Mount Airy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Airy clear sky chart from 2005-11-06 to 2026-01-17.

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% 6% 2 6% 4 4 5% 4 6% 8% 42%	127462
	Night	15% 6% 2 5% 4 4 4 3 5% 7% 44%	124243
Transparency	Day	39% 7% 12% 21% 16% 5%	131094
	Night	38% 6% 11% 21% 19% 6%	128680
Seeing	Day	18% 11% 23% 24% 16% 7%	16849
	Night	17% 8% 23% 31% 18% 3	26967

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 3 2 2 2 4 6% 53%	4146
	11th to 20th	Day	13% 5% 1 4 3 3 3 3 4 5% 57%	4114
	21st to end	Day	19% 5% 2 5% 4 3 3 2 4 4 48%	4466
February	1st to 10th	Day	13% 7% 2 6% 5% 4 4 3 5% 7% 43%	1800
	11th to 20th	Day	21% 6% 2 4 3 4 4 2 5% 6% 42%	1860
	21st to end	Day	19% 6% 2 5% 4 4 4 3 6% 6% 42%	1705
March	1st to 10th	Day	20% 5% 2 6% 4 4 4 3 4 6% 41%	4935
	11th to 20th	Day	12% 4 1 5% 3 3 3 3 5% 6% 54%	4980
	21st to end	Day	18% 7% 2 5% 4 3 3 3 5% 6% 45%	5465
April	1st to 10th	Day	12% 4 1 4 4 3 4 4 6% 8% 49%	2231
	11th to 20th	Day	15% 4 2 5% 4 3 4 4 5% 7% 47%	2374
	21st to end	Day	15% 6% 2 6% 4 4 6% 4 6% 6% 43%	2560
May	1st to 10th	Day	12% 7% 2 6% 5% 6% 6% 5% 8% 10% 32%	5862
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 7% 8% 27%	5861
	21st to end	Day	13% 5% 2 6% 5% 4 5% 4 7% 9% 39%	6433
June	1st to 10th	Day	10% 6% 3 6% 4 5% 6% 5% 8% 10% 38%	2600
	11th to 20th	Day	9% 5% 2 6% 5% 6% 6% 6% 7% 10% 39%	2600
	21st to end	Day	8% 4 2 6% 5% 7% 5% 5% 9% 10% 40%	2600
July	1st to 10th	Day	8% 5% 2 7% 5% 6% 6% 5% 8% 10% 37%	5900
	11th to 20th	Day	8% 5% 3 7% 6% 6% 7% 7% 9% 13% 30%	5900
	21st to end	Day	11% 6% 2 8% 6% 7% 7% 6% 8% 10% 28%	6424
August	1st to 10th	Day	16% 7% 3 8% 5% 5% 6% 5% 8% 11% 26%	4234
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 5% 7% 10% 37%	4174
	21st to end	Day	6% 4 2 4 4 4 5% 4 6% 10% 51%	4383
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 9% 45%	2293
	11th to 20th	Day	14% 6% 2 7% 4 5% 5% 3 6% 7% 42%	2200
	21st to end	Day	20% 7% 2 7% 4 4 5% 3 5% 7% 36%	2200
October	1st to 10th	Day	13% 5% 1 5% 4 3 4 3 3 6% 53%	2049
	11th to 20th	Day	15% 5% 1 4 3 3 3 2 4 5% 56%	2000
	21st to end	Day	15% 5% 2 5% 3 3 2 2 3 5% 55%	2200
November	1st to 10th	Day	13% 5% 1 5% 2 3 3 2 4 5% 56%	2057
	11th to 20th	Day	14% 4 2 4 3 3 4 3 5% 6% 54%	1918
	21st to end	Day	14% 5% 2 4 3 4 3 3 5% 6% 50%	1890
December	1st to 10th	Day	17% 6% 2 4 3 3 3 2 4 5% 51%	3020
	11th to 20th	Day	21% 6% 2 4 3 3 3 2 5% 6% 45%	3463
	21st to end	Day	24% 6% 2 4 3 4 4 3 5% 8% 39%	4565
January	1st to 10th	Night	13% 5% 2 4 3 3 3 3 4 5% 55%	6019
	11th to 20th	Night	13% 6% 2 4 3 2 3 3 4 5% 57%	5979
	21st to end	Night	20% 6% 2 4 2 3 2 2 4 5% 50%	6490
February	1st to 10th	Night	15% 7% 2 5% 4 4 4 4 5% 6% 44%	2600
	11th to 20th	Night	22% 6% 2 5% 3 3 4 3 5% 6% 43%	2423
	21st to end	Night	16% 7% 2 6% 5% 4 4 3 4 7% 43%	1925
