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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1601Z Apr 07, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 PM EDT TUE APR 07 2020

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

FORECAST DISCUSSION FROM APR 07/17UTC: A DEEP MID/UPPER LEVEL LOW
ON THE NOTHERN STREAM IS TO MEANDER EAST TO CENTER NEAR 40S 40W
LATER TODAY. ON WEDNESDAY...THE LOW IS TO STALL NEAR 40S 30W AS A
BUILDING RIDGE TO THE WEST AND SOUTH UNDERCUTS THE MID LEVEL
CYCLONIC CIRCULATION. SLOWING TO A CROLL...THE LOW IS TO THEN
EXTEND A TROUGH TO THE WEST-NORTHWEST ACROSS THE SOUTHERN STATES
OF BRASIL TO PARAGUAY. THIS PATTERN IS TO THEN HOLD THROUGH THE
END OF THE WEEK. AS THE TROUGH MEANDERS ACROSS THE
SOUTHERN/SOUTHEAST STATES OF BRASIL...AT 250 HPA...A SUBTROPICAL
JET IS TO ROUND THE BASE OF THE UPPER LEVEL TROUGH. DIVERGENCE ON
ITS LEFT ENTRANCE REGION IS TO THEN ENVELOP THE SOUTHEAST STATES
OF BRASIL. AT LOW LEVELS...THE MID LEVEL TROUGH SUSTAINS INTENSE
CYCLOGENESIS OVER THE WESTERN ATLANTIC...WITH A BROAD SURFACE
TROUGH ANCHORING ON A DEEP OCCLUDED 986 HPA LOW. ACROSS NORTHERN
ARGENTINA-PARAGUAY TO SANTA CRUZ IN EASTERN BOLIVIA THIS FAVORS A
SOUTHERLY LOW LEVEL JET. THIS IS ADVECTING A COOLER/DRYEAR AIR
MASS ACROSS MID SECTIONS OF SOUTH AMERICA..WITH SURFACE FRONT
ADVANCING ACROSS SAO PAULO IN BRASIL TO MATO GROSSO DO
SUL/PARAGUAY EARLY IN THE CYCLE. ON WEDNESDAY-THURSDAY THE FRONT
ADVANCES ACROSS RIO DE JANEIRO TO ESPIRITO SANTO...WHILE TRAILING
END REMAINS OVER MATO GROSSO DO SUL/PARAGUAY. AS THE FRONT STALLS
OVER MID SECTIONS OF SOUTH AMERICA...THE TROUGH ALOFT IS TO THEN
BUILD DOWNWARD TO SUSTAIN A SURFACE TROUGH ACROSS RIO DE
JANEIRO-TOCANTINS/GOIAS TO AMAZONAS IN WESTERN BRASIL. THIS TROUGH
WILL GRADUALLY BECOME THE FOCUS OF LOW LEVEL MOISTURE CONVERGENCE.
OVER CENTRAL BOLIVIA-SOUTHERN PERU/ACRE IN BRASIL...THE SOUTHERLY
WIND SURGE SUSTAINS ORGANIZED PREFRONTAL CONVECTION...WITH MAXIMA
OF 40-80MM. CONVECTIVE ACTIVITY IS TO THEN CLUSTER ALONG THE LOW
LEVEL TROUGH OVER BRASIL...WITH MAXIMA OF 20-35MM TO AFFECT
ACRE-MATO GROSSO. OVER RIO DE JANEIRO-MINAS
GERAIS-TOCANTINS/GOIAS...THE CONVECTION IS TO GRADUALLY BECOME
MORE ACTIVE/BETTER ORGANIZED ON THURSDAY. MEANWHILE...INITIALLY
EXPECTING RAINFALL AMOUNTS OF 15-25MM. ON WEDNESDAY-THURSDAY THIS
INCREASES TO 20-45MM...WITH PEAK ON THURSDAY WHEN THE MAXIMA
INCREASES TO 35-70MM. FURTHERMORE...AS THE MID LEVEL TROUGH
EXTENDS ACROSS THE SOUTHEAST STATES OF BRASIL...IT IS TO ENHANCE
CONVECTIVE INSTABILITY EARLY ON FRIDAY MORNING...TO TRIGGER
POTENTIALLY SEVERE CONVECTION ACROSS RIO GRANDE DO SUL.

