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 2025-02-06.

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% 6% 6% 6% 5% 7% 8% 34%	111776
	Night	3 8% 4 9% 6% 6% 6% 5% 8% 10% 35%	115127
Transparency	Day	39% 10% 16% 21% 11% 2	111516
	Night	38% 11% 17% 22% 10% 1	115033
Seeing	Day	14% 23% 31% 21% 9% 2	15879
	Night	9% 16% 38% 25% 10% 1	23954

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 8% 5% 12% 8% 8% 8% 6% 9% 10% 27%	3179
	11th to 20th	Day	1 6% 3 10% 6% 6% 6% 5% 8% 10% 38%	3159
	21st to end	Day	1 7% 3 8% 6% 7% 7% 6% 8% 11% 35%	3498
February	1st to 10th	Day	2 8% 3 13% 9% 8% 8% 6% 9% 10% 24%	1734
	11th to 20th	Day	1 8% 5% 12% 7% 7% 6% 6% 7% 8% 32%	1665
	21st to end	Day	1 9% 4 15% 9% 7% 9% 5% 8% 7% 27%	1413
March	1st to 10th	Day	5% 4 12% 8% 8% 7% 6% 9% 12% 29%	3212
	11th to 20th	Day	1 9% 4 9% 7% 6% 7% 6% 9% 10% 31%	3490
	21st to end	Day	2 13% 6% 14% 8% 6% 6% 5% 8% 7% 26%	3872
April	1st to 10th	Day	3 13% 6% 13% 9% 8% 6% 7% 7% 8% 21%	2302
	11th to 20th	Day	2 14% 7% 12% 6% 6% 6% 5% 8% 9% 26%	2438
	21st to end	Day	3 14% 5% 9% 7% 7% 6% 6% 8% 8% 25%	2533
May	1st to 10th	Day	3 11% 4 11% 7% 7% 7% 5% 6% 8% 30%	4420
	11th to 20th	Day	4 12% 4 11% 9% 9% 8% 6% 7% 7% 23%	4523
	21st to end	Day	9% 14% 5% 12% 7% 7% 6% 5% 7% 7% 20%	5161
June	1st to 10th	Day	11% 12% 4 10% 6% 5% 6% 4 6% 7% 28%	2850
	11th to 20th	Day	12% 14% 4 9% 6% 6% 6% 5% 7% 8% 23%	2850
	21st to end	Day	10% 10% 4 12% 7% 6% 5% 5% 6% 6% 29%	2850
July	1st to 10th	Day	6% 6% 2 6% 4 4 3 3 4 5% 57%	4740
	11th to 20th	Day	5% 5% 2 6% 5% 5% 4 3 5% 6% 54%	4740
	21st to end	Day	6% 8% 3 8% 6% 5% 5% 4 5% 7% 42%	5138
August	1st to 10th	Day	6% 5% 2 5% 3 4 4 4 6% 8% 53%	4471
	11th to 20th	Day	7% 10% 3 8% 6% 5% 5% 5% 6% 8% 37%	4026
	21st to end	Day	9% 9% 3 8% 5% 5% 5% 5% 7% 8% 37%	4521
September	1st to 10th	Day	6% 7% 2 7% 5% 4 5% 3 7% 8% 44%	2307
	11th to 20th	Day	9% 13% 4 7% 5% 5% 5% 5% 6% 7% 36%	2216
	21st to end	Day	7% 10% 3 8% 5% 4 5% 6% 7% 9% 36%	2043
October	1st to 10th	Day	4 10% 4 10% 6% 6% 5% 5% 7% 9% 34%	3180
	11th to 20th	Day	3 10% 2 8% 5% 5% 6% 5% 8% 11% 37%	3161
	21st to end	Day	1 8% 6% 11% 6% 5% 5% 5% 7% 8% 37%	2968
November	1st to 10th	Day	3 10% 4 10% 6% 5% 7% 7% 9% 11% 29%	1568
	11th to 20th	Day	2 6% 4 10% 7% 7% 6% 5% 9% 12% 32%	1600
	21st to end	Day	2 10% 4 9% 7% 8% 6% 5% 9% 9% 33%	1515
December	1st to 10th	Day	2 6% 3 12% 9% 6% 5% 5% 7% 9% 35%	2290
	11th to 20th	Day	1 11% 6% 11% 7% 7% 7% 6% 9% 8% 26%	2645
	21st to end	Day	4 4 11% 7% 6% 9% 7% 11% 11% 30%	3498
January	1st to 10th	Night	1 9% 5% 15% 8% 7% 7% 5% 8% 9% 26%	6766
	11th to 20th	Night	1 6% 3 8% 6% 8% 8% 6% 9% 12% 32%	6739
	21st to end	Night	1 6% 3 10% 6% 5% 7% 5% 8% 11% 37%	7458
February	1st to 10th	Night	2 8% 3 11% 8% 7% 8% 6% 8% 10% 27%	2553
	11th to 20th	Night	2 9% 4 11% 7% 5% 6% 5% 9% 9% 32%	2402
	21st to end	Night	1 8% 4 14% 9% 7% 6% 7% 8% 7% 30%	2041
