Iowa SkyNet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Iowa SkyNet Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	12% 8% 3 7% 5% 4 4 4 6% 7% 39%	101464
	Night	13% 8% 3 7% 4 4 4 3 5% 6% 42%	97636
Transparency	Day	43% 5% 12% 24% 15% 2	105085
	Night	42% 4 12% 24% 16% 2	102155
Seeing	Day	15% 9% 28% 27% 16% 4	15818
	Night	16% 9% 31% 31% 12% 1	25643

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% 11% 5% 17% 8% 7% 5% 4 6% 6% 22%	2527
	11th to 20th	Day	11% 12% 4 12% 8% 7% 6% 4 6% 5% 24%	2658
	21st to end	Day	15% 19% 7% 16% 6% 5% 3 3 4 5% 19%	3135
February	1st to 10th	Day	14% 12% 6% 9% 7% 4 4 4 5% 7% 27%	1710
	11th to 20th	Day	14% 10% 3 7% 4 6% 6% 3 5% 8% 34%	1702
	21st to end	Day	14% 9% 4 9% 6% 5% 3 4 4 6% 36%	1570
March	1st to 10th	Day	16% 12% 3 7% 4 3 3 2 4 4 41%	3268
	11th to 20th	Day	9% 7% 3 6% 4 4 4 4 6% 7% 47%	3480
	21st to end	Day	22% 13% 4 9% 5% 4 4 3 5% 6% 25%	3940
April	1st to 10th	Day	16% 12% 3 8% 5% 4 4 3 5% 5% 35%	2280
	11th to 20th	Day	17% 8% 3 8% 5% 4 4 3 4 6% 37%	2254
	21st to end	Day	22% 8% 3 6% 4 4 5% 3 5% 6% 34%	2280
May	1st to 10th	Day	16% 7% 2 7% 5% 5% 5% 4 5% 8% 34%	4188
	11th to 20th	Day	16% 7% 3 7% 5% 4 4 4 4 7% 41%	4399
	21st to end	Day	12% 6% 2 6% 4 5% 4 4 5% 7% 44%	4824
June	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 45%	2660
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 3 7% 8% 47%	2660
	21st to end	Day	10% 5% 2 7% 5% 4 5% 5% 7% 9% 40%	2660
July	1st to 10th	Day	9% 8% 3 7% 5% 5% 6% 4 7% 9% 37%	4440
	11th to 20th	Day	6% 4 1 5% 4 4 5% 4 6% 9% 52%	4440
	21st to end	Day	5% 5% 2 6% 5% 5% 6% 5% 8% 12% 40%	4659
August	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 5% 8% 11% 45%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 9% 40%	3931
	21st to end	Day	7% 5% 2 6% 4 4 4 4 5% 9% 50%	4180
September	1st to 10th	Day	13% 4 2 4 3 4 4 3 6% 7% 51%	2280
	11th to 20th	Day	10% 4 2 5% 3 3 3 3 6% 9% 52%	2280
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 7% 48%	2014
October	1st to 10th	Day	12% 7% 2 5% 5% 4 3 3 4 6% 49%	1900
	11th to 20th	Day	15% 7% 2 6% 4 3 3 3 4 6% 45%	1900
	21st to end	Day	17% 8% 2 6% 4 4 4 3 5% 6% 41%	2071
November	1st to 10th	Day	11% 7% 3 6% 4 4 4 3 5% 7% 45%	1699
	11th to 20th	Day	16% 10% 3 6% 4 4 4 3 5% 7% 37%	1630
	21st to end	Day	17% 10% 3 6% 3 4 3 4 4 6% 40%	1520
December	1st to 10th	Day	14% 13% 3 9% 5% 4 5% 3 4 6% 33%	1520
	11th to 20th	Day	13% 10% 5% 8% 5% 5% 4 4 5% 7% 34%	1918
	21st to end	Day	22% 18% 7% 12% 5% 4 3 3 4 4 18%	2783
January	1st to 10th	Night	12% 11% 7% 14% 6% 4 4 3 4 5% 29%	4428
	11th to 20th	Night	12% 16% 6% 11% 5% 5% 5% 3 8% 5% 24%	4309
	21st to end	Night	18% 17% 6% 12% 5% 4 3 3 4 5% 24%	4532
February	1st to 10th	Night	15% 12% 4 8% 5% 5% 4 3 5% 6% 34%	2470
	11th to 20th	Night	13% 8% 3 7% 5% 4 4 3 6% 6% 40%	2363
	21st to end	Night	14% 10% 4 9% 4 3 3 2 4 5% 42%	1884
