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 2026-05-17.

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 10% 5% 5% 4 4 5% 7% 30%	131559
	Night	16% 13% 4 10% 5% 4 4 3 5% 6% 30%	131217
Transparency	Day	53% 5% 10% 19% 11% 1	135191
	Night	54% 5% 10% 19% 11% 1	135654
Seeing	Day	23% 16% 27% 20% 10% 4	16531
	Night	22% 13% 27% 26% 11% 1	26502

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	15% 21% 7% 23% 6% 4 3 2 3 4 12%	5258
	11th to 20th	Day	11% 22% 8% 19% 9% 6% 5% 2 3 4 12%	5280
	21st to end	Day	19% 18% 8% 13% 8% 7% 4 3 4 3 13%	5780
February	1st to 10th	Day	16% 20% 5% 12% 7% 4 4 3 4 5% 21%	1890
	11th to 20th	Day	15% 14% 7% 14% 9% 4 5% 3 4 4 21%	1911
	21st to end	Day	16% 15% 4 13% 7% 4 4 3 5% 5% 23%	1730
March	1st to 10th	Day	18% 12% 7% 13% 5% 4 3 3 5% 5% 26%	4909
	11th to 20th	Day	12% 12% 5% 11% 5% 4 4 3 4 6% 35%	5090
	21st to end	Day	20% 13% 5% 9% 5% 4 4 3 5% 5% 27%	5586
April	1st to 10th	Day	16% 14% 4 8% 5% 5% 4 3 5% 7% 29%	2344
	11th to 20th	Day	18% 12% 3 7% 5% 5% 5% 4 5% 6% 32%	2675
	21st to end	Day	19% 11% 4 7% 5% 4 3 3 4 6% 33%	2730
May	1st to 10th	Day	22% 10% 3 8% 5% 5% 4 4 5% 6% 29%	5992
	11th to 20th	Day	19% 8% 3 7% 4 4 4 4 5% 8% 32%	5939
	21st to end	Day	18% 8% 2 6% 5% 4 5% 4 6% 8% 34%	6433
June	1st to 10th	Day	14% 8% 2 7% 5% 5% 5% 4 6% 8% 37%	2800
	11th to 20th	Day	13% 7% 3 8% 5% 5% 5% 5% 6% 8% 36%	2800
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 10% 39%	2753
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 6% 10% 42%	5900
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 4 7% 11% 37%	5900
	21st to end	Day	11% 6% 3 6% 5% 4 5% 4 6% 8% 40%	6424
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 8% 35%	4234
	11th to 20th	Day	11% 7% 2 7% 4 5% 6% 5% 8% 9% 36%	4174
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 9% 40%	4609
September	1st to 10th	Day	13% 6% 2 5% 4 5% 4 4 5% 8% 44%	2284
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 3 5% 9% 44%	2200
	21st to end	Day	19% 9% 3 7% 4 4 4 3 4 6% 38%	2200
October	1st to 10th	Day	14% 7% 3 7% 4 3 4 4 6% 7% 41%	2071
	11th to 20th	Day	19% 9% 3 8% 4 4 4 4 5% 5% 35%	2000
	21st to end	Day	22% 11% 3 9% 4 5% 4 3 6% 6% 29%	2190
November	1st to 10th	Day	13% 11% 5% 7% 5% 5% 4 3 5% 6% 37%	1852
	11th to 20th	Day	18% 16% 3 9% 6% 3 4 3 5% 6% 27%	1881
	21st to end	Day	19% 19% 7% 9% 5% 4 5% 3 5% 5% 18%	1680
December	1st to 10th	Day	17% 17% 7% 16% 6% 4 4 3 4 4 18%	2680
	11th to 20th	Day	23% 20% 7% 11% 5% 4 3 2 3 5% 16%	3070
	21st to end	Day	25% 23% 7% 13% 5% 4 4 3 3 3 9%	4310
January	1st to 10th	Night	15% 20% 8% 23% 6% 4 3 3 3 3 11%	7635
	11th to 20th	Night	12% 20% 10% 18% 9% 6% 6% 3 3 3 11%	7680
	21st to end	Night	18% 18% 6% 12% 5% 5% 4 3 4 5% 18%	8401
February	1st to 10th	Night	19% 15% 6% 13% 7% 4 4 3 4 5% 21%	2730
	11th to 20th	Night	16% 14% 6% 12% 7% 6% 5% 4 5% 4 21%	2591
