Norwich
Clear Sky Chart
History

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

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	17% 11% 4 8% 5% 4 4 4 5% 7% 29%	101501
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 30%	97533
Transparency	Day	53% 6% 11% 19% 9% 1	105023
	Night	55% 6% 11% 19% 9% 1	102100
Seeing	Day	27% 15% 28% 19% 9% 3	14745
	Night	24% 15% 27% 24% 9% 1	23903

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	13% 19% 11% 12% 5% 4 4 3 4 4 21%	2517
	11th to 20th	Day	15% 18% 9% 15% 8% 5% 4 2 3 3 17%	2520
	21st to end	Day	18% 21% 10% 10% 9% 4 4 3 4 4 15%	3042
February	1st to 10th	Day	17% 17% 5% 14% 9% 5% 5% 4 5% 4 16%	1710
	11th to 20th	Day	13% 14% 7% 16% 9% 5% 5% 4 3 5% 19%	1737
	21st to end	Day	20% 14% 3 12% 9% 4 3 3 3 5% 22%	1570
March	1st to 10th	Day	24% 15% 5% 11% 5% 3 3 3 3 3 24%	3116
	11th to 20th	Day	11% 21% 6% 10% 5% 4 3 2 4 5% 28%	3480
	21st to end	Day	20% 13% 5% 10% 4 3 3 3 4 4 30%	4032
April	1st to 10th	Day	19% 15% 3 8% 4 4 4 3 4 4 30%	2280
	11th to 20th	Day	18% 11% 3 7% 5% 5% 5% 3 4 5% 34%	2254
	21st to end	Day	20% 13% 3 7% 5% 4 4 3 4 6% 31%	2280
May	1st to 10th	Day	25% 10% 3 6% 4 3 4 3 4 6% 32%	4366
	11th to 20th	Day	19% 8% 3 8% 6% 5% 5% 4 6% 7% 28%	4398
	21st to end	Day	14% 6% 2 6% 5% 4 4 5% 7% 8% 39%	4837
June	1st to 10th	Day	19% 8% 2 7% 5% 5% 5% 4 5% 8% 32%	2660
	11th to 20th	Day	17% 7% 3 6% 5% 5% 5% 4 6% 9% 33%	2660
	21st to end	Day	17% 6% 3 7% 5% 5% 5% 5% 6% 9% 31%	2660
July	1st to 10th	Day	11% 7% 3 6% 5% 5% 6% 5% 8% 11% 35%	4440
	11th to 20th	Day	11% 5% 2 7% 5% 5% 7% 6% 9% 11% 32%	4440
	21st to end	Day	14% 6% 3 8% 6% 6% 6% 4 7% 8% 34%	4814
August	1st to 10th	Day	20% 6% 3 7% 5% 5% 5% 4 6% 8% 30%	4182
	11th to 20th	Day	16% 8% 3 8% 5% 6% 6% 4 7% 10% 29%	3863
	21st to end	Day	19% 6% 2 7% 4 4 4 3 6% 8% 36%	4180
September	1st to 10th	Day	17% 7% 2 5% 5% 4 4 4 6% 8% 38%	2280
	11th to 20th	Day	15% 7% 2 6% 3 4 4 3 5% 7% 44%	2266
	21st to end	Day	20% 6% 3 7% 5% 4 6% 4 6% 6% 33%	2057
October	1st to 10th	Day	21% 9% 3 8% 5% 5% 4 3 6% 6% 31%	1900
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 4 5% 6% 33%	1900
	21st to end	Day	23% 15% 3 6% 4 3 4 3 6% 6% 26%	1981
November	1st to 10th	Day	14% 13% 3 7% 5% 5% 4 3 5% 6% 35%	1708
	11th to 20th	Day	18% 17% 3 10% 5% 4 5% 4 4 5% 26%	1653
	21st to end	Day	18% 17% 5% 9% 7% 5% 5% 3 4 6% 22%	1520
December	1st to 10th	Day	20% 19% 7% 12% 6% 4 4 3 4 5% 16%	1520
	11th to 20th	Day	20% 17% 8% 12% 5% 4 4 3 4 3 22%	1906
	21st to end	Day	23% 21% 8% 10% 5% 4 4 2 5% 4 14%	2772
January	1st to 10th	Night	16% 15% 8% 15% 6% 5% 5% 4 5% 5% 16%	4429
	11th to 20th	Night	13% 17% 8% 17% 9% 5% 3 2 4 4 18%	4440
	21st to end	Night	22% 16% 6% 14% 7% 5% 4 3 4 3 14%	4599
February	1st to 10th	Night	13% 16% 5% 14% 8% 5% 5% 3 4 5% 20%	2470
	11th to 20th	Night	12% 13% 8% 14% 9% 6% 6% 5% 5% 5% 18%	2328
