656
FXUS63 KIWX 201907
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
307 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
(THIS EVENING THROUGH TUESDAY)
ISSUED AT 305 PM EDT MON MAY 20 2013
REMNANT GRAVITY WAVE FROM OVERNIGHT CONVECTION AND
ASSOCIATED WITH A ~10F DEGREE DEWPOINT DROP IN ITS WAKE HAS WASHED
OUT AS IT MOVED INTO OUR FORECAST AREA. THIS HAS KEPT MODERATELY
UNSTABLE AIRMASS ACROSS THE EASTERN TWO-THIRDS OF OUR FORECAST AREA.
ADDED SLIGHT CHANCE POPS FOR THE EAST THIS EVENING AS CONVECTION
COULD FIRE ALONG OR IN FRONT OF THIS BOUNDARY WHERE THE AIRMASS IS
CHARACTERIZED BY SBCAPE VALUES IN EXCESS OF 3000 J/KG. THE GREATEST
LIMITING FACTOR IS THE LACK OF SIGNIFICANT FORCING...ALTHOUGH
CONVECTION ACROSS MICHIGAN AND ADDITIONAL CONVECTION FIRING ALONG
THE BOUNDARY ACROSS EASTERN ILLINOIS AT 1830Z INDICATES THIS
BOUNDARY MAY PROVIDE JUST ENOUGH FORCED ASCENT FOR ISOLATED STORM
DEVELOPMENT.
STILL SOME UNCERTAINTY REGARDING CONVECTIVE EVOLUTION AND IMPACTS
ACROSS OUR AREA TONIGHT. DECAYING STORM CLUSTER ACROSS WESTERN
ILLINOIS SHOULD CONTINUE ITS WEAKENING TREND AS IT MOVES INTO A
MOISTURE VOID AREA ACROSS ILLINOIS WITH SURFACE DEWPOINTS IN THE
UPPER 50S. WITH THAT BEING SAID...SOME SHORT TERM MODEL GUIDANCE IS
INDICATING A QUICK RECOVERY OF THE MOISTURE PROFILE IN THAT AREA AS
850 MOISTURE TRANSPORT INCREASES THIS AFTERNOON. IF THE AIRMASS
AHEAD OF THESE STORMS CAN DESTABILIZE OVER THE NEXT FEW HOURS...AS
THE HRRR SUGGESTS...UPSCALE GROWTH OF THAT CLUSTER AS WELL AS
ADDITIONAL STORM DEVELOPMENT MAY TRACK ACROSS THE NORTHWEST PORTION
OF OUR FORECAST AREA DURING THE LATE EVENING. IF STORMS CAN
DEVELOP...SEVERE POTENTIAL DOES EXIST AS 0-6 KM SHEAR OF 35-45 KNOTS
OVERSPREADS THE NORTHWEST PORTION OF OUR FORECAST AREA WITH THE MAIN
THREATS BEING SEVERE HAIL AND WIND.
REMAIN MORE CONFIDENT IN PRECIPITATION CHANCES AFTER 06Z WHEN
REMNANT CONVECTION FROM MISSOURI TRACKS TOWARDS THE AREA. SEVERE
THREAT WILL BE MINIMAL WITH THIS CONVECTION DUE TO ITS TIMING DURING
THE EARLY MORNING HOURS.
TUESDAY LOOKS TO BE COOLER THAN TODAY AS LITTLE SUN WILL BE SEEN
ACROSS OUR FORECAST AREA DUE TO CLOUD DEBRIS FROM FROM OVERNIGHT
CONVECTION AS WELL AS ADDITIONAL DYNAMIC LIFT FROM 40-50 KT LLJ.
SEVERE THREAT DOES EXIST IF A FEW BREAKS IN THE CLOUDS CAN PROVIDE
SIGNIFICANT SURFACE HEATING FOR EVEN MARGINAL SURFACE BASED
INSTABILITY. THE MAIN THREAT WILL BE LARGE HAIL AND DAMAGING WINDS
AS UNIDIRECTIONAL 35-40 KNOT SHEAR OVERSPREADS THE AREA.
LONG TERM
(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 305 PM EDT MON MAY 20 2013
ONE OR TWO MORE ROUNDS OF CONVECTION TO BEGIN THE FORECAST PERIOD.
MODELS IN PRETTY GOOD AGREEMENT IN SHORT WAVE COMING OUT OF BASE OF
CLOSED LOW AND IMPACTING THE AREA TUE NIGHT. GOOD SUPPORT WILL
ACCOMPANY THIS FEATURE AND 50-60KT MID LEVEL SPEED MAX WILL COMBINE
WITH INFLUX OF LOW LEVEL MOISTURE WITH AT LEAST SUFFICIENT
INSTABILITY TO INITIATE OR MAINTAIN CONVECTION. UNIDIRECTIONAL WIND
PROFILE WITH AROUND 30KT OF SPEED SHEAR WILL HAVE DAMAGING WINDS AS
THE MAIN SEVERE THREAT. CLOSED LOW FINALLY OPENS UP AND WILL MOVE
EASTWARD INTO THE GREAT LAKES REGION WEDNESDAY NIGHT...BRINGING SFC
LOW AND MAIN COLD FRONT WITH IT. MODELS OFFERING VARYING
TIMING/PLACEMENT OF THESE FEATURES BUT ONE MORE ROUND OF CONVECTION
POSSIBLE WEDNESDAY...MAINLY FOR THE EASTERN HALF OF THE CWA. UPPER
TROF AXIS ROTATES THROUGH THE AREA WEDNESDAY NIGHT INTO THURSDAY
KEEPING CHANCE FOR A FEW SHOWERS BEFORE COOLER DRIER CANADIAN HIGH
PRESSURE BEGINS TO BUILD INTO THE GREAT LAKES REGION ON FRIDAY. THIS
WILL PROVIDE A NICE START TO THE HOLIDAY WEEKEND...QUESTIONS REMAIN
AS TO WHETHER IT WILL LAST THROUGH MONDAY. SFC RIDGE AXIS WILL
PROGRESS EASTWARD SUNDAY AND MONDAY...PLACING OUR AREA ON THE
WESTERN PERIPHERY OF THE HIGH WHILE MEDIUM RANGE MODELS ATTEMPTING
TO BRING SHORT WAVE ENERGY DOWN IN NW FLOW. GETTING BETTER MODEL
AGREEMENT WITH THIS SOLN BUT LOTS OF VARIATION IN TIMING AND
PLACEMENT. ENSEMBLE GUIDANCE NEAR OR MOSTLY BELOW CLIMO FOR POPS AS
WELL SO WILL STILL HOLD OUT FOR DRY FORECAST FOR AT LEAST ONE MORE
ISSUANCE. TEMPS TRENDING SEASONABLY COOLER WITH AOB NORMAL FOR MOST
OF THE FCST PERIOD.
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...BENTLEY
LONG TERM...JAL
AVIATION...BENTLEY
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