Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 192334
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
634 PM CDT SAT APR 19 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 354 PM CDT SAT APR 19 2014

WITH AN AREA OF HIGH PRESSURE NEAR THE OHIO VALLEY REGION AND A
SOMEWHAT DEEP AND NEGATIVELY TILTED TROUGH ALONG THE US CANADA
BORDER...CENTRAL IOWA WILL BE SANDWICHED IN SOUTHWESTERLY FLOW FOR
THE SHORT TERM. MOST IMPORTANT SHORT TERM ISSUE IS THE EVER SLOWING
BOUNDARY/WEAK COLD FRONT CURRENTLY EXTENDING FROM NE NEBRASKA INTO
FAR WEST CENTRAL MINNESOTA. THE AFOREMENTIONED HIGH PRESSURE HAS
SERVED TO SLOW THE PROGRESSION OF THE BOUNDARY AND INTRODUCTION OF
MOISTURE IN THE LOW LEVELS TO THIS SYSTEM. IT SEEMS THAT WITH EVERY
MODEL RUN THE PAST FEW DAYS...THE PROGRESSION/EVOLUTION OF THIS
BOUNDARY HAS TRENDED SLOWER AND DRIER. AS A RESULT...HAVE PUSHED
BOUNDARY ARRIVAL IN OUR CWA BACK TO AROUND THE 09Z TIME PERIOD. NOT
A LOT OF DYNAMICS TO SUPPORT SYSTEM UNTIL A WEAK SHORTWAVE
PROPAGATES OFF THE ROCKIES AND IS INTRODUCED TO THE BOUNDARY AROUND
12Z SUNDAY. AROUND THIS TIME...THERE SHOULD BE A SUFFICIENT AMOUNT OF
SHEAR TO HELP GENERATE AND SUSTAIN SOME CONVECTION WHICH WILL BE
DISCUSSED IN THE LONG TERM DISCUSSION.

FOR TEMPERATURES...MOST MODEL RUNS INITIALIZING WAY TOO MOIST AND
COOL AT 18Z. SOUTHWESTERLY FLOW SHOULD HELP KEEP TEMPERATURES WELL
ABOVE NORMAL INTO THE OVERNIGHT. RAP/RUC INITIALIZING THE BEST...SO
WILL LEAN ON THEM FOR TEMP TRENDS INTO SUNDAY MORNING. PRESSURE
GRADIENT TO GRADUALLY RELAX INTO SUNDAY MORNING WHICH SHOULD AID IN
DECREASING THE WINDS DURING SUNDAY MORNING.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 354 PM CDT SAT APR 19 2014

PRECIPITATION TRENDS THROUGH MONDAY WILL BE THE FORECAST CHALLENGE
DURING THE EARLY PORTION OF THE PERIOD. THE FRONTAL BOUNDARY
MOVING INTO NW IA TODAY WILL WEAKEN INTO SUNDAY AS THE UPPER LEVEL
ENERGY SPLITS THE AREA WELL TO THE NORTH AND WELL TO THE SOUTH.
PROFILES WILL CONTINUE TO MOISTEN DURING THIS TIME WITH SURGES OF
THETA-E ADVECTION PASSING OVERHEAD AND WILL RESULT IN MOSTLY
CLOUDY CONDITIONS WITH PERIODS OF SHOWERS AND THUNDERSTORMS OVER
THE NORTHWEST HALF TO THIRD ON SUNDAY THEN GRADUALLY SETTLING
SOUTH SUNDAY NIGHT. THE BEST POTENTIAL FOR PRECIPITATION OVER
CENTRAL IOWA WILL BE SUNDAY NIGHT THOUGH SOME DRY AIR IN THE LOWER
LEVELS DOES MAINTAIN THROUGH THAT TIME. THE POTENTIAL FOR SEVERE
WEATHER WILL BE LOW WITH MUCAPES AT 500 J/KG OR LESS AND LAPSE
RATES NEAR MOIST ADIABATIC IN THE MID TO UPPER LEVELS RESULTING IN
SKINNY CAPES AND LOW POTENTIAL FOR GOOD VERTICAL ACCELERATIONS AND
UPDRAFTS. DRY AIR SURGES SOUTHEAST INTO THE NORTHWEST HALF ON
MONDAY AS THE NEXT BOUNDARY PASSES THROUGH. POSSIBLE FOR A
DIURNALLY DRIVEN LINE OF THUNDERSTORMS TO DEVELOP IN THE AFTERNOON
OVER THE SOUTHEAST THAT COULD YIELD SOME SMALL HAIL PRODUCERS.

HIGH PRESSURE ARRIVES TUESDAY AND WILL BE THE COOLEST DAY OF THE
WEEK BUT STILL PLEASANT. UPPER LOW MOVES INTO THE WESTERN DAKOTAS
AND NEBRASKA ON WEDNESDAY. THE CURRENT SET UP WOULD FAVOR STRONG
TO SEVERE STORMS DEVELOP IN THE VICINITY OF A DRY LINE FROM
CENTRAL NEBRASKA AND SOUTH TO THE OKLAHOMA AND TEXAS PANHANDLES.
THIS WOULD LEAVE CENTRAL IOWA IN THE MORE FAVORABLE REGION FOR
ELEVATED CONVECTION EARLY WEDNESDAY THEN POSSIBLE MCS ROLLING
THROUGH WEDNESDAY NIGHT. PENDING THE FRONTAL BOUNDARY
POSITION...LIKELY REDEVELOPMENT OF STORMS THURSDAY AFTERNOON
THROUGH THE MID MISSISSIPPI VALLEY WHICH MAY CLIP THE FAR EAST
FORECAST AREA. MORE UNCERTAINTY BEYOND THURSDAY WITH THE
PROGRESSION OF THE UPPER RIDGE WEST AND HOW DEEP THE DEPARTING
UPPER LOW DEVELOPS OVER THE GREAT LAKES.

&&

.AVIATION...20/00Z
ISSUED AT 632 PM CDT SAT APR 19 2014

FRONTAL BOUNDARY WILL BEGIN TO PUSH SE ACROSS SITES THROUGH THE
PERIOD. THIS WILL SHIFT WINDS TO THE WEST NEAR BOUNDARY. IN
ADDITION...SHRA AND TSRA ARE POSSIBLE NEAR BOUNDARY...WITH WESTERN
AND NORTHERN SITES KFOD/KMCW SEEING PRECIPITATION FIRST BEFORE
SHIFTING TO OTHER SITES. HAVE LEFT TSRA MENTION OUT FOR
NOW GIVEN UNCERTAINTIES IN TIMING AND LOCATION...THOUGH IS
POSSIBLE AT SITES. EXPECT CONDITIONS TO REMAIN VFR...THOUGH COULD
SEE MVFR OR IFR CEILINGS AND VISIBILITIES AT TIMES WITH SHRA.

&&

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

$$

SHORT TERM...KOTENBERG
LONG TERM...DONAVON
AVIATION...AWB



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