Morehead Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morehead Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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% 43%	74624
	Night	14% 5% 2 5% 5% 3 4 4 5% 7% 45%	75128
Transparency	Day	39% 5% 12% 22% 18% 4	74346
	Night	39% 5% 10% 21% 20% 5%	74925
Seeing	Day	17% 11% 25% 24% 17% 6%	14204
	Night	17% 10% 24% 30% 17% 2	24528

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	17% 6% 2 6% 4 3 4 3 3 5% 46%	1706
	11th to 20th	Day	18% 6% 3 4 4 2 4 4 5% 6% 45%	1647
	21st to end	Day	16% 6% 3 4 3 2 4 4 4 5% 48%	1782
February	1st to 10th	Day	15% 7% 2 5% 5% 3 5% 4 6% 7% 43%	1620
	11th to 20th	Day	22% 6% 2 4 4 2 3 3 4 4 46%	1573
	21st to end	Day	19% 7% 3 6% 4 3 2 4 4 6% 41%	1627
March	1st to 10th	Day	14% 5% 1 4 4 2 4 4 5% 6% 52%	1980
	11th to 20th	Day	14% 7% 3 5% 5% 2 5% 5% 4 9% 42%	1980
	21st to end	Day	17% 7% 3 5% 6% 3 4 4 4 6% 41%	2178
April	1st to 10th	Day	11% 4 2 3 4 2 4 4 5% 8% 55%	2083
	11th to 20th	Day	11% 5% 2 5% 4 4 4 5% 5% 8% 48%	2134
	21st to end	Day	15% 5% 3 4 4 3 5% 4 6% 7% 45%	2160
May	1st to 10th	Day	12% 5% 2 5% 4 3 5% 5% 7% 8% 42%	2333
	11th to 20th	Day	14% 6% 2 5% 6% 3 6% 6% 6% 8% 39%	2301
	21st to end	Day	12% 5% 2 5% 5% 4 6% 5% 6% 8% 40%	2531
June	1st to 10th	Day	10% 5% 2 5% 6% 4 5% 7% 8% 10% 39%	2340
	11th to 20th	Day	9% 5% 2 5% 6% 3 5% 5% 7% 10% 43%	2340
	21st to end	Day	7% 5% 3 5% 6% 4 6% 7% 7% 11% 40%	2340
July	1st to 10th	Day	8% 5% 2 7% 7% 5% 7% 7% 8% 10% 36%	2340
	11th to 20th	Day	7% 5% 3 6% 6% 4 6% 8% 10% 13% 33%	2340
	21st to end	Day	7% 5% 2 6% 7% 5% 8% 7% 7% 12% 34%	2547
August	1st to 10th	Day	10% 5% 3 6% 7% 4 6% 7% 9% 11% 31%	2327
	11th to 20th	Day	10% 7% 3 8% 7% 5% 6% 7% 7% 8% 32%	2245
	21st to end	Day	11% 6% 3 5% 6% 4 6% 6% 7% 10% 36%	2376
September	1st to 10th	Day	9% 4 2 5% 5% 3 5% 5% 7% 9% 46%	2160
	11th to 20th	Day	15% 5% 2 5% 5% 3 5% 5% 5% 8% 42%	2022
	21st to end	Day	21% 7% 2 6% 4 2 4 4 5% 6% 39%	1949
October	1st to 10th	Day	15% 5% 2 6% 4 2 3 3 4 6% 50%	1800
	11th to 20th	Day	13% 5% 2 4 3 2 4 3 4 5% 56%	1800
	21st to end	Day	12% 5% 1 4 4 2 3 3 4 4 56%	1980
November	1st to 10th	Day	14% 4 2 4 4 2 3 3 4 5% 56%	1857
	11th to 20th	Day	15% 4 2 4 3 2 3 3 4 6% 53%	1877
	21st to end	Day	14% 4 2 4 4 2 3 4 4 6% 51%	1630
December	1st to 10th	Day	18% 7% 3 4 5% 2 5% 4 4 7% 42%	1520
	11th to 20th	Day	16% 4 2 4 3 2 2 3 4 6% 56%	2075
	21st to end	Day	17% 6% 2 5% 4 3 4 4 5% 7% 42%	3124
January	1st to 10th	Night	16% 6% 2 5% 4 3 3 4 4 6% 47%	2459
	11th to 20th	Night	15% 7% 3 6% 4 3 4 4 4 6% 44%	2386
	21st to end	Night	16% 5% 2 4 4 2 4 3 4 5% 50%	2574
February	1st to 10th	Night	18% 5% 2 5% 4 3 3 4 5% 6% 45%	2340
	11th to 20th	Night	20% 6% 3 5% 3 2 4 4 4 5% 44%	2271
	21st to end	Night	16% 6% 2 4 4 3 3 4 5% 6% 45%	1628
March	1st to 10th	Night	13% 5% 2 4 4 2 4 4 4 5% 52%	1980
