Arundel
Clear Sky Chart
History

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

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	18% 11% 4 9% 5% 4 4 3 5% 6% 30%	101546
	Night	18% 13% 4 9% 5% 4 4 3 5% 5% 30%	97420
Transparency	Day	54% 6% 11% 19% 9% 1	101307
	Night	55% 6% 11% 18% 9% 1	97279
Seeing	Day	26% 17% 30% 18% 7% 2	14483
	Night	25% 14% 28% 24% 8% 1	23461

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% 6% 16% 8% 5% 3 2 3 4 16%	2517
	11th to 20th	Day	13% 17% 7% 18% 9% 4 3 2 3 5% 19%	2520
	21st to end	Day	12% 17% 9% 14% 6% 5% 6% 3 5% 5% 18%	2772
February	1st to 10th	Day	12% 18% 6% 14% 8% 5% 4 3 3 6% 22%	1700
	11th to 20th	Day	12% 20% 6% 12% 6% 5% 4 3 4 4 25%	1710
	21st to end	Day	17% 17% 5% 10% 8% 5% 3 3 4 4 24%	1570
March	1st to 10th	Day	18% 16% 4 9% 6% 5% 4 3 5% 5% 25%	3116
	11th to 20th	Day	13% 19% 7% 12% 5% 4 4 3 4 4 24%	3368
	21st to end	Day	14% 10% 3 9% 6% 4 4 3 5% 6% 36%	4102
April	1st to 10th	Day	21% 15% 3 8% 4 4 3 3 4 5% 30%	2280
	11th to 20th	Day	22% 11% 4 6% 4 3 4 3 4 5% 33%	2254
	21st to end	Day	22% 12% 3 7% 5% 4 4 3 5% 4 30%	2431
May	1st to 10th	Day	22% 11% 3 7% 5% 5% 5% 4 6% 6% 28%	4426
	11th to 20th	Day	19% 8% 3 8% 5% 6% 5% 4 5% 7% 32%	4398
	21st to end	Day	19% 7% 3 7% 5% 4 5% 3 5% 7% 35%	4837
June	1st to 10th	Day	23% 9% 3 7% 5% 5% 5% 4 6% 7% 26%	2660
	11th to 20th	Day	17% 7% 3 6% 5% 5% 6% 4 6% 7% 34%	2660
	21st to end	Day	23% 9% 2 7% 6% 5% 6% 4 5% 7% 27%	2660
July	1st to 10th	Day	14% 8% 3 8% 6% 5% 6% 4 6% 9% 32%	4440
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 8% 33%	4440
	21st to end	Day	13% 7% 2 6% 4 4 4 4 6% 7% 43%	4814
August	1st to 10th	Day	16% 7% 3 8% 6% 6% 5% 4 6% 9% 29%	4423
	11th to 20th	Day	17% 7% 2 7% 4 4 5% 4 6% 9% 34%	4018
	21st to end	Day	17% 6% 2 7% 5% 5% 5% 3 6% 8% 37%	4180
September	1st to 10th	Day	18% 6% 2 5% 4 4 5% 3 5% 6% 41%	2280
	11th to 20th	Day	16% 6% 2 5% 4 3 5% 3 5% 8% 44%	2236
	21st to end	Day	21% 7% 2 5% 4 3 4 3 6% 7% 38%	2090
October	1st to 10th	Day	22% 9% 3 6% 4 4 4 4 5% 7% 32%	1905
	11th to 20th	Day	24% 14% 3 8% 4 4 4 3 5% 5% 25%	1891
	21st to end	Day	25% 14% 3 8% 5% 3 3 4 5% 6% 24%	1881
November	1st to 10th	Day	16% 14% 3 8% 4 4 5% 4 5% 6% 31%	1681
	11th to 20th	Day	21% 16% 5% 9% 6% 4 4 3 5% 5% 21%	1568
	21st to end	Day	23% 15% 7% 9% 6% 4 4 3 4 4 21%	1520
December	1st to 10th	Day	23% 21% 6% 10% 5% 4 3 3 4 4 17%	1520
	11th to 20th	Day	21% 17% 6% 12% 6% 4 4 3 3 4 21%	1906
	21st to end	Day	23% 21% 6% 10% 5% 4 3 3 3 4 18%	2772
January	1st to 10th	Night	16% 19% 8% 12% 6% 4 3 3 4 4 21%	4429
	11th to 20th	Night	12% 16% 6% 16% 9% 5% 4 3 5% 5% 20%	4440
	21st to end	Night	12% 18% 8% 15% 7% 6% 4 3 4 5% 18%	4884
February	1st to 10th	Night	12% 17% 7% 12% 7% 5% 4 4 5% 4 23%	2479
	11th to 20th	Night	13% 17% 6% 12% 6% 5% 3 3 4 5% 25%	2354
