Easton Woods Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Easton Woods Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	131115
	Night	14% 10% 4 8% 5% 4 4 3 5% 7% 35%	129728
Transparency	Day	47% 6% 10% 22% 14% 2	134788
	Night	47% 5% 10% 22% 14% 2	134125
Seeing	Day	21% 12% 27% 22% 13% 6%	16553
	Night	20% 10% 25% 29% 15% 2	26695

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% 18% 6% 11% 6% 4 3 3 4 5% 21%	5258
	11th to 20th	Day	13% 16% 7% 14% 6% 4 3 3 3 4 27%	5280
	21st to end	Day	18% 13% 6% 11% 9% 6% 5% 3 4 4 21%	5780
February	1st to 10th	Day	21% 12% 4 9% 5% 3 3 2 5% 5% 30%	1890
	11th to 20th	Day	19% 13% 5% 10% 4 4 4 4 4 6% 27%	1979
	21st to end	Day	20% 13% 4 8% 4 3 3 3 4 5% 32%	1650
March	1st to 10th	Day	18% 15% 4 8% 4 4 4 3 4 5% 31%	4748
	11th to 20th	Day	12% 7% 3 7% 4 4 4 4 6% 7% 41%	4980
	21st to end	Day	18% 8% 3 7% 4 4 5% 4 5% 7% 34%	5465
April	1st to 10th	Day	16% 9% 3 9% 4 5% 4 3 5% 6% 34%	2202
	11th to 20th	Day	16% 9% 3 6% 5% 4 5% 3 5% 6% 39%	2528
	21st to end	Day	18% 8% 2 7% 6% 5% 4 4 5% 7% 34%	2600
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 6% 4 6% 8% 27%	5862
	11th to 20th	Day	19% 9% 3 8% 5% 4 5% 4 6% 7% 30%	5861
	21st to end	Day	14% 7% 2 7% 5% 5% 6% 4 7% 9% 34%	6433
June	1st to 10th	Day	11% 6% 2 6% 6% 5% 4 5% 8% 9% 38%	2600
	11th to 20th	Day	9% 6% 3 7% 6% 6% 6% 5% 7% 9% 38%	2600
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 6% 8% 10% 38%	2600
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 5% 4 6% 8% 44%	5900
	11th to 20th	Day	10% 7% 3 7% 5% 5% 6% 6% 8% 10% 33%	5900
	21st to end	Day	11% 7% 3 8% 6% 6% 6% 5% 7% 9% 32%	6424
August	1st to 10th	Day	7% 5% 2 7% 5% 6% 6% 6% 8% 11% 37%	4234
	11th to 20th	Day	7% 6% 2 7% 5% 5% 6% 5% 7% 10% 39%	4174
	21st to end	Day	5% 3 2 5% 4 4 5% 4 6% 8% 54%	4562
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 3 6% 6% 47%	2200
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 3 6% 8% 50%	2200
	21st to end	Day	18% 6% 2 5% 4 3 4 3 5% 6% 42%	2200
October	1st to 10th	Day	12% 5% 2 5% 3 4 4 3 6% 7% 48%	2135
	11th to 20th	Day	14% 7% 2 5% 4 4 3 3 5% 6% 47%	2000
	21st to end	Day	19% 9% 2 7% 4 4 3 2 4 6% 40%	2190
November	1st to 10th	Day	12% 6% 3 5% 4 4 4 4 4 5% 50%	1852
	11th to 20th	Day	16% 12% 3 7% 4 3 3 4 5% 5% 37%	1890
	21st to end	Day	17% 11% 4 6% 5% 5% 4 3 5% 6% 34%	1890
December	1st to 10th	Day	19% 13% 3 9% 6% 4 4 3 4 5% 29%	3020
	11th to 20th	Day	23% 15% 5% 8% 5% 4 4 3 4 5% 24%	3463
	21st to end	Day	19% 18% 5% 12% 6% 4 4 3 5% 5% 20%	4565
January	1st to 10th	Night	14% 15% 6% 15% 6% 5% 5% 4 5% 4 19%	7635
	11th to 20th	Night	15% 15% 6% 14% 7% 4 4 3 4 5% 23%	7680
	21st to end	Night	18% 11% 4 9% 6% 5% 4 3 4 5% 29%	8401
February	1st to 10th	Night	20% 13% 4 8% 4 4 4 3 5% 5% 29%	2730
	11th to 20th	Night	20% 13% 3 10% 5% 4 4 3 4 5% 29%	2415
	21st to end	Night	21% 15% 4 7% 4 4 4 2 4 5% 30%	1980
