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 2024-11-05.

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% 3 9% 6% 5% 5% 5% 6% 8% 33%	106041
	Night	8% 9% 4 10% 6% 5% 5% 5% 7% 8% 33%	101544
Transparency	Day	46% 8% 17% 22% 7%	105777
	Night	47% 7% 16% 21% 8% 1	101454
Seeing	Day	14% 7% 27% 29% 18% 5%	16135
	Night	13% 5% 28% 35% 16% 2	24515

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	4 16% 6% 13% 13% 6% 6% 6% 6% 7% 17%	2031
	11th to 20th	Day	5% 9% 4 11% 6% 7% 6% 7% 8% 9% 30%	2199
	21st to end	Day	6% 13% 4 10% 6% 5% 6% 5% 6% 8% 32%	2574
February	1st to 10th	Day	8% 12% 4 11% 10% 6% 7% 5% 8% 7% 23%	1520
	11th to 20th	Day	6% 11% 6% 12% 7% 6% 6% 5% 8% 8% 25%	1579
	21st to end	Day	4 12% 5% 11% 8% 8% 7% 6% 7% 8% 24%	1459
March	1st to 10th	Day	4 12% 6% 12% 8% 8% 6% 4 5% 8% 27%	3138
	11th to 20th	Day	4 10% 5% 11% 5% 5% 5% 4 5% 9% 37%	3442
	21st to end	Day	9% 15% 5% 18% 6% 5% 5% 4 6% 6% 21%	3909
April	1st to 10th	Day	7% 13% 4 9% 6% 5% 6% 6% 6% 8% 29%	2375
	11th to 20th	Day	9% 12% 3 9% 6% 6% 6% 5% 6% 7% 31%	2440
	21st to end	Day	12% 11% 4 9% 7% 5% 5% 5% 7% 8% 28%	2485
May	1st to 10th	Day	18% 10% 3 7% 5% 5% 5% 4 5% 7% 32%	4708
	11th to 20th	Day	13% 11% 3 8% 6% 5% 5% 4 6% 8% 30%	4694
	21st to end	Day	11% 8% 3 10% 7% 6% 7% 5% 7% 9% 26%	5161
June	1st to 10th	Day	15% 8% 3 8% 6% 6% 5% 4 6% 7% 31%	2912
	11th to 20th	Day	20% 10% 3 8% 5% 5% 5% 5% 7% 9% 23%	3040
	21st to end	Day	10% 6% 2 7% 6% 6% 6% 6% 7% 9% 35%	3040
July	1st to 10th	Day	8% 4 2 6% 5% 5% 6% 5% 7% 9% 42%	5060
	11th to 20th	Day	8% 5% 2 6% 5% 4 5% 5% 7% 9% 45%	4790
	21st to end	Day	14% 5% 2 5% 4 4 5% 4 6% 8% 43%	5138
August	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 5% 8% 43%	4567
	11th to 20th	Day	10% 5% 3 6% 5% 4 5% 5% 7% 9% 41%	4210
	21st to end	Day	11% 5% 2 7% 4 5% 5% 4 7% 9% 40%	4521
September	1st to 10th	Day	11% 7% 2 8% 5% 5% 5% 4 6% 8% 40%	2426
	11th to 20th	Day	14% 7% 2 6% 4 5% 5% 4 6% 9% 39%	2095
	21st to end	Day	9% 6% 3 7% 5% 4 5% 4 6% 9% 42%	2090
October	1st to 10th	Day	11% 7% 3 9% 5% 5% 6% 4 6% 10% 33%	3301
	11th to 20th	Day	12% 10% 4 8% 4 5% 5% 5% 5% 7% 34%	2846
	21st to end	Day	9% 12% 5% 9% 5% 5% 5% 4 6% 8% 32%	3024
November	1st to 10th	Day	10% 15% 4 10% 8% 7% 6% 4 6% 7% 25%	1509
	11th to 20th	Day	7% 12% 6% 11% 7% 4 5% 4 6% 7% 29%	1330
	21st to end	Day	5% 12% 4 14% 7% 5% 6% 4 6% 8% 28%	1330
December	1st to 10th	Day	4 13% 4 11% 9% 7% 6% 4 6% 7% 29%	1330
	11th to 20th	Day	7% 13% 4 10% 7% 6% 7% 6% 6% 7% 26%	1678
	21st to end	Day	3 7% 3 8% 6% 6% 5% 5% 7% 9% 40%	2090
January	1st to 10th	Night	5% 12% 6% 16% 8% 6% 5% 5% 6% 6% 23%	4910
	11th to 20th	Night	4 10% 4 10% 7% 7% 7% 6% 7% 6% 34%	4699
