Island Lake State Recreation Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Island Lake State Recreation Area clear sky chart from 2005-11-06 to 2025-08-05.

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	14% 10% 4 9% 5% 5% 5% 4 6% 7% 33%	124857
	Night	14% 11% 4 8% 5% 4 4 3 5% 6% 34%	123295
Transparency	Day	48% 6% 12% 20% 12% 1	128427
	Night	48% 6% 12% 21% 12% 1	127783
Seeing	Day	18% 12% 29% 23% 13% 5%	16508
	Night	19% 10% 29% 29% 12% 1	26527

By Month

Percentage Cloud Cover SE (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% 18% 6% 17% 6% 5% 4 3 4 5% 22%	3617
	11th to 20th	Day	14% 15% 6% 18% 8% 9% 6% 3 5% 5% 10%	3620
	21st to end	Day	22% 19% 6% 12% 5% 4 5% 3 4 4 16%	4331
February	1st to 10th	Day	14% 14% 6% 13% 8% 5% 5% 4 4 7% 21%	1800
	11th to 20th	Day	14% 13% 5% 12% 9% 5% 4 3 5% 6% 23%	1910
	21st to end	Day	14% 17% 4 12% 5% 5% 4 3 5% 6% 26%	1650
March	1st to 10th	Day	15% 12% 4 11% 6% 4 4 3 5% 6% 30%	4561
	11th to 20th	Day	12% 11% 4 8% 5% 4 4 4 5% 8% 35%	4980
	21st to end	Day	18% 14% 4 9% 5% 4 4 3 4 6% 28%	5465
April	1st to 10th	Day	16% 13% 3 7% 5% 4 5% 4 5% 6% 30%	2348
	11th to 20th	Day	16% 10% 3 7% 5% 5% 4 3 6% 6% 35%	2521
	21st to end	Day	16% 9% 3 8% 5% 4 4 4 5% 7% 35%	2600
May	1st to 10th	Day	19% 9% 3 8% 4 4 4 3 5% 6% 34%	5862
	11th to 20th	Day	16% 8% 2 7% 5% 4 5% 4 7% 8% 33%	5861
	21st to end	Day	14% 7% 3 7% 4 4 4 3 5% 8% 41%	6476
June	1st to 10th	Day	10% 5% 3 7% 5% 4 5% 5% 6% 9% 42%	2800
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 9% 39%	2800
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 8% 11% 38%	2800
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 4 7% 10% 40%	6360
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 4 6% 9% 47%	6360
	21st to end	Day	8% 5% 2 6% 4 4 4 4 7% 9% 45%	6588
August	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 4 6% 9% 42%	4156
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 8% 40%	4044
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 4 8% 9% 40%	4445
September	1st to 10th	Day	10% 6% 2 7% 5% 6% 5% 4 6% 9% 40%	2161
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 9% 47%	2090
	21st to end	Day	13% 7% 3 8% 4 5% 5% 5% 6% 7% 37%	2090
October	1st to 10th	Day	13% 6% 3 6% 5% 5% 4 4 5% 6% 42%	2052
	11th to 20th	Day	17% 9% 4 7% 6% 5% 4 3 5% 7% 33%	1900
	21st to end	Day	19% 10% 3 8% 5% 4 4 4 5% 6% 31%	1916
November	1st to 10th	Day	12% 10% 3 8% 5% 5% 4 4 5% 7% 38%	1762
	11th to 20th	Day	15% 13% 4 9% 6% 5% 4 4 5% 6% 29%	1800
	21st to end	Day	19% 13% 4 10% 5% 5% 4 3 5% 5% 27%	1757
December	1st to 10th	Day	12% 15% 7% 13% 8% 7% 5% 4 5% 6% 19%	2600
	11th to 20th	Day	19% 21% 6% 10% 5% 5% 4 4 4 5% 17%	2792
	21st to end	Day	26% 20% 8% 11% 5% 3 3 2 3 4 13%	3982
January	1st to 10th	Night	13% 14% 6% 13% 6% 5% 5% 3 5% 5% 24%	6348
	11th to 20th	Night	12% 15% 8% 15% 8% 6% 6% 4 6% 6% 15%	6360
	21st to end	Night	18% 16% 8% 11% 5% 5% 4 3 4 5% 21%	6628