	21st to end	Night	19% 15% 5% 12% 6% 4 4 3 4 5% 23%	2076
March	1st to 10th	Night	21% 14% 4 9% 4 3 3 2 3 5% 31%	5151
	11th to 20th	Night	13% 10% 3 7% 4 4 5% 3 5% 7% 38%	5090
	21st to end	Night	18% 12% 4 9% 4 4 4 3 5% 5% 33%	5588
April	1st to 10th	Night	18% 13% 3 7% 5% 5% 4 3 5% 7% 29%	2274
	11th to 20th	Night	15% 11% 3 7% 5% 5% 6% 4 5% 6% 33%	1911
	21st to end	Night	15% 8% 3 7% 5% 5% 5% 3 6% 6% 36%	1890
May	1st to 10th	Night	24% 10% 3 8% 4 4 4 4 5% 6% 27%	4123
	11th to 20th	Night	16% 9% 3 6% 4 4 4 3 5% 8% 38%	4086
	21st to end	Night	17% 7% 2 5% 3 4 4 4 7% 9% 38%	4404
June	1st to 10th	Night	9% 7% 3 6% 5% 5% 4 4 6% 7% 43%	1600
	11th to 20th	Night	10% 6% 2 7% 6% 5% 4 5% 8% 8% 40%	1600
	21st to end	Night	10% 5% 2 6% 4 4 6% 5% 7% 10% 41%	1639
July	1st to 10th	Night	9% 5% 2 7% 4 5% 5% 4 6% 10% 45%	4058
	11th to 20th	Night	9% 6% 2 6% 5% 4 5% 4 7% 9% 43%	4057
	21st to end	Night	8% 6% 2 7% 4 4 4 3 6% 9% 47%	4427
August	1st to 10th	Night	11% 8% 2 7% 5% 5% 4 3 6% 8% 40%	2915
	11th to 20th	Night	14% 8% 2 7% 4 4 3 3 4 7% 43%	2875
	21st to end	Night	8% 5% 3 7% 5% 5% 6% 4 6% 8% 44%	3256
September	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 5% 7% 48%	2112
	11th to 20th	Night	9% 5% 2 4 4 4 4 3 4 8% 54%	2200
	21st to end	Night	17% 7% 2 8% 5% 4 3 3 5% 7% 39%	2200
October	1st to 10th	Night	13% 6% 2 5% 4 4 5% 3 5% 7% 45%	2327
	11th to 20th	Night	19% 8% 3 7% 5% 5% 4 3 5% 5% 36%	2400
	21st to end	Night	22% 10% 3 7% 4 4 4 4 5% 6% 31%	2646
November	1st to 10th	Night	14% 8% 3 7% 4 4 5% 4 5% 6% 40%	2666
	11th to 20th	Night	16% 16% 4 9% 5% 4 4 3 5% 6% 28%	2735
	21st to end	Night	21% 16% 5% 7% 5% 4 5% 3 5% 5% 23%	2940
December	1st to 10th	Night	16% 16% 7% 12% 6% 5% 4 3 5% 6% 21%	4720
	11th to 20th	Night	19% 21% 7% 12% 5% 4 3 3 4 4 18%	5345
	21st to end	Night	24% 22% 7% 12% 5% 4 4 3 3 5% 12%	6869

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	79% 3 8% 7% 2	5259
	11th to 20th	Day	79% 2 6% 7% 6%	5280
	21st to end	Day	77% 3 6% 11% 3	5780
February	1st to 10th	Day	67% 3 10% 14% 6%	1890
	11th to 20th	Day	68% 4 8% 14% 6% 1	1920
	21st to end	Day	63% 4 13% 13% 6% 1	1730
March	1st to 10th	Day	60% 4 9% 21% 6%	4909
	11th to 20th	Day	51% 4 12% 24% 7% 1	5090
	21st to end	Day	59% 4 8% 18% 11% 1	5586
April	1st to 10th	Day	55% 5% 11% 17% 11% 1	2344
	11th to 20th	Day	52% 5% 11% 17% 12% 2	2675
	21st to end	Day	52% 5% 10% 21% 11% 2	2730
May	1st to 10th	Day	55% 6% 8% 18% 10% 3	6027
	11th to 20th	Day	50% 6% 11% 22% 11% 1	5943
	21st to end	Day	46% 7% 11% 20% 12% 3	6447
June	1st to 10th	Day	44% 7% 10% 25% 14% 1	2800
	11th to 20th	Day	43% 7% 13% 21% 14% 1	2800
	21st to end	Day	38% 7% 13% 24% 16% 2	2753
July	1st to 10th	Day	38% 6% 10% 28% 16% 2	5835
	11th to 20th	Day	40% 7% 12% 24% 15% 1	5831
	21st to end	Day	39% 7% 11% 21% 20% 2	6240
August	1st to 10th	Day	43% 8% 13% 23% 12%	4221
