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Palisades-Dows Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Palisades-Dows Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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	13% 8% 3 8% 5% 4 4 4 5% 7% 39%	127219
	Night	13% 9% 3 8% 5% 4 4 3 5% 6% 41%	123116
Transparency	Day	43% 5% 12% 24% 14% 1	130772
	Night	43% 5% 11% 24% 15% 2	127627
Seeing	Day	16% 10% 30% 27% 14% 4	17231
	Night	16% 9% 31% 31% 11% 1	27026

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	8% 11% 6% 20% 8% 7% 5% 3 5% 5% 22%	3617
	11th to 20th	Day	8% 9% 5% 10% 8% 7% 5% 5% 7% 5% 30%	3731
	21st to end	Day	12% 14% 5% 13% 5% 4 4 3 4 6% 29%	4488
February	1st to 10th	Day	13% 11% 5% 9% 6% 5% 5% 4 6% 7% 29%	1800
	11th to 20th	Day	14% 10% 4 8% 5% 5% 5% 4 5% 8% 33%	1792
	21st to end	Day	13% 10% 4 11% 5% 4 4 3 6% 7% 34%	1650
March	1st to 10th	Day	18% 10% 3 6% 3 2 2 2 3 5% 46%	4659
	11th to 20th	Day	10% 5% 3 6% 4 4 4 3 6% 8% 47%	4980
	21st to end	Day	21% 12% 4 11% 5% 4 5% 3 5% 6% 25%	5677
April	1st to 10th	Day	17% 12% 3 8% 5% 4 4 3 5% 6% 33%	2400
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 4 6% 6% 34%	2374
	21st to end	Day	21% 7% 3 7% 3 4 4 4 5% 6% 35%	2400
May	1st to 10th	Day	15% 7% 2 6% 5% 5% 5% 4 5% 7% 37%	6102
	11th to 20th	Day	15% 7% 2 6% 4 4 4 3 5% 7% 44%	6319
	21st to end	Day	15% 7% 3 7% 5% 4 5% 4 6% 7% 38%	6935
June	1st to 10th	Day	11% 5% 2 5% 4 5% 6% 4 7% 9% 44%	2800
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 5% 7% 46%	2800
	21st to end	Day	12% 6% 2 7% 4 4 5% 4 6% 8% 41%	2800
July	1st to 10th	Day	9% 7% 3 8% 5% 5% 5% 4 7% 9% 39%	6360
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 3 6% 8% 46%	6360
	21st to end	Day	10% 6% 3 7% 4 5% 5% 4 7% 9% 38%	6790
August	1st to 10th	Day	8% 5% 2 5% 4 4 5% 5% 7% 9% 45%	4234
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 7% 9% 42%	4077
	21st to end	Day	8% 4 2 5% 4 4 4 3 5% 9% 50%	4312
September	1st to 10th	Day	13% 5% 2 5% 3 4 3 3 5% 7% 51%	2400
	11th to 20th	Day	10% 4 1 5% 4 4 5% 4 5% 8% 51%	2400
	21st to end	Day	10% 5% 2 6% 5% 4 4 4 6% 8% 46%	2123
October	1st to 10th	Day	14% 6% 2 6% 5% 3 3 2 4 5% 50%	2000
	11th to 20th	Day	17% 7% 2 6% 4 3 3 3 5% 6% 42%	2000
	21st to end	Day	16% 9% 2 7% 4 4 3 3 4 6% 41%	2158
November	1st to 10th	Day	11% 9% 3 6% 4 4 3 4 6% 6% 44%	1780
	11th to 20th	Day	14% 12% 3 8% 5% 4 4 3 5% 7% 35%	1701
	21st to end	Day	16% 9% 3 8% 5% 3 4 4 4 6% 38%	1600
December	1st to 10th	Day	8% 9% 3 7% 4 3 4 3 5% 7% 46%	2610
	11th to 20th	Day	15% 11% 5% 14% 6% 6% 5% 4 5% 5% 25%	3008
	21st to end	Day	23% 22% 8% 12% 5% 3 3 2 3 4 16%	3982
January	1st to 10th	Night	10% 11% 6% 16% 5% 5% 4 3 4 5% 31%	6348
	11th to 20th	Night	10% 14% 5% 11% 7% 6% 5% 4 7% 6% 26%	6245
	21st to end	Night	13% 13% 6% 11% 5% 4 3 3 4 6% 32%	6490
February	1st to 10th	Night	12% 13% 4 8% 6% 5% 4 3 6% 6% 34%	2600
