Brandon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brandon clear sky chart from 2005-11-06 to 2024-05-13.

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	8% 6% 2 7% 6% 5% 6% 5% 7% 9% 39%	83999
	Night	9% 6% 2 7% 5% 5% 5% 4 7% 9% 42%	85509
Transparency	Day	39% 10% 14% 18% 14% 5%	83722
	Night	36% 9% 16% 19% 14% 5%	85305
Seeing	Day	8% 6% 19% 26% 24% 18%	14793
	Night	9% 4 21% 34% 25% 8%	24933

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	11% 6% 3 8% 4 4 5% 4 6% 8% 40%	2836
	11th to 20th	Day	21% 8% 3 7% 4 4 4 3 5% 8% 34%	2840
	21st to end	Day	10% 6% 2 6% 5% 4 4 4 6% 8% 44%	3358
February	1st to 10th	Day	11% 6% 2 5% 4 3 4 4 6% 8% 46%	1900
	11th to 20th	Day	7% 3 2 5% 4 4 4 4 5% 6% 55%	1848
	21st to end	Day	7% 6% 2 4 4 4 5% 3 5% 7% 52%	1632
March	1st to 10th	Day	6% 6% 3 9% 6% 5% 6% 5% 6% 9% 38%	3435
	11th to 20th	Day	6% 4 2 5% 4 3 4 4 7% 10% 51%	3480
	21st to end	Day	9% 4 2 4 3 3 3 3 6% 8% 52%	3815
April	1st to 10th	Day	7% 4 1 4 4 5% 5% 5% 6% 10% 49%	2090
	11th to 20th	Day	7% 5% 2 7% 5% 5% 4 5% 6% 8% 45%	2066
	21st to end	Day	4 3 2 4 4 4 5% 5% 5% 9% 53%	2260
May	1st to 10th	Day	4 2 2 3 4 3 4 4 6% 9% 58%	2470
	11th to 20th	Day	8% 5% 2 6% 6% 5% 7% 6% 7% 9% 40%	2329
	21st to end	Day	6% 6% 2 6% 8% 6% 7% 6% 8% 9% 37%	2531
June	1st to 10th	Day	12% 7% 3 9% 6% 6% 7% 7% 10% 10% 23%	2340
	11th to 20th	Day	6% 6% 3 8% 7% 7% 8% 7% 10% 12% 27%	2340
	21st to end	Day	7% 7% 2 8% 8% 7% 8% 6% 10% 11% 27%	2340
July	1st to 10th	Day	8% 6% 3 8% 10% 7% 9% 7% 9% 11% 22%	2340
	11th to 20th	Day	7% 7% 4 10% 10% 8% 8% 7% 9% 10% 22%	2340
	21st to end	Day	6% 7% 3 10% 9% 9% 8% 7% 9% 11% 22%	2547
August	1st to 10th	Day	7% 5% 3 10% 8% 9% 9% 6% 9% 11% 23%	2327
	11th to 20th	Day	6% 7% 3 11% 9% 9% 9% 6% 9% 10% 22%	2120
	21st to end	Day	11% 7% 3 10% 7% 7% 8% 5% 7% 11% 24%	2178
September	1st to 10th	Day	7% 7% 3 9% 7% 8% 8% 6% 10% 11% 23%	1980
	11th to 20th	Day	9% 8% 3 9% 7% 8% 8% 6% 8% 10% 24%	1980
	21st to end	Day	7% 8% 2 9% 7% 6% 6% 5% 9% 10% 31%	1980
October	1st to 10th	Day	7% 7% 2 8% 6% 7% 6% 5% 7% 9% 36%	1980
	11th to 20th	Day	6% 5% 2 6% 5% 6% 6% 5% 5% 8% 47%	1830
	21st to end	Day	7% 4 2 6% 4 4 4 4 6% 10% 49%	1980
November	1st to 10th	Day	7% 5% 2 5% 4 4 5% 4 5% 8% 50%	1857
	11th to 20th	Day	8% 6% 2 7% 5% 4 4 5% 5% 8% 46%	1900
	21st to end	Day	9% 5% 2 6% 4 5% 4 5% 7% 8% 45%	1763
December	1st to 10th	Day	8% 5% 2 5% 5% 5% 4 4 6% 10% 47%	1710
	11th to 20th	Day	11% 6% 2 7% 4 4 4 3 6% 8% 45%	2153
	21st to end	Day	13% 7% 4 9% 6% 5% 6% 4 5% 7% 35%	3124
January	1st to 10th	Night	11% 8% 3 8% 5% 5% 5% 3 6% 8% 37%	4109
	11th to 20th	Night	19% 11% 3 7% 4 4 4 3 5% 7% 32%	4120
	21st to end	Night	11% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	4294
February	1st to 10th	Night	10% 7% 2 5% 4 4 4 4 5% 8% 47%	2280
	11th to 20th	Night	9% 5% 2 5% 4 4 3 3 6% 7% 51%	2218
