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 2025-05-11.

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	9% 5% 2 5% 4 4 5% 4 7% 9% 46%	114204
	Night	9% 5% 2 5% 4 4 4 4 6% 9% 47%	114738
Transparency	Day	32% 9% 17% 19% 16% 7%	118101
	Night	32% 8% 15% 19% 18% 8%	118981
Seeing	Day	10% 3 12% 26% 31% 19%	15616
	Night	11% 4 15% 27% 30% 13%	25668

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% 5% 2 5% 4 3 4 3 4 6% 53%	4056
	11th to 20th	Day	15% 7% 2 6% 5% 4 4 4 5% 6% 43%	4262
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 9% 44%	4972
February	1st to 10th	Day	14% 9% 3 7% 4 3 3 4 5% 6% 42%	2000
	11th to 20th	Day	15% 7% 2 5% 3 3 3 3 5% 6% 48%	1948
	21st to end	Day	13% 7% 3 6% 4 5% 4 3 5% 7% 45%	1650
March	1st to 10th	Day	18% 7% 2 5% 3 3 3 3 6% 7% 42%	4617
	11th to 20th	Day	6% 5% 1 6% 4 4 4 4 6% 8% 53%	4980
	21st to end	Day	14% 6% 2 4 3 3 3 2 5% 8% 51%	5465
April	1st to 10th	Day	9% 5% 2 5% 5% 4 5% 4 5% 8% 47%	2215
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 7% 53%	2374
	21st to end	Day	5% 4 2 3 3 3 4 4 5% 8% 59%	2405
May	1st to 10th	Day	5% 4 2 5% 4 3 4 4 6% 9% 54%	4212
	11th to 20th	Day	8% 6% 2 7% 5% 4 5% 4 6% 8% 46%	4081
	21st to end	Day	3 3 1 3 3 3 4 4 7% 11% 58%	4476
June	1st to 10th	Day	8% 4 2 7% 5% 5% 6% 5% 9% 12% 37%	2470
	11th to 20th	Day	6% 4 1 5% 5% 5% 6% 5% 10% 13% 40%	2470
	21st to end	Day	6% 5% 2 6% 6% 7% 6% 6% 9% 11% 36%	2470
July	1st to 10th	Day	6% 4 2 6% 5% 5% 6% 6% 10% 16% 33%	4120
	11th to 20th	Day	5% 3 1 5% 5% 5% 6% 6% 10% 12% 41%	4120
	21st to end	Day	3 4 2 6% 5% 7% 7% 7% 12% 15% 31%	4390
August	1st to 10th	Day	7% 4 2 6% 5% 4 7% 6% 10% 13% 37%	3785
	11th to 20th	Day	7% 4 1 5% 4 4 5% 5% 9% 13% 43%	3729
	21st to end	Day	6% 5% 2 6% 6% 6% 7% 7% 10% 13% 33%	4148
September	1st to 10th	Day	9% 6% 2 7% 6% 4 6% 6% 11% 13% 30%	2090
	11th to 20th	Day	8% 5% 3 7% 6% 6% 6% 5% 10% 9% 36%	2090
	21st to end	Day	11% 4 2 5% 4 4 5% 4 6% 9% 46%	2090
October	1st to 10th	Day	11% 6% 2 5% 3 4 5% 4 5% 7% 48%	2090
	11th to 20th	Day	6% 3 1 3 2 3 3 3 5% 7% 64%	2085
	21st to end	Day	8% 4 2 6% 4 4 4 3 4 6% 56%	2090
November	1st to 10th	Day	7% 4 2 5% 3 4 4 4 6% 7% 55%	1885
	11th to 20th	Day	10% 4 2 5% 4 3 4 3 5% 7% 55%	1800
	21st to end	Day	9% 5% 2 5% 4 3 4 3 6% 8% 51%	1800
December	1st to 10th	Day	8% 5% 2 5% 4 4 4 3 4 7% 54%	2930
	11th to 20th	Day	10% 7% 2 6% 4 4 3 4 4 6% 50%	3373
	21st to end	Day	17% 9% 2 6% 4 3 4 4 4 5% 43%	4466
January	1st to 10th	Night	11% 6% 2 4 3 3 3 3 4 7% 53%	5889
	11th to 20th	Night	16% 7% 3 8% 5% 4 5% 4 6% 7% 36%	5693
	21st to end	Night	15% 8% 2 6% 3 4 4 3 6% 8% 41%	5984
February	1st to 10th	Night	15% 7% 2 6% 4 4 3 3 6% 5% 46%	2400
	11th to 20th	Night	14% 8% 2 6% 5% 3 3 3 4 5% 47%	2338
	21st to end	Night	13% 8% 3 5% 3 4 4 3 5% 5% 47%	1980
March	1st to 10th	Night	14% 9% 3 7% 5% 4 3 3 5% 7% 41%	5235
