Duluth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Duluth 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	13% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	75145
	Night	14% 10% 4 7% 6% 3 5% 4 5% 7% 36%	74655
Transparency	Day	32% 36% 10% 15% 6% 1	74849
	Night	33% 36% 9% 15% 6% 1	74485
Seeing	Day	16% 6% 25% 32% 17% 4	14933
	Night	17% 6% 28% 34% 14% 2	24968

By Month

Percentage Cloud Cover NE (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% 12% 7% 10% 8% 4 6% 4 5% 6% 31%	1517
	11th to 20th	Day	10% 14% 6% 12% 8% 4 6% 6% 6% 9% 20%	1480
	21st to end	Day	9% 11% 6% 11% 11% 5% 6% 6% 7% 8% 21%	1667
February	1st to 10th	Day	7% 13% 4 10% 7% 2 6% 5% 6% 6% 34%	1620
	11th to 20th	Day	8% 11% 5% 8% 6% 3 4 5% 5% 5% 38%	1574
	21st to end	Day	10% 11% 4 8% 8% 3 5% 4 4 7% 36%	1408
March	1st to 10th	Day	11% 11% 4 7% 7% 4 5% 6% 4 7% 34%	1852
	11th to 20th	Day	13% 8% 4 7% 6% 3 3 4 6% 6% 38%	1980
	21st to end	Day	17% 9% 4 8% 6% 3 5% 5% 5% 7% 32%	2251
April	1st to 10th	Day	15% 10% 5% 7% 7% 4 5% 5% 4 6% 32%	2160
	11th to 20th	Day	19% 10% 3 6% 7% 4 6% 4 5% 6% 31%	2134
	21st to end	Day	21% 10% 3 6% 6% 2 5% 4 5% 6% 33%	2356
May	1st to 10th	Day	18% 8% 4 6% 6% 3 5% 4 4 6% 36%	2520
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 5% 6% 7% 38%	2479
	21st to end	Day	15% 7% 3 6% 5% 4 4 5% 6% 8% 38%	2725
June	1st to 10th	Day	11% 6% 2 5% 6% 3 5% 5% 6% 9% 43%	2520
	11th to 20th	Day	13% 6% 3 6% 6% 3 5% 5% 6% 7% 40%	2601
	21st to end	Day	13% 5% 2 5% 6% 4 5% 7% 8% 9% 37%	2700
July	1st to 10th	Day	7% 3 2 4 4 3 4 5% 6% 10% 50%	2642
	11th to 20th	Day	8% 6% 2 5% 6% 3 5% 6% 6% 10% 44%	2520
	21st to end	Day	6% 4 2 5% 5% 3 5% 5% 7% 9% 49%	2743
August	1st to 10th	Day	9% 5% 2 6% 6% 3 6% 5% 7% 9% 43%	2448
	11th to 20th	Day	11% 6% 3 5% 5% 3 5% 4 5% 8% 44%	2301
	21st to end	Day	11% 6% 2 5% 4 2 4 4 6% 8% 47%	2448
September	1st to 10th	Day	11% 5% 2 5% 4 4 5% 5% 6% 9% 45%	2160
	11th to 20th	Day	12% 6% 3 6% 5% 3 5% 5% 5% 7% 43%	2160
	21st to end	Day	17% 7% 4 5% 5% 3 4 4 4 7% 39%	1895
October	1st to 10th	Day	18% 8% 3 6% 6% 3 5% 4 5% 6% 36%	1800
	11th to 20th	Day	15% 12% 4 7% 7% 4 5% 4 4 7% 32%	1800
	21st to end	Day	19% 10% 3 7% 8% 4 5% 4 4 7% 30%	1864
November	1st to 10th	Day	12% 10% 5% 7% 7% 4 5% 6% 6% 6% 33%	1563
	11th to 20th	Day	14% 13% 7% 10% 8% 3 5% 5% 5% 6% 25%	1520
	21st to end	Day	15% 11% 5% 9% 6% 4 4 5% 5% 6% 29%	1520
December	1st to 10th	Day	11% 12% 6% 10% 9% 5% 7% 6% 5% 7% 23%	1520
	11th to 20th	Day	12% 15% 8% 9% 8% 5% 5% 6% 5% 6% 21%	1914
	21st to end	Day	27% 18% 5% 10% 6% 3 3 3 2 4 19%	2783
January	1st to 10th	Night	10% 9% 6% 8% 7% 4 6% 6% 6% 7% 33%	2648
	11th to 20th	Night	10% 12% 6% 12% 9% 4 5% 4 5% 7% 26%	2591
	21st to end	Night	10% 13% 8% 10% 7% 5% 5% 5% 6% 6% 26%	2686
February	1st to 10th	Night	6% 11% 6% 10% 7% 4 5% 4 4 6% 36%	2340
