THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


SOUTH AMERICAN MODEL DISCUSSION




SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1213 PM EDT MON AUG 13 2018

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

MODEL DISCUSSION (VALID FROM AUG 13 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH THROUGH 120-132 HRS...WITH MODELS GENERALLY
AGREEING ON LONG WAVE PATTERN EVOLUTION OVER THE SOUTH AMERICAN
DOMAIN.

AT 500 HPA...A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO
MEANDER OFF THE SOUTHEAST COAST OF BRASIL WHILE CENTERING ON A
CLOSED LOW NEAR 20S 30W. AS IT MEANDERS EAST ACROSS 20W ON
WEDNESDAY THIS IS TO WEAKEN TO AN OPEN TROUGH...TO GRADUALLY
DISSIPATE LATER IN THE WEEK. AT LOW LEVELS THIS SUSTAINS A SURFACE
FRONT THAT TRAILS TO THE NORTHWEST TO EASTERN BAHIA IN BRASIL.
OVER THE NEXT COUPLE OF DAYS THIS IS TO ENHANCE COASTAL
CONVERGENCE TO FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY.

A PROGRESSIVE MID LEVEL TROUGH FOLLOWS...WITH AXIS TO PULL ACROSS
SOUTHERN/CENTRAL CHILE TO ARGENTINA LATER TROUGH. AT IT MEANDERS
ACROSS 50W EARLY ON TUESDAY THIS IS TO EVOLVE INTO A DEEP CLOSED
LOW TO THE EAST-SOUTHEAST OF URUGUAY. THIS IS TO THEN SLOWLY MOVE
ACROSS 25W/30W LATER ON THURSDAY. AT LOW LEVELS...THE TROUGH WILL
INTERACT WITH A FRONT OVER URUGUAY/NORTHERN ARGENTINA...TO INDUCE
CYCLOGENESIS OVER RIO DE LA PLATA BASIN EARLY IN THE CYCLE. DURING
THE DAY ON TUESDAY THE LOW IS FORECAST TO OCCLUDE WHILE
INTENSIFYING TO A 1000-1004 HPA LOW OFF THE COAST OF URUGUAY.
THIS...IN-TURN...WILL FAVOR A SOUTHERLY FLOW ACROSS
CENTRAL/NORTHERN ARGENTINA THAT IS TO DRIVE THE FRONT NORTH ACROSS
SOUTHERN BRASIL-PARAGUAY LATER ON TUESDAY. THE FRONT IS TO THEN
REMAIN NEARLY STATIONARY OVER MID SECTIONS OF SOUTH AMERICA WHILE
GRADUALLY WEAKENING ON WEDNESDAY TO THURSDAY. EARLY IN THE CYCLE
EXPECTING ISOLATED TO SCATTERED CONVECTION ACROSS URUGUAY-NORTHERN
ARGENTINA TO SUSTAIN MAXIMA OF 15-20MM. AS IT SURGES ACROSS
PARAGUAY TO SOUTHEAST BOLIVIA THIS DECREASES TO 10-15MM ON
TUESDAY...WHILE ACROSS THE BOLIVIAN JUNGLE THE MAXIMA ALONG THIS
BOUNDARY IS TO PEAK AT 20-40MM. ON WEDNESDAY-THURSDAY THIS
DECREASES TO 05-10MM/DAY...WITH MOST ACTIVE ON THE HIGH JUNGLE IN
SOUTHERN PERU-NORTHWEST BOLIVIA.

DEEPENING TROUGH ON THE SOUTHERN STREAM IS TO THEN DOMINATE THE
MESO-SYNOPTIC FLOW OVER THE EASTERN PACIFIC/SOUTHERN CONE OF SOUTH
AMERICA ON WEDNESDAY. THIS EVOLVES INTO A HIGH AMPLITUDE TROUGH
BETWEEN 110W-60W...WITH AXIS BOTTOMING OUT JUST SOUTH OF 25S. THIS
IS TO THEN FOCUS SHORT WAVE ENERGY AND SUBTROPICAL MOISTURE ACROSS
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. AT LOW LEVELS THE HIGH
AMPLITUDE TROUGH WILL SUSTAIN A PROGRESSIVE FRONT OVER SOUTHERN
CHILE LATER ON TUESDAY. FRONT IS TO THEN MEANDER EAST AND NORTH
ACROSS PATAGONIA IN ARGENTINA/SOUTHERN REGIONS OF CHILE. AS IT
ENTERS SOUTHERN CHILE ON TUESDAY-WEDNESDAY THIS IS TO SUSTAIN
MODERATE RAINFALL AMOUNTS...WITH MAXIMA OF 20-30MM/DAY. THROUGH
THURSDAY THIS DECREASES TO 15-20MM/DAY. OVER TIERRA DEL FUEGO/
EXTREME SOUTHERN PORTIONS OF CHILE THE DAILY MAXIMA WILL PEAK AT
05-10MM. ON THURSDAY THE ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE
FOR LIGHT SNOWFALL AMOUNTS TO RESULT IN ACCUMULATION OF 03-05CM.

NORTH OVER THE CONTINENT...AT 200 HPA...AN ILL ORGANIZED CELL OF
THE SUBTROPICAL RIDGE CONFINES TO EQUATORIAL SOUTH AMERICA.
THROUGH WEDNESDAY MORNING THE RIDGE IS TO BECOME BETTER ORGANIZED
WHILE BUILDING SOUTH ACROSS BRASIL TO NORTHERN BOLIVIA. AS THE
RIDGE BUILDS...THE CONVECTIVE ACTIVITY ACROSS NORTHWEST SOUTH
AMERICA IS TO INTENSIFY. IN THIS AREA INITIALLY EXPECTING
ACCUMULATION OF 15-20MM. ON WEDNESDAY THIS INCREASES TO 20-40MM
WHILE BUILDING NORTH ACROSS CENTRAL/NORTHERN PERU TO SOUTHERN
COLOMBIA. THROUGH THURSDAY THIS DECREASES TO 15-20MM/DAY.

SANCHEZ...SMN (ARGENTINA)
SALAZAR...SENAMHI (BOLIVIA)
DAVISON...WPC (USA)





Last Updated: 1213 PM EDT MON AUG 13 2018