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 2024-11-05.

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% 3 7% 5% 5% 5% 4 5% 6% 45%	105408
	Night	11% 9% 3 7% 5% 4 5% 4 5% 6% 40%	102315
Transparency	Day	20% 46% 7% 13% 9% 5%	105151
	Night	23% 47% 7% 13% 7% 3	102161
Seeing	Day	17% 14% 33% 22% 11% 3	14544
	Night	15% 9% 23% 34% 17% 2	23511

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	21% 22% 5% 14% 8% 6% 6% 3 4 4 7%	2539
	11th to 20th	Day	26% 16% 4 11% 7% 6% 5% 4 5% 5% 12%	2540
	21st to end	Day	31% 18% 6% 12% 5% 4 5% 3 5% 3 8%	2923
February	1st to 10th	Day	16% 15% 4 9% 7% 6% 6% 4 7% 6% 21%	1710
	11th to 20th	Day	12% 11% 3 9% 8% 7% 7% 5% 8% 8% 22%	1665
	21st to end	Day	11% 11% 4 10% 8% 8% 7% 6% 6% 7% 24%	1540
March	1st to 10th	Day	8% 11% 4 9% 8% 7% 7% 6% 7% 8% 25%	3166
	11th to 20th	Day	7% 8% 3 8% 5% 5% 5% 4 6% 5% 44%	3490
	21st to end	Day	10% 11% 4 10% 8% 7% 7% 6% 8% 8% 21%	3996
April	1st to 10th	Day	10% 10% 3 9% 7% 7% 7% 5% 8% 6% 27%	2280
	11th to 20th	Day	7% 10% 3 10% 6% 7% 5% 5% 6% 7% 34%	2249
	21st to end	Day	5% 7% 3 8% 5% 6% 6% 6% 7% 10% 37%	2425
May	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 6% 45%	4420
	11th to 20th	Day	5% 4 1 4 3 3 4 3 4 7% 61%	4377
	21st to end	Day	8% 6% 2 7% 5% 6% 6% 5% 7% 8% 39%	4813
June	1st to 10th	Day	8% 6% 2 7% 6% 6% 5% 5% 6% 7% 42%	2660
	11th to 20th	Day	4 5% 2 6% 5% 5% 5% 5% 7% 8% 48%	2660
	21st to end	Day	3 2 1 3 4 4 4 3 5% 7% 63%	2660
July	1st to 10th	Day	1 1 1 2 1 1 2 3 4 83%	4420
	11th to 20th	Day	1 2 1 1 2 2 2 2 3 3 82%	4420
	21st to end	Day	1 1 1 2 1 2 2 2 3 4 81%	4790
August	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 76%	4283
	11th to 20th	Day	1 2 1 3 3 3 4 3 5% 7% 69%	4026
	21st to end	Day	4 4 2 3 3 3 4 3 4 6% 65%	4220
September	1st to 10th	Day	2 1 1 2 2 2 2 3 5% 7% 72%	2280
	11th to 20th	Day	4 2 1 5% 4 5% 5% 4 5% 8% 57%	2280
	21st to end	Day	7% 4 2 5% 4 4 4 3 5% 7% 54%	2027
October	1st to 10th	Day	5% 4 2 5% 3 4 4 4 6% 8% 54%	3180
	11th to 20th	Day	7% 7% 3 8% 5% 6% 6% 5% 8% 8% 38%	3161
	21st to end	Day	13% 9% 4 9% 6% 5% 6% 4 7% 8% 27%	3260
November	1st to 10th	Day	15% 11% 4 9% 7% 5% 6% 6% 8% 7% 21%	1666
	11th to 20th	Day	15% 13% 5% 13% 7% 7% 7% 5% 6% 6% 16%	1520
	21st to end	Day	13% 14% 3 10% 7% 6% 7% 5% 6% 7% 21%	1520
December	1st to 10th	Day	14% 19% 6% 10% 6% 5% 5% 4 5% 5% 22%	1520
	11th to 20th	Day	21% 22% 9% 13% 6% 4 4 4 5% 5% 9%	1928
	21st to end	Day	21% 22% 8% 13% 6% 5% 5% 3 4 4 10%	2794
January	1st to 10th	Night	21% 22% 5% 14% 7% 5% 5% 4 4 4 8%	4406
	11th to 20th	Night	25% 16% 5% 11% 6% 5% 5% 3 4 8% 13%	4420
	21st to end	Night	32% 16% 6% 13% 4 4 3 3 3 4 11%	4734
February	1st to 10th	Night	16% 14% 3 8% 6% 6% 5% 6% 7% 7% 24%	2470