	11th to 20th	Night	7% 5% 1 5% 4 4 4 4 6% 8% 53%	4980
	21st to end	Night	14% 5% 2 5% 4 4 3 3 5% 7% 49%	5467
April	1st to 10th	Night	9% 6% 2 5% 5% 4 4 4 5% 7% 49%	2199
	11th to 20th	Night	9% 4 3 5% 4 3 3 3 6% 9% 51%	1975
	21st to end	Night	5% 4 2 4 4 4 4 3 6% 8% 57%	1993
May	1st to 10th	Night	5% 3 1 3 3 3 4 4 5% 10% 59%	2903
	11th to 20th	Night	9% 5% 2 7% 5% 4 5% 3 5% 8% 46%	2818
	21st to end	Night	3 2 1 3 3 4 4 4 6% 10% 60%	3079
June	1st to 10th	Night	7% 5% 3 5% 5% 5% 5% 5% 7% 11% 42%	1710
	11th to 20th	Night	6% 3 2 5% 5% 5% 5% 5% 9% 14% 43%	1710
	21st to end	Night	5% 4 2 5% 4 6% 6% 5% 9% 11% 43%	1710
July	1st to 10th	Night	4 4 2 6% 5% 6% 6% 7% 12% 17% 33%	2840
	11th to 20th	Night	3 3 1 4 3 5% 6% 5% 8% 13% 50%	2840
	21st to end	Night	2 3 1 5% 5% 6% 6% 7% 11% 16% 38%	3145
August	1st to 10th	Night	6% 3 1 4 4 5% 7% 5% 10% 14% 42%	3144
	11th to 20th	Night	3 3 1 5% 4 5% 6% 5% 8% 13% 47%	3100
	21st to end	Night	5% 4 2 6% 5% 6% 8% 7% 12% 13% 32%	3476
September	1st to 10th	Night	9% 6% 2 7% 6% 6% 7% 7% 8% 12% 30%	2088
	11th to 20th	Night	9% 7% 3 8% 6% 5% 7% 5% 7% 10% 33%	2090
	21st to end	Night	9% 5% 2 6% 4 4 4 4 7% 9% 45%	2090
October	1st to 10th	Night	8% 5% 2 6% 5% 4 4 5% 5% 8% 47%	2090
	11th to 20th	Night	5% 4 1 4 4 3 4 3 5% 7% 60%	2093
	21st to end	Night	8% 5% 2 6% 3 4 5% 4 4 8% 52%	2508
November	1st to 10th	Night	7% 4 2 5% 4 4 4 3 6% 6% 53%	2409
	11th to 20th	Night	9% 6% 2 6% 4 3 3 3 5% 7% 53%	2600
	21st to end	Night	11% 5% 3 5% 4 3 3 3 5% 7% 51%	2600
December	1st to 10th	Night	9% 4 1 4 4 4 4 4 5% 6% 55%	4250
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 5% 6% 54%	4822
	21st to end	Night	13% 8% 3 6% 4 4 4 3 5% 6% 45%	6490

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	31% 6% 9% 16% 28% 11%	4057
	11th to 20th	Day	41% 5% 7% 15% 21% 12%	4262
	21st to end	Day	35% 6% 12% 16% 21% 9%	4972
February	1st to 10th	Day	41% 7% 10% 14% 18% 10%	2000
	11th to 20th	Day	36% 6% 7% 18% 22% 11%	1958
	21st to end	Day	36% 7% 11% 16% 20% 9%	1650
March	1st to 10th	Day	39% 6% 10% 18% 19% 8%	4617
	11th to 20th	Day	27% 7% 13% 17% 20% 16%	4980
	21st to end	Day	32% 5% 12% 27% 15% 9%	5465
April	1st to 10th	Day	32% 8% 13% 19% 17% 11%	2215
	11th to 20th	Day	29% 7% 10% 22% 21% 10%	2374
	21st to end	Day	23% 6% 14% 28% 21% 9%	2405
May	1st to 10th	Day	22% 11% 18% 26% 18% 5%	4250
	11th to 20th	Day	33% 10% 16% 23% 16% 2	4085
	21st to end	Day	17% 8% 21% 34% 17% 2	4489
June	1st to 10th	Day	34% 14% 23% 24% 5% 1	2470
	11th to 20th	Day	31% 13% 26% 23% 8%	2470
	21st to end	Day	35% 15% 24% 18% 6% 1	2470
July	1st to 10th	Day	34% 15% 41% 10% 1	4055
	11th to 20th	Day	30% 15% 43% 10% 2	4051
	21st to end	Day	33% 22% 35% 10% 1	4250
August	1st to 10th	Day	32% 14% 25% 21% 7% 2	3773
	11th to 20th	Day	26% 14% 28% 24% 7%	3765
	21st to end	Day	36% 14% 29% 14% 6%	4148
