The Hughesville Sky-view Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Hughesville Sky-view Observatory 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% 6% 2 6% 4 4 4 4 6% 8% 42%	131522
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 44%	130617
Transparency	Day	38% 7% 12% 24% 17% 4	135113
	Night	38% 5% 11% 23% 18% 4	135095
Seeing	Day	19% 16% 30% 22% 10% 3	16877
	Night	18% 14% 29% 27% 11% 1	26494

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	14% 4 2 6% 4 4 4 4 5% 5% 47%	4780
	11th to 20th	Day	14% 8% 2 6% 3 3 3 2 3 4 51%	5280
	21st to end	Day	13% 7% 2 7% 4 4 4 4 5% 5% 45%	5780
February	1st to 10th	Day	13% 8% 3 6% 4 5% 5% 4 5% 6% 40%	1890
	11th to 20th	Day	19% 7% 2 5% 4 3 4 3 6% 6% 41%	1938
	21st to end	Day	16% 10% 3 6% 4 5% 4 3 4 6% 40%	1730
March	1st to 10th	Day	19% 6% 2 5% 4 3 4 3 5% 8% 41%	4903
	11th to 20th	Day	12% 6% 2 5% 3 3 4 3 5% 7% 51%	5090
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 7% 42%	5721
April	1st to 10th	Day	13% 7% 2 5% 4 4 4 4 5% 8% 44%	2520
	11th to 20th	Day	11% 7% 2 5% 4 4 4 3 5% 7% 48%	2446
	21st to end	Day	16% 7% 2 5% 4 4 4 4 5% 7% 43%	2400
May	1st to 10th	Day	20% 7% 2 6% 4 4 5% 4 6% 10% 30%	5635
	11th to 20th	Day	20% 6% 2 6% 5% 5% 5% 4 6% 9% 32%	6180
	21st to end	Day	15% 6% 2 6% 4 5% 5% 4 6% 9% 39%	6934
June	1st to 10th	Day	11% 5% 2 5% 5% 5% 5% 4 6% 10% 42%	2800
	11th to 20th	Day	11% 5% 1 5% 4 5% 5% 5% 7% 9% 43%	2800
	21st to end	Day	9% 3 2 5% 6% 5% 6% 5% 7% 11% 43%	2800
July	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 5% 7% 11% 44%	6360
	11th to 20th	Day	10% 6% 3 7% 6% 5% 6% 6% 9% 13% 30%	6186
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 10% 41%	6424
August	1st to 10th	Day	16% 7% 3 6% 5% 5% 6% 5% 7% 10% 32%	4234
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 8% 10% 38%	3930
	21st to end	Day	8% 4 2 5% 4 4 5% 4 6% 9% 48%	4312
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 5% 8% 46%	2400
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 6% 9% 45%	2400
	21st to end	Day	19% 9% 3 5% 4 4 4 4 5% 7% 36%	2119
October	1st to 10th	Day	15% 5% 2 4 4 4 4 3 5% 6% 48%	2000
	11th to 20th	Day	17% 4 2 5% 2 3 3 3 3 5% 53%	2000
	21st to end	Day	12% 6% 2 7% 3 4 3 3 5% 6% 49%	2200
November	1st to 10th	Day	12% 5% 1 4 4 3 3 3 5% 7% 54%	1931
	11th to 20th	Day	13% 6% 2 4 3 3 3 4 6% 5% 51%	1890
	21st to end	Day	14% 6% 3 5% 4 4 3 3 4 5% 50%	1711
December	1st to 10th	Day	12% 5% 2 6% 3 4 4 4 6% 7% 48%	2680
	11th to 20th	Day	17% 7% 2 6% 3 3 3 3 4 6% 46%	3070
	21st to end	Day	14% 8% 2 7% 4 3 4 4 6% 7% 41%	4048
January	1st to 10th	Night	12% 7% 2 6% 3 4 4 4 5% 7% 46%	8099
	11th to 20th	Night	13% 7% 2 6% 3 3 3 2 4 4 53%	7680
	21st to end	Night	14% 7% 2 6% 4 3 4 3 4 5% 48%	8401
February	1st to 10th	Night	15% 7% 2 6% 3 4 4 4 5% 7% 43%	2730
	11th to 20th	Night	19% 8% 3 6% 3 3 3 3 4 5% 43%	2565
