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 2025-03-12.

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%	108641
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	110344
Transparency	Day	38% 5% 12% 22% 18% 5%	112289
	Night	38% 5% 10% 21% 20% 6%	114835
Seeing	Day	19% 11% 26% 25% 15% 5%	15590
	Night	17% 10% 26% 30% 15% 2	25574

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	15% 5% 2 4 3 2 3 2 3 5% 55%	4056
	11th to 20th	Day	12% 7% 2 4 3 3 3 2 4 5% 56%	4060
	21st to end	Day	16% 6% 2 6% 4 3 4 3 4 5% 47%	4466
February	1st to 10th	Day	13% 7% 2 7% 4 5% 4 5% 6% 8% 41%	1800
	11th to 20th	Day	23% 6% 2 5% 3 3 3 3 4 5% 44%	1797
	21st to end	Day	18% 6% 2 5% 5% 4 4 4 5% 6% 41%	1720
March	1st to 10th	Day	21% 8% 3 6% 4 4 4 4 5% 6% 36%	3545
	11th to 20th	Day	11% 4 2 5% 3 3 4 3 5% 6% 54%	3491
	21st to end	Day	20% 6% 2 5% 4 3 4 4 5% 6% 40%	3815
April	1st to 10th	Day	12% 4 2 4 3 3 4 4 5% 7% 53%	2254
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 5% 6% 50%	2254
	21st to end	Day	15% 5% 2 6% 4 4 4 4 5% 7% 44%	2280
May	1st to 10th	Day	12% 7% 3 8% 6% 5% 6% 4 7% 10% 32%	3988
	11th to 20th	Day	19% 6% 2 7% 4 4 4 4 7% 9% 33%	4081
	21st to end	Day	9% 5% 2 4 4 4 4 4 7% 10% 48%	4593
June	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 8% 10% 42%	2660
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	2660
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 12% 40%	2636
July	1st to 10th	Day	6% 5% 2 6% 5% 6% 6% 6% 8% 12% 38%	4120
	11th to 20th	Day	11% 5% 3 7% 5% 5% 5% 5% 8% 11% 35%	4120
	21st to end	Day	11% 8% 3 8% 6% 6% 6% 5% 8% 9% 30%	4466
August	1st to 10th	Day	17% 9% 3 8% 5% 6% 6% 5% 7% 11% 26%	4104
	11th to 20th	Day	9% 6% 3 8% 6% 6% 6% 5% 7% 10% 35%	3867
	21st to end	Day	7% 4 2 6% 4 4 5% 4 6% 11% 49%	4180
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 4 4 6% 7% 44%	2280
	11th to 20th	Day	14% 6% 3 6% 5% 5% 5% 4 5% 8% 41%	2230
	21st to end	Day	20% 7% 3 6% 4 4 4 3 5% 6% 38%	2008
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 3 6% 48%	1900
	11th to 20th	Day	13% 5% 2 4 3 3 3 2 4 5% 55%	1900
	21st to end	Day	11% 5% 2 5% 4 4 3 3 4 5% 56%	2090
November	1st to 10th	Day	12% 5% 2 5% 4 3 3 3 4 5% 54%	1957
	11th to 20th	Day	15% 6% 2 5% 3 2 3 3 5% 5% 50%	1891
	21st to end	Day	14% 5% 1 5% 4 2 3 4 6% 5% 52%	1610
December	1st to 10th	Day	12% 6% 2 6% 3 3 4 3 5% 5% 52%	2600
	11th to 20th	Day	18% 6% 2 6% 4 3 4 3 4 5% 46%	2990
	21st to end	Day	14% 6% 2 6% 4 4 4 4 5% 7% 45%	4172
January	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 5% 53%	5889
	11th to 20th	Night	14% 7% 2 4 3 2 3 3 3 4 56%	5900
	21st to end	Night	17% 6% 2 5% 3 3 3 2 4 5% 50%	6490
February	1st to 10th	Night	17% 6% 2 5% 4 3 4 3 5% 7% 45%	2600
	11th to 20th	Night	20% 7% 2 5% 4 4 4 3 4 5% 41%	2488
	21st to end	Night	15% 7% 2 5% 3 3 2 3 5% 6% 48%	1905
