Marshfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marshfield clear sky chart from 2005-11-06 to 2025-03-27.

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	12% 8% 3 6% 4 4 4 3 5% 7% 44%	109010
	Night	12% 8% 3 6% 4 3 4 3 5% 6% 47%	110515
Transparency	Day	38% 6% 11% 24% 17% 4	112659
	Night	37% 6% 11% 24% 19% 4	115006
Seeing	Day	15% 13% 28% 26% 14% 3	15979
	Night	16% 13% 32% 27% 11% 1	25982

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	16% 11% 3 6% 5% 4 3 3 4 4 41%	4077
	11th to 20th	Day	7% 11% 5% 7% 4 4 4 3 4 5% 45%	4080
	21st to end	Day	17% 9% 3 8% 3 3 3 2 4 5% 41%	4488
February	1st to 10th	Day	15% 11% 4 8% 5% 5% 4 4 4 6% 34%	1800
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 3 4 5% 40%	1799
	21st to end	Day	14% 11% 3 6% 4 5% 4 3 5% 6% 40%	1692
March	1st to 10th	Day	14% 10% 4 6% 3 3 4 3 4 6% 45%	3546
	11th to 20th	Day	12% 8% 2 5% 3 3 3 3 4 7% 51%	3590
	21st to end	Day	16% 10% 4 7% 5% 5% 5% 4 5% 6% 34%	3880
April	1st to 10th	Day	11% 8% 3 6% 4 4 4 3 5% 7% 45%	2270
	11th to 20th	Day	15% 9% 3 6% 5% 4 4 3 5% 6% 40%	2254
	21st to end	Day	19% 8% 3 7% 4 4 4 4 5% 5% 36%	2280
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 6% 35%	3976
	11th to 20th	Day	14% 7% 3 6% 4 4 4 4 6% 7% 41%	4082
	21st to end	Day	13% 6% 2 6% 4 5% 5% 5% 5% 8% 40%	4746
June	1st to 10th	Day	9% 5% 2 6% 4 5% 4 4 6% 11% 45%	2660
	11th to 20th	Day	7% 4 2 5% 4 5% 4 4 7% 10% 48%	2660
	21st to end	Day	6% 4 1 4 4 4 5% 4 6% 9% 52%	2660
July	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 6% 10% 41%	4254
	11th to 20th	Day	6% 4 1 6% 5% 5% 5% 5% 7% 9% 47%	4120
	21st to end	Day	8% 5% 2 7% 6% 6% 6% 5% 9% 11% 37%	4465
August	1st to 10th	Day	5% 4 2 4 4 4 4 3 6% 9% 56%	4104
	11th to 20th	Day	10% 5% 2 7% 5% 4 4 4 6% 9% 46%	3896
	21st to end	Day	6% 4 2 5% 4 4 4 3 6% 9% 52%	4180
September	1st to 10th	Day	12% 4 2 4 5% 4 4 3 5% 8% 50%	2280
	11th to 20th	Day	10% 6% 3 7% 5% 5% 5% 3 4 6% 46%	2252
	21st to end	Day	8% 5% 1 5% 4 4 5% 4 6% 6% 51%	1995
October	1st to 10th	Day	10% 4 1 5% 3 4 3 3 4 7% 56%	1900
	11th to 20th	Day	12% 6% 2 5% 4 3 3 2 4 5% 54%	1900
	21st to end	Day	17% 7% 2 6% 3 3 3 3 4 6% 47%	2090
November	1st to 10th	Day	11% 6% 2 6% 3 3 3 2 3 5% 56%	1958
	11th to 20th	Day	13% 7% 3 5% 4 3 2 3 5% 8% 48%	1830
	21st to end	Day	14% 9% 3 6% 3 3 2 3 4 6% 48%	1600
December	1st to 10th	Day	10% 9% 3 6% 3 3 3 3 4 5% 52%	2610
	11th to 20th	Day	9% 11% 5% 7% 4 3 3 3 3 5% 47%	3008
	21st to end	Day	17% 19% 6% 10% 5% 4 4 3 4 4 27%	4028
January	1st to 10th	Night	14% 10% 5% 12% 6% 5% 4 3 4 4 34%	5888
	11th to 20th	Night	9% 8% 3 10% 7% 4 4 3 4 4 43%	5900
	21st to end	Night	15% 11% 4 8% 3 3 3 2 3 4 42%	6490
February	1st to 10th	Night	15% 10% 3 7% 4 3 3 3 4 6% 40%	2600
	11th to 20th	Night	14% 9% 3 8% 5% 3 3 2 5% 5% 43%	2485
	21st to end	Night	13% 9% 3 6% 6% 3 4 3 5% 5% 43%	1955