	21st to end	Night	6% 13% 5% 11% 7% 5% 6% 4 6% 7% 29%	5113
February	1st to 10th	Night	6% 12% 6% 12% 8% 7% 6% 5% 6% 8% 25%	2660
	11th to 20th	Night	6% 11% 4 10% 8% 7% 7% 5% 6% 7% 28%	2486
	21st to end	Night	4 10% 6% 10% 7% 6% 6% 6% 7% 8% 30%	1994
March	1st to 10th	Night	3 9% 5% 13% 8% 6% 5% 5% 6% 10% 29%	3736
	11th to 20th	Night	5% 8% 3 9% 6% 5% 5% 5% 7% 10% 37%	3537
	21st to end	Night	6% 12% 6% 16% 7% 6% 5% 4 6% 6% 26%	3741
April	1st to 10th	Night	6% 10% 3 10% 7% 5% 6% 5% 7% 8% 33%	1804
	11th to 20th	Night	10% 11% 3 9% 7% 6% 6% 5% 6% 7% 29%	1691
	21st to end	Night	10% 11% 4 9% 5% 5% 5% 5% 6% 7% 34%	1692
May	1st to 10th	Night	18% 11% 3 9% 5% 4 4 3 5% 6% 33%	2252
	11th to 20th	Night	12% 10% 3 8% 6% 5% 6% 5% 7% 8% 29%	2199
	21st to end	Night	13% 8% 3 9% 6% 5% 6% 5% 7% 10% 29%	2414
June	1st to 10th	Night	15% 7% 3 9% 6% 6% 6% 4 6% 6% 32%	1264
	11th to 20th	Night	16% 9% 3 9% 4 6% 5% 6% 8% 8% 25%	1140
	21st to end	Night	8% 7% 2 8% 6% 5% 6% 3 7% 9% 38%	1140
July	1st to 10th	Night	8% 5% 1 6% 4 5% 5% 5% 7% 8% 45%	1900
	11th to 20th	Night	8% 6% 2 5% 5% 4 5% 4 7% 11% 43%	2156
	21st to end	Night	14% 5% 2 5% 4 4 4 4 7% 8% 43%	2414
August	1st to 10th	Night	10% 6% 2 7% 5% 5% 4 4 6% 8% 43%	2360
	11th to 20th	Night	14% 6% 3 6% 4 4 5% 3 7% 8% 41%	2620
	21st to end	Night	13% 5% 2 6% 5% 4 4 4 7% 8% 43%	3146
September	1st to 10th	Night	12% 6% 3 7% 3 4 4 5% 6% 7% 44%	1753
	11th to 20th	Night	10% 7% 2 6% 5% 3 4 4 6% 8% 44%	2084
	21st to end	Night	9% 8% 2 6% 4 4 5% 4 5% 8% 44%	2090
October	1st to 10th	Night	7% 6% 3 9% 7% 5% 6% 4 7% 10% 35%	3672
	11th to 20th	Night	9% 7% 3 8% 4 5% 5% 4 7% 10% 36%	4081
	21st to end	Night	9% 8% 4 8% 5% 5% 6% 5% 8% 10% 33%	4502
November	1st to 10th	Night	12% 14% 5% 10% 6% 5% 5% 4 6% 6% 27%	2668
	11th to 20th	Night	8% 14% 5% 12% 8% 6% 5% 4 6% 7% 25%	2850
	21st to end	Night	6% 13% 5% 12% 8% 5% 5% 4 6% 8% 27%	2850
December	1st to 10th	Night	7% 12% 4 12% 7% 7% 5% 4 6% 8% 29%	2850
	11th to 20th	Night	8% 14% 5% 12% 7% 5% 5% 5% 7% 8% 23%	3510
	21st to end	Night	4 7% 3 8% 6% 5% 6% 4 7% 9% 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	63% 7% 11% 14% 4 1	2031
	11th to 20th	Day	48% 6% 12% 16% 16% 1	2220
	21st to end	Day	48% 8% 20% 17% 7%	2574
February	1st to 10th	Day	56% 7% 14% 15% 8%	1520
	11th to 20th	Day	53% 8% 14% 17% 7%	1587
	21st to end	Day	54% 7% 16% 17% 6%	1459
March	1st to 10th	Day	54% 6% 14% 20% 5%	3138
	11th to 20th	Day	43% 8% 20% 22% 7%	3443
	21st to end	Day	59% 8% 14% 16% 3	3909
April	1st to 10th	Day	49% 8% 18% 17% 7%	2375
	11th to 20th	Day	50% 6% 14% 21% 9%	2440
	21st to end	Day	51% 7% 13% 20% 7% 1	2485
May	1st to 10th	Day	51% 6% 10% 23% 10%	4708
