Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 231752
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1152 AM CST SUN NOV 23 2014

.UPDATE...
ISSUED AT 1041 AM CST SUN NOV 23 2014

MADE SOME MINOR CHANGES TO FORECAST THIS AFTERNOON...WITH
INCREASED POP FOR CENTRAL AS BANDING LIGHT RAIN HAS DEVELOPED.
PATCHY DENSE FOG AGAIN HAS DEVELOPED OVER FAR SOUTH CENTRAL AND
PATCHY FOG WILL CONTINUE UNTIL TROUGH/DEVELOPING COLD FRONT
PUSHES EAST THIS AFTERNOON AND EARLY EVENING. STILL COMPLICATED
FORECAST NEXT 24 HOURS WITH SEVERAL SHORTWAVES ROTATING THROUGH
FLOW. STILL APPEARS THAT THE COLD AIR MAY LAG THE FORCING LONG
ENOUGH TO FOCUS ANY HEAVIER SNOW OVER THE MIDWEST/GREAT LAKES
JUST EAST OF OUR AREA...BUT WILL NEED TO WATCH THE TIMING OF
PTYPE CHANGEOVER TONIGHT ACROSS THE EAST HALF OF OUR AREA.
MONITORING FOR ANY CHANGES AND CURRENTLY EVALUATING VARIOUS
SOLNS. /REV

&&

.SHORT TERM /TODAY/...
ISSUED AT 317 AM CST SUN NOV 23 2014

LOW PRESSURE IS BEGINNING TO TAKE SHAPE OVER SOUTHWEST KS INTO THE
OK PANHANDLE. COMPLICATING THE SITUATION IS THE FACT THAT THERE
ARE TWO SEPARATE SYSTEMS. AT THE SAME TIME THE NORTHERN SYSTEM IS
APPROACHING THE ND BORDER THIS MORNING. THE SOUTHERN SYSTEM WILL
DOMINATE THROUGH MOST OF THE DAY WITH RAIN SPREADING NORTH AND
WEST WITH THAT SYSTEM. THE TRICKY PART WILL BE AS THE TWO SYSTEMS
MERGE. THE BULK OF THAT WILL TAKE PLACE TONIGHT WITH THE SOUTHERN
SYSTEM BEING MORE DOMINANT DURING THE DAY...THE COLD AIR WILL BE
SLOWER TO MOVE IN. ONCE THE WIND SHIFTS...TEMPS WILL FALL AND DID
GO NON-DIURNAL WITH THE TEMP TRENDS TODAY. IT WILL BE VERY LATE
IN THE FORECAST PERIOD BEFORE IT WILL BE COLD ENOUGH FOR ANY
MIXING OF PRECIPITATION. WILL GO WITH A MIXTURE OVER THE FAR WEST
LATE IN THE PERIOD. THE SOUNDINGS INDICATE THE CHANGE OVER WILL BE
CLEAN AND NOT HAVE A FREEZING RAIN PERIOD IN THERE AND OPTED TO GO
THAT ROUTE.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 317 AM CST SUN NOV 23 2014

BY TONIGHT THE COLD FRONT DISCUSSED IN THE SHORT TERM SECTION WILL
BE MOVING EAST OF OUR AREA...HOWEVER IT WILL BE UNDERCUTTING
FAIRLY MOIST SOUTHWEST FLOW ALOFT FOR MUCH OF THE NIGHT. AS A
RESULT RAIN WILL CONTINUE...ESPECIALLY ACROSS THE SOUTHEAST
HALF...PROBABLY CHANGING BRIEFLY TO LIGHT SNOW BEFORE ENDING FROM
WEST TO EAST AFTER MIDNIGHT. FORECAST SOUNDINGS INDICATE THAT AS
COLD AIR ADVECTION KICKS IN BEHIND THE SURFACE FRONT LATE THE
TRANSITION SHOULD BE STRAIGHT RAIN TO SNOW...WITH MOST QPF COMING
IN THE FORM OF RAIN AND ONLY LIGHT SNOW ACCUMULATIONS POSSIBLE BY
MONDAY MORNING.

