Green Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green Bay clear sky chart from 2005-11-06 to 2025-08-05.

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	12% 9% 3 8% 5% 4 5% 4 6% 7% 39%	125945
	Night	12% 10% 3 8% 5% 4 4 3 5% 6% 39%	122381
Transparency	Day	43% 6% 12% 25% 13% 1	129419
	Night	44% 5% 12% 23% 14% 2	126968
Seeing	Day	16% 12% 30% 26% 13% 3	17026
	Night	16% 9% 32% 31% 11% 1	26869

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	8% 9% 4 14% 6% 6% 5% 4 5% 5% 34%	3617
	11th to 20th	Day	10% 12% 4 9% 5% 5% 6% 4 6% 7% 32%	3620
	21st to end	Day	13% 14% 5% 13% 5% 4 4 2 4 4 32%	3982
February	1st to 10th	Day	9% 12% 4 10% 7% 4 5% 3 5% 7% 32%	1751
	11th to 20th	Day	11% 11% 4 8% 5% 3 4 4 6% 6% 38%	1918
	21st to end	Day	11% 14% 4 9% 5% 5% 4 4 5% 6% 33%	1650
March	1st to 10th	Day	13% 7% 2 5% 3 3 4 3 5% 7% 47%	4480
	11th to 20th	Day	10% 8% 3 8% 4 5% 5% 4 6% 8% 39%	4683
	21st to end	Day	23% 12% 3 9% 4 4 4 3 4 4 30%	5967
April	1st to 10th	Day	15% 12% 4 8% 6% 5% 5% 4 6% 7% 30%	2400
	11th to 20th	Day	19% 9% 3 6% 4 4 4 4 5% 6% 36%	2374
	21st to end	Day	16% 10% 3 8% 5% 5% 5% 4 5% 7% 33%	2575
May	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 5% 6% 46%	5992
	11th to 20th	Day	10% 7% 3 7% 5% 4 4 4 6% 8% 44%	6319
	21st to end	Day	14% 8% 2 6% 4 5% 4 4 5% 8% 39%	6935
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 4 6% 7% 45%	2800
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 7% 8% 41%	2800
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 6% 9% 42%	2800
July	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 7% 9% 41%	6360
	11th to 20th	Day	6% 4 2 4 4 4 5% 4 8% 10% 48%	6360
	21st to end	Day	7% 6% 2 6% 4 5% 5% 4 6% 9% 45%	6924
August	1st to 10th	Day	8% 6% 3 7% 5% 5% 6% 4 7% 8% 41%	4480
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 47%	3937
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 3 6% 8% 40%	4180
September	1st to 10th	Day	12% 7% 2 7% 4 4 5% 4 6% 8% 42%	2280
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 6% 8% 47%	2166
	21st to end	Day	11% 8% 3 7% 5% 5% 4 4 6% 7% 39%	2090
October	1st to 10th	Day	14% 7% 3 7% 4 3 4 3 5% 5% 45%	2014
	11th to 20th	Day	19% 10% 3 8% 5% 6% 5% 2 5% 6% 31%	1842
	21st to end	Day	17% 9% 4 9% 5% 4 4 3 5% 6% 34%	1881
November	1st to 10th	Day	14% 9% 3 6% 5% 4 4 3 5% 8% 40%	1762
	11th to 20th	Day	12% 12% 4 10% 6% 6% 4 4 6% 7% 30%	1800
	21st to end	Day	15% 11% 3 8% 4 5% 5% 3 5% 7% 33%	1606
December	1st to 10th	Day	9% 12% 5% 9% 6% 5% 6% 4 7% 6% 30%	2610
	11th to 20th	Day	10% 16% 5% 12% 5% 4 5% 4 4 5% 28%	3008
	21st to end	Day	18% 18% 6% 13% 6% 5% 4 3 4 5% 18%	3982
January	1st to 10th	Night	9% 13% 5% 9% 5% 4 4 3 4 5% 38%	6348
	11th to 20th	Night	10% 13% 5% 12% 6% 5% 5% 3 5% 6% 30%	6360
	21st to end	Night	10% 15% 5% 12% 6% 5% 4 3 4 5% 31%	6996
February	1st to 10th	Night	9% 14% 5% 10% 6% 5% 5% 3 5% 5% 33%	2645
