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000
FXUS63 KIWX 201729
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
129 PM EDT MON MAY 20 2013

.SYNOPSIS...
ISSUED AT 1052 AM EDT MON MAY 20 2013

A SLOW MOVING LOW PRESSURE SYSTEM WILL BRING INCREASING CHANCES
FOR SHOWERS AND THUNDERSTORMS LATER TODAY THROUGH WEDNESDAY...WITH
A FEW SHOWERS POSSIBLY LINGERING INTO THURSDAY. THERE IS A SLIGHT
RISK FOR SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH TUESDAY
NIGHT. DRIER AND COOLER WEATHER IS ANTICIPATED LATE THIS WEEK
INTO NEXT WEEKEND.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 359 AM EDT MON MAY 20 2013

DEEP REX BLOCKED CUTOFF LOW CNTRD OVR NRN NE THIS
MORNING WILL MOVE LTL THIS PD. THUS W/LTL CHG IN JET
STRUCTURE/POSITIONING ALOFT XPC CONVN WILL ONCE AGAIN STAY FOCUSED
WWD INVOF MS VALLEY.

LG SCALE GRAVITY WAVE EMINATING FM SLOWLY DECAYING CONVN ACRS WRN
IL SWWD INTO ERN MO WILL CONT EWD THIS MORNING. HWVR DOWNSTREAM
AIRMASS OF MUCH POORER QUALITY AS EVIDENT IN 00Z RAOBS AND
W/LLJ/MID LVL JET STREAK AXIS REMAINING ANCHORED TO THE WEST SEE
LTL EVIDENCE OF A SUFFICIENT SYNOPIC TRIGGER FOR AFTN CONVN AGAIN
TDA ESP IN LIGHT OF 00Z MODEL GUIDANCE SFC MSTR BIAS. WILL RETAIN
A LWR BOUND CHC MENTION NW HALF IN PROXIMITY TO EWD EDGE OF BTR LL
MASS FLUX THIS AFTN AND IN COLLABORATION OF WRN/NRN NEIGHBORS BUT
SOME HIGHRES CONVN ALLOWING GUIDANCE DOES CAPTURE IL/ERN MO
DENSITY CURRENT THIS MORNING AND WOULD APPEAR TO MORE CORRECTLY
SUPPRESS CONVN HERE LOCALLY THIS AFTN/EVE WITHIN GENERALLY
SUBSIDENT/CAPPED AIRMASS.

OTRWS UPSTREAM CONVN XPCD TO INITIATE AND GROW UPSCALE THIS AFTN/EVE
VCNTY OF THE OZARK PLATUE AND LIFT NEWD IN REMNANT FASHION INTO AT
LEAST WRN AREAS LT TONIGHT AS LLJ FOCUSES INTO THE WRN LAKES.

&&

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 359 AM EDT MON MAY 20 2013

CONVECTION PLAGUING THE CENTRAL CONUS OVER THE PAST FEW NIGHTS WILL
FINALLY FULLY INFILTRATE THE SOUTHERN GREAT LAKES BY TUESDAY AS
CLOSED UPPER LOW SLOWLY MIGRATES EASTWARD. LACK OF ANY DISTINCT
SYNOPTIC FORCING WILL LEAD TO SEVERAL ROUNDS OF SHOWERS AND
THUNDERSTORMS SIMILAR TO WHAT HAS BEEN EXPERIENCED UPSTREAM. EXACT
TIMING AND LOCATION WILL DEPEND ON AMBIGUOUS MIDLEVEL WAVES ROTATING
THROUGH THE MEAN FLOW AND MESOSCALE SUBTLETIES DIFFICULT TO PINPOINT
THIS FAR OUT. ADDITIONALLY...HIGH THETA-E AIRMASS WILL BE FIRMLY IN
PLACE ACROSS THE REGION THANKS TO PERSISTENT SSW FLOW AND SURFACE
DEWPOINTS SHOULD BE HOVERING IN THE MID TO UPPER 60S. ATMOSPHERE
WILL BE LARGELY UNCAPPED BY TUESDAY AND THIS SHOULD SUPPORT MASS
CONVECTION IN WARM/HUMID AIRMASS. REASONABLY CONFIDENT IN PRECIP
OCCURRING AT SOME POINT TUESDAY BUT EXACT TIMING AND THE RESULTING
IMPACT ON BOTH HIGH TEMPS AND SEVERE CHANCES REMAINS NEBULOUS. WILL
LIKELY BE A FAIR AMOUNT OF NOCTURNAL CONVECTION CHURNING UPSTREAM
AND LATEST HI-RES GUIDANCE...AND EVEN THE COARSER NAM AND
GFS...SUGGEST THIS WILL MOVE OVER OUR AREA BY TUESDAY MORNING. THIS
WOULD SEVERELY LIMIT OUR DIURNAL INSTABILITY RECOVERY AND PREVENT US
FROM CAPITALIZING ON EXPECTED 30-40 KNOTS OF 0-6KM BULK SHEAR.
SEVERE WEATHER CHANCES WILL THEREFORE DEPEND ON FORTUITOUS BREAKS IN
CONVECTION THAT ALLOW INSTABILITY TO BUILD...WHICH MAY PROVE
DIFFICULT IN AN UNCAPPED ENVIRONMENT. SIMILARLY...HIGH TEMPS WILL BE
LARGELY DEPENDENT ON TIMING OF CONVECTION. THERMAL RIDGE WILL DAMPEN
EAST A BIT BY TUESDAY BUT 850MB TEMPS STILL LOOK TO BE AROUND 15C.
CERTAINLY WONT BE AS WARM AS TODAY BUT SHOULD STILL SQUEAK OUT MID
80S IN MOST PLACES...UPPER 80S IF ANY SUN PEAKS THROUGH.

