Lake Titus Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Titus Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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% 13% 4 10% 6% 5% 4 3 5% 6% 27%	126993
	Night	16% 15% 5% 12% 6% 5% 4 3 4 5% 25%	123025
Transparency	Day	58% 4 10% 18% 8% 1	130435
	Night	62% 4 10% 16% 8% 1	127656
Seeing	Day	31% 17% 29% 16% 6% 2	15873
	Night	29% 18% 26% 20% 7% 1	24853

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	11% 18% 8% 20% 14% 7% 3 2 3 3 10%	3597
	11th to 20th	Day	8% 18% 7% 24% 13% 5% 4 2 3 3 13%	3570
	21st to end	Day	11% 20% 8% 17% 7% 7% 6% 3 4 4 14%	3988
February	1st to 10th	Day	13% 21% 6% 16% 10% 5% 4 3 3 4 16%	1800
	11th to 20th	Day	11% 17% 8% 17% 9% 6% 4 2 4 4 16%	1847
	21st to end	Day	14% 19% 7% 14% 7% 6% 4 3 5% 4 17%	1650
March	1st to 10th	Day	17% 17% 8% 15% 5% 4 4 3 3 3 21%	4476
	11th to 20th	Day	10% 20% 7% 11% 6% 5% 4 3 5% 5% 25%	4784
	21st to end	Day	18% 15% 5% 9% 6% 4 4 2 3 4 30%	5917
April	1st to 10th	Day	19% 19% 5% 9% 4 4 3 2 4 4 27%	2400
	11th to 20th	Day	18% 16% 4 8% 5% 4 3 3 4 4 32%	2374
	21st to end	Day	22% 15% 3 7% 4 4 4 3 4 4 29%	2515
May	1st to 10th	Day	29% 15% 4 8% 4 4 4 3 4 5% 20%	6272
	11th to 20th	Day	20% 12% 3 8% 5% 5% 5% 4 6% 7% 26%	6318
	21st to end	Day	25% 10% 3 7% 4 4 4 3 5% 6% 29%	6949
June	1st to 10th	Day	28% 7% 2 6% 5% 5% 4 4 5% 6% 27%	2800
	11th to 20th	Day	19% 7% 2 6% 6% 5% 4 4 5% 8% 32%	2800
	21st to end	Day	25% 8% 3 7% 4 5% 4 4 5% 6% 28%	2800
July	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 4 7% 8% 32%	6360
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 5% 7% 8% 36%	6360
	21st to end	Day	17% 6% 2 5% 4 4 4 4 6% 9% 39%	6926
August	1st to 10th	Day	20% 8% 2 7% 4 5% 5% 4 6% 8% 31%	4563
	11th to 20th	Day	18% 6% 3 8% 5% 5% 5% 4 5% 7% 33%	4024
	21st to end	Day	19% 6% 2 5% 4 4 5% 4 6% 9% 36%	4312
September	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 5% 8% 40%	2400
	11th to 20th	Day	18% 6% 2 5% 3 3 3 3 4 7% 45%	2335
	21st to end	Day	19% 9% 2 6% 4 4 4 4 6% 7% 35%	2200
October	1st to 10th	Day	24% 10% 3 7% 4 4 4 3 4 5% 32%	2035
	11th to 20th	Day	21% 15% 4 8% 3 4 4 4 4 6% 28%	1996
	21st to end	Day	26% 19% 3 6% 4 3 3 2 4 5% 24%	1980
November	1st to 10th	Day	16% 19% 5% 8% 5% 4 4 3 4 5% 27%	1779
	11th to 20th	Day	16% 18% 6% 11% 6% 4 3 3 3 4 25%	1720
	21st to end	Day	16% 23% 7% 14% 6% 5% 4 2 3 4 17%	1600
December	1st to 10th	Day	14% 25% 9% 21% 10% 4 3 2 3 3 7%	2600
	11th to 20th	Day	16% 19% 6% 17% 6% 3 4 3 4 4 18%	2986
	21st to end	Day	16% 18% 7% 11% 7% 4 4 4 4 5% 20%	3960
January	1st to 10th	Night	9% 19% 8% 23% 12% 7% 3 2 2 3 11%	6349
	11th to 20th	Night	7% 19% 10% 24% 13% 6% 5% 3 3 3 8%	6315
	21st to end	Night	11% 17% 9% 18% 9% 8% 6% 4 4 3 13%	6951
February	1st to 10th	Night	13% 19% 8% 19% 9% 5% 4 2 3 4 16%	2600
