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 2024-02-10.

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	16% 10% 4 8% 7% 4 5% 5% 5% 7% 30%	78112
	Night	16% 11% 5% 9% 7% 4 5% 5% 5% 6% 29%	80845
Transparency	Day	53% 7% 11% 19% 10% 1	77817
	Night	53% 7% 11% 19% 9% 1	80674
Seeing	Day	25% 17% 28% 19% 8% 2	13729
	Night	22% 15% 27% 26% 9% 1	22827

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	11% 12% 7% 16% 10% 5% 4 4 4 5% 22%	2517
	11th to 20th	Day	13% 12% 6% 15% 13% 5% 5% 4 4 5% 21%	2520
	21st to end	Day	12% 16% 10% 13% 7% 5% 5% 4 4 4 19%	2772
February	1st to 10th	Day	11% 12% 7% 9% 9% 5% 6% 5% 5% 6% 24%	1648
	11th to 20th	Day	8% 13% 7% 12% 11% 5% 5% 5% 5% 7% 23%	1748
	21st to end	Day	12% 13% 6% 12% 8% 4 6% 5% 5% 6% 25%	1480
March	1st to 10th	Day	12% 12% 7% 11% 8% 4 6% 5% 4 5% 26%	1797
	11th to 20th	Day	15% 13% 6% 10% 6% 3 4 4 4 6% 29%	1847
	21st to end	Day	16% 12% 6% 8% 7% 3 4 4 4 5% 31%	2366
April	1st to 10th	Day	19% 12% 5% 8% 6% 3 4 4 4 6% 30%	2160
	11th to 20th	Day	17% 11% 4 6% 7% 3 4 5% 5% 6% 32%	2134
	21st to end	Day	22% 11% 5% 7% 6% 3 5% 4 5% 6% 26%	2334
May	1st to 10th	Day	21% 11% 4 6% 6% 3 5% 4 4 6% 29%	2350
	11th to 20th	Day	18% 9% 4 6% 5% 3 5% 4 4 7% 35%	2478
	21st to end	Day	14% 8% 3 6% 7% 4 5% 5% 6% 8% 35%	2725
June	1st to 10th	Day	23% 8% 3 7% 5% 3 6% 6% 5% 7% 27%	2520
	11th to 20th	Day	18% 7% 3 5% 6% 4 5% 6% 5% 7% 34%	2520
	21st to end	Day	19% 9% 4 8% 6% 4 5% 5% 6% 8% 26%	2520
July	1st to 10th	Day	16% 7% 3 5% 6% 3 5% 6% 6% 7% 36%	2520
	11th to 20th	Day	13% 6% 3 6% 8% 4 6% 7% 7% 8% 32%	2520
	21st to end	Day	16% 5% 2 5% 7% 3 7% 6% 7% 8% 33%	2744
August	1st to 10th	Day	13% 6% 3 7% 7% 4 7% 6% 6% 9% 33%	2473
	11th to 20th	Day	15% 7% 3 5% 6% 4 6% 6% 7% 10% 31%	2255
	21st to end	Day	13% 7% 3 6% 6% 3 6% 5% 6% 9% 37%	2376
September	1st to 10th	Day	13% 7% 2 4 4 4 4 5% 6% 8% 43%	2160
	11th to 20th	Day	15% 6% 2 6% 5% 2 4 3 4 6% 45%	2030
	21st to end	Day	15% 7% 3 5% 4 3 4 5% 6% 9% 39%	1980
October	1st to 10th	Day	22% 10% 3 7% 6% 3 4 4 4 6% 31%	1948
	11th to 20th	Day	14% 11% 4 7% 7% 3 4 5% 5% 7% 33%	1727
	21st to end	Day	23% 16% 5% 7% 5% 4 4 4 3 5% 24%	1782
November	1st to 10th	Day	13% 12% 5% 6% 6% 2 5% 4 5% 7% 35%	1671
	11th to 20th	Day	16% 12% 5% 10% 7% 4 5% 5% 5% 5% 26%	1710
	21st to end	Day	17% 12% 4 11% 7% 3 5% 5% 5% 6% 25%	1582
December	1st to 10th	Day	17% 18% 5% 12% 8% 4 4 4 4 7% 18%	1520
	11th to 20th	Day	19% 14% 5% 8% 6% 3 4 4 4 6% 25%	1906
	21st to end	Day	21% 14% 6% 13% 8% 4 4 4 3 4 19%	2772
January	1st to 10th	Night	14% 12% 5% 11% 9% 4 6% 6% 5% 6% 22%	4429
	11th to 20th	Night	11% 13% 6% 15% 13% 5% 6% 5% 5% 5% 16%	4440
	21st to end	Night	16% 15% 8% 14% 8% 5% 5% 4 4 4 19%	4884
February	1st to 10th	Night	12% 11% 6% 11% 10% 4 6% 5% 5% 6% 22%	2512
	11th to 20th	Night	10% 11% 5% 11% 10% 6% 7% 6% 5% 6% 24%	2098
