Sumpter
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sumpter clear sky chart from 2005-11-06 to 2026-08-30.

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	6% 8% 3 7% 5% 4 4 4 5% 6% 48%	152891
	Night	6% 8% 3 7% 5% 4 4 4 5% 7% 47%	146653
Transparency	Day	32% 8% 11% 21% 19% 10%	147645
	Night	33% 9% 12% 22% 17% 7%	142901
Seeing	Day	13% 16% 31% 26% 12% 3	16744
	Night	10% 9% 25% 35% 18% 3	25836

By Month

Percentage Cloud Cover SW (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	9% 16% 7% 15% 7% 6% 5% 4 5% 5% 20%	4722
	11th to 20th	Day	6% 9% 4 8% 3 3 3 3 5% 8% 48%	4740
	21st to end	Day	8% 13% 4 9% 5% 4 4 4 5% 6% 40%	5187
February	1st to 10th	Day	7% 16% 5% 9% 7% 6% 5% 4 6% 7% 29%	1822
	11th to 20th	Day	7% 16% 6% 12% 6% 6% 5% 4 6% 7% 26%	2003
	21st to end	Day	5% 14% 5% 13% 7% 5% 4 4 6% 7% 28%	1730
March	1st to 10th	Day	5% 11% 4 12% 7% 7% 6% 5% 6% 8% 28%	4618
	11th to 20th	Day	6% 13% 4 9% 6% 5% 5% 3 5% 6% 36%	4778
	21st to end	Day	6% 16% 5% 11% 7% 7% 6% 5% 6% 7% 24%	6101
April	1st to 10th	Day	8% 13% 5% 10% 7% 6% 6% 4 7% 7% 28%	2520
	11th to 20th	Day	6% 12% 4 10% 6% 6% 5% 4 6% 7% 35%	2489
	21st to end	Day	7% 12% 4 9% 7% 5% 4 4 6% 7% 36%	2700
May	1st to 10th	Day	6% 7% 3 6% 4 3 4 3 5% 7% 51%	7848
	11th to 20th	Day	6% 7% 2 7% 5% 4 5% 4 6% 7% 47%	8160
	21st to end	Day	6% 7% 2 6% 4 4 4 4 5% 7% 51%	8992
June	1st to 10th	Day	9% 10% 3 8% 6% 4 5% 4 6% 8% 37%	2940
	11th to 20th	Day	8% 8% 3 7% 5% 4 5% 3 5% 7% 45%	2940
	21st to end	Day	4 3 2 5% 4 4 4 4 5% 7% 60%	2940
July	1st to 10th	Day	2 2 1 2 2 2 3 3 4 5% 74%	8219
	11th to 20th	Day	3 3 1 4 2 3 3 2 4 4 71%	8220
	21st to end	Day	2 1 1 3 2 3 3 3 5% 6% 71%	8922
August	1st to 10th	Day	4 3 1 5% 4 4 4 3 5% 7% 58%	6350
	11th to 20th	Day	3 3 1 3 2 2 3 2 4 5% 73%	5801
	21st to end	Day	5% 4 2 5% 3 3 3 3 5% 6% 61%	6093
September	1st to 10th	Day	2 3 1 3 3 3 3 2 5% 7% 67%	2400
	11th to 20th	Day	6% 5% 2 5% 4 3 4 4 5% 7% 57%	2308
	21st to end	Day	5% 7% 2 6% 4 4 3 3 4 5% 57%	2200
October	1st to 10th	Day	5% 5% 2 5% 3 3 3 2 4 6% 64%	3444
	11th to 20th	Day	5% 7% 3 7% 5% 4 4 3 5% 8% 48%	3197
	21st to end	Day	8% 10% 3 9% 6% 5% 6% 5% 6% 7% 35%	3200
November	1st to 10th	Day	12% 12% 3 9% 6% 4 5% 4 6% 8% 31%	1854
	11th to 20th	Day	10% 12% 4 10% 6% 6% 6% 5% 6% 7% 29%	1873
