000
FXUS63 KLOT 172031
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
331 PM CDT THU MAY 17 2012

.DISCUSSION...
331 PM CDT

MAIN CONCERNS FOR THE AFTERNOON UPDATE WILL FOCUS ON INCREASING
TEMPERATURES OVER THE NEXT FEW DAYS AND THE CHANCES FOR SHOWERS AND
THUNDERSTORMS ON SUNDAY AND MONDAY.

FOR THE REST OF THIS AFTERNOON AND TONIGHT...CONDITIONS WILL REMAIN
QUIET AS HIGH PRESSURE REMAINS THE DOMINANT FEATURE ACROSS THE
REGION.  WHILE THE CENTER OF THE HIGH HAS MOVED TO THE EASTERN GREAT
LAKES...A SFC RIDGE AXIS STILL EXTENDS SWWD ACROSS NRN IL/IN AND
INTO THE MIDDLE MISSISSIPPI VALLEY.  THIS HAS EFFECTIVELY CUT OFF
THE LOCAL AREA FROM AND SIGNIFICANT SFC MOISTURE INFLUX...PROVIDING
A VERY PLEASANT...SUNNY SPRING DAY.  A WEAK SHORTWAVE OVERTOPPING A
BUILDING UPPER RIDGE IS SPREADING INCREASING CLOUDCOVER AND SCT
SHOWERS INTO THE UPPER MIDWEST...BUT EXPECT THE SHOWERS TO REMAIN
WELL NORTH OF THE CWA AND ONLY SOME INCREASING CLOUDINESS FOR THE
NRN TIER COUNTIES.  AS THE UPPER RIDGE CONTINUES TO BUILD THROUGH
THE NIGHT...THE CLOUDINESS AND SHOWERS WILL BE SHUNTED EVEN FARTHER
NORTH...WITH MOSTLY CLEAR SKIES RETURNING TO THE ENTIRE AREA
OVERNIGHT.  WITH DEWPOINTS REMAINING RATHER LOW...TEMPERATURES
OVERNIGHT ARE EXPECTED TO DROP TO AROUND 50F.

FOR FRIDAY AND SATURDAY...SFC FLOW WILL CONTINUE TO VEER THROUGH
SELY TO SOUTHERLY...BRINGING INCREASING TEMPERATURES TO THE REGION.
TEMPERATURES IN THE LOW TO MIDDLE 80S WILL RETURN TOMORROW...BUT
WITH PREVAILING SELY SFC WINDS...COASTAL LOCATIONS OF NRN COOK AND
LAKE COUNTIES WILL REMAIN MUCH COOLER...WITH TEMPERATURES TOPPING
OUT IN THE LOW 70S.  BY SATURDAY...THE SFC HIGH WILL MOVE FAR ENOUGH
EAST AND WITH LOW PRESSURE DEEPENING OVER THE CENTRAL PLAINS...SFC
WINDS WILL BECOME MORE SOUTHERLY...OR EVEN SLIGHTLY WEST OF
SOUTH...ALLOWING THE WARMER AIR TO FULLY OVERSPREAD THE CWA...WITH
MIDDLE TO UPPER 80S TEMPERATURES REACHING ALL THE WAY TO THE
LAKEFRONT.

