Elbow Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elbow Falls clear sky chart from 2005-11-06 to 2026-08-30.

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	6% 8% 3 8% 5% 5% 5% 4 7% 8% 40%	148695
	Night	3 7% 3 8% 5% 5% 5% 4 7% 9% 44%	142245
Transparency	Day	37% 8% 15% 24% 14% 2	148406
	Night	34% 8% 17% 24% 14% 3	142118
Seeing	Day	17% 23% 31% 19% 8% 2	17681
	Night	11% 24% 33% 22% 9% 2	26616

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	3 3 10% 6% 5% 7% 5% 9% 11% 42%	4125
	11th to 20th	Day	3 3 8% 5% 6% 6% 5% 8% 10% 47%	4393
	21st to end	Day	5% 3 10% 4 5% 5% 4 7% 9% 48%	5186
February	1st to 10th	Day	1 6% 3 10% 8% 9% 7% 6% 10% 9% 33%	1680
	11th to 20th	Day	1 6% 4 11% 7% 7% 7% 6% 8% 10% 34%	1803
	21st to end	Day	1 7% 4 15% 9% 6% 5% 5% 7% 8% 33%	1730
March	1st to 10th	Day	6% 3 10% 6% 5% 5% 4 6% 10% 44%	4618
	11th to 20th	Day	1 7% 5% 11% 5% 4 5% 4 8% 9% 41%	4988
	21st to end	Day	2 13% 8% 18% 7% 5% 4 4 6% 8% 25%	5781
April	1st to 10th	Day	4 15% 7% 11% 6% 6% 5% 4 7% 8% 27%	2541
	11th to 20th	Day	5% 17% 6% 13% 5% 4 5% 4 7% 8% 26%	2700
	21st to end	Day	7% 17% 6% 11% 5% 4 4 3 5% 8% 29%	2730
May	1st to 10th	Day	7% 18% 4 7% 4 4 4 3 5% 7% 37%	7998
	11th to 20th	Day	7% 16% 5% 9% 6% 6% 6% 5% 8% 8% 26%	8714
	21st to end	Day	11% 9% 3 6% 5% 5% 5% 5% 7% 9% 35%	9649
June	1st to 10th	Day	16% 12% 3 7% 6% 5% 4 4 6% 8% 28%	3150
	11th to 20th	Day	19% 11% 4 9% 5% 5% 5% 4 6% 5% 26%	3150
	21st to end	Day	12% 8% 3 7% 6% 5% 6% 5% 6% 8% 33%	3150
July	1st to 10th	Day	6% 5% 2 6% 4 4 5% 4 6% 8% 51%	8820
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 8% 47%	8820
	21st to end	Day	7% 5% 2 5% 3 4 4 4 5% 7% 54%	9152
August	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 4 8% 9% 38%	4681
	11th to 20th	Day	10% 5% 2 7% 5% 6% 5% 4 6% 8% 41%	4381
	21st to end	Day	9% 5% 2 5% 4 4 4 4 7% 9% 48%	4782
September	1st to 10th	Day	10% 8% 2 5% 4 4 4 4 6% 7% 46%	2445
	11th to 20th	Day	11% 9% 2 6% 4 4 4 5% 6% 6% 43%	2213
	21st to end	Day	7% 7% 3 5% 4 4 5% 5% 7% 8% 45%	2200
October	1st to 10th	Day	5% 7% 2 5% 4 4 4 4 6% 10% 50%	3511
	11th to 20th	Day	3 7% 3 6% 4 4 5% 4 7% 10% 46%	2942
	21st to end	Day	2 8% 3 7% 4 5% 5% 4 6% 8% 49%	3200
November	1st to 10th	Day	2 11% 5% 9% 6% 4 5% 4 7% 9% 37%	1775
	11th to 20th	Day	1 6% 3 9% 5% 4 4 4 7% 12% 45%	1570
	21st to end	Day	1 7% 2 9% 7% 5% 5% 5% 6% 9% 43%	1470
December	1st to 10th	Day	1 4 2 9% 5% 4 4 5% 9% 13% 44%	2360
	11th to 20th	Day	5% 2 8% 6% 6% 7% 6% 8% 10% 42%	2712
	21st to end	Day	7% 3 9% 6% 6% 6% 4 7% 8% 43%	3575
January	1st to 10th	Night	6% 4 11% 6% 5% 6% 5% 8% 10% 39%	8768
	11th to 20th	Night	3 2 8% 5% 5% 7% 6% 9% 10% 45%	8563
	21st to end	Night	5% 3 8% 6% 5% 6% 5% 8% 10% 45%	8994
February	1st to 10th	Night	1 6% 3 10% 8% 6% 8% 6% 7% 8% 36%	2940
	11th to 20th	Night	1 6% 5% 12% 7% 5% 7% 5% 7% 9% 37%	2699
	21st to end	Night	1 5% 4 11% 8% 7% 6% 6% 7% 9% 37%	2076
