National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KLSX 250213
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
913 PM CDT FRI MAY 24 2013

.UPDATE...
ISSUED AT 828 PM CDT FRI MAY 24 2013

MOST OF THE CONVECTION MOVING E-SEWD THROUGH CNTRL IA WILL LIKELY
REMAIN N OF OUR FORECAST AREA LATE THIS EVNG...AND SHOULD ALSO
WEAKEN AS IT GETS FURTHER E AND ENCOUNTERS DRIER AND MORE STABLE LOW
LEVEL AIR NEAR SFC RIDGE EXTENDING FROM THE GREAT LAKES REGION S
THROUGH ERN MO AND IL. MORE CONVECTION WILL DEVELOP ACROSS
NEBRASKA AND WRN IA AS A S-SWLY LOW LEVEL JET STRENGTHENS OVER THE
PLAINS. THIS ACTIVITY WILL LIKELY MOVE E-SEWD INTO PORTIONS OF NERN
MO AND W CNTRL IL LATE TGT INTO EARLY SAT MRNG...ALTHOUGH IT WILL
LIKELY WEAKEN AS IT GETS FURTHER E-SE INTO OUR FORECAST AREA. HIGH
LEVEL CONVECTIVE DEBRIS CLOUDINESS WILL STREAM NEWD INTO SERN MO
FROM CONVECTION OVER THE SRN PLAINS. MID-HIGH LEVEL CLOUDS WILL
DEVELOP AND ADVECT INTO NERN MO AND W CNTRL IL AS LOW-MID LEVEL
WAA INCREASES OVER THIS AREA LATE TGT. LOW TEMPERATURES TGT WILL BE
QUITE COOL AGAIN ACROSS SERN MO AND SWRN IL NEAR THE SFC RIDGE
AXIS...BUT LOW TEMPERATURES WILL BE WARMER THAN THE PREVIOUS NGT
ACROSS NERN AND CNTRL MO WHERE THERE WILL BE INCREASED CLOUD
COVER...INCREASING SELY/SLY SFC/BOUNDARY LAYER WINDS...AND RISING
OR AT LEAST HIGHER SFC DEW POINTS.

GKS

&&

.SHORT TERM...(THROUGH LATE TONIGHT)
ISSUED AT 353 PM CDT FRI MAY 24 2013

COOL CANADIAN SURFACE RIDGE HOLDING TOUGH LATE THIS AFTERNOON FROM
LAKE MICHIGAN TO SE MO.  RIDGE WILL LOOSEN ITS GRIP OVER THE REGION
OVERNIGHT AS IT CONTINUES TO DRIFT SE...ALLOWING SE FLOW THAT HAS
DEVELOPED OVER MID MO TODAY TO DEVELOP/STRENGTHEN ACROSS THE
REMAINDER OF THE CWA.  PRIMARY QUESTION FOR TONIGHT IS IF/WHEN
CONVECTION WILL BEGIN TO THREATEN AREA. CONSENSUS OF 12Z GUIDANCE
IS A BIT SLOWER WITH INTENSIFICATION OF LOW LEVEL JET INTO THE
MISSISSIPPI VALLEY...AND A BIT FURTHER N WITH THE 850MB THETA-E
BULLS-EYE...THAN INDICATED BY EARLIER RUNS. THIS WOULD SUGGEST POPS
BULLS-EYE WOULD PRIMARILY BE TO OUR N ACROSS IOWA...WITH SOME OF
THIS ELEVATED SHOWER AND ISOLATED THUNDERSTORM ACTIVITY POSSIBLY
DROPPING SOUTH DURING THE PREDAWN HOURS. I`VE DELAYED THE ONSET OF
THE PRECIP IN OUR N COUNTIES BY AN HOUR OR SO...BUT DO ALLOW
CHANCE POPS TO DROP AS FAR S AS A COU-PPQ LINE BY 6 AM. THIS MAY
BE TOO FAR S...BUT TRYING TO LEAVE SOME LEEWAY AS 850MB WAA DOES
SHOW A SUBTLE INCREASE FROM SE IA INTO N OZARKS DURING THE PREDAWN
HOURS.

TEMPERATURE-WISE...HAVE ATTEMPTED TO DEPICT IMPACT OF RETREATING
SURFACE RIDGE OVER SE PART OF THE CWA WITH MINS IN THE 40S...WHILE
INCREASING WINDS AND CLOUDS SHOULD MEAN LOWS IN THE L-M50S OVER NW
PART OF THE CWA.

