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 2025-05-26.

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	7% 8% 3 8% 5% 5% 5% 4 7% 8% 38%	117532
	Night	6% 9% 3 9% 5% 5% 5% 4 6% 8% 39%	120465
Transparency	Day	41% 6% 15% 25% 11% 2	117279
	Night	41% 6% 15% 24% 12% 2	120364
Seeing	Day	13% 10% 28% 30% 15% 4	15976
	Night	11% 7% 31% 36% 14% 2	25181

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 7% 6% 13% 8% 8% 5% 4 7% 8% 33%	3179
	11th to 20th	Day	2 7% 3 11% 7% 5% 5% 5% 7% 8% 40%	3272
	21st to end	Day	2 6% 2 8% 5% 4 4 4 6% 11% 48%	4004
February	1st to 10th	Day	3 9% 4 14% 7% 6% 7% 5% 7% 7% 32%	1600
	11th to 20th	Day	2 10% 4 11% 7% 8% 7% 5% 6% 8% 32%	1732
	21st to end	Day	2 11% 5% 11% 7% 7% 6% 5% 5% 8% 33%	1620
March	1st to 10th	Day	2 8% 4 10% 5% 5% 5% 4 5% 11% 39%	4518
	11th to 20th	Day	4 9% 5% 9% 5% 4 5% 4 6% 8% 41%	4924
	21st to end	Day	7% 20% 7% 13% 5% 5% 5% 4 6% 7% 20%	5607
April	1st to 10th	Day	8% 15% 4 10% 6% 5% 5% 4 6% 8% 29%	2443
	11th to 20th	Day	10% 14% 5% 9% 5% 5% 4 4 6% 7% 30%	2570
	21st to end	Day	11% 14% 4 8% 5% 5% 4 5% 6% 8% 30%	2600
May	1st to 10th	Day	16% 15% 4 8% 5% 5% 4 3 5% 6% 29%	4471
	11th to 20th	Day	11% 9% 4 9% 6% 6% 6% 5% 8% 8% 28%	4844
	21st to end	Day	17% 10% 4 10% 7% 6% 6% 4 6% 6% 24%	5239
June	1st to 10th	Day	17% 9% 3 8% 5% 5% 6% 5% 7% 7% 28%	2850
	11th to 20th	Day	21% 8% 3 8% 6% 5% 5% 5% 7% 7% 25%	2850
	21st to end	Day	9% 4 2 5% 6% 5% 5% 5% 8% 10% 39%	2850
July	1st to 10th	Day	7% 5% 2 5% 4 5% 5% 5% 7% 9% 47%	4740
	11th to 20th	Day	7% 3 1 4 3 4 5% 5% 8% 11% 50%	4740
	21st to end	Day	4 3 1 4 4 4 4 4 6% 9% 56%	4987
August	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 5% 8% 9% 42%	4401
	11th to 20th	Day	8% 4 2 6% 4 4 5% 5% 8% 10% 43%	4090
	21st to end	Day	9% 5% 2 5% 3 3 4 4 6% 8% 52%	4521
September	1st to 10th	Day	10% 6% 3 6% 4 4 4 4 5% 7% 50%	2349
	11th to 20th	Day	14% 8% 3 5% 4 3 4 4 6% 6% 45%	2090
	21st to end	Day	9% 7% 3 6% 4 4 5% 3 6% 8% 45%	2090
October	1st to 10th	Day	7% 6% 3 7% 4 4 4 4 6% 9% 46%	3369
	11th to 20th	Day	5% 7% 3 6% 4 5% 6% 4 8% 10% 41%	2887
	21st to end	Day	7% 7% 3 6% 5% 4 5% 3 6% 7% 47%	3101
November	1st to 10th	Day	6% 14% 4 9% 6% 5% 4 3 6% 7% 34%	1654
	11th to 20th	Day	4 10% 4 8% 6% 4 5% 4 6% 7% 42%	1510
	21st to end	Day	3 11% 4 10% 6% 4 6% 4 6% 9% 38%	1400
December	1st to 10th	Day	2 8% 5% 11% 7% 6% 7% 5% 6% 8% 35%	2290
	11th to 20th	Day	2 7% 4 11% 6% 7% 6% 4 8% 10% 34%	2642
	21st to end	Day	3 10% 4 9% 5% 5% 4 4 6% 8% 42%	3498
January	1st to 10th	Night	3 11% 5% 12% 9% 8% 6% 5% 7% 7% 27%	6766
	11th to 20th	Night	2 6% 4 13% 7% 6% 6% 5% 7% 8% 35%	6670
	21st to end	Night	2 8% 3 9% 5% 5% 5% 4 6% 8% 43%	6952
February	1st to 10th	Night	3 10% 4 9% 7% 7% 7% 5% 7% 8% 33%	2800
	11th to 20th	Night	3 12% 5% 11% 6% 6% 5% 5% 7% 9% 32%	2554
	21st to end	Night	3 9% 5% 12% 8% 5% 6% 4 6% 7% 37%	2005
