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South American Forecast Discussion
 
(Latest Discussion - Issued 1531Z Sep 29, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1131 AM EDT MON SEP 29 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 29 AT 00UTC): THE GLOBAL
MODELS AGREE ON PATTERN EVOLUTION THROUGH 132-144 HRS. THIS IS
WELL SUPPORTED BY THE CONSENSUS OF THE GLOBAL ENSEMBLES.
CONFIDENCE N THE FORECAST IS HIGH.

AT LOW LEVELS...MODELS INITIALIZED AN ELONGATED FRONT WITH AXIS
WEST ACROSS THE SOUTH ATLANTIC TO MID SECTIONS OF SOUTH
AMERICA...WITH BOUNDARY TRAILING ACROSS SOUTHERN STATES OF BRASIL
TO NORTHERN PROVINCES IN ARGENTINA. SUCCESSIVE SHORT WAVE
PERTURBATIONS CONTINUE TO INTERACT WITH THIS BOUNDARY AS IT
MEANDERS OVER THE CONTINENT...PROVIDING DYNAMICAL SUPPORT TO
ORGANIZED DEEP CONVECTION. IN THIS PATTERN...A MID LEVEL SHORT
WAVE TROUGH ENTERS NORTHERN CHILE EARLY IN THE CYCLE...AND THROUGH
48 HRS IT IS TO QUICKLY PULL ACROSS PARAGUAY-SOUTHERN STATES OF
BRASIL. AT 250 HPA...AN ANTICYCLONICALLY CURVED SUBTROPICAL JET
MAXIMA EXTENDS ACROSS NORTHERN CHILE/ARGENTINA-SOUTHERN STATES OF
BRASIL. THROUGH 60 HRS THE JET IS TO MIGRATE EAST INTO THE SOUTH
ATLANTIC. AS IT PULLS AWAY...THE SURFACE FRONT IS TO LOSE ITS
UPPER LEVEL SUPPORT. ALTHOUGH IT FRONTOLIZES OVER
PARAGUAY/SOUTHERN BRASIL...TRAILING END OVER THE ATLANTIC IS TO
PERSIST. BUILDING RIDGE TO THE SOUTH THEN DISPLACES THIS BOUNDARY
NORTH ACROSS SAO PAULO/RIO DE JANEIRO BY 72-84 HRS...TO ESPIRITO
SANTO/MINAS GERAIS BY 96-108 HRS. THROUGH 48-54 HRS CONDITIONS
REMAIN FAVORABLE FOR MCS DEVELOPMENT ACROSS PARAGUAY-MESOPOTAMIA
VALLEY IN ARGENTINA-SOUTHERN STATES OF BRASIL...WITH DAILY MAXIMA
OF 35-70MM. AS THE FRONT MOVES NORTH ACROSS SAO PAULO...IT IS TO
TRIGGER SCATTERED COASTAL CONVECTION WITH ACCUMULATION OF 15-30MM.
OVER MINAS GERAIS-BAHIA-ESPIRITO SANTO IT IS TO THEN FAVOR
RAINFALL AMOUNTS OF 20-40MM BY 96-132 HRS.

AT MID/UPPER LEVELS...A BLOCKING RIDGE ON THE SOUTHERN STREAM IS
TO DOMINATE FLOW ACROSS THE DRAKE PASSAGE/BELLINGSHAUSEN
SEA/ANTARCTIC PENINSULA DURING THE NEXT FEW DAYS. IN A SPLIT FLOW
PATTERN...A SHORT WAVE TROUGH IS TO TRACK JUST NORTH OF THIS AXIS.
THE DEEP MID LEVEL PERTURBATION REACHES CENTRAL CHILE BY 96-108
HRS...AND BY 120-132 HRS IT IS TO SPILL ACROSS THE ANDES INTO
CENTRAL PROVINCES IN ARGENTINA. INFLOW OF COLD AIR ALOFT WILL
RESULT IN HEIGHT FALLS OF 100-150GPM ACROSS CENTRAL
ARGENTINA-NORTHERN PATAGONIA. AT LOW LEVELS...BROAD RIDGE OVER THE
WESTERN ATLANTIC IS TO SUSTAIN A NORTHERLY JET ACROSS
PARAGUAY-ARGENTINA. AS AFOREMENTIONED FRONT WEAKENS OVER
PARAGUAY...A WARM/MOIST ADVECTIVE PATTERN IS TO ESTABLISH ACROSS
MID/SOUTHERN PORTIONS OF SOUTH AMERICA. THIS...IN COMBINATION WITH
COLD ADVECTION ALOFT...IS TO THEN FAVOR DEEP LAYER CONVECTIVE
INSTABILITY FROM NORTHERN PATAGONIA TO MENDOZA/CORDOBA IN
ARGENTINA. BY 96-108 HRS EXPECTING SCATTERED CONVECTION IN THIS
AREA TO SUSTAIN ACCUMULATION OF 15-20MM. THROUGH 120-132 HRS THIS
INCREASES TO 25-50MM IN POTENTIALLY SEVERE CONVECTION. OTHER
ACTIVITY IS EXPECTED TO THE NORTH ACROSS
JUJUY/SALTA-FORMOSA...WITH MAXIMA OF 15-30MM IN SCATTERED
CONVECTION.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE
PATTERN IS TO INITIALLY DOMINATE CONTINENTAL AREA TO THE NORTH OF
30S. THROUGH 72-96 HRS...AS SHORT WAVE TROUGH MOVES ACROSS PERU TO
BOLIVIA...RIDGE IS TO ERODE FROM THE WEST. BY THE END OF THE CYCLE
THE RIDGE IS TO LIMIT TO NORTHEAST BRASIL. EARLY IN THE CYCLE THE
RIDGE ALOFT IS TO VENT DEEP CONVECTION ALONG THE CENTRAL-SOUTHERN
SIERRA OF PERU...WITH MAXIMA OF 10-15MM. BUT THIS DECREASES TO
05-10MM. THROUGH 72-96 HRS FOCUS OF THE CONVECTION SHIFTS TO
SOUTHERN COLOMBIA/NORTHERN AMAZONAS IN BRASIL-NORTHERN JUNGLE OF
PERU...WITH MAXIMA OF 10-15MM. AS IT SETTLES TO THE EAST...THE
RIDGE IS TO THEN VENT THE AFOREMENTIONED CONVECTION OVER NORTHEAST
BRASIL...WHERE WE EXPECT MAXIMA OF 20-40MM BY 84-132 HRS.

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