Frost Climatology in Illinois

frost2It is that time of year to discuss the nemesis of every gardener out there – the late spring frost or freeze. We have a full suite of maps showing the earliest, 1 in 10 years, median, 9 in 10 years, and latest frost (32 degrees) and freeze (28 degrees).

One of the things you notice about this map, and all the others in the series, is that even though the date for the last spring frost/freeze gets later the farther north you go, you can get big differences between nearby locations. The reason for that is that most of these last frosts occur during calm, clear, cold nights. As a result, subtle local features can make a big difference. For example, cold air can settle in low-lying areas, causing frost pockets. Or locations out in the countryside may be just a few degrees cooler than in town, due to warm buildings, that may make them vulnerable to a later frost. Also, keep in mind that we measure the air temperature at 5 feet above the ground while the ground and some objects may cool to lower temperatures on calm, clear nights. Therefore, you may see frost even if the temperature is reported as 34 or 35 degrees.

Personally, I use these maps as a general guide. However, I watch the latest weather forecasts closely for a few weeks after I have new plants in the ground for any surprises. The NWS does put out hard freeze warnings (temperatures at or below 28 degrees with or without frost), freeze warning (temperatures at or below 32 degrees with or without frost), and frost advisories for widespread frost.

spring-freeze-32-median
Click to enlarge.

Frost in Illinois

frost2For much of Illinois April is typically the last month that we see freezing temperatures until Fall (at least we hope). Below are the maps showing the median dates when we see 28 and 32 degrees for the last time in Spring. The median represents the middle value in the range of dates and is less sensitive than the average to unusually early or late dates.
We have more discussion and maps, including the earliest and latest dates of freezes during the 1981-2010 period on our frost webpage.
In addition you can track the status of this spring (2013) in terms of how things stand on hitting 28 and 32 degrees from the Midwestern Regional Climate Center.

Click to enlarge.
Click to enlarge.

Click to enlarge.
Click to enlarge.

Frost on the Pumpkin in Illinois

Here are the median dates of the first time we hit 32 degrees in the fall. Since we don’t have reports of when frost occurs, we use 32 degrees as a proxy. It is no surprise that the frost date occurs earlier in northern Illinois than southern Illinois.
If you look closely, you may see differences of several days between neighboring sites. Nighttime temperatures, especially on calm, clear nights in the fall, can be very sensitive to the local conditions. Sites in town tend to be a little warmer than those in the countryside, and result in delaying the arrival of colder temperatures.
Chilly temperatures have already visited the northern part of the state this weekend. Mt. Carroll reported a low of 29 on September 23 and Elizabeth reported a low of 28 on September 24.
You can read more about frost and see many more maps on the state climatologist’s frost webpage.

Median date of first fall frost. Click to enlarge.

Frost Damage to Corn

There is an excellent article in the integrated pest management Bulletin at the University of Illinois by Emerson Nafziger about the damage of frost to corn this April and it’s impact on yield. You can read the full article at http://bulletin.ipm.illinois.edu/article.php?id=1619 

Here are the low temperatures reported last week, sorted from coldest to not so coldest. 