March	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 4 5% 44%	4918
	11th to 20th	Night	10% 3 2 4 3 3 3 3 5% 7% 57%	4980
	21st to end	Night	15% 6% 2 5% 4 4 4 3 6% 7% 44%	5467
April	1st to 10th	Night	14% 6% 2 5% 4 4 3 4 5% 7% 47%	2167
	11th to 20th	Night	14% 5% 2 5% 4 4 4 3 5% 8% 47%	1975
	21st to end	Night	15% 5% 2 5% 4 4 5% 3 5% 7% 46%	1855
May	1st to 10th	Night	16% 7% 2 6% 5% 5% 4 3 5% 9% 38%	4033
	11th to 20th	Night	21% 7% 3 8% 4 4 3 3 5% 8% 33%	4032
	21st to end	Night	18% 5% 2 5% 4 3 4 3 7% 9% 40%	4421
June	1st to 10th	Night	11% 4 2 6% 5% 4 5% 5% 7% 9% 43%	1800
	11th to 20th	Night	13% 6% 2 5% 4 4 4 3 7% 9% 43%	1800
	21st to end	Night	7% 5% 2 5% 6% 5% 5% 4 7% 11% 43%	1800
July	1st to 10th	Night	11% 7% 3 7% 5% 5% 5% 5% 7% 9% 35%	4058
	11th to 20th	Night	10% 6% 2 8% 6% 6% 7% 6% 8% 12% 29%	4057
	21st to end	Night	12% 8% 4 8% 6% 5% 6% 5% 8% 10% 28%	4427
August	1st to 10th	Night	18% 9% 3 8% 5% 5% 5% 4 7% 10% 27%	2915
	11th to 20th	Night	11% 6% 3 8% 5% 5% 5% 4 7% 9% 35%	2875
	21st to end	Night	7% 3 2 6% 4 4 4 4 6% 8% 51%	3480
September	1st to 10th	Night	11% 6% 1 5% 4 4 5% 5% 7% 8% 45%	2102
	11th to 20th	Night	16% 6% 3 8% 5% 4 5% 4 5% 7% 39%	2200
	21st to end	Night	20% 7% 3 7% 4 4 4 4 6% 5% 37%	2200
October	1st to 10th	Night	14% 6% 2 5% 4 3 4 3 5% 7% 47%	2350
	11th to 20th	Night	13% 5% 1 4 3 3 3 3 5% 5% 54%	2400
	21st to end	Night	15% 4 2 4 3 3 3 2 3 5% 56%	2640
November	1st to 10th	Night	15% 5% 2 4 3 3 3 2 4 4 53%	2461
	11th to 20th	Night	14% 4 1 4 3 2 3 3 5% 5% 55%	2699
	21st to end	Night	15% 5% 2 4 3 3 3 4 5% 7% 50%	2730
December	1st to 10th	Night	13% 7% 2 5% 3 4 4 3 4 5% 50%	4380
	11th to 20th	Night	22% 8% 2 5% 3 3 3 3 4 5% 42%	4952
	21st to end	Night	23% 5% 2 4 3 3 3 3 5% 6% 43%	6633

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 6% 20% 30% 7%	4147
	11th to 20th	Day	31% 3 6% 18% 33% 9%	4114
	21st to end	Day	40% 3 8% 23% 22% 5%	4466
February	1st to 10th	Day	41% 4 11% 21% 19% 4	1800
	11th to 20th	Day	43% 4 8% 21% 19% 5%	1869
	21st to end	Day	44% 5% 11% 16% 18% 6%	1705
March	1st to 10th	Day	44% 5% 6% 19% 15% 11%	4935
	11th to 20th	Day	31% 5% 7% 22% 23% 12%	4980
	21st to end	Day	41% 4 8% 24% 18% 5%	5465
April	1st to 10th	Day	32% 6% 13% 23% 20% 7%	2231
	11th to 20th	Day	37% 5% 11% 21% 20% 7%	2374
	21st to end	Day	41% 7% 11% 25% 14% 3	2560
May	1st to 10th	Day	43% 9% 16% 19% 12% 2	5897
	11th to 20th	Day	52% 9% 11% 19% 8% 1	5865
	21st to end	Day	39% 8% 15% 19% 15% 3	6447
June	1st to 10th	Day	39% 9% 15% 24% 11% 1	2600
	11th to 20th	Day	38% 11% 16% 19% 14% 2	2600
	21st to end	Day	35% 10% 19% 21% 14% 1	2600
July	1st to 10th	Day	38% 12% 18% 18% 11% 3	5835
	11th to 20th	Day	42% 13% 24% 16% 4 1	5831
	21st to end	Day	47% 12% 16% 18% 7%	6240
August	1st to 10th	Day	48% 10% 18% 19% 5%	4221
	11th to 20th	Day	37% 12% 21% 20% 8% 2	4213
	21st to end	Day	27% 8% 18% 34% 11% 2	4383
