Rensselaerville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rensselaerville clear sky chart from 2005-11-06 to 2025-07-21.

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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	120139
	Night	16% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	118960
Transparency	Day	47% 7% 12% 20% 12% 2	123672
	Night	46% 6% 13% 20% 12% 1	123588
Seeing	Day	25% 17% 29% 19% 8% 2	15692
	Night	23% 16% 29% 23% 8% 1	24767

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	9% 9% 4 15% 5% 6% 5% 4 5% 9% 28%	3597
	11th to 20th	Day	12% 13% 4 12% 6% 5% 5% 4 6% 6% 27%	3570
	21st to end	Day	13% 11% 5% 10% 6% 4 5% 4 5% 6% 32%	4167
February	1st to 10th	Day	13% 13% 4 10% 6% 6% 6% 5% 7% 6% 24%	1800
	11th to 20th	Day	10% 9% 5% 12% 7% 6% 6% 4 6% 7% 29%	1906
	21st to end	Day	16% 12% 3 8% 5% 4 4 5% 5% 6% 31%	1650
March	1st to 10th	Day	19% 10% 4 9% 6% 5% 5% 3 5% 5% 30%	4476
	11th to 20th	Day	13% 9% 4 8% 6% 5% 4 3 5% 6% 36%	4768
	21st to end	Day	17% 10% 3 8% 5% 5% 5% 4 5% 5% 34%	5920
April	1st to 10th	Day	16% 11% 4 8% 6% 4 4 3 5% 6% 33%	2400
	11th to 20th	Day	15% 10% 3 7% 5% 5% 5% 3 5% 5% 37%	2374
	21st to end	Day	18% 9% 2 8% 5% 5% 5% 4 5% 6% 34%	2465
May	1st to 10th	Day	29% 10% 3 7% 5% 5% 5% 3 5% 6% 24%	6040
	11th to 20th	Day	16% 8% 3 8% 6% 6% 5% 4 6% 7% 31%	6318
	21st to end	Day	18% 7% 2 6% 5% 5% 5% 5% 8% 9% 29%	6949
June	1st to 10th	Day	16% 7% 3 8% 6% 5% 5% 4 7% 9% 31%	2800
	11th to 20th	Day	15% 6% 3 7% 5% 5% 6% 5% 6% 9% 33%	2800
	21st to end	Day	15% 7% 2 7% 5% 5% 5% 5% 6% 8% 33%	2800
July	1st to 10th	Day	9% 6% 2 7% 6% 6% 7% 5% 7% 10% 35%	4580
	11th to 20th	Day	9% 5% 2 6% 5% 6% 6% 6% 8% 11% 35%	4580
	21st to end	Day	13% 6% 3 8% 6% 6% 6% 5% 7% 8% 33%	4814
August	1st to 10th	Day	16% 6% 2 8% 5% 5% 6% 4 6% 7% 33%	4360
	11th to 20th	Day	12% 7% 3 7% 6% 6% 5% 4 8% 10% 32%	3739
	21st to end	Day	12% 5% 2 6% 4 5% 6% 5% 8% 10% 38%	4180
September	1st to 10th	Day	13% 7% 2 6% 4 4 5% 4 5% 7% 42%	2280
	11th to 20th	Day	13% 5% 2 6% 3 4 4 3 5% 7% 48%	2207
	21st to end	Day	16% 6% 2 5% 4 4 5% 4 7% 8% 39%	2090
October	1st to 10th	Day	17% 9% 3 7% 4 5% 5% 4 5% 5% 36%	1962
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 4 5% 7% 40%	1900
	21st to end	Day	19% 9% 3 7% 6% 4 5% 4 5% 6% 31%	1910
November	1st to 10th	Day	12% 9% 3 6% 5% 5% 4 4 4 6% 42%	1761
	11th to 20th	Day	13% 9% 3 8% 5% 5% 6% 4 4 6% 36%	1800
	21st to end	Day	15% 10% 4 6% 6% 5% 6% 4 5% 6% 33%	1630
December	1st to 10th	Day	12% 13% 5% 11% 7% 6% 6% 5% 6% 7% 23%	2600
	11th to 20th	Day	18% 11% 3 8% 6% 4 5% 4 4 7% 30%	2986
	21st to end	Day	15% 11% 7% 9% 5% 4 5% 4 6% 8% 25%	3960
January	1st to 10th	Night	12% 9% 4 12% 7% 5% 5% 4 7% 8% 28%	6349
	11th to 20th	Night	9% 11% 4 11% 7% 5% 6% 5% 6% 8% 26%	6315
	21st to end	Night	14% 10% 4 10% 7% 6% 5% 3 5% 6% 30%	6787
February	1st to 10th	Night	13% 13% 4 8% 7% 5% 5% 4 6% 7% 28%	2600
