Washington(VT)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Washington(VT) clear sky chart from 2005-11-06 to 2026-07-16.

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	15% 11% 4 10% 6% 5% 5% 4 5% 7% 28%	137946
	Night	14% 12% 4 11% 7% 5% 5% 4 5% 6% 27%	134766
Transparency	Day	52% 7% 11% 19% 10% 1	141429
	Night	54% 7% 11% 18% 9% 1	139372
Seeing	Day	26% 18% 29% 18% 8% 2	16899
	Night	23% 15% 27% 25% 9% 1	25800

By Month

Percentage Cloud Cover NE (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	8% 12% 7% 21% 13% 7% 4 3 4 4 17%	4661
	11th to 20th	Day	9% 14% 6% 16% 14% 6% 4 3 5% 5% 19%	4650
	21st to end	Day	7% 13% 8% 13% 8% 9% 6% 3 5% 5% 23%	5124
February	1st to 10th	Day	10% 12% 6% 11% 9% 7% 5% 4 6% 6% 23%	1833
	11th to 20th	Day	7% 13% 6% 14% 9% 6% 5% 4 5% 7% 23%	2048
	21st to end	Day	11% 14% 5% 13% 7% 5% 5% 4 4 6% 25%	1730
March	1st to 10th	Day	17% 16% 6% 15% 5% 5% 4 3 3 4 23%	4576
	11th to 20th	Day	12% 12% 6% 11% 5% 5% 4 3 5% 6% 31%	4754
	21st to end	Day	19% 12% 5% 12% 6% 4 4 3 4 5% 27%	6091
April	1st to 10th	Day	18% 15% 4 9% 5% 4 4 3 4 6% 29%	2520
	11th to 20th	Day	17% 13% 3 7% 6% 4 4 4 5% 5% 31%	2494
	21st to end	Day	20% 12% 4 8% 5% 5% 5% 3 5% 5% 29%	2724
May	1st to 10th	Day	25% 14% 4 9% 5% 5% 5% 3 5% 5% 19%	7690
	11th to 20th	Day	15% 11% 3 9% 6% 5% 5% 4 6% 7% 28%	8221
	21st to end	Day	18% 9% 3 7% 5% 5% 5% 5% 6% 6% 29%	9060
June	1st to 10th	Day	21% 8% 3 8% 5% 5% 6% 5% 5% 7% 28%	2940
	11th to 20th	Day	16% 8% 3 6% 6% 6% 5% 5% 6% 7% 33%	2940
	21st to end	Day	18% 9% 3 8% 5% 5% 5% 4 6% 8% 27%	2940
July	1st to 10th	Day	12% 8% 2 7% 5% 5% 6% 6% 8% 10% 31%	6500
	11th to 20th	Day	11% 6% 2 7% 5% 5% 7% 5% 8% 9% 34%	6430
	21st to end	Day	14% 7% 2 6% 4 5% 5% 4 7% 8% 38%	6926
August	1st to 10th	Day	15% 7% 3 8% 6% 5% 6% 5% 6% 9% 31%	4501
	11th to 20th	Day	14% 10% 3 8% 5% 5% 6% 5% 7% 10% 27%	4081
	21st to end	Day	11% 8% 3 6% 4 5% 5% 4 6% 9% 39%	4312
September	1st to 10th	Day	12% 7% 2 5% 3 5% 4 4 6% 8% 45%	2400
	11th to 20th	Day	14% 6% 2 7% 4 3 4 3 5% 6% 47%	2255
	21st to end	Day	16% 8% 3 5% 4 4 4 3 6% 8% 39%	2200
October	1st to 10th	Day	20% 10% 3 8% 5% 4 3 3 4 6% 34%	2164
	11th to 20th	Day	15% 12% 4 8% 5% 4 4 4 5% 8% 33%	1918
	21st to end	Day	21% 17% 4 9% 5% 5% 4 3 3 4 26%	1980
November	1st to 10th	Day	13% 13% 5% 7% 5% 4 4 3 6% 6% 34%	1851
	11th to 20th	Day	15% 14% 5% 11% 6% 5% 5% 3 5% 5% 27%	1890
