Iowa City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Iowa City clear sky chart from 2005-11-06 to 2024-12-24.

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% 8% 3 8% 5% 4 5% 4 6% 7% 38%	101912
	Night	13% 8% 3 8% 4 4 4 3 5% 6% 41%	98299
Transparency	Day	42% 6% 12% 23% 14% 2	105520
	Night	42% 6% 12% 23% 15% 2	102831
Seeing	Day	15% 10% 29% 27% 15% 4	15985
	Night	16% 9% 31% 31% 12% 1	25900

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	9% 12% 5% 19% 7% 7% 5% 4 6% 5% 22%	2527
	11th to 20th	Day	11% 13% 4 10% 10% 7% 6% 4 7% 5% 24%	2626
	21st to end	Day	16% 18% 6% 17% 7% 5% 3 2 4 5% 17%	3135
February	1st to 10th	Day	12% 12% 4 10% 6% 5% 5% 5% 5% 7% 28%	1710
	11th to 20th	Day	14% 11% 3 7% 5% 6% 5% 3 5% 8% 33%	1702
	21st to end	Day	13% 10% 4 11% 5% 3 4 3 5% 6% 34%	1570
March	1st to 10th	Day	17% 11% 3 6% 3 3 3 2 4 5% 41%	3247
	11th to 20th	Day	10% 6% 3 7% 4 4 5% 4 5% 6% 47%	3480
	21st to end	Day	23% 13% 4 10% 5% 4 5% 3 5% 6% 22%	3959
April	1st to 10th	Day	16% 13% 3 8% 5% 5% 4 4 4 5% 34%	2280
	11th to 20th	Day	16% 9% 3 7% 6% 4 4 3 6% 7% 34%	2254
	21st to end	Day	21% 8% 3 7% 5% 3 4 4 4 6% 35%	2280
May	1st to 10th	Day	16% 8% 3 8% 5% 4 4 4 6% 7% 34%	4223
	11th to 20th	Day	16% 7% 2 6% 4 5% 4 3 4 7% 41%	4399
	21st to end	Day	13% 7% 2 6% 5% 4 4 4 5% 7% 43%	4824
June	1st to 10th	Day	9% 5% 2 6% 5% 4 6% 5% 7% 9% 44%	2660
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 7% 8% 46%	2660
	21st to end	Day	12% 6% 2 7% 5% 4 5% 4 6% 9% 39%	2660
July	1st to 10th	Day	9% 8% 3 7% 5% 6% 6% 5% 7% 9% 35%	4440
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 7% 9% 53%	4440
	21st to end	Day	5% 5% 2 6% 5% 6% 6% 6% 8% 12% 40%	4696
August	1st to 10th	Day	6% 5% 2 6% 4 4 6% 4 8% 10% 44%	4104
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 8% 9% 41%	3945
	21st to end	Day	8% 5% 2 5% 4 3 4 4 6% 8% 51%	4180
September	1st to 10th	Day	13% 4 2 5% 3 3 3 4 5% 8% 50%	2280
	11th to 20th	Day	10% 4 2 5% 4 4 4 3 5% 9% 51%	2280
	21st to end	Day	11% 6% 2 5% 4 4 4 4 5% 8% 47%	2017
October	1st to 10th	Day	13% 7% 2 7% 4 3 4 3 4 5% 49%	1900
	11th to 20th	Day	16% 7% 3 6% 4 3 4 3 5% 6% 43%	1900
	21st to end	Day	17% 9% 3 6% 4 4 3 3 5% 6% 41%	2057
November	1st to 10th	Day	11% 9% 3 5% 4 4 4 4 6% 6% 43%	1762
	11th to 20th	Day	15% 11% 3 7% 4 3 4 3 5% 8% 36%	1710
	21st to end	Day	16% 10% 3 6% 4 3 5% 3 4 7% 38%	1600
December	1st to 10th	Day	14% 11% 4 10% 4 4 5% 3 4 6% 34%	1600
	11th to 20th	Day	14% 10% 4 10% 6% 4 5% 4 5% 6% 32%	1998
	21st to end	Day	23% 19% 7% 11% 5% 4 4 3 3 4 17%	2807
January	1st to 10th	Night	11% 12% 7% 15% 5% 5% 4 3 5% 5% 28%	4428
	11th to 20th	Night	11% 16% 6% 13% 5% 4 5% 4 8% 5% 23%	4343
	21st to end	Night	17% 16% 7% 13% 5% 4 3 3 4 6% 23%	4532
February	1st to 10th	Night	14% 12% 4 8% 6% 4 4 4 5% 5% 34%	2470
	11th to 20th	Night	12% 9% 3 7% 5% 5% 4 3 5% 6% 41%	2364
