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000
FXUS63 KDMX 250447
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1147 PM CDT FRI MAY 24 2013

.UPDATE...
ISSUED AT 954 PM CDT FRI MAY 24 2013

BAND OF HIGH BASED SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE
FIRST WAVE OF THETA-E ADVECTION IS NOW ON THE FAR EASTERN EDGE OF
THE FORECAST AREA. ADDITIONAL THUNDERSTORMS ARE DEVELOPING ON THE
NOSE OF AN INCREASING LOW LEVEL JET OVER SOUTHWEST AND SOUTH
CENTRAL NEBRASKA. EXPECT THIS COMPLEX TO MAINTAIN AS IT SHIFTS
EAST ALONG THE EAST NORTHEAST 850-300 MB MEAN FLOW AS THE LOW
LEVEL JET CONTINUES TO STRENGTHEN AND FUEL THE COMPLEX. ADDITIONAL
ACTIVITY MAY DEVELOP AHEAD OF THE COMPLEX AS THE SECOND WAVE OF
THETA-E ADVECTION ARRIVES OVER THE WEST. WITH THIS...EXPECT
WIDESPREAD PRECIPITATION BETWEEN BETWEEN 4 AM AND 10 AM SATURDAY.
THE THREAT FOR SEVERE WEATHER REMAINS LOW THOUGH MARGINAL SEVERE
HAIL MAY BE POSSIBLE AS MUCAPES INCREASE AND LAPSE RATES INCREASE
A BIT. PRIMARY THREAT THOUGH WILL BE AREAS OF HEAVY RAIN
POTENTIAL AS PROFILES SATURATE WITH PWATS IN EXCESS OF 1.5 INCHES
ARRIVE. WILL CONTINUE TO HIGHLIGHT THE HEAVY RAIN POTENTIAL IN THE
HWO WITH THE POTENTIAL FOR LOCALIZED FLASH FLOODING.

&&

.SHORT TERM.../TONIGHT/
ISSUED AT 400 PM CDT FRI MAY 24 2013

SURFACE HIGH PRESSURE WILL REMAIN IN PLACE OVER THE GREAT LAKES AS A
SOUTH-SOUTHWEST FLOW ALOFT SETS UP A FEW THOUSAND FEET ALOFT AND
AIMS INTO IOWA. THIS WILL RESULT IN THE THERMAL GRADIENT AND ZONE OF
FRONTOGENESIS SETTING UP FROM NW TO SE ACROSS IOWA. LEADING EDGE OF
WARM ADVECTION IS PRODUCING ISOLATED TO SCATTERED THUNDER FROM THE
MISSOURI RIVER NORTH INTO THE DAKOTA/MINNESOTA BORDER REGION. THIS
WILL CONTINUE TO DRIBBLE EAST AND EVENTUALLY TURN SOUTHEAST ACROSS
NORTH AND NORTHEAST IOWA. AROUND MIDNIGHT THE SOUTHWESTERLY
LOW-LEVEL JET WILL INCREASE AND MORE WIDESPREAD THUNDERSTORMS ARE
EXPECTED TO DEVELOP ON THE BACK SIDE OF THIS REGION...MOST LIKELY
OVER NORTH CENTRAL IOWA AND THEN EXPANDING EAST AND SOUTH DURING THE
OVERNIGHT HOURS. SHEAR AND INSTABILITY ARE NOT FAVORABLE FOR SEVERE
WEATHER...BUT CONDITIONS ARE SOMEWHAT FAVORABLE FOR HEAVY RAINFALL
DUE TO FAIRLY SLOW STORM MOTION TO THE EAST AND POSSIBLE TRAINING OF
STORMS. PINPOINTING THE LOCATION OF HEAVIER RAIN IS DIFFICULT DUE TO
ELEVATED NATURE OF STORMS...BUT AGAIN NORTH CENTRAL INTO EAST
CENTRAL IOWA WOULD BE MOST LIKELY TO SEE OVER 1 INCH OF RAIN
OVERNIGHT. SHORT TERM RUNOFF PROBLEMS IN AREAS OF HIGH RAIN RATES
WOULD BE THE MOST LIKELY FLOOD THREAT TONIGHT SINCE WE HAVE NOT SEEN
RAINFALL IN SEVERAL DAYS.

