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 2025-04-26.

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% 9% 3 8% 5% 4 4 4 5% 6% 45%	117466
	Night	6% 9% 3 7% 5% 4 4 4 5% 7% 45%	119944
Transparency	Day	35% 8% 12% 20% 16% 9%	117211
	Night	35% 9% 13% 21% 16% 6%	119788
Seeing	Day	13% 16% 31% 26% 12% 3	14973
	Night	10% 9% 25% 34% 19% 3	24299

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	8% 14% 7% 16% 8% 6% 5% 4 5% 5% 22%	3639
	11th to 20th	Day	8% 12% 5% 10% 4 4 4 3 5% 7% 38%	3640
	21st to end	Day	10% 15% 4 10% 5% 3 3 3 4 5% 37%	4004
February	1st to 10th	Day	8% 16% 5% 10% 7% 6% 5% 4 6% 6% 28%	1735
	11th to 20th	Day	8% 16% 6% 12% 6% 6% 5% 4 6% 6% 26%	1905
	21st to end	Day	5% 15% 6% 13% 7% 6% 4 5% 7% 8% 27%	1650
March	1st to 10th	Day	5% 11% 4 12% 7% 7% 6% 5% 6% 8% 28%	4518
	11th to 20th	Day	6% 13% 4 9% 6% 5% 5% 3 5% 6% 37%	4676
	21st to end	Day	6% 16% 5% 11% 7% 7% 6% 5% 6% 7% 24%	5969
April	1st to 10th	Day	8% 13% 5% 10% 7% 6% 6% 4 7% 6% 27%	2400
	11th to 20th	Day	6% 12% 4 10% 6% 6% 5% 4 6% 7% 36%	2369
	21st to end	Day	7% 12% 4 8% 6% 4 4 5% 6% 7% 36%	2508
May	1st to 10th	Day	8% 11% 5% 9% 5% 4 4 4 5% 7% 38%	4229
	11th to 20th	Day	5% 6% 2 6% 4 4 4 3 5% 7% 53%	4377
	21st to end	Day	7% 11% 3 9% 5% 5% 5% 5% 5% 7% 38%	4813
June	1st to 10th	Day	10% 10% 3 8% 7% 5% 5% 5% 6% 9% 34%	2660
	11th to 20th	Day	8% 8% 3 7% 5% 4 5% 4 5% 8% 43%	2660
	21st to end	Day	4 3 2 4 3 3 4 4 5% 6% 61%	2660
July	1st to 10th	Day	1 2 1 2 2 2 3 3 4 4 78%	4420
	11th to 20th	Day	1 2 1 2 2 2 3 3 4 5% 75%	4420
	21st to end	Day	2 1 1 2 2 2 2 3 4 5% 75%	4790
August	1st to 10th	Day	4 3 1 5% 4 3 4 3 5% 8% 60%	4400
	11th to 20th	Day	2 3 1 3 3 3 3 3 4 5% 70%	3942
	21st to end	Day	3 3 1 4 3 3 3 3 4 5% 68%	4180
September	1st to 10th	Day	2 2 1 3 2 3 3 2 5% 7% 69%	2280
	11th to 20th	Day	6% 5% 2 5% 4 3 4 4 5% 7% 57%	2193
	21st to end	Day	4 7% 2 6% 4 4 3 3 4 5% 57%	2090
October	1st to 10th	Day	5% 5% 2 5% 2 3 3 2 3 6% 64%	3339
	11th to 20th	Day	5% 7% 3 8% 5% 4 4 3 5% 8% 48%	3099
	21st to end	Day	8% 10% 3 9% 6% 5% 6% 5% 6% 7% 35%	3101
November	1st to 10th	Day	12% 12% 3 9% 6% 4 5% 4 6% 8% 30%	1764
	11th to 20th	Day	10% 13% 4 10% 6% 6% 6% 4 6% 7% 28%	1784
	21st to end	Day	8% 10% 3 10% 6% 6% 5% 6% 7% 7% 33%	1600
December	1st to 10th	Day	5% 10% 4 7% 5% 4 4 4 4 6% 48%	2620
	11th to 20th	Day	9% 20% 7% 13% 7% 6% 5% 5% 5% 7% 17%	3028
	21st to end	Day	11% 16% 5% 13% 7% 7% 5% 4 5% 6% 20%	4004
January	1st to 10th	Night	9% 16% 6% 12% 8% 7% 6% 4 6% 6% 21%	6306
	11th to 20th	Night	8% 12% 6% 8% 5% 4 3 3 4 8% 40%	6320
	21st to end	Night	9% 16% 4 9% 4 3 3 3 4 5% 39%	6952
February	1st to 10th	Night	8% 13% 5% 11% 7% 5% 5% 4 6% 7% 29%	2660
	11th to 20th	Night	6% 13% 4 9% 7% 5% 5% 5% 7% 7% 32%	2382
	21st to end	Night	5% 11% 5% 10% 7% 7% 5% 4 7% 8% 30%	1980
March	1st to 10th	Night	4 10% 4 10% 6% 5% 6% 5% 7% 8% 35%	5376