	21st to end	Night	14% 10% 4 8% 5% 3 4 3 5% 4 40%	1884
March	1st to 10th	Night	17% 8% 3 6% 4 3 3 3 4 5% 43%	3623
	11th to 20th	Night	10% 6% 2 6% 4 4 3 3 4 6% 52%	3480
	21st to end	Night	22% 11% 5% 11% 5% 5% 5% 3 5% 4 23%	3672
April	1st to 10th	Night	15% 10% 3 7% 4 3 3 3 5% 6% 41%	1900
	11th to 20th	Night	16% 9% 3 7% 4 3 4 4 4 6% 40%	1875
	21st to end	Night	17% 8% 2 6% 4 5% 4 4 5% 7% 39%	1900
May	1st to 10th	Night	18% 7% 2 7% 4 4 4 3 5% 6% 39%	2678
	11th to 20th	Night	12% 5% 2 6% 5% 5% 5% 4 5% 6% 44%	2506
	21st to end	Night	8% 6% 2 6% 4 4 4 4 6% 7% 48%	2743
June	1st to 10th	Night	8% 6% 2 6% 4 4 4 4 7% 9% 47%	1520
	11th to 20th	Night	7% 5% 3 6% 4 4 4 4 7% 10% 45%	1520
	21st to end	Night	10% 5% 2 6% 4 4 5% 3 6% 8% 47%	1520
July	1st to 10th	Night	12% 4 2 7% 5% 5% 5% 5% 6% 9% 40%	2530
	11th to 20th	Night	5% 2 1 4 3 3 4 4 6% 10% 59%	2530
	21st to end	Night	6% 4 2 7% 5% 4 4 5% 8% 8% 48%	2864
August	1st to 10th	Night	4 3 2 5% 4 5% 5% 3 7% 8% 53%	2836
	11th to 20th	Night	6% 4 2 6% 4 4 4 4 5% 7% 54%	2889
	21st to end	Night	7% 4 2 6% 4 3 4 4 6% 8% 53%	3476
September	1st to 10th	Night	10% 4 2 4 3 3 3 4 5% 7% 55%	1900
	11th to 20th	Night	11% 5% 2 4 4 4 4 3 5% 7% 53%	1900
	21st to end	Night	7% 5% 2 6% 4 3 4 3 6% 7% 54%	2142
October	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 52%	2280
	11th to 20th	Night	14% 6% 2 5% 4 4 3 3 4 6% 49%	2280
	21st to end	Night	16% 8% 3 7% 5% 4 4 3 4 5% 42%	2539
November	1st to 10th	Night	11% 7% 2 4 3 3 3 3 5% 6% 52%	2536
	11th to 20th	Night	14% 9% 3 7% 5% 4 4 3 5% 5% 42%	2687
	21st to end	Night	16% 8% 3 8% 4 4 4 3 4 6% 39%	2800
December	1st to 10th	Night	12% 11% 4 8% 6% 4 4 3 6% 6% 36%	2800
	11th to 20th	Night	14% 11% 4 10% 5% 4 5% 3 5% 6% 35%	3419
	21st to end	Night	21% 16% 6% 11% 6% 5% 4 3 4 4 20%	4933

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	62% 7% 11% 14% 6%	2528
	11th to 20th	Day	60% 4 12% 16% 7%	2626
	21st to end	Day	71% 4 10% 10% 5%	3135
February	1st to 10th	Day	54% 7% 13% 19% 7% 1	1710
	11th to 20th	Day	49% 5% 14% 21% 9% 1	1711
	21st to end	Day	50% 5% 12% 21% 9% 2	1570
March	1st to 10th	Day	46% 5% 11% 23% 14% 1	3247
	11th to 20th	Day	37% 6% 12% 26% 18% 2	3480
	21st to end	Day	62% 7% 13% 14% 4 1	3959
April	1st to 10th	Day	52% 5% 11% 23% 9%	2280
	11th to 20th	Day	48% 6% 10% 23% 12% 2	2254
	21st to end	Day	50% 5% 10% 19% 14% 2	2280
May	1st to 10th	Day	46% 7% 12% 19% 15% 1	4261
	11th to 20th	Day	43% 7% 10% 27% 13%	4403
	21st to end	Day	39% 6% 10% 25% 18% 1	4837
June	1st to 10th	Day	34% 9% 15% 24% 16% 2	2660
	11th to 20th	Day	34% 8% 11% 22% 22% 4	2660
	21st to end	Day	40% 8% 14% 23% 15% 2	2660
July	1st to 10th	Day	42% 8% 13% 26% 9% 2	4371
	11th to 20th	Day	26% 8% 14% 32% 18% 2	4365
	21st to end	Day	32% 12% 18% 20% 18% 1	4548
August	1st to 10th	Day	31% 9% 18% 28% 13% 1	4090
	11th to 20th	Day	37% 8% 14% 25% 15% 1	3984
