Decatur(IL)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Decatur(IL) clear sky chart from 2005-11-06 to 2024-01-12.

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 6% 5% 3 5% 5% 5% 7% 39%	74784
	Night	14% 8% 3 6% 5% 3 4 4 5% 7% 41%	74952
Transparency	Day	44% 4 12% 24% 14% 2	74485
	Night	44% 3 11% 24% 15% 3	74772
Seeing	Day	16% 10% 28% 26% 15% 6%	14514
	Night	17% 10% 30% 29% 13% 1	24469

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	15% 13% 5% 10% 7% 4 5% 4 4 7% 27%	1517
	11th to 20th	Day	17% 15% 8% 9% 8% 4 4 3 4 5% 24%	1448
	21st to end	Day	14% 14% 8% 10% 6% 4 5% 3 4 4 28%	1750
February	1st to 10th	Day	16% 12% 6% 11% 6% 4 5% 4 4 5% 28%	1664
	11th to 20th	Day	14% 10% 4 8% 9% 4 5% 4 5% 6% 30%	1748
	21st to end	Day	18% 13% 5% 8% 6% 3 4 4 4 6% 30%	1480
March	1st to 10th	Day	17% 10% 4 8% 6% 3 4 4 4 5% 36%	1800
	11th to 20th	Day	15% 12% 4 7% 6% 2 5% 5% 5% 8% 33%	1892
	21st to end	Day	21% 13% 5% 7% 6% 3 4 4 5% 5% 26%	2361
April	1st to 10th	Day	14% 8% 4 5% 6% 4 4 4 6% 7% 37%	2160
	11th to 20th	Day	16% 9% 4 5% 4 3 4 4 4 6% 40%	2134
	21st to end	Day	20% 8% 4 5% 4 3 4 4 5% 6% 37%	2160
May	1st to 10th	Day	17% 8% 4 6% 5% 3 4 5% 6% 8% 33%	2340
	11th to 20th	Day	17% 9% 2 5% 5% 3 5% 5% 5% 7% 36%	2389
	21st to end	Day	11% 6% 3 6% 7% 3 6% 6% 7% 9% 36%	2725
June	1st to 10th	Day	8% 4 2 5% 5% 3 5% 6% 7% 9% 45%	2520
	11th to 20th	Day	9% 4 2 5% 4 3 5% 5% 6% 8% 48%	2520
	21st to end	Day	8% 5% 2 6% 6% 4 5% 6% 7% 10% 41%	2520
July	1st to 10th	Day	9% 4 2 4 5% 4 6% 6% 7% 10% 44%	2520
	11th to 20th	Day	6% 4 3 5% 5% 3 6% 5% 7% 10% 46%	2520
	21st to end	Day	9% 3 2 4 4 3 5% 6% 7% 10% 47%	2743
August	1st to 10th	Day	8% 4 2 4 5% 4 5% 5% 6% 11% 46%	2315
	11th to 20th	Day	8% 3 2 5% 5% 3 6% 7% 7% 10% 43%	2125
	21st to end	Day	7% 4 2 4 5% 3 5% 5% 7% 9% 49%	2376
September	1st to 10th	Day	13% 6% 2 5% 4 3 4 5% 5% 7% 46%	2160
	11th to 20th	Day	10% 5% 2 5% 4 3 5% 4 4 8% 50%	2075
	21st to end	Day	8% 5% 2 4 4 3 4 4 6% 8% 52%	1980
October	1st to 10th	Day	12% 5% 2 4 4 3 4 4 5% 6% 50%	1898
	11th to 20th	Day	17% 7% 3 5% 4 3 4 5% 5% 6% 43%	1800
	21st to end	Day	18% 9% 3 6% 5% 3 4 4 4 6% 38%	1850
November	1st to 10th	Day	10% 6% 3 4 4 2 3 4 4 9% 51%	1672
	11th to 20th	Day	16% 9% 5% 5% 4 2 3 5% 4 7% 41%	1710
	21st to end	Day	16% 11% 4 6% 5% 2 4 3 4 5% 39%	1691
December	1st to 10th	Day	15% 11% 6% 8% 7% 3 5% 4 5% 7% 30%	1520
	11th to 20th	Day	15% 12% 4 10% 6% 4 4 4 5% 7% 29%	1918
	21st to end	Day	21% 18% 6% 14% 5% 3 4 3 4 6% 16%	2783
January	1st to 10th	Night	13% 12% 5% 8% 6% 3 5% 4 5% 6% 33%	2648
	11th to 20th	Night	17% 11% 5% 10% 8% 4 5% 3 3 5% 30%	2541
	21st to end	Night	14% 12% 6% 9% 6% 4 4 4 4 6% 30%	2601
February	1st to 10th	Night	17% 12% 5% 9% 6% 4 4 3 4 6% 29%	2295
	11th to 20th	Night	15% 8% 4 8% 6% 4 4 3 5% 7% 36%	2098
