St Croix Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St Croix Falls clear sky chart from 2005-11-06 to 2024-01-16.

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 7% 6% 3 5% 5% 5% 7% 36%	74755
	Night	13% 9% 4 7% 6% 3 4 5% 5% 6% 38%	75078
Transparency	Day	47% 4 13% 24% 10% 1	74455
	Night	46% 4 13% 24% 11% 1	74898
Seeing	Day	17% 8% 30% 27% 14% 4	14868
	Night	17% 8% 31% 32% 11% 1	24899

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	9% 11% 6% 9% 9% 4 7% 6% 5% 6% 27%	1517
	11th to 20th	Day	11% 13% 8% 11% 10% 4 5% 5% 5% 6% 22%	1480
	21st to end	Day	9% 13% 7% 13% 8% 4 6% 6% 6% 6% 21%	1745
February	1st to 10th	Day	8% 11% 5% 9% 8% 3 6% 5% 6% 7% 31%	1620
	11th to 20th	Day	8% 12% 6% 8% 8% 5% 6% 4 4 7% 33%	1574
	21st to end	Day	11% 11% 6% 11% 6% 4 5% 5% 4 7% 31%	1406
March	1st to 10th	Day	13% 12% 6% 7% 6% 4 4 4 5% 7% 32%	1895
	11th to 20th	Day	14% 9% 4 6% 6% 3 4 3 4 8% 37%	1980
	21st to end	Day	18% 11% 4 7% 6% 3 5% 4 6% 7% 29%	2225
April	1st to 10th	Day	18% 10% 4 6% 6% 3 4 5% 5% 7% 33%	2160
	11th to 20th	Day	21% 12% 4 6% 5% 3 5% 4 4 6% 31%	2134
	21st to end	Day	21% 11% 3 7% 5% 3 5% 4 5% 5% 30%	2326
May	1st to 10th	Day	18% 7% 3 7% 6% 4 5% 5% 5% 7% 33%	2483
	11th to 20th	Day	17% 7% 3 6% 5% 3 5% 5% 5% 7% 37%	2479
	21st to end	Day	15% 6% 3 6% 6% 4 5% 5% 6% 7% 38%	2725
June	1st to 10th	Day	13% 6% 2 3 4 3 4 5% 6% 7% 45%	2520
	11th to 20th	Day	13% 6% 3 5% 5% 3 5% 6% 7% 9% 38%	2520
	21st to end	Day	10% 5% 2 4 6% 4 6% 6% 8% 10% 41%	2520
July	1st to 10th	Day	8% 3 2 4 4 3 5% 5% 6% 10% 50%	2520
	11th to 20th	Day	10% 4 2 4 5% 2 5% 5% 6% 8% 50%	2520
	21st to end	Day	8% 3 2 4 5% 3 5% 5% 7% 9% 49%	2743
August	1st to 10th	Day	10% 5% 2 5% 6% 4 6% 7% 7% 10% 41%	2360
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 5% 6% 6% 46%	2301
	21st to end	Day	10% 5% 3 4 4 3 3 4 5% 7% 51%	2445
September	1st to 10th	Day	12% 5% 2 6% 6% 3 4 5% 5% 8% 45%	2160
	11th to 20th	Day	13% 5% 2 5% 4 3 5% 5% 5% 8% 45%	2160
	21st to end	Day	17% 6% 3 5% 5% 3 4 4 5% 9% 41%	1881
October	1st to 10th	Day	17% 6% 2 5% 4 3 5% 5% 5% 7% 41%	1800
	11th to 20th	Day	17% 12% 3 6% 6% 3 4 5% 4 6% 35%	1800
	21st to end	Day	18% 11% 4 7% 5% 3 3 4 4 6% 35%	1918
November	1st to 10th	Day	11% 14% 5% 8% 6% 3 4 4 5% 6% 35%	1577
	11th to 20th	Day	13% 13% 8% 9% 9% 4 5% 3 4 6% 26%	1520
	21st to end	Day	14% 10% 5% 6% 5% 4 6% 4 6% 6% 33%	1520
December	1st to 10th	Day	11% 14% 6% 10% 9% 4 5% 6% 5% 6% 23%	1520
	11th to 20th	Day	12% 12% 8% 10% 8% 4 5% 5% 4 6% 26%	1918
	21st to end	Day	23% 15% 7% 13% 8% 2 4 3 3 4 18%	2783
January	1st to 10th	Night	9% 10% 6% 10% 9% 4 6% 6% 6% 5% 31%	2648
	11th to 20th	Night	11% 11% 7% 10% 8% 4 6% 6% 5% 6% 27%	2603
	21st to end	Night	12% 14% 6% 12% 7% 4 6% 5% 5% 6% 24%	2610
February	1st to 10th	Night	6% 10% 6% 9% 8% 4 6% 5% 5% 7% 34%	2340
