Bath Nature Preseve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bath Nature Preseve clear sky chart from 2005-11-06 to 2024-01-22.

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% 11% 4 7% 6% 3 5% 5% 5% 7% 30%	74666
	Night	16% 11% 4 8% 6% 3 5% 4 5% 6% 31%	75251
Transparency	Day	53% 6% 11% 19% 11% 1	74387
	Night	53% 5% 11% 18% 11% 1	75049
Seeing	Day	22% 15% 27% 20% 11% 4	13509
	Night	22% 12% 27% 26% 12% 1	23493

By Month

Percentage Cloud Cover SE (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	17% 18% 8% 12% 8% 4 5% 4 4 4 17%	1706
	11th to 20th	Day	19% 20% 9% 13% 8% 3 4 3 4 4 14%	1710
	21st to end	Day	16% 20% 9% 13% 9% 4 4 5% 4 4 12%	1791
February	1st to 10th	Day	18% 19% 6% 10% 9% 4 3 3 3 5% 19%	1620
	11th to 20th	Day	16% 13% 8% 13% 10% 3 5% 4 5% 4 20%	1631
	21st to end	Day	18% 15% 5% 12% 8% 3 4 3 4 4 23%	1480
March	1st to 10th	Day	19% 12% 7% 8% 6% 3 3 4 5% 6% 27%	1926
	11th to 20th	Day	16% 14% 6% 9% 5% 4 4 3 4 5% 28%	1980
	21st to end	Day	23% 11% 5% 8% 6% 3 4 4 4 5% 26%	2178
April	1st to 10th	Day	15% 13% 6% 6% 6% 3 5% 4 5% 6% 31%	2008
	11th to 20th	Day	18% 11% 4 6% 5% 3 5% 5% 4 6% 32%	2288
	21st to end	Day	21% 10% 5% 6% 6% 3 3 4 4 6% 32%	2340
May	1st to 10th	Day	18% 9% 3 7% 6% 4 5% 6% 4 7% 30%	2340
	11th to 20th	Day	18% 9% 4 6% 6% 4 5% 4 6% 7% 32%	2301
	21st to end	Day	10% 6% 3 6% 6% 3 5% 6% 7% 10% 37%	2531
June	1st to 10th	Day	14% 7% 3 6% 6% 4 5% 5% 6% 8% 37%	2520
	11th to 20th	Day	13% 7% 3 6% 6% 3 5% 6% 6% 8% 37%	2520
	21st to end	Day	12% 5% 2 5% 5% 4 6% 6% 7% 10% 39%	2479
July	1st to 10th	Day	10% 6% 3 6% 6% 4 5% 5% 6% 8% 41%	2340
	11th to 20th	Day	12% 4 3 5% 6% 4 7% 5% 6% 10% 39%	2340
	21st to end	Day	11% 5% 3 5% 6% 4 6% 6% 7% 9% 38%	2547
August	1st to 10th	Day	9% 6% 3 6% 6% 4 6% 6% 8% 8% 38%	2327
	11th to 20th	Day	10% 7% 3 6% 6% 4 6% 6% 8% 9% 35%	2303
	21st to end	Day	11% 5% 2 6% 6% 4 6% 7% 8% 9% 37%	2538
September	1st to 10th	Day	14% 6% 3 5% 5% 4 5% 5% 5% 8% 41%	2056
	11th to 20th	Day	12% 6% 2 6% 6% 3 5% 5% 5% 9% 41%	1980
	21st to end	Day	18% 8% 3 5% 4 3 4 4 4 6% 40%	1980
October	1st to 10th	Day	15% 8% 3 6% 5% 2 4 6% 6% 7% 38%	1865
	11th to 20th	Day	19% 10% 3 8% 5% 3 4 5% 5% 5% 33%	1800
	21st to end	Day	24% 11% 3 8% 5% 3 5% 4 5% 5% 27%	1972
November	1st to 10th	Day	12% 11% 4 7% 6% 3 4 4 5% 6% 38%	1672
	11th to 20th	Day	18% 15% 4 8% 6% 3 4 4 4 6% 28%	1703
	21st to end	Day	19% 16% 7% 8% 6% 3 6% 4 5% 6% 20%	1520
December	1st to 10th	Day	17% 22% 8% 10% 7% 3 5% 4 3 4 17%	1520
	11th to 20th	Day	19% 16% 8% 14% 6% 3 4 4 3 6% 16%	1910
	21st to end	Day	26% 24% 8% 9% 6% 3 3 3 3 4 10%	2944
January	1st to 10th	Night	19% 16% 7% 12% 7% 4 4 4 4 4 19%	2459
	11th to 20th	Night	21% 18% 6% 12% 8% 3 4 3 4 4 16%	2470
	21st to end	Night	17% 18% 7% 13% 8% 4 4 4 3 4 18%	2599
February	1st to 10th	Night	21% 14% 7% 11% 8% 4 4 3 4 5% 19%	2340
