Washington Road Scenic Overlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Washington Road Scenic Overlook clear sky chart from 2005-11-06 to 2026-06-01.

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	9% 6% 1 3 2 2 2 2 3 5% 64%	140935
	Night	11% 7% 1 3 2 2 3 2 4 5% 59%	139653
Transparency	Day	27% 2 6% 18% 25% 22%	135870
	Night	31% 3 6% 17% 23% 21%	135704
Seeing	Day	15% 14% 31% 27% 11% 3	17088
	Night	15% 7% 20% 33% 22% 4	26456

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	21% 13% 2 4 2 2 3 2 4 6% 40%	4722
	11th to 20th	Day	12% 7% 2 4 3 3 2 2 3 4 59%	5056
	21st to end	Day	15% 7% 2 5% 3 3 4 3 5% 6% 46%	5843
February	1st to 10th	Day	21% 10% 1 4 2 2 2 3 5% 5% 45%	1890
	11th to 20th	Day	16% 14% 2 4 3 3 3 3 5% 6% 41%	1988
	21st to end	Day	18% 15% 2 4 2 3 2 3 4 5% 43%	1730
March	1st to 10th	Day	16% 21% 5% 6% 3 3 3 2 4 5% 31%	4697
	11th to 20th	Day	15% 14% 3 5% 2 2 2 2 3 4 47%	5110
	21st to end	Day	20% 18% 3 6% 3 3 3 3 4 5% 33%	5867
April	1st to 10th	Day	16% 11% 2 5% 3 3 3 3 5% 7% 42%	2520
	11th to 20th	Day	13% 8% 2 4 4 3 4 3 4 5% 50%	2489
	21st to end	Day	12% 7% 1 4 2 3 3 3 5% 6% 54%	2520
May	1st to 10th	Day	6% 4 2 3 2 2 2 1 3 5% 70%	5776
	11th to 20th	Day	6% 3 1 3 2 2 2 2 3 5% 71%	6417
	21st to end	Day	5% 2 1 2 2 2 2 2 3 5% 76%	7056
June	1st to 10th	Day	8% 4 1 4 3 3 3 3 5% 6% 60%	2801
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 5% 77%	2800
	21st to end	Day	3 1 2 1 1 1 1 3 3 83%	2800
July	1st to 10th	Day	1 1 1 1 1 2 93%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 1 1 2 89%	6320
	21st to end	Day	1 1 1 2 1 1 2 2 3 4 82%	6561
August	1st to 10th	Day	1 1 1 2 2 1 2 2 2 3 83%	5777
	11th to 20th	Day	1 1 1 1 1 2 2 91%	5432
	21st to end	Day	2 2 1 2 2 2 2 1 3 3 82%	5984
September	1st to 10th	Day	2 1 1 1 1 1 2 1 2 4 85%	2400
	11th to 20th	Day	5% 2 1 2 2 2 2 2 4 4 74%	2400
	21st to end	Day	5% 3 1 2 2 2 1 2 3 5% 76%	2168
October	1st to 10th	Day	5% 3 1 2 1 2 2 3 4 5% 71%	3280
	11th to 20th	Day	8% 3 1 3 2 2 2 2 4 6% 68%	3261
	21st to end	Day	7% 4 1 4 4 4 4 3 4 6% 59%	3558
November	1st to 10th	Day	14% 7% 2 3 3 3 3 3 4 6% 53%	1857
	11th to 20th	Day	16% 5% 1 3 4 3 4 4 4 7% 48%	1890
	21st to end	Day	12% 8% 2 4 3 3 4 3 4 5% 53%	1746
December	1st to 10th	Day	11% 4 1 3 2 3 3 4 5% 7% 57%	2700
	11th to 20th	Day	27% 10% 2 5% 3 3 3 3 5% 6% 32%	3108
	21st to end	Day	25% 8% 3 6% 3 4 4 3 5% 7% 32%	4092
January	1st to 10th	Night	20% 13% 2 4 3 3 4 3 4 6% 37%	8172
	11th to 20th	Night	12% 5% 1 3 2 3 3 3 4 5% 59%	7918
	21st to end	Night	13% 9% 2 6% 4 4 4 3 4 6% 44%	8371
February	1st to 10th	Night	20% 7% 2 4 3 3 3 2 4 6% 48%	2730
	11th to 20th	Night	15% 12% 1 4 3 4 5% 3 5% 6% 42%	2520
	21st to end	Night	17% 10% 3 4 2 2 3 3 4 5% 46%	2076
March	1st to 10th	Night	18% 20% 3 5% 3 3 3 2 4 6% 35%	5411
