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 2024-11-02.

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	8% 9% 3 8% 5% 5% 5% 4 7% 8% 38%	101893
	Night	6% 9% 3 8% 5% 5% 5% 4 6% 8% 39%	97155
Transparency	Day	41% 7% 15% 24% 11% 2	101640
	Night	41% 6% 15% 24% 12% 2	97054
Seeing	Day	13% 10% 28% 30% 15% 4	15339
	Night	11% 7% 31% 36% 14% 2	24354

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 8% 6% 12% 7% 5% 5% 4 8% 10% 35%	2219
	11th to 20th	Day	2 9% 4 11% 7% 5% 6% 5% 7% 8% 37%	2270
	21st to end	Day	3 8% 3 8% 6% 5% 5% 4 6% 11% 41%	2794
February	1st to 10th	Day	3 10% 3 13% 7% 6% 7% 5% 7% 7% 33%	1520
	11th to 20th	Day	3 11% 4 10% 7% 8% 6% 5% 6% 8% 32%	1643
	21st to end	Day	2 11% 5% 11% 7% 7% 6% 5% 6% 7% 32%	1541
March	1st to 10th	Day	2 9% 4 12% 7% 7% 7% 5% 6% 8% 34%	3138
	11th to 20th	Day	5% 9% 3 6% 5% 4 4 4 6% 9% 46%	3440
	21st to end	Day	7% 21% 7% 13% 5% 5% 4 4 5% 6% 22%	3907
April	1st to 10th	Day	8% 16% 4 10% 6% 5% 5% 4 6% 8% 28%	2321
	11th to 20th	Day	11% 14% 5% 9% 5% 4 5% 4 6% 7% 30%	2440
	21st to end	Day	11% 14% 4 8% 5% 5% 4 5% 6% 7% 30%	2470
May	1st to 10th	Day	17% 15% 4 8% 5% 5% 4 3 5% 6% 28%	4334
	11th to 20th	Day	11% 9% 3 9% 6% 6% 6% 5% 8% 8% 29%	4694
	21st to end	Day	17% 10% 4 11% 7% 6% 6% 4 6% 6% 23%	5161
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	11% 9% 3 7% 5% 4 5% 4 5% 7% 41%	2021
	11th to 20th	Day	8% 10% 3 7% 5% 4 6% 4 5% 9% 39%	1743
	21st to end	Day	7% 10% 4 7% 5% 5% 6% 4 7% 8% 38%	1881
November	1st to 10th	Day	7% 15% 4 9% 6% 5% 4 3 6% 7% 35%	1579
	11th to 20th	Day	4 9% 4 8% 5% 4 5% 4 6% 7% 43%	1435
	21st to end	Day	3 11% 4 9% 6% 4 5% 4 6% 9% 40%	1330
December	1st to 10th	Day	4 8% 4 12% 7% 5% 6% 5% 6% 7% 36%	1330
	11th to 20th	Day	2 10% 5% 12% 7% 6% 7% 5% 8% 8% 31%	1682
	21st to end	Day	3 9% 3 7% 5% 5% 4 4 6% 9% 44%	2442
January	1st to 10th	Night	3 11% 5% 11% 8% 7% 6% 5% 8% 8% 29%	4726
	11th to 20th	Night	3 7% 4 13% 7% 6% 6% 6% 7% 8% 35%	4658
	21st to end	Night	3 10% 3 10% 7% 6% 5% 4 6% 8% 39%	4862
February	1st to 10th	Night	4 10% 4 9% 7% 6% 6% 5% 7% 9% 33%	2660
	11th to 20th	Night	3 12% 6% 11% 5% 6% 5% 4 7% 9% 32%	2423
	21st to end	Night	3 9% 5% 12% 8% 5% 5% 3 6% 7% 37%	1908
March	1st to 10th	Night	1 7% 4 14% 8% 7% 7% 6% 6% 9% 31%	3736
	11th to 20th	Night	5% 8% 2 6% 5% 4 4 4 7% 8% 48%	3538
	21st to end	Night	10% 20% 6% 13% 6% 5% 4 4 5% 5% 22%	3745
April	1st to 10th	Night	7% 16% 3 9% 5% 5% 5% 5% 5% 8% 32%	1858
	11th to 20th	Night	11% 13% 5% 10% 4 4 4 4 5% 7% 32%	1691
	21st to end	Night	10% 13% 4 8% 5% 4 5% 4 5% 7% 35%	1710
May	1st to 10th	Night	19% 13% 4 8% 4 4 4 3 4 6% 31%	2628
	11th to 20th	Night	11% 9% 3 8% 6% 5% 5% 4 7% 9% 35%	2199
	21st to end	Night	15% 9% 3 9% 5% 6% 6% 5% 7% 7% 29%	2414
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	10% 8% 2 6% 5% 4 4 4 6% 7% 43%	2158
	11th to 20th	Night	7% 8% 2 6% 4 4 5% 5% 6% 8% 44%	2436
	21st to end	Night	6% 10% 3 8% 5% 5% 5% 4 6% 8% 40%	2717
