Chena Hot Springs
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chena Hot Springs clear sky chart from 2005-11-06 to 2025-09-19.

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	12% 11% 4 11% 7% 6% 6% 4 6% 7% 26%	131792
	Night	6% 11% 5% 12% 7% 6% 6% 5% 6% 7% 29%	126014
Transparency	Day	55% 8% 15% 15% 6% 1	131393
	Night	52% 6% 13% 17% 10% 3	125991
Seeing	Day	17% 7% 17% 27% 23% 10%	19944
	Night	12% 5% 16% 31% 27% 8%	24008

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 9% 5% 11% 7% 4 5% 3 4 7% 42%	1227
	11th to 20th	Day	1 10% 5% 12% 9% 8% 6% 3 5% 8% 32%	1808
	21st to end	Day	3 8% 5% 13% 12% 9% 6% 6% 9% 6% 24%	2420
February	1st to 10th	Day	2 10% 5% 13% 7% 7% 5% 4 4 6% 38%	1200
	11th to 20th	Day	2 9% 6% 12% 8% 7% 7% 6% 9% 8% 25%	1458
	21st to end	Day	2 9% 8% 14% 8% 7% 7% 7% 6% 6% 26%	1320
March	1st to 10th	Day	1 11% 7% 17% 8% 6% 5% 4 5% 5% 31%	4356
	11th to 20th	Day	1 6% 5% 14% 7% 7% 6% 5% 8% 8% 32%	4694
	21st to end	Day	3 12% 5% 12% 7% 5% 5% 4 6% 7% 34%	5877
April	1st to 10th	Day	4 16% 6% 12% 7% 7% 7% 5% 6% 7% 23%	2565
	11th to 20th	Day	3 12% 4 10% 6% 5% 5% 4 6% 7% 37%	2796
	21st to end	Day	4 10% 4 8% 6% 7% 6% 5% 7% 8% 36%	3025
May	1st to 10th	Day	8% 15% 5% 12% 7% 6% 6% 5% 6% 8% 22%	7495
	11th to 20th	Day	5% 9% 3 9% 6% 6% 6% 5% 6% 7% 37%	7823
	21st to end	Day	12% 10% 3 10% 7% 7% 7% 6% 8% 9% 21%	9311
June	1st to 10th	Day	13% 9% 4 10% 7% 7% 6% 5% 7% 8% 25%	3920
	11th to 20th	Day	14% 7% 3 8% 7% 6% 6% 6% 8% 8% 27%	4000
	21st to end	Day	16% 8% 3 7% 6% 6% 5% 5% 7% 9% 28%	4000
July	1st to 10th	Day	26% 10% 3 7% 4 5% 5% 3 5% 6% 25%	9030
	11th to 20th	Day	17% 9% 4 9% 6% 6% 6% 5% 7% 8% 22%	8441
	21st to end	Day	23% 10% 3 8% 5% 6% 5% 4 6% 7% 23%	8775
August	1st to 10th	Day	25% 11% 3 9% 6% 4 5% 4 6% 7% 20%	5307
	11th to 20th	Day	22% 15% 3 10% 7% 6% 6% 4 6% 6% 15%	4963
	21st to end	Day	22% 17% 4 10% 7% 6% 6% 4 6% 5% 13%	5085
September	1st to 10th	Day	19% 13% 4 10% 5% 6% 5% 3 6% 7% 22%	2609
	11th to 20th	Day	21% 17% 5% 9% 6% 5% 4 4 6% 5% 19%	2321
	21st to end	Day	16% 20% 7% 10% 6% 5% 4 4 4 6% 18%	2090
October	1st to 10th	Day	8% 16% 6% 12% 5% 4 4 3 4 5% 31%	2950
	11th to 20th	Day	6% 14% 6% 16% 7% 6% 6% 4 5% 6% 24%	2791
	21st to end	Day	4 18% 6% 17% 9% 6% 5% 4 5% 6% 20%	2407
November	1st to 10th	Day	4 14% 5% 13% 8% 7% 5% 7% 8% 6% 23%	1195
