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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 2024-05-13.

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% 4 4 4 5% 7% 37%	83585
	Night	13% 9% 3 8% 5% 4 4 3 5% 6% 40%	85988
Transparency	Day	46% 5% 12% 22% 12% 1	83288
	Night	45% 5% 12% 23% 14% 2	85805
Seeing	Day	16% 10% 29% 27% 14% 4	15093
	Night	16% 9% 31% 31% 11% 1	25109

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	9% 11% 7% 20% 8% 7% 5% 3 5% 5% 20%	2527
	11th to 20th	Day	11% 11% 5% 11% 10% 7% 5% 4 7% 5% 24%	2599
	21st to end	Day	15% 18% 6% 16% 7% 5% 4 3 4 5% 17%	3135
February	1st to 10th	Day	13% 11% 5% 9% 6% 5% 5% 4 6% 7% 29%	1710
	11th to 20th	Day	14% 10% 3 7% 5% 5% 5% 4 5% 8% 33%	1700
	21st to end	Day	13% 10% 4 11% 5% 4 4 3 5% 7% 33%	1570
March	1st to 10th	Day	16% 11% 4 7% 3 3 3 2 4 5% 42%	3243
	11th to 20th	Day	10% 6% 3 7% 5% 4 4 3 6% 7% 45%	3480
	21st to end	Day	23% 13% 4 12% 5% 4 5% 3 5% 5% 21%	3959
April	1st to 10th	Day	17% 12% 3 8% 5% 4 4 3 5% 6% 32%	2280
	11th to 20th	Day	17% 11% 3 6% 5% 5% 4 4 6% 6% 34%	2254
	21st to end	Day	22% 7% 3 7% 3 4 4 4 5% 6% 35%	2280
May	1st to 10th	Day	18% 8% 3 7% 6% 5% 6% 4 6% 7% 31%	2562
	11th to 20th	Day	19% 9% 2 6% 4 5% 5% 3 5% 6% 35%	2510
	21st to end	Day	15% 7% 3 7% 6% 5% 5% 5% 6% 7% 34%	2725
June	1st to 10th	Day	11% 4 2 5% 4 5% 6% 4 7% 9% 43%	2520
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 5% 7% 47%	2520
	21st to end	Day	12% 6% 2 7% 5% 4 6% 4 6% 8% 40%	2520
July	1st to 10th	Day	8% 5% 2 6% 4 3 4 4 7% 10% 47%	2520
	11th to 20th	Day	9% 4 2 5% 4 5% 5% 4 7% 9% 47%	2520
	21st to end	Day	7% 5% 2 5% 4 4 5% 5% 8% 10% 45%	2690
August	1st to 10th	Day	7% 5% 2 5% 5% 5% 5% 5% 7% 8% 43%	2328
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 7% 47%	2252
	21st to end	Day	10% 4 2 5% 4 4 4 3 5% 8% 51%	2376
September	1st to 10th	Day	14% 5% 2 6% 3 4 3 3 5% 7% 48%	2160
	11th to 20th	Day	11% 4 1 5% 4 4 5% 3 5% 7% 52%	2160
	21st to end	Day	11% 5% 2 6% 4 5% 4 4 6% 8% 45%	1913
October	1st to 10th	Day	15% 7% 2 6% 5% 3 4 2 4 6% 46%	1800
	11th to 20th	Day	19% 7% 2 6% 4 3 3 3 6% 6% 41%	1800
	21st to end	Day	18% 9% 2 6% 4 4 3 3 4 6% 40%	1943
November	1st to 10th	Day	10% 9% 3 6% 4 4 3 4 6% 6% 45%	1672
	11th to 20th	Day	14% 12% 3 8% 5% 4 4 3 5% 7% 35%	1616
	21st to end	Day	17% 9% 3 7% 5% 3 4 3 4 6% 39%	1520
December	1st to 10th	Day	14% 13% 4 10% 5% 4 3 3 5% 7% 32%	1520
	11th to 20th	Day	15% 10% 5% 9% 5% 5% 5% 4 5% 6% 32%	1918
	21st to end	Day	23% 19% 8% 12% 5% 3 3 3 3 4 17%	2783
January	1st to 10th	Night	12% 11% 7% 16% 5% 5% 4 3 4 5% 27%	4428
	11th to 20th	Night	11% 16% 7% 12% 5% 5% 4 4 7% 5% 23%	4367
	21st to end	Night	17% 16% 7% 12% 5% 4 3 3 4 6% 23%	4532
February	1st to 10th	Night	12% 13% 4 8% 6% 5% 4 3 5% 6% 34%	2470
	11th to 20th	Night	12% 10% 3 8% 5% 4 4 3 5% 6% 40%	2366
