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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1500Z Jul 07, 2021)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EDT WED JUL 07 2021

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

FORECAST DISCUSSION FROM JUL 07/15UTC:  CONSISTENT WITH PREVIOUS
FORECAST...A MID/UPPER LEVEL SHORT WAVE TROUGH ON THE NORTHERN
STREAM LIFTS ACROSS THE RIO DE LA PLATA BASIN TO URUGUAY/SOUTHERN
STATES OF BRASIL EARLY IN THE CYCLE. THROUGH THURSDAY MORNING THE
PERTURBATION MOVES OFF THE SOUTH COAST OF BRASIL WHERE IT IS TO
INTERACT WITH AN OLD FRONTAL BOUNDARY...SUSTAINING CYCLOGENESIS
OFF THE SOUTHEAST COAST OF BRASIL. THE UPPER LEVEL PERTURBATION IS
THEN SLOWLY PULL TO THE EAST SOUTHEAST...WHILE THE SURFACE
PERTURBATION MEANDERS FARTHER OFFSHORE. MOST ACTIVE CONVECTION
WITH THIS FEATURE IS EXPECTED OVER THE WESTERN ATLANTIC OFF THE
SOUTHEAST COAST OF BRASIL.

UPSTREAM OVER THE EASTERN PACIFIC...A BROAD MID/UPPER LEVEL TROUGH
IS RAPIDLY BECOMING THE DOMINANT FEATURE...WITH AXIS NORTH BETWEEN
110W-70W TO 25S. THE TROUGH IS TO SLOWLY PULL OVER THE SOUTHERN
CONE ON THURSDAY...WHERE IT IS EXPECTED TO MEANDER THROUGH FRIDAY
EVENING. MEANWHILE...IT IS TO GRADUALLY WEAKEN WHILE SHEARING ITS
SHORT WAVE ENERGY ACROSS PATAGONIA TO THE WESTERN SOUTH ATLANTIC.
AT LOW LEVELS THIS SUSTAINS A BROAD TROUGH OVER THE SOUTHEAST
PACIFIC THAT INTRUDES ACROSS THE SOUTHERN CONE LATER TODAY. AS IT
MEANDERS EAST THIS IS TO FOCUS SHORT WAVE ENERGY AND SUBTROPICAL
MOISTURE ACROSS THE SOUTHERN REGIONS OF CHILE. THE BROAD POLAR
TROUGH IS TO THEN DOMINATE THE SOUTHERN CONE/SOUTHWEST ATLANTIC
THROUGH FRIDAY. UNDER THE STEERING INFLUENCE OF A BROAD RIDGE TO
THE WEST...PROGRESSIVE FRONTS ARE TO LIFT ACROSS THE SOUTHEAST
PACIFIC TO THEN REVOLVE AROUND THE MEANDERING POLAR TROUGH TO THE
EAST. THIS IS TO SUSTAIN A COLD ADVECTIVE PATTERN...LEADING TO A
PHASE CHANGE FROM LIQUID PRECIPITATION OVER THE NEXT TWO DAYS TO
SOLID (SNOW) ON FRIDAY TO SUNDAY. OVER SOUTHERN CHILE THE MOST
INTENSE RAINFALL IS EXPECTED TO CLUSTER BETWEEN CONCEPCION-PUERTO
MONTT...WITH RAINFALL AMOUNTS OF 20-45MM/DAY...WHILE TO THE SOUTH
IT INCREASES FROM 15-20MM EARLY IN THE CYCLE TO 20-35MM ON
THURSDAY IN DEEP CONVECTION. ON FRIDAY TO SATURDAY HEAVY SNOWFALL
AMOUNTS ARE TO AFFECT THE SOUTHERN ANDES OF CHILE AND TIERRA DEL
FUEGO...WITH STORM TOTAL AMOUNTS OF 20-30CM HIGHLY LIKELY.

NORTH OVER THE CONTINENT...AT 250 HPA...A SHORT WAVE TROUGH IS
FORECAST TO AMPLIFY ACROSS BOLIVIA TO WESTERN BRASIL EARLY IN THE
FORECAST CYCLE. ALTHOUGH THIS TENDS TO WEAKEN ON
SATURDAY-SUNDAY...ANOTHER TROUGH IS TO QUICKLY TAKE ITS PLACE
LATER DURING THE WEEKEND. UNDER THE INFLUENCE OF THESE
PERTURBATION THE DIURNAL RAINFALL PATTERN ACROSS NORTHERN SOUTH
AMERICA WILL REMAIN MORE ACTIVE THAN NORMAL...WITH DAILY MAXIMA OF
15-20MM ACROSS NORTHERN BRASIL TO NORTHERN JUNGLE OF PERU. HIGHER
AMOUNTS ARE EXPECTED TO THE WEST ACROSS SOUTHERN COLOMBIA TO
EASTERN ECUADOR...WHERE MODERATE RAINFALL AMOUNTS ARE EXPECTED ON
THURSDAY-SUNDAY...WITH ACCUMULATION OF 20-30MM/DAY IN SCATTERED
DEEP CONVECTION.

DAVISON...WPC (USA)