	11th to 20th	Night	6% 13% 4 9% 5% 4 4 3 5% 6% 40%	5320
	21st to end	Night	4 11% 5% 11% 7% 7% 6% 5% 8% 8% 27%	5006
April	1st to 10th	Night	7% 10% 3 8% 7% 6% 6% 4 7% 7% 37%	2000
	11th to 20th	Night	6% 9% 3 7% 5% 5% 4 3 6% 7% 45%	1979
	21st to end	Night	6% 9% 3 6% 4 4 4 5% 7% 9% 44%	1787
May	1st to 10th	Night	8% 8% 3 8% 6% 5% 4 3 5% 6% 43%	2732
	11th to 20th	Night	4 3 1 3 3 3 3 3 5% 6% 65%	2516
	21st to end	Night	6% 7% 2 7% 5% 5% 4 3 5% 7% 48%	2762
June	1st to 10th	Night	8% 9% 2 6% 5% 5% 5% 4 6% 9% 42%	1520
	11th to 20th	Night	6% 5% 3 5% 4 4 4 3 5% 8% 54%	1520
	21st to end	Night	3 4 1 4 3 3 3 4 6% 6% 64%	1520
July	1st to 10th	Night	1 1 1 1 2 2 2 2 4 83%	2540
	11th to 20th	Night	1 1 1 1 1 2 3 5% 6% 79%	2540
	21st to end	Night	2 2 1 2 3 2 3 2 4 5% 74%	2761
August	1st to 10th	Night	2 2 1 4 3 2 4 4 6% 7% 64%	2529
	11th to 20th	Night	1 2 1 3 2 2 3 3 4 5% 75%	2894
	21st to end	Night	2 2 1 3 3 2 3 2 4 5% 73%	3498
September	1st to 10th	Night	2 3 1 2 2 2 3 2 3 6% 74%	1900
	11th to 20th	Night	4 3 1 5% 3 3 4 4 6% 6% 61%	1985
	21st to end	Night	6% 5% 2 4 4 3 3 3 5% 6% 61%	2090
October	1st to 10th	Night	4 4 2 4 3 3 2 3 3 5% 69%	3639
	11th to 20th	Night	5% 5% 3 6% 3 4 4 3 6% 7% 54%	3835
	21st to end	Night	7% 7% 3 7% 4 5% 5% 4 7% 8% 44%	4457
November	1st to 10th	Night	10% 10% 4 8% 6% 5% 5% 4 6% 7% 35%	2535
	11th to 20th	Night	9% 11% 4 9% 5% 6% 6% 5% 6% 7% 32%	2615
	21st to end	Night	7% 10% 3 7% 6% 4 5% 5% 7% 9% 37%	2800
December	1st to 10th	Night	5% 8% 3 6% 4 4 3 4 5% 6% 52%	4560
	11th to 20th	Night	14% 17% 5% 11% 6% 6% 6% 4 6% 7% 18%	5176
	21st to end	Night	12% 17% 5% 11% 7% 6% 5% 4 6% 6% 21%	6952

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	55% 13% 13% 12% 7%	3639
	11th to 20th	Day	41% 11% 15% 22% 10% 1	3640
	21st to end	Day	46% 11% 8% 13% 16% 6%	4004
February	1st to 10th	Day	52% 11% 16% 15% 6% 1	1735
	11th to 20th	Day	52% 13% 13% 15% 6% 1	1915
	21st to end	Day	49% 12% 13% 18% 7% 1	1650
March	1st to 10th	Day	43% 11% 16% 17% 9% 4	4518
	11th to 20th	Day	41% 8% 14% 27% 10%	4676
	21st to end	Day	50% 15% 15% 16% 3	5969
April	1st to 10th	Day	51% 11% 16% 15% 5% 1	2400
	11th to 20th	Day	43% 10% 13% 20% 12% 2	2372
	21st to end	Day	42% 10% 14% 19% 14% 1	2508
May	1st to 10th	Day	38% 11% 13% 25% 13% 1	4229
	11th to 20th	Day	25% 6% 13% 32% 19% 6%	4380
	21st to end	Day	35% 13% 19% 24% 8%	4814
June	1st to 10th	Day	43% 10% 14% 24% 10%	2660
	11th to 20th	Day	35% 7% 15% 23% 15% 5%	2660
	21st to end	Day	21% 6% 10% 27% 28% 8%	2660
July	1st to 10th	Day	10% 4 6% 12% 20% 48%	4351
	11th to 20th	Day	11% 3 6% 9% 20% 50%	4345
	21st to end	Day	11% 3 5% 15% 35% 31%	4639
August	1st to 10th	Day	20% 4 7% 14% 31% 24%	4384
	11th to 20th	Day	15% 4 6% 19% 39% 17%	3982
	21st to end	Day	18% 4 7% 26% 25% 21%	4179
September	1st to 10th	Day	15% 5% 8% 21% 31% 20%	2280
