SUNY Ulster
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SUNY Ulster clear sky chart from 2005-11-06 to 2026-04-17.

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 5% 4 6% 7% 38%	131512
	Night	17% 7% 3 6% 4 4 4 3 5% 6% 40%	130659
Transparency	Day	42% 8% 13% 21% 14% 2	135013
	Night	42% 7% 13% 21% 15% 2	135245
Seeing	Day	20% 14% 28% 24% 11% 3	16664
	Night	19% 10% 29% 31% 10% 1	25903

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	11% 9% 5% 10% 4 4 4 3 5% 5% 40%	4661
	11th to 20th	Day	12% 8% 3 10% 6% 4 4 4 5% 6% 37%	4650
	21st to end	Day	13% 8% 2 7% 5% 4 5% 4 5% 6% 41%	5464
February	1st to 10th	Day	13% 9% 3 9% 6% 5% 5% 4 5% 6% 36%	1890
	11th to 20th	Day	12% 8% 3 9% 5% 4 5% 3 5% 6% 39%	2022
	21st to end	Day	18% 10% 2 6% 4 3 4 4 5% 5% 38%	1730
March	1st to 10th	Day	21% 8% 3 6% 4 4 4 3 4 4 40%	4576
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 7% 44%	4890
	21st to end	Day	19% 8% 3 6% 5% 4 4 3 5% 6% 38%	6051
April	1st to 10th	Day	18% 9% 3 7% 4 4 4 3 5% 6% 38%	2520
	11th to 20th	Day	15% 7% 3 6% 4 5% 4 4 6% 6% 40%	2446
	21st to end	Day	20% 5% 3 5% 5% 4 4 3 5% 6% 40%	2449
May	1st to 10th	Day	31% 7% 2 5% 3 4 4 3 5% 7% 28%	5971
	11th to 20th	Day	19% 7% 2 6% 4 4 5% 4 6% 7% 35%	6318
	21st to end	Day	20% 7% 2 6% 4 4 5% 4 6% 9% 33%	6949
June	1st to 10th	Day	16% 5% 2 6% 5% 5% 5% 5% 7% 8% 36%	2800
	11th to 20th	Day	15% 5% 2 6% 5% 4 5% 4 8% 8% 37%	2800
	21st to end	Day	13% 5% 2 5% 5% 5% 5% 5% 7% 9% 37%	2800
July	1st to 10th	Day	10% 6% 3 8% 5% 5% 6% 5% 7% 9% 36%	6360
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 5% 8% 13% 35%	6360
	21st to end	Day	13% 6% 2 6% 5% 4 5% 4 5% 8% 42%	6926
August	1st to 10th	Day	18% 6% 2 7% 4 5% 5% 4 6% 8% 34%	4422
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 7% 8% 41%	3850
	21st to end	Day	11% 5% 2 5% 4 5% 5% 4 7% 9% 43%	4312
September	1st to 10th	Day	13% 6% 2 6% 5% 4 4 2 5% 6% 46%	2400
	11th to 20th	Day	13% 4 1 5% 3 4 4 3 5% 7% 51%	2320
	21st to end	Day	18% 5% 2 5% 4 4 4 4 6% 7% 41%	2200
October	1st to 10th	Day	19% 6% 2 5% 3 4 3 3 4 6% 44%	2072
	11th to 20th	Day	14% 6% 2 6% 4 3 5% 4 5% 7% 43%	2000
	21st to end	Day	22% 5% 2 6% 4 5% 4 4 5% 6% 37%	2024
November	1st to 10th	Day	12% 8% 2 5% 5% 3 3 3 4 6% 49%	1851
	11th to 20th	Day	16% 7% 2 5% 4 3 5% 4 5% 6% 43%	1890
	21st to end	Day	17% 9% 3 5% 5% 4 5% 4 5% 7% 38%	1744
December	1st to 10th	Day	15% 6% 3 8% 5% 5% 5% 4 5% 7% 37%	2680
	11th to 20th	Day	22% 7% 2 5% 2 3 4 3 5% 6% 41%	3066
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 5% 5% 6% 34%	4048
January	1st to 10th	Night	14% 8% 3 9% 4 4 5% 3 5% 6% 39%	8234
	11th to 20th	Night	13% 9% 4 11% 6% 5% 4 3 5% 6% 34%	8235
	21st to end	Night	14% 9% 2 6% 6% 5% 4 4 6% 6% 39%	8701
February	1st to 10th	Night	14% 9% 3 6% 4 4 4 5% 6% 6% 39%	2730
	11th to 20th	Night	14% 8% 3 7% 5% 5% 5% 4 5% 6% 38%	2482