	21st to end	Night	16% 9% 3 4 3 3 4 3 5% 7% 43%	2076
March	1st to 10th	Night	16% 6% 3 6% 3 3 3 3 5% 6% 47%	5167
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 5% 7% 50%	5090
	21st to end	Night	14% 7% 2 6% 4 4 4 3 4 6% 45%	5451
April	1st to 10th	Night	15% 7% 2 5% 5% 4 4 3 5% 7% 42%	2100
	11th to 20th	Night	13% 5% 2 6% 4 3 4 3 5% 7% 48%	2036
	21st to end	Night	17% 5% 2 5% 4 4 4 3 6% 8% 42%	2000
May	1st to 10th	Night	18% 9% 3 7% 4 5% 5% 4 6% 8% 30%	4288
	11th to 20th	Night	21% 8% 2 5% 4 4 4 4 6% 9% 32%	3698
	21st to end	Night	17% 7% 2 6% 4 4 4 4 7% 8% 36%	3920
June	1st to 10th	Night	10% 6% 2 5% 4 4 5% 5% 7% 10% 41%	1600
	11th to 20th	Night	12% 6% 3 6% 5% 4 4 4 6% 10% 40%	1600
	21st to end	Night	8% 5% 2 5% 4 4 6% 5% 8% 11% 42%	1600
July	1st to 10th	Night	8% 5% 3 7% 5% 5% 6% 5% 8% 11% 39%	3598
	11th to 20th	Night	10% 8% 3 8% 5% 6% 6% 5% 7% 11% 30%	3767
	21st to end	Night	8% 6% 2 6% 6% 5% 6% 4 7% 9% 40%	4427
August	1st to 10th	Night	15% 7% 3 7% 4 4 5% 4 6% 9% 34%	2915
	11th to 20th	Night	11% 7% 3 8% 5% 5% 5% 6% 7% 9% 34%	3072
	21st to end	Night	9% 5% 3 5% 4 3 4 3 5% 7% 51%	3586
September	1st to 10th	Night	13% 6% 3 5% 4 4 4 3 5% 8% 47%	2000
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 6% 8% 48%	2000
	21st to end	Night	20% 8% 2 6% 4 4 4 4 5% 7% 36%	2275
October	1st to 10th	Night	15% 6% 2 6% 4 4 4 4 4 6% 46%	2400
	11th to 20th	Night	15% 5% 2 6% 3 3 3 2 5% 5% 51%	2400
	21st to end	Night	14% 5% 2 5% 4 3 4 3 4 7% 50%	2640
November	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 5% 53%	2584
	11th to 20th	Night	15% 7% 2 5% 3 4 3 3 5% 5% 49%	2730
	21st to end	Night	12% 5% 1 4 4 4 4 4 5% 6% 50%	2907
December	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 4 7% 54%	4720
	11th to 20th	Night	20% 7% 2 5% 4 4 4 3 5% 6% 40%	5345
	21st to end	Night	15% 8% 2 6% 4 4 4 4 5% 8% 41%	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	38% 5% 7% 25% 20% 6%	4781
	11th to 20th	Day	37% 3 6% 20% 24% 9%	5280
	21st to end	Day	39% 5% 8% 31% 14% 3	5780
February	1st to 10th	Day	42% 6% 11% 25% 13% 2	1890
	11th to 20th	Day	43% 5% 8% 23% 18% 3	1947
	21st to end	Day	46% 4 11% 19% 16% 4	1730
March	1st to 10th	Day	41% 5% 9% 21% 17% 7%	4903
	11th to 20th	Day	32% 5% 10% 26% 21% 6%	5090
	21st to end	Day	42% 5% 10% 19% 18% 7%	5721
April	1st to 10th	Day	37% 7% 11% 21% 19% 6%	2520
	11th to 20th	Day	35% 5% 11% 23% 20% 6%	2446
	21st to end	Day	40% 5% 10% 23% 16% 5%	2400
May	1st to 10th	Day	46% 9% 15% 18% 11% 1	5667
	11th to 20th	Day	46% 8% 11% 24% 10% 1	6184
	21st to end	Day	40% 8% 13% 23% 15% 2	6949
June	1st to 10th	Day	35% 8% 14% 26% 15% 1	2800
	11th to 20th	Day	35% 9% 14% 24% 17% 2	2800
	21st to end	Day	33% 8% 15% 25% 17% 2	2800
July	1st to 10th	Day	32% 10% 21% 20% 13% 4	6290
	11th to 20th	Day	41% 12% 20% 20% 6% 1	6111
	21st to end	Day	35% 9% 12% 22% 21% 1	6240
August	1st to 10th	Day	44% 8% 15% 25% 7%	4221