	21st to end	Night	18% 13% 5% 13% 6% 4 3 3 5% 6% 23%	1884
March	1st to 10th	Night	21% 15% 5% 9% 5% 4 3 4 4 5% 25%	3707
	11th to 20th	Night	14% 18% 6% 10% 5% 5% 4 3 4 5% 27%	3479
	21st to end	Night	17% 14% 4 11% 5% 4 3 3 4 4 31%	3599
April	1st to 10th	Night	20% 15% 4 7% 5% 5% 3 3 4 6% 29%	1900
	11th to 20th	Night	19% 12% 3 6% 5% 4 4 3 5% 6% 34%	1875
	21st to end	Night	20% 10% 4 7% 4 4 4 3 5% 6% 34%	1900
May	1st to 10th	Night	27% 8% 2 7% 4 3 4 2 5% 6% 31%	2601
	11th to 20th	Night	19% 9% 3 7% 5% 5% 4 3 6% 7% 32%	2495
	21st to end	Night	13% 8% 3 7% 4 5% 5% 4 6% 7% 38%	2738
June	1st to 10th	Night	16% 8% 2 6% 4 4 4 4 5% 7% 40%	1520
	11th to 20th	Night	17% 6% 2 5% 5% 3 4 4 7% 9% 38%	1520
	21st to end	Night	13% 5% 2 5% 4 4 4 4 6% 8% 43%	1520
July	1st to 10th	Night	10% 7% 3 7% 5% 4 6% 4 6% 9% 39%	2520
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 5% 8% 44%	2520
	21st to end	Night	15% 6% 2 6% 4 5% 4 4 5% 7% 43%	2739
August	1st to 10th	Night	23% 7% 2 6% 4 3 4 3 6% 6% 36%	2745
	11th to 20th	Night	18% 6% 3 7% 4 4 4 3 5% 5% 40%	2934
	21st to end	Night	15% 6% 2 5% 4 3 4 3 5% 7% 45%	3476
September	1st to 10th	Night	17% 6% 2 6% 3 3 4 3 5% 7% 44%	1900
	11th to 20th	Night	16% 5% 2 4 4 3 3 3 4 7% 49%	1914
	21st to end	Night	18% 8% 3 6% 4 4 5% 3 5% 7% 38%	2118
October	1st to 10th	Night	20% 8% 2 8% 5% 4 4 4 5% 5% 35%	2280
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 5% 6% 35%	2280
	21st to end	Night	25% 13% 3 8% 4 4 4 3 4 7% 26%	2615
November	1st to 10th	Night	13% 13% 4 8% 4 4 4 4 5% 7% 36%	2470
	11th to 20th	Night	20% 13% 3 8% 5% 4 4 3 5% 6% 29%	2526
	21st to end	Night	15% 15% 5% 9% 6% 5% 4 4 6% 7% 25%	2660
December	1st to 10th	Night	18% 18% 8% 11% 6% 4 4 4 5% 5% 18%	2660
	11th to 20th	Night	21% 14% 6% 13% 6% 5% 4 3 4 4 21%	3288
	21st to end	Night	25% 16% 8% 10% 5% 4 4 3 4 5% 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	67% 4 10% 14% 5% 1	2518
	11th to 20th	Day	72% 5% 7% 10% 4 1	2520
	21st to end	Day	74% 4 8% 9% 4 1	3042
February	1st to 10th	Day	71% 5% 7% 12% 4	1710
	11th to 20th	Day	68% 5% 5% 14% 6%	1746
	21st to end	Day	65% 5% 8% 14% 7%	1570
March	1st to 10th	Day	66% 4 9% 13% 7% 1	3119
	11th to 20th	Day	58% 5% 13% 13% 9% 1	3480
	21st to end	Day	57% 4 6% 16% 15% 2	4032
April	1st to 10th	Day	58% 4 6% 21% 9% 2	2280
	11th to 20th	Day	53% 5% 9% 19% 12% 1	2254
	21st to end	Day	55% 4 8% 19% 12% 3	2280
May	1st to 10th	Day	53% 5% 9% 19% 11% 1	4380
	11th to 20th	Day	53% 8% 10% 22% 6% 1	4402
	21st to end	Day	40% 7% 13% 26% 13% 1	4837
June	1st to 10th	Day	50% 7% 10% 20% 12% 1	2660
	11th to 20th	Day	48% 5% 13% 23% 10% 1	2660
	21st to end	Day	48% 7% 13% 21% 10% 1	2660
July	1st to 10th	Day	41% 8% 17% 24% 11%	4370
	11th to 20th	Day	40% 10% 17% 25% 8%	4365
	21st to end	Day	47% 7% 14% 22% 11%	4661
August	1st to 10th	Day	51% 7% 13% 18% 10%	4168
