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 2024-01-13.

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	15% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	74762
	Night	14% 9% 4 7% 6% 3 4 4 5% 7% 36%	75007
Transparency	Day	48% 7% 13% 21% 9% 1	74462
	Night	48% 7% 13% 21% 11% 1	74827
Seeing	Day	17% 11% 30% 25% 13% 4	14862
	Night	18% 8% 32% 31% 11% 1	24875

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	11% 12% 7% 9% 7% 3 6% 5% 6% 7% 26%	1517
	11th to 20th	Day	13% 14% 9% 13% 8% 4 5% 4 6% 7% 20%	1461
	21st to end	Day	11% 14% 7% 12% 8% 4 5% 5% 6% 8% 19%	1665
February	1st to 10th	Day	8% 12% 5% 10% 6% 3 5% 5% 6% 8% 32%	1620
	11th to 20th	Day	10% 10% 4 11% 7% 3 5% 4 6% 7% 33%	1574
	21st to end	Day	13% 11% 5% 9% 9% 4 4 6% 4 6% 29%	1471
March	1st to 10th	Day	13% 10% 6% 7% 6% 4 5% 5% 4 5% 34%	1813
	11th to 20th	Day	14% 9% 4 8% 6% 4 5% 4 4 6% 36%	1980
	21st to end	Day	19% 10% 4 6% 7% 3 5% 5% 5% 8% 29%	2285
April	1st to 10th	Day	15% 11% 4 8% 6% 3 5% 4 5% 7% 32%	2160
	11th to 20th	Day	22% 9% 5% 7% 5% 3 5% 5% 4 6% 30%	2134
	21st to end	Day	21% 10% 4 6% 6% 3 5% 5% 5% 5% 30%	2276
May	1st to 10th	Day	18% 7% 3 6% 6% 3 5% 5% 6% 7% 34%	2520
	11th to 20th	Day	18% 7% 3 6% 6% 3 5% 5% 5% 7% 36%	2479
	21st to end	Day	16% 6% 3 6% 5% 3 5% 5% 6% 8% 36%	2725
June	1st to 10th	Day	14% 5% 2 5% 5% 3 4 5% 6% 8% 41%	2520
	11th to 20th	Day	13% 7% 2 6% 6% 4 6% 6% 6% 7% 38%	2520
	21st to end	Day	11% 5% 2 5% 5% 3 6% 7% 7% 10% 38%	2520
July	1st to 10th	Day	8% 3 2 4 5% 3 5% 6% 7% 11% 47%	2520
	11th to 20th	Day	10% 5% 2 5% 4 3 5% 5% 6% 9% 44%	2520
	21st to end	Day	8% 4 2 5% 4 3 5% 5% 6% 10% 48%	2743
August	1st to 10th	Day	10% 5% 2 5% 6% 3 5% 7% 7% 9% 41%	2456
	11th to 20th	Day	14% 5% 2 4 5% 3 5% 6% 6% 7% 43%	2301
	21st to end	Day	13% 5% 2 4 5% 3 5% 4 6% 8% 45%	2382
September	1st to 10th	Day	13% 6% 2 5% 5% 3 5% 5% 6% 8% 43%	2160
	11th to 20th	Day	14% 6% 3 4 4 3 4 5% 6% 8% 44%	2160
	21st to end	Day	18% 6% 3 6% 5% 3 4 5% 5% 8% 39%	1915
October	1st to 10th	Day	18% 7% 2 6% 5% 3 4 5% 6% 6% 37%	1800
	11th to 20th	Day	18% 12% 4 7% 6% 4 5% 4 6% 6% 30%	1800
	21st to end	Day	20% 11% 3 7% 5% 3 4 4 4 6% 33%	1846
November	1st to 10th	Day	13% 11% 5% 6% 6% 4 4 5% 5% 7% 34%	1658
	11th to 20th	Day	16% 11% 6% 10% 8% 4 5% 4 5% 5% 25%	1520
	21st to end	Day	15% 12% 4 8% 6% 3 5% 5% 6% 8% 29%	1520
December	1st to 10th	Day	11% 13% 7% 13% 9% 5% 6% 5% 5% 6% 20%	1520
	11th to 20th	Day	14% 14% 7% 11% 9% 4 4 6% 5% 5% 20%	1918
	21st to end	Day	24% 18% 7% 13% 6% 3 3 3 2 3 17%	2783
January	1st to 10th	Night	10% 10% 6% 10% 8% 5% 6% 5% 6% 6% 28%	2648
	11th to 20th	Night	12% 14% 6% 13% 7% 4 5% 5% 5% 6% 24%	2561
	21st to end	Night	12% 16% 8% 12% 7% 3 4 5% 6% 7% 21%	2688
February	1st to 10th	Night	7% 11% 6% 9% 9% 4 6% 5% 5% 6% 32%	2340
	11th to 20th	Night	8% 10% 5% 7% 7% 4 6% 5% 6% 7% 36%	2273
