000
FXSA20 KWBC 091650
PMDSA 
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1149 AM EST THU FEB 09 2012
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
 
MODEL COMPARISON (VALID FROM 00 UTC FEB 09): THE MODELS GENERALLY
AGREE ON LONG WAVE PATTERN EVOLUTION THROUGH 168 HRS...WITH
LITTLE VARIABILITY NOTED AMONG THE ENSEMBLE MEMBERS INTO THE
MEDIUM/ LONG RANGE PERIOD. THE SYSTEM OF CONCERN REMAINS THE MID
LEVEL LOW ON THE NORTHERN STREAM THAT DEVELOPS OFF THE COAST OF
URUGUAY LATER ON DAY 01. THIS WILL THEN PERSIST THROUGH 72-84
HRS. THE EUROPEAN IS NOW THE ONE FAVORING THE DEEPEST MID/LOW
LEVEL CYCLONE...WHILE THE GFS-UKMET SETTLED IN FAVOR OF A WEAKER
SOLUTION. IN OUR CHARTS WE COMPROMISED...SHOWING A DEEPER LOW ON
DAY 02 THAN WHAT THE GFS-UKMET SUGGESTED...BUT NOT AS DEEP AS THE
ECMWF.

AS PREVIOUSLY INDICATED...A MID LEVEL TROUGH ON THE NORTHERN
STREAM WILL EVOLVE INTO A CLOSED LOW AS IT MEANDERS OFF THE COAST
OF URUGUAY/BUENOS AIRES PROVINCE LATER THIS EVENING. THE
LOW/TROUGH IS TO THEN STALL OFF THE COAST...TO MEANDER ALONG 50W
TO THE SOUTHERN STATES OF BRASIL THROUGH 84-90 HRS. BY 96-108 HRS
IT IS TO THEN FILL TO AN OPEN TROUGH WHILE IT BEGINS TO PULL TO
THE EAST-SOUTHEAST AHEAD OF AN AMPLIFYING POLAR TROUGH TO THE
SOUTH. AT LOW LEVELS...A FRONT WILL EXTEND ACROSS SOUTHERN
BRASIL-SOUTHEAST PARAGUAY TO NORTHWEST ARGENTINA EARLY IN THE
CYCLE. THE MID LEVEL LOW WILL INTERACT WITH THIS FRONT...INDUCING
A FRONTAL WAVE OFF THE SOUTHERN COAST OF BRASIL/URUGUAY EARLY IN
THE CYCLE. THROUGH 36-48 HRS THIS LOW WILL OCCLUDE AS IT DEEPENS
TO A 1006-1008 HPA LOW. THE SURFACE FRONT...MEANWHILE...IS TO
MEANDER NORTH ACROSS PARANA-PARAGUAY...TO THEN WEAKEN TO A
SURFACE TROUGH AS IT MEANDERS ACROSS SAO PAULO-MATO GROSSO DO
SUL-NORTHERN BOLIVIA/RONDONIA IN BRASIL. DURING THE 60-84 HRS
FORECAST PERIOD...THERE IS A SLIGHT RISK OF THIS SYSTEM EVOLVING
INTO A SUBTROPICAL CYCLONE AS UPPER LEVEL WIND SHEAR ABATES AND
IT REMAINS OVER WARM SEA SURFACE TEMPERATURES. IF A SUBTROPICAL
CYCLONE FORMS...OFFICIAL FORECAST WILL BE ISSUED BY THE
GOVERNMENTS OF BRASIL. UNDER INFLUENCE OF THIS SYSTEM...EXPECTING
SCATTERED DEEP CONVECTION ACROSS THE SOUTHERN STATES OF BRASIL
EARLY IN THE CYCLE...WITH RAINFALL AMOUNTS OF 20-35MM/DAY.
THROUGH 48-60 HRS THIS WILL INCREASE TO 25-50MM/DAY WHILE
EXPANDING NORTH ACROSS SAO PAULO-RIO DE JANEIRO AND MATO GROSSO
DO SUL IN BRASIL. BUT AS THE SYSTEM WEAKENS...EXPECTING MAXIMA TO
DECREASE TO 15-30MM/DAY BY 72-84 HRS. 