	21st to end	Night	7% 5% 2 7% 5% 4 4 3 6% 7% 51%	1820
March	1st to 10th	Night	13% 8% 3 9% 5% 5% 5% 4 5% 7% 37%	3418
	11th to 20th	Night	4 3 1 5% 3 4 5% 5% 9% 13% 48%	3480
	21st to end	Night	10% 5% 2 5% 3 3 5% 3 5% 7% 52%	3817
April	1st to 10th	Night	5% 5% 1 4 3 4 4 4 6% 11% 53%	2090
	11th to 20th	Night	6% 4 2 6% 4 4 5% 4 6% 9% 50%	2063
	21st to end	Night	6% 4 2 4 4 4 3 4 4 8% 58%	1926
May	1st to 10th	Night	3 3 1 4 3 3 3 3 5% 8% 63%	1713
	11th to 20th	Night	6% 6% 2 6% 4 5% 5% 5% 6% 8% 46%	1619
	21st to end	Night	6% 3 2 5% 4 5% 5% 4 6% 8% 52%	1744
June	1st to 10th	Night	11% 7% 3 6% 5% 5% 5% 5% 7% 10% 35%	1620
	11th to 20th	Night	5% 7% 2 6% 4 5% 6% 7% 8% 13% 38%	1620
	21st to end	Night	7% 4 2 7% 6% 7% 6% 6% 9% 13% 33%	1620
July	1st to 10th	Night	6% 6% 2 7% 5% 7% 7% 6% 9% 13% 31%	1620
	11th to 20th	Night	5% 6% 3 7% 7% 6% 9% 7% 11% 12% 28%	1620
	21st to end	Night	4 6% 3 9% 6% 6% 6% 7% 11% 13% 29%	1771
August	1st to 10th	Night	4 5% 2 6% 5% 6% 8% 8% 11% 13% 33%	1611
	11th to 20th	Night	4 6% 3 8% 6% 7% 7% 6% 8% 15% 31%	1763
	21st to end	Night	9% 7% 3 9% 7% 6% 6% 5% 8% 11% 29%	2171
September	1st to 10th	Night	6% 6% 2 8% 7% 6% 7% 7% 11% 13% 28%	1980
	11th to 20th	Night	9% 7% 3 9% 6% 6% 7% 6% 8% 11% 29%	1980
	21st to end	Night	8% 7% 3 9% 6% 6% 7% 5% 7% 9% 34%	1980
October	1st to 10th	Night	7% 5% 3 7% 5% 4 6% 4 7% 9% 42%	1980
	11th to 20th	Night	6% 5% 2 7% 4 5% 4 4 5% 7% 51%	2128
	21st to end	Night	7% 6% 2 7% 4 4 4 3 5% 8% 51%	2376
November	1st to 10th	Night	7% 5% 2 4 4 4 5% 3 5% 7% 54%	2221
	11th to 20th	Night	8% 5% 2 6% 5% 4 4 3 6% 6% 50%	2280
	21st to end	Night	7% 6% 3 7% 5% 5% 5% 4 6% 8% 46%	2413
December	1st to 10th	Night	8% 5% 2 6% 5% 4 4 4 6% 7% 49%	2470
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 7% 47%	3042
	21st to end	Night	13% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	4532

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	41% 6% 9% 19% 18% 8%	2837
	11th to 20th	Day	49% 4 7% 16% 17% 8%	2840
	21st to end	Day	36% 6% 8% 19% 23% 7%	3358
February	1st to 10th	Day	35% 7% 9% 19% 19% 11%	1900
	11th to 20th	Day	28% 5% 9% 19% 26% 12%	1858
	21st to end	Day	32% 5% 11% 16% 24% 11%	1632
March	1st to 10th	Day	39% 10% 13% 18% 14% 6%	3435
	11th to 20th	Day	27% 6% 13% 29% 20% 6%	3480
	21st to end	Day	29% 5% 9% 30% 17% 9%	3815
April	1st to 10th	Day	29% 8% 15% 22% 18% 8%	2090
	11th to 20th	Day	33% 9% 12% 17% 21% 8%	2066
	21st to end	Day	27% 6% 12% 23% 25% 8%	2260
May	1st to 10th	Day	21% 8% 12% 26% 23% 10%	2470
	11th to 20th	Day	38% 9% 14% 20% 16% 3	2333
	21st to end	Day	40% 11% 12% 19% 16% 3	2531
June	1st to 10th	Day	52% 12% 17% 14% 5%	2340
	11th to 20th	Day	45% 15% 19% 18% 3	2340
	21st to end	Day	47% 15% 22% 14% 2 1	2340
July	1st to 10th	Day	51% 17% 23% 7% 1	2275
	11th to 20th	Day	52% 17% 22% 9%	2271
	21st to end	Day	50% 16% 22% 11% 1	2405
August	1st to 10th	Day	48% 17% 26% 8%	2314