	11th to 20th	Night	11% 9% 4 11% 7% 6% 5% 5% 6% 8% 28%	2378
	21st to end	Night	15% 9% 3 8% 6% 5% 5% 4 6% 8% 30%	1980
March	1st to 10th	Night	17% 9% 3 8% 6% 4 4 4 6% 7% 32%	5364
	11th to 20th	Night	15% 8% 3 7% 6% 4 5% 4 5% 7% 37%	5173
	21st to end	Night	18% 10% 3 8% 5% 4 5% 3 5% 6% 34%	5010
April	1st to 10th	Night	16% 10% 3 9% 7% 6% 5% 4 6% 7% 28%	2000
	11th to 20th	Night	19% 8% 3 7% 4 5% 4 3 5% 7% 35%	1975
	21st to end	Night	18% 8% 3 7% 4 3 4 4 6% 5% 37%	1933
May	1st to 10th	Night	30% 9% 3 7% 4 4 4 3 5% 6% 25%	3930
	11th to 20th	Night	17% 9% 4 8% 4 5% 4 4 6% 6% 33%	3575
	21st to end	Night	17% 8% 3 8% 5% 4 5% 4 7% 8% 30%	3926
June	1st to 10th	Night	15% 7% 3 7% 5% 4 4 4 5% 7% 40%	1600
	11th to 20th	Night	14% 6% 2 5% 4 3 4 4 8% 10% 39%	1600
	21st to end	Night	10% 5% 1 5% 5% 5% 4 4 7% 11% 43%	1600
July	1st to 10th	Night	9% 6% 2 7% 6% 4 5% 5% 7% 8% 43%	2600
	11th to 20th	Night	13% 5% 3 5% 4 4 5% 4 7% 9% 42%	2600
	21st to end	Night	14% 6% 2 6% 4 5% 5% 4 6% 7% 41%	2739
August	1st to 10th	Night	18% 6% 2 6% 4 4 5% 4 6% 7% 38%	2565
	11th to 20th	Night	14% 7% 3 7% 4 4 4 4 5% 7% 42%	3057
	21st to end	Night	12% 5% 1 5% 3 3 4 3 5% 8% 49%	3476
September	1st to 10th	Night	12% 6% 2 5% 5% 4 5% 3 6% 6% 45%	1900
	11th to 20th	Night	13% 4 1 4 3 3 4 2 6% 6% 53%	1972
	21st to end	Night	14% 5% 2 6% 4 5% 4 4 4 7% 45%	2090
October	1st to 10th	Night	20% 7% 2 7% 3 4 4 3 5% 6% 38%	2213
	11th to 20th	Night	15% 7% 2 6% 4 4 4 4 6% 7% 41%	2280
	21st to end	Night	20% 8% 3 7% 4 4 4 4 6% 6% 34%	2687
November	1st to 10th	Night	13% 9% 2 7% 4 4 5% 3 5% 7% 42%	2537
	11th to 20th	Night	15% 9% 3 6% 5% 5% 5% 4 6% 7% 36%	2600
	21st to end	Night	13% 9% 3 7% 5% 5% 5% 4 6% 7% 36%	2765
December	1st to 10th	Night	15% 11% 3 8% 4 5% 6% 4 7% 9% 28%	4580
	11th to 20th	Night	22% 9% 3 7% 5% 4 4 4 5% 5% 33%	5208
	21st to end	Night	20% 11% 5% 9% 5% 5% 4 3 5% 6% 27%	6996

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	50% 5% 12% 22% 10% 1	3598
	11th to 20th	Day	55% 6% 11% 14% 10% 3	3600
	21st to end	Day	51% 6% 10% 20% 12% 1	4167
February	1st to 10th	Day	57% 6% 13% 14% 9% 1	1800
	11th to 20th	Day	51% 8% 9% 21% 10% 2	1915
	21st to end	Day	52% 6% 11% 18% 13% 1	1650
March	1st to 10th	Day	54% 5% 11% 14% 11% 5%	4479
	11th to 20th	Day	46% 6% 16% 21% 7% 4	4768
	21st to end	Day	50% 5% 7% 14% 20% 4	5920
April	1st to 10th	Day	51% 4 9% 21% 12% 2	2400
	11th to 20th	Day	48% 5% 11% 20% 15% 2	2374
	21st to end	Day	50% 5% 11% 18% 13% 3	2465
May	1st to 10th	Day	59% 8% 8% 15% 9% 1	6051
	11th to 20th	Day	49% 8% 12% 21% 9% 1	6322
	21st to end	Day	47% 9% 13% 22% 9% 1	6949
June	1st to 10th	Day	47% 7% 13% 20% 12% 1	2800
	11th to 20th	Day	45% 8% 15% 21% 11% 1	2800
	21st to end	Day	46% 7% 15% 21% 12% 1	2800
July	1st to 10th	Day	42% 8% 14% 23% 12% 1	4510
	11th to 20th	Day	40% 8% 17% 24% 11% 1	4505
	21st to end	Day	47% 7% 14% 20% 12% 1	4661
