Severe Thunderstorm Warning 233, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
323 PM CDT SAT JUL 19 2008

.SYNOPSIS...
COMPLICATED WEATHER SCENARIO ACROSS THE FORECAST AREA THIS
AFTERNOON.  THE MCS THAT MOVED THROUGH THE AREA OVERNIGHT HAD VERY
SCATTERED CONVECTION...SO WE HAD LOCATIONS WITH UP AROUND 2 INCHES
OF RAIN...BUT OTHER LOCATIONS THAT ONLY RECEIVED LESS THAN A TENTH
OF AN INCH.  A STRIPE FROM APPROXIMATELY CEDAR RAPIDS TO FREEPORT
GOT THE MOST RAIN...AND HAD A FEW LOCATIONS WITH 1 TO 2 INCHES OF
RAINFALL OR MORE.  THE MCV THAT WAS ASSOCIATED WITH THIS CONVECTION
HAS MOVED WELL OFF TO THE EAST...AND FOR NOW THE AREA IS DRY.  AN
MCS MOVED ACROSS SOUTH DAKOTA OVERNIGHT AND HAS BEEN DECAYING OVER
SOUTHERN MINNESOTA THIS MORNING.  IT APPEARS TO HAVE LAID OUT SOME
SORT OF OUTFLOW BOUNDARY/WARM FRONT FROM CENTRAL MINNESOTA SOUTHEAST
ACROSS THE ARX AREA AND INTO NORTHERN ILLINOIS. A COLD FRONT IS
DRAPED FROM WESTERN NEBRASKA NORTHEAST ACROSS TO SOUTHERN MINNESOTA
AND EAST INTO WISCONSIN AND MICHIGAN.  NEW CONVECTION HAS FIRED
ALONG THIS BOUNDARY OVER SOUTHEASTERN SOUTH DAKOTA...WHERE THERE IS
GOOD PRESSURE FALLS...MOISTURE CONVERGENCE AND PLENTY OF INSTABILITY.
&&

.SHORT TERM...TONIGHT...
FROM THE CONFUSED TANGLE OF BOUNDARIES AND FRONTS THIS AFTERNOON THE
MAIN CONCERN HAS BECOME WHERE THE NEXT MCS WILL FIRE.  THE
CONVECTION OVER SOUTH DAKOTA HAS BECOME SURFACE BASED AS IT HAS NOW
MOVED AWAY FROM THE INITIATING BOUNDARY AND INTO THE AREA OF
PRESSURE FALLS AND MOISTURE CONVERGENCE JUST TO THE EAST.  FOR OUR
FORECAST AREA...WE APPEAR TO BE WEAKLY CAPPED AND THE CLOUDINESS
AROUND THIS AFTERNOON IS KEEPING CONVECTION FROM DEVELOPING.
TONIGHTS CONVECTION...WHICH I HAVE ALREADY MENTIONED ABOVE OVER
SOUTHEAST SD AND SW MN...WILL SLIDE EAST ACROSS THE MN/IA BORDER
LATE THIS AFTERNOON AND EVENING.  IT WILL PUSH A WING OF CONVECTION
SOUTHEAST ACROSS THE CWA LATE THIS EVENING...LIKELY STARTING AROUND
THE 03Z TIME FRAME...AND LASTING MUCH OF THE NIGHT.  THE MAIN RISK
WILL BE HEAVY RAIN ACROSS THE NORTH AS THE PRECIPITABLE WATER VALUES
WILL BE UP IN THE 1.5 TO 2.0 INCH RANGE.  CONVECTION DOES LOOK LIKE
IT SHOULD BE FAIRLY PROGRESSIVE...BUT THERE IS SOME RISK OF REPEAT
THUNDERSTORMS LATER IN THE EVENT.  FOR NOW HAVE DECIDED TO HOLD
OFF...AND WILL LET THE EVENING SHIFT DECIDE IF THE POSSIBLE TRAINING
WILL SET UP IN THE RIGHT AREA OR NOT.  WHILE WE ARE IN A SLIGHT RISK
OF SEVERE WEATHER...FEEL THAT THE RISK IS GOING TO BE SOMEWHAT
ISOLATED AS CONVECTION CURRENTLY MOVING ALONG THE MN/IA BORDER WILL
HAVE TO PUSH SOMETHING DOWN INTO THE CWA BEFORE ABOUT 9-10 PM FOR US
TO HAVE A SIGNIFICANT RISK OF SEVERE...WHICH QUICKLY DIMINISHES
AFTER THAT.    ...LE...