	11th to 20th	Night	7% 10% 4 9% 7% 3 5% 4 5% 6% 40%	2273
	21st to end	Night	13% 12% 5% 7% 6% 3 4 4 5% 6% 36%	1847
March	1st to 10th	Night	10% 11% 4 8% 6% 4 5% 5% 4 7% 37%	2109
	11th to 20th	Night	13% 9% 4 7% 5% 2 5% 4 4 5% 42%	1979
	21st to end	Night	16% 10% 4 7% 6% 2 4 4 5% 5% 36%	2104
April	1st to 10th	Night	17% 11% 4 7% 5% 3 4 4 5% 7% 33%	1800
	11th to 20th	Night	19% 10% 3 7% 5% 3 4 5% 4 7% 33%	1775
	21st to end	Night	21% 11% 3 5% 5% 3 4 4 5% 6% 33%	1602
May	1st to 10th	Night	15% 8% 4 6% 7% 3 4 4 5% 7% 36%	1440
	11th to 20th	Night	16% 6% 3 5% 6% 3 3 5% 6% 6% 42%	1416
	21st to end	Night	16% 5% 3 6% 6% 4 5% 5% 6% 9% 36%	1551
June	1st to 10th	Night	12% 6% 3 6% 5% 4 5% 5% 6% 9% 39%	1440
	11th to 20th	Night	13% 6% 3 5% 5% 3 5% 5% 6% 8% 40%	1351
	21st to end	Night	12% 7% 2 5% 6% 3 6% 6% 6% 8% 40%	1260
July	1st to 10th	Night	5% 4 2 4 4 2 4 6% 6% 10% 54%	1314
	11th to 20th	Night	7% 4 2 4 4 3 4 6% 6% 9% 51%	1440
	21st to end	Night	6% 4 1 3 4 2 4 5% 7% 9% 53%	1575
August	1st to 10th	Night	7% 5% 2 4 5% 3 4 4 6% 8% 51%	1489
	11th to 20th	Night	12% 6% 3 5% 4 2 3 4 4 7% 51%	1600
	21st to end	Night	13% 6% 2 4 4 3 3 4 5% 7% 48%	1908
September	1st to 10th	Night	10% 6% 2 4 4 3 5% 5% 4 7% 50%	1800
	11th to 20th	Night	10% 5% 2 4 4 3 4 4 4 8% 51%	1800
	21st to end	Night	17% 6% 3 5% 4 3 4 5% 6% 7% 39%	2046
October	1st to 10th	Night	16% 7% 2 6% 6% 3 4 4 5% 6% 39%	2160
	11th to 20th	Night	15% 9% 3 6% 6% 3 5% 5% 5% 7% 35%	2160
	21st to end	Night	19% 9% 3 7% 6% 3 5% 4 5% 6% 32%	2492
November	1st to 10th	Night	14% 8% 4 7% 6% 4 5% 5% 4 8% 36%	2512
	11th to 20th	Night	15% 10% 5% 8% 5% 3 5% 4 5% 7% 32%	2660
	21st to end	Night	13% 9% 4 6% 6% 4 5% 5% 5% 7% 36%	2660
December	1st to 10th	Night	10% 13% 6% 10% 7% 5% 6% 5% 5% 7% 26%	2660
	11th to 20th	Night	12% 15% 5% 10% 7% 4 5% 5% 5% 6% 25%	3283
	21st to end	Night	27% 18% 5% 6% 5% 2 3 3 3 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	36% 40% 8% 13% 3	1518
	11th to 20th	Day	41% 41% 9% 7% 2	1480
	21st to end	Day	39% 38% 7% 10% 5%	1667
February	1st to 10th	Day	32% 36% 10% 13% 8% 1	1620
	11th to 20th	Day	30% 37% 11% 15% 6% 1	1583
	21st to end	Day	32% 36% 11% 12% 7% 1	1408
March	1st to 10th	Day	34% 36% 12% 13% 4	1854
	11th to 20th	Day	30% 36% 14% 15% 5%	1980
	21st to end	Day	35% 37% 10% 14% 4	2251
April	1st to 10th	Day	34% 35% 7% 14% 9% 1	2160
	11th to 20th	Day	37% 34% 8% 12% 7% 1	2134
	21st to end	Day	35% 35% 9% 14% 6% 1	2356
May	1st to 10th	Day	34% 36% 8% 14% 7% 1	2520
	11th to 20th	Day	28% 37% 10% 17% 6% 2	2483
	21st to end	Day	29% 37% 9% 15% 9%	2725
June	1st to 10th	Day	27% 37% 11% 17% 8%	2520
	11th to 20th	Day	27% 36% 10% 16% 10% 1	2601
	21st to end	Day	26% 37% 12% 18% 7% 1	2700
July	1st to 10th	Day	19% 38% 9% 21% 12% 1	2571
	11th to 20th	Day	21% 38% 10% 19% 10% 1	2445
	21st to end	Day	21% 38% 12% 19% 9% 1	2591
