Sutton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sutton clear sky chart from 2005-11-06 to 2024-01-22.

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	20% 12% 5% 8% 6% 3 5% 4 5% 6% 27%	74851
	Night	19% 13% 5% 9% 6% 3 4 4 4 5% 26%	75086
Transparency	Day	57% 6% 11% 17% 8% 1	74556
	Night	60% 6% 10% 16% 8% 1	74915
Seeing	Day	28% 17% 28% 18% 8% 2	13582
	Night	26% 15% 26% 23% 8% 1	22638

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	17% 23% 9% 12% 8% 3 5% 4 4 4 12%	1517
	11th to 20th	Day	16% 19% 7% 15% 7% 4 4 5% 4 5% 14%	1520
	21st to end	Day	11% 16% 7% 13% 9% 4 9% 5% 4 5% 18%	1592
February	1st to 10th	Day	15% 16% 8% 14% 10% 5% 6% 3 3 3 15%	1539
	11th to 20th	Day	13% 19% 9% 13% 8% 3 6% 5% 3 3 18%	1726
	21st to end	Day	14% 18% 8% 12% 8% 4 5% 4 4 4 19%	1480
March	1st to 10th	Day	15% 17% 8% 10% 7% 4 5% 4 4 4 22%	1797
	11th to 20th	Day	16% 17% 6% 8% 8% 4 3 3 3 5% 26%	1843
	21st to end	Day	21% 14% 6% 9% 6% 2 3 3 3 4 29%	2376
April	1st to 10th	Day	23% 16% 5% 8% 5% 3 4 3 4 4 25%	2160
	11th to 20th	Day	21% 14% 4 6% 4 3 4 4 4 5% 32%	2138
	21st to end	Day	25% 12% 3 6% 5% 4 5% 3 4 6% 26%	2340
May	1st to 10th	Day	23% 11% 4 5% 5% 3 4 3 4 6% 31%	2402
	11th to 20th	Day	21% 8% 3 6% 6% 3 5% 4 4 6% 33%	2478
	21st to end	Day	19% 7% 3 6% 5% 4 5% 6% 6% 8% 31%	2725
June	1st to 10th	Day	28% 7% 3 5% 5% 3 4 5% 6% 7% 27%	2520
	11th to 20th	Day	21% 6% 3 5% 4 4 4 5% 6% 8% 35%	2520
	21st to end	Day	25% 7% 3 6% 5% 3 5% 5% 5% 7% 28%	2520
July	1st to 10th	Day	17% 6% 3 7% 5% 3 5% 5% 6% 9% 34%	2520
	11th to 20th	Day	16% 6% 4 5% 6% 4 6% 6% 7% 8% 32%	2520
	21st to end	Day	17% 7% 3 5% 6% 4 6% 5% 7% 8% 31%	2744
August	1st to 10th	Day	18% 6% 3 6% 5% 4 6% 6% 7% 7% 32%	2506
	11th to 20th	Day	17% 6% 2 6% 5% 3 5% 6% 7% 7% 34%	2278
	21st to end	Day	18% 7% 3 4 4 3 5% 5% 6% 8% 36%	2376
September	1st to 10th	Day	18% 7% 3 5% 5% 2 4 5% 6% 7% 39%	2160
	11th to 20th	Day	20% 6% 2 4 4 2 3 3 4 6% 44%	2042
	21st to end	Day	19% 7% 2 5% 4 3 5% 4 6% 9% 35%	1980
October	1st to 10th	Day	26% 10% 3 6% 6% 3 5% 4 5% 5% 27%	1926
	11th to 20th	Day	23% 11% 3 6% 6% 3 5% 5% 5% 5% 28%	1720
	21st to end	Day	29% 18% 4 7% 5% 3 3 3 3 4 22%	1782
November	1st to 10th	Day	20% 15% 5% 7% 5% 4 4 4 4 6% 27%	1671
	11th to 20th	Day	19% 18% 7% 9% 7% 3 4 4 4 4 22%	1710
	21st to end	Day	18% 20% 7% 10% 6% 4 4 3 6% 4 19%	1525
December	1st to 10th	Day	22% 21% 8% 11% 8% 3 3 3 3 3 15%	1520
	11th to 20th	Day	19% 18% 8% 12% 5% 4 5% 3 3 4 19%	1906
	21st to end	Day	22% 18% 7% 13% 9% 3 4 3 3 3 15%	2772
January	1st to 10th	Night	17% 21% 8% 14% 8% 5% 5% 5% 4 3 11%	2649
	11th to 20th	Night	15% 18% 7% 15% 9% 4 6% 4 3 3 16%	2660
	21st to end	Night	12% 15% 7% 13% 10% 5% 6% 4 4 4 19%	2798
February	1st to 10th	Night	15% 18% 8% 15% 9% 4 5% 4 4 4 15%	2419
	11th to 20th	Night	14% 15% 8% 12% 9% 5% 6% 4 3 4 19%	2120
