Severe Thunderstorm Warning 45, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
321 PM CDT WED MAY 12 2010

.SYNOPSIS...
THUNDERSTORMS CONTINUE TO PERCOLATE EARLY THIS AFTERNOON ALONG
THE H8 FRONT THAT WAS ROUGHLY ALONG I-80 FROM CENTRAL TO EAST
CENTRAL IA. THE SURFACE FRONT REMAINS WELL TO THE SOUTH...
EXTENDING FROM LOW PRESSURE OVER S CENTRAL KS...EAST SOMEWHERE
NORTH OF THE I-70 CORRIDOR IN CENTRAL MO. SOUTH OF THE SURFACE
BOUNDARY...TEMPERATURES WERE IN THE 70S TO LOW 80S WITH DEWPOINTS
IN THE 60S...WHILE TO THE NORTH...WIDESPREAD TEMPERATURES AND
DEWPOINTS WERE ONLY IN THE 40S TO LOWER 50S ACROSS THE CWA WITH
BLUSTERY LOW LEVEL EAST WINDS. THE LEADING EDGE OF THE PLUME OF
VERY MOIST AIR AT H8 THAT WAS FEEDING THE ELEVATED CONVECTION IN
CENTRAL IA THIS AFTERNOON WAS ANALYZED AT 12Z REACHING FROM W TX
THROUGH NE KS. THIS WAS AHEAD OF A LONGWAVE UPPER TROUGH OVER THE
ROCKIES WITH EMBEDDED SHORTWAVES IN THE S-SWRLY FLOW ACROSS THE
CENTRAL PLAINS. AS THE SURFACE LOW AND JET LEVEL FORCING PROGRESS
NE TONIGHT...ALONG WITH THE FEED OF HIGH THETAE AIR...CONDITIONS
ARE SETTING UP FOR HEAVY RAINFALL ACROSS THE REGION.

&&

.SHORT TERM...TONIGHT AND THURSDAY...
POTENTIAL FOR HEAVY RAINFALL AND FLOODING TONIGHT AND THURSDAY IS
THE PRIMARY CONCERN. EARLY ON...WILL BE CLOSELY MONITORING
CURRENT CLUSTER OF ELEVATED STORMS N OF I-80 LATE THIS
AFTERNOON...WHICH MAY HAVE POTENTIAL FOR 1 INCH HAIL OR LARGER AND
NEAR SEVERE WIND GUSTS FROM DOWNDRAFTS AND GRAVITY WAVES. ALSO...WILL
NEED TO CLOSELY MONITOR THE FAR S AND SE...WHERE SOME THINNING IN
THE OVERCAST MAY LEAD TO SURFACE INSTABILITY IN PROXIMITY TO THE
BOUNDARY...ALTHOUGH THE CLOSEST ACTIVITY IS WELL WEST IN KS INTO
NW MO AT THIS TIME.

HEAVY RAIN POTENTIAL...12Z FORECAST MODELS HAD A POOR HANDLE ON
EVOLUTION OF THE MCS THAT MOVED ACROSS THE AREA THIS MORNING AND
ADDED SOME UNEXPECTED RAINFALL OVER ESPECIALLY E CENTRAL IA. THIS
WAS MISSED BY MOST MODELS...ALTHOUGH LATER RUC RUNS CAPTURED THE
WEAK MID LEVEL VORT RESPONSIBLE. THIS MODEL HAS A SIMILAR WEAK MID
LEVEL WAVE THAT IS LIKELY TRIGGERING THE NEXT ROUND OF MORE
SURFACE BASED CONVECTION CURRENTLY IN KS INTO NW MO. THIS LIFTS NE
INTO THE FORECAST AREA THIS EVENING...LIKELY IMPACTING THE W
EARLY. THEN...UPPER JET LEVEL COUPLET ABOVE STRONG LOW LEVEL
MOISTURE CONVERGENCE SETS UP OVER THE FORECAST AREA TOWARD
MIDNIGHT AS THE INITIAL AND FOLLOWING MID LEVEL WAVES RIPPLE
THROUGH. WHILE THERE IS SOME CONCERN THAT THE LOW LEVEL JET MAY
TRY TO FOCUS ACTIVITY ALONG THE H8 FRONT THAT WILL BE NORTH OF THE
REGION...THE STRONG FORCING OVER THE SURFACE WARM FRONT REACHING E
AND SE OF THE SURFACE LOW LIFTING THROUGH THE FORECAST AREA WILL
BE CAPABLE OF SUPPORTING CONVECTION WITH VERY HEAVY RAINFALL
RATES. HAVE RAISED OVERNIGHT QPF TO A WIDE SWATH OF 2 TO 3 INCHES
SW TO NE ACROSS THE MID SECTION OF THE CWA.

