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 2024-11-04.

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% 3 8% 5% 5% 5% 4 6% 7% 34%	100811
	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 35%	98199
Transparency	Day	47% 7% 12% 21% 12% 1	104425
	Night	47% 6% 12% 21% 12% 1	102713
Seeing	Day	17% 11% 29% 23% 14% 6%	15503
	Night	19% 9% 29% 29% 12% 1	25516

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	15% 21% 5% 10% 6% 5% 4 3 4 5% 21%	2527
	11th to 20th	Day	16% 18% 6% 12% 7% 7% 6% 4 6% 5% 13%	2530
	21st to end	Day	27% 22% 6% 10% 5% 3 3 3 3 4 14%	3028
February	1st to 10th	Day	13% 14% 6% 12% 8% 5% 5% 4 5% 6% 21%	1710
	11th to 20th	Day	14% 13% 5% 12% 9% 5% 4 3 5% 6% 24%	1811
	21st to end	Day	14% 17% 4 12% 5% 4 4 3 5% 6% 26%	1570
March	1st to 10th	Day	17% 16% 4 9% 6% 4 4 3 4 6% 27%	3173
	11th to 20th	Day	13% 11% 5% 8% 6% 5% 4 3 5% 7% 32%	3480
	21st to end	Day	19% 13% 3 9% 6% 4 4 3 4 6% 28%	3815
April	1st to 10th	Day	16% 13% 3 7% 5% 4 5% 4 5% 7% 31%	2230
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 3 6% 6% 35%	2393
	21st to end	Day	17% 10% 3 8% 5% 4 4 4 4 6% 35%	2470
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 4 3 6% 7% 35%	4082
	11th to 20th	Day	16% 7% 2 7% 5% 4 5% 4 6% 8% 35%	4081
	21st to end	Day	10% 6% 2 7% 4 4 4 3 5% 9% 45%	4505
June	1st to 10th	Day	10% 5% 3 7% 5% 4 5% 5% 6% 9% 41%	2660
	11th to 20th	Day	11% 6% 2 7% 5% 4 5% 4 6% 8% 40%	2660
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 8% 11% 37%	2660
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 4 7% 9% 38%	4440
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 6% 9% 48%	4440
	21st to end	Day	7% 5% 2 7% 5% 5% 5% 5% 7% 9% 42%	4574
August	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 4 6% 9% 42%	4104
	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%	1699
	11th to 20th	Day	14% 13% 4 9% 6% 5% 4 4 5% 6% 30%	1710
	21st to end	Day	19% 12% 4 9% 5% 5% 4 3 5% 6% 29%	1670
December	1st to 10th	Day	13% 17% 6% 12% 7% 5% 5% 3 4 6% 22%	1520
	11th to 20th	Day	15% 15% 5% 11% 5% 6% 5% 4 6% 6% 21%	1788
	21st to end	Day	26% 20% 7% 13% 5% 4 4 2 3 5% 10%	2783
January	1st to 10th	Night	15% 16% 7% 12% 6% 4 4 3 4 5% 24%	4428
	11th to 20th	Night	14% 17% 7% 14% 6% 6% 6% 4 6% 5% 14%	4440
	21st to end	Night	24% 17% 9% 11% 5% 4 3 2 4 4 17%	4628
February	1st to 10th	Night	17% 15% 5% 10% 7% 5% 5% 4 4 5% 24%	2470
	11th to 20th	Night	14% 14% 4 9% 6% 6% 4 4 5% 6% 27%	2252
	21st to end	Night	18% 11% 4 10% 5% 4 4 3 5% 6% 28%	1884
March	1st to 10th	Night	16% 12% 4 9% 5% 4 3 3 4 6% 35%	3679
	11th to 20th	Night	8% 8% 3 6% 5% 4 5% 5% 6% 8% 42%	3480
	21st to end	Night	16% 9% 3 8% 6% 4 4 3 4 6% 36%	3817
April	1st to 10th	Night	15% 10% 3 7% 6% 5% 3 4 5% 7% 36%	1967
	11th to 20th	Night	18% 9% 2 6% 4 3 4 4 6% 6% 36%	1735
	21st to end	Night	17% 8% 2 7% 5% 4 5% 4 4 7% 38%	1710
May	1st to 10th	Night	15% 10% 3 7% 4 4 4 3 6% 8% 35%	2813
	11th to 20th	Night	16% 7% 2 8% 4 4 3 3 5% 7% 41%	2812
	21st to end	Night	10% 5% 2 6% 4 4 5% 3 5% 8% 48%	3034
June	1st to 10th	Night	11% 5% 2 4 5% 4 4 3 6% 9% 47%	1520
