Largo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Largo clear sky chart from 2005-11-06 to 2025-12-03.

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% 4 2 6% 4 5% 5% 5% 8% 11% 43%	126880
	Night	8% 5% 2 6% 5% 5% 5% 4 7% 10% 44%	123823
Transparency	Day	20% 41% 13% 14% 9% 3	130653
	Night	23% 40% 12% 13% 9% 3	128119
Seeing	Day	8% 6% 20% 29% 24% 12%	16871
	Night	9% 5% 20% 32% 26% 9%	26887

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	9% 6% 2 6% 4 4 4 4 5% 8% 49%	4056
	11th to 20th	Day	21% 8% 3 7% 5% 4 4 3 5% 8% 31%	4060
	21st to end	Day	13% 5% 2 5% 3 3 5% 4 6% 9% 44%	4940
February	1st to 10th	Day	12% 5% 2 5% 3 3 5% 3 6% 8% 46%	2000
	11th to 20th	Day	9% 4 1 5% 3 4 4 3 5% 6% 55%	1948
	21st to end	Day	7% 5% 3 5% 3 3 3 3 5% 7% 55%	1675
March	1st to 10th	Day	8% 4 2 6% 4 4 4 4 5% 8% 49%	4935
	11th to 20th	Day	6% 3 1 4 3 3 3 3 6% 9% 60%	4980
	21st to end	Day	8% 4 2 5% 3 4 4 4 7% 9% 51%	5465
April	1st to 10th	Day	7% 3 1 3 3 4 4 4 7% 10% 55%	2200
	11th to 20th	Day	8% 4 2 6% 4 4 3 4 7% 8% 51%	2176
	21st to end	Day	5% 3 1 3 3 3 4 4 7% 8% 59%	2406
May	1st to 10th	Day	3 2 1 3 2 3 4 3 7% 10% 61%	5862
	11th to 20th	Day	9% 4 2 4 4 4 4 4 6% 9% 51%	5861
	21st to end	Day	3 3 1 4 3 3 4 4 7% 12% 56%	6433
June	1st to 10th	Day	10% 5% 3 8% 5% 7% 5% 6% 8% 11% 33%	2600
	11th to 20th	Day	5% 5% 2 5% 5% 6% 8% 6% 10% 13% 34%	2600
	21st to end	Day	7% 5% 2 6% 6% 6% 8% 6% 10% 13% 30%	2600
July	1st to 10th	Day	5% 4 2 7% 6% 7% 9% 8% 12% 16% 24%	5900
	11th to 20th	Day	3 3 2 7% 6% 8% 10% 8% 13% 15% 25%	5900
	21st to end	Day	3 4 2 6% 6% 6% 8% 8% 12% 17% 28%	6424
August	1st to 10th	Day	7% 4 2 7% 7% 6% 8% 7% 10% 14% 29%	4113
	11th to 20th	Day	4 4 2 5% 4 6% 7% 6% 10% 14% 37%	3849
	21st to end	Day	6% 4 2 7% 7% 6% 8% 7% 11% 14% 25%	3987
September	1st to 10th	Day	7% 6% 3 7% 6% 7% 7% 7% 11% 14% 25%	2200
	11th to 20th	Day	9% 7% 2 7% 7% 6% 7% 6% 8% 11% 30%	2200
	21st to end	Day	7% 6% 3 8% 6% 5% 6% 5% 9% 11% 34%	2200
October	1st to 10th	Day	8% 6% 3 8% 5% 6% 6% 5% 7% 10% 37%	2200
	11th to 20th	Day	5% 4 2 5% 4 4 4 4 6% 9% 54%	2071
	21st to end	Day	7% 4 2 6% 4 3 4 4 6% 9% 52%	2200
November	1st to 10th	Day	8% 4 2 4 4 4 4 4 6% 8% 52%	2057
	11th to 20th	Day	8% 5% 2 5% 4 4 4 5% 5% 8% 51%	2100
	21st to end	Day	7% 5% 2 5% 4 4 4 5% 6% 9% 50%	1895
December	1st to 10th	Day	4 3 1 4 4 3 4 3 5% 9% 60%	2948
	11th to 20th	Day	8% 5% 2 6% 4 4 4 3 6% 7% 50%	3373
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 5% 7% 39%	4466
January	1st to 10th	Night	8% 5% 3 6% 4 4 3 3 5% 8% 49%	5889
	11th to 20th	Night	19% 10% 4 9% 5% 4 5% 4 6% 7% 28%	5900
	21st to end	Night	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	6012
February	1st to 10th	Night	11% 7% 2 6% 3 4 5% 4 5% 7% 47%	2400
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 5% 7% 51%	2338
