Hugo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hugo clear sky chart from 2005-11-06 to 2026-02-16.

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	5% 4 2 4 3 3 4 3 6% 8% 58%	139451
	Night	5% 5% 2 5% 4 4 4 3 5% 7% 55%	138836
Transparency	Day	23% 5% 11% 25% 26% 10%	134439
	Night	27% 5% 10% 24% 24% 9%	134858
Seeing	Day	7% 8% 26% 31% 21% 7%	17267
	Night	7% 6% 31% 39% 15% 1	27383

By Month

Percentage Cloud Cover SW (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	2 7% 2 6% 4 3 4 4 5% 6% 56%	4720
	11th to 20th	Day	1 4 2 5% 5% 3 3 3 4 6% 63%	4740
	21st to end	Day	3 6% 2 6% 3 3 3 2 4 6% 63%	5742
February	1st to 10th	Day	2 6% 3 6% 4 2 4 3 4 7% 57%	2006
	11th to 20th	Day	2 6% 3 7% 4 4 4 3 5% 6% 56%	1999
	21st to end	Day	3 6% 2 6% 4 3 3 3 5% 6% 59%	1650
March	1st to 10th	Day	2 4 2 4 3 3 4 3 5% 6% 63%	4500
	11th to 20th	Day	5% 6% 2 4 4 3 4 3 5% 7% 59%	4698
	21st to end	Day	3 4 2 5% 3 3 5% 4 7% 9% 55%	5969
April	1st to 10th	Day	5% 6% 2 4 3 3 3 4 6% 8% 56%	2400
	11th to 20th	Day	8% 6% 2 5% 4 4 4 4 7% 7% 50%	2371
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 6% 7% 50%	2412
May	1st to 10th	Day	11% 5% 2 5% 4 3 3 3 5% 6% 52%	5900
	11th to 20th	Day	6% 4 2 5% 3 3 4 4 5% 8% 56%	5904
	21st to end	Day	10% 5% 2 4 3 3 4 3 6% 9% 50%	6925
June	1st to 10th	Day	6% 3 1 3 4 4 4 5% 7% 11% 53%	2800
	11th to 20th	Day	5% 3 1 3 3 3 3 4 6% 8% 59%	2800
	21st to end	Day	2 4 2 5% 3 4 5% 4 7% 9% 56%	2800
July	1st to 10th	Day	3 2 1 4 4 4 5% 4 6% 9% 57%	6339
	11th to 20th	Day	2 2 1 4 4 4 5% 4 8% 10% 56%	6340
	21st to end	Day	4 3 1 5% 4 4 5% 5% 8% 10% 52%	6903
August	1st to 10th	Day	9% 4 1 4 3 3 5% 5% 7% 10% 49%	5626
	11th to 20th	Day	3 3 1 4 3 3 5% 4 7% 10% 57%	5366
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 9% 50%	5984
September	1st to 10th	Day	4 3 1 4 4 3 4 4 6% 7% 61%	2400
	11th to 20th	Day	6% 3 1 3 2 3 3 3 5% 7% 64%	2295
	21st to end	Day	6% 4 1 3 2 3 3 2 4 6% 67%	2200
October	1st to 10th	Day	5% 3 1 2 1 1 2 2 3 4 77%	3509
	11th to 20th	Day	6% 4 1 4 3 2 2 2 4 6% 66%	3250
	21st to end	Day	5% 4 1 3 2 2 2 2 3 5% 71%	3288
November	1st to 10th	Day	4 3 2 3 3 2 3 3 5% 7% 65%	1853
	11th to 20th	Day	2 4 2 4 3 2 3 2 4 5% 67%	1890
