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 2026-09-29.

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% 8% 3 8% 5% 5% 5% 4 7% 8% 40%	154267
	Night	6% 8% 3 8% 5% 5% 5% 4 6% 8% 40%	145910
Transparency	Day	39% 6% 15% 26% 12% 2	153971
	Night	40% 6% 15% 24% 12% 2	145789
Seeing	Day	13% 10% 28% 30% 15% 4	17854
	Night	11% 7% 31% 36% 14% 2	26789

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	1 6% 5% 12% 8% 7% 6% 4 8% 9% 33%	4125
	11th to 20th	Day	1 7% 3 10% 6% 5% 5% 4 6% 7% 45%	4274
	21st to end	Day	2 6% 3 9% 5% 4 4 4 6% 11% 46%	5186
February	1st to 10th	Day	3 9% 4 13% 7% 6% 7% 5% 7% 7% 33%	1680
	11th to 20th	Day	2 10% 4 10% 7% 7% 7% 5% 6% 8% 33%	1821
	21st to end	Day	2 10% 5% 11% 7% 7% 6% 5% 6% 8% 34%	1699
March	1st to 10th	Day	2 8% 4 10% 5% 5% 5% 4 5% 11% 39%	4618
	11th to 20th	Day	4 9% 5% 9% 5% 4 5% 4 6% 8% 41%	5032
	21st to end	Day	6% 20% 7% 13% 5% 5% 5% 4 6% 7% 20%	5730
April	1st to 10th	Day	8% 15% 4 10% 6% 5% 5% 4 7% 8% 29%	2565
	11th to 20th	Day	10% 14% 5% 9% 5% 4 4 4 6% 7% 30%	2700
	21st to end	Day	10% 14% 5% 8% 5% 5% 4 5% 6% 8% 30%	2730
May	1st to 10th	Day	11% 10% 3 7% 4 5% 5% 4 6% 7% 37%	8019
	11th to 20th	Day	11% 11% 4 10% 6% 6% 7% 5% 7% 8% 25%	8755
	21st to end	Day	13% 7% 3 8% 5% 6% 5% 4 7% 8% 34%	9649
June	1st to 10th	Day	17% 8% 2 8% 5% 5% 6% 5% 7% 7% 29%	3150
	11th to 20th	Day	19% 8% 3 8% 6% 5% 5% 5% 7% 7% 27%	3150
	21st to end	Day	10% 4 2 5% 6% 5% 6% 5% 8% 10% 38%	3150
July	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 7% 9% 49%	8820
	11th to 20th	Day	9% 4 2 4 3 4 5% 4 7% 9% 49%	8820
	21st to end	Day	7% 4 2 4 3 3 4 3 5% 9% 55%	9278
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 7% 9% 48%	6441
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 41%	6015
	21st to end	Day	7% 4 1 4 3 3 4 4 6% 8% 55%	6570
September	1st to 10th	Day	11% 6% 3 6% 3 4 4 4 5% 6% 49%	2597
	11th to 20th	Day	13% 7% 3 5% 4 3 4 4 6% 6% 47%	2310
	21st to end	Day	8% 7% 3 6% 4 4 5% 3 6% 8% 47%	2289
October	1st to 10th	Day	7% 6% 3 7% 4 4 4 4 6% 9% 46%	3475
	11th to 20th	Day	5% 7% 3 6% 4 5% 6% 4 8% 10% 42%	2979
	21st to end	Day	7% 7% 3 5% 5% 4 5% 3 6% 7% 47%	3200
November	1st to 10th	Day	6% 14% 4 9% 5% 5% 4 4 6% 7% 35%	1738
	11th to 20th	Day	4 10% 4 8% 6% 4 5% 4 6% 7% 42%	1585
	21st to end	Day	3 11% 4 11% 6% 4 6% 4 6% 9% 37%	1470
December	1st to 10th	Day	2 8% 4 11% 7% 6% 7% 5% 7% 8% 35%	2360
	11th to 20th	Day	2 7% 4 11% 7% 7% 6% 4 8% 10% 34%	2712
	21st to end	Day	3 10% 4 9% 5% 5% 4 4 6% 8% 42%	3575
January	1st to 10th	Night	3 10% 5% 11% 8% 7% 6% 5% 7% 8% 30%	8768
	11th to 20th	Night	1 6% 4 11% 6% 5% 6% 5% 7% 9% 40%	8682
	21st to end	Night	2 7% 3 10% 6% 6% 6% 4 6% 8% 41%	8994
February	1st to 10th	Night	3 10% 4 9% 7% 7% 6% 5% 7% 9% 33%	2940
	11th to 20th	Night	3 11% 5% 11% 6% 6% 5% 5% 7% 9% 32%	2685
	21st to end	Night	3 9% 5% 11% 8% 5% 6% 4 6% 7% 37%	2102
