000
FXUS63 KLOT 160551
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1251 AM CDT THU MAY 16 2013

.DISCUSSION...
830 PM CDT

ONLY VERY MINOR TWEAKS MADE TO GOING FORECAST. HELD ON TO
SCATTERED CLOUDS THROUGH THE ENTIRE EVE ACROSS THE FORECAST AREA
WHICH COULD SLOW THE TEMPERATURE DROP SOME...BUT OTHER THAN
THAT MUCH OF THE FORECAST IS ON TRACK.

WATER VAPOR IMAGERY THIS EVE SHOWS THE CLOSED LOW OVER OK SLOWLY
MEANDERING NORTHEAST WITH A SHEARED SHORT WAVE RACING ESE ACROSS
LOWER MI TO NORTHERN IL TO EASTERN IA. THE STATIONARY FRONT AT THE
SURFACE IS DRAPED ACROSS CENTRAL IL JUST SOUTH OF THE FORECAST
AREA. ON THE ILX RADAR THIS BOUNDARY CAN BE SEEN INCHING BACK
NORTHWARD. CONVECTION THAT HAS DEVELOPED ACROSS NORTHERN MO IS ON
THE BEGINNINGS OF THE LOW-LEVEL JET NOSE WHICH WILL ORIENT ITSELF
INTO CENTRAL IL LATER IN THE NIGHT AND IMPROVE CONVERGENCE ATOP
THE LOW-LEVEL BOUNDARY. WITH COLUMN MOISTURE IMPROVING FROM THE
APPROACHING UPPER LOW...AND ELEVATED INSTABILITY OF AROUND 600
J/KG AT THIS POINT PER THE 00Z ILX RAOB...IT DOES LOOK LIKE
ISOLATED TO SCATTERED CONVECTION HAS A DECENT SHOT OF DEVELOPING
TO THE SOUTH OF THE AREA...ESPECIALLY GIVEN THE OBSERVED TRENDS
IN MO ALREADY. EVEN THE SOUTHERN PERIPHERY OF THE SHEARED SHORT
WAVE COULD HELP BE A TRIGGER. SOME OF THIS COULD GRAZE THE FAR
SOUTHERN/SOUTHEASTERN FORECAST AREA. THE SEVERE POTENTIAL IS QUITE
LOW DUE TO LIMITED DEEP LAYER SHEAR AND MARGINAL INSTABILITY. THE
AREA OF STORM CHANCES WAS WELL COVERED IN THE INHERITED FORECAST.

FOR TEMPERATURES...THE DRY LOW-LEVEL AIR MASS AND LIGHT WINDS NORTH
OF THE BOUNDARY INITIALLY POINTED TOWARDS A QUICK TEMPERATURE DROP.
HOWEVER...CLOUDS ASSOCIATED WITH THE MID-LEVEL SPEED MAX AND
FRONTOGENESIS IN THE 700-500MB LAYER LOOK TO SLOW THAT SOME. LAST
VISIBLE IMAGERY SHOWED MID-LEVEL CLOUDS ACTUALLY EXPANDING ACROSS
PORTIONS OF CENTRAL IA. SO HAVE INCREASED SKY COVER...DELAYING
CLEARING ACROSS NORTHERN IL AND FAR NW IN UNTIL LATE. HAVE
ADJUSTED HOURLY TEMPERATURES SOME BUT ALL IN ALL THE MINS STILL
LOOK REASONABLE. HAVE COME UP A DEGREE OR TWO IN CENTRAL AND
SOUTHERN LOCATIONS.

MTF

//PREV DISCUSSION...
513 PM CDT

MINOR UPDATE LATE THIS AFTERNOON TO INCLUDE A SMALL CHANCE FOR A
SHOWER OR SPRINKLES ACROSS NORTHERN ILLINOIS THROUGH EARLY
EVENING. A MID-LEVEL SHORT WAVE AND ASSOCIATED 60 KT 500 MB SPEED
MAX ACROSS WI INTO NORTHEAST IA LOOK TO CONTINUE TO PUSH EASTWARD
MAINLY NORTH OF THE AREA. THE SOUTHERN EXTENSION OF THIS HAS A
NICE 800-900MB CONVERGENCE SIGNATURE AND GENERATING JUST ENOUGH
SATURATION FOR SOME SUSTAINED SHOWERS FROM SOUTHERN WI INTO NW IL
AND EASTERN IA. THESE SHOULD MORE THAN LIKELY DISSIPATE WITH THE
LOSS OF DAYTIME HEATING FURTHER DWINDLING THE INSTABILITY PRESENT.
WHILE THERE HAVE BEEN A FEW LIGHTNING STRIKES NORTHWEST OF THE
QUAD CITIES...THE INSTABILITY ALOFT IS MEAGER SO DO NOT BELIEVE
THOSE WILL BECOME ANY MORE WIDESPREAD. SO WHILE WOULD NOT BE
SURPRISED IF WIDELY ISOLATED SHOWERS OR SPRINKLES HANG TOGETHER
AS THIS WAVE TRACKS ACROSS A GOOD PART OF THE CWA...THINKING THAT
WILL BE AT BEST THE COVERAGE AND EXTENT IN THE FORECAST AREA.

