North Lake Sinclair
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Lake Sinclair clear sky chart from 2005-11-06 to 2026-02-16.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	130986
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	129839
Transparency	Day	37% 7% 12% 19% 18% 7%	134749
	Night	36% 6% 11% 18% 20% 8%	134146
Seeing	Day	15% 10% 23% 24% 20% 9%	16703
	Night	15% 9% 22% 30% 21% 3	26799

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	14% 6% 2 5% 4 4 4 3 5% 6% 47%	5258
	11th to 20th	Day	11% 6% 2 4 3 2 2 2 4 6% 58%	5280
	21st to end	Day	18% 8% 2 7% 5% 4 4 2 4 6% 39%	5882
February	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 5% 7% 41%	2100
	11th to 20th	Day	20% 7% 2 5% 3 3 3 3 5% 6% 44%	1998
	21st to end	Day	17% 7% 2 6% 4 4 4 4 5% 6% 42%	1650
March	1st to 10th	Day	20% 8% 2 7% 4 4 3 3 5% 5% 38%	4772
	11th to 20th	Day	8% 4 1 5% 4 3 4 4 5% 7% 54%	4980
	21st to end	Day	15% 7% 3 7% 4 4 4 3 3 4 46%	5465
April	1st to 10th	Day	12% 5% 2 6% 5% 4 4 3 5% 6% 49%	2200
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 6% 7% 50%	2317
	21st to end	Day	8% 4 2 5% 4 4 5% 3 5% 8% 52%	2600
May	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 4 6% 9% 41%	5862
	11th to 20th	Day	17% 7% 2 7% 4 6% 5% 4 7% 9% 32%	5861
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 44%	6433
June	1st to 10th	Day	10% 6% 2 8% 6% 6% 6% 5% 8% 10% 33%	2600
	11th to 20th	Day	5% 4 2 6% 5% 5% 5% 5% 7% 11% 44%	2600
	21st to end	Day	5% 5% 2 6% 6% 7% 6% 6% 9% 10% 38%	2600
July	1st to 10th	Day	10% 6% 2 7% 6% 6% 8% 6% 9% 12% 28%	5900
	11th to 20th	Day	4 4 2 6% 6% 6% 7% 6% 10% 14% 37%	5900
	21st to end	Day	6% 7% 3 8% 6% 7% 7% 7% 9% 13% 26%	6424
August	1st to 10th	Day	13% 5% 2 7% 5% 6% 6% 6% 8% 13% 29%	4234
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 5% 7% 10% 45%	4022
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 6% 9% 48%	4199
September	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 5% 6% 10% 39%	2200
	11th to 20th	Day	13% 6% 3 6% 4 5% 4 4 7% 8% 42%	2200
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 7% 45%	2200
October	1st to 10th	Day	13% 5% 2 5% 3 4 4 3 4 7% 51%	2200
	11th to 20th	Day	13% 4 1 3 3 3 3 2 4 7% 58%	2040
	21st to end	Day	12% 5% 1 4 3 4 4 3 4 5% 56%	2200
November	1st to 10th	Day	13% 6% 2 4 4 3 3 3 4 5% 53%	1981
	11th to 20th	Day	13% 5% 2 4 3 2 3 2 4 7% 55%	1890
	21st to end	Day	13% 5% 2 5% 4 3 4 4 5% 7% 48%	1890
December	1st to 10th	Day	13% 7% 3 6% 3 4 3 3 4 6% 47%	3020
	11th to 20th	Day	16% 6% 2 5% 4 3 3 3 4 6% 48%	3463
	21st to end	Day	21% 7% 2 5% 2 3 3 3 4 6% 44%	4565
January	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 6% 48%	7635
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 5% 5% 50%	7680
	21st to end	Night	18% 10% 3 7% 4 3 4 3 4 5% 40%	8282
February	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 5% 6% 46%	2520
