Shelburne
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shelburne clear sky chart from 2005-11-06 to 2024-02-05.

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% 12% 5% 9% 7% 4 5% 5% 5% 7% 27%	78748
	Night	14% 11% 5% 10% 7% 4 5% 5% 5% 6% 28%	80097
Transparency	Day	55% 6% 11% 17% 10% 1	78459
	Night	55% 6% 11% 17% 9% 1	79921
Seeing	Day	21% 19% 32% 18% 8% 3	13848
	Night	20% 19% 32% 20% 8% 1	22910

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	14% 17% 9% 15% 9% 4 5% 4 4 5% 16%	2517
	11th to 20th	Day	10% 19% 11% 19% 12% 6% 7% 4 3 3 6%	2808
	21st to end	Day	16% 20% 10% 13% 9% 4 5% 3 3 4 11%	3124
February	1st to 10th	Day	12% 17% 7% 14% 14% 5% 6% 5% 4 3 13%	1656
	11th to 20th	Day	11% 13% 7% 15% 12% 3 5% 5% 6% 6% 17%	1573
	21st to end	Day	16% 15% 8% 11% 8% 4 6% 5% 4 5% 19%	1402
March	1st to 10th	Day	12% 13% 5% 11% 10% 5% 5% 4 3 6% 25%	1959
	11th to 20th	Day	11% 14% 7% 10% 7% 4 5% 4 4 5% 28%	1980
	21st to end	Day	16% 13% 5% 7% 7% 3 5% 5% 3 5% 30%	2178
April	1st to 10th	Day	16% 15% 6% 8% 6% 4 4 4 5% 7% 25%	2097
	11th to 20th	Day	17% 12% 3 6% 4 4 5% 4 5% 6% 34%	2253
	21st to end	Day	20% 10% 5% 6% 5% 3 4 4 5% 6% 31%	2340
May	1st to 10th	Day	17% 9% 4 8% 5% 4 4 4 5% 7% 33%	2340
	11th to 20th	Day	16% 8% 4 7% 5% 3 5% 5% 5% 7% 35%	2428
	21st to end	Day	13% 6% 3 5% 6% 3 6% 4 6% 9% 40%	2725
June	1st to 10th	Day	15% 6% 3 6% 6% 4 5% 5% 6% 9% 36%	2520
	11th to 20th	Day	12% 6% 2 6% 6% 3 5% 5% 6% 8% 40%	2668
	21st to end	Day	15% 5% 3 5% 6% 3 5% 5% 6% 9% 38%	2700
July	1st to 10th	Day	10% 5% 3 5% 5% 3 6% 6% 7% 9% 42%	2700
	11th to 20th	Day	11% 6% 3 6% 7% 4 6% 5% 7% 9% 35%	2538
	21st to end	Day	10% 7% 4 6% 7% 5% 6% 5% 8% 10% 32%	2547
August	1st to 10th	Day	11% 5% 3 7% 6% 5% 6% 6% 7% 10% 35%	2327
	11th to 20th	Day	10% 6% 3 7% 7% 5% 6% 6% 8% 9% 33%	2303
	21st to end	Day	13% 7% 3 6% 6% 4 6% 6% 6% 8% 36%	2514
September	1st to 10th	Day	16% 8% 3 7% 5% 4 4 5% 5% 7% 36%	2160
	11th to 20th	Day	13% 8% 3 6% 4 4 5% 5% 6% 8% 40%	2010
	21st to end	Day	16% 7% 4 7% 7% 4 5% 5% 6% 8% 32%	1972
October	1st to 10th	Day	18% 11% 5% 8% 5% 4 4 5% 5% 6% 30%	1800
	11th to 20th	Day	20% 14% 4 8% 7% 4 5% 5% 5% 6% 22%	1800
	21st to end	Day	26% 18% 5% 8% 6% 3 4 4 4 5% 18%	1976
November	1st to 10th	Day	13% 16% 6% 8% 7% 3 5% 5% 5% 6% 26%	1595
	11th to 20th	Day	13% 16% 6% 10% 7% 4 6% 5% 5% 6% 20%	1520
	21st to end	Day	15% 19% 9% 11% 7% 5% 5% 5% 4 6% 15%	1520
December	1st to 10th	Day	12% 23% 11% 16% 7% 3 5% 5% 5% 4 9%	1520
	11th to 20th	Day	16% 19% 7% 13% 10% 4 4 4 4 5% 14%	1906
	21st to end	Day	22% 23% 8% 17% 7% 4 4 3 3 2 7%	2772
January	1st to 10th	Night	15% 15% 10% 15% 8% 3 4 4 5% 6% 13%	4429
	11th to 20th	Night	13% 12% 9% 19% 16% 9% 7% 4 3 3 7%	4148
	21st to end	Night	17% 14% 8% 15% 9% 4 5% 6% 5% 5% 11%	4532
February	1st to 10th	Night	12% 14% 8% 12% 10% 6% 6% 6% 6% 6% 16%	2399
