 7% 10% 41%	3380
	11th to 20th	Day	8% 6% 3 8% 5% 6% 6% 5% 7% 9% 37%	2873
	21st to end	Day	7% 8% 4 8% 6% 5% 5% 4 6% 6% 40%	3101
November	1st to 10th	Day	7% 16% 5% 11% 7% 5% 5% 4 5% 7% 30%	1617
	11th to 20th	Day	6% 14% 4 10% 6% 4 5% 4 5% 7% 35%	1469
	21st to end	Day	5% 13% 4 10% 6% 6% 5% 4 7% 8% 31%	1400
December	1st to 10th	Day	6% 13% 4 11% 7% 7% 6% 5% 6% 8% 27%	2290
	11th to 20th	Day	5% 10% 5% 12% 8% 6% 6% 5% 6% 8% 29%	2642
	21st to end	Day	3 8% 4 11% 6% 5% 6% 4 5% 8% 40%	3498
January	1st to 10th	Night	3 12% 7% 15% 8% 6% 6% 5% 6% 7% 25%	6766
	11th to 20th	Night	2 10% 5% 12% 7% 6% 6% 5% 6% 7% 33%	6739
	21st to end	Night	3 9% 5% 10% 5% 5% 5% 5% 7% 9% 38%	6999
February	1st to 10th	Night	6% 12% 5% 13% 8% 6% 7% 4 6% 7% 26%	2800
	11th to 20th	Night	4 12% 6% 11% 8% 7% 6% 5% 6% 7% 27%	2581
	21st to end	Night	3 10% 5% 11% 7% 7% 6% 4 6% 8% 34%	2030
March	1st to 10th	Night	3 9% 4 12% 6% 6% 6% 4 6% 9% 34%	5376
	11th to 20th	Night	5% 10% 4 10% 6% 5% 7% 6% 8% 10% 30%	5089
	21st to end	Night	8% 18% 6% 14% 6% 6% 5% 4 5% 6% 22%	5360
April	1st to 10th	Night	7% 13% 4 8% 6% 6% 6% 5% 7% 8% 31%	1943
	11th to 20th	Night	9% 13% 5% 12% 6% 4 5% 3 6% 7% 29%	1781
	21st to end	Night	11% 10% 3 10% 5% 5% 5% 5% 8% 7% 31%	1800
May	1st to 10th	Night	17% 11% 4 7% 5% 3 3 3 5% 6% 36%	3568
	11th to 20th	Night	14% 10% 4 8% 6% 5% 5% 5% 8% 8% 27%	3159
	21st to end	Night	13% 8% 3 8% 6% 5% 5% 5% 7% 7% 33%	3470
June	1st to 10th	Night	15% 11% 4 8% 5% 5% 6% 4 7% 7% 29%	1400
	11th to 20th	Night	17% 9% 4 8% 7% 6% 6% 5% 6% 8% 24%	1400
	21st to end	Night	10% 7% 2 7% 5% 4 5% 6% 8% 9% 38%	1400
July	1st to 10th	Night	8% 7% 3 8% 5% 5% 5% 5% 6% 8% 41%	3180
	11th to 20th	Night	9% 4 2 6% 4 4 5% 5% 8% 9% 44%	3180
	21st to end	Night	11% 5% 2 5% 3 4 4 4 5% 11% 45%	3550
August	1st to 10th	Night	11% 8% 2 7% 4 4 5% 4 5% 7% 44%	2609
	11th to 20th	Night	8% 6% 3 7% 5% 5% 5% 5% 8% 12% 38%	2794
	21st to end	Night	9% 6% 2 6% 4 4 4 4 7% 8% 47%	3245
September	1st to 10th	Night	9% 6% 2 7% 3 3 5% 3 7% 7% 47%	1901
	11th to 20th	Night	15% 6% 3 6% 3 4 5% 3 5% 8% 43%	2198
	21st to end	Night	9% 7% 2 6% 3 4 5% 4 7% 7% 45%	2200
October	1st to 10th	Night	7% 6% 2 6% 5% 4 5% 5% 6% 9% 45%	3661
	11th to 20th	Night	6% 8% 3 8% 4 4 5% 4 7% 9% 41%	4053
	21st to end	Night	5% 9% 3 8% 6% 5% 5% 5% 7% 8% 40%	4457
November	1st to 10th	Night	9% 15% 4 9% 5% 4 6% 4 6% 7% 32%	2660