	11th to 20th	Night	18% 7% 2 6% 4 3 4 3 4 5% 44%	2399
	21st to end	Night	14% 7% 2 6% 4 4 4 3 5% 7% 45%	1980
March	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 5% 6% 40%	5079
	11th to 20th	Night	10% 4 2 4 3 3 4 4 6% 8% 52%	4980
	21st to end	Night	15% 5% 2 5% 3 4 4 4 5% 6% 46%	5467
April	1st to 10th	Night	11% 5% 2 6% 4 3 4 4 6% 7% 49%	2200
	11th to 20th	Night	12% 4 1 4 3 3 4 4 5% 8% 52%	2044
	21st to end	Night	7% 3 1 6% 4 4 5% 4 6% 7% 53%	1800
May	1st to 10th	Night	8% 6% 2 6% 5% 5% 5% 5% 7% 11% 39%	4033
	11th to 20th	Night	16% 5% 2 6% 4 5% 5% 5% 7% 9% 35%	4032
	21st to end	Night	9% 4 2 5% 4 4 4 4 6% 10% 47%	4421
June	1st to 10th	Night	9% 6% 2 6% 5% 6% 6% 5% 8% 10% 37%	1800
	11th to 20th	Night	4 4 2 6% 6% 6% 5% 5% 7% 11% 43%	1800
	21st to end	Night	6% 5% 2 5% 5% 5% 6% 7% 10% 14% 37%	1800
July	1st to 10th	Night	10% 8% 3 8% 6% 6% 6% 5% 8% 11% 29%	4058
	11th to 20th	Night	4 4 2 8% 6% 6% 7% 6% 9% 15% 33%	4057
	21st to end	Night	8% 7% 3 8% 6% 7% 6% 6% 9% 12% 28%	4427
August	1st to 10th	Night	12% 6% 3 7% 6% 7% 7% 5% 8% 12% 28%	2915
	11th to 20th	Night	7% 5% 2 7% 5% 5% 6% 5% 6% 10% 43%	3021
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 10% 48%	3652
September	1st to 10th	Night	9% 6% 2 7% 5% 5% 6% 5% 7% 10% 39%	2200
	11th to 20th	Night	12% 6% 2 7% 5% 5% 4 4 5% 7% 43%	2200
	21st to end	Night	12% 5% 2 6% 4 5% 4 3 6% 7% 46%	2200
October	1st to 10th	Night	13% 5% 1 5% 4 3 4 3 4 5% 52%	2200
	11th to 20th	Night	12% 4 1 4 3 2 3 3 4 6% 59%	2358
	21st to end	Night	11% 4 1 4 3 3 4 3 4 5% 56%	2640
November	1st to 10th	Night	12% 5% 2 5% 2 3 3 3 4 6% 54%	2534
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 3 5% 55%	2730
	21st to end	Night	12% 5% 2 6% 4 4 3 4 4 6% 50%	2730
December	1st to 10th	Night	13% 6% 2 5% 3 3 3 2 4 5% 54%	4380
	11th to 20th	Night	16% 5% 2 5% 4 3 3 3 5% 6% 48%	4952
	21st to end	Night	20% 7% 2 6% 4 4 3 3 4 5% 43%	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	38% 4 8% 20% 24% 7%	5259
	11th to 20th	Day	29% 2 4 17% 32% 15%	5280
	21st to end	Day	48% 3 5% 16% 20% 9%	5882
February	1st to 10th	Day	42% 4 8% 19% 19% 8%	2100
	11th to 20th	Day	42% 4 6% 19% 22% 6%	2008
	21st to end	Day	42% 5% 8% 14% 22% 9%	1650
March	1st to 10th	Day	47% 4 7% 11% 24% 7%	4772
	11th to 20th	Day	29% 5% 8% 15% 22% 21%	4980
	21st to end	Day	42% 4 5% 20% 18% 10%	5465
April	1st to 10th	Day	36% 5% 10% 21% 20% 9%	2200
	11th to 20th	Day	33% 5% 9% 20% 22% 11%	2317
	21st to end	Day	30% 6% 12% 24% 24% 4	2600
May	1st to 10th	Day	38% 8% 15% 22% 15% 2	5897
	11th to 20th	Day	46% 8% 17% 18% 10% 1	5865
	21st to end	Day	35% 8% 13% 21% 21% 2	6447
June	1st to 10th	Day	41% 10% 16% 19% 12% 2	2600
	11th to 20th	Day	31% 11% 18% 25% 15% 1	2600
	21st to end	Day	35% 12% 18% 19% 13% 3	2600
July	1st to 10th	Day	43% 14% 19% 19% 4 1	5835
	11th to 20th	Day	32% 14% 29% 21% 3 1	5831
	21st to end	Day	43% 15% 20% 19% 3	6240
August	1st to 10th	Day	43% 10% 19% 25% 3	4221