	21st to end	Day	3 6% 2 5% 4 3 3 2 4 6% 64%	1890
December	1st to 10th	Day	2 7% 1 3 2 2 3 2 4 6% 68%	2784
	11th to 20th	Day	2 4 2 3 3 2 3 3 5% 7% 66%	3106
	21st to end	Day	3 6% 3 5% 3 3 4 3 5% 7% 58%	4092
January	1st to 10th	Night	2 8% 3 6% 3 3 4 3 5% 7% 54%	8201
	11th to 20th	Night	1 5% 2 6% 3 4 4 3 4 6% 61%	8250
	21st to end	Night	2 6% 3 7% 4 3 3 3 4 5% 61%	8517
February	1st to 10th	Night	3 6% 2 5% 4 3 5% 3 5% 7% 56%	2612
	11th to 20th	Night	3 8% 3 7% 5% 4 4 4 6% 8% 48%	2398
	21st to end	Night	3 5% 2 5% 3 3 3 2 5% 6% 62%	1980
March	1st to 10th	Night	3 5% 3 7% 3 3 3 3 4 5% 61%	5374
	11th to 20th	Night	5% 8% 3 6% 4 3 4 3 4 6% 54%	5282
	21st to end	Night	7% 6% 2 7% 4 4 4 4 5% 8% 49%	4984
April	1st to 10th	Night	6% 7% 3 5% 4 4 4 4 6% 7% 51%	2000
	11th to 20th	Night	10% 7% 2 5% 3 4 3 3 7% 8% 47%	1977
	21st to end	Night	11% 7% 2 6% 4 3 4 3 6% 8% 47%	1985
May	1st to 10th	Night	12% 7% 2 5% 3 4 4 3 5% 7% 49%	4080
	11th to 20th	Night	7% 6% 2 5% 3 4 4 4 7% 8% 48%	3995
	21st to end	Night	15% 8% 2 5% 3 4 4 3 5% 7% 43%	3972
June	1st to 10th	Night	4 3 1 5% 4 5% 4 4 6% 11% 53%	1600
	11th to 20th	Night	4 4 2 4 4 4 4 4 7% 9% 55%	1600
	21st to end	Night	5% 4 2 5% 7% 5% 6% 4 6% 8% 48%	1600
July	1st to 10th	Night	6% 4 2 5% 5% 5% 5% 4 8% 8% 47%	3640
	11th to 20th	Night	6% 3 2 6% 5% 5% 5% 5% 7% 9% 47%	3640
	21st to end	Night	5% 4 2 7% 5% 6% 6% 5% 7% 8% 45%	3970
August	1st to 10th	Night	11% 6% 2 7% 5% 5% 6% 5% 7% 8% 38%	4181
	11th to 20th	Night	8% 4 2 5% 5% 5% 5% 5% 8% 9% 44%	4483
	21st to end	Night	13% 5% 2 5% 4 4 5% 5% 7% 9% 42%	4993
September	1st to 10th	Night	6% 5% 2 4 4 4 4 4 6% 8% 55%	2000
	11th to 20th	Night	5% 4 1 4 3 3 3 4 6% 8% 60%	2103
	21st to end	Night	6% 3 1 4 3 3 3 3 4 6% 65%	2200
October	1st to 10th	Night	5% 3 1 4 2 3 3 2 4 5% 68%	3656
	11th to 20th	Night	7% 4 1 4 2 2 3 3 5% 6% 63%	3898
	21st to end	Night	4 4 2 4 2 3 3 2 4 5% 67%	4480
November	1st to 10th	Night	3 3 1 3 2 3 4 3 5% 6% 67%	2665
	11th to 20th	Night	2 5% 2 3 2 2 2 3 4 5% 70%	2730
	21st to end	Night	4 5% 2 5% 3 2 2 3 5% 7% 60%	2730
December	1st to 10th	Night	1 3 1 4 3 2 3 2 4 5% 71%	4611
	11th to 20th	Night	2 5% 2 4 3 3 4 3 6% 8% 61%	5321
	21st to end	Night	3 5% 2 6% 4 4 4 4 6% 8% 53%	7128

