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 2026-08-15.

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	11% 7% 3 6% 4 4 4 4 5% 7% 44%	143272
	Night	11% 8% 3 6% 4 4 4 3 5% 7% 47%	138902
Transparency	Day	38% 6% 11% 25% 17% 4	146882
	Night	37% 5% 11% 25% 19% 4	143372
Seeing	Day	16% 13% 28% 26% 14% 3	18011
	Night	16% 13% 32% 27% 11% 1	27741

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	14% 10% 3 6% 5% 4 3 3 4 5% 43%	5289
	11th to 20th	Day	6% 10% 4 8% 4 4 4 3 4 6% 47%	5310
	21st to end	Day	16% 9% 4 8% 3 3 3 2 3 5% 44%	5812
February	1st to 10th	Day	14% 11% 4 8% 5% 5% 4 4 4 6% 35%	1890
	11th to 20th	Day	14% 9% 3 7% 5% 5% 5% 3 4 5% 41%	1892
	21st to end	Day	13% 11% 3 6% 4 5% 4 3 5% 6% 40%	1774
March	1st to 10th	Day	12% 10% 3 5% 3 3 4 3 4 6% 46%	5046
	11th to 20th	Day	9% 7% 2 4 3 3 3 3 5% 7% 53%	5090
	21st to end	Day	12% 9% 3 7% 5% 6% 5% 4 6% 8% 35%	5583
April	1st to 10th	Day	12% 8% 3 6% 4 3 4 3 6% 7% 44%	2509
	11th to 20th	Day	15% 9% 3 7% 5% 4 4 3 5% 7% 40%	2494
	21st to end	Day	19% 8% 3 7% 4 4 4 4 5% 6% 35%	2520
May	1st to 10th	Day	16% 7% 2 6% 4 5% 5% 4 6% 7% 39%	7413
	11th to 20th	Day	12% 6% 3 7% 4 5% 5% 4 6% 7% 40%	7627
	21st to end	Day	22% 8% 2 6% 4 4 5% 4 5% 7% 33%	8885
June	1st to 10th	Day	10% 5% 2 5% 4 5% 4 4 6% 10% 45%	2940
	11th to 20th	Day	7% 5% 2 5% 4 5% 4 5% 7% 10% 47%	2940
	21st to end	Day	6% 4 1 4 4 4 5% 4 6% 9% 52%	2940
July	1st to 10th	Day	8% 4 2 6% 4 5% 5% 4 7% 10% 45%	7926
	11th to 20th	Day	6% 4 2 7% 5% 5% 6% 5% 7% 10% 43%	7680
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 7% 11% 44%	8337
August	1st to 10th	Day	5% 4 2 4 4 4 4 3 6% 9% 56%	4364
	11th to 20th	Day	9% 5% 2 7% 5% 4 4 4 6% 9% 46%	4075
	21st to end	Day	7% 4 2 5% 4 4 4 4 6% 9% 52%	4312
September	1st to 10th	Day	12% 4 2 4 4 4 4 3 5% 8% 50%	2400
	11th to 20th	Day	10% 6% 3 7% 5% 5% 5% 4 5% 6% 45%	2370
	21st to end	Day	8% 5% 1 5% 4 4 4 4 6% 6% 51%	2100
October	1st to 10th	Day	10% 4 1 5% 3 4 3 3 4 7% 55%	2000
	11th to 20th	Day	12% 6% 2 5% 4 3 3 3 4 5% 54%	2000
	21st to end	Day	17% 8% 2 5% 3 3 3 3 4 6% 47%	2200
November	1st to 10th	Day	10% 6% 2 6% 3 3 3 3 3 5% 56%	2058
	11th to 20th	Day	13% 7% 3 5% 4 3 2 3 5% 8% 48%	1921
	21st to end	Day	14% 9% 3 6% 3 3 2 3 4 6% 47%	1680
December	1st to 10th	Day	10% 9% 3 6% 3 3 2 3 4 5% 52%	2690
	11th to 20th	Day	9% 10% 5% 7% 4 3 3 3 3 5% 47%	3088
	21st to end	Day	17% 19% 5% 9% 5% 4 4 2 4 4 27%	4117
January	1st to 10th	Night	12% 10% 4 11% 6% 4 4 3 3 4 39%	7634
	11th to 20th	Night	7% 7% 3 9% 6% 4 4 3 4 5% 48%	7680
	21st to end	Night	14% 10% 3 8% 4 5% 3 3 3 5% 42%	8402
February	1st to 10th	Night	14% 10% 3 7% 4 3 3 3 5% 6% 42%	2730
	11th to 20th	Night	14% 9% 3 8% 4 4 3 2 5% 5% 43%	2612
	21st to end	Night	13% 9% 3 6% 6% 3 4 3 5% 5% 44%	2050
March	1st to 10th	Night	15% 12% 3 7% 3 3 3 2 3 4 44%	5029
