Winchester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winchester clear sky chart from 2005-11-06 to 2024-11-04.

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	17% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	101560
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 31%	97447
Transparency	Day	51% 5% 12% 22% 9% 1	105043
	Night	53% 4 12% 20% 9% 1	102053
Seeing	Day	22% 13% 30% 22% 10% 3	14524
	Night	23% 10% 29% 28% 10% 1	23573

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% 16% 6% 12% 7% 5% 5% 3 4 4 21%	2517
	11th to 20th	Day	14% 14% 7% 11% 7% 6% 6% 4 5% 5% 21%	2520
	21st to end	Day	16% 18% 6% 12% 7% 6% 5% 4 4 5% 17%	2868
February	1st to 10th	Day	16% 15% 5% 11% 7% 5% 5% 3 5% 5% 24%	1710
	11th to 20th	Day	14% 15% 4 11% 7% 6% 3 3 4 6% 26%	1694
	21st to end	Day	19% 16% 4 10% 5% 4 4 4 4 5% 25%	1570
March	1st to 10th	Day	20% 12% 5% 10% 5% 4 4 3 4 5% 27%	3116
	11th to 20th	Day	13% 16% 5% 9% 6% 5% 5% 3 4 6% 28%	3439
	21st to end	Day	14% 8% 2 7% 6% 4 4 3 5% 7% 40%	4059
April	1st to 10th	Day	21% 13% 3 7% 4 3 4 3 5% 6% 31%	2280
	11th to 20th	Day	22% 9% 3 8% 4 4 3 3 3 6% 35%	2254
	21st to end	Day	24% 9% 2 7% 4 4 4 3 5% 5% 31%	2391
May	1st to 10th	Day	21% 8% 3 7% 5% 5% 4 4 6% 7% 31%	4426
	11th to 20th	Day	18% 9% 3 8% 5% 4 4 3 5% 7% 33%	4398
	21st to end	Day	15% 7% 3 6% 4 4 4 4 7% 7% 38%	4837
June	1st to 10th	Day	22% 8% 2 7% 5% 5% 5% 4 6% 6% 29%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 5% 4 4 6% 8% 38%	2660
	21st to end	Day	20% 7% 3 7% 5% 5% 5% 4 6% 7% 32%	2660
July	1st to 10th	Day	12% 6% 2 8% 5% 5% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 6% 5% 7% 9% 38%	4440
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 7% 9% 43%	4814
August	1st to 10th	Day	15% 8% 3 7% 5% 4 5% 4 6% 8% 35%	4378
	11th to 20th	Day	17% 6% 2 6% 4 4 5% 4 6% 8% 39%	3951
	21st to end	Day	17% 5% 2 5% 4 5% 5% 4 6% 8% 39%	4180
September	1st to 10th	Day	13% 5% 2 7% 4 4 5% 4 6% 7% 43%	2280
	11th to 20th	Day	14% 5% 2 5% 4 5% 3 3 5% 7% 47%	2262
	21st to end	Day	19% 5% 2 6% 3 5% 4 4 6% 7% 39%	2057
October	1st to 10th	Day	21% 6% 3 8% 4 4 5% 4 4 6% 35%	1900
	11th to 20th	Day	20% 9% 3 9% 6% 5% 5% 3 5% 6% 29%	1900
	21st to end	Day	26% 11% 3 7% 5% 4 4 3 5% 6% 27%	1920
November	1st to 10th	Day	16% 10% 3 7% 5% 4 4 5% 5% 8% 32%	1698
	11th to 20th	Day	18% 13% 3 8% 6% 4 5% 3 5% 5% 29%	1563
	21st to end	Day	20% 15% 4 10% 6% 5% 4 4 4 6% 21%	1520
December	1st to 10th	Day	24% 16% 4 10% 6% 5% 5% 3 4 6% 16%	1520
	11th to 20th	Day	23% 16% 4 8% 5% 4 4 4 5% 5% 23%	1906
	21st to end	Day	26% 18% 4 11% 4 5% 4 2 3 3 20%	2772
January	1st to 10th	Night	18% 16% 7% 12% 5% 5% 4 2 5% 5% 21%	4429
	11th to 20th	Night	13% 16% 6% 14% 7% 6% 6% 4 5% 4 18%	4440
	21st to end	Night	19% 19% 6% 11% 5% 5% 3 3 4 4 21%	4784
February	1st to 10th	Night	16% 17% 5% 11% 7% 5% 5% 4 5% 5% 22%	2470