	11th to 20th	Night	12% 10% 3 8% 5% 4 4 3 5% 6% 40%	2494
	21st to end	Night	13% 10% 3 9% 4 4 4 3 4 5% 40%	1980
March	1st to 10th	Night	17% 7% 3 6% 4 3 3 2 4 5% 46%	5238
	11th to 20th	Night	10% 7% 2 5% 4 4 3 3 4 7% 51%	4980
	21st to end	Night	19% 12% 5% 10% 6% 5% 4 3 4 5% 27%	5250
April	1st to 10th	Night	16% 9% 3 6% 4 4 3 2 5% 6% 41%	2000
	11th to 20th	Night	17% 9% 2 6% 4 3 3 3 5% 5% 41%	1975
	21st to end	Night	18% 8% 2 6% 4 3 4 4 6% 6% 39%	2000
May	1st to 10th	Night	17% 6% 2 6% 4 4 4 3 5% 7% 43%	3810
	11th to 20th	Night	10% 6% 2 6% 4 5% 4 4 6% 7% 46%	3596
	21st to end	Night	14% 7% 2 7% 4 4 4 3 5% 7% 43%	3942
June	1st to 10th	Night	8% 5% 2 5% 5% 4 4 3 6% 10% 48%	1600
	11th to 20th	Night	9% 5% 2 6% 4 4 4 4 8% 11% 44%	1600
	21st to end	Night	10% 5% 2 5% 4 3 4 4 6% 8% 49%	1600
July	1st to 10th	Night	10% 4 2 7% 5% 4 5% 4 7% 8% 43%	3618
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 6% 8% 54%	3617
	21st to end	Night	9% 5% 2 7% 4 5% 5% 4 6% 8% 45%	4077
August	1st to 10th	Night	5% 4 2 5% 4 4 4 4 6% 9% 53%	2926
	11th to 20th	Night	8% 4 2 7% 3 3 4 3 6% 7% 53%	2978
	21st to end	Night	8% 5% 1 5% 3 4 4 3 5% 8% 54%	3586
September	1st to 10th	Night	9% 4 2 5% 3 4 4 3 5% 6% 57%	2000
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 6% 7% 53%	2000
	21st to end	Night	6% 4 2 6% 4 4 4 3 4 7% 55%	2253
October	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 4 5% 54%	2400
	11th to 20th	Night	15% 7% 2 5% 3 4 4 3 4 6% 47%	2400
	21st to end	Night	17% 7% 3 6% 5% 4 3 3 4 6% 42%	2680
November	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 5% 6% 52%	2563
	11th to 20th	Night	14% 9% 3 7% 5% 3 4 4 5% 6% 41%	2695
	21st to end	Night	16% 9% 3 7% 5% 4 3 3 5% 5% 40%	2800
December	1st to 10th	Night	8% 7% 3 7% 5% 5% 4 4 5% 6% 48%	4580
	11th to 20th	Night	14% 12% 5% 10% 4 4 4 3 4 5% 33%	5199
	21st to end	Night	23% 17% 7% 12% 6% 4 4 3 3 4 15%	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	64% 4 9% 17% 6%	3618
	11th to 20th	Day	54% 3 10% 15% 16% 2	3731
	21st to end	Day	57% 4 14% 18% 7%	4488
February	1st to 10th	Day	54% 4 14% 19% 7% 1	1800
	11th to 20th	Day	49% 6% 12% 21% 10% 2	1801
	21st to end	Day	49% 5% 14% 21% 9% 2	1650
March	1st to 10th	Day	43% 3 9% 28% 14% 3	4659
	11th to 20th	Day	36% 4 10% 34% 16% 1	4980
	21st to end	Day	59% 5% 15% 15% 5% 1	5679
April	1st to 10th	Day	53% 5% 11% 22% 10%	2400
	11th to 20th	Day	49% 6% 10% 22% 12% 1	2374
	21st to end	Day	49% 5% 11% 22% 12% 2	2400
May	1st to 10th	Day	45% 6% 10% 20% 18% 1	6140
	11th to 20th	Day	39% 5% 11% 28% 14% 3	6323
	21st to end	Day	43% 7% 11% 24% 13% 1	6949
June	1st to 10th	Day	35% 8% 15% 24% 16% 2	2800
	11th to 20th	Day	36% 7% 11% 22% 21% 3	2800
	21st to end	Day	40% 7% 12% 24% 15% 2	2800
July	1st to 10th	Day	39% 8% 12% 28% 11% 1	6291
	11th to 20th	Day	35% 7% 13% 29% 15% 1	6285
	21st to end	Day	39% 9% 17% 20% 14% 1	6596
