005  
FXSA20 KWBC 191835  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
235 PM EDT WED MAR 19 2025  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/DATA/NCCF/COM/GFS/PROD/  
 
SOUTH AMERICAN FORECAST BULLETIN FROM 19 MARCH 2025 AT 18:15 UTC  
 
ANALYSIS AND FORECAST OF LARGE SCALE CONDITIONS  
-MJO AND TROPOSPHERIC WAVES: THE MJO IS PROPAGATING IN PHASE 4,  
WHILE LARGE SCALE UPPER CONVERGENCE STILL PERSISTS OVER THE  
AMERICAS. A TROPOSPHERIC KELVIN IS FORECAST TO ARRIVE EARLY NEXT  
WEEK TO PROVIDE ENHANCEMENT TO CONVECTION IN TROPICAL REGIONS.  
-SST: IMPORTANT POSITIVE ANOMALIES CONTINUE WEST OF ECUADOR AND  
COLOMBIA, WHICH WILL CONTINUE TO FUEL CONVECTION AND PRECIPITATION  
AMOUNTS DURING THE NEXT SEVERAL DAYS.  
 
SYNOPTIC ANALYSIS AND FORECAST FOR TROPICAL SOUTH AMERICA  
ANALYSIS: THE SUBTROPICAL UPPER RIDGE CENTERS ON A CELL OFF THE  
COAST OF SOUTHERN PERU AND CONTINUES VENTILATING CONVECTION OVER  
MOST OF WEST AND CENTRAL TROPICAL SOUTH AMERICA. DRIER CONDITIONS  
ARE OCCURING SOUTH OF 19S GIVEN ADVECTION OF A DRIER AIR MASS FROM  
THE PACIFIC BY MID-UPPER WESTERLIES. IN THE LOW-LEVELS, ENHANCED  
MOISTURE CONVERGENCE CENTERS IN EASTERN AMAZONAS-BRASIL, RONDONIA  
AND NORTH BOLIVIA, WHERE WIDESPREAD DEEP CONVECTION IS OCCURRING.  
INCREASING LOW-LEVEL WESTERLIES IN COASTAL ECUADOR ARE STIMULATING  
MOISTURE CONVERGENCE.  
 
WESTERN TROPICAL SOUTH AMERICA FORECAST: THE UPPER RIDGE IS  
FORECAST TO SLOWLY ROLL EASTWARD INTO SOUTHERN PERU STARTING  
TODAY, TO MAINTAIN VENTILATION NORTH OF 10S WHILE CONTINUING TO  
ADVECT DRY AIR INTO THE SOUTHERN ALTIPLANO, LIMITING CONVECTION IN  
SOUTHERN BOLIVIA. IN THE LOW LEVELS, HIGH VALUES OF AVAILABLE  
MOISTURE IN AMAZONAS, RONDONIA AND NORTH BOLIVIA WILL FAVOR HEAVY  
PRECIPITATION ON WEDNESDAY, DECREASING THEREAFTER. ANOTHER REGION  
OF INTEREST EAST OF THE ANDES IS ECUADOR AND SOUTHERN COLOMBIA,  
WHERE SOUTHEASTERLY LOW-LEVEL WINDS WILL ENHANCE MOISTURE  
CONVERGENCE ON WEDNESDAY, AND THE ARRIVAL OF THE MOIST PLUME  
THEREAFTER. IN COASTAL ECUADOR EXPECT WEAK LOW-LEVEL WESTERLIES  
AND INCREASING PRECIPITABLE WATER TO SUSTAIN ACTIVE CONVECTION  
THROUGH THE CYCLE, PEAKING ON THURSDAY.  
 
NOTEWORTHY QPF:  
-WEST AND CENTRAL AMAZON: MAXIMA OF 35 - 70MM AND A RISK OF MCS IN  
CENTRAL BRASIL ON WEDNESDAY, AND MAXIMA OF 25 - 50MM IN THE  
ORIENTE ECUATORIANO AND SOUTH COLOMBIA. ON THURSDAY MAXIMA  
INCREASES TO 35 - 70MM IN ORIENTE ECUATORIANO/SOUTHERN COLOMBIA,  
INCREASING FURTHER TO 40 - 80MM ON FRIDAY.  
-ALTIPLANO/PERUVIAN ANDES: SEASONAL CONVECTION, GENERALLY  
PRODUCING MAXIMA OF 15MM FROM NORTHWEST BOLIVIA INTO NORTHERN PERU  
ON A DAILY BASIS.  
-PACIFIC BASIN OF ECUADOR: MAXIMA OF 25 - 50MM ON WEDNESDAY,  
INCREASING TO 35 - 70MM ON THURSDAY, DECREASING TO 20 - 45MM ON  
FRIDAY. RISK OF LARGE RAINFALL RATES.  
 
