Robert Moses State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert Moses State Park clear sky chart from 2005-11-06 to 2026-03-03.

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	16% 7% 2 6% 4 4 4 3 5% 7% 41%	130785
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 42%	130398
Transparency	Day	42% 5% 12% 23% 16% 2	134325
	Night	43% 3 11% 23% 17% 3	134945
Seeing	Day	19% 11% 29% 27% 12% 2	16704
	Night	20% 11% 31% 28% 9% 1	25914

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% 6% 2 6% 4 3 4 3 4 6% 49%	4661
	11th to 20th	Day	15% 8% 3 5% 3 4 4 3 4 5% 47%	4650
	21st to end	Day	16% 8% 3 7% 4 4 4 3 5% 6% 42%	5458
February	1st to 10th	Day	16% 7% 3 6% 4 4 4 4 4 6% 41%	1964
	11th to 20th	Day	15% 6% 3 7% 4 4 4 3 4 6% 44%	2048
	21st to end	Day	19% 8% 2 7% 3 4 4 3 5% 6% 39%	1730
March	1st to 10th	Day	22% 8% 2 5% 3 3 3 3 4 5% 43%	4496
	11th to 20th	Day	11% 9% 3 6% 4 4 4 4 6% 7% 43%	4690
	21st to end	Day	18% 8% 2 6% 4 4 4 3 5% 6% 41%	5970
April	1st to 10th	Day	18% 8% 2 6% 4 4 4 4 5% 7% 37%	2400
	11th to 20th	Day	18% 6% 2 5% 3 4 3 4 5% 7% 42%	2374
	21st to end	Day	19% 7% 1 5% 4 4 3 4 6% 7% 41%	2465
May	1st to 10th	Day	28% 9% 2 5% 3 3 4 3 5% 9% 29%	5886
	11th to 20th	Day	23% 9% 3 6% 3 3 3 3 4 6% 36%	6105
	21st to end	Day	20% 8% 2 5% 4 4 4 4 6% 8% 35%	6949
June	1st to 10th	Day	17% 6% 2 5% 4 4 4 4 6% 9% 39%	2800
	11th to 20th	Day	15% 7% 3 5% 4 4 5% 4 6% 8% 39%	2800
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 6% 9% 43%	2800
July	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 6% 10% 37%	6360
	11th to 20th	Day	11% 7% 2 8% 5% 5% 6% 5% 8% 10% 34%	6360
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 7% 8% 40%	6926
August	1st to 10th	Day	17% 7% 2 7% 5% 4 5% 4 6% 9% 35%	4292
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 3 7% 9% 42%	3850
	21st to end	Day	8% 4 2 5% 4 4 5% 4 7% 10% 48%	4312
September	1st to 10th	Day	14% 5% 2 6% 4 4 3 3 5% 7% 47%	2400
	11th to 20th	Day	12% 6% 2 5% 3 3 4 3 5% 7% 51%	2275
	21st to end	Day	19% 7% 3 7% 4 4 4 3 5% 6% 39%	2200
October	1st to 10th	Day	19% 6% 2 5% 3 3 4 3 4 7% 44%	2150
	11th to 20th	Day	16% 4 2 5% 3 4 3 4 6% 7% 47%	2000
	21st to end	Day	18% 6% 2 5% 4 4 4 3 4 7% 44%	2000
November	1st to 10th	Day	14% 5% 2 5% 4 3 3 3 3 6% 52%	1851
	11th to 20th	Day	15% 6% 2 4 3 3 3 4 4 7% 48%	1890
	21st to end	Day	15% 7% 3 5% 4 3 3 3 6% 7% 44%	1879
December	1st to 10th	Day	16% 6% 2 6% 4 3 4 3 5% 7% 45%	2680
	11th to 20th	Day	23% 8% 2 4 2 2 2 2 4 5% 46%	3066
	21st to end	Day	17% 9% 3 6% 4 4 3 3 5% 6% 39%	4048
January	1st to 10th	Night	14% 8% 3 5% 3 3 3 2 4 5% 50%	8234
	11th to 20th	Night	16% 7% 3 6% 3 3 3 3 4 5% 46%	8235
	21st to end	Night	16% 9% 3 5% 4 5% 4 3 5% 5% 42%	8721
February	1st to 10th	Night	15% 10% 3 5% 4 4 4 3 5% 6% 41%	2655
	11th to 20th	Night	19% 8% 2 5% 3 4 4 3 5% 6% 40%	2458
