Cumberland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cumberland clear sky chart from 2005-11-06 to 2026-03-03.

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	17% 8% 2 6% 4 4 4 4 5% 7% 39%	130538
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 40%	130639
Transparency	Day	44% 5% 12% 21% 15% 3	134084
	Night	44% 5% 11% 21% 16% 3	135180
Seeing	Day	23% 18% 32% 18% 7% 2	16701
	Night	22% 15% 34% 22% 6%	25732

By Month

Percentage Cloud Cover NE (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	10% 8% 4 7% 4 4 4 4 5% 6% 44%	4661
	11th to 20th	Day	15% 9% 3 5% 3 4 3 3 4 5% 46%	4650
	21st to end	Day	15% 9% 2 5% 3 3 3 3 4 6% 46%	5124
February	1st to 10th	Day	18% 8% 2 5% 5% 5% 4 4 6% 6% 37%	1992
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 3 5% 7% 41%	2048
	21st to end	Day	18% 10% 3 6% 4 3 4 3 4 6% 38%	1730
March	1st to 10th	Day	22% 11% 2 6% 4 3 3 3 5% 5% 37%	4496
	11th to 20th	Day	15% 9% 2 6% 4 4 4 4 5% 7% 41%	4766
	21st to end	Day	25% 10% 2 5% 4 4 4 4 5% 6% 32%	5781
April	1st to 10th	Day	20% 9% 3 7% 4 3 3 4 5% 7% 37%	2400
	11th to 20th	Day	18% 7% 2 5% 4 4 4 3 6% 7% 40%	2374
	21st to end	Day	21% 6% 2 7% 4 4 4 3 5% 5% 39%	2600
May	1st to 10th	Day	29% 10% 3 6% 3 4 4 3 4 7% 25%	5886
	11th to 20th	Day	21% 9% 3 7% 5% 5% 4 3 5% 6% 32%	5924
	21st to end	Day	20% 7% 3 6% 4 4 4 4 5% 8% 35%	6949
June	1st to 10th	Day	18% 7% 2 5% 5% 4 5% 4 6% 9% 34%	2800
	11th to 20th	Day	16% 6% 2 7% 4 5% 5% 4 5% 9% 36%	2800
	21st to end	Day	16% 7% 2 6% 5% 4 4 4 7% 9% 37%	2800
July	1st to 10th	Day	17% 7% 2 7% 5% 5% 5% 5% 7% 9% 32%	6360
	11th to 20th	Day	12% 7% 3 7% 5% 5% 6% 5% 7% 11% 34%	6360
	21st to end	Day	16% 7% 2 6% 4 4 4 4 6% 7% 41%	6926
August	1st to 10th	Day	16% 7% 3 8% 5% 5% 5% 4 6% 8% 32%	4268
	11th to 20th	Day	12% 6% 3 7% 5% 6% 6% 4 5% 7% 39%	4083
	21st to end	Day	8% 4 2 6% 4 5% 6% 5% 7% 9% 45%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 3 5% 4 5% 6% 45%	2396
	11th to 20th	Day	14% 5% 2 5% 3 4 3 3 4 5% 51%	2200
	21st to end	Day	19% 6% 2 5% 4 4 3 4 5% 5% 42%	2200
October	1st to 10th	Day	22% 7% 2 5% 3 3 3 2 4 5% 44%	2200
	11th to 20th	Day	16% 4 2 6% 3 3 3 3 5% 7% 47%	1965
	21st to end	Day	18% 6% 2 6% 4 3 4 4 4 5% 44%	1980
November	1st to 10th	Day	16% 6% 2 5% 4 3 4 3 3 5% 49%	1851
	11th to 20th	Day	18% 6% 2 4 4 3 3 3 4 6% 47%	1890
	21st to end	Day	18% 7% 2 5% 4 3 3 3 5% 6% 44%	1890
December	1st to 10th	Day	15% 9% 2 4 4 3 3 3 4 6% 48%	2762
	11th to 20th	Day	19% 6% 2 4 4 3 3 2 4 4 49%	3066
	21st to end	Day	20% 10% 3 7% 3 3 3 2 4 5% 38%	4048
January	1st to 10th	Night	15% 7% 2 5% 3 3 4 3 4 6% 48%	8234
	11th to 20th	Night	15% 10% 4 8% 4 4 3 3 4 5% 40%	8235
	21st to end	Night	15% 9% 3 7% 4 4 4 3 4 5% 41%	9057
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 5% 6% 40%	2625
	11th to 20th	Night	16% 8% 2 7% 4 4 5% 4 5% 6% 41%	2458
