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 2025-08-05.

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	16% 11% 3 8% 5% 5% 4 3 5% 7% 33%	126189
	Night	17% 11% 4 9% 5% 4 4 4 5% 6% 32%	121867
Transparency	Day	50% 5% 11% 21% 11% 1	129706
	Night	51% 6% 11% 20% 11% 1	126437
Seeing	Day	24% 16% 31% 19% 8% 3	15391
	Night	22% 14% 31% 24% 9% 1	24537

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	12% 15% 5% 10% 6% 5% 5% 4 6% 6% 27%	3597
	11th to 20th	Day	11% 19% 8% 13% 6% 5% 5% 4 4 4 21%	3570
	21st to end	Day	14% 17% 7% 17% 6% 5% 4 2 3 4 20%	4351
February	1st to 10th	Day	14% 16% 4 12% 7% 5% 4 3 6% 6% 22%	1800
	11th to 20th	Day	13% 15% 5% 13% 6% 5% 5% 4 4 5% 28%	1753
	21st to end	Day	18% 15% 6% 9% 7% 6% 4 3 5% 4 23%	1614
March	1st to 10th	Day	19% 14% 4 9% 5% 4 3 3 4 6% 29%	4651
	11th to 20th	Day	10% 14% 4 8% 5% 6% 5% 4 5% 6% 32%	4980
	21st to end	Day	19% 12% 3 7% 4 3 3 2 4 5% 38%	5648
April	1st to 10th	Day	21% 13% 3 8% 5% 4 4 3 4 5% 31%	2400
	11th to 20th	Day	21% 10% 3 6% 4 4 4 3 4 5% 37%	2374
	21st to end	Day	21% 11% 3 8% 5% 4 4 3 4 4 33%	2535
May	1st to 10th	Day	24% 9% 3 8% 5% 4 5% 3 5% 6% 29%	6292
	11th to 20th	Day	18% 8% 3 8% 5% 4 4 4 5% 7% 34%	6318
	21st to end	Day	19% 9% 3 6% 5% 4 5% 4 5% 8% 33%	6949
June	1st to 10th	Day	19% 9% 3 7% 5% 5% 5% 4 6% 7% 30%	2800
	11th to 20th	Day	15% 5% 2 6% 5% 5% 5% 5% 6% 8% 38%	2800
	21st to end	Day	16% 8% 3 7% 6% 5% 5% 5% 5% 8% 33%	2800
July	1st to 10th	Day	12% 7% 2 7% 6% 5% 5% 4 6% 9% 36%	6360
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 6% 9% 42%	6360
	21st to end	Day	8% 6% 2 6% 4 5% 5% 4 6% 9% 45%	6926
August	1st to 10th	Day	16% 8% 3 7% 4 4 5% 4 6% 7% 36%	4232
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 4 6% 9% 35%	4044
	21st to end	Day	13% 6% 2 6% 4 4 5% 4 7% 10% 39%	4190
September	1st to 10th	Day	13% 7% 2 6% 5% 4 4 3 6% 7% 42%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 5% 7% 48%	2280
	21st to end	Day	19% 6% 2 6% 4 4 5% 2 6% 8% 38%	2003
October	1st to 10th	Day	19% 9% 3 7% 5% 4 4 3 5% 7% 35%	1900
	11th to 20th	Day	21% 10% 3 8% 6% 5% 4 3 6% 7% 28%	1900
	21st to end	Day	25% 12% 3 8% 5% 5% 4 3 5% 6% 25%	2006
November	1st to 10th	Day	15% 9% 3 8% 5% 5% 4 4 6% 6% 35%	1730
	11th to 20th	Day	17% 14% 5% 9% 5% 5% 4 3 4 5% 30%	1600
	21st to end	Day	22% 14% 5% 9% 5% 6% 4 3 5% 6% 22%	1600
December	1st to 10th	Day	22% 16% 5% 11% 5% 5% 4 3 5% 6% 18%	2600
	11th to 20th	Day	17% 21% 6% 10% 5% 4 4 3 4 4 23%	2986
	21st to end	Day	23% 18% 4 11% 5% 4 3 2 3 5% 23%	3960
January	1st to 10th	Night	15% 15% 7% 12% 6% 5% 5% 4 5% 5% 22%	6349
	11th to 20th	Night	11% 15% 6% 15% 8% 7% 5% 3 6% 5% 18%	6315
	21st to end	Night	15% 16% 7% 13% 6% 5% 4 3 5% 5% 21%	6604
February	1st to 10th	Night	14% 16% 5% 10% 7% 5% 4 5% 6% 6% 25%	2600
	11th to 20th	Night	13% 15% 5% 9% 6% 5% 4 3 6% 5% 28%	2533
