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000
FXUS63 KDVN 121728
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1228 PM CDT WED JUN 12 2013

.UPDATE...
ISSUED AT 1016 AM CDT WED JUN 12 2013

STRONG PRESSURE FALLS OCCURING ACROSS EASTERN IA WITH STRONG SHORT
WAVE IN SD. THERE IS JUST ENOUGH OF A CAP TO SUPPRESS ACTIVITY
THIS MORNING. VISIBLE SATELLITE SHOWS SKIES WILL BE CLEARING AS
THE MORNING PROGRESSES SETTING UP FOR A VOLATILE SITUATION.
STRONG DEEP LAYER SHEAR WILL BE IN PLACE WITH SWEAT INDEX OVER 400
AND HELICITY VALUES OVER 300 M2/S2. LCL WILL BE LOW AT AROUND 3K
FT. AS THE SHORT WAVE APPROACHES THE CAP WILL WEAKEN CONSIDERABLY
BY EARLY THIS AFTERNOON ALLOWING FOR EXPLOSIVE SUPERCELL
DEVELOPMENT. THIS WILL BE INITIALLY IN OUR NORTHERN CWA ALONG AND
NORTH OF A BOUNDARY AND THEN SPREADING SOUTHEAST DURING THE
AFTERNOON. THIS WILL EVENTUALLY CONGEAL INTO A WIDESPREAD DAMAGING
WIND EVENT INTO THE EARLY EVENING HOURS. SPC MESO ANALYSIS
INDICATES SIGNIFICANT TORNADO PARAMETERS SITUATED OVER THE DVN
CWA. SPC WILL BE UPGRADING PORTIONS OF EASTERN IA AND NORTHERN IL
INTO A HIGH RISK FOR STRONG TORNADOES AND WIDESPREAD DAMAGING
WINDS OF 80+ MPH. THIS IS A PARTICULARLY DANGEROUS WEATHER SITUATION.

THE WARMEST AIR MASS OF THE SEASON HAS SPREAD INTO THE CWA WITH
AFTERNOON MAXIMUM TEMPERATURES IN THE LOWER 90S SOUTH OF
INTERSTATE 80 WITH DEW POINTS IN THE LOWER 70S. THIS WILL CREATE
HEAT INDEX VALUES OF AROUND 100. HAVE ISSUED A SPECIAL WEATHER
STATEMENT.

&&

.SYNOPSIS...
ISSUED AT 258 AM CDT WED JUN 12 2013

A MAJOR SEVERE WEATHER OUTBREAK IS POSSIBLE TODAY IN IOWA AND
ILLINOIS.  AT MINIMUM...IT APPEARS A WIDESPREAD RISK FOR WIND AND
HAIL IS LIKELY OVER ALL OF THE CWA THIS AFTERNOON AND EARLY THIS
EVENING...WITH A RISK FOR TORNADOES PRIMARILY ALONG AND NORTH OF A
LINE FROM CEDAR RAPIDS...TO MUSCATINE...TO PEORIA ILLINOIS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 258 AM CDT WED JUN 12 2013

A VERY SOBERING SITUATION IS DEVELOPING EARLY THIS MORNING. A
CAPPED HIGH CAPE AIRMASS IS FOUND FROM IOWA SOUTHWARD...A STRONG
SHORT WAVE IS DROPPING INTO THE DAKOTAS...LOW PRESSURE IN SOUTH
CENTRAL NEBRASKA IS MOVING EAST ALONG A STALLED FRONTAL BOUNDARY.
THIS FRONT IS FOUND FROM OMAHA EASTWARD OVER IOWA TO THE QUAD
CITIES...TO NORTHERN INDIANA. MCS ACTIVITY IS OCCURRING JUST NORTH OF
THIS STALLED BOUNDARY...ENHANCING THE CONVERGENCE BY BACKING THE
WINDS ALONG IT.

