South River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South River clear sky chart from 2005-11-06 to 2026-08-30.

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	16% 12% 4 9% 5% 4 4 3 5% 6% 30%	144847
	Night	15% 14% 5% 11% 5% 4 4 3 4 5% 28%	137394
Transparency	Day	54% 5% 10% 20% 10% 1	148407
	Night	57% 5% 10% 18% 9% 1	141923
Seeing	Day	25% 17% 31% 18% 7% 2	17360
	Night	24% 15% 30% 22% 8% 1	26222

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	12% 18% 8% 17% 7% 6% 4 3 4 4 17%	4094
	11th to 20th	Day	9% 22% 8% 19% 7% 6% 5% 3 4 4 11%	4635
	21st to end	Day	9% 18% 8% 18% 8% 5% 5% 3 3 4 18%	5780
February	1st to 10th	Day	11% 22% 7% 13% 9% 6% 4 3 3 5% 18%	1890
	11th to 20th	Day	10% 19% 7% 15% 7% 5% 3 4 5% 5% 21%	1843
	21st to end	Day	13% 21% 7% 14% 7% 5% 3 2 4 5% 19%	1557
March	1st to 10th	Day	18% 15% 5% 12% 5% 5% 4 3 4 4 24%	5039
	11th to 20th	Day	13% 14% 6% 12% 6% 4 4 4 5% 7% 24%	5090
	21st to end	Day	16% 17% 6% 9% 5% 5% 3 2 3 4 29%	5586
April	1st to 10th	Day	20% 15% 6% 9% 4 4 3 3 5% 5% 26%	2501
	11th to 20th	Day	22% 13% 4 6% 4 4 3 3 4 5% 32%	2620
	21st to end	Day	22% 12% 3 8% 4 3 3 2 4 5% 33%	2730
May	1st to 10th	Day	16% 12% 3 8% 5% 5% 5% 4 6% 7% 29%	7875
	11th to 20th	Day	16% 10% 3 8% 4 4 4 3 5% 6% 36%	8221
	21st to end	Day	20% 9% 2 6% 4 4 3 3 4 6% 38%	9060
June	1st to 10th	Day	20% 9% 3 7% 5% 4 4 4 5% 6% 32%	3017
	11th to 20th	Day	16% 7% 3 7% 6% 4 4 4 6% 7% 36%	3150
	21st to end	Day	20% 8% 3 7% 5% 5% 4 4 6% 7% 31%	3150
July	1st to 10th	Day	16% 6% 2 6% 5% 4 5% 4 6% 9% 36%	8879
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 6% 8% 46%	8623
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 44%	8798
August	1st to 10th	Day	13% 8% 2 7% 5% 5% 6% 5% 6% 8% 33%	4364
	11th to 20th	Day	18% 8% 2 6% 4 4 4 4 6% 8% 35%	4304
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 42%	4662
September	1st to 10th	Day	16% 9% 3 7% 4 4 4 3 5% 8% 38%	2400
	11th to 20th	Day	16% 7% 2 5% 5% 3 4 3 5% 8% 43%	2303
	21st to end	Day	23% 10% 3 7% 4 4 4 3 4 5% 33%	2149
October	1st to 10th	Day	20% 12% 3 7% 3 4 4 3 4 6% 35%	2000
	11th to 20th	Day	25% 16% 3 7% 6% 4 3 3 5% 5% 23%	2000
	21st to end	Day	30% 18% 5% 8% 4 3 2 3 3 4 19%	2190
November	1st to 10th	Day	21% 16% 6% 9% 5% 4 4 3 5% 6% 23%	1656
	11th to 20th	Day	18% 20% 8% 10% 5% 5% 3 2 4 5% 19%	1680
	21st to end	Day	22% 25% 7% 10% 5% 5% 3 3 3 4 12%	1680
December	1st to 10th	Day	16% 23% 10% 19% 6% 5% 4 3 3 3 9%	2680
	11th to 20th	Day	18% 20% 7% 15% 7% 5% 3 2 2 3 19%	3066
	21st to end	Day	19% 23% 9% 15% 6% 3 2 2 3 4 13%	3575
January	1st to 10th	Night	11% 18% 10% 18% 9% 6% 4 3 4 3 14%	8831
	11th to 20th	Night	9% 22% 10% 19% 8% 5% 4 3 3 4 14%	8224
	21st to end	Night	8% 18% 10% 17% 7% 6% 5% 3 4 4 17%	8401
February	1st to 10th	Night	11% 17% 8% 13% 7% 5% 4 4 5% 5% 20%	2730