September	1st to 10th	Day	40% 17% 22% 13% 7% 2	2090
	11th to 20th	Day	40% 14% 21% 15% 9% 2	2090
	21st to end	Day	34% 9% 18% 18% 14% 7%	2090
October	1st to 10th	Day	44% 7% 9% 12% 16% 12%	3480
	11th to 20th	Day	13% 4 7% 22% 32% 23%	3441
	21st to end	Day	18% 5% 5% 20% 38% 13%	3428
November	1st to 10th	Day	28% 7% 11% 20% 21% 13%	1885
	11th to 20th	Day	29% 6% 10% 16% 28% 11%	1800
	21st to end	Day	31% 6% 11% 22% 22% 8%	1800
December	1st to 10th	Day	31% 5% 11% 20% 23% 9%	2930
	11th to 20th	Day	35% 6% 8% 19% 22% 9%	3370
	21st to end	Day	43% 5% 8% 17% 23% 4	4466
January	1st to 10th	Night	31% 4 8% 15% 29% 13%	5889
	11th to 20th	Night	46% 5% 6% 16% 20% 7%	5693
	21st to end	Night	40% 6% 10% 16% 19% 9%	5984
February	1st to 10th	Night	38% 6% 9% 15% 22% 11%	2400
	11th to 20th	Night	40% 5% 8% 15% 20% 13%	2339
	21st to end	Night	37% 6% 10% 17% 19% 11%	1980
March	1st to 10th	Night	42% 6% 9% 16% 18% 8%	5235
	11th to 20th	Night	27% 6% 11% 20% 18% 18%	4980
	21st to end	Night	34% 5% 9% 23% 18% 11%	5467
April	1st to 10th	Night	33% 7% 13% 18% 17% 12%	2199
	11th to 20th	Night	29% 5% 10% 21% 23% 11%	1975
	21st to end	Night	24% 7% 11% 28% 23% 8%	1993
May	1st to 10th	Night	18% 9% 21% 28% 18% 6%	2930
	11th to 20th	Night	32% 11% 16% 25% 14% 2	2819
	21st to end	Night	17% 7% 18% 37% 18% 2	3087
June	1st to 10th	Night	32% 11% 21% 28% 8% 1	1710
	11th to 20th	Night	28% 11% 27% 26% 8% 1	1710
	21st to end	Night	30% 13% 26% 20% 9% 1	1710
July	1st to 10th	Night	34% 15% 38% 12% 1	2795
	11th to 20th	Night	23% 16% 48% 12% 2	2786
	21st to end	Night	29% 18% 39% 13% 1	3045
August	1st to 10th	Night	27% 12% 29% 21% 10% 1	3132
	11th to 20th	Night	25% 12% 28% 29% 6%	3130
	21st to end	Night	36% 16% 27% 14% 7%	3476
September	1st to 10th	Night	41% 15% 20% 16% 6% 2	2088
	11th to 20th	Night	43% 12% 21% 15% 8% 1	2090
	21st to end	Night	33% 10% 17% 20% 16% 5%	2090
October	1st to 10th	Night	46% 7% 9% 12% 16% 11%	3480
	11th to 20th	Night	15% 4 6% 22% 31% 23%	3476
	21st to end	Night	19% 5% 6% 18% 39% 13%	4120
November	1st to 10th	Night	29% 5% 9% 22% 20% 14%	2409
	11th to 20th	Night	32% 6% 7% 17% 24% 14%	2600
	21st to end	Night	33% 5% 11% 18% 21% 11%	2600
December	1st to 10th	Night	30% 5% 10% 21% 22% 12%	4250
	11th to 20th	Night	32% 5% 11% 21% 21% 11%	4824
	21st to end	Night	39% 6% 8% 20% 21% 5%	6490

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% 2 30% 43% 14% 1	300
	11th to 20th	Day	12% 4 22% 40% 17% 3	300
	21st to end	Day	15% 7% 27% 42% 8%	330
February	1st to 10th	Day	15% 5% 17% 34% 27% 2	300
	11th to 20th	Day	20% 4 17% 40% 19% 1	300
	21st to end	Day	12% 5% 15% 46% 20% 2	249
March	1st to 10th	Day	11% 6% 20% 41% 21% 1	359
	11th to 20th	Day	10% 4 21% 39% 23% 2	500
	21st to end	Day	11% 6% 17% 40% 24% 2	550
April	1st to 10th	Day	10% 5% 21% 36% 26% 2	500
	11th to 20th	Day	12% 3 16% 37% 29% 4	492