	11th to 20th	Night	14% 14% 4 11% 6% 5% 4 3 5% 6% 27%	2371
	21st to end	Night	16% 15% 4 9% 6% 4 4 4 4 5% 29%	1884
March	1st to 10th	Night	21% 11% 4 8% 5% 4 4 3 4 5% 33%	3724
	11th to 20th	Night	19% 16% 4 10% 4 3 4 2 4 5% 27%	3516
	21st to end	Night	16% 11% 3 6% 4 4 3 3 4 4 41%	3572
April	1st to 10th	Night	21% 10% 3 8% 4 5% 4 3 4 5% 33%	1900
	11th to 20th	Night	19% 10% 3 6% 5% 4 4 4 5% 5% 35%	1875
	21st to end	Night	22% 9% 3 7% 5% 4 3 3 4 6% 35%	1806
May	1st to 10th	Night	22% 9% 3 7% 5% 5% 4 4 6% 7% 28%	2514
	11th to 20th	Night	20% 9% 3 7% 4 3 4 4 5% 5% 35%	2495
	21st to end	Night	13% 7% 2 6% 4 4 5% 4 5% 9% 39%	2738
June	1st to 10th	Night	18% 7% 3 7% 5% 5% 6% 4 6% 9% 29%	1520
	11th to 20th	Night	16% 6% 3 5% 4 4 4 3 6% 9% 40%	1520
	21st to end	Night	20% 7% 3 6% 4 4 4 3 6% 8% 35%	1520
July	1st to 10th	Night	13% 7% 3 8% 6% 5% 5% 4 6% 8% 35%	2520
	11th to 20th	Night	14% 6% 2 6% 4 5% 4 4 6% 8% 41%	2520
	21st to end	Night	11% 6% 2 6% 4 5% 5% 5% 6% 8% 41%	2739
August	1st to 10th	Night	14% 7% 3 7% 4 4 4 4 5% 8% 39%	2535
	11th to 20th	Night	13% 8% 3 7% 4 5% 4 4 6% 8% 39%	2844
	21st to end	Night	11% 7% 2 6% 4 5% 6% 4 6% 8% 41%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 4 5% 3 6% 6% 45%	1900
	11th to 20th	Night	14% 5% 2 4 4 3 3 3 5% 6% 50%	1917
	21st to end	Night	16% 6% 3 6% 4 4 4 4 5% 6% 43%	2121
October	1st to 10th	Night	18% 7% 3 6% 4 4 5% 4 5% 7% 37%	2280
	11th to 20th	Night	20% 8% 3 8% 5% 4 4 3 5% 6% 34%	2280
	21st to end	Night	25% 9% 3 8% 4 4 4 3 5% 6% 28%	2676
November	1st to 10th	Night	20% 10% 3 7% 4 4 4 3 3 7% 35%	2453
	11th to 20th	Night	18% 12% 3 7% 5% 5% 4 3 4 6% 32%	2616
	21st to end	Night	22% 13% 5% 9% 5% 4 4 3 5% 6% 24%	2660
December	1st to 10th	Night	21% 17% 5% 10% 5% 5% 4 4 5% 4 18%	2660
	11th to 20th	Night	22% 17% 3 9% 5% 4 4 2 3 4 26%	3288
	21st to end	Night	32% 15% 4 11% 4 4 3 2 3 3 18%	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	66% 5% 14% 9% 5% 1	2518
	11th to 20th	Day	63% 5% 13% 12% 7% 1	2520
	21st to end	Day	70% 5% 11% 10% 4	2868
February	1st to 10th	Day	63% 4 9% 20% 3 1	1710
	11th to 20th	Day	59% 5% 10% 17% 8% 1	1703
	21st to end	Day	62% 5% 11% 13% 9% 1	1570
March	1st to 10th	Day	60% 3 10% 19% 8% 1	3119
	11th to 20th	Day	57% 5% 12% 16% 9% 2	3439
	21st to end	Day	44% 4 8% 24% 17% 3	4059
April	1st to 10th	Day	55% 4 6% 20% 13% 2	2280
	11th to 20th	Day	51% 4 7% 21% 15% 2	2254
	21st to end	Day	54% 4 8% 16% 14% 3	2391
May	1st to 10th	Day	51% 6% 9% 22% 10% 2	4440
	11th to 20th	Day	51% 5% 12% 21% 9% 1	4402
	21st to end	Day	42% 6% 12% 24% 14% 1	4837
June	1st to 10th	Day	53% 6% 11% 18% 11% 1	2660
	11th to 20th	Day	43% 5% 12% 25% 12% 2	2660
	21st to end	Day	50% 6% 13% 20% 10% 1	2660
July	1st to 10th	Day	43% 4 13% 27% 12% 1	4370
	11th to 20th	Day	41% 4 15% 31% 8%	4365
	21st to end	Day	38% 6% 13% 33% 10%	4661