	11th to 20th	Night	11% 16% 7% 14% 7% 5% 4 4 5% 5% 22%	2663
	21st to end	Night	12% 20% 7% 14% 7% 6% 4 2 5% 4 19%	2244
March	1st to 10th	Night	14% 16% 5% 11% 5% 4 3 3 4 6% 28%	5020
	11th to 20th	Night	11% 16% 7% 11% 5% 5% 5% 3 5% 7% 26%	5089
	21st to end	Night	19% 13% 6% 8% 6% 4 4 3 4 4 29%	5588
April	1st to 10th	Night	20% 17% 4 7% 4 3 4 3 4 5% 28%	2118
	11th to 20th	Night	18% 12% 3 6% 5% 4 4 3 4 5% 35%	1967
	21st to end	Night	19% 12% 4 7% 5% 4 3 3 5% 5% 31%	1890
May	1st to 10th	Night	15% 10% 3 7% 4 4 5% 4 7% 7% 34%	5024
	11th to 20th	Night	17% 7% 2 6% 3 3 4 3 5% 7% 40%	4639
	21st to end	Night	17% 9% 2 6% 4 3 4 2 5% 8% 41%	5114
June	1st to 10th	Night	13% 9% 3 8% 6% 5% 4 4 5% 7% 35%	1598
	11th to 20th	Night	15% 6% 3 6% 4 4 4 4 6% 8% 41%	1470
	21st to end	Night	15% 9% 3 7% 4 4 4 4 6% 8% 36%	1470
July	1st to 10th	Night	14% 6% 3 7% 4 4 4 3 6% 8% 41%	4110
	11th to 20th	Night	14% 6% 2 6% 4 3 4 3 5% 7% 47%	4338
	21st to end	Night	13% 6% 2 5% 3 3 4 3 5% 7% 47%	5275
August	1st to 10th	Night	12% 6% 2 5% 4 5% 5% 4 6% 8% 43%	3005
	11th to 20th	Night	17% 8% 3 6% 3 4 4 3 5% 7% 41%	2965
	21st to end	Night	15% 5% 2 5% 4 4 3 3 4 7% 48%	3400
September	1st to 10th	Night	14% 5% 2 6% 4 4 4 3 5% 7% 47%	2000
	11th to 20th	Night	14% 6% 2 5% 4 4 4 2 5% 6% 48%	2094
	21st to end	Night	17% 8% 2 7% 4 4 3 3 5% 6% 40%	2250
October	1st to 10th	Night	18% 9% 3 7% 4 4 3 3 5% 6% 37%	2400
	11th to 20th	Night	24% 13% 4 8% 5% 4 4 3 4 6% 25%	2400
	21st to end	Night	26% 18% 4 9% 4 4 3 3 4 4 22%	2647
November	1st to 10th	Night	21% 16% 4 8% 5% 3 4 3 4 6% 27%	2862
	11th to 20th	Night	18% 17% 5% 9% 5% 5% 4 3 5% 5% 23%	2940
	21st to end	Night	22% 21% 7% 11% 6% 4 4 2 4 5% 14%	2940
December	1st to 10th	Night	16% 26% 8% 14% 8% 5% 4 3 3 3 9%	4720
	11th to 20th	Night	16% 22% 8% 14% 7% 4 3 3 4 4 17%	5348
	21st to end	Night	20% 20% 8% 16% 6% 4 3 2 3 4 15%	7620

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	71% 3 7% 13% 5% 1	4095
	11th to 20th	Day	77% 4 5% 7% 7% 1	4665
	21st to end	Day	72% 3 5% 10% 8% 1	5780
February	1st to 10th	Day	71% 3 6% 13% 6% 1	1890
	11th to 20th	Day	65% 4 10% 12% 8% 1	1852
	21st to end	Day	69% 4 7% 13% 7%	1557
March	1st to 10th	Day	62% 5% 9% 7% 14% 2	5042
	11th to 20th	Day	58% 6% 13% 15% 7% 1	5090
	21st to end	Day	59% 5% 7% 18% 10% 2	5586
April	1st to 10th	Day	59% 5% 9% 16% 9% 2	2501
	11th to 20th	Day	54% 5% 8% 21% 11% 1	2620
	21st to end	Day	55% 5% 8% 17% 13% 2	2730
May	1st to 10th	Day	52% 6% 10% 19% 9% 4	7884
	11th to 20th	Day	47% 6% 9% 24% 13% 1	8225
	21st to end	Day	48% 5% 10% 21% 15% 2	9061
June	1st to 10th	Day	51% 7% 9% 20% 13%	3017
	11th to 20th	Day	46% 7% 10% 24% 13% 1	3150
	21st to end	Day	51% 7% 12% 19% 10% 1	3150
July	1st to 10th	Day	43% 7% 15% 24% 11% 1	8806
	11th to 20th	Day	35% 5% 14% 36% 10%	8542
	21st to end	Day	38% 5% 14% 30% 12%	8603
August	1st to 10th	Day	46% 7% 13% 26% 8%	4351
