Salmon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salmon clear sky chart from 2005-11-06 to 2024-11-28.

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	4 6% 2 7% 5% 5% 6% 5% 7% 8% 45%	105292
	Night	4 7% 3 8% 6% 6% 6% 5% 7% 8% 41%	102916
Transparency	Day	34% 7% 14% 22% 15% 7%	105033
	Night	35% 8% 17% 23% 13% 4	102765
Seeing	Day	8% 14% 31% 29% 14% 3	15144
	Night	7% 6% 28% 40% 16% 2	24558

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	1 7% 3 12% 10% 10% 9% 8% 10% 10% 19%	2516
	11th to 20th	Day	1 5% 3 11% 10% 7% 9% 5% 7% 8% 34%	2540
	21st to end	Day	1 8% 4 12% 9% 8% 7% 7% 8% 8% 28%	2794
February	1st to 10th	Day	2 10% 4 11% 7% 5% 8% 8% 9% 10% 27%	1710
	11th to 20th	Day	1 8% 4 10% 8% 6% 8% 7% 9% 10% 30%	1744
	21st to end	Day	1 10% 3 12% 7% 8% 7% 6% 8% 9% 28%	1570
March	1st to 10th	Day	2 5% 3 9% 6% 7% 8% 7% 10% 10% 34%	3156
	11th to 20th	Day	2 7% 4 8% 6% 6% 7% 6% 7% 7% 41%	3490
	21st to end	Day	3 11% 5% 13% 9% 8% 8% 7% 8% 8% 20%	3825
April	1st to 10th	Day	4 11% 4 10% 9% 7% 7% 5% 8% 9% 28%	2255
	11th to 20th	Day	4 11% 3 8% 7% 7% 6% 5% 6% 7% 35%	2418
	21st to end	Day	7% 11% 4 9% 6% 6% 6% 4 7% 8% 33%	2470
May	1st to 10th	Day	9% 10% 3 9% 7% 6% 6% 5% 6% 8% 30%	4110
	11th to 20th	Day	4 5% 2 6% 5% 6% 5% 5% 8% 10% 44%	4071
	21st to end	Day	9% 10% 3 9% 6% 6% 6% 5% 7% 7% 32%	5023
June	1st to 10th	Day	9% 8% 3 8% 6% 6% 6% 5% 7% 8% 33%	2850
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	2850
	21st to end	Day	3 2 2 4 5% 5% 6% 4 6% 8% 56%	2850
July	1st to 10th	Day	1 2 1 3 3 4 4 4 5% 6% 69%	4621
	11th to 20th	Day	2 1 3 2 3 4 4 6% 7% 67%	4420
	21st to end	Day	2 3 1 3 3 4 4 4 5% 7% 64%	4790
August	1st to 10th	Day	3 3 1 5% 5% 5% 6% 4 7% 8% 53%	4101
	11th to 20th	Day	2 2 1 3 4 4 5% 4 6% 7% 64%	4028
	21st to end	Day	3 3 1 4 3 3 3 3 5% 6% 67%	4504
September	1st to 10th	Day	4 2 1 3 4 3 4 3 3 8% 65%	2213
	11th to 20th	Day	5% 5% 2 5% 5% 5% 5% 4 6% 7% 53%	2090
	21st to end	Day	7% 5% 2 4 3 4 4 2 5% 6% 60%	2090
October	1st to 10th	Day	4 5% 2 4 3 3 3 3 4 6% 64%	3427
	11th to 20th	Day	3 6% 2 4 3 3 4 3 5% 10% 56%	3095
	21st to end	Day	2 5% 2 6% 4 5% 6% 5% 6% 10% 49%	3101
November	1st to 10th	Day	5% 7% 2 6% 5% 6% 6% 5% 7% 10% 40%	1764
	11th to 20th	Day	3 9% 2 7% 6% 6% 6% 6% 7% 10% 37%	1735
	21st to end	Day	2 8% 4 7% 6% 6% 7% 5% 9% 9% 38%	1576
December	1st to 10th	Day	2 6% 3 7% 6% 8% 8% 7% 9% 11% 33%	1368
	11th to 20th	Day	2 6% 3 11% 8% 7% 7% 7% 10% 11% 28%	1685
	21st to end	Day	2 8% 3 13% 9% 7% 7% 6% 9% 10% 27%	2442
January	1st to 10th	Night	1 9% 5% 13% 10% 11% 11% 7% 8% 8% 17%	4457
	11th to 20th	Night	1 9% 4 17% 10% 8% 6% 5% 7% 8% 25%	4420
	21st to end	Night	2 10% 4 14% 11% 10% 8% 7% 8% 7% 19%	4861
February	1st to 10th	Night	3 11% 4 10% 8% 7% 9% 6% 9% 11% 22%	2470
	11th to 20th	Night	2 11% 5% 9% 8% 6% 7% 6% 9% 9% 29%	2322