BY SUNDAY...THE FOCUS OF CONCERN WITH SHIFT TO THE DEVELOPING LOW
PRESSURE AND ASSOCIATED COLD FRONT OVER THE PLAINS.  THE MODELS ARE
BEGINNING TO MERGE INTO A MORE CONSISTENT SOLUTION THROUGH SUNDAY
NIGHT.  THE CONSENSUS IS TO STEADILY PUSH THE COLD FRONT EASTWARD
ACROSS THE MISSISSIPPI RIVER BY EARLY SUNDAY EVENING...BEFORE
SLOWING OVER IL/WI AS THE PARENT SFC LOW LIFTS NEWD FROM SRN
MANITOBA TO JAMES BAY.  WHILE PCPN SHOULD DEVELOP WITH THE FRONT AS
IT CROSSES THE PLAINS...THE ONSET OF PCPN INTO NRN IL SHOULD BE
DELAYED OVER THE LOCAL AREA DUE TO THE DRY AIRMASS IN PLACE.  THE
SFC RIDGE THAT HAS CUT OFF THE AREA FROM THE GLFMEX WILL BE SLOW TO
ERODE...AND EVEN INTO SUNDAY...SFC TRAJECTORIES OFF THE GULF HAVE TO
GO THROUGH SERN TX BEFORE TURNING MORE NELY.  THE MODELS ARE FINALLY
CATCHING ON TO KEEPING LOWER DEWPOINTS OVER THE REGION...RATHER THAN
QUICKLY REBOUNDING TO CLIMATOLOGICAL NORMAL LEVELS...REINFORCING THE
IDEA OF DELAYING ONSET OF PCPN INTO NWRN IL UNTIL LATE SUNDAY
AFTERNOON AT THE EARLIEST.  WITH THE PROGRESSION OF THE FRONT
SLOWING ON SUNDAY AND MONDAY...AS HAD BEEN PREVIOUSLY ADVERTISED BY
THE ECMWF...AND WITH REINFORCEMENT BY THE GFS TRENDING TOWARD A
SLOWER SOLUTION...THE DURATION OF PCPN OVER THE AREA MAY BE A LITTLE
LONGER THAN PREVIOUSLY ANTICIPATED.  AS FOR THE THUNDER
POTENTIAL...CURRENTLY THINK THAT THERE IS STILL A GOOD CHANCE FOR AT
LEAST SCT THUNDER...ESPECIALLY ALONG THE FRONTAL BOUNDARY...BUT WITH
THE MAIN SFC LOW AND ASSOCIATED UPPER LEVEL FORCING SHIFTING A
LITTLE MORE NEWD...CONFIDENCE IS A LITTLE LOWER ON THE POTENTIAL FOR
STRONGER THUNDERSTORMS.  THE MAIN CHANGE TO THE GOING FORECAST WILL
FOCUS ON INCREASING QPF.  WHEN THE DEEP LAYER MOISTURE FINALLY DOES
RETURN BY SUNDAY AS THE EWD PROGRESSION OF THE FRONT SLOWS...
RAINFALL AMOUNTS MAY BE HEAVIER THAN PREVIOUSLY ANTICIPATED.  BY
SUNDAY EVENING...PWAT AMOUNTS INCREASE TO IN EXCESS OF 1.5 INCHES
PER THE LATEST GFS...SO THERE IS INCREASING POTENTIAL FOR LOCALLY
HEAVY RAINFALL WITH SOME THUNDERSTORMS...ESPECIALLY OVERNIGHT SUNDAY
NIGHT AND INTO MONDAY MORNING.

FOR THE REMAINDER OF THE FORECAST PERIOD...FOR MONDAY THROUGH
THURSDAY...SOME LINGERING SHOWERS ARE POSSIBLE INTO MONDAY NIGHT OR
TUESDAY MORNING.  FOLLOWING THE PASSAGE OF THE SFC COLD
FRONT...TEMPERATURES WILL DROP OFF TO CLOSER TO CLIMATOLOGICALLY
NORMAL LEVELS WITH HIGHS IN THE 70S AND LOWS IN THE 50S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* EAST WINDS AROUND 10KT THROUGH THE EARLY EVENING...DIMINISHING
  AND BECOMING MORE SOUTH SOUTHEAST TONIGHT.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

