Goose Island State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Goose Island State Park clear sky chart from 2005-11-06 to 2026-10-14.

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	11% 6% 2 6% 4 4 5% 4 6% 9% 43%	148822
	Night	13% 6% 2 5% 4 4 4 3 5% 8% 46%	143302
Transparency	Day	25% 35% 12% 16% 8% 4	152564
	Night	25% 35% 11% 16% 9% 5%	147626
Seeing	Day	11% 4 15% 29% 31% 10%	17162
	Night	14% 5% 16% 32% 29% 5%	26996

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	20% 9% 3 6% 3 3 3 3 4 5% 40%	5289
	11th to 20th	Day	15% 8% 2 6% 4 3 4 3 4 5% 45%	5310
	21st to end	Day	25% 9% 3 6% 4 3 4 3 5% 5% 33%	6152
February	1st to 10th	Day	20% 9% 3 5% 3 3 3 3 4 6% 41%	2100
	11th to 20th	Day	19% 9% 3 6% 3 3 3 3 5% 6% 40%	2049
	21st to end	Day	18% 8% 2 5% 4 3 3 3 5% 5% 45%	1822
March	1st to 10th	Day	17% 8% 3 7% 4 4 4 3 5% 7% 40%	5046
	11th to 20th	Day	17% 7% 3 6% 4 4 3 2 4 6% 46%	5090
	21st to end	Day	18% 7% 2 5% 3 4 4 3 5% 6% 43%	5583
April	1st to 10th	Day	15% 7% 3 5% 4 3 4 4 6% 8% 41%	2310
	11th to 20th	Day	16% 7% 3 6% 4 4 4 4 6% 7% 39%	2286
	21st to end	Day	12% 7% 3 6% 5% 4 4 4 6% 8% 41%	2520
May	1st to 10th	Day	20% 8% 3 8% 5% 6% 5% 4 6% 8% 27%	7498
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	7627
	21st to end	Day	9% 6% 2 7% 5% 6% 7% 6% 9% 11% 32%	8392
June	1st to 10th	Day	3 4 1 5% 3 3 5% 4 9% 13% 49%	2730
	11th to 20th	Day	5% 4 2 5% 3 5% 5% 5% 8% 14% 45%	2730
	21st to end	Day	6% 5% 1 4 4 5% 5% 6% 10% 13% 40%	2730
July	1st to 10th	Day	5% 5% 2 6% 5% 5% 6% 4 7% 10% 47%	7680
	11th to 20th	Day	5% 6% 2 7% 5% 5% 6% 5% 8% 13% 36%	7680
	21st to end	Day	5% 4 2 5% 4 4 5% 4 7% 12% 49%	8337
August	1st to 10th	Day	1 1 1 2 2 2 3 3 6% 9% 70%	6014
	11th to 20th	Day	2 2 1 2 3 4 5% 6% 9% 13% 55%	5579
	21st to end	Day	3 2 1 4 4 4 5% 5% 8% 12% 49%	5566
September	1st to 10th	Day	8% 5% 2 8% 6% 6% 7% 7% 7% 10% 35%	2310
	11th to 20th	Day	9% 5% 3 5% 5% 5% 5% 5% 7% 9% 42%	2310
	21st to end	Day	8% 4 2 5% 4 3 4 5% 8% 10% 48%	2310
October	1st to 10th	Day	6% 3 2 5% 4 4 4 4 5% 9% 55%	2310
	11th to 20th	Day	10% 5% 2 4 4 3 4 3 5% 7% 54%	2037
	21st to end	Day	9% 4 2 4 4 4 4 3 4 6% 57%	2200
November	1st to 10th	Day	10% 5% 2 5% 4 3 5% 4 6% 8% 48%	2058
	11th to 20th	Day	14% 5% 2 5% 4 4 3 3 5% 6% 48%	2100
	21st to end	Day	17% 5% 2 7% 4 5% 5% 3 5% 6% 41%	1969
December	1st to 10th	Day	26% 12% 3 7% 4 4 4 3 4 5% 28%	3030
	11th to 20th	Day	11% 8% 3 9% 4 4 5% 3 6% 7% 40%	3481
	21st to end	Day	13% 6% 2 6% 4 3 4 2 5% 6% 49%	4587
January	1st to 10th	Night	20% 7% 2 6% 4 4 3 3 4 5% 44%	7634
	11th to 20th	Night	13% 8% 2 7% 3 3 3 3 4 6% 48%	7680
	21st to end	Night	26% 8% 3 8% 4 4 4 3 5% 6% 30%	8104
February	1st to 10th	Night	19% 9% 2 6% 3 3 3 3 4 6% 42%	2520
	11th to 20th	Night	18% 7% 3 4 3 3 4 3 4 7% 44%	2458
	21st to end	Night	19% 9% 2 5% 4 4 4 3 4 6% 43%	1982
