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 2024-01-12.

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% 7% 3 6% 6% 4 5% 5% 6% 7% 36%	74618
	Night	13% 6% 3 5% 5% 3 5% 5% 6% 8% 40%	75088
Transparency	Day	46% 3 12% 23% 13% 2	74335
	Night	43% 3 12% 25% 14% 2	74890
Seeing	Day	26% 14% 26% 20% 11% 4	13695
	Night	24% 13% 23% 27% 13% 1	23443

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	11% 9% 4 8% 8% 4 5% 5% 6% 6% 33%	1663
	11th to 20th	Day	14% 9% 4 8% 8% 5% 6% 5% 6% 7% 28%	1629
	21st to end	Day	13% 12% 6% 9% 8% 3 5% 5% 5% 6% 28%	1782
February	1st to 10th	Day	13% 13% 5% 7% 6% 5% 5% 5% 4 7% 29%	1620
	11th to 20th	Day	12% 9% 3 9% 7% 4 6% 5% 7% 7% 30%	1573
	21st to end	Day	15% 9% 4 9% 7% 3 4 4 5% 7% 34%	1493
March	1st to 10th	Day	11% 8% 3 5% 6% 4 5% 4 5% 6% 42%	1980
	11th to 20th	Day	15% 8% 4 7% 6% 3 5% 4 7% 8% 34%	1980
	21st to end	Day	17% 8% 3 7% 7% 3 4 5% 6% 7% 33%	2178
April	1st to 10th	Day	11% 8% 5% 7% 6% 4 5% 5% 6% 6% 36%	2118
	11th to 20th	Day	14% 7% 4 6% 5% 3 5% 4 6% 7% 40%	2134
	21st to end	Day	20% 7% 3 6% 6% 3 4 4 6% 7% 35%	2268
May	1st to 10th	Day	18% 6% 2 7% 6% 4 6% 6% 6% 7% 32%	2340
	11th to 20th	Day	21% 6% 3 6% 5% 3 5% 5% 5% 7% 35%	2301
	21st to end	Day	15% 6% 2 5% 6% 4 5% 5% 7% 8% 37%	2724
June	1st to 10th	Day	13% 5% 2 5% 6% 4 5% 6% 8% 9% 38%	2520
	11th to 20th	Day	12% 5% 3 5% 6% 5% 6% 7% 7% 10% 34%	2520
	21st to end	Day	10% 4 2 4 6% 3 7% 6% 7% 10% 41%	2520
July	1st to 10th	Day	10% 5% 2 5% 6% 4 6% 6% 7% 8% 40%	2498
	11th to 20th	Day	8% 5% 3 6% 6% 4 6% 7% 7% 10% 40%	2340
	21st to end	Day	12% 5% 3 6% 5% 4 7% 7% 6% 8% 36%	2547
August	1st to 10th	Day	10% 5% 3 7% 6% 6% 7% 7% 8% 10% 32%	2327
	11th to 20th	Day	12% 5% 2 5% 6% 4 6% 6% 9% 9% 36%	2303
	21st to end	Day	13% 4 2 5% 5% 4 5% 6% 7% 9% 39%	2386
September	1st to 10th	Day	17% 5% 2 4 5% 3 5% 5% 5% 7% 42%	2160
	11th to 20th	Day	14% 5% 2 5% 5% 3 4 4 5% 8% 46%	2064
	21st to end	Day	19% 6% 2 5% 5% 4 5% 4 5% 7% 38%	1933
October	1st to 10th	Day	16% 7% 2 4 4 3 5% 5% 5% 6% 43%	1800
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 6% 5% 5% 40%	1800
	21st to end	Day	16% 5% 3 6% 5% 3 5% 4 6% 6% 42%	1980
November	1st to 10th	Day	10% 5% 3 5% 4 3 3 5% 6% 7% 49%	1857
	11th to 20th	Day	13% 8% 3 5% 5% 3 4 5% 5% 8% 41%	1558
	21st to end	Day	14% 8% 2 6% 6% 4 6% 5% 6% 7% 37%	1520
December	1st to 10th	Day	15% 9% 4 7% 7% 5% 7% 5% 6% 6% 28%	1520
	11th to 20th	Day	14% 9% 4 8% 6% 3 5% 5% 7% 6% 34%	1910
	21st to end	Day	17% 9% 4 8% 7% 4 6% 6% 5% 7% 26%	2772
January	1st to 10th	Night	11% 7% 4 7% 5% 4 6% 6% 6% 7% 38%	2497
	11th to 20th	Night	14% 9% 4 8% 7% 4 6% 5% 6% 8% 30%	2354
	21st to end	Night	12% 9% 4 7% 5% 4 6% 5% 6% 7% 36%	2574
February	1st to 10th	Night	12% 7% 3 6% 5% 4 6% 5% 6% 7% 37%	2340
	11th to 20th	Night	12% 9% 3 7% 7% 4 6% 5% 6% 7% 34%	2273
	21st to end	Night	15% 9% 3 7% 4 5% 5% 5% 7% 7% 34%	1757