	11th to 20th	Night	6% 9% 4 8% 7% 4 6% 5% 5% 7% 38%	2273
	21st to end	Night	12% 12% 5% 8% 7% 4 5% 5% 4 5% 34%	1848
March	1st to 10th	Night	12% 10% 3 8% 7% 3 5% 5% 5% 6% 36%	2080
	11th to 20th	Night	13% 9% 4 7% 5% 4 4 4 4 6% 41%	1980
	21st to end	Night	19% 8% 4 6% 5% 4 4 4 4 5% 37%	2129
April	1st to 10th	Night	19% 11% 3 6% 6% 3 3 4 5% 7% 34%	1800
	11th to 20th	Night	23% 9% 4 6% 5% 3 3 4 3 5% 35%	1775
	21st to end	Night	19% 10% 3 6% 5% 3 4 5% 5% 7% 35%	1633
May	1st to 10th	Night	17% 9% 3 7% 5% 3 4 4 5% 4 37%	1476
	11th to 20th	Night	16% 5% 2 5% 5% 3 4 5% 6% 7% 42%	1416
	21st to end	Night	12% 5% 2 6% 6% 3 5% 6% 6% 9% 40%	1551
June	1st to 10th	Night	11% 5% 3 5% 3 3 4 5% 6% 10% 45%	1440
	11th to 20th	Night	10% 4 3 6% 5% 3 5% 5% 5% 7% 47%	1440
	21st to end	Night	7% 4 2 4 5% 3 5% 5% 7% 9% 49%	1440
July	1st to 10th	Night	6% 3 1 3 3 3 4 5% 6% 10% 56%	1440
	11th to 20th	Night	7% 4 2 3 4 3 4 5% 5% 10% 53%	1440
	21st to end	Night	5% 3 1 3 3 2 4 4 6% 9% 60%	1575
August	1st to 10th	Night	7% 4 2 6% 6% 4 3 4 5% 9% 51%	1576
	11th to 20th	Night	13% 4 2 3 3 2 4 4 7% 7% 51%	1600
	21st to end	Night	10% 4 2 4 4 3 3 5% 5% 6% 54%	1909
September	1st to 10th	Night	10% 4 2 5% 4 3 4 4 4 8% 53%	1800
	11th to 20th	Night	10% 4 1 4 5% 2 4 5% 5% 7% 53%	1800
	21st to end	Night	15% 5% 2 4 5% 3 3 4 4 7% 47%	2058
October	1st to 10th	Night	15% 6% 2 4 4 2 4 4 4 6% 47%	2160
	11th to 20th	Night	17% 10% 3 5% 5% 3 5% 4 4 6% 39%	2160
	21st to end	Night	17% 11% 4 7% 5% 3 4 4 4 6% 36%	2438
November	1st to 10th	Night	15% 9% 3 6% 6% 3 4 4 5% 6% 39%	2497
	11th to 20th	Night	14% 11% 5% 10% 7% 3 4 4 4 5% 33%	2660
	21st to end	Night	14% 9% 4 8% 7% 3 4 4 6% 7% 36%	2660
December	1st to 10th	Night	9% 15% 5% 10% 8% 4 5% 4 5% 7% 28%	2660
	11th to 20th	Night	12% 15% 5% 11% 8% 4 5% 5% 4 6% 25%	3279
	21st to end	Night	23% 16% 5% 10% 7% 3 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	57% 5% 12% 20% 6%	1518
	11th to 20th	Day	64% 4 11% 13% 8%	1480
	21st to end	Day	62% 5% 12% 14% 7%	1745
February	1st to 10th	Day	52% 3 14% 21% 8% 1	1620
	11th to 20th	Day	52% 3 11% 24% 8% 1	1583
	21st to end	Day	54% 5% 9% 22% 10% 1	1406
March	1st to 10th	Day	54% 4 15% 19% 8% 1	1895
	11th to 20th	Day	48% 4 15% 24% 8% 1	1980
	21st to end	Day	55% 4 10% 22% 9% 1	2225
April	1st to 10th	Day	50% 5% 11% 21% 13% 1	2160
	11th to 20th	Day	55% 4 9% 19% 12% 1	2134
	21st to end	Day	55% 4 12% 20% 9%	2326
May	1st to 10th	Day	50% 5% 11% 23% 9% 1	2483
	11th to 20th	Day	47% 4 14% 23% 11% 1	2483
	21st to end	Day	45% 5% 11% 26% 12% 1	2725
June	1st to 10th	Day	36% 5% 15% 32% 11% 1	2520
	11th to 20th	Day	41% 5% 15% 25% 12% 1	2520
	21st to end	Day	37% 6% 18% 30% 8% 2	2520
July	1st to 10th	Day	29% 5% 17% 33% 15% 1	2451
	11th to 20th	Day	31% 6% 15% 29% 17% 2	2445
	21st to end	Day	30% 6% 17% 30% 16% 1	2591
August	1st to 10th	Day	38% 4 15% 31% 9% 2	2345