March	1st to 10th	Night	4 4 12% 8% 6% 5% 5% 8% 16% 31%	3655
	11th to 20th	Night	3 2 8% 6% 7% 8% 7% 9% 12% 38%	3489
	21st to end	Night	2 13% 5% 12% 5% 5% 5% 5% 7% 8% 32%	3781
April	1st to 10th	Night	2 9% 5% 13% 7% 6% 7% 6% 8% 10% 28%	1876
	11th to 20th	Night	2 11% 4 10% 6% 6% 6% 5% 8% 10% 31%	1691
	21st to end	Night	2 12% 5% 8% 8% 5% 6% 4 8% 9% 33%	1646
May	1st to 10th	Night	3 9% 3 9% 6% 5% 5% 4 6% 9% 41%	2540
	11th to 20th	Night	4 9% 2 7% 6% 7% 8% 6% 10% 11% 29%	2370
	21st to end	Night	11% 13% 5% 12% 7% 6% 6% 5% 6% 7% 22%	2414
June	1st to 10th	Night	11% 10% 3 8% 6% 7% 6% 4 7% 9% 31%	1330
	11th to 20th	Night	13% 8% 4 7% 5% 6% 5% 4 6% 9% 32%	1330
	21st to end	Night	12% 9% 3 7% 5% 5% 5% 4 6% 8% 37%	1330
July	1st to 10th	Night	5% 5% 2 4 4 4 4 3 5% 7% 56%	2220
	11th to 20th	Night	4 4 1 3 2 3 4 5% 5% 8% 61%	2220
	21st to end	Night	5% 6% 2 5% 4 4 4 4 6% 10% 49%	2414
August	1st to 10th	Night	6% 5% 2 5% 3 3 4 3 5% 7% 57%	2457
	11th to 20th	Night	8% 8% 3 6% 4 4 6% 5% 6% 8% 42%	2810
	21st to end	Night	9% 10% 3 7% 4 4 4 3 6% 7% 44%	3146
September	1st to 10th	Night	7% 7% 2 6% 4 4 4 4 6% 8% 50%	1872
	11th to 20th	Night	9% 10% 3 6% 4 5% 5% 4 6% 6% 41%	1962
	21st to end	Night	7% 9% 4 7% 4 5% 6% 5% 8% 9% 35%	2137
October	1st to 10th	Night	5% 10% 3 8% 5% 5% 6% 5% 7% 9% 36%	3800
	11th to 20th	Night	2 9% 3 7% 5% 7% 7% 7% 9% 11% 34%	3777
	21st to end	Night	2 9% 4 9% 5% 6% 5% 5% 7% 9% 40%	4583
November	1st to 10th	Night	2 9% 5% 12% 8% 7% 6% 5% 8% 10% 28%	2730
	11th to 20th	Night	2 8% 4 8% 6% 6% 7% 5% 10% 10% 34%	2800
	21st to end	Night	1 9% 3 10% 6% 7% 7% 6% 9% 10% 33%	2880
December	1st to 10th	Night	2 8% 4 9% 6% 7% 7% 6% 9% 10% 31%	4890
	11th to 20th	Night	2 9% 5% 13% 7% 7% 6% 6% 8% 9% 28%	5560
	21st to end	Night	5% 4 12% 8% 7% 8% 6% 10% 11% 30%	7458

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	45% 12% 13% 22% 7% 1	3179
	11th to 20th	Day	36% 9% 18% 22% 7% 8%	3180
	21st to end	Day	36% 12% 18% 20% 12% 1	3498
February	1st to 10th	Day	48% 12% 14% 15% 10% 1	1734
	11th to 20th	Day	44% 12% 13% 18% 12% 1	1674
	21st to end	Day	46% 10% 16% 18% 9% 1	1413
March	1st to 10th	Day	38% 13% 14% 15% 18% 1	3212
	11th to 20th	Day	39% 10% 16% 22% 12% 1	3490
	21st to end	Day	45% 14% 13% 17% 10% 1	3872
April	1st to 10th	Day	53% 12% 14% 13% 8%	2302
	11th to 20th	Day	49% 11% 12% 16% 12%	2438
	21st to end	Day	50% 10% 14% 19% 7% 1	2533
May	1st to 10th	Day	44% 11% 15% 21% 10%	4420
	11th to 20th	Day	48% 13% 13% 18% 7%	4526
	21st to end	Day	56% 10% 11% 18% 6%	5162
June	1st to 10th	Day	49% 8% 13% 16% 11% 3	2850
	11th to 20th	Day	51% 9% 15% 17% 8%	2850
	21st to end	Day	45% 10% 14% 19% 9% 2	2850
July	1st to 10th	Day	24% 7% 11% 20% 27% 12%	4666
	11th to 20th	Day	23% 6% 18% 25% 25% 3	4659
	21st to end	Day	30% 8% 19% 24% 16% 3	4976
August	1st to 10th	Day	23% 6% 13% 43% 15% 1	4453
	11th to 20th	Day	32% 11% 20% 28% 8% 2	4065