	11th to 20th	Day	40% 8% 11% 29% 11% 1	4213
	21st to end	Day	37% 8% 13% 29% 10% 2	4609
September	1st to 10th	Day	39% 6% 13% 22% 17% 3	2284
	11th to 20th	Day	37% 6% 14% 25% 16% 2	2200
	21st to end	Day	48% 5% 9% 21% 16% 1	2200
October	1st to 10th	Day	33% 5% 13% 29% 19% 1	3370
	11th to 20th	Day	46% 4 10% 20% 16% 3	3240
	21st to end	Day	43% 4 12% 24% 16% 1	3516
November	1st to 10th	Day	49% 4 10% 22% 14% 1	1852
	11th to 20th	Day	59% 4 9% 17% 9% 2	1881
	21st to end	Day	68% 4 9% 13% 6%	1680
December	1st to 10th	Day	70% 4 11% 12% 2	2680
	11th to 20th	Day	73% 3 8% 13% 3	3066
	21st to end	Day	81% 3 7% 7% 2	4310
January	1st to 10th	Night	80% 3 5% 9% 3	7636
	11th to 20th	Night	80% 3 6% 8% 3	7680
	21st to end	Night	70% 3 8% 13% 5%	8401
February	1st to 10th	Night	67% 4 9% 15% 5%	2730
	11th to 20th	Night	65% 5% 9% 15% 6%	2593
	21st to end	Night	64% 3 10% 13% 9% 1	2076
March	1st to 10th	Night	57% 3 11% 20% 8%	5151
	11th to 20th	Night	45% 5% 14% 24% 11% 2	5090
	21st to end	Night	53% 4 8% 20% 13% 1	5588
April	1st to 10th	Night	55% 5% 10% 16% 13% 1	2274
	11th to 20th	Night	50% 6% 11% 17% 14% 2	1911
	21st to end	Night	47% 5% 11% 20% 15% 2	1890
May	1st to 10th	Night	57% 6% 8% 15% 9% 5%	4150
	11th to 20th	Night	45% 6% 11% 23% 14% 2	4087
	21st to end	Night	41% 7% 13% 23% 13% 2	4411
June	1st to 10th	Night	40% 7% 10% 25% 16% 2	1600
	11th to 20th	Night	39% 6% 15% 20% 18% 2	1600
	21st to end	Night	35% 8% 13% 25% 17% 2	1639
July	1st to 10th	Night	35% 6% 13% 25% 18% 3	4015
	11th to 20th	Night	36% 7% 14% 27% 14% 1	4006
	21st to end	Night	34% 6% 12% 21% 26% 2	4297
August	1st to 10th	Night	41% 7% 12% 24% 15% 1	2904
	11th to 20th	Night	42% 4 10% 29% 13% 1	2902
	21st to end	Night	37% 7% 12% 28% 14% 2	3256
September	1st to 10th	Night	35% 5% 11% 27% 17% 4	2112
	11th to 20th	Night	30% 5% 13% 27% 23% 2	2200
	21st to end	Night	45% 5% 11% 19% 19% 1	2200
October	1st to 10th	Night	32% 4 9% 30% 24% 1	3808
	11th to 20th	Night	46% 4 9% 20% 18% 2	3899
	21st to end	Night	42% 3 10% 27% 16% 1	4270
November	1st to 10th	Night	44% 5% 12% 23% 14% 2	2666
	11th to 20th	Night	58% 3 9% 18% 9% 2	2735
	21st to end	Night	63% 4 11% 16% 5%	2940
December	1st to 10th	Night	64% 5% 11% 15% 4	4720
	11th to 20th	Night	71% 4 9% 14% 2	5348
	21st to end	Night	76% 4 9% 9% 1	6869

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	32% 25% 31% 9% 3 1	330
	11th to 20th	Day	36% 26% 28% 7% 2	330
	21st to end	Day	33% 30% 26% 8% 2	363
February	1st to 10th	Day	31% 25% 34% 9% 1	330
	11th to 20th	Day	32% 27% 33% 7% 1	330
	21st to end	Day	29% 34% 33% 4	273
March	1st to 10th	Day	28% 24% 31% 14% 4	477
	11th to 20th	Day	29% 21% 32% 13% 4 1	540
	21st to end	Day	33% 22% 26% 14% 4	594
April	1st to 10th	Day	27% 23% 28% 15% 6% 1	540
	11th to 20th	Day	30% 21% 24% 14% 8% 3	532
	21st to end	Day	26% 18% 33% 16% 6% 1	540
