Bremmon Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bremmon Road clear sky chart from 2005-11-06 to 2026-02-16.

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	10% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	139451
	Night	8% 8% 3 8% 6% 5% 6% 4 6% 7% 39%	138752
Transparency	Day	43% 5% 13% 26% 11% 1	134108
	Night	44% 5% 13% 24% 13% 1	135104
Seeing	Day	15% 11% 33% 28% 12% 2	17764
	Night	13% 9% 36% 32% 9% 1	27827

By Month

Percentage Cloud Cover SW (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	5% 12% 5% 14% 12% 11% 9% 7% 7% 6% 14%	4261
	11th to 20th	Day	3 7% 3 12% 8% 8% 11% 10% 11% 7% 19%	4740
	21st to end	Day	3 6% 5% 16% 10% 6% 6% 6% 7% 8% 28%	5374
February	1st to 10th	Day	7% 13% 5% 11% 7% 8% 6% 5% 6% 7% 25%	1890
	11th to 20th	Day	6% 10% 5% 12% 7% 8% 6% 6% 6% 7% 29%	1816
	21st to end	Day	8% 11% 5% 13% 7% 6% 6% 4 6% 7% 27%	1650
March	1st to 10th	Day	9% 9% 3 9% 5% 4 5% 3 4 7% 43%	4631
	11th to 20th	Day	8% 11% 3 9% 5% 4 4 3 5% 9% 37%	4980
	21st to end	Day	18% 13% 6% 13% 7% 5% 4 3 4 6% 20%	5464
April	1st to 10th	Day	14% 11% 3 6% 4 4 4 3 5% 7% 38%	2345
	11th to 20th	Day	16% 14% 4 7% 4 4 4 3 5% 6% 33%	2569
	21st to end	Day	18% 11% 3 7% 4 4 4 3 5% 6% 33%	2600
May	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 4 7% 50%	5900
	11th to 20th	Day	19% 9% 2 5% 3 3 3 3 5% 6% 42%	6017
	21st to end	Day	16% 7% 2 7% 5% 4 5% 4 6% 8% 36%	7292
June	1st to 10th	Day	13% 5% 2 5% 4 4 4 5% 6% 8% 43%	3000
	11th to 20th	Day	12% 6% 2 7% 4 5% 5% 4 6% 8% 41%	3000
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 8% 47%	3000
July	1st to 10th	Day	8% 4 2 5% 4 4 5% 4 7% 10% 47%	6799
	11th to 20th	Day	6% 5% 2 5% 4 3 4 3 6% 8% 55%	6576
	21st to end	Day	7% 4 2 6% 5% 5% 6% 5% 7% 10% 43%	6785
August	1st to 10th	Day	12% 5% 2 6% 4 4 4 4 6% 8% 43%	5801
	11th to 20th	Day	11% 7% 2 6% 5% 4 4 4 6% 9% 41%	5821
	21st to end	Day	6% 4 2 5% 4 4 4 4 5% 8% 55%	6490
September	1st to 10th	Day	9% 5% 2 4 3 4 4 3 5% 7% 54%	2372
	11th to 20th	Day	10% 6% 2 5% 4 3 5% 3 5% 8% 50%	2200
	21st to end	Day	13% 6% 2 5% 4 3 3 2 4 6% 52%	2200
October	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 8% 55%	3393
	11th to 20th	Day	11% 9% 3 7% 3 3 3 3 4 5% 50%	3240
	21st to end	Day	14% 9% 3 7% 3 3 4 3 5% 7% 41%	3230
November	1st to 10th	Day	12% 11% 5% 8% 5% 3 4 3 5% 7% 36%	1853
	11th to 20th	Day	9% 11% 5% 11% 6% 5% 4 4 5% 6% 34%	1685
