Trempealeau
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trempealeau clear sky chart from 2005-11-06 to 2024-01-17.

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% 6% 3 5% 5% 5% 7% 37%	74781
	Night	14% 9% 4 7% 5% 3 4 4 5% 6% 39%	75075
Transparency	Day	45% 8% 14% 22% 11% 1	74481
	Night	45% 7% 13% 22% 12% 1	74895
Seeing	Day	17% 13% 31% 24% 12% 3	14799
	Night	17% 10% 31% 30% 10% 1	24814

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	10% 10% 7% 9% 9% 5% 6% 4 5% 5% 30%	1517
	11th to 20th	Day	10% 18% 6% 10% 8% 5% 6% 5% 5% 5% 24%	1488
	21st to end	Day	13% 13% 7% 11% 7% 3 5% 5% 6% 8% 23%	1736
February	1st to 10th	Day	9% 12% 5% 9% 7% 5% 5% 5% 6% 7% 31%	1620
	11th to 20th	Day	12% 10% 4 8% 7% 4 5% 5% 5% 7% 34%	1574
	21st to end	Day	14% 11% 4 7% 7% 3 4 4 5% 8% 32%	1480
March	1st to 10th	Day	13% 10% 5% 7% 6% 3 5% 3 5% 5% 36%	1843
	11th to 20th	Day	14% 8% 3 6% 6% 4 4 4 5% 7% 39%	1980
	21st to end	Day	20% 11% 3 5% 5% 3 4 5% 6% 7% 32%	2267
April	1st to 10th	Day	19% 11% 4 7% 6% 3 4 4 4 7% 32%	2160
	11th to 20th	Day	21% 9% 4 5% 5% 3 5% 5% 4 6% 33%	2134
	21st to end	Day	21% 10% 3 5% 6% 3 5% 4 5% 6% 31%	2216
May	1st to 10th	Day	18% 8% 3 6% 6% 4 5% 5% 7% 7% 31%	2502
	11th to 20th	Day	17% 6% 3 6% 6% 3 6% 4 6% 7% 36%	2479
	21st to end	Day	16% 6% 2 6% 6% 3 4 5% 5% 7% 40%	2725
June	1st to 10th	Day	11% 5% 2 5% 4 3 5% 5% 6% 7% 47%	2520
	11th to 20th	Day	12% 5% 2 5% 6% 3 5% 5% 6% 8% 42%	2520
	21st to end	Day	12% 5% 2 5% 6% 4 5% 5% 6% 9% 41%	2520
July	1st to 10th	Day	8% 4 2 5% 5% 3 5% 5% 7% 9% 48%	2520
	11th to 20th	Day	8% 3 2 5% 5% 3 5% 5% 7% 9% 48%	2520
	21st to end	Day	8% 3 2 4 4 3 6% 6% 7% 10% 47%	2743
August	1st to 10th	Day	8% 4 2 5% 5% 4 5% 7% 7% 10% 43%	2377
	11th to 20th	Day	13% 5% 2 5% 5% 3 5% 4 6% 8% 43%	2293
	21st to end	Day	10% 4 3 4 5% 3 5% 5% 5% 7% 49%	2376
September	1st to 10th	Day	14% 6% 2 5% 4 2 4 4 5% 7% 47%	2160
	11th to 20th	Day	12% 5% 2 5% 5% 3 4 5% 5% 7% 47%	2160
	21st to end	Day	15% 7% 2 6% 5% 2 4 4 6% 7% 41%	1909
October	1st to 10th	Day	16% 5% 3 5% 6% 2 4 5% 5% 6% 43%	1800
	11th to 20th	Day	18% 9% 3 5% 4 3 5% 4 6% 7% 37%	1800
	21st to end	Day	18% 13% 4 6% 4 3 4 4 4 5% 37%	1890
November	1st to 10th	Day	13% 9% 3 6% 6% 3 4 5% 5% 7% 41%	1672
	11th to 20th	Day	15% 12% 5% 8% 7% 4 5% 4 4 8% 29%	1539
	21st to end	Day	13% 10% 4 7% 6% 3 3 4 4 6% 40%	1520
December	1st to 10th	Day	14% 12% 5% 9% 7% 3 7% 4 5% 5% 29%	1520
	11th to 20th	Day	12% 13% 6% 8% 6% 4 6% 5% 6% 7% 27%	1918
	21st to end	Day	20% 17% 9% 12% 6% 3 5% 3 3 4 17%	2783
January	1st to 10th	Night	11% 10% 6% 9% 7% 4 5% 5% 5% 6% 33%	2648
	11th to 20th	Night	12% 12% 6% 10% 8% 5% 4 4 6% 6% 26%	2617
	21st to end	Night	12% 15% 6% 11% 6% 4 5% 5% 5% 7% 25%	2618
February	1st to 10th	Night	8% 13% 6% 10% 7% 4 5% 5% 4 6% 32%	2340
	11th to 20th	Night	10% 9% 4 7% 6% 3 5% 5% 5% 7% 39%	2273
