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 2024-01-12.

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% 9% 4 7% 6% 4 6% 6% 6% 8% 35%	74610
	Night	8% 9% 4 8% 7% 4 6% 6% 6% 8% 34%	75104
Transparency	Day	44% 10% 17% 20% 8% 1	74293
	Night	45% 9% 15% 20% 9% 2	74939
Seeing	Day	13% 6% 25% 32% 19% 6%	14214
	Night	12% 5% 29% 38% 15% 2	23406

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% 13% 6% 9% 7% 3 5% 4 8% 9% 32%	1329
	11th to 20th	Day	7% 10% 5% 8% 7% 4 6% 5% 5% 8% 34%	1267
	21st to end	Day	6% 11% 5% 10% 7% 4 8% 6% 6% 9% 28%	1580
February	1st to 10th	Day	6% 12% 6% 9% 7% 5% 7% 5% 6% 8% 29%	1440
	11th to 20th	Day	6% 13% 5% 11% 9% 3 7% 7% 6% 8% 24%	1530
	21st to end	Day	3 9% 8% 11% 10% 4 7% 7% 7% 6% 28%	1435
March	1st to 10th	Day	5% 13% 6% 11% 10% 4 6% 6% 5% 7% 28%	1800
	11th to 20th	Day	6% 9% 5% 8% 7% 4 6% 6% 8% 9% 33%	1941
	21st to end	Day	9% 13% 6% 10% 6% 4 5% 5% 6% 7% 28%	2227
April	1st to 10th	Day	8% 12% 6% 8% 9% 4 6% 6% 7% 8% 28%	2210
	11th to 20th	Day	13% 14% 5% 9% 7% 3 5% 5% 5% 7% 27%	2310
	21st to end	Day	12% 11% 4 7% 7% 4 6% 5% 6% 8% 32%	2340
May	1st to 10th	Day	13% 11% 3 7% 7% 4 6% 6% 6% 8% 28%	2532
	11th to 20th	Day	9% 7% 3 8% 6% 4 6% 5% 7% 8% 38%	2654
	21st to end	Day	19% 7% 3 6% 5% 3 5% 6% 7% 8% 30%	2917
June	1st to 10th	Day	17% 7% 3 7% 6% 4 7% 7% 7% 7% 28%	2700
	11th to 20th	Day	19% 8% 4 7% 7% 4 5% 6% 6% 7% 25%	2700
	21st to end	Day	10% 5% 3 6% 6% 4 6% 7% 8% 9% 36%	2700
July	1st to 10th	Day	10% 6% 2 6% 5% 4 6% 7% 7% 10% 37%	2700
	11th to 20th	Day	13% 6% 3 4 4 3 5% 7% 8% 9% 39%	2700
	21st to end	Day	8% 4 2 4 4 3 5% 6% 7% 11% 46%	2906
August	1st to 10th	Day	11% 5% 2 5% 5% 2 5% 6% 7% 11% 40%	2507
	11th to 20th	Day	9% 4 2 4 4 3 4 5% 8% 9% 47%	2362
	21st to end	Day	10% 5% 2 4 5% 3 5% 6% 7% 9% 43%	2574
September	1st to 10th	Day	13% 6% 2 5% 4 3 4 6% 6% 7% 44%	2246
	11th to 20th	Day	15% 8% 2 5% 4 2 4 5% 4 7% 44%	1982
	21st to end	Day	10% 7% 3 6% 5% 3 5% 4 6% 9% 42%	1980
October	1st to 10th	Day	12% 9% 3 5% 5% 3 5% 5% 5% 8% 40%	1906
	11th to 20th	Day	11% 8% 4 7% 5% 3 5% 6% 6% 7% 38%	1638
	21st to end	Day	7% 10% 5% 9% 7% 5% 6% 5% 6% 7% 33%	1782
November	1st to 10th	Day	7% 15% 6% 10% 7% 4 5% 4 5% 7% 30%	1535
	11th to 20th	Day	7% 12% 5% 8% 8% 3 5% 5% 5% 7% 35%	1396
