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000
FXUS63 KDMX 081741
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1141 AM CST SUN DEC 8 2013

.SHORT TERM /TODAY/...
ISSUED AT 402 AM CST SUN DEC 8 2013

PRIMARY FOCUS OBVIOUSLY REMAINS SNOW TRENDS EARLY THIS MORNING.
LATEST GUIDANCE SUGGESTS LITTLE CHANGE TO PREVIOUS FORECAST WAS
NEEDED...2 TO 4 PLUS SE TO N...ALTHOUGH THERE ARE STILL SOME
CONCERNS.  PARENT SHORT WAVE IS STILL OVER UT/CO...BUT SEVERAL
WEAKER WAVES CONTINUE TO PRODUCE SNOW OUT AHEAD WITH MOST
SIGNIFICANT RESPONSE CURRENTLY CROSSING THE MO RIVER VALLEY.
FORCING WITH THIS AND SUBSEQUENT FEATURES IS QUITE DEEP...AND
MAINLY DRIVEN BY THERMODYNAMICS RATHER THAN KINEMATIC
EFFECTS...BUT IS STILL WEAK TO MODERATE. AIRMASS HAS STRUGGLED TO
SATURATE INTO IA FOR THE MOST PART WITH KDMX RADAR VIRGA DOUGHNUT
ONLY SLOWLY SHRINKING AND KDSM JUST NOW REPORTING FLURRIES. BEST
SATURATION HAS OCCURRED OVER NRN TWO TO THREE TIERS OF COUNTIES
WHICH HAVE RECEIVED HALF INCH PLUS BASED ON A FEW SPOTTER REPORTS
AND WEBCAMS.

MODELS ARE ALL FAIRLY SIMILAR HANDLING PROGRESSION OF SNOW TODAY
WITH NOTED DEEP DENDRITIC GROWTH ZONE...10KFT OR MORE AT TIMES.
OVERALL FORCING IS A BIT STRONGER THAN WHAT WAS SHOWN OVER THE PAST
FEW DAYS...BUT EVEN WITH SNOW RATIOS WELL INTO THE TEENS OR LOWER
20S QPF IS STILL NOT SUFFICIENT TO BUMP UP WIDESPREAD AMOUNTS THAT
MUCH.  HOWEVER WOULD NOT BE SURPRISED TO SEE SMALL HARD TO PREDICT
AREAS RECEIVE UP TO 6 INCHES AS IT WILL NOT TAKE MUCH ENHANCEMENT
IN THESE RATIOS TO INCREASE AMOUNTS. UPSTREAM REPORTS SUGGEST
THIS AS WELL. PAST TWO HI RES HOPWRF RUNS HAVE SUGGESTED AS
MUCH...BUT ONLY ON THE SCALE OF A FEW COUNTIES. THIS HAS SUGGESTED
JUST WEST OF DES MOINES METRO SO PLACED A LITTLE MINOR BULLSEYE
THERE FOR A START BUT DID NOT GO ALL IN WITH HIGHER AMOUNTS. NO
CHANGES TO HEADLINES...BUT CERTAINLY WILL NEED TO KEEP AN EYE ON
THESE TRENDS WITH MODEL CROSS SECTIONS SUGGESTING 16Z-22Z BEING
THE MOST INTENSE PERIODS OF SNOWFALL. ANOTHER CONCERN WOULD BE THE
GFS WHICH HOLDS ONTO STRONGER FORCING LONGER THAN OTHER
MODELS...CLOSELY ASSOCIATED WITH PARENT SHORT WAVE.

TEMPS SHOULD BE HIGHER THAN YESTERDAY WITH DEEP WEAK TO MODERATE
WARM ADVECTION IN PLACE...BUT MAINLY ALOFT.  ONCE AGAIN LEANED
TOWARD THE WARMER NAM AND NAM MOS WHICH SEEMS TO BE HANDLING
THINGS WELL.

.LONG TERM /TONIGHT THROUGH SATURDAY/...
ISSUED AT 402 AM CST SUN DEC 8 2013

LINGERING SNOW TONIGHT...CONTINUED COLD AS WELL AS INCREASING
CHANCES OF ACCUMULATING SNOW MID-WEEK WERE THE MAIN FORECAST
ISSUES DURING THE EXTENDED. LEANED TOWARD A BLEND OF THE
NAM/GFS/SREF TONIGHT INTO MONDAY...AND GFS THROUGH THE WORK WEEK.

