North-South Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North-South Lake clear sky chart from 2005-11-06 to 2024-01-12.

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% 7% 3 6% 6% 4 5% 5% 6% 7% 36%	74760
	Night	15% 7% 3 6% 5% 3 5% 5% 5% 7% 39%	74950
Transparency	Day	44% 6% 14% 21% 12% 2	74465
	Night	43% 6% 14% 22% 13% 2	74779
Seeing	Day	19% 14% 31% 23% 10% 3	13733
	Night	19% 12% 32% 28% 9% 1	22944

By Month

Percentage Cloud Cover NE (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	10% 10% 4 7% 6% 4 5% 5% 7% 8% 35%	1517
	11th to 20th	Day	11% 11% 5% 7% 8% 4 5% 8% 6% 7% 28%	1454
	21st to end	Day	8% 9% 4 9% 7% 4 5% 5% 5% 7% 35%	1670
February	1st to 10th	Day	13% 11% 5% 9% 7% 4 6% 6% 5% 7% 28%	1620
	11th to 20th	Day	11% 7% 4 7% 7% 4 6% 5% 6% 7% 37%	1723
	21st to end	Day	16% 12% 4 6% 6% 3 4 6% 5% 5% 35%	1480
March	1st to 10th	Day	11% 8% 4 8% 8% 3 4 4 6% 7% 37%	1797
	11th to 20th	Day	14% 9% 4 7% 6% 4 5% 4 6% 7% 35%	1890
	21st to end	Day	16% 9% 3 7% 6% 4 4 4 4 5% 38%	2358
April	1st to 10th	Day	15% 10% 4 7% 6% 3 4 4 5% 6% 36%	2160
	11th to 20th	Day	14% 7% 3 6% 6% 3 5% 5% 5% 6% 39%	2134
	21st to end	Day	19% 6% 3 5% 5% 3 5% 5% 6% 7% 36%	2216
May	1st to 10th	Day	20% 9% 3 7% 5% 3 5% 5% 5% 7% 31%	2376
	11th to 20th	Day	18% 6% 2 5% 6% 3 6% 5% 5% 8% 37%	2478
	21st to end	Day	13% 6% 2 5% 6% 3 6% 6% 6% 8% 39%	2725
June	1st to 10th	Day	15% 7% 3 6% 6% 4 5% 6% 7% 9% 33%	2520
	11th to 20th	Day	14% 5% 3 6% 6% 4 6% 5% 7% 10% 35%	2520
	21st to end	Day	15% 5% 2 6% 6% 4 7% 7% 7% 10% 32%	2520
July	1st to 10th	Day	10% 6% 3 6% 7% 5% 7% 6% 7% 8% 36%	2520
	11th to 20th	Day	9% 5% 2 5% 7% 4 6% 7% 8% 10% 37%	2520
	21st to end	Day	11% 6% 3 6% 6% 5% 7% 6% 7% 8% 35%	2744
August	1st to 10th	Day	9% 6% 2 5% 7% 4 7% 8% 7% 10% 35%	2463
	11th to 20th	Day	12% 6% 3 6% 7% 4 6% 7% 8% 10% 32%	2126
	21st to end	Day	12% 5% 2 6% 4 3 7% 6% 7% 9% 39%	2376
September	1st to 10th	Day	13% 6% 3 6% 5% 4 5% 5% 5% 8% 40%	2160
	11th to 20th	Day	13% 4 2 5% 5% 3 5% 4 5% 7% 47%	2086
	21st to end	Day	15% 6% 2 5% 4 3 5% 5% 6% 7% 43%	1980
October	1st to 10th	Day	18% 7% 3 6% 6% 3 4 4 5% 5% 39%	1868
	11th to 20th	Day	14% 8% 2 6% 5% 3 4 4 6% 8% 41%	1800
	21st to end	Day	21% 8% 3 5% 5% 3 6% 6% 6% 6% 33%	1811
November	1st to 10th	Day	12% 7% 3 5% 5% 3 4 5% 5% 6% 45%	1671
	11th to 20th	Day	15% 8% 3 6% 6% 3 4 5% 5% 6% 39%	1710
	21st to end	Day	15% 7% 3 6% 6% 3 5% 6% 5% 6% 36%	1569
December	1st to 10th	Day	14% 10% 4 10% 7% 5% 6% 5% 6% 7% 27%	1520
	11th to 20th	Day	20% 7% 4 6% 6% 2 4 4 5% 5% 37%	1906
	21st to end	Day	19% 10% 5% 8% 6% 4 4 5% 5% 8% 26%	2772
January	1st to 10th	Night	12% 9% 4 7% 6% 3 4 4 6% 7% 40%	2649
	11th to 20th	Night	13% 10% 4 8% 7% 3 5% 5% 5% 8% 32%	2546
	21st to end	Night	9% 8% 3 7% 7% 4 6% 4 5% 8% 38%	2682
February	1st to 10th	Night	13% 8% 4 9% 7% 4 5% 5% 5% 5% 33%	2340
