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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1623Z Feb 12, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1123 AM EST THU FEB 12 2015

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

MODEL DISCUSSION (VALID FROM FEBRUARY 12 AT 00UTC): GOOD
CONTINUITY OF THE FORECAST DURING THE SHORT TO MEDIUM RANGE
PERIOD...WITH MINOR CORRECTIONS NOTED LATER IN THE CYCLE.
CONFIDENCE IN THE FORECAST IS HIGH THROUGH 108-120 HRS.

DEEP MID LEVEL TROUGH DOMINATES FLOW ACROSS THE SOUTHERN CONE OF
SOUTH AMERICA TO THE WESTERN ATLANTIC. OVER THE NEXT COUPLE OF
DAYS THE BROAD TROUGH IS TO MEANDER EAST TO EXTEND BETWEEN 60W-10W
AND TO THE SOUTH OF 25S. AFTER 60 HRS IT THEN STARTS TO MIGRATE TO
THE EAST-SOUTHEAST...TO RAPIDLY ACCELERATE AS IT CROSSES 20W BY 96
HRS. AT LOW LEVELS...THE TROUGH WILL SUSTAIN A PROGRESSIVE POLAR
FRONT ACROSS RIO DE LA PLATA BASIN-MENDOZA IN ARGENTINA EARLY I
THE CYCLE. THIS MOVES NORTH TO SOUTHERN BRASIL-NORTHERN PROVINCES
IN ARGENTINA BY 48-60 HRS...WHERE IT IS TO THEN REMAIN THROUGH
84-96 HRS. AS IT MOVES ACROSS RIO DE LA PLATA BASIN THIS IS TO
TRIGGER ISOLATED CONVECTION WITH ACCUMULATION OF 05-10MM. HIGHER
AMOUNTS ARE EXPECTED TO THE NORTH...WITH ACTIVITY TO CLUSTER ALONG
A PREFRONTAL TROUGH OVER SOUTHERN BRASIL-PARAGUAY. IN THIS AREA
CONVECTION IS TO INCREASE TO 35-70MM/DAY THROUGH 48-60 HRS...WITH
HEAVY RAINS EXPECTED TO PERSIST THROUGH 84-96 HRS.

SHORT WAVE PERTURBATION ON THE SOUTHERN STREAM ARE TO THEN
PROPAGATE ACROSS THE EASTERN PACIFIC. THE MID LEVEL PERTURBATIONS
ARE FORECAST TO MOVE ACROSS THE DRAKE PASSAGE/SOUTHERN
CHILE-PATAGONIA IN ARGENTINA BY 60/72 HRS...96/108 HRS...AND BY
132 HRS. ASSOCIATED FRONTS ARE TO CONFINE TO EXTREME SOUTHERN
PORTIONS OF CHILE/TIERRA DEL FUEGO...WHERE THEY ARE TO FAVOR LIGHT
CONVECTION WITH ACCUMULATION OF 05-10MM.

THE SUBTROPICAL RIDGE IS TO DOMINATE FLOW OVER THE CONTINENT TO
THE NORTH OF 30S...WITH AXIS AT 200 HPA FORECAST TO INITIALLY
ANCHOR ON A HIGH OVER SOUTHEAST BOLIVIA-MATO GROSSO IN BRASIL.
THROUGH 48-72 HRS PATTERN IS EXPECTED TO CHANGE AS THE HIGH MOVES
WEST ACROSS NORTHERN CHILE TO THE EASTERN PACIFIC...WHERE IT IS TO
REMAIN THROUGH 132 HRS. AS THE HIGH RELOCATES...RIDGE OVER THE
CONTINENT IS FORECAST TO WEAKEN. THE RIDGE ALOFT IS TO VENT
DIURNAL CONVECTION ACROSS THE CENTRAL-SOUTHERN SIERRA OF PERU AND
THE ALTIPLANO OF BOLIVIA...TO FAVOR RAINFALL MAXIMA OF
15-20MM/DAY. HIGHER AMOUNTS ARE EXPECTED ALONG THE PERUVIAN
JUNGLE-ACRE/AMAZONAS IN BRASIL TO SOUTHERN COLOMBIA/EASTERN
ECUADOR...WHERE THE DAILY MAXIMA IS TO PEAK AT 20-45MM/DAY. OVER
EASTERN AMAZONAS-PARA IN BRASIL THE DAILY MAXIMA IS TO PEAK AT
15-20MM.

ALSO AT 200 HPA...A TUTT LOW/CAVADO DO NORDESTE IS TO DOMINATE THE
NORTHEAST STATES OF BRASIL WHILE CENTERING ON A LOW OVER EASTERN
BAHIA. THIS IS TO EXTEND A SHORT WAVE TROUGH ACROSS NORTHEAST
BRASIL. AS THE TROUGH HOLDS...A NORTHERN HEMISPHERE TROUGH IS TO
THEN AMPLIFY ALONG THE EQUATOR TO NORTHERN BRASIL. AS THE GRADIENT
BETWEEN THESE TROUGHS TIGHTEN THIS IS TO THEN FAVOR A SUBTROPICAL
JET MAXIMA ACROSS NORTHEAST BRASIL. THE JET MAXIMA IS TO FAVOR A
DIVERGENT PATTERN ALOFT...TO VENT DIURNAL/SEA BREEZE CONVECTION.
EARLY IN THE CYCLE EXPECTING RAINFALL AMOUNTS OF 15-30MM BETWEEN
PARA AND NORTHEAST BRASIL. THROUGH 72-84 HRS THIS INCREASES TO
20-40MM...WITH LOCALLY HIGHER AMOUNTS HIGHLY LIKELY.

ARREAGA...INAMHI (ECUADOR)
SCHNEIDER...INMET (BRASIL)
DAVISON...WPC (USA)