Morgantown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morgantown clear sky chart from 2005-11-06 to 2026-04-17.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 36%	131070
	Night	14% 10% 4 8% 5% 4 4 3 5% 7% 37%	131264
Transparency	Day	45% 5% 11% 23% 14% 2	134681
	Night	46% 5% 10% 22% 15% 2	135726
Seeing	Day	18% 13% 27% 22% 14% 5%	17433
	Night	18% 11% 29% 27% 13% 2	27347

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	15% 14% 6% 10% 4 4 4 3 6% 7% 27%	4691
	11th to 20th	Day	10% 12% 5% 15% 7% 5% 4 3 5% 4 30%	4710
	21st to end	Day	17% 14% 6% 13% 6% 5% 4 3 4 4 24%	5500
February	1st to 10th	Day	17% 14% 5% 8% 5% 4 3 3 4 6% 30%	2100
	11th to 20th	Day	16% 11% 5% 10% 5% 4 4 3 4 7% 31%	2048
	21st to end	Day	16% 14% 4 11% 3 3 2 3 4 6% 34%	1730
March	1st to 10th	Day	19% 14% 5% 7% 3 3 3 2 3 4 36%	4580
	11th to 20th	Day	11% 10% 3 6% 4 4 3 4 6% 7% 42%	4902
	21st to end	Day	15% 12% 3 8% 5% 4 4 4 5% 7% 32%	5853
April	1st to 10th	Day	15% 11% 3 7% 5% 5% 4 3 5% 7% 35%	2520
	11th to 20th	Day	15% 11% 2 7% 4 3 5% 3 5% 6% 38%	2446
	21st to end	Day	18% 8% 3 7% 5% 4 4 3 5% 7% 35%	2555
May	1st to 10th	Day	18% 10% 3 9% 5% 5% 5% 4 6% 8% 28%	5862
	11th to 20th	Day	19% 8% 3 6% 5% 4 4 4 5% 6% 35%	5861
	21st to end	Day	12% 8% 3 8% 6% 5% 6% 5% 7% 9% 32%	6521
June	1st to 10th	Day	11% 6% 3 6% 4 5% 4 5% 6% 8% 42%	2800
	11th to 20th	Day	9% 6% 2 5% 4 5% 5% 4 5% 9% 43%	2800
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	2800
July	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 7% 11% 40%	6360
	11th to 20th	Day	8% 6% 2 7% 5% 6% 6% 5% 8% 10% 38%	6360
	21st to end	Day	11% 7% 3 7% 5% 6% 6% 5% 7% 9% 33%	6683
August	1st to 10th	Day	8% 4 2 5% 4 4 5% 4 7% 10% 47%	4234
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 5% 8% 12% 39%	3950
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 9% 54%	4312
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 6% 7% 46%	2370
	11th to 20th	Day	10% 5% 2 5% 3 3 5% 4 6% 8% 49%	2200
	21st to end	Day	13% 5% 2 5% 4 4 3 4 5% 7% 49%	2200
October	1st to 10th	Day	10% 5% 2 6% 4 4 4 3 5% 7% 50%	2200
	11th to 20th	Day	12% 7% 2 6% 3 4 4 4 5% 6% 46%	2056
	21st to end	Day	18% 10% 3 7% 4 3 4 3 5% 6% 37%	1980
November	1st to 10th	Day	8% 6% 3 5% 4 4 4 3 5% 6% 52%	1852
	11th to 20th	Day	16% 11% 3 7% 3 3 4 3 6% 6% 38%	1890
	21st to end	Day	18% 12% 4 8% 4 4 2 3 4 6% 36%	1890
December	1st to 10th	Day	13% 13% 3 8% 4 3 2 3 4 5% 43%	3020
	11th to 20th	Day	15% 14% 6% 10% 4 5% 6% 3 4 6% 27%	3164
	21st to end	Day	23% 19% 7% 8% 5% 4 4 3 5% 5% 18%	4070
January	1st to 10th	Night	15% 15% 6% 13% 6% 4 4 3 5% 5% 25%	8232
	11th to 20th	Night	10% 16% 6% 15% 7% 6% 5% 3 4 4 24%	8280
	21st to end	Night	17% 12% 5% 8% 5% 5% 4 3 5% 6% 30%	8682
February	1st to 10th	Night	19% 12% 5% 10% 6% 4 4 3 5% 5% 27%	2520
	11th to 20th	Night	15% 12% 5% 9% 5% 4 4 3 6% 5% 32%	2458