	11th to 20th	Night	11% 10% 4 6% 6% 4 6% 5% 6% 7% 35%	2122
	21st to end	Night	15% 7% 4 6% 5% 4 5% 4 6% 6% 37%	1776
March	1st to 10th	Night	13% 10% 3 6% 4 3 4 5% 5% 7% 40%	2150
	11th to 20th	Night	14% 7% 3 5% 6% 3 6% 6% 6% 6% 38%	2065
	21st to end	Night	13% 8% 3 6% 5% 3 5% 4 6% 7% 40%	1997
April	1st to 10th	Night	15% 8% 4 6% 6% 4 6% 6% 5% 7% 34%	1800
	11th to 20th	Night	17% 7% 3 5% 5% 3 5% 5% 5% 6% 40%	1775
	21st to end	Night	19% 6% 2 6% 5% 3 4 4 5% 6% 39%	1742
May	1st to 10th	Night	21% 9% 3 6% 6% 4 4 4 4 7% 34%	1598
	11th to 20th	Night	16% 6% 2 5% 5% 3 4 5% 6% 8% 39%	1415
	21st to end	Night	12% 6% 3 5% 5% 3 6% 6% 5% 8% 42%	1550
June	1st to 10th	Night	15% 6% 3 5% 5% 2 4 5% 6% 7% 43%	1440
	11th to 20th	Night	13% 5% 2 6% 5% 2 5% 4 7% 9% 42%	1440
	21st to end	Night	11% 4 2 5% 5% 3 5% 4 6% 10% 45%	1440
July	1st to 10th	Night	11% 4 2 3 5% 3 5% 5% 7% 8% 47%	1440
	11th to 20th	Night	11% 4 3 5% 5% 3 6% 5% 7% 9% 42%	1440
	21st to end	Night	12% 5% 2 5% 4 3 5% 6% 6% 7% 44%	1574
August	1st to 10th	Night	8% 5% 2 5% 6% 4 5% 4 7% 9% 46%	1468
	11th to 20th	Night	11% 6% 2 7% 5% 4 5% 5% 6% 10% 40%	1761
	21st to end	Night	14% 5% 2 4 5% 3 5% 4 5% 7% 45%	1980
September	1st to 10th	Night	14% 5% 2 4 5% 3 5% 4 6% 8% 44%	1800
	11th to 20th	Night	14% 5% 1 3 3 2 4 3 4 6% 55%	1873
	21st to end	Night	15% 5% 2 5% 5% 2 3 4 5% 6% 47%	1980
October	1st to 10th	Night	19% 6% 3 6% 4 2 3 3 5% 7% 41%	2088
	11th to 20th	Night	16% 6% 2 5% 5% 3 4 4 5% 7% 43%	2160
	21st to end	Night	22% 7% 2 5% 6% 3 3 3 4 7% 36%	2543
November	1st to 10th	Night	12% 8% 3 5% 5% 3 3 4 5% 6% 46%	2407
	11th to 20th	Night	16% 7% 3 5% 4 3 4 4 6% 7% 40%	2470
	21st to end	Night	13% 6% 3 5% 5% 3 5% 5% 5% 8% 42%	2607
December	1st to 10th	Night	15% 9% 4 7% 6% 4 5% 5% 6% 6% 34%	2660
	11th to 20th	Night	18% 8% 3 5% 5% 3 4 5% 6% 7% 35%	3288
	21st to end	Night	20% 10% 3 8% 6% 3 4 5% 5% 6% 31%	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	43% 5% 16% 23% 11% 2	1518
	11th to 20th	Day	50% 9% 15% 16% 9% 2	1454
	21st to end	Day	45% 5% 14% 21% 12% 2	1670
February	1st to 10th	Day	53% 6% 13% 17% 9% 2	1620
	11th to 20th	Day	45% 7% 11% 23% 13% 3	1732
	21st to end	Day	50% 5% 12% 19% 12% 2	1480
March	1st to 10th	Day	44% 6% 16% 20% 12% 3	1800
	11th to 20th	Day	46% 5% 13% 20% 13% 2	1890
	21st to end	Day	48% 5% 8% 18% 17% 5%	2358
April	1st to 10th	Day	48% 6% 10% 21% 12% 3	2160
	11th to 20th	Day	42% 6% 12% 21% 16% 2	2134
	21st to end	Day	46% 5% 12% 19% 14% 4	2216
May	1st to 10th	Day	51% 4 10% 20% 12% 2	2376
	11th to 20th	Day	43% 7% 10% 23% 14% 2	2482
	21st to end	Day	40% 7% 18% 22% 11% 2	2725
June	1st to 10th	Day	44% 7% 17% 18% 12% 1	2520
	11th to 20th	Day	42% 8% 16% 22% 11% 1	2520
	21st to end	Day	43% 9% 14% 23% 10% 1	2520
July	1st to 10th	Day	42% 8% 14% 20% 15% 1	2450
	11th to 20th	Day	37% 8% 18% 24% 12%	2445
	21st to end	Day	41% 8% 15% 21% 13% 2	2591