	21st to end	Night	13% 17% 8% 11% 7% 5% 5% 3 3 4 24%	1776
March	1st to 10th	Night	16% 17% 7% 10% 7% 4 4 4 4 4 24%	2150
	11th to 20th	Night	18% 16% 6% 8% 7% 4 3 3 3 4 28%	2115
	21st to end	Night	19% 16% 4 8% 5% 2 3 3 3 4 32%	1980
April	1st to 10th	Night	23% 13% 6% 8% 6% 3 3 4 4 4 26%	1800
	11th to 20th	Night	23% 11% 4 6% 5% 3 4 3 3 6% 31%	1771
	21st to end	Night	23% 12% 4 6% 5% 3 3 4 4 4 31%	1620
May	1st to 10th	Night	23% 9% 4 8% 5% 3 5% 4 5% 6% 30%	1573
	11th to 20th	Night	20% 9% 3 5% 6% 3 4 4 4 6% 36%	1415
	21st to end	Night	19% 7% 3 5% 6% 4 4 5% 5% 8% 36%	1550
June	1st to 10th	Night	27% 7% 3 6% 5% 2 5% 4 5% 7% 30%	1440
	11th to 20th	Night	20% 6% 4 4 3 3 5% 5% 6% 7% 36%	1440
	21st to end	Night	21% 7% 3 5% 5% 3 6% 6% 7% 8% 30%	1440
July	1st to 10th	Night	15% 7% 3 6% 5% 3 5% 5% 7% 8% 36%	1440
	11th to 20th	Night	12% 5% 3 5% 6% 4 6% 5% 7% 10% 36%	1440
	21st to end	Night	17% 5% 3 5% 6% 4 6% 5% 6% 7% 37%	1574
August	1st to 10th	Night	16% 6% 2 5% 4 3 4 5% 6% 10% 39%	1432
	11th to 20th	Night	16% 7% 3 5% 6% 3 5% 5% 6% 6% 39%	1602
	21st to end	Night	16% 7% 2 5% 5% 4 4 5% 4 7% 40%	1980
September	1st to 10th	Night	19% 5% 2 5% 6% 3 4 5% 4 6% 40%	1800
	11th to 20th	Night	18% 6% 1 4 5% 3 3 4 5% 7% 45%	1917
	21st to end	Night	22% 5% 2 4 5% 2 4 4 5% 7% 40%	1980
October	1st to 10th	Night	21% 9% 3 7% 5% 3 4 4 5% 6% 33%	2032
	11th to 20th	Night	24% 11% 3 7% 6% 3 4 4 4 5% 28%	2238
	21st to end	Night	28% 14% 3 6% 5% 3 4 4 4 6% 24%	2574
November	1st to 10th	Night	21% 15% 4 7% 5% 3 4 5% 4 5% 27%	2407
	11th to 20th	Night	20% 16% 5% 9% 7% 3 3 4 4 5% 25%	2470
	21st to end	Night	19% 19% 7% 11% 6% 3 4 4 4 3 21%	2652
December	1st to 10th	Night	21% 23% 9% 11% 7% 3 4 4 3 3 12%	2660
	11th to 20th	Night	21% 20% 8% 14% 6% 4 4 3 3 3 14%	3288
	21st to end	Night	23% 20% 7% 13% 7% 3 4 3 2 3 16%	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	77% 3 9% 9% 2	1518
	11th to 20th	Day	73% 5% 8% 8% 5%	1520
	21st to end	Day	67% 6% 9% 12% 5% 1	1592
February	1st to 10th	Day	75% 4 6% 11% 4 1	1539
	11th to 20th	Day	71% 4 10% 10% 4 1	1735
	21st to end	Day	68% 5% 9% 11% 7% 1	1480
March	1st to 10th	Day	65% 4 9% 14% 5% 2	1800
	11th to 20th	Day	61% 5% 11% 12% 10% 1	1843
	21st to end	Day	61% 4 7% 18% 9% 2	2376
April	1st to 10th	Day	63% 4 8% 16% 8% 1	2160
	11th to 20th	Day	55% 4 7% 19% 13% 1	2138
	21st to end	Day	60% 5% 9% 15% 9% 2	2340
May	1st to 10th	Day	54% 4 9% 19% 12% 2	2402
	11th to 20th	Day	51% 6% 10% 19% 13% 1	2482
	21st to end	Day	49% 9% 13% 17% 11% 1	2725
June	1st to 10th	Day	55% 7% 13% 17% 8% 1	2520
	11th to 20th	Day	47% 6% 12% 23% 10% 2	2520
	21st to end	Day	55% 7% 12% 18% 7% 1	2520
July	1st to 10th	Day	44% 7% 15% 24% 10%	2450
	11th to 20th	Day	46% 8% 14% 26% 6%	2445
	21st to end	Day	48% 9% 15% 22% 6%	2591
August	1st to 10th	Day	49% 8% 17% 21% 5%	2492
