South Range
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Range clear sky chart from 2005-11-06 to 2026-09-14.

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	19% 12% 4 9% 5% 4 3 3 4 6% 30%	149548
	Night	20% 14% 5% 12% 6% 4 4 3 4 5% 24%	141652
Transparency	Day	56% 5% 11% 18% 10% 1	153099
	Night	62% 5% 10% 15% 7% 1	146190
Seeing	Day	30% 21% 30% 14% 4 1	19213
	Night	30% 18% 29% 18% 4	26885

By Month

Percentage Cloud Cover NE (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% 23% 9% 19% 11% 5% 3 1 2 3 9%	4093
	11th to 20th	Day	20% 21% 10% 23% 6% 4 2 2 2 2 7%	4980
	21st to end	Day	14% 15% 8% 22% 15% 7% 3 2 2 2 9%	5781
February	1st to 10th	Day	18% 20% 8% 17% 10% 4 3 2 3 4 11%	1890
	11th to 20th	Day	16% 17% 7% 17% 12% 4 3 1 3 4 16%	1843
	21st to end	Day	12% 17% 7% 11% 8% 5% 3 3 4 5% 24%	1667
March	1st to 10th	Day	23% 16% 6% 13% 9% 4 3 2 3 3 18%	4937
	11th to 20th	Day	18% 15% 4 10% 4 4 3 3 5% 6% 28%	5090
	21st to end	Day	27% 16% 6% 9% 4 4 4 3 4 4 20%	5587
April	1st to 10th	Day	24% 15% 4 6% 4 3 3 3 3 5% 30%	2425
	11th to 20th	Day	21% 11% 3 5% 3 4 3 2 5% 6% 37%	2682
	21st to end	Day	19% 13% 3 6% 3 3 3 3 4 5% 36%	2730
May	1st to 10th	Day	26% 12% 3 8% 4 4 3 3 4 5% 27%	7639
	11th to 20th	Day	17% 10% 3 7% 4 5% 4 4 6% 7% 34%	7999
	21st to end	Day	18% 11% 3 9% 4 4 4 3 5% 7% 33%	9059
June	1st to 10th	Day	23% 8% 2 7% 4 4 4 3 5% 7% 33%	3054
	11th to 20th	Day	21% 8% 3 5% 4 4 4 3 4 7% 38%	3150
	21st to end	Day	23% 8% 2 7% 5% 4 4 3 5% 6% 32%	3150
July	1st to 10th	Day	21% 7% 3 6% 4 4 4 3 6% 8% 34%	8880
	11th to 20th	Day	20% 7% 2 5% 3 3 3 3 5% 7% 42%	8532
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 8% 41%	8342
August	1st to 10th	Day	21% 9% 3 7% 3 4 3 3 5% 6% 36%	6015
	11th to 20th	Day	17% 7% 3 7% 4 4 4 3 5% 7% 39%	5953
	21st to end	Day	13% 6% 2 5% 3 4 3 3 5% 7% 49%	6506
September	1st to 10th	Day	19% 7% 2 4 3 3 3 2 4 6% 47%	2517
	11th to 20th	Day	16% 6% 2 5% 3 4 2 3 4 7% 48%	2233
	21st to end	Day	18% 7% 3 6% 4 3 3 3 4 5% 44%	2200
October	1st to 10th	Day	19% 7% 2 5% 3 4 4 4 5% 6% 41%	2014
	11th to 20th	Day	20% 12% 3 7% 3 4 4 3 5% 6% 33%	2000
	21st to end	Day	21% 13% 3 9% 4 4 4 3 4 5% 31%	2150
November	1st to 10th	Day	22% 12% 3 8% 5% 4 3 3 4 7% 29%	1789
	11th to 20th	Day	19% 21% 7% 8% 4 4 3 3 4 5% 20%	1680
	21st to end	Day	19% 21% 5% 14% 5% 4 3 2 3 4 18%	1680
