SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
327 PM EDT THU AUG 29 2024

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

SOUTH AMERICAN FORECAST BULLETIN FOR 29 AUG 2024 AT 1925 UTC:

OVER THE NEXT 3 DAYS...SEVERAL FACTORS WILL CONTRIBUTE TO CAUSE
AREAS OF ACTIVE WEATHER ACROSS SOUTH AMERICA...NAMELY OVER
PORTIONS OF SOUTHERN BRAZIL INTO URUGUAY AND EAST CENTRAL
ARGENTINA...WITH THE RISK OF SEVERE WEATHER ON FRIDAY INTO
SATURDAY...THEN AN ATMOSPHERIC RIVER THAT WILL BE AFFECTING
PORTIONS OF SOUTHERN CHILE.

BASED ON THE LATEST GUIDANCE...THE HEAVIEST PRECIPITATION EXPECTED
ANYWHERE WITHIN THE NEXT 3 DAYS WILL BE IN AND AROUND BUENOS
AIRES...BUT THE MOST UNSTABLE AREA WITH THE BEST CHANCE OF STRONG
THUNDERSTORMS WILL BE TO THE NORTH AND NORTHWEST OF BUENOS
AIRES...OVER THE ENTRE RIOS PROVINCE AND PORTIONS OF URUGUAY. THE
EXPECTED RAINFALL RELATED TO THESE THUNDERSTORMS COULD BE AS MUCH
AS 50-100MM OVER THE NEXT 3 DAYS...THOUGH MOST OF THE
PRECIPITATION...AROUND 40-80MM WOULD BE OBSERVED ON FRIDAY INTO
SATURDAY. THE AFOREMENTIONED ATMOSPHERIC RIVER THAT WILL AFFECT
SOUTHERN CHILE WILL GENERALLY AFFECT THE SECTORS OF AYSEN AND
MAGALLANES. THE PRECIPITABLE WATER ANOMALIES FOR FRIDAY AND
SATURDAY WILL BE NEAR 150 TO 200 PERCENT OF NORMAL...WHICH WILL
CONTRIBUTE TO SIGNIFICANT AMOUNTS OF RAIN AND SNOW OVER THE AREA.
THIS ATMOSPHERIC RIVER COULD CAUSE AS MUCH AS 30-60MM OF RAIN
ACROSS THE LOWER ELEVATIONS OF SOUTHERN CHILE...WHILE AS MUCH AS
30CM OF SNOW COULD BE OBSERVED OVER THE HIGHER ELEVATIONS OF
SOUTHERN CHILE. DAILY RAINFALL WILL BE OBSERVED ACROSS THE
TROPICAL SECTIONS OF SOUTH AMERICA DUE TO THE DEEP MOISTURE
INTERACTING WITH THE LOCAL OROGRAPHY AND DIURNAL PATTERNS..HAVING
A WIDESPREAD PRECIPITATION COVERAGE...BUT THE AMOUNTS WOULD BE
LIMITED ACROSS MOST AREAS OF TROPICAL SOUTH AMERICA...THOUGH
WESTERN AND NORTHWESTERN COLOMBIA IS EXPECTED TO HAVE SIGNIFICANT
RAINFALL ACCUMULATIONS...UP TO AROUND 100MM OVER THE NEXT 3 DAYS. 

A LOW LEVEL JET OVER SOUTH AMERICA WILL INTERACT WITH A STATIONARY
FRONT IN AND AROUND URUGUAY AND THE POOLING OF LOW LEVEL MOISTURE.
IN THE MID LEVELS...A CUTOFF LOW WILL MOVE FROM THE PACIFIC INTO
CHILE AND ARGENTINA...WHILE AN UPPER LEVEL LOW WILL ALSO MOVE FROM
THE PACIFIC INTO ARGENTINA. THIS VERTICALLY STACKED LOW WILL CAUSE
A LOW LEVEL TROUGH ACROSS ARGENTINA INTO URUGUAY FOR FRIDAY INTO
SATURDAY...WHICH WILL BE AMPLIFIED BY THE AFOREMENTIONED LLJ
ACROSS THE AREA TO HELP CAUSE SOME CYCLONIC ROTATION THAT WILL
GRADUALLY DEVELOP IN THE LOWER LEVELS. THE COMBINATION OF THESE
SYSTEMS WILL CAUSE AN INCREASE IN DIVERGENCE ALOFT AS WELL AS
INSTABILITY OVER THE AREA. THE LOW LEVEL WINDS COMING FROM THE
NORTH WILL INTERACT WITH THE DEEP MOISTURE AND WILL CAUSE THE
SIGNIFICANT RAINFALL TO THE SOUTH OF THE STATIONARY FRONT ON
FRIDAY. THAT BEING SAID...THE MODEL GUIDANCE IS SUGGESTING THE
COLDER AND MORE UNSTABLE MID TO UPPER LEVEL DYNAMICS ARE PRESENT
ON THE NORTH SIDE OF THE FRONTAL BOUNDARY AND THEREFORE THE BETTER
CHANCE OF SEVERE WEATHER WILL BE POSSIBLE TO THE NORTH OF THE
FRONTAL BOUNDARY. BY SATURDAY...THE STATIONARY FRONT WILL START
MOVING SOUTH AND A WARM FRONT WILL DEVELOP JUST OFFSHORE
URUGUAY...WHILE A COLD FRONT WILL PUSH NORTH AND EAST ACROSS
SOUTHERN BRAZIL INTO PARAGUAY. AN OCCLUDED FRONT ASSOCIATED WITH
THE AFOREMENTIONED WARM AND COLD FRONT WILL MOVE OVER EAST CENTRAL
ARGENTINA.

A MID TO UPPER LEVEL HIGH PRESSURE ACROSS SOUTHERN BRAZIL IS STILL
EXPECTED TO DEVELOP AND BECOME DOMINANT OVER THE NEXT SEVERAL
DAYS...CAUSING A BLOCKING PATTERN AND CREATE SUBSIDENCE OVER THE
AREA. THIS WILL KEEP THE OTHER SYSTEMS AND FRONTS FROM MOVING
FURTHER NORTH. FOR THIS REASON...MOST OF BRAZIL AND BOLIVIA IS
STILL EXPECTED TO REMAIN DRY THROUGH THE WEEKEND...WITH THE
EXCEPTION OF A SMALL SECTION OF BOLIVIA...ACROSS THE HIGHER
ELEVATIONS WHERE A MIX OF SNOW AND RAIN IS FORECAST FOR SATURDAY
INTO SUNDAY AS LIMITED MOISTURE MOVES INTO WESTERN BOLIVIA AND
INTERACTS WITH A STRONG UPPER JET OVER THE AREA.


ALAMO...(WPC)
LOPEZ...(DMH PARAGUAY)