Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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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) $$