Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 010532
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1132 PM CST SAT FEB 28 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 345 PM CST SAT FEB 28 2015

PRIMARY CONCERN WILL BE SHORT WAVE ON OUR IMMEDIATE DOORSTEP THIS
EVENING. ASSOCIATED FORCING IS FAIRLY DEEP...AS IS THE DEPTH OF
THE DENDRITIC GROWTH ZONE...BUT ONLY WEAK TO PATCHY MODERATE IN
MAGNITUDE. THIS DEGREE OF FORCING AND TRANSIENT NATURE OF THE LIFT
WILL ONLY RESULT IN LIGHT SNOW AMOUNTS...UP TO AN INCH OR LESS
ALONG THE IA/MO BORDER WITH ONLY FLURRIES OR JUST ABOVE TRACE
AMOUNTS NORTH TOWARD THE I80 CORRIDOR. HOURLY HI RES MODELS
SUGGEST SHOULD BE EXITING SRN I35 CORRIDOR BY 00-01Z AND MAINLY
OUT OF THE AREA ALTOGETHER BY 03Z. ECMWF AND GFS BOTH DEPICT
LINGERING STRATUS BUT GENERALLY SUBSIDENCE INTO THE NIGHT SO ONLY
HAVE TOKEN SLIGHT CHANCES SOUTH TO BLEND INTO BETTER POTENTIAL
INTO MO. WITH CLOUDS AND PERSISTENT LIGHT SLY FLOW DO NOT EXPECT
MINS ANYWHERE CLOSE TO LAST NIGHT...AND IN FACT ONLY FALL SLIGHTLY
FROM CURRENT VALUES.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 345 PM CST SAT FEB 28 2015

MAIN FORECAST CONCERN DEALT WITH THE POTENTIAL FOR A WINTRY MIX
MONDAY NIGHT INTO TUESDAY ACROSS CENTRAL AND SOUTHERN IOWA...AND
SNOW AND BLOWING SNOW OVER NORTHERN IOWA TUESDAY. MODELS ARE IN
DECENT AGREEMENT WITH THE LARGE SURFACE LOW PUSHING ACROSS THE
REGION MONDAY NIGHT INTO TUESDAY AND WITH THE LOCATION OF THE
DEFORMATION ZONE SETTING UP OVER WEST-CENTRAL TO NORTHERN IOWA
TUESDAY. THE GFS IS MORE BULLISH WITH QPF...ESPECIALLY WITH THE
FIRST ROUND OF PRECIP WRT TO THE WAA REGIME ON MONDAY NIGHT.
LEANED TOWARD A NAM/EC/SREF BLEND SUNDAY INTO TUESDAY...AND THEN
CLOSER TO THE ECMWF THROUGH THE REMAINDER OF THE WEEK.

SUNDAY INTO TUESDAY...STRONG AND BROAD AREA OF THETA-E ADVECTION AND
MOISTURE TRANSPORT INCREASE OVER WESTERN IOWA MONDAY AFTERNOON
AND CONTINUES INTO THE EVENING. GFS PEGS NORTHERN IOWA WITH A FAIR
AMOUNT OF SNOW PAST 00Z TUESDAY BUT NAM/ECMWF/SREF MUCH DRIER.
MODELS DO AGREE ON FORCING INCREASING OVERNIGHT MONDAY NIGHT
INTO TUESDAY OVER CENTRAL IOWA. LOWER POPS MONDAY NIGHT 00-06Z PER
THE DRIER ECMWF/NAM/SREF BUT KEPT THE LIKELY AND CATEGORICAL POPS
OVERNIGHT INTO TUESDAY.

THE THERMO PROFILES OVER SOUTHERN IOWA INDICATING MAINLY
RAIN/FREEZING RAIN POTENTIAL B/T 06-15Z TUESDAY BUT WITH THE
STRONG WAA AT 850MB AND AT THE SURFACE...LOW CONFIDENCE WITH MUCH
ICE ACCRUAL AND WRT TO THE DURATION OF ANY FREEZING RAIN IN THE
FAR SOUTH. HAVE A FEW HUNDREDTHS OF ICE MENTIONED OVER THE SOUTH
BUT WITH WAA AT THE SURFACE...EXPECT ANY TRAVEL ISSUES TO REMAIN
MINIMAL.

