Keechelus Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Keechelus Lake clear sky chart from 2005-11-06 to 2025-08-05.

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	15% 17% 4 8% 4 4 4 3 4 5% 31%	130428
	Night	16% 20% 5% 8% 5% 4 4 3 4 5% 26%	126342
Transparency	Day	49% 9% 11% 18% 11% 3	130151
	Night	53% 10% 10% 16% 9% 2	126196
Seeing	Day	28% 18% 28% 19% 6% 2	15692
	Night	30% 14% 21% 23% 11% 1	24208

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	20% 31% 7% 10% 5% 4 5% 3 4 4 8%	3639
	11th to 20th	Day	13% 16% 8% 10% 4 4 4 4 5% 5% 27%	3616
	21st to end	Day	22% 19% 4 8% 3 3 3 2 3 4 28%	4031
February	1st to 10th	Day	19% 27% 7% 11% 5% 4 4 3 3 4 12%	1800
	11th to 20th	Day	15% 34% 6% 7% 5% 3 3 2 3 3 18%	1755
	21st to end	Day	14% 33% 8% 9% 4 3 3 3 3 4 16%	1595
March	1st to 10th	Day	9% 21% 6% 12% 6% 6% 6% 4 6% 5% 21%	4518
	11th to 20th	Day	9% 28% 8% 12% 5% 3 3 2 3 3 25%	4999
	21st to end	Day	19% 27% 6% 11% 6% 5% 5% 3 4 4 10%	5744
April	1st to 10th	Day	18% 30% 7% 8% 5% 4 3 3 4 4 13%	2400
	11th to 20th	Day	16% 26% 5% 8% 5% 4 3 3 3 4 22%	2372
	21st to end	Day	17% 28% 5% 9% 5% 4 3 3 3 4 18%	2647
May	1st to 10th	Day	12% 19% 4 8% 5% 4 4 3 4 5% 32%	6320
	11th to 20th	Day	14% 25% 5% 11% 6% 5% 4 3 4 5% 19%	6277
	21st to end	Day	17% 20% 4 8% 5% 4 4 3 4 6% 24%	6903
June	1st to 10th	Day	26% 14% 3 7% 5% 4 4 3 4 5% 25%	2800
	11th to 20th	Day	24% 17% 4 9% 5% 5% 5% 3 5% 6% 18%	2877
	21st to end	Day	14% 10% 3 7% 4 4 4 3 6% 7% 37%	3000
July	1st to 10th	Day	6% 5% 2 3 3 3 3 3 4 6% 63%	6560
	11th to 20th	Day	4 4 1 3 3 2 3 2 4 4 69%	6320
	21st to end	Day	7% 5% 1 4 3 3 3 3 5% 7% 59%	6874
August	1st to 10th	Day	5% 5% 1 4 3 3 3 3 4 7% 62%	4458
	11th to 20th	Day	6% 8% 4 9% 4 4 5% 4 5% 7% 43%	4026
	21st to end	Day	14% 10% 3 7% 4 4 4 3 3 6% 42%	4258
September	1st to 10th	Day	11% 7% 2 5% 3 3 4 3 4 6% 51%	2280
	11th to 20th	Day	15% 9% 2 8% 5% 4 4 4 5% 6% 37%	2280
	21st to end	Day	18% 11% 3 7% 4 4 4 3 4 5% 37%	2028
October	1st to 10th	Day	15% 9% 2 6% 4 3 4 3 5% 9% 40%	3180
	11th to 20th	Day	24% 13% 3 8% 4 4 4 3 4 5% 28%	3161
	21st to end	Day	23% 20% 5% 10% 5% 5% 4 2 3 4 20%	3197
November	1st to 10th	Day	30% 21% 3 8% 4 4 3 3 4 5% 14%	1664
	11th to 20th	Day	27% 26% 5% 8% 4 3 2 2 3 3 16%	1600
	21st to end	Day	22% 26% 5% 9% 4 3 3 3 3 4 18%	1600
December	1st to 10th	Day	15% 17% 4 8% 5% 4 4 4 5% 6% 30%	2620
	11th to 20th	Day	22% 25% 6% 11% 6% 5% 5% 3 4 4 8%	3025
	21st to end	Day	22% 28% 6% 9% 5% 5% 5% 3 4 4 9%	4004
January	1st to 10th	Night	21% 29% 8% 11% 6% 5% 4 3 3 3 9%	6306
	11th to 20th	Night	14% 15% 7% 9% 3 3 4 4 5% 8% 27%	6282
	21st to end	Night	20% 18% 4 9% 5% 5% 4 2 3 4 27%	6925
February	1st to 10th	Night	17% 28% 8% 10% 6% 4 4 3 4 4 12%	2600
	11th to 20th	Night	15% 29% 7% 7% 5% 4 4 3 3 4 19%	2532
	21st to end	Night	14% 33% 7% 9% 4 3 4 2 4 3 17%	2035