December	1st to 10th	Day	21% 20% 10% 18% 5% 4 3 2 3 3 11%	2690
	11th to 20th	Day	23% 17% 6% 16% 5% 4 3 2 3 4 16%	3058
	21st to end	Day	19% 18% 9% 17% 7% 3 3 2 3 3 15%	3553
January	1st to 10th	Night	14% 23% 10% 23% 9% 4 3 2 2 2 9%	8831
	11th to 20th	Night	22% 23% 9% 20% 5% 3 2 2 2 2 9%	7897
	21st to end	Night	12% 15% 7% 25% 14% 7% 3 2 3 3 9%	8400
February	1st to 10th	Night	18% 18% 7% 19% 9% 5% 3 3 3 4 11%	2730
	11th to 20th	Night	17% 17% 6% 18% 11% 5% 4 2 3 3 14%	2663
	21st to end	Night	14% 16% 6% 13% 7% 5% 5% 4 5% 5% 20%	2137
March	1st to 10th	Night	23% 17% 7% 12% 9% 4 3 2 3 4 17%	5121
	11th to 20th	Night	18% 16% 5% 9% 5% 5% 4 3 5% 6% 24%	5089
	21st to end	Night	28% 12% 5% 8% 5% 4 3 2 4 4 25%	5587
April	1st to 10th	Night	24% 16% 4 6% 5% 3 4 3 4 5% 28%	2195
	11th to 20th	Night	23% 12% 2 7% 4 3 5% 3 5% 8% 29%	1884
	21st to end	Night	22% 13% 3 6% 4 4 4 3 4 6% 32%	1890
May	1st to 10th	Night	28% 15% 4 8% 4 4 3 2 3 4 24%	5259
	11th to 20th	Night	21% 11% 2 7% 5% 4 4 4 6% 6% 31%	4879
	21st to end	Night	17% 13% 3 8% 5% 4 4 3 5% 7% 31%	5147
June	1st to 10th	Night	24% 9% 3 5% 5% 3 4 3 6% 8% 29%	1582
	11th to 20th	Night	20% 8% 2 6% 4 3 4 3 6% 8% 36%	1470
	21st to end	Night	22% 8% 3 10% 5% 6% 4 3 5% 7% 27%	1470
July	1st to 10th	Night	20% 9% 3 8% 5% 5% 5% 4 6% 8% 27%	4110
	11th to 20th	Night	20% 7% 2 6% 4 4 4 3 5% 7% 38%	4375
	21st to end	Night	17% 7% 2 6% 4 4 4 3 5% 8% 39%	5736
August	1st to 10th	Night	25% 9% 2 7% 4 4 5% 3 5% 7% 29%	4135
	11th to 20th	Night	19% 10% 2 8% 5% 4 4 4 6% 7% 32%	4092
	21st to end	Night	17% 8% 2 5% 4 4 4 3 6% 7% 41%	4618
September	1st to 10th	Night	17% 5% 2 5% 4 3 4 3 5% 7% 44%	2100
	11th to 20th	Night	17% 7% 3 5% 3 3 3 3 5% 7% 44%	2234
	21st to end	Night	20% 8% 2 6% 4 4 5% 3 4 6% 38%	2200
October	1st to 10th	Night	19% 7% 2 6% 4 4 3 3 5% 6% 40%	2385
	11th to 20th	Night	18% 10% 3 7% 5% 4 4 3 4 6% 36%	2400
	21st to end	Night	25% 13% 3 8% 4 3 3 2 4 4 30%	2689
November	1st to 10th	Night	22% 13% 3 7% 5% 4 4 3 5% 5% 30%	2727
	11th to 20th	Night	20% 22% 4 10% 4 4 4 3 5% 5% 20%	2940
	21st to end	Night	20% 20% 6% 10% 5% 4 4 3 4 5% 21%	2940
December	1st to 10th	Night	17% 22% 9% 18% 5% 4 3 2 3 4 11%	4720
	11th to 20th	Night	19% 18% 6% 18% 5% 4 3 3 3 4 17%	5353
	21st to end	Night	22% 20% 7% 15% 6% 2 2 2 2 3 19%	7667

