679  
FXSA20 KWBC 131813  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
112 PM EST WED DEC 13 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM DEC 13 AT 0000 UTC): MINOR  
CORRECTIONS TO PREVIOUS FORECAST...WITH GLOBAL MODEL GUIDANCE  
FOLLOWING A SIMILAR EVOLUTION THROUGH DAY 06. THIS IS WELL  
SUPPORTED BY THE GLOBAL ENSEMBLE MEMBERS...LEADING TO A HIGH  
CONFIDENCE IN THE FORECAST.  
 
AS PREVIOUSLY FORECASTED...A PROGRESSIVE MID LEVEL TROUGH PULLS  
ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC EARLY IN THE  
CYCLE...CROSSING 50W LATER ON THURSDAY WHILE CONFINING TO THE  
SOUTH OF 40S. AT LOW LEVELS THE TROUGH ALOFT SUSTAINS A DEEP  
OCCLUDED LOW OVER THE BELLINGSHAUSEN SEA/SOUTHEAST PACIFIC. THIS  
IS TO GRADUALLY WEAKEN AS IT SLOWLY PULLS ACROSS THE DRAKE PASSAGE  
EARLY ON THURSDAY MORNING. MEANWHILE...THE ASSOCIATED FRONT IS TO  
MEANDER ACROSS CENTRAL PATAGONIA IN ARGENTINA-SOUTHERN REGIONS OF  
CHILE THROUGH THURSDAY EVENING...MEANDERING NORTH ACROSS LA PAMPA  
IN ARGENTINA ON FRIDAY. OVER SOUTHERN CHILE THIS IS TO FAVOR  
MODERATE RAINFALL AMOUNTS WITH MAXIMA OF 20-30MM THROUGH THURSDAY  
MORNING...AND 10-15MM ON THURSDAY TO FRIDAY. AS IT MEANDERS ACROSS  
LA PAMPA TO CENTRAL ARGENTINA ON FRIDAY THIS IS TO FAVOR SCATTERED  
CONVECTION WITH MAXIMA OF 05-10MM.  
 
A MID LEVEL TROUGH ON THE NORTHERN STREAM ENTERED THE CENTRAL  
REGIONS OF CHILE EARLY THIS MORNING. THIS IS TO THEN TRACK ACROSS  
CENTRAL ARGENTINA TO THE WESTERN ATLANTIC EARLY ON THURSDAY  
MORNING. AS IT SPILLS ACROSS THE CENTRAL ANDES...THE MID LEVEL  
TROUGH TRIGGERED CYCLOGENESIS OVER CENTRAL ARGENTINA. THROUGH THIS  
EVENING THE FRONT MOVES NORTH ACROSS THE BUENOS AIRES  
PROVINCE-CORDOBA IN ARGENTINA...AND ON THURSDAY IT CROSSES URUGUAY  
TO SOUTHERN BRASIL-NORTHERN PROVINCES IN ARGENTINA. OVER CENTRAL  
ARGENTINA THIS IS TO TRIGGER RAINFALL AMOUNTS OF 15-25MM THROUGH  
THURSDAY MORNING...WHILE OVER SOUTHERN BRASIL IT WILL SUSTAIN  
RAINFALL AMOUNTS OF 05-10MM.  
 
