Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 190458
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1158 PM CDT SAT APR 18 2015

.UPDATE...
ISSUED AT 721 PM CDT SAT APR 18 2015

INSTABILITY ACROSS THE CWA IS WEAKENING...WITH PRECIP SUPPORT
ALSO WEAKENING AS MOISTURE ADVECTION LESSENS. THEREFORE HAVE
CONFINED THUNDERSTORM WORDING TO THE HIGHER RADAR RETURNS AND
HIGHER AXIS OF MUCAPE NOSING UP INTO THE EASTERN CWA FOR THE
EVENING HOURS AND REMOVED THUNDER WORDING FOR LATE TONIGHT. EXPECT
A LULL IN ACTIVITY TOWARD THE LATE EVENING TO AROUND
MIDNIGHT...WITH MOISTURE ADVECTION PICKING BACK UP ACROSS THE
EASTERN CWA LATE TONIGHT TOWARD SUNRISE. THEREFORE COULD SEE AN
AREA OF SHOWERS FILL BACK IN ACROSS THE EAST LATE TONIGHT BEFORE
THE ENTIRE AREA LIFTS TO THE EAST NORTHEAST SUNDAY. THEREFORE HAVE
TRIED TO HIGHLIGHT WITH SOME FINER DETAIL IN THE POPS/WX.

&&

.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...19/06Z
ISSUED AT 1155 PM CDT SAT APR 18 2015

SCATTERED SHOWERS WILL PERSIST THROUGH MUCH OF THE TAF PERIOD WITH
PERIODS OF MVFR OR LOWER CONDITIONS IN THE HEAVIER RAIN. WINDS
WILL SWITCH TO THE NORTHWEST AND INCREASE TO 15 TO 20 KTS SUNDAY
AFTERNOON AND EVENING AS A COLD FRONT PUSHES ACROSS THE STATE.
THIS FRONT WILL ALSO BRING THE PRECIP TO AN END FROM NORTHWEST TO
SOUTHEAST.

&&

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

$$

UPDATE...BEERENDS
SHORT TERM...REV
LONG TERM...LEE
AVIATION...SKOW


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