	21st to end	Night	19% 8% 2 6% 4 4 3 3 5% 5% 42%	2076
March	1st to 10th	Night	20% 9% 3 5% 3 3 3 2 4 5% 44%	5389
	11th to 20th	Night	16% 9% 3 5% 3 4 3 3 5% 6% 43%	5266
	21st to end	Night	20% 9% 2 7% 4 4 4 3 5% 5% 39%	4962
April	1st to 10th	Night	20% 7% 3 6% 5% 4 5% 4 4 6% 37%	2000
	11th to 20th	Night	20% 7% 3 5% 4 3 4 4 5% 7% 40%	1975
	21st to end	Night	18% 8% 2 5% 4 3 3 3 4 6% 43%	1934
May	1st to 10th	Night	25% 11% 3 8% 4 4 4 3 5% 7% 27%	4054
	11th to 20th	Night	24% 11% 3 6% 4 3 4 3 5% 6% 34%	3818
	21st to end	Night	23% 8% 2 7% 4 4 3 3 5% 7% 34%	3926
June	1st to 10th	Night	19% 6% 2 5% 4 4 4 3 5% 8% 39%	1600
	11th to 20th	Night	16% 7% 2 5% 4 3 4 3 7% 9% 39%	1600
	21st to end	Night	12% 5% 2 7% 4 5% 5% 5% 7% 9% 39%	1600
July	1st to 10th	Night	13% 11% 4 8% 5% 5% 5% 4 6% 8% 33%	3600
	11th to 20th	Night	17% 11% 3 7% 4 5% 5% 4 6% 8% 30%	3600
	21st to end	Night	14% 7% 3 6% 4 4 4 3 6% 8% 40%	3926
August	1st to 10th	Night	22% 7% 2 6% 4 4 4 4 6% 8% 32%	2823
	11th to 20th	Night	14% 6% 3 6% 4 5% 5% 4 6% 9% 40%	3197
	21st to end	Night	9% 5% 2 4 4 4 4 4 5% 8% 52%	3586
September	1st to 10th	Night	14% 5% 2 7% 3 4 5% 4 6% 6% 44%	2000
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 51%	2125
	21st to end	Night	19% 6% 2 7% 4 4 3 4 5% 6% 41%	2200
October	1st to 10th	Night	18% 9% 2 5% 4 3 3 3 4 6% 42%	2245
	11th to 20th	Night	15% 5% 2 5% 3 4 3 3 5% 6% 49%	2400
	21st to end	Night	20% 6% 2 5% 3 3 4 3 4 6% 43%	2839
November	1st to 10th	Night	12% 6% 2 5% 4 4 4 3 5% 6% 51%	2667
	11th to 20th	Night	18% 6% 2 4 3 3 4 3 4 5% 49%	2730
	21st to end	Night	15% 5% 2 5% 4 4 4 3 5% 6% 47%	2739
December	1st to 10th	Night	16% 6% 2 5% 3 3 3 2 4 5% 49%	4720
	11th to 20th	Night	26% 7% 2 4 3 3 2 2 4 4 44%	5348
	21st to end	Night	18% 8% 3 6% 4 3 4 3 4 5% 43%	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	37% 3 9% 31% 18% 2	4662
	11th to 20th	Day	42% 3 8% 23% 18% 6%	4680
	21st to end	Day	44% 3 10% 27% 16% 1	5458
February	1st to 10th	Day	44% 5% 12% 23% 15% 2	1964
	11th to 20th	Day	43% 4 9% 26% 16% 2	2057
	21st to end	Day	46% 4 10% 22% 15% 2	1730
March	1st to 10th	Day	43% 5% 10% 18% 15% 9%	4499
	11th to 20th	Day	38% 6% 13% 28% 13% 2	4690
	21st to end	Day	44% 4 9% 14% 23% 6%	5970
April	1st to 10th	Day	45% 5% 8% 21% 16% 4	2400
	11th to 20th	Day	42% 5% 10% 22% 17% 3	2374
	21st to end	Day	42% 5% 10% 22% 18% 4	2465
May	1st to 10th	Day	54% 4 17% 15% 10% 1	5897
	11th to 20th	Day	49% 5% 11% 20% 14% 2	6109
	21st to end	Day	44% 6% 11% 24% 14% 1	6949
June	1st to 10th	Day	40% 7% 13% 23% 16% 2	2800
	11th to 20th	Day	41% 7% 13% 25% 13% 2	2800
	21st to end	Day	38% 7% 15% 23% 16% 1	2800
July	1st to 10th	Day	43% 7% 13% 21% 15% 1	6290
	11th to 20th	Day	43% 4 20% 22% 10% 1	6285
	21st to end	Day	42% 5% 11% 22% 19% 2	6728
August	1st to 10th	Day	47% 5% 16% 23% 9% 1	4278
	11th to 20th	Day	38% 5% 13% 34% 10% 1	3886
