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 2024-10-25.

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% 3 8% 5% 4 4 4 5% 7% 35%	101437
	Night	15% 12% 4 9% 5% 5% 4 3 5% 6% 31%	97436
Transparency	Day	47% 7% 13% 21% 11% 1	101189
	Night	53% 7% 12% 18% 9% 1	97304
Seeing	Day	18% 13% 30% 26% 11% 2	15307
	Night	21% 13% 29% 24% 11% 2	24528

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	19% 19% 11% 13% 5% 4 3 2 3 5% 17%	2239
	11th to 20th	Day	11% 15% 7% 20% 12% 6% 5% 3 5% 4 12%	2530
	21st to end	Day	16% 20% 7% 13% 7% 5% 4 4 5% 5% 14%	2967
February	1st to 10th	Day	11% 17% 7% 13% 8% 5% 5% 4 4 5% 22%	1710
	11th to 20th	Day	12% 14% 5% 12% 5% 5% 4 4 5% 6% 27%	1663
	21st to end	Day	11% 15% 5% 13% 6% 5% 4 4 6% 6% 26%	1559
March	1st to 10th	Day	16% 11% 4 7% 4 4 5% 3 5% 7% 34%	3263
	11th to 20th	Day	10% 13% 5% 10% 6% 6% 5% 4 5% 7% 30%	3480
	21st to end	Day	13% 10% 3 8% 5% 4 5% 4 6% 7% 36%	3815
April	1st to 10th	Day	17% 11% 3 6% 5% 4 4 3 6% 7% 32%	2229
	11th to 20th	Day	18% 8% 2 7% 5% 4 4 4 5% 7% 38%	2442
	21st to end	Day	19% 9% 3 7% 4 4 3 3 5% 7% 37%	2470
May	1st to 10th	Day	15% 6% 2 7% 5% 4 4 3 5% 7% 42%	4108
	11th to 20th	Day	13% 7% 3 8% 4 4 4 4 5% 7% 41%	4232
	21st to end	Day	14% 6% 2 7% 5% 4 4 3 5% 6% 45%	4990
June	1st to 10th	Day	13% 6% 2 6% 6% 5% 5% 4 6% 8% 39%	2850
	11th to 20th	Day	10% 6% 3 5% 5% 4 5% 5% 6% 9% 42%	2850
	21st to end	Day	14% 7% 2 6% 4 4 5% 4 7% 7% 39%	2850
July	1st to 10th	Day	13% 8% 3 8% 4 5% 4 4 5% 7% 39%	4760
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 6% 8% 50%	4650
	21st to end	Day	9% 5% 2 5% 4 4 4 3 5% 8% 52%	4656
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 10% 44%	4104
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 5% 8% 46%	4044
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 46%	4532
September	1st to 10th	Day	11% 6% 2 7% 5% 4 4 4 6% 8% 44%	2244
	11th to 20th	Day	12% 4 2 5% 4 3 5% 3 6% 8% 49%	2090
	21st to end	Day	16% 6% 3 7% 5% 4 4 4 6% 8% 39%	2090
October	1st to 10th	Day	16% 8% 3 6% 5% 4 4 4 6% 6% 36%	1957
	11th to 20th	Day	23% 11% 3 8% 6% 4 4 4 4 6% 27%	1900
	21st to end	Day	24% 12% 3 8% 7% 5% 4 3 4 6% 23%	1889
November	1st to 10th	Day	17% 13% 4 9% 5% 4 4 5% 5% 8% 25%	1650
	11th to 20th	Day	17% 16% 5% 11% 5% 5% 5% 3 6% 6% 20%	1520
	21st to end	Day	24% 21% 6% 9% 6% 4 4 4 5% 5% 13%	1520
December	1st to 10th	Day	15% 24% 7% 12% 6% 5% 5% 3 4 5% 14%	1482
	11th to 20th	Day	20% 20% 6% 13% 6% 5% 5% 3 4 4 16%	1671
	21st to end	Day	27% 24% 5% 12% 6% 5% 4 3 4 3 8%	2431
January	1st to 10th	Night	16% 20% 10% 14% 6% 4 4 3 4 5% 16%	4716
	11th to 20th	Night	12% 16% 7% 21% 8% 5% 5% 4 5% 4 14%	4440
	21st to end	Night	15% 20% 7% 13% 7% 5% 4 3 4 5% 18%	4692
February	1st to 10th	Night	11% 18% 6% 13% 7% 6% 4 4 5% 4 22%	2470
	11th to 20th	Night	10% 15% 5% 11% 7% 5% 5% 4 5% 5% 27%	2403