TONIGHT THROUGH MONDAY...ISENTROPIC LIFT AND THE DEEP MOISTURE
QUICKLY PUSH EAST THIS EVENING AND SHOULD SEE SNOW END BY 06Z IN
THE NORTHEAST...IF NOT SOONER. MAY SEE UP TO AN ADDITION INCH FROM
THE MCW TO ALO AREA FROM 00-06Z MONDAY. OTHERWISE...A HALF INCH OR
LESS CAN BE EXPECTED ELSEWHERE AS THE SNOW QUICKLY ENDS. CAA
DEVELOPS ON MONDAY WHEN SURFACE HIGH PRESSURE BUILDS INTO THE
STATE FROM THE CENTRAL PLAINS. THIS WILL PROVIDE BELOW ZERO WIND
CHILLS OVER THE NORTHERN HALF OF THE FORECAST AREA MONDAY
AFTERNOON...AND THEN THROUGHOUT THE ENTIRE AREA BY MONDAY NIGHT.
WINDS SHIFT SOUTH MONDAY NIGHT WITH THE HIGH MOVING EAST...BUT
REMAIN STRONG ENOUGH FOR WIND CHILLS CLOSE TO 20 BELOW IN THE
NORTH BY TUESDAY MORNING.

TUESDAY INTO WEDNESDAY...A QUICK MOVING 500MB SHORTWAVE CUTS
ACROSS THE DAKOTAS INTO MINNESOTA TUESDAY NIGHT INTO WEDNESDAY.
THE GFS/ECMWF SHOW SOME WEAK THETA-E ADVECTION AND ISENTROPIC LIFT
COMING ACROSS THE STATE B/T 00-12Z WEDNESDAY. THE DENDRITIC LAYER
EXTENDS FROM THE SURFACE TO AROUND 750MB BUT WITH THE WEAK
FORCING...EXPECTING ONLY AROUND AN INCH OR LESS WITH THE HIGHER
AMOUNTS IN NORTHERN IOWA ATTM. THIS SHORTWAVE BRINGS A REINFORCED
SHOT OF COLD AIR AND TEMPERATURES LOOK TO BOTTOM OUT WEDNESDAY
NIGHT WITH SURFACE HIGH OVERHEAD.

THURSDAY THROUGH SATURDAY...QUIET WEATHER AND SLIGHTLY WARMER
TEMPERATURES LATE IN THE WEEK WITH ZONAL TO PARTIAL NORTHWEST
FLOW. ECMWF HINTING ON A WEAK SHORTWAVE TO MOVE ACROSS THE
MISSOURI VALLEY AND MAINLY AFFECT SOUTHERN IOWA ON SATURDAY. GFS
IS EVEN FURTHER SOUTH WITH THE TRACK SO FORECAST REMAINS DRY ATTM
WITH EXCEPTION TO THE FAR SOUTHEAST FRIDAY NIGHT.

&&

.AVIATION...08/18Z
ISSUED AT 1141 AM CST SUN DEC 8 2013

LIGHT TO MOD SNOW CONTINUES WITH IFR/MVFR CONDITIONS THROUGH
06-08Z PRIOR TO SOME IMPROVEMENT AS THE SYSTEM LIFTS OUT.
EXPECTING THAT ONCE THE LIFT DIMINISHES...SCT CONDITIONS WILL GIVE
WAY TO CLEARING BY 12Z MOST AREAS. WINDS ON THE BACK SIDE PICK UP
WITH GUSTS 22 TO 25KTS WITH HIGHER GUSTS NORTH THROUGH END OF
PERIOD.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR BLACK
HAWK-BOONE-BREMER-BUTLER-CLARKE-DALLAS-FRANKLIN-GRUNDY-HAMILTON-
HARDIN-JASPER-MADISON-MARION-MARSHALL-POLK-POWESHIEK-STORY-TAMA-
UNION-WARREN-WRIGHT.

WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR ADAIR-
ADAMS-AUDUBON-CALHOUN-CARROLL-CASS-CERRO GORDO-CRAWFORD-EMMET-
GREENE-GUTHRIE-HANCOCK-HUMBOLDT-KOSSUTH-PALO ALTO-POCAHONTAS-SAC-
TAYLOR-WEBSTER-WINNEBAGO-WORTH.

&&

$$

SHORT TERM...SMALL
LONG TERM...PODRAZIK
AVIATION...REV