	21st to end	Night	18% 13% 5% 9% 4 4 4 3 4 5% 32%	2076
March	1st to 10th	Night	19% 15% 3 6% 4 3 3 3 3 5% 36%	5493
	11th to 20th	Night	12% 8% 3 6% 4 3 3 3 5% 7% 45%	5278
	21st to end	Night	16% 10% 3 8% 5% 5% 5% 3 5% 6% 34%	5362
April	1st to 10th	Night	14% 10% 3 7% 5% 3 4 3 5% 7% 39%	2100
	11th to 20th	Night	16% 9% 3 7% 4 4 4 3 5% 7% 40%	2035
	21st to end	Night	15% 7% 3 7% 4 5% 5% 4 7% 7% 37%	1845
May	1st to 10th	Night	19% 12% 3 7% 5% 4 5% 3 6% 8% 29%	4033
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 4 6% 9% 36%	4032
	21st to end	Night	13% 8% 3 7% 5% 5% 5% 4 6% 8% 36%	4320
June	1st to 10th	Night	9% 6% 3 6% 5% 3 4 4 5% 10% 46%	1600
	11th to 20th	Night	9% 5% 2 7% 4 4 4 4 6% 8% 47%	1600
	21st to end	Night	5% 5% 2 4 4 4 5% 4 7% 11% 48%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 8% 47%	3618
	11th to 20th	Night	8% 5% 2 6% 5% 4 5% 4 8% 10% 43%	3617
	21st to end	Night	9% 6% 2 7% 4 5% 5% 4 8% 11% 39%	4165
August	1st to 10th	Night	8% 6% 2 6% 3 4 4 3 5% 8% 50%	2915
	11th to 20th	Night	7% 5% 2 6% 5% 4 5% 4 6% 8% 48%	3096
	21st to end	Night	4 3 2 5% 4 4 5% 3 5% 8% 58%	3586
September	1st to 10th	Night	10% 6% 2 5% 4 4 4 3 5% 7% 50%	2010
	11th to 20th	Night	7% 5% 2 5% 3 3 4 4 5% 9% 55%	2200
	21st to end	Night	13% 5% 2 7% 4 4 3 3 4 6% 49%	2200
October	1st to 10th	Night	8% 4 2 5% 4 3 3 3 5% 7% 56%	2200
	11th to 20th	Night	15% 7% 2 5% 3 4 3 2 4 6% 48%	2340
	21st to end	Night	17% 8% 3 7% 4 4 4 3 4 6% 40%	2860
November	1st to 10th	Night	12% 7% 2 5% 4 4 3 3 5% 6% 48%	2666
	11th to 20th	Night	14% 9% 3 7% 4 3 3 4 5% 7% 41%	2730
	21st to end	Night	18% 13% 4 8% 5% 4 3 2 4 5% 33%	2730
December	1st to 10th	Night	17% 11% 4 8% 4 3 3 2 4 5% 38%	4380
	11th to 20th	Night	17% 14% 6% 11% 5% 4 4 3 4 5% 27%	5255
	21st to end	Night	25% 19% 7% 10% 4 4 4 2 4 4 17%	7150

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	57% 4 11% 21% 7% 1	4692
	11th to 20th	Day	57% 3 9% 17% 12% 2	4710
	21st to end	Day	65% 2 8% 16% 6% 4	5500
February	1st to 10th	Day	56% 3 12% 18% 9% 1	2100
	11th to 20th	Day	54% 5% 9% 21% 10% 1	2058
	21st to end	Day	52% 4 9% 22% 10% 2	1730
March	1st to 10th	Day	54% 3 5% 18% 16% 4	4580
	11th to 20th	Day	41% 4 10% 30% 13% 2	4902
	21st to end	Day	51% 6% 12% 19% 10% 2	5855
April	1st to 10th	Day	47% 6% 13% 20% 14% 1	2520
	11th to 20th	Day	46% 6% 11% 23% 12% 3	2446
	21st to end	Day	48% 6% 10% 22% 11% 2	2555
May	1st to 10th	Day	52% 7% 13% 19% 10%	5897
	11th to 20th	Day	48% 7% 9% 25% 11%	5865
	21st to end	Day	45% 8% 13% 20% 13% 2	6535
June	1st to 10th	Day	38% 7% 12% 24% 16% 3	2800
	11th to 20th	Day	36% 8% 12% 22% 20% 2	2800
	21st to end	Day	36% 9% 15% 19% 17% 4	2800
July	1st to 10th	Day	37% 5% 11% 27% 19% 1	6291
	11th to 20th	Day	40% 6% 15% 25% 13% 1	6285
	21st to end	Day	45% 6% 15% 21% 12% 2	6492
August	1st to 10th	Day	31% 6% 15% 32% 14% 1	4221
