Decorah
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Decorah 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	14% 8% 4 7% 5% 3 5% 5% 5% 7% 37%	74737
	Night	13% 8% 4 7% 6% 3 4 4 5% 6% 40%	75011
Transparency	Day	45% 7% 14% 22% 11% 1	74438
	Night	44% 7% 13% 22% 13% 2	74830
Seeing	Day	17% 11% 31% 25% 13% 4	14749
	Night	16% 10% 33% 30% 10% 1	24749

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% 11% 6% 4 7% 5% 5% 7% 28%	1517
	11th to 20th	Day	12% 13% 7% 13% 8% 3 5% 3 5% 7% 23%	1453
	21st to end	Day	13% 14% 5% 12% 8% 4 5% 4 5% 5% 23%	1782
February	1st to 10th	Day	9% 13% 5% 10% 8% 4 5% 6% 7% 7% 27%	1620
	11th to 20th	Day	13% 11% 5% 7% 6% 4 5% 6% 5% 6% 32%	1574
	21st to end	Day	15% 10% 4 9% 6% 4 5% 3 4 7% 33%	1476
March	1st to 10th	Day	14% 10% 5% 7% 6% 4 5% 4 5% 7% 33%	1870
	11th to 20th	Day	14% 9% 4 7% 5% 4 4 4 5% 8% 36%	1980
	21st to end	Day	21% 10% 4 6% 6% 4 4 5% 4 6% 29%	2250
April	1st to 10th	Day	19% 11% 4 7% 5% 3 4 5% 4 7% 31%	2160
	11th to 20th	Day	18% 12% 4 6% 5% 3 4 4 5% 5% 32%	2134
	21st to end	Day	23% 9% 3 6% 6% 3 4 5% 4 6% 31%	2216
May	1st to 10th	Day	18% 7% 4 7% 6% 4 6% 5% 6% 7% 30%	2462
	11th to 20th	Day	18% 7% 4 7% 6% 4 5% 5% 5% 7% 34%	2479
	21st to end	Day	17% 6% 3 5% 5% 4 6% 5% 5% 8% 37%	2725
June	1st to 10th	Day	11% 4 3 5% 4 3 4 5% 7% 8% 45%	2520
	11th to 20th	Day	13% 5% 2 6% 5% 3 5% 5% 5% 9% 42%	2520
	21st to end	Day	13% 5% 2 6% 6% 3 5% 6% 6% 9% 39%	2520
July	1st to 10th	Day	7% 4 1 4 5% 3 5% 6% 7% 10% 46%	2520
	11th to 20th	Day	8% 4 2 4 5% 4 5% 5% 6% 10% 47%	2520
	21st to end	Day	7% 4 2 5% 5% 3 5% 6% 7% 10% 46%	2738
August	1st to 10th	Day	7% 5% 2 5% 6% 5% 6% 6% 7% 9% 42%	2328
	11th to 20th	Day	13% 6% 2 5% 4 3 4 4 6% 9% 43%	2295
	21st to end	Day	11% 5% 2 4 4 3 4 4 6% 8% 48%	2376
September	1st to 10th	Day	15% 5% 3 5% 4 2 3 5% 4 7% 46%	2160
	11th to 20th	Day	12% 4 2 5% 4 3 4 4 6% 7% 47%	2160
	21st to end	Day	14% 7% 3 5% 5% 3 4 4 5% 8% 42%	1900
October	1st to 10th	Day	16% 7% 2 4 4 3 5% 4 5% 7% 43%	1800
	11th to 20th	Day	18% 9% 3 6% 5% 3 3 4 4 8% 38%	1800
	21st to end	Day	17% 11% 3 5% 5% 3 4 4 4 5% 39%	1923
November	1st to 10th	Day	10% 7% 3 6% 5% 3 4 5% 6% 7% 43%	1672
	11th to 20th	Day	14% 10% 6% 9% 7% 3 4 4 4 6% 32%	1546
	21st to end	Day	12% 11% 4 6% 6% 2 4 4 4 7% 39%	1520
December	1st to 10th	Day	13% 12% 5% 10% 7% 4 5% 5% 5% 6% 29%	1520
	11th to 20th	Day	12% 10% 6% 9% 7% 3 5% 5% 6% 8% 28%	1918
	21st to end	Day	20% 19% 10% 10% 6% 3 3 3 4 5% 18%	2783
January	1st to 10th	Night	9% 9% 6% 9% 9% 4 5% 5% 5% 6% 33%	2648
	11th to 20th	Night	12% 13% 6% 11% 7% 4 5% 4 5% 6% 27%	2544
	21st to end	Night	15% 12% 5% 10% 7% 3 5% 5% 5% 6% 26%	2574
February	1st to 10th	Night	10% 10% 6% 10% 8% 4 5% 4 5% 6% 31%	2340
	11th to 20th	Night	10% 10% 4 7% 7% 4 4 4 5% 7% 38%	2273
	21st to end	Night	15% 8% 5% 7% 7% 4 5% 4 5% 4 36%	1780
