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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1655Z Apr 01, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1255 PM EDT WED APR 01 2020

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

FORECAST DISCUSSION FROM MARCH 31/17UTC: MINOR CORRECTIONS TO
PREVIOUS FORECAST...WITH MODELS MAINTAINING GOOD CYCLE-TO-CYCLE
CONTINUITY THROUGH THE MEDIUM RANGE PERIOD. THIS LEADS TO HIGH
CONFIDENCE IN THE FORECAST.

AT 250 HPA...A CELL OF THE SUBTROPICAL RIDGE SPANS BETWEEN
NORTHWEST ARGENTINA AND ACRE IN WESTERN BRASIL...WITH AXIS
ANCHORING ON A CLOSED HIGH OVER THE ALTIPLANO OF BOLIVIA. THROUGH
FRIDAY...AS SHORT WAVE PERTURBATIONS STREAM TO THE SOUTH...THE
RIDGE TENDS TO WEAKEN/NEARLY COLLAPSE OVER NORTHWEST
ARGENTINA...WHILE PORTION OVER BOLIVIA-SOUTHERN PERU/ACRE-RONDONIA
IN BRASIL PERSISTS. AS IT HOLDS OVER THE CONTINENT...THE RIDGE
WILL SUSTAIN THE AMPLIFICATION OF A MID/UPPER LEVEL TROUGH OVER
THE WESTERN ATLANTIC TO THE SOUTHEAST STATES OF BRASIL. THROUGH
THURSDAY MORNING THIS IS TO THEN PULL TO THE EAST-SOUTHEAST. AT
LOW LEVELS...THE TROUGH ALOFT CONTINUES TO INTERACT WITH A SURFACE
FRONT THAT TRAILS ACROSS THE SOUTH ATLANTIC TO NORTHERN SAO
PAULO-RIO DE JANEIRO. THIS IS TO FAVOR ORGANIZED CONVECTION OVER
THE NEXT TWO DAYS...WITH MAXIMA OF 20-45MM OVER THE NEXT COUPLE OF
DAYS. ACTIVITY IS TO GRADUALLY WANE AS THE FRONT WEAKENS ON
THURSDAY.

GLOBAL MODELS CONTINUE TO FORECAST A MID LEVEL TROUGH ON THE
NORTHERN STREAM FLOW TO CLOSELY FOLLOW...ENTERING SOUTHERN/CENTRAL
CHILE LATER TODAY. THROUGH THURSDAY MORNING THE SHORT WAVE TROUGH
IS TO LIFT ACROSS THE RIO DE LA PLATA BASIN...WHERE UNDER
FAVORABLE JET DYNAMICS THE TROUGH IS FORECAST TO RAPIDLY INTENSIFY
THROUGH FRIDAY MORNING. DURING THE DAY THIS IS TO EVOLVE INTO A
CLOSED LOW. AT LOW LEVELS...THE MID LEVEL VORTEX WILL SUSTAIN
CYCLOGENESIS ALONG A MEANDERING FRONT OVER CENTRAL ARGENTINA LATER
TODAY. THE SURFACE LOW IS TO GRADUALLY DEEPEN AS IT LIFTS FROM LA
PAMPA TO THE RIO DE LA PLATA BASIN LATER ON WEDNESDAY...WHEN IT IS
TO CENTER ON A 1010 HPA LOW OVER URUGUAY. ON THURSDAY-FRIDAY THE
LOW IS TO EXPERIENCE A NEARLY EXPLOSIVE RATE OF INTENSIFICATION
(POSSIBLE METEOROLOGICAL BOMB)...TO SUSTAIN NEAR HURRICANE
INTENSITY WINDS AS IT DEEPENS TO A 980 HPA LOW OVER THE WESTERN
ATLANTIC EARLY ON FRIDAY MORNING. OVER ARGENTINA THIS IS TO
SUSTAIN A PAMPERO LOW LEVEL JET...THAT QUICKLY EXPANDS TO
PARAGUAY-BOLIVIA EARLY ON THURSDAY MORNING. THIS WILL THEN DRIVE A
SURFACE FRONT NORTH ACROSS CENTRAL TO NORTHERN ARGENTINA/URUGUAY
LATER ON WEDNESDAY...WHILE ALSO TRIGGERING A SEVERE WEATHER
PRODUCING PREFRONTAL SQUALL LINE. LATER ON THURSDAY THE FRONT
MOVES NORTH ACROSS PARANA/SANTA CATARINA IN SOUTHERN BRASIL TO
CHACO PARAGUAYO/SOUTHERN BOLIVIA...WITH THE BOUNDARY TO ALIGN
ALONG 20S LATER ON FRIDAY. ACROSS THE BUENOS AIRES PROVINCE TO
CENTRAL ARGENTINA THIS IS TO SUSTAIN MAXIMA OF 35-70MM IN
POTENTIALLY SEVERE CONVECTION LATER TODAY. THIS INCREASES TO
40-80MM ACROSS URUGUAY-NORTHERN ARGENTINA/SOUTHERN BOLIVIA ON
WEDNESDAY-THURSDAY. OVER CENTRAL BOLIVIA TO SOUTHERN PERU THE PEAK
IN CONVECTION IS EXPECTED ON THURSDAY-FRIDAY...WHEN THE SURGING
SOUTHERLY FLOW WILL LIKELY TRIGGER A HEAVY RAINFALL PRODUCING MCS
WITH MAXIMA OF 50-100MM. THROUGH FRIDAY THE ACTIVITY STARTS TO
WANE WHILE BUILDING WEST ACROSS SOUTHERN TO CENTRAL JUNGLE IN
PERU...WHERE IT IS TO SUSTAIN MAXIMA OF 20-40MM.

