203  
FXSA20 KWBC 291722  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1222 PM EST WED NOV 29 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 29 AT 0000 UTC): MINOR  
CORRECTIONS TO PREVIOUS FORECAST...WITH MODELS FOLLOWING A SIMILAR  
EVOLUTION THROUGH DAY 06. THE DETERMINISTIC SOLUTION IS WELL  
SUPPORTED BY THE MEAN OF THE GLOBAL ENSEMBLE MEMBERS...LEADING TO  
A HIGH CONFIDENCE IN THE FORECAST THROUGH THE END OF THE CYCLE.  
 
A SHORT WAVE TROUGH ON THE NORTHERN STREAM SPILLED ACROSS THE  
CENTRAL ANDES OF CHILE TO CUYO IN ARGENTINA. AT LOW LEVELS THIS IS  
INTERACTING WITH A SURFACE FRONT TRAILING ACROSS SOUTHERN BRASIL  
TO CENTRAL ARGENTINA....TRIGGERING CYCLOGENESIS OVER CUYO. THE  
FRONTAL WAVE IS TO THEN MEANDER TO THE EAST-SOUTHEAST ACROSS LA  
PAMPA/BUENOS AIRES PROVINCE. MEANWHILE...THIS IS TO SUSTAIN  
SCATTERED CONVECTION WITH ACCUMULATION OF 20-30MM/DAY ON WEDNESDAY  
AND THURSDAY.  
 
PROGRESSIVE MID LEVEL TROUGH ON THE SOUTHERN STREAM IS TO  
FOLLOW...TO MOVE TO THE BELLINGSHAUSEN SEA-SOUTHERN CHILE LATER  
TODAY. ON THURSDAY IT IS TO MOVE ACROSS THE DRAKE  
PASSAGE-PATAGONIA IN ARGENTINA...TO THEN MEANDER TO THE  
EAST-SOUTHEAST ACROSS THE SOUTH ATLANTIC LATER IN THE WEEK. THE  
TROUGH SUSTAINS A SURFACE FRONT ACROSS TIERRA DEL FUEGO LATER  
TODAY...THAT MOVES ACROSS PATAGONIA TO THE WESTERN ATLANTIC ON  
THURSDAY. IT IS TO THEN MERGE WITH/REINFORCE THE AFOREMENTIONED  
FRONT OVER CENTRAL ARGENTINA ON FRIDAY. AS THEY  
INTERACT...EXPECTING SCATTERED CONVECTION ACROSS LA PAMPA-CUYO IN  
ARGENTINA TO TRIGGER RAINFALL AMOUNTS OF 20-40MM. ON SATURDAY THIS  
SPREADS ACROSS THE BUENOS AIRES PROVINCE-ENTRE RIOS TO TRIGGER  
MAXIMA OF 20-30MM.  
 
FARTHER EAST...AT 500 HPA...A TROUGH EXTENDS OVER THE WESTERN  
ATLANTIC...WITH AXIS ENVELOPING AREA BETWEEN 50W-20W AND TO THE  
SOUTH OF 20S. THE SHORT WAVE TROUGH IS TO MEANDER OFF THE SOUTH  
COAST OF BRASIL THROUGH SATURDAY EVENING WHILE SLOWLY WEAKENING AS  
IT SHEARS SHORT WAVE ENERGY TO THE EAST-SOUTHEAST. AT LOW  
LEVELS... THE TROUGH SUSTAINS AN ELONGATED FRONT ACROSS THE SOUTH  
ATLANTIC TO RIO DE JANEIRO/SOUTHERN MINAS GERAIS TO MATO GROSSO DO  
SUL/PARAGUAY. THE BOUNDARY IS TO PERSIST DURING THE NEXT  
FOUR-TO-FIVE DAYS. MEANWHILE...THIS IS TO BECOME THE FOCUS OF LOW  
LEVEL MOISTURE CONVERGENCE ACROSS MID SECTIONS OF SOUTH AMERICA.  
UNDER FAVORABLE JET DYNAMICS EXPECTING ENVIRONMENTAL CONDITIONS  
OVER PARAGUAY-MATO GROSSO DO SUL IN BRASIL-SOUTHEAST BOLIVIA TO  
BECOME FAVORABLE FOR AN MCS TO FORM EARLY ON THURSDAY MORNING. IN  
THIS AREA EXPECTING MAXIMA OF 50-100MM. ON THURSDAY TO FRIDAY THIS  
INCREASES TO 75-125MM WHILE SPREADING NORTH ACROSS BOLIVIA TO  
RONDONIA IN BRASIL. ON FRIDAY THIS DECREASES TO 20-45MM WHILE  
CLUSTERING OVER CENTRAL BOLIVIA. OVER MINAS GERAIS-MATO GROSSO IN  
BRASIL...AS DEEP TROPICAL MOISTURE CONVERGES NORTH OF THIS  
BOUNDARY...EXPECTING RAINFALL MAXIMA OF 20-40MM. THROUGH FRIDAY  
THIS IS TO BECOME MORE ACTIVE/BETTER ORGANIZED...WITH MAXIMA OF  
40-80MM TO AFFECT MINAS GERAIS-BAHIA AND ESPIRITO SANTO IN BRASIL.  
ON SATURDAY-SUNDAY THE DAILY MAXIMA WILL THEN PEAK AT 30-60MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...MODELS CONTINUE TO  
FORECAST BROAD CELL OF THE SUBTROPICAL RIDGE TO BECOME THE  
DOMINANT FEATURE TO THE NORTH OF 30S...WITH AXIS TO ANCHOR ON A  
CLOSED HIGH THAT MEANDERS BETWEEN NORTHERN BOLIVIA-MATO  
GROSSO/RONDONIA IN BRASIL. THE RIDGE ALOFT IS TO VENT CONVECTION  
ACROSS NORTHERN SOUTH AMERICA...WITH MOST ACTIVE CLUSTERING ALONG  
AND NORTH OF THE AFOREMENTIONED SURFACE FRONT OVER  
BRASIL-PARAGUAY/BOLIVIA. OTHER CONVECTION IS EXPECTED ACROSS PARA  
IN BRASIL TO FAVOR MAXIMA OF 15-20MM/DAY. THROUGH FRIDAY THIS IS  
TO INTENSIFY...WITH MAXIMA OF 20-30MM. OVER ACRE-AMAZONAS IN  
WESTERN BRASIL TO THE NORTHERN JUNGLE OF PERU/EASTERN ECUADOR  
EXPECTING MAXIMA OF 10-15MM/DAY. THROUGH SATURDAY THIS IS TO  
INTENSIFY...WITH MAXIMA OVER AMAZONAS-SOUTHERN COLOMBIA-NORTHERN  
JUNGLE OF PERU TO PEAK AT 20-40MM. ON THE HIGH JUNGLE OF  
PERU...MEANWHILE...THE DAILY MAXIMA IS TO PEAK AT 20-35MM ON  
SATURDAY.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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