Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 211741
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1141 AM CST FRI NOV 21 2014

.UPDATE...
ISSUED AT 1141 AM CST FRI NOV 21 2014

SOME MINOR CHANGES WITH ONGOING FORECAST...MAINLY WITH THE ONSET
OF THE FZDZ/FZRA THIS EVENING AS DELAYED TIMING 1-2 HOURS NORTH OF
I-80. OTHERWISE...SOUNDINGS STILL BECOMES SATURATED UP TO AROUND
700MB BY 00Z SATURDAY AND THE HIRES MODELS DEPICTING A DECENT
CLUSTER/BAND OF PRECIP TO SPREAD ACROSS CENTRAL TO SOUTHERN IOWA
BETWEEN 00-03Z AND FURTHER NORTHEAST FROM 02-05Z TONIGHT. LOWERED
SURFACE TEMPS SLIGHTLY THIS EVENING...MAINLY NORTH OF HWY 34 AS
RAP/SREF/HRRR SLOWER WITH THE WAA INTO THE FORECAST AREA. THIS
WILL PROLONG THE FZDZ/FZRA POTENTIAL NORTH I80/EAST I35 INTO THE
OVERNIGHT HOURS.

&&

.SHORT TERM /TODAY/...
ISSUED AT 420 AM CST FRI NOV 21 2014

HIGH PRESSURE OVER IL WILL MOVE OFF TO THE EAST WITH WARMING
BEGINNING TO TAKE PLACE ALOFT ALREADY. THE SHALLOW INVERSION WILL
BE SLOW TO BREAK EVEN THOUGH H8 TEMPS WILL RISE WELL DURING THE
DAY. MOISTURE IS WORKING NORTH AS SEEN IN THE FOG PRODUCT THIS
MORNING WORKING INTO SOUTH CENTRAL KANSAS THROUGH SOUTHERN MO.
EVEN SO...IT WILL TAKE UNTIL MIDDAY TO REACH IA. SOUNDINGS
INDICATE IT WILL BE SHALLOW AND DON`T EXPECT TO SEE MORE THAN
DRIZZLE FORM THIS AFTERNOON OVER THE FAR SOUTH. MAX TEMPS FOR THE
DAY WILL COME AT 00Z WITH CONTINUED WARMING AFTER.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 420 AM CST FRI NOV 21 2014

MAIN FOCUS FOR THE EXTENDED HAS BEEN ON FREEZING DRIZZLE/RAIN
POTENTIAL FOR TONIGHT AND EARLY SATURDAY MORNING. DESPITE BEING
CLOSE TO THE ONSET OF THE EVENT THERE IS STILL CONSIDERABLE
UNCERTAINTY ON SEVERAL FRONTS. THE FIRST PERTAINS TO PRECIP TIMING
AND DURATION WITH MODEL SOLUTIONS HAVING SHIFTED SLIGHTLY FURTHER
EAST WITH THE BEST MOISTURE TRANSPORT AND PRECIP PLACEMENT...WITH
THE BEST CHANCE FOR FREEZING RAIN IN THE EASTERN CWA. RECENT RUNS
OF THE GFS AND SREF ALSO BEEN TRENDING WARMER OVER THE LAST FEW
RUNS AND NOW HAVE MUCH OF SOUTHERN IOWA ABOVE FREEZING FOR MIN
TEMPS OVERNIGHT FRIDAY. THE NAM REMAINS THE STOUT COLD OUTLIER OF
THE AVAILABLE GUIDANCE.

THAT BEING SAID...OUR RECORD-SETTING COLD SNAP OVER THE LAST WEEK
AND A HALF HAS LED TO FROST DEPTHS OF 6+ INCHES IN MOST
LOCATIONS. WITH THE WARMER AIR ARRIVING IN CONJUGATION WITH THE
PRECIP...GROUND SURFACES WILL NOT HAVE TIME TO THAW AND SHOULD BE
COLD ENOUGH TO FREEZE PRECIPITATION EVEN WITH AIR TEMPERATURES IN
THE 32-34 DEGREE RANGE. THE POINT AT WHICH THE WAA AND MOISTURE
ADVECTION IS ENOUGH TO OVERCOME THESE COLD GROUND TEMPS IS ANOTHER
MILLION DOLLAR QUESTION. USED AN ARBITRARY CUTOFF OF A 33 DEGREE
DEWPOINT TEMPERATURE TO MARK THE TRANSITION ZONE BETWEEN THE FZRA
AND RAIN. HAVE ISSUED A FREEZING RAIN ADVISORY FOR THE EASTERN
HALF OF THE CWA IN COORDINATION WITH ARX AND DVN...DRIVEN HEAVILY
BY ANTECEDENT CONDITIONS. THIS ADVISORY COVERS THE AREA THAT IS
MOST LIKELY TO EXPERIENCE FREEZING RAIN IMPACTS...WITH FZRA STILL
POSSIBLE OUTSIDE THIS ADVISORY.