February	1st to 10th	Night	16% 15% 5% 11% 7% 5% 5% 4 4 5% 24%	2600
	11th to 20th	Night	14% 14% 4 10% 7% 6% 4 4 5% 6% 27%	2373
	21st to end	Night	18% 10% 4 10% 5% 4 4 3 6% 6% 28%	1980
March	1st to 10th	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 36%	5291
	11th to 20th	Night	9% 9% 3 6% 4 4 5% 4 6% 8% 42%	4980
	21st to end	Night	16% 10% 3 8% 5% 4 4 3 4 6% 36%	5467
April	1st to 10th	Night	16% 10% 3 7% 5% 5% 3 3 5% 7% 36%	2070
	11th to 20th	Night	17% 9% 3 6% 4 4 4 4 6% 6% 37%	1827
	21st to end	Night	17% 7% 2 8% 5% 4 5% 4 4 7% 38%	1800
May	1st to 10th	Night	19% 11% 3 8% 4 4 4 3 5% 6% 32%	4033
	11th to 20th	Night	18% 9% 2 8% 4 4 3 2 5% 6% 39%	4032
	21st to end	Night	14% 6% 2 6% 4 3 5% 3 5% 7% 45%	4363
June	1st to 10th	Night	11% 5% 2 4 5% 4 4 3 6% 9% 47%	1600
	11th to 20th	Night	11% 6% 3 6% 4 4 5% 5% 7% 8% 43%	1600
	21st to end	Night	10% 5% 2 5% 4 3 4 4 7% 9% 48%	1600
July	1st to 10th	Night	8% 4 2 5% 4 5% 6% 5% 7% 9% 47%	3618
	11th to 20th	Night	8% 4 2 6% 4 4 4 4 6% 9% 50%	3617
	21st to end	Night	8% 5% 2 6% 5% 4 4 3 5% 8% 48%	4266
August	1st to 10th	Night	11% 5% 3 5% 4 4 4 3 6% 8% 48%	2861
	11th to 20th	Night	9% 6% 2 5% 4 4 5% 3 5% 7% 49%	2785
	21st to end	Night	8% 6% 2 7% 4 4 4 4 5% 8% 48%	3208
September	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 5% 7% 49%	2000
	11th to 20th	Night	10% 5% 1 4 4 4 3 3 5% 6% 55%	2090
	21st to end	Night	13% 7% 3 6% 4 4 5% 4 5% 7% 43%	2090
October	1st to 10th	Night	13% 7% 3 5% 4 4 4 3 4 6% 47%	2128
	11th to 20th	Night	19% 9% 3 7% 4 5% 4 4 4 6% 35%	2280
	21st to end	Night	20% 9% 3 8% 4 4 4 4 5% 6% 33%	2679
November	1st to 10th	Night	13% 8% 4 6% 5% 4 4 3 5% 6% 43%	2536
	11th to 20th	Night	16% 11% 3 8% 5% 5% 5% 4 6% 6% 30%	2600
	21st to end	Night	19% 14% 4 9% 5% 4 4 3 5% 5% 28%	2636
December	1st to 10th	Night	13% 13% 5% 15% 7% 6% 5% 4 5% 6% 22%	4580
	11th to 20th	Night	15% 20% 6% 12% 7% 5% 4 4 5% 5% 18%	5373
	21st to end	Night	25% 23% 7% 10% 4 4 3 3 4 4 14%	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	64% 6% 10% 14% 6% 1	3618
	11th to 20th	Day	74% 6% 10% 6% 4	3620
	21st to end	Day	72% 4 10% 8% 4	4331
February	1st to 10th	Day	63% 7% 9% 14% 7%	1800
	11th to 20th	Day	62% 5% 9% 15% 8% 1	1920
	21st to end	Day	59% 6% 11% 16% 7% 2	1650
March	1st to 10th	Day	55% 5% 12% 17% 9% 2	4561
	11th to 20th	Day	46% 5% 17% 22% 8% 2	4980
	21st to end	Day	57% 5% 10% 14% 12% 1	5465
April	1st to 10th	Day	53% 6% 11% 18% 12% 1	2348
	11th to 20th	Day	48% 5% 12% 21% 12% 2	2521
	21st to end	Day	47% 7% 13% 18% 14% 1	2600
May	1st to 10th	Day	49% 6% 10% 19% 13% 3	5897
	11th to 20th	Day	46% 9% 12% 20% 12% 2	5865
	21st to end	Day	40% 6% 10% 22% 19% 3	6490
June	1st to 10th	Day	37% 8% 12% 27% 14% 3	2800
	11th to 20th	Day	39% 7% 13% 23% 16% 2	2800
	21st to end	Day	38% 9% 14% 22% 16% 2	2800
July	1st to 10th	Day	36% 7% 15% 25% 15% 2	6291
	11th to 20th	Day	32% 7% 14% 28% 18% 1	6285