	11th to 20th	Day	38% 5% 15% 32% 10%	2301
	21st to end	Day	33% 4 15% 31% 16% 1	2445
September	1st to 10th	Day	37% 6% 12% 34% 11%	2160
	11th to 20th	Day	37% 4 18% 32% 8%	2160
	21st to end	Day	41% 5% 12% 33% 8%	1881
October	1st to 10th	Day	42% 4 13% 30% 10% 1	1800
	11th to 20th	Day	50% 4 13% 22% 11% 1	1800
	21st to end	Day	52% 3 13% 22% 10%	1918
November	1st to 10th	Day	51% 4 13% 19% 12% 2	1577
	11th to 20th	Day	60% 4 13% 15% 7% 1	1520
	21st to end	Day	51% 5% 16% 21% 6% 2	1520
December	1st to 10th	Day	61% 5% 14% 16% 4	1520
	11th to 20th	Day	60% 3 16% 15% 5% 1	1915
	21st to end	Day	72% 3 8% 11% 7%	2783
January	1st to 10th	Night	53% 4 13% 20% 9% 1	2648
	11th to 20th	Night	58% 5% 14% 16% 7% 1	2603
	21st to end	Night	61% 4 10% 16% 7% 1	2610
February	1st to 10th	Night	50% 4 13% 23% 9% 1	2340
	11th to 20th	Night	46% 5% 14% 25% 9% 1	2274
	21st to end	Night	53% 4 10% 21% 11% 1	1848
March	1st to 10th	Night	50% 5% 13% 23% 9% 1	2080
	11th to 20th	Night	46% 3 12% 23% 15% 1	1980
	21st to end	Night	50% 4 11% 23% 11% 1	2129
April	1st to 10th	Night	50% 4 7% 22% 16% 1	1800
	11th to 20th	Night	52% 3 8% 20% 14% 2	1775
	21st to end	Night	50% 3 9% 22% 14% 1	1633
May	1st to 10th	Night	49% 4 13% 19% 14% 1	1476
	11th to 20th	Night	40% 6% 13% 25% 13% 2	1417
	21st to end	Night	40% 5% 15% 23% 16% 2	1552
June	1st to 10th	Night	34% 5% 14% 31% 14% 1	1440
	11th to 20th	Night	36% 5% 13% 26% 18% 3	1440
	21st to end	Night	29% 6% 17% 32% 14% 3	1440
July	1st to 10th	Night	22% 5% 17% 37% 18% 1	1400
	11th to 20th	Night	27% 7% 14% 32% 18% 4	1392
	21st to end	Night	21% 5% 18% 33% 19% 4	1487
August	1st to 10th	Night	32% 4 13% 32% 15% 4	1567
	11th to 20th	Night	31% 5% 17% 31% 15% 2	1600
	21st to end	Night	31% 5% 13% 30% 17% 3	1909
September	1st to 10th	Night	31% 4 14% 34% 15% 1	1800
	11th to 20th	Night	30% 4 17% 34% 15%	1800
	21st to end	Night	37% 4 13% 34% 12% 1	2058
October	1st to 10th	Night	38% 4 11% 32% 13% 2	2160
	11th to 20th	Night	47% 4 13% 24% 12% 1	2160
	21st to end	Night	50% 4 13% 22% 10% 1	2438
November	1st to 10th	Night	45% 4 12% 25% 13% 1	2497
	11th to 20th	Night	55% 4 12% 18% 11% 1	2660
	21st to end	Night	49% 4 15% 24% 7% 1	2660
December	1st to 10th	Night	57% 4 14% 19% 6%	2660
	11th to 20th	Night	61% 4 12% 18% 5% 1	3281
	21st to end	Night	67% 2 11% 15% 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	17% 7% 34% 30% 10% 3	270
	11th to 20th	Day	18% 9% 38% 26% 7% 1	255
	21st to end	Day	16% 8% 40% 27% 9% 1	264
February	1st to 10th	Day	18% 12% 49% 17% 5%	240
	11th to 20th	Day	17% 15% 41% 20% 5% 1	240
	21st to end	Day	18% 14% 41% 25% 2	198
March	1st to 10th	Day	18% 12% 42% 19% 8% 1	240
	11th to 20th	Day	20% 8% 38% 23% 9% 2	240
	21st to end	Day	23% 14% 31% 19% 10% 3	311
April	1st to 10th	Day	23% 12% 36% 21% 6% 1	420
	11th to 20th	Day	30% 9% 25% 27% 8% 1	412
