Big Rapids
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Rapids clear sky chart from 2005-11-06 to 2025-10-04.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 33%	126316
	Night	14% 12% 4 10% 5% 5% 4 3 5% 6% 32%	123295
Transparency	Day	51% 3 10% 21% 13% 1	129829
	Night	53% 3 11% 21% 11% 1	127843
Seeing	Day	18% 15% 31% 22% 10% 3	17154
	Night	19% 12% 31% 28% 10% 1	26956

By Month

Percentage Cloud Cover SE (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	10% 20% 10% 23% 6% 5% 4 3 4 4 11%	3617
	11th to 20th	Day	11% 15% 8% 20% 15% 10% 8% 3 3 2 6%	3620
	21st to end	Day	14% 19% 11% 15% 7% 4 5% 4 3 4 14%	3982
February	1st to 10th	Day	12% 14% 7% 11% 11% 7% 7% 4 4 5% 18%	1784
	11th to 20th	Day	10% 16% 7% 16% 10% 6% 4 4 4 5% 18%	1948
	21st to end	Day	11% 18% 7% 12% 6% 5% 5% 4 5% 6% 21%	1650
March	1st to 10th	Day	12% 11% 4 11% 7% 5% 5% 4 4 6% 31%	4480
	11th to 20th	Day	12% 9% 6% 10% 5% 5% 5% 4 5% 8% 32%	4856
	21st to end	Day	21% 12% 7% 9% 5% 4 4 3 4 4 27%	5645
April	1st to 10th	Day	17% 15% 4 8% 5% 4 4 4 5% 6% 29%	2400
	11th to 20th	Day	18% 11% 3 7% 5% 4 4 3 4 6% 34%	2454
	21st to end	Day	16% 11% 3 8% 6% 4 4 4 6% 7% 33%	2600
May	1st to 10th	Day	18% 9% 2 7% 3 4 4 4 5% 7% 39%	5862
	11th to 20th	Day	13% 9% 2 7% 4 5% 5% 4 6% 7% 38%	5943
	21st to end	Day	14% 6% 3 7% 5% 4 5% 4 5% 7% 41%	6935
June	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 5% 8% 43%	2800
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 7% 8% 42%	2800
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 5% 6% 42%	2800
July	1st to 10th	Day	12% 6% 2 7% 4 5% 5% 4 7% 9% 39%	6360
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 47%	6360
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 6% 9% 46%	6924
August	1st to 10th	Day	10% 6% 3 6% 6% 5% 6% 5% 6% 8% 39%	4309
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 6% 7% 46%	4174
	21st to end	Day	9% 6% 2 6% 4 5% 5% 4 7% 8% 43%	4421
September	1st to 10th	Day	12% 5% 2 6% 5% 5% 6% 4 6% 9% 41%	2365
	11th to 20th	Day	11% 5% 2 5% 5% 5% 4 4 5% 7% 46%	2200
	21st to end	Day	14% 7% 3 7% 5% 5% 4 3 5% 7% 40%	2200
October	1st to 10th	Day	17% 8% 3 7% 4 4 4 3 4 6% 40%	2123
	11th to 20th	Day	21% 12% 3 7% 6% 6% 5% 3 4 6% 25%	1829
	21st to end	Day	21% 13% 3 9% 6% 5% 5% 4 5% 5% 23%	1881
November	1st to 10th	Day	14% 12% 4 8% 5% 4 4 3 5% 7% 33%	1762
	11th to 20th	Day	13% 19% 6% 12% 6% 6% 4 3 6% 5% 21%	1800
	21st to end	Day	20% 19% 7% 9% 5% 5% 3 2 4 5% 20%	1800
December	1st to 10th	Day	9% 23% 11% 16% 7% 5% 5% 3 4 4 12%	2642
	11th to 20th	Day	14% 22% 12% 13% 9% 5% 3 3 3 4 12%	3008
	21st to end	Day	24% 22% 7% 11% 5% 5% 4 3 3 4 12%	3982
January	1st to 10th	Night	10% 16% 10% 23% 7% 5% 4 3 4 4 14%	6348
	11th to 20th	Night	11% 16% 7% 20% 10% 12% 5% 3 4 4 8%	6360
	21st to end	Night	13% 19% 9% 17% 6% 5% 6% 4 4 5% 12%	6996
February	1st to 10th	Night	12% 16% 6% 12% 11% 6% 5% 4 4 5% 19%	2612
