SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 PM EST THU DEC 05 2024

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

SOUTH AMERICAN FORECAST BULLETIN FOR 05 DEC 2024 AT 2030 UTC:

OVER THE NEXT THREE DAYS SEVERAL SECTIONS OF SOUTH AMERICA WILL
RECEIVE SIGNIFICANT RAINFALL. THE MODEL GUIDANCE IS FAVORING 3-DAY
ACCUMULATIONS OF NEAR OR OVER 50MM ACROSS PORTIONS OF WESTERN
BRASIL...EASTERN PERU...AND PORTIONS OF EASTERN PARAGUAY INTO
SOUTHERN BRASIL AND NORTHERN URUGUAY...AS WELL AS A SMALL SECTION
OF NORTHEASTERN ARGENTINA...BORDERING PARAGUAY AND URUGUAY. IT CAN
BE EXPECTED FOR MOST OF THESE AREAS TO RECEIVE SOME RAIN EACH DAY 
OVER THE NEXT THREE DAYS.  NORTHERN PATAGONIA IS FORECAST TO
RECEIVE SIGNIFICANT RAIN...WITH THE RAINFALL FORECAST FOR TODAY
INTO FRIDAY INDICATING MAX VALUES BETWEEN 25-50MM WITH LOCALLY
HEAVY RAIN. THERE IS ALSO A RISK OF SEVERE WEATHER OVER PORTIONS
OF THE LLANURA PLATENSE INTO URUGUAY FOR THE REST OF TODAY THROUGH
FRIDAY. THE GR02T ALGORITHM DOES FAVOR THE TIME PERIOD OF LATE
TONIGHT INTO VERY EARLY FRIDAY TO HAVE THE HIGHEST RISK OF SEVERE
WEATHER.

MID AND UPPER LEVEL TROUGHS ARE MOVING NORTHEAST ACROSS SOUTHERN
SOUTH AMERICA...BEING STEERED BY A MID-UPPER POLAR TROUGH LOCATED
IN THE SOUTHWEST ATLANTIC. THE AXIS OF THE TROUGH MOVING THROUGH
SOUTHERN SOUTH AMERICA WILL MOVE FROM THE AUSTRAL SECTION OF CHILE
AND ARGENTINA...NORTHEAST INTO THE BUENOS AIRES REGION BY FRIDAY
EVENING. THE APPROACHING TROUGH INTO BUENOS AIRES COMBINED WITH
THE STRONG UPPER LEVEL WINDS WILL HELP IN THE DEVELOPMENT OF THE
SHOWERS AND THUNDERSTORMS THAT ARE EXPECTED OVER THE LLANURA
PLATENSE AND URUGUAY LATE TONIGHT INTO FRIDAY MORNING. THE UPPER
TROUGH IS DEVELOPING LOW-LEVEL EASTERLY FLOW IN CENTRAL
PATAGONIA...WHICH...COMBINED WITH INCREASING LOW LEVEL
MOISTURE...IS HELPING IN THE DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS TODAY INTO FRIDAY. ON FRIDAY INTO EARLY
SATURDAY...NORTHERLY WINDS WITH DEEP MOISTURE WILL MOVE INTO
BOLIVIA AND PARAGUAY...CAUSING CONVERGENCE IN SOUTHERN
PARAGUAY...NORTHEAST ARGENTINA AND PORTIONS OF SOUTHERN BRASIL.

IN THE TROPICAL REGION OF SOUTH AMERICA...THE BOLIVIAN HIGH
CONTINUES TO DOMINATE THE AREA. AN UPPER LOW CENTERED OVER
NORTHEAST BRASIL WILL ENHANCE THE SOUTHERLY UPPER FLOW AND
VENTILATION IN EASTERN BRASIL. THIS UPPER LOW WILL MOVE WEST...AND
THE BOLIVIAN HIGH WILL MOVE SOUTHWEST OVER THE NEXT FEW DAYS. THIS
WILL CAUSE DIFFLUENCE OVER WESTERN BRASIL ON SATURDAY...WHICH MAY
RESULT IN AN ENHANCED CHANCE OF THUNDERSTORMS OVER THE AREA. THE
ECMWF MODEL IS PICKING UP ON THIS AND ITS RAINFALL SOLUTION IS
SUGGESTING SIGNIFICANT RAINFALL OVER THE AREA. THE LATEST MJO
ANALYSIS AND GUIDANCE IS SUGGESTING AN UPPER CONVERGENT PATTERN
FOR THE NEXT SEVERAL DAYS. FOR THAT REASON WE DECIDED TO FORECAST
AMOUNTS AND COVERAGE A BIT MORE CONSERVATIVELY THAN THE MODEL
GUIDANCE WAS SUGGESTING...BUT STILL SHOWING AREAS WHERE
SIGNIFICANT RAIN AND SEVERE THUNDERSTORMS COULD OCCUR BASED ON THE
CURRENT SYNOPTIC PATTERN AND LOCAL EFFECTS.

ALAMO...(WPC)