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South American Forecast Discussion
 
(Latest Discussion - Issued 1626Z Feb 27, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1126 AM EST FRI FEB 27 2015

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

MODEL DISCUSSION (VALID FROM FEBRUARY 27 AT 00UTC): DEEP MID/UPPER
LEVEL TROUGH DOMINATES THE FLOW OVER THE WESTERN ATLANTIC...AS IT
EXTENDS NORTH BETWEEN 55W-20W TO 25S. THE TROUGH REACHES MAXIMUM
AMPLITUDE EARLY IN THE CYCLE...THEN STARTS TO SLOWLY WEAKEN AS IT
MIGRATES TO THE EAST-SOUTHEAST. THROUGH 48 HRS THE TROUGH IS TO
PULL ACROSS 20W...NEARING 05W BY 96 HRS. AT LOW LEVELS THIS
SUSTAINS A POLAR FRONT ACROSS ARGENTINA...FORECAST TO MOVE NORTH
INTO SOUTHERN BRASIL-NORTHERN PROVINCES IN ARGENTINA BY 24 HRS.
THE FRONT IS TO THEN STALL OVER SOUTHERN STATES OF BRASIL...WHERE
IT IS TO GRADUALLY WEAKEN THROUGH 84-96 HRS. AS IT MEANDERS OVER
SOUTHERN BRASIL-CORRIENTES IN ARGENTINA THIS IS TO TRIGGER
SCATTERED CONVECTION WITH ACCUMULATION OF 20-30MM. THROUGH 36-60
HRS THIS DECREASES TO 15-25MM. OTHER CONVECTION IS TO BUILD
FARTHER TO THE NORTH OVER SOUTHEAST BRASIL...WHERE THE AMPLIFYING
MID/UPPER LEVEL TROUGH IS TO ENHANCE CONVECTIVE DEVELOPMENT. OVER
SAO PAULO-RIO DE JANEIRO-ESPIRITO SANTO AND SOUTHEAST MINAS GERAIS
THIS IS TO SUSTAIN AN INCREASE IN CONVECTION THROUGH 48-60
HRS...WHEN THE DAILY RAINFALL MAXIMA IS TO PEAK AT 20-40MM. DUE TO
STRONG TOPOGRAPHICAL FORCING LOCALLY HIGHER AMOUNTS ARE HIGHLY
LIKELY.

THE NEXT MID/UPPER LEVEL LONG WAVE TROUGH MOVES ACROSS THE EASTERN
PACIFIC THROUGH 24 HRS. THIS IS TO NEAR THE SOUTH COAST OF CHILE
BY 60 HRS...AND THEN INLAND ACROSS THE SOUTHERN CONE INTO
ARGENTINA BY 84-96 HRS. BUT AS IT PRESSES AGAINST A RIDGE TO THE
EAST...THE TROUGH IS TO RAPIDLY WEAKEN. MEANWHILE...THE HIGH
AMPLITUDE/LONG WAVE TROUGH IS TO FOCUS SUBTROPICAL MOISTURE INTO
SOUTHERN PORTIONS OF CHILE. AT LOW LEVELS THIS IS TO SUSTAIN A
BROAD TROUGH ON THE SOUTHERN STREAM FLOW...FORECAST TO EXTEND
NORTHWARD ACROSS THE BELLINGSHAUSEN SEA/SOUTHEAST PACIFIC TO THE
SOUTHERN CONE OF SOUTH AMERICA. ASSOCIATED SURFACE FRONT IS TO
STRETCH ACROSS THE DRAKE PASSAGE/TIERRA DEL FUEGO BY 48 HRS. IT
THEN MOVES NORTH INTO PATAGONIA-SOUTHERN CHILE BY 72
HRS...REACHING THE BUENOS AIRES PROVINCE/MENDOZA IN ARGENTINA BY
96-120 HRS. AS THE PRESSURE GRADIENT TIGHTENS...STRONG BOUNDARY
LAYER WINDS ARE TO ACCOMPANY THIS BOUNDARY...WITH WINDS FORECAST
TO PEAK AT 35-45KT. THE INFLOW OF SUBTROPICAL MOISTURE IS TO
SUSTAIN MODERATE...LOCALLY HEAVY... CONVECTION ACROSS SOUTHERN
PORTIONS OF CHILE. IN THIS AREA THE DAILY  MAXIMA IS TO PEAK AT
15-20MM. OVER CENTRAL ARGENTINA THIS IS TO THEN FAVOR MAXIMA OF
20-35MM LATER IN THE CYCLE.

