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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1821Z Feb 07, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
121 PM EST WED FEB 07 2018

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

MODEL DISCUSSION (VALID FROM FEB 07 AT 0000 UTC): MODELS CONTINUE
SHOWING GOOD AGREEMENT THROUGH THE CYCLE. FORECAST CONFIDENCE IS
GOOD.

IN TROPICAL SOUTH AMERICA...THE SOUTH ATLANTIC CONVERGENCE ZONE IS
RAPIDLY LOSING ORGANIZATION WHILE THE UPPER FLOW PATTERN EVOLVES
AS WELL. THIS WILL ALLOW FOR THE DEVELOPMENT OF THE NORTHERLY
LOW-LEVEL JET TO THE EAST OF THE ANDES...AND SUSTAIN MOISTURE
TRANSPORT INTO ARGENTINA/PARAGUAY/URUGUAY. AT UPPER LEVELS...A
LONG WAVE TROUGH IS APPROACHING FROM THE PACIFIC AND PRODUCING
SIGNIFICANT HEIGHT FALLS ON WEDNESDAY...WHICH ARE EXCEEDING 150
GPM. AT LOW-LEVELS...A SURFACE FRONT IS MEANDERING NORTHEASTWARD
ACROSS EXTREME NORTHERN PATAGONIA. THIS WILL SUSTAIN SCATTERED
CONVECTION ON WEDNESDAY FROM CUYO INTO NORTHERN PATAGONIA/LA
PAMPA. YET...GIVEN THE LIMITATION IN MOISTURE AVAILABILITY
EXPECTING MAXIMA OF 05-10MM/DAY...WITH VERY ISOLATED HIGHER
AMOUNTS IN STRONGEST THUNDERSTORMS. MOISTURE CONTENT AND DYNAMICAL
FORCING INCREASE SIGNIFICANTLY DURING THURSDAY...WHICH WILL LEAD
TO AN INCREASE IN ACCUMULATIONS TO MAXIMA OF
20-35MM/DAY...STRETCHING FROM CUYO TO THE BUENOS AIRES PROVINCE.
NOTE THAT THERE IS A RISK FOR SEVERE CONVECTION. BY FRIDAY THE
FRONT WILL LOSE SPEED WHILE CROSSING THE RIO DE LA PLATA AND
EXTENDING INTO CORDOBA. EXPECTING 25-50MM/DAY WITH CONTINUED RISK
FOR SEVERE CONVECTION. BY SATURDAY...EXPECTING AN INCREASE IN
ACTIVITY IN NORTHERN ARGENTINA WHEN MAXIMA IS TO REACH
35-70MM/DAY. ALONG THE FRONT EXPECTING MAXIMA OF 20-35MM. BY
SUNDAY...MODELS ARE AGREEING ON A STRENGTHENING OF THE CHACO LOW
AND THE ASSOCIATED NORTHERLY AND SOUTHERLY LOW-LEVEL JETS. SINCE
PRECIPITABLE WATER WILL BE IN THE 65-70MM RANGE AND THE UPPER
DIVERGENT PATTERN WILL BE FAVORABLE...EXPECTING STRONG CONVECTION
TO DEVELOP...WITH THE RISK OF MCS FORMATION IN THE CHACO REGION.
TO THE EAST...NORTH OF THE FRONT...ENHANCED CONVECTIVE INSTABILITY
WILL FAVOR ACCUMULATIONS OF 25-50MM/DAY.

IN TROPICAL SOUTH AMERICA...THE WEAKENING OF THE SACZ WILL LEAD TO
A REORGANIZATION OF CONVECTION AND ASSOCIATED RAINFALL.
FURTHERMORE...THE UPPER FLOW PATTERN IS REORGANIZING AND THE UPPER
SUBTROPICAL RIDGE/BOLIVIAN HIGH IS FORECAST TO REFORM OVER MATO
GROSSO/EASTERN BOLIVIA BY FRIDAY. AS MOISTURE RETURNS WESTWARD
INTO THE PERUVIAN/BOLIVIAN EASTERN SLOPES...EXPECTING AN INCREASE
IN RAINFALL ACCUMULATIONS TO SUSTAIN MAXIMA OF 25-50MM/DAY ON
WEDNESDAY-THURSDAY...30-60MM/DAY ON THURSDAY-FRIDAY...DECREASING
TO 20-40MM/DAY BY FRIDAY-SATURDAY. THE ALTIPLANO/CENTRAL ANDEAN
CONVECTION WILL CONTINUE ENHANCED THROUGH THE CYCLE.
INITIALLY...EXPECTING MAXIMA OF 15-30MM/DAY FROM NORTHERN
ARGENTINA THROUGH SOUTHERN PERU ON WEDNESDAY. AMOUNTS WILL
DECREASE ON THURSDAY TO INCREASE AGAIN ON FRIDAY TO MAXIMA OF
15-25MM. DURING THE WEEKEND...UNDER THE INFLUENCE OF DEEP-LAYER
MOISTURE AND INSTABILITY...EXPECTING ACCUMULATIONS OF 15-30MM/DAY
ONCE AGAIN...WITH HEAVIEST PRECIPITATION RELOCATING FROM PERU ON
SATURDAY TO BOLIVIA/NORTHERN ARGENTINA/NORTHERN CHILE ON SUNDAY.

TO THE EAST...ACTIVE CONVECTION WILL PERSIST IN MOST OF BRASIL.
INITIALLY...LARGEST ACCUMULATION S ARE EXPECTED IN THE NORTHERN
COAST AND AMAZON DELTA...WHERE ENHANCED MOISTURE CONVERGENCE WILL
LEAD TO MAXIMA OF 40-80MM/DAY. ACCUMULATIONS WILL GRADUALLY
DECREASE AFTER THURSDAY. BY THE WEEKEND...MOST WIDESPREAD
CONVECTION WILL CLUSTER IN THE CENTRAL AMAZON BASIN WHERE
EXPECTING AMOUNTS OF 30-60MM/DAY.


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