March	1st to 10th	Night	16% 10% 3 6% 3 3 3 2 4 5% 45%	3529
	11th to 20th	Night	12% 8% 2 5% 3 3 4 3 5% 5% 51%	3590
	21st to end	Night	13% 9% 4 8% 5% 4 5% 4 5% 6% 38%	3889
April	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 5% 8% 51%	1910
	11th to 20th	Night	12% 8% 2 6% 3 3 4 3 5% 8% 45%	1875
	21st to end	Night	17% 7% 3 7% 4 4 3 4 6% 6% 40%	1900
May	1st to 10th	Night	14% 8% 2 6% 5% 3 3 3 5% 7% 44%	2923
	11th to 20th	Night	13% 9% 3 7% 5% 3 4 3 5% 8% 40%	2823
	21st to end	Night	12% 7% 3 6% 4 4 4 4 6% 8% 41%	2819
June	1st to 10th	Night	8% 5% 1 5% 3 3 3 4 6% 9% 52%	1520
	11th to 20th	Night	4 4 1 3 4 3 4 4 6% 11% 55%	1520
	21st to end	Night	3 2 1 3 3 3 4 3 5% 9% 65%	1520
July	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 6% 8% 48%	2711
	11th to 20th	Night	4 3 2 4 3 3 4 3 6% 9% 60%	2850
	21st to end	Night	6% 5% 2 5% 4 4 4 4 6% 10% 50%	3098
August	1st to 10th	Night	4 3 1 4 3 4 3 3 5% 8% 62%	2836
	11th to 20th	Night	9% 4 2 6% 4 4 4 3 5% 8% 50%	2936
	21st to end	Night	5% 3 1 4 3 3 3 3 5% 8% 61%	3476
September	1st to 10th	Night	9% 4 2 4 4 4 3 3 4 6% 56%	1900
	11th to 20th	Night	9% 4 2 5% 3 4 3 3 5% 7% 53%	1924
	21st to end	Night	9% 4 2 4 4 3 3 3 4 7% 58%	2166
October	1st to 10th	Night	7% 4 1 3 3 2 3 3 4 7% 61%	2280
	11th to 20th	Night	13% 5% 1 4 3 2 3 3 4 5% 55%	2280
	21st to end	Night	15% 7% 2 5% 3 2 3 3 4 6% 49%	2508
November	1st to 10th	Night	11% 6% 1 4 3 2 3 2 4 5% 58%	2340
	11th to 20th	Night	12% 7% 2 6% 3 3 3 3 5% 6% 51%	2566
	21st to end	Night	14% 8% 3 6% 3 3 3 3 4 5% 48%	2797
December	1st to 10th	Night	10% 9% 3 6% 4 3 3 3 4 6% 49%	4580
	11th to 20th	Night	14% 8% 4 7% 4 3 3 3 4 5% 46%	5199
	21st to end	Night	20% 17% 5% 8% 4 4 3 3 4 4 28%	6932

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	47% 4 9% 21% 17% 2	4078
	11th to 20th	Day	41% 4 7% 26% 16% 6%	4080
	21st to end	Day	47% 3 8% 16% 15% 11%	4488
February	1st to 10th	Day	51% 5% 11% 20% 12% 1	1800
	11th to 20th	Day	47% 4 10% 19% 16% 4	1808
	21st to end	Day	45% 4 8% 22% 16% 6%	1692
March	1st to 10th	Day	40% 6% 9% 20% 17% 9%	3546
	11th to 20th	Day	34% 6% 10% 28% 16% 8%	3590
	21st to end	Day	49% 8% 13% 19% 10% 1	3880
April	1st to 10th	Day	39% 6% 12% 22% 19% 2	2270
	11th to 20th	Day	44% 6% 11% 20% 15% 3	2254
	21st to end	Day	49% 7% 9% 23% 11% 1	2280
May	1st to 10th	Day	47% 9% 11% 19% 13% 1	4012
	11th to 20th	Day	40% 10% 14% 24% 12%	4086
	21st to end	Day	38% 11% 12% 24% 14% 1	4759
June	1st to 10th	Day	32% 9% 17% 25% 15% 1	2660
	11th to 20th	Day	29% 8% 15% 31% 14% 2	2660
	21st to end	Day	26% 9% 17% 28% 16% 4	2660
July	1st to 10th	Day	37% 8% 16% 25% 12% 2	4190
	11th to 20th	Day	30% 8% 14% 31% 17% 2	4051
	21st to end	Day	37% 9% 20% 24% 8% 1	4325
August	1st to 10th	Day	25% 6% 18% 28% 21% 1	4090
	11th to 20th	Day	37% 7% 14% 28% 14% 1	3935
