Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 180424
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1124 PM CDT FRI APR 17 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 322 PM CDT FRI APR 17 2015

CURRENT SCENARIO HAS MATURE UPPER LOW OVER THE CENTRAL ROCKIES
WITH LEADING SHORT WAVE LIFTING NORTHEAST THROUGH NE. SCATTERED
FAIRLY WEAK CONVECTION UPSTREAM IS MAINLY DRIVEN BY KINEMATIC
FORCING...UPPER LEVEL DIFFLUENCE AND DPVA...WITH LITTLE
BAROCLINICITY OR LOW LEVEL CONVERGENCE NOTED. SEVERAL HUNDRED
UNCAPPED MUCAPES ARE IN PLACE OVER IA BUT WITH NO TRIGGER OR
FOCUS.

THE PRIMARY QUESTION TONIGHT WILL BE PRECIP TRENDS AND SYSTEM
EVOLUTION. AFOREMENTIONED KINEMATIC FORCING WOULD APPEAR TO REMAIN
THE PRIMARY FOCUS INTO THE NIGHT. INFLOW ALONG THE 300K ISENT
SURFACE INTO THE POSITIVE AREA JUST ABOVE THE INVERSION DOES
INCREASE SOMEWHAT BY 06Z BUT IS STILL ONLY 10-15KTS. THERE IS
LITTLE BAROCLINICITY BUT SOME WEAK MOISTURE CONVERGENCE ON LEADING
EDGE OF MOISTURE RIBBON TO POSSIBLY AID THE KINEMATIC FOCUS. THUS
PRETTY MUCH EXPECT SLOW EXTRAPOLATION OF CURRENT SETUP WITH PATCHY
WEAK CONVECTION DRIFTING NORTH AND EAST INTO THE STATE...LESS
AGGRESSIVELY THAN PREVIOUSLY DEPICTED. SEVERAL MODELS...INCLUDING
12Z GFS...ARE ALREADY OVERZEALOUS WITH EASTWARD EXPANSION OF
QPF/PRECIP.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 322 PM CDT FRI APR 17 2015

SEVERAL CONCERNS OVER THE EXTENDED PERIOD WITH RAIN/THUNDER
CHANCES THIS WEEKEND...COLDER TEMPERATURES MOVING INTO THE REGION
SUNDAY NIGHT THROUGH MUCH OF NEXT WEEK RESULTING IN THE
FROST/FREEZE POTENTIAL FOR A COUPLE NIGHTS. LEANED TOWARD A BLEND
OF THE NAM/GFS/ECMWF OVER THE WEEKEND AND CLOSER TO THE ECMWF
MONDAY THROUGH MUCH OF NEXT WEEK.

SATURDAY THROUGH MONDAY...MODELS ARE IN DECENT AGREEMENT WITH THE
STUBBORN UPPER LEVEL CUTOFF LOW MEANDERING ACROSS THE CENTRAL
PLAINS. MAINLY LOOKING AT TWO POTENTIAL PERIODS OF RAIN AND
ISOLATED THUNDERSTORMS OVER THE WEEKEND WITH THE FIRST ROUND
DURING MUCH OF THE DAY TOMORROW AND A SECOND ROUND WITH THE COLD
FRONT SWEEPING ACROSS THE STATE ON SUNDAY.

SOME BROAD AND WEAK ISENTROPIC LIFT AND QG FORCING SPREADS OVER
THE STATE SATURDAY AHEAD OF THE UPPER LOW BEFORE THE LOW GETS
GETS PUSHED EAST SUNDAY AFTERNOON/EVENING WITH THE COLD FRONT. A
WEAK AREA OF SUBSIDENCE AND MID- LEVEL DRY AIR (PER THE ECMWF/GFS)
PUNCH INTO WESTERN TO NORTHERN IOWA SATURDAY EVENING AND SHOULD
PROVIDE A BRIEF BREAK IN THE RAIN. LOWERED POPS SLIGHTLY IN THIS
AREA SATURDAY EVENING. HOWEVER...ANOTHER BROAD AREA OF QG FORCING
MOVES INTO THE STATE EARLY SUNDAY MORNING AHEAD OF THE COLD FRONT
ANTICIPATED TO PUSH THROUGH THE FORECAST AREA BY THE AFTERNOON.
HAVE A NON-DIURNAL TEMP TREND GOING FOR HOURLY TEMPS SUNDAY WITH
THE CAA DEVELOPING AFTER 18Z. FORECAST SOUNDINGS BECOME DEEPLY
SATURATED SATURDAY MORNING AND OTHER THAN THE BRIEF PERIOD OF THE
AFOREMENTIONED MID- LEVEL DRY AIR SATURDAY EVENING...REMAIN DEEPLY
SATURATED UNTIL THE COLD FRONT MOVES THROUGH BY SUNDAY
AFTERNOON/EVENING. SHOULD BE PERIODIC RAIN AND SOME ISOLATED
THUNDER THROUGH MUCH OF THE WEEKEND.