March	1st to 10th	Night	17% 8% 3 6% 4 4 3 3 4 5% 43%	3615
	11th to 20th	Night	11% 5% 2 6% 3 4 4 3 4 6% 52%	3480
	21st to end	Night	21% 11% 5% 10% 5% 5% 5% 4 4 5% 24%	3690
April	1st to 10th	Night	16% 8% 3 6% 4 4 4 3 5% 6% 42%	1900
	11th to 20th	Night	16% 8% 2 5% 4 4 4 3 5% 6% 43%	1875
	21st to end	Night	17% 7% 2 6% 4 4 5% 3 5% 6% 39%	1900
May	1st to 10th	Night	19% 7% 2 7% 4 4 4 3 5% 6% 37%	2709
	11th to 20th	Night	13% 5% 2 6% 4 5% 5% 4 5% 6% 44%	2506
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 4 6% 8% 48%	2743
June	1st to 10th	Night	8% 5% 2 5% 4 4 5% 4 7% 9% 49%	1520
	11th to 20th	Night	8% 4 2 6% 4 4 4 4 7% 9% 48%	1520
	21st to end	Night	8% 5% 3 5% 5% 4 3 5% 6% 8% 48%	1520
July	1st to 10th	Night	12% 5% 2 6% 5% 5% 5% 4 6% 8% 42%	2530
	11th to 20th	Night	4 4 1 3 3 3 3 3 6% 9% 62%	2530
	21st to end	Night	6% 5% 2 5% 4 4 5% 4 7% 8% 49%	2900
August	1st to 10th	Night	4 4 1 5% 3 4 4 4 7% 10% 54%	2836
	11th to 20th	Night	7% 4 2 5% 4 3 3 3 5% 7% 55%	2891
	21st to end	Night	7% 4 2 5% 4 4 4 4 5% 9% 55%	3476
September	1st to 10th	Night	10% 4 1 4 3 2 3 3 4 7% 57%	1900
	11th to 20th	Night	10% 5% 1 5% 4 3 4 4 5% 7% 53%	1900
	21st to end	Night	7% 5% 1 5% 4 4 4 4 5% 7% 54%	2142
October	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 4 6% 53%	2280
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 5% 6% 49%	2280
	21st to end	Night	16% 8% 3 7% 4 5% 3 3 4 5% 42%	2526
November	1st to 10th	Night	9% 7% 2 4 3 3 3 3 4 7% 55%	2452
	11th to 20th	Night	13% 8% 3 7% 4 4 4 4 5% 6% 42%	2546
	21st to end	Night	16% 9% 2 7% 4 4 4 3 4 6% 40%	2660
December	1st to 10th	Night	14% 11% 3 8% 5% 4 5% 3 4 6% 37%	2660
	11th to 20th	Night	13% 11% 4 9% 5% 4 4 3 5% 6% 37%	3279
	21st to end	Night	21% 16% 7% 11% 5% 5% 4 3 4 4 21%	4884

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% 4 11% 15% 7%	2528
	11th to 20th	Day	61% 3 11% 18% 7%	2658
	21st to end	Day	70% 3 9% 12% 5%	3135
February	1st to 10th	Day	56% 3 14% 19% 7% 1	1710
	11th to 20th	Day	49% 4 13% 23% 10% 1	1711
	21st to end	Day	49% 4 12% 22% 10% 2	1570
March	1st to 10th	Day	48% 3 11% 23% 15% 1	3268
	11th to 20th	Day	37% 4 13% 26% 18% 1	3480
	21st to end	Day	61% 4 15% 16% 4 1	3940
April	1st to 10th	Day	51% 4 11% 24% 10%	2280
	11th to 20th	Day	48% 4 9% 24% 12% 2	2254
	21st to end	Day	50% 5% 10% 20% 13% 1	2280
May	1st to 10th	Day	49% 4 11% 20% 15% 1	4226
	11th to 20th	Day	45% 4 10% 28% 12%	4403
	21st to end	Day	39% 5% 10% 27% 18% 1	4837
June	1st to 10th	Day	34% 6% 16% 26% 15% 3	2660
	11th to 20th	Day	34% 6% 11% 24% 22% 4	2660
	21st to end	Day	38% 8% 15% 22% 16% 2	2660
July	1st to 10th	Day	43% 6% 11% 28% 10% 2	4371
	11th to 20th	Day	29% 7% 14% 31% 18% 2	4365
	21st to end	Day	33% 10% 19% 22% 16% 1	4512
August	1st to 10th	Day	31% 8% 16% 30% 14% 1	4090
	11th to 20th	Day	40% 6% 12% 27% 15% 1	3970