	11th to 20th	Night	12% 13% 6% 12% 9% 5% 6% 3 6% 5% 23%	2338
	21st to end	Night	14% 14% 5% 12% 6% 6% 4 3 5% 6% 25%	1980
March	1st to 10th	Night	16% 7% 4 8% 4 4 5% 3 5% 6% 36%	5373
	11th to 20th	Night	12% 10% 3 7% 4 4 4 3 6% 8% 40%	5103
	21st to end	Night	16% 14% 5% 8% 5% 4 4 3 5% 6% 31%	5312
April	1st to 10th	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 35%	2000
	11th to 20th	Night	19% 10% 3 6% 3 3 4 3 5% 7% 36%	1894
	21st to end	Night	18% 9% 3 7% 3 5% 4 3 6% 6% 37%	1800
May	1st to 10th	Night	15% 8% 3 6% 4 5% 4 3 6% 7% 38%	4033
	11th to 20th	Night	15% 9% 2 7% 4 4 4 3 5% 7% 40%	3953
	21st to end	Night	19% 7% 2 5% 3 3 3 2 4 6% 47%	3942
June	1st to 10th	Night	11% 7% 3 6% 5% 4 3 3 7% 9% 44%	1600
	11th to 20th	Night	11% 6% 2 7% 3 3 4 5% 7% 9% 43%	1600
	21st to end	Night	9% 5% 3 5% 5% 4 4 5% 5% 8% 47%	1600
July	1st to 10th	Night	9% 6% 2 7% 4 4 5% 4 6% 8% 45%	3618
	11th to 20th	Night	7% 5% 2 5% 3 4 4 3 5% 7% 55%	3617
	21st to end	Night	9% 6% 3 5% 4 4 4 3 5% 7% 52%	3947
August	1st to 10th	Night	10% 5% 2 6% 4 3 4 3 5% 10% 48%	2842
	11th to 20th	Night	12% 4 2 5% 4 3 4 3 5% 7% 50%	2875
	21st to end	Night	10% 5% 1 6% 4 4 4 4 5% 8% 49%	3474
September	1st to 10th	Night	9% 4 2 5% 4 5% 4 3 6% 6% 52%	2014
	11th to 20th	Night	11% 5% 1 5% 3 3 5% 3 4 7% 54%	2200
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 9% 42%	2200
October	1st to 10th	Night	17% 7% 2 5% 3 2 4 3 5% 6% 46%	2124
	11th to 20th	Night	19% 10% 3 7% 4 4 4 4 5% 7% 33%	2346
	21st to end	Night	22% 12% 4 6% 5% 5% 4 3 4 6% 31%	2717
November	1st to 10th	Night	12% 13% 3 8% 3 4 5% 4 5% 7% 36%	2536
	11th to 20th	Night	15% 15% 5% 11% 5% 4 5% 5% 5% 6% 24%	2600
	21st to end	Night	17% 17% 6% 10% 6% 5% 4 4 4 6% 22%	2600
December	1st to 10th	Night	11% 18% 7% 14% 7% 5% 5% 4 5% 7% 18%	4546
	11th to 20th	Night	16% 22% 7% 14% 8% 5% 4 3 4 5% 12%	5199
	21st to end	Night	24% 22% 6% 11% 5% 4 3 2 4 4 15%	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	78% 2 7% 10% 2	3618
	11th to 20th	Day	86% 3 4 6% 1	3620
	21st to end	Day	77% 1 9% 9% 3	3982
February	1st to 10th	Day	68% 4 7% 16% 5%	1784
	11th to 20th	Day	69% 3 7% 13% 7%	1958
	21st to end	Day	64% 3 10% 16% 6% 1	1650
March	1st to 10th	Day	55% 1 13% 18% 10% 2	4480
	11th to 20th	Day	52% 2 16% 18% 11% 1	4856
	21st to end	Day	61% 2 9% 16% 10% 1	5647
April	1st to 10th	Day	57% 3 9% 19% 12% 1	2400
	11th to 20th	Day	52% 2 9% 20% 14% 2	2454
	21st to end	Day	51% 3 11% 18% 14% 2	2600
May	1st to 10th	Day	47% 2 9% 22% 18% 2	5897
	11th to 20th	Day	46% 3 10% 23% 16% 2	5947
	21st to end	Day	44% 2 9% 23% 20% 2	6949
June	1st to 10th	Day	40% 3 10% 29% 17% 2	2800
	11th to 20th	Day	40% 3 13% 24% 19% 1	2800
	21st to end	Day	42% 4 12% 25% 16% 2	2800
July	1st to 10th	Day	40% 4 12% 26% 15% 2	6291
	11th to 20th	Day	34% 4 12% 31% 18% 1	6285
	21st to end	Day	33% 5% 13% 29% 19% 1	6728