	21st to end	Night	10% 11% 4 12% 9% 5% 5% 5% 5% 6% 27%	1776
March	1st to 10th	Night	12% 12% 6% 10% 9% 5% 5% 5% 5% 5% 27%	2150
	11th to 20th	Night	13% 12% 5% 10% 7% 4 6% 4 4 5% 28%	2110
	21st to end	Night	16% 11% 4 7% 7% 3 4 5% 4 6% 33%	1986
April	1st to 10th	Night	19% 12% 5% 7% 6% 3 4 5% 4 5% 30%	1800
	11th to 20th	Night	17% 12% 3 6% 5% 3 5% 4 6% 6% 33%	1775
	21st to end	Night	20% 11% 5% 6% 5% 4 4 4 4 6% 32%	1625
May	1st to 10th	Night	21% 12% 4 7% 5% 3 3 4 5% 6% 30%	1620
	11th to 20th	Night	17% 9% 3 5% 5% 3 4 5% 6% 6% 36%	1420
	21st to end	Night	14% 8% 3 5% 5% 3 5% 5% 7% 7% 37%	1550
June	1st to 10th	Night	19% 8% 3 5% 7% 3 6% 5% 6% 7% 31%	1440
	11th to 20th	Night	19% 6% 3 6% 5% 3 4 4 5% 7% 38%	1440
	21st to end	Night	18% 6% 3 6% 5% 4 5% 5% 6% 10% 34%	1440
July	1st to 10th	Night	15% 5% 2 5% 6% 3 4 6% 5% 8% 40%	1440
	11th to 20th	Night	15% 5% 2 4 4 3 4 6% 7% 10% 41%	1440
	21st to end	Night	12% 6% 2 5% 5% 3 6% 6% 6% 8% 41%	1574
August	1st to 10th	Night	13% 6% 2 5% 5% 3 4 5% 6% 8% 43%	1446
	11th to 20th	Night	13% 7% 4 4 5% 3 4 4 6% 10% 40%	1641
	21st to end	Night	13% 6% 3 4 5% 3 4 5% 6% 8% 42%	1980
September	1st to 10th	Night	13% 6% 3 5% 5% 2 3 5% 4 8% 46%	1800
	11th to 20th	Night	14% 6% 3 5% 4 2 3 5% 5% 6% 47%	1930
	21st to end	Night	14% 7% 3 4 5% 3 5% 4 6% 7% 42%	1980
October	1st to 10th	Night	20% 8% 3 7% 6% 3 5% 4 4 7% 33%	2009
	11th to 20th	Night	15% 12% 3 8% 6% 4 4 5% 5% 6% 32%	2232
	21st to end	Night	22% 14% 4 7% 6% 3 4 5% 5% 6% 25%	2574
November	1st to 10th	Night	15% 12% 4 8% 6% 3 4 5% 5% 6% 32%	2407
	11th to 20th	Night	16% 10% 6% 9% 6% 4 4 4 6% 6% 29%	2470
	21st to end	Night	16% 11% 6% 11% 7% 3 4 4 4 6% 26%	2595
December	1st to 10th	Night	17% 16% 6% 13% 8% 5% 5% 5% 4 5% 16%	2660
	11th to 20th	Night	19% 13% 6% 11% 6% 4 4 5% 5% 7% 20%	3288
	21st to end	Night	21% 13% 7% 15% 8% 4 4 4 4 4 17%	4884

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	58% 9% 9% 19% 5%	2518
	11th to 20th	Day	66% 7% 8% 14% 5% 1	2520
	21st to end	Day	66% 5% 9% 12% 6% 1	2772
February	1st to 10th	Day	59% 7% 10% 16% 7% 2	1648
	11th to 20th	Day	59% 6% 9% 16% 8% 1	1757
	21st to end	Day	59% 5% 10% 13% 11% 2	1480
March	1st to 10th	Day	59% 6% 10% 14% 10% 2	1800
	11th to 20th	Day	56% 4 10% 14% 13% 3	1847
	21st to end	Day	55% 5% 8% 16% 13% 4	2366
April	1st to 10th	Day	56% 5% 8% 18% 11% 2	2160
	11th to 20th	Day	50% 7% 8% 18% 15% 1	2134
	21st to end	Day	59% 5% 8% 15% 10% 2	2334
May	1st to 10th	Day	56% 4 7% 20% 10% 2	2350
	11th to 20th	Day	49% 6% 8% 20% 15% 2	2482
	21st to end	Day	46% 7% 14% 21% 10% 2	2725
June	1st to 10th	Day	54% 7% 13% 17% 9%	2520
	11th to 20th	Day	47% 6% 10% 21% 14% 1	2520
	21st to end	Day	54% 8% 11% 18% 8% 1	2520
July	1st to 10th	Day	42% 7% 13% 23% 14% 1	2450
	11th to 20th	Day	45% 9% 13% 24% 9%	2445
	21st to end	Day	44% 9% 13% 23% 11%	2591
August	1st to 10th	Day	44% 9% 15% 22% 9%	2459
