Tatlayoko Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tatlayoko Lake clear sky chart from 2005-11-06 to 2026-06-01.

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	4 9% 4 10% 7% 6% 6% 5% 7% 8% 33%	135684
	Night	3 8% 4 9% 6% 6% 6% 5% 8% 10% 35%	136147
Transparency	Day	39% 11% 17% 21% 11% 2	135380
	Night	37% 11% 18% 22% 11% 1	136029
Seeing	Day	15% 23% 31% 21% 9% 2	17636
	Night	10% 17% 38% 25% 10% 1	25604

By Month

Percentage Cloud Cover NW (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	1 7% 4 12% 7% 8% 8% 7% 10% 11% 26%	4125
	11th to 20th	Day	1 5% 3 8% 6% 5% 6% 5% 9% 10% 43%	4119
	21st to end	Day	1 9% 4 9% 6% 7% 7% 6% 8% 11% 32%	4529
February	1st to 10th	Day	2 7% 3 12% 9% 8% 7% 7% 9% 10% 25%	1867
	11th to 20th	Day	1 7% 5% 13% 7% 7% 6% 7% 7% 8% 31%	1845
	21st to end	Day	1 8% 4 15% 9% 7% 9% 5% 7% 7% 28%	1557
March	1st to 10th	Day	8% 5% 14% 8% 8% 7% 6% 8% 10% 25%	4717
	11th to 20th	Day	1 7% 5% 12% 8% 7% 8% 7% 9% 10% 27%	5110
	21st to end	Day	3 14% 7% 14% 8% 6% 6% 5% 8% 7% 22%	5668
April	1st to 10th	Day	2 12% 5% 13% 9% 8% 6% 7% 7% 8% 22%	2544
	11th to 20th	Day	2 13% 6% 13% 6% 6% 6% 5% 7% 9% 26%	2698
	21st to end	Day	3 14% 5% 9% 7% 7% 6% 6% 8% 9% 27%	2800
May	1st to 10th	Day	3 10% 4 11% 8% 7% 7% 5% 6% 7% 33%	6460
	11th to 20th	Day	4 15% 5% 13% 9% 8% 7% 5% 6% 7% 20%	6623
	21st to end	Day	7% 12% 4 13% 7% 6% 7% 5% 8% 8% 22%	7570
June	1st to 10th	Day	11% 12% 4 10% 6% 4 6% 4 6% 7% 30%	3001
	11th to 20th	Day	12% 15% 4 10% 6% 6% 6% 5% 7% 8% 22%	3000
	21st to end	Day	10% 10% 4 12% 7% 6% 5% 5% 6% 6% 29%	3000
July	1st to 10th	Day	6% 8% 3 8% 5% 5% 4 3 5% 6% 47%	6780
	11th to 20th	Day	6% 6% 2 7% 5% 5% 5% 4 5% 6% 48%	6780
	21st to end	Day	6% 7% 3 8% 6% 4 5% 4 6% 7% 46%	7375
August	1st to 10th	Day	6% 5% 2 5% 3 4 4 4 6% 8% 52%	4613
	11th to 20th	Day	7% 10% 3 9% 6% 5% 5% 5% 6% 8% 37%	4156
	21st to end	Day	9% 9% 3 8% 5% 5% 5% 5% 7% 8% 38%	4664
September	1st to 10th	Day	6% 7% 2 7% 5% 4 5% 4 6% 8% 45%	2428
	11th to 20th	Day	9% 13% 4 7% 5% 5% 5% 4 6% 8% 36%	2332
	21st to end	Day	7% 10% 3 8% 5% 4 5% 6% 7% 9% 36%	2150
October	1st to 10th	Day	4 10% 4 10% 6% 6% 5% 5% 8% 9% 34%	3280
	11th to 20th	Day	3 10% 2 8% 5% 5% 6% 5% 8% 11% 37%	3261
	21st to end	Day	1 8% 6% 11% 6% 5% 5% 5% 8% 8% 37%	3063
November	1st to 10th	Day	3 10% 4 11% 6% 5% 6% 6% 9% 10% 30%	1648