	11th to 20th	Night	17% 14% 6% 10% 8% 4 6% 5% 4 4 21%	2212
	21st to end	Night	21% 14% 6% 11% 7% 3 4 3 4 5% 23%	1776
March	1st to 10th	Night	17% 11% 6% 9% 5% 3 4 4 5% 5% 31%	2034
	11th to 20th	Night	17% 11% 4 7% 5% 2 5% 5% 5% 7% 33%	1980
	21st to end	Night	19% 11% 5% 8% 5% 3 4 4 5% 5% 31%	2178
April	1st to 10th	Night	16% 11% 4 7% 5% 3 5% 4 5% 8% 31%	1950
	11th to 20th	Night	15% 10% 3 6% 6% 3 6% 4 5% 6% 35%	1635
	21st to end	Night	16% 7% 3 6% 6% 4 6% 4 6% 6% 36%	1620
May	1st to 10th	Night	18% 8% 3 8% 7% 4 5% 5% 5% 7% 31%	1620
	11th to 20th	Night	15% 8% 3 6% 5% 3 4 5% 5% 9% 36%	1592
	21st to end	Night	10% 5% 2 5% 4 3 5% 5% 7% 11% 42%	1740
June	1st to 10th	Night	9% 6% 3 5% 6% 4 5% 5% 6% 8% 43%	1440
	11th to 20th	Night	10% 6% 2 5% 7% 4 5% 5% 8% 9% 41%	1440
	21st to end	Night	11% 4 2 5% 4 3 6% 6% 6% 11% 41%	1475
July	1st to 10th	Night	7% 5% 2 6% 6% 4 5% 4 6% 7% 48%	1620
	11th to 20th	Night	7% 5% 2 5% 5% 3 5% 4 7% 11% 46%	1620
	21st to end	Night	8% 5% 3 6% 6% 4 5% 4 6% 8% 45%	1771
August	1st to 10th	Night	6% 5% 2 5% 6% 3 6% 5% 6% 10% 47%	1611
	11th to 20th	Night	10% 6% 3 6% 5% 4 4 5% 5% 9% 44%	1598
	21st to end	Night	9% 5% 3 5% 5% 3 4 5% 6% 8% 47%	1800
September	1st to 10th	Night	13% 5% 2 5% 5% 3 5% 5% 5% 7% 46%	1900
	11th to 20th	Night	10% 5% 2 4 5% 3 4 4 4 8% 52%	1980
	21st to end	Night	15% 6% 2 7% 6% 3 4 4 5% 8% 41%	1980
October	1st to 10th	Night	14% 6% 2 5% 5% 3 5% 5% 5% 7% 43%	2093
	11th to 20th	Night	20% 8% 3 6% 6% 3 5% 4 5% 5% 34%	2160
	21st to end	Night	24% 10% 3 6% 6% 3 5% 4 5% 5% 29%	2380
November	1st to 10th	Night	15% 8% 3 6% 5% 3 5% 5% 5% 6% 40%	2406
	11th to 20th	Night	16% 15% 5% 8% 6% 3 4 3 4 6% 28%	2474
	21st to end	Night	21% 15% 5% 7% 6% 3 5% 5% 4 6% 24%	2660
December	1st to 10th	Night	21% 17% 9% 10% 5% 3 4 3 4 5% 19%	2660
	11th to 20th	Night	17% 18% 7% 11% 6% 3 4 3 4 5% 21%	3285
	21st to end	Night	26% 21% 8% 9% 7% 2 4 4 3 5% 11%	4693

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	73% 3 9% 11% 4	1707
	11th to 20th	Day	76% 4 10% 8% 3	1710
	21st to end	Day	75% 5% 8% 8% 3	1791
February	1st to 10th	Day	70% 3 10% 12% 5% 1	1620
	11th to 20th	Day	69% 4 8% 12% 6% 1	1640
	21st to end	Day	64% 3 12% 12% 7% 1	1480
March	1st to 10th	Day	59% 4 11% 20% 6%	1926
	11th to 20th	Day	58% 4 9% 17% 10% 1	1980
	21st to end	Day	61% 4 8% 18% 9% 1	2178
April	1st to 10th	Day	53% 5% 11% 18% 12% 1	2008
	11th to 20th	Day	53% 5% 11% 16% 13% 2	2288
	21st to end	Day	54% 5% 10% 20% 10% 2	2340
May	1st to 10th	Day	53% 6% 11% 19% 9% 2	2340
	11th to 20th	Day	50% 6% 11% 17% 14% 2	2305
	21st to end	Day	40% 7% 14% 24% 13% 1	2531
June	1st to 10th	Day	44% 7% 10% 25% 14% 1	2520
	11th to 20th	Day	43% 7% 14% 21% 14% 1	2520
	21st to end	Day	39% 7% 13% 24% 16% 2	2479
July	1st to 10th	Day	41% 6% 10% 25% 17% 2	2275
	11th to 20th	Day	40% 7% 12% 24% 15% 2	2271
	21st to end	Day	39% 8% 13% 24% 15% 2	2405