	11th to 20th	Night	15% 9% 3 9% 7% 5% 6% 4 6% 6% 30%	2402
	21st to end	Night	11% 13% 3 9% 6% 6% 6% 6% 8% 8% 24%	1913
March	1st to 10th	Night	8% 11% 3 10% 7% 6% 7% 6% 8% 9% 26%	3705
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 4 6% 7% 46%	3490
	21st to end	Night	10% 8% 4 11% 8% 7% 7% 5% 7% 8% 24%	3657
April	1st to 10th	Night	9% 10% 3 7% 7% 6% 6% 6% 7% 8% 32%	1900
	11th to 20th	Night	8% 7% 2 7% 5% 6% 7% 5% 6% 6% 40%	1879
	21st to end	Night	7% 5% 3 6% 4 4 6% 6% 9% 9% 41%	1751
May	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 5% 47%	2540
	11th to 20th	Night	4 3 1 4 3 3 3 3 5% 7% 63%	2516
	21st to end	Night	3 4 2 6% 5% 5% 6% 5% 8% 11% 45%	2762
June	1st to 10th	Night	9% 7% 2 6% 6% 5% 5% 3 7% 7% 44%	1520
	11th to 20th	Night	5% 4 2 4 4 4 3 4 6% 9% 55%	1520
	21st to end	Night	3 2 1 3 4 3 3 3 5% 6% 66%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 2 3 87%	2540
	11th to 20th	Night	1 1 2 1 2 2 2 3 3 84%	2540
	21st to end	Night	1 1 1 1 1 1 2 2 4 85%	2761
August	1st to 10th	Night	2 1 1 2 2 2 2 2 4 6% 77%	2646
	11th to 20th	Night	1 2 1 2 2 2 3 2 4 7% 74%	2812
	21st to end	Night	3 2 1 3 2 2 4 3 4 5% 71%	3456
September	1st to 10th	Night	2 1 1 3 2 2 2 2 3 5% 76%	1900
	11th to 20th	Night	5% 4 1 4 3 4 5% 4 4 7% 60%	1900
	21st to end	Night	7% 4 1 4 3 4 3 4 4 7% 59%	2148
October	1st to 10th	Night	5% 3 2 5% 3 4 4 3 5% 6% 59%	3800
	11th to 20th	Night	8% 5% 1 6% 4 5% 6% 5% 7% 8% 44%	3777
	21st to end	Night	12% 9% 4 10% 6% 5% 5% 4 6% 7% 32%	4301
November	1st to 10th	Night	16% 10% 3 7% 5% 6% 7% 4 7% 8% 28%	2511
	11th to 20th	Night	16% 11% 5% 10% 8% 6% 5% 5% 6% 6% 22%	2660
	21st to end	Night	11% 11% 4 10% 6% 6% 7% 5% 8% 7% 26%	2660
December	1st to 10th	Night	17% 16% 4 10% 7% 5% 5% 4 5% 5% 22%	2660
	11th to 20th	Night	22% 16% 7% 14% 7% 6% 5% 4 5% 4 10%	3276
	21st to end	Night	21% 21% 7% 11% 5% 4 5% 3 5% 4 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	48% 37% 6% 9% 1	2539
	11th to 20th	Day	46% 37% 10% 6%	2540
	21st to end	Day	56% 39% 3 2	2923
February	1st to 10th	Day	25% 66% 6% 3 1	1710
	11th to 20th	Day	24% 67% 4 4 1	1674
	21st to end	Day	21% 66% 5% 3 5%	1540
March	1st to 10th	Day	28% 42% 4 18% 7%	3166
	11th to 20th	Day	16% 40% 10% 27% 7%	3490
	21st to end	Day	34% 41% 8% 13% 4	3996
April	1st to 10th	Day	19% 66% 6% 7% 1	2280
	11th to 20th	Day	18% 65% 7% 5% 4	2252
	21st to end	Day	15% 67% 7% 8% 4	2425
May	1st to 10th	Day	21% 42% 6% 19% 12%	4420
	11th to 20th	Day	9% 40% 8% 26% 16% 2	4380
	21st to end	Day	21% 42% 19% 15% 3	4814
June	1st to 10th	Day	10% 65% 6% 13% 6% 1	2660
	11th to 20th	Day	10% 65% 5% 14% 6% 1	2660
	21st to end	Day	7% 63% 5% 15% 9% 1	2660
July	1st to 10th	Day	3 35% 3 7% 18% 34%	4351
