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000
FXUS63 KLOT 170239 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
939 PM CDT THU MAY 16 2013

.DISCUSSION...
930 PM CDT

THE FORECAST FOR TONIGHT HAS BEEN TWEAKED SLIGHTLY...TO CONTINUE
THE EVENING CHANCE OF THUNDER ACROSS THE SOUTHERN FORECAST AREA
THROUGH THE NIGHT...AND TO NUDGE IT NORTH SOME.

THE EVE WATER VAPOR LOOP DEPICTS THE CLOSED UPPER LOW ACROSS
NORTHERN AR EASING ITS WAY NORTHEAST. AT THE SURFACE...THE
PRIMARILY SYNOPTIC FRONT IS NEAR THE LOT/ILX CWA BORDER WITH A
LAKE BREEZE HAVING PUSHED WELL INLAND. BETWEEN THESE TWO A FEW
STORMS GENERATED...IT LOOKED LIKE ON A SLIGHTLY ELEVATED BOUNDARY
JUST NORTH OF THE SURFACE BOUNDARY PER ILX RADAR. THESE MAY FESTER
NORTHEAST ON THE AFOREMENTIONED MULTIPLE AREAS OF LOW-LEVEL
CONVERGENCE FOR SEVERAL MORE HOURS...BUT ANY CG LIGHTNING HAS BEEN
SPORADIC AT BEST AND WOULD EXPECT THAT TREND TO CONTINUE OR
DIMINISH ALTOGETHER. THE HRRR DOES INDICATE THESE SHOWERS TO SORT
OF OSCILLATE ALL THE WAY UP TO FAR NORTHEAST IL THROUGH EARLY
OVERNIGHT.

THE ILX VAD PROFILER INDICATES INCREASING SOUTHERLY FLOW BELOW 3K
FT...NOW UP TO 30 KT. THE LOW-LEVEL JET IS NOT EXPECTED TO
INCREASE MUCH FROM THAT MAGNITUDE AND POINT MORE INTO WESTERN IL.
MOISTURE TRANSPORT IS MORE LIMITED TONIGHT SO NOT EXPECTING AS
MUCH IF ANY ELEVATED CONVECTION...BUT COULD SEE SOME IN WESTERN IL
WHERE A LITTLE MORE THETA-E ADVECTION AND CONVERGENCE AROUND 850MB
IS FORECAST.

THE LAKE BREEZE MADE IMPRESSIVE PROGRESS WSW THROUGH EARLY EVE
AFTER SORT OF A SLOW START. A 30 DEGREE SPREAD AS OF 930 PM EXISTS
ACROSS THE CWA SIMPLY FROM JUST THIS MESOSCALE BOUNDARY. HAVE
ADJUSTED THE HOURLY TEMPERATURE FORECAST TO MEET TRENDS. THE LAV
GUIDANCE HAS VERY LITTLE TEMPERATURE DROP FOR MANY POINTS THROUGH
THE REST OF THE NIGHT...LIKELY DUE TO INCREASING CLOUD COVER.
WHILE CAA OFF THE LAKE LIKELY WILL CREATE A LITTLE MORE DROP THAN
IT ADVERTISES...THIS IS IN LINE WITH THE GOING MINIMUM TEMPERATURE
FORECASTS.

MTF

&&

.PREV DISCUSSION...
259 PM CDT

TODAY`S FORECAST CHALLENGES CONTINUE TO BE DEALING WITH FRONTAL
BOUNDARY CURRENTLY JUST SOUTH OF THE CWA...AND PERIODIC CONVECTIVE
CHANCES THROUGH MID NEXT WEEK.

TODAY AND TONIGHT...
THIS AFTERNOON THE FRONT IS LOCATED JUST NORTH OF QUINCY IL EAST TO
NEAR TERRE HAUTE INDIANA...AND HAS BEEN SLOWLY PUSHING NORTH THIS
AFTERNOON. MODERATE INSTABILITY EXISTS SOUTH OF THE FRONT AND MAY
LIFT INTO FAR SOUTHERN PORTIONS OF THE CWA LATE THIS EVENING BEFORE
FADING NOCTURNALLY. MAINTAINED SLT CHC POPS FOR A FEW HOURS THIS
EVENING WHEN THIS OCCURS...BUT OTHERWISE SHOULD BE FAIRLY QUIET
PERIOD THROUGH TONIGHT.

FRIDAY THROUGH SATURDAY...
COMPACT SHORTWAVE NOTED ON WV IMAGERY THIS AFTERNOON OVER WESTERN
NE/KS WILL CONTINUE ENE INTO WEST CENTRAL WISCONSIN BY FRIDAY
AFTERNOON. AS THIS HAPPENS...SOUTHERLY FLOW INCREASE AT THE SURFACE
AND SHOULD HELP PUSH THE BOUNDARY NORTH ACROSS THE AREA. DEWPOINTS
RISE INTO THE MID 60S AND MODEST INSTABILITY DEVELOPS OUTSIDE OF FAR
NE ILLINOIS WHERE ONSHORE WINDS WILL KEEP CONDITIONS COOLER/MORE
STABLE. THIS INSTABILITY IS UNCAPPED...AND GIVEN THERE IS NO WELL
DEFINED FOCUS FOR THUNDERSTORMS...EXPECT UNORGANIZED/SCATTERED
CONVECTION TO DEVELOP WITHIN THE WARM SECTOR. MID LEVEL LAPSE RATES
ARE PRETTY POOR...SO CONVECTION MAY STRUGGLE AT TIMES AND MAY LIMIT
THE THUNDER CHANCES TO SOME DEGREE. MUCH OF THE SAME IS EXPECTED
SATURDAY SO WILL MAINTAIN THE LOW POPS FOR DIURNALLY DRIVEN TSTORMS.

