St. George Island State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. George Island State Park clear sky chart from 2005-11-06 to 2026-09-14.

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	8% 5% 2 6% 4 4 5% 4 7% 10% 45%	148453
	Night	9% 5% 2 5% 4 4 5% 4 7% 10% 46%	142604
Transparency	Day	32% 10% 19% 19% 14% 6%	152306
	Night	32% 8% 17% 20% 16% 7%	146824
Seeing	Day	9% 3 11% 26% 32% 19%	17459
	Night	10% 4 15% 27% 31% 13%	27375

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	10% 6% 2 6% 4 4 4 3 4 7% 49%	5258
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 7% 43%	5538
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 9% 45%	6436
February	1st to 10th	Day	14% 8% 2 7% 4 3 3 3 5% 6% 44%	2100
	11th to 20th	Day	15% 7% 2 5% 3 3 4 3 5% 6% 48%	2048
	21st to end	Day	13% 7% 3 6% 3 5% 4 3 5% 7% 46%	1730
March	1st to 10th	Day	18% 7% 2 5% 3 3 3 3 6% 7% 43%	4720
	11th to 20th	Day	6% 5% 2 6% 4 4 4 4 6% 8% 53%	5090
	21st to end	Day	14% 5% 2 4 3 3 3 3 5% 8% 52%	5586
April	1st to 10th	Day	9% 5% 2 5% 5% 4 5% 4 5% 8% 47%	2326
	11th to 20th	Day	8% 4 2 5% 4 4 3 4 5% 7% 54%	2494
	21st to end	Day	5% 4 2 4 3 3 4 4 5% 8% 59%	2525
May	1st to 10th	Day	10% 7% 2 6% 4 4 4 3 6% 9% 44%	7616
	11th to 20th	Day	8% 4 2 5% 3 4 4 4 5% 9% 51%	7626
	21st to end	Day	3 3 2 5% 4 4 5% 4 8% 13% 49%	8391
June	1st to 10th	Day	8% 4 2 7% 5% 5% 5% 5% 9% 13% 37%	2730
	11th to 20th	Day	6% 4 1 6% 5% 5% 6% 5% 10% 13% 39%	2730
	21st to end	Day	6% 5% 2 6% 6% 7% 6% 6% 9% 11% 36%	2730
July	1st to 10th	Day	4 4 2 6% 5% 5% 6% 6% 10% 16% 36%	7680
	11th to 20th	Day	5% 3 2 6% 5% 6% 7% 6% 10% 12% 39%	7680
	21st to end	Day	3 3 2 5% 5% 6% 7% 7% 11% 15% 36%	8208
August	1st to 10th	Day	6% 4 2 7% 5% 5% 7% 6% 10% 13% 36%	5545
	11th to 20th	Day	5% 3 1 4 3 4 5% 5% 9% 14% 47%	5486
	21st to end	Day	5% 5% 2 7% 6% 7% 7% 7% 9% 14% 31%	6033
September	1st to 10th	Day	8% 5% 2 7% 6% 5% 6% 6% 11% 14% 30%	2310
	11th to 20th	Day	8% 5% 2 7% 5% 6% 6% 5% 9% 9% 38%	2233
	21st to end	Day	10% 4 2 5% 4 4 5% 4 6% 9% 47%	2200
October	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 5% 8% 48%	2200
	11th to 20th	Day	5% 3 1 3 3 3 3 3 5% 7% 64%	2195
	21st to end	Day	8% 4 2 6% 4 4 4 3 4 6% 56%	2200
November	1st to 10th	Day	7% 4 2 5% 3 4 4 4 6% 7% 55%	1981
	11th to 20th	Day	9% 4 2 5% 4 3 3 3 5% 7% 56%	1890
	21st to end	Day	8% 5% 2 5% 4 3 5% 3 6% 9% 50%	1890
December	1st to 10th	Day	9% 5% 2 5% 4 4 4 3 4 7% 53%	3020
	11th to 20th	Day	10% 7% 2 6% 4 4 3 4 4 6% 50%	3463
	21st to end	Day	17% 8% 2 6% 4 3 3 4 4 5% 43%	4565
January	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 5% 8% 51%	7635
	11th to 20th	Night	16% 6% 3 7% 4 4 5% 4 6% 7% 37%	7403
	21st to end	Night	14% 8% 3 7% 3 4 4 3 6% 8% 40%	7745
February	1st to 10th	Night	14% 6% 2 5% 4 4 3 3 5% 5% 47%	2520
	11th to 20th	Night	13% 8% 2 6% 5% 4 3 3 5% 6% 47%	2458
