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 2024-02-25.

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	7% 9% 4 8% 6% 4 5% 6% 7% 8% 36%	77895
	Night	4 7% 4 7% 6% 4 5% 6% 7% 9% 41%	81358
Transparency	Day	43% 8% 15% 21% 11% 2	77606
	Night	37% 8% 17% 23% 13% 3	81228
Seeing	Day	16% 23% 31% 20% 9% 2	14240
	Night	10% 23% 32% 23% 10% 2	23549

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 9% 9% 4 7% 6% 9% 13% 35%	2219
	11th to 20th	Day	4 5% 10% 7% 3 7% 6% 8% 11% 39%	2333
	21st to end	Day	6% 4 9% 6% 5% 6% 6% 8% 10% 41%	2794
February	1st to 10th	Day	1 5% 5% 9% 9% 7% 8% 6% 9% 10% 33%	1520
	11th to 20th	Day	1 6% 4 10% 8% 5% 8% 7% 8% 10% 32%	1626
	21st to end	Day	1 5% 5% 14% 12% 5% 6% 6% 6% 8% 32%	1521
March	1st to 10th	Day	1 7% 4 10% 9% 4 6% 7% 7% 10% 36%	1800
	11th to 20th	Day	2 8% 6% 8% 7% 3 5% 5% 7% 11% 37%	1926
	21st to end	Day	3 12% 7% 12% 9% 5% 5% 7% 7% 8% 25%	2245
April	1st to 10th	Day	5% 13% 8% 10% 7% 5% 6% 5% 7% 9% 26%	2178
	11th to 20th	Day	6% 17% 7% 11% 6% 3 4 5% 7% 7% 26%	2310
	21st to end	Day	8% 16% 7% 9% 6% 3 4 4 5% 9% 29%	2340
May	1st to 10th	Day	10% 18% 5% 8% 6% 4 5% 5% 6% 8% 25%	2453
	11th to 20th	Day	12% 12% 4 6% 5% 3 4 6% 7% 9% 33%	2640
	21st to end	Day	22% 12% 3 6% 6% 4 5% 5% 6% 7% 26%	2917
June	1st to 10th	Day	18% 11% 4 7% 8% 4 5% 5% 6% 8% 25%	2700
	11th to 20th	Day	22% 10% 4 9% 6% 4 6% 5% 6% 5% 23%	2700
	21st to end	Day	12% 8% 3 6% 6% 4 6% 7% 7% 8% 34%	2700
July	1st to 10th	Day	11% 6% 3 6% 6% 4 6% 6% 7% 8% 36%	2700
	11th to 20th	Day	10% 6% 2 6% 5% 3 6% 6% 6% 7% 41%	2700
	21st to end	Day	5% 5% 2 5% 5% 4 6% 6% 7% 8% 49%	2812
August	1st to 10th	Day	11% 6% 3 7% 6% 4 6% 6% 7% 7% 39%	2507
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 5% 5% 7% 46%	2350
	21st to end	Day	11% 7% 2 5% 5% 3 4 5% 6% 7% 43%	2574
September	1st to 10th	Day	11% 8% 2 5% 5% 3 4 5% 6% 7% 45%	2201
	11th to 20th	Day	11% 9% 2 5% 5% 3 4 6% 6% 7% 42%	1993
	21st to end	Day	8% 8% 3 5% 5% 3 5% 6% 6% 8% 43%	1980
October	1st to 10th	Day	9% 10% 4 6% 6% 4 5% 5% 6% 8% 37%	1936
	11th to 20th	Day	5% 10% 3 6% 6% 3 4 5% 7% 8% 42%	1630
	21st to end	Day	2 10% 4 9% 6% 4 5% 6% 8% 9% 38%	1782
November	1st to 10th	Day	2 11% 6% 9% 6% 4 5% 5% 7% 9% 37%	1603
	11th to 20th	Day	1 5% 3 8% 6% 3 4 5% 7% 12% 46%	1421
	21st to end	Day	2 5% 4 8% 7% 4 5% 6% 6% 9% 44%	1330
December	1st to 10th	Day	1 5% 3 10% 7% 3 6% 6% 7% 12% 40%	1330
	11th to 20th	Day	1 6% 3 9% 8% 5% 6% 7% 7% 9% 39%	1682
	21st to end	Day	1 7% 4 7% 7% 4 6% 5% 7% 8% 45%	2442
January	1st to 10th	Night	5% 4 11% 8% 4 7% 8% 8% 11% 33%	4726
	11th to 20th	Night	1 4 4 8% 8% 4 7% 8% 10% 10% 37%	4595
	21st to end	Night	1 7% 4 8% 7% 4 6% 6% 7% 10% 40%	4862
February	1st to 10th	Night	1 5% 3 9% 9% 4 6% 8% 7% 9% 37%	2660
	11th to 20th	Night	1 6% 5% 10% 8% 3 6% 7% 7% 10% 37%	2436
	21st to end	Night	1 5% 4 9% 9% 6% 6% 7% 6% 9% 37%	1829
