Sweetgum Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sweetgum Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	101090
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	98428
Transparency	Day	38% 7% 12% 20% 18% 5%	104908
	Night	37% 6% 11% 20% 20% 6%	102748
Seeing	Day	16% 9% 21% 23% 20% 11%	14747
	Night	15% 7% 21% 31% 22% 4	24757

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	18% 11% 2 6% 4 5% 5% 4 4 5% 36%	2836
	11th to 20th	Day	17% 7% 2 6% 4 3 3 2 4 4 47%	2840
	21st to end	Day	24% 9% 2 5% 3 3 3 2 3 5% 40%	3416
February	1st to 10th	Day	19% 9% 3 6% 4 4 3 3 6% 6% 38%	1900
	11th to 20th	Day	21% 9% 3 6% 4 3 4 3 4 5% 39%	1848
	21st to end	Day	20% 8% 2 9% 4 4 3 2 5% 4 38%	1570
March	1st to 10th	Day	23% 8% 3 7% 4 4 4 3 5% 6% 32%	3120
	11th to 20th	Day	14% 6% 3 7% 4 3 4 3 4 7% 44%	3439
	21st to end	Day	16% 6% 3 7% 5% 5% 4 4 6% 6% 39%	3833
April	1st to 10th	Day	11% 6% 2 5% 5% 4 4 4 5% 7% 46%	2280
	11th to 20th	Day	13% 5% 3 6% 5% 4 4 3 5% 6% 47%	2254
	21st to end	Day	10% 4 2 5% 3 5% 4 4 6% 7% 49%	2340
May	1st to 10th	Day	10% 5% 3 6% 4 5% 5% 4 6% 9% 43%	4082
	11th to 20th	Day	15% 6% 3 6% 5% 4 5% 3 5% 8% 40%	4081
	21st to end	Day	8% 5% 2 6% 5% 4 5% 5% 7% 10% 44%	4476
June	1st to 10th	Day	9% 7% 2 7% 6% 5% 6% 4 8% 10% 36%	2470
	11th to 20th	Day	4 4 2 5% 5% 5% 5% 5% 9% 10% 46%	2470
	21st to end	Day	7% 5% 2 6% 6% 5% 7% 6% 7% 10% 39%	2470
July	1st to 10th	Day	7% 5% 2 7% 6% 7% 7% 7% 9% 12% 29%	4120
	11th to 20th	Day	6% 5% 2 7% 6% 6% 7% 6% 8% 12% 35%	4120
	21st to end	Day	11% 10% 4 11% 6% 6% 7% 6% 8% 9% 21%	4466
August	1st to 10th	Day	4 3 1 4 4 5% 6% 6% 9% 13% 47%	3927
	11th to 20th	Day	6% 4 2 6% 5% 5% 5% 5% 7% 12% 45%	3729
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 8% 52%	4180
September	1st to 10th	Day	9% 5% 3 6% 5% 5% 5% 5% 7% 9% 42%	2176
	11th to 20th	Day	13% 6% 2 7% 4 4 5% 4 6% 7% 43%	2090
	21st to end	Day	12% 5% 2 6% 4 3 4 2 5% 7% 50%	2090
October	1st to 10th	Day	11% 4 2 5% 4 4 3 3 4 6% 55%	2090
	11th to 20th	Day	10% 6% 2 5% 3 3 3 3 4 7% 56%	2071
	21st to end	Day	13% 5% 2 4 3 3 4 2 4 5% 55%	1984
November	1st to 10th	Day	14% 5% 2 4 4 3 3 2 4 5% 53%	1762
	11th to 20th	Day	13% 6% 2 6% 4 4 3 3 4 6% 51%	1800
	21st to end	Day	15% 6% 2 4 3 3 4 3 6% 7% 45%	1773
December	1st to 10th	Day	20% 8% 2 6% 4 4 3 4 5% 6% 38%	1710
	11th to 20th	Day	18% 8% 2 6% 5% 4 4 3 4 5% 42%	2153
	21st to end	Day	20% 9% 3 7% 4 5% 5% 3 5% 7% 33%	3124
January	1st to 10th	Night	18% 10% 2 6% 4 4 4 3 5% 6% 39%	4109
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 4 6% 43%	4120
	21st to end	Night	22% 12% 2 5% 3 3 3 3 3 4 39%	4235
February	1st to 10th	Night	17% 8% 3 6% 4 4 3 3 4 6% 43%	2280
	11th to 20th	Night	21% 7% 3 7% 5% 2 3 3 4 4 42%	2218
	21st to end	Night	20% 7% 2 7% 4 4 4 3 4 6% 38%	1884
March	1st to 10th	Night	25% 8% 3 7% 4 4 4 3 4 5% 33%	3733
