Grand Marais
Clear Sky Chart
History

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

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% 4 4 4 4 6% 7% 37%	101695
	Night	13% 10% 3 8% 5% 4 4 4 6% 7% 37%	97513
Transparency	Day	45% 8% 15% 22% 10% 1	105142
	Night	46% 8% 14% 22% 10% 1	102153
Seeing	Day	18% 15% 34% 23% 8% 2	16159
	Night	17% 13% 31% 27% 10% 1	26038

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	9% 14% 5% 11% 6% 4 4 3 5% 6% 32%	2527
	11th to 20th	Day	6% 9% 6% 18% 9% 6% 4 3 6% 7% 27%	2530
	21st to end	Day	8% 18% 10% 13% 6% 4 4 3 6% 6% 22%	2783
February	1st to 10th	Day	8% 11% 4 10% 6% 6% 5% 3 7% 7% 33%	1676
	11th to 20th	Day	9% 10% 4 9% 5% 5% 4 4 6% 8% 37%	1664
	21st to end	Day	8% 15% 5% 11% 5% 4 4 4 5% 5% 34%	1555
March	1st to 10th	Day	10% 9% 3 7% 4 5% 4 3 5% 6% 43%	3118
	11th to 20th	Day	8% 10% 4 9% 4 5% 5% 4 5% 8% 38%	3411
	21st to end	Day	19% 14% 4 9% 4 4 4 3 4 5% 31%	4064
April	1st to 10th	Day	13% 11% 3 7% 5% 5% 5% 4 7% 7% 33%	2280
	11th to 20th	Day	17% 12% 4 9% 5% 3 4 4 5% 6% 31%	2254
	21st to end	Day	20% 10% 3 7% 4 5% 3 3 5% 5% 34%	2521
May	1st to 10th	Day	18% 8% 3 6% 4 4 3 3 4 6% 41%	4428
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 4 5% 8% 40%	4399
	21st to end	Day	19% 7% 2 7% 4 5% 4 3 5% 7% 37%	4837
June	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 6% 9% 41%	2660
	11th to 20th	Day	15% 5% 2 6% 4 4 5% 4 6% 8% 40%	2660
	21st to end	Day	17% 7% 2 6% 4 4 5% 4 7% 8% 38%	2660
July	1st to 10th	Day	10% 4 2 6% 4 4 5% 5% 8% 11% 41%	4440
	11th to 20th	Day	8% 4 2 4 4 4 4 5% 7% 10% 49%	4440
	21st to end	Day	10% 4 1 5% 4 4 4 4 6% 10% 48%	4814
August	1st to 10th	Day	7% 5% 2 7% 5% 6% 6% 5% 8% 10% 39%	4423
	11th to 20th	Day	12% 4 1 4 3 4 4 4 6% 10% 47%	4164
	21st to end	Day	13% 5% 2 5% 3 4 5% 5% 7% 9% 42%	4212
September	1st to 10th	Day	10% 5% 2 6% 4 4 5% 3 6% 8% 47%	2280
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 9% 41%	2266
	21st to end	Day	15% 7% 3 6% 4 4 4 4 5% 8% 39%	2044
October	1st to 10th	Day	16% 7% 4 7% 5% 5% 4 4 6% 8% 34%	1900
	11th to 20th	Day	17% 12% 3 7% 4 5% 4 4 5% 6% 33%	1891
	21st to end	Day	22% 13% 4 6% 5% 3 4 3 4 5% 32%	1881
November	1st to 10th	Day	15% 13% 3 7% 5% 5% 5% 4 5% 6% 33%	1656
	11th to 20th	Day	16% 16% 5% 8% 5% 6% 3 4 5% 5% 27%	1520
	21st to end	Day	15% 12% 4 8% 4 5% 4 3 6% 7% 32%	1520
December	1st to 10th	Day	11% 14% 6% 9% 5% 5% 6% 4 7% 6% 27%	1520
	11th to 20th	Day	12% 16% 5% 11% 6% 4 3 4 6% 6% 27%	1914
	21st to end	Day	24% 23% 6% 7% 3 3 2 2 3 3 23%	2783
January	1st to 10th	Night	11% 14% 5% 8% 5% 3 4 3 5% 6% 37%	4428
	11th to 20th	Night	6% 9% 6% 18% 10% 6% 5% 4 7% 7% 22%	4440
	21st to end	Night	9% 18% 9% 11% 6% 5% 4 3 5% 6% 24%	4884
February	1st to 10th	Night	8% 12% 4 9% 6% 6% 4 4 7% 6% 34%	2502
	11th to 20th	Night	8% 9% 3 9% 4 5% 4 5% 6% 7% 38%	2403
