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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1523Z Jan 23, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1023 AM EST FRI JAN 23 2015

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

MODEL DISCUSSION (VALID FROM JANUARY 23 AT 00UTC): GLOBAL MODELS
AGREE ON PATTERN EVOLUTION OVER THE NEXT FEW DAYS...WITH SHORT
WAVE PERTURBATIONS EXPECTED TO POPULATE THE SOUTHERN STREAM FLOW
ACROSS CHILE/ARGENTINA. IN THIS PATTERN...MODELS CONTINUE TO MAKE
CYCLE-TO-CYCLE CORRECTIONS...ADJUSTING THE TIMING/AMPLITUDE OF
THESE PERTURBATIONS. THIS ADDS TO THE UNCERTAINTY AND LACK OF
CONFIDENCE IN THE FORECAST BEYOND 84-96 HRS.

AT MID LEVELS...A WEST-TO-EAST RIDGE IS TO EXTEND FROM THE EASTERN
PACIFIC...ACROSS NORTHERN CHILE TO NORTHERN
ARGENTINA/PARAGUAY-SOUTHERN STATES OF BRASIL...WITH AXIS TO
GENERALLY ANCHOR ON A CLOSED HIGH OFF THE NORTH COAST OF CHILE.
ALTHOUGH RIDGE TENDS TO WEAKEN LATER IN THE CYCLE...IT WILL
SUSTAIN A CAP INVERSION ACROSS MID SECTIONS OF SOUTH AMERICA.
ISOLATED DIURNAL CONVECTION IS TO LIMIT TO THE LEE OF THE ANDES
OVER NORTHWEST ARGENTINA.

AS THE MID LEVEL RIDGE HOLDS TO THE NORTH...IT IS TO CONTINUE
STEERING SHORT WAVE VORTICES EASTWARD ACROSS THE SOUTHERN CONE. IN
THIS PATTERN...A STRONG SHORT WAVE TROUGH IS TO PULL ACROSS
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA THROUGH 30-36 HRS...AND
OFF THE COAST INTO THE WESTERN ATLANTIC BY 48 HRS. THROUGH 72 HRS
IT IS TO THEN MEANDER ACROSS 40W...NEARING 20W LATER IN THE CYCLE.
AT LOW LEVELS...A MEANDERING FRONT IS TO EXTEND ACROSS THE SOUTH
ATLANTIC TO THE BUENOS AIRES PROVINCE/LA PAMPA IN
ARGENTINA-CENTRAL CHILE TO THE EASTERN PACIFIC EARLY THIS CYCLE.
THIS BOUNDARY IS TO REMAIN NEARLY STATIONARY WHILE ANOTHER FRONT
APPROACHES FROM THE SOUTH. THE LATTER MOVES INTO PATAGONIA IN
ARGENTINA BY 36-42 HRS...THEN NORTH TO THE BUENOS AIRES PROVINCE
BY 72-84 HRS WHERE IT IS TO REINFORCE THE OLD FRONT TO THE NORTH.
OVER SOUTHERN CHILE THESE ARE TO ONLY TRIGGER ISOLATED CONVECTION
WITH LIGHT AMOUNTS. OVER LA PAMPA/BUENOS AIRES PROVINCE EXPECTING
ISOLATED TO SCATTERED CONVECTION LATER ON DAY 03 TO RESULT IN
ACCUMULATION OF 00-05MM...WITH LOCALLY HIGHER AMOUNTS POSSIBLE ON
DAY 04 WHEN MAXIMA IS TO PEAK AT 10-15MM.

THE NEXT MID LEVEL PERTURBATION REACHES THE BELLINGSHAUSEN
SEA/SOUTHERN CHILE BY 96 HRS. THIS IS TO THEN STREAM ACROSS THE
SOUTHERN CONE TO THE WESTERN ATLANTIC BY 120 HRS. ASSOCIATED FRONT
IS TO CONFINE TO SOUTHERN CHILE-PATAGONIA IN ARGENTINA...WHERE IT
IS TO SUSTAIN ISOLATED TO SCATTERED CONVECTION WITH ACCUMULATION
OF 00-05MM.

A 200 HPA HIGH OVER NORTHERN CHILE/SOUTHWEST BOLIVIA ANCHORS THE
SUBTROPICAL RIDGE OVER THE NORTHERN CHILE/NORTHWEST
ARGENTINA-BOLIVIA. CONSISTENT WITH PREVIOUS FORECASTS...THE HIGH
IS TO DRIFT WEST INTO THE EASTERN PACIFIC EARLY IN THE
CYCLE...WITH RIDGE OVER PERU/BOLIVIA TO WEAKEN TO A NARROW AND
ELONGATED AXIS AS THE CYCLE PROGRESSES. ACROSS SOUTHERN PERU TO
THE ALTIPLANO OF BOLIVIA EXPECTING SCATTERED CONVECTION TO SUSTAIN
RAINFALL AMOUNTS OF 10-15MM/DAY. ON THE CENTRAL/NORTHERN JUNGLE OF
PERU TO ECUADOR DAILY MAXIMA IS TO PEAK AT 15-20MM. AN UPPER
TROUGH LIES TO THE EAST OF THE SUBTROPICAL RIDGE...WITH AXIS
NORTHWEST ACROSS NORTHEAST BRASIL TO NORTHERN AMAZONAS/PARA. AS
THE RIDGE TO THE WEST WEAKENS...THE TROUGH IS TO ALSO WEAKEN
THROUGH 48-72 HRS. MEANWHILE...THIS IS TO ENHANCE CONVECTIVE
DEVELOPMENT ACROSS PARA-AMAZONAS-MATO GROSSO IN BRASIL...WHERE WE
EXPECT RAINFALL MAXIMA OF 20-45MM. BUT AS THE TROUGH WEAKENS THIS
DECREASES TO 15-25MM LATER ON DAY 03. MODELS THEN CARVE A SHORT
WAVE TROUGH ACROSS SOUTHERN BRASIL TO MATO GROSSO DO SUL BY 48-72
HRS...WHERE IT IS TO REMAIN THROUGH 108-120 HRS. AS THE TROUGH
AMPLIFIES...IT IS TO TRIGGER SCATTERED CONVECTION ACROSS SAO
PAULO/RIO DE JANEIRO-MINAS GERAIS...WITH MAXIMA IN THIS AREA
EXPECTED TO PEAK AT 20-35MM.

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