Lake Thunderbird
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Thunderbird clear sky chart from 2005-11-06 to 2024-01-13.

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	14% 8% 4 6% 5% 3 5% 4 5% 7% 38%	74780
	Night	14% 8% 4 6% 5% 3 4 4 5% 7% 40%	74971
Transparency	Day	46% 4 12% 24% 13% 2	74481
	Night	45% 3 11% 24% 15% 2	74791
Seeing	Day	17% 9% 27% 26% 16% 5%	14614
	Night	18% 8% 29% 31% 13% 1	24585

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	14% 11% 5% 8% 8% 5% 5% 5% 5% 7% 27%	1517
	11th to 20th	Day	15% 17% 6% 10% 8% 4 4 4 4 5% 23%	1456
	21st to end	Day	15% 16% 7% 10% 7% 3 4 3 4 5% 25%	1729
February	1st to 10th	Day	17% 13% 5% 10% 6% 4 5% 4 5% 5% 28%	1620
	11th to 20th	Day	14% 10% 3 8% 8% 3 5% 5% 4 5% 35%	1726
	21st to end	Day	16% 12% 6% 10% 5% 3 4 4 4 6% 29%	1480
March	1st to 10th	Day	15% 12% 6% 7% 5% 2 4 4 5% 6% 34%	1800
	11th to 20th	Day	14% 8% 4 7% 6% 4 5% 4 6% 7% 35%	1920
	21st to end	Day	21% 10% 5% 8% 6% 4 4 5% 5% 6% 25%	2340
April	1st to 10th	Day	16% 10% 5% 6% 5% 3 4 4 5% 8% 34%	2160
	11th to 20th	Day	18% 10% 3 5% 5% 3 4 4 5% 7% 37%	2134
	21st to end	Day	21% 7% 3 6% 6% 4 5% 4 4 6% 34%	2169
May	1st to 10th	Day	17% 7% 4 7% 6% 4 5% 4 6% 8% 32%	2346
	11th to 20th	Day	19% 8% 3 6% 5% 3 5% 5% 5% 6% 35%	2479
	21st to end	Day	15% 6% 3 6% 6% 3 5% 5% 7% 8% 35%	2725
June	1st to 10th	Day	10% 4 2 5% 4 4 5% 6% 7% 8% 45%	2520
	11th to 20th	Day	7% 6% 2 6% 5% 3 6% 6% 6% 7% 46%	2520
	21st to end	Day	11% 5% 3 6% 6% 4 6% 6% 7% 8% 39%	2520
July	1st to 10th	Day	8% 4 2 6% 5% 3 5% 4 6% 10% 47%	2520
	11th to 20th	Day	8% 5% 2 4 5% 3 5% 5% 6% 10% 47%	2520
	21st to end	Day	7% 5% 2 4 5% 4 6% 6% 7% 9% 45%	2743
August	1st to 10th	Day	7% 5% 3 5% 6% 4 5% 6% 7% 11% 41%	2398
	11th to 20th	Day	8% 4 3 5% 4 4 5% 5% 6% 10% 46%	2133
	21st to end	Day	8% 4 2 3 4 3 5% 5% 6% 8% 52%	2376
September	1st to 10th	Day	12% 6% 2 4 5% 3 4 4 5% 8% 46%	2160
	11th to 20th	Day	12% 3 2 4 4 2 3 3 5% 7% 54%	2099
	21st to end	Day	8% 5% 3 5% 5% 3 5% 4 5% 8% 47%	1980
October	1st to 10th	Day	11% 7% 2 5% 5% 3 4 5% 5% 6% 47%	1850
	11th to 20th	Day	17% 8% 3 6% 5% 3 4 4 5% 5% 40%	1800
	21st to end	Day	22% 8% 3 5% 4 3 4 3 5% 6% 39%	1850
November	1st to 10th	Day	11% 7% 2 5% 5% 2 3 4 6% 7% 48%	1672
	11th to 20th	Day	17% 9% 4 6% 6% 3 4 4 4 6% 37%	1710
	21st to end	Day	18% 10% 4 7% 5% 3 3 3 4 4 39%	1587
December	1st to 10th	Day	13% 12% 5% 7% 5% 3 5% 5% 3 6% 35%	1520
	11th to 20th	Day	14% 13% 4 10% 7% 4 5% 4 4 6% 29%	1918
	21st to end	Day	24% 19% 8% 11% 6% 2 3 3 3 4 16%	2783
January	1st to 10th	Night	13% 10% 5% 8% 7% 3 4 4 4 6% 35%	2648
	11th to 20th	Night	14% 14% 6% 9% 7% 3 4 4 4 5% 30%	2549
	21st to end	Night	14% 11% 7% 9% 6% 4 5% 5% 5% 6% 28%	2624
February	1st to 10th	Night	17% 12% 5% 7% 7% 4 4 4 4 6% 30%	2340
	11th to 20th	Night	13% 10% 5% 7% 6% 4 4 4 5% 6% 37%	2120