August	1st to 10th	Day	48% 8% 14% 19% 10% 1	4346
	11th to 20th	Day	44% 8% 17% 26% 5%	3775
	21st to end	Day	36% 7% 14% 31% 10% 1	4180
September	1st to 10th	Day	40% 6% 13% 25% 16% 1	2280
	11th to 20th	Day	35% 6% 13% 26% 19% 2	2207
	21st to end	Day	40% 7% 13% 24% 14% 2	2090
October	1st to 10th	Day	42% 6% 10% 21% 20% 1	3261
	11th to 20th	Day	35% 5% 11% 26% 18% 4	3140
	21st to end	Day	35% 7% 15% 27% 12% 3	3122
November	1st to 10th	Day	41% 6% 13% 25% 14% 2	1761
	11th to 20th	Day	47% 5% 12% 19% 15% 2	1800
	21st to end	Day	50% 6% 15% 20% 8% 1	1630
December	1st to 10th	Day	57% 7% 11% 19% 4	2600
	11th to 20th	Day	52% 5% 14% 18% 10% 1	2986
	21st to end	Day	54% 6% 11% 15% 11% 2	3960
January	1st to 10th	Night	50% 7% 14% 17% 12% 1	6349
	11th to 20th	Night	52% 6% 16% 13% 10% 3	6360
	21st to end	Night	53% 5% 12% 13% 15% 3	6787
February	1st to 10th	Night	53% 7% 12% 18% 9% 1	2600
	11th to 20th	Night	52% 7% 12% 18% 11% 1	2380
	21st to end	Night	50% 6% 13% 20% 9% 2	1980
March	1st to 10th	Night	50% 5% 13% 17% 13% 2	5374
	11th to 20th	Night	45% 6% 18% 20% 8% 2	5174
	21st to end	Night	50% 5% 7% 16% 20% 2	5010
April	1st to 10th	Night	53% 5% 12% 19% 10% 1	2000
	11th to 20th	Night	47% 5% 12% 19% 15% 1	1975
	21st to end	Night	45% 6% 12% 19% 15% 3	1933
May	1st to 10th	Night	59% 7% 11% 12% 10% 2	3936
	11th to 20th	Night	48% 8% 11% 23% 9% 1	3576
	21st to end	Night	49% 8% 14% 18% 10% 1	3927
June	1st to 10th	Night	42% 7% 11% 24% 14% 2	1600
	11th to 20th	Night	39% 8% 16% 26% 12%	1600
	21st to end	Night	34% 9% 17% 25% 13% 1	1600
July	1st to 10th	Night	37% 8% 16% 22% 15% 1	2560
	11th to 20th	Night	36% 8% 17% 25% 13%	2552
	21st to end	Night	42% 6% 12% 26% 12% 1	2651
August	1st to 10th	Night	44% 8% 15% 24% 9%	2555
	11th to 20th	Night	41% 7% 16% 27% 9%	3087
	21st to end	Night	31% 7% 12% 38% 12% 1	3476
September	1st to 10th	Night	38% 7% 11% 29% 15% 1	1900
	11th to 20th	Night	31% 5% 14% 26% 23% 1	1972
	21st to end	Night	40% 5% 13% 24% 17% 1	2090
October	1st to 10th	Night	45% 5% 12% 23% 14% 1	3694
	11th to 20th	Night	32% 6% 14% 24% 21% 4	3779
	21st to end	Night	37% 6% 16% 29% 11% 1	4425
November	1st to 10th	Night	41% 5% 12% 22% 17% 2	2537
	11th to 20th	Night	45% 6% 13% 22% 13% 2	2600
	21st to end	Night	45% 6% 18% 23% 7% 1	2765
December	1st to 10th	Night	48% 8% 14% 25% 5%	4580
	11th to 20th	Night	53% 4 14% 15% 14% 1	5208
	21st to end	Night	56% 6% 10% 14% 11% 3	6996

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	32% 25% 31% 10% 4 1	200
	11th to 20th	Day	39% 23% 26% 10% 3 1	200
	21st to end	Day	28% 24% 34% 11% 3	265
February	1st to 10th	Day	38% 27% 26% 8% 1	300
	11th to 20th	Day	36% 27% 27% 9% 1	454
	21st to end	Day	32% 22% 33% 12% 1	414
March	1st to 10th	Day	33% 21% 32% 12% 2	500
	11th to 20th	Day	34% 23% 28% 12% 3 1	500
	21st to end	Day	35% 23% 26% 10% 3 2	550
April	1st to 10th	Day	36% 23% 24% 11% 5% 1	500
	11th to 20th	Day	31% 26% 24% 13% 4 2	492
