Arden
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arden clear sky chart from 2005-11-06 to 2024-04-03.

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% 4 7% 6% 3 5% 5% 5% 6% 32%	78712
	Night	17% 10% 4 7% 6% 3 5% 4 5% 6% 32%	81410
Transparency	Day	51% 6% 12% 19% 11% 1	78417
	Night	52% 6% 12% 19% 10% 1	81239
Seeing	Day	23% 16% 31% 19% 8% 3	13628
	Night	22% 14% 31% 24% 9% 1	22989

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	15% 17% 5% 9% 7% 4 5% 4 5% 4 25%	2517
	11th to 20th	Day	14% 16% 8% 11% 8% 4 5% 5% 4 4 22%	2520
	21st to end	Day	19% 19% 7% 13% 7% 4 4 3 3 4 19%	3037
February	1st to 10th	Day	15% 16% 4 11% 8% 3 5% 4 6% 6% 22%	1710
	11th to 20th	Day	13% 14% 5% 11% 7% 3 5% 5% 3 5% 28%	1663
	21st to end	Day	19% 14% 6% 8% 7% 4 5% 4 5% 5% 24%	1535
March	1st to 10th	Day	16% 12% 4 9% 8% 4 5% 4 4 5% 29%	1964
	11th to 20th	Day	13% 15% 5% 8% 7% 4 4 4 5% 4 31%	2090
	21st to end	Day	19% 12% 3 6% 4 3 2 3 4 5% 38%	2375
April	1st to 10th	Day	20% 12% 4 7% 6% 3 4 3 4 6% 31%	2184
	11th to 20th	Day	21% 9% 3 5% 4 3 4 4 4 6% 39%	2134
	21st to end	Day	22% 10% 3 7% 6% 3 4 4 4 5% 32%	2281
May	1st to 10th	Day	19% 7% 3 6% 6% 3 6% 4 5% 7% 34%	2494
	11th to 20th	Day	16% 6% 3 7% 6% 3 4 5% 5% 6% 39%	2478
	21st to end	Day	13% 5% 2 6% 6% 3 5% 6% 5% 8% 40%	2725
June	1st to 10th	Day	20% 8% 3 6% 5% 4 5% 5% 6% 7% 31%	2520
	11th to 20th	Day	17% 5% 2 5% 5% 4 6% 5% 6% 8% 38%	2520
	21st to end	Day	16% 7% 4 6% 6% 4 5% 5% 5% 8% 33%	2520
July	1st to 10th	Day	11% 5% 2 5% 7% 4 5% 5% 6% 9% 40%	2520
	11th to 20th	Day	12% 6% 2 5% 5% 3 6% 6% 7% 10% 37%	2520
	21st to end	Day	11% 5% 3 6% 6% 4 7% 6% 7% 9% 36%	2744
August	1st to 10th	Day	10% 6% 3 6% 7% 4 6% 6% 6% 8% 38%	2373
	11th to 20th	Day	12% 6% 3 6% 6% 4 5% 6% 6% 9% 37%	2303
	21st to end	Day	14% 7% 2 5% 5% 3 5% 5% 7% 9% 38%	2386
September	1st to 10th	Day	13% 6% 3 5% 5% 3 5% 4 6% 7% 42%	2160
	11th to 20th	Day	12% 6% 2 4 5% 3 4 4 5% 8% 47%	2160
	21st to end	Day	19% 6% 2 5% 5% 3 5% 4 6% 8% 38%	1898
October	1st to 10th	Day	20% 8% 4 6% 6% 3 4 4 5% 7% 35%	1800
	11th to 20th	Day	22% 9% 3 7% 7% 3 5% 5% 6% 8% 27%	1800
	21st to end	Day	27% 11% 3 7% 6% 3 4 4 5% 6% 24%	1901
November	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 5% 6% 6% 35%	1642
	11th to 20th	Day	18% 13% 5% 8% 6% 4 4 4 4 5% 30%	1520
	21st to end	Day	22% 13% 5% 8% 5% 4 4 5% 4 6% 23%	1520
December	1st to 10th	Day	22% 16% 5% 9% 7% 4 4 5% 4 6% 18%	1520
	11th to 20th	Day	20% 14% 6% 8% 5% 4 4 4 4 5% 26%	1906
	21st to end	Day	27% 18% 5% 10% 6% 3 3 2 3 4 19%	2772
January	1st to 10th	Night	18% 14% 7% 9% 8% 4 5% 5% 5% 5% 20%	4429
	11th to 20th	Night	14% 14% 5% 11% 10% 5% 5% 4 6% 5% 20%	4440
	21st to end	Night	19% 16% 7% 10% 8% 4 4 4 4 4 20%	4618
February	1st to 10th	Night	14% 15% 5% 9% 7% 3 5% 6% 5% 6% 24%	2470
	11th to 20th	Night	14% 13% 6% 8% 7% 4 4 4 5% 6% 29%	2403
