Fond du Lac
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fond du Lac clear sky chart from 2005-11-06 to 2024-01-12.

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% 4 7% 6% 3 5% 5% 5% 8% 37%	74782
	Night	13% 9% 4 7% 6% 3 4 4 5% 6% 38%	74954
Transparency	Day	46% 6% 13% 23% 11% 1	74483
	Night	46% 6% 12% 22% 13% 1	74774
Seeing	Day	16% 10% 30% 26% 14% 4	14750
	Night	17% 10% 32% 29% 11% 1	24747

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	11% 12% 5% 10% 8% 4 5% 5% 7% 6% 28%	1517
	11th to 20th	Day	11% 16% 7% 13% 7% 4 5% 4 4 6% 21%	1448
	21st to end	Day	11% 14% 6% 13% 8% 4 5% 5% 4 7% 23%	1585
February	1st to 10th	Day	11% 13% 6% 9% 6% 4 6% 4 4 7% 30%	1620
	11th to 20th	Day	13% 11% 3 7% 5% 4 5% 5% 3 7% 36%	1716
	21st to end	Day	13% 13% 5% 8% 7% 4 4 5% 4 6% 30%	1480
March	1st to 10th	Day	14% 11% 4 8% 5% 3 5% 5% 5% 7% 35%	1800
	11th to 20th	Day	12% 11% 4 7% 6% 3 5% 4 5% 6% 39%	1859
	21st to end	Day	17% 11% 4 8% 6% 3 4 5% 4 6% 32%	2376
April	1st to 10th	Day	16% 13% 4 6% 6% 3 5% 4 6% 8% 30%	2160
	11th to 20th	Day	20% 10% 3 5% 5% 3 4 4 4 6% 34%	2134
	21st to end	Day	19% 9% 3 6% 7% 3 4 5% 5% 5% 33%	2281
May	1st to 10th	Day	16% 9% 3 6% 5% 4 5% 5% 6% 8% 33%	2384
	11th to 20th	Day	16% 5% 3 6% 6% 4 5% 4 5% 8% 39%	2479
	21st to end	Day	12% 6% 3 5% 7% 3 5% 5% 6% 9% 39%	2725
June	1st to 10th	Day	10% 5% 3 5% 5% 3 5% 5% 6% 9% 45%	2520
	11th to 20th	Day	11% 6% 3 6% 6% 3 4 5% 6% 9% 43%	2520
	21st to end	Day	10% 5% 2 4 5% 3 5% 5% 6% 9% 45%	2520
July	1st to 10th	Day	6% 4 2 3 4 3 5% 6% 7% 11% 49%	2520
	11th to 20th	Day	9% 4 1 5% 5% 3 5% 6% 6% 9% 46%	2520
	21st to end	Day	7% 4 2 4 4 4 5% 5% 6% 10% 49%	2743
August	1st to 10th	Day	7% 4 2 5% 5% 4 5% 6% 8% 11% 44%	2507
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 5% 6% 9% 43%	2202
	21st to end	Day	11% 6% 3 5% 4 3 4 5% 5% 8% 45%	2376
September	1st to 10th	Day	13% 6% 3 6% 4 3 5% 4 5% 8% 44%	2160
	11th to 20th	Day	13% 5% 2 5% 4 3 4 4 5% 8% 48%	2066
	21st to end	Day	14% 7% 2 6% 6% 4 4 5% 5% 8% 40%	1980
October	1st to 10th	Day	15% 7% 2 6% 4 3 4 4 4 7% 43%	1890
	11th to 20th	Day	20% 12% 3 7% 5% 3 5% 4 5% 7% 29%	1774
	21st to end	Day	18% 12% 4 7% 5% 3 4 3 4 5% 35%	1782
November	1st to 10th	Day	13% 9% 4 6% 4 3 4 4 5% 7% 42%	1672
	11th to 20th	Day	12% 12% 5% 9% 8% 4 5% 5% 5% 6% 28%	1710
	21st to end	Day	16% 12% 4 6% 6% 3 4 4 5% 6% 34%	1535
December	1st to 10th	Day	13% 11% 7% 10% 8% 5% 6% 5% 6% 6% 24%	1520
	11th to 20th	Day	12% 14% 6% 10% 7% 4 6% 5% 4 7% 24%	1918
	21st to end	Day	18% 19% 8% 12% 8% 4 4 5% 3 5% 14%	2783
January	1st to 10th	Night	12% 11% 6% 10% 8% 4 4 4 4 5% 33%	2648
	11th to 20th	Night	14% 14% 6% 11% 6% 3 5% 4 4 5% 26%	2541
	21st to end	Night	12% 13% 6% 10% 8% 4 5% 5% 5% 6% 26%	2768
February	1st to 10th	Night	11% 14% 6% 8% 6% 4 5% 4 3 5% 33%	2340
	11th to 20th	Night	10% 9% 4 9% 6% 4 6% 4 4 5% 38%	2129