	21st to end	Night	14% 11% 4 9% 4 4 4 3 4 5% 39%	1884
March	1st to 10th	Night	18% 8% 2 6% 4 4 3 3 4 5% 44%	3640
	11th to 20th	Night	10% 6% 2 6% 5% 4 3 3 4 6% 51%	3480
	21st to end	Night	24% 12% 4 11% 5% 4 4 3 4 5% 23%	3670
April	1st to 10th	Night	16% 9% 3 7% 4 4 3 3 5% 6% 40%	1900
	11th to 20th	Night	17% 9% 2 6% 4 3 3 3 5% 5% 41%	1875
	21st to end	Night	18% 8% 2 5% 4 3 4 4 6% 6% 39%	1900
May	1st to 10th	Night	16% 6% 3 6% 5% 5% 4 3 6% 7% 40%	1615
	11th to 20th	Night	16% 8% 2 5% 4 5% 4 4 6% 6% 39%	1440
	21st to end	Night	11% 5% 2 8% 6% 5% 4 4 6% 7% 43%	1551
June	1st to 10th	Night	8% 5% 3 5% 5% 4 4 3 6% 10% 48%	1440
	11th to 20th	Night	9% 5% 2 6% 4 4 4 4 8% 10% 45%	1440
	21st to end	Night	10% 5% 2 5% 4 3 4 5% 6% 8% 49%	1440
July	1st to 10th	Night	7% 3 1 5% 4 3 4 4 7% 9% 53%	1440
	11th to 20th	Night	5% 4 1 3 3 3 4 3 7% 9% 59%	1440
	21st to end	Night	6% 3 2 6% 4 5% 5% 4 7% 8% 51%	1624
August	1st to 10th	Night	5% 3 2 5% 4 4 4 4 6% 10% 52%	1611
	11th to 20th	Night	7% 4 1 6% 4 3 5% 3 6% 8% 53%	1648
	21st to end	Night	9% 5% 1 4 3 3 4 3 5% 7% 56%	1980
September	1st to 10th	Night	10% 4 2 5% 3 4 4 3 5% 6% 54%	1800
	11th to 20th	Night	10% 5% 2 4 3 3 4 2 5% 6% 55%	1800
	21st to end	Night	7% 4 2 6% 4 4 4 3 4 7% 54%	2026
October	1st to 10th	Night	13% 5% 2 5% 4 3 3 3 4 5% 53%	2160
	11th to 20th	Night	16% 7% 2 5% 3 4 4 3 4 6% 46%	2160
	21st to end	Night	17% 7% 3 6% 5% 3 3 3 4 6% 42%	2412
November	1st to 10th	Night	10% 6% 2 5% 4 3 4 2 5% 6% 53%	2406
	11th to 20th	Night	13% 9% 3 8% 5% 3 4 4 5% 6% 41%	2560
	21st to end	Night	16% 9% 2 6% 5% 4 3 3 5% 5% 41%	2660
December	1st to 10th	Night	13% 11% 4 9% 6% 5% 4 4 5% 6% 35%	2660
	11th to 20th	Night	13% 11% 4 9% 5% 5% 4 3 5% 6% 34%	3279
	21st to end	Night	21% 16% 6% 11% 6% 5% 4 3 4 5% 19%	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	65% 4 11% 13% 6%	2528
	11th to 20th	Day	61% 3 12% 16% 8%	2599
	21st to end	Day	70% 4 10% 10% 5%	3135
February	1st to 10th	Day	54% 4 14% 20% 7% 1	1710
	11th to 20th	Day	49% 6% 12% 22% 10% 2	1709
	21st to end	Day	50% 5% 13% 20% 9% 2	1570
March	1st to 10th	Day	46% 4 11% 24% 14% 2	3243
	11th to 20th	Day	38% 4 12% 29% 15% 1	3480
	21st to end	Day	64% 5% 14% 13% 3 1	3959
April	1st to 10th	Day	53% 4 11% 22% 9%	2280
	11th to 20th	Day	49% 6% 10% 22% 12% 1	2254
	21st to end	Day	49% 5% 10% 21% 12% 2	2280
May	1st to 10th	Day	51% 6% 12% 20% 9% 1	2562
	11th to 20th	Day	49% 5% 12% 22% 11% 1	2514
	21st to end	Day	47% 8% 11% 18% 13% 2	2725
June	1st to 10th	Day	35% 8% 16% 24% 16% 1	2520
	11th to 20th	Day	36% 7% 11% 21% 22% 3	2520
	21st to end	Day	41% 7% 13% 23% 15% 1	2520
July	1st to 10th	Day	32% 8% 14% 29% 15% 3	2451
	11th to 20th	Day	32% 9% 14% 26% 15% 3	2445
	21st to end	Day	30% 8% 19% 26% 16% 2	2540
August	1st to 10th	Day	35% 9% 15% 28% 12% 1	2314
	11th to 20th	Day	35% 7% 15% 25% 17% 1	2252
