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 2025-11-18.

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 7% 5% 5% 5% 4 6% 8% 36%	126939
	Night	14% 8% 3 7% 4 4 4 4 6% 7% 39%	123402
Transparency	Day	43% 6% 14% 22% 13% 2	130427
	Night	42% 6% 14% 22% 15% 2	127988
Seeing	Day	20% 15% 31% 22% 9% 3	16182
	Night	19% 12% 32% 27% 8% 1	25251

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	9% 8% 3 10% 5% 6% 5% 4 5% 6% 39%	3597
	11th to 20th	Day	8% 11% 5% 11% 7% 5% 4 4 6% 8% 31%	3570
	21st to end	Day	11% 9% 5% 11% 5% 4 4 4 5% 6% 36%	4172
February	1st to 10th	Day	12% 12% 4 9% 6% 5% 5% 5% 6% 8% 30%	1800
	11th to 20th	Day	11% 8% 4 8% 6% 5% 5% 4 7% 6% 36%	1920
	21st to end	Day	15% 12% 2 6% 5% 4 3 5% 5% 5% 36%	1650
March	1st to 10th	Day	18% 9% 3 8% 4 4 4 3 5% 6% 36%	4476
	11th to 20th	Day	11% 8% 3 7% 4 5% 4 3 5% 7% 43%	4750
	21st to end	Day	15% 10% 2 6% 5% 4 5% 3 6% 6% 37%	5924
April	1st to 10th	Day	16% 11% 3 8% 5% 4 4 4 5% 6% 35%	2400
	11th to 20th	Day	15% 8% 2 7% 5% 4 5% 4 6% 6% 38%	2374
	21st to end	Day	18% 7% 2 7% 4 5% 5% 4 5% 7% 37%	2463
May	1st to 10th	Day	28% 8% 2 6% 4 4 5% 3 5% 7% 26%	5992
	11th to 20th	Day	18% 7% 2 7% 5% 5% 5% 4 6% 7% 35%	6318
	21st to end	Day	19% 7% 2 6% 5% 5% 5% 5% 7% 9% 31%	6949
June	1st to 10th	Day	15% 8% 2 7% 5% 5% 5% 5% 7% 9% 32%	2800
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 4 7% 9% 34%	2800
	21st to end	Day	14% 6% 2 7% 5% 5% 6% 5% 7% 9% 33%	2800
July	1st to 10th	Day	8% 6% 3 8% 7% 6% 7% 5% 8% 10% 33%	6360
	11th to 20th	Day	7% 5% 2 6% 6% 6% 7% 6% 9% 12% 34%	6360
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	6926
August	1st to 10th	Day	15% 7% 3 7% 6% 5% 6% 5% 7% 8% 31%	4462
	11th to 20th	Day	12% 7% 3 7% 5% 5% 6% 4 7% 10% 34%	3850
	21st to end	Day	8% 4 2 7% 4 6% 7% 5% 8% 10% 39%	4312
September	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 5% 7% 42%	2400
	11th to 20th	Day	12% 4 2 6% 4 4 4 3 5% 7% 49%	2317
	21st to end	Day	15% 6% 2 6% 3 4 6% 4 6% 7% 41%	2200
October	1st to 10th	Day	16% 7% 2 6% 5% 4 4 4 5% 6% 41%	2075
	11th to 20th	Day	13% 8% 2 7% 4 4 4 3 6% 7% 41%	2000
	21st to end	Day	19% 8% 2 5% 5% 4 5% 5% 5% 6% 35%	2011
November	1st to 10th	Day	11% 8% 3 6% 4 5% 4 4 5% 6% 44%	1851
	11th to 20th	Day	14% 8% 3 6% 6% 4 4 4 5% 6% 40%	1863
	21st to end	Day	15% 9% 3 6% 6% 5% 4 5% 5% 6% 35%	1651
December	1st to 10th	Day	9% 10% 4 12% 6% 6% 6% 4 6% 7% 30%	2600
	11th to 20th	Day	18% 8% 3 6% 4 3 4 3 5% 6% 38%	2986
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 4 7% 10% 31%	3960
January	1st to 10th	Night	12% 8% 3 6% 4 4 5% 3 6% 9% 40%	6349
	11th to 20th	Night	9% 12% 4 10% 6% 5% 5% 4 6% 10% 31%	6315
	21st to end	Night	13% 10% 3 8% 6% 5% 5% 4 5% 6% 35%	6766
February	1st to 10th	Night	12% 9% 4 9% 6% 6% 5% 4 5% 5% 34%	2600
	11th to 20th	Night	10% 11% 3 7% 6% 5% 6% 4 6% 7% 35%	2365
	21st to end	Night	14% 8% 3 7% 5% 5% 4 4 6% 7% 36%	1980