March	1st to 10th	Night	18% 12% 3 6% 4 3 4 3 4 6% 37%	5103
	11th to 20th	Night	12% 9% 3 6% 4 3 4 3 6% 9% 42%	4980
	21st to end	Night	16% 10% 4 8% 6% 5% 5% 3 5% 6% 33%	5467
April	1st to 10th	Night	16% 10% 3 6% 5% 4 4 3 5% 7% 37%	2200
	11th to 20th	Night	13% 8% 2 7% 5% 4 4 4 7% 7% 40%	1833
	21st to end	Night	15% 8% 3 7% 4 4 5% 4 5% 6% 38%	1800
May	1st to 10th	Night	22% 11% 3 7% 5% 5% 4 4 5% 7% 28%	4033
	11th to 20th	Night	16% 7% 3 6% 4 4 5% 4 7% 9% 35%	4032
	21st to end	Night	13% 7% 3 7% 4 5% 5% 4 6% 9% 36%	4421
June	1st to 10th	Night	9% 5% 2 5% 5% 5% 5% 4 7% 9% 45%	1800
	11th to 20th	Night	7% 6% 2 6% 4 4 5% 5% 8% 10% 44%	1800
	21st to end	Night	8% 4 2 5% 5% 4 5% 5% 7% 10% 45%	1800
July	1st to 10th	Night	8% 7% 2 7% 4 4 5% 4 7% 8% 44%	4058
	11th to 20th	Night	8% 7% 3 7% 5% 5% 5% 5% 7% 11% 37%	4057
	21st to end	Night	7% 7% 3 8% 5% 6% 5% 4 7% 10% 37%	4427
August	1st to 10th	Night	7% 6% 3 7% 5% 6% 5% 5% 8% 9% 40%	2915
	11th to 20th	Night	9% 6% 3 8% 5% 5% 5% 4 5% 7% 43%	2875
	21st to end	Night	5% 3 1 5% 4 4 5% 4 7% 10% 52%	3284
September	1st to 10th	Night	11% 4 2 5% 3 3 4 4 6% 6% 53%	2200
	11th to 20th	Night	9% 5% 2 6% 3 4 4 3 5% 7% 54%	2200
	21st to end	Night	15% 7% 2 6% 4 4 3 3 5% 6% 46%	2200
October	1st to 10th	Night	11% 5% 2 5% 3 3 2 3 5% 6% 53%	2265
	11th to 20th	Night	13% 6% 3 5% 3 3 4 4 6% 8% 46%	2400
	21st to end	Night	18% 7% 3 6% 4 3 4 3 5% 5% 42%	2646
November	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 4 6% 49%	2666
	11th to 20th	Night	16% 10% 3 6% 4 4 4 3 5% 6% 39%	2730
	21st to end	Night	19% 13% 4 7% 4 3 3 2 4 6% 34%	2730
December	1st to 10th	Night	18% 12% 3 9% 5% 4 4 3 4 5% 32%	4380
	11th to 20th	Night	18% 15% 7% 9% 5% 4 4 3 4 6% 26%	4952
	21st to end	Night	19% 17% 5% 10% 6% 5% 5% 3 5% 6% 19%	6633

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	65% 4 11% 15% 5%	5259
	11th to 20th	Day	62% 3 7% 14% 13% 2	5280
	21st to end	Day	66% 4 7% 16% 6% 1	5780
February	1st to 10th	Day	57% 4 11% 19% 9% 1	1890
	11th to 20th	Day	58% 5% 9% 17% 10% 1	1989
	21st to end	Day	54% 4 8% 22% 10% 2	1650
March	1st to 10th	Day	55% 3 7% 22% 10% 3	4748
	11th to 20th	Day	40% 5% 9% 27% 17% 2	4980
	21st to end	Day	48% 5% 10% 22% 13% 2	5465
April	1st to 10th	Day	49% 6% 10% 22% 11% 3	2202
	11th to 20th	Day	45% 5% 10% 21% 16% 4	2528
	21st to end	Day	49% 6% 10% 20% 12% 3	2600
May	1st to 10th	Day	52% 6% 11% 19% 10% 2	5897
	11th to 20th	Day	51% 6% 10% 22% 10% 1	5865
	21st to end	Day	43% 8% 12% 21% 14% 3	6447
June	1st to 10th	Day	39% 8% 13% 24% 15% 2	2600
	11th to 20th	Day	40% 8% 14% 21% 16% 2	2600
	21st to end	Day	38% 8% 14% 23% 15% 2	2600
July	1st to 10th	Day	37% 7% 11% 27% 16% 2	5835
	11th to 20th	Day	41% 10% 14% 24% 11% 1	5831
	21st to end	Day	45% 8% 12% 18% 15% 2	6240
August	1st to 10th	Day	36% 9% 16% 29% 11% 1	4221
	11th to 20th	Day	35% 7% 11% 30% 16% 1	4213
