Deer Ridge Lookout
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deer Ridge Lookout clear sky chart from 2005-11-06 to 2026-01-17.

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% 13% 4 7% 4 4 4 3 5% 6% 37%	131216
	Night	12% 16% 4 8% 4 4 4 3 5% 6% 35%	129132
Transparency	Day	47% 6% 13% 20% 10% 3	130933
	Night	50% 7% 13% 18% 10% 2	128991
Seeing	Day	22% 17% 27% 21% 10% 2	16544
	Night	20% 11% 21% 31% 15% 1	25783

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	12% 35% 11% 13% 5% 3 3 2 3 3 10%	3437
	11th to 20th	Day	10% 17% 5% 11% 6% 4 4 4 5% 7% 26%	3664
	21st to end	Day	18% 24% 5% 9% 4 3 3 2 3 5% 26%	4004
February	1st to 10th	Day	16% 27% 6% 11% 6% 3 4 3 4 6% 16%	1600
	11th to 20th	Day	11% 25% 7% 12% 7% 4 4 3 3 4 20%	1812
	21st to end	Day	13% 24% 7% 12% 6% 5% 3 3 3 5% 20%	1650
March	1st to 10th	Day	8% 19% 5% 8% 5% 5% 5% 4 7% 7% 28%	4518
	11th to 20th	Day	10% 24% 4 7% 4 3 3 2 3 6% 33%	4792
	21st to end	Day	18% 25% 4 9% 5% 4 5% 3 5% 6% 15%	5783
April	1st to 10th	Day	15% 20% 4 8% 5% 5% 5% 4 6% 6% 20%	2400
	11th to 20th	Day	17% 15% 4 9% 5% 5% 5% 3 4 5% 27%	2512
	21st to end	Day	15% 13% 4 9% 6% 6% 5% 4 5% 6% 26%	2600
May	1st to 10th	Day	13% 10% 4 8% 5% 5% 5% 4 5% 5% 38%	6139
	11th to 20th	Day	15% 11% 3 10% 7% 7% 6% 5% 7% 7% 22%	6277
	21st to end	Day	12% 11% 3 9% 5% 5% 5% 4 6% 6% 33%	7405
June	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 3 5% 7% 31%	3000
	11th to 20th	Day	18% 9% 2 8% 7% 6% 6% 4 6% 6% 28%	3000
	21st to end	Day	11% 5% 2 5% 4 5% 5% 4 6% 8% 45%	3000
July	1st to 10th	Day	5% 3 1 4 3 3 3 3 4 5% 65%	6780
	11th to 20th	Day	4 2 1 2 2 2 2 2 4 6% 72%	6444
	21st to end	Day	5% 3 1 3 2 2 3 3 4 6% 67%	6874
August	1st to 10th	Day	5% 3 1 4 3 3 5% 3 6% 8% 59%	4541
	11th to 20th	Day	5% 3 1 3 3 3 3 3 5% 7% 64%	4235
	21st to end	Day	7% 4 2 5% 4 4 4 3 5% 7% 55%	4553
September	1st to 10th	Day	6% 4 2 5% 3 4 4 3 5% 7% 56%	2400
	11th to 20th	Day	11% 7% 2 6% 3 3 4 3 6% 8% 48%	2245
	21st to end	Day	13% 7% 2 6% 4 4 4 3 5% 8% 43%	2200
October	1st to 10th	Day	11% 6% 2 4 3 3 4 4 6% 8% 50%	3551
	11th to 20th	Day	17% 8% 2 6% 4 4 4 3 6% 8% 39%	2947
	21st to end	Day	21% 18% 5% 6% 4 4 4 3 4 5% 26%	3200
November	1st to 10th	Day	25% 21% 4 9% 4 4 2 4 5% 5% 17%	1854
	11th to 20th	Day	23% 24% 4 9% 4 3 4 3 4 4 18%	1682
	21st to end	Day	17% 27% 6% 11% 6% 4 3 2 4 5% 14%	1470
December	1st to 10th	Day	14% 15% 5% 10% 6% 4 4 3 6% 7% 27%	2360
	11th to 20th	Day	18% 30% 7% 11% 5% 4 3 2 4 4 12%	2712
	21st to end	Day	19% 29% 8% 11% 5% 4 4 3 4 4 9%	3575
January	1st to 10th	Night	16% 32% 10% 14% 4 4 3 2 3 3 9%	6758
	11th to 20th	Night	11% 14% 5% 12% 5% 5% 4 3 4 6% 29%	6366
	21st to end	Night	16% 24% 4 9% 4 3 3 2 3 4 25%	6952
February	1st to 10th	Night	16% 24% 6% 9% 5% 4 4 3 4 5% 20%	2800
	11th to 20th	Night	15% 22% 5% 9% 4 4 4 3 4 6% 24%	2471
