NAA Minooka
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NAA Minooka clear sky chart from 2005-11-06 to 2025-09-04.

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% 9% 3 8% 5% 4 5% 4 6% 8% 37%	126188
	Night	14% 9% 3 8% 5% 4 4 3 5% 6% 38%	122784
Transparency	Day	44% 6% 12% 23% 13% 2	129709
	Night	44% 6% 11% 22% 15% 2	127325
Seeing	Day	16% 10% 27% 26% 16% 6%	16960
	Night	17% 9% 29% 31% 12% 1	26739

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	12% 12% 5% 14% 6% 6% 5% 4 6% 6% 25%	3617
	11th to 20th	Day	10% 11% 5% 12% 6% 6% 5% 6% 7% 4 28%	3620
	21st to end	Day	15% 15% 7% 10% 5% 3 3 3 5% 6% 28%	4194
February	1st to 10th	Day	16% 14% 5% 8% 5% 6% 5% 4 6% 6% 26%	1825
	11th to 20th	Day	15% 10% 4 8% 7% 5% 4 3 4 6% 34%	1948
	21st to end	Day	14% 12% 6% 10% 4 4 3 3 5% 6% 31%	1650
March	1st to 10th	Day	18% 12% 3 6% 4 3 3 2 3 5% 41%	4480
	11th to 20th	Day	9% 7% 3 7% 4 4 5% 4 7% 8% 43%	4711
	21st to end	Day	20% 11% 6% 11% 6% 5% 4 4 5% 6% 22%	5967
April	1st to 10th	Day	16% 13% 3 8% 5% 4 4 3 5% 7% 31%	2400
	11th to 20th	Day	16% 10% 3 7% 5% 4 4 4 6% 6% 36%	2374
	21st to end	Day	20% 7% 3 8% 5% 5% 4 4 5% 6% 34%	2471
May	1st to 10th	Day	17% 8% 2 7% 5% 5% 5% 4 6% 9% 33%	5862
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 8% 41%	6217
	21st to end	Day	13% 6% 3 7% 4 4 5% 4 7% 9% 38%	6935
June	1st to 10th	Day	9% 5% 2 6% 5% 4 4 4 6% 7% 46%	2800
	11th to 20th	Day	9% 6% 2 6% 5% 4 5% 4 6% 8% 46%	2800
	21st to end	Day	10% 6% 2 7% 5% 6% 6% 4 6% 8% 40%	2800
July	1st to 10th	Day	8% 6% 3 7% 5% 5% 5% 5% 8% 10% 37%	6360
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 11% 41%	6360
	21st to end	Day	10% 7% 3 7% 5% 5% 6% 5% 6% 10% 37%	6924
August	1st to 10th	Day	6% 5% 2 6% 5% 4 5% 4 7% 10% 45%	4432
	11th to 20th	Day	9% 5% 2 6% 4 5% 4 5% 7% 11% 42%	3849
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 6% 10% 48%	4312
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 6% 7% 49%	2316
	11th to 20th	Day	10% 4 2 4 3 4 4 3 6% 8% 53%	2176
	21st to end	Day	9% 7% 3 7% 3 4 4 4 6% 8% 46%	2090
October	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 7% 47%	2014
	11th to 20th	Day	16% 9% 2 6% 4 4 5% 3 5% 7% 39%	1900
	21st to end	Day	18% 9% 3 7% 5% 3 4 4 5% 6% 37%	1899
November	1st to 10th	Day	12% 8% 2 6% 4 4 4 3 5% 6% 46%	1762
	11th to 20th	Day	16% 10% 4 9% 5% 4 4 3 5% 7% 33%	1800
	21st to end	Day	19% 10% 3 9% 5% 4 4 3 5% 4 34%	1723
December	1st to 10th	Day	8% 9% 3 8% 5% 4 4 3 4 6% 45%	2610
	11th to 20th	Day	12% 15% 5% 11% 6% 6% 6% 4 5% 6% 23%	3008
	21st to end	Day	27% 20% 7% 12% 5% 4 4 2 3 4 12%	3982
January	1st to 10th	Night	13% 12% 6% 13% 5% 4 4 3 4 5% 31%	6348
	11th to 20th	Night	12% 15% 6% 12% 7% 5% 5% 4 6% 4 23%	6360
	21st to end	Night	17% 14% 6% 9% 4 4 4 3 4 4 31%	6768
February	1st to 10th	Night	16% 15% 5% 8% 5% 4 4 2 4 5% 32%	2574
	11th to 20th	Night	14% 10% 3 8% 6% 4 5% 3 4 6% 37%	2338
