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 2024-03-18.

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	19% 11% 4 8% 6% 3 5% 4 5% 6% 29%	78445
	Night	18% 12% 5% 8% 6% 3 4 4 4 6% 30%	81335
Transparency	Day	55% 6% 10% 18% 9% 1	78150
	Night	56% 6% 11% 18% 9% 1	81164
Seeing	Day	27% 18% 30% 17% 7% 2	13580
	Night	25% 14% 28% 23% 8% 1	22767

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% 18% 7% 15% 9% 4 4 2 3 4 16%	2517
	11th to 20th	Day	13% 16% 8% 15% 11% 3 3 3 3 5% 19%	2520
	21st to end	Day	12% 17% 9% 13% 7% 3 6% 5% 5% 5% 18%	2772
February	1st to 10th	Day	12% 17% 6% 12% 8% 4 4 3 4 6% 22%	1700
	11th to 20th	Day	12% 19% 6% 11% 6% 4 4 5% 4 4 25%	1710
	21st to end	Day	17% 16% 6% 9% 8% 4 5% 3 4 5% 24%	1570
March	1st to 10th	Day	16% 13% 6% 8% 7% 4 4 4 4 6% 27%	1897
	11th to 20th	Day	15% 15% 5% 8% 7% 3 4 4 5% 5% 28%	1985
	21st to end	Day	19% 10% 4 7% 6% 2 4 4 4 6% 34%	2340
April	1st to 10th	Day	22% 13% 4 8% 4 3 3 4 4 5% 31%	2160
	11th to 20th	Day	22% 10% 4 5% 5% 2 4 4 3 5% 34%	2134
	21st to end	Day	22% 11% 4 7% 6% 3 4 4 5% 4 30%	2302
May	1st to 10th	Day	22% 10% 4 6% 5% 3 4 4 4 6% 31%	2520
	11th to 20th	Day	20% 8% 3 6% 6% 4 5% 4 4 6% 35%	2478
	21st to end	Day	21% 7% 3 6% 5% 3 5% 4 5% 7% 34%	2725
June	1st to 10th	Day	23% 8% 3 6% 6% 3 5% 5% 6% 7% 27%	2520
	11th to 20th	Day	18% 7% 3 5% 5% 3 6% 5% 5% 8% 35%	2520
	21st to end	Day	22% 8% 3 6% 7% 3 6% 5% 5% 7% 28%	2520
July	1st to 10th	Day	15% 6% 3 5% 6% 4 5% 6% 5% 8% 37%	2520
	11th to 20th	Day	16% 5% 3 6% 7% 4 6% 5% 6% 10% 33%	2520
	21st to end	Day	14% 7% 3 6% 6% 4 6% 6% 7% 8% 33%	2744
August	1st to 10th	Day	16% 7% 3 7% 7% 4 6% 5% 6% 8% 33%	2506
	11th to 20th	Day	15% 6% 2 7% 6% 4 6% 5% 6% 9% 35%	2294
	21st to end	Day	17% 6% 3 6% 6% 3 5% 4 5% 7% 38%	2376
September	1st to 10th	Day	18% 6% 2 5% 5% 3 5% 5% 5% 7% 41%	2160
	11th to 20th	Day	17% 6% 3 5% 4 2 4 5% 5% 7% 43%	2119
	21st to end	Day	21% 7% 3 4 5% 2 4 4 5% 7% 38%	1980
October	1st to 10th	Day	23% 8% 3 5% 5% 3 5% 5% 5% 7% 32%	1805
	11th to 20th	Day	26% 13% 4 6% 6% 3 4 4 5% 5% 24%	1792
	21st to end	Day	27% 14% 3 7% 5% 3 3 4 5% 5% 23%	1782
November	1st to 10th	Day	17% 13% 3 7% 5% 2 5% 4 5% 7% 31%	1671
	11th to 20th	Day	22% 15% 6% 8% 6% 3 4 4 5% 5% 21%	1568
	21st to end	Day	23% 14% 7% 8% 7% 3 4 4 4 4 21%	1520
December	1st to 10th	Day	24% 19% 6% 9% 6% 4 3 3 4 4 17%	1520
	11th to 20th	Day	21% 15% 6% 11% 7% 2 5% 4 3 4 21%	1906
	21st to end	Day	23% 20% 7% 9% 6% 3 4 3 3 4 19%	2772
January	1st to 10th	Night	17% 18% 8% 10% 7% 3 4 4 4 4 21%	4429
	11th to 20th	Night	13% 15% 7% 14% 11% 4 4 4 5% 5% 20%	4440
	21st to end	Night	12% 17% 8% 14% 8% 5% 5% 4 4 5% 18%	4884
February	1st to 10th	Night	13% 15% 8% 10% 8% 4 5% 5% 5% 5% 23%	2479
	11th to 20th	Night	13% 15% 7% 11% 8% 4 4 3 4 6% 25%	2354
	21st to end	Night	14% 15% 6% 9% 6% 3 5% 4 5% 6% 27%	1884
March	1st to 10th	Night	17% 12% 6% 8% 7% 4 6% 4 4 5% 28%	2270
	11th to 20th	Night	17% 14% 6% 7% 7% 3 3 3 4 5% 30%	2138
	21st to end	Night	18% 11% 3 6% 5% 3 3 4 4 5% 38%	2016
April	1st to 10th	Night	23% 11% 4 6% 5% 3 3 3 4 6% 31%	1800
	11th to 20th	Night	20% 9% 4 5% 5% 2 3 5% 5% 6% 36%	1775