ON THE SOUTHERN STREAM...A MID LEVEL PERTURBATION WILL RACE
ACROSS THE EASTERN PACIFIC TO THE SOUTHERN CONE BY 24 HRS...TO
QUICKLY PULL ACROSS THE DRAKE PASSAGE. A STRONGER PERTURBATION
WILL FOLLOW...TO REACH THE SOUTHERN CONE BY 84 HRS. THE
LATTER WILL INDUCE HEIGHT FALLS OF 150-200GPM AS IT MOVES
ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. THROUGH 120
HRS THIS WILL EVOLVE INTO A BROAD TROUGH ACROSS THE EASTERN
PACIFIC/SOUTHERN CONE OF SOUTH AMERICA. AT LOW LEVELS...ELONGATED
FRONTS WILL STREAM ACROSS SOUTHERN CHILE/TIERRA DEL FUEGO DURING
THE NEXT FEW DAYS...WITH A GRADUAL NORTHWARD MODULATION ACROSS 
PATAGONIA BY 72 HRS...INTO CENTRAL PROVINCES IN ARGENTINA BY 96-
108 HRS. THESE ARE TO FAVOR STRONG BOUNDARY LAYER WINDS AND
MODERATE TO HEAVY RAINFALL AMOUNTS...WITH MOST INTENSE ON DAY 01
WHEN MAXIMA ACROSS CHILE SOUTH OF ISLA DE CHILOE IS FORECAST TO
PEAK AT 15-20MM. OTHERWISE...DAILY MAXIMA IN THIS AREA WILL PEAK
AT 10-15MM/DAY. OVER LA PAMPA/SOUTHERN BUENOS AIRES IN ARGENTINA
EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY IN SCATTERED
CONVECTION.

AT 200 HPA...THE BOLIVIAN HIGH IS TO MEANDER OVER NORTHWEST
ARGENTINA/SOUTHERN BOLIVIA EARLY IN THE CYCLE. THIS WILL ANCHOR A
RIDGE OVER THE CONTINENT THAT IS TO EXTENDS BETWEEN 30S-15S.
THROUGH 36-48 HRS THE HIGH WILL LIFT TO SOUTHERN BOLIVIA...WHILE
RIDGE MEANDERS ACROSS BOLIVIA TO CENTRAL BRASIL. AS IT MEANDERS
ACROSS MID SECTIONS OF SOUTH AMERICA...THE RIDGE ALOFT WILL VENT
LATE AFTERNOON CONVECTION ACROSS NORTHWEST ARGENTINA...WHERE IT
IS TO GENERALLY FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY. IT IS TO
ALSO VENT DIURNAL CONVECTION ACROSS THE SIERRA OF PERU-ALTIPLANO
OF BOLIVIA TO NORTHWEST PROVINCES IN ARGENTINA...WITH RAINFALL
MAXIMA OF 15-20MM/DAY EXPECTED OVER THE NEXT FEW DAYS. 

ALSO AT UPPER LEVELS...A TROUGH LIES TO THE NORTH OF THE
SUBTROPICAL RIDGE...WITH AXIS WEST ALONG 13S/14S TO PARA IN
BRASIL. A WANING LOW NEAR 14S 50W IS TO ANCHOR THIS TROUGH EARLY
IN THE CYCLE...AND THROUGH 48-72 HRS IT IS TO FILL TO AN OPEN
TROUGH. THIS IS TO ENHANCE DIURNAL CONVECTION AS IT BUILDS ACROSS
THE CONTINENT TO THE NORTH OF 13S...WITH RAINFALL AMOUNTS OF 20-
35MM/DAY. LOCALLY HIGHER AMOUNTS ARE EXPECTED ACROSS PARA AND
CENTRAL PORTIONS OF BRASIL. THROUGH 72-96 HRS CONVECTION BECOMES
MORE ACTIVE/BETTER ORGANIZED. 

GONZALEZ...SHIN (ARGENTINA)
VILLELA...INMET (BRASIL)
DAVISON...HPC (USA)$$