	21st to end	Night	14% 11% 5% 7% 8% 4 5% 5% 5% 6% 31%	1785
March	1st to 10th	Night	13% 8% 4 6% 6% 3 5% 5% 5% 6% 39%	2160
	11th to 20th	Night	13% 10% 3 7% 6% 3 4 3 5% 6% 40%	1980
	21st to end	Night	18% 9% 4 6% 6% 3 5% 4 4 5% 35%	2070
April	1st to 10th	Night	19% 10% 4 6% 5% 2 5% 5% 5% 7% 33%	1800
	11th to 20th	Night	25% 8% 3 6% 4 3 3 3 4 6% 35%	1775
	21st to end	Night	20% 9% 3 5% 5% 3 4 4 7% 7% 34%	1681
May	1st to 10th	Night	20% 7% 3 7% 6% 5% 4 5% 5% 7% 32%	1440
	11th to 20th	Night	18% 6% 3 5% 5% 3 4 4 5% 5% 41%	1416
	21st to end	Night	14% 6% 3 6% 5% 3 4 6% 5% 8% 40%	1551
June	1st to 10th	Night	12% 5% 3 5% 4 2 4 4 7% 9% 44%	1440
	11th to 20th	Night	11% 6% 3 5% 5% 3 4 5% 6% 8% 44%	1440
	21st to end	Night	8% 5% 2 4 5% 3 6% 6% 6% 9% 45%	1440
July	1st to 10th	Night	6% 5% 1 3 4 3 4 6% 7% 9% 53%	1440
	11th to 20th	Night	9% 4 2 4 4 3 4 5% 7% 9% 48%	1440
	21st to end	Night	7% 3 2 4 5% 2 3 4 7% 10% 54%	1575
August	1st to 10th	Night	10% 4 2 4 5% 3 4 4 5% 7% 52%	1479
	11th to 20th	Night	15% 6% 2 4 4 2 3 3 6% 8% 47%	1600
	21st to end	Night	14% 5% 2 4 4 2 3 4 5% 7% 50%	1972
September	1st to 10th	Night	10% 5% 2 4 5% 2 4 4 5% 6% 53%	1800
	11th to 20th	Night	10% 5% 2 4 5% 2 4 5% 5% 7% 50%	1800
	21st to end	Night	15% 5% 3 5% 5% 2 4 4 5% 8% 44%	2025
October	1st to 10th	Night	15% 6% 2 5% 5% 2 3 4 5% 6% 46%	2160
	11th to 20th	Night	16% 9% 3 7% 5% 3 4 4 5% 5% 37%	2160
	21st to end	Night	19% 9% 3 7% 6% 3 5% 4 5% 6% 33%	2510
November	1st to 10th	Night	17% 8% 4 5% 5% 2 4 5% 4 8% 37%	2415
	11th to 20th	Night	15% 11% 5% 9% 6% 4 4 4 5% 7% 31%	2660
	21st to end	Night	14% 11% 4 8% 6% 3 5% 5% 5% 7% 32%	2660
December	1st to 10th	Night	11% 13% 7% 10% 8% 4 5% 4 5% 6% 27%	2660
	11th to 20th	Night	13% 14% 6% 10% 8% 4 5% 6% 5% 6% 23%	3279
	21st to end	Night	25% 16% 6% 9% 5% 3 3 4 4 5% 19%	4884

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	56% 8% 11% 18% 6% 1	1518
	11th to 20th	Day	65% 7% 8% 11% 8%	1461
	21st to end	Day	62% 6% 12% 14% 7%	1665
February	1st to 10th	Day	50% 7% 13% 20% 9% 1	1620
	11th to 20th	Day	50% 5% 13% 21% 9% 1	1583
	21st to end	Day	56% 6% 10% 17% 9% 1	1471
March	1st to 10th	Day	52% 6% 14% 18% 8% 1	1813
	11th to 20th	Day	49% 6% 14% 19% 10% 1	1980
	21st to end	Day	54% 6% 12% 19% 8% 1	2285
April	1st to 10th	Day	51% 7% 10% 19% 12% 1	2160
	11th to 20th	Day	55% 6% 10% 17% 10% 2	2134
	21st to end	Day	56% 6% 11% 17% 9%	2276
May	1st to 10th	Day	48% 8% 12% 22% 9% 1	2520
	11th to 20th	Day	48% 7% 13% 20% 11% 1	2483
	21st to end	Day	45% 7% 12% 22% 12% 2	2725
June	1st to 10th	Day	38% 9% 14% 27% 11% 1	2520
	11th to 20th	Day	44% 9% 13% 21% 14% 1	2520
	21st to end	Day	38% 9% 19% 24% 10% 1	2520
July	1st to 10th	Day	29% 9% 17% 33% 12%	2451
	11th to 20th	Day	34% 9% 14% 25% 15% 2	2445
	21st to end	Day	31% 8% 18% 27% 15% 1	2591
August	1st to 10th	Day	36% 10% 16% 27% 8% 2	2441