Station Name Low Temp(°F) Month/Day
PAXTON 20 11-Apr
CHAMPAIGN 9 SW 21 11-Apr
PAW PAW  23 11-Apr
JERSEYVILLE 2 SW 23 17-Apr
MT CARROLL 24 11-Apr
SIDELL 5 NW  24 11-Apr
WATSEKA 2 NW 24 11-Apr
LISLE-MORTON ARBORETUM 25 11-Apr
SHABBONA 5 NNE 25 10-Apr
ALTONA 25 11-Apr
MONMOUTH 4 NW  25 11-Apr
NORMAL 4NE 25 11-Apr
CONGERVILLE 2 NW 25 11-Apr
NORMAL 4NE 25 11-Apr
PERRY 6 NW 25 12-Apr
GALENA 26 11-Apr
STOCKTON 3 NNE 26 11-Apr
MARSEILLES LOCK  26 11-Apr
LA HARPE 26 11-Apr
PRINCEVILLE 2W 26 11-Apr
DWIGHT 26 11-Apr
HOOPESTON 1 NE 26 11-Apr
NEOGA 4NW  26 11-Apr
SULLIVAN 26 11-Apr
ELIZABETH  27 11-Apr
KEWANEE 1 E  27 12-Apr
ROCKFORD GTR ROCKFORD AP 27 11-Apr
DE KALB  27 11-Apr
MCHENRY STRATTON L&D 27 11-Apr
MUNDELEIN 4 WSW  27 11-Apr
BENTLEY  27 12-Apr
GALESBURG  27 11-Apr
PRAIRIE CITY 2S  27 11-Apr
CHENOA 27 11-Apr
DANVILLE 27 11-Apr
EFFINGHAM  27 11-Apr
NEWTON 27 11-Apr
PARIS WTR WKS  27 11-Apr
TUSCOLA  27 11-Apr
WINDSOR  27 12-Apr
FREEPORT WWP 28 11-Apr
HENNEPIN 28 12-Apr
MOLINE QUAD CITY INTL AP 28 12-Apr
ROCHELLE 28 11-Apr
ROCHELLE 28 11-Apr
BARRINGTON 3 SW  28 11-Apr
ELGIN  28 11-Apr
MARENGO  28 11-Apr
MORRIS 28 11-Apr
KNOXVILLE  28 11-Apr
BLOOMINGTON 5W 28 11-Apr
DECATUR  28 11-Apr
MINONK 28 11-Apr
OGDEN  28 12-Apr
PONTIAC  28 11-Apr
CARLINVILLE  28 11-Apr
MORRISONVILLE  28 11-Apr
SPRINGFIELD CAPITAL AP 28 11-Apr
CHARLESTON 28 11-Apr
PALESTINE 2W 28 11-Apr
RAMSEY 28 11-Apr
ROBINSON 28 11-Apr
SHELBYVILLE DAM  28 11-Apr
ALEDO  29 11-Apr
CHICAGO BOTANICAL GARDEN 29 11-Apr
OTTAWA 29 11-Apr
ROMEOVILLE LEWIS UNIV AP 29 11-Apr
QUINCY RGNL AP 29 11-Apr
RUSHVILLE  29 11-Apr
URBANA 29 11-Apr
GRIGGSVILLE  29 13-Apr
PITTSFIELD #2  29 12-Apr
SPRINGFIELD #2 29 11-Apr
WHITE HALL 1 E 29 12-Apr
WINCHESTER 29 11-Apr
HIDALGO 3SW  29 11-Apr
PANA 29 11-Apr
MT VERNON 3 NE 29 12-A
pr
GENESEO  30 11-Apr
NEW BOSTON DAM 17  30 13-Apr
AURORA 30 11-Apr
JOLIET BRANDON RD DM 30 11-Apr
LITTLE RED SCHOOL HSE  30 11-Apr
PARK FOREST  30 11-Apr
PEORIA GTR PEORIA AP 30 11-Apr
FISHER 30 11-Apr
RANTOUL  30 11-Apr
JACKSONVILLE 2 E 30 12-Apr
OLNEY 2S 30 11-Apr
TRIMBLE 1E 30 11-Apr
VANDALIA 30 11-Apr
CARBONDALE SEWAGE PLT  30 12-Apr
SPARTA 30 11-Apr
FAIRFIELD RADIO WFIW 30 12-Apr
ILLINOIS CITY DAM 16 31 12-Apr
CHANNAHON DRESDEN ISLAND 31 12-Apr
CHICAGO MIDWAY AP  31 11-Apr
CHICAGO MIDWAY AP 3 SW 31 11-Apr
KANKAKEE METRO WWTP  31 11-Apr
FLORA  31 12-Apr
IUKA 31 11-Apr
BELLEVILLE SIU RSRCH 31 12-Apr
DU QUOIN 4 SE  31 12-Apr
ROCK ISLAND L&D 15 32 11-Apr
ROCK ISLAND L&D 15 32 11-Apr
CHICAGO OHARE INTL AP  32 11-Apr
QUINCY DAM 21  32 12-Apr
STREATOR 32 11-Apr
JACKSONVILLE 2 32 11-Apr
CARLYLE RSVR 32 11-Apr
KASKASKIA RIV NAV LO 32 12-Apr
LEBANON  32 12-Apr
SMITHLAND L&D  32 12-Apr
MORRISON 33 17-Apr
GLADSTONE DAM 18 33 11-Apr
BIRDS 2E 33 11-Apr
LAWRENCEVILLE  33 11-Apr
SALEM  33 11-Apr
NASHVILLE 1 E  33 12-Apr
CAIRO 3 N  34 12-Apr
GRAND CHAIN DAM 53 34 12-Apr
BROOKPORT DAM 52 34 12-Apr
ALTON MELVIN PRICE 41 10-Apr
GRAYVILLE  44 10-Apr