March	1st to 10th	Night	7% 4 10% 6% 5% 5% 5% 8% 10% 39%	5496
	11th to 20th	Night	1 6% 4 8% 5% 4 5% 5% 8% 10% 45%	5231
	21st to end	Night	1 12% 7% 14% 6% 5% 3 4 7% 9% 32%	5433
April	1st to 10th	Night	3 12% 5% 9% 6% 4 6% 4 6% 9% 36%	2079
	11th to 20th	Night	5% 11% 5% 12% 4 5% 5% 4 6% 8% 35%	1871
	21st to end	Night	3 11% 6% 11% 6% 5% 4 4 6% 7% 36%	1890
May	1st to 10th	Night	6% 15% 4 7% 4 3 3 3 4 7% 44%	4928
	11th to 20th	Night	6% 13% 4 9% 6% 5% 5% 4 7% 9% 32%	4132
	21st to end	Night	9% 8% 3 6% 5% 5% 5% 4 7% 8% 40%	4522
June	1st to 10th	Night	12% 13% 3 7% 5% 4 4 4 6% 7% 34%	1470
	11th to 20th	Night	17% 10% 3 7% 6% 4 5% 4 5% 7% 34%	1470
	21st to end	Night	9% 5% 2 6% 5% 4 5% 5% 7% 7% 46%	1470
July	1st to 10th	Night	5% 5% 2 5% 4 4 5% 4 6% 7% 52%	4140
	11th to 20th	Night	8% 5% 1 4 3 3 4 4 5% 7% 56%	4140
	21st to end	Night	10% 5% 1 3 2 2 3 3 5% 6% 60%	4912
August	1st to 10th	Night	10% 10% 2 5% 4 3 4 4 7% 8% 43%	2689
	11th to 20th	Night	6% 5% 2 5% 4 5% 5% 4 7% 9% 48%	2894
	21st to end	Night	7% 4 1 4 3 4 4 4 7% 9% 53%	3326
September	1st to 10th	Night	8% 7% 2 5% 3 3 4 3 5% 7% 52%	1952
	11th to 20th	Night	10% 7% 2 5% 3 3 3 4 7% 8% 47%	2186
	21st to end	Night	7% 7% 2 5% 3 4 4 4 6% 8% 51%	2200
October	1st to 10th	Night	4 7% 3 5% 3 3 4 4 5% 7% 53%	3686
	11th to 20th	Night	3 5% 3 5% 3 3 4 3 7% 10% 54%	4203
	21st to end	Night	2 6% 3 8% 4 4 4 4 7% 8% 51%	4600
November	1st to 10th	Night	2 9% 4 9% 4 5% 5% 5% 7% 9% 39%	2723
	11th to 20th	Night	1 6% 4 7% 5% 5% 5% 5% 7% 11% 44%	3049
	21st to end	Night	1 8% 3 8% 6% 5% 5% 4 8% 10% 42%	3150
December	1st to 10th	Night	5% 3 7% 5% 5% 5% 5% 8% 12% 46%	5040
	11th to 20th	Night	1 5% 3 10% 7% 7% 6% 6% 8% 11% 37%	5700
	21st to end	Night	1 8% 4 11% 6% 5% 5% 4 7% 8% 40%	7623

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	31% 8% 14% 26% 19% 3	4125
	11th to 20th	Day	30% 6% 19% 24% 16% 4	4415
	21st to end	Day	29% 7% 19% 27% 16% 2	5187
February	1st to 10th	Day	40% 8% 16% 20% 12% 4	1680
	11th to 20th	Day	39% 8% 16% 24% 11% 3	1812
	21st to end	Day	46% 7% 14% 18% 14% 2	1730
March	1st to 10th	Day	33% 5% 20% 17% 23% 2	4618
	11th to 20th	Day	34% 6% 21% 20% 18% 1	4989
	21st to end	Day	53% 8% 13% 15% 11%	5781
April	1st to 10th	Day	51% 8% 17% 16% 7%	2541
	11th to 20th	Day	52% 7% 14% 18% 7% 1	2700
	21st to end	Day	53% 6% 14% 18% 7% 1	2730
May	1st to 10th	Day	45% 6% 12% 25% 11%	7998
	11th to 20th	Day	49% 9% 13% 21% 8% 1	8718
	21st to end	Day	41% 9% 17% 24% 9%	9650
June	1st to 10th	Day	53% 8% 12% 16% 10% 1	3150
	11th to 20th	Day	55% 9% 11% 14% 10% 1	3150
	21st to end	Day	44% 10% 14% 20% 10% 1	3150
July	1st to 10th	Day	28% 7% 13% 26% 25% 2	8746
	11th to 20th	Day	31% 9% 12% 24% 17% 7%	8739
	21st to end	Day	27% 7% 11% 27% 22% 6%	8955
August	1st to 10th	Day	39% 9% 12% 27% 11% 1	4664
	11th to 20th	Day	37% 9% 18% 28% 7% 1	4422
	21st to end	Day	29% 7% 17% 33% 13% 1	4781
