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 2025-11-03.

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 7% 5% 4 4 4 6% 7% 38%	127749
	Night	13% 10% 4 8% 5% 4 4 4 5% 7% 37%	122529
Transparency	Day	44% 8% 15% 22% 10% 1	131226
	Night	47% 8% 14% 21% 10% 1	127139
Seeing	Day	16% 8% 27% 32% 15% 3	17524
	Night	17% 8% 29% 31% 13% 1	27364

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% 11% 5% 12% 6% 4 4 3 4 7% 35%	3617
	11th to 20th	Day	6% 13% 7% 12% 8% 6% 7% 5% 7% 8% 22%	3589
	21st to end	Day	5% 15% 7% 14% 7% 6% 5% 4 6% 6% 24%	4120
February	1st to 10th	Day	8% 12% 5% 10% 6% 5% 6% 5% 6% 8% 31%	1800
	11th to 20th	Day	8% 11% 4 7% 5% 4 4 5% 6% 6% 39%	1754
	21st to end	Day	7% 11% 4 8% 7% 5% 5% 4 7% 6% 36%	1587
March	1st to 10th	Day	11% 8% 2 6% 5% 5% 4 4 5% 8% 42%	4565
	11th to 20th	Day	7% 10% 4 9% 5% 6% 5% 5% 6% 8% 36%	4980
	21st to end	Day	20% 11% 3 7% 4 4 4 3 4 5% 35%	5693
April	1st to 10th	Day	15% 10% 4 8% 5% 5% 5% 4 5% 5% 33%	2400
	11th to 20th	Day	17% 10% 3 8% 6% 5% 5% 4 5% 6% 31%	2374
	21st to end	Day	21% 9% 3 7% 4 5% 4 3 5% 7% 32%	2626
May	1st to 10th	Day	16% 6% 2 5% 4 3 4 3 4 6% 48%	6348
	11th to 20th	Day	15% 7% 2 6% 4 4 5% 3 5% 6% 42%	6319
	21st to end	Day	14% 8% 2 7% 5% 4 4 3 5% 6% 41%	6949
June	1st to 10th	Day	11% 6% 2 5% 4 5% 5% 4 6% 9% 44%	2800
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 4 6% 7% 38%	2854
	21st to end	Day	14% 5% 3 6% 5% 4 4 5% 7% 9% 37%	3000
July	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 45%	6562
	11th to 20th	Day	12% 4 2 4 3 4 4 4 6% 9% 49%	6360
	21st to end	Day	8% 4 2 5% 4 4 4 3 6% 10% 50%	6926
August	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 8% 43%	4508
	11th to 20th	Day	13% 4 1 5% 3 4 4 4 6% 9% 48%	4171
	21st to end	Day	13% 7% 2 7% 4 4 4 4 6% 7% 43%	4416
September	1st to 10th	Day	9% 5% 2 6% 5% 4 4 4 6% 8% 46%	2400
	11th to 20th	Day	14% 6% 2 6% 5% 4 5% 4 5% 7% 42%	2400
	21st to end	Day	16% 7% 2 6% 5% 3 5% 4 5% 6% 41%	2110
October	1st to 10th	Day	16% 6% 3 7% 5% 5% 5% 4 6% 6% 36%	2000
	11th to 20th	Day	16% 10% 4 7% 4 4 4 4 6% 7% 34%	2000
	21st to end	Day	20% 9% 3 8% 5% 5% 4 3 4 5% 33%	2045
November	1st to 10th	Day	15% 10% 3 8% 4 5% 6% 3 5% 7% 33%	1680
	11th to 20th	Day	14% 13% 6% 10% 8% 5% 4 4 5% 5% 26%	1600
	21st to end	Day	14% 12% 5% 8% 7% 5% 5% 4 6% 6% 29%	1600
December	1st to 10th	Day	11% 14% 5% 11% 8% 6% 5% 4 5% 5% 26%	2610
	11th to 20th	Day	13% 18% 5% 9% 5% 4 5% 4 6% 5% 26%	3004
	21st to end	Day	23% 20% 6% 14% 5% 4 3 2 3 3 17%	3982
January	1st to 10th	Night	8% 11% 5% 12% 7% 5% 5% 3 6% 6% 33%	6348
	11th to 20th	Night	7% 11% 5% 13% 7% 6% 6% 5% 6% 8% 26%	6316
	21st to end	Night	7% 17% 6% 12% 5% 5% 4 4 5% 6% 29%	6842
February	1st to 10th	Night	8% 12% 5% 10% 6% 5% 5% 4 6% 8% 33%	2600
	11th to 20th	Night	7% 9% 3 8% 6% 5% 5% 3 6% 6% 41%	2533
	21st to end	Night	10% 13% 4 7% 6% 5% 5% 4 5% 7% 36%	2042
