Edgewood Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edgewood Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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	16% 11% 4 9% 5% 5% 4 4 5% 7% 31%	126677
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 31%	123689
Transparency	Day	51% 6% 11% 20% 10% 1	130280
	Night	52% 6% 11% 19% 11% 2	128156
Seeing	Day	23% 15% 27% 20% 11% 4	16054
	Night	22% 12% 26% 27% 11% 1	25691

By Month

Percentage Cloud Cover SE (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% 9% 22% 5% 3 3 2 3 4 14%	3982
	11th to 20th	Day	13% 22% 9% 18% 9% 6% 2 2 2 2 14%	4060
	21st to end	Day	21% 20% 6% 12% 7% 5% 3 3 4 4 16%	4466
February	1st to 10th	Day	20% 17% 6% 12% 7% 5% 3 3 3 4 21%	1800
	11th to 20th	Day	17% 15% 6% 14% 5% 4 5% 3 4 5% 21%	1753
	21st to end	Day	20% 15% 5% 10% 6% 4 3 3 4 5% 24%	1647
March	1st to 10th	Day	17% 13% 5% 9% 5% 4 4 3 4 5% 32%	4935
	11th to 20th	Day	13% 10% 5% 8% 5% 5% 5% 4 5% 6% 35%	4980
	21st to end	Day	17% 11% 4 9% 6% 4 5% 4 5% 6% 30%	5465
April	1st to 10th	Day	17% 13% 3 8% 4 5% 4 4 5% 7% 29%	2321
	11th to 20th	Day	16% 11% 3 8% 5% 4 5% 4 5% 6% 33%	2386
	21st to end	Day	21% 9% 3 7% 5% 4 4 3 5% 7% 34%	2600
May	1st to 10th	Day	21% 10% 3 7% 5% 5% 5% 5% 6% 7% 26%	5862
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 9% 29%	5861
	21st to end	Day	19% 7% 2 7% 4 4 5% 4 7% 8% 32%	6885
June	1st to 10th	Day	14% 7% 3 6% 5% 5% 5% 4 7% 8% 35%	2800
	11th to 20th	Day	14% 7% 3 6% 5% 5% 5% 5% 7% 9% 33%	2800
	21st to end	Day	13% 6% 2 6% 6% 5% 4 4 6% 10% 37%	2800
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 4 6% 8% 41%	6268
	11th to 20th	Day	11% 7% 3 8% 5% 5% 5% 5% 7% 11% 32%	5900
	21st to end	Day	12% 7% 3 8% 5% 5% 5% 4 6% 8% 39%	6424
August	1st to 10th	Day	14% 9% 3 7% 5% 6% 6% 4 7% 8% 31%	4234
	11th to 20th	Day	12% 7% 2 7% 5% 5% 6% 4 6% 9% 35%	4174
	21st to end	Day	9% 4 2 6% 5% 5% 6% 5% 7% 10% 41%	4422
September	1st to 10th	Day	16% 6% 2 5% 3 4 4 3 5% 6% 46%	2400
	11th to 20th	Day	12% 6% 2 6% 5% 3 4 5% 5% 7% 46%	2231
	21st to end	Day	21% 7% 3 7% 5% 5% 4 3 5% 6% 34%	2184
October	1st to 10th	Day	17% 6% 2 5% 4 4 4 4 5% 7% 42%	2000
	11th to 20th	Day	19% 7% 2 7% 4 5% 6% 3 5% 6% 35%	2000
	21st to end	Day	22% 9% 3 8% 4 4 3 3 5% 7% 33%	2200
November	1st to 10th	Day	12% 10% 2 7% 5% 4 4 3 5% 6% 41%	1993
	11th to 20th	Day	18% 15% 3 7% 5% 4 4 3 5% 5% 30%	1694
	21st to end	Day	19% 16% 5% 9% 5% 4 4 3 5% 5% 25%	1600
December	1st to 10th	Day	18% 14% 7% 19% 6% 4 3 3 4 4 18%	2600
	11th to 20th	Day	24% 18% 6% 10% 4 3 3 2 3 5% 22%	2990
	21st to end	Day	22% 21% 6% 11% 5% 5% 4 3 5% 5% 14%	3960
January	1st to 10th	Night	15% 17% 7% 23% 5% 4 3 2 4 3 15%	5958
	11th to 20th	Night	15% 17% 8% 17% 9% 6% 4 3 3 4 15%	5900
	21st to end	Night	22% 16% 6% 12% 6% 5% 5% 3 3 3 20%	6490
February	1st to 10th	Night	21% 14% 5% 10% 6% 5% 4 3 4 5% 24%	2600
