National Weather Service Weather Forecast Office

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

000
FXUS63 KLSX 232033
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
333 PM CDT THU MAY 23 2013

.SHORT TERM...(THROUGH LATE TONIGHT)
ISSUED AT 325 PM CDT THU MAY 23 2013

SECONDARY SHORTWAVE DROPPING DOWN BACK SIDE OF GREAT LAKES TROF HAS
MAINTAINED A FEW SPOTTY SHOWERS OVER THE AREA THIS AFTERNOON.  THINK
MOST OF THIS ACTIVITY WILL EITHER ADVECT OUT OF OUR AREA OR
DISSIPATE BY 00Z...BUT WILL WATCH RADAR TRENDS TO DETERMINE IF ANY
OF THIS ACTIVITY WILL PERSIST INTO THE EARLY EVENING.  IF IT
DOES...IT SHOULDN`T LAST MUCH PAST SUNSET.

RATHER EXTENSIVE AND PERSISTENT SC DECK IS ALSO HOLDING TOUGH ACROSS
AREA.  HOWEVER CEILINGS HAVE BEEN INCREASING AND VISIBLE SATELLITE
IMAGERY SUGGESTS CLOUDS ARE BECOMING A BIT MORE CUMULIFORM WITH
TIME....SO BELIEVE CLEARING IS STILL IN THE OFFING DURING THE EARLY
EVENING HOURS.

SINCE WE`RE STILL LEANING TOWARDS A DECREASING CLOUD TREND
TONIGHT...I`VE REMAINED ON THE COOL SIDE OF GUIDANCE FOR MINS.
TEMPERATURES WILL BEGIN THE EVENING ON THE CHILLY SIDE...AND WITH
THE SWD PUSH OF THE SURFACE RIDGE INTO THE AREA WINDS SHOULD BE
RATHER LIGHT AND DEWPOINTS SHOULD BE FAIRLY LOW DURING TIME OF MAX
RADIATIONAL COOLING.

TRUETT

.LONG TERM...(FRIDAY THROUGH NEXT THURSDAY)
ISSUED AT 325 PM CDT THU MAY 23 2013

THE MAIN FCST ISSUES CONTINUE TO BE TEMPERATURE TRENDS AND PCPN CHCS.

A STRONG SFC HIGH WILL CONTINUE BUILDING INTO THE WRN GRTLKS ON FRI
WITH THE RIDGE AXIS EXTENDING SWD INTO MO/IL. ELY SFC FLOW AROUND
THE HIGH WILL KEEP TEMPERATURES SEASONABLY COOL ON FRI/FRI NIGHT
IN ADDITION TO REINFORCING A BAROCLINIC ZONE ACROSS THE PLAINS.
MEANWHILE...A DVLPG LOW PRESSURE SYSTEM OVER THE PLAINS WILL
REORIENT THE AFOREMENTIONED BAROCLINIC ZONE AND LIFT IT NEWD AS A
WMFNT. TEMPERATURES WILL WARM UP QUICKLY ON SAT ACROSS CENTRAL MO
DUE TO BOTH THE WMFNT AND THE LATE MAY SUN ANGLE. THE EXTENT OF
WARMING ACROSS WRN/SWRN IL FOR THE WEEKEND IS MORE IN QUESTION
BECAUSE OF UNCERTAINTIES REGARDING THE LOCATION OF NOCTURNAL
MESOSCALE CONVECTIVE SYSTEMS AND THE EFFECT OF THEIR OUTFLOWS ON
THE POSITION OF THE EFFECTIVE FRONT. TEMPERATURES ACROSS WRN/SWRN
IL WILL WARM UP ONCE THE FRONT LIFTS FARTHER NORTH...BUT THAT MAY
NOT HAPPEN UNTIL MONDAY. TEMPERATURES ACROSS THE AREA WILL ALSO
DEPEND ON THE EXTENT OF REMNANT CLOUD COVER FROM OVERNIGHT
CONVECTION THAT OCCURS UPSTREAM.