	21st to end	Night	18% 10% 5% 7% 5% 3 3 3 4 5% 36%	1776
March	1st to 10th	Night	15% 10% 3 7% 6% 3 4 5% 4 5% 38%	2160
	11th to 20th	Night	15% 7% 4 5% 6% 4 4 5% 4 7% 39%	2055
	21st to end	Night	21% 10% 4 7% 6% 3 4 4 5% 6% 30%	2014
April	1st to 10th	Night	15% 9% 4 6% 5% 2 4 3 6% 6% 39%	1800
	11th to 20th	Night	17% 9% 3 4 6% 3 4 3 4 6% 42%	1775
	21st to end	Night	18% 8% 3 5% 6% 2 5% 4 5% 8% 37%	1789
May	1st to 10th	Night	16% 7% 3 6% 5% 4 5% 5% 6% 9% 34%	1611
	11th to 20th	Night	18% 6% 2 5% 5% 3 4 5% 5% 7% 40%	1416
	21st to end	Night	11% 5% 3 6% 6% 4 5% 4 7% 9% 41%	1551
June	1st to 10th	Night	8% 6% 2 5% 4 3 4 4 6% 7% 52%	1440
	11th to 20th	Night	9% 4 2 6% 5% 3 4 4 7% 9% 47%	1440
	21st to end	Night	9% 4 2 5% 5% 3 4 6% 6% 9% 46%	1440
July	1st to 10th	Night	7% 4 1 4 4 2 4 5% 7% 11% 51%	1440
	11th to 20th	Night	7% 3 2 3 4 2 5% 4 6% 8% 56%	1440
	21st to end	Night	4 3 2 4 4 3 5% 5% 7% 9% 53%	1575
August	1st to 10th	Night	5% 5% 2 5% 5% 3 4 5% 5% 9% 53%	1539
	11th to 20th	Night	6% 4 3 4 5% 3 5% 4 5% 7% 54%	1767
	21st to end	Night	7% 4 1 4 4 3 4 4 5% 7% 57%	1980
September	1st to 10th	Night	13% 4 2 3 4 2 3 4 4 6% 54%	1800
	11th to 20th	Night	10% 4 2 4 4 3 3 5% 6% 7% 54%	1842
	21st to end	Night	8% 5% 2 4 4 2 5% 6% 6% 8% 48%	1980
October	1st to 10th	Night	10% 5% 2 6% 4 3 4 4 4 6% 53%	2107
	11th to 20th	Night	16% 6% 3 5% 4 2 3 4 4 6% 46%	2160
	21st to end	Night	19% 8% 2 6% 5% 3 4 4 5% 5% 38%	2506
November	1st to 10th	Night	11% 6% 2 5% 3 2 3 4 5% 6% 51%	2406
	11th to 20th	Night	15% 8% 3 6% 5% 2 4 4 5% 6% 41%	2470
	21st to end	Night	17% 8% 4 6% 5% 3 4 4 4 6% 39%	2588
December	1st to 10th	Night	16% 10% 4 8% 5% 3 6% 4 5% 6% 35%	2660
	11th to 20th	Night	15% 12% 5% 9% 6% 3 4 4 4 6% 34%	3279
	21st to end	Night	22% 17% 7% 10% 7% 4 4 4 4 4 18%	4884

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	58% 3 12% 16% 10% 1	1518
	11th to 20th	Day	64% 2 11% 16% 6% 1	1456
	21st to end	Day	64% 3 11% 14% 8% 1	1729
February	1st to 10th	Day	59% 2 13% 18% 6% 2	1620
	11th to 20th	Day	53% 3 11% 23% 9% 1	1736
	21st to end	Day	58% 3 9% 21% 7% 2	1480
March	1st to 10th	Day	52% 3 13% 23% 9% 1	1800
	11th to 20th	Day	50% 3 14% 22% 10% 1	1920
	21st to end	Day	59% 4 10% 21% 5% 1	2340
April	1st to 10th	Day	49% 3 12% 23% 12%	2160
	11th to 20th	Day	48% 3 10% 25% 12% 3	2134
	21st to end	Day	52% 4 10% 18% 14% 2	2169
May	1st to 10th	Day	50% 4 14% 23% 9%	2346
	11th to 20th	Day	50% 5% 10% 23% 12%	2483
	21st to end	Day	45% 5% 12% 19% 16% 2	2725
June	1st to 10th	Day	35% 4 13% 29% 16% 2	2520
	11th to 20th	Day	35% 5% 11% 23% 23% 3	2520
	21st to end	Day	41% 5% 13% 23% 16% 2	2520
July	1st to 10th	Day	34% 3 14% 30% 16% 3	2451
	11th to 20th	Day	33% 5% 14% 31% 16% 2	2445
	21st to end	Day	34% 5% 15% 28% 17% 2	2591
August	1st to 10th	Day	35% 5% 15% 31% 12% 2	2383
	11th to 20th	Day	33% 5% 15% 28% 18% 2	2133
