LAT26 RAO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the LAT26 RAO clear sky chart from 2005-11-06 to 2026-01-02.

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% 5% 2 7% 6% 6% 7% 6% 8% 11% 35%	126615
	Night	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 42%	124746
Transparency	Day	37% 11% 19% 21% 10% 2	130268
	Night	35% 10% 19% 22% 11% 2	129149
Seeing	Day	7% 4 20% 31% 25% 13%	17621
	Night	8% 4 17% 32% 28% 11%	27751

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	7% 5% 2 6% 4 4 4 4 6% 10% 48%	4065
	11th to 20th	Day	17% 7% 3 8% 6% 5% 6% 4 7% 9% 28%	4060
	21st to end	Day	10% 7% 3 8% 6% 5% 5% 4 6% 8% 39%	4528
February	1st to 10th	Day	9% 7% 3 6% 5% 5% 5% 5% 6% 10% 40%	2000
	11th to 20th	Day	7% 5% 2 5% 4 4 4 5% 7% 9% 48%	2076
	21st to end	Day	7% 5% 2 6% 5% 4 5% 5% 7% 10% 43%	1815
March	1st to 10th	Day	5% 4 2 7% 6% 6% 6% 6% 8% 10% 40%	4935
	11th to 20th	Day	4 3 1 3 3 3 4 5% 6% 9% 59%	4980
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 9% 42%	5465
April	1st to 10th	Day	4 3 2 5% 5% 5% 5% 6% 8% 13% 45%	2200
	11th to 20th	Day	6% 4 2 7% 5% 5% 6% 5% 8% 10% 41%	2278
	21st to end	Day	6% 4 1 6% 5% 6% 6% 5% 9% 10% 42%	2400
May	1st to 10th	Day	2 2 1 3 4 4 5% 5% 8% 11% 55%	5405
	11th to 20th	Day	6% 5% 2 5% 5% 5% 5% 5% 8% 10% 44%	5440
	21st to end	Day	4 4 2 6% 5% 6% 8% 7% 10% 11% 36%	6433
June	1st to 10th	Day	13% 9% 4 11% 8% 9% 8% 6% 8% 8% 16%	2600
	11th to 20th	Day	8% 7% 3 11% 8% 8% 7% 7% 9% 11% 20%	2600
	21st to end	Day	7% 7% 3 9% 8% 8% 9% 8% 10% 11% 20%	2600
July	1st to 10th	Day	5% 7% 3 9% 7% 7% 7% 7% 9% 13% 24%	5900
	11th to 20th	Day	5% 5% 3 9% 7% 7% 9% 7% 10% 12% 27%	5900
	21st to end	Day	3 3 2 6% 5% 5% 7% 6% 10% 16% 36%	6424
August	1st to 10th	Day	4 5% 3 11% 8% 8% 9% 9% 11% 13% 19%	4139
	11th to 20th	Day	4 4 2 7% 6% 8% 9% 9% 12% 14% 25%	3850
	21st to end	Day	5% 5% 2 7% 7% 9% 9% 8% 12% 17% 19%	4031
September	1st to 10th	Day	7% 7% 3 11% 7% 10% 9% 7% 9% 12% 18%	2200
	11th to 20th	Day	7% 6% 3 11% 9% 9% 9% 8% 8% 10% 20%	2200
	21st to end	Day	11% 9% 4 10% 7% 8% 7% 7% 8% 9% 19%	2200
October	1st to 10th	Day	8% 8% 3 10% 7% 8% 8% 7% 9% 11% 20%	2096
	11th to 20th	Day	10% 5% 3 9% 7% 6% 9% 7% 8% 10% 27%	2000
	21st to end	Day	11% 6% 3 8% 5% 5% 6% 6% 5% 11% 35%	2200
November	1st to 10th	Day	8% 5% 2 7% 5% 6% 7% 6% 9% 10% 36%	2057
	11th to 20th	Day	9% 6% 3 9% 8% 6% 6% 6% 6% 9% 32%	2100
	21st to end	Day	8% 5% 2 7% 5% 5% 6% 6% 8% 9% 39%	2100
December	1st to 10th	Day	5% 4 2 5% 4 4 5% 5% 7% 7% 52%	3310
	11th to 20th	Day	8% 5% 2 7% 5% 6% 6% 5% 8% 11% 37%	3463
	21st to end	Day	11% 6% 3 8% 6% 6% 7% 5% 8% 10% 30%	4565
January	1st to 10th	Night	6% 5% 2 7% 5% 5% 5% 5% 7% 10% 44%	5903
	11th to 20th	Night	15% 9% 3 9% 5% 5% 5% 4 5% 7% 31%	5900
	21st to end	Night	10% 9% 3 7% 5% 4 4 4 5% 7% 41%	6424
February	1st to 10th	Night	8% 6% 2 5% 4 5% 4 4 7% 10% 47%	2400