March	1st to 10th	Night	9% 8% 3 6% 4 4 5% 3 5% 7% 47%	5318
	11th to 20th	Night	11% 10% 4 11% 5% 5% 5% 5% 5% 6% 32%	4979
	21st to end	Night	21% 13% 4 7% 5% 4 3 2 4 4 32%	5224
April	1st to 10th	Night	16% 12% 3 7% 5% 4 4 3 5% 6% 34%	2000
	11th to 20th	Night	18% 10% 4 6% 5% 3 4 3 4 6% 36%	1975
	21st to end	Night	21% 9% 3 6% 4 4 4 3 4 5% 36%	1768
May	1st to 10th	Night	16% 6% 2 5% 3 3 4 3 4 6% 48%	3613
	11th to 20th	Night	15% 6% 2 5% 4 4 4 3 5% 6% 45%	3596
	21st to end	Night	15% 7% 3 6% 5% 4 4 4 5% 7% 40%	3949
June	1st to 10th	Night	14% 6% 2 5% 5% 5% 4 4 6% 9% 41%	1600
	11th to 20th	Night	14% 8% 2 6% 5% 4 5% 4 5% 8% 39%	1536
	21st to end	Night	13% 6% 2 6% 5% 4 5% 4 7% 8% 42%	1400
July	1st to 10th	Night	9% 5% 2 5% 3 4 4 4 6% 9% 49%	3397
	11th to 20th	Night	11% 3 2 4 3 3 3 3 5% 7% 56%	3620
	21st to end	Night	10% 6% 2 6% 4 4 4 3 6% 8% 47%	3948
August	1st to 10th	Night	12% 4 1 5% 4 4 4 3 6% 7% 49%	2649
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 6% 8% 49%	2888
	21st to end	Night	20% 6% 2 5% 4 3 4 3 5% 7% 41%	3485
September	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 7% 52%	2000
	11th to 20th	Night	14% 5% 1 5% 3 4 4 4 6% 8% 47%	2000
	21st to end	Night	16% 6% 2 5% 4 4 4 3 6% 7% 43%	2267
October	1st to 10th	Night	16% 5% 3 6% 4 4 5% 3 5% 6% 43%	2400
	11th to 20th	Night	16% 8% 2 7% 4 5% 5% 4 5% 7% 37%	2400
	21st to end	Night	19% 9% 3 7% 5% 4 5% 4 5% 6% 33%	2795
November	1st to 10th	Night	15% 9% 3 6% 4 5% 4 4 7% 8% 34%	2662
	11th to 20th	Night	17% 11% 4 7% 5% 5% 5% 4 5% 7% 31%	2800
	21st to end	Night	13% 11% 4 7% 4 4 6% 5% 6% 6% 34%	2800
December	1st to 10th	Night	11% 14% 5% 11% 7% 5% 6% 5% 7% 7% 23%	4580
	11th to 20th	Night	12% 15% 5% 11% 5% 6% 5% 4 5% 6% 24%	5203
	21st to end	Night	25% 19% 6% 10% 3 2 3 3 3 5% 22%	6996

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	51% 6% 14% 17% 12%	3618
	11th to 20th	Day	60% 11% 12% 13% 4	3620
	21st to end	Day	59% 9% 11% 16% 5%	4120
February	1st to 10th	Day	50% 9% 17% 17% 7% 1	1800
	11th to 20th	Day	44% 7% 16% 23% 8% 1	1763
	21st to end	Day	46% 9% 14% 17% 11% 2	1587
March	1st to 10th	Day	40% 7% 17% 22% 11% 4	4567
	11th to 20th	Day	45% 8% 15% 19% 12% 1	4980
	21st to end	Day	50% 7% 11% 20% 11%	5693
April	1st to 10th	Day	50% 9% 10% 17% 12% 2	2400
	11th to 20th	Day	52% 7% 12% 18% 10% 2	2374
	21st to end	Day	50% 7% 11% 20% 10% 1	2626
May	1st to 10th	Day	37% 7% 14% 25% 16% 1	6357
	11th to 20th	Day	42% 9% 13% 22% 9% 5%	6323
	21st to end	Day	42% 8% 11% 24% 14% 1	6949
June	1st to 10th	Day	34% 12% 17% 24% 12% 1	2800
	11th to 20th	Day	43% 8% 15% 21% 13%	2854
	21st to end	Day	41% 10% 16% 23% 8% 1	3000
July	1st to 10th	Day	33% 9% 21% 28% 10%	6494
	11th to 20th	Day	30% 8% 21% 31% 10% 1	6285
	21st to end	Day	29% 9% 18% 31% 13% 1	6728
August	1st to 10th	Day	36% 9% 17% 25% 11% 1	4493
