Elbow Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elbow Valley clear sky chart from 2005-11-06 to 2024-03-06.

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	9% 8% 4 7% 6% 4 5% 6% 6% 8% 37%	77977
	Night	6% 9% 4 7% 6% 4 5% 5% 6% 8% 39%	81496
Transparency	Day	43% 7% 15% 23% 11% 2	77684
	Night	41% 6% 15% 23% 11% 3	81369
Seeing	Day	13% 10% 28% 30% 15% 4	14323
	Night	11% 7% 31% 36% 14% 2	23642

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	2 7% 6% 11% 8% 4 5% 5% 8% 10% 35%	2219
	11th to 20th	Day	2 8% 4 9% 8% 4 6% 6% 7% 8% 37%	2270
	21st to end	Day	3 7% 3 7% 8% 4 5% 5% 6% 10% 42%	2794
February	1st to 10th	Day	3 9% 4 11% 9% 4 7% 7% 6% 7% 33%	1520
	11th to 20th	Day	3 9% 5% 9% 8% 6% 7% 6% 6% 8% 32%	1643
	21st to end	Day	2 10% 6% 10% 9% 5% 7% 5% 5% 8% 32%	1541
March	1st to 10th	Day	3 9% 6% 10% 9% 4 7% 6% 5% 9% 32%	1851
	11th to 20th	Day	3 9% 5% 7% 7% 4 5% 6% 7% 9% 38%	1943
	21st to end	Day	7% 14% 6% 10% 7% 4 5% 6% 6% 8% 26%	2222
April	1st to 10th	Day	9% 14% 5% 9% 7% 4 5% 5% 6% 9% 27%	2198
	11th to 20th	Day	11% 14% 5% 8% 6% 3 5% 5% 5% 7% 30%	2310
	21st to end	Day	11% 13% 5% 7% 6% 4 5% 6% 6% 7% 31%	2340
May	1st to 10th	Day	13% 11% 4 7% 7% 4 6% 5% 7% 8% 28%	2458
	11th to 20th	Day	14% 7% 3 6% 6% 4 6% 5% 7% 7% 33%	2654
	21st to end	Day	22% 8% 3 6% 6% 4 6% 5% 6% 7% 27%	2917
June	1st to 10th	Day	18% 8% 3 7% 6% 4 6% 6% 6% 7% 28%	2700
	11th to 20th	Day	22% 7% 3 7% 7% 3 5% 6% 7% 7% 25%	2700
	21st to end	Day	10% 4 3 5% 7% 3 6% 7% 8% 10% 39%	2700
July	1st to 10th	Day	9% 5% 3 5% 5% 3 5% 7% 7% 10% 41%	2700
	11th to 20th	Day	10% 5% 2 4 4 3 5% 6% 7% 9% 44%	2700
	21st to end	Day	5% 3 2 4 5% 3 5% 6% 6% 9% 53%	2854
August	1st to 10th	Day	10% 5% 2 4 5% 3 5% 6% 7% 8% 44%	2507
	11th to 20th	Day	10% 4 2 5% 4 3 4 5% 5% 10% 49%	2337
	21st to end	Day	10% 5% 2 5% 4 3 4 5% 7% 8% 48%	2574
September	1st to 10th	Day	10% 6% 3 5% 4 3 4 5% 5% 6% 50%	2227
	11th to 20th	Day	14% 7% 3 4 5% 2 4 5% 6% 6% 45%	1980
	21st to end	Day	9% 7% 3 5% 5% 3 5% 4 5% 8% 45%	1980
October	1st to 10th	Day	12% 9% 4 6% 6% 3 5% 5% 4 6% 40%	1915
	11th to 20th	Day	8% 9% 4 6% 6% 3 6% 5% 5% 9% 39%	1652
	21st to end	Day	7% 10% 4 6% 6% 3 5% 6% 7% 9% 37%	1782
November	1st to 10th	Day	7% 14% 4 8% 7% 4 5% 4 6% 7% 34%	1570
	11th to 20th	Day	5% 9% 5% 7% 6% 3 5% 5% 6% 8% 43%	1435