	11th to 20th	Day	2 7% 4 10% 7% 7% 6% 5% 10% 12% 31%	1680
	21st to end	Day	2 10% 4 9% 7% 8% 6% 5% 9% 9% 33%	1591
December	1st to 10th	Day	2 6% 3 12% 10% 6% 5% 5% 8% 9% 34%	2360
	11th to 20th	Day	1 10% 6% 11% 8% 7% 7% 6% 9% 9% 26%	2715
	21st to end	Day	4 4 11% 7% 6% 9% 7% 11% 11% 29%	3575
January	1st to 10th	Night	1 7% 5% 15% 8% 7% 7% 5% 8% 10% 26%	8770
	11th to 20th	Night	1 5% 2 7% 5% 6% 7% 6% 8% 12% 41%	8779
	21st to end	Night	1 7% 4 10% 6% 5% 6% 5% 7% 10% 38%	9651
February	1st to 10th	Night	2 8% 3 10% 8% 7% 8% 6% 8% 11% 28%	2749
	11th to 20th	Night	2 8% 4 11% 7% 6% 6% 5% 9% 9% 32%	2662
	21st to end	Night	1 7% 4 14% 9% 7% 7% 6% 8% 8% 30%	2249
March	1st to 10th	Night	1 6% 5% 13% 7% 6% 5% 5% 8% 14% 29%	5374
	11th to 20th	Night	3 3 10% 6% 7% 8% 7% 9% 11% 34%	5109
	21st to end	Night	3 14% 6% 12% 5% 5% 5% 5% 7% 8% 30%	5549
April	1st to 10th	Night	2 9% 5% 13% 7% 6% 7% 5% 8% 10% 28%	2074
	11th to 20th	Night	2 10% 4 10% 6% 6% 6% 5% 8% 10% 32%	1871
	21st to end	Night	2 12% 4 8% 7% 5% 6% 4 8% 9% 34%	1819
May	1st to 10th	Night	2 8% 3 9% 6% 5% 6% 4 8% 10% 40%	3720
	11th to 20th	Night	4 12% 3 8% 6% 6% 7% 6% 9% 11% 26%	3476
	21st to end	Night	8% 11% 4 11% 7% 6% 7% 5% 7% 9% 25%	3547
June	1st to 10th	Night	10% 9% 3 8% 6% 7% 6% 4 7% 8% 33%	1400
	11th to 20th	Night	13% 9% 4 7% 5% 6% 5% 4 7% 9% 33%	1400
	21st to end	Night	11% 10% 3 7% 5% 5% 5% 4 6% 8% 37%	1400
July	1st to 10th	Night	5% 6% 2 5% 4 4 5% 3 6% 8% 51%	3180
	11th to 20th	Night	5% 5% 2 4 3 4 4 4 6% 8% 54%	3180
	21st to end	Night	7% 7% 2 5% 4 5% 4 4 6% 9% 48%	3468
August	1st to 10th	Night	6% 5% 2 5% 3 3 4 3 5% 7% 57%	2535
	11th to 20th	Night	8% 8% 3 6% 4 4 6% 5% 6% 7% 42%	2900
	21st to end	Night	8% 9% 3 7% 3 4 4 3 6% 7% 45%	3245
September	1st to 10th	Night	7% 7% 2 6% 4 4 4 4 6% 8% 50%	1971
	11th to 20th	Night	9% 10% 3 6% 4 5% 5% 4 6% 7% 42%	2065
	21st to end	Night	7% 9% 4 7% 5% 6% 5% 5% 8% 9% 35%	2250
October	1st to 10th	Night	5% 10% 3 8% 5% 5% 6% 5% 7% 10% 36%	3920
	11th to 20th	Night	2 9% 3 7% 5% 7% 7% 7% 8% 10% 34%	3897
	21st to end	Night	2 8% 4 9% 5% 6% 5% 5% 7% 9% 39%	4730
November	1st to 10th	Night	2 9% 4 11% 7% 7% 6% 6% 8% 11% 28%	2870
	11th to 20th	Night	2 8% 3 8% 7% 6% 6% 5% 10% 10% 34%	2940
	21st to end	Night	1 8% 3 10% 6% 7% 7% 6% 9% 10% 33%	3024
December	1st to 10th	Night	2 8% 4 9% 6% 7% 7% 6% 9% 10% 31%	5040