	11th to 20th	Night	11% 6% 2 5% 4 3 4 4 6% 7% 49%	3519
	21st to end	Night	18% 8% 2 7% 5% 4 3 4 5% 5% 40%	3817
April	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 7% 9% 48%	1910
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 7% 50%	1875
	21st to end	Night	9% 4 2 6% 4 4 4 3 4 7% 53%	1838
May	1st to 10th	Night	11% 5% 2 7% 5% 4 5% 4 6% 9% 41%	2813
	11th to 20th	Night	15% 7% 3 6% 5% 4 4 4 6% 7% 40%	2812
	21st to end	Night	6% 4 2 5% 4 4 6% 5% 7% 11% 46%	3079
June	1st to 10th	Night	7% 5% 2 7% 6% 6% 6% 5% 9% 9% 39%	1710
	11th to 20th	Night	3 3 1 5% 4 5% 5% 4 7% 11% 52%	1710
	21st to end	Night	5% 5% 2 5% 5% 5% 5% 6% 6% 11% 47%	1710
July	1st to 10th	Night	8% 5% 3 8% 5% 5% 6% 5% 8% 12% 34%	2840
	11th to 20th	Night	7% 5% 2 5% 5% 4 5% 6% 8% 13% 40%	2840
	21st to end	Night	10% 9% 4 11% 7% 6% 7% 5% 7% 9% 25%	3087
August	1st to 10th	Night	3 3 2 5% 4 4 5% 4 9% 11% 51%	2998
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 5% 9% 49%	3100
	21st to end	Night	8% 5% 2 5% 3 3 4 3 5% 7% 55%	3476
September	1st to 10th	Night	8% 5% 3 6% 5% 5% 6% 5% 7% 8% 44%	1983
	11th to 20th	Night	13% 5% 3 6% 5% 4 4 3 6% 8% 43%	2090
	21st to end	Night	10% 6% 2 5% 3 4 4 3 5% 7% 51%	2090
October	1st to 10th	Night	10% 3 2 4 3 3 3 3 4 6% 59%	2090
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 4 5% 55%	2109
	21st to end	Night	12% 5% 2 5% 3 4 3 3 4 4 55%	2611
November	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 53%	2536
	11th to 20th	Night	13% 6% 2 4 3 3 3 2 4 6% 54%	2600
	21st to end	Night	15% 6% 2 5% 3 3 4 4 4 7% 47%	2562
December	1st to 10th	Night	19% 8% 3 6% 5% 3 4 3 5% 6% 38%	2470
	11th to 20th	Night	17% 7% 2 6% 3 3 3 2 4 6% 48%	3042
	21st to end	Night	19% 8% 3 7% 5% 4 4 4 6% 8% 32%	4532

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	49% 5% 7% 14% 21% 3	2837
	11th to 20th	Day	41% 4 7% 23% 23% 2	2840
	21st to end	Day	49% 3 8% 18% 19% 5%	3416
February	1st to 10th	Day	47% 5% 8% 18% 19% 3	1900
	11th to 20th	Day	48% 4 5% 19% 19% 5%	1858
	21st to end	Day	49% 5% 7% 13% 20% 6%	1570
March	1st to 10th	Day	52% 6% 9% 11% 14% 9%	3120
	11th to 20th	Day	40% 5% 7% 19% 23% 6%	3439
	21st to end	Day	44% 6% 11% 16% 18% 4	3833
April	1st to 10th	Day	38% 5% 12% 21% 19% 6%	2280
	11th to 20th	Day	38% 6% 8% 17% 24% 7%	2254
	21st to end	Day	31% 7% 12% 25% 21% 3	2340
May	1st to 10th	Day	36% 8% 13% 25% 16% 2	4120
	11th to 20th	Day	41% 8% 14% 25% 12% 1	4085
	21st to end	Day	33% 9% 13% 25% 18% 2	4489
June	1st to 10th	Day	40% 11% 16% 19% 12% 2	2470
	11th to 20th	Day	29% 10% 19% 24% 16% 1	2470
	21st to end	Day	36% 12% 16% 22% 12% 3	2470
July	1st to 10th	Day	40% 15% 21% 17% 6% 1	4055
	11th to 20th	Day	38% 12% 23% 19% 7% 1	4051
	21st to end	Day	56% 12% 14% 13% 5%	4324
August	1st to 10th	Day	25% 10% 16% 36% 13%	3914
	11th to 20th	Day	30% 9% 18% 26% 14% 3	3765
	21st to end	Day	30% 9% 14% 19% 24% 4	4179