	21st to end	Night	15% 10% 2 7% 4 4 4 4 5% 5% 40%	2076
March	1st to 10th	Night	20% 8% 3 5% 3 3 4 3 4 6% 42%	5484
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 5% 7% 42%	5287
	21st to end	Night	17% 10% 3 7% 4 4 3 3 4 5% 39%	5122
April	1st to 10th	Night	19% 8% 3 7% 4 6% 4 4 6% 7% 33%	2100
	11th to 20th	Night	17% 7% 2 6% 5% 5% 4 4 5% 8% 37%	2036
	21st to end	Night	20% 7% 3 5% 4 3 4 3 4 5% 42%	1950
May	1st to 10th	Night	33% 6% 2 6% 3 3 3 3 5% 6% 29%	4012
	11th to 20th	Night	22% 8% 2 7% 4 3 4 3 5% 7% 35%	3575
	21st to end	Night	20% 8% 3 7% 3 4 4 4 6% 7% 34%	3926
June	1st to 10th	Night	16% 5% 2 6% 4 4 4 4 5% 8% 42%	1600
	11th to 20th	Night	14% 6% 3 5% 4 4 4 4 6% 10% 41%	1600
	21st to end	Night	13% 4 2 5% 3 4 4 4 6% 10% 45%	1600
July	1st to 10th	Night	11% 6% 3 6% 4 4 5% 4 6% 8% 42%	3600
	11th to 20th	Night	12% 6% 3 7% 5% 5% 5% 5% 7% 10% 37%	3600
	21st to end	Night	12% 5% 2 5% 4 4 4 4 5% 6% 49%	3926
August	1st to 10th	Night	21% 6% 2 6% 4 4 4 4 5% 8% 36%	2702
	11th to 20th	Night	15% 6% 2 6% 5% 4 5% 4 5% 6% 42%	3188
	21st to end	Night	13% 5% 2 5% 3 3 3 3 5% 6% 52%	3586
September	1st to 10th	Night	14% 5% 2 5% 5% 4 4 3 4 7% 47%	2000
	11th to 20th	Night	13% 5% 1 4 3 3 4 3 4 7% 55%	2080
	21st to end	Night	17% 6% 2 5% 4 4 3 3 5% 7% 45%	2200
October	1st to 10th	Night	20% 7% 3 6% 3 4 4 3 4 5% 43%	2325
	11th to 20th	Night	17% 6% 2 5% 3 3 4 3 5% 6% 48%	2400
	21st to end	Night	23% 6% 2 7% 3 3 3 3 4 7% 39%	2815
November	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 47%	2667
	11th to 20th	Night	17% 8% 2 5% 3 4 4 4 5% 5% 43%	2730
	21st to end	Night	15% 7% 2 5% 5% 4 4 3 6% 6% 43%	2872
December	1st to 10th	Night	15% 9% 2 7% 4 4 4 3 4 6% 42%	4720
	11th to 20th	Night	26% 8% 2 5% 3 3 3 3 4 5% 38%	5348
	21st to end	Night	19% 10% 3 7% 4 4 3 3 5% 6% 35%	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	44% 5% 12% 24% 12% 2	4662
	11th to 20th	Day	44% 7% 11% 19% 15% 6%	4680
	21st to end	Day	41% 7% 12% 24% 16% 1	5464
February	1st to 10th	Day	47% 7% 12% 19% 14% 1	1890
	11th to 20th	Day	44% 7% 10% 22% 14% 3	2031
	21st to end	Day	47% 5% 11% 21% 13% 2	1730
March	1st to 10th	Day	46% 6% 12% 17% 11% 8%	4579
	11th to 20th	Day	38% 7% 16% 27% 8% 4	4890
	21st to end	Day	46% 6% 8% 13% 21% 6%	6051
April	1st to 10th	Day	47% 6% 10% 20% 14% 4	2520
	11th to 20th	Day	43% 7% 12% 21% 15% 2	2446
	21st to end	Day	44% 6% 10% 20% 15% 4	2449
May	1st to 10th	Day	54% 9% 13% 14% 10% 1	5982
	11th to 20th	Day	45% 9% 14% 19% 12% 1	6322
	21st to end	Day	44% 9% 14% 22% 11% 1	6949
June	1st to 10th	Day	42% 9% 16% 19% 13% 1	2800
	11th to 20th	Day	41% 9% 16% 22% 10% 1	2800
	21st to end	Day	39% 11% 13% 23% 12% 1	2800
July	1st to 10th	Day	42% 10% 13% 19% 14% 1	6290
	11th to 20th	Day	35% 12% 18% 24% 10%	6285
	21st to end	Day	39% 7% 13% 23% 17% 1	6728
August	1st to 10th	Day	46% 9% 16% 19% 9% 1	4408
	11th to 20th	Day	37% 9% 18% 27% 9%	3886
