THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


SOUTH AMERICAN MODEL DISCUSSION




SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1248 PM EST FRI FEB 23 2018

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

MODEL DISCUSSION (VALID FROM FEB 23 AT 0000 UTC): THE GFS AND
EUROPEAN MODELS FOLLOW SIMILAR PATTERN EVOLUTION OVER THE
CONTINENT-WESTERN ATLANTIC THROUGH TUESDAY EVENING. OVER THE
EASTERN SOUTH PACIFIC THEY AGREE THROUGH 108-120 HRS...THEN
DIVERGE ON HOW A SHORT WAVE TROUGH STREAMING TOWARDS THE DRAKE
PASSAGE/SOUTHERN CONE IS GOING TO EVOLVE. THE GFS FORESEES A
STRONGER/DEEPER PERTURBATION WHILE THE ECMWF FORECASTS A WEAKER
WAVE. THE DIFFERENCES AMONG THE DETERMINISTIC MODELS ARE ALSO
EVIDENT AMONG THE GLOBAL ENSEMBLE MEMBERS. AS A
RESULT...CONFIDENCE IN THE FORECAST BEYOND 108-120 HRS IS LOW.

CONSISTENT WITH PREVIOUS FORECAST...A MID/UPPER LEVEL SHORT WAVE
TROUGH MEANDERS OFF THE COAST OF URUGUAY/SOUTHERN BRASIL...WITH
AXIS TO DRIFT ACROSS 35W LATER THIS EVENING. THE SHORT WAVE TROUGH
IS TO THEN ACCELERATE AS IT MOVES TO THE EASTERN SOUTH ATLANTIC
LATER DURING THE WEEKEND/EARLY NEXT WEEK. AT LOW LEVELS...THESE
WILL COMBINE IN SUPPORT OF AN ELONGATED FRONT OVER THE SOUTH
ATLANTIC. THE FRONT IS TO EXTEND TO THE WEST-NORTHWEST TO RIO DE
JANEIRO IN EASTERN BRASIL. OVER THE CONTINENT...IT IS TO THEN
REFLECT AS AN OPEN TROUGH WITH AXIS WEST BETWEEN NORTHERN
BOLIVIA-SOUTHERN MINAS GERAIS. MOISTURE CONVERGES ALONG THE LOW
LEVEL FEATURE...FEEDING CONVECTIVE DEVELOPMENT ACROSS
BRASIL-BOLIVIA. ACROSS AMAZONAS-RONDONIA-MATO GROSSO TO ESPIRITO
SANTO/SOUTHERN MINAS GERAIS INITIALLY EXPECTING RAINFALL MAXIMA OF
35-70MM/DAY. THROUGH SUNDAY THIS DECREASES TO 25-50MM/DAY IN
SCATTERED CONVECTION. 

ANOTHER SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO FOLLOW. THE
MID LEVEL TROUGH SPILLS ACROSS THE CENTRAL ANDES OF CHILE TO CUYO
IN ARGENTINA LATER TODAY...AND ON SATURDAY IT MOVES OFF THE COAST
OF URUGUAY/SOUTHERN BRASIL. THIS IS TO EVOLVE INTO A CLOSED LOW
NEAR 40S 40W LATER ON SUNDAY...WHERE IT IS TO REMAIN THROUGH AT
LEAST TUESDAY MORNING. AS IT MEANDERS OFF THE COAST OF
URUGUAY/SOUTHERN BRASIL THIS WILL THEN PROVIDE SUPPORT TO THE
MEANDERING FRONT OFF THE COAST OF BRASIL WHILE ALSO ENHANCING
CONVECTION ACROSS NORTHERN SOUTH AMERICA. OVER ARGENTINA...THE
TROUGH SUSTAINS AN UNDULATING FRONT OVER THE BUENOS AIRES
PROVINCE-MENDOZA. EARLY IN THE CYCLE EXPECTING MODERATE TO HEAVY
CONVECTION WITH MAXIMA OF 25-50MM. BUT AS THE MID LEVEL TROUGH
MEANDERS AWAY ON SATURDAY IT WILL DECREASE TO 15-20MM/DAY ON
SATURDAY-MONDAY.

