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 2024-03-01.

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	7% 9% 4 8% 6% 3 5% 5% 5% 7% 41%	78390
	Night	7% 9% 4 7% 6% 4 5% 5% 6% 7% 40%	81030
Transparency	Day	39% 9% 13% 18% 14% 6%	78094
	Night	38% 11% 15% 19% 13% 4	80847
Seeing	Day	12% 16% 31% 26% 12% 3	13482
	Night	10% 9% 24% 34% 19% 3	22833

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	6% 14% 9% 18% 11% 5% 6% 5% 5% 5% 17%	2539
	11th to 20th	Day	12% 16% 7% 12% 6% 3 5% 4 5% 7% 24%	2540
	21st to end	Day	14% 19% 6% 12% 8% 3 5% 5% 5% 5% 18%	2794
February	1st to 10th	Day	8% 15% 5% 9% 7% 4 6% 5% 6% 7% 29%	1648
	11th to 20th	Day	8% 14% 7% 10% 7% 4 6% 5% 6% 7% 26%	1807
	21st to end	Day	4 13% 7% 12% 8% 4 5% 6% 7% 8% 25%	1570
March	1st to 10th	Day	10% 13% 6% 11% 8% 5% 6% 5% 5% 6% 24%	1801
	11th to 20th	Day	8% 17% 6% 10% 7% 4 7% 5% 5% 7% 26%	1838
	21st to end	Day	9% 16% 7% 10% 9% 5% 6% 4 5% 5% 22%	2376
April	1st to 10th	Day	9% 12% 6% 10% 9% 5% 7% 6% 7% 6% 25%	2160
	11th to 20th	Day	7% 11% 5% 10% 7% 4 5% 4 6% 7% 33%	2129
	21st to end	Day	7% 12% 4 7% 7% 3 5% 5% 6% 7% 36%	2313
May	1st to 10th	Day	6% 8% 4 7% 7% 4 4 6% 6% 8% 40%	2407
	11th to 20th	Day	10% 9% 3 8% 6% 4 6% 6% 6% 8% 34%	2477
	21st to end	Day	11% 10% 4 9% 7% 3 6% 6% 6% 7% 31%	2723
June	1st to 10th	Day	10% 8% 4 8% 7% 4 6% 5% 6% 9% 34%	2520
	11th to 20th	Day	9% 8% 3 6% 6% 3 5% 5% 5% 8% 43%	2520
	21st to end	Day	5% 3 2 3 4 3 4 4 5% 7% 61%	2520
July	1st to 10th	Day	1 2 1 3 3 2 4 5% 5% 6% 66%	2520
	11th to 20th	Day	1 2 1 2 3 2 3 3 4 6% 73%	2520
	21st to end	Day	2 2 1 3 3 2 3 3 4 5% 74%	2741
August	1st to 10th	Day	4 2 1 4 4 2 4 4 6% 8% 62%	2507
	11th to 20th	Day	3 2 1 2 3 2 3 3 4 6% 71%	2254
	21st to end	Day	3 3 1 4 3 2 3 4 4 6% 67%	2376
September	1st to 10th	Day	2 2 1 3 3 2 3 3 4 7% 70%	2160
	11th to 20th	Day	6% 4 2 4 5% 2 4 5% 5% 7% 58%	2078
	21st to end	Day	5% 7% 3 6% 5% 3 4 3 4 5% 55%	1980
October	1st to 10th	Day	8% 7% 4 6% 5% 2 4 4 4 6% 49%	1894
	11th to 20th	Day	7% 8% 3 6% 5% 2 4 4 5% 8% 48%	1765
	21st to end	Day	10% 9% 3 7% 6% 4 5% 5% 6% 7% 39%	1782
November	1st to 10th	Day	12% 11% 3 8% 7% 3 5% 5% 6% 8% 31%	1674
	11th to 20th	Day	9% 11% 5% 9% 7% 4 6% 6% 6% 7% 30%	1695
	21st to end	Day	8% 9% 3 8% 7% 4 6% 7% 6% 7% 33%	1520
December	1st to 10th	Day	8% 14% 6% 9% 7% 4 6% 7% 5% 7% 27%	1520
	11th to 20th	Day	10% 19% 7% 10% 8% 4 6% 5% 5% 6% 19%	1928
	21st to end	Day	9% 12% 6% 12% 10% 6% 6% 6% 5% 6% 21%	2794
January	1st to 10th	Night	7% 13% 6% 12% 11% 6% 7% 6% 7% 6% 17%	4406
	11th to 20th	Night	12% 16% 7% 9% 7% 3 4 4 5% 7% 26%	4420
	21st to end	Night	13% 21% 5% 9% 6% 3 4 4 5% 6% 22%	4862
February	1st to 10th	Night	9% 12% 4 9% 8% 4 6% 6% 6% 7% 30%	2527
	11th to 20th	Night	6% 12% 5% 8% 7% 4 5% 6% 7% 7% 33%	2260
	21st to end	Night	6% 10% 5% 9% 8% 6% 6% 6% 7% 8% 29%	1884
