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 2025-04-26.

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% 9% 3 9% 5% 5% 5% 4 7% 8% 39%	117119
	Night	3 7% 3 8% 5% 5% 5% 5% 7% 9% 42%	120218
Transparency	Day	39% 8% 15% 22% 13% 2	116871
	Night	35% 8% 17% 23% 14% 3	120113
Seeing	Day	16% 23% 31% 20% 8% 2	15794
	Night	11% 24% 33% 22% 9% 2	25059

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 12% 7% 6% 7% 5% 9% 11% 37%	3179
	11th to 20th	Day	4 3 10% 6% 7% 7% 5% 8% 10% 39%	3363
	21st to end	Day	4 2 8% 4 5% 5% 4 7% 9% 51%	4004
February	1st to 10th	Day	6% 3 10% 8% 9% 7% 6% 10% 9% 33%	1600
	11th to 20th	Day	1 6% 4 12% 7% 7% 7% 6% 8% 10% 32%	1715
	21st to end	Day	1 7% 4 16% 10% 6% 5% 5% 7% 8% 32%	1650
March	1st to 10th	Day	1 6% 4 10% 6% 5% 5% 4 6% 10% 44%	4518
	11th to 20th	Day	1 7% 5% 11% 5% 4 5% 4 8% 8% 41%	4881
	21st to end	Day	2 13% 8% 19% 7% 5% 4 4 6% 8% 25%	5656
April	1st to 10th	Day	4 15% 7% 11% 6% 6% 5% 4 7% 8% 27%	2420
	11th to 20th	Day	5% 17% 6% 13% 6% 4 5% 4 7% 8% 26%	2570
	21st to end	Day	7% 17% 6% 10% 6% 4 4 4 5% 8% 29%	2537
May	1st to 10th	Day	11% 25% 4 7% 5% 4 4 3 5% 6% 24%	4314
	11th to 20th	Day	7% 11% 4 7% 6% 5% 6% 6% 9% 9% 29%	4680
	21st to end	Day	14% 13% 3 8% 6% 6% 6% 4 7% 8% 25%	5161
June	1st to 10th	Day	17% 11% 3 8% 6% 5% 4 4 6% 8% 26%	2850
	11th to 20th	Day	21% 11% 4 10% 6% 5% 5% 4 6% 5% 24%	2850
	21st to end	Day	11% 8% 3 7% 6% 5% 6% 5% 6% 8% 34%	2850
July	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 4 6% 7% 46%	4740
	11th to 20th	Day	6% 4 2 5% 4 5% 6% 5% 7% 9% 48%	4740
	21st to end	Day	4 4 2 5% 3 5% 5% 4 6% 8% 54%	4917
August	1st to 10th	Day	11% 7% 2 7% 5% 4 5% 4 8% 9% 37%	4401
	11th to 20th	Day	10% 5% 2 7% 5% 6% 5% 4 6% 8% 41%	4115
	21st to end	Day	9% 6% 2 5% 4 4 4 4 7% 8% 47%	4521
September	1st to 10th	Day	10% 8% 2 6% 4 4 4 4 6% 7% 46%	2323
	11th to 20th	Day	11% 9% 2 6% 4 4 4 5% 6% 7% 42%	2103
	21st to end	Day	7% 8% 3 6% 4 4 5% 5% 7% 8% 44%	2090
October	1st to 10th	Day	5% 7% 2 5% 4 4 4 3 6% 10% 50%	3404
	11th to 20th	Day	3 7% 3 6% 4 4 5% 4 8% 10% 45%	2852
	21st to end	Day	2 8% 3 7% 4 5% 5% 4 6% 8% 48%	3101
November	1st to 10th	Day	2 11% 5% 9% 6% 4 5% 4 7% 9% 37%	1689
	11th to 20th	Day	1 6% 3 8% 5% 4 4 4 8% 12% 45%	1495
	21st to end	Day	1 7% 3 9% 7% 5% 6% 5% 6% 9% 43%	1400
December	1st to 10th	Day	1 5% 2 9% 5% 4 4 5% 9% 12% 44%	2290
	11th to 20th	Day	5% 2 8% 6% 6% 7% 6% 8% 10% 42%	2642
	21st to end	Day	7% 3 10% 6% 6% 6% 4 7% 8% 43%	3498
January	1st to 10th	Night	6% 4 14% 7% 6% 7% 6% 8% 10% 32%	6766
	11th to 20th	Night	4 3 9% 6% 6% 7% 6% 10% 10% 39%	6579
	21st to end	Night	5% 3 8% 6% 5% 5% 5% 8% 10% 45%	6952
February	1st to 10th	Night	1 6% 3 10% 8% 6% 7% 6% 7% 8% 37%	2800
	11th to 20th	Night	1 6% 5% 12% 7% 5% 6% 5% 7% 9% 37%	2567
	21st to end	Night	1 5% 3 11% 8% 7% 6% 6% 7% 9% 37%	1980
