Tainter Lake Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tainter Lake Skies Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	13% 9% 3 8% 5% 4 4 4 5% 7% 37%	120019
	Night	12% 10% 4 9% 5% 4 4 4 5% 6% 37%	118445
Transparency	Day	45% 5% 12% 25% 12% 1	123576
	Night	46% 5% 12% 23% 13% 1	123015
Seeing	Day	17% 10% 30% 26% 14% 4	16799
	Night	17% 9% 31% 32% 11% 1	26760

By Month

Percentage Cloud Cover SE (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	7% 14% 7% 17% 7% 6% 4 3 3 4 28%	3617
	11th to 20th	Day	6% 12% 6% 12% 7% 7% 9% 9% 6% 5% 21%	3620
	21st to end	Day	8% 15% 7% 12% 5% 4 3 3 4 6% 31%	4327
February	1st to 10th	Day	9% 11% 5% 10% 6% 5% 5% 5% 6% 7% 31%	1800
	11th to 20th	Day	9% 10% 4 10% 6% 5% 3 5% 5% 7% 35%	1754
	21st to end	Day	11% 12% 5% 10% 5% 4 4 4 6% 7% 33%	1614
March	1st to 10th	Day	13% 8% 2 5% 4 3 3 3 4 8% 47%	4635
	11th to 20th	Day	11% 8% 3 7% 4 5% 5% 4 6% 8% 40%	4980
	21st to end	Day	22% 10% 4 9% 5% 4 4 3 5% 6% 28%	5663
April	1st to 10th	Day	16% 12% 4 7% 5% 4 5% 3 5% 7% 32%	2400
	11th to 20th	Day	20% 10% 4 8% 5% 4 4 3 5% 5% 31%	2374
	21st to end	Day	21% 11% 3 7% 5% 5% 5% 4 5% 6% 29%	2520
May	1st to 10th	Day	14% 6% 2 6% 4 3 4 3 4 5% 49%	6309
	11th to 20th	Day	15% 8% 2 6% 4 4 5% 4 5% 6% 40%	6319
	21st to end	Day	17% 9% 3 6% 4 4 4 3 5% 6% 38%	6935
June	1st to 10th	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 43%	2787
	11th to 20th	Day	12% 7% 2 7% 6% 5% 5% 4 6% 9% 36%	2660
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 8% 10% 39%	2660
July	1st to 10th	Day	13% 5% 2 6% 5% 5% 6% 5% 7% 9% 38%	4440
	11th to 20th	Day	6% 3 1 5% 4 3 4 4 6% 10% 55%	4440
	21st to end	Day	8% 5% 2 6% 4 5% 6% 4 7% 8% 45%	4813
August	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 6% 7% 43%	4210
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 45%	4041
	21st to end	Day	10% 7% 2 7% 5% 5% 5% 4 6% 8% 42%	4222
September	1st to 10th	Day	11% 6% 2 6% 4 4 3 3 5% 9% 47%	2280
	11th to 20th	Day	13% 5% 2 5% 5% 4 4 4 5% 8% 45%	2280
	21st to end	Day	16% 6% 3 6% 3 4 4 3 5% 8% 43%	2004
October	1st to 10th	Day	15% 7% 2 6% 4 3 4 3 6% 6% 43%	1900
	11th to 20th	Day	15% 10% 4 8% 5% 5% 5% 3 4 7% 36%	1900
	21st to end	Day	19% 11% 4 7% 4 3 3 3 5% 5% 36%	1993
November	1st to 10th	Day	14% 10% 3 7% 4 4 4 3 5% 7% 37%	1722
	11th to 20th	Day	13% 14% 5% 9% 7% 4 4 4 7% 4 29%	1600
	21st to end	Day	14% 12% 4 7% 6% 4 4 3 5% 5% 36%	1600
December	1st to 10th	Day	8% 10% 5% 16% 13% 7% 5% 4 4 5% 23%	2610
	11th to 20th	Day	11% 18% 6% 10% 7% 4 4 3 4 5% 28%	3008
	21st to end	Day	20% 20% 8% 16% 5% 5% 3 3 3 3 14%	3982
January	1st to 10th	Night	7% 12% 6% 14% 9% 5% 3 3 4 6% 32%	6348
	11th to 20th	Night	7% 12% 6% 12% 7% 6% 8% 8% 6% 5% 22%	6360
	21st to end	Night	8% 17% 6% 12% 5% 4 3 3 5% 6% 31%	6647
February	1st to 10th	Night	7% 12% 5% 11% 6% 5% 4 4 5% 6% 34%	2600
	11th to 20th	Night	7% 10% 4 9% 5% 6% 5% 4 6% 6% 39%	2533