	21st to end	Night	14% 15% 4 8% 6% 5% 4 4 6% 6% 29%	2015
March	1st to 10th	Night	19% 13% 4 10% 5% 5% 4 3 4 5% 29%	5185
	11th to 20th	Night	12% 12% 3 8% 4 5% 5% 5% 7% 9% 30%	4979
	21st to end	Night	19% 10% 4 8% 4 4 4 3 4 6% 35%	5284
April	1st to 10th	Night	21% 11% 3 6% 5% 3 4 3 5% 6% 33%	2000
	11th to 20th	Night	18% 9% 3 7% 5% 3 4 3 5% 5% 38%	1975
	21st to end	Night	20% 9% 2 7% 4 4 4 4 5% 7% 34%	1881
May	1st to 10th	Night	25% 10% 3 7% 4 4 4 4 5% 6% 28%	3646
	11th to 20th	Night	15% 8% 3 6% 3 3 4 3 5% 7% 42%	3575
	21st to end	Night	19% 7% 3 6% 5% 5% 4 4 5% 7% 36%	3926
June	1st to 10th	Night	16% 7% 3 7% 6% 6% 4 4 6% 8% 34%	1600
	11th to 20th	Night	12% 6% 3 5% 5% 4 5% 4 6% 9% 42%	1600
	21st to end	Night	15% 5% 3 8% 5% 5% 5% 3 6% 8% 37%	1600
July	1st to 10th	Night	11% 6% 3 7% 6% 5% 5% 5% 6% 9% 37%	3600
	11th to 20th	Night	12% 5% 2 6% 3 4 3 3 6% 8% 47%	3600
	21st to end	Night	9% 5% 2 5% 4 4 4 4 6% 8% 50%	3926
August	1st to 10th	Night	12% 7% 2 6% 4 4 4 4 5% 8% 44%	2782
	11th to 20th	Night	14% 6% 2 6% 4 4 4 3 4 8% 44%	2785
	21st to end	Night	11% 4 2 6% 4 5% 5% 5% 7% 9% 41%	3434
September	1st to 10th	Night	11% 7% 2 6% 4 3 4 3 5% 9% 46%	1900
	11th to 20th	Night	12% 4 2 5% 4 3 4 4 4 8% 51%	1900
	21st to end	Night	17% 5% 3 6% 4 4 4 4 6% 5% 43%	2171
October	1st to 10th	Night	15% 9% 3 6% 5% 4 5% 3 5% 6% 39%	2280
	11th to 20th	Night	21% 8% 3 8% 4 4 5% 4 6% 5% 32%	2280
	21st to end	Night	23% 10% 3 7% 5% 5% 5% 4 4 5% 29%	2591
November	1st to 10th	Night	17% 10% 3 6% 4 4 5% 4 5% 6% 36%	2567
	11th to 20th	Night	18% 11% 3 8% 5% 5% 5% 4 5% 6% 32%	2800
	21st to end	Night	21% 13% 4 9% 5% 5% 4 4 5% 6% 25%	2800
December	1st to 10th	Night	20% 16% 4 10% 7% 5% 5% 4 6% 6% 18%	4580
	11th to 20th	Night	21% 17% 5% 9% 5% 4 4 3 4 5% 24%	5208
	21st to end	Night	27% 16% 4 10% 5% 4 4 3 4 4 21%	6996

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	56% 6% 12% 18% 8% 1	3598
	11th to 20th	Day	67% 4 11% 11% 7%	3600
	21st to end	Day	69% 4 7% 10% 9% 1	4351
February	1st to 10th	Day	62% 6% 9% 17% 6% 1	1800
	11th to 20th	Day	59% 4 10% 15% 10% 1	1762
	21st to end	Day	64% 4 9% 11% 10% 1	1614
March	1st to 10th	Day	57% 4 10% 13% 14% 2	4654
	11th to 20th	Day	51% 5% 16% 15% 11% 2	4980
	21st to end	Day	49% 4 5% 22% 17% 3	5648
April	1st to 10th	Day	56% 4 7% 18% 13% 3	2400
	11th to 20th	Day	49% 5% 7% 21% 16% 2	2374
	21st to end	Day	55% 4 8% 16% 14% 3	2535
May	1st to 10th	Day	56% 6% 8% 18% 10% 3	6303
	11th to 20th	Day	50% 6% 11% 18% 15% 1	6322
	21st to end	Day	48% 6% 12% 22% 11% 1	6949
June	1st to 10th	Day	51% 7% 10% 19% 13% 1	2800
	11th to 20th	Day	43% 5% 12% 25% 13% 2	2800
	21st to end	Day	47% 6% 14% 20% 12% 1	2800
July	1st to 10th	Day	42% 6% 13% 26% 12% 1	6290
	11th to 20th	Day	35% 7% 13% 28% 16%	6285
	21st to end	Day	34% 7% 13% 35% 11%	6728
August	1st to 10th	Day	45% 6% 14% 23% 12%	4218
