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South American Forecast Discussion
 
(Latest Discussion - Issued 1544Z Aug 17, 2017)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1144 AM EDT THU AUG 17 2017

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

MODEL DISCUSSION (VALID FROM AUG 17 AT 0000 UTC): AN ELONGATED
FRONT IS TO MEANDER ACROSS THE SOUTH ATLANTIC TO SOUTHEAST
BRASIL...THEN INLAND ACROSS NORTHERN SAO PAULO/SOUTHERN MINAS
GERAIS TO RONDONIA/ NORTHERN BOLIVIA. A SUBTROPICAL JET MAXIMA
ALOFT IS TO HELP SUSTAIN THIS BOUNDARY DURING THE NEXT TWO
DAYS...WITH AXIS TO THEN WEAKEN EARLY ON SATURDAY MORNING.
MEANWHILE...THIS WILL BE THE FOCUS OF MOISTURE CONVERGENCE OVER
MID SECTIONS OF SOUTH AMERICA. MOST ACTIVE CONVECTION IS TO
CLUSTER ALONG THE TRAILING END OF THIS FRONT OVER ACRE/SOUTHERN
AMAZONAS IN BRASIL-THE SOUTHERN JUNGLE OF PERU AND NORTHERN
BOLIVIA...WITH MAXIMA OF 20-45MM. OVER CENTRAL/EASTERN
BOLIVIA-MATO GROSSO DO SUL EXPECTING RAINFALL AMOUNTS OF
15-20MM/DAY...WHILE OVER SAO PAULO/RIO DE JANEIRO THE MAXIMA IS TO
PEAK AT 20-35MM.

A BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES THE MID/UPPER
LEVEL FLOW OVER THE EASTERN PACIFIC. THE RIDGE HOLDS NEARLY
UNCHANGED DURING THE NEXT THREE DAYS. MEANWHILE...THIS IS TO FAVOR
A TIGHT BELT OF MID LATITUDE WESTERLIES ACROSS THE SOUTHEAST
PACIFIC-SOUTHERN CONE OF SOUTH AMERICA. EMBEDDED IN THIS FLOW...A
STRONG MID LEVEL TROUGH IS TO MOVE TOWARDS SOUTHERN CHILE LATER
TODAY/EARLY FRIDAY MORNING. AS IT ENTERS THE SOUTHERN CONE THIS IS
TO INDUCE HEIGHT FALLS OF 150-200 GPM. FURTHERMORE...THIS IS TO
ALSO ESTABLISH A SUBTROPICAL CONNECTION AS IT ENTERS THE SOUTHERN
REGIONS OF CHILE. THIS IS TO FAVOR MODERATE TO HEAVY CONVECTION
THROUGH FRIDAY MORNING...WITH MAXIMA OF 20-45MM BETWEEN
TEMUCO-ISLA DE CHILOE. OVER CONCEPCION-TEMUCO THE MAXIMA IS TO
PEAK AT 15-20MM THROUGH FRIDAY MORNING...AND 10-15MM ON
FRIDAY-SATURDAY. ON THE CENTRAL ANDES THIS IS TO THEN FAVOR
MODERATE TO HEAVY SNOWFALL AMOUNTS...WITH ACCUMULATION OF 15-30CM.