	21st to end	Night	18% 10% 2 7% 4 3 4 3 4 5% 41%	2076
March	1st to 10th	Night	23% 9% 2 5% 3 3 4 3 5% 6% 38%	5389
	11th to 20th	Night	16% 10% 3 6% 4 4 4 3 5% 6% 39%	5192
	21st to end	Night	25% 10% 2 6% 3 3 4 3 5% 5% 34%	5146
April	1st to 10th	Night	19% 9% 3 7% 4 5% 4 4 4 6% 36%	2000
	11th to 20th	Night	19% 8% 2 6% 5% 4 4 3 5% 5% 38%	1974
	21st to end	Night	20% 8% 2 6% 4 3 3 3 4 6% 40%	1800
May	1st to 10th	Night	29% 9% 3 7% 4 4 4 3 4 7% 26%	4054
	11th to 20th	Night	19% 9% 3 8% 5% 6% 5% 4 6% 7% 28%	3998
	21st to end	Night	20% 8% 3 7% 5% 5% 5% 4 6% 7% 32%	3926
June	1st to 10th	Night	15% 8% 3 6% 6% 4 5% 5% 6% 7% 37%	1600
	11th to 20th	Night	19% 7% 3 6% 4 3 5% 4 5% 8% 36%	1600
	21st to end	Night	15% 6% 3 6% 4 4 5% 4 6% 8% 41%	1600
July	1st to 10th	Night	16% 8% 3 6% 4 4 4 4 6% 10% 35%	3600
	11th to 20th	Night	15% 7% 3 7% 4 5% 4 4 6% 9% 36%	3600
	21st to end	Night	13% 8% 3 6% 5% 4 4 4 6% 6% 41%	3926
August	1st to 10th	Night	21% 7% 3 8% 4 5% 5% 4 6% 7% 30%	2848
	11th to 20th	Night	10% 8% 3 8% 5% 6% 7% 5% 6% 7% 36%	2961
	21st to end	Night	9% 4 1 5% 3 3 4 3 5% 7% 55%	3586
September	1st to 10th	Night	12% 7% 2 7% 4 5% 5% 4 5% 6% 44%	2002
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 4 6% 52%	2200
	21st to end	Night	19% 8% 2 6% 4 3 4 3 5% 5% 41%	2200
October	1st to 10th	Night	19% 8% 2 5% 4 3 3 3 4 6% 44%	2200
	11th to 20th	Night	16% 5% 2 4 4 3 4 3 5% 7% 47%	2431
	21st to end	Night	20% 7% 2 7% 4 4 4 2 4 5% 40%	2860
November	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 6% 48%	2667
	11th to 20th	Night	18% 6% 2 5% 3 3 3 2 4 6% 47%	2730
	21st to end	Night	16% 6% 2 4 3 4 4 4 5% 7% 45%	2730
December	1st to 10th	Night	17% 9% 1 5% 4 3 3 3 3 5% 47%	4636
	11th to 20th	Night	22% 8% 2 5% 3 3 3 3 4 5% 42%	5348
	21st to end	Night	17% 11% 3 6% 4 3 3 3 4 5% 40%	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	41% 3 10% 25% 19% 2	4662
	11th to 20th	Day	41% 4 9% 20% 18% 7%	4680
	21st to end	Day	39% 4 10% 24% 21% 2	5124
February	1st to 10th	Day	45% 6% 13% 18% 15% 3	1992
	11th to 20th	Day	43% 6% 10% 22% 16% 3	2057
	21st to end	Day	48% 4 10% 20% 15% 3	1730
March	1st to 10th	Day	48% 4 11% 14% 12% 11%	4499
	11th to 20th	Day	40% 7% 14% 27% 10% 2	4766
	21st to end	Day	53% 5% 6% 15% 15% 7%	5781
April	1st to 10th	Day	47% 5% 11% 18% 16% 3	2400
	11th to 20th	Day	42% 6% 11% 20% 18% 3	2374
	21st to end	Day	46% 6% 9% 19% 17% 4	2600
May	1st to 10th	Day	58% 6% 14% 12% 8% 1	5897
	11th to 20th	Day	52% 6% 14% 16% 11% 2	5928
	21st to end	Day	46% 7% 12% 21% 13% 1	6949
June	1st to 10th	Day	45% 8% 13% 21% 12% 1	2800
	11th to 20th	Day	44% 8% 13% 20% 14% 2	2800
	21st to end	Day	43% 7% 14% 20% 14% 1	2800
July	1st to 10th	Day	49% 6% 11% 20% 13% 2	6290
	11th to 20th	Day	44% 5% 18% 22% 10% 1	6285
	21st to end	Day	42% 5% 11% 25% 16% 2	6728
August	1st to 10th	Day	49% 6% 16% 20% 8% 1	4254