AS PREVIOUSLY INDICATED...A MID LEVEL RIDGE TO THE WEST EXTENDS
SOUTH FROM CENTRAL ARGENTINA TO THE ANTARCTIC PENINSULA. POLAR
TROUGH LIFTING ACROSS THE SOUTHEAST PACIFIC WILL SLIDE UNDER THIS
AXIS...MEANWHILE FOCUSING SHORT WAVE ENERGY AND SUBTROPICAL
MOISTURE ACROSS SOUTHERN CHILE. THIS IS TO THEN LEAD TO THE
GRADUAL EROSION OF THE MID LEVEL RIDGE PATTERN LATER IN THE
WEEK...WHEN MID/UPPER LEVEL TROUGH IS TO THEN PUSH EAST ACROSS THE
SOUTHERN CONE. AT LOW LEVELS...BROAD TROUGH ON THE SOUTHERN STREAM
IS TO DOMINATE THE MESO-SYNOPTIC PATTERN DURING THE NEXT FEW
DAYS...WITH AXIS TO INTIALLY CONFINE TO THE SOUTHEAST
PACIFIC/BELLINGSHAUSEN SEA. THROUGH THURSDAY...AS A RIDGE TO THE
EAST AND NORTH WEAKENS...THE POLAR TROUGH IS TO FINALLY PRESS
EASTWARD ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. THIS IS
TO THEN DRIVE A FRONT EAST AND NORTH ACROSS THE SOUTHERN CONE TO
CENTRAL ARGENTINA LATER IN THE CYCLE. OVER SOUTHERN CHILE/TIERRA
DEL FUEGO THIS IS TO INITIALLY TRIGGER LIGHT TO MODERATE
CONVECTION...WITH ACCUMULATION OF 15-20MM. THROUGH THURSDAY/FRIDAY
THIS DECREASES TO 10-15MM WHILE BUILDING NORTH ACROSS THE SOUTHERN
REGIONS OF CHILE. 

AT 250 HPA...AN ILL ORGANIZED CELL OF THE SUBTROPICAL RIDGE WILL
CONFINE TO CENTRAL BRASIL-BOLIVIA-NORTHERN PARAGUAY DURING THE
NEXT FEW DAYS. AS A DRYER AIR MASS ADVECTS ACROSS PARAGUAY TO MATO
GROSSO DO SUL IN BRASIL/PARAGUAY...THE UPPER LEVEL RIDGE TENDS TO
WEAKEN. MEANWHILE...THIS WILL VENT THE AFOREMENTIONED CONVECTION
OVER TOCANTINS/GOIAS-MINAS GERAIS AND THE CENTRAL STATES OF
BRASIL. THE RIDGE ALOFT IS TO VENT CONVECTION ALONG THE NEAR
EQUATORIAL TROUGH OVER NORTHERN SOUTH AMERICA. THIS...AS
ITINTERACTS WITH THE ITCZ...WILL SUSTAIN A SURGE IN ACTIVITY
ACROSS THE AMAZON RIVER DELTA REGION TO PARA...WITH MAXIMA LIKELY
TO PEAK ABOVE 35-70MM. ACTIVITY IS TO THEN GRADUALLY BUILD ACROSS
ACRE TO AMAZONAS IN BRASIL...WITH MAXIMA INCREASING TO 40-80MM.
OTHER CONVECTION IS TO CLUSTER ALONG THE SIERRA OF PERU...WITH
ACTIVITY INCRESING FROM 10-15MM EARLY IN THE CYCLE TO 30-60MM ON
WEDNESDAY TO THURSDAY.

DAVISON...WPC (USA)
GALVEZ...WPC (USA)