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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1714Z Mar 03, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 PM EST TUE MAR 03 2015

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

MODEL DISCUSSION (VALID FROM MARCH 03 AT 00UTC): THE GLOBAL MODELS
AGREE ON PATTERN EVOLUTION THROUGH 96-108 HRS...THEN START TO
DIVERGE ON HOW UPSTREAM PATTERN OVER THE EASTERN PACIFIC IS GOING
TO UNFOLD. CYCLE-TO-CYCLE INCONSISTENCIES ABOUND...LEADING TO LOW
CONFIDENCE IN THE FORECAST LATER ON DAY 06.

IN A TIGHT BELT OF MID LATITUDE WESTERLIES...PROGRESSIVE MID LEVEL
TROUGHS ARE TO STREAM ACROSS THE SOUTH PACIFIC. IN THIS
PATTERN...A STRONG PERTURBATION IS TO ENTER SOUTHERN CHILE BY
48-60 HRS...WITH AXIS TO THEN MOVE ACROSS PATAGONIA TO THE WESTERN
ATLANTIC BY 66-72 HRS. IT IS TO THEN QUICKLY MIGRATE ACROSS THE
SOUTH GEORGIA ISLANDS BY 96 HRS. AT LOW LEVELS...AN ELONGATED
FRONT IS TO STRETCH ACROSS SOUTHERN PATAGONIA-CHILE...WITH DEEP
FRONTAL WAVE/LOW TO REACH THE SOUTH COAST OF CHILE BY 48-54 HRS.
THIS IS TO QUICKLY MOVE ACROSS THE SOUTHERN CONE...DRIVING THE
FRONT NORTH ACROSS PATAGONIA-TEMUCO CHILE. IN A TIGHT PRESSURE
GRADIENT...EXPECT STRONG BOUNDARY LAYER WINDS OVER THE SOUTHERN
CONE TO PEAK AT 30-40KT. THIS IS TO ENHANCE MOISTURE CONVERGENCE
OVER SOUTHERN PORTIONS OF CHILE WHERE WE EXPECT DAILY MAXIMA OF
10-15MM THROUGH 36 HRS. BY 48-60 HRS THIS INCREASES TO 15-25MM AS
THE APPROACHING MID/UPPER LEVEL TROUGH ESTABLISHES A SUBTROPICAL
CONNECTION.

THIS SETS THE STAGE FOR THE NEXT PERTURBATION...WITH MODELS
AGREEING ON A DEEP MID LEVEL TROUGH TO REACH SOUTHERN PORTIONS OF
CHILE BY 84-96 HRS. AS IT MOVES ACROSS CHILE TO PATAGONIA THIS IS
TO SUSTAIN HEIGHT FALLS OF 150-200GPM. AT LOW LEVELS THIS IS TO
SUSTAIN A DEEP OCCLUDED LOW OFF THE SOUTH COAST OF CHILE LATER ON
DAY 04...WITH ASSOCIATED FRONT TO QUICKLY PULL ACROSS SOUTHERN
CHILE-PATAGONIA IN ARGENTINA BY 96-108 HRS. DUE TO STRONG
MESO/SYNOPTIC FORCING EXPECTING ORGANIZED CONVECTION ACROSS
SOUTHERN PORTIONS OF CHILE TO SUSTAIN RAINFALL MAXIMA OF 15-20MM.
LOCALLY HIGHER AMOUNTS ARE HIGHLY LIKELY.

NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE
SUBTROPICAL RIDGE IS TO DOMINATE THE UPPER LEVELS WHILE CENTERING
ON A CLOSED HIGH OVER WESTERN BOLIVIA/SOUTHERN PERU. AN
ANTICYCLONICALLY CURVED SUBTROPICAL JET MAXIMA IS TO BOUND THE
SOUTHERN FRINGES OF THIS RIDGE...WITH AXIS ACROSS NORTHERN
CHILE-ARGENTINA-RIO DE LA PLATA BASIN/SOUTHERN STATES OF BRASIL.
THE JET ALOFT IS TO FAVOR A DIVERGENT PATTERN ACROSS NORTHERN
PROVINCES IN ARGENTINA-SOUTHERN STATES OF BRASIL...WHILE ALSO
FAVORING GENERATION OF LEESIDE PERTURBATIONS. AT LOW
LEVELS...UNDER INFLUENCE OF EL CHACO LOW OVER NORTHWEST
ARGENTINA...A MOIST NORTHERLY FLOW IS TO PERSIST ACROSS PARAGUAY
TO NORTHERN ARGENTINA/RIO DE LA PLATA BASIN. MOISTURE IS TO THEN
CONVERGE ACROSS URUGUAY/MESOPOTAMIA VALLEY IN ARGENTINA TO
JUJUY/SALTA TO THE NORTHWEST...WITH PRECIPITABLE WATER CONTENT TO
PEAK AT 50MM OVER THE NEXT FEW DAYS. HEAVY...POTENTIALLY
SEVERE...CONVECTION IS EXPECTED IN THIS AREA THROUGH 36 HRS...WITH
RAINFALL MAXIMA TO PEAK AT 30-60MM. SCATTERED CONVECTION IS TO
THEN PERSIST THROUGH 84 HRS...WITH RAINFALL MAXIMA OF 20-45MM. BY
96-108 HRS FOCUS OF THE CONVECTION SHIFTS EAST AND NORTH ACROSS
SOUTHERN BRASIL-PARAGUAY...WITH MODELS SHOWING SLIGHT RISK OF
SEVERE CONVECTION AS MID LEVEL TROUGH PULLS ACROSS SOUTHERN
BRASIL. IN THIS AREA...ALTHOUGH WE EXPECT RAINFALL MAXIMA OF
20-45MM...LOCALLY HIGHER AMOUNTS ARE POSSIBLE DUE TO TOPOGRAPHICAL
FORCING.

ALSO AT 200 HPA...AN UPPER LEVEL TROUGH BOUNDS THE
EASTERN-NORTHERN FRINGES OF THE SUBTROPICAL RIDGE...WITH AXIS
NORTH ACROSS NORTHEAST BRASIL. UNDER INFLUENCE OF THE RIDGE TO THE
WEST AND SOUTH...THE TROUGH IS FORECAST TO GRADUALLY AMPLIFY
ACROSS THE NORTHEAST TO CENTRAL STATES OF BRASIL...WITH BROAD AREA
OF DIFFLUENCE TO ESTABLISH ACROSS PARA-AMAZONAS-RORAIMA TO
COLOMBIA-ECUADOR/NORTHERN PERU LATER ON DAY 02/. DEEP MOISTURE IS
TO THEN CLUSTER ALONG THE EQUATORIAL TROUGH TO THE NORTH...WITH
MAXIMA OF 20-40MM. AN INCREASE IN ACTIVITY...HOWEVER...IS EXPECTED
ACROSS ACRE-AMAZONAS IN BRASIL TO THE PERUVIAN JUNGLE/EASTERN
ECUADOR BY 36-84 HRS...WITH MAXIMA IN THIS AREA EXPECTED TO PEAK
AT 25-50MM/DAY. ACROSS NORTHERN AND NORTHEAST BRASIL THE DAILY
MAXIMA PEAKS AT 20-40MM EARLY IN THE CYCLE...BUT THROUGH 72 HRS IT
DECREASES TO 20-35MM/DAY. OVER WESTERN ECUADOR MODERATE TO HEAVY
CONVECTION IS EXPECTED THROUGH 36-48 HRS...WHEN THE DAILY MAXIMA
IS TO PEAK AT 20-45MM. BUT THIS THEN DECREASES TO 10-15MM/DAY.

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