	11th to 20th	Day	32% 9% 20% 30% 8%	4210
	21st to end	Day	39% 9% 17% 25% 10%	4415
September	1st to 10th	Day	34% 9% 19% 28% 9%	2400
	11th to 20th	Day	38% 11% 19% 26% 6%	2400
	21st to end	Day	43% 8% 13% 27% 8%	2110
October	1st to 10th	Day	37% 7% 18% 29% 9% 1	3260
	11th to 20th	Day	43% 6% 13% 25% 13%	3240
	21st to end	Day	51% 7% 16% 20% 6%	3283
November	1st to 10th	Day	51% 7% 12% 20% 8% 1	1680
	11th to 20th	Day	62% 6% 14% 12% 5%	1600
	21st to end	Day	57% 8% 15% 14% 5% 1	1600
December	1st to 10th	Day	62% 9% 13% 15% 1	2610
	11th to 20th	Day	62% 7% 9% 8% 14%	3005
	21st to end	Day	73% 6% 9% 9% 3	3982
January	1st to 10th	Night	52% 9% 13% 13% 12%	6348
	11th to 20th	Night	57% 11% 17% 10% 5%	6360
	21st to end	Night	56% 9% 14% 16% 6%	6842
February	1st to 10th	Night	50% 8% 15% 18% 8% 1	2600
	11th to 20th	Night	44% 7% 16% 22% 11% 1	2534
	21st to end	Night	48% 6% 14% 21% 9% 2	2042
March	1st to 10th	Night	37% 6% 15% 18% 18% 6%	5329
	11th to 20th	Night	52% 7% 12% 19% 9%	4980
	21st to end	Night	57% 5% 8% 15% 14% 1	5224
April	1st to 10th	Night	51% 6% 9% 17% 15% 1	2000
	11th to 20th	Night	49% 7% 11% 21% 12% 1	1975
	21st to end	Night	50% 6% 9% 24% 11% 1	1768
May	1st to 10th	Night	36% 7% 14% 30% 13%	3620
	11th to 20th	Night	39% 8% 10% 23% 15% 6%	3597
	21st to end	Night	42% 9% 10% 25% 12% 1	3950
June	1st to 10th	Night	41% 8% 15% 23% 12% 2	1600
	11th to 20th	Night	41% 8% 13% 22% 14% 2	1536
	21st to end	Night	40% 8% 12% 28% 12% 1	1400
July	1st to 10th	Night	32% 8% 19% 27% 13% 1	3358
	11th to 20th	Night	28% 7% 18% 38% 9% 1	3572
	21st to end	Night	35% 7% 14% 30% 12% 1	3832
August	1st to 10th	Night	34% 8% 14% 26% 15% 2	2640
	11th to 20th	Night	34% 7% 16% 34% 8% 1	2915
	21st to end	Night	43% 8% 14% 25% 10% 1	3485
September	1st to 10th	Night	32% 8% 16% 32% 11% 1	2000
	11th to 20th	Night	34% 9% 19% 30% 8%	2000
	21st to end	Night	40% 8% 14% 28% 10%	2267
October	1st to 10th	Night	31% 5% 11% 34% 18% 2	3920
	11th to 20th	Night	43% 5% 12% 25% 14%	3899
	21st to end	Night	52% 7% 14% 19% 9%	4507
November	1st to 10th	Night	48% 8% 14% 22% 7% 1	2662
	11th to 20th	Night	55% 10% 15% 13% 7%	2800
	21st to end	Night	50% 11% 18% 16% 5% 1	2800
December	1st to 10th	Night	62% 10% 15% 11% 2	4580
	11th to 20th	Night	62% 8% 14% 11% 5%	5201
	21st to end	Night	68% 6% 9% 13% 4	6996

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	14% 7% 37% 29% 12%	300
	11th to 20th	Day	15% 7% 38% 29% 11%	300
	21st to end	Day	13% 10% 38% 29% 9% 1	330
February	1st to 10th	Day	10% 12% 41% 29% 6% 1	300
	11th to 20th	Day	13% 15% 40% 21% 10% 1	300
	21st to end	Day	12% 12% 44% 30% 2	249
March	1st to 10th	Day	15% 11% 33% 32% 9% 1	300
	11th to 20th	Day	14% 8% 42% 26% 10% 1	300
	21st to end	Day	24% 9% 29% 27% 8% 2	430
April	1st to 10th	Day	18% 13% 34% 27% 7%	500
	11th to 20th	Day	22% 11% 26% 30% 11% 1	492