March	1st to 10th	Night	22% 7% 2 6% 5% 5% 5% 3 5% 5% 36%	3528
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 52%	3498
	21st to end	Night	17% 5% 2 5% 3 3 3 3 3 5% 51%	3817
April	1st to 10th	Night	13% 6% 3 5% 4 3 3 3 6% 7% 46%	1924
	11th to 20th	Night	11% 6% 1 5% 3 3 4 4 5% 7% 49%	1875
	21st to end	Night	14% 6% 2 5% 4 4 4 4 5% 7% 47%	1900
May	1st to 10th	Night	15% 8% 3 7% 4 4 4 3 6% 7% 38%	2921
	11th to 20th	Night	23% 6% 3 7% 4 4 4 4 4 7% 35%	2812
	21st to end	Night	10% 4 2 6% 4 4 4 3 6% 10% 46%	2957
June	1st to 10th	Night	9% 6% 2 6% 6% 3 5% 5% 7% 9% 43%	1520
	11th to 20th	Night	10% 6% 2 7% 4 4 5% 5% 7% 10% 41%	1520
	21st to end	Night	7% 5% 2 6% 6% 5% 5% 4 7% 10% 42%	1536
July	1st to 10th	Night	7% 5% 2 7% 6% 6% 5% 5% 9% 11% 38%	2840
	11th to 20th	Night	12% 7% 3 7% 4 6% 6% 5% 7% 8% 35%	2840
	21st to end	Night	14% 9% 4 9% 7% 6% 6% 4 6% 8% 28%	3087
August	1st to 10th	Night	19% 8% 2 7% 5% 5% 5% 4 8% 10% 26%	2825
	11th to 20th	Night	7% 5% 3 7% 5% 6% 5% 5% 8% 10% 40%	2929
	21st to end	Night	8% 4 2 6% 5% 4 5% 5% 7% 9% 45%	3476
September	1st to 10th	Night	11% 6% 2 6% 3 4 4 3 6% 8% 47%	1900
	11th to 20th	Night	13% 6% 2 7% 5% 4 3 4 5% 8% 43%	1946
	21st to end	Night	20% 9% 3 7% 4 4 4 3 5% 5% 36%	2171
October	1st to 10th	Night	14% 7% 2 6% 4 3 3 3 5% 5% 48%	2280
	11th to 20th	Night	13% 7% 2 4 3 3 3 3 5% 5% 53%	2280
	21st to end	Night	12% 5% 2 5% 3 3 4 3 5% 6% 53%	2508
November	1st to 10th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 51%	2341
	11th to 20th	Night	13% 6% 2 4 3 3 4 3 5% 6% 50%	2505
	21st to end	Night	13% 5% 2 4 4 3 3 4 4 6% 52%	2785
December	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 4 5% 53%	4580
	11th to 20th	Night	18% 7% 2 7% 5% 4 4 3 5% 4 40%	5205
	21st to end	Night	14% 7% 2 5% 3 4 4 3 5% 7% 46%	6766

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	34% 2 4 21% 29% 9%	4057
	11th to 20th	Day	33% 2 5% 19% 31% 10%	4060
	21st to end	Day	41% 3 6% 26% 18% 5%	4466
February	1st to 10th	Day	40% 5% 11% 23% 17% 4	1800
	11th to 20th	Day	44% 3 6% 21% 21% 6%	1806
	21st to end	Day	44% 3 12% 16% 19% 6%	1720
March	1st to 10th	Day	48% 5% 7% 18% 13% 7%	3545
	11th to 20th	Day	30% 4 9% 22% 23% 12%	3491
	21st to end	Day	44% 5% 11% 19% 17% 4	3815
April	1st to 10th	Day	31% 5% 11% 24% 22% 8%	2254
	11th to 20th	Day	34% 4 12% 23% 21% 6%	2254
	21st to end	Day	40% 4 12% 23% 16% 5%	2280
May	1st to 10th	Day	45% 7% 16% 21% 11% 2	4024
	11th to 20th	Day	46% 6% 12% 25% 10% 1	4085
	21st to end	Day	30% 6% 17% 25% 20% 2	4607
June	1st to 10th	Day	35% 8% 14% 25% 16% 1	2660
	11th to 20th	Day	33% 7% 17% 24% 16% 2	2660
	21st to end	Day	34% 9% 18% 23% 15% 1	2636
July	1st to 10th	Day	35% 11% 19% 20% 11% 4	4055
	11th to 20th	Day	40% 9% 24% 20% 6% 1	4051
	21st to end	Day	46% 9% 14% 18% 12%	4324
August	1st to 10th	Day	52% 6% 18% 19% 5%	4091
	11th to 20th	Day	41% 7% 18% 22% 10% 1	3906
