552
FXSA20 KWBC 181852
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
251 PM EDT WED SEP 18 2024
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
SOUTH AMERICAN FORECAST BULLETIN FOR 18 SEP 2024 AT 1845 UTC:
OVER THE NEXT COUPLE OF DAYS...SOME AREAS IN AND AROUND
NORTHEASTERN ARGENTINA...URUGUAY...SOUTHERN BRAZIL AND SOUTHERN
PARAGUAY MAY OBSERVE SEVERE WEATHER. CENTRAL TO SOUTHERN
CHILE...WILL BE SUBJECT TO HIGHER THAN NORMAL MOISTURE TODAY
THROUGH EARLY THURSDAY...AS A COLD FRONT AND A SFC LOW MOVES IN
LATE TODAY 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 TO
ELEVATED RISK OF SEVERE WEATHER PARTICULARLY TONIGHT THROUGH VERY
EARLY FRIDAY. THERE IS A MODERATE RISK OF SEVER WEATHER MORE OVER
SOUTHERN BRAZIL INTO PARAGUAY ON FRIDAY INTO SATURDAY. THIS RISK
OF SEVERE WEATHER...INCLUDING 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 ARGENTINA...JUST AHEAD OF A FRONTAL
BOUNDARY THAT IS MOVING NORTHEAST. IN THE MID LEVELS...A TROUGH
WILL MOVE THROUGH 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
TODAY AND THURSDAY. THE GRO2T SEVERITY ALGORITHM DOES INDICATE A
MODERATE TO ELEVATED RISK FOR SEVERE WEATHER ACROSS THE AREA EACH
DAY OVER THE NEXT THREE DAYS...THOUGH THE HIGHEST AND MOST
SIGNIFICANT RISK FOR SEVERE WEATHER IS BEING SUGGESTED BY THE
ALGORITHM TO BE ON THURSDAY.
THE PRECIPITABLE WATER IS FORECAST TO CONTINUE ABOVE NORMAL TODAY
INTO THURSDAY ACROSS CENTRAL TO SOUTHERN CHILE...THEN DECREASE ON
FRIDAY...BEFORE AN ATMOSPHERIC RIVER MOVES INTO CENTRAL CHILE LATE
ON FRIDAY INTO THE WEEKEND. THE MODEL GUIDANCE HAS BEEN
OVERESTIMATING THE PRECIPITATION OVER THE AREA THESE 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 20-30MM
TODAY...AND UP TO 20-35 ON THURSDAY. FOR FRIDAY INTO EARLY
SATURDAY...THE ATMOSPHERIC RIVER WILL BE MORE PERPENDICULAR TO THE
COAST OF CHILE...PLUS IT HAS SOME UPPER LEVEL SUPPORT WITH A
STRONG JET...SO THE FORECAST PRECIPITATION HAS A MAX VALUE NEAR
20-45MM. IT IS WORTH MENTIONING THAT THE MODEL GUIDANCE CONTINUES
TO SUGGEST RAINFALL IN THE LOWER ELEVATIONS AND SNOW ACROSS THE
HIGHER ELEVATIONS. THERE IS ALSO SNOW IN THE FORECAST FOR THE
SOUTHERNMOST SECTIONS OF CHILE OVER THE NEXT THREE DAYS.
AS MENTIONED ABOVE...PORTIONS OF EAST CENTRAL ARGENTINA IN TO
SOUTHERN BRAZIL AND SOUTHERN PARAGUAY ARE AT RISK OF OBSERVING
SEVERE WEATHER FROM THIS EVENING THROUGH THE NEXT FEW DAYS. IN
TERMS OF RAINFALL AMOUNTS...THE LATEST MODEL GUIDANCE IS
SUGGESTING UP TO 45MM OR SO FOR THIS EVENING INTO EARLY THURSDAY.
FOR THURSDAY INTO FRIDAY...PRECIPITATION MAXIMA NEAR 35-70MM ARE
FORECAST FOR SOUTHERN BRAZIL...NORTHERN URUGUAY AND SOUTHERN
PARAGUAY...WITH EASTERN AND NORTHEASTERN ARGENTINA OBSERVING LESS
RAINFALL...UP TO AROUND 35MM. FRIDAY INTO SATURDAY...THE LATEST
GUIDANCE 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. ONCE AGAIN...THE GR02T
ALGORITHM DOES SUGGEST A MODERATE TO ELEVATED RISK OF SEVERE
WEATHER AND HAIL ACROSS THE AREA OVER THE NEXT FEW DAYS.
PERU IS FORECAST TO OBSERVE SOME RAINFALL EACH DAY BUT THE AMOUNTS
WILL BE RELATIVELY MODEST. MAX VALUES OF 25MM OR LESS ARE FORECAST
EACH DAY OVER PERU...WITH EACH PASSING DAY HAVING LESS RAIN IN THE
FORECAST THAN THE PREVIOUS DAY INTO THE WEEKEND. ALSO AREAS NEAR
ESPIRITO SANTO AND BAHIA IN BRAZIL COULD OBSERVE MAX VALUES NEAR
10-25MM EACH DAY OVER THE NEXT THREE DAYS.
ALAMO...(WPC)
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