	11th to 20th	Night	6% 4 1 5% 3 3 4 4 6% 7% 56%	2207
	21st to end	Night	5% 3 2 5% 3 4 5% 4 6% 9% 55%	1815
March	1st to 10th	Night	5% 4 2 6% 4 4 5% 4 6% 8% 51%	4918
	11th to 20th	Night	4 3 1 4 3 4 4 3 5% 9% 60%	4980
	21st to end	Night	6% 4 2 6% 4 5% 5% 4 6% 8% 49%	5467
April	1st to 10th	Night	3 3 1 4 3 3 4 4 7% 10% 58%	2200
	11th to 20th	Night	4 3 2 4 4 5% 5% 4 7% 9% 52%	2070
	21st to end	Night	6% 5% 2 4 4 3 4 4 7% 10% 52%	2000
May	1st to 10th	Night	2 2 1 2 3 3 4 4 7% 11% 61%	4490
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 7% 9% 51%	4490
	21st to end	Night	4 4 2 6% 5% 5% 6% 6% 9% 12% 42%	4424
June	1st to 10th	Night	11% 8% 3 10% 7% 6% 7% 7% 7% 10% 26%	1800
	11th to 20th	Night	7% 6% 3 6% 5% 5% 6% 6% 8% 14% 34%	1800
	21st to end	Night	5% 5% 2 6% 6% 6% 7% 7% 11% 13% 31%	1800
July	1st to 10th	Night	4 6% 3 8% 6% 6% 6% 5% 8% 12% 35%	4058
	11th to 20th	Night	3 5% 3 7% 5% 5% 7% 6% 9% 12% 38%	4057
	21st to end	Night	2 3 2 5% 4 4 5% 5% 8% 13% 50%	4427
August	1st to 10th	Night	4 3 2 6% 6% 6% 7% 7% 9% 13% 35%	2976
	11th to 20th	Night	2 3 1 7% 5% 6% 7% 7% 9% 15% 38%	3197
	21st to end	Night	4 4 2 6% 6% 6% 8% 8% 14% 15% 26%	3846
September	1st to 10th	Night	6% 5% 3 8% 6% 8% 8% 7% 9% 13% 28%	2200
	11th to 20th	Night	7% 7% 3 8% 7% 6% 7% 5% 8% 12% 28%	2200
	21st to end	Night	8% 7% 3 9% 8% 8% 8% 7% 8% 10% 25%	2200
October	1st to 10th	Night	8% 6% 3 8% 8% 7% 7% 7% 9% 10% 27%	2300
	11th to 20th	Night	8% 6% 2 7% 5% 5% 5% 6% 7% 10% 38%	2400
	21st to end	Night	10% 6% 2 6% 5% 5% 5% 5% 6% 9% 41%	2640
November	1st to 10th	Night	8% 5% 2 7% 4 5% 6% 4 5% 9% 45%	2461
	11th to 20th	Night	7% 7% 3 7% 6% 6% 6% 5% 6% 8% 40%	2520
	21st to end	Night	7% 5% 2 6% 5% 4 5% 4 7% 9% 45%	2520
December	1st to 10th	Night	6% 5% 2 5% 3 4 4 4 6% 9% 53%	4071
	11th to 20th	Night	12% 7% 3 7% 5% 4 5% 4 7% 8% 37%	4952
	21st to end	Night	9% 8% 3 9% 7% 6% 6% 5% 8% 9% 30%	6633

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	30% 6% 10% 29% 19% 6%	4066
	11th to 20th	Day	51% 8% 14% 18% 7% 2	4060
	21st to end	Day	41% 7% 7% 28% 13% 4	4528
February	1st to 10th	Day	37% 7% 12% 24% 15% 4	2000
	11th to 20th	Day	29% 7% 11% 27% 21% 6%	2086
	21st to end	Day	32% 8% 11% 19% 23% 7%	1815
March	1st to 10th	Day	33% 11% 12% 21% 20% 4	4935
	11th to 20th	Day	18% 8% 14% 29% 19% 11%	4980
	21st to end	Day	33% 8% 11% 29% 15% 4	5465
April	1st to 10th	Day	25% 10% 18% 28% 16% 3	2200
	11th to 20th	Day	33% 8% 17% 21% 17% 5%	2278
	21st to end	Day	30% 9% 12% 26% 20% 3	2400
May	1st to 10th	Day	17% 8% 19% 36% 17% 3	5437
	11th to 20th	Day	31% 10% 20% 32% 7% 1	5444
	21st to end	Day	30% 13% 21% 29% 7%	6447
June	1st to 10th	Day	58% 13% 16% 11% 3	2600
	11th to 20th	Day	51% 15% 19% 13% 2	2600
	21st to end	Day	48% 16% 26% 10%	2600
July	1st to 10th	Day	41% 16% 31% 11%	5835
	11th to 20th	Day	41% 16% 30% 13% 1	5831
	21st to end	Day	27% 15% 35% 23% 1	6240
