212  
FXSA20 KWBC 061801  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
101 PM EST TUE FEB 06 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM FEB 06 AT 0000 UTC): MINOR CHANGES TO  
PREVIOUS RUN...WITH MODELS REMAINING IN CLOSE AGREEMENT ON LONG  
WAVE PATTERN EVOLUTION THROUGH DAY 06. CONFIDENCE IN THE FORECAST  
IS HIGH.  
 
SHORT WAVE TROUGH ON THE NORTHERN STREAM MOVES ACROSS SOUTHERN  
CHILE-PATAGONIA IN ARGENTINA EARLY IN THE CYCLE...WITH THE MID  
LEVEL VORTEX MOVING TO THE WESTERN ATLANTIC LATER TODAY. ON  
WEDNESDAY IT IS THEN FORECAST TO MERGE INTO A BROAD LONG WAVE  
TROUGH TO THE SOUTH. AT LOW LEVELS THIS SUSTAINS A DEEP SURFACE  
LOW THAT STREAMS ACROSS SOUTHERN CHILE-PATAGONIA IN ARGENTINA TO  
THE WESTERN ATLANTIC LATER ON TUESDAY...DRIVING A FRONT NORTH  
ACROSS LA PAMPA TO THE BUENOS AIRES PROVINCE ON TUESDAY-WEDNESDAY.  
AS IT SURFACES ACROSS CENTRAL ARGENTINA THIS IS TO SUSTAIN  
RAINFALL AMOUNTS OF 15-20MM. ON WEDNESDAY...AS THE TROUGH PULLS  
AWAY...THIS DECREASES TO 05-10MM.  
 
A DEEPER MID/UPPER LEVEL TROUGH LIES TO THE SOUTH...WITH AXIS  
ACROSS THE SOUTHEAST PACIFIC/BELLINGSHAUSEN SEA. THE DEEP TROUGH  
IS TO MEANDER OVER THE SOUTHEAST PACIFIC DURING THE NEXT 24-36  
HRS. LATER ON WEDNESDAY THE TROUGH MEANDERS ACROSS THE ANTARCTIC  
PENINSULA TO THE WEDDELL SEA...AND NORTH ACROSS SOUTHERN CHILE TO  
PATAGONIA IN ARGENTINA. AS IT AMPLIFIES ACROSS THE SOUTHERN CONE  
THE TROUGH IS TO FOCUS SHORT WAVE ENERGY ACROSS CONTINENTAL AREA  
TO THE SOUTH OF 35S. ON THURSDAY...UNDER THE INFLUENCE OF A  
BUILDING RIDGE TO THE WEST...THE TROUGH IS EXPECTED TO AMPLIFY  
FARTHER NORTH ACROSS ARGENTINA TO MID SECTIONS OF SOUTH AMERICA.  
AT LOW LEVELS THE ASSOCIATED SURFACE FRONT IS TO MEANDERS ACROSS  
SOUTHERN CHILE-TIERRA DEL FUEGO DURING THE NEXT COUPLE OF DAYS. ON  
THURSDAY...BUILDING RIDGE OVER THE SOUTHEAST PACIFIC WILL THEN  
FAVOR A STRONG SOUTHERLY JET ACROSS PATAGONIA TO CENTRAL  
ARGENTINA. THIS IS TO DRIVE THE FRONT NORTH ACROSS LA PAMPA/BUENOS  
AIRES PROVINCE TO THE RIO DE LA PLATA BASIN LATER ON FRIDAY. EARLY  
IN THE CYCLE...AS THE FRONT MEANDERS OVER TIERRA DEL FUEGO...IT IS  
TO FAVOR LIGHT CONVECTION WITH ACCUMULATION OF 05-10MM/DAY. AS THE  
FRONT SURGES ACROSS LA PAMPA TO THE BUENOS AIRES PROVINCE ON  
THURSDAY EVENING...THIS INCREASES TO 20-35MM IN POTENTIALLY SEVERE  
CONVECTION. ON FRIDAY THE MAXIMA ACROSS URUGUAY-ENTRE RIOS-CENTRAL  
ARGENTINA IS TO PEAK AT 25-50MM...WITH RISK OF SEVERE CONVECTION  
TO PERSIST.  
 