	21st to end	Night	15% 14% 4 7% 6% 4 4 5% 5% 6% 30%	1918
March	1st to 10th	Night	15% 12% 4 8% 7% 3 4 4 4 6% 32%	2199
	11th to 20th	Night	17% 13% 6% 7% 5% 2 4 4 5% 6% 33%	2089
	21st to end	Night	16% 9% 4 7% 5% 3 4 4 4 4 40%	2223
April	1st to 10th	Night	20% 10% 4 5% 4 3 4 3 5% 6% 35%	1821
	11th to 20th	Night	18% 8% 3 6% 6% 2 4 5% 5% 5% 39%	1775
	21st to end	Night	20% 8% 2 6% 4 3 5% 5% 5% 7% 34%	1693
May	1st to 10th	Night	21% 8% 2 6% 5% 3 4 4 4 6% 38%	1464
	11th to 20th	Night	14% 6% 3 5% 4 4 4 4 5% 8% 43%	1415
	21st to end	Night	11% 5% 2 4 5% 3 5% 5% 5% 9% 46%	1550
June	1st to 10th	Night	17% 6% 3 6% 7% 4 5% 5% 6% 8% 34%	1440
	11th to 20th	Night	13% 6% 3 4 5% 3 4 5% 6% 9% 42%	1440
	21st to end	Night	14% 5% 3 7% 5% 3 5% 4 6% 9% 38%	1440
July	1st to 10th	Night	9% 4 3 5% 5% 3 5% 5% 5% 9% 47%	1440
	11th to 20th	Night	11% 5% 2 5% 5% 3 5% 5% 6% 10% 44%	1440
	21st to end	Night	10% 5% 2 4 4 3 5% 5% 7% 8% 47%	1574
August	1st to 10th	Night	9% 6% 2 4 5% 3 4 5% 5% 8% 46%	1562
	11th to 20th	Night	9% 5% 2 6% 6% 5% 5% 5% 5% 9% 44%	1598
	21st to end	Night	11% 5% 3 5% 5% 2 4 5% 6% 8% 46%	1952
September	1st to 10th	Night	11% 7% 2 5% 5% 3 4 4 5% 9% 45%	1800
	11th to 20th	Night	13% 4 2 4 5% 2 4 5% 4 8% 50%	1800
	21st to end	Night	17% 5% 3 6% 4 3 4 4 5% 5% 44%	2056
October	1st to 10th	Night	16% 9% 3 5% 6% 3 5% 5% 5% 6% 37%	2160
	11th to 20th	Night	22% 8% 3 7% 6% 3 5% 4 6% 5% 31%	2160
	21st to end	Night	23% 10% 4 6% 6% 3 5% 5% 4 5% 29%	2454
November	1st to 10th	Night	18% 9% 3 5% 4 3 5% 5% 5% 6% 37%	2435
	11th to 20th	Night	19% 10% 3 7% 5% 3 5% 5% 5% 6% 32%	2660
	21st to end	Night	21% 12% 4 8% 6% 3 5% 5% 5% 6% 25%	2660
December	1st to 10th	Night	21% 15% 5% 9% 7% 4 5% 4 5% 5% 20%	2660
	11th to 20th	Night	20% 16% 5% 7% 6% 3 4 3 3 5% 27%	3288
	21st to end	Night	29% 17% 4 8% 6% 3 4 4 4 4 17%	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	58% 8% 15% 12% 6% 2	2518
	11th to 20th	Day	65% 5% 12% 11% 7%	2520
	21st to end	Day	72% 4 8% 10% 5% 1	3037
February	1st to 10th	Day	62% 6% 9% 17% 5% 1	1710
	11th to 20th	Day	58% 5% 10% 15% 10% 1	1672
	21st to end	Day	62% 4 9% 12% 11% 1	1535
March	1st to 10th	Day	58% 4 11% 15% 10% 2	1967
	11th to 20th	Day	56% 5% 10% 16% 11% 2	2090
	21st to end	Day	49% 4 7% 21% 14% 6%	2375
April	1st to 10th	Day	56% 3 7% 18% 13% 3	2184
	11th to 20th	Day	47% 5% 7% 23% 16% 2	2134
	21st to end	Day	55% 3 9% 16% 14% 4	2281
May	1st to 10th	Day	50% 6% 10% 17% 15% 3	2494
	11th to 20th	Day	45% 5% 10% 22% 15% 3	2482
	21st to end	Day	42% 7% 15% 20% 13% 3	2725
June	1st to 10th	Day	51% 7% 10% 18% 13% 1	2520
	11th to 20th	Day	43% 5% 12% 25% 14% 2	2520
	21st to end	Day	47% 7% 14% 19% 12% 1	2520
July	1st to 10th	Day	38% 8% 12% 27% 15% 1	2450
	11th to 20th	Day	39% 8% 16% 27% 10%	2445
	21st to end	Day	42% 8% 15% 23% 11% 1	2591
August	1st to 10th	Day	41% 8% 15% 24% 11% 1	2359