MTF

//PREV DISCUSSION...
241 PM CDT

FORECAST CHALLENGES THIS AFTERNOON MAINLY REVOLVE AROUND PERIODIC
CONVECTIVE CHANCES ASSOCIATED WITH FRONTAL BOUNDARY THAT HAS STALLED
SOUTH OF I-80.

TODAY AND TONIGHT...
MODEST SURFACE RIDGE IS BUILDING ACROSS THE NORTHERN PLAINS INTO
NORTHERN ILLINOIS THIS AFTERNOON WHILE A COLD FRONT HAS SLOWLY
SAGGED SOUTH ACROSS OUR SOUTHERN TIER OF COUNTIES THIS AFTERNOON.
DEWPOINTS POOLING INTO THE LOW 60S AHEAD THE FRONT WITH TEMPS WELL
INTO THE 80S HAS LED TO MODERATE INSTABILITY DEVELOPING JUST TO OUR
SOUTH. AN ELONGATED TROUGH DROPPING ACROSS THE GREAT LAKES THIS
EVENING WILL LEAD TO MODEST HEIGHT FALLS ALOFT ASSISTING DIURNAL
EROSION OF THE CAP TO KICK OFF A FEW THUNDERSTORMS LATE THIS
EVENING. APPEARS THE MAIN THREAT WILL REMAIN SOUTH OF THE CWA NEAR
AN OUTFLOW/EFFECTIVE FRONTAL BOUNDARY CURRENTLY JUST SOUTH OF
BLOOMINGTON EAST TO LAFAYETTE. TRIMMED POPS...LEAVING ONLY SLT CHC
POPS SOUTH OF THE KANKAKEE RIVER TO ACCOUNT FOR SOME UNCERTAINTY.
MANY CONVECTIVE ALLOWING MODELS SUGGEST THAT COVERAGE WILL BE PRETTY
SPARSE...AND GIVEN THE WEAKLY FORCED SETUP...SEEMS REASONABLE.

THURSDAY THROUGH SATURDAY...
CLOSED LOW NOTED ON WV IMAGERY THIS AFTERNOON MOVING INTO SOUTHERN
UTAH WILL CONTINUE EAST ACROSS THE PLAINS THURSDAY. BROAD AREA OF
SURFACE LOW PRESSURE OVER THE PLAINS WILL LEAD TO MOISTURE RETURN
INTO THE UPPER MISSISSIPPI VALLEY AND NORTHERN PLAINS...AND SHOULD
HELP LIFT THE STATIONARY BOUNDARY BACK INTO THE CWA. MEANWHILE...THE
MID LEVEL DISTURBANCE BECOMES MASKED WITHIN THE MID/UPPER LEVEL
RIDGING WHICH IS AMPLIFYING ACROSS THE CENTRAL CONUS. MODEL
SOUNDINGS INDICATE WEAK IF ANY CIN IN PLACE THURSDAY AFTERNOON...SO
WON`T TAKE MUCH IMPETUS FOR THUNDERSTORMS TO DEVELOP. EXPECT MAIN
FOCUS TO BE ALONG THE FRONT AS IT LIFTS NORTH ACROSS THE MISSISSIPPI
VALLEY SOUTHEAST INTO EAST CENTRAL ILLINOIS...AND SHOULD LARGELY BE
DIURNALLY DRIVEN GIVEN OVERALL LACK OF SUPPORT ALOFT. EXPECT BETTER
CHANCES FOR CONVECTION ACROSS ALL BUT FAR NORTHEAST ILLINOIS //WHERE
INSTABILITY IS FORECAST TO BE MUCH WEAKER// ON FRIDAY AS THE
AFOREMENTIONED MID LEVEL DISTURBANCE FINALLY MOVES ACROSS THE AREA.
DETAILS FOR SATURDAY ARE PRETTY MURKY. STILL EXPECT THE MODEST
INSTABILITY ACROSS THE AREA AND CANNOT RULE OUT AFTERNOON
THUNDERSTORMS...THOUGH MID LEVEL RIDGE AXIS MOVING DIRECTLY OVERHEAD
MAY INHIBIT VERTICAL GROWTH...SO CAPPED POPS IN THE SLT CHC
CATEGORY. EACH DAY THIS PERIOD EXPECT AN ONSHORE COMPONENT TO THE
WINDS EITHER SYNOPTICALLY OR DUE TO LAKE BREEZES DEVELOPING...WHICH
WILL MEAN TEMPERATURES QUITE A BIT COOLER ALONG THE LAKE FRONT.