	11th to 20th	Night	10% 6% 3 6% 4 4 5% 5% 7% 8% 43%	1520
	21st to end	Night	10% 5% 2 5% 4 3 4 4 7% 9% 47%	1520
July	1st to 10th	Night	9% 3 1 5% 4 5% 6% 4 7% 9% 47%	2530
	11th to 20th	Night	8% 3 2 5% 4 3 4 4 5% 8% 54%	2530
	21st to end	Night	5% 4 2 6% 6% 5% 5% 4 7% 10% 47%	2978
August	1st to 10th	Night	11% 5% 3 5% 4 4 4 3 6% 8% 48%	2825
	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 5% 5% 4 4 3 5% 6% 43%	2452
	11th to 20th	Night	16% 11% 3 8% 5% 5% 5% 4 6% 7% 31%	2470
	21st to end	Night	19% 14% 4 8% 5% 4 4 3 5% 5% 29%	2504
December	1st to 10th	Night	18% 15% 5% 11% 7% 6% 4 4 5% 6% 20%	2660
	11th to 20th	Night	14% 15% 5% 12% 6% 5% 5% 4 6% 6% 23%	3397
	21st to end	Night	26% 24% 6% 11% 5% 4 3 2 4 4 12%	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	64% 7% 11% 13% 6%	2528
	11th to 20th	Day	70% 7% 13% 7% 3	2530
	21st to end	Day	76% 4 10% 7% 3 1	3028
February	1st to 10th	Day	62% 7% 9% 14% 7%	1710
	11th to 20th	Day	61% 5% 9% 15% 8% 1	1821
	21st to end	Day	59% 6% 11% 16% 7% 2	1570
March	1st to 10th	Day	58% 6% 11% 17% 6% 1	3173
	11th to 20th	Day	49% 6% 14% 21% 8% 1	3480
	21st to end	Day	56% 6% 12% 13% 10% 2	3815
April	1st to 10th	Day	52% 6% 11% 19% 12%	2230
	11th to 20th	Day	48% 5% 12% 20% 12% 2	2393
	21st to end	Day	48% 7% 13% 16% 14% 2	2470
May	1st to 10th	Day	46% 7% 12% 22% 11% 2	4120
	11th to 20th	Day	43% 10% 14% 23% 9% 1	4085
	21st to end	Day	36% 7% 11% 19% 23% 4	4518
June	1st to 10th	Day	37% 8% 12% 27% 13% 3	2660
	11th to 20th	Day	39% 7% 13% 23% 17% 2	2660
	21st to end	Day	38% 9% 14% 22% 16% 2	2660
July	1st to 10th	Day	40% 7% 15% 20% 16% 2	4371
	11th to 20th	Day	30% 7% 13% 32% 17% 1	4365
	21st to end	Day	36% 9% 13% 19% 21% 1	4429
August	1st to 10th	Day	38% 7% 13% 25% 16% 1	4091
	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% 7% 12% 22% 13% 1	1699
	11th to 20th	Day	54% 5% 13% 19% 7% 2	1710
	21st to end	Day	57% 5% 12% 18% 7%	1670
December	1st to 10th	Day	63% 7% 11% 14% 4	1520
	11th to 20th	Day	61% 7% 13% 15% 4	1784
	21st to end	Day	77% 5% 9% 6% 3	2783
January	1st to 10th	Night	62% 6% 12% 15% 6% 1	4428
	11th to 20th	Night	68% 7% 13% 8% 4	4440
	21st to end	Night	71% 5% 10% 11% 3 1	4628
February	1st to 10th	Night	62% 7% 10% 13% 7% 1	2470
	11th to 20th	Night	56% 5% 11% 17% 9% 1	2253
	21st to end	Night	56% 5% 13% 17% 8% 2	1884
March	1st to 10th	Night	50% 5% 12% 25% 7% 1	3679
	11th to 20th	Night	37% 7% 15% 21% 19% 1	3480
	21st to end	Night	48% 6% 12% 22% 11% 1	3817
April	1st to 10th	Night	48% 6% 10% 21% 14% 2	1967
	11th to 20th	Night	46% 6% 11% 18% 18% 2	1735
	21st to end	Night	45% 7% 11% 18% 16% 3	1710
May	1st to 10th	Night	46% 7% 11% 21% 13% 3	2840
	11th to 20th	Night	41% 8% 10% 27% 13% 2	2813
	21st to end	Night	33% 8% 13% 21% 21% 5%	3042
June	1st to 10th	Night	34% 6% 11% 28% 18% 3	1520
	11th to 20th	Night	35% 8% 14% 24% 17% 2	1520
	21st to end	Night	32% 7% 14% 26% 20% 1	1520
July	1st to 10th	Night	32% 6% 13% 28% 14% 6%	2490
	11th to 20th	Night	28% 5% 13% 31% 22% 2	2482
	21st to end	Night	31% 8% 18% 19% 22% 2	2883
