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 2024-01-13.

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% 10% 5% 9% 8% 4 6% 6% 6% 7% 26%	74253
	Night	6% 11% 5% 11% 9% 5% 6% 6% 6% 7% 28%	75493
Transparency	Day	55% 8% 16% 15% 5% 1	73848
	Night	53% 7% 13% 16% 8% 2	75417
Seeing	Day	17% 6% 17% 26% 24% 10%	17390
	Night	12% 5% 16% 31% 28% 8%	22008

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% 6% 9% 7% 3 6% 5% 5% 7% 40%	512
	11th to 20th	Day	4 8% 5% 10% 9% 6% 9% 6% 7% 8% 27%	728
	21st to end	Day	2 9% 7% 14% 10% 6% 5% 6% 7% 7% 28%	956
February	1st to 10th	Day	2 9% 5% 11% 8% 5% 6% 5% 4 6% 38%	1080
	11th to 20th	Day	3 9% 7% 12% 9% 6% 8% 8% 8% 7% 24%	1308
	21st to end	Day	2 9% 9% 12% 9% 4 8% 9% 5% 6% 27%	1184
March	1st to 10th	Day	1 11% 6% 12% 9% 5% 6% 6% 7% 6% 30%	1743
	11th to 20th	Day	1 6% 6% 10% 8% 5% 5% 6% 8% 7% 37%	1862
	21st to end	Day	3 9% 5% 10% 8% 4 6% 5% 6% 7% 38%	2340
April	1st to 10th	Day	4 14% 6% 10% 9% 5% 7% 6% 6% 8% 25%	2308
	11th to 20th	Day	4 10% 4 8% 8% 5% 5% 6% 6% 8% 38%	2512
	21st to end	Day	4 10% 4 7% 7% 5% 6% 6% 7% 8% 36%	2722
May	1st to 10th	Day	7% 11% 5% 10% 8% 5% 8% 6% 6% 9% 27%	2972
	11th to 20th	Day	7% 9% 4 8% 8% 5% 7% 6% 7% 8% 31%	3071
	21st to end	Day	12% 8% 4 7% 7% 4 7% 7% 8% 8% 28%	3647
June	1st to 10th	Day	14% 8% 4 9% 8% 5% 6% 6% 6% 8% 26%	3528
	11th to 20th	Day	15% 7% 3 8% 8% 5% 6% 7% 7% 8% 26%	3600
	21st to end	Day	18% 7% 4 6% 7% 4 6% 6% 6% 9% 27%	3600
July	1st to 10th	Day	16% 8% 3 6% 6% 4 7% 7% 7% 9% 27%	3596
	11th to 20th	Day	23% 10% 5% 8% 8% 5% 6% 6% 6% 7% 18%	3353
	21st to end	Day	22% 9% 4 8% 7% 5% 6% 6% 7% 9% 19%	3493
August	1st to 10th	Day	26% 9% 4 9% 8% 3 6% 5% 6% 7% 18%	2924
	11th to 20th	Day	25% 10% 4 7% 8% 4 6% 6% 6% 6% 18%	2742
	21st to end	Day	25% 11% 5% 8% 8% 4 5% 6% 5% 5% 18%	2804
September	1st to 10th	Day	20% 13% 4 8% 7% 4 5% 4 6% 7% 23%	2349
	11th to 20th	Day	21% 16% 5% 8% 7% 3 5% 5% 5% 5% 21%	2110
	21st to end	Day	17% 18% 7% 8% 8% 4 5% 5% 4 6% 18%	1980
October	1st to 10th	Day	12% 19% 6% 11% 8% 4 5% 4 6% 6% 20%	1681
	11th to 20th	Day	7% 15% 6% 12% 9% 4 6% 5% 4 7% 24%	1602
	21st to end	Day	6% 16% 5% 9% 11% 4 4 6% 6% 9% 24%	1386
November	1st to 10th	Day	5% 14% 5% 11% 8% 5% 6% 7% 8% 6% 24%	1135
	11th to 20th	Day	6% 11% 5% 11% 11% 6% 7% 4 6% 7% 26%	950
	21st to end	Day	5% 13% 5% 13% 10% 3 6% 5% 5% 7% 28%	671
December	1st to 10th	Day	6% 14% 6% 10% 7% 5% 4 5% 7% 11% 25%	570
	11th to 20th	Day	1 12% 5% 13% 10% 5% 10% 7% 8% 7% 21%	530
	21st to end	Day	1 10% 5% 10% 9% 6% 7% 7% 10% 10% 26%	704
January	1st to 10th	Night	2 8% 4 10% 8% 4 6% 5% 6% 8% 37%	3653
	11th to 20th	Night	3 11% 5% 10% 9% 5% 6% 6% 7% 8% 29%	3307
	21st to end	Night	3 9% 6% 11% 8% 4 7% 8% 6% 8% 29%	3399
February	1st to 10th	Night	1 7% 6% 12% 8% 4 6% 4 5% 5% 42%	2880
	11th to 20th	Night	2 9% 6% 11% 9% 5% 7% 6% 7% 8% 30%	2537
