Schroon Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Schroon Lake clear sky chart from 2005-11-06 to 2024-01-27.

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% 4 7% 6% 4 5% 5% 6% 7% 32%	74875
	Night	16% 8% 4 7% 6% 3 5% 5% 5% 7% 34%	75169
Transparency	Day	51% 4 11% 21% 11% 1	74580
	Night	50% 4 12% 21% 11% 1	74998
Seeing	Day	22% 16% 30% 20% 9% 3	13632
	Night	21% 13% 28% 28% 10% 1	22803

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% 12% 6% 9% 9% 5% 6% 6% 6% 6% 25%	1517
	11th to 20th	Day	14% 13% 3 10% 8% 4 5% 6% 5% 7% 26%	1520
	21st to end	Day	10% 10% 6% 11% 8% 5% 7% 5% 6% 7% 26%	1647
February	1st to 10th	Day	12% 12% 6% 9% 9% 5% 7% 5% 7% 6% 24%	1620
	11th to 20th	Day	10% 11% 6% 9% 8% 4 5% 5% 6% 7% 28%	1699
	21st to end	Day	16% 11% 5% 8% 8% 4 6% 4 4 6% 27%	1480
March	1st to 10th	Day	12% 10% 5% 9% 9% 4 7% 5% 5% 7% 29%	1797
	11th to 20th	Day	15% 11% 5% 8% 6% 4 4 5% 5% 6% 31%	1868
	21st to end	Day	17% 11% 3 7% 6% 3 4 4 3 6% 36%	2371
April	1st to 10th	Day	19% 10% 3 7% 5% 4 5% 4 4 6% 34%	2160
	11th to 20th	Day	17% 8% 4 7% 5% 3 4 5% 5% 5% 37%	2134
	21st to end	Day	22% 9% 3 8% 6% 4 5% 4 5% 6% 29%	2268
May	1st to 10th	Day	21% 9% 3 7% 6% 4 4 4 4 6% 31%	2423
	11th to 20th	Day	19% 8% 3 6% 5% 3 4 4 4 6% 38%	2478
	21st to end	Day	17% 6% 3 6% 6% 4 5% 6% 5% 7% 37%	2725
June	1st to 10th	Day	19% 6% 3 7% 6% 4 6% 6% 7% 8% 28%	2520
	11th to 20th	Day	17% 6% 3 5% 5% 4 6% 6% 6% 8% 34%	2520
	21st to end	Day	19% 6% 3 6% 6% 4 5% 6% 7% 8% 30%	2520
July	1st to 10th	Day	14% 5% 3 6% 6% 3 6% 6% 7% 8% 35%	2520
	11th to 20th	Day	13% 6% 3 5% 6% 4 6% 6% 6% 9% 36%	2520
	21st to end	Day	16% 4 2 5% 5% 4 6% 6% 8% 8% 35%	2744
August	1st to 10th	Day	12% 5% 2 6% 7% 4 7% 7% 6% 8% 36%	2506
	11th to 20th	Day	14% 5% 2 5% 7% 4 6% 5% 8% 10% 33%	2186
	21st to end	Day	14% 5% 2 5% 5% 3 6% 7% 6% 8% 38%	2376
September	1st to 10th	Day	14% 5% 2 4 6% 3 5% 5% 6% 8% 41%	2160
	11th to 20th	Day	15% 6% 2 5% 4 2 4 4 5% 7% 46%	2080
	21st to end	Day	19% 5% 3 5% 4 3 4 4 6% 8% 39%	1980
October	1st to 10th	Day	24% 8% 3 6% 6% 4 4 4 5% 5% 32%	1872
	11th to 20th	Day	18% 9% 3 6% 5% 3 4 5% 7% 6% 34%	1788
	21st to end	Day	23% 10% 3 7% 7% 3 5% 4 5% 6% 27%	1782
November	1st to 10th	Day	14% 8% 3 7% 6% 5% 5% 5% 6% 8% 35%	1671
	11th to 20th	Day	15% 8% 3 8% 6% 4 6% 5% 5% 6% 32%	1705
	21st to end	Day	17% 9% 5% 9% 6% 4 5% 5% 6% 6% 29%	1520
December	1st to 10th	Day	19% 14% 6% 8% 9% 3 5% 5% 5% 6% 20%	1520
	11th to 20th	Day	21% 11% 5% 7% 6% 4 4 5% 5% 7% 27%	1906
	21st to end	Day	21% 16% 6% 9% 6% 3 4 3 4 4 23%	2772
January	1st to 10th	Night	13% 10% 5% 8% 8% 5% 5% 5% 6% 7% 28%	2649
	11th to 20th	Night	13% 12% 6% 10% 7% 5% 5% 5% 5% 7% 25%	2660
	21st to end	Night	10% 9% 5% 9% 9% 4 4 6% 5% 7% 32%	2850
February	1st to 10th	Night	11% 11% 5% 12% 8% 4 6% 6% 6% 7% 24%	2340
	11th to 20th	Night	9% 10% 5% 8% 8% 4 7% 6% 6% 7% 31%	2147