August	1st to 10th	Day	46% 18% 25% 10% 1	4126
	11th to 20th	Day	34% 18% 31% 17% 1	3886
	21st to end	Day	41% 18% 35% 5% 1	4031
September	1st to 10th	Day	49% 20% 21% 10% 1	2200
	11th to 20th	Day	49% 18% 21% 9% 3	2200
	21st to end	Day	55% 14% 16% 10% 5%	2200
October	1st to 10th	Day	47% 13% 20% 14% 5% 1	3408
	11th to 20th	Day	47% 10% 15% 17% 10% 1	3240
	21st to end	Day	37% 7% 11% 27% 14% 4	3538
November	1st to 10th	Day	38% 10% 12% 17% 17% 6%	2057
	11th to 20th	Day	44% 8% 10% 17% 16% 4	2100
	21st to end	Day	38% 8% 11% 18% 20% 4	2100
December	1st to 10th	Day	28% 6% 14% 29% 18% 4	3310
	11th to 20th	Day	38% 8% 12% 19% 18% 4	3460
	21st to end	Day	46% 9% 13% 16% 15% 2	4565
January	1st to 10th	Night	34% 8% 12% 25% 17% 4	5903
	11th to 20th	Night	51% 7% 16% 16% 8% 2	5900
	21st to end	Night	40% 7% 8% 28% 12% 4	6424
February	1st to 10th	Night	32% 7% 13% 27% 17% 4	2400
	11th to 20th	Night	25% 7% 11% 28% 22% 7%	2208
	21st to end	Night	26% 8% 11% 23% 25% 6%	1815
March	1st to 10th	Night	28% 9% 12% 23% 24% 4	4918
	11th to 20th	Night	20% 8% 18% 27% 18% 10%	4980
	21st to end	Night	30% 7% 12% 27% 20% 3	5467
April	1st to 10th	Night	20% 7% 18% 34% 16% 3	2200
	11th to 20th	Night	27% 8% 18% 21% 21% 4	2070
	21st to end	Night	26% 8% 14% 28% 20% 4	2000
May	1st to 10th	Night	16% 8% 24% 37% 13% 2	4520
	11th to 20th	Night	26% 9% 19% 34% 11% 1	4491
	21st to end	Night	28% 13% 25% 28% 6%	4432
June	1st to 10th	Night	50% 13% 22% 14% 2	1800
	11th to 20th	Night	38% 15% 26% 18% 3	1800
	21st to end	Night	37% 18% 32% 12% 1	1800
July	1st to 10th	Night	39% 13% 35% 13%	4015
	11th to 20th	Night	35% 14% 39% 12%	4006
	21st to end	Night	24% 12% 40% 22% 3	4297
August	1st to 10th	Night	37% 16% 28% 16% 2	2965
	11th to 20th	Night	30% 15% 35% 20%	3227
	21st to end	Night	37% 20% 35% 6% 1	3846
September	1st to 10th	Night	43% 19% 26% 11% 1	2200
	11th to 20th	Night	44% 19% 23% 12% 2	2200
	21st to end	Night	50% 16% 15% 13% 6%	2200
October	1st to 10th	Night	49% 14% 18% 15% 3 1	3755
	11th to 20th	Night	47% 9% 17% 15% 11% 1	3899
	21st to end	Night	38% 7% 11% 27% 14% 3	4252
November	1st to 10th	Night	35% 9% 13% 20% 17% 6%	2461
	11th to 20th	Night	41% 9% 9% 22% 15% 4	2520
	21st to end	Night	35% 8% 14% 19% 18% 5%	2520
December	1st to 10th	Night	29% 8% 13% 30% 17% 3	4071
	11th to 20th	Night	42% 7% 11% 20% 15% 5%	4954
	21st to end	Night	46% 10% 14% 16% 13% 2	6633

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	7% 12% 37% 37% 8%	303
	11th to 20th	Day	16% 11% 33% 32% 8% 1	300
	21st to end	Day	10% 9% 48% 28% 5%	330
February	1st to 10th	Day	7% 8% 30% 42% 11% 1	300
	11th to 20th	Day	6% 7% 32% 37% 15% 2	429
	21st to end	Day	5% 6% 27% 42% 19% 1	414
March	1st to 10th	Day	5% 9% 38% 34% 13% 1	500
	11th to 20th	Day	6% 8% 34% 35% 16% 1	500
	21st to end	Day	5% 5% 35% 35% 18% 2	550
April	1st to 10th	Day	2 5% 40% 34% 16% 3	500