	11th to 20th	Day	25% 6% 11% 23% 24% 12%	2193
	21st to end	Day	28% 5% 10% 26% 22% 8%	2090
October	1st to 10th	Day	23% 4 8% 19% 37% 8%	3339
	11th to 20th	Day	33% 5% 15% 28% 17% 3	3099
	21st to end	Day	43% 8% 12% 24% 12% 1	3101
November	1st to 10th	Day	47% 9% 16% 18% 9% 1	1764
	11th to 20th	Day	49% 11% 17% 19% 4 1	1784
	21st to end	Day	45% 10% 16% 18% 9% 2	1600
December	1st to 10th	Day	35% 8% 12% 33% 11%	2620
	11th to 20th	Day	61% 13% 13% 11% 1	3028
	21st to end	Day	54% 15% 14% 12% 5%	4004
January	1st to 10th	Night	55% 15% 13% 11% 6%	6306
	11th to 20th	Night	40% 9% 15% 23% 12% 1	6320
	21st to end	Night	44% 11% 10% 15% 11% 8%	6952
February	1st to 10th	Night	50% 12% 16% 16% 5% 1	2660
	11th to 20th	Night	46% 11% 16% 16% 9% 1	2383
	21st to end	Night	45% 14% 13% 18% 7% 2	1980
March	1st to 10th	Night	35% 10% 14% 24% 12% 5%	5376
	11th to 20th	Night	39% 8% 13% 29% 11%	5320
	21st to end	Night	42% 17% 18% 17% 5%	5006
April	1st to 10th	Night	41% 11% 17% 22% 8% 1	2000
	11th to 20th	Night	36% 9% 15% 26% 12% 2	1979
	21st to end	Night	31% 12% 18% 23% 15% 1	1787
May	1st to 10th	Night	32% 10% 18% 26% 13% 1	2732
	11th to 20th	Night	19% 7% 12% 35% 26% 1	2516
	21st to end	Night	32% 11% 23% 28% 7%	2762
June	1st to 10th	Night	36% 10% 16% 28% 10% 1	1520
	11th to 20th	Night	28% 9% 14% 29% 17% 4	1520
	21st to end	Night	18% 6% 13% 31% 25% 7%	1520
July	1st to 10th	Night	8% 2 5% 15% 23% 47%	2500
	11th to 20th	Night	6% 3 7% 12% 25% 47%	2492
	21st to end	Night	12% 3 5% 14% 38% 28%	2674
August	1st to 10th	Night	17% 4 9% 15% 35% 20%	2521
	11th to 20th	Night	12% 3 6% 21% 43% 15%	2920
	21st to end	Night	13% 3 8% 28% 27% 21%	3498
September	1st to 10th	Night	13% 4 8% 24% 33% 19%	1900
	11th to 20th	Night	20% 7% 11% 24% 25% 13%	1985
	21st to end	Night	22% 5% 10% 28% 25% 10%	2090
October	1st to 10th	Night	20% 5% 7% 22% 37% 9%	3639
	11th to 20th	Night	27% 6% 17% 22% 25% 2	3835
	21st to end	Night	34% 9% 12% 27% 17% 1	4457
November	1st to 10th	Night	42% 11% 14% 21% 11% 1	2535
	11th to 20th	Night	46% 12% 14% 20% 7%	2615
	21st to end	Night	39% 12% 17% 17% 13% 2	2800
December	1st to 10th	Night	29% 9% 14% 28% 18% 1	4560
	11th to 20th	Night	60% 11% 13% 13% 3	5176
	21st to end	Night	53% 15% 15% 12% 5%	6952

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	24% 14% 27% 21% 12% 3	200
	11th to 20th	Day	25% 15% 24% 22% 12% 4	200
	21st to end	Day	12% 14% 34% 25% 12% 3	220
February	1st to 10th	Day	19% 26% 32% 18% 4 1	335
	11th to 20th	Day	17% 23% 36% 18% 5% 1	472
	21st to end	Day	19% 21% 34% 22% 5%	414
March	1st to 10th	Day	18% 23% 36% 20% 4	500
	11th to 20th	Day	17% 23% 30% 20% 8% 1	500
	21st to end	Day	21% 25% 25% 22% 6% 1	550
April	1st to 10th	Day	20% 21% 29% 19% 10% 2	500
	11th to 20th	Day	17% 24% 32% 18% 7% 3	492
	21st to end	Day	15% 22% 34% 20% 7% 2	481
May	1st to 10th	Day	14% 23% 30% 23% 7% 3	463