August	1st to 10th	Day	33% 8% 16% 29% 13% 1	4220
	11th to 20th	Day	36% 7% 16% 24% 16% 1	4116
	21st to end	Day	32% 5% 14% 31% 17% 2	4311
September	1st to 10th	Day	33% 5% 11% 26% 22% 3	2400
	11th to 20th	Day	32% 5% 13% 30% 18% 2	2400
	21st to end	Day	35% 5% 11% 29% 19% 2	2123
October	1st to 10th	Day	24% 2 6% 30% 36% 2	3260
	11th to 20th	Day	30% 3 12% 24% 26% 5%	3240
	21st to end	Day	40% 3 10% 30% 14% 3	3460
November	1st to 10th	Day	41% 4 13% 26% 13% 3	1780
	11th to 20th	Day	49% 3 13% 22% 12% 1	1701
	21st to end	Day	47% 4 16% 24% 9% 1	1600
December	1st to 10th	Day	39% 3 14% 37% 7% 1	2610
	11th to 20th	Day	61% 4 12% 13% 9% 1	3005
	21st to end	Day	75% 3 9% 10% 3	3982
January	1st to 10th	Night	56% 3 13% 19% 8% 1	6348
	11th to 20th	Night	56% 5% 12% 12% 14% 1	6245
	21st to end	Night	55% 3 10% 19% 12% 1	6490
February	1st to 10th	Night	51% 5% 11% 22% 11% 1	2600
	11th to 20th	Night	46% 5% 11% 24% 13% 2	2495
	21st to end	Night	47% 4 10% 22% 15% 2	1980
March	1st to 10th	Night	42% 3 8% 27% 19% 2	5238
	11th to 20th	Night	33% 4 10% 32% 18% 3	4980
	21st to end	Night	60% 5% 12% 14% 8% 1	5250
April	1st to 10th	Night	45% 4 9% 26% 14% 2	2000
	11th to 20th	Night	46% 4 9% 23% 16% 3	1975
	21st to end	Night	44% 5% 12% 22% 14% 2	2000
May	1st to 10th	Night	41% 6% 9% 22% 20% 2	3837
	11th to 20th	Night	36% 7% 13% 23% 17% 3	3597
	21st to end	Night	40% 6% 10% 28% 14% 1	3950
June	1st to 10th	Night	32% 6% 15% 27% 18% 3	1600
	11th to 20th	Night	32% 6% 14% 25% 19% 4	1600
	21st to end	Night	33% 6% 16% 24% 17% 4	1600
July	1st to 10th	Night	36% 7% 13% 29% 13% 2	3580
	11th to 20th	Night	28% 6% 14% 32% 19% 1	3572
	21st to end	Night	34% 9% 18% 23% 14% 2	3960
August	1st to 10th	Night	26% 7% 17% 33% 15% 2	2916
	11th to 20th	Night	29% 7% 15% 31% 16% 1	3005
	21st to end	Night	29% 6% 11% 30% 18% 5%	3586
September	1st to 10th	Night	29% 5% 10% 28% 26% 3	2000
	11th to 20th	Night	32% 5% 10% 32% 18% 4	2000
	21st to end	Night	30% 5% 9% 29% 25% 2	2253
October	1st to 10th	Night	23% 3 6% 28% 36% 3	3920
	11th to 20th	Night	28% 3 10% 22% 31% 6%	3899
	21st to end	Night	46% 3 8% 22% 17% 4	4316
November	1st to 10th	Night	34% 5% 13% 27% 18% 4	2563
	11th to 20th	Night	45% 4 13% 24% 13% 2	2695
	21st to end	Night	47% 3 12% 26% 11% 1	2800
December	1st to 10th	Night	37% 4 13% 35% 10% 1	4580
	11th to 20th	Night	54% 4 13% 23% 6% 1	5201
	21st to end	Night	73% 4 8% 10% 4	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	21% 10% 35% 23% 8% 2	300
	11th to 20th	Day	20% 16% 41% 18% 5% 1	300
	21st to end	Day	20% 14% 39% 20% 6% 1	330
February	1st to 10th	Day	20% 15% 39% 21% 4	300
	11th to 20th	Day	19% 20% 35% 21% 4 1	300
	21st to end	Day	21% 14% 44% 16% 4	249
March	1st to 10th	Day	21% 20% 40% 14% 5%	300
	11th to 20th	Day	23% 18% 30% 22% 6% 2	300
	21st to end	Day	30% 16% 33% 15% 5% 1	416
April	1st to 10th	Day	23% 15% 38% 17% 7%	500
	11th to 20th	Day	23% 18% 29% 21% 9%	492