EASTERN AND SOUTHERN TROPICAL SOUTH AMERICA FORECAST: ITCZ  
CONVERGENCE WILL BE THE PRIMARY FACTOR ENHANCING CONVECTION,  
PARTICULARLY ALONG THE NORTH COAST OF BRASIL/AMAZON DELTA. A WEAK  
PERTURBATION IS PROPAGATING ALONG CEARA/PIAUI ON WEDNESDAY AND IS  
FORECAST TO REACH THE AMAZON DELTA ON FRIDAY, TO PROVIDE SOME  
ENHANCEMENT IN CONVECTION AND ASSOCIATED ACCUMULATIONS. IN  
SOUTHEAST BRASIL, A MID-UPPER TROUGH IS FORECAST TO MOVE SLOWLY  
FROM PARANA-MG SUL TO WESTERN SAO PAULO-SOUTHEASTERN MG BY FRIDAY  
EVENING. THIS WILL STIMULATE DIURNAL CONVECTION FROM ESPIRITO  
SANTO/RIO DE JANEIRO INTO SOUTHEASTERN MG ON A DAILY BASIS. THE  
LARGEST AMOUNTS ARE EXPECTED ON WEDNESDAY WHERE ONSHORE FLOW AND  
ENHANCED UPPER DIVERGENCE ARE EXPECTED TO COUPLE.  
 
NOTEWORTHY QPF:  
-NORTHERN COAST OF BRASIL: MAX. OF 20 - 40MM ON WEDNESDAY  
DECREASING AFTER.  
INTERIOR NORDESTE/TOCANTINS: PEAK ON THURSDAY WHEN EXPECT MAX. OF  
30 - 60MM.  
-SOUTHEASTERN BRASIL: MAX. OF 35 - 70MM ON WEDNESDAY, DECREASING  
AFTER.  
 
SYNOPTIC ANALYSIS AND FORECAST FOR EXTRATROPICAL SOUTH AMERICA:  
ANALYSIS: A BROAD MID-UPPER TROUGH IN THE SOUTHERN STREAM  
ASSOCIATES WITH AN ATMOSPHERIC RIVER THAT IS ENTERING AYSEN IN  
AUSTRAL CHILE. ALTHOUGH IT CONTAINS 20-25MM OF PRECIPITABLE WATER,  
IT IS LOSING MOISTURE, WIND SPEEDS AND SUPPORT IN THE UPPER  
TROPOSPHERE. IN THE NORTHERN STREAM, A SHORT WAVE MID-UPPER TROUGH  
EXTENDS ALONG 86W. IT IS RELEVANT GIVEN ITS POTENTIAL ROLE IN  
TRIGGERING STRONG CONVECTION IN THE CHACO ON FRIDAY.  
 
FORECAST: THE ATMOSPHERIC RIVER WILL STILL FAVOR MODERATE AMOUNTS  
IN AUSTRAL CHILE ON WEDNESDAY, GRADUALLY DECREASING THEREAFTER  
WHILE CHANCES OF MOUNTAIN SNOW INCREASE AS A COOLER AIR MASS MOVES  
IN. EAST OF THE ANDES, EXPECT A GRADUAL ACTIVATION OF CONVECTION  
IN ARGENTINA AS SEVERAL MID-UPPER TROUGHS STIMULATE NORTHERLY  
LOW-LEVEL WINDS. THE SALLJ WILL LIKELY INCREASE PRECIPITABLE WATER  
TO NEAR 50MM IN THE CHACO ON FRIDAY, WHICH WILL FAVOR MODERATE  
PRECIPITATION AND A MARGINAL RISK FOR SEVERE CONVECTION ON FRIDAY  
INTO SATURDAY.  
 
NOTEWORTHY QPF:  
-AUSTRAL CHILE: MAX OF 20 - 35MM ON WEDNESDAY, DECREASING AFTER.  
-INTERIOR NW ARGENTINA/CHACO: MAXIMA OF 20 - 35MM ON THURSDAY. MAX  
OF 30 - 60MM IN THE CHACO ON FRIDAY WITH A MARGINAL RISK FOR  
SEVERITY.  
 
FOR ASSOCIATED QPF GRAPHICAL INFORMATION:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/INTERNATIONAL/SAM_DAY1-3.SHTML  
 
GALVEZ...(WPC)  
ALAMO...(WPC)  

 
 
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