	21st to end	Night	15% 11% 4 8% 6% 3 4 4 4 6% 35%	1776
March	1st to 10th	Night	14% 10% 5% 5% 5% 3 6% 5% 5% 6% 37%	2133
	11th to 20th	Night	14% 8% 3 7% 6% 3 5% 5% 5% 5% 38%	1980
	21st to end	Night	19% 10% 3 5% 6% 3 4 5% 4 6% 35%	2088
April	1st to 10th	Night	18% 10% 4 5% 5% 3 4 4 5% 6% 36%	1800
	11th to 20th	Night	21% 9% 3 6% 4 2 4 4 4 6% 36%	1775
	21st to end	Night	18% 8% 3 5% 6% 3 4 4 6% 7% 36%	1742
May	1st to 10th	Night	20% 9% 3 5% 4 2 5% 5% 5% 8% 35%	1458
	11th to 20th	Night	18% 5% 3 5% 4 2 4 6% 5% 6% 43%	1416
	21st to end	Night	14% 4 2 5% 4 3 5% 5% 5% 7% 45%	1551
June	1st to 10th	Night	10% 5% 2 5% 5% 3 4 4 6% 8% 48%	1440
	11th to 20th	Night	13% 4 2 5% 5% 2 4 4 5% 8% 45%	1440
	21st to end	Night	8% 4 2 6% 4 2 5% 6% 6% 8% 51%	1440
July	1st to 10th	Night	6% 4 2 4 3 2 4 5% 5% 9% 57%	1440
	11th to 20th	Night	8% 3 1 4 4 3 4 4 5% 8% 55%	1440
	21st to end	Night	6% 2 1 3 4 2 4 5% 6% 10% 56%	1575
August	1st to 10th	Night	6% 2 2 4 5% 3 5% 5% 5% 10% 52%	1559
	11th to 20th	Night	12% 4 2 3 4 2 3 4 4 8% 53%	1607
	21st to end	Night	10% 4 2 5% 4 2 4 4 4 7% 54%	1980
September	1st to 10th	Night	11% 5% 2 4 5% 3 4 4 5% 6% 51%	1800
	11th to 20th	Night	11% 4 2 4 3 3 3 4 4 7% 54%	1800
	21st to end	Night	13% 5% 2 4 4 3 4 4 5% 5% 52%	2029
October	1st to 10th	Night	14% 6% 2 5% 4 2 3 4 4 6% 50%	2160
	11th to 20th	Night	17% 7% 3 5% 4 3 4 4 5% 7% 40%	2160
	21st to end	Night	17% 9% 4 6% 5% 3 4 4 4 7% 36%	2465
November	1st to 10th	Night	14% 8% 4 5% 4 3 4 4 4 6% 44%	2406
	11th to 20th	Night	14% 10% 6% 8% 6% 3 5% 5% 4 6% 33%	2636
	21st to end	Night	15% 11% 4 7% 6% 3 4 3 4 6% 37%	2660
December	1st to 10th	Night	12% 11% 6% 10% 7% 4 5% 5% 5% 6% 29%	2660
	11th to 20th	Night	13% 14% 5% 10% 7% 4 5% 4 4 6% 27%	3279
	21st to end	Night	22% 15% 6% 11% 7% 2 4 4 4 4 22%	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	56% 5% 14% 17% 7%	1518
	11th to 20th	Day	62% 6% 10% 14% 8%	1488
	21st to end	Day	59% 7% 15% 12% 7% 1	1736
February	1st to 10th	Day	52% 6% 15% 16% 9% 1	1620
	11th to 20th	Day	50% 6% 12% 22% 9% 1	1583
	21st to end	Day	51% 8% 10% 19% 10% 1	1480
March	1st to 10th	Day	50% 7% 13% 19% 9% 1	1843
	11th to 20th	Day	46% 6% 13% 22% 12% 1	1980
	21st to end	Day	52% 7% 12% 20% 8% 1	2267
April	1st to 10th	Day	52% 7% 11% 19% 10% 1	2160
	11th to 20th	Day	52% 6% 10% 19% 11% 2	2134
	21st to end	Day	53% 7% 13% 16% 10% 1	2216
May	1st to 10th	Day	50% 8% 14% 19% 8% 1	2502
	11th to 20th	Day	46% 8% 14% 19% 11% 1	2483
	21st to end	Day	44% 9% 10% 22% 13% 2	2725
June	1st to 10th	Day	34% 9% 15% 28% 13% 2	2520
	11th to 20th	Day	39% 8% 14% 24% 14% 1	2520
	21st to end	Day	39% 9% 15% 24% 11% 1	2520
July	1st to 10th	Day	31% 10% 18% 27% 12% 2	2451
	11th to 20th	Day	31% 10% 16% 23% 18% 2	2445
	21st to end	Day	30% 10% 16% 28% 14% 2	2591
August	1st to 10th	Day	32% 10% 17% 28% 10% 2	2362