	11th to 20th	Day	45% 6% 14% 26% 8%	4343
	21st to end	Day	38% 6% 13% 33% 10%	4662
September	1st to 10th	Day	44% 7% 14% 23% 12%	2400
	11th to 20th	Day	40% 7% 12% 29% 12%	2303
	21st to end	Day	54% 6% 10% 23% 8%	2149
October	1st to 10th	Day	51% 6% 12% 23% 9% 1	3260
	11th to 20th	Day	55% 7% 11% 21% 6%	3240
	21st to end	Day	68% 4 11% 11% 4	3516
November	1st to 10th	Day	62% 7% 12% 15% 5%	1656
	11th to 20th	Day	66% 7% 10% 10% 6% 1	1680
	21st to end	Day	77% 6% 7% 8% 3	1680
December	1st to 10th	Day	81% 4 7% 6% 1 1	2680
	11th to 20th	Day	72% 4 5% 12% 7%	3066
	21st to end	Day	76% 3 4 12% 5%	3575
January	1st to 10th	Night	74% 5% 6% 10% 4	8831
	11th to 20th	Night	75% 5% 6% 6% 7%	8269
	21st to end	Night	71% 3 6% 10% 9% 1	8401
February	1st to 10th	Night	65% 6% 9% 13% 6% 1	2730
	11th to 20th	Night	64% 5% 9% 16% 6% 1	2665
	21st to end	Night	68% 5% 8% 13% 6% 1	2244
March	1st to 10th	Night	57% 5% 9% 12% 12% 4	5030
	11th to 20th	Night	57% 6% 13% 14% 8% 1	5090
	21st to end	Night	58% 5% 6% 17% 12% 2	5588
April	1st to 10th	Night	58% 5% 8% 18% 10% 2	2118
	11th to 20th	Night	51% 5% 7% 22% 14% 1	1967
	21st to end	Night	54% 6% 7% 16% 14% 2	1890
May	1st to 10th	Night	46% 6% 8% 26% 11% 3	5031
	11th to 20th	Night	41% 8% 10% 23% 16% 2	4640
	21st to end	Night	43% 5% 9% 28% 15% 1	5115
June	1st to 10th	Night	48% 6% 11% 19% 13% 3	1598
	11th to 20th	Night	40% 6% 11% 26% 17% 1	1470
	21st to end	Night	44% 8% 13% 22% 11% 1	1470
July	1st to 10th	Night	40% 6% 14% 27% 11% 1	4075
	11th to 20th	Night	37% 4 14% 33% 11% 1	4296
	21st to end	Night	36% 5% 12% 34% 13%	5155
August	1st to 10th	Night	38% 7% 16% 25% 13% 2	2994
	11th to 20th	Night	42% 7% 16% 25% 9% 1	2992
	21st to end	Night	37% 5% 13% 33% 12% 1	3400
September	1st to 10th	Night	37% 8% 14% 28% 12% 1	2000
	11th to 20th	Night	37% 7% 14% 30% 13%	2094
	21st to end	Night	45% 6% 13% 24% 12%	2250
October	1st to 10th	Night	43% 5% 10% 29% 14%	3920
	11th to 20th	Night	53% 6% 13% 19% 8%	3899
	21st to end	Night	61% 5% 16% 12% 5%	4271
November	1st to 10th	Night	58% 6% 12% 18% 5%	2862
	11th to 20th	Night	62% 7% 11% 13% 6% 1	2940
	21st to end	Night	73% 7% 9% 8% 3	2940
December	1st to 10th	Night	80% 5% 7% 6% 2	4720
	11th to 20th	Night	72% 3 6% 10% 8%	5348
	21st to end	Night	76% 3 5% 10% 5%	7620

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	20% 31% 30% 13% 5% 1	220
	11th to 20th	Day	24% 21% 35% 16% 4	242
	21st to end	Day	25% 18% 36% 16% 4	363
February	1st to 10th	Day	31% 26% 33% 7% 2 1	330
	11th to 20th	Day	24% 30% 36% 8% 1	330
	21st to end	Day	36% 19% 37% 6% 1	273
March	1st to 10th	Day	29% 22% 36% 11% 2	537
	11th to 20th	Day	26% 25% 32% 13% 4 1	540
	21st to end	Day	31% 23% 28% 14% 3 1	594
April	1st to 10th	Day	30% 22% 30% 13% 4 1	540
	11th to 20th	Day	37% 18% 23% 13% 7% 2	532
	21st to end	Day	31% 18% 30% 14% 5% 1	540