	21st to end	Day	29% 5% 12% 29% 21% 4	2376
September	1st to 10th	Day	37% 3 12% 25% 19% 5%	2160
	11th to 20th	Day	31% 2 12% 29% 22% 4	2099
	21st to end	Day	36% 4 9% 29% 21% 2	1980
October	1st to 10th	Day	38% 4 10% 27% 19% 2	1850
	11th to 20th	Day	47% 2 8% 24% 17% 2	1800
	21st to end	Day	48% 2 12% 24% 10% 3	1850
November	1st to 10th	Day	37% 3 16% 26% 16% 3	1672
	11th to 20th	Day	50% 2 12% 23% 12% 1	1710
	21st to end	Day	51% 3 13% 24% 10%	1587
December	1st to 10th	Day	53% 4 13% 21% 9% 1	1520
	11th to 20th	Day	58% 2 9% 23% 7% 1	1915
	21st to end	Day	75% 3 8% 10% 5%	2783
January	1st to 10th	Night	52% 3 12% 20% 13%	2648
	11th to 20th	Night	58% 2 14% 16% 9%	2549
	21st to end	Night	57% 3 12% 18% 9% 1	2624
February	1st to 10th	Night	57% 3 11% 18% 10% 1	2340
	11th to 20th	Night	50% 2 11% 24% 12% 1	2121
	21st to end	Night	53% 2 9% 21% 12% 2	1776
March	1st to 10th	Night	49% 3 12% 24% 11% 1	2160
	11th to 20th	Night	46% 3 11% 23% 13% 3	2055
	21st to end	Night	56% 3 11% 20% 9% 1	2014
April	1st to 10th	Night	46% 3 11% 24% 14% 3	1800
	11th to 20th	Night	45% 2 8% 26% 14% 5%	1775
	21st to end	Night	46% 3 14% 21% 12% 4	1789
May	1st to 10th	Night	47% 4 11% 24% 13% 1	1611
	11th to 20th	Night	43% 4 10% 26% 16% 1	1417
	21st to end	Night	40% 5% 14% 23% 16% 3	1552
June	1st to 10th	Night	33% 3 14% 26% 20% 4	1440
	11th to 20th	Night	34% 3 12% 23% 23% 4	1440
	21st to end	Night	35% 6% 15% 21% 19% 3	1440
July	1st to 10th	Night	28% 5% 15% 32% 16% 4	1400
	11th to 20th	Night	27% 4 14% 30% 22% 3	1392
	21st to end	Night	26% 4 16% 30% 20% 4	1487
August	1st to 10th	Night	30% 4 16% 31% 17% 2	1530
	11th to 20th	Night	29% 4 14% 30% 21% 2	1767
	21st to end	Night	28% 4 11% 29% 23% 5%	1980
September	1st to 10th	Night	33% 3 9% 26% 24% 5%	1800
	11th to 20th	Night	29% 3 10% 30% 24% 4	1842
	21st to end	Night	32% 5% 11% 29% 21% 3	1980
October	1st to 10th	Night	35% 3 10% 24% 24% 3	2107
	11th to 20th	Night	40% 3 7% 27% 20% 3	2160
	21st to end	Night	47% 3 10% 24% 14% 2	2506
November	1st to 10th	Night	34% 3 11% 29% 18% 4	2406
	11th to 20th	Night	45% 2 11% 24% 15% 2	2470
	21st to end	Night	48% 3 10% 25% 13% 1	2588
December	1st to 10th	Night	52% 3 12% 23% 9% 1	2660
	11th to 20th	Night	53% 2 11% 23% 9% 1	3281
	21st to end	Night	72% 2 8% 13% 5%	4884

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	24% 13% 32% 23% 8%	270
	11th to 20th	Day	28% 18% 33% 15% 5% 1	246
	21st to end	Day	21% 20% 33% 19% 7%	264
February	1st to 10th	Day	22% 18% 43% 15% 2	240
	11th to 20th	Day	23% 17% 38% 16% 6%	240
	21st to end	Day	27% 14% 45% 11% 3	198
March	1st to 10th	Day	21% 21% 36% 17% 4	240
	11th to 20th	Day	26% 15% 33% 18% 7%	240
	21st to end	Day	29% 13% 31% 19% 7% 1	426
April	1st to 10th	Day	21% 11% 34% 25% 7% 1	420
	11th to 20th	Day	22% 15% 27% 20% 13% 2	412
	21st to end	Day	26% 9% 31% 23% 10% 1	420
