225  
FXSA20 KWBC 031620  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1120 AM EST WED JAN 03 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 03 AT 0000 UTC): GLOBAL MODELS  
CONTINUE TO FOLLOW A SIMILAR EVOLUTION THROUGH 132-144  
HRS...FORECASTING A HIGHLY AMPLIFIED SINUSOIDAL FLOW TO ESTABLISH  
ACROSS THE DOMAIN. THIS FORECAST IS WELL SUPPORTED BY A LARGE  
MAJORITY OF THE GLOBAL ENSEMBLE MEMBERS... LEADING TO A HIGH  
CONFIDENCE IN THE FORECAST.  
 
SHORT WAVE TROUGH ON THE NORTHERN STREAM EXTENDED OVER THE  
SOUTHERN STATES OF BRASIL-PARAGUAY EARLY THIS MORNING...WITH AXIS  
TO PULL ACROSS 45W LATER TODAY. CONSISTENT WITH PREVIOUS  
FORECAST...THE TROUGH IS TO THEN RAPIDLY WEAKEN AS IT ACCELERATES  
ACROSS THE SOUTH ATLANTIC. MEANWHILE...THIS WILL SUSTAIN AN  
ELONGATED FRONT ACROSS SOUTHEAST BRASIL-PARAGUAY. THE FRONT IS TO  
REMAIN NEARLY STATIONARY WHILE GRADUALLY WEAKENING EARLY ON FRIDAY  
MORNING. DEEP TROPICAL MOISTURE CONVERGES ALONG AND NORTH OF THIS  
BOUNDARY. THIS WILL FEED CONVECTIVE DEVELOPMENT ACROSS NORTHERN  
SAO PAULO-MINAS GERAIS EARLY IN THE CYCLE...TO FAVOR RAINFALL  
MAXIMA OF 30-60MM. ON THURSDAY...UNDER FAVORABLE JET  
DYNAMICS...ACTIVITY IS TO INTENSIFY WHILE BUILDING NORTH ACROSS  
TOCANTINS-GOIAS...WITH RAINFALL MAXIMA OF 40-80MM. OTHER  
CONVECTION TO THE WEST IS EXPECTED ACROSS NORTHERN  
BOLIVIA-SOUTHERN PERU...WITH MAXIMA OF 25-50MM. ON THURSDAY TO  
FRIDAY THIS DECREASES TO 15-25MM.  
 
FARTHER UPSTREAM OVER THE EASTERN PACIFIC...IN A TIGHT BELT OF MID  
LATITUDE WESTERLIES...A PROGRESSIVE MID LEVEL TROUGH WILL RACE  
ACROSS THE EASTERN PACIFIC TO SOUTHERN CHILE LATER THIS  
EVENING...TO QUICKLY MOVE ACROSS PATAGONIA IN SOUTHERN ARGENTINA  
ON THURSDAY AFTERNOON. AT LOW LEVELS THE ASSOCIATED SURFACE TROUGH  
MOVES ACROSS PATAGONIA TO THE WESTERN ATLANTIC LATER TODAY. THIS  
SUSTAINS A SURFACE FRONT ACROSS NORTHERN PATAGONIA-LA PAMPA IN  
ARGENTINA TO TEMUCO IN SOUTHERN CHILE LATER THIS AFTERNOON...TO  
MEANDER NORTH ACROSS LA PAMPA-CENTRAL CHILE ON THURSDAY. AS IT  
ENTERS SOUTHERN CHILE THIS WILL SUSTAIN SCATTERED CONVECTION OVER  
CHILE BETWEEN PUERTO MONTT AND CONCEPCION...TO FAVOR MODERATE  
RAINFALL AMOUNTS WITH MAXIMA OF 15-20MM. MODERATE CONVECTION IS TO  
PERSIST THROUGH THURSDAY AS AN OCCLUDED LOW/TROUGH MEANDERS OVER  
THE SOUTHERN CONE. OVER CENTRAL ARGENTINA THIS IS TO SUSTAIN  
RAINFALL AMOUNTS OF 05-10MM ON THURSDAY.  
 
