SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1137 AM EDT TUE MAY 07 2013

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

MODEL COMPARISON (VALID FROM 00 UTC MAY 07): GLOBAL MODELS AND
ENSEMBLE MEMBERS AGREE ON FORECAST EVOLUTION THROUGH 84-96 HRS.
DISCREPANCIES ON TIMING/EVOLUTION OF TROUGH CROSSING THE ANDES
BETWEEN 96-120 HRS LEAD TO LOW CONFIDENCE ON THE EVOLUTION OF THE
SYSTEM.

BROAD MID LEVEL TROUGH OVER THE SOUTH ATLANTIC CONTINUES
SUSTAINING SHORT WAVE VORTICES REVOLVING AROUND MAIN AXIS.  ONE IS
AMPLIFYING AND SUSTAINING A COLD FRONT TO EXTEND ACROSS SAO
PAULO-SOUTHEASTERN MATO GROSSO DO SUL BY 24 HRS. AIR MASS IS DRY
DUE TO FRONTAL PASSAGE DURING THE WEEKEND...THUS...EXPECTING ONLY
LIGHT CONVECTION ACROSS COASTAL AREAS WITH THIS SYSTEM.

IN THE WESTERLIES...MID-UPPER TROUGH IS APPROACHING SOUTHERN
CHILE. AT LOW-LEVELS THE SYSTEM WILL SUSTAIN A WEAK SUBTROPICAL
CONNECTION THAT WILL ENHANCE AVAILABLE PWAT AND ACCUMULATIONS
ACROSS SOUTHERN CHILE. STRONG 50-60KT BOUNDARY-LAYER WINDS AND
MOISTURE POOL WILL LEAD HEAVIEST AMOUNTS NEAR AND TO THE SOUTH OF
ISLA CHILOE...WHERE EXPECTING AMOUNTS OF 20-35MM/DAY THROUGH 36
HRS. BY 36-60 HRS...HEAVIEST PRECIPITATION WILL CONCENTRATE FROM
ISLA CHILOE INTO PUERTO MONTT/OSORNO...WITH ACCUMULATIONS OF
10-15MM/DAY. ISOLATED HIGHER AMOUNTS ARE POSSIBLE IN INTERACTION
WITH OROGRAPHY.

TROUGH IN THE NORTHERN STREAM WILL APPROACH THE ANDES BY LATE
CYCLE. THIS...IN COMBINATION WITH INCREASING LOW-LEVEL MOISTURE IN
MID SECTIONS OF THE CONTINENT...WILL LEAD TO ANOTHER PERIOD WITH
CONVECTION AND RAINFALL ACROSS NORTHERN ARGENTINA/PARAGUAY. BY
LATE CYCLE. CONFIDENCE ON THE TIMING AND INTENSITY OF THIS SYSTEM
CONTINUES LIMITED. IT APPEARS THAT SYSTEM WILL ORGANIZE LATE ON
DAY 04 INTO DAY 05 TO PRODUCE STRONGEST CONVECTION ACROSS
NORTHEASTERN ARGENTINA INTO NORTHERN URUGUAY/RIO GRANDE DO SUL.

NORTH ACROSS THE CONTINENT...FOCUS FOR CONVECTION WILL BE ACROSS
AMAZONAS IN BRASIL/NORTHERN PERU EARLY IN THE CYCLE...ASSOCIATED
WITH SOUTHERLY SURGE AT LOW-LEVELS. AT UPPER LEVELS...THE REGION
LIES IN THE PERIPHERY OF UPPER RIDGE...WITH FAVORABLE UPPER
DIVERGENCE TO VENT ORGANIZED DEEP CONVECTION. THROUGH 36
HRS...EXPECTING AMOUNTS OF 30-60MM/DAY WITH THE RISK OF MCS
FORMATION. ACCUMULATIONS ARE TO START DECREASING AFTERWARDS...AS
MAIN FOCUS FOR CONVECTION MEANDERS NORTHWARD INTO EASTERN
ECUADOR/COLOMBIA. OTHER REGION OF ACTIVE CONVECTION IN TROPICAL
SOUTH AMERICA WILL BE THE AMAZON DELTA INTO AMAPA AND THE SOUTHERN
GUIANAS. ACTIVE ATLANTIC ITCZ WILL INTERACT WITH VENTILATION IN
THE PERIPHERY OF UPPER RIDGE. SEVERAL ROUNDS OF DEEP CONVECTION
WILL PRODUCE ACCUMULATIONS OF 20-50MM FROM NORTHWESTERN MARANHAO
TO THE WEST INTO AMAPA/EASTERN PARA/SOUTHERN GUIANAS. LOCALLY
HIGHER AMOUNTS ARE POSSIBLE. TO THE EAST ACROSS THE NORDESTE...AN
INCREASE IN SOUTHEASTERLY WINDS AND MOISTURE POOL WILL LEAD TO AN
INCREASE IN ACTIVITY ACROSS COASTAL AREAS BETWEEN SALVADOR DE
BAHIA AND RECIFE/JOAO PESSOA. EXPECTING AMOUNTS PEAKING AT MAXIMA
OF 20-35MM/DAY ON DAY 03.

MAQUEDA...DINAC (PARAGUAY)
SILVA DE SOUZA...INMET (BRASIL)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)