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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1405Z Sep 16, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1005 AM EDT WED SEP 16 2020

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

FORECAST DISCUSSION FROM SEPT 16/14UTC: A BUILDING MID/UPPER LEVEL
RIDGE OVER THE EASTERN PACIFIC IS TO SUSTAIN THE GRADUAL
AMPLIFICATION OF A TROUGH OVER THE WESTERN ATLANTIC. THROUGH
FRIDAY THE TROUGH IS TO REACH MAXIMUM AMPLITUDE/INTENSITY...WHEN
IT IS TO ENVELOP AREA BETWEEN 75W AND 40W WHILE BOTTOMING OUT TO
THE SOUTH OF 25S. AT LOW LEVELS THIS WILL SUSTAIN A DEEP/BROAD
TROUGH OVER THE DRAKE PASSAGE/SOUTHERN CONE EARLY IN THE
CYCLE...WITH AXIS TO MEANDER EAST ACROSS THE SOUTHERN CONE TO THE
WESTERN ATLANTIC ON THURSDAY-FRIDAY WHILE SIMULTANEOUSLY A POLAR
RIDGE BUILDS ACROSS ARGENTINA. THIS WILL BE ACCOMPANIED BY STRONG
BOUNDARY LAYER WINDS...PEAKING AT 35-50KT ACROSS PATAGONIA IN
ARGENTINA/SOUTHERN REGIONS OF CHILE AND TIERRA DEL FUEGO. THE DEEP
TROUGH ALSO SUSTAINS A SURFACE FRONT OVER SOUTHERN ARGENTINA/CHILE
LATER THIS EVENING...ON FRIDAY...AS A THE POLAR RIDGE BUILDS NORTH
ALONG THE LEE OF THE ANDES...THIS WILL THEN SUSTAIN A PAMPERO LOW
LEVEL JET THAT DISPLACES THE FRONT NORTH ACROSS URUGUAY TO CORDOBA
IN ARGENTINA. THROUGH SATURDAY THE FRONT ADVANCES FARTHER NORTH
ACROSS SAO PAULO-MATO GROSSO DO SUL TO CHACO PARAGUAYO...WITH
BOUNDARY SLOWING DOWN OVER THE WEEKEND AS IT LOSES ITS UPPER LEVEL
SUPPORT. OVER SOUTHERN CHILE THIS WILL SUSTAIN MODERATE RAINFALL
AMOUNTS...WITH MAXIMA OF 20-30MM/DAY EXPECTED OVER THE NEXT COUPLE
OF DAYS. OVER TIERRA DEL FUEGO AND THE SOUTHERN ANDES...IN A COLD
ADVECTIVE PATTERN...MODERATE TO HEAVY SNOWFALL AMOUNTS ARE
EXPECTED ON THURSDAY-FRIDAY...WITH MAXIMA OF 10-15CM. AS THE FRONT
SURGES ACROSS ARGENTINA ONLY EXPECTING A FEW CONVECTIVE CELLS.
OVER SAO PAULO/RIO DE JANEIRO THIS IS EXPECTED TO INTENSIFY...WITH
MAXIMA INCREASING FROM 20-30MM ON SATURDAY TO 20-40MM ON
SUNDAY...WHILE OVER CHACO PARAGUAYO EXPECTING MODERATE CONVECTION
AND SEVERE THUNDERSTORMS ON SATURDAY...WITH MAXIMA OF 20-30MM.
LIKEWISE...ACROSS CENTRAL-NORTHERN BOLIVIA ON
SATURDAY-SUNDAY...WITH MAXIMA INCREASING TO 20-40MM IN SCATTERED
DEEP CONVECTION

A WANING/OLD FRONTAL BOUNDARY LIES TO THE NORTH...WITH AXIS
STRETCHING ACROSS THE SOUTH ATLANTIC TO MID SECTIONS OF SOUTH
AMERICA. A MID/UPPER LEVEL TROUGH ON THE NORTHERN STREAM IS
INTERACTING WITH THIS FRONT...SUSTAINING SCATTERED/POTENTIALLY
SEVERE CONVECTION ACROSS RIO GRANDE DO SUL IN BRASIL AND THE CHACO
ARGENTINO. MOST INTENSE IS EXPECTED OVER THE NEXT 12-18 HRS WITH
MAXIMA OF 20-30MM.

NORTH OVER THE CONTINENT...AT 250 HPA...THE SUBTROPICAL RIDGE OVER
BRASIL-PERU ANCHORS ON A CLOSED HIGH OVER MATO GROSSO. THROUGH
FRIDAY EVENING THE HIGH RELOCATES TO AMAZONAS IN THE NORTHWEST OF
BRASIL. BUT LATER IN THE CYCLE...EARLY NEXT WEEK...THE HIGH
COLLAPSES AND RIDGE FLATTENS UNDER PRESSURE FROM POLAR TROUGH
STREAMING TO THE SOUTH. INITIALLY THIS IS TO VENT DEEP CONVECTION
OVER EQUATORIAL SOUTH AMERICA...WITH FOCUS OF THE ACTIVITY
SHIFTING TO THE PERUVIAN JUNGLE-EASTERN ECUADOR ON THURSDAY TO
FRIDAY. MAXIMA IN THIS AREA PEAKS AT 15-20MM/DAY...WITH
POTENTIALLY FOR LOCALLY HIGHER AMOUNTS DUE TO STRONG TOPOGRAPHICAL
FORCING ALONG THE LEE OF THE ANDES.

DAVISON/GALVEZ...WPC (USA)