	11th to 20th	Night	18% 5% 2 4 5% 3 5% 4 5% 6% 42%	1980
	21st to end	Night	15% 6% 3 5% 4 3 4 4 5% 7% 44%	2178
April	1st to 10th	Night	14% 5% 2 4 4 2 4 4 4 7% 49%	1877
	11th to 20th	Night	14% 4 2 5% 5% 2 3 4 4 6% 51%	1775
	21st to end	Night	12% 4 2 5% 5% 2 6% 5% 5% 7% 47%	1800
May	1st to 10th	Night	10% 4 2 5% 6% 3 5% 5% 6% 9% 45%	1641
	11th to 20th	Night	16% 4 3 6% 5% 3 4 4 5% 8% 41%	1592
	21st to end	Night	11% 6% 2 5% 5% 3 5% 5% 6% 10% 42%	1744
June	1st to 10th	Night	10% 6% 2 4 6% 4 5% 6% 8% 9% 40%	1620
	11th to 20th	Night	10% 5% 3 6% 6% 3 5% 5% 8% 10% 40%	1620
	21st to end	Night	8% 5% 3 5% 6% 3 5% 5% 7% 12% 40%	1620
July	1st to 10th	Night	8% 5% 3 6% 7% 4 5% 6% 8% 11% 38%	1620
	11th to 20th	Night	7% 5% 2 5% 5% 3 6% 7% 9% 12% 38%	1620
	21st to end	Night	6% 4 2 6% 7% 4 7% 7% 7% 13% 37%	1771
August	1st to 10th	Night	11% 5% 3 6% 7% 4 5% 6% 8% 12% 33%	1611
	11th to 20th	Night	11% 6% 3 5% 6% 4 6% 6% 8% 9% 35%	1636
	21st to end	Night	9% 5% 2 6% 7% 4 5% 5% 7% 11% 38%	1980
September	1st to 10th	Night	12% 5% 2 5% 4 3 4 4 6% 8% 47%	1800
	11th to 20th	Night	14% 6% 2 5% 5% 2 5% 4 6% 7% 45%	1934
	21st to end	Night	18% 8% 3 6% 5% 3 4 5% 6% 6% 37%	2010
October	1st to 10th	Night	15% 6% 3 5% 5% 2 3 4 4 5% 50%	2160
	11th to 20th	Night	14% 6% 2 5% 4 2 3 3 4 6% 52%	2160
	21st to end	Night	13% 5% 2 4 4 3 3 3 4 5% 55%	2376
November	1st to 10th	Night	14% 6% 2 5% 4 2 3 3 3 5% 53%	2221
	11th to 20th	Night	12% 5% 2 5% 4 3 5% 4 4 6% 51%	2300
	21st to end	Night	14% 4 2 3 4 2 3 5% 5% 6% 51%	2543
December	1st to 10th	Night	17% 7% 3 5% 6% 3 4 4 4 5% 42%	2660
	11th to 20th	Night	16% 6% 2 4 4 2 3 4 5% 5% 49%	3109
	21st to end	Night	18% 6% 3 4 4 2 3 3 5% 7% 46%	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	42% 2 7% 24% 19% 5%	1707
	11th to 20th	Day	41% 4 6% 21% 23% 4	1647
	21st to end	Day	39% 3 6% 22% 23% 7%	1782
February	1st to 10th	Day	41% 3 11% 21% 18% 5%	1620
	11th to 20th	Day	43% 3 7% 20% 22% 6%	1582
	21st to end	Day	46% 3 10% 16% 19% 6%	1627
March	1st to 10th	Day	34% 4 8% 23% 24% 7%	1980
	11th to 20th	Day	41% 5% 10% 20% 18% 7%	1980
	21st to end	Day	46% 4 9% 20% 18% 4	2178
April	1st to 10th	Day	29% 3 10% 25% 24% 8%	2083
	11th to 20th	Day	35% 3 10% 23% 20% 8%	2134
	21st to end	Day	38% 4 10% 24% 19% 4	2160
May	1st to 10th	Day	37% 6% 16% 21% 17% 3	2333
	11th to 20th	Day	43% 5% 15% 23% 12% 2	2305
	21st to end	Day	42% 5% 15% 25% 14% 1	2531
June	1st to 10th	Day	37% 7% 15% 24% 15% 1	2340
	11th to 20th	Day	35% 7% 17% 24% 16% 2	2340
	21st to end	Day	36% 8% 16% 23% 15% 2	2340
July	1st to 10th	Day	41% 8% 15% 19% 14% 3	2275
	11th to 20th	Day	38% 9% 20% 21% 10% 2	2271
	21st to end	Day	39% 8% 20% 24% 8%	2405
August	1st to 10th	Day	44% 8% 17% 22% 9% 1	2314
	11th to 20th	Day	46% 8% 16% 20% 10% 1	2245
	21st to end	Day	41% 7% 16% 21% 11% 3	2376