August	1st to 10th	Day	38% 8% 17% 24% 12% 1	2449
	11th to 20th	Day	43% 8% 17% 23% 8%	2126
	21st to end	Day	38% 7% 14% 25% 15% 1	2376
September	1st to 10th	Day	41% 6% 14% 23% 14% 1	2160
	11th to 20th	Day	36% 6% 11% 24% 22% 2	2086
	21st to end	Day	38% 5% 14% 24% 17% 2	1980
October	1st to 10th	Day	45% 5% 11% 22% 14% 2	1868
	11th to 20th	Day	40% 7% 14% 28% 12% 1	1800
	21st to end	Day	50% 6% 13% 18% 10% 3	1811
November	1st to 10th	Day	38% 6% 14% 26% 14% 2	1671
	11th to 20th	Day	45% 5% 13% 21% 15% 2	1710
	21st to end	Day	45% 5% 16% 24% 8% 2	1569
December	1st to 10th	Day	55% 5% 15% 16% 9% 1	1520
	11th to 20th	Day	47% 6% 16% 21% 8% 2	1906
	21st to end	Day	56% 8% 13% 16% 6%	2772
January	1st to 10th	Night	43% 6% 15% 20% 15% 2	2649
	11th to 20th	Night	49% 8% 14% 18% 9% 2	2546
	21st to end	Night	43% 6% 12% 22% 14% 3	2682
February	1st to 10th	Night	50% 5% 14% 18% 10% 2	2340
	11th to 20th	Night	46% 7% 11% 20% 13% 2	2124
	21st to end	Night	46% 5% 11% 24% 11% 3	1776
March	1st to 10th	Night	42% 5% 13% 24% 13% 2	2160
	11th to 20th	Night	44% 6% 14% 20% 13% 2	2066
	21st to end	Night	43% 7% 10% 21% 16% 4	1997
April	1st to 10th	Night	48% 5% 12% 21% 12% 2	1800
	11th to 20th	Night	45% 5% 11% 20% 18% 1	1775
	21st to end	Night	46% 5% 11% 21% 14% 3	1742
May	1st to 10th	Night	51% 5% 10% 17% 14% 2	1598
	11th to 20th	Night	42% 6% 11% 22% 16% 2	1416
	21st to end	Night	39% 8% 18% 22% 13% 1	1551
June	1st to 10th	Night	40% 7% 12% 26% 14% 2	1440
	11th to 20th	Night	38% 7% 17% 26% 11% 1	1440
	21st to end	Night	34% 9% 16% 26% 15% 1	1440
July	1st to 10th	Night	34% 8% 15% 25% 15% 3	1400
	11th to 20th	Night	36% 8% 17% 28% 11%	1392
	21st to end	Night	35% 9% 15% 23% 15% 3	1486
August	1st to 10th	Night	32% 8% 18% 27% 14% 1	1458
	11th to 20th	Night	37% 10% 17% 25% 11%	1761
	21st to end	Night	37% 6% 12% 26% 16% 1	1980
September	1st to 10th	Night	39% 7% 11% 29% 15% 1	1800
	11th to 20th	Night	32% 4 11% 27% 24% 1	1873
	21st to end	Night	38% 4 12% 25% 20% 1	1980
October	1st to 10th	Night	43% 6% 13% 23% 14% 1	2088
	11th to 20th	Night	41% 5% 16% 24% 13% 1	2160
	21st to end	Night	49% 5% 13% 21% 11% 1	2543
November	1st to 10th	Night	38% 7% 12% 24% 17% 3	2407
	11th to 20th	Night	43% 6% 13% 22% 13% 3	2470
	21st to end	Night	41% 5% 18% 27% 8% 1	2607
December	1st to 10th	Night	48% 6% 15% 21% 9% 1	2660
	11th to 20th	Night	47% 6% 16% 17% 12% 1	3288
	21st to end	Night	53% 6% 15% 19% 7%	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	21% 17% 39% 16% 7%	180
	11th to 20th	Day	23% 26% 35% 12% 2 1	164
	21st to end	Day	16% 23% 40% 16% 4	214
February	1st to 10th	Day	31% 20% 38% 10% 1	240
	11th to 20th	Day	24% 26% 37% 12% 1	391
	21st to end	Day	28% 23% 32% 15% 2	346
March	1st to 10th	Day	22% 19% 39% 18% 3	420
	11th to 20th	Day	21% 23% 37% 16% 3 1	420
	21st to end	Day	27% 25% 26% 15% 5% 3	462
April	1st to 10th	Day	25% 24% 27% 15% 7% 1	420