August	1st to 10th	Day	41% 4 10% 29% 15% 1	4294
	11th to 20th	Day	37% 5% 11% 28% 18% 1	4213
	21st to end	Day	37% 5% 13% 28% 16% 1	4420
September	1st to 10th	Day	39% 4 13% 29% 13% 2	2365
	11th to 20th	Day	37% 3 12% 32% 16% 1	2200
	21st to end	Day	44% 3 12% 27% 14%	2200
October	1st to 10th	Day	33% 2 7% 34% 21% 3	3513
	11th to 20th	Day	48% 2 12% 25% 13%	3006
	21st to end	Day	56% 3 13% 20% 7%	3081
November	1st to 10th	Day	52% 3 11% 23% 10% 1	1762
	11th to 20th	Day	64% 3 12% 15% 6%	1800
	21st to end	Day	69% 2 12% 13% 4	1800
December	1st to 10th	Day	75% 4 9% 10% 1	2642
	11th to 20th	Day	77% 2 8% 11% 1	3005
	21st to end	Day	78% 2 6% 10% 4	3982
January	1st to 10th	Night	75% 3 7% 11% 5%	6348
	11th to 20th	Night	81% 2 7% 6% 4	6360
	21st to end	Night	75% 2 9% 10% 4	6996
February	1st to 10th	Night	68% 2 7% 15% 6% 1	2612
	11th to 20th	Night	63% 3 8% 17% 8% 1	2339
	21st to end	Night	61% 3 11% 17% 7% 1	1980
March	1st to 10th	Night	49% 2 15% 23% 10% 1	5373
	11th to 20th	Night	44% 2 18% 23% 12% 1	5103
	21st to end	Night	56% 2 10% 20% 11% 1	5312
April	1st to 10th	Night	51% 3 8% 23% 15% 1	2000
	11th to 20th	Night	49% 2 8% 22% 16% 2	1894
	21st to end	Night	48% 2 11% 22% 14% 3	1800
May	1st to 10th	Night	47% 2 11% 18% 17% 3	4060
	11th to 20th	Night	46% 2 9% 26% 15% 1	3954
	21st to end	Night	42% 2 7% 25% 20% 4	3950
June	1st to 10th	Night	37% 3 12% 29% 17% 2	1600
	11th to 20th	Night	37% 4 14% 24% 21% 1	1600
	21st to end	Night	35% 4 14% 29% 16% 2	1600
July	1st to 10th	Night	37% 4 12% 27% 14% 5%	3580
	11th to 20th	Night	30% 4 12% 31% 22% 1	3572
	21st to end	Night	33% 4 15% 26% 20% 2	3832
August	1st to 10th	Night	33% 4 13% 31% 18% 1	2833
	11th to 20th	Night	33% 3 13% 34% 16% 1	2902
	21st to end	Night	34% 4 12% 29% 19% 1	3474
September	1st to 10th	Night	33% 4 10% 33% 18% 2	2014
	11th to 20th	Night	31% 3 11% 37% 17% 1	2200
	21st to end	Night	41% 3 13% 29% 13% 1	2200
October	1st to 10th	Night	30% 3 10% 39% 17% 1	3514
	11th to 20th	Night	42% 4 12% 26% 17% 1	3895
	21st to end	Night	48% 2 11% 29% 10%	4467
November	1st to 10th	Night	48% 4 10% 24% 13% 1	2536
	11th to 20th	Night	60% 4 13% 16% 7% 1	2600
	21st to end	Night	64% 2 14% 16% 4 1	2600
December	1st to 10th	Night	66% 5% 15% 11% 2	4546
	11th to 20th	Night	76% 2 8% 10% 3	5201
	21st to end	Night	75% 2 9% 9% 7%	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	21% 17% 37% 19% 4 1	300
	11th to 20th	Day	25% 22% 37% 12% 4	300
	21st to end	Day	23% 20% 36% 17% 4	330
February	1st to 10th	Day	18% 28% 33% 17% 2 1	300
	11th to 20th	Day	21% 30% 35% 12% 2	300
	21st to end	Day	26% 31% 33% 9% 1	249
March	1st to 10th	Day	24% 24% 39% 10% 3	300
	11th to 20th	Day	24% 18% 29% 22% 6% 1	441
	21st to end	Day	27% 17% 32% 18% 5% 1	550
April	1st to 10th	Day	26% 20% 31% 18% 4 1	500
	11th to 20th	Day	28% 21% 30% 13% 6% 2	492
	21st to end	Day	24% 16% 30% 21% 8% 1	500