	11th to 20th	Day	38% 9% 16% 26% 10%	2301
	21st to end	Day	36% 8% 14% 26% 15% 1	2382
September	1st to 10th	Day	39% 7% 15% 27% 12%	2160
	11th to 20th	Day	37% 8% 18% 28% 7%	2160
	21st to end	Day	44% 6% 15% 28% 7%	1915
October	1st to 10th	Day	44% 8% 13% 28% 7% 1	1800
	11th to 20th	Day	55% 6% 12% 18% 9% 1	1800
	21st to end	Day	53% 6% 14% 20% 8%	1846
November	1st to 10th	Day	48% 7% 12% 21% 11% 1	1658
	11th to 20th	Day	60% 7% 13% 14% 6% 1	1520
	21st to end	Day	52% 6% 16% 18% 6% 1	1520
December	1st to 10th	Day	64% 7% 13% 13% 4	1520
	11th to 20th	Day	63% 6% 12% 13% 4 1	1915
	21st to end	Day	74% 4 7% 10% 5%	2783
January	1st to 10th	Night	55% 6% 13% 18% 7% 1	2648
	11th to 20th	Night	60% 6% 12% 15% 6%	2561
	21st to end	Night	62% 6% 9% 15% 8% 1	2688
February	1st to 10th	Night	51% 6% 12% 21% 9% 1	2340
	11th to 20th	Night	47% 7% 13% 22% 9% 1	2274
	21st to end	Night	53% 6% 13% 18% 8% 2	1785
March	1st to 10th	Night	46% 7% 15% 20% 10% 2	2160
	11th to 20th	Night	45% 6% 12% 22% 14% 1	1980
	21st to end	Night	52% 5% 9% 21% 11% 1	2070
April	1st to 10th	Night	50% 6% 9% 18% 16% 1	1800
	11th to 20th	Night	52% 5% 9% 19% 13% 3	1775
	21st to end	Night	47% 7% 11% 20% 14% 1	1681
May	1st to 10th	Night	51% 8% 13% 17% 11% 1	1440
	11th to 20th	Night	45% 7% 11% 22% 13% 3	1417
	21st to end	Night	40% 8% 14% 21% 15% 1	1552
June	1st to 10th	Night	34% 8% 17% 27% 14% 1	1440
	11th to 20th	Night	37% 8% 15% 23% 16% 2	1440
	21st to end	Night	33% 9% 16% 28% 12% 2	1440
July	1st to 10th	Night	25% 8% 15% 31% 20% 1	1400
	11th to 20th	Night	30% 9% 16% 26% 17% 3	1392
	21st to end	Night	24% 8% 18% 31% 16% 3	1487
August	1st to 10th	Night	32% 7% 13% 31% 14% 3	1470
	11th to 20th	Night	35% 8% 15% 25% 15% 2	1600
	21st to end	Night	34% 8% 12% 28% 15% 3	1972
September	1st to 10th	Night	32% 7% 13% 31% 16% 1	1800
	11th to 20th	Night	32% 7% 16% 32% 12%	1800
	21st to end	Night	39% 7% 15% 30% 10% 1	2025
October	1st to 10th	Night	39% 6% 13% 29% 12% 1	2160
	11th to 20th	Night	47% 7% 14% 22% 10% 1	2160
	21st to end	Night	51% 6% 12% 19% 11%	2510
November	1st to 10th	Night	45% 6% 13% 23% 12%	2415
	11th to 20th	Night	53% 7% 15% 15% 10% 1	2660
	21st to end	Night	52% 6% 15% 20% 6% 1	2660
December	1st to 10th	Night	58% 7% 12% 18% 5%	2660
	11th to 20th	Night	60% 7% 11% 16% 4	3281
	21st to end	Night	68% 5% 8% 14% 4	4884

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	17% 12% 34% 24% 10% 3	270
	11th to 20th	Day	21% 13% 35% 23% 7% 1	248
	21st to end	Day	20% 9% 36% 26% 9%	264
February	1st to 10th	Day	14% 13% 49% 18% 6%	240
	11th to 20th	Day	15% 16% 47% 17% 5% 1	240
	21st to end	Day	18% 12% 48% 22% 1	198
March	1st to 10th	Day	17% 16% 38% 20% 8% 1	240
	11th to 20th	Day	19% 13% 38% 18% 10% 3	240
	21st to end	Day	25% 14% 29% 20% 8% 4	371
April	1st to 10th	Day	19% 17% 36% 22% 6% 1	420
	11th to 20th	Day	27% 12% 27% 24% 9% 1	412
