River Flood Warning 135, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
340 PM CDT THU OCT 29 2009

.SYNOPSIS...
VIGOROUS FALL STORM SYSTEM WILL CONTINUE TO IMPACT THE REGION
TONIGHT AND FRIDAY. THE UPPER LOW WAS MOVING OUT OF THE 4 CORNERS
REGION AT MIDDAY. OUT AHEAD OF THE DEEP TROUGH...GULF MOISTURE AND
WIDESPREAD SHOWERS AND THUNDERSTORMS EXTENDED FROM EASTERN TX NORTH
INTO IA AND IL. AT THE SURFACE...THE MAIN AREA OF LOW PRESSURE
WAS CENTERED JUST EAST OF WICHITA WITH MSAS INDICATING A LARGE
AREA OF 3 TO 4 MB PRESSURE FALLS OUT AHEAD FROM EASTERN IA SOUTH
INTO AR. A SERIES OF SHORTWAVES LIFTING N-NE AHEAD OF THE UPPER
TROUGH CONTINUES TO PRODUCE WIDESPREAD SHOWERS IN THE 50 TO 60KT
MOISTURE RICH RETURN FLOW WITH MODERATE TO SEASONALLY HEAVY
RAINFALL RATES OVER MUCH OF THE REGION.

&&

.SHORT TERM...TONIGHT AND FRIDAY...
CHALLENGING FORECAST CONTINUES WITH PRIMARY FOCUS NOW ON RAINFALL
AMOUNTS AND FLOODING POTENTIAL THIS EVENING. ONCE THE DEEPER
MOISTURE ADVECTED INTO THE AREA FOLLOWING THE FIRST ROUND OF RAIN
THIS MORNING...IT WAS NOTED THAT RAINFALL EFFICIENCY HAD
INCREASED...AS RADAR ESTIMATES WENT FROM WAY OVERESTIMATING
RAINFALL AMOUNTS TO NEARLY UNDERESTIMATING...BASED ON GROUND
TRUTH EARLY THIS AFTERNOON. RADAR STP HAS INDICATED THE HEAVIEST
RAIN SO FAR HAS FALLEN IN A SWATH FROM SCOTLAND COUNTY MO N-NE
THROUGH JEFFERSON AND WASHINGTON COUNTIES IN SE IA. 1 TO 2 INCH AMOUNTS
HAVE BEEN REPORTED IN THIS AREA AND A FEW CREEKS AND STREAMS WERE
REPORTED RUNNING AT AND ABOVE BANKFUL.

MORE MODERATE TO HEAVY SHOWERS AND THUNDERSTORMS ARE DEVELOPING IN N
CENTRAL MO HEADING TOWARD THESE ALREADY SATURATED AREAS. THESE HAVE
BEEN INCREASING IN INTENSITY OVER THE PAST HOUR. PARAMETERS
SUPPORTING ADDITIONAL MODERATE TO HEAVY RAIN...INCLUDING HIGH PW AIR
AND ADDITIONAL MID LEVEL SHORTWAVES...SHIFTS EAST TO TARGET THE
EASTERN HALF OF THE CWA THIS EVENING. THE 12Z ECMWF HAS EXTENDED A
LARGE 1 TO 2 INCH QPF AREA FURTHER NW FROM PREVIOUS RUNS INTO MUCH
OF THE CWA EAST OF THE MS RIVER AND ESPECIALLY SOUTH OF I-80 FOR
THE 12 HOURS ENDING 12Z...WHICH IS LOOKING REASONABLE. CONSIDERING
THIS...AND THE ALREADY SATURATED GROUND IN SE IA...HAVE GONE WITH
A FLASH FLOOD WATCH FOR ROUGHLY THE SOUTHERN HALF OF THE FORECAST
AREA FOR OVERNIGHT.

THREAT FOR HEAVY RAIN WILL ENDS FOLLOWING THE PASSAGE OF THE COLD
FRONT EARLY FRI MORNING. HAVE FOLLOWED A MODEL BLEND FRONTAL TIMING.
THE UPPER TROUGH REMAINS OUT WEST THROUGH THE DAY AND WILL KEEP
CHANCES FOR MAINLY DRIZZLE OR VERY LIGHT RAIN IN THE LINGERING
CYCLONIC CURVATURE FRI. DEEP MIXING IN THE DRY SLOT EARLY IN THE
DAY WILL MIX DOWN WARMER TEMPERATURES EARLY IN THE DAY FOLLOWED BY
STEADY TO FALLING TEMPERATURES IN THE AFTERNOON. THUS HAVE EARLY
HIGHS IN THE MID 50S WEST TO LOWER 60S FAR EAST BEFORE COLD
ADVECTION INCREASES ALOFT BEHIND THE STRONG LOW LIFTING N INTO
CANADA. RESULTING PRESSURE GRADIENT WILL KEEP WINDS BRISK FROM THE
SW TO W THROUGH THE DAY.
..SHEETS..