	11th to 20th	Day	5% 12% 5% 14% 9% 8% 5% 4 6% 7% 25%	1000
	21st to end	Day	4 15% 5% 16% 8% 4 6% 4 5% 7% 27%	705
December	1st to 10th	Day	4 12% 3 9% 5% 5% 4 4 8% 9% 36%	980
	11th to 20th	Day	2 11% 5% 14% 6% 6% 8% 5% 7% 7% 29%	836
	21st to end	Day	1 10% 5% 12% 8% 7% 5% 5% 8% 9% 31%	1012
January	1st to 10th	Night	2 8% 4 11% 6% 6% 5% 4 5% 6% 43%	8738
	11th to 20th	Night	2 9% 4 12% 8% 6% 6% 5% 6% 8% 34%	8156
	21st to end	Night	2 9% 5% 13% 9% 8% 7% 6% 8% 7% 25%	8552
February	1st to 10th	Night	1 8% 5% 14% 8% 6% 4 3 5% 4 42%	3200
	11th to 20th	Night	2 8% 5% 12% 7% 7% 6% 5% 7% 9% 31%	2827
	21st to end	Night	3 11% 6% 17% 9% 7% 7% 5% 4 6% 25%	2310
March	1st to 10th	Night	2 10% 6% 18% 8% 7% 5% 4 4 5% 31%	5500
	11th to 20th	Night	2 7% 4 12% 8% 7% 6% 5% 7% 10% 34%	5264
	21st to end	Night	3 11% 4 10% 7% 6% 6% 5% 7% 9% 33%	5038
April	1st to 10th	Night	4 15% 6% 11% 7% 6% 6% 5% 7% 7% 27%	1835
	11th to 20th	Night	3 11% 5% 11% 7% 5% 5% 5% 6% 7% 35%	1551
	21st to end	Night	5% 9% 3 9% 7% 6% 5% 4 6% 8% 37%	1374
May	1st to 10th	Night	8% 12% 3 10% 7% 7% 6% 5% 7% 9% 25%	2474
	11th to 20th	Night	5% 7% 3 7% 6% 6% 6% 4 7% 10% 39%	2077
	21st to end	Night	13% 10% 3 8% 6% 6% 7% 6% 8% 9% 24%	1586
June	1st to 10th	Night	7% 10% 2 13% 7% 7% 6% 6% 5% 8% 28%	480
	11th to 20th	Night	13% 7% 4 8% 4 5% 6% 7% 8% 7% 31%	400
	21st to end	Night	15% 7% 4 6% 6% 5% 7% 5% 9% 9% 28%	400
July	1st to 10th	Night	27% 10% 3 8% 5% 4 5% 3 4 5% 27%	937
	11th to 20th	Night	18% 12% 4 9% 5% 5% 6% 4 6% 8% 23%	1537
	21st to end	Night	23% 11% 3 8% 5% 5% 5% 3 6% 7% 25%	2084
August	1st to 10th	Night	25% 13% 3 7% 5% 4 4 4 7% 8% 21%	1848
	11th to 20th	Night	25% 14% 3 10% 6% 6% 4 3 4 5% 18%	2095
	21st to end	Night	23% 17% 4 9% 6% 5% 5% 4 5% 6% 17%	2822
September	1st to 10th	Night	18% 12% 3 9% 6% 5% 4 5% 5% 6% 27%	1791
	11th to 20th	Night	17% 16% 5% 10% 6% 5% 5% 5% 5% 6% 21%	2034
	21st to end	Night	16% 16% 5% 9% 6% 5% 7% 4 6% 5% 21%	2090
October	1st to 10th	Night	8% 16% 6% 10% 6% 5% 5% 4 4 6% 28%	4014
	11th to 20th	Night	6% 15% 6% 17% 6% 5% 5% 5% 5% 7% 23%	4135
	21st to end	Night	5% 14% 7% 19% 9% 6% 5% 3 4 5% 23%	5152
November	1st to 10th	Night	5% 16% 6% 13% 7% 6% 5% 4 4 5% 28%	3100
	11th to 20th	Night	6% 11% 6% 16% 9% 6% 5% 4 5% 6% 25%	3400
	21st to end	Night	5% 14% 4 15% 7% 6% 6% 4 6% 6% 28%	3673
