Browns Summit
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Browns Summit clear sky chart from 2005-11-06 to 2024-02-10.

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	13% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	78704
	Night	14% 5% 2 5% 5% 3 4 4 5% 7% 45%	80276
Transparency	Day	38% 4 12% 23% 18% 4	78426
	Night	39% 4 10% 22% 20% 5%	80073
Seeing	Day	15% 7% 22% 24% 21% 10%	14343
	Night	16% 7% 25% 32% 19% 2	24526

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	18% 5% 2 4 3 2 3 3 4 5% 52%	2836
	11th to 20th	Day	13% 6% 2 5% 3 2 4 3 4 4 52%	2840
	21st to end	Day	21% 9% 3 5% 4 2 3 4 3 4 41%	3124
February	1st to 10th	Day	14% 5% 2 5% 6% 3 4 5% 4 8% 44%	1701
	11th to 20th	Day	20% 7% 2 4 5% 2 4 4 4 5% 45%	1613
	21st to end	Day	19% 7% 3 5% 5% 2 4 4 5% 7% 40%	1583
March	1st to 10th	Day	15% 4 2 4 4 2 4 4 4 7% 51%	1980
	11th to 20th	Day	16% 5% 2 5% 4 3 5% 4 6% 8% 41%	1980
	21st to end	Day	16% 8% 3 6% 5% 2 4 3 5% 7% 41%	2178
April	1st to 10th	Day	10% 3 1 4 3 3 4 4 5% 8% 54%	2052
	11th to 20th	Day	12% 5% 2 5% 4 3 4 4 5% 8% 48%	2134
	21st to end	Day	14% 5% 2 4 6% 3 5% 5% 5% 7% 45%	2220
May	1st to 10th	Day	12% 5% 2 5% 5% 3 4 6% 7% 9% 41%	2340
	11th to 20th	Day	13% 6% 3 6% 6% 4 6% 5% 6% 8% 38%	2301
	21st to end	Day	11% 5% 2 6% 6% 4 6% 6% 6% 9% 38%	2531
June	1st to 10th	Day	9% 5% 2 5% 5% 3 5% 5% 8% 11% 42%	2340
	11th to 20th	Day	8% 5% 2 5% 5% 3 5% 6% 6% 11% 42%	2340
	21st to end	Day	7% 5% 2 6% 6% 3 6% 6% 7% 11% 41%	2340
July	1st to 10th	Day	9% 4 2 5% 6% 4 7% 7% 8% 10% 38%	2340
	11th to 20th	Day	6% 4 2 6% 7% 3 7% 7% 9% 14% 36%	2340
	21st to end	Day	7% 5% 2 6% 7% 5% 7% 7% 7% 11% 37%	2547
August	1st to 10th	Day	11% 5% 2 6% 6% 5% 6% 6% 7% 10% 35%	2327
	11th to 20th	Day	10% 7% 3 6% 7% 5% 6% 6% 7% 9% 34%	2290
	21st to end	Day	9% 5% 3 6% 5% 3 5% 6% 7% 9% 41%	2376
September	1st to 10th	Day	10% 4 2 5% 6% 3 5% 5% 5% 8% 47%	2142
	11th to 20th	Day	13% 6% 2 5% 6% 2 4 4 5% 8% 44%	1980
	21st to end	Day	21% 7% 2 5% 4 2 4 4 5% 6% 40%	1980
October	1st to 10th	Day	15% 6% 2 4 4 2 3 3 3 6% 52%	1800
	11th to 20th	Day	14% 6% 1 4 4 2 4 3 4 5% 54%	1800
	21st to end	Day	12% 4 2 4 4 2 2 4 4 5% 56%	1980
November	1st to 10th	Day	14% 5% 2 4 3 2 4 3 4 4 55%	1857
	11th to 20th	Day	13% 5% 2 4 4 2 3 4 4 7% 52%	1815
	21st to end	Day	13% 5% 2 4 5% 3 4 4 5% 6% 50%	1710
December	1st to 10th	Day	16% 7% 2 4 5% 3 4 4 6% 7% 41%	1710
	11th to 20th	Day	16% 4 2 3 3 2 3 3 4 7% 55%	2153
	21st to end	Day	18% 6% 1 4 4 3 5% 4 6% 8% 41%	3124
January	1st to 10th	Night	15% 6% 2 5% 4 3 4 4 5% 6% 49%	4109
	11th to 20th	Night	14% 7% 2 5% 4 2 4 4 4 5% 49%	4120
	21st to end	Night	21% 7% 2 5% 4 3 3 3 4 5% 44%	4532
February	1st to 10th	Night	15% 7% 2 4 5% 2 4 5% 5% 6% 45%	2464
	11th to 20th	Night	20% 7% 2 4 3 2 3 4 5% 6% 44%	2228
	21st to end	Night	17% 5% 3 6% 4 3 3 4 5% 7% 43%	1672