	21st to end	Night	18% 10% 4 8% 4 3 3 2 4 5% 37%	1980
March	1st to 10th	Night	17% 11% 3 6% 4 4 3 3 4 5% 41%	5373
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 4 6% 47%	5293
	21st to end	Night	18% 11% 4 10% 5% 5% 4 3 5% 5% 28%	4962
April	1st to 10th	Night	15% 11% 3 6% 5% 4 3 3 4 7% 39%	2000
	11th to 20th	Night	18% 8% 2 6% 4 4 3 2 5% 7% 41%	1975
	21st to end	Night	18% 7% 3 7% 5% 4 5% 4 6% 7% 35%	1927
May	1st to 10th	Night	18% 8% 3 7% 4 5% 4 3 6% 7% 35%	4033
	11th to 20th	Night	12% 6% 2 6% 3 4 5% 4 6% 10% 43%	3692
	21st to end	Night	13% 8% 3 6% 5% 4 5% 3 6% 8% 39%	3942
June	1st to 10th	Night	9% 5% 2 6% 3 3 4 4 6% 7% 50%	1600
	11th to 20th	Night	8% 5% 2 6% 5% 4 5% 4 7% 9% 45%	1600
	21st to end	Night	8% 6% 2 7% 4 5% 5% 5% 7% 7% 44%	1600
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 4 7% 9% 41%	3618
	11th to 20th	Night	7% 5% 2 6% 5% 4 4 4 6% 8% 50%	3617
	21st to end	Night	8% 6% 3 7% 5% 4 5% 5% 7% 8% 42%	3947
August	1st to 10th	Night	4 4 2 6% 4 5% 5% 4 8% 10% 48%	2720
	11th to 20th	Night	7% 4 2 5% 4 4 5% 4 5% 9% 51%	3200
	21st to end	Night	8% 4 2 5% 3 4 3 4 5% 10% 53%	3586
September	1st to 10th	Night	10% 6% 2 5% 3 3 2 2 4 7% 56%	1930
	11th to 20th	Night	8% 4 2 5% 3 4 4 3 6% 7% 54%	1984
	21st to end	Night	9% 6% 3 5% 4 5% 4 4 6% 7% 47%	2090
October	1st to 10th	Night	10% 5% 2 6% 4 3 4 3 4 6% 53%	2163
	11th to 20th	Night	17% 7% 2 5% 3 3 3 2 4 5% 48%	2280
	21st to end	Night	19% 8% 3 7% 4 3 3 2 5% 7% 39%	2698
November	1st to 10th	Night	12% 8% 2 5% 3 3 3 3 5% 6% 49%	2536
	11th to 20th	Night	15% 8% 3 7% 5% 4 5% 3 6% 6% 38%	2600
	21st to end	Night	17% 10% 3 8% 4 4 4 3 4 5% 38%	2675
December	1st to 10th	Night	12% 9% 3 7% 4 4 4 3 5% 6% 44%	4580
	11th to 20th	Night	17% 13% 4 10% 5% 4 4 3 4 5% 32%	5199
	21st to end	Night	24% 18% 6% 10% 5% 4 4 3 4 5% 16%	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	59% 5% 12% 16% 8%	3618
	11th to 20th	Day	55% 5% 9% 11% 15% 4	3620
	21st to end	Day	58% 4 13% 17% 8%	4194
February	1st to 10th	Day	58% 6% 11% 15% 8% 2	1825
	11th to 20th	Day	51% 5% 11% 23% 8% 2	1958
	21st to end	Day	54% 5% 12% 19% 8% 2	1650
March	1st to 10th	Day	47% 5% 9% 24% 13% 3	4480
	11th to 20th	Day	37% 6% 12% 33% 11% 1	4711
	21st to end	Day	61% 8% 11% 13% 7% 1	5969
April	1st to 10th	Day	52% 6% 10% 21% 10%	2400
	11th to 20th	Day	47% 6% 11% 21% 11% 3	2374
	21st to end	Day	50% 7% 12% 17% 12% 2	2471
May	1st to 10th	Day	45% 8% 11% 21% 14% 1	5897
	11th to 20th	Day	41% 7% 10% 26% 15% 2	6221
	21st to end	Day	40% 7% 12% 24% 14% 4	6949
June	1st to 10th	Day	34% 7% 12% 27% 17% 3	2800
	11th to 20th	Day	35% 7% 12% 23% 20% 3	2800
	21st to end	Day	40% 9% 13% 21% 15% 3	2800
July	1st to 10th	Day	39% 7% 13% 26% 14% 1	6291
	11th to 20th	Day	35% 7% 15% 29% 14% 1	6285
	21st to end	Day	40% 8% 18% 20% 13% 2	6728
August	1st to 10th	Day	32% 7% 17% 30% 12% 1	4417
