145  
FXSA20 KWBC 041915  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
215 PM EST WED DEC 04 2024  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
SOUTH AMERICAN FORECAST BULLETIN FOR 04 DEC 2024 AT 1810 UTC: A  
MID-UPPER TROUGH IS PROPAGATING ACROSS SOUTHERN SOUTH AMERICA FROM  
SOUTHWEST TO NORTHEAST...AS IT IS BEING STEERED BY A LARGER  
MID-UPPER POLAR TROUGH LOCATED IN THE SOUTHWEST ATLANTIC. THE  
TROUGH IS FORECAST TO PROPAGATE FROM SOUTHERN PATAGONIA...TAITAO  
PENINSULA...31S 88W ON WEDNESDAY TO 50S 53W...SOUTHWEST BUENOS  
AIRES PROVINCE...MENDOZA BY FRIDAY EVENING. THE SLOW EVOLUTION OF  
THE UPPER TROUGH IS DEVELOPING LOW-LEVEL EASTERLY FLOW IN CENTRAL  
PATAGONIA...WHICH IS RESULTING IN THE DEVELOPMENT OF DEEP  
CONVECTION AND MODERATE PRECIPITATION FOR THE REGION. THROUGH  
EARLY THURSDAY EXPECT MAXIMA OF 15-20MM. FROM THURSDAY INTO EARLY  
FRIDAY THIS IS EXPECTED TO INCREASE TO 15-20MM/DAY AND MAXIMA OF  
25-50MM IN EASTERN RIO NEGRO. THIS DECREASES THEREAFTER. ALSO ON  
THURSDAY...AS AVAILABLE LOW-LEVEL MOISTURE RECOVERS IN CENTRAL  
ARGENTINA AND THE RIO DE LA PLATA REGION AND A SURFACE FRONT  
ORGANIZES...EXPECT THE DEVELOPMENT OF SCATTERED MOIST CONVECTION.  
GIVEN LOW TEMPERATURES IN THE MID-TROPOSPHERE...EXPECT SUFFICIENT  
INSTABILITY TO STIMULATE THE DEVELOPMENT OF SEVERE CONVECTION. BY  
THURSDAY INTO EARLY FRIDAY...EXPECT MAXIMA OF 20-45MM DEVELOPING  
FROM ENTRE RIOS INTO CENTRAL AND NORTHERN URUGUAY AND SOUTHERN RIO  
GRANDE DO SUL...WITH A MODERATE RISK OF SEVERITY. ACROSS CENTRAL  
ARGENTINA FROM CORDOBA INTO MOST OF THE BUENOS AIRES PROVINCE  
EXPECT MAXIMA OF 15-20MM/DAY ALSO WITH A MODERATE RISK FOR  
SEVERITY. ON FRIDAY INTO EARLY SATURDAY...EXPECT A  
REINTENSIFICATION OF THE SALLJ ACROSS BOLIVIA AND PARAGUAY...WHICH  
WILL STIMULATE MOISTURE CONVERGENCE IN SOUTHERN  
PARAGUAY...NORTHEAST ARGENTINA AND PORTIONS OF SOUTHERN BRASIL.  
INTERACTIONS WITH SHORT WAVE MID-UPPER TROUGHS WILL FAVOR PERIODS  
OF HEAVY RAINFALL. EXPECT AMOUNTS OF 20-40MM WITH POTENTIAL MAXIMA  
OF 75-125MM AND A RISK FOR MCS FORMATION. IN NORTHWEST ARGENTINA  
AS WELL AS IN SOUTHERN RIO GRANDE DO SUL EXPECT 05-10MM/DAY AND  
MAXIMA OF 15-30MM.  
 
IN TROPICAL SOUTH AMERICA...THE BOLIVIAN HIGH CONTINUES BEING THE  
DOMINANT FEATURE WHILE CENTERING OVER WESTERN MATO GROSSO AND  
EXTENDING FROM SOUTHEAST BRASIL INTO NORTHWEST BRASIL/NORTHERN  
PERU. A CLOSED UPPER LOW (OR VORTICE CICLONIC DE ALTOS NIVELS -  
VCAN) CENTERS OVER FAR NORTHEAST BRASIL. THIS IS ENHANCING  
SOUTHERLY UPPER FLOW AND VENTILATION IN EASTERN BRASIL. THE VCAN  
IS FORECAST TO RETROGRADE TO CENTER OVER SOUTHEAST PARA BY  
SATURDAY EVENING...WHICH WILL RESULT IN A GRADUAL WESTWARD  
MIGRATION OF THE REGION OF HIGHEST VENTILATION/UPPER DIVERGENCE  
BETWEEN THE BOLIVIAN HIGH AND THE VCAN. FURTHERMORE...A GRADUAL  
DECREASE IN UPPER CONVERGENCE IN THE LARGE SCALE...IN ASSOCIATION  
WITH THE MJO...WILL FAVOR MODERATE RAINFALL DEVELOPING IN PORTIONS  
OF THE CENTRAL AND WESTERN AMAZON AS THE FORECAST CYCLE  
PROGRESSES. IN TERMS OF THE AREAS WHERE THE HEAVIEST PRECIPITATION  
IS EXPECTED...ON WEDNESDAY EXPECT MAXIMA OF 30-60MM FROM SOUTHERN  
MARANHAO INTO PARA IN BRASIL...AND MAXIMA OF 20-45MM FROM GOIAS  
INTO MINAS GERAIS AND RIO DE JANEIRO. IN NORTHWEST BRASIL/NORTHERN  
PERU EXPECT MAXIMA OF 15-30MM. EXPECT SIMILAR AMOUNTS ALONG A  
TROUGH LOCATED FROM THE PANTANAL INTO NORTHERN BOLIVIA AND  
SOUTHERN PERU. ON THURSDAY...EXPECT THE HEAVIEST PRECIPITATION TO  
CLUSTER FROM CENTRAL PARA AND CENTRAL AMAZONAS SOUTH INTO MATO  
GROSSO AND RONDONIA...WHERE EXPECT MAXIMA OF 35-70MM. IN SOUTHEAST  
BRASIL...EXPECT MAXIMA OF 15-30MM ALONG A SURFACE TROUGH FORECAST  
TO EXTEND FROM RIO DE JANEIRO INTO NORTHERN MATO GROSSO DO SUL. ON  
FRIDAY EXPECT MAXIMA OF 20-45MM ACROSS MOST OF THE CENTRAL AMAZOBN  
FROM NORTHERN PARA INTO AMAZONAS AND RONDONIA. ALSO ON  
FRIDAY...ENHANCED VENTILATION AND CYCLONIC VORTICITY ALONG THE  
NORTHERLY LOW-LEVEL JET WILL FAVOR MAXIMA OF 40-80MM ALONG THE  
CENTRAL AND SOUTHERN AMAZON OF PERU AND NORTHWEST BOLIVIA.  
 
GALVEZ...(WPC)  
 
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