Linslaw Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Linslaw Point clear sky chart from 2005-11-06 to 2025-09-19.

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	17% 9% 3 7% 4 4 4 3 5% 6% 38%	135485
	Night	19% 10% 3 7% 4 4 4 3 4 5% 36%	130932
Transparency	Day	45% 7% 11% 18% 14% 5%	130263
	Night	48% 7% 12% 17% 11% 4	127152
Seeing	Day	24% 13% 25% 25% 11% 2	15922
	Night	27% 7% 15% 29% 19% 2	24829

By Month

Percentage Cloud Cover SW (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	36% 18% 5% 10% 5% 4 4 3 3 3 8%	3639
	11th to 20th	Day	27% 10% 3 5% 3 4 4 3 5% 7% 29%	3801
	21st to end	Day	26% 10% 3 7% 5% 5% 4 3 4 5% 29%	4510
February	1st to 10th	Day	28% 16% 4 11% 6% 5% 4 4 4 6% 13%	1800
	11th to 20th	Day	28% 15% 4 10% 5% 4 4 4 4 5% 17%	1755
	21st to end	Day	30% 18% 4 8% 5% 4 3 2 4 4 17%	1540
March	1st to 10th	Day	20% 17% 4 9% 6% 6% 5% 4 6% 5% 17%	4900
	11th to 20th	Day	29% 15% 4 9% 4 4 3 2 3 4 24%	5000
	21st to end	Day	27% 14% 4 11% 7% 7% 5% 4 5% 5% 10%	5486
April	1st to 10th	Day	29% 15% 4 11% 6% 5% 4 3 4 4 15%	2400
	11th to 20th	Day	24% 14% 4 9% 6% 4 4 3 4 5% 23%	2383
	21st to end	Day	22% 11% 4 8% 5% 4 5% 3 6% 6% 25%	2600
May	1st to 10th	Day	15% 8% 3 8% 5% 5% 5% 3 4 6% 39%	5985
	11th to 20th	Day	12% 9% 3 8% 5% 5% 4 4 6% 7% 37%	6277
	21st to end	Day	13% 7% 3 7% 5% 5% 6% 5% 6% 8% 36%	6902
June	1st to 10th	Day	22% 9% 3 7% 4 3 4 4 5% 6% 34%	2800
	11th to 20th	Day	15% 9% 3 7% 6% 4 5% 4 6% 8% 34%	2800
	21st to end	Day	10% 6% 2 5% 4 3 3 2 5% 7% 52%	2800
July	1st to 10th	Day	2 2 1 2 2 2 2 2 3 5% 77%	6319
	11th to 20th	Day	4 2 1 2 2 2 2 2 3 5% 76%	6320
	21st to end	Day	3 3 1 3 2 2 2 2 4 5% 73%	6620
August	1st to 10th	Day	2 4 2 5% 3 3 3 3 5% 7% 63%	5777
	11th to 20th	Day	5% 5% 2 5% 3 3 3 3 5% 8% 57%	5796
	21st to end	Day	5% 5% 1 5% 4 3 4 3 6% 8% 55%	6191
September	1st to 10th	Day	6% 3 1 3 3 2 3 3 5% 7% 64%	2400
	11th to 20th	Day	10% 6% 3 7% 4 3 4 4 5% 7% 47%	2314
	21st to end	Day	14% 6% 2 6% 4 3 3 3 5% 6% 46%	2035
October	1st to 10th	Day	12% 8% 2 6% 4 3 3 2 4 5% 50%	3180
	11th to 20th	Day	17% 7% 3 9% 6% 6% 6% 5% 6% 8% 28%	3161
	21st to end	Day	22% 11% 4 9% 5% 6% 5% 4 6% 7% 22%	3448
November	1st to 10th	Day	31% 10% 5% 9% 5% 5% 4 4 5% 5% 18%	1694
	11th to 20th	Day	33% 10% 4 9% 5% 5% 4 4 4 6% 17%	1600
