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 2026-03-18.

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% 8% 3 7% 4 4 4 4 5% 7% 38%	131100
	Night	16% 8% 3 7% 4 4 4 3 5% 6% 40%	130407
Transparency	Day	44% 5% 11% 23% 15% 2	134614
	Night	43% 4 11% 23% 16% 3	134980
Seeing	Day	24% 16% 29% 20% 9% 2	16616
	Night	22% 14% 30% 25% 8% 1	25841

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	12% 9% 3 7% 5% 5% 5% 4 5% 6% 41%	4661
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 3 4 5% 42%	4650
	21st to end	Day	15% 9% 3 7% 4 4 4 4 5% 6% 40%	5459
February	1st to 10th	Day	15% 9% 3 8% 5% 5% 4 4 5% 7% 36%	1897
	11th to 20th	Day	15% 8% 3 7% 4 5% 5% 3 5% 6% 38%	2048
	21st to end	Day	19% 9% 3 5% 4 4 4 3 4 6% 38%	1730
March	1st to 10th	Day	21% 8% 3 7% 5% 4 3 3 4 5% 38%	4576
	11th to 20th	Day	12% 7% 3 7% 5% 4 5% 4 5% 7% 42%	4808
	21st to end	Day	18% 8% 2 7% 5% 4 4 4 5% 6% 37%	5960
April	1st to 10th	Day	19% 9% 3 8% 4 4 4 3 5% 6% 35%	2400
	11th to 20th	Day	17% 7% 2 7% 4 4 4 3 5% 7% 39%	2374
	21st to end	Day	20% 7% 2 5% 4 4 5% 4 5% 6% 39%	2455
May	1st to 10th	Day	28% 8% 3 6% 4 4 4 3 5% 8% 27%	5886
	11th to 20th	Day	19% 9% 3 7% 5% 4 5% 3 5% 6% 35%	6308
	21st to end	Day	20% 7% 2 6% 4 4 5% 4 6% 8% 35%	6949
June	1st to 10th	Day	17% 5% 2 5% 5% 5% 5% 4 7% 8% 36%	2800
	11th to 20th	Day	15% 8% 3 7% 5% 4 5% 5% 7% 8% 35%	2800
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 5% 6% 9% 38%	2800
July	1st to 10th	Day	10% 8% 3 8% 5% 5% 6% 4 7% 9% 34%	6360
	11th to 20th	Day	9% 7% 3 7% 5% 6% 7% 5% 8% 10% 33%	6360
	21st to end	Day	13% 7% 2 7% 5% 4 5% 4 5% 8% 40%	6926
August	1st to 10th	Day	20% 7% 2 6% 4 5% 5% 4 6% 7% 33%	4386
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 42%	3850
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 9% 46%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 5% 5% 6% 44%	2400
	11th to 20th	Day	12% 5% 2 5% 4 4 3 3 5% 7% 49%	2305
	21st to end	Day	16% 6% 2 7% 4 4 5% 4 5% 7% 39%	2200
October	1st to 10th	Day	20% 7% 2 5% 4 3 4 3 4 5% 43%	2100
	11th to 20th	Day	15% 6% 2 6% 3 4 4 3 5% 8% 44%	2000
	21st to end	Day	20% 6% 3 6% 4 4 4 3 6% 5% 39%	2015
November	1st to 10th	Day	14% 6% 2 5% 4 4 3 2 5% 6% 50%	1851
	11th to 20th	Day	16% 6% 2 5% 4 4 3 3 5% 7% 44%	1890
	21st to end	Day	17% 8% 3 5% 4 4 4 4 5% 6% 40%	1790
December	1st to 10th	Day	14% 9% 3 7% 4 4 5% 3 5% 6% 41%	2680
	11th to 20th	Day	20% 9% 2 5% 3 3 3 3 5% 6% 43%	3066
	21st to end	Day	17% 10% 4 8% 5% 3 4 3 5% 7% 34%	4048
January	1st to 10th	Night	13% 8% 3 8% 5% 4 5% 3 5% 6% 40%	8234
	11th to 20th	Night	13% 9% 3 9% 5% 4 4 3 5% 6% 38%	8235
	21st to end	Night	14% 8% 3 7% 4 4 3 3 5% 6% 42%	8717
February	1st to 10th	Night	15% 10% 3 7% 4 4 4 3 5% 5% 40%	2721
	11th to 20th	Night	16% 8% 3 7% 5% 4 5% 4 6% 6% 37%	2458
	21st to end	Night	17% 7% 3 7% 5% 4 4 3 6% 5% 39%	2076
