309  
FXSA20 KWBC 061701  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EST WED DEC 06 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM DEC 06 AT 0000 UTC): THE GLOBAL  
MODELS ARE IN BETTER AGREEMENT...FOLLOWING SIMILAR EVOLUTION  
THROUGH 132-144 HRS. DURING THE LATTER PART OF THE FORECAST...THE  
GFS AND UKMET MADE PATTERN CORRECTIONS...AND THEY NO LONGER  
FORECAST A LOW TO CLOSE OVER THE SOUTHERN STATES OF BRASIL. THIS  
IS SIMILAR TO WHAT THE ECMWF PREVIOUSLY FORECASTED...WITH THE  
ENSEMBLE MEMBERS PROVIDING MORE SUPPORT TO THIS SOLUTION.  
 
A BROAD MID/UPPER LEVEL TROUGH EXTENDS OVER THE ATLANTIC ALONG 20W  
TO 20S. CONSISTENT WITH PREVIOUS FORECAST...THIS IS TO GRADUALLY  
WEAKEN AS IT MEANDERS EAST ACROSS THE SOUTH ATLANTIC. AT LOW  
LEVELS...THE TROUGH ALOFT SUSTAINS AN ELONGATED FRONT THAT EXTENDS  
ACROSS THE SOUTH ATLANTIC TO THE SOUTHERN STATES OF BRASIL. THE  
SEGMENT OVER SOUTHERN BRASIL IS FORECAST TO FRONTOLIZE LATER ON  
THURSDAY...WHILE THE REMNANTS OVER THE ATLANTIC DISSIPATE LATER ON  
SATURDAY. AN OLD BOUNDARY LIES TO THE NORTH...EXTENDING ACROSS THE  
SOUTH ATLANTIC TO RIO DE JANEIRO/ESPIRITO SANTO IN BRASIL. THIS IS  
TO ALSO WEAKEN/NEARLY DISSIPATE ON THURSDAY TO FRIDAY. OVER  
SOUTHEAST BRASIL...THE LATTER SUSTAINS A LOW/MID LEVEL TROUGH  
ACROSS ESPIRITO SANTO-MINAS GERAIS TO MATO GROSSO DO SUL. ALTHOUGH  
THE FRONT TENDS TO DISSIPATE...THE TROUGH IS TO PERSIST THROUGH  
THE END OF THE WEEK. AT 250 HPA AN ANTICYCLONICALLY CURVED  
SUBTROPICAL JET EXTENDS ACROSS NORTHERN ARGENTINA-SOUTHERN BRASIL.  
THE JET ALOFT FAVORS AN UPPER DIVERGENT PATTERN THAT IS TO VENT  
DEEP CONVECTION ALONG THE LOW LEVEL TROUGH. MOST ACTIVE CONVECTION  
IS TO CLUSTER ACROSS MINAS GERAIS-ESPIRITO SANTO AND BAHIA. IN  
THIS AREA THE ENVIRONMENTAL CONDITIONS ARE FAVORABLE FOR MCS TO  
FORM DURING THE NEXT FEW DAYS...WITH DAILY RAINFALL AMOUNTS OF  
40-80MM WITH LOCALLY HIGHER AMOUNTS IN EXCESS OF 125MM HIGHLY  
PROBABLE. ON FRIDAY TO SATURDAY THE FOCUS OF THE HEAVY CONVECTION  
SHIFTS TO BAHIA-TOCANTINS/GOIAS IN NORTHEAST BRASIL.  
 
IN A TIGHT BELT OF MID LATITUDE WESTERLIES...PROGRESSIVE MID LEVEL  
PERTURBATIONS ARE TO STREAM ACROSS THE SOUTHEAST PACIFIC TO THE  
SOUTHERN CONE OF SOUTH AMERICA. ONE MOVES ACROSS 50W EARLY IN THE  
CYCLE AS ANOTHER MAKES LANDFALL OVER SOUTHERN CHILE EARLY ON  
THURSDAY MORNING. AT LOW LEVELS POLAR FRONT MOVES NORTH ACROSS LA  
PAMPA TO THE BUENOS AIRES PROVINCE LATER TODAY...REACHING RIO DE  
LA PLATA BASIN/URUGUAY ON THURSDAY. ANOTHER FRONT  
FOLLOWS...ENTERING SOUTHERN CHILE EARLY ON THURSDAY  
MORNING...CROSSING PATAGONIA TO LA PAMPA-CENTRAL CHILE LATER IN  
THE DAY. UNDER INFLUENCE OF THESE FRONTS...SCATTERED CONVECTION  
ACROSS EXTREME SOUTHERN PORTIONS OF CHILE IS TO SUSTAIN RAINFALL  
AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM. ACROSS CENTRAL  
ARGENTINA EXPECTING MAXIMA OF 20-35MM EARLY IN THE CYCLE...WHILE  
ON THURSDAY IT DECREASES TO 00-05MM. ON FRIDAY MOST ACTIVE IS TO  
CLUSTER BETWEEN MENDOZA-BUENOS AIRES PROVINCE AND URUGUAY...WITH  
MAXIMA OF 15-25MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE  
SUBTROPICAL RIDGE CONTINUES TO DOMINATE THE FLOW TO THE NORTH OF  
30S...WITH AXIS ANCHORING ON A CLOSED HIGH OVER MATO GROSSO IN  
BRASIL. AN ELONGATED TROUGH LIES TO THE NORTH OF THIS  
RIDGE...EXTENDING ACROSS NORTH COAST OF BRASIL TO THE GUIANAS. THE  
TROUGH ALOFT FAVORS AN UPPER CONVERGENT PATTERN THAT IS TO INHIBIT  
DEEP CONVECTION ALONG THE NORTH COAST OF BRASIL TO PARA. THE RIDGE  
ALOFT IS TO VENT CONVECTION TO THE SOUTH. MOST INTENSE IS TO  
CLUSTER ACROSS MINAS GERAIS-BAHIA-TOCANTINS/GOIAS WHERE THE DAILY  
MAXIMA IS TO RANGE BETWEEN 40-80MM AS MCS FORM OVER NORTHEAST  
SOUTH AMERICA. ON THE CENTRAL/SOUTHERN SIERRA OF PERU TO THE  
ALTIPLANO OF BOLIVIA THIS IS TO FAVOR MODERATE RAINFALL AMOUNTS  
WITH ACCUMULATION OF 20-35MM/DAY. OVER EASTERN ECUADOR/SOUTHERN  
COLOMBIA-NORTHERN JUNGLE OF PERU INITIALLY EXPECTING RAINFALL  
AMOUNTS OF 15-20MM/DAY. ON THURSDAY-SATURDAY THIS WILL INCREASE TO  
20-30MM/DAY IN SCATTERED DEEP CONVECTION.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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