	11th to 20th	Day	52% 17% 21% 9% 1	2120
	21st to end	Day	52% 16% 20% 11% 2	2178
September	1st to 10th	Day	48% 18% 20% 12% 2	1980
	11th to 20th	Day	50% 15% 19% 11% 5%	1980
	21st to end	Day	45% 13% 14% 15% 10% 3	1980
October	1st to 10th	Day	43% 11% 12% 16% 11% 8%	1980
	11th to 20th	Day	34% 7% 11% 21% 22% 5%	1830
	21st to end	Day	31% 7% 12% 18% 21% 12%	1980
November	1st to 10th	Day	30% 7% 11% 21% 19% 12%	1857
	11th to 20th	Day	36% 7% 9% 20% 20% 9%	1900
	21st to end	Day	36% 6% 10% 20% 20% 8%	1763
December	1st to 10th	Day	33% 7% 12% 26% 16% 6%	1710
	11th to 20th	Day	37% 5% 11% 18% 18% 12%	2150
	21st to end	Day	46% 6% 11% 16% 15% 5%	3124
January	1st to 10th	Night	44% 6% 10% 17% 18% 6%	4109
	11th to 20th	Night	52% 4 8% 19% 13% 5%	4120
	21st to end	Night	40% 7% 12% 15% 19% 7%	4294
February	1st to 10th	Night	36% 6% 11% 18% 20% 10%	2280
	11th to 20th	Night	31% 6% 12% 18% 23% 10%	2219
	21st to end	Night	31% 5% 14% 18% 23% 8%	1820
March	1st to 10th	Night	45% 9% 11% 16% 14% 5%	3418
	11th to 20th	Night	24% 9% 22% 25% 15% 5%	3480
	21st to end	Night	31% 5% 10% 26% 22% 6%	3817
April	1st to 10th	Night	26% 6% 19% 25% 16% 7%	2090
	11th to 20th	Night	29% 8% 14% 23% 21% 6%	2063
	21st to end	Night	25% 6% 13% 26% 24% 7%	1926
May	1st to 10th	Night	19% 6% 14% 29% 23% 9%	1713
	11th to 20th	Night	32% 10% 20% 20% 16% 2	1620
	21st to end	Night	29% 9% 19% 23% 19% 2	1745
June	1st to 10th	Night	41% 12% 21% 20% 6%	1620
	11th to 20th	Night	36% 12% 28% 21% 4	1620
	21st to end	Night	38% 18% 25% 14% 5%	1620
July	1st to 10th	Night	40% 20% 30% 8% 2	1575
	11th to 20th	Night	42% 21% 28% 9% 1	1566
	21st to end	Night	39% 21% 29% 11%	1672
August	1st to 10th	Night	34% 20% 35% 10% 1	1600
	11th to 20th	Night	38% 17% 32% 12%	1763
	21st to end	Night	46% 19% 20% 13% 2	2171
September	1st to 10th	Night	41% 21% 23% 13% 2	1980
	11th to 20th	Night	46% 15% 22% 15% 2	1980
	21st to end	Night	43% 12% 17% 16% 9% 3	1980
October	1st to 10th	Night	35% 12% 14% 19% 13% 7%	1980
	11th to 20th	Night	30% 7% 12% 24% 22% 5%	2128
	21st to end	Night	32% 6% 13% 18% 22% 10%	2376
November	1st to 10th	Night	28% 6% 14% 20% 21% 11%	2221
	11th to 20th	Night	34% 7% 10% 20% 20% 9%	2280
	21st to end	Night	35% 7% 10% 23% 19% 7%	2413
December	1st to 10th	Night	32% 7% 14% 27% 16% 5%	2470
	11th to 20th	Night	36% 6% 10% 19% 17% 13%	3044
	21st to end	Night	45% 8% 13% 16% 15% 4	4532

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	9% 15% 41% 25% 9% 1	270
	11th to 20th	Day	10% 13% 33% 31% 10% 2	270
	21st to end	Day	15% 15% 46% 17% 6%	297
February	1st to 10th	Day	12% 12% 33% 28% 14% 1	270
	11th to 20th	Day	9% 10% 37% 28% 11% 4	270
	21st to end	Day	6% 12% 31% 32% 18% 1	287
March	1st to 10th	Day	3 12% 39% 34% 11% 1	460
	11th to 20th	Day	8% 9% 29% 32% 20% 2	460
	21st to end	Day	6% 10% 28% 34% 19% 3	506
April	1st to 10th	Day	7% 9% 33% 30% 17% 3	460
