Ladysmith
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ladysmith 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	14% 9% 3 8% 5% 4 4 4 5% 7% 36%	127762
	Night	13% 10% 4 9% 5% 4 4 4 5% 6% 36%	123897
Transparency	Day	46% 6% 13% 23% 11% 1	131248
	Night	47% 6% 12% 22% 12% 1	128484
Seeing	Day	17% 11% 30% 25% 13% 4	17622
	Night	18% 8% 32% 31% 10% 1	27557

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	8% 13% 6% 17% 8% 5% 4 3 4 5% 26%	3625
	11th to 20th	Day	6% 12% 7% 13% 6% 8% 9% 6% 7% 6% 19%	3620
	21st to end	Day	8% 17% 9% 13% 5% 4 4 3 5% 7% 25%	4189
February	1st to 10th	Day	8% 14% 5% 10% 5% 4 4 4 6% 8% 31%	1800
	11th to 20th	Day	9% 10% 4 12% 5% 5% 5% 4 5% 7% 34%	1754
	21st to end	Day	12% 11% 5% 10% 7% 5% 4 5% 4 6% 31%	1640
March	1st to 10th	Day	13% 8% 3 5% 4 4 4 3 5% 7% 45%	4521
	11th to 20th	Day	10% 9% 3 9% 4 5% 4 4 6% 8% 37%	4980
	21st to end	Day	23% 9% 3 10% 4 4 4 3 4 6% 29%	5736
April	1st to 10th	Day	16% 13% 3 9% 5% 4 4 4 5% 7% 31%	2400
	11th to 20th	Day	21% 10% 4 8% 5% 4 5% 4 5% 5% 30%	2374
	21st to end	Day	21% 11% 3 7% 6% 4 4 4 5% 5% 29%	2531
May	1st to 10th	Day	16% 6% 2 5% 4 3 3 3 5% 6% 49%	6319
	11th to 20th	Day	15% 6% 3 6% 5% 4 5% 4 6% 6% 40%	6319
	21st to end	Day	18% 10% 3 6% 4 4 4 3 5% 6% 37%	6935
June	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 7% 8% 41%	2800
	11th to 20th	Day	15% 7% 2 7% 5% 5% 6% 4 6% 7% 36%	2800
	21st to end	Day	12% 5% 2 6% 4 5% 5% 5% 8% 10% 37%	2800
July	1st to 10th	Day	12% 4 2 5% 3 4 4 4 7% 10% 46%	6360
	11th to 20th	Day	10% 4 2 4 3 3 4 4 6% 10% 50%	6360
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 9% 45%	6924
August	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 6% 8% 41%	4467
	11th to 20th	Day	14% 5% 2 5% 4 4 4 4 6% 8% 47%	4171
	21st to end	Day	15% 6% 3 6% 5% 5% 5% 4 6% 7% 38%	4318
September	1st to 10th	Day	12% 6% 2 6% 4 4 5% 3 6% 7% 44%	2400
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 6% 9% 43%	2400
	21st to end	Day	16% 6% 2 6% 4 3 4 4 5% 8% 42%	2125
October	1st to 10th	Day	17% 7% 2 7% 4 4 4 4 5% 6% 40%	2000
	11th to 20th	Day	18% 13% 3 8% 5% 5% 4 3 6% 6% 31%	2000
	21st to end	Day	19% 11% 3 7% 4 4 4 4 4 6% 33%	2050
November	1st to 10th	Day	14% 12% 3 8% 5% 5% 5% 3 5% 7% 34%	1836
	11th to 20th	Day	15% 12% 5% 11% 6% 5% 5% 3 5% 5% 27%	1680
	21st to end	Day	15% 14% 4 10% 5% 4 4 4 6% 7% 28%	1680
December	1st to 10th	Day	8% 14% 7% 20% 10% 6% 5% 3 5% 5% 17%	2690
	11th to 20th	Day	12% 19% 6% 11% 7% 4 3 3 4 5% 25%	3088
	21st to end	Day	23% 19% 6% 16% 5% 5% 3 3 3 3 14%	4070
January	1st to 10th	Night	8% 11% 6% 16% 9% 5% 4 3 4 5% 29%	6363
	11th to 20th	Night	7% 13% 6% 14% 7% 7% 9% 6% 7% 6% 19%	6360
	21st to end	Night	8% 18% 9% 14% 5% 4 4 3 5% 6% 25%	6786
February	1st to 10th	Night	7% 11% 5% 10% 7% 6% 5% 4 6% 6% 32%	2600
	11th to 20th	Night	8% 10% 4 8% 6% 6% 5% 4 6% 6% 36%	2533