	21st to end	Day	17% 15% 5% 13% 6% 4 4 4 5% 6% 23%	1748
December	1st to 10th	Day	10% 19% 6% 23% 8% 5% 4 3 4 5% 13%	2680
	11th to 20th	Day	16% 14% 7% 12% 6% 5% 5% 3 4 5% 25%	3066
	21st to end	Day	16% 13% 6% 14% 7% 5% 5% 3 4 4 23%	4048
January	1st to 10th	Night	9% 11% 6% 19% 11% 8% 6% 4 4 4 17%	8234
	11th to 20th	Night	8% 14% 6% 20% 13% 7% 5% 4 4 5% 13%	8235
	21st to end	Night	9% 11% 5% 13% 9% 11% 8% 4 5% 5% 21%	9057
February	1st to 10th	Night	11% 12% 6% 13% 9% 6% 5% 5% 6% 6% 22%	2782
	11th to 20th	Night	8% 11% 5% 14% 9% 7% 6% 5% 5% 6% 24%	2458
	21st to end	Night	10% 11% 4 14% 8% 6% 5% 3 5% 6% 28%	2076
March	1st to 10th	Night	19% 14% 4 11% 7% 6% 5% 3 5% 5% 22%	5484
	11th to 20th	Night	13% 14% 5% 11% 6% 5% 4 3 4 6% 28%	5423
	21st to end	Night	19% 15% 5% 11% 5% 4 4 3 3 5% 27%	5078
April	1st to 10th	Night	19% 13% 4 9% 5% 4 5% 4 4 5% 29%	2100
	11th to 20th	Night	18% 14% 3 7% 5% 5% 4 3 5% 6% 31%	2075
	21st to end	Night	19% 11% 4 7% 4 4 4 4 4 5% 34%	1895
May	1st to 10th	Night	26% 15% 4 7% 4 4 3 3 5% 6% 23%	5259
	11th to 20th	Night	16% 11% 3 8% 5% 5% 5% 4 6% 7% 30%	4644
	21st to end	Night	17% 10% 3 7% 5% 4 4 4 7% 7% 31%	5114
June	1st to 10th	Night	18% 9% 2 7% 6% 5% 5% 3 6% 7% 33%	1680
	11th to 20th	Night	18% 8% 2 6% 5% 4 4 4 5% 7% 36%	1680
	21st to end	Night	19% 7% 2 6% 5% 5% 4 4 6% 9% 33%	1680
July	1st to 10th	Night	11% 7% 3 8% 6% 5% 6% 5% 7% 9% 34%	3680
	11th to 20th	Night	16% 7% 3 8% 5% 4 5% 4 5% 8% 36%	3640
	21st to end	Night	10% 8% 2 7% 5% 4 5% 4 5% 7% 43%	3926
August	1st to 10th	Night	19% 10% 3 7% 4 4 4 3 5% 6% 35%	2615
	11th to 20th	Night	15% 8% 4 6% 4 4 5% 3 6% 8% 37%	2962
	21st to end	Night	10% 9% 2 6% 4 4 4 4 7% 9% 42%	3586
September	1st to 10th	Night	12% 7% 2 6% 4 3 3 3 4 8% 47%	2000
	11th to 20th	Night	13% 6% 3 5% 4 4 3 4 5% 6% 48%	2145
	21st to end	Night	14% 8% 2 5% 4 4 5% 4 6% 7% 41%	2200
October	1st to 10th	Night	18% 8% 3 7% 5% 4 4 3 4 7% 35%	2233
	11th to 20th	Night	14% 12% 3 9% 5% 4 3 4 5% 6% 34%	2481
	21st to end	Night	21% 14% 3 8% 5% 4 5% 3 5% 6% 25%	2860
November	1st to 10th	Night	16% 13% 4 9% 4 3 4 4 5% 5% 32%	2667
	11th to 20th	Night	15% 11% 6% 10% 5% 4 4 4 6% 6% 29%	2730
	21st to end	Night	15% 12% 6% 13% 6% 4 4 3 5% 6% 26%	2869
December	1st to 10th	Night	12% 15% 6% 20% 8% 6% 5% 3 4 4 14%	4720
	11th to 20th	Night	18% 16% 6% 12% 6% 5% 4 3 4 5% 21%	5348
	21st to end	Night	16% 14% 6% 16% 7% 6% 5% 3 4 4 20%	7150