	21st to end	Night	7% 6% 2 5% 4 4 4 3 5% 7% 53%	1952
March	1st to 10th	Night	10% 5% 3 7% 5% 4 4 3 6% 7% 46%	4918
	11th to 20th	Night	4 3 1 4 3 3 4 4 7% 10% 58%	4980
	21st to end	Night	9% 5% 2 5% 4 4 4 4 5% 7% 51%	5467
April	1st to 10th	Night	6% 4 2 4 4 3 4 4 8% 9% 53%	2200
	11th to 20th	Night	7% 4 2 5% 4 4 5% 4 6% 9% 51%	2173
	21st to end	Night	6% 3 1 4 3 4 4 3 5% 7% 59%	2004
May	1st to 10th	Night	3 2 1 3 4 4 4 4 7% 10% 58%	4033
	11th to 20th	Night	9% 4 2 5% 3 3 4 4 5% 8% 54%	4032
	21st to end	Night	3 3 1 4 3 4 4 5% 6% 10% 58%	4421
June	1st to 10th	Night	11% 5% 3 6% 5% 4 5% 4 6% 12% 40%	1800
	11th to 20th	Night	5% 4 2 6% 6% 5% 5% 7% 9% 12% 39%	1800
	21st to end	Night	7% 5% 2 6% 5% 5% 7% 5% 9% 13% 36%	1800
July	1st to 10th	Night	4 4 3 9% 7% 8% 8% 8% 10% 15% 24%	4058
	11th to 20th	Night	3 3 2 7% 6% 7% 8% 7% 12% 15% 29%	4057
	21st to end	Night	3 4 2 9% 8% 7% 8% 8% 12% 15% 23%	4427
August	1st to 10th	Night	5% 4 2 6% 5% 5% 7% 6% 10% 13% 36%	3029
	11th to 20th	Night	3 3 2 5% 4 5% 7% 6% 9% 16% 40%	3200
	21st to end	Night	6% 5% 3 9% 6% 7% 7% 5% 10% 13% 29%	3877
September	1st to 10th	Night	6% 5% 2 9% 7% 7% 7% 7% 10% 13% 27%	2200
	11th to 20th	Night	8% 7% 3 9% 7% 6% 6% 6% 9% 9% 31%	2200
	21st to end	Night	8% 5% 2 8% 6% 5% 7% 5% 8% 9% 37%	2200
October	1st to 10th	Night	9% 6% 2 7% 5% 4 6% 4 8% 9% 39%	2200
	11th to 20th	Night	6% 4 1 5% 4 4 5% 4 6% 8% 52%	2326
	21st to end	Night	8% 5% 2 6% 4 4 4 3 5% 9% 49%	2640
November	1st to 10th	Night	8% 4 2 5% 4 4 5% 3 5% 9% 52%	2461
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 6% 7% 50%	2520
	21st to end	Night	6% 6% 2 6% 4 5% 4 4 6% 9% 47%	2720
December	1st to 10th	Night	5% 3 1 4 3 3 3 3 5% 9% 61%	4277
	11th to 20th	Night	10% 6% 2 6% 4 4 3 3 5% 7% 51%	4822
	21st to end	Night	13% 7% 3 7% 6% 5% 5% 5% 6% 8% 35%	6490

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	25% 27% 7% 12% 19% 9%	4057
	11th to 20th	Day	45% 27% 3 12% 10% 4	4060
	21st to end	Day	27% 29% 7% 22% 12% 3	4940
February	1st to 10th	Day	12% 63% 5% 8% 8% 4	2000
	11th to 20th	Day	8% 61% 3 11% 13% 4	1958
	21st to end	Day	12% 62% 5% 9% 8% 4	1675
March	1st to 10th	Day	27% 31% 11% 14% 12% 4	4935
	11th to 20th	Day	16% 29% 9% 17% 14% 15%	4980
	21st to end	Day	21% 31% 6% 24% 15% 3	5465
April	1st to 10th	Day	8% 63% 7% 12% 7% 4	2200
	11th to 20th	Day	8% 63% 6% 7% 11% 5%	2176
	21st to end	Day	7% 63% 5% 12% 12% 1	2406
May	1st to 10th	Day	14% 32% 22% 21% 9% 2	5897
	11th to 20th	Day	22% 30% 15% 23% 10% 1	5865
	21st to end	Day	11% 32% 17% 29% 11%	6447
June	1st to 10th	Day	15% 65% 11% 8% 2	2600
	11th to 20th	Day	16% 66% 10% 7%	2600
	21st to end	Day	10% 67% 15% 8% 1	2600
July	1st to 10th	Day	27% 36% 32% 5%	5835
	11th to 20th	Day	27% 38% 31% 5%	5831
	21st to end	Day	25% 38% 23% 13%	6240
August	1st to 10th	Day	25% 43% 20% 8% 3	4100
	11th to 20th	Day	15% 43% 22% 18% 3	3885