	11th to 20th	Day	43% 5% 14% 27% 10%	4122
	21st to end	Day	33% 6% 14% 27% 18% 2	4312
September	1st to 10th	Day	38% 7% 11% 22% 20% 2	2396
	11th to 20th	Day	35% 5% 10% 24% 24% 3	2200
	21st to end	Day	43% 5% 9% 20% 22% 2	2200
October	1st to 10th	Day	40% 4 9% 22% 22% 4	3590
	11th to 20th	Day	31% 4 7% 25% 29% 4	3181
	21st to end	Day	32% 4 13% 28% 20% 3	3180
November	1st to 10th	Day	39% 5% 13% 22% 20% 2	1851
	11th to 20th	Day	38% 5% 10% 22% 21% 3	1890
	21st to end	Day	42% 5% 12% 27% 12% 3	1890
December	1st to 10th	Day	39% 4 14% 27% 15% 1	2762
	11th to 20th	Day	40% 3 14% 17% 19% 6%	3066
	21st to end	Day	48% 6% 8% 19% 15% 4	4048
January	1st to 10th	Night	38% 3 11% 29% 17% 2	8234
	11th to 20th	Night	47% 4 10% 19% 15% 5%	8280
	21st to end	Night	45% 4 8% 18% 20% 4	9057
February	1st to 10th	Night	44% 6% 12% 21% 15% 2	2625
	11th to 20th	Night	44% 6% 10% 20% 17% 4	2460
	21st to end	Night	46% 4 8% 22% 15% 4	2076
March	1st to 10th	Night	47% 5% 9% 16% 16% 7%	5399
	11th to 20th	Night	44% 6% 17% 18% 12% 3	5193
	21st to end	Night	52% 4 6% 12% 20% 6%	5146
April	1st to 10th	Night	48% 5% 10% 19% 15% 3	2000
	11th to 20th	Night	46% 6% 9% 18% 18% 3	1974
	21st to end	Night	46% 6% 10% 18% 16% 4	1800
May	1st to 10th	Night	57% 8% 15% 11% 8% 1	4060
	11th to 20th	Night	53% 8% 15% 14% 8% 2	3999
	21st to end	Night	50% 8% 14% 18% 10% 1	3927
June	1st to 10th	Night	44% 9% 14% 20% 13% 1	1600
	11th to 20th	Night	45% 7% 13% 21% 13% 1	1600
	21st to end	Night	39% 9% 16% 23% 13% 1	1600
July	1st to 10th	Night	45% 7% 12% 23% 14%	3560
	11th to 20th	Night	45% 5% 18% 22% 10% 1	3552
	21st to end	Night	43% 5% 11% 26% 15% 1	3809
August	1st to 10th	Night	52% 7% 13% 18% 9% 1	2838
	11th to 20th	Night	45% 7% 14% 25% 9%	2988
	21st to end	Night	28% 5% 15% 29% 22% 1	3586
September	1st to 10th	Night	40% 6% 11% 23% 18% 1	2002
	11th to 20th	Night	34% 7% 9% 23% 26% 2	2200
	21st to end	Night	45% 6% 8% 20% 19% 2	2200
October	1st to 10th	Night	39% 5% 12% 24% 17% 3	3590
	11th to 20th	Night	27% 4 9% 27% 31% 3	3954
	21st to end	Night	35% 3 11% 28% 20% 2	4610
November	1st to 10th	Night	36% 7% 11% 23% 19% 3	2667
	11th to 20th	Night	40% 3 10% 22% 21% 4	2730
	21st to end	Night	39% 5% 13% 28% 14% 2	2730
December	1st to 10th	Night	42% 3 11% 28% 14% 1	4636
	11th to 20th	Night	46% 4 14% 15% 19% 2	5348
	21st to end	Night	45% 5% 8% 21% 17% 3	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	29% 28% 30% 12% 2	220
	11th to 20th	Day	32% 26% 33% 5% 3	220
	21st to end	Day	27% 31% 31% 9% 2 1	242
February	1st to 10th	Day	31% 25% 31% 12% 1	461
	11th to 20th	Day	30% 32% 29% 8% 1	536
	21st to end	Day	30% 24% 31% 11% 3	446
March	1st to 10th	Day	32% 21% 32% 12% 3	508
	11th to 20th	Day	29% 26% 30% 12% 3	500
	21st to end	Day	31% 23% 32% 10% 4 2	550
April	1st to 10th	Day	35% 23% 26% 11% 5% 1	500
	11th to 20th	Day	29% 26% 29% 12% 3 1	492