	11th to 20th	Night	9% 11% 3 10% 6% 5% 5% 4 4 6% 37%	2368
	21st to end	Night	14% 13% 3 9% 5% 4 4 4 4 5% 35%	1980
March	1st to 10th	Night	14% 7% 3 6% 3 4 3 3 5% 6% 46%	5373
	11th to 20th	Night	10% 8% 3 8% 5% 4 5% 4 6% 8% 39%	5320
	21st to end	Night	21% 10% 4 8% 4 4 4 4 4 6% 31%	4962
April	1st to 10th	Night	17% 11% 3 7% 5% 4 4 3 5% 6% 34%	2000
	11th to 20th	Night	21% 8% 2 6% 4 3 4 3 5% 6% 39%	1975
	21st to end	Night	16% 10% 3 8% 5% 3 3 4 5% 6% 38%	1825
May	1st to 10th	Night	14% 8% 2 7% 4 4 3 3 5% 8% 43%	3906
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 5% 7% 8% 43%	3596
	21st to end	Night	18% 9% 3 6% 4 3 4 3 5% 6% 39%	3942
June	1st to 10th	Night	10% 7% 2 5% 5% 4 4 4 7% 8% 45%	1600
	11th to 20th	Night	14% 6% 2 6% 5% 3 4 3 6% 9% 41%	1600
	21st to end	Night	9% 6% 2 5% 5% 4 5% 5% 6% 8% 46%	1600
July	1st to 10th	Night	12% 6% 2 5% 4 4 5% 3 6% 8% 45%	3618
	11th to 20th	Night	8% 4 1 4 3 3 4 3 6% 9% 55%	3617
	21st to end	Night	5% 4 2 5% 4 4 5% 3 6% 9% 53%	3947
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 9% 46%	2549
	11th to 20th	Night	12% 6% 2 5% 4 3 4 3 5% 7% 49%	2876
	21st to end	Night	8% 6% 2 6% 3 4 4 4 6% 7% 48%	3476
September	1st to 10th	Night	9% 4 2 5% 4 4 4 3 5% 7% 54%	1900
	11th to 20th	Night	11% 4 2 5% 4 4 4 2 5% 7% 52%	1994
	21st to end	Night	12% 7% 2 7% 5% 3 4 3 5% 6% 46%	2090
October	1st to 10th	Night	13% 7% 2 6% 4 3 3 3 5% 6% 47%	2163
	11th to 20th	Night	15% 9% 3 8% 5% 4 4 3 5% 6% 38%	2337
	21st to end	Night	18% 11% 4 8% 5% 5% 3 3 5% 6% 33%	2717
November	1st to 10th	Night	13% 9% 2 6% 5% 3 4 3 5% 7% 43%	2536
	11th to 20th	Night	13% 11% 4 9% 6% 5% 4 4 5% 6% 34%	2600
	21st to end	Night	15% 11% 3 7% 5% 4 4 3 5% 6% 35%	2790
December	1st to 10th	Night	11% 10% 4 8% 5% 5% 4 3 5% 7% 37%	4580
	11th to 20th	Night	12% 16% 7% 11% 5% 5% 4 3 4 5% 28%	5199
	21st to end	Night	20% 17% 5% 10% 5% 5% 4 3 4 5% 21%	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	50% 5% 15% 19% 10% 1	3618
	11th to 20th	Day	50% 5% 11% 21% 11% 2	3620
	21st to end	Day	56% 4 10% 18% 12%	3982
February	1st to 10th	Day	50% 6% 12% 20% 11% 1	1751
	11th to 20th	Day	47% 4 12% 23% 13% 2	1928
	21st to end	Day	51% 5% 12% 21% 9% 2	1650
March	1st to 10th	Day	37% 4 14% 22% 17% 6%	4480
	11th to 20th	Day	41% 6% 15% 22% 15% 1	4683
	21st to end	Day	58% 4 9% 18% 10% 1	5969
April	1st to 10th	Day	52% 7% 11% 19% 11%	2400
	11th to 20th	Day	49% 5% 9% 22% 14% 2	2374
	21st to end	Day	50% 5% 12% 19% 13% 2	2575
May	1st to 10th	Day	37% 6% 13% 25% 17% 2	6027
	11th to 20th	Day	37% 6% 12% 28% 16% 1	6323
	21st to end	Day	42% 6% 10% 24% 16% 2	6949
June	1st to 10th	Day	37% 6% 12% 28% 15% 2	2800
	11th to 20th	Day	40% 5% 15% 24% 15% 1	2800
	21st to end	Day	37% 7% 15% 25% 15% 1	2800
July	1st to 10th	Day	37% 6% 13% 32% 11% 1	6291
	11th to 20th	Day	27% 7% 15% 35% 15% 1	6285
	21st to end	Day	34% 7% 12% 26% 19% 1	6728
August	1st to 10th	Day	38% 6% 14% 27% 14% 1	4465
