000
FXUS63 KDVN 110930
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
330 AM CST WED FEB 11 2009

.SYNOPSIS...
POTENT SHORTWAVE TROUGH WAS LOCATED OVER TX PANHANDLE EARLY THIS
MORNING. MSAS ANALYSIS PLACES LEAD SFC CYCLONE SW OF STL IN
RRQ OF 105+ KT H3 JET ARCING FROM MIDWEST INTO NEW ENGLAND.
COUPLED JET STRUCTURE EXISTS WITH SECONDARY 100+ KT JET UNDERCUTTING
POTENT TROUGH IN SOUTHERN PLAINS. SATELLITE AND RADARS SHOW
COLDEST CLOUD TOPS AND BRUNT OF CONVECTION APPEARS TIED TO COUPLING
OF JETS AND SFC CYCLONE ACROSS LOWER MISSISSIPPI VALLEY... ALSO
IN REGION OF STRONG UPPER DIFFLUENCE AND MOISTURE ADVECTION... WITH
ACTIVE SEVERE WX ONGOING WITH SQUALL LINE EXTENDING SOUTH TO
LA GULF COAST AHEAD OF VIGOROUS SFC DRYLINE. RADAR SHOWS RAIN SHIELD
ADVANCING N/NE MAINLY SOUTHEAST OF FFL-MLI-SQI LINE AT 0830Z.
COUPLE OF LIGHTNING STRIKES EARLIER IN WARREN COUNTY...AND PERHAPS
A FEW MORE FAIRLY ISOLD ACROSS EAST WHERE SOME TINY 50+ DBZ CORES
EXIST. LIGHT WIND AND MOISTURE POOLING IN EAST RESULTING IN SOME
DENSE FOG ACROSS PORTIONS OF BUREAU AND PUTNAM COUNTIES. ..MCCLURE..

&&

.SHORT TERM...TODAY AND TONIGHT...
MAIN CHALLENGES INCLUDE POPS WITH EXPECTED SHARP CUTOFF TO PCPN...
WINDS WITH POTENTIAL FOR ADVISORY CRITERIA... AND POTENTIAL
FOR -SN.

NEGATIVE TILT POTENT SHORTWAVE TROUGH OVER TX PANHANDLE AND ATTENDANT
SFC CYCLONE WILL DEEPEN TODAY WHILE LIFTING RAPIDLY NORTHEAST TO
THE OHIO VALLEY BY THIS EVE. LOOKS AS THOUGH BRUNT OF HEAVIEST PCPN
WITH WARM ADVECTION TO PASS SOUTH/EAST. STILL...SLUG OF MODERATE RAIN
WITH ISOLD EMBEDDED THUNDER TO CONTINUE LIFTING N/NE INTO MID
MORNING. DRIER AIR TO NORTHWEST RESULTING IN SHARP
DELINEATION/CUTOFF TO PCPN SHIELD... WHICH PER LATEST RADAR TRENDS
APPEARS WILL LAY OUT NEAR AWG-MLI LINE THIS MORNING. BUT THEN EXPECT
STRONG DEFORMATION ZONE TO DEVELOP ON NORTHWEST FLANK OF
INTENSIFYING/DEEPENING SYSTEM BY THIS AFTN... WHICH COULD SPREAD
PCPN FARTHER NW... BUT STAYING MAINLY SE OF CID-DBQ AXIS DUE TO
DRIER AIR. DEFORMATION THEN QUICKLY PULLS AWAY BY LATE PM FROM SW TO
NE. ALL OF THIS TRANSLATES TO HEAVIEST PCPN AND HIGHEST POPS SE
1/3-1/2 TODAY...WITH RAPID DROP OFF HEADING NW OF THE QUAD CITIES.
NORTHWEST FRINGE OF PCPN SHIELD COULD SEE MIX OR EVEN CHANGE TO -SN
FOR BRIEF PERIOD WITH EVAPORATIONAL COOLING. WINDS NEXT ITEM... AS
EXPECT WINDY CONDITIONS DEVELOPING TODAY AS MSLP GRADIENT TIGHTENS
IN RESPONSE TO DEEPENING SFC CYCLONE. CANT RULE OUT SOME AREAS
ESPECIALLY ACROSS THE SOUTH AND EAST CLOSE TO ADVISORY CRITERIA.
OVERALL TEMPS STEADY TO SLOWLY FALLING TODAY AS WINDS BECOME
NORTHERLY AND STRENGTHEN. TONIGHT...AREA ENTRENCHED IN CYCLONIC FLOW
WITH LOW CLOUDS RETREATING TO NORTH HALF OR SO. FCST SOUNDINGS
SUPPORT SOME POTENTIAL FOR -DZ/-FZDZ WITH DRY MID/UPPER LEVELS...
BUT NO REAL SUPPORT IT APPEARS FOR WEAK LIFT/OMEGAS WITH MODELS
GENERALLY SHOWING DVM... THEREFORE WILL NOT MENTION. LOWS NEAR
GUIDANCE BLEND.        ..MCCLURE..