	21st to end	Night	14% 17% 4 9% 6% 4 5% 4 6% 6% 25%	1893
March	1st to 10th	Night	13% 8% 3 7% 5% 5% 4 3 5% 6% 42%	3577
	11th to 20th	Night	8% 12% 4 8% 5% 5% 4 3 5% 6% 38%	3479
	21st to end	Night	11% 9% 5% 9% 5% 5% 5% 3 5% 7% 36%	3817
April	1st to 10th	Night	20% 9% 2 7% 4 4 4 4 5% 6% 35%	1967
	11th to 20th	Night	19% 8% 3 6% 3 4 4 4 5% 8% 37%	1687
	21st to end	Night	18% 10% 4 8% 5% 5% 4 3 5% 6% 34%	1710
May	1st to 10th	Night	15% 6% 3 9% 6% 5% 4 4 5% 5% 39%	2833
	11th to 20th	Night	10% 6% 3 8% 5% 5% 5% 5% 6% 8% 39%	2659
	21st to end	Night	13% 7% 3 7% 4 4 3 4 5% 7% 41%	2587
June	1st to 10th	Night	11% 8% 2 6% 5% 4 5% 5% 7% 7% 39%	1330
	11th to 20th	Night	10% 6% 2 5% 4 4 7% 4 7% 8% 44%	1330
	21st to end	Night	12% 6% 2 7% 5% 5% 5% 4 6% 7% 40%	1330
July	1st to 10th	Night	12% 6% 2 6% 5% 4 4 4 5% 8% 45%	2210
	11th to 20th	Night	10% 4 2 5% 4 3 6% 4 6% 7% 51%	2303
	21st to end	Night	8% 5% 3 7% 4 4 4 3 5% 6% 51%	2900
August	1st to 10th	Night	8% 6% 2 7% 4 4 5% 5% 6% 8% 45%	2825
	11th to 20th	Night	11% 5% 2 6% 3 4 5% 3 7% 8% 45%	2785
	21st to end	Night	8% 6% 3 6% 4 4 4 3 5% 7% 50%	3124
September	1st to 10th	Night	12% 5% 2 6% 3 4 4 4 5% 8% 47%	1914
	11th to 20th	Night	10% 5% 2 5% 4 5% 4 3 6% 7% 50%	2090
	21st to end	Night	17% 6% 2 6% 5% 4 5% 3 5% 8% 39%	2090
October	1st to 10th	Night	18% 8% 3 7% 6% 4 4 4 5% 6% 36%	2223
	11th to 20th	Night	23% 9% 3 8% 6% 5% 4 3 5% 6% 26%	2280
	21st to end	Night	25% 12% 4 8% 6% 4 4 3 5% 6% 23%	2571
November	1st to 10th	Night	19% 14% 3 7% 4 5% 4 4 5% 7% 28%	2426
	11th to 20th	Night	17% 18% 5% 10% 7% 6% 5% 3 4 6% 19%	2660
	21st to end	Night	21% 19% 6% 9% 6% 5% 4 3 5% 5% 16%	2660
December	1st to 10th	Night	19% 23% 7% 11% 6% 4 3 3 4 4 14%	2693
	11th to 20th	Night	18% 21% 5% 11% 6% 5% 4 3 5% 5% 17%	3526
	21st to end	Night	24% 21% 6% 13% 5% 5% 4 2 4 4 12%	5236

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	72% 9% 11% 7% 1	2240
	11th to 20th	Day	78% 8% 7% 5% 2	2530
	21st to end	Day	72% 10% 10% 7% 2	2967
February	1st to 10th	Day	65% 7% 12% 13% 3	1710
	11th to 20th	Day	57% 8% 14% 14% 6% 1	1672
	21st to end	Day	56% 8% 14% 18% 5%	1559
March	1st to 10th	Day	48% 8% 16% 15% 11% 1	3266
	11th to 20th	Day	51% 9% 13% 20% 6% 1	3480
	21st to end	Day	44% 9% 16% 15% 13% 3	3815
April	1st to 10th	Day	49% 7% 13% 19% 11% 1	2229
	11th to 20th	Day	45% 5% 10% 25% 14% 2	2442
	21st to end	Day	46% 5% 13% 20% 14% 3	2470
May	1st to 10th	Day	39% 7% 12% 23% 17% 2	4120
	11th to 20th	Day	38% 8% 14% 25% 14% 1	4236
	21st to end	Day	39% 7% 13% 17% 22% 3	4990
June	1st to 10th	Day	40% 7% 13% 25% 13% 2	2850
	11th to 20th	Day	36% 7% 13% 26% 17% 2	2850
	21st to end	Day	41% 7% 12% 24% 13% 2	2850
July	1st to 10th	Day	43% 6% 14% 23% 13% 1	4686
	11th to 20th	Day	29% 8% 16% 34% 13% 1	4569
	21st to end	Day	29% 7% 12% 29% 23% 1	4509