	11th to 20th	Day	49% 7% 10% 24% 9% 1	4698
	21st to end	Day	49% 11% 16% 16% 7% 1	5162
June	1st to 10th	Day	50% 8% 13% 20% 7% 1	2912
	11th to 20th	Day	56% 10% 13% 17% 4	3040
	21st to end	Day	41% 11% 19% 20% 7%	3040
July	1st to 10th	Day	35% 10% 18% 26% 11% 1	4981
	11th to 20th	Day	33% 9% 16% 29% 12%	4707
	21st to end	Day	37% 9% 21% 26% 7%	4976
August	1st to 10th	Day	39% 9% 20% 30% 2	4549
	11th to 20th	Day	36% 9% 22% 24% 8%	4252
	21st to end	Day	38% 8% 28% 23% 3	4520
September	1st to 10th	Day	42% 8% 19% 23% 7% 1	2426
	11th to 20th	Day	42% 8% 20% 23% 6%	2095
	21st to end	Day	38% 10% 17% 26% 9% 1	2090
October	1st to 10th	Day	46% 5% 24% 21% 4	3301
	11th to 20th	Day	48% 6% 15% 25% 5%	2846
	21st to end	Day	50% 5% 18% 24% 3	3024
November	1st to 10th	Day	56% 8% 14% 16% 6%	1509
	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	58% 8% 11% 15% 6% 1	4910
	11th to 20th	Night	48% 6% 13% 16% 16% 1	4740
	21st to end	Night	52% 7% 21% 13% 6%	5113
February	1st to 10th	Night	56% 6% 12% 17% 8% 1	2660
	11th to 20th	Night	52% 7% 15% 17% 9% 1	2488
	21st to end	Night	48% 6% 14% 21% 9% 1	1994
March	1st to 10th	Night	49% 6% 16% 22% 6%	3736
	11th to 20th	Night	40% 7% 22% 20% 10% 1	3537
	21st to end	Night	55% 9% 12% 17% 7%	3741
April	1st to 10th	Night	46% 9% 12% 20% 11% 1	1804
	11th to 20th	Night	50% 7% 10% 19% 12% 2	1691
	21st to end	Night	47% 7% 10% 23% 13% 1	1692
May	1st to 10th	Night	51% 4 11% 20% 13% 1	2252
	11th to 20th	Night	47% 8% 12% 22% 10% 1	2199
	21st to end	Night	45% 11% 19% 15% 9% 1	2414
June	1st to 10th	Night	49% 8% 13% 18% 9% 1	1264
	11th to 20th	Night	52% 9% 14% 20% 5%	1140
	21st to end	Night	40% 9% 18% 25% 6% 1	1140
July	1st to 10th	Night	34% 8% 17% 26% 14% 1	1870
	11th to 20th	Night	34% 8% 17% 31% 11%	2116
	21st to end	Night	36% 7% 21% 28% 7%	2337
August	1st to 10th	Night	38% 8% 19% 33% 2	2353
	11th to 20th	Night	40% 8% 19% 22% 10%	2644
	21st to end	Night	37% 7% 26% 25% 5%	3146
September	1st to 10th	Night	38% 8% 17% 27% 7% 2	1753
	11th to 20th	Night	37% 6% 18% 30% 9% 1	2084
	21st to end	Night	37% 8% 15% 27% 12% 2	2090
October	1st to 10th	Night	40% 8% 22% 23% 7%	3672
	11th to 20th	Night	43% 6% 15% 31% 5%	4081
	21st to end	Night	44% 6% 24% 20% 5%	4502
November	1st to 10th	Night	57% 7% 11% 20% 5%	2668
	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% 32% 21% 3	180
	11th to 20th	Day	11% 7% 36% 26% 16% 4	180
	21st to end	Day	11% 9% 31% 30% 16% 4	198
February	1st to 10th	Day	12% 11% 34% 26% 12% 4	180
	11th to 20th	Day	11% 7% 31% 30% 16% 5%	228
	21st to end	Day	5% 11% 30% 35% 14% 6%	271
March	1st to 10th	Day	9% 11% 30% 32% 14% 3	460