	11th to 20th	Night	20% 14% 2 3 2 2 2 2 3 5% 46%	5110
	21st to end	Night	19% 17% 2 5% 3 3 4 3 5% 6% 33%	5348
April	1st to 10th	Night	15% 11% 2 4 3 3 2 3 6% 6% 45%	2100
	11th to 20th	Night	14% 8% 2 4 3 3 3 3 4 6% 50%	2079
	21st to end	Night	11% 6% 1 3 3 2 3 2 5% 6% 58%	2100
May	1st to 10th	Night	4 6% 1 3 2 3 3 2 3 5% 68%	4427
	11th to 20th	Night	4 3 1 4 3 3 2 3 3 4 71%	3696
	21st to end	Night	4 2 1 2 1 2 2 2 3 4 77%	4060
June	1st to 10th	Night	8% 4 1 2 2 3 3 3 4 7% 64%	1600
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 5% 78%	1600
	21st to end	Night	3 2 1 2 2 1 2 1 3 3 81%	1600
July	1st to 10th	Night	1 1 1 1 1 1 1 93%	3640
	11th to 20th	Night	2 1 1 2 1 1 1 1 1 2 87%	3640
	21st to end	Night	1 1 1 2 2 2 2 2 4 5% 78%	4288
August	1st to 10th	Night	3 2 1 2 1 1 2 2 3 4 80%	4035
	11th to 20th	Night	1 1 1 1 1 1 2 3 90%	4435
	21st to end	Night	2 2 1 2 1 1 2 2 3 3 80%	5015
September	1st to 10th	Night	2 1 1 1 1 1 1 2 4 84%	2000
	11th to 20th	Night	4 2 1 3 2 2 3 2 3 4 76%	2000
	21st to end	Night	4 2 1 2 2 2 2 2 4 4 76%	2228
October	1st to 10th	Night	4 3 1 3 2 2 2 2 2 2 77%	3920
	11th to 20th	Night	4 2 1 2 2 1 2 2 3 4 76%	3897
	21st to end	Night	11% 3 1 3 2 2 3 3 4 6% 62%	4253
November	1st to 10th	Night	15% 6% 1 3 2 2 3 3 3 7% 54%	2660
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 8% 51%	2730
	21st to end	Night	13% 7% 2 4 3 3 3 3 3 6% 54%	2872
December	1st to 10th	Night	12% 4 1 2 1 2 3 3 4 6% 62%	4700
	11th to 20th	Night	25% 12% 2 4 3 3 4 3 6% 8% 29%	5316
	21st to end	Night	28% 11% 3 6% 4 3 4 3 4 5% 30%	7106

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	47% 3 10% 17% 16% 7%	4723
	11th to 20th	Day	32% 2 4 13% 21% 28%	5056
	21st to end	Day	40% 2 5% 18% 19% 16%	5843
February	1st to 10th	Day	42% 3 9% 17% 19% 11%	1890
	11th to 20th	Day	45% 3 7% 19% 19% 7%	1998
	21st to end	Day	44% 2 9% 22% 14% 8%	1730
March	1st to 10th	Day	57% 3 5% 13% 16% 6%	4697
	11th to 20th	Day	43% 2 9% 28% 15% 4	5110
	21st to end	Day	55% 4 11% 18% 11% 1	5867
April	1st to 10th	Day	44% 4 11% 22% 16% 3	2520
	11th to 20th	Day	37% 5% 12% 23% 17% 7%	2492
	21st to end	Day	31% 4 12% 28% 21% 4	2520
May	1st to 10th	Day	21% 2 9% 26% 29% 13%	5776
	11th to 20th	Day	19% 2 9% 28% 35% 7%	6420
	21st to end	Day	15% 3 6% 33% 37% 6%	7058
June	1st to 10th	Day	24% 5% 10% 23% 29% 9%	2801
	11th to 20th	Day	12% 3 7% 21% 36% 20%	2800
	21st to end	Day	10% 1 3 16% 39% 32%	2800
July	1st to 10th	Day	3 1 1 6% 21% 68%	6251
	11th to 20th	Day	6% 1 1 5% 14% 72%	6245
	21st to end	Day	10% 1 2 16% 30% 42%	6372
August	1st to 10th	Day	13% 1 1 8% 25% 52%	4206
	11th to 20th	Day	5% 1 2 7% 43% 43%	3924
	21st to end	Day	8% 1 1 11% 45% 35%	4311
September	1st to 10th	Day	8% 1 2 11% 33% 45%	2400
	11th to 20th	Day	16% 3 4 21% 38% 19%	2400
	21st to end	Day	15% 2 5% 18% 35% 25%	2168
