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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1721Z Feb 12, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1221 PM EST MON FEB 12 2018

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

MODEL DISCUSSION (VALID FROM FEB 12 AT 0000 UTC): FORECAST MODELS
AND ENSEMBLE MEMBERS CONTINUE IN FAIRLY GOOD AGREEMENT ON FORECAST
EVOLUTION THROUGH THE CYCLE. DIFFERENCES ARISE AROUND 96 HRS. THE
STRUGGLE IS RESOLVING THE DETAILS OF AN UPPER TROUGH THAT WILL
MEANDER OFF THE COAST OF RIO DE JANEIRO AND SAO PAULO.
ALSO...PROBLEMS ARISE ON PERTURBATIONS ARRIVING IN THE WESTERLIES.

SOUTHERN SOUTH AMERICA

A CHANGE OF PATTERN FOR EXTREME SOUTHERN CHILE INTO A WETTER ONE
IS STARTING TUESDAY. A RAPIDLY-PROPAGATING UPPER TROUGH IN THE
WESTERLIES WILL CROSS THE ANDES TO THE SOUTH OF 45S DURING IN
TUESDAY EVENING. THE ASSOCIATED TRAIN OF SURFACE FRONTS WILL
ARRIVE INTO SOUTHERN CHILE ACCOMPANIED BY A SUBTROPICAL MOISTURE
CONNECTION...PRECIPITABLE WATER VALUES ARE FORECAST TO SURPASS
35MM. THIS WILL SUSTAIN MODERATE RAINFALL IN AYSEN AND MAGALLANES
WHERE MAXIMA WILL REACH 20-40MM/DAY DURING TUESDAY-EARLY
WEDNESDAY. MOISTURE WILL REMAIN AVAILABLE THROUGH AT LEAST THROUGH
THE WEEKEND. THIS WILL SUSTAIN SEVERAL ROUNDS OF RAINFALL IN
SOUTHERN CHILE...FOR THE MOST PART...ENHANCED BY PASSING UPPER
TROUGHS. THIS WILL ENHANCE PRECIPITATION ON THURSDAY-FRIDAY TO
SUSTAIN MAXIMA OF 20-40MM/DAY. OTHERWISE...ENHANCED MOISTURE
CONVERGENCE WILL SUSTAIN MAXIMA OF 15-20MM ON TUESDAY. IN
ARGENTINA AND URUGUAY...CONDITIONS WILL BE QUIET FOR THE MOST
PART...WITH THE EXCEPTION OF A FEW THUNDERSTORMS IN URUGUAY ON
MONDAY.

CENTRAL SOUTH AMERICA

A MID-LEVEL TROUGH PROPAGATING ACROSS SOUTHERN BRASIL WILL
STRUGGLE TO CONTINUE EAST ONCE IT REACHES A RIDGE THAT EXTENDS
FROM ESPIRITO SANTO SOUTHEAST TO 30S 20W. THIS WILL LEAD TO THE
UPPER TROUGH TO WEAKEN BUT LINGER IN THE AREA TO BE REINFORCED BY
ANOTHER TROUGH ARRIVING ON WEDNESDAY FROM SOUTHERN BRASIL. UPPER
TROUGH DYNAMICS AND THERMODYNAMICS WILL INTERACT WITH MOIST PLUME
PRESENT IN CENTRAL SOUTH AMERICA AND THE SAO PAULO-PARANA AREA.
OFF THE COAST OF BRASIL...A PRECIPITABLE WATER PLUME OF OVER 55MM
LIGERS BETWEEN PARANA AND RIO DE JANEIRO. MODELS SHOW THIS PLUME
LINGERING WHILE MOISTURE CONTENT DECREASES TO 50MM BY
THURSDAY...STILL A LARGE VALUE. MODELS ALSO SUGGEST ONSHORE WINDS
IMPINGING INTO THE SERRA DO MAR...WHICH WILL LIKELY TRIGGER HEAVY
RAINFALL. INITIALLY...THROUGH EARLY TUESDAY...EXPECTING 25-50MM
ALONG THE SERRA DO MAR OF PARANA AND SAO PAULO. INLAND ACROSS MATO
GROSSO DO SUL/SAO PAULO EXPECTING MAXIMA OD 20-35MM. BY
TUESDAY-WEDNESDAY...EXPECTING MAXIMA OF 40-80MM/DAY IN THE SERRA
DO MAR OF SAO PAULO AND WESTERN RIO DE JANEIRO. INLAND EXPECTING
MAXIMA OF 15-25MM. BY WEDNESDAY-THURSDAY EXPECTING MAXIMA OF
25-50MM/DAY BETWEEN SAO PAULO AND CENTRAL RIO DE JANEIRO. BY
THURSDAY-FRIDAY EXPECTING MAXIMA OF 10-15MM IN RIO DE JANEIRO.

