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 2024-01-17.

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	18% 10% 4 7% 6% 3 5% 5% 5% 6% 31%	74792
	Night	17% 10% 4 7% 6% 3 5% 4 5% 6% 33%	75023
Transparency	Day	52% 6% 11% 19% 10% 1	74497
	Night	51% 6% 11% 20% 10% 1	74852
Seeing	Day	23% 17% 32% 19% 7% 2	13413
	Night	22% 13% 31% 25% 8% 1	22462

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	14% 15% 6% 10% 9% 4 5% 4 5% 5% 24%	1517
	11th to 20th	Day	15% 16% 6% 10% 8% 3 4 4 3 6% 26%	1488
	21st to end	Day	11% 12% 5% 10% 8% 3 5% 5% 5% 6% 30%	1584
February	1st to 10th	Day	11% 17% 7% 11% 8% 4 5% 3 4 5% 24%	1526
	11th to 20th	Day	12% 16% 7% 9% 6% 4 4 4 4 5% 29%	1667
	21st to end	Day	15% 16% 7% 9% 6% 4 5% 3 5% 4 27%	1480
March	1st to 10th	Day	13% 12% 4 9% 8% 4 6% 4 5% 5% 30%	1797
	11th to 20th	Day	15% 12% 6% 7% 6% 4 5% 4 5% 6% 30%	1853
	21st to end	Day	17% 12% 3 6% 6% 4 5% 4 5% 5% 32%	2376
April	1st to 10th	Day	21% 14% 4 7% 5% 3 4 4 4 6% 29%	2160
	11th to 20th	Day	22% 8% 3 6% 5% 3 4 4 4 6% 35%	2138
	21st to end	Day	22% 10% 4 6% 5% 3 4 4 5% 5% 30%	2340
May	1st to 10th	Day	22% 9% 3 7% 4 3 4 4 4 6% 34%	2489
	11th to 20th	Day	19% 7% 3 6% 6% 4 4 5% 5% 6% 34%	2478
	21st to end	Day	20% 7% 3 7% 6% 3 5% 4 5% 7% 33%	2725
June	1st to 10th	Day	22% 7% 4 7% 6% 3 6% 5% 5% 7% 27%	2520
	11th to 20th	Day	18% 7% 3 6% 6% 4 6% 5% 6% 8% 33%	2520
	21st to end	Day	23% 8% 3 7% 8% 3 5% 6% 6% 7% 25%	2520
July	1st to 10th	Day	15% 5% 3 6% 7% 5% 6% 5% 7% 8% 34%	2520
	11th to 20th	Day	14% 6% 3 7% 6% 3 6% 6% 7% 9% 32%	2520
	21st to end	Day	14% 6% 3 7% 7% 4 7% 6% 7% 9% 31%	2744
August	1st to 10th	Day	16% 7% 3 6% 6% 5% 6% 7% 7% 9% 28%	2506
	11th to 20th	Day	15% 6% 2 6% 6% 4 7% 6% 7% 7% 34%	2344
	21st to end	Day	14% 6% 2 6% 6% 3 5% 6% 6% 9% 37%	2376
September	1st to 10th	Day	15% 5% 2 6% 5% 3 5% 5% 6% 8% 40%	2160
	11th to 20th	Day	15% 6% 2 5% 6% 3 4 5% 5% 7% 43%	2070
	21st to end	Day	21% 7% 3 6% 3 2 5% 4 4 6% 40%	1980
October	1st to 10th	Day	24% 7% 3 6% 4 3 5% 4 5% 7% 33%	1877
	11th to 20th	Day	22% 10% 4 8% 7% 4 5% 5% 5% 5% 25%	1726
	21st to end	Day	26% 13% 3 6% 4 3 4 4 4 6% 26%	1782
November	1st to 10th	Day	16% 13% 3 8% 5% 4 3 4 5% 5% 32%	1671
	11th to 20th	Day	19% 13% 4 8% 6% 3 5% 4 4 6% 26%	1620
	21st to end	Day	20% 17% 4 6% 6% 3 5% 5% 4 6% 24%	1520
December	1st to 10th	Day	23% 16% 5% 8% 6% 3 4 3 5% 4 22%	1520
	11th to 20th	Day	21% 13% 5% 8% 6% 3 4 4 4 6% 26%	1906
	21st to end	Day	20% 16% 6% 10% 5% 3 4 4 3 5% 23%	2772
January	1st to 10th	Night	16% 17% 7% 10% 6% 4 5% 5% 4 5% 22%	2649
	11th to 20th	Night	14% 16% 5% 9% 7% 4 4 4 4 6% 28%	2616
	21st to end	Night	9% 11% 5% 10% 8% 4 5% 4 4 6% 32%	2772
February	1st to 10th	Night	11% 13% 6% 8% 7% 5% 7% 5% 5% 5% 28%	2430
	11th to 20th	Night	11% 14% 5% 9% 7% 4 5% 4 5% 7% 30%	2177
	21st to end	Night	14% 12% 5% 8% 6% 3 5% 5% 5% 6% 32%	1776