	21st to end	Night	3 11% 7% 15% 10% 6% 6% 6% 4 6% 26%	2072
March	1st to 10th	Night	2 9% 6% 13% 11% 6% 7% 5% 5% 6% 30%	2214
	11th to 20th	Night	2 8% 5% 8% 8% 5% 5% 6% 5% 8% 40%	2096
	21st to end	Night	3 9% 5% 10% 7% 4 5% 5% 5% 8% 39%	2014
April	1st to 10th	Night	4 13% 6% 9% 9% 4 7% 6% 7% 8% 28%	1652
	11th to 20th	Night	3 9% 4 10% 9% 4 5% 6% 6% 8% 36%	1395
	21st to end	Night	6% 8% 3 8% 7% 4 6% 6% 6% 8% 37%	1238
May	1st to 10th	Night	6% 11% 4 8% 7% 5% 7% 6% 7% 8% 30%	988
	11th to 20th	Night	7% 8% 4 6% 7% 4 7% 6% 6% 11% 36%	821
	21st to end	Night	11% 7% 4 6% 7% 4 7% 6% 6% 9% 33%	628
June	1st to 10th	Night	8% 7% 4 10% 9% 5% 7% 7% 5% 10% 29%	432
	11th to 20th	Night	14% 5% 4 9% 5% 5% 6% 8% 8% 6% 30%	360
	21st to end	Night	16% 7% 4 6% 6% 4 8% 6% 7% 10% 28%	360
July	1st to 10th	Night	12% 5% 3 9% 7% 7% 5% 5% 7% 10% 28%	364
	11th to 20th	Night	23% 10% 5% 8% 6% 4 6% 3 5% 7% 24%	605
	21st to end	Night	16% 10% 4 8% 6% 4 7% 5% 8% 9% 24%	824
August	1st to 10th	Night	23% 13% 4 7% 8% 4 5% 4 5% 7% 20%	1013
	11th to 20th	Night	25% 8% 3 8% 8% 5% 6% 4 6% 5% 20%	1158
	21st to end	Night	23% 15% 4 9% 7% 3 5% 5% 5% 5% 21%	1550
September	1st to 10th	Night	18% 11% 3 7% 7% 4 5% 6% 6% 6% 27%	1611
	11th to 20th	Night	17% 14% 4 9% 7% 4 5% 6% 5% 6% 22%	1848
	21st to end	Night	16% 16% 5% 8% 7% 4 7% 6% 6% 5% 21%	1980
October	1st to 10th	Night	13% 19% 6% 10% 6% 4 6% 6% 5% 6% 19%	2276
	11th to 20th	Night	7% 15% 6% 13% 7% 4 5% 6% 7% 7% 24%	2356
	21st to end	Night	6% 14% 6% 10% 9% 5% 6% 5% 5% 7% 25%	2970
November	1st to 10th	Night	5% 16% 7% 11% 8% 4 6% 4 4 5% 28%	2941
	11th to 20th	Night	6% 11% 7% 14% 10% 5% 5% 5% 5% 6% 25%	3230
	21st to end	Night	5% 12% 5% 12% 9% 4 7% 6% 6% 7% 28%	3488
December	1st to 10th	Night	6% 12% 6% 10% 8% 6% 6% 6% 6% 9% 26%	3610
	11th to 20th	Night	3 11% 8% 13% 12% 6% 8% 7% 7% 6% 20%	4660
	21st to end	Night	2 10% 6% 11% 9% 5% 7% 8% 7% 10% 26%	6963

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% 8% 12% 21% 13% 4	512
	11th to 20th	Day	52% 7% 9% 20% 9% 3	728
	21st to end	Day	52% 7% 12% 16% 11% 3	956
February	1st to 10th	Day	45% 6% 6% 16% 18% 8%	1080
	11th to 20th	Day	55% 7% 10% 18% 9% 1	1315
	21st to end	Day	55% 6% 7% 19% 10% 3	1184
March	1st to 10th	Day	50% 7% 12% 17% 11% 3	1743
	11th to 20th	Day	42% 6% 10% 26% 14% 2	1862
	21st to end	Day	45% 6% 17% 15% 13% 4	2340
April	1st to 10th	Day	56% 6% 13% 15% 8% 1	2308
	11th to 20th	Day	43% 8% 17% 23% 8% 2	2512
	21st to end	Day	44% 7% 16% 25% 8%	2722
May	1st to 10th	Day	55% 7% 15% 18% 5%	2972
	11th to 20th	Day	49% 7% 16% 20% 7%	3074
	21st to end	Day	50% 10% 17% 20% 3	3648
June	1st to 10th	Day	54% 9% 17% 17% 3	3528
	11th to 20th	Day	53% 9% 18% 18% 1	3600
	21st to end	Day	53% 9% 22% 14% 2	3600
July	1st to 10th	Day	51% 12% 21% 14% 2	3497
	11th to 20th	Day	64% 10% 16% 9% 1	3248
	21st to end	Day	58% 12% 21% 8%	3299
August	1st to 10th	Day	64% 10% 19% 7%	2904