	21st to end	Day	30% 5% 16% 31% 16% 1	4180
September	1st to 10th	Day	38% 7% 14% 16% 20% 5%	2280
	11th to 20th	Day	41% 6% 9% 23% 19% 3	2230
	21st to end	Day	46% 5% 9% 20% 16% 4	2008
October	1st to 10th	Day	36% 4 6% 20% 27% 6%	3160
	11th to 20th	Day	22% 2 6% 22% 31% 18%	3140
	21st to end	Day	23% 3 7% 27% 28% 12%	3428
November	1st to 10th	Day	32% 3 8% 24% 26% 6%	1957
	11th to 20th	Day	36% 2 10% 22% 23% 8%	1891
	21st to end	Day	34% 3 8% 24% 27% 5%	1610
December	1st to 10th	Day	34% 3 8% 27% 22% 6%	2600
	11th to 20th	Day	42% 3 11% 20% 19% 5%	2986
	21st to end	Day	38% 4 11% 25% 20% 1	4172
January	1st to 10th	Night	34% 3 5% 19% 27% 12%	5889
	11th to 20th	Night	34% 3 5% 18% 34% 6%	5900
	21st to end	Night	39% 2 5% 25% 23% 5%	6490
February	1st to 10th	Night	41% 3 10% 22% 19% 4	2600
	11th to 20th	Night	45% 4 7% 18% 20% 6%	2490
	21st to end	Night	38% 3 8% 23% 19% 9%	1905
March	1st to 10th	Night	50% 5% 7% 17% 17% 4	3528
	11th to 20th	Night	34% 5% 6% 16% 26% 14%	3498
	21st to end	Night	37% 3 8% 26% 21% 5%	3817
April	1st to 10th	Night	37% 5% 10% 18% 24% 6%	1924
	11th to 20th	Night	33% 6% 10% 23% 23% 6%	1875
	21st to end	Night	37% 5% 10% 26% 18% 4	1900
May	1st to 10th	Night	45% 5% 14% 22% 12% 2	2950
	11th to 20th	Night	49% 7% 10% 22% 12% 1	2813
	21st to end	Night	33% 6% 16% 25% 18% 2	2964
June	1st to 10th	Night	36% 7% 16% 24% 15% 1	1520
	11th to 20th	Night	37% 8% 17% 21% 15% 2	1520
	21st to end	Night	36% 8% 13% 22% 17% 3	1536
July	1st to 10th	Night	37% 13% 18% 19% 11% 3	2795
	11th to 20th	Night	44% 11% 19% 19% 6% 2	2786
	21st to end	Night	54% 6% 13% 17% 10%	2988
August	1st to 10th	Night	51% 7% 19% 16% 6%	2814
	11th to 20th	Night	37% 8% 19% 24% 11% 1	2956
	21st to end	Night	33% 6% 13% 27% 19% 2	3476
September	1st to 10th	Night	35% 7% 14% 20% 19% 4	1900
	11th to 20th	Night	40% 6% 11% 19% 21% 3	1946
	21st to end	Night	49% 6% 10% 16% 16% 4	2171
October	1st to 10th	Night	41% 4 9% 18% 24% 4	3800
	11th to 20th	Night	26% 2 5% 21% 30% 16%	3779
	21st to end	Night	24% 3 5% 30% 23% 15%	4120
November	1st to 10th	Night	35% 4 9% 20% 26% 6%	2341
	11th to 20th	Night	36% 3 8% 19% 23% 11%	2505
	21st to end	Night	34% 3 7% 22% 27% 6%	2785
December	1st to 10th	Night	35% 3 6% 24% 26% 6%	4580
	11th to 20th	Night	47% 4 8% 18% 16% 7%	5208
	21st to end	Night	38% 4 11% 27% 19% 2	6766

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	31% 24% 31% 10% 4	300
	11th to 20th	Day	28% 29% 32% 9% 2	300
	21st to end	Day	24% 23% 39% 13% 1	330
February	1st to 10th	Day	25% 23% 38% 13% 2	300
	11th to 20th	Day	42% 22% 28% 7% 1	344
	21st to end	Day	27% 19% 35% 17% 2	414
March	1st to 10th	Day	26% 21% 31% 18% 5%	500
	11th to 20th	Day	23% 22% 34% 15% 5% 1	464
	21st to end	Day	24% 17% 37% 17% 5% 1	506
April	1st to 10th	Day	23% 18% 33% 19% 6% 1	460
	11th to 20th	Day	19% 15% 33% 19% 10% 3	452
	21st to end	Day	22% 13% 32% 23% 9% 1	460