	21st to end	Day	5% 10% 6% 8% 8% 4 5% 6% 7% 9% 33%	1330
December	1st to 10th	Day	6% 12% 5% 11% 9% 5% 6% 5% 4 7% 30%	1330
	11th to 20th	Day	3 9% 5% 12% 8% 4 7% 7% 6% 9% 29%	1682
	21st to end	Day	4 8% 4 9% 7% 3 5% 5% 5% 8% 41%	2442
January	1st to 10th	Night	4 10% 6% 11% 9% 5% 7% 6% 6% 7% 28%	2836
	11th to 20th	Night	5% 12% 5% 9% 7% 4 6% 6% 7% 9% 30%	2722
	21st to end	Night	6% 13% 6% 9% 7% 4 6% 6% 7% 8% 28%	2791
February	1st to 10th	Night	6% 12% 6% 12% 9% 4 6% 6% 5% 8% 27%	2520
	11th to 20th	Night	5% 12% 6% 10% 9% 5% 7% 6% 6% 8% 26%	2316
	21st to end	Night	3 9% 6% 10% 8% 5% 7% 5% 6% 7% 34%	1821
March	1st to 10th	Night	5% 11% 4 8% 9% 5% 7% 6% 7% 9% 29%	2160
	11th to 20th	Night	5% 9% 5% 9% 8% 3 7% 7% 7% 9% 31%	2017
	21st to end	Night	6% 12% 7% 9% 7% 4 6% 7% 6% 8% 27%	2126
April	1st to 10th	Night	8% 11% 5% 8% 7% 5% 6% 6% 7% 8% 30%	1749
	11th to 20th	Night	10% 13% 6% 10% 7% 3 5% 5% 6% 7% 29%	1601
	21st to end	Night	13% 10% 3 8% 6% 3 6% 5% 7% 8% 32%	1620
May	1st to 10th	Night	14% 12% 5% 7% 7% 3 4 5% 5% 8% 29%	1424
	11th to 20th	Night	11% 8% 3 4 6% 3 5% 5% 8% 8% 39%	1239
	21st to end	Night	20% 7% 3 6% 6% 4 4 5% 7% 8% 31%	1358
June	1st to 10th	Night	15% 10% 4 7% 5% 4 6% 5% 7% 8% 29%	1260
	11th to 20th	Night	18% 9% 4 7% 7% 5% 6% 6% 6% 9% 23%	1260
	21st to end	Night	10% 6% 2 6% 6% 4 5% 6% 8% 10% 38%	1260
July	1st to 10th	Night	11% 6% 3 5% 4 4 6% 7% 7% 9% 39%	1260
	11th to 20th	Night	10% 4 3 6% 5% 4 6% 6% 9% 9% 37%	1260
	21st to end	Night	8% 4 2 4 3 3 6% 5% 6% 10% 50%	1408
August	1st to 10th	Night	9% 6% 2 6% 6% 4 5% 6% 6% 8% 42%	1432
	11th to 20th	Night	9% 6% 3 5% 5% 4 4 5% 6% 10% 43%	1537
	21st to end	Night	9% 5% 2 6% 5% 3 5% 5% 7% 9% 44%	1782
September	1st to 10th	Night	10% 6% 2 6% 5% 2 5% 4 6% 8% 46%	1710
	11th to 20th	Night	15% 6% 3 5% 4 3 4 5% 5% 8% 42%	1978
	21st to end	Night	10% 7% 2 5% 4 3 6% 5% 7% 7% 44%	1980
October	1st to 10th	Night	11% 8% 3 6% 6% 3 4 5% 5% 7% 41%	2053
	11th to 20th	Night	8% 8% 3 8% 5% 4 5% 6% 7% 9% 36%	2320
	21st to end	Night	7% 11% 4 9% 7% 4 5% 5% 6% 8% 34%	2574
November	1st to 10th	Night	9% 13% 5% 8% 6% 3 5% 6% 6% 7% 32%	2523
	11th to 20th	Night	5% 11% 5% 9% 7% 4 6% 6% 7% 9% 32%	2783
	21st to end	Night	4 10% 5% 9% 7% 4 5% 5% 7% 9% 34%	2850
December	1st to 10th	Night	6% 11% 5% 8% 7% 5% 6% 4 5% 7% 34%	2850
