Norfolk County
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norfolk County clear sky chart from 2005-11-06 to 2024-08-15.

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% 10% 4 8% 5% 5% 5% 4 6% 7% 32%	95547
	Night	15% 10% 3 8% 5% 4 4 4 5% 7% 34%	93078
Transparency	Day	48% 8% 14% 19% 10% 1	95278
	Night	49% 8% 12% 19% 11% 1	92901
Seeing	Day	18% 11% 28% 25% 14% 5%	14300
	Night	19% 10% 29% 28% 12% 2	23693

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% 19% 8% 10% 5% 4 4 3 4 5% 21%	2626
	11th to 20th	Day	12% 21% 9% 17% 8% 5% 4 3 4 5% 13%	2840
	21st to end	Day	23% 20% 7% 13% 6% 5% 4 3 4 3 14%	3124
February	1st to 10th	Day	16% 18% 4 11% 8% 6% 5% 4 4 4 19%	1710
	11th to 20th	Day	14% 13% 8% 14% 7% 5% 4 3 5% 5% 21%	1663
	21st to end	Day	19% 13% 5% 12% 7% 5% 5% 4 4 5% 22%	1522
March	1st to 10th	Day	20% 13% 4 9% 6% 5% 4 3 4 6% 27%	3418
	11th to 20th	Day	11% 15% 5% 10% 6% 4 4 3 5% 7% 29%	3480
	21st to end	Day	18% 10% 3 9% 5% 5% 4 3 4 5% 33%	3815
April	1st to 10th	Day	17% 13% 4 8% 5% 4 4 3 6% 7% 29%	2194
	11th to 20th	Day	17% 10% 4 8% 5% 4 3 3 5% 7% 34%	2366
	21st to end	Day	19% 10% 3 7% 5% 4 4 3 5% 6% 33%	2470
May	1st to 10th	Day	19% 7% 3 7% 5% 5% 6% 4 5% 7% 31%	4108
	11th to 20th	Day	16% 9% 4 8% 5% 5% 4 4 6% 8% 31%	4176
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 8% 45%	4837
June	1st to 10th	Day	12% 7% 2 6% 5% 4 4 4 6% 8% 41%	2660
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 4 8% 9% 39%	2660
	21st to end	Day	12% 6% 2 6% 4 4 4 4 7% 10% 40%	2785
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 11% 42%	4454
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 5% 7% 10% 41%	4231
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 6% 8% 10% 42%	4466
August	1st to 10th	Day	10% 5% 2 5% 5% 5% 6% 5% 7% 9% 42%	2457
	11th to 20th	Day	9% 5% 3 7% 4 6% 8% 6% 8% 10% 36%	2357
	21st to end	Day	11% 6% 2 8% 4 4 5% 4 6% 8% 42%	2505
September	1st to 10th	Day	13% 5% 2 6% 4 5% 6% 4 6% 8% 40%	2160
	11th to 20th	Day	9% 5% 2 5% 5% 4 4 4 7% 8% 46%	1984
	21st to end	Day	15% 6% 2 7% 5% 5% 5% 4 6% 7% 38%	1980
October	1st to 10th	Day	17% 7% 3 7% 5% 5% 4 4 6% 6% 36%	1805
	11th to 20th	Day	18% 11% 4 8% 5% 5% 4 4 5% 6% 30%	1800
	21st to end	Day	23% 10% 4 9% 6% 4 4 3 6% 6% 24%	1980
November	1st to 10th	Day	14% 9% 3 8% 5% 4 4 4 5% 7% 36%	1676
	11th to 20th	Day	16% 11% 3 7% 6% 5% 4 4 6% 8% 30%	1520
	21st to end	Day	21% 14% 3 9% 4 4 5% 5% 6% 6% 23%	1520
December	1st to 10th	Day	16% 17% 4 10% 7% 5% 5% 4 5% 6% 22%	1520
	11th to 20th	Day	18% 16% 5% 10% 6% 5% 4 5% 6% 5% 19%	1906
	21st to end	Day	28% 20% 6% 9% 6% 4 4 3 4 4 12%	2772
January	1st to 10th	Night	17% 15% 6% 11% 6% 4 4 3 4 6% 22%	4305
	11th to 20th	Night	15% 15% 6% 13% 7% 5% 6% 5% 6% 6% 17%	4120
	21st to end	Night	24% 17% 7% 14% 6% 4 4 3 3 4 14%	4532
February	1st to 10th	Night	16% 16% 5% 10% 6% 5% 4 4 5% 5% 23%	2470
