Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3
000
FXSA20 KWBC 121753
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1252 PM EST TUE DEC 12 2017

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

MODEL DISCUSSION (VALID FROM DEC 12 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH...WITH MODELS FOLLOWING A SIMILAR EVOLUTION
THROUGH DAY 06. THE DETERMINISTIC SOLUTION IS WELL SUPPORTED BY
THE MEAN OF THE GLOBAL ENSEMBLE MEMBERS.

A PROGRESSIVE MID LEVEL TROUGH ON THE SOUTHERN STREAM IS TO ENTER
THE SOUTHERN REGIONS OF CHILE EARLY ON WEDNESDAY
MORNING...CROSSING PATAGONIA IN ARGENTINA LATER IN THE DAY. AT LOW
LEVELS THIS SUSTAINS A BROAD TROUGH OVER THE SOUTHEAST PACIFIC
LATER THIS AFTERNOON...WITH ASSOCIATED FRONT MOVING ACROSS
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA ON WEDNESDAY
MORNING...WHILE TRAILING ACROSS THE SOUTHERN REGIONS OF CHILE. AS
IT MEANDERS OVER THE SOUTHERN CONE THIS IS TO SUSTAIN A
SUBTROPICAL CONNECTION. THIS IS TO THEN FEED CONVECTIVE
DEVELOPMENT OVER CHILE BETWEEN ISLA DE CHILOE AND TEMUCO TO THE
NORTH. ON WEDNESDAY THIS IS TO FAVOR MODERATE CONVECTION WITH
ACCUMULATION OF 20-30MM.

AN ELONGATED FRONT TO THE NORTH...MEANWHILE...IS TO EXTEND FROM
THE SOUTH GEORGIA ISLANDS TO LA PAMPA IN ARGENTINA. THE FRONT IS
TO REMAIN NEARLY STATIONARY THROUGH WEDNESDAY EVENING...SURGING
ACROSS RIO DE LA PLATA BASIN/URUGUAY TO SOUTHERN BRASIL-NORTHERN
PROVINCES IN ARGENTINA ON THURSDAY. AS IT MEANDERS OVER THE
SOUTHERN CONE...A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO
ENTER CENTRAL CHILE EARLY ON WEDNESDAY MORNING...TO MOVE ACROSS LA
PAMPA/CENTRAL ARGENTINA LATER ON WEDNESDAY. AS IT STREAMS ACROSS
CENTRAL ARGENTINA THIS WILL INTERACT WITH MEANDERING FRONT OT THE
NORTH. EARLY IN THE CYCLE THE FRONT IS TO TRIGGER LIGHT TO
MODERATE CONVECTION OVER CENTRAL ARGENTINA WITH ACCUMULATION OF
15-20MM ON TUESDAY-WEDNESDAY. ON WEDNESDAY TO THURSDAY THIS
INCREASES TO 10-15MM. OTHER CONVECTION TO THE NORTH IS TO AFFECT
RIO GRANDE DO SUL IN BRASIL-CORRIENTES/MISIONES IN
ARGENTINA...WITH RAINFALL AMOUNTS OF 05-10MM ON FRIDAY TO
SATURDAY. ON SATURDAY TO SUNDAY EXPECTING AN INCREASE IN ACTIVITY
ACROSS URUGUAY-ENTRE RIOS IN ARGENTINA...WITH MAXIMA OF 25-50MM IN
POTENTIALLY SEVERE CONVECTION. OVER NORTHWEST
ARGENTINA...MEANWHILE... THE MAXIMA PEAKS AT 15-20MM.