SUNDAY AND MONDAY...
MODELS CONTINUE TO INDICATE A RETURN OF HEAT THIS PERIOD WITH
INCREASING STRONG TO SEVERE THUNDERSTORM CHANCES AS LOW PRESSURE
DEEPENS OVER THE CENTRAL PLAINS AND LIFTS NORTH INTO THE DAKOTAS.
EML BEGINS TO MOVE OVER THE AREA SUNDAY WITH H85 TEMPS INCREASING TO
17-19C PROVIDING A FAIRLY STOUT CAPPED FOR SURFACE BASED CONVECTION.
LOCAL CLIMATOLOGY SHOWS THESE H85 TEMPS WITH H92 TEMPS OF 19-20C
RESULTING IN MEAN TEMPERATURES INTO THE UPPER 80S. BUMPED UP
TEMPERATURES TOWARDS THE BIAS CORRECTED GEM...AND BUMPED DOWN POPS
ACROSS THE CWA SUNDAY...THOUGH STILL MAINTAINED SOME LOW CHANCE/SLT
CHC POPS.

GUIDANCE CURRENTLY INDICATES THAT MONDAY WILL BE THE DAY TO KEEP AN
EYE ON SEVERE WEATHER-WISE...THOUGH HAS BEEN HAVING TROUBLE TIMING
THIS SYSTEM THUS FAR. THAT SAID...MAIN INSTABILITY AXIS IS CURRENTLY
PROGGED TO BE OVERHEAD MONDAY AS A NEGATIVELY TILTED TROUGH LIFTS
INTO THE UPPER MISSISSIPPI VALLEY. MODERATE TO STRONG INSTABILITY
COUPLED WITH MARGINAL SHEAR DEEP LAYER SHEAR INDICATE THE POTENTIAL
FOR SEVERE WEATHER...THOUGH THE USUAL CAVEATS THIS FAR OUT APPLY.
UPSTREAM CONVECTION...CLOUD COVER...AND UNCERTAINTY IN THE TIMING OF
THE UPPER LEVEL DISTURBANCE ALL CLOUD THE PICTURE SOMEWHAT.

DEUBELBEISS

&&

.AVIATION...

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

* NO CONCERNS IN THE NEAR TERM.

* LIGHT/VARIABLE WINDS THIS MORNING BECOMING EASTERLY BY MID
  MORNING.

RODRIGUEZ

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

QUIET AT THE TERMINALS EARLY THIS MORNING WITH THE BULK OF ANY
ACTIVITY OCCURRING SOUTH/SOUTHWEST OF THE TERMINALS...AND EXPECT
THIS TO CONTINUE FOR THE REMAINDER OF THE FORECAST PERIOD WITH
ONLY HIGH LEVEL CLOUD COVER EXPECTED TO MOVE ACROSS THE TERMINALS.
LIGHT AND VARIABLE WINDS WILL BE REPLACED WITH AN EASTERLY LIGHT
WIND BY MID MORNING...CONTINUING THROUGH THE AFTERNOON BEFORE LAKE
BREEZE INFLUENCE GIVES A STRONGER PUSH OF AN EAST NORTHEAST WIND.
WINDS WILL DIMINISH THIS EVENING...AND HOLD ONTO THIS EAST
NORTHEAST WIND.

RODRIGUEZ


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

* HIGH CONFIDENCE WITH VFR CONDITIONS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

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

FRIDAY THROUGH TUESDAY...PERIODIC CHANCES FOR SHRA/TSRA WITH
LOCALIZED MVFR CONDITIONS.  OTHERWISE...VFR.

KREIN

&&

.MARINE...
205 PM CDT

OVERALL...IT APPEARS TO BE RATHER QUIET ACROSS THE LAKE FOR THE NEXT
COUPLE OF DAYS. A SURFACE RIDGE OF HIGH PRESSURE WILL BUILD IN
ACROSS THE UPPER LAKES ON THURSDAY IN THE WAKE OF A LOW MOVING
EASTWARD ACROSS SOUTHERN QUEBEC. THIS WILL LEAD TO A PERIOD OF
NORTHERLY WINDS ACROSS THE LAKE LATER THURSDAY AND INTO FRIDAY.
HOWEVER...WIND SPEEDS DO NOT LOOK TO GET OVER 20 KT.

IN THE EXTENDED FORECAST PERIOD...LATER THIS WEEKEND AND INTO EARLY
NEXT WEEK...IT APPEARS THAT A POTENT STORM SYSTEM WILL TAKE SHAPE
ACROSS THE PLAINS STATES. THIS SYSTEM LOOKS TO PRODUCE SOME STRONGER
SOUTHERLY FLOW OVER THE LAKE DURING THIS PERIOD ALONG WITH
INCREASING THREATS FOR THUNDERSTORMS INTO EARLY NEXT WEEK.

KJB

&&

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

$$

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