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 2024-11-08.

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% 3 8% 5% 4 4 4 6% 7% 37%	101572
	Night	13% 9% 3 8% 5% 4 4 3 5% 6% 40%	97638
Transparency	Day	43% 7% 13% 23% 12% 1	105154
	Night	43% 6% 12% 23% 14% 2	102196
Seeing	Day	17% 11% 31% 25% 12% 4	15945
	Night	16% 10% 32% 30% 10% 1	25792

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	8% 15% 8% 19% 5% 4 5% 3 4 6% 23%	2527
	11th to 20th	Day	9% 11% 5% 13% 9% 6% 5% 8% 8% 7% 19%	2530
	21st to end	Day	15% 18% 9% 13% 5% 4 4 3 5% 6% 19%	3135
February	1st to 10th	Day	8% 13% 4 11% 6% 6% 4 5% 7% 7% 28%	1710
	11th to 20th	Day	12% 11% 4 8% 5% 5% 5% 5% 6% 7% 33%	1664
	21st to end	Day	14% 10% 4 10% 5% 5% 5% 2 5% 7% 33%	1565
March	1st to 10th	Day	15% 8% 3 6% 4 4 4 3 4 5% 45%	3246
	11th to 20th	Day	11% 8% 2 8% 5% 4 4 4 5% 8% 41%	3480
	21st to end	Day	24% 13% 4 10% 5% 4 4 3 4 5% 25%	3941
April	1st to 10th	Day	19% 13% 3 8% 5% 3 4 3 4 7% 31%	2280
	11th to 20th	Day	18% 13% 4 7% 4 4 4 3 5% 6% 32%	2254
	21st to end	Day	22% 10% 3 7% 5% 4 4 4 5% 6% 31%	2340
May	1st to 10th	Day	19% 7% 3 6% 5% 4 5% 4 6% 7% 36%	4301
	11th to 20th	Day	15% 7% 3 7% 4 4 4 3 5% 8% 41%	4399
	21st to end	Day	18% 7% 2 6% 4 5% 5% 4 5% 7% 38%	4824
June	1st to 10th	Day	11% 5% 3 6% 4 4 4 4 6% 8% 45%	2660
	11th to 20th	Day	13% 6% 2 7% 5% 4 5% 4 6% 8% 41%	2660
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 5% 6% 9% 38%	2660
July	1st to 10th	Day	9% 6% 3 6% 5% 5% 6% 6% 7% 10% 36%	4440
	11th to 20th	Day	5% 4 1 5% 4 4 4 5% 6% 9% 53%	4440
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 5% 7% 9% 42%	4795
August	1st to 10th	Day	10% 6% 2 7% 4 6% 5% 5% 7% 7% 41%	4104
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 9% 43%	4021
	21st to end	Day	8% 6% 2 5% 4 4 4 4 7% 8% 47%	4180
September	1st to 10th	Day	14% 5% 3 5% 3 3 4 4 5% 7% 48%	2280
	11th to 20th	Day	12% 5% 2 6% 4 4 4 3 6% 7% 47%	2280
	21st to end	Day	13% 7% 3 6% 4 4 4 3 5% 8% 43%	2005
October	1st to 10th	Day	15% 7% 1 5% 3 4 4 3 5% 6% 45%	1900
	11th to 20th	Day	17% 9% 2 6% 4 4 3 3 4 7% 39%	1900
	21st to end	Day	16% 12% 3 6% 4 4 3 3 4 6% 40%	2029
November	1st to 10th	Day	11% 8% 3 7% 4 5% 4 4 6% 7% 42%	1735
	11th to 20th	Day	14% 11% 5% 10% 6% 4 4 3 5% 6% 32%	1546
	21st to end	Day	12% 12% 4 7% 5% 3 4 3 5% 7% 39%	1520
December	1st to 10th	Day	13% 12% 5% 11% 6% 5% 5% 4 5% 5% 28%	1520
	11th to 20th	Day	12% 12% 5% 10% 6% 4 4 4 6% 8% 28%	1918
	21st to end	Day	20% 20% 9% 12% 4 4 3 2 4 5% 17%	2783
January	1st to 10th	Night	10% 13% 8% 17% 6% 4 4 3 5% 5% 26%	4428
	11th to 20th	Night	9% 15% 5% 13% 7% 5% 5% 5% 9% 5% 22%	4437
