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 2024-11-30.

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	11% 8% 3 8% 5% 4 4 4 6% 7% 40%	105520
	Night	9% 9% 3 8% 5% 5% 5% 4 6% 7% 40%	102733
Transparency	Day	42% 6% 13% 26% 11% 1	105254
	Night	42% 6% 13% 24% 13% 2	102589
Seeing	Day	15% 11% 32% 28% 12% 2	16136
	Night	13% 9% 36% 32% 9% 1	26071

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	7% 15% 6% 13% 8% 8% 6% 5% 8% 6% 18%	2286
	11th to 20th	Day	4 9% 4 12% 8% 6% 11% 10% 10% 7% 20%	2540
	21st to end	Day	5% 11% 5% 21% 9% 6% 4 4 6% 7% 22%	2889
February	1st to 10th	Day	7% 12% 4 11% 7% 8% 6% 5% 6% 7% 26%	1710
	11th to 20th	Day	6% 10% 5% 12% 7% 8% 6% 6% 5% 6% 27%	1680
	21st to end	Day	8% 12% 5% 13% 7% 6% 6% 4 5% 7% 27%	1570
March	1st to 10th	Day	10% 12% 4 10% 6% 5% 5% 3 4 7% 35%	3222
	11th to 20th	Day	8% 14% 3 9% 6% 4 4 3 5% 8% 36%	3480
	21st to end	Day	20% 15% 5% 14% 7% 4 3 3 3 5% 20%	3814
April	1st to 10th	Day	14% 11% 3 6% 4 4 4 4 5% 7% 38%	2228
	11th to 20th	Day	16% 14% 4 7% 4 4 4 3 5% 6% 33%	2439
	21st to end	Day	18% 12% 4 7% 4 4 4 4 5% 6% 33%	2470
May	1st to 10th	Day	13% 9% 3 7% 4 4 4 4 5% 6% 40%	4120
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 6% 7% 43%	4195
	21st to end	Day	17% 7% 2 7% 5% 4 5% 4 6% 8% 36%	5077
June	1st to 10th	Day	13% 5% 2 5% 4 4 4 5% 6% 8% 43%	2850
	11th to 20th	Day	11% 6% 2 7% 4 5% 5% 4 6% 8% 42%	2850
	21st to end	Day	9% 5% 2 6% 4 4 5% 5% 6% 8% 47%	2850
July	1st to 10th	Day	10% 5% 2 5% 4 4 5% 5% 7% 9% 44%	4750
	11th to 20th	Day	4 3 1 3 3 3 4 3 6% 9% 61%	4596
	21st to end	Day	5% 3 1 6% 5% 5% 6% 5% 7% 10% 48%	4723
August	1st to 10th	Day	11% 5% 2 5% 3 4 4 4 6% 8% 47%	4103
	11th to 20th	Day	14% 7% 2 6% 5% 5% 4 3 6% 8% 40%	4041
	21st to end	Day	7% 5% 2 5% 4 4 4 3 5% 8% 53%	4532
September	1st to 10th	Day	10% 5% 2 4 3 4 4 3 5% 7% 54%	2254
	11th to 20th	Day	10% 6% 2 5% 3 3 4 3 5% 8% 51%	2090
	21st to end	Day	13% 7% 2 5% 4 3 3 2 4 6% 51%	2090
October	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 7% 55%	3289
	11th to 20th	Day	11% 9% 3 6% 3 3 3 2 4 5% 51%	3140
	21st to end	Day	14% 9% 3 7% 3 3 4 3 5% 7% 41%	3130
November	1st to 10th	Day	13% 12% 5% 7% 5% 3 4 3 5% 7% 37%	1763
	11th to 20th	Day	9% 12% 5% 12% 7% 5% 4 4 5% 5% 33%	1605
	21st to end	Day	8% 11% 3 11% 6% 5% 4 3 6% 6% 34%	1597
December	1st to 10th	Day	7% 11% 4 14% 8% 5% 6% 6% 5% 5% 26%	1422
	11th to 20th	Day	8% 11% 5% 11% 6% 6% 5% 4 7% 9% 28%	1683
	21st to end	Day	16% 12% 6% 16% 5% 5% 4 3 4 4 25%	2442
January	1st to 10th	Night	6% 10% 5% 13% 8% 9% 9% 6% 7% 6% 21%	4664
	11th to 20th	Night	4 9% 4 10% 8% 8% 12% 9% 9% 6% 21%	4430
	21st to end	Night	5% 11% 6% 17% 7% 5% 5% 5% 7% 6% 26%	4776
February	1st to 10th	Night	6% 10% 5% 12% 7% 7% 7% 5% 6% 6% 30%	2470
	11th to 20th	Night	7% 10% 4 10% 6% 5% 7% 5% 6% 7% 33%	2403
