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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1549Z Sep 03, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1149 AM EDT WED SEP 03 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 03 AT 00UTC): MINOR
CORRECTIONS TO PREVIOUS FORECAST PACKAGE...AS GLOBAL MODELS
CONTINUE TO FORECAST A SIMILAR EVOLUTION ACROSS THE SOUTH AMERICAN
DOMAIN DURING THE NEXT FEW DAYS. CONFIDENCE IN THE FORECAST IS
HIGH. THE GLOBAL MODELS INITIALIZE A HIGHLY AMPLIFIED LONG WAVE
PATTERN ACROSS THE SOUTH AMERICAN DOMAIN...WITH A NORTH-TO-SOUTH
RIDGE OVER THE WESTERN ATLANTIC SEPARATING TWO TROUGHS. ONE LIES
ACROSS THE FAR EASTERN PACIFIC AND THE OTHER OVER THE
CENTRAL-EASTERN ATLANTIC.

THE LATTER EXTENDS BETWEEN 45W-00W AND TO THE SOUTH OF 15S. THE
TROUGH IS FORECAST TO MEANDER TO THE EAST-SOUTHEAST AS THE CYCLE
PROGRESSES. THROUGH 72 HRS THE TROUGH IS TO SHEAR A SHORT WAVE
TROUGH ON THE NORTHERN STREAM...WHILE MAIN BODY TO THE SOUTH IS TO
QUICKLY PULL ACROSS THE SOUTH ATLANTIC. THE NORTHERN STREAM VORTEX
IS TO MEANDER ACROSS 20W/25W AND TO THE SOUTH OF 15S BY 96 HRS...
NEARING 10W BY 120 HRS. AT LOW LEVELS...A BROAD RIDGE DOMINATES
THE WESTERN ATLANTIC. AN ELONGATED FRONT LIES TO THE EAST AND
NORTH OF THIS AXIS...EXTENDING WEST ALONG 20S 20W...SOUTHEAST
BRASIL-PARAGUAY TO NORTHERN ARGENTINA. THE TRAILING END OF THE
FRONT...AS IT MEANDERS OVER THE CONTINENT...IS TO FRONTOLIZE
THROUGH 36 HRS. THE  REMNANTS OVER THE ATLANTIC...MEANWHILE...MOVE
NORTH ACROSS ESPIRITO SANTO IN BRASIL EARLY IN THE CYCLE...INTO
EASTERN BAHIA BY 48-72 HRS...AND PERNAMBUCO/RIO GRANDE DO NORTE
LATER IN THE CYCLE. IN A NORTHERLY LOW LEVEL FLOW...MOISTURE IS TO
INITIALLY CONVERGE ACROSS NORTHERN ARGENTINA-PARAGUAY...WHERE WE
EXPECT ISOLATED TO SCATTERED CONVECTION TO RESULT IN RAINFALL
AMOUNTS OF 05-10MM. HIGHER AMOUNTS ARE EXPECTED ACROSS SAO
PAULO-RIO DE JANEIRO/SOUTHERN MINAS GERAIS...WHERE THE FRONT WILL
FAVOR RAINFALL AMOUNTS OF 10-15MM. BY 36-60 HRS SCATTERED
CONVECTION ACROSS ESPIRITO SANTO/EASTERN BAHIA WILL FAVOR MAXIMA
OF 10-15MM. LATER IN THE CYCLE...AS THE EASTERLY TRADES SURGE
ACROSS NORTHEAST BRASIL...THIS INCREASES TO 15-20MM/DAY.

THE TROUGH OVER THE EASTERN PACIFIC...MEANWHILE...IS TO BOUND
BETWEEN 95W-60W AND TO THE SOUTH OF 15S...WHILE CENTERING ON A
DEEP LOW NEAR 41S 85W. THIS TROUGH IS TO PRESS AGAINST MID/UPPER
LEVEL 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 48 HRS THE RIDGE WEAKENS ENOUGH AND THE
TROUGH IS TO THEN ENTER CENTRAL CHILE...QUICKLY SPILLING ACROSS
THE CENTRAL ANDES INTO ARGENTINA BY 72 HRS. THIS IS TO THEN
TRIGGER HEIGHT FALLS OF 75-125GPM. AS IT MOVES EAST OF
PATAGONIA/BUENOS AIRES PROVINCE BY 84-96 HRS...UNDER COUPLED JETS
ALOFT...THE TROUGH/LOW IS FORECAST TO RAPIDLY 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...WITH
POLAR FRONT PUSHING EAST ACROSS CHILE TO CENTRAL ARGENTINA EARLY
IN THE CYCLE. THE FRONT IS TO THEN REMAIN OVER CENTRAL ARGENTINA
WHILE THE OCCLUDED LOW/FRONT OVER THE EASTERN PACIFIC WEAKENS. A
NEW LOW FORMS ALONG THE MEANDERING FRONT OVER NORTHERN
PATAGONIA/LA PAMPA BY 66-72 HRS. THROUGH 96 HRS THIS IS TO DEEPEN
FROM A 1008 TO A 990 HPA LOW...WITH SOME OF THE MODELS SUGGESTING
POSSIBLE METEOROLOGICAL BOMB FORMING DURING THIS PERIOD. 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 72 HRS...MOVING NORTH TO
RIO GRANDE DO SUL-NORTHERN PROVINCES IN ARGENTINA BY 96-108 HRS.
AS THE FRONT MOVES INTO CENTRAL ARGENTINA EARLY IN THE CYCLE...IT
IS TO SUSTAIN SCATTERED CONVECTION WITH ACCUMULATION OF 15-250MM.
AS IT SURGES TOWARDS NORTHERN ARGENTINA/URUGUAY BY 60-72 HRS THIS
INCREASES TO 30-60MM IN POTENTIALLY SEVERE CONVECTION. BY 96-120
HRS FOCUS OF THE CONVECTION IS GOING TO BE SOUTHERN
BRASIL-PARAGUAY-CORRIENTES/MISIONES IN ARGENTINA...WHERE
MEANDERING FRONT WILL FAVOR MAXIMA OF 20-45MM. OTHER ACTIVITY TO
THE WEST IS EXPECTED ACROSS CHACO PARAGUAYO TO SOUTHERN
BOLIVIA...WITH ACCUMULATION OF 10-15MM.

NORTH OVER THE CONTINENT...AT 200 HPA...A RIDGE IS TO SLOWLY BUILD
WEST ACROSS THE TROPICAL ATLANTIC TO NORTHERN SOUTH AMERICA.
THROUGH 72 HRS THE RIDGE WILL ESTABLISH A FOOTHOLD ACROSS
CENTRAL/WESTERN BRASIL...WHILE ANCHORING ON A CLOSED HIGH OVER
NORTHERN PARA/AMAZONAS. AS THE RIDGE BUILDS...THIS WILL SUSTAIN
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. EARLY IN THE
CYCLE EXPECTING MAXIMA IN THIS AREA TO PEAK AT 15-20MM. THROUGH 72
HRS THIS DECREASES TO 05-10MM IN ISOLATED TO SCATTERED
CONVECTION...WITH MOST ACTIVE OVER CENTRAL/NORTHERN JUNGLE OF
PERU. 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.

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