March	1st to 10th	Night	15% 12% 5% 9% 8% 4 5% 4 5% 6% 28%	2150
	11th to 20th	Night	16% 13% 4 8% 6% 4 5% 5% 4 5% 31%	2103
	21st to end	Night	15% 9% 4 7% 5% 4 5% 5% 4 5% 37%	1980
April	1st to 10th	Night	22% 10% 5% 7% 6% 4 4 5% 5% 6% 29%	1800
	11th to 20th	Night	18% 6% 3 6% 5% 2 5% 4 6% 6% 39%	1769
	21st to end	Night	22% 9% 3 6% 5% 2 3 4 5% 6% 34%	1620
May	1st to 10th	Night	22% 8% 3 6% 5% 2 4 3 4 7% 37%	1486
	11th to 20th	Night	20% 6% 3 6% 4 2 4 5% 4 7% 39%	1415
	21st to end	Night	18% 5% 3 6% 5% 3 5% 4 5% 6% 40%	1550
June	1st to 10th	Night	20% 6% 3 6% 5% 3 5% 5% 6% 6% 36%	1440
	11th to 20th	Night	18% 6% 3 6% 5% 4 5% 4 5% 7% 37%	1440
	21st to end	Night	19% 5% 3 6% 6% 3 5% 5% 6% 7% 34%	1440
July	1st to 10th	Night	13% 5% 2 6% 5% 3 5% 5% 6% 9% 41%	1440
	11th to 20th	Night	13% 4 2 6% 6% 4 4 5% 5% 8% 43%	1440
	21st to end	Night	13% 5% 2 5% 4 3 4 6% 6% 9% 42%	1574
August	1st to 10th	Night	10% 5% 3 6% 5% 3 5% 5% 6% 9% 43%	1432
	11th to 20th	Night	14% 5% 3 5% 5% 3 4 5% 5% 7% 43%	1535
	21st to end	Night	15% 6% 2 4 4 2 3 4 5% 7% 47%	1980
September	1st to 10th	Night	13% 6% 3 4 4 3 5% 5% 5% 6% 47%	1800
	11th to 20th	Night	16% 5% 2 4 4 2 3 4 6% 6% 48%	1890
	21st to end	Night	18% 6% 2 4 4 3 4 4 3 7% 46%	1980
October	1st to 10th	Night	17% 9% 3 6% 4 2 4 4 4 5% 41%	2078
	11th to 20th	Night	23% 8% 3 7% 5% 3 3 4 4 7% 34%	2233
	21st to end	Night	24% 9% 3 6% 6% 3 5% 4 5% 6% 30%	2574
November	1st to 10th	Night	16% 10% 4 7% 6% 3 4 5% 5% 6% 34%	2407
	11th to 20th	Night	18% 11% 4 7% 6% 3 5% 5% 5% 6% 30%	2555
	21st to end	Night	19% 14% 5% 7% 6% 3 4 3 5% 6% 28%	2660
December	1st to 10th	Night	19% 15% 5% 9% 6% 4 5% 5% 4 6% 22%	2660
	11th to 20th	Night	21% 13% 6% 8% 6% 4 5% 4 4 4 26%	3288
	21st to end	Night	21% 16% 6% 9% 6% 3 4 3 4 5% 23%	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	62% 6% 9% 15% 8%	1518
	11th to 20th	Day	61% 4 7% 16% 10% 1	1488
	21st to end	Day	54% 6% 8% 18% 12% 2	1584
February	1st to 10th	Day	62% 4 7% 16% 9% 2	1526
	11th to 20th	Day	58% 5% 9% 14% 11% 1	1676
	21st to end	Day	60% 5% 7% 16% 9% 3	1480
March	1st to 10th	Day	57% 4 8% 18% 11% 2	1800
	11th to 20th	Day	54% 6% 10% 14% 13% 3	1853
	21st to end	Day	53% 5% 8% 18% 12% 4	2376
April	1st to 10th	Day	57% 6% 9% 15% 12% 3	2160
	11th to 20th	Day	50% 5% 9% 21% 12% 3	2138
	21st to end	Day	55% 5% 8% 16% 12% 3	2340
May	1st to 10th	Day	51% 6% 8% 20% 13% 2	2489
	11th to 20th	Day	49% 6% 10% 18% 15% 2	2482
	21st to end	Day	50% 7% 11% 18% 13% 2	2725
June	1st to 10th	Day	55% 8% 9% 18% 9% 2	2520
	11th to 20th	Day	48% 7% 11% 21% 11% 2	2520
	21st to end	Day	57% 7% 11% 15% 9%	2520
July	1st to 10th	Day	44% 8% 15% 22% 9%	2450
	11th to 20th	Day	44% 9% 16% 22% 9%	2445
	21st to end	Day	47% 10% 15% 20% 7%	2591
August	1st to 10th	Day	49% 10% 16% 20% 4	2492
	11th to 20th	Day	43% 11% 16% 22% 9%	2344
