156  
FXSA20 KWBC 071821  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
121 PM EST WED FEB 07 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM FEB 07 AT 0000 UTC): MODELS CONTINUE  
SHOWING GOOD AGREEMENT THROUGH THE CYCLE. FORECAST CONFIDENCE IS  
GOOD.  
 
IN TROPICAL SOUTH AMERICA...THE SOUTH ATLANTIC CONVERGENCE ZONE IS  
RAPIDLY LOSING ORGANIZATION WHILE THE UPPER FLOW PATTERN EVOLVES  
AS WELL. THIS WILL ALLOW FOR THE DEVELOPMENT OF THE NORTHERLY  
LOW-LEVEL JET TO THE EAST OF THE ANDES...AND SUSTAIN MOISTURE  
TRANSPORT INTO ARGENTINA/PARAGUAY/URUGUAY. AT UPPER LEVELS...A  
LONG WAVE TROUGH IS APPROACHING FROM THE PACIFIC AND PRODUCING  
SIGNIFICANT HEIGHT FALLS ON WEDNESDAY...WHICH ARE EXCEEDING 150  
GPM. AT LOW-LEVELS...A SURFACE FRONT IS MEANDERING NORTHEASTWARD  
ACROSS EXTREME NORTHERN PATAGONIA. THIS WILL SUSTAIN SCATTERED  
CONVECTION ON WEDNESDAY FROM CUYO INTO NORTHERN PATAGONIA/LA  
PAMPA. YET...GIVEN THE LIMITATION IN MOISTURE AVAILABILITY  
EXPECTING MAXIMA OF 05-10MM/DAY...WITH VERY ISOLATED HIGHER  
AMOUNTS IN STRONGEST THUNDERSTORMS. MOISTURE CONTENT AND DYNAMICAL  
FORCING INCREASE SIGNIFICANTLY DURING THURSDAY...WHICH WILL LEAD  
TO AN INCREASE IN ACCUMULATIONS TO MAXIMA OF  
20-35MM/DAY...STRETCHING FROM CUYO TO THE BUENOS AIRES PROVINCE.  
NOTE THAT THERE IS A RISK FOR SEVERE CONVECTION. BY FRIDAY THE  
FRONT WILL LOSE SPEED WHILE CROSSING THE RIO DE LA PLATA AND  
EXTENDING INTO CORDOBA. EXPECTING 25-50MM/DAY WITH CONTINUED RISK  
FOR SEVERE CONVECTION. BY SATURDAY...EXPECTING AN INCREASE IN  
ACTIVITY IN NORTHERN ARGENTINA WHEN MAXIMA IS TO REACH  
35-70MM/DAY. ALONG THE FRONT EXPECTING MAXIMA OF 20-35MM. BY  
SUNDAY...MODELS ARE AGREEING ON A STRENGTHENING OF THE CHACO LOW  
AND THE ASSOCIATED NORTHERLY AND SOUTHERLY LOW-LEVEL JETS. SINCE  
PRECIPITABLE WATER WILL BE IN THE 65-70MM RANGE AND THE UPPER  
DIVERGENT PATTERN WILL BE FAVORABLE...EXPECTING STRONG CONVECTION  
TO DEVELOP...WITH THE RISK OF MCS FORMATION IN THE CHACO REGION.  
TO THE EAST...NORTH OF THE FRONT...ENHANCED CONVECTIVE INSTABILITY  
WILL FAVOR ACCUMULATIONS OF 25-50MM/DAY.  
 
IN TROPICAL SOUTH AMERICA...THE WEAKENING OF THE SACZ WILL LEAD TO  
A REORGANIZATION OF CONVECTION AND ASSOCIATED RAINFALL.  
FURTHERMORE...THE UPPER FLOW PATTERN IS REORGANIZING AND THE UPPER  
SUBTROPICAL RIDGE/BOLIVIAN HIGH IS FORECAST TO REFORM OVER MATO  
GROSSO/EASTERN BOLIVIA BY FRIDAY. AS MOISTURE RETURNS WESTWARD  
INTO THE PERUVIAN/BOLIVIAN EASTERN SLOPES...EXPECTING AN INCREASE  
IN RAINFALL ACCUMULATIONS TO SUSTAIN MAXIMA OF 25-50MM/DAY ON  
WEDNESDAY-THURSDAY...30-60MM/DAY ON THURSDAY-FRIDAY...DECREASING  
TO 20-40MM/DAY BY FRIDAY-SATURDAY. THE ALTIPLANO/CENTRAL ANDEAN  
CONVECTION WILL CONTINUE ENHANCED THROUGH THE CYCLE.  
INITIALLY...EXPECTING MAXIMA OF 15-30MM/DAY FROM NORTHERN  
ARGENTINA THROUGH SOUTHERN PERU ON WEDNESDAY. AMOUNTS WILL  
DECREASE ON THURSDAY TO INCREASE AGAIN ON FRIDAY TO MAXIMA OF  
15-25MM. DURING THE WEEKEND...UNDER THE INFLUENCE OF DEEP-LAYER  
MOISTURE AND INSTABILITY...EXPECTING ACCUMULATIONS OF 15-30MM/DAY  
ONCE AGAIN...WITH HEAVIEST PRECIPITATION RELOCATING FROM PERU ON  
SATURDAY TO BOLIVIA/NORTHERN ARGENTINA/NORTHERN CHILE ON SUNDAY.  
 
TO THE EAST...ACTIVE CONVECTION WILL PERSIST IN MOST OF BRASIL.  
INITIALLY...LARGEST ACCUMULATION S ARE EXPECTED IN THE NORTHERN  
COAST AND AMAZON DELTA...WHERE ENHANCED MOISTURE CONVERGENCE WILL  
LEAD TO MAXIMA OF 40-80MM/DAY. ACCUMULATIONS WILL GRADUALLY  
DECREASE AFTER THURSDAY. BY THE WEEKEND...MOST WIDESPREAD  
CONVECTION WILL CLUSTER IN THE CENTRAL AMAZON BASIN WHERE  
EXPECTING AMOUNTS OF 30-60MM/DAY.  
 
BALBINO...INMET (BRASIL)  
POMIER...SENAMHI (BOLIVIA)  
GALVEZ...WPC (USA)  

 
 
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