887
FXSA20 KWBC 192103
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
503 PM EDT THU SEP 19 2024

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

SOUTH AMERICAN FORECAST BULLETIN FOR 19 SEP 2024 AT 2100 UTC:

SOME AREAS IN AND AROUND NORTHEASTERN ARGENTINA AND URUGUAY
OBSERVED SEVERE WEATHER TODAY...AS IT WAS EXPECTED. HOWEVER...THE
ACTIVE AND SEVERE WEATHER RISK CONTINUES TONIGHT INTO FRIDAY FOR
PORTIONS MAINLY OVER URUGUAY...SOUTHERN BRAZIL AND SOUTHERN
PARAGUAY...THOUGH PORTIONS OF NORTHEASTERN ARGENTINA MAY ALSO
OBSERVE ACTIVE WEATHER INTO LATE THIS AFTERNOON. CENTRAL TO
SOUTHERN CHILE...WILL BE SUBJECT TO HIGHER THAN NORMAL MOISTURE
FOR THE NEXT FEW DAYS...STARTING MAINLY FRIDAY AFTERNOON...AS AN
ATMOSPHERIC RIVER AFFECTS THE AREA. FOR TODAY INTO EARLY
FRIDAY...THERE WILL BE DIRECT ONSHORE FLOW INTO CENTRAL TO SOUTH
CENTRAL  CHILE. THERE IS RAIN THAT IS FORECAST ACROSS THE LOWER
ELEVATIONS OF THESE SECTIONS OF CHILE...WHILE SNOW IS FORECAST
OVER THE HIGHEST ELEVATIONS.

THERE IS AN ELEVATED RISK OF SEVERE WEATHER EVENT OVER ARGENTINA
INTO URUGUAY FOR THE REST OF TODAY INTO EARLY FRIDAY...LARGE HAIL
AND STRONG GUSTY WINDS HAVE ALREADY BEEN REPORTED OVER THE AREA.
THE STRONG STORMS THAT ARE FORECAST TONIGHT INTO FRIDAY COULD
PRODUCE FREQUENT LIGHTNING...STRONG GUSTY WINDS...HEAVY RAIN AND
SOME HAIL. BASED ON THE LATEST GUIDANCE...THE MODERATE RISK OF
SEVERE WEATHER WILL BE MAINLY OVER SOUTHERN BRAZIL INTO PARAGUAY
ON FRIDAY INTO SATURDAY. THE STRONG GUSTY WINDS AND THE RISK OF
HAIL IS DUE TO THE COMBINATION OF A WARM AND NORTHERLY LOW LEVEL
JET OVER THE CONTINENT INTO THE AREA...JUST AHEAD OF A FRONTAL
BOUNDARY THAT IS MOVING NORTHEAST. IN THE MID LEVELS...ALTHOUGH
THE STRONG MID LEVEL TROUGH HAS PASSED...THERE IS STILL A MID
LEVEL SHORTWAVE TROUGH OVER THE AREA. THERE IS ALSO AN UPPER
TROUGH WITH  STRONG WINDS THAT ARE PROVIDING SOME
DIVERGENCE...THOUGH THERE IS ALSO DIFLUENCE EXPECTED IN THE UPPER
LEVELS OVER THE AREA THROUGH FRIDAY NIGHT. THE GRO2T SEVERITY
ALGORITHM DOES INDICATE A MODERATE TO ELEVATED RISK FOR SEVERE
WEATHER THROUGH EARLY FRIDAY...THEN SLIGHT TO MODERATE ON FRIDAY
OVER PARAGUAY AND SOUTHERN BRAZIL...THEN ALSO SLIGHT TO MODERATE
OVER ARGENTINA IN AND AROUND THE BUENOS AIRES PROVINCE.

