Ucon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ucon 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	7% 8% 3 6% 4 4 4 3 5% 6% 51%	139791
	Night	9% 10% 3 7% 4 4 4 3 5% 7% 45%	138810
Transparency	Day	34% 5% 11% 21% 19% 11%	134497
	Night	38% 6% 13% 20% 15% 8%	135108
Seeing	Day	13% 11% 24% 28% 18% 6%	16981
	Night	14% 7% 20% 38% 19% 2	26724

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	14% 22% 6% 11% 5% 4 4 2 4 6% 21%	4562
	11th to 20th	Day	7% 12% 5% 11% 5% 4 3 2 4 6% 42%	4895
	21st to end	Day	10% 14% 5% 9% 4 3 3 3 4 6% 38%	5844
February	1st to 10th	Day	12% 15% 6% 11% 5% 5% 5% 4 4 6% 26%	1890
	11th to 20th	Day	12% 14% 6% 10% 6% 5% 5% 3 6% 6% 27%	1856
	21st to end	Day	8% 15% 5% 10% 5% 5% 4 4 5% 6% 33%	1730
March	1st to 10th	Day	9% 13% 5% 9% 5% 4 4 3 5% 7% 35%	4776
	11th to 20th	Day	9% 13% 3 7% 4 4 4 3 4 6% 43%	5000
	21st to end	Day	9% 12% 5% 11% 6% 6% 6% 5% 6% 7% 28%	5486
April	1st to 10th	Day	9% 11% 3 7% 4 4 5% 4 6% 8% 37%	2274
	11th to 20th	Day	7% 10% 3 7% 4 4 3 4 6% 7% 44%	2567
	21st to end	Day	9% 9% 2 8% 4 4 5% 4 6% 8% 40%	2600
May	1st to 10th	Day	8% 7% 3 5% 4 3 4 4 5% 6% 52%	5880
	11th to 20th	Day	8% 6% 2 6% 4 5% 5% 4 6% 7% 46%	5841
	21st to end	Day	6% 7% 2 4 3 3 4 3 4 7% 57%	6876
June	1st to 10th	Day	7% 4 2 5% 5% 4 5% 4 7% 9% 48%	2932
	11th to 20th	Day	7% 5% 2 6% 3 4 4 3 6% 7% 54%	3000
	21st to end	Day	2 2 1 3 2 3 3 3 4 6% 70%	3000
July	1st to 10th	Day	1 2 1 3 3 2 3 3 4 6% 73%	6737
	11th to 20th	Day	1 2 1 2 2 3 3 3 5% 6% 73%	6283
	21st to end	Day	2 2 1 3 2 3 3 3 5% 7% 68%	6401
August	1st to 10th	Day	3 3 1 4 3 3 4 3 5% 7% 62%	5779
	11th to 20th	Day	2 2 1 2 3 3 3 3 4 7% 71%	5798
	21st to end	Day	4 4 1 4 3 3 3 3 5% 5% 65%	6468
September	1st to 10th	Day	4 3 1 3 2 3 3 3 4 5% 70%	2324
	11th to 20th	Day	7% 4 1 4 3 2 3 3 4 7% 62%	2200
	21st to end	Day	7% 5% 1 3 3 2 2 2 5% 6% 64%	2200
October	1st to 10th	Day	7% 4 2 4 2 3 3 2 3 4 66%	3411
	11th to 20th	Day	6% 5% 2 5% 3 4 3 2 4 5% 62%	3250
	21st to end	Day	8% 9% 3 7% 4 3 5% 4 5% 7% 46%	3391
November	1st to 10th	Day	13% 11% 3 6% 4 3 4 3 4 6% 42%	1854
	11th to 20th	Day	11% 11% 3 7% 5% 5% 4 4 6% 8% 38%	1748
	21st to end	Day	9% 14% 4 8% 5% 4 4 3 4 5% 41%	1680
December	1st to 10th	Day	8% 10% 5% 10% 4 3 2 2 4 6% 47%	2700
	11th to 20th	Day	15% 19% 6% 11% 6% 5% 4 3 4 6% 21%	2983
	21st to end	Day	15% 16% 5% 10% 5% 4 4 3 4 7% 26%	3575
January	1st to 10th	Night	14% 18% 6% 14% 5% 4 4 3 4 6% 21%	8371
	11th to 20th	Night	10% 15% 4 11% 5% 3 2 2 4 6% 37%	8069
	21st to end	Night	11% 14% 5% 8% 4 3 3 3 5% 8% 38%	8370
February	1st to 10th	Night	14% 15% 4 9% 5% 5% 4 3 6% 6% 29%	2730
	11th to 20th	Night	14% 16% 5% 8% 5% 4 4 3 5% 6% 31%	2648
	21st to end	Night	9% 13% 6% 12% 5% 5% 4 4 5% 8% 30%	2076
March	1st to 10th	Night	8% 14% 4 8% 5% 5% 4 3 5% 9% 35%	5163
