South Baymouth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Baymouth 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	14% 10% 4 8% 5% 4 4 4 5% 7% 36%	144128
	Night	14% 12% 4 10% 5% 5% 4 3 5% 6% 31%	138280
Transparency	Day	46% 7% 13% 22% 11% 1	147642
	Night	52% 7% 12% 18% 10% 1	142855
Seeing	Day	18% 12% 30% 26% 11% 2	17733
	Night	20% 13% 29% 25% 11% 2	26897

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% 17% 8% 13% 5% 4 3 2 3 5% 24%	4153
	11th to 20th	Day	10% 19% 9% 19% 10% 5% 5% 3 4 3 13%	4679
	21st to end	Day	10% 15% 7% 16% 8% 6% 5% 4 5% 6% 19%	5494
February	1st to 10th	Day	11% 17% 6% 13% 8% 5% 4 3 4 5% 23%	1890
	11th to 20th	Day	12% 14% 5% 12% 6% 6% 5% 5% 5% 6% 26%	1843
	21st to end	Day	11% 15% 5% 13% 6% 5% 4 4 6% 6% 25%	1719
March	1st to 10th	Day	16% 10% 3 8% 4 4 5% 3 5% 7% 35%	4783
	11th to 20th	Day	11% 12% 5% 10% 6% 6% 5% 5% 6% 7% 29%	5090
	21st to end	Day	16% 10% 4 8% 5% 4 4 3 5% 5% 34%	5586
April	1st to 10th	Day	17% 11% 3 6% 5% 4 4 3 6% 7% 33%	2464
	11th to 20th	Day	18% 8% 2 7% 4 3 4 3 5% 6% 39%	2702
	21st to end	Day	18% 9% 3 7% 4 4 3 3 5% 8% 36%	2730
May	1st to 10th	Day	13% 6% 2 7% 4 4 4 3 5% 7% 44%	7642
	11th to 20th	Day	14% 8% 3 8% 5% 4 4 4 5% 6% 40%	7917
	21st to end	Day	15% 7% 3 7% 4 4 4 3 5% 6% 43%	9353
June	1st to 10th	Day	13% 6% 2 6% 6% 5% 5% 4 6% 7% 40%	3150
	11th to 20th	Day	11% 6% 3 6% 5% 4 5% 5% 6% 9% 42%	3150
	21st to end	Day	14% 7% 2 6% 4 4 5% 4 7% 8% 39%	3150
July	1st to 10th	Day	12% 7% 3 8% 5% 5% 5% 4 5% 8% 38%	8879
	11th to 20th	Day	8% 5% 2 6% 4 4 4 3 6% 8% 51%	8686
	21st to end	Day	7% 5% 2 6% 4 4 4 3 5% 9% 50%	8694
August	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 44%	4364
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 5% 8% 46%	4304
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 45%	4792
September	1st to 10th	Day	11% 6% 2 7% 5% 5% 4 4 6% 8% 43%	2361
	11th to 20th	Day	12% 4 2 5% 4 3 5% 4 6% 8% 49%	2200
	21st to end	Day	16% 7% 3 7% 5% 4 4 4 6% 8% 38%	2200
October	1st to 10th	Day	16% 8% 3 6% 5% 4 4 4 6% 6% 38%	2060
	11th to 20th	Day	23% 10% 3 8% 6% 4 4 4 5% 7% 28%	2000
	21st to end	Day	23% 11% 3 8% 7% 5% 5% 3 5% 6% 23%	2048
November	1st to 10th	Day	18% 13% 4 9% 5% 4 4 4 5% 8% 25%	1827
	11th to 20th	Day	17% 16% 5% 11% 5% 5% 5% 3 6% 6% 21%	1680
	21st to end	Day	22% 22% 6% 10% 6% 4 4 4 5% 5% 13%	1680
December	1st to 10th	Day	15% 24% 7% 11% 6% 5% 4 3 5% 5% 14%	2614
	11th to 20th	Day	21% 19% 6% 14% 5% 4 5% 3 4 5% 13%	2691
	21st to end	Day	27% 24% 6% 11% 5% 4 3 3 5% 4 8%	3553
January	1st to 10th	Night	12% 17% 8% 13% 5% 5% 4 3 4 6% 22%	8771
	11th to 20th	Night	10% 21% 7% 18% 7% 5% 4 3 5% 5% 15%	8236
	21st to end	Night	8% 16% 8% 16% 8% 7% 4 3 4 5% 21%	8700
February	1st to 10th	Night	11% 17% 6% 13% 6% 6% 5% 4 5% 4 23%	2730
	11th to 20th	Night	10% 16% 5% 12% 7% 5% 5% 4 5% 5% 27%	2663