	11th to 20th	Night	11% 13% 6% 13% 10% 5% 6% 5% 6% 6% 19%	2273
	21st to end	Night	12% 13% 6% 12% 8% 4 6% 5% 5% 6% 22%	1852
March	1st to 10th	Night	12% 10% 5% 11% 7% 4 6% 5% 5% 7% 28%	1988
	11th to 20th	Night	11% 13% 5% 8% 6% 4 5% 5% 4 5% 34%	1979
	21st to end	Night	13% 11% 3 7% 7% 3 5% 4 5% 6% 35%	2178
April	1st to 10th	Night	18% 11% 5% 8% 6% 4 4 4 4 6% 30%	1862
	11th to 20th	Night	14% 10% 3 6% 5% 3 4 4 4 7% 38%	1671
	21st to end	Night	14% 12% 4 7% 6% 3 5% 5% 5% 6% 32%	1620
May	1st to 10th	Night	15% 8% 3 5% 5% 3 5% 5% 5% 7% 37%	1620
	11th to 20th	Night	15% 6% 2 4 5% 3 4 4 4 7% 45%	1464
	21st to end	Night	9% 5% 2 5% 4 3 4 5% 6% 8% 50%	1550
June	1st to 10th	Night	12% 6% 3 6% 6% 3 5% 4 5% 10% 41%	1440
	11th to 20th	Night	10% 5% 2 5% 5% 3 6% 5% 8% 8% 44%	1288
	21st to end	Night	11% 6% 2 5% 5% 3 4 4 5% 9% 45%	1260
July	1st to 10th	Night	5% 5% 3 4 3 2 4 4 4 8% 58%	1260
	11th to 20th	Night	8% 6% 2 4 6% 3 4 5% 6% 8% 48%	1415
	21st to end	Night	7% 6% 2 5% 6% 3 4 5% 6% 8% 49%	1771
August	1st to 10th	Night	9% 5% 1 5% 5% 3 4 5% 6% 8% 50%	1611
	11th to 20th	Night	6% 3 2 5% 5% 4 4 6% 6% 9% 50%	1598
	21st to end	Night	10% 6% 2 6% 5% 4 4 4 5% 7% 46%	1822
September	1st to 10th	Night	9% 6% 3 6% 5% 3 5% 4 7% 8% 45%	1800
	11th to 20th	Night	11% 5% 2 4 4 3 4 4 6% 6% 50%	1948
	21st to end	Night	14% 9% 4 7% 5% 2 5% 3 5% 6% 40%	1988
October	1st to 10th	Night	16% 8% 3 7% 6% 3 5% 4 6% 6% 36%	2160
	11th to 20th	Night	19% 12% 4 7% 5% 4 5% 4 4 6% 29%	2160
	21st to end	Night	19% 14% 5% 8% 8% 4 4 5% 5% 7% 22%	2377
November	1st to 10th	Night	15% 12% 4 8% 6% 4 4 5% 6% 6% 29%	2482
	11th to 20th	Night	15% 13% 5% 8% 7% 4 6% 5% 6% 7% 23%	2660
	21st to end	Night	16% 15% 7% 10% 8% 4 5% 5% 5% 7% 19%	2660
December	1st to 10th	Night	16% 17% 8% 15% 8% 4 5% 5% 5% 5% 13%	2660
	11th to 20th	Night	12% 20% 8% 14% 10% 4 5% 4 4 5% 14%	3288
	21st to end	Night	23% 20% 9% 17% 7% 4 4 3 3 4 7%	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	67% 7% 12% 9% 4	2518
	11th to 20th	Day	80% 5% 7% 4 3	2808
	21st to end	Day	75% 6% 7% 7% 4	3124
February	1st to 10th	Day	73% 5% 7% 11% 3 1	1656
	11th to 20th	Day	65% 5% 10% 12% 6% 2	1582
	21st to end	Day	66% 4 8% 14% 7% 1	1402
March	1st to 10th	Day	60% 5% 11% 13% 10% 1	1962
	11th to 20th	Day	57% 5% 9% 17% 11% 2	1980
	21st to end	Day	55% 4 10% 15% 13% 2	2178
April	1st to 10th	Day	59% 4 8% 17% 10% 1	2097
	11th to 20th	Day	49% 5% 10% 20% 15% 1	2253
	21st to end	Day	53% 4 11% 18% 12% 3	2340
May	1st to 10th	Day	51% 4 10% 21% 14% 1	2340
	11th to 20th	Day	47% 6% 10% 23% 13% 1	2432
	21st to end	Day	41% 6% 14% 23% 15% 2	2725
June	1st to 10th	Day	43% 7% 12% 21% 15% 1	2520
	11th to 20th	Day	40% 6% 12% 25% 16% 1	2668
	21st to end	Day	42% 6% 13% 25% 14% 1	2700
July	1st to 10th	Day	36% 8% 12% 24% 18% 2	2626
	11th to 20th	Day	41% 7% 13% 27% 11% 1	2461
	21st to end	Day	44% 8% 13% 22% 13% 1	2405