THE PRECIPITABLE WATER IS FORECAST TO BE NEAR TO BELOW NORMAL
TONIGHT INTO EARLY FRIDAY ACROSS CENTRAL TO SOUTHERN CHILE...THEN
INCREASE ON FRIDAY ONWARD...AS AN ATMOSPHERIC RIVER MOVES IN AND
AFFECTS PORTIONS OF CENTRAL CHILE. THE MODEL GUIDANCE CONTINUES TO
OVERESTIMATE THE PRECIPITATION OVER THE AREA...AS IT HAS BEEN
DOING OVER THE PAST FEW DAYS. FOR THAT REASON...THE FORECAST
PRECIPITATION OVER CENTRAL TO SOUTHERN CHILE WILL BE LOWER THAN
WHAT THE MODEL GUIDANCE IS SUGGESTING. OUR FORECAST SUGGESTS MAX
VALUES NEAR 20-40MM TODAY AND FRIDAY...WHILE SATURDAY INTO SUNDAY
UP TO 50MM IS FORECAST. THE REASON FOR THE HIGHER AMOUNT ON
SATURDAY INTO FRIDAY IS BECAUSE THERE WILL BE A MID LEVEL TROUGH
MOVING INTO THE AREA AS WELL AS STRONG UPPER LEVEL WINDS...WHICH
WILL CAUSE AN INCREASE IN INSTABILITY. THE GFS MODEL IS VERY
AGGRESSIVE WITH THE AMOUNTS...WHILE THE ECMWF IS MORE
MODEST...THEREFORE AT THIS TIME WE SHOWED AN INCREASE IN
PRECIPITATION BUT SPLITTING THE DIFFERENCE BETWEEN THE MODELS. WE
WILL ADJUST AS WE FIND MORE CONSISTENCY AMONG THE MODELS. IT IS
WORTH MENTIONING THAT THERE IS ALSO A CHANCE OF ISOLATED
THUNDERSTORMS ON FRIDAY INTO EARLY SATURDAY ACROSS CENTRAL CHILE.

AS MENTIONED ABOVE...PORTIONS OF EAST CENTRAL ARGENTINA IN TO
SOUTHERN BRAZIL AND SOUTHERN PARAGUAY ARE AT RISK OF OBSERVING
SEVERE WEATHER THIS EVENING INTO THE WEEKEND...THOUGH MORE
ISOLATED WITH EACH PASSING DAY. THE PRECIPITATION FORECAST
SUGGESTS A MAXIMA NEAR 35-70MM FOR SOUTHERN BRAZIL...NORTHERN
URUGUAY AND SOUTHERN PARAGUAY...WITH EASTERN AND NORTHEASTERN
ARGENTINA OBSERVING UP TO AROUND 35MM. PRECIPITATION FORECAST FROM
FRIDAY INTO SATURDAY...SUGGESTS LITTLE RAIN OVER ARGENTINA....BUT
SOUTHERN BRAZIL AND SOUTHERN PARAGUAY IS FORECAST TO OBSERVE UP TO
35-70MM OF RAIN...WITH THE ECMWF MODEL HAVING A LARGER COVERAGE
AREA IN THE FORECAST COMPARED TO THE GFS MODEL. THEN SATURDAY INTO
SUNDAY...UP TO 25MM IS FORECAST OVER SOUTHERN BRAZIL...BUT AREAS
IN AND AROUND BUENOS AIRES ARE FORECAST UP TO 35MM WITH A SLIGHT
RISK OF SVR WEATHER.

PERU IS FORECAST TO OBSERVE SOME RAINFALL EACH DAY BUT THE AMOUNTS
WILL BE RELATIVELY MODEST. GENERALLY MAX VALUES OF 25MM OR LESS
ARE FORECAST EACH DAY OVER PERU...WITH THE CHANCE OF ISOLATED
THUNDERSTORMS. THAT BEING SAID...NORTHERN PERU COULD OBSERVE UP TO
35MM ON SATURDAY INTO SUNDAY.


ALAMO...(WPC)
$$