Two Harbors
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Two Harbors clear sky chart from 2005-11-06 to 2024-05-13.

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% 5% 5% 4 6% 7% 36%	83743
	Night	13% 11% 4 8% 5% 4 4 3 5% 7% 36%	85792
Transparency	Day	33% 36% 10% 14% 7% 1	83449
	Night	35% 34% 10% 14% 6% 1	85621
Seeing	Day	16% 8% 28% 31% 14% 2	15366
	Night	18% 8% 30% 31% 13% 1	25431

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	11% 14% 6% 12% 6% 4 4 4 4 7% 28%	2527
	11th to 20th	Day	7% 13% 6% 13% 8% 7% 8% 6% 6% 7% 19%	2530
	21st to end	Day	6% 16% 7% 14% 7% 6% 6% 5% 5% 6% 21%	2879
February	1st to 10th	Day	8% 12% 5% 10% 6% 5% 5% 5% 6% 8% 31%	1710
	11th to 20th	Day	9% 11% 4 7% 5% 4 4 4 6% 6% 39%	1664
	21st to end	Day	7% 12% 4 8% 7% 5% 5% 4 6% 6% 36%	1510
March	1st to 10th	Day	11% 10% 3 7% 5% 5% 5% 4 5% 6% 40%	3177
	11th to 20th	Day	7% 10% 4 8% 5% 5% 5% 4 6% 7% 38%	3480
	21st to end	Day	19% 12% 4 9% 4 4 4 3 5% 6% 30%	3973
April	1st to 10th	Day	15% 10% 4 8% 5% 5% 5% 4 5% 5% 33%	2280
	11th to 20th	Day	18% 10% 3 8% 6% 5% 4 4 5% 6% 31%	2254
	21st to end	Day	21% 9% 3 7% 4 5% 4 3 5% 7% 32%	2494
May	1st to 10th	Day	17% 9% 2 8% 5% 5% 5% 3 5% 6% 36%	2660
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 4 6% 7% 39%	2510
	21st to end	Day	16% 7% 2 7% 5% 5% 5% 4 6% 8% 36%	2725
June	1st to 10th	Day	11% 5% 2 5% 5% 5% 5% 4 6% 9% 44%	2520
	11th to 20th	Day	15% 5% 2 6% 4 5% 4 4 7% 8% 40%	2568
	21st to end	Day	14% 5% 3 6% 5% 5% 4 5% 7% 10% 37%	2700
July	1st to 10th	Day	7% 4 1 5% 4 4 4 4 8% 10% 50%	2606
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 4 7% 9% 46%	2520
	21st to end	Day	6% 4 1 4 4 4 5% 4 7% 10% 51%	2743
August	1st to 10th	Day	9% 4 3 5% 5% 4 5% 4 7% 9% 45%	2482
	11th to 20th	Day	11% 4 2 6% 4 4 5% 5% 5% 8% 47%	2301
	21st to end	Day	12% 5% 2 6% 4 4 3 4 6% 7% 47%	2435
September	1st to 10th	Day	9% 5% 2 5% 5% 4 4 4 6% 8% 46%	2160
	11th to 20th	Day	14% 6% 2 6% 5% 4 5% 4 6% 7% 43%	2160
	21st to end	Day	17% 8% 2 6% 5% 3 5% 4 5% 6% 38%	1900
October	1st to 10th	Day	17% 7% 3 7% 5% 5% 6% 4 6% 6% 34%	1800
	11th to 20th	Day	16% 11% 4 8% 4 4 4 4 6% 7% 32%	1800
	21st to end	Day	21% 9% 3 8% 6% 5% 4 3 5% 5% 32%	1841
November	1st to 10th	Day	14% 10% 4 8% 4 5% 6% 3 5% 7% 34%	1577
	11th to 20th	Day	14% 13% 6% 11% 8% 5% 4 4 5% 5% 26%	1520
	21st to end	Day	14% 12% 5% 8% 7% 5% 5% 4 6% 6% 29%	1520
December	1st to 10th	Day	11% 13% 5% 11% 7% 6% 5% 5% 6% 6% 25%	1520
	11th to 20th	Day	14% 18% 7% 10% 6% 4 4 4 6% 5% 21%	1914
	21st to end	Day	27% 20% 4 9% 4 4 3 3 3 4 20%	2783
January	1st to 10th	Night	12% 14% 6% 9% 5% 4 4 3 6% 7% 30%	4428
	11th to 20th	Night	7% 12% 5% 14% 9% 7% 6% 4 6% 7% 23%	4440
	21st to end	Night	9% 21% 8% 12% 5% 5% 4 3 4 5% 25%	4786
February	1st to 10th	Night	7% 11% 5% 10% 6% 4 5% 4 6% 8% 34%	2470
	11th to 20th	Night	8% 9% 3 8% 6% 5% 4 4 6% 6% 41%	2403