August	1st to 10th	Day	33% 8% 17% 29% 13% 1	4091
	11th to 20th	Day	35% 7% 18% 29% 11%	4083
	21st to end	Day	33% 9% 15% 33% 10% 1	4531
September	1st to 10th	Day	37% 8% 16% 28% 10% 1	2244
	11th to 20th	Day	33% 7% 17% 31% 11% 1	2090
	21st to end	Day	43% 9% 15% 23% 9%	2090
October	1st to 10th	Day	47% 8% 12% 20% 13%	1957
	11th to 20th	Day	57% 7% 14% 16% 6%	1900
	21st to end	Day	62% 7% 12% 13% 5%	1889
November	1st to 10th	Day	56% 8% 14% 17% 5%	1650
	11th to 20th	Day	64% 8% 14% 10% 5%	1520
	21st to end	Day	72% 6% 12% 8% 2	1520
December	1st to 10th	Day	74% 8% 10% 6% 2	1482
	11th to 20th	Day	74% 6% 9% 10% 1	1671
	21st to end	Day	80% 9% 6% 5%	2431
January	1st to 10th	Night	70% 10% 10% 8% 2	4716
	11th to 20th	Night	74% 9% 9% 6% 2	4440
	21st to end	Night	71% 7% 11% 9% 2	4692
February	1st to 10th	Night	65% 5% 10% 14% 4	2470
	11th to 20th	Night	58% 8% 13% 15% 5% 1	2405
	21st to end	Night	57% 8% 13% 14% 7%	1893
March	1st to 10th	Night	43% 7% 16% 22% 11% 1	3587
	11th to 20th	Night	44% 6% 14% 23% 10% 2	3480
	21st to end	Night	45% 8% 13% 20% 11% 2	3817
April	1st to 10th	Night	49% 6% 10% 20% 13% 2	1967
	11th to 20th	Night	43% 6% 9% 23% 17% 2	1687
	21st to end	Night	50% 6% 9% 17% 15% 3	1710
May	1st to 10th	Night	44% 6% 12% 21% 15% 2	2840
	11th to 20th	Night	39% 7% 12% 22% 17% 2	2660
	21st to end	Night	40% 8% 12% 19% 16% 5%	2588
June	1st to 10th	Night	39% 8% 10% 23% 18% 2	1330
	11th to 20th	Night	34% 8% 13% 23% 20% 2	1330
	21st to end	Night	41% 7% 14% 22% 13% 2	1330
July	1st to 10th	Night	37% 5% 13% 24% 16% 4	2175
	11th to 20th	Night	30% 7% 11% 38% 13% 1	2261
	21st to end	Night	33% 6% 12% 23% 26% 1	2808
August	1st to 10th	Night	34% 8% 14% 30% 13% 1	2814
	11th to 20th	Night	35% 8% 18% 25% 13%	2812
	21st to end	Night	33% 7% 14% 32% 13% 1	3124
September	1st to 10th	Night	35% 7% 14% 28% 14% 2	1914
	11th to 20th	Night	33% 7% 16% 33% 11% 1	2090
	21st to end	Night	43% 8% 15% 23% 10%	2090
October	1st to 10th	Night	49% 6% 11% 22% 12%	2223
	11th to 20th	Night	58% 7% 12% 17% 5%	2280
	21st to end	Night	62% 7% 12% 13% 5%	2571
November	1st to 10th	Night	55% 7% 12% 19% 6%	2426
	11th to 20th	Night	67% 7% 12% 10% 4	2660
	21st to end	Night	70% 7% 12% 9% 2	2660
December	1st to 10th	Night	75% 7% 9% 8% 1	2693
	11th to 20th	Night	70% 7% 11% 9% 3	3525
	21st to end	Night	77% 9% 8% 5% 1	5236

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	27% 21% 32% 16% 4	189
	11th to 20th	Day	21% 17% 37% 20% 5%	270
	21st to end	Day	28% 13% 32% 19% 8%	297
February	1st to 10th	Day	22% 25% 34% 13% 5%	270
	11th to 20th	Day	19% 23% 38% 17% 2	270
	21st to end	Day	25% 28% 37% 8% 1	225
March	1st to 10th	Day	21% 18% 36% 19% 4 1	351
	11th to 20th	Day	19% 15% 37% 23% 5% 1	460
	21st to end	Day	21% 17% 32% 23% 5% 1	506
April	1st to 10th	Day	23% 15% 32% 23% 7% 1	460
	11th to 20th	Day	27% 17% 27% 17% 9% 3	452