	11th to 20th	Day	42% 7% 16% 24% 10% 1	2303
	21st to end	Day	41% 6% 14% 26% 12% 1	2386
September	1st to 10th	Day	39% 6% 14% 27% 13% 1	2160
	11th to 20th	Day	36% 6% 12% 30% 15% 1	2160
	21st to end	Day	44% 5% 14% 28% 9%	1898
October	1st to 10th	Day	49% 6% 11% 22% 12% 1	1800
	11th to 20th	Day	54% 7% 13% 18% 6% 1	1800
	21st to end	Day	60% 5% 10% 16% 7%	1901
November	1st to 10th	Day	48% 7% 15% 21% 9% 1	1642
	11th to 20th	Day	56% 6% 12% 16% 10% 1	1520
	21st to end	Day	61% 8% 12% 10% 8%	1520
December	1st to 10th	Day	67% 6% 12% 11% 5%	1520
	11th to 20th	Day	61% 6% 14% 12% 6%	1906
	21st to end	Day	71% 4 7% 14% 5%	2772
January	1st to 10th	Night	64% 6% 14% 12% 4	4429
	11th to 20th	Night	64% 6% 13% 11% 5% 1	4440
	21st to end	Night	67% 6% 10% 11% 6% 1	4618
February	1st to 10th	Night	59% 6% 11% 18% 6%	2470
	11th to 20th	Night	56% 5% 10% 20% 9% 1	2405
	21st to end	Night	55% 5% 10% 19% 11% 1	1918
March	1st to 10th	Night	53% 6% 10% 18% 12% 1	2209
	11th to 20th	Night	53% 4 11% 19% 11% 1	2090
	21st to end	Night	48% 4 8% 21% 16% 3	2223
April	1st to 10th	Night	51% 4 7% 22% 14% 2	1821
	11th to 20th	Night	47% 5% 9% 21% 17% 2	1775
	21st to end	Night	50% 6% 9% 16% 16% 3	1693
May	1st to 10th	Night	47% 5% 8% 19% 17% 4	1464
	11th to 20th	Night	39% 6% 11% 26% 16% 3	1416
	21st to end	Night	34% 6% 17% 20% 19% 3	1551
June	1st to 10th	Night	46% 8% 12% 22% 12% 1	1440
	11th to 20th	Night	38% 7% 13% 21% 19% 2	1440
	21st to end	Night	42% 9% 15% 21% 12% 1	1440
July	1st to 10th	Night	33% 7% 12% 26% 19% 3	1400
	11th to 20th	Night	35% 7% 13% 31% 14%	1392
	21st to end	Night	33% 7% 15% 32% 12% 1	1486
August	1st to 10th	Night	34% 8% 16% 29% 12% 1	1552
	11th to 20th	Night	36% 7% 16% 28% 12% 1	1598
	21st to end	Night	34% 8% 14% 30% 13%	1952
September	1st to 10th	Night	36% 6% 14% 29% 14% 1	1800
	11th to 20th	Night	32% 6% 16% 32% 13% 1	1800
	21st to end	Night	42% 4 12% 31% 10% 1	2056
October	1st to 10th	Night	46% 7% 11% 21% 14% 1	2160
	11th to 20th	Night	52% 7% 13% 18% 8%	2160
	21st to end	Night	57% 7% 12% 15% 9%	2454
November	1st to 10th	Night	47% 6% 14% 22% 10% 1	2435
	11th to 20th	Night	52% 7% 11% 19% 10% 2	2660
	21st to end	Night	58% 7% 13% 16% 6%	2660
December	1st to 10th	Night	64% 6% 11% 14% 4	2660
	11th to 20th	Night	61% 5% 11% 15% 8% 1	3288
	21st to end	Night	71% 5% 9% 12% 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	27% 22% 32% 16% 3 1	180
	11th to 20th	Day	31% 19% 31% 15% 3 1	180
	21st to end	Day	26% 19% 35% 15% 4	274
February	1st to 10th	Day	31% 27% 30% 10% 2	270
	11th to 20th	Day	29% 26% 40% 5%	270
	21st to end	Day	36% 22% 30% 10% 1	347
March	1st to 10th	Day	27% 21% 33% 16% 4	460
	11th to 20th	Day	28% 20% 33% 15% 4	460
	21st to end	Day	34% 19% 27% 13% 5% 1	506
April	1st to 10th	Day	30% 22% 28% 15% 4	428
	11th to 20th	Day	32% 22% 20% 16% 8% 3	412
	21st to end	Day	30% 20% 31% 11% 6% 1	420
