South Hill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Hill clear sky chart from 2005-11-06 to 2026-07-31.

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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	137549
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 45%	135448
Transparency	Day	38% 5% 12% 22% 18% 5%	141153
	Night	39% 5% 10% 21% 20% 6%	139915
Seeing	Day	19% 11% 27% 24% 15% 5%	17482
	Night	17% 10% 27% 30% 14% 2	27338

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	14% 6% 2 5% 3 3 3 3 4 5% 52%	5258
	11th to 20th	Day	12% 6% 2 4 3 3 3 2 3 5% 58%	5280
	21st to end	Day	16% 7% 2 7% 4 3 3 2 3 5% 47%	5780
February	1st to 10th	Day	13% 7% 2 7% 4 4 4 5% 6% 7% 42%	1890
	11th to 20th	Day	22% 6% 2 5% 3 3 3 3 4 5% 44%	1889
	21st to end	Day	20% 7% 2 5% 5% 4 4 4 5% 6% 40%	1803
March	1st to 10th	Day	18% 8% 3 6% 5% 4 4 4 5% 6% 39%	5045
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 5% 6% 52%	5090
	21st to end	Day	15% 6% 2 5% 4 4 4 4 5% 6% 44%	5586
April	1st to 10th	Day	12% 4 2 4 3 3 4 4 5% 7% 52%	2492
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 5% 6% 51%	2494
	21st to end	Day	14% 5% 2 7% 4 4 4 4 5% 7% 44%	2520
May	1st to 10th	Day	12% 6% 2 7% 5% 4 5% 4 7% 10% 37%	7438
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 6% 8% 40%	7626
	21st to end	Day	17% 6% 2 6% 4 4 5% 4 6% 9% 38%	8606
June	1st to 10th	Day	9% 4 2 5% 4 4 5% 4 8% 10% 43%	2940
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	2940
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 8% 12% 41%	2913
July	1st to 10th	Day	7% 5% 3 6% 5% 5% 6% 6% 8% 11% 38%	6030
	11th to 20th	Day	9% 5% 3 8% 6% 5% 7% 6% 9% 13% 30%	6030
	21st to end	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 11% 37%	6554
August	1st to 10th	Day	17% 9% 3 7% 5% 6% 6% 5% 6% 10% 26%	4234
	11th to 20th	Day	9% 6% 3 8% 6% 6% 6% 5% 8% 10% 35%	3992
	21st to end	Day	7% 4 2 6% 4 4 5% 4 6% 11% 49%	4312
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 4 4 6% 7% 45%	2400
	11th to 20th	Day	14% 6% 3 6% 5% 5% 4 4 5% 8% 41%	2347
	21st to end	Day	20% 7% 3 6% 4 4 4 3 5% 7% 36%	2113
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 3 6% 48%	2000
	11th to 20th	Day	14% 6% 2 4 3 3 3 2 4 5% 55%	2000
	21st to end	Day	12% 5% 2 5% 3 4 3 3 4 5% 56%	2200
November	1st to 10th	Day	12% 4 2 5% 4 3 3 3 4 5% 55%	2057
	11th to 20th	Day	14% 5% 2 5% 3 2 3 3 5% 6% 51%	1985
	21st to end	Day	14% 5% 1 5% 4 2 3 3 5% 5% 52%	1690
December	1st to 10th	Day	12% 6% 2 6% 3 3 4 3 5% 6% 51%	2680
	11th to 20th	Day	18% 6% 2 6% 4 3 3 3 4 5% 46%	3070
	21st to end	Day	14% 6% 2 6% 4 4 4 4 5% 7% 45%	4265
January	1st to 10th	Night	12% 6% 2 6% 3 3 4 3 4 6% 51%	7635
	11th to 20th	Night	13% 6% 2 4 3 2 3 2 3 4 57%	7680
	21st to end	Night	17% 7% 2 5% 3 3 3 3 4 5% 48%	8401
February	1st to 10th	Night	16% 6% 2 5% 4 3 4 3 4 7% 45%	2730
	11th to 20th	Night	20% 7% 2 5% 3 4 4 3 4 5% 41%	2616