SUNDAY THROUGH TUESDAY...
THIS PERIOD CONTINUES TO LOOK ACTIVE AS THE OVERALL PATTERN
AMPLIFIES WITH DEEP TROUGHING DEVELOPING ACROSS THE WESTERN
CONUS...AND STRONG RIDGING EAST. THE H85 THERMAL RIDGE BEGINS TO
WORK INTO THE AREA SUNDAY...AS WELL AS DRY AIR ALOFT AND THE EML
LATER IN THE DAY HELPING TO STEEPEN LAPSE RATES ALOFT. NEGATIVELY
TILTED TROUGH IS EXPECTED TO ROUND THE BASE OF THE LONGWAVE TROUGH
SUNDAY LIFTING INTO THE MID MISSOURI VALLEY SUNDAY NIGHT. MODELS ARE
MIXED ON WHETHER OR NOT THE CIN ERODES DURING THE DAYTIME...BUT IF
IT DOES CHANCES WILL BE BEST OVER WESTERN PORTIONS OF THE CWA...SO
HAVE MAINTAINED LOWER POPS. THERE MAY BE A BETTER CHANCE FOR
CONVECTION OVERNIGHT AS A LOW LEVEL JET DEVELOPS JUST TO OUR WEST
WITH LARGE SCALE ASCENT ASSOCIATED WITH AFOREMENTIONED TROUGH.

ON MONDAY...THE GFS INDICATES ANOTHER LOWER AMPLITUDE DISTURBANCE
WILL ROUND THE BASE OF THE LONGWAVE TROUGH AND LIFT INTO THE MID
MISSISSIPPI VALLEY. THIS CONTINUES TO BE A DAY TO KEEP AN EYE ON FOR
SEVERE WEATHER POTENTIAL. MODELS CONTINUE TO ADVERTISE MODERATE TO
STRONG INSTABILITY IN PLACE OVERHEAD WITH MARGINAL SHEAR CONDITIONS
TO SUPPORT SEVERE WEATHER. AS PREVIOUSLY MENTIONED...CONVECTION FROM
THE PREVIOUS NIGHT...CLOUD COVER...AND OTHER SMALL SCALE FEATURES
CANNOT BE RESOLVED THIS FAR OUT AND ADD A CONSIDERABLE AMOUNT OF
UNCERTAINTY. WE SHOULD BEGIN TO GET A BETTER PICTURE THIS WEEKEND SO
STAY TUNED FOR FORECAST UPDATES. DEPENDING ON THE SPEED OF THE
SYSTEM...TUESDAY WILL ALSO HAVE TO BE MONITORED...PERHAPS WITH THE
THREAT MORE FOCUSED ON THE EASTERN PORTIONS OF THE CWA.

IN ADDITION TO THE SEVERE THREAT...MULTIPLE ROUNDS OF THUNDERSTORMS
MOVING ALONG THE SLOW MOVING BOUNDARY SUNDAY NIGHT THROUGH TUESDAY
WILL LEAD TO A INCREASED HEAVY RAIN AND FLOODING THREAT.

FOR TEMPERATURES SUNDAY AND MONDAY...CONTINUE TO LEAN ON THE WARMER
BIAS CORRECTED GEM WHICH HAPPENED TO VERIFY BEST WITH THE
UNSEASONABLY HEAT TUESDAY. DEPENDING ON THE SPEED OF THE
SYSTEM...CURRENT FORECAST TEMPS MAY BE A BIT ON THE COOL SIDE
TUESDAY...PARTICULARLY THE EASTERN CWA. H85 TEMPS OF 16-18C AND H92
TEMPS OF 19-22C SHOULD SUPPORT TEMPERATURES WELL INTO THE 80S AND
WOULDN`T BE SURPRISED TO SEE PLACES HIT 90S THOSE DAYS...BUT WILL
REMAIN A BIT CONSERVATIVE GIVEN THE PRECIP CHANCES AND CLOUD COVER.

DEUBELBEISS

&&

.AVIATION...

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

* ENELY WINDS 5-10KT FOLLOWING LAKE BREEZE PASSAGE.

* SELY WINDS TOMORROW MORNING BACKING ELY IN THE AFTERNOON.

* CHANCE TSRA/SHRA TOMORROW AFTERNOON/EVENING.

