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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1412Z Sep 10, 2020)
 
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Abbreviations and acronyms used in this product


SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1012 AM EDT THU SEP 10 2020

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

FORECAST DISCUSSION FROM SEP 10/14UTC: THE GFS AND EUROPEAN MODELS
MADE PATTERN CORRECTIONS AND NOW FAVOR A SIMILAR EVOLUTION THROUGH
THE MEDIUM RANGE PERIOD. OVER THE EASTERN PACIFIC THEY AGREE ON
THE SOUTHWARD AMPLIFICATION OF A MID/UPPER LEVEL RIDGE BETWEEN
120W-90W TO 60S...WITH AXIS EXPECTED TO HOLD DURING THE NEXT
SEVERAL DAYS. UNDER INFLUENCE OF THIS RIDGE...SUCCESSIVE SHORT
WAVE PERTURBATIONS ON THE SOUTHERN STREAM WILL RACE ACROSS THE
SOUTHEAST PACIFIC. THESE ARE THEN FORECAST TO AMPLIFY AS THEY
ENTER THE SOUTHERN CONE OF SOUTH AMERICA...WITH SHORT WAVE TROUGHS
BOTTOMING OUT TO THE SOUTH OF 30S. AT UPPER LEVELS...THE INFLOW OF
MID LEVEL ENERGY WILL HELP SUSTAIN A FAIRLY PERSISTENT JET MAXIMA
ACROSS MID SECTIONS OF SOUTH AMERICA...WITH JET ALOFT FAVORING
AREAS OF UPPER DIVERGENCE THAT ARE TO VENT ORGANIZED DEEP
CONVECTION. AT LOW LEVELS...THE PROGRESSIVE MID LEVEL
PERTURBATIONS WILL HELP SUSTAIN PROGRESSIVE FRONTS...STRONG
BOUNDARY LAYER WINDS AND A COLD ADVECTIVE PATTERN. THIS WILL BE
COLD ENOUGH TO HELP SUSTAIN PERIODS OF HEAVY SNOWFALL AMOUNTS
ACROSS TIERRA DEL FUEGO AND THE SOUTHERN ANDES OF CHILE/ARGENTINA
DURING THE NEXT THREE DAYS...WITH WARMER TEMPERATURES LATER IN THE
CYCLE TO SUSTAIN A TRANSITION TO LIQUID PRECIPITATION. ACROSS MID
SECTIONS OF SOUTH AMERICA THESE WILL COMBINE IN SUPPORT OF A
MEANDERING FRONT...WITH AXIS TO UNDULATE BACK-AND-FORTH ACROSS THE
SOUTHERN STATES OF BRASIL-PARAGUAY/NORTHERN ARGENTINA DURING THE
NEXT 84-96 HRS...WITH A NORTHWARD SURGE INTO MATO GROSSO DO
SUL/BOLIVIA ON MONDAY. MEANWHILE...THIS WILL ACT AS THE FOCUS OF
LOW LEVEL MOISTURE CONVERGENCE...HELPING SUSTAIN MODERATE TO HEAVY
CONVECTION. UNDER FAVORABLE JET DYNAMICS...THERE IS ALSO A RISK OF
SEVERE CONVECTION...TO INITIALLY AFFECT THE BUENOS AIRES PROVINCE
IN ARGENTINA. ON FRIDAY-SUNDAY THE FOCUS OF THE HEAVY RAINS AND
SEVERE CONVECTION SHIFTS TO RIO GRANDE DO SUL/CORRIENTES-MISIONES
IN ARGENTINA...WHILE SLOWLY BUILDING NORTH TO ALSO AFFECT PORTIONS
OF BOLIVIA AND PARAGUAY. 

NORTH OVER THE CONTINENT...AT 250 HPA...CELL OF THE SUBTROPICAL
RIDGE IS TO SLOWLY BUILD FROM THE WEST ACROSS THE TROPICAL PACIFIC
TO NORTHWEST SOUTH AMERICA...WITH AXIS TO GRADUALLY STRENGTHEN ITS
FOOTHOLD OVER THE CONTINENT EARLY NEXT WEEK. AS THE RIDGE
BUILDS...THIS WILL DISPLACE A SHORT WAVE TROUGH TO THE SOUTH TO
MEANDER EAST ACROSS NORTHERN CHILE TO BOLIVIA/NORTHWEST ARGENTINA.
THIS WILL BE ACCOMPANIED BY INTENSIFICATION OF A SUBEQUATORIAL JET
MAXIMA. UNDER INFLUENCE OF THE RIDGE ALOFT...DIURNAL ACTIVITY IS
TO BUILD ACROSS NORTHWEST SOUTH AMERICA...AFFECTING THE BRAZILIAN
STATES OF AMAZONAS-ACRE...THE PERUVIAN JUNGLE AND SOUTHERN
COLOMBIA/EASTERN ECUADOR. IN THIS AREA SCATTERED CONVECTION IS
LIKELY DURING THE NEXT SEVERAL DAYS. FURTHERMORE...CONDITIONS ARE
SLOWLY BECOMING MORE FAVORABLE FOR CONVECTION TO BUILD ALONG THE
CENTRAL AND SOUTHERN ANDES OF PERU.

DAVISON/GALVEZ...WPC (USA)