	11th to 20th	Day	46% 7% 19% 20% 9%	2278
	21st to end	Day	45% 8% 14% 22% 11%	2376
September	1st to 10th	Day	43% 7% 14% 25% 10% 1	2160
	11th to 20th	Day	41% 4 13% 30% 12%	2042
	21st to end	Day	44% 7% 15% 24% 9% 1	1980
October	1st to 10th	Day	57% 6% 12% 16% 8%	1926
	11th to 20th	Day	56% 7% 15% 15% 6%	1720
	21st to end	Day	68% 4 9% 13% 5% 1	1782
November	1st to 10th	Day	58% 7% 11% 16% 7%	1671
	11th to 20th	Day	66% 5% 10% 11% 6% 2	1710
	21st to end	Day	67% 6% 14% 9% 4	1525
December	1st to 10th	Day	76% 5% 9% 8% 2	1520
	11th to 20th	Day	70% 4 8% 13% 5%	1906
	21st to end	Day	75% 5% 8% 9% 3	2772
January	1st to 10th	Night	77% 6% 7% 7% 2	2649
	11th to 20th	Night	73% 5% 8% 10% 4	2660
	21st to end	Night	67% 5% 9% 11% 7% 1	2798
February	1st to 10th	Night	73% 5% 6% 10% 5%	2419
	11th to 20th	Night	69% 5% 8% 13% 5%	2122
	21st to end	Night	65% 4 8% 13% 8% 1	1776
March	1st to 10th	Night	64% 5% 8% 15% 7% 1	2160
	11th to 20th	Night	61% 4 9% 15% 9% 1	2116
	21st to end	Night	58% 4 7% 19% 10% 3	1980
April	1st to 10th	Night	62% 5% 7% 15% 10% 1	1800
	11th to 20th	Night	55% 5% 8% 18% 13%	1771
	21st to end	Night	56% 5% 8% 17% 11% 2	1620
May	1st to 10th	Night	55% 6% 6% 16% 14% 3	1573
	11th to 20th	Night	50% 5% 11% 17% 16% 2	1416
	21st to end	Night	47% 7% 13% 20% 12% 2	1551
June	1st to 10th	Night	53% 5% 10% 22% 8% 1	1440
	11th to 20th	Night	46% 8% 11% 22% 11% 2	1440
	21st to end	Night	48% 10% 14% 18% 9%	1440
July	1st to 10th	Night	43% 9% 14% 21% 13% 1	1400
	11th to 20th	Night	38% 10% 15% 28% 9%	1392
	21st to end	Night	43% 8% 16% 24% 9%	1486
August	1st to 10th	Night	38% 10% 20% 24% 7%	1422
	11th to 20th	Night	42% 8% 17% 22% 10%	1602
	21st to end	Night	43% 7% 15% 24% 11%	1980
September	1st to 10th	Night	43% 7% 13% 26% 11% 1	1800
	11th to 20th	Night	39% 5% 16% 29% 10%	1917
	21st to end	Night	44% 7% 12% 25% 12% 1	1980
October	1st to 10th	Night	52% 6% 11% 21% 11%	2032
	11th to 20th	Night	58% 6% 11% 18% 6%	2238
	21st to end	Night	62% 6% 10% 13% 7% 1	2574
November	1st to 10th	Night	58% 6% 11% 17% 7% 1	2407
	11th to 20th	Night	62% 6% 9% 14% 8% 2	2470
	21st to end	Night	68% 5% 10% 12% 4	2652
December	1st to 10th	Night	77% 5% 8% 8% 2	2660
	11th to 20th	Night	76% 4 7% 9% 4	3288
	21st to end	Night	75% 5% 7% 11% 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	31% 21% 30% 13% 6%	180
	11th to 20th	Day	29% 29% 27% 12% 3 1	180
	21st to end	Day	26% 22% 33% 15% 3 1	178
February	1st to 10th	Day	40% 28% 25% 5% 1	204
	11th to 20th	Day	34% 26% 29% 9% 2	394
	21st to end	Day	33% 20% 29% 16% 2	346
March	1st to 10th	Day	33% 19% 30% 16% 3	420
	11th to 20th	Day	31% 22% 29% 14% 4 1	420
	21st to end	Day	35% 20% 22% 15% 6% 1	462
April	1st to 10th	Day	37% 17% 26% 15% 5%	420
	11th to 20th	Day	36% 19% 23% 14% 6% 2	412
	21st to end	Day	35% 17% 29% 13% 5% 2	420
May	1st to 10th	Day	35% 18% 26% 13% 6% 2	423