	11th to 20th	Night	7% 10% 3 7% 4 4 4 4 6% 9% 42%	5000
	21st to end	Night	8% 11% 3 8% 5% 5% 6% 5% 7% 9% 35%	5489
April	1st to 10th	Night	10% 11% 3 7% 5% 4 4 3 6% 8% 39%	2121
	11th to 20th	Night	8% 10% 3 7% 5% 5% 4 4 5% 7% 41%	1781
	21st to end	Night	9% 8% 2 7% 4 4 4 3 6% 7% 45%	1800
May	1st to 10th	Night	8% 9% 3 6% 4 4 4 3 5% 6% 49%	4100
	11th to 20th	Night	7% 6% 3 6% 4 5% 5% 4 6% 9% 47%	4074
	21st to end	Night	7% 5% 1 5% 4 4 5% 4 6% 9% 51%	4019
June	1st to 10th	Night	7% 4 1 5% 4 4 6% 4 7% 9% 49%	1463
	11th to 20th	Night	8% 5% 2 5% 4 3 2 4 5% 7% 54%	1400
	21st to end	Night	3 3 1 3 2 2 3 2 4 8% 68%	1400
July	1st to 10th	Night	2 1 1 3 3 3 4 3 5% 5% 69%	3217
	11th to 20th	Night	1 1 1 3 2 3 4 3 5% 8% 70%	3676
	21st to end	Night	2 2 1 3 3 3 4 4 6% 8% 65%	4472
August	1st to 10th	Night	3 3 2 4 2 3 4 3 6% 8% 62%	4033
	11th to 20th	Night	1 1 1 3 3 4 3 3 5% 7% 68%	4051
	21st to end	Night	6% 5% 2 4 3 2 3 3 4 6% 62%	4509
September	1st to 10th	Night	4 3 1 4 2 3 3 3 4 4 69%	2072
	11th to 20th	Night	6% 4 2 4 3 3 4 3 5% 7% 59%	2200
	21st to end	Night	7% 4 1 3 3 2 2 3 5% 6% 64%	2200
October	1st to 10th	Night	5% 3 2 3 3 2 2 2 3 5% 70%	3782
	11th to 20th	Night	10% 7% 2 4 3 3 4 3 4 5% 54%	3898
	21st to end	Night	8% 9% 3 6% 4 4 4 4 5% 8% 46%	4406
November	1st to 10th	Night	12% 10% 3 5% 3 3 4 4 5% 6% 45%	2665
	11th to 20th	Night	11% 12% 3 6% 6% 4 4 4 5% 6% 39%	2848
	21st to end	Night	9% 11% 4 8% 5% 4 4 3 5% 6% 40%	2940
December	1st to 10th	Night	9% 11% 3 8% 5% 3 3 2 4 7% 44%	4710
	11th to 20th	Night	14% 19% 5% 8% 5% 3 4 3 5% 7% 26%	5434
	21st to end	Night	16% 16% 5% 10% 4 4 4 3 4 7% 26%	7623

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	65% 6% 14% 11% 3	4563
	11th to 20th	Day	45% 5% 23% 16% 9% 2	4895
	21st to end	Day	48% 6% 13% 21% 11% 1	5844
February	1st to 10th	Day	58% 8% 12% 16% 4 1	1890
	11th to 20th	Day	55% 9% 13% 16% 5% 1	1865
	21st to end	Day	50% 7% 15% 20% 7% 1	1730
March	1st to 10th	Day	47% 6% 16% 21% 8% 2	4776
	11th to 20th	Day	42% 4 11% 30% 12% 1	5000
	21st to end	Day	52% 9% 17% 18% 4	5486
April	1st to 10th	Day	44% 8% 16% 18% 13% 2	2274
	11th to 20th	Day	38% 6% 12% 26% 15% 3	2570
	21st to end	Day	40% 7% 13% 25% 14% 1	2600
May	1st to 10th	Day	30% 5% 11% 27% 21% 5%	5880
	11th to 20th	Day	33% 6% 9% 25% 19% 6%	5844
	21st to end	Day	26% 6% 8% 34% 23% 3	6877
June	1st to 10th	Day	30% 7% 13% 29% 20% 1	2932
	11th to 20th	Day	28% 6% 10% 22% 23% 12%	3000
	21st to end	Day	15% 3 6% 23% 34% 19%	3000
July	1st to 10th	Day	13% 2 4 11% 29% 40%	6664
	11th to 20th	Day	12% 2 5% 11% 29% 41%	6208
	21st to end	Day	16% 3 5% 11% 37% 29%	6217
August	1st to 10th	Day	21% 4 7% 15% 29% 24%	4208
	11th to 20th	Day	15% 3 5% 20% 37% 20%	4197
	21st to end	Day	16% 3 5% 20% 29% 27%	4663
September	1st to 10th	Day	17% 4 6% 18% 32% 23%	2324
	11th to 20th	Day	23% 4 10% 24% 27% 13%	2200