	21st to end	Night	19% 9% 4 7% 6% 3 4 4 4 5% 35%	1776
March	1st to 10th	Night	16% 10% 4 6% 5% 3 4 4 4 5% 37%	2160
	11th to 20th	Night	16% 9% 3 6% 5% 3 5% 4 5% 7% 37%	2084
	21st to end	Night	21% 10% 4 6% 5% 3 4 4 4 6% 33%	1994
April	1st to 10th	Night	13% 6% 4 6% 6% 3 4 5% 5% 6% 43%	1800
	11th to 20th	Night	17% 7% 2 5% 4 2 3 4 4 6% 45%	1775
	21st to end	Night	22% 7% 2 6% 5% 3 5% 4 4 6% 36%	1798
May	1st to 10th	Night	15% 6% 3 6% 6% 3 5% 5% 5% 8% 39%	1620
	11th to 20th	Night	16% 7% 3 5% 5% 3 5% 5% 4 7% 42%	1502
	21st to end	Night	10% 6% 3 7% 5% 4 5% 5% 6% 9% 40%	1551
June	1st to 10th	Night	9% 5% 1 4 4 2 4 5% 5% 10% 51%	1440
	11th to 20th	Night	7% 4 2 5% 5% 2 4 6% 5% 8% 53%	1440
	21st to end	Night	7% 5% 2 5% 5% 2 5% 5% 7% 11% 46%	1440
July	1st to 10th	Night	10% 4 2 5% 4 3 5% 5% 6% 10% 47%	1440
	11th to 20th	Night	5% 3 2 3 3 3 4 5% 6% 10% 57%	1440
	21st to end	Night	5% 3 2 4 4 3 4 5% 5% 10% 54%	1575
August	1st to 10th	Night	7% 3 1 4 5% 2 4 5% 8% 9% 52%	1618
	11th to 20th	Night	6% 4 2 5% 6% 3 5% 5% 5% 8% 52%	1776
	21st to end	Night	5% 3 1 4 4 3 5% 4 5% 8% 55%	1980
September	1st to 10th	Night	11% 4 2 5% 3 3 4 4 5% 8% 51%	1800
	11th to 20th	Night	8% 4 2 3 4 2 4 4 6% 9% 55%	1867
	21st to end	Night	8% 5% 2 5% 4 2 4 4 5% 7% 54%	1980
October	1st to 10th	Night	10% 4 2 4 4 3 4 4 4 7% 54%	2060
	11th to 20th	Night	15% 6% 2 4 4 2 3 3 4 6% 49%	2160
	21st to end	Night	19% 8% 2 5% 5% 3 3 3 4 6% 42%	2506
November	1st to 10th	Night	10% 6% 2 4 5% 2 3 4 5% 6% 53%	2406
	11th to 20th	Night	12% 8% 3 5% 5% 3 4 3 4 6% 46%	2470
	21st to end	Night	18% 8% 4 6% 4 2 4 3 4 6% 40%	2488
December	1st to 10th	Night	17% 10% 4 8% 6% 3 5% 4 5% 7% 32%	2660
	11th to 20th	Night	17% 9% 5% 9% 5% 3 3 3 3 5% 37%	3279
	21st to end	Night	24% 19% 6% 9% 6% 3 4 3 3 4 17%	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	59% 3 8% 19% 10% 1	1518
	11th to 20th	Day	65% 2 10% 16% 7%	1448
	21st to end	Day	60% 3 12% 17% 7%	1750
February	1st to 10th	Day	59% 3 11% 17% 8% 1	1664
	11th to 20th	Day	55% 3 10% 21% 9% 1	1758
	21st to end	Day	57% 3 8% 21% 9% 2	1480
March	1st to 10th	Day	51% 4 10% 24% 10% 1	1800
	11th to 20th	Day	51% 4 12% 23% 9% 1	1892
	21st to end	Day	60% 4 10% 19% 6% 1	2361
April	1st to 10th	Day	46% 4 12% 24% 14%	2160
	11th to 20th	Day	47% 3 10% 25% 11% 3	2134
	21st to end	Day	49% 3 13% 21% 12% 3	2160
May	1st to 10th	Day	49% 4 15% 23% 8% 1	2340
	11th to 20th	Day	47% 5% 13% 20% 14% 1	2393
	21st to end	Day	43% 6% 14% 21% 14% 2	2725
June	1st to 10th	Day	34% 5% 15% 27% 16% 3	2520
	11th to 20th	Day	33% 5% 11% 27% 21% 4	2520
	21st to end	Day	37% 6% 15% 23% 16% 3	2520
July	1st to 10th	Day	35% 4 14% 29% 15% 3	2451
	11th to 20th	Day	32% 7% 15% 29% 15% 2	2445
	21st to end	Day	31% 5% 15% 31% 16% 2	2591
August	1st to 10th	Day	32% 6% 16% 32% 12% 2	2300
	11th to 20th	Day	33% 7% 15% 29% 15% 2	2125
