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 2025-03-12.

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% 29%	108678
	Night	15% 12% 4 11% 6% 5% 5% 4 5% 6% 28%	110327
Transparency	Day	52% 7% 11% 19% 10% 1	112207
	Night	53% 7% 11% 18% 10% 1	114962
Seeing	Day	25% 18% 28% 18% 8% 2	15123
	Night	23% 15% 27% 26% 9% 1	24201

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	9% 12% 7% 21% 13% 6% 4 3 4 4 18%	3597
	11th to 20th	Day	10% 12% 5% 15% 12% 5% 4 4 5% 6% 22%	3570
	21st to end	Day	8% 14% 9% 15% 7% 6% 4 3 4 5% 25%	3960
February	1st to 10th	Day	11% 13% 6% 11% 9% 7% 5% 4 5% 6% 23%	1745
	11th to 20th	Day	8% 13% 6% 14% 10% 6% 5% 4 5% 7% 22%	1948
	21st to end	Day	12% 14% 4 13% 7% 5% 5% 4 5% 6% 25%	1650
March	1st to 10th	Day	19% 18% 6% 12% 5% 5% 4 3 3 4 22%	3216
	11th to 20th	Day	13% 15% 8% 14% 6% 4 4 3 4 5% 25%	3259
	21st to end	Day	17% 12% 5% 11% 6% 4 4 3 4 4 30%	4156
April	1st to 10th	Day	18% 15% 4 9% 5% 4 4 3 4 6% 29%	2280
	11th to 20th	Day	17% 12% 3 7% 5% 4 4 4 5% 6% 32%	2254
	21st to end	Day	21% 12% 4 8% 5% 5% 5% 4 5% 5% 27%	2464
May	1st to 10th	Day	22% 13% 4 8% 5% 5% 4 3 4 6% 25%	4130
	11th to 20th	Day	16% 10% 3 9% 6% 5% 6% 5% 6% 8% 28%	4398
	21st to end	Day	12% 7% 2 7% 5% 6% 5% 5% 7% 8% 36%	4837
June	1st to 10th	Day	22% 8% 3 8% 5% 5% 5% 5% 6% 7% 27%	2660
	11th to 20th	Day	17% 8% 3 6% 6% 5% 4 5% 6% 7% 33%	2660
	21st to end	Day	19% 10% 3 8% 5% 6% 5% 5% 6% 8% 26%	2660
July	1st to 10th	Day	13% 7% 2 6% 5% 4 6% 6% 8% 10% 33%	4440
	11th to 20th	Day	11% 6% 2 7% 6% 5% 7% 5% 8% 10% 33%	4440
	21st to end	Day	15% 8% 3 7% 5% 5% 6% 4 6% 7% 35%	4814
August	1st to 10th	Day	15% 8% 3 8% 6% 5% 6% 4 6% 9% 30%	4363
	11th to 20th	Day	14% 10% 3 8% 5% 5% 6% 5% 7% 10% 26%	3954
	21st to end	Day	11% 9% 3 6% 4 5% 5% 4 6% 9% 39%	4180
September	1st to 10th	Day	13% 7% 2 5% 3 5% 5% 4 6% 8% 44%	2280
	11th to 20th	Day	14% 6% 2 7% 4 3 4 3 5% 6% 46%	2142
	21st to end	Day	15% 8% 3 5% 4 4 4 4 7% 8% 38%	2090
October	1st to 10th	Day	21% 10% 3 8% 5% 4 3 3 5% 6% 32%	2056
	11th to 20th	Day	14% 12% 4 8% 5% 4 4 4 5% 7% 34%	1822
	21st to end	Day	21% 16% 4 8% 4 5% 4 3 3 5% 26%	1881
November	1st to 10th	Day	13% 12% 5% 7% 5% 4 4 4 6% 6% 35%	1761
	11th to 20th	Day	15% 14% 4 11% 6% 5% 5% 4 6% 5% 27%	1800
	21st to end	Day	17% 14% 4 12% 6% 4 4 4 5% 6% 24%	1665
December	1st to 10th	Day	10% 19% 6% 24% 8% 5% 4 2 4 5% 12%	2600
	11th to 20th	Day	16% 14% 7% 12% 6% 5% 5% 3 4 5% 25%	2986
	21st to end	Day	17% 13% 6% 14% 6% 5% 5% 3 3 4 23%	3960
January	1st to 10th	Night	10% 11% 6% 20% 11% 8% 5% 3 4 5% 16%	6349
	11th to 20th	Night	9% 14% 6% 18% 13% 7% 5% 4 5% 5% 14%	6315
	21st to end	Night	11% 12% 6% 14% 8% 7% 5% 4 5% 5% 23%	6996
February	1st to 10th	Night	11% 12% 6% 12% 9% 6% 5% 5% 6% 6% 22%	2650
	11th to 20th	Night	9% 11% 5% 14% 9% 7% 6% 5% 5% 6% 24%	2338
	21st to end	Night	10% 11% 4 13% 9% 6% 5% 3 5% 6% 27%	1980