March	1st to 10th	Night	2 7% 3 12% 6% 6% 6% 5% 6% 11% 36%	5496
	11th to 20th	Night	3 8% 3 9% 6% 5% 5% 5% 7% 8% 39%	5186
	21st to end	Night	9% 18% 6% 13% 6% 5% 4 4 6% 7% 24%	5485
April	1st to 10th	Night	7% 15% 4 8% 5% 5% 5% 4 5% 8% 32%	2054
	11th to 20th	Night	10% 14% 5% 10% 4 4 4 4 5% 7% 33%	1871
	21st to end	Night	9% 13% 4 9% 6% 4 5% 4 5% 7% 34%	1890
May	1st to 10th	Night	14% 11% 3 7% 3 3 4 3 6% 7% 41%	4911
	11th to 20th	Night	11% 11% 4 8% 6% 4 5% 4 7% 10% 31%	4105
	21st to end	Night	10% 6% 2 7% 5% 6% 6% 6% 7% 8% 37%	4522
June	1st to 10th	Night	15% 9% 2 7% 6% 5% 5% 4 6% 8% 34%	1470
	11th to 20th	Night	17% 9% 3 7% 4 5% 4 4 7% 9% 32%	1470
	21st to end	Night	8% 4 1 5% 5% 5% 6% 5% 7% 9% 44%	1470
July	1st to 10th	Night	5% 5% 2 5% 4 4 5% 4 6% 9% 51%	4140
	11th to 20th	Night	7% 5% 2 5% 3 3 4 4 7% 9% 53%	4140
	21st to end	Night	9% 4 1 4 2 3 3 2 5% 8% 57%	4786
August	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 7% 7% 48%	3709
	11th to 20th	Night	11% 4 2 5% 4 5% 5% 5% 8% 10% 40%	4046
	21st to end	Night	6% 4 1 3 3 3 4 4 6% 10% 55%	4578
September	1st to 10th	Night	9% 7% 2 5% 3 4 4 3 6% 8% 49%	2021
	11th to 20th	Night	14% 7% 2 5% 3 3 4 3 5% 7% 49%	2310
	21st to end	Night	9% 7% 2 5% 3 3 4 3 5% 8% 50%	2288
October	1st to 10th	Night	7% 6% 2 5% 4 3 5% 4 6% 8% 51%	3720
	11th to 20th	Night	5% 7% 2 5% 4 4 4 4 7% 8% 50%	4168
	21st to end	Night	5% 9% 3 6% 4 4 5% 4 6% 7% 47%	4600
November	1st to 10th	Night	5% 14% 4 8% 5% 5% 5% 5% 7% 7% 37%	2760
	11th to 20th	Night	3 9% 4 8% 5% 5% 6% 4 7% 8% 40%	3030
	21st to end	Night	3 10% 4 9% 5% 6% 5% 4 6% 9% 39%	3150
December	1st to 10th	Night	2 9% 4 9% 6% 5% 6% 5% 8% 10% 36%	5040
	11th to 20th	Night	2 9% 5% 12% 8% 6% 6% 5% 7% 9% 31%	5700
	21st to end	Night	3 11% 4 9% 6% 4 5% 4 6% 7% 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	44% 6% 11% 22% 13% 3	4125
	11th to 20th	Day	36% 4 14% 25% 17% 3	4295
	21st to end	Day	31% 6% 16% 31% 15% 1	5187
February	1st to 10th	Day	48% 6% 14% 18% 10% 3	1680
	11th to 20th	Day	46% 6% 14% 23% 10% 2	1830
	21st to end	Day	46% 7% 13% 20% 13% 2	1699
March	1st to 10th	Day	39% 5% 15% 23% 17% 1	4618
	11th to 20th	Day	39% 5% 14% 25% 16% 1	5033
	21st to end	Day	59% 7% 12% 14% 6% 1	5730
April	1st to 10th	Day	50% 8% 16% 19% 7% 1	2565
	11th to 20th	Day	51% 7% 12% 20% 10% 1	2700
	21st to end	Day	50% 5% 14% 21% 8% 1	2730
May	1st to 10th	Day	44% 5% 9% 26% 14% 2	8019
	11th to 20th	Day	50% 8% 10% 21% 9% 2	8759
	21st to end	Day	44% 6% 15% 25% 8% 1	9650
June	1st to 10th	Day	50% 8% 14% 18% 9% 1	3150
	11th to 20th	Day	53% 7% 13% 19% 7% 1	3150
	21st to end	Day	36% 9% 19% 24% 10% 2	3150
July	1st to 10th	Day	29% 7% 16% 30% 15% 3	8746
	11th to 20th	Day	30% 6% 17% 29% 13% 5%	8739
	21st to end	Day	26% 5% 14% 28% 20% 6%	9076
August	1st to 10th	Day	30% 7% 16% 34% 9% 4	6424
	11th to 20th	Day	36% 7% 25% 25% 6% 1	6055
	21st to end	Day	26% 5% 17% 38% 12% 1	6569
