Lac Sacacomie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Sacacomie clear sky chart from 2005-11-06 to 2026-05-02.

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	16% 11% 4 9% 5% 5% 5% 4 5% 6% 30%	131799
	Night	15% 11% 4 9% 5% 5% 4 4 5% 6% 31%	130693
Transparency	Day	52% 6% 12% 19% 10% 1	135231
	Night	52% 5% 12% 20% 10% 1	135348
Seeing	Day	23% 18% 32% 18% 7% 2	16299
	Night	22% 13% 31% 25% 8% 1	25341

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	11% 16% 6% 13% 7% 4 5% 3 5% 6% 25%	4661
	11th to 20th	Day	8% 18% 7% 16% 9% 5% 4 3 4 5% 23%	4650
	21st to end	Day	6% 10% 6% 15% 7% 6% 5% 4 5% 6% 30%	5124
February	1st to 10th	Day	10% 16% 6% 13% 8% 6% 4 3 4 5% 26%	1780
	11th to 20th	Day	11% 17% 6% 10% 6% 5% 4 3 4 5% 29%	1954
	21st to end	Day	13% 17% 6% 10% 6% 5% 4 3 5% 4 27%	1730
March	1st to 10th	Day	17% 18% 4 12% 7% 4 4 3 3 3 24%	4576
	11th to 20th	Day	11% 13% 5% 10% 5% 5% 5% 3 5% 6% 31%	4760
	21st to end	Day	14% 16% 4 8% 4 4 4 3 4 5% 33%	6102
April	1st to 10th	Day	20% 15% 4 8% 5% 3 4 4 4 5% 29%	2520
	11th to 20th	Day	23% 9% 3 7% 5% 4 3 3 4 6% 34%	2500
	21st to end	Day	21% 11% 4 7% 4 4 4 3 6% 6% 30%	2730
May	1st to 10th	Day	27% 10% 3 7% 4 4 5% 4 5% 6% 27%	6300
	11th to 20th	Day	22% 8% 3 7% 4 4 4 3 5% 7% 33%	6318
	21st to end	Day	22% 9% 3 8% 5% 5% 5% 4 5% 6% 28%	6949
June	1st to 10th	Day	21% 8% 3 8% 5% 5% 5% 4 6% 6% 27%	2800
	11th to 20th	Day	17% 7% 2 7% 5% 5% 6% 4 6% 8% 32%	2800
	21st to end	Day	23% 9% 2 8% 6% 5% 4 5% 6% 7% 25%	2800
July	1st to 10th	Day	17% 6% 3 8% 6% 6% 6% 4 7% 8% 29%	6360
	11th to 20th	Day	13% 6% 2 7% 5% 5% 7% 5% 8% 9% 35%	6360
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 4 7% 9% 40%	6926
August	1st to 10th	Day	14% 6% 2 7% 5% 6% 7% 5% 7% 9% 32%	4563
	11th to 20th	Day	18% 6% 2 7% 5% 5% 5% 4 6% 8% 32%	4228
	21st to end	Day	17% 6% 3 7% 5% 4 5% 5% 5% 8% 36%	4312
September	1st to 10th	Day	14% 5% 2 7% 4 4 4 4 6% 8% 41%	2400
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 6% 45%	2299
	21st to end	Day	20% 8% 2 6% 3 4 4 3 4 6% 40%	2200
October	1st to 10th	Day	22% 7% 3 7% 3 4 4 3 5% 7% 34%	2085
	11th to 20th	Day	21% 10% 3 9% 6% 6% 4 4 5% 5% 27%	1917
	21st to end	Day	25% 13% 3 7% 4 4 4 3 4 6% 27%	1980
November	1st to 10th	Day	16% 14% 3 9% 5% 5% 3 3 5% 5% 31%	1851
	11th to 20th	Day	18% 15% 3 10% 5% 4 4 3 4 6% 27%	1790
	21st to end	Day	20% 18% 4 7% 5% 4 5% 4 4 6% 23%	1680
December	1st to 10th	Day	18% 16% 7% 13% 5% 5% 3 3 5% 4 20%	2680
	11th to 20th	Day	17% 13% 5% 11% 5% 4 4 3 4 5% 28%	3066
	21st to end	Day	17% 15% 6% 11% 6% 4 4 3 4 5% 26%	4048
January	1st to 10th	Night	10% 18% 8% 14% 5% 4 4 3 4 6% 23%	8234
	11th to 20th	Night	9% 16% 7% 17% 8% 5% 4 3 4 5% 22%	8235
	21st to end	Night	6% 10% 5% 13% 8% 7% 6% 4 6% 7% 27%	9057
February	1st to 10th	Night	9% 13% 6% 9% 6% 7% 6% 4 5% 6% 29%	2835
	11th to 20th	Night	10% 14% 4 11% 6% 5% 5% 4 5% 6% 29%	2550
