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 2025-09-04.

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	14% 5% 2 6% 4 4 4 4 6% 8% 42%	126135
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	122598
Transparency	Day	38% 7% 12% 21% 17% 5%	129767
	Night	38% 6% 11% 20% 19% 6%	127035
Seeing	Day	17% 8% 22% 24% 19% 9%	16396
	Night	17% 6% 24% 32% 19% 2	26451

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	16% 6% 2 4 2 3 2 2 3 5% 56%	4056
	11th to 20th	Day	14% 5% 1 3 3 3 3 2 3 5% 58%	4060
	21st to end	Day	19% 6% 2 5% 4 3 3 2 3 5% 48%	4466
February	1st to 10th	Day	14% 6% 2 7% 5% 4 4 3 5% 7% 43%	1800
	11th to 20th	Day	20% 7% 1 4 4 4 4 3 4 6% 44%	1857
	21st to end	Day	19% 7% 2 6% 3 4 3 3 5% 7% 41%	1713
March	1st to 10th	Day	20% 6% 2 5% 4 3 4 3 4 6% 42%	4935
	11th to 20th	Day	12% 4 2 4 3 3 3 3 5% 6% 54%	4980
	21st to end	Day	18% 7% 2 5% 3 3 3 3 4 6% 45%	5465
April	1st to 10th	Day	13% 3 2 4 3 3 4 4 6% 8% 51%	2235
	11th to 20th	Day	16% 4 2 4 4 3 4 3 4 8% 48%	2374
	21st to end	Day	15% 6% 2 5% 4 4 4 4 5% 7% 44%	2546
May	1st to 10th	Day	12% 6% 2 7% 5% 5% 6% 6% 8% 9% 34%	5862
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 8% 29%	5861
	21st to end	Day	14% 5% 2 5% 5% 4 5% 5% 7% 9% 40%	6433
June	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 8% 10% 39%	2600
	11th to 20th	Day	9% 4 2 6% 6% 6% 6% 5% 8% 10% 39%	2600
	21st to end	Day	8% 4 1 6% 5% 5% 6% 5% 8% 12% 40%	2600
July	1st to 10th	Day	8% 5% 2 7% 5% 7% 6% 5% 7% 10% 38%	5900
	11th to 20th	Day	8% 6% 3 7% 6% 6% 7% 6% 8% 12% 31%	5900
	21st to end	Day	11% 7% 3 8% 6% 6% 7% 6% 9% 9% 29%	6424
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 5% 8% 10% 27%	4234
	11th to 20th	Day	10% 5% 2 7% 6% 5% 6% 5% 7% 10% 36%	4174
	21st to end	Day	6% 4 2 5% 3 4 5% 4 6% 11% 50%	4361
September	1st to 10th	Day	12% 4 2 6% 4 5% 4 3 6% 8% 47%	2220
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 6% 7% 42%	2090
	21st to end	Day	20% 6% 3 7% 4 3 4 3 5% 6% 38%	2090
October	1st to 10th	Day	14% 5% 1 6% 4 3 3 3 3 6% 54%	1943
	11th to 20th	Day	14% 4 1 4 3 2 3 2 4 6% 57%	1900
	21st to end	Day	14% 5% 2 5% 3 3 2 2 4 5% 55%	2090
November	1st to 10th	Day	13% 5% 2 5% 3 2 3 2 4 6% 55%	1957
	11th to 20th	Day	14% 4 2 4 3 3 3 3 4 6% 54%	1840
	21st to end	Day	15% 5% 1 5% 4 3 3 3 5% 6% 50%	1800
December	1st to 10th	Day	16% 6% 1 4 3 3 3 2 4 5% 52%	2930
	11th to 20th	Day	20% 6% 1 4 4 3 3 3 5% 6% 44%	3373
	21st to end	Day	24% 5% 2 4 3 3 4 3 5% 8% 41%	4466
January	1st to 10th	Night	13% 5% 1 4 3 3 3 2 4 5% 57%	5889
	11th to 20th	Night	14% 5% 2 4 3 2 2 2 4 4 58%	5900
	21st to end	Night	19% 5% 2 4 3 3 3 3 4 5% 49%	6490
February	1st to 10th	Night	16% 6% 2 5% 4 4 4 4 6% 6% 44%	2600
	11th to 20th	Night	21% 7% 2 5% 3 2 3 3 4 6% 44%	2424
	21st to end	Night	16% 7% 2 5% 5% 3 4 3 5% 6% 44%	1915
March	1st to 10th	Night	18% 6% 2 6% 4 4 3 3 4 5% 45%	4918