March	1st to 10th	Night	8% 12% 5% 10% 7% 4 5% 6% 6% 7% 31%	2165
	11th to 20th	Night	8% 9% 3 7% 7% 5% 7% 7% 8% 9% 31%	2118
	21st to end	Night	6% 9% 5% 10% 8% 4 6% 7% 8% 9% 29%	1980
April	1st to 10th	Night	7% 9% 4 7% 7% 5% 6% 5% 7% 7% 35%	1800
	11th to 20th	Night	6% 8% 4 6% 7% 4 4 4 6% 7% 43%	1779
	21st to end	Night	6% 9% 3 6% 4 3 5% 6% 7% 9% 43%	1646
May	1st to 10th	Night	5% 6% 3 6% 6% 3 5% 4 5% 7% 51%	1548
	11th to 20th	Night	8% 5% 2 5% 6% 4 5% 6% 7% 9% 43%	1416
	21st to end	Night	6% 6% 3 6% 8% 5% 6% 6% 6% 9% 40%	1552
June	1st to 10th	Night	8% 9% 3 5% 5% 4 5% 5% 6% 10% 41%	1440
	11th to 20th	Night	6% 5% 3 4 4 3 3 4 6% 8% 54%	1440
	21st to end	Night	3 3 1 3 4 2 3 4 6% 6% 64%	1440
July	1st to 10th	Night	2 2 1 2 3 2 4 4 5% 6% 71%	1440
	11th to 20th	Night	1 1 2 2 1 2 2 4 5% 80%	1440
	21st to end	Night	1 2 1 1 2 1 3 3 5% 5% 76%	1576
August	1st to 10th	Night	3 2 1 3 2 1 3 5% 6% 8% 66%	1432
	11th to 20th	Night	1 1 1 2 3 2 3 3 4 5% 76%	1641
	21st to end	Night	2 2 1 2 3 2 3 3 4 6% 72%	1980
September	1st to 10th	Night	2 3 1 2 3 2 2 3 3 5% 75%	1800
	11th to 20th	Night	3 2 1 4 3 2 4 5% 6% 6% 63%	1880
	21st to end	Night	6% 5% 2 3 4 2 3 4 5% 6% 60%	1980
October	1st to 10th	Night	6% 5% 2 4 4 3 3 5% 5% 7% 56%	2064
	11th to 20th	Night	7% 6% 2 6% 4 4 4 4 5% 7% 51%	2193
	21st to end	Night	8% 7% 2 6% 7% 3 5% 5% 5% 7% 44%	2574
November	1st to 10th	Night	10% 9% 4 7% 7% 4 5% 6% 6% 7% 35%	2405
	11th to 20th	Night	9% 9% 4 7% 6% 4 7% 7% 6% 7% 33%	2484
	21st to end	Night	6% 9% 4 7% 6% 3 5% 6% 7% 9% 37%	2660
December	1st to 10th	Night	9% 12% 5% 8% 7% 4 5% 5% 7% 7% 30%	2660
	11th to 20th	Night	12% 16% 5% 8% 8% 4 6% 5% 6% 9% 23%	3276
	21st to end	Night	8% 14% 5% 11% 10% 5% 6% 5% 6% 8% 22%	4862

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% 16% 16% 8% 2	2539
	11th to 20th	Day	56% 12% 13% 14% 4 1	2540
	21st to end	Day	61% 16% 11% 8% 3 1	2794
February	1st to 10th	Day	52% 11% 16% 16% 5% 1	1648
	11th to 20th	Day	52% 13% 13% 15% 6% 1	1817
	21st to end	Day	50% 12% 13% 17% 7% 1	1570
March	1st to 10th	Day	56% 11% 15% 12% 5% 1	1801
	11th to 20th	Day	53% 9% 14% 18% 7%	1838
	21st to end	Day	59% 11% 13% 13% 3	2376
April	1st to 10th	Day	53% 11% 16% 14% 6% 2	2160
	11th to 20th	Day	46% 10% 13% 18% 11% 2	2132
	21st to end	Day	44% 9% 14% 19% 13% 1	2313
May	1st to 10th	Day	36% 9% 15% 28% 12% 1	2407
	11th to 20th	Day	43% 9% 16% 23% 9% 1	2480
	21st to end	Day	48% 10% 14% 20% 7%	2724
June	1st to 10th	Day	43% 9% 14% 24% 9%	2520
	11th to 20th	Day	36% 8% 15% 23% 14% 5%	2520
	21st to end	Day	22% 6% 10% 27% 27% 8%	2520
July	1st to 10th	Day	16% 6% 10% 21% 28% 20%	2451
	11th to 20th	Day	12% 4 9% 14% 30% 30%	2445
	21st to end	Day	12% 3 5% 13% 37% 30%	2589
August	1st to 10th	Day	18% 6% 9% 22% 29% 17%	2490
	11th to 20th	Day	14% 4 7% 22% 34% 18%	2254
	21st to end	Day	17% 5% 8% 23% 34% 14%	2376
