Clarence Fahnestock Memorial State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clarence Fahnestock Memorial State Park clear sky chart from 2005-11-06 to 2024-01-15.

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% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	74788
	Night	17% 7% 3 5% 5% 3 4 4 5% 7% 40%	74992
Transparency	Day	44% 5% 12% 23% 15% 2	74493
	Night	43% 5% 12% 23% 15% 2	74821
Seeing	Day	23% 16% 29% 21% 9% 3	13828
	Night	22% 13% 30% 26% 8% 1	23056

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	13% 7% 3 5% 5% 4 5% 4 6% 6% 41%	1517
	11th to 20th	Day	15% 9% 4 7% 6% 4 5% 6% 5% 6% 34%	1478
	21st to end	Day	13% 8% 3 6% 5% 4 4 5% 6% 6% 40%	1683
February	1st to 10th	Day	17% 10% 3 6% 6% 3 5% 5% 5% 8% 33%	1625
	11th to 20th	Day	15% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	1748
	21st to end	Day	20% 9% 3 5% 5% 3 5% 4 4 7% 36%	1480
March	1st to 10th	Day	14% 7% 3 6% 6% 3 5% 4 5% 8% 39%	1797
	11th to 20th	Day	16% 8% 3 6% 6% 3 5% 5% 6% 7% 36%	1877
	21st to end	Day	19% 9% 3 6% 5% 2 3 4 4 5% 39%	2366
April	1st to 10th	Day	18% 8% 3 7% 4 3 5% 5% 4 7% 37%	2160
	11th to 20th	Day	17% 6% 3 6% 5% 4 4 4 5% 7% 41%	2134
	21st to end	Day	21% 6% 2 4 5% 3 5% 5% 5% 6% 38%	2209
May	1st to 10th	Day	23% 7% 3 6% 5% 3 4 4 5% 6% 35%	2340
	11th to 20th	Day	18% 7% 3 5% 5% 3 4 5% 6% 6% 38%	2468
	21st to end	Day	14% 6% 2 5% 5% 3 5% 5% 5% 8% 41%	2725
June	1st to 10th	Day	18% 5% 2 5% 4 4 5% 5% 7% 9% 37%	2520
	11th to 20th	Day	15% 7% 3 6% 6% 3 5% 6% 6% 8% 35%	2520
	21st to end	Day	13% 5% 3 6% 6% 3 5% 6% 6% 8% 39%	2520
July	1st to 10th	Day	12% 7% 2 5% 6% 3 6% 5% 6% 9% 39%	2520
	11th to 20th	Day	11% 5% 3 5% 5% 4 6% 6% 7% 10% 39%	2520
	21st to end	Day	12% 5% 3 6% 6% 4 6% 7% 6% 9% 37%	2744
August	1st to 10th	Day	11% 7% 2 5% 5% 4 7% 6% 8% 8% 38%	2417
	11th to 20th	Day	12% 6% 3 5% 6% 3 6% 6% 6% 10% 38%	2126
	21st to end	Day	13% 5% 2 5% 6% 3 5% 5% 5% 9% 42%	2376
September	1st to 10th	Day	14% 6% 2 5% 5% 4 5% 6% 6% 6% 42%	2160
	11th to 20th	Day	13% 5% 3 4 5% 3 3 4 5% 7% 49%	2075
	21st to end	Day	16% 5% 2 6% 5% 3 5% 4 5% 7% 42%	1980
October	1st to 10th	Day	22% 7% 3 5% 4 2 4 4 3 5% 41%	1890
	11th to 20th	Day	15% 5% 2 4 4 3 5% 4 6% 8% 44%	1800
	21st to end	Day	22% 6% 3 5% 5% 3 4 4 6% 5% 37%	1814
November	1st to 10th	Day	15% 6% 2 4 4 3 3 3 5% 6% 50%	1671
	11th to 20th	Day	18% 6% 2 4 4 3 3 4 5% 7% 44%	1710
	21st to end	Day	17% 6% 3 4 5% 3 4 4 5% 7% 42%	1620
December	1st to 10th	Day	19% 7% 4 7% 6% 3 5% 3 4 7% 35%	1520
	11th to 20th	Day	21% 7% 2 4 3 2 4 4 5% 6% 42%	1906
	21st to end	Day	19% 10% 5% 7% 7% 3 5% 4 5% 7% 29%	2772
January	1st to 10th	Night	15% 7% 3 5% 4 2 4 5% 5% 7% 43%	2649
	11th to 20th	Night	18% 7% 3 6% 6% 3 5% 5% 5% 6% 36%	2588
	21st to end	Night	12% 8% 4 5% 4 3 4 4 6% 8% 42%	2668
February	1st to 10th	Night	17% 10% 3 6% 5% 3 4 4 4 6% 38%	2333