	21st to end	Night	1 9% 4 11% 7% 8% 7% 6% 9% 8% 29%	1884
March	1st to 10th	Night	1 8% 4 10% 7% 6% 7% 5% 9% 11% 31%	3717
	11th to 20th	Night	2 7% 3 7% 4 6% 7% 6% 7% 10% 41%	3490
	21st to end	Night	3 11% 5% 11% 7% 7% 7% 5% 9% 11% 25%	3828
April	1st to 10th	Night	3 10% 3 7% 7% 5% 7% 4 8% 10% 36%	1923
	11th to 20th	Night	4 9% 3 8% 6% 6% 5% 6% 7% 8% 38%	1709
	21st to end	Night	6% 7% 3 8% 6% 6% 6% 4 7% 7% 39%	1710
May	1st to 10th	Night	10% 12% 3 8% 5% 4 5% 4 6% 7% 36%	2860
	11th to 20th	Night	5% 6% 3 6% 4 4 4 4 6% 10% 49%	2834
	21st to end	Night	9% 12% 3 8% 5% 6% 6% 4 6% 8% 33%	2546
June	1st to 10th	Night	9% 6% 2 7% 5% 5% 6% 4 5% 9% 42%	1330
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 6% 7% 46%	1330
	21st to end	Night	3 2 1 3 3 4 4 4 6% 7% 62%	1330
July	1st to 10th	Night	1 1 1 2 2 3 3 3 4 6% 75%	2335
	11th to 20th	Night	1 1 3 1 2 3 2 4 8% 73%	2540
	21st to end	Night	1 1 1 2 3 3 4 3 5% 6% 71%	2761
August	1st to 10th	Night	2 2 1 4 3 4 4 3 6% 9% 62%	2837
	11th to 20th	Night	1 1 1 2 2 2 4 3 6% 8% 70%	2811
	21st to end	Night	4 2 1 3 3 3 4 3 5% 6% 66%	3162
September	1st to 10th	Night	4 3 1 4 3 3 2 3 4 6% 66%	1966
	11th to 20th	Night	6% 4 2 6% 4 3 4 3 5% 7% 55%	2090
	21st to end	Night	6% 5% 2 4 3 3 3 2 4 6% 61%	2090
October	1st to 10th	Night	4 5% 1 4 3 3 3 2 4 6% 66%	3550
	11th to 20th	Night	6% 5% 2 4 3 3 3 3 5% 7% 57%	3831
	21st to end	Night	6% 6% 2 6% 4 4 5% 3 6% 8% 49%	4457
November	1st to 10th	Night	6% 8% 3 6% 6% 5% 5% 5% 8% 9% 39%	2535
	11th to 20th	Night	4 9% 3 8% 7% 6% 8% 6% 7% 10% 33%	2644
	21st to end	Night	3 6% 2 7% 6% 6% 7% 6% 9% 10% 38%	2759
December	1st to 10th	Night	2 8% 3 8% 7% 7% 7% 6% 9% 12% 30%	2807
	11th to 20th	Night	2 10% 4 11% 8% 8% 9% 6% 9% 9% 23%	3506
	21st to end	Night	3 8% 5% 13% 9% 10% 9% 7% 8% 9% 18%	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	49% 10% 24% 14% 3	2516
	11th to 20th	Day	45% 8% 20% 17% 8% 1	2540
	21st to end	Day	46% 11% 22% 17% 4	2794
February	1st to 10th	Day	48% 11% 19% 17% 4	1710
	11th to 20th	Day	47% 10% 21% 16% 7%	1753
	21st to end	Day	51% 8% 14% 19% 7% 1	1570
March	1st to 10th	Day	39% 11% 16% 23% 11%	3156
	11th to 20th	Day	35% 8% 23% 30% 4	3490
	21st to end	Day	58% 8% 19% 12% 3	3825
April	1st to 10th	Day	52% 9% 16% 17% 6% 1	2255
	11th to 20th	Day	47% 7% 15% 20% 9% 1	2421
	21st to end	Day	49% 7% 13% 23% 7% 1	2470
May	1st to 10th	Day	48% 9% 13% 19% 9% 2	4110
	11th to 20th	Day	33% 8% 13% 28% 13% 5%	4074
	21st to end	Day	46% 10% 14% 23% 5%	5024
June	1st to 10th	Day	45% 9% 16% 21% 8% 1	2850
	11th to 20th	Day	39% 8% 10% 22% 15% 6%	2850
	21st to end	Day	26% 6% 9% 25% 27% 7%	2850
July	1st to 10th	Day	14% 5% 7% 15% 29% 30%	4550
	11th to 20th	Day	13% 5% 6% 14% 26% 36%	4345
	21st to end	Day	18% 4 6% 18% 28% 26%	4639
August	1st to 10th	Day	26% 6% 9% 22% 23% 14%	4086
	11th to 20th	Day	17% 5% 9% 30% 31% 7%	4067