SPC HAS ALREADY OUTLINED THE THREATS TODAY VERY WELL IN THEIR DAY 1
GRAPHICS...AS I STRONGLY BELIEVE THERE WILL BE SEVERAL HOURS OF
SUPERCELL THUNDERSTORMS THIS AFTERNOON OVER THE NORTHERN 1/2 OF THE
CWA...ALONG THE STALLED BOUNDARY. THIS PLACES A TORNADO RISK INTO THE
CEDAR RAPIDS...DUBUQUE...CLINTON...QUAD CITIES...FREEPORT...STERLING
...GENESEO...AND PRINCETON METRO AREAS. AS NOTED BY SPC...THERE IS A
RISK FOR A FEW STRONG TORNADOES...ESPECIALLY RIGHT NEAR THE BOUNDARY
WHERE THE STRONGEST LOW LEVEL INSTABILITY SHOULD BE FOUND...ALONG
WITH BACKED WINDS...CREATING A MORE STRONGLY CURVED HODOGRAPH. AT
THIS TIME...THIS APPEARS TO BE LOCATIONS ROUGHLY ALONG INTERSTATE
80...EAST OF IOWA CITY.

THE CAP WHICH PREVENTED CONVECTION YESTERDAY IS NOW WORKING AGAINST
US. THUS FAR THROUGH 2 AM...IT HAS PREVENTED STORMS FROM FORMING IN
THE SOUTH HALF IOWA. OUR SAVIOR OUT OF THIS EVENT IS MOST CERTAINLY
GETTING STORMS TO PUSH THE BOUNDARY SOUTH...BUT EVEN WITH A LARGE
FLARE UP IN STORMS IN NORTHWEST IOWA...THE CAP IS SO STRONG THAT
STORMS MAY ONLY SWIPE THE NORTHERN 2 ROWS OF COUNTIES. AT THIS
POINT...SINCE MODELS ARE CORRECTLY SHOWING THE STORMS TO THE
NORTHWEST REMAINING ON AN EAST TO NORTHEAST PROGRESS...I HAVE TO
BELIEVE THE BOUNDARY WILL NOT DROP FARTHER SOUTH...AND STRONG
HEATING/HIGH CAPE WILL OCCUR IN THE SOUTHERN 1/2 OF THE CWA SETTING
THE STAGE FOR OUR POTENTIAL SEVERE EVENT.  THIS SAID...I WILL
CONTINUE TO MONITOR CONVECTIVE TRENDS...AND HOPE OUR CAPPING
WEAKENS...BUT THAT SEEMS UNLIKELY AHEAD OF THE COMING STRONG SHORT
WAVE IN THE DAKOTA.   AFTER HIGHS REACH THE UPPER 80S TODAY...THE
LOW SHOULD BE POISED NEAR DES MOINES...AND WILL SWEEP EAST TO THE
MISSISSIPPI RIVER BY 7 PM THIS EVENING. THUS...SUPERCELLS SHOULD
BREAK OUT BY EARLY TO MID AFTERNOON...WITH A TORNADO RISK IN THE
AFOREMENTIONED AREAS...THIS SHOULD THEN CONGEAL WITH STORMS NEAR THE
LOW AND ALONG THE COLD FRONT IN CENTRAL IOWA THIS LATE AFTERNOON.
FROM THIS POINT ON A INTENSE DERECHO SHOULD FORM...AND SWEEP
EASTWARD. WIDESPREAD WIND THREAT IS EXPECTED...WITH WINDS THAT
SHOULD EASILY REACH 80 MPH IN BOWING SEGMENTS. THIS IS POSSIBLE IN
ALL AREAS EAST OF I-280...BUT ESPECIALLY IN THE ILLINOIS COUNTIES.
IN SOUTHEAST IOWA...NORTHERN MISSOURI...AND WEST CENTRAL
ILLINOIS...IT IS THE DAMAGING WINDS WITH THE MAIN LOW PASSAGE THAT
WILL BE THE PRIMARY THREAT...UNLESS THE BOUNDARY DROPS WELL SOUTH AS
MENTIONED AS A LOWER POSSIBILITY.