May	1st to 10th	Day	17% 15% 37% 20% 9% 3	463
	11th to 20th	Day	20% 7% 26% 29% 15% 3	487
	21st to end	Day	21% 4 22% 26% 21% 6%	529
June	1st to 10th	Day	11% 5% 28% 30% 20% 6%	490
	11th to 20th	Day	10% 6% 22% 32% 23% 6%	490
	21st to end	Day	11% 4 20% 37% 22% 6%	490
July	1st to 10th	Day	10% 3 13% 34% 29% 11%	485
	11th to 20th	Day	5% 2 15% 37% 32% 9%	484
	21st to end	Day	11% 2 19% 36% 25% 8%	532
August	1st to 10th	Day	14% 5% 16% 31% 25% 9%	486
	11th to 20th	Day	12% 3 14% 32% 29% 11%	479
	21st to end	Day	9% 2 14% 30% 29% 16%	539
September	1st to 10th	Day	13% 4 16% 27% 24% 15%	490
	11th to 20th	Day	18% 4 14% 30% 22% 12%	490
	21st to end	Day	27% 6% 21% 28% 14% 4	490
October	1st to 10th	Day	20% 5% 22% 25% 22% 6%	490
	11th to 20th	Day	15% 11% 27% 28% 17% 3	490
	21st to end	Day	14% 13% 27% 27% 16% 4	539
November	1st to 10th	Day	16% 11% 32% 25% 14% 3	495
	11th to 20th	Day	20% 16% 30% 22% 10% 1	445
	21st to end	Day	25% 15% 25% 23% 8% 3	210
December	1st to 10th	Day	23% 20% 40% 10% 7% 1	200
	11th to 20th	Day	25% 16% 35% 21% 3 2	200
	21st to end	Day	25% 17% 31% 19% 5% 2	267
January	1st to 10th	Night	20% 19% 34% 23% 3	800
	11th to 20th	Night	23% 16% 31% 26% 4	800
	21st to end	Night	19% 16% 39% 23% 3	880
February	1st to 10th	Night	21% 16% 36% 24% 4	800
	11th to 20th	Night	28% 19% 37% 16% 1	783
	21st to end	Night	20% 15% 38% 24% 2	660
March	1st to 10th	Night	20% 16% 35% 25% 5%	800
	11th to 20th	Night	20% 16% 35% 23% 6%	767
	21st to end	Night	19% 14% 39% 22% 6%	836
April	1st to 10th	Night	19% 14% 37% 24% 6%	760
	11th to 20th	Night	16% 12% 35% 28% 9%	751
	21st to end	Night	16% 7% 37% 32% 8%	760
May	1st to 10th	Night	17% 10% 31% 32% 10%	641
	11th to 20th	Night	20% 5% 24% 37% 13% 1	561
	21st to end	Night	14% 1 20% 39% 24% 2	546
June	1st to 10th	Night	12% 2 19% 45% 22% 1	380
	11th to 20th	Night	10% 3 17% 43% 23% 3	380
	21st to end	Night	8% 3 17% 47% 23% 3	396
July	1st to 10th	Night	10% 2 12% 40% 32% 4	555
	11th to 20th	Night	7% 3 9% 39% 38% 4	552
	21st to end	Night	8% 3 15% 39% 31% 4	624
August	1st to 10th	Night	13% 2 10% 42% 28% 4	567
	11th to 20th	Night	12% 3 10% 39% 33% 4	643
	21st to end	Night	12% 2 9% 34% 36% 7%	836
September	1st to 10th	Night	13% 2 11% 36% 32% 5%	760
	11th to 20th	Night	16% 5% 14% 31% 30% 5%	760
	21st to end	Night	24% 4 20% 32% 19% 1	760
October	1st to 10th	Night	17% 6% 19% 30% 24% 5%	760
	11th to 20th	Night	16% 9% 26% 30% 18% 2	760
	21st to end	Night	15% 9% 26% 30% 17% 3	836
November	1st to 10th	Night	16% 7% 29% 31% 16% 2	780
	11th to 20th	Night	17% 12% 29% 33% 9% 1	800
	21st to end	Night	16% 12% 29% 31% 12% 1	800
December	1st to 10th	Night	23% 14% 32% 24% 8%	800
	11th to 20th	Night	19% 11% 33% 31% 6%	800
	21st to end	Night	22% 15% 27% 31% 5%	880

Page generated at 2025-03-09 08:08:44. Version ac07

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