	21st to end	Day	26% 13% 34% 18% 8% 1	460
May	1st to 10th	Day	20% 9% 37% 24% 8% 2	463
	11th to 20th	Day	17% 10% 29% 30% 13% 2	487
	21st to end	Day	13% 8% 33% 29% 15% 3	617
June	1st to 10th	Day	14% 9% 32% 31% 13% 1	680
	11th to 20th	Day	12% 8% 31% 34% 13% 1	680
	21st to end	Day	17% 8% 30% 31% 11% 2	680
July	1st to 10th	Day	9% 4 28% 39% 17% 2	671
	11th to 20th	Day	10% 6% 28% 38% 14% 4	668
	21st to end	Day	11% 3 30% 36% 16% 4	644
August	1st to 10th	Day	12% 6% 25% 33% 20% 5%	486
	11th to 20th	Day	12% 5% 21% 35% 20% 8%	479
	21st to end	Day	13% 8% 28% 29% 18% 4	539
September	1st to 10th	Day	13% 10% 28% 26% 18% 5%	490
	11th to 20th	Day	13% 7% 23% 31% 19% 7%	490
	21st to end	Day	19% 11% 24% 26% 17% 4	490
October	1st to 10th	Day	19% 19% 24% 24% 12% 2	490
	11th to 20th	Day	24% 19% 34% 17% 6% 1	490
	21st to end	Day	28% 23% 32% 14% 3 1	376
November	1st to 10th	Day	28% 18% 34% 15% 5%	259
	11th to 20th	Day	26% 22% 34% 14% 3	180
	21st to end	Day	33% 23% 31% 11% 2	180
December	1st to 10th	Day	27% 24% 29% 15% 5%	180
	11th to 20th	Day	32% 23% 35% 9% 2	180
	21st to end	Day	31% 28% 33% 5% 3 1	198
January	1st to 10th	Night	23% 22% 30% 20% 4	950
	11th to 20th	Night	25% 19% 31% 20% 5% 1	950
	21st to end	Night	22% 12% 35% 22% 8% 1	931
February	1st to 10th	Night	19% 21% 35% 20% 4	760
	11th to 20th	Night	18% 17% 34% 24% 6%	743
	21st to end	Night	21% 17% 37% 20% 4	628
March	1st to 10th	Night	17% 17% 37% 22% 6% 1	760
	11th to 20th	Night	17% 15% 36% 23% 8% 1	760
	21st to end	Night	19% 12% 32% 29% 8% 1	836
April	1st to 10th	Night	25% 11% 33% 25% 5% 1	701
	11th to 20th	Night	23% 11% 30% 23% 11% 2	563
	21st to end	Night	22% 11% 28% 25% 13% 1	570
May	1st to 10th	Night	15% 6% 28% 34% 14% 3	570
	11th to 20th	Night	16% 7% 26% 33% 16% 1	473
	21st to end	Night	14% 5% 26% 34% 19% 2	411
June	1st to 10th	Night	15% 4 31% 34% 13% 2	380
	11th to 20th	Night	11% 8% 22% 38% 20% 2	380
	21st to end	Night	14% 3 21% 37% 22% 2	380
July	1st to 10th	Night	10% 3 20% 42% 23% 1	370
	11th to 20th	Night	8% 3 20% 39% 25% 4	422
	21st to end	Night	9% 4 23% 34% 27% 4	624
August	1st to 10th	Night	10% 4 21% 37% 24% 4	567
	11th to 20th	Night	11% 4 17% 31% 32% 5%	564
	21st to end	Night	12% 4 22% 32% 23% 6%	627
September	1st to 10th	Night	14% 6% 26% 27% 20% 7%	708
	11th to 20th	Night	12% 6% 24% 30% 18% 10%	760
	21st to end	Night	18% 9% 24% 26% 19% 4	760
October	1st to 10th	Night	21% 12% 26% 26% 13% 2	760
	11th to 20th	Night	28% 15% 28% 19% 10%	760
	21st to end	Night	29% 17% 29% 20% 4 1	812
November	1st to 10th	Night	26% 15% 30% 21% 7% 1	740
	11th to 20th	Night	26% 23% 28% 17% 6%	760
	21st to end	Night	32% 18% 29% 16% 5%	760
December	1st to 10th	Night	31% 22% 29% 12% 5%	793
	11th to 20th	Night	28% 22% 32% 12% 4 1	950
	21st to end	Night	34% 17% 30% 14% 4	1045

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