	11th to 20th	Day	37% 8% 16% 26% 12% 1	3968
	21st to end	Day	30% 8% 14% 28% 18% 2	4312
September	1st to 10th	Day	37% 6% 13% 21% 19% 4	2400
	11th to 20th	Day	35% 6% 10% 26% 20% 3	2400
	21st to end	Day	47% 5% 9% 20% 15% 3	2119
October	1st to 10th	Day	36% 5% 7% 18% 28% 5%	3260
	11th to 20th	Day	26% 4 6% 27% 27% 11%	3240
	21st to end	Day	23% 3 8% 30% 25% 11%	3538
November	1st to 10th	Day	31% 4 11% 28% 21% 5%	1931
	11th to 20th	Day	34% 4 11% 23% 23% 5%	1890
	21st to end	Day	37% 3 9% 28% 20% 3	1711
December	1st to 10th	Day	35% 6% 13% 25% 17% 4	2680
	11th to 20th	Day	40% 4 13% 28% 12% 3	3066
	21st to end	Day	40% 7% 13% 24% 15% 1	4048
January	1st to 10th	Night	37% 4 10% 24% 20% 4	8100
	11th to 20th	Night	35% 3 7% 24% 23% 8%	7680
	21st to end	Night	39% 4 7% 29% 19% 3	8401
February	1st to 10th	Night	41% 4 11% 25% 17% 2	2730
	11th to 20th	Night	44% 3 8% 21% 18% 5%	2567
	21st to end	Night	41% 4 11% 22% 16% 6%	2076
March	1st to 10th	Night	38% 5% 8% 24% 17% 9%	5167
	11th to 20th	Night	32% 5% 10% 25% 21% 7%	5090
	21st to end	Night	40% 5% 8% 22% 19% 6%	5451
April	1st to 10th	Night	41% 5% 10% 20% 20% 5%	2100
	11th to 20th	Night	35% 5% 12% 22% 21% 5%	2036
	21st to end	Night	39% 6% 11% 25% 15% 5%	2000
May	1st to 10th	Night	49% 8% 14% 18% 9% 3	4318
	11th to 20th	Night	47% 7% 13% 21% 11% 1	3699
	21st to end	Night	43% 7% 14% 23% 12% 2	3927
June	1st to 10th	Night	35% 8% 13% 25% 17% 2	1600
	11th to 20th	Night	38% 7% 14% 24% 14% 3	1600
	21st to end	Night	33% 8% 17% 20% 19% 3	1600
July	1st to 10th	Night	37% 11% 19% 18% 13% 2	3560
	11th to 20th	Night	44% 11% 21% 16% 6% 1	3722
	21st to end	Night	37% 8% 15% 23% 17%	4297
August	1st to 10th	Night	45% 8% 18% 21% 8%	2904
	11th to 20th	Night	42% 9% 14% 23% 11% 1	3099
	21st to end	Night	32% 5% 11% 28% 21% 1	3586
September	1st to 10th	Night	36% 5% 13% 22% 17% 6%	2000
	11th to 20th	Night	33% 6% 11% 26% 21% 3	2000
	21st to end	Night	47% 6% 11% 18% 15% 3	2275
October	1st to 10th	Night	38% 5% 10% 20% 20% 6%	3920
	11th to 20th	Night	24% 3 10% 22% 32% 9%	3899
	21st to end	Night	22% 3 9% 31% 25% 10%	4252
November	1st to 10th	Night	34% 4 9% 26% 22% 5%	2584
	11th to 20th	Night	38% 3 9% 22% 22% 7%	2730
	21st to end	Night	33% 4 11% 26% 22% 4	2907
December	1st to 10th	Night	32% 4 12% 28% 22% 3	4720
	11th to 20th	Night	45% 4 11% 20% 15% 5%	5348
	21st to end	Night	40% 6% 14% 24% 15% 1	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% 29% 10% 5%	242
	11th to 20th	Day	28% 29% 30% 10% 2	330
	21st to end	Day	21% 33% 35% 9% 2	363
February	1st to 10th	Day	24% 28% 35% 10% 2	330
	11th to 20th	Day	34% 25% 31% 9% 1	425
	21st to end	Day	29% 24% 32% 12% 2	446
March	1st to 10th	Day	24% 27% 32% 14% 2 1	540
	11th to 20th	Day	26% 25% 31% 13% 4 1	540
	21st to end	Day	23% 23% 37% 13% 3 1	594
April	1st to 10th	Day	21% 24% 35% 14% 5%	540
	11th to 20th	Day	18% 21% 37% 15% 7% 2	516
