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 2025-05-11.

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 8% 3 9% 6% 6% 6% 5% 7% 9% 36%	117094
	Night	4 8% 4 9% 6% 6% 6% 5% 8% 9% 34%	120564
Transparency	Day	41% 11% 16% 21% 10% 2	116834
	Night	41% 12% 17% 20% 9% 1	120470
Seeing	Day	11% 18% 32% 24% 12% 3	16261
	Night	8% 10% 37% 31% 13% 1	24291

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 12% 5% 12% 8% 7% 8% 7% 10% 9% 20%	3179
	11th to 20th	Day	2 7% 4 8% 6% 5% 6% 6% 10% 12% 34%	3159
	21st to end	Day	2 8% 3 9% 6% 6% 7% 5% 8% 9% 35%	3498
February	1st to 10th	Day	3 8% 3 11% 8% 7% 7% 6% 9% 10% 28%	1760
	11th to 20th	Day	1 10% 5% 9% 6% 7% 5% 6% 8% 9% 35%	1755
	21st to end	Day	1 7% 4 10% 7% 7% 8% 6% 9% 9% 31%	1485
March	1st to 10th	Day	1 8% 4 12% 8% 6% 6% 6% 9% 12% 28%	4613
	11th to 20th	Day	2 7% 3 8% 6% 7% 8% 7% 10% 11% 30%	5000
	21st to end	Day	4 12% 4 12% 8% 7% 7% 5% 7% 8% 26%	5528
April	1st to 10th	Day	2 11% 5% 11% 8% 7% 8% 5% 7% 9% 27%	2436
	11th to 20th	Day	3 10% 3 12% 7% 7% 7% 6% 7% 8% 31%	2568
	21st to end	Day	3 12% 4 9% 6% 6% 6% 5% 8% 8% 31%	2665
May	1st to 10th	Day	4 10% 3 9% 7% 6% 6% 5% 7% 8% 35%	4560
	11th to 20th	Day	5% 10% 4 11% 7% 7% 7% 5% 8% 8% 28%	4560
	21st to end	Day	11% 11% 4 11% 7% 7% 7% 5% 6% 7% 23%	5161
June	1st to 10th	Day	11% 9% 3 9% 6% 6% 6% 5% 7% 7% 31%	2850
	11th to 20th	Day	10% 11% 3 9% 7% 6% 7% 5% 7% 8% 27%	2850
	21st to end	Day	9% 7% 3 9% 7% 7% 6% 5% 8% 8% 33%	2850
July	1st to 10th	Day	5% 4 2 4 3 3 4 3 4 6% 62%	4740
	11th to 20th	Day	4 4 2 4 4 3 3 3 5% 7% 62%	4740
	21st to end	Day	4 5% 3 7% 5% 5% 5% 5% 7% 8% 47%	5138
August	1st to 10th	Day	4 3 1 4 3 3 4 3 5% 8% 61%	4486
	11th to 20th	Day	5% 6% 2 6% 5% 6% 6% 5% 6% 9% 44%	4026
	21st to end	Day	6% 7% 2 7% 5% 4 5% 5% 7% 9% 42%	4521
September	1st to 10th	Day	6% 5% 2 7% 5% 5% 5% 4 6% 8% 47%	2317
	11th to 20th	Day	8% 8% 3 6% 6% 6% 5% 4 5% 7% 41%	2207
	21st to end	Day	7% 7% 3 7% 5% 4 5% 4 7% 10% 41%	2049
October	1st to 10th	Day	4 7% 3 8% 6% 7% 7% 5% 8% 9% 35%	3180
	11th to 20th	Day	6% 6% 2 6% 6% 5% 6% 5% 9% 11% 38%	3161
	21st to end	Day	2 9% 3 8% 6% 5% 6% 4 7% 10% 39%	2957
November	1st to 10th	Day	3 9% 5% 8% 5% 7% 7% 6% 9% 10% 31%	1568
	11th to 20th	Day	2 6% 3 8% 7% 6% 8% 7% 10% 10% 33%	1600
	21st to end	Day	2 10% 4 10% 5% 5% 6% 5% 8% 10% 34%	1494
December	1st to 10th	Day	2 7% 3 8% 8% 8% 9% 7% 8% 9% 32%	2290
	11th to 20th	Day	3 10% 6% 15% 8% 7% 8% 6% 9% 8% 19%	2645
	21st to end	Day	1 6% 4 11% 7% 7% 8% 7% 10% 10% 28%	3498
January	1st to 10th	Night	2 13% 7% 15% 8% 8% 8% 7% 8% 8% 16%	6766
	11th to 20th	Night	3 7% 3 8% 7% 7% 9% 6% 12% 9% 30%	6739
	21st to end	Night	2 7% 4 10% 7% 6% 6% 5% 8% 10% 35%	7458
February	1st to 10th	Night	3 9% 4 10% 8% 7% 7% 6% 7% 9% 32%	2636
	11th to 20th	Night	2 9% 4 11% 7% 6% 6% 5% 7% 8% 36%	2532
	21st to end	Night	2 10% 4 11% 8% 7% 6% 6% 8% 8% 31%	2145