	21st to end	Night	15% 7% 2 5% 4 3 3 4 5% 6% 46%	1997
March	1st to 10th	Night	17% 6% 2 5% 4 4 4 3 5% 5% 44%	5028
	11th to 20th	Night	12% 4 1 4 3 3 4 3 5% 7% 52%	5090
	21st to end	Night	13% 5% 2 5% 4 3 4 3 5% 7% 49%	5588
April	1st to 10th	Night	13% 6% 3 5% 4 3 4 4 6% 7% 46%	2126
	11th to 20th	Night	10% 6% 2 5% 3 3 4 4 6% 8% 50%	2075
	21st to end	Night	13% 5% 2 5% 4 5% 4 4 5% 7% 47%	2100
May	1st to 10th	Night	12% 7% 3 7% 5% 4 5% 4 7% 9% 37%	5457
	11th to 20th	Night	17% 7% 3 6% 4 4 4 3 5% 7% 41%	5234
	21st to end	Night	21% 7% 3 7% 4 4 4 3 5% 8% 34%	5528
June	1st to 10th	Night	9% 6% 2 6% 5% 3 5% 5% 7% 9% 44%	1680
	11th to 20th	Night	9% 6% 2 7% 5% 4 5% 4 7% 10% 40%	1680
	21st to end	Night	7% 5% 2 6% 6% 5% 5% 4 7% 10% 42%	1698
July	1st to 10th	Night	10% 6% 3 7% 5% 5% 5% 5% 8% 10% 35%	4148
	11th to 20th	Night	12% 8% 3 9% 5% 6% 6% 5% 7% 9% 28%	4147
	21st to end	Night	11% 7% 3 8% 6% 6% 6% 5% 7% 10% 31%	4517
August	1st to 10th	Night	19% 8% 2 7% 5% 5% 5% 4 7% 10% 26%	2915
	11th to 20th	Night	7% 5% 3 7% 5% 6% 5% 5% 8% 10% 39%	3023
	21st to end	Night	8% 5% 2 6% 5% 4 5% 4 7% 9% 45%	3586
September	1st to 10th	Night	11% 7% 2 6% 3 4 4 3 5% 8% 48%	2000
	11th to 20th	Night	13% 6% 2 7% 5% 4 3 4 5% 8% 43%	2049
	21st to end	Night	20% 9% 3 7% 4 4 5% 3 5% 6% 35%	2285
October	1st to 10th	Night	14% 7% 2 6% 4 3 3 3 5% 5% 48%	2400
	11th to 20th	Night	13% 7% 2 4 3 3 3 3 4 5% 53%	2400
	21st to end	Night	13% 5% 2 5% 3 3 4 3 4 6% 53%	2640
November	1st to 10th	Night	13% 6% 2 5% 4 2 3 3 5% 6% 51%	2461
	11th to 20th	Night	13% 6% 2 4 3 3 4 3 5% 6% 50%	2630
	21st to end	Night	12% 5% 2 5% 4 3 4 3 4 6% 52%	2924
December	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 4 5% 53%	4720
	11th to 20th	Night	18% 7% 2 7% 5% 4 4 3 5% 4 41%	5345
	21st to end	Night	14% 7% 2 5% 3 4 4 3 5% 7% 46%	6915

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	35% 3 9% 22% 25% 7%	5259
	11th to 20th	Day	31% 2 4 16% 32% 14%	5280
	21st to end	Day	43% 2 5% 26% 18% 6%	5780
February	1st to 10th	Day	40% 4 11% 22% 18% 4	1890
	11th to 20th	Day	44% 3 6% 21% 21% 5%	1898
	21st to end	Day	45% 3 11% 17% 18% 5%	1803
March	1st to 10th	Day	46% 4 7% 18% 16% 10%	5045
	11th to 20th	Day	32% 4 8% 21% 23% 12%	5090
	21st to end	Day	41% 4 11% 20% 19% 6%	5586
April	1st to 10th	Day	31% 5% 11% 24% 22% 7%	2492
	11th to 20th	Day	33% 4 12% 24% 20% 6%	2494
	21st to end	Day	40% 4 12% 24% 16% 4	2520
May	1st to 10th	Day	41% 6% 15% 23% 14% 1	7471
	11th to 20th	Day	43% 5% 12% 24% 15% 1	7630
	21st to end	Day	43% 6% 13% 21% 15% 3	8621
June	1st to 10th	Day	34% 8% 14% 26% 17% 2	2940
	11th to 20th	Day	33% 7% 18% 25% 16% 2	2940
	21st to end	Day	33% 9% 18% 25% 15% 1	2913
July	1st to 10th	Day	36% 10% 19% 20% 12% 3	5965
	11th to 20th	Day	42% 12% 25% 16% 4 1	5961
	21st to end	Day	38% 9% 15% 25% 13%	6370
August	1st to 10th	Day	52% 6% 17% 19% 5%	4221