August	1st to 10th	Day	24% 37% 9% 21% 7% 2	2433
	11th to 20th	Day	25% 35% 10% 19% 10%	2301
	21st to end	Day	22% 36% 9% 21% 11% 1	2448
September	1st to 10th	Day	22% 36% 13% 22% 6%	2160
	11th to 20th	Day	27% 35% 13% 20% 4	2160
	21st to end	Day	29% 36% 10% 20% 4	1895
October	1st to 10th	Day	31% 36% 11% 19% 4	1800
	11th to 20th	Day	39% 36% 10% 10% 4	1800
	21st to end	Day	36% 37% 9% 13% 5%	1864
November	1st to 10th	Day	32% 40% 8% 13% 6% 1	1563
	11th to 20th	Day	41% 39% 8% 10% 2	1520
	21st to end	Day	34% 41% 10% 12% 2 1	1520
December	1st to 10th	Day	38% 40% 11% 9% 1	1520
	11th to 20th	Day	46% 33% 8% 10% 3 1	1915
	21st to end	Day	58% 24% 5% 8% 4	2783
January	1st to 10th	Night	33% 40% 10% 14% 3	2648
	11th to 20th	Night	40% 42% 9% 8% 2	2591
	21st to end	Night	38% 37% 6% 12% 5%	2686
February	1st to 10th	Night	34% 35% 8% 14% 7% 1	2340
	11th to 20th	Night	30% 37% 9% 15% 8% 1	2274
	21st to end	Night	34% 35% 9% 16% 5% 1	1847
March	1st to 10th	Night	33% 37% 11% 13% 6% 1	2120
	11th to 20th	Night	29% 36% 10% 17% 7%	1980
	21st to end	Night	37% 35% 8% 14% 6% 1	2104
April	1st to 10th	Night	34% 36% 5% 12% 11% 1	1800
	11th to 20th	Night	35% 35% 7% 14% 9%	1775
	21st to end	Night	36% 35% 7% 15% 7%	1602
May	1st to 10th	Night	34% 35% 8% 13% 9% 1	1440
	11th to 20th	Night	27% 37% 7% 19% 9% 2	1417
	21st to end	Night	31% 38% 8% 14% 8% 1	1552
June	1st to 10th	Night	30% 37% 10% 17% 6% 1	1440
	11th to 20th	Night	24% 37% 9% 17% 11% 2	1351
	21st to end	Night	27% 37% 10% 16% 10%	1260
July	1st to 10th	Night	18% 38% 10% 19% 14% 1	1276
	11th to 20th	Night	20% 38% 8% 19% 12% 2	1392
	21st to end	Night	19% 38% 13% 19% 9% 2	1487
August	1st to 10th	Night	22% 36% 8% 24% 7% 3	1480
	11th to 20th	Night	22% 35% 10% 20% 11% 2	1600
	21st to end	Night	23% 36% 8% 19% 14% 1	1908
September	1st to 10th	Night	21% 36% 9% 24% 9%	1800
	11th to 20th	Night	22% 36% 11% 26% 5%	1800
	21st to end	Night	26% 37% 11% 20% 6%	2046
October	1st to 10th	Night	29% 36% 9% 20% 5% 1	2160
	11th to 20th	Night	36% 36% 9% 14% 4	2160
	21st to end	Night	33% 37% 9% 15% 5%	2492
November	1st to 10th	Night	31% 40% 9% 14% 5% 1	2512
	11th to 20th	Night	35% 39% 8% 12% 6%	2660
	21st to end	Night	30% 40% 12% 13% 4 1	2660
December	1st to 10th	Night	37% 40% 10% 10% 2	2660
	11th to 20th	Night	42% 34% 9% 12% 3	3281
	21st to end	Night	54% 25% 8% 11% 2	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	12% 6% 25% 37% 20% 1	270
	11th to 20th	Day	19% 8% 21% 35% 16%	255
	21st to end	Day	13% 3 27% 37% 16% 4	264
February	1st to 10th	Day	12% 8% 35% 39% 7%	240
	11th to 20th	Day	13% 7% 38% 29% 10% 3	240
	21st to end	Day	18% 6% 30% 40% 7%	198
March	1st to 10th	Day	12% 8% 27% 35% 17% 2	240
	11th to 20th	Day	14% 5% 26% 41% 9% 5%	240
	21st to end	Day	20% 7% 27% 30% 13% 4	337
April	1st to 10th	Day	21% 11% 25% 31% 10% 1	420
	11th to 20th	Day	26% 5% 20% 33% 14% 3	412