March	1st to 10th	Night	20% 8% 2 6% 3 3 3 3 5% 7% 40%	5029
	11th to 20th	Night	16% 7% 2 6% 4 4 3 3 3 5% 47%	5090
	21st to end	Night	18% 6% 2 4 2 3 3 3 4 5% 51%	5588
April	1st to 10th	Night	14% 9% 3 6% 5% 4 4 4 5% 7% 39%	2310
	11th to 20th	Night	18% 7% 2 6% 3 3 3 3 4 8% 43%	2280
	21st to end	Night	14% 8% 2 6% 5% 4 4 4 6% 8% 38%	2100
May	1st to 10th	Night	23% 9% 3 7% 5% 5% 4 3 5% 7% 29%	5350
	11th to 20th	Night	12% 6% 2 6% 3 4 4 4 7% 10% 43%	5265
	21st to end	Night	10% 7% 3 9% 6% 5% 6% 5% 7% 11% 33%	5793
June	1st to 10th	Night	5% 3 1 4 3 4 5% 4 8% 11% 52%	1890
	11th to 20th	Night	5% 4 2 4 5% 4 5% 5% 7% 13% 46%	1890
	21st to end	Night	6% 5% 1 5% 4 4 5% 7% 8% 12% 43%	1890
July	1st to 10th	Night	4 4 1 6% 4 4 5% 4 6% 10% 51%	5308
	11th to 20th	Night	4 5% 2 6% 6% 6% 6% 5% 8% 13% 39%	5307
	21st to end	Night	5% 4 2 5% 4 4 5% 4 7% 11% 49%	5770
August	1st to 10th	Night	1 1 2 2 2 4 9% 77%	4156
	11th to 20th	Night	1 1 1 3 3 3 4 4 7% 14% 60%	4477
	21st to end	Night	2 2 1 3 2 3 4 4 6% 14% 61%	5560
September	1st to 10th	Night	6% 5% 1 7% 4 5% 7% 5% 7% 9% 43%	2310
	11th to 20th	Night	7% 5% 2 6% 5% 4 4 4 5% 9% 48%	2310
	21st to end	Night	7% 3 1 5% 3 4 4 4 7% 9% 52%	2310
October	1st to 10th	Night	5% 3 1 4 4 4 5% 4 5% 8% 58%	2310
	11th to 20th	Night	9% 5% 1 3 2 2 2 3 5% 7% 60%	2406
	21st to end	Night	8% 4 2 4 3 3 3 3 4 6% 62%	2640
November	1st to 10th	Night	9% 4 1 4 4 4 3 3 5% 7% 54%	2460
	11th to 20th	Night	14% 6% 2 5% 4 3 3 2 5% 6% 51%	2520
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 6% 43%	2646
December	1st to 10th	Night	30% 12% 4 7% 3 3 2 2 3 4 29%	4380
	11th to 20th	Night	14% 8% 3 6% 4 4 4 4 5% 7% 43%	4946
	21st to end	Night	11% 6% 2 6% 4 4 3 3 5% 6% 50%	6633

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	39% 23% 9% 17% 7% 5%	5290
	11th to 20th	Day	32% 24% 6% 14% 15% 8%	5310
	21st to end	Day	43% 23% 5% 9% 13% 6%	6152
February	1st to 10th	Day	21% 60% 4 4 6% 5%	2100
	11th to 20th	Day	19% 58% 5% 10% 7% 2	2059
	21st to end	Day	19% 60% 3 8% 6% 4	1822
March	1st to 10th	Day	34% 32% 6% 13% 3 11%	5046
	11th to 20th	Day	29% 30% 4 9% 13% 14%	5090
	21st to end	Day	30% 30% 6% 16% 13% 4	5585
April	1st to 10th	Day	17% 59% 5% 6% 7% 5%	2310
	11th to 20th	Day	19% 61% 6% 6% 5% 3	2286
	21st to end	Day	17% 61% 6% 10% 5% 2	2520
May	1st to 10th	Day	43% 27% 12% 12% 6% 1	7535
	11th to 20th	Day	28% 25% 14% 19% 11% 4	7631
	21st to end	Day	33% 28% 14% 22% 3	8405
June	1st to 10th	Day	9% 62% 10% 15% 4	2730
	11th to 20th	Day	14% 61% 8% 11% 5%	2730
	21st to end	Day	12% 61% 11% 13% 3	2730
July	1st to 10th	Day	23% 23% 33% 20% 1	7616
	11th to 20th	Day	33% 24% 29% 11% 2	7611
	21st to end	Day	23% 22% 19% 29% 6%	8155
August	1st to 10th	Day	7% 28% 17% 39% 9%	6000
	11th to 20th	Day	12% 29% 33% 24% 2	5618
	21st to end	Day	17% 29% 20% 27% 5% 1	5565