	21st to end	Night	13% 13% 4 9% 5% 5% 5% 4 5% 6% 31%	2076
March	1st to 10th	Night	19% 15% 5% 12% 6% 4 4 3 4 4 24%	5484
	11th to 20th	Night	12% 14% 4 9% 5% 5% 5% 4 5% 6% 29%	5402
	21st to end	Night	15% 10% 4 10% 5% 5% 4 4 5% 6% 32%	5072
April	1st to 10th	Night	21% 11% 4 7% 5% 4 4 4 5% 6% 30%	2100
	11th to 20th	Night	18% 8% 3 6% 5% 3 5% 3 6% 5% 37%	2067
	21st to end	Night	22% 9% 3 7% 4 3 3 3 6% 6% 35%	1890
May	1st to 10th	Night	24% 10% 3 7% 5% 4 4 4 5% 6% 27%	3706
	11th to 20th	Night	24% 7% 2 6% 4 3 4 4 4 6% 35%	3575
	21st to end	Night	21% 9% 3 8% 5% 5% 4 4 5% 7% 30%	3926
June	1st to 10th	Night	20% 6% 3 7% 4 4 4 3 6% 6% 36%	1600
	11th to 20th	Night	18% 7% 3 6% 5% 5% 4 4 5% 7% 37%	1600
	21st to end	Night	20% 7% 3 7% 6% 4 4 4 6% 7% 34%	1600
July	1st to 10th	Night	13% 5% 2 6% 5% 6% 6% 6% 7% 10% 35%	3600
	11th to 20th	Night	14% 5% 2 6% 5% 4 4 4 5% 7% 43%	3600
	21st to end	Night	10% 4 1 5% 4 3 4 5% 6% 9% 48%	3926
August	1st to 10th	Night	12% 5% 3 7% 5% 5% 5% 4 5% 7% 40%	2586
	11th to 20th	Night	16% 6% 2 6% 4 4 4 4 5% 7% 42%	2784
	21st to end	Night	16% 6% 2 7% 5% 4 4 3 5% 6% 42%	3586
September	1st to 10th	Night	12% 6% 3 5% 3 4 5% 4 5% 6% 48%	2000
	11th to 20th	Night	14% 5% 1 5% 3 3 3 3 6% 6% 50%	2100
	21st to end	Night	17% 6% 2 5% 4 4 3 3 4 7% 45%	2200
October	1st to 10th	Night	17% 9% 3 6% 3 4 4 3 4 5% 42%	2310
	11th to 20th	Night	21% 8% 2 7% 4 3 4 4 5% 7% 36%	2482
	21st to end	Night	23% 9% 3 8% 4 4 5% 3 5% 6% 30%	2860
November	1st to 10th	Night	17% 10% 4 8% 5% 4 4 4 5% 6% 33%	2667
	11th to 20th	Night	18% 12% 3 8% 5% 4 4 4 6% 6% 30%	2825
	21st to end	Night	19% 15% 5% 9% 5% 4 3 3 5% 5% 26%	2940
December	1st to 10th	Night	13% 15% 5% 11% 6% 6% 5% 5% 6% 7% 22%	4720
	11th to 20th	Night	21% 14% 4 9% 5% 5% 5% 3 4 4 26%	5348
	21st to end	Night	19% 15% 6% 11% 5% 3 3 3 3 4 28%	7150

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	58% 6% 11% 17% 7%	4662
	11th to 20th	Day	63% 5% 7% 14% 9% 2	4680
	21st to end	Day	54% 5% 8% 17% 15% 1	5124
February	1st to 10th	Day	60% 4 7% 17% 9% 2	1780
	11th to 20th	Day	57% 5% 9% 17% 11% 1	1963
	21st to end	Day	59% 4 7% 16% 10% 3	1730
March	1st to 10th	Day	63% 5% 7% 11% 10% 4	4579
	11th to 20th	Day	52% 6% 14% 13% 12% 3	4760
	21st to end	Day	54% 4 7% 16% 17% 3	6102
April	1st to 10th	Day	56% 5% 9% 15% 12% 2	2520
	11th to 20th	Day	51% 5% 8% 21% 12% 2	2500
	21st to end	Day	54% 5% 9% 17% 12% 2	2730
May	1st to 10th	Day	57% 5% 9% 16% 11% 1	6311
	11th to 20th	Day	49% 7% 16% 18% 7% 2	6322
	21st to end	Day	54% 7% 9% 14% 13% 2	6949
June	1st to 10th	Day	54% 8% 9% 18% 10% 1	2800
	11th to 20th	Day	46% 7% 13% 22% 11% 2	2800
	21st to end	Day	57% 7% 12% 15% 9% 1	2800
July	1st to 10th	Day	49% 7% 14% 23% 7%	6290
	11th to 20th	Day	41% 8% 18% 26% 7%	6285
	21st to end	Day	37% 8% 17% 30% 8%	6728
August	1st to 10th	Day	45% 9% 18% 21% 7%	4549