December	1st to 10th	Night	4 10% 4 10% 7% 7% 6% 5% 7% 8% 31%	6210
	11th to 20th	Night	3 10% 6% 13% 7% 7% 6% 5% 7% 6% 30%	7364
	21st to end	Night	1 10% 5% 13% 7% 6% 7% 5% 7% 9% 29%	9966

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% 5% 11% 17% 13% 11%	1227
	11th to 20th	Day	51% 6% 10% 19% 8% 6%	1820
	21st to end	Day	55% 5% 8% 15% 10% 7%	2420
February	1st to 10th	Day	46% 6% 6% 15% 19% 9%	1200
	11th to 20th	Day	51% 7% 11% 18% 11% 2	1465
	21st to end	Day	55% 6% 7% 18% 10% 3	1320
March	1st to 10th	Day	54% 5% 7% 18% 15% 1	4356
	11th to 20th	Day	44% 8% 8% 18% 17% 5%	4694
	21st to end	Day	47% 6% 13% 18% 15% 2	5877
April	1st to 10th	Day	58% 6% 13% 14% 8% 1	2565
	11th to 20th	Day	44% 7% 17% 22% 8% 3	2796
	21st to end	Day	44% 7% 15% 26% 8%	3025
May	1st to 10th	Day	58% 7% 11% 18% 5%	7495
	11th to 20th	Day	43% 8% 13% 19% 10% 6%	7826
	21st to end	Day	56% 10% 15% 16% 3	9312
June	1st to 10th	Day	54% 9% 16% 18% 3	3920
	11th to 20th	Day	51% 9% 18% 20% 2	4000
	21st to end	Day	51% 9% 23% 15% 2	4000
July	1st to 10th	Day	60% 7% 15% 14% 4	8931
	11th to 20th	Day	57% 9% 20% 14% 1	8336
	21st to end	Day	59% 9% 19% 10% 2	8528
August	1st to 10th	Day	63% 8% 19% 9% 1	5287
	11th to 20th	Day	68% 9% 16% 7%	5011
	21st to end	Day	71% 8% 16% 5%	5084
September	1st to 10th	Day	61% 8% 19% 11% 1	2609
	11th to 20th	Day	65% 8% 16% 11%	2321
	21st to end	Day	66% 8% 11% 13% 2	2090
October	1st to 10th	Day	56% 5% 10% 20% 9%	2950
	11th to 20th	Day	60% 6% 11% 20% 2	2791
	21st to end	Day	65% 5% 13% 14% 3	2407
November	1st to 10th	Day	56% 9% 14% 15% 4 2	1195
	11th to 20th	Day	57% 7% 14% 15% 7%	1000
	21st to end	Day	55% 7% 11% 16% 10% 1	705
December	1st to 10th	Day	43% 6% 20% 21% 9% 1	980
	11th to 20th	Day	50% 7% 17% 16% 6% 5%	838
	21st to end	Day	45% 8% 14% 14% 17% 2	1012
January	1st to 10th	Night	42% 4 10% 20% 14% 10%	8738
	11th to 20th	Night	47% 6% 14% 19% 9% 4	8206
	21st to end	Night	54% 5% 8% 12% 16% 5%	8552
February	1st to 10th	Night	43% 4 7% 15% 22% 8%	3200
	11th to 20th	Night	47% 6% 11% 20% 13% 3	2831
	21st to end	Night	59% 5% 9% 14% 11% 3	2310
March	1st to 10th	Night	55% 3 6% 23% 12% 1	5500
	11th to 20th	Night	41% 7% 8% 20% 19% 5%	5266
	21st to end	Night	44% 7% 13% 17% 17% 2	5038
April	1st to 10th	Night	52% 8% 15% 19% 6% 1	1835
	11th to 20th	Night	46% 6% 17% 21% 8% 2	1551
