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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1634Z Sep 04, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1234 PM EDT THU SEP 04 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 04 AT 00UTC): CONTINUITY
WITH PREVIOUS FORECAST IS GOOD THROUGH 84-96 HRS...WITH MODELS
MAKING PATTERN CORRECTIONS DURING THE MEDIUM RANGE. IN THIS PERIOD
THE ENSEMBLE MEMBERS FAIL TO REACH A CONSENSUS ON HOW THE PATTERN
IS GOING TO EVOLVE...SO EXPECTING FURTHER CORRECTIONS IN THE NEXT
FEW RUNS.

OVER THE EASTERN PACIFIC...AT MID/UPPER LEVELS...A TROUGH EXTENDS
BETWEEN 90W-65W TO 15S. THIS IS PRESSING AGAINST A RIDGE TO THE
EAST...AND AS A RESULT IT IS TO SLOWLY MOVE EAST WHILE SHEARING
SHORT WAVE ENERGY ACROSS THE CENTRAL ANDES OF CHILE TO ARGENTINA.
BY 24 HRS THE RIDGE WEAKENS ENOUGH AND THE TROUGH IS TO ENTER
CENTRAL CHILE...QUICKLY SPILLING ACROSS THE CENTRAL ANDES INTO
ARGENTINA BY 48 HRS. THIS IS TO THEN SUSTAIN HEIGHT FALLS OF
75-150GPM AS IT PULLS ACROSS THE CENTRAL PROVINCES IN ARGENTINA.
AS IT MOVES EAST OF PATAGONIA/BUENOS AIRES PROVINCE BY 60-72
HRS...UNDER FAVORABLE JET DYNAMICS...THE TROUGH/LOW IS FORECAST
DEEPEN/INTENSIFY. IT IS TO THEN MEANDER TO THE EAST-SOUTHEAST. AT
LOW LEVELS...IT IS TO SUSTAIN A BROAD OCCLUDED TROUGH OVER THE
EASTERN PACIFIC AND A POLAR FRONT ACROSS CENTRAL PROVINCES IN
ARGENTINA. INFLOW OF SHORT WAVE ENERGY IS TO THEN SUSTAIN
CYCLOGENESIS ALONG THIS BOUNDARY BY 48 HRS...WITH A LOW TO FORM
OVER NORTHERN PATAGONIA. AS IT MOVES TO THE WESTERN ATLANTIC THE
LOW IS TO RAPIDLY OCCLUDE...WITH MODELS SUGGESTING POSSIBLE
METEOROLOGICAL BOMB AS THE CYCLONE DEEPENS FROM A 1010 HPA LOW BY
48 HRS TO A 986 HPA LOW BY 72 HRS. AS THE LOW DEEPENS AND A POLAR
RIDGE BUILDS ACROSS CENTRAL ARGENTINA...THE SURFACE FRONT IS TO
SURGE ACROSS BUENOS AIRES PROVINCE-CORDOBA/MENDOZA IN ARGENTINA BY
48 HRS...MOVING NORTH TO RIO GRANDE DO SUL-NORTHERN PROVINCES IN
ARGENTINA BY 72-84 HRS. BOUNDARY IS TO THEN FRONTOLIZE LATER IN
THE CYCLE. AS THE FRONT MOVES MEANDERS OVER CENTRAL ARGENTINA
EARLY IN THE CYCLE...IT IS TO SUSTAIN SCATTERED CONVECTION WITH
ACCUMULATION OF 10-15MM. BUT IN A MOIST NORTHERLY FLOW...EXPECTING
MAXIMA OF 30-60MM AND POTENTIALLY SEVERE CONVECTION ACROSS
CORRIENTES-MESOPOTAMIA VALLEY/BUENOS AIRES PROVINCE AND URUGUAY
OVER THE NEXT TWO DAYS. FURTHERMORE...AS THE FRONT PUSHES NORTH
ACROSS SOUTHERN BRASIL TO NORTHERN ARGENTINA AND INTERACTS WITH EL
CHACO LOW...CONDITIONS WILL BECOME FAVORABLE FOR AN MCC TO DEVELOP
LATER ON DAY 03. AS THE FRONT WEAKENS ON DAYS 04-05...MAXIMA ALONG
THE WEAKENING FRONT WILL GRADUALLY DECREASE TO 05-10MM.

A BROAD MID/UPPER LEVEL TROUGH EXTENDS ACROSS THE CENTRAL-EASTERN
SOUTH ATLANTIC. THE TROUGH IS FORECAST TO MEANDER TO THE
EAST-SOUTHEAST AS THE CYCLE PROGRESSES. AS IT PULLS AWAY...IT IS
TO SHEAR A SHORT WAVE TROUGH ON THE NORTHERN STREAM LATER ON DAY
02. THE NORTHERN STREAM VORTEX IS TO THEN MEANDER ACROSS 20W/25W
AND TO THE SOUTH OF 15S BY 72 HRS...NEARING 00W BY 120 HRS. AT LOW
LEVELS...A BROAD RIDGE DOMINATES THE WESTERN ATLANTIC...SUSTAINING
A BRISK SOUTHEASTERLY FLOW ACROSS THE NORTHEAST STATES OF BRASIL.
AN ELONGATED FRONT LIES TO THE EAST AND NORTH OF THIS AXIS. EARLY
IN THE CYCLE THE FRONT IS TO EXTEND TO ESPIRITO SANTO IN
BRASIL...WHERE IT IS TO FAVOR RAINFALL AMOUNTS OF 10-15MM. THROUGH
48-60 HRS IT MOVES NORTH ACROSS BAHIA TO PERNAMBUCO/RIO GRANDE DO
NORTE. AS IT PUSHES NORTH...DAILY MAXIMA INCREASES TO 15-20MM.

NORTH OVER THE CONTINENT...AT 200 HPA...MODELS CONTINUE TO
FORECAST GRADUAL INTENSIFICATION OF THE SUBTROPICAL RIDGE PATTERN
ACROSS BRASIL/PERU. THROUGH 48 HRS THE RIDGE IS TO BECOME WELL
ENTRENCHED OVER CENTRAL/WESTERN BRASIL...AS IT IS TO CENTER ON A
CLOSED HIGH OVER NORTHERN PARA/AMAZONAS. AS THE RIDGE BUILDS
SOUTH...THIS WILL THEN INDUCE THE NORTHWARD AMPLIFICATION OF A
TROUGH ACROSS NORTHEAST BRASIL. EVOLVING UPPER LEVEL PATTERN WILL
SUSTAIN A GRADUAL DRYING TREND OVER NORTHWEST BRASIL-SOUTHERN
COLOMBIA AND ECUADOR. BY 24-72 HRS CONVECTION IS TO LIMIT TO THE
JUNGLE OF PERU WITH ACCUMULATION OF 05-10MM/DAY. AS THE TROUGH
DEEPENS ACROSS NORTHEAST BRASIL...AND COOL AIR ADVECTS ACROSS
MINAS GERAIS/BHAI TO TOCANTINS/GOIAS...IT IS TO ENHANCE DIURNAL
CONVECTIVE DEVELOPMENT TO RESULT IN RAINFALL AMOUNTS OF 05-10MM.
THIS INCREASES TO 15-20MM BY 72-96 HRS.

JALFIN...SMN (ARGENTINA)
CAROCA...DMC (CHILE)
DAVISON...WPC (USA)