	11th to 20th	Day	39% 8% 13% 27% 13%	2293
	21st to end	Day	34% 8% 12% 27% 17% 1	2376
September	1st to 10th	Day	37% 7% 14% 26% 16%	2160
	11th to 20th	Day	35% 9% 15% 30% 10% 1	2160
	21st to end	Day	41% 7% 13% 28% 11%	1909
October	1st to 10th	Day	40% 8% 11% 28% 12%	1800
	11th to 20th	Day	45% 8% 13% 22% 11% 1	1800
	21st to end	Day	51% 6% 12% 22% 9% 1	1890
November	1st to 10th	Day	44% 8% 13% 20% 14% 2	1672
	11th to 20th	Day	57% 6% 11% 18% 8% 1	1539
	21st to end	Day	46% 7% 17% 22% 7% 1	1520
December	1st to 10th	Day	56% 7% 14% 15% 7% 1	1520
	11th to 20th	Day	54% 8% 17% 14% 7%	1915
	21st to end	Day	72% 5% 8% 12% 3	2783
January	1st to 10th	Night	52% 6% 13% 21% 8% 1	2648
	11th to 20th	Night	58% 7% 13% 15% 7%	2617
	21st to end	Night	59% 7% 11% 14% 8% 1	2618
February	1st to 10th	Night	53% 5% 11% 21% 8% 2	2340
	11th to 20th	Night	45% 8% 13% 23% 10% 2	2274
	21st to end	Night	50% 6% 11% 20% 11% 2	1776
March	1st to 10th	Night	48% 7% 14% 21% 8% 2	2133
	11th to 20th	Night	46% 7% 12% 22% 12% 2	1980
	21st to end	Night	49% 7% 12% 21% 10% 1	2088
April	1st to 10th	Night	49% 6% 9% 20% 15% 2	1800
	11th to 20th	Night	49% 6% 10% 18% 15% 3	1775
	21st to end	Night	46% 8% 12% 18% 13% 2	1742
May	1st to 10th	Night	47% 8% 12% 19% 13% 1	1458
	11th to 20th	Night	41% 8% 14% 22% 15% 1	1417
	21st to end	Night	38% 9% 11% 24% 17% 1	1552
June	1st to 10th	Night	31% 9% 15% 25% 17% 2	1440
	11th to 20th	Night	36% 7% 13% 23% 19% 2	1440
	21st to end	Night	30% 8% 16% 28% 14% 4	1440
July	1st to 10th	Night	25% 7% 14% 34% 19% 2	1400
	11th to 20th	Night	26% 7% 17% 30% 18% 3	1392
	21st to end	Night	22% 8% 18% 29% 18% 4	1487
August	1st to 10th	Night	27% 9% 17% 28% 17% 3	1550
	11th to 20th	Night	30% 8% 15% 28% 18% 2	1607
	21st to end	Night	29% 7% 14% 29% 16% 4	1980
September	1st to 10th	Night	33% 7% 10% 29% 20% 1	1800
	11th to 20th	Night	30% 7% 15% 31% 16% 1	1800
	21st to end	Night	34% 6% 13% 29% 18% 1	2029
October	1st to 10th	Night	35% 6% 11% 29% 16% 2	2160
	11th to 20th	Night	42% 7% 14% 22% 15% 1	2160
	21st to end	Night	48% 6% 12% 21% 12% 1	2465
November	1st to 10th	Night	42% 6% 12% 23% 15% 2	2406
	11th to 20th	Night	52% 8% 13% 17% 10% 1	2636
	21st to end	Night	50% 5% 15% 22% 7% 1	2660
December	1st to 10th	Night	54% 7% 14% 19% 5%	2660
	11th to 20th	Night	57% 8% 12% 17% 6%	3281
	21st to end	Night	66% 6% 11% 13% 4	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	16% 18% 33% 23% 9% 1	270
	11th to 20th	Day	20% 19% 38% 18% 3 1	258
	21st to end	Day	20% 17% 40% 17% 6%	264
February	1st to 10th	Day	14% 26% 43% 13% 4	240
	11th to 20th	Day	20% 26% 32% 17% 5%	240
	21st to end	Day	22% 21% 44% 14%	198
March	1st to 10th	Day	20% 24% 36% 13% 7% 1	240
	11th to 20th	Day	22% 18% 38% 14% 6% 2	240
	21st to end	Day	30% 12% 31% 16% 9% 1	353
April	1st to 10th	Day	27% 16% 34% 18% 5%	420
	11th to 20th	Day	29% 15% 28% 18% 9% 1	412