	21st to end	Day	27% 6% 14% 29% 21% 2	4562
September	1st to 10th	Day	36% 5% 10% 22% 21% 6%	2200
	11th to 20th	Day	33% 5% 10% 27% 23% 2	2200
	21st to end	Day	42% 5% 8% 24% 19% 1	2200
October	1st to 10th	Day	24% 4 8% 30% 33% 2	3473
	11th to 20th	Day	30% 3 9% 31% 24% 3	3240
	21st to end	Day	34% 4 10% 28% 22% 2	3516
November	1st to 10th	Day	37% 4 10% 28% 19% 3	1852
	11th to 20th	Day	48% 4 8% 22% 16% 3	1890
	21st to end	Day	51% 4 9% 22% 13% 1	1890
December	1st to 10th	Day	58% 4 8% 23% 7%	3020
	11th to 20th	Day	62% 5% 9% 18% 6%	3460
	21st to end	Day	67% 5% 10% 13% 6%	4565
January	1st to 10th	Night	66% 5% 9% 14% 5%	7636
	11th to 20th	Night	64% 4 7% 14% 9% 2	7680
	21st to end	Night	57% 5% 10% 20% 8% 1	8401
February	1st to 10th	Night	57% 4 10% 19% 9% 1	2730
	11th to 20th	Night	58% 4 8% 18% 12% 1	2416
	21st to end	Night	57% 4 10% 17% 9% 3	1980
March	1st to 10th	Night	48% 4 6% 27% 12% 2	5103
	11th to 20th	Night	38% 4 8% 31% 18% 1	4980
	21st to end	Night	52% 5% 7% 23% 12% 2	5467
April	1st to 10th	Night	47% 6% 8% 22% 16% 3	2200
	11th to 20th	Night	41% 4 11% 21% 17% 6%	1833
	21st to end	Night	45% 6% 9% 22% 16% 2	1800
May	1st to 10th	Night	55% 7% 10% 15% 9% 3	4060
	11th to 20th	Night	44% 8% 13% 22% 11% 1	4033
	21st to end	Night	41% 8% 15% 23% 10% 3	4429
June	1st to 10th	Night	34% 7% 11% 25% 20% 3	1800
	11th to 20th	Night	33% 8% 16% 20% 20% 3	1800
	21st to end	Night	32% 8% 15% 23% 19% 3	1800
July	1st to 10th	Night	35% 8% 11% 25% 19% 3	4015
	11th to 20th	Night	37% 10% 17% 23% 12% 1	4006
	21st to end	Night	39% 9% 12% 22% 14% 4	4297
August	1st to 10th	Night	36% 9% 15% 28% 11% 1	2904
	11th to 20th	Night	38% 7% 10% 24% 21%	2902
	21st to end	Night	26% 6% 14% 30% 22% 3	3284
September	1st to 10th	Night	31% 5% 14% 23% 21% 7%	2200
	11th to 20th	Night	30% 5% 10% 25% 27% 3	2200
	21st to end	Night	40% 4 9% 21% 25% 1	2200
October	1st to 10th	Night	26% 4 6% 27% 33% 3	3707
	11th to 20th	Night	27% 5% 8% 27% 26% 7%	3899
	21st to end	Night	32% 4 8% 26% 26% 5%	4270
November	1st to 10th	Night	36% 4 10% 25% 21% 4	2666
	11th to 20th	Night	46% 4 7% 23% 17% 3	2730
	21st to end	Night	52% 4 9% 22% 12% 1	2730
December	1st to 10th	Night	54% 4 12% 23% 7%	4380
	11th to 20th	Night	60% 4 11% 18% 6% 1	4954
	21st to end	Night	66% 5% 9% 15% 5%	6633

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	32% 19% 34% 10% 4	330
	11th to 20th	Day	37% 22% 30% 10% 1	330
	21st to end	Day	29% 27% 33% 9% 2	363
February	1st to 10th	Day	33% 19% 30% 15% 3	330
	11th to 20th	Day	41% 25% 27% 5% 1 1	315
	21st to end	Day	31% 24% 36% 9%	249
March	1st to 10th	Day	29% 21% 32% 16% 3	412
	11th to 20th	Day	29% 19% 33% 14% 5% 1	500
	21st to end	Day	33% 18% 29% 17% 3	550
April	1st to 10th	Day	26% 19% 29% 17% 9% 1	500
	11th to 20th	Day	25% 15% 31% 19% 8% 2	492
	21st to end	Day	25% 15% 33% 19% 6% 2	500
