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 2024-11-04.

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	16% 18% 4 8% 4 4 4 3 4 5% 31%	105782
	Night	17% 21% 5% 8% 5% 4 4 3 4 5% 25%	101836
Transparency	Day	50% 9% 10% 16% 11% 3	105547
	Night	54% 11% 10% 14% 9% 3	101717
Seeing	Day	28% 18% 27% 19% 6% 2	14773
	Night	30% 14% 21% 23% 11% 1	23319

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% 31% 7% 10% 5% 4 5% 2 4 4 6%	2539
	11th to 20th	Day	18% 21% 7% 11% 4 4 3 4 5% 5% 18%	2516
	21st to end	Day	30% 26% 6% 10% 4 3 3 2 3 3 10%	2807
February	1st to 10th	Day	20% 28% 7% 11% 5% 4 4 3 3 4 12%	1710
	11th to 20th	Day	15% 34% 6% 7% 5% 3 3 2 3 3 18%	1665
	21st to end	Day	14% 33% 9% 9% 4 3 3 3 3 4 16%	1517
March	1st to 10th	Day	10% 23% 6% 12% 6% 5% 5% 4 4 4 20%	3138
	11th to 20th	Day	11% 25% 5% 8% 4 2 3 2 3 3 35%	3489
	21st to end	Day	16% 29% 6% 11% 6% 5% 4 3 3 3 13%	4005
April	1st to 10th	Day	18% 31% 6% 8% 5% 4 3 3 4 4 13%	2280
	11th to 20th	Day	17% 27% 5% 9% 5% 4 3 3 3 4 20%	2252
	21st to end	Day	18% 29% 5% 10% 5% 4 3 3 3 3 17%	2515
May	1st to 10th	Day	14% 21% 5% 8% 5% 4 4 3 4 5% 28%	4420
	11th to 20th	Day	12% 18% 3 9% 6% 5% 4 3 5% 7% 27%	4377
	21st to end	Day	24% 26% 5% 9% 5% 4 3 2 3 5% 13%	4813
June	1st to 10th	Day	27% 14% 3 7% 5% 4 4 3 4 5% 23%	2660
	11th to 20th	Day	25% 18% 4 9% 5% 5% 5% 3 4 5% 17%	2733
	21st to end	Day	15% 10% 3 7% 4 4 4 3 5% 7% 37%	2850
July	1st to 10th	Day	7% 5% 2 3 3 3 3 3 4 5% 63%	4590
	11th to 20th	Day	5% 5% 2 3 3 3 3 2 4 4 66%	4420
	21st to end	Day	8% 5% 2 4 3 3 3 3 4 5% 60%	4790
August	1st to 10th	Day	5% 5% 1 4 3 3 3 3 4 7% 63%	4401
	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%	1606
	11th to 20th	Day	27% 26% 4 8% 4 3 2 2 3 3 17%	1520
	21st to end	Day	23% 26% 4 9% 4 3 3 3 3 3 19%	1520
December	1st to 10th	Day	19% 23% 4 9% 6% 4 4 3 3 5% 20%	1520
	11th to 20th	Day	21% 23% 6% 10% 5% 5% 5% 4 6% 5% 11%	1925
	21st to end	Day	20% 23% 6% 10% 6% 6% 6% 3 4 4 12%	2794
January	1st to 10th	Night	22% 31% 9% 10% 6% 5% 3 2 3 3 6%	4406
	11th to 20th	Night	20% 18% 8% 11% 4 3 3 3 5% 7% 17%	4382
	21st to end	Night	26% 25% 5% 10% 5% 5% 4 2 3 4 10%	4848
February	1st to 10th	Night	18% 28% 7% 10% 6% 4 4 3 4 5% 12%	2470
	11th to 20th	Night	15% 28% 7% 7% 5% 4 5% 3 4 4 19%	2402
	21st to end	Night	13% 34% 7% 9% 4 3 4 2 4 3 16%	1937
March	1st to 10th	Night	10% 19% 7% 12% 7% 6% 6% 5% 6% 6% 16%	3736
	11th to 20th	Night	11% 21% 6% 7% 3 3 3 2 3 5% 37%	3489
	21st to end	Night	16% 32% 7% 10% 4 4 4 3 4 4 12%	3648
April	1st to 10th	Night	15% 30% 7% 8% 4 5% 4 4 4 5% 13%	1900
	11th to 20th	Night	16% 25% 5% 8% 4 4 4 3 4 5% 21%	1879
	21st to end	Night	18% 29% 6% 9% 4 3 3 3 4 4 18%	1660
May	1st to 10th	Night	13% 26% 4 6% 4 4 3 3 4 4 29%	2540
	11th to 20th	Night	10% 22% 3 8% 4 4 4 4 5% 6% 30%	2516
	21st to end	Night	17% 37% 4 8% 4 3 4 3 4 3 12%	2762
June	1st to 10th	Night	23% 17% 4 8% 5% 4 4 3 5% 6% 22%	1520
	11th to 20th	Night	23% 20% 5% 9% 6% 5% 5% 4 3 4 18%	1439
	21st to end	Night	14% 11% 4 10% 6% 5% 4 3 5% 5% 34%	1330
July	1st to 10th	Night	7% 8% 2 5% 3 3 4 3 4 4 56%	2363
	11th to 20th	Night	5% 5% 2 4 3 2 3 2 3 4 66%	2540
	21st to end	Night	8% 6% 2 5% 5% 5% 4 3 5% 5% 52%	2762
August	1st to 10th	Night	4 5% 2 4 2 4 3 3 5% 7% 61%	2529
	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 3 14%	2542
	11th to 20th	Night	26% 24% 4 8% 4 4 3 3 3 4 17%	2660
	21st to end	Night	21% 26% 5% 8% 4 4 3 3 4 4 17%	2660
December	1st to 10th	Night	19% 25% 5% 9% 6% 4 4 3 4 3 18%	2660
