White Salmon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Salmon clear sky chart from 2005-11-06 to 2024-01-12.

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% 7% 3 6% 6% 3 5% 5% 6% 7% 42%	74753
	Night	11% 8% 4 7% 6% 3 5% 5% 6% 7% 39%	74967
Transparency	Day	38% 4 14% 24% 15% 4	74456
	Night	40% 5% 16% 23% 12% 3	74785
Seeing	Day	17% 14% 33% 22% 11% 3	13420
	Night	15% 9% 23% 34% 17% 2	22535

By Month

Percentage Cloud Cover SW (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	18% 17% 7% 14% 10% 4 7% 5% 4 5% 9%	1519
	11th to 20th	Day	19% 13% 5% 12% 10% 6% 7% 5% 5% 6% 11%	1448
	21st to end	Day	13% 15% 7% 12% 8% 4 7% 6% 8% 6% 14%	1657
February	1st to 10th	Day	16% 13% 5% 8% 8% 4 6% 6% 6% 6% 21%	1620
	11th to 20th	Day	12% 9% 4 8% 8% 5% 7% 7% 8% 8% 24%	1575
	21st to end	Day	10% 10% 5% 9% 9% 6% 7% 7% 6% 6% 24%	1452
March	1st to 10th	Day	12% 11% 3 9% 9% 5% 7% 7% 6% 9% 23%	1815
	11th to 20th	Day	11% 10% 5% 10% 9% 5% 7% 7% 6% 7% 24%	1980
	21st to end	Day	10% 10% 5% 10% 9% 5% 8% 8% 8% 8% 21%	2272
April	1st to 10th	Day	11% 9% 4 8% 8% 5% 8% 6% 8% 7% 27%	2160
	11th to 20th	Day	8% 9% 4 8% 7% 5% 6% 6% 6% 7% 33%	2129
	21st to end	Day	5% 6% 3 7% 6% 4 8% 6% 7% 10% 38%	2296
May	1st to 10th	Day	6% 4 3 6% 6% 3 5% 5% 7% 7% 48%	2520
	11th to 20th	Day	8% 6% 3 6% 5% 3 5% 6% 6% 10% 41%	2477
	21st to end	Day	9% 6% 2 5% 6% 3 5% 6% 6% 9% 42%	2723
June	1st to 10th	Day	8% 6% 2 6% 6% 4 6% 6% 7% 8% 43%	2520
	11th to 20th	Day	4 4 3 5% 6% 4 6% 6% 7% 9% 48%	2520
	21st to end	Day	3 1 2 3 5% 3 4 4 4 6% 64%	2520
July	1st to 10th	Day	1 1 1 2 3 2 2 3 4 7% 73%	2520
	11th to 20th	Day	2 2 1 2 2 2 3 4 4 4 75%	2520
	21st to end	Day	1 1 1 1 1 1 2 2 2 3 84%	2741
August	1st to 10th	Day	1 1 1 2 2 1 2 3 3 6% 77%	2442
	11th to 20th	Day	2 1 1 1 2 2 4 3 3 6% 76%	2298
	21st to end	Day	2 1 1 2 4 3 4 4 5% 8% 68%	2403
September	1st to 10th	Day	2 1 1 2 3 2 2 3 5% 7% 72%	2160
	11th to 20th	Day	5% 2 2 4 5% 3 5% 5% 6% 8% 57%	2160
	21st to end	Day	7% 5% 2 5% 4 3 5% 4 4 7% 53%	1921
October	1st to 10th	Day	7% 5% 3 6% 5% 3 5% 5% 6% 9% 45%	1800
	11th to 20th	Day	9% 6% 3 7% 5% 3 6% 6% 8% 8% 39%	1800
	21st to end	Day	14% 8% 3 7% 7% 4 6% 5% 7% 7% 33%	1873
November	1st to 10th	Day	15% 10% 5% 8% 7% 4 6% 8% 7% 8% 22%	1630
	11th to 20th	Day	15% 12% 6% 12% 9% 5% 7% 7% 6% 6% 16%	1520
	21st to end	Day	14% 12% 4 9% 8% 5% 7% 6% 6% 7% 21%	1520
December	1st to 10th	Day	14% 17% 8% 9% 7% 4 5% 5% 5% 5% 22%	1520
	11th to 20th	Day	21% 21% 9% 12% 7% 3 5% 4 5% 5% 9%	1928
	21st to end	Day	21% 21% 8% 11% 8% 4 5% 4 3 4 10%	2794
January	1st to 10th	Night	19% 16% 6% 14% 9% 4 5% 5% 5% 6% 12%	2646
	11th to 20th	Night	19% 15% 6% 11% 8% 4 6% 5% 5% 6% 15%	2534
	21st to end	Night	16% 12% 5% 11% 7% 4 6% 6% 6% 7% 20%	2696
February	1st to 10th	Night	16% 12% 4 7% 6% 4 6% 7% 7% 7% 24%	2340
	11th to 20th	Night	14% 8% 4 8% 7% 4 6% 5% 6% 6% 31%	2272