March	1st to 10th	Night	16% 10% 4 6% 4 3 4 5% 4 6% 37%	2106
	11th to 20th	Night	13% 9% 3 6% 5% 3 5% 5% 6% 6% 39%	1980
	21st to end	Night	18% 11% 4 7% 6% 3 5% 5% 5% 6% 31%	2106
April	1st to 10th	Night	15% 10% 5% 6% 6% 2 4 4 3 6% 40%	1800
	11th to 20th	Night	19% 9% 2 5% 5% 3 4 5% 5% 6% 37%	1775
	21st to end	Night	19% 8% 3 6% 5% 3 4 4 5% 6% 37%	1742
May	1st to 10th	Night	19% 6% 2 4 5% 3 4 5% 5% 6% 39%	1496
	11th to 20th	Night	16% 7% 2 5% 5% 3 5% 4 5% 7% 42%	1416
	21st to end	Night	14% 6% 2 5% 4 2 4 4 6% 8% 45%	1551
June	1st to 10th	Night	9% 5% 2 6% 4 3 5% 5% 6% 7% 47%	1440
	11th to 20th	Night	10% 4 2 7% 6% 3 3 6% 5% 9% 45%	1440
	21st to end	Night	9% 4 2 5% 4 3 4 5% 5% 7% 53%	1440
July	1st to 10th	Night	7% 3 2 4 3 3 4 4 6% 8% 55%	1440
	11th to 20th	Night	5% 3 1 4 4 3 5% 3 6% 10% 55%	1440
	21st to end	Night	6% 3 1 3 3 3 4 5% 6% 10% 56%	1577
August	1st to 10th	Night	6% 3 2 3 4 4 4 6% 6% 9% 53%	1611
	11th to 20th	Night	10% 4 2 3 5% 2 3 4 4 8% 53%	1604
	21st to end	Night	8% 4 2 5% 4 2 3 4 5% 7% 56%	1980
September	1st to 10th	Night	10% 5% 2 5% 4 3 3 5% 4 5% 54%	1800
	11th to 20th	Night	11% 5% 2 5% 4 2 3 3 4 6% 55%	1800
	21st to end	Night	11% 5% 2 4 4 2 3 3 5% 6% 54%	2037
October	1st to 10th	Night	13% 5% 2 5% 4 2 3 4 5% 7% 51%	2160
	11th to 20th	Night	16% 7% 2 5% 4 3 4 4 5% 6% 44%	2160
	21st to end	Night	16% 9% 3 6% 5% 3 3 4 5% 6% 40%	2431
November	1st to 10th	Night	12% 7% 3 5% 5% 2 3 4 5% 6% 48%	2406
	11th to 20th	Night	13% 11% 6% 9% 6% 3 4 3 4 5% 36%	2631
	21st to end	Night	14% 10% 3 7% 6% 3 4 4 5% 6% 39%	2660
December	1st to 10th	Night	11% 12% 4 10% 7% 3 5% 5% 6% 7% 30%	2660
	11th to 20th	Night	13% 11% 4 10% 7% 4 5% 4 5% 7% 30%	3279
	21st to end	Night	19% 15% 6% 11% 7% 3 4 4 4 4 20%	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	55% 7% 13% 15% 9%	1518
	11th to 20th	Day	61% 5% 11% 15% 7%	1453
	21st to end	Day	62% 5% 13% 12% 7% 1	1782
February	1st to 10th	Day	53% 7% 14% 17% 8% 1	1620
	11th to 20th	Day	50% 7% 12% 21% 9% 1	1583
	21st to end	Day	53% 5% 12% 18% 10% 2	1476
March	1st to 10th	Day	51% 7% 14% 18% 9% 1	1870
	11th to 20th	Day	46% 6% 14% 23% 10% 1	1980
	21st to end	Day	55% 7% 11% 19% 6% 1	2250
April	1st to 10th	Day	52% 6% 13% 19% 9% 1	2160
	11th to 20th	Day	51% 7% 11% 20% 10% 1	2134
	21st to end	Day	53% 7% 13% 16% 11% 1	2216
May	1st to 10th	Day	51% 8% 14% 18% 8% 1	2462
	11th to 20th	Day	49% 8% 12% 20% 9% 1	2483
	21st to end	Day	45% 8% 12% 21% 12% 2	2725
June	1st to 10th	Day	34% 9% 14% 28% 13% 1	2520
	11th to 20th	Day	39% 8% 13% 22% 17% 1	2520
	21st to end	Day	40% 9% 15% 22% 13% 1	2520
July	1st to 10th	Day	29% 10% 18% 28% 13% 2	2451
	11th to 20th	Day	31% 10% 16% 25% 16% 3	2445
	21st to end	Day	30% 9% 17% 26% 15% 2	2586
August	1st to 10th	Day	36% 9% 15% 28% 10% 2	2314
	11th to 20th	Day	37% 8% 13% 27% 13% 1	2295
	21st to end	Day	33% 8% 12% 27% 18% 2	2376
