Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 182023
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
323 PM CDT SAT APR 18 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 323 PM CDT SAT APR 18 2015

LONGWAVE TROUGH CONTINUES TO DRIFT EAST TONIGHT WITH WAVE CURRENTLY
ROTATING INTO THE AREA THIS AFTERNOON/EVENING WILL PROVIDE
SUFFICIENT FORCING TO CONTINUE SCT THUNDER OVERNIGHT. TEMPS WILL
SETTLE INTO THE 50S OVERNIGHT AS CHANCES FOR THUNDER DIMINISH TOWARD
MORNING. INSTABILITY CONTINUES TO GEN UP SOME IMPRESSIVE UPDRAFTS
BUT AS THE RAIN FALLS WITH THE PULSE STORMS...CORES ARE COLLAPSING
FAST. THUS...ANY HAIL STILL LOOKS MINOR AND WILL LIKELY REMAIN
BELOW SEVERE LIMITS. CAPE ACROSS THE SOUTHEAST/EAST STILL RANGES
FROM 500 TO 1000 J/KG WITH LLCAPE BETWEEN 125 AND 175 J/KG OVER
THE SOUTHEAST. NST PARAMETER SUGGESTED POTENTIAL FOR
LANDSPOUTS...BUT FOR NOW THE BOUNDARY THAT MIGHT HAVE HELPED
INITIATE SOME HAS MOVED FARTHER NORTH TOWARD US 20. THUS...NOT AS
CONCERNED AT THIS POINT...BUT WILL BE MONITORING. CLOUDS WILL
CONTINUE TONIGHT WITH SOUTH SOUTHEAST FLOW AND BRIEF HEAVY
DOWNPOURS IN SOME OF THE MORE VIGOROUS STORMS. RAINFALL AMOUNTS
MAY REACH UP TO AN INCH OVERNIGHT WITH PONDING OF WATER IN URBAN
AREAS THE MAIN CONCERNS WITH ANY HIGH RAINFALL RATES THAT MAY
OCCUR.

.LONG TERM /SUNDAY THROUGH SATURDAY/...
ISSUED AT 323 PM CDT SAT APR 18 2015

THE TROUGH CURRENTLY TO OUR WEST THAT IS GENERATING SHOWERS AND
STORMS TODAY AND TONIGHT...AS DISCUSSED IN THE SHORT TERM SECTION
ABOVE...BUT WILL FINALLY MOVE ACROSS THE AREA AND CLEAR THINGS OUT
ON SUNDAY NIGHT. DURING THE DAY SUNDAY WE WILL REMAIN WITHIN THE
MODEST WARM ADVECTION REGION AHEAD OF THE TROUGH...RESULTING IN
SCATTERED TO NUMEROUS SHOWERS SIMILAR TO TODAY...AND THEN WILL
LIKELY SEE AN INCREASE IN COVERAGE ACROSS THE EAST AND SOUTHEAST
COINCIDENT WITH THE SURFACE FRONTAL PASSAGE AND DIURNAL
TEMPERATURE MAX. LIKELY TO CATEGORICAL POPS HAVE BEEN MAINTAINED
ACCORDINGLY. HOWEVER...INSTABILITY AND SHEAR ARE LIMITED AND
SEVERE WEATHER IS NOT ANTICIPATED.

ONCE THE FRONT BLOWS THROUGH AND SCOURS THINGS OUT WE WILL SEE
COOL AND RELATIVELY DRY WEATHER FOR THE REMAINDER OF THE WEEK. AN
UPPER LEVEL CYCLONE OVER CENTRAL CANADA WILL SWING DOWN ACROSS THE
GREAT LAKES...PROVIDING REINFORCING SHOTS OF COOL AIR AS WELL AS
AN IMPETUS FOR STRATUS CLOUDS AND A FEW LIGHT SHOWERS AT TIMES.
HAVE TAKEN A BEST GUESS AT TIMING THESE LIGHT SHOWER CHANCES...AND
THEY SHOULD BE CLOSELY TIED TO A DIURNAL CYCLE WITH THE MOST
LIKELY PERIODS IN THE AFTERNOONS AND EVENINGS ON MONDAY AND
TUESDAY.

ANOTHER CONSEQUENCE OF THE TROUGH PASSAGE AND SOUTHWARD DROP OF
THE CANADIAN CYCLONE EARLY IN THE WEEK WILL BE STRONG WINDS. WIND
SPEEDS WILL BE AIDED NOT ONLY BY A FAIRLY TIGHT PRESSURE GRADIENT
BUT ALSO COLD AIR ADVECTION AND EFFICIENT MIXING PER FORECAST
SOUNDINGS. THE STRONGEST WINDS WILL LIKELY COME DURING THE
AFTERNOON HOURS EACH DAY AND MAY REQUIRE ONE OR MORE WIND
ADVISORIES. AT THIS TIME IT APPEARS THAT THE SURFACE BOUNDARY
PASSAGE ON SUNDAY WILL COME LATE ENOUGH IN THE DAY THAT WINDS MAY
NOT REACH CRITERIA BEFORE SUNSET...BUT MONDAY LOOKS PARTICULARLY
WINDY WITH A HIGHER CHANCE OF A HEADLINE BECOMING NECESSARY. THIS
WILL BE CLOSELY MONITORED OVER THE NEXT COUPLE OF DAYS.

FINALLY...AS THE LARGE GYRE THAT MOVED SOUTH OVER THE GREAT LAKES
AS REFERENCED ABOVE FINALLY BEGINS TO MOVE EASTWARD AROUND THE
MIDDLE OF THE WEEK...IT WILL ALLOW A COLD SURFACE HIGH PRESSURE
RIDGE TO SPILL DOWN ACROSS THE MIDWEST FROM WEDNESDAY INTO FRIDAY.
THIS WILL DECREASE THE WINDS BUT ALSO REINFORCE THE COOL AIR IN
PLACE...AND LIKELY LEAD TO FROST AND POSSIBLY EVEN FREEZING
TEMPERATURES ACROSS PORTIONS OF THE AREA DURING THE EARLY MORNING
HOURS THURSDAY AND FRIDAY.

&&

.AVIATION...18/18Z
ISSUED AT 1228 PM CDT SAT APR 18 2015

MAIN CONCERN ARE CONVECTIVE CHANCES THROUGH THE PERIOD WITH CIGS
ADDING SOME COMPLEXITY AS WELL. ISO TO SCT THUNDER NOW DEVELOPING
IN BROAD WARM AIR ADVECTION ZONE OF SOUTHEAST IOWA ALONG A WARM
FRONT. UPPER LEVEL WAVE APPROACHING THE REGION FROM THE WEST ALSO
AIDING IN LARGE SCALE LIFT OVER WESTERN SECTIONS WHICH WILL BEGIN
TO PROGRESS/DEVELOP EAST AFT 20Z AND CONTINUE THROUGH 06Z...WITH
ANOTHER SHOT OF SHOWERS OR THUNDER AFT 15Z SUNDAY. WINDS WILL
REMAIN NEAR 10-12KTS WITH THE EXCEPTION OF TROUGH AXIS WHERE LIGHT
WINDS AND MVFR BR MAY DEVELOP. /REV

&&

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

&&

$$

SHORT TERM...REV
LONG TERM...LEE
AVIATION...REV


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