SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1231 PM EDT THU APR 28 2022

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

FORECAST DISCUSSION FROM APR 28/17 UTC: IN A SINUSOIDAL
PATTERN...A RIDGE IS INITIALIZED OVER THE EASTERN PACIFIC WITH
AXIS SOUTH BETWEEN 80W/90W...WHILE TO THE EAST A BROAD TROUGH
EXTENDS OVER THE CONTINENT BETWEEN 70W-50W TO 20S. THE LATTER
SLOWLY RELOCATES TO THE WESTERN ATLANTIC THROUGH FRIDAY
AFTERNOON...WHERE IT BECOMES THE DOMINANT SYNOPTIC SCALE FEATURE.
MEANWHILE...UNDER THE INFLUENCE OF THE RIDGE TO THE WEST...SHORT
WAVE PERTURBATIONS ARE TO LIFT ACROSS THE SOUTHERN CONE AND FEED
INTO THE BROAD TROUGH TO THE EAST. THROUGH THE WEEKEND THE INFLOW
OF SHORT WAVE ENERGY WILL SUSTAIN THE NORTHWARD AMPLIFICATION OF A
SECONDARY TROUGH ACROSS ARGENTINA LATER ON SUNDAY. THROUGH MONDAY
THE TROUGH IS EXPECTED TO SPLIT IN TWO...SHEARING A SHORT WAVE
TROUGH OVER THE RIO DE LA PLATA BASIN/NORTHERN ARGENTINA. THIS
EVOLVES INTO A CLOSED LOW AS IT LIFTS ACROSS URUGUAY TO SOUTHERN
BRASIL EARLY NEXT WEEK.

AT LOW LEVELS...A POLAR RIDGE IS BUILDING NORTH ACROSS
ARGENTINA...WHILE TO THE EAST A BROAD TROUGH DOMINATES THE
CENTRAL/WESTERN SOUTH ATLANTIC. THE TROUGH ANCHOR ON AN INTENSE
936 HPA LOW NEAR THE SOUTH GEORGIA ISLANDS...WITH POLAR FRONT
SURGING ACROSS SOUTHERN BRASIL-PARAGUAY TO CENTRAL BOLIVIA LATER
THIS AFTERNOON. THE FRONT WILL REMAIN NEARLY STATIONARY OVER MID
SECTIONS OF SOUTH AMERICA THROUGH THE WEEKEND. BUT EARLY NEXT
WEEK...AS THE AFOREMENTIONED MID LEVEL SHORT WAVE TROUGH LIFTS
ACROSS ARGENTINA...THIS WILL STRENGTHEN THE BAROCLINIC BOUNDARY
WHILE TRIGGERING CYCLOGENESIS OVER SOUTHERN BRASIL. AS THE SURFACE
LOW DEEPENS...IT WILL DRIVE THE FRONT FARTHER NORTH ACROSS
BRASIL...SURGING ACROSS SAO PAULO-MATO GROSSO TO AMAZONAS ON
TUESDAY TO WEDNESDAY. OVER SOUTHERN BRASIL...THE FRONT WILL
INITIALLY FAVOR RAINFALL MAXIMA OF 30-60MM. THROUGH THE WEEKEND
THIS IS EXPECTED TO INTENSIFY...WITH MAXIMA INCREASING TO 40-80MM
IN POTENTIALLY SEVERE CONVECTION. MOST INTENSE...HOWEVER...IS
EXPECTED EARLY NEXT WEEK AS THE FRONT EXPERIENCES CYCLOGENESIS. ON
TUESDAY THIS COULD LEAD TO AN ECHO TRAINING PATTERN...WITH MAXIMA
SURGING TO 75-150MM. OTHER CONVECTION IS EXPECTED TO THE NORTH
ACROSS CENTRAL BOLIVIA...WHERE THE MAXIMA ALSO PEAKS AT 30-60MM
EARLY IN THE CYCLE. THIS...HOWEVER...RAPIDLY WEAKENS ON FRIDAY TO
SATURDAY.

SIMULTANEOUSLY...AS SHORT WAVE TROUGH REVOLVE AROUND THE RIDGE TO
THE WEST AND FEED INTO THE POLAR TROUGH TO THE EAST...THEY ARE TO
FAVOR PROGRESSIVE FRONTAL PERTURBATIONS. THESE LIFT ACROSS THE
SOUTHEAST PACIFIC TO THE SOUTHERN REGIONS OF CHILE/TIERRA DEL
FUEGO IN AN ALMOST DAILY BASIS. THE FRONTAL LOWS WILL ENHANCE THE
TRANSPORT OF SUBTROPICAL MOISTURE ACROSS THE SOUTHEAST
PACIFIC...FEEDING CONVECTIVE DEVELOPMENT TO THE SOUTH OF PUERTO
MONTT. ON FRIDAY AND SATURDAY THIS WILL RESULT IN RAINFALL AMOUNTS
OF 15-20MM/DAY...WHILE ON MONDAY AND TUESDAY IT IS TO INCREASE TO
25-50MM/DAY.

NORTH OVER THE CONTINENT...THE DOMINANT FEATURE IS A BROAD CELL OF
THE SUBTROPICAL RIDGE...WITH UPPER LEVEL AXIS ENVELOPING AREA TO
THE NORTH OF 20S. OVER THE EQUATOR...UPPER FLOW SPLITS BETWEEN
THIS AXIS AND A CELL OF THE SUBEQUATORIAL RIDGE OVER THE
CARIBBEAN/NORTHERN SOUTH AMERICA. THIS FAVORS AN UPPER DIVERGENT
PATTERN THAT IS VENTING DIURNAL CONVECTION OVER EQUATORIAL SOUTH
AMERICA. MOST ACTIVE IS CLUSTERING ALONG THE NORTH COAST OF BRASIL
INTO AMAPA-PARA-AMAZONAS TO THE NORTH AND WEST. GDI FORECAST OVER
THE NEXT FEW DAYS SHOWS AN ENHANCED POTENTIAL FOR MODERATE TO
HEAVY RAINFALL AMOUNTS...WITH ACTIVITY FLARING UP LATER IN THE DAY
INTO THE LATE EVENING HOURS.

DAVISON...WPC (USA)