	11th to 20th	Day	8% 10% 28% 32% 19% 4	452
	21st to end	Day	5% 6% 23% 32% 27% 7%	460
May	1st to 10th	Day	5% 4 17% 35% 29% 11%	463
	11th to 20th	Day	8% 3 17% 28% 29% 14%	456
	21st to end	Day	8% 2 8% 21% 33% 27%	485
June	1st to 10th	Day	15% 3 10% 19% 28% 26%	450
	11th to 20th	Day	6% 3 8% 22% 30% 31%	450
	21st to end	Day	4 2 4 13% 31% 46%	450
July	1st to 10th	Day	7% 1 3 11% 24% 54%	445
	11th to 20th	Day	4 1 3 15% 31% 46%	444
	21st to end	Day	7% 2 3 19% 27% 41%	488
August	1st to 10th	Day	7% 1 4 11% 31% 46%	446
	11th to 20th	Day	8% 1 6% 12% 25% 48%	439
	21st to end	Day	9% 2 7% 18% 30% 35%	495
September	1st to 10th	Day	9% 1 8% 14% 29% 40%	450
	11th to 20th	Day	9% 2 6% 24% 31% 27%	450
	21st to end	Day	7% 2 6% 24% 34% 26%	450
October	1st to 10th	Day	7% 4 18% 36% 27% 8%	450
	11th to 20th	Day	6% 3 18% 32% 33% 8%	450
	21st to end	Day	6% 4 18% 40% 28% 4	495
November	1st to 10th	Day	10% 5% 23% 33% 25% 5%	455
	11th to 20th	Day	11% 7% 24% 35% 19% 4	460
	21st to end	Day	8% 7% 33% 32% 17% 3	323
December	1st to 10th	Day	6% 11% 35% 27% 16% 6%	270
	11th to 20th	Day	10% 11% 33% 30% 13% 2	270
	21st to end	Day	8% 11% 31% 34% 15% 2	297
January	1st to 10th	Night	11% 10% 29% 37% 13%	760
	11th to 20th	Night	12% 8% 27% 40% 12% 1	760
	21st to end	Night	14% 9% 35% 33% 9%	836
February	1st to 10th	Night	16% 5% 31% 34% 14%	760
	11th to 20th	Night	11% 7% 29% 39% 12% 1	743
	21st to end	Night	9% 6% 31% 44% 10%	628
March	1st to 10th	Night	6% 7% 36% 41% 8% 1	760
	11th to 20th	Night	7% 6% 31% 41% 14% 1	760
	21st to end	Night	7% 5% 31% 41% 15%	836
April	1st to 10th	Night	6% 6% 30% 43% 15%	760
	11th to 20th	Night	7% 5% 33% 40% 14% 1	751
	21st to end	Night	7% 4 26% 46% 17%	760
May	1st to 10th	Night	4 1 16% 47% 28% 2	573
	11th to 20th	Night	7% 2 17% 42% 29% 3	540
	21st to end	Night	5% 2 11% 38% 39% 6%	584
June	1st to 10th	Night	10% 3 9% 27% 42% 9%	540
	11th to 20th	Night	6% 1 5% 20% 45% 24%	540
	21st to end	Night	5% 1 4 18% 42% 29%	540
July	1st to 10th	Night	8% 1 2 11% 46% 33%	525
	11th to 20th	Night	7% 3 10% 44% 36%	522
	21st to end	Night	5% 1 4 12% 46% 34%	591
August	1st to 10th	Night	4 2 10% 50% 33%	537
	11th to 20th	Night	5% 1 3 9% 42% 39%	534
	21st to end	Night	11% 1 8% 21% 36% 23%	785
September	1st to 10th	Night	8% 1 9% 22% 42% 18%	720
	11th to 20th	Night	10% 2 9% 26% 37% 15%	720
	21st to end	Night	11% 2 11% 30% 35% 11%	720
October	1st to 10th	Night	9% 2 19% 41% 25% 4	720
	11th to 20th	Night	6% 3 17% 39% 31% 3	720
	21st to end	Night	10% 3 20% 41% 24% 2	792
November	1st to 10th	Night	9% 3 27% 37% 21% 3	740
	11th to 20th	Night	10% 4 23% 41% 20% 2	760
	21st to end	Night	9% 5% 29% 43% 14% 1	760
December	1st to 10th	Night	8% 4 27% 39% 22% 1	760
	11th to 20th	Night	11% 6% 25% 38% 19% 1	760
	21st to end	Night	10% 7% 28% 39% 16% 1	836

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