	21st to end	Day	24% 44% 23% 10%	3987
September	1st to 10th	Day	17% 63% 12% 7%	2200
	11th to 20th	Day	15% 60% 13% 8% 3	2200
	21st to end	Day	16% 60% 7% 12% 4 1	2200
October	1st to 10th	Day	41% 42% 8% 6% 3	3590
	11th to 20th	Day	12% 36% 5% 14% 29% 4	3350
	21st to end	Day	16% 36% 5% 17% 21% 5%	3538
November	1st to 10th	Day	13% 55% 6% 13% 9% 4	2057
	11th to 20th	Day	16% 55% 5% 11% 7% 6%	2100
	21st to end	Day	14% 55% 4 14% 9% 4	1895
December	1st to 10th	Day	12% 36% 11% 19% 17% 5%	2948
	11th to 20th	Day	20% 33% 7% 14% 16% 9%	3370
	21st to end	Day	35% 29% 8% 18% 8% 2	4466
January	1st to 10th	Night	25% 27% 6% 13% 25% 4	5889
	11th to 20th	Night	47% 28% 6% 9% 9% 1	5900
	21st to end	Night	30% 30% 6% 17% 13% 4	6012
February	1st to 10th	Night	14% 63% 6% 9% 7% 2	2400
	11th to 20th	Night	10% 61% 4 9% 12% 4	2339
	21st to end	Night	12% 62% 5% 8% 11% 2	1952
March	1st to 10th	Night	31% 30% 9% 13% 12% 5%	4918
	11th to 20th	Night	14% 30% 14% 14% 14% 14%	4980
	21st to end	Night	25% 30% 6% 19% 16% 3	5467
April	1st to 10th	Night	9% 62% 8% 12% 7% 2	2200
	11th to 20th	Night	10% 63% 5% 9% 10% 4	2173
	21st to end	Night	8% 62% 6% 12% 11% 2	2004
May	1st to 10th	Night	15% 33% 19% 23% 7% 2	4060
	11th to 20th	Night	21% 30% 13% 23% 12% 1	4033
	21st to end	Night	13% 31% 15% 30% 10%	4429
June	1st to 10th	Night	14% 63% 11% 10% 2	1800
	11th to 20th	Night	16% 66% 11% 7%	1800
	21st to end	Night	11% 65% 14% 7% 2	1800
July	1st to 10th	Night	34% 35% 28% 3	4015
	11th to 20th	Night	28% 37% 31% 4	4006
	21st to end	Night	36% 35% 19% 9%	4297
August	1st to 10th	Night	23% 43% 20% 8% 5%	3018
	11th to 20th	Night	15% 42% 25% 17% 1	3230
	21st to end	Night	26% 44% 21% 7% 1	3877
September	1st to 10th	Night	20% 62% 10% 7% 1	2200
	11th to 20th	Night	16% 60% 13% 9% 2	2200
	21st to end	Night	17% 60% 10% 10% 4	2200
October	1st to 10th	Night	44% 40% 7% 6% 3	3590
	11th to 20th	Night	13% 37% 5% 19% 22% 4	3786
	21st to end	Night	17% 36% 5% 19% 20% 3	4252
November	1st to 10th	Night	14% 54% 9% 11% 9% 4	2461
	11th to 20th	Night	17% 55% 5% 9% 11% 4	2520
	21st to end	Night	15% 55% 4 13% 9% 5%	2720
December	1st to 10th	Night	10% 35% 13% 21% 11% 9%	4277
	11th to 20th	Night	20% 33% 9% 15% 16% 7%	4824
	21st to end	Night	36% 30% 11% 14% 8% 1	6490

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	9% 16% 46% 24% 5%	300
	11th to 20th	Day	11% 18% 34% 28% 8% 1	300
	21st to end	Day	16% 17% 40% 24% 3	330
February	1st to 10th	Day	9% 13% 30% 33% 13% 1	300
	11th to 20th	Day	9% 11% 39% 29% 9% 2	300
	21st to end	Day	5% 14% 35% 32% 12% 1	274
March	1st to 10th	Day	5% 14% 42% 31% 8% 1	500
	11th to 20th	Day	11% 12% 28% 33% 15% 1	500
	21st to end	Day	5% 11% 35% 32% 15% 2	550
April	1st to 10th	Day	7% 12% 34% 32% 13% 2	500
	11th to 20th	Day	7% 11% 30% 35% 14% 3	492
	21st to end	Day	5% 5% 25% 37% 23% 4	500