	21st to end	Night	14% 16% 6% 10% 5% 5% 4 3 5% 6% 27%	1884
March	1st to 10th	Night	20% 13% 5% 8% 5% 4 4 2 4 4 31%	3724
	11th to 20th	Night	17% 19% 6% 10% 4 4 3 2 4 4 27%	3589
	21st to end	Night	14% 12% 5% 8% 6% 4 4 3 4 5% 35%	3516
April	1st to 10th	Night	22% 13% 4 6% 5% 3 3 3 4 6% 31%	1900
	11th to 20th	Night	21% 10% 3 6% 5% 3 4 3 5% 5% 35%	1875
	21st to end	Night	20% 11% 3 7% 4 4 4 3 5% 5% 33%	1763
May	1st to 10th	Night	20% 10% 3 8% 5% 3 5% 4 5% 7% 31%	2514
	11th to 20th	Night	20% 8% 3 6% 4 3 4 3 5% 7% 38%	2495
	21st to end	Night	18% 7% 3 7% 5% 4 6% 5% 6% 6% 34%	2738
June	1st to 10th	Night	19% 9% 2 7% 5% 5% 5% 4 7% 7% 31%	1520
	11th to 20th	Night	17% 8% 3 6% 5% 3 5% 4 5% 8% 37%	1520
	21st to end	Night	21% 8% 2 6% 4 4 4 4 5% 5% 36%	1520
July	1st to 10th	Night	14% 8% 3 8% 5% 5% 5% 4 6% 7% 34%	2520
	11th to 20th	Night	17% 7% 3 5% 4 3 4 3 6% 7% 40%	2520
	21st to end	Night	12% 5% 2 5% 4 4 4 4 7% 9% 45%	2739
August	1st to 10th	Night	14% 8% 3 7% 5% 4 4 4 6% 7% 39%	2506
	11th to 20th	Night	17% 7% 2 7% 4 4 4 3 6% 6% 41%	2775
	21st to end	Night	16% 7% 3 7% 4 4 3 4 5% 6% 41%	3476
September	1st to 10th	Night	15% 7% 2 5% 4 3 4 3 4 6% 46%	1900
	11th to 20th	Night	16% 6% 2 4 3 3 3 3 4 7% 48%	1943
	21st to end	Night	19% 7% 2 4 3 3 4 3 4 7% 43%	2090
October	1st to 10th	Night	18% 8% 3 7% 4 5% 3 3 5% 5% 37%	2271
	11th to 20th	Night	23% 11% 3 7% 5% 4 4 3 4 5% 30%	2289
	21st to end	Night	24% 13% 4 8% 4 3 4 3 4 6% 27%	2717
November	1st to 10th	Night	21% 12% 4 6% 5% 4 4 3 6% 6% 29%	2431
	11th to 20th	Night	19% 14% 5% 10% 5% 4 5% 3 4 5% 26%	2607
	21st to end	Night	21% 18% 6% 10% 5% 4 3 3 4 4 21%	2660
December	1st to 10th	Night	21% 20% 6% 12% 6% 4 3 3 4 4 16%	2660
	11th to 20th	Night	21% 18% 6% 12% 5% 4 3 2 3 4 22%	3288
	21st to end	Night	24% 22% 5% 10% 5% 3 3 3 3 4 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	70% 7% 8% 11% 4	2518
	11th to 20th	Day	68% 6% 5% 13% 7% 1	2520
	21st to end	Day	66% 6% 10% 11% 6% 1	2772
February	1st to 10th	Day	65% 3 7% 17% 6% 2	1700
	11th to 20th	Day	62% 5% 10% 12% 9% 1	1719
	21st to end	Day	64% 4 7% 14% 9% 2	1570
March	1st to 10th	Day	61% 7% 7% 13% 11% 1	3119
	11th to 20th	Day	62% 6% 9% 12% 9% 2	3368
	21st to end	Day	47% 6% 8% 20% 17% 2	4102
April	1st to 10th	Day	57% 4 9% 17% 11% 3	2280
	11th to 20th	Day	54% 6% 7% 20% 12% 2	2254
	21st to end	Day	57% 5% 7% 15% 12% 3	2431
May	1st to 10th	Day	53% 8% 8% 21% 8% 2	4440
	11th to 20th	Day	48% 9% 17% 16% 8% 1	4402
	21st to end	Day	48% 7% 11% 20% 14% 1	4837
June	1st to 10th	Day	56% 7% 9% 18% 10% 1	2660
	11th to 20th	Day	47% 8% 12% 20% 11% 3	2660
	21st to end	Day	57% 7% 10% 17% 8%	2660
July	1st to 10th	Day	47% 7% 15% 24% 7%	4370
	11th to 20th	Day	46% 8% 16% 24% 6%	4365
	21st to end	Day	39% 7% 15% 31% 8%	4661
August	1st to 10th	Day	50% 7% 16% 21% 6%	4409
	11th to 20th	Day	45% 7% 16% 27% 5%	4060
