Tanaeum Ridge and Peoh Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tanaeum Ridge and Peoh Point clear sky chart from 2005-11-06 to 2025-08-05.

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	5% 8% 3 8% 5% 5% 5% 4 6% 7% 44%	129876
	Night	6% 8% 3 8% 5% 5% 5% 5% 6% 8% 40%	126895
Transparency	Day	31% 10% 15% 24% 15% 5%	129600
	Night	34% 11% 17% 23% 12% 3	126747
Seeing	Day	17% 20% 34% 20% 7% 2	15304
	Night	14% 17% 30% 26% 11% 2	24235

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	7% 16% 6% 14% 7% 6% 6% 5% 7% 8% 17%	3639
	11th to 20th	Day	6% 12% 4 8% 5% 5% 5% 4 7% 7% 37%	3616
	21st to end	Day	12% 14% 5% 9% 5% 4 5% 4 5% 6% 32%	4004
February	1st to 10th	Day	8% 11% 5% 13% 9% 6% 5% 5% 7% 7% 25%	1800
	11th to 20th	Day	7% 14% 4 10% 6% 6% 6% 5% 7% 8% 28%	1755
	21st to end	Day	6% 12% 5% 12% 7% 7% 6% 6% 6% 8% 25%	1620
March	1st to 10th	Day	3 9% 3 9% 7% 9% 7% 6% 8% 8% 30%	4518
	11th to 20th	Day	4 10% 4 13% 8% 6% 5% 4 5% 5% 36%	4951
	21st to end	Day	6% 12% 5% 12% 10% 8% 7% 5% 7% 8% 19%	5785
April	1st to 10th	Day	8% 12% 3 12% 9% 7% 8% 5% 7% 7% 23%	2400
	11th to 20th	Day	6% 12% 4 9% 8% 5% 6% 4 6% 7% 33%	2372
	21st to end	Day	5% 10% 4 10% 7% 6% 6% 5% 7% 7% 34%	2628
May	1st to 10th	Day	5% 6% 2 8% 5% 4 5% 4 6% 7% 49%	6320
	11th to 20th	Day	5% 6% 3 9% 7% 6% 6% 5% 7% 9% 37%	6277
	21st to end	Day	6% 7% 3 8% 6% 5% 6% 5% 6% 8% 41%	6903
June	1st to 10th	Day	8% 7% 3 8% 6% 5% 5% 4 7% 7% 40%	2800
	11th to 20th	Day	5% 5% 2 6% 6% 6% 6% 6% 8% 9% 41%	2800
	21st to end	Day	4 4 2 5% 4 5% 4 4 5% 8% 55%	2800
July	1st to 10th	Day	1 2 1 2 2 2 2 2 4 5% 78%	6320
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 80%	6320
	21st to end	Day	2 2 1 3 3 2 3 2 4 7% 73%	6874
August	1st to 10th	Day	1 1 1 3 2 2 3 3 5% 6% 72%	4458
	11th to 20th	Day	2 2 1 5% 3 3 4 3 6% 8% 64%	4043
	21st to end	Day	5% 5% 2 5% 4 3 4 3 5% 7% 58%	4223
September	1st to 10th	Day	4 2 1 3 3 4 3 3 5% 8% 64%	2280
	11th to 20th	Day	4 4 2 5% 5% 5% 6% 6% 7% 7% 50%	2280
	21st to end	Day	7% 6% 2 7% 4 4 4 3 6% 8% 50%	2034
October	1st to 10th	Day	5% 5% 2 6% 4 3 4 4 6% 10% 52%	3180
	11th to 20th	Day	7% 7% 3 9% 6% 6% 5% 4 6% 9% 38%	3161
	21st to end	Day	8% 9% 4 10% 6% 7% 7% 4 7% 7% 31%	3169
November	1st to 10th	Day	9% 12% 5% 12% 6% 6% 6% 4 7% 7% 26%	1697
	11th to 20th	Day	8% 15% 4 11% 7% 7% 5% 4 7% 7% 25%	1600
	21st to end	Day	8% 15% 4 9% 7% 6% 6% 5% 7% 6% 27%	1600
December	1st to 10th	Day	6% 10% 3 9% 5% 5% 4 5% 7% 8% 38%	2620
	11th to 20th	Day	9% 15% 6% 15% 9% 6% 7% 4 7% 6% 17%	3025
	21st to end	Day	10% 16% 6% 15% 8% 6% 6% 5% 5% 6% 18%	4004
January	1st to 10th	Night	8% 15% 7% 13% 8% 7% 7% 6% 6% 7% 18%	6306
	11th to 20th	Night	7% 10% 3 9% 5% 5% 5% 4 6% 10% 36%	6282
	21st to end	Night	9% 15% 5% 9% 5% 5% 5% 4 5% 6% 32%	6938
February	1st to 10th	Night	7% 12% 5% 9% 6% 5% 6% 5% 8% 10% 27%	2600
	11th to 20th	Night	7% 12% 4 9% 5% 5% 6% 5% 7% 8% 34%	2532
