Glens Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glens Falls clear sky chart from 2005-11-06 to 2025-10-19.

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 8% 5% 5% 5% 4 6% 7% 33%	126687
	Night	17% 10% 3 8% 5% 5% 5% 4 5% 6% 33%	123043
Transparency	Day	48% 7% 13% 20% 10% 1	130165
	Night	50% 6% 12% 19% 11% 1	127652
Seeing	Day	21% 15% 30% 22% 10% 3	16004
	Night	21% 11% 30% 29% 9% 1	24978

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% 11% 7% 16% 7% 6% 5% 3 5% 5% 24%	3597
	11th to 20th	Day	11% 13% 6% 11% 7% 6% 6% 5% 5% 6% 24%	3570
	21st to end	Day	13% 10% 3 10% 6% 6% 5% 4 5% 7% 29%	4029
February	1st to 10th	Day	13% 13% 3 10% 7% 5% 5% 4 6% 7% 27%	1800
	11th to 20th	Day	12% 13% 5% 10% 5% 5% 5% 4 6% 6% 29%	1913
	21st to end	Day	18% 11% 4 8% 5% 4 4 3 5% 5% 32%	1650
March	1st to 10th	Day	20% 11% 5% 11% 5% 4 4 3 3 5% 30%	4476
	11th to 20th	Day	14% 10% 3 9% 5% 4 4 3 5% 6% 36%	4694
	21st to end	Day	20% 10% 3 7% 5% 4 4 3 4 5% 34%	5970
April	1st to 10th	Day	19% 10% 4 7% 5% 4 4 3 5% 6% 35%	2400
	11th to 20th	Day	17% 8% 2 8% 6% 4 4 4 5% 6% 37%	2374
	21st to end	Day	20% 8% 3 7% 5% 5% 4 4 5% 6% 33%	2513
May	1st to 10th	Day	30% 10% 3 8% 4 4 4 3 5% 6% 23%	6039
	11th to 20th	Day	15% 8% 4 10% 6% 5% 5% 5% 6% 7% 30%	6318
	21st to end	Day	18% 8% 3 7% 4 5% 5% 4 6% 8% 33%	6949
June	1st to 10th	Day	16% 7% 3 7% 6% 6% 5% 5% 7% 8% 31%	2800
	11th to 20th	Day	17% 6% 2 6% 5% 5% 5% 5% 6% 9% 34%	2800
	21st to end	Day	16% 7% 2 8% 6% 5% 5% 5% 6% 9% 32%	2800
July	1st to 10th	Day	9% 7% 2 8% 5% 6% 5% 5% 8% 10% 36%	6360
	11th to 20th	Day	8% 6% 2 7% 5% 6% 6% 6% 9% 12% 33%	6360
	21st to end	Day	13% 5% 2 6% 5% 6% 5% 5% 6% 9% 39%	6926
August	1st to 10th	Day	14% 5% 2 7% 5% 6% 6% 5% 6% 9% 35%	4563
	11th to 20th	Day	13% 6% 3 6% 5% 6% 6% 5% 8% 10% 31%	3895
	21st to end	Day	10% 6% 3 7% 4 5% 6% 5% 7% 9% 37%	4312
September	1st to 10th	Day	13% 4 1 5% 4 4 6% 4 6% 8% 45%	2400
	11th to 20th	Day	13% 5% 1 4 4 4 3 4 5% 8% 49%	2304
	21st to end	Day	16% 5% 3 5% 4 4 5% 4 5% 7% 41%	2200
October	1st to 10th	Day	19% 8% 2 8% 5% 5% 4 4 5% 5% 36%	2091
	11th to 20th	Day	15% 8% 2 7% 4 4 4 4 6% 7% 38%	1971
	21st to end	Day	24% 8% 3 7% 5% 6% 4 3 5% 6% 30%	1881
November	1st to 10th	Day	12% 9% 3 8% 4 4 4 3 6% 7% 39%	1761
	11th to 20th	Day	16% 8% 3 6% 5% 5% 5% 4 6% 6% 36%	1800
	21st to end	Day	19% 8% 3 7% 6% 5% 5% 4 5% 7% 33%	1625
December	1st to 10th	Day	19% 12% 6% 11% 6% 6% 4 3 5% 6% 22%	2600
	11th to 20th	Day	21% 11% 3 7% 5% 4 5% 3 4 7% 29%	2986
	21st to end	Day	23% 16% 4 7% 5% 3 4 3 5% 5% 26%	3960
January	1st to 10th	Night	13% 12% 6% 11% 6% 5% 4 4 5% 6% 28%	6349
	11th to 20th	Night	10% 12% 5% 14% 8% 7% 6% 4 6% 6% 22%	6315
	21st to end	Night	15% 12% 4 9% 6% 5% 5% 4 5% 6% 29%	6925
February	1st to 10th	Night	13% 13% 5% 10% 7% 5% 6% 4 6% 6% 26%	2600
	11th to 20th	Night	12% 11% 4 9% 6% 5% 4 5% 6% 6% 32%	2372
