000
FXUS63 KLOT 172003
AFDLOT

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

.MESOSCALE DISCUSSION...
201 PM CDT

A CLUSTER OF STORMS IS TRYING TO TAKE SHAPE ACROSS THE SOUTHERN
PORTION OF THE CWA THIS AFTERNOON ALONG A STATIONARY SURFACE
BOUNDARY AND MOISTURE CONVERGENCE AXIS...BUT AT THIS TIME WE ARE NOT
EXPECTING ANYTHING SEVERE TO DEVELOP.  LOCALIZED FLOODING WOULD BE
MORE OF A CONCERN.  SFC-BASED CAPE VALUES HAVE REACHED SEVERAL
HUNDRED J/KG...BUT DEEP LAYER SHEAR IS VIRTUALLY NONEXISTENT...WITH
BOTH FORECAST AND LATEST ACARS SOUNDINGS FROM ORD SHOWING WINDS
THROUGH MOST OF THE TROPOSPHERE AT 20 KTS OR LESS.

STORMS THAT DO PULSE UP IN THIS LOW SHEAR AND MODERATE CAPE
ENVIRONMENT COULD POSE A HAIL OR WIND THREAT...BUT ACARS -20C
HEIGHTS AROUND 23 KFT PROVIDE AN IDEA OF HOW HIGH 60 DBZ ECHOES
WOULD HAVE TO GET TO SUPPORT SEVERE HAIL...AND STORMS SO FAR HAVE
ONLY BEEN REACHING HALF THAT LEVEL.  FAIRLY SATURATED LOW LEVELS IN
FORECAST SOUNDINGS ALSO SUGGEST THE THREAT OF STRONG DOWNBURST WINDS
WOULD NOT BE HIGH.  AGAIN...LOCALIZED FLOODING WOULD BE MORE OF A
CONCERN GIVEN THE COMBINATION OF SATURATED SOUNDINGS SOMEWHAT
TROPICAL IN NATURE...SLOW STORM MOTION...MINIMAL SHEAR...THE
PRESENCE OF A FOCUSING BOUNDARY...AND PRECIPITABLE WATER VALUES
AROUND 1.4 INCHES.  AT THIS POINT THE STORMS ARE REMAINING GENERALLY
SCATTERED AND DISCRETE...AND HAVE NOT BEEN TRAINING.  THESE WILL
CONTINUE TO BE MONITORED FOR ANY CHANGES AS WE PROGRESS THROUGH PEAK
MIDAFTERNOON HEATING.

LENNING

&&

.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 20Z...

* ISOLD-SCT SHRA/TSRA TO THE WEST AND SOUTH WHICH MAY REACH MDW
  LATE AFTERNOON...WITH LOWER CHANCE OF REACHING ORD.

* NORTHEAST WINDS 10-12KT WITH SOME GUSTS NEAR 20 KT AT
  TIMES...TRENDING MORE EASTERLY LATE AFTERNOON.

* MVFR CIGS/VSBY POSSIBLE LATE TONIGHT/EARLY SATURDAY MORNING.

MDB

//DISCUSSION...UPDATED 20Z...

BAND OF SCATTERED SHRA/TSRA FROM ENE OF KVYS TO KC09 TO KRZL
CONTINUES TO LIFT NORTHWARD AT 20Z. LAKE REINFORCED BOUNDARY IS
POSITIONED NEAR THE LEADING EDGE OF THE ACTIVITY AND WITH MUCH MORE
STABLE AIR TO ITS NORTH SO THE NORTHWARD PUSH MAY BE LIMITED. WILL
REMOVE TS MENTION FROM MDW WITH THE CHANCE FOR TSRA ONLY AROUND 30
PERCENT IF THAT...WITH A BETTER CHANCE FOR JUST SHRA SO WILL KEEP
TEMPO FOR SHRA FOR NOW. GYY STILL HAS A FAIR CHANCE FOR TSRA GIVEN
THAT THE BOUNDARY ARCS BACK TO THE LAKESHORE JUST TO THE EAST SO
UNSTABLE AIR IS NEARBY...AND OUT FLOW FROM CELLS NEAR IKK MAY PUSH
THAT PORTION OF THE BOUNDARY NORTHWARD SOMEWHAT. CHANCES FOR
SHRA/TSRA AT ORD ARE LOWER...PROBABLY LESS THAN 30 PERCENT SO
REMOVED VCTS MENTION BUT BRIEF SHRA IS POSSIBLE LATE THIS AFTERNOON.
RFD LOOKS TO BE IN A SIMILAR SITUATION BUT WITH A BETTER CHANCE FOR
SHRA AND A REDUCED CHANCE FOR TSRA. ANY BETTER ORGANIZED SHRA/TSRA
THAT DOES PASS OVER A TERMINAL WILL LIKELY DROP VSBY TO IFR FOR A
SHORT PERIOD. WINDS REMAIN A CHALLENGE WITH THE BOUNDARY IN THE AREA
AND POTENTIAL OUTFLOWS FROM CONVECTION. STILL FAVOR THE PREVAILING
NORTHEAST TO EAST DIRECTION THROUGH THE EVENING HOWEVER.