	21st to end	Day	3 9% 5% 8% 6% 3 5% 5% 6% 9% 40%	1330
December	1st to 10th	Day	4 7% 5% 10% 8% 4 7% 6% 5% 8% 36%	1330
	11th to 20th	Day	2 9% 5% 10% 8% 5% 7% 7% 7% 8% 31%	1682
	21st to end	Day	3 9% 3 6% 6% 4 4 5% 6% 9% 45%	2442
January	1st to 10th	Night	3 11% 5% 10% 9% 5% 6% 7% 8% 9% 29%	4726
	11th to 20th	Night	3 6% 4 11% 9% 4 6% 7% 6% 8% 35%	4658
	21st to end	Night	3 9% 4 9% 8% 4 5% 5% 6% 8% 39%	4862
February	1st to 10th	Night	4 9% 5% 9% 7% 5% 7% 6% 6% 9% 33%	2660
	11th to 20th	Night	3 11% 6% 10% 6% 4 5% 6% 7% 9% 33%	2423
	21st to end	Night	3 7% 6% 11% 8% 4 6% 4 6% 7% 37%	1908
March	1st to 10th	Night	2 9% 5% 10% 9% 4 6% 6% 6% 9% 32%	2225
	11th to 20th	Night	4 8% 4 7% 8% 3 6% 6% 7% 9% 38%	2015
	21st to end	Night	5% 12% 7% 9% 7% 4 5% 6% 7% 7% 32%	2133
April	1st to 10th	Night	7% 15% 4 8% 6% 3 6% 6% 5% 8% 32%	1761
	11th to 20th	Night	11% 13% 5% 9% 5% 3 4 4 5% 8% 32%	1601
	21st to end	Night	10% 12% 5% 8% 5% 3 5% 5% 5% 8% 35%	1620
May	1st to 10th	Night	12% 11% 4 7% 6% 3 6% 4 5% 8% 34%	1500
	11th to 20th	Night	11% 8% 3 5% 5% 2 4 5% 6% 9% 41%	1239
	21st to end	Night	19% 7% 3 7% 5% 4 5% 6% 6% 7% 32%	1358
June	1st to 10th	Night	16% 8% 3 5% 6% 4 6% 4 6% 8% 35%	1260
	11th to 20th	Night	19% 7% 3 6% 4 3 5% 5% 7% 8% 32%	1260
	21st to end	Night	8% 4 2 4 5% 4 6% 6% 7% 10% 45%	1260
July	1st to 10th	Night	8% 4 2 4 6% 3 5% 5% 7% 9% 48%	1260
	11th to 20th	Night	8% 5% 1 5% 4 3 5% 6% 7% 10% 46%	1260
	21st to end	Night	5% 3 2 4 3 2 4 4 5% 8% 58%	1459
August	1st to 10th	Night	10% 5% 1 4 4 3 4 5% 7% 8% 48%	1432
	11th to 20th	Night	9% 4 2 3 3 3 3 4 8% 10% 51%	1563
	21st to end	Night	9% 4 2 4 3 2 4 4 6% 8% 54%	1782
September	1st to 10th	Night	10% 7% 2 4 4 2 3 4 6% 8% 48%	1732
	11th to 20th	Night	14% 7% 2 4 3 2 3 3 5% 7% 49%	1980
	21st to end	Night	10% 8% 3 4 4 2 4 4 5% 8% 48%	1980
October	1st to 10th	Night	11% 8% 3 5% 6% 3 5% 5% 5% 7% 43%	2044
	11th to 20th	Night	7% 8% 3 5% 5% 3 5% 6% 7% 9% 43%	2307
	21st to end	Night	6% 10% 4 7% 6% 3 5% 5% 6% 8% 40%	2574
November	1st to 10th	Night	6% 13% 4 7% 5% 4 5% 5% 6% 6% 37%	2490
	11th to 20th	Night	4 8% 4 7% 6% 3 5% 5% 6% 9% 42%	2740
	21st to end	Night	3 9% 5% 8% 6% 4 5% 5% 6% 9% 40%	2850
December	1st to 10th	Night	3 10% 5% 8% 7% 4 7% 6% 6% 9% 35%	2850
	11th to 20th	Night	2 8% 5% 9% 9% 4 7% 7% 7% 9% 34%	3510