	21st to end	Night	16% 16% 7% 12% 5% 5% 4 3 5% 5% 22%	4532
February	1st to 10th	Night	9% 12% 5% 11% 7% 6% 5% 4 5% 6% 32%	2470
	11th to 20th	Night	9% 10% 4 8% 6% 5% 4 4 5% 7% 39%	2403
	21st to end	Night	14% 9% 4 8% 6% 4 5% 3 5% 4 37%	1889
March	1st to 10th	Night	14% 9% 3 6% 3 3 4 4 5% 6% 44%	3637
	11th to 20th	Night	10% 8% 3 7% 4 5% 4 4 6% 7% 44%	3480
	21st to end	Night	25% 12% 4 10% 4 3 3 3 4 4 27%	3690
April	1st to 10th	Night	15% 12% 3 6% 5% 4 3 3 4 5% 39%	1900
	11th to 20th	Night	19% 9% 2 5% 5% 4 4 4 5% 6% 38%	1875
	21st to end	Night	19% 9% 2 7% 5% 3 4 4 5% 6% 37%	1838
May	1st to 10th	Night	18% 7% 2 6% 4 4 4 4 5% 6% 41%	2602
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 3 5% 6% 47%	2506
	21st to end	Night	12% 7% 2 6% 4 4 4 3 6% 7% 46%	2743
June	1st to 10th	Night	9% 5% 3 6% 4 4 4 4 7% 7% 47%	1520
	11th to 20th	Night	10% 4 2 8% 5% 4 3 5% 6% 9% 44%	1520
	21st to end	Night	10% 5% 2 6% 4 3 4 3 5% 7% 51%	1520
July	1st to 10th	Night	11% 6% 3 6% 4 4 4 3 6% 8% 45%	2530
	11th to 20th	Night	3 3 1 4 4 4 4 3 7% 10% 56%	2530
	21st to end	Night	6% 4 1 5% 3 4 5% 4 7% 9% 52%	2765
August	1st to 10th	Night	10% 4 2 5% 4 4 4 4 6% 7% 49%	2836
	11th to 20th	Night	11% 5% 2 4 4 3 3 3 4 7% 54%	2815
	21st to end	Night	9% 5% 2 6% 4 3 4 3 5% 7% 52%	3476
September	1st to 10th	Night	10% 5% 1 6% 4 3 3 4 4 5% 56%	1900
	11th to 20th	Night	11% 5% 2 5% 3 4 3 2 4 5% 55%	1900
	21st to end	Night	10% 6% 1 5% 3 3 3 2 5% 6% 55%	2151
October	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 52%	2280
	11th to 20th	Night	15% 7% 2 5% 3 4 3 3 5% 6% 46%	2280
	21st to end	Night	16% 9% 3 7% 4 4 3 3 5% 6% 40%	2567
November	1st to 10th	Night	12% 8% 3 6% 4 3 3 3 5% 6% 47%	2504
	11th to 20th	Night	13% 12% 5% 10% 6% 4 4 3 4 4 36%	2631
	21st to end	Night	14% 11% 3 7% 5% 4 3 3 5% 6% 39%	2660
December	1st to 10th	Night	11% 12% 4 11% 7% 5% 5% 4 6% 7% 30%	2660
	11th to 20th	Night	13% 12% 3 11% 6% 5% 5% 3 5% 7% 29%	3279
	21st to end	Night	19% 16% 5% 13% 6% 4 4 3 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	63% 6% 12% 12% 5%	2528
	11th to 20th	Day	57% 8% 12% 14% 8%	2530
	21st to end	Day	66% 6% 13% 11% 4	3135
February	1st to 10th	Day	51% 7% 14% 17% 9% 1	1710
	11th to 20th	Day	48% 8% 12% 23% 8% 1	1673
	21st to end	Day	50% 6% 13% 19% 10% 2	1565
March	1st to 10th	Day	41% 6% 12% 24% 15% 3	3246
	11th to 20th	Day	37% 8% 12% 32% 11% 1	3480
	21st to end	Day	62% 7% 12% 13% 6% 1	3941
April	1st to 10th	Day	52% 6% 13% 19% 9% 1	2280
	11th to 20th	Day	51% 6% 11% 20% 11% 1	2254
	21st to end	Day	52% 7% 13% 16% 11% 1	2340
May	1st to 10th	Day	46% 8% 13% 20% 14% 1	4340
	11th to 20th	Day	39% 8% 12% 31% 9% 1	4403