May	1st to 10th	Day	23% 18% 32% 18% 6% 3	503
	11th to 20th	Day	19% 14% 31% 23% 9% 3	557
	21st to end	Day	15% 14% 32% 25% 11% 3	789
June	1st to 10th	Day	13% 13% 38% 24% 9% 3	730
	11th to 20th	Day	15% 12% 34% 27% 8% 3	730
	21st to end	Day	14% 13% 35% 25% 10% 3	730
July	1st to 10th	Day	9% 9% 30% 30% 17% 5%	721
	11th to 20th	Day	8% 11% 30% 28% 16% 6%	718
	21st to end	Day	9% 7% 34% 28% 15% 7%	794
August	1st to 10th	Day	10% 8% 26% 25% 22% 9%	576
	11th to 20th	Day	13% 6% 21% 29% 21% 11%	519
	21st to end	Day	13% 7% 24% 30% 18% 8%	583
September	1st to 10th	Day	15% 10% 24% 25% 18% 8%	530
	11th to 20th	Day	9% 7% 22% 27% 26% 9%	530
	21st to end	Day	17% 13% 20% 28% 16% 5%	530
October	1st to 10th	Day	20% 14% 28% 22% 14% 2	502
	11th to 20th	Day	26% 17% 31% 20% 5%	390
	21st to end	Day	31% 20% 31% 13% 4 2	330
November	1st to 10th	Day	25% 20% 33% 17% 4 1	300
	11th to 20th	Day	23% 24% 38% 12% 3	300
	21st to end	Day	31% 21% 30% 14% 4	300
December	1st to 10th	Day	25% 26% 30% 14% 5%	300
	11th to 20th	Day	24% 24% 37% 13% 2	300
	21st to end	Day	29% 23% 32% 11% 3 1	330
January	1st to 10th	Night	20% 19% 34% 21% 5% 1	1000
	11th to 20th	Night	23% 16% 34% 22% 5%	1000
	21st to end	Night	20% 12% 35% 27% 6%	1100
February	1st to 10th	Night	18% 17% 36% 26% 3	847
	11th to 20th	Night	21% 15% 37% 22% 4	783
	21st to end	Night	23% 19% 36% 19% 2	660
March	1st to 10th	Night	19% 15% 35% 24% 7% 1	800
	11th to 20th	Night	18% 16% 36% 23% 6% 1	800
	21st to end	Night	21% 14% 33% 25% 6%	815
April	1st to 10th	Night	22% 14% 34% 25% 5% 1	600
	11th to 20th	Night	28% 12% 30% 24% 5% 1	593
	21st to end	Night	21% 14% 33% 25% 7% 1	600
May	1st to 10th	Night	16% 12% 35% 29% 7% 1	600
	11th to 20th	Night	18% 9% 33% 29% 10% 1	591
	21st to end	Night	14% 8% 31% 31% 16% 1	650
June	1st to 10th	Night	13% 9% 31% 34% 12% 1	600
	11th to 20th	Night	12% 7% 29% 38% 13% 1	600
	21st to end	Night	11% 5% 30% 40% 14% 1	600
July	1st to 10th	Night	7% 4 22% 42% 23% 3	585
	11th to 20th	Night	7% 6% 22% 42% 20% 2	582
	21st to end	Night	9% 3 25% 41% 21% 1	657
August	1st to 10th	Night	7% 3 22% 44% 21% 2	597
	11th to 20th	Night	10% 3 21% 39% 23% 4	594
	21st to end	Night	13% 4 20% 40% 21% 2	660
September	1st to 10th	Night	8% 6% 25% 36% 21% 4	614
	11th to 20th	Night	11% 6% 20% 36% 24% 4	800
	21st to end	Night	17% 9% 23% 31% 17% 3	800
October	1st to 10th	Night	20% 9% 25% 32% 14% 1	773
	11th to 20th	Night	24% 12% 30% 25% 7% 1	760
	21st to end	Night	29% 12% 31% 22% 6%	836
November	1st to 10th	Night	19% 15% 32% 26% 6% 1	780
	11th to 20th	Night	23% 16% 36% 20% 5%	800
	21st to end	Night	25% 15% 32% 24% 3	800
December	1st to 10th	Night	22% 18% 32% 24% 3	979
	11th to 20th	Night	26% 15% 37% 18% 4 1	1000
	21st to end	Night	31% 14% 35% 19% 2	1100

Page generated at 2025-10-01 01:39:06. Version ac07

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