	21st to end	Night	3 8% 3 7% 7% 4 5% 6% 6% 7% 44%	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	42% 6% 13% 26% 10% 3	2219
	11th to 20th	Day	43% 6% 10% 19% 19% 3	2291
	21st to end	Day	36% 7% 16% 31% 9% 1	2794
February	1st to 10th	Day	48% 6% 15% 19% 9% 3	1520
	11th to 20th	Day	46% 6% 15% 21% 9% 2	1652
	21st to end	Day	48% 7% 12% 18% 12% 2	1541
March	1st to 10th	Day	48% 7% 17% 18% 8% 1	1851
	11th to 20th	Day	41% 7% 14% 23% 12% 2	1944
	21st to end	Day	54% 8% 14% 17% 6% 1	2222
April	1st to 10th	Day	51% 8% 15% 18% 7% 1	2198
	11th to 20th	Day	52% 6% 11% 20% 9% 1	2310
	21st to end	Day	51% 5% 15% 20% 8% 1	2340
May	1st to 10th	Day	53% 7% 14% 20% 7%	2458
	11th to 20th	Day	46% 7% 13% 23% 10% 1	2658
	21st to end	Day	54% 7% 13% 20% 6% 1	2918
June	1st to 10th	Day	52% 8% 14% 17% 8% 1	2700
	11th to 20th	Day	55% 7% 14% 16% 6% 1	2700
	21st to end	Day	36% 9% 19% 24% 10% 2	2700
July	1st to 10th	Day	37% 9% 18% 22% 11% 2	2626
	11th to 20th	Day	35% 8% 17% 27% 12% 2	2619
	21st to end	Day	27% 7% 16% 32% 15% 2	2695
August	1st to 10th	Day	35% 8% 18% 28% 10% 2	2490
	11th to 20th	Day	30% 8% 23% 28% 10% 2	2337
	21st to end	Day	32% 6% 17% 30% 13% 2	2574
September	1st to 10th	Day	34% 6% 16% 26% 15% 3	2227
	11th to 20th	Day	39% 6% 14% 26% 14% 2	1980
	21st to end	Day	37% 7% 15% 27% 12% 2	1980
October	1st to 10th	Day	44% 6% 13% 25% 10% 2	1915
	11th to 20th	Day	43% 6% 14% 24% 10% 3	1652
	21st to end	Day	42% 8% 13% 24% 12% 2	1782
November	1st to 10th	Day	48% 6% 13% 20% 12% 2	1570
	11th to 20th	Day	39% 5% 17% 27% 10% 2	1435
	21st to end	Day	39% 7% 17% 24% 10% 3	1330
December	1st to 10th	Day	45% 6% 15% 18% 13% 4	1330
	11th to 20th	Day	45% 8% 17% 19% 10% 1	1684
	21st to end	Day	35% 5% 11% 25% 19% 5%	2442
January	1st to 10th	Night	48% 7% 14% 21% 8% 2	4726
	11th to 20th	Night	46% 6% 11% 18% 14% 6%	4699
	21st to end	Night	41% 7% 14% 25% 12% 1	4862
February	1st to 10th	Night	46% 6% 13% 21% 12% 3	2660
	11th to 20th	Night	46% 7% 13% 20% 13% 2	2424
	21st to end	Night	46% 4 12% 23% 13% 3	1908
March	1st to 10th	Night	46% 7% 15% 23% 7% 1	2225
	11th to 20th	Night	39% 7% 15% 24% 12% 2	2015
	21st to end	Night	47% 7% 16% 19% 9% 2	2133
April	1st to 10th	Night	50% 5% 12% 21% 11% 1	1761
	11th to 20th	Night	50% 6% 14% 20% 9% 1	1601
	21st to end	Night	46% 6% 15% 21% 9% 2	1620