	11th to 20th	Night	3 9% 5% 10% 9% 5% 8% 6% 6% 9% 30%	3510
	21st to end	Night	3 10% 4 7% 6% 3 5% 5% 6% 7% 44%	5214

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	48% 8% 13% 21% 8% 2	1329
	11th to 20th	Day	48% 8% 13% 20% 9% 2	1267
	21st to end	Day	51% 8% 15% 15% 10% 1	1580
February	1st to 10th	Day	50% 9% 13% 18% 8% 2	1440
	11th to 20th	Day	53% 10% 14% 14% 7% 1	1539
	21st to end	Day	52% 8% 13% 17% 10% 1	1435
March	1st to 10th	Day	53% 8% 15% 16% 7% 1	1800
	11th to 20th	Day	43% 11% 14% 21% 10% 1	1942
	21st to end	Day	53% 9% 17% 15% 5% 1	2227
April	1st to 10th	Day	48% 12% 18% 15% 6%	2210
	11th to 20th	Day	54% 8% 11% 19% 8%	2310
	21st to end	Day	49% 9% 15% 20% 6% 2	2340
May	1st to 10th	Day	50% 9% 16% 18% 7%	2532
	11th to 20th	Day	41% 10% 16% 22% 11%	2658
	21st to end	Day	47% 11% 16% 19% 7% 1	2918
June	1st to 10th	Day	49% 11% 16% 18% 5% 1	2700
	11th to 20th	Day	55% 11% 14% 15% 5% 1	2700
	21st to end	Day	38% 13% 20% 22% 5% 1	2700
July	1st to 10th	Day	38% 13% 22% 21% 6% 1	2626
	11th to 20th	Day	37% 12% 23% 23% 5%	2619
	21st to end	Day	30% 12% 24% 28% 6%	2744
August	1st to 10th	Day	34% 14% 22% 25% 6%	2490
	11th to 20th	Day	29% 12% 26% 23% 9% 1	2362
	21st to end	Day	34% 11% 18% 26% 9% 1	2574
September	1st to 10th	Day	36% 9% 21% 22% 9% 3	2246
	11th to 20th	Day	39% 7% 15% 27% 10% 1	1982
	21st to end	Day	38% 9% 16% 24% 11% 2	1980
October	1st to 10th	Day	42% 8% 17% 23% 9% 1	1906
	11th to 20th	Day	42% 8% 18% 20% 10% 1	1638
	21st to end	Day	48% 8% 13% 20% 11% 1	1782
November	1st to 10th	Day	53% 8% 13% 17% 8% 2	1535
	11th to 20th	Day	47% 9% 13% 21% 10% 1	1396
	21st to end	Day	46% 9% 17% 18% 9% 2	1330
December	1st to 10th	Day	53% 7% 12% 17% 9% 2	1330
	11th to 20th	Day	47% 10% 18% 18% 5% 2	1684
	21st to end	Day	36% 9% 13% 20% 18% 4	2442
January	1st to 10th	Night	53% 8% 11% 16% 9% 3	2836
	11th to 20th	Night	48% 9% 14% 19% 6% 3	2722
	21st to end	Night	50% 8% 13% 17% 11% 2	2791
February	1st to 10th	Night	54% 6% 11% 18% 9% 1	2520
	11th to 20th	Night	54% 7% 14% 15% 9% 1	2317
	21st to end	Night	46% 7% 13% 20% 12% 2	1821
March	1st to 10th	Night	49% 10% 13% 21% 7% 1	2160
	11th to 20th	Night	45% 9% 16% 18% 12% 1	2017
	21st to end	Night	51% 10% 13% 18% 6% 1	2126
April	1st to 10th	Night	48% 10% 14% 18% 10%	1749
	11th to 20th	Night	52% 7% 14% 18% 7% 1	1601