	21st to end	Night	10% 13% 3 7% 6% 4 5% 3 5% 7% 36%	1943
March	1st to 10th	Night	8% 9% 3 7% 4 4 5% 3 5% 6% 44%	3692
	11th to 20th	Night	10% 9% 4 12% 5% 5% 4 4 5% 6% 36%	3479
	21st to end	Night	22% 14% 4 8% 5% 4 4 2 3 4 30%	3644
April	1st to 10th	Night	15% 12% 3 8% 5% 4 5% 3 5% 6% 34%	1900
	11th to 20th	Night	18% 10% 3 6% 5% 4 4 3 5% 6% 35%	1875
	21st to end	Night	20% 10% 3 6% 4 4 4 3 4 5% 35%	1680
May	1st to 10th	Night	17% 9% 3 6% 5% 4 4 3 5% 7% 37%	1520
	11th to 20th	Night	15% 8% 2 5% 5% 4 4 4 6% 6% 41%	1440
	21st to end	Night	17% 6% 2 6% 5% 5% 4 4 5% 8% 38%	1551
June	1st to 10th	Night	14% 6% 2 5% 4 5% 4 4 6% 9% 41%	1440
	11th to 20th	Night	13% 8% 2 6% 5% 5% 5% 4 5% 8% 39%	1383
	21st to end	Night	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	1260
July	1st to 10th	Night	8% 3 2 3 3 3 3 4 5% 9% 56%	1347
	11th to 20th	Night	8% 4 2 5% 5% 4 4 4 6% 8% 51%	1440
	21st to end	Night	6% 4 2 4 3 4 4 3 7% 9% 54%	1575
August	1st to 10th	Night	9% 3 1 5% 4 4 4 3 5% 8% 54%	1454
	11th to 20th	Night	12% 6% 2 6% 3 3 3 2 5% 8% 51%	1600
	21st to end	Night	16% 5% 2 4 3 3 3 3 4 7% 50%	1921
September	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 6% 52%	1800
	11th to 20th	Night	13% 5% 1 5% 3 4 4 4 6% 8% 49%	1800
	21st to end	Night	17% 6% 2 5% 4 4 4 3 6% 8% 40%	2039
October	1st to 10th	Night	18% 6% 3 6% 4 5% 5% 3 5% 6% 41%	2160
	11th to 20th	Night	16% 8% 3 8% 4 5% 5% 3 6% 8% 36%	2160
	21st to end	Night	20% 8% 3 7% 5% 4 5% 3 5% 6% 33%	2515
November	1st to 10th	Night	14% 9% 3 6% 4 5% 4 4 7% 8% 35%	2500
	11th to 20th	Night	16% 11% 4 7% 5% 5% 5% 4 6% 7% 31%	2660
	21st to end	Night	13% 11% 3 6% 4 4 5% 5% 6% 6% 35%	2660
December	1st to 10th	Night	11% 15% 5% 10% 7% 5% 4 5% 7% 7% 25%	2660
	11th to 20th	Night	12% 15% 5% 10% 6% 5% 5% 5% 6% 8% 23%	3283
	21st to end	Night	27% 20% 4 8% 4 2 2 2 3 5% 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	46% 26% 12% 11% 4	2528
	11th to 20th	Day	50% 29% 13% 7% 1	2530
	21st to end	Day	50% 27% 10% 9% 3	2879
February	1st to 10th	Day	33% 38% 11% 11% 6% 1	1710
	11th to 20th	Day	29% 38% 13% 13% 5% 1	1673
	21st to end	Day	33% 38% 10% 10% 7% 2	1510
March	1st to 10th	Day	36% 25% 11% 17% 10% 2	3179
	11th to 20th	Day	35% 25% 15% 15% 10%	3480
	21st to end	Day	45% 25% 8% 17% 5%	3973
April	1st to 10th	Day	34% 36% 7% 13% 8% 1	2280
	11th to 20th	Day	37% 35% 8% 12% 7% 1	2254
	21st to end	Day	35% 37% 8% 14% 6% 1	2494
May	1st to 10th	Day	34% 37% 7% 13% 8% 1	2660
	11th to 20th	Day	28% 38% 9% 15% 7% 2	2514
	21st to end	Day	29% 40% 9% 13% 9% 1	2725
June	1st to 10th	Day	24% 41% 12% 15% 8% 1	2520
	11th to 20th	Day	26% 38% 10% 15% 11% 1	2568
	21st to end	Day	26% 40% 11% 17% 6%	2700
July	1st to 10th	Day	17% 40% 11% 20% 11% 1	2537
	11th to 20th	Day	20% 40% 11% 18% 10% 1	2445
	21st to end	Day	19% 42% 10% 18% 9% 1	2591