	21st to end	Day	33% 7% 14% 24% 21% 1	6401
August	1st to 10th	Day	37% 7% 13% 25% 17% 1	4143
	11th to 20th	Day	39% 7% 12% 31% 11% 1	4083
	21st to end	Day	37% 8% 14% 28% 12% 1	4444
September	1st to 10th	Day	40% 7% 14% 23% 14% 2	2161
	11th to 20th	Day	32% 8% 12% 32% 16% 1	2090
	21st to end	Day	43% 6% 12% 24% 13%	2090
October	1st to 10th	Day	31% 5% 11% 31% 20% 1	3416
	11th to 20th	Day	39% 5% 12% 25% 19%	3140
	21st to end	Day	45% 5% 14% 24% 12% 1	3128
November	1st to 10th	Day	45% 6% 11% 23% 13% 1	1762
	11th to 20th	Day	55% 5% 12% 19% 7% 2	1800
	21st to end	Day	58% 5% 12% 17% 7%	1757
December	1st to 10th	Day	64% 7% 15% 11% 3	2600
	11th to 20th	Day	69% 5% 9% 13% 4	2788
	21st to end	Day	75% 4 8% 8% 4	3982
January	1st to 10th	Night	60% 5% 10% 18% 6% 1	6348
	11th to 20th	Night	67% 6% 12% 10% 5%	6360
	21st to end	Night	65% 5% 11% 12% 7%	6628
February	1st to 10th	Night	62% 6% 10% 14% 7% 1	2600
	11th to 20th	Night	57% 5% 11% 17% 9% 1	2374
	21st to end	Night	56% 5% 14% 17% 8% 2	1980
March	1st to 10th	Night	49% 5% 13% 23% 10% 1	5291
	11th to 20th	Night	38% 6% 14% 26% 15% 1	4980
	21st to end	Night	49% 5% 11% 19% 14% 2	5467
April	1st to 10th	Night	48% 6% 10% 21% 13% 2	2070
	11th to 20th	Night	45% 6% 11% 18% 18% 2	1827
	21st to end	Night	45% 7% 12% 18% 16% 3	1800
May	1st to 10th	Night	52% 6% 10% 16% 12% 4	4060
	11th to 20th	Night	45% 6% 9% 25% 11% 3	4033
	21st to end	Night	37% 6% 12% 22% 18% 4	4371
June	1st to 10th	Night	34% 6% 11% 27% 20% 3	1600
	11th to 20th	Night	35% 8% 14% 25% 16% 2	1600
	21st to end	Night	32% 7% 15% 26% 20% 1	1600
July	1st to 10th	Night	32% 7% 14% 28% 15% 5%	3580
	11th to 20th	Night	30% 6% 14% 29% 20% 1	3572
	21st to end	Night	34% 6% 14% 21% 24% 2	4140
August	1st to 10th	Night	33% 7% 13% 28% 19% 1	2850
	11th to 20th	Night	33% 7% 11% 36% 12% 2	2812
	21st to end	Night	35% 7% 12% 31% 14% 1	3208
September	1st to 10th	Night	33% 8% 12% 27% 18% 2	2000
	11th to 20th	Night	30% 5% 10% 31% 22% 2	2090
	21st to end	Night	40% 6% 12% 28% 14% 1	2090
October	1st to 10th	Night	26% 4 10% 32% 27% 1	3544
	11th to 20th	Night	43% 4 12% 24% 18%	3779
	21st to end	Night	40% 4 11% 31% 13% 1	4405
November	1st to 10th	Night	42% 5% 12% 25% 15% 1	2536
	11th to 20th	Night	52% 5% 14% 19% 9% 1	2600
	21st to end	Night	57% 6% 12% 18% 7%	2636
December	1st to 10th	Night	61% 7% 15% 14% 4	4580
	11th to 20th	Night	66% 6% 11% 13% 4 1	5376
	21st to end	Night	74% 5% 9% 7% 6%	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	23% 17% 39% 14% 5% 1	300
	11th to 20th	Day	24% 17% 45% 12% 1 1	300
	21st to end	Day	27% 17% 34% 17% 4 1	330
February	1st to 10th	Day	24% 23% 37% 13% 2 1	300
	11th to 20th	Day	25% 22% 37% 15% 2	300
	21st to end	Day	27% 25% 35% 11% 1	249
March	1st to 10th	Day	25% 24% 33% 15% 3	329
	11th to 20th	Day	24% 14% 34% 22% 6%	500
	21st to end	Day	27% 17% 31% 20% 5% 1	550
April	1st to 10th	Day	22% 15% 35% 19% 8% 1	500