	21st to end	Night	14% 17% 4 9% 6% 4 4 4 6% 6% 25%	2085
March	1st to 10th	Night	16% 9% 4 8% 5% 4 4 3 4 6% 39%	5277
	11th to 20th	Night	12% 10% 3 8% 6% 5% 5% 4 6% 7% 34%	5089
	21st to end	Night	17% 10% 5% 10% 5% 4 4 3 4 5% 34%	5588
April	1st to 10th	Night	19% 9% 2 7% 5% 4 4 4 5% 6% 34%	2174
	11th to 20th	Night	18% 8% 3 6% 3 4 3 4 5% 8% 38%	1867
	21st to end	Night	17% 10% 4 8% 5% 5% 4 3 5% 6% 34%	1890
May	1st to 10th	Night	13% 7% 2 8% 5% 4 5% 4 5% 7% 39%	5257
	11th to 20th	Night	14% 7% 3 8% 4 4 4 4 4 6% 43%	4941
	21st to end	Night	16% 8% 3 7% 3 3 3 3 5% 6% 42%	4833
June	1st to 10th	Night	11% 8% 2 6% 5% 4 5% 5% 6% 7% 41%	1470
	11th to 20th	Night	11% 7% 2 5% 3 4 6% 4 6% 8% 43%	1470
	21st to end	Night	12% 6% 3 7% 5% 5% 6% 4 6% 7% 40%	1470
July	1st to 10th	Night	11% 5% 3 7% 5% 4 5% 4 5% 8% 43%	4110
	11th to 20th	Night	9% 4 2 5% 4 4 5% 4 6% 8% 49%	4287
	21st to end	Night	9% 6% 3 7% 4 4 4 3 5% 8% 48%	5398
August	1st to 10th	Night	8% 6% 2 7% 4 5% 5% 4 6% 8% 45%	3005
	11th to 20th	Night	11% 5% 2 6% 4 4 5% 3 7% 8% 45%	2965
	21st to end	Night	9% 6% 3 6% 4 4 4 3 5% 7% 50%	3304
September	1st to 10th	Night	12% 5% 2 6% 3 4 4 4 5% 8% 47%	2015
	11th to 20th	Night	10% 4 2 5% 4 5% 4 3 6% 7% 51%	2200
	21st to end	Night	17% 6% 2 6% 5% 4 5% 3 5% 8% 39%	2200
October	1st to 10th	Night	17% 7% 3 7% 6% 4 4 4 5% 6% 37%	2340
	11th to 20th	Night	23% 9% 3 8% 6% 5% 4 3 5% 7% 26%	2400
	21st to end	Night	23% 11% 4 8% 6% 4 4 3 5% 6% 25%	2790
November	1st to 10th	Night	18% 14% 3 7% 5% 5% 5% 4 5% 7% 28%	2689
	11th to 20th	Night	17% 18% 5% 10% 7% 5% 5% 3 5% 6% 20%	2940
	21st to end	Night	21% 21% 6% 9% 6% 5% 4 3 5% 5% 16%	2940
December	1st to 10th	Night	17% 21% 6% 11% 5% 5% 4 3 5% 5% 18%	4783
	11th to 20th	Night	18% 20% 6% 16% 6% 5% 4 3 4 4 14%	5736
	21st to end	Night	24% 22% 7% 11% 4 5% 4 3 5% 4 12%	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	63% 8% 11% 14% 3 1	4154
	11th to 20th	Day	78% 6% 5% 6% 5%	4710
	21st to end	Day	65% 7% 9% 12% 7%	5494
February	1st to 10th	Day	64% 7% 11% 14% 4	1890
	11th to 20th	Day	58% 8% 14% 13% 6%	1852
	21st to end	Day	57% 8% 13% 18% 4	1719
March	1st to 10th	Day	48% 7% 14% 13% 15% 3	4786
	11th to 20th	Day	53% 7% 14% 16% 8% 1	5090
	21st to end	Day	49% 8% 15% 15% 11% 2	5586
April	1st to 10th	Day	48% 6% 13% 20% 11% 1	2464
	11th to 20th	Day	45% 5% 10% 25% 14% 1	2702
	21st to end	Day	45% 5% 13% 21% 13% 3	2730
May	1st to 10th	Day	37% 7% 12% 27% 14% 3	7651
	11th to 20th	Day	41% 7% 10% 22% 17% 2	7921
	21st to end	Day	41% 5% 11% 23% 17% 3	9354
June	1st to 10th	Day	39% 7% 12% 25% 14% 2	3150
	11th to 20th	Day	37% 7% 13% 27% 16% 1	3150
	21st to end	Day	42% 7% 13% 24% 13% 2	3150
July	1st to 10th	Day	42% 7% 15% 23% 12% 1	8806
	11th to 20th	Day	29% 6% 14% 40% 11% 1	8605
	21st to end	Day	30% 7% 13% 32% 18%	8503
August	1st to 10th	Day	33% 8% 17% 29% 13% 1	4351