	21st to end	Day	22% 19% 34% 18% 6% 1	500
May	1st to 10th	Day	25% 18% 31% 17% 7% 2	503
	11th to 20th	Day	23% 16% 32% 22% 7% 1	527
	21st to end	Day	19% 9% 28% 27% 13% 3	573
June	1st to 10th	Day	12% 12% 31% 27% 16% 3	530
	11th to 20th	Day	14% 7% 33% 29% 14% 3	530
	21st to end	Day	11% 8% 29% 33% 14% 4	530
July	1st to 10th	Day	11% 4 22% 36% 20% 7%	525
	11th to 20th	Day	5% 3 20% 43% 21% 8%	524
	21st to end	Day	10% 3 25% 35% 20% 6%	576
August	1st to 10th	Day	12% 7% 23% 33% 18% 6%	526
	11th to 20th	Day	12% 5% 20% 36% 19% 8%	519
	21st to end	Day	10% 4 25% 32% 18% 11%	583
September	1st to 10th	Day	15% 7% 24% 27% 15% 12%	530
	11th to 20th	Day	13% 7% 27% 29% 13% 10%	530
	21st to end	Day	28% 10% 27% 22% 9% 3	530
October	1st to 10th	Day	18% 10% 28% 23% 15% 6%	530
	11th to 20th	Day	19% 17% 28% 24% 10% 2	530
	21st to end	Day	16% 18% 36% 19% 9% 2	583
November	1st to 10th	Day	16% 16% 36% 20% 9% 3	469
	11th to 20th	Day	21% 22% 31% 19% 7% 1	430
	21st to end	Day	21% 25% 29% 16% 8%	251
December	1st to 10th	Day	23% 23% 38% 12% 3 1	220
	11th to 20th	Day	25% 24% 30% 17% 4	220
	21st to end	Day	24% 24% 28% 19% 3	242
January	1st to 10th	Night	22% 25% 33% 17% 3	840
	11th to 20th	Night	22% 22% 31% 21% 4	840
	21st to end	Night	21% 22% 37% 18% 2	924
February	1st to 10th	Night	20% 21% 35% 22% 3	840
	11th to 20th	Night	25% 27% 33% 13% 1	823
	21st to end	Night	24% 22% 35% 16% 2	692
March	1st to 10th	Night	20% 23% 34% 20% 3	840
	11th to 20th	Night	23% 20% 35% 17% 5% 1	840
	21st to end	Night	20% 20% 40% 17% 3	924
April	1st to 10th	Night	21% 23% 35% 18% 3	840
	11th to 20th	Night	15% 17% 36% 25% 6%	816
	21st to end	Night	20% 14% 34% 24% 8%	800
May	1st to 10th	Night	20% 11% 36% 24% 9% 1	715
	11th to 20th	Night	18% 10% 32% 32% 8%	452
	21st to end	Night	15% 6% 25% 35% 16% 2	433
June	1st to 10th	Night	12% 5% 27% 42% 15% 1	400
	11th to 20th	Night	13% 6% 24% 41% 15% 2	400
	21st to end	Night	9% 6% 27% 42% 15% 2	400
July	1st to 10th	Night	9% 4 19% 41% 24% 2	390
	11th to 20th	Night	7% 2 16% 43% 28% 4	454
	21st to end	Night	8% 3 22% 39% 25% 3	657
August	1st to 10th	Night	11% 2 16% 43% 25% 3	597
	11th to 20th	Night	12% 4 18% 41% 24% 2	713
	21st to end	Night	11% 4 18% 35% 26% 5%	880
September	1st to 10th	Night	16% 4 19% 34% 23% 4	800
	11th to 20th	Night	12% 5% 15% 39% 25% 4	800
	21st to end	Night	25% 6% 24% 28% 17% 1	800
October	1st to 10th	Night	19% 7% 20% 31% 17% 5%	800
	11th to 20th	Night	18% 14% 26% 26% 15% 1	800
	21st to end	Night	18% 14% 30% 25% 12% 1	880
November	1st to 10th	Night	14% 14% 32% 27% 10% 2	820
	11th to 20th	Night	19% 19% 31% 23% 7%	840
	21st to end	Night	16% 20% 31% 24% 8% 1	840
December	1st to 10th	Night	23% 18% 31% 18% 8% 1	840
	11th to 20th	Night	21% 17% 35% 22% 5%	840
	21st to end	Night	20% 18% 31% 27% 3	924

Page generated at 2026-04-14 02:44:23. Version ac07

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