.LONG TERM...FRIDAY NIGHT THROUGH NEXT THURSDAY...
POOR RUN-RUN CONTINUITY PLAGUING NOT ONLY NA MODELS BUT TYPICALLY MORE
STABLE ECMWF AS WELL... AS SHIFT TO SEMI-ZONAL/WEST NORTHWEST FLOW
GIVING MODELS FITS WITH RESPECT TO FEATURES/TIMING... THUS CONFIDENCE
IS AVERAGE TO BELOW ON FCST DETAILS NEXT 7 DAYS. PRIOR THOUGH TO THE
PATTERN CHG MODELS HAVE ESPECIALLY DIFFICULT TIME RESOLVING STRENGTH
AND TRACK OF RESIDUAL ENERGY HANGING BACK IN THE SOUTHWEST. WED 12Z
GFS HAD CLOSED LOW ALONG THE KS/MO BORDER AND WAS FURTHEST NW WITH
TRACK AND SWIPED SE 1/2 WITH PCPN LATE SAT/SAT NGT. SUBSEQUENT RUNS
HAVE GONE BACK AND FORTH BETWEEN OPEN WAVE AND CLOSED SYSTEM... WITH
PAST COUPLE OF RUNS BACK TO A CLOSED LOW BUT NOW TRACKING MUCH
FURTHER SOUTH ACROSS THE TN VALLEY. ECMWF BACK AND FORTH AS WELL...
AND NOW OPENS SYSTEM UP WITH GENERAL LONGWAVE TROUGH SWEEPING THROUGH
MID MISSISSIPPI VALLEY SAT AM. APPEARS AS DEGREE OF PHASING AND
INTERACTION WITH NORTHWEST CANADA ENERGY GIVING MODELS FITS HERE...
AND TRENDS APPEAR TO BE WEAKER THUS SIDING TOWARD LITTLE/NO IMPACTS
FROM RESIDUAL ENERGY SW. BUT...WITH MID/UPPER LEVEL TROUGH STILL TO
PASS FRI NGT CANT RULE OUT SOME DRIZZLE WITH FAVORABLE FCST SOUNDINGS
AND TSECTS SHOWING WEAK/NIL LIFT AND DRY MID LEVELS AND TRAPPED LLVL
MOISTURE BENEATH INVERSION. SMALL POPS MAY NEED TO BE INCLUDED ESPECIALLY
NORTH FRI NGT INTO EARLY SAT AM WHERE SOME MODELS PROG CURRENT WAVE
OF MANITOBA TO PROPAGATE SE IN BEHIND DEPARTING SYSTEM HEADED FOR JAMES
BAY. GIVEN POOR MODEL RUN-RUN CONTINUITY HAVE OPTED TO LEAVE OUT ATTIM.
BEYOND THIS...WITH SEMI-ZONAL TO WEST/NORTHWEST FLOW DOMINATING EXPECT
THE REST OF THE PERIOD TO FEATURE NEAR NORMAL TEMPS WITH A LOT OF
DRY TIME. THIS DOES NOT MEAN PCPN CHCS WILL BE NIL. IN FACT POTENTIAL
FOR COUPLE SYSTEMS ONE LATE SUN-EARLY MON WHICH MAY BRING SOME -RA WITH
WARM ADVECTION/ISENTROPIC LIFT AHEAD OF NEXT FRONT... WITH ANOTHER CHC
POTENTIALLY AROUND MIDWEEK AS PATTERN WOULD SUGGEST ABOUT EVERY COUPLE
DAYS OR SO. WITH GULF OF MEXICO MOISTURE COMPLETELY CUT OFF ANY PCPN
SHOULD BE LIGHT.  ..MCCLURE..

&&

.AVIATION...
SHOWERS WITH MODERATE RAINFALL AND IFR CONDITIONS WILL CONTINUE TO
STREAM NORTHWARD THROUGH THE TERMINALS UNTIL WELL AFTER MIDNIGHT
TONIGHT AS A STRONG FALL STORM SYSTEM INTENSIFIES AND MOVES THROUGH
THE CENTRAL PLAINS. THERE WILL BE EMBEDDED THUNDERSTORMS...BUT THE
PROBABILITY OF IMPACTING ANY SITE IS TOO LOW FOR INCLUSION IN
FORECASTS BEYOND USING CB IN THE CLOUD GROUP. THERE WILL BE A FEW
GAPS IN THE LOW CLOUDS AND PERIODS OF MVFR AND EVEN VFR CIGS THIS
AFTERNOON BEFORE CONDITIONS RETURN TO PREVAILING IFR AFTER SUNSET.
HEAVIER SHOWERS OVERNIGHT WILL LOWER CIGS TO LIFR. SOUTHEAST WINDS
FROM 15 TO 25KTS WILL VEER TO THE SOUTHWEST FRIDAY MORNING WITH THE
PASSAGE OF A COLD FRONT. CURRENT THINKING IS THAT CONDITIONS WILL
THEN IMPROVE TO MVFR AND POSSIBLY VFR LATER FRIDAY MORNING.
..SHEETS..

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...FLASH FLOOD WATCH THROUGH FRIDAY MORNING FOR DES MOINES-HENRY IA-
     JEFFERSON-KEOKUK-LEE-LOUISA-MUSCATINE-SCOTT-VAN BUREN-
     WASHINGTON.

IL...FLASH FLOOD WATCH THROUGH FRIDAY MORNING FOR BUREAU-HANCOCK-
     HENDERSON-HENRY IL-MCDONOUGH-MERCER-PUTNAM-ROCK ISLAND-
     WARREN.

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

&&

SHEETS/MCCLURE