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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1602Z May 17, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1202 PM EDT THU MAY 17 2018

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM MAY 17 AT 0000 UTC): DEEPENING MID
LEVEL TROUGH ON THE NORTHERN STREAM FLOW IS THE SYSTEM OF
CONCERN...WITH SHORT WAVE PERTURBATION LIFTING ACROSS CENTRAL
ARGENTINA/RIO DE LA PLATA BASIN LATER TODAY. THIS IS TO THEN
EXPERIENCE A RAPID RATE OF INTENSIFICATION ON FRIDAY-TO-SATURDAY
WHILE LIFTING NORTH ACROSS URUGUAY TO THE SOUTHERN STATES OF
BRASIL. ON FRIDAY THIS IS TO THEN TRIGGER HEIGHT FALLS OF
75-125GPM...INCREASING TO 150-175GPM FALLS ON SATURDAY. THE TROUGH
IS TO THEN EVOLVE INTO A CLOSED LOW OFF THE SOUTH COAST OF BRASIL
LATER DURING THE WEEKEND. AS IT STREAMS ACROSS MID SECTIONS OF
SOUTH AMERICA THE MID LEVEL TROUGH IS TO INTERACT WITH A
MEANDERING FRONT OVER SOUTHERN BRASIL-PARAGUAY...TRIGGERING
CYCLOGENESIS ALONG THIS BOUNDARY. THE LOW IS TO TRACK TO THE
EAST-SOUTHEAST ACROSS SOUTHERN BRASIL TO THE WESTERN ATLANTIC
LATER ON FRIDAY...WHERE IT IS FORECAST TO RAPIDLY OCCLUDE. AS THE
LOW DEEPENS...AND A POLAR RIDGE BUILDS ACROSS ARGENTINA...THIS IS
TO THEN INDUCE A SOUTHERLY LOW LEVEL JET ACROSS PARAGUAY/EASTERN
BOLIVIA. THE WIND SURGE IS TO THEN DRIVE THE ASSOCIATED FRONT
NORTH ACROSS THE SOUTHEAST STATES OF BRASIL-MATO GROSSO TO
NORTHERN BOLIVIA/SOUTHERN PERU ON SATURDAY. LATER ON SUNDAY IT IS
TO MOVE EAST AND NORTH ACROSS SAO PAULO/RIO DE JANEIRO TO MINAS
GERAIS...WHILE TRAILING END REMAINS OVER ACRE/RONDONIA-SOUTHERN
PERU. INITIALLY...AS THE FRONT MEANDERS OVER SOUTHERN
BRASIL-PARAGUAY...EXPECTING MAXIMA OF 15-30MM. ON FRIDAY...AS THE
LOW FORMS...THIS INCREASES TO 30-60MM WHILE BUILDING NORTH ACROSS
MATO GROSSO DO SUL TO SANTA CRUZ IN EASTERN BOLIVIA. OVER CENTRAL
BOLIVIA PREFRONTAL CONVECTION IS TO THEN TRIGGER MAXIMA OF
20-45MM. ON SATURDAY THE FRONTAL CONVECTION OVER RIO DE
JANEIRO/NORTHERN SAO PAULO-MATO GROSSO-RONDONIA IN BRASIL IS TO
TRIGGER MAXIMA OF 15-25MM....WHILE OVER PARA-AMAZONAS IN BRASIL
THE MAXIMA IS TO PEAK AT 20-40MM IN PREFRONTAL CONVECTION. HIGHER
AMOUNTS ARE EXPECTED OVER NORTHWEST BOLIVIA-ACRE IN BRASIL AND THE
PERUVIAN JUNGLE...WHERE THE SURGING LOW LEVEL JET IS TO TRIGGER
MAXIMA OF 40-80MM ON SATURDAY. ON SUNDAY FOCUS OF THE HEAVY
CONVECTION SHIFTS TO THE NORTHERN JUNGLE OF PERU-EASTERN
ECUADOR/SOUTHERN COLOMBIA WITH MAXIMA OF 30-60MM.

UPSTREAM OVER THE SOUTH PACIFIC...A BROAD MID LEVEL TROUGH ON THE
SOUTHERN STREAM IS TO PROPAGATE ACROSS THE SOUTHEAST PACIFIC TO
SOUTHERN PORTIONS OF CHILE/DRAKE PASSAGE LATER ON FRIDAY. THE
TROUGH PUSHES EAST ACROSS THE SOUTHERN ANDES TO PATAGONIA IN
ARGENTINA ON SATURDAY. BUT AS IS PRESSES AGAINST A RIDGE TO THE
EAST THE TROUGH IS FORECAST TO GRADUALLY WEAKEN LATER ON
SUNDAY/MONDAY. AT LOW LEVELS THE TROUGH ALOFT  WILL SUSTAIN A
BROAD SURFACE TROUGH OVER THE SOUTHEAST PACIFIC ON FRIDAY...WITH
ASSOCIATED FRONT STREAMING ACROSS SOUTHERN CHILE TO PATAGONIA IN
ARGENTINA DURING THE WEEKEND. AS IT ENTERS THE SOUTHERN CONE THE
FRONT/POLAR TROUGH WILL SUSTAIN A SUBTROPICAL
CONNECTION...FAVORING MODERATE RAINFALL AMOUNTS BETWEEN
TEMUCO-ISLA DE CHILOE IN SOUTHERN CHILE. IN THIS AREA EXPECTING
MAXIMA OF 15-20MM LATER ON FRIDAY TO SATURDAY.

AT 200 HPA...A SHORT WAVE RIDGE EXTENDS ACROSS NORTHERN SOUTH
AMERICA. THIS HIGH/RIDGE IS TO DOMINATE THE FLOW TO THE NORTH OF
10S DURING THE NEXT TWO DAYS. LATER DURING THE WEEKEND...AS THE
AFOREMENTIONED POLAR TROUGH DEEPENS ACROSS BRASIL...EXPECTING
RAPID EROSION/COLLAPSE OF THE UPPER LEVEL RIDGE PATTERN.
MEANWHILE...THE RIDGE ALOFT IS TO VENT DIURNAL CONVECTION ACROSS
PARA-AMAZONAS-RORAIMA IN BRASIL...WITH RAINFALL MAXIMA OF
20-40MM/DAY. SEA BREEZE CONVERGENCE ALONG THE NORTH COAST OF
BRASIL IS TO SUSTAIN ACCUMULATION OF 10-15MM IN ISOLATED TO
SCATTERED CONVECTION. AS THE RIDGE COLLAPSES...CONVECTION IS TO
SPREAD ACROSS EQUATORIAL SOUTH AMERICA LATER DURING THE
WEEKEND...FAVORING MAXIMA OF 20-45MM/DAY.

BALBINO...INMET (BRASIL)
DIAZ...INUMET (URUGUAY)
DAVISON/GALVEZ...WPC (USA)