October	1st to 10th	Day	17% 2 3 12% 33% 33%	3280
	11th to 20th	Day	20% 2 4 18% 40% 17%	3261
	21st to end	Day	27% 1 5% 23% 30% 14%	3558
November	1st to 10th	Day	34% 3 8% 19% 22% 13%	1857
	11th to 20th	Day	37% 3 10% 18% 22% 10%	1890
	21st to end	Day	34% 3 6% 19% 23% 14%	1746
December	1st to 10th	Day	28% 2 7% 21% 26% 16%	2700
	11th to 20th	Day	54% 2 7% 15% 14% 8%	3108
	21st to end	Day	51% 3 11% 18% 13% 4	4092
January	1st to 10th	Night	48% 3 10% 17% 15% 6%	8172
	11th to 20th	Night	29% 2 5% 10% 22% 31%	7918
	21st to end	Night	43% 3 4 12% 18% 20%	8371
February	1st to 10th	Night	41% 3 6% 18% 19% 13%	2730
	11th to 20th	Night	44% 4 7% 18% 20% 8%	2521
	21st to end	Night	42% 3 8% 21% 19% 7%	2076
March	1st to 10th	Night	54% 3 6% 17% 14% 7%	5411
	11th to 20th	Night	44% 2 7% 22% 21% 5%	5110
	21st to end	Night	53% 5% 10% 19% 10% 2	5348
April	1st to 10th	Night	40% 4 12% 22% 18% 5%	2100
	11th to 20th	Night	36% 4 13% 22% 18% 7%	2079
	21st to end	Night	29% 3 12% 32% 20% 3	2100
May	1st to 10th	Night	20% 5% 9% 26% 30% 10%	4424
	11th to 20th	Night	18% 3 8% 28% 31% 13%	3696
	21st to end	Night	13% 4 8% 30% 36% 9%	4060
June	1st to 10th	Night	21% 7% 10% 25% 26% 11%	1600
	11th to 20th	Night	11% 3 7% 22% 34% 23%	1600
	21st to end	Night	12% 1 4 14% 35% 35%	1600
July	1st to 10th	Night	3 1 1 6% 21% 68%	3600
	11th to 20th	Night	9% 1 1 5% 15% 70%	3592
	21st to end	Night	12% 1 2 13% 27% 45%	4166
August	1st to 10th	Night	15% 1 2 7% 24% 51%	2929
	11th to 20th	Night	5% 1 2 8% 39% 45%	3211
	21st to end	Night	9% 1 2 12% 36% 40%	3608
September	1st to 10th	Night	8% 1 3 9% 31% 48%	2000
	11th to 20th	Night	14% 2 5% 20% 38% 21%	2000
	21st to end	Night	13% 3 4 19% 33% 27%	2228
October	1st to 10th	Night	17% 2 3 11% 28% 40%	3920
	11th to 20th	Night	15% 1 4 24% 38% 18%	3897
	21st to end	Night	25% 2 4 22% 30% 17%	4253
November	1st to 10th	Night	33% 4 7% 21% 20% 15%	2660
	11th to 20th	Night	32% 4 10% 20% 22% 11%	2730
	21st to end	Night	33% 3 6% 20% 23% 15%	2872
December	1st to 10th	Night	26% 3 5% 20% 23% 22%	4700
	11th to 20th	Night	53% 2 5% 12% 20% 7%	5316
	21st to end	Night	57% 3 7% 15% 11% 6%	7106

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	41% 14% 19% 18% 7% 1	220
	11th to 20th	Day	23% 13% 22% 28% 11% 2	328
	21st to end	Day	24% 14% 24% 23% 12% 2	473
February	1st to 10th	Day	30% 14% 24% 22% 8% 1	430
	11th to 20th	Day	30% 19% 29% 18% 4	502
	21st to end	Day	26% 16% 33% 18% 6%	446
March	1st to 10th	Day	34% 23% 24% 13% 5% 1	540
	11th to 20th	Day	30% 18% 24% 17% 8% 2	540
	21st to end	Day	28% 23% 26% 17% 4 1	594
April	1st to 10th	Day	23% 22% 29% 17% 6% 2	540
	11th to 20th	Day	23% 21% 29% 20% 6% 1	532
	21st to end	Day	15% 20% 32% 24% 9% 1	540
May	1st to 10th	Day	16% 23% 29% 22% 7% 3	543
	11th to 20th	Day	16% 19% 31% 21% 9% 4	568