	21st to end	Day	8% 11% 3 11% 7% 5% 5% 3 6% 6% 34%	1680
December	1st to 10th	Day	6% 9% 4 16% 10% 8% 7% 6% 6% 7% 21%	2509
	11th to 20th	Day	7% 12% 6% 13% 7% 7% 6% 5% 7% 8% 22%	2713
	21st to end	Day	12% 11% 5% 16% 8% 5% 5% 3 6% 5% 24%	3575
January	1st to 10th	Night	4 8% 4 13% 10% 10% 12% 7% 8% 7% 17%	8642
	11th to 20th	Night	3 8% 4 10% 8% 7% 13% 9% 10% 7% 22%	8250
	21st to end	Night	3 7% 5% 12% 7% 6% 7% 5% 8% 7% 33%	8838
February	1st to 10th	Night	6% 11% 5% 12% 7% 7% 6% 4 6% 6% 29%	2730
	11th to 20th	Night	6% 9% 4 10% 5% 5% 7% 6% 7% 7% 35%	2599
	21st to end	Night	8% 11% 4 9% 6% 5% 5% 5% 5% 6% 35%	1980
March	1st to 10th	Night	8% 7% 3 7% 5% 5% 5% 4 5% 8% 42%	5236
	11th to 20th	Night	8% 9% 3 9% 6% 5% 4 4 6% 8% 37%	4980
	21st to end	Night	17% 12% 4 9% 6% 5% 4 3 5% 7% 28%	5467
April	1st to 10th	Night	12% 11% 3 7% 4 4 5% 3 6% 6% 39%	2052
	11th to 20th	Night	16% 10% 5% 6% 4 3 3 3 4 6% 39%	1779
	21st to end	Night	16% 11% 4 7% 5% 4 5% 4 5% 5% 35%	1800
May	1st to 10th	Night	13% 5% 2 4 3 2 3 3 5% 6% 55%	4080
	11th to 20th	Night	15% 8% 2 5% 4 4 4 3 5% 6% 44%	3898
	21st to end	Night	14% 7% 2 6% 4 3 5% 3 6% 7% 42%	3602
June	1st to 10th	Night	11% 4 1 4 4 4 4 4 5% 8% 50%	1400
	11th to 20th	Night	9% 6% 1 4 4 4 5% 5% 6% 9% 46%	1400
	21st to end	Night	6% 4 2 4 3 3 4 3 5% 8% 58%	1400
July	1st to 10th	Night	7% 5% 2 6% 3 3 4 3 6% 9% 51%	3180
	11th to 20th	Night	6% 3 1 4 3 3 4 3 5% 7% 60%	3400
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 7% 10% 46%	4085
August	1st to 10th	Night	10% 6% 3 6% 4 4 5% 3 6% 7% 46%	4011
	11th to 20th	Night	10% 6% 3 6% 4 4 4 3 5% 7% 49%	4028
	21st to end	Night	6% 4 1 4 3 4 3 4 5% 8% 57%	4487
September	1st to 10th	Night	7% 4 1 4 3 2 3 3 5% 6% 60%	2025
	11th to 20th	Night	10% 5% 1 5% 4 3 4 2 5% 6% 55%	2200
	21st to end	Night	12% 5% 1 4 3 3 3 3 4 5% 57%	2200
October	1st to 10th	Night	8% 5% 1 4 3 2 3 2 4 5% 63%	3753
	11th to 20th	Night	12% 7% 2 5% 4 4 3 3 6% 7% 47%	3899
	21st to end	Night	12% 9% 3 7% 4 3 4 3 5% 6% 44%	4568
November	1st to 10th	Night	8% 11% 3 9% 5% 5% 5% 4 5% 7% 40%	2665
	11th to 20th	Night	7% 10% 5% 12% 6% 5% 3 3 4 6% 38%	2934
	21st to end	Night	8% 10% 3 10% 6% 5% 4 3 5% 8% 38%	2940
December	1st to 10th	Night	4 10% 4 13% 8% 9% 6% 4 5% 7% 31%	4885
	11th to 20th	Night	6% 11% 6% 13% 8% 7% 7% 4 5% 6% 25%	5714
	21st to end	Night	11% 13% 5% 14% 8% 5% 5% 4 5% 5% 25%	7645

