THE WEATHER PREDICTION CENTER

CAMP SPRINGS, MD


SOUTH AMERICAN MODEL DISCUSSION



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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER CAMP SPRINGS MD
1210 PM EDT FRI JUN 24 2011
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
 
MODEL COMPARISON (VALID FROM 00UTC JUNE 24):  THE GLOBAL MODELS
HAVE REACHED A CONSENSUS ON THE PATTERN EVOLUTION...AND NOW AGREE
THROUGH DAY 05.

A MID LEVEL TROUGH ON THE SOUTHERN STREAM ENTERED THE DRAKE
PASSAGE/SOUTHERN CONE. AS IT PULLS EAST...THE TROUGH IS FORECAST
TO SPLIT IN TWO...SHEARING A SHORT WAVE TROUGH ON THE NORTHERN
STREAM FLOW. THE LATTER IS TO MEANDER NORTH ACROSS BUENOS AIRES
PROVINCE/RIO DE LA PLATA BY 30-36 HRS...AND IT IS TO THEN STALL
OFF THE COAST OF RIO GRANDE DO SUL/URUGUAY...WHERE IT WILL REMAIN
THROUGH 96-108 HRS. AS IT MEANDERS OVER RIO DE LA PLATA BASIN/RIO
GRANDE DO SUL IN BRASIL IT IS TO FAVOR HEIGHT FALLS OF 50-75GPM.
MOST INTENSE EXPECTED THROUGH 60-72 HRS. THIS WILL ENHANCE
INSTABILITY ALONG THE COAST OF URUGUAY AND THE SOUTHERN STATES OF
BRASIL. AT LOW LEVELS...THE ASSOCIATED FRONT WILL PUSH NORTH
ACROSS BUENOS AIRES PROVINCE/RIO DE LA PLATA THROUGH 24 HRS...
INTO RIO GRANDE DO SUL BY 48 HRS. IT IS TO THEN MERGE WITH AN OLD
MEANDERING FRONT TO THE NORTH...AS THE LATTER EXTENDS ACROSS
SOUTHERN BRASIL TO SANTA CRUZ IN EASTERN BOLIVIA. THIS WILL
REINFORCE THE OLD BOUNDARY WHILE SUSTAINING CYCLOGENESIS OVER THE
WESTERN ATLANTIC THROUGH 60-72 HRS. THE NASCENT LOW WILL QUICKLY
DEEPEN/OCCLUDE THROUGH 96-108 HRS WHILE SLOWLY PULLING TO THE
SOUTHEAST. AS THEY MERGE/COMBINE...THE FRONT WILL THEN MOVE NORTH
TO SAO PAULO/MATO GROSSO DO SUL IN BRASIL-NORTHERN BOLIVIA...TO
REACH RIO DE JANEIRO/SOUTHERN MINAS GERAIS BY 96-108 HRS. THE
MEANDERING FRONT TO THE NORTH WILL FAVOR SCATTERED CONVECTION
ACROSS SOUTHERN BRASIL-MESOPOTAMIA VALLE/SOUTHEAST PARAGUAY
THROUGH 36-48 HRS...WITH DAILY MAXIMA TO PEAK AT 15-25MM/DAY.
OVER EASTERN SAO PAULO IT IS TO FAVOR MAXIMA OF 15-20MM/DAY...
WITH MOST INTENSE ALONG THE SERRA DO MAR.

A STRONG PERTURBATION IN THE SOUTHERN STREAM FOLLOWS...WITH MID
LEVEL TROUGH TO ENTER THE BELLINGSHAUSEN SEA EARLY IN THE CYCLE.
THROUGH 48 HRS IT WILL EXPAND ACROSS THE ANTARCTIC PENINSULA TO
THE WEDDELL SEA/SOUTH ATLANTIC...WHERE IT WILL REMAIN THE
DOMINANT FEATURE THROUGH 72-84 HRS. AT LOW LEVELS IT WILL SUSTAIN
AN ELONGATED FRONT ACROSS SOUTHERN CHILE/SOUTHERN
PATAGONIA...WHERE IT IS TO MEANDER THROUGH 84-96 HRS. THIS WILL
FAVOR SCATTERED CONVECTION WITH ACCUMULATION OF 05-10MM/DAY.
LOCALLY HIGHER AMOUNTS ARE POSSIBLE. 

THE MODELS THEN FORECAST A STRONG MID LEVEL TROUGH THAT QUICKLY
PROPAGATES ACROSS THE SOUTH PACIFIC TO THE BELLINGSHAUSEN
SEA/ANTARCTIC PENINSULA BY 108-120 HRS. UNDER INFLUENCE OF A
BUILDING RIDGE TO THE WEST...THE TROUGH WILL AMPLIFY NORTH ACROSS
SOUTHERN CHILE/ARGENTINA THROUGH 132-144 HRS...FOCUSING ITS SHORT
WAVE ENERGY ACROSS SOUTHERN/CENTRAL CHILE. THE DEEP TROUGH
PATTERN IS TO INDUCE HEIGHT FALLS OF 250-300GPM. AT LOW LEVELS IT
WILL SUSTAIN A DEEP OCCLUDED LOW OVER TIERRA DEL FUEGO/SOUTHERN
PATAGONIA BY 120 HRS...WHILE THE ASSOCIATED FRONT QUICKLY
PROPAGATES NORTH ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA/
CENTRAL CHILE. THE AIR MASS WILL BE COLD ENOUGH TO SUSTAIN
ORGANIZED SNOW SHOWERS ACROSS SOUTHERN CHILE-TIERRA DEL FUEGO...
TO START AROUND 120 HRS AND PERSIST THROUGH 144 HRS. LIQUID WATER
EQUIVALENT WILL RANGE BETWEEN 20-40MM.

NORTH OVER THE CONTINENT...AT 200 HPA...THE MODELS CONTINUE TO
FORECAST AN UNSEASONABLY STRONG CELL OF THE SUBTROPICAL RIDGE TO
ESTABLISH A FOOTHOLD OVER NORTHERN SOUTH AMERICA. THE CLOSED HIGH
IS TO CENTER NEAR 10S 70W EARLY IN THE CYCLE...AND THROUGH 60-72
HRS IT WILL MIGRATE ACROSS 10S 60W. THE BUILDING RIDGE WILL
INDUCE A SHORT WAVE TROUGH ACROSS NORTHEAST BRASIL BY 36-54
HRS...WITH AXIS TO SLOWLY MOVE OFFSHORE THROUGH 72-84 HRS.
MEANWHILE...IT IS TO ENHANCE COASTAL CONVECTION WHILE TRIGGERING
MAXIMA OF 20-40MM/DAY. THIS RIDGE IS TO ALSO VENT DEEP CONVECTION
ACROSS NORTHERN AMAZONAS IN BRASIL TO THE PERUVIAN JUNGLE...WHERE
WE EXPECT SCATTERED CONVECTION OVER THE NEXT FEW DAYS TO SUSTAIN
MAXIMA OF 15-25MM/DAY.

PEREYRA...DNM (URUGUAY)
SANTACRUZ...DMH (PARAGUAY)
DAVISON...WPC (USA)




Last Updated: 1210 PM EDT FRI JUN 24 2011