	21st to end	Night	6% 12% 4 11% 6% 6% 6% 5% 6% 7% 30%	2010
March	1st to 10th	Night	4 6% 3 8% 7% 7% 8% 7% 8% 9% 33%	5376
	11th to 20th	Night	3 8% 4 11% 7% 6% 6% 5% 6% 6% 40%	5045
	21st to end	Night	6% 9% 3 11% 8% 7% 8% 6% 9% 9% 24%	5189
April	1st to 10th	Night	6% 8% 3 9% 7% 7% 8% 7% 8% 9% 28%	2000
	11th to 20th	Night	4 8% 3 8% 6% 4 6% 5% 7% 8% 40%	1979
	21st to end	Night	5% 8% 3 8% 7% 5% 7% 6% 10% 8% 31%	1767
May	1st to 10th	Night	4 5% 2 8% 5% 4 4 4 5% 7% 50%	3640
	11th to 20th	Night	4 6% 2 8% 6% 7% 5% 5% 6% 7% 42%	3616
	21st to end	Night	4 5% 3 8% 6% 6% 8% 6% 9% 10% 36%	3972
June	1st to 10th	Night	7% 5% 1 8% 6% 5% 6% 4 7% 8% 44%	1600
	11th to 20th	Night	4 5% 3 6% 7% 5% 6% 5% 8% 11% 40%	1600
	21st to end	Night	2 3 2 5% 5% 5% 6% 5% 7% 6% 55%	1600
July	1st to 10th	Night	1 1 1 2 2 2 2 2 5% 5% 76%	3640
	11th to 20th	Night	1 1 2 2 1 2 2 2 5% 82%	3640
	21st to end	Night	1 1 1 2 2 2 3 2 4 7% 75%	3969
August	1st to 10th	Night	1 2 1 2 2 2 2 2 4 6% 75%	2561
	11th to 20th	Night	1 2 1 3 3 4 4 4 6% 7% 67%	2780
	21st to end	Night	4 3 1 7% 4 4 4 3 5% 6% 58%	3453
September	1st to 10th	Night	3 2 1 3 3 2 3 3 5% 6% 67%	1900
	11th to 20th	Night	3 4 2 7% 4 5% 5% 4 6% 9% 52%	1900
	21st to end	Night	4 4 3 5% 4 4 4 4 6% 9% 51%	2141
October	1st to 10th	Night	4 5% 2 6% 4 4 4 4 6% 9% 52%	3800
	11th to 20th	Night	6% 5% 2 7% 5% 6% 6% 5% 7% 9% 42%	3777
	21st to end	Night	8% 9% 3 9% 6% 6% 6% 4 6% 9% 32%	4390
November	1st to 10th	Night	11% 11% 3 9% 5% 6% 6% 5% 7% 9% 29%	2600
	11th to 20th	Night	8% 11% 4 10% 5% 6% 6% 5% 8% 9% 29%	2800
	21st to end	Night	8% 11% 4 10% 7% 5% 6% 5% 7% 8% 29%	2800
December	1st to 10th	Night	5% 9% 3 7% 5% 5% 6% 4 6% 8% 41%	4560
	11th to 20th	Night	9% 17% 6% 13% 8% 7% 7% 5% 6% 7% 16%	5180
	21st to end	Night	10% 17% 6% 15% 7% 6% 5% 4 6% 7% 17%	6952

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	55% 13% 15% 14% 2	3639
	11th to 20th	Day	39% 9% 18% 25% 9% 1	3640
	21st to end	Day	47% 10% 10% 20% 13%	4004
February	1st to 10th	Day	50% 14% 16% 14% 4 1	1800
	11th to 20th	Day	46% 14% 15% 17% 8% 1	1764
	21st to end	Day	46% 17% 15% 15% 6% 1	1620
March	1st to 10th	Day	37% 11% 15% 19% 16% 1	4518
	11th to 20th	Day	38% 10% 12% 32% 7%	4951
	21st to end	Day	48% 15% 18% 15% 4	5785
April	1st to 10th	Day	48% 14% 16% 17% 5%	2400
	11th to 20th	Day	39% 13% 16% 20% 10% 1	2372
	21st to end	Day	37% 16% 14% 22% 10% 1	2628
May	1st to 10th	Day	24% 8% 14% 31% 20% 3	6320
	11th to 20th	Day	24% 12% 27% 25% 11%	6280
	21st to end	Day	29% 13% 23% 28% 7%	6904
June	1st to 10th	Day	35% 11% 14% 25% 13% 2	2800
	11th to 20th	Day	26% 12% 19% 27% 13% 2	2800
	21st to end	Day	22% 9% 18% 30% 18% 3	2800
July	1st to 10th	Day	9% 4 10% 25% 28% 24%	6251
	11th to 20th	Day	10% 3 6% 21% 32% 29%	6245
	21st to end	Day	11% 4 8% 36% 32% 10%	6681
August	1st to 10th	Day	11% 5% 8% 23% 36% 17%	4441