September	1st to 10th	Day	16% 59% 8% 10% 6% 1	2310
	11th to 20th	Day	13% 56% 11% 14% 6% 1	2310
	21st to end	Day	14% 57% 9% 15% 3 2	2310
October	1st to 10th	Day	12% 36% 5% 8% 18% 21%	3700
	11th to 20th	Day	14% 37% 8% 12% 21% 7%	3277
	21st to end	Day	17% 38% 4 16% 20% 5%	3538
November	1st to 10th	Day	19% 56% 8% 7% 7% 3	2058
	11th to 20th	Day	22% 55% 5% 8% 4 6%	2100
	21st to end	Day	22% 55% 6% 8% 8% 2	1969
December	1st to 10th	Day	45% 35% 3 6% 10% 2	3030
	11th to 20th	Day	26% 34% 6% 15% 11% 9%	3479
	21st to end	Day	27% 27% 5% 17% 13% 10%	4587
January	1st to 10th	Night	36% 23% 7% 15% 12% 7%	7635
	11th to 20th	Night	31% 22% 4 15% 18% 9%	7680
	21st to end	Night	45% 23% 5% 10% 11% 6%	8104
February	1st to 10th	Night	20% 59% 4 4 6% 7%	2520
	11th to 20th	Night	16% 59% 5% 9% 7% 4	2458
	21st to end	Night	18% 59% 3 8% 7% 5%	1982
March	1st to 10th	Night	36% 30% 7% 12% 7% 8%	5029
	11th to 20th	Night	31% 29% 5% 7% 13% 15%	5090
	21st to end	Night	25% 30% 7% 17% 17% 4	5588
April	1st to 10th	Night	18% 59% 5% 7% 6% 5%	2310
	11th to 20th	Night	17% 61% 6% 6% 5% 5%	2280
	21st to end	Night	17% 60% 7% 9% 5% 2	2100
May	1st to 10th	Night	47% 25% 10% 12% 5% 2	5377
	11th to 20th	Night	27% 27% 10% 22% 11% 4	5266
	21st to end	Night	36% 26% 16% 19% 2	5805
June	1st to 10th	Night	10% 60% 8% 16% 6%	1890
	11th to 20th	Night	15% 60% 5% 13% 6%	1890
	21st to end	Night	14% 60% 8% 14% 3	1890
July	1st to 10th	Night	21% 23% 30% 25% 1	5265
	11th to 20th	Night	31% 25% 29% 13% 1	5256
	21st to end	Night	24% 23% 18% 27% 8%	5641
August	1st to 10th	Night	4 26% 18% 41% 10%	4146
	11th to 20th	Night	10% 29% 32% 27% 2	4504
	21st to end	Night	8% 29% 24% 32% 6%	5560
September	1st to 10th	Night	12% 58% 12% 11% 6% 2	2310
	11th to 20th	Night	11% 56% 10% 14% 7% 1	2310
	21st to end	Night	13% 57% 9% 15% 4 2	2310
October	1st to 10th	Night	11% 36% 5% 9% 14% 24%	3700
	11th to 20th	Night	9% 35% 8% 14% 23% 10%	3892
	21st to end	Night	13% 37% 4 17% 23% 6%	4252
November	1st to 10th	Night	19% 55% 6% 8% 8% 4	2460
	11th to 20th	Night	21% 55% 5% 8% 6% 5%	2520
	21st to end	Night	23% 55% 5% 8% 7% 3	2646
December	1st to 10th	Night	47% 34% 3 5% 7% 3	4380
	11th to 20th	Night	25% 33% 7% 13% 12% 10%	4947
	21st to end	Night	26% 28% 5% 15% 15% 11%	6633

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	19% 10% 26% 31% 12% 2	330
	11th to 20th	Day	23% 10% 22% 35% 9% 1	330
	21st to end	Day	21% 8% 32% 27% 11% 1	363
February	1st to 10th	Day	24% 8% 25% 27% 15% 2	330
	11th to 20th	Day	25% 8% 25% 31% 11%	330
	21st to end	Day	19% 4 38% 32% 7%	273
March	1st to 10th	Day	18% 6% 32% 33% 10% 1	330
	11th to 20th	Day	17% 9% 32% 32% 9% 1	330
	21st to end	Day	13% 7% 34% 36% 9% 2	363
April	1st to 10th	Day	16% 5% 37% 30% 11% 1	330
	11th to 20th	Day	18% 10% 28% 30% 13% 1	324
	21st to end	Day	14% 7% 30% 37% 11% 1	540
