Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 232328
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
627 PM CDT THU JUL 23 2015

...UPDATED FOR 24/00Z AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
ISSUED AT 402 PM CDT THU JUL 23 2015

CWA STILL SANDWICHED BETWEEN HIGH PRESSURE TO THE EAST AND AN AREA
OF LOW PRESSURE TO THE WEST...WITH THE AREA OF HIGH PRESSURE HAVING
MOVED VERY LITTLE THE PAST 24 TO 48 HOURS. SOUTHERLY FLOW STILL
EXPECTED OVERNIGHT AHEAD OF THE LOW TO THE WEST...AND AS THE HIGH
CONTINUES TO SLOWLY DRIFT EAST. MAINLY CLEAR SKIES EXPECTED THIS
EVENING...WITH CLOUD COVER TO INCREASE FROM THE WEST NORTHWEST WITH
A PUSH OF THETA-E ADVECTION AND WAA AHEAD OF AN UPPER WAVE LIFTING
NORTHEASTWARD THROUGH THE DAKOTAS. NAM TRIES TO INITIATE SOME STORMS
ON THE LEADING EDGE OF THE WAA/MOISTURE ADVECTION LATE TONIGHT
TOWARD SUNRISE FRIDAY MORNING ACROSS THE NORTHWESTERN/NORTHERN CWA.
HAVE INTRODUCED SOME POPS ACROSS THIS AREA...BUT BETTER CHANCES FOR
CONVECTION WILL BE FURTHER NORTH ON THE NOSE OF THE THETA-E RIDGE
INTO CENTRAL/NORTHERN MN. WITH DEWPOINTS INCREASING
TONIGHT...WAA...AND MORE SOUTHERLY COMPONENT TO THE WIND WILL KEEP
OVERNIGHT TEMPS A BIT WARMER THAN IN PREVIOUS NIGHTS WITH MUCH OF
CENTRAL AND WESTERN AREAS IN THE UPPER 60S TO AROUND 70. AREAS
FURTHER EAST WITH A BIT DRIER DEWPOINTS TO STILL COOL OFF MORE
TOWARD THE MID 60S.

.LONG TERM /FRIDAY THROUGH THURSDAY/...
ISSUED AT 402 PM CDT THU JUL 23 2015

FRIDAY WILL SEE THE INFLUENCE OF THE RIDGE SET IN...BRINGING WITH
IT STRONG 850MB WAA AND THETA-E ADVECTION. ALONG AND AHEAD OF
THAT ADVECTION AND A WEAK FRONTAL BOUNDARY...AN MCS MAY BE ONGOING
IN SOUTHERN MINNESOTA AND NORTHERN IOWA FRIDAY MORNING. NAM
GUIDANCE HAS BEEN AGGRESSIVE IN BRINGING IT SOUTH INTO CENTRAL
AND SOUTHEASTERN IOWA AS FAR AS I-80...BUT IS THE LONE WOLF IN
THAT REGARD. POPS REFLECT MORE OF A NORTHERLY TRACK IN LINE WITH
GFS...EURO...AND OTHERS. EVEN SO...POPS MAY BE A BIT AGGRESSIVE
INTO CENTRAL IOWA AS BEST FORCING REMAINS ACROSS NORTHERN IOWA AND
INTO MINNESOTA. CONVECTION WILL BE ELEVATED..AND GIVEN THE AM TIME
FRAME CHANCES FOR SEVERE WILL BE HIGHLY LIMITED. WESTERN COUNTIES
DURING THE AFTERNOON WILL SEE HIGHS AROUND 90 AND WITH DEW PTS
APPROACHING 80...HEAT INDEX VALUES WILL BE NEAR 105 AND A HEAT
ADVISORY HAS BEEN ISSUED FOR THE AFTERNOON.

FRIDAY EVENING A WEAK COLD FRONT WILL PUSH INTO THE
AREA...PROVIDING ANOTHER ROUND OF STORMS. AFTERNOON INSTABILITY
WILL BE QUITE HIGH WITH VALUES APPROACHING 3000-4000+ J/KG MUCAPE.
WITH THE WEAK BOUNDARY...CONVECTION ACROSS NORTHERN AND CENTRAL
IOWA LIKELY WILL NOT GET GOING UNTIL THE LLJ KICKS IN...EVEN WITH
THE CAP EXPECTED TO ERODE BY LATE AFTERNOON. A SEVERE WEATHER
THREAT CERTAINLY EXISTS WITH THE HIGH CAPE VALUES BUT BORDERLINE
SUPPORTIVE SHEAR HINTS AT A LIMITED WINDOW BEFORE STORMS CONGEAL
AND EVOLVE MORE INTO A HEAVY RAIN EVENT IN THE EVENING AND
OVERNIGHT HOURS. THE AFTERNOON/EARLY EVENING THREAT WILL BE FOR
LARGE HAIL AND DAMAGING WINDS.

SATURDAY AND SUNDAY WILL SEE CONTINUED STORM CHANCES ACROSS
CENTRAL AND SOUTHERN IOWA AS THE BOUNDARY STALLS AND LINGERS IN
THE AREA. SEVERE POTENTIAL WILL BE FAIRLY SMALL WITH LIMITED
INSTABILITY FROM EXPECTED LINGERING CLOUD COVER. CHANCES CONTINUE
EARLY IN THE WEEK AS WAVES TOP THE RIDGE...BUT MODEL DISAGREEMENT
SUGGESTS THAT POPS ARE LIKELY OVER DONE EARLY IN THE WEEK. THE
REGION WILL REMAIN UNDER THE INFLUENCE OF THE UPPER LEVEL RIDGE
THROUGH TUESDAY BEFORE A COLD FRONT MOVES THROUGH TUESDAY EVENING AND
NORTHWEST FLOW LOOKS TO SET BACK IN AND TAKE TEMPERATURES BACK
INTO THE LOW TO MID 80S WEDNESDAY AND TO ROUND OUT THE WEEK. IN
THE MEANTIME...TEMPERATURES SHOULD REMAIN SEASONABLE...IN THE
UPPER 80S AND LOW 90S THROUGH TUESDAY.

&&

.AVIATION...24/00Z
ISSUED AT 627 PM CDT THU JUL 23 2015

VFR CONDITIONS EXPECTED FOR THE CRITICAL TAF PERIOD. ISOLD-SCT TSTMS
ARE POSSIBLE ACROSS NORTHERN IOWA LATER TONIGHT...AND HAVE ADDED
VCTS TO THE KMCW AND KALO TAFS. ISOLD-SCT TSTMS MAY PERSIST INTO
CENTRAL IOWA DURG THE DAY FRI...SO HAVE ADDED VCTS TO KDSM TAF.
CONSIDERABLE UNCERTAINTY EXISTS AS TO HOW FAR SOUTH THE CONVECTION
WILL GO HOWEVER.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY FROM 1 PM TO 8 PM CDT FRIDAY FOR ADAIR-ADAMS-
AUDUBON-CARROLL-CASS-CRAWFORD-GUTHRIE-RINGGOLD-SAC-TAYLOR-UNION.

&&

$$

SHORT TERM...BEERENDS
LONG TERM...CURTIS
AVIATION...ZOGG


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