Troy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Troy clear sky chart from 2005-11-06 to 2026-01-02.

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	11% 6% 2 6% 4 5% 5% 4 6% 8% 42%	126921
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	124469
Transparency	Day	37% 7% 12% 19% 18% 7%	130765
	Night	37% 6% 11% 18% 19% 9%	128696
Seeing	Day	14% 9% 22% 25% 20% 11%	16210
	Night	14% 8% 22% 30% 22% 5%	26199

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	14% 7% 2 5% 3 3 3 3 5% 5% 51%	4065
	11th to 20th	Day	12% 6% 3 4 3 3 3 3 4 6% 52%	4272
	21st to end	Day	20% 9% 3 6% 3 3 4 3 5% 5% 40%	4972
February	1st to 10th	Day	15% 9% 3 6% 5% 4 5% 4 5% 6% 39%	2000
	11th to 20th	Day	18% 7% 3 6% 3 3 4 3 6% 6% 43%	1948
	21st to end	Day	15% 7% 3 7% 4 4 4 4 5% 6% 40%	1650
March	1st to 10th	Day	16% 8% 3 6% 5% 4 5% 4 6% 5% 39%	4480
	11th to 20th	Day	9% 5% 2 6% 3 4 4 4 5% 6% 52%	4905
	21st to end	Day	15% 6% 2 5% 4 4 4 4 5% 6% 43%	5498
April	1st to 10th	Day	12% 6% 3 6% 4 4 4 4 5% 7% 46%	2400
	11th to 20th	Day	10% 6% 2 6% 5% 4 4 3 5% 7% 48%	2374
	21st to end	Day	6% 4 1 5% 3 5% 5% 4 6% 8% 53%	2400
May	1st to 10th	Day	13% 7% 3 8% 4 5% 4 4 6% 7% 40%	5803
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 4 8% 10% 36%	5861
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 10% 45%	6433
June	1st to 10th	Day	8% 6% 3 8% 5% 7% 6% 6% 9% 10% 33%	2600
	11th to 20th	Day	6% 4 2 6% 7% 6% 6% 7% 10% 11% 36%	2600
	21st to end	Day	5% 5% 3 8% 7% 8% 8% 7% 9% 10% 31%	2600
July	1st to 10th	Day	8% 6% 3 8% 7% 8% 8% 7% 10% 11% 25%	5900
	11th to 20th	Day	5% 4 2 7% 6% 7% 8% 6% 10% 12% 34%	5900
	21st to end	Day	5% 5% 3 8% 7% 7% 8% 7% 11% 14% 25%	6253
August	1st to 10th	Day	6% 4 2 5% 5% 6% 7% 6% 10% 13% 37%	3905
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 5% 6% 8% 48%	3849
	21st to end	Day	6% 5% 2 6% 5% 7% 7% 6% 9% 10% 38%	4312
September	1st to 10th	Day	10% 6% 2 6% 6% 6% 6% 6% 8% 9% 34%	2285
	11th to 20th	Day	13% 7% 2 7% 4 5% 6% 4 6% 9% 39%	2200
	21st to end	Day	10% 4 2 7% 4 5% 4 4 5% 8% 47%	2200
October	1st to 10th	Day	9% 6% 2 6% 4 4 4 3 5% 6% 51%	2200
	11th to 20th	Day	10% 4 2 4 3 3 3 2 5% 7% 58%	2200
	21st to end	Day	10% 5% 2 5% 3 3 3 3 4 6% 56%	2176
November	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 4 5% 54%	1852
	11th to 20th	Day	12% 6% 1 4 3 3 4 3 3 5% 55%	1890
	21st to end	Day	13% 6% 2 5% 4 3 4 3 5% 7% 47%	1890
December	1st to 10th	Day	17% 6% 2 5% 3 3 3 3 4 5% 49%	3020
	11th to 20th	Day	13% 8% 2 6% 4 4 4 3 4 5% 48%	3463
	21st to end	Day	19% 6% 3 5% 3 3 4 3 3 5% 45%	4565
January	1st to 10th	Night	15% 6% 4 5% 3 3 4 3 4 5% 49%	5903
	11th to 20th	Night	13% 8% 3 7% 4 4 4 3 4 6% 44%	5670
	21st to end	Night	18% 11% 2 6% 3 3 3 2 5% 6% 40%	5984
February	1st to 10th	Night	15% 8% 3 6% 4 4 3 3 5% 6% 42%	2400
	11th to 20th	Night	19% 8% 2 5% 3 3 3 3 3 6% 46%	2338
