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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1500Z Apr 09, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EDT THU APR 09 2015

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

MODEL DISCUSSION (VALID FROM APRIL 08 AT 0000 UTC): THE AGREEMENT
OF GLOBAL MODELS AND ENSEMBLE MEMBERS ON FORECAST EVOLUTION VARIES
LARGELY WITH LATITUDE. TO THE NORTH OF 30S THERE IS GOOD AGREEMENT
THROUGH 96-108 HRS WITH A GRADUAL DECREASE IN CONFIDENCE
AFTERWARDS. TO THE SOUTH OF 30S HOWEVER CONFIDENCE DECREASES
RAPIDLY AFTER 84-96 HRS.

LONG WAVE UPPER TROUGH IS ORGANIZING OVER THE EASTERN PACIFIC
ALONG 110W. MODELS ARE SHOWING THIS TROUGH ORGANIZING AND BECOMING
WELL DEFINED DURING FRIDAY-SATURDAY AS IT APPROACHES THE
CONTINENT. THE DIVERGENT TIER OF THE TROUGH WILL ENTER SOUTHERN
CHILE DURING SUNDAY WHEN IT IS TO ENHANCE PRECIPITATION. TROUGH
WILL THEN CROSS INTO ARGENTINA TO ENHANCE ACTIVITY ACROSS NORTHERN
PATAGONIA/CENTRAL ARGENTINA DURING MONDAY. IN TERMS OF
ACCUMULATIONS...EXPECTING AN INCREASE IN ACCUMULATIONS ON SATURDAY
INTO EARLY SUNDAY WITH MAXIMA OF 10-15MM/DAY EXPECTED BETWEEN
PUERTO MONTT AND THE MAGALLANES REGION IN CHILE. DURING SUNDAY
INTO EARLY MONDAY ACCUMULATIONS ARE TO PEAK BETWEEN ISLA CHILOE
AND CONCEPCION IN CHILE WITH MAXIMA OT 20-30MM/DAY. AMOUNTS ARE TO
RAPIDLY DECREASE DURING MONDAY INTO TUESDAY. IN
ARGENTINA...MOISTURE WILL BE STILL LIMITED AS THE UPPER TROUGH
ARRIVES. YET...THE ENVIRONMENT WILL BE MORE FAVORABLE FOR
ACCUMULATIONS COMPARED TO PREVIOUS WEEKS. EXPECTING MAXIMA OF
20-35MM/DAY IN THUNDERSTORMS THAT DEVELOP DURING MONDAY INTO
TUESDAY.

A FEATURE OF INTEREST IS SURFACE FRONT STALLING IN THE COAST OF
BAHIA. THE FRONT WILL MEANDER IN THIS REGION THROUGH THE WEEKEND
TO AND INTO EARLY NEXT WEEK...TO WEAKEN VERY SLOWLY. PRECIPITABLE
WATER IS VERY LARGE IN THE WARM SECTOR OF THE FRONT AS IT IS
APPROACHING 60MM. THIS WILL LEAD TO LOCALLY HEAVY RAINS IN COASTAL
AREAS IN INTERACTION WITH ENHANCED TRADE WIND CONVERGENCE.
EXPECTING MAXIMA IN THE ORDER OF 25-50MM/DAY THROUGH EARLY
FRIDAY...DECREASING GRADUALLY AFTERWARDS. YET...EXPECTING WET
PATTERN TO PERSIST INTO THE WEEKEND. NOTE THAT ISOLATED HIGHER
AMOUNTS ARE EXPECTED IN INTERACTION WITH OROGRAPHY.

ANOTHER SYSTEM OF INTEREST IS A SHORT WAVE UPPER TROUGH
APPROACHING FROM THE WEST INTO SOUTHERN PERU/BOLIVIA DURING
WEDNESDAY-EARLY FRIDAY. THIS TROUGH IS SETTING A DIVERGENT PATTERN
AHEAD OF THE MAIN AXIS. THIS WILL INITIALLY STIMULATE CONVECTION
DEVELOPMENT ACROSS THE ANDES OF CENTRAL/SOUTHERN PERU INTO WESTERN
BOLIVIA TO PRODUCE SCATTERED MAXIMA OF 20-40MM/DAY THROUGH EARLY
FRIDAY. UPPER TROUGH WILL ALSO INTERACT WITH MOISTURE POOL
BUILDING IN THE AMAZON BASIN. THIS WILL LEAD TO STRONG
THUNDERSTORMS AND THE RISK OF MCS FORMATION ACROSS THE
BOLIVIAN/PERUVIAN AMAZON BY LATE THURSDAY INTO EARLY FRIDAY. THEN
EXPECTING MAXIMA OF 30-60MM/DAY WITH ISOLATED LARGER AMOUNTS.
SIMILAR CONDITIONS ARE TO EXTEND INTO EARLY SATURDAY ACROSS
CENTRAL/NORTHERN PERU/EASTERN ECUADOR AND SOUTHERN
COLOMBIA/WESTERN BRASIL. AMOUNTS WILL START DECREASING AFTERWARDS.
TO THE SOUTHEAST...UPPER DIVERGENT PATTERN BETWEEN AFOREMENTIONED
UPPER TROUGH AND A GRADUALLY STRENGTHENING SUBTROPICAL RIDGE WILL
INTERACT WITH MOISTURE POOL BUILDING ACROSS PARAGUAY/SOUTHERN
BOLIVIA/NORTHWESTERN ARGENTINA. THIS WILL LEAD TO STRONG
THUNDERSTORMS DURING SATURDAY INTO EARLY SUNDAY ACROSS EXTREME
NORTHWESTERN ARGENTINA/SOUTHERN BOLIVIA TO PRODUCE ACCUMULATIONS
OF 20-45MM/DAY. CONVECTION WILL THEN MEANDER/REBUILD ACROSS
PARAGUAY WITH ISOLATED MAXIMA OF 25-50MM/DAY DURING SUNDAY INTO
EARLY MONDAY.

SCHNEIDER...INMET (BRASIL)
CALLE...UNALM (PERU)
CHARPENTIER...DMC (CHILE)
DAVISON/GALVEZ...WPC (USA)