	21st to end	Day	28% 22% 31% 15% 2 2	500
May	1st to 10th	Day	31% 24% 28% 14% 3 1	503
	11th to 20th	Day	23% 18% 41% 14% 5%	527
	21st to end	Day	19% 16% 36% 22% 6% 2	573
June	1st to 10th	Day	21% 14% 36% 20% 8% 1	530
	11th to 20th	Day	18% 17% 38% 21% 5% 1	530
	21st to end	Day	17% 15% 36% 23% 7% 2	530
July	1st to 10th	Day	18% 9% 35% 24% 12% 2	525
	11th to 20th	Day	15% 8% 34% 27% 14% 2	524
	21st to end	Day	14% 8% 41% 26% 9% 1	576
August	1st to 10th	Day	11% 11% 34% 30% 11% 2	526
	11th to 20th	Day	14% 8% 33% 29% 12% 3	519
	21st to end	Day	11% 11% 36% 24% 12% 5%	583
September	1st to 10th	Day	18% 14% 28% 24% 13% 4	530
	11th to 20th	Day	18% 11% 27% 25% 11% 7%	530
	21st to end	Day	23% 12% 33% 21% 9% 3	530
October	1st to 10th	Day	27% 12% 26% 20% 10% 5%	530
	11th to 20th	Day	20% 17% 33% 17% 9% 3	475
	21st to end	Day	25% 18% 31% 18% 8% 1	462
November	1st to 10th	Day	23% 17% 34% 16% 8% 2	425
	11th to 20th	Day	27% 24% 29% 16% 5%	430
	21st to end	Day	28% 22% 30% 15% 5%	430
December	1st to 10th	Day	24% 30% 29% 13% 4	276
	11th to 20th	Day	33% 27% 31% 6% 2	220
	21st to end	Day	27% 27% 31% 9% 3 2	242
January	1st to 10th	Night	23% 21% 38% 15% 3	840
	11th to 20th	Night	28% 21% 34% 14% 2	840
	21st to end	Night	21% 24% 35% 18% 3	924
February	1st to 10th	Night	24% 19% 38% 18% 1	840
	11th to 20th	Night	26% 22% 36% 14% 1	823
	21st to end	Night	27% 21% 34% 15% 3	692
March	1st to 10th	Night	25% 21% 34% 16% 3	809
	11th to 20th	Night	21% 24% 36% 17% 3	800
	21st to end	Night	27% 20% 35% 15% 4	880
April	1st to 10th	Night	25% 22% 33% 17% 3	800
	11th to 20th	Night	24% 21% 35% 17% 4	790
	21st to end	Night	24% 19% 39% 16% 3	600
May	1st to 10th	Night	31% 15% 32% 20% 3	600
	11th to 20th	Night	22% 16% 39% 20% 3	583
	21st to end	Night	18% 9% 39% 29% 5%	433
June	1st to 10th	Night	18% 8% 37% 30% 8%	400
	11th to 20th	Night	19% 7% 38% 31% 5%	400
	21st to end	Night	16% 6% 40% 32% 6%	400
July	1st to 10th	Night	14% 5% 33% 39% 8%	390
	11th to 20th	Night	16% 4 31% 38% 11% 1	388
	21st to end	Night	13% 6% 36% 38% 7%	438
August	1st to 10th	Night	14% 5% 35% 39% 8%	556
	11th to 20th	Night	14% 5% 29% 40% 12%	642
	21st to end	Night	14% 6% 28% 37% 13% 2	880
September	1st to 10th	Night	16% 6% 33% 34% 11% 1	800
	11th to 20th	Night	17% 7% 28% 29% 17% 2	800
	21st to end	Night	23% 8% 28% 28% 11% 2	800
October	1st to 10th	Night	25% 11% 28% 24% 12% 2	800
	11th to 20th	Night	20% 12% 34% 23% 11% 1	800
	21st to end	Night	26% 16% 33% 19% 7%	880
November	1st to 10th	Night	18% 17% 33% 23% 9% 1	820
	11th to 20th	Night	23% 19% 35% 17% 6%	840
	21st to end	Night	23% 20% 32% 20% 4 1	840
December	1st to 10th	Night	26% 18% 34% 18% 4	840
	11th to 20th	Night	27% 18% 33% 19% 2	840
	21st to end	Night	26% 20% 35% 17% 2	924

Page generated at 2026-02-28 01:40:23. Version ac07

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