	21st to end	Day	33% 8% 16% 29% 13% 1	4312
September	1st to 10th	Day	39% 7% 12% 23% 18% 2	2400
	11th to 20th	Day	33% 6% 12% 24% 23% 2	2320
	21st to end	Day	40% 7% 13% 20% 17% 3	2200
October	1st to 10th	Day	37% 7% 10% 20% 23% 3	3371
	11th to 20th	Day	32% 6% 10% 28% 22% 3	3240
	21st to end	Day	32% 6% 15% 25% 18% 4	3249
November	1st to 10th	Day	37% 5% 14% 25% 17% 2	1851
	11th to 20th	Day	41% 7% 11% 22% 17% 2	1890
	21st to end	Day	45% 6% 14% 25% 8% 2	1744
December	1st to 10th	Day	45% 7% 15% 24% 8% 1	2680
	11th to 20th	Day	43% 6% 15% 22% 12% 3	3066
	21st to end	Day	48% 7% 13% 19% 13% 1	4048
January	1st to 10th	Night	44% 6% 14% 19% 15% 2	8234
	11th to 20th	Night	47% 6% 14% 15% 12% 5%	8280
	21st to end	Night	41% 7% 12% 19% 17% 3	8701
February	1st to 10th	Night	44% 7% 15% 21% 12% 2	2730
	11th to 20th	Night	45% 6% 12% 18% 15% 4	2484
	21st to end	Night	45% 5% 11% 22% 13% 4	2076
March	1st to 10th	Night	43% 6% 13% 19% 15% 5%	5494
	11th to 20th	Night	41% 7% 17% 22% 10% 3	5288
	21st to end	Night	46% 6% 7% 14% 23% 4	5122
April	1st to 10th	Night	49% 7% 11% 18% 13% 2	2100
	11th to 20th	Night	44% 7% 12% 17% 18% 1	2036
	21st to end	Night	44% 6% 10% 20% 17% 3	1950
May	1st to 10th	Night	55% 6% 13% 14% 10% 1	4018
	11th to 20th	Night	48% 9% 13% 16% 14% 1	3576
	21st to end	Night	46% 8% 14% 21% 10% 1	3927
June	1st to 10th	Night	41% 7% 12% 23% 17% 1	1600
	11th to 20th	Night	38% 9% 18% 25% 10% 1	1600
	21st to end	Night	33% 9% 16% 26% 14% 2	1600
July	1st to 10th	Night	39% 9% 15% 20% 15% 3	3560
	11th to 20th	Night	41% 10% 16% 22% 11% 1	3552
	21st to end	Night	34% 8% 13% 27% 17% 1	3809
August	1st to 10th	Night	46% 10% 15% 19% 9% 1	2692
	11th to 20th	Night	40% 8% 16% 26% 10%	3218
	21st to end	Night	32% 7% 13% 33% 15% 1	3586
September	1st to 10th	Night	38% 7% 12% 25% 18% 1	2000
	11th to 20th	Night	30% 6% 12% 26% 24% 1	2080
	21st to end	Night	39% 6% 11% 22% 21% 1	2200
October	1st to 10th	Night	41% 6% 11% 21% 18% 2	3806
	11th to 20th	Night	29% 4 11% 29% 25% 2	3899
	21st to end	Night	34% 5% 13% 30% 16% 2	4540
November	1st to 10th	Night	37% 6% 12% 23% 19% 3	2667
	11th to 20th	Night	42% 5% 11% 21% 17% 3	2730
	21st to end	Night	40% 6% 16% 27% 10% 1	2872
December	1st to 10th	Night	42% 6% 14% 29% 8% 1	4720
	11th to 20th	Night	48% 5% 15% 16% 15% 2	5348
	21st to end	Night	48% 6% 13% 17% 12% 3	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	22% 24% 28% 18% 8%	220
	11th to 20th	Day	28% 24% 32% 13% 2	220
	21st to end	Day	21% 23% 35% 16% 4	305
February	1st to 10th	Day	25% 22% 34% 16% 3	330
	11th to 20th	Day	24% 23% 35% 16% 2	510
	21st to end	Day	27% 20% 33% 16% 3	446
March	1st to 10th	Day	24% 18% 32% 20% 5%	540
	11th to 20th	Day	25% 22% 30% 17% 4 1	540
	21st to end	Day	27% 20% 29% 17% 5% 1	594
April	1st to 10th	Day	30% 19% 27% 15% 6% 2	540
	11th to 20th	Day	24% 24% 28% 14% 8% 2	516
