199  
FXSA20 KWBC 171643  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1242 PM EDT TUE OCT 17 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
NOTE: THERE IS A RISK FOR SEVERE CONVECTION IN NORTH-CENTRAL AND  
NORTHEASTERN ARGENTINA ON TUESDAY AND ESPECIALLY WEDNESDAY. NOTE  
THAT THE RISK FOR HAIL IS HIGH...PARTICULARLY DURING THE DAY ON  
WEDNESDAY...WHEN A RISK FOR LARGE HAIL EXISTS FROM LA PAMPA-BUENOS  
AIRES PROVINCE NORTH ACROSS CORDOBA/SANTA FE.  
 
MODEL DISCUSSION (VALID FROM OCT 17 AT 0000 UTC): GLOBAL MODELS  
AND ENSEMBLE MEMBERS CONTINUE AGREEING ON THE FORECAST EVOLUTION  
THROUGH 96-108 HRS. AFTER THIS PERIOD...THE CONFIDENCE DECREASES  
VERY RAPIDLY TO THE SOUTH OF 45S...ESPECIALLY IN THE EASTERN  
PACIFIC.  
 
ACTIVE WEATHER PATTERN IS UNRAVELING FOR NORTHEASTERN  
ARGENTINA-URUGUAY-SOUTHERN BRASIL AND PARAGUAY. SEVERAL SHORT WAVE  
TROUGHS ARE TO CROSS THE ANDES AND INTERACT WITH A MOIST AND  
UNSTABLE AIR MASS BREWING IN THE REGION. AT LOW-LEVELS...AN  
UNSEASONABLY WARM AIR MASS IS LEADING TO EXTREME TEMPERATURES IN  
THE REGIONS. NOTE THAT FORECAST MINIMUM TEMPERATURES CLOSE TO 30C  
ARE EXPECTED FOR THE PARAGUAYAN CHACO AND EXTREME NORTHERN  
ARGENTINA. THE WARM AIR MASS WILL FAVOR THE DEVELOPMENT OF STRONG  
INSTABILITY ON WEDNESDAY...WITH LIFTED INDEX VALUES APPROACHING  
-10C. DURING TUESDAY...SEVERE CONVECTION WILL CONTINUE DEVELOPING  
IN ENTRE RIOS-CORRIENTES/NORTHERN BUENOS AIRES PROVINCE INTO  
URUGUAY...TO PRODUCE MAXIMUM ACCUMULATIONS OF 40-80MM/DAY.  
ALSO...STRONG CONVECTION IS TO DEVELOP IN LA PAMPA/SOUTHERN BUENOS  
AIRES PROVINCE...TO PRODUCE ISOLATED MAXIMA OF 15-25MM. BY  
WEDNESDAY-THURSDAY...THE RISK FOR SEVERE CONVECTION WILL PEAK  
DURING THE DAY...ESPECIALLY BETWEEN CORRIENTES-ENTRE RIOS-SANTA FE  
AND URUGUAY/SOUTHERN RIO GRANDE DO SUL. EXPECTING ACCUMULATIONS OF  
50-100MM/DAY...YET ISOLATED LARGER AMOUNTS ARE POSSIBLE IN AREAS  
UNDER THE INFLUENCE OF STRONGEST THUNDERSTORMS. BY  
THURSDAY...LARGEST ACCUMULATIONS WILL CLUSTER BETWEEN SOUTHERN  
BOLIVIA AND MOST OF PARAGUAY...WHERE SCATTERED CONVECTION WILL  
LEAD TO MAXIMA OF 35-70MM. ENHANCED CONVECTION ALONG THE BOLIVIAN  
YUNGAS AND SOUTHERN PERU WILL LEAD TO MAXIMA OF 25-50MM. IN  
SOUTHERN BRASIL/MISIONES...EXPECTING MAXIMA OF 20-30MM/DAY. DURING  
FRIDAY...A SHORT WAVE TROUGH WILL INTERACT WITH MOISTURE POOL  
SITTING IN PARAGUAY TO LEAD ONCE AGAIN TO STRONG CONVECTION.  
EXPECTING ACCUMULATIONS OF 75-125MM/DAY AND THE RISK FOR MCS  
FORMATION IN SOUTHEASTERN PARAGUAY/MISIONES/PARANA AND WESTERN  
SANTA CATARINA IN BRASIL. BY SATURDAY-SUNDAY...CONVECTION WILL  
REMAIN ACTIVE ALONG THE SURFACE FRONT THAT IS FORECAST TO MEANDER  
NORTHWARD INTO SOUTHERN BOLIVIA-NORTHERN PARAGUAY-SOUTHERN MATO  
GROSSO DO SUL...WHERE EXPECTING MAXIMA OF 30-60MM.  
 
ELSEWHERE IN SOUTH AMERICA...FRONTAL CONVECTION IN ESPIRITO SANTO  
WILL LEAD TO ISOLATED MAXIMA OF 15-20MM/DAY ON MONDAY-TUESDAY.  
MAXIMA WILL SHIFT TO SALVADOR DE BAHIA ON TUESDAY-WEDNESDAY WHERE  
EXPECTING AMOUNTS OF 15-25MM/DAY IN A REGION OF ENHANCED TRADE  
WIND CONVERGENCE. AMOUNTS WILL DECREASE AFTER.  
 
ALSO IN TROPICAL SOUTH AMERICA...UNSEASONABLY ACTIVE CONVECTION IS  
EXPECTED IN THE PERUVIAN/BOLIVIAN ANDES EARLY IN THE CYCLE AS  
UPPER TROUGH TO THE SOUTH WEST INTERACTS WITH MOIST AIR MASS IN  
PLACE. THIS WILL LEAD TO MAXIMA OF 10-15MM/DAY ON  
TUESDAY-WEDNESDAY...DECREASING AFTER.  
 
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
GALVEZ...WPC (USA)  

 
 
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