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 2024-11-06.

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% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	102073
	Night	14% 10% 3 7% 5% 4 4 3 5% 7% 37%	97117
Transparency	Day	44% 9% 15% 22% 9% 1	105567
	Night	47% 8% 14% 21% 9% 1	101711
Seeing	Day	16% 8% 28% 31% 14% 3	16132
	Night	17% 8% 29% 31% 13% 1	26008

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	20% 7% 2 6% 4 4 4 3 4 6% 40%	4428
	11th to 20th	Day	17% 5% 2 6% 4 4 5% 4 5% 6% 42%	4399
	21st to end	Day	19% 8% 3 7% 5% 4 5% 4 6% 6% 34%	4837
June	1st to 10th	Day	11% 6% 2 5% 4 5% 5% 4 6% 8% 44%	2660
	11th to 20th	Day	16% 6% 2 6% 4 5% 4 4 7% 8% 39%	2711
	21st to end	Day	14% 5% 3 6% 5% 5% 4 5% 7% 9% 37%	2850
July	1st to 10th	Day	10% 5% 2 5% 4 4 4 4 8% 11% 44%	4578
	11th to 20th	Day	6% 4 1 4 4 4 4 4 7% 10% 52%	4440
	21st to end	Day	7% 4 2 5% 4 4 4 4 6% 10% 51%	4814
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 8% 43%	4370
	11th to 20th	Day	13% 4 1 5% 3 3 4 4 5% 9% 49%	4041
	21st to end	Day	14% 7% 2 7% 4 4 4 4 6% 7% 42%	4281
September	1st to 10th	Day	9% 5% 2 5% 5% 4 4 4 6% 8% 48%	2280
	11th to 20th	Day	13% 5% 2 6% 5% 4 5% 4 5% 7% 44%	2280
	21st to end	Day	16% 7% 2 6% 5% 3 5% 4 5% 6% 41%	2004
October	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 6% 6% 35%	1900
	11th to 20th	Day	16% 10% 4 7% 4 4 4 4 6% 7% 34%	1900
	21st to end	Day	21% 9% 3 8% 5% 5% 4 3 5% 5% 32%	1943
November	1st to 10th	Day	15% 10% 4 8% 5% 5% 6% 3 5% 7% 33%	1622
	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	19% 8% 2 5% 4 3 4 3 5% 7% 39%	2523
	11th to 20th	Night	14% 7% 2 5% 4 4 4 4 5% 6% 44%	2506
	21st to end	Night	19% 7% 3 7% 5% 5% 5% 5% 5% 6% 33%	2750
June	1st to 10th	Night	14% 6% 2 5% 4 5% 4 4 6% 9% 40%	1520
	11th to 20th	Night	14% 7% 2 6% 5% 4 5% 4 5% 8% 39%	1459
	21st to end	Night	12% 5% 2 6% 5% 4 5% 4 7% 8% 42%	1330
July	1st to 10th	Night	9% 5% 2 4 3 3 4 4 6% 10% 49%	2372
	11th to 20th	Night	5% 3 2 4 3 3 3 3 6% 8% 60%	2530
	21st to end	Night	7% 5% 2 4 3 3 3 3 6% 9% 55%	2750
August	1st to 10th	Night	11% 3 1 5% 4 4 4 3 6% 7% 49%	2567
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 6% 8% 49%	2798
	21st to end	Night	21% 6% 2 5% 4 3 4 3 5% 7% 41%	3378
September	1st to 10th	Night	9% 5% 2 5% 4 3 4 3 5% 7% 53%	1900
	11th to 20th	Night	13% 4 1 5% 3 4 4 4 6% 8% 49%	1900
	21st to end	Night	16% 6% 2 5% 4 4 4 3 6% 8% 43%	2154
October	1st to 10th	Night	17% 5% 2 6% 4 4 5% 3 5% 6% 43%	2280
	11th to 20th	Night	15% 8% 2 8% 4 5% 5% 4 5% 7% 36%	2280
	21st to end	Night	20% 8% 3 7% 5% 4 5% 4 5% 6% 33%	2655
