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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1529Z Jun 18, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1129 AM EDT MON JUN 18 2018

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

MODEL DISCUSSION (VALID FROM JUNE 18 AT 0000 UTC): THE GLOBAL
MODELS MAINTAIN GOOD CONTINUITY WITH PREVIOUS RUN...ONLY MAKING
MINOR CORRECTIONS TO SHORT WAVE PATTERN DURING THE LATTER PART OF
THE FORECAST. OVERALL CONFIDENCE IN THE FORECAST IS HIGH.

A DEEP LAYER TROUGH ON THE SOUTHERN STREAM IS TO DOMINATE THE FLOW
ACROSS THE DRAKE PASSAGE/SOUTHERN CONE OF SOUTH AMERICA DURING THE
NEXT FIVE-TO-SIX DAYS. EARLY IN THE CYCLE THE TROUGH IS TO CONFINE
TO CONTINENTAL AREA TO THE SOUTH OF 40S...AND THROUGH WEDNESDAY
EVENING IT AMPLIFIES TO 30S. THE BROAD TROUGH IS TO REMAIN THE
DOMINANT FEATURE THROUGH THE END OF THE WORKWEEK. AT LOW LEVELS
THIS WILL SUSTAIN A BROAD TROUGH ACROSS THE SOUTHERN CONE. AN
ELONGATED FRONT IS TO BOUND THE NORTHERN FRINGES OF THIS AXIS...TO
MEANDER ACROSS NORTHERN PATAGONIA IN ARGENTINA-SOUTHERN CHILE
DURING THE NEXT THREE DAYS. ON THURSDAY...THE BOUNDARY SURGES
ACROSS RIO DE LA PLATA BASIN/URUGUAY TO SOUTHERN BRASIL-NORTHERN
ARGENTINA...WHERE IT IS FORECAST TO STALL. MEANWHILE...THIS WILL
ENHANCE MOISTURE CONVERGENCE BETWEEN TEMUCO-PUERTO MONTT IN
SOUTHERN CHILE T FAVOR SCATTERED CONVECTION. MOST ACTIVE IS
EXPECTED TODAY WITH MAXIMA OF 20-35MM. ON TUESDAY-WEDNESDAY THE
RAINFALL DECREASES TO 00-05MM/DAY. ON THURSDAY...AS THE FRONT
SURGES ACROSS URUGUAY...IT IS TO ALSO TRIGGER LIGHT RAINFALL
AMOUNTS WITH MAXIMA OF 00-05MM. SIMILAR AMOUNTS ARE EXPECTED OVER
SOUTHERN BRASIL-CORRIENTES IN ARGENTINA LATER ON THURSDAY-FRIDAY
MORNING.

FURTHERMORE...AS THE DEEP POLAR TROUGH MEANDERS ACROSS THE
SOUTHERN CONE...PROGRESSIVE FRONTS ON THE SOUTHERN STREAM ARE TO
LIFT ACROSS THE BELLINGSHAUSEN SEA TO EXTREME SOUTHERN REGIONS OF
CHILE/TIERRA DEL FUEGO. THESE WILL FAVOR A COLD ADVECTIVE PATTERN
WHILE SUSTAINING ENVIRONMENTAL CONDITIONS HIGHLY FAVORABLE FOR
SNOWFALL TO ACCUMULATE ACROSS THE SOUTHERN ANDES AND PORTIONS OF
TIERRA DEL FUEGO. IN THIS AREA INITIALLY EXPECTING ACCUMULATION OF
15-20CM. ON TUESDAY AND WEDNESDAY EXPECTING ADDITIONAL SNOWFALL
AMOUNTS OF 10-15CM/DAY. DUE TO STRONG TOPOGRAPHICAL
FORCING...LOCALLY HIGHER AMOUNTS ARE HIGHLY PROBABLE.

ANOTHER MID/UPPER LEVEL TROUGH TO THE EAST DOMINATES THE FLOW
ACROSS THE CENTRAL/EASTERN SOUTH ATLANTIC. THIS TROUGH SUSTAINS AN
ELONGATED FRONT THAT EXTENDS WEST ACROSS RIO DE JANEIRO/MINAS
GERAIS TO MATO GROSSO DO SUL IN BRASIL. THE FRONT LOSES ITS UPPER
LEVEL SUPPORT EARLY IN THE CYCLE...WITH PORTION OVER THE CONTINENT
FORECAST TO FRONTOLIZE ON TUESDAY. MEANWHILE...OVER NORTHERN SAO
PAULO-RIO DE JANEIRO THIS WILL FAVOR MODERATE RAINFALL AMOUNTS
WITH ACCUMULATION OF 15-20MM. OTHER CONVECTION TO THE NORTH IS TO
AFFECT EASTERN BAHIA...WHERE UNDER THE INFLUENCE OF A PREFRONTAL
SHEAR LINE EXPECTING MAXIMA OF 15-20MM/DAY OVER THE NEXT FOUR DAYS.

NORTH OVER THE CONTINENT...AT 200 HPA...A RIDGE EXTENDS WEST
ACROSS NORTHERN SOUTH AMERICA TO AMAZONAS IN BRASIL. A TROUGH TO
THE SOUTH...MEANWHILE...LIES OFF THE NORTH COAST OF CHILE/SOUTHERN
PERU. ON TUESDAY-WEDNESDAY THE SHORT WAVE TROUGH IS TO MEANDER
EAST ACROSS THE ANDES TO BOLIVIA...WHERE IT IS TO REMAIN THROUGH
THE END OF THE WEEK. ON THE SOUTHERN SIERRA OF PERU AND THE
ALTIPLANO OF BOLIVIA THIS IS TO TRIGGER ISOLATED SNOW SHOWERS.
MOST ACTIVE CONVECTION...HOWEVER...IS EXPECTED TO THE NORTH ACROSS
EQUATORIAL SOUTH AMERICA. OVER RORAIMA/NORTHERN AMAZONAS IN BRASIL
TO SOUTHERN COLOMBIA EXPECTING DAILY MAXIMA OF 20-30MM. ACROSS
NORTHERN PARA AND ALONG THE NORTH COAST SEA BREEZE CONVERGENCE IS
TO FAVOR MAXIMA OF 10-15MM IN ISOLATED TO SCATTERED CONVECTION.

DIAZ...INUMET (URUGUAY)
SANCHEZ...SMN (ARGENTINA)
DAVISON...WPC (USA)