THUS...THE FLASH FLOOD WATCH REMAINS AND HAVE EXPANDED IT FURTHER
N AND NW DUE TO THE HIGHER ANTICIPATED AMOUNTS AND SATURATION
CAUSED BY TODAY/S RAINFALL. ALSO...EXTENDED THE EAST TO EXPIRE AT
MIDDAY THURSDAY AS RAIN WILL CONTINUE THERE MUCH OF THE DAY...BUT
POTENTIAL FOR HEAVY RAINFALL RATES WILL BE LIMITED TO THE MORNING.

OTHERWISE...HAVE A NON DIURNAL TEMPERATURE CURVE FOR TONIGHT INTO
THU...WITH THE SE GETTING INTO THE WARM SECTOR AND TEMPERATURES IN
THE 60S TO AROUND 70 LATE TONIGHT INTO EARLY THU. TEMPERATURES
THEN FALL BACK TO THE 50S TO LOW 60S DURING THE DAY.
..SHEETS..

.LONG TERM...THURSDAY NIGHT THROUGH NEXT WEDNESDAY...
...SLIGHTLY BELOW NORMAL TEMPS WITH A CHANCE OF SHOWERS AND POSSIBLY
SOME STORMS SUNDAY INTO MONDAY...

OVERALL...SOLUTIONS HAVING PROBLEMS WITH ONGOING CONVECTION.
VERIFICATION AT 18Z SUPPORTS A 70/30 BLEND OF NAM-WRF WITH HI-RES
ECMWF/UKMET INTO SATURDAY. THEN WENT WITH MODEL RUN-TO-RUN CONTINUITY
OF A 60/40 BLEND OF GFS AND HI-RES ECMWF BEYOND SATURDAY.  NEXT LOW
TRACK AND TIMING SHOULD BE CLARIFIED NEXT 24 HOURS FROM CONVECTION
THAT OCCURS TONIGHT INTERACTING WITH UPSTREAM ENERGY AND ALSO BETTER
RESOLUTION OF PHASING.

THURSDAY NIGHT THROUGH SATURDAY...DRY AND QUIET WITH TEMPERATURES
MAINLY 2 TO 5 DEGREES BELOW NORMAL.  LOW DEWPOINTS SUGGEST SLIGHTLY
LARGER DIURNAL RANGES WITH MANY/MOST LOCATIONS POSSIBLY A COUPLE OF
DEGREES HIGHER ON MAX TEMPS AND ALSO COLDER ON MIN TEMPS.  PASS TO
LATER SHIFTS TO RECONSIDER.

SUNDAY AND MONDAY...LARGE SCALE ANALYSIS SUGGEST LOTS OF CLOUDS WITH
SOME RAIN AND EMBEDDED THUNDER.  RAISED POPS TO CHANCE BUT TRACK THE
MAIN ISSUE.  HIGHS MAY BE UP TO 5 DEGREES TOO WARM IF CLOUDS AND RAIN
ARE SIGNIFICANT.  LOWS ALSO MAY A FEW TOO COOL DUE TO LIMITED
RADIATIONAL COOLING.  AGAIN...SHOULD BE ABLE TO CLARIFY EXTENT OF ANY
PRECIPITATION BY THURSDAY AFTERNOON.

TUESDAY AND WEDNESDAY...NEXT MODERATE STRENGTH SURFACE HIGH TO KEEP
AREA QUIET AND GENERALLY SLIGHTLY BELOW NORMAL.  LOWS WITH SURFACE
HIGH OVERHEAD MAY NEED LOWERING UP TO 5 DEGREES NEXT FEW DAYS AS
TIMING BETTER CONFIRMED.  WARMING TREND TO BEGIN BY LATE NEXT WEEK
WITH DECENT UPPER TROUGH TO WEST AND SOUTH WINDS.   ..NICHOLS..

&&

.AVIATION...
SCATTERED THUNDERSTORMS WILL BECOME WIDESPREAD THIS EVENING AND
OVERNIGHT AS LOW PRESSURE OVER THE PLAINS MOVES ACROSS EASTERN IA.
CONDITIONS WILL REMAIN PREDOMINANTLY IFR MAINLY DUE TO LOW CIGS
TONIGHT THROUGH THU MORNING. EVEN OUTSIDE OF THUNDERSTORMS...
PERIODS OF STRONG EASTERLY WINDS AS HIGH AS 20 TO 30 KTS WILL BE
POSSIBLE THIS AFTERNOON AND OVERNIGHT. SOME STORMS IN THE
AFTERNOON AND EARLY EVENING PERIOD COULD PRODUCE SMALL HAIL AND
WIND GUSTS TO 45 KTS. RAIN WILL END FROM W TO E ON THU AS SYSTEM
SENDS A COLD FRONT THROUGH THE AREA. THIS WILL VEER WINDS AROUND
TO THE SW THEN W BY AFTERNOON.
..SHEETS..
&&

.HYDROLOGY...
A HEAVY RAIN EVENT IS FORECAST TO AFFECT THE AREA MAINLY TONIGHT.
THERE IS STILL SOME UNCERTAINTY REGARDING THE TIMING...AMOUNT...AND
LOCATION OF THE HEAVY RAIN. HOWEVER...BASED ON FORECASTED RAINFALL
THAT HAS BEEN INPUT INTO THE RIVER MODELS...SEVERAL RIVERS ARE
EXPECTED TO GO INTO FLOOD. RIVERS THAT DO NOT GO INTO FLOOD WILL SEE
SIGNIFICANT RISES.