March	1st to 10th	Night	20% 16% 4 8% 7% 5% 4 3 5% 5% 24%	3844
	11th to 20th	Night	12% 15% 6% 12% 6% 5% 4 3 4 5% 28%	3727
	21st to end	Night	17% 15% 5% 11% 5% 3 3 3 3 4 31%	3472
April	1st to 10th	Night	18% 13% 5% 9% 5% 4 5% 3 5% 5% 30%	1900
	11th to 20th	Night	17% 14% 2 7% 5% 4 4 3 5% 6% 32%	1875
	21st to end	Night	20% 11% 4 7% 4 4 4 4 4 5% 33%	1715
May	1st to 10th	Night	24% 13% 3 6% 4 4 4 3 6% 6% 26%	2834
	11th to 20th	Night	18% 11% 3 8% 5% 5% 5% 4 6% 5% 30%	2500
	21st to end	Night	14% 7% 2 6% 5% 4 5% 4 7% 8% 38%	2738
June	1st to 10th	Night	19% 9% 2 6% 6% 5% 5% 3 6% 7% 31%	1520
	11th to 20th	Night	18% 8% 2 6% 5% 3 5% 4 5% 7% 37%	1520
	21st to end	Night	19% 7% 2 6% 5% 5% 4 4 6% 9% 32%	1520
July	1st to 10th	Night	13% 7% 3 8% 6% 5% 6% 5% 6% 8% 33%	2520
	11th to 20th	Night	16% 6% 2 6% 4 4 4 4 6% 8% 39%	2520
	21st to end	Night	13% 9% 3 7% 5% 4 5% 4 6% 7% 37%	2739
August	1st to 10th	Night	20% 10% 3 8% 4 4 4 3 5% 5% 35%	2534
	11th to 20th	Night	15% 8% 4 6% 4 4 5% 4 6% 8% 36%	2869
	21st to end	Night	10% 9% 2 5% 4 4 4 4 7% 9% 42%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 3 3 3 4 8% 46%	1900
	11th to 20th	Night	14% 7% 3 5% 3 3 3 4 5% 6% 47%	2038
	21st to end	Night	14% 8% 2 5% 4 4 5% 4 6% 7% 42%	2090
October	1st to 10th	Night	19% 9% 3 8% 5% 4 5% 3 4 7% 33%	2121
	11th to 20th	Night	15% 13% 3 8% 5% 5% 3 4 5% 6% 33%	2357
	21st to end	Night	21% 14% 3 8% 5% 4 5% 3 5% 6% 26%	2717
November	1st to 10th	Night	15% 13% 4 9% 5% 4 4 4 5% 5% 32%	2537
	11th to 20th	Night	15% 11% 5% 10% 6% 4 4 4 6% 6% 30%	2600
	21st to end	Night	16% 13% 6% 12% 6% 4 4 3 5% 6% 26%	2732
December	1st to 10th	Night	12% 16% 6% 20% 8% 6% 5% 3 4 4 14%	4580
	11th to 20th	Night	19% 16% 6% 12% 6% 4 4 3 4 5% 21%	5208
	21st to end	Night	16% 14% 6% 16% 7% 6% 5% 3 4 4 20%	6996

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	65% 7% 8% 15% 4	3598
	11th to 20th	Day	60% 7% 9% 14% 8% 2	3600
	21st to end	Day	59% 5% 9% 14% 11% 1	3960
February	1st to 10th	Day	59% 7% 9% 16% 7% 2	1745
	11th to 20th	Day	59% 7% 9% 16% 8% 1	1957
	21st to end	Day	58% 6% 10% 14% 11% 2	1650
March	1st to 10th	Day	66% 5% 7% 10% 10% 2	3219
	11th to 20th	Day	57% 7% 10% 13% 10% 2	3259
	21st to end	Day	57% 4 6% 13% 17% 2	4156
April	1st to 10th	Day	56% 5% 8% 17% 11% 2	2280
	11th to 20th	Day	51% 7% 8% 18% 14% 1	2254
	21st to end	Day	57% 6% 8% 16% 11% 2	2464
May	1st to 10th	Day	59% 7% 9% 19% 6% 1	4144
	11th to 20th	Day	51% 10% 14% 15% 9% 1	4402
	21st to end	Day	40% 9% 12% 26% 12% 1	4837
June	1st to 10th	Day	53% 7% 13% 18% 9%	2660
	11th to 20th	Day	47% 6% 11% 21% 13% 1	2660
	21st to end	Day	54% 8% 11% 18% 8% 1	2660
July	1st to 10th	Day	40% 9% 16% 23% 11%	4370
	11th to 20th	Day	39% 11% 16% 27% 6%	4365
	21st to end	Day	45% 8% 11% 25% 11%	4661
August	1st to 10th	Day	47% 9% 15% 21% 8%	4349
	11th to 20th	Day	48% 9% 17% 21% 5%	3993