	11th to 20th	Day	33% 7% 13% 35% 11% 1	3976
	21st to end	Day	41% 7% 13% 22% 16% 1	4179
September	1st to 10th	Day	39% 6% 12% 27% 15% 1	2280
	11th to 20th	Day	34% 5% 18% 32% 11% 1	2166
	21st to end	Day	42% 6% 13% 28% 11%	2090
October	1st to 10th	Day	25% 4 11% 34% 25% 2	3352
	11th to 20th	Day	47% 5% 9% 25% 14% 1	3032
	21st to end	Day	44% 5% 13% 28% 10%	3081
November	1st to 10th	Day	42% 6% 13% 24% 13% 1	1762
	11th to 20th	Day	52% 5% 15% 18% 9%	1800
	21st to end	Day	51% 5% 16% 21% 6% 1	1606
December	1st to 10th	Day	50% 7% 17% 22% 4	2610
	11th to 20th	Day	58% 4 10% 15% 11% 2	3005
	21st to end	Day	70% 4 6% 15% 5%	3982
January	1st to 10th	Night	48% 4 9% 24% 13% 1	6348
	11th to 20th	Night	55% 4 9% 17% 14% 1	6360
	21st to end	Night	56% 4 12% 17% 11%	6996
February	1st to 10th	Night	52% 5% 9% 21% 11% 2	2645
	11th to 20th	Night	49% 4 10% 24% 11% 2	2369
	21st to end	Night	51% 4 12% 21% 10% 2	1980
March	1st to 10th	Night	38% 3 16% 26% 13% 3	5373
	11th to 20th	Night	41% 5% 17% 22% 13% 2	5320
	21st to end	Night	55% 4 10% 18% 12% 1	4962
April	1st to 10th	Night	50% 6% 6% 20% 17% 1	2000
	11th to 20th	Night	47% 4 8% 24% 14% 3	1975
	21st to end	Night	46% 5% 11% 22% 14% 1	1825
May	1st to 10th	Night	40% 5% 12% 21% 20% 2	3933
	11th to 20th	Night	36% 8% 14% 24% 17% 2	3597
	21st to end	Night	46% 5% 9% 24% 12% 4	3950
June	1st to 10th	Night	35% 7% 12% 30% 16% 1	1600
	11th to 20th	Night	40% 5% 11% 26% 17% 2	1600
	21st to end	Night	34% 8% 15% 25% 15% 3	1600
July	1st to 10th	Night	36% 5% 14% 32% 9% 4	3580
	11th to 20th	Night	26% 5% 15% 35% 16% 2	3572
	21st to end	Night	28% 5% 16% 26% 23% 2	3832
August	1st to 10th	Night	35% 7% 13% 27% 18% 1	2540
	11th to 20th	Night	35% 5% 11% 31% 16% 1	2903
	21st to end	Night	34% 7% 13% 23% 21% 3	3476
September	1st to 10th	Night	30% 6% 12% 31% 20% 1	1900
	11th to 20th	Night	31% 5% 14% 34% 15% 1	1994
	21st to end	Night	38% 5% 13% 29% 14% 1	2090
October	1st to 10th	Night	29% 4 9% 38% 19% 1	3605
	11th to 20th	Night	37% 5% 12% 29% 15% 2	3873
	21st to end	Night	46% 5% 11% 23% 15%	4467
November	1st to 10th	Night	41% 5% 12% 26% 15% 2	2536
	11th to 20th	Night	51% 4 12% 19% 12% 1	2600
	21st to end	Night	48% 5% 14% 25% 7% 1	2790
December	1st to 10th	Night	45% 5% 22% 21% 5% 1	4580
	11th to 20th	Night	60% 4 11% 13% 11% 1	5201
	21st to end	Night	65% 5% 8% 14% 8%	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	13% 14% 35% 27% 10% 1	300
	11th to 20th	Day	22% 15% 32% 26% 5%	300
	21st to end	Day	20% 13% 34% 26% 5% 1	330
February	1st to 10th	Day	14% 16% 41% 21% 7% 1	300
	11th to 20th	Day	12% 23% 40% 18% 7%	300
	21st to end	Day	20% 19% 40% 18% 2	249
March	1st to 10th	Day	13% 24% 39% 19% 5%	300
	11th to 20th	Day	21% 17% 31% 21% 9% 2	329
	21st to end	Day	25% 14% 29% 24% 8% 1	550
April	1st to 10th	Day	24% 15% 33% 21% 7% 1	500
	11th to 20th	Day	25% 19% 26% 20% 8% 2	492
