Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 241131
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
631 AM CDT SUN AUG 24 2014

.SHORT TERM /TODAY/...
ISSUED AT 400 AM CDT SUN AUG 24 2014

THE FORECAST FOR TODAY IS A BIT WARMER AND GENERALLY DRY WITH MODEST
SOUTHERLY FLOW AND WARMER TEMPERATURES ALOFT. CURRENTLY SCATTERED
THUNDERSTORMS ARE MOVING NORTHWARD ALONG THE IOWA/NEBRASKA BORDER
BUT SLOWLY DEVELOPING EASTWARD ON FORWARD PROPAGATING OUTFLOW
BOUNDARIES. A FEW STORMS COULD MAKE IT INTO OUR WESTERN COUNTIES
EARLY THIS MORNING BUT SHOULD FADE THE FURTHER EAST THEY GET AND NO
IMPACTS ARE ANTICIPATED AS THE STORMS QUICKLY DIE OFF AROUND
SUNRISE. THE NEXT FORECAST CHALLENGE FOR THE DAY WILL BE THE DEGREE
OF WARMING. MODEL GUIDANCE HAS BEEN TOO WARM THE PAST FOUR
CONSECUTIVE DAYS BUT THERE WAS CONSIDERABLE EARLY MORNING CONVECTION
AND ENSUING CLOUD DEBRIS ON EACH OF THOSE DAYS...WHICH SHOULD NOT BE
THE CASE TODAY AND IMPLIES WARMER TEMPERATURES. HOWEVER...LOW LEVEL
WINDS WILL STILL BE MORE IN THE 160 TO 180 RANGE RATHER THAN WEST OF
SOUTH...AND DEWPOINTS WILL CONTINUE TO HOVER IN THE LOW TO MID 70S
MITIGATING SURFACE HEATING. GIVEN THESE FACTORS WILL STICK WITH A
MAX TEMP FORECAST WARMER THAN YESTERDAY...BUT SLIGHTLY BELOW
GUIDANCE AND THE PREVIOUS FORECAST AS CONSIDERABLE UNCERTAINTY
REMAINS IN THIS AREA. FINALLY...LATE IN THE DAY MORE THUNDERSTORMS
SHOULD DEVELOP AROUND NORTHWEST IOWA ALONG A SLOWLY ADVANCING AND
DECAYING FRONTAL BOUNDARY. AT THIS TIME IT APPEARS ANY STORMS WILL
NOT ENTER OUR AREA UNTIL NEAR OR AFTER 00Z AND HAVE GONE WITH ONLY
LOW POPS IN THE NORTHWEST AND WEST THROUGH THAT TIME...LEAVING
HIGHER POPS FOR THE TONIGHT PERIOD AS OUTLINED IN THE LONG TERM
DISCUSSION.

.LONG TERM /TONIGHT THROUGH SATURDAY/...
ISSUED AT 400 AM CDT SUN AUG 24 2014

AN ACTIVE PATTERN FOR MUCH OF THE WEEK AS A SFC BOUNDARY SINKS
SLOWLY SOUTH THROUGH THE AREA MONDAY THROUGH WEDNESDAY THEN RETURN
NORTH AGAIN ON THURSDAY. PEAK THUNDERSTORM CHANCES WILL ARRIVE
WITH PASSING SHORT WAVES DURING THE PERIOD WITH THE FOCUS ON
MONDAY AND TUESDAY NIGHTS. THUNDERSTORMS ARE POSSIBLE
TONIGHT WITH THE INITIAL BOUNDARY INTRUSION. THE OVERALL FORCING
IS MODEST THEREFORE EXPECT STORMS TO REMAIN SCATTERED ALONG THE
BOUNDARY. THIS ACTIVITY WILL LINGER INTO MONDAY BEFORE
DIMINISHING. CONVECTIVE DEBRIS LINGERING INTO MONDAY MAY HAVE AN
IMPACT ON HIGH TEMPERATURES BUT AT THIS TIME EXPECT AROUND 80 FAR
NORTHWEST TO THE LOWER 90S SOUTHEAST.