September	1st to 10th	Day	35% 9% 14% 20% 19% 4	2293
	11th to 20th	Day	41% 7% 12% 22% 16% 2	2200
	21st to end	Day	48% 5% 11% 18% 16% 3	2200
October	1st to 10th	Day	30% 4 9% 20% 27% 10%	3335
	11th to 20th	Day	23% 3 5% 24% 28% 17%	3240
	21st to end	Day	28% 4 9% 24% 22% 14%	3538
November	1st to 10th	Day	31% 3 9% 24% 24% 8%	2057
	11th to 20th	Day	32% 4 9% 22% 27% 7%	1918
	21st to end	Day	35% 4 9% 23% 26% 4	1890
December	1st to 10th	Day	37% 4 6% 21% 25% 7%	3020
	11th to 20th	Day	41% 3 11% 18% 22% 6%	3460
	21st to end	Day	44% 5% 12% 23% 14% 2	4565
January	1st to 10th	Night	31% 3 8% 19% 28% 10%	6019
	11th to 20th	Night	31% 5% 6% 17% 33% 8%	5979
	21st to end	Night	39% 2 5% 23% 25% 5%	6490
February	1st to 10th	Night	40% 4 9% 23% 19% 4	2600
	11th to 20th	Night	44% 4 8% 19% 18% 7%	2425
	21st to end	Night	42% 4 10% 20% 18% 6%	1925
March	1st to 10th	Night	41% 5% 7% 19% 20% 9%	4918
	11th to 20th	Night	27% 4 7% 21% 25% 15%	4980
	21st to end	Night	39% 4 8% 26% 18% 5%	5467
April	1st to 10th	Night	37% 5% 11% 20% 21% 5%	2167
	11th to 20th	Night	36% 4 11% 21% 20% 7%	1975
	21st to end	Night	37% 7% 11% 25% 17% 3	1855
May	1st to 10th	Night	43% 9% 15% 21% 12% 1	4060
	11th to 20th	Night	49% 8% 12% 20% 10% 1	4033
	21st to end	Night	39% 8% 16% 24% 10% 3	4429
June	1st to 10th	Night	36% 10% 15% 24% 14% 2	1800
	11th to 20th	Night	36% 8% 18% 23% 13% 1	1800
	21st to end	Night	34% 8% 18% 21% 14% 4	1800
July	1st to 10th	Night	42% 12% 15% 18% 11% 2	4015
	11th to 20th	Night	44% 12% 24% 15% 4 1	4006
	21st to end	Night	47% 9% 18% 18% 7%	4297
August	1st to 10th	Night	51% 9% 18% 16% 6%	2904
	11th to 20th	Night	41% 10% 20% 20% 9% 1	2902
	21st to end	Night	30% 8% 14% 36% 10% 2	3480
September	1st to 10th	Night	35% 8% 15% 20% 17% 6%	2102
	11th to 20th	Night	43% 6% 11% 20% 19% 1	2200
	21st to end	Night	48% 6% 10% 18% 16% 3	2200
October	1st to 10th	Night	35% 6% 9% 18% 24% 9%	3844
	11th to 20th	Night	22% 4 7% 24% 29% 14%	3899
	21st to end	Night	26% 5% 7% 23% 25% 14%	4252
November	1st to 10th	Night	36% 3 8% 22% 24% 8%	2461
	11th to 20th	Night	31% 3 9% 22% 26% 9%	2699
	21st to end	Night	34% 4 7% 24% 24% 6%	2730
December	1st to 10th	Night	36% 4 8% 22% 27% 3	4380
	11th to 20th	Night	46% 3 9% 17% 17% 8%	4954
	21st to end	Night	41% 4 15% 22% 17% 1	6633

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% 26% 31% 10% 4	330
	11th to 20th	Day	29% 24% 31% 13% 3	318
	21st to end	Day	25% 25% 35% 13% 2	330
February	1st to 10th	Day	22% 21% 37% 17% 3	300
	11th to 20th	Day	41% 19% 30% 8% 1	300
	21st to end	Day	27% 22% 34% 14% 3	304
March	1st to 10th	Day	24% 17% 32% 20% 6%	500
	11th to 20th	Day	22% 22% 32% 19% 5% 1	500
	21st to end	Day	25% 18% 31% 20% 5%	550
April	1st to 10th	Day	21% 19% 30% 19% 10% 1	500
	11th to 20th	Day	18% 18% 26% 22% 13% 2	492
	21st to end	Day	20% 12% 30% 21% 13% 4	500
