792  
FXSA20 KWBC 181638  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1238 PM EDT WED OCT 18 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
NOTE: THE RISK FOR SEVERE CONVECTION IN NORTH-CENTRAL AND  
NORTHEASTERN ARGENTINA-URUGUAY AND SOUTHERN BRASIL ON WEDNESDAY  
CONTINUE. 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 18 AT 0000 UTC): THE CONFIDENCE  
ON THE FORECAST HAS DECREASED WITH RESPECT TO YESTERDAY...AS  
GLOBAL MODELS AND ENSEMBLE MEMBERS START DIVERGING AFTER 96 HRS TO  
THE SOUTH OF 40S. THE DIFFERENCES ARE PARTICULARLY LARGE WHEN  
RESOLVING A TROUGH THAT APPROACHES THE SOUTHERN CONE BY 120-132  
HRS.  
 
SEVERE WEATHER EVENT IN NORTHEASTERN AND CENTRAL  
ARGENTINA/URUGUAY/RIO GRANDE DO SUL CONTINUES UNRAVELING. AT  
LOW-LEVELS...AN UNSEASONABLY WARM AIR MASS IS LEADING TO EXTREME  
TEMPERATURES NORTHERN ARGENTINA/PARAGUAY...WHERE MINIMUM  
TEMPERATURES HAVE OSCILLATED BETWEEN 25 AND 29C. AS SEVERAL SHORT  
WAVE TROUGHS CROSS THE ANDES AND THE MID-LEVELS COOL...INSTABILITY  
IS FORECAST TO PEAK DURING WEDNESDAY AFTERNOON. LIFTED INDEX  
VALUES ARE FORECAST TO BECOME LOWER THAN -9...AND CAPE HIGHER THAN  
5000 J/KG IN ENTRE RIOS/NORTHWESTERN URUGUAY ON WEDNESDAY  
AFTERNOON...WHICH WILL SUSTAIN STRONG CONVECTION. THE UPPER  
DYNAMICS WILL ALSO BE FAVORABLE...AS THE DIVERGENT RIGHT ENTRANCE  
OF AN UPPER JET ENHANCES VENTILATION. THROUGH EARLY  
THURSDAY...EXPECTING ACCUMULATIONS PEAKING AT 50-100MM/DAY FROM  
SANTA FE/ENTRE RIOS/CORRIENTES EAST INTO URUGUAY AND RIO GRANDE DO  
SUL. IN THE BUENOS AIRES PROVINCE...EXPECTING MAXIMA OF 25-50MM.  
BOTH REGIONS ARE PRONE TO SEVERE CONVECTION WITH THE RISK OF LARGE  
HAIL. IN SANTIAGO DEL ESTERO/CORDOBA...EXPECTING MAXIMA OF  
15-20MM. BY THURSDAY INTO EARLY FRIDAY...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 40-80MM. BY SUNDAY-MONDAY...THE SOUTHERLY WIND  
SURGE WILL REACH SOUTHERN PERU/NORTHERN BOLIVIA/ACRE...WHERE  
EXPECTING MAXIMA OF 50-100MM. ACROSS THE SERRA DO MAR OF PARANA  
AND SAO PAULO IN BRASIL EXPECTING MAXIMA OF 20-40MM/DAY. IN  
MID-SECTIONS OF THE CONTINENT... IN MATO GROSSO/WESTERN SAO  
PAULO...EXPECTING MAXIMA OF 20-30MM.  
 
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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