August	1st to 10th	Day	24% 39% 9% 19% 7% 1	2467
	11th to 20th	Day	22% 39% 10% 19% 10%	2301
	21st to end	Day	22% 39% 8% 19% 11% 1	2435
September	1st to 10th	Day	22% 39% 11% 21% 6%	2160
	11th to 20th	Day	25% 40% 12% 19% 4	2160
	21st to end	Day	30% 38% 9% 19% 4	1900
October	1st to 10th	Day	31% 41% 9% 16% 4	1800
	11th to 20th	Day	36% 39% 11% 9% 4	1800
	21st to end	Day	35% 39% 8% 12% 5%	1841
November	1st to 10th	Day	31% 41% 7% 13% 6% 1	1577
	11th to 20th	Day	39% 41% 8% 9% 3	1520
	21st to end	Day	32% 43% 11% 11% 2 1	1520
December	1st to 10th	Day	37% 43% 12% 7% 2	1520
	11th to 20th	Day	46% 34% 7% 8% 3 1	1915
	21st to end	Day	56% 25% 7% 7% 4	2783
January	1st to 10th	Night	44% 29% 11% 12% 4	4428
	11th to 20th	Night	48% 30% 14% 6% 1	4440
	21st to end	Night	49% 25% 12% 11% 2	4786
February	1st to 10th	Night	34% 38% 11% 12% 5% 1	2470
	11th to 20th	Night	28% 37% 11% 15% 7% 1	2404
	21st to end	Night	34% 35% 10% 15% 5% 2	1943
March	1st to 10th	Night	33% 24% 13% 14% 14% 2	3703
	11th to 20th	Night	40% 23% 11% 18% 7% 1	3480
	21st to end	Night	52% 23% 6% 11% 8% 1	3644
April	1st to 10th	Night	36% 34% 6% 11% 12% 1	1900
	11th to 20th	Night	33% 34% 8% 16% 9%	1875
	21st to end	Night	36% 35% 6% 16% 7% 1	1680
May	1st to 10th	Night	34% 35% 9% 13% 8% 1	1520
	11th to 20th	Night	26% 39% 7% 17% 9% 2	1441
	21st to end	Night	30% 39% 6% 15% 8% 1	1552
June	1st to 10th	Night	28% 40% 11% 14% 7% 1	1440
	11th to 20th	Night	25% 37% 8% 17% 10% 2	1383
	21st to end	Night	26% 38% 9% 16% 10%	1260
July	1st to 10th	Night	18% 39% 10% 19% 14% 1	1308
	11th to 20th	Night	20% 40% 9% 17% 11% 3	1392
	21st to end	Night	19% 40% 11% 18% 10% 2	1487
August	1st to 10th	Night	21% 38% 8% 22% 8% 3	1445
	11th to 20th	Night	21% 37% 10% 20% 11% 1	1600
	21st to end	Night	21% 38% 9% 18% 14% 1	1921
September	1st to 10th	Night	20% 39% 8% 23% 10%	1800
	11th to 20th	Night	21% 39% 11% 24% 5%	1800
	21st to end	Night	26% 39% 11% 19% 6%	2039
October	1st to 10th	Night	29% 37% 9% 19% 5%	2160
	11th to 20th	Night	36% 37% 11% 12% 4 1	2160
	21st to end	Night	32% 39% 10% 13% 5%	2515
November	1st to 10th	Night	30% 42% 9% 13% 5% 1	2500
	11th to 20th	Night	35% 41% 9% 9% 5%	2660
	21st to end	Night	30% 43% 12% 11% 4 1	2660
December	1st to 10th	Night	37% 45% 9% 8% 2	2660
	11th to 20th	Night	41% 36% 11% 8% 4	3281
	21st to end	Night	54% 27% 7% 9% 4	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% 8% 39% 27% 10%	270
	11th to 20th	Day	16% 7% 40% 29% 9%	270
	21st to end	Day	12% 11% 36% 30% 9% 1	297
February	1st to 10th	Day	11% 12% 43% 27% 6% 1	270
	11th to 20th	Day	14% 16% 41% 18% 9% 1	270
	21st to end	Day	13% 13% 44% 28% 1	225
March	1st to 10th	Day	15% 11% 32% 33% 8% 1	270
	11th to 20th	Day	14% 8% 43% 24% 11% 1	270
	21st to end	Day	23% 9% 31% 26% 8% 2	392
April	1st to 10th	Day	18% 13% 35% 26% 7%	460
	11th to 20th	Day	23% 11% 25% 29% 11% 1	452