	21st to end	Day	43% 8% 11% 23% 14% 1	4837
June	1st to 10th	Day	34% 9% 14% 27% 14% 1	2660
	11th to 20th	Day	39% 8% 13% 22% 17% 1	2660
	21st to end	Day	40% 8% 15% 22% 12% 2	2660
July	1st to 10th	Day	40% 10% 18% 24% 8% 1	4371
	11th to 20th	Day	27% 8% 15% 31% 18% 1	4365
	21st to end	Day	36% 9% 15% 21% 17% 1	4644
August	1st to 10th	Day	39% 7% 13% 26% 13% 2	4090
	11th to 20th	Day	37% 7% 13% 30% 13% 1	4060
	21st to end	Day	33% 7% 15% 28% 16% 1	4179
September	1st to 10th	Day	35% 6% 13% 27% 18% 1	2280
	11th to 20th	Day	35% 7% 14% 31% 13%	2280
	21st to end	Day	38% 7% 11% 28% 14% 1	2005
October	1st to 10th	Day	25% 4 7% 41% 23% 1	3160
	11th to 20th	Day	34% 4 12% 28% 20% 2	3140
	21st to end	Day	41% 3 11% 31% 12% 1	3319
November	1st to 10th	Day	40% 7% 15% 23% 13% 2	1735
	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	59% 7% 11% 16% 7% 1	4428
	11th to 20th	Night	57% 6% 11% 16% 9%	4437
	21st to end	Night	62% 6% 11% 15% 5% 1	4532
February	1st to 10th	Night	52% 6% 11% 18% 12% 1	2470
	11th to 20th	Night	44% 6% 13% 23% 12% 2	2404
	21st to end	Night	48% 7% 11% 20% 12% 2	1889
March	1st to 10th	Night	39% 6% 11% 27% 14% 2	3637
	11th to 20th	Night	35% 7% 11% 28% 18% 2	3480
	21st to end	Night	60% 5% 9% 16% 8% 1	3690
April	1st to 10th	Night	47% 5% 11% 21% 14% 2	1900
	11th to 20th	Night	46% 7% 11% 19% 15% 3	1875
	21st to end	Night	45% 8% 10% 22% 13% 2	1838
May	1st to 10th	Night	41% 8% 11% 17% 21% 1	2628
	11th to 20th	Night	36% 8% 12% 24% 16% 4	2507
	21st to end	Night	34% 9% 13% 26% 16% 1	2751
June	1st to 10th	Night	33% 9% 14% 26% 17% 2	1520
	11th to 20th	Night	35% 8% 12% 22% 20% 3	1520
	21st to end	Night	32% 7% 16% 25% 16% 4	1520
July	1st to 10th	Night	36% 7% 17% 27% 12% 2	2490
	11th to 20th	Night	23% 7% 17% 36% 15% 2	2482
	21st to end	Night	26% 9% 19% 23% 21% 2	2677
August	1st to 10th	Night	33% 6% 13% 29% 18% 1	2826
	11th to 20th	Night	30% 6% 15% 33% 15% 1	2842
	21st to end	Night	33% 6% 14% 26% 18% 3	3476
September	1st to 10th	Night	30% 7% 10% 29% 23% 1	1900
	11th to 20th	Night	31% 5% 13% 33% 17% 1	1900
	21st to end	Night	30% 6% 10% 31% 20% 2	2151
October	1st to 10th	Night	23% 4 7% 35% 29% 2	3800
	11th to 20th	Night	29% 4 12% 25% 27% 4	3779
	21st to end	Night	44% 4 10% 24% 16% 1	4227
November	1st to 10th	Night	38% 5% 14% 24% 17% 2	2504
	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	21% 16% 38% 20% 4 1	270
	21st to end	Day	19% 17% 39% 20% 6% 1	297
February	1st to 10th	Day	15% 21% 43% 17% 3 1	270
	11th to 20th	Day	21% 24% 32% 18% 3 1	270
	21st to end	Day	20% 19% 40% 17% 3	225
March	1st to 10th	Day	14% 20% 43% 16% 6% 1	270