	21st to end	Day	8% 10% 3 9% 6% 6% 5% 6% 7% 7% 33%	1680
December	1st to 10th	Day	5% 10% 4 7% 5% 4 4 4 4 6% 46%	2700
	11th to 20th	Day	9% 20% 7% 12% 7% 6% 5% 5% 5% 7% 17%	3108
	21st to end	Day	11% 16% 5% 13% 7% 7% 5% 4 5% 6% 21%	4092
January	1st to 10th	Night	10% 16% 6% 13% 7% 7% 6% 4 6% 6% 20%	8172
	11th to 20th	Night	6% 9% 4 6% 4 3 3 3 4 8% 49%	8220
	21st to end	Night	7% 14% 4 8% 4 4 4 3 5% 6% 39%	8994
February	1st to 10th	Night	8% 13% 5% 10% 7% 5% 5% 4 6% 7% 31%	2793
	11th to 20th	Night	6% 13% 4 9% 7% 6% 6% 4 7% 7% 32%	2504
	21st to end	Night	5% 11% 5% 10% 7% 7% 5% 4 7% 8% 30%	2076
March	1st to 10th	Night	4 10% 4 10% 6% 5% 6% 5% 7% 8% 35%	5496
	11th to 20th	Night	6% 13% 4 9% 5% 4 4 3 5% 6% 41%	5438
	21st to end	Night	4 11% 5% 11% 7% 7% 6% 5% 8% 8% 28%	5116
April	1st to 10th	Night	7% 10% 3 8% 7% 6% 5% 4 7% 7% 37%	2100
	11th to 20th	Night	6% 9% 3 7% 5% 5% 4 4 6% 7% 45%	2079
	21st to end	Night	6% 9% 3 6% 4 4 4 5% 7% 8% 44%	1919
May	1st to 10th	Night	5% 5% 2 5% 4 4 3 3 5% 8% 58%	5083
	11th to 20th	Night	4 5% 2 4 3 4 4 4 6% 7% 59%	4700
	21st to end	Night	6% 5% 2 5% 4 4 4 3 4 7% 56%	5181
June	1st to 10th	Night	7% 9% 2 6% 4 4 4 4 6% 9% 44%	1680
	11th to 20th	Night	6% 6% 3 5% 4 4 4 3 5% 8% 54%	1680
	21st to end	Night	3 4 1 4 4 3 3 4 6% 6% 63%	1680
July	1st to 10th	Night	1 2 1 2 2 3 3 3 4 5% 75%	4740
	11th to 20th	Night	1 2 1 3 2 2 3 2 4 5% 76%	4740
	21st to end	Night	3 2 1 2 2 2 3 3 5% 5% 72%	5153
August	1st to 10th	Night	2 2 1 4 3 3 4 5% 6% 7% 63%	3662
	11th to 20th	Night	1 2 1 3 2 2 3 2 3 5% 75%	4268
	21st to end	Night	3 4 2 4 3 3 3 2 4 6% 65%	5105
September	1st to 10th	Night	2 3 1 2 2 2 3 2 3 6% 72%	2000
	11th to 20th	Night	4 3 1 5% 3 4 4 4 6% 6% 61%	2090
	21st to end	Night	6% 5% 2 4 3 3 4 3 5% 6% 62%	2200
October	1st to 10th	Night	3 4 2 4 3 3 2 3 3 5% 69%	3754
	11th to 20th	Night	5% 6% 3 6% 3 4 4 3 6% 7% 53%	3957
	21st to end	Night	7% 7% 3 7% 4 5% 5% 4 6% 8% 45%	4600
November	1st to 10th	Night	10% 9% 4 8% 6% 5% 5% 4 6% 7% 35%	2665
	11th to 20th	Night	9% 11% 4 9% 6% 6% 6% 5% 6% 7% 32%	2746
	21st to end	Night	7% 10% 3 7% 6% 4 5% 5% 7% 9% 36%	2940
December	1st to 10th	Night	6% 8% 3 6% 4 4 3 4 5% 7% 52%	4700
	11th to 20th	Night	14% 17% 5% 10% 6% 6% 6% 4 6% 7% 19%	5316
	21st to end	Night	12% 17% 5% 11% 7% 6% 5% 4 6% 6% 21%	7106