August	1st to 10th	Day	40% 9% 12% 26% 12% 1	2314
	11th to 20th	Day	41% 9% 14% 23% 11% 2	2303
	21st to end	Day	39% 9% 12% 22% 14% 4	2538
September	1st to 10th	Day	41% 7% 14% 20% 16% 3	2056
	11th to 20th	Day	40% 7% 14% 24% 15% 1	1980
	21st to end	Day	46% 5% 9% 23% 16% 1	1980
October	1st to 10th	Day	44% 7% 11% 23% 14% 1	1865
	11th to 20th	Day	51% 5% 11% 21% 10% 1	1800
	21st to end	Day	59% 4 12% 15% 9% 1	1972
November	1st to 10th	Day	48% 4 11% 21% 14% 1	1672
	11th to 20th	Day	58% 4 9% 18% 8% 2	1703
	21st to end	Day	66% 5% 9% 14% 6%	1520
December	1st to 10th	Day	73% 3 9% 12% 3	1520
	11th to 20th	Day	71% 5% 8% 13% 3	1906
	21st to end	Day	80% 4 9% 6% 2	2944
January	1st to 10th	Night	69% 4 8% 13% 6%	2459
	11th to 20th	Night	73% 4 9% 11% 2	2470
	21st to end	Night	70% 4 9% 12% 4 1	2599
February	1st to 10th	Night	69% 4 9% 14% 4	2340
	11th to 20th	Night	65% 5% 9% 14% 7%	2214
	21st to end	Night	65% 3 10% 13% 9% 1	1776
March	1st to 10th	Night	56% 3 8% 23% 9% 1	2034
	11th to 20th	Night	50% 5% 11% 19% 12% 2	1980
	21st to end	Night	56% 4 8% 19% 11% 2	2178
April	1st to 10th	Night	52% 5% 11% 17% 14% 1	1950
	11th to 20th	Night	49% 5% 10% 17% 15% 3	1635
	21st to end	Night	47% 4 12% 19% 15% 3	1620
May	1st to 10th	Night	52% 5% 10% 18% 12% 3	1620
	11th to 20th	Night	46% 5% 12% 18% 15% 4	1593
	21st to end	Night	34% 8% 16% 25% 16% 1	1741
June	1st to 10th	Night	38% 7% 10% 26% 15% 2	1440
	11th to 20th	Night	38% 6% 15% 20% 18% 2	1440
	21st to end	Night	35% 9% 13% 25% 17% 2	1475
July	1st to 10th	Night	36% 6% 12% 23% 19% 4	1575
	11th to 20th	Night	32% 7% 14% 26% 19% 2	1566
	21st to end	Night	37% 6% 13% 23% 17% 3	1672
August	1st to 10th	Night	32% 8% 14% 27% 19% 1	1600
	11th to 20th	Night	37% 6% 15% 27% 12% 2	1598
	21st to end	Night	35% 6% 13% 25% 18% 3	1800
September	1st to 10th	Night	37% 6% 12% 25% 16% 4	1900
	11th to 20th	Night	31% 5% 14% 26% 22% 1	1980
	21st to end	Night	42% 6% 11% 21% 19% 1	1980
October	1st to 10th	Night	39% 6% 13% 22% 19% 1	2093
	11th to 20th	Night	52% 4 10% 21% 13% 1	2160
	21st to end	Night	57% 4 10% 19% 9% 2	2380
November	1st to 10th	Night	45% 5% 12% 22% 14% 2	2406
	11th to 20th	Night	58% 3 9% 17% 10% 2	2474
	21st to end	Night	63% 4 11% 16% 6%	2660
December	1st to 10th	Night	69% 5% 9% 12% 5%	2660
	11th to 20th	Night	66% 5% 11% 15% 3	3288
	21st to end	Night	77% 4 10% 8% 2	4693

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	31% 23% 30% 10% 4 1	270
	11th to 20th	Day	30% 26% 31% 9% 3	270
	21st to end	Day	27% 33% 28% 9% 3	267
February	1st to 10th	Day	35% 23% 35% 7%	240
	11th to 20th	Day	30% 29% 35% 6% 1	240
	21st to end	Day	30% 32% 33% 5%	198
March	1st to 10th	Day	27% 23% 31% 15% 4	366
	11th to 20th	Day	27% 19% 33% 15% 5% 1	420
	21st to end	Day	33% 20% 25% 16% 5%	462
April	1st to 10th	Day	24% 22% 29% 17% 7% 1	420
	11th to 20th	Day	28% 19% 26% 14% 10% 4	412