March	1st to 10th	Night	19% 9% 3 6% 3 3 3 3 4 6% 40%	5484
	11th to 20th	Night	13% 8% 3 7% 5% 4 4 3 5% 7% 41%	5303
	21st to end	Night	18% 9% 3 7% 3 4 4 2 4 5% 38%	4971
April	1st to 10th	Night	18% 9% 3 7% 5% 6% 4 4 5% 6% 34%	2000
	11th to 20th	Night	19% 8% 3 7% 4 4 4 4 4 6% 37%	1975
	21st to end	Night	19% 8% 2 6% 4 4 4 3 5% 5% 40%	1944
May	1st to 10th	Night	30% 9% 2 7% 5% 3 4 3 5% 7% 25%	4054
	11th to 20th	Night	19% 9% 3 7% 5% 5% 4 3 5% 6% 33%	3628
	21st to end	Night	20% 7% 2 6% 4 4 4 3 6% 8% 36%	3926
June	1st to 10th	Night	16% 6% 3 6% 5% 3 4 4 5% 8% 40%	1600
	11th to 20th	Night	14% 6% 3 6% 5% 4 5% 4 7% 9% 39%	1600
	21st to end	Night	11% 6% 2 6% 4 4 4 5% 7% 10% 41%	1600
July	1st to 10th	Night	11% 7% 3 7% 4 5% 4 5% 7% 8% 38%	3600
	11th to 20th	Night	12% 8% 3 9% 6% 5% 5% 5% 6% 9% 33%	3600
	21st to end	Night	11% 8% 3 5% 4 4 4 4 5% 6% 46%	3926
August	1st to 10th	Night	20% 7% 2 8% 4 5% 5% 3 6% 7% 32%	2714
	11th to 20th	Night	14% 8% 2 7% 4 4 4 4 5% 7% 40%	3197
	21st to end	Night	12% 5% 2 5% 3 3 3 3 5% 7% 52%	3586
September	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 4 6% 46%	2000
	11th to 20th	Night	13% 5% 1 4 3 3 3 3 5% 7% 53%	2095
	21st to end	Night	17% 7% 3 5% 3 4 3 3 4 7% 44%	2200
October	1st to 10th	Night	18% 7% 3 5% 3 3 4 3 4 5% 44%	2296
	11th to 20th	Night	15% 6% 2 6% 4 4 3 3 5% 7% 47%	2400
	21st to end	Night	21% 6% 2 6% 4 4 4 3 5% 6% 39%	2825
November	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 5% 7% 47%	2667
	11th to 20th	Night	17% 8% 2 5% 4 3 3 3 4 6% 44%	2730
	21st to end	Night	15% 7% 2 5% 5% 4 3 4 6% 7% 43%	2827
December	1st to 10th	Night	15% 9% 2 6% 4 4 4 3 5% 6% 43%	4720
	11th to 20th	Night	23% 10% 2 5% 3 3 3 3 4 5% 39%	5348
	21st to end	Night	18% 11% 3 7% 4 3 4 3 4 6% 37%	7150

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% 10% 28% 15% 2	4662
	11th to 20th	Day	44% 3 8% 22% 16% 6%	4680
	21st to end	Day	44% 3 10% 26% 16% 1	5459
February	1st to 10th	Day	47% 4 11% 21% 15% 2	1897
	11th to 20th	Day	46% 4 9% 24% 16% 2	2057
	21st to end	Day	48% 3 11% 23% 14% 2	1730
March	1st to 10th	Day	47% 3 11% 18% 12% 8%	4579
	11th to 20th	Day	40% 5% 13% 29% 9% 4	4808
	21st to end	Day	47% 4 8% 14% 22% 6%	5960
April	1st to 10th	Day	48% 4 9% 21% 14% 4	2400
	11th to 20th	Day	44% 4 11% 21% 17% 2	2374
	21st to end	Day	45% 5% 9% 22% 16% 3	2455
May	1st to 10th	Day	56% 5% 13% 15% 10% 1	5897
	11th to 20th	Day	50% 5% 10% 21% 12% 1	6312
	21st to end	Day	46% 6% 11% 23% 13% 1	6949
June	1st to 10th	Day	43% 6% 13% 23% 14% 1	2800
	11th to 20th	Day	45% 6% 13% 24% 11% 1	2800
	21st to end	Day	41% 7% 12% 24% 13% 1	2800
July	1st to 10th	Day	45% 7% 11% 21% 14% 1	6290
	11th to 20th	Day	44% 6% 17% 22% 11% 1	6285
	21st to end	Day	42% 5% 10% 23% 19% 1	6728
August	1st to 10th	Day	50% 6% 13% 22% 9% 1	4372
	11th to 20th	Day	39% 5% 17% 29% 10%	3886