	11th to 20th	Night	16% 8% 3 6% 5% 3 5% 5% 6% 6% 37%	2098
	21st to end	Night	18% 6% 3 7% 5% 3 4 4 6% 5% 39%	1776
March	1st to 10th	Night	16% 7% 2 4 4 3 4 5% 6% 7% 41%	2150
	11th to 20th	Night	17% 7% 3 6% 5% 3 4 4 5% 6% 39%	2079
	21st to end	Night	18% 7% 4 4 4 3 5% 4 5% 6% 40%	1989
April	1st to 10th	Night	17% 9% 3 6% 5% 4 6% 5% 4 7% 35%	1800
	11th to 20th	Night	19% 7% 3 5% 5% 2 5% 5% 4 7% 38%	1775
	21st to end	Night	21% 7% 3 5% 5% 2 4 4 5% 5% 39%	1750
May	1st to 10th	Night	22% 7% 3 7% 7% 2 4 4 6% 6% 31%	1620
	11th to 20th	Night	18% 8% 3 5% 6% 3 5% 4 5% 7% 38%	1440
	21st to end	Night	15% 5% 2 4 5% 3 5% 5% 6% 8% 41%	1550
June	1st to 10th	Night	17% 5% 3 5% 5% 2 5% 5% 5% 9% 40%	1440
	11th to 20th	Night	14% 5% 3 6% 5% 3 5% 5% 6% 9% 38%	1440
	21st to end	Night	11% 5% 2 5% 4 3 5% 5% 7% 10% 43%	1440
July	1st to 10th	Night	12% 7% 3 5% 5% 4 5% 5% 8% 7% 41%	1440
	11th to 20th	Night	12% 5% 2 7% 5% 3 5% 5% 6% 11% 39%	1440
	21st to end	Night	10% 6% 3 5% 4 3 5% 7% 7% 9% 42%	1574
August	1st to 10th	Night	8% 5% 2 7% 5% 3 6% 5% 7% 8% 43%	1500
	11th to 20th	Night	12% 7% 2 7% 6% 4 5% 6% 6% 8% 36%	1774
	21st to end	Night	16% 5% 2 4 4 3 4 4 6% 7% 44%	1980
September	1st to 10th	Night	16% 6% 2 5% 5% 2 5% 4 4 6% 45%	1800
	11th to 20th	Night	14% 5% 1 4 3 2 4 3 4 7% 53%	1885
	21st to end	Night	16% 6% 2 4 4 2 4 4 4 7% 46%	1980
October	1st to 10th	Night	20% 8% 3 4 4 3 3 4 4 4 42%	2066
	11th to 20th	Night	15% 6% 3 5% 5% 3 3 4 5% 8% 45%	2160
	21st to end	Night	22% 7% 2 5% 5% 3 4 4 4 6% 38%	2542
November	1st to 10th	Night	13% 7% 3 4 5% 3 4 4 5% 7% 46%	2407
	11th to 20th	Night	18% 7% 2 4 4 2 3 4 4 6% 44%	2470
	21st to end	Night	15% 6% 3 5% 5% 4 3 4 6% 7% 43%	2557
December	1st to 10th	Night	20% 8% 3 5% 4 3 5% 4 5% 7% 37%	2660
	11th to 20th	Night	20% 8% 3 5% 4 3 4 5% 5% 6% 37%	3288
	21st to end	Night	21% 10% 3 6% 5% 3 4 4 4 6% 33%	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	41% 5% 11% 28% 12% 4	1518
	11th to 20th	Day	49% 5% 13% 19% 13% 2	1478
	21st to end	Day	42% 4 12% 25% 15% 2	1683
February	1st to 10th	Day	49% 4 11% 20% 14% 1	1625
	11th to 20th	Day	45% 4 10% 23% 16% 2	1757
	21st to end	Day	50% 3 10% 22% 14% 2	1480
March	1st to 10th	Day	44% 3 14% 22% 14% 3	1800
	11th to 20th	Day	45% 5% 11% 24% 14% 1	1877
	21st to end	Day	49% 3 7% 19% 17% 5%	2366
April	1st to 10th	Day	47% 4 10% 22% 14% 4	2160
	11th to 20th	Day	43% 4 11% 22% 18% 3	2134
	21st to end	Day	46% 5% 9% 22% 15% 3	2209
May	1st to 10th	Day	50% 4 9% 20% 14% 2	2340
	11th to 20th	Day	45% 6% 10% 22% 16% 3	2472
	21st to end	Day	41% 7% 16% 21% 13% 2	2725
June	1st to 10th	Day	43% 6% 14% 22% 13% 1	2520
	11th to 20th	Day	45% 6% 12% 24% 11% 1	2520
	21st to end	Day	41% 8% 12% 25% 13% 1	2520
July	1st to 10th	Day	41% 7% 13% 21% 16% 2	2450
	11th to 20th	Day	38% 7% 16% 24% 14% 1	2445
	21st to end	Day	41% 7% 12% 20% 16% 3	2591
August	1st to 10th	Day	41% 8% 12% 25% 13% 1	2403