	21st to end	Night	15% 8% 3 6% 4 4 4 3 5% 6% 44%	1980
March	1st to 10th	Night	21% 9% 3 6% 4 3 3 3 5% 6% 36%	5373
	11th to 20th	Night	11% 7% 2 5% 4 4 4 3 5% 7% 48%	5054
	21st to end	Night	11% 6% 3 7% 4 4 4 3 5% 6% 47%	5467
April	1st to 10th	Night	12% 5% 2 5% 5% 3 4 4 5% 7% 47%	2005
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 6% 8% 49%	1975
	21st to end	Night	7% 4 2 5% 4 4 4 3 6% 7% 55%	2000
May	1st to 10th	Night	10% 6% 2 6% 5% 4 4 4 6% 10% 42%	4089
	11th to 20th	Night	15% 6% 2 6% 4 5% 4 4 6% 9% 38%	4032
	21st to end	Night	6% 4 2 6% 4 4 6% 5% 9% 12% 43%	4421
June	1st to 10th	Night	8% 6% 3 7% 7% 6% 5% 5% 9% 10% 35%	1800
	11th to 20th	Night	5% 5% 2 5% 4 5% 6% 5% 8% 13% 43%	1800
	21st to end	Night	5% 4 3 7% 7% 6% 6% 6% 9% 12% 36%	1800
July	1st to 10th	Night	8% 7% 3 9% 6% 6% 8% 7% 10% 12% 23%	4058
	11th to 20th	Night	5% 4 2 6% 6% 6% 7% 6% 10% 15% 34%	4057
	21st to end	Night	6% 7% 3 9% 7% 7% 7% 7% 8% 13% 27%	4594
August	1st to 10th	Night	6% 5% 3 7% 5% 6% 6% 7% 9% 14% 33%	3244
	11th to 20th	Night	5% 4 2 5% 4 6% 6% 4 8% 11% 46%	3200
	21st to end	Night	7% 5% 2 5% 4 5% 6% 5% 8% 12% 41%	3586
September	1st to 10th	Night	9% 7% 3 7% 4 6% 5% 5% 9% 9% 36%	2093
	11th to 20th	Night	13% 6% 2 6% 5% 4 5% 4 5% 8% 42%	2200
	21st to end	Night	8% 6% 2 6% 4 5% 4 4 6% 7% 49%	2200
October	1st to 10th	Night	7% 6% 2 6% 4 3 4 3 5% 6% 55%	2200
	11th to 20th	Night	8% 4 2 3 3 3 4 3 5% 5% 61%	2200
	21st to end	Night	11% 6% 2 5% 3 3 3 2 4 5% 57%	2655
November	1st to 10th	Night	10% 4 2 3 3 3 4 3 5% 6% 58%	2666
	11th to 20th	Night	12% 5% 1 4 3 3 3 2 4 6% 57%	2730
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 6% 49%	2730
December	1st to 10th	Night	15% 7% 2 5% 3 2 2 2 4 7% 52%	4380
	11th to 20th	Night	15% 5% 2 5% 4 3 3 3 4 5% 51%	4952
	21st to end	Night	18% 7% 2 5% 3 3 3 3 4 5% 45%	6633

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	34% 4 5% 18% 32% 7%	4066
	11th to 20th	Day	33% 4 5% 15% 32% 12%	4272
	21st to end	Day	46% 4 8% 13% 16% 13%	4972
February	1st to 10th	Day	46% 5% 7% 14% 20% 9%	2000
	11th to 20th	Day	42% 4 5% 16% 23% 10%	1958
	21st to end	Day	43% 5% 6% 17% 17% 11%	1650
March	1st to 10th	Day	45% 4 8% 16% 18% 9%	4480
	11th to 20th	Day	31% 6% 7% 14% 22% 21%	4905
	21st to end	Day	40% 5% 9% 18% 17% 11%	5500
April	1st to 10th	Day	37% 6% 9% 21% 17% 11%	2400
	11th to 20th	Day	36% 4 8% 19% 23% 10%	2374
	21st to end	Day	28% 6% 11% 25% 25% 5%	2400
May	1st to 10th	Day	41% 7% 11% 25% 15% 2	5839
	11th to 20th	Day	39% 8% 18% 23% 11% 1	5865
	21st to end	Day	32% 8% 15% 25% 18% 1	6447
June	1st to 10th	Day	42% 10% 15% 21% 10% 2	2600
	11th to 20th	Day	36% 10% 19% 20% 13% 2	2600
	21st to end	Day	41% 12% 17% 18% 9% 3	2600
July	1st to 10th	Day	44% 15% 23% 14% 4	5835
	11th to 20th	Day	37% 14% 29% 17% 2	5831
	21st to end	Day	42% 16% 23% 16% 2	6072
August	1st to 10th	Day	33% 10% 18% 26% 12% 1	3893