	21st to end	Day	25% 17% 31% 20% 7% 2	476
May	1st to 10th	Day	21% 19% 31% 22% 6% 1	603
	11th to 20th	Day	20% 14% 30% 22% 11% 3	625
	21st to end	Day	19% 11% 26% 25% 15% 4	679
June	1st to 10th	Day	9% 8% 31% 31% 18% 3	630
	11th to 20th	Day	14% 9% 32% 30% 12% 2	630
	21st to end	Day	13% 10% 31% 27% 14% 5%	630
July	1st to 10th	Day	8% 5% 20% 31% 25% 10%	621
	11th to 20th	Day	9% 7% 29% 30% 18% 7%	618
	21st to end	Day	7% 4 29% 36% 18% 7%	684
August	1st to 10th	Day	7% 5% 26% 32% 22% 8%	626
	11th to 20th	Day	13% 7% 20% 28% 25% 7%	607
	21st to end	Day	11% 9% 25% 30% 20% 6%	495
September	1st to 10th	Day	17% 8% 26% 28% 16% 5%	450
	11th to 20th	Day	13% 6% 30% 29% 18% 4	450
	21st to end	Day	20% 15% 26% 24% 13% 1	356
October	1st to 10th	Day	16% 14% 31% 24% 12% 3	270
	11th to 20th	Day	26% 18% 35% 14% 7%	270
	21st to end	Day	26% 18% 34% 16% 4 1	297
November	1st to 10th	Day	20% 15% 35% 22% 7% 1	270
	11th to 20th	Day	21% 22% 34% 18% 4	270
	21st to end	Day	21% 17% 39% 17% 5%	270
December	1st to 10th	Day	16% 14% 44% 17% 9% 1	270
	11th to 20th	Day	23% 15% 37% 19% 6% 1	270
	21st to end	Day	28% 17% 41% 12% 2	297
January	1st to 10th	Night	14% 15% 35% 28% 7% 1	950
	11th to 20th	Night	19% 15% 33% 28% 5% 1	935
	21st to end	Night	21% 12% 34% 27% 6%	990
February	1st to 10th	Night	15% 15% 38% 26% 6% 1	900
	11th to 20th	Night	15% 15% 40% 22% 8%	879
	21st to end	Night	21% 14% 35% 25% 5%	592
March	1st to 10th	Night	17% 14% 35% 26% 7% 1	693
	11th to 20th	Night	20% 12% 31% 29% 7% 1	540
	21st to end	Night	23% 10% 28% 29% 9% 1	594
April	1st to 10th	Night	20% 14% 37% 25% 4	540
	11th to 20th	Night	25% 10% 30% 29% 6%	533
	21st to end	Night	22% 9% 33% 27% 9% 1	540
May	1st to 10th	Night	23% 9% 34% 29% 5% 1	540
	11th to 20th	Night	17% 9% 32% 32% 9% 1	531
	21st to end	Night	15% 7% 27% 36% 14% 1	584
June	1st to 10th	Night	11% 6% 28% 45% 11%	540
	11th to 20th	Night	14% 6% 29% 41% 9%	540
	21st to end	Night	10% 4 25% 44% 16% 1	540
July	1st to 10th	Night	6% 3 22% 36% 31% 2	525
	11th to 20th	Night	8% 4 25% 39% 23% 1	522
	21st to end	Night	6% 2 16% 53% 20% 3	591
August	1st to 10th	Night	7% 2 16% 48% 26% 1	537
	11th to 20th	Night	13% 2 18% 34% 29% 3	534
	21st to end	Night	11% 4 21% 38% 23% 2	594
September	1st to 10th	Night	12% 5% 24% 37% 18% 5%	540
	11th to 20th	Night	11% 4 28% 35% 19% 3	540
	21st to end	Night	17% 9% 27% 33% 14% 1	677
October	1st to 10th	Night	16% 8% 32% 28% 17% 1	720
	11th to 20th	Night	19% 13% 31% 28% 8%	720
	21st to end	Night	22% 12% 29% 30% 7%	792
November	1st to 10th	Night	18% 12% 34% 28% 7% 1	740
	11th to 20th	Night	19% 14% 39% 22% 6%	926
	21st to end	Night	20% 15% 34% 24% 7%	950
December	1st to 10th	Night	18% 12% 37% 26% 6% 1	950
	11th to 20th	Night	22% 13% 35% 23% 6% 1	950
	21st to end	Night	27% 13% 33% 24% 3	1045

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