May	1st to 10th	Day	28% 20% 28% 16% 6% 2	543
	11th to 20th	Day	22% 17% 30% 19% 8% 4	551
	21st to end	Day	17% 14% 25% 24% 16% 4	573
June	1st to 10th	Day	17% 11% 32% 28% 9% 3	530
	11th to 20th	Day	18% 10% 24% 32% 12% 4	530
	21st to end	Day	13% 11% 32% 26% 12% 5%	530
July	1st to 10th	Day	13% 6% 24% 28% 20% 9%	525
	11th to 20th	Day	12% 6% 27% 28% 19% 7%	524
	21st to end	Day	11% 7% 24% 31% 19% 7%	576
August	1st to 10th	Day	13% 8% 20% 30% 23% 7%	526
	11th to 20th	Day	16% 9% 22% 26% 18% 9%	519
	21st to end	Day	11% 6% 24% 28% 20% 10%	583
September	1st to 10th	Day	17% 8% 20% 27% 18% 10%	530
	11th to 20th	Day	11% 4 17% 30% 27% 11%	530
	21st to end	Day	25% 10% 23% 22% 14% 6%	530
October	1st to 10th	Day	15% 10% 27% 24% 19% 4	530
	11th to 20th	Day	23% 18% 33% 16% 8% 2	530
	21st to end	Day	29% 19% 30% 18% 3 1	573
November	1st to 10th	Day	22% 23% 32% 13% 8% 2	330
	11th to 20th	Day	34% 25% 25% 12% 3 1	324
	21st to end	Day	31% 24% 37% 7% 1	220
December	1st to 10th	Day	28% 23% 35% 10% 2 2	220
	11th to 20th	Day	32% 28% 28% 10% 2	220
	21st to end	Day	35% 24% 30% 10% 1	305
January	1st to 10th	Night	29% 21% 32% 15% 4	840
	11th to 20th	Night	33% 22% 28% 14% 3	840
	21st to end	Night	29% 21% 28% 20% 2	924
February	1st to 10th	Night	28% 19% 31% 20% 3	840
	11th to 20th	Night	27% 20% 32% 18% 2	823
	21st to end	Night	29% 19% 36% 14% 2	692
March	1st to 10th	Night	25% 16% 35% 19% 5%	840
	11th to 20th	Night	24% 18% 30% 21% 5% 1	840
	21st to end	Night	25% 14% 32% 21% 6% 1	924
April	1st to 10th	Night	26% 16% 30% 23% 4 1	840
	11th to 20th	Night	24% 14% 33% 20% 8% 1	667
	21st to end	Night	19% 12% 34% 29% 5% 1	630
May	1st to 10th	Night	21% 10% 29% 30% 8% 1	630
	11th to 20th	Night	18% 10% 27% 34% 10% 1	609
	21st to end	Night	15% 3 25% 36% 19% 2	645
June	1st to 10th	Night	11% 5% 34% 36% 14% 1	400
	11th to 20th	Night	13% 5% 28% 41% 13% 1	400
	21st to end	Night	11% 7% 26% 37% 19% 1	439
July	1st to 10th	Night	10% 3 15% 41% 28% 3	585
	11th to 20th	Night	9% 4 21% 37% 26% 3	582
	21st to end	Night	9% 5% 15% 42% 26% 2	657
August	1st to 10th	Night	10% 4 14% 43% 26% 3	597
	11th to 20th	Night	13% 3 14% 37% 31% 3	594
	21st to end	Night	10% 3 19% 34% 30% 3	680
September	1st to 10th	Night	13% 6% 18% 32% 27% 4	800
	11th to 20th	Night	11% 3 16% 35% 31% 4	800
	21st to end	Night	19% 8% 22% 28% 18% 4	800
October	1st to 10th	Night	16% 9% 23% 30% 20% 2	800
	11th to 20th	Night	25% 12% 28% 26% 10% 1	800
	21st to end	Night	28% 14% 27% 25% 5%	880
November	1st to 10th	Night	20% 15% 30% 26% 9% 1	820
	11th to 20th	Night	28% 18% 28% 19% 6% 1	840
	21st to end	Night	32% 18% 29% 15% 6%	840
December	1st to 10th	Night	31% 18% 30% 16% 4	840
	11th to 20th	Night	28% 21% 32% 16% 3	840
	21st to end	Night	31% 17% 31% 19% 2	924

Page generated at 2026-05-14 01:59:01. Version ac07

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