	21st to end	Day	32% 5% 11% 28% 20% 3	2376
September	1st to 10th	Day	35% 5% 10% 25% 21% 3	2160
	11th to 20th	Day	31% 5% 12% 31% 18% 3	2160
	21st to end	Day	36% 5% 11% 30% 17% 1	1913
October	1st to 10th	Day	42% 3 10% 26% 19% 1	1800
	11th to 20th	Day	44% 4 11% 25% 15% 2	1800
	21st to end	Day	46% 3 13% 23% 14% 2	1943
November	1st to 10th	Day	40% 4 13% 26% 14% 3	1672
	11th to 20th	Day	49% 3 13% 22% 12% 1	1616
	21st to end	Day	47% 4 16% 24% 9% 1	1520
December	1st to 10th	Day	53% 4 14% 20% 8% 1	1520
	11th to 20th	Day	52% 4 15% 18% 9% 2	1915
	21st to end	Day	72% 4 9% 10% 4	2783
January	1st to 10th	Night	59% 4 13% 15% 9%	4428
	11th to 20th	Night	60% 4 12% 14% 10% 1	4367
	21st to end	Night	64% 4 10% 15% 6% 1	4532
February	1st to 10th	Night	51% 5% 10% 22% 11% 1	2470
	11th to 20th	Night	44% 5% 11% 25% 13% 2	2367
	21st to end	Night	48% 5% 10% 21% 14% 2	1884
March	1st to 10th	Night	44% 4 10% 25% 16% 2	3640
	11th to 20th	Night	34% 4 11% 32% 16% 3	3480
	21st to end	Night	64% 5% 13% 12% 5% 1	3670
April	1st to 10th	Night	45% 4 9% 25% 14% 2	1900
	11th to 20th	Night	46% 4 8% 22% 16% 4	1875
	21st to end	Night	44% 5% 12% 22% 14% 3	1900
May	1st to 10th	Night	43% 6% 12% 23% 14% 1	1615
	11th to 20th	Night	43% 6% 14% 23% 13% 2	1441
	21st to end	Night	40% 7% 12% 22% 16% 3	1552
June	1st to 10th	Night	32% 6% 15% 26% 18% 3	1440
	11th to 20th	Night	32% 6% 14% 24% 20% 5%	1440
	21st to end	Night	32% 6% 17% 25% 16% 4	1440
July	1st to 10th	Night	25% 7% 16% 32% 15% 5%	1400
	11th to 20th	Night	22% 6% 16% 35% 19% 3	1392
	21st to end	Night	27% 7% 15% 30% 18% 3	1534
August	1st to 10th	Night	26% 7% 17% 34% 12% 3	1601
	11th to 20th	Night	29% 7% 12% 30% 21% 2	1648
	21st to end	Night	28% 5% 10% 28% 23% 6%	1980
September	1st to 10th	Night	31% 5% 10% 26% 25% 3	1800
	11th to 20th	Night	30% 5% 10% 34% 18% 4	1800
	21st to end	Night	31% 4 9% 30% 23% 2	2026
October	1st to 10th	Night	34% 4 10% 25% 24% 3	2160
	11th to 20th	Night	39% 5% 12% 23% 19% 3	2160
	21st to end	Night	45% 4 11% 22% 16% 2	2412
November	1st to 10th	Night	33% 5% 13% 26% 18% 4	2406
	11th to 20th	Night	44% 4 13% 24% 13% 2	2560
	21st to end	Night	46% 3 12% 26% 11% 1	2660
December	1st to 10th	Night	51% 4 13% 22% 9% 1	2660
	11th to 20th	Night	51% 4 13% 24% 7% 1	3281
	21st to end	Night	68% 5% 8% 13% 5%	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	22% 10% 34% 24% 8% 2	270
	11th to 20th	Day	22% 15% 39% 19% 5% 1	270
	21st to end	Day	21% 13% 37% 21% 6% 1	297
February	1st to 10th	Day	20% 15% 40% 20% 4	270
	11th to 20th	Day	20% 18% 34% 23% 5% 1	270
	21st to end	Day	22% 14% 45% 15% 4	225
March	1st to 10th	Day	20% 21% 39% 15% 6%	270
	11th to 20th	Day	23% 17% 30% 22% 6% 2	270
	21st to end	Day	31% 15% 32% 15% 6% 1	378
April	1st to 10th	Day	23% 14% 39% 17% 6%	460
	11th to 20th	Day	23% 17% 29% 21% 9%	452
	21st to end	Day	24% 15% 32% 19% 10% 1	460