.LONG TERM...SUNDAY THROUGH SATURDAY...
AREA REMAINS IN ACTIVE PATTERN THROUGH AT LEAST MONDAY NIGHT AS THE
LOW LEVEL BOUNDARY REMAINING IN THE VICINITY...WITH HIGH PW AIRMASS
AND FAST ZONAL UPPER FLOW JUST TO THE NORTH KEEPING FAVORABLE
CONDITIONS FOR PERIODIC MCS ACTIVITY. THIS LOOKS TO CHANGE BY EARLY
NEXT WEEK AS MODELS IN AGREEMENT WITH UPPER LEVEL RIDGE BUILDING OUT
WEST WITH SURFACE HIGH OVER GREAT LAKES FEEDING DRIER LOW LEVEL
AIRMASS INTO THE CWFA. THIS WILL PROVIDE A BREAK FROM DAILY
THUNDERSTORM CHANCES AND THE SUMMER HEAT AND HUMIDITY TUE AND WED.
PATTERN AGAIN BECOMES ACTIVE THU THROUGH SAT AS UPPER RIDGE FLATTENS
AND DEEPER MOISTURE/HIGH PW AIRMASS RETURNS UPSTREAM INTO THE
NORTHERN PLAINS.

SUNDAY...CHALLENGE WILL BE HOW FAR SOUTH THE SYNOPTIC FRONT GETS
PUSHED BY OVERNIGHT CONVECTION TONIGHT...AND RESULTING AFFECT ON
LOCATION OF LATE DAY AND EVENING CONVECTION. BULK OF THE DAY LOOKS
TO BE BETWEEN PERIODS OF SYNOPTIC FORCING WITH H7 TEMPERATURES CLOSE
TO 10 DEG C CAPPING CONVECTION AND HAVE MAINTAINED ONLY SLIGHT
CHANCE POPS. DECENT WAA DEVELOPS AT H8 ACROSS THE SOUTH...WITH
VALUES APPROACHING 22 DEG BY AFTERNOON RESULTING IN HIGHS REACHING
LOWER 90S OVER AT LEAST THE SOUTH.

SUN NIGHT INTO MON...FORCING AHEAD OF STRONGER SHORTWAVE CURRENTLY
MOVING INTO ND ARRIVES SUN NIGHT WITH SUPPLY OF HIGH PW AIRMASS
ALREADY POOLING OVER THE CWA AT THE TIME SETTING THE STAGE FOR AN
MCS TO DEVELOP OVER OR NEAR THE CWA AND HAVE RIBBON OF HIGH CHANCE
POPS ACROSS THE CENTRAL CWA WHERE THE LOW LEVEL BOUNDARY WILL LIKELY
RESIDE. WITH GFS PW VALUES AGAIN PROGGED TO EXCEED 2 INCHES...WILL
CONTINUE THE THREAT OF HEAVY RAINFALL AND WILL HAVE TO MONITOR FOR
FLASH FLOOD WATCH NEED IN ESPECIALLY E CENTRAL IA THAT HAS ALREADY
BEEN HIT BY SEVERAL HEAVY RAINFALL EVENTS THE PAST COUPLE DAYS. WILL
KEEP CHANCE POPS OVER AREA THROUGH MON UNTIL SYNOPTIC SUBSIDENCE
ARRIVES MON NIGHT AND SURFACE FRONT SHIFTS SOUTH.