	21st to end	Day	28% 6% 14% 34% 14% 4	4179
September	1st to 10th	Day	32% 7% 13% 24% 15% 8%	2280
	11th to 20th	Day	37% 7% 9% 22% 23% 1	2252
	21st to end	Day	31% 7% 9% 26% 23% 3	1995
October	1st to 10th	Day	18% 3 5% 18% 36% 19%	3160
	11th to 20th	Day	23% 2 5% 22% 33% 15%	3140
	21st to end	Day	28% 3 8% 31% 24% 4	3428
November	1st to 10th	Day	33% 4 9% 25% 23% 5%	1958
	11th to 20th	Day	36% 5% 8% 21% 24% 7%	1830
	21st to end	Day	40% 4 9% 24% 20% 3	1600
December	1st to 10th	Day	36% 4 9% 34% 17% 1	2610
	11th to 20th	Day	42% 4 6% 25% 21% 2	3005
	21st to end	Day	61% 5% 8% 16% 9% 1	4028
January	1st to 10th	Night	54% 4 8% 19% 13% 2	5888
	11th to 20th	Night	43% 5% 8% 21% 21% 2	5900
	21st to end	Night	47% 3 7% 19% 18% 5%	6490
February	1st to 10th	Night	45% 5% 11% 23% 14% 3	2600
	11th to 20th	Night	44% 5% 10% 21% 17% 4	2486
	21st to end	Night	43% 4 9% 21% 18% 5%	1955
March	1st to 10th	Night	42% 6% 9% 19% 18% 6%	3529
	11th to 20th	Night	34% 7% 10% 24% 20% 4	3590
	21st to end	Night	44% 9% 14% 22% 10% 1	3889
April	1st to 10th	Night	31% 6% 13% 24% 22% 5%	1910
	11th to 20th	Night	36% 7% 12% 23% 17% 6%	1875
	21st to end	Night	44% 6% 11% 24% 14% 1	1900
May	1st to 10th	Night	39% 8% 13% 22% 15% 3	2952
	11th to 20th	Night	39% 10% 12% 24% 13% 1	2824
	21st to end	Night	38% 11% 14% 26% 12%	2827
June	1st to 10th	Night	27% 7% 17% 28% 18% 3	1520
	11th to 20th	Night	22% 7% 16% 32% 21% 3	1520
	21st to end	Night	16% 6% 20% 32% 20% 6%	1520
July	1st to 10th	Night	34% 8% 14% 25% 16% 4	2666
	11th to 20th	Night	20% 6% 12% 39% 21% 2	2796
	21st to end	Night	28% 7% 21% 34% 10%	2999
August	1st to 10th	Night	20% 6% 16% 33% 24% 1	2826
	11th to 20th	Night	33% 6% 16% 28% 16% 1	2963
	21st to end	Night	21% 5% 15% 38% 17% 4	3476
September	1st to 10th	Night	28% 6% 11% 27% 20% 7%	1900
	11th to 20th	Night	31% 6% 11% 24% 26% 3	1924
	21st to end	Night	28% 5% 10% 23% 30% 3	2166
October	1st to 10th	Night	14% 4 6% 17% 44% 16%	3800
	11th to 20th	Night	22% 3 6% 21% 28% 20%	3779
	21st to end	Night	29% 4 7% 30% 25% 5%	4120
November	1st to 10th	Night	30% 4 10% 26% 23% 7%	2340
	11th to 20th	Night	34% 4 8% 23% 25% 7%	2566
	21st to end	Night	39% 5% 8% 24% 21% 3	2797
December	1st to 10th	Night	37% 4 9% 32% 17% 1	4580
	11th to 20th	Night	42% 3 8% 23% 22% 2	5201
	21st to end	Night	60% 5% 9% 17% 7% 2	6932

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% 27% 37% 13% 2	300
	11th to 20th	Day	26% 28% 37% 9%	300
	21st to end	Day	18% 32% 38% 12% 1	330
February	1st to 10th	Day	23% 27% 40% 9% 2	300
	11th to 20th	Day	28% 30% 29% 11% 2	300
	21st to end	Day	28% 28% 35% 8% 2	249
March	1st to 10th	Day	21% 27% 39% 10% 3	300
	11th to 20th	Day	29% 23% 34% 11% 2	300
	21st to end	Day	31% 24% 34% 9% 1	315
April	1st to 10th	Day	19% 22% 36% 18% 3 1	450
	11th to 20th	Day	23% 24% 32% 16% 4	452