	11th to 20th	Night	5% 12% 4 11% 7% 5% 5% 5% 7% 9% 31%	2930
	21st to end	Night	4 12% 4 10% 7% 6% 5% 4 7% 9% 32%	3000
December	1st to 10th	Night	7% 13% 4 11% 7% 7% 6% 4 6% 7% 29%	4890
	11th to 20th	Night	4 13% 5% 13% 8% 7% 6% 5% 6% 8% 24%	5550
	21st to end	Night	2 9% 4 10% 5% 5% 5% 4 7% 7% 41%	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	51% 6% 12% 19% 11% 2	3179
	11th to 20th	Day	46% 7% 10% 14% 19% 3	3180
	21st to end	Day	38% 7% 15% 30% 11%	3986
February	1st to 10th	Day	52% 9% 12% 16% 9% 2	1600
	11th to 20th	Day	51% 10% 13% 15% 9% 2	1714
	21st to end	Day	50% 9% 13% 17% 10% 1	1600
March	1st to 10th	Day	41% 7% 16% 22% 13%	4518
	11th to 20th	Day	41% 8% 14% 23% 14% 1	4910
	21st to end	Day	60% 8% 11% 14% 7%	5612
April	1st to 10th	Day	48% 11% 17% 17% 7%	2456
	11th to 20th	Day	52% 9% 11% 19% 8% 1	2570
	21st to end	Day	48% 9% 15% 21% 6% 1	2600
May	1st to 10th	Day	44% 7% 10% 23% 15% 1	6392
	11th to 20th	Day	50% 12% 14% 18% 6%	6738
	21st to end	Day	41% 11% 16% 22% 9% 1	7406
June	1st to 10th	Day	47% 11% 15% 18% 7% 1	3000
	11th to 20th	Day	54% 10% 14% 17% 5% 1	3000
	21st to end	Day	39% 12% 20% 23% 5% 1	3000
July	1st to 10th	Day	29% 8% 19% 31% 11% 2	6706
	11th to 20th	Day	35% 8% 21% 30% 6%	6699
	21st to end	Day	34% 8% 19% 26% 11% 2	7084
August	1st to 10th	Day	36% 10% 18% 28% 7%	4524
	11th to 20th	Day	32% 11% 24% 26% 7%	4301
	21st to end	Day	32% 8% 22% 29% 8% 1	4663
September	1st to 10th	Day	34% 8% 20% 24% 10% 3	2495
	11th to 20th	Day	38% 7% 15% 29% 11% 1	2202
	21st to end	Day	37% 9% 16% 25% 11% 3	2200
October	1st to 10th	Day	37% 7% 20% 29% 6% 1	3380
	11th to 20th	Day	41% 7% 19% 20% 11% 2	2873
	21st to end	Day	43% 6% 11% 32% 8% 1	3101
November	1st to 10th	Day	53% 8% 13% 17% 8% 2	1617
	11th to 20th	Day	48% 8% 12% 20% 10% 1	1469
	21st to end	Day	48% 8% 16% 17% 8% 2	1400
December	1st to 10th	Day	53% 7% 16% 17% 5% 1	2290
	11th to 20th	Day	51% 9% 19% 16% 4 1	2644
	21st to end	Day	39% 8% 12% 23% 16% 3	3498
January	1st to 10th	Night	55% 8% 12% 17% 6% 2	6766
	11th to 20th	Night	47% 7% 12% 16% 14% 4	6780
	21st to end	Night	38% 9% 17% 25% 10% 1	6999
February	1st to 10th	Night	55% 6% 11% 17% 10% 1	2800
	11th to 20th	Night	52% 7% 13% 16% 10% 1	2582
	21st to end	Night	46% 7% 13% 21% 12% 2	2030
March	1st to 10th	Night	43% 9% 16% 21% 11%	5376
	11th to 20th	Night	42% 11% 16% 19% 11% 1	5089