May	1st to 10th	Night	49% 5% 14% 22% 9% 1	1500
	11th to 20th	Night	38% 6% 15% 30% 9% 1	1239
	21st to end	Night	50% 5% 15% 22% 7% 1	1358
June	1st to 10th	Night	47% 6% 15% 22% 10%	1260
	11th to 20th	Night	48% 6% 18% 19% 8% 2	1260
	21st to end	Night	33% 8% 20% 28% 9% 1	1260
July	1st to 10th	Night	31% 8% 21% 27% 13% 1	1225
	11th to 20th	Night	33% 8% 20% 26% 11% 3	1218
	21st to end	Night	23% 7% 17% 32% 18% 3	1378
August	1st to 10th	Night	31% 7% 19% 29% 10% 2	1424
	11th to 20th	Night	25% 7% 25% 30% 12% 1	1563
	21st to end	Night	26% 7% 15% 32% 16% 3	1782
September	1st to 10th	Night	33% 5% 18% 25% 16% 3	1732
	11th to 20th	Night	35% 5% 16% 27% 13% 4	1980
	21st to end	Night	33% 5% 19% 26% 14% 4	1980
October	1st to 10th	Night	40% 6% 14% 24% 13% 2	2044
	11th to 20th	Night	37% 7% 16% 26% 12% 3	2307
	21st to end	Night	41% 6% 16% 25% 11% 1	2574
November	1st to 10th	Night	45% 7% 13% 21% 13% 2	2490
	11th to 20th	Night	39% 5% 17% 22% 15% 2	2740
	21st to end	Night	40% 5% 17% 22% 11% 4	2850
December	1st to 10th	Night	45% 5% 14% 20% 11% 4	2850
	11th to 20th	Night	43% 9% 18% 22% 7% 1	3507
	21st to end	Night	37% 6% 12% 25% 14% 6%	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	2 9% 23% 40% 14% 11%	180
	11th to 20th	Day	9% 6% 26% 37% 19% 3	180
	21st to end	Day	8% 9% 21% 43% 16% 4	198
February	1st to 10th	Day	9% 14% 30% 32% 7% 7%	180
	11th to 20th	Day	7% 11% 31% 37% 12% 2	260
	21st to end	Day	5% 14% 28% 36% 15% 2	353
March	1st to 10th	Day	7% 16% 39% 25% 11% 3	441
	11th to 20th	Day	9% 14% 35% 29% 11% 3	420
	21st to end	Day	12% 19% 32% 23% 11% 3	462
April	1st to 10th	Day	14% 17% 35% 25% 8% 1	420
	11th to 20th	Day	19% 14% 28% 25% 12% 2	412
	21st to end	Day	18% 17% 29% 24% 10% 2	420
May	1st to 10th	Day	21% 12% 26% 24% 13% 5%	445
	11th to 20th	Day	17% 8% 24% 26% 20% 4	625
	21st to end	Day	21% 6% 21% 29% 19% 4	679
June	1st to 10th	Day	19% 8% 27% 30% 12% 3	630
	11th to 20th	Day	24% 10% 26% 25% 12% 3	630
	21st to end	Day	11% 6% 27% 29% 22% 5%	630
July	1st to 10th	Day	12% 6% 24% 30% 24% 5%	621
	11th to 20th	Day	13% 5% 26% 32% 20% 3	618
	21st to end	Day	6% 6% 28% 35% 19% 7%	600
August	1st to 10th	Day	13% 5% 26% 33% 18% 5%	447
	11th to 20th	Day	11% 4 24% 38% 17% 6%	437
	21st to end	Day	11% 8% 26% 31% 16% 8%	495
September	1st to 10th	Day	14% 8% 30% 28% 16% 4	450