	21st to end	Day	17% 5% 7% 26% 31% 13%	4503
September	1st to 10th	Day	20% 5% 9% 24% 28% 14%	2213
	11th to 20th	Day	29% 6% 13% 23% 23% 6%	2090
	21st to end	Day	26% 4 14% 31% 22% 3	2090
October	1st to 10th	Day	24% 3 12% 29% 28% 4	3427
	11th to 20th	Day	24% 5% 23% 29% 17% 1	3095
	21st to end	Day	31% 6% 19% 29% 15% 1	3101
November	1st to 10th	Day	39% 9% 18% 23% 8% 2	1764
	11th to 20th	Day	40% 10% 25% 20% 5% 1	1735
	21st to end	Day	39% 8% 22% 21% 8% 1	1576
December	1st to 10th	Day	42% 12% 21% 18% 7% 1	1368
	11th to 20th	Day	43% 10% 28% 17% 2	1684
	21st to end	Day	42% 10% 20% 18% 9% 1	2442
January	1st to 10th	Night	47% 13% 17% 20% 3	4457
	11th to 20th	Night	53% 9% 15% 15% 7% 1	4420
	21st to end	Night	48% 13% 19% 16% 4	4861
February	1st to 10th	Night	52% 9% 19% 15% 5%	2470
	11th to 20th	Night	47% 8% 21% 17% 7%	2323
	21st to end	Night	46% 9% 16% 20% 8% 1	1884
March	1st to 10th	Night	34% 12% 18% 22% 13% 1	3717
	11th to 20th	Night	29% 9% 28% 28% 5%	3490
	21st to end	Night	44% 14% 23% 17% 2	3828
April	1st to 10th	Night	42% 9% 19% 22% 6% 1	1923
	11th to 20th	Night	41% 8% 18% 23% 10%	1709
	21st to end	Night	42% 8% 20% 23% 7%	1710
May	1st to 10th	Night	45% 7% 14% 24% 9%	2860
	11th to 20th	Night	30% 8% 13% 31% 16% 2	2835
	21st to end	Night	45% 10% 17% 23% 5%	2546
June	1st to 10th	Night	37% 10% 19% 25% 8% 1	1330
	11th to 20th	Night	36% 7% 13% 25% 14% 5%	1330
	21st to end	Night	19% 6% 14% 28% 26% 7%	1330
July	1st to 10th	Night	10% 4 8% 20% 29% 28%	2297
	11th to 20th	Night	10% 3 6% 19% 33% 29%	2492
	21st to end	Night	13% 4 8% 24% 31% 20%	2674
August	1st to 10th	Night	18% 5% 10% 32% 24% 10%	2829
	11th to 20th	Night	10% 4 14% 38% 26% 7%	2838
	21st to end	Night	16% 5% 8% 30% 31% 9%	3162
September	1st to 10th	Night	18% 4 9% 28% 25% 15%	1966
	11th to 20th	Night	27% 6% 14% 22% 25% 6%	2090
	21st to end	Night	25% 3 13% 30% 24% 5%	2090
October	1st to 10th	Night	20% 4 13% 30% 30% 2	3550
	11th to 20th	Night	28% 5% 21% 33% 13% 1	3831
	21st to end	Night	33% 6% 21% 27% 14%	4457
November	1st to 10th	Night	38% 8% 19% 25% 8% 2	2535
	11th to 20th	Night	42% 10% 21% 22% 5% 1	2644
	21st to end	Night	37% 8% 22% 24% 9% 1	2759
December	1st to 10th	Night	41% 12% 20% 19% 7% 1	2807
	11th to 20th	Night	45% 10% 24% 18% 3	3507
	21st to end	Night	46% 10% 19% 14% 9% 1	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	4 12% 36% 28% 18% 1	180
	11th to 20th	Day	4 8% 38% 29% 14% 6%	180
	21st to end	Day	6% 10% 37% 33% 10% 3	198
February	1st to 10th	Day	11% 15% 43% 27% 4	270
	11th to 20th	Day	5% 17% 40% 29% 9% 1	349
	21st to end	Day	10% 21% 36% 26% 7%	382
March	1st to 10th	Day	9% 21% 39% 26% 4 1	460
	11th to 20th	Day	9% 20% 30% 28% 11% 1	460
	21st to end	Day	10% 25% 37% 21% 7% 1	506
April	1st to 10th	Day	14% 22% 33% 22% 8% 1	460
	11th to 20th	Day	11% 27% 33% 21% 6% 2	452