	21st to end	Night	16% 12% 4 7% 5% 3 4 4 5% 5% 34%	1776
March	1st to 10th	Night	14% 11% 3 6% 5% 3 5% 5% 5% 7% 36%	2160
	11th to 20th	Night	13% 8% 3 5% 5% 3 5% 5% 5% 8% 40%	2116
	21st to end	Night	17% 9% 4 7% 5% 3 5% 5% 4 6% 35%	1980
April	1st to 10th	Night	18% 11% 4 7% 4 3 4 4 5% 6% 34%	1800
	11th to 20th	Night	20% 9% 3 5% 5% 2 4 4 4 5% 37%	1775
	21st to end	Night	16% 8% 4 7% 5% 3 4 4 6% 6% 37%	1678
May	1st to 10th	Night	15% 9% 3 6% 6% 3 4 6% 6% 8% 33%	1574
	11th to 20th	Night	15% 6% 3 7% 6% 4 5% 5% 6% 7% 37%	1416
	21st to end	Night	11% 5% 2 5% 6% 3 5% 6% 5% 10% 42%	1551
June	1st to 10th	Night	10% 5% 2 5% 5% 2 4 5% 6% 8% 48%	1440
	11th to 20th	Night	11% 7% 2 5% 4 3 4 4 6% 9% 45%	1440
	21st to end	Night	8% 5% 2 5% 5% 2 4 6% 5% 8% 51%	1440
July	1st to 10th	Night	7% 3 1 4 3 3 4 4 5% 8% 57%	1440
	11th to 20th	Night	5% 4 2 4 4 3 5% 5% 7% 9% 52%	1440
	21st to end	Night	6% 3 2 5% 4 3 4 5% 7% 10% 53%	1575
August	1st to 10th	Night	7% 4 2 4 5% 3 4 4 7% 11% 49%	1432
	11th to 20th	Night	8% 5% 2 5% 5% 2 4 5% 5% 7% 52%	1694
	21st to end	Night	9% 5% 2 3 4 3 4 5% 5% 7% 51%	1980
September	1st to 10th	Night	10% 5% 2 4 5% 3 4 4 5% 8% 51%	1800
	11th to 20th	Night	13% 4 2 4 4 3 4 4 4 5% 53%	1875
	21st to end	Night	13% 6% 2 6% 5% 3 3 4 5% 6% 48%	1980
October	1st to 10th	Night	13% 6% 3 6% 5% 3 4 4 5% 6% 47%	2067
	11th to 20th	Night	18% 9% 3 6% 5% 3 5% 4 4 7% 38%	2184
	21st to end	Night	18% 11% 3 6% 5% 3 4 5% 5% 7% 33%	2574
November	1st to 10th	Night	12% 7% 3 6% 5% 3 4 4 5% 6% 45%	2406
	11th to 20th	Night	14% 10% 5% 9% 7% 4 5% 5% 4 6% 31%	2470
	21st to end	Night	15% 10% 4 7% 6% 4 4 4 5% 6% 35%	2642
December	1st to 10th	Night	13% 12% 5% 8% 7% 4 5% 5% 5% 6% 29%	2660
	11th to 20th	Night	12% 14% 7% 10% 7% 4 5% 4 5% 5% 27%	3279
	21st to end	Night	18% 16% 7% 10% 7% 4 4 4 4 4 21%	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% 6% 12% 17% 9%	1518
	11th to 20th	Day	64% 5% 9% 15% 8%	1448
	21st to end	Day	61% 6% 11% 15% 7% 1	1585
February	1st to 10th	Day	54% 6% 11% 20% 8% 1	1620
	11th to 20th	Day	49% 6% 10% 22% 11% 2	1726
	21st to end	Day	55% 5% 10% 17% 10% 2	1480
March	1st to 10th	Day	48% 6% 14% 21% 9% 2	1800
	11th to 20th	Day	46% 6% 11% 22% 14% 2	1859
	21st to end	Day	53% 5% 13% 19% 7% 1	2376
April	1st to 10th	Day	53% 6% 12% 19% 10%	2160
	11th to 20th	Day	50% 6% 8% 21% 13% 2	2134
	21st to end	Day	51% 7% 11% 20% 10% 1	2281
May	1st to 10th	Day	48% 7% 14% 23% 9% 1	2384
	11th to 20th	Day	44% 6% 13% 23% 12% 1	2483
	21st to end	Day	41% 9% 12% 24% 13% 2	2725
June	1st to 10th	Day	36% 7% 13% 28% 15% 2	2520
	11th to 20th	Day	39% 6% 13% 25% 15% 1	2520
	21st to end	Day	34% 9% 15% 26% 14% 1	2520
July	1st to 10th	Day	28% 8% 14% 32% 15% 2	2451
	11th to 20th	Day	32% 8% 15% 28% 16% 2	2445
	21st to end	Day	29% 7% 17% 29% 15% 3	2591
August	1st to 10th	Day	32% 9% 17% 29% 11% 2	2492
