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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1415Z Sep 14, 2020)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1015 AM EDT MON SEP 14 2020

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

FORECAST DISCUSSION FROM SEP 14/14UTC: A MID/UPPER LEVEL RIDGE ON
THE NORTHERN STREAM IS TO BECOME THE DOMINANT FEATURE OVER THE
EASTERN PACIFIC EARLY IN THE CYCLE...WITH AXIS TO DOMINATE AREA
BETWEEN 115W-80W AND TO THE NORTH OF 45S. AS THE RIDGE HOLDS...IT
IS TO STEER SUCCESSIVE SHORT WAVE PERTURBATIONS ACROSS THE
SOUTHEAST PACIFIC/BELLINGSHAUSEN SEA. AS THESE CLEAR THE FRINGES
OF THE RIDGE TO THE WEST...THE SHORT WAVE TROUGHS ARE TO THEN
AMPLIFY OVER THE WESTERN ATLANTIC TO MID SECTIONS OF SOUTH
AMERICA. THROUGH THE END OF THE CYCLE...THE INFLOW OF SHORT WAVE
ENERGY WILL HELP CARVE A BROAD/HIGH AMPLITUDE TROUGH OVER THE
WESTERN ATLANTIC...WITH AXIS BOTTOMING OUT TO THE SOUTH OF 30S. AT
LOW LEVELS...THE PROGRESSIVE MID LEVEL PERTURBATIONS WILL SUSTAIN
A TRAIN OF SURFACE FRONTS THAT ARE TO STREAM ACROSS SOUTHERN
CHILE-PATAGONIA IN ARGENTINA DURING THE NEXT 72-84 HRS. LATER IN
THE CYCLE...AS THE TROUGH BECOMES BETTER ORGANIZED OVER THE
WESTERN ATLANTIC AND A RIDGE BUILDS TO THE WEST...THE SURFACE
FRONT WILL SURGE ACROSS THE RIO DE LA PLATA BASIN TO MID SECTIONS
OF SOUTH AMERICA. MEANWHILE...THESE FRONTS ARE TO FAVOR MODERATE
CONVECTION OVER SOUTHERN CHILE BETWEEN ISLA DE CHILOE AND PUERTO
MONTT...WITH DAILY MAXIMA PEAKING AT 15-30MM. A LULL IN
ACTIVITY...HOWEVER...IS EXPECTED ON TUESDAY. THIS IS TO ALSO
RESULT IN MODERATE SNOWFALL AMOUNTS OVER THE SOUTHERN ANDES-TIERRA
DEL FUEGO IN SOUTHERN CHILE.

ALSO...AS THE MID LEVEL RIDGE SETTLES OVER THE EASTERN
PACIFIC...IT IS TO DISPLACE A SHORT WAVE TROUGH ON THE NORTHERN
STREAM EAST ACROSS THE NORTHERN ANDES OF CHILE TO
BOLIVIA/NORTHWEST ARGENTINA EARLY ON TUESDAY...WITH AXIS TO THEN
MEANDER EAST ACROSS MID SECTIONS OF SOUTH AMERICA ON
WEDNESDAY-THURSDAY. AT 250 HPA...A SUBTROPICAL JET MAXIMA IS TO
ACCOMPANY THIS TROUGH AS IT STREAMS ACROSS CENTRAL SOUTH
AMERICA...WITH JET ALOFT FAVORING AN UPPER DIVERGENT PATTERN THAT
IS TO VENT DEEP CONVECTION. AT LOW LEVELS...A FRONT EXTENDS FROM A
DEEPENING LOW OVER THE WESTERN ATLANTIC TO SOUTHERN
BRASIL-NORTHERN BOLIVIA. THE MID LEVEL TROUGH WILL SUSTAIN
CYCLOGENESIS ALONG THIS BOUNDARY ON TUESDAY...WITH THE LOW TO
GRADUALLY OCCLUDE AS IT MOVES ACROSS CORRIENTES/MISIONES IN
ARGENTINA TO SOUTHERN BRASIL EARLY ON WEDNESDAY MORNING. IN THIS
PROCESS THIS IS TO SUSTAIN MODERATE TO HEAVY POTENTIALLY SEVERE
CONVECTION AS IT MOVES ACROSS THE MESOPOTAMIA VALLEY IN
ARGENTINA/SOUTHEAST PARAGUAY TO SOUTHERN BRASIL. IT IS TO ALSO
TRIGGER SCATTERED SNOW SHOWERS ACROSS THE SOUTHERN SIERRA OF PERU
AND THE ALTIPLANO OF BOLIVIA EARLY IN THE CYCLE...WHILE ON THE
SOUTHERN JUNGLE OF PERU AND ACROSS CENTRAL BOLIVIA EXPECTING
MODERATE RAINFALL AMOUNTS.

OVER NORTHERN SOUTH AMERICA...AT 200 HPA...AN ILL ORGANIZED CELL
OF THE SUBTROPICAL RIDGE IS TO DOMINATE FLOW TO THE NORTH OF 20S.
THE RIDGE ALOFT IS TO VENT DEEP CONVECTION OVER AMAZONAS IN
BRASIL-SOUTHERN COLOMBIA-NORTHERN JUNGLE OF PERU. MOST ACTIVE IS
EXPECTED OVER THE NEXT DAY OR SO...WITH ACTIVITY FORECAST TO
GRADUALLY WANE AS THE WEEK WEARS OFF.

DAVISON/GALVEZ...WPC (USA)