Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 252142
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
342 PM CST SUN JAN 25 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 340 PM CST SUN JAN 25 2015

ANOTHER SYSTEM WILL IMPACT IOWA AGAIN TONIGHT. AN UPPER LEVEL SHORT
WAVE OVER MANITOBA THIS AFTERNOON WILL RACE SOUTHEAST INTO MINNESOTA
OVERNIGHT. A COUPLE FORCING MECHANISMS TO CONTEND OVERNIGHT.
INCREASING THETA-E ADVECTION WILL DEVELOP SOUTH OF THE APPROACHING
SYSTEM AND MOVE EAST ACROSS THE STATE AFTER 06Z. AS THIS
OCCURS...MID LEVEL LAPSE RATES INCREASE AND MAY BE ENOUGH FOR A FEW
CONVECTIVE SNOW SHOWERS TO DEVELOP. MOISTURE AVAILABILITY WILL BE
THE PRIMARY LIMITING FACTOR AND SHOULD LIMIT AREAL COVERAGE. THE
KINEMATIC FORCING ASSOCIATED WITH THE SHORT WAVE WILL ARRIVE OVER
MAINLY NORTHEAST IOWA AFT 09Z AND WILL HAVE SOME OVERLAP WITH THE
THERMODYNAMIC FORCING. THIS WILL BE THE REGION WITH THE BEST
POTENTIAL FOR SOME LIGHT SNOW TO DEVELOP LATE. TEMPERATURES WILL
DROP INITIALLY THEN BEGIN TO RISE OVER WESTERN IA TOWARD DAYBREAK
WITH THE ARRIVAL OF WESTERLY DOWNSLOPE FLOW.

.LONG TERM /MONDAY THROUGH SUNDAY/...
ISSUED AT 340 PM CST SUN JAN 25 2015

TODAY THE MODELS ARE IN LESS AGREEMENT WITH THE LONG TERM THAN THEY
WERE YESTERDAY.  THE GFS HAS DONE THE BIGGEST TURN AROUND AND NOW
ONLY BRINGS A QUICK SHOT OF COLD AIR INTO THE STATE FRIDAY INTO
SATURDAY THEN WARMS THE STATE BACK UP.  THERE WILL CERTAINLY BE
SEVERAL MORE ITERATIONS TO THE FORECAST TO BE SURE.

ON MONDAY A LARGE UPPER RIDGE BUILDS OVER THE ROCKIES AND HIGH
PLAINS WITH A DEEP TROUGH OVER THE EAST COAST INTO THE GREAT LAKES.
A WEAK SHORTWAVE SLIDES DOWN THE FLOW ACROSS EASTERN MN AND IA
THROUGH WI AND INTO IL.  THE WAVE IS WEAK BUT THERE IS SOME FORCING
IN THE DENDRITIC LAYER.  HOWEVER MOISTURE IS SOMEWHAT IN QUESTION AS
THERE IS A DRY LAYER BETWEEN THE DENDRITIC ZONE AND THE SURFACE.  AT
ANY RATE IT WOULD BE A QUICK SHOT IN THE MORNING BEFORE THE BUILDING
RIDGE TO THE WEST PUSHES EVERYTHING INTO ILLINOIS.

THE UPPER RIDGE THEN BUILDS INTO THE UPPER MIDWEST THROUGH MIDWEEK
AND TEMPS WILL RESPOND NICELY WITH HIGHS BOUNCING BACK INTO THE 40S
AND 50S...POSSIBLY UPPER 50S SOUTHWEST.  AT THIS POINT I WILL BE
PLAYING HIGHS ON WEDNESDAY A LITTLE CONSERVATIVELY WITH A POTENT
SHORTWAVE APPROACHING THROUGH THE DAY.  AT THIS POINT MODELS ARE
PRETTY CONSISTENT WITH BRINGING THE WAVE INTO THE WEST BY 00Z
THURSDAY BUT MY CONFIDENCE IN THE MODELS...AT LEAST THE GFS...IN
GENERAL IS NOT GREAT DUE TO THE SHIFT IT HAS DONE IN THE LATER
PERIODS.

