Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 230749
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
249 AM CDT WED JUL 23 2014

.DISCUSSION...
248 AM CDT

TODAY THROUGH TONIGHT...
EARLY THIS MORNING IR IMAGERY DEPICTS A CHANNEL OF COOLER CLOUDS
STRETCHING FROM FORD COUNTY NORTHEAST THROUGH NORTHWEST INDIANA.
RADAR CONTINUES TO SHOW A RAGGED LINE OF CONVECTION UNDER THESE
CLOUDS...WHICH SHOULD CONTINUE TO SAG SOUTHEAST AS THE FRONTAL
BOUNDARY PUSHES SOUTH ACROSS THE FORECAST AREA THIS MORNING.
INSTABILITY ALONG AND SOUTH OF THE BOUNDARY REMAINS...WITH MOST OF
THE CONVECTION BEING ROOTED IN THE MID-LVLS AS LAPSE RATES CONTINUE
TO REMAIN RATHER STEEP. FORTUNATELY THOUGH THE INTENSITY OF THE
STORMS SHUD CONTINUE TO REMAIN SUB-SEVERE AND PERHAPS ANOTHER SPS
WILL BE NEEDED BEFORE ACTIVITY PUSHES SOUTH OF THE FORECAST AREA.

OTHERWISE HIGH PRESSURE WILL BUILD INTO THE REGION TODAY...WITH
WINDS SHIFTING NORTHERLY TO SLIGHTLY NORTHEASTERLY. THIS WILL
PROVIDE AN INVERSE AIRMASS FROM THE PAST 48 HOURS...TO A MUCH DRIER
AND SUB-SEASONAL TEMPS. THE PRESSURE GRADIENT WILL REMAIN TIGHT ON
THE LEE-SIDE OF THE SFC RIDGE...RESULTING IN A STRONGER MARINE
INFLUENCE ON TEMPS ALONG THE IMMEDIATE SHORELINE TODAY. THUS IT IS
LIKELY THAT AFTN HIGHS MAY STRUGGLE TO TOUCH 70...MEANWHILE INLAND
AREAS WILL BE GENERALLY IN THE LOW/MID 70S.

TONIGHT HIGH PRESSURE WILL BE OVERHEAD WITH JUST A LIGHT NORTHERLY
FLOW AND PERHAPS WINDS WILL BECOME CALM FOR THE NORTHERN CWFA. TEMPS
SHUD EASILY RADIATE INTO THE LOWER 50S. A FEW LOCATIONS COULD DIP
INTO THE UPR 40S JUST BEFORE SUNRISE THUR...MAINLY ACROSS THE FOX
VALLEY.

THURSDAY...
ANTI-CYCLONIC FLOW WILL CONTINUE TO DOMINATE THE REGION THRU
THUR...WITH MINIMAL CLOUD COVER AND TEMPS GENERALLY IN THE MID 70S.
THE EXCEPTION WILL BE LOCATIONS ADJACENT TO LAKE MICHIGAN WHERE A
LAKE BREEZE/ONSHORE FLOW WILL KEEP TEMPS ARND 70.

MID-LVL TROUGH AXIS BEGINS TO PIVOT EAST THUR NGT...WITH THE SFC
RIDGE DRIFTING EAST AND ALLOWING WINDS TO SLOWLY TURN SOUTHERLY
AHEAD OF THE NEXT WAVE SET TO ARRIVE FRI.

CONFIDENCE...HIGH.

FRIDAY THROUGH TUESDAY...
MID-LVL RIDGE CENTERED OVER THE SOUTHERN PLAINS WILL BEGIN TO
FLATTEN ALONG THE NORTHERN FRINGES...ALLOWING FOR AN EASE OF SYSTEMS
TO TRAVERSE THE NORTHERN TIER STATES EAST ACROSS THE GREAT LAKES
REGION. GUIDANCE HAS CONTINUED TO POINT TOWARDS A WEAK SFC WAVE
SLIDING EAST FROM THE CENTRAL PLAINS FRI...ARRIVING OVER THE
FORECAST AREA WITH SOME ENHANCEMENT TO THE PRECIP OUTPUT DUE TO WARM
AIR ADVECTION AND ASCENT TO PARCELS. THUS HAVE NUDGED POPS UP
SLIGHTLY DURING THE DAY FRI...WITH THE FOCUS LIKELY MIDDAY THRU
EARLY EVENING.

