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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1842Z Apr 02, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
242 PM EDT THU APR 02 2020

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

FORECAST DISCUSSION FROM APR 02/17UTC: THE CONFIDENCE IN THE
FORECAST OVER THE WESTERN ATLANTIC AND SOUTH AMERICA IS HIGH
THROUGH DAY 05...WITH THE GLOBAL MODELS MAINTAINING GOOD
CYCLE-TO-CYCLE CONTINUITY. OVER THE EASTERN PACIFIC THE FOLLOW A
SIMILAR EVOLUTION THROUGH 96-108 HRS...THEN DIVERGE ON THE
AMPLITUDE AND SPEED OF A BROAD TROUGH PROPAGATING ACROSS THE
SOUTHEAST PACIFIC DURING THE LATTER PART OF THE FORECAST.

CONSISTENT WITH PREVIOUS FORECASTS...A MID LEVEL SHORT WAVE TROUGH
LIFTS ACROSS THE RIO DE LA PLATA BASIN/URUGUAY EARLY IN THE CYCLE.
AS IT MOVES OFF THE COAST...UNDER FAVORABLE JET DYNAMICS...THE
TROUGH IS FORECAST TO RAPIDLY INTENSIFY...EVOLVING INTO A DEEP MID
LEVEL LOW LATER TODAY/EARLY ON  FRIDAY MORNING. THE CLOSED LOW IS
TO THEN MEANDER EAST ACROSS 40W LATER IN THE DAY...TO SLOWLY PULL
ACROSS 30W ON SATURDAY-SUNDAY. AT LOW LEVELS THIS SUSTAIN A
DEEPENING LOW THAT IS FORECAST TO RAPIDLY INTENSIFY THROUGH FRIDAY
MORNING...FAVORING TROPICAL STORM INTENSITY WINDS OVER THE WESTERN
ATLANTIC ON FRIDAY. OVER ARGENTINA THE DEEPENING LOW SUSTAINS A
PAMPERO LOW LEVEL JET. THIS PROPAGATES ACROSS NORTHERN ARGENTINA
TO PARAGUAY/EASTERN BOLIVIA LATER TODAY. THIS...IN-TURN...WILL
DRIVE THE ASSOCIATED SURFACE FRONT NORTH ACROSS SOUTHERN BRASIL TO
SAO PAULO-CHACO PARAGUAYO-SOUTHEAST BOLIVIA LATER TODAY. THIS WILL
THEN MEANDER NORTH ALONG 20S LATER ON FRIDAY...WITH BOUNDARY OVER
THE CONTINENT TO DISSIPATE ON SATURDAY. REMNANTS OVER THE ATLANTIC
ARE TO THEN WEAKEN TO A SHEAR LINE OVER ESPIRITO SANTO/MINAS
GERAIS IN BRASIL. ACROSS BOLIVIA THIS IS TO SUSTAIN HEAVY
CONVECTION EARLY IN THE CYCLE...WITH ACTIVITY BUILDING WEST ALONG
THE LEE OF THE ANDES TO THE SOUTHERN JUNGLE OF PERU...TO RESULT IN
MAXIMA OF 40-80MM. OVER PARANA-SAO PAULO-MISIONES ARGENTINA AND
SOUTHEAST PARAGUAY EXPECTING MAXIMA OF 20-35MM. ON FRIDAY ACTIVITY
ACROSS CENTRAL PERU WEAKENS TO 20-40MM...WHILE OVER SOUTHEAST
BRASIL THIS WILL SUSTAIN ACCUMULATION OF 20-30MM. ON
SATURDAY-SUNDAY...AS THE SHEAR LINE ESTABLISHES ACROSS ESPIRITO
SANTO TO MINAS GERAIS...ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE
FOR AN ECHO TRAINING EVENT...WITH MAXIMA ALONG THE COAST TO PEAK
AT 35-70MM. LOCALLY HIGHER AMOUNTS ARE HIGHLY PROBABLE.

