AllSky Camera - Tatla Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AllSky Camera - Tatla Lake clear sky chart from 2005-11-06 to 2026-09-14.

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 7% 3 9% 6% 6% 6% 5% 7% 9% 37%	153826
	Night	4 8% 3 9% 6% 6% 6% 5% 8% 9% 35%	145979
Transparency	Day	39% 10% 16% 22% 10% 1	153522
	Night	40% 12% 17% 21% 9% 1	145865
Seeing	Day	11% 17% 32% 24% 12% 3	18154
	Night	7% 10% 37% 32% 13% 1	25864

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	2 10% 4 11% 8% 8% 9% 7% 11% 10% 21%	4125
	11th to 20th	Day	1 5% 3 7% 5% 5% 6% 6% 10% 14% 38%	4119
	21st to end	Day	2 9% 4 9% 6% 7% 8% 5% 8% 10% 32%	4529
February	1st to 10th	Day	2 8% 3 10% 8% 7% 8% 6% 9% 11% 28%	1848
	11th to 20th	Day	1 10% 5% 10% 6% 7% 6% 6% 8% 9% 34%	1845
	21st to end	Day	1 7% 4 10% 7% 7% 8% 6% 9% 9% 31%	1557
March	1st to 10th	Day	1 8% 4 12% 8% 6% 6% 6% 9% 12% 28%	4715
	11th to 20th	Day	2 6% 3 8% 6% 7% 8% 7% 10% 11% 30%	5110
	21st to end	Day	3 12% 4 11% 8% 7% 7% 5% 8% 8% 27%	5650
April	1st to 10th	Day	2 11% 4 11% 7% 7% 7% 5% 8% 9% 28%	2558
	11th to 20th	Day	3 10% 3 11% 7% 6% 7% 6% 8% 9% 31%	2698
	21st to end	Day	3 12% 4 9% 6% 7% 6% 5% 8% 8% 32%	2798
May	1st to 10th	Day	3 7% 3 9% 7% 6% 6% 5% 7% 7% 40%	8195
	11th to 20th	Day	4 10% 4 12% 7% 7% 7% 6% 7% 8% 27%	8494
	21st to end	Day	7% 9% 3 11% 7% 7% 7% 6% 7% 9% 28%	9649
June	1st to 10th	Day	10% 8% 3 9% 6% 6% 6% 5% 7% 7% 33%	3150
	11th to 20th	Day	10% 10% 3 9% 7% 6% 6% 5% 7% 8% 29%	3150
	21st to end	Day	9% 7% 3 8% 6% 7% 6% 5% 8% 8% 33%	3150
July	1st to 10th	Day	4 6% 2 6% 4 5% 5% 4 5% 8% 50%	8820
	11th to 20th	Day	4 4 2 5% 4 4 5% 4 6% 9% 53%	8820
	21st to end	Day	3 5% 3 7% 5% 5% 5% 5% 7% 8% 47%	9567
August	1st to 10th	Day	3 3 1 4 3 3 4 3 5% 8% 62%	6571
	11th to 20th	Day	4 5% 2 6% 5% 7% 6% 5% 7% 10% 43%	5923
	21st to end	Day	5% 6% 2 7% 4 5% 6% 5% 7% 10% 42%	6569
September	1st to 10th	Day	6% 5% 2 7% 5% 5% 6% 4 5% 8% 47%	2561
	11th to 20th	Day	8% 8% 3 6% 5% 6% 5% 4 5% 7% 42%	2360
	21st to end	Day	7% 7% 3 8% 5% 4 5% 5% 7% 10% 39%	2157
October	1st to 10th	Day	4 8% 3 8% 6% 7% 7% 5% 8% 9% 35%	3280
	11th to 20th	Day	5% 6% 2 6% 5% 5% 6% 5% 9% 11% 39%	3261
	21st to end	Day	3 9% 3 8% 5% 5% 6% 4 7% 10% 39%	3051
November	1st to 10th	Day	3 9% 5% 8% 5% 6% 7% 6% 9% 10% 32%	1648