November	1st to 10th	Night	15% 10% 3 6% 4 5% 4 4 7% 8% 34%	2578
	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	58% 7% 17% 14% 4	2528
	11th to 20th	Day	64% 10% 14% 10% 2	2530
	21st to end	Day	62% 11% 12% 11% 4	2879
February	1st to 10th	Day	49% 9% 17% 17% 7% 1	1710
	11th to 20th	Day	44% 8% 16% 23% 8% 1	1673
	21st to end	Day	47% 9% 13% 17% 12% 2	1510
March	1st to 10th	Day	43% 8% 14% 23% 10% 2	3179
	11th to 20th	Day	43% 9% 16% 20% 11%	3480
	21st to end	Day	52% 9% 12% 21% 6% 1	3973
April	1st to 10th	Day	49% 9% 11% 17% 12% 2	2280
	11th to 20th	Day	52% 7% 12% 18% 10% 2	2254
	21st to end	Day	50% 8% 11% 21% 10% 1	2494
May	1st to 10th	Day	44% 7% 13% 22% 13% 1	4440
	11th to 20th	Day	41% 9% 14% 26% 9% 2	4403
	21st to end	Day	47% 10% 13% 18% 12% 1	4837
June	1st to 10th	Day	35% 12% 17% 23% 12% 1	2660
	11th to 20th	Day	42% 8% 15% 21% 14%	2711
	21st to end	Day	41% 10% 16% 24% 8% 1	2850
July	1st to 10th	Day	33% 9% 21% 23% 13% 1	4509
	11th to 20th	Day	26% 9% 19% 33% 12% 1	4365
	21st to end	Day	27% 9% 17% 31% 14% 1	4662
August	1st to 10th	Day	36% 9% 17% 25% 11% 1	4355
	11th to 20th	Day	32% 9% 20% 30% 9%	4080
	21st to end	Day	40% 9% 17% 24% 10%	4280
September	1st to 10th	Day	33% 9% 19% 28% 10%	2280
	11th to 20th	Day	37% 11% 19% 26% 6%	2280
	21st to end	Day	43% 8% 14% 27% 7%	2004
October	1st to 10th	Day	37% 7% 18% 28% 9% 1	3160
	11th to 20th	Day	43% 6% 14% 25% 13%	3140
	21st to end	Day	51% 7% 16% 19% 6%	3181
November	1st to 10th	Day	51% 7% 12% 20% 8% 1	1622
	11th to 20th	Day	63% 6% 14% 12% 5%	1520
	21st to end	Day	57% 8% 15% 14% 5% 1	1520
December	1st to 10th	Day	61% 9% 17% 11% 2	1520
	11th to 20th	Day	66% 8% 11% 11% 4 1	1915
	21st to end	Day	71% 7% 9% 9% 4	2783
January	1st to 10th	Night	54% 11% 17% 13% 4	4428
	11th to 20th	Night	60% 13% 17% 9% 1	4440
	21st to end	Night	62% 8% 14% 14% 3	4786
February	1st to 10th	Night	50% 8% 15% 18% 8% 1	2470
	11th to 20th	Night	43% 7% 16% 22% 11% 1	2404
	21st to end	Night	48% 5% 14% 21% 10% 2	1943
March	1st to 10th	Night	40% 8% 15% 19% 16% 2	3703
	11th to 20th	Night	47% 8% 13% 22% 10%	3480
	21st to end	Night	60% 5% 8% 15% 11% 1	3644
April	1st to 10th	Night	51% 6% 10% 17% 16% 1	1900
	11th to 20th	Night	49% 7% 10% 21% 12% 1	1875
	21st to end	Night	50% 6% 9% 24% 11% 1	1680
May	1st to 10th	Night	43% 8% 14% 25% 9% 1	2530
	11th to 20th	Night	39% 9% 10% 24% 15% 3	2507
	21st to end	Night	48% 11% 12% 18% 10% 1	2751
June	1st to 10th	Night	40% 8% 16% 22% 12% 1	1520
	11th to 20th	Night	40% 8% 13% 21% 15% 2	1459
	21st to end	Night	39% 8% 13% 28% 12% 1	1330
July	1st to 10th	Night	31% 9% 21% 23% 16% 1	2333
	11th to 20th	Night	22% 7% 15% 43% 11% 2	2482