	11th to 20th	Day	3 35% 3 7% 17% 36%	4345
	21st to end	Day	7% 35% 6% 15% 24% 13%	4639
August	1st to 10th	Day	10% 36% 2 11% 22% 19%	4267
	11th to 20th	Day	11% 37% 10% 30% 9% 2	4065
	21st to end	Day	17% 37% 8% 16% 19% 3	4219
September	1st to 10th	Day	6% 60% 6% 16% 10% 3	2280
	11th to 20th	Day	13% 60% 7% 10% 8% 3	2280
	21st to end	Day	13% 60% 6% 12% 7% 1	2027
October	1st to 10th	Day	14% 37% 8% 23% 16% 1	3180
	11th to 20th	Day	27% 39% 11% 15% 6%	3161
	21st to end	Day	34% 39% 7% 17% 4	3260
November	1st to 10th	Day	24% 60% 6% 9% 2	1666
	11th to 20th	Day	27% 61% 4 4 3	1520
	21st to end	Day	24% 61% 3 6% 5% 1	1520
December	1st to 10th	Day	31% 60% 4 4 1	1520
	11th to 20th	Day	43% 49% 4 3 1	1928
	21st to end	Day	49% 37% 6% 6% 2	2794
January	1st to 10th	Night	46% 38% 6% 7% 2	4406
	11th to 20th	Night	47% 37% 8% 7%	4420
	21st to end	Night	52% 39% 5% 3	4734
February	1st to 10th	Night	25% 65% 5% 5% 1	2470
	11th to 20th	Night	23% 66% 4 6% 1	2404
	21st to end	Night	19% 65% 6% 7% 3	1913
March	1st to 10th	Night	23% 42% 8% 20% 8%	3705
	11th to 20th	Night	14% 40% 9% 29% 7%	3490
	21st to end	Night	31% 41% 11% 16% 1	3657
April	1st to 10th	Night	16% 67% 8% 7% 2	1900
	11th to 20th	Night	13% 67% 7% 8% 5%	1879
	21st to end	Night	12% 66% 6% 12% 3	1751
May	1st to 10th	Night	21% 41% 3 23% 11% 1	2540
	11th to 20th	Night	7% 40% 6% 31% 13% 2	2516
	21st to end	Night	16% 40% 28% 15% 2	2762
June	1st to 10th	Night	11% 65% 5% 14% 4 1	1520
	11th to 20th	Night	8% 66% 5% 14% 7%	1520
	21st to end	Night	6% 64% 5% 15% 9% 2	1520
July	1st to 10th	Night	3 34% 2 9% 22% 29%	2500
	11th to 20th	Night	5% 35% 3 9% 17% 31%	2492
	21st to end	Night	4 35% 5% 15% 28% 13%	2674
August	1st to 10th	Night	9% 36% 2 12% 23% 19%	2638
	11th to 20th	Night	7% 38% 14% 28% 10% 2	2839
	21st to end	Night	12% 38% 10% 19% 16% 6%	3456
September	1st to 10th	Night	6% 60% 6% 14% 11% 3	1900
	11th to 20th	Night	13% 61% 5% 12% 6% 3	1900
	21st to end	Night	12% 60% 6% 13% 8% 1	2148
October	1st to 10th	Night	12% 39% 5% 26% 17%	3800
	11th to 20th	Night	22% 39% 15% 16% 7%	3777
	21st to end	Night	33% 39% 6% 18% 4	4301
November	1st to 10th	Night	22% 60% 5% 10% 3	2511
	11th to 20th	Night	25% 61% 6% 5% 3	2660
	21st to end	Night	20% 61% 5% 9% 5% 1	2660
December	1st to 10th	Night	30% 61% 4 4 1	2660
	11th to 20th	Night	38% 52% 5% 4 1	3276
	21st to end	Night	44% 38% 7% 9% 2	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	27% 13% 28% 25% 7% 1	180
	11th to 20th	Day	36% 6% 24% 22% 11% 1	180
	21st to end	Day	30% 7% 23% 26% 14%	275
February	1st to 10th	Day	28% 17% 24% 22% 8% 1	370
	11th to 20th	Day	28% 18% 31% 18% 5% 1	365
	21st to end	Day	27% 14% 33% 19% 6% 1	368
March	1st to 10th	Day	25% 16% 33% 17% 7% 1	460