	11th to 20th	Day	2 6% 3 9% 7% 6% 8% 7% 10% 10% 32%	1680
	21st to end	Day	2 10% 4 10% 6% 6% 6% 5% 8% 10% 34%	1568
December	1st to 10th	Day	2 7% 3 8% 8% 8% 9% 7% 8% 9% 32%	2360
	11th to 20th	Day	3 10% 6% 15% 8% 8% 8% 6% 9% 8% 19%	2715
	21st to end	Day	1 6% 4 11% 7% 7% 8% 7% 10% 10% 28%	3575
January	1st to 10th	Night	2 11% 7% 15% 9% 8% 8% 6% 8% 9% 17%	8770
	11th to 20th	Night	2 5% 2 6% 6% 6% 8% 6% 11% 13% 35%	8779
	21st to end	Night	1 7% 4 11% 7% 7% 7% 6% 8% 10% 33%	9651
February	1st to 10th	Night	3 9% 3 10% 8% 7% 7% 6% 8% 9% 32%	2768
	11th to 20th	Night	2 9% 4 11% 6% 6% 6% 5% 7% 8% 36%	2662
	21st to end	Night	2 9% 4 11% 8% 7% 6% 6% 8% 8% 31%	2249
March	1st to 10th	Night	1 9% 4 13% 6% 5% 6% 6% 9% 12% 30%	5390
	11th to 20th	Night	1 6% 4 7% 5% 5% 7% 6% 10% 10% 39%	5109
	21st to end	Night	4 15% 4 9% 5% 5% 6% 5% 7% 9% 30%	5566
April	1st to 10th	Night	2 10% 4 10% 7% 5% 6% 6% 8% 10% 32%	2058
	11th to 20th	Night	3 10% 3 9% 6% 6% 6% 6% 7% 9% 36%	1871
	21st to end	Night	3 9% 4 10% 6% 6% 5% 5% 7% 8% 37%	1822
May	1st to 10th	Night	2 6% 3 7% 5% 5% 6% 5% 8% 9% 44%	4724
	11th to 20th	Night	5% 8% 3 9% 6% 7% 7% 6% 9% 10% 31%	4353
	21st to end	Night	9% 9% 3 9% 6% 6% 7% 5% 7% 8% 31%	4522
June	1st to 10th	Night	9% 7% 3 8% 7% 5% 6% 5% 8% 8% 34%	1470
	11th to 20th	Night	10% 8% 3 7% 5% 4 5% 5% 8% 9% 36%	1470
	21st to end	Night	11% 6% 3 7% 5% 5% 6% 5% 6% 6% 40%	1470
July	1st to 10th	Night	4 4 2 5% 4 5% 5% 4 7% 8% 53%	4140
	11th to 20th	Night	5% 4 2 5% 4 4 5% 3 5% 7% 55%	4140
	21st to end	Night	4 5% 2 6% 4 4 5% 4 6% 8% 52%	4501
August	1st to 10th	Night	4 4 2 4 3 3 4 3 4 7% 61%	3575
	11th to 20th	Night	7% 6% 3 8% 5% 5% 6% 4 6% 9% 41%	4142
	21st to end	Night	7% 6% 3 7% 5% 4 5% 4 6% 8% 45%	4579
September	1st to 10th	Night	8% 6% 3 5% 4 3 4 3 7% 8% 50%	2059
	11th to 20th	Night	9% 7% 3 6% 5% 5% 5% 3 5% 6% 46%	2105
	21st to end	Night	8% 7% 3 9% 5% 4 5% 4 7% 7% 40%	2243
October	1st to 10th	Night	6% 8% 3 8% 5% 6% 5% 5% 7% 9% 38%	3920
	11th to 20th	Night	3 7% 2 7% 5% 5% 7% 6% 9% 10% 37%	3897
	21st to end	Night	4 9% 3 7% 5% 6% 6% 5% 8% 10% 36%	4741
November	1st to 10th	Night	3 10% 4 10% 7% 6% 6% 7% 8% 10% 30%	2870
	11th to 20th	Night	3 8% 3 9% 6% 6% 7% 6% 9% 10% 33%	2940
	21st to end	Night	2 10% 3 9% 7% 7% 6% 6% 9% 10% 30%	3050
December	1st to 10th	Night	3 9% 4 9% 7% 8% 9% 7% 9% 9% 27%	5040