	11th to 20th	Day	19% 6% 24% 32% 15% 4	450
	21st to end	Day	13% 14% 28% 29% 13% 3	450
October	1st to 10th	Day	15% 8% 29% 29% 16% 5%	385
	11th to 20th	Day	16% 10% 25% 31% 13% 4	270
	21st to end	Day	14% 15% 34% 23% 10% 3	297
November	1st to 10th	Day	20% 9% 30% 29% 10% 2	270
	11th to 20th	Day	12% 13% 31% 32% 10% 2	230
	21st to end	Day	6% 9% 32% 32% 12% 9%	180
December	1st to 10th	Day	7% 6% 29% 42% 12% 4	180
	11th to 20th	Day	3 12% 32% 39% 9% 4	180
	21st to end	Day	7% 6% 24% 38% 22% 4	198
January	1st to 10th	Night	8% 12% 33% 35% 10% 2	950
	11th to 20th	Night	7% 8% 37% 37% 9% 1	922
	21st to end	Night	8% 13% 34% 36% 9% 1	836
February	1st to 10th	Night	8% 11% 32% 31% 13% 4	760
	11th to 20th	Night	9% 8% 33% 35% 13% 2	744
	21st to end	Night	6% 6% 35% 32% 17% 4	628
March	1st to 10th	Night	6% 6% 38% 34% 13% 3	742
	11th to 20th	Night	7% 8% 37% 34% 12% 2	720
	21st to end	Night	11% 6% 33% 34% 13% 3	792
April	1st to 10th	Night	12% 7% 32% 33% 13% 2	681
	11th to 20th	Night	20% 6% 33% 30% 11%	533
	21st to end	Night	16% 7% 31% 34% 10% 1	540
May	1st to 10th	Night	17% 7% 26% 34% 16% 1	442
	11th to 20th	Night	15% 6% 24% 37% 18% 1	354
	21st to end	Night	22% 4 22% 34% 18% 1	389
June	1st to 10th	Night	20% 5% 24% 35% 14% 1	360
	11th to 20th	Night	20% 5% 26% 33% 16% 1	360
	21st to end	Night	10% 2 20% 38% 28% 1	360
July	1st to 10th	Night	10% 4 14% 46% 25% 2	350
	11th to 20th	Night	11% 2 20% 46% 18% 2	348
	21st to end	Night	6% 5% 16% 46% 26% 2	394
August	1st to 10th	Night	11% 3 12% 42% 28% 3	358
	11th to 20th	Night	9% 3 18% 43% 25% 3	495
	21st to end	Night	9% 5% 19% 43% 22% 2	594
September	1st to 10th	Night	15% 4 22% 36% 20% 3	648
	11th to 20th	Night	18% 4 17% 38% 21% 3	720
	21st to end	Night	14% 5% 29% 35% 14% 4	720
October	1st to 10th	Night	16% 4 25% 36% 16% 3	720
	11th to 20th	Night	12% 6% 31% 34% 15% 3	720
	21st to end	Night	10% 7% 34% 37% 10% 1	792
November	1st to 10th	Night	14% 8% 36% 33% 9% 1	825
	11th to 20th	Night	9% 11% 40% 32% 6% 1	950
	21st to end	Night	7% 8% 40% 33% 11% 2	950
December	1st to 10th	Night	9% 8% 36% 32% 13% 2	950
	11th to 20th	Night	4 8% 37% 41% 9% 1	950
	21st to end	Night	8% 7% 35% 37% 12% 2	1045

Page generated at 2024-03-03 04:28:57. Version ac07

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