	21st to end	Day	15% 23% 31% 22% 7% 3	460
May	1st to 10th	Day	12% 22% 27% 26% 11% 1	463
	11th to 20th	Day	16% 16% 28% 26% 11% 2	488
	21st to end	Day	12% 16% 24% 26% 19% 4	651
June	1st to 10th	Day	10% 13% 26% 31% 16% 4	680
	11th to 20th	Day	14% 17% 28% 28% 12% 1	680
	21st to end	Day	4 11% 24% 36% 22% 2	680
July	1st to 10th	Day	3 10% 29% 34% 20% 3	607
	11th to 20th	Day	3 10% 38% 32% 15% 2	484
	21st to end	Day	4 11% 31% 34% 17% 5%	531
August	1st to 10th	Day	5% 8% 32% 34% 16% 5%	487
	11th to 20th	Day	3 7% 29% 36% 18% 7%	477
	21st to end	Day	6% 9% 29% 31% 18% 6%	539
September	1st to 10th	Day	4 10% 26% 31% 23% 6%	490
	11th to 20th	Day	9% 10% 26% 32% 18% 5%	490
	21st to end	Day	10% 10% 26% 31% 19% 3	490
October	1st to 10th	Day	10% 11% 28% 28% 18% 5%	453
	11th to 20th	Day	9% 11% 25% 29% 17% 10%	300
	21st to end	Day	7% 13% 35% 32% 11% 2	330
November	1st to 10th	Day	9% 10% 38% 26% 16% 2	300
	11th to 20th	Day	5% 13% 41% 30% 9% 2	300
	21st to end	Day	4 8% 36% 39% 11% 1	291
December	1st to 10th	Day	5% 11% 38% 25% 18% 4	198
	11th to 20th	Day	9% 10% 42% 27% 11% 2	180
	21st to end	Day	7% 9% 42% 28% 13% 1	198
January	1st to 10th	Night	7% 6% 36% 41% 10%	785
	11th to 20th	Night	6% 6% 39% 36% 12% 1	760
	21st to end	Night	5% 6% 36% 42% 10% 1	836
February	1st to 10th	Night	8% 7% 43% 35% 7% 1	760
	11th to 20th	Night	6% 9% 39% 37% 8% 1	744
	21st to end	Night	4 11% 37% 37% 10% 1	628
March	1st to 10th	Night	4 6% 41% 40% 9% 1	760
	11th to 20th	Night	5% 9% 32% 40% 13% 1	760
	21st to end	Night	7% 10% 31% 41% 10% 1	836
April	1st to 10th	Night	8% 9% 29% 40% 14% 1	760
	11th to 20th	Night	7% 10% 35% 38% 9% 1	581
	21st to end	Night	9% 9% 30% 37% 14% 1	570
May	1st to 10th	Night	11% 10% 24% 40% 16% 1	570
	11th to 20th	Night	10% 9% 21% 36% 23% 1	561
	21st to end	Night	15% 6% 20% 33% 24% 2	411
June	1st to 10th	Night	12% 4 18% 41% 23% 2	380
	11th to 20th	Night	16% 3 22% 40% 18% 1	380
	21st to end	Night	4 1 17% 49% 27% 1	380
July	1st to 10th	Night	2 1 12% 50% 34% 2	370
	11th to 20th	Night	1 2 14% 56% 27%	368
	21st to end	Night	2 1 10% 52% 33% 1	416
August	1st to 10th	Night	4 2 14% 49% 29% 2	557
	11th to 20th	Night	2 2 12% 50% 31% 3	564
	21st to end	Night	6% 4 17% 41% 30% 1	630
September	1st to 10th	Night	6% 1 15% 41% 32% 4	760
	11th to 20th	Night	7% 3 11% 43% 31% 5%	760
	21st to end	Night	8% 3 19% 38% 27% 5%	760
October	1st to 10th	Night	10% 6% 21% 39% 21% 2	760
	11th to 20th	Night	10% 6% 20% 43% 17% 4	760
	21st to end	Night	9% 7% 27% 41% 12% 3	836
November	1st to 10th	Night	8% 7% 29% 43% 12% 1	780
	11th to 20th	Night	8% 9% 36% 37% 9% 1	844
	21st to end	Night	5% 7% 34% 41% 12% 1	986
December	1st to 10th	Night	7% 5% 38% 39% 10% 2	950
	11th to 20th	Night	7% 7% 36% 40% 9% 1	950
	21st to end	Night	6% 8% 41% 33% 11% 1	1045

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