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	66% 8% 8% 14% 4	4662
	11th to 20th	Day	62% 7% 9% 12% 8% 2	4680
	21st to end	Day	57% 6% 10% 14% 11% 1	5124
February	1st to 10th	Day	58% 7% 9% 17% 7% 2	1833
	11th to 20th	Day	59% 7% 9% 16% 8% 1	2057
	21st to end	Day	58% 6% 10% 14% 11% 2	1730
March	1st to 10th	Day	64% 5% 7% 10% 9% 5%	4579
	11th to 20th	Day	52% 6% 14% 17% 9% 3	4754
	21st to end	Day	58% 4 6% 13% 16% 2	6091
April	1st to 10th	Day	56% 5% 8% 17% 12% 2	2520
	11th to 20th	Day	52% 7% 8% 17% 15% 1	2494
	21st to end	Day	56% 6% 8% 17% 12% 2	2724
May	1st to 10th	Day	63% 7% 8% 14% 7% 1	7702
	11th to 20th	Day	51% 9% 14% 17% 8% 1	8225
	21st to end	Day	49% 9% 11% 22% 8%	9061
June	1st to 10th	Day	53% 7% 12% 18% 10%	2940
	11th to 20th	Day	47% 7% 11% 21% 13% 1	2940
	21st to end	Day	53% 8% 11% 19% 8% 1	2940
July	1st to 10th	Day	42% 9% 17% 22% 10%	6430
	11th to 20th	Day	40% 10% 15% 24% 10%	6355
	21st to end	Day	40% 8% 12% 30% 10%	6728
August	1st to 10th	Day	46% 9% 15% 21% 9%	4487
	11th to 20th	Day	47% 9% 17% 22% 5%	4120
	21st to end	Day	38% 9% 17% 22% 13% 1	4312
September	1st to 10th	Day	35% 7% 12% 32% 13% 1	2400
	11th to 20th	Day	36% 6% 9% 31% 17% 1	2255
	21st to end	Day	41% 6% 14% 24% 12% 2	2200
October	1st to 10th	Day	45% 8% 11% 22% 13% 1	3528
	11th to 20th	Day	44% 5% 13% 24% 12% 1	3095
	21st to end	Day	47% 5% 10% 27% 9% 1	3180
November	1st to 10th	Day	49% 6% 13% 20% 12%	1851
	11th to 20th	Day	55% 8% 10% 13% 13% 2	1890
	21st to end	Day	59% 7% 13% 15% 4	1748
December	1st to 10th	Day	71% 7% 10% 8% 3	2680
	11th to 20th	Day	61% 5% 7% 16% 10% 1	3066
	21st to end	Day	63% 6% 6% 12% 11% 3	4048
January	1st to 10th	Night	63% 10% 11% 12% 4	8234
	11th to 20th	Night	66% 10% 9% 7% 6% 1	8280
	21st to end	Night	59% 7% 9% 14% 10% 2	9057
February	1st to 10th	Night	58% 8% 10% 15% 9% 1	2782
	11th to 20th	Night	56% 7% 9% 18% 9% 1	2460
	21st to end	Night	52% 7% 11% 17% 9% 3	2076
March	1st to 10th	Night	61% 5% 9% 13% 10% 2	5494
	11th to 20th	Night	53% 8% 15% 13% 10% 2	5424
	21st to end	Night	57% 5% 6% 13% 16% 2	5078
April	1st to 10th	Night	55% 5% 8% 18% 13% 2	2100
	11th to 20th	Night	52% 6% 8% 22% 12%	2075
	21st to end	Night	51% 5% 8% 18% 15% 3	1895
May	1st to 10th	Night	60% 6% 10% 14% 9% 1	5265
	11th to 20th	Night	51% 8% 12% 20% 8% 1	4645
	21st to end	Night	48% 8% 12% 23% 9% 1	5115
June	1st to 10th	Night	48% 8% 11% 22% 11% 1	1680
	11th to 20th	Night	45% 9% 13% 20% 11% 2	1680
	21st to end	Night	47% 7% 13% 23% 9% 1	1680
July	1st to 10th	Night	42% 9% 18% 21% 10%	3640
	11th to 20th	Night	44% 8% 13% 25% 11%	3592
	21st to end	Night	36% 9% 15% 31% 8%	3809
August	1st to 10th	Night	49% 7% 12% 23% 9%	2605
	11th to 20th	Night	42% 8% 18% 22% 10%	2989
	21st to end	Night	34% 9% 19% 26% 12% 1	3586
September	1st to 10th	Night	36% 6% 14% 31% 13%	2000
	11th to 20th	Night	36% 6% 11% 31% 15% 1	2145
	21st to end	Night	39% 7% 12% 25% 14% 2	2200
October	1st to 10th	Night	48% 8% 12% 23% 10% 1	3649
	11th to 20th	Night	46% 5% 12% 21% 14% 2	4043
	21st to end	Night	47% 6% 12% 25% 9% 1	4610
November	1st to 10th	Night	51% 7% 12% 20% 9% 2	2667
	11th to 20th	Night	51% 7% 11% 18% 11% 2	2730
	21st to end	Night	56% 7% 12% 18% 6%	2869
December	1st to 10th	Night	67% 8% 10% 12% 2	4720
	11th to 20th	Night	62% 7% 8% 12% 12%	5348
	21st to end	Night	66% 6% 6% 13% 6% 3	7150

