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 2024-10-25.

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%	101371
	Night	6% 9% 3 7% 5% 4 4 4 6% 7% 44%	97592
Transparency	Day	34% 9% 12% 19% 16% 10%	101116
	Night	35% 11% 14% 20% 15% 7%	97436
Seeing	Day	12% 16% 31% 26% 12% 3	14429
	Night	10% 9% 25% 34% 19% 3	23573

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% 20% 9% 7% 5% 4 5% 5% 16%	2539
	11th to 20th	Day	11% 17% 7% 13% 5% 4 4 3 5% 6% 24%	2540
	21st to end	Day	13% 19% 6% 14% 7% 4 5% 4 5% 5% 18%	2794
February	1st to 10th	Day	8% 16% 5% 10% 7% 6% 5% 4 6% 6% 29%	1648
	11th to 20th	Day	7% 16% 6% 12% 6% 6% 5% 4 6% 6% 26%	1807
	21st to end	Day	4 15% 6% 13% 7% 6% 4 5% 7% 8% 25%	1570
March	1st to 10th	Day	7% 14% 5% 14% 7% 7% 6% 4 5% 6% 26%	3138
	11th to 20th	Day	5% 11% 3 8% 5% 4 5% 3 4 5% 48%	3270
	21st to end	Day	7% 16% 6% 12% 8% 8% 7% 5% 6% 5% 21%	4165
April	1st to 10th	Day	8% 14% 5% 11% 7% 6% 6% 4 7% 6% 26%	2280
	11th to 20th	Day	6% 13% 4 10% 6% 6% 5% 4 6% 7% 34%	2249
	21st to end	Day	7% 12% 4 9% 6% 4 5% 4 6% 7% 36%	2442
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	7% 8% 4 7% 4 3 4 3 4 6% 51%	1999
	11th to 20th	Day	7% 8% 3 7% 4 3 4 3 5% 8% 47%	1863
	21st to end	Day	10% 9% 3 8% 5% 5% 5% 4 6% 7% 38%	1822
November	1st to 10th	Day	12% 12% 3 9% 6% 4 5% 4 6% 8% 30%	1674
	11th to 20th	Day	9% 12% 4 10% 6% 6% 5% 4 6% 7% 29%	1695
	21st to end	Day	8% 10% 3 10% 6% 6% 5% 6% 7% 7% 33%	1520
December	1st to 10th	Day	8% 16% 5% 9% 7% 5% 6% 5% 6% 6% 27%	1520
	11th to 20th	Day	10% 19% 7% 11% 7% 6% 5% 5% 5% 6% 19%	1928
	21st to end	Day	9% 13% 5% 14% 8% 8% 6% 5% 6% 6% 21%	2794
January	1st to 10th	Night	7% 14% 6% 14% 9% 8% 7% 4 7% 6% 17%	4406
	11th to 20th	Night	12% 17% 7% 10% 6% 4 4 3 5% 7% 26%	4420
	21st to end	Night	13% 21% 5% 10% 5% 4 4 4 5% 6% 22%	4862
February	1st to 10th	Night	8% 13% 4 10% 7% 5% 5% 4 7% 7% 30%	2527
	11th to 20th	Night	6% 12% 4 9% 7% 5% 6% 5% 7% 7% 32%	2260
	21st to end	Night	5% 11% 5% 10% 7% 8% 5% 4 7% 8% 29%	1884
March	1st to 10th	Night	5% 13% 5% 11% 6% 5% 5% 4 6% 7% 33%	3736
	11th to 20th	Night	5% 9% 2 7% 4 4 4 4 6% 6% 48%	3706
	21st to end	Night	5% 9% 4 12% 7% 7% 7% 6% 9% 8% 24%	3488
April	1st to 10th	Night	7% 10% 3 9% 7% 6% 6% 4 6% 7% 36%	1900
	11th to 20th	Night	6% 9% 3 7% 6% 5% 4 4 6% 7% 44%	1879
	21st to end	Night	6% 9% 3 6% 4 4 4 5% 7% 9% 43%	1737
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	6% 5% 2 4 3 4 3 4 5% 7% 57%	2179
	11th to 20th	Night	7% 6% 2 7% 3 4 4 3 6% 7% 51%	2315
	21st to end	Night	8% 7% 3 8% 5% 5% 5% 4 6% 6% 44%	2639
November	1st to 10th	Night	10% 9% 4 8% 6% 5% 6% 4 7% 7% 35%	2405
	11th to 20th	Night	9% 10% 4 9% 5% 5% 7% 5% 6% 7% 33%	2484
	21st to end	Night	6% 10% 3 7% 6% 4 5% 5% 7% 9% 37%	2660
December	1st to 10th	Night	9% 12% 5% 9% 6% 6% 4 5% 7% 7% 30%	2660
	11th to 20th	Night	11% 16% 5% 9% 7% 5% 5% 4 6% 9% 23%	3276
	21st to end	Night	8% 15% 5% 13% 8% 6% 6% 4 6% 7% 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	45% 13% 15% 17% 9% 1	3138
	11th to 20th	Day	33% 9% 13% 34% 11%	3270
	21st to end	Day	51% 18% 15% 13% 4	4165
April	1st to 10th	Day	52% 11% 16% 14% 5% 1	2280
	11th to 20th	Day	44% 11% 13% 18% 12% 2	2252
	21st to end	Day	43% 10% 15% 19% 13% 1	2442
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	34% 6% 10% 21% 24% 5%	1999
	11th to 20th	Day	32% 7% 13% 27% 17% 3	1863
	21st to end	Day	41% 9% 13% 22% 14% 1	1822
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% 17% 7% 2	1884
March	1st to 10th	Night	38% 12% 16% 23% 10% 1	3736
	11th to 20th	Night	30% 9% 15% 36% 10%	3706
	21st to end	Night	40% 21% 19% 13% 6%	3488
April	1st to 10th	Night	42% 12% 17% 21% 7% 1	1900
	11th to 20th	Night	37% 9% 16% 25% 11% 2	1879
	21st to end	Night	32% 12% 18% 23% 14% 1	1737
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	26% 8% 11% 24% 24% 6%	2179
	11th to 20th	Night	30% 7% 15% 23% 23% 3	2315
	21st to end	Night	36% 10% 16% 18% 19% 2	2639
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% 35% 22% 5%	382
March	1st to 10th	Day	18% 23% 36% 20% 3	460
	11th to 20th	Day	15% 23% 30% 22% 8% 2	460
	21st to end	Day	22% 25% 25% 23% 6%	506
April	1st to 10th	Day	22% 21% 28% 18% 9% 2	460
	11th to 20th	Day	17% 25% 31% 17% 7% 3	452
	21st to end	Day	15% 23% 35% 20% 7% 1	460
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% 18% 23% 28% 13% 3	311
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% 14% 32% 27% 14% 2	628
March	1st to 10th	Night	11% 13% 29% 30% 14% 2	760
	11th to 20th	Night	10% 12% 29% 29% 18% 2	760
	21st to end	Night	10% 16% 28% 34% 11% 1	836
April	1st to 10th	Night	11% 12% 29% 33% 13% 2	760
	11th to 20th	Night	9% 13% 32% 28% 14% 4	751
	21st to end	Night	10% 15% 28% 34% 12% 1	597
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% 22% 34% 19% 5%	812
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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