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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1701Z Dec 04, 2017)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 PM EST MON DEC 04 2017

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

MODEL DISCUSSION (VALID FROM DEC 04 AT 0000 UTC): AT MID/UPPER
LEVELS...A HIGH AMPLITUDE TROUGH EXTENDS NORTH ALONG 40W TO 25S.
LATER THIS EVENING THE TROUGH IS TO MEANDER EAST ACROSS
20W...NEARING 10W LATER ON TUESDAY. AT LOW LEVELS...THIS SUSTAIN A
SURFACE FRONT THAT EXTENDS WEST ACROSS THE SOUTH ATLANTIC TO THE
SOUTHERN STATES OF BRASIL/NORTHERN PROVINCES IN ARGENTINA. THE
FRONTAL BOUNDARY IS TO REMAIN NEARLY STATIONARY DURING THE NEXT
48-72 HRS...WITH BOUNDARY TO WEAKEN OVER THE CONTINENT LATER ON
THURSDAY. AS IT MEANDERS OVER SOUTHERN BRASIL-NORTHERN
ARGENTINA...THE FRONT SUSTAINS A DEEP LAYER TROUGH TO THE NORTH.
AT 850-700 HPA THE TROUGH EXTENDS TO THE SOUTHEAST FROM THE
BOLIVIAN JUNGLE...ACROSS MATO GROSSO DO SUL TO PARAGUAY/SOUTHERN
STATES OF BRASIL. THIS BOUNDARY IS TO PERSIST DURING THE NEXT FEW
DAYS...WITH MOISTURE CLUSTERING ALONG THIS FEATURE. AT 200
HPA...BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES CONTINENTAL
AREA TO THE NORTH OF 30S...WITH AXIS ANCHORING ON A CLOSED HIGH
THAT MEANDERS BETWEEN MATO GROSSO-SANTA CRUZ IN EASTERN BOLIVIA.
THE RIDGE ALOFT IS VENTING DEEP CONVECTION ALONG THIS BOUNDARY.
EARLY IN THE CYCLE THE ENVIRONMENTAL CONDITIONS OVER MID SECTIONS
OF SOUTH AMERICA WILL BECOME FAVORABLE FOR AN MCS TO FORM OVER
BOLIVIA-MATO GROSSO...WITH MAXIMA OF 50-100MM. ON TUESDAY THE
MAXIMA DECREASES TO 30-60MM...WHILE ON WEDNESDAY IT PEAKS AT
20-45MM. FOCUS OF THE HEAVY CONVECTION WILL THEN SHIFT TO THE
SOUTHEAST STATES OF BRASIL. ACROSS RIO DE JANEIRO-ESPIRITO
SANTO-MINAS GERAIS INITIALLY EXPECTING MAXIMA OF 20-30MM. ON
WEDNESDAY-THURSDAY AN MCS IS LIKELY TO FORM...TO TRIGGER MAXIMA OF
40-80MM/DAY.

ON THE SOUTHERN STRING...IN A TIGHT BELT OF MID LATITUDE
WESTERLIES...PROGRESSIVE SHORT WAVE PERTURBATIONS ARE STREAMING
ACROSS THE SOUTHEAST PACIFIC TO THE DRAKE PASSAGE/SOUTHERN CONE OF
SOUTH AMERICA. AT LOW LEVELS THE ASSOCIATED FRONT IS TO INITIALLY
LIMIT TO EXTREME SOUTHERN CHILE-PATAGONIA IN ARGENTINA. ON
WEDNESDAY...AS A RIDGE BUILDS TO THE SOUTH ACROSS PATAGONIA... THE
FRONT MOVES NORTH ACROSS NORTHERN PATAGONIA-LA PAMPA TO THE BUENOS
AIRES PROVINCE IN ARGENTINA. OVER SOUTHERN CHILE THIS IS TO FAVOR
SCATTERED RAINFALL WITH ACCUMULATION OF 00-05MM/DAY.

AS BROAD CELL OF THE SUBTROPICAL RIDGE PERSIST TO THE NORTH...IT
IS TO ALSO VENT DIURNAL CONVECTION ACROSS MID SECTIONS OF SOUTH
AMERICA. ACROSS ACRE/RONDONIA TO BAHIA/MINAS GERAIS EXPECTING
MODERATE RAINFALL AMOUNTS OVER THE NEXT FEW DAYS TO TRIGGER
RAINFALL AMOUNTS OF 20-35MM. OTHER CONVECTION TO THE NORTH IS TO
CLUSTER ACROSS NORTHERN PERU-SOUTHERN COLOMBIA-EASTERN
ECUADOR...WITH MAXIMA OF 20-45MM/DAY. THROUGH WEDNESDAY EVENING
THE MAXIMA IN THIS AREA DECREASES TO 20-35MM/DAY.
FURTHERMORE...THE RIDGE ALOFT IS TO ALSO VENT DEEP CONVECTION ON
THE SOUTHERN SIERRA OF PERU-ALTIPLANO OF BOLIVIA...WITH MAXIMA OF
20-35MM ON TUESDAY AND 20-40MM ON WEDNESDAY-THURSDAY.
GE OVER BRASIL.

OVIEDO...SHN (ARGENTINA)
RIVAS...SENAMHI (PERU)
DAVISON...WPC (USA)