	21st to end	Night	42% 8% 17% 25% 8%	1374
May	1st to 10th	Night	53% 7% 16% 21% 3	2471
	11th to 20th	Night	38% 7% 12% 25% 13% 5%	2077
	21st to end	Night	50% 10% 15% 20% 5%	1586
June	1st to 10th	Night	51% 9% 18% 18% 4	480
	11th to 20th	Night	45% 12% 20% 22% 3	400
	21st to end	Night	46% 15% 24% 15% 1	400
July	1st to 10th	Night	61% 6% 14% 14% 5%	927
	11th to 20th	Night	60% 8% 18% 14% 1	1519
	21st to end	Night	59% 9% 20% 10% 3	2026
August	1st to 10th	Night	60% 8% 21% 8% 3	1843
	11th to 20th	Night	69% 7% 16% 7%	2113
	21st to end	Night	67% 8% 15% 10%	2822
September	1st to 10th	Night	57% 8% 21% 13% 2	1791
	11th to 20th	Night	63% 7% 16% 13% 1	2034
	21st to end	Night	63% 8% 12% 15% 3	2090
October	1st to 10th	Night	57% 6% 9% 23% 5%	4014
	11th to 20th	Night	59% 7% 15% 16% 3	4135
	21st to end	Night	64% 5% 10% 19% 2	5152
November	1st to 10th	Night	57% 7% 13% 17% 4 2	3100
	11th to 20th	Night	59% 6% 13% 16% 5%	3400
	21st to end	Night	55% 6% 11% 18% 9% 1	3673
December	1st to 10th	Night	48% 7% 15% 20% 9% 1	6210
	11th to 20th	Night	52% 6% 15% 15% 8% 3	7361
	21st to end	Night	47% 7% 15% 11% 16% 3	9966

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 10% 31% 30% 20% 5%	100
	11th to 20th	Day	7% 5% 25% 32% 25% 6%	100
	21st to end	Day	7% 10% 18% 29% 23% 13%	175
February	1st to 10th	Day	5% 8% 14% 32% 29% 13%	300
	11th to 20th	Day	7% 8% 20% 33% 24% 9%	378
	21st to end	Day	7% 8% 22% 33% 23% 7%	331
March	1st to 10th	Day	6% 4 17% 37% 28% 9%	400
	11th to 20th	Day	6% 8% 24% 36% 15% 11%	400
	21st to end	Day	7% 10% 21% 29% 25% 8%	620
April	1st to 10th	Day	11% 8% 23% 32% 20% 5%	683
	11th to 20th	Day	8% 9% 24% 30% 23% 6%	690
	21st to end	Day	7% 6% 19% 29% 30% 10%	700
May	1st to 10th	Day	14% 8% 22% 24% 24% 9%	703
	11th to 20th	Day	8% 9% 22% 30% 23% 8%	794
	21st to end	Day	19% 6% 15% 29% 23% 8%	1172
June	1st to 10th	Day	14% 5% 16% 28% 25% 11%	1130
	11th to 20th	Day	14% 5% 13% 25% 29% 13%	1130
	21st to end	Day	16% 3 13% 25% 30% 13%	1130
July	1st to 10th	Day	22% 4 14% 24% 27% 10%	1111
	11th to 20th	Day	23% 4 15% 24% 23% 11%	1031
	21st to end	Day	23% 5% 14% 24% 21% 13%	972
August	1st to 10th	Day	29% 6% 16% 22% 20% 7%	726
	11th to 20th	Day	33% 8% 16% 21% 16% 6%	715
	21st to end	Day	32% 7% 16% 26% 15% 5%	803
September	1st to 10th	Day	27% 6% 16% 22% 20% 10%	730