	21st to end	Day	27% 17% 29% 18% 7% 3	500
May	1st to 10th	Day	31% 15% 26% 18% 8% 2	503
	11th to 20th	Day	18% 15% 32% 24% 10% 2	527
	21st to end	Day	20% 9% 25% 29% 14% 3	573
June	1st to 10th	Day	18% 12% 26% 28% 14% 3	530
	11th to 20th	Day	16% 11% 27% 30% 13% 2	530
	21st to end	Day	16% 13% 26% 27% 16% 3	530
July	1st to 10th	Day	13% 5% 28% 32% 18% 4	525
	11th to 20th	Day	11% 6% 26% 35% 17% 6%	524
	21st to end	Day	13% 7% 27% 34% 15% 4	576
August	1st to 10th	Day	12% 7% 21% 35% 17% 8%	526
	11th to 20th	Day	14% 6% 21% 31% 21% 7%	519
	21st to end	Day	10% 8% 25% 31% 19% 8%	583
September	1st to 10th	Day	17% 10% 20% 28% 17% 8%	530
	11th to 20th	Day	13% 6% 25% 23% 20% 12%	530
	21st to end	Day	20% 9% 24% 28% 13% 6%	530
October	1st to 10th	Day	24% 9% 21% 22% 17% 6%	530
	11th to 20th	Day	16% 15% 28% 25% 12% 3	530
	21st to end	Day	23% 13% 29% 25% 9% 1	486
November	1st to 10th	Day	17% 13% 29% 28% 9% 3	425
	11th to 20th	Day	22% 17% 30% 23% 7% 1	430
	21st to end	Day	22% 15% 33% 25% 4 1	284
December	1st to 10th	Day	20% 26% 29% 16% 8%	220
	11th to 20th	Day	27% 21% 30% 18% 4	220
	21st to end	Day	22% 14% 38% 21% 4 1	242
January	1st to 10th	Night	18% 14% 37% 27% 3	840
	11th to 20th	Night	22% 14% 34% 27% 4	840
	21st to end	Night	16% 13% 39% 28% 3	924
February	1st to 10th	Night	19% 13% 37% 29% 2	840
	11th to 20th	Night	20% 16% 37% 25% 1	823
	21st to end	Night	22% 14% 38% 22% 4	692
March	1st to 10th	Night	22% 13% 36% 26% 4	840
	11th to 20th	Night	20% 16% 35% 25% 5%	840
	21st to end	Night	19% 16% 36% 22% 5%	924
April	1st to 10th	Night	25% 15% 33% 21% 5%	840
	11th to 20th	Night	21% 13% 34% 25% 7%	816
	21st to end	Night	23% 13% 29% 27% 7%	750
May	1st to 10th	Night	26% 12% 28% 26% 8%	584
	11th to 20th	Night	19% 8% 30% 36% 6%	394
	21st to end	Night	16% 7% 21% 38% 18% 1	433
June	1st to 10th	Night	17% 5% 23% 41% 14% 1	400
	11th to 20th	Night	16% 5% 23% 41% 16% 1	400
	21st to end	Night	14% 4 20% 46% 16% 1	400
July	1st to 10th	Night	14% 3 15% 47% 20% 1	390
	11th to 20th	Night	11% 4 17% 47% 20% 1	388
	21st to end	Night	11% 5% 16% 47% 19% 1	438
August	1st to 10th	Night	13% 3 12% 46% 24% 2	462
	11th to 20th	Night	12% 4 16% 39% 27% 3	781
	21st to end	Night	15% 4 16% 39% 24% 2	880
September	1st to 10th	Night	16% 3 21% 37% 20% 3	800
	11th to 20th	Night	15% 4 19% 33% 24% 5%	800
	21st to end	Night	18% 5% 21% 36% 18% 2	800
October	1st to 10th	Night	23% 7% 23% 28% 16% 3	800
	11th to 20th	Night	19% 8% 26% 37% 10% 1	800
	21st to end	Night	26% 9% 29% 30% 6%	880
November	1st to 10th	Night	17% 9% 31% 34% 9%	820
	11th to 20th	Night	22% 12% 31% 27% 7% 1	840
	21st to end	Night	19% 12% 33% 30% 6% 1	840
December	1st to 10th	Night	23% 14% 33% 25% 5%	840
	11th to 20th	Night	25% 11% 32% 28% 4	840
	21st to end	Night	24% 11% 35% 27% 3	924

Page generated at 2026-04-14 02:44:23. Version ac07

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