March	1st to 10th	Night	8% 19% 7% 11% 7% 6% 6% 5% 6% 6% 18%	5376
	11th to 20th	Night	11% 25% 8% 9% 4 3 3 2 3 4 27%	4999
	21st to end	Night	21% 29% 7% 10% 4 4 4 3 4 5% 10%	5231
April	1st to 10th	Night	14% 31% 7% 8% 4 5% 5% 4 5% 5% 13%	2000
	11th to 20th	Night	15% 24% 5% 8% 4 4 4 3 4 5% 23%	1979
	21st to end	Night	17% 28% 5% 9% 4 3 3 3 4 4 18%	1747
May	1st to 10th	Night	11% 22% 5% 5% 3 3 3 3 4 5% 34%	3640
	11th to 20th	Night	11% 32% 3 8% 4 4 4 3 4 5% 22%	3616
	21st to end	Night	15% 30% 4 8% 4 4 4 3 5% 5% 18%	3972
June	1st to 10th	Night	21% 16% 4 8% 5% 4 4 3 5% 6% 25%	1600
	11th to 20th	Night	22% 20% 4 9% 6% 4 5% 4 4 4 19%	1515
	21st to end	Night	13% 11% 4 10% 6% 5% 4 3 5% 5% 34%	1400
July	1st to 10th	Night	7% 8% 2 5% 3 3 3 3 3 5% 58%	3379
	11th to 20th	Night	4 4 2 3 2 2 3 3 4 5% 68%	3640
	21st to end	Night	6% 6% 2 5% 5% 5% 4 3 5% 7% 53%	3969
August	1st to 10th	Night	4 5% 2 4 2 4 3 3 5% 7% 60%	2561
	11th to 20th	Night	8% 16% 4 8% 6% 5% 4 3 4 5% 37%	2808
	21st to end	Night	17% 12% 2 6% 3 4 3 2 3 4 44%	3417
September	1st to 10th	Night	12% 6% 3 6% 4 3 4 3 4 4 51%	1900
	11th to 20th	Night	17% 13% 3 7% 4 4 4 3 4 4 36%	1900
	21st to end	Night	17% 12% 4 8% 4 4 4 3 5% 5% 34%	2149
October	1st to 10th	Night	16% 12% 3 5% 4 4 3 3 5% 8% 36%	3800
	11th to 20th	Night	24% 15% 4 7% 4 3 4 2 4 4 29%	3777
	21st to end	Night	24% 22% 4 7% 4 4 4 3 4 3 20%	4363
November	1st to 10th	Night	28% 22% 5% 9% 5% 4 3 3 4 4 15%	2632
	11th to 20th	Night	27% 24% 5% 8% 4 3 3 2 3 4 16%	2800
	21st to end	Night	21% 25% 5% 8% 5% 4 4 3 4 4 16%	2800
December	1st to 10th	Night	14% 19% 4 8% 6% 4 5% 3 5% 5% 28%	4560
	11th to 20th	Night	22% 25% 6% 11% 5% 5% 5% 3 5% 4 9%	5180
	21st to end	Night	22% 29% 7% 11% 5% 5% 5% 2 3 3 7%	6952

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	73% 11% 7% 8% 2	3639
	11th to 20th	Day	52% 11% 7% 20% 10% 1	3640
	21st to end	Day	59% 6% 3 18% 13% 1	4031
February	1st to 10th	Day	74% 7% 8% 7% 4 1	1800
	11th to 20th	Day	68% 9% 7% 9% 7% 1	1764
	21st to end	Day	70% 8% 7% 11% 4 1	1595
March	1st to 10th	Day	55% 11% 13% 11% 10% 1	4518
	11th to 20th	Day	59% 10% 6% 23% 2	4999
	21st to end	Day	72% 10% 10% 6% 2	5744
April	1st to 10th	Day	69% 11% 10% 9% 1	2400
	11th to 20th	Day	62% 9% 9% 13% 6% 1	2372
	21st to end	Day	66% 8% 9% 10% 5% 1	2647
May	1st to 10th	Day	45% 9% 12% 23% 11% 1	6320
	11th to 20th	Day	54% 15% 15% 13% 3	6280
	21st to end	Day	49% 14% 18% 16% 3	6904
June	1st to 10th	Day	55% 10% 13% 14% 8% 1	2800
	11th to 20th	Day	59% 11% 11% 12% 6% 1	2877
	21st to end	Day	40% 10% 16% 20% 12% 2	3000
July	1st to 10th	Day	20% 5% 12% 24% 23% 16%	6490
	11th to 20th	Day	16% 4 9% 25% 31% 15%	6245
	21st to end	Day	20% 6% 13% 35% 22% 4	6681
August	1st to 10th	Day	20% 5% 8% 23% 34% 10%	4441
	11th to 20th	Day	27% 13% 14% 32% 12% 2	4065
	21st to end	Day	38% 8% 12% 23% 18% 2	4257