September	1st to 10th	Day	34% 6% 16% 26% 14% 4	2597
	11th to 20th	Day	37% 6% 15% 27% 14% 1	2310
	21st to end	Day	35% 7% 15% 28% 12% 3	2289
October	1st to 10th	Day	34% 5% 17% 35% 8% 1	3475
	11th to 20th	Day	35% 5% 20% 23% 13% 3	2979
	21st to end	Day	35% 6% 11% 34% 14% 1	3200
November	1st to 10th	Day	47% 6% 12% 20% 12% 2	1738
	11th to 20th	Day	40% 5% 16% 27% 10% 2	1585
	21st to end	Day	42% 7% 15% 24% 9% 3	1470
December	1st to 10th	Day	46% 6% 14% 24% 8% 2	2360
	11th to 20th	Day	43% 8% 20% 20% 8% 1	2714
	21st to end	Day	38% 5% 10% 25% 18% 4	3575
January	1st to 10th	Night	49% 7% 12% 20% 11% 2	8769
	11th to 20th	Night	40% 5% 15% 21% 13% 6%	8723
	21st to end	Night	39% 6% 16% 25% 13% 1	8994
February	1st to 10th	Night	46% 6% 12% 21% 13% 3	2940
	11th to 20th	Night	47% 6% 12% 19% 14% 2	2686
	21st to end	Night	46% 4 12% 23% 12% 3	2102
March	1st to 10th	Night	41% 5% 16% 22% 13% 2	5496
	11th to 20th	Night	39% 7% 14% 24% 15% 1	5186
	21st to end	Night	59% 5% 11% 15% 9% 1	5485
April	1st to 10th	Night	49% 5% 13% 21% 11% 1	2054
	11th to 20th	Night	49% 6% 13% 21% 10% 1	1871
	21st to end	Night	47% 6% 15% 21% 9% 2	1890
May	1st to 10th	Night	44% 4 10% 25% 16% 1	4908
	11th to 20th	Night	46% 6% 13% 27% 8% 1	4105
	21st to end	Night	41% 6% 17% 28% 7% 1	4526
June	1st to 10th	Night	47% 6% 14% 23% 10% 1	1470
	11th to 20th	Night	47% 6% 16% 20% 8% 2	1470
	21st to end	Night	34% 8% 20% 28% 10% 1	1470
July	1st to 10th	Night	29% 7% 17% 31% 14% 2	4105
	11th to 20th	Night	27% 6% 20% 30% 11% 5%	4098
	21st to end	Night	26% 4 16% 29% 19% 6%	4683
August	1st to 10th	Night	33% 6% 15% 29% 13% 3	3701
	11th to 20th	Night	35% 8% 29% 22% 6%	4072
	21st to end	Night	24% 6% 21% 35% 12% 1	4578
September	1st to 10th	Night	32% 5% 18% 25% 15% 4	2021
	11th to 20th	Night	35% 5% 16% 28% 13% 4	2310
	21st to end	Night	31% 5% 18% 28% 14% 4	2288
October	1st to 10th	Night	31% 6% 16% 26% 19% 2	3720
	11th to 20th	Night	31% 5% 19% 27% 16% 2	4168
	21st to end	Night	35% 5% 11% 34% 13% 1	4600
November	1st to 10th	Night	44% 7% 13% 22% 13% 2	2760
	11th to 20th	Night	40% 6% 16% 23% 14% 2	3030
	21st to end	Night	41% 6% 17% 23% 11% 3	3150
December	1st to 10th	Night	42% 7% 20% 21% 8% 2	5040
	11th to 20th	Night	47% 8% 18% 18% 9% 1	5697
	21st to end	Night	41% 5% 10% 25% 15% 4	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	2 10% 30% 36% 14% 9%	220
	11th to 20th	Day	10% 7% 31% 33% 16% 2	220
	21st to end	Day	7% 10% 26% 40% 14% 3	242
February	1st to 10th	Day	9% 14% 31% 32% 8% 6%	220
	11th to 20th	Day	7% 9% 33% 38% 11% 2	318
	21st to end	Day	7% 16% 30% 33% 13% 2	415
March	1st to 10th	Day	7% 14% 39% 26% 11% 2	540
	11th to 20th	Day	10% 13% 35% 29% 11% 3	540
	21st to end	Day	13% 19% 32% 23% 9% 3	594
April	1st to 10th	Day	14% 15% 36% 24% 9% 1	540
	11th to 20th	Day	17% 16% 29% 24% 12% 2	532
	21st to end	Day	16% 17% 30% 24% 10% 3	540