September	1st to 10th	Day	36% 6% 13% 26% 16% 1	2160
	11th to 20th	Day	35% 7% 15% 30% 13%	2160
	21st to end	Day	39% 8% 12% 28% 13% 1	1900
October	1st to 10th	Day	40% 7% 12% 27% 15%	1800
	11th to 20th	Day	45% 5% 14% 23% 12% 1	1800
	21st to end	Day	47% 5% 13% 22% 12% 1	1923
November	1st to 10th	Day	39% 7% 15% 24% 14% 2	1672
	11th to 20th	Day	53% 5% 13% 19% 9% 1	1546
	21st to end	Day	46% 5% 18% 22% 9% 1	1520
December	1st to 10th	Day	55% 7% 12% 17% 7% 1	1520
	11th to 20th	Day	52% 7% 17% 15% 8% 1	1915
	21st to end	Day	70% 6% 8% 12% 4	2783
January	1st to 10th	Night	50% 6% 13% 19% 11% 1	2648
	11th to 20th	Night	57% 6% 14% 15% 9%	2544
	21st to end	Night	57% 6% 12% 16% 8% 1	2574
February	1st to 10th	Night	53% 5% 12% 18% 11% 1	2340
	11th to 20th	Night	45% 6% 13% 22% 12% 2	2274
	21st to end	Night	50% 7% 10% 20% 12% 2	1780
March	1st to 10th	Night	46% 7% 13% 23% 9% 1	2106
	11th to 20th	Night	43% 7% 13% 21% 13% 2	1980
	21st to end	Night	53% 6% 13% 18% 8% 2	2106
April	1st to 10th	Night	46% 6% 11% 20% 15% 2	1800
	11th to 20th	Night	47% 7% 11% 19% 14% 3	1775
	21st to end	Night	46% 8% 9% 22% 13% 2	1742
May	1st to 10th	Night	44% 7% 13% 23% 13% 1	1496
	11th to 20th	Night	42% 8% 14% 23% 13% 1	1417
	21st to end	Night	37% 9% 14% 24% 15% 2	1552
June	1st to 10th	Night	33% 9% 14% 25% 17% 2	1440
	11th to 20th	Night	34% 9% 12% 22% 20% 3	1440
	21st to end	Night	30% 7% 17% 26% 16% 4	1440
July	1st to 10th	Night	25% 8% 13% 33% 18% 2	1400
	11th to 20th	Night	23% 9% 17% 30% 17% 3	1392
	21st to end	Night	22% 9% 19% 30% 17% 4	1489
August	1st to 10th	Night	26% 7% 17% 31% 17% 2	1601
	11th to 20th	Night	29% 7% 14% 30% 18% 2	1604
	21st to end	Night	28% 8% 15% 25% 19% 5%	1980
September	1st to 10th	Night	31% 7% 11% 28% 22% 1	1800
	11th to 20th	Night	31% 5% 13% 33% 17% 1	1800
	21st to end	Night	31% 6% 11% 31% 19% 2	2037
October	1st to 10th	Night	33% 6% 12% 28% 19% 2	2160
	11th to 20th	Night	40% 5% 14% 22% 17% 1	2160
	21st to end	Night	45% 6% 13% 21% 15% 1	2431
November	1st to 10th	Night	37% 5% 14% 24% 18% 2	2406
	11th to 20th	Night	51% 6% 11% 20% 11% 1	2631
	21st to end	Night	47% 4 14% 25% 9% 1	2660
December	1st to 10th	Night	53% 6% 13% 19% 7% 1	2660
	11th to 20th	Night	53% 7% 15% 18% 7% 1	3281
	21st to end	Night	65% 7% 10% 12% 6%	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% 17% 37% 20% 7% 2	270
	11th to 20th	Day	23% 13% 38% 21% 4 1	245
	21st to end	Day	19% 16% 39% 20% 6% 1	264
February	1st to 10th	Day	15% 21% 45% 16% 2 1	240
	11th to 20th	Day	23% 25% 30% 18% 3 2	240
	21st to end	Day	23% 19% 40% 16% 3	198
March	1st to 10th	Day	13% 21% 44% 14% 7% 1	240
	11th to 20th	Day	23% 16% 35% 18% 8% 1	240
	21st to end	Day	29% 17% 29% 17% 7% 2	336
April	1st to 10th	Day	26% 14% 37% 16% 6%	420
	11th to 20th	Day	23% 19% 28% 21% 10%	412
	21st to end	Day	26% 14% 29% 21% 7% 2	476
