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 2025-05-11.

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	20% 12% 4 10% 5% 4 3 3 4 6% 29%	113854
	Night	19% 15% 5% 12% 6% 4 4 3 4 5% 23%	115157
Transparency	Day	57% 6% 11% 17% 9% 1	117447
	Night	62% 6% 10% 15% 7% 1	119728
Seeing	Day	30% 21% 30% 14% 4 1	17290
	Night	30% 18% 30% 18% 4	25224

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% 25% 9% 20% 9% 3 3 1 2 3 9%	3157
	11th to 20th	Day	16% 21% 10% 25% 7% 4 2 2 2 2 8%	3816
	21st to end	Day	15% 17% 10% 20% 11% 6% 3 2 3 3 11%	4466
February	1st to 10th	Day	19% 20% 7% 16% 10% 5% 3 2 3 4 11%	1800
	11th to 20th	Day	16% 17% 7% 17% 12% 4 3 1 3 4 14%	1753
	21st to end	Day	12% 18% 7% 11% 8% 5% 3 3 4 5% 23%	1590
March	1st to 10th	Day	24% 17% 6% 13% 9% 4 3 2 3 3 18%	4830
	11th to 20th	Day	18% 15% 4 10% 4 4 3 3 5% 6% 28%	4980
	21st to end	Day	27% 16% 6% 9% 4 4 4 3 4 4 20%	5466
April	1st to 10th	Day	24% 15% 4 6% 4 3 3 3 3 5% 30%	2310
	11th to 20th	Day	20% 11% 3 5% 3 4 3 3 5% 6% 38%	2553
	21st to end	Day	20% 13% 3 6% 3 3 3 3 4 6% 36%	2600
May	1st to 10th	Day	20% 13% 3 9% 5% 4 4 4 5% 7% 27%	4236
	11th to 20th	Day	18% 9% 3 7% 5% 4 4 4 5% 7% 33%	4287
	21st to end	Day	17% 7% 2 6% 4 4 4 3 6% 9% 37%	4836
June	1st to 10th	Day	24% 9% 2 7% 4 4 3 3 5% 6% 33%	2763
	11th to 20th	Day	21% 8% 2 5% 4 4 3 3 4 7% 38%	2850
	21st to end	Day	23% 8% 3 7% 5% 4 4 4 4 6% 32%	2850
July	1st to 10th	Day	22% 7% 3 7% 4 3 4 4 5% 7% 34%	4760
	11th to 20th	Day	27% 8% 2 5% 4 3 3 3 5% 7% 33%	4580
	21st to end	Day	16% 7% 2 6% 4 4 4 4 6% 9% 37%	4467
August	1st to 10th	Day	26% 9% 3 8% 4 3 3 3 5% 6% 31%	4105
	11th to 20th	Day	15% 7% 3 7% 4 4 4 4 6% 7% 41%	4045
	21st to end	Day	12% 5% 2 5% 3 4 3 3 4 7% 53%	4474
September	1st to 10th	Day	18% 6% 2 4 3 3 3 2 4 6% 48%	2277
	11th to 20th	Day	17% 6% 2 5% 3 3 2 3 4 7% 47%	2090
	21st to end	Day	19% 7% 3 6% 4 3 3 3 4 5% 44%	2090
October	1st to 10th	Day	20% 8% 2 5% 4 4 4 4 5% 6% 39%	1914
	11th to 20th	Day	20% 11% 3 7% 3 4 4 3 5% 6% 34%	1900
	21st to end	Day	22% 13% 3 8% 4 3 4 3 4 5% 31%	2043
November	1st to 10th	Day	22% 12% 3 8% 5% 4 3 3 4 7% 29%	1702
	11th to 20th	Day	19% 20% 7% 8% 4 4 3 3 5% 6% 21%	1600
	21st to end	Day	20% 21% 5% 14% 5% 4 3 2 3 4 18%	1600
December	1st to 10th	Day	21% 20% 10% 18% 4 4 3 2 3 3 11%	2610
	11th to 20th	Day	24% 17% 6% 16% 5% 4 3 2 3 4 16%	2978
	21st to end	Day	20% 18% 9% 17% 7% 3 3 2 3 3 16%	3476
January	1st to 10th	Night	14% 24% 10% 25% 6% 3 3 2 2 2 10%	6808
	11th to 20th	Night	17% 22% 10% 23% 6% 3 3 2 3 2 10%	6061
	21st to end	Night	13% 15% 7% 23% 13% 6% 4 2 3 3 10%	6490
February	1st to 10th	Night	19% 19% 7% 18% 9% 5% 3 3 3 3 11%	2600
	11th to 20th	Night	17% 18% 6% 18% 12% 5% 4 2 3 3 12%	2533
	21st to end	Night	14% 16% 6% 14% 8% 5% 5% 4 5% 5% 20%	2038