	11th to 20th	Day	19% 19% 28% 18% 13% 2	488
	21st to end	Day	15% 17% 23% 29% 12% 4	529
June	1st to 10th	Day	13% 18% 28% 25% 12% 5%	490
	11th to 20th	Day	15% 19% 34% 22% 8% 2	490
	21st to end	Day	3 14% 35% 30% 13% 4	490
July	1st to 10th	Day	3 8% 37% 35% 13% 2	486
	11th to 20th	Day	2 10% 40% 29% 15% 3	484
	21st to end	Day	2 8% 35% 33% 17% 5%	531
August	1st to 10th	Day	5% 6% 32% 34% 17% 6%	487
	11th to 20th	Day	4 7% 26% 36% 21% 7%	477
	21st to end	Day	6% 10% 30% 30% 17% 7%	539
September	1st to 10th	Day	4 10% 26% 36% 18% 6%	490
	11th to 20th	Day	9% 10% 26% 32% 17% 5%	490
	21st to end	Day	8% 13% 31% 30% 15% 3	490
October	1st to 10th	Day	11% 17% 25% 28% 18% 2	490
	11th to 20th	Day	13% 15% 29% 25% 16% 3	453
	21st to end	Day	15% 17% 25% 28% 12% 3	330
November	1st to 10th	Day	16% 17% 31% 23% 12% 1	300
	11th to 20th	Day	16% 15% 28% 28% 10% 2	292
	21st to end	Day	15% 13% 31% 30% 11% 2	200
December	1st to 10th	Day	15% 15% 28% 17% 17% 9%	200
	11th to 20th	Day	18% 20% 38% 19% 5% 2	200
	21st to end	Day	14% 19% 35% 22% 8% 2	220
January	1st to 10th	Night	14% 13% 28% 28% 15% 3	800
	11th to 20th	Night	15% 12% 27% 26% 17% 2	800
	21st to end	Night	13% 8% 26% 34% 18% 3	880
February	1st to 10th	Night	14% 15% 30% 29% 10% 3	800
	11th to 20th	Night	12% 11% 31% 30% 15% 2	784
	21st to end	Night	11% 14% 31% 28% 14% 2	660
March	1st to 10th	Night	11% 13% 30% 31% 14% 2	800
	11th to 20th	Night	11% 12% 30% 28% 17% 2	800
	21st to end	Night	10% 16% 29% 34% 11% 1	880
April	1st to 10th	Night	10% 12% 29% 34% 13% 2	800
	11th to 20th	Night	9% 14% 31% 29% 14% 4	791
	21st to end	Night	9% 14% 28% 34% 13% 1	615
May	1st to 10th	Night	8% 14% 31% 31% 15% 1	494
	11th to 20th	Night	12% 7% 20% 32% 26% 3	374
	21st to end	Night	9% 6% 24% 34% 22% 4	411
June	1st to 10th	Night	9% 8% 25% 36% 20% 2	380
	11th to 20th	Night	8% 11% 25% 39% 17% 1	380
	21st to end	Night	5% 3 18% 49% 24% 1	380
July	1st to 10th	Night	2 3 18% 48% 27% 2	370
	11th to 20th	Night	2 2 20% 57% 20%	368
	21st to end	Night	1 2 17% 52% 26% 1	416
August	1st to 10th	Night	2 3 13% 49% 30% 3	378
	11th to 20th	Night	2 1 17% 41% 31% 7%	606
	21st to end	Night	2 3 20% 42% 30% 4	836
September	1st to 10th	Night	3 3 18% 40% 31% 5%	760
	11th to 20th	Night	4 4 16% 37% 32% 8%	760
	21st to end	Night	7% 6% 19% 34% 27% 6%	760
October	1st to 10th	Night	8% 5% 23% 35% 25% 4	760
	11th to 20th	Night	10% 8% 18% 36% 19% 8%	760
	21st to end	Night	10% 10% 23% 34% 18% 4	836
November	1st to 10th	Night	11% 12% 23% 35% 18% 1	780
	11th to 20th	Night	14% 12% 25% 33% 14% 3	800
	21st to end	Night	12% 12% 23% 31% 17% 6%	800
December	1st to 10th	Night	14% 10% 25% 30% 17% 4	800
	11th to 20th	Night	18% 8% 28% 31% 12% 2	800
	21st to end	Night	16% 14% 30% 29% 10% 1	880

Page generated at 2025-04-23 06:25:08. Version ac07

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