	11th to 20th	Day	26% 9% 17% 23% 20% 5%	552
	21st to end	Day	28% 8% 17% 21% 16% 10%	390
October	1st to 10th	Day	19% 11% 19% 22% 17% 12%	390
	11th to 20th	Day	15% 6% 18% 23% 26% 12%	390
	21st to end	Day	12% 9% 13% 25% 24% 17%	429
November	1st to 10th	Day	12% 7% 14% 30% 28% 10%	259
	11th to 20th	Day	9% 6% 9% 28% 26% 22%	100
	21st to end	Day	11% 4 15% 32% 28% 10%	100
December	1st to 10th	Day	11% 7% 23% 34% 23% 2	100
	11th to 20th	Day	7% 8% 27% 24% 29% 5%	100
	21st to end	Day	10% 12% 17% 33% 24% 5%	110
January	1st to 10th	Night	6% 5% 22% 33% 25% 9%	1200
	11th to 20th	Night	8% 5% 20% 40% 20% 6%	1020
	21st to end	Night	6% 7% 23% 35% 23% 6%	1040
February	1st to 10th	Night	5% 7% 19% 32% 26% 11%	900
	11th to 20th	Night	6% 7% 20% 37% 25% 5%	884
	21st to end	Night	8% 6% 21% 38% 23% 5%	743
March	1st to 10th	Night	6% 3 19% 37% 30% 4	756
	11th to 20th	Night	5% 4 21% 42% 22% 6%	664
	21st to end	Night	7% 5% 17% 35% 27% 9%	660
April	1st to 10th	Night	10% 7% 15% 34% 27% 7%	600
	11th to 20th	Night	8% 3 17% 36% 28% 8%	593
	21st to end	Night	10% 2 11% 32% 35% 10%	574
May	1st to 10th	Night	11% 4 13% 27% 36% 8%	297
	11th to 20th	Night	10% 3 12% 37% 35% 4	197
	21st to end	Night	17% 4 8% 32% 34% 5%	217
June	1st to 10th	Night	13% 4 13% 28% 33% 10%	200
	11th to 20th	Night	15% 2 8% 27% 39% 10%	200
	21st to end	Night	17% 3 5% 21% 46% 10%	200
July	1st to 10th	Night	19% 3 6% 25% 40% 8%	195
	11th to 20th	Night	24% 4 10% 20% 33% 9%	194
	21st to end	Night	21% 2 10% 24% 36% 7%	219
August	1st to 10th	Night	31% 5% 9% 19% 29% 8%	331
	11th to 20th	Night	32% 5% 10% 21% 26% 6%	496
	21st to end	Night	30% 5% 8% 22% 24% 12%	660
September	1st to 10th	Night	24% 5% 10% 24% 26% 12%	600
	11th to 20th	Night	27% 5% 10% 24% 29% 5%	594
	21st to end	Night	24% 5% 15% 24% 26% 7%	570
October	1st to 10th	Night	22% 6% 17% 24% 25% 6%	798
	11th to 20th	Night	15% 6% 16% 25% 29% 9%	860
	21st to end	Night	11% 4 14% 33% 28% 10%	946
November	1st to 10th	Night	13% 6% 18% 31% 25% 6%	880
	11th to 20th	Night	11% 5% 14% 29% 28% 12%	900
	21st to end	Night	11% 5% 16% 33% 26% 10%	1100
December	1st to 10th	Night	11% 7% 19% 36% 22% 5%	1200
	11th to 20th	Night	9% 5% 20% 28% 29% 8%	1200
	21st to end	Night	8% 7% 17% 32% 26% 9%	1320

Page generated at 2025-09-15 21:49:11. Version ac07

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