Long Island Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Island Lake clear sky chart from 2005-11-06 to 2024-01-12.

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	10% 9% 4 8% 7% 4 6% 6% 6% 8% 32%	74794
	Night	9% 9% 4 8% 7% 4 6% 6% 6% 8% 33%	74924
Transparency	Day	48% 9% 17% 20% 6%	74467
	Night	48% 8% 15% 21% 8% 1	74769
Seeing	Day	14% 7% 26% 29% 19% 5%	14925
	Night	13% 5% 28% 35% 16% 2	23565

By Month

Percentage Cloud Cover NW (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	6% 12% 8% 11% 11% 5% 7% 6% 6% 8% 20%	1219
	11th to 20th	Day	8% 11% 6% 10% 7% 5% 6% 6% 6% 9% 26%	1270
	21st to end	Day	7% 12% 6% 12% 9% 3 7% 5% 6% 8% 23%	1462
February	1st to 10th	Day	8% 11% 4 10% 10% 6% 7% 7% 7% 7% 24%	1440
	11th to 20th	Day	6% 11% 7% 11% 8% 5% 5% 7% 7% 8% 23%	1494
	21st to end	Day	5% 10% 6% 10% 9% 6% 8% 8% 7% 8% 24%	1375
March	1st to 10th	Day	6% 14% 7% 10% 10% 6% 8% 6% 6% 7% 20%	1800
	11th to 20th	Day	8% 11% 5% 11% 7% 4 5% 6% 5% 7% 32%	1945
	21st to end	Day	10% 13% 7% 10% 7% 4 6% 6% 8% 7% 22%	2224
April	1st to 10th	Day	8% 11% 5% 8% 6% 4 6% 8% 6% 8% 29%	2250
	11th to 20th	Day	10% 12% 4 7% 7% 5% 6% 6% 5% 7% 31%	2310
	21st to end	Day	12% 10% 4 8% 7% 4 6% 6% 7% 9% 29%	2354
May	1st to 10th	Day	12% 9% 5% 7% 7% 5% 6% 7% 7% 8% 28%	2682
	11th to 20th	Day	11% 6% 3 5% 6% 4 5% 5% 7% 9% 40%	2654
	21st to end	Day	16% 7% 3 6% 6% 4 5% 5% 6% 8% 34%	2917
June	1st to 10th	Day	15% 8% 3 7% 7% 4 6% 5% 6% 7% 31%	2758
	11th to 20th	Day	21% 9% 4 7% 6% 4 5% 6% 7% 9% 22%	2880
	21st to end	Day	10% 5% 2 6% 6% 5% 7% 7% 7% 10% 36%	2880
July	1st to 10th	Day	12% 5% 3 5% 6% 4 6% 6% 7% 10% 36%	2880
	11th to 20th	Day	12% 6% 3 6% 7% 3 5% 6% 7% 11% 34%	2736
	21st to end	Day	10% 5% 2 4 5% 4 5% 6% 7% 10% 42%	2938
August	1st to 10th	Day	10% 5% 2 5% 6% 4 6% 6% 7% 10% 36%	2603
	11th to 20th	Day	8% 5% 3 6% 6% 3 5% 6% 7% 9% 42%	2407
	21st to end	Day	11% 6% 2 6% 6% 4 6% 6% 7% 9% 38%	2574
September	1st to 10th	Day	12% 7% 2 7% 6% 4 5% 5% 6% 8% 38%	2299
	11th to 20th	Day	15% 7% 2 5% 5% 3 5% 5% 6% 9% 39%	1985
	21st to end	Day	9% 6% 3 6% 6% 3 5% 6% 6% 9% 42%	1980
October	1st to 10th	Day	12% 8% 3 9% 5% 4 6% 4 5% 8% 36%	1875
	11th to 20th	Day	11% 7% 4 6% 6% 3 6% 7% 5% 8% 36%	1624
	21st to end	Day	12% 11% 5% 8% 8% 4 6% 4 5% 7% 30%	1744
November	1st to 10th	Day	10% 13% 6% 9% 8% 6% 6% 6% 5% 7% 25%	1477