August	1st to 10th	Night	33% 7% 13% 28% 18% 1	2814
	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	2452
	11th to 20th	Night	52% 5% 14% 19% 8% 1	2470
	21st to end	Night	56% 6% 12% 19% 7%	2504
December	1st to 10th	Night	64% 7% 11% 13% 6%	2660
	11th to 20th	Night	59% 7% 13% 14% 6% 1	3400
	21st to end	Night	76% 6% 10% 6% 2	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	24% 17% 37% 15% 6% 1	270
	11th to 20th	Day	25% 14% 45% 14% 1 1	270
	21st to end	Day	28% 15% 34% 18% 4 1	297
February	1st to 10th	Day	23% 21% 38% 14% 2 1	270
	11th to 20th	Day	24% 21% 38% 15% 2	270
	21st to end	Day	27% 26% 35% 11% 1	225
March	1st to 10th	Day	26% 24% 31% 15% 3	297
	11th to 20th	Day	23% 13% 34% 23% 7%	460
	21st to end	Day	26% 17% 31% 21% 5% 1	506
April	1st to 10th	Day	20% 15% 35% 20% 8% 1	460
	11th to 20th	Day	25% 18% 31% 15% 6% 5%	452
	21st to end	Day	24% 15% 30% 18% 11% 2	460
May	1st to 10th	Day	24% 13% 28% 21% 11% 3	463
	11th to 20th	Day	20% 10% 28% 22% 13% 7%	487
	21st to end	Day	14% 6% 23% 28% 19% 9%	545
June	1st to 10th	Day	11% 8% 29% 30% 18% 4	680
	11th to 20th	Day	13% 7% 31% 28% 18% 4	680
	21st to end	Day	12% 8% 30% 29% 16% 5%	680
July	1st to 10th	Day	8% 6% 24% 26% 25% 11%	671
	11th to 20th	Day	10% 7% 27% 28% 19% 9%	668
	21st to end	Day	9% 4 24% 30% 23% 9%	601
August	1st to 10th	Day	8% 5% 20% 28% 26% 14%	486
	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	16% 18% 36% 19% 10% 1	279
	11th to 20th	Day	22% 22% 31% 17% 6% 1	270
	21st to end	Day	26% 19% 36% 14% 4	250
December	1st to 10th	Day	24% 19% 34% 14% 7% 1	180
	11th to 20th	Day	24% 19% 41% 12% 4 1	196
	21st to end	Day	28% 22% 33% 16% 1	297
January	1st to 10th	Night	22% 15% 35% 22% 6% 1	950
	11th to 20th	Night	25% 14% 34% 22% 5% 1	950
	21st to end	Night	21% 12% 34% 28% 5%	893
February	1st to 10th	Night	24% 12% 37% 23% 3	760
	11th to 20th	Night	22% 15% 35% 24% 4	743
	21st to end	Night	26% 13% 38% 21% 2	628
March	1st to 10th	Night	21% 12% 35% 26% 5% 1	760
	11th to 20th	Night	17% 15% 36% 25% 5% 1	760
	21st to end	Night	23% 11% 30% 27% 8% 1	836
April	1st to 10th	Night	19% 15% 34% 28% 4 1	637
	11th to 20th	Night	23% 9% 34% 26% 7% 1	563
	21st to end	Night	20% 9% 32% 30% 8%	570
May	1st to 10th	Night	18% 9% 31% 32% 8% 1	570
	11th to 20th	Night	22% 4 26% 34% 12% 1	561
	21st to end	Night	12% 4 24% 37% 20% 2	617
June	1st to 10th	Night	12% 4 24% 47% 13% 1	570
	11th to 20th	Night	12% 4 24% 41% 19%	570
	21st to end	Night	10% 4 22% 43% 19% 1	570
July	1st to 10th	Night	8% 2 17% 41% 28% 4	555
	11th to 20th	Night	10% 3 18% 40% 24% 5%	552
	21st to end	Night	5% 2 18% 48% 26% 2	624
August	1st to 10th	Night	8% 2 17% 43% 28% 3	567
	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% 31% 29% 11% 1	755
	11th to 20th	Night	22% 14% 35% 22% 7% 1	760
	21st to end	Night	25% 13% 34% 21% 6%	760
December	1st to 10th	Night	23% 17% 34% 21% 6%	760
	11th to 20th	Night	24% 14% 38% 21% 3	893
	21st to end	Night	32% 12% 35% 19% 2	1045

Page generated at 2024-11-01 22:47:41. Version ac07

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