	21st to end	Day	31% 7% 13% 31% 16% 2	4179
September	1st to 10th	Day	32% 6% 10% 25% 23% 4	2280
	11th to 20th	Day	30% 6% 12% 31% 19% 3	2280
	21st to end	Day	34% 5% 10% 30% 18% 2	2017
October	1st to 10th	Day	23% 3 6% 29% 37% 2	3160
	11th to 20th	Day	28% 3 11% 23% 29% 6%	3140
	21st to end	Day	39% 4 10% 29% 15% 3	3371
November	1st to 10th	Day	39% 6% 14% 24% 14% 3	1762
	11th to 20th	Day	47% 4 14% 21% 13% 1	1710
	21st to end	Day	46% 6% 14% 24% 9%	1600
December	1st to 10th	Day	51% 5% 13% 22% 8% 1	1600
	11th to 20th	Day	51% 6% 14% 18% 9% 1	1995
	21st to end	Day	71% 4 10% 11% 4	2807
January	1st to 10th	Night	57% 6% 12% 16% 9%	4428
	11th to 20th	Night	59% 4 12% 13% 10% 1	4343
	21st to end	Night	63% 5% 10% 15% 6% 1	4532
February	1st to 10th	Night	51% 5% 11% 21% 11% 1	2470
	11th to 20th	Night	44% 6% 12% 25% 13% 2	2365
	21st to end	Night	46% 4 11% 22% 14% 2	1884
March	1st to 10th	Night	44% 4 9% 25% 16% 1	3623
	11th to 20th	Night	33% 5% 11% 32% 15% 4	3480
	21st to end	Night	63% 8% 12% 12% 5% 1	3672
April	1st to 10th	Night	44% 4 9% 26% 14% 2	1900
	11th to 20th	Night	44% 5% 9% 22% 17% 4	1875
	21st to end	Night	44% 6% 11% 22% 14% 3	1900
May	1st to 10th	Night	45% 7% 10% 19% 17% 2	2705
	11th to 20th	Night	39% 8% 12% 25% 14% 1	2507
	21st to end	Night	33% 7% 11% 27% 20% 2	2751
June	1st to 10th	Night	31% 8% 13% 27% 17% 4	1520
	11th to 20th	Night	32% 6% 12% 25% 20% 5%	1520
	21st to end	Night	33% 7% 17% 22% 17% 5%	1520
July	1st to 10th	Night	39% 8% 14% 26% 11% 3	2490
	11th to 20th	Night	19% 7% 18% 33% 22% 1	2482
	21st to end	Night	29% 9% 19% 22% 18% 2	2773
August	1st to 10th	Night	26% 8% 16% 32% 17% 2	2826
	11th to 20th	Night	28% 8% 14% 31% 18% 1	2916
	21st to end	Night	28% 7% 12% 29% 18% 5%	3476
September	1st to 10th	Night	28% 6% 11% 26% 26% 4	1900
	11th to 20th	Night	32% 5% 8% 32% 19% 4	1900
	21st to end	Night	30% 5% 10% 29% 24% 3	2142
October	1st to 10th	Night	23% 3 6% 26% 37% 3	3800
	11th to 20th	Night	26% 3 10% 22% 32% 6%	3779
	21st to end	Night	46% 4 8% 22% 17% 4	4175
November	1st to 10th	Night	33% 5% 14% 26% 18% 4	2536
	11th to 20th	Night	44% 4 12% 25% 14% 2	2687
	21st to end	Night	46% 4 11% 26% 11% 1	2800
December	1st to 10th	Night	48% 5% 13% 24% 9% 1	2800
	11th to 20th	Night	50% 5% 13% 24% 7% 1	3421
	21st to end	Night	67% 5% 9% 13% 5%	4933

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% 13% 31% 24% 9% 1	270
	11th to 20th	Day	21% 16% 40% 19% 4	270
	21st to end	Day	20% 12% 40% 21% 5% 1	297
February	1st to 10th	Day	19% 18% 38% 20% 5%	270
	11th to 20th	Day	22% 17% 32% 22% 7%	270
	21st to end	Day	19% 18% 42% 18% 3	225
March	1st to 10th	Day	19% 21% 41% 13% 7%	270
	11th to 20th	Day	21% 19% 33% 20% 7% 1	270
	21st to end	Day	31% 15% 32% 16% 5% 1	378
April	1st to 10th	Day	22% 16% 37% 20% 5% 1	460
	11th to 20th	Day	21% 17% 31% 21% 10% 1	452
	21st to end	Day	24% 14% 33% 18% 10% 1	460