.LONG TERM...THURSDAY THROUGH NEXT TUESDAY...
PRIMARY CHALLENGE IS POTENTIAL FOR HEAVY SNOW LATE FRIDAY AND FRIDAY
NIGHT. LATEST WV LOOP SHOWS AN UPPER LOW SPINNING OVER THE
PACIFIC OFF THE COAST OF OREGON. THIS IS PROGGED TO BE THE NEXT IN A
SERIES OF SYSTEMS EJECTING EAST OUT OF THE BROAD WESTERN UPPER
TROUGH. 00Z MODELS IN GOOD AGREEMENT FOR A SYSTEM THIS FAR OUT...
WITH ESPECIALLY THE TIMING OF BOTH THE SURFACE LOW AND SHARP UPPER
TROUGH TRACKING ALONG THE H8 BAROCLINIC AXIS THAT WILL LAY OUT
ACROSS KS...MO AND IL IN THE WAKE OF THE CURRENT SYSTEM. HAVE KEPT
THE FORECAST CLOSEST TO A BLEND OF ECMWF...GFS AND NAM...FAVORING
THE SLOWER TIMING OF THE GFS...TRACKING THE SURFACE LOW FROM SW
KS/OK PANHANDLE FRI MORNING NORTHEAST TO E CENTRAL IL SAT MORNING.
THE STRONG UPPER VORT TRACKS ALONG OR ROUGHLY 100 MILES SOUTH OF THE
IA/MO BORDER...DEPENDING ON MODEL...LATE FRI AND FRI NIGHT WITH
STRONG FORCING IMPACTING AT LEAST THE SOUTHERN 2/3RDS OF THE
FORECAST AREA.

CONFIDENCE INCREASING FOR MODERATE AND POSSIBLY HEAVY SNOWFALL
AMOUNTS AND HAVE RAISED FRI NIGHT POPS TO LIKELY. MOISTURE SHOULD BE
MORE THAN ADEQUATE AS RETURN FLOW OFF THE GULF IS SHOWN DEVELOPING
WITH SEASONABLY HIGH PW VALUES ADVECTING INTO THE AREA FRI AND FRI
NIGHT. MODELS DEPICT STRONG AND DEEP LIFT IN DEF ZONE OF THE UPPER
SHORTWAVE...WITH HIGH OMEGA VALUES IN THE FAVORED DENDRITIC GROWTH
FOR HEAVY SNOWFALL RATES OVER THE AREA FRI NIGHT. GARCIA METHOD
SUPPORTS A LARGE SWATH OF MINIMAL 4 TO 6 INCH AMOUNTS IN THE PRIMARY
PERIOD OF LIFT FRI NIGHT. HAVE PLACED THESE AMOUNTS IN THE FORECAST
FOR NOW...NOTING THAT THESE COULD BE TOO CONSERVATIVE. A WINTER
STORM WATCH MAY BE NEEDED AS THIS PERIOD GETS CLOSER IN TIME. FOR
NOW...WILL MENTION THIS HEAVY SNOW POTENTIAL IN THE HAZARDOUS
WEATHER OUTLOOK.