	21st to end	Night	8% 11% 4 9% 7% 6% 5% 5% 5% 6% 33%	1884
March	1st to 10th	Night	8% 8% 3 8% 6% 5% 5% 5% 5% 7% 39%	3638
	11th to 20th	Night	8% 11% 4 10% 7% 5% 4 4 5% 7% 36%	3480
	21st to end	Night	19% 13% 4 9% 7% 4 4 4 5% 7% 24%	3817
April	1st to 10th	Night	12% 11% 3 7% 4 4 5% 3 6% 6% 39%	1950
	11th to 20th	Night	17% 10% 5% 6% 4 3 3 3 4 5% 39%	1689
	21st to end	Night	15% 11% 4 7% 5% 4 4 4 5% 5% 36%	1710
May	1st to 10th	Night	15% 6% 2 5% 3 3 4 4 5% 7% 46%	2850
	11th to 20th	Night	10% 5% 2 6% 5% 5% 5% 4 6% 7% 45%	2710
	21st to end	Night	12% 7% 2 7% 4 3 5% 4 6% 8% 42%	2507
June	1st to 10th	Night	10% 4 1 4 4 4 4 4 5% 9% 49%	1330
	11th to 20th	Night	9% 6% 1 4 4 4 5% 5% 6% 9% 47%	1330
	21st to end	Night	7% 3 2 3 3 3 4 3 5% 8% 59%	1330
July	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 7% 10% 46%	2220
	11th to 20th	Night	3 2 1 3 3 3 3 3 4 6% 69%	2370
	21st to end	Night	4 3 2 5% 4 4 5% 5% 7% 11% 51%	2837
August	1st to 10th	Night	8% 5% 3 6% 3 4 5% 3 5% 7% 52%	2836
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 5% 7% 48%	2798
	21st to end	Night	8% 5% 2 5% 4 4 3 4 5% 7% 53%	3135
September	1st to 10th	Night	7% 5% 1 4 3 2 3 3 5% 6% 61%	1924
	11th to 20th	Night	9% 5% 1 5% 4 3 4 2 4 6% 56%	2090
	21st to end	Night	12% 5% 1 4 3 3 3 3 4 6% 56%	2090
October	1st to 10th	Night	8% 5% 1 4 3 2 3 2 4 5% 63%	3638
	11th to 20th	Night	11% 7% 2 5% 4 4 3 3 6% 7% 48%	3779
	21st to end	Night	12% 9% 3 7% 4 3 4 3 5% 6% 44%	4426
November	1st to 10th	Night	9% 11% 3 8% 4 4 5% 4 5% 6% 40%	2535
	11th to 20th	Night	8% 10% 5% 12% 6% 5% 3 3 4 6% 38%	2794
	21st to end	Night	8% 10% 3 9% 6% 5% 3 3 6% 8% 39%	2799
December	1st to 10th	Night	6% 12% 4 12% 9% 6% 5% 4 5% 7% 30%	2755
	11th to 20th	Night	8% 12% 5% 12% 6% 5% 5% 4 6% 7% 30%	3514
	21st to end	Night	15% 15% 5% 14% 6% 4 4 3 4 5% 26%	5225

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	60% 8% 10% 15% 5% 1	2287
	11th to 20th	Day	55% 10% 13% 19% 4	2540
	21st to end	Day	57% 11% 9% 19% 4	2889
February	1st to 10th	Day	54% 5% 13% 19% 7% 1	1710
	11th to 20th	Day	53% 8% 12% 19% 6% 1	1689
	21st to end	Day	55% 7% 14% 16% 8%	1570
March	1st to 10th	Day	49% 7% 11% 26% 7% 1	3222
	11th to 20th	Day	45% 6% 13% 27% 8% 1	3480
	21st to end	Day	67% 5% 11% 12% 4 1	3814
April	1st to 10th	Day	45% 6% 12% 25% 11% 1	2228
	11th to 20th	Day	51% 5% 11% 21% 12% 1	2442
	21st to end	Day	51% 5% 12% 23% 8%	2470
May	1st to 10th	Day	43% 6% 9% 26% 14% 1	4120
	11th to 20th	Day	38% 8% 10% 29% 13% 3	4199
	21st to end	Day	42% 9% 13% 25% 9%	5077
June	1st to 10th	Day	36% 6% 16% 29% 11% 1	2850
	11th to 20th	Day	39% 8% 14% 25% 12% 2	2850
	21st to end	Day	33% 7% 18% 28% 12% 1	2850
July	1st to 10th	Day	36% 5% 18% 29% 12% 1	4676
	11th to 20th	Day	21% 4 15% 39% 18% 2	4515
	21st to end	Day	30% 5% 18% 31% 14% 1	4573
August	1st to 10th	Day	34% 5% 14% 30% 14% 3	4090