	21st to end	Night	14% 11% 4 8% 6% 3 5% 4 5% 7% 31%	1776
March	1st to 10th	Night	13% 11% 3 7% 7% 4 6% 6% 6% 6% 31%	2150
	11th to 20th	Night	16% 10% 4 8% 6% 3 6% 4 5% 6% 33%	2087
	21st to end	Night	15% 7% 3 7% 6% 3 5% 4 4 5% 39%	1985
April	1st to 10th	Night	18% 8% 4 6% 6% 3 4 5% 5% 6% 35%	1800
	11th to 20th	Night	17% 8% 4 6% 5% 3 4 5% 5% 8% 34%	1775
	21st to end	Night	21% 8% 3 7% 5% 2 5% 5% 5% 6% 35%	1692
May	1st to 10th	Night	23% 8% 3 7% 4 3 5% 4 5% 5% 33%	1552
	11th to 20th	Night	18% 7% 2 6% 5% 3 4 5% 5% 6% 39%	1415
	21st to end	Night	15% 6% 2 5% 5% 3 5% 4 7% 8% 40%	1550
June	1st to 10th	Night	19% 5% 3 5% 5% 3 4 5% 5% 8% 39%	1440
	11th to 20th	Night	18% 5% 2 4 4 3 4 4 5% 8% 41%	1440
	21st to end	Night	16% 5% 2 5% 5% 4 5% 5% 6% 8% 38%	1440
July	1st to 10th	Night	12% 4 3 5% 5% 3 7% 5% 5% 8% 45%	1440
	11th to 20th	Night	11% 4 2 4 5% 3 4 6% 6% 10% 44%	1440
	21st to end	Night	11% 4 3 4 5% 3 4 6% 5% 8% 46%	1574
August	1st to 10th	Night	11% 4 1 5% 4 3 6% 6% 6% 8% 46%	1432
	11th to 20th	Night	14% 5% 2 5% 5% 3 4 5% 7% 8% 41%	1692
	21st to end	Night	13% 4 2 5% 4 2 4 6% 5% 8% 47%	1980
September	1st to 10th	Night	12% 5% 2 5% 5% 3 4 4 7% 8% 45%	1800
	11th to 20th	Night	14% 5% 2 5% 3 2 4 4 4 6% 50%	1880
	21st to end	Night	17% 5% 1 5% 4 2 4 4 5% 7% 45%	1980
October	1st to 10th	Night	19% 8% 3 7% 6% 3 5% 4 5% 6% 34%	2086
	11th to 20th	Night	16% 6% 3 6% 6% 4 6% 5% 6% 7% 35%	2170
	21st to end	Night	21% 9% 3 6% 6% 3 5% 5% 5% 7% 29%	2574
November	1st to 10th	Night	13% 8% 3 7% 6% 3 6% 5% 6% 6% 38%	2407
	11th to 20th	Night	17% 8% 3 7% 5% 3 5% 4 5% 7% 35%	2474
	21st to end	Night	16% 9% 4 7% 6% 4 5% 5% 6% 8% 31%	2660
December	1st to 10th	Night	17% 12% 5% 10% 7% 3 5% 5% 6% 8% 22%	2660
	11th to 20th	Night	19% 10% 4 8% 7% 3 5% 5% 5% 6% 28%	3288
	21st to end	Night	22% 14% 6% 10% 6% 4 4 4 4 6% 21%	4884

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	58% 3 9% 21% 8% 1	1518
	11th to 20th	Day	58% 5% 11% 16% 9% 2	1520
	21st to end	Day	56% 3 11% 16% 11% 2	1647
February	1st to 10th	Day	59% 5% 11% 17% 6% 2	1620
	11th to 20th	Day	56% 4 11% 16% 11% 2	1708
	21st to end	Day	59% 3 10% 15% 12% 2	1480
March	1st to 10th	Day	55% 3 11% 17% 11% 3	1800
	11th to 20th	Day	55% 4 11% 14% 14% 3	1868
	21st to end	Day	52% 3 6% 17% 17% 4	2371
April	1st to 10th	Day	52% 4 9% 21% 12% 3	2160
	11th to 20th	Day	49% 4 8% 20% 16% 2	2134
	21st to end	Day	57% 3 10% 16% 11% 3	2268
May	1st to 10th	Day	55% 4 7% 20% 13% 2	2423
	11th to 20th	Day	48% 3 7% 23% 16% 3	2482
	21st to end	Day	46% 5% 15% 21% 11% 1	2725
June	1st to 10th	Day	52% 5% 13% 19% 10% 1	2520
	11th to 20th	Day	47% 5% 12% 22% 13% 2	2520
	21st to end	Day	50% 5% 14% 20% 11% 1	2520
July	1st to 10th	Day	44% 5% 12% 25% 13%	2450
	11th to 20th	Day	42% 5% 14% 30% 8%	2445
	21st to end	Day	44% 5% 14% 25% 12% 1	2591