March	1st to 10th	Night	2 8% 3 12% 7% 6% 6% 5% 6% 11% 35%	5376
	11th to 20th	Night	4 8% 3 9% 6% 5% 5% 5% 7% 8% 39%	5074
	21st to end	Night	9% 18% 6% 13% 6% 5% 4 4 6% 6% 24%	5367
April	1st to 10th	Night	7% 15% 4 8% 5% 5% 5% 5% 5% 8% 32%	1956
	11th to 20th	Night	10% 13% 5% 10% 4 4 4 4 5% 7% 33%	1781
	21st to end	Night	9% 12% 4 9% 5% 4 5% 4 5% 8% 35%	1800
May	1st to 10th	Night	18% 13% 4 8% 4 4 4 3 4 6% 32%	2711
	11th to 20th	Night	11% 9% 3 8% 6% 5% 5% 4 7% 9% 34%	2269
	21st to end	Night	15% 9% 3 9% 5% 6% 6% 5% 7% 7% 29%	2452
June	1st to 10th	Night	15% 9% 2 7% 6% 5% 5% 3 6% 8% 34%	1330
	11th to 20th	Night	18% 8% 3 7% 4 5% 5% 4 7% 8% 32%	1330
	21st to end	Night	8% 5% 1 5% 5% 5% 6% 5% 7% 10% 45%	1330
July	1st to 10th	Night	6% 5% 2 6% 6% 4 4 4 6% 7% 49%	2220
	11th to 20th	Night	4 4 1 4 3 4 5% 5% 8% 11% 51%	2220
	21st to end	Night	4 4 1 5% 2 4 4 3 5% 7% 61%	2561
August	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 8% 9% 43%	2529
	11th to 20th	Night	6% 3 2 5% 4 5% 5% 5% 8% 10% 47%	2746
	21st to end	Night	8% 4 2 4 3 3 3 4 6% 9% 54%	3146
September	1st to 10th	Night	10% 7% 2 5% 3 3 3 3 6% 8% 50%	1829
	11th to 20th	Night	14% 7% 2 4 3 3 3 3 5% 7% 49%	2090
	21st to end	Night	9% 8% 2 5% 3 3 4 3 6% 8% 49%	2090
October	1st to 10th	Night	7% 6% 2 5% 4 4 5% 4 6% 8% 51%	3606
	11th to 20th	Night	5% 7% 2 5% 4 4 4 4 6% 8% 50%	4040
	21st to end	Night	5% 9% 3 6% 4 4 5% 4 6% 7% 47%	4457
November	1st to 10th	Night	6% 14% 4 8% 5% 5% 5% 4 6% 6% 37%	2625
	11th to 20th	Night	4 9% 4 8% 6% 5% 6% 4 6% 8% 41%	2885
	21st to end	Night	3 10% 4 10% 5% 6% 5% 4 6% 9% 39%	3000
December	1st to 10th	Night	2 9% 4 9% 6% 5% 6% 5% 8% 10% 36%	4890
	11th to 20th	Night	2 9% 5% 12% 8% 6% 6% 5% 7% 9% 31%	5550
	21st to end	Night	3 11% 4 9% 5% 4 5% 4 7% 7% 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	47% 6% 10% 23% 11% 3	3179
	11th to 20th	Day	41% 4 12% 20% 19% 3	3293
	21st to end	Day	30% 6% 16% 32% 15% 1	4004
February	1st to 10th	Day	49% 6% 14% 18% 9% 3	1600
	11th to 20th	Day	46% 6% 15% 22% 9% 2	1741
	21st to end	Day	47% 7% 13% 19% 13% 2	1620
March	1st to 10th	Day	39% 5% 15% 23% 17% 1	4518
	11th to 20th	Day	39% 5% 14% 25% 16% 1	4925
	21st to end	Day	60% 7% 12% 14% 6% 1	5607
April	1st to 10th	Day	50% 8% 15% 19% 8% 1	2443
	11th to 20th	Day	51% 7% 12% 20% 10% 1	2570
	21st to end	Day	50% 6% 15% 21% 8% 1	2600
May	1st to 10th	Day	55% 5% 10% 23% 7%	4471
	11th to 20th	Day	46% 10% 12% 23% 9%	4848
	21st to end	Day	56% 8% 12% 17% 7% 1	5240
June	1st to 10th	Day	51% 8% 14% 17% 8% 1	2850
	11th to 20th	Day	55% 7% 13% 17% 7% 2	2850
	21st to end	Day	35% 9% 19% 24% 11% 2	2850
July	1st to 10th	Day	32% 7% 14% 26% 17% 4	4666
	11th to 20th	Day	27% 7% 19% 34% 12% 2	4659
	21st to end	Day	22% 6% 11% 29% 24% 7%	4829
August	1st to 10th	Day	34% 7% 16% 35% 6% 1	4384
	11th to 20th	Day	32% 8% 25% 27% 7% 1	4130