	11th to 20th	Day	46% 7% 16% 22% 9%	2255
	21st to end	Day	41% 8% 13% 24% 13% 1	2376
September	1st to 10th	Day	37% 7% 12% 30% 13% 1	2160
	11th to 20th	Day	38% 5% 8% 30% 16% 2	2030
	21st to end	Day	41% 6% 15% 24% 12% 2	1980
October	1st to 10th	Day	54% 5% 9% 19% 11% 1	1948
	11th to 20th	Day	49% 7% 14% 23% 6% 1	1727
	21st to end	Day	63% 5% 8% 15% 8% 2	1782
November	1st to 10th	Day	48% 6% 13% 20% 13%	1671
	11th to 20th	Day	55% 8% 10% 13% 11% 2	1710
	21st to end	Day	57% 7% 14% 16% 4 1	1582
December	1st to 10th	Day	66% 6% 11% 12% 4	1520
	11th to 20th	Day	59% 6% 9% 16% 9% 1	1906
	21st to end	Day	68% 6% 7% 11% 7%	2772
January	1st to 10th	Night	55% 10% 14% 16% 5%	4429
	11th to 20th	Night	63% 11% 11% 10% 5% 1	4440
	21st to end	Night	67% 6% 7% 12% 6% 1	4884
February	1st to 10th	Night	58% 7% 10% 14% 9% 1	2512
	11th to 20th	Night	56% 7% 9% 17% 10% 1	2100
	21st to end	Night	53% 7% 11% 17% 9% 2	1776
March	1st to 10th	Night	57% 5% 9% 17% 10% 2	2160
	11th to 20th	Night	56% 6% 9% 17% 10% 2	2111
	21st to end	Night	49% 5% 10% 19% 14% 3	1986
April	1st to 10th	Night	55% 4 8% 19% 12% 2	1800
	11th to 20th	Night	49% 6% 8% 23% 13% 1	1775
	21st to end	Night	53% 5% 8% 17% 13% 3	1625
May	1st to 10th	Night	54% 4 7% 18% 14% 2	1620
	11th to 20th	Night	46% 6% 10% 20% 16% 2	1421
	21st to end	Night	44% 7% 15% 23% 11% 1	1551
June	1st to 10th	Night	50% 8% 12% 20% 10% 1	1440
	11th to 20th	Night	46% 8% 12% 20% 11% 2	1440
	21st to end	Night	46% 8% 14% 23% 10%	1440
July	1st to 10th	Night	39% 8% 17% 22% 14% 1	1400
	11th to 20th	Night	35% 8% 18% 27% 12%	1392
	21st to end	Night	37% 9% 14% 28% 11% 1	1486
August	1st to 10th	Night	37% 7% 15% 30% 10%	1436
	11th to 20th	Night	40% 6% 17% 26% 11%	1641
	21st to end	Night	38% 7% 15% 27% 12%	1980
September	1st to 10th	Night	36% 7% 15% 30% 11%	1800
	11th to 20th	Night	38% 6% 11% 30% 14% 1	1930
	21st to end	Night	39% 7% 12% 25% 14% 2	1980
October	1st to 10th	Night	50% 6% 11% 21% 11% 1	2009
	11th to 20th	Night	50% 6% 13% 23% 7%	2232
	21st to end	Night	59% 6% 9% 16% 9% 1	2574
November	1st to 10th	Night	50% 7% 11% 20% 10% 2	2407
	11th to 20th	Night	51% 7% 11% 18% 10% 2	2470
	21st to end	Night	56% 7% 12% 18% 6%	2595
December	1st to 10th	Night	68% 7% 9% 13% 4	2660
	11th to 20th	Night	60% 9% 10% 13% 9%	3288
	21st to end	Night	69% 5% 7% 14% 4	4884

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	22% 24% 28% 21% 5% 1	180
	11th to 20th	Day	31% 26% 26% 12% 4 1	180
	21st to end	Day	22% 25% 33% 14% 6% 1	198
February	1st to 10th	Day	34% 30% 27% 6% 3	249
	11th to 20th	Day	31% 23% 30% 13% 3	416
	21st to end	Day	30% 22% 31% 14% 3 1	346
March	1st to 10th	Day	31% 16% 35% 15% 4	420
	11th to 20th	Day	28% 27% 27% 12% 5%	420
	21st to end	Day	32% 20% 25% 15% 7% 2	462
April	1st to 10th	Day	35% 20% 25% 13% 6% 1	420
	11th to 20th	Day	33% 22% 22% 16% 6% 2	412
	21st to end	Day	34% 19% 27% 11% 7% 1	420