May	1st to 10th	Day	30% 15% 29% 20% 5% 1	543
	11th to 20th	Day	22% 21% 27% 19% 9% 2	567
	21st to end	Day	24% 18% 30% 17% 10% 1	617
June	1st to 10th	Day	24% 14% 33% 23% 5% 1	647
	11th to 20th	Day	21% 16% 35% 18% 8% 2	780
	21st to end	Day	24% 14% 35% 18% 8% 1	780
July	1st to 10th	Day	15% 12% 35% 29% 8% 1	771
	11th to 20th	Day	17% 14% 30% 28% 9% 2	680
	21st to end	Day	15% 11% 33% 27% 11% 2	620
August	1st to 10th	Day	17% 10% 30% 28% 11% 4	566
	11th to 20th	Day	18% 7% 30% 27% 13% 5%	559
	21st to end	Day	21% 11% 31% 22% 11% 3	619
September	1st to 10th	Day	20% 14% 31% 20% 11% 5%	530
	11th to 20th	Day	18% 8% 27% 25% 12% 9%	530
	21st to end	Day	25% 15% 25% 24% 10% 2	530
October	1st to 10th	Day	25% 16% 25% 21% 11% 2	530
	11th to 20th	Day	31% 18% 34% 13% 2 1	530
	21st to end	Day	38% 17% 28% 14% 2	573
November	1st to 10th	Day	36% 18% 32% 11% 2	225
	11th to 20th	Day	29% 25% 36% 7% 3 1	220
	21st to end	Day	32% 25% 35% 6% 1 1	220
December	1st to 10th	Day	30% 20% 34% 14% 2	220
	11th to 20th	Day	32% 22% 34% 10% 3	220
	21st to end	Day	32% 24% 28% 12% 4 1	242
January	1st to 10th	Night	26% 19% 34% 16% 4	1050
	11th to 20th	Night	28% 19% 32% 17% 4	885
	21st to end	Night	21% 15% 34% 22% 7% 1	924
February	1st to 10th	Night	21% 24% 33% 19% 3	840
	11th to 20th	Night	20% 22% 35% 19% 4	823
	21st to end	Night	21% 25% 33% 18% 2	692
March	1st to 10th	Night	21% 24% 33% 18% 4	840
	11th to 20th	Night	25% 22% 32% 17% 5% 1	840
	21st to end	Night	22% 17% 32% 22% 6% 1	924
April	1st to 10th	Night	31% 15% 32% 18% 4	840
	11th to 20th	Night	28% 18% 24% 21% 9% 1	723
	21st to end	Night	28% 12% 30% 22% 8%	630
May	1st to 10th	Night	23% 8% 30% 29% 9% 1	551
	11th to 20th	Night	21% 11% 34% 27% 7% 1	414
	21st to end	Night	19% 10% 36% 27% 8%	455
June	1st to 10th	Night	18% 9% 32% 31% 9%	420
	11th to 20th	Night	19% 11% 27% 34% 9%	420
	21st to end	Night	18% 7% 31% 31% 12% 1	420
July	1st to 10th	Night	15% 5% 30% 38% 12%	410
	11th to 20th	Night	16% 6% 28% 34% 17%	408
	21st to end	Night	14% 5% 28% 36% 17% 1	524
August	1st to 10th	Night	17% 4 22% 38% 17% 2	627
	11th to 20th	Night	16% 4 24% 34% 20% 3	624
	21st to end	Night	20% 9% 26% 28% 16% 2	744
September	1st to 10th	Night	18% 7% 29% 29% 15% 2	800
	11th to 20th	Night	20% 7% 26% 25% 20% 3	800
	21st to end	Night	22% 9% 24% 28% 15% 2	800
October	1st to 10th	Night	23% 12% 30% 25% 9% 1	800
	11th to 20th	Night	32% 14% 29% 17% 7% 1	800
	21st to end	Night	36% 16% 27% 18% 3	880
November	1st to 10th	Night	33% 13% 29% 18% 6% 1	820
	11th to 20th	Night	29% 18% 30% 18% 5%	840
	21st to end	Night	33% 19% 28% 18% 2	840
December	1st to 10th	Night	32% 19% 30% 15% 5%	840
	11th to 20th	Night	28% 19% 34% 16% 2 1	840
	21st to end	Night	32% 18% 30% 17% 3	1134

Page generated at 2026-08-27 04:07:10. Version ac07

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