Frostburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Frostburg clear sky chart from 2005-11-06 to 2025-10-19.

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% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	126365
	Night	13% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	123306
Transparency	Day	45% 3 11% 25% 14% 2	129967
	Night	43% 2 12% 25% 15% 3	127773
Seeing	Day	26% 14% 26% 20% 10% 4	16079
	Night	24% 13% 23% 27% 12% 1	25690

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	12% 8% 3 8% 7% 7% 7% 5% 6% 7% 33%	3946
	11th to 20th	Day	9% 11% 5% 12% 8% 7% 6% 4 6% 6% 25%	4060
	21st to end	Day	13% 9% 4 8% 6% 5% 4 4 5% 8% 33%	4466
February	1st to 10th	Day	12% 13% 4 8% 5% 6% 5% 4 5% 7% 31%	1800
	11th to 20th	Day	12% 9% 3 9% 6% 6% 5% 4 7% 7% 31%	1753
	21st to end	Day	14% 9% 4 9% 5% 4 4 3 6% 7% 35%	1665
March	1st to 10th	Day	14% 9% 3 6% 5% 5% 5% 4 5% 6% 39%	4935
	11th to 20th	Day	10% 6% 3 7% 4 4 4 4 6% 8% 43%	4980
	21st to end	Day	11% 8% 3 7% 6% 5% 5% 4 6% 6% 39%	5465
April	1st to 10th	Day	13% 10% 3 8% 5% 5% 5% 4 6% 6% 34%	2354
	11th to 20th	Day	13% 7% 3 6% 5% 5% 5% 4 6% 7% 40%	2374
	21st to end	Day	18% 7% 2 8% 5% 4 4 3 6% 7% 36%	2520
May	1st to 10th	Day	20% 7% 2 8% 5% 6% 6% 5% 7% 7% 29%	5862
	11th to 20th	Day	24% 7% 2 6% 4 4 5% 5% 7% 9% 28%	5861
	21st to end	Day	16% 5% 2 6% 5% 5% 6% 5% 8% 9% 33%	6933
June	1st to 10th	Day	12% 6% 2 5% 6% 5% 5% 5% 7% 9% 38%	2800
	11th to 20th	Day	12% 5% 3 6% 5% 6% 6% 5% 7% 9% 35%	2800
	21st to end	Day	10% 4 2 5% 5% 5% 6% 5% 7% 10% 41%	2800
July	1st to 10th	Day	5% 4 2 7% 5% 6% 6% 5% 7% 8% 45%	6282
	11th to 20th	Day	7% 5% 2 8% 6% 7% 7% 5% 9% 11% 33%	5900
	21st to end	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 9% 39%	6424
August	1st to 10th	Day	16% 5% 2 7% 5% 6% 6% 5% 7% 9% 31%	4234
	11th to 20th	Day	9% 4 2 7% 5% 6% 7% 5% 8% 9% 38%	4174
	21st to end	Day	10% 4 2 5% 4 6% 5% 4 7% 9% 44%	4322
September	1st to 10th	Day	15% 5% 2 6% 4 4 4 4 5% 6% 46%	2400
	11th to 20th	Day	14% 6% 1 6% 4 3 4 4 5% 7% 47%	2292
	21st to end	Day	21% 7% 2 6% 5% 5% 5% 3 5% 6% 35%	2147
October	1st to 10th	Day	15% 7% 2 5% 4 4 5% 4 5% 7% 45%	2000
	11th to 20th	Day	16% 7% 3 6% 4 4 4 4 5% 6% 41%	1980
	21st to end	Day	15% 6% 2 6% 4 4 5% 3 6% 6% 43%	2090
November	1st to 10th	Day	9% 6% 2 5% 4 4 4 4 6% 7% 49%	1957
	11th to 20th	Day	13% 9% 3 6% 5% 4 4 4 6% 8% 40%	1639
	21st to end	Day	13% 9% 2 7% 6% 5% 6% 3 6% 7% 36%	1600
December	1st to 10th	Day	11% 7% 4 8% 5% 6% 6% 4 6% 7% 36%	2600
	11th to 20th	Day	19% 11% 4 7% 4 4 4 4 7% 6% 31%	2990
	21st to end	Day	17% 9% 4 11% 7% 7% 5% 4 5% 7% 24%	3960
January	1st to 10th	Night	9% 8% 4 10% 6% 6% 5% 4 6% 8% 33%	5981
	11th to 20th	Night	9% 10% 4 8% 6% 6% 5% 4 6% 7% 33%	5900
	21st to end	Night	13% 8% 3 8% 5% 5% 4 3 5% 6% 39%	6490
February	1st to 10th	Night	12% 8% 3 7% 5% 5% 5% 4 6% 7% 38%	2600