March	1st to 10th	Night	1 9% 4 13% 6% 5% 6% 6% 9% 12% 29%	5272
	11th to 20th	Night	1 7% 4 7% 5% 5% 7% 6% 10% 10% 39%	4999
	21st to end	Night	4 15% 4 9% 5% 5% 6% 5% 8% 9% 30%	5446
April	1st to 10th	Night	2 9% 4 10% 8% 5% 6% 6% 8% 10% 32%	1960
	11th to 20th	Night	3 10% 3 9% 5% 6% 6% 5% 7% 9% 36%	1781
	21st to end	Night	3 9% 4 10% 7% 6% 5% 5% 7% 8% 36%	1735
May	1st to 10th	Night	3 8% 3 8% 6% 4 6% 4 7% 8% 42%	2620
	11th to 20th	Night	6% 8% 2 7% 5% 6% 7% 6% 9% 11% 34%	2340
	21st to end	Night	13% 10% 3 11% 7% 6% 6% 6% 6% 6% 26%	2414
June	1st to 10th	Night	10% 7% 3 8% 7% 5% 6% 5% 8% 8% 33%	1330
	11th to 20th	Night	10% 8% 3 7% 5% 5% 5% 5% 8% 10% 34%	1330
	21st to end	Night	11% 5% 3 8% 5% 5% 5% 5% 6% 6% 41%	1330
July	1st to 10th	Night	5% 4 1 3 3 4 4 3 6% 6% 61%	2220
	11th to 20th	Night	5% 2 1 4 3 3 4 3 4 7% 65%	2220
	21st to end	Night	5% 6% 2 5% 3 3 6% 4 6% 9% 52%	2414
August	1st to 10th	Night	5% 5% 3 5% 4 4 4 4 4 6% 56%	2440
	11th to 20th	Night	8% 5% 2 7% 5% 5% 5% 4 6% 9% 44%	2812
	21st to end	Night	8% 7% 3 6% 5% 4 4 4 6% 8% 45%	3146
September	1st to 10th	Night	7% 6% 3 6% 4 3 4 3 7% 8% 49%	1863
	11th to 20th	Night	9% 7% 3 6% 5% 5% 5% 3 6% 6% 46%	1971
	21st to end	Night	7% 7% 3 9% 5% 4 5% 4 7% 8% 40%	2131
October	1st to 10th	Night	6% 8% 3 8% 5% 6% 5% 5% 7% 10% 38%	3800
	11th to 20th	Night	3 7% 2 7% 5% 5% 7% 6% 9% 11% 36%	3777
	21st to end	Night	4 9% 3 7% 5% 6% 6% 5% 8% 10% 37%	4594
November	1st to 10th	Night	3 10% 4 10% 7% 6% 6% 7% 7% 9% 30%	2730
	11th to 20th	Night	2 8% 3 9% 6% 6% 7% 6% 9% 10% 33%	2800
	21st to end	Night	2 10% 3 9% 7% 7% 6% 6% 9% 10% 31%	2905
December	1st to 10th	Night	3 9% 4 8% 7% 8% 9% 7% 9% 9% 27%	4890
	11th to 20th	Night	3 11% 5% 15% 8% 8% 7% 5% 8% 10% 19%	5560
	21st to end	Night	1 7% 4 10% 7% 7% 8% 7% 11% 12% 25%	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	50% 15% 13% 17% 4 1	3179
	11th to 20th	Day	40% 11% 18% 20% 6% 6%	3180
	21st to end	Day	36% 16% 19% 20% 9%	3498
February	1st to 10th	Day	48% 13% 15% 14% 9% 1	1760
	11th to 20th	Day	44% 11% 15% 18% 11% 1	1764
	21st to end	Day	44% 11% 15% 21% 8% 1	1485
March	1st to 10th	Day	42% 11% 15% 20% 11%	4613
	11th to 20th	Day	39% 10% 16% 20% 14% 1	5000
	21st to end	Day	51% 11% 15% 15% 8% 1	5528
April	1st to 10th	Day	49% 12% 16% 14% 8%	2436
	11th to 20th	Day	47% 12% 11% 18% 12%	2568
	21st to end	Day	47% 11% 15% 18% 8% 1	2665
May	1st to 10th	Day	41% 11% 16% 24% 9%	4560
	11th to 20th	Day	48% 14% 14% 18% 6% 1	4563
	21st to end	Day	53% 13% 13% 16% 5%	5162
June	1st to 10th	Day	48% 10% 14% 16% 10% 3	2850
	11th to 20th	Day	51% 10% 15% 17% 7%	2850
	21st to end	Day	45% 12% 14% 19% 8% 2	2850
July	1st to 10th	Day	24% 6% 9% 22% 27% 12%	4666
	11th to 20th	Day	23% 6% 14% 31% 24% 2	4659
	21st to end	Day	32% 8% 19% 23% 15% 3	4976
August	1st to 10th	Day	21% 7% 14% 40% 17% 1	4468
	11th to 20th	Day	32% 11% 19% 27% 9% 1	4065