KEPT IDEA OF SNOW OVERSPREADING THE AREA FROM WEST TO EAST FRI...
AND AS MENTIONED IN PREVIOUS DISCUSSION...THE ONSET OF ISENTROPIC
LIFT WILL HAVE TO OVERCOME INITIALLY DRY LOW LEVELS. THIS...COMBINED
WITH TEMPERATURES RECOVERING BACK ABOVE FREEZING BEFORE ONSET...WILL
LIMIT POTENTIAL THE FOR ACCUMULATING SNOW DURING THE DAY FRI. HAVE
THUS KEPT DAYTIME ACCUMULATIONS LIGHT AND MAINLY WEST OF THE MS
RIVER. LOW LEVEL THERMAL FIELDS AND SOUNDINGS SUGGEST RAIN/SNOW MIX
POSSIBLE AT ONSET IN THE FAR SOUTH.

EARLIER ON...THU AND THU NIGHT WILL BE A QUIET PERIOD WITH A WEAK
SURFACE RIDGE OVER THE AREA. WITH SUNSHINE AND LACK OF SNOW
COVER...KEPT IDEA OF TEMPERATURES RECOVERING INTO THE 40S THU. LIGHT
WINDS AND RADIATIONAL COOLING WILL PUSH MINS BACK INTO THE 20S FRI
MORNING.

OVER THE WEEKEND...KEPT LOW CHANCE POPS FOR LIGHT SNOW LINGERING IN
ESPECIALLY THE EAST SAT MORNING...OTHERWISE...ANOTHER SURFACE RIDGE
SLIDES ACROSS THE AREA. MADE ONLY MINOR ADJUSTMENTS TO MAXES AND
MINS IN 30S AND 20S RESPECTIVELY...NOTING THAT THESE COULD BE TOO
OPTIMISTIC IF HEAVY SNOW EVENT MATERIALIZES.
..SHEETS..

&&

.AVIATION...
RAIN WITH ISOLD THUNDER WILL LIFT NORTH/NORTHEAST THIS MORNING AND
MAINLY IMPACT KBRL AND KMLI TERMINALS. CIGS VFR TO MVFR WITH
POTENTIAL FOR PERIOD OF IFR CIGS/VSBYS AT KBRL. DEFORMATION ZONE ON
NORTHWEST FLANK OF INTENSIFYING STORM SYSTEM TRACKING FROM MID
MISSISSIPPI TO OHIO VALLEY BY EVE WILL SWIPE TERMINALS WITH MORE
RAIN LATE AM THROUGH MID AFTN. BULK OF THIS PCPN ALSO APPEARS TO
IMPACT MAINLY KBRL AND KMLI TERMINALS. COLDER AIR FILTERING IN ON
THE BACKSIDE ALONG WITH EVAPORATIONAL COOLING COULD BRING MIX OR
EVEN BRIEF CHANGEOVER TO -SN BEFORE PCPN ENDS LATE PM. WINDS TO
BECOME NORTHERLY AND STRENGTHEN AT 15-25 KTS WITH GUSTS IN EXCESS OF
30 KTS AT KBRL AND POSSIBLY KMLI... DUE TO TIGHTENING MSLP GRADIENT.
WINDS SHIFT TO NORTHWEST TONIGHT WITH GUSTS LINGERING AT LEAST
THROUGH THE EVE AS SYSTEM PULLS AWAY. SOME MVFR CIGS LIKELY TO
LINGER AS WELL THIS EVE INTO OVERNIGHT WITH COLD ADVECTION... THOUGH
EXPECT TO RETREAT NORTHWARD WITH TIME.

&&

.HYDROLOGY...
LOOKS LIKE HEAVIEST PCPN WITH THIS STORM SYSTEM WILL BE FOUND S/E OF
THE HSA. STILL MODERATE TO LOCALLY HEAVY AMOUNTS OF 0.5 TO 1.25 INCH
BUT THIS FALLING OUTSIDE OF SWOLLEN ROCK...IOWA AND MAQUOKETA BASINS
AND MAINLY OVER FAR SOUTHEAST IA...NORTHEAST MO AND WEST CENTRAL IL.
THIS LIKELY TO BRING RISES TO FOX AND LA MOINE RIVERS... WHICH WILL
NEED WATCHING.
..MCCLURE..

&&

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

&&

$$

MCCLURE/SHEETS