	11th to 20th	Day	13% 6% 17% 42% 19% 4	4082
	21st to end	Day	24% 5% 14% 27% 26% 3	4222
September	1st to 10th	Day	16% 6% 13% 31% 26% 8%	2280
	11th to 20th	Day	25% 10% 17% 23% 21% 5%	2280
	21st to end	Day	29% 7% 18% 26% 16% 4	2034
October	1st to 10th	Day	22% 8% 13% 41% 16% 1	3180
	11th to 20th	Day	31% 13% 17% 25% 13%	3161
	21st to end	Day	35% 12% 17% 22% 11% 4	3169
November	1st to 10th	Day	49% 13% 13% 18% 7% 1	1697
	11th to 20th	Day	51% 14% 15% 13% 5% 1	1600
	21st to end	Day	47% 14% 15% 16% 7% 1	1600
December	1st to 10th	Day	37% 11% 21% 24% 7%	2620
	11th to 20th	Day	60% 13% 13% 11% 3	3028
	21st to end	Day	59% 12% 12% 13% 4	4004
January	1st to 10th	Night	57% 13% 17% 10% 3	6306
	11th to 20th	Night	35% 10% 19% 27% 8% 1	6320
	21st to end	Night	49% 9% 11% 20% 10% 1	6938
February	1st to 10th	Night	46% 15% 17% 16% 5%	2600
	11th to 20th	Night	41% 13% 18% 20% 7% 1	2534
	21st to end	Night	45% 14% 16% 18% 7%	2010
March	1st to 10th	Night	31% 12% 18% 23% 14% 1	5376
	11th to 20th	Night	32% 12% 19% 30% 7%	5046
	21st to end	Night	42% 16% 19% 19% 4	5189
April	1st to 10th	Night	38% 17% 20% 19% 6%	2000
	11th to 20th	Night	33% 13% 18% 22% 13% 1	1979
	21st to end	Night	32% 18% 19% 22% 9% 1	1767
May	1st to 10th	Night	23% 10% 11% 35% 20% 1	3637
	11th to 20th	Night	23% 12% 25% 29% 10% 1	3616
	21st to end	Night	25% 18% 27% 25% 5%	3972
June	1st to 10th	Night	30% 13% 19% 24% 13% 1	1600
	11th to 20th	Night	27% 13% 20% 27% 12% 1	1600
	21st to end	Night	19% 11% 18% 34% 15% 3	1600
July	1st to 10th	Night	8% 5% 10% 30% 22% 25%	3600
	11th to 20th	Night	6% 4 7% 26% 32% 26%	3592
	21st to end	Night	7% 4 13% 34% 30% 13%	3857
August	1st to 10th	Night	9% 4 8% 24% 39% 15%	2553
	11th to 20th	Night	11% 6% 25% 36% 18% 4	2806
	21st to end	Night	18% 8% 18% 27% 26% 3	3453
September	1st to 10th	Night	14% 7% 14% 29% 29% 6%	1900
	11th to 20th	Night	23% 9% 17% 25% 20% 7%	1900
	21st to end	Night	24% 9% 19% 28% 16% 5%	2141
October	1st to 10th	Night	20% 7% 17% 41% 14% 1	3800
	11th to 20th	Night	27% 12% 19% 28% 13% 1	3777
	21st to end	Night	35% 12% 19% 20% 13% 1	4390
November	1st to 10th	Night	45% 12% 16% 19% 8% 1	2600
	11th to 20th	Night	46% 14% 16% 17% 6% 1	2800
	21st to end	Night	46% 12% 17% 15% 9% 1	2800
December	1st to 10th	Night	36% 12% 18% 29% 6%	4560
	11th to 20th	Night	61% 13% 12% 10% 4	5176
	21st to end	Night	56% 12% 16% 12% 3	6952

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% 14% 28% 18% 12% 2	200
	11th to 20th	Day	29% 10% 23% 27% 9% 4	200
	21st to end	Day	19% 12% 31% 26% 10% 2	220
February	1st to 10th	Day	24% 27% 29% 15% 5%	400
	11th to 20th	Day	28% 23% 32% 14% 3	395
	21st to end	Day	23% 21% 35% 16% 5% 1	399
March	1st to 10th	Day	21% 25% 29% 19% 5% 1	500
	11th to 20th	Day	19% 24% 33% 16% 7% 1	500
	21st to end	Day	25% 28% 31% 12% 4	550
April	1st to 10th	Day	26% 24% 29% 15% 5% 1	500
	11th to 20th	Day	22% 28% 29% 15% 3 2	492
