1209 PM CDT
PRELIMINARY SHORT TERM DISCUSSION FOR THIS AFTERNOON THROUGH SAT
NIGHT...
THE UPPER LOW CENTER OF CIRCULATION WAS OVER LAKE ERIE AT MIDDAY AND
LIFTING TO THE NNE. SHORT RANGE MODEL OUTPUT HAS A GOOD HANDLE ON
THIS MOVEMENT AND CONTINUE TO LIFT THE UPPER LOW NNE-NE TO CENTRAL
QUEBEC BY 12Z FRI. WITH THE SYSTEM MOVING OFF TO THE NNE AND NE THE
REST OF TODAY AND THROUGH THE NIGHT THE BACK EDGE OF THE RAIN THAT
HAS BEEN SLOWLY ERODING/BREAKING UP OVER EASTERN WI AND NE IL AS
DRIER MID LEVEL AIR PER 12Z RAOBS...700HPA DEW POINT DEPRESSION OF
7C AT KMPX AND 12C AT KINL...GETS ENTRAINED INTO THE WEST SECTOR OF
THE GREAT LAKES SYSTEM.
THIS TREND WILL CONTINUE THE REST OF THE DAY AND BY THIS EVENING THE
WEST EDGE OF ANY SIGNIFICANT THREAT OF RAIN WILL HAVE SHIFTED OUT
OVER LAKE MI. ONLY EXCEPTION WILL BE PORTER COUNTY OF FAR NW IN
WHERE FORECAST THERMAL PROFILE STILL SUPPORTIVE OF LAKE EFFECT RAIN
BUT CLOUD BEARING LAYER FLOW FROM THE NNW-NW KEEPS MOST OF THE
REMAINING LAKE EFFECT MORE TOWARD N CENTRAL IN AND SW LOWER MI.
WITH THE WEAKENING OF THE LOW LEVEL PRESSURE GRADIENT CONTINUING
THIS AFTERNOON WINDS WILL CORRESPONDINGLY GRADUALLY DIMINISH
THOUGH REMAIN BREEZY.
MODELS SHOW THE SHORT WAVE TROUGH OVER GRB AT MIDDAY DROPPING S-SSE
AND CROSSING SE WI...NW IL AND NW IN OVERNIGHT. WHILE CONTINUED
DRYING OF LOWER AND MID WILL BE OCCURRING...THE SHORT WAVE TROUGH
WILL BRING SOME HIGH CLOUDINESS ACROSS THE LOCAL FORECAST AREA. HIGH
CLOUDS WILL CLEAR DURING OVERNIGHT BEFORE SUNRISE ALLOWING FOR
RADIATIONAL COOLING THUS THREAT OF FROST FOR EARLY MORNING FRI
REMAINS ACROSS THE WESTERN PORTIONS OF THE FORECAST AREA WHERE
COLDER TEMPERATURES AND LIGHTER WINDS WILL BE.
WITH THE UPPER LOW CONTINUING TO MOVE EVEN FARTHER AWAY FRI RIDGING
BUILDS FROM THE MID MO AND UPPER MS VALLEYS OVER THE UPPER MIDWEST
AND WESTERN GREAT LAKES. THIS WILL RESULT IN CLEAR SKIES AND A BIT
OF MODERATION IN TEMPERATURES FRI.
A SHORT WAVE IS PROGGED TO MOVE ESE FROM TO NORTHERN PLAINS TO THE
UPPER MIDWEST FRI NIGHT AND SAT. THIS SYSTEM WILL BE MOISTURE
STARVED WITH ONLY AN INCREASE IN HIGH AND SOME MID LEVEL CLOUDINESS.
THE SHORT WAVE DOES EVENTUALLY PUSH A COLD FRONT ACROSS INTO THE
LOCAL AREA SAT NIGHT WITH MODERATELY STRONG LOW LEVEL WARM AIR
ADVECTION OCCURRING AHEAD OF THE FRONT DURING SAT AS THE FLOW BACKS
TO SOUTHWESTERLY AHEAD OF THE APPROACHING SHORT WAVE TROUGH AND
ASSOCIATED COLD FRONT. THIS WARMING COMBINED WITH MAINLY SUNNY SKIES
AT LEAST FOR THE FIRST HALF OF THE DAY SHOULD ALLOW AFTERNOON
TEMPERATURES TO REACH FROM THE UPPER 50S TO THE MID 60S ACROSS THE
AREA.