	11th to 20th	Day	35% 6% 18% 30% 11%	4343
	21st to end	Day	33% 9% 15% 32% 9% 1	4791
September	1st to 10th	Day	37% 8% 16% 28% 10% 1	2361
	11th to 20th	Day	32% 7% 18% 31% 11% 1	2200
	21st to end	Day	44% 9% 15% 22% 10%	2200
October	1st to 10th	Day	37% 6% 11% 28% 18%	3359
	11th to 20th	Day	46% 6% 15% 25% 8%	3240
	21st to end	Day	56% 6% 14% 17% 6%	3285
November	1st to 10th	Day	56% 8% 13% 18% 5%	1827
	11th to 20th	Day	63% 7% 14% 11% 5%	1680
	21st to end	Day	72% 6% 12% 8% 2	1680
December	1st to 10th	Day	72% 6% 14% 7% 1	2614
	11th to 20th	Day	72% 6% 10% 10% 2	2691
	21st to end	Day	80% 8% 6% 5% 1	3553
January	1st to 10th	Night	62% 9% 13% 13% 4 1	8771
	11th to 20th	Night	72% 6% 7% 9% 5%	8280
	21st to end	Night	67% 6% 9% 9% 8% 1	8700
February	1st to 10th	Night	64% 5% 11% 15% 5% 1	2730
	11th to 20th	Night	58% 8% 12% 15% 6% 1	2665
	21st to end	Night	58% 7% 12% 16% 7%	2085
March	1st to 10th	Night	46% 6% 14% 17% 13% 3	5287
	11th to 20th	Night	48% 6% 17% 20% 9% 1	5090
	21st to end	Night	52% 6% 10% 17% 13% 2	5588
April	1st to 10th	Night	50% 5% 11% 20% 13% 1	2174
	11th to 20th	Night	44% 5% 9% 22% 18% 2	1867
	21st to end	Night	50% 6% 9% 17% 15% 3	1890
May	1st to 10th	Night	42% 6% 9% 24% 15% 3	5264
	11th to 20th	Night	41% 6% 9% 23% 19% 2	4942
	21st to end	Night	42% 5% 8% 24% 17% 4	4834
June	1st to 10th	Night	38% 7% 10% 23% 19% 3	1470
	11th to 20th	Night	35% 8% 13% 23% 19% 2	1470
	21st to end	Night	41% 7% 14% 22% 13% 2	1470
July	1st to 10th	Night	38% 7% 12% 24% 16% 3	4075
	11th to 20th	Night	30% 7% 12% 38% 13%	4245
	21st to end	Night	34% 5% 11% 29% 20% 1	5276
August	1st to 10th	Night	34% 8% 14% 29% 14% 1	2994
	11th to 20th	Night	35% 8% 18% 26% 13%	2992
	21st to end	Night	33% 7% 15% 32% 12% 1	3304
September	1st to 10th	Night	35% 7% 15% 28% 13% 2	2015
	11th to 20th	Night	32% 7% 16% 34% 11% 1	2200
	21st to end	Night	43% 8% 15% 23% 11%	2200
October	1st to 10th	Night	36% 5% 10% 31% 18%	3821
	11th to 20th	Night	46% 6% 15% 23% 10%	3899
	21st to end	Night	52% 7% 18% 18% 5%	4503
November	1st to 10th	Night	55% 7% 12% 19% 6%	2689
	11th to 20th	Night	66% 7% 12% 11% 4	2940
	21st to end	Night	70% 7% 11% 9% 2	2940
December	1st to 10th	Night	68% 7% 15% 8% 2	4783
	11th to 20th	Night	73% 7% 8% 8% 3	5735
	21st to end	Night	76% 9% 8% 5% 2	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	26% 19% 34% 17% 4	231
	11th to 20th	Day	21% 18% 40% 18% 4	330
	21st to end	Day	24% 14% 33% 21% 8%	363
February	1st to 10th	Day	22% 25% 34% 15% 5%	330
	11th to 20th	Day	20% 22% 38% 17% 3 1	330
	21st to end	Day	24% 26% 36% 12% 2	273
March	1st to 10th	Day	21% 18% 38% 19% 4	419
	11th to 20th	Day	20% 16% 37% 21% 5% 1	540
	21st to end	Day	22% 17% 32% 22% 5% 1	594
April	1st to 10th	Day	23% 15% 31% 22% 8% 1	540
	11th to 20th	Day	26% 16% 27% 18% 10% 3	532
	21st to end	Day	25% 13% 35% 19% 8% 1	540