MAIN SURFACE RIDGE AXIS WILL CONTINUE TO SLOWLY SHIFT TO THE EAST
BUT WITH QUIET/VFR CONDITIONS TO PREVAIL THROUGH THE ENTIRE
FORECAST PERIOD. LAKE BREEZE SLOWLY PUSHING INLAND WITH MDW
ALREADY SHIFTING TO THE EAST...BUT WITH ORD SLOWLY SEEING THIS
TRANSITION AS THIS BOUNDARY MEANDERS OVER THE TERMINAL.
ALTHOUGH...EXPECT PREVAILING DIRECTION FOR ORD TO BE MORE EASTERLY
EARLY THIS AFTERNOON BUT WITH ALL TERMINALS TO SHIFT MORE SOUTHEAST
THIS EVENING. AS HIGH PRESSURE CONTINUES EAST ON FRIDAY...A MORE
SOUTHERLY DIRECTION WITH HIGHER SPEEDS AROUND 12KT CAN BE EXPECTED
BY MID MORNING FRIDAY. A SLIGHT DEVIATION TOWARDS A SOUTHEAST
COMPONENT MIGHT BE OBSERVED FRIDAY AFTERNOON WITH A LAKE
INFLUENCE...BUT WITH LAKE BREEZE ANTICIPATED TO REMAIN EAST OF THE
TERMINALS.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE WITH VFR CONDITIONS.

* HIGH CONFIDENCE WITH WIND SPEED AND DIRECTION.

RODRIGUEZ

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

* FRIDAY NIGHT THROUGH SATURDAY...VFR.
* SUNDAY...CHANCE OF TSRA.
* SUNDAY NIGHT AND MONDAY...GOOD CHANCE OF TSRA.
* TUESDAY...CHANCE OF RAIN.
* WEDNESDAY...VFR.

KJB

&&

.MARINE...
250 PM CDT

HIGH PRES CENTERED OVER SOUTHERN LAKE HURON AT MID AFTERNOON WILL
CONTINUE TO MOVE E AND OVER THE LOWER GREAT LAKES THIS EVENING.
OVERNIGHT...THE HIGH CONTINUES ON TO THE NORTHEASTERN AND NEW
ENGLAND STATES WHILE A BROAD AREA OF LOW PRESSURE MOVES EAST TO
SOUTHERN MANITOBA...THE NORTHERN PLAINS AND THE CENTRAL ROCKIES...
LIFTING A WARM FRONT N ACROSS THE UPPER MIDWEST AND INTO THE
WESTERN GREAT LAKES. THE PRESSURE GRADIENT BETWEEN TO HIGH MOVING
OFF TO THE E AND THE LOW MOVING IN FROM THE W WILL GRADUALLY
INCREASE THE PRESSURE GRADIENT OVER LAKE MI. HOWEVER...THE WARM
FRONT WILL SPREAD VERY WARM AIR ACROSS THE REGION AND WITH STILL
COOL LAKE WATERS A STABLE LAYER AT AND NEAR THE WATER SURFACE
WILL KEEP STRONGER WINDS HIGHER ABOVE THE WATER FROM REACHING
DOWN TOWARDS THE SURFACE. THIS WILL LIMIT BOTH THE WIND STRENGTH
AND GROWTH OF WAVES DURING FRI THROUGH SUN NIGHT. THE AREA OF LOW
PRES GRADUALLY CONTINUES E DURING FRI AND SAT...REACHING WESTERN
ONTARIO...THE UPPER MS VALLEY AND THE MID MO VALLEY BY SUN
MORNING. LATE SUN NIGHT AND EARLY MON MORNING THE COMBINATION OF
THE TROUGH AND A COLD FRONT WILL MOVE E ACROSS LAKE MI. WINDS
WILL VEER TO OUT OF THE NORTHWEST AND NORTH BEHIND THE COLD FRONT
AS HIGH PRES BUILDS INTO THE UPPER MIDWEST...WESTERN GREAT LAKES
AND MID MS VALLEY BEHIND THE DEPARTING COLD FRONT DURING MON.
THESE NW-N WINDS ARE ONLY EXPECTED TO BE LIGHT BREEZES AS THE SLOW
EASTWARD PROGRESSION OF THE SURFACE FEATURES WILL RESULT IN ONLY A
GRADUAL RISE IN PRESSURE AS THE HIGH BUILDS IN.

TRS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

NWS LOT Office Area Forecast Discussion