Pilot Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pilot Mountain clear sky chart from 2005-11-06 to 2024-03-28.

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	15% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	79182
	Night	16% 5% 2 5% 5% 3 4 4 5% 7% 45%	80823
Transparency	Day	38% 7% 12% 21% 17% 4	78904
	Night	39% 6% 11% 20% 19% 5%	80620
Seeing	Day	17% 8% 22% 24% 19% 10%	14401
	Night	17% 6% 24% 32% 19% 2	24594

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	19% 4 1 3 3 2 3 3 4 6% 52%	2836
	11th to 20th	Day	16% 5% 2 4 5% 2 3 3 4 5% 51%	2840
	21st to end	Day	26% 6% 2 4 4 2 3 3 3 4 43%	3124
February	1st to 10th	Day	14% 5% 3 6% 5% 3 4 4 5% 7% 44%	1710
	11th to 20th	Day	19% 6% 2 3 5% 3 4 4 4 6% 45%	1761
	21st to end	Day	20% 6% 3 5% 4 3 4 4 5% 7% 40%	1630
March	1st to 10th	Day	16% 4 2 3 3 2 4 4 6% 6% 49%	2090
	11th to 20th	Day	19% 5% 2 5% 4 3 4 5% 6% 7% 41%	2090
	21st to end	Day	19% 7% 2 6% 5% 2 4 4 4 6% 41%	2255
April	1st to 10th	Day	12% 3 2 3 4 2 4 4 6% 8% 53%	2011
	11th to 20th	Day	16% 4 2 4 4 2 4 4 4 8% 47%	2134
	21st to end	Day	15% 5% 2 5% 5% 3 4 4 5% 7% 44%	2290
May	1st to 10th	Day	13% 4 2 4 5% 3 6% 6% 7% 8% 41%	2340
	11th to 20th	Day	16% 5% 3 5% 6% 4 5% 5% 6% 9% 37%	2301
	21st to end	Day	14% 5% 2 4 6% 3 5% 5% 6% 9% 41%	2531
June	1st to 10th	Day	11% 5% 2 5% 5% 4 6% 5% 7% 10% 39%	2340
	11th to 20th	Day	10% 4 2 5% 7% 4 6% 6% 7% 10% 40%	2340
	21st to end	Day	8% 4 2 6% 6% 4 6% 6% 8% 12% 38%	2340
July	1st to 10th	Day	10% 5% 3 5% 6% 5% 6% 6% 7% 11% 35%	2340
	11th to 20th	Day	8% 5% 2 6% 6% 4 7% 9% 8% 11% 33%	2340
	21st to end	Day	9% 5% 3 6% 7% 5% 7% 7% 8% 8% 35%	2547
August	1st to 10th	Day	13% 5% 2 6% 6% 3 7% 7% 9% 10% 33%	2327
	11th to 20th	Day	11% 5% 2 6% 8% 5% 7% 7% 7% 9% 32%	2303
	21st to end	Day	10% 5% 2 5% 5% 3 6% 6% 7% 11% 39%	2409
September	1st to 10th	Day	13% 4 2 5% 5% 3 4 4 6% 8% 46%	2070
	11th to 20th	Day	14% 5% 2 5% 4 2 5% 5% 6% 8% 44%	1980
	21st to end	Day	20% 6% 3 6% 5% 2 4 4 5% 6% 39%	1980
October	1st to 10th	Day	15% 4 1 5% 4 2 3 3 3 6% 53%	1841
	11th to 20th	Day	15% 4 1 4 4 2 3 3 4 6% 55%	1800
	21st to end	Day	15% 5% 2 4 4 2 2 3 3 5% 55%	1980
November	1st to 10th	Day	13% 5% 2 4 3 2 3 2 3 6% 56%	1857
	11th to 20th	Day	14% 4 2 4 3 2 4 3 4 6% 54%	1748
	21st to end	Day	16% 4 1 4 4 3 3 4 4 6% 51%	1710
December	1st to 10th	Day	20% 8% 2 5% 4 3 4 3 4 6% 40%	1710
	11th to 20th	Day	16% 4 1 3 3 2 3 3 5% 7% 54%	2153
	21st to end	Day	21% 5% 2 4 4 2 4 5% 5% 7% 40%	3124
January	1st to 10th	Night	16% 5% 2 4 5% 3 4 3 4 5% 49%	4109
	11th to 20th	Night	16% 6% 2 5% 4 2 3 3 4 5% 49%	4120
	21st to end	Night	26% 5% 2 4 4 2 4 4 4 4 42%	4532
February	1st to 10th	Night	16% 6% 2 4 5% 3 4 5% 5% 6% 44%	2470
	11th to 20th	Night	20% 6% 2 4 3 2 3 4 4 6% 45%	2300
	21st to end	Night	17% 7% 2 5% 5% 3 4 3 5% 6% 42%	1822