	21st to end	Day	23% 8% 26% 27% 14% 2	590
May	1st to 10th	Day	21% 8% 26% 31% 11% 3	603
	11th to 20th	Day	20% 8% 24% 28% 15% 5%	625
	21st to end	Day	18% 6% 22% 30% 20% 3	679
June	1st to 10th	Day	10% 6% 28% 35% 18% 4	630
	11th to 20th	Day	14% 6% 27% 37% 14% 2	630
	21st to end	Day	14% 5% 23% 32% 21% 5%	630
July	1st to 10th	Day	9% 3 20% 33% 26% 9%	621
	11th to 20th	Day	12% 5% 24% 31% 21% 8%	618
	21st to end	Day	7% 2 21% 39% 23% 8%	684
August	1st to 10th	Day	11% 3 19% 35% 27% 6%	626
	11th to 20th	Day	14% 4 17% 31% 28% 6%	615
	21st to end	Day	14% 6% 19% 30% 23% 7%	567
September	1st to 10th	Day	12% 4 20% 38% 22% 4	450
	11th to 20th	Day	14% 4 21% 35% 21% 4	450
	21st to end	Day	24% 9% 27% 24% 13% 3	315
October	1st to 10th	Day	22% 8% 22% 29% 14% 5%	270
	11th to 20th	Day	19% 10% 34% 25% 12% 1	270
	21st to end	Day	24% 8% 35% 26% 6% 1	297
November	1st to 10th	Day	18% 13% 29% 30% 10%	270
	11th to 20th	Day	17% 13% 32% 28% 10% 1	270
	21st to end	Day	17% 10% 28% 34% 10%	270
December	1st to 10th	Day	16% 8% 33% 32% 10% 1	270
	11th to 20th	Day	20% 11% 31% 28% 9%	270
	21st to end	Day	27% 9% 27% 29% 7% 1	297
January	1st to 10th	Night	13% 8% 32% 35% 11% 1	950
	11th to 20th	Night	16% 6% 34% 33% 10% 1	926
	21st to end	Night	17% 6% 34% 33% 9% 1	990
February	1st to 10th	Night	12% 7% 35% 37% 8% 1	900
	11th to 20th	Night	13% 5% 38% 32% 10% 1	879
	21st to end	Night	18% 5% 31% 35% 11% 1	663
March	1st to 10th	Night	16% 7% 29% 36% 11% 1	680
	11th to 20th	Night	19% 4 33% 34% 9% 1	540
	21st to end	Night	19% 7% 26% 33% 13% 3	594
April	1st to 10th	Night	23% 4 30% 33% 9% 1	540
	11th to 20th	Night	23% 7% 22% 37% 11% 1	533
	21st to end	Night	27% 5% 20% 33% 13% 2	540
May	1st to 10th	Night	18% 6% 31% 33% 11% 2	540
	11th to 20th	Night	19% 3 24% 35% 16% 2	531
	21st to end	Night	17% 5% 18% 38% 21% 1	584
June	1st to 10th	Night	14% 4 21% 41% 18% 1	540
	11th to 20th	Night	16% 3 21% 46% 14% 1	540
	21st to end	Night	15% 5% 17% 41% 20% 3	540
July	1st to 10th	Night	7% 2 15% 39% 32% 4	525
	11th to 20th	Night	9% 2 23% 36% 26% 3	522
	21st to end	Night	8% 2 17% 44% 26% 3	591
August	1st to 10th	Night	9% 3 16% 44% 25% 3	537
	11th to 20th	Night	14% 3 16% 33% 30% 4	534
	21st to end	Night	16% 5% 17% 34% 25% 3	594
September	1st to 10th	Night	12% 3 17% 41% 24% 3	540
	11th to 20th	Night	13% 5% 19% 37% 24% 2	540
	21st to end	Night	21% 6% 27% 29% 15% 2	652
October	1st to 10th	Night	20% 6% 25% 35% 13% 1	720
	11th to 20th	Night	20% 10% 32% 27% 10% 1	720
	21st to end	Night	25% 8% 30% 30% 8%	792
November	1st to 10th	Night	19% 9% 31% 32% 9%	846
	11th to 20th	Night	20% 11% 32% 26% 9% 1	950
	21st to end	Night	18% 9% 36% 30% 7%	950
December	1st to 10th	Night	16% 11% 32% 33% 7% 1	950
	11th to 20th	Night	20% 10% 35% 24% 9% 1	950
	21st to end	Night	28% 8% 30% 26% 7% 1	1045

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