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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1627Z Jul 21, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1227 PM EDT MON JUL 21 2014

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

MODEL DISCUSSION (VALID FROM 21 JULY 00UTC): GLOBAL MODEL GUIDANCE
CONVERGE ON A SIMILAR SOLUTION THROUGH 84-96 HRS. THEY THEN
DIVERGE ON AMPLITUDE/SPEED OF SHORT WAVE PERTURBATIONS ENTERING
THE SOUTHERN CONE...WITH BOTH THE GFS AND ECMWF FAVORING A
DEEPER/STRONGER TROUGH PATTERN THAN WHAT THE UKMET FORECASTS. HIGH
VARIABILITY IS ALSO NOTED AMONG THE GLOBAL ENSEMBLE MEMBERS DURING
THE LATTER PART OF THE FORECAST...LEADING TO LOWER CONFIDENCE
LATER IN THE CYCLE.

AT MID LEVELS...A TROUGH ON THE SOUTHERN STREAM IS TO ENTER THE
SOUTHERN CONE EARLY IN THE CYCLE. UNDER INFLUENCE OF A BUILDING
RIDGE TO THE WEST...PROGRESSIVE PERTURBATIONS ARE TO LIFT ACROSS
THE BELLINGSHAUSEN SEA/ANTARCTIC PENINSULA. THESE ARE TO THEN
REVOLVE AROUND THE TROUGH AS IT MEANDERS OVER THE SOUTHERN CONE.
THE INFLOW OF COLD/POLAR AIR...AND A CONTINENTAL AIR MASS...IS TO
THEN INDUCE THE GRADUAL AMPLIFICATION/INTENSIFICATION OF THIS
TROUGH AS THE CYCLE PROGRESSES. AT LOW LEVELS...BROAD TROUGH PULLS
ACROSS THE BELLINGSHAUSEN SEA TO THE ANTARCTIC PENINSULA THROUGH
30-36 HRS. BUILDING RIDGE TO THE WEST DISPLACES THIS AXIS ACROSS
THE ANTARCTIC PENINSULA TO THE WEDDELL SEA...WITH AXIS NORTH INTO
THE WESTERN ATLANTIC. PROGRESSIVE POLAR FRONTS ARE TO REVOLVE
AROUND THIS TROUGH AS IT MEANDERS OVER SOUTHERN CHILE/PATAGONIA IN
ARGENTINA. THROUGH 48-72 HRS INFLOW OF COLD/POLAR AIR IS TO
INTENSIFY ACROSS THE SOUTHERN CONE. OVER EXTREME SOUTHERN PORTIONS
OF CHILE AND TIERRA DEL FUEGO THIS WILL LIKELY FAVOR SOLID
PRECIPITATION (SNOW) ON DAYS 02-03...WITH ACCUMULATION OF
10-15CM/DAY. THROUGH 96-108 HRS INFLOW OF COLD/POLAR AIR WILL
EXPAND ACROSS PATAGONIA TO LA PAMPA/BUENOS AIRES PROVINCE IN
ARGENTINA. AS A SOUTHERLY FLOW ESTABLISHES ALONG THE COAST OF
PATAGONIA...THE COLD ADEVECTION WILL ENHANCE CONVECTIVE
INSTABILITY AND GENERATION OF SHALLOW CONVECTION ACROSS SOUTHERN
BUENOS AIRES TO LA SIERRA DE LA VENTANA/TANDIL...WHERE WE EXPECT
SNOW SHOWERS BY 96-108 HRS WITH ACCUMULATION OF 05-10CM OVER
HIGHER ELEVATIONS.

MEANWHILE...A MID LEVEL SHORT WAVE TROUGH TO THE NORTH IS TO REACH
THE CENTRAL/NORTH COAST OF CHILE EARLY IN THE CYCLE. THROUGH 60-72
HRS THIS IS TO SPILL ACROSS THE ANDES INTO THE NORTHWEST PROVINCES
IN ARGENTINA...MEANWHILE TRIGGERING HEIGHT FALLS OF 75-100GPM OVER
MID SECTIONS OF SOUTH AMERICA. AT LOW LEVELS THIS IS TO SUSTAIN A
POLAR FRONT ACROSS NORTHERN PATAGONIA/LA PAMPA IN ARGENTINA EARLY
IN THE CYCLE. BUILDING POLAR RIDGE AND PAMPERO JET WILL DISPLACE
THIS BOUNDARY NORTH ACROSS URUGUAY/NORTHERN PROVINCES IN ARGENTINA
BY 48 HRS. THROUGH 72-96 HRS...AS THE POLAR HIGH BUILDS TO A 1027
HPA CIRCULATION...THE FRONT WILL SURGE ACROSS SOUTHERN
BRASIL-PARAGUAY TO BOLIVIA...REACHING SAO PAULO/RIO DE
JANEIRO-MATO GROSSO/RONDONIA IN BRASIL-NORTHERN BOLIVIA BY 96 HRS.
EARLY IN THE CYCLE THIS WILL SUSTAIN SCATTERED CONVECTION ACROSS
URUGUAY/RIO DE LA PLATA WITH ACCUMULATION OF 20-35MM. THROUGH
42/48 HRS THIS INCREASES TO 35-70MM WITH MOST INTENSE ACROSS RIO
GRANDE DO SUL IN BRASIL-URUGUAY-MESOPOTAMIA VALLEY IN ARGENTINA TO
CENTRAL PARAGUAY. THROUGH 72-84 HRS CONVECTION ACROSS SOUTHERN
BRASIL WILL INCREASE TO 75-125MM IN POTENTIALLY SEVERE
CONVECTION...WHILE ACROSS BOLIVIA TO SOUTHERN PERU IT IS TO PEAK
AT 40-80MM. THROUGH 96-108 HRS THIS IS TO BUILD WEST ACROSS ACRE
IN BRASIL TO SOUTHERN PERU...WHERE WE EXPECT MAXIMA OF 30-60MM.
DUE TO STRONG TOPOGRAPHICAL FORCING...LOCALLY HIGHER AMOUNTS ARE
HIGHLY LIKELY.

OVER NORTHERN SOUTH AMERICA...A NEAR ZONAL WESTERLY FLOW IS
EXPECTED AT 200 HPA TO ENVELOP AREA TO THE NORTH OF 20S. THIS IS
TO GENERALLY FAVOR LIGHT CONVECTION ALONG THE LEE OF THE ANDES
OVER NORTHERN JUNGLE OF PERU/EASTERN ECUADOR-NORTHERN AMAZONAS IN
BRASIL...WITH RAINFALL AMOUNTS IN THIS AREA TO PEAK AT 05-10MM. A
SLIGHT INCREASE...HOWEVER...IS POSSIBLE LATER IN THE CYCLE AS
POLAR TROUGH PATTERN OVER ARGENTINA-PARAGUAY STRENGTHENS. ACROSS
NORTHEAST BRASIL...MEANWHILE...A SURFACE FRONT IS TO MEANDER
ACROSS THE SOUTH ATLANTIC TO NORTHERN ESPIRITO SANTO/SOUTHERN
BAHIA. THIS IS TO ENHANCE LOW LEVEL MOISTURE CONVERGENCE WHILE
FAVOR SCATTERED CONVECTION. EARLY IN THE CYCLE THIS IS TO RESULT
IN RAINFALL AMOUNTS OF 20-35MM. THROUGH 72-96 HRS THIS IS TO
DECREASE TO 15-20MM/DAY.

FERNANDES...INMET (BRASIL)
JALFIN...SMN (ARGENTINA)
DAVISON...WPC (USA)