	11th to 20th	Day	37% 7% 14% 29% 12% 1	2202
	21st to end	Day	36% 7% 13% 26% 17% 2	2376
September	1st to 10th	Day	39% 6% 12% 26% 15% 1	2160
	11th to 20th	Day	36% 5% 15% 32% 12% 1	2066
	21st to end	Day	43% 6% 12% 30% 10%	1980
October	1st to 10th	Day	42% 5% 11% 27% 14% 1	1890
	11th to 20th	Day	54% 6% 12% 20% 8% 1	1774
	21st to end	Day	52% 5% 12% 20% 11%	1782
November	1st to 10th	Day	42% 5% 15% 23% 13% 1	1672
	11th to 20th	Day	54% 5% 14% 19% 7% 1	1710
	21st to end	Day	52% 4 15% 22% 7%	1535
December	1st to 10th	Day	58% 6% 14% 15% 6%	1520
	11th to 20th	Day	58% 5% 14% 15% 6% 1	1915
	21st to end	Day	74% 4 8% 10% 4	2783
January	1st to 10th	Night	55% 4 11% 18% 11% 1	2648
	11th to 20th	Night	61% 4 11% 16% 7% 1	2541
	21st to end	Night	59% 4 11% 16% 9% 1	2768
February	1st to 10th	Night	53% 5% 9% 20% 11% 2	2340
	11th to 20th	Night	49% 5% 10% 22% 12% 2	2130
	21st to end	Night	51% 5% 12% 20% 11% 2	1776
March	1st to 10th	Night	46% 7% 13% 21% 11% 2	2160
	11th to 20th	Night	41% 6% 14% 22% 15% 2	2116
	21st to end	Night	50% 5% 9% 22% 11% 2	1980
April	1st to 10th	Night	50% 5% 9% 17% 17% 1	1800
	11th to 20th	Night	48% 5% 8% 20% 16% 3	1775
	21st to end	Night	46% 6% 12% 21% 14% 1	1678
May	1st to 10th	Night	48% 7% 12% 21% 11% 1	1574
	11th to 20th	Night	46% 6% 11% 23% 13% 2	1417
	21st to end	Night	38% 7% 14% 24% 15% 2	1552
June	1st to 10th	Night	32% 7% 15% 28% 17% 1	1440
	11th to 20th	Night	35% 6% 12% 27% 18% 2	1440
	21st to end	Night	31% 8% 16% 27% 16% 3	1440
July	1st to 10th	Night	25% 7% 15% 31% 19% 4	1400
	11th to 20th	Night	27% 7% 15% 30% 18% 3	1392
	21st to end	Night	26% 7% 16% 30% 17% 4	1487
August	1st to 10th	Night	29% 7% 17% 29% 15% 3	1423
	11th to 20th	Night	30% 7% 15% 32% 16%	1694
	21st to end	Night	31% 6% 13% 28% 20% 3	1980
September	1st to 10th	Night	32% 7% 12% 25% 23% 2	1800
	11th to 20th	Night	33% 4 11% 35% 16% 1	1875
	21st to end	Night	37% 6% 11% 30% 16% 1	1980
October	1st to 10th	Night	38% 5% 9% 29% 17% 2	2067
	11th to 20th	Night	47% 6% 13% 20% 13% 1	2184
	21st to end	Night	50% 6% 12% 21% 11%	2574
November	1st to 10th	Night	40% 5% 11% 26% 16% 2	2406
	11th to 20th	Night	53% 5% 12% 18% 10% 1	2470
	21st to end	Night	49% 5% 16% 23% 7% 1	2642
December	1st to 10th	Night	54% 6% 14% 19% 7% 1	2660
	11th to 20th	Night	60% 5% 11% 16% 8% 1	3281
	21st to end	Night	67% 6% 9% 14% 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	16% 14% 37% 26% 8% 1	270
	11th to 20th	Day	17% 16% 35% 26% 6%	243
	21st to end	Day	19% 11% 39% 24% 6% 1	264
February	1st to 10th	Day	13% 18% 45% 19% 6%	240
	11th to 20th	Day	20% 21% 35% 19% 6%	240
	21st to end	Day	20% 18% 45% 15% 2 1	198
March	1st to 10th	Day	18% 18% 43% 16% 5%	240
	11th to 20th	Day	19% 15% 34% 21% 8% 3	248
	21st to end	Day	24% 11% 33% 23% 7% 2	462
April	1st to 10th	Day	25% 12% 34% 24% 5%	420
	11th to 20th	Day	25% 17% 26% 20% 9% 2	412