FURTHER NORTH...SLEET/SNOW/FZRA PROFILES FROM DENISON TO DES
MOINES TO MARSHALLTOWN AND EVEN SOUTHEAST TOWARDS OSKALOOSA
THROUGH 18Z TUESDAY. HERE...A LARGE WARM NOSE CREEPS INTO THE
SOUNDINGS AND LOOKS TO MELT ANY SNOW FALLING THROUGH THIS LAYER
AND DEPENDING ON HOW QUICKLY THE WAA DEVELOPS AT THE
SURFACE...SLEET AND FREEZING RAIN POTENTIAL LINGERS THROUGH MUCH
OF THE MORNING TUESDAY BEFORE THE CAA DEVELOPS. THAT BEING
SAID...THE TIMING OF THE CAA DEVELOPING WILL BE THE CHALLENGING
PART OF SWITCHING PRECIP OVER TO ALL SNOW TUESDAY. CONFIDENT
NORTH OF HIGHWAY 20 WILL REMAIN ALL SNOW AND THUS INCREASED SNOW
AMOUNTS TO 2 TO NEAR 5 INCHES CLOSE TO THE MINNESOTA BORDER.
NAM/GFS HINTING ON STRONG FRONTOGENETICAL FORCING ON THE BACKSIDE
OF THE SURFACE LOW TO DEVELOP LATE TUESDAY MORNING INTO THE
AFTERNOON HOURS OVER NORTHERN IOWA SUGGESTING SOME DECENT SNOWFALL
RATIOS TUESDAY AFTERNOON. THIS MATCHES UP WELL WITH THE
MCW/FRM/FOD SOUNDINGS AS THE COLUMN COOLS TO NEARLY ENTIRELY
WITHIN THE DENDRITIC LAYER BY TUESDAY AFTERNOON. THIS COUPLED WITH
WINDS ATOP THE MIXED LAYER RANGING FROM 35 TO 45 KNOTS...LIKELY TO
SEE SOME BLOWING SNOW TUESDAY AFTERNOON INTO TUESDAY NIGHT OVER
THE NORTH. HENCE...HAVE INTRODUCED THE MENTION OF BLOWING SNOW
DURING THIS TIME FRAME.

WEDNESDAY THROUGH SATURDAY...COLD AND DRY WEDNESDAY AND THURSDAY
BEFORE A DECENT WARM UP BEGINS BY FRIDAY AND INTO NEXT WEEKEND.
LOWERED MINIMUM TEMPERATURES WEDNESDAY NIGHT INTO THURSDAY WITH
THE SURFACE HIGH OVERHEAD PROVIDING A STRONG RADIATIONAL COOLING
SET UP.

&&

.AVIATION...01/06Z
ISSUED AT 1128 PM CST SAT FEB 28 2015

WEAK UPPER LEVEL TROUGH CONTINUES TO MOVE SLOWLY ACROSS THE AREA
TONIGHT. MVFR STRATUS HAS FILLED IN AND SLOWLY DRIFTING ENE WITH
TIME. WITH WEAK LIFT...VERY LIGHT SNOW OR FLURRIES CONTINUE TO
DEVELOP IN THE SHALLOW CLOUD DECK. WILL MAINTAIN FLURRIES AND
MODEST REDUCTION IN VSBY FROM 4SM TO 6SM THROUGH 14Z...LONGER
SOUTHEAST AT KOTM. OTHERWISE MVFR CIGS WILL GIVE WAY TO VFR CIGS
AS MID LEVEL DECK ACCOMPANIES SFC WIND SHIFT THROUGH THE DAY. MORE
PROBLEMATIC SYSTEM STILL ON TRACK FOR LATE MONDAY/TUESDAY./REV

&&

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

$$

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



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