AFTER ANOTHER VERY MILD NIGHT ON TUESDAY NIGHT...HIGHS ON WEDNESDAY
WILL LIKELY BE A CATEGORY COOLER AS AIRMASS BECOMES INCREASINGLY
HOMOGENEOUS AND ABUNDANT CLOUDS/PRECIP TEMPER DIURNAL RESPONSE.
ASSOCIATED WEAKENING OF LAPSE RATES ALOFT WILL FURTHER LIMIT OUR
SEVERE CHANCES BY WEDNESDAY. CAPE VALUES EXPECTED TO BE IN THE
500-1000 J/KG RANGE...ENOUGH FOR THUNDER MENTION BUT NO ORGANIZATION
EXPECTED. WIDESPREAD PRECIP STILL EXPECTED TO CONTINUE THOUGH WITH
SIMILAR SETUP TO THE PRIOR DAY. COULD SEE SOME LOCALLY HEAVY
RAINFALL TOTALS WHEN ALL IS SAID AND DONE GIVEN PW VALUES HOVERING
AROUND 1.5 INCHES FOR MUCH OF THE EVENT. WEAK SURFACE LOW AND
OCCLUDED FRONT WILL PASS THROUGH THE SOUTHERN GREAT LAKES BY LATE
WEDNESDAY AND WESTERLY FLOW WILL FINALLY ADVECT SOME DRIER AIR INTO
THE AREA. COULD STILL BE SOME SHOWERS ON THURSDAY AS THE OLD
MIDLEVEL VORT MAX ROTATES THROUGH BUT HEAVIER/WIDESPREAD PRECIP
SHOULD TAPER OFF WEDNESDAY NIGHT. TANGIBLE AIRMASS CHANGE WONT
ARRIVE UNTIL FRIDAY THOUGH WHEN 1030MB CANADIAN SURFACE HIGH SETTLES
OVER THE GREAT LAKES. EXPECT HIGHS ONLY IN THE MID TO UPPER 60S
FRI/SAT. LATTER HALF OF THE HOLIDAY WEEKEND CONTINUES TO BE A
STRUGGLE FOR VARIOUS DETERMINISTIC NWP WITH POTENTIAL INTRUSION OF
PRECIP ON BACKSIDE OF AFOREMENTIONED SURFACE HIGH. PLACEMENT OF
RELEVANT SYNOPTIC FEATURES AND RELATIVELY COLD LAKES FAVOR STRONGER
HIGH AND DRY FORECAST BUT THIS WILL CERTAINLY HAVE TO BE WATCHED AS
TIME GOES ON.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 128 PM EDT MON MAY 20 2013

VFR CONDITIONS EXPECTED FOR THE REST OF TODAY AND INTO
THE OVERNIGHT HOURS. SLIGHT CHANCE THAT A STRAY SHOWER OR ISOLATED
STORM COULD POP UP NEAR KFWA...BUT CONFIDENCE WAS TOO LOW FOR
INCLUSION IN 18Z TAF ISSUANCE. STORMS WILL FIRE ACROSS MISSOURI
TODAY AND WILL LIKELY TRACK INTO NORTHERN INDIANA DURING THE EARLY
MORNING HOURS. THIS THREAT IS GREATEST AT KSBN. WILL WAIT FOR LATER
TAF ISSUANCES BEFORE INCLUDING THESE STORMS AS SUBTLE TIMING
DIFFERENCES AND EXACT LOCATION WILL NOT BE KNOWN UNTIL THE
CONVECTION HAS FIRED AND BEGINS TRACKING TOWARDS THE AREA.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...STEINWEDEL
SHORT TERM...T
LONG TERM...AGD
AVIATION...BENTLEY


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