TRS
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* CIG TRENDS AND TIMING OF IMPROVEMENT TO VFR LATER THIS
AFTERNOON/EVENING.
* GUSTY WINDS THIS AFTERNOON.
KJB
//DISCUSSION...UPDATED 18Z...
LOW PRESSURE ACROSS THE EASTERN GREAT LAKES WILL CONTINUE TO LOSS
ITS GRIP ON NORTHERN ILLINOIS AND NORTHWEST INDIANA AS IT MOVES
NORTHEAST THROUGH QUEBEC TONIGHT. HOWEVER...GUSTY NORTHWEST WINDS UP
TO 25 KT WILL CONTINUE THOROUGH MUCH OF THE AFTERNOON...BEFORE THE
WINDS ABATE THIS EVENING. CIGS SHOULD ALSO BE IMPROVING TO LOW END
VFR LATER THIS AFTERNOON AND SKIES SHOULD BECOME MOSTLY CLEAR
OVERNIGHT. A SURFACE RIDGE OF HIGH PRESSURE WILL BUILD IN ACROSS THE
AREA FOR FRIDAY. THIS SHOULD PRODUCE LIGHT WESTERLY FLOW ACROSS THE
TERMINALS.
KJB
//ORD AND MDW CONFIDENCE...UPDATED 18Z...
* MEDIUM TO HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* MEDIUM TO HIGH CONFIDENCE IN MVFR CIGS THROUGH MID AFTERNOON.
* MEDIUM CONFIDENCE IN CIGS IMPROVING LATE THIS AFTERNOON.
KJB
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
FRIDAY NIGHT...VFR.
SATURDAY...VFR.
SUNDAY...CHC SHRA.
MONDAY...VFR.
TUESDAY...CHC SHRA.
WEDNESDAY...CHC SHRA.
BMD
&&
.MARINE...
258 AM CDT
STRONG LOW PRESSURE NOW CENTERED NEAR TOLEDO IS NOT EXPECTED TO
MOVE MUCH FURTHER WEST AS IT BEGINS TO WEAKEN AND ELONGATE
NORTHEAST INTO SOUTHWEST QUEBEC BY THIS EVENING. BUT THE GRADIENT
DID TIGHTEN ENOUGH FOR STORM FORCE GUSTS ACROSS MUCH OF SOUTHERN
LAKE MICHIGAN. EVEN THOUGH THE LOW WILL BE WEAKENING...SLOWLY...
THE GRADIENT WILL STILL REMAIN QUITE STRONG THIS MORNING. THUS
WILL LET THE STORM WARNING CONTINUE. WINDS SLOWLY DIMINISH THROUGH
GALE FORCE THIS AFTERNOON INTO TONIGHT...SO ONCE THE STORM FORCE
WINDS ARE DONE...A GALE WARNING WILL BE NEEDED. WINDS SHOULD RELAX
BELOW GALE FORCE BY LATE THIS EVENING OR EARLY FRIDAY MORNING...
AND THEN CONTINUE TO STEADILY WEAKEN AS A RIDGE OF HIGH PRESSURE
MOVES ACROSS THE WESTERN LAKES FRIDAY AFTERNOON/EVENING. ANOTHER
AREA OF LOW PRESSURE IS EXPECTED TO MOVE ACROSS SOUTHERN CANADA
SATURDAY NIGHT INTO SUNDAY WHICH MAY INCREASE SOUTHWESTERLY FLOW
DURING THAT TIME. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKESHORE FLOOD WARNING...ILZ006-ILZ014 UNTIL 4 PM THURSDAY.
FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ019-ILZ020-ILZ021-ILZ032...1 AM FRIDAY TO 9 AM
FRIDAY.
IN...LAKESHORE FLOOD WARNING...INZ001-INZ002 UNTIL 9 PM THURSDAY.
LM...STORM WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ744-LMZ745-LMZ777-
LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM
THURSDAY.
GALE WARNING...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 7 PM THURSDAY.
&&
$$
