Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 261402
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
902 AM CDT TUE APR 26 2016

.UPDATE...
ISSUED AT 902 AM CDT TUE APR 26 2016

A WAKE LOW SITUATION DEVELOPING ACROSS THE SOUTHERN CWA...WITH
STRONG WINDS BEING REPORTED AT SITES JUST TO THE SOUTHWEST OF THE
CWA BEHIND THE AREA OF THUNDERSTORMS MOVING THROUGH SOUTHERN IOWA.
HAVE ISSUED A WIND ADVISORY FOR A FEW HOURS THIS MORNING FOR THE
STRONG WINDS EXPECTED TO PUSH THROUGH THE SOUTHERN CWA WITH THIS
CONVECTIVE ACTIVITY. ALSO UPDATED POPS EARLIER TO ACCOUNT FOR THE
AREA OF STORM MOVING THROUGH THE SOUTHERN THIRD OF THE CWA.

&&

.SHORT TERM.../TODAY/
ISSUED AT 358 AM CDT TUE APR 26 2016

A NUMBER OF CHALLENGES TODAY...INCLUDING TEMPERATURES AND EXTENT OF
CONVECTION THIS MORNING OVER THE SOUTH...TIMING OF THE ONSET OF LATE
AFTERNOON CONVECTION AGAIN OVER THE SOUTHWEST. HIRES MODELS
CAPTURING THE PRESENT MID LEVEL WARM AIR ADVECTION STRATUS NICELY
ACROSS SOUTHERN NEBRASKA AND IOWA. SUBJECTIVE SFC ANALYSIS SHOWS SFC
STATIONARY BOUNDARY DRAPED ACROSS THE IA/MO BORDER. ALOFT SUBJECTIVE
00Z H850 ANALYSIS INDICATES BOUNDARY ALOFT WITH MOISTURE FEEDING
INTO EASTERN KS BEFORE IT TURNS NORTHEAST INTO SOUTHERN IOWA EARLY
TODAY. THUS...A FEW POCKETS OF CONVECTION HAVE BEEN PERCOLATING OVER
THE SOUTH WITHIN ISENTROPICALLY LIFTED PARCELS...THEN DIMINISHING AS
THEY DRIFT NORTH INTO DRIER AIR THROUGH 18Z. HAVE INCLUDED SLIGHT
POP OVER THE FAR SOUTH THROUGH 12-16Z...THEN DRYING OFF THROUGH LATE
DAY. OF SECOND CONCERN IS MAX TEMP FOR TODAY...ESPECIALLY SOUTH.
GUIDANCE LOWER OVERALL...AND WITH CLOUDS DEVELOPING ALONG WITH
LITTLE MIXING AND EASTERLY FLOW THROUGH THE DAY...NOT LIKELY TO SEE
A GREAT WARMUP FOR THE AFTERNOON HOURS. DESPITE THOSE NEGATIVES...WE
REMAIN MILD ALOFT WITH 8C NORTH TO 12C SOUTH AT H850 TODAY. HAVE
TRIMMED HIGHS BACK MOST AREAS ~4 TO 5 DEGREES WITH EXPECTED
SUN/CLOUD MIX AND EASTERLY FLOW. RETURN OF CONVECTION...OTHER THAN
EARLY MORNING... WILL BE DELAYED UNTIL LATE AFTERNOON AND ONLY OVER
THE SOUTHWEST AS DEEPENING LOW OVER TX PANHANDLE BEGINS TO FORCE
H850 MOISTURE INTO EASTERN KS AND NEBRASKA BY 00Z AND SFC
CONVERGENCE INCREASES RAPIDLY INTO THE SAME AREAS. OUR BEST CHANCES
FOR CONVECTION APPEAR TO BE INTO THE LATE AFTERNOON HOURS SOUTHWEST
AND THEN THE EVENING ACROSS THE SOUTH AS THE H850 LOW DRIVES INTO
SOUTHERN NE AT 06Z AND FORCING INCREASES FROM 21Z THROUGH OVERNIGHT.
HAVE POPS INCREASING OVER THE SOUTHWEST BETWEEN 21-00Z WITH LESSER
CHANCES ELSEWHERE. GFS PROGS MUCAPE ACROSS THE SOUTH AT 1600-
3000 J/KG WITH HIGHER FORECASTS ALONG THE SW BORDER COUNTIES.