AT 200 HPA...A MEANDERING HIGH OVER NORTHERN CHILE-SOUTHERN PERU  
ANCHORS A CELL OF THE SUBTROPICAL RIDGE THAT EXTENDS  
NORTH-TO-SOUTH OVER THE CONTINENT TO THE WEST OF 60W. EAST OF THIS  
AXIS...A TROUGH EXTENDS ACROSS SOUTHEAST BRASIL TO MATO  
GROSSO/SOUTHERN PARA. THIS PATTERN IS TO GRADUALLY WEAKEN DURING  
THE NEXT THREE DAYS...WITH THE RIDGE TO NEARLY COLLAPSE AND THE  
TROUGH TO GRADUALLY FILL. AT LOW LEVELS...THE SOUTH ATLANTIC  
CONVERGENCE ZONE (SACZ) EXTENDS TO THE NORTHWEST ACROSS MINAS  
GERAIS/MATO GROSSO TO RONDONIA IN BRASIL/NORTHERN BOLIVIA. AS THE  
UPPER PATTERN EVOLVES AND THE SACZ LOSES ITS UPPER LEVEL  
SUPPORT...THE CONVERGENCE ZONE IS FORECAST TO GRADUALLY WEAKEN TO  
AN OPEN TROUGH ON WEDNESDAY. CONVECTION OVER NORTHERN SOUTH  
AMERICA IS TO THEN CLUSTER BETWEEN THE WANING SACZ AND THE NEAR  
EQUATORIAL TROUGH TO THE NORTH. OVER ACRE-RONDONIA-AMAZONAS IN  
BRASIL TO CENTRAL/NORTHERN PERU EXPECTING MAXIMA OF 25-50MM. ON  
WEDNESDAY-THURSDAY THIS DECREASES TO 15-30MM/DAY. OVER NORTHEAST  
BRASIL...MEANWHILE...EXPECTING MAXIMA OF 75-125MM THROUGH  
WEDNESDAY MORNING...AND 40-80MM/DAY ON WEDNESDAY THROUGH FRIDAY.  
 
THE RIDGE ALOFT IS TO ALSO VENT CONVECTION ALONG THE NORTHERN  
ANDES OF ARGENTINA...WITH RAINFALL AMOUNTS OF 05-10MM/DAY AND  
MAXIMA OF 15-20MM. HIGHER AMOUNTS ARE EXPECTED ACROSS THE  
ALTIPLANO OF BOLIVIA-NORTHERN CHILE TO SOUTHERN PERU. IN THIS AREA  
GDI CONTINUE TO SHOW HIGH RISK OF MODERATE TO HEAVY RAINFALL  
AMOUNTS TO SUSTAIN ACCUMULATION OF 15-30MM/DAY ON  
TUESDAY-WEDNESDAY...AND 05-10MM ON WEDNESDAY TO THURSDAY MORNING.  
ON FRIDAY TO SATURDAY FOCUS OF THE HEAVY CONVECTION SHIFTS TO  
SOUTHERN BOLIVIA...WHERE THE MAXIMA IS TO PEAK AT 25-50MM. LOCALLY  
HIGHER AMOUNTS ARE HIGHLY PROBABLE. FATHER NORTH...THE PANAMANIAN  
LOW/TROUGH WILL ENHANCE COASTAL CONVERGENCE ACROSS ECUADOR...TO  
FAVOR MODERATE RAINFALL AMOUNTS WITH ACCUMULATION OF 15-25MM OVER  
THE NEXT COUPLE OF DAYS. ON THURSDAY-FRIDAY THIS DECREASES TO  
05-10MM AS THE MOIST INFLOW WEAKENS.  
 
BALBINO...INMET (BRASIL)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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