	11th to 20th	Night	10% 3 1 4 3 3 4 3 5% 6% 57%	4980
	21st to end	Night	15% 5% 2 5% 4 3 4 4 5% 8% 45%	5467
April	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 7% 47%	2165
	11th to 20th	Night	13% 5% 3 4 4 4 4 3 6% 7% 48%	1975
	21st to end	Night	14% 5% 2 5% 5% 4 4 4 4 7% 47%	1870
May	1st to 10th	Night	16% 6% 2 7% 4 4 4 4 6% 9% 38%	4033
	11th to 20th	Night	20% 7% 3 8% 5% 4 4 3 5% 7% 33%	4032
	21st to end	Night	17% 5% 2 5% 4 4 3 4 6% 9% 41%	4421
June	1st to 10th	Night	11% 4 2 6% 5% 5% 6% 4 8% 10% 40%	1800
	11th to 20th	Night	11% 5% 2 6% 5% 4 5% 4 7% 10% 41%	1800
	21st to end	Night	8% 5% 2 6% 6% 6% 5% 4 7% 10% 42%	1800
July	1st to 10th	Night	10% 7% 3 9% 6% 5% 6% 5% 8% 9% 33%	4058
	11th to 20th	Night	11% 7% 3 9% 6% 6% 6% 5% 9% 11% 28%	4057
	21st to end	Night	11% 7% 3 8% 6% 6% 6% 5% 8% 11% 27%	4427
August	1st to 10th	Night	19% 8% 3 8% 5% 5% 5% 5% 7% 8% 27%	2915
	11th to 20th	Night	11% 6% 3 8% 6% 5% 6% 6% 9% 9% 32%	2875
	21st to end	Night	7% 3 2 6% 4 5% 5% 4 7% 9% 50%	3502
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 5% 7% 7% 45%	2022
	11th to 20th	Night	17% 6% 3 7% 4 5% 4 4 6% 7% 37%	2090
	21st to end	Night	20% 7% 3 6% 4 4 4 4 4 6% 37%	2090
October	1st to 10th	Night	15% 5% 3 5% 4 3 3 3 5% 6% 48%	2237
	11th to 20th	Night	14% 4 1 5% 4 3 3 3 4 5% 55%	2280
	21st to end	Night	14% 4 2 5% 3 3 3 3 3 5% 57%	2508
November	1st to 10th	Night	15% 6% 2 5% 4 3 3 2 4 5% 53%	2341
	11th to 20th	Night	14% 5% 1 5% 3 3 3 3 5% 5% 54%	2555
	21st to end	Night	14% 4 2 4 3 3 3 4 5% 6% 52%	2600
December	1st to 10th	Night	14% 6% 2 4 4 3 4 3 5% 6% 51%	4250
	11th to 20th	Night	23% 8% 3 5% 3 3 3 2 4 4 42%	4822
	21st to end	Night	22% 4 1 4 3 3 4 3 5% 7% 44%	6490

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	33% 2 6% 21% 30% 8%	4057
	11th to 20th	Day	31% 3 5% 18% 35% 9%	4060
	21st to end	Day	40% 3 6% 23% 23% 5%	4466
February	1st to 10th	Day	40% 5% 11% 20% 19% 5%	1800
	11th to 20th	Day	41% 5% 8% 21% 19% 5%	1866
	21st to end	Day	44% 5% 11% 15% 18% 7%	1713
March	1st to 10th	Day	43% 4 6% 18% 17% 12%	4935
	11th to 20th	Day	31% 5% 7% 19% 24% 15%	4980
	21st to end	Day	41% 4 8% 23% 19% 5%	5465
April	1st to 10th	Day	30% 6% 13% 22% 22% 7%	2235
	11th to 20th	Day	35% 5% 11% 21% 21% 8%	2374
	21st to end	Day	40% 7% 11% 24% 15% 4	2546
May	1st to 10th	Day	42% 10% 16% 18% 12% 2	5897
	11th to 20th	Day	51% 9% 11% 20% 8% 1	5865
	21st to end	Day	37% 9% 15% 20% 16% 4	6447
June	1st to 10th	Day	37% 8% 16% 24% 13% 1	2600
	11th to 20th	Day	37% 11% 17% 19% 14% 2	2600
	21st to end	Day	34% 11% 18% 22% 14% 1	2600
July	1st to 10th	Day	38% 12% 16% 19% 12% 3	5835
	11th to 20th	Day	40% 13% 24% 18% 4 1	5831
	21st to end	Day	45% 13% 15% 19% 8%	6240
August	1st to 10th	Day	48% 11% 17% 19% 5%	4221
	11th to 20th	Day	39% 13% 19% 19% 8% 2	4213
	21st to end	Day	27% 8% 17% 34% 13% 2	4361
