SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
333 PM EDT WED AUG 28 2024

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

SOUTH AMERICAN FORECAST BULLETIN FOR 28 AUG 2024 AT 1935 UTC:

THERE HAS BEEN ONLY MINOR CHANGES IN THE 3-DAY FORECAST FOR THE
SOUTH AMERICAN CONTINENT...WITH THE MOST SIGNIFICANT EVENT
POSSIBLY TAKING PLACE ON FRIDAY INTO EARLY SATURDAY WHERE THERE IS
A RISK OF SEVERE WEATHER OVER PORTIONS OF EASTERN ARGENTINA...NEAR
THE PROVINCE OF ENTRE RIOS...AS WELL AS MANY SECTORS OF URUGUAY.
THAT BEING SAID...THE HEAVIEST PRECIPITATION...AS SUGGESTED BY THE
MODEL GUIDANCE WILL BE IN AND AROUND BUENOS AIRES...BUT THE MOST
INSTABILITY WITH THE BEST CHANCE OF STRONG THUNDERSTORMS WOULD BE
TO THE NORTH AND NORTHWEST OF BUENOS AIRES...OVER ENTRE RIOS AND
PORTIONS OF URUGUAY. ELSEWHERE OVER SOUTH AMERICA...DAILY
PRECIPITATION IS EXPECTED TO BE OVER THE NORTHERN AND TROPICAL
SECTIONS OF SOUTH AMERICA...CENTRAL PERU...THE EAST COAST OF EAST
CENTRAL BRAZIL FROM RIO DE JANEIRO DE BAHIA...AND SOUTHERN CHILE
FROM AYSEN TO MAGALLANES. THERE IS ALSO SOME SNOW FORECAST ACROSS
THE MOUNTAINOUS SECTIONS OF SAN JUAN AND MENDOZA IN ARGENTINA
ALONG THE BORDER WITH CHILE...AS WELL AS SOME RAIN ALONG A LINE
FROM CORDOBA TO ENTRE RIOS IN ARGENTINA INTO SOUTHERN URUGUAY ON
THURSDAY INTO FRIDAY...THOUGH WITH MUCH LOWER ACCUMULATIONS THAN
WHAT IS EXPECTED ON FRIDAY INTO SATURDAY.

BASED ON THE LATEST GUIDANCE...IN TERMS OF LIQUID
PRECIPITATION...NORTHERN SOUTH AMERICA IS EXPECTED TO HAVE THE
WIDEST RAINFALL COVERAGE...BUT IN TERMS OF AMOUNTS...THE EVENT
OVER EASTERN ARGENTINA INTO URUGUAY COULD BE THE MOST
SIGNIFICANT...WITH MAX TOTALS RANGING BETWEEN
50-100MM...ESPECIALLY WHEN MOST OF THAT RAINFALL IS EXPECTED TO
OCCUR IN A 24-HR PERIOD FROM FRIDAY INTO SATURDAY. THE 3-DAY
PRECIPITATION AMOUNTS ACROSS NORTHERN SOUTH AMERICA COULD RANGE
BETWEEN 25 AND 50MM WITH ISOLATED HIGHER AMOUNTS POSSIBLY REACHING
75MM ACROSS PORTIONS OF CENTRAL VENEZUELA AND WESTERN COLOMBIA.
THIS WOULD BE DUE TO A COMBINATION OF FACTORS...INCLUDING DEEP
TROPICAL MOISTURE...TROPICAL WAVES PASSING BY AND SURFACE
TROUGHS...ALL THAT INTERACTING WITH THE LOCAL OROGRAPHIC AND
DIURNAL EFFECTS.