September	1st to 10th	Day	30% 7% 13% 24% 21% 6%	2280
	11th to 20th	Day	41% 10% 11% 18% 17% 4	2280
	21st to end	Day	46% 7% 14% 17% 13% 3	2028
October	1st to 10th	Day	38% 7% 9% 33% 13% 1	3180
	11th to 20th	Day	56% 7% 9% 17% 11%	3161
	21st to end	Day	63% 8% 7% 10% 8% 4	3197
November	1st to 10th	Day	68% 8% 9% 9% 4 1	1664
	11th to 20th	Day	72% 7% 6% 8% 5% 1	1600
	21st to end	Day	65% 9% 7% 10% 6% 3	1600
December	1st to 10th	Day	52% 8% 8% 17% 14% 1	2620
	11th to 20th	Day	75% 6% 9% 9% 1	3028
	21st to end	Day	75% 7% 8% 6% 3	4004
January	1st to 10th	Night	76% 10% 4 7% 3 1	6306
	11th to 20th	Night	49% 10% 8% 21% 10% 1	6320
	21st to end	Night	57% 8% 5% 18% 11% 1	6925
February	1st to 10th	Night	71% 9% 7% 9% 5%	2600
	11th to 20th	Night	64% 10% 8% 10% 6% 2	2534
	21st to end	Night	69% 9% 8% 11% 4	2035
March	1st to 10th	Night	49% 16% 12% 12% 9% 1	5376
	11th to 20th	Night	54% 9% 12% 21% 3	5000
	21st to end	Night	69% 10% 10% 9% 1	5231
April	1st to 10th	Night	67% 13% 10% 9% 2	2000
	11th to 20th	Night	58% 10% 10% 12% 9% 1	1979
	21st to end	Night	61% 12% 8% 11% 7% 1	1747
May	1st to 10th	Night	42% 10% 11% 25% 12%	3637
	11th to 20th	Night	51% 15% 15% 17% 3	3616
	21st to end	Night	53% 16% 15% 14% 2	3972
June	1st to 10th	Night	51% 13% 15% 13% 8%	1600
	11th to 20th	Night	58% 13% 12% 12% 5%	1515
	21st to end	Night	43% 10% 15% 20% 10% 2	1400
July	1st to 10th	Night	21% 7% 12% 23% 18% 19%	3340
	11th to 20th	Night	13% 6% 12% 23% 33% 13%	3592
	21st to end	Night	19% 10% 16% 27% 21% 7%	3857
August	1st to 10th	Night	19% 6% 9% 22% 37% 7%	2553
	11th to 20th	Night	28% 20% 15% 22% 12% 3	2835
	21st to end	Night	38% 8% 11% 21% 19% 3	3417
September	1st to 10th	Night	30% 10% 12% 21% 22% 5%	1900
	11th to 20th	Night	42% 12% 8% 16% 16% 5%	1900
	21st to end	Night	44% 11% 11% 17% 12% 5%	2149
October	1st to 10th	Night	41% 7% 9% 33% 10%	3800
	11th to 20th	Night	54% 8% 7% 19% 12% 1	3777
	21st to end	Night	62% 8% 8% 10% 9% 3	4363
November	1st to 10th	Night	68% 9% 9% 10% 4 1	2632
	11th to 20th	Night	69% 7% 9% 9% 5% 1	2800
	21st to end	Night	67% 7% 7% 10% 6% 2	2800
December	1st to 10th	Night	54% 8% 7% 18% 12% 1	4560
	11th to 20th	Night	74% 8% 7% 9% 2	5176
	21st to end	Night	75% 10% 7% 6% 2	6952

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	37% 26% 24% 12% 2 1	200
	11th to 20th	Day	35% 24% 27% 12% 4	200
	21st to end	Day	34% 19% 25% 18% 3 1	234
February	1st to 10th	Day	42% 22% 21% 13% 3	400
	11th to 20th	Day	41% 22% 23% 13% 1	395
	21st to end	Day	35% 22% 26% 15% 2	387
March	1st to 10th	Day	32% 21% 28% 16% 3 1	500
	11th to 20th	Day	31% 21% 27% 12% 8% 1	500
	21st to end	Day	39% 19% 27% 11% 4	550
April	1st to 10th	Day	38% 22% 22% 14% 4 1	500
	11th to 20th	Day	34% 24% 23% 15% 3 1	492
	21st to end	Day	36% 19% 25% 13% 6% 1	500
May	1st to 10th	Day	32% 17% 28% 18% 5% 1	503