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	68% 6% 8% 12% 6% 1	4263
	11th to 20th	Day	56% 7% 12% 17% 7%	4740
	21st to end	Day	51% 7% 14% 19% 10%	5374
February	1st to 10th	Day	56% 5% 13% 18% 7% 1	1890
	11th to 20th	Day	51% 8% 11% 21% 8% 1	1825
	21st to end	Day	54% 7% 15% 16% 8%	1650
March	1st to 10th	Day	41% 5% 15% 29% 8% 1	4631
	11th to 20th	Day	44% 5% 12% 28% 10% 1	4980
	21st to end	Day	65% 4 12% 15% 3 1	5464
April	1st to 10th	Day	46% 6% 12% 25% 11% 1	2345
	11th to 20th	Day	51% 5% 11% 21% 12% 1	2572
	21st to end	Day	51% 5% 12% 23% 8% 1	2600
May	1st to 10th	Day	34% 5% 9% 30% 21%	5900
	11th to 20th	Day	43% 5% 8% 22% 17% 5%	6021
	21st to end	Day	43% 7% 11% 27% 11%	7293
June	1st to 10th	Day	37% 6% 16% 29% 11% 1	3000
	11th to 20th	Day	40% 7% 15% 24% 12% 2	3000
	21st to end	Day	34% 7% 18% 28% 13% 1	3000
July	1st to 10th	Day	33% 4 20% 32% 12% 1	6726
	11th to 20th	Day	29% 4 13% 38% 14% 1	6495
	21st to end	Day	36% 4 20% 28% 11% 1	6588
August	1st to 10th	Day	35% 5% 14% 29% 14% 3	4220
	11th to 20th	Day	41% 4 14% 32% 7% 1	4210
	21st to end	Day	31% 5% 16% 33% 13% 2	4674
September	1st to 10th	Day	30% 5% 13% 36% 14% 1	2372
	11th to 20th	Day	34% 5% 19% 31% 11% 1	2200
	21st to end	Day	35% 4 12% 31% 16% 2	2200
October	1st to 10th	Day	30% 3 9% 31% 24% 3	3393
	11th to 20th	Day	38% 3 9% 30% 18% 3	3240
	21st to end	Day	44% 3 15% 24% 15%	3230
November	1st to 10th	Day	47% 5% 12% 21% 13% 2	1853
	11th to 20th	Day	50% 6% 15% 18% 9% 1	1685
	21st to end	Day	50% 5% 15% 21% 7% 2	1680
December	1st to 10th	Day	60% 6% 14% 15% 4 1	2509
	11th to 20th	Day	58% 7% 15% 17% 3	2710
	21st to end	Day	60% 5% 11% 16% 7%	3575
January	1st to 10th	Night	60% 7% 12% 14% 6%	8643
	11th to 20th	Night	54% 7% 12% 16% 9% 1	8250
	21st to end	Night	45% 8% 14% 21% 12%	8838
February	1st to 10th	Night	53% 6% 13% 16% 11% 1	2730
	11th to 20th	Night	45% 6% 12% 23% 13% 2	2600
	21st to end	Night	48% 6% 12% 19% 13% 2	1980
March	1st to 10th	Night	39% 5% 13% 29% 12% 2	5236
	11th to 20th	Night	43% 5% 13% 25% 12%	4980
	21st to end	Night	55% 6% 12% 20% 6% 1	5467
April	1st to 10th	Night	44% 5% 11% 25% 13% 1	2052
	11th to 20th	Night	46% 4 9% 24% 15% 2	1779
	21st to end	Night	50% 5% 10% 24% 10% 1	1800
May	1st to 10th	Night	30% 5% 11% 30% 22% 2	4080
	11th to 20th	Night	40% 6% 7% 22% 20% 5%	3899
	21st to end	Night	39% 6% 11% 32% 12%	3603
June	1st to 10th	Night	32% 5% 17% 30% 13% 3	1400
	11th to 20th	Night	33% 6% 17% 25% 15% 3	1400
	21st to end	Night	25% 5% 20% 31% 17% 2	1400
July	1st to 10th	Night	30% 5% 16% 34% 14% 1	3145
	11th to 20th	Night	25% 3 12% 42% 16% 2	3358
	21st to end	Night	33% 4 21% 28% 12% 2	3969
August	1st to 10th	Night	31% 4 15% 29% 16% 3	2916
	11th to 20th	Night	36% 4 16% 30% 12% 1	2915
	21st to end	Night	31% 5% 15% 29% 18% 2	3234
September	1st to 10th	Night	25% 5% 13% 36% 20% 1	2025
	11th to 20th	Night	31% 4 16% 31% 17% 1	2200
	21st to end	Night	29% 5% 12% 31% 20% 3	2200
October	1st to 10th	Night	25% 4 8% 31% 30% 3	3753
	11th to 20th	Night	37% 3 10% 27% 21% 2	3899
	21st to end	Night	42% 4 12% 27% 14% 1	4568
November	1st to 10th	Night	44% 5% 11% 22% 16% 3	2665
	11th to 20th	Night	48% 5% 14% 20% 13% 2	2934
	21st to end	Night	45% 4 17% 23% 9% 1	2940
December	1st to 10th	Night	52% 4 20% 16% 7%	4885
	11th to 20th	Night	58% 5% 15% 17% 4	5716
	21st to end	Night	61% 4 10% 18% 6%	7645