	21st to end	Night	47% 9% 16% 20% 6% 1	1620
May	1st to 10th	Night	51% 8% 16% 16% 8%	1424
	11th to 20th	Night	40% 10% 16% 22% 13%	1239
	21st to end	Night	47% 10% 17% 18% 7% 1	1358
June	1st to 10th	Night	49% 12% 14% 18% 7%	1260
	11th to 20th	Night	56% 11% 12% 15% 4 1	1260
	21st to end	Night	38% 13% 20% 22% 6% 1	1260
July	1st to 10th	Night	38% 13% 21% 23% 5% 1	1225
	11th to 20th	Night	38% 13% 23% 17% 8% 1	1218
	21st to end	Night	28% 11% 23% 28% 10%	1330
August	1st to 10th	Night	37% 12% 23% 22% 6%	1424
	11th to 20th	Night	34% 9% 23% 25% 7% 1	1537
	21st to end	Night	34% 10% 18% 25% 12% 2	1782
September	1st to 10th	Night	34% 9% 18% 25% 11% 3	1710
	11th to 20th	Night	39% 9% 16% 23% 10% 4	1978
	21st to end	Night	35% 8% 17% 23% 13% 3	1980
October	1st to 10th	Night	41% 8% 17% 22% 12% 1	2053
	11th to 20th	Night	41% 9% 17% 22% 9% 2	2320
	21st to end	Night	46% 10% 16% 20% 8% 1	2574
November	1st to 10th	Night	49% 8% 12% 19% 10% 2	2523
	11th to 20th	Night	47% 8% 16% 17% 11% 1	2783
	21st to end	Night	44% 9% 18% 18% 7% 3	2850
December	1st to 10th	Night	49% 7% 12% 19% 10% 3	2850
	11th to 20th	Night	49% 10% 15% 19% 6% 1	3507
	21st to end	Night	36% 7% 14% 23% 15% 5%	5214

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% 3 26% 35% 22% 9%	180
	11th to 20th	Day	9% 2 30% 36% 17% 7%	162
	21st to end	Day	6% 8% 27% 33% 19% 7%	176
February	1st to 10th	Day	9% 9% 25% 36% 12% 8%	160
	11th to 20th	Day	14% 5% 27% 40% 12% 3	220
	21st to end	Day	5% 3 29% 36% 21% 7%	301
March	1st to 10th	Day	9% 7% 31% 34% 14% 5%	420
	11th to 20th	Day	7% 5% 30% 36% 15% 7%	420
	21st to end	Day	14% 6% 29% 28% 15% 6%	462
April	1st to 10th	Day	9% 10% 33% 31% 14% 4	420
	11th to 20th	Day	17% 8% 25% 28% 17% 5%	412
	21st to end	Day	16% 7% 28% 28% 17% 4	420
May	1st to 10th	Day	16% 8% 25% 29% 18% 5%	485
	11th to 20th	Day	11% 8% 21% 33% 21% 5%	625
	21st to end	Day	18% 5% 18% 32% 21% 7%	679
June	1st to 10th	Day	17% 6% 23% 38% 13% 3	630
	11th to 20th	Day	21% 7% 23% 31% 14% 4	630
	21st to end	Day	11% 5% 22% 31% 22% 9%	630
July	1st to 10th	Day	13% 3 19% 32% 24% 9%	621
	11th to 20th	Day	14% 4 19% 34% 24% 5%	618
	21st to end	Day	7% 4 21% 33% 26% 9%	652
August	1st to 10th	Day	11% 4 24% 30% 22% 10%	447
	11th to 20th	Day	7% 5% 22% 33% 28% 5%	437
	21st to end	Day	11% 6% 21% 31% 24% 8%	495
