Flash Flood Watch 2, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
330 PM CDT SAT APR 24 2010

.SYNOPSIS...
LOW PRESSURE CONTINUES TO EVOLVE OVER SRN MO EARLY THIS AFTERNOON AS
POTENT S/W MOVES NE AHEAD OF SRN PLAINS UPPER LOW.  EASTERLY LOW
LEVEL FLOW IS IN PLACE OVER THE CWFA THIS AFTERNOON KEEPING LOW
CLOUDS AND AREAS OF BR/HZ IN PLACE THROUGH EARLY AFTERNOON.
DIFFLUENT UPPER FLOW AHEAD OF THE SRN PLAINS UPPER LOW HAS
SUPPORTED SOME ISOLD-SCT -SHRA/-TSRA OVER THE AREA SO FAR TODAY WITH
MORE WIDE SPREAD SHRA/TSRA LIFTING N THROUGH CENTRAL/NRN MO.

&&

.SHORT TERM...TONIGHT AND SUNDAY...
MODELS ARE CONSISTENT WITH DEEPENING SE MO SFC LOW LIFTING N INTO NE
MO/WCNTRL IL BY EARLY THIS EVENING THEN TURNING EAST AND MVNG INTO
ECNTRL IL/WCNTRL IN BY MIDDAY SUNDAY. THIS TRAJECTORY WILL BRING
EXPANDING AREA OF SHRA/TSRA THROUGH THE CWFA LATE THIS AFTERNOON AND
TONIGHT WITH LINGERING -RA OVER MUCH OF THE AREA IN STRONG CYCLONIC
FLOW SUNDAY.

THE SEVERE THREAT IS EXPECTED TO BE LOW AS THE STRONGEST FORCING
SPREADS N THROUGH CWFA LATE THIS AFTERNOON AND THIS EVENING.
BELIEVE ATMOSPHERE WILL SATURATE QUICKLY LIMITING THE CHANCE FOR ANY
SIGNIFICANT HAIL.  THE BIGGEST CONCERN MAY BE DAMAGING WINDS EARLY
THIS EVENING AS LOW LEVEL EASTERLY FLOW STRENGTHENS AHEAD OF THE
DEEPENING SURFACE LOW.  ANY STRONG TSRA WILL HAVE THE POTENTIAL TO
MIX DOWN STRONGER WINDS JUST OFF THE SURFACE.  THE WIND THREAT
THOUGH WOULD BE LIMITED TO THE FAR SRN CWFA.

HEAVY RAIN POTENTIAL/FLOODING IS ALSO A CONCERN ESPECIALLY IN WEST
CENTRAL IL ALONG AND SOUTH OF HIGHWAY 34 SO WILL ISSUE A FLASH FLOOD
WATCH FOR THIS EVENING.  RECENT RAINS IN THIS AREA HAVE MOISTENED
THE GROUND AND FFG VALUES ARE IN THE 1 TO 2 INCH RANGE.  HEAVIEST
QPF TO OCCUR THIS EVENING OVER THE FAR SRN CWFA AND SHOULD APPROACH
THE FFG.

ALSO EXPECT WINDY CONDITIONS TONIGHT INTO SUNDAY JUST NORTH AND WEST
OF THE SURFACE LOW. POTENTIAL EXISTS TO REACH ADVISORY CRITERIA IN
THE SOUTH. SINCE THE STRONGEST GRADIENT WILL BE OVER THE AREA AT
NIGHT WILL TAKE WINDS UP TO JUST UNDER ADVISORY CRITERIA AND
MONITOR.

SUNDAY EXPECTED TO BE A BLUSTERY/RAINY DAY OVER THE AREA AS THE
SURFACE LOW PULLS AWAY FROM THE REGION.  TEMPS ARE NOT EXPECTED TO
RECOVER MUCH AND ONLY ALLOW FOR ABOUT A 5 DEGREE RISE.  ..DLF...

.LONG TERM...SUNDAY NIGHT THROUGH NEXT SATURDAY...
FIRST HALF OF THE WEEK...THE AREA WILL BE IN A WEAK NW FLOW ALOFT
WITH EMBEDDED SHORTWAVES TO KEEP SEASONABLY COOL AND UNSETTLED
WEATHER IN PLACE. LATE WEEK INTO THE WEEKEND...DEVELOPING UPPER LOW
OVER THE NORTHERN ROCKIES/HIGH PLAINS INDUCES RETURN FLOW WITH
WARMING TEMPERATURES AND RETURNING RAIN CHANCES.