September	1st to 10th	Day	36% 6% 14% 26% 15% 3	2445
	11th to 20th	Day	38% 6% 15% 25% 13% 2	2213
	21st to end	Day	34% 10% 17% 26% 13% 2	2200
October	1st to 10th	Day	29% 5% 19% 34% 12% 1	3511
	11th to 20th	Day	30% 9% 22% 20% 16% 4	2942
	21st to end	Day	32% 6% 15% 30% 15% 2	3200
November	1st to 10th	Day	42% 9% 15% 19% 13% 2	1775
	11th to 20th	Day	32% 8% 22% 24% 12% 2	1570
	21st to end	Day	36% 8% 20% 23% 9% 3	1470
December	1st to 10th	Day	29% 8% 28% 21% 11% 2	2360
	11th to 20th	Day	32% 10% 21% 27% 9% 1	2714
	21st to end	Day	35% 7% 12% 24% 17% 5%	3575
January	1st to 10th	Night	36% 9% 16% 23% 15% 2	8769
	11th to 20th	Night	29% 8% 19% 21% 14% 9%	8603
	21st to end	Night	31% 8% 21% 23% 16% 1	8994
February	1st to 10th	Night	41% 7% 14% 19% 15% 4	2940
	11th to 20th	Night	40% 8% 18% 18% 13% 3	2700
	21st to end	Night	40% 7% 14% 22% 15% 3	2076
March	1st to 10th	Night	35% 6% 19% 19% 16% 4	5496
	11th to 20th	Night	30% 6% 22% 22% 19% 1	5231
	21st to end	Night	46% 8% 16% 18% 11% 1	5433
April	1st to 10th	Night	43% 7% 16% 20% 12% 1	2079
	11th to 20th	Night	45% 7% 16% 21% 9% 1	1871
	21st to end	Night	45% 8% 14% 22% 9% 2	1890
May	1st to 10th	Night	40% 5% 13% 27% 15% 1	4925
	11th to 20th	Night	44% 7% 12% 30% 7%	4132
	21st to end	Night	38% 8% 19% 25% 10%	4526
June	1st to 10th	Night	46% 9% 13% 22% 9%	1470
	11th to 20th	Night	48% 7% 14% 18% 12% 1	1470
	21st to end	Night	32% 10% 17% 29% 11% 1	1470
July	1st to 10th	Night	27% 8% 15% 26% 21% 3	4105
	11th to 20th	Night	24% 7% 16% 27% 20% 6%	4098
	21st to end	Night	24% 5% 14% 29% 22% 5%	4805
August	1st to 10th	Night	33% 9% 14% 31% 11% 2	2681
	11th to 20th	Night	29% 8% 25% 28% 9% 1	2919
	21st to end	Night	24% 8% 22% 32% 13% 1	3326
September	1st to 10th	Night	30% 6% 17% 29% 15% 3	1952
	11th to 20th	Night	34% 6% 15% 27% 14% 4	2186
	21st to end	Night	32% 6% 18% 28% 15% 2	2200
October	1st to 10th	Night	29% 7% 15% 28% 20% 1	3686
	11th to 20th	Night	24% 7% 20% 30% 17% 2	4203
	21st to end	Night	29% 6% 15% 33% 16% 1	4600
November	1st to 10th	Night	38% 11% 16% 20% 12% 2	2723
	11th to 20th	Night	32% 9% 18% 24% 16% 2	3049
	21st to end	Night	34% 8% 19% 22% 12% 4	3150
December	1st to 10th	Night	28% 10% 27% 23% 9% 3	5040
	11th to 20th	Night	37% 10% 21% 20% 12% 1	5697
	21st to end	Night	38% 7% 12% 23% 16% 5%	7623

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	14% 27% 29% 21% 6% 3	220
	11th to 20th	Day	10% 28% 36% 20% 5% 1	220
	21st to end	Day	11% 36% 35% 10% 5% 2	242
February	1st to 10th	Day	15% 27% 37% 14% 5% 1	220
	11th to 20th	Day	8% 25% 43% 16% 7%	309
	21st to end	Day	19% 26% 30% 19% 6%	446
March	1st to 10th	Day	15% 30% 34% 14% 6% 1	540
	11th to 20th	Day	13% 30% 35% 15% 5% 1	540
	21st to end	Day	15% 32% 32% 15% 5% 2	594
April	1st to 10th	Day	15% 30% 36% 15% 4	540
	11th to 20th	Day	16% 28% 32% 16% 7% 2	532
	21st to end	Day	19% 27% 26% 18% 9% 1	540
