000
FXUS63 KIWX 181709
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
109 PM EDT SAT MAY 18 2013

.SYNOPSIS...
ISSUED AT 1111 AM EDT SAT MAY 18 2013

A STALLED FRONTAL BOUNDARY ACROSS THE REGION WILL BEGIN TO LIFT
NORTHWARD AS A WARM FRONT SUNDAY AND SUNDAY NIGHT. WARM CONDITIONS
CAN BE EXPECTED SUNDAY AND MONDAY IN ADVANCE OF A COLD FRONT AND
UPPER LEVEL DISTURBANCE THAT WILL BRING A GOOD CHANCE OF SHOWERS
AND THUNDERSTORMS TO THE REGION MONDAY THROUGH WEDNESDAY.

&&

.UPDATE...
ISSUED AT 1111 AM EDT SAT MAY 18 2013

SCATTERED LIGHT SHOWERS OR SPRINKLES HAVE DIMINISHED ACROSS
SOUTHEAST PORTIONS OF THE AREA THIS MORNING. SHOULD SEE SOME
DIURNAL RAMP UP OVER NEXT FEW HOURS OF THESE SHOWERS REDEVELOPING
PARTICULARLY ACROSS SOUTHEAST/SOUTH CENTRAL PORTIONS OF THE
FORECAST AREA IN CLOSER PROXIMITY TO DPVA WITH SLOW SE MOVING VORT
MAX...AND WHERE SFC DEW POINTS REMAIN IN THE UPPER 50S TO LOWER
60S. JUST SOME SMALL TWEAKS MADE TO HOURLY TEMPERATURE TRENDS BUT
MAX TEMPS STILL APPEAR TO BE IN GOOD SHAPE FROM UPPER 70S TO
LOWER 80S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 416 AM EDT SAT MAY 18 2013

A VERY TIGHT MOISTURE GRADIENT CONTINUED OVER THE AREA AGAIN
TODAY...WITH DEW POINTS IN THE 30S NORTH OF THE BOUNDARY TO LOWER
60S FARTHER SOUTH. GIVEN VERY WEAK SYNOPTIC SCALE FORCING AND LIGHT
WIND PROFILES...INCLUDING WIND GENERALLY AROUND OR UNDER 20 KNOTS
INTO THE UPPER LEVELS...CURRENT THINKING SHOWERS AND ISOLATED STORMS
WILL BE HIGHLY DIURNAL TODAY...INCLUDING LATE AFTERNOON AND EARLY
EVENING. CAPE VALUES SHOULD REMAIN VERY LIMITED AND CONVECTION
SHOULD BE MAINLY CONFINED TO THE MUCH HIGHER SFC THETA E AREAS ALONG
AND SOUTH OF THE FRONT. RAISED HIGHS A LITTLE TODAY GIVEN VERY LARGE
DIURNAL TEMPERATURE SWINGS EXPECTED TODAY...ESPECIALLY NORTH OF THE
BOUNDARY. NCEP MOS GUIDANCE FOR HIGHS HAS BEEN RUNNING 2 TO 4
DEGREES TOO COOL.

&&

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 416 AM EDT SAT MAY 18 2013

STRONG PACIFIC JET CURRENTLY CRASHING INTO THE WESTERN CONUS WILL
CARVE OUT A VERY LARGE BAROTROPIC LOW PRESSURE SYSTEM EAST OF THE
ROCKIES BY EARLY NEXT WEEK. THE GRADUAL EASTWARD PROGRESSION OF THIS
FEATURE WILL BRING INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS
TO THE LOCAL FORECAST AREA THROUGH MIDWEEK. BEGINNING WITH SUNDAY
THOUGH...MIDLEVEL RIDGE AXIS DIRECTLY OVER THE GREAT LAKES MAKES FOR
A SOMEWHAT PRECARIOUS PRECIP FORECAST. LOW LEVEL WINDS BEGIN TO VEER
TO A MORE SOUTHERLY DIRECTION DURING THIS TIME...ADVECTING MORE
WARM/MOIST AIR INTO THE REGION. LATEST MOS GUIDANCE SUPPORTS HIGHS
SOLIDLY IN THE MID 80S WITH DEWPOINTS CREEPING INTO THE LOW TO MID
60S. NAM AND GFS MLCAPE FIELDS/FORECAST SOUNDINGS CONTINUE TO SHOW A
MODERATELY UNSTABLE AND WEAKLY CAPPED ENVIRONMENT...THANKS TO STRONG
SOLAR INSOLATION AND INCREASING LOW LEVEL THETA-E ADVECTION.
HOWEVER...WITH THE LACK OF ANY SYNOPTIC SCALE LIFTING MECHANISM...
CONVECTION WILL BE RELIANT ON INEFFICIENT PBL MIXING TO REACH THE
LFC. ALSO...GIVEN PLACEMENT AND EVOLUTION OF RIDGING ALOFT...EXPECT
THE CAP MAY BE A BIT STRONGER THAN WHAT CURRENT BUFR SOUNDINGS
INDICATE. Q VECTOR DIVERGENCE FIELDS SHOW WEAKLY SUBSIDENT AIR MASS
THAT WILL LIKELY INHIBIT CONVECTION. RELATIVELY DRY TROPOSPHERIC
COLUMN SHOULD ALSO TEND TO INHIBIT EXPANDING CONVECTION. ALL OF THAT
BEING SAID...WOULDNT COMPLETELY RULE OUT AN ISOLATED THUNDERSTORM
BUT COVERAGE WILL BE VERY LIMITED AND DECIDED TO CUT POPS TO AROUND
10 PERCENT AND REMOVE BLANKET SLIGHT CHANCE WORDING.