	21st to end	Day	33% 19% 30% 12% 5% 2	500
May	1st to 10th	Day	33% 19% 27% 14% 5% 2	503
	11th to 20th	Day	20% 20% 30% 21% 7% 2	527
	21st to end	Day	20% 11% 33% 24% 10% 3	573
June	1st to 10th	Day	21% 14% 31% 23% 10% 1	530
	11th to 20th	Day	19% 13% 32% 24% 10% 2	530
	21st to end	Day	17% 16% 32% 24% 9% 2	530
July	1st to 10th	Day	12% 11% 31% 29% 14% 3	525
	11th to 20th	Day	13% 8% 30% 32% 13% 4	524
	21st to end	Day	13% 8% 37% 25% 13% 3	532
August	1st to 10th	Day	12% 8% 29% 30% 16% 5%	486
	11th to 20th	Day	14% 7% 30% 29% 13% 6%	479
	21st to end	Day	14% 11% 28% 27% 14% 7%	539
September	1st to 10th	Day	17% 10% 28% 23% 16% 7%	490
	11th to 20th	Day	15% 9% 27% 22% 17% 11%	490
	21st to end	Day	22% 9% 28% 24% 13% 4	490
October	1st to 10th	Day	26% 12% 26% 19% 14% 4	490
	11th to 20th	Day	23% 17% 28% 24% 8% 2	490
	21st to end	Day	27% 17% 30% 19% 7% 1	444
November	1st to 10th	Day	24% 19% 25% 21% 10% 1	395
	11th to 20th	Day	31% 21% 26% 17% 4 1	400
	21st to end	Day	29% 23% 29% 18% 1	230
December	1st to 10th	Day	31% 25% 26% 15% 4 1	200
	11th to 20th	Day	39% 19% 33% 8% 2	200
	21st to end	Day	30% 19% 35% 13% 4	220
January	1st to 10th	Night	27% 24% 31% 16% 2	800
	11th to 20th	Night	28% 18% 32% 18% 3	800
	21st to end	Night	22% 24% 36% 17% 2	880
February	1st to 10th	Night	26% 22% 35% 16% 1	800
	11th to 20th	Night	27% 25% 32% 16%	783
	21st to end	Night	29% 21% 32% 15% 3	660
March	1st to 10th	Night	29% 21% 32% 15% 3	800
	11th to 20th	Night	25% 26% 28% 18% 3	800
	21st to end	Night	29% 22% 30% 15% 4 1	880
April	1st to 10th	Night	28% 22% 31% 17% 3	800
	11th to 20th	Night	26% 21% 30% 17% 6%	791
	21st to end	Night	25% 20% 29% 20% 6%	733
May	1st to 10th	Night	31% 15% 27% 21% 5% 1	554
	11th to 20th	Night	20% 16% 34% 24% 5% 1	394
	21st to end	Night	16% 8% 30% 34% 11% 1	433
June	1st to 10th	Night	19% 10% 31% 26% 13% 1	400
	11th to 20th	Night	19% 11% 28% 31% 12%	400
	21st to end	Night	12% 7% 32% 35% 13% 1	400
July	1st to 10th	Night	12% 7% 22% 39% 18% 1	390
	11th to 20th	Night	14% 7% 21% 38% 18% 2	388
	21st to end	Night	14% 5% 24% 42% 14%	416
August	1st to 10th	Night	12% 4 25% 37% 20% 2	411
	11th to 20th	Night	14% 6% 23% 36% 17% 4	722
	21st to end	Night	15% 7% 22% 35% 19% 2	836
September	1st to 10th	Night	15% 7% 27% 30% 19% 2	760
	11th to 20th	Night	16% 7% 25% 27% 19% 6%	760
	21st to end	Night	17% 9% 26% 33% 13% 2	760
October	1st to 10th	Night	24% 12% 22% 25% 15% 1	760
	11th to 20th	Night	21% 13% 29% 27% 9%	760
	21st to end	Night	27% 18% 27% 22% 6%	836
November	1st to 10th	Night	22% 17% 27% 25% 8% 1	780
	11th to 20th	Night	25% 18% 29% 21% 6% 2	800
	21st to end	Night	26% 20% 27% 22% 5% 1	800
December	1st to 10th	Night	25% 23% 32% 16% 4	800
	11th to 20th	Night	29% 18% 32% 19% 3	800
	21st to end	Night	30% 24% 26% 17% 3	880

Page generated at 2025-07-18 01:09:59. Version ac07

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