August	1st to 10th	Day	47% 5% 15% 24% 9%	4364
	11th to 20th	Day	43% 4 16% 29% 8%	3990
	21st to end	Day	43% 4 17% 25% 11%	4180
September	1st to 10th	Day	39% 6% 13% 29% 12%	2280
	11th to 20th	Day	37% 5% 12% 33% 14%	2262
	21st to end	Day	43% 5% 14% 27% 10%	2057
October	1st to 10th	Day	47% 4 11% 30% 8%	3160
	11th to 20th	Day	48% 3 16% 26% 7%	3140
	21st to end	Day	49% 3 17% 24% 7%	3145
November	1st to 10th	Day	49% 5% 14% 24% 7% 1	1698
	11th to 20th	Day	55% 5% 13% 17% 9% 1	1563
	21st to end	Day	63% 6% 13% 13% 5%	1520
December	1st to 10th	Day	69% 7% 11% 10% 2	1520
	11th to 20th	Day	64% 5% 13% 14% 4	1906
	21st to end	Day	72% 3 7% 15% 3	2772
January	1st to 10th	Night	66% 4 15% 11% 4	4429
	11th to 20th	Night	67% 6% 13% 10% 5%	4440
	21st to end	Night	68% 4 11% 11% 5% 1	4784
February	1st to 10th	Night	64% 4 10% 16% 6% 1	2470
	11th to 20th	Night	58% 5% 9% 20% 8%	2373
	21st to end	Night	58% 4 8% 18% 11% 1	1884
March	1st to 10th	Night	55% 3 9% 21% 9% 2	3734
	11th to 20th	Night	59% 4 14% 15% 7% 1	3517
	21st to end	Night	47% 4 5% 25% 17% 3	3572
April	1st to 10th	Night	54% 3 9% 19% 13% 2	1900
	11th to 20th	Night	50% 6% 7% 20% 15% 2	1875
	21st to end	Night	52% 3 9% 17% 16% 3	1806
May	1st to 10th	Night	53% 5% 10% 19% 9% 3	2520
	11th to 20th	Night	49% 6% 11% 21% 11% 2	2496
	21st to end	Night	42% 5% 14% 20% 17% 2	2739
June	1st to 10th	Night	49% 7% 13% 19% 11% 1	1520
	11th to 20th	Night	41% 5% 13% 22% 17% 2	1520
	21st to end	Night	47% 6% 13% 20% 13% 1	1520
July	1st to 10th	Night	46% 4 14% 21% 14% 1	2480
	11th to 20th	Night	40% 4 14% 33% 8%	2472
	21st to end	Night	40% 6% 15% 24% 15%	2651
August	1st to 10th	Night	44% 4 16% 26% 10%	2525
	11th to 20th	Night	44% 3 16% 29% 8%	2871
	21st to end	Night	41% 4 16% 26% 13% 1	3476
September	1st to 10th	Night	39% 6% 11% 28% 15% 1	1900
	11th to 20th	Night	35% 4 13% 34% 13% 1	1917
	21st to end	Night	41% 5% 12% 29% 13%	2121
October	1st to 10th	Night	43% 4 14% 30% 10%	3800
	11th to 20th	Night	45% 3 15% 28% 9%	3779
	21st to end	Night	50% 3 16% 21% 9%	4401
November	1st to 10th	Night	51% 4 14% 22% 9% 1	2453
	11th to 20th	Night	54% 5% 12% 18% 10% 1	2616
	21st to end	Night	61% 5% 12% 16% 5%	2660
December	1st to 10th	Night	68% 5% 10% 14% 3	2660
	11th to 20th	Night	63% 3 10% 16% 7% 1	3288
	21st to end	Night	72% 4 8% 13% 3	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	23% 17% 31% 21% 8%	180
	11th to 20th	Day	28% 19% 32% 14% 6% 1	180
	21st to end	Day	23% 13% 36% 21% 7%	225
February	1st to 10th	Day	29% 20% 34% 12% 4	270
	11th to 20th	Day	23% 20% 41% 15% 2	301
	21st to end	Day	27% 15% 37% 19% 2	382
March	1st to 10th	Day	23% 13% 36% 20% 7%	460
	11th to 20th	Day	23% 16% 36% 19% 5% 1	460
	21st to end	Day	27% 16% 30% 18% 7% 2	506
April	1st to 10th	Day	27% 16% 33% 17% 6% 1	460
	11th to 20th	Day	28% 20% 25% 18% 6% 3	452
	21st to end	Day	28% 17% 32% 12% 9% 2	460