	11th to 20th	Night	3 11% 5% 15% 8% 8% 7% 5% 8% 10% 19%	5710
	21st to end	Night	1 7% 4 10% 7% 7% 8% 7% 11% 12% 25%	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	49% 16% 13% 16% 6%	4125
	11th to 20th	Day	33% 11% 18% 23% 10% 5%	4140
	21st to end	Day	40% 15% 17% 18% 9%	4530
February	1st to 10th	Day	47% 12% 15% 15% 10% 1	1848
	11th to 20th	Day	45% 11% 15% 18% 11% 1	1854
	21st to end	Day	44% 11% 16% 21% 8% 1	1557
March	1st to 10th	Day	42% 11% 15% 20% 11% 1	4715
	11th to 20th	Day	39% 10% 16% 21% 14% 1	5110
	21st to end	Day	50% 11% 15% 15% 8% 1	5650
April	1st to 10th	Day	48% 12% 16% 15% 8%	2558
	11th to 20th	Day	46% 12% 12% 18% 11%	2698
	21st to end	Day	46% 11% 14% 19% 9% 1	2798
May	1st to 10th	Day	38% 9% 13% 28% 11%	8195
	11th to 20th	Day	48% 11% 15% 18% 7%	8497
	21st to end	Day	46% 13% 16% 18% 6% 1	9650
June	1st to 10th	Day	46% 10% 13% 17% 11% 3	3150
	11th to 20th	Day	50% 9% 14% 18% 8% 1	3150
	21st to end	Day	44% 11% 14% 20% 9% 1	3150
July	1st to 10th	Day	31% 7% 11% 26% 19% 7%	8746
	11th to 20th	Day	26% 7% 16% 32% 17% 1	8739
	21st to end	Day	31% 8% 19% 25% 14% 2	9360
August	1st to 10th	Day	20% 7% 14% 39% 19% 2	6553
	11th to 20th	Day	31% 11% 22% 28% 8% 1	5962
	21st to end	Day	35% 9% 24% 25% 7%	6568
September	1st to 10th	Day	33% 8% 20% 26% 10% 2	2561
	11th to 20th	Day	39% 8% 17% 25% 9% 2	2360
	21st to end	Day	38% 12% 17% 22% 10% 1	2157
October	1st to 10th	Day	42% 10% 20% 17% 8% 2	3280
	11th to 20th	Day	36% 12% 17% 27% 8%	3261
	21st to end	Day	37% 11% 17% 25% 9% 1	3051
November	1st to 10th	Day	43% 13% 18% 20% 6%	1648
	11th to 20th	Day	42% 13% 19% 16% 10%	1680
	21st to end	Day	43% 12% 17% 19% 7% 2	1568
December	1st to 10th	Day	47% 12% 14% 20% 6% 1	2360
	11th to 20th	Day	57% 11% 14% 10% 8%	2718
	21st to end	Day	41% 15% 16% 20% 5% 1	3575
January	1st to 10th	Night	57% 13% 12% 11% 7%	8770
	11th to 20th	Night	35% 13% 17% 24% 8% 3	8820
	21st to end	Night	40% 13% 20% 18% 8%	9651
February	1st to 10th	Night	46% 11% 16% 15% 11% 1	2768
	11th to 20th	Night	45% 10% 14% 20% 11% 1	2664
	21st to end	Night	47% 9% 13% 21% 8% 1	2249
March	1st to 10th	Night	42% 10% 17% 17% 14%	5390
	11th to 20th	Night	33% 9% 16% 24% 16% 2	5110
	21st to end	Night	47% 12% 15% 16% 11% 1	5566
April	1st to 10th	Night	41% 14% 21% 17% 7% 1	2058
	11th to 20th	Night	40% 12% 17% 22% 9% 1	1871