	21st to end	Day	37% 9% 25% 21% 7% 1	4520
September	1st to 10th	Day	33% 9% 20% 26% 10% 2	2317
	11th to 20th	Day	40% 8% 16% 24% 9% 2	2207
	21st to end	Day	37% 11% 17% 23% 10% 1	2049
October	1st to 10th	Day	42% 11% 20% 18% 8% 2	3180
	11th to 20th	Day	37% 12% 16% 27% 8%	3161
	21st to end	Day	38% 11% 17% 25% 9% 1	2957
November	1st to 10th	Day	43% 13% 18% 20% 6%	1568
	11th to 20th	Day	41% 13% 19% 16% 11%	1600
	21st to end	Day	43% 11% 17% 20% 7% 2	1494
December	1st to 10th	Day	47% 12% 14% 19% 6% 1	2290
	11th to 20th	Day	57% 11% 14% 10% 8%	2648
	21st to end	Day	41% 15% 16% 20% 5% 1	3498
January	1st to 10th	Night	57% 13% 12% 13% 5%	6766
	11th to 20th	Night	40% 13% 15% 19% 7% 4	6780
	21st to end	Night	38% 14% 22% 18% 8%	7458
February	1st to 10th	Night	47% 11% 16% 14% 11% 1	2636
	11th to 20th	Night	44% 10% 14% 20% 11% 1	2534
	21st to end	Night	47% 10% 13% 21% 9% 1	2145
March	1st to 10th	Night	42% 10% 17% 17% 14%	5272
	11th to 20th	Night	33% 9% 16% 24% 16% 2	5000
	21st to end	Night	47% 12% 15% 15% 11%	5446
April	1st to 10th	Night	41% 14% 21% 17% 7%	1960
	11th to 20th	Night	40% 12% 16% 22% 9%	1781
	21st to end	Night	43% 10% 15% 23% 9%	1735
May	1st to 10th	Night	33% 12% 21% 25% 8%	2620
	11th to 20th	Night	38% 13% 21% 23% 4	2340
	21st to end	Night	52% 13% 13% 18% 4	2414
June	1st to 10th	Night	43% 12% 16% 17% 8% 3	1330
	11th to 20th	Night	44% 12% 13% 23% 7%	1330
	21st to end	Night	41% 11% 15% 21% 9% 2	1330
July	1st to 10th	Night	23% 7% 11% 19% 30% 9%	2185
	11th to 20th	Night	20% 7% 14% 41% 18%	2178
	21st to end	Night	28% 7% 20% 23% 19% 3	2337
August	1st to 10th	Night	26% 8% 12% 40% 13% 1	2433
	11th to 20th	Night	34% 11% 21% 26% 6% 2	2839
	21st to end	Night	37% 9% 27% 22% 4	3146
September	1st to 10th	Night	30% 9% 19% 29% 11% 2	1863
	11th to 20th	Night	38% 9% 16% 24% 11% 3	1971
	21st to end	Night	39% 11% 18% 23% 7% 1	2131
October	1st to 10th	Night	41% 11% 16% 24% 7%	3800
	11th to 20th	Night	38% 14% 18% 23% 7%	3777
	21st to end	Night	37% 14% 21% 22% 6%	4594
November	1st to 10th	Night	47% 13% 16% 17% 6% 1	2730
	11th to 20th	Night	43% 11% 18% 19% 9%	2800
	21st to end	Night	44% 12% 18% 16% 6% 3	2905
December	1st to 10th	Night	50% 12% 15% 17% 5% 1	4890
	11th to 20th	Night	54% 16% 13% 12% 5%	5556
	21st to end	Night	40% 18% 15% 18% 9%	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	4 12% 42% 29% 8% 6%	200
	11th to 20th	Day	3 15% 36% 31% 13% 3	200
	21st to end	Day	4 10% 44% 26% 14% 3	220
February	1st to 10th	Day	8% 21% 39% 22% 8% 1	397
	11th to 20th	Day	8% 15% 39% 27% 10% 1	395
	21st to end	Day	11% 22% 42% 16% 8% 1	331
March	1st to 10th	Day	6% 25% 31% 22% 14% 2	463
	11th to 20th	Day	7% 23% 34% 22% 12% 1	500
	21st to end	Day	13% 22% 32% 20% 11% 1	550
April	1st to 10th	Day	14% 25% 31% 22% 8% 1	500
	11th to 20th	Day	10% 24% 32% 21% 11% 3	492
	21st to end	Day	16% 22% 26% 22% 10% 4	500