	11th to 20th	Day	11% 7% 32% 31% 14% 5%	460
	21st to end	Day	17% 6% 30% 29% 17% 2	506
April	1st to 10th	Day	9% 13% 35% 26% 13% 3	460
	11th to 20th	Day	14% 9% 27% 32% 13% 5%	452
	21st to end	Day	15% 12% 31% 27% 12% 3	460
May	1st to 10th	Day	16% 10% 27% 29% 15% 4	634
	11th to 20th	Day	13% 8% 25% 29% 20% 4	675
	21st to end	Day	17% 4 21% 29% 20% 8%	734
June	1st to 10th	Day	19% 6% 28% 28% 14% 3	742
	11th to 20th	Day	21% 6% 21% 25% 20% 7%	870
	21st to end	Day	10% 4 20% 32% 25% 9%	870
July	1st to 10th	Day	12% 4 20% 31% 27% 7%	856
	11th to 20th	Day	13% 4 22% 29% 25% 7%	703
	21st to end	Day	11% 4 20% 31% 24% 10%	739
August	1st to 10th	Day	13% 5% 18% 28% 23% 14%	588
	11th to 20th	Day	8% 6% 29% 32% 20% 5%	477
	21st to end	Day	12% 8% 23% 30% 22% 5%	539
September	1st to 10th	Day	16% 10% 28% 24% 16% 6%	490
	11th to 20th	Day	20% 7% 24% 29% 17% 3	490
	21st to end	Day	12% 12% 33% 24% 18% 2	490
October	1st to 10th	Day	17% 11% 27% 26% 17% 3	379
	11th to 20th	Day	15% 7% 34% 25% 16% 2	300
	21st to end	Day	18% 10% 37% 21% 11% 3	330
November	1st to 10th	Day	19% 7% 29% 30% 14% 2	276
	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	11% 7% 30% 37% 12% 1	950
	21st to end	Night	16% 9% 33% 29% 10% 3	983
February	1st to 10th	Night	10% 7% 28% 34% 19% 3	760
	11th to 20th	Night	11% 4 32% 34% 17% 2	744
	21st to end	Night	7% 5% 29% 37% 18% 4	628
March	1st to 10th	Night	10% 5% 29% 39% 14% 3	760
	11th to 20th	Night	13% 4 31% 35% 14% 3	760
	21st to end	Night	14% 6% 29% 33% 16% 2	836
April	1st to 10th	Night	10% 7% 28% 34% 18% 3	664
	11th to 20th	Night	13% 7% 28% 34% 15% 3	563
	21st to end	Night	15% 8% 26% 33% 17% 1	552
May	1st to 10th	Night	14% 8% 22% 35% 18% 3	380
	11th to 20th	Night	13% 4 26% 40% 16% 3	374
	21st to end	Night	21% 4 21% 31% 20% 2	411
June	1st to 10th	Night	21% 6% 22% 35% 16% 2	380
	11th to 20th	Night	16% 4 19% 33% 24% 3	380
	21st to end	Night	10% 3 14% 42% 27% 4	380
July	1st to 10th	Night	12% 2 16% 42% 25% 2	370
	11th to 20th	Night	13% 4 19% 39% 22% 4	368
	21st to end	Night	9% 3 16% 39% 28% 5%	416
August	1st to 10th	Night	8% 3 15% 37% 29% 6%	378
	11th to 20th	Night	12% 2 21% 37% 26% 2	447
	21st to end	Night	14% 3 19% 41% 21% 2	627
September	1st to 10th	Night	16% 4 20% 37% 22% 3	613
	11th to 20th	Night	14% 4 21% 41% 20% 1	760
	21st to end	Night	12% 5% 31% 36% 14% 3	760
October	1st to 10th	Night	13% 4 30% 37% 14% 2	760
	11th to 20th	Night	14% 5% 29% 37% 13% 2	760
	21st to end	Night	15% 7% 33% 31% 13% 1	857
November	1st to 10th	Night	18% 6% 30% 33% 10% 2	950
	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 2024-11-03 00:11:30. Version ac07

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