STAY INFORMED. TAKE WARNINGS VERY SERIOUSLY TODAY. KNOW WHERE YOU
WILL TAKE SHELTER THIS AFTERNOON IF IT IS REQUIRED. SHUT YOUR GARAGE
DOOR.
ERVIN

.LONG TERM...(THURSDAY THROUGH NEXT TUESDAY)
ISSUED AT 258 AM CDT WED JUN 12 2013

THURSDAY AND FRIDAY...THE 00Z MODEL RUNS CONTINUE TO BE CONSISTENT
WITH PREVIOUS RUNS IN ADVERTISING A SEASONABLY ROBUST SFC HIGH
DUMPING DOWN THE UPPER MS RVR VALLEY WHILE UPPER RIDGE AMPLIFIES ACRS
THE PLAINS/MO RVR VALLEY IN THE WAKE OF THE DIGGING GRT LKS TROF. THU
CONTINUE TO LOOK DRY...LESS HUMID AND A BIT COOLER IN THE MID 70S TO
AROUND 80. THU NIGHT COOLER IN THE MID 50S TO AROUND 60 WITH
VALLEY/LOW LYING AREA FOG POSSIBLE...BUT CI DEBRIS OFF SHOWERS/
CONVECTION RIDGE-RIDING OFF TO THE WEST MAY BLEED ACRS THE CWA AND
INHIBIT MORE WIDESPREAD FOG FORMATION. SFC HIGH SHIFTS ACRS THE
WESTERN GRT LKS FOR CONTINUED FAIR WX PERIOD ON FRI...BUT
DEBRIS/DECAYING SHOWERS AND A POSSIBLE STORM MAY TRY TO MAKE IT INTO
THE FAR WESTERN CWA. SOUTHERLY LLJ WITH RICH THTA-E FEED RELOADS ACRS
WESTERN IA FRI EVENING...THUS THE POTENTIAL FOR ANOTHER RIDGE-RIDING
MCS TO DEVELOP UPSTREAM AND PROPAGATE EASTWARD INTO THE DVN CWA
OVERNIGHT INTO SAT MORNING. HEAVY RAIN POSSIBLE AS WELL AS ISOLATED
SVR WX IN FORM OF MAINLY LARGE HAIL.

SATURDAY THROUGH NEXT TUESDAY...LATEST MEDIUM RANGE MODELS AND
ENSEMBLES STILL SUGGEST A FLATTENING FLOW PATTERN ACRS THE UPPER
MIDWEST SAT INTO SUNDAY. THE SAT MORNING MCS MAY DECAY WITH OUTFLOW
AND BOUNDARIES SETTLING TO THE SOUTH...ACTING AS A FOCAL POINT FOR
NEW CONVECTIVE DEVELOPMENT SAT NIGHT. HOW FAR NORTH OR SOUTH THIS
OCCUR STILL VERY MUCH UNCERTAIN AT THIS POINT...WITH THE NEW RUNS
TRENDING BACK NORTH UNFORTUNATELY WITH NEW MCS TRACK LAY OUT ACRS IA
INTO NORTHERN IL FOR BOTH SAT NIGHT AND INTO SUNDAY. HIGH CHC POPS
FOR THESE PERIODS WILL CONTINUE.  LONGER RANGE INDICATIONS SUGGEST
DIGGING WESTERN GRT LKS UPPER TROF MAY BRING A REPRIEVE FROM THE
STORMS LATER MON INTO TUE WITH THE CONVECTIVE FOCUS SHIFTING TO THE
SOUTH.    ..12..

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1217 PM CDT WED JUN 12 2013

VFR CONDS EARLY THIS AFTERNOON THEN SCATTERED SUPERCELLS WILL
DEVELOP NORTH OF INTERSTATE 80 EARLY TO MID AFTERNOON...WITH
THUNDERSTORMS GRADUALLY BECOMING WIDESPREAD AND SPREADING
SOUTHEAST ACROSS ALL THE TAF SITES LATER IN THE AFTERNOON INTO THE
EVENING. ISOLATED STRONG TORNADOES AND WIDESPREAD DESTRUCTIVE
WINDS IN EXCESS OF 70 KNOTS CAN BE EXPECTED THIS AFTERNOON INTO
THIS EVENING. MVFR/OCNL IFR CONDS IN THUNDERSTORMS.

HIGH PRESSURE BUILDS INTO THE REGION LATE TONIGHT AND THURSDAY
WITH VFR CONDS WITH CLEAR SKIES. SOUTH WINDS 10 TO 15 KNOTS THIS
AFTERNOON BECOMING NORTH 10 TO 15 KNOTS THIS EVENING AND OVERNIGHT.
NORTH WINDS AROUND 10 KNOTS ON THURSDAY.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...HAASE
SYNOPSIS...ERVIN
SHORT TERM...ERVIN
LONG TERM...12
AVIATION...HAASE