March	1st to 10th	Night	12% 6% 2 4 5% 3 5% 5% 6% 7% 46%	1980
	11th to 20th	Night	16% 7% 3 5% 5% 2 3 5% 5% 7% 41%	1980
	21st to end	Night	15% 7% 3 5% 5% 2 5% 6% 5% 7% 39%	2178
April	1st to 10th	Night	13% 8% 3 7% 6% 3 4 5% 6% 6% 39%	1841
	11th to 20th	Night	13% 5% 3 5% 6% 3 5% 5% 5% 9% 41%	1775
	21st to end	Night	18% 5% 2 5% 5% 3 4 4 5% 7% 42%	1706
May	1st to 10th	Night	18% 5% 2 5% 5% 3 4 6% 6% 9% 37%	1620
	11th to 20th	Night	21% 5% 3 5% 5% 3 4 4 5% 6% 39%	1592
	21st to end	Night	11% 5% 2 4 4 3 4 6% 7% 10% 44%	1550
June	1st to 10th	Night	11% 4 2 4 4 3 5% 6% 6% 8% 47%	1440
	11th to 20th	Night	13% 5% 1 5% 5% 4 5% 5% 6% 9% 42%	1440
	21st to end	Night	10% 4 1 3 5% 3 4 6% 7% 12% 45%	1440
July	1st to 10th	Night	10% 4 2 5% 5% 3 5% 5% 6% 10% 45%	1458
	11th to 20th	Night	7% 4 2 4 4 3 5% 5% 6% 10% 49%	1620
	21st to end	Night	8% 4 2 4 5% 3 5% 6% 8% 10% 45%	1771
August	1st to 10th	Night	6% 5% 2 5% 6% 4 5% 6% 7% 10% 45%	1611
	11th to 20th	Night	11% 4 2 5% 4 3 5% 5% 6% 8% 47%	1598
	21st to end	Night	11% 5% 2 4 5% 3 5% 4 5% 8% 48%	1951
September	1st to 10th	Night	15% 5% 3 5% 4 3 4 4 5% 6% 47%	1800
	11th to 20th	Night	14% 5% 1 3 4 2 3 3 5% 6% 53%	1894
	21st to end	Night	19% 5% 2 4 5% 3 3 4 6% 7% 42%	2026
October	1st to 10th	Night	17% 6% 3 5% 4 3 3 4 5% 6% 44%	2160
	11th to 20th	Night	16% 5% 2 3 4 3 4 5% 5% 8% 46%	2160
	21st to end	Night	16% 5% 2 5% 4 3 4 4 5% 7% 44%	2376
November	1st to 10th	Night	10% 7% 2 4 5% 3 4 4 5% 6% 49%	2221
	11th to 20th	Night	14% 6% 4 5% 5% 3 5% 5% 6% 7% 41%	2616
	21st to end	Night	14% 7% 2 6% 5% 4 5% 5% 6% 7% 38%	2660
December	1st to 10th	Night	15% 9% 4 6% 6% 4 5% 5% 5% 7% 33%	2660
	11th to 20th	Night	14% 7% 3 6% 5% 4 5% 6% 7% 8% 36%	3285
	21st to end	Night	16% 9% 5% 7% 7% 4 6% 5% 6% 7% 27%	4884

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	51% 3 9% 25% 11% 2	1664
	11th to 20th	Day	55% 2 13% 20% 9% 1	1629
	21st to end	Day	58% 2 9% 18% 10% 1	1782
February	1st to 10th	Day	56% 3 12% 19% 9% 1	1620
	11th to 20th	Day	53% 3 11% 21% 11% 1	1582
	21st to end	Day	51% 2 12% 19% 13% 2	1493
March	1st to 10th	Day	44% 3 12% 25% 15% 1	1980
	11th to 20th	Day	49% 3 11% 21% 13% 3	1980
	21st to end	Day	50% 3 10% 22% 12% 2	2178
April	1st to 10th	Day	48% 3 12% 19% 15% 3	2118
	11th to 20th	Day	44% 3 11% 19% 18% 4	2134
	21st to end	Day	49% 3 9% 25% 12% 2	2268
May	1st to 10th	Day	51% 4 11% 20% 13% 1	2340
	11th to 20th	Day	50% 4 12% 21% 12% 2	2305
	21st to end	Day	44% 5% 15% 25% 10% 2	2724
June	1st to 10th	Day	41% 5% 13% 26% 14% 1	2520
	11th to 20th	Day	44% 5% 14% 24% 13% 1	2520
	21st to end	Day	38% 5% 16% 27% 12% 1	2520
July	1st to 10th	Day	42% 5% 12% 24% 15% 3	2429
	11th to 20th	Day	38% 5% 14% 25% 17% 2	2271
	21st to end	Day	44% 4 12% 23% 16% 2	2405
August	1st to 10th	Day	45% 5% 15% 24% 10%	2314
	11th to 20th	Day	43% 4 13% 27% 13%	2303