August	1st to 10th	Day	43% 5% 16% 26% 9%	2492
	11th to 20th	Day	44% 5% 16% 25% 10%	2186
	21st to end	Day	41% 5% 12% 27% 13% 1	2376
September	1st to 10th	Day	39% 6% 11% 30% 12% 1	2160
	11th to 20th	Day	38% 3 10% 30% 18% 1	2080
	21st to end	Day	42% 4 13% 25% 13% 2	1980
October	1st to 10th	Day	54% 4 8% 21% 12% 1	1872
	11th to 20th	Day	49% 4 14% 25% 8% 1	1788
	21st to end	Day	59% 4 11% 16% 9% 1	1782
November	1st to 10th	Day	47% 4 15% 21% 12%	1671
	11th to 20th	Day	51% 5% 11% 18% 13% 3	1705
	21st to end	Day	55% 4 15% 18% 7% 1	1520
December	1st to 10th	Day	65% 3 11% 15% 5% 1	1520
	11th to 20th	Day	58% 3 14% 16% 8% 1	1906
	21st to end	Day	67% 3 7% 16% 8%	2772
January	1st to 10th	Night	55% 4 11% 20% 10%	2649
	11th to 20th	Night	58% 5% 13% 15% 8% 1	2660
	21st to end	Night	52% 3 9% 19% 14% 2	2850
February	1st to 10th	Night	59% 5% 11% 15% 8% 1	2340
	11th to 20th	Night	52% 5% 10% 20% 12% 1	2149
	21st to end	Night	54% 3 11% 21% 10% 2	1776
March	1st to 10th	Night	54% 3 10% 20% 11% 2	2160
	11th to 20th	Night	53% 3 10% 19% 13% 2	2088
	21st to end	Night	48% 4 8% 19% 16% 4	1985
April	1st to 10th	Night	51% 4 8% 22% 13% 2	1800
	11th to 20th	Night	50% 3 11% 22% 13% 1	1775
	21st to end	Night	51% 4 9% 20% 13% 4	1692
May	1st to 10th	Night	54% 4 7% 16% 17% 2	1552
	11th to 20th	Night	47% 4 10% 20% 17% 2	1416
	21st to end	Night	43% 4 16% 22% 13% 2	1551
June	1st to 10th	Night	45% 4 16% 21% 12% 1	1440
	11th to 20th	Night	43% 4 16% 22% 14% 2	1440
	21st to end	Night	44% 5% 14% 26% 10% 1	1440
July	1st to 10th	Night	36% 6% 16% 26% 15% 1	1400
	11th to 20th	Night	35% 6% 17% 31% 11%	1392
	21st to end	Night	34% 7% 17% 29% 12% 1	1486
August	1st to 10th	Night	35% 5% 18% 29% 12% 1	1422
	11th to 20th	Night	40% 6% 15% 28% 11%	1692
	21st to end	Night	35% 5% 15% 31% 13% 1	1980
September	1st to 10th	Night	37% 6% 15% 31% 11% 1	1800
	11th to 20th	Night	36% 4 12% 31% 18% 1	1880
	21st to end	Night	40% 3 13% 28% 13% 2	1980
October	1st to 10th	Night	52% 3 11% 21% 12% 1	2086
	11th to 20th	Night	48% 4 14% 25% 8% 1	2170
	21st to end	Night	56% 4 13% 17% 9% 1	2574
November	1st to 10th	Night	48% 4 13% 21% 12% 2	2407
	11th to 20th	Night	50% 4 12% 21% 11% 3	2474
	21st to end	Night	52% 5% 15% 20% 8% 1	2660
December	1st to 10th	Night	62% 4 12% 17% 4	2660
	11th to 20th	Night	57% 4 11% 17% 10% 1	3288
	21st to end	Night	66% 3 9% 18% 5%	4884

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% 17% 33% 19% 8%	180
	11th to 20th	Day	24% 28% 31% 13% 2 1	180
	21st to end	Day	16% 24% 38% 17% 5%	195
February	1st to 10th	Day	30% 38% 23% 8% 1	240
	11th to 20th	Day	23% 30% 32% 13% 2	367
	21st to end	Day	29% 18% 33% 17% 3	346
March	1st to 10th	Day	23% 21% 34% 18% 4	420
	11th to 20th	Day	28% 22% 30% 14% 5% 1	420
	21st to end	Day	29% 24% 22% 15% 8% 2	462
April	1st to 10th	Day	32% 17% 29% 15% 7%	420
	11th to 20th	Day	29% 22% 24% 15% 7% 3	412
