FXUS63 KDMX 242137
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
337 PM CST THU DEC 24 2009

.SHORT TERM.../TONIGHT/
MAIN PLAYER JUST ROUNDING THE BEND OVER THE SOUTHERN PLAINS.  STILL 
SOME WRINKLES AND CREASES FOR THE FCST TNT...BUT MORE CONSENSUS ON 
THE SPECIFICS.  INVERTED TROUGH TO REMAIN OVER THE STATE TNT AND 
ACTUALLY BACK TO THE WEST A BIT OVERNIGHT AS THE SOUTHWEST AREAS 
COOL OFF BOTH ALOFT AND AT THE SFC WHILE THE EASTERN AREAS REWARM 
AGAIN TOWARD SUNRISE. THUS THE WINTER STORM WATCH FOR THE EASTERN 
SECTIONS WILL BE UPGRADED TO A WINTER WEATHER ADV BEGINNING AT 12Z 
FRIDAY. WITH THE TROUGH EXTENDING ACROSS THE STATE TNT...THE BULK OF 
THE HEAVIER SNOW WILL BE WEST AND CENTRAL FOR THE NEXT 12 HOURS. THE 
GFS APPEARS TO BE MODEL OF CHOICE AFTER LOOKING AT SFC AND UPPER 
LEVEL FEATURES AND PREFERRED AREAS OF FORCING. H850 BAROCLINIC ZONE 
PICKED UP WELL OVER THE WEST AT NOON AND AREAL COVERAGE INCREASED 
RAPIDLY THERE AND CONTINUES.  SFC LOW TRACKS COMING INTO LINE FOR 
12Z FRIDAY WITH SFC LOW OVER SOUTHEAST IA NEAR KEOKUK. NAM/GFS SEEM 
TO BE BETTER CHOICES FOR NOW. EURO/GEM A BIT WARMER...BUT APPEARS 
THAT CONVECTION ACROSS THE SOUTH MAY HELP TO KEEP THE LOW SLIGHTLY 
MORE EAST. BOTTOM LINE IS THAT THE MODELS ARE WARMER OVER THE EAST 
AND HAVE CUT SNOW AMTS DOWN THERE FOR TNT...AND LEANED HEAVILY 
TOWARD LIQUID QPF FOR THAT AREA AS WELL. SOME OF THE WINTER STORM 
WARNING BORDER COUNTIES...BLACK HAWK...TAMA MAY NOT SEE SIGNIFICANT 
IMPACTS TNT...AND LESSENED IMPACTS OF SNOWFALL FRIDAY/SAT. 
THUS...WILL PASS ALONG TO THE EVENING SHIFT THE POTENTIAL FOR SOME 
MODIFICATIONS TO WARNING OUTLINE THERE.  THE TREMENDOUS CHALLENGE IS 
THE CHANGEOVER FROM RAIN TO SNOW LINE. IT LOOKS TO BE NEAR 
MARSHALLTOWN TO NEWTON TO NEAR CHARITON. JUST WEST OF THAT 
BOUNDARY...SNOWFALL TONIGHT MAY QUICKLY PILE UP TO 5 TO 7 INCHES 
THROUGH 12Z FRIDAY. HIGHER AMOUNTS WILL OCCUR WEST AS PREVIOUSLY 
EXPECTED. SOME INSTABILITY IS NOTED IN THE SOUNDINGS EAST...AND THIS 
COULD ENHANCE THE TOTALS IN THE ZONE OF CHANGEOVER. SIGNIFICANT 
FORCING AND WINDS WILL OCCUR ON THE BACK SIDE OF THE LOW OVERNIGHT 
WITH GUSTS TO 35 TO 40 MPH ALONG OUR WESTERN COUNTIES.  THE STRONGER 
WINDS OF 45 MPH ARE EXPECTED ALONG THE MO RIVER VALLEY. BORDERLINE 
TO BLIZZARD CONDITIONS WILL BE POSSIBLE OVER THE FAR WEST PORTION OF 
THE FORECAST AREA LATE TNT AND EARLY FRIDAY MORNING. WILL BE 
REEVALUATING THE CONDITIONS THIS EVENING BEFORE MAKING ANY 
ADJUSTMENTS THERE. OVERALL STORM TOTALS WILL STILL BE RATHER HIGH 
ACROSS CENTRAL SECTIONS AND WEST...WITH SOME DOWNWARD REFINEMENT 
ACROSS THE EAST. DYNAMICS... MOISTURE TRANSPORT...WIND AND DURATION 
OF THE EVENT THROUGH SATURDAY WILL CERTAINLY LEAVE A LASTING 
IMPRESSION. 