	21st to end	Night	20% 11% 3 6% 5% 3 5% 3 5% 6% 33%	1671
May	1st to 10th	Night	20% 10% 3 6% 5% 2 3 5% 5% 6% 36%	1440
	11th to 20th	Night	18% 7% 3 6% 4 2 5% 5% 5% 6% 39%	1415
	21st to end	Night	16% 6% 4 5% 5% 3 5% 6% 4 7% 40%	1550
June	1st to 10th	Night	19% 8% 2 6% 6% 4 5% 5% 7% 8% 31%	1440
	11th to 20th	Night	17% 7% 3 5% 5% 2 5% 5% 5% 8% 38%	1440
	21st to end	Night	19% 8% 3 5% 4 3 5% 5% 5% 6% 37%	1440
July	1st to 10th	Night	12% 5% 3 6% 5% 3 5% 4 5% 8% 44%	1440
	11th to 20th	Night	14% 5% 2 5% 5% 3 3 6% 7% 8% 42%	1440
	21st to end	Night	12% 5% 2 5% 5% 3 5% 6% 6% 9% 41%	1574
August	1st to 10th	Night	11% 6% 2 6% 5% 3 4 6% 6% 8% 42%	1432
	11th to 20th	Night	13% 5% 2 6% 5% 3 5% 4 5% 7% 45%	1585
	21st to end	Night	15% 6% 3 4 4 3 3 5% 5% 7% 45%	1980
September	1st to 10th	Night	15% 7% 3 5% 4 2 3 5% 4 6% 45%	1800
	11th to 20th	Night	17% 5% 2 4 4 3 3 4 5% 7% 46%	1840
	21st to end	Night	19% 6% 2 4 4 2 4 4 4 7% 44%	1980
October	1st to 10th	Night	19% 8% 3 6% 5% 3 4 4 5% 6% 37%	2151
	11th to 20th	Night	24% 11% 3 6% 6% 3 4 4 4 6% 30%	2168
	21st to end	Night	25% 12% 4 7% 6% 2 4 4 4 6% 27%	2574
November	1st to 10th	Night	21% 12% 5% 6% 5% 3 4 4 5% 6% 30%	2407
	11th to 20th	Night	19% 13% 6% 9% 6% 3 5% 4 4 5% 26%	2607
	21st to end	Night	21% 17% 6% 9% 6% 2 4 4 4 4 21%	2660
December	1st to 10th	Night	21% 18% 7% 11% 7% 3 4 4 4 4 17%	2660
	11th to 20th	Night	22% 17% 6% 10% 7% 3 4 3 3 4 23%	3288
	21st to end	Night	24% 21% 5% 9% 7% 2 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	59% 5% 8% 16% 10% 2	1900
	11th to 20th	Day	58% 5% 9% 14% 11% 3	1985
	21st to end	Day	52% 5% 9% 18% 13% 4	2340
April	1st to 10th	Day	57% 4 9% 16% 11% 3	2160
	11th to 20th	Day	53% 6% 7% 20% 12% 2	2134
	21st to end	Day	57% 5% 7% 14% 12% 4	2302
May	1st to 10th	Day	54% 5% 7% 19% 12% 3	2520
	11th to 20th	Day	51% 5% 8% 19% 15% 2	2482
	21st to end	Day	50% 6% 11% 18% 13% 2	2725
June	1st to 10th	Day	56% 7% 9% 18% 10% 1	2520
	11th to 20th	Day	48% 8% 11% 20% 11% 3	2520
	21st to end	Day	56% 7% 10% 17% 9% 1	2520
July	1st to 10th	Day	42% 8% 15% 25% 10%	2450
	11th to 20th	Day	45% 8% 14% 23% 10%	2445
	21st to end	Day	46% 8% 16% 21% 8%	2591
August	1st to 10th	Day	49% 7% 16% 22% 6%	2492
	11th to 20th	Day	44% 8% 17% 23% 8% 1	2294
	21st to end	Day	45% 6% 13% 24% 11% 1	2376
September	1st to 10th	Day	43% 6% 13% 25% 12%	2160
	11th to 20th	Day	40% 7% 13% 29% 10% 1	2119
	21st to end	Day	45% 6% 14% 26% 9%	1980
October	1st to 10th	Day	51% 5% 12% 21% 10% 1	1805
	11th to 20th	Day	61% 6% 11% 16% 5% 1	1792
	21st to end	Day	63% 5% 11% 14% 6% 1	1782
November	1st to 10th	Day	52% 6% 14% 19% 7% 1	1671
	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	59% 5% 8% 17% 10% 2	2280
	11th to 20th	Night	57% 5% 9% 15% 12% 2	2139
	21st to end	Night	50% 5% 8% 18% 15% 4	2016
April	1st to 10th	Night	55% 4 8% 17% 13% 2	1800
	11th to 20th	Night	48% 5% 9% 21% 14% 2	1775
	21st to end	Night	53% 5% 9% 18% 12% 3	1671
May	1st to 10th	Night	50% 6% 7% 20% 14% 3	1440
	11th to 20th	Night	46% 6% 9% 19% 17% 3	1416
	21st to end	Night	43% 8% 11% 21% 14% 3	1551
June	1st to 10th	Night	48% 8% 12% 22% 9%	1440