	11th to 20th	Night	15% 13% 5% 9% 7% 6% 5% 4 6% 6% 25%	2403
	21st to end	Night	18% 13% 4 10% 7% 4 5% 4 6% 6% 23%	1928
March	1st to 10th	Night	18% 10% 3 8% 5% 5% 4 3 4 5% 34%	3422
	11th to 20th	Night	13% 10% 4 7% 4 4 4 3 5% 7% 38%	3479
	21st to end	Night	16% 9% 3 7% 4 4 4 3 4 5% 40%	3817
April	1st to 10th	Night	19% 10% 3 7% 5% 4 4 4 5% 7% 32%	1986
	11th to 20th	Night	17% 9% 2 6% 4 4 4 5% 6% 7% 36%	1778
	21st to end	Night	15% 6% 3 8% 5% 5% 5% 4 7% 8% 35%	1710
May	1st to 10th	Night	19% 8% 3 6% 4 4 4 3 5% 7% 37%	2833
	11th to 20th	Night	11% 9% 3 8% 5% 5% 6% 4 6% 8% 36%	2703
	21st to end	Night	10% 5% 2 5% 4 4 3 3 6% 9% 48%	2738
June	1st to 10th	Night	12% 6% 2 6% 5% 5% 3 5% 7% 8% 42%	1520
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 4 7% 10% 41%	1520
	21st to end	Night	10% 5% 2 5% 4 4 5% 3 7% 8% 46%	1376
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 3 6% 9% 50%	2475
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 7% 8% 49%	2711
	21st to end	Night	6% 4 2 6% 5% 4 5% 4 6% 8% 49%	3087
August	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 9% 46%	1701
	11th to 20th	Night	8% 4 2 5% 4 4 4 4 6% 10% 50%	1643
	21st to end	Night	8% 4 2 6% 5% 4 5% 3 6% 9% 49%	1831
September	1st to 10th	Night	12% 8% 3 7% 4 4 4 3 5% 7% 45%	1800
	11th to 20th	Night	10% 4 2 5% 3 4 3 3 6% 6% 54%	1973
	21st to end	Night	15% 5% 2 7% 5% 4 4 4 6% 6% 41%	1980
October	1st to 10th	Night	15% 6% 3 7% 4 3 4 3 5% 8% 42%	2155
	11th to 20th	Night	17% 11% 3 7% 5% 4 3 3 5% 6% 35%	2160
	21st to end	Night	22% 9% 3 7% 5% 4 4 4 5% 6% 31%	2376
November	1st to 10th	Night	14% 8% 2 6% 4 4 4 4 5% 8% 41%	2394
	11th to 20th	Night	15% 11% 3 8% 6% 5% 5% 4 6% 8% 30%	2660
	21st to end	Night	19% 13% 4 8% 5% 4 5% 4 5% 7% 27%	2660
December	1st to 10th	Night	19% 17% 4 9% 6% 4 4 4 5% 6% 22%	2660
	11th to 20th	Night	15% 17% 5% 10% 6% 5% 4 4 5% 6% 23%	3288
	21st to end	Night	27% 19% 5% 10% 5% 4 4 3 4 5% 14%	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	65% 10% 10% 9% 7%	2627
	11th to 20th	Day	74% 11% 7% 6% 3	2840
	21st to end	Day	74% 8% 9% 7% 3	3124
February	1st to 10th	Day	67% 6% 11% 11% 5% 1	1710
	11th to 20th	Day	63% 6% 10% 15% 6%	1672
	21st to end	Day	63% 7% 11% 14% 5% 1	1522
March	1st to 10th	Day	57% 8% 11% 20% 4	3421
	11th to 20th	Day	51% 7% 19% 16% 6% 1	3480
	21st to end	Day	50% 6% 12% 20% 10% 1	3815
April	1st to 10th	Day	52% 6% 13% 17% 12% 1	2194
	11th to 20th	Day	49% 6% 12% 19% 12% 1	2366
	21st to end	Day	49% 7% 13% 18% 12% 2	2470
May	1st to 10th	Day	48% 9% 13% 18% 10% 2	4120
	11th to 20th	Day	47% 9% 16% 19% 7% 1	4180
	21st to end	Day	34% 9% 14% 22% 18% 4	4837
June	1st to 10th	Day	39% 8% 14% 24% 14% 2	2660
	11th to 20th	Day	38% 9% 16% 22% 14% 2	2660
	21st to end	Day	37% 8% 14% 26% 15% 1	2785
July	1st to 10th	Day	35% 5% 14% 27% 16% 3	4384
	11th to 20th	Day	36% 5% 15% 30% 14% 1	4158
	21st to end	Day	35% 7% 17% 21% 19% 1	4324