	11th to 20th	Day	44% 6% 14% 27% 8% 1	4083
	21st to end	Day	39% 6% 14% 30% 10%	4190
September	1st to 10th	Day	39% 6% 14% 28% 13% 1	2280
	11th to 20th	Day	35% 6% 12% 31% 15% 1	2280
	21st to end	Day	44% 5% 14% 27% 10%	2003
October	1st to 10th	Day	43% 5% 12% 31% 9%	3160
	11th to 20th	Day	46% 5% 14% 25% 10% 1	3140
	21st to end	Day	52% 5% 14% 21% 7%	3283
November	1st to 10th	Day	48% 7% 14% 22% 8% 1	1730
	11th to 20th	Day	55% 5% 11% 17% 11% 1	1600
	21st to end	Day	62% 8% 12% 10% 8%	1600
December	1st to 10th	Day	67% 5% 15% 9% 3	2600
	11th to 20th	Day	65% 5% 10% 14% 7%	2986
	21st to end	Day	66% 4 7% 16% 7%	3960
January	1st to 10th	Night	63% 5% 12% 14% 6%	6349
	11th to 20th	Night	66% 5% 11% 10% 6%	6360
	21st to end	Night	65% 5% 8% 9% 12% 1	6604
February	1st to 10th	Night	58% 5% 11% 18% 7%	2600
	11th to 20th	Night	56% 5% 10% 19% 9% 1	2535
	21st to end	Night	55% 5% 10% 19% 10% 1	2015
March	1st to 10th	Night	58% 4 6% 17% 11% 5%	5195
	11th to 20th	Night	48% 7% 18% 17% 8% 2	4980
	21st to end	Night	48% 6% 8% 21% 14% 2	5284
April	1st to 10th	Night	53% 4 7% 21% 14% 2	2000
	11th to 20th	Night	48% 5% 8% 21% 17% 1	1975
	21st to end	Night	49% 6% 9% 16% 16% 3	1881
May	1st to 10th	Night	56% 6% 9% 17% 9% 4	3652
	11th to 20th	Night	41% 6% 14% 23% 14% 2	3576
	21st to end	Night	46% 6% 13% 19% 14% 1	3927
June	1st to 10th	Night	46% 8% 11% 21% 12% 1	1600
	11th to 20th	Night	38% 7% 13% 22% 18% 2	1600
	21st to end	Night	44% 8% 14% 21% 13% 1	1600
July	1st to 10th	Night	42% 6% 15% 20% 16% 1	3560
	11th to 20th	Night	35% 6% 13% 33% 13%	3552
	21st to end	Night	32% 7% 12% 35% 13% 1	3809
August	1st to 10th	Night	38% 7% 14% 27% 14% 1	2772
	11th to 20th	Night	38% 6% 14% 31% 10% 1	2812
	21st to end	Night	36% 8% 15% 29% 11% 1	3434
September	1st to 10th	Night	35% 6% 14% 30% 14% 1	1900
	11th to 20th	Night	32% 6% 15% 32% 14% 1	1900
	21st to end	Night	42% 4 11% 30% 11% 1	2171
October	1st to 10th	Night	39% 5% 11% 27% 17%	3800
	11th to 20th	Night	44% 5% 15% 26% 10%	3779
	21st to end	Night	50% 6% 13% 24% 8%	4264
November	1st to 10th	Night	47% 6% 13% 23% 10% 1	2567
	11th to 20th	Night	52% 6% 11% 20% 10% 2	2800
	21st to end	Night	59% 7% 13% 16% 6%	2800
December	1st to 10th	Night	65% 6% 13% 13% 3	4580
	11th to 20th	Night	63% 6% 9% 14% 8% 1	5208
	21st to end	Night	68% 4 7% 11% 9%	6996

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% 23% 35% 14% 3 1	200
	11th to 20th	Day	30% 19% 32% 15% 4 1	200
	21st to end	Day	25% 22% 35% 13% 4	305
February	1st to 10th	Day	32% 27% 29% 9% 2	300
	11th to 20th	Day	32% 26% 37% 5%	300
	21st to end	Day	35% 21% 32% 10% 1	378
March	1st to 10th	Day	28% 21% 31% 16% 3	500
	11th to 20th	Day	28% 21% 32% 15% 4	500
	21st to end	Day	36% 19% 27% 13% 5% 1	550
April	1st to 10th	Day	31% 23% 28% 14% 4	500
	11th to 20th	Day	34% 22% 21% 14% 7% 2	492
	21st to end	Day	31% 21% 30% 11% 6% 1	500