TRUETT

.LONG TERM...(SATURDAY THROUGH NEXT FRIDAY)
ISSUED AT 353 PM CDT FRI MAY 24 2013

SFC HIGH PRESSURE CENTER OVER THE GRTLKS WILL SHIFT EWD ON
SATURDAY WHILE A PERSISTENT LEE SIDE LOW OVER THE PLAINS PUSHES A
BAROCLINIC ZONE NEWD AS A WMFNT. THIS WILL CAUSE WINDS TO BECOME
SELY TO SLY ACROSS THE LSX CWA WITH THE WMFNT STRETCHING ALONG THE
MO/IL BORDER THROUGH SUNDAY BEFORE THE BDRY LIFTS FARTHER NWD. A
GENERAL WARMING TREND IS EXPECTED THROUGH NEXT WEEK HOWEVER THERE
WILL PROBABLY BE A COUPLE OF COOLER DAYS MIXED IN DUE TO THE
EFFECTS OF NOCTURNAL MESOSCALE CONVECTIVE SYSTEMS /EITHER UPSTREAM
OR OVERHEAD/. THESE EFFECTS MAY INCLUDE LINGERING SHRA...THICK
CLOUD COVER...AN MCV WHICH FOCUSES SCT AFTN TSRA...AND/OR OUTFLOW
BDRYS WHICH PUSH THE EFFECTIVE WMFNT FARTHER SOUTH THAN WAS
PREVIOUSLY FCST. TEMPERATURE TRENDS IN THE PREVIOUS FCST LOOK
REASONABLE AND FEW CHANGES WERE REQUIRED.

AS FOR PCPN CHCS...MODELS CONTINUE TO SHOW A COUPLE OF VORT MAXES
WHICH MAY SUPPORT SCT AFTN SHRA/TSRA AS THEY MOVE ACROSS THE AREA
OVER THE NEXT SEVERAL DAYS. A PERSISTENT AND REDEVELOPING LLJ
INTERACTING WITH A BAROCLINIC ZONE WILL ALSO SUPPORT NOCTURNAL
THUNDERSTORM DVLPMT ACROSS PARTS OF THE CENTRAL CONUS OVER THE NEXT
COUPLE OF NIGHTS. SOME OF THE TSRA CLUSTERS WILL PROBABLY CONGEAL
INTO MESOSCALE CONVECTIVE SYSTEMS AND COULD MOVE INTO THE LSX CWA
/BASED ON CORFIDI VECTOR FCSTS/ DEPENDING ON WHERE THEY INITIALLY
FORM...AND WHERE THEY INITIALLY FORM EACH NIGHT WILL DEPEND ON THE
POSITION OF THE EFFECTIVE WMFNT WHICH MAY END UP BEING PUSHED
FARTHER SOUTH BY OUTFLOW BDRYS. THESE MESOSCALE DETAILS CANNOT BE
ACCURATELY FCST VERY FAR IN ADVANCE. IN OTHER WORDS...WE EXPECT TO
SEE UNSETTLED WEATHER THROUGH EARLY NEXT WEEK BEFORE THE WARM FRONT
LIFTS FAR ENOUGH NORTH TO LIMIT THE MCS POTENTIAL.

BY THE MIDDLE OF NEXT WEEK...THE UPPER AIR PATTN OVER THE CENTRAL
CONUS WILL SHIFT FROM RIDGING TO SW FLOW AFTER A TROF BECOMES
ESTABLISHED OVER THE WRN HALF OF THE COUNTRY. GFS/ECMWF DISAGREE ON
THE AMPLITUDE OF THE TROF AND ON THE POSITION OF A STRONG VORT MAX
WITHIN IT. THE VORT MAX MAY BRING A CHANCE OF PCPN TO MO/IL WHEN IT
LIFTS THROUGH THE PLAINS LATE NEXT WEEK HOWEVER THERE IS
CONSIDERABLE UNCERTAINTY ATTM DUE TO MODEL DISAGREEMENT.

KANOFSKY

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 649 PM CDT FRI MAY 24 2013

WHILE THERE ARE CHANCES FOR SHRA/TSRA OVER THE AREA BEGINNING
LATE TONIGHT AND CONTINUING THROUGH THE TAF PERIOD... CONFIDENCE
IS NOT HIGH ENOUGH TO INCLUDE MENTION OF RAIN AT THIS POINT. ONE
EXCEPTION IS THAT I HAVE INCLUDED A PROB30 GROUP AT KUIN TOMORROW
MORNING WHEN I EXPECT AN AREA OF -SHRA TO BE DROPPING SOUTHWARD
OUT OF IOWA. THIS AREA COULD DROP FURTHER INTO THE ST. LOUIS METRO
TAF SITES MID- LATE MORNING...BUT THERE IS TOO MUCH UNCERTAINTY TO
INCLUDE AT THIS POINT. THERE IS ALSO THE POTENTIAL FOR STORMS TO
GENERATE AS A WARM FRONT MOVES NORTHEAST THROUGH THE REGION DURING
THE LATE AFTERNOON/EARLY EVENING HOURS.

EXPECT MAINLY VFR CONDITIONS THE NEXT 24-30 HOURS. THE EXCEPTION WILL
BE MVFR/POSSIBLY IFR CEILINGS/VISIBILITIES ASSOCIATED WITH THE HEAVIER
-SHRA/-TSRA.

SPECIFICS FOR KSTL...EXPECT DRY AND VFR CONDITIONS THE NEXT 30 HOURS.
THERE IS A SMALL CHANCE OF -SHRA/-TSRA ON SATURDAY AFTERNOON/
EVENING AS A WARM FRONT APPROACHES THE TERMINAL FROM THE
SOUTHWEST. HOWEVER...CHANCES ARE TOO LOW TO INCLUDE IN THE
FORECAST AT THIS TIME.

BRITT

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&

$$

WFO LSX