	21st to end	Day	27% 11% 3 8% 6% 5% 5% 3 5% 6% 22%	1600
December	1st to 10th	Day	20% 9% 3 7% 5% 4 5% 4 5% 8% 31%	2620
	11th to 20th	Day	31% 14% 4 10% 6% 5% 4 4 6% 5% 10%	3028
	21st to end	Day	34% 19% 5% 11% 5% 4 4 3 4 4 7%	4004
January	1st to 10th	Night	38% 17% 4 9% 6% 4 3 2 3 3 10%	6306
	11th to 20th	Night	27% 12% 3 7% 4 3 4 3 4 5% 28%	6162
	21st to end	Night	30% 12% 3 6% 3 2 2 2 3 4 33%	6468
February	1st to 10th	Night	25% 14% 5% 9% 5% 5% 5% 4 5% 5% 18%	2600
	11th to 20th	Night	27% 13% 4 8% 4 4 4 3 5% 4 25%	2532
	21st to end	Night	27% 15% 3 8% 5% 5% 4 3 5% 5% 21%	2090
March	1st to 10th	Night	20% 17% 4 9% 5% 5% 4 4 6% 5% 20%	4989
	11th to 20th	Night	25% 16% 3 8% 5% 4 3 3 3 3 26%	5000
	21st to end	Night	28% 17% 4 10% 5% 4 4 3 4 5% 15%	5489
April	1st to 10th	Night	25% 17% 4 8% 5% 5% 4 3 4 5% 22%	2000
	11th to 20th	Night	19% 14% 3 7% 5% 3 4 3 6% 6% 32%	1960
	21st to end	Night	19% 11% 3 8% 4 3 5% 3 5% 7% 31%	1800
May	1st to 10th	Night	18% 8% 2 5% 4 3 3 3 4 5% 46%	3990
	11th to 20th	Night	10% 12% 3 7% 5% 4 4 4 4 6% 40%	3616
	21st to end	Night	12% 8% 3 6% 4 3 4 3 5% 7% 44%	3972
June	1st to 10th	Night	17% 8% 3 5% 4 4 4 3 5% 7% 42%	1600
	11th to 20th	Night	11% 7% 3 5% 3 3 4 4 6% 8% 48%	1600
	21st to end	Night	9% 4 2 4 3 4 4 3 4 6% 58%	1600
July	1st to 10th	Night	1 2 1 3 2 2 3 3 3 5% 75%	3640
	11th to 20th	Night	3 2 1 2 2 2 3 3 3 3 77%	3640
	21st to end	Night	3 3 1 3 3 2 2 2 4 6% 70%	4239
August	1st to 10th	Night	2 4 2 5% 3 3 4 4 5% 7% 62%	4035
	11th to 20th	Night	7% 5% 2 6% 4 5% 4 4 5% 7% 53%	4052
	21st to end	Night	3 3 2 5% 3 4 3 4 5% 7% 61%	4785
September	1st to 10th	Night	5% 4 1 4 3 3 3 3 5% 6% 63%	2000
	11th to 20th	Night	8% 6% 2 6% 3 4 3 3 5% 7% 53%	2039
	21st to end	Night	11% 6% 2 5% 3 3 3 3 5% 6% 52%	2144
October	1st to 10th	Night	9% 6% 2 6% 3 3 3 2 4 6% 55%	3800
	11th to 20th	Night	15% 9% 4 8% 5% 5% 5% 4 6% 8% 33%	3777
	21st to end	Night	25% 12% 4 9% 4 4 4 3 5% 5% 25%	4121
November	1st to 10th	Night	28% 10% 4 7% 4 4 4 4 5% 5% 25%	2598
	11th to 20th	Night	32% 11% 3 8% 6% 5% 3 3 5% 5% 19%	2800
	21st to end	Night	23% 10% 3 7% 5% 4 5% 4 5% 6% 27%	2800
December	1st to 10th	Night	17% 9% 2 6% 4 4 5% 4 7% 8% 33%	4560
	11th to 20th	Night	35% 13% 5% 10% 6% 5% 4 3 4 5% 11%	5176
	21st to end	Night	34% 15% 4 10% 6% 5% 4 3 4 4 11%	6952