March	1st to 10th	Night	14% 5% 2 5% 4 2 4 4 5% 6% 50%	2090
	11th to 20th	Night	17% 5% 2 5% 5% 3 5% 5% 5% 5% 44%	2090
	21st to end	Night	18% 5% 2 5% 5% 2 4 5% 4 7% 42%	2256
April	1st to 10th	Night	14% 6% 2 5% 4 3 3 4 5% 7% 47%	1949
	11th to 20th	Night	14% 5% 3 3 4 3 4 4 5% 7% 48%	1775
	21st to end	Night	15% 4 3 4 5% 2 5% 4 4 7% 47%	1684
May	1st to 10th	Night	13% 5% 2 6% 4 2 5% 4 5% 7% 45%	1620
	11th to 20th	Night	16% 6% 3 6% 6% 3 5% 5% 5% 7% 38%	1592
	21st to end	Night	14% 6% 2 5% 6% 3 5% 5% 6% 9% 40%	1744
June	1st to 10th	Night	10% 4 2 5% 5% 3 6% 6% 8% 11% 40%	1620
	11th to 20th	Night	11% 5% 2 5% 5% 3 5% 5% 6% 11% 43%	1620
	21st to end	Night	9% 4 1 5% 6% 4 6% 5% 7% 10% 41%	1620
July	1st to 10th	Night	9% 5% 3 6% 6% 4 5% 7% 8% 10% 37%	1620
	11th to 20th	Night	8% 3 2 6% 5% 4 6% 7% 10% 11% 38%	1620
	21st to end	Night	8% 5% 2 5% 6% 4 7% 7% 9% 12% 36%	1771
August	1st to 10th	Night	15% 5% 3 6% 6% 4 5% 7% 7% 9% 34%	1611
	11th to 20th	Night	12% 5% 3 6% 8% 4 5% 7% 8% 9% 34%	1598
	21st to end	Night	10% 4 2 6% 6% 4 6% 6% 8% 11% 37%	1927
September	1st to 10th	Night	11% 5% 2 4 5% 3 5% 6% 7% 8% 45%	1886
	11th to 20th	Night	16% 6% 3 6% 5% 4 4 5% 6% 7% 39%	1980
	21st to end	Night	19% 7% 3 5% 5% 3 4 5% 4 6% 38%	1980
October	1st to 10th	Night	16% 4 3 4 5% 3 3 4 5% 6% 47%	2119
	11th to 20th	Night	14% 4 2 4 4 2 4 3 4 5% 54%	2160
	21st to end	Night	15% 4 2 4 4 2 3 3 3 5% 56%	2376
November	1st to 10th	Night	16% 5% 2 3 4 2 3 2 4 5% 54%	2221
	11th to 20th	Night	14% 4 2 4 3 2 4 3 5% 5% 54%	2427
	21st to end	Night	15% 4 2 4 3 2 4 4 5% 6% 51%	2470
December	1st to 10th	Night	19% 6% 3 5% 5% 3 3 4 4 6% 43%	2470
	11th to 20th	Night	18% 5% 2 3 4 2 3 3 4 5% 50%	3042
	21st to end	Night	23% 5% 2 4 4 3 4 4 5% 7% 38%	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	34% 3 8% 27% 20% 7%	2837
	11th to 20th	Day	37% 4 7% 18% 30% 5%	2840
	21st to end	Day	45% 4 7% 19% 21% 4	3124
February	1st to 10th	Day	40% 5% 11% 21% 19% 5%	1710
	11th to 20th	Day	41% 5% 8% 21% 19% 5%	1770
	21st to end	Day	45% 5% 12% 15% 17% 7%	1630
March	1st to 10th	Day	35% 4 8% 24% 22% 7%	2090
	11th to 20th	Day	41% 6% 9% 19% 17% 7%	2090
	21st to end	Day	45% 6% 9% 21% 16% 3	2255
April	1st to 10th	Day	28% 6% 13% 23% 22% 7%	2011
	11th to 20th	Day	36% 5% 10% 20% 21% 8%	2134
	21st to end	Day	40% 6% 11% 24% 16% 4	2290
May	1st to 10th	Day	38% 9% 16% 18% 15% 4	2340
	11th to 20th	Day	42% 10% 15% 21% 9% 2	2305
	21st to end	Day	37% 11% 15% 25% 10% 1	2531
June	1st to 10th	Day	38% 8% 16% 24% 12% 1	2340
	11th to 20th	Day	37% 11% 16% 19% 14% 2	2340
	21st to end	Day	36% 11% 18% 21% 13% 1	2340
July	1st to 10th	Day	40% 13% 15% 17% 13% 3	2275
	11th to 20th	Day	39% 13% 19% 18% 10% 2	2271
	21st to end	Day	40% 13% 19% 18% 10% 1	2405
August	1st to 10th	Day	42% 12% 16% 21% 9% 1	2314
	11th to 20th	Day	45% 14% 15% 17% 9% 1	2303
	21st to end	Day	37% 10% 19% 21% 10% 3	2409