September	1st to 10th	Day	17% 4 27% 30% 17% 5%	450
	11th to 20th	Day	19% 6% 22% 28% 19% 6%	450
	21st to end	Day	13% 10% 28% 29% 14% 6%	450
October	1st to 10th	Day	15% 8% 26% 27% 16% 8%	376
	11th to 20th	Day	13% 8% 30% 27% 16% 6%	270
	21st to end	Day	12% 11% 35% 27% 13% 2	297
November	1st to 10th	Day	17% 4 23% 38% 13% 4	270
	11th to 20th	Day	15% 6% 31% 33% 14% 1	211
	21st to end	Day	4 6% 31% 37% 12% 10%	180
December	1st to 10th	Day	11% 4 26% 32% 22% 4	180
	11th to 20th	Day	9% 6% 37% 31% 16% 3	180
	21st to end	Day	6% 5% 24% 31% 29% 6%	198
January	1st to 10th	Night	10% 6% 33% 35% 15% 1	950
	11th to 20th	Night	11% 6% 32% 38% 13% 1	908
	21st to end	Night	11% 9% 31% 37% 10% 2	811
February	1st to 10th	Night	10% 8% 28% 36% 16% 2	720
	11th to 20th	Night	9% 6% 33% 40% 12% 1	704
	21st to end	Night	6% 3 27% 37% 23% 5%	592
March	1st to 10th	Night	9% 4 31% 38% 16% 3	720
	11th to 20th	Night	8% 5% 30% 41% 14% 2	720
	21st to end	Night	12% 4 28% 39% 14% 3	792
April	1st to 10th	Night	11% 5% 31% 36% 15% 1	669
	11th to 20th	Night	16% 5% 32% 35% 12%	533
	21st to end	Night	16% 7% 25% 38% 12% 1	540
May	1st to 10th	Night	17% 8% 25% 36% 12% 1	406
	11th to 20th	Night	12% 6% 27% 37% 18% 1	354
	21st to end	Night	21% 5% 19% 37% 18% 1	389
June	1st to 10th	Night	21% 3 23% 37% 14% 2	360
	11th to 20th	Night	21% 3 24% 36% 16%	360
	21st to end	Night	12% 2 21% 40% 23% 2	360
July	1st to 10th	Night	14% 3 14% 44% 23% 1	350
	11th to 20th	Night	12% 3 19% 47% 18% 1	348
	21st to end	Night	9% 2 17% 43% 28% 2	394
August	1st to 10th	Night	9% 3 18% 35% 32% 3	358
	11th to 20th	Night	12% 3 17% 42% 25% 2	469
	21st to end	Night	11% 3 21% 44% 21%	594
September	1st to 10th	Night	14% 3 21% 43% 17% 2	630
	11th to 20th	Night	17% 4 19% 38% 20% 2	720
	21st to end	Night	12% 3 28% 39% 16% 1	720
October	1st to 10th	Night	16% 4 25% 38% 16% 2	720
	11th to 20th	Night	12% 4 31% 37% 16% 1	720
	21st to end	Night	10% 7% 34% 37% 11%	792
November	1st to 10th	Night	17% 7% 32% 32% 11% 2	858
	11th to 20th	Night	11% 6% 41% 31% 10% 1	950
	21st to end	Night	7% 4 37% 39% 11% 2	950
December	1st to 10th	Night	11% 7% 30% 36% 14% 2	950
	11th to 20th	Night	8% 5% 35% 37% 13% 2	950
	21st to end	Night	11% 4 32% 37% 15% 2	1045

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