SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1147 AM EDT THU JUN 06 2013

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

MODEL COMPARISON (VALID FROM 00 UTC JUNE 06): AS A RESULT OF THE
PROGRESSIVE SHORT WAVE PERTURBATIONS POPULATING THE DOMAIN...THE
GLOBAL AND ENSEMBLE MODELS CONTINUE TO DISPLAY LITTLE TO NO
CYCLE-TO-CYCLE CONSISTENCY IN THEIR FORECASTS INTO THE MEDIUM
RANGE PERIOD. AS A RESULT...CONFIDENCE IN THE FORECAST BEYOND
72/84 HRS IS LOW.

MID LEVEL TROUGH DOMINATING THE WESTERN ATLANTIC HAS STARTED ITS
EASTWARD MIGRATION...AND THROUGH 24 HRS IT IS TO PULL ACROSS 45W
TO SOUTHEAST BRASIL. BY 48 HRS IT IS TO MOVE ACROSS
20W/25W...NEARING 00W BY 72 HRS. AS IT PULLS AWAY...THE TROUGH IS
FORECAST TO GRADUALLY WEAKEN. AT LOW LEVELS THIS SUSTAINS A
SURFACE FRONT ACROSS THE SOUTHERN STATES OF BRASIL TO CHACO
ARGENTINO. THE BOUNDARY OVER THE CONTINENT IS TO FRONTOLIZE
THROUGH 30-36 HRS...WHILE REMNANTS OVER THE ATLANTIC WEAKEN BY
60-72 HRS AS THE FRONT MEANDERS NORTH ALONG THE COAST OF SAO
PAULO/RIO DE JANEIRO. MODELS CONTINUE TO FORESEE LITTLE TO NO
CONVECTION WITH THIS BOUNDARY.

A VERY INTENSE MID LEVEL PERTURBATION IN THE SOUTHERN STREAM
FOLLOWS...WITH AXIS ACROSS SOUTHERN CHILE TO PATAGONIA IN
ARGENTINA BY 24 HRS. AS IT CLEARS THE COAST OF ARGENTINA BY 36-42
HRS...THE SYSTEM IS THEN FORECAST TO DEEPEN/AMPLIFY TO RIO DE LA
PLATA BASIN/URUGUAY. BY 48 HRS THE TROUGH WILL LIE ALONG 50W TO
30S. THROUGH 60-72 HRS...AS THE TROUGH PRESSES AGAINST A RIDGE TO
THE EAST AND SOUTH...IT IS FORECAST TO SPLIT IN TWO. IN THIS
PROCESS IT IS TO THEN SHEAR A CLOSED LOW ON THE NORTHERN STREAM
NEAR 47S 37W. BY 120 HRS THE LOW IS TO PULL ACROSS 50S 00W. AT LOW
LEVELS THIS  SUSTAIN A PROGRESSIVE FRONT ACROSS THE SOUTHERN CONE
TO THE WESTERN ATLANTIC EARLY IN THE CYCLE. THE POLAR FRONT THEN
MOVES NORTH ACROSS RIO DE LA PLATA BASIN/URUGUAY-MENDOZA IN
ARGENTINA BY 48 HRS. AT 72-108 HRS IT IS TO THEN STALL OVER
SOUTHERN BRASIL-NORTHERN PROVINCES IN ARGENTINA. AS THE FRONTAL
TROUGH MOVES ACROSS SOUTHERN CHILE TO PATAGONIA EARLY IN THE CYCLE
EXPECTING RAINFALL AMOUNTS OF 10-15MM IN SCATTERED CONVECTION. IT
IS TO ALSO FAVOR STRONG BOUNDARY LAYER WINDS OF 35-50KT. ACROSS
ARGENTINA...LITTLE TO NO CONVECTION IS EXPECTED IN ASSOCIATION
WITH THIS FEATURE THROUGH 54-60 HRS.

