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South American Forecast Discussion
 
(Latest Discussion - Issued 1628Z Oct 24, 2014)
 
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Abbreviations and acronyms used in this product


SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1228 PM EDT FRI OCT 24 2014

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

NOTE: THERE IS A RISK OF SEVERAL ROUNDS WITH SEVERE WEATHER
AFFECTING CENTRAL ARGENTINA. THE STRONGEST EVENT IS EXPECTED TO
DEVELOP TUESDAY INTO WEDNESDAY NEXT WEEK...WHEN SEVERE
THUNDERSTORMS WILL BE ACCOMPANIED BY HEAVY PRECIPITATION. MODE
DETAILS WILL BECOME CLEAR DURING THE WEEKEND.

MODEL DISCUSSION (VALID FROM OCTOBER 24 AT 00UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS CONTINUE IN EXCELLENT AGREEMENT REGARDING
FORECAST EVOLUTION. FORECAST CONFIDENCE IS HIGH.

NEXT SYSTEM TO AFFECT CHILE AND PORTIONS OF CENTRAL ARGENTINA IS A
LARGE NORTHERN STREAM TROUGH CURRENTLY STALLED IN THE EASTERN
PACIFIC. THIS TROUGH WILL START MOVING TOWARDS THE CONTINENT
DURING SATURDAY...CROSSING THE ANDES DURING SUNDAY INTO EARLY
MONDAY. MODELS CONTINUE FORECASTING A STRONG RIDGE BUILDING FROM
THE NORTHEAST AHEAD OF THE TROUGH...FROM THE TROPICAL EASTERN
PACIFIC INTO NORTHERN AND CENTRAL ARGENTINA. THIS WILL CAUSE THE
TROUGH TO BECOME NEGATIVELY TILTED AND DEVELOP STRONG UPPER
DIVERGENCE AHEAD OF MAIN AXIS. HEIGHT FALLS WILL ALSO BE
LARGE...EXCEEDING 100 GPM/DAY ACROSS CENTRAL ARGENTINA DURING
SUNDAY INTO MONDAY. ACROSS CHILE...THIS WILL ONLY CAUSE ISOLATED
SHOWERS AND SNOW SHOWERS IN THE CORDILLERA AS MOISTURE WILL BE
LIMITED. IN ARGENTINA HOWEVER...STRONG MOISTURE CONVERGENCE ALONG
A WEAKENING SURFACE FRONT WILL GE THE FOCUS FOR CYCLOGENESIS AND
FRONTOGENESIS. THIS WILL LEAD TO STRONG THUNDERSTORMS DEVELOPING
SUNDAY AFTERNOON INTO SUNDAY EVENING ACROSS LA PAMPA AND SOUTHERN
BUENOS AIRES PROVINCE. EXPECTING MAXIMA OF 40-80MM/DAY IN SEVERE
CONVECTION. THE FRONT WILL  ADVANCE INTO THE RIO DE LA PLATA
REGION BY MONDAY EVENING...TO THEN START RETREATING. THROUGH EARLY
TUESDAY...THUNDERSTORMS ARE TO PRODUCE SCATTERED MAXIMA OF
20-40MM/DAY. AMOUNTS ARE TO INCREASE ONCE AGAIN TO MAXIMA OF
40-80MM/DAY IN CONVECTION DEVELOPING DURING TUESDAY INTO EARLY
WEDNESDAY...AS NEW TROUGH ARRIVES AND FRONT REORGANIZES. LARGER
AMOUNTS ARE EXPECTED ON WEDNESDAY...YET FORECAST WILL BECOME MORE
CLEAR IN COMING DAYS.

NORTH ACROSS THE CONTINENT...A SHORT WAVE TROUGH IS PROGRESSING
EAST ACROSS BOLIVIA. THIS TROUGH IS INTERACTING WITH AN UNSTABLE
AIR MASS ESTABLISHED ACROSS SOUTHERN BOLIVIA AND NORTHWESTERN
ARGENTINA. THIS WAVE IS FORECASTED TO AMPLIFY ACROSS SOUTHERN
BRASIL...TO SUSTAIN AN ACTIVE PATTERN OF CONVECTION IN REGIONS OF
SOUTHEASTERN BRASIL DURING SEVERAL DAYS. ACTIVITY WILL START
INCREASING TODAY TO PRODUCE MAXIMA OF 20-45MM/DAY IN WESTERN MINAS
GERAIS/NORTHERN SAO PAULO INTO MATO GROSSO DO SUL/BOLIVIA/RONDONIA
THROUGH EARLY SATURDAY. DURING SATURDAY INTO EARLY SUNDAY LARGEST
ACROSS MINAS GERAIS/RIO/ESPIRITO SANTO WITH SCATTERED MAXIMA OF
25-50MM/DAY. AMOUNTS ARE TO INCREASE TO MAXIMA OF 30-60MM/DAY FROM
SUNDAY INTO TUESDAY IN HEAVY DIURNAL THUNDERSTORMS.

ELSEWHERE IN TROPICAL SOUTH AMERICA CONVECTION WILL CONCENTRATE IN
CENTRAL AMAZONIA...GRADUALLY FOCUSING TO THE WEST. AS VENTILATION
WILL REMAIN FAVORABLE AND CONVECTIVE INSTABILITY LARGE...EXPECTING
MAXIMA IN THE ORDER OF 20-45MM/DAY.

CAROCA...DMC (CHILE)
DURAN...SENAHMI (PERU)
GALVEZ...WPC (USA)