	11th to 20th	Day	65% 11% 17% 8%	2742
	21st to end	Day	67% 8% 18% 6% 1	2804
September	1st to 10th	Day	60% 9% 19% 11% 1	2349
	11th to 20th	Day	64% 8% 16% 12%	2110
	21st to end	Day	66% 8% 11% 12% 2	1980
October	1st to 10th	Day	65% 7% 13% 9% 5%	1681
	11th to 20th	Day	60% 7% 16% 13% 3	1602
	21st to end	Day	54% 9% 17% 17% 3 1	1386
November	1st to 10th	Day	55% 9% 14% 16% 4 2	1135
	11th to 20th	Day	56% 7% 15% 14% 8%	950
	21st to end	Day	54% 7% 11% 16% 11% 1	671
December	1st to 10th	Day	51% 9% 12% 18% 9% 2	570
	11th to 20th	Day	57% 8% 9% 18% 6% 1	532
	21st to end	Day	46% 9% 11% 19% 15% 1	704
January	1st to 10th	Night	44% 7% 14% 20% 11% 4	3653
	11th to 20th	Night	49% 7% 12% 20% 11% 1	3307
	21st to end	Night	50% 8% 12% 17% 11% 3	3399
February	1st to 10th	Night	43% 5% 8% 16% 21% 8%	2880
	11th to 20th	Night	49% 6% 11% 21% 11% 2	2541
	21st to end	Night	59% 5% 9% 14% 10% 3	2072
March	1st to 10th	Night	54% 5% 9% 19% 11% 3	2214
	11th to 20th	Night	40% 7% 9% 26% 16% 3	2098
	21st to end	Night	43% 5% 15% 17% 15% 4	2014
April	1st to 10th	Night	50% 8% 14% 20% 7% 1	1652
	11th to 20th	Night	45% 7% 19% 21% 8% 1	1395
	21st to end	Night	43% 7% 17% 24% 9%	1238
May	1st to 10th	Night	49% 8% 17% 21% 4	988
	11th to 20th	Night	41% 9% 16% 27% 8%	821
	21st to end	Night	44% 8% 15% 27% 6%	628
June	1st to 10th	Night	49% 9% 19% 18% 5%	432
	11th to 20th	Night	47% 12% 19% 19% 3	360
	21st to end	Night	47% 15% 22% 15% 1	360
July	1st to 10th	Night	52% 8% 21% 15% 4	354
	11th to 20th	Night	61% 9% 17% 11% 2	587
	21st to end	Night	52% 13% 27% 8%	778
August	1st to 10th	Night	63% 8% 21% 8%	1008
	11th to 20th	Night	63% 9% 18% 10%	1158
	21st to end	Night	65% 9% 17% 10%	1550
September	1st to 10th	Night	55% 9% 22% 13% 2	1611
	11th to 20th	Night	61% 8% 17% 14% 1	1848
	21st to end	Night	63% 8% 12% 14% 3	1980
October	1st to 10th	Night	65% 9% 11% 11% 4	2276
	11th to 20th	Night	56% 8% 18% 13% 4	2356
	21st to end	Night	57% 8% 14% 16% 3 1	2970
November	1st to 10th	Night	57% 7% 13% 17% 4 2	2941
	11th to 20th	Night	59% 6% 13% 16% 4	3230
	21st to end	Night	55% 6% 11% 18% 9% 1	3488
December	1st to 10th	Night	54% 8% 12% 16% 9% 2	3610
	11th to 20th	Night	61% 8% 9% 14% 8%	4657
	21st to end	Night	49% 8% 11% 14% 16% 3	6963

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 11% 27% 31% 22% 4	90
	11th to 20th	Day	7% 4 18% 33% 30% 7%	82
	21st to end	Day	8% 8% 14% 29% 26% 15%	146
February	1st to 10th	Day	5% 8% 14% 32% 28% 13%	260
	11th to 20th	Day	7% 7% 18% 31% 26% 10%	321
	21st to end	Day	7% 8% 22% 33% 23% 7%	280
March	1st to 10th	Day	6% 4 17% 35% 29% 10%	340
	11th to 20th	Day	6% 7% 25% 37% 14% 10%	340
	21st to end	Day	8% 11% 23% 28% 25% 7%	536
April	1st to 10th	Day	10% 8% 24% 30% 22% 6%	586
	11th to 20th	Day	7% 8% 23% 29% 26% 7%	590
	21st to end	Day	8% 6% 20% 28% 29% 10%	600
May	1st to 10th	Day	13% 5% 20% 25% 27% 10%	603