A MID-LVL VORT PROGGED TO BE OVER THE CANADIAN PRAIRIES FRI...WILL
SLOWLY MOVE EAST FRI NGT BEFORE SLIDING SOUTHEAST ACROSS THE GREAT
LAKES REGION LATER IN THE WEEKEND. ENSEMBLES CONTINUE TO POINT
TOWARDS ANOTHER PATTERN ADJUSTMENT OVER THE SECOND HALF OF THE
WEEKEND INTO EARLY NEXT WEEK...AS THE NORTH ATLANTIC RIDGE RETURNS
AND PREVENTS THE AFOREMENTIONED UPPER MIDWEST SHORTWAVE FROM
DEPARTING. IN ADDITION A HIGH AMPLITUDE RIDGE CONTINUES TO BE
PROGGED ACROSS THE WESTERN CONUS...KEEPING THE MID-LVL TROUGH OVER
HUDSON BAY/GREAT LAKES THRU MON/TUE.

THE OVERALL THEME CONTINUES TO BE A BRIEF RETURN TO SEASONAL TEMPS
FOR THE WEEKEND IN THE LOW 80S...HOWEVER ONCE THE TROUGH RETURNS TO
THE GREAT LAKES REGION SO WILL THE UNSEASONABLY COOLER AIR. TEMPS BY
EARLY NEXT WEEK WILL MAINLY BE IN THE MID/UPR 70S.

CONFIDENCE...HIGH.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* POTENTIAL FOR MVFR CIGS OVERNIGHT.
* GUSTY NNE/NE WINDS TONIGHT THROUGH WEDNESDAY EVENING.

BMD

//DISCUSSION...UPDATED 06Z...

A COLD FRONT IS DROPPING SOUTH ACROSS THE REGION TONIGHT WITH A
BROKEN LINE OF THUNDERSTORMS ALREADY MOVING SOUTH OF THE TERMINALS.
BEHIND THE FRONT WINDS HAVE TURNED NORTHEAST WITH GUSTS INTO THE LOW
TO MID 20 KT RANGE. SOME STRATUS IS ALSO EVIDENT ON SPLIT CHANNEL IR
IMAGERY HUGGING THE LAKE MICHIGAN SHORES WITH CEILINGS BETWEEN
ROUGHLY 025 AND 035. FARTHER UPSTREAM VFR CONDITIONS PREVAIL WITH
JUST SOME PATCHY MID AND HIGH CLOUDS. WITH COLD ADVECTION INTO THE
AREA...MODERATE WINDS TO AROUND 30 KT ARE EVIDENT IN SOUNDINGS AS
LOW AS AROUND 010 AND MAY BE ABLE TO MIX DOWN TO THE SURFACE AT
TIMES OVERNIGHT RESULTING IN CONTINUED GUSTINESS THROUGH THE
OVERNIGHT HOURS. IN FACT...WINDS MAY NOT BEGIN TO TAPER UNTIL CLOSER
TO SUNSET WEDNESDAY EVENING.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION...MEDIUM IN WIND GUSTS SPEEDS.
* LOW CONFIDENCE IN PREVAILING MVFR CIGS OVERNIGHT.
* HIGH CONFIDENCE IN VFR CONDITIONS THROUGH THE DAY WEDNESDAY.

BMD

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

THURSDAY...VFR. NORTHEAST WINDS.
FRIDAY...CHANCE OF TSRA DURING THE NIGHT.
SATURDAY-MONDAY...PERIODIC CHANCES OF TSRA.

MTF

&&

.MARINE...
300 PM CDT

LOW PRESSURE OVER SOUTHERN QUEBEC WILL CONTINUE TO DEEPEN AS IT
MOVES ACROSS QUEBEC TONIGHT WHILE HIGH PRESSURE MOVES OFF THE MID
ATLANTIC COAST. A STRONG COLD FRONT ASSOCIATED WITH THE LOW WILL
PUSH SOUTH DOWN THE LENGTH OF THE LAKE TONIGHT. MODERATELY STRONG
SOUTH TO SOUTHWEST WINDS WILL VEER TO NORTHERLY FOLLOWING THE
FRONTAL PASSAGE WITH WINDS INCREASING TO 30 KT WITH OCCASIONAL 35
KT GALE FORCE GUSTS POSSIBLE. A SMALL CRAFT ADVISORY ASSOCIATED
WITH THE STRONG NORTH WINDS WILL GO INTO EFFECT LATE TONIGHT AND
REMAIN IN EFFECT THROUGH THURSDAY MORNING WHEN WINDS AND WAVES
WILL TAPER OFF AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE
REGION.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ006-ILZ014 UNTIL 10 AM THURSDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 10 AM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM THURSDAY.

&&

$$

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