	21st to end	Night	12% 11% 4 8% 7% 5% 5% 4 6% 6% 32%	1990
March	1st to 10th	Night	10% 6% 2 7% 4 4 4 3 5% 7% 47%	5373
	11th to 20th	Night	10% 9% 4 10% 6% 5% 5% 4 7% 8% 33%	4980
	21st to end	Night	22% 12% 4 8% 5% 4 4 3 4 5% 29%	5192
April	1st to 10th	Night	19% 11% 3 7% 4 3 5% 3 4 7% 34%	2000
	11th to 20th	Night	23% 8% 3 7% 4 4 3 3 4 6% 36%	1975
	21st to end	Night	20% 9% 2 6% 4 3 3 3 7% 7% 35%	1866
May	1st to 10th	Night	15% 6% 2 6% 4 4 3 3 5% 7% 46%	3596
	11th to 20th	Night	14% 5% 2 6% 4 3 3 2 4 5% 51%	3596
	21st to end	Night	16% 7% 2 7% 5% 4 4 4 5% 7% 40%	3942
June	1st to 10th	Night	12% 6% 2 6% 4 3 4 4 7% 9% 43%	1600
	11th to 20th	Night	13% 7% 2 6% 5% 4 4 4 7% 8% 42%	1600
	21st to end	Night	10% 6% 2 5% 5% 5% 5% 4 6% 9% 43%	1600
July	1st to 10th	Night	9% 5% 2 6% 4 4 5% 4 6% 9% 47%	3618
	11th to 20th	Night	9% 4 2 5% 3 3 3 3 6% 8% 54%	3617
	21st to end	Night	11% 5% 2 6% 4 3 4 3 6% 8% 48%	3947
August	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 6% 6% 46%	2689
	11th to 20th	Night	14% 5% 1 5% 3 3 3 3 6% 8% 49%	2888
	21st to end	Night	16% 6% 3 5% 4 4 3 4 5% 7% 43%	3578
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 5% 6% 53%	2000
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 5% 7% 49%	2000
	21st to end	Night	13% 5% 2 6% 4 3 4 3 5% 7% 47%	2252
October	1st to 10th	Night	14% 6% 2 6% 4 3 4 3 5% 6% 47%	2400
	11th to 20th	Night	16% 9% 3 8% 4 4 4 3 5% 5% 38%	2400
	21st to end	Night	18% 10% 3 8% 5% 4 4 4 5% 6% 33%	2790
November	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 5% 8% 37%	2677
	11th to 20th	Night	14% 13% 4 9% 5% 4 4 3 5% 6% 33%	2940
	21st to end	Night	14% 12% 4 11% 6% 5% 5% 3 5% 7% 30%	2940
December	1st to 10th	Night	8% 12% 6% 14% 8% 7% 5% 4 5% 6% 24%	4720
	11th to 20th	Night	12% 17% 7% 13% 6% 5% 4 4 5% 5% 21%	5339
	21st to end	Night	24% 15% 6% 13% 5% 4 3 3 4 5% 18%	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	61% 5% 8% 16% 9%	3626
	11th to 20th	Day	62% 6% 6% 15% 10%	3620
	21st to end	Day	59% 5% 13% 17% 6%	4189
February	1st to 10th	Day	50% 6% 13% 20% 10% 1	1800
	11th to 20th	Day	49% 5% 13% 22% 10% 1	1763
	21st to end	Day	53% 5% 12% 19% 9% 2	1640
March	1st to 10th	Day	39% 5% 16% 22% 14% 5%	4521
	11th to 20th	Day	43% 6% 16% 21% 13% 2	4980
	21st to end	Day	58% 4 10% 16% 12% 1	5738
April	1st to 10th	Day	52% 7% 10% 19% 12% 1	2400
	11th to 20th	Day	54% 6% 10% 18% 10% 2	2374
	21st to end	Day	56% 6% 11% 17% 10%	2531
May	1st to 10th	Day	36% 6% 11% 29% 16% 2	6357
	11th to 20th	Day	41% 7% 13% 23% 13% 3	6323
	21st to end	Day	47% 5% 10% 23% 14% 1	6949
June	1st to 10th	Day	37% 9% 14% 27% 12% 1	2800
	11th to 20th	Day	46% 9% 13% 20% 13% 1	2800
	21st to end	Day	39% 9% 18% 23% 10% 1	2800
July	1st to 10th	Day	33% 7% 17% 36% 7%	6291
	11th to 20th	Day	30% 6% 18% 34% 12% 1	6285
	21st to end	Day	36% 6% 15% 28% 15%	6728
August	1st to 10th	Day	40% 7% 15% 24% 13% 1	4452
