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South American Forecast Discussion
 
(Latest Discussion - Issued 1406Z Sep 30, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1006 AM EDT TUE SEP 30 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 30 AT 00UTC): THE GFS AND
THE UKMET ARE IN EXCELLENT AGREEMENT THROUGH 132-144 HRS...WHILE
THE ECMWF DIVERGES ON LONG RANGE PATTERN EVOLUTION. LATER IN THE
CYCLE...THE ECMWF IS TRENDING TOWARDS A FASTER EVOLUTION...WHILE
THE GFS/UKMET AND THE MEAN OF THE GLOBAL ENSEMBLES FAVOR SLOWER
DEVELOPMENT.

AT LOW LEVELS...AN ELONGATED FRONT EXTENDS ACROSS THE SOUTH
ATLANTIC TO MID SECTIONS OF SOUTH AMERICA. THE FRONT TRAILS ACROSS
SOUTHERN STATES OF BRASIL TO NORTHERN PROVINCES IN
ARGENTINA/PARAGUAY BORDER. UNDER INFLUENCE OF MID LEVEL SHORT WAVE
PERTURBATIONS...AND FAVORABLE JET DYNAMICS...THIS REMAINS FOCUS OF
MOISTURE CONVERGENCE AND ORGANIZED CONVECTIVE DEVELOPMENT. BUT
THROUGH 42-48 HRS THE FRONT LOOSES ITS UPPER LEVEL SUPPORT...AND
IT IS FORECAST TO FRONTOLIZE. MEANWHILE...ANOTHER ROUND OF MESO
SCALE CONVECTIVE SYSTEMS IS EXPECTED ACROSS SOUTHERN
BRASIL-MESOPOTAMIA VALLEY IN ARGENTINA...WITH RAINFALL MAXIMA TO
PEAK AT 35-70MM.

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 48-60 HRS...TO ESPIRITO SANTO/MINAS GERAIS BY 72-84 HRS. AS THE
FRONT SURGES ALONG THE COAST OF BRASIL...A PREFRONTAL SHEAR LINE
IS TO THEN DEVELOP ACROSS NORTHEAST BRASIL. THIS IS TO ENHANCE
MOISTURE CONVERGENCE WHILE SUSTAINING ORGANIZED DEEP CONVECTION.
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 72-108 HRS.

AT MID/UPPER LEVELS...A BLOCKING RIDGE ON THE SOUTHERN STREAM IS
TO DOMINATE FLOW ACROSS THE SOUTHERN CONE/DRAKE PASSAGE TO THE
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 72-84 HRS...AND BY 96-108 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. THIS PERTURBATION IS TO THEN
MEANDER EAST ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC
THROUGH 132-144 HRS. 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 72-84 HRS
EXPECTING SCATTERED CONVECTION IN THIS AREA TO SUSTAIN
ACCUMULATION OF 15-20MM. THROUGH 96-108 HRS THIS INCREASES TO
25-50MM IN POTENTIALLY SEVERE CONVECTION. MODERATE TO HEAVY
AMOUNTS ARE TO THEN PERSISTS ACROSS CENTRAL ARGENTINA THROUGH 132
HRS. 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 48-72 HRS...AS A SHORT WAVE TROUGH MOVES ACROSS PERU
TO BOLIVIA...RIDGE IS TO ERODE FROM THE WEST. BY THE 72-96 HRS THE
RIDGE IS TO THEN 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 05-10MM. THROUGH 72 HRS THE FOCUS
OF THE CONVECTION SHIFTS TO SOUTHERN COLOMBIA/NORTHERN AMAZONAS IN
BRASIL-NORTHERN JUNGLE OF PERU...WITH MAXIMA OF 15-25MM. 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 60-108 HRS.

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