September	1st to 10th	Day	35% 9% 13% 22% 17% 4	2070
	11th to 20th	Day	38% 9% 11% 21% 18% 3	1980
	21st to end	Day	47% 7% 9% 18% 17% 3	1980
October	1st to 10th	Day	34% 5% 9% 22% 24% 4	1841
	11th to 20th	Day	32% 5% 9% 27% 21% 7%	1800
	21st to end	Day	33% 4 7% 26% 22% 9%	1980
November	1st to 10th	Day	32% 4 8% 22% 27% 8%	1857
	11th to 20th	Day	32% 3 8% 23% 26% 8%	1748
	21st to end	Day	35% 4 8% 22% 26% 5%	1710
December	1st to 10th	Day	45% 6% 7% 20% 18% 4	1710
	11th to 20th	Day	32% 4 9% 22% 24% 9%	2150
	21st to end	Day	42% 5% 11% 23% 17% 2	3124
January	1st to 10th	Night	37% 3 9% 21% 24% 6%	4109
	11th to 20th	Night	38% 4 8% 17% 27% 6%	4120
	21st to end	Night	46% 3 7% 19% 20% 6%	4532
February	1st to 10th	Night	39% 6% 9% 21% 20% 4	2470
	11th to 20th	Night	42% 4 8% 19% 20% 7%	2302
	21st to end	Night	43% 4 10% 18% 18% 6%	1822
March	1st to 10th	Night	36% 6% 7% 21% 24% 7%	2090
	11th to 20th	Night	41% 6% 8% 22% 18% 6%	2090
	21st to end	Night	42% 6% 9% 20% 18% 4	2256
April	1st to 10th	Night	35% 6% 11% 20% 22% 5%	1949
	11th to 20th	Night	36% 5% 9% 21% 21% 8%	1775
	21st to end	Night	37% 6% 10% 24% 18% 4	1684
May	1st to 10th	Night	37% 8% 13% 24% 16% 2	1620
	11th to 20th	Night	44% 9% 13% 19% 15% 1	1593
	21st to end	Night	40% 9% 15% 24% 10% 1	1745
June	1st to 10th	Night	36% 10% 16% 24% 12% 2	1620
	11th to 20th	Night	35% 10% 17% 23% 15% 1	1620
	21st to end	Night	36% 11% 16% 19% 14% 4	1620
July	1st to 10th	Night	38% 13% 15% 18% 12% 3	1575
	11th to 20th	Night	34% 14% 20% 19% 9% 3	1566
	21st to end	Night	35% 13% 22% 22% 8% 1	1672
August	1st to 10th	Night	44% 12% 16% 18% 10% 1	1600
	11th to 20th	Night	43% 11% 17% 18% 10% 2	1598
	21st to end	Night	37% 12% 16% 24% 9% 2	1927
September	1st to 10th	Night	35% 9% 14% 21% 16% 5%	1886
	11th to 20th	Night	43% 9% 10% 18% 19% 2	1980
	21st to end	Night	47% 7% 10% 17% 17% 3	1980
October	1st to 10th	Night	38% 4 10% 22% 22% 4	2119
	11th to 20th	Night	33% 5% 8% 26% 21% 7%	2160
	21st to end	Night	32% 4 7% 21% 25% 10%	2376
November	1st to 10th	Night	35% 4 8% 20% 25% 9%	2221
	11th to 20th	Night	33% 4 8% 19% 26% 10%	2427
	21st to end	Night	34% 4 8% 24% 25% 6%	2470
December	1st to 10th	Night	44% 5% 8% 20% 19% 5%	2470
	11th to 20th	Night	37% 4 8% 19% 22% 9%	3044
	21st to end	Night	42% 5% 12% 20% 19% 2	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	27% 17% 32% 17% 6%	270
	11th to 20th	Day	28% 17% 29% 20% 5%	270
	21st to end	Day	24% 17% 38% 17% 4	297
February	1st to 10th	Day	19% 17% 37% 19% 7%	270
	11th to 20th	Day	33% 16% 36% 12% 3	270
	21st to end	Day	26% 19% 32% 19% 4	285
March	1st to 10th	Day	21% 13% 32% 25% 9% 1	460
	11th to 20th	Day	20% 12% 39% 22% 6% 1	460
	21st to end	Day	25% 12% 31% 24% 7% 1	490
April	1st to 10th	Day	18% 14% 31% 22% 12% 3	420
	11th to 20th	Day	17% 13% 25% 25% 17% 3	412
	21st to end	Day	19% 11% 25% 24% 17% 4	420
