Washington(VT)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Washington(VT) clear sky chart from 2005-11-05 to 2024-10-14.

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 9% 6% 5% 5% 4 5% 7% 29%	101207
	Night	16% 12% 4 10% 6% 5% 4 4 5% 6% 29%	97359
Transparency	Day	52% 7% 11% 19% 10% 1	100966
	Night	53% 7% 11% 18% 9% 1	97225
Seeing	Day	25% 17% 28% 19% 8% 3	14716
	Night	22% 15% 27% 26% 9% 1	23605

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% 13% 6% 18% 7% 5% 4 3 4 5% 22%	2517
	11th to 20th	Day	13% 12% 6% 17% 11% 6% 4 3 4 4 21%	2520
	21st to end	Day	12% 17% 9% 15% 6% 6% 4 3 4 4 19%	2772
February	1st to 10th	Day	11% 13% 6% 10% 9% 7% 5% 4 5% 6% 23%	1657
	11th to 20th	Day	8% 14% 6% 15% 9% 6% 4 4 5% 6% 23%	1848
	21st to end	Day	12% 13% 4 13% 7% 5% 5% 4 5% 6% 26%	1570
March	1st to 10th	Day	19% 18% 6% 11% 5% 5% 4 3 3 4 22%	3116
	11th to 20th	Day	13% 15% 8% 14% 6% 4 4 3 4 5% 25%	3249
	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% 6% 4 4 4 5% 7% 33%	1757
	21st to end	Day	23% 17% 4 9% 4 5% 4 3 3 5% 24%	1782
November	1st to 10th	Day	13% 13% 5% 7% 5% 4 4 4 6% 6% 35%	1671
	11th to 20th	Day	16% 13% 4 11% 6% 5% 5% 4 6% 5% 26%	1710
	21st to end	Day	17% 13% 4 12% 6% 4 4 4 5% 6% 25%	1582
December	1st to 10th	Day	16% 19% 5% 13% 7% 6% 4 3 5% 6% 18%	1520
	11th to 20th	Day	19% 15% 4 10% 5% 4 4 3 4 6% 25%	1906
	21st to end	Day	21% 15% 6% 14% 6% 5% 4 3 3 4 19%	2772
January	1st to 10th	Night	13% 12% 5% 13% 7% 6% 6% 4 5% 6% 22%	4429
	11th to 20th	Night	11% 13% 6% 17% 11% 7% 5% 4 5% 5% 16%	4440
	21st to end	Night	16% 16% 7% 15% 7% 6% 4 3 4 4 18%	4884
February	1st to 10th	Night	11% 12% 6% 12% 9% 6% 5% 5% 6% 6% 22%	2518
	11th to 20th	Night	9% 11% 5% 14% 8% 7% 6% 5% 5% 6% 24%	2218
	21st to end	Night	10% 11% 4 13% 8% 6% 5% 3 5% 6% 28%	1884
March	1st to 10th	Night	20% 16% 4 8% 6% 4 4 3 5% 5% 25%	3724
	11th to 20th	Night	12% 16% 6% 12% 6% 5% 4 3 4 5% 28%	3708
	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% 12% 3 9% 5% 5% 4 4 5% 6% 32%	2275
	21st to end	Night	21% 15% 4 8% 5% 4 5% 3 5% 6% 25%	2574
November	1st to 10th	Night	15% 13% 4 10% 5% 3 4 4 5% 5% 32%	2407
	11th to 20th	Night	16% 11% 5% 10% 6% 4 4 4 6% 6% 29%	2470
	21st to end	Night	16% 12% 6% 13% 6% 4 4 3 5% 6% 26%	2595
December	1st to 10th	Night	17% 17% 6% 14% 7% 6% 5% 4 4 5% 16%	2660
	11th to 20th	Night	19% 14% 5% 12% 5% 5% 4 4 5% 6% 20%	3288
	21st to end	Night	21% 14% 6% 17% 6% 5% 4 3 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% 9% 17% 7% 2	1657
	11th to 20th	Day	59% 7% 9% 16% 8% 1	1857
	21st to end	Day	57% 5% 10% 15% 11% 2	1570
March	1st to 10th	Day	66% 5% 7% 10% 10% 1	3119
	11th to 20th	Day	58% 7% 9% 13% 10% 2	3249
	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	53% 6% 9% 20% 12% 1	2056
	11th to 20th	Day	49% 7% 14% 23% 7% 1	1758
	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% 8% 10% 14% 9% 1	2518
	11th to 20th	Night	56% 7% 9% 18% 10% 1	2220
	21st to end	Night	52% 7% 11% 18% 9% 3	1884
March	1st to 10th	Night	61% 4 9% 15% 9% 2	3734
	11th to 20th	Night	55% 8% 9% 15% 11% 1	3709
	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	50% 6% 11% 21% 11% 1	2121
	11th to 20th	Night	50% 6% 14% 23% 7%	2279
	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% 31% 26% 7% 2	252
	11th to 20th	Day	31% 24% 30% 12% 2	456
	21st to end	Day	31% 21% 30% 14% 3 1	382
March	1st to 10th	Day	32% 16% 33% 16% 3	460
	11th to 20th	Day	28% 28% 27% 12% 5%	460
	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% 26% 22% 9% 2	425
	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% 18% 34% 23% 4	760
	11th to 20th	Night	20% 23% 34% 20% 3	743
	21st to end	Night	21% 19% 32% 23% 4	628
March	1st to 10th	Night	25% 17% 32% 23% 3	760
	11th to 20th	Night	25% 21% 27% 22% 5% 1	760
	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	735
	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 2024-10-11 10:50:01. Version ac07

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