March	1st to 10th	Night	23% 17% 7% 12% 9% 4 3 2 3 4 16%	5008
	11th to 20th	Night	18% 16% 5% 9% 5% 5% 4 3 5% 6% 24%	4979
	21st to end	Night	28% 12% 5% 8% 5% 4 3 2 4 4 24%	5466
April	1st to 10th	Night	23% 16% 4 6% 5% 3 4 3 4 5% 28%	2090
	11th to 20th	Night	23% 11% 2 7% 4 3 5% 3 5% 8% 30%	1793
	21st to end	Night	22% 13% 3 6% 5% 4 4 3 5% 6% 31%	1800
May	1st to 10th	Night	20% 17% 4 8% 3 4 3 3 4 6% 28%	2924
	11th to 20th	Night	19% 10% 3 8% 5% 5% 4 4 6% 6% 30%	2620
	21st to end	Night	16% 10% 3 9% 5% 5% 5% 3 6% 8% 30%	2749
June	1st to 10th	Night	25% 9% 3 5% 4 3 4 3 6% 9% 28%	1432
	11th to 20th	Night	21% 8% 2 6% 4 3 4 4 5% 8% 35%	1330
	21st to end	Night	22% 8% 3 10% 5% 5% 4 4 5% 7% 27%	1330
July	1st to 10th	Night	24% 12% 3 8% 4 4 4 4 6% 7% 25%	2210
	11th to 20th	Night	26% 8% 2 6% 4 4 4 4 6% 8% 28%	2352
	21st to end	Night	16% 7% 2 7% 5% 5% 5% 4 6% 8% 37%	3087
August	1st to 10th	Night	27% 10% 3 7% 3 3 4 3 5% 7% 29%	2825
	11th to 20th	Night	18% 9% 2 8% 5% 5% 5% 4 6% 8% 30%	2782
	21st to end	Night	11% 8% 2 5% 4 4 4 3 6% 7% 47%	3181
September	1st to 10th	Night	17% 5% 2 5% 4 3 4 3 5% 7% 45%	1900
	11th to 20th	Night	18% 7% 3 5% 3 3 3 3 5% 7% 43%	2090
	21st to end	Night	20% 8% 2 6% 4 4 5% 3 4 6% 38%	2090
October	1st to 10th	Night	20% 8% 2 6% 5% 4 3 3 5% 6% 38%	2266
	11th to 20th	Night	17% 9% 3 7% 6% 4 4 3 4 6% 37%	2280
	21st to end	Night	25% 14% 3 8% 3 3 3 2 4 5% 29%	2554
November	1st to 10th	Night	21% 12% 3 7% 5% 4 4 3 5% 5% 30%	2594
	11th to 20th	Night	21% 21% 4 10% 4 4 4 3 5% 5% 21%	2800
	21st to end	Night	20% 20% 5% 11% 5% 4 4 3 4 5% 21%	2800
December	1st to 10th	Night	17% 22% 9% 18% 5% 4 3 2 4 4 11%	4580
	11th to 20th	Night	19% 17% 6% 18% 6% 4 3 3 3 4 17%	5213
	21st to end	Night	22% 21% 7% 14% 6% 2 2 2 2 3 19%	7502

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% 5% 9% 3 1	3158
	11th to 20th	Day	82% 5% 7% 4 2	3849
	21st to end	Day	76% 5% 11% 4 3	4466
February	1st to 10th	Day	77% 5% 8% 5% 3	1800
	11th to 20th	Day	75% 4 8% 9% 3	1761
	21st to end	Day	63% 5% 12% 13% 6% 1	1590
March	1st to 10th	Day	73% 3 8% 11% 5% 1	4834
	11th to 20th	Day	57% 5% 13% 18% 7%	4980
	21st to end	Day	70% 3 5% 12% 9% 1	5466
April	1st to 10th	Day	60% 4 9% 13% 13% 1	2310
	11th to 20th	Day	48% 5% 10% 23% 12% 2	2553
	21st to end	Day	50% 4 10% 19% 14% 2	2600
May	1st to 10th	Day	55% 7% 12% 18% 7% 1	4250
	11th to 20th	Day	47% 9% 16% 18% 9% 1	4291
	21st to end	Day	43% 8% 17% 18% 13%	4836
June	1st to 10th	Day	52% 6% 10% 20% 11% 1	2763
	11th to 20th	Day	47% 6% 12% 20% 13% 2	2850
	21st to end	Day	54% 8% 10% 18% 9% 2	2850
July	1st to 10th	Day	49% 6% 11% 20% 12% 1	4685
	11th to 20th	Day	51% 6% 11% 22% 10%	4499
	21st to end	Day	45% 7% 14% 22% 12% 1	4325
August	1st to 10th	Day	56% 6% 10% 18% 10%	4092
