Flood in Iowa, May 1, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
258 PM CDT THU APR 30 2009

.SYNOPSIS...
LATEST SFC ANALYSIS WAS INDICATING SFC INDUCED LOW BY THIS MORNING/S
MCV OVER SOUTHERN LK MI ATTM...BUT MAIN SYNOPTIC SCALE SFC LOW WAS
NOTED NEAR INTERNATIONAL FALLS MN UNDER MAIN NORTHERN STREAM S/W.
THE TRAILING SFC FRONT OFF THIS FEATURE WAS ALMOST BI-SECTING IA
FROM NORTHEAST-TO-SOUTHWEST AT THIS TIME...WITH AN UPPER 50 TO
LOWER 60 DPT FIELD POOLED TO THE LEE OF IT. OTHERWISE...MEAN LARGE
SCALE FLOW PATTERN ACRS THE SOUTH HALF OF THE CONUS REMAINED ZONAL.

&&

.SHORT TERM...TONIGHT AND FRIDAY...
WITH A SFC WAVE ON THE UPSTREAM FRONT NOTED NORTHEAST OF MCI AND SFC
PRESSURE FALLS INCREASING AHEAD OF THE FRONT OVER MUCH OF EASTERN
IA...THESE AND OTHER NOWCAST TOOLS SUGGEST IT PRUDENT TO KEEP AT
LEAST LOW TO MODERATE CHC POPS OVER THE CWA THIS EVENING FOR SCTRD
SHOWERS AND EVEN POSSIBLY A THUNDERSTORM TO DEVELOP IN SOME OF THE
INSTABILITY THAT HAS DEVELOPED LOCALLY DUE TO FEW CLOUD BREAKS
ALLOWING TEMPS TO WARM INTO THE UPPER 60S TO AROUND 70. THEN WITH A
RATHER BROAD/UN-SHARP FROPA PROCESS MAKING ITS WAY THROUGH THE
REGION...WILL TREND OUT MOST OF THE LOW CLOUDS AND HIGHER DPTS. SOME
CLEARING AND THE EXTENT OF CAA LOOKING UPSTREAM SUGGEST THE
NORTHWESTERN CWA MAY DIP CLOSE TO 40 DEGREES FOR OVERNIGHT LOWS...
WHILE THE FAR SOUTH AND SOUTHEASTERN CWA REMAIN UP AROUND 50. WILL
BANK ON POST-FRONTAL NORTHWESTERLY BOUNDARY LAYER FLOW TO INHIBIT
MUCH OF ANY FOG DEVELOPMENT OVERNIGHT.

ON FRIDAY...SHORT RANGE MODELS IN GOOD AGREEMENT OF SUGGESTING THE
MAIN STORM TRACK TO SET UP WELL SOUTH OF THE DVN FCST AREA ALONG A
VERY TIGHT LLVL THTA-E GRADIENT ACRS KS/CENTRAL MO/SW IL. BUT A
SECONDARY ELEVATED FRONTOGENETICAL FORCING BAND AND NICE ISENTROPIC
LIFT ZONE/LOOKING AT 300K SFCS/ SWEEPS ACRS AND JUST NORTH OF THE
IA/MO BORDER FRI AFTERNOON. IN FACT...EXTENT OF SATURATION AND
CONVERGENT MIXING RATIO FEED SUGGEST .1-.3 INCHES OF RAIN POSSIBLE
ACRS THE FAR SOUTHERN 2 TIERS OF COUNTIES OR 15 MILES NORTH OF THE
HWY 34 CORRIDOR BY FRI EVENING. SOUTHERN EDGE UPPER LIFT OFF SD/MN/WI
100+ KT UPPER JET MAX WILL ALSO ADD TO OVERALL POTENTIAL. FOR NOW
WILL KEEP MODERATE CHC POPS ACRS THE SOUTHERN THIRD...AND SLIGHT
CHCS UP TO I80 FOR MAINLY OVERRUNNING RAIN AS OPPOSED TO SHOWERS.
VERY MARGINAL MID LAYER INSTABILITY PLUME AND MU CAPES SUGGEST
ISOLATED THUNDER MAY BE STILL OVERDOING IT IN THE FAR SOUTH...BUT
WILL KEEP MENTION ONE MORE PACKAGE. EXPECT WIDESPREAD MID TO UPPER
50S WITH CLOUDS REESTABLISHING...SOME EVAPO COOLING AND FRESHLY
ARRIVED CAA. THE SOUTHERN CWA MAY NOT GET OUT OF THE MID 50S IN VCNTY
OF MORE EVAPO COOLING AND RAIN.     ..12..

.LONG TERM...FRIDAY NIGHT THROUGH NEXT THURSDAY...
FRIDAY NIGHT THROUGH SUNDAY NIGHT...GENERALLY QUITE WEATHER IS
EXPECTED THROUGH THE WEEKEND WITH REGION TO REMAIN UNDER BROAD MID
LEVEL CYCLONIC FLOW ASSOCIATED WITH EASTERN CANADIAN UPPER LOW AND
WEAK RIDGE AT THE SURFACE. DRY WEATHER SHOULD DOMINATE MOST OF THE
CWFA THROUGH THE WEEKEND.  HOWEVER...SOME LOW POPS WERE PLACED OVER
THE FAR SOUTHERN CWFA WITH SOME INDICATION THAT THE NORTHERN EXTENT
OF SHRA/TSRA DEVELOPING ALONG STALLED FRONT OVER MO MAY SET UP AS
FAR NORTH AS HIGHWAY 34.  TEMPS THROUGH THE PERIOD ARE EXPECTED TO
BE CLOSE TO NORMAL FOR EARLY MAY. HOWEVER KEPT COOLEST TEMPS IN THE
SOUTH WITH CLOUD COVER ASSOCIATED WITH STALLED FRONT IN MO AND ALSO
WITH THE PCPN THREAT.