	21st to end	Day	24% 8% 27% 28% 11% 1	621
May	1st to 10th	Day	18% 11% 31% 29% 8% 2	653
	11th to 20th	Day	18% 6% 27% 32% 14% 3	637
	21st to end	Day	18% 6% 25% 33% 17% 2	679
June	1st to 10th	Day	10% 4 29% 39% 14% 3	630
	11th to 20th	Day	14% 8% 27% 37% 13% 1	630
	21st to end	Day	14% 4 24% 37% 18% 3	630
July	1st to 10th	Day	9% 2 20% 39% 24% 5%	621
	11th to 20th	Day	11% 5% 22% 36% 20% 6%	618
	21st to end	Day	7% 3 19% 43% 21% 7%	684
August	1st to 10th	Day	11% 4 19% 40% 23% 4	626
	11th to 20th	Day	13% 5% 16% 34% 28% 4	615
	21st to end	Day	17% 6% 19% 31% 24% 4	554
September	1st to 10th	Day	11% 4 24% 38% 20% 2	450
	11th to 20th	Day	16% 8% 25% 28% 20% 3	450
	21st to end	Day	24% 9% 28% 22% 14% 3	338
October	1st to 10th	Day	20% 6% 28% 30% 14% 2	270
	11th to 20th	Day	18% 16% 34% 24% 7% 1	270
	21st to end	Day	25% 12% 39% 21% 3	297
November	1st to 10th	Day	20% 11% 36% 24% 9%	270
	11th to 20th	Day	21% 14% 36% 23% 6%	270
	21st to end	Day	19% 15% 34% 26% 6%	270
December	1st to 10th	Day	16% 17% 34% 24% 7% 1	270
	11th to 20th	Day	21% 17% 38% 19% 4	270
	21st to end	Day	28% 13% 33% 21% 5%	297
January	1st to 10th	Night	15% 11% 37% 29% 7%	950
	11th to 20th	Night	17% 9% 42% 24% 8% 1	950
	21st to end	Night	17% 9% 39% 27% 7% 1	1045
February	1st to 10th	Night	13% 11% 39% 29% 7% 1	950
	11th to 20th	Night	13% 11% 39% 26% 10% 1	929
	21st to end	Night	17% 7% 37% 31% 7% 1	687
March	1st to 10th	Night	14% 9% 34% 34% 9% 1	743
	11th to 20th	Night	17% 8% 36% 28% 11% 1	570
	21st to end	Night	21% 6% 29% 29% 12% 3	627
April	1st to 10th	Night	21% 9% 34% 29% 7% 1	570
	11th to 20th	Night	24% 7% 25% 32% 11% 1	563
	21st to end	Night	25% 6% 23% 31% 13% 2	570
May	1st to 10th	Night	19% 6% 29% 34% 10% 2	570
	11th to 20th	Night	19% 4 25% 36% 14% 3	540
	21st to end	Night	17% 5% 19% 38% 21% 1	584
June	1st to 10th	Night	16% 3 21% 40% 19% 1	540
	11th to 20th	Night	18% 2 21% 41% 17% 1	540
	21st to end	Night	15% 3 18% 40% 21% 2	540
July	1st to 10th	Night	8% 2 16% 41% 31% 3	525
	11th to 20th	Night	9% 2 22% 38% 27% 1	522
	21st to end	Night	8% 2 16% 45% 26% 3	591
August	1st to 10th	Night	10% 2 16% 42% 27% 2	537
	11th to 20th	Night	14% 3 16% 35% 26% 5%	534
	21st to end	Night	17% 3 15% 36% 25% 3	594
September	1st to 10th	Night	12% 4 21% 36% 23% 4	540
	11th to 20th	Night	14% 4 21% 38% 20% 2	540
	21st to end	Night	20% 7% 25% 30% 16% 2	669
October	1st to 10th	Night	20% 8% 26% 31% 14% 1	720
	11th to 20th	Night	19% 9% 34% 26% 10% 1	720
	21st to end	Night	25% 10% 30% 28% 7%	792
November	1st to 10th	Night	19% 11% 32% 29% 8% 1	834
	11th to 20th	Night	20% 12% 34% 23% 10% 1	950
	21st to end	Night	18% 15% 36% 25% 7%	950
December	1st to 10th	Night	19% 13% 36% 26% 7%	950
	11th to 20th	Night	21% 13% 36% 21% 8%	950
	21st to end	Night	29% 11% 34% 21% 5% 1	1045

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