March	1st to 10th	Night	7% 4 10% 6% 5% 5% 5% 8% 10% 39%	5376
	11th to 20th	Night	1 6% 4 8% 5% 4 5% 5% 8% 10% 45%	5118
	21st to end	Night	1 13% 7% 15% 5% 5% 3 4 7% 9% 32%	5316
April	1st to 10th	Night	3 12% 5% 9% 6% 4 6% 4 6% 9% 36%	1980
	11th to 20th	Night	5% 11% 5% 12% 4 5% 5% 4 7% 8% 35%	1781
	21st to end	Night	3 12% 6% 10% 6% 5% 4 4 6% 7% 37%	1759
May	1st to 10th	Night	9% 21% 5% 9% 5% 4 3 3 5% 5% 30%	2646
	11th to 20th	Night	6% 10% 4 8% 6% 6% 5% 4 7% 9% 35%	2213
	21st to end	Night	12% 12% 3 7% 5% 5% 5% 4 6% 8% 33%	2414
June	1st to 10th	Night	12% 13% 3 7% 5% 4 4 5% 6% 7% 34%	1330
	11th to 20th	Night	18% 11% 3 7% 6% 4 5% 4 5% 7% 32%	1330
	21st to end	Night	8% 5% 1 6% 5% 4 5% 5% 7% 8% 47%	1330
July	1st to 10th	Night	5% 5% 2 4 4 4 5% 4 6% 7% 54%	2220
	11th to 20th	Night	5% 4 1 3 4 3 4 5% 6% 8% 57%	2220
	21st to end	Night	5% 3 1 3 3 3 3 3 6% 5% 64%	2631
August	1st to 10th	Night	10% 10% 2 5% 4 3 4 4 7% 8% 43%	2529
	11th to 20th	Night	6% 5% 2 5% 4 5% 5% 4 7% 9% 49%	2720
	21st to end	Night	8% 4 1 4 3 4 4 4 7% 9% 52%	3146
September	1st to 10th	Night	9% 7% 2 5% 3 3 4 4 5% 7% 52%	1854
	11th to 20th	Night	11% 8% 2 6% 3 3 3 4 7% 8% 46%	2076
	21st to end	Night	7% 7% 2 5% 3 4 4 3 6% 8% 50%	2090
October	1st to 10th	Night	4 7% 3 5% 3 3 4 4 5% 7% 52%	3573
	11th to 20th	Night	3 5% 3 5% 3 3 4 3 7% 10% 54%	4073
	21st to end	Night	2 6% 3 8% 4 4 4 4 7% 9% 50%	4457
November	1st to 10th	Night	2 9% 4 9% 4 5% 5% 5% 7% 9% 39%	2590
	11th to 20th	Night	1 6% 4 7% 5% 4 5% 5% 7% 11% 45%	2904
	21st to end	Night	1 7% 3 9% 6% 5% 6% 4 8% 10% 41%	3000
December	1st to 10th	Night	5% 3 7% 5% 5% 5% 5% 8% 12% 46%	4890
	11th to 20th	Night	1 5% 3 10% 7% 7% 6% 6% 8% 10% 37%	5550
	21st to end	Night	1 8% 4 11% 6% 5% 5% 4 7% 8% 40%	7458

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	35% 9% 13% 24% 16% 3	3179
	11th to 20th	Day	36% 6% 19% 19% 16% 4	3385
	21st to end	Day	26% 7% 19% 30% 16% 2	4004
February	1st to 10th	Day	41% 8% 16% 20% 12% 4	1600
	11th to 20th	Day	40% 8% 16% 23% 10% 3	1724
	21st to end	Day	47% 8% 14% 17% 13% 2	1650
March	1st to 10th	Day	33% 5% 19% 17% 23% 3	4518
	11th to 20th	Day	34% 6% 21% 20% 18% 1	4882
	21st to end	Day	54% 8% 13% 15% 11%	5656
April	1st to 10th	Day	51% 8% 17% 16% 8%	2420
	11th to 20th	Day	53% 7% 14% 18% 8% 1	2570
	21st to end	Day	53% 6% 15% 18% 7% 1	2537
May	1st to 10th	Day	59% 6% 11% 18% 5%	4314
	11th to 20th	Day	43% 10% 15% 24% 8%	4684
	21st to end	Day	52% 10% 13% 15% 11%	5162
June	1st to 10th	Day	54% 8% 12% 15% 9% 1	2850
	11th to 20th	Day	57% 9% 11% 14% 8% 1	2850
	21st to end	Day	43% 10% 14% 20% 11% 2	2850
July	1st to 10th	Day	33% 8% 11% 20% 25% 4	4666
	11th to 20th	Day	28% 10% 12% 28% 18% 3	4659
	21st to end	Day	25% 7% 10% 25% 26% 7%	4762
August	1st to 10th	Day	39% 9% 12% 27% 11% 1	4384
	11th to 20th	Day	37% 9% 18% 28% 7% 1	4156
	21st to end	Day	30% 7% 17% 32% 12% 1	4520