	21st to end	Day	22% 13% 28% 23% 12% 1	420
May	1st to 10th	Day	20% 12% 32% 25% 9% 2	467
	11th to 20th	Day	18% 10% 33% 24% 12% 3	625
	21st to end	Day	15% 9% 30% 25% 17% 5%	679
June	1st to 10th	Day	10% 8% 31% 31% 17% 4	630
	11th to 20th	Day	13% 7% 32% 27% 15% 5%	630
	21st to end	Day	12% 9% 25% 33% 16% 4	630
July	1st to 10th	Day	6% 4 20% 31% 27% 11%	621
	11th to 20th	Day	10% 5% 26% 34% 18% 8%	618
	21st to end	Day	6% 4 28% 33% 21% 7%	684
August	1st to 10th	Day	8% 3 22% 36% 22% 9%	626
	11th to 20th	Day	13% 5% 15% 27% 27% 13%	464
	21st to end	Day	14% 7% 20% 28% 21% 9%	495
September	1st to 10th	Day	16% 7% 20% 28% 22% 8%	450
	11th to 20th	Day	12% 5% 20% 34% 20% 9%	450
	21st to end	Day	15% 13% 26% 22% 20% 4	450
October	1st to 10th	Day	19% 12% 24% 27% 14% 4	360
	11th to 20th	Day	22% 18% 32% 20% 8%	270
	21st to end	Day	27% 12% 36% 18% 7% 1	297
November	1st to 10th	Day	18% 14% 34% 24% 9% 2	270
	11th to 20th	Day	16% 18% 39% 21% 7%	270
	21st to end	Day	24% 12% 40% 20% 4	270
December	1st to 10th	Day	17% 19% 41% 17% 5%	270
	11th to 20th	Day	21% 16% 39% 16% 6% 1	270
	21st to end	Day	25% 19% 38% 16% 3	297
January	1st to 10th	Night	16% 15% 38% 23% 7%	950
	11th to 20th	Night	20% 13% 37% 24% 6% 1	908
	21st to end	Night	18% 11% 38% 27% 6%	990
February	1st to 10th	Night	19% 13% 37% 25% 5%	900
	11th to 20th	Night	14% 17% 37% 25% 7%	734
	21st to end	Night	24% 14% 35% 22% 5% 1	592
March	1st to 10th	Night	20% 12% 33% 26% 8% 1	720
	11th to 20th	Night	17% 9% 39% 28% 7% 1	684
	21st to end	Night	22% 8% 28% 32% 10% 1	594
April	1st to 10th	Night	23% 11% 37% 23% 6%	540
	11th to 20th	Night	24% 10% 31% 29% 7% 1	533
	21st to end	Night	19% 9% 33% 31% 8% 1	540
May	1st to 10th	Night	18% 10% 37% 28% 7%	540
	11th to 20th	Night	16% 10% 34% 29% 11% 1	531
	21st to end	Night	13% 6% 28% 37% 15% 1	584
June	1st to 10th	Night	11% 4 29% 40% 16%	540
	11th to 20th	Night	14% 4 32% 37% 13% 1	540
	21st to end	Night	10% 3 26% 42% 17% 1	540
July	1st to 10th	Night	8% 2 18% 42% 28% 2	525
	11th to 20th	Night	8% 3 24% 39% 24% 2	522
	21st to end	Night	8% 2 21% 45% 24% 1	591
August	1st to 10th	Night	9% 2 15% 50% 22% 2	537
	11th to 20th	Night	10% 2 17% 40% 28% 4	534
	21st to end	Night	11% 2 19% 45% 20% 3	594
September	1st to 10th	Night	11% 4 24% 37% 20% 4	540
	11th to 20th	Night	15% 5% 21% 33% 22% 4	615
	21st to end	Night	15% 8% 28% 29% 18% 2	720
October	1st to 10th	Night	16% 7% 28% 31% 17% 1	720
	11th to 20th	Night	22% 12% 33% 26% 7% 1	720
	21st to end	Night	25% 10% 30% 25% 10%	792
November	1st to 10th	Night	16% 12% 36% 26% 9% 1	740
	11th to 20th	Night	19% 16% 38% 21% 5%	760
	21st to end	Night	19% 14% 38% 22% 7%	932
December	1st to 10th	Night	19% 15% 38% 21% 5%	950
	11th to 20th	Night	21% 13% 39% 21% 5% 1	950
	21st to end	Night	24% 15% 36% 22% 3	1045

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