May	1st to 10th	Day	19% 11% 37% 25% 6% 2	639
	11th to 20th	Day	20% 12% 28% 27% 12% 2	675
	21st to end	Day	15% 10% 27% 27% 15% 5%	734
June	1st to 10th	Day	7% 5% 29% 33% 21% 6%	680
	11th to 20th	Day	12% 6% 29% 33% 18% 3	680
	21st to end	Day	12% 8% 31% 30% 14% 5%	680
July	1st to 10th	Day	8% 4 17% 32% 25% 13%	671
	11th to 20th	Day	9% 3 24% 34% 24% 7%	668
	21st to end	Day	6% 3 23% 38% 25% 6%	739
August	1st to 10th	Day	6% 3 24% 36% 23% 7%	676
	11th to 20th	Day	10% 5% 19% 34% 24% 8%	608
	21st to end	Day	9% 4 18% 35% 26% 9%	539
September	1st to 10th	Day	13% 7% 18% 31% 24% 7%	490
	11th to 20th	Day	8% 4 18% 39% 22% 9%	490
	21st to end	Day	13% 9% 28% 23% 23% 4	388
October	1st to 10th	Day	17% 8% 28% 30% 13% 5%	300
	11th to 20th	Day	19% 20% 33% 18% 10%	300
	21st to end	Day	28% 13% 30% 22% 5% 1	330
November	1st to 10th	Day	17% 11% 41% 20% 9% 3	300
	11th to 20th	Day	22% 16% 32% 20% 8% 2	300
	21st to end	Day	23% 11% 36% 23% 6%	300
December	1st to 10th	Day	14% 14% 42% 23% 6% 3	300
	11th to 20th	Day	16% 15% 37% 23% 8%	300
	21st to end	Day	27% 15% 37% 17% 3	306
January	1st to 10th	Night	15% 12% 39% 27% 7% 1	950
	11th to 20th	Night	18% 14% 35% 27% 6%	950
	21st to end	Night	19% 11% 37% 27% 6%	1045
February	1st to 10th	Night	21% 11% 37% 26% 4	950
	11th to 20th	Night	17% 13% 36% 29% 5%	890
	21st to end	Night	22% 12% 40% 22% 3 1	628
March	1st to 10th	Night	20% 12% 39% 23% 6% 1	702
	11th to 20th	Night	16% 11% 32% 31% 8%	570
	21st to end	Night	23% 12% 35% 24% 5% 1	627
April	1st to 10th	Night	20% 14% 39% 24% 3	570
	11th to 20th	Night	21% 13% 32% 28% 6%	563
	21st to end	Night	20% 10% 32% 29% 8% 1	570
May	1st to 10th	Night	18% 8% 39% 28% 7% 1	570
	11th to 20th	Night	18% 8% 29% 34% 11%	561
	21st to end	Night	13% 4 31% 34% 17% 1	617
June	1st to 10th	Night	10% 4 25% 44% 16% 1	570
	11th to 20th	Night	9% 4 28% 45% 15%	570
	21st to end	Night	13% 3 28% 38% 17% 1	570
July	1st to 10th	Night	9% 2 11% 42% 32% 4	555
	11th to 20th	Night	5% 3 20% 43% 26% 3	552
	21st to end	Night	6% 2 19% 43% 27% 2	624
August	1st to 10th	Night	5% 2 16% 47% 29% 2	567
	11th to 20th	Night	6% 3 15% 43% 27% 5%	564
	21st to end	Night	9% 2 16% 43% 28% 3	627
September	1st to 10th	Night	11% 5% 19% 37% 25% 3	570
	11th to 20th	Night	12% 2 18% 39% 24% 5%	570
	21st to end	Night	9% 7% 27% 37% 19% 2	712
October	1st to 10th	Night	16% 6% 26% 32% 18% 2	760
	11th to 20th	Night	18% 11% 30% 31% 11%	760
	21st to end	Night	21% 11% 32% 28% 8%	836
November	1st to 10th	Night	16% 9% 36% 29% 9% 1	780
	11th to 20th	Night	18% 13% 39% 23% 6%	887
	21st to end	Night	21% 12% 34% 27% 7%	1000
December	1st to 10th	Night	18% 13% 38% 26% 6% 1	1000
	11th to 20th	Night	21% 10% 34% 29% 6%	1000
	21st to end	Night	25% 14% 34% 24% 3	1063

Page generated at 2024-12-21 03:13:49. Version ac07

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