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	28% 4 7% 32% 22% 8%	4723
	11th to 20th	Day	22% 5% 8% 25% 29% 11%	4740
	21st to end	Day	25% 3 7% 27% 30% 9%	5742
February	1st to 10th	Day	26% 4 11% 26% 23% 9%	2006
	11th to 20th	Day	29% 4 9% 27% 25% 7%	2009
	21st to end	Day	26% 4 8% 20% 26% 15%	1650
March	1st to 10th	Day	19% 5% 7% 20% 32% 17%	4500
	11th to 20th	Day	24% 4 7% 24% 33% 7%	4698
	21st to end	Day	22% 7% 12% 39% 18% 3	5969
April	1st to 10th	Day	25% 6% 11% 25% 23% 9%	2400
	11th to 20th	Day	31% 5% 11% 24% 19% 10%	2374
	21st to end	Day	31% 6% 12% 25% 21% 5%	2412
May	1st to 10th	Day	31% 6% 10% 26% 19% 8%	5900
	11th to 20th	Day	23% 6% 12% 22% 26% 11%	5908
	21st to end	Day	28% 7% 14% 24% 19% 7%	6926
June	1st to 10th	Day	23% 7% 17% 28% 16% 8%	2800
	11th to 20th	Day	21% 7% 11% 22% 23% 16%	2800
	21st to end	Day	21% 7% 11% 23% 25% 13%	2800
July	1st to 10th	Day	21% 7% 11% 20% 29% 12%	6271
	11th to 20th	Day	19% 7% 18% 26% 22% 7%	6265
	21st to end	Day	25% 7% 16% 19% 18% 14%	6705
August	1st to 10th	Day	29% 7% 17% 28% 15% 5%	4093
	11th to 20th	Day	23% 7% 14% 23% 26% 7%	3882
	21st to end	Day	22% 5% 11% 26% 24% 11%	4311
September	1st to 10th	Day	22% 5% 9% 22% 28% 14%	2400
	11th to 20th	Day	19% 5% 9% 19% 30% 18%	2295
	21st to end	Day	20% 4 6% 20% 35% 15%	2200
October	1st to 10th	Day	14% 2 6% 16% 37% 25%	3509
	11th to 20th	Day	20% 3 7% 27% 33% 9%	3250
	21st to end	Day	18% 2 5% 25% 36% 13%	3288
November	1st to 10th	Day	19% 4 9% 27% 27% 14%	1853
	11th to 20th	Day	20% 3 6% 27% 34% 11%	1890
	21st to end	Day	24% 2 9% 21% 30% 14%	1890
December	1st to 10th	Day	20% 3 7% 31% 32% 8%	2784
	11th to 20th	Day	18% 2 9% 30% 35% 6%	3104
	21st to end	Day	25% 5% 9% 28% 24% 8%	4092
January	1st to 10th	Night	29% 4 7% 31% 24% 5%	8202
	11th to 20th	Night	23% 5% 10% 23% 27% 12%	8250
	21st to end	Night	27% 4 7% 25% 26% 10%	8517
February	1st to 10th	Night	28% 5% 10% 25% 24% 8%	2612
	11th to 20th	Night	33% 5% 11% 27% 19% 5%	2398
	21st to end	Night	24% 3 7% 23% 29% 14%	1980
March	1st to 10th	Night	24% 5% 6% 15% 34% 15%	5374
	11th to 20th	Night	29% 5% 11% 15% 28% 12%	5282
	21st to end	Night	30% 7% 13% 31% 17% 2	4984
April	1st to 10th	Night	30% 6% 11% 23% 22% 9%	2000
	11th to 20th	Night	32% 7% 12% 24% 19% 7%	1977
	21st to end	Night	36% 6% 12% 25% 18% 4	1985
May	1st to 10th	Night	33% 8% 14% 27% 13% 5%	4080
	11th to 20th	Night	29% 8% 15% 24% 17% 7%	3996
	21st to end	Night	38% 8% 15% 23% 12% 4	3972
June	1st to 10th	Night	24% 9% 23% 25% 14% 4	1600
	11th to 20th	Night	23% 8% 16% 23% 20% 12%	1600
	21st to end	Night	31% 7% 11% 23% 19% 9%	1600
July	1st to 10th	Night	31% 7% 13% 26% 20% 3	3600
	11th to 20th	Night	31% 7% 19% 20% 19% 4	3592
	21st to end	Night	35% 8% 13% 16% 20% 8%	3856
August	1st to 10th	Night	45% 8% 15% 18% 9% 4	3038
	11th to 20th	Night	38% 8% 13% 22% 16% 3	3243
	21st to end	Night	28% 8% 14% 26% 17% 6%	3597
September	1st to 10th	Night	27% 6% 11% 19% 26% 11%	2000
	11th to 20th	Night	21% 5% 12% 23% 26% 14%	2103
	21st to end	Night	21% 5% 7% 23% 32% 12%	2200
October	1st to 10th	Night	18% 5% 6% 18% 32% 21%	3656
	11th to 20th	Night	22% 4 8% 27% 27% 11%	3898
	21st to end	Night	21% 4 7% 26% 30% 13%	4480
November	1st to 10th	Night	18% 4 9% 25% 28% 15%	2665
	11th to 20th	Night	17% 3 7% 27% 33% 12%	2730
	21st to end	Night	24% 3 9% 22% 29% 13%	2730
December	1st to 10th	Night	17% 3 8% 33% 30% 9%	4611
	11th to 20th	Night	21% 3 6% 30% 33% 6%	5322
	21st to end	Night	27% 5% 10% 24% 27% 7%	7128