September	1st to 10th	Day	14% 5% 8% 22% 30% 21%	2160
	11th to 20th	Day	24% 6% 11% 22% 25% 12%	2078
	21st to end	Day	29% 6% 10% 26% 21% 8%	1980
October	1st to 10th	Day	36% 6% 11% 22% 22% 4	1894
	11th to 20th	Day	32% 7% 13% 28% 18% 3	1765
	21st to end	Day	41% 9% 13% 21% 14% 1	1782
November	1st to 10th	Day	47% 9% 16% 19% 8% 1	1674
	11th to 20th	Day	49% 10% 17% 19% 4 1	1695
	21st to end	Day	45% 10% 16% 18% 9% 2	1520
December	1st to 10th	Day	51% 13% 15% 13% 7% 1	1520
	11th to 20th	Day	58% 15% 12% 13% 2	1928
	21st to end	Day	50% 19% 15% 12% 5%	2794
January	1st to 10th	Night	53% 19% 17% 8% 2	4406
	11th to 20th	Night	54% 12% 14% 14% 6% 1	4420
	21st to end	Night	56% 15% 14% 10% 4 1	4862
February	1st to 10th	Night	49% 13% 16% 16% 5% 1	2527
	11th to 20th	Night	46% 11% 17% 16% 9% 1	2261
	21st to end	Night	45% 15% 14% 18% 7% 2	1884
March	1st to 10th	Night	46% 10% 17% 18% 7% 2	2165
	11th to 20th	Night	41% 12% 20% 21% 6%	2118
	21st to end	Night	43% 15% 19% 18% 5%	1980
April	1st to 10th	Night	43% 12% 16% 21% 8% 1	1800
	11th to 20th	Night	38% 9% 15% 25% 11% 2	1779
	21st to end	Night	33% 12% 17% 22% 14% 1	1646
May	1st to 10th	Night	28% 9% 18% 31% 13% 1	1548
	11th to 20th	Night	33% 11% 18% 28% 9%	1416
	21st to end	Night	37% 11% 20% 25% 8%	1552
June	1st to 10th	Night	37% 10% 16% 29% 9%	1440
	11th to 20th	Night	28% 9% 15% 29% 15% 4	1440
	21st to end	Night	18% 6% 13% 32% 24% 7%	1440
July	1st to 10th	Night	14% 4 9% 26% 27% 20%	1400
	11th to 20th	Night	8% 3 10% 19% 32% 27%	1392
	21st to end	Night	10% 3 5% 17% 38% 26%	1488
August	1st to 10th	Night	14% 5% 11% 24% 30% 15%	1424
	11th to 20th	Night	11% 4 8% 22% 35% 20%	1641
	21st to end	Night	12% 4 11% 24% 33% 16%	1980
September	1st to 10th	Night	13% 4 8% 24% 33% 19%	1800
	11th to 20th	Night	18% 8% 11% 24% 26% 14%	1880
	21st to end	Night	23% 6% 10% 27% 24% 10%	1980
October	1st to 10th	Night	27% 8% 12% 25% 23% 5%	2064
	11th to 20th	Night	30% 7% 15% 23% 22% 3	2193
	21st to end	Night	36% 10% 16% 18% 19% 2	2574
November	1st to 10th	Night	42% 11% 14% 21% 11% 1	2405
	11th to 20th	Night	45% 12% 15% 21% 7%	2484
	21st to end	Night	38% 12% 17% 16% 14% 2	2660
December	1st to 10th	Night	47% 13% 16% 14% 8% 1	2660
	11th to 20th	Night	53% 14% 15% 14% 4	3276
	21st to end	Night	47% 19% 17% 10% 7%	4862

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% 13% 27% 19% 13% 3	180
	11th to 20th	Day	27% 16% 23% 19% 12% 4	180
	21st to end	Day	14% 14% 34% 26% 10% 2	198
February	1st to 10th	Day	19% 25% 33% 19% 4 1	308
	11th to 20th	Day	17% 22% 36% 18% 6% 1	434
	21st to end	Day	17% 22% 34% 22% 5%	382
March	1st to 10th	Day	18% 23% 37% 19% 3	421
	11th to 20th	Day	15% 24% 32% 23% 6%	420
	21st to end	Day	23% 24% 24% 23% 6%	462
April	1st to 10th	Day	23% 20% 28% 18% 9% 1	420
	11th to 20th	Day	19% 25% 31% 16% 7% 3	412
	21st to end	Day	16% 24% 33% 19% 7% 1	420
