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South American Forecast Discussion
 
(Latest Discussion - Issued 1629Z Dec 22, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1129 AM EST MON DEC 22 2014

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

MODEL DISCUSSION (VALID FROM DECEMBER 22 AT 00UTC): GLOBAL MODELS
CONTINUE TO MAINTAIN CYCLE-TO-CYCLE CONTINUITY...AND THEY AGREE ON
A SIMILAR SOLUTION THROUGH 108-120 HRS. AS A RESULT...CONFIDENCE
IN THE FORECAST IS HIGH.

UNDER INFLUENCE OF A HIGH AMPLITUDE MID/UPPER LEVEL RIDGE OVER THE
EASTERN PACIFIC...A LONG WAVE TROUGH EXTENDS NORTH ACROSS THE
CONTINENT TO PARAGUAY/SOUTHERN STATES OF BRASIL. THROUGH 30-36 HRS
THE RIDGE TO THE WEST IS TO FLATTEN...AND AS A RESULT THE TROUGH
OVER THE CONTINENT WILL RAPIDLY PULL TO THE EAST-SOUTHEAST. AS IT
MOVES TO THE WESTERN ATLANTIC IT IS TO SHEAR A SHORT WAVE TROUGH
ON THE NORTHERN STREAM OVER RIO DE LA PLATA BASIN. THIS MOVES EAST
TO 35S 45W LATER ON DAY 02...AND THROUGH 84-96 HRS IT MEANDERS
EAST TO 35S 30W. AT LOW LEVELS THE TROUGH ALOFT SUSTAINS A
BAROCLINIC BOUNDARY ACROSS SOUTHERN BRASIL-PARAGUAY-NORTHERN
ARGENTINA. THIS IS TO REMAIN NEARLY STATIONARY THROUGH 48-60
HRS...FRONTOLIZING BY 72-84 HRS. UNDER FAVORABLE JET DYNAMICS THIS
IS TO SUSTAIN ORGANIZED DEEP CONVECTION ACROSS SOUTHEAST
BRASIL...WITH MAXIMA OF 50-100MM EXPECTED THROUGH 36 HRS...AND
35-70MM AT 36-60 HRS. STRONG TOPOGRAPHICAL FORCING ALONG THE SERRA
DO MAR IS LIKELY TO RESULT IN LOCALLY HIGHER RAINFALL AMOUNTS.
FURTHERMORE...A POLAR RIDGE OVER ARGENTINA SUSTAINS A STRONG
SOUTHEASTERLY FLOW ACROSS PARAGUAY-BOLIVIA. THIS IS TO ENHANCE
MOISTURE CONVERGENCE ACROSS NORTHERN BOLIVIA-SOUTHERN PERU AND
ACROSS ACRE-RONDONIA IN BRASIL...WHERE WE EXPECT RAINFALL MAXIMA
OF 40-80MM THROUGH 36 HRS. BY 36-60 HRS THE FOCUS OF THE
CONVECTION SHIFTS TO CENTRAL-NORTHERN PERU/EASTERN
ECUADOR-SOUTHERN COLOMBIA AND AMAZONAS IN BRASIL WITH MAXIMA OF
25-50MM. THIS DECREASES TO 20-35MM LATER ON DAY 03.

A NEAR ZONAL WESTERLY FLOW IS TO THEN ESTABLISH ACROSS THE EASTERN
SOUTH PACIFIC...WITH MID LEVEL PERTURBATIONS TO STREAM TOWARDS THE
DRAKE PASSAGE-SOUTHERN CONE OF SOUTH AMERICA. THREE STRONG
PERTURBATIONS ARE FORECAST TO MAKE LANDFALL DURING THE NEXT FIVE
DAYS...WITH ONE TO ENTER SOUTHERN CHILE/PATAGONIA IN ARGENTINA
EARLY IN THE FORECAST CYCLE. THE NEXT IS EXPECTED BY 78-84
HRS...WHILE A THIRD IS TO ARRIVE BY 132-144 HRS. AS THEY STREAM
ACROSS THE SOUTH PACIFIC THESE ARE TO SUSTAIN A SUBTROPICAL
CONNECTION...ENHANCING MOISTURE TRANSPORT/CONVERGENCE ACROSS
TIERRA DEL FUEGO/SOUTHERN PORTIONS OF CHILE. IN THIS AREA
EXPECTING MODERATE CONVECTION WITH LOCALLY HEAVY AMOUNTS...TO
SUSTAIN RAINFALL MAXIMA OF 15-20MM.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS
TO EXTEND TO THE NORTHWEST ACROSS SAO PAULO IN BRASIL TO THE
PERUVIAN JUNGLE/ECUADOR. EARLY IN THE CYCLE THE RIDGE IS TO ANCHOR
ON A CLOSED HIGH OVER SOUTHEAST BRASIL. THROUGH 72-84 HRS THE HIGH
RELOCATES TO CENTRAL BOLIVIA...WHERE IT IS TO THEN REMAIN. RIDGE
ALOFT IS TO VENT AFOREMENTIONED DEEP CONVECTION ACROSS SOUTHEAST
BRASIL-BOLIVIA-PERU. LATER IN THE CYCLE IT IS TO THEN ENHANCE
CONVECTIVE DEVELOPMENT OVER AMAZONAS IN WESTERN
BRASIL-CENTRAL/NORTHERN PERU AND EASTERN ECUADOR...WITH RAINFALL
MAXIMA OF 20-35MM.

EAST OF THE UPPER LEVEL RIDGE...A TUTT LOW MEANDERS OFF THE
NORTHEAST COAST OF BRASIL. THIS IS TO MOVE INLAND LATER ON
TUESDAY...TO SETTLE NEAR 10S 40W LATER ON THURSDAY. AS IT
RETROGRESSES TO NORTHEAST BRASIL THE TROUGH ALOFT IS TO FAVOR AN
UPPER CONVERGENT PATTERN THAT IS EXPECTED TO CONTINUE INHIBITING
ORGANIZED DEEP CONVECTION.

ARREAGA...INAMHI (ECUADOR)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)