	11th to 20th	Night	1 9% 5% 13% 8% 7% 6% 6% 8% 9% 28%	5710
	21st to end	Night	5% 4 12% 8% 8% 8% 6% 10% 11% 30%	7623

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% 12% 16% 22% 9% 1	4125
	11th to 20th	Day	30% 9% 16% 25% 14% 6%	4140
	21st to end	Day	38% 11% 17% 19% 14% 1	4530
February	1st to 10th	Day	46% 12% 14% 15% 11% 2	1867
	11th to 20th	Day	45% 11% 13% 19% 11% 1	1854
	21st to end	Day	45% 10% 17% 18% 9% 1	1557
March	1st to 10th	Day	41% 13% 15% 16% 14% 1	4717
	11th to 20th	Day	38% 10% 14% 20% 16% 1	5110
	21st to end	Day	48% 13% 12% 17% 9% 1	5668
April	1st to 10th	Day	50% 12% 15% 15% 8%	2544
	11th to 20th	Day	48% 11% 13% 16% 12%	2698
	21st to end	Day	47% 10% 15% 20% 8%	2800
May	1st to 10th	Day	40% 11% 15% 22% 12%	6460
	11th to 20th	Day	48% 13% 14% 17% 7%	6626
	21st to end	Day	48% 12% 16% 18% 5% 1	7571
June	1st to 10th	Day	47% 8% 14% 17% 11% 3	3001
	11th to 20th	Day	51% 9% 15% 17% 8%	3000
	21st to end	Day	45% 10% 15% 19% 9% 1	3000
July	1st to 10th	Day	30% 9% 13% 19% 20% 8%	6706
	11th to 20th	Day	26% 9% 20% 24% 18% 2	6699
	21st to end	Day	27% 8% 20% 27% 16% 2	7168
August	1st to 10th	Day	23% 7% 13% 42% 15% 1	4595
	11th to 20th	Day	32% 11% 20% 28% 8% 2	4195
	21st to end	Day	37% 10% 26% 19% 8% 1	4663
September	1st to 10th	Day	32% 7% 19% 28% 11% 3	2428
	11th to 20th	Day	41% 7% 14% 26% 9% 3	2332
	21st to end	Day	38% 11% 18% 21% 11% 1	2150
October	1st to 10th	Day	39% 11% 20% 19% 11% 1	3280
	11th to 20th	Day	34% 10% 19% 27% 10%	3261
	21st to end	Day	35% 11% 19% 26% 10% 1	3063
November	1st to 10th	Day	42% 11% 18% 22% 5% 1	1648
	11th to 20th	Day	40% 14% 17% 19% 10%	1680
	21st to end	Day	41% 10% 20% 20% 7% 2	1591
December	1st to 10th	Day	41% 12% 15% 23% 8% 1	2360
	11th to 20th	Day	45% 13% 19% 14% 9%	2718
	21st to end	Day	35% 13% 22% 22% 8% 1	3575
January	1st to 10th	Night	46% 11% 16% 17% 9% 1	8770
	11th to 20th	Night	28% 12% 16% 24% 15% 4	8820
	21st to end	Night	35% 12% 19% 20% 13% 1	9651
February	1st to 10th	Night	43% 11% 17% 14% 13% 2	2749
	11th to 20th	Night	43% 9% 14% 20% 12% 2	2664
	21st to end	Night	45% 9% 15% 21% 10%	2249
March	1st to 10th	Night	40% 10% 17% 17% 16% 1	5374
	11th to 20th	Night	30% 10% 15% 23% 20% 2	5110
	21st to end	Night	44% 12% 13% 18% 12%	5549
April	1st to 10th	Night	43% 10% 20% 21% 6% 1	2074