	21st to end	Night	12% 24% 6% 9% 5% 4 4 2 5% 5% 25%	1980
March	1st to 10th	Night	8% 19% 5% 8% 5% 4 4 3 4 6% 34%	5376
	11th to 20th	Night	11% 23% 4 7% 4 3 3 2 4 5% 35%	5206
	21st to end	Night	17% 19% 4 10% 6% 5% 5% 4 6% 6% 18%	5192
April	1st to 10th	Night	13% 15% 4 7% 3 4 4 4 6% 9% 31%	2000
	11th to 20th	Night	14% 11% 4 7% 5% 4 5% 4 4 5% 36%	1838
	21st to end	Night	11% 10% 4 9% 5% 5% 4 4 6% 8% 34%	1800
May	1st to 10th	Night	9% 9% 3 8% 5% 4 5% 4 6% 6% 40%	3824
	11th to 20th	Night	13% 9% 3 8% 5% 4 5% 4 6% 8% 36%	3599
	21st to end	Night	13% 8% 3 6% 4 4 4 4 6% 9% 40%	3470
June	1st to 10th	Night	15% 7% 2 7% 5% 4 4 4 5% 8% 40%	1400
	11th to 20th	Night	16% 6% 2 5% 5% 6% 7% 5% 7% 8% 34%	1400
	21st to end	Night	6% 4 2 5% 4 3 4 4 7% 8% 53%	1400
July	1st to 10th	Night	5% 2 1 2 2 2 3 3 4 6% 71%	3180
	11th to 20th	Night	5% 2 1 2 2 2 2 2 3 5% 75%	3499
	21st to end	Night	4 2 1 3 2 2 2 2 4 6% 72%	3969
August	1st to 10th	Night	4 3 1 3 2 2 3 3 5% 9% 65%	2609
	11th to 20th	Night	3 3 2 4 3 3 4 3 6% 8% 62%	2807
	21st to end	Night	5% 3 1 5% 4 3 4 4 5% 7% 60%	3344
September	1st to 10th	Night	4 3 1 5% 2 3 4 3 5% 6% 63%	2000
	11th to 20th	Night	7% 5% 2 6% 3 4 4 4 6% 8% 50%	2154
	21st to end	Night	12% 6% 2 4 3 2 3 3 6% 7% 51%	2200
October	1st to 10th	Night	9% 5% 2 4 3 3 4 3 5% 8% 54%	3646
	11th to 20th	Night	14% 8% 2 5% 3 3 3 4 6% 7% 46%	4200
	21st to end	Night	17% 13% 3 6% 4 3 3 3 5% 9% 33%	4600
November	1st to 10th	Night	23% 18% 4 6% 4 4 4 4 5% 6% 21%	2665
	11th to 20th	Night	21% 23% 4 8% 5% 4 4 3 5% 5% 20%	2914
	21st to end	Night	20% 24% 5% 10% 5% 4 3 3 3 5% 19%	3150
December	1st to 10th	Night	12% 16% 5% 12% 5% 4 3 3 5% 5% 30%	5040
	11th to 20th	Night	17% 26% 8% 13% 6% 5% 4 3 3 5% 12%	5700
	21st to end	Night	16% 31% 8% 12% 5% 4 4 3 3 4 10%	7623

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	78% 7% 7% 7% 2	3437
	11th to 20th	Day	54% 9% 17% 12% 5% 3	3688
	21st to end	Day	61% 7% 11% 15% 7%	4004
February	1st to 10th	Day	73% 5% 8% 7% 5% 2	1600
	11th to 20th	Day	71% 6% 9% 9% 5%	1821
	21st to end	Day	70% 6% 9% 10% 5%	1650
March	1st to 10th	Day	53% 7% 11% 15% 14%	4518
	11th to 20th	Day	56% 5% 21% 16% 2	4793
	21st to end	Day	72% 6% 10% 10% 3	5783
April	1st to 10th	Day	65% 6% 13% 13% 2	2400
	11th to 20th	Day	59% 6% 13% 17% 5%	2512
	21st to end	Day	60% 6% 13% 17% 4 1	2600
May	1st to 10th	Day	48% 5% 11% 22% 14%	6139
	11th to 20th	Day	57% 8% 13% 17% 4	6280
	21st to end	Day	49% 7% 17% 22% 5%	7406
June	1st to 10th	Day	55% 5% 13% 18% 8%	3000
	11th to 20th	Day	56% 7% 12% 17% 8% 1	3000
	21st to end	Day	37% 6% 16% 27% 13% 1	3000
July	1st to 10th	Day	20% 6% 11% 27% 25% 11%	6706
	11th to 20th	Day	15% 4 13% 26% 24% 19%	6366
	21st to end	Day	18% 4 10% 35% 22% 11%	6681
August	1st to 10th	Day	21% 6% 15% 31% 22% 6%	4524
	11th to 20th	Day	20% 4 14% 41% 18% 1	4275
	21st to end	Day	28% 6% 15% 32% 17% 2	4552