	21st to end	Night	8% 14% 5% 9% 5% 4 4 3 6% 8% 33%	1899
March	1st to 10th	Night	9% 9% 2 8% 5% 5% 5% 4 5% 6% 41%	3722
	11th to 20th	Night	10% 12% 3 7% 5% 5% 5% 4 6% 7% 34%	3575
	21st to end	Night	18% 13% 3 8% 5% 4 4 4 4 5% 31%	3566
April	1st to 10th	Night	15% 11% 3 8% 5% 4 4 4 6% 5% 35%	1900
	11th to 20th	Night	17% 11% 2 8% 4 4 4 3 5% 6% 35%	1875
	21st to end	Night	20% 10% 3 6% 4 4 4 3 5% 5% 34%	1655
May	1st to 10th	Night	20% 6% 2 5% 4 4 4 3 5% 6% 41%	2523
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 6% 6% 43%	2506
	21st to end	Night	20% 6% 2 5% 5% 4 5% 3 6% 7% 36%	2750
June	1st to 10th	Night	14% 6% 3 5% 4 4 5% 4 6% 8% 41%	1520
	11th to 20th	Night	15% 6% 2 5% 4 4 4 5% 7% 7% 41%	1520
	21st to end	Night	15% 5% 2 5% 4 4 5% 3 8% 7% 44%	1520
July	1st to 10th	Night	8% 6% 2 5% 4 4 4 4 6% 9% 48%	2530
	11th to 20th	Night	6% 3 1 4 4 3 4 3 5% 7% 59%	2530
	21st to end	Night	8% 5% 1 5% 3 3 3 3 6% 9% 54%	2750
August	1st to 10th	Night	10% 4 2 5% 4 5% 5% 4 6% 8% 48%	2517
	11th to 20th	Night	12% 4 2 5% 4 3 4 4 6% 7% 50%	2672
	21st to end	Night	18% 5% 2 5% 3 3 3 3 4 7% 46%	3444
September	1st to 10th	Night	11% 4 2 5% 3 3 4 4 6% 6% 52%	1900
	11th to 20th	Night	12% 5% 2 6% 4 4 4 4 5% 6% 48%	1900
	21st to end	Night	17% 6% 2 5% 3 3 4 3 5% 8% 42%	2128
October	1st to 10th	Night	15% 8% 3 7% 4 4 5% 3 5% 6% 41%	2280
	11th to 20th	Night	16% 8% 3 5% 5% 4 4 3 5% 6% 39%	2289
	21st to end	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 33%	2717
November	1st to 10th	Night	16% 9% 3 8% 6% 5% 5% 3 7% 7% 33%	2521
	11th to 20th	Night	17% 14% 4 7% 5% 4 4 3 5% 6% 32%	2660
	21st to end	Night	14% 13% 4 7% 5% 4 3 3 6% 6% 33%	2660
December	1st to 10th	Night	11% 14% 5% 9% 5% 4 4 4 7% 8% 29%	2660
	11th to 20th	Night	11% 14% 5% 10% 5% 4 4 4 6% 7% 30%	3283
	21st to end	Night	23% 22% 6% 9% 3 3 2 2 3 3 23%	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	53% 8% 10% 21% 8%	2528
	11th to 20th	Day	57% 7% 9% 23% 4	2530
	21st to end	Day	62% 10% 10% 11% 6%	2783
February	1st to 10th	Day	48% 8% 12% 19% 11% 2	1676
	11th to 20th	Day	46% 6% 15% 21% 12% 1	1673
	21st to end	Day	50% 6% 14% 13% 15% 2	1555
March	1st to 10th	Day	41% 7% 15% 20% 15% 2	3120
	11th to 20th	Day	43% 9% 16% 17% 13% 1	3411
	21st to end	Day	56% 6% 9% 16% 12% 1	4064
April	1st to 10th	Day	50% 7% 12% 17% 12% 2	2280
	11th to 20th	Day	55% 6% 12% 17% 9% 1	2254
	21st to end	Day	52% 6% 10% 18% 12% 1	2521
May	1st to 10th	Day	43% 7% 15% 21% 13% 1	4440
	11th to 20th	Day	41% 9% 14% 25% 10% 1	4403
	21st to end	Day	46% 9% 12% 16% 16% 1	4837
June	1st to 10th	Day	39% 9% 17% 21% 13% 1	2660
	11th to 20th	Day	41% 8% 14% 24% 13%	2660
	21st to end	Day	42% 10% 16% 23% 9%	2660
July	1st to 10th	Day	36% 10% 19% 23% 12%	4371
	11th to 20th	Day	28% 8% 22% 34% 7%	4365
	21st to end	Day	31% 9% 18% 32% 9% 1	4662
August	1st to 10th	Day	37% 10% 19% 23% 10% 1	4408
