044  
FXSA20 KWBC 021633  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1133 AM EST TUE JAN 02 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 02 AT 0000 UTC): CONFIDENCE IN  
THE FORECAST IS HIGH THROUGH 108-120 HRS...WITH MODELS AGREEING  
QUITE WELL ON THE LONG/SHORT WAVE PATTERN EVOLUTION THROUGHOUT THE  
SHORT RANGE PERIOD. THIS FORECAST IS WELL SUPPORTED BY THE MEAN OF  
THE GLOBAL ENSEMBLES.  
 
ON THE NORTHERN STREAM...A MID LEVEL TROUGH IS TO MOVE ACROSS  
SOUTHERN BRASIL-PARAGUAY LATER TODAY...AND OFF THE SOUTH COAST OF  
BRASIL EARLY ON WEDNESDAY MORNING. LATER IN THE DAY THE TROUGH  
WILL CONTINUE ACROSS 40W TO 30S...ACCELERATING ACROSS 10W ON  
THURSDAY EVENING. AT LOW LEVELS THIS SUSTAINS A SURFACE FRONT THAT  
EXTENDS ACROSS THE SOUTH ATLANTIC TO SAO PAULO-PARAGUAY. BOUNDARY  
IS TO REMAIN NEARLY STATIONARY WHILE GRADUALLY DISSIPATING ON  
THURSDAY. MEANWHILE...DEEP TROPICAL MOISTURE IS TO CONVERGE ALONG  
AND NORTH OF THIS BOUNDARY. OVER SOUTHEAST BRASIL-MATO GROSSO DO  
SUL TO PARAGUAY THIS IS TO INITIALLY FAVOR RAINFALL MAXIMA OF  
40-80MM. ON WEDNESDAY...AS ASSOCIATED JET MAXIMA ALOFT MEANDERS  
AWAY...THIS DECREASES TO 30-60MM. OTHER CONVECTION TO THE WEST IS  
TO CLUSTER ACROSS CENTRAL BOLIVIA TO THE SOUTHERN/CENTRAL JUNGLE  
OF PERU...WHERE IT IS TO SUSTAIN RAINFALL MAXIMA OF 30-60MM. ON  
WEDNESDAY-THURSDAY THIS DECREASES TO 20-30MM/DAY.  
 
IN TIGHT BELT OF MID LATITUDE WESTERLIES...A PROGRESSIVE MID LEVE  
TROUGH IS TO MOVE BETWEEN 80W-100W AND TO THE SOUTH OF 35S LATER  
TODAY...MOVING ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA ON  
WEDNESDAY. AS IT ENTERS THE SOUTHERN CONE THE SHORT WAVE TROUGH  
WILL SUSTAIN A SUBTROPICAL CONNECTION. THIS WILL FEED CONVECTIVE  
DEVELOPMENT TO THE SOUTH. AT LOW LEVELS THE TROUGH ALOFT SUSTAINS  
A PROGRESSIVE FRONT ENTERING SOUTHERN REGIONS OF CHILE LATER THIS  
EVENING...THEN QUICKLY MOVE ACROSS PATAGONIA IN ARGENTINA ON  
WEDNESDAY...INTO THE BUENOS AIRES PROVINCE/URUGUAY ON  
THURSDAY-FRIDAY. AS IT ENTERS SOUTHERN CHILE THIS WILL RESULT IN  
SCATTERED CONVECTION WITH MAXIMA OF 15-25MM. ON WEDNESDAY  
CONVECTION BUILDS NORTH ACROSS TEMUCO TO CONCEPCION...TO FAVOR  
MODERATE RAINFALL AMOUNTS WITH MAXIMA OF 15-20MM. ON THURSDAY ALSO  
EXPECTING MAXIMA OF 15-20MM BETWEEN PUERTO MONTT AND SOUTHERN  
PATAGONIA/TIERRA DEL FUEGO. OVER CENTRAL ARGENTINA THIS IS TO  
SUSTAIN RAINFALL AMOUNTS OF 05-10MM ON THURSDAY...WHILE ON FRIDAY  
MOST INTENSE IS TO FOCUS ON THE NORTHWEST PROVINCES TO TRIGGER  
RAINFALL MAXIMA OF 20-30MM.  
 
LATER IN THE CYCLE...AS A HIGH AMPLITUDE TROUGH DEEPENS BETWEEN  
130W-90W TO 30S THIS IS TO THEN SUSTAIN THE SOUTHWARD  
AMPLIFICATION OF A RIDGE ALONG 80W TO THE BELLINGSHAUSEN SEA. AS  
THE RIDGE BUILDS...A TROUGH IS TO AMPLIFY OVER THE WESTERN  
ATLANTIC WHILE MEANDERING OFF THE COAST OF ARGENTINA LATER ON  
SATURDAY-SUNDAY. AS THE TROUGH DEEPENS THIS IS TO INTERACT WITH  
AFOREMENTIONED FRONT STREAMING ACROSS CENTRAL-NORTHERN  
ARGENTINA/RIO DE LA PLATA BASIN. THIS IS TO THEN FAVOR AN INCREASE  
IN CONVECTION ACROSS BOLIVIA-SOUTHERN PERU TO MATO GROSSO IN  
BRASIL...WHERE WE EXPECT MAXIMA OF 25-50MM.  
 
AT 200 HPA...A RIDGE EXTENDS FROM SOUTHERN PERU...ACROSS  
BOLIVIA-SOUTHEAST STATES OF BRASIL INTO THE CENTRAL ATLANTIC. THE  
RIDGE ALOFT UNDERCUTS A MEANDERING TROUGH TO THE NORTH...WITH AXIS  
EXTENDING ACROSS NORTHWEST BRASIL TO THE GUIANAS. THROUGH THURSDAY  
MORNING THE TROUGH MEANDERS EAST AND NORTH. AS THE PATTERN EVOLVES  
FOCUS OF THE HEAVY CONVECTION WILL GRADUALLY SHIFT FROM SAO  
PAULO-MATO GROSSO DO SUL TO MINAS GERAIS-BAHIA-TOCANTINS/GOIAS IN  
BRASIL...WITH MAXIMA INCREASING FROM 20-30MM EARLY IN THE CYCLE T  
35-70MM ON THURSDAY. OTHER CONVECTION ALONG THE NEAR EQUATORIAL  
TROUGH IS TO CLUSTER ACROSS NORTHERN PARA-AMAZONAS IN BRASIL...TO  
FAVOR MAXIMA OF 15-25MM/DAY.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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