	11th to 20th	Day	48% 8% 16% 22% 6%	3902
	21st to end	Day	44% 6% 12% 30% 7% 1	4180
September	1st to 10th	Day	44% 6% 12% 26% 12% 1	2280
	11th to 20th	Day	41% 4 11% 24% 19% 1	2266
	21st to end	Day	49% 6% 11% 21% 12% 1	2057
October	1st to 10th	Day	47% 6% 11% 25% 11% 1	3160
	11th to 20th	Day	46% 5% 12% 20% 16%	3140
	21st to end	Day	44% 6% 15% 24% 9% 1	3245
November	1st to 10th	Day	49% 5% 13% 19% 12% 1	1708
	11th to 20th	Day	62% 4 10% 15% 8% 2	1653
	21st to end	Day	64% 3 13% 14% 5%	1520
December	1st to 10th	Day	72% 4 10% 11% 4	1520
	11th to 20th	Day	70% 3 12% 11% 4	1906
	21st to end	Day	75% 4 7% 10% 4	2772
January	1st to 10th	Night	68% 6% 12% 9% 5%	4429
	11th to 20th	Night	69% 5% 7% 12% 6% 1	4440
	21st to end	Night	75% 4 7% 10% 4 1	4599
February	1st to 10th	Night	67% 5% 9% 13% 6%	2470
	11th to 20th	Night	67% 6% 8% 13% 6% 1	2330
	21st to end	Night	61% 5% 10% 15% 8% 1	1884
March	1st to 10th	Night	62% 5% 9% 16% 8%	3717
	11th to 20th	Night	60% 5% 10% 19% 5%	3480
	21st to end	Night	57% 5% 5% 19% 13% 2	3599
April	1st to 10th	Night	58% 5% 10% 17% 9% 2	1900
	11th to 20th	Night	51% 5% 10% 18% 15% 1	1875
	21st to end	Night	52% 5% 9% 19% 13% 3	1900
May	1st to 10th	Night	54% 5% 10% 18% 9% 3	2607
	11th to 20th	Night	50% 8% 14% 19% 8% 1	2496
	21st to end	Night	44% 7% 12% 20% 15% 1	2739
June	1st to 10th	Night	43% 6% 12% 24% 14% 1	1520
	11th to 20th	Night	41% 8% 15% 24% 11% 1	1520
	21st to end	Night	38% 8% 14% 27% 12% 1	1520
July	1st to 10th	Night	40% 8% 15% 21% 14% 1	2480
	11th to 20th	Night	39% 7% 14% 27% 13%	2472
	21st to end	Night	42% 6% 11% 26% 14% 1	2651
August	1st to 10th	Night	48% 7% 15% 22% 8% 1	2735
	11th to 20th	Night	45% 6% 15% 26% 8%	2961
	21st to end	Night	38% 6% 13% 32% 11%	3476
September	1st to 10th	Night	41% 5% 14% 25% 14% 1	1900
	11th to 20th	Night	36% 5% 11% 28% 19% 1	1914
	21st to end	Night	46% 5% 11% 23% 13% 1	2118
October	1st to 10th	Night	51% 6% 11% 22% 10% 1	3800
	11th to 20th	Night	46% 5% 13% 18% 14% 3	3779
	21st to end	Night	45% 6% 15% 26% 8%	4301
November	1st to 10th	Night	49% 5% 11% 20% 14% 2	2470
	11th to 20th	Night	56% 6% 10% 18% 8% 2	2526
	21st to end	Night	58% 5% 15% 16% 5%	2660
December	1st to 10th	Night	69% 4 11% 13% 3	2660
	11th to 20th	Night	67% 6% 10% 13% 4	3288
	21st to end	Night	71% 6% 9% 11% 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	34% 18% 29% 14% 4 1	180
	11th to 20th	Day	44% 24% 20% 9% 2 1	180
	21st to end	Day	30% 26% 30% 11% 3	276
February	1st to 10th	Day	35% 30% 28% 6%	270
	11th to 20th	Day	37% 27% 27% 8%	344
	21st to end	Day	40% 19% 27% 12% 3	382
March	1st to 10th	Day	33% 20% 29% 13% 4	460
	11th to 20th	Day	36% 21% 25% 15% 3	460
	21st to end	Day	38% 21% 23% 12% 4 2	506
April	1st to 10th	Day	38% 17% 26% 14% 5% 1	460
	11th to 20th	Day	33% 20% 25% 11% 7% 4	452
	21st to end	Day	35% 15% 27% 14% 6% 2	460