	11th to 20th	Day	41% 6% 17% 23% 12%	2126
	21st to end	Day	39% 5% 11% 25% 17% 2	2376
September	1st to 10th	Day	41% 7% 10% 23% 17% 2	2160
	11th to 20th	Day	36% 5% 8% 25% 24% 2	2075
	21st to end	Day	42% 5% 9% 24% 17% 3	1980
October	1st to 10th	Day	47% 5% 8% 23% 15% 3	1890
	11th to 20th	Day	39% 4 13% 28% 15% 1	1800
	21st to end	Day	48% 4 10% 22% 14% 2	1814
November	1st to 10th	Day	36% 3 13% 27% 18% 3	1671
	11th to 20th	Day	41% 4 11% 23% 18% 3	1710
	21st to end	Day	41% 4 14% 29% 11% 2	1620
December	1st to 10th	Day	50% 4 14% 18% 13% 1	1520
	11th to 20th	Day	44% 2 16% 22% 13% 2	1906
	21st to end	Day	54% 5% 11% 22% 8% 1	2772
January	1st to 10th	Night	40% 3 13% 26% 15% 3	2649
	11th to 20th	Night	47% 5% 13% 24% 9% 2	2588
	21st to end	Night	40% 3 11% 24% 18% 3	2668
February	1st to 10th	Night	47% 4 13% 22% 12% 2	2333
	11th to 20th	Night	45% 4 11% 19% 17% 4	2100
	21st to end	Night	46% 3 8% 24% 16% 3	1776
March	1st to 10th	Night	40% 3 14% 24% 16% 3	2160
	11th to 20th	Night	45% 4 10% 22% 16% 3	2080
	21st to end	Night	44% 4 9% 19% 19% 5%	1989
April	1st to 10th	Night	48% 3 10% 22% 14% 3	1800
	11th to 20th	Night	46% 5% 9% 20% 19% 1	1775
	21st to end	Night	46% 4 8% 23% 15% 4	1750
May	1st to 10th	Night	51% 5% 10% 19% 14% 2	1620
	11th to 20th	Night	45% 5% 9% 20% 18% 2	1441
	21st to end	Night	40% 7% 17% 22% 12% 2	1551
June	1st to 10th	Night	41% 6% 11% 23% 17% 2	1440
	11th to 20th	Night	40% 8% 17% 25% 10% 1	1440
	21st to end	Night	35% 6% 17% 26% 15% 1	1440
July	1st to 10th	Night	40% 7% 14% 23% 14% 3	1400
	11th to 20th	Night	40% 7% 13% 28% 11% 1	1392
	21st to end	Night	35% 7% 17% 21% 16% 2	1486
August	1st to 10th	Night	36% 7% 16% 25% 15% 1	1490
	11th to 20th	Night	45% 7% 14% 22% 11% 1	1774
	21st to end	Night	38% 6% 12% 23% 20% 1	1980
September	1st to 10th	Night	40% 5% 10% 27% 16% 1	1800
	11th to 20th	Night	33% 4 11% 25% 25% 2	1885
	21st to end	Night	39% 6% 9% 22% 23% 1	1980
October	1st to 10th	Night	45% 5% 11% 22% 15% 2	2066
	11th to 20th	Night	39% 4 13% 30% 14% 1	2160
	21st to end	Night	47% 4 11% 23% 14% 1	2542
November	1st to 10th	Night	37% 4 12% 23% 21% 3	2407
	11th to 20th	Night	41% 3 9% 24% 18% 4	2470
	21st to end	Night	39% 3 14% 31% 12% 1	2557
December	1st to 10th	Night	47% 4 11% 23% 13% 1	2660
	11th to 20th	Night	46% 4 13% 20% 15% 3	3288
	21st to end	Night	51% 3 12% 22% 12%	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	26% 27% 29% 13% 4	180
	11th to 20th	Day	33% 25% 26% 14% 2	170
	21st to end	Day	21% 29% 34% 12% 3 2	220
February	1st to 10th	Day	38% 22% 30% 8% 1	245
	11th to 20th	Day	29% 25% 32% 13%	416
	21st to end	Day	32% 22% 31% 13% 2	346
March	1st to 10th	Day	29% 21% 30% 17% 3	420
	11th to 20th	Day	27% 26% 30% 13% 2 1	420
	21st to end	Day	30% 21% 30% 12% 4 2	462
April	1st to 10th	Day	30% 21% 28% 13% 7% 1	420
	11th to 20th	Day	24% 24% 29% 15% 7% 1	412