	11th to 20th	Night	10% 9% 2 5% 3 3 4 3 5% 6% 52%	5090
	21st to end	Night	11% 8% 3 7% 4 4 5% 3 5% 7% 42%	5588
April	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 5% 8% 51%	2110
	11th to 20th	Night	13% 8% 2 6% 3 2 4 3 5% 8% 46%	2075
	21st to end	Night	16% 7% 3 7% 4 4 3 4 5% 6% 41%	2100
May	1st to 10th	Night	15% 9% 2 6% 4 3 3 3 5% 7% 43%	5444
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 6% 9% 42%	5265
	21st to end	Night	20% 10% 3 7% 4 4 4 4 5% 6% 33%	5284
June	1st to 10th	Night	8% 5% 1 5% 3 3 3 4 6% 9% 51%	1680
	11th to 20th	Night	6% 4 1 4 4 3 4 4 7% 10% 53%	1680
	21st to end	Night	3 2 1 4 3 3 4 3 5% 8% 64%	1680
July	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 9% 49%	5043
	11th to 20th	Night	3 3 2 4 4 4 5% 4 7% 10% 55%	5307
	21st to end	Night	5% 4 2 5% 3 4 4 4 6% 11% 52%	5770
August	1st to 10th	Night	4 3 1 4 3 4 3 3 5% 8% 63%	3016
	11th to 20th	Night	9% 4 2 6% 4 4 4 3 5% 8% 51%	3066
	21st to end	Night	5% 3 1 4 3 3 3 3 5% 9% 61%	3586
September	1st to 10th	Night	10% 4 2 4 4 4 3 3 4 6% 55%	2000
	11th to 20th	Night	9% 4 2 5% 4 4 3 3 6% 7% 52%	2025
	21st to end	Night	9% 4 2 4 4 3 3 3 4 7% 57%	2280
October	1st to 10th	Night	7% 4 1 3 3 3 3 3 5% 7% 61%	2400
	11th to 20th	Night	13% 5% 1 4 3 2 4 3 4 6% 55%	2400
	21st to end	Night	16% 8% 2 5% 3 2 3 3 4 5% 49%	2640
November	1st to 10th	Night	11% 6% 1 4 3 2 3 2 4 5% 58%	2460
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 52%	2695
	21st to end	Night	15% 8% 3 6% 3 3 3 3 4 5% 47%	2937
December	1st to 10th	Night	10% 9% 3 7% 4 3 3 3 4 6% 49%	4720
	11th to 20th	Night	14% 8% 3 7% 4 3 3 3 4 5% 46%	5339
	21st to end	Night	20% 17% 5% 8% 4 4 3 3 4 4 29%	7085

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	44% 4 8% 25% 17% 2	5290
	11th to 20th	Day	39% 3 6% 28% 18% 6%	5310
	21st to end	Day	46% 2 8% 18% 16% 10%	5812
February	1st to 10th	Day	49% 5% 11% 21% 13% 1	1890
	11th to 20th	Day	46% 4 10% 19% 16% 4	1901
	21st to end	Day	44% 4 7% 21% 17% 6%	1774
March	1st to 10th	Day	39% 5% 8% 20% 16% 12%	5046
	11th to 20th	Day	31% 4 8% 23% 22% 12%	5090
	21st to end	Day	46% 7% 12% 24% 10% 1	5585
April	1st to 10th	Day	40% 6% 12% 21% 19% 2	2509
	11th to 20th	Day	44% 6% 11% 19% 15% 3	2494
	21st to end	Day	49% 7% 10% 23% 10% 1	2520
May	1st to 10th	Day	44% 6% 11% 22% 16% 1	7449
	11th to 20th	Day	41% 8% 12% 22% 16% 1	7631
	21st to end	Day	49% 8% 11% 21% 11%	8899
June	1st to 10th	Day	33% 9% 16% 25% 16% 1	2940
	11th to 20th	Day	31% 8% 14% 31% 14% 2	2940
	21st to end	Day	27% 8% 17% 28% 16% 4	2940
July	1st to 10th	Day	33% 7% 16% 25% 17% 2	7862
	11th to 20th	Day	34% 8% 16% 25% 13% 3	7611
	21st to end	Day	33% 7% 19% 32% 8%	8155
August	1st to 10th	Day	25% 6% 18% 29% 21% 1	4350
	11th to 20th	Day	35% 7% 14% 30% 13% 1	4114
	21st to end	Day	29% 6% 13% 34% 15% 4	4311