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	58% 12% 15% 10% 6%	4723
	11th to 20th	Day	32% 8% 13% 24% 18% 4	4740
	21st to end	Day	43% 9% 10% 15% 18% 6%	5187
February	1st to 10th	Day	51% 11% 16% 16% 5% 1	1822
	11th to 20th	Day	52% 13% 13% 15% 6% 1	2013
	21st to end	Day	49% 11% 12% 18% 8% 2	1730
March	1st to 10th	Day	43% 11% 16% 17% 9% 4	4618
	11th to 20th	Day	41% 8% 13% 27% 10%	4778
	21st to end	Day	50% 14% 15% 16% 4	6101
April	1st to 10th	Day	49% 11% 16% 17% 5% 1	2520
	11th to 20th	Day	43% 10% 13% 20% 12% 2	2492
	21st to end	Day	42% 10% 14% 20% 14% 1	2700
May	1st to 10th	Day	28% 7% 9% 29% 26% 1	7848
	11th to 20th	Day	29% 8% 14% 27% 19% 4	8163
	21st to end	Day	26% 9% 15% 30% 17% 2	8994
June	1st to 10th	Day	41% 9% 14% 24% 12% 1	2940
	11th to 20th	Day	34% 7% 14% 23% 18% 5%	2940
	21st to end	Day	23% 6% 10% 26% 27% 8%	2940
July	1st to 10th	Day	13% 3 5% 16% 31% 32%	8151
	11th to 20th	Day	16% 3 5% 9% 26% 42%	8145
	21st to end	Day	13% 4 5% 19% 31% 27%	8723
August	1st to 10th	Day	20% 4 7% 14% 30% 25%	4664
	11th to 20th	Day	15% 4 6% 20% 39% 17%	4237
	21st to end	Day	18% 4 7% 26% 24% 21%	4420
September	1st to 10th	Day	16% 5% 8% 22% 30% 19%	2400
	11th to 20th	Day	25% 6% 12% 23% 24% 11%	2308
	21st to end	Day	28% 5% 10% 26% 23% 8%	2200
October	1st to 10th	Day	23% 4 8% 20% 37% 8%	3444
	11th to 20th	Day	32% 5% 15% 28% 17% 3	3197
	21st to end	Day	42% 8% 12% 25% 12% 1	3200
November	1st to 10th	Day	47% 9% 16% 19% 8% 1	1854
	11th to 20th	Day	50% 10% 17% 19% 4 1	1873
	21st to end	Day	44% 11% 17% 18% 8% 2	1680
December	1st to 10th	Day	36% 8% 12% 32% 11%	2700
	11th to 20th	Day	60% 13% 13% 11% 2	3108
	21st to end	Day	54% 15% 14% 12% 5%	4092
January	1st to 10th	Night	56% 13% 14% 11% 5%	8172
	11th to 20th	Night	32% 8% 13% 25% 19% 4	8220
	21st to end	Night	42% 10% 10% 18% 12% 8%	8994
February	1st to 10th	Night	49% 12% 16% 17% 6% 1	2793
	11th to 20th	Night	46% 10% 16% 17% 9% 1	2505
	21st to end	Night	44% 14% 13% 18% 8% 2	2076
March	1st to 10th	Night	35% 10% 13% 24% 12% 5%	5496
	11th to 20th	Night	39% 8% 13% 29% 11%	5438
	21st to end	Night	42% 17% 18% 17% 5%	5116
April	1st to 10th	Night	40% 11% 17% 24% 7% 1	2100
	11th to 20th	Night	36% 9% 15% 26% 12% 2	2079
	21st to end	Night	32% 12% 17% 23% 16% 1	1919
May	1st to 10th	Night	22% 6% 12% 32% 26% 2	5081
	11th to 20th	Night	22% 7% 14% 34% 23% 1	4700
	21st to end	Night	27% 7% 15% 35% 16% 1	5182
June	1st to 10th	Night	34% 9% 14% 29% 13% 1	1680
	11th to 20th	Night	28% 8% 13% 27% 19% 4	1680
	21st to end	Night	20% 6% 13% 30% 25% 7%	1680
July	1st to 10th	Night	12% 2 4 21% 29% 30%	4700
	11th to 20th	Night	12% 2 5% 10% 30% 40%	4692
	21st to end	Night	13% 3 5% 21% 34% 24%	5040
August	1st to 10th	Night	17% 4 9% 15% 34% 21%	2681
	11th to 20th	Night	12% 3 6% 21% 43% 15%	3105
	21st to end	Night	14% 4 8% 28% 27% 20%	3698
September	1st to 10th	Night	13% 4 8% 24% 33% 18%	2000
	11th to 20th	Night	20% 7% 10% 24% 26% 13%	2090
	21st to end	Night	22% 5% 10% 27% 26% 10%	2200
October	1st to 10th	Night	20% 5% 7% 23% 36% 9%	3754
	11th to 20th	Night	27% 6% 17% 22% 25% 2	3957
	21st to end	Night	33% 9% 12% 28% 17% 1	4600
November	1st to 10th	Night	42% 11% 15% 21% 10% 1	2665
	11th to 20th	Night	47% 11% 15% 20% 7%	2746
	21st to end	Night	39% 12% 17% 17% 12% 2	2940
December	1st to 10th	Night	30% 9% 14% 28% 17% 1	4700
	11th to 20th	Night	59% 11% 13% 13% 3	5316
	21st to end	Night	53% 15% 15% 12% 5%	7106