RIVERS THAT MAY BE AFFECTED INCLUDE THE LOWER WAPSIPINICON...ROCK...
PORTIONS OF THE IOWA...ENGLISH...NORTH SKUNK...SKUNK...LA MOINE...
MISSISSIPPI BELOW DAM 15...AND THE LOWER DES MOINES.

THE CURRENT WEATHER AND RIVER LEVELS WILL BE MONITORED CLOSELY
TONIGHT. ADDITIONAL RIVER FLOOD WARNINGS ARE LIKELY DEPENDING UPON
HOW THE HEAVY RAIN THREAT EVOLVES TONIGHT INTO THURSDAY MORNING.
..08..

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY
     MORNING FOR BENTON-CEDAR-CLINTON-HENRY IA-IOWA-JACKSON-
     JEFFERSON-JOHNSON-JONES-KEOKUK-LINN-LOUISA-MUSCATINE-SCOTT-
     VAN BUREN-WASHINGTON.

     FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY
     MORNING FOR DES MOINES-LEE.

IL...FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY
     MORNING FOR JO DAVIESS.

     FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY
     MORNING FOR BUREAU-CARROLL-HANCOCK-HENDERSON-HENRY IL-
     MCDONOUGH-MERCER-PUTNAM-ROCK ISLAND-STEPHENSON-WARREN-
     WHITESIDE.

MO...FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY
     MORNING FOR SCOTLAND.

     FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY
     MORNING FOR CLARK.

&&

SHEETS/NICHOLS/08

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
514 AM CDT WED MAY 12 2010

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-131015-
BUCHANAN-DELAWARE-DUBUQUE-BENTON-LINN-JONES-JACKSON-IOWA-JOHNSON-
CEDAR-CLINTON-MUSCATINE-SCOTT-KEOKUK-WASHINGTON-LOUISA-JEFFERSON-
HENRY IA-DES MOINES-VAN BUREN-LEE-JO DAVIESS-STEPHENSON-CARROLL-
WHITESIDE-ROCK ISLAND-HENRY IL-BUREAU-PUTNAM-MERCER-HENDERSON-
WARREN-HANCOCK-MCDONOUGH-SCOTLAND-CLARK-
514 AM CDT WED MAY 12 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
ILLINOIS...NORTHWEST ILLINOIS...WEST CENTRAL ILLINOIS...EAST
CENTRAL IOWA...NORTHEAST IOWA...SOUTHEAST IOWA AND NORTHEAST
MISSOURI.

.DAY ONE...TODAY AND TONIGHT

SEVERAL PERIODS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED
THROUGH TONIGHT AS A WARM FRONT LIFTS INTO THE OUTLOOK
AREA. THE MAIN THREAT WILL BE HEAVY RAINFALL OF 1 TO 2
INCHES... WITH LOCALLY HIGHER AMOUNTS POSSIBLE. A FLASH
FLOOD WATCH IS IN EFFECT FOR TONIGHT FOR AREAS ROUGHLY
ALONG AND SOUTH OF INTERSTATE 80 WHERE SOILS ARE SATURATED
FROM RECENT HEAVY RAINFALL. ANY ADDITIONAL HEAVY RAINFALL
IN THESE AREAS WILL LIKELY GO MOSTLY INTO RUNOFF AND RESULT
IN SIGNIFICANT RISES ON AREA TRIBUTARY RIVERS... STREAMS
AND CREEKS. IN ADDITION TO HEAVY RAIN...THERE IS THE
POTENTIAL FOR HAIL WITH THE STRONGER STORMS OVER THE ENTIRE
OUTLOOK AREA... MAINLY THIS AFTERNOON AND EVENING. THE
STORM PREDICTION CENTER DOES HAVE THE AREA MAINLY SOUTH OF
HIGHWAY 34 IN A SLIGHT RISK OF SEVERE STORMS THIS AFTERNOON
AND EVENING... AND THIS IS MAINLY FOR THE POTENTIAL OF
A STORM TO PRODUCE DAMAGING WINDS OR AN ISOLATED TORNADO
ALONG THE WARM FRONT. CURRENT INFORMATION SUGGESTS
HOWEVER... THAT THIS THREAT LIKELY RESIDES SOUTH OF THE
OUTLOOK AREA.

AREA RIVERS ARE EXPERIENCING FLOODING. PLEASE SEE THE LATEST
FLOOD STATEMENTS AND FLOOD WARNINGS FOR DETAILS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS NOT ANTICIPATED TODAY OR TONIGHT.
HOWEVER... SPOTTERS ARE ENCOURAGED TO REPORT FLASH
FLOODING AND RAINFALL AMOUNTS IN EXCESS OF 1 INCH TO THE
NATIONAL WEATHER SERVICE IN THE QUAD CITIES.

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