September	1st to 10th	Day	35% 9% 12% 22% 17% 4	2220
	11th to 20th	Day	39% 9% 11% 21% 18% 3	2090
	21st to end	Day	47% 7% 9% 17% 17% 3	2090
October	1st to 10th	Day	29% 5% 8% 19% 27% 11%	3229
	11th to 20th	Day	21% 3 5% 23% 25% 23%	3140
	21st to end	Day	26% 4 9% 25% 21% 15%	3428
November	1st to 10th	Day	33% 4 7% 22% 26% 7%	1957
	11th to 20th	Day	33% 3 8% 23% 26% 7%	1840
	21st to end	Day	35% 4 8% 22% 26% 4	1800
December	1st to 10th	Day	36% 4 6% 20% 27% 7%	2930
	11th to 20th	Day	41% 4 10% 17% 22% 5%	3370
	21st to end	Day	42% 4 12% 25% 15% 2	4466
January	1st to 10th	Night	31% 2 7% 19% 31% 10%	5889
	11th to 20th	Night	32% 3 6% 17% 34% 8%	5900
	21st to end	Night	39% 2 7% 22% 26% 5%	6490
February	1st to 10th	Night	40% 6% 10% 21% 19% 4	2600
	11th to 20th	Night	42% 4 9% 19% 20% 7%	2426
	21st to end	Night	42% 4 10% 18% 19% 7%	1915
March	1st to 10th	Night	42% 4 6% 17% 22% 9%	4918
	11th to 20th	Night	27% 5% 6% 19% 25% 17%	4980
	21st to end	Night	38% 5% 7% 26% 20% 5%	5467
April	1st to 10th	Night	36% 6% 12% 19% 22% 5%	2165
	11th to 20th	Night	35% 5% 10% 21% 21% 8%	1975
	21st to end	Night	37% 7% 11% 24% 17% 4	1870
May	1st to 10th	Night	43% 9% 14% 20% 13% 1	4060
	11th to 20th	Night	49% 8% 12% 18% 12% 1	4033
	21st to end	Night	39% 7% 13% 25% 12% 4	4429
June	1st to 10th	Night	35% 10% 16% 23% 13% 2	1800
	11th to 20th	Night	36% 10% 16% 22% 14% 1	1800
	21st to end	Night	34% 11% 16% 20% 15% 4	1800
July	1st to 10th	Night	44% 12% 14% 18% 12% 1	4015
	11th to 20th	Night	45% 16% 21% 13% 4 1	4006
	21st to end	Night	47% 11% 17% 19% 6%	4297
August	1st to 10th	Night	52% 10% 17% 16% 5%	2904
	11th to 20th	Night	41% 12% 20% 17% 9% 1	2902
	21st to end	Night	29% 9% 12% 36% 12% 3	3502
September	1st to 10th	Night	35% 9% 13% 21% 15% 6%	2022
	11th to 20th	Night	44% 9% 10% 17% 19% 2	2090
	21st to end	Night	48% 7% 10% 16% 16% 3	2090
October	1st to 10th	Night	37% 5% 9% 16% 24% 9%	3731
	11th to 20th	Night	22% 3 6% 24% 29% 16%	3779
	21st to end	Night	26% 3 6% 25% 25% 15%	4120
November	1st to 10th	Night	35% 4 8% 20% 24% 9%	2341
	11th to 20th	Night	33% 4 8% 19% 26% 9%	2555
	21st to end	Night	33% 4 8% 24% 25% 6%	2600
December	1st to 10th	Night	35% 4 7% 22% 29% 4	4250
	11th to 20th	Night	48% 4 7% 17% 16% 9%	4824
	21st to end	Night	39% 4 16% 21% 18% 2	6490

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	28% 20% 31% 16% 5%	300
	11th to 20th	Day	27% 19% 30% 19% 5%	300
	21st to end	Day	22% 17% 38% 18% 4	330
February	1st to 10th	Day	19% 18% 39% 18% 6%	300
	11th to 20th	Day	36% 16% 34% 11% 2	300
	21st to end	Day	24% 19% 33% 20% 4	312
March	1st to 10th	Day	22% 13% 32% 24% 8% 1	500
	11th to 20th	Day	21% 12% 38% 22% 6% 1	500
	21st to end	Day	24% 14% 33% 23% 6% 1	550
April	1st to 10th	Day	20% 16% 31% 20% 11% 3	500
	11th to 20th	Day	17% 14% 26% 24% 15% 3	492
	21st to end	Day	18% 11% 26% 25% 16% 4	500