May	1st to 10th	Day	35% 21% 23% 12% 7% 2	423
	11th to 20th	Day	22% 20% 34% 16% 5% 2	447
	21st to end	Day	18% 19% 32% 22% 8% 1	485
June	1st to 10th	Day	27% 14% 35% 17% 6% 1	450
	11th to 20th	Day	22% 16% 30% 21% 8% 2	450
	21st to end	Day	20% 15% 32% 23% 7% 2	450
July	1st to 10th	Day	18% 12% 29% 27% 11% 3	445
	11th to 20th	Day	15% 9% 35% 27% 11% 3	444
	21st to end	Day	14% 11% 37% 26% 10% 2	488
August	1st to 10th	Day	14% 12% 29% 25% 16% 3	446
	11th to 20th	Day	19% 9% 28% 23% 14% 7%	439
	21st to end	Day	14% 14% 28% 24% 13% 6%	495
September	1st to 10th	Day	15% 15% 25% 25% 14% 7%	450
	11th to 20th	Day	19% 12% 25% 20% 14% 10%	450
	21st to end	Day	20% 11% 30% 22% 12% 6%	450
October	1st to 10th	Day	28% 14% 23% 18% 12% 5%	450
	11th to 20th	Day	22% 20% 25% 23% 9% 2	413
	21st to end	Day	36% 17% 23% 18% 6%	396
November	1st to 10th	Day	25% 18% 23% 23% 11% 1	365
	11th to 20th	Day	28% 23% 26% 17% 5% 1	370
	21st to end	Day	33% 17% 26% 18% 6%	242
December	1st to 10th	Day	31% 20% 28% 15% 6% 1	180
	11th to 20th	Day	31% 23% 31% 13% 2	180
	21st to end	Day	34% 19% 28% 15% 4	198
January	1st to 10th	Night	21% 20% 33% 22% 4	760
	11th to 20th	Night	27% 18% 28% 23% 4	760
	21st to end	Night	17% 20% 34% 24% 4	836
February	1st to 10th	Night	21% 19% 34% 23% 4	759
	11th to 20th	Night	20% 23% 35% 19% 3	703
	21st to end	Night	21% 20% 32% 23% 4	592
March	1st to 10th	Night	24% 17% 33% 23% 3	720
	11th to 20th	Night	25% 21% 27% 22% 5% 1	720
	21st to end	Night	26% 17% 28% 21% 7% 1	792
April	1st to 10th	Night	28% 17% 28% 22% 5%	720
	11th to 20th	Night	23% 21% 27% 22% 7%	711
	21st to end	Night	29% 16% 29% 21% 5%	545
May	1st to 10th	Night	29% 14% 28% 22% 6% 1	540
	11th to 20th	Night	18% 14% 31% 30% 6% 1	359
	21st to end	Night	19% 9% 29% 31% 12%	389
June	1st to 10th	Night	23% 8% 26% 33% 11%	360
	11th to 20th	Night	20% 9% 26% 32% 13% 1	360
	21st to end	Night	20% 4 27% 36% 12% 1	360
July	1st to 10th	Night	18% 4 21% 39% 16% 1	350
	11th to 20th	Night	16% 3 23% 37% 20% 2	348
	21st to end	Night	14% 5% 22% 40% 19% 1	394
August	1st to 10th	Night	15% 4 17% 40% 24%	372
	11th to 20th	Night	17% 5% 23% 34% 18% 3	577
	21st to end	Night	17% 7% 17% 35% 21% 3	792
September	1st to 10th	Night	14% 8% 25% 31% 19% 2	720
	11th to 20th	Night	18% 10% 21% 28% 20% 4	720
	21st to end	Night	18% 10% 24% 27% 19% 2	720
October	1st to 10th	Night	26% 12% 17% 29% 14% 2	720
	11th to 20th	Night	22% 14% 23% 28% 12% 1	720
	21st to end	Night	31% 14% 26% 23% 6%	792
November	1st to 10th	Night	23% 16% 25% 28% 8%	740
	11th to 20th	Night	22% 17% 29% 22% 8% 2	760
	21st to end	Night	25% 19% 26% 23% 7% 1	760
December	1st to 10th	Night	28% 20% 30% 19% 4	760
	11th to 20th	Night	28% 18% 27% 23% 4	760
	21st to end	Night	28% 20% 27% 21% 4	836

Page generated at 2024-02-07 06:11:57. Version ac07

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