000
FXUS63 KLOT 172358
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
658 PM CDT FRI MAY 17 2013

.DISCUSSION...

303 PM...MULTIPLE FORECAST CONCERNS THROUGH THE MIDDLE OF NEXT
WEEK INCLUDING CONVECTIVE CHANCES THIS EVENING AND THEN FROM
SUNDAY AFTERNOON THROUGH NEXT WEDNESDAY...IN ADDITION TO
TEMPERATURES...WINDS AND POTENTIAL LAKE BREEZES...AND POTENTIAL
FOR PERIODS OF HEAVY RAIN NEXT WEEK.

IN THE SHORT TERM...CONVECTION CONTINUES TO DEVELOP AND SPREAD
NORTH ACROSS THE SOUTHERN HALF OR SO OF THE CWA WHILE AN OUTFLOW/
WIND SHIFT FROM CONVECTION EARLIER THIS MORNING ACROSS WI
CONTINUES TO MOVE SOUTH OF THE I-80 CORRIDOR AND IS NOW
INTERSECTING WITH A CONVECTIVE OUTFLOW LIFTING NORTH. THIS
BOUNDARY WILL LIKELY AID ADDITIONAL DEVELOPMENT THROUGH THE
AFTERNOON. AS NOTED IN THE MESOSCALE DISCUSSION ABOVE...MAIN
CONCERN WITH ONGOING CONVECTION IS LOCALLY HEAVY RAIN WITH SLOW
STORM MOVEMENT. SHORT TERM GUIDANCE IN GOOD AGREEMENT WITH THIS
ACTIVITY QUICKLY DISSIPATING AFTER SUNSET WITH LINGERING SHOWERS
POSSIBLE INTO THE EARLY OVERNIGHT HOURS.

LITTLE TO FOCUS ADDITIONAL PRECIP DEVELOPMENT FROM LATE TONIGHT
THROUGH MIDDAY SUNDAY AND HAVE MAINTAINED A GENERALLY DRY
FORECAST. WITH LOW LEVEL MOISTURE SLOWLY INCREASING OVER THE
WEEKEND...POSSIBLE FOR ISOLATED SHOWERS BUT EXPECTED COVERAGE TOO
LOW FOR ANY MENTION AT THIS TIME. CONVECTIVE CHANCES THEN BEGIN TO
INCREASE FROM SUNDAY AFTERNOON/EVENING INTO SUNDAY NIGHT.
CONSENSUS SEEMS TO BE FOCUSING ON A MCS DEVELOPING OVER THE PLAINS
SUNDAY AFTERNOON/EVENING AND MOVING INTO THE WESTERN LAKES SUNDAY
NIGHT. STILL TIME TO EVALUATE THIS BUT HAVE MAINTAINED SLIGHT
CHANCE POPS SUNDAY AFTERNOON AND THEN INCREASED POPS THROUGH
SUNDAY EVENING AND OVERNIGHT INTO MONDAY MORNING. AND SHOULD THIS
PAN OUT THEN MONDAY AFTERNOON INTO MONDAY AFTERNOON COULD
POTENTIALLY BE FAIRLY DRY.

AS FOR TEMPERATURES...WITH MUCH OF SUNDAY NOW LOOKING DRY AS WELL
AS MONDAY AFTERNOON POTENTIALLY BEING DRY OR DRY ENOUGH TO ALLOW
GOOD HEATING...HAVE BUMPED TEMPS UP MORE IN LINE WITH THE GEM...
WHICH WAS ONE OF THE BETTER PERFORMING MODELS FOR HIGH TEMPS WITH
THE WARM UP EARLIER THIS WEEK WHICH PUSHES HIGHS FOR BOTH DAYS
INTO THE MID/UPPER 80S AND WOULDN/T BE SURPRISED TO SEE SOME
LOCATIONS TAG 90. WINDS STILL SOUTHEASTERLY SUNDAY WILL LIKELY
KEEP THE IL SHORE COOLER BUT BY MONDAY WINDS INCREASE AND SHOULD
TURN ENOUGH SOUTHWESTERLY TO PREVENT ANY COOLING ALONG THE LAKE.
FORECAST SOUNDINGS SUGGEST WINDS COULD BE GUSTING WELL INTO THE
25-30 MPH RANGE.

DEWPOINTS WILL ALSO BE INCREASING THROUGH THE WEEKEND AND COULD
POTENTIALLY REACH THE UPPER 60S BY SUNDAY AFTERNOON AND ONLY DROP
MODESTLY SUNDAY NIGHT WITH LOWS WELL IN THE 60S. HOWEVER...SHOULD
STRONGER WINDS MATERIALIZE ON MONDAY...LOW LEVEL MIXING WOULD
LIKELY ALLOW SOME AMOUNT OF DRIER AIR TO MIX TO THE SURFACE.

BY MONDAY NIGHT AND BEYOND...TIMING VARIOUS WAVES BECOMES MORE
DIFFICULT AND WHILE THERE WILL BE DRY PERIODS...AT TIMES... HAVE
OPTED TO KEEP LIKELY POPS FOR SHOWERS/TSRA AND THE 12Z ECMWF SHOWS
SEVERAL WAVES TO AFFECT THE REGION DURING THE MIDDLE OF NEXT WEEK.
CLOUD COVER/PRECIP/POTENTIAL FLOW OFF THE LAKE ALL SIGNIFICANTLY
INCREASE TEMPERATURE FORECAST DIFFICULTY AND HAVE GENERALLY GONE
MIDDLE OF THE ROAD ON TEMPS. WITH DEWPOINTS EXPECTED TO STAY IN
THE 60S THROUGH WEDNESDAY MORNING AND PRECIPITABLE WATER VALUES IN
THE 1 TO 1.5 INCH RANGE...WHICH MAY END UP TOO LOW...ROUNDS OF
HEAVY RAIN WILL CERTAINLY BE POSSIBLE. CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* SCATTERED SPRINKLES/LIGHT SHOWERS ENDING EARLY EVENING.