	21st to end	Day	38% 10% 26% 19% 6% 1	4520
September	1st to 10th	Day	33% 7% 18% 27% 11% 3	2307
	11th to 20th	Day	41% 8% 13% 25% 9% 3	2216
	21st to end	Day	38% 11% 18% 21% 11% 1	2043
October	1st to 10th	Day	38% 11% 20% 19% 11% 1	3180
	11th to 20th	Day	34% 10% 19% 27% 10%	3161
	21st to end	Day	35% 11% 19% 25% 10% 1	2968
November	1st to 10th	Day	43% 12% 19% 21% 5% 1	1568
	11th to 20th	Day	39% 13% 17% 19% 10%	1600
	21st to end	Day	41% 11% 19% 20% 7% 2	1515
December	1st to 10th	Day	41% 12% 16% 23% 8% 1	2290
	11th to 20th	Day	46% 13% 19% 13% 9%	2648
	21st to end	Day	35% 13% 22% 22% 7% 1	3498
January	1st to 10th	Night	50% 11% 12% 18% 8% 1	6766
	11th to 20th	Night	35% 12% 18% 21% 8% 5%	6780
	21st to end	Night	35% 13% 20% 20% 11% 1	7458
February	1st to 10th	Night	45% 11% 17% 14% 11% 1	2553
	11th to 20th	Night	43% 10% 14% 19% 12% 2	2404
	21st to end	Night	45% 9% 15% 21% 9%	2041
March	1st to 10th	Night	36% 10% 18% 15% 20% 1	3655
	11th to 20th	Night	30% 10% 16% 26% 17%	3490
	21st to end	Night	42% 13% 13% 19% 12% 1	3781
April	1st to 10th	Night	43% 11% 19% 21% 6%	1876
	11th to 20th	Night	42% 10% 17% 20% 11%	1691
	21st to end	Night	42% 9% 18% 22% 9%	1646
May	1st to 10th	Night	34% 10% 21% 26% 9%	2540
	11th to 20th	Night	39% 13% 21% 23% 3	2370
	21st to end	Night	56% 10% 12% 18% 4	2414
June	1st to 10th	Night	44% 10% 16% 20% 9% 2	1330
	11th to 20th	Night	45% 10% 19% 19% 7%	1330
	21st to end	Night	42% 10% 15% 24% 8% 2	1330
July	1st to 10th	Night	24% 8% 12% 22% 26% 9%	2185
	11th to 20th	Night	18% 9% 14% 38% 20% 1	2178
	21st to end	Night	25% 9% 21% 22% 20% 4	2337
August	1st to 10th	Night	25% 7% 13% 41% 14% 1	2450
	11th to 20th	Night	34% 11% 22% 25% 7% 1	2837
	21st to end	Night	36% 8% 28% 24% 4	3146
September	1st to 10th	Night	31% 7% 18% 30% 11% 3	1872
	11th to 20th	Night	38% 8% 16% 24% 11% 3	1962
	21st to end	Night	40% 9% 20% 24% 7% 1	2137
October	1st to 10th	Night	40% 12% 16% 26% 7%	3800
	11th to 20th	Night	35% 12% 21% 23% 8%	3777
	21st to end	Night	34% 11% 20% 26% 9%	4583
November	1st to 10th	Night	47% 11% 18% 16% 7% 1	2730
	11th to 20th	Night	39% 12% 19% 19% 10%	2800
	21st to end	Night	40% 14% 19% 16% 7% 3	2880
December	1st to 10th	Night	41% 13% 19% 19% 7% 1	4890
	11th to 20th	Night	47% 13% 17% 18% 6%	5556
	21st to end	Night	36% 12% 16% 22% 13% 1	7458

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	9% 19% 40% 22% 7% 4	200
	11th to 20th	Day	11% 22% 35% 23% 8% 2	200
	21st to end	Day	6% 22% 40% 18% 14%	220
February	1st to 10th	Day	14% 27% 37% 18% 4	381
	11th to 20th	Day	8% 28% 39% 19% 6% 1	365
	21st to end	Day	13% 31% 36% 13% 7% 1	307
March	1st to 10th	Day	13% 27% 28% 20% 11% 2	431
	11th to 20th	Day	11% 30% 33% 18% 6% 2	460
	21st to end	Day	16% 25% 32% 17% 8% 1	506
April	1st to 10th	Day	19% 28% 30% 17% 4 1	460
	11th to 20th	Day	16% 25% 31% 18% 8% 2	452