	21st to end	Night	15% 10% 4 9% 5% 4 5% 4 5% 5% 33%	1980
March	1st to 10th	Night	21% 9% 3 8% 6% 5% 4 4 5% 5% 30%	5364
	11th to 20th	Night	16% 11% 3 7% 4 4 4 3 4 7% 36%	5261
	21st to end	Night	20% 12% 4 9% 4 4 4 3 4 4 32%	4962
April	1st to 10th	Night	20% 8% 3 7% 5% 4 4 3 4 6% 35%	2000
	11th to 20th	Night	19% 9% 3 7% 5% 5% 3 3 5% 6% 35%	1975
	21st to end	Night	19% 9% 2 6% 4 4 4 4 5% 5% 38%	1885
May	1st to 10th	Night	31% 9% 3 7% 5% 4 4 3 4 6% 24%	3944
	11th to 20th	Night	17% 10% 4 9% 6% 5% 5% 3 5% 7% 30%	3575
	21st to end	Night	17% 9% 3 8% 5% 5% 5% 5% 5% 7% 31%	3926
June	1st to 10th	Night	19% 6% 2 5% 5% 5% 5% 4 7% 6% 37%	1600
	11th to 20th	Night	17% 7% 3 7% 4 4 4 3 6% 8% 39%	1600
	21st to end	Night	16% 5% 2 5% 5% 5% 5% 4 6% 7% 40%	1600
July	1st to 10th	Night	10% 7% 3 7% 5% 5% 5% 5% 7% 9% 38%	3600
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 4 6% 8% 36%	3600
	21st to end	Night	10% 6% 2 6% 4 5% 4 4 6% 8% 46%	3926
August	1st to 10th	Night	18% 8% 3 6% 4 4 5% 3 6% 7% 37%	2586
	11th to 20th	Night	15% 6% 3 7% 4 4 5% 4 7% 8% 36%	3117
	21st to end	Night	10% 5% 2 5% 4 4 6% 6% 8% 9% 41%	3586
September	1st to 10th	Night	13% 6% 2 6% 4 3 4 4 5% 7% 46%	2000
	11th to 20th	Night	12% 5% 1 5% 3 3 3 3 5% 7% 52%	2095
	21st to end	Night	15% 5% 2 5% 4 4 5% 4 6% 6% 45%	2200
October	1st to 10th	Night	19% 9% 3 7% 5% 5% 3 4 5% 5% 35%	2305
	11th to 20th	Night	15% 7% 3 7% 5% 5% 4 4 6% 6% 38%	2386
	21st to end	Night	24% 8% 3 7% 5% 4 4 3 5% 6% 31%	2717
November	1st to 10th	Night	14% 8% 2 9% 4 5% 4 3 4 6% 40%	2537
	11th to 20th	Night	18% 8% 3 7% 5% 3 3 3 6% 6% 39%	2600
	21st to end	Night	16% 10% 3 7% 5% 4 5% 4 5% 7% 34%	2771
December	1st to 10th	Night	17% 13% 5% 9% 6% 5% 5% 4 6% 7% 24%	4580
	11th to 20th	Night	26% 10% 3 7% 5% 4 4 3 4 5% 29%	5208
	21st to end	Night	23% 16% 4 7% 4 4 4 3 4 5% 25%	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	59% 8% 10% 18% 5%	3598
	11th to 20th	Day	59% 7% 11% 13% 8% 2	3600
	21st to end	Day	53% 6% 10% 17% 12% 2	4029
February	1st to 10th	Day	55% 8% 14% 15% 7% 1	1800
	11th to 20th	Day	56% 6% 12% 15% 9% 1	1922
	21st to end	Day	54% 6% 12% 16% 11% 1	1650
March	1st to 10th	Day	58% 6% 9% 13% 9% 7%	4479
	11th to 20th	Day	45% 9% 19% 16% 8% 3	4694
	21st to end	Day	52% 5% 7% 15% 17% 5%	5970
April	1st to 10th	Day	51% 6% 9% 20% 12% 3	2400
	11th to 20th	Day	47% 8% 10% 19% 14% 2	2374
	21st to end	Day	50% 8% 10% 17% 12% 3	2513
May	1st to 10th	Day	61% 7% 9% 16% 7% 1	6050
	11th to 20th	Day	50% 9% 14% 18% 8% 1	6322
	21st to end	Day	48% 7% 14% 21% 9% 1	6949
June	1st to 10th	Day	47% 10% 14% 18% 10% 1	2800
	11th to 20th	Day	45% 8% 14% 19% 13% 1	2800
	21st to end	Day	47% 8% 14% 19% 11% 1	2800
July	1st to 10th	Day	41% 6% 15% 23% 13% 1	6290
	11th to 20th	Day	40% 7% 16% 26% 11% 1	6285
	21st to end	Day	41% 5% 14% 30% 10%	6728
August	1st to 10th	Day	45% 7% 16% 20% 12% 1	4549