	21st to end	Day	41% 8% 15% 25% 12%	2376
September	1st to 10th	Day	39% 7% 18% 24% 12% 1	2160
	11th to 20th	Day	40% 7% 14% 28% 11% 1	2070
	21st to end	Day	45% 5% 13% 27% 10%	1980
October	1st to 10th	Day	50% 5% 12% 24% 8% 1	1877
	11th to 20th	Day	59% 6% 12% 19% 4	1726
	21st to end	Day	59% 6% 11% 15% 9% 1	1782
November	1st to 10th	Day	52% 6% 13% 19% 10% 1	1671
	11th to 20th	Day	57% 5% 11% 16% 10%	1620
	21st to end	Day	60% 7% 10% 16% 7%	1520
December	1st to 10th	Day	65% 4 10% 15% 6%	1520
	11th to 20th	Day	59% 5% 8% 19% 8%	1906
	21st to end	Day	64% 4 8% 15% 8% 1	2772
January	1st to 10th	Night	63% 5% 9% 16% 6%	2649
	11th to 20th	Night	60% 5% 11% 14% 8% 2	2616
	21st to end	Night	53% 4 10% 18% 14% 1	2772
February	1st to 10th	Night	57% 5% 9% 18% 9% 1	2430
	11th to 20th	Night	55% 5% 10% 18% 11% 1	2179
	21st to end	Night	53% 4 8% 18% 14% 2	1776
March	1st to 10th	Night	56% 6% 9% 17% 11% 2	2160
	11th to 20th	Night	56% 5% 8% 16% 13% 3	2104
	21st to end	Night	50% 4 8% 21% 14% 3	1980
April	1st to 10th	Night	55% 5% 8% 16% 13% 2	1800
	11th to 20th	Night	45% 5% 10% 24% 14% 2	1769
	21st to end	Night	51% 4 8% 20% 14% 2	1620
May	1st to 10th	Night	50% 5% 10% 17% 15% 4	1486
	11th to 20th	Night	45% 6% 10% 21% 14% 4	1416
	21st to end	Night	44% 7% 12% 19% 15% 2	1551
June	1st to 10th	Night	46% 7% 13% 22% 11% 1	1440
	11th to 20th	Night	46% 7% 10% 21% 13% 3	1440
	21st to end	Night	48% 7% 14% 18% 13%	1440
July	1st to 10th	Night	38% 7% 19% 23% 12% 1	1400
	11th to 20th	Night	40% 7% 16% 26% 9% 1	1392
	21st to end	Night	39% 7% 19% 26% 9%	1486
August	1st to 10th	Night	38% 9% 19% 27% 7%	1422
	11th to 20th	Night	39% 7% 18% 25% 11%	1535
	21st to end	Night	38% 6% 17% 29% 10%	1980
September	1st to 10th	Night	37% 6% 17% 26% 14% 1	1800
	11th to 20th	Night	36% 6% 16% 32% 10% 1	1890
	21st to end	Night	40% 4 13% 30% 13%	1980
October	1st to 10th	Night	46% 5% 10% 25% 13% 1	2078
	11th to 20th	Night	50% 6% 14% 23% 7%	2233
	21st to end	Night	54% 6% 12% 19% 9% 1	2574
November	1st to 10th	Night	50% 5% 13% 22% 8% 1	2407
	11th to 20th	Night	53% 7% 11% 18% 10% 1	2555
	21st to end	Night	58% 5% 11% 17% 8% 1	2660
December	1st to 10th	Night	63% 6% 11% 16% 5%	2660
	11th to 20th	Night	60% 6% 7% 16% 10% 1	3288
	21st to end	Night	64% 4 8% 17% 6% 1	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	24% 17% 37% 17% 5%	180
	11th to 20th	Day	23% 20% 36% 17% 4 1	172
	21st to end	Day	17% 18% 44% 15% 4 1	176
February	1st to 10th	Day	30% 27% 35% 7% 1	198
	11th to 20th	Day	25% 24% 39% 11% 1	334
	21st to end	Day	26% 25% 31% 15% 3	346
March	1st to 10th	Day	25% 18% 35% 18% 4	420
	11th to 20th	Day	24% 21% 36% 14% 5%	420
	21st to end	Day	29% 23% 25% 15% 6% 2	462
April	1st to 10th	Day	28% 17% 32% 16% 6%	420
	11th to 20th	Day	29% 20% 28% 14% 7% 2	412
	21st to end	Day	30% 20% 34% 10% 5% 1	420