	11th to 20th	Night	13% 10% 2 8% 6% 5% 5% 4 5% 6% 34%	2533
	21st to end	Night	14% 9% 3 7% 4 6% 5% 4 8% 7% 35%	1958
March	1st to 10th	Night	16% 8% 3 5% 4 3 5% 3 5% 7% 41%	4918
	11th to 20th	Night	9% 5% 4 6% 4 3 4 3 5% 8% 48%	4980
	21st to end	Night	10% 7% 2 6% 5% 4 5% 4 5% 7% 45%	5467
April	1st to 10th	Night	15% 9% 3 8% 5% 5% 4 4 6% 6% 36%	2045
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 4 6% 8% 41%	1975
	21st to end	Night	16% 5% 2 6% 4 4 4 3 5% 8% 42%	1895
May	1st to 10th	Night	23% 7% 2 7% 5% 4 5% 4 6% 8% 28%	4033
	11th to 20th	Night	26% 7% 2 5% 3 4 4 4 6% 7% 33%	4032
	21st to end	Night	17% 6% 2 6% 4 4 5% 5% 7% 9% 36%	3920
June	1st to 10th	Night	11% 5% 2 5% 4 4 5% 5% 6% 8% 47%	1600
	11th to 20th	Night	13% 5% 1 6% 4 5% 6% 4 7% 9% 42%	1600
	21st to end	Night	9% 5% 1 4 5% 4 4 5% 8% 12% 44%	1600
July	1st to 10th	Night	7% 4 2 6% 5% 5% 6% 5% 7% 10% 44%	3644
	11th to 20th	Night	6% 6% 3 8% 6% 6% 6% 6% 8% 10% 35%	4057
	21st to end	Night	6% 5% 2 6% 5% 5% 5% 5% 8% 10% 43%	4427
August	1st to 10th	Night	15% 4 2 5% 4 5% 4 5% 7% 10% 39%	2915
	11th to 20th	Night	10% 5% 2 6% 5% 4 5% 4 7% 8% 44%	2875
	21st to end	Night	13% 5% 2 4 4 4 4 3 5% 8% 47%	3542
September	1st to 10th	Night	14% 5% 2 5% 3 3 4 3 5% 6% 49%	2000
	11th to 20th	Night	13% 5% 1 4 4 3 3 3 5% 6% 53%	2105
	21st to end	Night	22% 6% 2 5% 4 4 4 3 6% 7% 39%	2252
October	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 5% 6% 47%	2400
	11th to 20th	Night	15% 5% 2 4 3 3 4 3 5% 8% 48%	2377
	21st to end	Night	16% 5% 1 5% 4 4 4 4 5% 7% 45%	2508
November	1st to 10th	Night	10% 7% 2 5% 4 4 4 3 5% 6% 50%	2341
	11th to 20th	Night	14% 7% 3 6% 4 4 4 4 6% 7% 40%	2755
	21st to end	Night	14% 8% 2 7% 5% 5% 5% 4 6% 7% 37%	2800
December	1st to 10th	Night	10% 7% 3 7% 5% 5% 6% 4 6% 8% 40%	4580
	11th to 20th	Night	15% 9% 3 8% 5% 5% 5% 5% 6% 7% 33%	5205
	21st to end	Night	15% 9% 5% 10% 7% 6% 6% 4 7% 7% 24%	6996

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	50% 1 7% 24% 15% 3	3947
	11th to 20th	Day	60% 1 7% 13% 16% 4	4060
	21st to end	Day	52% 1 10% 23% 13% 1	4466
February	1st to 10th	Day	54% 2 12% 21% 11% 1	1800
	11th to 20th	Day	53% 3 11% 21% 12% 1	1762
	21st to end	Day	50% 2 13% 19% 14% 2	1665
March	1st to 10th	Day	47% 1 7% 24% 14% 6%	4935
	11th to 20th	Day	39% 1 10% 31% 15% 3	4980
	21st to end	Day	46% 2 10% 22% 18% 3	5465
April	1st to 10th	Day	50% 3 11% 19% 14% 3	2354
	11th to 20th	Day	44% 2 11% 20% 19% 4	2374
	21st to end	Day	48% 2 8% 26% 12% 2	2520
May	1st to 10th	Day	54% 2 11% 21% 9% 2	5897
	11th to 20th	Day	53% 3 9% 29% 6% 1	5865
	21st to end	Day	46% 3 12% 24% 12% 2	6948
June	1st to 10th	Day	41% 4 13% 26% 14% 1	2800
	11th to 20th	Day	43% 5% 14% 24% 13% 1	2800
	21st to end	Day	38% 5% 16% 26% 14% 1	2800
July	1st to 10th	Day	36% 6% 12% 29% 14% 3	6213
	11th to 20th	Day	42% 4 19% 25% 10% 1	5831
	21st to end	Day	41% 3 10% 27% 18% 1	6240
August	1st to 10th	Day	48% 4 15% 24% 9%	4221