May	1st to 10th	Day	5% 5% 25% 38% 20% 7%	503
	11th to 20th	Day	9% 4 20% 34% 24% 9%	527
	21st to end	Day	7% 3 11% 32% 32% 15%	573
June	1st to 10th	Day	12% 2 9% 34% 29% 14%	530
	11th to 20th	Day	7% 3 9% 28% 32% 22%	530
	21st to end	Day	4 1 6% 22% 35% 32%	530
July	1st to 10th	Day	5% 1 4 18% 35% 37%	525
	11th to 20th	Day	6% 3 18% 36% 36%	524
	21st to end	Day	10% 2 5% 18% 37% 28%	576
August	1st to 10th	Day	7% 1 4 18% 37% 32%	526
	11th to 20th	Day	8% 2 4 14% 36% 36%	519
	21st to end	Day	10% 2 6% 22% 36% 25%	583
September	1st to 10th	Day	8% 3 6% 21% 39% 23%	530
	11th to 20th	Day	11% 3 8% 26% 35% 18%	530
	21st to end	Day	7% 3 8% 29% 37% 16%	530
October	1st to 10th	Day	13% 2 19% 36% 24% 5%	530
	11th to 20th	Day	6% 5% 19% 36% 28% 5%	530
	21st to end	Day	9% 5% 23% 39% 22% 3	583
November	1st to 10th	Day	10% 5% 24% 39% 19% 4	535
	11th to 20th	Day	12% 7% 23% 39% 15% 3	540
	21st to end	Day	7% 9% 34% 30% 17% 2	335
December	1st to 10th	Day	6% 11% 37% 31% 11% 4	306
	11th to 20th	Day	11% 8% 38% 30% 11% 1	300
	21st to end	Day	9% 15% 27% 37% 12% 1	330
January	1st to 10th	Night	11% 11% 32% 31% 14% 1	800
	11th to 20th	Night	13% 11% 24% 37% 14% 1	800
	21st to end	Night	15% 10% 32% 31% 11%	880
February	1st to 10th	Night	12% 8% 30% 34% 15%	800
	11th to 20th	Night	10% 9% 30% 36% 14% 2	783
	21st to end	Night	10% 6% 27% 44% 13%	660
March	1st to 10th	Night	6% 8% 35% 40% 10% 1	800
	11th to 20th	Night	8% 8% 25% 38% 19% 1	800
	21st to end	Night	7% 6% 29% 40% 16% 1	880
April	1st to 10th	Night	7% 8% 25% 41% 18% 1	800
	11th to 20th	Night	7% 7% 30% 39% 16% 1	791
	21st to end	Night	7% 4 27% 42% 20% 1	734
May	1st to 10th	Night	4 2 14% 45% 31% 4	600
	11th to 20th	Night	8% 2 16% 40% 30% 4	591
	21st to end	Night	6% 1 11% 36% 39% 7%	650
June	1st to 10th	Night	12% 3 7% 27% 40% 12%	600
	11th to 20th	Night	5% 2 7% 20% 40% 25%	600
	21st to end	Night	6% 1 6% 16% 42% 30%	600
July	1st to 10th	Night	7% 1 3 10% 43% 36%	585
	11th to 20th	Night	5% 1 1 12% 40% 41%	582
	21st to end	Night	4 2 4 11% 42% 37%	657
August	1st to 10th	Night	5% 1 2 12% 45% 34%	597
	11th to 20th	Night	6% 2 2 9% 42% 39%	594
	21st to end	Night	10% 2 6% 21% 38% 23%	834
September	1st to 10th	Night	9% 2 8% 22% 41% 19%	800
	11th to 20th	Night	10% 3 9% 29% 37% 13%	800
	21st to end	Night	10% 3 10% 29% 37% 11%	800
October	1st to 10th	Night	12% 3 19% 37% 24% 5%	800
	11th to 20th	Night	7% 3 18% 41% 28% 3	800
	21st to end	Night	10% 4 27% 37% 20% 2	880
November	1st to 10th	Night	8% 4 30% 36% 19% 3	820
	11th to 20th	Night	11% 6% 21% 41% 19% 2	840
	21st to end	Night	8% 7% 26% 39% 19% 1	840
December	1st to 10th	Night	8% 5% 28% 36% 22% 1	809
	11th to 20th	Night	10% 6% 28% 35% 20% 1	800
	21st to end	Night	11% 8% 27% 35% 18% 1	880

Page generated at 2025-11-30 01:00:51. Version ac07

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