	11th to 20th	Day	33% 7% 12% 32% 15%	3885
	21st to end	Day	31% 7% 12% 31% 17% 2	4311
September	1st to 10th	Day	33% 7% 13% 24% 18% 5%	2316
	11th to 20th	Day	29% 5% 13% 28% 21% 3	2176
	21st to end	Day	35% 7% 10% 26% 20% 2	2090
October	1st to 10th	Day	25% 4 7% 28% 33% 2	3352
	11th to 20th	Day	29% 4 11% 25% 28% 2	3140
	21st to end	Day	41% 4 10% 27% 15% 3	3099
November	1st to 10th	Day	38% 5% 14% 24% 16% 2	1762
	11th to 20th	Day	51% 5% 11% 21% 11% 1	1800
	21st to end	Day	53% 4 11% 22% 9%	1723
December	1st to 10th	Day	41% 4 15% 31% 9%	2610
	11th to 20th	Day	59% 6% 11% 16% 7% 1	3005
	21st to end	Day	78% 4 7% 7% 4	3982
January	1st to 10th	Night	55% 5% 10% 19% 10%	6348
	11th to 20th	Night	62% 5% 10% 9% 13% 1	6360
	21st to end	Night	57% 4 11% 17% 11% 1	6768
February	1st to 10th	Night	55% 4 11% 17% 11% 2	2574
	11th to 20th	Night	49% 5% 9% 24% 12% 1	2339
	21st to end	Night	49% 5% 12% 20% 12% 3	1980
March	1st to 10th	Night	46% 5% 10% 24% 11% 5%	5373
	11th to 20th	Night	37% 5% 12% 29% 15% 3	5293
	21st to end	Night	57% 6% 9% 19% 8% 1	4962
April	1st to 10th	Night	46% 5% 11% 23% 13% 2	2000
	11th to 20th	Night	44% 5% 9% 22% 16% 4	1975
	21st to end	Night	45% 8% 11% 22% 11% 3	1927
May	1st to 10th	Night	47% 7% 12% 17% 14% 3	4060
	11th to 20th	Night	35% 9% 14% 26% 13% 4	3693
	21st to end	Night	41% 7% 11% 23% 15% 3	3950
June	1st to 10th	Night	32% 7% 14% 26% 19% 4	1600
	11th to 20th	Night	33% 7% 12% 25% 21% 3	1600
	21st to end	Night	37% 8% 14% 21% 16% 3	1600
July	1st to 10th	Night	39% 6% 13% 23% 16% 3	3580
	11th to 20th	Night	31% 6% 13% 28% 20% 1	3572
	21st to end	Night	37% 8% 15% 22% 17% 3	3832
August	1st to 10th	Night	29% 8% 18% 26% 18% 1	2711
	11th to 20th	Night	29% 7% 16% 29% 18% 1	3230
	21st to end	Night	27% 6% 12% 33% 18% 3	3586
September	1st to 10th	Night	29% 5% 11% 27% 24% 4	1930
	11th to 20th	Night	28% 5% 9% 29% 25% 3	1984
	21st to end	Night	34% 7% 12% 26% 18% 3	2090
October	1st to 10th	Night	22% 3 7% 36% 29% 3	3605
	11th to 20th	Night	32% 4 8% 23% 31% 3	3779
	21st to end	Night	39% 4 9% 25% 19% 4	4436
November	1st to 10th	Night	36% 5% 10% 27% 18% 4	2536
	11th to 20th	Night	46% 6% 12% 21% 13% 2	2600
	21st to end	Night	49% 4 11% 23% 12% 1	2675
December	1st to 10th	Night	42% 4 14% 28% 11% 1	4580
	11th to 20th	Night	55% 4 13% 18% 10% 1	5201
	21st to end	Night	70% 5% 8% 10% 5%	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	22% 10% 32% 27% 9%	300
	11th to 20th	Day	21% 16% 37% 20% 5% 1	300
	21st to end	Day	24% 16% 28% 25% 6%	330
February	1st to 10th	Day	20% 18% 35% 22% 5%	300
	11th to 20th	Day	21% 17% 37% 20% 5%	300
	21st to end	Day	22% 13% 43% 17% 4	249
March	1st to 10th	Day	24% 19% 33% 21% 3	300
	11th to 20th	Day	24% 18% 32% 19% 7% 1	305
	21st to end	Day	27% 15% 33% 17% 7% 2	550
April	1st to 10th	Day	24% 13% 33% 23% 6% 1	500
	11th to 20th	Day	21% 18% 28% 20% 12% 2	492
	21st to end	Day	23% 13% 30% 23% 9% 1	500