CONSISTENT WITH THE PREVIOUS FORECAST...THE NEXT MID LEVEL  
PERTURBATION ENTERS SOUTHERN CHILE EARLY ON FRIDAY MORNING. THIS  
IS TO QUICKLY PULL ACROSS THE SOUTHERN CONE TO THE WESTERN  
ATLANTIC EARLY ON SATURDAY... NEARING 40W LATER ON SUNDAY. AT LOW  
LEVELS THIS IS TO SUSTAIN A DEEP FRONTAL LOW THAT MOVES ACROSS  
SOUTHERN CHILE/PATAGONIA IN ARGENTINA ON FRIDAY. ON  
SATURDAY...UNDER INFLUENCE OF A PAMPERO LOW LEVEL JET AND BUILDING  
POLAR RIDGE OVER ARGENTINA...THE FRONT SURGES ACROSS LA  
PAMPA/CENTRAL ARGENTINA ON SATURDAY. ON SUNDAY IT CONTINUES NORTH  
ACROSS SOUTHERN BRASIL-PARAGUAY TO SOUTHERN BOLIVIA. AS IT MAKES  
LANDFALL OVER SOUTHERN CHILE ON FRIDAY THIS WILL SUSTAIN MODERATE  
CONVECTION WITH ACCUMULATION OF 15-20MM. MOST INTENSE IS EXPECTED  
OVER ENTRE RIOS IN ARGENTINA-URUGUAY ON SATURDAY...WHEN THE FRONT  
SURGES ACROSS CENTRAL ARGENTINA WHILE TRIGGERING MODERATE TO HEAVY  
CONVECTION WITH MAXIMA OF 25-50MM. DURING THIS PERIOD...THE MODELS  
CONTINUE TO FORESEE AN ELEVATED POTENTIAL OF SEVERE THUNDERSTORMS.  
ON SUNDAY...AS THE FRONT MEANDERS OVER SOUTHERN  
BRASIL-PARAGUAY...MOST ACTIVE CONVECTION IS EXPECTED ACROSS  
SOUTHERN BOLIVIA-NORTHWEST ARGENTINA AND THE CHACO  
PARAGUAYO...WITH MAXIMA OF 30-60MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...AN ILL ORGANIZED CELL OF  
THE SUBTROPICAL RIDGE IS INITIALIZED OVER NORTHERN BRASIL. THIS...  
HOWEVER...IS FORECAST TO GRADUALLY BUILD ACROSS WESTERN  
BRASIL-PERU DURING THE NEXT THREE DAYS. AXIS IS TO THEN CENTER ON  
A CLOSED HIGH OVER NORTHERN BOLIVIA. AS THE RIDGE BUILDS TO THE  
WEST...IT IS TO INDUCE THE NORTHWARD AMPLIFICATION OF A TROUGH  
ACROSS SOUTHEAST BRASIL. IN THIS PATTERN...THE MOST INTENSE  
CONVECTION IS EXPECTED OVER THE CONTINENT TO THE NORTH OF 20S. ON  
THE NORTHEAST STATES OF BRASIL INITIALLY EXPECTING RAINFALL MAXIMA  
OF 35-70MM...WITH LOCALLY HIGHER AMOUNTS HIGHLY PROBABLE. THIS  
DECREASES TO 20-30MM ON FRIDAY. ON SATURDAY-SUNDAY THIS SURGES  
ACROSS TOCANTINS-GOIAS TO PARA IN BRASIL...WHERE IT IS TO TRIGGER  
RAINFALL MAXIMA OF 40-80MM. ACROSS PARA-AMAZONAS IN BRASIL  
INITIALLY EXPECTING RAINFALL MAXIMA OF 20-35MM. ON THURSDAY THIS  
INCREASES TO MAXIMA OF 20-45MM...WHILE ON FRIDAY IT WILL PEAK AT  
30-60MM. ON THE NORTHERN JUNGLE OF PERU-EASTERN ECUADOR EXPECTING  
RAINFALL MAXIMA OF 15-20MM IN SCATTERED DEEP CONVECTION...WHILE ON  
THE SOUTHERN SIERRA/ALTIPLANO THE CONVECTIVE ACTIVITY IS TO  
GRADUALLY BECOME MORE ACTIVE/BETTER ORGANIZED...WITH MAXIMA OF  
00-05MM/DAY EARLY IN THE CYCLE INCREASING TO 10-15MM ON  
FRIDAY-SATURDAY.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
DAVISON/GALVEZ...WPC (USA)  

 
 
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