	21st to end	Day	35% 5% 11% 32% 16% 1	4312
September	1st to 10th	Day	40% 6% 10% 24% 18% 2	2400
	11th to 20th	Day	35% 5% 8% 26% 24% 2	2305
	21st to end	Day	44% 6% 9% 22% 16% 3	2200
October	1st to 10th	Day	40% 4 8% 20% 24% 4	3425
	11th to 20th	Day	30% 4 8% 28% 25% 5%	3240
	21st to end	Day	31% 3 15% 26% 21% 4	3227
November	1st to 10th	Day	36% 3 13% 26% 19% 2	1851
	11th to 20th	Day	40% 4 10% 24% 19% 3	1890
	21st to end	Day	43% 4 13% 28% 10% 2	1790
December	1st to 10th	Day	44% 3 15% 27% 10% 1	2680
	11th to 20th	Day	44% 2 14% 22% 15% 2	3066
	21st to end	Day	50% 4 8% 22% 14% 3	4048
January	1st to 10th	Night	43% 3 12% 25% 16% 2	8234
	11th to 20th	Night	45% 4 11% 20% 15% 6%	8280
	21st to end	Night	43% 2 9% 22% 20% 4	8717
February	1st to 10th	Night	46% 4 13% 23% 13% 2	2721
	11th to 20th	Night	45% 4 10% 20% 17% 4	2460
	21st to end	Night	46% 3 8% 24% 15% 3	2076
March	1st to 10th	Night	44% 4 12% 19% 15% 6%	5494
	11th to 20th	Night	42% 3 15% 25% 11% 4	5304
	21st to end	Night	48% 3 6% 15% 23% 4	4971
April	1st to 10th	Night	49% 3 10% 21% 14% 3	2000
	11th to 20th	Night	47% 5% 9% 19% 19% 1	1975
	21st to end	Night	45% 4 8% 23% 17% 3	1944
May	1st to 10th	Night	58% 5% 12% 14% 10% 1	4060
	11th to 20th	Night	51% 4 13% 16% 14% 2	3629
	21st to end	Night	47% 5% 14% 23% 10% 2	3927
June	1st to 10th	Night	42% 6% 10% 23% 18% 2	1600
	11th to 20th	Night	40% 7% 17% 25% 10% 1	1600
	21st to end	Night	36% 6% 16% 25% 15% 2	1600
July	1st to 10th	Night	43% 6% 14% 21% 14% 2	3560
	11th to 20th	Night	48% 6% 14% 21% 11%	3552
	21st to end	Night	37% 5% 13% 25% 19% 1	3809
August	1st to 10th	Night	51% 6% 15% 19% 9% 1	2704
	11th to 20th	Night	43% 5% 14% 28% 9% 1	3227
	21st to end	Night	31% 5% 11% 36% 16% 1	3586
September	1st to 10th	Night	39% 5% 10% 27% 18% 1	2000
	11th to 20th	Night	32% 4 11% 25% 26% 2	2095
	21st to end	Night	41% 5% 9% 22% 22% 2	2200
October	1st to 10th	Night	41% 4 10% 22% 20% 2	3751
	11th to 20th	Night	28% 3 10% 29% 26% 4	3899
	21st to end	Night	35% 3 13% 30% 18% 2	4563
November	1st to 10th	Night	36% 4 12% 25% 20% 3	2667
	11th to 20th	Night	40% 3 9% 24% 20% 4	2730
	21st to end	Night	40% 3 13% 30% 12% 1	2827
December	1st to 10th	Night	41% 4 12% 32% 10% 1	4720
	11th to 20th	Night	48% 3 12% 20% 16% 3	5348
	21st to end	Night	48% 3 9% 19% 16% 4	7150

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	29% 28% 28% 12% 4	220
	11th to 20th	Day	36% 25% 26% 11% 1	220
	21st to end	Day	27% 28% 31% 10% 2 2	303
February	1st to 10th	Day	34% 26% 32% 8% 1	337
	11th to 20th	Day	32% 25% 32% 12%	536
	21st to end	Day	32% 23% 30% 13% 3	446
March	1st to 10th	Day	31% 21% 29% 15% 3	540
	11th to 20th	Day	29% 26% 29% 13% 3 1	528
	21st to end	Day	31% 22% 29% 12% 3 2	550
April	1st to 10th	Day	33% 22% 26% 12% 6% 1	500
	11th to 20th	Day	27% 25% 28% 13% 6% 1	492
	21st to end	Day	30% 17% 32% 16% 5% 1	500
