128  
FXSA20 KWBC 251702  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
102 PM EDT WED OCT 25 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM OCT 25 AT 0000 UTC): MINOR  
CORRECTIONS TO PREVIOUS FORECAST...WITH MODELS FOLLOWING A SIMILAR  
EVOLUTION THROUGH THE END OF THE FORECAST CYCLE. CONFIDENCE IN THE  
FORECAST REMAINS HIGH.  
 
A PROGRESSIVE MID LEVEL TROUGH PULLS ACROSS PATAGONIA IN ARGENTINA  
TO THE MALVINAS/FALKLAND ISLANDS LATER TODAY...NEARING THE SOUTH  
GEORGIA ISLANDS LATER ON THURSDAY. AT LOW LEVELS THIS SUSTAINS AN  
ELONGATED FRONT ACROSS SOUTHERN PATAGONIA IN ARGENTINA/SOUTHERN  
CHILE TO THE EASTERN PACIFIC. THIS IS ENHANCING LOW LEVEL MOISTURE  
CONVERGENCE ACROSS SOUTHERN PORTIONS OF CHILE...WHERE IT IS TO  
TRIGGER SCATTERED CONVECTION WITH ACCUMULATION OF 05-10MM.  
 
A DEEPENING SHORT WAVE TROUGH IS TO FOLLOW...WITH MID LEVEL AXIS  
TO MOVE ACROSS 95W TO 35S LATER ON THURSDAY. ON FRIDAY...AS IT  
NEARS THE SOUTH COAST OF CHILE...THE MID LEVEL PERTURBATION IS TO  
RAPIDLY INTENSIFY...CENTERING ON A DEEP CLOSED LOW JUST WEST OF  
ISLA DE CHILOE. THROUGH SATURDAY THIS EVOLVES INTO A BROAD TROUGH  
ACROSS THE SOUTHERN CONE...FOCUSING ITS SHORT WAVE ENERGY ACROSS  
PATAGONIA IN ARGENTINA-LA PAMPA TO CUYO. AT LOW LEVELS THIS WILL  
SUSTAIN A DEEP OCCLUDED LOW OFF THE SOUTH COAST OF CHILE LATER ON  
FRIDAY...WHILE THE ASSOCIATED FRONT PUSHES EAST ACROSS PATAGONIA  
IN ARGENTINA. ON SATURDAY IT IS TO MEANDER EAST ACROSS LA  
PAMPA-SOUTHERN CUYO IN ARGENTINA-CENTRAL CHILE TO THE EASTERN  
PACIFIC. BUILDING POLAR RIDGE IS TO THEN DISPLACE THIS BOUNDARY  
NORTH ACROSS RIO DE LA PLATA BASIN-CORDOBA IN ARGENTINA ON SUNDAY.  
AS IT ENTERS SOUTHERN CHILE ON FRIDAY THE DEEP LOW IS TO SUSTAIN  
MODERATE CONVECTION WITH MAXIMA OF 20-30MM. OVER SOUTHERN  
PATAGONIA...THE DEEP OCCLUDED LOW WILL THEN FAVOR A MOIST  
ADVECTIVE PATTERN TO CONVERGE ON THE ARGENTINEAN SIDE OF THE  
ANDES. IN THIS AREA EXPECTING MAXIMA OF 15-20MM ON  
THURSDAY-FRIDAY...WHILE ON FRIDAY TO SATURDAY THE MAXIMA INCREASES  
TO 20-30MM. AS THE FRONT SURGES ACROSS LA PAMPA-CENTRAL  
ARGENTINA...UNDER FAVORABLE JET DYNAMICS...IT IS NOW FORECAST TO  
TRIGGER HEAVY RAINFALL AMOUNTS...WITH ACCUMULATION OF 30-60MM IN  
POTENTIALLY SEVERE CONVECTION.  
 
SHORT WAVE PERTURBATIONS POPULATE THE NORTHERN STREAM FLOW...WITH  
ONE MOVING ACROSS URUGUAY/SOUTHERN BRASIL AS ANOTHER NEARS THE  
CENTRAL REGIONS OF CHILE. THE LATTER SPILLS ACROSS THE CENTRAL  
ANDES TO CUYO IN ARGENTINA EARLY ON THURSDAY...AND DURING THE  
EARLY MORNING HOURS ON FRIDAY IT IS TO MIGRATE ACROSS  
URUGUAY/SOUTHERN BRASIL TO THE WESTERN ATLANTIC. THIS IS TO THEN  
INTENSIFY WHILE MEANDERING TO THE EAST-SOUTHEAST. THE MID LEVEL  
PERTURBATIONS...IN INTERACTION WITH MEANDERING FRONT OVER MID  
SECTIONS OF SOUTH AMERICA...WILL FAVOR GENERATION OF MESO SCALE  
CONVECTIVE SYSTEMS AND POTENTIALLY SEVERE CONVECTION. ACTIVITY IS  
EXPECTED TO PEAK OVER THE NEXT THREE DAYS. MOST ACTIVE IS TO  
CLUSTER BETWEEN PARAGUAY-SOUTHERN BRASIL...WHERE THE MAXIMA IS TO  
PEAK AT 50-100MM. ACTIVITY IS TO GRADUALLY WANE AS THE CYCLE  
PROGRESSES.  
 
NORTH OVER THE CONTINENT...A 200 HPA RIDGE ENVELOPS CONTINENTAL  
AREA TO THE NORTH OF 20S. MODELS CONTINUE TO FORECAST UPPER LEVEL  
RIDGE PATTERN TO GRADUALLY BECOME BETTER ORGANIZED...WITH AXIS TO  
CENTER ON A CLOSED HIGH OVER AMAZONAS IN WESTERN BRASIL. THE BROAD  
UPPER LEVEL RIDGE PATTERN IS TO VENT DEEP CONVECTION ACROSS  
NORTHWEST SOUTH AMERICA. OVER AMAZONAS IN BRASIL-AMAZONIA IN  
SOUTHERN COLOMBIA AND THE NORTHERN JUNGLE OF PERU THIS IS TO FAVOR  
MAXIMA OF 20-35MM/DAY...WITH LOCALLY HIGHER AMOUNTS EXPECTED ON  
SATURDAY. OVER MATO GROSSO-SOUTHERN PARA AND RORAIMA IN BRASIL  
EXPECTING SCATTERED CONVECTION TO BUILD IN A DIURNAL  
PATTERN...WITH ACCUMULATION OF 15-25MM/DAY. ON THE  
CENTRAL-SOUTHERN JUNGLE OF PERU THE DAILY MAXIMA IS TO PEAK AT  
15-20MM. THIS IS TO GENERALLY PERSIST OVER THE NEXT COUPLE OF DAYS.  
 
OVIEDO...SHIN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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