SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
303 PM EDT TUE SEP 17 2024

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

SOUTH AMERICAN FORECAST BULLETIN FOR 17 SEP 2024 AT 1900 UTC:

OVER THE NEXT THREE DAYS...SOME AREAS OF THE SOUTH AMERICAN
CONTINENT WILL RECEIVE SIGNIFICANT RAIN...AND SNOW...WHILE SOME
AREAS MAY OBSERVE SEVERE WEATHER. CENTRAL TO SOUTHERN CHILE...WILL
BE SUBJECT TO SLIGHTLY HIGHER THAN NORMAL MOISTURE TODAY THROUGH
EARLY THURSDAY. A COLD FRONT AND A SFC LOW MOVES IN LATE WEDNESDAY
INTO THURSDAY. THESE FEATURES WILL CAUSE SOME RAIN ACROSS CENTRAL
CHILE ACROSS THE LOWER ELEVATIONS...WHILE SNOW COULD BE OBSERVE
OVER THE HIGHEST ELEVATIONS.

AN AREA ACROSS EAST CENTRAL ARGENTINA WILL HAVE A MODERATE RISK OF
SEVERE WEATHER ON WEDNESDAY...NAMELY IN THE REGION NEAR THE
PROVINCES OF LA PAMPA...RIO NEGRO...AND BUENOS AIRES. FOR THURSDAY
INTO FRIDAY...THE RISK OF SEVERE WEATHER MOVES NORTH...POSSIBLY
AFFECTING SOUTHERN BRAZIL...NORTHERN URUGUAY AND SOUTHERN
PARAGUAY...WITH A SMALL SECTION OF NORTHEASTERN ARGENTINA. THIS
RISK OF SEVERE WEATHER...INCLUDING STRONG GUSTY WINDS AND THE RISK
OF HAIL IS DUE TO THE COMBINATION OF SEVERAL FACTORS. THERE IS
WARM AIR MOVING IN FROM THE LOW LEVELS...JUST AHEAD OF A FRONTAL
BOUNDARY THAT IS MOVING NORTH. IN THE MID LEVELS...A TROUGH WILL
MOVE THROUGH THE CONTINENT FROM WEST TO EAST...WITH THE VORTICITY
MAXIMA MOVING ACROSS THE CONTINENT AS WELL...WHILE A STRONG UPPER
LEVEL JET PROVIDES PLENTY OF DIVERGENCE AND SOME DIFLUENCE OVER
THE AREA ON WEDNESDAY AND THURSDAY. THE COMBINATION OF THESE
FACTORS WILL PROVIDE GOOD INSTABILITY AND THE CHANCE OF SEVERE
WEATHER. THE GRO2T SEVERITY ALGORITHM DOES INDICATE A MODERATE TO
PERHAPS ELEVATED RISK FOR SEVERE WEATHER ACROSS THE AREA.

THE ATMOSPHERIC RIVER THAT AFFECTED CHILE WILL BE WEAKER BY
WEDNESDAY...AND THE PRECIPITABLE WATER IS FORECAST TO DECREASE
OVER SOUTH CENTRAL CHILE. THE MODEL GUIDANCE OVERESTIMATED THE
PRECIPITATION OVER THE AREA ON THE PAST SEVERAL MODEL RUNS...FOR
THAT REASON...THE FORECAST PRECIPITATION OVER CENTRAL TO SOUTHERN
CHILE WILL BE LOWER THAN WHAT THE MODEL GUIDANCE IS
SUGGESTING...WITH OUR FORECAST SUGGESTING MAX VALUES NEAR 15-25MM
TODAY AND ON WEDNESDAY. BY THURSDAY INTO EARLY FRIDAY...THE LOW
HAS MOVE IN AND THERE IS PERSISTENT LIGHT TO MODERATE
PRECIPITATION OVER CENTRAL TO SOUTHERN CHILE. THE CENTRAL SECTIONS
WILL OBSERVE RAIN IN THE LOWER ELEVATIONS...WHILE THE HIGHER
ELEVATIONS WILL OBSERVE SNOW. THERE IS ALSO NOW IN THE FORECAST
FOR THE SOUTHERNMOST SECTIONS OF CHILE ON THURSDAY INTO
FRIDAY...BEHIND A COLD FRONT.

PORTIONS OF EAST CENTRAL ARGENTINA IN TO SOUTHERN CHILE AND
SOUTHERN PARAGUAY ARE AT RISK OF OBSERVING SEVERE WEATHER ON
WEDNESDAY AND THURSDAY INTO EARLY FRIDAY. THE MAIN FEATURES THAT
WILL AFFECT THE AREA WERE DISCUSSED ABOVE...AND IN TERMS OF
RAINFALL AMOUNTS...THE LATEST MODEL GUIDANCE IS SUGGESTING LITTLE
RAIN TODAY INTO WEDNESDAY...BUT FROM WEDNESDAY INTO THURSDAY...UP
TO 45MM OR SO COULD BE OBSERVED ACROSS PORTIONS OF LA PAMPA...RIO
NEGRO...AND THE BUENOS AIRES PROVINCES...WHILE LOWER AMOUNTS OF
RAIN...MAX NEAR 20 TO 35MM IS FORECAST FURTHER NORTH...THOUGH
STILL WITH A CHANCE OF STRONG STORMS. HOWEVER...FOR THURSDAY INTO
FRIDAY...CONSIDERING THE AFOREMENTIONED FEATURES THAT COULD CAUSE
SEVERE WEATHER OVER THE AREA...PRECIPITATION MAXIMA NEAR 35-70MM
ARE FORECAST FOR SOUTHERN BRAZIL...NORTHERN URUGUAY AND SOUTHERN
BRAZIL...WITH NORTHEASTERN ARGENTINA OBSERVING LESS RAINFALL...UP
TO AROUND 35MM. ONCE AGAIN...THE GR02T ALGORITHM DOES SUGGEST A
MODERATE TO ELEVATED RISK OF SEVERE WEATHER ACROSS THE AREA...WITH
AN ELEVATED RISK OF HAIL.

OTHER AREAS WITH SOME PRECIPITATION WILL BE OVER PERU...WHERE THE
HIGHER ELEVATIONS ARE FORECAST TO OBSERVE MAX VALUES OF 15-25MM
EACH DAY. ALSO AREAS NEAR RIO DE JANEIRO IN BRAZIL...NORTH INTO
ESPIRITO SANTO AND BAHIA COULD OBSERVE MAX VALUES NEAR 10-30MM
TODAY AS A STATIONARY FRONT AND SFC TROUGH IS LOCATED OVER THE
AREA...CAUSING LOCALLY HIGHER MOISTURE CONVERGENCE. THE AMOUNTS OF
RAIN OVER THE AREA IS FORECAST TO DECREASE EACH DAY THEREAFTER AS
THE FRONT WEAKENS AND MOVES AWAY. 


ALAMO...(WPC)