MONDAY THROUGH THURSDAY...
THE GFS/ECMWF ARE STILL SHOWING THE TRANSITION TO A MORE WESTERLY
MID LEVEL FLOW REGIME THROUGH NEXT WEEK. HOWEVER THE MODELS ARE
HAVING DIFFICULTY WITH THE INDIVIDUAL PIECES OF ENERGY MOVING
THROUGH THE WESTERLY FLOW.  THE GFS PUTS MORE EMPHASIS ON THE LEAD
S/W THAT/S PROGGED TO MOVE THROUGH THE LOWER/MID MS VALLEY SUNDAY
NIGHT OR MONDAY WHILE THE 30/00Z ECMWF DAMPENS THIS FEATURE OUT AS
IT MOVES INTO THE CENTRAL U.S. AND PUTS MORE EMPHASIS ON THE
TRAILING S/W THAT PROGGED TO REACH WITH MID MS VALLEY TUESDAY NIGHT
OR WEDNESDAY.  IT APPEARS THE 30/00Z RUN OF THE ECMWF WAS TRENDING
FASTER WITH BOTH S/WS AND WAS AN OUTLIER COMPARED TO ITS PREVIOUS
RUNS.  HAVE STAYED CLOSER TO THE HPC/GFS GUIDANCE SINCE THE GFS HAS
HAD BETTER RUN TO RUN CONTINUITY OVER THE PAST SEVERAL MODEL RUNS.

AS A RESULT HAVE ADDED LOW POPS TO MOST PERIODS WITH SYSTEMS PROGGED
TO MOVED THROUGH REGION MONDAY AND AGAIN TUESDAY NIGHT AND
WEDNESDAY.  DUE TO THE HIGH DEGREE OF UNCERTAINTY DURING THIS PERIOD
HAVE KEPT POPS IN THE SLIGHT CHANCE OR LOW CHANCE CATEGORY.  LATER
FORECASTS WILL HAVE TO REFINE THE TIMING AND LOCATION OF THE GREATER
PCPN THREAT.  TEMPS THROUGH THE PERIOD ARE EXPECTED TO BE NEAR
NORMAL.  ..DLF..

&&

.AVIATION...
WITH INCREASING POST-FRONTAL NW FLOW IN THE BOUNDARY LAYER...EXPECT
MAINLY A VFR NIGHT TONIGHT BUT WITH A FEW LINGERING BOUTS OF MVFR
CIGS THROUGH 03Z. SOME SHOWERS AND POSSIBLY A THUNDERSTORM WILL BE
IN THE VCNTY OF THE BRL TERMINAL AND POSSIBLY MLI THROUGH 03Z
BEFORE THE FRONT FINALLY PUSHES THROUGH. MID DECK TO REESTABLISH FRI
MORNING AHEAD OF NEXT UPPER AIR DISTURBANCE WITH HIGH BASED LIGHT
RAIN POSSIBLE JUST WEST OF BRL BY LATE FRI MORNING.   ..12..

&&

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

&&

12/DLF

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
449 AM CDT THU APR 30 2009

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-011000-
BENTON IA-BUCHANAN IA-BUREAU IL-CARROLL IL-CEDAR IA-CLARK MO-
CLINTON IA-DELAWARE IA-DES MOINES IA-DUBUQUE IA-HANCOCK IL-
HENDERSON IL-HENRY IA-HENRY IL-IOWA IA-JACKSON IA-JEFFERSON IA-
JO DAVIESS IL-JOHNSON IA-JONES IA-KEOKUK IA-LEE IA-LINN IA-LOUISA IA-
MCDONOUGH IL-MERCER IL-MUSCATINE IA-PUTNAM IL-ROCK ISLAND IL-
SCOTLAND MO-SCOTT IA-STEPHENSON IL-VAN BUREN IA-WARREN IL-
WASHINGTON IA-WHITESIDE IL-
449 AM CDT THU APR 30 2009

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

A FLASH FLOOD WATCH CONTINUES THIS MORNING FOR PORTIONS OF SOUTHEAST
IOWA...NORTHEAST MISSOURI...AND WEST CENTRAL ILLINOIS...AS WELL AS
PUTNAM COUNTY ILLINOIS.  A LARGE AREA OF MODERATE RAIN...WITH SOME
EMBEDDED HEAVY RAIN...WILL MOVE EAST OUT OF THE AREA THIS MORNING.
ADDITIONAL RAINFALL AFTER 7 AM IS EXPECTED TO BE LESS THAN A HALF
INCH.  THE WIDESPREAD OVERNIGHT RAINS OF 1 TO 2 INCHES THAT OCCURRED
ALONG AND SOUTH OF HIGHWAY 30...ARE EXPECTED TO CAUSE ALREADY HIGH
RIVER LEVELS TO RISE FURTHER AND MAY WORSEN ANY FLOODING THAT IS
OCCURRING.

SEVERAL AREA RIVERS ARE EXPERIENCING MINOR TO MODERATE FLOODING. SEE
THE LATEST FLOOD STATEMENTS FOR UPDATES.

A FEW NON SEVERE THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON.
ISOLATED HEAVY RAINS COULD OCCUR WITH THESE STORMS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THERE IS A CHANCE OF THUNDERSTORMS ALONG AND SOUTH OF HIGHWAY 34
FRIDAY AFTERNOON AND EARLY EVENING. THESE STORMS ARE NOT EXPECTED TO
BE SEVERE.

ALTHOUGH NOT AS CLEAR...THERE MAY BE A CHANCE OF THUNDERSTORMS
SUNDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY OR TONIGHT.

ERVIN/08