Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 251748
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1248 PM CDT SAT JUL 25 2015

.SHORT TERM /TODAY/...
ISSUED AT 350 AM CDT SAT JUL 25 2015

TODAY WILL REMAIN ACTIVE AND ONCE AGAIN THE MODELS...INCLUDING
THE HI-RES MODELS HAVE FAILED TO INITIALIZE VERY WELL. THE COLD
FRONT WILL CONTINUE TO SINK SOUTH AND EAST SETTLING MOST LIKELY
IN NORTHERN MISSOURI. IF IT HAPPENS TO BE FURTHER NORTH THEN
THERE WILL BE BETTER PRECIP CHANCES IN SOUTHERN IOWA THAN WHAT WE
HAVE GOING.

IN GENERAL THE ONGOING (CURRENT)CONVECTION IS WEAKENING AND
SINKING SOUTHEAST. WHILE AN ISOLATED STORM MAY PRODUCE STRONG WIND
OR LARGE HAIL THE OVERALL THREAT FOR NOW IS DIMINISHING. RAINFALL
IS PRETTY IMPRESSIVE WITH RADAR ESTIMATED 1+ INCH AMOUNTS ACROSS
FAR SOUTHERN IOWA. UNLIKE YESTERDAY THESE STORMS ARE MOVING OFF
AND THE STORMS BEHIND THE INITIAL BAND ARE WEAKER AND PROGRESSIVE.
FLASH FLOODING THREAT APPEARS MINIMAL AT THIS TIME BUT THIS WILL
CONTINUE TO BE MONITORED.

LATER TODAY A SHORTWAVE WILL MOVE ACROSS IOWA AND WITH THE
FRONTAL BOUNDARY IN THE VICINITY SO I EXPECT ADDITIONAL STORMS
THIS AFTERNOON INTO THE EVENING. HOWEVER...SHEAR OR AT LEAST DEEP
SHEAR IS MINIMAL AND OUR BEST INSTABILITY SETTLES SOUTH OF THE
STATE BY MID TO LATE AFTERNOON. I HAVE NO DOUBT THAT A FEW STORMS
MAY BE SEVERE AND OF COURSE THE HEAVY RAINFALL POTENTIAL WILL
EXIST BUT THE AREAL EXTENT OF THE SLIGHT RISK CATEGORY WE ARE IN
MAY BE A BIT OVERDONE. HOWEVER IF ORGANIZED CONVECTION CAN GET
GOING WEST OF US IT WILL ROLL INTO US AN PROVIDE THE POTENTIAL FOR
SEVERE STORMS...AT LEAST ACROSS THE SOUTH AND INTO THE EVENING
HOURS.

TEMPERATURES WILL NOT BE AS WARM TODAY ALTHOUGH OUR DEWPOINTS
WILL BE IN THE LOWER TO MIDDLE 70S. IT WILL BE ANOTHER MUGGY DAY
BUT HEAT INDICES WILL REMAIN WELL BELOW ADVISORY LIMITS FOR TODAY
SO NO HEADLINES ARE EXPECTED AT THIS POINT.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 350 AM CDT SAT JUL 25 2015

A DEEP LAYER RIDGE WILL PERSIST ACROSS THE SOUTH CENTRAL U.S. FOR
THE NEXT SEVERAL DAYS...WITH THE TOP PRETTY FLATTENED OVER IOWA
THROUGH TONIGHT THEN BUILDING OVERHEAD FROM SUNDAY THROUGH MONDAY.
TONIGHT IT IS EXPECTED THAT...SIMILAR TO THE CURRENT TIME /FRIDAY
NIGHT/...CLUSTERS OF THUNDERSTORMS WILL DEVELOP OVER EASTERN
NEBRASKA AND DRIFT EASTWARD ACROSS SOUTHWESTERN AND SOUTHERN IOWA
OVERNIGHT...WITH ISOLATED TO SCATTERED THUNDERSTORMS POSSIBLE
FURTHER NORTH DEPENDING ON DEGREE OF DESTABILIZATION AND LOCATION
OF LINGERING BOUNDARIES. ONCE AGAIN THERE WILL BE A MARGINAL
THREAT OF SEVERE WIND/HAIL ALONG WITH A DISTINCT THREAT OF LOCALLY
HEAVY RAIN/FLOODING AS THE ATMOSPHERE WILL BE LITTLE CHANGED FROM
THE PREVIOUS NIGHT. ONCE ANY OVERNIGHT ACTIVITY EXITS TO THE
SOUTH/SOUTHEAST ON SUNDAY MORNING...THE BUILDING 500 MB RIDGE
SHOULD MINIMIZE CONVECTIVE POTENTIAL FROM SUNDAY AFTERNOON THROUGH
MONDAY BUT THERE WILL BE ENOUGH INSTABILITY AND OLD OUTFLOW
BOUNDARIES THAT ANY SUBTLE IMPULSES TRAVELING THROUGH THE STEERING
FLOW MAY BE ABLE TO KICK OFF A FEW STORMS...THUS HAVE MAINTAINED
SLIGHT CHANCE POPS DURING MUCH OF THIS TIME FRAME THROUGH THE
SEVERE WEATHER THREAT IS PRETTY MINIMAL.