	21st to end	Day	6% 3 13% 33% 38% 6%	500
May	1st to 10th	Day	6% 2 12% 35% 37% 8%	503
	11th to 20th	Day	7% 2 9% 29% 36% 17%	487
	21st to end	Day	5% 2 5% 18% 46% 24%	529
June	1st to 10th	Day	11% 1 3 19% 43% 23%	490
	11th to 20th	Day	8% 1 4 17% 39% 31%	490
	21st to end	Day	6% 2 3 11% 43% 35%	490
July	1st to 10th	Day	8% 2 3 6% 29% 52%	485
	11th to 20th	Day	7% 2 3 5% 26% 57%	484
	21st to end	Day	4 1 4 11% 38% 43%	532
August	1st to 10th	Day	10% 1 5% 6% 32% 46%	486
	11th to 20th	Day	11% 3 5% 31% 49%	479
	21st to end	Day	9% 2 5% 11% 34% 40%	539
September	1st to 10th	Day	11% 2 7% 12% 35% 34%	490
	11th to 20th	Day	11% 2 6% 17% 39% 24%	490
	21st to end	Day	10% 2 7% 14% 42% 25%	490
October	1st to 10th	Day	13% 2 11% 30% 34% 10%	490
	11th to 20th	Day	5% 2 11% 28% 38% 16%	490
	21st to end	Day	7% 4 11% 35% 34% 9%	539
November	1st to 10th	Day	10% 2 13% 30% 36% 8%	423
	11th to 20th	Day	11% 3 14% 40% 29% 3	300
	21st to end	Day	12% 2 16% 39% 26% 5%	300
December	1st to 10th	Day	11% 4 25% 34% 21% 5%	300
	11th to 20th	Day	12% 2 21% 42% 19% 3	300
	21st to end	Day	14% 6% 16% 37% 22% 4	330
January	1st to 10th	Night	15% 8% 30% 32% 13% 1	800
	11th to 20th	Night	12% 7% 26% 34% 18% 4	800
	21st to end	Night	19% 6% 29% 32% 13% 1	880
February	1st to 10th	Night	18% 7% 22% 30% 22% 2	800
	11th to 20th	Night	16% 7% 25% 33% 17% 2	783
	21st to end	Night	16% 4 24% 39% 17% 1	660
March	1st to 10th	Night	12% 4 23% 38% 22% 2	800
	11th to 20th	Night	10% 5% 21% 36% 25% 3	800
	21st to end	Night	10% 5% 20% 34% 29% 3	880
April	1st to 10th	Night	10% 4 19% 37% 27% 3	799
	11th to 20th	Night	10% 4 17% 36% 29% 4	593
	21st to end	Night	5% 3 18% 32% 36% 7%	600
May	1st to 10th	Night	5% 2 14% 35% 36% 9%	600
	11th to 20th	Night	8% 2 10% 28% 40% 10%	563
	21st to end	Night	4 1 5% 21% 53% 15%	617
June	1st to 10th	Night	9% 5% 19% 49% 18%	570
	11th to 20th	Night	5% 1 4 14% 45% 31%	570
	21st to end	Night	7% 1 2 11% 44% 34%	570
July	1st to 10th	Night	6% 2 3 7% 40% 42%	555
	11th to 20th	Night	5% 2 6% 35% 52%	552
	21st to end	Night	4 3 7% 42% 45%	624
August	1st to 10th	Night	7% 1 2 5% 43% 42%	567
	11th to 20th	Night	7% 1 3 7% 37% 46%	564
	21st to end	Night	10% 5% 13% 37% 34%	627
September	1st to 10th	Night	10% 2 4 14% 39% 30%	758
	11th to 20th	Night	11% 1 6% 20% 42% 20%	760
	21st to end	Night	10% 1 7% 20% 43% 19%	760
October	1st to 10th	Night	11% 2 14% 31% 33% 10%	760
	11th to 20th	Night	7% 3 13% 31% 37% 11%	760
	21st to end	Night	10% 3 16% 32% 34% 6%	836
November	1st to 10th	Night	9% 4 16% 36% 30% 5%	780
	11th to 20th	Night	12% 6% 20% 34% 25% 3	800
	21st to end	Night	13% 5% 23% 33% 21% 5%	800
December	1st to 10th	Night	13% 4 24% 29% 25% 5%	800
	11th to 20th	Night	15% 6% 23% 33% 20% 3	800
	21st to end	Night	17% 6% 20% 37% 19% 2	880

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