	21st to end	Day	24% 7% 26% 30% 11% 1	670
May	1st to 10th	Day	17% 10% 30% 29% 11% 3	703
	11th to 20th	Day	18% 6% 27% 31% 14% 3	725
	21st to end	Day	18% 6% 24% 34% 16% 2	789
June	1st to 10th	Day	11% 6% 28% 38% 15% 3	730
	11th to 20th	Day	15% 8% 25% 38% 12% 1	730
	21st to end	Day	15% 4 22% 39% 17% 3	730
July	1st to 10th	Day	9% 2 18% 38% 26% 6%	721
	11th to 20th	Day	10% 5% 20% 36% 22% 8%	718
	21st to end	Day	7% 3 17% 43% 23% 7%	794
August	1st to 10th	Day	12% 4 18% 37% 25% 4	726
	11th to 20th	Day	14% 4 15% 34% 29% 4	715
	21st to end	Day	16% 6% 18% 31% 25% 4	648
September	1st to 10th	Day	11% 4 22% 38% 20% 5%	530
	11th to 20th	Day	17% 7% 22% 28% 23% 3	530
	21st to end	Day	21% 7% 24% 24% 19% 4	405
October	1st to 10th	Day	18% 6% 27% 31% 15% 3	330
	11th to 20th	Day	18% 15% 31% 28% 7% 1	330
	21st to end	Day	23% 10% 35% 24% 6% 1	363
November	1st to 10th	Day	21% 10% 33% 25% 9% 1	306
	11th to 20th	Day	20% 14% 35% 24% 7%	300
	21st to end	Day	19% 14% 32% 28% 7%	300
December	1st to 10th	Day	15% 16% 34% 25% 8% 2	300
	11th to 20th	Day	20% 16% 38% 22% 4	300
	21st to end	Day	28% 12% 30% 23% 7%	330
January	1st to 10th	Night	15% 11% 37% 29% 8%	1000
	11th to 20th	Night	16% 9% 41% 25% 8% 1	1000
	21st to end	Night	17% 9% 39% 28% 6% 1	1100
February	1st to 10th	Night	13% 11% 39% 29% 7% 1	1000
	11th to 20th	Night	12% 10% 39% 27% 10% 1	979
	21st to end	Night	16% 7% 37% 31% 8% 1	722
March	1st to 10th	Night	14% 9% 34% 34% 8% 1	782
	11th to 20th	Night	17% 8% 36% 29% 10% 1	600
	21st to end	Night	21% 6% 29% 30% 12% 3	660
April	1st to 10th	Night	22% 8% 33% 29% 7% 1	600
	11th to 20th	Night	24% 7% 24% 32% 12% 1	593
	21st to end	Night	26% 6% 22% 32% 13% 2	600
May	1st to 10th	Night	19% 6% 28% 35% 11% 3	600
	11th to 20th	Night	18% 4 25% 36% 15% 2	591
	21st to end	Night	17% 5% 19% 38% 20% 1	650
June	1st to 10th	Night	16% 4 21% 40% 19% 1	600
	11th to 20th	Night	19% 2 20% 42% 17% 1	600
	21st to end	Night	16% 3 17% 41% 21% 2	600
July	1st to 10th	Night	8% 2 14% 39% 32% 4	585
	11th to 20th	Night	10% 2 20% 37% 29% 2	582
	21st to end	Night	8% 2 15% 43% 29% 4	657
August	1st to 10th	Night	11% 3 15% 41% 28% 3	597
	11th to 20th	Night	14% 3 15% 35% 27% 5%	594
	21st to end	Night	17% 3 15% 36% 26% 3	660
September	1st to 10th	Night	12% 4 21% 35% 23% 5%	600
	11th to 20th	Night	15% 4 20% 38% 21% 3	600
	21st to end	Night	19% 6% 23% 29% 19% 4	744
October	1st to 10th	Night	18% 8% 27% 32% 15% 1	800
	11th to 20th	Night	19% 9% 33% 28% 10% 1	800
	21st to end	Night	24% 10% 29% 28% 8%	880
November	1st to 10th	Night	20% 11% 31% 30% 8% 1	888
	11th to 20th	Night	20% 12% 33% 23% 10% 1	1000
	21st to end	Night	18% 14% 35% 25% 7%	1000
December	1st to 10th	Night	19% 13% 35% 26% 7%	1000
	11th to 20th	Night	21% 13% 36% 21% 8%	1000
	21st to end	Night	29% 10% 33% 21% 6% 1	1100

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