	11th to 20th	Day	35% 7% 12% 31% 14% 1	3989
	21st to end	Day	27% 6% 14% 32% 18% 4	4311
September	1st to 10th	Day	35% 7% 11% 25% 18% 4	2370
	11th to 20th	Day	32% 5% 11% 28% 21% 3	2200
	21st to end	Day	35% 5% 11% 23% 25% 2	2200
October	1st to 10th	Day	23% 4 7% 31% 34% 2	3590
	11th to 20th	Day	32% 4 9% 26% 27% 2	3324
	21st to end	Day	39% 3 9% 23% 24% 2	3180
November	1st to 10th	Day	34% 4 11% 30% 17% 4	1852
	11th to 20th	Day	46% 4 10% 21% 15% 4	1890
	21st to end	Day	52% 4 8% 22% 13% 1	1890
December	1st to 10th	Day	46% 3 10% 27% 14%	3020
	11th to 20th	Day	59% 4 8% 20% 8% 1	3161
	21st to end	Day	68% 4 11% 12% 5%	4070
January	1st to 10th	Night	61% 4 10% 17% 7%	8233
	11th to 20th	Night	64% 3 8% 12% 11% 3	8280
	21st to end	Night	56% 3 9% 22% 9% 1	8682
February	1st to 10th	Night	59% 5% 11% 18% 6% 1	2520
	11th to 20th	Night	52% 5% 11% 19% 12% 1	2459
	21st to end	Night	55% 4 10% 18% 11% 2	2076
March	1st to 10th	Night	52% 3 6% 24% 11% 3	5493
	11th to 20th	Night	37% 5% 10% 26% 20% 1	5278
	21st to end	Night	50% 5% 9% 27% 8% 1	5362
April	1st to 10th	Night	45% 5% 11% 24% 13% 2	2100
	11th to 20th	Night	44% 5% 11% 19% 16% 5%	2035
	21st to end	Night	44% 7% 10% 23% 13% 3	1845
May	1st to 10th	Night	52% 8% 11% 18% 9% 2	4060
	11th to 20th	Night	44% 6% 12% 26% 11%	4033
	21st to end	Night	43% 7% 16% 20% 11% 3	4328
June	1st to 10th	Night	34% 7% 11% 23% 22% 3	1600
	11th to 20th	Night	33% 8% 11% 24% 21% 4	1600
	21st to end	Night	27% 9% 16% 23% 20% 4	1600
July	1st to 10th	Night	34% 6% 10% 27% 20% 4	3580
	11th to 20th	Night	35% 5% 17% 27% 15% 1	3572
	21st to end	Night	39% 4 17% 25% 12% 3	4043
August	1st to 10th	Night	32% 6% 13% 35% 12% 1	2904
	11th to 20th	Night	34% 5% 13% 30% 18% 1	3123
	21st to end	Night	25% 5% 13% 31% 22% 4	3586
September	1st to 10th	Night	33% 6% 11% 24% 20% 6%	2010
	11th to 20th	Night	26% 6% 11% 26% 28% 4	2200
	21st to end	Night	36% 5% 10% 21% 24% 4	2200
October	1st to 10th	Night	19% 3 7% 23% 45% 3	3590
	11th to 20th	Night	27% 3 8% 24% 36% 3	3811
	21st to end	Night	36% 3 8% 23% 25% 5%	4610
November	1st to 10th	Night	37% 5% 9% 25% 21% 3	2666
	11th to 20th	Night	43% 5% 10% 22% 17% 4	2730
	21st to end	Night	54% 3 10% 21% 12% 1	2730
December	1st to 10th	Night	49% 3 11% 24% 12%	4380
	11th to 20th	Night	59% 4 10% 16% 10% 1	5257
	21st to end	Night	71% 4 8% 11% 5%	7150

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% 20% 33% 16% 3 1	330
	11th to 20th	Day	32% 23% 31% 13% 2	330
	21st to end	Day	30% 25% 30% 14% 2	363
February	1st to 10th	Day	28% 25% 33% 12% 2	330
	11th to 20th	Day	27% 29% 28% 14% 2	330
	21st to end	Day	29% 23% 40% 7%	273
March	1st to 10th	Day	27% 28% 32% 12% 2	330
	11th to 20th	Day	29% 22% 33% 11% 4	456
	21st to end	Day	31% 20% 31% 13% 4 1	594
April	1st to 10th	Day	25% 19% 31% 20% 5% 1	540
	11th to 20th	Day	22% 21% 28% 19% 8% 2	516
	21st to end	Day	22% 20% 35% 15% 7% 2	500