	11th to 20th	Day	46% 9% 17% 23% 6%	4270
	21st to end	Day	45% 6% 14% 21% 13% 1	4312
September	1st to 10th	Day	38% 7% 19% 25% 11% 1	2400
	11th to 20th	Day	38% 7% 14% 30% 11% 1	2299
	21st to end	Day	45% 5% 13% 26% 11%	2200
October	1st to 10th	Day	47% 5% 13% 28% 7% 1	3397
	11th to 20th	Day	49% 6% 14% 25% 6%	3094
	21st to end	Day	47% 6% 21% 19% 8% 1	3180
November	1st to 10th	Day	53% 6% 12% 19% 10% 1	1851
	11th to 20th	Day	56% 5% 11% 17% 11%	1790
	21st to end	Day	62% 6% 10% 15% 6%	1680
December	1st to 10th	Day	66% 4 9% 16% 5%	2680
	11th to 20th	Day	57% 4 7% 19% 13%	3066
	21st to end	Day	61% 3 8% 16% 11%	4048
January	1st to 10th	Night	62% 4 10% 17% 6% 1	8234
	11th to 20th	Night	65% 4 9% 15% 6% 1	8280
	21st to end	Night	55% 6% 9% 16% 15%	9057
February	1st to 10th	Night	55% 4 10% 19% 10% 1	2835
	11th to 20th	Night	55% 5% 10% 18% 11% 1	2552
	21st to end	Night	53% 4 9% 19% 13% 2	2076
March	1st to 10th	Night	63% 5% 8% 11% 11% 2	5494
	11th to 20th	Night	53% 6% 12% 15% 12% 3	5403
	21st to end	Night	53% 4 6% 23% 12% 3	5072
April	1st to 10th	Night	54% 5% 8% 17% 14% 2	2100
	11th to 20th	Night	48% 5% 10% 22% 13% 2	2067
	21st to end	Night	49% 4 8% 21% 15% 2	1890
May	1st to 10th	Night	57% 5% 12% 15% 9% 1	3712
	11th to 20th	Night	49% 6% 13% 20% 9% 2	3576
	21st to end	Night	52% 7% 11% 16% 12% 1	3927
June	1st to 10th	Night	46% 7% 13% 22% 12% 1	1600
	11th to 20th	Night	45% 7% 11% 21% 13% 3	1600
	21st to end	Night	49% 6% 13% 18% 13% 1	1600
July	1st to 10th	Night	43% 7% 22% 22% 6%	3560
	11th to 20th	Night	40% 6% 20% 28% 6%	3552
	21st to end	Night	33% 6% 19% 31% 11%	3809
August	1st to 10th	Night	42% 7% 18% 25% 8%	2576
	11th to 20th	Night	42% 5% 20% 24% 8%	2808
	21st to end	Night	44% 5% 15% 24% 11%	3586
September	1st to 10th	Night	36% 6% 17% 28% 14% 1	2000
	11th to 20th	Night	34% 5% 16% 33% 10% 1	2100
	21st to end	Night	41% 4 13% 29% 13%	2200
October	1st to 10th	Night	46% 5% 13% 26% 10%	3778
	11th to 20th	Night	42% 5% 14% 30% 8%	4044
	21st to end	Night	46% 4 18% 19% 11% 2	4610
November	1st to 10th	Night	51% 5% 13% 22% 8% 1	2667
	11th to 20th	Night	52% 6% 12% 19% 10% 1	2825
	21st to end	Night	60% 4 11% 16% 8% 1	2940
December	1st to 10th	Night	59% 6% 14% 16% 5%	4720
	11th to 20th	Night	60% 5% 7% 17% 10% 1	5348
	21st to end	Night	62% 3 6% 15% 13% 1	7150

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	24% 19% 37% 16% 4	220
	11th to 20th	Day	24% 21% 36% 15% 3	220
	21st to end	Day	16% 21% 42% 15% 5% 1	242
February	1st to 10th	Day	25% 26% 39% 8% 1	272
	11th to 20th	Day	24% 27% 37% 12% 1	441
	21st to end	Day	25% 26% 32% 14% 4	446
March	1st to 10th	Day	27% 21% 33% 16% 4	540
	11th to 20th	Day	25% 22% 36% 13% 4	540
	21st to end	Day	29% 25% 25% 14% 5% 1	594
April	1st to 10th	Day	31% 19% 31% 14% 5%	540
	11th to 20th	Day	32% 20% 27% 14% 5% 2	532
	21st to end	Day	31% 21% 32% 10% 5% 1	540