ON THE SOUTHERN STREAM FLOW...A BROAD MID LEVEL TROUGH IS TO
AMPLIFY BETWEEN 110W-80W TO 30S LATER TODAY...WITH AXIS TO FOCUS
ITS SHORT WAVE ENERGY ACROSS THE DRAKE PASSAGE-EXTREME SOUTHERN
PORTIONS OF CHILE. THE TROUGH IS TO SLOWLY PULL ACROSS THE
SOUTHERN CONE TO THE WESTERN ATLANTIC LATER ON MONDAY. BUT AS IT
PULLS ACROSS CHILE TO ARGENTINA IT IS TO SHEAR A SHORT WAVE
TROUGH. THE SHORT WAVE TROUGH IS TO THEN LIFT ALONG THE COAST TO
CENTRAL CHILE DURING THE DAY ON TUESDAY...TO THEN FOCUS SHORT WAVE
ENERGY ACROSS CUYO-CENTRAL PROVINCES IN ARGENTINA. AT LOW LEVELS
THE TROUGH ALOFT WILL SUSTAIN A BROAD TROUGH OVER THE
BELLINGSHAUSEN SEA-SOUTHEAST PACIFIC EARLY IN THE CYCLE...WHILE
THE ASSOCIATED FRONT MOVES OVER TIERRA DEL FUEGO/SOUTHERN
PATAGONIA ON SATURDAY. ON SUNDAY-MONDAY THIS IS TO MEANDER NORTH
ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA-CENTRAL REGIONS OF
CHILE. AS IT ENTERS SOUTHERN CHILE THIS IS TO TRIGGER LIGHT
CONVECTION ON SATURDAY WITH ACCUMULATION OF 10-15MM...DECREASING
TO 00-05MM/DAY ON SUNDAY TO MONDAY. DEEPER CONVECTION IS TO THEN
CLUSTER AHEAD OF THIS FRONT OVER NORTHERN PATAGONIA-LA PAMPA ON
MONDAY-TUESDAY...WHEN IT IS TO SUSTAIN RAINFALL AMOUNTS OF 10-15MM
IN SCATTERED DEEP CONVECTION. ON TUESDAY THIS INCREASES TO
20-30MM...WITH MOST INTENSE EXPECTED BETWEEN MENDOZA/SAN LUIS AND
NORTHERN NEUQUEN.

NORTH OF 30S...AT 200 HPA...BROAD CELL OF THE SUBTROPICAL RIDGE
WILL REMAIN THE DOMINANT FEATURE. THE RIDGE IS TO ANCHOR ON A
MEANDERING HIGH OVER MATO GROSSO IN BRASIL. THIS IS TO GENERALLY
HOLD DURING THE NEXT FEW DAYS...MEANWHILE FAVORING AN UPPER
DIVERGENT PATTERN THAT IS TO VENT DEEP CONVECTION ALONG THE NEAR
EQUATORIAL TROUGH. OVER NORTHERN BRASIL INITIALLY EXPECTING MAXIMA
OF 30-60MM. ON SATURDAY AND ONWARD THIS DECREASES TO
20-45MM/DAY...WITH MOST ACTIVE BETWEEN CEARA AND PARA. ACROSS
AMAZONAS TO THE WEST THE DAILY MAXIMA DECREASES TO 15-20MM/DAY.
OVER WESTERN ECUADOR...UNDER INFLUENCE OF THE PANAMANIAN TROUGH...
MODERATE CONVECTION IS EXPECTED OVER THE NEXT DAY OR SO TO TRIGGER
RAINFALL MAXIMA OF 20-30MM. THIS DECREASES TO 15-20MM/DAY ON
SATURDAY-MONDAY. ON THE SOUTHERN SIERRA OF PERU ALSO EXPECTING
MODERATE RAINFALL AMOUNTS...WITH ACCUMULATION OF 15-20MM/DAY.
HIGHER AMOUNTS... HOWEVER...ARE EXPECTED ON FRIDAY-SATURDAY WHEN
THE MAXIMA IS TO PEAK AT 20-30MM/DAY. LIKEWISE...OVER THE
ALTIPLANO OF BOLIVIA EXPECTING DAILY MAXIMA OF 15-20MM...WITH A
PEAK IN CONVECTION ON SATURDAY TO SUSTAIN ACCUMULATION OF
20-30MM/DAY. 

BALBINO...INMET (BRASIL)
POMIER...SENAMHI (BOLIVIA)
DAVISON...WPC (USA)




Last Updated: 1248 PM EST FRI FEB 23 2018