May	1st to 10th	Day	27% 15% 32% 17% 7% 3	423
	11th to 20th	Day	18% 17% 38% 17% 9% 2	447
	21st to end	Day	17% 17% 33% 19% 10% 4	485
June	1st to 10th	Day	26% 10% 35% 21% 7% 1	450
	11th to 20th	Day	16% 17% 32% 21% 13% 2	450
	21st to end	Day	20% 13% 32% 23% 10% 2	450
July	1st to 10th	Day	13% 9% 29% 31% 16% 3	445
	11th to 20th	Day	16% 10% 29% 27% 14% 4	444
	21st to end	Day	14% 9% 36% 25% 11% 4	488
August	1st to 10th	Day	11% 8% 32% 29% 15% 5%	446
	11th to 20th	Day	12% 6% 29% 29% 17% 6%	439
	21st to end	Day	16% 11% 29% 24% 13% 7%	495
September	1st to 10th	Day	15% 11% 33% 22% 12% 7%	450
	11th to 20th	Day	14% 9% 28% 24% 16% 10%	450
	21st to end	Day	19% 12% 30% 22% 13% 5%	450
October	1st to 10th	Day	27% 14% 28% 16% 11% 4	450
	11th to 20th	Day	27% 21% 30% 17% 5% 1	450
	21st to end	Day	31% 19% 27% 18% 4	455
November	1st to 10th	Day	28% 16% 29% 18% 9%	336
	11th to 20th	Day	29% 21% 31% 13% 4 2	180
	21st to end	Day	27% 23% 32% 13% 3 1	180
December	1st to 10th	Day	31% 23% 32% 11% 2 1	180
	11th to 20th	Day	36% 23% 27% 11% 3 1	180
	21st to end	Day	36% 20% 31% 10% 3 1	198
January	1st to 10th	Night	28% 19% 30% 19% 4	760
	11th to 20th	Night	28% 17% 29% 20% 5% 1	760
	21st to end	Night	21% 16% 36% 22% 5%	836
February	1st to 10th	Night	23% 20% 36% 18% 3	760
	11th to 20th	Night	22% 19% 39% 16% 4	743
	21st to end	Night	25% 20% 34% 18% 3	628
March	1st to 10th	Night	23% 17% 35% 21% 3	760
	11th to 20th	Night	27% 18% 30% 21% 4 1	760
	21st to end	Night	23% 16% 34% 19% 7% 1	836
April	1st to 10th	Night	26% 17% 32% 22% 3	729
	11th to 20th	Night	23% 21% 29% 20% 6% 1	711
	21st to end	Night	25% 13% 29% 23% 10%	613
May	1st to 10th	Night	26% 8% 25% 29% 10% 2	384
	11th to 20th	Night	16% 9% 35% 32% 8%	354
	21st to end	Night	12% 9% 40% 25% 13% 1	389
June	1st to 10th	Night	17% 8% 33% 33% 9% 1	360
	11th to 20th	Night	15% 10% 31% 29% 13% 2	360
	21st to end	Night	18% 6% 27% 37% 12%	360
July	1st to 10th	Night	8% 5% 32% 39% 16%	350
	11th to 20th	Night	13% 3 30% 36% 18% 1	348
	21st to end	Night	11% 4 30% 42% 12% 1	394
August	1st to 10th	Night	12% 5% 24% 37% 20% 2	488
	11th to 20th	Night	12% 4 21% 37% 23% 3	534
	21st to end	Night	13% 6% 31% 29% 18% 3	764
September	1st to 10th	Night	13% 6% 32% 29% 18% 3	720
	11th to 20th	Night	14% 7% 24% 28% 23% 5%	720
	21st to end	Night	20% 11% 23% 27% 18% 2	720
October	1st to 10th	Night	22% 12% 28% 22% 14% 2	720
	11th to 20th	Night	26% 13% 31% 22% 7% 1	720
	21st to end	Night	29% 14% 30% 22% 5%	792
November	1st to 10th	Night	24% 14% 30% 23% 8%	740
	11th to 20th	Night	25% 16% 33% 17% 8% 1	760
	21st to end	Night	30% 17% 28% 19% 6%	760
December	1st to 10th	Night	31% 18% 30% 18% 3	760
	11th to 20th	Night	27% 20% 33% 18% 2 1	760
	21st to end	Night	35% 15% 32% 16% 2	836

Page generated at 2024-03-31 06:08:55. Version ac07

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