	21st to end	Night	12% 8% 3 5% 3 4 4 3 5% 5% 48%	2076
March	1st to 10th	Night	13% 9% 3 7% 5% 3 3 3 5% 7% 41%	5352
	11th to 20th	Night	7% 5% 1 5% 4 4 4 3 6% 8% 53%	5090
	21st to end	Night	14% 5% 2 5% 4 4 3 3 5% 7% 50%	5588
April	1st to 10th	Night	9% 6% 2 5% 5% 4 4 4 6% 7% 48%	2309
	11th to 20th	Night	8% 4 2 5% 4 3 4 3 6% 9% 51%	2075
	21st to end	Night	5% 4 2 4 4 4 4 3 6% 8% 57%	2093
May	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 5% 9% 51%	5237
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 4 6% 9% 49%	5234
	21st to end	Night	3 3 2 4 4 4 5% 4 7% 12% 53%	5761
June	1st to 10th	Night	6% 5% 3 5% 5% 5% 6% 5% 8% 11% 41%	1890
	11th to 20th	Night	5% 3 1 5% 5% 5% 5% 5% 9% 14% 43%	1890
	21st to end	Night	5% 3 2 5% 4 6% 6% 5% 9% 12% 43%	1890
July	1st to 10th	Night	3 3 2 5% 4 6% 6% 7% 11% 16% 37%	5278
	11th to 20th	Night	3 3 1 5% 5% 5% 7% 6% 9% 14% 42%	5277
	21st to end	Night	3 3 1 5% 5% 6% 6% 6% 11% 18% 37%	5850
August	1st to 10th	Night	5% 3 1 5% 5% 5% 7% 5% 9% 13% 42%	4604
	11th to 20th	Night	2 3 1 4 3 5% 5% 5% 8% 14% 50%	4560
	21st to end	Night	4 4 2 6% 5% 6% 8% 7% 12% 15% 32%	5046
September	1st to 10th	Night	8% 6% 2 7% 6% 6% 7% 7% 8% 12% 31%	2308
	11th to 20th	Night	9% 6% 3 7% 6% 5% 6% 5% 6% 10% 36%	2234
	21st to end	Night	9% 5% 2 6% 4 4 4 4 7% 10% 45%	2200
October	1st to 10th	Night	8% 5% 2 6% 5% 4 4 5% 6% 8% 46%	2200
	11th to 20th	Night	5% 4 1 4 3 3 4 3 5% 8% 61%	2203
	21st to end	Night	8% 5% 2 6% 3 4 4 4 4 7% 52%	2640
November	1st to 10th	Night	7% 4 2 5% 4 4 4 3 6% 7% 54%	2533
	11th to 20th	Night	9% 5% 2 5% 4 3 3 3 4 7% 54%	2730
	21st to end	Night	10% 5% 2 5% 4 4 3 3 5% 7% 51%	2730
December	1st to 10th	Night	10% 4 2 4 4 4 4 4 5% 6% 54%	4380
	11th to 20th	Night	10% 6% 2 5% 3 3 3 3 5% 6% 54%	4952
	21st to end	Night	13% 7% 3 6% 4 4 4 3 5% 6% 46%	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	34% 7% 11% 15% 25% 9%	5259
	11th to 20th	Day	39% 5% 6% 17% 19% 13%	5538
	21st to end	Day	35% 6% 12% 16% 20% 11%	6436
February	1st to 10th	Day	40% 7% 9% 15% 18% 11%	2100
	11th to 20th	Day	36% 6% 8% 19% 21% 10%	2058
	21st to end	Day	36% 7% 11% 17% 20% 9%	1730
March	1st to 10th	Day	39% 6% 10% 18% 19% 8%	4720
	11th to 20th	Day	27% 7% 13% 17% 20% 16%	5090
	21st to end	Day	31% 5% 12% 27% 15% 9%	5586
April	1st to 10th	Day	33% 8% 14% 19% 16% 10%	2326
	11th to 20th	Day	28% 7% 10% 22% 23% 10%	2494
	21st to end	Day	23% 6% 15% 28% 20% 8%	2525
May	1st to 10th	Day	36% 8% 16% 23% 14% 4	7651
	11th to 20th	Day	27% 8% 18% 28% 16% 2	7630
	21st to end	Day	25% 12% 24% 25% 13% 1	8405
June	1st to 10th	Day	34% 13% 23% 23% 5% 1	2730
	11th to 20th	Day	31% 13% 28% 21% 7%	2730
	21st to end	Day	35% 15% 25% 19% 6% 1	2730
July	1st to 10th	Day	32% 15% 39% 12% 2	7615
	11th to 20th	Day	33% 14% 40% 11% 1	7611
	21st to end	Day	30% 17% 33% 19%	8026
August	1st to 10th	Day	35% 13% 26% 19% 6% 1	5533
	11th to 20th	Day	22% 14% 37% 22% 5%	5522