May	1st to 10th	Day	17% 10% 30% 25% 14% 5%	423
	11th to 20th	Day	15% 5% 20% 29% 20% 11%	447
	21st to end	Day	19% 4 13% 25% 24% 15%	485
June	1st to 10th	Day	13% 2 17% 29% 25% 14%	450
	11th to 20th	Day	11% 3 18% 23% 26% 19%	450
	21st to end	Day	12% 2 13% 33% 26% 15%	450
July	1st to 10th	Day	10% 1 9% 25% 32% 22%	445
	11th to 20th	Day	5% 1 10% 23% 34% 26%	444
	21st to end	Day	8% 1 10% 24% 33% 23%	488
August	1st to 10th	Day	15% 3 12% 23% 28% 20%	446
	11th to 20th	Day	12% 2 8% 26% 27% 24%	439
	21st to end	Day	12% 2 8% 22% 35% 22%	495
September	1st to 10th	Day	13% 3 10% 22% 29% 23%	450
	11th to 20th	Day	16% 2 11% 21% 31% 18%	450
	21st to end	Day	23% 5% 21% 24% 21% 6%	450
October	1st to 10th	Day	18% 5% 17% 28% 23% 10%	450
	11th to 20th	Day	14% 6% 24% 27% 23% 5%	450
	21st to end	Day	17% 8% 20% 35% 15% 5%	495
November	1st to 10th	Day	19% 6% 25% 30% 15% 4	455
	11th to 20th	Day	18% 13% 31% 23% 12% 3	308
	21st to end	Day	16% 13% 28% 26% 13% 3	270
December	1st to 10th	Day	27% 11% 34% 21% 6%	270
	11th to 20th	Day	20% 13% 27% 28% 11% 1	270
	21st to end	Day	27% 11% 31% 22% 8% 1	297
January	1st to 10th	Night	21% 9% 36% 29% 5%	760
	11th to 20th	Night	20% 9% 37% 30% 5%	760
	21st to end	Night	19% 8% 39% 32% 2	836
February	1st to 10th	Night	19% 9% 36% 32% 4	760
	11th to 20th	Night	23% 14% 36% 25% 2	743
	21st to end	Night	18% 11% 39% 30% 2	628
March	1st to 10th	Night	18% 10% 31% 34% 6%	760
	11th to 20th	Night	19% 11% 34% 28% 7% 1	760
	21st to end	Night	19% 8% 33% 33% 6%	821
April	1st to 10th	Night	17% 12% 30% 32% 9%	720
	11th to 20th	Night	16% 9% 29% 32% 13%	711
	21st to end	Night	17% 6% 30% 35% 12%	604
May	1st to 10th	Night	14% 5% 29% 34% 17% 1	540
	11th to 20th	Night	17% 3 22% 32% 23% 2	531
	21st to end	Night	16% 2 11% 34% 34% 4	584
June	1st to 10th	Night	11% 2 11% 39% 33% 3	540
	11th to 20th	Night	12% 1 12% 30% 39% 6%	540
	21st to end	Night	9% 1 10% 34% 42% 4	540
July	1st to 10th	Night	10% 2 10% 29% 44% 6%	525
	11th to 20th	Night	7% 2 5% 32% 46% 8%	522
	21st to end	Night	8% 2 8% 33% 43% 7%	591
August	1st to 10th	Night	15% 1 8% 27% 42% 7%	537
	11th to 20th	Night	11% 2 7% 32% 39% 8%	534
	21st to end	Night	11% 1 9% 26% 44% 9%	739
September	1st to 10th	Night	12% 2 9% 29% 41% 8%	720
	11th to 20th	Night	17% 2 13% 29% 33% 7%	720
	21st to end	Night	23% 3 16% 30% 27% 1	720
October	1st to 10th	Night	15% 5% 18% 30% 28% 5%	720
	11th to 20th	Night	16% 5% 24% 35% 19% 2	720
	21st to end	Night	17% 6% 23% 37% 16% 2	792
November	1st to 10th	Night	18% 6% 20% 39% 15% 2	740
	11th to 20th	Night	16% 8% 26% 38% 12%	760
	21st to end	Night	16% 6% 29% 36% 12% 1	760
December	1st to 10th	Night	22% 6% 31% 32% 8%	760
	11th to 20th	Night	20% 4 32% 36% 8%	760
	21st to end	Night	26% 5% 28% 35% 6%	836

Page generated at 2024-03-24 23:37:03. Version ac07

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