September	1st to 10th	Day	36% 6% 13% 26% 15% 3	2323
	11th to 20th	Day	39% 6% 16% 24% 13% 2	2103
	21st to end	Day	35% 10% 16% 25% 13% 2	2090
October	1st to 10th	Day	30% 5% 19% 33% 12% 1	3404
	11th to 20th	Day	30% 9% 22% 20% 15% 3	2852
	21st to end	Day	33% 6% 14% 31% 14% 1	3101
November	1st to 10th	Day	42% 9% 15% 20% 12% 2	1689
	11th to 20th	Day	31% 9% 22% 24% 11% 2	1495
	21st to end	Day	36% 9% 21% 22% 9% 4	1400
December	1st to 10th	Day	29% 8% 29% 21% 11% 2	2290
	11th to 20th	Day	32% 10% 21% 27% 9% 1	2644
	21st to end	Day	36% 7% 12% 24% 17% 5%	3498
January	1st to 10th	Night	41% 10% 15% 22% 10% 2	6766
	11th to 20th	Night	34% 9% 16% 19% 15% 8%	6619
	21st to end	Night	30% 8% 20% 23% 18% 2	6952
February	1st to 10th	Night	41% 8% 14% 20% 15% 3	2800
	11th to 20th	Night	40% 8% 18% 18% 12% 3	2568
	21st to end	Night	40% 7% 14% 21% 15% 2	1980
March	1st to 10th	Night	35% 6% 19% 19% 16% 5%	5376
	11th to 20th	Night	30% 6% 21% 22% 19% 1	5118
	21st to end	Night	46% 8% 16% 18% 11% 1	5316
April	1st to 10th	Night	43% 8% 16% 20% 12% 1	1980
	11th to 20th	Night	45% 7% 16% 21% 9% 1	1781
	21st to end	Night	45% 8% 14% 23% 8% 2	1759
May	1st to 10th	Night	54% 7% 12% 22% 6%	2646
	11th to 20th	Night	39% 9% 16% 29% 7%	2213
	21st to end	Night	46% 8% 15% 19% 11%	2414
June	1st to 10th	Night	46% 10% 13% 22% 9% 1	1330
	11th to 20th	Night	50% 8% 14% 17% 11% 1	1330
	21st to end	Night	31% 10% 18% 28% 12% 1	1330
July	1st to 10th	Night	26% 8% 15% 25% 21% 5%	2185
	11th to 20th	Night	22% 8% 16% 32% 19% 4	2178
	21st to end	Night	20% 6% 12% 28% 26% 8%	2548
August	1st to 10th	Night	34% 9% 14% 31% 11% 2	2521
	11th to 20th	Night	28% 8% 25% 28% 9% 1	2745
	21st to end	Night	25% 8% 22% 31% 12% 1	3146
September	1st to 10th	Night	31% 6% 17% 28% 15% 3	1854
	11th to 20th	Night	35% 7% 15% 26% 13% 4	2076
	21st to end	Night	32% 6% 18% 27% 15% 2	2090
October	1st to 10th	Night	29% 7% 15% 27% 21% 1	3573
	11th to 20th	Night	23% 7% 21% 31% 17% 2	4073
	21st to end	Night	30% 6% 15% 33% 15% 1	4457
November	1st to 10th	Night	39% 11% 17% 20% 12% 2	2590
	11th to 20th	Night	32% 9% 18% 24% 15% 2	2904
	21st to end	Night	35% 8% 20% 22% 12% 4	3000
December	1st to 10th	Night	28% 10% 28% 23% 9% 3	4890
	11th to 20th	Night	37% 10% 21% 19% 12% 1	5547
	21st to end	Night	38% 7% 12% 22% 16% 5%	7458

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	9% 28% 31% 23% 7% 3	200
	11th to 20th	Day	9% 27% 36% 22% 6% 1	200
	21st to end	Day	10% 35% 35% 11% 6% 2	220
February	1st to 10th	Day	13% 27% 39% 15% 6% 2	200
	11th to 20th	Day	9% 24% 43% 16% 8%	281
	21st to end	Day	17% 26% 31% 20% 7%	414
March	1st to 10th	Day	12% 31% 34% 15% 6% 1	500
	11th to 20th	Day	10% 31% 36% 16% 5% 2	500
	21st to end	Day	14% 31% 32% 16% 5% 2	550
April	1st to 10th	Day	15% 31% 35% 15% 4	500
	11th to 20th	Day	15% 28% 32% 17% 7% 2	492
	21st to end	Day	19% 27% 26% 18% 9% 1	481