FROM 18Z...

COMPLEX FORECAST CONTINUES WITH LAKE MICHIGAN HELPING TO PUSH A
FRONTAL BOUNDARY SOUTHWESTWARD ACROSS THE CHICAGO/NW INDIANA METRO
AREA. THIS HAS RESULTED IN A SHIFT TO STEADY NORTHEAST WINDS AT
ORD/MDW/DPA AND GYY SHORTLY WITH SOME GUSTS TO NEAR 20 KT. WINDS
SHOULD STAY NORTHEASTERLY FOR THE NEXT FEW HOURS AND TREND MORE
EASTERLY THROUGH THE AFTERNOON BUT THIS MAY BE SLOWER TO OCCUR
THAN FORECAST. SHRA/TSRA HAS BEGUN TO DEVELOP SOUTH OF THE
TERMINALS AND WILL BE MOVING NORTHWARD THROUGH THE AFTERNOON. ONE
QUESTION IS HOW FAR NORTH IT WILL BE ABLE TO MAKE IT NOW THAT THE
FRONTAL BOUNDARY HAS PUSHED THROUGH THE TERMINALS. AM THINKING
THAT THE BOUNDARY ITSELF MAY ACT TO TRIGGER MORE STORMS BUT THAT
IT WILL NEED TO MOVE FURTHER SOUTH TOWARD/PAST JOT/KC09 WHERE THE
NORTHERN EDGE OF DECENT INSTABILITY EXISTS IN ORDER TO DO SO. WILL
CONTINUE WITH THE IDEA OF THE HIGHEST POTENTIAL AT GYY AND MDW AND
INCLUDE TEMPO TS THERE BY MID AFTERNOON. ORD/DPA/RFD HAVE A CHANCE
AS WELL BUT IT IS MUCH LESS CLEAR WHETHER OR NOT THEY WILL BE
DIRECTLY AFFECTED. WHERE SHRA/TSRA DO PASS OVER THEN BRIEF IFR
VSBY IS POSSIBLE IN HEAVY DOWNPOURS.

SHRA/TSRA ACTIVITY WILL WANE THIS EVENING AND WINDS WILL LIKELY
REMAIN EAST OR EAST-NORTHEAST FOR THE MOST PART BUT MAY TURN
SOUTHEAST OVERNIGHT. BETTER LOW LEVEL MOISTURE WILL BE IN
PLACE..ESPECIALLY IF RAIN CAN FALL...AND MVFR VSBY IS A DECENT
POSSIBILITY TOWARD DAYBREAK. SCT-BKN MVFR CLOUDS MAY ALSO DEVELOP
DURING THIS TIME. EXPECT THAT ANY MVFR VSBY/CIGS WOULD IMPROVE
AFTER DAYBREAK. WINDS WILL CONTINUE TO BE TRICKY WITH A EASTERLY
DIRECTION CONTINUING WITH VARIABILITY LIKELY.

MDB

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

* HIGH CONFIDENCE IN SHRA/TSRA REMAINING MAINLY SOUTH OF THE
  TERMINALS...LOW-MEDIUM CONFIDENCE IN ACTIVITY NEAR MDW THIS
  AFTERNOON...MEDIUM CONFIDENCE THAT SHRA/TSRA POTENTIAL NEAR ORD
  IS LOW.

* MEDIUM CONFIDENCE IN WIND TRENDS THROUGH THE PERIOD.

* MEDIUM CONFIDENCE IN MVFR VSBY LATE TONIGHT...LOW CONFIDENCE IN
  MVFR CIG POTENTIAL.

MDB

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

SATURDAY NIGHT...VFR.
SUNDAY THROUGH WEDNESDAY...VFR. PERIODIC CHANCES FOR SHRA/TSRA.
THURSDAY...VFR. PSBL MVFR WITH CHANCE FOR SHRA.

BEACHLER

&&

.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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