	21st to end	Day	31% 5% 14% 32% 16% 2	4179
September	1st to 10th	Day	32% 5% 10% 27% 21% 5%	2280
	11th to 20th	Day	30% 4 12% 32% 19% 3	2280
	21st to end	Day	34% 5% 9% 30% 19% 2	2014
October	1st to 10th	Day	23% 3 6% 23% 43% 2	3160
	11th to 20th	Day	27% 3 10% 23% 30% 7%	3140
	21st to end	Day	41% 2 9% 28% 17% 3	3397
November	1st to 10th	Day	38% 4 14% 25% 16% 3	1699
	11th to 20th	Day	47% 3 13% 22% 14% 1	1630
	21st to end	Day	47% 4 14% 25% 10%	1520
December	1st to 10th	Day	53% 4 13% 21% 8% 1	1520
	11th to 20th	Day	51% 4 13% 21% 10% 1	1915
	21st to end	Day	72% 3 7% 12% 4	2783
January	1st to 10th	Night	60% 3 10% 18% 9% 1	4428
	11th to 20th	Night	60% 3 12% 13% 11% 1	4309
	21st to end	Night	64% 3 11% 16% 6% 1	4532
February	1st to 10th	Night	51% 3 10% 23% 11% 1	2470
	11th to 20th	Night	44% 5% 12% 25% 12% 2	2364
	21st to end	Night	46% 2 10% 25% 15% 2	1884
March	1st to 10th	Night	45% 4 9% 25% 16% 1	3615
	11th to 20th	Night	35% 3 11% 32% 15% 4	3480
	21st to end	Night	62% 4 15% 13% 5% 1	3690
April	1st to 10th	Night	44% 3 10% 26% 14% 2	1900
	11th to 20th	Night	43% 4 9% 24% 17% 4	1875
	21st to end	Night	45% 4 10% 24% 14% 3	1900
May	1st to 10th	Night	47% 4 11% 21% 17% 1	2736
	11th to 20th	Night	39% 5% 14% 26% 14% 1	2507
	21st to end	Night	33% 6% 10% 27% 22% 2	2751
June	1st to 10th	Night	31% 6% 16% 28% 17% 3	1520
	11th to 20th	Night	30% 7% 12% 26% 22% 4	1520
	21st to end	Night	32% 7% 15% 23% 19% 4	1520
July	1st to 10th	Night	39% 5% 14% 27% 12% 3	2490
	11th to 20th	Night	21% 4 16% 35% 23% 1	2482
	21st to end	Night	30% 7% 17% 25% 19% 2	2808
August	1st to 10th	Night	24% 6% 18% 33% 17% 2	2826
	11th to 20th	Night	28% 5% 15% 33% 18% 1	2918
	21st to end	Night	28% 6% 13% 31% 17% 5%	3476
September	1st to 10th	Night	28% 5% 8% 29% 26% 4	1900
	11th to 20th	Night	32% 4 10% 30% 20% 5%	1900
	21st to end	Night	29% 5% 9% 31% 24% 3	2142
October	1st to 10th	Night	23% 3 6% 24% 41% 3	3800
	11th to 20th	Night	27% 2 9% 23% 31% 8%	3779
	21st to end	Night	45% 3 7% 22% 19% 4	4150
November	1st to 10th	Night	31% 5% 15% 27% 19% 4	2452
	11th to 20th	Night	42% 3 12% 27% 14% 2	2546
	21st to end	Night	46% 3 12% 25% 13% 1	2660
December	1st to 10th	Night	49% 4 12% 24% 10% 1	2660
	11th to 20th	Night	49% 4 12% 26% 9% 1	3281
	21st to end	Night	67% 3 9% 15% 6%	4884

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% 14% 32% 22% 9% 2	270
	11th to 20th	Day	22% 16% 39% 18% 4	270
	21st to end	Day	20% 14% 36% 25% 5%	297
February	1st to 10th	Day	19% 20% 35% 21% 4	270
	11th to 20th	Day	20% 18% 32% 23% 7%	270
	21st to end	Day	22% 14% 43% 17% 4	225
March	1st to 10th	Day	18% 19% 43% 16% 5%	270
	11th to 20th	Day	21% 17% 33% 22% 7% 1	270
	21st to end	Day	33% 15% 31% 15% 6% 1	372
April	1st to 10th	Day	23% 15% 35% 20% 6% 1	460
	11th to 20th	Day	21% 15% 31% 22% 10% 1	452
	21st to end	Day	23% 13% 33% 19% 10% 1	460