	11th to 20th	Day	43% 7% 15% 25% 9%	4084
	21st to end	Day	33% 5% 13% 26% 21% 2	4474
September	1st to 10th	Day	40% 5% 11% 26% 17% 2	2277
	11th to 20th	Day	39% 5% 11% 26% 17% 2	2090
	21st to end	Day	43% 5% 8% 25% 16% 2	2090
October	1st to 10th	Day	47% 5% 10% 26% 11% 1	3174
	11th to 20th	Day	46% 4 9% 24% 16%	3140
	21st to end	Day	47% 3 12% 24% 12% 1	3345
November	1st to 10th	Day	56% 5% 12% 19% 8% 1	1702
	11th to 20th	Day	65% 6% 10% 14% 5% 1	1600
	21st to end	Day	69% 6% 11% 11% 2	1600
December	1st to 10th	Day	78% 6% 6% 9% 1	2610
	11th to 20th	Day	72% 4 10% 9% 4 1	2977
	21st to end	Day	73% 5% 10% 6% 6%	3476
January	1st to 10th	Night	82% 5% 6% 6% 1	6808
	11th to 20th	Night	81% 4 7% 6% 2	6103
	21st to end	Night	75% 6% 9% 7% 2	6490
February	1st to 10th	Night	77% 5% 8% 7% 4	2600
	11th to 20th	Night	76% 6% 7% 8% 3	2536
	21st to end	Night	64% 7% 11% 12% 5% 1	2038
March	1st to 10th	Night	73% 3 8% 9% 6% 1	5017
	11th to 20th	Night	60% 6% 13% 16% 5%	4980
	21st to end	Night	63% 4 7% 16% 9% 1	5466
April	1st to 10th	Night	59% 4 9% 14% 11% 2	2090
	11th to 20th	Night	53% 5% 10% 21% 10% 1	1793
	21st to end	Night	54% 5% 10% 17% 13% 2	1800
May	1st to 10th	Night	58% 6% 11% 17% 7%	2930
	11th to 20th	Night	50% 10% 13% 20% 6% 1	2621
	21st to end	Night	49% 10% 15% 20% 5%	2750
June	1st to 10th	Night	53% 7% 12% 20% 8% 1	1432
	11th to 20th	Night	47% 7% 13% 21% 11% 1	1330
	21st to end	Night	57% 6% 11% 16% 8% 2	1330
July	1st to 10th	Night	57% 6% 11% 14% 11%	2175
	11th to 20th	Night	54% 6% 14% 15% 10%	2310
	21st to end	Night	44% 8% 12% 22% 12% 1	2989
August	1st to 10th	Night	56% 6% 11% 22% 6%	2813
	11th to 20th	Night	48% 8% 16% 22% 6%	2809
	21st to end	Night	35% 7% 14% 26% 17% 1	3180
September	1st to 10th	Night	38% 7% 10% 28% 15% 2	1900
	11th to 20th	Night	41% 5% 10% 28% 16% 1	2090
	21st to end	Night	47% 6% 9% 22% 16% 1	2090
October	1st to 10th	Night	48% 4 13% 22% 12% 1	3786
	11th to 20th	Night	42% 5% 12% 23% 18% 1	3779
	21st to end	Night	50% 3 9% 24% 13%	4202
November	1st to 10th	Night	54% 7% 13% 18% 8%	2594
	11th to 20th	Night	64% 7% 11% 13% 6%	2800
	21st to end	Night	65% 6% 14% 11% 3	2800
December	1st to 10th	Night	75% 6% 8% 9% 1	4580
	11th to 20th	Night	70% 5% 11% 11% 3	5215
	21st to end	Night	72% 4 7% 10% 5%	7502

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	41% 27% 24% 8% 1	200
	11th to 20th	Day	39% 28% 22% 10% 2	309
	21st to end	Day	28% 30% 32% 9% 1	440
February	1st to 10th	Day	39% 22% 31% 6% 3	400
	11th to 20th	Day	40% 28% 23% 7% 2	396
	21st to end	Day	34% 25% 28% 11% 2	384
March	1st to 10th	Day	35% 27% 31% 7% 1	500
	11th to 20th	Day	36% 25% 27% 9% 3	500
	21st to end	Day	35% 28% 23% 10% 2 1	550
April	1st to 10th	Day	42% 28% 22% 6% 2	500
	11th to 20th	Day	35% 23% 29% 10% 2	492
	21st to end	Day	32% 24% 27% 13% 4	500
