Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 201205
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
705 AM CDT SUN APR 20 2014

...UPDATED AVIATION DISCUSSION...

.SHORT TERM /TODAY/...
ISSUED AT 351 AM CDT SUN APR 20 2014

FRONTAL BOUNDARY STALLED UP ACROSS NORTHWEST IOWA WILL SLOWLY
TRANSITION SOUTHEAST THROUGHOUT THE DAY TODAY. MAIN CONCERN IS
WITH PRECIP ASSOCIATED WITH THE FRONT AND MAX TEMPERATURES.

UTILIZED A BLEND OF THE 20.03Z HOPWRF...20.05Z HRRR...AND 20.00Z
RUNS OF THE NMM/ARW-EAST AS THEY WERE IN GREAT AGREEMENT WITH SMALL
BATCH OF SHOWERS TO AFFECT NORTHERN IOWA THROUGH THE EARLY THIS
MORNING HOURS. THERE LOOKS TO BE A BRIEF BREAK LATE IN THE MORNING
INTO THE EARLY AFTERNOON BEFORE SHOWERS/STORMS DEVELOP ALONG THE
FRONT WITH DEEPER MOISTURE MOVING INTO THE STATE AND BETTER
INSTABILITY. STRONG MOISTURE TRANSPORT AND THETA-E ADVECTION WILL
CONTINUE PUSH SURFACE DEW POINTS INTO THE UPPER 40S/LOWER 50S
THROUGH THE DAY. SOUNDINGS DEPICTING ELEVATED LCL (AROUND 5000-6000
FEET) AND RAIN LOOKS TO HAVE TO FIGHT THROUGH A FAIRLY DEEP DRY
LAYER TO THE SURFACE THIS MORNING. THERE ARE A FEW ISOLATED SHOWERS
DEVELOPING ALONG THE 300-310K ISENTROPIC SURFACE WHERE ENOUGH LIFT
AND MOISTURE TRANSPORT PRESENT. BUT NOT ANTICIPATING THESE SHOWERS
TO PERSIST PAST 12Z AS THEY LOOK TO MOVE INTO MORE STABLE AIR
FURTHER EAST. AFTER THESE LITTLE SHOWERS MOVE THROUGH CENTRAL IOWA
THIS MORNING...NOT EXPECTING PRECIP UNTIL LATE THIS AFTERNOON AND
CONFINED POPS TO THE NORTH AND WEST UNTIL 21Z.

LATER INTO THE AFTERNOON...BETTER INSTABILITY BY 21Z SUNDAY ACROSS
WESTERN TO NORTHERN IOWA AND EXPECTING FRONT TO TRIGGER SCATTERED
SHOWERS/TSTMS OVER THIS AREA. PRECIPITABLE WATER VALUES AROUND 1.20"
THIS AFTERNOON AND WITH THE DEEPER MOISTURE MOVING INTO THE
STATE...COULD SEE A FEW ISOLATED HALF INCH AMOUNTS.

WITH THE WAA CONTINUING OVERNIGHT TONIGHT...TEMPERATURES REMAINED
SLIGHTLY WARMER THAN ANTICIPATED. THEREFORE...WAS CONFIDENT TO BUMP
MAX TEMPS UP A DEGREE OR TWO ACROSS THE FORECAST...WHICH WAS NEAR
OR SLIGHTLY WARMER THAN MOS.