August	1st to 10th	Day	40% 9% 15% 23% 11% 2	2314
	11th to 20th	Day	43% 8% 16% 22% 10%	2303
	21st to end	Day	44% 7% 14% 23% 11% 1	2514
September	1st to 10th	Day	44% 7% 13% 24% 10% 2	2160
	11th to 20th	Day	41% 6% 12% 28% 12%	2010
	21st to end	Day	49% 7% 12% 24% 7% 1	1972
October	1st to 10th	Day	54% 5% 12% 16% 12% 1	1800
	11th to 20th	Day	62% 5% 10% 16% 6% 1	1800
	21st to end	Day	68% 5% 10% 11% 6%	1976
November	1st to 10th	Day	56% 7% 11% 17% 8% 1	1595
	11th to 20th	Day	62% 5% 11% 13% 7% 1	1520
	21st to end	Day	68% 7% 11% 10% 3	1520
December	1st to 10th	Day	74% 7% 8% 8% 3	1520
	11th to 20th	Day	71% 7% 9% 10% 3	1906
	21st to end	Day	83% 4 5% 7% 1	2772
January	1st to 10th	Night	68% 8% 11% 10% 3	4429
	11th to 20th	Night	78% 7% 8% 4 3	4148
	21st to end	Night	69% 11% 9% 7% 3 1	4532
February	1st to 10th	Night	65% 6% 9% 15% 4	2399
	11th to 20th	Night	62% 6% 10% 14% 7%	2275
	21st to end	Night	60% 6% 10% 15% 8% 1	1852
March	1st to 10th	Night	54% 6% 11% 17% 10% 1	1998
	11th to 20th	Night	52% 5% 9% 20% 12% 2	1980
	21st to end	Night	49% 4 9% 20% 15% 3	2178
April	1st to 10th	Night	55% 3 9% 18% 14% 1	1862
	11th to 20th	Night	47% 4 9% 21% 17% 2	1671
	21st to end	Night	51% 4 11% 16% 16% 2	1620
May	1st to 10th	Night	45% 5% 11% 21% 16% 2	1620
	11th to 20th	Night	40% 4 10% 26% 17% 3	1465
	21st to end	Night	30% 6% 16% 27% 17% 4	1551
June	1st to 10th	Night	40% 5% 10% 25% 19% 2	1440
	11th to 20th	Night	34% 5% 15% 26% 20% 1	1288
	21st to end	Night	36% 6% 13% 28% 15% 1	1260
July	1st to 10th	Night	26% 6% 12% 29% 24% 3	1225
	11th to 20th	Night	33% 5% 12% 33% 16% 1	1369
	21st to end	Night	32% 7% 15% 29% 15% 2	1672
August	1st to 10th	Night	31% 5% 18% 31% 14% 1	1600
	11th to 20th	Night	28% 8% 15% 32% 16% 1	1598
	21st to end	Night	37% 5% 13% 28% 15% 1	1822
September	1st to 10th	Night	35% 6% 16% 28% 13% 2	1800
	11th to 20th	Night	32% 5% 13% 32% 17% 1	1948
	21st to end	Night	44% 6% 13% 27% 10% 1	1988
October	1st to 10th	Night	48% 7% 11% 19% 15% 1	2160
	11th to 20th	Night	54% 6% 12% 20% 7% 1	2160
	21st to end	Night	61% 6% 10% 14% 9%	2377
November	1st to 10th	Night	52% 6% 11% 20% 10% 1	2482
	11th to 20th	Night	57% 7% 13% 14% 7% 2	2660
	21st to end	Night	62% 7% 14% 12% 3 1	2660
December	1st to 10th	Night	70% 7% 10% 10% 3	2660
	11th to 20th	Night	70% 7% 10% 10% 3	3288
	21st to end	Night	82% 5% 5% 6% 2	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	24% 29% 28% 16% 3	180
	11th to 20th	Day	21% 34% 31% 10% 3	261
	21st to end	Day	27% 25% 35% 12% 1	297
February	1st to 10th	Day	30% 33% 29% 6% 2	252
	11th to 20th	Day	27% 33% 35% 4 1	240
	21st to end	Day	39% 30% 27% 4	198
March	1st to 10th	Day	26% 26% 32% 12% 3	402
	11th to 20th	Day	25% 21% 37% 12% 4	420
	21st to end	Day	31% 21% 30% 14% 3	462
April	1st to 10th	Day	26% 23% 35% 11% 4	420
	11th to 20th	Day	29% 23% 27% 11% 7% 3	412
	21st to end	Day	29% 20% 31% 13% 5% 2	420