	21st to end	Night	42% 10% 15% 23% 9%	1822
May	1st to 10th	Night	30% 11% 23% 28% 8%	4721
	11th to 20th	Night	42% 11% 19% 23% 5%	4353
	21st to end	Night	47% 12% 17% 20% 5%	4526
June	1st to 10th	Night	43% 11% 15% 18% 10% 3	1470
	11th to 20th	Night	43% 12% 13% 25% 8%	1470
	21st to end	Night	41% 12% 16% 21% 9% 2	1470
July	1st to 10th	Night	28% 8% 15% 24% 20% 5%	4105
	11th to 20th	Night	26% 8% 16% 38% 12%	4098
	21st to end	Night	28% 8% 21% 25% 17% 2	4403
August	1st to 10th	Night	23% 8% 13% 40% 16% 1	3568
	11th to 20th	Night	36% 12% 22% 24% 5% 1	4169
	21st to end	Night	36% 8% 25% 26% 4	4579
September	1st to 10th	Night	30% 9% 20% 28% 10% 2	2059
	11th to 20th	Night	38% 8% 17% 24% 10% 3	2105
	21st to end	Night	40% 11% 18% 23% 7% 1	2243
October	1st to 10th	Night	41% 12% 17% 24% 7%	3920
	11th to 20th	Night	38% 14% 18% 23% 7%	3897
	21st to end	Night	38% 14% 21% 22% 6%	4741
November	1st to 10th	Night	46% 14% 16% 17% 7% 1	2870
	11th to 20th	Night	44% 11% 18% 19% 8%	2940
	21st to end	Night	44% 13% 19% 16% 6% 3	3050
December	1st to 10th	Night	50% 12% 15% 17% 5% 1	5040
	11th to 20th	Night	54% 15% 13% 12% 5%	5706
	21st to end	Night	40% 18% 15% 18% 9%	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	4 11% 40% 31% 9% 5%	220
	11th to 20th	Day	2 14% 35% 32% 14% 4	220
	21st to end	Day	4 10% 42% 28% 14% 3	242
February	1st to 10th	Day	8% 20% 41% 22% 8% 1	427
	11th to 20th	Day	8% 15% 38% 28% 11% 1	425
	21st to end	Day	12% 21% 41% 17% 8% 1	355
March	1st to 10th	Day	7% 25% 31% 22% 13% 2	499
	11th to 20th	Day	8% 24% 34% 22% 11% 1	540
	21st to end	Day	13% 22% 32% 21% 11% 1	594
April	1st to 10th	Day	14% 24% 31% 23% 8% 1	540
	11th to 20th	Day	10% 23% 31% 22% 11% 4	532
	21st to end	Day	15% 21% 27% 22% 10% 4	540
May	1st to 10th	Day	10% 20% 27% 31% 10% 1	543
	11th to 20th	Day	14% 17% 31% 24% 12% 3	679
	21st to end	Day	18% 20% 31% 19% 11% 2	845
June	1st to 10th	Day	15% 21% 35% 20% 7% 1	780
	11th to 20th	Day	17% 21% 30% 20% 10% 2	780
	21st to end	Day	12% 14% 32% 25% 13% 3	780
July	1st to 10th	Day	12% 15% 31% 24% 14% 4	771
	11th to 20th	Day	10% 15% 30% 25% 15% 4	768
	21st to end	Day	7% 14% 30% 27% 17% 6%	849
August	1st to 10th	Day	8% 9% 23% 31% 20% 8%	636
	11th to 20th	Day	6% 12% 23% 29% 20% 9%	557
	21st to end	Day	8% 14% 29% 27% 17% 6%	627
