Heavy snow and blizzard conditions spreading across northern Illinois into the Chicago Metro area tonight

The latest mesoscale discussion from the Storm Prediction Center in Norman, Oklahoma highlights the latest storm status

MESOSCALE DISCUSSION 1664

NWS STORM PREDICTION CENTER NORMAN OK

0654 PM CST SUN NOV 25 2018

AREAS AFFECTED...NORTHERN IL AND ADJACENT PORTIONS OF EASTERN

IA/SOUTHERN WI



CONCERNING...BLIZZARD 

VALID 260054Z - 260700Z

SUMMARY...HEAVY SNOW WILL SPREAD INTO A LARGER PORTION OF NORTHERN

IL THIS EVENING. AS STRONGER WINDS MOVE IN FROM THE WEST, BLIZZARD

CONDITIONS WILL EXPAND LATER TONIGHT ACROSS THE REGION.



DISCUSSION...00Z SURFACE ANALYSIS DEPICTS A 993 MB SURFACE CYCLONE

JUST NORTHEAST OF ST. LOUIS. TO THE NORTH AND NORTHWEST OF THE LOW,

HEAVY SNOW IS ONGOING FROM NORTHEAST MO INTO NORTHWEST IL, WITH

STRONGER WINDS IN THE NORTHWESTERN QUADRANT OF THE CYCLONE PRODUCING



BLIZZARD CONDITIONS. DUAL POL PRODUCTS FROM KILX/KLOT AND RECENT

SURFACE OBS AND MPING REPORTS INDICATE THAT THE RAIN/SNOW LINE IS

MOVING EASTWARD ACROSS NORTHERN IL, AND THIS TREND IS EXPECTED TO

CONTINUE AS BACKING SURFACE WINDS RESULT IN INCREASING LOW-LEVEL

COLD ADVECTION TO THE NORTH AND NORTHWEST OF THE EAST-NORTHEASTWARD

MOVING SURFACE LOW. SNOW SHOULD CONTINUE SPREADING INTO MOST OF THE

CHICAGOLAND AREA BETWEEN NOW AND 02Z, THOUGH AREAS IN THE IMMEDIATE

VICINITY OF LAKE MICHIGAN MAY SEE A LONGER PERIOD OF MIXED

PRECIPITATION AS NORTHEASTERLY WINDS OFF OF THE LAKE MAINTAIN A

SLIGHTLY WARMER NEAR-SURFACE LAYER. 

SUBSTANTIAL CONVECTION HAS BEEN NOTED NEAR THE SURFACE LOW MOVING

INTO SOUTHERN IL, WITH A CONVECTIVE CHARACTER TO THE PRECIP (AND

SOME THUNDERSNOW REPORTS) ALSO NOTED WITHIN COOLING CLOUD TOPS

ACROSS NORTHERN IL. STRONG LOW/MIDLEVEL FRONTOGENESIS WILL CONTINUE

TO FAVOR MODERATE-TO-HEAVY SNOW TO THE NORTH OF THE MIDLEVEL LOW,

WITH SOME CONVECTIVE ENHANCEMENT POSSIBLE JUST NORTH OF THE MIDLEVEL

DRY SLOT, WHERE RELATIVELY STEEP LAPSE RATES (IN EXCESS OF 7 C/KM AS

NOTED ON ILX/DVN 00Z SOUNDINGS) WILL BE MAINTAINED. SNOW RATES OF

1-3 INCHES PER HOUR ARE EXPECTED WITHIN THE PRIMARY SNOW BAND, WHICH

SHOULD SHIFT GRADUALLY EASTWARD INTO NORTHEAST IL BY LATE TONIGHT. 

STRONG WINDS (GUSTS IN EXCESS OF 40 KT) ARE RESULTING IN ONGOING

BLIZZARD CONDITIONS FROM NORTHEAST MO INTO NORTHWEST IL. THESE

STRONGER WINDS WILL EXPAND EASTWARD WITH TIME TONIGHT IN CONJUNCTION

WITH THE MOVEMENT OF THE SURFACE LOW, RESULTING IN AN EXPANSION OF

BLIZZARD CONDITIONS INTO NORTHEAST IL AND PERHAPS FAR SOUTHEAST WI

AFTER 03Z TONIGHT.
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