KREIN

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

THE LAKE BREEZE HAS FINALLY PUSHED INLAND OF ORD/MDW/GYY AND
SHOULD PUSH THROUGH DPA SOON AS WELL. THIS WILL SET UP ENELY WINDS
OVER NERN IL/NWRN IN...BUT WILL LIKELY NOT IMPACT RFD WHICH SHOULD
REMAIN SELY THROUGH THE NIGHT. HAVE BEEN MONITORING THE
PROGRESSION OF THE LAKE BREEZE BOUNDARY TO THE SOUTHWEST ALONG
WITH ANOTHER WEAK BOUNDARY MOVING NORTHWARD ALONG THE
ILLINOIS/KANKAKEE RIVERS. THIS WEAK BOUNDARY SEPARATES SOUTHERLY
FLOW WITH SLIGHTLY HIGHER DEWPOINTS. WILL NEED TO MONITOR THESE
BOUNDARYS CLOSELY AS THEY APPROACH EACH OTHER FOR ANY SHRA/TSRA
DEVELOPMENT...WHICH BASED ON CURRENT TRACK/TIMING WOULD BE INVOF
KJOT AREA. OTHERWISE THE REMAINDER OF THE NIGHT SHOULD BE QUIET AT
THE TERMINALS. FOCUS WILL THEN SHIFT TO TSRA POTENTIAL TOMORROW
AFTERNOON. LATEST GUIDANCE INDICATES A WARM FRONT LIFTING INTO NRN
IL/IN BY LATE TOMORROW AFTERNOON. MOISTURE POOLING ALONG THE
BOUNDARY AND ISENTROPIC LIFT ALONG THE FRONTAL ZONE WILL PROVIDE
ENOUGH FOCUS TO NECESSATE ADDING A PROB30 GROUP TO THE FORECAST.
TIMING WILL BE THE MAIN QUESTION...BUT GENERALLY EXPECT THE BEST
TIMING TO BE DURG THE LATE AFTERNOON/EARLY EVENING HOURS.

KREIN

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

* MODERATE TO HIGH CONFIDENCE IN WIND TRENDS.

* MODERATE CONFIDENCE IN TSRA/SHRA CHANCES TOMORROW...BUT LOWER
  CONFIDENCE IN EXACT TIMING.

KREIN

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

SATURDAY THROUGH WEDNESDAY...PERIODIC CHANCES FOR SHRA/TSRA...
OTHERWISE...VFR.

KREIN

&&

.MARINE...
228 PM CDT

RIDGING FROM HIGH PRESSURE CENTERED OVER WESTERN ONTARIO EXTENDS
ACROSS LAKE MICHIGAN THIS AFTERNOON. WEAK LOW PRESSURE WILL DEVELOP
AND MOVE UP THE OHIO RIVER VALLEY FRIDAY WITH ADDITIONAL LOW
PRESSURE DEVELOPING ACROSS THE CENTRAL HIGH PLAINS. EAST TO
NORTHEAST FLOW OVERALL WILL CONTINUE ACROSS THE LAKE...WITH ONSHORE
FLOW IN AREAS WHERE THE PRESSURE GRADIENT IS WEAKER CAUSING SOME
ERRATIC DIRECTIONS AT TIMES. STEADIER AND MORE UNIFORM WINDS WILL
DEVELOP WITH TIME THROUGH TOMORROW WITH MORE OF AN EAST TO SOUTHEAST
TREND. THE STRONGEST WINDS WILL OCCUR FRIDAY EVENING/NIGHT
COINCIDENT WITH THE STRONGEST PRESSURE GRADIENT THANKS TO THE LOW
PASSING TO THE SOUTHEAST. THE GRADIENT WEAKENS DURING THE DAY
SATURDAY AS THE LOW DEPARTS TO THE EAST. LOW PRESSURE STRENGTHENS
ACROSS THE CENTRAL/NORTHERN HIGH PLAINS INTO SUNDAY WHICH WILL
GRADUALLY TIGHTEN THE PRESSURE GRADIENT ACROSS THE LAKE. THIS WILL
ALLOW A STEADY SOUTH TO SOUTHEAST WIND TO DEVELOP ACROSS MOST OF THE
LAKE...WITH A MORE EASTERLY DIRECTION ACROSS THE FAR NORTH WHERE A
WARM FRONTAL BOUNDARY IS EXPECTED TO SET UP. THE MAIN LOW WILL
MEANDER NORTHWARD BEFORE BEING PUSHED EASTWARD ACROSS MINNESOTA/IOWA
SOMETIME TUESDAY OR WEDNESDAY WHICH WILL LIKELY PUSH THE FRONTAL
BOUNDARY FURTHER SOUTH ACROSS THE LAKE LEADING TO EAST TO NORTHEAST
WINDS NORTH AND SOUTH TO SOUTHWEST WINDS SOUTH BY MID WEEK. THE MAIN
CONCERN WILL BE THE POTENTIAL FOR INCREASED GUSTINESS ACROSS THE
NORTH AS COLDER AIR SETTLES IN ALLOWING SLIGHTLY INCREASED MIXING.
OTHERWISE...GENERALLY STABLE LOW LEVEL AIR ACROSS THE LAKE WILL KEEP
GUSTS TO A MINIMUM FROM TONIGHT THROUGH THE WEEKEND.

MDB

&&

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

$$

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