	21st to end	Day	26% 13% 27% 23% 9% 2	500
May	1st to 10th	Day	22% 13% 31% 26% 8% 1	603
	11th to 20th	Day	21% 12% 28% 24% 12% 4	625
	21st to end	Day	20% 10% 27% 23% 16% 4	679
June	1st to 10th	Day	13% 8% 29% 29% 17% 4	630
	11th to 20th	Day	13% 8% 34% 29% 12% 3	630
	21st to end	Day	12% 7% 31% 27% 16% 7%	630
July	1st to 10th	Day	9% 5% 20% 31% 24% 11%	621
	11th to 20th	Day	11% 8% 26% 30% 17% 8%	618
	21st to end	Day	8% 4 28% 31% 20% 8%	684
August	1st to 10th	Day	11% 6% 23% 29% 24% 7%	626
	11th to 20th	Day	15% 6% 19% 29% 25% 7%	615
	21st to end	Day	14% 7% 23% 30% 21% 6%	501
September	1st to 10th	Day	14% 10% 24% 29% 20% 4	450
	11th to 20th	Day	12% 6% 30% 31% 19% 2	450
	21st to end	Day	22% 11% 27% 27% 12% 2	373
October	1st to 10th	Day	17% 12% 27% 29% 12% 3	270
	11th to 20th	Day	22% 20% 33% 18% 7% 1	270
	21st to end	Day	28% 13% 37% 18% 3 1	297
November	1st to 10th	Day	17% 14% 36% 22% 9% 1	270
	11th to 20th	Day	21% 19% 34% 20% 6%	270
	21st to end	Day	21% 16% 37% 20% 6%	270
December	1st to 10th	Day	14% 16% 41% 21% 8% 1	270
	11th to 20th	Day	23% 17% 33% 20% 7% 1	270
	21st to end	Day	27% 15% 36% 18% 3	297
January	1st to 10th	Night	14% 10% 38% 28% 9%	950
	11th to 20th	Night	20% 9% 35% 28% 6% 2	915
	21st to end	Night	20% 10% 35% 29% 6% 1	990
February	1st to 10th	Night	14% 9% 41% 30% 6% 1	900
	11th to 20th	Night	14% 12% 39% 27% 7%	879
	21st to end	Night	19% 11% 37% 26% 6%	601
March	1st to 10th	Night	16% 13% 34% 29% 7% 1	720
	11th to 20th	Night	18% 11% 34% 29% 8% 1	540
	21st to end	Night	21% 10% 30% 28% 9% 2	594
April	1st to 10th	Night	22% 9% 34% 28% 7% 1	540
	11th to 20th	Night	30% 8% 26% 28% 7%	533
	21st to end	Night	24% 8% 29% 31% 7% 1	540
May	1st to 10th	Night	24% 9% 33% 28% 6% 1	540
	11th to 20th	Night	20% 8% 31% 30% 9% 2	531
	21st to end	Night	16% 7% 25% 36% 15% 1	584
June	1st to 10th	Night	12% 7% 30% 39% 11%	540
	11th to 20th	Night	15% 5% 30% 41% 9% 1	540
	21st to end	Night	12% 4 24% 45% 14% 1	540
July	1st to 10th	Night	8% 2 25% 36% 28% 2	525
	11th to 20th	Night	11% 3 26% 40% 19% 2	522
	21st to end	Night	7% 2 18% 48% 23% 2	591
August	1st to 10th	Night	10% 4 17% 45% 23% 2	537
	11th to 20th	Night	16% 2 20% 32% 27% 3	534
	21st to end	Night	16% 3 21% 33% 25% 2	594
September	1st to 10th	Night	11% 4 23% 40% 17% 4	540
	11th to 20th	Night	13% 3 30% 34% 18% 3	540
	21st to end	Night	17% 8% 32% 31% 11% 1	689
October	1st to 10th	Night	18% 7% 30% 30% 15% 1	720
	11th to 20th	Night	20% 12% 33% 28% 8%	720
	21st to end	Night	23% 10% 28% 29% 9%	792
November	1st to 10th	Night	22% 7% 33% 29% 8% 1	749
	11th to 20th	Night	20% 12% 37% 24% 7%	950
	21st to end	Night	20% 13% 36% 25% 6%	950
December	1st to 10th	Night	18% 10% 38% 27% 7% 1	950
	11th to 20th	Night	21% 9% 38% 23% 7% 1	950
	21st to end	Night	26% 10% 35% 23% 6% 1	1045

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