September	1st to 10th	Day	32% 7% 13% 25% 15% 8%	2400
	11th to 20th	Day	38% 7% 9% 22% 22% 1	2370
	21st to end	Day	31% 7% 9% 25% 24% 4	2100
October	1st to 10th	Day	18% 3 5% 18% 36% 19%	3260
	11th to 20th	Day	23% 2 5% 23% 33% 14%	3240
	21st to end	Day	29% 3 8% 31% 24% 4	3538
November	1st to 10th	Day	33% 4 9% 26% 23% 5%	2058
	11th to 20th	Day	36% 4 8% 21% 23% 7%	1921
	21st to end	Day	40% 4 9% 25% 20% 2	1680
December	1st to 10th	Day	36% 4 9% 33% 17% 1	2690
	11th to 20th	Day	41% 4 6% 26% 21% 2	3085
	21st to end	Day	60% 5% 8% 16% 10% 1	4117
January	1st to 10th	Night	49% 4 8% 25% 13% 1	7635
	11th to 20th	Night	38% 4 7% 22% 26% 3	7680
	21st to end	Night	47% 3 8% 20% 17% 4	8402
February	1st to 10th	Night	43% 5% 12% 24% 14% 2	2730
	11th to 20th	Night	44% 4 10% 22% 17% 3	2613
	21st to end	Night	42% 3 9% 21% 19% 6%	2050
March	1st to 10th	Night	45% 4 7% 17% 21% 6%	5029
	11th to 20th	Night	33% 5% 8% 23% 19% 10%	5090
	21st to end	Night	40% 7% 14% 24% 14% 1	5588
April	1st to 10th	Night	32% 6% 14% 23% 22% 4	2110
	11th to 20th	Night	36% 6% 12% 23% 17% 6%	2075
	21st to end	Night	43% 6% 11% 25% 14% 1	2100
May	1st to 10th	Night	40% 7% 13% 25% 14% 2	5473
	11th to 20th	Night	37% 8% 11% 24% 16% 3	5266
	21st to end	Night	51% 8% 10% 19% 9% 2	5295
June	1st to 10th	Night	28% 7% 16% 28% 18% 2	1680
	11th to 20th	Night	25% 6% 15% 31% 20% 3	1680
	21st to end	Night	18% 6% 20% 31% 20% 6%	1680
July	1st to 10th	Night	31% 6% 15% 25% 20% 2	5000
	11th to 20th	Night	24% 8% 17% 32% 18% 2	5256
	21st to end	Night	26% 7% 19% 38% 10%	5641
August	1st to 10th	Night	20% 6% 16% 33% 24% 1	3006
	11th to 20th	Night	32% 6% 16% 29% 16% 1	3093
	21st to end	Night	21% 5% 15% 37% 17% 4	3586
September	1st to 10th	Night	30% 6% 11% 27% 20% 7%	2000
	11th to 20th	Night	31% 6% 11% 24% 24% 3	2025
	21st to end	Night	28% 5% 10% 23% 30% 4	2280
October	1st to 10th	Night	14% 4 6% 17% 43% 15%	3920
	11th to 20th	Night	22% 3 6% 21% 28% 20%	3899
	21st to end	Night	30% 4 6% 30% 25% 5%	4252
November	1st to 10th	Night	30% 4 10% 27% 23% 6%	2460
	11th to 20th	Night	33% 4 8% 25% 24% 6%	2695
	21st to end	Night	41% 5% 8% 24% 20% 3	2937
December	1st to 10th	Night	38% 4 9% 32% 17% 1	4720
	11th to 20th	Night	42% 3 8% 23% 22% 2	5341
	21st to end	Night	59% 5% 9% 18% 7% 2	7085

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% 26% 39% 13% 2	330
	11th to 20th	Day	25% 28% 38% 8%	330
	21st to end	Day	18% 31% 39% 11% 1	363
February	1st to 10th	Day	22% 26% 41% 10% 2	330
	11th to 20th	Day	28% 30% 30% 10% 2	330
	21st to end	Day	28% 27% 36% 8% 1	273
March	1st to 10th	Day	22% 28% 38% 10% 3	330
	11th to 20th	Day	29% 22% 35% 11% 2	330
	21st to end	Day	29% 24% 37% 9% 1	363
April	1st to 10th	Day	23% 21% 35% 17% 3 1	529
	11th to 20th	Day	23% 26% 32% 15% 4	532