.LONG TERM.../SATURDAY THROUGH FRIDAY/
ISSUED AT 400 PM CDT FRI MAY 24 2013

THE PRIMARY CONCERN THROUGH THIS PERIOD WILL REMAIN CONVECTIVE
TRENDS AND HEAVY RAINS...AND EVENTUALLY BETTER SEVERE POTENTIAL INTO
NEXT WEEK.  EVALUATION WILL CHANGE LITTLE FROM AS OUTLIER IN ABOVE
SHORT TERM DISCUSSION WITH DETAILS HARD TO COME BY.  MAIN THEME WILL
BE NOCTURNAL/WARM ADVECTION MAX WITH BETTER CHANCES DURING THE
NIGHTTIME AND EARLY MORNING HOURS.  EXPECT MCS TO BE ONGOING AT
BEGINNING OF THE PERIOD WITH THETA-E ADVECTION STILL FOCUSED RIGHT
INTO CENTRAL IA.  TYPICAL DIURNAL DECREASE IN POPS IS ANTICIPATED
LATER IN THE DAY UNTIL THE NEXT ROUND OF OVERNIGHT CONVECTION CYCLES
UP.  THETA-E ADVECTION SAT NIGHT DOES NOT APPEAR TO BE AS STRONG AS
WHAT MAY OCCUR TONIGHT...BUT WHAT OCCURS MAY BE MORE CONDUCTIVE FOR
HEAVY RAINS.  PRECIPITATION POTENTIAL PLACEMENT...WARM CLOUD DEPTHS
AND PRECIPITABLE WATER WILL ALL EITHER APPRECIABLY INCREASE OR BE
MORE ENTRENCHED INTO IA WITH MEAN WIND EVEN A TAD WEAKER.  THIS
COULD CERTAINLY RESULT IN LOCALLY HEAVY RAINS AND EFFICIENT RAINFALL
PRODUCERS.  DO NOT EXPECT WIDESPREAD RAINFALL WITH ANY PARTICULAR
MCS...BUT CUMULATIVE EFFECTS FROM NIGHT AFTER NIGHT WILL LIKELY
PRODUCE WIDESPREAD ONE TO TWO INCH AMOUNTS BY MONDAY WITH LOCALLY
HIGHER AMOUNTS POSSIBLE.  TEMPERATURE FORECASTS WILL BE PROBLEMATIC
THIS WEEKEND TOO DUE TO UNCERTAINTY WITH REGARD TO
MIXING...CLIMATOLOGY VS MODELS SELY FLOW/STRATUS SIGNAL.  GENERALLY
PLAYED A MIDDLE OF THE ROAD APPROACHING BUT LESS CONVECTION COULD
CERTAINLY END UP WITH HIGHER TEMPS.

AIRMASS WILL DEFINITELY BECOME MORE SUMMER-LIKE INTO NEXT WEEK WITH
PERSISTENT 1KM SOUTHERLY FETCH BOOSTING DEWPOINTS INTO THE 60S.
THIS MAY ALSO INCREASE OUR SEVERE AND SURFACE BASED POTENTIAL
SETTING UP SOMEWHERE IN THE VICINITY OF IA...WHOSE LATITUDINAL
EXTENT WILL BE DIFFICULT TO PINPOINT DUE TO REPETITIVE CONVECTIVE
OUTFLOW.  THERE MAY BE SOMEWHAT OF A LULL AROUND WED AS WARM SECTOR
BECOMES BETTER ENTRENCHED INTO IA AND WARM ADVECTION ZONE LIFTS
NORTHWARD.  HOWEVER SHORTLY AFTER THIS TIME LONG WAVE TROUGH WILL
FINALLY ADVANCE INTO THE PLAINS INCREASING KINEMATIC FORCING.  THIS
MAY INCREASE SEVERE THREAT ALTHOUGH SURFACE FEATURES AND ASSOCIATED
CONVERGENCE ZONES STILL LOOK TO BE OFF TO OUR NORTH AND
WEST...ESPECIALLY IF THE ECMWF VERIFIES.

&&

.AVIATION...25/06Z
ISSUED AT 1146 PM CDT FRI MAY 24 2013

THE FORECAST PERIOD WILL BE DOMINATED BY PRECIPITATION CHANCES AND
LOWERING CEILINGS. EXPECT SHOWERS AND THUNDERSTORMS TO EXPAND
ACROSS THE AREA OVERNIGHT AND INTO SATURDAY MORNING. CIGS WILL
LOWER TO MVFR WITH PRECIPITATION AND POSSIBLE LOWER SATURDAY
AFTERNOON OVER THE NORTH. THE PRECIPITATION WILL BECOME LESS
INTENSE BY SATURDAY AFTERNOON INTO THE EVENING WITH THE PRIMARY
ISSUE BEING CIGS BY THAT TIME. WINDS WILL BE OUT OF THE SOUTHEAST
THROUGH MUCH OF THE PERIOD.

&&

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

$$

UPDATE...DONAVON
SHORT TERM...JUNGBLUTH
LONG TERM...SMALL
AVIATION...DONAVON