	21st to end	Night	10% 12% 4 8% 8% 4 6% 7% 8% 8% 25%	1803
March	1st to 10th	Night	12% 10% 3 8% 8% 4 6% 7% 6% 9% 27%	2142
	11th to 20th	Night	12% 7% 3 7% 7% 4 9% 6% 7% 11% 29%	1980
	21st to end	Night	10% 8% 4 9% 9% 5% 7% 6% 7% 7% 28%	2084
April	1st to 10th	Night	10% 9% 4 6% 7% 4 6% 7% 7% 8% 33%	1800
	11th to 20th	Night	8% 7% 2 6% 6% 4 7% 7% 6% 7% 40%	1779
	21st to end	Night	7% 4 3 6% 5% 3 6% 6% 8% 9% 42%	1660
May	1st to 10th	Night	4 5% 3 5% 6% 3 5% 5% 7% 7% 50%	1440
	11th to 20th	Night	7% 5% 2 4 5% 3 4 5% 7% 9% 48%	1416
	21st to end	Night	4 5% 2 5% 5% 3 6% 6% 8% 10% 47%	1552
June	1st to 10th	Night	9% 5% 2 4 7% 4 6% 4 7% 8% 44%	1440
	11th to 20th	Night	5% 4 3 4 4 3 4 4 6% 10% 54%	1440
	21st to end	Night	3 2 1 3 3 2 4 3 5% 6% 67%	1440
July	1st to 10th	Night	2 1 1 2 2 1 2 3 3 5% 77%	1440
	11th to 20th	Night	1 1 2 2 1 2 3 3 5% 81%	1440
	21st to end	Night	1 1 1 1 1 2 2 2 3 86%	1576
August	1st to 10th	Night	2 1 1 2 2 1 2 3 3 6% 77%	1493
	11th to 20th	Night	2 2 1 2 1 3 3 3 4 79%	1602
	21st to end	Night	1 2 1 2 2 1 2 4 4 6% 75%	1952
September	1st to 10th	Night	2 1 1 2 3 1 2 3 3 5% 77%	1800
	11th to 20th	Night	5% 3 2 3 4 3 5% 5% 4 7% 61%	1800
	21st to end	Night	7% 4 1 3 4 3 4 4 4 7% 58%	2034
October	1st to 10th	Night	9% 4 2 5% 4 2 4 4 5% 6% 53%	2160
	11th to 20th	Night	11% 5% 1 5% 5% 3 5% 5% 6% 7% 45%	2160
	21st to end	Night	13% 7% 3 6% 6% 3 4 5% 6% 7% 40%	2481
November	1st to 10th	Night	16% 8% 4 7% 6% 4 7% 6% 7% 8% 29%	2447
	11th to 20th	Night	16% 10% 5% 9% 9% 4 6% 5% 6% 6% 23%	2660
	21st to end	Night	11% 10% 5% 9% 7% 4 7% 7% 7% 7% 26%	2660
December	1st to 10th	Night	17% 14% 6% 10% 7% 4 5% 5% 5% 5% 22%	2660
	11th to 20th	Night	22% 15% 8% 14% 8% 4 6% 5% 5% 4 10%	3276
	21st to end	Night	21% 20% 7% 10% 6% 3 5% 4 5% 5% 13%	4862

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	68% 8% 13% 10% 1	1519
	11th to 20th	Day	63% 7% 15% 10% 4 1	1448
	21st to end	Day	56% 8% 15% 16% 5%	1657
February	1st to 10th	Day	54% 9% 19% 15% 3 1	1620
	11th to 20th	Day	47% 8% 20% 19% 6% 1	1584
	21st to end	Day	48% 8% 17% 17% 10%	1452
March	1st to 10th	Day	53% 5% 13% 22% 7%	1815
	11th to 20th	Day	52% 5% 15% 23% 4	1980
	21st to end	Day	55% 7% 17% 18% 3	2272
April	1st to 10th	Day	49% 6% 16% 21% 8%	2160
	11th to 20th	Day	47% 5% 17% 17% 13% 2	2132
	21st to end	Day	37% 6% 18% 26% 11% 2	2296
May	1st to 10th	Day	34% 4 16% 32% 14%	2520
	11th to 20th	Day	39% 3 18% 27% 13% 1	2480
	21st to end	Day	36% 5% 19% 29% 10% 1	2724
June	1st to 10th	Day	37% 5% 16% 29% 12% 2	2520
	11th to 20th	Day	30% 3 18% 35% 12% 1	2520
	21st to end	Day	20% 3 15% 36% 18% 7%	2520
July	1st to 10th	Day	12% 2 13% 31% 29% 13%	2451
	11th to 20th	Day	13% 2 8% 23% 35% 19%	2445
	21st to end	Day	8% 1 4 24% 42% 20%	2589
August	1st to 10th	Day	11% 2 11% 31% 33% 12%	2425
	11th to 20th	Day	12% 2 11% 31% 34% 11%	2298
