National Weather Service National Headquarters

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

000
FXUS63 KLSX 150838
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
338 AM CDT WED MAY 15 2013

.SHORT TERM...(THROUGH LATE THIS AFTERNOON)
ISSUED AT 322 AM CDT WED MAY 15 2013

MAIN CONCERN IS THE POTENTIAL FOR A FEW STRONG THUNDERSTORMS THIS
AFTERNOON.  A COLD FRONT CURRENTLY STRETCHES ACROSS EASTERN AND
SOUTHERN IOWA INTO SOUTHERN NEBRASKA.  THIS FRONT WILL BE ABLE TO
MOVE INTO NORTHERN MO/CENTRAL IL THIS AFTERNOON BEFORE IT STALLS
BETWEEN THE STRONG WESTERLIES OVER THE UPPER MIDWEST AND THE UPPER
LOW OVER THE SOUTHERN PLAINS.  THIS FRONT WILL PRODUCE SOME WEAK
CONVERGENCE OVER THE NORTHERN PART OF THE CWA.  AT THE SAME TIME...
THERE WILL BE SOME WEAK ASCENT THAT WILL MOVE INTO THE AREA FROM THE
SOUTHWEST AHEAD OF A VORT LOBE AND ASSOCIATED 925-850MB MOISTURE
CONVERGENCE.

WHILE NONE OF THIS FORCING IS PARTICULARLY IMPRESSIVE...INSTABILITY
WILL BE INCREASING TODAY AS DEWPOINTS INCREASE TO NEAR 60.  THESE
VALUES ARE BELOW THE FORECAST VALUES OF THE MODELS BECAUSE THEY HAVE
HAD A WET BIAS THE PAST FEW DAYS...BUT DO THINK THAT TEMPERATURES
COULD VERY WELL BE A FEW DEGREES WARMER THAN MOS GUIDANCE GIVEN THE
CURRENT READINGS ARE RELATIVELY WARM AND FORECAST SOUNDINGS SHOW
MIXING INTO THE 850-800MB RANGE.  CURRENTLY THINK THAT ANY
THUNDERSTORM DEVELOPMENT WILL BE SCATTERED AS A PROGGED WARM LAYER
BETWEEN 800-700MB WILL LIMIT AREAL EXTENT.  DO NOT EXPECT ORGANIZED
THUNDERSTORMS TODAY...THOUGH WITH MLCAPES AROUND 1500 J/KG AND DEEP
MIXING SUGGEST THAT SOME LOCALLY STRONG WIND GUSTS WILL BE POSSIBLE
WITH A FEW STORMS.