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	11% 11% 40% 30% 7% 1	330
	11th to 20th	Day	12% 16% 40% 27% 6%	330
	21st to end	Day	13% 14% 39% 26% 8%	363
February	1st to 10th	Day	15% 15% 42% 24% 3 1	330
	11th to 20th	Day	12% 14% 41% 24% 7% 2	315
	21st to end	Day	14% 12% 45% 27% 2	249
March	1st to 10th	Day	16% 16% 39% 24% 4 1	300
	11th to 20th	Day	13% 14% 39% 23% 9% 2	300
	21st to end	Day	18% 15% 28% 25% 10% 3	330
April	1st to 10th	Day	22% 16% 36% 20% 7%	445
	11th to 20th	Day	27% 15% 30% 19% 8% 1	690
	21st to end	Day	24% 12% 31% 22% 9% 2	700
May	1st to 10th	Day	18% 12% 31% 28% 11% 1	703
	11th to 20th	Day	21% 10% 26% 29% 12% 2	725
	21st to end	Day	17% 11% 26% 30% 14% 2	789
June	1st to 10th	Day	11% 10% 27% 30% 18% 4	730
	11th to 20th	Day	14% 11% 40% 23% 11% 2	730
	21st to end	Day	14% 7% 34% 30% 13% 2	730
July	1st to 10th	Day	8% 4 26% 34% 22% 5%	721
	11th to 20th	Day	7% 7% 31% 36% 16% 4	718
	21st to end	Day	6% 5% 27% 38% 20% 4	794
August	1st to 10th	Day	11% 6% 23% 38% 19% 3	726
	11th to 20th	Day	14% 5% 28% 31% 17% 5%	715
	21st to end	Day	11% 5% 28% 35% 17% 4	803
September	1st to 10th	Day	13% 9% 29% 32% 16% 2	502
	11th to 20th	Day	13% 9% 40% 23% 12% 2	330
	21st to end	Day	18% 13% 29% 25% 12% 3	330
October	1st to 10th	Day	18% 10% 29% 28% 12% 2	330
	11th to 20th	Day	14% 20% 35% 25% 5% 1	330
	21st to end	Day	20% 17% 39% 17% 6% 1	363
November	1st to 10th	Day	20% 15% 35% 22% 6% 1	330
	11th to 20th	Day	18% 14% 42% 19% 7%	330
	21st to end	Day	17% 15% 42% 21% 4 1	330
December	1st to 10th	Day	15% 9% 46% 19% 9% 1	330
	11th to 20th	Day	13% 16% 46% 22% 3	330
	21st to end	Day	19% 15% 39% 22% 5% 1	363
January	1st to 10th	Night	10% 11% 43% 28% 7% 1	1050
	11th to 20th	Night	12% 11% 42% 30% 4	1050
	21st to end	Night	12% 11% 42% 28% 6%	1155
February	1st to 10th	Night	12% 12% 39% 30% 6% 1	1050
	11th to 20th	Night	10% 10% 44% 27% 8% 1	1005
	21st to end	Night	15% 9% 38% 25% 10% 3	660
March	1st to 10th	Night	14% 11% 39% 27% 9% 1	740
	11th to 20th	Night	16% 12% 37% 27% 7% 1	600
	21st to end	Night	15% 9% 35% 28% 12% 1	660
April	1st to 10th	Night	17% 11% 39% 28% 6%	600
	11th to 20th	Night	22% 13% 29% 27% 9% 1	593
	21st to end	Night	21% 10% 33% 27% 8% 1	600
May	1st to 10th	Night	17% 8% 33% 33% 8% 1	600
	11th to 20th	Night	14% 8% 32% 35% 10%	591
	21st to end	Night	14% 8% 31% 35% 12% 1	650
June	1st to 10th	Night	12% 7% 27% 40% 12% 1	600
	11th to 20th	Night	13% 5% 36% 40% 7%	600
	21st to end	Night	9% 3 32% 43% 12% 1	600
July	1st to 10th	Night	8% 4 26% 41% 19% 2	585
	11th to 20th	Night	4 2 29% 49% 15% 1	582
	21st to end	Night	5% 3 25% 50% 15% 1	657
August	1st to 10th	Night	8% 3 23% 50% 16% 1	597
	11th to 20th	Night	10% 3 27% 40% 17% 3	594
	21st to end	Night	7% 3 31% 41% 18% 1	660
September	1st to 10th	Night	10% 5% 32% 39% 13% 2	600
	11th to 20th	Night	12% 6% 31% 36% 14% 1	600
	21st to end	Night	13% 6% 35% 32% 14% 1	600
October	1st to 10th	Night	16% 11% 33% 30% 9%	698
	11th to 20th	Night	20% 9% 37% 27% 7%	800
	21st to end	Night	20% 10% 37% 26% 6%	1070
November	1st to 10th	Night	14% 10% 39% 30% 7%	1025
	11th to 20th	Night	13% 12% 40% 26% 8% 1	1050
	21st to end	Night	14% 12% 44% 27% 4	1050
December	1st to 10th	Night	12% 12% 41% 28% 7%	1050
	11th to 20th	Night	15% 12% 43% 24% 5% 1	1050
	21st to end	Night	19% 11% 40% 24% 5%	1155

Page generated at 2026-02-13 00:42:12. Version ac07

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