	11th to 20th	Day	23% 18% 34% 17% 7% 1	270
	21st to end	Day	28% 18% 29% 17% 6% 2	373
April	1st to 10th	Day	27% 14% 38% 16% 6%	460
	11th to 20th	Day	24% 20% 27% 20% 9%	452
	21st to end	Day	27% 14% 30% 20% 7% 2	520
May	1st to 10th	Day	22% 12% 33% 25% 7% 1	653
	11th to 20th	Day	21% 14% 27% 24% 12% 3	675
	21st to end	Day	19% 11% 28% 24% 15% 4	734
June	1st to 10th	Day	11% 8% 30% 31% 17% 3	680
	11th to 20th	Day	15% 9% 32% 29% 13% 2	680
	21st to end	Day	14% 9% 31% 29% 13% 5%	680
July	1st to 10th	Day	9% 5% 21% 32% 21% 11%	671
	11th to 20th	Day	7% 4 29% 31% 21% 7%	668
	21st to end	Day	6% 3 28% 36% 19% 7%	739
August	1st to 10th	Day	7% 4 23% 37% 21% 8%	676
	11th to 20th	Day	14% 6% 20% 31% 20% 9%	658
	21st to end	Day	9% 7% 25% 32% 19% 7%	539
September	1st to 10th	Day	15% 7% 25% 28% 20% 5%	490
	11th to 20th	Day	10% 7% 26% 32% 20% 5%	490
	21st to end	Day	17% 13% 28% 24% 15% 2	367
October	1st to 10th	Day	19% 9% 32% 25% 13% 2	300
	11th to 20th	Day	21% 21% 32% 19% 6%	300
	21st to end	Day	24% 15% 37% 17% 6% 2	330
November	1st to 10th	Day	17% 14% 37% 24% 5% 2	291
	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% 15% 40% 26% 6%	950
	11th to 20th	Night	17% 14% 37% 26% 5% 1	950
	21st to end	Night	20% 12% 35% 27% 5%	1045
February	1st to 10th	Night	15% 14% 37% 26% 7%	950
	11th to 20th	Night	15% 16% 40% 23% 6% 1	929
	21st to end	Night	19% 14% 37% 24% 5%	633
March	1st to 10th	Night	19% 13% 38% 25% 5% 1	703
	11th to 20th	Night	18% 12% 36% 27% 7% 1	570
	21st to end	Night	24% 11% 32% 26% 6% 1	627
April	1st to 10th	Night	21% 14% 37% 25% 3	570
	11th to 20th	Night	22% 13% 33% 26% 6% 1	563
	21st to end	Night	21% 8% 36% 27% 7% 1	570
May	1st to 10th	Night	20% 9% 33% 31% 6% 1	570
	11th to 20th	Night	17% 9% 32% 32% 9% 1	561
	21st to end	Night	16% 6% 27% 37% 13% 1	617
June	1st to 10th	Night	11% 5% 28% 43% 12% 1	570
	11th to 20th	Night	11% 6% 29% 42% 11%	570
	21st to end	Night	12% 4 28% 42% 14% 1	570
July	1st to 10th	Night	7% 2 19% 42% 27% 3	555
	11th to 20th	Night	6% 2 24% 41% 24% 3	552
	21st to end	Night	6% 2 19% 48% 21% 3	624
August	1st to 10th	Night	6% 2 19% 49% 24% 1	567
	11th to 20th	Night	11% 2 17% 40% 25% 5%	564
	21st to end	Night	9% 3 21% 41% 23% 3	627
September	1st to 10th	Night	11% 5% 24% 36% 19% 4	570
	11th to 20th	Night	12% 3 26% 35% 22% 2	570
	21st to end	Night	11% 9% 27% 36% 16% 1	702
October	1st to 10th	Night	14% 7% 30% 32% 16% 1	760
	11th to 20th	Night	19% 12% 34% 27% 9%	760
	21st to end	Night	21% 11% 32% 30% 6%	836
November	1st to 10th	Night	15% 12% 37% 26% 8% 1	771
	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

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