SUNDAY NIGHT THROUGH WED...WRAP AROUND MOISTURE AND LINGERING
PRESSURE GRADIENT BEHIND DEPARTING STRONG CYCLONE OVER OHIO WILL
KEEP SCATTERED SHOWERS AND BRISK WINDS THROUGH SUNDAY EVENING...THEN
HAVE TRENDED DOWN RAIN CHANCES FROM NW TO SE AFTER MIDNIGHT AS THE
FILLING SURFACE LOW CONTINUES EAST. MID LEVEL SHORTWAVE CURRENTLY
MOVING INTO THE PACIFIC NW IS DEPICTED PASSING OVER OR SW OF THE
FORECAST AREA MONDAY AFTERNOON AND EVENING. WITH LOW TO MID LEVEL
MOISTURE LACKING...HAVE KEPT POPS ONLY IN SLIGHT CHANCE RANGE
THROUGH MON NIGHT AND EARLY TUE. SURFACE AND UPPER LEVEL RIDGE THEN
MIGRATES EAST THROUGH THE AREA TUE AFTERNOON INTO WED...PROVIDING DRY
WEATHER AND ALLOWING MINS WED MORNING TO DROP INTO THE UPPER 30S
ACROSS THE NORTH. FOR NOW HAVE A RANGE FROM AROUND 37 NORTH TO LOWER
40S SOUTH...BUT WILL NEED TO WATCH THIS SETUP IN LATER FORECASTS...
FOR POSSIBILITY OF COLDER MINS AND FROST ACROSS ESPECIALLY THE
NORTH. OTHERWISE...KEPT TEMPERATURES CLOSE TO SEASONAL NORMS MON
THROUGH WED.

WED NIGHT THROUGH FRI...LOW LEVEL JET AND MOISTURE RETURN FLOW
DEVELOPS WED NIGHT AND HAVE SLIGHT CHANCES FOR POSSIBLE ELEVATED
THUNDERSTORMS ON NOSE OF THE JET ACROSS THE NORTH. THUNDERSTORM
CHANCES THEN INCREASE THU INTO FRI AS GULF MOISTURE THETA E RIDGE
AXIS SETS UP OVER THE REGION. HOWEVER...OVERALL CONFIDENCE IN THE
TIMING AND PLACEMENT OF SYNOPTIC FEATURES AND PERIODS OF BETTER
FORCING IS LOW DUE TO POOR AGREEMENT AMONG THE ECMWF...GFS AND UKMET
HANDLING OF THE UPPER SHORTWAVES. WILL THUS CONTINUE BROAD-BRUSH
APPROACH...WITH HIGHEST POPS CENTERED ON THU NIGHT AND FRI.
TEMPERATURES RETURN TO ABOVE NORMAL WITH HIGHS IN THE 70S AND LOWS
IN THE 50S.

..SHEETS..

&&

.AVIATION...
VFR TO ISOLD IFR CONDITIONS WILL EVOLVE TO WIDESPREAD IFR THIS
EVENING AS LARGE AREA OF SHRA AND ISOLD-SCT TSRA SPREAD N OVER THE
AREA.  THE MAIN TSRA THREAT WILL BE AT KMLI/KBRL THROUGH THE EVENING
THEN PCPN SHOULD BE MAINLY RA/SHRA.  STRONG EAST WIND WILL DEVELOP
OVER THE AREA BY EARLY EVENING AND THEN TURN TO THE N-NNW
OVERNIGHT.  GUSTS IN EXCESS OF 30 MPH ARE EXPECTED AT KMLI/KBRL.
..DLF..

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...FLASH FLOOD WATCH THROUGH SUNDAY MORNING FOR LEE-VAN BUREN.

IL...FLASH FLOOD WATCH THROUGH SUNDAY MORNING FOR HANCOCK-MCDONOUGH.

MO...FLASH FLOOD WATCH THROUGH SUNDAY MORNING FOR CLARK-SCOTLAND.

&&

DLF/SHEETS

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