.LONG TERM.../TONIGHT THROUGH MONDAY/
ISSUED AT 358 AM CDT TUE APR 26 2016

OVERALL THE PATTERN CHANGES LITTLE THROUGH THE ENTIRE PERIOD WITH A
BLOCKY...WEAK FLOW ACROSS THE NRN ROCKIES. OUR MAIN WEATHER WILL BE
DRIVEN BY THE SUB-TROPICAL JET WHICH LOOKS TO KEEP THE MAIN STORM
TRACK JUST TO OUR SOUTH AND A GOOD DOSE OF SEASONALLY COOL DAMP ELY
FLOW IN PLACE. AT ONSET ALL EYES WILL BE JUST TO OUR SOUTH AND WEST
ALONG AND SW OF THE DRYLINE/WARM FRONT INTERSECTION. EXTREME
INSTABILITY WILL BE IN PLACE WITH DECENT CONFIDENCE IN DIURNAL
SEVERE CONVECTIVE INITIATION ACROSS THE CENTRAL PLAINS. MUCH LIKE
YESTERDAY...THE PRIMARY QUESTION WILL BE WHETHER ADEQUATE LOW
LEVEL CONVERGENCE AND REDUCED CINH CAN PHASE TO INITIATE OUR OWN
CONVECTION DOWN IN THE SW CORNER...OR WHETHER WE WILL HAVE TO
WAIT FOR UPSTREAM STORMS TO EVENTUALLY REACH US PER NEAR SLY MEAN
WIND AND BUNKERS SUPERCELL MOTION. CONVECTION ALLOWING MODEL /CAM/
CONSENSUS SUGGESTS THE LATTER WILL BE MOST LIKELY WITH A VERY
SMALL SEVERE WEATHER WINDOW FAR SOUTHWEST WHERE ADEQUATE SHEAR AND
INSTABILITY CAN BE REALIZED. CONVECTIVE DEBRIS FROM CURRENT KS
MCS MAY ALSO HINDER LIKELIHOOD OF SURFACE BASED CONVECTION THIS
FAR NORTH AND WEST. THUS MOST LIKELY SCENARIO WILL BE WEAKENING
CONVECTION SLOWLY CROSSING IA SW-NE DURING THE NIGHT IN PERSISTENT
WARM ADVECTION REGIME WAITING FOR LARGE SCALE MECHANICAL AND
THERMODYNAMIC FORCING FROM PARENT SYSTEM TO REACH THE STATE INTO
WED. THE NAM AND GFS ONLY DEPICT WEAK ELEVATED INSTABILITY SO DO
NOT EXPECT MUCH IN THE WAY OF SEVERE WEATHER POTENTIAL AFTER 03Z
WHEN MLCAPES FADE.

LOOKING INTO WED THE MAIN CONCERN WILL BE THE WARM FRONTAL PLACEMENT
AND OUR LOW LEVEL DESTABILIZATION. THE 00Z ECMWF REMAINS EMPHATIC
THAT THE WARM FRONT WILL CROSS THE MO BORDER PLACING FAR SRN IA
UNDER THE GUN FOR SEVERE WEATHER OF ALL MODES...ISOLATED TORNADOES
WIND AND HAIL...AND THE GFS IS NOT FAR BEHIND WITH THE FRONT
RIGHT ALONG THE BORDER. THE NAM AND CAMS ARE LESS BULLISH HOWEVER
KEEPING THE FRONT TO OUR SOUTH...POSSIBLY LATCHING ONTO EFFECTS OF
PREVIOUS MCS OUTFLOW. ANY SEVERE WINDOW WOULD BE BRIEF AND
DIURNALLY DRIVEN...BUT WILL CERTAINLY NEED TO WATCH THE BOUNDARY
PLACEMENT AND POTENTIAL FOR UPGRADE BEYOND CURRENT DAY 2 MARGINAL.
FARTHER TO THE NORTH EXPECT MORE WIDESPREAD WEAK CONVECTION
LIFTING NORTH TO SOUTH THROUGH THE REMAINDER OF THE STATE WITH
LOBE OF FORCING IMMEDIATELY AHEAD OF THE UPPER LOW.