	11th to 20th	Day	20% 24% 31% 16% 8% 1	412
	21st to end	Day	29% 16% 32% 16% 5% 2	420
May	1st to 10th	Day	29% 16% 30% 16% 8% 1	423
	11th to 20th	Day	19% 15% 36% 19% 8% 2	447
	21st to end	Day	17% 9% 31% 26% 13% 4	485
June	1st to 10th	Day	17% 9% 35% 24% 13% 3	450
	11th to 20th	Day	15% 11% 32% 30% 11% 2	450
	21st to end	Day	17% 9% 28% 29% 14% 2	450
July	1st to 10th	Day	11% 5% 30% 33% 18% 2	445
	11th to 20th	Day	10% 5% 25% 40% 16% 4	444
	21st to end	Day	13% 5% 32% 32% 16% 2	488
August	1st to 10th	Day	9% 6% 27% 37% 16% 6%	446
	11th to 20th	Day	15% 4 24% 35% 15% 7%	439
	21st to end	Day	11% 6% 28% 32% 16% 7%	495
September	1st to 10th	Day	17% 8% 26% 26% 17% 6%	450
	11th to 20th	Day	14% 9% 28% 24% 15% 10%	450
	21st to end	Day	17% 11% 27% 28% 13% 4	450
October	1st to 10th	Day	24% 10% 23% 23% 14% 5%	450
	11th to 20th	Day	15% 16% 32% 28% 8% 2	450
	21st to end	Day	24% 17% 32% 22% 5%	410
November	1st to 10th	Day	19% 18% 30% 22% 11% 1	365
	11th to 20th	Day	21% 21% 31% 21% 5% 1	370
	21st to end	Day	18% 19% 38% 21% 3 1	229
December	1st to 10th	Day	20% 21% 41% 12% 6% 1	180
	11th to 20th	Day	27% 24% 33% 12% 4	180
	21st to end	Day	23% 19% 41% 15% 2 1	198
January	1st to 10th	Night	18% 16% 41% 22% 3	760
	11th to 20th	Night	20% 18% 36% 24% 2	728
	21st to end	Night	15% 19% 40% 24% 2	792
February	1st to 10th	Night	18% 19% 39% 22% 2	720
	11th to 20th	Night	19% 19% 42% 19% 1	703
	21st to end	Night	22% 16% 41% 18% 3	592
March	1st to 10th	Night	20% 17% 38% 22% 3	720
	11th to 20th	Night	21% 14% 41% 19% 3	720
	21st to end	Night	20% 21% 33% 20% 6%	792
April	1st to 10th	Night	20% 18% 36% 22% 4	720
	11th to 20th	Night	21% 16% 35% 21% 6%	711
	21st to end	Night	23% 15% 31% 25% 6% 1	662
May	1st to 10th	Night	26% 13% 29% 24% 8%	518
	11th to 20th	Night	18% 11% 32% 32% 7%	354
	21st to end	Night	16% 7% 27% 37% 12% 1	389
June	1st to 10th	Night	18% 6% 29% 34% 13% 1	360
	11th to 20th	Night	16% 7% 26% 36% 14% 1	360
	21st to end	Night	12% 3 26% 44% 14% 1	360
July	1st to 10th	Night	15% 3 20% 41% 20% 1	350
	11th to 20th	Night	14% 3 20% 43% 20% 1	348
	21st to end	Night	12% 4 19% 47% 17% 1	394
August	1st to 10th	Night	10% 3 20% 44% 21% 2	394
	11th to 20th	Night	12% 3 16% 41% 23% 4	697
	21st to end	Night	16% 5% 18% 36% 23% 3	792
September	1st to 10th	Night	17% 4 25% 34% 17% 2	720
	11th to 20th	Night	17% 7% 25% 27% 19% 6%	720
	21st to end	Night	18% 6% 25% 35% 14% 2	720
October	1st to 10th	Night	23% 8% 24% 28% 14% 3	720
	11th to 20th	Night	20% 9% 31% 32% 8%	720
	21st to end	Night	26% 13% 30% 26% 6% 1	792
November	1st to 10th	Night	18% 14% 32% 28% 8%	740
	11th to 20th	Night	21% 12% 36% 24% 6% 1	760
	21st to end	Night	16% 15% 36% 27% 6% 1	760
December	1st to 10th	Night	21% 14% 38% 22% 4	760
	11th to 20th	Night	21% 13% 38% 25% 3	760
	21st to end	Night	23% 16% 41% 19% 2	836

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