	21st to end	Day	29% 6% 19% 33% 12% 1	4520
September	1st to 10th	Day	33% 6% 15% 26% 15% 4	2349
	11th to 20th	Day	39% 6% 15% 25% 13% 1	2090
	21st to end	Day	36% 7% 15% 27% 12% 3	2090
October	1st to 10th	Day	34% 5% 17% 35% 7% 1	3369
	11th to 20th	Day	35% 5% 21% 23% 12% 3	2887
	21st to end	Day	36% 6% 11% 34% 13% 1	3101
November	1st to 10th	Day	47% 6% 13% 20% 12% 2	1654
	11th to 20th	Day	40% 5% 16% 26% 10% 2	1510
	21st to end	Day	41% 7% 16% 24% 9% 3	1400
December	1st to 10th	Day	45% 6% 14% 24% 8% 2	2290
	11th to 20th	Day	43% 8% 20% 20% 8% 1	2644
	21st to end	Day	39% 5% 10% 25% 18% 4	3498
January	1st to 10th	Night	53% 6% 12% 21% 6% 2	6766
	11th to 20th	Night	45% 5% 12% 20% 13% 5%	6711
	21st to end	Night	37% 6% 14% 27% 15% 1	6952
February	1st to 10th	Night	46% 6% 12% 21% 12% 3	2800
	11th to 20th	Night	47% 6% 13% 19% 13% 2	2555
	21st to end	Night	46% 4 12% 23% 13% 3	2005
March	1st to 10th	Night	42% 5% 16% 22% 13% 2	5376
	11th to 20th	Night	39% 7% 14% 24% 15% 1	5074
	21st to end	Night	59% 5% 11% 15% 8% 1	5367
April	1st to 10th	Night	49% 5% 13% 21% 11% 1	1956
	11th to 20th	Night	50% 6% 13% 21% 10% 1	1781
	21st to end	Night	46% 7% 15% 21% 9% 2	1800
May	1st to 10th	Night	54% 4 11% 24% 7%	2711
	11th to 20th	Night	42% 7% 13% 29% 8% 1	2269
	21st to end	Night	50% 7% 15% 20% 8% 1	2452
June	1st to 10th	Night	47% 6% 15% 23% 9% 1	1330
	11th to 20th	Night	48% 6% 17% 18% 9% 2	1330
	21st to end	Night	32% 8% 20% 28% 10% 1	1330
July	1st to 10th	Night	33% 7% 14% 25% 18% 3	2185
	11th to 20th	Night	25% 8% 23% 31% 9% 4	2178
	21st to end	Night	23% 5% 10% 33% 24% 6%	2480
August	1st to 10th	Night	34% 7% 15% 30% 12% 1	2521
	11th to 20th	Night	29% 7% 29% 25% 9% 1	2772
	21st to end	Night	27% 6% 20% 34% 12% 2	3146
September	1st to 10th	Night	32% 5% 18% 24% 16% 4	1829
	11th to 20th	Night	35% 5% 16% 28% 13% 4	2090
	21st to end	Night	32% 5% 19% 26% 14% 4	2090
October	1st to 10th	Night	31% 7% 15% 26% 20% 2	3606
	11th to 20th	Night	31% 5% 19% 27% 16% 2	4040
	21st to end	Night	36% 5% 11% 34% 13% 1	4457
November	1st to 10th	Night	45% 7% 13% 22% 12% 2	2625
	11th to 20th	Night	40% 6% 16% 22% 15% 2	2885
	21st to end	Night	41% 6% 17% 22% 11% 4	3000
December	1st to 10th	Night	41% 7% 21% 21% 8% 2	4890
	11th to 20th	Night	47% 8% 18% 18% 9%	5547
	21st to end	Night	41% 5% 10% 25% 15% 4	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	2 10% 26% 38% 15% 10%	200
	11th to 20th	Day	9% 8% 28% 36% 18% 3	200
	21st to end	Day	8% 9% 24% 41% 14% 3	220
February	1st to 10th	Day	9% 14% 31% 34% 8% 6%	200
	11th to 20th	Day	7% 10% 33% 38% 11% 2	289
	21st to end	Day	5% 16% 29% 34% 14% 2	384
March	1st to 10th	Day	7% 14% 38% 26% 12% 3	500
	11th to 20th	Day	8% 12% 35% 29% 11% 3	500
	21st to end	Day	13% 19% 31% 24% 10% 3	550
April	1st to 10th	Day	14% 16% 36% 25% 8% 1	500
	11th to 20th	Day	17% 16% 29% 24% 12% 2	492
