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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1723Z Jan 09, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1223 PM EST FRI JAN 09 2015

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

MODEL DISCUSSION (VALID FROM JANUARY 09 AT 00UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS ARE IN GOOD AGREEMENT ON FORECAST EVOLUTION.
ONLY SIGNIFICANT DIFFERENCES ARE ON THE EVOLUTION OF A SHORT WAVE
TROUGH APPROACHING SOUTHERN CHILE DURING TUESDAY...AS MODELS ARE
TENDING TO DELAY ITS ARRIVAL.

WET PATTERN ACROSS THE ALTIPLANO AND NORTHERN
ARGENTINA/URUGUAY/SOUTHERN BRASIL CONTINUES. MOIST AND UNSTABLE
AIRMASS IS TO REMAIN IN PLACE AIDED BY MOISTURE TRANSPORT AND
CONVERGENCE ASSOCIATED WITH AN ACTIVE LOW-LEVEL JET FROM THE
NORTH. AT UPPER LEVELS...THE SUBTROPICAL RIDGE IS DISPLACED TO THE
SOUTHEAST OF ITS CLIMATOLOGICAL POSITION AIDED BY PERSISTENT
POSITIVE SEA SURFACE TEMPERATURE ANOMALIES OFF THE COAST OF
SOUTHERN BRASIL AND THE RIO DE LA PLATA. TO THE WEST...A
PERSISTENT UPPER TROUGH PATTERN DOMINATES OVER THE EASTERN PACIFIC
OFF THE COAST OF PERU AND NORTHERN CHILE AIDED BY PERSISTENT
NEGATIVE SEA SURFACE TEMPERATURE ANOMALIES. THIS PATTERN IS
FAVORING THE A PERSISTENT SUBTROPICAL JET THAT HAS A CURVED
DIVERGENT ENTRANCE THAT ELONGATES FROM THE ALTIPLANO INTO PARTS OF
NORTHERN ARGENTINA. ALTHOUGH STRONGEST FORCING FROM TROUGHS
ARRIVING IN THE WESTERLIES WILL BE PRESENT IN PATAGONIA AND
REGIONS SOUTH...HEAVY THUNDERSTORMS ARE TO REGENERATE DAILY
BETWEEN LATITUDES 28S AND 35S. INITIALLY...EXPECTING MAXIMA OF
25-50MM/DAY FROM CORRIENTES/EASTERN URUGUAY INTO RIO GRANDE DO
SUL. BY SATURDAY INTO EARLY SUNDAY MAXIMA IS TO DECREASE TO
20-35MM/DAY TO STRETCH FROM SANTIAGO DEL ESTERO/CATAMARCA EAST
INTO CORRIENTES. BY SUNDAY INTO MONDAY...EXPECTING AN INCREASE IN
AMOUNTS TO MAXIMA OF 25-50MM/DAY ACROSS CENTRAL/NORTHERN
ARGENTINA. A MORE SIGNIFICANT EVENT IS EXPECTED ON MONDAY INTO
TUESDAY AS A TROUGH IN THE WESTERLIES UNDULATES A SURFACE FRONT
AND ENHANCES UPPER DIVERGENCE IN CENTRAL ARGENTINA. THIS WILL LEAD
TO SEVERE THUNDERSTORMS WITH ACCUMULATIONS IN THE ORDER OF
50-100MM/DAY. SIMILAR AMOUNTS ARE EXPECTED FROM TUESDAY INTO
WEDNESDAY IN A SLOW-MOVING SYSTEM.

IN NORTHERN SECTIONS OF THE CONTINENT AND AT UPPER LEVELS THE
CAVADO DO NORDESTE CONTINUES DOMINATING WHILE THE SUBTROPICAL HIGH
IS RELOCATING TO THE SOUTHEAST INTO SOUTHERN BRASIL. UNDER THIS
VERY UNUSUAL PATTERN...CONVECTION IN THE AMAZON BASIN IS OCCURRING
IN A MORE ISOLATED MANNER THAN USUAL. STRONGEST CONVECTION WILL
CLUSTER IN THE PERIPHERY OF THE RETROGRESSING CAVADO...IN REGIONS
WHERE INCREASED VENTILATION ENTERS IN PHASE WITH INSTABILITY
MAXIMA AT LOWER LEVELS. THESE REGIONS WILL EXTEND ACROSS CENTRAL
AMAZONIA FROM WESTERN PARA INTO SOUTHWESTERN AMAZONIA ACROSS
SOUTHEASTERN PERU/NORTHERN BOLIVIA/RONDONIA. EXPECTING DIURNAL
CONVECTION TO PRODUCE MAXIMA IN THE ORDER OF 20-35MM/DAY. ANOTHER
REGION WHERE ACTIVATION IS EXPECTED IS THE AMAZON DELTA...WHERE
EXPECTING ALSO SCATTERED MAXIMA IN THE ORDER OF 20-35MM/DAY WITH
ISOLATED HIGHER AMOUNTS. ACROSS THE ANDES...ACTIVE PATTERN WILL
CONTINUE DOMINATING OVER THE ALTIPLANO THROUGH MID-CYCLE WITH
WIDESPREAD DIURNAL CONVECTION PRODUCING ISOLATED MAXIMA OF
15-20MM/DAY. THIS LOCALLY HIGH RAINFALL AMOUNTS ARE TO DISPLACE
NORTHWESTWARD INTO THE CENTRAL ANDES OF PERU INTO MONDAY AND
TUESDAY DUE TO A DECREASE IN VENTILATION OVER THE ALTIPLANO...IN
RESPONSE TO A SOUTHEASTWARD MIGRATION OF THE SUBTROPICAL HIGH AND
THE SUBTROPICAL JET TO THE SOUTH.

ARREAGA...INAMHI (ECUADOR)
DURAN...SENAHMI (PERU)
GALVEZ...WPC (USA)