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	82% 4 9% 4 1	4094
	11th to 20th	Day	85% 4 6% 4 2	5013
	21st to end	Day	81% 4 9% 3 3	5781
February	1st to 10th	Day	78% 5% 8% 6% 3	1890
	11th to 20th	Day	74% 4 8% 10% 4	1851
	21st to end	Day	63% 4 12% 13% 6% 1	1667
March	1st to 10th	Day	72% 3 8% 11% 5% 1	4941
	11th to 20th	Day	57% 5% 13% 18% 7%	5090
	21st to end	Day	70% 3 5% 12% 9% 1	5587
April	1st to 10th	Day	60% 4 9% 13% 14% 1	2425
	11th to 20th	Day	49% 5% 10% 22% 12% 1	2682
	21st to end	Day	50% 4 10% 19% 14% 3	2730
May	1st to 10th	Day	60% 5% 10% 17% 8%	7651
	11th to 20th	Day	48% 6% 15% 19% 9% 2	8003
	21st to end	Day	52% 6% 12% 16% 13% 1	9060
June	1st to 10th	Day	52% 6% 10% 20% 11% 1	3054
	11th to 20th	Day	47% 6% 11% 21% 13% 2	3150
	21st to end	Day	53% 8% 10% 18% 9% 2	3150
July	1st to 10th	Day	49% 6% 14% 21% 10% 1	8805
	11th to 20th	Day	43% 4 11% 28% 13%	8451
	21st to end	Day	43% 5% 13% 25% 14% 1	8159
August	1st to 10th	Day	50% 5% 12% 21% 10% 1	6002
	11th to 20th	Day	45% 6% 16% 25% 7%	5992
	21st to end	Day	37% 5% 13% 27% 16% 2	6506
September	1st to 10th	Day	41% 4 10% 26% 17% 1	2517
	11th to 20th	Day	38% 5% 11% 26% 18% 2	2233
	21st to end	Day	42% 5% 8% 24% 18% 3	2200
October	1st to 10th	Day	46% 5% 10% 26% 11% 1	3274
	11th to 20th	Day	46% 4 9% 24% 16%	3240
	21st to end	Day	47% 3 12% 24% 12% 1	3452
November	1st to 10th	Day	57% 5% 12% 19% 7% 1	1789
	11th to 20th	Day	65% 6% 10% 13% 5% 1	1680
	21st to end	Day	69% 6% 11% 11% 2	1680
December	1st to 10th	Day	78% 6% 6% 9% 1	2690
	11th to 20th	Day	72% 4 10% 9% 4 1	3057
	21st to end	Day	74% 5% 9% 6% 6%	3553
January	1st to 10th	Night	84% 4 5% 5% 1	8831
	11th to 20th	Night	82% 4 6% 7% 2	7939
	21st to end	Night	79% 5% 7% 6% 2	8400
February	1st to 10th	Night	77% 5% 7% 7% 3	2730
	11th to 20th	Night	74% 6% 7% 10% 3	2666
	21st to end	Night	64% 7% 11% 13% 5% 1	2137
March	1st to 10th	Night	72% 3 8% 9% 7% 1	5130
	11th to 20th	Night	60% 6% 13% 16% 5%	5090
	21st to end	Night	63% 4 7% 16% 9% 1	5587
April	1st to 10th	Night	60% 4 9% 13% 12% 2	2195
	11th to 20th	Night	54% 5% 10% 20% 11% 1	1884
	21st to end	Night	53% 5% 10% 17% 13% 2	1890
May	1st to 10th	Night	64% 5% 8% 15% 7%	5265
	11th to 20th	Night	53% 7% 12% 19% 8% 2	4880
	21st to end	Night	52% 7% 12% 19% 9% 1	5148
June	1st to 10th	Night	52% 6% 12% 21% 8% 1	1582
	11th to 20th	Night	46% 7% 13% 22% 11% 1	1470
	21st to end	Night	56% 6% 11% 16% 9% 2	1470
July	1st to 10th	Night	55% 6% 13% 18% 8%	4075
	11th to 20th	Night	46% 5% 12% 22% 14% 1	4333
	21st to end	Night	44% 6% 11% 24% 14% 1	5605
August	1st to 10th	Night	55% 6% 12% 20% 8%	4123
	11th to 20th	Night	50% 6% 17% 22% 5%	4119
	21st to end	Night	42% 6% 14% 25% 13% 1	4617
September	1st to 10th	Night	39% 6% 10% 27% 15% 1	2100
	11th to 20th	Night	40% 5% 10% 28% 17% 1	2234
	21st to end	Night	46% 6% 9% 22% 16% 1	2200
October	1st to 10th	Night	47% 4 13% 22% 13% 1	3905
	11th to 20th	Night	43% 5% 12% 22% 17% 1	3899
	21st to end	Night	50% 3 9% 24% 13%	4337
November	1st to 10th	Night	55% 7% 12% 17% 8%	2727
	11th to 20th	Night	65% 6% 11% 12% 5%	2940
	21st to end	Night	65% 6% 14% 11% 3	2940
December	1st to 10th	Night	76% 6% 8% 10% 1	4720
	11th to 20th	Night	71% 5% 11% 11% 3	5355
	21st to end	Night	72% 4 7% 10% 6%	7667