May	1st to 10th	Day	24% 13% 29% 23% 8% 2	463
	11th to 20th	Day	18% 14% 36% 20% 10% 3	487
	21st to end	Day	18% 16% 30% 21% 13% 2	529
June	1st to 10th	Day	26% 11% 27% 26% 9% 2	490
	11th to 20th	Day	16% 13% 30% 26% 11% 4	490
	21st to end	Day	23% 12% 30% 21% 10% 4	490
July	1st to 10th	Day	13% 8% 26% 34% 15% 4	485
	11th to 20th	Day	13% 8% 28% 32% 15% 3	484
	21st to end	Day	14% 7% 29% 33% 14% 2	532
August	1st to 10th	Day	16% 7% 23% 34% 16% 4	486
	11th to 20th	Day	15% 5% 23% 29% 20% 8%	479
	21st to end	Day	15% 10% 27% 26% 14% 8%	539
September	1st to 10th	Day	14% 9% 29% 26% 13% 10%	490
	11th to 20th	Day	12% 7% 23% 23% 21% 14%	490
	21st to end	Day	19% 9% 30% 20% 17% 4	490
October	1st to 10th	Day	22% 12% 28% 19% 13% 6%	490
	11th to 20th	Day	24% 19% 27% 23% 7% 1	490
	21st to end	Day	31% 15% 26% 22% 5%	449
November	1st to 10th	Day	26% 19% 27% 20% 7% 1	374
	11th to 20th	Day	25% 18% 35% 14% 8%	223
	21st to end	Day	26% 22% 31% 13% 7% 1	180
December	1st to 10th	Day	31% 14% 32% 19% 4	180
	11th to 20th	Day	27% 25% 33% 11% 4 1	180
	21st to end	Day	34% 18% 29% 15% 3 2	198
January	1st to 10th	Night	27% 14% 31% 24% 4	760
	11th to 20th	Night	29% 13% 30% 23% 5% 1	760
	21st to end	Night	21% 10% 33% 29% 6%	836
February	1st to 10th	Night	21% 14% 36% 24% 4	760
	11th to 20th	Night	21% 15% 37% 23% 4	743
	21st to end	Night	24% 15% 32% 26% 4	628
March	1st to 10th	Night	25% 13% 32% 26% 5%	760
	11th to 20th	Night	24% 16% 32% 22% 5%	760
	21st to end	Night	23% 12% 30% 27% 8%	836
April	1st to 10th	Night	26% 12% 29% 28% 4	760
	11th to 20th	Night	24% 14% 31% 22% 8%	751
	21st to end	Night	27% 11% 28% 25% 8% 1	666
May	1st to 10th	Night	26% 8% 29% 27% 9% 2	380
	11th to 20th	Night	19% 7% 34% 31% 8%	374
	21st to end	Night	14% 7% 39% 27% 13%	411
June	1st to 10th	Night	18% 7% 29% 37% 9%	380
	11th to 20th	Night	18% 7% 29% 33% 13% 1	380
	21st to end	Night	19% 5% 30% 32% 13% 1	380
July	1st to 10th	Night	11% 6% 27% 43% 14%	370
	11th to 20th	Night	16% 3 21% 40% 18% 1	368
	21st to end	Night	12% 3 25% 49% 11% 1	416
August	1st to 10th	Night	15% 3 22% 41% 18% 1	394
	11th to 20th	Night	15% 2 19% 38% 25% 2	597
	21st to end	Night	15% 5% 26% 34% 18% 2	836
September	1st to 10th	Night	15% 7% 25% 35% 18% 1	760
	11th to 20th	Night	16% 5% 19% 32% 23% 4	760
	21st to end	Night	17% 7% 26% 28% 21% 2	760
October	1st to 10th	Night	21% 8% 29% 26% 15% 2	760
	11th to 20th	Night	24% 11% 30% 26% 9% 1	760
	21st to end	Night	28% 12% 27% 25% 7%	836
November	1st to 10th	Night	26% 12% 27% 26% 8% 1	755
	11th to 20th	Night	25% 15% 31% 21% 9%	760
	21st to end	Night	27% 15% 28% 23% 7%	760
December	1st to 10th	Night	30% 13% 28% 24% 4	760
	11th to 20th	Night	29% 13% 31% 21% 5% 1	760
	21st to end	Night	33% 12% 29% 22% 3	836

Page generated at 2024-11-01 22:47:44. Version ac07

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