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 2024-03-23.

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	19% 18% 5% 7% 5% 3 4 4 4 5% 27%	78901
	Night	19% 20% 6% 7% 6% 3 4 4 4 5% 22%	80933
Transparency	Day	55% 9% 10% 15% 9% 2	78627
	Night	58% 10% 9% 13% 8% 2	80787
Seeing	Day	29% 17% 27% 19% 6% 2	13862
	Night	30% 14% 21% 23% 11% 1	22643

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	21% 30% 8% 9% 7% 3 5% 3 4 4 6%	2539
	11th to 20th	Day	19% 20% 7% 9% 6% 3 4 4 5% 5% 18%	2516
	21st to end	Day	30% 26% 6% 9% 5% 3 3 2 3 3 10%	2807
February	1st to 10th	Day	21% 26% 7% 9% 6% 3 4 4 3 5% 12%	1710
	11th to 20th	Day	16% 33% 7% 6% 5% 3 3 3 3 3 18%	1665
	21st to end	Day	14% 32% 10% 8% 5% 2 3 3 3 4 16%	1517
March	1st to 10th	Day	16% 25% 8% 9% 6% 4 4 4 3 3 18%	1900
	11th to 20th	Day	17% 28% 7% 8% 6% 2 3 3 4 4 18%	2089
	21st to end	Day	18% 31% 7% 9% 6% 3 5% 4 4 4 10%	2304
April	1st to 10th	Day	19% 29% 7% 8% 6% 3 4 4 4 4 13%	2160
	11th to 20th	Day	19% 25% 6% 7% 6% 3 4 4 3 3 19%	2132
	21st to end	Day	18% 28% 5% 9% 6% 3 4 4 3 4 17%	2381
May	1st to 10th	Day	16% 23% 5% 6% 6% 3 5% 4 4 5% 24%	2520
	11th to 20th	Day	19% 17% 4 7% 7% 3 5% 5% 6% 7% 21%	2477
	21st to end	Day	27% 18% 4 6% 6% 3 4 4 4 6% 19%	2723
June	1st to 10th	Day	28% 13% 3 7% 6% 3 4 4 4 5% 22%	2520
	11th to 20th	Day	26% 17% 4 8% 6% 4 5% 4 4 5% 16%	2589
	21st to end	Day	15% 10% 3 6% 5% 3 4 4 5% 7% 38%	2700
July	1st to 10th	Day	12% 8% 3 5% 5% 3 4 4 5% 6% 45%	2620
	11th to 20th	Day	9% 8% 3 5% 4 3 5% 4 5% 5% 49%	2520
	21st to end	Day	7% 6% 2 3 3 2 2 3 3 4 63%	2741
August	1st to 10th	Day	9% 7% 2 4 4 2 4 4 5% 7% 52%	2507
	11th to 20th	Day	8% 5% 2 4 4 2 3 4 4 7% 57%	2298
	21st to end	Day	11% 8% 3 6% 5% 3 4 5% 4 7% 43%	2428
September	1st to 10th	Day	12% 7% 3 4 4 2 4 4 4 6% 51%	2160
	11th to 20th	Day	16% 9% 2 7% 6% 3 4 5% 5% 6% 38%	2160
	21st to end	Day	19% 11% 3 7% 5% 3 4 3 4 5% 37%	1922
October	1st to 10th	Day	20% 12% 4 5% 5% 3 4 4 5% 7% 32%	1800
	11th to 20th	Day	25% 13% 4 6% 4 2 3 3 4 5% 31%	1800
	21st to end	Day	29% 15% 4 7% 4 2 3 3 3 5% 25%	1838
November	1st to 10th	Day	31% 20% 4 7% 4 3 4 4 4 5% 14%	1579
	11th to 20th	Day	27% 25% 5% 6% 5% 3 2 3 3 4 17%	1520
	21st to end	Day	24% 23% 6% 8% 5% 2 3 4 3 3 19%	1520
December	1st to 10th	Day	19% 22% 6% 8% 6% 3 4 4 3 5% 20%	1520
	11th to 20th	Day	21% 22% 6% 9% 6% 3 6% 5% 5% 5% 11%	1925
	21st to end	Day	20% 22% 7% 9% 7% 5% 6% 4 4 4 12%	2794
January	1st to 10th	Night	22% 30% 9% 9% 7% 4 4 3 3 3 6%	4406
	11th to 20th	Night	21% 17% 8% 10% 5% 3 3 4 5% 7% 17%	4382
	21st to end	Night	27% 24% 5% 9% 7% 4 4 3 3 4 10%	4848
February	1st to 10th	Night	19% 27% 7% 9% 6% 3 5% 3 4 5% 13%	2470
	11th to 20th	Night	16% 27% 8% 6% 5% 3 4 4 4 4 19%	2402
	21st to end	Night	14% 32% 8% 8% 5% 3 4 4 4 3 16%	1937
March	1st to 10th	Night	18% 22% 7% 7% 6% 4 4 5% 4 6% 18%	2280