	21st to end	Day	24% 15% 32% 19% 9% 1	500
May	1st to 10th	Day	18% 12% 36% 24% 7% 2	695
	11th to 20th	Day	20% 13% 26% 25% 14% 2	725
	21st to end	Day	14% 11% 29% 28% 14% 5%	789
June	1st to 10th	Day	9% 5% 28% 32% 21% 5%	730
	11th to 20th	Day	12% 6% 29% 34% 16% 3	730
	21st to end	Day	11% 9% 31% 33% 13% 4	730
July	1st to 10th	Day	9% 3 20% 33% 23% 12%	721
	11th to 20th	Day	9% 4 24% 33% 23% 7%	718
	21st to end	Day	8% 3 22% 37% 23% 5%	794
August	1st to 10th	Day	7% 3 25% 35% 23% 7%	726
	11th to 20th	Day	11% 3 20% 33% 24% 8%	660
	21st to end	Day	8% 4 19% 36% 26% 7%	583
September	1st to 10th	Day	13% 8% 17% 32% 22% 8%	530
	11th to 20th	Day	8% 4 19% 38% 23% 8%	530
	21st to end	Day	13% 8% 29% 24% 22% 4	424
October	1st to 10th	Day	18% 7% 28% 29% 13% 5%	330
	11th to 20th	Day	19% 21% 36% 15% 8% 1	330
	21st to end	Day	24% 14% 34% 20% 6% 2	363
November	1st to 10th	Day	16% 12% 37% 23% 9% 2	306
	11th to 20th	Day	21% 18% 32% 19% 8% 2	300
	21st to end	Day	24% 11% 38% 21% 6%	300
December	1st to 10th	Day	13% 15% 44% 20% 6% 2	300
	11th to 20th	Day	17% 16% 35% 24% 8% 1	300
	21st to end	Day	27% 17% 37% 16% 3	330
January	1st to 10th	Night	15% 13% 38% 27% 7% 1	1000
	11th to 20th	Night	19% 14% 34% 27% 6%	1000
	21st to end	Night	19% 11% 37% 27% 5%	1100
February	1st to 10th	Night	20% 13% 38% 24% 5%	1000
	11th to 20th	Night	18% 13% 37% 26% 5%	940
	21st to end	Night	19% 13% 40% 23% 4 1	660
March	1st to 10th	Night	20% 13% 38% 22% 6% 1	743
	11th to 20th	Night	17% 11% 34% 30% 8% 1	600
	21st to end	Night	22% 13% 37% 24% 4 1	660
April	1st to 10th	Night	20% 14% 40% 23% 3	600
	11th to 20th	Night	21% 16% 29% 27% 6%	593
	21st to end	Night	23% 9% 32% 28% 8% 1	600
May	1st to 10th	Night	17% 8% 39% 28% 7% 1	600
	11th to 20th	Night	17% 9% 29% 33% 12%	591
	21st to end	Night	14% 5% 30% 33% 17% 1	650
June	1st to 10th	Night	9% 5% 26% 43% 16% 2	600
	11th to 20th	Night	10% 4 30% 42% 14%	600
	21st to end	Night	12% 4 28% 41% 14% 1	600
July	1st to 10th	Night	9% 1 13% 44% 30% 3	585
	11th to 20th	Night	6% 3 20% 42% 26% 3	582
	21st to end	Night	6% 4 18% 44% 27% 1	657
August	1st to 10th	Night	5% 2 16% 47% 27% 2	597
	11th to 20th	Night	7% 3 14% 42% 29% 5%	594
	21st to end	Night	11% 2 13% 46% 26% 2	660
September	1st to 10th	Night	11% 4 17% 40% 23% 4	600
	11th to 20th	Night	11% 3 20% 37% 25% 4	600
	21st to end	Night	9% 6% 27% 36% 20% 1	750
October	1st to 10th	Night	15% 6% 27% 32% 19% 1	800
	11th to 20th	Night	19% 10% 33% 30% 9%	800
	21st to end	Night	21% 12% 32% 27% 7%	880
November	1st to 10th	Night	14% 10% 37% 29% 9% 1	789
	11th to 20th	Night	19% 14% 39% 22% 6%	895
	21st to end	Night	20% 12% 36% 26% 6% 1	1000
December	1st to 10th	Night	17% 13% 38% 26% 5% 1	1000
	11th to 20th	Night	22% 10% 35% 28% 6%	1000
	21st to end	Night	26% 13% 33% 24% 4	1100

Page generated at 2025-10-31 01:02:42. Version ac07

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