	11th to 20th	Night	20% 25% 6% 9% 5% 5% 5% 3 5% 4 11%	3280
	21st to end	Night	20% 26% 7% 12% 6% 5% 6% 3 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	57% 13% 10% 13% 7% 1	3138
	11th to 20th	Day	49% 11% 7% 31% 3	3489
	21st to end	Day	69% 12% 10% 7% 2	4005
April	1st to 10th	Day	70% 11% 10% 9% 1	2280
	11th to 20th	Day	64% 9% 9% 12% 6% 1	2252
	21st to end	Day	68% 8% 9% 8% 6% 1	2515
May	1st to 10th	Day	49% 9% 12% 18% 11% 1	4420
	11th to 20th	Day	40% 19% 20% 18% 4	4380
	21st to end	Day	63% 15% 13% 9% 1	4814
June	1st to 10th	Day	57% 10% 13% 12% 7% 1	2660
	11th to 20th	Day	61% 12% 11% 11% 5% 1	2733
	21st to end	Day	40% 10% 16% 20% 12% 2	2850
July	1st to 10th	Day	21% 5% 8% 17% 27% 22%	4520
	11th to 20th	Day	19% 5% 6% 18% 32% 21%	4345
	21st to end	Day	20% 6% 10% 29% 29% 5%	4639
August	1st to 10th	Day	20% 5% 8% 24% 34% 10%	4384
	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	69% 8% 9% 9% 5% 1	1606
	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	52% 18% 12% 11% 6% 1	3736
	11th to 20th	Night	44% 11% 14% 28% 3	3490
	21st to end	Night	67% 12% 11% 8% 2	3648
April	1st to 10th	Night	66% 14% 9% 9% 2	1900
	11th to 20th	Night	59% 10% 10% 11% 9% 1	1879
	21st to end	Night	63% 12% 7% 10% 7% 1	1660
May	1st to 10th	Night	48% 11% 11% 19% 11% 1	2540
	11th to 20th	Night	38% 18% 19% 20% 4	2516
	21st to end	Night	58% 19% 12% 9% 1	2762
June	1st to 10th	Night	53% 13% 15% 11% 8%	1520
	11th to 20th	Night	60% 13% 12% 11% 4	1439
	21st to end	Night	43% 10% 15% 20% 11% 2	1330
July	1st to 10th	Night	21% 8% 8% 18% 19% 26%	2324
	11th to 20th	Night	17% 6% 7% 18% 34% 19%	2492
	21st to end	Night	20% 10% 12% 20% 27% 10%	2674
August	1st to 10th	Night	19% 6% 9% 22% 37% 7%	2521
	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% 8% 10% 4 1	2542
	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	38% 19% 26% 12% 4	506
April	1st to 10th	Day	39% 21% 20% 14% 5% 1	460
	11th to 20th	Day	34% 24% 23% 15% 3 1	452
	21st to end	Day	38% 20% 24% 12% 4 1	460
May	1st to 10th	Day	32% 17% 28% 18% 4 1	463
	11th to 20th	Day	32% 17% 26% 16% 7% 2	488
	21st to end	Day	36% 16% 22% 19% 6% 2	529
June	1st to 10th	Day	32% 17% 25% 19% 6% 2	490
	11th to 20th	Day	34% 22% 27% 12% 4 1	563
	21st to end	Day	18% 19% 32% 22% 7% 2	680
July	1st to 10th	Day	16% 14% 39% 24% 5% 2	590
	11th to 20th	Day	12% 17% 36% 23% 11% 3	484
	21st to end	Day	8% 13% 36% 26% 12% 4	531
August	1st to 10th	Day	11% 12% 32% 26% 13% 6%	487
	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	47% 12% 24% 14% 3	234
	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	32% 21% 20% 18% 6% 1	836
April	1st to 10th	Night	32% 19% 16% 24% 7% 1	760
	11th to 20th	Night	30% 16% 23% 23% 7% 2	751
	21st to end	Night	36% 14% 19% 22% 8%	520
May	1st to 10th	Night	26% 16% 18% 26% 14% 1	380
	11th to 20th	Night	25% 12% 17% 29% 17% 2	374
	21st to end	Night	32% 14% 12% 25% 16% 1	411
June	1st to 10th	Night	30% 11% 16% 27% 15% 1	380
	11th to 20th	Night	32% 17% 15% 23% 12% 1	380
	21st to end	Night	19% 10% 19% 30% 21% 1	380
July	1st to 10th	Night	15% 12% 11% 37% 23% 1	370
	11th to 20th	Night	11% 11% 17% 32% 27% 2	368
	21st to end	Night	10% 6% 13% 36% 32% 3	416
August	1st to 10th	Night	10% 6% 11% 33% 38% 3	378
	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	41% 15% 25% 17% 3	754
	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 2024-11-01 19:47:42. Version ac07

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