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	23% 27% 27% 18% 4	220
	11th to 20th	Day	32% 25% 27% 11% 4 1	220
	21st to end	Day	26% 25% 31% 14% 5%	242
February	1st to 10th	Day	33% 30% 28% 7% 2	308
	11th to 20th	Day	32% 24% 31% 11% 2	536
	21st to end	Day	30% 24% 30% 13% 3	446
March	1st to 10th	Day	33% 18% 32% 14% 3	540
	11th to 20th	Day	31% 27% 27% 11% 4	540
	21st to end	Day	36% 21% 24% 12% 5% 2	594
April	1st to 10th	Day	37% 21% 25% 11% 5% 1	540
	11th to 20th	Day	38% 21% 22% 13% 5% 2	532
	21st to end	Day	34% 21% 26% 11% 6% 1	540
May	1st to 10th	Day	37% 21% 24% 11% 6% 2	543
	11th to 20th	Day	24% 20% 33% 17% 5% 2	567
	21st to end	Day	20% 20% 32% 20% 7% 1	617
June	1st to 10th	Day	25% 14% 35% 18% 8% 1	570
	11th to 20th	Day	22% 17% 32% 20% 7% 2	570
	21st to end	Day	21% 17% 33% 21% 6% 2	570
July	1st to 10th	Day	15% 12% 36% 25% 10% 2	565
	11th to 20th	Day	15% 11% 35% 27% 10% 3	544
	21st to end	Day	15% 12% 35% 27% 9% 2	576
August	1st to 10th	Day	13% 12% 29% 27% 15% 4	526
	11th to 20th	Day	20% 9% 27% 22% 14% 7%	519
	21st to end	Day	13% 14% 29% 25% 13% 6%	583
September	1st to 10th	Day	15% 16% 25% 24% 13% 7%	530
	11th to 20th	Day	17% 11% 24% 22% 15% 12%	530
	21st to end	Day	21% 11% 28% 22% 12% 5%	530
October	1st to 10th	Day	26% 14% 23% 19% 13% 5%	530
	11th to 20th	Day	23% 20% 25% 21% 9% 2	484
	21st to end	Day	35% 17% 25% 18% 5%	462
November	1st to 10th	Day	28% 20% 22% 20% 10% 1	425
	11th to 20th	Day	27% 23% 28% 17% 5% 1	430
	21st to end	Day	36% 19% 24% 16% 5%	288
December	1st to 10th	Day	30% 20% 29% 15% 5%	220
	11th to 20th	Day	34% 22% 30% 11% 2	220
	21st to end	Day	33% 18% 29% 17% 3	242
January	1st to 10th	Night	22% 21% 33% 20% 4	840
	11th to 20th	Night	27% 18% 29% 22% 4	840
	21st to end	Night	17% 22% 34% 23% 4	924
February	1st to 10th	Night	21% 19% 34% 23% 3	840
	11th to 20th	Night	21% 23% 34% 19% 3	823
	21st to end	Night	21% 19% 34% 22% 4	692
March	1st to 10th	Night	26% 18% 32% 21% 3	840
	11th to 20th	Night	26% 20% 27% 21% 5%	840
	21st to end	Night	27% 18% 29% 19% 6%	924
April	1st to 10th	Night	29% 19% 28% 20% 5%	840
	11th to 20th	Night	26% 20% 27% 20% 6%	831
	21st to end	Night	29% 17% 28% 20% 6%	635
May	1st to 10th	Night	29% 14% 29% 21% 6% 1	630
	11th to 20th	Night	18% 14% 33% 30% 5% 1	419
	21st to end	Night	20% 10% 29% 30% 11%	455
June	1st to 10th	Night	21% 8% 26% 34% 12%	420
	11th to 20th	Night	20% 11% 26% 30% 13%	420
	21st to end	Night	21% 5% 27% 35% 11% 1	420
July	1st to 10th	Night	17% 6% 21% 41% 15% 1	410
	11th to 20th	Night	16% 5% 21% 37% 19% 2	398
	21st to end	Night	14% 6% 22% 40% 18%	438
August	1st to 10th	Night	15% 5% 16% 38% 25%	414
	11th to 20th	Night	18% 5% 22% 33% 19% 3	643
	21st to end	Night	15% 8% 18% 36% 21% 3	880
September	1st to 10th	Night	15% 9% 25% 31% 19% 2	800
	11th to 20th	Night	16% 9% 20% 29% 22% 5%	800
	21st to end	Night	18% 10% 24% 28% 19% 2	800
October	1st to 10th	Night	24% 12% 18% 28% 16% 2	800
	11th to 20th	Night	22% 15% 23% 28% 12% 1	800
	21st to end	Night	30% 14% 27% 23% 6%	880
November	1st to 10th	Night	24% 17% 25% 26% 8%	820
	11th to 20th	Night	22% 18% 29% 21% 8% 1	840
	21st to end	Night	24% 20% 26% 23% 6%	840
December	1st to 10th	Night	28% 20% 30% 19% 4	840
	11th to 20th	Night	29% 18% 26% 22% 4	840
	21st to end	Night	28% 20% 27% 20% 4	924

Page generated at 2026-07-13 03:14:54. Version ac07

Copyright © 2026 Attilla Danko.