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000
FXUS63 KDMX 181746
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1246 PM CDT SAT MAY 18 2013

.SHORT TERM.../TODAY /...
ISSUED AT 352 AM CDT SAT MAY 18 2013

UPPER LEVEL RIDGING TO BUILD OVER THE STATE TODAY...WITH SOUTHERLY
FLOW AHEAD OF A DEVELOPING AREA OF SFC LOW PRESSURE ACROSS THE
WESTERN HIGH PLAINS OF SD/NE/CO. DRY CONDITIONS ARE EXPECTED ACROSS
THE CWA TODAY...HOWEVER PUSH OF MOISTURE ADVECTION COULD ALLOW FOR
SOME THUNDERSTORM DEVELOPMENT JUST TO THE WEST OF THE CWA BY LATE
AFTERNOON/EARLY EVENING. FOR NOW LOOKS LIKE ANY ACTIVITY WILL HOLD
OFF UNTIL AFTER 00Z ACROSS THE AREA...SO HAVE KEPT THE GRIDS DRY.
TEMPS ARE TRICKY TODAY...WITH CLOUD SHIELD INITIALLY OVER PORTIONS
OF THE CWA FROM ONGOING MCS ACTIVITY ACROSS CNTRL NE/SD/MN. DO
EXPECT SKIES TO CLEAR SOME THROUGH THE MORNING...WITH DECENT MIXING
ALLOWING TEMPS TO PUSH INTO THE 80S ACROSS THE CWA. COULD ALSO SEE
SOME BREEZY CONDITIONS AS STRONGER WINDS ALOFT MIX DOWN THROUGH THE
DAY.

.LONG TERM.../TONIGHT THROUGH FRIDAY/...
ISSUED AT 352 AM CDT SAT MAY 18 2013

SHORTWAVE WILL EJECT TOWARDS THE STATE TONIGHT WITH MID LEVEL QG
FORCING INCREASING. INSTABILITY WILL ALREADY BE IN PLACE WITH THE
ARRIVAL OF THE FORCING AND ANTICIPATE CONVECTION DEVELOPING/MOVING
INTO THE WEST AND SPREADING NORTHEAST WITH TIME. THIS CONVECTION
PERSIST INTO SUNDAY MORNING ACROSS A BROAD SWATH OF THE FORECAST
AREA BEFORE THE FORCING PASSES TO THE NORTHEAST. WILL LIKELY SEE
SOME BREAK IN THE ACTIVITY LATE SUNDAY MORNING INTO THE EARLY
AFTERNOON IN SUBSIDENCE BEHIND THIS INITIAL WAVE AND HAVE
DECREASED POPS EARLY IN THE AFTERNOON. HOWEVER...NEXT SHORTWAVE
WILL BE QUICKLY APPROACHING BY LATE AFTERNOON/EVENING WITH VERY
GOOD UPPER LEVEL DIVERGENCE. GOOD MID LEVEL LAPSE RATES MOVE INTO
THE STATE DURING THIS TIME AS SURFACE LOW MOVES INTO EASTERN
NEBRASKA. STILL SOME QUESTION AS TO RECOVERY BEHIND DEPARTING
CONVECTION DURING THE MORNING BUT THE SOUTHWEST SHOULD SEE THE
BEST CHANCE OF THIS OCCURRING BY LATE AFTERNOON. SPC HAS ALSO
HIGHLIGHTED THIS AREA WITH BEST POTENTIAL FOR SEVERE CONVECTION
DURING THE AFTERNOON AS BULK SHEAR WILL BE INCREASING WITH
APPROACHING MID LEVEL SPEED MAX AND LOW LEVEL HELICITY WILL ALSO
BE INCREASING AS SURFACE LOW MOVES INTO NEBRASKA. SOME CONCERN
WITH A WARM LAYER IN THE LOW LEVELS OF FORECAST SOUNDINGS THAT MAY
AT LEAST SLOW PARCEL ACCELERATION IN THE 0-3KM LAYER. OVERALL
STILL PLENTY UNCERTAINTY AS TO THE EVENTUAL EVOLUTION...BUT SEVERE
WEATHER WITH AT LEAST LARGE HAIL APPEARS A GOOD BET WITH THE
POSSIBILITY OF A FEW TORNADOES IN THE SOUTH LATE AFTERNOON/EVENING
TIMEFRAME.

THE THREAT OF CONVECTION WILL PERSIST INTO SUNDAY NIGHT...ALTHOUGH
DRY SLOT MOVING UP INTO THE STATE MAY BEGIN TO CUT OFF MORE
SIGNIFICANT PRECIPITATION WITH TIME. UPPER LOW WILL THEN SIT AND
SPIN NEAR IOWA THROUGH WEDNESDAY WITH ONGOING THREATS OF PCPN
DURING THIS TIME. MAY SEE THE POTENTIAL FOR MORE SEVERE WEATHER IN
THE SOUTHEAST ON MONDAY WITH OTHER CONVECTION ACROSS FAR NORTHERN
IOWA UNDERNEATH THE UPPER LOW. CHANCES OF SHOWERS/ISOLD THUNDER
WILL LINGER INTO TUESDAY/WEDNESDAY AS LOW SLOWLY MOVES THROUGH THE
STATE WITH QUIET WEATHER ARRIVING LATE IN THE WEEK.

&&

.AVIATION...18/18Z
 ISSUED AT 1246 PM CDT SAT MAY 18 2013

OVERNIGHT CONCERNS REGARDING CONVECTION AND OVERALL COVERAGE.
MODELS SUGGESTING MCS DEVELOPMENT NEAR/IN AREA BY 10-15Z SUNDAY
BUT PLACEMENT SOMEWHAT CHALLENGING FOR NOW. HAVE CONSIDERED WARM
AIR ADVECTION AND NOSE OF INCREASING SOUTHERLY JET WITH WARM
FRONTAL PLACEMENT...ALL POINTING TO DEVELOPMENT AFFECTING EITHER
KDSM OR KFOD GREATER THAN AREAS EAST/NORTH. THUS...FOR NOW HAVE
INCREASED LIKELIHOOD OF TSRA AT THOSE TWO SITES FOR EARLY MORNING
HOURS. WINDS WILL LIKELY REMAIN JUST UNDER 12KT OVERNIGHT WITH
INCREASING SOUTHERLY FLOW AFT 04Z. WITH OVERNIGHT CONVECTION...
BEGIN TO EXPECT THE MCS TO DIMINISH TOWARD THE END OF PERIOD AS
JET WEAKENS AFTER 12Z. NEXT ROUND OF CONVECTION MORE LIKELY LATE
AFTERNOON OR AFT 20/00Z AS SHORTWAVE APPROACHES FROM WEST.

&&

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

$$

SHORT TERM...BEERENDS
LONG TERM...COGIL
AVIATION...REV