THUNDERSTORM CHANCES INCREASE MONDAY NIGHT AS A 35 KT LOW LEVEL
JET DEVELOPS AND BRINGS ANOTHER SURGE OF MOISTURE ADVECTION THE
STATE WITH PWATS SURPASSING 1.75 INCHES. THE OVERALL SCENARIO WILL
FEATURE A FOCUSED AREA OF ISENTROPIC LIFT AND THUNDERSTORM
DEVELOPMENT. THE POTENTIAL FOR TRAINING OF SLOW MOVING STORMS
ALONG THE INSTABILITY AXIS EXISTS MONDAY NIGHT AND WITH CONDITIONS
AGAIN FAVORABLE FOR EFFICIENT RAINFALL PRODUCING STORMS...AN AREA
OF HEAVY RAIN IS POSSIBLE. THE POTENTIAL FOR THUNDERSTORMS WILL
RETURN AGAIN TUESDAY NIGHT INTO WEDNESDAY. WHILE THE SFC BOUNDARY
WILL DROP SOUTH OF THE STATE...STRONG MOISTURE ADVECTION WILL
OVERRIDE THE SFC BOUNDARY WITH GOOD ISENTROPIC UPGLIDE FOCUSED
OVER IOWA AGAIN. THIS ROUND OF STORMS WILL HAVE STRONGER KINEMATIC
FORCING THAN MONDAY NIGHT AS A COUPLE IMPULSES PASS OVER THE AREA.
PWAT VALUES WILL BE NEAR 2 INCHES DURING THIS EVENT AND AGAIN
HEAVY RAINFALL IS A CONCERN. THE THREAT OF HEAVY RAINFALL LOOKS TO
BE MORE WIDESPREAD MONDAY NIGHT AND ESPECIALLY TUESDAY NIGHT THAN
THE PAST SEVERAL DAYS AND CERTAINLY HYDRO IMPACTS MAY OCCUR. THE
THREAT FOR SOME SEVERE WEATHER DOES EXIST WITH THE PRIMARY THREAT
BEING DAMAGING WINDS.

CONTINUE TO PREFER THE SLOWER EC/GEM SOLUTIONS FOR THE CLOSED LOW
MOVING OUT OF THE WEST AND TOWARDS THE AREA MID TO LATE WEEK. THE
GFS CONTINUES TO BE MORE PROGRESSIVE HOWEVER...ITS ENSEMBLE MEAN
IS TRENDING SLOWER AND MORE ECMWF LIKE. THIS SOLUTION WILL KEEP
POPS AROUND INTO AT LEAST THURSDAY. TEMPERATURES FOR THE WEEK WILL
BE ON THE DOWNWARD TREND TUESDAY AND WEDNESDAY AND MAY BE EVER
COOLER SHOULD CONVECTIVE DEBRIS LINGER ALL DAY.

&&

.AVIATION...24/12Z
ISSUED AT 631 AM CDT SUN AUG 24 2014

FOG/STRATUS HAS DEVELOPED ACROSS EASTERN IOWA EARLY THIS MORNING
AND IS PRODUCING IFR OR LOWER CONDITIONS AT MCW/ALO/OTM. THIS
SHOULD BURN OFF BY AROUND 14Z...PERHAPS A LITTLE LATER AT
ALO...AFTER WHICH VFR CONDITIONS WILL PREVAIL THROUGH THE
REMAINDER OF THE TAF PERIOD. THERE ARE THUNDERSTORM CHANCES AFTER
DARK TONIGHT MAINLY AT FOD/MCW...BUT THE PROBABILITY IS TOO LOW
FOR INCLUSION IN TAFS ATTM. THERE IS ALSO SOME POSSIBILITY OF MORE
FOG/STRATUS DEVELOPMENT AFTER 06Z MONDAY MORNING...BUT AGAIN
CONFIDENCE TOO LOW TO MENTION IN TAFS AT THIS RANGE.

&&

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

&&

$$

SHORT TERM...LEE
LONG TERM...DONAVON
AVIATION...LEE


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