September	1st to 10th	Day	30% 4 12% 32% 17% 4	2400
	11th to 20th	Day	38% 4 14% 27% 15% 1	2245
	21st to end	Day	41% 6% 22% 21% 10% 1	2200
October	1st to 10th	Day	33% 5% 19% 35% 7%	3551
	11th to 20th	Day	42% 7% 18% 21% 11%	2947
	21st to end	Day	61% 7% 13% 13% 6%	3200
November	1st to 10th	Day	70% 8% 9% 10% 3	1854
	11th to 20th	Day	70% 8% 10% 7% 4 1	1682
	21st to end	Day	73% 6% 10% 8% 3	1470
December	1st to 10th	Day	52% 13% 19% 14% 2	2360
	11th to 20th	Day	76% 7% 12% 4 1	2714
	21st to end	Day	77% 7% 8% 6% 2	3575
January	1st to 10th	Night	78% 6% 7% 7% 1	6758
	11th to 20th	Night	53% 8% 12% 15% 9% 3	6404
	21st to end	Night	63% 6% 10% 14% 8%	6952
February	1st to 10th	Night	67% 6% 10% 10% 6% 2	2800
	11th to 20th	Night	63% 8% 11% 12% 5% 1	2472
	21st to end	Night	64% 4 12% 12% 7% 1	1980
March	1st to 10th	Night	51% 5% 15% 14% 14% 1	5376
	11th to 20th	Night	53% 5% 17% 22% 3	5206
	21st to end	Night	66% 7% 11% 13% 2	5192
April	1st to 10th	Night	50% 9% 18% 17% 6%	2000
	11th to 20th	Night	50% 6% 14% 20% 10%	1838
	21st to end	Night	48% 7% 15% 21% 8% 1	1800
May	1st to 10th	Night	44% 6% 12% 20% 17% 1	3821
	11th to 20th	Night	46% 7% 15% 23% 8%	3599
	21st to end	Night	39% 7% 19% 29% 7%	3470
June	1st to 10th	Night	44% 5% 16% 23% 10% 2	1400
	11th to 20th	Night	44% 8% 15% 21% 11% 1	1400
	21st to end	Night	29% 6% 18% 28% 17% 2	1400
July	1st to 10th	Night	15% 4 10% 31% 27% 13%	3145
	11th to 20th	Night	14% 3 11% 25% 23% 24%	3455
	21st to end	Night	15% 3 10% 32% 25% 14%	3857
August	1st to 10th	Night	18% 4 14% 31% 24% 10%	2601
	11th to 20th	Night	21% 5% 13% 38% 20% 3	2832
	21st to end	Night	23% 5% 15% 32% 22% 3	3344
September	1st to 10th	Night	24% 4 12% 32% 21% 7%	2000
	11th to 20th	Night	31% 7% 15% 28% 16% 3	2154
	21st to end	Night	34% 5% 22% 25% 12% 2	2200
October	1st to 10th	Night	29% 5% 20% 35% 9%	3646
	11th to 20th	Night	36% 9% 14% 25% 15% 1	4200
	21st to end	Night	49% 10% 17% 18% 6%	4600
November	1st to 10th	Night	65% 8% 13% 11% 3 1	2665
	11th to 20th	Night	68% 7% 11% 9% 5%	2914
	21st to end	Night	68% 6% 11% 11% 3	3150
December	1st to 10th	Night	53% 13% 15% 15% 3	5040
	11th to 20th	Night	77% 6% 12% 4 1	5697
	21st to end	Night	76% 8% 9% 5% 2	7623

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% 19% 27% 18% 7% 1	220
	11th to 20th	Day	21% 19% 32% 18% 9%	212
	21st to end	Day	20% 23% 27% 21% 7% 1	220
February	1st to 10th	Day	28% 23% 32% 15% 3 1	200
	11th to 20th	Day	27% 20% 27% 19% 7%	380
	21st to end	Day	27% 21% 31% 17% 5%	414
March	1st to 10th	Day	31% 21% 25% 16% 6% 2	500
	11th to 20th	Day	27% 18% 22% 19% 12% 2	500
	21st to end	Day	34% 21% 23% 14% 6% 1	550
April	1st to 10th	Day	30% 20% 25% 18% 5% 1	500
	11th to 20th	Day	28% 25% 23% 16% 7% 2	492
	21st to end	Day	26% 18% 27% 18% 7% 3	500
May	1st to 10th	Day	24% 16% 27% 23% 7% 3	503