	21st to end	Day	19% 26% 26% 20% 7% 2	460
May	1st to 10th	Day	13% 21% 34% 25% 7% 1	463
	11th to 20th	Day	17% 20% 29% 22% 10% 2	567
	21st to end	Day	20% 22% 29% 20% 8% 2	735
June	1st to 10th	Day	16% 28% 34% 16% 6% 1	680
	11th to 20th	Day	19% 25% 29% 18% 8% 1	680
	21st to end	Day	13% 21% 33% 23% 8% 2	680
July	1st to 10th	Day	11% 20% 33% 22% 11% 3	671
	11th to 20th	Day	12% 18% 31% 25% 11% 2	668
	21st to end	Day	9% 17% 32% 27% 10% 4	739
August	1st to 10th	Day	12% 11% 26% 30% 16% 5%	532
	11th to 20th	Day	8% 14% 28% 32% 14% 4	477
	21st to end	Day	14% 18% 32% 25% 10% 2	539
September	1st to 10th	Day	10% 21% 33% 23% 11% 2	490
	11th to 20th	Day	18% 20% 25% 24% 10% 3	490
	21st to end	Day	23% 26% 27% 17% 6% 1	490
October	1st to 10th	Day	23% 23% 25% 17% 11% 3	490
	11th to 20th	Day	18% 27% 27% 19% 7% 2	490
	21st to end	Day	17% 26% 30% 17% 8% 2	336
November	1st to 10th	Day	17% 30% 32% 17% 6%	200
	11th to 20th	Day	10% 25% 30% 25% 9% 2	200
	21st to end	Day	18% 21% 30% 17% 10% 6%	200
December	1st to 10th	Day	9% 22% 28% 28% 9% 6%	200
	11th to 20th	Day	9% 23% 43% 15% 8% 4	200
	21st to end	Day	11% 19% 37% 25% 8% 1	220
January	1st to 10th	Night	8% 23% 43% 19% 6% 2	900
	11th to 20th	Night	8% 21% 44% 22% 5% 1	900
	21st to end	Night	7% 22% 43% 19% 8% 1	990
February	1st to 10th	Night	9% 21% 40% 22% 7% 1	787
	11th to 20th	Night	5% 19% 40% 26% 9%	744
	21st to end	Night	6% 20% 44% 24% 6% 1	628
March	1st to 10th	Night	7% 19% 43% 22% 9%	760
	11th to 20th	Night	3 21% 44% 22% 9%	760
	21st to end	Night	8% 17% 38% 26% 10% 1	836
April	1st to 10th	Night	9% 14% 40% 28% 8% 1	736
	11th to 20th	Night	6% 15% 45% 24% 10%	563
	21st to end	Night	9% 14% 41% 28% 6% 1	506
May	1st to 10th	Night	10% 11% 36% 29% 13%	380
	11th to 20th	Night	11% 11% 34% 35% 9% 1	374
	21st to end	Night	18% 9% 33% 31% 8%	411
June	1st to 10th	Night	14% 10% 37% 30% 8%	380
	11th to 20th	Night	13% 9% 39% 29% 9%	380
	21st to end	Night	13% 8% 33% 37% 9%	380
July	1st to 10th	Night	10% 6% 32% 38% 14%	370
	11th to 20th	Night	9% 8% 32% 35% 15%	368
	21st to end	Night	5% 4 31% 36% 22% 2	416
August	1st to 10th	Night	10% 3 21% 38% 28% 2	378
	11th to 20th	Night	6% 3 25% 37% 27% 1	562
	21st to end	Night	12% 9% 32% 32% 14%	627
September	1st to 10th	Night	12% 9% 29% 32% 17% 1	732
	11th to 20th	Night	14% 11% 25% 28% 20% 2	760
	21st to end	Night	16% 19% 33% 21% 10%	760
October	1st to 10th	Night	19% 19% 27% 23% 11% 1	760
	11th to 20th	Night	12% 20% 37% 19% 11%	760
	21st to end	Night	11% 20% 41% 19% 7% 1	836
November	1st to 10th	Night	12% 22% 43% 17% 6%	780
	11th to 20th	Night	8% 23% 44% 20% 5% 1	800
	21st to end	Night	9% 22% 43% 18% 7% 1	840
December	1st to 10th	Night	6% 19% 42% 24% 9% 2	900
	11th to 20th	Night	8% 19% 43% 22% 6% 1	900
	21st to end	Night	8% 17% 49% 20% 5%	990

Page generated at 2025-02-03 00:05:50. Version ac07

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