922  
FXSA20 KWBC 101719  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
118 PM EDT TUE OCT 10 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM OCT 10 AT 0000 UTC): MODEL CONFIDENCE  
REMAINS HIGH THROUGH THE CYCLE. THEY ALL AGREE ON THE TRANSITION  
INTO A LONG-WAVE PATTERN BY DAYS 05 AND 06. DISCREPANCIES ON THE  
FORECAST ONLY START ARISING AFTER 108-120 HRS.  
 
AN UPPER TROUGH CROSSING THE SOUTHERN CONE IS FORECAST TO EXIT  
INTO THE SOUTH ATLANTIC ON TUESDAY...WHILE ITS NORTHERN TIER  
REMAINS DELAYED TO THE WEST OF THE ANDES. THIS WILL SUSTAIN  
SCATTERED SHOWERS IN MAULE AND BIO BIO ON TUESDAY WITH MAXIMUM  
ACCUMULATIONS OF 05-10MM/DAY. TO THE EAST...THE TROUGH IS TO  
INTERACT WITH THE CONVERGENT EXIT OF A LOW-LEVEL JET FROM THE EAST  
ACROSS LA PAMPA/MENDOZA...WHERE EXPECTING THUNDERSTORMS  
DEVELOPMENT WITH MAXIMA OF 15-20MM/DAY. AS THE UPPER TROUGH  
LINGERS...SIMILAR ACCUMULATIONS IN CUYO ON BOTH WEDNESDAY AND  
THURSDAY...DECREASING LATER.  
 
ALSO IN THE SOUTHERN CONE...A TROUGH WILL RAPIDLY ARRIVE FROM THE  
WEST LATE ON THURSDAY AND CROSS THE SOUTHERN CONE ON FRIDAY. THIS  
SYSTEM WILL ARRIVE ACCOMPANIED WITH 40-45KT WINDS TO THE SOUTH OF  
ISLA CHILOE...AND WITH A SUBTROPICAL MOISTURE CONNECTION. THIS  
WILL LEAD TO MAXIMA OF 20-35MM/DAY ON FRIDAY-SATURDAY BETWEEN ISLA  
CHILOE AND MOST OF THE AYSEN REGION. TO THE SOUTH...EXPECTING  
MAXIMA OF 10-15MM/DAY.  
 
A SURFACE FRONT CONTINUES MEANDERING IN MID-SECTIONS OF THE  
CONTINENT..AND AS SUCH...WILL CONTINUE BEING THE FICUS FOR  
MOISTURE CONVERGENCE THROUGH THE CYCLE. PRECIPITABLE WATER WILL  
LINGER BETWEEN 45 AND 50MM THROUGH THE CYCLE...WHICH WILL SUSTAIN  
MODERATE RAINFALL AMOUNTS...ESPECIALLY IN THE MISIONES/CORRIENTES  
REGIONS IN ARGENTINA AND IN NORTHER RIO GRANDE DO SUL AND SANTA  
CATARINA IN BRASIL. THROUGH EARLY WEDNESDAY...LARGEST AMOUNTS WILL  
REACH 30-60MM/DAY FROM CORRIENTES EAST INTO MOST OF RIO GRANDE DO  
SUL. ACCUMULATIONS ARE TO INCREASE TO MAXIMA OF 35-70MM BETWEEN  
MISIONES-ARGENTINA AND RIO GRANDE DO SUL/SANTA CATARINA BY  
WEDNESDAY-THURSDAY. BY THURSDAY-FRIDAY EXPECTING LARGEST AMOUNTS  
ACROSS PARANA/SANTA CATARINA WHERE SCATTERED CONVECTION WILL  
PRODUCE MAXIMA OF 35-70MM. INLAND ACROSS SOUTHERN PARAGUAY  
EXPECTING MAXIMA OF 10-15MM/DAY. AMOUNTS WILL DECREASE AFTER. AS  
THE FRONT INTERACTS WITH THE SERRA DO MAR ON  
SATURDAY-SUNDAY...EXPECTING LOCALIZED MAXIMA OF 20-40MM/DAY IN  
COASTAL AREAS/EASTERN AND SOUTHERN SLOPES...WHILE INLAND EXPECTING  
MAXIMA OF 15-20MM/DAY.  
 
NORTH ACROSS THE CONTINENT...IN THE AMAZON BASIN...SCATTERED  
DIURNAL CONVECTION IS FORECAST TO INCREASE AS THE CYCLE  
PROGRESSES. LARGEST AMOUNTS ARE EXPECTED IN PARA/EASTERN AMAZONAS  
ON TUESDAY...WHERE SCATTERED DIURNAL THUNDERSTORMS ARE TO PRODUCE  
MAXIMA OF 15-25MM. AMOUNTS WILL INCREASE TO MAXIMA OF 20-35MM FROM  
THURSDAY AND ON...AS MOST ACTIVE CONVECTION EXPANDS WESTWARD. BY  
SATURDAY...A DEVELOPING SOUTHEASTERLY SURGE IN THE WESTERN AMAZON  
WILL ENHANCE LOW-LEVEL MOISTURE CONVERGENCE TO ENHANCE  
ACCUMULATIONS TO MAXIMA OF 25-50MM. ANDEAN CONVECTION IN THE  
CENTRAL ANDES IS ALSO ACTIVATING TWO PERIODS ARE FAVORABLE FOR  
MODERATE AMOUNTS...WEDNESDAY...WHEN EXPECTING MAXIMA OF  
05-10MM/DAY FROM NORTHERN PERU INTO BOLIVIA...AND SATURDAY...WHEN  
EXPECTING ISOLATED MAXIMA OF 10-15MM/DAY IN THE ALTIPLANO.  
 
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENMAHI (PERU)  
GALVEZ...WPC (USA)  

 
 
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