May	1st to 10th	Day	17% 16% 29% 22% 12% 5%	503
	11th to 20th	Day	20% 8% 25% 25% 15% 7%	527
	21st to end	Day	20% 6% 19% 25% 21% 9%	573
June	1st to 10th	Day	13% 5% 22% 32% 19% 10%	530
	11th to 20th	Day	12% 6% 16% 29% 23% 14%	530
	21st to end	Day	10% 5% 15% 34% 25% 10%	530
July	1st to 10th	Day	10% 2 12% 27% 32% 17%	525
	11th to 20th	Day	7% 2 11% 27% 33% 20%	524
	21st to end	Day	12% 3 12% 27% 30% 17%	576
August	1st to 10th	Day	18% 4 12% 26% 23% 16%	526
	11th to 20th	Day	11% 4 13% 27% 26% 18%	519
	21st to end	Day	10% 4 10% 27% 30% 19%	583
September	1st to 10th	Day	13% 3 12% 28% 28% 16%	530
	11th to 20th	Day	16% 4 12% 27% 27% 15%	530
	21st to end	Day	21% 9% 20% 26% 18% 5%	530
October	1st to 10th	Day	16% 5% 18% 30% 23% 7%	530
	11th to 20th	Day	15% 11% 22% 30% 19% 3	530
	21st to end	Day	19% 12% 23% 31% 11% 4	583
November	1st to 10th	Day	18% 12% 29% 26% 12% 2	535
	11th to 20th	Day	19% 20% 31% 20% 9% 1	358
	21st to end	Day	18% 20% 31% 22% 8% 2	330
December	1st to 10th	Day	27% 19% 38% 13% 3 1	330
	11th to 20th	Day	23% 18% 30% 20% 8%	330
	21st to end	Day	30% 15% 28% 19% 6% 1	363
January	1st to 10th	Night	21% 15% 33% 26% 5%	840
	11th to 20th	Night	20% 15% 33% 28% 4	825
	21st to end	Night	19% 12% 38% 29% 2	880
February	1st to 10th	Night	19% 13% 33% 33% 3	800
	11th to 20th	Night	26% 15% 34% 23% 2	783
	21st to end	Night	18% 15% 35% 29% 2	660
March	1st to 10th	Night	19% 13% 32% 30% 6%	800
	11th to 20th	Night	21% 13% 33% 26% 6% 1	800
	21st to end	Night	20% 13% 32% 30% 5%	880
April	1st to 10th	Night	17% 16% 30% 29% 8%	800
	11th to 20th	Night	17% 12% 29% 29% 12% 1	791
	21st to end	Night	17% 8% 28% 34% 12%	655
May	1st to 10th	Night	16% 7% 26% 35% 16% 1	600
	11th to 20th	Night	17% 7% 20% 34% 20% 2	591
	21st to end	Night	17% 3 12% 31% 31% 6%	650
June	1st to 10th	Night	12% 4 12% 38% 32% 4	600
	11th to 20th	Night	14% 2 13% 28% 37% 6%	600
	21st to end	Night	9% 1 9% 34% 42% 5%	600
July	1st to 10th	Night	11% 3 6% 28% 46% 6%	585
	11th to 20th	Night	7% 2 5% 29% 48% 9%	582
	21st to end	Night	9% 3 7% 32% 42% 8%	657
August	1st to 10th	Night	17% 2 7% 30% 39% 5%	597
	11th to 20th	Night	14% 3 8% 29% 38% 8%	594
	21st to end	Night	11% 2 8% 27% 43% 9%	813
September	1st to 10th	Night	11% 3 9% 32% 35% 9%	800
	11th to 20th	Night	18% 4 12% 28% 32% 7%	800
	21st to end	Night	22% 5% 18% 30% 23% 2	800
October	1st to 10th	Night	15% 7% 19% 27% 27% 5%	800
	11th to 20th	Night	15% 6% 25% 35% 17% 3	800
	21st to end	Night	16% 10% 19% 38% 15% 2	880
November	1st to 10th	Night	17% 9% 24% 34% 15% 2	820
	11th to 20th	Night	17% 10% 28% 35% 9% 1	840
	21st to end	Night	17% 10% 28% 33% 10% 1	840
December	1st to 10th	Night	23% 10% 31% 30% 7%	840
	11th to 20th	Night	20% 9% 33% 31% 7%	840
	21st to end	Night	28% 10% 25% 32% 5%	924

Page generated at 2026-01-14 01:14:30. Version ac07

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