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000
FXUS63 KDVN 171201
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
701 AM CDT FRI MAY 17 2013

.UPDATE...
ISSUED AT 649 AM CDT FRI MAY 17 2013

THE NOCTURNAL MCS WILL CONTINUE MOVING EAST FROM MN INTO WI THIS
MORNING BEFORE SLOWLY DISSIPATING. BOUNDARIES LEFT OVER FROM THAT
CONVECTION WILL BE THE PRIMARY FOCUS FOR DIURNAL CONVECTION TODAY.

MCS AND LIFT TOOLS PER RAP TRENDS SHOW THE THETA E GRADIENT AND
ASSOCIATED CONVERGENCE/LIFT IS JUST NORTH OF THE AREA. THUS DRY
CONDITIONS ARE EXPECTED THROUGH MID DAY ACROSS THE AREA. THE
CURRENT FCST HAS CONVECTION DEVELOPING IN THE AFTERNOON BUT IT IS
DEPENDENT ON WHEN CONVECTIVE TEMPERATURE IS ACHIEVED. IF THE RAP IS
CORRECT WE WOULD REMAIN BELOW CONVECTIVE TEMPERATURE. HOWEVER...
THE RAP TRENDS DO SHOW AREAS OF CONVERGENCE DEVELOPING DURING THE
AFTERNOON ALONG WITH WEAK THETA E GRADIENTS.

SO...ISOLATED TO SCATTERED CONVECTION IS EXPECTED THIS AFTERNOON
WITH THE NORTH THIRD MORE FAVORED DUE TO THE PROXIMITY OF THE
FRONTAL BOUNDARY. STORMS WILL BE SLOW MOVING DUE TO THE UPPER
RIDGE SO ANY THUNDERSTORM THAT DEVELOPS WILL HAVE THE POTENTIAL TO
PRODUCE VERY LOCALIZED HEAVY RAINFALL OF AN INCH OR MORE.  ..08..

&&

.SYNOPSIS...
ISSUED AT 229 AM CDT FRI MAY 17 2013

06Z SFC ANALYSIS HAS A WEAK LOW IN WESTERN IOWA JUST EAST OF KSUX
AND ANOTHER IN SOUTHERN SOUTH DAKOTA. AN EAST/WEST FRONTAL BOUNDARY
RAN FROM NORTHERN OHIO...THROUGH CENTRAL INDIANA...AND TO THE LOW
NEAR KSUX. FLOW OFF LAKE MICHIGAN HAD DEW POINTS RANGING FROM THE
UPPER 30S NORTH OF THE FRONT TO 50S AND LOW 60S SOUTH OF THE FRONT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 229 AM CDT FRI MAY 17 2013

THE CURRENT CONVECTION ON RADAR IS OCCURRING ALONG A THETA E
GRADIENT AND MOISTURE/TEMPERATURE GRADIENTS FROM THE 850MB FRONT.
MOST OF THE AREA WILL REMAIN DRY THROUGH SUNRISE EXCEPT FOR VERY
ISOLATED CONVECTION IN THE HWY 20 CORRIDOR.

THE MORNING HOURS ARE EXPECTED TO BE MAINLY DRY WITH PASSING CLOUDS
AS THE THETA E GRADIENT MOVES NORTH INTO WISCONSIN. DIFFERENTIAL
HEATING COMBINED WITH AN APPROACHING VORT MAX SHOULD RESULT IN
ISOLATED TO SCATTERED CONVECTION DEVELOPING BY LATE MORNING IN THE
EASTERN CWFA.

DURING THE AFTERNOON HOURS...ISOLATED TO SCATTERED CONVECTION WILL
EXPAND TO MOST OF THE CWFA AS CONVECTIVE TEMPERATURES ARE REACHED.

THE PROXIMITY OF THE UPPER RIDGE MEANS THAT STEERING CURRENTS FOR
THE CONVECTION ARE VERY WEAK. THUS THOSE AREAS THAT DO SEE RAIN THIS
AFTERNOON WILL HAVE THE POTENTIAL TO SEE LOCALLY HEAVY RAINFALL.

CONVECTION WILL SLOWLY DIMINISH WITH SUNSET BUT ISOLATED TO
SCATTERED CONVECTION IS EXPECTED TO CONTINUE INTO THE EVENING OVER
ROUGHLY THE NORTHEAST HALF OF THE CWFA. BY LATE EVENING MAINLY DRY
CONDITIONS ARE EXPECTED WITH LITTLE IF ANY CONVECTION AFTER
MIDNIGHT.

08

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 229 AM CDT FRI MAY 17 2013

MAIN CHALLENGE IS THE PROBABLE SEVERE WEATHER RISKS SUN/MON.

OVERVIEW...INITIALIZATION AND VERIFICATION FAIR WITH ALL SOLUTIONS
HAVING DIFFICULTY WITH ONGOING CENTRAL IOWA MCS EVENT. COUPLED
WITH BL DEWPOINT ISSUES SUGGEST AGAIN USE OF CONCEPTUAL
PRECIPITATION EVOLUTION TOOLS DERIVED FROM THE FORCING OF A BLEND
OF GEM-NH /HI-RES ECMWF/GFS. THIS SUPPORTS A DECENT RISK OF SEVERE
STORMS SUN/MON WITH PHASING AND CONVECTIVE ISSUES THAT SHOULD
BETTER CLARIFIED IN THE NEXT 24 HOURS. HIGHER END SEVERE STORM
EVENTS FOR REGION APPEAR MARGINAL ATTM FOR THE AREA WITH LOW/MODERATE
SEVERE EVENTS SUGGESTED ATTM.