	11th to 20th	Day	42% 7% 18% 22% 10% 1	4031
	21st to end	Day	30% 5% 16% 31% 17% 1	4312
September	1st to 10th	Day	37% 7% 14% 17% 20% 5%	2400
	11th to 20th	Day	41% 5% 9% 23% 19% 3	2347
	21st to end	Day	47% 6% 10% 20% 15% 3	2113
October	1st to 10th	Day	36% 4 6% 21% 27% 6%	3260
	11th to 20th	Day	22% 2 5% 22% 30% 18%	3240
	21st to end	Day	23% 3 7% 27% 28% 12%	3538
November	1st to 10th	Day	31% 3 8% 26% 26% 6%	2057
	11th to 20th	Day	35% 2 10% 23% 23% 7%	1985
	21st to end	Day	34% 3 8% 24% 26% 5%	1690
December	1st to 10th	Day	35% 3 7% 27% 22% 6%	2680
	11th to 20th	Day	41% 3 11% 20% 19% 6%	3066
	21st to end	Day	38% 4 11% 26% 19% 1	4265
January	1st to 10th	Night	35% 3 10% 20% 22% 10%	7636
	11th to 20th	Night	34% 3 4 17% 34% 9%	7680
	21st to end	Night	40% 2 5% 24% 22% 7%	8401
February	1st to 10th	Night	40% 3 10% 22% 20% 5%	2730
	11th to 20th	Night	45% 4 7% 18% 20% 6%	2618
	21st to end	Night	39% 3 8% 22% 19% 8%	1997
March	1st to 10th	Night	43% 4 7% 16% 22% 10%	5028
	11th to 20th	Night	32% 4 7% 16% 26% 14%	5090
	21st to end	Night	36% 3 10% 24% 22% 6%	5588
April	1st to 10th	Night	37% 5% 11% 19% 23% 6%	2126
	11th to 20th	Night	32% 6% 11% 24% 22% 6%	2075
	21st to end	Night	37% 5% 10% 26% 18% 4	2100
May	1st to 10th	Night	43% 6% 15% 23% 12% 2	5486
	11th to 20th	Night	43% 5% 11% 23% 16% 1	5235
	21st to end	Night	49% 5% 11% 20% 13% 2	5536
June	1st to 10th	Night	36% 7% 15% 24% 17% 2	1680
	11th to 20th	Night	38% 8% 17% 21% 15% 2	1680
	21st to end	Night	36% 8% 13% 23% 17% 3	1698
July	1st to 10th	Night	41% 10% 17% 19% 10% 2	4105
	11th to 20th	Night	50% 12% 19% 14% 4 1	4096
	21st to end	Night	46% 7% 15% 20% 12%	4387
August	1st to 10th	Night	51% 7% 18% 17% 6%	2904
	11th to 20th	Night	38% 8% 19% 24% 11% 1	3050
	21st to end	Night	34% 6% 13% 27% 19% 2	3586
September	1st to 10th	Night	35% 7% 14% 21% 19% 4	2000
	11th to 20th	Night	41% 6% 10% 20% 21% 3	2049
	21st to end	Night	50% 6% 10% 15% 15% 4	2285
October	1st to 10th	Night	41% 4 9% 19% 24% 4	3920
	11th to 20th	Night	26% 2 5% 21% 30% 15%	3899
	21st to end	Night	25% 3 5% 29% 23% 15%	4252
November	1st to 10th	Night	34% 4 8% 21% 27% 5%	2461
	11th to 20th	Night	35% 3 9% 19% 24% 10%	2630
	21st to end	Night	34% 3 7% 22% 27% 6%	2924
December	1st to 10th	Night	35% 3 7% 24% 26% 6%	4720
	11th to 20th	Night	47% 4 8% 18% 17% 7%	5348
	21st to end	Night	38% 4 11% 27% 19% 2	6915

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	30% 23% 32% 11% 4	330
	11th to 20th	Day	29% 29% 32% 8% 2	330
	21st to end	Day	25% 24% 38% 12% 1	363
February	1st to 10th	Day	24% 24% 38% 12% 2	330
	11th to 20th	Day	41% 22% 28% 7% 2	376
	21st to end	Day	29% 19% 34% 16% 3	446
March	1st to 10th	Day	26% 20% 31% 18% 5%	540
	11th to 20th	Day	23% 22% 35% 15% 5% 1	540
	21st to end	Day	22% 18% 39% 16% 5% 1	594
April	1st to 10th	Day	21% 18% 35% 19% 6% 1	540
	11th to 20th	Day	19% 14% 36% 20% 9% 3	532