SIMULTANEOUSLY...OVER THE EASTERN PACIFIC...A BROAD TROUGH
AMPLIFIES ACROSS THE BELLINGSHAUSEN SEA TO THE SOUTHERN CONE OF
SOUTH AMERICA EARLY IN THE CYCLE. THIS SETS THE STAGE FOR A
PROGRESSIVE CLIPPER LOW TO LIFT ACROSS SOUTHERN CHILE TO PATAGONIA
IN ARGENTINA EARLY ON SATURDAY MORNING. AT LOW LEVELS THESE ARE TO
FAVOR A BROAD TROUGH OVER THE SOUTHEAST PACIFIC/SOUTHERN CONE OF
SOUTH AMERICA...WITH POLAR FRONT STREAMING ACROSS SOUTHERN CHILE
TO PATAGONIA/LA PAMPA IN ARGENTINA. THIS IS TO SUSTAIN STRONG
BOUNDARY LAYER WINDS DURING THE NEXT FEW DAYS...WITH MODERATE
CONVECTION EXPECTED OVER CHILE TO THE SOUTH OF PUERTO MONTT...WITH
MAXIMA PEAKING AT 15-20MM/DAY. ALSO ON SATURDAY...AS THE CLIPPER
LOW LIFTS ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA...THIS
IS TO FAVOR SNOW SHOWERS...WITH ACCUMULATION OF 10-15CM TO THE
SOUTH OF 50S.

ANOTHER MID LEVEL TROUGH LIFTS ACROSS PATAGONIA ON SUNDAY
MORNING...WITH MID LEVEL VORTEX TO RAPIDLY DEEPEN AS IT CLEARS THE
COAST OF PATAGONIA LATER IN THE AFTERNOON. AT LOW LEVELS THIS IS
TO ALSO SUSTAIN CYCLOGENESIS OVER THE WESTERN ATLANTIC LATER ON
SUNDAY/EARLY MORNING ON MONDAY...WITH PERTURBATION EXPECTED TO
FOLLOW A NEAR EXPLOSIVE INTENSIFICATION THROUGH THE DAY. THE
DEEPENING LOW IS TO ALSO FAVOR TROPICAL STORM INTENSITY WINDS OVER
THE SOUTHWEST ATLANTIC ON MONDAY...WITH DEEPENING LOW TO DRIVE A
PROGRESSIVE FRONT NORTH ACROSS CENTRAL TO NORTHERN ARGENTINA ON
MONDAY. AS IT ACCELERATES ACROSS SOUTHERN BRASIL TO NORTHERN
ARGENTINA THIS WILL THEN TRIGGER A SEVERE WEATHER PRODUCING
PREFRONTAL SQUALL LINE ACROSS PARAGUAY-CHACO ARGENTINO TO SOUTHERN
BOLIVIA...TO SUSTAIN HEAVY RAINFALL AMOUNTS WITH MAXIMA OF
50-100MM.

AT 250 HPA...THE SUBTROPICAL RIDGE CONFINES TO BOLIVIA-WESTERN
BRASIL-PERU. ON FRIDAY...AS SHORT WAVE PERTURBATIONS STREAM ACROSS
NORTHERN ARGENTINA-SOUTHERN BRASIL...THE RIDGE TENDS TO
WEAKEN/NEARLY COLLAPSE. THE REMNANTS ARE TO VENT DIURNAL
CONVECTION ON THE SIERRA OF PERU...WITH ACCUMULATION OF
05-10MM/DAY. THIS TENDS TO INTENSIFY ON SUNDAY-MONDAY...WHEN THE
RIDGE BEGINS TO BUILD. OTHER CONVECTION TO THE NORTH IS TO CLUSTER
ALONG THE NEAR EQUATORIAL TROUGH. OVER PARA-AMAZONAS IN BRASIL
THIS IS TO INITIALLY FAVOR HEAVY CONVECTION WITH MAXIMA OF
40-80MM...DECREASING TO 250-50MM AS IT SPREADS TO SOUTHERN
COLOMBIA/NORTHERN JUNGLE OF PERU TO EASTER ECUADOR ON
SATURDAY-SUNDAY. EARLY NEXT WEEK...ACTIVITY OVER AMAZONAS IN
BRASIL-NORTHERN PERU IS TO INTENSIFY...WITH DAILY MAXIMA
INCREASING TO 35-70MM.

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