SURFACE HIGH OVER GREAT LAKES TO FEED DRIER AND SLIGHTLY COOLER
AIRMASS INTO AREA TUE AND WED...THEN HEAT AND HUMIDITY RETURNS THU
THROUGH SAT. BEST POTENTIAL FOR WIDESPREAD THUNDERSTORMS ARE
CENTERED ON THU AND THU NIGHT...WHEN MODELS...ESPECIALLY THE
ECMWF...DEPICT THE NEXT FROPA AND POTENT SURFACE LOW IMPACTING THE
REGION WITH HEAVY RAIN POTENTIAL. BROUGHT IN SAT AS DRY WITH TEMPS
NEAR CLIMO FOR NOW...BUT WITH ACTIVE PATTERN AND CURRENT POOR
AGREEMENT AMONG MODELS THAT FAR OUT...FORECAST CONFIDENCE IS BELOW
AVERAGE. ..SHEETS..

&&

.AVIATION...
SCT-BKN MVFR CIGS ACROSS THE TAF LOCATIONS THIS AFTERNOON AND EARLY
EVENING...IN A VERY HUMID AIRMASS.  THUNDERSTORMS EXPECTED TO MOVE
INTO TAF LOCATIONS LATE EVENING AND OVERNIGHT WITH MAINLY MVFR CIGS
AND VSBYS...WITH OCCASIONAL IFR CONDITIONS IN STRONGER CELLS.  MVFR
CONDITIONS TO LINGER INTO SUNDAY MORNING BEHIND CONVECTION. ...LE...

&&

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

&&

LE/SHEETS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
450 AM CDT SAT JUL 19 2008

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-201000-
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-
450 AM CDT SAT JUL 19 2008

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

AREAS OF SHOWERS AND A FEW THUNDERSTORMS WILL MOVE EAST...AND OUT
OF THE OUTLOOK AREA EARLY THIS MORNING. BY AFTERNOON...PARTLY
CLOUDY SKIES WILL ALLOW TEMPERATURES TO WARM INTO THE LOWER TO MID
80S...AND ALONG WITH HIGH HUMIDITY LEVELS...THIS WILL PROVIDE THE
FUEL FOR ADDITIONAL SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND
TONIGHT. THE STORM PREDICTION CENTER IS FORECASTING A SLIGHT RISK
FOR SEVERE THUNDERSTORMS NORTH OF HIGHWAY 34 IN IOWA AND ILLINOIS.
THE PRIMARY RISK WITH STORMS WILL BE HEAVY RAIN ONCE AGAIN...BUT
DAMAGING WINDS WILL ALSO BE POSSIBLE. TONIGHT...A LARGE COMPLEX OF
THUNDERSTORMS WILL MOVE EAST AND SOUTHEAST OVER
IOWA...ILLINOIS...AND WISCONSIN. THIS AREA OF STORMS MAY BRING
ADDITIONAL HEAVY RAIN...AND A RISK FOR FLASH FLOODING TO PORTIONS
OF THE OUTLOOK AREA.

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

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE STORM PREDICTION CENTER IS FORECASTING A SLIGHT RISK
FOR SEVERE THUNDERSTORMS ACROSS THE ENTIRE OUTLOOK AREA SUNDAY AND
SUNDAY NIGHT. HEAVY RAIN WILL BE LIKELY WITH THUNDERSTORMS SUNDAY
NIGHT.  OTHER THUNDERSTORMS WILL BE POSSIBLE THROUGH MUCH OF NEXT
WEEK...BUT IT IS TOO EARLY TO DETERMINE THE THREAT OF SEVERE
WEATHER.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE THIS AFTERNOON AND TONIGHT. HEAVY
RAINFALL REPORTS WOULD BE APPRECIATED.

ERVIN

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