May	1st to 10th	Day	26% 21% 32% 15% 5% 1	423
	11th to 20th	Day	21% 20% 32% 20% 5% 1	447
	21st to end	Day	21% 22% 34% 16% 5% 1	485
June	1st to 10th	Day	22% 16% 40% 15% 6%	450
	11th to 20th	Day	18% 21% 30% 20% 9% 1	450
	21st to end	Day	26% 11% 31% 24% 7% 1	450
July	1st to 10th	Day	14% 11% 37% 28% 9% 2	445
	11th to 20th	Day	14% 14% 35% 29% 7% 2	444
	21st to end	Day	14% 9% 31% 31% 12% 2	488
August	1st to 10th	Day	15% 10% 33% 27% 13% 2	446
	11th to 20th	Day	16% 7% 29% 29% 13% 5%	439
	21st to end	Day	16% 14% 28% 23% 13% 6%	495
September	1st to 10th	Day	16% 13% 34% 20% 11% 5%	450
	11th to 20th	Day	16% 13% 30% 23% 13% 5%	450
	21st to end	Day	22% 14% 30% 19% 10% 5%	450
October	1st to 10th	Day	26% 15% 27% 20% 9% 2	450
	11th to 20th	Day	26% 19% 30% 16% 9% 1	412
	21st to end	Day	34% 16% 28% 18% 4	396
November	1st to 10th	Day	24% 20% 29% 19% 7% 1	365
	11th to 20th	Day	25% 21% 32% 17% 5%	280
	21st to end	Day	23% 30% 30% 14% 2 1	180
December	1st to 10th	Day	31% 18% 28% 16% 6% 1	180
	11th to 20th	Day	30% 23% 33% 12% 2 1	180
	21st to end	Day	32% 21% 28% 15% 4 1	198
January	1st to 10th	Night	26% 15% 34% 20% 4	760
	11th to 20th	Night	25% 15% 33% 21% 6%	748
	21st to end	Night	16% 13% 38% 27% 7%	792
February	1st to 10th	Night	19% 14% 37% 23% 6%	720
	11th to 20th	Night	20% 17% 36% 21% 5%	703
	21st to end	Night	21% 16% 35% 23% 4	592
March	1st to 10th	Night	25% 13% 34% 23% 4	720
	11th to 20th	Night	23% 20% 32% 18% 6% 1	720
	21st to end	Night	22% 16% 30% 24% 7% 1	792
April	1st to 10th	Night	28% 13% 30% 23% 6%	720
	11th to 20th	Night	23% 15% 31% 23% 7%	705
	21st to end	Night	27% 16% 30% 21% 6%	540
May	1st to 10th	Night	26% 13% 30% 23% 7% 1	406
	11th to 20th	Night	24% 11% 31% 27% 7%	354
	21st to end	Night	20% 9% 41% 21% 8%	389
June	1st to 10th	Night	23% 9% 29% 33% 6%	360
	11th to 20th	Night	20% 8% 28% 31% 13%	360
	21st to end	Night	19% 5% 32% 31% 12%	360
July	1st to 10th	Night	13% 6% 33% 33% 14% 1	350
	11th to 20th	Night	12% 4 29% 39% 14% 1	348
	21st to end	Night	17% 4 28% 37% 13% 1	394
August	1st to 10th	Night	11% 4 24% 43% 16% 1	358
	11th to 20th	Night	15% 4 26% 36% 17% 2	471
	21st to end	Night	18% 6% 27% 30% 17% 2	792
September	1st to 10th	Night	15% 6% 31% 34% 12% 1	720
	11th to 20th	Night	18% 7% 30% 26% 18% 1	720
	21st to end	Night	20% 11% 29% 24% 14% 2	720
October	1st to 10th	Night	21% 13% 29% 26% 11%	720
	11th to 20th	Night	25% 12% 30% 23% 8% 1	720
	21st to end	Night	28% 14% 30% 22% 5% 1	792
November	1st to 10th	Night	24% 14% 29% 24% 7% 1	740
	11th to 20th	Night	23% 15% 32% 21% 8% 1	760
	21st to end	Night	26% 20% 25% 23% 5% 1	760
December	1st to 10th	Night	29% 13% 30% 22% 6%	760
	11th to 20th	Night	26% 15% 33% 20% 5% 1	760
	21st to end	Night	30% 16% 29% 20% 4	836

Page generated at 2024-01-14 09:55:01. Version ac07

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