	21st to end	Day	27% 18% 30% 17% 6% 2	420
May	1st to 10th	Day	26% 17% 29% 17% 8% 2	423
	11th to 20th	Day	23% 15% 31% 19% 9% 4	447
	21st to end	Day	15% 12% 26% 26% 17% 5%	485
June	1st to 10th	Day	16% 10% 32% 30% 10% 3	450
	11th to 20th	Day	18% 10% 23% 31% 14% 4	450
	21st to end	Day	13% 11% 33% 26% 11% 5%	450
July	1st to 10th	Day	13% 6% 22% 28% 22% 10%	445
	11th to 20th	Day	13% 6% 25% 28% 20% 7%	444
	21st to end	Day	11% 7% 25% 30% 20% 7%	488
August	1st to 10th	Day	13% 7% 20% 28% 24% 8%	446
	11th to 20th	Day	17% 8% 22% 25% 18% 10%	439
	21st to end	Day	12% 6% 23% 28% 20% 11%	495
September	1st to 10th	Day	18% 7% 20% 28% 17% 10%	450
	11th to 20th	Day	13% 5% 18% 28% 26% 10%	450
	21st to end	Day	24% 10% 22% 22% 15% 6%	450
October	1st to 10th	Day	16% 10% 28% 24% 18% 4	450
	11th to 20th	Day	24% 18% 34% 16% 8%	450
	21st to end	Day	32% 17% 29% 18% 3 1	487
November	1st to 10th	Day	20% 24% 30% 15% 9% 2	270
	11th to 20th	Day	32% 23% 26% 14% 4 1	266
	21st to end	Day	27% 23% 41% 8% 1	180
December	1st to 10th	Day	27% 24% 33% 10% 3 2	180
	11th to 20th	Day	28% 28% 32% 9% 2	180
	21st to end	Day	33% 25% 30% 11% 1	249
January	1st to 10th	Night	29% 21% 32% 14% 4	760
	11th to 20th	Night	33% 20% 28% 15% 4	760
	21st to end	Night	27% 20% 29% 21% 3	800
February	1st to 10th	Night	29% 19% 32% 18% 2	720
	11th to 20th	Night	28% 18% 33% 18% 2	703
	21st to end	Night	29% 19% 35% 14% 2	592
March	1st to 10th	Night	24% 17% 35% 19% 5%	720
	11th to 20th	Night	23% 17% 31% 23% 6% 1	720
	21st to end	Night	25% 13% 30% 23% 8% 1	792
April	1st to 10th	Night	24% 15% 31% 24% 5% 1	720
	11th to 20th	Night	23% 13% 33% 20% 10% 1	571
	21st to end	Night	19% 11% 36% 28% 6% 1	540
May	1st to 10th	Night	20% 10% 29% 31% 9% 1	540
	11th to 20th	Night	19% 8% 27% 35% 10% 2	531
	21st to end	Night	13% 3 25% 36% 21% 2	580
June	1st to 10th	Night	10% 4 33% 37% 15% 1	360
	11th to 20th	Night	13% 5% 27% 41% 14% 1	360
	21st to end	Night	11% 6% 27% 37% 18% 1	395
July	1st to 10th	Night	10% 3 15% 41% 29% 3	525
	11th to 20th	Night	8% 4 21% 38% 25% 3	522
	21st to end	Night	9% 5% 16% 43% 25% 2	591
August	1st to 10th	Night	9% 4 15% 43% 27% 3	537
	11th to 20th	Night	13% 2 14% 37% 32% 3	534
	21st to end	Night	11% 3 20% 32% 31% 4	612
September	1st to 10th	Night	14% 6% 17% 32% 27% 5%	720
	11th to 20th	Night	12% 3 17% 34% 30% 4	720
	21st to end	Night	17% 8% 23% 28% 19% 4	720
October	1st to 10th	Night	16% 9% 24% 30% 19% 2	720
	11th to 20th	Night	25% 12% 28% 26% 8% 1	720
	21st to end	Night	29% 14% 27% 24% 5%	792
November	1st to 10th	Night	20% 14% 30% 26% 10% 1	740
	11th to 20th	Night	28% 18% 28% 19% 6% 1	760
	21st to end	Night	31% 18% 29% 16% 6%	760
December	1st to 10th	Night	32% 18% 30% 16% 5%	760
	11th to 20th	Night	27% 20% 32% 17% 3	760
	21st to end	Night	31% 17% 31% 19% 2	836

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