	21st to end	Night	59% 9% 9% 15% 7% 1	5360
April	1st to 10th	Night	46% 10% 15% 18% 10%	1943
	11th to 20th	Night	52% 7% 14% 18% 8% 1	1781
	21st to end	Night	48% 9% 15% 21% 6% 1	1800
May	1st to 10th	Night	48% 6% 10% 20% 14% 2	3565
	11th to 20th	Night	47% 12% 17% 18% 6%	3159
	21st to end	Night	43% 12% 16% 20% 8% 1	3470
June	1st to 10th	Night	49% 12% 13% 18% 8% 1	1400
	11th to 20th	Night	55% 10% 12% 16% 5% 1	1400
	21st to end	Night	38% 12% 20% 22% 6% 1	1400
July	1st to 10th	Night	38% 9% 18% 22% 11% 2	3145
	11th to 20th	Night	33% 8% 22% 28% 5% 3	3138
	21st to end	Night	34% 7% 23% 25% 10% 1	3451
August	1st to 10th	Night	39% 8% 17% 28% 7%	2601
	11th to 20th	Night	35% 9% 25% 24% 6% 1	2819
	21st to end	Night	34% 8% 20% 29% 8% 1	3245
September	1st to 10th	Night	33% 9% 18% 26% 12% 3	1901
	11th to 20th	Night	38% 8% 15% 24% 11% 3	2198
	21st to end	Night	34% 8% 17% 25% 13% 3	2200
October	1st to 10th	Night	34% 7% 19% 27% 13% 1	3661
	11th to 20th	Night	37% 7% 18% 28% 9% 1	4053
	21st to end	Night	40% 8% 14% 29% 8%	4457
November	1st to 10th	Night	49% 8% 13% 19% 9% 2	2660
	11th to 20th	Night	47% 8% 16% 17% 10% 1	2930
	21st to end	Night	46% 9% 18% 18% 7% 3	3000
December	1st to 10th	Night	54% 6% 16% 16% 6% 2	4890
	11th to 20th	Night	57% 8% 14% 14% 6% 1	5547
	21st to end	Night	39% 7% 11% 24% 16% 4	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	5% 4 26% 34% 23% 9%	200
	11th to 20th	Day	8% 3 31% 38% 17% 6%	200
	21st to end	Day	6% 8% 26% 34% 20% 7%	220
February	1st to 10th	Day	9% 8% 24% 37% 15% 8%	200
	11th to 20th	Day	11% 4 26% 39% 16% 4	275
	21st to end	Day	4 4 29% 35% 21% 6%	364
March	1st to 10th	Day	8% 6% 30% 34% 16% 5%	500
	11th to 20th	Day	7% 5% 29% 37% 16% 7%	500
	21st to end	Day	15% 7% 28% 30% 15% 6%	550
April	1st to 10th	Day	10% 10% 31% 30% 14% 5%	500
	11th to 20th	Day	16% 9% 27% 28% 15% 5%	492
	21st to end	Day	16% 8% 26% 29% 17% 4	500
May	1st to 10th	Day	16% 9% 25% 29% 17% 4	573
	11th to 20th	Day	12% 9% 22% 33% 19% 5%	725
	21st to end	Day	16% 6% 18% 31% 21% 7%	789
June	1st to 10th	Day	16% 7% 24% 36% 14% 3	730
	11th to 20th	Day	20% 7% 23% 29% 16% 5%	730
	21st to end	Day	11% 6% 22% 31% 22% 9%	730
July	1st to 10th	Day	13% 3 18% 32% 25% 9%	721
	11th to 20th	Day	14% 4 18% 33% 24% 7%	718
	21st to end	Day	9% 4 20% 32% 26% 9%	758
August	1st to 10th	Day	11% 3 23% 30% 23% 10%	527