	11th to 20th	Day	25% 19% 31% 15% 6% 5%	492
	21st to end	Day	24% 14% 30% 19% 11% 2	500
May	1st to 10th	Day	24% 13% 28% 21% 11% 3	503
	11th to 20th	Day	21% 11% 27% 22% 13% 7%	527
	21st to end	Day	15% 8% 24% 26% 18% 8%	590
June	1st to 10th	Day	11% 8% 30% 30% 16% 4	730
	11th to 20th	Day	13% 7% 32% 28% 17% 4	730
	21st to end	Day	12% 8% 29% 31% 16% 5%	730
July	1st to 10th	Day	8% 6% 24% 27% 24% 11%	721
	11th to 20th	Day	10% 7% 27% 28% 19% 8%	718
	21st to end	Day	9% 4 24% 30% 23% 9%	649
August	1st to 10th	Day	7% 4 20% 28% 25% 15%	502
	11th to 20th	Day	14% 4 18% 28% 24% 12%	479
	21st to end	Day	10% 4 21% 27% 25% 12%	539
September	1st to 10th	Day	12% 6% 24% 24% 23% 11%	490
	11th to 20th	Day	10% 3 18% 25% 29% 16%	490
	21st to end	Day	16% 9% 25% 23% 18% 9%	490
October	1st to 10th	Day	17% 9% 26% 24% 16% 8%	490
	11th to 20th	Day	21% 15% 28% 26% 9% 1	490
	21st to end	Day	27% 16% 35% 17% 5%	365
November	1st to 10th	Day	17% 19% 36% 18% 10% 1	300
	11th to 20th	Day	24% 22% 31% 17% 5% 1	300
	21st to end	Day	26% 21% 36% 14% 4	277
December	1st to 10th	Day	23% 20% 36% 14% 8% 1	200
	11th to 20th	Day	27% 19% 39% 11% 4	218
	21st to end	Day	29% 22% 32% 15% 2	330
January	1st to 10th	Night	22% 15% 35% 22% 5% 1	1000
	11th to 20th	Night	24% 15% 35% 21% 4 1	1000
	21st to end	Night	21% 13% 34% 27% 5%	940
February	1st to 10th	Night	24% 13% 38% 23% 3	800
	11th to 20th	Night	23% 15% 35% 23% 4	783
	21st to end	Night	25% 13% 39% 20% 2	660
March	1st to 10th	Night	21% 13% 35% 25% 5% 1	800
	11th to 20th	Night	17% 16% 36% 25% 5% 1	800
	21st to end	Night	23% 12% 30% 27% 7% 1	880
April	1st to 10th	Night	20% 16% 34% 27% 3 1	670
	11th to 20th	Night	23% 10% 33% 25% 8% 1	593
	21st to end	Night	20% 10% 32% 30% 8%	600
May	1st to 10th	Night	19% 9% 32% 31% 8% 1	600
	11th to 20th	Night	22% 6% 27% 33% 12% 1	591
	21st to end	Night	12% 5% 25% 37% 19% 2	650
June	1st to 10th	Night	12% 4 24% 46% 13% 1	600
	11th to 20th	Night	13% 4 24% 41% 19%	600
	21st to end	Night	10% 4 23% 43% 19% 2	600
July	1st to 10th	Night	8% 2 16% 42% 28% 4	585
	11th to 20th	Night	10% 3 19% 40% 24% 5%	582
	21st to end	Night	5% 2 17% 48% 25% 2	657
August	1st to 10th	Night	8% 2 18% 42% 28% 3	579
	11th to 20th	Night	9% 2 20% 38% 28% 4	564
	21st to end	Night	10% 3 17% 35% 33% 3	627
September	1st to 10th	Night	12% 4 20% 34% 26% 4	670
	11th to 20th	Night	12% 4 16% 33% 31% 4	760
	21st to end	Night	15% 7% 20% 32% 21% 5%	760
October	1st to 10th	Night	16% 6% 28% 30% 17% 3	760
	11th to 20th	Night	23% 12% 29% 26% 9% 1	760
	21st to end	Night	25% 10% 35% 24% 6%	836
November	1st to 10th	Night	18% 10% 32% 28% 11% 1	780
	11th to 20th	Night	21% 15% 35% 22% 6% 1	800
	21st to end	Night	25% 14% 34% 21% 6%	800
December	1st to 10th	Night	22% 17% 34% 21% 6%	800
	11th to 20th	Night	24% 14% 37% 21% 3	940
	21st to end	Night	32% 12% 35% 19% 2	1100

Page generated at 2025-08-02 01:32:22. Version ac07

Copyright © 2025 Attilla Danko.