March	1st to 10th	Night	4 5% 8% 8% 4 5% 6% 8% 10% 40%	2160
	11th to 20th	Night	2 6% 5% 7% 6% 3 4 5% 7% 11% 43%	2033
	21st to end	Night	2 10% 5% 9% 7% 4 5% 6% 8% 10% 35%	2108
April	1st to 10th	Night	4 9% 7% 9% 6% 3 6% 5% 6% 9% 35%	1782
	11th to 20th	Night	6% 10% 5% 11% 6% 4 5% 4 6% 8% 34%	1601
	21st to end	Night	4 11% 6% 8% 7% 4 4 4 6% 7% 37%	1620
May	1st to 10th	Night	7% 13% 5% 8% 8% 4 5% 5% 7% 7% 33%	1504
	11th to 20th	Night	9% 9% 3 6% 5% 3 6% 4 8% 8% 39%	1253
	21st to end	Night	19% 12% 3 6% 6% 3 4 4 5% 7% 32%	1358
June	1st to 10th	Night	13% 11% 3 6% 6% 3 5% 5% 6% 7% 33%	1260
	11th to 20th	Night	19% 9% 3 6% 6% 3 5% 5% 5% 7% 31%	1260
	21st to end	Night	8% 4 2 4 6% 3 5% 7% 7% 7% 47%	1260
July	1st to 10th	Night	7% 6% 2 4 5% 3 4 6% 5% 7% 51%	1260
	11th to 20th	Night	9% 5% 2 3 5% 2 4 7% 5% 8% 50%	1260
	21st to end	Night	6% 3 1 4 4 2 4 4 7% 7% 57%	1501
August	1st to 10th	Night	9% 5% 2 4 5% 1 4 5% 6% 8% 50%	1432
	11th to 20th	Night	8% 5% 2 4 3 3 3 4 6% 10% 52%	1550
	21st to end	Night	9% 5% 1 3 4 2 4 4 6% 9% 52%	1782
September	1st to 10th	Night	9% 7% 2 4 4 2 4 4 6% 7% 50%	1756
	11th to 20th	Night	11% 7% 2 5% 4 2 3 5% 7% 8% 46%	1966
	21st to end	Night	8% 7% 2 5% 3 3 4 5% 5% 8% 49%	1980
October	1st to 10th	Night	7% 9% 4 6% 4 3 5% 5% 5% 7% 45%	2024
	11th to 20th	Night	5% 7% 4 6% 5% 3 4 4 7% 9% 45%	2327
	21st to end	Night	3 8% 3 9% 7% 3 5% 6% 8% 10% 38%	2574
November	1st to 10th	Night	2 9% 5% 8% 5% 4 5% 6% 7% 9% 39%	2457
	11th to 20th	Night	1 5% 4 5% 6% 3 5% 6% 7% 12% 46%	2758
	21st to end	Night	1 6% 4 7% 7% 3 6% 6% 8% 10% 42%	2850
December	1st to 10th	Night	1 5% 5% 8% 7% 4 6% 6% 7% 11% 41%	2850
	11th to 20th	Night	1 5% 3 9% 7% 5% 7% 6% 8% 11% 37%	3510
	21st to end	Night	1 7% 4 9% 8% 4 6% 6% 7% 8% 42%	5214

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	36% 9% 15% 24% 13% 3	2219
	11th to 20th	Day	37% 7% 14% 19% 17% 6%	2355
	21st to end	Day	33% 9% 18% 29% 9% 2	2794
February	1st to 10th	Day	41% 9% 15% 21% 11% 3	1520
	11th to 20th	Day	40% 9% 16% 22% 10% 3	1635
	21st to end	Day	48% 8% 13% 17% 12% 2	1521
March	1st to 10th	Day	40% 9% 20% 20% 10% 1	1800
	11th to 20th	Day	38% 8% 19% 22% 11% 3	1927
	21st to end	Day	53% 9% 16% 14% 7% 1	2245
April	1st to 10th	Day	52% 8% 17% 15% 7%	2178
	11th to 20th	Day	54% 7% 13% 17% 7% 1	2310
	21st to end	Day	53% 6% 15% 18% 7% 1	2340
May	1st to 10th	Day	56% 8% 15% 17% 5%	2453
	11th to 20th	Day	47% 8% 15% 21% 8% 1	2644
	21st to end	Day	57% 7% 11% 18% 6%	2918
June	1st to 10th	Day	56% 8% 12% 15% 8%	2700
	11th to 20th	Day	58% 9% 12% 14% 7% 1	2700
	21st to end	Day	43% 11% 15% 20% 9% 2	2700
July	1st to 10th	Day	41% 10% 14% 19% 13% 2	2626
	11th to 20th	Day	39% 8% 11% 22% 16% 2	2619
	21st to end	Day	30% 9% 12% 28% 19% 2	2656
August	1st to 10th	Day	41% 10% 12% 23% 13% 2	2490
	11th to 20th	Day	34% 7% 17% 29% 10% 2	2350
	21st to end	Day	36% 8% 13% 28% 13% 1	2574