May	1st to 10th	Day	21% 12% 28% 26% 11% 3	503
	11th to 20th	Day	20% 9% 28% 25% 13% 5%	675
	21st to end	Day	14% 8% 30% 23% 16% 8%	789
June	1st to 10th	Day	10% 9% 27% 27% 20% 6%	730
	11th to 20th	Day	11% 6% 29% 30% 20% 5%	730
	21st to end	Day	12% 7% 31% 28% 17% 5%	730
July	1st to 10th	Day	10% 3 17% 28% 25% 16%	721
	11th to 20th	Day	12% 5% 20% 30% 22% 11%	718
	21st to end	Day	8% 3 21% 34% 27% 8%	794
August	1st to 10th	Day	6% 3 15% 36% 27% 13%	686
	11th to 20th	Day	11% 4 17% 27% 27% 14%	519
	21st to end	Day	7% 3 16% 31% 30% 14%	583
September	1st to 10th	Day	13% 5% 20% 26% 28% 8%	502
	11th to 20th	Day	9% 2 15% 30% 30% 13%	490
	21st to end	Day	13% 9% 24% 25% 21% 7%	490
October	1st to 10th	Day	13% 7% 28% 28% 19% 6%	414
	11th to 20th	Day	18% 19% 30% 23% 9% 1	300
	21st to end	Day	28% 12% 31% 22% 6% 2	330
November	1st to 10th	Day	14% 14% 36% 22% 10% 4	300
	11th to 20th	Day	22% 16% 33% 20% 7% 2	300
	21st to end	Day	25% 12% 32% 24% 7%	300
December	1st to 10th	Day	18% 15% 39% 19% 7% 1	300
	11th to 20th	Day	17% 14% 39% 23% 7%	300
	21st to end	Day	28% 17% 34% 17% 3	330
January	1st to 10th	Night	20% 15% 36% 24% 5%	1000
	11th to 20th	Night	21% 13% 37% 24% 5% 1	1000
	21st to end	Night	21% 12% 34% 29% 4	1100
February	1st to 10th	Night	23% 11% 36% 25% 4 1	974
	11th to 20th	Night	20% 12% 35% 28% 5%	783
	21st to end	Night	22% 11% 38% 24% 3	660
March	1st to 10th	Night	21% 15% 34% 25% 6%	800
	11th to 20th	Night	17% 11% 35% 30% 6% 1	749
	21st to end	Night	24% 11% 35% 24% 5% 1	660
April	1st to 10th	Night	19% 13% 36% 26% 6%	600
	11th to 20th	Night	21% 12% 33% 27% 7%	593
	21st to end	Night	19% 10% 33% 30% 7% 1	600
May	1st to 10th	Night	19% 7% 35% 31% 8% 1	600
	11th to 20th	Night	18% 5% 29% 36% 11% 1	591
	21st to end	Night	13% 6% 26% 38% 17%	650
June	1st to 10th	Night	11% 4 24% 45% 16% 1	600
	11th to 20th	Night	10% 4 27% 46% 13% 1	600
	21st to end	Night	9% 4 26% 41% 19% 1	600
July	1st to 10th	Night	9% 2 14% 42% 30% 4	585
	11th to 20th	Night	8% 2 19% 40% 28% 3	582
	21st to end	Night	4 3 13% 49% 29% 2	657
August	1st to 10th	Night	5% 1 12% 47% 30% 4	597
	11th to 20th	Night	6% 4 10% 43% 34% 3	594
	21st to end	Night	8% 1 14% 41% 33% 3	660
September	1st to 10th	Night	12% 3 16% 36% 30% 3	579
	11th to 20th	Night	9% 3 18% 38% 28% 5%	654
	21st to end	Night	13% 5% 23% 35% 21% 2	760
October	1st to 10th	Night	12% 6% 25% 36% 19% 1	760
	11th to 20th	Night	20% 12% 29% 28% 11%	760
	21st to end	Night	24% 11% 30% 26% 8%	836
November	1st to 10th	Night	18% 9% 37% 26% 10% 1	780
	11th to 20th	Night	20% 13% 34% 27% 7%	800
	21st to end	Night	22% 11% 35% 27% 6%	875
December	1st to 10th	Night	22% 10% 37% 26% 6%	1000
	11th to 20th	Night	23% 10% 33% 28% 6%	1000
	21st to end	Night	28% 14% 32% 23% 3	1100

Page generated at 2025-09-01 00:51:09. Version ac07

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