SOUTHWESTERLY LLJ BEGINS TO RAMP UP SUNDAY NIGHT AND MONDAY AS THE
APPROACHING MIDLEVEL HEIGHT ANOMALY FORCES A TIGHTENING OF THE LOW
LEVEL GRADIENT. WARM FRONT BEGINS TO REALLY TAKE SHAPE AND LIFT
NORTH SUNDAY NIGHT AS THE RIDGE AXIS SHIFTS EAST. ASSOCIATED
ISENTROPIC ASCENT AND MOISTURE FLUX CONVERGENCE IN REGION OF MODEST
ELEVATED INSTABILITY COULD SPARK OFF A FEW
SHOWERS/THUNDERSTORMS...BUT AGAIN COVERAGE WILL BE LIMITED. CWA WILL
BE FIRMLY IN THE WARM SECTOR BY MONDAY AFTERNOON. 850MB TEMPS LOOK
TO CLIMB TO AROUND 17C...SUPPORTING HIGHS IN THE MID TO UPPER 80S
WITH DEWPOINTS IN THE MID TO UPPER 60S. PRECIP CHANCES WILL HINGE ON
EXACT TIMING OF APPROACHING TROUGH AND ASSOCIATED WEAKENING OF THE
CAPPING INVERSION. LATEST 00Z GFS IS MUCH SLOWER THAN ITS NAM AND
ECMWF COUNTERPARTS AND MAINTAINS A PREDOMINATELY DRY FORECAST.
SYMPATHETIC TO A SLOWER SOLUTION GIVEN OVERALL PATTERN BUT
CONFIDENCE TOO LOW TO MAKE SIGNIFICANT ADJUSTMENTS TO POPS AT THIS
TIME AND WILL GO WITH LOW CHANCE WORDING. IF CONVECTION DOES
OCCUR...SEVERE WEATHER IS A DISTINCT POSSIBILITY GIVEN STRONG
INSTABILITY AND MODERATE SHEAR PROFILES. AS SUCH...SPC HAS PLACED
OUR CWA IN DAY3 SLIGHT RISK TO COVER THIS CONDITIONAL THREAT.

MUCH BETTER PRECIP CHANCES EXPECTED TUES AND WED AS VERTICALLY
STACKED LOW APPROACHES AND LOW LEVEL MOISTURE ADVECTION CONTINUES.
EXPECT SEVERAL ROUNDS OF SHOWERS AND THUNDERSTORMS WITH EXACT TIMING
DEPENDENT ON EVOLUTION OF FRONTAL FEATURES AS WELL AS POTENTIALLY
MEDDLESOME MCS DEVELOPMENT. SEVERE WEATHER REMAINS POSSIBLE DURING
THIS TIME BUT WEAKENING DYNAMICS ALOFT AND INCREASINGLY STABLE
AIRMASS DOES NOT BODE WELL. A FEW LINGERING SHOWERS ARE POSSIBLE ON
THURSDAY BUT 1030 MB CANADIAN SURFACE HIGH IS EXPECTED TO BUILD OVER
THE GREAT LAKES BY THE END OF THE WEEK. THIS SHOULD RESULT IN A
PLEASANT...ALBEIT COOL...MEMORIAL DAY WEEKEND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 102 PM EDT SAT MAY 18 2013

VFR CONDITIONS EXPECTED THROUGH THE TAF PD WITH LIGHT EAST
SOUTHEAST FLOW NORTH OF A STATIONARY FRONT. ANY STRAY SHOWER THAT
DEVELOPS ALONG THE FRONT THIS AFTERNOON EXPECTED TO BE ISOLATED
AND WELL SOUTH OF TERMINALS. MOS GUIDANCE INDICATES A POSSIBLE
DROP TO MVFR CONDITIONS TOWARD DAYBREAK...HOWEVER KEPT TAFS VFR AS
MODEL SFC DEWPOINTS NORTH OF THE BOUNDARY ARE WELL OVERDONE...AND
EXPECT ADVECTION OF SFC BOUNDARY/HIGHER SFC MOISTURE NORTHWARD
INTO KFWA TO BE AFTER 12Z AND COINCIDENT WITH BEGINNING OF DAYTIME
MIXING.

&&

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

$$

UPDATE...MARSILI
SYNOPSIS...MARSILI
SHORT TERM...SKIPPER
LONG TERM...AGD
AVIATION...NG


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