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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1541Z Sep 26, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1141 AM EDT FRI SEP 26 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 26 AT 00UTC): GOOD
AGREEMENT AMONG GLOBAL MODEL GUIDANCE THROUGH 108-120 HRS.
CONFIDENCE IN THE FORECAST IS HIGH...AS THE GLOBAL ENSEMBLES
PROVIDE GOOD SUPPORT TO THE DETERMINISTIC SOLUTION.

AT 500 HPA...A RIDGE ON THE SOUTHERN STREAM IS TO EXTEND ALONG
90W/95W AND TO THE SOUTH OF 45S OVER THE NEXT FEW DAYS. DOWNSTREAM
FROM THIS AXIS...A BROAD TROUGH EXTENDS BETWEEN 80W-20W AND TO THE
SOUTH OF 35S...WITH AXIS ANCHORING ON A DEEP LOW JUST EAST OF THE
ANTARCTIC PENINSULA. AS THE RIDGE MEANDERS TO THE WEST...THIS WILL
STEER SHORT WAVE VORTICES NORTHWARD ACROSS THE ANTARCTIC
PENINSULA/ DRAKE PASSAGE TO THE SOUTHERN CONE OF SOUTH AMERICA.
THESE ARE TO THEN FEED INTO THE TROUGH...SUSTAINING ITS GRADUAL
INTENSIFICATION AS IT BUILDS EAST ACROSS THE SOUTH ATLANTIC. AT
LOW LEVELS...BROAD TROUGH IS TO DOMINATE FLOW ACROSS THE ATLANTIC
TO THE SOUTH OF 40S...WHILE ANCHORING ON A DEEP/OCCLUDED LOW OVER
THE WEDDELL SEA. PROGRESSIVE FRONTS ARE TO REVOLVE AROUND THIS
AXIS...TO STREAM ACROSS SOUTHERN CHILE/TIERRA DEL FUEGO TO
PATAGONIA IN ARGENTINA. IN A COLD ADVECTIVE PATTERN...THIS IS TO
THEN TRIGGER SNOW SHOWERS ACROSS THE SOUTHERN ANDES AND PORTIONS
OF TIERRA DEL FUEGO. IN THIS AREA LIQUID WATER EQUIVALENT IS TO
PEAK AT 05-10MM/DAY...WITH MODERATE SNOWFALL AMOUNTS EXPECTED ON
DAY 01.

A SHORT WAVE TROUGH IS TO THEN PULL ACROSS THE EASTERN
PACIFIC...WITH AXIS TO MOVE ACROSS 100W AND SOUTH OF 40S BY 48
HRS. THIS IS TO THEN ENTER SOUTHERN CHILE BY 84-96 HRS...TO PULL
ACROSS ARGENTINA THROUGH 120 HRS. AT LOW LEVELS IT IS TO SUSTAIN A
FRONTAL SYSTEM ACROSS SOUTHERN CHILE BY 96 HRS...WEAKENING OVER
PATAGONIA THROUGH 120 HRS. THIS IS TO TRIGGER SCATTERED CONVECTION
WITH ACCUMULATION OF 05-10MM.

ON THE NORTHERN STREAM...A TIGHT BELT OF MID LATITUDE WESTERLIES
IS TO DOMINATE FLOW ACROSS THE EASTERN PACIFIC-MID SECTIONS OF
SOUTH AMERICA. SHORT WAVE PERTURBATIONS ARE TO EMBED IN THIS
FLOW...WITH A STRONG VORTEX TO ENTER CENTRAL CHILE EARLY IN THE
CYCLE...WHILE ANOTHER IS TO MAKE LANDFALL BY 96-108 HRS. THESE ARE
TO THEN STREAM ACROSS NORTHERN ARGENTINA/PARAGUAY-SOUTHERN STATES
OF BRASIL TO THE WESTERN ATLANTIC. THIS IS TO ALSO FOCUS A
SUBTROPICAL JET ACROSS CENTRAL/NORTHERN CHILE-NORTHERN
ARGENTINA/SOUTHERN BRASIL. AS THE FLOW IS TO REMAIN AT A
PERPENDICULAR ANGLE TO THE ANDES...THIS IS TO THEN FAVOR
GENERATION OF LEESIDE PERTURBATIONS ACROSS NORTHERN
ARGENTINA-PARAGUAY. AT LOW LEVELS...A MEANDERING FRONT EXTENDS
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 25-50MM.

THE SUBTROPICAL RIDGE...AT 200 HPA...IS TO DOMINATE FLOW OVER THE
CONTINENT TO THE NORTH OF 30S. THE RIDGE ALOFT...AS IT HOLDS OVER
THE CONTINENT...IS TO STEER A SHORT WAVE TROUGH ACROSS EQUATORIAL
SOUTH AMERICA. UPPER VORTEX ENTERS THE GUIANAS/AMAPA IN BRASIL
EARLY IN THE CYCLE...AND THROUGH 48-60 HRS IT MOVES TO RORAIMA IN
NORTHERN BRASIL. LATER IN THE CYCLE IT WEAKENS AS IT PULLS ACROSS
AMAZONAS IN BRASIL TO THE PERUVIAN JUNGLE. THIS VORTEX IS TO
ENHANCE DIURNAL CONVECTION BETWEEN NORTHERN AMAZONAS IN BRASIL TO
AMAPA/ILHA DE MARAJO...TO FAVOR RAINFALL AMOUNTS OF 10-15MM IN
SCATTERED CONVECTION. THIS STARTS AROUND 72/84 HRS AND IT IS TO
THEN PERSIST THROUGH 132 HRS. DIURNAL CONVECTION TO THE WEST IS TO
CLUSTER ALONG THE SIERRA/JUNGLE OF PERU AND EASTERN ECUADOR...WITH
ACCUMULATION OF 10-15MM/DAY.

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