	11th to 20th	Day	7% 12% 6% 10% 8% 3 5% 5% 6% 8% 29%	1330
	21st to end	Day	6% 11% 5% 12% 9% 4 5% 6% 6% 7% 29%	1330
December	1st to 10th	Day	5% 11% 5% 9% 10% 5% 7% 5% 6% 7% 29%	1330
	11th to 20th	Day	7% 12% 4 9% 9% 5% 7% 7% 6% 7% 26%	1678
	21st to end	Day	3 7% 4 8% 6% 4 6% 6% 7% 9% 41%	2090
January	1st to 10th	Night	7% 12% 5% 11% 9% 5% 6% 7% 6% 7% 24%	2942
	11th to 20th	Night	6% 12% 5% 8% 8% 5% 7% 6% 6% 8% 29%	2730
	21st to end	Night	7% 13% 7% 12% 7% 5% 6% 6% 7% 7% 22%	2911
February	1st to 10th	Night	6% 10% 6% 11% 10% 5% 7% 6% 6% 8% 26%	2520
	11th to 20th	Night	7% 11% 5% 10% 9% 5% 7% 7% 6% 7% 27%	2351
	21st to end	Night	4 9% 6% 9% 8% 5% 6% 7% 7% 9% 30%	1880
March	1st to 10th	Night	6% 10% 6% 10% 9% 4 6% 6% 5% 9% 30%	2160
	11th to 20th	Night	9% 10% 3 7% 8% 4 6% 6% 6% 9% 31%	2014
	21st to end	Night	9% 13% 5% 8% 7% 4 5% 5% 7% 8% 29%	2129
April	1st to 10th	Night	7% 10% 4 8% 8% 4 5% 6% 6% 8% 34%	1710
	11th to 20th	Night	10% 11% 4 8% 8% 5% 6% 6% 6% 7% 30%	1601
	21st to end	Night	11% 10% 4 8% 5% 3 6% 6% 6% 8% 34%	1603
May	1st to 10th	Night	11% 9% 5% 7% 7% 3 6% 5% 6% 8% 33%	1278
	11th to 20th	Night	11% 7% 3 6% 5% 3 6% 5% 6% 8% 39%	1239
	21st to end	Night	18% 8% 3 5% 6% 3 5% 5% 6% 8% 32%	1358
June	1st to 10th	Night	14% 7% 3 7% 7% 4 7% 5% 6% 7% 32%	1198
	11th to 20th	Night	16% 9% 4 8% 5% 3 7% 7% 8% 8% 25%	1080
	21st to end	Night	7% 6% 3 7% 8% 3 6% 5% 7% 9% 38%	1080
July	1st to 10th	Night	11% 6% 2 4 5% 4 6% 6% 8% 9% 38%	1080
	11th to 20th	Night	11% 5% 2 5% 7% 4 5% 6% 7% 11% 38%	1224
	21st to end	Night	8% 5% 2 5% 6% 3 6% 5% 8% 8% 44%	1379
August	1st to 10th	Night	7% 5% 2 5% 6% 4 6% 6% 7% 10% 41%	1333
	11th to 20th	Night	10% 4 2 5% 5% 3 5% 4 7% 8% 46%	1491
	21st to end	Night	12% 6% 2 6% 7% 3 4 5% 6% 7% 41%	1782
September	1st to 10th	Night	12% 6% 3 6% 4 3 4 6% 6% 7% 42%	1660
	11th to 20th	Night	10% 6% 3 5% 6% 3 3 5% 6% 9% 45%	1974
	21st to end	Night	9% 7% 3 5% 5% 3 5% 4 5% 8% 45%	1980
October	1st to 10th	Night	11% 8% 3 7% 7% 3 5% 5% 6% 8% 37%	2084
	11th to 20th	Night	10% 7% 4 8% 6% 4 5% 5% 7% 8% 37%	2335
	21st to end	Night	11% 9% 5% 8% 7% 4 5% 5% 6% 7% 34%	2593
November	1st to 10th	Night	12% 13% 6% 9% 7% 3 5% 5% 6% 7% 27%	2599
	11th to 20th	Night	8% 12% 5% 10% 9% 5% 6% 5% 6% 7% 25%	2850
	21st to end	Night	6% 11% 6% 11% 9% 4 5% 5% 6% 8% 27%	2850