	11th to 20th	Night	41% 10% 18% 20% 11%	1871
	21st to end	Night	40% 9% 18% 24% 9%	1819
May	1st to 10th	Night	32% 9% 23% 25% 10%	3717
	11th to 20th	Night	41% 12% 21% 23% 3	3476
	21st to end	Night	46% 13% 17% 20% 5%	3547
June	1st to 10th	Night	42% 10% 16% 20% 10% 2	1400
	11th to 20th	Night	45% 10% 18% 20% 8%	1400
	21st to end	Night	41% 10% 15% 24% 8% 2	1400
July	1st to 10th	Night	27% 10% 16% 21% 20% 6%	3145
	11th to 20th	Night	21% 12% 20% 33% 14% 1	3138
	21st to end	Night	27% 9% 24% 22% 16% 3	3370
August	1st to 10th	Night	24% 8% 13% 41% 13% 1	2528
	11th to 20th	Night	34% 11% 22% 25% 7% 1	2927
	21st to end	Night	35% 8% 28% 24% 5%	3245
September	1st to 10th	Night	30% 7% 19% 30% 11% 3	1971
	11th to 20th	Night	38% 8% 17% 24% 11% 3	2065
	21st to end	Night	40% 9% 20% 23% 7% 1	2250
October	1st to 10th	Night	40% 12% 16% 26% 7%	3920
	11th to 20th	Night	35% 12% 21% 23% 8%	3897
	21st to end	Night	33% 11% 20% 26% 9%	4730
November	1st to 10th	Night	46% 12% 18% 16% 7% 1	2870
	11th to 20th	Night	39% 12% 19% 19% 10%	2940
	21st to end	Night	40% 14% 20% 16% 7% 3	3024
December	1st to 10th	Night	41% 13% 19% 19% 7% 1	5040
	11th to 20th	Night	46% 13% 17% 18% 6%	5706
	21st to end	Night	36% 12% 16% 22% 14% 1	7623

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	10% 20% 39% 21% 6% 3	220
	11th to 20th	Day	12% 21% 32% 24% 9% 1	220
	21st to end	Day	8% 22% 36% 20% 14%	242
February	1st to 10th	Day	16% 27% 36% 17% 4	425
	11th to 20th	Day	8% 26% 40% 20% 6% 1	425
	21st to end	Day	17% 30% 35% 12% 6% 1	355
March	1st to 10th	Day	17% 27% 27% 18% 10% 1	505
	11th to 20th	Day	15% 29% 33% 17% 5% 1	540
	21st to end	Day	19% 25% 32% 16% 7% 1	594
April	1st to 10th	Day	19% 28% 30% 18% 4 1	540
	11th to 20th	Day	16% 25% 30% 19% 8% 2	532
	21st to end	Day	19% 26% 27% 19% 7% 2	540
May	1st to 10th	Day	15% 21% 33% 24% 7% 1	543
	11th to 20th	Day	17% 21% 30% 21% 9% 2	655
	21st to end	Day	21% 25% 26% 19% 7% 2	845
June	1st to 10th	Day	16% 28% 34% 16% 5% 1	731
	11th to 20th	Day	19% 25% 30% 17% 8% 1	730
	21st to end	Day	14% 20% 32% 23% 9% 2	730
July	1st to 10th	Day	12% 21% 33% 21% 10% 3	721
	11th to 20th	Day	12% 19% 31% 25% 11% 2	718
	21st to end	Day	9% 17% 32% 28% 10% 4	794
August	1st to 10th	Day	11% 12% 27% 30% 16% 5%	574
	11th to 20th	Day	11% 15% 28% 30% 13% 4	517
	21st to end	Day	13% 17% 30% 25% 13% 3	583