	21st to end	Day	30% 5% 13% 26% 18% 7%	2376
September	1st to 10th	Day	39% 4 8% 26% 18% 5%	2160
	11th to 20th	Day	33% 4 8% 27% 23% 4	2075
	21st to end	Day	31% 4 8% 30% 23% 3	1980
October	1st to 10th	Day	35% 3 11% 27% 21% 3	1898
	11th to 20th	Day	41% 4 8% 23% 22% 2	1800
	21st to end	Day	48% 3 9% 24% 15% 2	1850
November	1st to 10th	Day	33% 3 14% 28% 19% 4	1672
	11th to 20th	Day	44% 3 10% 25% 15% 3	1710
	21st to end	Day	50% 3 11% 23% 13%	1691
December	1st to 10th	Day	54% 3 11% 21% 10%	1520
	11th to 20th	Day	55% 3 8% 25% 7% 1	1915
	21st to end	Day	71% 3 9% 11% 5%	2783
January	1st to 10th	Night	53% 4 8% 21% 14%	2648
	11th to 20th	Night	58% 2 10% 21% 8%	2541
	21st to end	Night	55% 3 12% 20% 9% 1	2601
February	1st to 10th	Night	57% 3 11% 17% 9% 2	2295
	11th to 20th	Night	49% 3 10% 23% 13% 2	2099
	21st to end	Night	51% 3 10% 23% 10% 3	1776
March	1st to 10th	Night	50% 4 9% 22% 14% 1	2160
	11th to 20th	Night	47% 3 13% 21% 13% 2	2084
	21st to end	Night	53% 4 11% 21% 10% 1	1994
April	1st to 10th	Night	42% 3 11% 26% 16% 2	1800
	11th to 20th	Night	41% 3 9% 26% 16% 4	1775
	21st to end	Night	50% 4 10% 20% 12% 4	1798
May	1st to 10th	Night	44% 4 15% 26% 11% 1	1620
	11th to 20th	Night	42% 4 14% 23% 16% 1	1503
	21st to end	Night	40% 6% 14% 20% 16% 4	1552
June	1st to 10th	Night	31% 4 14% 28% 19% 4	1440
	11th to 20th	Night	30% 4 11% 27% 23% 5%	1440
	21st to end	Night	31% 5% 18% 24% 18% 5%	1440
July	1st to 10th	Night	33% 5% 14% 29% 15% 4	1400
	11th to 20th	Night	22% 4 14% 34% 21% 3	1392
	21st to end	Night	26% 6% 16% 31% 19% 3	1487
August	1st to 10th	Night	26% 6% 16% 32% 18% 2	1609
	11th to 20th	Night	30% 5% 11% 31% 20% 2	1776
	21st to end	Night	27% 5% 14% 26% 21% 7%	1980
September	1st to 10th	Night	32% 4 10% 27% 20% 8%	1800
	11th to 20th	Night	27% 4 8% 28% 28% 5%	1867
	21st to end	Night	30% 3 9% 28% 25% 5%	1980
October	1st to 10th	Night	31% 4 10% 26% 24% 5%	2060
	11th to 20th	Night	36% 3 7% 28% 22% 4	2160
	21st to end	Night	45% 3 8% 23% 18% 2	2506
November	1st to 10th	Night	34% 3 10% 28% 20% 6%	2406
	11th to 20th	Night	40% 3 9% 28% 19% 2	2470
	21st to end	Night	48% 2 10% 24% 16% 1	2488
December	1st to 10th	Night	52% 4 12% 20% 11% 1	2660
	11th to 20th	Night	52% 2 11% 24% 11% 1	3281
	21st to end	Night	73% 2 6% 12% 6% 1	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	26% 17% 34% 16% 7%	270
	11th to 20th	Day	27% 17% 37% 15% 3	243
	21st to end	Day	17% 21% 40% 19% 3	264
February	1st to 10th	Day	26% 18% 39% 16% 2	240
	11th to 20th	Day	25% 20% 34% 16% 3 2	240
	21st to end	Day	28% 13% 47% 10% 2	198
March	1st to 10th	Day	23% 20% 35% 18% 3	240
	11th to 20th	Day	33% 14% 35% 14% 5%	240
	21st to end	Day	32% 13% 32% 16% 6%	447
April	1st to 10th	Day	20% 12% 36% 24% 7%	420
	11th to 20th	Day	20% 17% 29% 21% 11% 1	412
	21st to end	Day	25% 13% 37% 17% 7% 2	420