May	1st to 10th	Day	18% 14% 27% 25% 11% 4	569
	11th to 20th	Day	16% 11% 24% 26% 19% 4	775
	21st to end	Day	19% 7% 22% 29% 18% 4	844
June	1st to 10th	Day	18% 10% 28% 29% 12% 3	780
	11th to 20th	Day	21% 11% 27% 26% 12% 3	780
	21st to end	Day	11% 8% 26% 30% 21% 4	780
July	1st to 10th	Day	11% 5% 26% 30% 23% 5%	771
	11th to 20th	Day	12% 6% 25% 33% 20% 3	768
	21st to end	Day	7% 6% 27% 35% 18% 6%	750
August	1st to 10th	Day	12% 6% 25% 34% 18% 6%	567
	11th to 20th	Day	11% 5% 24% 36% 18% 6%	557
	21st to end	Day	11% 7% 26% 31% 17% 8%	627
September	1st to 10th	Day	14% 7% 28% 28% 16% 6%	570
	11th to 20th	Day	17% 6% 24% 32% 17% 5%	570
	21st to end	Day	12% 14% 30% 30% 11% 2	563
October	1st to 10th	Day	13% 8% 31% 29% 15% 4	457
	11th to 20th	Day	15% 10% 26% 32% 13% 4	330
	21st to end	Day	13% 16% 34% 24% 9% 3	363
November	1st to 10th	Day	19% 11% 30% 29% 9% 2	330
	11th to 20th	Day	11% 14% 30% 31% 11% 3	280
	21st to end	Day	7% 8% 33% 33% 11% 8%	220
December	1st to 10th	Day	6% 9% 31% 40% 10% 4	220
	11th to 20th	Day	5% 12% 33% 37% 10% 4	220
	21st to end	Day	7% 7% 27% 38% 19% 3	242
January	1st to 10th	Night	9% 11% 35% 34% 10% 2	1050
	11th to 20th	Night	7% 9% 39% 35% 8% 1	1018
	21st to end	Night	7% 12% 37% 35% 8% 1	924
February	1st to 10th	Night	8% 11% 32% 33% 12% 4	840
	11th to 20th	Night	9% 8% 34% 35% 13% 1	824
	21st to end	Night	6% 6% 37% 32% 16% 3	692
March	1st to 10th	Night	6% 7% 38% 34% 12% 3	840
	11th to 20th	Night	7% 7% 38% 35% 11% 2	840
	21st to end	Night	12% 7% 33% 33% 13% 2	924
April	1st to 10th	Night	13% 8% 32% 32% 13% 2	794
	11th to 20th	Night	18% 7% 34% 31% 10%	623
	21st to end	Night	16% 8% 31% 34% 11%	630
May	1st to 10th	Night	17% 7% 25% 36% 14% 1	515
	11th to 20th	Night	16% 7% 24% 35% 18%	414
	21st to end	Night	19% 4 23% 33% 20% 1	455
June	1st to 10th	Night	20% 6% 24% 36% 13% 1	420
	11th to 20th	Night	18% 5% 28% 33% 15% 1	420
	21st to end	Night	11% 3 20% 39% 26% 1	420
July	1st to 10th	Night	9% 4 14% 47% 24% 2	410
	11th to 20th	Night	12% 2 20% 47% 17% 2	408
	21st to end	Night	7% 5% 18% 44% 25% 2	460
August	1st to 10th	Night	11% 4 12% 43% 28% 3	418
	11th to 20th	Night	9% 3 17% 44% 24% 3	579
	21st to end	Night	8% 6% 19% 44% 21% 1	693
September	1st to 10th	Night	14% 4 22% 36% 21% 3	756
	11th to 20th	Night	18% 4 16% 38% 23% 2	840
	21st to end	Night	12% 6% 30% 36% 13% 3	832
October	1st to 10th	Night	15% 5% 27% 36% 16% 3	800
	11th to 20th	Night	12% 6% 32% 35% 14% 2	800
	21st to end	Night	10% 7% 36% 36% 10% 1	880
November	1st to 10th	Night	13% 9% 37% 32% 9% 1	915
	11th to 20th	Night	9% 11% 40% 32% 7% 1	1050
	21st to end	Night	7% 8% 39% 34% 10% 2	1050
December	1st to 10th	Night	9% 8% 38% 31% 12% 2	1050
	11th to 20th	Night	4 8% 38% 40% 9% 1	1050
	21st to end	Night	8% 7% 36% 36% 11% 2	1155

Page generated at 2026-09-26 02:18:40. Version ac07

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