May	1st to 10th	Day	16% 11% 29% 25% 14% 5%	503
	11th to 20th	Day	17% 6% 20% 28% 19% 10%	527
	21st to end	Day	20% 5% 16% 23% 22% 13%	573
June	1st to 10th	Day	11% 3 19% 30% 24% 13%	530
	11th to 20th	Day	10% 3 17% 25% 27% 18%	530
	21st to end	Day	10% 2 12% 32% 29% 15%	530
July	1st to 10th	Day	9% 1 9% 26% 33% 21%	525
	11th to 20th	Day	6% 2 9% 23% 34% 27%	524
	21st to end	Day	10% 2 11% 23% 32% 22%	576
August	1st to 10th	Day	17% 3 12% 23% 28% 17%	526
	11th to 20th	Day	12% 2 9% 27% 27% 22%	519
	21st to end	Day	11% 2 9% 24% 33% 21%	583
September	1st to 10th	Day	12% 3 11% 24% 29% 21%	502
	11th to 20th	Day	17% 3 12% 20% 30% 17%	490
	21st to end	Day	24% 5% 22% 23% 20% 6%	490
October	1st to 10th	Day	17% 5% 17% 30% 22% 9%	490
	11th to 20th	Day	14% 7% 23% 27% 23% 5%	490
	21st to end	Day	15% 8% 20% 34% 17% 6%	539
November	1st to 10th	Day	19% 6% 26% 30% 14% 4	495
	11th to 20th	Day	18% 12% 31% 24% 12% 3	340
	21st to end	Day	16% 16% 28% 26% 12% 3	300
December	1st to 10th	Day	28% 13% 34% 20% 6%	300
	11th to 20th	Day	21% 13% 27% 27% 10% 1	300
	21st to end	Day	27% 12% 29% 22% 9% 1	330
January	1st to 10th	Night	21% 10% 37% 28% 5%	800
	11th to 20th	Night	20% 10% 37% 30% 4	800
	21st to end	Night	19% 8% 40% 31% 2	880
February	1st to 10th	Night	19% 9% 37% 32% 4	800
	11th to 20th	Night	24% 14% 36% 24% 2	783
	21st to end	Night	17% 12% 39% 30% 2	660
March	1st to 10th	Night	18% 11% 32% 34% 6%	800
	11th to 20th	Night	19% 11% 35% 28% 7% 1	800
	21st to end	Night	18% 10% 35% 32% 6%	880
April	1st to 10th	Night	17% 13% 30% 31% 8%	800
	11th to 20th	Night	16% 9% 30% 32% 12%	791
	21st to end	Night	15% 7% 30% 36% 12%	670
May	1st to 10th	Night	14% 5% 28% 35% 17% 1	600
	11th to 20th	Night	17% 5% 22% 32% 22% 2	591
	21st to end	Night	16% 3 13% 34% 31% 4	650
June	1st to 10th	Night	11% 2 13% 39% 33% 3	600
	11th to 20th	Night	12% 2 12% 31% 39% 5%	600
	21st to end	Night	8% 1 9% 32% 46% 4	600
July	1st to 10th	Night	10% 2 9% 30% 44% 5%	585
	11th to 20th	Night	7% 2 5% 31% 46% 8%	582
	21st to end	Night	9% 2 8% 32% 42% 7%	657
August	1st to 10th	Night	16% 2 8% 27% 40% 6%	597
	11th to 20th	Night	11% 2 8% 33% 38% 8%	594
	21st to end	Night	11% 1 10% 26% 43% 8%	822
September	1st to 10th	Night	12% 2 10% 30% 39% 7%	773
	11th to 20th	Night	17% 2 13% 29% 32% 6%	760
	21st to end	Night	24% 3 16% 30% 26% 1	760
October	1st to 10th	Night	15% 5% 17% 31% 27% 5%	760
	11th to 20th	Night	15% 6% 24% 35% 19% 2	760
	21st to end	Night	16% 6% 22% 37% 18% 1	836
November	1st to 10th	Night	18% 6% 21% 39% 15% 2	780
	11th to 20th	Night	16% 8% 26% 38% 11%	800
	21st to end	Night	16% 6% 30% 36% 11% 1	800
December	1st to 10th	Night	21% 7% 32% 32% 8%	800
	11th to 20th	Night	21% 5% 31% 35% 8%	800
	21st to end	Night	26% 5% 28% 35% 6%	880

Page generated at 2025-09-01 01:51:05. Version ac07

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