	11th to 20th	Day	31% 10% 17% 28% 14% 1	4061
	21st to end	Day	31% 8% 16% 28% 15% 3	4199
September	1st to 10th	Day	39% 10% 14% 18% 16% 4	2200
	11th to 20th	Day	39% 8% 11% 20% 20% 3	2200
	21st to end	Day	39% 6% 10% 21% 19% 5%	2200
October	1st to 10th	Day	30% 3 7% 14% 33% 12%	3590
	11th to 20th	Day	17% 2 5% 16% 28% 31%	3306
	21st to end	Day	23% 3 5% 20% 35% 14%	3538
November	1st to 10th	Day	34% 4 8% 14% 27% 13%	1981
	11th to 20th	Day	31% 3 7% 21% 26% 12%	1890
	21st to end	Day	35% 5% 9% 18% 26% 8%	1890
December	1st to 10th	Day	38% 4 6% 16% 26% 9%	3020
	11th to 20th	Day	39% 4 8% 20% 21% 8%	3460
	21st to end	Day	41% 4 8% 21% 23% 3	4565
January	1st to 10th	Night	36% 4 8% 21% 24% 6%	7636
	11th to 20th	Night	35% 3 6% 18% 28% 10%	7680
	21st to end	Night	47% 3 5% 14% 23% 8%	8282
February	1st to 10th	Night	39% 5% 7% 18% 22% 9%	2520
	11th to 20th	Night	43% 4 6% 17% 21% 9%	2400
	21st to end	Night	40% 5% 8% 15% 19% 13%	1980
March	1st to 10th	Night	45% 4 9% 14% 17% 11%	5079
	11th to 20th	Night	28% 4 10% 12% 25% 20%	4980
	21st to end	Night	38% 4 7% 18% 20% 13%	5467
April	1st to 10th	Night	34% 5% 10% 21% 20% 11%	2200
	11th to 20th	Night	30% 5% 7% 24% 23% 11%	2044
	21st to end	Night	29% 8% 11% 22% 23% 7%	1800
May	1st to 10th	Night	35% 10% 16% 23% 13% 3	4060
	11th to 20th	Night	42% 9% 16% 21% 11% 1	4033
	21st to end	Night	31% 7% 15% 24% 20% 3	4429
June	1st to 10th	Night	38% 11% 17% 19% 15% 1	1800
	11th to 20th	Night	31% 10% 19% 26% 12% 2	1800
	21st to end	Night	31% 14% 22% 17% 12% 4	1800
July	1st to 10th	Night	46% 13% 21% 16% 4 1	4015
	11th to 20th	Night	35% 14% 30% 18% 3	4006
	21st to end	Night	46% 15% 20% 16% 4	4297
August	1st to 10th	Night	46% 10% 20% 20% 3	2904
	11th to 20th	Night	34% 10% 18% 24% 12% 2	3048
	21st to end	Night	30% 8% 17% 27% 16% 2	3652
September	1st to 10th	Night	39% 10% 16% 17% 14% 4	2200
	11th to 20th	Night	39% 8% 12% 18% 19% 5%	2200
	21st to end	Night	37% 7% 12% 17% 21% 6%	2200
October	1st to 10th	Night	33% 4 9% 12% 31% 10%	3590
	11th to 20th	Night	17% 3 5% 13% 30% 32%	3831
	21st to end	Night	21% 3 5% 19% 32% 19%	4252
November	1st to 10th	Night	32% 5% 8% 14% 27% 14%	2534
	11th to 20th	Night	32% 4 6% 17% 27% 14%	2730
	21st to end	Night	36% 5% 7% 18% 25% 10%	2730
December	1st to 10th	Night	33% 4 6% 19% 30% 8%	4380
	11th to 20th	Night	37% 4 11% 17% 22% 8%	4954
	21st to end	Night	44% 3 6% 23% 21% 3	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	21% 21% 44% 12% 3	330
	11th to 20th	Day	23% 24% 33% 12% 7% 1	330
	21st to end	Day	25% 25% 36% 11% 4	363
February	1st to 10th	Day	23% 17% 40% 18% 2	330
	11th to 20th	Day	36% 17% 31% 15% 1	315
	21st to end	Day	24% 20% 39% 13% 4	249
March	1st to 10th	Day	23% 21% 26% 22% 6% 1	423
	11th to 20th	Day	20% 16% 36% 19% 9%	500
	21st to end	Day	19% 17% 36% 21% 7%	550
April	1st to 10th	Day	21% 16% 28% 23% 12%	500
	11th to 20th	Day	12% 15% 29% 29% 13% 3	492