	11th to 20th	Day	35% 7% 14% 34% 10%	4210
	21st to end	Day	43% 7% 15% 24% 11% 1	4317
September	1st to 10th	Day	38% 7% 15% 28% 12%	2400
	11th to 20th	Day	37% 8% 19% 28% 7% 1	2400
	21st to end	Day	41% 6% 14% 30% 9%	2125
October	1st to 10th	Day	30% 5% 12% 35% 18%	3260
	11th to 20th	Day	47% 4 10% 23% 15% 1	3240
	21st to end	Day	46% 4 18% 23% 8%	3288
November	1st to 10th	Day	49% 7% 12% 20% 11% 1	1836
	11th to 20th	Day	58% 7% 12% 17% 6% 1	1680
	21st to end	Day	54% 6% 15% 18% 5% 1	1680
December	1st to 10th	Day	69% 5% 9% 14% 3	2690
	11th to 20th	Day	61% 4 9% 15% 10% 1	3085
	21st to end	Day	75% 4 6% 9% 5%	4070
January	1st to 10th	Night	57% 5% 10% 17% 11%	6363
	11th to 20th	Night	61% 6% 10% 13% 10%	6360
	21st to end	Night	60% 5% 10% 18% 8%	6786
February	1st to 10th	Night	51% 5% 12% 20% 10% 1	2600
	11th to 20th	Night	46% 7% 13% 23% 10% 1	2534
	21st to end	Night	50% 6% 14% 19% 8% 2	1990
March	1st to 10th	Night	36% 5% 17% 23% 15% 4	5373
	11th to 20th	Night	46% 6% 15% 21% 11% 1	4980
	21st to end	Night	59% 4 9% 15% 12%	5192
April	1st to 10th	Night	50% 6% 9% 19% 16% 1	2000
	11th to 20th	Night	50% 5% 10% 19% 13% 3	1975
	21st to end	Night	46% 7% 10% 21% 14% 1	1866
May	1st to 10th	Night	37% 6% 11% 25% 18% 1	3620
	11th to 20th	Night	36% 5% 12% 24% 19% 5%	3597
	21st to end	Night	42% 7% 13% 23% 14% 1	3950
June	1st to 10th	Night	35% 8% 16% 26% 14% 1	1600
	11th to 20th	Night	39% 8% 14% 22% 15% 2	1600
	21st to end	Night	35% 9% 15% 27% 13% 2	1600
July	1st to 10th	Night	32% 7% 19% 31% 11% 1	3580
	11th to 20th	Night	28% 6% 16% 35% 15% 1	3572
	21st to end	Night	34% 6% 14% 26% 18% 1	3832
August	1st to 10th	Night	38% 5% 14% 27% 14% 2	2680
	11th to 20th	Night	33% 6% 15% 32% 12% 2	2915
	21st to end	Night	40% 7% 14% 27% 11% 2	3578
September	1st to 10th	Night	32% 6% 13% 32% 15% 1	2000
	11th to 20th	Night	33% 7% 17% 32% 11%	2000
	21st to end	Night	36% 6% 14% 31% 11% 1	2252
October	1st to 10th	Night	28% 4 8% 34% 23% 3	3920
	11th to 20th	Night	39% 5% 12% 26% 17% 1	3899
	21st to end	Night	52% 5% 10% 22% 11%	4502
November	1st to 10th	Night	46% 6% 13% 23% 12%	2677
	11th to 20th	Night	52% 6% 15% 17% 9% 1	2940
	21st to end	Night	54% 6% 14% 19% 6% 1	2940
December	1st to 10th	Night	60% 7% 14% 16% 3	4720
	11th to 20th	Night	64% 5% 9% 15% 7%	5341
	21st to end	Night	69% 4 7% 12% 7%	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	16% 12% 35% 25% 10% 3	303
	11th to 20th	Day	18% 12% 37% 24% 8% 1	300
	21st to end	Day	17% 10% 38% 26% 9%	330
February	1st to 10th	Day	14% 14% 47% 18% 6% 2	300
	11th to 20th	Day	13% 16% 44% 20% 6% 1	300
	21st to end	Day	15% 15% 46% 22% 2	249
March	1st to 10th	Day	17% 15% 41% 20% 7% 1	300
	11th to 20th	Day	18% 14% 40% 17% 8% 3	300
	21st to end	Day	26% 13% 30% 20% 7% 3	449
April	1st to 10th	Day	21% 18% 35% 20% 5% 1	500
	11th to 20th	Day	27% 13% 29% 22% 8% 1	492
