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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1646Z Jun 07, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1246 PM EDT THU JUN 07 2018

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

COR

MODEL DISCUSSION (VALID FROM JUNE 07 AT 0000 UTC): MODELS CONTINUE
TO AGREE QUITE WELL ON HOW PATTERN IS GOING TO UNFOLD OVER THE
CONTINENT DURING THE NEXT FEW DAYS. UPSTREAM PATTERN DIFFERENCES
LIMIT TO THE EASTERN PACIFIC DURING THE MEDIUM RANGE PERIOD...WITH
MODELS DISAGREEING ON THE AMPLITUDE AND SPEED OF PROPAGATION OF
SHORT WAVE PERTURBATIONS STREAMING TOWARDS THE CONTINENT.

CONSISTENT WITH THE PREVIOUS FORECAST...A 500 HPA SHORT WAVE
TROUGH IS TO MEANDER OVER THE WESTERN ATLANTIC/OFF THE COAST OF
ARGENTINA/URUGUAY THROUGH FRIDAY MORNING. LATER IN THE DAY...AS IT
MOVES ACROSS 35W...THE WAVE WILL START TO ACCELERATE...CROSSING
15W LATER ON SATURDAY. AT LOW LEVELS...THE ASSOCIATED TROUGH IS
FORECAST TO DEEPEN WHILE MEANDERING TO THE
EAST-SOUTHEAST...REACHING MAXIMUM INTENSITY OVER THE CENTRAL SOUTH
ATLANTIC LATER ON SATURDAY. AS THE LOW/TROUGH DEEPENS...THE
ASSOCIATED SURFACE FRONT IS TO MOVE TO SOUTHEAST BRASIL-MATO
GROSSO DO SUL LATER TODAY...WHERE IT IS TO THEN MERGE WITH AN OLD
BOUNDARY TO THE NORTH EARLY ON FRIDAY MORNING. ON SATURDAY...UNDER
INFLUENCE OF A NORTHERLY LOW LEVEL JET...THE FRONT IS TO THEN
RETROGRESS ACROSS PARAGUAY TO SOUTHERN BRASIL-NORTHERN PROVINCES
IN ARGENTINA. OVER SAO PAULO/RIO DE JANEIRO THIS IS TO FAVOR
MODERATE RAINFALL AMOUNTS WITH ACCUMULATION OF 15-20MM EARLY IN
THE CYCLE. ON FRIDAY THIS DECREASES TO 05-10MM. OTHER CONVECTION
ALONG THE TRAILING END OF THIS BOUNDARY IS TO BUILD BETWEEN
WESTERN BOLIVIA AND SOUTHERN PERU...WITH MAXIMA IN THIS AREA
PEAKING AT 05-10MM OVER THE NEXT DAY OR SO.