	11th to 20th	Night	19% 13% 5% 13% 5% 4 4 3 5% 4 24%	2533
	21st to end	Night	20% 13% 4 11% 5% 4 5% 3 5% 5% 25%	1976
March	1st to 10th	Night	21% 12% 4 9% 5% 3 3 3 3 5% 32%	4918
	11th to 20th	Night	14% 11% 4 6% 3 3 3 3 4 7% 41%	4980
	21st to end	Night	17% 10% 4 8% 5% 5% 4 3 4 5% 35%	5467
April	1st to 10th	Night	19% 14% 2 7% 4 4 4 3 4 5% 34%	2078
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 5% 6% 37%	1975
	21st to end	Night	16% 9% 3 7% 4 4 4 3 5% 8% 36%	1804
May	1st to 10th	Night	26% 12% 3 8% 4 4 4 3 5% 6% 25%	4033
	11th to 20th	Night	17% 9% 3 8% 5% 4 3 3 5% 8% 35%	4032
	21st to end	Night	20% 8% 2 6% 4 4 5% 4 6% 8% 34%	3965
June	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 4 6% 8% 44%	1600
	11th to 20th	Night	12% 7% 2 7% 5% 4 5% 5% 6% 8% 40%	1600
	21st to end	Night	11% 5% 2 5% 5% 4 6% 5% 7% 10% 41%	1600
July	1st to 10th	Night	11% 8% 3 8% 5% 4 4 3 5% 8% 41%	3684
	11th to 20th	Night	12% 7% 2 8% 5% 5% 6% 5% 7% 9% 35%	4057
	21st to end	Night	10% 7% 3 7% 5% 4 5% 4 6% 8% 42%	4427
August	1st to 10th	Night	12% 8% 4 8% 5% 4 6% 4 7% 8% 35%	2915
	11th to 20th	Night	13% 7% 3 7% 4 4 4 4 5% 7% 42%	2875
	21st to end	Night	8% 6% 2 6% 4 5% 5% 5% 7% 8% 44%	3441
September	1st to 10th	Night	13% 5% 2 4 4 4 5% 4 5% 7% 49%	2000
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 6% 8% 52%	2165
	21st to end	Night	17% 9% 2 7% 5% 4 4 3 5% 6% 39%	2215
October	1st to 10th	Night	15% 6% 3 5% 4 3 4 3 5% 7% 45%	2400
	11th to 20th	Night	18% 6% 2 6% 5% 4 5% 4 4 6% 40%	2400
	21st to end	Night	22% 9% 3 5% 4 4 3 3 3 7% 38%	2640
November	1st to 10th	Night	13% 9% 2 6% 4 3 4 3 5% 7% 43%	2523
	11th to 20th	Night	19% 12% 3 8% 5% 5% 4 3 5% 6% 31%	2857
	21st to end	Night	20% 14% 4 7% 5% 4 4 3 4 7% 29%	2800
December	1st to 10th	Night	19% 16% 10% 14% 5% 3 3 3 4 5% 18%	4580
	11th to 20th	Night	23% 15% 7% 10% 4 4 3 3 4 5% 23%	5205
	21st to end	Night	22% 18% 6% 10% 5% 5% 4 3 4 5% 17%	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	74% 5% 8% 9% 4	3983
	11th to 20th	Day	78% 4 6% 8% 3 1	4060
	21st to end	Day	72% 4 7% 11% 5%	4466
February	1st to 10th	Day	68% 4 8% 14% 5% 1	1800
	11th to 20th	Day	65% 5% 12% 13% 6%	1762
	21st to end	Day	62% 5% 11% 14% 6% 1	1647
March	1st to 10th	Day	53% 6% 11% 22% 8% 1	4935
	11th to 20th	Day	48% 6% 13% 24% 8% 2	4980
	21st to end	Day	53% 6% 9% 19% 12% 1	5465
April	1st to 10th	Day	53% 7% 11% 17% 10% 2	2321
	11th to 20th	Day	49% 8% 11% 17% 13% 2	2386
	21st to end	Day	49% 7% 11% 21% 10% 2	2600
May	1st to 10th	Day	54% 8% 11% 17% 8% 3	5897
	11th to 20th	Day	50% 8% 11% 21% 9% 1	5865
	21st to end	Day	46% 9% 13% 20% 9% 2	6900
June	1st to 10th	Day	43% 10% 15% 20% 11% 1	2800
	11th to 20th	Day	44% 10% 14% 19% 12% 1	2800
	21st to end	Day	41% 9% 13% 24% 12% 1	2800
July	1st to 10th	Day	41% 6% 9% 27% 15% 2	6200
	11th to 20th	Day	45% 6% 14% 24% 11%	5831
	21st to end	Day	42% 5% 10% 22% 19% 1	6240