	11th to 20th	Day	41% 4 14% 32% 7% 1	4080
	21st to end	Day	31% 5% 16% 33% 13% 2	4531
September	1st to 10th	Day	30% 5% 13% 36% 15% 1	2254
	11th to 20th	Day	32% 5% 18% 33% 12% 1	2090
	21st to end	Day	36% 4 13% 30% 15% 2	2090
October	1st to 10th	Day	31% 3 9% 31% 24% 2	3289
	11th to 20th	Day	37% 3 9% 30% 18% 3	3140
	21st to end	Day	44% 3 15% 24% 14%	3130
November	1st to 10th	Day	47% 5% 12% 21% 13% 2	1763
	11th to 20th	Day	51% 6% 15% 18% 9% 1	1605
	21st to end	Day	49% 6% 15% 22% 7% 2	1597
December	1st to 10th	Day	56% 7% 12% 17% 6% 1	1422
	11th to 20th	Day	50% 8% 17% 20% 4	1680
	21st to end	Day	60% 7% 8% 19% 5%	2442
January	1st to 10th	Night	57% 10% 10% 17% 6%	4664
	11th to 20th	Night	54% 10% 13% 16% 7% 1	4430
	21st to end	Night	53% 11% 11% 18% 7%	4776
February	1st to 10th	Night	53% 6% 13% 16% 11% 1	2470
	11th to 20th	Night	47% 6% 12% 22% 11% 2	2404
	21st to end	Night	49% 6% 12% 18% 12% 2	1884
March	1st to 10th	Night	42% 6% 13% 27% 10% 2	3638
	11th to 20th	Night	45% 7% 12% 27% 9% 1	3480
	21st to end	Night	57% 7% 12% 16% 6% 1	3817
April	1st to 10th	Night	44% 5% 11% 25% 13% 1	1950
	11th to 20th	Night	47% 4 9% 23% 15% 2	1689
	21st to end	Night	49% 6% 10% 24% 10% 1	1710
May	1st to 10th	Night	37% 5% 11% 29% 15% 3	2850
	11th to 20th	Night	35% 8% 10% 29% 16% 2	2711
	21st to end	Night	37% 8% 13% 31% 10%	2508
June	1st to 10th	Night	31% 5% 18% 29% 14% 3	1330
	11th to 20th	Night	32% 7% 16% 25% 16% 4	1330
	21st to end	Night	24% 5% 20% 32% 16% 2	1330
July	1st to 10th	Night	34% 6% 20% 25% 14% 1	2185
	11th to 20th	Night	16% 3 11% 45% 21% 2	2328
	21st to end	Night	27% 5% 21% 28% 16% 3	2748
August	1st to 10th	Night	31% 5% 15% 29% 17% 4	2826
	11th to 20th	Night	36% 4 16% 30% 12% 1	2825
	21st to end	Night	31% 5% 15% 29% 18% 2	3135
September	1st to 10th	Night	25% 5% 12% 35% 21% 2	1924
	11th to 20th	Night	30% 4 15% 32% 18% 1	2090
	21st to end	Night	30% 5% 12% 30% 20% 3	2090
October	1st to 10th	Night	25% 4 8% 30% 30% 3	3638
	11th to 20th	Night	36% 3 11% 28% 21% 2	3779
	21st to end	Night	42% 4 12% 27% 15% 1	4426
November	1st to 10th	Night	43% 5% 11% 22% 17% 3	2535
	11th to 20th	Night	47% 5% 13% 20% 13% 2	2794
	21st to end	Night	44% 5% 17% 24% 9% 1	2799
December	1st to 10th	Night	52% 6% 16% 19% 8%	2755
	11th to 20th	Night	52% 7% 18% 18% 5%	3516
	21st to end	Night	62% 5% 9% 17% 7%	5225

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	12% 11% 38% 31% 7% 1	270
	11th to 20th	Day	12% 13% 39% 30% 6%	270
	21st to end	Day	16% 11% 36% 28% 9%	297
February	1st to 10th	Day	13% 13% 44% 27% 3	270
	11th to 20th	Day	14% 16% 41% 24% 6% 1	270
	21st to end	Day	15% 12% 44% 26% 3	225
March	1st to 10th	Day	17% 17% 37% 24% 4 1	270
	11th to 20th	Day	13% 12% 40% 23% 10% 2	270
	21st to end	Day	18% 15% 26% 27% 11% 3	297
April	1st to 10th	Day	22% 17% 35% 19% 7%	408
	11th to 20th	Day	28% 15% 29% 19% 8% 1	640