	21st to end	Day	38% 9% 17% 22% 13% 1	4180
September	1st to 10th	Day	36% 7% 12% 32% 13% 1	2280
	11th to 20th	Day	37% 6% 9% 31% 16% 1	2142
	21st to end	Day	42% 6% 14% 24% 12% 2	2090
October	1st to 10th	Day	46% 8% 11% 22% 12% 1	3420
	11th to 20th	Day	45% 5% 13% 24% 13% 1	2999
	21st to end	Day	47% 5% 11% 27% 9% 1	3081
November	1st to 10th	Day	48% 6% 13% 21% 12%	1761
	11th to 20th	Day	54% 8% 10% 13% 13% 2	1800
	21st to end	Day	58% 7% 14% 16% 4	1665
December	1st to 10th	Day	72% 7% 10% 8% 3	2600
	11th to 20th	Day	61% 5% 7% 16% 10% 1	2986
	21st to end	Day	63% 6% 6% 12% 11% 3	3960
January	1st to 10th	Night	65% 9% 11% 12% 4	6349
	11th to 20th	Night	65% 10% 10% 8% 5% 1	6360
	21st to end	Night	59% 7% 8% 13% 11% 2	6996
February	1st to 10th	Night	59% 7% 10% 14% 9% 1	2650
	11th to 20th	Night	56% 7% 9% 17% 10% 1	2340
	21st to end	Night	53% 7% 11% 18% 8% 3	1980
March	1st to 10th	Night	61% 4 9% 15% 9% 2	3854
	11th to 20th	Night	55% 8% 9% 15% 11% 1	3728
	21st to end	Night	55% 5% 7% 14% 17% 3	3472
April	1st to 10th	Night	55% 4 8% 18% 12% 2	1900
	11th to 20th	Night	51% 6% 8% 23% 12%	1875
	21st to end	Night	52% 5% 9% 17% 14% 3	1715
May	1st to 10th	Night	56% 7% 10% 18% 8% 1	2840
	11th to 20th	Night	53% 9% 12% 17% 9% 1	2501
	21st to end	Night	40% 9% 16% 21% 13% 1	2739
June	1st to 10th	Night	49% 9% 11% 21% 9% 1	1520
	11th to 20th	Night	44% 9% 13% 20% 11% 2	1520
	21st to end	Night	48% 7% 13% 22% 10% 1	1520
July	1st to 10th	Night	43% 9% 16% 19% 12%	2480
	11th to 20th	Night	40% 8% 15% 27% 10%	2472
	21st to end	Night	43% 9% 11% 27% 10%	2651
August	1st to 10th	Night	50% 6% 12% 23% 8%	2524
	11th to 20th	Night	43% 8% 18% 21% 10%	2896
	21st to end	Night	34% 8% 19% 26% 12% 1	3476
September	1st to 10th	Night	36% 6% 14% 30% 12%	1900
	11th to 20th	Night	37% 6% 12% 31% 14% 1	2038
	21st to end	Night	39% 7% 12% 25% 14% 2	2090
October	1st to 10th	Night	49% 8% 12% 22% 9% 1	3537
	11th to 20th	Night	46% 5% 11% 21% 14% 2	3919
	21st to end	Night	47% 6% 12% 25% 9% 1	4467
November	1st to 10th	Night	50% 7% 12% 20% 9% 2	2537
	11th to 20th	Night	50% 7% 11% 18% 12% 2	2600
	21st to end	Night	57% 7% 12% 18% 6%	2732
December	1st to 10th	Night	68% 8% 10% 11% 2	4580
	11th to 20th	Night	62% 7% 8% 12% 12%	5208
	21st to end	Night	66% 6% 6% 13% 6% 3	6996

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% 28% 27% 19% 5% 1	200
	11th to 20th	Day	31% 25% 27% 12% 4 1	200
	21st to end	Day	25% 25% 30% 14% 5%	220
February	1st to 10th	Day	35% 31% 25% 6% 2	280
	11th to 20th	Day	33% 23% 30% 11% 2	496
	21st to end	Day	31% 22% 30% 13% 3	414
March	1st to 10th	Day	33% 17% 32% 15% 3	500
	11th to 20th	Day	28% 28% 27% 12% 5%	464
	21st to end	Day	33% 21% 24% 14% 6% 2	506
April	1st to 10th	Day	36% 20% 25% 13% 6% 1	460
	11th to 20th	Day	36% 21% 21% 15% 5% 2	452
	21st to end	Day	33% 21% 26% 12% 7% 1	460