THE AFOREMENTIONED CUTOFF LOW GETS BROKEN UP WITHIN THE 500MB LOW
WITH ONE PIECE OF THE UPPER LEVEL VORT MAX QUICKLY SHIFTING
NORTHEAST WHILE THE REMAINDER PORTIONS OF THE SYSTEM GETS
INGESTED INTO THE SOUTHERN MORE ZONAL FLOW AND MOVES EAST INTO THE
OHIO VALLEY BY SUNDAY NIGHT. LOWERED POPS SUNDAY NIGHT WITH THE
SYSTEM MOVING OUT OF THE AREA QUICKER. WENT COOLER ON MONDAY WITH
THE STRONG CAA DEVELOPING. TWEAKED UP WINDS AS WELL WITH WINDS
ATOP THE MIXED LAYER FROM 35-40 KNOTS. MCW NAM/GFS FORECAST
SOUNDINGS SUGGEST SOME ICE INTRODUCTION AND EVEN THOUGH THE
SURFACE WET BULBS REMAIN WARM ENOUGH TO SUPPORT RAIN...THERE MAY
BE SOME GRAUPEL AND POSSIBLY SNOW MIXED INTO THE LIGHT RAIN
SHOWERS ACROSS THE NORTH WITHIN THE STRONG CAA. INTRODUCED LIGHT
SNOW SHOWERS ACROSS THE FAR NORTH.

TUESDAY THROUGH FRIDAY...MAIN CONCERN DURING THIS TIME FRAME IS
THE FROST/FREEZE POTENTIAL. WINDS REMAIN TOO STRONG TUESDAY
MORNING FOR FROST...BUT SOME AREAS ACROSS THE NORTH MAY DIP TO
AROUND FREEZING. ANOTHER WEAK SHORTWAVE BRINGS A REINFORCED SHOT
OF COLD AIR WEDNESDAY MORNING. DID GO COLDER FOR MAX TEMPS
WEDNESDAY. SO THE BEST PERIOD FOR FROST POTENTIAL LOOKS TO BE
THURSDAY MORNING WITH THE SURFACE RIDGE BUILDING INTO THE STATE
AND ALLOWING FOR SOME RADIATIONAL COOLING SETUP. WENT DRY THURSDAY
NIGHT INTO FRIDAY WITH THE GFS/ECMWF REMAINING DRY AS WELL.

&&

.AVIATION...18/06Z
ISSUED AT 1124 PM CDT FRI APR 17 2015

A FEW ISOLATED SHOWERS AND WEAK THUNDERSTORMS HAVE DEVELOPED
ACROSS FAR SOUTHERN IOWA...WITH MID AND HIGH LEVEL CLOUDS IN
PLACE. CHANCES FOR PRECIP TO INCREASE THROUGH THE PERIOD AS BETTER
MOISTURE LIFTS INTO THE STATE...WITH THE BEST TIMES EXPECTED
DURING THE DAY SATURDAY INTO SATURDAY EVENING. MORE SPOTTY
ACTIVITY EXPECTED PRIOR TO THEN...AND COULD MAINLY BE CONFINED TO
THE WESTERN AND SOUTHERN AREAS OF THE STATE. MVFR CIGS EXPECTED
TOWARD THE END OF THE PERIOD AS LOW LEVEL MOISTURE REALLY
INCREASES. ADDITIONALLY WINDS TO PICK UP SOME AND BECOME MORE
SOUTHEASTERLY FOR SATURDAY.

&&

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

&&

$$

SHORT TERM...SMALL
LONG TERM...PODRAZIK
AVIATION...BEERENDS


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