May	1st to 10th	Day	34% 18% 26% 14% 6% 1	503
	11th to 20th	Day	24% 13% 35% 19% 7% 1	527
	21st to end	Day	22% 12% 27% 25% 12% 2	573
June	1st to 10th	Day	22% 11% 31% 25% 11% 2	530
	11th to 20th	Day	17% 17% 29% 24% 12% 1	530
	21st to end	Day	15% 14% 27% 28% 13% 3	530
July	1st to 10th	Day	14% 8% 30% 28% 15% 4	525
	11th to 20th	Day	13% 8% 28% 31% 17% 3	524
	21st to end	Day	14% 8% 31% 33% 12% 2	576
August	1st to 10th	Day	16% 8% 25% 31% 16% 5%	526
	11th to 20th	Day	14% 7% 25% 33% 15% 6%	519
	21st to end	Day	12% 10% 30% 27% 15% 7%	583
September	1st to 10th	Day	16% 13% 25% 23% 16% 6%	530
	11th to 20th	Day	14% 8% 30% 26% 13% 9%	530
	21st to end	Day	22% 10% 30% 23% 10% 5%	530
October	1st to 10th	Day	27% 10% 24% 21% 15% 4	530
	11th to 20th	Day	23% 17% 29% 20% 10% 1	530
	21st to end	Day	28% 14% 29% 20% 9%	481
November	1st to 10th	Day	20% 16% 30% 22% 10% 2	425
	11th to 20th	Day	27% 24% 26% 17% 5% 1	430
	21st to end	Day	27% 22% 29% 18% 3 1	330
December	1st to 10th	Day	27% 23% 32% 13% 5%	220
	11th to 20th	Day	39% 19% 30% 11% 1	220
	21st to end	Day	27% 24% 30% 15% 5%	242
January	1st to 10th	Night	23% 18% 37% 19% 3	840
	11th to 20th	Night	26% 20% 30% 22% 2	840
	21st to end	Night	20% 23% 34% 20% 3	924
February	1st to 10th	Night	23% 19% 35% 21% 2	840
	11th to 20th	Night	25% 20% 39% 15% 1	823
	21st to end	Night	25% 19% 35% 18% 2	692
March	1st to 10th	Night	25% 21% 32% 19% 3	840
	11th to 20th	Night	25% 22% 31% 19% 3	829
	21st to end	Night	24% 20% 34% 18% 4 1	880
April	1st to 10th	Night	25% 20% 33% 19% 4	800
	11th to 20th	Night	26% 16% 33% 21% 4	791
	21st to end	Night	24% 16% 35% 21% 5%	744
May	1st to 10th	Night	27% 15% 31% 22% 5%	600
	11th to 20th	Night	23% 13% 34% 24% 6%	421
	21st to end	Night	20% 7% 26% 36% 10% 1	433
June	1st to 10th	Night	19% 7% 29% 35% 11%	400
	11th to 20th	Night	16% 6% 31% 32% 14% 1	400
	21st to end	Night	14% 3 28% 43% 13%	400
July	1st to 10th	Night	16% 5% 20% 39% 18% 1	390
	11th to 20th	Night	14% 3 25% 41% 16% 2	388
	21st to end	Night	14% 3 23% 42% 18% 1	438
August	1st to 10th	Night	13% 3 21% 43% 19% 1	474
	11th to 20th	Night	16% 3 20% 36% 22% 2	790
	21st to end	Night	18% 6% 20% 35% 21% 2	880
September	1st to 10th	Night	17% 6% 25% 35% 14% 2	800
	11th to 20th	Night	16% 5% 24% 33% 18% 4	800
	21st to end	Night	21% 6% 25% 30% 15% 2	800
October	1st to 10th	Night	22% 9% 27% 26% 15% 2	800
	11th to 20th	Night	20% 13% 29% 28% 9%	800
	21st to end	Night	26% 12% 32% 22% 8%	880
November	1st to 10th	Night	17% 13% 34% 26% 9% 1	820
	11th to 20th	Night	25% 17% 30% 21% 6% 1	840
	21st to end	Night	21% 19% 30% 24% 6%	840
December	1st to 10th	Night	27% 17% 33% 18% 5%	840
	11th to 20th	Night	27% 16% 32% 23% 3	840
	21st to end	Night	27% 16% 35% 19% 2	924

Page generated at 2026-03-15 02:23:51. Version ac07

Copyright © 2026 Attilla Danko.