BRITT

.LONG TERM...(TONIGHT THROUGH TUESDAY)
ISSUED AT 322 AM CDT WED MAY 15 2013

THE HIGHEST PROBABILITY FOR SHOWERS AND STORMS SHOULD OCCUR ACROSS
NERN MO AND W CNTRL IL TGT ALONG AN E-W FRONT. MORE SCATTERED
ACTIVITY IS EXPECTED FURTHER S ACROSS PORTIONS OF SERN MO AHEAD OF
A SLOW MOVING UPPER LEVEL TROUGH/LOW. THIS FRONT SHOULD WEAKEN AND
BECOME MORE NW TO SE ORIENTED THU AS A SFC RIDGE MOVES EWD
THROUGH THE GREAT LAKES REGION WITH THE WRN PORTION OF THE FRONT
LIFTING NWD. THE UPPER LEVEL LOW/TROUGH WILL MOVE EWD THROUGH SRN
MO AND NRN AR. THERE SHOULD BE AT LEAST SCATTERED STORMS OVER MUCH
OF THE FORECAST AREA ON THU. HIGH TEMPERATURES ON THU WILL BE COOLER
...ALBEIT STILL ABOVE SEASONAL NORMALS. MAY GET A BREAK IN THE
CONVECTION THU NGT AS THE FRONT MOVES N-NE OF OUR FORECAST AREA
AND THE UPPER LEVEL TROUGH/LOW SHIFTS SE OF THE REGION. A MID LEVEL
VORT MAX MOVING E-SEWD THROUGH NRN MO MAY LEAD TO SCATTERED
CONVECTION ON FRI...ALTHOUGH IT APPEARS THAT THE GFS MODEL IS TOO
STRONG WITH THIS FEATURE AND OVERDONE WITH ITS QPF. THE UPPER
LEVEL RIDGE WILL BUILD BACK OVER THE CNTRL US FRI NGT INTO THE
WEEKEND. THIS ALONG WITH CONTINUED SLY SFC/LOW LEVEL FLOW WILL
LEAD TO WARMER HIGH TEMPERATURES WELL INTO THE 80S FOR THE
WEEKEND. THE GFS MODEL STILL APPEARS OVERDONE WITH ITS QPF...
ALTHOUGH THERE MAY BE ISOLATED TO WIDELY SCATTERED SHOWERS AND
STORMS MAINLY DURING THE AFTN INTO THE EARLY EVNG ON SAT. THE
POPS SHOULD BEGIN TO RAMP UP BEGINNING SUN AFTN...MAINLY ACROSS
NERN AND CNTRL MO AS SW FLOW SHORTWAVES AHEAD OF AN APPROACHING
UPPER LEVEL TROUGH MOVE NEWD THROUGH THIS REGION. THE MODELS
CONTINUE TO SLOW THE PROGRESSION OF THE UPPER LEVEL TROUGH/LOW
MOVING EWD THROUGH THE NRN PLAINS AND ITS ASSOCIATED COLD FRONT.
WE SHOULD SEE MORE WIDESPREAD AND ORGANIZED CONVECTION MON AND
MON NGT AHEAD OF THIS UPPER LEVEL TROUGH AND ASSOCIATED COLD
FRONT. THE COLD FRONT SHOULD FINALLY MOVE SEWD THROUGH OUR
FORECAST AREA TUE AND TUE EVNG WITH TEMPERATURES DROPPING BACK
DOWN TO SEASONAL NORMALS FOR TUE AND TUE NGT.

GKS

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1157 PM CDT TUE MAY 14 2013

VFR CONDITIONS WILL PREVAIL THRU THE VALID TAF PERIOD. DRY
CONDITIONS ARE ALSO EXPECTED THRU AT LEAST MIDDAY WEDNESDAY. A
CDFNT WILL EDGE INTO NEAR THE KUIN WEDNESDAY AFTERNOON AND IS
EXPECTED TO ULTIMATELY ACT AS A FOCUS FOR TSRA DEVELOPMENT BY LATE
AFTERNOON AND CONTINUE INTO THE EVENING. MAINTAINED VCTS AT THE
KUIN TAF DURING THIS TIME PERIOD. TSRA CHCS FOR THE OTHER TAF
SITES LOOKS MORE UP IN THE AIR AND HARD TO GET A FIRM HANDLE ON
FOR INCLUSION IN THE TAF AS THE COVERAGE SHOULD BE MORE SPARSE.
WHAT DOES DEVELOP S OF THE CDFNT LATE WEDNESDAY AFTERNOON SHOULD
DISSIPATE BY MID EVENING WITH LITTLE TO SUSTAIN IT. GUSTY SW SFC
WNDS WILL DIMINISH AROUND OR SHORTLY AFTER SUNSET. 50KT LO LEVEL
JET IN PROGRESS THE REST OF THE OVERNIGHT...AND LLWS WITH A LO
BASE JET AROUND 1100FT AND MAGNITUDE OF 40-45KTS OR MORE IS
JUSTIFIED.

SPECIFICS FOR KSTL...VFR THRU THE PERIOD...TSRA A POSSIBILITY LATE
WED AFTERNOON AND EARLY EVENING BUT PROBS TOO LO TO INCLUDE AT
THIS TIME...GUSTY SW SFC WNDS TO DIMINISH SHORTLY AFTER SUNSET...
LLWS ADDED WITH 40-45KT LO BASE JET MOVING THRU.

TES

&&

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

$$

WFO LSX