	11th to 20th	Night	12% 16% 7% 16% 9% 6% 5% 3 3 3 19%	2439
	21st to end	Night	12% 19% 6% 13% 8% 6% 3 2 4 5% 21%	1980
March	1st to 10th	Night	16% 15% 6% 13% 7% 6% 4 3 3 4 24%	5364
	11th to 20th	Night	12% 18% 7% 10% 5% 5% 4 3 4 6% 27%	5173
	21st to end	Night	16% 17% 6% 12% 6% 3 3 2 3 3 27%	5014
April	1st to 10th	Night	19% 18% 4 10% 4 4 4 3 4 4 26%	2000
	11th to 20th	Night	21% 14% 3 8% 5% 5% 4 3 3 5% 29%	1975
	21st to end	Night	21% 13% 3 7% 4 4 3 3 5% 5% 32%	1885
May	1st to 10th	Night	28% 15% 3 7% 4 4 4 4 5% 5% 20%	3697
	11th to 20th	Night	21% 12% 3 7% 5% 4 4 3 5% 6% 31%	3575
	21st to end	Night	20% 12% 3 7% 5% 4 4 3 5% 7% 29%	3926
June	1st to 10th	Night	25% 8% 3 6% 5% 4 4 5% 6% 7% 28%	1600
	11th to 20th	Night	19% 6% 3 6% 5% 4 4 4 6% 6% 37%	1600
	21st to end	Night	21% 8% 2 6% 5% 4 5% 4 6% 7% 32%	1600
July	1st to 10th	Night	15% 5% 2 7% 6% 5% 5% 4 6% 8% 36%	3600
	11th to 20th	Night	18% 7% 2 5% 4 4 4 4 5% 7% 41%	3600
	21st to end	Night	14% 8% 2 6% 5% 4 4 4 5% 6% 42%	3926
August	1st to 10th	Night	21% 7% 2 6% 4 4 3 4 4 6% 38%	2586
	11th to 20th	Night	19% 8% 3 8% 4 4 4 3 5% 6% 37%	2975
	21st to end	Night	16% 7% 2 5% 4 4 4 4 6% 7% 41%	3586
September	1st to 10th	Night	18% 6% 2 6% 5% 4 4 3 4 5% 43%	2000
	11th to 20th	Night	16% 7% 2 5% 3 3 3 3 5% 6% 47%	2064
	21st to end	Night	20% 8% 2 6% 4 3 4 3 5% 7% 39%	2200
October	1st to 10th	Night	21% 10% 3 6% 4 4 3 3 5% 6% 34%	2360
	11th to 20th	Night	20% 14% 3 6% 5% 4 4 4 4 5% 30%	2402
	21st to end	Night	26% 18% 4 7% 4 4 3 2 4 5% 23%	2860
November	1st to 10th	Night	19% 17% 4 9% 4 5% 4 4 5% 4 26%	2564
	11th to 20th	Night	18% 17% 6% 10% 4 4 3 3 4 5% 26%	2675
	21st to end	Night	17% 22% 7% 13% 5% 4 4 2 3 4 18%	2800
December	1st to 10th	Night	15% 24% 12% 21% 6% 4 3 2 3 3 8%	4580
	11th to 20th	Night	18% 22% 8% 15% 5% 3 3 3 3 3 17%	5208
	21st to end	Night	18% 19% 6% 14% 6% 5% 5% 3 3 3 19%	6996

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	81% 3 7% 8% 2	3598
	11th to 20th	Day	78% 2 6% 6% 6% 2	3600
	21st to end	Day	73% 4 9% 8% 6% 1	3988
February	1st to 10th	Day	75% 2 4 14% 3 2	1800
	11th to 20th	Day	72% 3 6% 12% 6% 1	1856
	21st to end	Day	71% 3 6% 11% 7% 2	1650
March	1st to 10th	Day	69% 2 8% 11% 8% 3	4479
	11th to 20th	Day	62% 4 12% 12% 8% 3	4784
	21st to end	Day	59% 3 5% 14% 17% 2	5917
April	1st to 10th	Day	62% 2 6% 18% 10% 2	2400
	11th to 20th	Day	57% 3 6% 18% 14% 2	2374
	21st to end	Day	59% 3 9% 15% 11% 2	2515
May	1st to 10th	Day	67% 4 7% 15% 6% 1	6283
	11th to 20th	Day	57% 5% 14% 15% 8% 1	6322
	21st to end	Day	56% 4 11% 21% 8% 1	6949
June	1st to 10th	Day	57% 5% 10% 18% 10% 1	2800
	11th to 20th	Day	49% 4 12% 24% 9% 2	2800
	21st to end	Day	56% 5% 11% 19% 9% 1	2800
July	1st to 10th	Day	46% 7% 14% 24% 8%	6290
	11th to 20th	Day	41% 8% 14% 27% 10%	6285
	21st to end	Day	40% 7% 12% 35% 6%	6728
August	1st to 10th	Day	51% 5% 15% 22% 7%	4549