	11th to 20th	Day	9% 8% 22% 29% 24% 8%	686
	21st to end	Day	19% 6% 15% 29% 23% 8%	1022
June	1st to 10th	Day	14% 5% 15% 27% 26% 12%	990
	11th to 20th	Day	16% 5% 14% 25% 28% 12%	990
	21st to end	Day	17% 3 14% 24% 28% 13%	990
July	1st to 10th	Day	19% 4 13% 25% 29% 10%	971
	11th to 20th	Day	24% 4 16% 24% 22% 11%	899
	21st to end	Day	21% 5% 13% 24% 22% 14%	845
August	1st to 10th	Day	27% 7% 15% 24% 20% 7%	626
	11th to 20th	Day	31% 8% 17% 23% 16% 6%	615
	21st to end	Day	30% 5% 15% 26% 17% 6%	693
September	1st to 10th	Day	27% 7% 14% 20% 21% 11%	630
	11th to 20th	Day	25% 9% 16% 24% 21% 5%	485
	21st to end	Day	29% 9% 18% 21% 16% 8%	360
October	1st to 10th	Day	20% 12% 19% 22% 16% 12%	360
	11th to 20th	Day	15% 5% 19% 23% 26% 13%	360
	21st to end	Day	12% 8% 12% 26% 24% 18%	396
November	1st to 10th	Day	12% 8% 13% 29% 28% 10%	239
	11th to 20th	Day	10% 7% 9% 27% 26% 22%	90
	21st to end	Day	11% 3 14% 32% 29% 10%	90
December	1st to 10th	Day	11% 7% 20% 37% 23% 2	90
	11th to 20th	Day	7% 8% 28% 22% 30% 6%	90
	21st to end	Day	9% 11% 18% 34% 24% 3	99
January	1st to 10th	Night	6% 5% 20% 33% 27% 9%	1130
	11th to 20th	Night	8% 5% 17% 40% 22% 7%	915
	21st to end	Night	6% 6% 21% 35% 25% 7%	920
February	1st to 10th	Night	5% 7% 19% 32% 26% 12%	800
	11th to 20th	Night	6% 7% 18% 37% 27% 5%	784
	21st to end	Night	9% 5% 21% 38% 23% 5%	658
March	1st to 10th	Night	6% 3 19% 36% 31% 5%	671
	11th to 20th	Night	5% 3 20% 42% 23% 7%	592
	21st to end	Night	8% 5% 16% 34% 27% 10%	594
April	1st to 10th	Night	9% 5% 14% 34% 29% 7%	540
	11th to 20th	Night	8% 3 15% 35% 30% 9%	533
	21st to end	Night	11% 2 11% 29% 36% 11%	518
May	1st to 10th	Night	11% 3 10% 28% 39% 9%	268
	11th to 20th	Night	11% 2 11% 37% 36% 3	177
	21st to end	Night	16% 4 8% 31% 35% 6%	195
June	1st to 10th	Night	13% 3 13% 25% 34% 11%	180
	11th to 20th	Night	17% 2 7% 28% 36% 11%	180
	21st to end	Night	18% 2 5% 20% 44% 11%	180
July	1st to 10th	Night	17% 2 5% 25% 44% 8%	175
	11th to 20th	Night	26% 3 10% 18% 32% 10%	174
	21st to end	Night	20% 2 10% 24% 36% 8%	197
August	1st to 10th	Night	31% 5% 9% 17% 29% 8%	297
	11th to 20th	Night	30% 4 10% 22% 28% 6%	446
	21st to end	Night	29% 5% 6% 23% 25% 13%	594
September	1st to 10th	Night	24% 5% 8% 23% 28% 13%	540
	11th to 20th	Night	26% 4 10% 24% 31% 6%	540
	21st to end	Night	24% 5% 14% 25% 26% 6%	540
October	1st to 10th	Night	23% 6% 16% 24% 25% 5%	751
	11th to 20th	Night	15% 6% 16% 24% 30% 9%	810
	21st to end	Night	11% 3 13% 34% 29% 11%	891
November	1st to 10th	Night	14% 5% 18% 31% 26% 6%	830
	11th to 20th	Night	12% 5% 14% 29% 28% 12%	850
	21st to end	Night	11% 4 16% 33% 26% 10%	1035
December	1st to 10th	Night	12% 7% 18% 36% 22% 6%	1130
	11th to 20th	Night	9% 5% 19% 28% 30% 9%	1130
	21st to end	Night	8% 7% 17% 32% 26% 10%	1243

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