A BROAD/LOW AMPLITUDE MID LEVEL TROUGH IS TO THEN SETTLE OVER THE
SOUTHEAST PACIFIC LATER ON THURSDAY...WITH THE BROAD TROUGH TO
ESTABLISH A SUBTROPICAL CONNECTION AS IT NEARS THE SOUTHERN CONE
OF SOUTH AMERICA. ON FRIDAY THIS IS TO THEN MOVE EAST ACROSS
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA...WHERE IT IS TO SLOWLY
AMPLIFY TO LA PAMPA. AT LOW LEVELS THIS WILL SUSTAIN A BROAD
TROUGH OVER THE SOUTHEAST PACIFIC LATER ON WEDNESDAY...THAT
AMPLIFIES ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA THROUGH
FRIDAY EVENING. THE ASSOCIATED FRONT MOVES ACROSS TIERRA DEL FUEGO
TO SOUTHERN PATAGONIA LATER ON WEDNESDAY/EARLY ON THURSDAY
MORNING...THEN NORTH ACROSS LA PAMPA TO CENTRAL ARGENTINA/CHILE ON
SATURDAY-SUNDAY. OVER SOUTHERN CHILE THIS WILL TRIGGER MODERATE
RAINFALL AMOUNTS WITH MAXIMA OF 10-15MM EARLY ON THURSDAY. THROUGH
THE DAY THIS IS TO INTENSIFY WHILE BUILDING NORTH TO ISLA DE
CHILOE...WITH MAXIMA INCREASING TO 15-20MM. ON FRIDAY-SATURDAY
EXPECTING ADDITIONAL RAINFALL AMOUNTS OF 05-10MM.

OTHER CONVECTION TO THE NORTH IS TO CLUSTER ALONG THE NEAR
EQUATORIAL TROUGH/ATLANTIC ITCZ AS IT MEANDERS OVER NORTHERN
BRASIL. IN THIS AREA...AS ENHANCED BY EASTERLY WAVES STREAMING
ACROSS NORTHERN BRASIL/EQUATORIAL SOUTH AMERICA...THERE IS A HIGH
RISK OF MODERATE TO HEAVY AMOUNTS DURING THE NEXT FEW DAYS. ALONG
THE NORTH COAST OF BRASIL TO NORTHERN PARA THE MAXIMA IS TO PEAK
AT 35-70MM EARLY IN THE CYCLE...INCREASING TO 40-80MM ON
WEDNESDAY-THURSDAY. HEAVY CONVECTION IS TO PERSIST ON
THURSDAY-FRIDAY AS THE EASTERLY WAVE PROPAGATES TO AMAZONAS IN
WESTERN BRASIL...WITH MAXIMA OF 35-70MM. ON FRIDAY-SATURDAY THIS
DECREASES TO 20-40MM WHILE BUILDING WEST ACROSS COLOMBIA TO THE
NORTHERN JUNGLE OF PERU. DURING THE WEEKEND THIS SURGES...WITH
MAXIMA INCREASING TO 30-60MM AS IT BUILDS INTO EASTERN ECUADOR.

DAVISON...WPC (USA)
GALVEZ...WPC (USA)