	21st to end	Day	23% 3 8% 28% 29% 10%	2200
October	1st to 10th	Day	24% 3 7% 21% 35% 10%	3411
	11th to 20th	Day	26% 4 9% 37% 18% 6%	3250
	21st to end	Day	37% 6% 13% 27% 16% 1	3391
November	1st to 10th	Day	43% 5% 17% 23% 11% 1	1854
	11th to 20th	Day	43% 8% 18% 22% 6% 2	1748
	21st to end	Day	46% 5% 19% 21% 7% 1	1680
December	1st to 10th	Day	40% 6% 24% 25% 4 1	2700
	11th to 20th	Day	64% 6% 14% 13% 2	2981
	21st to end	Day	58% 7% 15% 15% 6%	3575
January	1st to 10th	Night	64% 6% 10% 16% 4	8372
	11th to 20th	Night	49% 6% 23% 16% 5% 1	8069
	21st to end	Night	45% 6% 15% 22% 9% 3	8370
February	1st to 10th	Night	55% 7% 15% 16% 6% 1	2730
	11th to 20th	Night	53% 7% 13% 19% 7% 1	2649
	21st to end	Night	52% 7% 14% 17% 8% 1	2076
March	1st to 10th	Night	45% 7% 14% 22% 9% 2	5163
	11th to 20th	Night	38% 6% 14% 29% 13% 1	5000
	21st to end	Night	42% 9% 17% 25% 6%	5489
April	1st to 10th	Night	43% 7% 14% 21% 13% 3	2121
	11th to 20th	Night	41% 6% 11% 24% 16% 2	1781
	21st to end	Night	36% 6% 13% 27% 17% 1	1800
May	1st to 10th	Night	34% 6% 10% 24% 23% 3	4097
	11th to 20th	Night	30% 6% 12% 27% 19% 5%	4075
	21st to end	Night	26% 7% 11% 25% 27% 4	4019
June	1st to 10th	Night	29% 9% 13% 22% 24% 3	1463
	11th to 20th	Night	29% 5% 9% 21% 25% 12%	1400
	21st to end	Night	16% 3 6% 19% 31% 25%	1400
July	1st to 10th	Night	16% 3 5% 11% 22% 44%	3182
	11th to 20th	Night	12% 2 4 11% 27% 44%	3628
	21st to end	Night	15% 3 5% 11% 30% 34%	4344
August	1st to 10th	Night	19% 3 6% 12% 29% 29%	2928
	11th to 20th	Night	17% 3 5% 20% 32% 23%	2928
	21st to end	Night	17% 3 5% 17% 27% 31%	3245
September	1st to 10th	Night	19% 3 6% 13% 32% 27%	2072
	11th to 20th	Night	24% 5% 8% 22% 25% 17%	2200
	21st to end	Night	22% 4 7% 24% 32% 11%	2200
October	1st to 10th	Night	20% 3 7% 20% 36% 15%	3782
	11th to 20th	Night	33% 4 7% 33% 17% 7%	3898
	21st to end	Night	36% 5% 12% 28% 17% 1	4406
November	1st to 10th	Night	38% 6% 15% 25% 13% 2	2665
	11th to 20th	Night	44% 7% 17% 23% 7% 2	2848
	21st to end	Night	45% 5% 18% 21% 9% 1	2940
December	1st to 10th	Night	42% 5% 25% 23% 4 1	4710
	11th to 20th	Night	57% 7% 20% 13% 2	5435
	21st to end	Night	58% 6% 13% 15% 7%	7623

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	26% 10% 18% 23% 20% 4	220
	11th to 20th	Day	18% 7% 19% 29% 23% 4	248
	21st to end	Day	19% 10% 18% 33% 18% 1	363
February	1st to 10th	Day	23% 13% 25% 24% 13% 1	330
	11th to 20th	Day	21% 15% 24% 27% 12% 1	341
	21st to end	Day	19% 18% 26% 27% 8% 1	446
March	1st to 10th	Day	17% 19% 29% 25% 8% 2	509
	11th to 20th	Day	13% 16% 32% 25% 13% 2	500
	21st to end	Day	18% 21% 30% 22% 8% 1	550
April	1st to 10th	Day	18% 17% 28% 22% 13% 3	500
	11th to 20th	Day	16% 19% 31% 22% 10% 2	492
	21st to end	Day	15% 10% 31% 27% 12% 4	500
May	1st to 10th	Day	12% 14% 25% 28% 15% 6%	503
	11th to 20th	Day	12% 14% 29% 24% 16% 5%	528