August	1st to 10th	Day	33% 9% 18% 26% 13% 1	2444
	11th to 20th	Day	36% 10% 18% 25% 9% 1	2357
	21st to end	Day	37% 8% 14% 26% 12% 2	2505
September	1st to 10th	Day	38% 9% 17% 24% 11% 1	2160
	11th to 20th	Day	33% 8% 16% 28% 15%	1984
	21st to end	Day	42% 8% 15% 23% 11% 1	1980
October	1st to 10th	Day	46% 8% 14% 19% 12% 1	1805
	11th to 20th	Day	53% 8% 14% 16% 9% 1	1800
	21st to end	Day	58% 8% 14% 14% 6% 1	1980
November	1st to 10th	Day	45% 8% 13% 23% 8% 2	1676
	11th to 20th	Day	50% 9% 16% 15% 9%	1520
	21st to end	Day	59% 9% 14% 13% 4	1520
December	1st to 10th	Day	63% 9% 13% 12% 2	1520
	11th to 20th	Day	63% 12% 11% 9% 4	1906
	21st to end	Day	75% 6% 10% 7% 2	2772
January	1st to 10th	Night	61% 10% 12% 11% 5% 1	4305
	11th to 20th	Night	65% 17% 8% 7% 3	4120
	21st to end	Night	74% 7% 7% 8% 3 1	4532
February	1st to 10th	Night	61% 8% 11% 15% 5% 1	2470
	11th to 20th	Night	57% 8% 12% 17% 6%	2405
	21st to end	Night	59% 6% 11% 16% 7% 1	1928
March	1st to 10th	Night	51% 7% 14% 21% 7% 1	3432
	11th to 20th	Night	43% 8% 16% 18% 13% 1	3480
	21st to end	Night	44% 6% 11% 21% 16% 2	3817
April	1st to 10th	Night	51% 6% 12% 17% 13% 1	1986
	11th to 20th	Night	47% 6% 9% 20% 15% 2	1778
	21st to end	Night	45% 8% 11% 19% 15% 3	1710
May	1st to 10th	Night	46% 6% 12% 19% 13% 5%	2840
	11th to 20th	Night	43% 10% 15% 22% 8% 2	2704
	21st to end	Night	30% 7% 15% 23% 22% 2	2739
June	1st to 10th	Night	38% 7% 11% 24% 16% 3	1520
	11th to 20th	Night	36% 8% 13% 24% 17% 2	1520
	21st to end	Night	35% 7% 14% 24% 18% 1	1376
July	1st to 10th	Night	32% 4 12% 26% 20% 6%	2435
	11th to 20th	Night	32% 5% 13% 32% 16% 2	2662
	21st to end	Night	31% 7% 17% 22% 20% 3	2988
August	1st to 10th	Night	32% 8% 13% 30% 15% 1	1690
	11th to 20th	Night	29% 8% 17% 31% 13% 1	1643
	21st to end	Night	32% 8% 14% 29% 16% 2	1831
September	1st to 10th	Night	37% 8% 13% 24% 16% 2	1800
	11th to 20th	Night	30% 6% 13% 32% 19% 1	1973
	21st to end	Night	42% 7% 12% 25% 13% 1	1980
October	1st to 10th	Night	40% 7% 12% 24% 15% 1	2155
	11th to 20th	Night	49% 7% 13% 20% 11%	2160
	21st to end	Night	53% 7% 11% 18% 10% 1	2376
November	1st to 10th	Night	41% 7% 13% 24% 14% 1	2394
	11th to 20th	Night	50% 9% 13% 17% 10% 1	2660
	21st to end	Night	56% 9% 16% 14% 4 1	2660
December	1st to 10th	Night	62% 8% 14% 13% 3	2660
	11th to 20th	Night	61% 10% 12% 12% 4	3288
	21st to end	Night	73% 8% 11% 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	25% 19% 32% 13% 8% 2	213
	11th to 20th	Day	26% 17% 37% 14% 4 1	270
	21st to end	Day	26% 17% 33% 19% 5% 1	297
February	1st to 10th	Day	23% 17% 42% 14% 4	270
	11th to 20th	Day	21% 24% 35% 18% 2	270
	21st to end	Day	25% 26% 34% 13% 1	225
March	1st to 10th	Day	24% 11% 32% 25% 7%	446
	11th to 20th	Day	21% 15% 36% 21% 5% 1	460
	21st to end	Day	27% 13% 32% 20% 7% 1	506
April	1st to 10th	Day	19% 16% 33% 24% 7% 1	460
	11th to 20th	Day	24% 15% 28% 21% 9% 3	452