	11th to 20th	Night	17% 24% 6% 7% 6% 2 4 3 4 5% 22%	2089
	21st to end	Night	19% 29% 8% 7% 5% 3 4 4 4 4 14%	2097
April	1st to 10th	Night	16% 27% 8% 7% 5% 4 5% 5% 5% 5% 13%	1800
	11th to 20th	Night	17% 24% 5% 8% 5% 3 4 4 4 5% 20%	1779
	21st to end	Night	19% 26% 7% 8% 5% 2 3 4 4 4 18%	1574
May	1st to 10th	Night	15% 25% 4 5% 5% 4 4 3 4 5% 26%	1440
	11th to 20th	Night	17% 16% 4 8% 6% 3 5% 6% 6% 6% 23%	1416
	21st to end	Night	22% 21% 4 7% 6% 3 4 5% 5% 5% 18%	1552
June	1st to 10th	Night	23% 15% 5% 7% 5% 4 4 4 4 6% 23%	1440
	11th to 20th	Night	24% 19% 5% 8% 7% 4 4 5% 4 3 17%	1364
	21st to end	Night	14% 10% 4 9% 6% 4 4 4 5% 5% 36%	1260
July	1st to 10th	Night	11% 11% 3 7% 6% 3 4 4 5% 6% 40%	1333
	11th to 20th	Night	9% 8% 3 6% 5% 3 5% 4 4 6% 48%	1440
	21st to end	Night	8% 7% 2 4 4 3 3 3 4 6% 58%	1576
August	1st to 10th	Night	7% 8% 2 4 4 3 4 3 4 8% 55%	1432
	11th to 20th	Night	7% 6% 3 4 4 3 4 4 5% 7% 54%	1598
	21st to end	Night	12% 8% 2 6% 4 3 5% 4 4 5% 46%	1927
September	1st to 10th	Night	13% 6% 3 5% 4 3 4 4 4 4 51%	1800
	11th to 20th	Night	17% 11% 3 6% 5% 3 4 4 4 4 38%	1800
	21st to end	Night	17% 12% 4 7% 6% 3 4 4 5% 5% 34%	2035
October	1st to 10th	Night	22% 11% 4 5% 5% 3 4 3 4 6% 34%	2160
	11th to 20th	Night	23% 13% 5% 6% 4 3 4 3 4 4 31%	2160
	21st to end	Night	28% 15% 3 6% 5% 3 3 4 4 4 26%	2517
November	1st to 10th	Night	29% 21% 5% 8% 6% 2 4 4 4 4 15%	2497
	11th to 20th	Night	27% 22% 5% 8% 5% 3 3 3 3 4 17%	2660
	21st to end	Night	22% 24% 6% 7% 5% 3 4 4 4 4 17%	2660
December	1st to 10th	Night	20% 23% 7% 9% 7% 3 5% 3 4 4 18%	2660
	11th to 20th	Night	20% 24% 7% 8% 6% 4 5% 4 5% 5% 11%	3280
	21st to end	Night	21% 25% 7% 10% 7% 4 6% 4 4 3 8%	4862

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% 13% 7% 5% 1 1	2539
	11th to 20th	Day	64% 8% 8% 13% 5% 2	2540
	21st to end	Day	78% 7% 4 7% 4 1	2807
February	1st to 10th	Day	74% 7% 8% 7% 4 1	1710
	11th to 20th	Day	68% 9% 7% 9% 7% 1	1674
	21st to end	Day	70% 8% 7% 10% 3 1	1517
March	1st to 10th	Day	66% 9% 9% 11% 4	1900
	11th to 20th	Day	67% 9% 8% 13% 4	2089
	21st to end	Day	73% 11% 9% 6% 1	2304
April	1st to 10th	Day	70% 11% 9% 9% 1	2160
	11th to 20th	Day	66% 9% 8% 11% 5% 1	2132
	21st to end	Day	68% 8% 9% 8% 6% 1	2381
May	1st to 10th	Day	56% 11% 13% 15% 5%	2520
	11th to 20th	Day	55% 12% 15% 14% 4	2480
	21st to end	Day	61% 12% 12% 13% 2	2724
June	1st to 10th	Day	58% 10% 13% 13% 6% 1	2520
	11th to 20th	Day	62% 12% 12% 10% 4 1	2589
	21st to end	Day	40% 10% 16% 20% 12% 2	2700
July	1st to 10th	Day	34% 8% 13% 24% 17% 4	2550
	11th to 20th	Day	29% 8% 9% 25% 23% 5%	2445
	21st to end	Day	20% 4 10% 29% 30% 6%	2589
August	1st to 10th	Day	28% 7% 13% 24% 23% 5%	2490
	11th to 20th	Day	23% 8% 14% 32% 21% 3	2298
	21st to end	Day	33% 10% 12% 26% 16% 2	2428