	21st to end	Day	12% 14% 31% 27% 11% 5%	617
June	1st to 10th	Day	9% 14% 33% 28% 11% 5%	531
	11th to 20th	Day	8% 16% 39% 23% 10% 4	530
	21st to end	Day	2 11% 37% 32% 12% 6%	530
July	1st to 10th	Day	1 7% 41% 33% 13% 5%	526
	11th to 20th	Day	1 4 39% 35% 15% 7%	524
	21st to end	Day	1 6% 35% 37% 15% 6%	575
August	1st to 10th	Day	4 5% 39% 34% 14% 5%	527
	11th to 20th	Day	2 9% 33% 38% 13% 5%	517
	21st to end	Day	2 6% 36% 40% 13% 4	583
September	1st to 10th	Day	2 9% 42% 31% 14% 2	530
	11th to 20th	Day	8% 12% 33% 32% 12% 3	530
	21st to end	Day	7% 13% 33% 35% 10% 2	530
October	1st to 10th	Day	8% 17% 30% 30% 12% 3	530
	11th to 20th	Day	9% 13% 27% 33% 14% 3	530
	21st to end	Day	13% 14% 27% 30% 13% 3	583
November	1st to 10th	Day	18% 12% 19% 27% 20% 4	333
	11th to 20th	Day	18% 12% 25% 27% 14% 4	330
	21st to end	Day	19% 11% 22% 28% 17% 3	254
December	1st to 10th	Day	22% 12% 20% 25% 14% 8%	220
	11th to 20th	Day	27% 11% 20% 22% 16% 4	220
	21st to end	Day	30% 11% 26% 21% 10% 2	242
January	1st to 10th	Night	27% 9% 23% 25% 12% 4	840
	11th to 20th	Night	19% 9% 29% 31% 10% 1	840
	21st to end	Night	23% 10% 24% 25% 16% 2	924
February	1st to 10th	Night	24% 10% 24% 29% 12% 1	840
	11th to 20th	Night	23% 10% 22% 28% 14% 3	824
	21st to end	Night	23% 12% 25% 30% 8% 2	692
March	1st to 10th	Night	28% 10% 23% 25% 12% 2	840
	11th to 20th	Night	25% 10% 17% 28% 19% 2	840
	21st to end	Night	26% 9% 23% 29% 13% 1	924
April	1st to 10th	Night	21% 7% 21% 33% 16% 2	840
	11th to 20th	Night	17% 10% 24% 31% 15% 3	831
	21st to end	Night	14% 7% 19% 36% 20% 3	840
May	1st to 10th	Night	11% 11% 23% 31% 21% 3	737
	11th to 20th	Night	10% 5% 19% 39% 23% 4	414
	21st to end	Night	11% 3 15% 35% 31% 5%	455
June	1st to 10th	Night	8% 3 14% 39% 31% 4	400
	11th to 20th	Night	3 5% 17% 42% 30% 4	400
	21st to end	Night	3 1 14% 43% 35% 4	400
July	1st to 10th	Night	1 12% 37% 47% 3	390
	11th to 20th	Night	1 1 11% 44% 39% 5%	388
	21st to end	Night	2 1 9% 34% 48% 7%	577
August	1st to 10th	Night	4 1 11% 39% 40% 6%	597
	11th to 20th	Night	1 1 12% 42% 36% 8%	759
	21st to end	Night	1 1 10% 44% 39% 5%	880
September	1st to 10th	Night	2 2 12% 43% 36% 4	800
	11th to 20th	Night	4 2 14% 39% 32% 9%	800
	21st to end	Night	5% 4 20% 37% 26% 8%	800
October	1st to 10th	Night	7% 6% 18% 42% 24% 4	800
	11th to 20th	Night	9% 6% 18% 36% 26% 4	800
	21st to end	Night	11% 7% 21% 30% 24% 6%	880
November	1st to 10th	Night	18% 5% 18% 30% 23% 5%	820
	11th to 20th	Night	15% 7% 26% 32% 17% 3	840
	21st to end	Night	16% 7% 26% 31% 16% 4	840
December	1st to 10th	Night	23% 8% 23% 31% 13% 3	840
	11th to 20th	Night	30% 8% 20% 28% 12% 2	840
	21st to end	Night	31% 11% 24% 24% 10%	924

Page generated at 2026-05-28 22:53:26. Version ac07

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