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	40% 28% 24% 8%	220
	11th to 20th	Day	41% 28% 21% 9% 1	335
	21st to end	Day	29% 30% 32% 8% 1	473
February	1st to 10th	Day	36% 23% 30% 8% 2	430
	11th to 20th	Day	38% 28% 24% 8% 2	426
	21st to end	Day	34% 27% 27% 11% 1	413
March	1st to 10th	Day	34% 27% 31% 6% 1	540
	11th to 20th	Day	37% 25% 27% 8% 3	540
	21st to end	Day	37% 27% 23% 9% 2 1	594
April	1st to 10th	Day	42% 28% 22% 6% 2 1	540
	11th to 20th	Day	36% 23% 29% 10% 2	532
	21st to end	Day	31% 23% 28% 13% 4	540
May	1st to 10th	Day	34% 25% 30% 9% 1 1	543
	11th to 20th	Day	27% 23% 31% 15% 4	694
	21st to end	Day	31% 18% 32% 16% 3 1	845
June	1st to 10th	Day	31% 19% 29% 17% 4	780
	11th to 20th	Day	25% 20% 31% 19% 5%	780
	21st to end	Day	31% 16% 32% 17% 3 1	780
July	1st to 10th	Day	23% 13% 38% 18% 6% 1	770
	11th to 20th	Day	24% 13% 34% 21% 7% 1	733
	21st to end	Day	21% 14% 40% 18% 6%	620
August	1st to 10th	Day	19% 12% 39% 23% 6% 1	566
	11th to 20th	Day	20% 10% 38% 22% 8% 1	559
	21st to end	Day	20% 16% 33% 21% 9% 1	627
September	1st to 10th	Day	21% 16% 36% 19% 6% 1	570
	11th to 20th	Day	23% 17% 32% 19% 7% 2	542
	21st to end	Day	21% 19% 32% 18% 7% 2	530
October	1st to 10th	Day	25% 15% 29% 21% 8% 2	427
	11th to 20th	Day	30% 17% 30% 16% 5% 1	420
	21st to end	Day	32% 23% 27% 12% 5% 1	462
November	1st to 10th	Day	34% 20% 28% 13% 3 1	425
	11th to 20th	Day	42% 22% 25% 8% 3	430
	21st to end	Day	36% 28% 25% 7% 3	430
December	1st to 10th	Day	39% 26% 25% 9% 1	430
	11th to 20th	Day	44% 27% 20% 8% 1	425
	21st to end	Day	39% 27% 26% 7% 2	242
January	1st to 10th	Night	36% 24% 26% 13% 1	950
	11th to 20th	Night	40% 21% 25% 12% 3	840
	21st to end	Night	30% 27% 29% 12% 3	924
February	1st to 10th	Night	35% 24% 28% 11% 2	840
	11th to 20th	Night	35% 25% 27% 10% 2	823
	21st to end	Night	26% 26% 32% 14% 2	692
March	1st to 10th	Night	31% 25% 31% 13% 1	840
	11th to 20th	Night	30% 21% 28% 17% 3	840
	21st to end	Night	31% 22% 29% 13% 5%	924
April	1st to 10th	Night	39% 19% 28% 12% 2	725
	11th to 20th	Night	32% 21% 31% 14% 2	624
	21st to end	Night	31% 16% 31% 17% 4	630
May	1st to 10th	Night	31% 16% 32% 18% 3	630
	11th to 20th	Night	28% 17% 32% 20% 3	622
	21st to end	Night	22% 17% 39% 19% 2 1	682
June	1st to 10th	Night	28% 14% 33% 21% 4	532
	11th to 20th	Night	23% 11% 37% 23% 5% 1	420
	21st to end	Night	26% 10% 35% 22% 6%	420
July	1st to 10th	Night	22% 8% 40% 25% 5%	410
	11th to 20th	Night	21% 10% 36% 25% 8%	465
	21st to end	Night	20% 7% 39% 29% 5%	689
August	1st to 10th	Night	19% 8% 37% 30% 6% 1	628
	11th to 20th	Night	21% 10% 33% 28% 8%	622
	21st to end	Night	17% 10% 35% 29% 10%	693
September	1st to 10th	Night	20% 11% 35% 25% 9%	630
	11th to 20th	Night	21% 11% 28% 27% 12% 1	813
	21st to end	Night	24% 14% 29% 24% 8% 2	800
October	1st to 10th	Night	25% 11% 29% 24% 11% 1	800
	11th to 20th	Night	24% 19% 28% 20% 8% 1	800
	21st to end	Night	34% 21% 23% 18% 4	880
November	1st to 10th	Night	33% 18% 26% 17% 5%	852
	11th to 20th	Night	36% 19% 24% 15% 5%	950
	21st to end	Night	35% 24% 25% 13% 4	950
December	1st to 10th	Night	38% 21% 26% 13% 2	950
	11th to 20th	Night	38% 28% 24% 9% 2	950
	21st to end	Night	38% 23% 24% 12% 3	1045

Page generated at 2026-09-11 05:11:58. Version ac07

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