	21st to end	Day	41% 4 14% 26% 13% 3	2386
September	1st to 10th	Day	43% 4 11% 20% 19% 4	2160
	11th to 20th	Day	38% 2 10% 29% 18% 2	2064
	21st to end	Day	48% 3 10% 22% 17% 1	1933
October	1st to 10th	Day	42% 4 11% 25% 15% 3	1800
	11th to 20th	Day	47% 3 8% 27% 15% 1	1800
	21st to end	Day	44% 2 9% 27% 17% 2	1980
November	1st to 10th	Day	35% 2 12% 25% 21% 4	1857
	11th to 20th	Day	43% 2 10% 22% 20% 3	1558
	21st to end	Day	48% 2 12% 25% 12% 1	1520
December	1st to 10th	Day	56% 3 12% 19% 8% 1	1520
	11th to 20th	Day	50% 1 11% 27% 9% 1	1906
	21st to end	Day	58% 1 13% 16% 11%	2772
January	1st to 10th	Night	46% 3 10% 24% 16% 2	2497
	11th to 20th	Night	53% 3 13% 20% 9% 1	2354
	21st to end	Night	48% 2 10% 25% 12% 2	2574
February	1st to 10th	Night	46% 3 14% 24% 12% 1	2340
	11th to 20th	Night	51% 3 10% 20% 14% 1	2275
	21st to end	Night	49% 3 11% 23% 11% 3	1757
March	1st to 10th	Night	39% 3 12% 30% 15% 2	1980
	11th to 20th	Night	44% 3 11% 24% 16% 2	1980
	21st to end	Night	45% 4 10% 22% 14% 4	2178
April	1st to 10th	Night	47% 2 11% 20% 17% 3	1841
	11th to 20th	Night	40% 4 12% 23% 16% 4	1775
	21st to end	Night	43% 3 10% 27% 13% 4	1706
May	1st to 10th	Night	44% 4 12% 24% 12% 4	1620
	11th to 20th	Night	46% 4 13% 20% 15% 2	1593
	21st to end	Night	35% 6% 19% 27% 12% 1	1551
June	1st to 10th	Night	34% 6% 13% 29% 16% 1	1440
	11th to 20th	Night	38% 6% 15% 29% 11% 1	1440
	21st to end	Night	32% 6% 18% 27% 16% 1	1440
July	1st to 10th	Night	36% 6% 14% 28% 13% 4	1417
	11th to 20th	Night	31% 5% 17% 29% 16% 2	1566
	21st to end	Night	32% 5% 20% 25% 15% 2	1672
August	1st to 10th	Night	35% 6% 18% 28% 14% 1	1600
	11th to 20th	Night	36% 5% 16% 28% 15% 1	1598
	21st to end	Night	36% 4 13% 29% 15% 3	1951
September	1st to 10th	Night	38% 3 15% 23% 18% 4	1800
	11th to 20th	Night	34% 2 10% 32% 20% 2	1894
	21st to end	Night	42% 3 10% 24% 19% 1	2026
October	1st to 10th	Night	42% 3 11% 28% 15% 2	2160
	11th to 20th	Night	38% 2 11% 31% 17% 2	2160
	21st to end	Night	41% 2 8% 29% 18% 2	2376
November	1st to 10th	Night	37% 2 11% 25% 20% 5%	2221
	11th to 20th	Night	42% 3 8% 27% 16% 4	2616
	21st to end	Night	46% 2 12% 24% 14% 2	2660
December	1st to 10th	Night	52% 3 12% 23% 9% 1	2660
	11th to 20th	Night	46% 2 12% 24% 15% 1	3288
	21st to end	Night	57% 2 15% 17% 9%	4884

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	43% 20% 24% 8% 4 1	249
	11th to 20th	Day	39% 23% 28% 7% 3	243
	21st to end	Day	37% 26% 22% 12% 3	264
February	1st to 10th	Day	41% 22% 29% 6% 2	240
	11th to 20th	Day	45% 22% 28% 5%	240
	21st to end	Day	41% 18% 29% 11% 1	292
March	1st to 10th	Day	35% 19% 26% 17% 3	420
	11th to 20th	Day	36% 23% 23% 13% 4 1	420
	21st to end	Day	32% 21% 27% 13% 4 2	462
April	1st to 10th	Day	33% 21% 23% 16% 7%	420
	11th to 20th	Day	25% 17% 27% 17% 9% 3	412
	21st to end	Day	34% 17% 27% 15% 7% 1	420