May	1st to 10th	Day	21% 19% 29% 20% 9% 2	543
	11th to 20th	Day	22% 15% 25% 24% 12% 2	759
	21st to end	Day	25% 16% 23% 21% 13% 2	844
June	1st to 10th	Day	22% 22% 29% 18% 8% 1	780
	11th to 20th	Day	25% 22% 25% 20% 7% 1	780
	21st to end	Day	16% 18% 29% 23% 10% 4	780
July	1st to 10th	Day	13% 15% 33% 23% 13% 2	771
	11th to 20th	Day	15% 19% 30% 24% 10% 2	768
	21st to end	Day	10% 18% 36% 25% 10% 3	702
August	1st to 10th	Day	14% 17% 31% 26% 11% 1	567
	11th to 20th	Day	14% 17% 32% 26% 8% 2	557
	21st to end	Day	15% 17% 33% 23% 9% 3	620
September	1st to 10th	Day	16% 23% 29% 22% 8% 2	530
	11th to 20th	Day	18% 18% 30% 26% 7% 1	530
	21st to end	Day	21% 32% 27% 15% 5% 1	530
October	1st to 10th	Day	17% 23% 31% 19% 10% 1	480
	11th to 20th	Day	15% 28% 32% 17% 6% 1	330
	21st to end	Day	20% 32% 31% 12% 5% 1	363
November	1st to 10th	Day	21% 35% 30% 10% 5% 1	330
	11th to 20th	Day	22% 29% 35% 10% 3	272
	21st to end	Day	14% 34% 29% 12% 7% 5%	220
December	1st to 10th	Day	16% 30% 35% 11% 5% 2	220
	11th to 20th	Day	11% 35% 38% 14% 1 1	220
	21st to end	Day	15% 22% 40% 14% 6% 2	242
January	1st to 10th	Night	12% 32% 38% 15% 3	1050
	11th to 20th	Night	9% 33% 39% 16% 2 2	976
	21st to end	Night	9% 35% 35% 15% 6%	924
February	1st to 10th	Night	9% 30% 31% 19% 9% 2	840
	11th to 20th	Night	7% 27% 37% 20% 8%	824
	21st to end	Night	11% 21% 34% 22% 11% 2	692
March	1st to 10th	Night	7% 26% 38% 20% 8% 2	840
	11th to 20th	Night	8% 25% 39% 21% 6% 1	840
	21st to end	Night	9% 22% 31% 27% 9% 2	924
April	1st to 10th	Night	11% 21% 32% 27% 8% 1	819
	11th to 20th	Night	13% 21% 34% 25% 8%	623
	21st to end	Night	13% 18% 32% 26% 9% 1	630
May	1st to 10th	Night	14% 14% 30% 29% 12% 1	494
	11th to 20th	Night	14% 13% 29% 25% 16% 3	414
	21st to end	Night	23% 11% 24% 24% 16% 1	455
June	1st to 10th	Night	20% 14% 26% 27% 10% 3	420
	11th to 20th	Night	23% 13% 26% 27% 12%	420
	21st to end	Night	12% 12% 29% 28% 18% 1	420
July	1st to 10th	Night	12% 9% 22% 37% 18% 1	410
	11th to 20th	Night	11% 10% 31% 32% 14% 2	408
	21st to end	Night	9% 10% 24% 37% 18% 2	460
August	1st to 10th	Night	13% 7% 21% 33% 23% 2	418
	11th to 20th	Night	11% 9% 24% 32% 21% 3	563
	21st to end	Night	11% 12% 27% 33% 15% 2	687
September	1st to 10th	Night	12% 13% 26% 31% 14% 4	752
	11th to 20th	Night	15% 12% 27% 28% 13% 5%	800
	21st to end	Night	14% 26% 30% 20% 9% 3	800
October	1st to 10th	Night	14% 19% 31% 26% 9% 2	800
	11th to 20th	Night	12% 26% 32% 23% 7% 1	800
	21st to end	Night	12% 29% 34% 19% 4 1	880
November	1st to 10th	Night	12% 31% 40% 12% 4 1	878
	11th to 20th	Night	11% 37% 36% 14% 1 1	1050
	21st to end	Night	9% 33% 38% 14% 5% 1	1050
December	1st to 10th	Night	11% 31% 35% 14% 8% 1	1050
	11th to 20th	Night	7% 34% 37% 16% 4 1	1050
	21st to end	Night	8% 31% 38% 15% 6% 1	1155

Page generated at 2026-08-27 02:07:10. Version ac07

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