May	1st to 10th	Day	35% 20% 24% 13% 6% 2	463
	11th to 20th	Day	21% 19% 34% 18% 5% 2	487
	21st to end	Day	18% 19% 32% 22% 8% 1	529
June	1st to 10th	Day	26% 14% 34% 17% 7% 1	490
	11th to 20th	Day	21% 16% 31% 22% 8% 2	490
	21st to end	Day	22% 16% 32% 21% 7% 2	490
July	1st to 10th	Day	16% 12% 31% 27% 11% 3	485
	11th to 20th	Day	14% 10% 36% 27% 10% 3	484
	21st to end	Day	14% 11% 36% 26% 9% 2	532
August	1st to 10th	Day	15% 12% 30% 25% 15% 3	486
	11th to 20th	Day	21% 9% 27% 23% 13% 7%	479
	21st to end	Day	14% 14% 29% 24% 13% 6%	539
September	1st to 10th	Day	15% 16% 26% 24% 13% 7%	490
	11th to 20th	Day	18% 11% 23% 21% 15% 12%	490
	21st to end	Day	21% 11% 28% 22% 13% 5%	490
October	1st to 10th	Day	27% 14% 24% 18% 12% 5%	490
	11th to 20th	Day	22% 20% 24% 22% 10% 2	448
	21st to end	Day	35% 17% 25% 18% 6%	429
November	1st to 10th	Day	27% 18% 23% 21% 10% 1	395
	11th to 20th	Day	28% 22% 27% 17% 5% 1	400
	21st to end	Day	37% 18% 23% 16% 5%	265
December	1st to 10th	Day	30% 20% 30% 16% 5% 1	200
	11th to 20th	Day	33% 23% 31% 13% 2	200
	21st to end	Day	32% 19% 29% 17% 4	220
January	1st to 10th	Night	22% 21% 33% 21% 4	800
	11th to 20th	Night	27% 18% 29% 22% 4 1	800
	21st to end	Night	17% 21% 34% 24% 4	880
February	1st to 10th	Night	22% 19% 34% 22% 4	800
	11th to 20th	Night	21% 23% 33% 19% 3	783
	21st to end	Night	21% 20% 33% 22% 4	660
March	1st to 10th	Night	25% 18% 32% 22% 3	800
	11th to 20th	Night	25% 21% 27% 22% 5% 1	767
	21st to end	Night	26% 17% 28% 21% 7%	836
April	1st to 10th	Night	27% 18% 28% 21% 5%	760
	11th to 20th	Night	25% 20% 27% 21% 7%	751
	21st to end	Night	29% 17% 28% 21% 6%	575
May	1st to 10th	Night	28% 15% 28% 22% 6% 1	570
	11th to 20th	Night	18% 14% 32% 30% 6% 1	379
	21st to end	Night	19% 9% 29% 31% 11%	411
June	1st to 10th	Night	22% 7% 26% 33% 11%	380
	11th to 20th	Night	19% 10% 25% 31% 14% 1	380
	21st to end	Night	22% 5% 27% 34% 11% 1	380
July	1st to 10th	Night	18% 5% 20% 40% 16% 1	370
	11th to 20th	Night	17% 4 22% 37% 19% 2	368
	21st to end	Night	15% 5% 21% 40% 18%	416
August	1st to 10th	Night	16% 5% 17% 38% 24%	393
	11th to 20th	Night	18% 5% 23% 33% 18% 3	610
	21st to end	Night	16% 7% 17% 35% 21% 3	836
September	1st to 10th	Night	15% 9% 25% 31% 19% 2	760
	11th to 20th	Night	17% 9% 20% 28% 21% 5%	760
	21st to end	Night	18% 10% 24% 28% 19% 2	760
October	1st to 10th	Night	25% 12% 18% 29% 15% 2	760
	11th to 20th	Night	22% 15% 23% 28% 12% 1	760
	21st to end	Night	30% 14% 26% 23% 6%	836
November	1st to 10th	Night	22% 17% 25% 27% 8%	780
	11th to 20th	Night	22% 18% 28% 22% 8% 2	800
	21st to end	Night	24% 20% 26% 22% 6% 1	800
December	1st to 10th	Night	28% 20% 30% 19% 4	800
	11th to 20th	Night	29% 18% 26% 23% 4	800
	21st to end	Night	27% 20% 27% 21% 4	880

Page generated at 2025-03-09 08:08:42. Version ac07

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