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	25% 15% 25% 20% 11% 3	220
	11th to 20th	Day	22% 13% 23% 24% 14% 4	220
	21st to end	Day	11% 13% 34% 27% 12% 2	242
February	1st to 10th	Day	18% 25% 31% 18% 5% 2	362
	11th to 20th	Day	16% 23% 36% 18% 5% 1	510
	21st to end	Day	19% 22% 33% 21% 5%	446
March	1st to 10th	Day	19% 23% 34% 19% 4	540
	11th to 20th	Day	18% 24% 30% 20% 7% 1	540
	21st to end	Day	22% 24% 26% 21% 6% 1	594
April	1st to 10th	Day	20% 21% 28% 20% 10% 2	540
	11th to 20th	Day	18% 23% 32% 17% 7% 3	532
	21st to end	Day	15% 21% 34% 20% 7% 2	540
May	1st to 10th	Day	13% 22% 31% 22% 8% 3	543
	11th to 20th	Day	21% 21% 29% 17% 11% 2	568
	21st to end	Day	14% 17% 24% 28% 12% 4	617
June	1st to 10th	Day	14% 18% 28% 24% 12% 5%	570
	11th to 20th	Day	14% 20% 34% 22% 8% 2	570
	21st to end	Day	4 15% 35% 29% 13% 4	570
July	1st to 10th	Day	4 8% 38% 34% 13% 2	566
	11th to 20th	Day	3 11% 40% 29% 15% 3	564
	21st to end	Day	3 9% 33% 33% 17% 5%	619
August	1st to 10th	Day	6% 6% 32% 33% 17% 6%	567
	11th to 20th	Day	4 7% 28% 35% 20% 6%	557
	21st to end	Day	5% 11% 31% 30% 17% 6%	620
September	1st to 10th	Day	4 9% 25% 36% 18% 7%	530
	11th to 20th	Day	9% 10% 25% 33% 17% 5%	530
	21st to end	Day	8% 12% 30% 30% 15% 4	530
October	1st to 10th	Day	11% 17% 26% 28% 17% 2	530
	11th to 20th	Day	14% 14% 29% 25% 15% 3	491
	21st to end	Day	15% 17% 25% 29% 12% 2	363
November	1st to 10th	Day	17% 17% 31% 23% 12% 1	330
	11th to 20th	Day	16% 15% 28% 29% 10% 2	321
	21st to end	Day	15% 13% 30% 30% 10% 1	220
December	1st to 10th	Day	18% 15% 27% 16% 15% 8%	220
	11th to 20th	Day	18% 19% 38% 19% 5% 2	220
	21st to end	Day	17% 18% 34% 21% 8% 2	242
January	1st to 10th	Night	15% 13% 27% 28% 14% 3	840
	11th to 20th	Night	14% 11% 27% 28% 18% 3	840
	21st to end	Night	12% 7% 25% 35% 18% 3	924
February	1st to 10th	Night	13% 14% 30% 30% 11% 2	840
	11th to 20th	Night	11% 11% 31% 30% 15% 2	824
	21st to end	Night	11% 14% 32% 27% 14% 2	692
March	1st to 10th	Night	11% 13% 30% 31% 13% 2	840
	11th to 20th	Night	11% 12% 31% 27% 16% 2	840
	21st to end	Night	10% 16% 29% 33% 11% 1	924
April	1st to 10th	Night	10% 12% 29% 34% 13% 2	840
	11th to 20th	Night	9% 14% 31% 29% 14% 3	831
	21st to end	Night	9% 14% 29% 35% 11% 1	659
May	1st to 10th	Night	8% 14% 30% 33% 15% 1	546
	11th to 20th	Night	11% 8% 23% 30% 24% 3	414
	21st to end	Night	9% 6% 24% 35% 22% 4	455
June	1st to 10th	Night	9% 8% 24% 36% 21% 2	420
	11th to 20th	Night	7% 10% 26% 40% 16% 1	420
	21st to end	Night	5% 4 19% 48% 24% 1	420
July	1st to 10th	Night	2 2 18% 49% 27% 2	410
	11th to 20th	Night	2 2 19% 57% 20%	408
	21st to end	Night	1 2 16% 53% 27% 1	460
August	1st to 10th	Night	2 3 13% 50% 29% 2	418
	11th to 20th	Night	2 2 17% 44% 29% 6%	671
	21st to end	Night	3 3 19% 43% 28% 4	916
September	1st to 10th	Night	3 3 18% 40% 31% 5%	800
	11th to 20th	Night	4 4 16% 37% 32% 8%	800
	21st to end	Night	7% 7% 19% 33% 29% 6%	800
October	1st to 10th	Night	8% 5% 23% 35% 25% 4	800
	11th to 20th	Night	10% 9% 19% 36% 19% 7%	800
	21st to end	Night	10% 10% 22% 35% 18% 4	880
November	1st to 10th	Night	11% 12% 23% 35% 17% 1	820
	11th to 20th	Night	14% 12% 24% 34% 14% 3	840
	21st to end	Night	11% 12% 24% 31% 16% 6%	840
December	1st to 10th	Night	15% 10% 26% 29% 17% 4	840
	11th to 20th	Night	18% 8% 28% 32% 11% 2	840
	21st to end	Night	17% 14% 30% 28% 10% 1	924

Page generated at 2026-08-27 01:07:14. Version ac07

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