	11th to 20th	Day	41% 3 10% 31% 14%	4213
	21st to end	Day	37% 4 13% 31% 14% 2	4322
September	1st to 10th	Day	40% 4 10% 21% 21% 4	2400
	11th to 20th	Day	38% 2 10% 29% 19% 2	2292
	21st to end	Day	51% 3 9% 20% 16% 1	2147
October	1st to 10th	Day	33% 2 9% 28% 24% 5%	3260
	11th to 20th	Day	37% 1 10% 27% 16% 9%	3220
	21st to end	Day	28% 1 11% 33% 24% 2	3428
November	1st to 10th	Day	35% 2 12% 25% 21% 4	1957
	11th to 20th	Day	43% 2 10% 22% 20% 3	1639
	21st to end	Day	49% 2 12% 24% 12% 1	1600
December	1st to 10th	Day	47% 2 15% 25% 6% 4	2600
	11th to 20th	Day	53% 1 14% 21% 10% 1	2986
	21st to end	Day	60% 1 13% 14% 12%	3960
January	1st to 10th	Night	48% 1 6% 23% 19% 2	5981
	11th to 20th	Night	49% 1 9% 19% 17% 6%	5900
	21st to end	Night	47% 2 10% 26% 14% 2	6490
February	1st to 10th	Night	45% 2 14% 25% 12% 1	2600
	11th to 20th	Night	51% 3 10% 20% 14% 1	2535
	21st to end	Night	48% 3 11% 22% 12% 4	1958
March	1st to 10th	Night	44% 1 9% 27% 12% 6%	4918
	11th to 20th	Night	37% 1 12% 34% 12% 4	4980
	21st to end	Night	39% 2 12% 24% 20% 4	5467
April	1st to 10th	Night	48% 2 11% 20% 16% 2	2045
	11th to 20th	Night	41% 4 12% 24% 16% 4	1975
	21st to end	Night	41% 3 10% 29% 14% 3	1895
May	1st to 10th	Night	55% 3 13% 17% 9% 3	4060
	11th to 20th	Night	51% 2 9% 28% 9% 1	4033
	21st to end	Night	44% 3 16% 27% 7% 3	3927
June	1st to 10th	Night	36% 6% 12% 29% 17% 2	1600
	11th to 20th	Night	38% 5% 15% 28% 12% 1	1600
	21st to end	Night	33% 5% 17% 27% 17% 1	1600
July	1st to 10th	Night	36% 5% 15% 27% 12% 4	3605
	11th to 20th	Night	42% 5% 19% 24% 10% 1	4006
	21st to end	Night	35% 4 14% 27% 19% 1	4297
August	1st to 10th	Night	41% 5% 19% 27% 9%	2904
	11th to 20th	Night	37% 4 12% 29% 17% 1	2902
	21st to end	Night	37% 2 12% 33% 14% 2	3542
September	1st to 10th	Night	37% 3 14% 23% 19% 4	2000
	11th to 20th	Night	34% 2 10% 32% 20% 2	2105
	21st to end	Night	46% 3 10% 23% 17% 1	2252
October	1st to 10th	Night	35% 2 9% 30% 23% 2	3920
	11th to 20th	Night	28% 1 10% 27% 24% 9%	3876
	21st to end	Night	28% 1 10% 33% 23% 4	4120
November	1st to 10th	Night	37% 2 11% 25% 20% 5%	2341
	11th to 20th	Night	43% 3 8% 27% 16% 4	2755
	21st to end	Night	47% 2 12% 24% 14% 2	2800
December	1st to 10th	Night	42% 2 14% 30% 10% 1	4580
	11th to 20th	Night	50% 1 13% 23% 11% 1	5208
	21st to end	Night	58% 2 12% 17% 11%	6996

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	44% 21% 23% 8% 3 1	277
	11th to 20th	Day	42% 21% 28% 6% 3	300
	21st to end	Day	36% 25% 25% 12% 3	330
February	1st to 10th	Day	40% 21% 29% 9% 2	300
	11th to 20th	Day	47% 21% 26% 4 1	300
	21st to end	Day	39% 19% 29% 11% 1	354
March	1st to 10th	Day	36% 19% 26% 17% 3	500
	11th to 20th	Day	36% 24% 23% 12% 4 1	500
	21st to end	Day	33% 21% 28% 13% 4 1	550
April	1st to 10th	Day	36% 21% 23% 14% 6%	500
	11th to 20th	Day	27% 20% 26% 16% 9% 2	492
	21st to end	Day	31% 17% 29% 15% 6% 1	500