December	1st to 10th	Night	8% 10% 5% 10% 8% 5% 6% 5% 5% 8% 29%	2850
	11th to 20th	Night	8% 13% 6% 10% 9% 4 5% 6% 7% 8% 23%	3510
	21st to end	Night	4 6% 3 7% 6% 4 6% 6% 7% 10% 41%	5566

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	61% 7% 11% 14% 6% 1	1219
	11th to 20th	Day	54% 9% 14% 15% 6% 1	1270
	21st to end	Day	57% 7% 11% 16% 7%	1462
February	1st to 10th	Day	55% 7% 14% 15% 8%	1440
	11th to 20th	Day	55% 8% 14% 16% 6%	1502
	21st to end	Day	54% 7% 15% 16% 7%	1375
March	1st to 10th	Day	61% 7% 14% 13% 5%	1800
	11th to 20th	Day	51% 7% 12% 21% 9%	1946
	21st to end	Day	57% 10% 14% 14% 4	2224
April	1st to 10th	Day	50% 8% 19% 17% 6%	2250
	11th to 20th	Day	51% 7% 14% 21% 8%	2310
	21st to end	Day	51% 7% 13% 21% 7% 1	2354
May	1st to 10th	Day	52% 8% 12% 19% 9% 1	2682
	11th to 20th	Day	39% 8% 13% 28% 12% 1	2658
	21st to end	Day	47% 7% 12% 23% 11% 1	2918
June	1st to 10th	Day	50% 9% 13% 21% 7%	2758
	11th to 20th	Day	57% 10% 13% 16% 4	2880
	21st to end	Day	41% 12% 20% 21% 6% 1	2880
July	1st to 10th	Day	40% 11% 19% 24% 5% 1	2801
	11th to 20th	Day	42% 12% 24% 20% 1	2653
	21st to end	Day	35% 12% 24% 26% 2	2775
August	1st to 10th	Day	40% 12% 26% 19% 2	2585
	11th to 20th	Day	36% 10% 24% 25% 5%	2407
	21st to end	Day	40% 9% 23% 23% 5%	2574
September	1st to 10th	Day	43% 9% 19% 21% 6% 1	2299
	11th to 20th	Day	42% 9% 21% 23% 7%	1985
	21st to end	Day	37% 10% 17% 26% 9% 1	1980
October	1st to 10th	Day	47% 5% 19% 21% 7%	1875
	11th to 20th	Day	45% 8% 16% 25% 6%	1624
	21st to end	Day	54% 6% 13% 22% 5%	1744
November	1st to 10th	Day	56% 8% 14% 16% 6%	1477
	11th to 20th	Day	53% 7% 18% 16% 5%	1330
	21st to end	Day	52% 10% 14% 19% 5% 1	1330
December	1st to 10th	Day	52% 8% 14% 17% 8% 1	1330
	11th to 20th	Day	53% 9% 16% 16% 6%	1680
	21st to end	Day	39% 6% 11% 29% 13% 1	2090
January	1st to 10th	Night	57% 8% 13% 14% 7% 1	2942
	11th to 20th	Night	52% 8% 15% 16% 7% 1	2730
	21st to end	Night	59% 7% 14% 12% 8%	2911
February	1st to 10th	Night	56% 6% 13% 17% 8% 1	2520
	11th to 20th	Night	55% 7% 15% 16% 8%	2353
	21st to end	Night	48% 7% 14% 21% 9% 1	1880
March	1st to 10th	Night	50% 7% 14% 22% 7%	2160
	11th to 20th	Night	48% 7% 12% 21% 11% 1	2014
	21st to end	Night	50% 9% 15% 17% 8% 1	2129
April	1st to 10th	Night	46% 9% 12% 21% 11% 1	1710
	11th to 20th	Night	50% 7% 9% 19% 12% 2	1601