May	1st to 10th	Day	13% 21% 31% 23% 7% 3	423
	11th to 20th	Day	21% 19% 27% 18% 13% 2	448
	21st to end	Day	16% 17% 23% 29% 12% 4	485
June	1st to 10th	Day	13% 18% 27% 25% 12% 5%	450
	11th to 20th	Day	14% 19% 34% 22% 8% 2	450
	21st to end	Day	3 13% 35% 31% 14% 4	450
July	1st to 10th	Day	3 8% 37% 36% 14% 2	446
	11th to 20th	Day	2 9% 41% 30% 16% 3	444
	21st to end	Day	2 7% 34% 34% 17% 5%	487
August	1st to 10th	Day	5% 6% 31% 36% 17% 5%	447
	11th to 20th	Day	4 6% 24% 37% 22% 8%	437
	21st to end	Day	5% 10% 31% 30% 17% 6%	495
September	1st to 10th	Day	4 11% 26% 36% 18% 6%	450
	11th to 20th	Day	10% 10% 25% 33% 17% 5%	450
	21st to end	Day	7% 14% 31% 30% 15% 3	450
October	1st to 10th	Day	11% 17% 25% 27% 17% 2	450
	11th to 20th	Day	12% 15% 30% 24% 15% 3	415
	21st to end	Day	15% 18% 23% 28% 13% 3	297
November	1st to 10th	Day	14% 17% 32% 24% 11%	270
	11th to 20th	Day	14% 15% 27% 30% 11% 3	263
	21st to end	Day	15% 12% 31% 31% 12% 1	180
December	1st to 10th	Day	16% 16% 29% 18% 13% 7%	180
	11th to 20th	Day	18% 18% 40% 18% 5% 2	180
	21st to end	Day	10% 20% 36% 22% 9% 3	198
January	1st to 10th	Night	13% 13% 28% 28% 15% 3	760
	11th to 20th	Night	16% 12% 26% 26% 18% 3	760
	21st to end	Night	13% 8% 25% 33% 18% 3	836
February	1st to 10th	Night	14% 15% 29% 30% 11% 3	760
	11th to 20th	Night	11% 11% 31% 29% 16% 2	744
	21st to end	Night	11% 15% 32% 27% 14% 2	628
March	1st to 10th	Night	12% 13% 29% 30% 14% 2	722
	11th to 20th	Night	10% 12% 29% 29% 17% 2	720
	21st to end	Night	11% 16% 28% 34% 11% 1	792
April	1st to 10th	Night	10% 12% 28% 33% 14% 2	720
	11th to 20th	Night	9% 13% 31% 28% 15% 4	711
	21st to end	Night	10% 15% 27% 34% 13% 1	566
May	1st to 10th	Night	8% 14% 30% 32% 16% 1	468
	11th to 20th	Night	13% 7% 19% 32% 26% 3	354
	21st to end	Night	9% 6% 24% 33% 23% 4	389
June	1st to 10th	Night	9% 8% 25% 35% 21% 2	360
	11th to 20th	Night	8% 11% 24% 39% 18% 1	360
	21st to end	Night	5% 2 17% 50% 25% 1	360
July	1st to 10th	Night	2 3 18% 47% 27% 2	350
	11th to 20th	Night	2 2 21% 55% 21%	348
	21st to end	Night	1 2 16% 52% 27% 2	394
August	1st to 10th	Night	3 3 13% 47% 31% 3	358
	11th to 20th	Night	2 1 17% 40% 32% 8%	573
	21st to end	Night	2 3 20% 41% 30% 4	792
September	1st to 10th	Night	3 3 19% 40% 30% 5%	720
	11th to 20th	Night	3 4 16% 36% 33% 8%	720
	21st to end	Night	7% 6% 19% 33% 28% 6%	720
October	1st to 10th	Night	8% 5% 23% 34% 25% 5%	720
	11th to 20th	Night	11% 8% 18% 35% 19% 8%	720
	21st to end	Night	10% 10% 22% 34% 19% 5%	792
November	1st to 10th	Night	10% 12% 23% 36% 18% 1	740
	11th to 20th	Night	13% 12% 25% 34% 15% 3	760
	21st to end	Night	11% 12% 24% 31% 16% 6%	760
December	1st to 10th	Night	14% 10% 26% 29% 17% 3	760
	11th to 20th	Night	18% 8% 28% 31% 12% 2	760
	21st to end	Night	16% 14% 30% 29% 10% 1	836

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