August	1st to 10th	Day	49% 8% 14% 20% 9%	4221
	11th to 20th	Day	43% 7% 11% 28% 11% 1	4213
	21st to end	Day	36% 7% 13% 28% 13% 2	4422
September	1st to 10th	Day	39% 7% 10% 21% 20% 3	2400
	11th to 20th	Day	36% 6% 15% 26% 16% 1	2231
	21st to end	Day	50% 5% 11% 20% 13% 1	2184
October	1st to 10th	Day	33% 5% 10% 31% 20% 1	3260
	11th to 20th	Day	44% 7% 10% 22% 14% 5%	3240
	21st to end	Day	37% 4 12% 28% 18% 1	3538
November	1st to 10th	Day	43% 6% 12% 20% 16% 2	1993
	11th to 20th	Day	54% 5% 11% 17% 10% 2	1694
	21st to end	Day	61% 6% 12% 16% 5% 1	1600
December	1st to 10th	Day	72% 4 11% 9% 4	2600
	11th to 20th	Day	67% 4 12% 14% 3	2986
	21st to end	Day	72% 5% 8% 12% 4	3960
January	1st to 10th	Night	73% 5% 7% 11% 4	5958
	11th to 20th	Night	73% 5% 9% 10% 2 1	5900
	21st to end	Night	70% 4 8% 11% 5% 1	6490
February	1st to 10th	Night	63% 6% 9% 16% 6%	2600
	11th to 20th	Night	62% 5% 11% 16% 7%	2535
	21st to end	Night	61% 6% 10% 15% 9% 1	1976
March	1st to 10th	Night	55% 5% 9% 22% 8% 1	4918
	11th to 20th	Night	43% 5% 13% 27% 8% 3	4980
	21st to end	Night	50% 6% 10% 18% 15% 1	5467
April	1st to 10th	Night	52% 6% 10% 18% 13% 2	2078
	11th to 20th	Night	45% 7% 12% 17% 15% 3	1975
	21st to end	Night	46% 6% 10% 23% 11% 3	1804
May	1st to 10th	Night	59% 6% 10% 13% 9% 3	4060
	11th to 20th	Night	48% 7% 10% 23% 10% 1	4033
	21st to end	Night	44% 10% 12% 21% 9% 3	3972
June	1st to 10th	Night	37% 10% 13% 23% 15% 2	1600
	11th to 20th	Night	39% 9% 15% 23% 13% 1	1600
	21st to end	Night	37% 9% 13% 23% 16% 1	1600
July	1st to 10th	Night	42% 6% 9% 24% 17% 2	3645
	11th to 20th	Night	43% 6% 17% 22% 11% 1	4006
	21st to end	Night	39% 6% 11% 19% 24% 1	4297
August	1st to 10th	Night	46% 8% 14% 22% 10% 1	2904
	11th to 20th	Night	41% 6% 10% 29% 14% 1	2902
	21st to end	Night	36% 7% 12% 31% 13% 2	3441
September	1st to 10th	Night	33% 8% 12% 23% 20% 4	2000
	11th to 20th	Night	30% 6% 14% 28% 22% 1	2165
	21st to end	Night	46% 6% 11% 21% 15% 1	2215
October	1st to 10th	Night	36% 6% 8% 26% 23% 1	3920
	11th to 20th	Night	38% 4 11% 24% 15% 7%	3899
	21st to end	Night	36% 3 10% 28% 21% 2	4252
November	1st to 10th	Night	41% 5% 12% 21% 17% 3	2523
	11th to 20th	Night	53% 6% 11% 19% 10% 2	2857
	21st to end	Night	56% 6% 11% 20% 7% 1	2800
December	1st to 10th	Night	70% 4 10% 13% 3	4580
	11th to 20th	Night	66% 4 14% 14% 3	5208
	21st to end	Night	68% 7% 10% 12% 2	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	31% 28% 24% 11% 4 2	283
	11th to 20th	Day	34% 29% 27% 7% 2 1	300
	21st to end	Day	29% 31% 28% 8% 3 1	330
February	1st to 10th	Day	33% 26% 33% 7% 1	300
	11th to 20th	Day	38% 28% 27% 7% 1	300
	21st to end	Day	38% 25% 30% 7% 1	296
March	1st to 10th	Day	28% 24% 29% 14% 4	500
	11th to 20th	Day	34% 20% 30% 11% 5% 1	500
	21st to end	Day	32% 19% 29% 15% 4 1	550
April	1st to 10th	Day	30% 22% 25% 16% 7% 1	500
	11th to 20th	Day	25% 23% 26% 15% 8% 3	492