* POSSIBLE MVFR CIG/VSBY DEVELOPING LATE TONIGHT/EARLY SATURDAY MORNING.

ALLSOPP

//DISCUSSION...UPDATED 00Z...

SPRINKLES/LIGHT SHOWERS DISSIPATING EARLY THIS EVENING...OTHERWISE
JUST BROKEN MID AND HIGH CLOUD LAYERS FOR MOST OF THE NIGHT. SOME
MVFR VISIBILITIES MAY DEVELOP LATE TONIGHT AND EARLY SATURDAY AS
WINDS DIMINISH AND LOW LEVEL INVERSION STRENGTHENS. THE LIGHT
SHOWERS LATE THIS AFTERNOON AND EARLY THIS EVENING MAY HAVE ADDED
ENOUGH ADDITIONAL LOW LEVEL MOISTURE TO ALLOW SOME LIGHT FOG AND
HAZE DEVELOP. THIS SHOULD MIX OUT BY MID MORNING.

NEARLY STATIONARY WARM FRONT EXTENDS FROM NEAR MLI TO PNT TO
LAF THIS EVENING...WITH ENE WINDS PREVAILING NORTH OF THE BOUNDARY.
PRESSURE GRADIENT WILL BE WEAKENING AS UPPER LEVEL RIDGE BUILDS
OVER THE REGION AND SURFACE HIGH PRESSURE OVER THE GREAT LAKES
SHIFTS EAST. WINDS WILL GRADUALLY TURN SOUTHEAST OVER MUCH OF
NORTHERN IL AND IN SATURDAY EXCEPT NEAR THE LAKE WHERE ONSHORE
FLOW WILL KEEP WINDS MORE EAST. THEREFORE DONT EXPECT WINDS TO BE
QUITE AS STRONG OR GUSTY SATURDAY AS THEY WERE TODAY. WITH
BUILDING UPPER RIDGE SATURDAY AND OLD WARM FRONTAL BOUNDARY
WASHING OUT...THERE DOESN`T SEEM TO BE MUCH FOCUS FOR CONVECTION
SATURDAY. ALSO BUILDING RIDGE SHOULD KEEP ATMOSPHERE CAPPED.
THERFORE NOT ANTICIPATING ANY SHOWERS OR THUNDERSTORMS IN THE AREA
SATURDAY.

ALLSOPP


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND FORECAST.

* LOW CONFIDENCE IN SHOWERS NEXT COUPLE HOURS.

* MEDIUM CONFIDENCE IN MVFR VISIBILITY LATE TONIGHT/EARLY SATURDAY
  MORNING. LOW CONFIDENCE IN MVFR CIG DEVELOPING.

ALLSOPP

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...VFR.

SUNDAY NIGHT THROUGH WEDNESDAY...PERIODS OF TSRA.

THURSDAY...CHC SHRA.

ALLSOPP

&&

.MARINE...
206 PM CDT

A SURFACE RIDGE OF HIGH PRESSURE CONTINUES TO BUILD
EAST-SOUTHEASTWARD ACROSS ONTARIO AND THE CENTRAL AND EASTERN LAKES
THIS AFTERNOON. A HYBRID LAKE BREEZE/OUTFLOW BOUNDARY FROM
CONVECTION ACROSS WISCONSIN THIS MORNING HAS PUSHED ACROSS SOUTHERN
LAKE MICHIGAN EARLY THIS AFTERNOON. THIS LED TO A SUBSTANTIAL
INCREASE IN THE WINDS FOR A PERIOD OUT OF THE NORTH-NORTHEAST UP TO
25 TO 30 KT. THESE NORTHEAST WINDS UP TO AROUND 20 KT WILL CONTINUE
FOR THE NEXT FEW HOUR BEFORE SLOWLY EASING AND BECOMING MORE
EASTERLY TONIGHT.

A STORM SYSTEM IS EXPECTED TO TAKE SHAPE ACROSS THE HIGH PLAINS ON
SATURDAY BEFORE IT MOVES EAST-NORTHEASTWARD TOWARDS THE MID MISSOURI
VALLEY BY LATE SUNDAY. THIS SYSTEM LOOKS TO LIFT A WARM FRONT
NORTHWARD ACROSS AT LEAST THE SOUTHERN HALF TO TWO THIRDS OF THE
LAKE THROUGH MONDAY. BEHIND THIS FRONT WINDS LOOKS TO INCREASE OUT
OF THE SOUTH IN THE 15 TO 25 KT RANGE ON MONDAY. IT APPEARS THAT
THIS LOW WILL SLOWLY MOVE EASTWARD ACROSS THE MID MISSISSIPPI VALLEY
INTO MID WEEK AND THEN TO THE OHIO VALLEY LATER IN THE WEEK. THIS
SHOULD ALLOW THIS FRONT TO MOVE BACK SOUTH. DURING THIS TIME...THE
WINDS LOOK TO BECOME MORE NORTHERLY WITH TIME...ESPECIALLY BY MID TO
LATE WEEK AS THE SURFACE LOW PASSES TO THE SOUTH OF THE LAKE. THIS
COULD RESULT IN SOME STRONGER NORTHERLY WINDS BY LATE NEXT WEEK.

KJB

&&

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

$$

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