May	1st to 10th	Day	32% 18% 27% 13% 7% 4	423
	11th to 20th	Day	30% 16% 27% 18% 7% 2	447
	21st to end	Day	23% 10% 25% 21% 12% 9%	485
June	1st to 10th	Day	18% 11% 29% 25% 13% 4	450
	11th to 20th	Day	20% 15% 28% 20% 13% 5%	450
	21st to end	Day	14% 14% 31% 23% 13% 5%	450
July	1st to 10th	Day	16% 5% 27% 26% 17% 10%	445
	11th to 20th	Day	7% 5% 31% 30% 18% 9%	444
	21st to end	Day	15% 7% 24% 30% 16% 7%	488
August	1st to 10th	Day	13% 8% 21% 29% 19% 10%	446
	11th to 20th	Day	15% 5% 24% 29% 15% 11%	439
	21st to end	Day	15% 6% 25% 25% 17% 13%	495
September	1st to 10th	Day	22% 6% 20% 23% 19% 10%	450
	11th to 20th	Day	18% 5% 20% 29% 22% 6%	450
	21st to end	Day	27% 9% 25% 21% 15% 3	450
October	1st to 10th	Day	24% 8% 23% 23% 18% 4	450
	11th to 20th	Day	26% 14% 26% 22% 11% 1	450
	21st to end	Day	26% 17% 29% 20% 7% 1	495
November	1st to 10th	Day	22% 15% 29% 22% 11% 2	455
	11th to 20th	Day	29% 18% 29% 19% 5%	213
	21st to end	Day	32% 22% 32% 11% 3 1	180
December	1st to 10th	Day	38% 19% 27% 9% 5% 1	180
	11th to 20th	Day	41% 15% 27% 14% 3	180
	21st to end	Day	35% 14% 26% 20% 5% 1	198
January	1st to 10th	Night	32% 19% 29% 16% 4	760
	11th to 20th	Night	32% 18% 29% 20% 1	725
	21st to end	Night	29% 22% 28% 19% 2	792
February	1st to 10th	Night	30% 18% 23% 26% 3	720
	11th to 20th	Night	31% 24% 28% 15% 1	703
	21st to end	Night	32% 17% 30% 19% 2	592
March	1st to 10th	Night	28% 18% 28% 22% 3	720
	11th to 20th	Night	33% 18% 25% 18% 6% 1	720
	21st to end	Night	26% 17% 29% 21% 6% 1	792
April	1st to 10th	Night	27% 21% 28% 19% 5%	720
	11th to 20th	Night	20% 17% 25% 29% 9% 1	711
	21st to end	Night	27% 13% 24% 27% 9%	626
May	1st to 10th	Night	25% 10% 21% 29% 15%	540
	11th to 20th	Night	26% 9% 21% 30% 13% 1	531
	21st to end	Night	12% 8% 16% 32% 27% 4	389
June	1st to 10th	Night	12% 6% 23% 38% 21% 1	360
	11th to 20th	Night	17% 6% 21% 34% 20% 2	360
	21st to end	Night	13% 5% 24% 38% 19% 1	360
July	1st to 10th	Night	11% 3 18% 38% 26% 4	367
	11th to 20th	Night	7% 4 16% 34% 34% 5%	522
	21st to end	Night	11% 3 21% 37% 27% 2	591
August	1st to 10th	Night	10% 3 14% 37% 33% 3	537
	11th to 20th	Night	12% 5% 11% 40% 27% 5%	534
	21st to end	Night	14% 4 13% 37% 28% 5%	763
September	1st to 10th	Night	19% 4 15% 31% 25% 6%	720
	11th to 20th	Night	18% 6% 13% 32% 27% 4	720
	21st to end	Night	23% 9% 16% 29% 20% 4	720
October	1st to 10th	Night	22% 10% 18% 26% 21% 3	720
	11th to 20th	Night	24% 11% 24% 28% 12% 2	720
	21st to end	Night	26% 15% 23% 24% 11% 1	792
November	1st to 10th	Night	20% 13% 22% 31% 13% 1	740
	11th to 20th	Night	29% 15% 21% 27% 8% 1	760
	21st to end	Night	28% 14% 25% 26% 6% 1	760
December	1st to 10th	Night	32% 18% 24% 20% 6% 1	760
	11th to 20th	Night	30% 18% 24% 24% 4	760
	21st to end	Night	29% 16% 27% 25% 3	836

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