	11th to 20th	Day	46% 7% 15% 25% 6%	3932
	21st to end	Day	41% 6% 15% 27% 11% 1	4312
September	1st to 10th	Day	36% 8% 13% 30% 13% 1	2400
	11th to 20th	Day	34% 7% 11% 28% 19% 1	2304
	21st to end	Day	40% 8% 13% 25% 13% 1	2200
October	1st to 10th	Day	47% 5% 7% 25% 14% 1	3403
	11th to 20th	Day	41% 6% 13% 26% 14% 1	3199
	21st to end	Day	40% 6% 13% 29% 11% 1	3081
November	1st to 10th	Day	42% 8% 16% 23% 11% 1	1761
	11th to 20th	Day	46% 8% 12% 17% 15% 1	1800
	21st to end	Day	52% 7% 17% 18% 6% 1	1625
December	1st to 10th	Day	62% 5% 13% 16% 3	2600
	11th to 20th	Day	55% 6% 12% 19% 8% 1	2986
	21st to end	Day	61% 5% 8% 14% 11%	3960
January	1st to 10th	Night	56% 8% 13% 14% 9%	6349
	11th to 20th	Night	61% 8% 10% 12% 8% 1	6360
	21st to end	Night	55% 5% 11% 13% 12% 4	6925
February	1st to 10th	Night	57% 8% 13% 15% 6% 1	2600
	11th to 20th	Night	52% 8% 12% 18% 9% 2	2374
	21st to end	Night	52% 7% 14% 19% 8% 2	1980
March	1st to 10th	Night	53% 8% 10% 14% 13% 3	5374
	11th to 20th	Night	47% 7% 19% 17% 8% 2	5262
	21st to end	Night	56% 4 6% 16% 17% 2	4962
April	1st to 10th	Night	51% 6% 10% 20% 11% 2	2000
	11th to 20th	Night	50% 6% 10% 20% 13% 1	1975
	21st to end	Night	47% 7% 10% 18% 15% 3	1885
May	1st to 10th	Night	61% 8% 10% 13% 8% 1	3950
	11th to 20th	Night	53% 8% 12% 18% 8% 1	3576
	21st to end	Night	51% 8% 12% 16% 11% 1	3927
June	1st to 10th	Night	44% 9% 13% 21% 11% 2	1600
	11th to 20th	Night	42% 8% 15% 22% 12% 1	1600
	21st to end	Night	41% 11% 13% 23% 12% 1	1600
July	1st to 10th	Night	43% 5% 17% 23% 12% 1	3560
	11th to 20th	Night	47% 5% 13% 19% 14%	3552
	21st to end	Night	38% 5% 12% 33% 11% 1	3809
August	1st to 10th	Night	47% 7% 15% 22% 9% 1	2576
	11th to 20th	Night	45% 6% 18% 21% 9%	3146
	21st to end	Night	39% 6% 15% 29% 11%	3586
September	1st to 10th	Night	37% 7% 14% 28% 14% 1	2000
	11th to 20th	Night	32% 6% 14% 29% 18% 1	2095
	21st to end	Night	40% 7% 12% 23% 15% 2	2200
October	1st to 10th	Night	51% 5% 10% 21% 12% 1	3773
	11th to 20th	Night	38% 6% 12% 26% 17% 1	3897
	21st to end	Night	46% 5% 12% 28% 9% 1	4467
November	1st to 10th	Night	45% 6% 13% 22% 13% 2	2537
	11th to 20th	Night	46% 6% 12% 21% 12% 2	2600
	21st to end	Night	49% 8% 17% 19% 7%	2771
December	1st to 10th	Night	61% 6% 13% 16% 4	4580
	11th to 20th	Night	57% 5% 11% 14% 11% 1	5208
	21st to end	Night	61% 6% 9% 15% 9% 1	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	24% 21% 32% 17% 7% 1	200
	11th to 20th	Day	27% 26% 31% 15% 1 1	200
	21st to end	Day	23% 22% 33% 17% 5% 1	235
February	1st to 10th	Day	27% 29% 31% 12% 1	300
	11th to 20th	Day	27% 25% 34% 12% 2	461
	21st to end	Day	27% 18% 36% 16% 3	414
March	1st to 10th	Day	27% 15% 34% 20% 4 1	500
	11th to 20th	Day	28% 21% 31% 15% 5%	500
	21st to end	Day	29% 21% 26% 15% 7% 2	550
April	1st to 10th	Day	31% 20% 25% 16% 7% 1	500
	11th to 20th	Day	30% 22% 26% 13% 7% 2	492