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	79% 6% 6% 6% 3 1	3639
	11th to 20th	Day	54% 7% 7% 18% 11% 2	3801
	21st to end	Day	57% 6% 6% 11% 14% 6%	4510
February	1st to 10th	Day	71% 7% 9% 9% 4 1	1800
	11th to 20th	Day	68% 7% 9% 8% 5% 2	1764
	21st to end	Day	70% 6% 8% 9% 6% 2	1540
March	1st to 10th	Day	62% 9% 11% 14% 4	4900
	11th to 20th	Day	63% 5% 7% 16% 8% 1	5000
	21st to end	Day	71% 10% 10% 7% 2	5486
April	1st to 10th	Day	70% 6% 11% 9% 4	2400
	11th to 20th	Day	62% 6% 10% 12% 7% 2	2386
	21st to end	Day	58% 8% 13% 14% 7% 1	2600
May	1st to 10th	Day	43% 8% 11% 23% 15%	5985
	11th to 20th	Day	42% 8% 16% 23% 10% 1	6280
	21st to end	Day	41% 11% 26% 20% 3	6904
June	1st to 10th	Day	50% 7% 14% 23% 6%	2800
	11th to 20th	Day	46% 9% 18% 21% 7%	2800
	21st to end	Day	30% 6% 17% 29% 14% 3	2800
July	1st to 10th	Day	12% 4 10% 25% 27% 22%	6251
	11th to 20th	Day	13% 3 6% 15% 37% 26%	6245
	21st to end	Day	13% 3 13% 37% 27% 7%	6429
August	1st to 10th	Day	18% 5% 11% 25% 30% 10%	4206
	11th to 20th	Day	23% 6% 15% 36% 16% 4	4195
	21st to end	Day	25% 6% 12% 25% 24% 8%	4458
September	1st to 10th	Day	21% 5% 12% 29% 22% 12%	2400
	11th to 20th	Day	35% 7% 13% 22% 17% 5%	2314
	21st to end	Day	37% 7% 12% 22% 17% 5%	2035
October	1st to 10th	Day	36% 5% 7% 16% 24% 10%	3180
	11th to 20th	Day	48% 9% 15% 16% 11% 1	3161
	21st to end	Day	56% 8% 9% 15% 11% 2	3448
November	1st to 10th	Day	66% 8% 9% 12% 5%	1694
	11th to 20th	Day	67% 7% 9% 8% 6% 3	1600
	21st to end	Day	62% 8% 8% 8% 11% 3	1600
December	1st to 10th	Day	50% 8% 9% 14% 18% 2	2620
	11th to 20th	Day	73% 9% 8% 7% 2	3028
	21st to end	Day	80% 7% 6% 6% 2 1	4004
January	1st to 10th	Night	79% 5% 5% 6% 4 1	6306
	11th to 20th	Night	57% 8% 7% 15% 10% 2	6162
	21st to end	Night	57% 3 5% 12% 15% 7%	6468
February	1st to 10th	Night	66% 8% 10% 11% 4 1	2600
	11th to 20th	Night	61% 7% 11% 11% 7% 2	2534
	21st to end	Night	63% 9% 9% 11% 6% 2	2090
March	1st to 10th	Night	61% 7% 13% 13% 4 1	4989
	11th to 20th	Night	62% 6% 10% 13% 7% 1	5000
	21st to end	Night	67% 9% 13% 10% 1	5489
April	1st to 10th	Night	63% 8% 11% 13% 4 1	2000
	11th to 20th	Night	51% 8% 15% 17% 6% 3	1960
	21st to end	Night	51% 9% 13% 18% 7% 2	1800
May	1st to 10th	Night	38% 6% 11% 30% 14% 1	3987
	11th to 20th	Night	41% 7% 15% 26% 9% 2	3616
	21st to end	Night	35% 10% 32% 20% 3	3972
June	1st to 10th	Night	42% 7% 17% 29% 5% 1	1600
	11th to 20th	Night	31% 9% 23% 28% 9% 1	1600
	21st to end	Night	24% 6% 21% 32% 13% 4	1600
July	1st to 10th	Night	10% 4 12% 29% 22% 24%	3600
	11th to 20th	Night	10% 3 8% 18% 30% 30%	3592
	21st to end	Night	15% 4 15% 35% 26% 6%	4119
August	1st to 10th	Night	13% 6% 12% 30% 30% 10%	2929
	11th to 20th	Night	22% 8% 17% 32% 16% 4	2929
	21st to end	Night	19% 5% 12% 31% 26% 7%	3443
September	1st to 10th	Night	20% 6% 12% 27% 24% 12%	2000
	11th to 20th	Night	30% 6% 16% 25% 15% 8%	2039
	21st to end	Night	31% 7% 15% 23% 17% 8%	2144
October	1st to 10th	Night	30% 6% 9% 23% 24% 8%	3800
	11th to 20th	Night	45% 9% 16% 18% 10% 2	3777
	21st to end	Night	58% 7% 9% 14% 9% 3	4121
November	1st to 10th	Night	58% 9% 11% 12% 10% 1	2598
	11th to 20th	Night	66% 7% 9% 10% 6% 2	2800
	21st to end	Night	56% 8% 11% 9% 11% 5%	2800
December	1st to 10th	Night	47% 8% 10% 18% 17% 1	4560
	11th to 20th	Night	74% 7% 9% 6% 3	5176
	21st to end	Night	72% 12% 8% 6% 2 1	6952