May	1st to 10th	Day	27% 21% 31% 15% 5% 1	507
	11th to 20th	Day	21% 20% 31% 22% 5% 1	527
	21st to end	Day	24% 22% 33% 16% 5% 1	573
June	1st to 10th	Day	22% 16% 39% 17% 6%	530
	11th to 20th	Day	19% 20% 32% 20% 8% 2	530
	21st to end	Day	27% 13% 31% 21% 6% 1	530
July	1st to 10th	Day	15% 12% 37% 25% 8% 2	525
	11th to 20th	Day	13% 14% 37% 27% 7% 2	524
	21st to end	Day	13% 12% 33% 29% 12% 2	576
August	1st to 10th	Day	14% 10% 34% 28% 12% 2	526
	11th to 20th	Day	17% 7% 29% 28% 14% 5%	519
	21st to end	Day	16% 15% 28% 22% 14% 5%	583
September	1st to 10th	Day	17% 14% 34% 21% 10% 5%	530
	11th to 20th	Day	14% 12% 29% 25% 15% 6%	530
	21st to end	Day	22% 15% 29% 19% 11% 4	530
October	1st to 10th	Day	24% 15% 28% 20% 9% 2	530
	11th to 20th	Day	26% 18% 30% 17% 8% 1	483
	21st to end	Day	31% 16% 31% 18% 4	462
November	1st to 10th	Day	28% 21% 27% 18% 6% 1	425
	11th to 20th	Day	25% 20% 33% 18% 5% 1	330
	21st to end	Day	25% 28% 31% 13% 2	220
December	1st to 10th	Day	30% 17% 31% 15% 5% 1	220
	11th to 20th	Day	30% 23% 33% 11% 2	220
	21st to end	Day	29% 20% 32% 15% 3 2	242
January	1st to 10th	Night	25% 15% 35% 21% 4	840
	11th to 20th	Night	25% 16% 33% 21% 6%	840
	21st to end	Night	15% 13% 38% 27% 7%	924
February	1st to 10th	Night	18% 14% 37% 24% 6% 1	840
	11th to 20th	Night	19% 19% 36% 21% 4	823
	21st to end	Night	21% 16% 35% 24% 4	692
March	1st to 10th	Night	26% 15% 34% 22% 4	840
	11th to 20th	Night	24% 20% 33% 18% 5% 1	840
	21st to end	Night	23% 16% 31% 23% 6% 1	924
April	1st to 10th	Night	29% 14% 31% 21% 5%	840
	11th to 20th	Night	25% 16% 31% 21% 6%	823
	21st to end	Night	27% 17% 31% 19% 5%	630
May	1st to 10th	Night	28% 13% 30% 22% 6% 1	454
	11th to 20th	Night	23% 10% 32% 26% 9%	394
	21st to end	Night	21% 9% 40% 21% 9%	433
June	1st to 10th	Night	22% 9% 29% 34% 6%	400
	11th to 20th	Night	20% 8% 28% 32% 12%	400
	21st to end	Night	22% 5% 32% 30% 11%	400
July	1st to 10th	Night	13% 6% 32% 35% 13% 1	390
	11th to 20th	Night	13% 4 28% 40% 13% 1	388
	21st to end	Night	16% 5% 28% 37% 13% 1	438
August	1st to 10th	Night	11% 5% 23% 43% 17% 1	398
	11th to 20th	Night	14% 5% 25% 36% 19% 2	526
	21st to end	Night	19% 6% 26% 31% 17% 2	880
September	1st to 10th	Night	15% 6% 31% 35% 12% 1	800
	11th to 20th	Night	16% 7% 29% 27% 20% 1	800
	21st to end	Night	20% 10% 28% 26% 15% 2	800
October	1st to 10th	Night	21% 13% 29% 26% 11%	800
	11th to 20th	Night	23% 13% 30% 24% 8% 1	800
	21st to end	Night	27% 15% 30% 22% 6%	880
November	1st to 10th	Night	25% 14% 29% 24% 7% 1	820
	11th to 20th	Night	23% 15% 31% 21% 8% 1	840
	21st to end	Night	26% 19% 26% 23% 5% 1	840
December	1st to 10th	Night	27% 14% 29% 23% 6%	840
	11th to 20th	Night	27% 16% 32% 19% 5% 1	840
	21st to end	Night	30% 16% 30% 20% 5%	924

Page generated at 2026-04-29 02:21:41. Version ac07

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