ANY SEVERE WEATHER THREAT WANES INTO WED NIGHT WITH LOSS OF
INSTABILITY AS UPPER LOW TAKES ITS TIME DRIFTING ACROSS IA INTO THU.
THIS WILL RESULT IN A COOL DAMP ELY TO NELY FLOW AND PERIODS OF
LIGHT RAIN OR SHOWERS...WITH POPS GRADUALLY DECREASING THU BEFORE
ENDING BY THU EVENING AT THE LATEST. FLOW BECOMES WEAK BY
THEN...AND ITS NOT IN THE FORECAST THIS FAR OUT...BUT WOULD NOT
BE SURPRISED TO SEE FOG DEVELOP THU NIGHT AS PRECIP ENDS AND WEAK
NELY WIND IN PLACE. THE NEXT SYSTEM LOOKS TO TAKE A SLIGHTLY
FARTHER SOUTH PATH BUT WITH SIMILAR RESULTS INTO IA...A PROLONGED
PERIOD OF INTERMITTENT STRATIFORM AND WEAK CONVECTIVE RAINS WITH
ELY TO NELY FLOW THROUGH THE WEEKEND. THE UPPER LOW WILL BE QUITE
SLOW MOVING WITH NEUTRAL FORCING WRAP AROUND MOISTURE STILL
POSSIBLY DRIBBLING OVER IA INTO MON.

&&

.AVIATION.../FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING/
ISSUED AT 646 AM CDT TUE APR 26 2016

ISO THUNDER CONTINUES SOUTH OF KDSM EARLY TODAY...BUT WILL
DISSIPATE BY 15Z. SOME LIFR CIGS AND BR HAVE DEVELOPED NORTH AT
KMCW AND KALO ALONG A COLD FRONT. AS SYSTEM APPROACHES TONIGHT
MAINLY VFR CONDITIONS AFT NORTH CIGS LIFT AT 15-16Z. OVER THE
SOUTH VFR CONDITIONS WILL CONTINUE THROUGH 03-04Z WHEN MVFR CIGS
RETURN. EAST WINDS WILL INCREASE TO NEAR 15KTS 18-21Z WITH GUSTS
INCREASING TO 24-28KTS AFT 00Z ALL LOCATIONS. UNCERTAINTY ABOUT
COVERAGE OF THUNDER THIS EVENING...AND HAVE COVERED MOST SITES
WITH VC WORDING FOR NOW. COVERAGE OF SHRA WILL INCREASE AFT 03Z. /REV


&&

.HYDROLOGY...
ISSUED AT 358 AM CDT TUE APR 26 2016

QPF HAS BEEN TEMPERED A BIT FROM THIS TIME LAST NIGHT WITH BETTER
RAINS STAYING JUST TO OUR WEST. STILL EXPECT WIDESPREAD 1-2 INCH
RAINS THROUGH MIDWEEK...BUT POSSIBLY NOT EXCEEDING 2 INCHES SW AS
NOTED BEFORE. RFC SIMULATIONS SUGGEST THAT THE VAST MAJORITY OF
SITES SHOULD ONLY EXPERIENCE WITHIN BANK RISES...HOWEVER THERE IS
AN OUTSIDE POSSIBILITY THAT PORTIONS OF THE DES MOINES AND
RACCOON BASINS COULD JUST REACH FLOOD STAGE DEPENDING ON THE
LOCATION OF HEAVIER CONVECTIVE RAINS. SITES ACROSS PARTS OF THE
RACCOON BASIN ARE CURRENTLY EXPERIENCING STREAMFLOWS IN THE 75TH
PERCENTILE OR BETTER.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL NOON CDT TODAY FOR ADAIR-ADAMS-CASS-CLARKE-
DECATUR-LUCAS-MADISON-RINGGOLD-TAYLOR-UNION-WARREN-WAYNE.

&&

$$

UPDATE...BEERENDS
SHORT TERM...REV
LONG TERM...SMALL
AVIATION...REV
HYDROLOGY...SMALL



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