September	1st to 10th	Day	9% 19% 32% 24% 13% 2	530
	11th to 20th	Day	18% 20% 25% 25% 9% 3	530
	21st to end	Day	25% 26% 27% 16% 5% 1	530
October	1st to 10th	Day	23% 23% 25% 16% 10% 3	530
	11th to 20th	Day	20% 26% 26% 19% 7% 2	530
	21st to end	Day	20% 25% 31% 16% 7% 2	365
November	1st to 10th	Day	20% 29% 30% 15% 5%	220
	11th to 20th	Day	11% 25% 30% 23% 8% 2	220
	21st to end	Day	16% 21% 31% 18% 9% 5%	220
December	1st to 10th	Day	10% 24% 27% 26% 8% 5%	220
	11th to 20th	Day	13% 22% 41% 13% 7% 4	220
	21st to end	Day	11% 21% 36% 24% 7% 1	242
January	1st to 10th	Night	8% 23% 42% 19% 5% 2	950
	11th to 20th	Night	8% 21% 43% 23% 5% 1	950
	21st to end	Night	7% 23% 42% 20% 8% 1	1045
February	1st to 10th	Night	10% 21% 39% 22% 7% 1	848
	11th to 20th	Night	5% 19% 40% 27% 9%	824
	21st to end	Night	8% 21% 43% 23% 5% 1	692
March	1st to 10th	Night	8% 20% 43% 21% 8%	840
	11th to 20th	Night	5% 22% 44% 21% 9%	840
	21st to end	Night	9% 18% 37% 25% 10% 1	924
April	1st to 10th	Night	9% 16% 39% 28% 8% 1	814
	11th to 20th	Night	6% 16% 45% 24% 9%	623
	21st to end	Night	9% 14% 41% 29% 6% 1	559
May	1st to 10th	Night	9% 12% 36% 30% 13%	420
	11th to 20th	Night	12% 10% 35% 34% 8% 1	414
	21st to end	Night	18% 12% 33% 30% 7%	455
June	1st to 10th	Night	14% 10% 39% 30% 8%	400
	11th to 20th	Night	14% 9% 39% 30% 9%	400
	21st to end	Night	13% 7% 34% 37% 9%	400
July	1st to 10th	Night	10% 7% 32% 37% 14%	390
	11th to 20th	Night	10% 8% 32% 35% 15%	388
	21st to end	Night	5% 5% 30% 37% 21% 2	438
August	1st to 10th	Night	10% 3 21% 38% 26% 2	398
	11th to 20th	Night	7% 4 26% 36% 25% 1	592
	21st to end	Night	12% 8% 31% 34% 15%	660
September	1st to 10th	Night	11% 9% 29% 33% 18% 1	771
	11th to 20th	Night	14% 11% 25% 28% 20% 2	800
	21st to end	Night	17% 20% 32% 21% 9%	800
October	1st to 10th	Night	18% 19% 28% 23% 11% 1	800
	11th to 20th	Night	13% 20% 37% 19% 11%	800
	21st to end	Night	13% 20% 40% 19% 7% 1	880
November	1st to 10th	Night	13% 23% 42% 16% 6%	820
	11th to 20th	Night	8% 23% 44% 20% 5% 1	840
	21st to end	Night	9% 21% 43% 19% 6% 1	884
December	1st to 10th	Night	7% 20% 41% 23% 8% 2	950
	11th to 20th	Night	10% 19% 42% 21% 6% 1	950
	21st to end	Night	8% 19% 49% 19% 5%	1045

Page generated at 2026-05-28 22:53:32. Version ac07

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