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	51% 16% 19% 9% 6%	200
	11th to 20th	Day	40% 12% 20% 18% 9% 1	270
	21st to end	Day	36% 12% 19% 21% 11% 1	440
February	1st to 10th	Day	40% 12% 19% 21% 7% 1	400
	11th to 20th	Day	40% 17% 18% 19% 5% 1	395
	21st to end	Day	41% 16% 19% 18% 5%	359
March	1st to 10th	Day	39% 17% 21% 18% 5% 1	500
	11th to 20th	Day	36% 15% 21% 19% 8% 1	500
	21st to end	Day	40% 16% 21% 17% 6%	550
April	1st to 10th	Day	40% 15% 18% 18% 8% 1	500
	11th to 20th	Day	34% 20% 22% 17% 6% 3	492
	21st to end	Day	29% 17% 27% 19% 7% 2	500
May	1st to 10th	Day	22% 18% 28% 20% 9% 3	503
	11th to 20th	Day	31% 14% 25% 19% 9% 4	528
	21st to end	Day	21% 15% 26% 23% 12% 2	573
June	1st to 10th	Day	22% 13% 26% 25% 11% 2	530
	11th to 20th	Day	19% 20% 29% 22% 9% 1	530
	21st to end	Day	11% 9% 28% 34% 15% 2	530
July	1st to 10th	Day	6% 8% 34% 33% 16% 3	526
	11th to 20th	Day	5% 9% 32% 35% 17% 2	524
	21st to end	Day	2 6% 28% 41% 18% 5%	575
August	1st to 10th	Day	4 8% 28% 39% 17% 5%	527
	11th to 20th	Day	5% 6% 22% 40% 21% 6%	517
	21st to end	Day	8% 8% 30% 32% 18% 4	583
September	1st to 10th	Day	10% 8% 29% 31% 19% 3	530
	11th to 20th	Day	15% 10% 26% 30% 16% 4	523
	21st to end	Day	19% 11% 27% 29% 10% 4	490
October	1st to 10th	Day	22% 11% 25% 23% 16% 3	490
	11th to 20th	Day	23% 12% 19% 25% 17% 4	490
	21st to end	Day	32% 13% 23% 21% 7% 4	539
November	1st to 10th	Day	36% 14% 21% 20% 8% 1	288
	11th to 20th	Day	38% 13% 27% 14% 7% 2	200
	21st to end	Day	33% 14% 19% 28% 6%	200
December	1st to 10th	Day	35% 11% 24% 21% 9% 1	200
	11th to 20th	Day	45% 11% 27% 14% 3 1	200
	21st to end	Day	45% 12% 21% 18% 5%	220
January	1st to 10th	Night	47% 9% 16% 17% 9% 2	800
	11th to 20th	Night	39% 7% 16% 23% 13% 2	800
	21st to end	Night	35% 7% 14% 29% 13% 2	880
February	1st to 10th	Night	34% 9% 13% 28% 14% 2	800
	11th to 20th	Night	36% 8% 16% 28% 12% 1	784
	21st to end	Night	38% 11% 13% 25% 12%	660
March	1st to 10th	Night	35% 10% 16% 27% 11% 1	800
	11th to 20th	Night	34% 9% 15% 27% 14% 1	800
	21st to end	Night	39% 9% 16% 22% 13% 1	880
April	1st to 10th	Night	37% 10% 14% 23% 15% 1	800
	11th to 20th	Night	25% 12% 21% 26% 15% 2	772
	21st to end	Night	26% 8% 17% 30% 19% 1	600
May	1st to 10th	Night	20% 8% 21% 30% 20% 2	555
	11th to 20th	Night	22% 7% 16% 29% 24% 2	394
	21st to end	Night	18% 6% 20% 31% 23% 1	433
June	1st to 10th	Night	19% 5% 16% 38% 21% 2	400
	11th to 20th	Night	13% 6% 19% 44% 16% 2	400
	21st to end	Night	12% 3 14% 41% 29% 1	400
July	1st to 10th	Night	5% 2 14% 43% 35% 1	390
	11th to 20th	Night	7% 2 14% 49% 28%	388
	21st to end	Night	3 3 10% 42% 39% 3	554
August	1st to 10th	Night	4 3 10% 39% 39% 6%	597
	11th to 20th	Night	6% 2 9% 35% 43% 6%	594
	21st to end	Night	8% 4 16% 40% 29% 3	780
September	1st to 10th	Night	9% 4 17% 37% 32% 2	800
	11th to 20th	Night	12% 4 14% 31% 32% 7%	792
	21st to end	Night	16% 5% 14% 34% 28% 3	760
October	1st to 10th	Night	18% 5% 18% 32% 25% 3	760
	11th to 20th	Night	22% 5% 11% 31% 25% 5%	760
	21st to end	Night	30% 10% 16% 24% 16% 4	836
November	1st to 10th	Night	34% 6% 14% 28% 15% 1	780
	11th to 20th	Night	38% 11% 15% 23% 12% 1	800
	21st to end	Night	28% 9% 17% 30% 14% 2	800
December	1st to 10th	Night	31% 8% 18% 27% 15% 2	800
	11th to 20th	Night	42% 8% 16% 21% 13% 1	800
	21st to end	Night	46% 11% 14% 23% 7%	880

Page generated at 2025-09-15 22:49:17. Version ac07

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