	21st to end	Day	15% 2 10% 35% 31% 7%	2403
September	1st to 10th	Day	13% 2 11% 33% 28% 13%	2160
	11th to 20th	Day	25% 3 14% 28% 23% 7%	2160
	21st to end	Day	31% 3 14% 29% 18% 5%	1921
October	1st to 10th	Day	35% 4 13% 28% 17% 3	1800
	11th to 20th	Day	35% 5% 20% 25% 15% 1	1800
	21st to end	Day	45% 5% 14% 25% 10%	1873
November	1st to 10th	Day	53% 6% 14% 21% 5%	1630
	11th to 20th	Day	57% 8% 15% 16% 4	1520
	21st to end	Day	50% 7% 17% 17% 8% 1	1520
December	1st to 10th	Day	59% 5% 12% 18% 5%	1520
	11th to 20th	Day	71% 6% 11% 11% 2	1928
	21st to end	Day	72% 4 10% 11% 3	2794
January	1st to 10th	Night	65% 8% 14% 11% 2	2646
	11th to 20th	Night	59% 6% 15% 15% 5%	2534
	21st to end	Night	54% 8% 16% 18% 4	2696
February	1st to 10th	Night	52% 6% 21% 18% 3	2340
	11th to 20th	Night	46% 8% 17% 22% 6%	2274
	21st to end	Night	45% 7% 17% 22% 8% 1	1803
March	1st to 10th	Night	46% 7% 16% 24% 6% 1	2142
	11th to 20th	Night	46% 5% 18% 25% 5% 1	1980
	21st to end	Night	49% 6% 21% 19% 5%	2084
April	1st to 10th	Night	43% 8% 19% 22% 7% 1	1800
	11th to 20th	Night	37% 6% 19% 24% 10% 3	1779
	21st to end	Night	34% 6% 20% 27% 11% 2	1660
May	1st to 10th	Night	29% 3 18% 35% 13% 1	1440
	11th to 20th	Night	31% 4 23% 28% 11% 3	1416
	21st to end	Night	31% 5% 28% 28% 8% 1	1552
June	1st to 10th	Night	37% 5% 17% 31% 10% 1	1440
	11th to 20th	Night	26% 3 21% 37% 12% 1	1440
	21st to end	Night	19% 3 13% 40% 19% 6%	1440
July	1st to 10th	Night	13% 2 14% 27% 30% 15%	1400
	11th to 20th	Night	9% 3 13% 23% 33% 20%	1392
	21st to end	Night	7% 1 5% 23% 41% 22%	1488
August	1st to 10th	Night	11% 2 10% 34% 32% 12%	1485
	11th to 20th	Night	12% 1 12% 30% 33% 11%	1602
	21st to end	Night	12% 2 10% 36% 32% 8%	1952
September	1st to 10th	Night	12% 2 12% 33% 27% 14%	1800
	11th to 20th	Night	23% 3 14% 30% 18% 12%	1800
	21st to end	Night	25% 3 14% 31% 20% 7%	2034
October	1st to 10th	Night	30% 4 12% 28% 23% 3	2160
	11th to 20th	Night	33% 5% 18% 25% 15% 3	2160
	21st to end	Night	38% 5% 14% 26% 17% 1	2481
November	1st to 10th	Night	48% 5% 15% 24% 8%	2447
	11th to 20th	Night	52% 7% 18% 19% 5%	2660
	21st to end	Night	47% 7% 17% 22% 6% 1	2660
December	1st to 10th	Night	57% 7% 14% 18% 5%	2660
	11th to 20th	Night	65% 7% 14% 12% 2	3276
	21st to end	Night	65% 5% 12% 15% 3	4862

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	26% 12% 29% 25% 7% 1	180
	11th to 20th	Day	35% 6% 23% 23% 12% 1	162
	21st to end	Day	29% 8% 22% 27% 13%	249
February	1st to 10th	Day	29% 17% 24% 22% 7% 1	340
	11th to 20th	Day	28% 17% 31% 19% 4 1	335
	21st to end	Day	27% 15% 34% 19% 6%	334
March	1st to 10th	Day	26% 16% 33% 16% 7% 1	420
	11th to 20th	Day	20% 17% 30% 23% 8% 1	420
	21st to end	Day	26% 19% 31% 16% 7%	462
April	1st to 10th	Day	28% 20% 29% 15% 7% 1	420
	11th to 20th	Day	23% 20% 33% 15% 6% 3	412
	21st to end	Day	21% 20% 33% 18% 5% 3	420