May	1st to 10th	Day	19% 12% 36% 24% 7% 2	645
	11th to 20th	Day	21% 13% 27% 25% 13% 2	637
	21st to end	Day	15% 10% 27% 28% 15% 5%	679
June	1st to 10th	Day	8% 4 27% 33% 23% 5%	630
	11th to 20th	Day	11% 6% 28% 35% 18% 2	630
	21st to end	Day	11% 9% 29% 33% 14% 4	630
July	1st to 10th	Day	8% 3 19% 33% 24% 14%	621
	11th to 20th	Day	9% 4 23% 35% 23% 6%	618
	21st to end	Day	7% 2 23% 38% 24% 5%	684
August	1st to 10th	Day	7% 3 23% 36% 24% 8%	626
	11th to 20th	Day	11% 3 19% 33% 24% 8%	566
	21st to end	Day	9% 4 19% 36% 24% 8%	495
September	1st to 10th	Day	15% 8% 17% 31% 21% 7%	450
	11th to 20th	Day	9% 5% 20% 38% 21% 8%	450
	21st to end	Day	14% 9% 29% 21% 23% 3	356
October	1st to 10th	Day	21% 7% 27% 30% 11% 4	270
	11th to 20th	Day	21% 22% 34% 14% 9%	270
	21st to end	Day	27% 12% 34% 19% 7% 2	297
November	1st to 10th	Day	14% 13% 38% 23% 10% 2	270
	11th to 20th	Day	20% 18% 32% 20% 9% 2	270
	21st to end	Day	26% 11% 37% 20% 6%	270
December	1st to 10th	Day	13% 15% 41% 21% 7% 3	270
	11th to 20th	Day	16% 14% 37% 24% 9% 1	270
	21st to end	Day	27% 17% 38% 15% 2	297
January	1st to 10th	Night	15% 13% 38% 27% 7% 1	950
	11th to 20th	Night	19% 13% 34% 27% 7%	950
	21st to end	Night	20% 11% 36% 27% 6%	1045
February	1st to 10th	Night	20% 12% 38% 25% 5%	950
	11th to 20th	Night	18% 12% 37% 27% 5%	892
	21st to end	Night	20% 13% 40% 23% 4 1	628
March	1st to 10th	Night	20% 13% 39% 22% 7% 1	706
	11th to 20th	Night	17% 11% 33% 31% 8% 1	570
	21st to end	Night	22% 12% 36% 24% 5% 1	627
April	1st to 10th	Night	19% 14% 40% 24% 3	570
	11th to 20th	Night	22% 15% 29% 28% 7%	563
	21st to end	Night	23% 8% 32% 28% 8% 1	570
May	1st to 10th	Night	18% 8% 39% 27% 7% 1	570
	11th to 20th	Night	18% 9% 30% 32% 11%	540
	21st to end	Night	14% 4 30% 33% 18% 1	584
June	1st to 10th	Night	9% 4 26% 43% 16% 2	540
	11th to 20th	Night	10% 3 29% 44% 14%	540
	21st to end	Night	11% 4 27% 42% 15% 1	540
July	1st to 10th	Night	8% 1 13% 43% 32% 4	525
	11th to 20th	Night	6% 2 21% 43% 26% 3	522
	21st to end	Night	6% 3 18% 45% 27% 1	591
August	1st to 10th	Night	5% 2 15% 47% 28% 3	537
	11th to 20th	Night	7% 3 15% 41% 29% 5%	534
	21st to end	Night	11% 2 14% 45% 26% 3	594
September	1st to 10th	Night	12% 4 17% 40% 22% 4	540
	11th to 20th	Night	11% 3 21% 36% 24% 4	540
	21st to end	Night	10% 7% 28% 35% 19% 1	674
October	1st to 10th	Night	16% 6% 28% 31% 18% 2	720
	11th to 20th	Night	19% 11% 32% 30% 9%	720
	21st to end	Night	22% 12% 32% 27% 8%	792
November	1st to 10th	Night	13% 10% 37% 29% 10% 1	740
	11th to 20th	Night	19% 14% 39% 22% 7%	850
	21st to end	Night	21% 11% 36% 26% 6% 1	950
December	1st to 10th	Night	17% 13% 37% 26% 6% 1	950
	11th to 20th	Night	22% 9% 35% 28% 6%	950
	21st to end	Night	26% 13% 33% 24% 4	1045

Page generated at 2024-05-10 11:39:05. Version ac07

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