	11th to 20th	Day	33% 8% 23% 28% 7%	4206
	21st to end	Day	36% 9% 20% 25% 9%	4211
September	1st to 10th	Day	36% 9% 17% 29% 9%	2280
	11th to 20th	Day	40% 9% 24% 22% 5% 1	2266
	21st to end	Day	45% 9% 16% 23% 7%	2044
October	1st to 10th	Day	39% 8% 14% 28% 10% 1	3160
	11th to 20th	Day	48% 6% 12% 25% 8%	3119
	21st to end	Day	54% 6% 15% 17% 7%	3081
November	1st to 10th	Day	53% 8% 15% 16% 7% 1	1656
	11th to 20th	Day	61% 7% 12% 15% 6%	1520
	21st to end	Day	52% 8% 18% 14% 7% 2	1520
December	1st to 10th	Day	54% 10% 14% 16% 5%	1520
	11th to 20th	Day	58% 7% 12% 12% 9% 3	1915
	21st to end	Day	68% 5% 7% 14% 5% 1	2783
January	1st to 10th	Night	48% 8% 16% 20% 7%	4428
	11th to 20th	Night	60% 8% 10% 18% 4	4440
	21st to end	Night	60% 9% 13% 13% 6%	4884
February	1st to 10th	Night	47% 8% 13% 19% 12% 1	2502
	11th to 20th	Night	43% 7% 15% 21% 12% 2	2404
	21st to end	Night	49% 7% 11% 18% 12% 2	1899
March	1st to 10th	Night	43% 7% 14% 15% 18% 3	3733
	11th to 20th	Night	46% 8% 15% 19% 10% 1	3576
	21st to end	Night	53% 7% 9% 15% 13% 2	3566
April	1st to 10th	Night	49% 7% 11% 17% 16% 1	1900
	11th to 20th	Night	50% 5% 11% 21% 12% 2	1875
	21st to end	Night	50% 6% 8% 20% 14% 1	1655
May	1st to 10th	Night	42% 7% 12% 25% 13%	2530
	11th to 20th	Night	40% 8% 13% 22% 13% 4	2507
	21st to end	Night	43% 11% 12% 21% 12% 2	2751
June	1st to 10th	Night	40% 9% 13% 22% 15% 2	1520
	11th to 20th	Night	40% 7% 13% 25% 15% 1	1520
	21st to end	Night	37% 9% 17% 25% 11% 1	1520
July	1st to 10th	Night	31% 8% 21% 24% 14% 1	2490
	11th to 20th	Night	23% 8% 21% 39% 9% 1	2482
	21st to end	Night	27% 7% 16% 37% 13% 1	2662
August	1st to 10th	Night	34% 7% 17% 29% 12% 1	2508
	11th to 20th	Night	32% 7% 19% 33% 8%	2696
	21st to end	Night	38% 7% 18% 28% 9%	3444
September	1st to 10th	Night	31% 9% 17% 32% 10% 1	1900
	11th to 20th	Night	34% 9% 22% 30% 5%	1900
	21st to end	Night	40% 8% 18% 26% 7% 1	2128
October	1st to 10th	Night	32% 7% 11% 32% 16% 1	3800
	11th to 20th	Night	44% 6% 13% 25% 13% 1	3800
	21st to end	Night	52% 7% 16% 18% 6%	4467
November	1st to 10th	Night	50% 10% 15% 18% 7%	2521
	11th to 20th	Night	53% 9% 15% 15% 7%	2660
	21st to end	Night	52% 8% 15% 16% 8% 1	2660
December	1st to 10th	Night	52% 9% 14% 20% 4	2660
	11th to 20th	Night	53% 8% 15% 16% 7%	3281
	21st to end	Night	69% 4 7% 14% 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	17% 17% 40% 19% 7%	270
	11th to 20th	Day	16% 17% 37% 22% 7% 1	270
	21st to end	Day	16% 19% 39% 21% 5%	297
February	1st to 10th	Day	14% 17% 48% 14% 6% 1	270
	11th to 20th	Day	14% 28% 40% 12% 5% 1	270
	21st to end	Day	18% 24% 43% 13% 2	225
March	1st to 10th	Day	12% 21% 43% 21% 3	270
	11th to 20th	Day	13% 23% 40% 18% 6%	270
	21st to end	Day	22% 18% 35% 17% 7% 1	444
April	1st to 10th	Day	20% 17% 35% 21% 6% 1	460
	11th to 20th	Day	25% 15% 26% 24% 9% 1	452