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	5% 8% 31% 35% 17% 4	330
	11th to 20th	Day	10% 12% 27% 38% 12% 1	330
	21st to end	Day	6% 10% 36% 32% 14% 3	363
February	1st to 10th	Day	5% 10% 43% 31% 9% 2	330
	11th to 20th	Day	3 7% 48% 29% 12% 2	315
	21st to end	Day	4 12% 43% 27% 12% 2	249
March	1st to 10th	Day	4 10% 33% 30% 17% 6%	300
	11th to 20th	Day	10% 11% 33% 28% 14% 3	347
	21st to end	Day	11% 18% 33% 26% 10% 2	550
April	1st to 10th	Day	9% 17% 35% 23% 12% 3	500
	11th to 20th	Day	12% 15% 40% 22% 10% 2	492
	21st to end	Day	13% 15% 33% 26% 11% 2	512
May	1st to 10th	Day	12% 15% 29% 28% 13% 4	703
	11th to 20th	Day	13% 9% 27% 29% 19% 4	725
	21st to end	Day	11% 10% 29% 27% 18% 5%	789
June	1st to 10th	Day	7% 5% 21% 31% 26% 10%	730
	11th to 20th	Day	5% 7% 25% 31% 24% 7%	730
	21st to end	Day	4 4 24% 36% 23% 8%	730
July	1st to 10th	Day	5% 3 17% 33% 31% 11%	721
	11th to 20th	Day	4 1 11% 34% 37% 13%	718
	21st to end	Day	7% 2 10% 31% 36% 14%	794
August	1st to 10th	Day	5% 2 14% 35% 30% 13%	588
	11th to 20th	Day	4 3 20% 35% 28% 11%	517
	21st to end	Day	3 2 19% 38% 28% 10%	583
September	1st to 10th	Day	4 2 18% 37% 26% 12%	530
	11th to 20th	Day	3 5% 18% 39% 25% 10%	425
	21st to end	Day	9% 6% 18% 24% 29% 14%	330
October	1st to 10th	Day	9% 4 23% 26% 23% 15%	330
	11th to 20th	Day	5% 5% 31% 33% 18% 8%	330
	21st to end	Day	6% 12% 30% 25% 21% 6%	363
November	1st to 10th	Day	6% 10% 29% 30% 22% 4	330
	11th to 20th	Day	5% 5% 32% 34% 20% 4	330
	21st to end	Day	8% 10% 28% 33% 16% 5%	330
December	1st to 10th	Day	7% 9% 30% 36% 14% 3	330
	11th to 20th	Day	6% 9% 34% 31% 17% 2	330
	21st to end	Day	7% 13% 32% 37% 10% 1	363
January	1st to 10th	Night	7% 5% 35% 39% 12% 2	1050
	11th to 20th	Night	5% 8% 37% 36% 11% 1	1050
	21st to end	Night	3 8% 37% 42% 9% 1	980
February	1st to 10th	Night	6% 6% 43% 39% 6% 1	840
	11th to 20th	Night	6% 6% 44% 35% 9% 1	804
	21st to end	Night	6% 6% 41% 39% 7%	660
March	1st to 10th	Night	7% 10% 35% 37% 11% 1	800
	11th to 20th	Night	9% 8% 37% 35% 10% 1	790
	21st to end	Night	9% 10% 40% 34% 8%	660
April	1st to 10th	Night	11% 12% 39% 31% 7%	600
	11th to 20th	Night	15% 10% 38% 31% 7%	593
	21st to end	Night	13% 14% 30% 32% 10% 1	600
May	1st to 10th	Night	12% 10% 31% 35% 11% 1	600
	11th to 20th	Night	14% 6% 29% 36% 14% 1	591
	21st to end	Night	14% 9% 33% 33% 10% 1	650
June	1st to 10th	Night	6% 5% 27% 42% 19% 1	600
	11th to 20th	Night	5% 5% 35% 43% 12%	600
	21st to end	Night	6% 3 27% 46% 18%	600
July	1st to 10th	Night	6% 3 19% 47% 23% 2	585
	11th to 20th	Night	5% 3 9% 49% 31% 2	582
	21st to end	Night	7% 2 12% 43% 33% 3	657
August	1st to 10th	Night	7% 2 16% 43% 29% 3	597
	11th to 20th	Night	6% 3 15% 53% 22% 1	594
	21st to end	Night	7% 2 13% 46% 28% 3	660
September	1st to 10th	Night	8% 2 17% 49% 23% 1	600
	11th to 20th	Night	6% 4 21% 45% 22% 3	600
	21st to end	Night	7% 4 25% 42% 20% 2	600
October	1st to 10th	Night	11% 7% 27% 38% 15% 3	640
	11th to 20th	Night	5% 6% 32% 36% 18% 3	800
	21st to end	Night	7% 8% 28% 36% 17% 3	1020
November	1st to 10th	Night	5% 5% 29% 43% 16% 2	1025
	11th to 20th	Night	5% 6% 33% 41% 13% 2	1050
	21st to end	Night	6% 8% 31% 39% 14% 2	1050
December	1st to 10th	Night	5% 6% 36% 40% 11% 2	1050
	11th to 20th	Night	6% 6% 36% 38% 12% 2	1050
	21st to end	Night	6% 10% 37% 37% 10% 1	1155

Page generated at 2026-02-12 23:42:11. Version ac07

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