.LONG TERM /TONIGHT THROUGH SATURDAY/...
ISSUED AT 351 AM CDT SUN APR 20 2014

SYSTEM TRACKING MORE OR LESS AS EXPECTED TONIGHT...AS WEAKENED
INVERTED TROUGH WITH VERY WEAK SFC IMPULSE DRIFTING NORTHEAST INTO
WESTERN WI BY 12Z MONDAY. SO FAR...MOISTURE HAS BEEN LACKING BOTH
AT THE SFC AND ALOFT. SUBJECTIVE SFC ANALYSIS TONIGHT SHOWS
SECONDARY WARM FRONT FROM LOW OVER THE NE/KS BORDER SOUTHEAST
ACROSS SOUTHEAST KS TO NORTHERN AR. DEW POINTS POOLING IN THE
50-55F RANGE OVER THE SOUTHERN PLAINS BUT SFC WINDS NOT HELPING
MUCH TO TRANSPORT MOISTURE NORTH. ALOFT AT H850...A THIN RIBBON OF
5C DEW POINTS HAS WORKED NORTH TO MINNEAPOLIS BUT DEEPER MOISTURE
STILL STUCK SOUTH IN THE SOUTHERN PLAINS AND THIS SHOULD EXPAND
INTO IOWA TONIGHT. H850 MOISTURE CHANNEL HAS BEEN HELD IN CHECK BY
EXPANSIVE HIGH PRESSURE ALOFT TO OUR EAST. BY TONIGHT THIS FEATURE
WILL DRIFT EAST AND ALLOW WEAK SFC SYSTEM SOUTHWEST OF US TO MOVE
ACROSS THE REGION AND TUG THE WEAK BOUNDARY SOUTHEAST THROUGH
MONDAY AFTERNOON. SHOWERS AND SCT THUNDER WILL INCREASE NORTH THIS
EVENING AS THE WEAK SFC LOW BEGINS TO MOVE NORTHEAST. AFTER 06Z TO
12Z THE ENTIRE AREA DRIFTS SOUTHEAST BUT THE FAR SOUTHEAST SHOULD
STILL BE MAINLY DRY UNTIL 12Z. THROUGH THE DAY MONDAY THE SYSTEM
WILL MOVE EAST OF THE REGION WITH A SECONDARY COLD FRONT DROPPING
INTO NORTHERN IA BY 00Z TUE FOLLOWED BY CANADIAN HIGH PRESSURE FOR
TUESDAY. LOWS TONIGHT WILL REMAIN RATHER MILD WITH BOUNDARY TO THE
NORTH AND THICK CLOUD COVER. WITH THE MILD START TO THE DAY
MONDAY...HIGHS SHOULD REACH THE UPPER 60S TO NEAR 70. AS THE
SECONDARY FRONT DROPS SOUTH MONDAY NIGHT...COLDER AIR FILTERS INTO
THE REGION THROUGH 12Z TUES WITH LOWS IN THE 30S AND 40S. TUES
LOOKS PLEASANT WITH SEASONAL READINGS AS NORTHEAST FLOW KEEPS WARM
AIR ADVECTION WELL TO THE WEST. HIGHS RANGE FROM THE UPPER 50S
NORTHEAST TO THE MID 60S SOUTH. NEXT UPSTREAM WAVE OVER THE
ROCKIES WILL SPREAD SOME CLOUDS INTO WEST LATE IN THE DAY...AND
SHOWERS ARRIVE BY 12Z WED WEST. THROUGH WED...ENHANCED LIFT AS
WARM FRONT AND THETAE ADVECTION RETURN WILL KEEP TEMPS COOL...AND
MAY STRUGGLE TO REACH 60 ACROSS THE NORTHEAST HALF OF THE FORECAST
AREA AS SHOWERS WILL OCCUR THERE AND ISO THUNDER DEVELOPS
SOUTHWEST. MODELS CONTINUE TO ADVERTISE VIGOROUS WAVE FOR WED/THUR
WITH EXTENSIVE H500 LONGWAVE TROUGH EXTENDING ALL THE WAY BACK TO
DUTCH HARBOR AK ALONG THE ALEUTIAN CHAIN. AS MENTIONED IN LAST
NIGHTS AFD...WIND FIELDS ALOFT STILL SOMEWHAT IMPRESSIVE BY
WED/THU OVER THE PLAINS. SYSTEM SHOULD GEN UP SHOWERS AS WARM AIR
ADVECTION INCREASES WED WITH POTENTIAL FOR ISO THUNDER. FOR THE
MOST PART WE REMAIN IN THE COOL SECTOR THROUGH WED AFTERNOON. AS
WAVE BUCKLES AND CROSSES THE REGION...CENTRAL/EASTERN AREAS
BRIEFLY GET IN WARM SECTOR LATE WED NIGHT INTO MIDDAY THUR. BEST
CHANCE FOR ORGANIZED SVR WILL OCCUR WED EVE OVER EASTERN NE AND
WESTERN HALF OF IOWA ...WEAKENING SLOWLY AS IT CROSSES THE REGION
WED NIGHT AND REINTENSIFYING LATE THU MORNING/EARLY AFTERNOON AS
THE WARM SECTOR MOVES EAST INTO EASTERN AND SOUTHEAST IOWA.
POTENTIAL FOR EVENING AND LATE NIGHT SVR WED NIGHT/EARLY MORNING
THUR IS INCREASING WITH EURO SLOWING THE SYSTEM DOWN. GFS APPEARS
FASTER AT THIS POINT. WILL NEED TO WATCH PROGRESSION OF WAVE FOR
SEVERE POTENTIAL. THOUGH WINDS ALOFT ARE NOT LINING UP VERY WELL
FOR A SIGNIFICANT EVENT OVER OUR AREA...ENOUGH OF A SIGNAL WITH
SHEAR/CAPE TO BE WEARY OF OVERNIGHT SUSTAINED SVR CONVECTION LATE
WED NIGHT. TEMPS THURS WILL STILL BE MILD BUT ON THE DOWNSWING
LATE AS ANOTHER COOL FRONT DROPS SOUTH INTO THE AREA BY FRIDAY
MORNING. AIRMASS BEHIND THAT BOUNDARY MODERATES A BIT AS IT
ARRIVES FRIDAY...LEAVING MOST OF THE AREA IN THE 50S TO LOWER 60S.
LONG WAVE CONTINUES TO PUSH ENERGY EAST INTO THE WESTERN STATES
WHICH QUICKLY IS PROGGED TO ARRIVE IN THE PLAINS ALREADY ON
SATURDAY AND SUNDAY. NEXT WEEKEND IS BEGINNING TO LOOK WET ONCE
AGAIN. MEDIUM CONFIDENCE RIGHT NOW...WITH EXTENSIVE H500 WAVE
TRAIN HEADING OUR WAY.

&&

.AVIATION...20/12Z
ISSUED AT 704 AM CDT SUN APR 20 2014

ONGOING LIGHT SHOWER ACTIVITY WILL CONTINUE TO MOVE NORTHEAST AND
AFFECT MCW/ALO AND POSSIBLY FOD THROUGH 15Z THIS MORNING.
HOWEVER...EXPECTING VFR CONDITIONS. THE MAIN SHORTWAVE WILL
FINALLY MAKES ITS WAY ACROSS THE STATE TONIGHT AND SHOULD INCREASE
SHOWER AND THUNDERSTORM ACTIVITY ALONG THE FRONT STALLED ACROSS
NORTHWEST IOWA. HAVE INTRODUCED MVFR VIS/CIGS AT ALL SITES EXCEPT
OTM SINCE PRECIP WILL NOT REACH SOUTHEAST IOWA UNTIL EARLY MONDAY
MORNING. LOW CONFIDENCE WITH EXTENDED PERIOD OF PRECIP AT ANY TAF
SITE...BUT EVEN LOWER CONFIDENCE IS TRYING TO TIME THE PERIODIC
PRECIP TONIGHT.

&&

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

&&

$$

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



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