IN A HIGHLY AMPLIFIED SINUSOIDAL PATTERN A RIDGE IS TO THEN  
AMPLIFY ALONG 90W TO THE BELLINGSHAUSEN SEA/POLAR ICECAP LATER ON  
THURSDAY. AS THE RIDGE BUILDS TO THE WEST THIS IS TO THEN SUSTAIN  
THE NORTHWARD AMPLIFICATION OF A TROUGH ALONG THE COAST OF  
ARGENTINA TO URUGUAY/ENTRE RIOS IN ARGENTINA LATER ON FRIDAY.  
BROAD/HIGH AMPLITUDE TROUGH IS TO MEANDER EAST TO EXTEND BETWEEN  
60W-20W TO 30S LATER ON SUNDAY. AT LOW LEVELS...A RIDGE IS TO  
THEN BUILD ACROSS THE SOUTHERN CONE ON FRIDAY...TO SUSTAIN A  
PAMPERO LOW LEVEL JET THAT DRIVES THE SURFACE FRONT NORTH TO  
SOUTHERN BRASIL-NORTHERN ARGENTINA LATER IN THE DAY. THE FRONT IS  
TO THEN REMAIN NEARLY STATIONARY WHILE SLOWLY WEAKENING LATER  
DURING THE WEEKEND. AS IT SURGES ACROSS NORTHERN ARGENTINA THIS  
WILL TRIGGER MODERATE CONVECTION ACROSS JUJUY/SALTA TO THE  
NORTHWEST...WITH MAXIMA OF 20-30MM. LOCALLY HIGHER AMOUNTS ARE  
HIGHLY PROBABLE DUE TO STRONG TOPOGRAPHICAL FORCING. ON SATURDAY  
EXPECTING HEAVY CONVECTION ACROSS CENTRAL-NORTHERN BOLIVIA-MATO  
GROSSO IN BRASIL TO TRIGGER MAXIMA OF 50-100MM IN AN MCS...WHILE  
OVER SOUTHERN JUNGLE OF PERU EXPECTING MAXIMA OF 25-50MM. ON  
SUNDAY FOCUS OF THE CONVECTION IS EXPECTED ACROSS NORTHERN  
BOLIVIA-RONDONIA-MATO GROSSO IN BRASIL TO FAVOR MAXIMA OF 30-60MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...AN EAST-TO-WEST RIDGE  
TRAVERSES THE CONTINENT BETWEEN 05S-20S. EARLY IN THE CYCLE THIS  
IS TO ANCHOR ON A CLOSED HIGH OVER SOUTHEAST BRASIL. BUT AS  
CONVECTION ACROSS BOLIVIA INTENSIFIES LATER DURING THE  
WEEKEND...AND LATENT HEAT IS RELEASED TO THE ATMOSPHERE...THE HIGH  
WILL RELOCATE TO CENTRAL BOLIVIA. A TROUGH TO THE NORTH IS TO  
MEANDER OVER NORTHEAST BRASIL TO THE GUIANAS...WHILE ORIGINATING  
ON A CLOSED LOW EAST OF RECIFE. IN A DIVERGENT PATTERN BETWEEN  
THIS TROUGH AND THE RIDGE TO THE SOUTH ORGANIZED DEEP CONVECTION  
IS TO CLUSTER BETWEEN PARA AND BAHIA IN BRASIL...WITH MAXIMA OF  
20-35MM EARLY IN THE CYCLE. ON THURSDAY THIS INCREASES TO  
40-80MM...WHILE ON FRIDAY THE MAXIMA PEAKS AT 30-60MM. DURING THE  
WEEKEND THE FOCUS OF THE CONVECTION SHIFTS ALONG THE NEAR  
EQUATORIAL TROUGH OVER PARA-AMAZONAS IN BRASIL...WITH MAXIMA OF  
20-40MM. OVER ECUADOR INITIALLY EXPECTING MAXIMA OF  
15-25MM...INCREASING TO 20-35MM/DAY ON THURSDAY-SUNDAY.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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