	21st to end	Day	33% 15% 33% 11% 7% 2	420
May	1st to 10th	Day	29% 19% 29% 12% 7% 4	423
	11th to 20th	Day	20% 17% 34% 21% 5% 2	447
	21st to end	Day	19% 14% 33% 22% 11% 2	485
June	1st to 10th	Day	24% 15% 32% 19% 9% 2	450
	11th to 20th	Day	18% 14% 38% 21% 9% 2	450
	21st to end	Day	19% 13% 35% 22% 8% 3	450
July	1st to 10th	Day	15% 8% 27% 33% 14% 3	445
	11th to 20th	Day	17% 7% 33% 27% 13% 2	444
	21st to end	Day	14% 9% 34% 30% 10% 2	488
August	1st to 10th	Day	11% 10% 28% 30% 15% 6%	446
	11th to 20th	Day	15% 7% 29% 27% 14% 7%	439
	21st to end	Day	13% 13% 28% 25% 15% 6%	495
September	1st to 10th	Day	15% 8% 28% 26% 13% 9%	450
	11th to 20th	Day	14% 12% 26% 21% 15% 11%	450
	21st to end	Day	20% 10% 29% 23% 12% 6%	450
October	1st to 10th	Day	28% 15% 23% 16% 14% 4	450
	11th to 20th	Day	21% 18% 27% 24% 10% 1	444
	21st to end	Day	30% 14% 28% 22% 6%	396
November	1st to 10th	Day	22% 19% 24% 24% 11% 1	365
	11th to 20th	Day	24% 21% 28% 19% 7% 1	365
	21st to end	Day	23% 23% 33% 17% 4	180
December	1st to 10th	Day	26% 24% 27% 18% 4 1	180
	11th to 20th	Day	27% 26% 33% 13% 1	180
	21st to end	Day	29% 23% 30% 16% 3	198
January	1st to 10th	Night	21% 18% 33% 24% 4	760
	11th to 20th	Night	22% 18% 32% 24% 3	760
	21st to end	Night	16% 20% 33% 25% 6%	820
February	1st to 10th	Night	20% 18% 37% 23% 2	720
	11th to 20th	Night	18% 21% 37% 22% 3	703
	21st to end	Night	23% 19% 33% 22% 3	592
March	1st to 10th	Night	21% 17% 34% 25% 3	720
	11th to 20th	Night	24% 18% 29% 24% 5%	720
	21st to end	Night	22% 16% 28% 25% 7% 1	792
April	1st to 10th	Night	25% 14% 30% 26% 5%	720
	11th to 20th	Night	22% 21% 27% 22% 7% 1	711
	21st to end	Night	27% 14% 28% 23% 8%	612
May	1st to 10th	Night	30% 12% 24% 23% 10%	472
	11th to 20th	Night	19% 13% 28% 31% 9%	354
	21st to end	Night	17% 8% 25% 35% 14% 1	389
June	1st to 10th	Night	22% 6% 26% 30% 15%	360
	11th to 20th	Night	18% 6% 25% 36% 15%	360
	21st to end	Night	19% 6% 26% 34% 14% 1	360
July	1st to 10th	Night	14% 3 19% 42% 20% 2	350
	11th to 20th	Night	12% 4 20% 41% 20% 2	348
	21st to end	Night	12% 5% 20% 44% 18% 1	394
August	1st to 10th	Night	11% 3 18% 42% 24% 1	358
	11th to 20th	Night	14% 4 18% 39% 22% 3	628
	21st to end	Night	16% 5% 19% 37% 21% 2	792
September	1st to 10th	Night	14% 6% 22% 38% 17% 3	720
	11th to 20th	Night	16% 8% 21% 30% 21% 4	720
	21st to end	Night	18% 7% 27% 27% 17% 3	720
October	1st to 10th	Night	24% 12% 20% 27% 16% 2	720
	11th to 20th	Night	20% 12% 24% 31% 12% 1	720
	21st to end	Night	27% 13% 27% 27% 8%	792
November	1st to 10th	Night	20% 15% 29% 28% 8% 1	740
	11th to 20th	Night	23% 18% 26% 24% 8% 2	760
	21st to end	Night	21% 18% 29% 25% 7%	760
December	1st to 10th	Night	26% 17% 33% 21% 4	760
	11th to 20th	Night	25% 18% 28% 23% 6%	760
	21st to end	Night	26% 16% 33% 22% 3	836

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