	21st to end	Day	22% 10% 35% 23% 8% 2	460
May	1st to 10th	Day	22% 11% 28% 24% 9% 6%	463
	11th to 20th	Day	18% 8% 23% 27% 20% 4	487
	21st to end	Day	13% 5% 23% 32% 19% 8%	529
June	1st to 10th	Day	12% 6% 31% 34% 14% 3	490
	11th to 20th	Day	13% 9% 23% 33% 18% 4	490
	21st to end	Day	14% 6% 30% 33% 14% 3	615
July	1st to 10th	Day	9% 4 20% 29% 27% 11%	499
	11th to 20th	Day	15% 5% 21% 30% 19% 11%	484
	21st to end	Day	9% 4 22% 36% 22% 7%	532
August	1st to 10th	Day	10% 4 19% 33% 23% 12%	486
	11th to 20th	Day	9% 5% 18% 33% 23% 12%	456
	21st to end	Day	12% 5% 21% 29% 23% 11%	495
September	1st to 10th	Day	15% 5% 19% 29% 22% 11%	450
	11th to 20th	Day	8% 3 19% 27% 28% 14%	450
	21st to end	Day	15% 9% 24% 28% 16% 7%	450
October	1st to 10th	Day	18% 10% 25% 21% 19% 6%	450
	11th to 20th	Day	18% 17% 34% 23% 7% 2	450
	21st to end	Day	26% 15% 30% 21% 7%	495
November	1st to 10th	Day	19% 18% 33% 18% 10% 2	282
	11th to 20th	Day	23% 23% 29% 16% 7% 2	180
	21st to end	Day	28% 17% 35% 17% 3	180
December	1st to 10th	Day	26% 24% 28% 16% 5% 1	180
	11th to 20th	Day	27% 24% 32% 13% 4	180
	21st to end	Day	28% 21% 33% 13% 5%	198
January	1st to 10th	Night	24% 18% 36% 17% 6%	760
	11th to 20th	Night	27% 16% 33% 19% 4	760
	21st to end	Night	21% 14% 35% 25% 6%	836
February	1st to 10th	Night	26% 14% 36% 23% 2	760
	11th to 20th	Night	22% 14% 34% 26% 4	743
	21st to end	Night	23% 16% 36% 23% 3	628
March	1st to 10th	Night	18% 11% 36% 28% 6%	760
	11th to 20th	Night	21% 11% 36% 25% 8%	760
	21st to end	Night	22% 10% 31% 27% 9% 1	836
April	1st to 10th	Night	22% 11% 34% 27% 6% 1	760
	11th to 20th	Night	22% 9% 31% 28% 9% 1	654
	21st to end	Night	17% 8% 31% 36% 9%	570
May	1st to 10th	Night	18% 6% 28% 31% 15% 1	570
	11th to 20th	Night	14% 5% 26% 39% 14% 1	504
	21st to end	Night	14% 2 24% 34% 24% 2	411
June	1st to 10th	Night	13% 4 27% 39% 15% 1	380
	11th to 20th	Night	11% 3 24% 43% 18%	380
	21st to end	Night	11% 5% 23% 42% 18% 1	380
July	1st to 10th	Night	8% 2 19% 43% 25% 4	370
	11th to 20th	Night	11% 3 19% 39% 25% 5%	480
	21st to end	Night	8% 2 18% 44% 25% 3	624
August	1st to 10th	Night	8% 3 14% 41% 29% 4	567
	11th to 20th	Night	9% 3 16% 34% 33% 5%	549
	21st to end	Night	10% 3 19% 38% 26% 4	643
September	1st to 10th	Night	14% 6% 19% 32% 24% 5%	720
	11th to 20th	Night	12% 4 16% 33% 30% 5%	720
	21st to end	Night	16% 7% 21% 30% 21% 5%	720
October	1st to 10th	Night	18% 7% 23% 29% 19% 3	720
	11th to 20th	Night	22% 13% 27% 28% 9% 1	720
	21st to end	Night	26% 11% 32% 26% 5%	792
November	1st to 10th	Night	20% 11% 29% 28% 12% 1	740
	11th to 20th	Night	20% 19% 31% 22% 7% 2	760
	21st to end	Night	26% 14% 33% 21% 6%	760
December	1st to 10th	Night	30% 17% 32% 16% 5% 1	760
	11th to 20th	Night	24% 18% 35% 19% 4	760
	21st to end	Night	31% 13% 34% 20% 2	836

Page generated at 2024-08-12 09:52:50. Version ac07

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