	21st to end	Night	12% 10% 4 9% 6% 5% 5% 4 5% 6% 36%	2015
March	1st to 10th	Night	10% 6% 3 6% 4 4 4 3 5% 7% 46%	5249
	11th to 20th	Night	9% 8% 3 9% 6% 5% 5% 4 6% 8% 38%	4980
	21st to end	Night	24% 11% 4 10% 4 3 3 2 4 5% 29%	5252
April	1st to 10th	Night	17% 11% 3 7% 4 4 3 3 6% 6% 36%	2000
	11th to 20th	Night	22% 10% 3 6% 4 3 4 3 5% 5% 35%	1975
	21st to end	Night	20% 8% 3 6% 3 4 5% 3 5% 6% 36%	1876
May	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 47%	3606
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 7% 50%	3596
	21st to end	Night	15% 8% 3 7% 5% 4 4 3 5% 6% 39%	3942
June	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 7% 8% 45%	1597
	11th to 20th	Night	11% 6% 2 5% 4 4 5% 4 6% 8% 45%	1520
	21st to end	Night	8% 5% 1 5% 4 4 6% 4 7% 8% 47%	1520
July	1st to 10th	Night	11% 4 2 5% 4 4 4 4 6% 8% 47%	2530
	11th to 20th	Night	5% 3 1 4 4 4 4 4 6% 10% 56%	2530
	21st to end	Night	5% 4 2 5% 4 4 4 4 5% 7% 56%	2750
August	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 3 6% 6% 45%	2726
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 6% 7% 50%	2798
	21st to end	Night	12% 6% 3 7% 5% 4 4 3 4 6% 45%	3434
September	1st to 10th	Night	9% 5% 2 6% 3 3 4 4 4 8% 52%	1900
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 6% 7% 51%	1900
	21st to end	Night	14% 5% 2 5% 3 3 4 3 5% 6% 49%	2152
October	1st to 10th	Night	13% 6% 2 6% 3 4 3 3 5% 6% 49%	2280
	11th to 20th	Night	16% 8% 3 6% 4 5% 4 3 5% 7% 41%	2280
	21st to end	Night	17% 11% 3 6% 4 4 4 3 5% 6% 36%	2603
November	1st to 10th	Night	13% 11% 4 6% 4 3 3 3 5% 7% 40%	2571
	11th to 20th	Night	14% 10% 4 10% 5% 5% 4 3 5% 6% 34%	2800
	21st to end	Night	14% 11% 4 9% 5% 3 4 4 5% 6% 35%	2800
December	1st to 10th	Night	8% 9% 4 15% 7% 6% 6% 4 5% 7% 29%	4580
	11th to 20th	Night	10% 18% 7% 13% 6% 5% 4 4 5% 5% 22%	5199
	21st to end	Night	22% 16% 6% 16% 6% 4 3 2 4 4 18%	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	60% 4 9% 19% 8%	3618
	11th to 20th	Day	60% 5% 7% 17% 11%	3620
	21st to end	Day	54% 4 16% 18% 7%	4327
February	1st to 10th	Day	51% 6% 13% 18% 10% 1	1800
	11th to 20th	Day	46% 6% 13% 25% 10% 1	1763
	21st to end	Day	49% 5% 14% 20% 10% 1	1614
March	1st to 10th	Day	37% 4 17% 25% 13% 4	4635
	11th to 20th	Day	42% 4 14% 28% 11% 1	4980
	21st to end	Day	58% 4 9% 18% 10% 1	5665
April	1st to 10th	Day	51% 5% 11% 20% 13% 1	2400
	11th to 20th	Day	54% 5% 10% 18% 12% 2	2374
	21st to end	Day	55% 6% 11% 18% 9% 1	2520
May	1st to 10th	Day	37% 4 11% 30% 16% 2	6347
	11th to 20th	Day	42% 6% 12% 23% 14% 3	6323
	21st to end	Day	46% 5% 8% 29% 11% 1	6949
June	1st to 10th	Day	36% 7% 13% 29% 13% 2	2787
	11th to 20th	Day	43% 9% 12% 22% 13% 1	2660
	21st to end	Day	37% 8% 15% 28% 10% 1	2660
July	1st to 10th	Day	40% 8% 17% 24% 11% 1	4371
	11th to 20th	Day	24% 5% 16% 35% 18% 1	4365
	21st to end	Day	33% 8% 14% 27% 17% 1	4662
August	1st to 10th	Day	38% 6% 13% 27% 15% 1	4195