	21st to end	Day	27% 14% 27% 22% 8% 2	590
May	1st to 10th	Day	21% 13% 29% 26% 9% 2	703
	11th to 20th	Day	20% 13% 27% 24% 13% 4	725
	21st to end	Day	21% 10% 26% 24% 15% 4	789
June	1st to 10th	Day	13% 9% 29% 29% 16% 4	730
	11th to 20th	Day	16% 9% 33% 28% 11% 3	730
	21st to end	Day	14% 8% 31% 26% 15% 6%	730
July	1st to 10th	Day	10% 4 19% 31% 24% 11%	721
	11th to 20th	Day	11% 8% 24% 31% 17% 9%	718
	21st to end	Day	8% 4 28% 32% 20% 9%	794
August	1st to 10th	Day	11% 6% 24% 28% 24% 7%	726
	11th to 20th	Day	15% 6% 18% 30% 24% 7%	715
	21st to end	Day	15% 6% 22% 30% 22% 5%	589
September	1st to 10th	Day	13% 9% 25% 28% 20% 5%	530
	11th to 20th	Day	12% 6% 28% 32% 19% 3	530
	21st to end	Day	20% 9% 26% 25% 16% 4	443
October	1st to 10th	Day	15% 13% 28% 29% 11% 4	330
	11th to 20th	Day	22% 20% 33% 17% 7% 1	330
	21st to end	Day	25% 13% 39% 18% 4 2	363
November	1st to 10th	Day	19% 15% 36% 21% 8% 1	330
	11th to 20th	Day	20% 19% 33% 21% 6% 1	330
	21st to end	Day	22% 14% 37% 21% 6%	330
December	1st to 10th	Day	13% 15% 41% 23% 7% 1	330
	11th to 20th	Day	22% 18% 33% 20% 6% 1	330
	21st to end	Day	27% 14% 36% 18% 4 1	363
January	1st to 10th	Night	13% 10% 38% 29% 9%	1006
	11th to 20th	Night	19% 9% 37% 28% 6% 2	1000
	21st to end	Night	18% 10% 35% 30% 5%	1100
February	1st to 10th	Night	14% 9% 40% 30% 6% 1	1000
	11th to 20th	Night	14% 12% 40% 27% 6%	979
	21st to end	Night	18% 11% 38% 28% 5%	670
March	1st to 10th	Night	16% 12% 36% 29% 6% 1	800
	11th to 20th	Night	16% 13% 35% 28% 7% 1	600
	21st to end	Night	22% 10% 30% 29% 8% 2	660
April	1st to 10th	Night	23% 10% 32% 29% 6% 1	600
	11th to 20th	Night	28% 9% 27% 28% 7%	593
	21st to end	Night	24% 8% 30% 31% 7% 1	600
May	1st to 10th	Night	23% 9% 33% 29% 7% 1	600
	11th to 20th	Night	19% 8% 31% 31% 9% 2	591
	21st to end	Night	17% 7% 26% 36% 13% 1	650
June	1st to 10th	Night	12% 8% 29% 39% 11%	600
	11th to 20th	Night	17% 5% 30% 40% 8% 1	600
	21st to end	Night	14% 4 24% 44% 13% 1	600
July	1st to 10th	Night	8% 2 23% 37% 26% 2	585
	11th to 20th	Night	11% 3 24% 40% 20% 2	582
	21st to end	Night	8% 2 18% 48% 22% 2	657
August	1st to 10th	Night	10% 4 17% 44% 23% 2	597
	11th to 20th	Night	15% 3 20% 33% 26% 3	594
	21st to end	Night	16% 3 21% 34% 25% 2	660
September	1st to 10th	Night	12% 4 23% 39% 18% 4	600
	11th to 20th	Night	12% 3 28% 36% 18% 3	600
	21st to end	Night	15% 7% 29% 32% 15% 1	767
October	1st to 10th	Night	17% 7% 30% 31% 14% 1	800
	11th to 20th	Night	19% 11% 34% 28% 8%	800
	21st to end	Night	24% 10% 28% 29% 8%	880
November	1st to 10th	Night	22% 8% 34% 29% 7% 1	831
	11th to 20th	Night	20% 12% 36% 24% 7%	1050
	21st to end	Night	20% 13% 36% 25% 6%	1050
December	1st to 10th	Night	18% 9% 38% 27% 8% 1	1050
	11th to 20th	Night	20% 11% 37% 24% 7% 1	1050
	21st to end	Night	26% 10% 34% 24% 6% 1	1155

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