EASTERN BRAZIL...ESPECIALLY OVER BAHIA COULD OBSERVE UP TO 50-60MM
OVER THE 3-DAY PERIOD...AS A FRONTAL BOUNDARY THAT MOVES OVER THE
ATLANTIC AND SKIRTS THE EAST COAST OF BRAZIL. THIS FRONTAL
BOUNDARY WILL BECOME STATIONARY...EXTENDING FROM THE BRAZILIAN
STATE OF BAHIA EXTENDING INTO THE ATLANTIC...BUT WILL WEAKEN
SLIGHTLY EACH DAY OVER THE NEXT 3 DAYS. THE DEEPER MOISTURE AHEAD
OF THE FRONTAL BOUNDARY WILL BE PUSHED INLAND AND THEN INTERACT
WITH THE LOCAL TERRAIN. MEANWHILE...SOUTHERN CHILE COULD OBSERVE A
RAIN AND SNOW MIX...WITH THE HIGHER ELEVATIONS OF MAGALLANES
POSSIBLY OBSERVING AS MUCH AS 15CM OF SNOW OVER THE 3-DAY
PERIOD...THOUGH MOST OF THE SNOW IS EXPECTED TODAY INTO THURSDAY
MORNING...WITH LESS AND LESS SNOWFALL ACCUMULATIONS WITH EACH
PASSING DAY...FAVORING RAINFALL OVER THE LOWER
ELEVATIONS...LEAVING THE SNOW FOR THE HIGHER ELEVATIONS. ANOTHER
AREA WITH EXPECTED SNOW WOULD BE ACROSS THE HIGHEST ELEVATIONS OF
SAN JUAN AND MENDOZA IN ARGENTINA...WHICH CAN BE UP TO 30CM FOR
THE 3-DAY PERIOD...BUT ALMOST ALL OF THE PRECIPITATION IN THE AREA
IS EXPECTED TO BE OBSERVED FROM THURSDAY INTO FRIDAY.

ACROSS THE REGION...THERE ARE SEVERAL SURFACE LOW AND HIGH
PRESSURE SYSTEMS OVER THE WATERS. HOWEVER...ONE SYSTEM OF
PARTICULAR INTEREST IS A GRADUAL DEVELOPING OF CYCLOGENESIS ACROSS
CENTRAL TO EAST CENTRAL ARGENTINA. A LOW LEVEL JET WITH A
NORTHERLY FLOW IS MOVING FROM BRAZIL AND PARAGUAY INTO
ARGENTINA...WHICH WILL PROVIDE WARM ADVECTION TO THE AREA.
ADDITIONALLY THERE IS A STATIONARY FRONT DEVELOPING OVER EASTERN
ARGENTINA INTO SOUTHERN BRAZIL AND URUGUAY. THIS WILL ALLOW FOR
LOW LEVEL MOISTURE TO POOL OVER THE AREA OVER THE NEXT FEW DAYS AS
THE CYCLONIC ROTATION STARTS TO GRADUALLY DEVELOP IN THE LOWER
LEVELS. IN THE MID LEVELS...THERE IS A CUTOFF LOW THAT WILL BE
MOVING INLAND FROM THE PACIFIC INTO CHILE AND ARGENTINA BY FRIDAY.
THERE IS ALSO AN UPPER LEVEL TROUGH WITH STRONG WINDS ALOFT OVER
THE AREA. THE COMBINATION OF THESE SYSTEMS WILL CAUSE AN INCREASE
IN DIVERGENCE ALOFT AS WELL AS INSTABILITY OVER THE AREA. THIS
WILL TRANSLATE TO HEAVY RAIN AND THE POTENTIAL OF STRONG
THUNDERSTORMS ON FRIDAY INTO SATURDAY. THAT BEING SAID...THE MODEL
GUIDANCE IS SUGGESTING THE MOST OF THE HEAVY RAINFALL WILL OCCUR
OVER THE PROVINCE OF BUENOS AIRES...WHICH IS SOUTH OF THE
STATIONARY FRONT...BUT THE COLDER AND MORE UNSTABLE MID TO UPPER
LEVEL DYNAMICS ARE PRESENT ON THE NORTH SIDE OF THE FRONTAL
BOUNDARY.

ACROSS BRAZIL...A MID LEVEL HIGH PRESSURE ACROSS SOUTHEASTERN
BRAZIL IS STILL EXPECTED TO CREATE A BLOCKING PATTERN...WHICH WILL
KEEP THE OTHER SYSTEMS AND FRONTS FROM MOVING FURTHER NORTH WHILE
CREATING SUBSIDENCE OVER THE AREA. FOR THIS REASON...MOST OF
BRAZIL AND BOLIVIA IS STILL EXPECTED TO REMAIN DRY THROUGH THE
WEEKEND.


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