	21st to end	Day	33% 4 13% 28% 21% 2	4312
September	1st to 10th	Day	38% 5% 13% 22% 20% 2	2400
	11th to 20th	Day	34% 4 11% 25% 24% 2	2275
	21st to end	Day	45% 4 10% 19% 19% 2	2200
October	1st to 10th	Day	37% 4 10% 20% 24% 5%	3501
	11th to 20th	Day	27% 3 10% 23% 32% 5%	3240
	21st to end	Day	30% 3 14% 26% 24% 3	3212
November	1st to 10th	Day	36% 3 14% 23% 22% 2	1851
	11th to 20th	Day	38% 3 10% 23% 23% 3	1890
	21st to end	Day	40% 4 14% 28% 12% 2	1879
December	1st to 10th	Day	40% 3 15% 28% 13% 1	2680
	11th to 20th	Day	42% 3 13% 23% 17% 3	3066
	21st to end	Day	47% 5% 8% 22% 15% 3	4048
January	1st to 10th	Night	39% 2 11% 25% 21% 3	8234
	11th to 20th	Night	42% 2 10% 22% 18% 6%	8280
	21st to end	Night	45% 2 8% 22% 19% 4	8721
February	1st to 10th	Night	44% 4 12% 24% 13% 2	2655
	11th to 20th	Night	45% 4 9% 22% 16% 4	2460
	21st to end	Night	45% 3 7% 24% 16% 4	2076
March	1st to 10th	Night	45% 3 10% 20% 14% 8%	5399
	11th to 20th	Night	44% 3 13% 25% 12% 4	5267
	21st to end	Night	48% 3 5% 14% 24% 5%	4962
April	1st to 10th	Night	48% 4 9% 18% 17% 3	2000
	11th to 20th	Night	45% 5% 10% 19% 21% 2	1975
	21st to end	Night	44% 4 8% 21% 18% 5%	1934
May	1st to 10th	Night	58% 4 13% 14% 10% 1	4060
	11th to 20th	Night	52% 4 13% 15% 13% 2	3819
	21st to end	Night	50% 4 12% 22% 11% 2	3927
June	1st to 10th	Night	44% 5% 9% 21% 20% 1	1600
	11th to 20th	Night	41% 6% 14% 26% 12% 1	1600
	21st to end	Night	39% 8% 12% 25% 14% 2	1600
July	1st to 10th	Night	48% 6% 12% 22% 11% 1	3560
	11th to 20th	Night	51% 4 14% 21% 9% 1	3552
	21st to end	Night	41% 4 14% 24% 16% 1	3809
August	1st to 10th	Night	50% 6% 17% 18% 9% 1	2813
	11th to 20th	Night	42% 5% 14% 30% 9% 1	3227
	21st to end	Night	30% 5% 11% 34% 19% 1	3586
September	1st to 10th	Night	39% 6% 10% 26% 19% 1	2000
	11th to 20th	Night	35% 4 10% 25% 23% 3	2125
	21st to end	Night	44% 5% 8% 21% 19% 3	2200
October	1st to 10th	Night	41% 3 10% 24% 20% 3	3674
	11th to 20th	Night	25% 3 10% 28% 30% 4	3899
	21st to end	Night	32% 3 13% 29% 21% 3	4577
November	1st to 10th	Night	36% 4 11% 24% 21% 4	2667
	11th to 20th	Night	39% 3 8% 24% 20% 5%	2730
	21st to end	Night	38% 4 12% 30% 15% 1	2739
December	1st to 10th	Night	40% 3 12% 30% 13% 2	4720
	11th to 20th	Night	47% 3 9% 24% 15% 3	5348
	21st to end	Night	45% 4 9% 21% 17% 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	25% 22% 32% 17% 3	220
	11th to 20th	Day	21% 30% 32% 13% 3	220
	21st to end	Day	21% 18% 40% 15% 4 1	303
February	1st to 10th	Day	23% 15% 43% 17% 3	404
	11th to 20th	Day	23% 20% 37% 18% 2	536
	21st to end	Day	24% 19% 34% 18% 5%	446
March	1st to 10th	Day	17% 19% 36% 23% 4	508
	11th to 20th	Day	18% 14% 39% 24% 4 1	500
	21st to end	Day	24% 15% 36% 18% 6% 1	550
April	1st to 10th	Day	24% 17% 35% 16% 8% 1	500
	11th to 20th	Day	21% 15% 32% 23% 8%	492
	21st to end	Day	24% 13% 32% 24% 5% 1	500