May	1st to 10th	Day	21% 16% 33% 19% 8% 3	503
	11th to 20th	Day	24% 12% 26% 23% 10% 5%	527
	21st to end	Day	14% 9% 28% 24% 18% 7%	609
June	1st to 10th	Day	12% 9% 28% 28% 18% 4	730
	11th to 20th	Day	12% 6% 26% 32% 17% 6%	730
	21st to end	Day	12% 6% 30% 25% 21% 6%	730
July	1st to 10th	Day	12% 5% 19% 25% 24% 15%	721
	11th to 20th	Day	7% 4 23% 34% 23% 9%	718
	21st to end	Day	11% 2 20% 33% 24% 9%	692
August	1st to 10th	Day	9% 4 16% 31% 28% 13%	526
	11th to 20th	Day	13% 4 18% 29% 26% 9%	519
	21st to end	Day	7% 3 19% 28% 32% 12%	583
September	1st to 10th	Day	10% 6% 18% 30% 28% 9%	530
	11th to 20th	Day	10% 2 16% 27% 30% 14%	530
	21st to end	Day	16% 10% 21% 24% 22% 8%	530
October	1st to 10th	Day	12% 7% 25% 32% 19% 5%	530
	11th to 20th	Day	16% 14% 32% 24% 12% 2	457
	21st to end	Day	32% 14% 36% 16% 1	363
November	1st to 10th	Day	13% 22% 32% 22% 7% 2	330
	11th to 20th	Day	24% 23% 29% 16% 6% 1	330
	21st to end	Day	28% 15% 35% 18% 4	330
December	1st to 10th	Day	21% 27% 35% 14% 3 1	330
	11th to 20th	Day	24% 20% 38% 14% 3 1	330
	21st to end	Day	28% 24% 36% 10% 3	363
January	1st to 10th	Night	22% 19% 34% 21% 3	1050
	11th to 20th	Night	26% 19% 37% 16% 2	1050
	21st to end	Night	23% 19% 35% 21% 3	1051
February	1st to 10th	Night	26% 15% 38% 19% 2	840
	11th to 20th	Night	23% 21% 35% 20% 2	823
	21st to end	Night	27% 16% 36% 19% 1	692
March	1st to 10th	Night	25% 18% 33% 23% 2	840
	11th to 20th	Night	22% 15% 37% 21% 5%	840
	21st to end	Night	25% 13% 35% 22% 4	827
April	1st to 10th	Night	17% 14% 40% 22% 7%	630
	11th to 20th	Night	19% 15% 33% 24% 9% 1	611
	21st to end	Night	19% 11% 39% 24% 7% 1	600
May	1st to 10th	Night	19% 9% 36% 27% 9% 1	600
	11th to 20th	Night	17% 8% 26% 30% 17% 3	591
	21st to end	Night	10% 5% 26% 36% 22% 2	650
June	1st to 10th	Night	11% 4 23% 40% 21% 1	600
	11th to 20th	Night	11% 3 21% 44% 21% 1	600
	21st to end	Night	7% 4 23% 37% 27% 3	600
July	1st to 10th	Night	10% 2 13% 36% 32% 8%	585
	11th to 20th	Night	6% 5% 16% 36% 33% 5%	582
	21st to end	Night	9% 3 13% 41% 32% 3	657
August	1st to 10th	Night	8% 2 14% 38% 34% 4	597
	11th to 20th	Night	6% 3 14% 38% 35% 5%	594
	21st to end	Night	6% 2 16% 35% 35% 6%	660
September	1st to 10th	Night	12% 4 12% 38% 30% 4	610
	11th to 20th	Night	8% 3 14% 34% 37% 4	800
	21st to end	Night	16% 5% 21% 31% 24% 3	800
October	1st to 10th	Night	10% 6% 24% 34% 23% 4	800
	11th to 20th	Night	18% 10% 27% 28% 15% 2	800
	21st to end	Night	22% 12% 35% 24% 7% 1	880
November	1st to 10th	Night	16% 10% 34% 28% 11% 1	820
	11th to 20th	Night	20% 16% 32% 24% 8%	840
	21st to end	Night	27% 13% 26% 27% 6%	840
December	1st to 10th	Night	25% 14% 36% 20% 5%	840
	11th to 20th	Night	26% 14% 33% 21% 6% 1	992
	21st to end	Night	30% 16% 34% 17% 3	1155

Page generated at 2026-04-14 02:44:29. Version ac07

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