May	1st to 10th	Day	19% 9% 34% 26% 10% 2	429
	11th to 20th	Day	24% 9% 27% 25% 12% 3	625
	21st to end	Day	18% 6% 25% 25% 16% 9%	679
June	1st to 10th	Day	10% 3 27% 31% 22% 7%	630
	11th to 20th	Day	9% 3 27% 33% 22% 5%	630
	21st to end	Day	13% 7% 28% 30% 16% 6%	630
July	1st to 10th	Day	11% 2 15% 31% 26% 15%	621
	11th to 20th	Day	11% 3 21% 32% 25% 9%	618
	21st to end	Day	7% 3 19% 38% 26% 7%	684
August	1st to 10th	Day	7% 4 18% 34% 25% 12%	626
	11th to 20th	Day	10% 4 15% 28% 29% 14%	447
	21st to end	Day	8% 2 19% 31% 29% 11%	495
September	1st to 10th	Day	15% 4 16% 30% 28% 7%	450
	11th to 20th	Day	10% 2 15% 30% 31% 12%	450
	21st to end	Day	10% 7% 28% 24% 25% 7%	450
October	1st to 10th	Day	16% 8% 27% 29% 16% 4	320
	11th to 20th	Day	18% 20% 36% 19% 6% 1	270
	21st to end	Day	35% 9% 27% 24% 4 1	297
November	1st to 10th	Day	12% 15% 39% 21% 9% 4	270
	11th to 20th	Day	23% 16% 36% 16% 9% 1	270
	21st to end	Day	24% 9% 38% 24% 4	270
December	1st to 10th	Day	18% 15% 40% 20% 6% 2	270
	11th to 20th	Day	20% 12% 37% 24% 6% 1	270
	21st to end	Day	27% 17% 37% 16% 2	297
January	1st to 10th	Night	18% 13% 39% 24% 5% 1	950
	11th to 20th	Night	22% 11% 37% 25% 5%	911
	21st to end	Night	20% 11% 36% 28% 5%	990
February	1st to 10th	Night	25% 10% 38% 23% 4	900
	11th to 20th	Night	18% 13% 37% 27% 5%	725
	21st to end	Night	24% 12% 38% 21% 4	592
March	1st to 10th	Night	21% 13% 35% 26% 5%	720
	11th to 20th	Night	20% 8% 33% 31% 7%	615
	21st to end	Night	25% 10% 33% 24% 7% 1	594
April	1st to 10th	Night	21% 11% 36% 26% 6%	540
	11th to 20th	Night	23% 9% 30% 29% 8%	533
	21st to end	Night	21% 11% 30% 30% 8%	540
May	1st to 10th	Night	21% 6% 33% 31% 8% 1	540
	11th to 20th	Night	19% 4 30% 34% 12% 1	531
	21st to end	Night	14% 3 27% 36% 18% 2	584
June	1st to 10th	Night	10% 3 21% 48% 17% 1	540
	11th to 20th	Night	10% 4 23% 45% 18% 1	540
	21st to end	Night	11% 4 25% 39% 20% 1	540
July	1st to 10th	Night	8% 2 11% 41% 32% 6%	525
	11th to 20th	Night	7% 2 16% 45% 26% 4	522
	21st to end	Night	5% 1 14% 49% 29% 2	591
August	1st to 10th	Night	7% 1 14% 42% 31% 5%	537
	11th to 20th	Night	7% 2 10% 41% 34% 6%	534
	21st to end	Night	10% 1 14% 38% 33% 3	594
September	1st to 10th	Night	15% 4 16% 36% 27% 3	540
	11th to 20th	Night	12% 3 18% 32% 31% 4	582
	21st to end	Night	9% 7% 25% 32% 24% 2	720
October	1st to 10th	Night	13% 5% 27% 33% 21% 2	720
	11th to 20th	Night	21% 12% 28% 26% 12% 1	720
	21st to end	Night	25% 10% 33% 25% 7%	792
November	1st to 10th	Night	15% 9% 38% 28% 10% 1	740
	11th to 20th	Night	19% 14% 34% 26% 6% 1	760
	21st to end	Night	22% 11% 34% 26% 6%	878
December	1st to 10th	Night	23% 11% 35% 25% 6%	950
	11th to 20th	Night	23% 11% 32% 28% 6%	950
	21st to end	Night	29% 13% 33% 22% 3	1045

Page generated at 2024-01-10 00:25:01. Version ac07

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