May	1st to 10th	Day	22% 19% 27% 21% 10% 3	463
	11th to 20th	Day	22% 13% 24% 25% 13% 2	661
	21st to end	Day	26% 14% 22% 21% 14% 2	734
June	1st to 10th	Day	21% 20% 30% 19% 8% 1	680
	11th to 20th	Day	26% 21% 23% 20% 8% 1	680
	21st to end	Day	16% 17% 29% 24% 11% 4	680
July	1st to 10th	Day	14% 13% 32% 24% 15% 3	671
	11th to 20th	Day	13% 18% 29% 26% 11% 3	668
	21st to end	Day	8% 15% 37% 26% 10% 3	606
August	1st to 10th	Day	14% 18% 30% 26% 11% 1	487
	11th to 20th	Day	13% 17% 31% 27% 9% 3	477
	21st to end	Day	18% 17% 32% 22% 9% 2	539
September	1st to 10th	Day	17% 25% 30% 20% 7% 2	490
	11th to 20th	Day	19% 19% 31% 23% 6% 1	490
	21st to end	Day	21% 32% 26% 15% 5% 1	490
October	1st to 10th	Day	17% 23% 29% 19% 10% 1	443
	11th to 20th	Day	15% 27% 32% 18% 6% 1	300
	21st to end	Day	19% 31% 31% 13% 5% 1	330
November	1st to 10th	Day	17% 36% 31% 11% 5% 1	300
	11th to 20th	Day	21% 30% 34% 11% 3	247
	21st to end	Day	13% 34% 28% 12% 8% 6%	200
December	1st to 10th	Day	13% 31% 36% 13% 6% 2	200
	11th to 20th	Day	8% 34% 41% 15% 2 1	200
	21st to end	Day	13% 21% 41% 15% 7% 2	220
January	1st to 10th	Night	11% 32% 38% 16% 3	1000
	11th to 20th	Night	7% 34% 39% 17% 2 2	930
	21st to end	Night	9% 34% 36% 15% 6%	880
February	1st to 10th	Night	8% 29% 32% 20% 9% 2	800
	11th to 20th	Night	7% 27% 37% 21% 8%	784
	21st to end	Night	9% 21% 34% 23% 11% 2	660
March	1st to 10th	Night	7% 25% 38% 21% 8% 2	800
	11th to 20th	Night	7% 25% 39% 22% 6% 1	800
	21st to end	Night	9% 21% 30% 28% 10% 3	880
April	1st to 10th	Night	11% 21% 32% 27% 8% 1	780
	11th to 20th	Night	12% 20% 34% 25% 8% 1	593
	21st to end	Night	13% 17% 32% 26% 10% 1	587
May	1st to 10th	Night	15% 13% 27% 31% 14% 1	447
	11th to 20th	Night	14% 12% 27% 26% 18% 3	374
	21st to end	Night	25% 12% 21% 24% 18% 1	411
June	1st to 10th	Night	19% 14% 25% 28% 11% 3	380
	11th to 20th	Night	23% 13% 25% 26% 13%	380
	21st to end	Night	11% 12% 27% 28% 19% 1	380
July	1st to 10th	Night	13% 8% 20% 37% 20% 2	370
	11th to 20th	Night	11% 10% 29% 34% 15% 2	368
	21st to end	Night	8% 10% 23% 37% 19% 2	416
August	1st to 10th	Night	13% 6% 19% 34% 25% 3	378
	11th to 20th	Night	10% 9% 24% 32% 22% 3	509
	21st to end	Night	12% 13% 26% 31% 16% 2	627
September	1st to 10th	Night	13% 13% 27% 29% 14% 4	714
	11th to 20th	Night	15% 12% 28% 26% 13% 6%	760
	21st to end	Night	14% 25% 29% 20% 9% 3	760
October	1st to 10th	Night	14% 18% 30% 26% 9% 2	760
	11th to 20th	Night	12% 24% 32% 24% 7% 1	760
	21st to end	Night	11% 30% 35% 20% 4 1	836
November	1st to 10th	Night	10% 31% 40% 13% 5% 1	835
	11th to 20th	Night	10% 37% 36% 14% 1 1	1000
	21st to end	Night	9% 34% 37% 14% 5% 2	1000
December	1st to 10th	Night	9% 31% 36% 15% 8% 1	1000
	11th to 20th	Night	6% 34% 38% 17% 5% 1	1000
	21st to end	Night	8% 31% 37% 16% 7% 1	1100

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