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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1724Z Nov 12, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1224 PM EST WED NOV 12 2014

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

NOTE: ENVIRONMENTAL AND MJO CONDITIONS APPEAR FAVORABLE FOR THE
SOUTH ATLANTIC CONVERGENCE ZONE (SACZ) TO DEVELOP ACROSS CENTRAL
BRASIL-PERU EARLY IN THE CYCLE. THIS IS TO FAVOR HEAVY RAINFALL
AMOUNTS...WITH MCS TO CLUSTER ACROSS NORTHERN
BOLIVIA-ACRE/RONDONIA IN BRASIL TO CENTRAL/SOUTHERN PERU OVER THE
NEXT THREE DAYS...AND ACROSS MATO GROSSO-GOIAS-MINAS GERAIS/BAHIA
IN BRASIL DURING THE MEDIUM RANGE PERIOD.

MODEL DISCUSSION (VALID FROM NOVEMBER 12 AT 00UTC): GLOBAL MODELS
ARE IN EXCELLENT AGREEMENT THROUGH DAY 07...WITH HIGH CORRELATION
AMONG THE GLOBAL MODELS THROUGH DAY 10. AS A RESULT...OUR
CONFIDENCE IN THE FORECAST IS HIGH.

MID/UPPER LEVEL RIDGE OVER THE EASTERN PACIFIC IS TO DRIVE A LONG
WAVE TROUGH EAST ACROSS CHILE TO ARGENTINA EARLY IN THE CYCLE.
THROUGH THURSDAY EVENING THE TROUGH IS TO SPLIT...SHEARING A SHORT
WAVE TROUGH ON THE NORTHERN STREAM WHILE THE SOUTHERN HALF
ACCELERATES ACROSS THE SOUTH ATLANTIC. THE NORTHERN STREAM
VORTEX... MEANWHILE...IS TO MEANDER OFF THE SOUTH COAST OF
BRASIL/URUGUAY THROUGH AT LEAST SATURDAY MORNING...THEN PULL TO
THE EAST-SOUTHEAST LATER IN THE CYCLE. AS THE TROUGH MOVES EAST
ACROSS THE CONTINENT... A SUBTROPICAL JET MAXIMA IS TO ACCOMPANY
THIS VORTEX...PULLING ACROSS NORTHERN CHILE/ARGENTINA TO SOUTHERN
BRASIL EARLY IN THE CYCLE. THROUGH FRIDAY EVENING THIS IS TO MOVE
EAST ACROSS SOUTHEAST BRASIL TO THE EASTERN PACIFIC. AS IT
MIGRATES ACROSS THE CONTINENT...DIVERGENCE ON ITS LEFT ENTRANCE
REGION IS TO ENHANCE CONVECTIVE DEVELOPMENT. THIS IS TO COUPLE
WITH PERSISTENT CELL OF THE SUBTROPICAL RIDGE AT 200 HPA OVER
WESTERN BRASIL-PERU TO ENHANCE CONVECTION ACROSS NORTHERN
BOLIVIA-SOUTHERN PERU/WESTERN BRASIL EARLY IN THE CYCLE AND ACROSS
MINAS GERAIS-GOIAS/BAHIA LATER IN THE PERIOD.

AT LOW LEVELS...BUILDING RIDGE OVER ARGENTINA IS TO SUSTAIN A
35-45KT SOUTHERLY JET ACROSS PARAGUAY TO BOLIVIA EARLY IN THE
CYCLE. A POLAR FRONT OVER RIO DE LA PLATA BASIN IS TO THEN SURGE
ACROSS URUGUAY TO SOUTHERN BRASIL-NORTHERN ARGENTINA EARLY IN THE
CYCLE...WHERE IT IS TO WEAKEN TO A TROUGH. LATER ON THURSDAY/EARLY
FRIDAY MORNING THE TROUGH EVOLVES INTO THE SACZ...AS IT IS TO
EXTEND FROM SAO PAULO TO NORTHERN BOLIVIA/SOUTHERN PERU. LATER ON
SATURDAY...AS LOW LEVEL WINDS WEAKEN TO 20-25KT...THE SACZ IS TO
MEANDER NORTH ACROSS MINAS GERAIS/ESPIRITO SANTO-GOIAS TO NORTHERN
BOLIVIA/CENTRAL PERU. HEAVY RAINS ARE TO INITIALLY CLUSTER ACROSS
BOLIVIA-MATO GROSSO IN BRASIL...WITH MAXIMA OF 50-100MM. THROUGH
FRIDAY MORNING THIS INCREASES TO 75-125MM WHILE BUILDING WEST AND
NORTH ACROSS ACRE/AMAZONAS IN BRASIL TO THE SOUTHERN-CENTRAL
JUNGLE OF PERU. LATER ON SATURDAY THIS IS TO DECREASE TO 20-40MM
AS UPPER JET DYNAMICS WANE TO THE WEST.
SIMULTANEOUSLY...CONVECTION ACROSS SOUTHEAST BRASIL IS TO
GRADUALLY BECOME MORE ACTIVE/BETTER ORGANIZED...WITH MAXIMA OF
30-60MM EXPECTED FROM MATO GROSSO TO ESPIRITO SANTO/BAHIA LATER ON
THURSDAY/EARLY FRIDAY MORNING. BUT AS UPPER JET DYNAMICS
IMPROVE...THIS IS TO INCREASE TO 50-100MM EARLY ON SATURDAY.

BEST BAROCLINIC ENVIRONMENT IS EXPECTED FAR TO THE SOUTH...WITH
PROGRESSIVE MID LEVEL PERTURBATIONS STREAMING ACROSS THE ANTARCTIC
PENINSULA/DRAKE PASSAGE TO SUSTAIN A SERIES OF PROGRESSIVE
BOUNDARIES THAT ARE TO STREAM ACROSS SOUTHERN CHILE/PATAGONIA IN
ARGENTINA OVER THE NEXT FEW DAYS...FAVORING SCATTERED CONVECTION
WITH DAILY MAXIMA OF 10-15MM. THROUGH SUNDAY EVENING PATTERN
BECOMES BETTER ORGANIZED AS DEEP PERTURBATION ON THE SOUTHERN
STREAM MERGES WITH A NORTHERN STREAM VORTEX MEANDERING OVER THE
EASTERN PACIFIC. AS THEY COMBINE...MODELS SHOWING RAPID
INTENSIFICATION AND DEEPENING OF MID LEVEL TROUGH
PATTERN...PROJECTING HEIGHT FALLS OF NEARLY 300 GPM LATER IN THE
CYCLE. DEEPENING TROUGH PATTERN IS TO THEN ESTABLISH A SUBTROPICAL
CONNECTION INTO SOUTHERN PORTIONS OF CHILE...AND THIS IS LIKELY TO
RESULT IN MODERATE TO HEAVY RAINS LATER ON SUNDAY.

CAROCA...DMC (CHILE)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)