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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1643Z Nov 18, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1143 AM EST TUE NOV 18 2014

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

MODEL DISCUSSION (VALID FROM NOVEMBER 18 AT 00UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS AGREE VERY WELL ON FORECAST EVOLUTION.
FORECAST CONFIDENCE IS HIGH.

LONG WAVE UPPER TROUGH IS APPROACHING THE SOUTHERN CONE FROM THE
SOUTHWEST. THE TROUGH IS TO EXTEND ALONG THE NORTHERN
PATAGONIA-CONCEPCION BY TUESDAY EVENING...TO THE SOUTHWESTERN
BUENOS AIRES PROVINCE-MENDOZA BY WEDNESDAY EVENING. THE TROUGH
WILL BE REINFORCED BY ANOTHER RAPIDLY MOVING SHORT WAVE TROUGH.
THESE TWO ARE TO MERGE DURING LATE WEDNESDAY/EARLY THURSDAY TO
FORM A LARGER AND STRONGER UPPER TROUGH. THIS ONE WILL EXTEND FROM
VIEDMA INTO MENDOZA-COQUIMBO BY THURSDAY EVENING TO SLOWLY MOVE
INTO THE RIO DE LA PLATA-CORDOBA-TUCUMAN BY FRIDAY EVENING...TO
SANTA CATARINA-PARAGUAY BY SATURDAY EVENING. A NORTHERLY LOW-LEVEL
JET IS REESTABLISHING AT LOW-LEVELS AND IS STARTING TO INCREASE
MOISTURE AND CONVECTIVE INSTABILITY IN PORTIONS OF CENTRAL AND
NORTHERN ARGENTINA. AS FIRST TROUGH MOVES IN...EXPECTING
DEVELOPING COLD FRONT TO EXTEND ACROSS BAHIA BLANCA INTO SOUTHERN
MENDOZA BY TUESDAY EVENING...CROSS THE RIO DE LA PLATA REGION
DURING WEDNESDAY MORNING...TO EXTEND ACROSS SOUTHERN URUGUAY-SANTA
FE-SOUTHERN SANTIAGO DEL ESTERO BY WEDNESDAY EVENING. AS TROUGH
MOVES VERY SLOWLY WHILE REORGANIZING...FRONT WILL THEN MEANDER
ACROSS NORTHERN URUGUAY INTO THE CHACO ARGENTINO AS DEEP-LAYER
MOISTURE AND ENHANCE CONVERGENCE DEVELOPS ACROSS WESTERN PORTIONS
OF THE CHACO DURING THURSDAY. THE FRONT WILL START TO MOVE AGAIN
LATE ON FRIDAY TO EXTEND ACROSS RIO GRANDE DO SUL-SOUTHWESTERN
MATO GROSSO DO SUL INTO SOUTHERN BOLIVIA BY FRIDAY EVENING. BY
SATURDAY...FRONT WILL EXTEND INTO EASTERN SAO PAULO IN BRASIL. IN
TERMS OF ACCUMULATIONS...EXPECTING STORMS TO DEVELOP ON TUESDAY
AND LEAD TO SCATTERED MAXIMA OF 20-45MM/DAY BETWEEN CORDOBA/SAN
LUIS INTO LA PAMPA/MOST OF THE BUENOS AIRES PROVINCE...WITH THE
RISK OF SEVERE WEATHER. BY WEDNESDAY...FOCUS FOR STRONGEST
CONVECTION WILL MOVE INTO NORTHWESTERN ARGENTINA WHERE EXPECTING
MAXIMA OF 25-50MM/DAY. BY THURSDAY INTO EARLY FRIDAY...A
STRENGTHENING OF THE CHACO LOW AND INCREASE IN MOISTURE AND
CONVECTIVE INSTABILITY WILL ENTER IN PHASE WITH DIVERGENT TIER OF
REORGANIZING UPPER TROUGH. THIS WILL LEAD TO SCATTERED MAXIMA OF
35-70MM/DAY WITH THE RISK OF MCS FORMATION. BY FRIDAY INTO
SATURDAY...EXPECTING ANOTHER ROUND OF SEVERE WEATHER TO DEVELOP
FROM NORTHERN ARGENTINA/SOUTHERN PARAGUAY INTO SOUTHERN BRASIL
WITH MAXIMA OF 30-60MM/DAY. INLAND ACROSS THE LOWLANDS OF
BOLIVIA...THE DEVELOPMENT OF A SOUTHERLY JET WILL ENHANCE
LOW-LEVEL CONVERGENCE AND LEAD TO MAXIMA OF 40-80MM/DAY.

NORTHERN STREAM TROUGH IS CROSSING THE ANDES ACROSS NORTHERN
CHILE/NORTHERN ARGENTINA WHILE WEAKENING. MOISTURE IS LIMITED
HOWEVER...THIS THIS TROUGH WILL STRUGGLE ENHANCING ACTIVITY EARLY
IN THE CYCLE. HOWEVER...AS MOISTURE INCREASES IN THE CONVERGENT
SIDE OF LOW-LEVEL JET...EXPECTING SOME STORMS TO DEVELOP DURING
EARLY WEDNESDAY MORNING ACROSS CENTRAL/EASTERN PARAGUAY INTO MATO
GROSSO DO SUL. THESE WILL LEAD TO ACCUMULATIONS OF 25-50MM/DAY
ESPECIALLY DURING WEDNESDAY INTO EARLY THURSDAY. AMOUNTS ARE TO
DECREASE TO MAXIMA OF 15-30MM/DAY AS THE FOCUS FOR CONVECTION
MOVES INTO MATO GROSSO DO SUL/PARANA IN BRASIL DURING THURSDAY.

NORTH ACROSS THE CONTINENT...SUBTROPICAL HIGH IS WEAKENING AS
FOCUS FOR CONVECTION HAS MIGRATED NORTH. INITIALLY...STRONGEST
ACTIVITY IS EXPECTED ACROSS THE BRASILIAN NORDESTE WITH
ACCUMULATIONS OF 20-40MM/DAY. FOCUS FOR CONVECTION WILL GRADUALLY
MEANDER WESTWARD TO EXTEND ACROSS CENTRAL/EASTERN AMAZONIA INTO
GOIAS/TOCANTINS BY WEDNESDAY INTO FRIDAY. ACTIVITY WILL THEN START
MEANDERING INTO WESTERN AMAZONIA. OTHER REGION WITH ISOLATED
ACTIVATING CONVECTION WILL BE THE EASTERN SLOPES OF PERU AND
NORTHEASTERN SLOPES OF THE BOLIVIAN ANDES. NOCTURNAL/EARLY MORNING
CONVECTION WILL LEAD TO ISOLATED MAXIMA OF 15-30MM/DAY. ALONG THE
CENTRAL ANDES...SEASONAL CONVECTION WILL PRODUCE ISOLATED MAXIMA
IN THE ORDER OF 05-10MM/DAY.

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