	21st to end	Day	44% 7% 15% 22% 12% 1	4180
September	1st to 10th	Day	43% 6% 13% 26% 12%	2280
	11th to 20th	Day	39% 6% 13% 30% 11% 1	2236
	21st to end	Day	45% 6% 13% 25% 10%	2090
October	1st to 10th	Day	51% 5% 12% 22% 10% 1	1905
	11th to 20th	Day	60% 6% 11% 17% 5% 1	1891
	21st to end	Day	61% 6% 12% 14% 6% 1	1881
November	1st to 10th	Day	53% 6% 14% 19% 7% 1	1681
	11th to 20th	Day	64% 5% 11% 12% 8%	1568
	21st to end	Day	66% 7% 11% 12% 4 1	1520
December	1st to 10th	Day	71% 5% 9% 10% 4	1520
	11th to 20th	Day	65% 7% 10% 13% 5%	1906
	21st to end	Day	70% 4 6% 13% 7%	2772
January	1st to 10th	Night	65% 7% 13% 11% 3	4429
	11th to 20th	Night	64% 8% 10% 12% 4 1	4440
	21st to end	Night	67% 6% 9% 9% 7% 1	4884
February	1st to 10th	Night	62% 5% 9% 17% 6% 1	2479
	11th to 20th	Night	61% 5% 9% 16% 8% 1	2356
	21st to end	Night	57% 6% 9% 16% 10% 2	1884
March	1st to 10th	Night	57% 5% 10% 14% 11% 3	3734
	11th to 20th	Night	60% 7% 8% 14% 11% 1	3590
	21st to end	Night	50% 6% 7% 20% 13% 4	3516
April	1st to 10th	Night	55% 4 8% 18% 13% 2	1900
	11th to 20th	Night	49% 6% 9% 21% 14% 2	1875
	21st to end	Night	52% 5% 9% 19% 12% 3	1763
May	1st to 10th	Night	51% 9% 12% 19% 8% 2	2520
	11th to 20th	Night	44% 9% 16% 16% 12% 2	2496
	21st to end	Night	47% 8% 9% 20% 14% 2	2739
June	1st to 10th	Night	48% 9% 12% 22% 10%	1520
	11th to 20th	Night	44% 7% 11% 23% 13% 2	1520
	21st to end	Night	49% 7% 11% 20% 12% 1	1520
July	1st to 10th	Night	48% 5% 18% 19% 9%	2480
	11th to 20th	Night	42% 7% 18% 27% 6%	2472
	21st to end	Night	35% 7% 19% 28% 11%	2651
August	1st to 10th	Night	44% 7% 15% 26% 7%	2496
	11th to 20th	Night	43% 7% 19% 26% 6%	2799
	21st to end	Night	42% 7% 15% 23% 11% 2	3476
September	1st to 10th	Night	38% 6% 14% 28% 13% 1	1900
	11th to 20th	Night	37% 5% 15% 32% 10% 1	1943
	21st to end	Night	42% 5% 13% 29% 11%	2090
October	1st to 10th	Night	48% 6% 10% 23% 12% 1	2271
	11th to 20th	Night	56% 5% 12% 20% 7%	2289
	21st to end	Night	59% 5% 11% 16% 7% 1	2717
November	1st to 10th	Night	54% 6% 14% 19% 6%	2431
	11th to 20th	Night	59% 6% 11% 15% 7% 2	2607
	21st to end	Night	66% 5% 10% 13% 5%	2660
December	1st to 10th	Night	71% 5% 8% 12% 4	2660
	11th to 20th	Night	66% 5% 7% 15% 7% 1	3288
	21st to end	Night	70% 5% 6% 13% 6%	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	26% 21% 37% 13% 4	180
	11th to 20th	Day	28% 22% 33% 11% 6% 1	180
	21st to end	Day	25% 21% 36% 13% 5% 1	198
February	1st to 10th	Day	36% 28% 28% 7% 1	265
	11th to 20th	Day	28% 30% 35% 6% 1	317
	21st to end	Day	34% 24% 28% 12% 2	382
March	1st to 10th	Day	28% 21% 34% 14% 2 1	460
	11th to 20th	Day	30% 21% 33% 13% 3	460
	21st to end	Day	33% 21% 25% 15% 6% 1	506
April	1st to 10th	Day	32% 20% 30% 13% 3 1	460
	11th to 20th	Day	35% 19% 24% 12% 8% 2	452
	21st to end	Day	33% 18% 31% 12% 4 1	460