	21st to end	Day	39% 14% 28% 14% 4	6033
September	1st to 10th	Day	38% 17% 23% 14% 7% 1	2310
	11th to 20th	Day	38% 13% 20% 17% 10% 2	2233
	21st to end	Day	33% 9% 18% 19% 14% 6%	2200
October	1st to 10th	Day	44% 7% 9% 13% 16% 11%	3590
	11th to 20th	Day	13% 4 7% 21% 32% 23%	3551
	21st to end	Day	19% 5% 5% 20% 38% 13%	3538
November	1st to 10th	Day	27% 7% 11% 19% 21% 14%	1981
	11th to 20th	Day	28% 6% 9% 17% 29% 11%	1890
	21st to end	Day	31% 6% 12% 22% 21% 8%	1890
December	1st to 10th	Day	32% 5% 11% 20% 23% 9%	3020
	11th to 20th	Day	35% 6% 8% 19% 22% 9%	3460
	21st to end	Day	42% 5% 8% 17% 23% 4	4565
January	1st to 10th	Night	30% 5% 11% 18% 25% 10%	7636
	11th to 20th	Night	44% 5% 6% 17% 18% 10%	7403
	21st to end	Night	41% 6% 9% 16% 19% 9%	7745
February	1st to 10th	Night	36% 6% 9% 15% 22% 12%	2520
	11th to 20th	Night	39% 5% 9% 16% 19% 12%	2459
	21st to end	Night	36% 6% 10% 18% 18% 11%	2076
March	1st to 10th	Night	41% 6% 9% 17% 18% 8%	5352
	11th to 20th	Night	27% 6% 11% 20% 18% 18%	5090
	21st to end	Night	34% 5% 9% 23% 18% 11%	5588
April	1st to 10th	Night	33% 7% 13% 18% 17% 11%	2309
	11th to 20th	Night	29% 5% 9% 21% 25% 11%	2075
	21st to end	Night	24% 7% 11% 27% 23% 8%	2093
May	1st to 10th	Night	30% 7% 17% 27% 14% 6%	5264
	11th to 20th	Night	30% 8% 15% 27% 16% 3	5235
	21st to end	Night	22% 9% 25% 29% 13% 1	5771
June	1st to 10th	Night	32% 11% 22% 26% 9%	1890
	11th to 20th	Night	28% 11% 29% 24% 7%	1890
	21st to end	Night	30% 13% 27% 21% 9% 1	1890
July	1st to 10th	Night	31% 14% 42% 12% 1	5235
	11th to 20th	Night	29% 15% 44% 11% 1	5226
	21st to end	Night	29% 14% 37% 19% 1	5719
August	1st to 10th	Night	30% 12% 27% 22% 8%	4592
	11th to 20th	Night	22% 13% 35% 26% 4	4590
	21st to end	Night	35% 16% 30% 14% 5%	5046
September	1st to 10th	Night	40% 15% 21% 16% 6% 2	2308
	11th to 20th	Night	41% 12% 21% 16% 10% 1	2234
	21st to end	Night	32% 9% 17% 21% 16% 5%	2200
October	1st to 10th	Night	46% 7% 9% 12% 16% 10%	3590
	11th to 20th	Night	15% 4 6% 21% 31% 22%	3586
	21st to end	Night	20% 5% 6% 17% 39% 13%	4252
November	1st to 10th	Night	29% 5% 9% 22% 21% 15%	2533
	11th to 20th	Night	30% 5% 7% 18% 24% 14%	2730
	21st to end	Night	33% 5% 11% 19% 21% 11%	2730
December	1st to 10th	Night	31% 5% 10% 21% 22% 12%	4380
	11th to 20th	Night	31% 5% 11% 21% 21% 11%	4954
	21st to end	Night	39% 6% 8% 20% 22% 5%	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	10% 3 28% 42% 16% 1	330
	11th to 20th	Day	13% 4 22% 41% 17% 3	330
	21st to end	Day	15% 9% 26% 42% 9%	363
February	1st to 10th	Day	14% 5% 18% 35% 26% 2	330
	11th to 20th	Day	19% 4 16% 41% 19% 1	330
	21st to end	Day	11% 6% 16% 45% 20% 1	273
March	1st to 10th	Day	11% 5% 19% 40% 23% 2	392
	11th to 20th	Day	9% 4 21% 40% 24% 2	540
	21st to end	Day	11% 5% 16% 38% 27% 3	594
April	1st to 10th	Day	10% 5% 21% 34% 26% 3	540
	11th to 20th	Day	11% 3 15% 36% 30% 6%	532