May	1st to 10th	Day	19% 20% 32% 18% 9% 2	423
	11th to 20th	Day	18% 13% 35% 21% 10% 3	448
	21st to end	Day	15% 16% 34% 23% 9% 2	485
June	1st to 10th	Day	17% 17% 33% 18% 12% 2	450
	11th to 20th	Day	18% 22% 36% 15% 6% 2	450
	21st to end	Day	8% 17% 39% 25% 10% 2	450
July	1st to 10th	Day	6% 12% 50% 24% 8% 1	446
	11th to 20th	Day	5% 14% 46% 23% 9% 2	444
	21st to end	Day	3 10% 44% 22% 16% 5%	487
August	1st to 10th	Day	5% 8% 40% 23% 17% 7%	447
	11th to 20th	Day	4 11% 34% 27% 16% 8%	437
	21st to end	Day	7% 16% 33% 23% 15% 5%	495
September	1st to 10th	Day	6% 13% 32% 27% 18% 4	450
	11th to 20th	Day	10% 10% 32% 31% 14% 4	450
	21st to end	Day	13% 12% 31% 27% 14% 3	450
October	1st to 10th	Day	17% 11% 29% 25% 15% 3	450
	11th to 20th	Day	16% 14% 24% 26% 16% 5%	450
	21st to end	Day	26% 11% 24% 23% 12% 4	388
November	1st to 10th	Day	27% 7% 23% 31% 10% 1	248
	11th to 20th	Day	29% 8% 30% 26% 6% 2	180
	21st to end	Day	27% 6% 28% 28% 11% 1	180
December	1st to 10th	Day	21% 12% 24% 22% 17% 3	180
	11th to 20th	Day	31% 8% 29% 27% 4 1	180
	21st to end	Day	24% 14% 22% 28% 11% 1	198
January	1st to 10th	Night	25% 10% 20% 29% 15% 1	760
	11th to 20th	Night	23% 8% 18% 34% 15% 2	724
	21st to end	Night	20% 6% 17% 36% 18% 3	792
February	1st to 10th	Night	22% 13% 18% 31% 15% 1	720
	11th to 20th	Night	23% 8% 19% 32% 16% 2	704
	21st to end	Night	20% 12% 21% 34% 12% 1	592
March	1st to 10th	Night	18% 11% 21% 35% 14% 1	720
	11th to 20th	Night	15% 10% 20% 39% 15% 1	720
	21st to end	Night	18% 14% 21% 33% 11% 2	792
April	1st to 10th	Night	19% 13% 24% 30% 13% 1	720
	11th to 20th	Night	14% 14% 28% 27% 15% 2	711
	21st to end	Night	13% 12% 30% 30% 14% 1	580
May	1st to 10th	Night	10% 15% 28% 29% 17% 2	360
	11th to 20th	Night	10% 10% 27% 31% 21% 2	354
	21st to end	Night	7% 10% 28% 36% 16% 2	389
June	1st to 10th	Night	14% 13% 29% 27% 16% 1	360
	11th to 20th	Night	9% 16% 39% 26% 10%	360
	21st to end	Night	6% 12% 34% 31% 16% 1	360
July	1st to 10th	Night	5% 8% 35% 35% 16% 1	350
	11th to 20th	Night	2 8% 43% 35% 11% 1	348
	21st to end	Night	3 8% 35% 35% 19% 2	394
August	1st to 10th	Night	3 6% 31% 39% 19% 3	419
	11th to 20th	Night	3 5% 20% 34% 31% 7%	534
	21st to end	Night	4 11% 31% 30% 21% 4	764
September	1st to 10th	Night	4 8% 27% 31% 26% 3	720
	11th to 20th	Night	6% 7% 24% 30% 28% 5%	720
	21st to end	Night	8% 8% 17% 36% 27% 4	720
October	1st to 10th	Night	12% 6% 18% 39% 23% 3	720
	11th to 20th	Night	13% 6% 18% 34% 24% 4	720
	21st to end	Night	17% 7% 17% 37% 18% 3	792
November	1st to 10th	Night	17% 7% 18% 40% 17% 1	740
	11th to 20th	Night	22% 8% 20% 35% 13% 2	760
	21st to end	Night	14% 9% 19% 38% 18% 2	760
December	1st to 10th	Night	19% 9% 21% 34% 16% 2	760
	11th to 20th	Night	24% 5% 21% 35% 13%	760
	21st to end	Night	23% 10% 24% 33% 8% 1	836

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