March	1st to 10th	Night	19% 8% 2 6% 3 3 4 4 5% 8% 39%	5364
	11th to 20th	Night	12% 9% 4 7% 4 5% 4 3 5% 7% 41%	5191
	21st to end	Night	14% 10% 3 7% 4 4 4 3 5% 6% 38%	4993
April	1st to 10th	Night	15% 9% 3 8% 6% 5% 6% 5% 6% 6% 32%	2000
	11th to 20th	Night	17% 8% 3 5% 4 4 5% 4 5% 6% 39%	1975
	21st to end	Night	18% 7% 2 6% 4 4 4 3 5% 6% 40%	1935
May	1st to 10th	Night	28% 8% 2 6% 4 4 4 3 5% 7% 29%	3990
	11th to 20th	Night	19% 7% 2 5% 4 3 4 4 9% 8% 35%	3575
	21st to end	Night	18% 8% 3 6% 5% 4 5% 4 6% 8% 33%	3926
June	1st to 10th	Night	16% 6% 3 6% 4 4 4 4 6% 7% 42%	1600
	11th to 20th	Night	13% 6% 2 6% 5% 4 4 4 7% 10% 41%	1600
	21st to end	Night	11% 4 2 6% 5% 4 5% 3 7% 10% 44%	1600
July	1st to 10th	Night	8% 5% 2 6% 5% 5% 5% 4 7% 8% 44%	3600
	11th to 20th	Night	9% 5% 3 7% 5% 6% 5% 5% 7% 10% 39%	3600
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 6% 49%	3926
August	1st to 10th	Night	17% 6% 2 6% 5% 5% 5% 4 6% 8% 37%	2666
	11th to 20th	Night	12% 6% 2 7% 4 4 4 3 5% 9% 42%	3183
	21st to end	Night	10% 4 2 4 4 4 4 3 5% 7% 53%	3586
September	1st to 10th	Night	13% 5% 2 5% 4 4 5% 4 5% 8% 46%	2000
	11th to 20th	Night	13% 4 1 4 3 3 3 2 4 7% 55%	2082
	21st to end	Night	15% 6% 2 7% 4 3 4 3 5% 6% 45%	2200
October	1st to 10th	Night	18% 6% 3 6% 3 3 4 2 5% 7% 42%	2320
	11th to 20th	Night	16% 6% 2 6% 4 4 4 4 5% 6% 44%	2400
	21st to end	Night	21% 7% 2 5% 5% 4 4 2 5% 7% 38%	2827
November	1st to 10th	Night	12% 8% 2 6% 4 3 3 3 6% 6% 46%	2667
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 6% 7% 40%	2692
	21st to end	Night	14% 7% 3 6% 5% 4 4 4 5% 7% 41%	2745
December	1st to 10th	Night	11% 11% 3 8% 5% 4 4 3 6% 8% 37%	4580
	11th to 20th	Night	21% 9% 3 6% 4 3 3 3 5% 6% 37%	5208
	21st to end	Night	18% 10% 3 8% 4 4 4 4 5% 7% 33%	6996

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	41% 4 15% 22% 14% 3	3598
	11th to 20th	Day	48% 5% 13% 17% 13% 4	3600
	21st to end	Day	46% 5% 13% 21% 14% 2	4172
February	1st to 10th	Day	50% 6% 14% 18% 10% 2	1800
	11th to 20th	Day	45% 7% 10% 23% 13% 3	1929
	21st to end	Day	48% 4 12% 20% 13% 2	1650
March	1st to 10th	Day	47% 5% 14% 15% 11% 9%	4479
	11th to 20th	Day	38% 5% 20% 24% 8% 5%	4750
	21st to end	Day	46% 5% 7% 15% 21% 6%	5924
April	1st to 10th	Day	49% 5% 9% 20% 12% 4	2400
	11th to 20th	Day	43% 6% 12% 21% 16% 2	2374
	21st to end	Day	44% 5% 13% 20% 15% 3	2463
May	1st to 10th	Day	55% 7% 12% 16% 9% 1	6003
	11th to 20th	Day	45% 7% 14% 22% 11% 1	6322
	21st to end	Day	45% 8% 14% 23% 10% 1	6949
June	1st to 10th	Day	44% 7% 17% 19% 13% 1	2800
	11th to 20th	Day	42% 8% 17% 21% 11% 1	2800
	21st to end	Day	42% 9% 14% 23% 11% 1	2800
July	1st to 10th	Day	42% 9% 15% 19% 14% 1	6290
	11th to 20th	Day	36% 10% 18% 26% 9% 1	6285
	21st to end	Day	39% 7% 13% 26% 15% 1	6728
August	1st to 10th	Day	47% 7% 17% 20% 9% 1	4448
	11th to 20th	Day	41% 7% 17% 28% 7%	3886