GENERALLY DRY CONDITIONS ARE EXPECTED THROUGH FRI NIGHT HOWEVER
NOCTURNAL CONVECTION DRIVEN BY THE LLJ MAY REACH THE NWRN CWA ON
LATE FRI NIGHT/EARLY SAT MORNING. A FEW VORT MAXES MAY TRY TO
UNDERCUT THE UPPER RIDGE THAT WILL BE IN PLACE OVER THE CENTRAL
CONUS THROUGH EARLY NEXT WEEK...AND THESE FEATURES MAY SUPPORT SCT
SHRA/TSRA AT TIMES. ADDITIONALLY...THE FCST WX PATTERN WILL BE
CONDUCIVE FOR NIGHTLY MCS DVLPMT ACROSS VARIOUS PARTS OF THE
CENTRAL CONUS. SOME OF THESE THUNDERSTORM COMPLEXES MAY MOVE
ACROSS THE LSX CWA DEPENDING ON THE POSITION OF THE EFFECTIVE
FRONT EACH NIGHT AND ITS ORIENTATION WITH RESPECT TO THE LLJ AXIS.
UPSTREAM CONVECTION COULD ALSO PRODUCE AN MCV WHICH THEN FOCUSES
TSRA DVLPMT IN OUR AREA ON THE FOLLOWING AFTN. THESE KINDS OF
MESOSCALE DETAILS CANNOT BE FCST VERY FAR IN ADVANCE THEREFORE
THIS FCST PACKAGE MAINTAINS CHC POPS /HIGHER VALUES WHERE MODELS
SEEM TO BE IN SLIGHTLY BETTER AGREEMENT/ FOR SEVERAL DAYS WHERE
THUNDERSTORMS ARE POSSIBLE BUT MESOSCALE DETAILS ARE UNKNOWN ATTM.

A PATTERN SHIFT WILL BE UNDERWAY BY THE MIDDLE OF NEXT WEEK ONCE A
CLOSED LOW PRESSURE SYSTEM DVLPS OVER THE SWRN CONUS AND SHIFTS THE
UPPER AIR PATTN OVER MO/IL FROM RIDGING TO SW FLOW. GFS/ECMWF DEPICT
VERY DIFFERENT SCENARIOS FOR HOW THE LOW LIFTS INTO THE PLAINS
THEREFORE GENERALLY FOLLOWED THE RECOMMENDED CR INITIALIZATION FOR
TUE AND BEYOND.

KANOFSKY

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1225 PM CDT THU MAY 23 2013

BEGINNING TO SEE SOME THIN SPOTS IN THE HIGH END MVFR CIGS THAT
BLANKET AREA. THIS SHOULD ALLOW FOR AN INCREASE IN LOW LEVEL
MIXING THAT SHOULD CAUSE CEILING HEIGHTS TO INCREASE TO LOW END
MVFR NO LATER THAN MID AFTERNOON. THIS TREND TOWARDS THE CLOUD
DECK BECOMING MORE CUMULIFORM SHOULD ALSO MEAN A GRADUAL CLEARING
TREND DURING THE LATE AFTERNOON AND EARLY EVENING HOURS AS HEATING
EBBS AND AS CYCLONIC LOW LEVEL CURVATURE DECREASES WITH THE SWD
PUSH OF THE SURFACE RIDGE. ONCE CLEARING OCCURS...EXPECTING CLEAR
SKIES AND LIGHT NE/E WINDS FOR THE REMAINDER OF THE OVERNIGHT
HOURS AND INTO FRIDAY MORNING.

SPECIFICS FOR KSTL...CIGS OVER KSTL SHOULD INCREASE TO 3-4KFT BY
MID AFTERNOON WITH N WINDS 10-15KTS. THIS VFR CLOUD DECK SHOULD
ERODE DURING THE EVENING...LEAVING CLEAR SKIES FOR MUCH OF THE
NIGHT WITH NE WINDS 4-8KTS.

TRUETT

&&

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

$$

WFO LSX