Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXSA20 KWBC 211547
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1147 AM EDT THU AUG 21 2014

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

MODEL DISCUSSION (VALID FROM AUGUST 21 AT 00UTC): BROAD TROUGH
OVER THE EASTERN PACIFIC IS THE SYSTEM OF CONCERN...WITH
CYCLE-TO-CYCLE INCONSISTENCIES ADDING TO THE UNCERTAINTY. IN THIS
CYCLE THE GFS AND ECMWF REVERSED COURSE...AND NOW FORESEE A DEEPER
TROUGH TO EMERGE ACROSS ARGENTINA DURING THE MEDIUM RANGE PERIOD.
THE LATEST CHANGE IS WELL SUPPORTED BY THE UKMET MODEL AND THE
MEAN OF THE GLOBAL ENSEMBLES. THIS SYSTEM IS LIKELY TO FAVOR
ORGANIZED/POTENTIALLY SEVERE CONVECTION ACROSS CENTRAL ARGENTINA
AND RIO DE LA PLATA BASIN.

DEEP TROUGH CONTINUES TO DOMINATE THE FLOW ACROSS THE EASTERN
PACIFIC...WITH MID LEVEL PERTURBATION ENVELOPING AREA BETWEEN
105W-75W AND TO THE SOUTH OF 15S. EAST OF THIS AXIS...A
NORTH-TO-SOUTH RIDGE EXTENDS ACROSS ARGENTINA WHILE ORIGINATING ON
A CLOSED HIGH OVER SOUTHERN BRASIL. THE TROUGH TO THE WEST IS TO
PRESS AGAINST THIS AXIS...LEADING TO GRADUAL EROSION/WEAKENING OF
RIDGE PATTERN AS SHORT WAVE ENERGY SHEARS UNDER THIS AXIS. BY
48-72 HRS THE RIDGE WILL WEAKEN ENOUGH TO ALLOW A STRONG VORTEX TO
SPILL ACROSS THE CENTRAL ANDES OF CHILE TO ARGENTINA...TRIGGERING
HEIGHT FALLS OF 100-150GPM ON THE CENTRAL PROVINCES IN ARGENTINA.
BY 72-96 HRS THE FOCUS OF THE SHORT WAVE ENERGY SHIFTS TO RIO DE
LA PLATA BASIN/URUGUAY AS A MID LEVEL LOW RAPIDLY DEEPENS TO THE
SOUTH. AT LOW LEVELS...THE TROUGH ALOFT SUSTAINS A BROAD TROUGH
OVER THE FAR EASTERN PACIFIC AND A POLAR FRONT ACROSS CENTRAL
ARGENTINA. THROUGH 36 HRS THE TROUGH PUSHES FARTHER EAST INTO THE
SOUTHERN CONE OF SOUTH AMERICA...WITH POLAR FRONT UNDULATING NORTH
INTO THE CENTRAL PROVINCES IN ARGENTINA. BY 72 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/LA PAMPA IN ARGENTINA. THROUGH 96-120 HRS THIS IS
FORECAST TO OCCLUDE/RAPIDLY DEEPEN WHILE DRIFTING EAST-SOUTHEAST
INTO THE 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 05-10MM. THROUGH 48-60 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 10-15CM EXPECTED BY 48-72 HRS. ACROSS
ARGENTINA...UNDULATING FRONT WILL SUSTAIN MODERATE CONVECTION
LATER ON DAY 01...WITH MAXIMA OF 15-20MM. THIS INCREASES TO
20-45MM IN POTENTIALLY SEVERE CONVECTION ON DAY 02. MOST ACTIVE
CONVECTION IS EXPECTED ON DAY 03...WHEN OCCLUDING LOW AND
PROGRESSIVE SURFACE FRONT WILL SUSTAIN MODERATE TO HEAVY
CONVECTION WITH ACCUMULATION OF 25-50MM. THIS IS TO QUICKLY BUILD
NORTH ACROSS URUGUAY TO SOUTHERN BRASIL...WHERE IT IS TO FAVOR
RAINFALL AMOUNTS OF 20-35MM.

NORTH OVER THE CONTINENT...AT 200 HPA...MODELS CONTINUE TO
FORECAST A CELL OF THE SUBTROPICAL RIDGE TO BUILD WEST ACROSS
NORTHERN SOUTH AMERICA INTO THE NORTHERN STATES OF BRASIL. AS THE
RIDGE TO THE NORTH BECOMES BETTER ORGANIZED...A SHORT WAVE TROUGH
TO THE SOUTH IS EXPECTED TO WEAKEN. THIS IS TO INITIALLY EXTEND
ACROSS MATO GROSSO TO BOLIVIA. BY 48 HRS IT IS TO CONFINE TO
PARAGUAY-MATO GROSSO/EASTERN BOLIVIA. BY 96-108 HRS IT WILL LIFT
ACROSS NORTHEAST BRASIL AS RIDGE PATTERN SETTLES TO THE WEST
ACROSS PERU/WESTERN BRASIL. 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 A STRONG NORTHERN HEMISPHERE
TROPICAL WAVE MOVES ACROSS VENEZUELA TO COLOMBIA...SUSTAINING
MAXIMA OF 15-30MM ACROSS RORAIMA-NORTHERN PARA AND EXTREME
NORTHERN PORTIONS OF AMAZONAS IN BRASIL TO SOUTHERN COLOMBIA.

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




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.