	21st to end	Day	24% 17% 35% 18% 5%	540
May	1st to 10th	Day	19% 19% 35% 22% 5%	677
	11th to 20th	Day	19% 13% 31% 23% 12% 1	775
	21st to end	Day	16% 10% 33% 24% 13% 3	844
June	1st to 10th	Day	11% 7% 22% 31% 23% 5%	780
	11th to 20th	Day	8% 3 25% 37% 23% 3	780
	21st to end	Day	7% 5% 30% 38% 17% 3	780
July	1st to 10th	Day	9% 3 18% 35% 27% 9%	771
	11th to 20th	Day	5% 3 17% 42% 28% 5%	768
	21st to end	Day	9% 2 15% 36% 30% 8%	849
August	1st to 10th	Day	9% 4 17% 42% 23% 5%	776
	11th to 20th	Day	8% 4 17% 37% 28% 6%	652
	21st to end	Day	10% 3 15% 32% 30% 10%	583
September	1st to 10th	Day	10% 3 13% 41% 26% 7%	530
	11th to 20th	Day	9% 3 19% 40% 22% 7%	500
	21st to end	Day	12% 8% 28% 30% 18% 4	330
October	1st to 10th	Day	10% 8% 33% 34% 13% 2	330
	11th to 20th	Day	16% 16% 38% 21% 9%	330
	21st to end	Day	29% 19% 31% 18% 2	363
November	1st to 10th	Day	14% 17% 44% 18% 5% 1	330
	11th to 20th	Day	17% 22% 37% 18% 4 1	330
	21st to end	Day	25% 21% 32% 18% 4	330
December	1st to 10th	Day	18% 28% 34% 15% 4 2	330
	11th to 20th	Day	22% 23% 37% 14% 3	330
	21st to end	Day	21% 33% 34% 10% 2	363
January	1st to 10th	Night	18% 23% 37% 18% 4	1050
	11th to 20th	Night	19% 25% 39% 14% 3	1050
	21st to end	Night	19% 23% 40% 18% 1	1155
February	1st to 10th	Night	20% 20% 43% 15% 2	1050
	11th to 20th	Night	22% 22% 40% 15% 2	978
	21st to end	Night	20% 24% 39% 16% 2	666
March	1st to 10th	Night	21% 19% 38% 20% 2	630
	11th to 20th	Night	25% 16% 36% 19% 4	630
	21st to end	Night	20% 18% 40% 19% 3	693
April	1st to 10th	Night	15% 18% 39% 25% 4	630
	11th to 20th	Night	19% 17% 39% 21% 5%	623
	21st to end	Night	20% 15% 40% 20% 6%	630
May	1st to 10th	Night	16% 9% 39% 30% 7%	630
	11th to 20th	Night	15% 9% 32% 29% 14% 1	621
	21st to end	Night	15% 7% 30% 29% 16% 2	683
June	1st to 10th	Night	10% 4 20% 40% 23% 2	630
	11th to 20th	Night	7% 3 26% 43% 20% 1	630
	21st to end	Night	3 2 25% 48% 21% 1	630
July	1st to 10th	Night	10% 1 12% 42% 31% 4	615
	11th to 20th	Night	4 1 15% 44% 33% 3	612
	21st to end	Night	5% 1 13% 46% 32% 3	690
August	1st to 10th	Night	6% 3 16% 43% 30% 2	627
	11th to 20th	Night	8% 1 16% 44% 28% 3	606
	21st to end	Night	6% 2 14% 40% 33% 5%	660
September	1st to 10th	Night	11% 2 16% 40% 29% 3	600
	11th to 20th	Night	12% 2 15% 42% 26% 4	600
	21st to end	Night	11% 5% 25% 37% 19% 3	680
October	1st to 10th	Night	8% 6% 31% 32% 21% 3	800
	11th to 20th	Night	15% 12% 36% 28% 8%	800
	21st to end	Night	22% 12% 35% 25% 6%	880
November	1st to 10th	Night	13% 14% 40% 25% 7%	820
	11th to 20th	Night	16% 17% 38% 22% 7%	840
	21st to end	Night	21% 16% 35% 21% 7%	1047
December	1st to 10th	Night	20% 17% 39% 19% 4	1050
	11th to 20th	Night	21% 18% 38% 20% 3	1050
	21st to end	Night	22% 21% 39% 17% 2	1155

Page generated at 2026-08-12 02:37:18. Version ac07

Copyright © 2026 Attilla Danko.