	21st to end	Day	5% 3 13% 34% 38% 6%	540
May	1st to 10th	Day	5% 3 12% 36% 36% 8%	543
	11th to 20th	Day	8% 2 8% 30% 37% 16%	567
	21st to end	Day	4 2 6% 19% 46% 23%	617
June	1st to 10th	Day	10% 1 3 19% 45% 21%	570
	11th to 20th	Day	7% 1 4 16% 38% 32%	570
	21st to end	Day	5% 2 3 11% 43% 36%	570
July	1st to 10th	Day	7% 2 3 6% 30% 52%	565
	11th to 20th	Day	6% 2 3 6% 29% 54%	564
	21st to end	Day	3 1 4 11% 39% 42%	620
August	1st to 10th	Day	9% 1 4 6% 33% 47%	566
	11th to 20th	Day	9% 3 5% 31% 52%	559
	21st to end	Day	9% 2 5% 11% 33% 40%	627
September	1st to 10th	Day	10% 2 7% 13% 36% 33%	570
	11th to 20th	Day	10% 2 6% 16% 41% 26%	542
	21st to end	Day	10% 2 7% 14% 43% 25%	530
October	1st to 10th	Day	12% 2 11% 30% 34% 10%	530
	11th to 20th	Day	5% 2 11% 27% 38% 17%	530
	21st to end	Day	7% 4 11% 35% 34% 8%	583
November	1st to 10th	Day	10% 2 13% 30% 37% 8%	459
	11th to 20th	Day	10% 2 13% 38% 31% 5%	330
	21st to end	Day	11% 2 16% 40% 27% 4	330
December	1st to 10th	Day	14% 4 25% 33% 20% 5%	330
	11th to 20th	Day	12% 2 21% 42% 20% 3	330
	21st to end	Day	13% 6% 17% 36% 24% 5%	363
January	1st to 10th	Night	14% 8% 29% 32% 15% 1	840
	11th to 20th	Night	12% 7% 26% 33% 18% 3	840
	21st to end	Night	19% 6% 29% 33% 12% 1	924
February	1st to 10th	Night	17% 7% 22% 31% 22% 1	840
	11th to 20th	Night	15% 6% 24% 35% 17% 2	823
	21st to end	Night	15% 4 24% 39% 16% 1	692
March	1st to 10th	Night	11% 4 22% 37% 23% 2	840
	11th to 20th	Night	10% 5% 21% 36% 26% 3	840
	21st to end	Night	10% 5% 19% 33% 30% 3	924
April	1st to 10th	Night	10% 4 19% 36% 27% 4	839
	11th to 20th	Night	9% 4 17% 35% 31% 4	623
	21st to end	Night	5% 3 17% 33% 36% 7%	630
May	1st to 10th	Night	6% 2 14% 36% 34% 8%	630
	11th to 20th	Night	8% 2 10% 29% 41% 10%	621
	21st to end	Night	4 1 5% 21% 53% 15%	683
June	1st to 10th	Night	8% 1 5% 20% 49% 17%	630
	11th to 20th	Night	5% 1 3 14% 45% 32%	630
	21st to end	Night	7% 1 2 11% 44% 35%	630
July	1st to 10th	Night	5% 2 3 7% 39% 44%	615
	11th to 20th	Night	5% 3 6% 35% 51%	612
	21st to end	Night	3 3 8% 42% 43%	690
August	1st to 10th	Night	6% 1 2 6% 43% 42%	627
	11th to 20th	Night	6% 1 3 6% 36% 48%	624
	21st to end	Night	10% 5% 13% 38% 34%	693
September	1st to 10th	Night	10% 2 4 15% 39% 30%	838
	11th to 20th	Night	11% 1 5% 20% 43% 20%	813
	21st to end	Night	10% 1 7% 20% 43% 19%	800
October	1st to 10th	Night	10% 3 13% 31% 33% 10%	800
	11th to 20th	Night	7% 3 12% 31% 37% 11%	800
	21st to end	Night	10% 3 16% 33% 33% 6%	880
November	1st to 10th	Night	8% 4 16% 36% 30% 5%	820
	11th to 20th	Night	12% 6% 19% 34% 27% 3	840
	21st to end	Night	12% 5% 23% 33% 21% 5%	840
December	1st to 10th	Night	14% 4 24% 30% 24% 4	840
	11th to 20th	Night	15% 5% 23% 33% 21% 3	840
	21st to end	Night	16% 6% 19% 36% 20% 3	924

Page generated at 2026-09-11 04:11:58. Version ac07

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