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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1623Z Aug 25, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1223 PM EDT MON AUG 25 2014

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

MODEL DISCUSSION (VALID FROM AUGUST 25 AT 00UTC): CONFIDENCE IN
THE FORECAST IS HIGH...AS THE GLOBAL MODELS AGREE ON PATTERN
EVOLUTION THROUGH DAY 06. THE DETERMINISTIC SOLUTION IS WELL
SUPPORTED BY THE MEAN OF THE GLOBAL ENSEMBLES.

DEEP TROUGH ON THE NORTHERN STREAM DOMINATES THE FLOW OVER MID
SECTIONS OF SOUTH AMERICA...WITH MID LEVEL TROUGH FORECAST TO PULL
ACROSS RIO DE LA PLATA BASIN TO SOUTHERN BRASIL EARLY IN THE
CYCLE. THIS TROUGH IS TO ANCHOR ON A CLOSED LOW JUST EAST OF THE
BUENOS AIRES PROVINCE. THROUGH 48 HRS THE TROUGH WILL DRIFT EAST
TO EXTEND BETWEEN 60W-30W TO SAO PAULO/RIO DE JANEIRO IN
BRASIL....WITH CLOSED LOW TO MEANDER TO 42S 45W. BY 96-120 HRS THE
CLOSED LOW FILLS TO AN OPEN TROUGH...WITH AXIS TO STRETCH TO THE
NORTHWEST ALONG 35S 25W TO RIO DE JANEIRO. AT LOW LEVELS IT
SUSTAINS AN OCCLUDED 1006 HPA LOW OVER LA PAMPA/SOUTHERN BUENOS
AIRES. BY 24 HRS THE LOW DEEPENS TO A 992 HPA LOW WHILE MOVING
JUST EAST OF THE BUENOS AIRES PROVINCE/ URUGUAY...AND THROUGH 48
HRS IT IS TO INTENSIFY TO A 984 HPA LOW WHILE MEANDERING TO THE
EAST-SOUTHEAST. THE DEEPENING LOW WILL SUSTAIN A TIGHT PRESSURE
GRADIENT ACROSS RIO DE LA PLATA BASIN EARLY IN THE CYCLE...WITH
850 HPA WINDS FORECAST TO PEAK AT 60-70KT. THE ASSOCIATED FRONT
MOVES NORTH ACROSS PARAGUAY TO SAO PAULO-MATO GROSSO IN BRASIL TO
CENTRAL BOLIVIA...WHERE IT IS TO REMAIN THROUGH 60-72 HRS. LATER
IN THE CYCLE IT IS TO MEANDER SOUTH ACROSS PARAGUAY. UNDER
INFLUENCE OF THE OCCLUDING LOW...MODERATE RAINFALL IS EXPECTED
ACROSS THE BUENOS AIRES PROVINCE WITH ACCUMULATION OF 20-35MM.
LOCALLY HIGHER AMOUNTS ARE EXPECTED ACROSS SIERRA DE LA VENTANA.
OVER SOUTHERN BRASIL-MATO GROSSO THIS IS TO SUSTAIN RAINFALL
AMOUNTS OF 20-40MM THROUGH 36 HRS. OVER SOUTHERN PERU-WESTERN
ECUADOR...PREFRONTAL CONVECTION IS TO RESULT IN ACCUMULATION OF
15-20MM EARLY IN THE CYCLE. OTHER ACTIVITY IS EXPECTED ACROSS RIO
DE JANEIRO-NORTHERN SAO PAULO AS THE FRONT MEANDERS NORTH...WITH
ACCUMULATION OF 05-10MM.

BLOCKING RIDGE PATTERN IS TO THEN ESTABLISH ACROSS THE FAR EASTERN
PACIFIC/SOUTHERN CONE OF SOUTH AMERICA...WITH MID LEVEL AXIS TO
INITIALLY EXTEND ALONG THE COAST OF CHILE. THROUGH 48-72 HRS THE
RIDGE RELOCATES ACROSS CHILE TO ARGENTINA...WHERE IT IS TO REMAIN
THROUGH 96-120 HRS. SHORT WAVE PERTURBATIONS WILL THEN PRESS
AGAINST THE LONG WAVE RIDGE. THROUGH 48-72 HRS THESE EVOLVE INTO A
BROAD TROUGH OVER THE EASTERN PACIFIC BETWEEN 100W-75W AND TO THE
SOUTH OF 15S. LATER IN THE CYCLE THE RIDGE WILL WEAKEN ENOUGH TO
ALLOW SOME OF THE SHORT WAVE ENERGY TO SPILL ACROSS
SOUTHERN-CENTRAL PORTIONS OF CHILE. AT LOW LEVELS...RIDGE ALOFT IS
TO SUSTAIN A SURFACE RIDGE ACROSS CHILE-ARGENTINA OVER THE NEXT
FEW DAYS...WHILE THE TROUGH ALOFT SUSTAINS A BROAD AREA OF LOW
PRESSURE TO THE WEST. POLAR FRONTS ARE TO REVOLVE AROUND THE
MEANDERING PRESSURE TROUGH. BUT AS THEY CLASH WITH THE RIDGE TO
THE EAST...THEY ARE TO SHEAR SOUTH ACROSS TIERRA DEL FUEGO/DRAKE
PASSAGE...WHERE IT IS TO FAVOR LIGHT CONVECTION. LATER IN THE
CYCLE...AS THE SURFACE RIDGE STARTS TO WEAKEN...FRONTS WILL PUSH
EAST INTO SOUTHERN-CENTRAL PORTIONS OF CHILE WHERE THEY ARE TO
ENHANCE MOISTURE CONVERGENCE WHILE TRIGGERING MODERATE RAINFALL
AMOUNTS.

AT 200 HPA...AN UPPER LEVEL RIDGE EXTENDS FROM PERU INTO THE
EASTERN PACIFIC. THROUGH 48 HRS THE HIGH IS TO RELOCATE ACROSS
BRASIL AS THE RIDGE BUILDS EAST ACROSS NORTHERN SOUTH AMERICA.
RIDGE PATTERN IS TO THEN HOLD THROUGH 96-120 HRS WHILE CENTERING
ON A CLOSED HIGH OVER AMAPA/AMAZON RIVER DELTA REGION. THE RIDGE
ALOFT IS TO VENT CONVECTION ACROSS EQUATORIAL SOUTH AMERICA...WITH
ACCUMULATION OF 10-15MM. HIGHER AMOUNTS...HOWEVER...ARE EXPECTED
ON THE LEE OF THE ANDES OVER PERU-ECUADOR...WHERE MAXIMA IS TO
PEAK AT 15-25MM.

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