September	1st to 10th	Day	37% 10% 16% 15% 16% 6%	2176
	11th to 20th	Day	40% 8% 11% 20% 18% 3	2090
	21st to end	Day	35% 6% 13% 18% 22% 7%	2090
October	1st to 10th	Day	24% 5% 6% 11% 37% 16%	3480
	11th to 20th	Day	21% 3 5% 16% 30% 25%	3427
	21st to end	Day	24% 4 7% 23% 32% 10%	3247
November	1st to 10th	Day	34% 4 7% 17% 29% 9%	1762
	11th to 20th	Day	34% 4 8% 18% 27% 9%	1800
	21st to end	Day	38% 5% 8% 18% 26% 6%	1773
December	1st to 10th	Day	46% 5% 8% 17% 19% 5%	1710
	11th to 20th	Day	46% 3 7% 18% 20% 6%	2150
	21st to end	Day	49% 5% 10% 18% 16% 2	3124
January	1st to 10th	Night	45% 4 7% 18% 23% 3	4109
	11th to 20th	Night	42% 5% 7% 22% 18% 6%	4120
	21st to end	Night	51% 3 5% 15% 22% 4	4235
February	1st to 10th	Night	44% 3 7% 19% 20% 6%	2280
	11th to 20th	Night	47% 3 6% 17% 19% 8%	2219
	21st to end	Night	47% 5% 8% 14% 18% 8%	1884
March	1st to 10th	Night	52% 6% 9% 12% 15% 6%	3733
	11th to 20th	Night	33% 5% 10% 19% 24% 9%	3519
	21st to end	Night	45% 4 7% 20% 20% 4	3817
April	1st to 10th	Night	33% 7% 12% 21% 21% 6%	1910
	11th to 20th	Night	35% 5% 6% 21% 22% 11%	1875
	21st to end	Night	32% 5% 11% 27% 20% 5%	1838
May	1st to 10th	Night	36% 10% 14% 20% 18% 2	2840
	11th to 20th	Night	40% 8% 15% 25% 12% 1	2813
	21st to end	Night	27% 10% 16% 27% 18% 2	3087
June	1st to 10th	Night	35% 11% 15% 21% 15% 2	1710
	11th to 20th	Night	23% 10% 24% 23% 18% 2	1710
	21st to end	Night	29% 10% 19% 21% 16% 5%	1710
July	1st to 10th	Night	40% 12% 21% 19% 7% 1	2795
	11th to 20th	Night	30% 13% 24% 24% 7% 2	2786
	21st to end	Night	51% 14% 14% 14% 6% 1	2988
August	1st to 10th	Night	24% 9% 15% 38% 12% 1	2987
	11th to 20th	Night	30% 8% 17% 28% 16% 2	3130
	21st to end	Night	28% 7% 14% 17% 28% 5%	3476
September	1st to 10th	Night	34% 11% 16% 17% 15% 6%	1983
	11th to 20th	Night	38% 9% 11% 19% 20% 3	2090
	21st to end	Night	31% 5% 12% 21% 22% 8%	2090
October	1st to 10th	Night	23% 4 6% 16% 33% 17%	3480
	11th to 20th	Night	19% 3 4 17% 29% 27%	3492
	21st to end	Night	22% 4 5% 24% 31% 13%	4298
November	1st to 10th	Night	32% 5% 9% 19% 24% 11%	2536
	11th to 20th	Night	32% 4 6% 20% 28% 10%	2600
	21st to end	Night	37% 4 8% 21% 23% 7%	2562
December	1st to 10th	Night	46% 6% 9% 17% 19% 3	2470
	11th to 20th	Night	40% 4 8% 16% 28% 4	3044
	21st to end	Night	48% 5% 11% 19% 16% 2	4532

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% 23% 36% 16% 3	270
	11th to 20th	Day	27% 20% 32% 15% 5% 1	270
	21st to end	Day	23% 22% 39% 11% 4 1	297
February	1st to 10th	Day	28% 17% 32% 19% 4	270
	11th to 20th	Day	37% 20% 28% 13% 3	270
	21st to end	Day	29% 24% 36% 11%	225
March	1st to 10th	Day	25% 19% 34% 16% 4 2	270
	11th to 20th	Day	21% 17% 34% 21% 6% 2	432
	21st to end	Day	20% 16% 36% 21% 7%	506
April	1st to 10th	Day	21% 14% 29% 20% 14% 2	460
	11th to 20th	Day	17% 15% 30% 24% 13% 1	452
	21st to end	Day	15% 11% 28% 27% 16% 3	460