	11th to 20th	Day	36% 7% 13% 34% 10%	4080
	21st to end	Day	39% 7% 14% 28% 12% 1	4221
September	1st to 10th	Day	34% 7% 15% 30% 14%	2280
	11th to 20th	Day	36% 7% 16% 31% 8%	2280
	21st to end	Day	39% 5% 13% 31% 11%	2004
October	1st to 10th	Day	28% 4 9% 38% 21%	3160
	11th to 20th	Day	40% 4 11% 26% 17% 2	3140
	21st to end	Day	43% 4 15% 27% 10%	3257
November	1st to 10th	Day	46% 6% 13% 20% 13% 2	1722
	11th to 20th	Day	56% 6% 12% 17% 8% 1	1600
	21st to end	Day	50% 5% 16% 21% 7% 2	1600
December	1st to 10th	Day	63% 5% 11% 16% 5%	2610
	11th to 20th	Day	59% 4 10% 20% 7% 1	3005
	21st to end	Day	76% 5% 7% 9% 4	3982
January	1st to 10th	Night	55% 4 11% 20% 10%	6348
	11th to 20th	Night	61% 5% 10% 13% 12%	6360
	21st to end	Night	54% 5% 11% 20% 9% 1	6647
February	1st to 10th	Night	51% 5% 12% 21% 10% 2	2600
	11th to 20th	Night	45% 6% 13% 26% 9% 1	2534
	21st to end	Night	48% 6% 11% 22% 11% 2	2015
March	1st to 10th	Night	37% 4 15% 24% 15% 5%	5249
	11th to 20th	Night	42% 4 16% 23% 13% 1	4980
	21st to end	Night	59% 3 10% 15% 13% 1	5252
April	1st to 10th	Night	48% 6% 8% 19% 17% 2	2000
	11th to 20th	Night	50% 5% 9% 19% 15% 2	1975
	21st to end	Night	48% 5% 9% 21% 15% 2	1876
May	1st to 10th	Night	38% 5% 10% 24% 21% 1	3630
	11th to 20th	Night	34% 5% 11% 25% 20% 6%	3597
	21st to end	Night	45% 6% 10% 26% 13% 1	3950
June	1st to 10th	Night	33% 8% 12% 28% 17% 1	1597
	11th to 20th	Night	34% 8% 14% 24% 18% 1	1520
	21st to end	Night	31% 9% 14% 32% 13% 3	1520
July	1st to 10th	Night	34% 6% 20% 26% 14% 1	2490
	11th to 20th	Night	22% 6% 14% 36% 20% 1	2482
	21st to end	Night	25% 7% 15% 30% 21% 3	2662
August	1st to 10th	Night	38% 5% 12% 28% 14% 3	2717
	11th to 20th	Night	33% 7% 13% 32% 13% 2	2825
	21st to end	Night	39% 6% 14% 27% 13% 2	3434
September	1st to 10th	Night	30% 7% 12% 34% 16% 1	1900
	11th to 20th	Night	31% 6% 15% 33% 16%	1900
	21st to end	Night	34% 6% 13% 32% 14% 1	2152
October	1st to 10th	Night	25% 3 7% 35% 25% 4	3800
	11th to 20th	Night	34% 5% 11% 27% 23% 1	3779
	21st to end	Night	47% 4 11% 24% 13%	4276
November	1st to 10th	Night	43% 5% 11% 25% 14% 1	2571
	11th to 20th	Night	52% 5% 13% 18% 12% 1	2800
	21st to end	Night	49% 6% 15% 22% 7% 1	2800
December	1st to 10th	Night	53% 6% 17% 20% 4	4580
	11th to 20th	Night	63% 4 10% 16% 6%	5201
	21st to end	Night	71% 3 8% 12% 6%	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	13% 13% 34% 26% 10% 3	300
	11th to 20th	Day	16% 12% 38% 26% 7% 1	300
	21st to end	Day	15% 9% 39% 26% 9% 1	330
February	1st to 10th	Day	16% 14% 43% 19% 7% 2	300
	11th to 20th	Day	14% 18% 38% 21% 9%	300
	21st to end	Day	18% 12% 45% 22% 3	249
March	1st to 10th	Day	16% 13% 40% 21% 10% 1	300
	11th to 20th	Day	19% 13% 36% 23% 7% 2	300
	21st to end	Day	24% 14% 31% 20% 9% 2	415
April	1st to 10th	Day	25% 15% 32% 21% 5% 1	500
	11th to 20th	Day	29% 13% 28% 22% 7% 1	492
	21st to end	Day	27% 14% 28% 19% 9% 2	620