May	1st to 10th	Day	27% 16% 32% 17% 7% 2	503
	11th to 20th	Day	18% 17% 38% 18% 8% 1	527
	21st to end	Day	18% 17% 32% 20% 9% 3	573
June	1st to 10th	Day	25% 11% 35% 21% 7% 1	530
	11th to 20th	Day	15% 17% 35% 20% 12% 2	530
	21st to end	Day	20% 14% 33% 22% 9% 2	530
July	1st to 10th	Day	13% 9% 32% 30% 14% 3	525
	11th to 20th	Day	15% 10% 30% 27% 15% 3	524
	21st to end	Day	13% 10% 36% 26% 11% 4	576
August	1st to 10th	Day	13% 8% 31% 28% 15% 5%	502
	11th to 20th	Day	13% 7% 28% 29% 17% 6%	479
	21st to end	Day	16% 11% 29% 25% 13% 7%	539
September	1st to 10th	Day	15% 12% 32% 23% 12% 6%	490
	11th to 20th	Day	13% 8% 26% 23% 18% 12%	490
	21st to end	Day	19% 11% 29% 22% 14% 4	490
October	1st to 10th	Day	26% 13% 29% 16% 11% 4	490
	11th to 20th	Day	25% 21% 30% 17% 5% 1	490
	21st to end	Day	30% 19% 28% 19% 4	494
November	1st to 10th	Day	29% 15% 29% 17% 8%	364
	11th to 20th	Day	27% 20% 35% 12% 5% 2	200
	21st to end	Day	30% 23% 31% 13% 3 1	200
December	1st to 10th	Day	32% 22% 32% 12% 3 1	200
	11th to 20th	Day	38% 23% 26% 10% 3 1	200
	21st to end	Day	35% 18% 30% 12% 4	220
January	1st to 10th	Night	28% 19% 32% 19% 4	800
	11th to 20th	Night	27% 18% 30% 20% 5% 1	800
	21st to end	Night	21% 16% 36% 22% 5%	880
February	1st to 10th	Night	23% 20% 36% 18% 3	800
	11th to 20th	Night	22% 20% 38% 16% 4	783
	21st to end	Night	25% 20% 34% 18% 3	660
March	1st to 10th	Night	24% 18% 34% 21% 3	800
	11th to 20th	Night	26% 18% 31% 21% 3 1	800
	21st to end	Night	23% 16% 34% 19% 7% 1	880
April	1st to 10th	Night	27% 17% 32% 21% 3	800
	11th to 20th	Night	24% 21% 29% 19% 6% 1	791
	21st to end	Night	25% 13% 30% 23% 9%	681
May	1st to 10th	Night	27% 8% 25% 30% 9% 1	426
	11th to 20th	Night	15% 10% 35% 32% 7%	394
	21st to end	Night	13% 9% 39% 27% 12%	433
June	1st to 10th	Night	17% 8% 32% 34% 9% 1	400
	11th to 20th	Night	15% 10% 31% 31% 12% 2	400
	21st to end	Night	19% 7% 27% 36% 11%	400
July	1st to 10th	Night	8% 6% 32% 39% 14%	390
	11th to 20th	Night	13% 3 29% 37% 18% 1	388
	21st to end	Night	11% 4 30% 42% 12% 1	438
August	1st to 10th	Night	13% 5% 24% 38% 19% 2	526
	11th to 20th	Night	13% 5% 21% 36% 23% 2	564
	21st to end	Night	13% 6% 30% 30% 18% 2	807
September	1st to 10th	Night	12% 6% 31% 30% 17% 3	760
	11th to 20th	Night	14% 6% 23% 27% 25% 6%	760
	21st to end	Night	20% 11% 22% 28% 18% 2	760
October	1st to 10th	Night	21% 12% 28% 23% 14% 2	760
	11th to 20th	Night	26% 13% 30% 23% 8% 1	760
	21st to end	Night	29% 14% 30% 22% 6%	836
November	1st to 10th	Night	24% 15% 30% 23% 8%	780
	11th to 20th	Night	25% 16% 34% 18% 8% 1	800
	21st to end	Night	30% 17% 29% 18% 6%	800
December	1st to 10th	Night	31% 17% 31% 18% 4	800
	11th to 20th	Night	27% 20% 33% 17% 2 1	800
	21st to end	Night	35% 14% 31% 17% 3	880

Page generated at 2025-08-02 01:32:22. Version ac07

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