Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXSA20 KWBC 311643
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1243 PM EDT WED AUG 31 2016

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

MODEL DISCUSSION (VALID FROM AUG 31 AT 0000 UTC): HIGH AMPLITUDE
TROUGH ON THE SOUTHERN STREAM FLOW DOMINATES THE DRAKE
PASSAGE/SOUTHERN CONE OF SOUTH AMERICA. CONSISTENT WITH PREVIOUS
FORECASTS THE TROUGH IS FORECAST TO SLOWLY PULL TO THE
EAST-SOUTHEAST WHILE GRADUALLY AMPLIFYING ACROSS CENTRAL
ARGENTINA. ON  FRIDAY EVENING THE TROUGH REACHES MAXIMUM AMPLITUDE
AS IT IS FORECAST TO EXTEND ACROSS THE SOUTH ATLANTIC TO CENTRAL
CHILE/ ARGENTINA. SIMULTANEOUSLY...A SHORT WAVE RIDGE IS TO BUILD
OVER THE EASTERN PACIFIC BETWEEN 80W/90W TO THE BELLINGSHAUSEN
SEA. AS THE RIDGE BUILDS IT IS TO UNDERCUT THE LONG WAVE TROUGH.
THIS IS TO THEN FAVOR THE GENERATION OF A CUT OFF LOW OVER CENTRAL
CHILE LATER IN THE DAY/EARLY SATURDAY MORNING. THROUGH MIDDAY ON
SUNDAY THE CLOSED LOW IS TO THEN MEANDER OVER CENTRAL CHILE/CUYO
IN ARGENTINA. AS IT AMPLIFIES ACROSS CENTRAL CHILE THE TROUGH WILL
PROVIDE THE DYNAMICAL SUPPORT TO FAVOR ORGANIZED CONVECTION ACROSS
THE CENTRAL ANDES. THROUGH THURSDAY MORNING THIS IS TO RESULT IN
SNOWFALL AMOUNTS OF 15-30CM...WHILE ON SATURDAY IT IS TO PEAK AT
10-15CM.

AT LOW LEVELS IT SUSTAINS A DEEP TROUGH ACROSS THE ANTARCTIC
PENINSULA TO PATAGONIA IN ARGENTINA. LATER TODAY THE TROUGH
MEANDERS EAST ACROSS THE SOUTHERN CONE TO THE SOUTH ATLANTIC WHILE
YIELDING TO A BUILDING RIDGE. EARLY ON THURSDAY THE RIDGE IS TO
MOVE FARTHER EAST ACROSS THE CENTRAL PROVINCES IN ARGENTINA...AND
THROUGH SUNDAY MORNING IT IS TO DOMINATE THE FLOW ACROSS SOUTHERN
PORTIONS OF SOUTH AMERICA. AN ELONGATED FRONT LIES TO THE
NORTH...FORECAST TO EXTEND ACROSS RIO DE LA PLATA BASIN TO MENDOZA
IN ARGENTINA LATER TODAY. THROUGH THURSDAY MORNING IT IS TO MOVE
NORTH INTO URUGUAY/RIO GRANDE DO SUL IN BRASIL-NORTHERN ARGENTINA.
BUILDING RIDGE TO THE SOUTH WILL FAVOR A MOIST/COOL ADVECTIVE
PATTERN ACROSS URUGUAY-ENTRE RIOS IN ARGENTINA...TO RESULT IN
SCATTERED POST FRONTAL CONVECTION. IN THIS AREA THE DAILY MAXIMA
WILL PEAK AT 05-10MM STARTING ON THURSDAY AND TO PERSIST THROUGH
SATURDAY MORNING.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM FLOW MOVES ACROSS
PARAGUAY-SOUTHERN BRASIL LATER TODAY. THROUGH THURSDAY EVENING
THIS WILL THEN MERGE WITH BROAD POLAR TROUGH TO THE SOUTH. THE
TROUGH SUSTAINS AN ELONGATED FRONT ACROSS THE SOUTH
ATLANTIC-SOUTHEAST BRASIL-NORTHERN BOLIVIA/ACRE IN WESTERN BRASIL.
EARLY ON THURSDAY THE TAIL END OF THE FRONT WILL START TO
RETROGRESS ACROSS MATO GROSSO TO PARAGUAY...AND ON FRIDAY IT IS
EXPECTED TO STALL. AS IT MEANDERS OVER NORTHERN SAO PAULO THIS
WILL SUSTAIN SCATTERED CONVECTION WITH ACCUMULATION OF 15-30MM
EXPECTED THROUGH THURSDAY MORNING...AND 00-05MM ON THURSDAY TO
FRIDAY.

THE MID LEVEL LOW/TROUGH OVER CHILE/CUYO ARGENTINA WILL THEN
INTERACT WITH THE SURFACE FRONT. UNDER COUPLED JETS...THE SURFACE
BOUNDARY IS FORECAST TO STRENGTHEN...AND DURING THE DAY ON
SATURDAY IT IS TO ONCE AGAIN ADVANCE ACROSS MATO GROSSO-RONDONIA
IN BRASIL TO NORTHERN BOLIVIA. ACROSS PARAGUAY THIS WILL RESULT IN
LIGHT CONVECTION WITH ACCUMULATION OF 05-10MM LATER ON
FRIDAY/EARLY ON SATURDAY...WHILE OVER CENTRAL-NORTHERN BOLIVIA TO
SOUTHERN PERU THE MAXIMA WILL PEAK AT 35-70MM. ON SATURDAY THIS
WILL DECREASE TO MAXIMA OF 25-50MM.

NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE
SUBTROPICAL RIDGE WILL DOMINATE AREA TO THE NORTH OF 20S. THIS
WILL PERSIST NEARLY UNCHANGED THROUGH SATURDAY EVENING...WITH AXIS
EXPECTED TO FLATTEN LATER DURING THE WEEKEND AS THE POLAR TROUGH
PULLS ACROSS CHILE TO ARGENTINA. MEANWHILE...RIDGE ALOFT WILL VENT
DEEP CONVECTION ACROSS NORTHWEST SOUTH AMERICA. OVER NORTHERN
AMAZONAS IN BRASIL TO AMAZONIA IN SOUTHERN COLOMBIA/NORTHERN
JUNGLE OF PERU THIS WILL FAVOR SCATTERED DEEP CONVECTION WITH
ACCUMULATION OF 20-35MM. THROUGH THURSDAY EVENING THIS WILL
DECREASE TO 15-20MM...AND DURING THE DAY ON FRIDAY IT WILL PEAK AT
10-15MM.

OSORIO...DMC (CHILE)
ALVA...SENAMHI (PERU)
DAVISON...WPC (USA)
$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.