NORTHWEST WINDS WILL INCREASE BEHIND THE FRONT ON SUNDAY
NIGHT...THEN STRENGTHEN FURTHER ON MONDAY AS THE DEPARTING SURFACE
LOW DEEPENS TO OUR NORTHEAST AND THE PRESSURE GRADIENT TIGHTENS
ACROSS IOWA. MEANWHILE THE SUNDAY NIGHT PRECIP WILL DEPART TO THE
EAST...HOWEVER A SECOND LOBE OF VORTICITY ALOFT WILL GENERATE
CLOUDS AND FLURRIES/LIGHT SNOW SHOWERS ESPECIALLY MONDAY
AFTERNOON. WHILE THERMAL PROFILES APPEAR FAVORABLE FOR SOME
DENDRITIC SNOW GROWTH...THE FORCING WITHIN THE SNOW LAYER IS
FAIRLY WEAK AND ONLY VERY LIGHT ACCUMULATION IS ANTICIPATED.
HOWEVER...GIVEN THE STRONG WINDS IF THERE ARE ANY MORE MODERATE
SNOW SHOWERS THEN BLOWING SNOW COULD CAUSE BRIEF AND SPOTTY
ISSUES. AT THIS POINT THIS APPEARS UNLIKELY GIVEN THE EXPECTED
LIGHTER NATURE OF THE SNOW BUT IT DOES BEAR MONITORING.

FROM MONDAY NIGHT INTO TUESDAY NIGHT A WEAK SURFACE RIDGE WILL
SLIDE ACROSS THE REGION...BRINGING A REPRIEVE FROM POPS AS WELL AS
SLOWLY MODERATING TEMPERATURES. PROGNOSTIC MODELS ARE NOW
UNANIMOUS IN BARRELING A COMPACT BUT ROBUST CLIPPER SYSTEM
SOUTHEASTWARD ACROSS THE UPPER MIDWEST ON TUESDAY NIGHT AND
WEDNESDAY...WITH CONSENSUS TAKING THE TRACK OF THE SYSTEM JUST
NORTHEAST OF OUR AREA. THIS WILL LIKELY RESULT IN SOME LIGHT
SNOWFALL...ESPECIALLY ACROSS OUR NORTH/NORTHEAST...FOLLOWED BY
MORE NORTHWEST WINDS ON WEDNESDAY. RIGHT NOW THE SNOW POTENTIAL
APPEARS LIMITED IN OUR FORECAST AREA...HOWEVER IF THE TRACK OF THE
LOW SHIFTS SOUTHWARD THIS MAY NEED TO BE REVISED SO WE WILL
CONTINUE TO MONITOR THIS SYSTEM.

FROM WEDNESDAY NIGHT THROUGH THE REMAINDER OF THE WORK WEEK A
LARGE CANADIAN HIGH PRESSURE CENTER WILL EXERT ITS INFLUENCE
ACROSS THE REGION...RESULTING IN DRY BUT MUCH COOLER WEATHER
DURING THIS PERIOD. THE COLDEST TEMPERATURES WILL LIKELY COME
THURSDAY AND THURSDAY NIGHT WITH FORECAST HIGHS ONLY IN THE TEENS
AND 20S AND LOWS IN THE SINGLE DIGITS AND TEENS. THIS WILL MAKE
FOR COLD BUT GENERALLY BENIGN TRAVELING WEATHER FOR THE
THANKSGIVING HOLIDAY.

&&

.AVIATION...23/18Z
ISSUED AT 1152 AM CST SUN NOV 23 2014

MANY CHALLENGES INCLUDING RAIN TO SNOW CHANGEOVER LATER
TONIGHT...VSBY/CIGS AND WINDS. MULTI WAVE SYSTEM TRACKING OVER THE
CENTRAL CONUS NEXT 24 HOURS. LOW CIGS/VSBY CONTINUE THIS AFTERNOON
AHEAD OF TROUGH/COOL FRONT IN IOWA NOW. EXPECTING SOME IMPROVEMENT
IN VSBY THROUGH EVENING WEST/CENTRAL. AS COLDER AIR WRAPS INTO
SYSTEM TONIGHT...RAIN TO SNOW CHANGEOVER AFT 05-06Z WEST AND
CLOSER TO 08-10Z EAST. WINDS INCREASE WITH STEEPENING BUFR LAPSE
RATES AS COLDER AIR SPILLS IN. WILL SEE SUSTAINED 20 TO 26KTS
NORTHWEST WINDS GUSTS 28 TO 33KTS THROUGH END OF PERIOD. /REV

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...REV
SHORT TERM...MS NOV 14
LONG TERM...LEE
AVIATION...REV


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