	21st to end	Day	35% 7% 17% 28% 12% 1	4312
September	1st to 10th	Day	39% 6% 13% 25% 16% 1	2400
	11th to 20th	Day	34% 5% 12% 26% 22% 2	2317
	21st to end	Day	41% 5% 14% 23% 16% 2	2200
October	1st to 10th	Day	38% 5% 10% 22% 23% 2	3374
	11th to 20th	Day	32% 4 9% 29% 23% 3	3240
	21st to end	Day	32% 6% 15% 28% 15% 4	3223
November	1st to 10th	Day	38% 6% 14% 25% 15% 2	1851
	11th to 20th	Day	44% 5% 12% 20% 16% 2	1863
	21st to end	Day	46% 5% 16% 24% 8% 2	1651
December	1st to 10th	Day	51% 5% 14% 23% 7%	2600
	11th to 20th	Day	45% 5% 14% 22% 11% 2	2986
	21st to end	Day	47% 7% 12% 17% 15% 2	3960
January	1st to 10th	Night	39% 6% 14% 21% 18% 1	6349
	11th to 20th	Night	47% 6% 14% 15% 13% 5%	6360
	21st to end	Night	47% 5% 13% 14% 16% 5%	6766
February	1st to 10th	Night	48% 5% 15% 20% 10% 2	2600
	11th to 20th	Night	45% 7% 11% 20% 14% 3	2367
	21st to end	Night	45% 5% 12% 23% 12% 3	1980
March	1st to 10th	Night	42% 5% 13% 19% 15% 6%	5374
	11th to 20th	Night	42% 6% 20% 21% 9% 3	5192
	21st to end	Night	45% 6% 7% 16% 23% 3	4993
April	1st to 10th	Night	50% 5% 12% 20% 12% 2	2000
	11th to 20th	Night	45% 6% 11% 20% 18% 1	1975
	21st to end	Night	45% 5% 11% 21% 16% 3	1935
May	1st to 10th	Night	55% 6% 14% 14% 10% 2	3996
	11th to 20th	Night	43% 9% 14% 20% 12% 1	3576
	21st to end	Night	47% 7% 16% 19% 10% 1	3927
June	1st to 10th	Night	40% 7% 12% 24% 15% 2	1600
	11th to 20th	Night	38% 7% 18% 26% 11% 1	1600
	21st to end	Night	35% 8% 16% 25% 15% 1	1600
July	1st to 10th	Night	36% 8% 16% 22% 16% 2	3560
	11th to 20th	Night	38% 9% 15% 24% 13% 1	3552
	21st to end	Night	33% 6% 12% 30% 17% 1	3809
August	1st to 10th	Night	43% 8% 17% 21% 10% 1	2656
	11th to 20th	Night	38% 8% 16% 29% 10%	3213
	21st to end	Night	29% 6% 12% 38% 15% 1	3586
September	1st to 10th	Night	37% 7% 10% 29% 17% 1	2000
	11th to 20th	Night	31% 4 11% 29% 24% 1	2082
	21st to end	Night	40% 5% 12% 24% 19% 1	2200
October	1st to 10th	Night	38% 6% 12% 24% 18% 1	3788
	11th to 20th	Night	30% 3 11% 27% 25% 4	3899
	21st to end	Night	35% 5% 15% 31% 14% 2	4565
November	1st to 10th	Night	37% 6% 12% 25% 18% 3	2667
	11th to 20th	Night	42% 6% 13% 22% 15% 3	2692
	21st to end	Night	41% 5% 18% 27% 9% 1	2745
December	1st to 10th	Night	43% 6% 14% 29% 8% 1	4580
	11th to 20th	Night	48% 5% 14% 16% 15% 2	5208
	21st to end	Night	49% 6% 13% 15% 13% 4	6996

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	23% 21% 35% 15% 7%	200
	11th to 20th	Day	23% 26% 36% 13% 2 1	200
	21st to end	Day	19% 22% 40% 15% 4	267
February	1st to 10th	Day	29% 24% 37% 9% 1	300
	11th to 20th	Day	25% 28% 34% 11% 1	468
	21st to end	Day	26% 25% 32% 15% 2	414
March	1st to 10th	Day	26% 18% 36% 17% 3	500
	11th to 20th	Day	22% 24% 35% 15% 3 1	500
	21st to end	Day	27% 25% 27% 14% 5% 2	550
April	1st to 10th	Day	29% 24% 27% 13% 6% 1	500
	11th to 20th	Day	24% 24% 30% 14% 7% 1	492