September	1st to 10th	Day	31% 7% 13% 23% 20% 6%	2160
	11th to 20th	Day	41% 9% 10% 17% 18% 4	2160
	21st to end	Day	46% 7% 13% 17% 13% 3	1922
October	1st to 10th	Day	48% 8% 10% 23% 10% 1	1800
	11th to 20th	Day	53% 7% 11% 17% 11%	1800
	21st to end	Day	59% 8% 7% 13% 11% 1	1838
November	1st to 10th	Day	68% 8% 9% 9% 5% 1	1579
	11th to 20th	Day	72% 7% 7% 8% 5% 1	1520
	21st to end	Day	66% 8% 7% 10% 6% 3	1520
December	1st to 10th	Day	66% 8% 7% 10% 7% 1	1520
	11th to 20th	Day	67% 9% 11% 11% 2	1928
	21st to end	Day	69% 9% 10% 8% 4	2794
January	1st to 10th	Night	75% 13% 5% 4 2 1	4406
	11th to 20th	Night	61% 10% 8% 13% 5% 2	4420
	21st to end	Night	74% 9% 5% 7% 4 1	4848
February	1st to 10th	Night	71% 9% 7% 9% 4	2470
	11th to 20th	Night	64% 10% 9% 9% 7% 1	2404
	21st to end	Night	69% 9% 8% 10% 4	1937
March	1st to 10th	Night	62% 11% 10% 13% 5%	2280
	11th to 20th	Night	58% 10% 11% 15% 5% 1	2090
	21st to end	Night	68% 11% 10% 9% 2	2097
April	1st to 10th	Night	67% 14% 9% 9% 2	1800
	11th to 20th	Night	61% 10% 10% 11% 7% 1	1779
	21st to end	Night	63% 12% 7% 10% 8% 1	1574
May	1st to 10th	Night	52% 13% 15% 13% 5% 1	1440
	11th to 20th	Night	52% 14% 14% 15% 5% 1	1416
	21st to end	Night	57% 12% 14% 14% 2	1552
June	1st to 10th	Night	54% 13% 14% 12% 7%	1440
	11th to 20th	Night	61% 13% 12% 11% 4	1364
	21st to end	Night	42% 10% 15% 20% 11% 2	1260
July	1st to 10th	Night	34% 10% 14% 24% 14% 4	1294
	11th to 20th	Night	27% 10% 11% 24% 21% 6%	1392
	21st to end	Night	21% 6% 11% 23% 29% 9%	1488
August	1st to 10th	Night	25% 8% 13% 22% 27% 6%	1424
	11th to 20th	Night	23% 10% 13% 28% 21% 5%	1598
	21st to end	Night	32% 10% 12% 25% 19% 3	1927
September	1st to 10th	Night	31% 10% 13% 21% 21% 5%	1800
	11th to 20th	Night	43% 10% 8% 17% 17% 5%	1800
	21st to end	Night	45% 11% 10% 17% 12% 5%	2035
October	1st to 10th	Night	47% 7% 11% 23% 12% 1	2160
	11th to 20th	Night	52% 10% 8% 16% 13% 2	2160
	21st to end	Night	56% 8% 8% 13% 13% 1	2517
November	1st to 10th	Night	68% 9% 8% 10% 4 1	2497
	11th to 20th	Night	68% 7% 9% 9% 6% 1	2660
	21st to end	Night	67% 7% 7% 10% 6% 2	2660
December	1st to 10th	Night	69% 7% 7% 11% 6%	2660
	11th to 20th	Night	68% 9% 10% 10% 3	3276
	21st to end	Night	70% 13% 8% 6% 2	4862

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	36% 26% 23% 13% 2 1	180
	11th to 20th	Day	37% 23% 25% 11% 3	180
	21st to end	Day	36% 19% 25% 16% 2 1	211
February	1st to 10th	Day	42% 21% 21% 13% 3	370
	11th to 20th	Day	42% 21% 22% 13% 1	365
	21st to end	Day	34% 22% 26% 15% 2	357
March	1st to 10th	Day	33% 22% 27% 15% 2 1	460
	11th to 20th	Day	30% 21% 27% 12% 8% 1	460
	21st to end	Day	39% 20% 25% 11% 4	471
April	1st to 10th	Day	39% 22% 20% 14% 5% 1	420
	11th to 20th	Day	36% 23% 22% 15% 3 1	412
	21st to end	Day	38% 20% 24% 13% 4 1	420
May	1st to 10th	Day	32% 17% 29% 17% 4 1	423