SHORT WAVE PERTURBATIONS ON THE NORTHERN STREAM...AS THEY MEANDER
EAST ACROSS NORTHERN CHILE TO ARGENTINA...ARE THEN FORECAST TO
INTERACT WITH THE SURFACE FRONT. THE INFLOW OF SHORT WAVE
ENERGY/COLD AIR ALOFT WILL SUSTAIN HEIGHT FALLS OF 30-60GPM. A
SUBTROPICAL JET MAXIMA IS TO ACCOMPANY THIS PERTURBATION AS IT
PULLS ACROSS THE CONTINENT...WITH DIVERGENCE ON ITS LEFT ENTRANCE
REGION TO PROVIDE VENTILATION ALOFT TO DEEP CONVECTION. AT LOW
LEVELS THE SHORT WAVE TROUGH WILL INTERACT WITH SURFACE FRONT
MEANDERING OVER SOUTHERN BRASIL-NORTHERN ARGENTINA. THIS WILL
STRENGTHEN THE FRONTAL BOUNDARY WHILE TRIGGERING SCATTERED DEEP
CONVECTION. ACROSS NORTHERN ARGENTINA/CHACO-CENTRAL PARAGUAY THIS
WILL SUSTAIN RAINFALL AMOUNTS OF 20-35MM BY 72-96 HRS.

OTHER SHORT WAVE PERTURBATIONS ON THE SOUTHERN STREAM...AS THEY
EMBED IN A TIGHT BELT OF MID LATITUDE WESTERLIES...ARE TO THEN
QUICKLY MOVE ACROSS THE SOUTH PACIFIC TO THE DRAKE
PASSAGE-SOUTHERN CONE OF SOUTH AMERICA. TWO FAIRLY INTENSE
PERTURBATIONS ARE OF PARTICULAR INTEREST...WITH ONE MAKING
LANDFALL AT 84-96 HRS...AND THE OTHER BY 120-132 HRS. NOTE THAT
THE MODELS DIVERGE ON THE INTENSITY AND TIMING OF THESE
PERTURBATIONS...SO FURTHER CORRECTIONS TO THE FORECAST ARE
EXPECTED. AS THEY STREAM ACROSS THE EASTERN PACIFIC/SOUTHERN CONE
THESE WILL SUSTAIN AN ELONGATED FRONT ACROSS PATAGONIA IN
ARGENTINA-SOUTHERN CHILE...WITH FRONTAL WAVES TO QUICKLY PULL EAST
ACROSS SOUTHERN CHILE. THESE ARE TO CONTINUE FAVORING STRONG
BOUNDARY LAYER WINDS AND TOPOGRAPHICALLY INDUCED CONVECTION ACROSS
SOUTHERN CHILE...WITH RAINFALL AMOUNTS OF 05-10MM/DAY.

NORTH OVER THE CONTINENT...AT 200 HPA...A LOW AMPLITUDE TROUGH IS
INITIALIZE OVER THE NORTHERN STATES OF BRASIL OF PARA-AMAZONAS.
THIS IS TO REMAIN NEARLY STATIONARY THROUGH 36-48 HRS. BY 60-72
HRS...AS A SHORT WAVE RIDGE ESTABLISHES ACROSS NORTHERN AMAZONAS
IN BRASIL/ SOUTHERN COLOMBIA...THE TROUGH WILL THEN MIGRATE EAST
ACROSS 50W. EARLY IN THE CYCLE EXPECTING WIDELY ISOLATED
CONVECTION OVER THE CONTINENT TO THE NORTH OF 10S. THROUGH 48-60
HRS CONVECTIVE ACTIVITY WILL BECOME MORE WIDESPREAD WHILE
EXPANDING ACROSS PARA-AMAZONAS TO SOUTHERN COLOMBIA/EASTERN
ECUADOR-NORTHERN PERU. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF
10-15MM/DAY. OTHER ACTIVITY IS EXPECTED ALONG THE NORTH COAST OF
BRASIL IN ASSOCIATION WITH NORTHERN HEMISPHERE TROPICAL WAVES.
MOST ACTIVE IS TO CLUSTER ACROSS AMAPA...WHERE THE DAILY MAXIMA IS
TO PEAK AT 15-20MM. FURTHERMORE... TRADE WINDS CONVERGENCE ACROSS
ESPIRITO SANTO/EASTERN BAHIA IN BRASIL IS TO SUSTAIN SCATTERED
CONVECTION WITH ACCUMULATION OF 10-15MM. LOCALLY HIGHER AMOUNTS
ARE HIGHLY LIKELY DUE TO STRONG TOPOGRAPHICAL FORCING.

OLIVARES...SENAMHI (PERU)
SILVA DE SOUZA...INMET (BRASIL)
DAVISON...WPC (USA)