	11th to 20th	Night	45% 7% 10% 23% 13% 3	1440
	21st to end	Night	48% 7% 12% 21% 12%	1440
July	1st to 10th	Night	37% 6% 16% 27% 13% 1	1400
	11th to 20th	Night	38% 8% 14% 30% 10%	1392
	21st to end	Night	38% 9% 18% 25% 10%	1486
August	1st to 10th	Night	37% 10% 19% 26% 8%	1422
	11th to 20th	Night	38% 8% 17% 27% 10%	1585
	21st to end	Night	39% 7% 16% 28% 10%	1980
September	1st to 10th	Night	39% 6% 14% 27% 12% 1	1800
	11th to 20th	Night	38% 5% 15% 31% 10% 1	1840
	21st to end	Night	42% 6% 12% 30% 11%	1980
October	1st to 10th	Night	48% 6% 10% 24% 11% 1	2151
	11th to 20th	Night	56% 5% 12% 19% 7%	2168
	21st to end	Night	60% 6% 11% 16% 7% 1	2574
November	1st to 10th	Night	54% 7% 14% 19% 6%	2407
	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	31% 21% 31% 14% 3	449
	21st to end	Day	34% 19% 24% 16% 6% 1	462
April	1st to 10th	Day	32% 20% 31% 13% 4	420
	11th to 20th	Day	34% 18% 24% 14% 8% 2	412
	21st to end	Day	32% 19% 31% 13% 4 1	420
May	1st to 10th	Day	29% 19% 31% 15% 5% 1	423
	11th to 20th	Day	26% 18% 33% 17% 5% 1	447
	21st to end	Day	24% 19% 34% 18% 5%	485
June	1st to 10th	Day	27% 17% 34% 15% 6%	450
	11th to 20th	Day	21% 18% 30% 20% 10% 1	450
	21st to end	Day	26% 14% 33% 18% 8% 2	450
July	1st to 10th	Day	18% 11% 33% 26% 9% 2	445
	11th to 20th	Day	16% 13% 36% 27% 8% 1	444
	21st to end	Day	16% 10% 38% 26% 8% 1	488
August	1st to 10th	Day	18% 12% 28% 30% 10% 2	446
	11th to 20th	Day	18% 9% 26% 29% 12% 6%	439
	21st to end	Day	20% 17% 26% 21% 11% 6%	495
September	1st to 10th	Day	22% 10% 31% 19% 12% 5%	450
	11th to 20th	Day	17% 13% 28% 21% 14% 8%	450
	21st to end	Day	21% 17% 22% 24% 10% 6%	450
October	1st to 10th	Day	29% 18% 22% 18% 11% 2	450
	11th to 20th	Day	33% 21% 25% 14% 7% 1	446
	21st to end	Day	37% 13% 31% 14% 5%	396
November	1st to 10th	Day	35% 15% 26% 18% 4 1	365
	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	752
	21st to end	Night	27% 15% 30% 22% 6% 1	792
April	1st to 10th	Night	30% 17% 27% 22% 4	720
	11th to 20th	Night	27% 14% 30% 22% 6%	711
	21st to end	Night	27% 18% 27% 20% 9%	591
May	1st to 10th	Night	26% 11% 30% 24% 8% 1	360
	11th to 20th	Night	22% 11% 31% 27% 8% 1	354
	21st to end	Night	18% 12% 38% 24% 8%	389
June	1st to 10th	Night	23% 8% 32% 29% 8%	360
	11th to 20th	Night	22% 8% 26% 32% 12% 1	360
	21st to end	Night	21% 7% 21% 36% 15% 1	360
July	1st to 10th	Night	13% 8% 24% 38% 16% 1	350
	11th to 20th	Night	15% 5% 24% 37% 17% 1	348
	21st to end	Night	13% 7% 26% 39% 14% 1	394
August	1st to 10th	Night	14% 4 19% 45% 17% 1	358
	11th to 20th	Night	14% 5% 20% 35% 24% 2	521
	21st to end	Night	18% 7% 24% 33% 16% 2	792
September	1st to 10th	Night	18% 6% 28% 32% 15% 1	720
	11th to 20th	Night	21% 6% 21% 32% 19% 1	720
	21st to end	Night	22% 9% 25% 25% 17% 2	720
October	1st to 10th	Night	23% 13% 25% 26% 12% 1	720
	11th to 20th	Night	31% 12% 27% 23% 7% 1	720
	21st to end	Night	31% 13% 28% 23% 5%	792
November	1st to 10th	Night	29% 14% 26% 23% 6% 1	740
	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 2024-03-15 14:01:42. Version ac07

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