SIMULTANEOUSLY...A PROGRESSIVE SHORT WAVE TROUGH ON THE SOUTHERN
STREAM IS TO ENTER THE DRAKE PASSAGE/SOUTHERN CONE OF SOUTH
AMERICA EARLY ON FRIDAY MORNING. AS THE MID LEVEL TROUGH PULLS
ACROSS THE SOUTHERN CONE...IT IS TO INTERACT WITH ANOTHER SHORT
WAVE TROUGH TO THE NORTH. IT IS TO THEN DRAW THE LATTER TO THE
CENTRAL REGIONS OF CHILE ON FRIDAY EVENING/EARLY MORNING HOURS ON
SATURDAY. AS IT MAKES LANDFALL THIS IS TO THEN FOCUS SHORT WAVE
ENERGY AND A PLUME OF SUBTROPICAL MOISTURE ACROSS CENTRAL REGIONS
OF CHILE. ON SATURDAY-SUNDAY THIS EVOLVES INTO A LONG WAVE TROUGH
OVER THE CONTINENT TO THE SOUTH OF 18S. AS IT INTENSIFIES...THIS
WILL SUSTAIN HEIGHT FALLS OF 75-150GPM OVER CENTRAL ARGENTINA ON
SATURDAY AND ACROSS URUGUAY/NORTHERN ARGENTINA ON SUNDAY. AT 250
HPA A SUBTROPICAL AND A POLAR JET ARE TO ACCOMPANY THIS TROUGH AS
IT MOVES ACROSS CHILE TO ARGENTINA. AS THE JETS INTERACT...THIS
WILL SUSTAIN A BROAD AREA OF DIVERGENCE ACROSS CENTRAL CHILE ON
FRIDAY-SATURDAY...AND THE NORTHERN PROVINCES OF
ARGENTINA/PARAGUAY-SOUTHERN BRASIL ON SATURDAY TO SUNDAY. AT LOW
LEVELS...DEEPENING POLAR TROUGH MOVES ACROSS SOUTHERN CHILE TO
PATAGONIA IN ARGENTINA LATER THIS AFTERNOON. ON FRIDAY...AS IT
CLEARS THE COAST OF ARGENTINA...THE TROUGH IS TO INTENSIFY WHILE
THE LOW GRADUALLY OCCLUDES. THIS WILL DRIVE THE FRONT NORTH ACROSS
THE BUENOS AIRES PROVINCE-CENTRAL CHILE ON SATURDAY. ON
SUNDAY...AS A BUILDING POLAR RIDGE TO THE SOUTH INDUCES A PAMPERO
JET ACROSS ARGENTINA...THE FRONT WILL ACCELERATE ACROSS URUGUAY TO
SOUTHERN BRASIL-NORTHERN PROVINCES IN ARGENTINA. ON MONDAY THIS
WILL CONTINUE FARTHER NORTH ACROSS THE SOUTHERN STATES OF
BRASIL-PARAGUAY TO BOLIVIA. AS IT ENTERS SOUTHERN CHILE EARLY IN
THE CYCLE THIS WILL SUSTAIN MODERATE TO HEAVY CONVECTION...WITH
MAXIMA OF 20-40MM IN DEEP CONVECTION. ON FRIDAY EXPECTING SIMILAR
AMOUNTS OVER SANTIAGO AND VICINITY...WHILE ADDITIONAL RAINFALL
AMOUNTS OF 20-30MM ON SATURDAY. OVER THE CENTRAL ANDES HEAVY
SNOWFALL ARE EXPECTED ON FRIDAY AND SATURDAY...TO RESULT IN
SNOWFALL AMOUNTS OF 25-50CM/DAY...WITH STORM TOTAL AMOUNTS OF
NEARLY ONE METER. ON SUNDAY...AS THE FRONT ACCELERATES ACROSS MID
SECTIONS OF SOUTH AMERICA...ENVIRONMENTAL CONDITIONS COULD BECOME
FAVORABLE FOR SEVERE CONVECTION TO DEVELOP ACROSS RIO GRANDE DO
SUL-MISIONES IN ARGENTINA AND SOUTHEAST PARAGUAY...WITH MAXIMA OF
35-70MM. ON MONDAY IT IS TO THEN SUSTAIN MAXIMA OF 20-40MM IN
SCATTERED DEEP CONVECTION. OTHER CONVECTION TO THE NORTH IS TO
BUILD ACROSS CENTRAL BOLIVIA LATER ON SUNDAY...WITH MAXIMA OF
15-20MM. ON MONDAY THIS INCREASES TO 20-30MM.

AS THE MID/UPPER LEVEL TROUGH AMPLIFIES ACROSS SOUTH AMERICA...IT
WILL PRESS AGAINST A WANING CELL OF THE SUBTROPICAL RIDGE TO THE
NORTH. AT 200 HPA...THE RIDGE IS TO INITIALLY CENTER ON A CLOSED
HIGH OVER PARA IN BRASIL WHILE TRAVERSING THE CONTINENT FROM
EAST-TO-WEST ALONG 05S. ON FRIDAY THE CLOSED HIGH COLLAPSES...WITH
AN OPEN RIDGE TO THEN CONFINE TO EQUATORIAL SOUTH AMERICA.
MEANWHILE...THIS WILL VENT DIURNAL CONVECTION ACROSS NORTHERN
SOUTH AMERICA....WITH MODERATE TO HEAVY CONVECTION ACROSS
PARA-AMAZONAS IN BRASIL TO SUSTAIN MAXIMA OF 20-40MM DURING THE
NEXT COUPLE OF DAYS. THROUGH SATURDAY THIS WILL DECREASES TO
15-20MM/DAY...WITH LESSER AMOUNTS ON SUNDAY-MONDAY. OVER
COLOMBIA-NORTHERN PERU AND EASTERN ECUADOR ALSO EXPECTING MAXIMA
OF 20-40MM/DAY DURING THE NEXT THREE DAYS...DECREASING TO 15-30MM
ON SUNDAY-MONDAY. OVER CENTRAL JUNGLE PERU...UNDER THE INFLUENCE
OF THE LONG WAVE TROUGH TO THE SOUTH...CONVECTION OVER THE JUNGLE
WILL RESULT IN ACCUMULATION OF 10-15MM/DAY...INCREASING TO 15-20MM
LATER IN THE PERIOD. LIKEWISE...OVER SOUTHERN PERU-CENTRAL BOLIVIA
EXPECTING ACCUMULATION OF 10-15MM/DAY...INCREASING TO 20-30MM ON
MONDAY.

DIAZ...INUMET (URUGUAY)
SANCHEZ...SMN (ARGENTINA)
DAVISON...WPC (USA)