SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
320 PM EDT MON SEP 16 2024

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

SOUTH AMERICAN FORECAST BULLETIN FOR 16 SEP 2024 AT 1920 UTC:

MOST OF THE SOUTH AMERICAN CONTINENT WILL REMAIN RELATIVELY CALM
OVER THE NEXT THREE DAYS IN TERMS OF RAINFALL. HOWEVER...SOME
AREAS OF INTEREST ARE CENTRAL TO SOUTHERN CHILE...WHICH WILL BE
SUBJECT TO HIGHER THAN NORMAL MOISTURE AS AN ATMOSPHERIC RIVER
AFFECT THE AREA TODAY AND TUESDAY...AND THEN A COLD FRONT AND A
SFC LOW MOVES IN LATE WEDNESDAY INTO THURSDAY. THERE IS ALSO AN
AREA ACROSS EAST CENTRAL ARGENTINA...NAMELY IN THE REGION NEAR THE
PROVINCES OF LA PAMPA...RIO NEGRO...AND BUENOS AIRES. THESE AREAS
HAVE A MODERATE RISK OF SEVERE WEATHER LATE WEDNESDAY INTO
THURSDAY AS A SMALL SFC LOW MOVES EAST ACROSS THE PATAGONIA INTO
THE ATLANTIC COAST...CAUSING WARM MOIST AIR FROM THE NORTH TO MOVE
IN AHEAD OF A COLD FRONT. THERE IS ALSO A MID LEVEL TROUGH THAT
WILL MOVE INTO THE AREA LATE WEDNESDAY INTO THURSDAY...AS WELL AS
AN UPPER LEVEL TROUGH...WHICH WILL PROVIDE STRONG DIVERGENCE ALOFT
VERY EARLY THURSDAY MORNING. FOR THAT...THE GRO2T SEVERITY
ALGORITHM DOES INDICATE A MODERATE RISK FOR SEVERE WEATHER ACROSS
THE AREA.

TODAY...THE AFOREMENTIONED ATMOSPHERIC RIVER WILL BRING RAIN AND
SNOW TO SOUTH CENTRAL AND SOUTHERN CHILE AS A COUPLE OF FRONTAL
BOUNDARIES MOVE THROUGH THE AREA. A SFC LOW ACROSS THE WESTERN
ATLANTIC...WILL CAUSE ONSHORE WIND FLOW INTO RIO DE
JANEIRO...WHICH WILL CAUSE RAIN TO DEVELOP ALONG THE COAST.
NORTHWESTERN SOUTH AMERICA...IN PARTICULAR THE NORTHERN HALF OF
PERU AND WESTERN BRAZIL IS FORECAST TO OBSERVE SHOWERS AND
THUNDERSTORMS AS DEEP TROPICAL MOISTURE INTERACTS WITH THE LOCAL
TERRAIN EFFECTS.

THE FRONTAL BOUNDARIES MOVE QUICKLY OVER THE AREA WATERS...AND BY
WEDNESDAY THE ATMOSPHERIC RIVER WILL BE WEAKER...AND THE
PRECIPITABLE WATER IS FORECAST TO DECREASE OVER SOUTH CENTRAL
CHILE FROM AROUND 0.9 INCHES ON TUESDAY...TO AROUND 0.7 INCHES ON
WEDNESDAY MORNING. THEREFORE THE AMOUNTS OF RAIN AND SNOW FORECAST
ON WEDNESDAY OVER CHILE WILL BE A BIT MORE MODEST COMPARED TO WHAT
IS FORECAST FOR THE REST OF TODAY INTO EARLY TUESDAY.

BY LATE WEDNESDAY INTO THURSDAY...THE MAIN AREA TO OBSERVE IS THE
AFOREMENTIONED AREA IN EAST CENTRAL ARGENTINA. THE LATEST MODEL
GUIDANCE AND FORECAST ALGORITHMS INDICATE THAT THERE IS A MODERATE
RISK FOR SEVERE WEATHER AND SOME HAIL. IN TERMS OF RAINFALL
AMOUNTS...THE LATEST MODEL GUIDANCE IS SUGGESTING UP TO 45MM OR
SO...WHICH SEEMS CONSERVATIVE GIVEN THE EXPECTED INCREASE IN
MOISTURE AHEAD OF A SMALL COLD FRONT WITH WARM AIR MOVING IN FROM
THE NORTH. THERE IS ALSO A MID LEVEL TROUGH WITH VORTICITY MAX
OVER THE AREA OVERNIGHT WEDNESDAY INTO THURSDAY...AND A STRONG
UPPER JET TO THE SOUTHEAST OF THE AREA FOR THE TIME FRAME. OVERALL
THE SYNOPTIC PATTERN LOOKS ADEQUATE FOR SEVERE WEATHER...BUT THE
AMOUNTS OF RAIN IN THE FORECAST SEEMS A BIT LOW...HENCE WE WILL
WAIT FOR MODEL CONSISTENCY AND UPDATE TOMORROW. CENTRAL TO
SOUTHERN CHILE WILL RECEIVE ADDITIONAL PRECIPITATION ON WEDNESDAY
INTO THURSDAY...AS A SFC LOW PRESSURE MOVES IN WITH ITS ASSOCIATED
COLD FRONT. A COMBINATION OF RAIN AND SNOW IS FORECAST FOR THE
CENTRAL TO SOUTHERN HALF OF CHILE.  OTHER AREAS OF SEVERE WEATHER
COULD BE OBSERVED ALONG EASTERN ARGENTINA LATER ON IN THE
WEEK...THIS PATTERN WILL BE CLOSELY MONITORED.


ALAMO...(WPC)