	21st to end	Night	47% 6% 10% 24% 13% 1	1603
May	1st to 10th	Night	48% 5% 14% 21% 11% 1	1278
	11th to 20th	Night	41% 7% 10% 26% 15% 1	1239
	21st to end	Night	49% 9% 10% 20% 11% 1	1358
June	1st to 10th	Night	49% 8% 14% 19% 9% 1	1198
	11th to 20th	Night	52% 10% 13% 19% 5%	1080
	21st to end	Night	40% 10% 19% 25% 5% 1	1080
July	1st to 10th	Night	39% 10% 19% 24% 7% 1	1050
	11th to 20th	Night	39% 11% 24% 23% 3	1184
	21st to end	Night	33% 10% 23% 29% 4	1302
August	1st to 10th	Night	35% 12% 24% 27% 2	1326
	11th to 20th	Night	33% 10% 23% 27% 7% 1	1491
	21st to end	Night	41% 8% 17% 26% 8%	1782
September	1st to 10th	Night	39% 8% 18% 25% 7% 2	1660
	11th to 20th	Night	37% 6% 18% 29% 9% 1	1974
	21st to end	Night	36% 8% 15% 28% 12% 1	1980
October	1st to 10th	Night	43% 9% 13% 26% 9%	2084
	11th to 20th	Night	43% 7% 15% 27% 8%	2335
	21st to end	Night	49% 7% 14% 22% 8%	2593
November	1st to 10th	Night	56% 7% 11% 20% 5%	2599
	11th to 20th	Night	56% 8% 14% 16% 6%	2850
	21st to end	Night	54% 8% 15% 18% 4 1	2850
December	1st to 10th	Night	53% 6% 11% 20% 9% 1	2850
	11th to 20th	Night	56% 8% 14% 15% 6%	3507
	21st to end	Night	38% 6% 16% 24% 13% 2	5566

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	8% 4 32% 31% 21% 3	180
	11th to 20th	Day	12% 7% 36% 26% 17% 4	163
	21st to end	Day	10% 9% 31% 30% 16% 4	176
February	1st to 10th	Day	10% 11% 35% 26% 13% 4	160
	11th to 20th	Day	12% 8% 32% 30% 13% 5%	203
	21st to end	Day	5% 8% 28% 37% 16% 6%	241
March	1st to 10th	Day	10% 10% 29% 32% 15% 3	420
	11th to 20th	Day	11% 6% 31% 31% 14% 5%	420
	21st to end	Day	17% 6% 30% 29% 17% 2	462
April	1st to 10th	Day	9% 12% 35% 27% 14% 4	420
	11th to 20th	Day	15% 8% 26% 34% 13% 5%	412
	21st to end	Day	15% 11% 32% 27% 13% 3	420
May	1st to 10th	Day	14% 10% 27% 29% 15% 4	585
	11th to 20th	Day	13% 6% 25% 29% 22% 5%	625
	21st to end	Day	18% 4 20% 30% 20% 8%	679
June	1st to 10th	Day	19% 6% 27% 30% 15% 4	688
	11th to 20th	Day	21% 6% 20% 26% 20% 7%	810
	21st to end	Day	10% 5% 20% 31% 25% 9%	810
July	1st to 10th	Day	13% 4 20% 31% 27% 6%	796
	11th to 20th	Day	13% 4 22% 30% 24% 6%	652
	21st to end	Day	10% 4 20% 31% 24% 11%	684
August	1st to 10th	Day	12% 5% 18% 28% 22% 15%	543
	11th to 20th	Day	8% 6% 30% 32% 19% 5%	437
	21st to end	Day	12% 8% 23% 29% 23% 5%	495