May	1st to 10th	Day	10% 21% 28% 30% 11% 1	503
	11th to 20th	Day	15% 17% 29% 24% 12% 3	589
	21st to end	Day	18% 20% 30% 18% 11% 2	735
June	1st to 10th	Day	16% 22% 35% 19% 7% 1	680
	11th to 20th	Day	17% 21% 30% 20% 10% 2	680
	21st to end	Day	12% 16% 34% 24% 12% 3	680
July	1st to 10th	Day	12% 15% 30% 24% 15% 4	671
	11th to 20th	Day	10% 15% 29% 26% 15% 4	668
	21st to end	Day	7% 15% 31% 25% 17% 5%	739
August	1st to 10th	Day	9% 9% 23% 31% 20% 7%	550
	11th to 20th	Day	6% 12% 23% 31% 21% 7%	477
	21st to end	Day	9% 16% 32% 26% 14% 3	539
September	1st to 10th	Day	10% 14% 30% 26% 15% 4	490
	11th to 20th	Day	15% 12% 27% 27% 15% 5%	490
	21st to end	Day	16% 22% 30% 21% 10% 1	490
October	1st to 10th	Day	18% 17% 27% 22% 13% 4	490
	11th to 20th	Day	13% 20% 34% 22% 9% 2	490
	21st to end	Day	15% 18% 38% 15% 11% 2	332
November	1st to 10th	Day	12% 20% 38% 22% 9% 1	200
	11th to 20th	Day	4 15% 33% 33% 13% 3	200
	21st to end	Day	11% 19% 31% 21% 11% 9%	200
December	1st to 10th	Day	5% 10% 35% 31% 14% 6%	200
	11th to 20th	Day	6% 15% 37% 26% 11% 6%	200
	21st to end	Day	7% 15% 37% 28% 13% 1	220
January	1st to 10th	Night	6% 13% 44% 26% 9% 2	900
	11th to 20th	Night	5% 11% 41% 34% 6% 2	900
	21st to end	Night	4 13% 44% 27% 11% 2	990
February	1st to 10th	Night	7% 13% 41% 27% 11% 1	817
	11th to 20th	Night	7% 8% 40% 31% 14% 1	784
	21st to end	Night	6% 12% 39% 33% 8% 2	660
March	1st to 10th	Night	3 14% 42% 28% 13% 1	800
	11th to 20th	Night	2 12% 43% 31% 11% 1	800
	21st to end	Night	7% 13% 35% 30% 14% 1	880
April	1st to 10th	Night	7% 11% 34% 35% 12% 1	760
	11th to 20th	Night	7% 8% 40% 33% 12%	593
	21st to end	Night	7% 11% 37% 33% 12% 1	535
May	1st to 10th	Night	3 9% 38% 39% 12%	400
	11th to 20th	Night	10% 9% 29% 42% 8% 1	375
	21st to end	Night	17% 9% 31% 34% 9%	411
June	1st to 10th	Night	11% 10% 37% 34% 7%	380
	11th to 20th	Night	13% 8% 34% 32% 11% 1	380
	21st to end	Night	13% 5% 29% 40% 13%	380
July	1st to 10th	Night	10% 5% 29% 39% 16%	370
	11th to 20th	Night	10% 6% 29% 39% 17%	368
	21st to end	Night	6% 3 27% 40% 22% 2	416
August	1st to 10th	Night	10% 2 17% 38% 31% 2	379
	11th to 20th	Night	5% 4 21% 37% 31% 2	564
	21st to end	Night	9% 7% 29% 37% 18% 1	627
September	1st to 10th	Night	12% 6% 24% 36% 21% 1	723
	11th to 20th	Night	13% 7% 25% 28% 24% 4	760
	21st to end	Night	11% 14% 34% 28% 12% 1	760
October	1st to 10th	Night	14% 11% 31% 29% 13% 2	760
	11th to 20th	Night	9% 11% 40% 25% 14% 1	760
	21st to end	Night	12% 12% 39% 27% 9% 2	836
November	1st to 10th	Night	6% 17% 42% 27% 7% 1	780
	11th to 20th	Night	5% 14% 46% 26% 8% 1	800
	21st to end	Night	5% 13% 46% 26% 8% 2	853
December	1st to 10th	Night	5% 11% 38% 31% 14% 2	900
	11th to 20th	Night	6% 10% 42% 30% 10% 2	900
	21st to end	Night	5% 9% 47% 29% 8% 1	990

Page generated at 2025-05-08 06:33:55. Version ac07

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