May	1st to 10th	Day	20% 13% 34% 24% 7% 2	635
	11th to 20th	Day	20% 10% 28% 25% 13% 3	675
	21st to end	Day	15% 9% 26% 27% 16% 6%	734
June	1st to 10th	Day	8% 5% 26% 34% 20% 7%	680
	11th to 20th	Day	10% 5% 28% 34% 20% 3	680
	21st to end	Day	12% 9% 31% 30% 15% 3	680
July	1st to 10th	Day	8% 3 16% 35% 24% 13%	671
	11th to 20th	Day	11% 4 21% 34% 24% 7%	668
	21st to end	Day	7% 2 20% 36% 28% 6%	739
August	1st to 10th	Day	7% 3 21% 36% 25% 8%	676
	11th to 20th	Day	11% 4 17% 33% 28% 6%	607
	21st to end	Day	9% 2 18% 34% 29% 8%	539
September	1st to 10th	Day	15% 4 18% 32% 24% 7%	490
	11th to 20th	Day	9% 3 17% 38% 23% 10%	490
	21st to end	Day	13% 9% 27% 22% 25% 4	382
October	1st to 10th	Day	17% 8% 30% 26% 14% 5%	300
	11th to 20th	Day	14% 23% 32% 20% 11%	300
	21st to end	Day	27% 14% 30% 23% 5% 1	330
November	1st to 10th	Day	16% 7% 43% 22% 10% 3	279
	11th to 20th	Day	21% 15% 30% 22% 9% 2	270
	21st to end	Day	24% 11% 34% 26% 5%	270
December	1st to 10th	Day	14% 16% 38% 22% 8% 3	270
	11th to 20th	Day	16% 16% 36% 23% 9%	270
	21st to end	Day	25% 17% 39% 15% 3	297
January	1st to 10th	Night	15% 13% 39% 24% 7% 1	950
	11th to 20th	Night	18% 13% 37% 25% 6%	950
	21st to end	Night	20% 11% 36% 27% 6%	1045
February	1st to 10th	Night	22% 10% 37% 25% 5%	950
	11th to 20th	Night	18% 13% 35% 29% 4	889
	21st to end	Night	21% 13% 40% 22% 4 1	628
March	1st to 10th	Night	18% 12% 40% 23% 6% 1	694
	11th to 20th	Night	18% 11% 34% 30% 7%	570
	21st to end	Night	25% 11% 36% 23% 5% 1	627
April	1st to 10th	Night	21% 13% 38% 25% 3	570
	11th to 20th	Night	20% 12% 31% 29% 7%	563
	21st to end	Night	20% 9% 34% 28% 8% 1	570
May	1st to 10th	Night	18% 8% 37% 28% 8% 1	570
	11th to 20th	Night	19% 6% 30% 32% 12%	561
	21st to end	Night	12% 4 32% 33% 19%	617
June	1st to 10th	Night	10% 3 24% 45% 17% 1	570
	11th to 20th	Night	9% 4 26% 44% 17% 1	570
	21st to end	Night	10% 6% 25% 41% 17% 1	570
July	1st to 10th	Night	7% 3 14% 42% 31% 3	555
	11th to 20th	Night	5% 2 20% 43% 27% 3	552
	21st to end	Night	8% 2 14% 47% 28% 2	624
August	1st to 10th	Night	6% 2 15% 45% 28% 3	567
	11th to 20th	Night	9% 2 15% 44% 26% 4	564
	21st to end	Night	10% 1 13% 44% 29% 3	627
September	1st to 10th	Night	13% 2 18% 39% 26% 3	570
	11th to 20th	Night	13% 2 18% 38% 24% 5%	570
	21st to end	Night	8% 6% 27% 36% 21% 2	708
October	1st to 10th	Night	15% 6% 28% 32% 18% 2	760
	11th to 20th	Night	19% 11% 30% 31% 10%	760
	21st to end	Night	20% 11% 34% 27% 7%	836
November	1st to 10th	Night	14% 10% 38% 28% 9% 1	755
	11th to 20th	Night	17% 13% 40% 24% 6%	836
	21st to end	Night	22% 10% 34% 27% 6%	950
December	1st to 10th	Night	19% 10% 38% 27% 5% 1	950
	11th to 20th	Night	21% 12% 32% 29% 6%	950
	21st to end	Night	25% 14% 33% 24% 3	1045

Page generated at 2024-11-01 21:47:30. Version ac07

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