BY MONDAY NIGHT A FAIRLY ROBUST 500 MB TROUGH WILL BE MOVING OVER
THE NORTHERN ROCKIES...AND SUBSEQUENTLY ACROSS THE UPPER MIDWEST
ON TUESDAY NIGHT AND WEDNESDAY. THIS TROUGH WILL THEN DIG DOWN THE
EASTERN U.S. AND PUSH THE AFOREMENTIONED DEEP LAYER RIDGE FURTHER
WEST OVER THE ROCKIES DURING THE LATTER HALF OF THE WEEK.
INITIALLY...THE APPROACHING TROUGH ON MONDAY NIGHT INTO TUESDAY
MAY BE ABLE TO KICK OFF SOME CONVECTION IN A WARM AIR ADVECTION
REGIME PARTICULARLY ON MONDAY NIGHT AND HAVE INCLUDED POPS FOR
MOST OF THE AREA TO ACCOUNT FOR THIS POSSIBILITY. SAID LOW LEVEL
WARM AIR ADVECTION COMBINED WITH WARM TEMPERATURES MOVING OVERHEAD
DURING THE DAY ON TUESDAY SHOULD PUSH HIGHS UP INTO THE LOWER TO
POSSIBLY MID 90S ACROSS THE AREA...AND COMBINED WITH DEWPOINTS IN
THE MID 70S WILL LIKELY RESULT IN HEAT INDEX VALUES PEAKING IN
THE 100 TO 105 RANGE WITH ATTENDANT HEAT CONCERNS. THE BEST CHANCE
OF RAIN WILL THEN COME AROUND TUESDAY NIGHT AS THE UPPER TROUGH
BEGINS TO MOVE OFF TO THE NORTHEAST BUT THE LAST SHOT OF VORTICITY
ROUNDING ITS BASE PUSHES A SURFACE FRONT SOUTHEASTWARD ACROSS
IOWA. EXPECT THAT THE FORCING ASSOCIATED WITH THIS VORTICITY LOBE
AND THE INSTABILITY POOLED ALONG/SOUTH OF THE BOUNDARY...ESPECIALLY
IN THE PRESENCE OF A DEVELOPING LOW LEVEL JET...WILL BE SUFFICIENT
TO GENERATE THUNDERSTORMS ACROSS MUCH OF THE AREA TUESDAY NIGHT
AND HAVE RAISED POPS ACCORDINGLY.

ANY LINGERING STORMS FROM THE FRONTAL PASSAGE WILL CLEAR OUT OF
OUR FORECAST AREA ON WEDNESDAY MORNING...WITH RELATIVELY COOL AND
DRY WEATHER THEN SETTLING IN FOR THE REMAINDER OF THE WEEK AS THE
AFOREMENTIONED WESTERN RIDGE/EASTERN TROUGH PATTERN SETTING UP
PLACES US BENEATH BENIGN NORTHWEST FLOW. THIS SHOULD GIVE US A
NICE BREAK FROM THE HOT...HUMID...AND SOMEWHAT ACTIVE WEATHER
LEADING UP TO IT.

&&

.AVIATION...25/18Z
ISSUED AT 1248 PM CDT SAT JUL 25 2015

CONFIDENCE ADMITTEDLY LOW THROUGH THE VALID PERIOD...MAINLY DUE TO
UNCERTAIN PRECIP TRENDS. CONVECTION OF VARIED STRENGTH WILL CROSS
THE MO RIVER INTO IA SHORTLY WHICH MAY BRING A PERIOD OF PRECIP TO
TAF SITES BUT COVERAGE AND AREAL EXTENT REMAINS QUESTIONABLE.
ADDITIONAL CONVECTION MAY ALSO DEVELOP FARTHER UPSTREAM IN THE
DAKOTAS REACHING IA DURING THE EARLY MORNING HOURS SUN. THUS HAVE
NOTHING MORE THAN VFR/VCSH WORDING FOR NOW UNTIL TRENDS IN LOWER
CONDITIONS AND THUNDER BECOME MORE CLEAR.

&&

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

&&

$$

SHORT TERM...FAB
LONG TERM...LEE
AVIATION...SMALL



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