May	1st to 10th	Day	20% 12% 35% 25% 6% 3	423
	11th to 20th	Day	19% 10% 26% 28% 13% 4	535
	21st to end	Day	12% 6% 33% 28% 12% 9%	679
June	1st to 10th	Day	8% 6% 24% 35% 20% 7%	630
	11th to 20th	Day	10% 5% 25% 35% 19% 6%	630
	21st to end	Day	9% 8% 31% 28% 19% 6%	630
July	1st to 10th	Day	10% 3 14% 30% 25% 17%	621
	11th to 20th	Day	7% 4 19% 35% 25% 10%	618
	21st to end	Day	10% 2 17% 35% 27% 9%	684
August	1st to 10th	Day	8% 1 18% 32% 30% 11%	564
	11th to 20th	Day	11% 2 17% 30% 29% 11%	439
	21st to end	Day	7% 2 18% 31% 32% 10%	495
September	1st to 10th	Day	13% 6% 18% 28% 28% 7%	450
	11th to 20th	Day	10% 3 14% 30% 31% 12%	450
	21st to end	Day	10% 7% 24% 28% 19% 11%	450
October	1st to 10th	Day	15% 7% 27% 29% 17% 5%	368
	11th to 20th	Day	16% 20% 32% 24% 7% 1	270
	21st to end	Day	32% 12% 36% 16% 4	297
November	1st to 10th	Day	12% 13% 37% 23% 11% 4	270
	11th to 20th	Day	22% 17% 36% 16% 7% 2	270
	21st to end	Day	26% 11% 36% 21% 5%	270
December	1st to 10th	Day	16% 18% 41% 16% 6% 3	270
	11th to 20th	Day	19% 17% 39% 22% 3 1	270
	21st to end	Day	26% 19% 37% 15% 3	297
January	1st to 10th	Night	19% 15% 40% 22% 4	950
	11th to 20th	Night	21% 16% 36% 20% 6%	908
	21st to end	Night	20% 15% 36% 26% 3	990
February	1st to 10th	Night	24% 13% 37% 23% 3	855
	11th to 20th	Night	20% 15% 38% 24% 3	703
	21st to end	Night	25% 15% 37% 20% 3	592
March	1st to 10th	Night	22% 14% 35% 25% 4	720
	11th to 20th	Night	20% 11% 35% 27% 6%	644
	21st to end	Night	25% 11% 34% 22% 8%	594
April	1st to 10th	Night	16% 15% 37% 26% 6%	540
	11th to 20th	Night	19% 12% 32% 28% 9%	533
	21st to end	Night	26% 9% 34% 24% 7% 1	540
May	1st to 10th	Night	18% 7% 35% 30% 8% 1	540
	11th to 20th	Night	17% 7% 27% 31% 16% 2	531
	21st to end	Night	11% 5% 26% 35% 20% 2	584
June	1st to 10th	Night	10% 4 23% 44% 20%	540
	11th to 20th	Night	9% 2 22% 45% 20% 1	540
	21st to end	Night	9% 4 24% 39% 23% 1	540
July	1st to 10th	Night	12% 2 11% 33% 36% 6%	525
	11th to 20th	Night	5% 1 18% 41% 31% 3	522
	21st to end	Night	6% 2 13% 47% 31% 2	591
August	1st to 10th	Night	8% 1 13% 42% 32% 4	537
	11th to 20th	Night	7% 2 13% 41% 33% 4	534
	21st to end	Night	5% 2 13% 39% 36% 4	594
September	1st to 10th	Night	11% 3 19% 37% 25% 4	540
	11th to 20th	Night	9% 2 17% 39% 29% 5%	607
	21st to end	Night	10% 6% 23% 32% 27% 3	720
October	1st to 10th	Night	11% 6% 27% 34% 19% 3	720
	11th to 20th	Night	19% 10% 29% 29% 12%	720
	21st to end	Night	22% 13% 34% 24% 6%	792
November	1st to 10th	Night	14% 10% 40% 26% 10% 1	740
	11th to 20th	Night	18% 16% 33% 27% 6% 1	760
	21st to end	Night	24% 14% 32% 25% 6%	778
December	1st to 10th	Night	23% 12% 38% 22% 5%	950
	11th to 20th	Night	24% 10% 33% 27% 6% 1	950
	21st to end	Night	31% 15% 31% 21% 3	1045

Page generated at 2024-01-09 06:14:43. Version ac07

Copyright 2024 Attilla Danko