	21st to end	Day	19% 13% 33% 24% 10% 1	540
May	1st to 10th	Day	16% 15% 39% 20% 8% 2	543
	11th to 20th	Day	20% 8% 27% 29% 14% 2	567
	21st to end	Day	23% 7% 22% 24% 19% 5%	617
June	1st to 10th	Day	10% 5% 30% 28% 20% 6%	570
	11th to 20th	Day	10% 6% 24% 34% 21% 6%	570
	21st to end	Day	10% 4 20% 36% 24% 6%	570
July	1st to 10th	Day	10% 3 13% 34% 30% 11%	565
	11th to 20th	Day	6% 2 15% 37% 31% 9%	564
	21st to end	Day	12% 2 18% 34% 25% 10%	616
August	1st to 10th	Day	16% 5% 16% 31% 24% 9%	526
	11th to 20th	Day	12% 3 13% 33% 29% 10%	519
	21st to end	Day	8% 3 16% 31% 27% 15%	583
September	1st to 10th	Day	13% 5% 17% 28% 23% 15%	530
	11th to 20th	Day	18% 4 15% 30% 22% 12%	530
	21st to end	Day	26% 7% 21% 28% 14% 4	530
October	1st to 10th	Day	19% 5% 22% 25% 21% 7%	530
	11th to 20th	Day	17% 11% 27% 27% 16% 3	530
	21st to end	Day	16% 13% 26% 26% 15% 3	583
November	1st to 10th	Day	16% 11% 34% 24% 13% 3	535
	11th to 20th	Day	21% 16% 30% 22% 10% 1	479
	21st to end	Day	25% 17% 24% 23% 8% 3	230
December	1st to 10th	Day	24% 20% 40% 9% 6% 1	220
	11th to 20th	Day	25% 15% 37% 20% 3 1	220
	21st to end	Day	26% 18% 32% 18% 4 2	294
January	1st to 10th	Night	19% 19% 35% 23% 3	840
	11th to 20th	Night	22% 17% 32% 25% 3	840
	21st to end	Night	20% 16% 39% 23% 2	924
February	1st to 10th	Night	21% 16% 36% 24% 4	840
	11th to 20th	Night	28% 19% 36% 16% 1	823
	21st to end	Night	21% 16% 37% 23% 2	692
March	1st to 10th	Night	20% 16% 34% 25% 4	840
	11th to 20th	Night	20% 16% 35% 23% 5%	840
	21st to end	Night	19% 14% 40% 22% 5%	924
April	1st to 10th	Night	19% 13% 38% 24% 5%	840
	11th to 20th	Night	15% 12% 37% 27% 9%	831
	21st to end	Night	15% 7% 37% 33% 8%	840
May	1st to 10th	Night	16% 11% 32% 31% 9%	709
	11th to 20th	Night	19% 6% 25% 38% 12%	621
	21st to end	Night	17% 2 20% 37% 22% 2	604
June	1st to 10th	Night	12% 3 20% 44% 21%	420
	11th to 20th	Night	11% 3 18% 42% 23% 3	420
	21st to end	Night	7% 3 16% 46% 24% 3	438
July	1st to 10th	Night	11% 2 11% 40% 33% 4	615
	11th to 20th	Night	8% 2 10% 38% 38% 4	612
	21st to end	Night	9% 3 15% 37% 32% 3	687
August	1st to 10th	Night	15% 2 10% 42% 27% 4	597
	11th to 20th	Night	12% 3 10% 38% 33% 4	677
	21st to end	Night	12% 2 10% 35% 34% 6%	880
September	1st to 10th	Night	13% 3 11% 37% 31% 5%	800
	11th to 20th	Night	16% 5% 14% 31% 30% 5%	800
	21st to end	Night	24% 4 20% 33% 18% 1	800
October	1st to 10th	Night	16% 6% 19% 30% 25% 5%	800
	11th to 20th	Night	17% 9% 26% 29% 18% 2	800
	21st to end	Night	15% 10% 26% 30% 16% 2	880
November	1st to 10th	Night	16% 9% 28% 30% 15% 2	820
	11th to 20th	Night	17% 12% 30% 32% 9% 1	840
	21st to end	Night	15% 13% 29% 31% 11% 1	840
December	1st to 10th	Night	23% 13% 32% 24% 8%	840
	11th to 20th	Night	19% 11% 33% 31% 5%	840
	21st to end	Night	22% 15% 28% 30% 5%	924

Page generated at 2026-07-28 03:25:21. Version ac07

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