	11th to 20th	Day	48% 7% 15% 24% 6%	4064
	21st to end	Day	43% 7% 17% 22% 10%	4312
September	1st to 10th	Day	42% 4 13% 28% 12% 1	2400
	11th to 20th	Day	40% 4 10% 31% 14% 1	2335
	21st to end	Day	47% 5% 13% 24% 10% 1	2200
October	1st to 10th	Day	49% 4 10% 26% 11%	3308
	11th to 20th	Day	52% 4 13% 20% 11% 1	3224
	21st to end	Day	52% 3 14% 24% 6% 1	3180
November	1st to 10th	Day	60% 4 10% 17% 7%	1779
	11th to 20th	Day	65% 3 8% 12% 8% 3	1720
	21st to end	Day	73% 3 10% 10% 4	1600
December	1st to 10th	Day	84% 3 6% 6% 1	2600
	11th to 20th	Day	69% 4 9% 11% 7%	2986
	21st to end	Day	69% 2 7% 13% 8% 1	3960
January	1st to 10th	Night	81% 3 7% 7% 2	6349
	11th to 20th	Night	82% 3 6% 6% 3 1	6360
	21st to end	Night	75% 3 7% 7% 8% 1	6951
February	1st to 10th	Night	75% 2 6% 10% 6% 1	2600
	11th to 20th	Night	71% 3 6% 13% 7%	2441
	21st to end	Night	67% 3 6% 14% 9% 1	1980
March	1st to 10th	Night	65% 2 9% 12% 11% 1	5374
	11th to 20th	Night	58% 5% 15% 13% 7% 3	5174
	21st to end	Night	63% 4 3 16% 13% 1	5014
April	1st to 10th	Night	62% 3 6% 17% 11% 1	2000
	11th to 20th	Night	60% 3 8% 17% 11% 1	1975
	21st to end	Night	55% 3 8% 19% 12% 3	1885
May	1st to 10th	Night	65% 5% 9% 13% 7% 1	3703
	11th to 20th	Night	54% 4 13% 19% 9% 1	3576
	21st to end	Night	55% 4 11% 20% 10% 1	3927
June	1st to 10th	Night	53% 6% 13% 18% 10% 1	1600
	11th to 20th	Night	46% 5% 14% 21% 13% 1	1600
	21st to end	Night	50% 5% 13% 22% 10%	1600
July	1st to 10th	Night	44% 6% 17% 23% 9%	3560
	11th to 20th	Night	41% 6% 15% 28% 10%	3552
	21st to end	Night	41% 7% 14% 30% 8%	3809
August	1st to 10th	Night	47% 4 16% 24% 8%	2576
	11th to 20th	Night	48% 5% 19% 20% 8% 1	3000
	21st to end	Night	41% 6% 16% 26% 11% 1	3586
September	1st to 10th	Night	44% 5% 12% 28% 11%	2000
	11th to 20th	Night	39% 3 13% 33% 12% 1	2064
	21st to end	Night	45% 5% 13% 24% 13% 1	2200
October	1st to 10th	Night	49% 5% 11% 23% 11% 1	3854
	11th to 20th	Night	52% 4 12% 20% 10% 2	3913
	21st to end	Night	57% 4 14% 18% 6% 1	4610
November	1st to 10th	Night	61% 3 11% 15% 8% 1	2564
	11th to 20th	Night	61% 4 10% 14% 8% 3	2675
	21st to end	Night	71% 3 9% 11% 5% 1	2800
December	1st to 10th	Night	84% 3 6% 6% 1	4580
	11th to 20th	Night	74% 3 5% 10% 7%	5208
	21st to end	Night	72% 2 6% 9% 8% 2	6996

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	29% 24% 29% 14% 4 1	200
	11th to 20th	Day	31% 27% 31% 10% 1 1	200
	21st to end	Day	30% 25% 33% 10% 1	227
February	1st to 10th	Day	44% 28% 23% 4 1	300
	11th to 20th	Day	38% 26% 30% 5% 1	394
	21st to end	Day	37% 24% 29% 8% 2	414
March	1st to 10th	Day	34% 25% 26% 11% 4	500
	11th to 20th	Day	32% 23% 32% 9% 3 1	500
	21st to end	Day	38% 20% 26% 11% 5% 1	550
April	1st to 10th	Day	39% 21% 25% 11% 4	500
	11th to 20th	Day	42% 14% 25% 13% 4 2	492
	21st to end	Day	40% 17% 27% 9% 5% 1	500