May	1st to 10th	Day	32% 18% 27% 13% 7% 4	503
	11th to 20th	Day	30% 16% 27% 17% 8% 2	527
	21st to end	Day	24% 11% 26% 20% 11% 8%	573
June	1st to 10th	Day	19% 13% 28% 23% 13% 4	530
	11th to 20th	Day	20% 13% 27% 22% 12% 5%	530
	21st to end	Day	13% 14% 30% 23% 14% 5%	530
July	1st to 10th	Day	14% 5% 30% 27% 16% 8%	525
	11th to 20th	Day	7% 7% 31% 30% 17% 8%	524
	21st to end	Day	14% 7% 25% 30% 16% 7%	576
August	1st to 10th	Day	14% 9% 22% 28% 19% 9%	526
	11th to 20th	Day	15% 6% 25% 30% 14% 10%	519
	21st to end	Day	14% 7% 24% 26% 17% 11%	583
September	1st to 10th	Day	20% 8% 21% 24% 18% 10%	530
	11th to 20th	Day	18% 4 21% 28% 22% 7%	530
	21st to end	Day	31% 8% 24% 21% 13% 3	530
October	1st to 10th	Day	23% 8% 23% 24% 17% 4	530
	11th to 20th	Day	26% 15% 26% 21% 11% 1	522
	21st to end	Day	24% 16% 30% 21% 8% 1	539
November	1st to 10th	Day	22% 15% 30% 21% 10% 1	495
	11th to 20th	Day	29% 18% 30% 18% 5%	234
	21st to end	Day	34% 21% 33% 10% 3 1	200
December	1st to 10th	Day	37% 21% 29% 9% 5% 1	200
	11th to 20th	Day	42% 15% 28% 13% 3	200
	21st to end	Day	36% 14% 26% 20% 4	220
January	1st to 10th	Night	33% 20% 28% 15% 4	800
	11th to 20th	Night	32% 18% 30% 19% 1	800
	21st to end	Night	30% 22% 28% 18% 2	880
February	1st to 10th	Night	30% 17% 24% 26% 3	800
	11th to 20th	Night	34% 23% 27% 14% 1	783
	21st to end	Night	31% 16% 31% 18% 3	660
March	1st to 10th	Night	30% 18% 28% 22% 4	800
	11th to 20th	Night	33% 18% 25% 18% 6% 1	800
	21st to end	Night	26% 19% 29% 20% 5% 1	880
April	1st to 10th	Night	28% 20% 28% 19% 5%	800
	11th to 20th	Night	22% 17% 25% 28% 8% 1	791
	21st to end	Night	25% 13% 24% 28% 8%	695
May	1st to 10th	Night	25% 10% 22% 29% 14%	600
	11th to 20th	Night	27% 9% 21% 29% 13% 1	591
	21st to end	Night	14% 8% 18% 30% 26% 3	433
June	1st to 10th	Night	13% 6% 23% 38% 20% 1	400
	11th to 20th	Night	17% 6% 21% 35% 20% 2	400
	21st to end	Night	13% 5% 25% 38% 20% 1	400
July	1st to 10th	Night	11% 2 18% 41% 24% 4	409
	11th to 20th	Night	7% 5% 16% 34% 33% 4	582
	21st to end	Night	10% 3 20% 38% 27% 2	657
August	1st to 10th	Night	12% 3 13% 39% 30% 3	597
	11th to 20th	Night	12% 4 12% 41% 26% 5%	594
	21st to end	Night	15% 4 14% 37% 26% 4	849
September	1st to 10th	Night	18% 4 16% 32% 24% 5%	800
	11th to 20th	Night	18% 5% 12% 33% 28% 4	800
	21st to end	Night	26% 8% 16% 29% 18% 3	800
October	1st to 10th	Night	21% 9% 19% 26% 22% 3	800
	11th to 20th	Night	23% 12% 25% 27% 12% 1	793
	21st to end	Night	25% 15% 23% 25% 11% 1	836
November	1st to 10th	Night	19% 13% 23% 32% 12% 1	780
	11th to 20th	Night	29% 15% 21% 27% 7% 1	800
	21st to end	Night	29% 15% 25% 25% 6% 1	800
December	1st to 10th	Night	32% 19% 24% 19% 5% 1	800
	11th to 20th	Night	31% 17% 24% 24% 4	800
	21st to end	Night	29% 15% 27% 26% 3	880

Page generated at 2025-10-16 01:50:27. Version ac07

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