	21st to end	Day	25% 18% 35% 17% 4	460
May	1st to 10th	Day	21% 19% 33% 21% 6%	584
	11th to 20th	Day	19% 12% 31% 25% 13% 1	675
	21st to end	Day	13% 10% 36% 24% 14% 4	734
June	1st to 10th	Day	9% 6% 22% 33% 24% 6%	680
	11th to 20th	Day	7% 3 24% 39% 24% 4	680
	21st to end	Day	6% 5% 31% 37% 17% 3	680
July	1st to 10th	Day	10% 3 19% 33% 27% 8%	671
	11th to 20th	Day	4 3 17% 42% 29% 5%	668
	21st to end	Day	9% 1 16% 34% 30% 9%	739
August	1st to 10th	Day	10% 3 16% 41% 25% 5%	676
	11th to 20th	Day	9% 4 19% 36% 26% 5%	585
	21st to end	Day	10% 2 13% 32% 31% 11%	539
September	1st to 10th	Day	10% 3 13% 40% 26% 7%	490
	11th to 20th	Day	9% 2 21% 41% 21% 7%	462
	21st to end	Day	11% 8% 29% 29% 18% 4	300
October	1st to 10th	Day	11% 8% 33% 32% 14% 2	300
	11th to 20th	Day	17% 15% 39% 21% 8%	300
	21st to end	Day	27% 20% 31% 19% 2	330
November	1st to 10th	Day	15% 16% 44% 19% 5% 1	300
	11th to 20th	Day	18% 22% 36% 19% 4 1	300
	21st to end	Day	24% 21% 32% 19% 4	300
December	1st to 10th	Day	17% 30% 33% 15% 4 2	300
	11th to 20th	Day	23% 24% 35% 14% 4	300
	21st to end	Day	22% 34% 32% 10% 2	330
January	1st to 10th	Night	18% 23% 37% 18% 4	1000
	11th to 20th	Night	20% 25% 39% 14% 3	1000
	21st to end	Night	19% 22% 40% 18% 1	1100
February	1st to 10th	Night	21% 21% 42% 15% 2	1000
	11th to 20th	Night	21% 22% 39% 15% 2	931
	21st to end	Night	20% 24% 39% 16% 1	635
March	1st to 10th	Night	21% 19% 37% 21% 2	600
	11th to 20th	Night	25% 16% 36% 19% 4	600
	21st to end	Night	21% 18% 39% 19% 3	647
April	1st to 10th	Night	14% 19% 38% 25% 4	570
	11th to 20th	Night	18% 16% 39% 22% 5%	563
	21st to end	Night	20% 15% 40% 19% 6%	570
May	1st to 10th	Night	15% 9% 40% 29% 7%	570
	11th to 20th	Night	16% 8% 32% 29% 14% 1	561
	21st to end	Night	13% 8% 31% 29% 17% 2	617
June	1st to 10th	Night	9% 4 20% 40% 25% 2	570
	11th to 20th	Night	5% 2 26% 44% 21% 2	570
	21st to end	Night	3 2 25% 49% 21% 1	570
July	1st to 10th	Night	9% 2 12% 43% 30% 4	555
	11th to 20th	Night	3 1 15% 45% 32% 3	552
	21st to end	Night	5% 1 14% 45% 32% 3	624
August	1st to 10th	Night	7% 2 14% 43% 31% 2	567
	11th to 20th	Night	8% 1 17% 43% 27% 3	564
	21st to end	Night	7% 2 14% 39% 34% 5%	627
September	1st to 10th	Night	10% 2 15% 40% 30% 3	570
	11th to 20th	Night	12% 2 15% 43% 25% 3	570
	21st to end	Night	11% 5% 26% 36% 19% 3	646
October	1st to 10th	Night	8% 6% 31% 31% 21% 3	760
	11th to 20th	Night	16% 13% 37% 27% 7%	760
	21st to end	Night	21% 12% 35% 26% 6%	836
November	1st to 10th	Night	13% 13% 41% 25% 8%	780
	11th to 20th	Night	17% 17% 38% 21% 7%	800
	21st to end	Night	20% 17% 36% 21% 7%	997
December	1st to 10th	Night	21% 17% 38% 20% 4	1000
	11th to 20th	Night	22% 17% 38% 21% 3	1000
	21st to end	Night	22% 22% 38% 17% 2	1100

Page generated at 2025-03-24 08:04:30. Version ac07

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