May	1st to 10th	Day	25% 16% 30% 17% 10% 2	503
	11th to 20th	Day	21% 12% 27% 24% 10% 5%	527
	21st to end	Day	16% 8% 27% 26% 17% 7%	573
June	1st to 10th	Day	15% 7% 25% 29% 18% 6%	530
	11th to 20th	Day	14% 8% 24% 30% 16% 8%	530
	21st to end	Day	12% 6% 30% 25% 18% 9%	530
July	1st to 10th	Day	13% 2 20% 26% 18% 20%	525
	11th to 20th	Day	9% 5% 21% 32% 23% 11%	524
	21st to end	Day	12% 5% 17% 30% 23% 13%	576
August	1st to 10th	Day	11% 4 18% 29% 27% 11%	526
	11th to 20th	Day	11% 3 21% 34% 20% 12%	519
	21st to end	Day	9% 3 17% 33% 25% 13%	583
September	1st to 10th	Day	13% 5% 16% 27% 26% 12%	530
	11th to 20th	Day	9% 3 14% 28% 31% 15%	530
	21st to end	Day	21% 8% 20% 25% 20% 5%	530
October	1st to 10th	Day	13% 7% 24% 29% 20% 7%	530
	11th to 20th	Day	17% 12% 32% 22% 13% 4	530
	21st to end	Day	25% 12% 31% 23% 8%	573
November	1st to 10th	Day	18% 16% 36% 22% 7% 1	330
	11th to 20th	Day	30% 15% 33% 16% 5% 2	330
	21st to end	Day	24% 20% 36% 16% 4	330
December	1st to 10th	Day	31% 20% 32% 13% 4 1	330
	11th to 20th	Day	28% 21% 37% 11% 3 1	330
	21st to end	Day	32% 18% 32% 13% 4 1	363
January	1st to 10th	Night	28% 17% 31% 20% 5%	840
	11th to 20th	Night	30% 20% 29% 19% 3	840
	21st to end	Night	26% 17% 34% 21% 2	924
February	1st to 10th	Night	29% 15% 29% 25% 2	840
	11th to 20th	Night	30% 18% 32% 18% 1	804
	21st to end	Night	29% 16% 33% 20% 2	660
March	1st to 10th	Night	26% 13% 30% 27% 4	800
	11th to 20th	Night	25% 15% 31% 20% 8% 1	800
	21st to end	Night	25% 14% 31% 23% 7%	880
April	1st to 10th	Night	22% 15% 33% 23% 7%	800
	11th to 20th	Night	16% 13% 34% 24% 12% 1	607
	21st to end	Night	18% 9% 38% 27% 7% 1	600
May	1st to 10th	Night	21% 8% 27% 31% 11% 2	600
	11th to 20th	Night	19% 6% 25% 31% 18% 1	591
	21st to end	Night	10% 5% 19% 34% 27% 4	650
June	1st to 10th	Night	10% 3 21% 40% 24% 2	600
	11th to 20th	Night	9% 3 18% 42% 26% 2	600
	21st to end	Night	9% 2 21% 36% 29% 3	600
July	1st to 10th	Night	12% 4 13% 33% 30% 8%	585
	11th to 20th	Night	7% 3 15% 36% 34% 4	582
	21st to end	Night	10% 2 14% 32% 38% 4	657
August	1st to 10th	Night	8% 2 11% 39% 36% 3	597
	11th to 20th	Night	11% 2 12% 37% 32% 7%	594
	21st to end	Night	8% 2 16% 31% 35% 8%	660
September	1st to 10th	Night	12% 3 13% 35% 33% 6%	800
	11th to 20th	Night	11% 3 12% 35% 32% 7%	800
	21st to end	Night	18% 6% 19% 33% 21% 3	800
October	1st to 10th	Night	13% 5% 20% 34% 25% 4	800
	11th to 20th	Night	17% 10% 24% 34% 14% 1	800
	21st to end	Night	21% 10% 26% 30% 11% 1	880
November	1st to 10th	Night	17% 10% 27% 30% 15% 1	820
	11th to 20th	Night	22% 16% 27% 25% 9% 1	840
	21st to end	Night	26% 12% 25% 29% 8% 1	840
December	1st to 10th	Night	31% 13% 29% 23% 5%	840
	11th to 20th	Night	25% 14% 31% 24% 5%	840
	21st to end	Night	27% 17% 27% 26% 3	924

Page generated at 2026-02-13 01:42:18. Version ac07

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