	21st to end	Day	26% 17% 34% 16% 5% 1	500
May	1st to 10th	Day	30% 17% 29% 16% 7% 1	503
	11th to 20th	Day	21% 16% 33% 20% 9% 2	527
	21st to end	Day	19% 10% 31% 25% 12% 3	573
June	1st to 10th	Day	17% 10% 34% 25% 12% 3	530
	11th to 20th	Day	15% 13% 32% 29% 10% 2	530
	21st to end	Day	17% 10% 31% 28% 13% 2	530
July	1st to 10th	Day	11% 6% 34% 31% 16% 2	525
	11th to 20th	Day	9% 7% 27% 38% 15% 4	524
	21st to end	Day	13% 7% 33% 31% 15% 2	576
August	1st to 10th	Day	10% 7% 28% 35% 14% 6%	526
	11th to 20th	Day	14% 4 26% 35% 13% 8%	519
	21st to end	Day	10% 7% 30% 32% 14% 7%	583
September	1st to 10th	Day	17% 8% 26% 27% 16% 6%	530
	11th to 20th	Day	12% 8% 27% 25% 18% 10%	530
	21st to end	Day	19% 10% 27% 28% 12% 4	530
October	1st to 10th	Day	22% 11% 24% 23% 14% 5%	530
	11th to 20th	Day	16% 18% 30% 26% 7% 2	530
	21st to end	Day	22% 17% 33% 21% 6%	478
November	1st to 10th	Day	20% 21% 29% 20% 10% 1	425
	11th to 20th	Day	21% 21% 33% 20% 5% 1	421
	21st to end	Day	21% 19% 38% 19% 2 1	251
December	1st to 10th	Day	21% 21% 39% 13% 7% 1	200
	11th to 20th	Day	28% 25% 34% 11% 4	200
	21st to end	Day	22% 20% 42% 15% 2	220
January	1st to 10th	Night	18% 18% 41% 21% 3	800
	11th to 20th	Night	19% 18% 37% 23% 2	800
	21st to end	Night	16% 18% 41% 23% 2	880
February	1st to 10th	Night	18% 19% 40% 21% 2	800
	11th to 20th	Night	19% 20% 42% 19% 1	783
	21st to end	Night	22% 16% 41% 18% 3	660
March	1st to 10th	Night	21% 17% 38% 21% 3	800
	11th to 20th	Night	21% 15% 42% 19% 3	800
	21st to end	Night	20% 21% 34% 20% 5%	880
April	1st to 10th	Night	21% 19% 36% 21% 4	800
	11th to 20th	Night	23% 17% 34% 20% 6%	791
	21st to end	Night	22% 16% 31% 25% 6% 1	735
May	1st to 10th	Night	27% 13% 29% 24% 7%	575
	11th to 20th	Night	18% 12% 31% 32% 7% 1	394
	21st to end	Night	16% 7% 29% 37% 11%	433
June	1st to 10th	Night	18% 6% 30% 34% 12% 1	400
	11th to 20th	Night	16% 7% 28% 36% 13% 1	400
	21st to end	Night	13% 4 26% 42% 15% 1	400
July	1st to 10th	Night	14% 3 22% 42% 18% 1	390
	11th to 20th	Night	13% 4 22% 42% 19% 1	388
	21st to end	Night	12% 5% 21% 47% 15% 1	438
August	1st to 10th	Night	11% 3 19% 45% 20% 2	439
	11th to 20th	Night	13% 4 17% 40% 23% 4	776
	21st to end	Night	16% 5% 19% 36% 22% 2	880
September	1st to 10th	Night	17% 5% 25% 35% 17% 2	800
	11th to 20th	Night	16% 6% 24% 29% 20% 6%	800
	21st to end	Night	18% 6% 25% 35% 15% 2	800
October	1st to 10th	Night	22% 9% 24% 28% 15% 3	800
	11th to 20th	Night	21% 9% 31% 31% 8%	800
	21st to end	Night	24% 12% 31% 27% 6%	880
November	1st to 10th	Night	19% 14% 33% 27% 7%	820
	11th to 20th	Night	21% 13% 36% 23% 6% 1	829
	21st to end	Night	17% 15% 36% 26% 6% 1	800
December	1st to 10th	Night	21% 14% 38% 23% 4	800
	11th to 20th	Night	22% 13% 38% 25% 3	800
	21st to end	Night	22% 16% 40% 19% 3	880

Page generated at 2025-11-15 00:56:00. Version ac07

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