	21st to end	Day	32% 16% 32% 14% 5% 1	420
May	1st to 10th	Day	34% 18% 27% 13% 6% 1	423
	11th to 20th	Day	24% 13% 38% 19% 5% 1	447
	21st to end	Day	20% 12% 26% 27% 14% 2	485
June	1st to 10th	Day	22% 11% 30% 23% 12% 2	450
	11th to 20th	Day	17% 17% 29% 24% 12% 1	450
	21st to end	Day	15% 14% 26% 29% 14% 3	450
July	1st to 10th	Day	15% 8% 28% 28% 16% 5%	445
	11th to 20th	Day	14% 7% 28% 31% 17% 3	444
	21st to end	Day	14% 7% 30% 34% 13% 2	488
August	1st to 10th	Day	14% 7% 24% 33% 17% 5%	446
	11th to 20th	Day	15% 7% 24% 33% 15% 6%	439
	21st to end	Day	14% 9% 28% 27% 16% 7%	495
September	1st to 10th	Day	17% 13% 24% 23% 16% 7%	450
	11th to 20th	Day	16% 9% 31% 23% 11% 10%	450
	21st to end	Day	21% 11% 30% 22% 11% 6%	450
October	1st to 10th	Day	29% 8% 26% 21% 14% 3	450
	11th to 20th	Day	20% 16% 30% 22% 10% 1	450
	21st to end	Day	29% 13% 28% 20% 9%	412
November	1st to 10th	Day	19% 14% 29% 24% 11% 3	365
	11th to 20th	Day	28% 22% 26% 17% 5% 1	370
	21st to end	Day	23% 20% 31% 21% 4 1	280
December	1st to 10th	Day	25% 22% 34% 13% 5%	180
	11th to 20th	Day	36% 21% 31% 11% 2	180
	21st to end	Day	25% 26% 28% 15% 5%	198
January	1st to 10th	Night	21% 17% 39% 20% 3	760
	11th to 20th	Night	25% 19% 30% 23% 2	740
	21st to end	Night	19% 22% 34% 22% 3	792
February	1st to 10th	Night	24% 18% 36% 20% 2	720
	11th to 20th	Night	23% 21% 40% 15% 1	703
	21st to end	Night	25% 20% 34% 19% 2	592
March	1st to 10th	Night	24% 21% 33% 19% 3	720
	11th to 20th	Night	24% 22% 32% 19% 3	720
	21st to end	Night	23% 21% 32% 19% 4 1	792
April	1st to 10th	Night	23% 20% 33% 19% 4	720
	11th to 20th	Night	25% 15% 33% 23% 4	711
	21st to end	Night	25% 16% 34% 21% 4	670
May	1st to 10th	Night	25% 15% 32% 23% 5%	540
	11th to 20th	Night	23% 12% 35% 23% 6%	379
	21st to end	Night	20% 7% 23% 38% 11% 1	389
June	1st to 10th	Night	20% 6% 29% 34% 11%	360
	11th to 20th	Night	16% 5% 31% 33% 15% 1	360
	21st to end	Night	13% 3 27% 45% 13%	360
July	1st to 10th	Night	17% 5% 19% 39% 20% 1	350
	11th to 20th	Night	14% 2 24% 42% 17% 2	348
	21st to end	Night	13% 3 22% 42% 19% 1	394
August	1st to 10th	Night	11% 3 22% 44% 19% 1	426
	11th to 20th	Night	16% 3 19% 37% 23% 2	710
	21st to end	Night	18% 5% 18% 36% 21% 2	792
September	1st to 10th	Night	18% 5% 25% 35% 14% 2	720
	11th to 20th	Night	17% 6% 25% 32% 17% 4	720
	21st to end	Night	20% 6% 25% 31% 16% 2	720
October	1st to 10th	Night	23% 9% 26% 26% 14% 2	720
	11th to 20th	Night	20% 12% 29% 29% 9%	720
	21st to end	Night	28% 11% 32% 21% 7%	792
November	1st to 10th	Night	16% 12% 33% 27% 10% 1	740
	11th to 20th	Night	24% 16% 30% 22% 7% 1	760
	21st to end	Night	19% 18% 31% 24% 7%	760
December	1st to 10th	Night	28% 16% 32% 18% 5%	760
	11th to 20th	Night	25% 16% 32% 23% 3	760
	21st to end	Night	25% 16% 36% 19% 2	836

Page generated at 2024-01-12 16:17:48. Version ac07

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