September	1st to 10th	Day	35% 6% 15% 20% 18% 6%	2160
	11th to 20th	Day	40% 5% 11% 18% 22% 4	2022
	21st to end	Day	46% 4 8% 21% 17% 4	1949
October	1st to 10th	Day	37% 3 9% 22% 25% 4	1800
	11th to 20th	Day	32% 3 7% 29% 21% 8%	1800
	21st to end	Day	33% 3 6% 24% 25% 9%	1980
November	1st to 10th	Day	33% 2 8% 22% 27% 8%	1857
	11th to 20th	Day	34% 2 8% 22% 27% 7%	1877
	21st to end	Day	35% 3 7% 23% 26% 6%	1630
December	1st to 10th	Day	44% 3 10% 21% 18% 4	1520
	11th to 20th	Day	32% 2 7% 26% 24% 9%	2072
	21st to end	Day	42% 3 10% 23% 20% 2	3124
January	1st to 10th	Night	40% 3 8% 20% 23% 7%	2459
	11th to 20th	Night	42% 4 10% 19% 21% 5%	2386
	21st to end	Night	38% 2 5% 23% 26% 6%	2574
February	1st to 10th	Night	41% 3 9% 21% 20% 6%	2340
	11th to 20th	Night	43% 3 7% 17% 21% 8%	2273
	21st to end	Night	39% 3 9% 21% 20% 8%	1628
March	1st to 10th	Night	35% 3 7% 22% 24% 9%	1980
	11th to 20th	Night	42% 4 9% 20% 19% 6%	1980
	21st to end	Night	41% 5% 9% 22% 19% 5%	2178
April	1st to 10th	Night	37% 4 9% 18% 26% 7%	1877
	11th to 20th	Night	35% 3 9% 23% 21% 8%	1775
	21st to end	Night	37% 4 10% 25% 19% 5%	1800
May	1st to 10th	Night	36% 5% 14% 24% 17% 4	1641
	11th to 20th	Night	42% 5% 13% 22% 16% 2	1593
	21st to end	Night	37% 7% 16% 25% 14% 1	1745
June	1st to 10th	Night	38% 7% 16% 22% 15% 2	1620
	11th to 20th	Night	38% 7% 18% 20% 15% 2	1620
	21st to end	Night	36% 9% 16% 21% 15% 3	1620
July	1st to 10th	Night	38% 9% 16% 20% 14% 3	1575
	11th to 20th	Night	35% 10% 22% 22% 8% 3	1566
	21st to end	Night	36% 9% 20% 22% 12%	1672
August	1st to 10th	Night	42% 8% 19% 20% 10% 1	1600
	11th to 20th	Night	42% 10% 17% 20% 9% 2	1636
	21st to end	Night	39% 7% 18% 24% 9% 3	1980
September	1st to 10th	Night	35% 7% 14% 21% 17% 6%	1800
	11th to 20th	Night	38% 6% 11% 20% 22% 3	1934
	21st to end	Night	47% 6% 11% 17% 15% 4	2010
October	1st to 10th	Night	38% 4 8% 23% 23% 4	2160
	11th to 20th	Night	36% 3 7% 23% 24% 8%	2160
	21st to end	Night	33% 3 7% 21% 26% 11%	2376
November	1st to 10th	Night	36% 3 7% 19% 27% 9%	2221
	11th to 20th	Night	36% 3 8% 17% 25% 12%	2300
	21st to end	Night	34% 3 6% 24% 26% 7%	2543
December	1st to 10th	Night	46% 3 7% 20% 19% 4	2660
	11th to 20th	Night	38% 3 7% 21% 22% 9%	3111
	21st to end	Night	40% 2 7% 25% 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	27% 21% 36% 14% 3	270
	11th to 20th	Day	26% 23% 34% 13% 4	249
	21st to end	Day	21% 23% 42% 11% 3	264
February	1st to 10th	Day	23% 20% 41% 13% 3	240
	11th to 20th	Day	39% 20% 33% 7% 1	240
	21st to end	Day	26% 21% 32% 17% 3	345
March	1st to 10th	Day	23% 19% 34% 17% 7%	420
	11th to 20th	Day	21% 23% 39% 11% 5% 1	420
	21st to end	Day	21% 20% 36% 18% 4 1	462
April	1st to 10th	Day	22% 18% 33% 18% 7% 2	420
	11th to 20th	Day	15% 19% 30% 23% 10% 4	412
	21st to end	Day	19% 12% 30% 26% 11% 2	420