	11th to 20th	Day	7% 5% 22% 33% 27% 6%	517
	21st to end	Day	11% 5% 19% 30% 26% 9%	583
September	1st to 10th	Day	15% 4 25% 29% 19% 8%	530
	11th to 20th	Day	18% 5% 20% 28% 20% 8%	530
	21st to end	Day	12% 10% 31% 28% 13% 5%	530
October	1st to 10th	Day	14% 8% 26% 26% 18% 8%	424
	11th to 20th	Day	12% 8% 29% 30% 16% 5%	300
	21st to end	Day	12% 10% 34% 29% 13% 3	330
November	1st to 10th	Day	17% 5% 23% 37% 14% 4	300
	11th to 20th	Day	15% 6% 31% 31% 16% 1	234
	21st to end	Day	5% 5% 31% 39% 11% 10%	200
December	1st to 10th	Day	12% 5% 25% 33% 22% 4	200
	11th to 20th	Day	10% 5% 35% 31% 17% 4	200
	21st to end	Day	6% 4 22% 32% 29% 6%	220
January	1st to 10th	Night	9% 6% 33% 35% 16% 1	1000
	11th to 20th	Night	10% 6% 33% 38% 12% 1	1000
	21st to end	Night	10% 9% 31% 38% 10% 2	901
February	1st to 10th	Night	10% 8% 27% 37% 16% 3	800
	11th to 20th	Night	8% 5% 32% 40% 14% 1	784
	21st to end	Night	6% 4 29% 37% 21% 4	660
March	1st to 10th	Night	9% 4 30% 39% 16% 3	800
	11th to 20th	Night	8% 5% 30% 42% 14% 2	800
	21st to end	Night	13% 4 28% 38% 14% 3	880
April	1st to 10th	Night	12% 5% 32% 36% 14% 1	743
	11th to 20th	Night	15% 6% 33% 35% 11%	593
	21st to end	Night	16% 8% 26% 37% 13% 1	600
May	1st to 10th	Night	18% 8% 25% 36% 12% 1	450
	11th to 20th	Night	12% 7% 27% 36% 17% 1	394
	21st to end	Night	20% 5% 19% 37% 18% 1	433
June	1st to 10th	Night	20% 5% 26% 35% 13% 2	400
	11th to 20th	Night	20% 3 24% 36% 17%	400
	21st to end	Night	12% 3 21% 40% 23% 2	400
July	1st to 10th	Night	13% 3 15% 45% 23% 1	390
	11th to 20th	Night	12% 3 19% 46% 18% 2	388
	21st to end	Night	10% 2 17% 41% 29% 2	438
August	1st to 10th	Night	10% 3 18% 35% 32% 2	398
	11th to 20th	Night	12% 3 18% 41% 25% 2	523
	21st to end	Night	11% 3 21% 45% 21%	660
September	1st to 10th	Night	13% 3 21% 42% 19% 2	701
	11th to 20th	Night	17% 4 18% 38% 22% 2	800
	21st to end	Night	12% 3 30% 39% 14% 1	800
October	1st to 10th	Night	15% 3 26% 39% 15% 1	772
	11th to 20th	Night	11% 4 31% 38% 15% 1	760
	21st to end	Night	10% 7% 33% 38% 11% 1	836
November	1st to 10th	Night	17% 7% 31% 32% 11% 2	905
	11th to 20th	Night	11% 6% 40% 31% 11% 1	1000
	21st to end	Night	8% 4 37% 38% 11% 2	1000
December	1st to 10th	Night	11% 7% 31% 36% 14% 2	1000
	11th to 20th	Night	9% 5% 35% 36% 13% 2	1000
	21st to end	Night	10% 4 31% 38% 15% 2	1100

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