	11th to 20th	Day	32% 7% 16% 26% 18% 1	3885
	21st to end	Day	35% 11% 22% 20% 12% 1	4311
September	1st to 10th	Day	42% 11% 16% 13% 14% 4	2285
	11th to 20th	Day	42% 8% 11% 18% 17% 4	2200
	21st to end	Day	35% 7% 10% 20% 23% 6%	2200
October	1st to 10th	Day	32% 3 6% 12% 21% 26%	3590
	11th to 20th	Day	17% 3 4 16% 25% 35%	3568
	21st to end	Day	20% 2 4 16% 41% 16%	3490
November	1st to 10th	Day	32% 4 7% 16% 26% 15%	1852
	11th to 20th	Day	32% 4 7% 15% 28% 14%	1890
	21st to end	Day	36% 4 9% 18% 22% 11%	1890
December	1st to 10th	Day	38% 3 7% 16% 29% 6%	3020
	11th to 20th	Day	39% 4 7% 21% 23% 8%	3460
	21st to end	Day	42% 4 4 21% 25% 4	4565
January	1st to 10th	Night	37% 4 5% 15% 30% 8%	5903
	11th to 20th	Night	41% 4 5% 14% 26% 10%	5670
	21st to end	Night	46% 3 6% 16% 21% 8%	5984
February	1st to 10th	Night	43% 4 6% 15% 20% 11%	2400
	11th to 20th	Night	42% 4 6% 14% 22% 13%	2339
	21st to end	Night	42% 3 8% 17% 17% 14%	1980
March	1st to 10th	Night	48% 4 6% 13% 19% 9%	5373
	11th to 20th	Night	36% 4 8% 13% 19% 20%	5054
	21st to end	Night	37% 4 9% 19% 19% 12%	5467
April	1st to 10th	Night	37% 5% 9% 16% 20% 12%	2005
	11th to 20th	Night	33% 4 8% 20% 24% 11%	1975
	21st to end	Night	28% 4 9% 27% 23% 8%	2000
May	1st to 10th	Night	36% 9% 17% 20% 15% 3	4116
	11th to 20th	Night	40% 8% 15% 24% 10% 2	4033
	21st to end	Night	29% 9% 18% 26% 16% 2	4429
June	1st to 10th	Night	40% 10% 15% 19% 14% 1	1800
	11th to 20th	Night	30% 10% 22% 23% 13% 2	1800
	21st to end	Night	36% 12% 17% 20% 10% 4	1800
July	1st to 10th	Night	46% 16% 24% 11% 3 1	4015
	11th to 20th	Night	34% 15% 31% 15% 3	4006
	21st to end	Night	45% 14% 20% 17% 3	4461
August	1st to 10th	Night	35% 13% 19% 25% 7% 2	3232
	11th to 20th	Night	29% 10% 20% 24% 15% 2	3230
	21st to end	Night	33% 10% 21% 22% 12% 2	3586
September	1st to 10th	Night	40% 10% 17% 14% 13% 6%	2093
	11th to 20th	Night	39% 8% 12% 18% 18% 6%	2200
	21st to end	Night	34% 7% 11% 18% 21% 9%	2200
October	1st to 10th	Night	33% 4 8% 12% 23% 20%	3590
	11th to 20th	Night	16% 2 4 14% 30% 33%	3571
	21st to end	Night	21% 2 4 17% 36% 20%	4291
November	1st to 10th	Night	29% 3 7% 19% 25% 17%	2666
	11th to 20th	Night	31% 3 6% 16% 31% 14%	2730
	21st to end	Night	36% 4 8% 18% 21% 13%	2730
December	1st to 10th	Night	35% 3 6% 20% 28% 8%	4380
	11th to 20th	Night	37% 4 6% 21% 25% 7%	4954
	21st to end	Night	41% 4 5% 19% 27% 3	6633

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	23% 19% 38% 17% 3	303
	11th to 20th	Day	20% 19% 37% 17% 6% 2	300
	21st to end	Day	22% 23% 38% 14% 3 1	330
February	1st to 10th	Day	25% 20% 30% 21% 4	300
	11th to 20th	Day	29% 22% 35% 13% 1	300
	21st to end	Day	18% 23% 44% 13% 2	249
March	1st to 10th	Day	19% 22% 37% 17% 4	300
	11th to 20th	Day	18% 17% 34% 22% 8% 1	464
	21st to end	Day	18% 18% 30% 25% 8% 1	550
April	1st to 10th	Day	19% 16% 29% 23% 12% 2	500
	11th to 20th	Day	14% 11% 36% 24% 12% 2	492