SATURDAY...MINOR CHANGES WITH AREA LIKELY PARTLY SUNNY AND DRY AHEAD
OF SEASONABLY STRONG UPPER LEVEL SYSTEM MOVING INTO WEST CENTRAL
PLAINS. WARM AND A BIT HUMID WITH HIGHS IN THE LOWER 80S AND LOWS
MOSTLY IN THE LOWER 60S WITH DEWPOINTS 60-64F. SOME PATCHY FOG
POSSIBLE WITH ANY CLEARING FOR LATER SHIFTS TO CONSIDER.

SUNDAY AND MONDAY. GOOD SHEAR AND AT LEAST MODERATE INSTABILITY
SUPPORT ONE OR MORE CONVECTIVE EVENTS SUGGESTED WITH ENVIRONMENT
MOSTLY FAVORABLE FOR CONVECTIVE BOWING SEGMENTS ATTM. SEVERE
WEATHER AREAL TOOL AND BLEP/HELP ALGORITHMS SUGGEST WITH T/TDS
AOA 83/63 OF 60-70 MPH STRAIGHT LINE WINDS AND SOME HAIL THAT
COULD APPROACH 1.75 INCHES WITH WBZ OF ~11K AGL AND SBCAPE OF
2000-3000 J/KG. IF ANY WAVE FORMS IN LATE PM/EVENING THERE IS A
RISK OF ISOLATED TORNADOES BUT THIS APPEARS MARGINAL DUE TO
CURRENT JET STRUCTURE AND TIMING. HIGHS SUGGESTED BASED ON PARTLY
SUNNY SKIES SHOULD BE IN THE LOWER/MIDDLE 80S AND MINS MOSTLY IN
THE MIDDLE 60S. PW/S OF 1.25+ INCHES DO SUPPORT LOCALLY HEAVY
RAINFALL WITH ANY TRAINING OF STORMS. POPS IN THE LIKELY CATEGORY TO THE
MID/HIGH CHANCE WITH TIMING MAIN ISSUE. LOCAL FORCING AND HEAVY
RAIN TECHNIQUES DO SUPPORT MOST AREAS TO PICK UP AN INCH OR MORE
OF RAIN WITH PASSAGE OF UPPER LEVEL SYSTEM OVER NEXT 96+ HOURS.

TUESDAY...A CHALLENGE WITH WAVE BASED ON CONVECTION FIRING OVER
SOUTHERN PLAINS THE KEY ISSUE. JET STRUCTURE SUPPORTS DECENT RAIN
EVENT WITH LOTS OF CLOUDS AND THIS WOULD IMPACT HIGH TEMPERATURES
FOR LATER SHIFTS THAT MAY NEED LOWERING OVER CENTRAL AND SE SECTIONS.
POPS MAY NEED RAISING AS WELL BY 10-20 PERCENT WITH MODERATE TO
LOW END HEAVY AMOUNTS SUGGESTED. CONVECTIVE FEEDBACK QUESTION
SHOULD BE CLARIFIED MORE IN THE NEXT 24-36 HOURS. TUESDAY
NIGHT...UPPER LOW MOVES INTO AREA WITH CHANCE OF LOW TOP CONVECTION
OF SHOWERS AND BRIEF THUNDERSTORMS. MINS OF 55-60F WITH TEMPS
POSSIBLY A BIT TOO COOL IN FAR SE SECTIONS WITH CLOUDS.

WEDNESDAY AND THURSDAY...UPPER LOW TO SLIDE SLOWLY EAST WITH CHANCE
SHOWERS AND POSSIBLY ISOLATED THUNDER WITH PARTLY TO MOSTLY CLOUDY
SKIES. HIGH TEMPERATURES 67-77F SUGGESTED.  LOWS IN THE 50S WED AM
AND MID/UPPER 40S TO LOWER 50S SE SECTIONS THU AM. SEASONABLY STRONG
CANADIAN HIGH PRESSURE TO THEN DOMINATE AND KEEP AREA COOL WITH LOW
DEWPOINTS AND BELOW NORMAL INTO NEXT WEEKEND.

NICHOLS

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 649 AM CDT FRI MAY 17 2013

VFR WX WILL BE SEEN THROUGH 12Z/18. NEW CONVECTION WILL DVLP AFT
18Z/17 BUT THE PROBABILITY OF A SHRA OR TSRA AFFECTING A TAF SITE
IS 15 PERCENT. VCTS OR VCSH WAS INCLUDED IN THE 12Z TAFS TO
REFLECT THE POTENTIAL FOR NEARBY CONVECTION FROM 20Z/17 TO 03Z/18.
IF A SHRA/TSRA AFFECTS A TAF SITE CIGS SHOULD REMAIN VFR. VSBYS
MAY DROP TO MVFR OR IFR FROM HEAVY RAIN.          ..08..

&&

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

$$

UPDATE...08
SYNOPSIS...08
SHORT TERM...08
LONG TERM...NICHOLS
AVIATION...08