	21st to end	Day	12% 11% 27% 28% 20% 3	500
May	1st to 10th	Day	11% 12% 26% 29% 15% 7%	503
	11th to 20th	Day	15% 6% 23% 27% 20% 9%	527
	21st to end	Day	13% 6% 18% 29% 23% 11%	573
June	1st to 10th	Day	10% 5% 19% 27% 28% 12%	530
	11th to 20th	Day	5% 3 17% 28% 27% 19%	530
	21st to end	Day	6% 3 12% 31% 30% 18%	530
July	1st to 10th	Day	8% 2 9% 22% 33% 26%	525
	11th to 20th	Day	6% 2 6% 21% 39% 27%	524
	21st to end	Day	5% 2 9% 24% 39% 22%	576
August	1st to 10th	Day	16% 3 13% 23% 28% 17%	526
	11th to 20th	Day	9% 2 8% 21% 39% 20%	519
	21st to end	Day	13% 2 10% 29% 29% 17%	583
September	1st to 10th	Day	10% 4 13% 29% 29% 14%	530
	11th to 20th	Day	15% 4 13% 26% 32% 10%	530
	21st to end	Day	16% 5% 17% 26% 28% 8%	530
October	1st to 10th	Day	16% 7% 21% 29% 19% 8%	530
	11th to 20th	Day	12% 8% 21% 30% 22% 6%	530
	21st to end	Day	16% 9% 24% 26% 21% 4	583
November	1st to 10th	Day	21% 6% 26% 28% 16% 3	459
	11th to 20th	Day	16% 15% 39% 22% 6% 2	330
	21st to end	Day	15% 15% 32% 28% 9% 2	330
December	1st to 10th	Day	28% 17% 33% 15% 6% 1	330
	11th to 20th	Day	25% 15% 32% 17% 10% 1	330
	21st to end	Day	28% 16% 31% 19% 6% 1	363
January	1st to 10th	Night	21% 18% 32% 23% 5%	840
	11th to 20th	Night	19% 16% 31% 26% 8%	840
	21st to end	Night	19% 18% 35% 25% 3	924
February	1st to 10th	Night	20% 13% 31% 30% 6%	840
	11th to 20th	Night	22% 17% 31% 27% 3	804
	21st to end	Night	17% 16% 34% 28% 4	660
March	1st to 10th	Night	17% 15% 31% 32% 5%	800
	11th to 20th	Night	17% 14% 32% 27% 9%	800
	21st to end	Night	18% 14% 30% 29% 9%	880
April	1st to 10th	Night	16% 14% 31% 28% 12%	800
	11th to 20th	Night	14% 12% 27% 32% 14% 1	671
	21st to end	Night	9% 8% 24% 40% 19% 1	600
May	1st to 10th	Night	8% 8% 26% 40% 18% 2	600
	11th to 20th	Night	12% 3 22% 35% 24% 4	591
	21st to end	Night	12% 3 16% 34% 30% 6%	650
June	1st to 10th	Night	11% 2 13% 40% 30% 4	600
	11th to 20th	Night	4 4 13% 33% 36% 11%	600
	21st to end	Night	7% 2 8% 35% 42% 7%	600
July	1st to 10th	Night	9% 1 8% 28% 41% 13%	585
	11th to 20th	Night	6% 2 5% 23% 49% 14%	582
	21st to end	Night	6% 2 6% 29% 48% 9%	657
August	1st to 10th	Night	11% 2 8% 30% 38% 12%	597
	11th to 20th	Night	11% 1 7% 28% 44% 9%	594
	21st to end	Night	14% 3 8% 29% 37% 9%	700
September	1st to 10th	Night	10% 2 12% 31% 38% 8%	800
	11th to 20th	Night	14% 2 11% 29% 40% 4	800
	21st to end	Night	14% 3 16% 31% 33% 4	800
October	1st to 10th	Night	14% 3 21% 32% 26% 5%	800
	11th to 20th	Night	14% 7% 19% 33% 24% 4	800
	21st to end	Night	13% 8% 24% 31% 23% 2	880
November	1st to 10th	Night	15% 7% 21% 35% 21% 2	820
	11th to 20th	Night	15% 12% 26% 31% 15% 1	840
	21st to end	Night	13% 13% 28% 31% 15% 1	840
December	1st to 10th	Night	19% 13% 29% 29% 9% 1	840
	11th to 20th	Night	21% 12% 27% 30% 10%	840
	21st to end	Night	25% 12% 25% 30% 7%	924

Page generated at 2026-02-13 01:42:17. Version ac07

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