Skip Navigation Links weather.gov 
NOAA logo - Click to go to the NOAA homepage National Weather Service   NWS logo - Click to go to the NWS homepage
The Weather Prediction Center
 
South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1626Z Sep 25, 2014)
 
Version Selection
Versions back from latest:  0   1   2   3   4   5   6   7   8   9   10   
 
Abbreviations and acronyms used in this product


SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1226 PM EDT THU SEP 25 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 25 AT 00UTC): THE GLOBAL
MODELS ARE IN BETTER AGREEMENT...SHOWING SIMILAR PATTERN EVOLUTION
THROUGH 96-108 HRS. LATER IN THE CYCLE THEY DIVERGE ON INTENSITY
OF SHORT WAVE TROUGH ON THE NORTHERN STREAM ENTERING CENTRAL
CHILE. IN THIS ARE BOTH EUROPEAN MODELS FAVOR A DEEPER/STRONGER
PERTURBATION THAN WHAT THE GFS SUGGESTS. ALTHOUGH THE GFS HAS BEEN
TRENDING TOWARDS A DEEPER PERTURBATION...HIGH VARIABILITY AMONG
THE ENSEMBLE MEMBERS SUGGEST POSSIBILITY OF FURTHER ADJUSTMENTS.

SOUTH OVER THE CONTINENT...AT 500 HPA...A TROUGH EXTENDS ACROSS
THE SOUTHERN CONE. UNDER INFLUENCE OF A BUILDING RIDGE TO THE
WEST...THE TROUGH RELOCATES TO THE SOUTHWEST ATLANTIC/WEDDELL SEA
EARLY IN THE CYCLE. THROUGH 96-108 HRS THIS IS TO EVOLVE INTO A
BROAD/HIGH AMPLITUDE TROUGH ACROSS THE SOUTH ATLANTIC...WITH AXIS
TO ENVELOP AREA TO THE SOUTH OF 30S. A SIMILAR PATTERN IS EXPECTED
AT LOW LEVELS OF THE ATMOSPHERE...WITH BROAD TROUGH FORECAST TO
DOMINATE THE SOUTHERN STREAM FLOW. OVER THE NEXT TWO DAYS...AS THE
TROUGH CONFINES TO THE WEDDELL SEA/SOUTHWEST ATLANTIC...CLIPPER
LOWS/ PROGRESSIVE FRONTS ARE TO LIFT NORTH ACROSS THE
BELLINGSHAUSEN SEA/DRAKE PASSAGE TO TIERRA DEL FUEGO/SOUTHERN
CHILE-PATAGONIA IN ARGENTINA. THE INFLOW OF COLD ANTARCTIC AIR
ACROSS THE DRAKE PASSAGE IS LIKELY TO TRIGGER SNOW SHOWERS ACROSS
THE SOUTHERN ANDES OF CHILE AND PORTIONS OF TIERRA DEL FUEGO. IN
THIS AREA LIQUID WATER EQUIVALENT IS TO PEAK AT 05-10MM/DAY...WITH
MODERATE SNOWFALL AMOUNTS LIKELY ON DAY 02.