May	1st to 10th	Day	15% 5% 32% 37% 11%	711
	11th to 20th	Day	10% 4 25% 41% 16% 3	775
	21st to end	Day	8% 3 16% 45% 26% 3	844
June	1st to 10th	Day	5% 1 7% 38% 40% 8%	780
	11th to 20th	Day	7% 1 8% 38% 39% 7%	780
	21st to end	Day	7% 2 6% 31% 43% 12%	780
July	1st to 10th	Day	6% 2 4 23% 48% 16%	771
	11th to 20th	Day	4 1 2 17% 58% 18%	768
	21st to end	Day	6% 1 3 17% 53% 20%	849
August	1st to 10th	Day	2 1 13% 56% 27%	776
	11th to 20th	Day	3 1 14% 57% 24%	604
	21st to end	Day	7% 1 2 11% 44% 35%	396
September	1st to 10th	Day	9% 1 2 17% 49% 22%	360
	11th to 20th	Day	6% 1 2 15% 52% 24%	360
	21st to end	Day	5% 1 6% 20% 48% 20%	360
October	1st to 10th	Day	8% 2 4 30% 48% 9%	360
	11th to 20th	Day	11% 3 9% 27% 35% 15%	339
	21st to end	Day	12% 5% 16% 31% 29% 7%	363
November	1st to 10th	Day	14% 4 12% 31% 33% 7%	330
	11th to 20th	Day	18% 4 12% 34% 23% 9%	330
	21st to end	Day	22% 7% 25% 27% 13% 5%	330
December	1st to 10th	Day	23% 6% 19% 33% 16% 3	330
	11th to 20th	Day	22% 9% 18% 30% 19% 2	330
	21st to end	Day	18% 7% 23% 31% 19% 2	363
January	1st to 10th	Night	22% 8% 25% 32% 14%	1050
	11th to 20th	Night	20% 8% 23% 37% 12%	1050
	21st to end	Night	22% 9% 26% 33% 11%	1050
February	1st to 10th	Night	24% 8% 22% 35% 12%	840
	11th to 20th	Night	23% 9% 21% 37% 11%	824
	21st to end	Night	22% 7% 27% 34% 9% 1	598
March	1st to 10th	Night	22% 7% 23% 36% 13%	630
	11th to 20th	Night	18% 10% 21% 40% 10% 1	630
	21st to end	Night	16% 6% 25% 40% 13% 1	693
April	1st to 10th	Night	16% 7% 28% 39% 11%	630
	11th to 20th	Night	20% 8% 25% 35% 13%	623
	21st to end	Night	18% 5% 25% 39% 14%	630
May	1st to 10th	Night	17% 4 25% 42% 11%	630
	11th to 20th	Night	11% 3 21% 46% 17% 1	621
	21st to end	Night	8% 2 14% 44% 30% 2	683
June	1st to 10th	Night	5% 2 4 37% 47% 4	630
	11th to 20th	Night	7% 6% 43% 41% 3	630
	21st to end	Night	7% 1 7% 31% 44% 11%	630
July	1st to 10th	Night	6% 1 3 25% 49% 15%	615
	11th to 20th	Night	4 1 2 18% 58% 17%	612
	21st to end	Night	3 1 2 20% 60% 13%	690
August	1st to 10th	Night	2 12% 65% 21%	627
	11th to 20th	Night	4 1 1 12% 65% 18%	624
	21st to end	Night	4 1 14% 55% 25%	693
September	1st to 10th	Night	10% 1 2 18% 51% 17%	630
	11th to 20th	Night	8% 1 4 19% 50% 18%	630
	21st to end	Night	6% 1 5% 22% 54% 11%	630
October	1st to 10th	Night	6% 1 5% 26% 50% 12%	630
	11th to 20th	Night	9% 2 9% 35% 39% 5%	782
	21st to end	Night	10% 5% 14% 36% 31% 4	880
November	1st to 10th	Night	10% 3 11% 34% 37% 5%	820
	11th to 20th	Night	17% 3 16% 34% 27% 3	840
	21st to end	Night	19% 5% 22% 34% 18% 2	966
December	1st to 10th	Night	22% 5% 20% 30% 20% 3	1050
	11th to 20th	Night	20% 7% 22% 32% 17% 1	1050
	21st to end	Night	19% 7% 22% 34% 16% 1	1155

Page generated at 2026-10-11 04:06:32. Version ac07

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