May	1st to 10th	Day	28% 12% 30% 22% 7% 1	503
	11th to 20th	Day	21% 10% 28% 31% 10% 1	527
	21st to end	Day	19% 5% 21% 33% 20% 3	573
June	1st to 10th	Day	19% 5% 24% 33% 17% 2	530
	11th to 20th	Day	17% 8% 27% 34% 12% 2	530
	21st to end	Day	13% 5% 27% 33% 19% 2	530
July	1st to 10th	Day	14% 4 19% 37% 23% 4	525
	11th to 20th	Day	10% 4 21% 37% 23% 5%	524
	21st to end	Day	13% 5% 21% 41% 17% 3	576
August	1st to 10th	Day	13% 3 19% 37% 21% 6%	526
	11th to 20th	Day	14% 4 20% 35% 23% 4	519
	21st to end	Day	12% 5% 23% 36% 19% 6%	583
September	1st to 10th	Day	18% 6% 22% 27% 20% 6%	530
	11th to 20th	Day	14% 3 22% 32% 19% 9%	530
	21st to end	Day	23% 4 28% 27% 15% 4	530
October	1st to 10th	Day	23% 8% 23% 24% 16% 6%	530
	11th to 20th	Day	17% 13% 29% 26% 13% 2	530
	21st to end	Day	21% 13% 31% 23% 10% 2	473
November	1st to 10th	Day	16% 15% 26% 31% 10% 2	425
	11th to 20th	Day	19% 21% 31% 22% 6%	430
	21st to end	Day	21% 16% 32% 23% 7% 1	419
December	1st to 10th	Day	23% 18% 35% 18% 6%	220
	11th to 20th	Day	31% 20% 28% 16% 5%	220
	21st to end	Day	26% 16% 39% 12% 8%	242
January	1st to 10th	Night	20% 18% 39% 19% 4	840
	11th to 20th	Night	26% 17% 32% 23% 2	840
	21st to end	Night	20% 17% 40% 20% 2	924
February	1st to 10th	Night	21% 15% 39% 23% 2	840
	11th to 20th	Night	25% 16% 39% 18% 1	823
	21st to end	Night	23% 17% 36% 19% 4	692
March	1st to 10th	Night	22% 17% 36% 21% 5%	809
	11th to 20th	Night	20% 13% 39% 22% 5% 1	800
	21st to end	Night	22% 14% 39% 20% 5%	880
April	1st to 10th	Night	23% 13% 36% 23% 5%	800
	11th to 20th	Night	22% 13% 32% 27% 5%	791
	21st to end	Night	21% 10% 35% 28% 6% 1	734
May	1st to 10th	Night	24% 8% 33% 27% 7% 1	600
	11th to 20th	Night	22% 9% 35% 28% 5%	507
	21st to end	Night	22% 5% 20% 36% 16% 2	433
June	1st to 10th	Night	20% 5% 26% 34% 15%	400
	11th to 20th	Night	19% 4 21% 42% 15% 1	400
	21st to end	Night	12% 4 23% 47% 13% 1	400
July	1st to 10th	Night	13% 3 23% 42% 18% 2	390
	11th to 20th	Night	13% 6% 17% 43% 19% 3	388
	21st to end	Night	15% 2 18% 47% 17% 1	438
August	1st to 10th	Night	12% 2 21% 45% 20% 1	531
	11th to 20th	Night	15% 3 17% 38% 25% 2	790
	21st to end	Night	13% 5% 17% 38% 23% 3	880
September	1st to 10th	Night	16% 3 24% 35% 18% 4	800
	11th to 20th	Night	16% 4 19% 35% 20% 6%	800
	21st to end	Night	21% 3 24% 33% 17% 2	800
October	1st to 10th	Night	22% 7% 25% 27% 16% 3	800
	11th to 20th	Night	18% 11% 29% 29% 12% 1	800
	21st to end	Night	23% 11% 34% 25% 8%	880
November	1st to 10th	Night	15% 11% 33% 27% 11% 2	820
	11th to 20th	Night	21% 15% 33% 22% 8%	840
	21st to end	Night	18% 17% 33% 25% 7% 1	840
December	1st to 10th	Night	25% 16% 34% 19% 5% 1	840
	11th to 20th	Night	24% 15% 36% 22% 3	840
	21st to end	Night	23% 15% 38% 21% 3	924

Page generated at 2026-02-28 01:40:21. Version ac07

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