	21st to end	Day	20% 13% 32% 20% 13% 2	500
May	1st to 10th	Day	17% 12% 36% 24% 9% 2	555
	11th to 20th	Day	16% 12% 33% 26% 11% 2	725
	21st to end	Day	15% 10% 30% 27% 14% 5%	789
June	1st to 10th	Day	11% 9% 34% 30% 14% 3	730
	11th to 20th	Day	17% 8% 32% 28% 12% 2	730
	21st to end	Day	13% 10% 30% 30% 15% 2	730
July	1st to 10th	Day	9% 4 22% 35% 22% 8%	721
	11th to 20th	Day	8% 7% 26% 34% 18% 6%	718
	21st to end	Day	7% 4 27% 35% 20% 7%	794
August	1st to 10th	Day	9% 5% 22% 34% 23% 7%	697
	11th to 20th	Day	12% 5% 20% 28% 25% 10%	504
	21st to end	Day	14% 6% 22% 27% 24% 7%	539
September	1st to 10th	Day	14% 9% 24% 27% 18% 7%	490
	11th to 20th	Day	11% 4 22% 34% 21% 7%	490
	21st to end	Day	15% 11% 26% 26% 17% 6%	490
October	1st to 10th	Day	16% 14% 27% 24% 16% 3	414
	11th to 20th	Day	19% 20% 32% 23% 6%	300
	21st to end	Day	22% 21% 35% 17% 4 1	330
November	1st to 10th	Day	18% 15% 36% 22% 8% 1	300
	11th to 20th	Day	16% 20% 38% 21% 5% 1	300
	21st to end	Day	22% 14% 43% 17% 4	300
December	1st to 10th	Day	16% 18% 41% 21% 4	300
	11th to 20th	Day	18% 21% 38% 17% 5% 1	300
	21st to end	Day	27% 14% 36% 16% 6% 1	330
January	1st to 10th	Night	15% 11% 41% 26% 7%	1000
	11th to 20th	Night	19% 13% 35% 25% 8% 1	1000
	21st to end	Night	17% 9% 37% 29% 8%	1100
February	1st to 10th	Night	15% 12% 37% 28% 7% 1	1000
	11th to 20th	Night	15% 11% 41% 27% 6%	813
	21st to end	Night	20% 11% 37% 27% 4	660
March	1st to 10th	Night	17% 10% 36% 29% 8% 1	800
	11th to 20th	Night	16% 11% 38% 27% 6% 1	788
	21st to end	Night	23% 7% 30% 29% 10% 1	660
April	1st to 10th	Night	23% 8% 37% 26% 5%	600
	11th to 20th	Night	24% 9% 31% 28% 7% 1	593
	21st to end	Night	18% 10% 34% 29% 9% 1	600
May	1st to 10th	Night	18% 9% 34% 30% 9% 1	600
	11th to 20th	Night	17% 6% 34% 34% 9% 1	591
	21st to end	Night	13% 6% 25% 40% 14% 1	650
June	1st to 10th	Night	12% 6% 29% 40% 13% 1	600
	11th to 20th	Night	17% 7% 27% 38% 12% 1	600
	21st to end	Night	11% 5% 26% 43% 15%	600
July	1st to 10th	Night	8% 2 20% 46% 22% 2	585
	11th to 20th	Night	10% 3 22% 41% 24% 1	582
	21st to end	Night	7% 2 22% 45% 22% 2	657
August	1st to 10th	Night	9% 3 17% 43% 26% 2	579
	11th to 20th	Night	9% 3 19% 39% 27% 3	564
	21st to end	Night	10% 3 22% 41% 22% 2	627
September	1st to 10th	Night	10% 5% 25% 34% 22% 4	570
	11th to 20th	Night	12% 6% 24% 34% 21% 4	664
	21st to end	Night	15% 8% 23% 34% 19% 2	760
October	1st to 10th	Night	17% 9% 26% 30% 18% 1	760
	11th to 20th	Night	19% 11% 33% 29% 7%	760
	21st to end	Night	23% 11% 33% 25% 9% 1	836
November	1st to 10th	Night	16% 11% 37% 28% 7% 1	780
	11th to 20th	Night	18% 14% 39% 23% 5% 1	800
	21st to end	Night	19% 14% 36% 24% 7%	990
December	1st to 10th	Night	19% 13% 39% 24% 6%	1000
	11th to 20th	Night	21% 12% 35% 24% 6% 1	1000
	21st to end	Night	26% 11% 34% 25% 4	1100

Page generated at 2025-08-02 00:32:25. Version ac07

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