May	1st to 10th	Day	22% 12% 34% 25% 6% 1	603
	11th to 20th	Day	23% 14% 26% 23% 11% 3	625
	21st to end	Day	19% 9% 28% 24% 15% 4	679
June	1st to 10th	Day	11% 7% 29% 32% 18% 4	630
	11th to 20th	Day	15% 8% 32% 29% 14% 3	630
	21st to end	Day	13% 8% 31% 30% 14% 5%	630
July	1st to 10th	Day	9% 4 20% 33% 22% 12%	621
	11th to 20th	Day	8% 5% 30% 31% 21% 5%	618
	21st to end	Day	7% 3 28% 36% 19% 7%	684
August	1st to 10th	Day	7% 2 23% 37% 22% 8%	626
	11th to 20th	Day	13% 6% 20% 30% 21% 10%	609
	21st to end	Day	10% 6% 25% 33% 19% 7%	495
September	1st to 10th	Day	16% 7% 24% 28% 19% 5%	450
	11th to 20th	Day	10% 7% 27% 32% 19% 5%	450
	21st to end	Day	18% 13% 29% 23% 14% 2	334
October	1st to 10th	Day	20% 10% 30% 26% 12% 2	270
	11th to 20th	Day	22% 23% 31% 18% 6%	270
	21st to end	Day	24% 15% 36% 16% 6% 2	297
November	1st to 10th	Day	16% 14% 39% 23% 5% 3	270
	11th to 20th	Day	19% 22% 33% 19% 7% 1	270
	21st to end	Day	22% 14% 40% 19% 5%	270
December	1st to 10th	Day	14% 17% 40% 20% 8%	270
	11th to 20th	Day	21% 12% 39% 20% 7%	270
	21st to end	Day	29% 12% 41% 15% 2	297
January	1st to 10th	Night	13% 14% 40% 26% 6%	950
	11th to 20th	Night	17% 14% 36% 27% 5% 1	910
	21st to end	Night	21% 12% 36% 26% 5%	990
February	1st to 10th	Night	16% 14% 38% 25% 6%	900
	11th to 20th	Night	16% 16% 40% 22% 6% 1	879
	21st to end	Night	19% 14% 37% 24% 6%	596
March	1st to 10th	Night	19% 12% 37% 26% 5% 1	666
	11th to 20th	Night	18% 11% 35% 28% 7% 1	540
	21st to end	Night	23% 10% 32% 26% 7% 1	594
April	1st to 10th	Night	20% 14% 37% 25% 3	540
	11th to 20th	Night	23% 12% 32% 26% 6% 1	533
	21st to end	Night	21% 8% 36% 27% 7% 1	540
May	1st to 10th	Night	20% 9% 33% 31% 6% 1	540
	11th to 20th	Night	18% 8% 32% 32% 8% 1	531
	21st to end	Night	17% 5% 27% 36% 14% 1	584
June	1st to 10th	Night	11% 5% 28% 43% 13% 1	540
	11th to 20th	Night	12% 6% 29% 42% 12%	540
	21st to end	Night	11% 4 27% 42% 15% 1	540
July	1st to 10th	Night	7% 2 19% 41% 28% 3	525
	11th to 20th	Night	7% 2 24% 41% 24% 2	522
	21st to end	Night	6% 2 19% 48% 21% 3	591
August	1st to 10th	Night	5% 1 18% 49% 25% 1	537
	11th to 20th	Night	11% 2 17% 38% 27% 5%	534
	21st to end	Night	9% 4 22% 39% 23% 3	594
September	1st to 10th	Night	11% 5% 24% 35% 19% 5%	540
	11th to 20th	Night	12% 3 26% 35% 21% 2	540
	21st to end	Night	12% 9% 28% 35% 15% 1	665
October	1st to 10th	Night	15% 7% 31% 31% 16% 1	720
	11th to 20th	Night	20% 12% 33% 27% 8%	720
	21st to end	Night	21% 11% 31% 30% 6%	792
November	1st to 10th	Night	15% 12% 38% 26% 8% 1	740
	11th to 20th	Night	18% 16% 40% 20% 6%	921
	21st to end	Night	19% 14% 38% 21% 8%	950
December	1st to 10th	Night	17% 13% 40% 24% 5% 1	950
	11th to 20th	Night	20% 12% 38% 23% 6%	950
	21st to end	Night	25% 15% 34% 22% 4	1045

Page generated at 2024-01-09 15:24:26. Version ac07

Copyright 2024 Attilla Danko