	11th to 20th	Day	24% 16% 27% 23% 8% 2	528
	21st to end	Day	23% 12% 21% 24% 16% 3	789
June	1st to 10th	Day	25% 15% 23% 23% 11% 3	730
	11th to 20th	Day	23% 20% 25% 20% 10% 2	730
	21st to end	Day	14% 15% 25% 24% 17% 5%	730
July	1st to 10th	Day	9% 13% 29% 30% 17% 3	721
	11th to 20th	Day	8% 20% 36% 22% 11% 3	580
	21st to end	Day	7% 14% 38% 26% 12% 3	575
August	1st to 10th	Day	8% 13% 35% 26% 14% 3	527
	11th to 20th	Day	7% 13% 35% 25% 15% 5%	517
	21st to end	Day	12% 15% 31% 25% 12% 5%	583
September	1st to 10th	Day	14% 17% 25% 26% 15% 3	530
	11th to 20th	Day	16% 13% 30% 26% 12% 3	530
	21st to end	Day	24% 18% 27% 19% 11% 1	530
October	1st to 10th	Day	22% 16% 30% 20% 11% 2	530
	11th to 20th	Day	30% 15% 22% 19% 10% 3	345
	21st to end	Day	30% 19% 25% 18% 6% 2	363
November	1st to 10th	Day	37% 15% 20% 23% 5%	330
	11th to 20th	Day	35% 17% 24% 16% 7%	283
	21st to end	Day	31% 20% 24% 13% 11% 1	220
December	1st to 10th	Day	30% 19% 20% 18% 12% 2	220
	11th to 20th	Day	32% 19% 23% 19% 7% 1	220
	21st to end	Day	26% 15% 29% 20% 10%	242
January	1st to 10th	Night	31% 17% 23% 23% 5%	983
	11th to 20th	Night	23% 16% 26% 29% 7%	824
	21st to end	Night	18% 14% 29% 30% 9% 1	880
February	1st to 10th	Night	25% 14% 25% 27% 7% 1	800
	11th to 20th	Night	23% 11% 26% 30% 10%	784
	21st to end	Night	22% 15% 21% 28% 12% 1	660
March	1st to 10th	Night	23% 16% 20% 28% 13% 1	800
	11th to 20th	Night	23% 13% 19% 30% 14% 1	800
	21st to end	Night	24% 14% 22% 26% 13% 2	880
April	1st to 10th	Night	19% 11% 20% 31% 18% 1	800
	11th to 20th	Night	19% 15% 25% 29% 11% 2	650
	21st to end	Night	17% 11% 29% 30% 13% 1	600
May	1st to 10th	Night	18% 6% 21% 35% 18% 2	480
	11th to 20th	Night	13% 6% 20% 33% 26% 2	394
	21st to end	Night	19% 9% 18% 28% 23% 2	433
June	1st to 10th	Night	22% 8% 18% 31% 19% 4	400
	11th to 20th	Night	18% 7% 22% 33% 19% 2	400
	21st to end	Night	8% 7% 14% 44% 26% 2	400
July	1st to 10th	Night	5% 3 10% 43% 37% 1	390
	11th to 20th	Night	4 2 17% 49% 26% 2	388
	21st to end	Night	4 4 12% 45% 34% 1	438
August	1st to 10th	Night	4 4 14% 40% 35% 4	398
	11th to 20th	Night	5% 4 14% 37% 35% 4	536
	21st to end	Night	8% 4 17% 42% 27% 3	720
September	1st to 10th	Night	7% 4 19% 40% 25% 6%	800
	11th to 20th	Night	11% 5% 14% 33% 32% 5%	800
	21st to end	Night	15% 8% 16% 37% 19% 5%	800
October	1st to 10th	Night	20% 7% 16% 39% 18% 1	800
	11th to 20th	Night	22% 7% 17% 33% 19% 2	800
	21st to end	Night	25% 11% 23% 29% 11% 2	880
November	1st to 10th	Night	32% 13% 19% 31% 5%	820
	11th to 20th	Night	30% 16% 21% 25% 6% 1	940
	21st to end	Night	27% 14% 22% 27% 9%	1050
December	1st to 10th	Night	23% 15% 25% 28% 10%	1050
	11th to 20th	Night	26% 16% 27% 25% 5%	1050
	21st to end	Night	27% 14% 28% 26% 5%	1155

Page generated at 2026-01-13 22:14:28. Version ac07

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