NORTH OVER THE CONTINENT...A BROAD CELL OF THE SUBTROPICAL RIDGE
IS TO EXTEND ACROSS CENTRAL BRASIL TO NORTHERN BOLIVIA. THE POLAR
TROUGH TO THE SOUTH OVER CHILE/ARGENTINA IS TO PRESS AGAINST THIS
RIDGE. IN A TIGHT GRADIENT...A SUBTROPICAL JET SEPARATES THE
TROUGH TO THE SOUTH FROM THE RIDGE TO THE NORTH. THE
ANTICYCLONICALLY CURVED JET IS TO EXTEND ACROSS NORTHERN
CHILE/ARGENTINA-SOUTHERN STATES OF BRASIL TO THE SOUTH ATLANTIC.
AS THE FLOW IS TO REMAIN AT A PERPENDICULAR ANGLE TO THE CENTRAL
ANDES...THIS IS TO FAVOR GENERATION OF LEESIDE PERTURBATIONS
ACROSS ARGENTINA. AT LOW LEVELS...A MEANDERING FRONT IS TO EXTEND
ACROSS THE SOUTH ATLANTIC TO SOUTHERN BRASIL-PARAGUAY/NORTHERN
ARGENTINA. THE BAROCLINIC BOUNDARY IS TO PERSIST OVER THE NEXT FEW
DAY...BLOCKING MOISTURE TRANSPORT TO THE MID SECTIONS OF SOUTH
AMERICA. IN A PERSISTENT NORTHERLY FLOW ACROSS BOLIVIA-MATO GROSSO
IN BRASIL...PRECIPITABLE WATER CONTENT VALUES ALONG THE MEANDERING
FRONT ARE TO PEAK BETWEEN 45-55MM OVER THE NEXT FEW DAYS. THIS
WILL COMBINE WITH FAVORABLE UPPER DYNAMICS AND INFLOW OF MID LEVEL
SHORT WAVE VORTICES TO SUSTAIN GENERATION OF MESO SCALE CONVECTIVE
SYSTEMS ACROSS PARAGUAY-SOUTHERN/SOUTHEAST BRASIL OVER THE NEXT
FEW DAYS. IN THIS AREA...THE DAILY MAXIMA PEAKS AT 30-60MM THROUGH
36 HRS...AND 25-50MM/DAY THEREAFTER THROUGH 108 HRS. A SLIGHT
DECREASE IS EXPECTED LATER IN THE CYCLE...WHEN MAXIMA IS TO PEAK
AT 20-40MM IN SCATTERED CONVECTION.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO THEN MIGRATE
ACROSS THE EASTERN PACIFIC...MOVING ACROSS 80W TO 20S BY 72-96
HRS...AND TO MEANDER ALONG THE CENTRAL/NORTHERN COAST OF CHILE BY
120-132 HRS. ASSOCIATED FRONT MEANDERS EAST ACROSS THE SOUTH
PACIFIC. THROUGH 108-120 HRS THE FRONT AND ASSOCIATED FRONTAL LOW
SPILLS ACROSS THE CENTRAL ANDES OF CHILE TO CUYO IN ARGENTINA.
OVER CENTRAL CHILE THIS IS TO FAVOR LIGHT CONVECTION...WHILE OVER
CENTRAL ARGENTINA EXPECTING MAXIMA OF 05-10MM.

AT 200 HPA...NORTHERN SOUTH AMERICA WILL BE UNDER INFLUENCE OF THE
SUBTROPICAL RIDGE PATTERN. THIS IS TO DOMINATE AREA TO THE NORTH
OF 30S DURING THE NEXT FEW DAYS. AS THE RIDGE HOLDS OVER THE
CONTINENT...IT IS TO STEER A SHORT WAVE TROUGH ACROSS EQUATORIAL
SOUTH AMERICA. UPPER VORTEX ENTERS THE GUIANAS/AMAPA IN BRASIL BY
24-36 HRS...AND THROUGH 72-84 HRS IT MOVES TO RORAIMA IN NORTHERN
BRASIL. THIS IS TO THEN ENHANCE DIURNAL CONVECTION BETWEEN
NORTHERN AMAZONAS IN BRASIL TO AMAPA/ILHA DE MARAJO...TO FAVOR
RAINFALL AMOUNTS OF 10-15MM IN SCATTERED CONVECTION. DIURNAL
CONVECTION TO THE WEST IS TO CLUSTER ALONG THE SIERRA/JUNGLE OF
PERU AND EASTERN ECUADOR...WITH ACCUMULATION OF 05-10MM/DAY IN
SCATTERED CONVECTION. THROUGH 48 HRS THIS IS TO INCREASE TO
10-15MM/DAY.

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