	11th to 20th	Day	8% 6% 32% 34% 16% 4	492
	21st to end	Day	4 3 27% 42% 20% 5%	500
May	1st to 10th	Day	3 2 22% 42% 24% 7%	503
	11th to 20th	Day	9% 3 20% 35% 25% 7%	527
	21st to end	Day	8% 3 10% 32% 34% 14%	573
June	1st to 10th	Day	11% 3 11% 30% 29% 16%	530
	11th to 20th	Day	8% 2 7% 25% 34% 23%	530
	21st to end	Day	3 2 6% 19% 35% 35%	530
July	1st to 10th	Day	4 2 4 15% 40% 36%	525
	11th to 20th	Day	4 2 3 19% 41% 30%	524
	21st to end	Day	3 1 4 21% 35% 36%	576
August	1st to 10th	Day	4 1 6% 19% 38% 31%	526
	11th to 20th	Day	4 1 3 22% 37% 33%	519
	21st to end	Day	9% 1 7% 23% 34% 26%	583
September	1st to 10th	Day	7% 2 4 19% 35% 32%	530
	11th to 20th	Day	7% 2 6% 18% 36% 30%	530
	21st to end	Day	11% 2 9% 24% 33% 21%	530
October	1st to 10th	Day	12% 2 13% 35% 29% 9%	530
	11th to 20th	Day	12% 4 19% 31% 24% 11%	530
	21st to end	Day	10% 6% 22% 36% 21% 5%	583
November	1st to 10th	Day	8% 6% 24% 38% 19% 5%	535
	11th to 20th	Day	10% 7% 25% 35% 20% 3	540
	21st to end	Day	6% 7% 26% 39% 20% 1	540
December	1st to 10th	Day	9% 6% 25% 40% 19% 1	516
	11th to 20th	Day	7% 7% 32% 35% 17% 2	330
	21st to end	Day	10% 9% 31% 32% 16% 2	363
January	1st to 10th	Night	8% 7% 24% 39% 19% 2	805
	11th to 20th	Night	10% 9% 28% 35% 17% 1	800
	21st to end	Night	9% 9% 30% 40% 13%	880
February	1st to 10th	Night	11% 6% 24% 38% 21% 1	800
	11th to 20th	Night	7% 6% 27% 39% 21% 1	783
	21st to end	Night	6% 4 26% 47% 17%	660
March	1st to 10th	Night	5% 7% 33% 39% 15% 1	800
	11th to 20th	Night	7% 5% 24% 45% 17% 2	800
	21st to end	Night	5% 6% 27% 43% 17% 1	880
April	1st to 10th	Night	4 4 22% 47% 21% 2	800
	11th to 20th	Night	6% 4 25% 44% 20% 1	791
	21st to end	Night	7% 3 21% 44% 23% 2	800
May	1st to 10th	Night	4 2 18% 46% 28% 3	800
	11th to 20th	Night	10% 2 17% 42% 27% 2	789
	21st to end	Night	7% 3 7% 32% 42% 9%	653
June	1st to 10th	Night	11% 2 7% 25% 40% 14%	600
	11th to 20th	Night	7% 2 3 18% 44% 27%	600
	21st to end	Night	4 1 4 13% 42% 37%	600
July	1st to 10th	Night	5% 2 3 10% 43% 38%	585
	11th to 20th	Night	4 1 3 13% 42% 37%	582
	21st to end	Night	2 1 3 10% 40% 44%	657
August	1st to 10th	Night	8% 1 3 12% 45% 32%	632
	11th to 20th	Night	3 1 4 15% 44% 33%	790
	21st to end	Night	8% 1 6% 20% 39% 26%	880
September	1st to 10th	Night	7% 2 6% 16% 40% 31%	800
	11th to 20th	Night	7% 3 7% 19% 36% 29%	800
	21st to end	Night	9% 3 9% 20% 37% 23%	800
October	1st to 10th	Night	9% 3 11% 34% 34% 10%	800
	11th to 20th	Night	11% 4 11% 31% 34% 9%	800
	21st to end	Night	13% 2 21% 35% 23% 5%	880
November	1st to 10th	Night	10% 6% 24% 33% 24% 4	820
	11th to 20th	Night	11% 5% 20% 34% 27% 4	840
	21st to end	Night	8% 5% 22% 40% 22% 3	840
December	1st to 10th	Night	8% 5% 19% 39% 28% 2	840
	11th to 20th	Night	11% 7% 23% 34% 22% 3	840
	21st to end	Night	8% 7% 24% 34% 23% 3	924

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