	21st to end	Day	23% 12% 31% 23% 9% 2	650
May	1st to 10th	Day	19% 12% 32% 27% 10%	653
	11th to 20th	Day	19% 11% 26% 29% 12% 2	675
	21st to end	Day	17% 11% 27% 30% 12% 2	734
June	1st to 10th	Day	10% 9% 27% 31% 18% 4	680
	11th to 20th	Day	13% 11% 40% 23% 11% 2	680
	21st to end	Day	13% 7% 34% 30% 13% 2	680
July	1st to 10th	Day	8% 5% 25% 34% 22% 6%	671
	11th to 20th	Day	6% 7% 30% 36% 16% 4	668
	21st to end	Day	5% 5% 26% 39% 21% 4	739
August	1st to 10th	Day	10% 5% 23% 39% 20% 4	676
	11th to 20th	Day	14% 5% 27% 32% 17% 5%	665
	21st to end	Day	11% 5% 29% 34% 17% 4	748
September	1st to 10th	Day	13% 9% 28% 33% 15% 2	464
	11th to 20th	Day	12% 10% 40% 25% 12% 2	300
	21st to end	Day	20% 14% 30% 22% 11% 2	300
October	1st to 10th	Day	19% 11% 29% 27% 12% 2	300
	11th to 20th	Day	14% 17% 36% 27% 5% 1	300
	21st to end	Day	20% 18% 38% 17% 6% 1	330
November	1st to 10th	Day	21% 14% 34% 24% 6% 1	300
	11th to 20th	Day	18% 14% 42% 18% 8%	300
	21st to end	Day	17% 17% 40% 21% 4 1	299
December	1st to 10th	Day	15% 9% 45% 21% 10% 1	270
	11th to 20th	Day	12% 14% 49% 23% 3	270
	21st to end	Day	21% 15% 37% 22% 4 1	297
January	1st to 10th	Night	10% 12% 42% 28% 6% 1	950
	11th to 20th	Night	13% 11% 41% 31% 5%	950
	21st to end	Night	14% 10% 41% 29% 6%	1045
February	1st to 10th	Night	11% 12% 39% 31% 7% 1	950
	11th to 20th	Night	11% 10% 44% 27% 7% 2	929
	21st to end	Night	15% 8% 38% 26% 10% 3	628
March	1st to 10th	Night	14% 11% 39% 26% 9% 1	703
	11th to 20th	Night	17% 11% 37% 28% 7% 1	570
	21st to end	Night	15% 10% 34% 28% 13% 1	627
April	1st to 10th	Night	17% 11% 38% 28% 6%	570
	11th to 20th	Night	22% 12% 28% 27% 9% 1	563
	21st to end	Night	21% 10% 33% 27% 9% 1	570
May	1st to 10th	Night	17% 8% 33% 33% 8% 1	570
	11th to 20th	Night	13% 8% 32% 36% 11%	561
	21st to end	Night	13% 9% 32% 35% 11%	617
June	1st to 10th	Night	12% 7% 27% 40% 12% 1	570
	11th to 20th	Night	12% 5% 35% 39% 7%	570
	21st to end	Night	9% 3 31% 44% 13% 1	570
July	1st to 10th	Night	7% 4 26% 41% 20% 1	555
	11th to 20th	Night	4 2 29% 50% 15% 1	552
	21st to end	Night	5% 3 24% 51% 16% 1	624
August	1st to 10th	Night	7% 3 22% 51% 17% 1	567
	11th to 20th	Night	10% 3 27% 40% 17% 3	564
	21st to end	Night	7% 2 32% 40% 17% 1	627
September	1st to 10th	Night	10% 4 33% 39% 12% 2	570
	11th to 20th	Night	11% 6% 31% 36% 15% 1	570
	21st to end	Night	14% 6% 36% 31% 12% 1	570
October	1st to 10th	Night	17% 11% 32% 31% 9%	663
	11th to 20th	Night	19% 9% 36% 28% 7%	760
	21st to end	Night	20% 10% 37% 26% 6%	1016
November	1st to 10th	Night	14% 10% 38% 30% 7%	975
	11th to 20th	Night	13% 12% 40% 26% 8% 1	1000
	21st to end	Night	13% 12% 44% 27% 4	1000
December	1st to 10th	Night	12% 11% 41% 28% 7% 1	950
	11th to 20th	Night	16% 11% 42% 25% 5% 1	950
	21st to end	Night	20% 11% 38% 25% 5%	1045

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