	21st to end	Day	20% 25% 34% 15% 4 1	500
May	1st to 10th	Day	20% 19% 37% 17% 6% 1	503
	11th to 20th	Day	21% 20% 33% 17% 6% 2	528
	21st to end	Day	16% 20% 34% 22% 8% 1	573
June	1st to 10th	Day	18% 21% 34% 19% 7% 1	530
	11th to 20th	Day	18% 27% 38% 12% 3 1	530
	21st to end	Day	8% 23% 36% 23% 8% 1	530
July	1st to 10th	Day	5% 17% 50% 24% 4	526
	11th to 20th	Day	8% 19% 45% 22% 6% 1	524
	21st to end	Day	5% 15% 45% 25% 9% 2	575
August	1st to 10th	Day	5% 13% 40% 27% 11% 2	504
	11th to 20th	Day	4 12% 38% 30% 12% 4	477
	21st to end	Day	9% 17% 38% 22% 10% 4	539
September	1st to 10th	Day	8% 18% 39% 22% 11% 3	490
	11th to 20th	Day	10% 18% 37% 24% 10% 1	490
	21st to end	Day	14% 18% 34% 22% 9% 2	490
October	1st to 10th	Day	17% 18% 27% 22% 12% 3	490
	11th to 20th	Day	17% 17% 30% 20% 12% 3	490
	21st to end	Day	25% 15% 31% 17% 9% 3	374
November	1st to 10th	Day	28% 15% 28% 23% 6% 1	265
	11th to 20th	Day	29% 15% 29% 17% 8% 3	200
	21st to end	Day	22% 16% 25% 24% 11% 3	200
December	1st to 10th	Day	26% 10% 25% 21% 12% 8%	200
	11th to 20th	Day	21% 19% 32% 21% 7% 2	200
	21st to end	Day	21% 17% 29% 23% 7% 2	220
January	1st to 10th	Night	23% 13% 24% 27% 11% 2	800
	11th to 20th	Night	21% 13% 25% 28% 12% 2	800
	21st to end	Night	18% 12% 25% 29% 14% 2	880
February	1st to 10th	Night	19% 16% 27% 27% 9% 1	800
	11th to 20th	Night	18% 18% 26% 27% 10% 1	784
	21st to end	Night	21% 18% 23% 25% 11% 2	660
March	1st to 10th	Night	16% 15% 27% 31% 10% 1	800
	11th to 20th	Night	14% 17% 28% 29% 11% 1	800
	21st to end	Night	18% 20% 28% 25% 8% 1	880
April	1st to 10th	Night	14% 23% 32% 23% 8% 1	800
	11th to 20th	Night	13% 23% 29% 24% 9% 2	791
	21st to end	Night	12% 27% 35% 17% 9% 1	567
May	1st to 10th	Night	14% 23% 32% 23% 7% 1	400
	11th to 20th	Night	13% 17% 35% 22% 11% 2	394
	21st to end	Night	11% 18% 35% 26% 9%	433
June	1st to 10th	Night	14% 21% 38% 19% 8% 1	400
	11th to 20th	Night	11% 31% 38% 16% 4	400
	21st to end	Night	7% 24% 38% 23% 8% 1	400
July	1st to 10th	Night	5% 17% 50% 23% 6%	390
	11th to 20th	Night	2 24% 49% 20% 5%	388
	21st to end	Night	3 18% 46% 24% 8%	438
August	1st to 10th	Night	3 15% 45% 25% 10% 1	386
	11th to 20th	Night	3 13% 37% 27% 16% 4	544
	21st to end	Night	6% 20% 36% 22% 14% 3	804
September	1st to 10th	Night	5% 17% 34% 26% 15% 3	760
	11th to 20th	Night	8% 15% 28% 27% 17% 5%	760
	21st to end	Night	9% 16% 27% 28% 18% 2	760
October	1st to 10th	Night	12% 15% 25% 28% 18% 2	760
	11th to 20th	Night	14% 11% 25% 30% 16% 4	760
	21st to end	Night	17% 17% 26% 25% 12% 3	836
November	1st to 10th	Night	18% 17% 25% 30% 10%	780
	11th to 20th	Night	21% 15% 25% 25% 13% 2	800
	21st to end	Night	16% 14% 25% 29% 13% 3	800
December	1st to 10th	Night	17% 14% 24% 28% 15% 2	800
	11th to 20th	Night	19% 13% 31% 28% 9% 1	800
	21st to end	Night	21% 18% 27% 27% 6%	880

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