	21st to end	Day	9% 10% 27% 32% 17% 5%	500
May	1st to 10th	Day	10% 8% 26% 29% 21% 5%	503
	11th to 20th	Day	9% 4 24% 33% 21% 10%	527
	21st to end	Day	10% 4 18% 30% 22% 16%	573
June	1st to 10th	Day	10% 3 14% 32% 27% 15%	530
	11th to 20th	Day	9% 3 11% 27% 32% 19%	530
	21st to end	Day	6% 2 12% 25% 32% 24%	530
July	1st to 10th	Day	7% 2 7% 20% 36% 28%	525
	11th to 20th	Day	6% 2 4 17% 38% 33%	524
	21st to end	Day	3 2 6% 22% 38% 29%	576
August	1st to 10th	Day	10% 3 6% 19% 33% 29%	526
	11th to 20th	Day	8% 2 7% 20% 36% 28%	519
	21st to end	Day	9% 3 10% 26% 30% 21%	583
September	1st to 10th	Day	12% 3 10% 25% 31% 18%	530
	11th to 20th	Day	16% 2 10% 29% 30% 12%	530
	21st to end	Day	11% 2 15% 28% 32% 12%	530
October	1st to 10th	Day	13% 5% 25% 32% 20% 5%	530
	11th to 20th	Day	11% 5% 21% 33% 23% 6%	530
	21st to end	Day	16% 9% 24% 29% 19% 3	513
November	1st to 10th	Day	18% 8% 24% 34% 12% 4	330
	11th to 20th	Day	14% 12% 36% 27% 10% 2	330
	21st to end	Day	14% 18% 35% 25% 7% 1	330
December	1st to 10th	Day	25% 14% 35% 20% 6% 1	330
	11th to 20th	Day	26% 16% 31% 21% 5% 1	330
	21st to end	Day	23% 12% 32% 26% 6% 1	363
January	1st to 10th	Night	20% 17% 31% 27% 5%	805
	11th to 20th	Night	19% 16% 28% 29% 8%	800
	21st to end	Night	20% 15% 36% 26% 3	880
February	1st to 10th	Night	20% 12% 31% 31% 7%	800
	11th to 20th	Night	23% 14% 31% 26% 7%	783
	21st to end	Night	18% 14% 38% 27% 3	660
March	1st to 10th	Night	15% 14% 33% 31% 6%	800
	11th to 20th	Night	13% 13% 35% 27% 12%	800
	21st to end	Night	15% 13% 32% 29% 10%	880
April	1st to 10th	Night	15% 11% 30% 31% 13%	605
	11th to 20th	Night	12% 9% 32% 27% 18% 2	593
	21st to end	Night	7% 9% 26% 36% 21% 1	600
May	1st to 10th	Night	9% 4 28% 32% 24% 4	600
	11th to 20th	Night	9% 5% 22% 33% 26% 4	591
	21st to end	Night	9% 1 12% 37% 36% 5%	650
June	1st to 10th	Night	11% 2 11% 35% 34% 8%	600
	11th to 20th	Night	5% 2 9% 32% 41% 11%	600
	21st to end	Night	5% 1 8% 30% 44% 12%	600
July	1st to 10th	Night	7% 2 5% 22% 47% 17%	585
	11th to 20th	Night	8% 1 3 20% 46% 21%	582
	21st to end	Night	5% 2 6% 25% 47% 15%	657
August	1st to 10th	Night	9% 1 4 26% 37% 23%	597
	11th to 20th	Night	8% 2 6% 20% 52% 12%	594
	21st to end	Night	12% 3 7% 26% 37% 16%	660
September	1st to 10th	Night	12% 1 8% 28% 38% 12%	693
	11th to 20th	Night	15% 3 9% 34% 33% 6%	800
	21st to end	Night	11% 2 13% 31% 36% 7%	800
October	1st to 10th	Night	9% 4 23% 38% 23% 4	800
	11th to 20th	Night	10% 5% 23% 32% 27% 3	800
	21st to end	Night	14% 6% 23% 34% 21% 2	880
November	1st to 10th	Night	12% 6% 23% 36% 21% 2	820
	11th to 20th	Night	14% 10% 26% 33% 16% 1	840
	21st to end	Night	16% 11% 28% 30% 14% 1	840
December	1st to 10th	Night	18% 11% 28% 31% 11% 1	840
	11th to 20th	Night	20% 8% 30% 30% 10% 1	840
	21st to end	Night	24% 11% 27% 28% 9%	924

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