September	1st to 10th	Day	10% 13% 28% 26% 17% 6%	570
	11th to 20th	Day	14% 12% 27% 27% 15% 5%	543
	21st to end	Day	15% 21% 32% 21% 9% 2	530
October	1st to 10th	Day	18% 17% 27% 22% 13% 3	530
	11th to 20th	Day	12% 20% 33% 22% 10% 2	530
	21st to end	Day	16% 18% 39% 15% 11% 2	360
November	1st to 10th	Day	11% 20% 39% 21% 8%	220
	11th to 20th	Day	5% 14% 34% 34% 11% 3	220
	21st to end	Day	10% 18% 31% 23% 10% 8%	220
December	1st to 10th	Day	5% 10% 36% 31% 12% 5%	220
	11th to 20th	Day	6% 15% 36% 26% 10% 5%	220
	21st to end	Day	6% 13% 38% 30% 12% 1	242
January	1st to 10th	Night	6% 12% 44% 27% 9% 2	950
	11th to 20th	Night	5% 10% 41% 35% 7% 2	950
	21st to end	Night	4 12% 42% 28% 12% 2	1045
February	1st to 10th	Night	7% 13% 41% 28% 11% 1	859
	11th to 20th	Night	6% 8% 39% 32% 14% 1	824
	21st to end	Night	6% 13% 39% 33% 8% 2	692
March	1st to 10th	Night	4 14% 42% 28% 12%	840
	11th to 20th	Night	2 12% 44% 31% 10% 1	840
	21st to end	Night	7% 13% 36% 30% 14% 1	924
April	1st to 10th	Night	7% 12% 33% 35% 13% 1	798
	11th to 20th	Night	7% 8% 39% 33% 13%	623
	21st to end	Night	7% 11% 37% 33% 12% 1	562
May	1st to 10th	Night	3 8% 36% 40% 12%	420
	11th to 20th	Night	9% 9% 29% 42% 9% 1	414
	21st to end	Night	17% 8% 31% 35% 9%	455
June	1st to 10th	Night	11% 10% 37% 35% 7%	420
	11th to 20th	Night	13% 9% 34% 31% 12%	420
	21st to end	Night	12% 6% 27% 40% 14%	420
July	1st to 10th	Night	10% 5% 30% 40% 16%	410
	11th to 20th	Night	10% 5% 28% 40% 17%	408
	21st to end	Night	6% 4 25% 42% 22% 2	460
August	1st to 10th	Night	9% 2 16% 41% 30% 2	419
	11th to 20th	Night	6% 4 20% 37% 31% 2	624
	21st to end	Night	8% 7% 26% 36% 22% 1	693
September	1st to 10th	Night	12% 6% 23% 35% 23% 1	799
	11th to 20th	Night	13% 7% 24% 29% 24% 3	812
	21st to end	Night	11% 14% 34% 28% 12% 1	800
October	1st to 10th	Night	14% 11% 30% 31% 13% 2	800
	11th to 20th	Night	9% 11% 40% 25% 14% 1	800
	21st to end	Night	11% 12% 39% 28% 9% 2	880
November	1st to 10th	Night	6% 16% 43% 27% 7% 1	820
	11th to 20th	Night	5% 13% 45% 28% 8% 1	840
	21st to end	Night	5% 12% 45% 28% 8% 2	898
December	1st to 10th	Night	5% 11% 38% 31% 13% 2	950
	11th to 20th	Night	6% 10% 43% 30% 9% 2	950
	21st to end	Night	5% 9% 47% 30% 8% 1	1045

Page generated at 2026-09-11 01:11:55. Version ac07

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