March	1st to 10th	Night	13% 6% 2 4 3 2 4 3 4 5% 53%	1980
	11th to 20th	Night	17% 6% 2 5% 5% 3 5% 5% 5% 7% 41%	1980
	21st to end	Night	16% 5% 3 5% 5% 3 4 4 5% 7% 43%	2178
April	1st to 10th	Night	12% 5% 2 5% 4 3 4 4 5% 7% 49%	1908
	11th to 20th	Night	12% 5% 2 4 5% 2 4 4 6% 7% 49%	1775
	21st to end	Night	13% 6% 2 4 5% 3 4 5% 4 6% 47%	1755
May	1st to 10th	Night	10% 4 3 5% 6% 4 4 4 6% 8% 48%	1620
	11th to 20th	Night	13% 6% 3 6% 6% 2 5% 5% 6% 10% 38%	1592
	21st to end	Night	12% 6% 3 6% 4 3 3 5% 6% 11% 42%	1744
June	1st to 10th	Night	10% 4 2 6% 5% 4 6% 7% 7% 11% 39%	1620
	11th to 20th	Night	9% 5% 2 5% 6% 4 5% 5% 7% 10% 43%	1620
	21st to end	Night	8% 5% 2 5% 6% 4 5% 6% 7% 12% 41%	1620
July	1st to 10th	Night	7% 5% 2 5% 6% 4 7% 7% 9% 11% 37%	1620
	11th to 20th	Night	6% 4 2 6% 6% 5% 8% 7% 7% 11% 39%	1620
	21st to end	Night	7% 5% 2 5% 5% 4 6% 7% 9% 12% 39%	1771
August	1st to 10th	Night	10% 6% 3 6% 7% 4 5% 6% 9% 10% 33%	1611
	11th to 20th	Night	10% 6% 3 5% 6% 4 7% 6% 7% 10% 37%	1598
	21st to end	Night	10% 5% 2 6% 5% 3 6% 6% 7% 12% 38%	1974
September	1st to 10th	Night	11% 5% 2 5% 5% 3 4 5% 6% 8% 46%	1813
	11th to 20th	Night	13% 5% 2 5% 5% 3 4 5% 5% 8% 45%	1980
	21st to end	Night	19% 7% 3 5% 5% 2 5% 5% 3 6% 39%	1980
October	1st to 10th	Night	16% 5% 2 5% 4 2 3 3 4 6% 50%	2159
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 5% 55%	2160
	21st to end	Night	13% 4 1 3 4 3 3 3 3 5% 57%	2376
November	1st to 10th	Night	15% 5% 3 5% 3 2 3 3 3 5% 54%	2221
	11th to 20th	Night	12% 4 2 4 4 2 4 4 3 6% 53%	2362
	21st to end	Night	13% 4 2 4 3 2 4 4 5% 6% 51%	2470
December	1st to 10th	Night	17% 7% 3 5% 5% 3 3 4 4 6% 42%	2470
	11th to 20th	Night	16% 6% 2 4 4 3 4 4 4 5% 49%	3042
	21st to end	Night	19% 5% 2 4 4 2 4 4 5% 8% 43%	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	36% 2 4 29% 22% 6%	2837
	11th to 20th	Day	36% 3 5% 19% 32% 5%	2840
	21st to end	Day	48% 3 4 19% 22% 4	3124
February	1st to 10th	Day	40% 3 10% 22% 21% 5%	1701
	11th to 20th	Day	44% 3 6% 23% 18% 6%	1622
	21st to end	Day	45% 3 11% 16% 19% 7%	1583
March	1st to 10th	Day	34% 3 8% 26% 22% 6%	1980
	11th to 20th	Day	41% 5% 10% 22% 16% 6%	1980
	21st to end	Day	44% 3 10% 22% 17% 4	2178
April	1st to 10th	Day	29% 3 10% 25% 24% 8%	2052
	11th to 20th	Day	35% 2 12% 22% 21% 8%	2134
	21st to end	Day	38% 4 11% 26% 17% 4	2220
May	1st to 10th	Day	39% 4 17% 21% 15% 4	2340
	11th to 20th	Day	43% 5% 16% 23% 11% 2	2305
	21st to end	Day	41% 5% 15% 27% 12% 1	2531
June	1st to 10th	Day	35% 5% 17% 27% 14% 1	2340
	11th to 20th	Day	35% 5% 18% 24% 15% 2	2340
	21st to end	Day	35% 7% 18% 25% 14% 2	2340
July	1st to 10th	Day	38% 8% 17% 21% 14% 3	2275
	11th to 20th	Day	35% 7% 24% 23% 10% 1	2271
	21st to end	Day	39% 7% 20% 22% 11% 1	2405
August	1st to 10th	Day	41% 7% 18% 26% 8% 1	2314
	11th to 20th	Day	44% 6% 18% 20% 11% 1	2290