THE NEXT MID LEVEL PERTURBATION ENTERS SOUTHERN CHILE EARLY ON
FRIDAY MORNING. BUILDING RIDGE TO THE WEST IS TO THEN INDUCE THE
NORTHWARD AMPLIFICATION OF THIS TROUGH ACROSS PATAGONIA IN
ARGENTINA TO LA PAMPA/SOUTHERN BUENOS AIRES PROVINCE ON FRIDAY. AS
IT SPILLS ACROSS THE ANDES TO CENTRAL PROVINCES IN ARGENTINA THIS
WILL SUSTAIN SURFACE CYCLOGENESIS. ON FRIDAY TO SATURDAY THE
TROUGH MOVES ACROSS THE SOUTHERN CONE TO CENTRAL ARGENTINA...WHILE
LATER ON MONDAY IT WILL EXTEND ALONG 60W TO ENTRE RIOS IN
ARGENTINA. AS IT AMPLIFIES TO MID SECTION OF ARGENTINA THIS TROUGH
IS TO TRIGGER MODERATE TO HEAVY CONVECTION...WITH POTENTIAL FOR
SEVERE THUNDERSTORMS. AT LOW LEVELS THIS IS TO SUSTAIN AN
ELONGATED FRONT ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA.
THIS MOVES NORTH TO THE MESOPOTAMIA VALLEY IN ARGENTINA LATER ON
FRIDAY/EARLY SATURDAY MORNING. OVER SOUTHERN CHILE THIS IS TO
FAVOR MODERATE RAINFALL AMOUNTS...WITH MAXIMA OF 05-10MM/DAY.
THROUGH FRIDAY THIS INCREASES TO 10-15MM/DAY...WHILE ON SATURDAY
THE MAXIMA PEAKS AT 15-20MM. OVER CENTRAL ARGENTINA THE  MAXIMA ON
SATURDAY WILL PEAK AT 15-20MM/DAY...WITH HIGHER AMOUNTS TO THE
NORTH AS THE MID/UPPER LEVEL TROUGH INTERACTS WITH A SURFACE FRONT
OVER SOUTHERN BRASIL-NORTHERN ARGENTINA.

AT 200 HPA...AN ILL ORGANIZED CELL OF THE SUBTROPICAL RIDGE
CONFINES TO CONTINENTAL AREA TO THE NORTH OF 12S/14S. THROUGH
THURSDAY THIS CELL OF THE SUBTROPICAL RIDGE IS TO BECOME BETTER
ORGANIZED WHILE CENTERING ON A CLOSED HIGH OVER NORTHERN BOLIVIA.
THIS...IN-TURN...WILL SUSTAIN THE NORTHWARD AMPLIFICATION OF A
TROUGH ACROSS THE SOUTHEAST STATES OF BRASIL. THE TROUGH REACHES
MAXIMUM AMPLITUDE LATER DURING THE WEEKEND. EARLY IN THE CYCLE
SCATTERED DEEP CONVECTION IS TO CLUSTER ALONG THE SOUTH ATLANTIC
CONVERGENCE ZONE...AS IT EXTENDS FROM ESPIRITO SANTO/MINAS GERAIS
TO RONDONIA/SOUTHERN AMAZONAS IN BRASIL. THE SACZ IS TO WEAKEN TO
AN OPEN TROUGH LATER ON TUESDAY...TO THEN REMAIN ILL ORGANIZED
WHILE CONFINING TO MATO GROSSO-RONDONIA. EARLY IN THE CYCLE
MODERATE TO HEAVY CONVECTION IS TO BUILD FROM BAHIA/MINAS GERAIS
IN BRASIL TO PARA...WITH MAXIMA OF 40-80MM. AS THE UPPER PATTERN
EVOLVES...AND THE SACZ WEAKENS TO AN OPEN TROUGH...MOST ACTIVE IS
TO CLUSTERS ACROSS BAHIA-TOCANTINS AND GOIAS...WITH MAXIMA IN THIS
AREA PEAKING AT 35-70MM/DAY. ON SATURDAY THIS DECREASES TO
30-60MM...WHILE ON SUNDAY A MAXIMA OF 40-80MM IS TO CLUSTER OVER
EASTERN PARA-GOIAS IN BRASIL. ON THE NORTHERN JUNGLE OF PERU TO
EASTERN ECUADOR THE DAILY MAXIMA WILL PEAK AT 15-20MM IN DIURNAL
CONVECTION.

OVIEDO...SHN (ARGENTINA)
POMIER...SENAMHI (BOLIVIA)
RIVAS...SENAMHI (PERU)
DAVISON/GALVEZ...WPC (USA)
$$





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