May	1st to 10th	Day	26% 17% 30% 18% 7% 2	423
	11th to 20th	Day	21% 15% 34% 19% 8% 4	447
	21st to end	Day	16% 14% 32% 23% 11% 4	485
June	1st to 10th	Day	18% 15% 34% 23% 8% 2	450
	11th to 20th	Day	15% 15% 33% 24% 10% 2	598
	21st to end	Day	16% 15% 37% 21% 8% 3	630
July	1st to 10th	Day	13% 10% 31% 29% 14% 4	621
	11th to 20th	Day	16% 10% 33% 24% 11% 6%	470
	21st to end	Day	11% 9% 41% 25% 10% 4	488
August	1st to 10th	Day	10% 9% 31% 28% 15% 7%	446
	11th to 20th	Day	10% 8% 30% 27% 18% 8%	439
	21st to end	Day	15% 12% 30% 27% 13% 4	495
September	1st to 10th	Day	16% 12% 30% 24% 12% 6%	450
	11th to 20th	Day	12% 11% 27% 25% 17% 7%	450
	21st to end	Day	17% 17% 27% 20% 14% 5%	450
October	1st to 10th	Day	23% 19% 24% 18% 11% 4	450
	11th to 20th	Day	26% 26% 31% 14% 3	450
	21st to end	Day	33% 23% 28% 13% 2	491
November	1st to 10th	Day	28% 27% 28% 14% 3	233
	11th to 20th	Day	28% 21% 37% 9% 3 2	180
	21st to end	Day	28% 25% 38% 8% 1	180
December	1st to 10th	Day	29% 31% 34% 6%	180
	11th to 20th	Day	29% 31% 29% 8% 2 1	180
	21st to end	Day	27% 36% 30% 6% 2	198
January	1st to 10th	Night	22% 31% 30% 14% 2	760
	11th to 20th	Night	26% 25% 30% 16% 2 1	760
	21st to end	Night	18% 20% 39% 18% 5%	836
February	1st to 10th	Night	22% 30% 34% 13% 1	739
	11th to 20th	Night	23% 25% 37% 13% 2	703
	21st to end	Night	23% 29% 33% 12% 2	592
March	1st to 10th	Night	21% 24% 35% 18% 2	720
	11th to 20th	Night	22% 24% 35% 14% 4	720
	21st to end	Night	21% 20% 33% 21% 5%	792
April	1st to 10th	Night	26% 20% 35% 17% 2	720
	11th to 20th	Night	22% 19% 32% 18% 8% 1	607
	21st to end	Night	23% 17% 31% 22% 7%	540
May	1st to 10th	Night	19% 13% 31% 28% 8% 2	540
	11th to 20th	Night	19% 10% 35% 25% 10%	403
	21st to end	Night	12% 12% 33% 30% 13%	389
June	1st to 10th	Night	16% 9% 39% 27% 8% 1	360
	11th to 20th	Night	13% 9% 30% 36% 11%	360
	21st to end	Night	14% 10% 34% 28% 13% 1	360
July	1st to 10th	Night	7% 6% 32% 34% 19% 1	350
	11th to 20th	Night	10% 7% 35% 29% 18% 1	355
	21st to end	Night	10% 7% 34% 34% 15% 1	591
August	1st to 10th	Night	10% 4 32% 32% 20% 2	537
	11th to 20th	Night	8% 6% 26% 36% 22% 3	534
	21st to end	Night	14% 7% 30% 27% 20% 2	634
September	1st to 10th	Night	13% 8% 30% 29% 15% 5%	720
	11th to 20th	Night	14% 9% 29% 28% 16% 5%	720
	21st to end	Night	19% 11% 25% 26% 16% 4	720
October	1st to 10th	Night	21% 15% 31% 20% 12% 3	720
	11th to 20th	Night	27% 17% 32% 17% 6% 1	720
	21st to end	Night	26% 22% 32% 16% 4	792
November	1st to 10th	Night	24% 21% 32% 17% 6% 1	740
	11th to 20th	Night	22% 29% 28% 14% 6% 1	760
	21st to end	Night	24% 25% 33% 15% 3	760
December	1st to 10th	Night	27% 25% 33% 11% 3	760
	11th to 20th	Night	22% 29% 35% 11% 3 1	760
	21st to end	Night	30% 28% 28% 13% 1	836

Page generated at 2024-02-02 05:20:30. Version ac07

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