TROPICAL SOUTH AMERICA

THE BOLIVIAN HIGH/SUBTROPICAL RIDGE HAS REFORMED OVER BOLIVIA
WHERE IT WILL MEANDER SLOWLY NORTHWESTWARD TO CENTER OVER EXTREME
SOUTHERN PERU BY FRIDAY. TO THE NORTHEAST...A CLOSE LOW HAS
RETROGRESSED FROM THE TROPICAL ATLANTIC AND NOW CENTERS OVER CEARA
IN THE NORDESTE. THIS UPPER LOW WILL INTERACT WITH THE ATLANTIC
AND ITCZ TO VENTILATE CONVECTION THROUGH THE CYCLE.
INITIALLY...EXPECTING MAXIMA OF 20-40MM/DAY. THIS IS TO INCREASE
TO MAXIMA OF 25-50MM BY WEDNESDAY IN RESPONSE TO AN INCREASE IN
LOW-LEVEL CONVERGENCE. THIS IS TO DECREASE TO MAXIMA OF
20-35MM...WHILE CONVECTION REMAINS ACTIVE THROUGH THE CYCLE. TO
THE WEST...ENHANCED CONVECTION IN THE AMAZON WILL MEANDER WESTWARD
THROUGH THE CYCLE. INITIALLY...IT WILL EXTEND ACROSS
AMAZONAS/WESTERN PARA/RONDONIA IN BRASIL...WHILE IT WILL EXTEND
ACROSS PERU/SOUTHERN COLOMBIA/WESTERN BRASIL BY WEDNESDAY. THIS
WILL BE ENHANCED NOT ONLY BY PERSISTENT VENTILATION IN THE
NORTHEASTERN PERIPHERY OF THE BOLIVIAN HIGH/SUBTROPICAL
RIDGE...BUT BY A SOUTHERLY WIND SURGE ALONG THE EASTERN FLANKS OF
THE ANDES. THE SURGE...WILL EXTEND ACROSS CENTRAL/NORTHERN BOLIVIA
ON MONDAY EVENING...TO THEN DEVELOP A BARRIER JET INTO CENTRAL
PERU. THIS WILL SUSTAIN ACCUMULATIONS OF 50-100MM/DAY IN NORTHERN
BOLIVIA/SOUTHERN PERU ON MONDAY...40-80MM/DAY IN SOUTHERN AND
CENTRAL PERU ON TUESDAY...DECREASING TO 30-60MM/DAY BY WEDNESDAY.
AS MOISTURE POOL ARRIVES FROM THE EAST AND THE NORTHERLY LOW-LEVEL
JET STRENGTHENS ACROSS COLOMBIA NORTHERN PERU...EXPECTING A BURST
IN MOISTURE CONVERGENCE TO SUSTAIN AN INCREASE IN PRECIPITATION ON
THURSDAY. THIS WILL SUSTAIN MAXIMA OF 50-100 BY THURSDAY-EARLY
FRIDAY ACROSS EASTERN PERU/WESTERN BRAZIL...TO DECREASE AFTER.

IN ECUADOR...AN INCREASE IN THE WINDS ACROSS THE PANAMA ISTHMUS
WILL LEAD TO A NEW INCREASE IN PRECIPITATION ON WEDNESDAY...TO
SUSTAIN MAXIMA OF 30-60MM/DAY IN INTERIOR PORTIONS OF THE
COAST/WESTERN SLOPES. OTHERWISE...EXPECTING MAXIMA OF 15-20MM/DAY.

BALBINO...INMET (BRASIL)
POMIER...SENAMHI (BOLIVIA)
GALVEZ...WPC (USA)