May	1st to 10th	Day	20% 14% 29% 27% 9% 2	703
	11th to 20th	Day	19% 13% 26% 25% 13% 4	725
	21st to end	Day	19% 11% 25% 26% 16% 4	789
June	1st to 10th	Day	11% 8% 26% 32% 18% 4	726
	11th to 20th	Day	16% 10% 33% 27% 12% 2	680
	21st to end	Day	14% 7% 29% 29% 16% 6%	680
July	1st to 10th	Day	9% 5% 22% 28% 26% 10%	671
	11th to 20th	Day	9% 5% 27% 29% 20% 10%	668
	21st to end	Day	6% 4 25% 36% 21% 9%	739
August	1st to 10th	Day	12% 5% 22% 32% 22% 7%	676
	11th to 20th	Day	13% 4 20% 29% 27% 7%	665
	21st to end	Day	13% 6% 24% 29% 23% 5%	568
September	1st to 10th	Day	13% 6% 28% 30% 18% 6%	490
	11th to 20th	Day	11% 6% 27% 31% 22% 3	490
	21st to end	Day	21% 13% 22% 25% 15% 4	363
October	1st to 10th	Day	19% 10% 32% 22% 15% 2	300
	11th to 20th	Day	22% 15% 34% 23% 5% 1	300
	21st to end	Day	25% 18% 34% 16% 6% 2	330
November	1st to 10th	Day	20% 11% 34% 24% 9% 1	300
	11th to 20th	Day	21% 16% 38% 18% 6% 1	300
	21st to end	Day	24% 12% 42% 14% 7%	300
December	1st to 10th	Day	16% 13% 38% 24% 8% 1	300
	11th to 20th	Day	19% 18% 36% 20% 6% 1	300
	21st to end	Day	28% 12% 36% 20% 3 1	330
January	1st to 10th	Night	13% 13% 32% 32% 9% 1	1000
	11th to 20th	Night	18% 10% 36% 30% 6% 1	1000
	21st to end	Night	18% 10% 33% 31% 7%	1100
February	1st to 10th	Night	14% 13% 37% 29% 7% 1	1000
	11th to 20th	Night	13% 12% 40% 27% 7%	979
	21st to end	Night	17% 13% 33% 29% 7%	695
March	1st to 10th	Night	15% 11% 37% 30% 6% 1	754
	11th to 20th	Night	17% 10% 35% 32% 6%	600
	21st to end	Night	22% 9% 31% 26% 10% 2	660
April	1st to 10th	Night	24% 13% 32% 26% 6% 1	600
	11th to 20th	Night	27% 9% 30% 27% 6% 1	593
	21st to end	Night	24% 7% 33% 27% 8% 1	600
May	1st to 10th	Night	21% 10% 32% 31% 7%	600
	11th to 20th	Night	19% 8% 28% 32% 12% 1	591
	21st to end	Night	15% 6% 26% 39% 14% 1	650
June	1st to 10th	Night	10% 7% 28% 41% 14% 1	599
	11th to 20th	Night	12% 6% 31% 40% 11%	570
	21st to end	Night	9% 4 25% 44% 17% 1	570
July	1st to 10th	Night	8% 2 21% 39% 27% 2	555
	11th to 20th	Night	8% 5% 22% 41% 22% 2	552
	21st to end	Night	6% 2 19% 46% 24% 3	624
August	1st to 10th	Night	8% 3 16% 47% 25% 1	567
	11th to 20th	Night	13% 2 19% 35% 26% 3	564
	21st to end	Night	14% 2 22% 36% 24% 1	627
September	1st to 10th	Night	11% 4 24% 38% 18% 5%	570
	11th to 20th	Night	12% 4 27% 36% 19% 2	570
	21st to end	Night	15% 10% 28% 30% 16% 1	699
October	1st to 10th	Night	17% 8% 28% 31% 14% 1	760
	11th to 20th	Night	20% 9% 34% 29% 7%	760
	21st to end	Night	22% 11% 29% 30% 8%	836
November	1st to 10th	Night	18% 10% 35% 29% 7%	815
	11th to 20th	Night	19% 13% 35% 25% 8%	1000
	21st to end	Night	20% 14% 34% 26% 6%	1000
December	1st to 10th	Night	17% 11% 35% 29% 8% 1	1000
	11th to 20th	Night	21% 10% 36% 25% 7% 2	1000
	21st to end	Night	26% 9% 33% 25% 6% 1	1100

Page generated at 2025-06-07 09:28:16. Version ac07

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