ON THE NORTHERN STREAM...A MID LEVEL LOW AND ASSOCIATED SHORT WAVE
TROUGH ARE TO MEANDER OFF THE COAST OF CHILE THROUGH 36-48 HRS.
THROUGH 60 HRS THE LOW WEAKENS TO AN OPEN TROUGH. THIS IS TO THEN
RAPIDLY SHEAR EASTWARD ACROSS THE ANDES INTO CENTRAL ARGENTINA AS
THE AFOREMENTIONED LONG WAVE TROUGH NEARS THE SOUTHERN PORTIONS OF
CHILE. INFLOW OF SHORT WAVE ENERGY IS TO TRIGGER SCATTERED
CONVECTION ALONG THE CENTRAL ANDES OF CHILE...WITH ACCUMULATION OF
05-10MM EXPECTED ON DAYS 01-02. OVER ARGENTINA...INFLOW OF MID
LEVEL ENERGY IS TO THEN INTERACT WITH THE THERMAL LOW...TO SUSTAIN
AN INCREASE IN CONVECTION ACROSS THE NORTHERN PROVINCES IN
ARGENTINA TO NORTHERN URUGUAY/SOUTHERN STATES OF BRASIL. IN THIS
AREA EXPECTING DEEP CONVECTION TO SUSTAIN RAINFALL MAXIMA OF
30-60MM IN POTENTIALLY SEVERE CONVECTION LATER ON DAY
03...DECREASING TO 20-40MM THROUGH DAY 04.

NORTH OVER THE CONTINENT...AT 200 HPA...DISORGANIZED SUBTROPICAL
RIDGE PATTERN IS TO DOMINATE PERU-WESTERN BRASIL-BOLIVIA EARLY IN
THE CYCLE. THROUGH 48-72 HRS THE HIGH/RIDGE PATTERN IS TO
GRADUALLY STRENGTHEN...BUILDING EASTWARD ACROSS BRASIL. AS THE
RIDGE BECOMES BETTER ORGANIZED DIURNAL/TROPICAL CONVECTION OVER
NORTHERN PORTIONS OF THE CONTINENT IS TO ALSO BECOME MORE ACTIVE.
MOST ACTIVE CONVECTION...HOWEVER...IS EXPECTED ALONG THE NEAR
EQUATORIAL TROUGH OVER NORTHERN BRASIL-PERU/EASTERN ECUADOR...WITH
MAXIMA OF 20-40MM/DAY. OVER WESTERN ECUADOR...AN INCREASE IN
CONVECTION IS EXPECTED THROUGH 48-72 HRS...WHEN STRONG ONSHORE
FLOW IS TO ENHANCE MOISTURE CONVERGENCE ALONG THE COAST INTO THE
ANDES MOUNTAINS...TO RESULT IN RAINFALL MAXIMA OF 20-40MM. ACROSS
NORTHEAST BRASIL SCATTERED CONVECTION IS TO SUSTAIN MAXIMA OF
15-20MM/DAY. ON THE SIERRA OF PERU-ALTIPLANO OF BOLIVIA THE DAILY
MAXIMA IS TO PEAK AT 05-10MM.

ARREAGA...INAMHI (ECUADOR)
SCHNEIDER...INMET (BRASIL)
DAVISON...WPC (USA)