May	1st to 10th	Day	19% 10% 36% 25% 8% 1	543
	11th to 20th	Day	16% 11% 29% 29% 13% 2	567
	21st to end	Day	14% 7% 33% 28% 14% 3	715
June	1st to 10th	Day	13% 8% 32% 32% 14% 1	780
	11th to 20th	Day	13% 8% 31% 34% 13% 1	780
	21st to end	Day	16% 8% 30% 32% 11% 2	780
July	1st to 10th	Day	9% 4 27% 41% 17% 2	771
	11th to 20th	Day	10% 7% 28% 38% 14% 4	768
	21st to end	Day	10% 4 29% 38% 15% 3	744
August	1st to 10th	Day	12% 6% 25% 34% 20% 4	566
	11th to 20th	Day	11% 4 23% 36% 19% 7%	559
	21st to end	Day	13% 8% 27% 30% 18% 4	619
September	1st to 10th	Day	12% 10% 28% 26% 18% 6%	530
	11th to 20th	Day	12% 6% 22% 31% 20% 9%	530
	21st to end	Day	19% 11% 22% 27% 17% 3	530
October	1st to 10th	Day	18% 18% 24% 26% 13% 2	530
	11th to 20th	Day	24% 18% 33% 18% 6% 1	530
	21st to end	Day	26% 22% 34% 15% 3	431
November	1st to 10th	Day	30% 18% 33% 16% 4	316
	11th to 20th	Day	26% 20% 34% 17% 3	220
	21st to end	Day	31% 25% 31% 12% 1	220
December	1st to 10th	Day	28% 23% 29% 15% 5%	220
	11th to 20th	Day	32% 24% 32% 10% 2	220
	21st to end	Day	33% 25% 31% 8% 2 1	242
January	1st to 10th	Night	22% 21% 32% 20% 4	1050
	11th to 20th	Night	25% 19% 31% 20% 5% 1	1050
	21st to end	Night	21% 13% 36% 22% 7% 1	1029
February	1st to 10th	Night	19% 20% 35% 20% 5%	840
	11th to 20th	Night	18% 18% 33% 24% 7%	823
	21st to end	Night	21% 17% 36% 22% 5%	692
March	1st to 10th	Night	18% 17% 37% 22% 6% 1	840
	11th to 20th	Night	18% 16% 35% 23% 7% 1	840
	21st to end	Night	20% 12% 32% 29% 8% 1	924
April	1st to 10th	Night	24% 12% 34% 25% 5% 1	775
	11th to 20th	Night	22% 11% 30% 24% 11% 2	623
	21st to end	Night	21% 11% 28% 25% 13% 1	630
May	1st to 10th	Night	14% 7% 28% 34% 14% 2	630
	11th to 20th	Night	15% 8% 27% 33% 16% 1	523
	21st to end	Night	15% 5% 26% 34% 19% 2	455
June	1st to 10th	Night	15% 4 30% 34% 15% 2	420
	11th to 20th	Night	12% 8% 23% 38% 19% 2	420
	21st to end	Night	14% 4 20% 39% 22% 2	420
July	1st to 10th	Night	10% 3 20% 44% 23% 1	410
	11th to 20th	Night	9% 3 20% 40% 25% 4	468
	21st to end	Night	9% 4 23% 35% 26% 3	690
August	1st to 10th	Night	10% 4 20% 38% 24% 4	627
	11th to 20th	Night	11% 4 17% 33% 29% 5%	624
	21st to end	Night	12% 4 22% 32% 24% 6%	687
September	1st to 10th	Night	14% 7% 26% 27% 19% 8%	745
	11th to 20th	Night	12% 6% 23% 30% 19% 11%	800
	21st to end	Night	18% 9% 24% 26% 20% 4	800
October	1st to 10th	Night	21% 11% 26% 27% 14% 2	800
	11th to 20th	Night	28% 15% 28% 20% 10%	800
	21st to end	Night	27% 16% 31% 20% 5% 1	880
November	1st to 10th	Night	26% 16% 30% 21% 7% 1	820
	11th to 20th	Night	26% 22% 28% 17% 7%	840
	21st to end	Night	33% 18% 30% 15% 4	840
December	1st to 10th	Night	30% 23% 29% 12% 5%	877
	11th to 20th	Night	28% 22% 32% 13% 4 1	1050
	21st to end	Night	34% 18% 30% 14% 5%	1155

Page generated at 2026-08-27 04:07:09. Version ac07

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