	11th to 20th	Day	20% 17% 30% 23% 8% 2	460
	21st to end	Day	26% 19% 32% 16% 7%	506
April	1st to 10th	Day	27% 20% 29% 15% 7% 1	460
	11th to 20th	Day	22% 20% 34% 14% 7% 3	452
	21st to end	Day	22% 20% 34% 17% 5% 3	460
May	1st to 10th	Day	20% 19% 32% 18% 9% 2	463
	11th to 20th	Day	17% 14% 35% 21% 10% 3	488
	21st to end	Day	16% 16% 35% 22% 9% 2	529
June	1st to 10th	Day	18% 17% 34% 18% 11% 2	490
	11th to 20th	Day	19% 22% 35% 15% 7% 2	490
	21st to end	Day	8% 17% 38% 24% 10% 2	490
July	1st to 10th	Day	6% 13% 48% 23% 10% 1	486
	11th to 20th	Day	5% 15% 44% 24% 10% 3	484
	21st to end	Day	4 10% 44% 22% 15% 5%	531
August	1st to 10th	Day	5% 8% 39% 24% 17% 7%	487
	11th to 20th	Day	4 11% 34% 27% 16% 8%	477
	21st to end	Day	8% 16% 31% 24% 15% 6%	539
September	1st to 10th	Day	6% 12% 32% 28% 17% 6%	490
	11th to 20th	Day	10% 11% 33% 29% 13% 3	490
	21st to end	Day	13% 12% 31% 27% 14% 3	490
October	1st to 10th	Day	17% 11% 29% 24% 16% 2	490
	11th to 20th	Day	16% 13% 24% 26% 14% 5%	490
	21st to end	Day	26% 12% 25% 22% 12% 4	426
November	1st to 10th	Day	29% 7% 23% 30% 9% 1	260
	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	24% 8% 18% 34% 14% 2	760
	21st to end	Night	21% 6% 17% 36% 18% 2	836
February	1st to 10th	Night	22% 12% 18% 31% 15% 1	760
	11th to 20th	Night	23% 9% 19% 32% 16% 2	744
	21st to end	Night	21% 12% 21% 33% 11% 1	628
March	1st to 10th	Night	17% 11% 21% 36% 14% 1	760
	11th to 20th	Night	15% 10% 19% 39% 15% 2	760
	21st to end	Night	18% 14% 22% 33% 11% 2	836
April	1st to 10th	Night	18% 14% 24% 29% 13% 1	760
	11th to 20th	Night	14% 15% 28% 27% 15% 2	751
	21st to end	Night	13% 12% 31% 29% 14% 1	611
May	1st to 10th	Night	11% 16% 27% 29% 16% 2	380
	11th to 20th	Night	10% 11% 27% 30% 20% 2	374
	21st to end	Night	7% 10% 30% 36% 15% 2	411
June	1st to 10th	Night	15% 12% 29% 28% 15% 1	380
	11th to 20th	Night	10% 16% 39% 25% 10%	380
	21st to end	Night	7% 12% 33% 32% 16% 1	380
July	1st to 10th	Night	5% 8% 36% 35% 15% 1	370
	11th to 20th	Night	2 8% 43% 35% 11% 1	368
	21st to end	Night	2 8% 35% 35% 18% 2	416
August	1st to 10th	Night	3 6% 30% 40% 18% 3	443
	11th to 20th	Night	3 5% 22% 34% 30% 7%	564
	21st to end	Night	4 11% 31% 30% 21% 4	807
September	1st to 10th	Night	4 7% 27% 32% 27% 3	760
	11th to 20th	Night	6% 7% 26% 29% 27% 5%	760
	21st to end	Night	9% 8% 17% 35% 27% 4	760
October	1st to 10th	Night	11% 6% 18% 40% 22% 3	760
	11th to 20th	Night	12% 6% 18% 36% 23% 4	760
	21st to end	Night	17% 8% 19% 37% 18% 3	836
November	1st to 10th	Night	18% 8% 18% 40% 16% 1	760
	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

Page generated at 2024-11-02 23:11:18. Version ac07

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