	21st to end	Day	15% 8% 20% 26% 21% 9%	766
June	1st to 10th	Day	8% 10% 24% 29% 21% 8%	730
	11th to 20th	Day	13% 13% 25% 31% 16% 2	730
	21st to end	Day	4 7% 26% 32% 25% 6%	730
July	1st to 10th	Day	3 7% 23% 34% 27% 6%	705
	11th to 20th	Day	2 8% 25% 37% 21% 5%	524
	21st to end	Day	3 5% 22% 33% 27% 10%	575
August	1st to 10th	Day	5% 6% 26% 31% 25% 7%	527
	11th to 20th	Day	5% 4 21% 34% 24% 11%	517
	21st to end	Day	6% 10% 22% 28% 22% 13%	583
September	1st to 10th	Day	4 6% 23% 27% 29% 12%	530
	11th to 20th	Day	10% 9% 24% 29% 19% 9%	530
	21st to end	Day	9% 10% 22% 25% 23% 12%	530
October	1st to 10th	Day	12% 7% 16% 29% 24% 11%	419
	11th to 20th	Day	12% 13% 19% 23% 18% 14%	330
	21st to end	Day	18% 13% 17% 29% 20% 4	363
November	1st to 10th	Day	24% 9% 20% 24% 15% 8%	330
	11th to 20th	Day	16% 10% 21% 33% 15% 5%	330
	21st to end	Day	17% 8% 21% 32% 21% 2	330
December	1st to 10th	Day	23% 9% 19% 27% 15% 6%	330
	11th to 20th	Day	29% 9% 21% 25% 14% 2	300
	21st to end	Day	29% 11% 17% 23% 15% 6%	242
January	1st to 10th	Night	23% 8% 15% 34% 18% 2	913
	11th to 20th	Night	23% 7% 15% 35% 18% 3	840
	21st to end	Night	19% 5% 18% 40% 16% 2	924
February	1st to 10th	Night	24% 8% 23% 32% 13% 1	840
	11th to 20th	Night	22% 8% 20% 35% 13% 2	824
	21st to end	Night	14% 11% 24% 36% 12% 2	692
March	1st to 10th	Night	15% 10% 23% 36% 14% 1	808
	11th to 20th	Night	12% 9% 25% 37% 16% 2	800
	21st to end	Night	15% 8% 26% 38% 12% 1	880
April	1st to 10th	Night	16% 8% 26% 34% 15% 1	750
	11th to 20th	Night	13% 11% 31% 35% 9% 1	593
	21st to end	Night	13% 7% 25% 40% 15% 2	600
May	1st to 10th	Night	11% 8% 25% 36% 19% 1	600
	11th to 20th	Night	10% 7% 25% 32% 23% 3	591
	21st to end	Night	13% 6% 21% 40% 17% 3	650
June	1st to 10th	Night	8% 8% 20% 37% 24% 2	463
	11th to 20th	Night	9% 10% 28% 37% 17% 1	400
	21st to end	Night	4 3 20% 46% 24% 5%	400
July	1st to 10th	Night	3 1 17% 47% 28% 3	390
	11th to 20th	Night	2 1 16% 55% 25%	398
	21st to end	Night	3 1 19% 45% 30% 3	657
August	1st to 10th	Night	5% 4 17% 48% 25% 1	597
	11th to 20th	Night	3 2 18% 44% 30% 3	594
	21st to end	Night	6% 5% 16% 44% 27% 2	660
September	1st to 10th	Night	5% 2 18% 43% 27% 5%	697
	11th to 20th	Night	8% 4 15% 38% 29% 6%	800
	21st to end	Night	9% 4 17% 38% 26% 7%	800
October	1st to 10th	Night	11% 5% 18% 39% 26% 2	800
	11th to 20th	Night	13% 8% 20% 33% 22% 4	800
	21st to end	Night	11% 8% 20% 40% 16% 4	880
November	1st to 10th	Night	17% 8% 22% 33% 18% 2	820
	11th to 20th	Night	17% 9% 23% 36% 13% 1	958
	21st to end	Night	16% 8% 19% 36% 20% 1	1050
December	1st to 10th	Night	20% 9% 19% 36% 14% 3	1050
	11th to 20th	Night	23% 10% 17% 36% 13% 1	1050
	21st to end	Night	27% 9% 19% 31% 12% 1	1155

Page generated at 2026-02-27 23:40:24. Version ac07

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