	21st to end	Day	27% 15% 29% 22% 7% 1	569
May	1st to 10th	Day	20% 19% 37% 18% 5% 2	653
	11th to 20th	Day	18% 14% 36% 23% 7% 2	675
	21st to end	Day	20% 12% 33% 25% 8% 2	734
June	1st to 10th	Day	14% 15% 35% 25% 7% 2	680
	11th to 20th	Day	18% 14% 37% 21% 9% 2	680
	21st to end	Day	19% 10% 33% 25% 10% 3	680
July	1st to 10th	Day	9% 8% 37% 31% 12% 4	671
	11th to 20th	Day	11% 11% 34% 27% 13% 4	668
	21st to end	Day	10% 7% 36% 30% 12% 5%	739
August	1st to 10th	Day	12% 9% 34% 32% 11% 2	676
	11th to 20th	Day	13% 8% 28% 35% 14% 3	665
	21st to end	Day	18% 11% 29% 27% 14% 2	558
September	1st to 10th	Day	14% 13% 28% 30% 14% 1	490
	11th to 20th	Day	15% 11% 32% 28% 11% 3	490
	21st to end	Day	20% 17% 30% 22% 11% 1	444
October	1st to 10th	Day	24% 18% 29% 18% 10% 1	300
	11th to 20th	Day	20% 23% 36% 18% 2	300
	21st to end	Day	31% 22% 33% 13% 1	330
November	1st to 10th	Day	21% 21% 34% 17% 6%	282
	11th to 20th	Day	27% 27% 31% 11% 3 1	270
	21st to end	Day	25% 23% 30% 17% 4	270
December	1st to 10th	Day	22% 18% 37% 18% 4	270
	11th to 20th	Day	22% 24% 38% 14% 2	270
	21st to end	Day	25% 19% 39% 14% 2 1	297
January	1st to 10th	Night	16% 18% 43% 19% 4	950
	11th to 20th	Night	15% 19% 41% 19% 5% 1	950
	21st to end	Night	18% 16% 37% 24% 5%	1045
February	1st to 10th	Night	15% 18% 38% 22% 6% 1	950
	11th to 20th	Night	13% 19% 36% 23% 8% 1	929
	21st to end	Night	15% 16% 37% 26% 5%	643
March	1st to 10th	Night	13% 16% 35% 28% 8% 1	760
	11th to 20th	Night	18% 14% 34% 27% 7% 1	627
	21st to end	Night	18% 13% 30% 26% 11% 3	627
April	1st to 10th	Night	18% 12% 33% 29% 6% 1	570
	11th to 20th	Night	20% 13% 27% 29% 10% 1	563
	21st to end	Night	23% 9% 25% 29% 12% 2	570
May	1st to 10th	Night	22% 10% 28% 29% 9% 2	570
	11th to 20th	Night	16% 9% 27% 32% 14% 3	561
	21st to end	Night	18% 9% 20% 37% 15% 1	617
June	1st to 10th	Night	16% 6% 24% 36% 15% 2	570
	11th to 20th	Night	17% 6% 24% 38% 14% 1	570
	21st to end	Night	17% 4 23% 37% 17% 2	570
July	1st to 10th	Night	8% 4 24% 44% 18% 2	555
	11th to 20th	Night	8% 5% 26% 40% 19% 2	552
	21st to end	Night	8% 3 26% 38% 23% 3	624
August	1st to 10th	Night	11% 3 28% 38% 19% 1	567
	11th to 20th	Night	12% 5% 20% 32% 28% 3	564
	21st to end	Night	15% 7% 21% 34% 20% 3	627
September	1st to 10th	Night	13% 5% 25% 35% 19% 3	570
	11th to 20th	Night	14% 5% 25% 35% 18% 2	570
	21st to end	Night	20% 10% 25% 31% 14% 1	755
October	1st to 10th	Night	20% 12% 30% 25% 12% 1	760
	11th to 20th	Night	20% 16% 33% 25% 6% 1	760
	21st to end	Night	24% 15% 31% 23% 7%	836
November	1st to 10th	Night	21% 15% 32% 25% 6% 1	811
	11th to 20th	Night	22% 18% 32% 20% 8% 1	950
	21st to end	Night	22% 20% 33% 20% 5%	950
December	1st to 10th	Night	16% 19% 39% 20% 5%	950
	11th to 20th	Night	19% 20% 35% 19% 6% 1	950
	21st to end	Night	27% 17% 34% 18% 5%	1045

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