May	1st to 10th	Day	18% 17% 31% 22% 8% 4	423
	11th to 20th	Day	16% 9% 23% 30% 18% 5%	447
	21st to end	Day	21% 5% 18% 27% 21% 8%	485
June	1st to 10th	Day	12% 4 23% 32% 22% 6%	450
	11th to 20th	Day	9% 8% 22% 29% 25% 8%	450
	21st to end	Day	12% 3 21% 33% 25% 6%	450
July	1st to 10th	Day	10% 2 11% 33% 33% 11%	445
	11th to 20th	Day	6% 2 12% 31% 36% 12%	444
	21st to end	Day	9% 2 15% 35% 27% 12%	488
August	1st to 10th	Day	15% 3 17% 28% 26% 11%	446
	11th to 20th	Day	12% 2 13% 29% 27% 16%	439
	21st to end	Day	12% 4 11% 29% 27% 16%	495
September	1st to 10th	Day	12% 4 17% 25% 28% 15%	450
	11th to 20th	Day	17% 4 12% 30% 27% 11%	450
	21st to end	Day	25% 6% 22% 26% 17% 3	450
October	1st to 10th	Day	18% 8% 21% 24% 21% 8%	450
	11th to 20th	Day	16% 8% 25% 28% 18% 5%	450
	21st to end	Day	15% 13% 25% 29% 14% 4	495
November	1st to 10th	Day	19% 10% 30% 24% 14% 3	455
	11th to 20th	Day	19% 15% 28% 26% 11% 1	437
	21st to end	Day	14% 18% 31% 21% 13% 2	232
December	1st to 10th	Day	23% 18% 38% 12% 8% 1	180
	11th to 20th	Day	21% 18% 35% 19% 7% 1	234
	21st to end	Day	26% 17% 30% 17% 9% 1	297
January	1st to 10th	Night	21% 18% 31% 24% 5%	760
	11th to 20th	Night	20% 17% 31% 26% 7%	735
	21st to end	Night	19% 16% 37% 24% 3	792
February	1st to 10th	Night	22% 13% 35% 27% 4	720
	11th to 20th	Night	25% 20% 34% 20% 1	703
	21st to end	Night	19% 16% 36% 24% 4	592
March	1st to 10th	Night	17% 16% 35% 27% 5%	720
	11th to 20th	Night	22% 16% 31% 21% 9% 1	720
	21st to end	Night	18% 14% 37% 26% 5%	792
April	1st to 10th	Night	18% 17% 31% 26% 8%	720
	11th to 20th	Night	15% 14% 33% 25% 12% 1	711
	21st to end	Night	16% 9% 33% 34% 8%	720
May	1st to 10th	Night	14% 10% 33% 33% 9%	561
	11th to 20th	Night	17% 5% 24% 34% 18% 1	531
	21st to end	Night	14% 3 13% 40% 28% 3	584
June	1st to 10th	Night	13% 3 16% 41% 25% 2	540
	11th to 20th	Night	12% 4 15% 37% 27% 5%	540
	21st to end	Night	10% 3 14% 39% 31% 3	540
July	1st to 10th	Night	8% 1 13% 33% 41% 4	525
	11th to 20th	Night	8% 2 9% 38% 36% 7%	522
	21st to end	Night	6% 3 13% 40% 34% 5%	591
August	1st to 10th	Night	13% 2 9% 36% 35% 4	537
	11th to 20th	Night	13% 3 9% 33% 34% 7%	572
	21st to end	Night	12% 3 9% 31% 38% 7%	792
September	1st to 10th	Night	15% 2 10% 33% 33% 7%	720
	11th to 20th	Night	17% 3 14% 30% 31% 5%	720
	21st to end	Night	25% 4 16% 33% 22% 1	720
October	1st to 10th	Night	18% 5% 17% 30% 25% 6%	720
	11th to 20th	Night	17% 9% 23% 28% 20% 2	720
	21st to end	Night	16% 10% 26% 29% 18% 2	792
November	1st to 10th	Night	17% 8% 24% 34% 14% 2	740
	11th to 20th	Night	15% 13% 29% 32% 11%	760
	21st to end	Night	16% 13% 27% 30% 13% 1	760
December	1st to 10th	Night	21% 14% 29% 28% 8%	760
	11th to 20th	Night	19% 11% 31% 31% 8%	760
	21st to end	Night	22% 15% 26% 29% 7%	836

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