May	1st to 10th	Day	16% 7% 28% 27% 16% 6%	463
	11th to 20th	Day	11% 6% 20% 30% 23% 10%	487
	21st to end	Day	11% 5% 17% 27% 23% 17%	529
June	1st to 10th	Day	13% 3 18% 26% 24% 15%	490
	11th to 20th	Day	5% 3 16% 23% 28% 25%	490
	21st to end	Day	10% 3 13% 25% 28% 21%	490
July	1st to 10th	Day	8% 3 8% 25% 28% 27%	485
	11th to 20th	Day	7% 2 6% 21% 33% 30%	484
	21st to end	Day	8% 2 9% 18% 36% 26%	532
August	1st to 10th	Day	9% 1 10% 21% 35% 23%	486
	11th to 20th	Day	10% 2 8% 29% 34% 18%	479
	21st to end	Day	13% 4 8% 21% 30% 24%	539
September	1st to 10th	Day	9% 4 9% 29% 32% 18%	490
	11th to 20th	Day	16% 4 11% 23% 31% 15%	490
	21st to end	Day	13% 4 14% 24% 34% 10%	490
October	1st to 10th	Day	13% 3 20% 30% 24% 10%	490
	11th to 20th	Day	10% 9% 22% 33% 24% 3	490
	21st to end	Day	15% 12% 18% 29% 23% 3	433
November	1st to 10th	Day	20% 9% 27% 28% 14% 3	300
	11th to 20th	Day	15% 12% 36% 25% 9% 1	300
	21st to end	Day	16% 11% 35% 25% 11% 1	291
December	1st to 10th	Day	29% 17% 31% 17% 6% 1	270
	11th to 20th	Day	25% 16% 27% 24% 6% 1	270
	21st to end	Day	28% 17% 32% 17% 5%	297
January	1st to 10th	Night	22% 15% 32% 25% 6%	760
	11th to 20th	Night	21% 15% 29% 28% 7%	760
	21st to end	Night	21% 15% 35% 26% 3	836
February	1st to 10th	Night	20% 12% 29% 33% 5%	760
	11th to 20th	Night	24% 14% 31% 27% 3	743
	21st to end	Night	24% 14% 35% 25% 2	628
March	1st to 10th	Night	20% 12% 32% 32% 5%	760
	11th to 20th	Night	18% 12% 33% 28% 9% 1	760
	21st to end	Night	20% 13% 27% 31% 10%	836
April	1st to 10th	Night	14% 10% 31% 30% 14% 1	580
	11th to 20th	Night	16% 10% 29% 31% 13% 1	563
	21st to end	Night	11% 8% 25% 38% 18% 1	570
May	1st to 10th	Night	11% 5% 24% 32% 25% 2	570
	11th to 20th	Night	11% 4 16% 35% 27% 6%	561
	21st to end	Night	8% 2 11% 35% 38% 6%	617
June	1st to 10th	Night	8% 2 12% 36% 37% 5%	570
	11th to 20th	Night	2 1 10% 33% 39% 15%	570
	21st to end	Night	6% 1 9% 29% 44% 11%	570
July	1st to 10th	Night	8% 2 6% 24% 46% 14%	555
	11th to 20th	Night	5% 1 4 23% 48% 17%	552
	21st to end	Night	6% 2 6% 27% 46% 12%	624
August	1st to 10th	Night	6% 1 5% 27% 49% 12%	567
	11th to 20th	Night	11% 1 7% 28% 43% 10%	564
	21st to end	Night	14% 2 7% 25% 40% 11%	627
September	1st to 10th	Night	8% 3 8% 30% 41% 10%	653
	11th to 20th	Night	14% 3 10% 30% 38% 6%	760
	21st to end	Night	12% 3 15% 32% 36% 2	760
October	1st to 10th	Night	11% 3 18% 35% 27% 6%	760
	11th to 20th	Night	13% 5% 23% 34% 22% 2	760
	21st to end	Night	15% 7% 20% 36% 19% 2	836
November	1st to 10th	Night	13% 7% 20% 37% 21% 1	780
	11th to 20th	Night	15% 7% 30% 35% 13% 1	800
	21st to end	Night	17% 9% 27% 35% 12% 1	789
December	1st to 10th	Night	23% 11% 28% 28% 9% 1	760
	11th to 20th	Night	23% 9% 29% 30% 9%	760
	21st to end	Night	28% 10% 27% 29% 6%	836

Page generated at 2024-11-24 23:22:18. Version ac07

Copyright © 2024 Attilla Danko.