	21st to end	Day	17% 17% 30% 23% 10% 3	500
May	1st to 10th	Day	19% 13% 26% 26% 11% 4	528
	11th to 20th	Day	16% 9% 24% 26% 19% 5%	725
	21st to end	Day	20% 7% 21% 29% 19% 4	760
June	1st to 10th	Day	19% 10% 28% 29% 12% 3	680
	11th to 20th	Day	23% 11% 25% 25% 12% 4	680
	21st to end	Day	10% 7% 28% 29% 21% 5%	680
July	1st to 10th	Day	12% 6% 24% 31% 23% 5%	671
	11th to 20th	Day	12% 5% 25% 33% 22% 4	668
	21st to end	Day	6% 6% 27% 35% 19% 6%	650
August	1st to 10th	Day	13% 5% 25% 34% 17% 6%	487
	11th to 20th	Day	10% 5% 23% 37% 18% 6%	477
	21st to end	Day	12% 8% 27% 30% 16% 8%	539
September	1st to 10th	Day	13% 8% 29% 28% 17% 6%	490
	11th to 20th	Day	19% 6% 25% 31% 16% 3	490
	21st to end	Day	13% 15% 30% 28% 12% 2	490
October	1st to 10th	Day	14% 8% 30% 29% 15% 4	421
	11th to 20th	Day	15% 10% 26% 32% 13% 4	300
	21st to end	Day	14% 15% 35% 23% 10% 4	330
November	1st to 10th	Day	18% 10% 30% 30% 10% 2	300
	11th to 20th	Day	11% 14% 30% 31% 11% 2	255
	21st to end	Day	7% 8% 33% 33% 12% 9%	200
December	1st to 10th	Day	7% 7% 31% 42% 11% 4	200
	11th to 20th	Day	3 11% 32% 39% 11% 5%	200
	21st to end	Day	7% 6% 25% 38% 20% 3	220
January	1st to 10th	Night	9% 11% 34% 34% 10% 2	1000
	11th to 20th	Night	7% 8% 38% 36% 9% 1	970
	21st to end	Night	8% 13% 36% 34% 8% 1	880
February	1st to 10th	Night	8% 11% 32% 33% 13% 4	800
	11th to 20th	Night	9% 8% 34% 35% 13% 2	784
	21st to end	Night	6% 6% 36% 32% 17% 4	660
March	1st to 10th	Night	6% 6% 38% 35% 13% 3	800
	11th to 20th	Night	7% 7% 37% 36% 12% 2	800
	21st to end	Night	12% 6% 32% 33% 13% 3	880
April	1st to 10th	Night	13% 8% 33% 32% 13% 2	756
	11th to 20th	Night	18% 7% 34% 30% 11%	593
	21st to end	Night	16% 8% 32% 34% 11% 1	600
May	1st to 10th	Night	17% 7% 26% 35% 15% 1	490
	11th to 20th	Night	16% 7% 24% 36% 18% 1	394
	21st to end	Night	20% 4 23% 33% 19% 1	422
June	1st to 10th	Night	20% 6% 25% 35% 13% 1	380
	11th to 20th	Night	20% 5% 27% 32% 16% 1	380
	21st to end	Night	10% 2 21% 38% 27% 1	380
July	1st to 10th	Night	9% 4 15% 47% 24% 2	370
	11th to 20th	Night	11% 2 19% 46% 19% 2	368
	21st to end	Night	6% 5% 17% 45% 25% 2	416
August	1st to 10th	Night	11% 3 12% 42% 29% 3	378
	11th to 20th	Night	9% 3 17% 43% 25% 3	523
	21st to end	Night	9% 5% 19% 43% 21% 2	627
September	1st to 10th	Night	14% 4 22% 36% 20% 3	684
	11th to 20th	Night	18% 4 16% 39% 20% 2	760
	21st to end	Night	13% 5% 30% 34% 13% 4	760
October	1st to 10th	Night	15% 5% 27% 35% 16% 3	760
	11th to 20th	Night	12% 6% 31% 34% 14% 3	760
	21st to end	Night	10% 7% 35% 37% 10% 1	836
November	1st to 10th	Night	13% 8% 36% 33% 9% 1	870
	11th to 20th	Night	9% 11% 40% 32% 7% 1	1000
	21st to end	Night	7% 8% 39% 34% 10% 2	1000
December	1st to 10th	Night	9% 8% 37% 32% 12% 2	1000
	11th to 20th	Night	4 8% 37% 41% 9% 1	1000
	21st to end	Night	8% 7% 35% 36% 12% 2	1100

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