May	1st to 10th	Day	33% 25% 30% 10% 2 1	503
	11th to 20th	Day	26% 21% 31% 16% 5%	602
	21st to end	Day	29% 19% 32% 17% 3 1	735
June	1st to 10th	Day	32% 18% 30% 15% 4	680
	11th to 20th	Day	24% 18% 32% 20% 5%	680
	21st to end	Day	32% 15% 31% 17% 4 1	680
July	1st to 10th	Day	24% 13% 36% 19% 7% 1	670
	11th to 20th	Day	23% 11% 35% 22% 7% 1	637
	21st to end	Day	22% 14% 40% 18% 6%	532
August	1st to 10th	Day	21% 12% 38% 23% 6% 1	486
	11th to 20th	Day	22% 9% 37% 22% 9% 1	479
	21st to end	Day	20% 16% 31% 22% 9% 2	539
September	1st to 10th	Day	20% 17% 36% 20% 6% 1	490
	11th to 20th	Day	24% 17% 32% 18% 7% 2	490
	21st to end	Day	22% 19% 32% 19% 7% 2	490
October	1st to 10th	Day	26% 15% 28% 21% 8% 2	397
	11th to 20th	Day	29% 17% 30% 16% 6% 2	390
	21st to end	Day	32% 23% 27% 13% 5% 1	429
November	1st to 10th	Day	32% 20% 30% 13% 4 1	395
	11th to 20th	Day	42% 22% 24% 9% 3	400
	21st to end	Day	36% 28% 26% 7% 3 1	400
December	1st to 10th	Day	38% 27% 25% 10% 1	400
	11th to 20th	Day	43% 28% 20% 8% 2	395
	21st to end	Day	38% 28% 25% 7% 2	220
January	1st to 10th	Night	36% 23% 26% 13% 1	900
	11th to 20th	Night	39% 21% 25% 12% 3	800
	21st to end	Night	29% 27% 29% 12% 3	880
February	1st to 10th	Night	36% 24% 27% 11% 2	800
	11th to 20th	Night	36% 26% 27% 9% 2	783
	21st to end	Night	26% 25% 32% 15% 2	660
March	1st to 10th	Night	31% 24% 30% 13% 1	800
	11th to 20th	Night	30% 22% 28% 17% 4	800
	21st to end	Night	30% 22% 29% 14% 5%	880
April	1st to 10th	Night	38% 19% 29% 12% 2	690
	11th to 20th	Night	32% 20% 32% 14% 2	594
	21st to end	Night	31% 17% 31% 17% 4	600
May	1st to 10th	Night	30% 15% 33% 19% 4 1	600
	11th to 20th	Night	28% 16% 33% 21% 3	565
	21st to end	Night	22% 16% 40% 19% 3 1	616
June	1st to 10th	Night	29% 14% 33% 19% 4	482
	11th to 20th	Night	23% 10% 37% 24% 5% 1	380
	21st to end	Night	27% 10% 36% 21% 6%	380
July	1st to 10th	Night	23% 7% 39% 26% 5%	370
	11th to 20th	Night	21% 10% 37% 24% 8%	419
	21st to end	Night	19% 7% 40% 30% 4	623
August	1st to 10th	Night	19% 8% 38% 28% 6% 1	568
	11th to 20th	Night	21% 11% 34% 26% 8%	562
	21st to end	Night	17% 9% 34% 29% 10%	627
September	1st to 10th	Night	20% 10% 36% 25% 9% 1	570
	11th to 20th	Night	22% 11% 28% 27% 11% 1	760
	21st to end	Night	24% 14% 28% 24% 9% 2	760
October	1st to 10th	Night	25% 10% 29% 24% 11% 1	760
	11th to 20th	Night	23% 20% 29% 19% 8% 1	760
	21st to end	Night	35% 21% 23% 18% 3	836
November	1st to 10th	Night	31% 18% 27% 18% 5%	809
	11th to 20th	Night	36% 20% 24% 15% 5%	900
	21st to end	Night	35% 23% 25% 14% 4	900
December	1st to 10th	Night	38% 21% 27% 12% 2	900
	11th to 20th	Night	37% 28% 24% 9% 2	900
	21st to end	Night	38% 23% 24% 13% 3	990

Page generated at 2025-05-08 10:33:58. Version ac07

Copyright © 2025 Attilla Danko.