	21st to end	Day	37% 5% 20% 23% 12% 3	2376
September	1st to 10th	Day	35% 5% 14% 23% 18% 4	2142
	11th to 20th	Day	40% 4 10% 21% 22% 3	1980
	21st to end	Day	46% 3 8% 21% 18% 3	1980
October	1st to 10th	Day	36% 3 8% 25% 24% 4	1800
	11th to 20th	Day	34% 2 7% 28% 21% 7%	1800
	21st to end	Day	33% 2 7% 25% 25% 8%	1980
November	1st to 10th	Day	34% 2 7% 23% 27% 8%	1857
	11th to 20th	Day	34% 2 8% 24% 25% 7%	1815
	21st to end	Day	35% 3 8% 23% 26% 5%	1710
December	1st to 10th	Day	44% 4 9% 21% 19% 4	1710
	11th to 20th	Day	32% 2 7% 24% 25% 9%	2150
	21st to end	Day	43% 3 9% 25% 19% 2	3124
January	1st to 10th	Night	38% 2 6% 22% 26% 6%	4109
	11th to 20th	Night	39% 3 6% 19% 27% 6%	4120
	21st to end	Night	45% 3 5% 21% 20% 6%	4532
February	1st to 10th	Night	41% 3 8% 23% 21% 4	2464
	11th to 20th	Night	43% 3 8% 18% 21% 7%	2230
	21st to end	Night	42% 3 9% 20% 19% 7%	1672
March	1st to 10th	Night	35% 3 7% 23% 25% 7%	1980
	11th to 20th	Night	43% 4 8% 21% 19% 6%	1980
	21st to end	Night	42% 4 10% 22% 18% 4	2178
April	1st to 10th	Night	36% 3 10% 19% 26% 5%	1908
	11th to 20th	Night	35% 3 10% 23% 22% 8%	1775
	21st to end	Night	37% 4 11% 25% 18% 5%	1755
May	1st to 10th	Night	35% 5% 14% 27% 16% 3	1620
	11th to 20th	Night	42% 4 15% 22% 14% 2	1593
	21st to end	Night	36% 5% 17% 29% 12% 1	1745
June	1st to 10th	Night	37% 7% 16% 25% 14% 1	1620
	11th to 20th	Night	37% 6% 17% 24% 14% 2	1620
	21st to end	Night	34% 10% 18% 21% 13% 4	1620
July	1st to 10th	Night	36% 9% 19% 20% 13% 3	1575
	11th to 20th	Night	37% 9% 21% 20% 10% 4	1566
	21st to end	Night	35% 6% 22% 24% 12%	1672
August	1st to 10th	Night	43% 8% 18% 20% 10% 1	1600
	11th to 20th	Night	41% 8% 17% 19% 12% 2	1598
	21st to end	Night	37% 7% 20% 25% 8% 3	1974
September	1st to 10th	Night	35% 6% 14% 23% 16% 6%	1813
	11th to 20th	Night	38% 5% 11% 20% 23% 2	1980
	21st to end	Night	48% 5% 8% 18% 17% 4	1980
October	1st to 10th	Night	38% 2 7% 26% 23% 4	2159
	11th to 20th	Night	34% 2 8% 26% 23% 7%	2160
	21st to end	Night	33% 2 6% 23% 26% 11%	2376
November	1st to 10th	Night	36% 3 7% 20% 26% 10%	2221
	11th to 20th	Night	35% 2 7% 19% 25% 11%	2362
	21st to end	Night	34% 3 6% 24% 27% 6%	2470
December	1st to 10th	Night	44% 3 8% 21% 19% 5%	2470
	11th to 20th	Night	39% 3 6% 20% 23% 9%	3044
	21st to end	Night	41% 2 8% 24% 23% 3	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	23% 14% 36% 19% 7%	270
	11th to 20th	Day	18% 16% 41% 21% 4	270
	21st to end	Day	20% 16% 39% 21% 4	297
February	1st to 10th	Day	17% 13% 40% 21% 8% 1	267
	11th to 20th	Day	31% 15% 38% 12% 3	240
	21st to end	Day	28% 15% 35% 20% 3	301
March	1st to 10th	Day	20% 11% 35% 26% 8%	420
	11th to 20th	Day	19% 11% 41% 22% 6% 1	420
	21st to end	Day	18% 15% 34% 26% 6% 1	462
April	1st to 10th	Day	17% 12% 31% 26% 13% 2	420
	11th to 20th	Day	12% 13% 28% 25% 17% 5%	412