.LONG TERM.../SAT THROUGH THU/
COMPLEX SITUATION WITH UPPER LO PRES SYS DOING A FUJIWARA OVER THE
CENTRAL U.S. ON SAT. MODELS HAVING A DIFFICULT TIME HANDLING THE
FINE POINTS...WHICH WILL MAKE FOR A DIFFICULT FCST ALONG THE I-35
CORRIDOR. WARM AIR STREAMING OVER THE TOP OF THE LOW ON SAT WILL
KEEP A MIXTURE OF PCPN OVR THE EAST THROUGH A GOOD PART OF THE
DAY...THUS KEEPING ACCUMS DOWN IN THOSE AREAS. LOW WILL BOTTOM OUT
TNGT AND DO A TOUR AROUND IA FRI INTO SAT AS WHOLE SYSTEM FILLS.
EXPECT TO SEE AN EXTENDED PERIOD OF SNOW LASTING INTO
SUN...HOWEVER THE BULK OF THE ACCUM SNOW WILL TAKE PLACE TONIGHT
THROUGH FRI MRNG. WITH COMBO OF LOW FILLING AND SLOW MOVEMENT OF
STACKED SYS...DO NOT EXPECT TO SEE WINDS AS STRONG AS WOULD
OTHEWISE BE EXPECTED WITH THIS SYS. STRONGEST WINDS WILL TAKE
PLACE TNGT INTO FRI MRNG. WEATHER TURNS MUCH QUIETER AFTER SUN
WITH HI PRES BLDG INTO THE AREA. TEMPS WILL FALL BELOW NORMAL OVER
THE WKND INTO NEXT WEEK...BUT NOT SIGIFICANTLY SO. ANOTHER WEAK
SYS WILL MOVE THROUGH THE AREA ON WED...BUT SNOWFALL FROM THIS
WILL BE OF LITTLE CONSEQUENCE. 

&&

.AVIATION...
24/18Z...NO MAJOR CHANGES GO PREVIOUS FORECAST. LOW CIGS TO 
CONTINUE...IFR TO VLIFR CONDITIONS WILL BE WIDESPREAD DURING THE 
PERIOD. A MIX OF PRECIPITATION IS ANTICIPATED THROUGH EARLY 
AFTERNOON WEST WITH A TRANSITION TO SNOW LATE THIS AFTERNOON AND 
EVENING. THE EASTERN TAF SITES...KALO AND KOTM WILL TAKE INTO THE 
MID TO LATE EVENING TO FULLY TRANSITION TO ALL SNOW.  THE MOST 
INTENSE PRECIPITATION WILL OCCUR OVERNIGHT TONIGHT AND CONTINUE INTO 
EARLY FRIDAY. EXPECT WINDS TO BECOME MORE NORTHERLY DURING THE 
PERIOD AND INCREASE OVER THE NORTHWEST...CREATING HAZARDOUS 
CONDITIONS. 

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR ADAIR-ADAMS-
AUDUBON-BLACK HAWK-BOONE-BREMER-BUTLER-CALHOUN-CARROLL-CASS-
CERRO GORDO-CLARKE-CRAWFORD-DALLAS-DECATUR-EMMET-FRANKLIN-GREENE-
GRUNDY-GUTHRIE-HAMILTON-HANCOCK-HARDIN-HUMBOLDT-JASPER-KOSSUTH-
MADISON-MARSHALL-PALO ALTO-POCAHONTAS-POLK-RINGGOLD-SAC-STORY-
TAMA-TAYLOR-UNION-WARREN-WEBSTER-WINNEBAGO-WORTH-WRIGHT.

WINTER WEATHER ADVISORY FROM 6 AM FRIDAY TO 6 AM CST SATURDAY 
FOR APPANOOSE-DAVIS-LUCAS-MAHASKA-MARION-MONROE-POWESHIEK-
WAPELLO-WAYNE.

&&

$$

SHORT TERM/AVIATION...REV
LONG TERM...MS DEC 09