THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


SOUTH AMERICAN MODEL DISCUSSION




SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1219 PM EDT MON APR 24 2017

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

MODEL DISCUSSION (VALID FROM APRIL 24 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH THROUGH 96-108 HRS. MODELS THEN DISAGREE ON
HOW SYSTEM ENTERING THE SOUTHERN CONE IS GOING TO EVOLVE. DUE TO
THE HIGH VARIABILITY AMONG THE GLOBAL ENSEMBLE MEMBERS...THE
CONFIDENCE IN THE FORECAST IS LOW BEYOND 108 HRS.

THE GLOBAL MODELS AGREE ON RISK OF EXPLOSIVE CYCLOGENESIS OVER THE
WESTERN SOUTH ATLANTIC DURING THE SHORT RANGE PERIOD...WITH
DEEPENING TROUGH TO PULL ACROSS THE SOUTHERN CONE TO THE WESTERN
ATLANTIC ON TUESDAY. UNDER COUPLED JETS ALOFT...THE TROUGH IS TO
THEN EXPERIENCE A RAPID RATE OF INTENSIFICATION...WITH ASSOCIATED
SURFACE LOW DEEPENING FROM A 1002 HPA LOW ON TUESDAY EVENING TO A
962 HPA LOW ON WEDNESDAY EVENING. THIS WILL COMBINE WITH BUILDING
POLAR RIDGE OVER ARGENTINA AND A PAMPERO LOW LEVEL JET TO SUSTAIN
A PROGRESSIVE FRONT THAT SURGES ACROSS LA PAMPA-CENTRAL ARGENTINA
LATER TODAY. ON TUESDAY THE FRONT MOVES FARTHER NORTH ACROSS THE
CONTINENT...REACHING THE SOUTHERN STATES OF BRASIL-MID SECTIONS OF
SOUTH AMERICA. THE FRONTAL SYSTEM WILL THEN SLOW DOWN AS IT MOVES
ACROSS SAO PAULO-MATO GROSSO IN BRASIL TO BOLIVIA ON WEDNESDAY TO
THURSDAY. THE SURGING FRONT WILL TRIGGER SCATTERED DEEP CONVECTION
AS IT SURGES ACROSS THE CENTRAL PROVINCES IN ARGENTINA LATER
TODAY... WITH ACCUMULATION OF 20-40MM. OVER
PARAGUAY-CORRIENTES/MISIONES-CHACO IN ARGENTINA THIS IS LIKELY TO
TRIGGER AN MCS...WITH RAINFALL MAXIMA OF 40-80MM. UNDER INFLUENCE
OF LOW LEVEL JET...CONVECTION WILL RAPIDLY SPREAD ACROSS
BOLIVIA/ACRE-RONDONIA IN BRASIL TO SOUTHERN/CENTRAL JUNGLE OF
PERU...WHERE IT IS TO FAVOR SIMILAR RAINFALL AMOUNTS ON
WEDNESDAY-THURSDAY.

NEXT MID/UPPER LEVEL TROUGH IS TO PULL ACROSS THE SOUTH PACIFIC ON
WEDNESDAY TO THURSDAY. ALTHOUGH THE MODELS INITIALLY AGREE ON ITS
EVOLUTION DURING THE SHORT RANGE PERIOD...LATER ON THEY DISAGREE
ON HOW IT IS GOING TO EVOLVE. BOTH EUROPEAN MODELS FORECAST THE
TROUGH TO DAMPEN AS IT PRESSES AGAINST A LONG WAVE RIDGE OVER THE
SOUTHERN CONE. THE GFS...IN CONTRAST...FORECASTS THE TROUGH TO
REMAIN WELL ORGANIZED AS IT ENTERS SOUTHERN CHILE ON FRIDAY. AS
SUGGESTED BY THE GLOBAL ENSEMBLE MEMBERS...THIS IS LIKELY TO BE
WEAKER THAN WHAT THE GFS IS FORECASTING...BUT STRONGER THAN WHAT
THE EUROPEAN MODELS SUGGEST. AT LOW LEVELS IT IS TO SUSTAIN A
BROAD POLAR TROUGH OVER THE SOUTHEAST PACIFIC LATER ON FRIDAY.
THIS WILL SUSTAIN AN ELONGATED FRONT THAT MOVES ACROSS THE
SOUTHERN CONE LATER IN THE WEEK. AS IT APPROACHES THE CONTINENT
THE TROUGH WILL SUSTAIN A SUBTROPICAL CONNECTION. IF THIS
REMAINS...AS SOME OF THE MODELS SUGGEST...MODERATE TO HEAVY
RAINFALL AMOUNTS ARE PROBABLE OVER SOUTHERN CHILE LATER IN THE
WEEK.

NORTHERN SOUTH AMERICA...MEANWHILE...WILL REMAIN UNDER THE
INFLUENCE OF A CELL OF THE SUBTROPICAL RIDGE...WITH AXIS AT 200
HPA TO ENVELOP CONTINENTAL AREA TO THE NORTH OF 20S. A HIGH OVER
AMAZONAS IN BRASIL IS TO ANCHOR THIS RIDGE DURING THE NEXT FEW
DAYS. RIDGE ALOFT WILL VENT DIURNAL CONVECTION OVER THE
CONTINENT...WITH MOST ACTIVE TO THE NORTH OF 10S. ACROSS
EQUATORIAL SOUTH AMERICA THE DAILY MAXIMA IS TO RANGE BETWEEN
20-35MM...AS CONVECTION CLUSTERS ALONG THE NEAR EQUATORIAL TROUGH.
ON THE PERUVIAN JUNGLE DAILY MAXIMA WILL PEAK AT
15-20MM...INCREASING ON THURSDAY TO 35-70MM AS POLAR FRONT SURGES
ACROSS MID SECTIONS OF SOUTH AMERICA (SEE ABOVE). OVER EASTERN
ECUADOR/NORTHERN PERU...INITIALLY EXPECTING MAXIMA OF
20-45MM...DECREASING TO 20-35MM/DAY ON WEDNESDAY-THURSDAY. LOW
LEVEL WESTERLIES OVER THE EASTERN PACIFIC ARE TO FAVOR HIGHER
AMOUNTS OVER WESTERN ECUADOR...WITH MAXIMA O 35-70MM ON MONDAY TO
TUESDAY. ON TUESDAY-WEDNESDAY THE WINDS SHIFT TO THE
NORTH-NORTHEAST...AND RAINFALL AMOUNTS ARE TO PEAK AT 20-40MM.

ABDEMUR...FAA (ARGENTINA)
ESPINOLA...DNM (PARAGUAY)
DAVISON...WPC (USA)




Last Updated: 1219 PM EDT MON APR 24 2017