May	1st to 10th	Day	29% 19% 31% 15% 5% 1	463
	11th to 20th	Day	24% 17% 34% 19% 5% 1	487
	21st to end	Day	25% 18% 33% 18% 5%	529
June	1st to 10th	Day	27% 16% 34% 16% 6%	490
	11th to 20th	Day	20% 18% 32% 20% 9% 1	490
	21st to end	Day	27% 14% 32% 17% 7% 2	490
July	1st to 10th	Day	18% 11% 33% 26% 9% 2	485
	11th to 20th	Day	17% 13% 35% 26% 8% 1	484
	21st to end	Day	16% 10% 37% 27% 8% 2	532
August	1st to 10th	Day	19% 13% 27% 30% 10% 2	486
	11th to 20th	Day	18% 9% 26% 28% 13% 6%	479
	21st to end	Day	19% 16% 27% 22% 11% 6%	539
September	1st to 10th	Day	22% 10% 31% 20% 12% 5%	490
	11th to 20th	Day	16% 12% 26% 22% 16% 8%	490
	21st to end	Day	21% 17% 23% 23% 10% 6%	490
October	1st to 10th	Day	28% 17% 22% 19% 12% 2	490
	11th to 20th	Day	31% 21% 26% 14% 6% 1	485
	21st to end	Day	36% 13% 31% 15% 4	429
November	1st to 10th	Day	35% 15% 26% 18% 4 1	369
	11th to 20th	Day	29% 25% 29% 13% 4	228
	21st to end	Day	34% 24% 28% 13% 1	180
December	1st to 10th	Day	35% 19% 28% 13% 4	180
	11th to 20th	Day	32% 28% 28% 9% 1 1	180
	21st to end	Day	36% 24% 27% 10% 3 1	198
January	1st to 10th	Night	29% 16% 36% 16% 3	760
	11th to 20th	Night	30% 20% 29% 16% 5%	760
	21st to end	Night	19% 19% 36% 20% 6% 1	836
February	1st to 10th	Night	22% 21% 34% 19% 4 1	760
	11th to 20th	Night	23% 22% 34% 18% 3	743
	21st to end	Night	25% 18% 32% 22% 3	628
March	1st to 10th	Night	26% 17% 33% 21% 3	760
	11th to 20th	Night	26% 21% 31% 18% 3 1	760
	21st to end	Night	26% 16% 31% 21% 6% 1	836
April	1st to 10th	Night	30% 17% 27% 22% 4	760
	11th to 20th	Night	27% 15% 30% 21% 6%	751
	21st to end	Night	27% 17% 28% 19% 8%	623
May	1st to 10th	Night	26% 11% 30% 24% 8% 1	380
	11th to 20th	Night	22% 11% 30% 28% 8% 1	374
	21st to end	Night	18% 12% 38% 24% 8%	411
June	1st to 10th	Night	22% 9% 31% 29% 9%	380
	11th to 20th	Night	21% 7% 26% 33% 12% 1	380
	21st to end	Night	22% 7% 21% 35% 14% 1	380
July	1st to 10th	Night	14% 8% 24% 38% 15% 1	370
	11th to 20th	Night	14% 6% 24% 38% 17% 1	368
	21st to end	Night	13% 7% 25% 39% 15% 1	416
August	1st to 10th	Night	14% 4 19% 46% 17% 1	378
	11th to 20th	Night	14% 5% 21% 34% 24% 2	551
	21st to end	Night	18% 7% 23% 33% 16% 2	836
September	1st to 10th	Night	18% 6% 27% 33% 14% 1	760
	11th to 20th	Night	20% 6% 20% 31% 21% 1	760
	21st to end	Night	22% 9% 25% 25% 17% 2	760
October	1st to 10th	Night	23% 13% 25% 26% 12% 1	760
	11th to 20th	Night	30% 12% 26% 23% 7% 1	760
	21st to end	Night	31% 13% 28% 23% 5%	836
November	1st to 10th	Night	29% 15% 26% 23% 6% 1	748
	11th to 20th	Night	27% 18% 31% 15% 8% 1	760
	21st to end	Night	33% 18% 26% 17% 6%	760
December	1st to 10th	Night	31% 21% 27% 17% 4 1	760
	11th to 20th	Night	31% 21% 26% 16% 4 1	760
	21st to end	Night	36% 17% 28% 17% 3	836

Page generated at 2024-10-30 13:19:24. Version ac07

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