THE MID LEVEL TROUGH IS TO THEN PULL ACROSS ARGENTINA TO THE
WESTERN ATLANTIC ON SATURDAY. ON SUNDAY-MONDAY THE TROUGH IS TO
THEN STRETCH TO THE NORTHWEST ACROSS SOUTHERN BRASIL-PARAGUAY TO
BOLIVIA. THE HIGH AMPLITUDE TROUGH IS TO THEN PROVIDE DYNAMICAL
SUPPORT TO ASSOCIATED SURFACE FRONT AS IT RACES ACROSS THE
CONTINENT. LATER ON FRIDAY THE FRONT WILL MOVE NORTH ACROSS THE
BUENOS AIRES PROVINCE-CUYO IN ARGENTINA-CENTRAL CHILE. ON
SATURDAY...AS A POLAR RIDGE BUILDS ACROSS ARGENTINA AND A
SOUTHERLY/PAMPERO LOW LEVEL JET ESTABLISHES ACROSS THE
CONTINENT...THE FRONT WILL THEN RACE NORTH ACROSS SOUTHERN BRASIL
TO NORTHERN ARGENTINA. ON SUNDAY-MONDAY THE FRONT IS TO CONTINUE
NORTH ACROSS SAO PAULO/RIO DE JANEIRO TO MATO GROSSO-ACRE IN
BRASIL/CENTRAL JUNGLE OF PERU AS THE STRONG SOUTHERLY JET EXPANDS
ACROSS PARAGUAY TO MATO GROSSO/BOLIVIA. AS THE FRONT SURGES ACROSS
THE BUENOS AIRES PROVINCE ON FRIDAY IT IS TO TRIGGER SCATTERED
CONVECTION WITH ACCUMULATION OF 10-15MM. OVER URUGUAY-ENTRE
RIOS/CORRIENTES-RIO GRANDE DO SUL THE MAXIMA WILL THEN PEAK AT
15-20MM ON SATURDAY...WHILE OVER SOUTHEAST BRASIL-SOUTHEAST
PARAGUAY EXPECTING MAXIMA OF 40-80MM IN POTENTIALLY SEVERE
CONVECTION. AS IT MOVES NORTH ACROSS SAO PAULO TO RIO DE JANEIRO
THE MAXIMA IS TO THEN PEAK AT 20-35MM ON SUNDAY. ALSO UNDER THE
INFLUENCE OF THE SOUTHERLY WIND SURGE...EXPECTING HEAVY CONVECTION
ACROSS NORTHERN BOLIVIA-SOUTHERN JUNGLE OF PERU ON
SATURDAY-SUNDAY...WITH ACCUMULATION OF 30-60MM. ON SUNDAY-MONDAY
THE CONVECTION WILL THEN BUILD NORTH ALONG THE LEE OF THE ANDES
ACROSS CENTRAL/NORTHERN PERU TO EASTERN ECUADOR/SOUTHERN
COLOMBIA...WITH MAXIMA OF 35-70MM. LOCALLY HIGHER AMOUNTS ARE
HIGHLY LIKELY. ON MONDAY THE MAXIMA DECREASES TO 20-45MM WHILE
CLUSTERING OVER SOUTHERN COLOMBIA/EASTERN ECUADOR.
A HIGH AMPLITUDE LONG WAVE TROUGH IS TO FOLLOW...WITH MID LEVEL
AXIS TO MOVE TO THE SOUTHEAST PACIFIC ON SUNDAY. THIS IS TO
CONTINUE EAST ACROSS THE SOUTHERN CONE ON MONDAY. THE HIGH
AMPLITUDE LONG WAVE TROUGH...AS IT APPROACHES THE SOUTHERN REGIONS
OF CHILE...IS TO SUSTAIN A SUBTROPICAL CONNECTION...ADVECTING DEEP
MOISTURE EASTWARD ACROSS SOUTHERN CHILE. AT UPPER LEVELS THIS WILL
BE ACCOMPANIED BY VERY STRONG SUBTROPICAL-POLAR JETS. OVER
SOUTHERN CHILE THE JETS ARE TO COUPLE ON THEIR RESPECTIVE
DIVERGENT EXIT/ENTRANCE REGIONS...TO RESULT IN BROAD AREA OF
DIVERGENCE THAT IS TO VENT ORGANIZED CONVECTION ON SUNDAY AND
MONDAY. AT LOW LEVELS...DEEP POLAR TROUGH IS TO DOMINATE THE FLOW
OVER THE SOUTHEAST PACIFIC ON SUNDAY-MONDAY...WITH ASSOCIATED
FRONT TO STREAM ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA.
THIS IS TO FAVOR A TIGHT GRADIENT AND STRONG BOUNDARY LAYER WINDS.
OVER CHILE...BETWEEN TEMUCO AND ISLA DE CHILOE...IT IS TO SUSTAIN
HEAVY RAINFALL AMOUNTS...WITH ACCUMULATION OF 35-70MM ON SUNDAY
AND 30-60MM ON MONDAY. OVER TIERRA DEL FUEGO THE MAXIMA IS TO PEAK
AT 10-15MM/DAY.

GONZALEZ...DMC (CHILE)
VANNUCCI...SMN (ARGENTINA)
DAVISON...WPC (USA)