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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1615Z Aug 20, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1215 PM EDT WED AUG 20 2014

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM AUGUST 20 AT 00UTC): MODELS CONTINUE
TO MAKE PATTERN CORRECTIONS TO MID LEVEL TROUGH ENTERING THE
CONTINENT DURING THE MEDIUM RANGE PERIOD. BOTH THE GFS AND UKMET
MADE MAJOR PATTERN CORRECTIONS...WITH THE GFS NOW FAVORING A
WEAKER PERTURBATION TO CROSS THE ANDES INTO ARGENTINA. THE
UKMET... MEANWHILE...IS NOW TRENDING TOWARDS A DEEPER TROUGH TO
MOVE ACROSS ARGENTINA. THE ECMWF IS THE ONLY ONE THAT IS
MAINTAINING CYCLE-TO-CYCLE CONTINUITY...FAVORING A STRONGER WAVE
THAN WHAT THE GFS SUGGESTS BUT NOT AS INTENSE AS FORECASTED BY THE
UKMET. THESE APPEARS AS THE COMPROMISE SOLUTION...AND IT IS WELL
SUPPORTED BY THE MEAN OF THE ENSEMBLE MODEL GUIDANCE. CONFIDENCE
IN THE FORECAST IS HIGH.

DEEP TROUGH ON THE NORTHERN STREAM DOMINATES FLOW ACROSS THE
EASTERN PACIFIC...WITH MID LEVEL PERTURBATION ENVELOPING AREA
BETWEEN 110W-90W AND TO THE SOUTH OF 15S. THIS IS PRESSING AGAINST
A BLOCKING RIDGE TO THE EAST. AS THEY COLLIDE...THE TROUGH IS TO
FOCUS SUBTROPICAL MOISTURE AND SHORT WAVE ENERGY ACROSS CHILE
SOUTH OF CONCEPCION.  THROUGH 72 HRS THE RIDGE TO THE EAST IS TO
WEAKEN ENOUGH TO ALLOW TROUGH TO SPILL ACROSS THE CENTRAL ANDES OF
CHILE INTO ARGENTINA. AS SHORT WAVE ENERGY SPILLS ACROSS THE ANDES
THIS WILL THEN FAVOR HEIGHT FALLS OF 75-125GPM ACROSS THE CENTRAL
PROVINCES IN ARGENTINA ON DAYS 03 AND 04...WITH FOCUS OF THE
ENERGY ACROSS THE BUENOS AIRES PROVINCE/RIO DE LA PLATA BASIN ON
DAY 05. AT LOW LEVELS THIS WILL SUSTAIN A BROAD TROUGH ACROSS THE
FAR EASTERN PACIFIC...WITH ASSOCIATED FRONT ENTERING SOUTHERN
CHILE/PATAGONIA IN ARGENTINA. THROUGH 48-60 HRS TROUGH PATTERN IS
TO PUSH FARTHER EAST INTO THE SOUTHERN CONE OF SOUTH
AMERICA...WITH POLAR FRONT UNDULATING NORTH INTO THE CENTRAL
PROVINCES IN ARGENTINA. THROUGH 96 HRS...AS THE FOCUS OF SHORT
WAVE ENERGY SHIFTS TO RIO DE LA PLATA BASIN AND UNDER FAVORABLE
JET DYNAMICS...A FRONTAL LOW IS TO FORM OVER THE BUENOS AIRES
PROVINCE. THROUGH 120-132 HRS THIS IS TO THEN DEEPEN WHILE
DRIFTING EAST-SOUTHEAST INTO THE WESTERN ATLANTIC. AS THE
LOW/TROUGH DEEPENS...THIS WILL THEN SUSTAIN THE RAPID PROGRESSION
OF THE SURFACE FRONT INTO MID SECTIONS OF SOUTH AMERICA. INFLOW OF
SHORT WAVE ENERGY AND SUBTROPICAL MOISTURE WILL FAVOR SCATTERED
CONVECTION ACROSS CHILE BETWEEN CONCEPCION AND ISLA DE
CHILOE...WITH DAILY MAXIMA TO PEAK AT 15-20MM. THROUGH 72-84 HRS
ACTIVITY WILL BUILD NORTH ALONG THE COAST TO TALCA/CURICO...WITH
MAXIMA OF 15-25MM. THIS IS TO ALSO FAVOR SCATTERED SNOW SHOWERS
ACROSS THE CENTRAL ANDES...WITH SNOWFALL AMOUNTS OF 10-15CMM
EXPECTED BETWEEN 72-96 HRS. ACROSS ARGENTINA...UNDULATING FRONT
WILL SUSTAIN MODERATE CONVECTION LATER ON DAY 02...WITH MAXIMA OF
15-20MM. THIS INCREASES TO 20-45MM IN POTENTIALLY SEVERE
CONVECTION ON DAY 03. THROUGH 96-108 HRS...AS SURFACE LOW DEEPENS
AND BEGINS TO OCCLUDE...HEAVY CONVECTION IS EXPECTED ACROSS
SOUTHERN BUENOS AIRES PROVINCE TO LA PAMPA...WITH MAXIMA TO PEAK
AT 35-70MM DUE TO POSSIBILITY OF ECHO TRAINING.

NORTH OVER THE CONTINENT...AT 200 HPA...SUBTROPICAL RIDGE IS TO
STRENGTHEN ACROSS THE GUIANAS-NORTHERN BRASIL OVER THE NEXT FEW
DAYS. AS THE RIDGE BECOMES BETTER ORGANIZED...A SHORT WAVE TROUGH
TO THE SOUTH IS EXPECTED TO WEAKEN. THIS IS TO INITIALLY EXTEND
ACROSS MATO GROSSO TO CENTRAL BRASIL. BY 72 HRS IT IS TO CONFINE
TO PARAGUAY-MATO GROSSO...AND LATER IN THE CYCLE IT WILL MIGRATE
ACROSS ESPIRITO SANTO/MINAS GERAIS. UNDER INFLUENCE OF THE UPPER
LEVEL RIDGE...TROPICAL CONVECTION WILL LIMIT TO EQUATORIAL SOUTH
AMERICA AND NORTHWARD...WITH CONVECTION ACROSS THE GUIANAS-RORAIMA
IN BRASIL TO SOUTHERN COLOMBIA. IN THIS AREA EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY IN SCATTERED CONVECTION. LOCALLY HIGHER
AMOUNTS...HOWEVER...ARE EXPECTED AS NORTHERN HEMISPHERE TROPICAL
WAVES ENTER NORTHERN SOUTH AMERICA OVER THE NEXT FEW DAYS.

JALFIN...SMN (ARGENTINA)
CAROCA...DMC (CHILE)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)