	11th to 20th	Day	24% 19% 32% 16% 7% 2	447
	21st to end	Day	20% 19% 32% 21% 6% 1	485
June	1st to 10th	Day	32% 14% 32% 15% 6% 1	450
	11th to 20th	Day	22% 13% 33% 22% 9% 1	450
	21st to end	Day	26% 12% 35% 18% 7% 2	450
July	1st to 10th	Day	19% 9% 31% 28% 11% 1	445
	11th to 20th	Day	17% 11% 36% 25% 9% 3	444
	21st to end	Day	19% 10% 34% 27% 8% 1	488
August	1st to 10th	Day	18% 12% 28% 26% 15% 1	446
	11th to 20th	Day	20% 8% 29% 25% 14% 4	439
	21st to end	Day	21% 14% 24% 24% 11% 6%	495
September	1st to 10th	Day	20% 12% 28% 21% 13% 6%	450
	11th to 20th	Day	20% 12% 23% 22% 16% 7%	450
	21st to end	Day	19% 13% 26% 25% 12% 5%	450
October	1st to 10th	Day	28% 18% 22% 18% 12% 3	450
	11th to 20th	Day	33% 18% 21% 19% 9% 1	410
	21st to end	Day	41% 16% 24% 15% 5%	396
November	1st to 10th	Day	33% 18% 28% 15% 5% 1	365
	11th to 20th	Day	32% 24% 22% 15% 5% 2	370
	21st to end	Day	32% 21% 30% 16% 2	185
December	1st to 10th	Day	33% 21% 28% 12% 5%	180
	11th to 20th	Day	32% 27% 31% 9% 1 1	180
	21st to end	Day	38% 23% 24% 12% 3	198
January	1st to 10th	Night	28% 23% 29% 17% 3	760
	11th to 20th	Night	28% 24% 28% 17% 4	760
	21st to end	Night	21% 20% 31% 22% 5%	800
February	1st to 10th	Night	26% 22% 31% 17% 3	720
	11th to 20th	Night	24% 22% 32% 19% 3	703
	21st to end	Night	27% 19% 30% 21% 2	592
March	1st to 10th	Night	29% 18% 28% 22% 3	720
	11th to 20th	Night	30% 18% 25% 20% 6%	720
	21st to end	Night	29% 17% 25% 19% 8% 1	792
April	1st to 10th	Night	31% 16% 27% 21% 4	720
	11th to 20th	Night	31% 16% 24% 21% 8%	707
	21st to end	Night	32% 14% 29% 19% 6%	540
May	1st to 10th	Night	26% 13% 29% 24% 8% 1	493
	11th to 20th	Night	24% 12% 27% 29% 7% 1	354
	21st to end	Night	20% 11% 29% 32% 7% 1	389
June	1st to 10th	Night	30% 8% 25% 29% 8% 1	360
	11th to 20th	Night	22% 8% 26% 31% 13% 1	360
	21st to end	Night	19% 11% 24% 38% 9% 1	360
July	1st to 10th	Night	15% 4 31% 36% 13%	350
	11th to 20th	Night	12% 5% 24% 41% 17% 1	348
	21st to end	Night	15% 5% 24% 40% 15%	394
August	1st to 10th	Night	16% 6% 19% 37% 21% 1	358
	11th to 20th	Night	17% 6% 20% 37% 18% 2	538
	21st to end	Night	18% 7% 24% 32% 18% 2	792
September	1st to 10th	Night	19% 8% 24% 33% 14% 2	720
	11th to 20th	Night	21% 8% 19% 30% 21% 2	720
	21st to end	Night	23% 10% 25% 25% 16% 1	720
October	1st to 10th	Night	26% 13% 23% 26% 11% 1	720
	11th to 20th	Night	28% 14% 25% 22% 9% 1	720
	21st to end	Night	36% 14% 27% 19% 4	792
November	1st to 10th	Night	31% 16% 27% 19% 6% 1	740
	11th to 20th	Night	27% 22% 25% 16% 8% 2	760
	21st to end	Night	31% 23% 24% 16% 6% 1	760
December	1st to 10th	Night	36% 21% 24% 15% 4	760
	11th to 20th	Night	31% 20% 28% 16% 4 1	760
	21st to end	Night	33% 22% 25% 18% 3	836

Page generated at 2024-01-19 09:28:30. Version ac07

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