	21st to end	Day	28% 16% 32% 15% 7% 2	500
May	1st to 10th	Day	32% 15% 30% 14% 8% 2	503
	11th to 20th	Day	18% 15% 35% 22% 8% 2	527
	21st to end	Day	16% 15% 29% 26% 11% 2	573
June	1st to 10th	Day	17% 15% 31% 25% 10% 2	530
	11th to 20th	Day	18% 14% 32% 25% 9% 3	530
	21st to end	Day	18% 13% 32% 25% 10% 2	530
July	1st to 10th	Day	12% 8% 33% 28% 16% 3	525
	11th to 20th	Day	11% 8% 32% 31% 15% 3	524
	21st to end	Day	14% 5% 36% 31% 12% 3	576
August	1st to 10th	Day	11% 8% 27% 30% 19% 6%	526
	11th to 20th	Day	15% 6% 28% 27% 19% 6%	519
	21st to end	Day	11% 9% 27% 31% 15% 7%	583
September	1st to 10th	Day	12% 10% 23% 30% 16% 8%	530
	11th to 20th	Day	13% 10% 23% 23% 19% 12%	530
	21st to end	Day	18% 9% 28% 24% 14% 7%	530
October	1st to 10th	Day	23% 11% 26% 20% 14% 6%	530
	11th to 20th	Day	17% 17% 32% 22% 9% 2	517
	21st to end	Day	29% 14% 26% 24% 6% 1	429
November	1st to 10th	Day	20% 16% 29% 23% 13% 1	395
	11th to 20th	Day	26% 16% 28% 23% 6% 2	400
	21st to end	Day	29% 18% 32% 16% 4	225
December	1st to 10th	Day	25% 20% 34% 16% 6%	200
	11th to 20th	Day	32% 20% 32% 14% 3	200
	21st to end	Day	27% 18% 31% 20% 4	220
January	1st to 10th	Night	21% 15% 37% 25% 2	800
	11th to 20th	Night	24% 16% 33% 24% 3	800
	21st to end	Night	18% 13% 38% 27% 4	880
February	1st to 10th	Night	20% 16% 40% 23% 2	800
	11th to 20th	Night	19% 18% 40% 22% 2	783
	21st to end	Night	22% 15% 37% 22% 4	660
March	1st to 10th	Night	22% 17% 34% 24% 3	800
	11th to 20th	Night	24% 16% 32% 24% 4	800
	21st to end	Night	23% 16% 33% 22% 7%	880
April	1st to 10th	Night	26% 16% 31% 23% 4	800
	11th to 20th	Night	24% 17% 31% 21% 7%	791
	21st to end	Night	24% 15% 30% 25% 6%	685
May	1st to 10th	Night	27% 12% 27% 26% 8%	555
	11th to 20th	Night	19% 10% 36% 29% 6% 1	394
	21st to end	Night	16% 9% 25% 37% 12% 1	433
June	1st to 10th	Night	21% 3 27% 37% 12% 1	400
	11th to 20th	Night	18% 7% 28% 38% 11%	400
	21st to end	Night	15% 5% 27% 42% 11%	400
July	1st to 10th	Night	12% 4 22% 46% 15% 2	390
	11th to 20th	Night	14% 3 19% 45% 18% 1	388
	21st to end	Night	12% 2 22% 47% 16% 1	438
August	1st to 10th	Night	13% 2 19% 47% 19% 1	398
	11th to 20th	Night	15% 4 20% 37% 22% 3	734
	21st to end	Night	14% 5% 19% 40% 21% 1	880
September	1st to 10th	Night	15% 4 22% 39% 18% 3	800
	11th to 20th	Night	14% 6% 21% 31% 23% 5%	800
	21st to end	Night	17% 6% 24% 34% 17% 2	800
October	1st to 10th	Night	23% 9% 22% 29% 16% 2	800
	11th to 20th	Night	20% 9% 27% 34% 10% 1	793
	21st to end	Night	28% 11% 28% 28% 6%	836
November	1st to 10th	Night	17% 12% 34% 30% 7%	780
	11th to 20th	Night	21% 13% 33% 26% 7% 1	800
	21st to end	Night	21% 12% 35% 25% 6% 1	800
December	1st to 10th	Night	27% 13% 33% 23% 4	800
	11th to 20th	Night	28% 12% 32% 25% 4	800
	21st to end	Night	27% 13% 32% 23% 3	880

Page generated at 2025-10-16 01:50:23. Version ac07

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