	11th to 20th	Day	32% 17% 26% 16% 7% 2	448
	21st to end	Day	33% 17% 22% 19% 6% 2	485
June	1st to 10th	Day	31% 18% 24% 18% 6% 2	450
	11th to 20th	Day	34% 22% 28% 11% 5% 1	519
	21st to end	Day	17% 19% 31% 23% 7% 2	630
July	1st to 10th	Day	17% 13% 39% 25% 5% 2	545
	11th to 20th	Day	12% 18% 36% 22% 10% 2	444
	21st to end	Day	7% 13% 36% 27% 13% 4	487
August	1st to 10th	Day	13% 12% 31% 26% 13% 6%	447
	11th to 20th	Day	8% 10% 31% 31% 14% 5%	437
	21st to end	Day	16% 15% 32% 23% 9% 4	495
September	1st to 10th	Day	16% 17% 32% 25% 8% 2	450
	11th to 20th	Day	22% 14% 28% 24% 10% 1	450
	21st to end	Day	25% 14% 27% 25% 8% 1	450
October	1st to 10th	Day	27% 15% 23% 24% 9% 2	450
	11th to 20th	Day	32% 16% 20% 21% 10% 1	450
	21st to end	Day	41% 12% 24% 14% 7% 1	353
November	1st to 10th	Day	48% 10% 25% 14% 3	225
	11th to 20th	Day	45% 12% 23% 14% 6%	180
	21st to end	Day	38% 16% 26% 18% 3	180
December	1st to 10th	Day	40% 19% 15% 18% 7%	180
	11th to 20th	Day	41% 23% 24% 11% 1	180
	21st to end	Day	35% 18% 26% 18% 3	198
January	1st to 10th	Night	40% 18% 24% 15% 3	760
	11th to 20th	Night	34% 20% 24% 16% 6%	760
	21st to end	Night	36% 15% 25% 20% 4	836
February	1st to 10th	Night	37% 16% 26% 17% 4	760
	11th to 20th	Night	33% 15% 25% 20% 6% 1	744
	21st to end	Night	33% 18% 25% 18% 5%	628
March	1st to 10th	Night	29% 16% 23% 22% 9% 1	760
	11th to 20th	Night	30% 18% 23% 20% 7% 1	760
	21st to end	Night	33% 21% 20% 18% 7% 2	800
April	1st to 10th	Night	32% 19% 17% 24% 7% 2	720
	11th to 20th	Night	30% 16% 22% 23% 7% 2	711
	21st to end	Night	36% 13% 19% 22% 9%	494
May	1st to 10th	Night	26% 16% 18% 26% 14% 1	360
	11th to 20th	Night	25% 12% 15% 30% 16% 2	354
	21st to end	Night	31% 13% 13% 25% 17% 1	389
June	1st to 10th	Night	30% 11% 17% 28% 14% 1	360
	11th to 20th	Night	32% 17% 14% 23% 13%	360
	21st to end	Night	18% 10% 19% 30% 21% 1	360
July	1st to 10th	Night	16% 11% 11% 36% 23% 1	350
	11th to 20th	Night	12% 12% 17% 31% 26% 2	348
	21st to end	Night	9% 6% 13% 35% 33% 3	394
August	1st to 10th	Night	11% 6% 10% 32% 38% 3	358
	11th to 20th	Night	11% 6% 11% 30% 33% 9%	530
	21st to end	Night	16% 7% 17% 32% 24% 3	739
September	1st to 10th	Night	17% 6% 19% 35% 19% 3	720
	11th to 20th	Night	21% 11% 13% 26% 25% 4	720
	21st to end	Night	24% 8% 17% 33% 17% 1	720
October	1st to 10th	Night	27% 8% 18% 30% 16% 1	720
	11th to 20th	Night	31% 11% 17% 27% 12% 2	720
	21st to end	Night	37% 11% 22% 21% 7% 2	792
November	1st to 10th	Night	40% 14% 25% 17% 3	740
	11th to 20th	Night	41% 16% 23% 17% 2 1	760
	21st to end	Night	33% 17% 26% 21% 3	760
December	1st to 10th	Night	33% 16% 26% 20% 5%	760
	11th to 20th	Night	39% 19% 25% 14% 3	760
	21st to end	Night	39% 21% 25% 13% 2	836

Page generated at 2024-03-19 20:31:07. Version ac07

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