September	1st to 10th	Day	17% 10% 29% 24% 15% 5%	450
	11th to 20th	Day	20% 8% 25% 28% 17% 3	450
	21st to end	Day	12% 11% 31% 24% 19% 3	450
October	1st to 10th	Day	17% 9% 26% 27% 18% 3	345
	11th to 20th	Day	15% 7% 35% 24% 17% 3	270
	21st to end	Day	18% 11% 36% 22% 10% 3	297
November	1st to 10th	Day	19% 7% 29% 31% 13% 2	264
	11th to 20th	Day	11% 8% 35% 28% 14% 4	180
	21st to end	Day	4 12% 39% 27% 12% 7%	180
December	1st to 10th	Day	10% 7% 37% 27% 14% 5%	180
	11th to 20th	Day	12% 6% 31% 36% 12% 3	180
	21st to end	Day	9% 4 27% 36% 20% 5%	198
January	1st to 10th	Night	13% 5% 32% 35% 14% 2	1000
	11th to 20th	Night	12% 8% 30% 37% 13% 1	910
	21st to end	Night	16% 9% 33% 29% 10% 3	931
February	1st to 10th	Night	9% 7% 28% 34% 19% 3	720
	11th to 20th	Night	12% 4 32% 33% 17% 2	704
	21st to end	Night	6% 4 29% 37% 19% 4	592
March	1st to 10th	Night	10% 4 29% 39% 14% 3	720
	11th to 20th	Night	14% 3 31% 35% 14% 3	720
	21st to end	Night	15% 5% 28% 33% 17% 2	792
April	1st to 10th	Night	10% 6% 27% 35% 19% 3	630
	11th to 20th	Night	13% 7% 28% 34% 15% 3	533
	21st to end	Night	16% 8% 26% 33% 17% 1	523
May	1st to 10th	Night	13% 8% 23% 35% 19% 3	360
	11th to 20th	Night	13% 4 24% 41% 16% 3	354
	21st to end	Night	22% 4 21% 31% 20% 2	389
June	1st to 10th	Night	21% 4 20% 36% 17% 2	360
	11th to 20th	Night	16% 4 19% 33% 25% 3	360
	21st to end	Night	9% 3 14% 41% 29% 4	360
July	1st to 10th	Night	13% 2 17% 42% 24% 2	350
	11th to 20th	Night	13% 3 19% 39% 21% 3	348
	21st to end	Night	9% 3 16% 40% 27% 5%	394
August	1st to 10th	Night	8% 4 16% 37% 30% 6%	358
	11th to 20th	Night	12% 2 20% 38% 26% 2	423
	21st to end	Night	14% 3 18% 41% 22% 2	594
September	1st to 10th	Night	17% 4 20% 36% 22% 3	580
	11th to 20th	Night	14% 4 21% 40% 20% 1	720
	21st to end	Night	12% 4 29% 37% 15% 3	720
October	1st to 10th	Night	14% 3 29% 37% 15% 2	720
	11th to 20th	Night	14% 5% 28% 37% 13% 2	720
	21st to end	Night	15% 8% 32% 31% 14% 1	811
November	1st to 10th	Night	18% 6% 30% 34% 10% 2	925
	11th to 20th	Night	15% 6% 36% 29% 11% 3	950
	21st to end	Night	9% 7% 39% 32% 11% 1	950
December	1st to 10th	Night	13% 7% 34% 29% 13% 4	950
	11th to 20th	Night	11% 8% 32% 36% 11% 2	950
	21st to end	Night	10% 4 29% 38% 16% 3	1144

Page generated at 2024-01-09 14:24:26. Version ac07

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