	21st to end	Day	19% 8% 28% 24% 19% 3	420
May	1st to 10th	Day	13% 14% 26% 28% 15% 4	423
	11th to 20th	Day	14% 6% 20% 25% 23% 11%	447
	21st to end	Day	17% 2 16% 26% 25% 14%	485
June	1st to 10th	Day	12% 3 14% 28% 30% 13%	450
	11th to 20th	Day	11% 3 18% 25% 26% 18%	450
	21st to end	Day	10% 2 13% 26% 36% 13%	450
July	1st to 10th	Day	11% 1 6% 25% 33% 24%	445
	11th to 20th	Day	4 1 9% 21% 39% 26%	444
	21st to end	Day	8% 1 8% 23% 41% 19%	488
August	1st to 10th	Day	14% 2 12% 23% 28% 22%	446
	11th to 20th	Day	10% 2 7% 23% 33% 25%	439
	21st to end	Day	10% 2 8% 22% 31% 26%	495
September	1st to 10th	Day	14% 1 9% 20% 31% 25%	450
	11th to 20th	Day	15% 3 13% 18% 30% 21%	450
	21st to end	Day	27% 2 16% 25% 21% 8%	450
October	1st to 10th	Day	18% 5% 14% 26% 26% 11%	450
	11th to 20th	Day	15% 4 22% 28% 25% 7%	450
	21st to end	Day	14% 8% 24% 32% 19% 4	495
November	1st to 10th	Day	18% 7% 23% 29% 18% 5%	455
	11th to 20th	Day	15% 10% 33% 25% 15% 3	375
	21st to end	Day	10% 11% 32% 27% 16% 3	270
December	1st to 10th	Day	20% 11% 37% 23% 8% 1	270
	11th to 20th	Day	17% 11% 33% 25% 12% 2	270
	21st to end	Day	23% 12% 30% 22% 11% 2	297
January	1st to 10th	Night	19% 12% 36% 27% 5%	760
	11th to 20th	Night	20% 11% 37% 27% 5%	760
	21st to end	Night	18% 11% 40% 28% 3	836
February	1st to 10th	Night	19% 11% 36% 31% 4	759
	11th to 20th	Night	24% 13% 40% 21% 1	703
	21st to end	Night	20% 12% 38% 26% 4	592
March	1st to 10th	Night	16% 13% 36% 30% 4	720
	11th to 20th	Night	20% 13% 34% 26% 7% 1	720
	21st to end	Night	18% 8% 35% 32% 6%	792
April	1st to 10th	Night	14% 13% 35% 31% 7%	720
	11th to 20th	Night	15% 9% 32% 30% 14%	711
	21st to end	Night	16% 7% 29% 37% 10%	675
May	1st to 10th	Night	11% 8% 32% 35% 14% 1	540
	11th to 20th	Night	16% 4 21% 35% 22% 2	531
	21st to end	Night	16% 2 10% 35% 33% 5%	584
June	1st to 10th	Night	11% 2 15% 39% 32% 2	540
	11th to 20th	Night	10% 1 13% 34% 35% 6%	540
	21st to end	Night	10% 2 14% 34% 37% 3	540
July	1st to 10th	Night	11% 1 9% 30% 42% 7%	525
	11th to 20th	Night	7% 1 5% 32% 48% 7%	522
	21st to end	Night	9% 1 7% 38% 38% 8%	591
August	1st to 10th	Night	13% 1 8% 36% 35% 7%	537
	11th to 20th	Night	13% 2 8% 30% 40% 7%	534
	21st to end	Night	12% 1 8% 33% 38% 9%	786
September	1st to 10th	Night	13% 2 7% 31% 39% 8%	720
	11th to 20th	Night	16% 3 10% 29% 37% 5%	720
	21st to end	Night	22% 3 15% 30% 28% 1	720
October	1st to 10th	Night	18% 3 17% 29% 28% 6%	720
	11th to 20th	Night	17% 5% 26% 31% 20% 2	720
	21st to end	Night	14% 7% 26% 35% 16% 2	792
November	1st to 10th	Night	16% 7% 23% 36% 17% 2	740
	11th to 20th	Night	14% 9% 31% 33% 12% 1	760
	21st to end	Night	15% 8% 30% 33% 13% 1	760
December	1st to 10th	Night	21% 8% 33% 31% 8%	760
	11th to 20th	Night	18% 5% 37% 32% 8%	760
	21st to end	Night	23% 8% 28% 33% 7%	836

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