May	1st to 10th	Day	38% 14% 28% 12% 5% 2	503
	11th to 20th	Day	28% 19% 28% 19% 5% 2	527
	21st to end	Day	28% 18% 27% 19% 8%	573
June	1st to 10th	Day	35% 13% 30% 16% 5% 1	530
	11th to 20th	Day	24% 15% 33% 18% 8% 2	530
	21st to end	Day	29% 16% 33% 16% 5% 1	530
July	1st to 10th	Day	22% 11% 34% 22% 10% 1	525
	11th to 20th	Day	21% 13% 34% 24% 7% 2	524
	21st to end	Day	18% 12% 40% 23% 6% 1	576
August	1st to 10th	Day	21% 11% 29% 25% 11% 3	526
	11th to 20th	Day	20% 8% 34% 22% 12% 4	519
	21st to end	Day	25% 13% 27% 21% 9% 4	583
September	1st to 10th	Day	22% 11% 31% 18% 13% 5%	530
	11th to 20th	Day	20% 9% 24% 22% 17% 8%	530
	21st to end	Day	22% 12% 29% 23% 9% 4	530
October	1st to 10th	Day	31% 13% 24% 18% 10% 4	530
	11th to 20th	Day	33% 21% 26% 13% 7% 1	527
	21st to end	Day	40% 17% 24% 16% 3	462
November	1st to 10th	Day	37% 17% 26% 15% 5%	401
	11th to 20th	Day	40% 23% 21% 11% 4 2	320
	21st to end	Day	40% 20% 30% 9% 2	200
December	1st to 10th	Day	37% 19% 32% 10% 3	200
	11th to 20th	Day	43% 24% 26% 7% 1 1	200
	21st to end	Day	39% 22% 25% 10% 4 1	220
January	1st to 10th	Night	30% 26% 31% 11% 2	800
	11th to 20th	Night	31% 27% 26% 12% 3 1	800
	21st to end	Night	22% 28% 29% 17% 4 1	880
February	1st to 10th	Night	28% 26% 31% 13% 2	800
	11th to 20th	Night	29% 28% 29% 13% 1	783
	21st to end	Night	28% 23% 32% 14% 2	660
March	1st to 10th	Night	32% 23% 25% 16% 3 1	800
	11th to 20th	Night	31% 22% 28% 15% 3 1	800
	21st to end	Night	31% 21% 24% 17% 6% 1	880
April	1st to 10th	Night	33% 19% 27% 19% 3	800
	11th to 20th	Night	33% 21% 23% 17% 7%	791
	21st to end	Night	33% 16% 28% 18% 6% 1	685
May	1st to 10th	Night	35% 11% 26% 20% 7% 1	451
	11th to 20th	Night	28% 11% 30% 22% 8% 1	394
	21st to end	Night	20% 13% 30% 26% 10% 1	433
June	1st to 10th	Night	29% 10% 28% 25% 8% 1	400
	11th to 20th	Night	24% 8% 29% 27% 11% 1	400
	21st to end	Night	25% 9% 29% 28% 9% 1	400
July	1st to 10th	Night	13% 10% 27% 36% 13%	390
	11th to 20th	Night	15% 6% 28% 36% 14% 1	388
	21st to end	Night	18% 7% 30% 34% 10% 1	438
August	1st to 10th	Night	18% 7% 23% 35% 17% 2	398
	11th to 20th	Night	21% 3 23% 31% 21% 1	653
	21st to end	Night	22% 8% 27% 30% 13% 1	880
September	1st to 10th	Night	21% 9% 27% 29% 14% 1	800
	11th to 20th	Night	20% 7% 20% 29% 22% 2	800
	21st to end	Night	25% 12% 23% 22% 18% 1	800
October	1st to 10th	Night	28% 13% 24% 21% 13% 1	800
	11th to 20th	Night	31% 16% 26% 20% 7% 1	800
	21st to end	Night	39% 18% 21% 19% 3	880
November	1st to 10th	Night	36% 17% 25% 15% 6% 1	789
	11th to 20th	Night	33% 23% 22% 13% 7% 2	800
	21st to end	Night	34% 24% 23% 14% 5% 1	800
December	1st to 10th	Night	37% 22% 25% 13% 3	800
	11th to 20th	Night	34% 26% 23% 13% 4 1	800
	21st to end	Night	36% 23% 24% 12% 4	880

Page generated at 2025-10-31 02:02:40. Version ac07

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