OTHERWISE DID NOT MAKE MANY CHANGES TO THE GOING FORECAST BEYOND
SUNDAY. MOISTURE PROFILES STILL SHOW LOW CLOUDS HANGING AROUND
THROUGH THE DAY ON SATURDAY. MOS GUIDANCE STILL HAS THE SOUTHERN
CWA SITES BREAKING 50 DEGREES ON SATURDAY AND SUNDAY...BUT HELD
HIGH TEMPERATURES DOWN A FEW DEGREES GIVEN THE EXPANSIVE CLOUDS
AND PRECIPITATION. DEEPENING SURFACE CYCLONE LIFTS NORTHEASTWARD
FROM TEXAS INTO THE WESTERN GREAT LAKES BY EARLY MONDAY. RECENT
GFS/EC RUNS HAVE TAKEN THE LOW ON A SLIGHTLY MORE EASTWARD
TRACK...WHICH WOULD PULL THE HEAVIEST PRECIP FURTHER TOWARDS THE
EASTERN CWA BORDER. LOWERED QPF AMOUNTS ON SUNDAY SLIGHTLY BASED
ON THESE TRENDS. COLDER AIR SPILLS IN BEHIND THE LOW ON SUNDAY
NIGHT AND CHANGES ANY REMAINING PRECIP TO SNOW. AFTERWARDS THERE
MAY BE SEVERAL MORE SHOTS OF SNOW THROUGH THE WEEK...FIRST AS AN
INVERTED TROUGH WRAPS AROUND THE BACKSIDE OF THE DEPARTING UPPER
LEVEL LOW ON MONDAY AND EARLY TUESDAY (ACCOMPANIED BY STRONG
WINDS)...AND AGAIN ON WEDNESDAY AS A CLIPPER SYSTEM DIVES THROUGH
THE REGION.

&&

.AVIATION...21/18Z
ISSUED AT 1141 AM CST FRI NOV 21 2014

EXPECTING CIGS TO DECREASE LATE THIS AFTERNOON INTO THE EVENING
HOURS DOWN TO AT LEAST MVFR AND POSSIBLE IFR AT TIMES. HIGHER
CONFIDENCE WITH MENTIONING IFR CIGS OVERNIGHT WITH SLUG OF
MOISTURE MOVING ACROSS THE EASTERN HALF OF THE STATE AND MODEL
SOUNDINGS SATURATED FROM THE SURFACE TO AROUND 5000 FEET. MANY
STATIONS ALREADY REPORTING IFR/LOWER MVFR CIGS UNDER THE STRATUS
SHIELD EXPECTED TO MOVE INTO THE STATE THIS EVENING. FZDZ/FZRA
LIKELY TONIGHT AND ONLY CHANGE WAS A SLIGHT DELAY WITH THE ONSET
AND THEN WARMER TEMPS MOVING IN OVERNIGHT SHOULD SWITCH IT OVER TO
DZ/RA BY THE 12Z TAF ISSUANCE. MVFR CIGS HANG AROUND THROUGH MUCH
OF SATURDAY MORNING.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FREEZING RAIN ADVISORY FROM 9 PM THIS EVENING TO 6 AM CST
SATURDAY FOR BLACK HAWK-BOONE-BREMER-BUTLER-CERRO GORDO-DALLAS-
FRANKLIN-GRUNDY-HAMILTON-HARDIN-JASPER-MADISON-MAHASKA-MARION-
MARSHALL-POLK-POWESHIEK-STORY-TAMA-WARREN-WORTH-WRIGHT.

FREEZING RAIN ADVISORY FROM 6 PM THIS EVENING TO 3 AM CST
SATURDAY FOR APPANOOSE-CLARKE-DAVIS-DECATUR-LUCAS-MONROE-WAPELLO-
WAYNE.

&&

$$

UPDATE...PODRAZIK
SHORT TERM...MS NOV 14
LONG TERM...SKOW
AVIATION...PODRAZIK



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