May	1st to 10th	Day	34% 15% 27% 13% 8% 4	463
	11th to 20th	Day	23% 12% 33% 20% 7% 4	487
	21st to end	Day	19% 11% 32% 26% 9% 4	529
June	1st to 10th	Day	26% 14% 25% 22% 10% 2	490
	11th to 20th	Day	19% 11% 30% 26% 11% 2	490
	21st to end	Day	22% 12% 34% 23% 7% 2	490
July	1st to 10th	Day	15% 8% 28% 27% 16% 6%	485
	11th to 20th	Day	15% 6% 27% 33% 14% 5%	484
	21st to end	Day	18% 6% 34% 27% 12% 3	532
August	1st to 10th	Day	14% 9% 28% 26% 17% 5%	486
	11th to 20th	Day	17% 9% 26% 27% 14% 8%	479
	21st to end	Day	17% 11% 27% 24% 14% 8%	539
September	1st to 10th	Day	19% 10% 24% 23% 15% 9%	490
	11th to 20th	Day	15% 8% 26% 21% 19% 11%	490
	21st to end	Day	24% 11% 25% 22% 13% 5%	490
October	1st to 10th	Day	27% 13% 24% 19% 12% 7%	490
	11th to 20th	Day	29% 16% 28% 17% 9% 2	490
	21st to end	Day	36% 14% 26% 20% 4	482
November	1st to 10th	Day	27% 20% 24% 19% 9% 2	378
	11th to 20th	Day	34% 23% 23% 14% 5% 1	313
	21st to end	Day	36% 18% 32% 13% 1	180
December	1st to 10th	Day	37% 22% 26% 12% 3 1	180
	11th to 20th	Day	37% 20% 32% 10% 1	180
	21st to end	Day	38% 21% 32% 7% 1 1	198
January	1st to 10th	Night	27% 24% 32% 15% 2	760
	11th to 20th	Night	28% 22% 28% 19% 3	760
	21st to end	Night	23% 22% 33% 18% 3	836
February	1st to 10th	Night	28% 21% 30% 19% 2	760
	11th to 20th	Night	27% 23% 32% 15% 2	743
	21st to end	Night	30% 21% 29% 17% 2	628
March	1st to 10th	Night	27% 21% 29% 19% 3	760
	11th to 20th	Night	29% 20% 28% 19% 3	760
	21st to end	Night	27% 22% 24% 20% 7% 1	836
April	1st to 10th	Night	30% 15% 31% 21% 3	760
	11th to 20th	Night	26% 17% 28% 20% 8% 1	751
	21st to end	Night	29% 13% 27% 23% 7%	760
May	1st to 10th	Night	31% 10% 22% 29% 9%	441
	11th to 20th	Night	20% 9% 32% 30% 8% 1	374
	21st to end	Night	14% 6% 31% 36% 12% 1	411
June	1st to 10th	Night	18% 8% 26% 36% 12% 1	380
	11th to 20th	Night	18% 7% 23% 35% 16%	380
	21st to end	Night	14% 4 27% 40% 14% 1	380
July	1st to 10th	Night	11% 3 22% 44% 19% 2	370
	11th to 20th	Night	13% 2 21% 42% 21% 2	368
	21st to end	Night	16% 2 22% 44% 14% 2	416
August	1st to 10th	Night	15% 3 22% 36% 22% 2	513
	11th to 20th	Night	17% 4 13% 37% 25% 4	648
	21st to end	Night	18% 6% 18% 35% 22% 2	836
September	1st to 10th	Night	19% 6% 23% 33% 17% 2	760
	11th to 20th	Night	18% 6% 20% 27% 25% 4	760
	21st to end	Night	21% 9% 24% 28% 16% 2	760
October	1st to 10th	Night	24% 11% 24% 24% 15% 2	760
	11th to 20th	Night	25% 12% 27% 27% 8% 1	760
	21st to end	Night	32% 12% 28% 22% 5%	836
November	1st to 10th	Night	21% 16% 30% 24% 8%	760
	11th to 20th	Night	31% 17% 27% 17% 6% 1	760
	21st to end	Night	25% 19% 31% 20% 5%	760
December	1st to 10th	Night	31% 23% 25% 17% 3	760
	11th to 20th	Night	30% 21% 28% 18% 3	760
	21st to end	Night	30% 23% 30% 16% 2	836

Page generated at 2024-11-03 02:11:24. Version ac07

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