	21st to end	Day	26% 20% 28% 18% 7% 2	500
May	1st to 10th	Day	30% 17% 26% 17% 8% 3	503
	11th to 20th	Day	22% 14% 30% 19% 11% 4	527
	21st to end	Day	20% 8% 25% 25% 15% 6%	573
June	1st to 10th	Day	16% 11% 32% 25% 14% 4	530
	11th to 20th	Day	18% 14% 24% 26% 15% 3	530
	21st to end	Day	14% 9% 30% 28% 15% 4	530
July	1st to 10th	Day	12% 7% 23% 27% 21% 10%	525
	11th to 20th	Day	12% 7% 26% 29% 17% 8%	524
	21st to end	Day	14% 6% 24% 32% 18% 6%	576
August	1st to 10th	Day	12% 8% 23% 27% 21% 9%	526
	11th to 20th	Day	15% 6% 21% 27% 20% 10%	519
	21st to end	Day	10% 6% 26% 26% 23% 9%	583
September	1st to 10th	Day	16% 10% 20% 26% 19% 10%	530
	11th to 20th	Day	13% 3 18% 31% 23% 11%	530
	21st to end	Day	26% 11% 21% 25% 12% 5%	530
October	1st to 10th	Day	17% 9% 26% 24% 18% 5%	530
	11th to 20th	Day	23% 16% 28% 22% 8% 2	530
	21st to end	Day	28% 17% 30% 16% 8% 1	583
November	1st to 10th	Day	21% 17% 31% 20% 9% 3	471
	11th to 20th	Day	33% 18% 30% 12% 5% 2	233
	21st to end	Day	26% 24% 39% 10% 2 1	200
December	1st to 10th	Day	33% 28% 24% 12% 4 1	200
	11th to 20th	Day	35% 23% 30% 11% 3	200
	21st to end	Day	34% 22% 29% 13% 2	220
January	1st to 10th	Night	27% 24% 30% 15% 3	800
	11th to 20th	Night	31% 20% 30% 17% 3	800
	21st to end	Night	29% 20% 30% 19% 3	880
February	1st to 10th	Night	29% 18% 29% 23% 2	800
	11th to 20th	Night	30% 20% 34% 15% 1	783
	21st to end	Night	28% 17% 34% 19% 2	660
March	1st to 10th	Night	25% 18% 31% 22% 3	800
	11th to 20th	Night	27% 18% 28% 21% 6% 1	800
	21st to end	Night	24% 17% 33% 21% 5% 1	880
April	1st to 10th	Night	27% 17% 29% 22% 5%	800
	11th to 20th	Night	23% 12% 31% 24% 9% 1	791
	21st to end	Night	19% 11% 33% 30% 6%	604
May	1st to 10th	Night	23% 11% 25% 33% 8% 1	600
	11th to 20th	Night	21% 8% 27% 32% 11%	591
	21st to end	Night	12% 5% 26% 32% 23% 2	453
June	1st to 10th	Night	12% 6% 25% 41% 16% 1	400
	11th to 20th	Night	14% 4 26% 36% 19% 1	400
	21st to end	Night	12% 3 29% 36% 19% 1	400
July	1st to 10th	Night	9% 2 22% 41% 21% 4	423
	11th to 20th	Night	11% 3 19% 34% 29% 4	582
	21st to end	Night	11% 3 16% 41% 27% 2	657
August	1st to 10th	Night	8% 4 15% 43% 28% 2	597
	11th to 20th	Night	12% 4 15% 37% 28% 4	594
	21st to end	Night	11% 5% 18% 34% 27% 5%	787
September	1st to 10th	Night	14% 4 20% 35% 24% 4	800
	11th to 20th	Night	11% 4 15% 37% 28% 4	800
	21st to end	Night	20% 9% 23% 28% 19% 3	800
October	1st to 10th	Night	17% 7% 22% 30% 22% 2	800
	11th to 20th	Night	21% 11% 29% 29% 10% 1	800
	21st to end	Night	25% 14% 26% 27% 8%	880
November	1st to 10th	Night	18% 11% 29% 30% 11%	820
	11th to 20th	Night	27% 16% 27% 23% 6% 1	829
	21st to end	Night	29% 16% 29% 21% 6% 1	800
December	1st to 10th	Night	31% 18% 29% 17% 5%	800
	11th to 20th	Night	28% 20% 29% 20% 3	800
	21st to end	Night	28% 18% 30% 22% 2	880

Page generated at 2025-11-15 00:55:55. Version ac07

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