WEDNESDAY NIGHT INTO THURSDAY THERE WILL BE TWO SHORT WAVES BACK TO
BACK AFFECTING THE STATE.  MODELS VARY WITH THE INTENSITY OF THE
WEDNESDAY SHORTWAVE PUSHING ACROSS THE AREA.  THE GFS IS THE
STRONGEST WITH THE CANADIAN BEING WEAKEST AND THE EURO SOMEWHERE IN
THE MIDDLE BEING A WEAKER THAN THE GFS BUT A LITTLE FASTER THAN THE
CANADIAN. THE GFS IS SUGGESTING ADEQUATE FORCING WITH THE WAVE AND
ALL MODELS ARE LACKING MOISTURE WITH THIS SYSTEM.  AT THIS POINT I
WENT DRY WITH THE INITIAL WAVE ON WEDNESDAY.  THE SECOND WAVE COMES
IN OUT OF THE NORTHERN PLAINS ON THE HEELS OF THE FIRST WAVE.  THE
TIMEFRAME FOR THIS IS FROM ABOUT 09Z THURSDAY THROUGH ABOUT 18Z
THURSDAY.  MODELS ARE ONCE AGAIN ALL OVER THE PLACE WITH INTENSITY
AND TIMING.  HERE THE EURO IS MORE INTENSE WITH THE WAVE WHILE THE
GFS IS A LITTLE WEATHER AND FASTER.  THE CANADIAN IS THE WEAKEST OF
THE THREE.  THE EURO ALSO HAS A MUCH BROADER AREA OF QPF WITH THIS
SYSTEM AND WITH COLDER AIR COMING IN THE ONLY CERTAINTY...SNOW WILL
BE POSSIBLE.  HOWEVER GIVEN THE MODEL DIFFERENCES I FELT THAT SLIGHT
CHANCE/ LOW END CHANCE POPS ESPECIALLY NE/ECEN WERE ALL THAT WAS
WARRANTIED.

THE NEXT WAVE APPROACHES FOR FRIDAY NIGHT/SATURDAY AND MODEL
DIFFERENCES CONTINUE THIS TIME WITH THE GFS BEING STRONGER AND
FASTER.  IF YOU BELIEVE THE GFS THE NORTH/NORTHEAST WILL GET CLIPPED
BY THIS SYSTEM WITH LITTLE PRECIP AFFECTING THE AREA.  THE EURO
KEEPS PRECIP IN MN AND WI.  MODEL DIFFERENCES REALLY KICK IN FOR THE
REST OF THE WEEKEND AND WHAT LOOKED TO BE A COLD WEEKEND NOW IS IN
QUESTION.  THE EURO IS STILL ADVERTISING AN EVEN STRONGER TROUGH
OVER THE UPPER MIDWEST AND GREAT LAKES AREA WITH AN EQUALLY INTENSE
RIDGE OVER THE WEST COAST WHILE THE GFS HAS COMPLETELY FLIPPED FROM
YESTERDAY AND NOW HAS WEAK TROUGHING FURTHER EAST WITH RIDGING
BUILDING BACK OVER THE ROCKIES.  WILE THIS WOULD MEAN COOLER TEMPS
THAN MID WEEK IT IS FAR FROM THE MID 20S ADVERTISED YESTERDAY. FOR
NOW I DID NOT GO CRAZY WITH TEMPS BUT DID WARM AT LEAST SOUTHERN
IOWA UP AT LEAST A CATEGORY AND IF THE GFS IS RIGHT...WE`LL BE MUCH
WARMER THAN THAT BUT IF THE EURO VERIFIES...WE`LL BE MUCH COLDER.
LOTS OF THINGS TO KEEP AN EYE ON OVER THE UPCOMING WEEK.&&

.AVIATION...25/18Z
ISSUED AT 1155 AM CST SUN JAN 25 2015

IFR CIGS AND VSBYS TIED TO THE DEPARTING SNOW SYSTEM WILL COME TO
AN END OVER THE SOUTHEAST BY EARLY AFTERNOON. CIGS ACROSS THE REST
OF CENTRAL IOWA WILL GENERALLY BE LOW TO MID MVFR WITH SOME
POCKETS OF IFR AND VFR CIGS. THERE IS MEDIUM CONFIDENCE IN THIS
STRATUS DECK LINGERING ON INTO THE OVERNIGHT...BUT WITH SOME
POCKETS OF CLEARING UPSTREAM SOME SITES MAY RISE TO VFR CONDITIONS
AT TIMES DURING THE TAF PERIOD. GUSTY NORTH TO NORTHEAST WINDS
WILL LESSEN THIS AFTERNOON AND SWITCH TO THE SOUTH AROUND
MIDNIGHT.

&&

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

$$

SHORT TERM...DONAVON
LONG TERM...FAB
AVIATION...SKOW


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