233  
FXSA20 KWBC 211609  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1208 PM EDT THU JUN 21 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JUNE 21 AT 0000 UTC): GOOD AGREEMENT  
AMONG THE GLOBAL MODEL GUIDANCE THROUGH 84-96 HRS. UPSTREAM OVER  
THE EASTERN PACIFIC...THE MODELS START TO DIVERGE AT 108-120  
HRS...AS THEY DISAGREE ON THE AMPLITUDE OF A MID LEVEL TROUGH ON  
THE SOUTHERN STREAM NEARING THE SOUTHERN CONE LATER ON DAY 06. THE  
HIGH VARIABILITY AMONG THE DETERMINISTIC MODELS IS ALSO EVIDENT  
AMONG THE GLOBAL ENSEMBLE MEMBERS. AS A RESULT...LONG RANGE  
FORECAST CONFIDENCE IS LOW.  
 
BROAD TROUGH DOMINATES THE FLOW ACROSS THE SOUTHERN CONE...WITH  
MID LEVEL AXIS ENVELOPING AREA BETWEEN 85W-50W AND TO THE SOUTH OF  
30S. THIS IS FOCUSING ITS SHORT WAVE ENERGY ACROSS PATAGONIA-LA  
PAMPA IN ARGENTINA. LATER TODAY THE TROUGH MIGRATES EAST TO THE  
WESTERN SOUTH ATLANTIC...NEARING 20W LATER ON FRIDAY. AT LOW  
LEVELS...THE ASSOCIATED SURFACE FRONT MOVES NORTH TO SOUTHERN  
BRASIL-SOUTHEAST PARAGUAY/NORTHERN ARGENTINA LATER THIS  
EVENING...WHERE IT IS EXPECTED TO STALL THROUGH SATURDAY MORNING.  
OVER SOUTHERN BRASIL-CORRIENTES/MISIONES IN ARGENTINA THIS IS TO  
FAVOR LIGHT RAINFALL AMOUNTS...WITH ACCUMULATION OF 00-05MM/DAY IN  
STRATIFORM PRECIPITATION.  
 
SIMULTANEOUSLY...AS A RIDGE BUILDS SOUTH ALONG 100W TO THE POLAR  
ICECAP...THIS IS TO STEER A SHORT WAVE TROUGH ON THE SOUTHERN  
STREAM NORTHWARD ACROSS THE BELLINGSHAUSEN SEA-DRAKE PASSAGE TO  
TIERRA DEL FUEGO LATER TODAY. AS IT ENTERS SOUTHERN ARGENTINA ON  
FRIDAY THIS WILL PHASE WITH ANOTHER SHORT WAVE TROUGH TO THE  
NORTH. THESE WILL THEN COMBINE INTO A LONG WAVE TROUGH OVER THE  
WESTERN ATLANTIC/MID SECTIONS OF SOUTH AMERICA LATER ON SATURDAY.  
THE BROAD TROUGH IS TO THEN MEANDER EAST ACROSS THE WESTERN TO THE  
CENTRAL ATLANTIC LATER DURING THE WEEKEND/EARLY NEXT WEEK. AS IT  
LIFTS ACROSS THE DRAKE PASSAGE...THE MID LEVEL TROUGH WILL SUSTAIN  
A PROGRESSIVE FRONT. THIS WILL ENTER TIERRA DEL FUEGO/EXTREME  
SOUTHERN PORTIONS OF CHILE LATER THIS EVENING. THE SURFACE TROUGH  
IS TO THEN INTENSIFY AS IT MEANDERS EAST ACROSS PATAGONIA IN  
ARGENTINA TO THE WESTERN ATLANTIC. AS THE TROUGH DEEPENS...AND A  
POLAR RIDGE BUILDS ACROSS THE SOUTHERN CONE...THE SURFACE FRONT  
WILL SURGE ACROSS CENTRAL ARGENTINA ON FRIDAY...REACHING SOUTHERN  
BRASIL-NORTHERN ARGENTINA ON SATURDAY AFTERNOON. THE FRONT IS OT  
THEN STALL OVER SOUTHERN BRASIL-PARAGUAY LATER DURING THE WEEKEND.  
IN A COLD ADVECTIVE PATTERN... BELOW FREEZING TEMPERATURES ARE  
EXPECTED OVER PATAGONIA-CENTRAL ARGENTINA/BUENOS AIRES PROVINCE ON  
SUNDAY-MONDAY. THE COLD ADVECTION WILL TRIGGER SNOW SHOWERS ACROSS  
THE SOUTHERN PORTIONS OF THE BUENOS AIRES PROVINCE...WITH LIGHT  
SNOWFALL TO ACCUMULATE OVER SIERRA DE LA VENTANA AND TANDIL...WITH  
ACCUMULATION OF 03-05CM. AS THE FRONT SURGES ACROSS URUGUAY TO  
SOUTHERN BRASIL/NORTHERN ARGENTINA ON SATURDAY THIS WILL TRIGGER  
SCATTERED DEEP CONVECTION WITH MAXIMA OF 15-20MM. THROUGH SUNDAY  
THIS DECREASES TO 05-10MM/DAY.  
 
FARTHER NORTH...AT 200 HPA...A RIDGE EXTENDS WEST ACROSS NORTHERN  
SOUTH AMERICA...WITH AXIS ENVELOPING CONTINENTAL AREA TO THE NORTH  
OF 10S. THROUGH SUNDAY EVENING THE RIDGE WILL BUILD SOUTH ACROSS  
WESTERN BRASIL TO NORTHERN BOLIVIA...WITH AXIS TO ANCHOR ON A  
CLOSED HIGH OVER SOUTHERN AMAZONAS/ACRE IN BRASIL. AS THE RIDGE  
BUILDS...CONVECTION OVER NORTHWEST SOUTH AMERICA IS TO INTENSIFY.  
INITIALLY EXPECTING RAINFALL AMOUNTS OF 20-30MM/DAY. THROUGH  
SUNDAY THIS INCREASES TO 20-45MM WITH MOST ACTIVE NORTH OF THE  
EQUATOR OVER COLOMBIA/NORTHERN PERU AND EASTERN ECUADOR. ACROSS  
CENTRAL PERU THIS IS TO THEN FAVOR SCATTERED CONVECTION ON THE  
SIERRA/JUNGLE WITH ACCUMULATION OF 10-15MM. ALONG THE NORTH COAST  
OF BRASIL-PARA...MEANWHILE...DIURNAL CONVECTION WILL SUSTAIN  
MAXIMA OF 10-15MM/DAY.  
 
DIAZ...INUMET (URUGUAY)  
SANCHEZ...SMN (ARGENTINA)  
DAVISON...WPC (USA)  

 
 
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