	11th to 20th	Day	34% 17% 25% 15% 6% 2	528
	21st to end	Day	35% 16% 22% 18% 6% 2	573
June	1st to 10th	Day	30% 17% 26% 19% 6% 2	530
	11th to 20th	Day	33% 22% 29% 12% 4 1	607
	21st to end	Day	18% 19% 32% 22% 7% 2	730
July	1st to 10th	Day	15% 14% 40% 23% 5% 2	635
	11th to 20th	Day	11% 17% 37% 22% 11% 3	524
	21st to end	Day	8% 13% 36% 26% 12% 5%	575
August	1st to 10th	Day	11% 12% 33% 27% 12% 5%	504
	11th to 20th	Day	9% 11% 32% 30% 13% 5%	477
	21st to end	Day	17% 15% 32% 23% 9% 4	539
September	1st to 10th	Day	15% 16% 32% 26% 8% 2	490
	11th to 20th	Day	22% 16% 30% 23% 9% 1	490
	21st to end	Day	24% 15% 28% 24% 8% 1	490
October	1st to 10th	Day	27% 16% 23% 24% 9% 2	490
	11th to 20th	Day	32% 17% 21% 20% 10% 1	490
	21st to end	Day	40% 13% 24% 15% 7% 1	389
November	1st to 10th	Day	48% 10% 25% 14% 2	250
	11th to 20th	Day	46% 13% 24% 13% 5%	200
	21st to end	Day	37% 15% 28% 19% 3	200
December	1st to 10th	Day	38% 19% 17% 21% 7%	200
	11th to 20th	Day	42% 25% 23% 10% 1	200
	21st to end	Day	38% 18% 25% 16% 2	220
January	1st to 10th	Night	40% 19% 25% 14% 3	800
	11th to 20th	Night	33% 20% 25% 17% 5%	800
	21st to end	Night	34% 15% 26% 22% 4	880
February	1st to 10th	Night	35% 18% 26% 17% 4	800
	11th to 20th	Night	33% 16% 26% 19% 6% 1	784
	21st to end	Night	33% 18% 26% 18% 5%	660
March	1st to 10th	Night	28% 16% 23% 23% 9% 1	800
	11th to 20th	Night	30% 19% 23% 20% 7% 1	800
	21st to end	Night	33% 21% 21% 18% 6% 1	880
April	1st to 10th	Night	32% 19% 17% 24% 7% 1	800
	11th to 20th	Night	29% 16% 23% 24% 6% 2	791
	21st to end	Night	35% 14% 19% 22% 9%	547
May	1st to 10th	Night	26% 16% 18% 27% 14% 1	400
	11th to 20th	Night	25% 12% 17% 28% 16% 2	394
	21st to end	Night	30% 14% 12% 26% 17% 1	433
June	1st to 10th	Night	29% 11% 16% 28% 16% 1	400
	11th to 20th	Night	31% 17% 16% 24% 12% 1	400
	21st to end	Night	19% 11% 19% 30% 20% 1	400
July	1st to 10th	Night	15% 12% 12% 36% 23% 1	390
	11th to 20th	Night	11% 11% 18% 32% 26% 2	388
	21st to end	Night	9% 7% 14% 35% 32% 3	438
August	1st to 10th	Night	10% 6% 11% 34% 37% 3	386
	11th to 20th	Night	12% 6% 12% 29% 32% 8%	560
	21st to end	Night	17% 8% 17% 33% 23% 3	781
September	1st to 10th	Night	17% 6% 19% 36% 19% 3	760
	11th to 20th	Night	22% 11% 13% 26% 24% 4	760
	21st to end	Night	24% 9% 17% 32% 17% 1	760
October	1st to 10th	Night	26% 9% 18% 30% 16% 1	760
	11th to 20th	Night	31% 11% 18% 27% 11% 2	760
	21st to end	Night	37% 12% 23% 20% 7% 2	836
November	1st to 10th	Night	40% 14% 26% 17% 3	780
	11th to 20th	Night	41% 16% 23% 16% 2 1	800
	21st to end	Night	32% 17% 26% 22% 3	800
December	1st to 10th	Night	32% 15% 28% 20% 5%	800
	11th to 20th	Night	40% 19% 25% 13% 3	800
	21st to end	Night	40% 21% 25% 12% 2	880

Page generated at 2025-08-01 22:32:25. Version ac07

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