September	1st to 10th	Day	37% 6% 14% 25% 15% 3	2201
	11th to 20th	Day	39% 6% 16% 24% 13% 2	1993
	21st to end	Day	36% 10% 16% 25% 12% 1	1980
October	1st to 10th	Day	42% 7% 12% 25% 11% 1	1936
	11th to 20th	Day	38% 9% 16% 22% 13% 2	1630
	21st to end	Day	40% 9% 16% 21% 13% 2	1782
November	1st to 10th	Day	43% 9% 15% 19% 12% 2	1603
	11th to 20th	Day	31% 9% 22% 25% 11% 2	1421
	21st to end	Day	35% 8% 21% 22% 9% 4	1330
December	1st to 10th	Day	36% 8% 22% 17% 15% 3	1330
	11th to 20th	Day	37% 11% 17% 25% 10% 2	1684
	21st to end	Day	34% 8% 11% 24% 17% 7%	2442
January	1st to 10th	Night	39% 11% 15% 21% 11% 3	4726
	11th to 20th	Night	36% 9% 15% 17% 14% 9%	4635
	21st to end	Night	35% 10% 19% 22% 13% 1	4862
February	1st to 10th	Night	40% 8% 14% 20% 14% 3	2660
	11th to 20th	Night	40% 9% 18% 18% 12% 3	2437
	21st to end	Night	41% 7% 12% 21% 16% 3	1829
March	1st to 10th	Night	36% 10% 18% 22% 13% 1	2160
	11th to 20th	Night	33% 8% 20% 23% 14% 1	2033
	21st to end	Night	41% 10% 16% 22% 9% 2	2108
April	1st to 10th	Night	44% 8% 16% 19% 13% 1	1782
	11th to 20th	Night	47% 7% 16% 20% 9% 1	1601
	21st to end	Night	45% 8% 14% 22% 8% 2	1620
May	1st to 10th	Night	47% 8% 17% 20% 8%	1504
	11th to 20th	Night	40% 9% 16% 28% 7% 1	1253
	21st to end	Night	51% 8% 13% 21% 7%	1358
June	1st to 10th	Night	47% 10% 13% 21% 8%	1260
	11th to 20th	Night	50% 8% 15% 17% 10% 1	1260
	21st to end	Night	31% 10% 18% 28% 11% 1	1260
July	1st to 10th	Night	31% 8% 17% 27% 15% 1	1225
	11th to 20th	Night	31% 9% 16% 27% 16% 2	1218
	21st to end	Night	22% 9% 17% 29% 21% 2	1418
August	1st to 10th	Night	31% 8% 16% 30% 12% 3	1424
	11th to 20th	Night	27% 7% 20% 35% 11% 1	1550
	21st to end	Night	27% 7% 15% 32% 16% 2	1782
September	1st to 10th	Night	32% 6% 17% 28% 15% 2	1756
	11th to 20th	Night	35% 7% 16% 26% 13% 4	1966
	21st to end	Night	33% 6% 17% 26% 15% 2	1980
October	1st to 10th	Night	38% 7% 15% 25% 15% 1	2024
	11th to 20th	Night	34% 7% 18% 25% 13% 3	2327
	21st to end	Night	38% 9% 16% 24% 12% 1	2574
November	1st to 10th	Night	39% 11% 17% 20% 12% 2	2457
	11th to 20th	Night	31% 9% 19% 25% 15% 2	2758
	21st to end	Night	35% 8% 20% 21% 12% 4	2850
December	1st to 10th	Night	36% 9% 16% 22% 12% 5%	2850
	11th to 20th	Night	36% 10% 21% 22% 10% 1	3507
	21st to end	Night	36% 7% 13% 23% 14% 7%	5214

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	8% 29% 28% 24% 7% 3	180
	11th to 20th	Day	8% 24% 38% 23% 6% 1	180
	21st to end	Day	7% 37% 35% 12% 7% 3	198
February	1st to 10th	Day	14% 28% 36% 14% 6% 2	180
	11th to 20th	Day	9% 25% 41% 15% 9%	252
	21st to end	Day	12% 26% 32% 22% 7%	363
March	1st to 10th	Day	10% 32% 36% 14% 6% 2	420
	11th to 20th	Day	10% 32% 35% 16% 6% 2	420
	21st to end	Day	14% 32% 30% 18% 5% 2	462
April	1st to 10th	Day	15% 29% 36% 15% 4	420
	11th to 20th	Day	17% 26% 31% 18% 7% 2	412
	21st to end	Day	20% 28% 24% 17% 9% 2	420
