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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1558Z Feb 24, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1058 AM EST TUE FEB 24 2015

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

MODEL DISCUSSION (VALID FROM FEBRUARY 24 AT 00UTC): SHORT WAVE
TROUGH ON THE NORTHERN STREAM REMAINS THE SYSTEM OF CONCERN...WITH
MID LEVEL AXIS FORECAST TO MEANDER OFF THE CENTRAL COAST OF CHILE
OVER THE NEXT FEW DAYS. AS IT MEANDERS TO THE EAST...THIS IS TO
SHEAR SHORT WAVE VORTICES ACROSS THE CENTRAL ANDES INTO CENTRAL
ARGENTINA...WITH STRONG VORTEX TO SPILL ACROSS THE ANDES INTO CUYO
BY 24-30 HRS. THIS IS TO THEN TRACK TO THE EAST-NORTHEAST ACROSS
URUGUAY/RIO DE LA PLATA BASIN BY 36-48 HRS. SECONDARY SHORT WAVE
VORTICES ARE TO FOLLOW...BUT THEY ARE TO LACK THE INTENSITY OF THE
FORMER. EARLY IN THE CYCLE...INFLOW OF SHORT WAVE ENERGY WILL BE
ACCOMPANIED BY A 250 HPA SUBTROPICAL JET MAXIMA. THIS JET IS TO
SUSTAIN A DIVERGENT PATTERN ALOFT ACROSS CENTRAL ARGENTINA THROUGH
48-60 HRS. AT LOW LEVELS...A NORTHERLY JET ACROSS
PARAGUAY-NORTHERN ARGENTINA IS TO SUSTAIN A MOIST ADVECTIVE
PATTERN. MOISTURE IS FORECAST TO CONVERGE ACROSS CENTRAL ARGENTINA
AND ALONG A MEANDERING FRONT TO THE SOUTH. OVER THE NEXT FEW
DAYS...THE PRECIPITABLE WATER CONTENT IS FORECAST TO INCREASE TO
50MM. THIS IS TO THEN HELP FEED ORGANIZED DEEP CONVECTION ACROSS
THE CENTRAL PROVINCES. RISK OF SEVERE CONVECTION IS HIGH ON DAYS
01-02...WITH EXCESSIVE RAINFALL AMOUNTS EXPECTED ON DAY 02 AS AN
MCS DEVELOPS OVER ARGENTINA. INITIALLY EXPECTING MAXIMA OF
35-70MM...BUT THROUGH WEDNESDAY MORNING THIS INCREASES TO
75-150MM. LOCALLY HIGHER AMOUNTS IS HIGHLY LIKELY AS SUGGESTED BY
THE GLOBAL ENSEMBLE MEMBERS. BY 60-84 HRS MODERATE TO HEAVY
CONVECTION IS EXPECTED ACROSS ENTRE RIOS IN
ARGENTINA/URUGUAY...WHERE THE MAXIMA IS TO PEAK AT 30-60MM.

ON THE SOUTHERN STREAM...A TIGHT BELT OF MID LEVEL WESTERLIES
DOMINATES THE FAR EASTERN PACIFIC-SOUTHERN CONE/ANTARCTIC
PENINSULA-SOUTH ATLANTIC. THIS PATTERN IS TO REMAIN NEARLY
UNCHANGED THROUGH 48 HRS...BUT THEN RAPIDLY CHANGES BY 72 HRS AS A
DEEP/HIGH AMPLITUDE TROUGH ENTERS THE EASTERN PACIFIC. THE TROUGH
IS TO ENVELOP AREA BETWEEN 120W-80W AND TO THE SOUTH OF
30S...WHILE FOCUSING SHORT WAVE ENERGY INTO EXTREME SOUTHERN
PORTIONS OF CHILE/TIERRA DEL FUEGO. AT LOW LEVELS IT IS TO SUSTAIN
A BROAD TROUGH ACROSS THE BELLINGSHAUSEN SEA TO THE DRAKE
PASSAGE/TIERRA DEL FUEGO...WITH POLAR FRONTS FORECAST TO REVOLVE
AROUND THIS AXIS. IN A TIGHT PRESSURE GRADIENT EXPECTING LIGHT
CONVECTION OVER THE SOUTHERN CONE TO RESULT IN RAINFALL AMOUNTS OF
05-10MM/DAY...TO START ON DAY 04 AND PERSIST THROUGH DAY 05.

AS A TROUGH DEEPENS TO THE WEST...A LONG WAVE RIDGE IS TO THEN
BUILD SOUTH ACROSS THE CONTINENT TO THE WESTERN ATLANTIC...WITH
MID LEVEL AXIS FORECAST TO EXTEND ALONG 60W/65W. AS THE RIDGE
BUILDS...A HIGH AMPLITUDE/LONG WAVE TROUGH IS TO GRADUALLY AMPLIFY
ACROSS THE WESTERN SOUTH ATLANTIC BY 84-132 HRS. THIS TROUGH IS TO
EXTEND BETWEEN 60W-20W AND TO THE SOUTH OF 25S. AT LOW LEVELS IT
IS TO ALSO SUSTAIN A BROAD TROUGH OVER THE SOUTHWEST
ATLANTIC...WITH ASSOCIATED FRONT TO SURGE ACROSS PATAGONIA TO LA
PAMPA IN ARGENTINA BY 72-84 HRS...INTO THE SOUTHERN STATES OF
BRASIL BY 96-108 HRS. ACROSS SOUTHERN-SOUTHEAST BRASIL THIS IS TO
FAVOR SCATTERED DEEP CONVECTION WITH ACCUMULATION OF
20-35MM...WITH MOST INTENSE EXPECTED BETWEEN 96-120 HRS.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE
DOMINATES AREA TO THE NORTH OF 30S AND WEST OF 50W...WHILE
ANCHORING ON A HIGH OVER NORTHERN CHILE/SOUTHERN PERU. RIDGE
PATTERN ALOFT IS TO GRADUALLY WEAKEN THROUGH 84-96 HRS. EARLY IN
THE CYCLE THIS IS TO VENT DEEP CONVECTION ACROSS SOUTHERN
COLOMBIA-NORTHERN PERU-EASTERN ECUADOR AND NORTHWEST BRASIL...WITH
MAXIMA FORECAST TO PEAK AT 20-45MM/DAY. BUT AS THE RIDGE WEAKENS
THIS IS TO GRADUALLY DECREASE IN INTENSITY/AREA COVERAGE. OVER
NORTHERN BOLIVIA-SOUTHERN PERU THE MAXIMA IS TO PEAK AT
15-25MM...WITH AN INCREASE POSSIBLE LATER IN THE CYCLE. A TUTT LOW
TO THE EAST DOMINATES FLOW ACROSS NORTHEAST BRASIL-EQUATORIAL
SOUTH AMERICA. THIS TROUGH IS CUT OFF FROM THE FLOW...AND AS SUCH
IT IS TO GRADUALLY FILL AS THE CYCLE PROGRESSES. MEANWHILE...THIS
IS TO ENHANCE CONVECTIVE DEVELOPMENT ACROSS NORTHEAST BRASIL TO
FAVOR MAXIMA OF 20-35MM. BUT AS THE TROUGH WEAKENS...MOST ACTIVE
IS TO DEVELOP ALONG THE NORTH COAST AS ENHANCED BY SEA BREEZE
CONVERGENCE.

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