November	1st to 10th	Night	6% 14% 4 8% 5% 5% 5% 4 6% 6% 37%	2503
	11th to 20th	Night	4 9% 4 8% 5% 4 6% 4 6% 8% 42%	2740
	21st to end	Night	3 10% 4 9% 5% 6% 5% 4 6% 9% 40%	2850
December	1st to 10th	Night	3 11% 4 9% 6% 6% 6% 5% 7% 8% 35%	2850
	11th to 20th	Night	2 8% 4 11% 7% 6% 6% 6% 7% 9% 34%	3510
	21st to end	Night	3 8% 3 9% 6% 5% 5% 5% 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	46% 7% 15% 17% 13% 1	3138
	11th to 20th	Day	34% 6% 18% 26% 14% 1	3441
	21st to end	Day	60% 7% 13% 16% 5%	3907
April	1st to 10th	Day	51% 8% 15% 18% 7% 1	2321
	11th to 20th	Day	51% 7% 11% 20% 10% 1	2440
	21st to end	Day	50% 6% 15% 21% 8% 1	2470
May	1st to 10th	Day	56% 5% 10% 23% 6%	4334
	11th to 20th	Day	45% 10% 12% 23% 9%	4698
	21st to end	Day	56% 8% 12% 16% 7% 1	5162
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	43% 6% 14% 26% 10% 2	2021
	11th to 20th	Day	42% 6% 15% 24% 10% 3	1743
	21st to end	Day	41% 8% 13% 25% 12% 1	1881
November	1st to 10th	Day	48% 6% 12% 20% 12% 2	1579
	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	47% 6% 13% 23% 11% 1	3736
	11th to 20th	Night	31% 9% 18% 25% 16% 1	3538
	21st to end	Night	62% 6% 11% 15% 5% 1	3745
April	1st to 10th	Night	49% 5% 13% 21% 11% 1	1858
	11th to 20th	Night	50% 6% 14% 20% 9% 1	1691
	21st to end	Night	47% 6% 15% 21% 9% 2	1710
May	1st to 10th	Night	55% 4 11% 24% 6%	2628
	11th to 20th	Night	42% 7% 13% 29% 9% 1	2199
	21st to end	Night	50% 7% 15% 19% 8% 1	2414
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	39% 6% 15% 25% 14% 2	2158
	11th to 20th	Night	36% 6% 16% 25% 13% 3	2436
	21st to end	Night	41% 6% 15% 26% 11% 1	2717
November	1st to 10th	Night	45% 7% 13% 21% 13% 2	2503
	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% 15% 39% 25% 11% 3	460
	11th to 20th	Day	9% 13% 33% 30% 12% 3	460
	21st to end	Day	13% 19% 31% 23% 10% 3	506
April	1st to 10th	Day	15% 17% 36% 24% 7% 1	460
	11th to 20th	Day	18% 14% 29% 25% 12% 2	452
	21st to end	Day	17% 17% 31% 23% 9% 2	460
May	1st to 10th	Day	21% 13% 25% 25% 12% 5%	487
	11th to 20th	Day	16% 9% 24% 26% 20% 4	675
	21st to end	Day	20% 7% 21% 29% 19% 4	734
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% 34% 23% 11% 3	330
November	1st to 10th	Day	19% 9% 30% 29% 10% 2	273
	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% 39% 35% 12% 3	760
	11th to 20th	Night	7% 7% 37% 35% 12% 2	760
	21st to end	Night	12% 7% 32% 34% 13% 3	836
April	1st to 10th	Night	13% 8% 33% 32% 12% 2	718
	11th to 20th	Night	19% 6% 33% 31% 11%	563
	21st to end	Night	16% 8% 32% 34% 10% 1	570
May	1st to 10th	Night	17% 7% 25% 34% 15% 1	466
	11th to 20th	Night	15% 6% 24% 37% 17% 1	374
	21st to end	Night	21% 4 23% 34% 18% 1	411
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% 11% 1	836
November	1st to 10th	Night	14% 8% 36% 33% 9% 1	829
	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

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