	21st to end	Night	26% 7% 14% 36% 14% 2	2662
August	1st to 10th	Night	33% 8% 15% 26% 15% 3	2558
	11th to 20th	Night	33% 7% 17% 34% 8% 1	2825
	21st to end	Night	43% 8% 14% 24% 10% 1	3378
September	1st to 10th	Night	31% 8% 16% 33% 11% 1	1900
	11th to 20th	Night	32% 9% 19% 31% 8%	1900
	21st to end	Night	40% 8% 15% 28% 9%	2154
October	1st to 10th	Night	31% 5% 11% 34% 18% 2	3800
	11th to 20th	Night	44% 6% 12% 24% 14%	3779
	21st to end	Night	52% 7% 14% 19% 8%	4367
November	1st to 10th	Night	48% 8% 14% 22% 7% 1	2578
	11th to 20th	Night	55% 10% 15% 13% 7%	2660
	21st to end	Night	49% 11% 18% 16% 5% 1	2660
December	1st to 10th	Night	61% 10% 14% 12% 3	2660
	11th to 20th	Night	61% 9% 15% 12% 3	3281
	21st to end	Night	68% 7% 10% 11% 3	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% 28% 32% 13% 3	675
	21st to end	Day	18% 7% 25% 32% 16% 2	734
June	1st to 10th	Day	10% 6% 29% 39% 13% 3	680
	11th to 20th	Day	14% 8% 27% 37% 12% 1	680
	21st to end	Day	15% 5% 23% 38% 17% 3	680
July	1st to 10th	Day	9% 2 19% 38% 25% 6%	671
	11th to 20th	Day	10% 5% 21% 35% 21% 8%	668
	21st to end	Day	7% 3 18% 42% 23% 7%	739
August	1st to 10th	Day	12% 4 18% 38% 24% 4	676
	11th to 20th	Day	13% 4 15% 34% 29% 5%	665
	21st to end	Day	17% 6% 19% 31% 23% 4	601
September	1st to 10th	Day	10% 4 22% 39% 21% 3	490
	11th to 20th	Day	15% 7% 23% 28% 23% 3	490
	21st to end	Day	22% 8% 25% 25% 16% 4	371
October	1st to 10th	Day	20% 6% 28% 30% 14% 2	300
	11th to 20th	Day	18% 15% 31% 28% 7% 1	300
	21st to end	Day	25% 11% 37% 23% 5%	330
November	1st to 10th	Day	21% 11% 34% 25% 9%	285
	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% 2	561
	21st to end	Night	17% 5% 19% 38% 20% 1	617
June	1st to 10th	Night	16% 4 21% 40% 18% 1	570
	11th to 20th	Night	19% 2 20% 42% 17% 1	570
	21st to end	Night	15% 3 18% 41% 21% 2	570
July	1st to 10th	Night	8% 2 15% 40% 32% 4	555
	11th to 20th	Night	9% 2 22% 37% 29% 3	552
	21st to end	Night	8% 2 15% 43% 28% 4	624
August	1st to 10th	Night	10% 3 15% 42% 28% 2	567
	11th to 20th	Night	14% 3 15% 35% 27% 5%	564
	21st to end	Night	18% 4 15% 35% 26% 3	627
September	1st to 10th	Night	12% 4 21% 35% 23% 4	570
	11th to 20th	Night	14% 4 21% 38% 21% 2	570
	21st to end	Night	19% 6% 24% 30% 18% 3	707
October	1st to 10th	Night	19% 8% 27% 31% 14% 1	760
	11th to 20th	Night	19% 9% 34% 27% 10% 1	760
	21st to end	Night	25% 10% 30% 28% 7%	836
November	1st to 10th	Night	19% 11% 31% 30% 8% 1	859
	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

Page generated at 2024-11-03 12:19:04. Version ac07

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