	21st to end	Day	25% 11% 32% 22% 9% 2	586
May	1st to 10th	Day	21% 11% 30% 27% 8% 2	603
	11th to 20th	Day	21% 10% 27% 25% 13% 4	625
	21st to end	Day	20% 7% 27% 26% 16% 4	679
June	1st to 10th	Day	11% 8% 26% 34% 17% 4	630
	11th to 20th	Day	13% 9% 34% 31% 11% 2	630
	21st to end	Day	13% 5% 30% 28% 17% 7%	630
July	1st to 10th	Day	9% 3 24% 28% 25% 10%	621
	11th to 20th	Day	10% 6% 25% 31% 18% 9%	618
	21st to end	Day	7% 3 24% 36% 21% 8%	684
August	1st to 10th	Day	11% 3 21% 34% 25% 7%	626
	11th to 20th	Day	14% 4 19% 31% 26% 7%	615
	21st to end	Day	13% 5% 23% 33% 21% 5%	564
September	1st to 10th	Day	15% 5% 28% 30% 18% 4	450
	11th to 20th	Day	13% 4 29% 32% 18% 4	450
	21st to end	Day	21% 10% 29% 25% 11% 4	283
October	1st to 10th	Day	21% 10% 29% 21% 16% 3	270
	11th to 20th	Day	20% 19% 28% 26% 8%	270
	21st to end	Day	24% 13% 39% 16% 6% 2	297
November	1st to 10th	Day	21% 12% 36% 21% 9% 1	270
	11th to 20th	Day	21% 14% 39% 22% 3	270
	21st to end	Day	24% 12% 37% 21% 6%	270
December	1st to 10th	Day	17% 9% 43% 22% 8% 1	270
	11th to 20th	Day	20% 15% 36% 23% 6%	270
	21st to end	Day	28% 13% 39% 18% 2	297
January	1st to 10th	Night	13% 11% 37% 30% 9% 1	950
	11th to 20th	Night	17% 8% 38% 29% 7% 1	930
	21st to end	Night	19% 9% 35% 29% 7% 1	990
February	1st to 10th	Night	12% 10% 41% 29% 7% 1	900
	11th to 20th	Night	11% 13% 40% 28% 7% 1	879
	21st to end	Night	19% 12% 34% 27% 8%	664
March	1st to 10th	Night	16% 12% 36% 27% 7% 1	640
	11th to 20th	Night	18% 8% 39% 29% 6%	540
	21st to end	Night	22% 10% 30% 25% 11% 3	594
April	1st to 10th	Night	26% 8% 33% 26% 6%	540
	11th to 20th	Night	28% 6% 30% 28% 7% 1	533
	21st to end	Night	25% 8% 29% 29% 8% 1	540
May	1st to 10th	Night	21% 7% 35% 30% 7%	540
	11th to 20th	Night	17% 8% 31% 32% 11% 2	531
	21st to end	Night	12% 7% 26% 39% 14% 1	584
June	1st to 10th	Night	13% 4 27% 42% 13% 1	540
	11th to 20th	Night	11% 5% 30% 43% 10%	540
	21st to end	Night	9% 4 24% 44% 16% 2	540
July	1st to 10th	Night	7% 2 21% 40% 28% 2	525
	11th to 20th	Night	9% 4 20% 45% 20% 1	522
	21st to end	Night	5% 2 22% 47% 22% 3	591
August	1st to 10th	Night	9% 1 14% 55% 19% 2	537
	11th to 20th	Night	14% 1 19% 36% 27% 4	534
	21st to end	Night	11% 3 23% 37% 25% 2	594
September	1st to 10th	Night	11% 5% 23% 39% 19% 4	540
	11th to 20th	Night	13% 2 30% 35% 18% 2	540
	21st to end	Night	17% 9% 31% 29% 13% 1	633
October	1st to 10th	Night	19% 7% 28% 32% 14% 2	720
	11th to 20th	Night	23% 10% 30% 28% 8% 1	720
	21st to end	Night	25% 10% 28% 29% 9%	792
November	1st to 10th	Night	20% 9% 32% 31% 7% 1	831
	11th to 20th	Night	20% 12% 33% 27% 8%	950
	21st to end	Night	19% 13% 36% 25% 6%	950
December	1st to 10th	Night	16% 10% 36% 29% 8% 1	950
	11th to 20th	Night	21% 8% 38% 25% 7% 1	950
	21st to end	Night	25% 10% 33% 26% 6%	1045

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