May	1st to 10th	Day	20% 20% 27% 21% 10% 3	423
	11th to 20th	Day	23% 13% 23% 25% 14% 3	611
	21st to end	Day	26% 13% 21% 22% 14% 3	679
June	1st to 10th	Day	20% 21% 29% 20% 8% 2	630
	11th to 20th	Day	26% 21% 23% 20% 8% 1	630
	21st to end	Day	15% 17% 29% 24% 11% 4	630
July	1st to 10th	Day	14% 13% 32% 23% 15% 3	621
	11th to 20th	Day	14% 19% 30% 24% 11% 2	618
	21st to end	Day	8% 15% 36% 26% 11% 4	558
August	1st to 10th	Day	14% 18% 30% 27% 10% 1	447
	11th to 20th	Day	14% 18% 31% 27% 8% 3	437
	21st to end	Day	16% 18% 33% 22% 9% 2	495
September	1st to 10th	Day	17% 26% 30% 18% 6% 2	450
	11th to 20th	Day	19% 19% 30% 24% 7% 1	450
	21st to end	Day	19% 30% 27% 17% 5% 2	450
October	1st to 10th	Day	17% 22% 29% 20% 11% 1	406
	11th to 20th	Day	14% 27% 31% 20% 7% 1	270
	21st to end	Day	18% 32% 32% 13% 5% 1	297
November	1st to 10th	Day	16% 34% 32% 11% 6% 1	270
	11th to 20th	Day	18% 31% 37% 12% 2	223
	21st to end	Day	14% 34% 26% 12% 8% 6%	180
December	1st to 10th	Day	11% 31% 36% 14% 7% 2	180
	11th to 20th	Day	6% 36% 40% 16% 2 1	180
	21st to end	Day	11% 20% 43% 16% 7% 3	198
January	1st to 10th	Night	11% 32% 38% 15% 3	950
	11th to 20th	Night	6% 33% 39% 18% 2 2	884
	21st to end	Night	8% 34% 36% 16% 6%	836
February	1st to 10th	Night	8% 29% 31% 19% 10% 3	760
	11th to 20th	Night	8% 27% 35% 21% 9%	744
	21st to end	Night	7% 20% 36% 24% 12% 2	610
March	1st to 10th	Night	6% 26% 37% 21% 8% 2	720
	11th to 20th	Night	7% 26% 36% 22% 7% 1	720
	21st to end	Night	9% 20% 30% 29% 10% 3	792
April	1st to 10th	Night	10% 20% 31% 28% 9% 1	702
	11th to 20th	Night	13% 20% 31% 26% 9% 1	533
	21st to end	Night	13% 18% 32% 25% 11% 1	540
May	1st to 10th	Night	14% 12% 27% 32% 14% 1	424
	11th to 20th	Night	15% 11% 26% 26% 19% 3	354
	21st to end	Night	26% 11% 21% 24% 18% 2	389
June	1st to 10th	Night	18% 14% 24% 29% 11% 3	360
	11th to 20th	Night	24% 11% 25% 26% 13%	360
	21st to end	Night	11% 13% 26% 29% 21% 1	360
July	1st to 10th	Night	13% 8% 19% 38% 21% 2	350
	11th to 20th	Night	11% 10% 29% 32% 15% 2	348
	21st to end	Night	8% 9% 22% 38% 21% 2	394
August	1st to 10th	Night	13% 6% 18% 34% 26% 3	358
	11th to 20th	Night	11% 9% 23% 32% 22% 3	482
	21st to end	Night	12% 12% 26% 31% 16% 2	594
September	1st to 10th	Night	14% 13% 26% 28% 14% 5%	676
	11th to 20th	Night	16% 12% 27% 26% 14% 6%	720
	21st to end	Night	13% 24% 28% 21% 10% 3	720
October	1st to 10th	Night	14% 17% 29% 27% 10% 2	720
	11th to 20th	Night	11% 24% 31% 25% 8% 2	720
	21st to end	Night	10% 30% 35% 20% 5% 1	792
November	1st to 10th	Night	10% 30% 41% 13% 5% 1	792
	11th to 20th	Night	10% 37% 36% 14% 1 1	950
	21st to end	Night	9% 34% 36% 15% 5% 2	950
December	1st to 10th	Night	8% 31% 36% 16% 8% 1	950
	11th to 20th	Night	5% 34% 38% 17% 5% 1	950
	21st to end	Night	7% 30% 39% 17% 7% 1	1045

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