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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1632Z Jul 09, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1232 PM EDT WED JUL 09 2014

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

MODEL DISCUSSION (VALID FROM 09 JULY 00UTC): ACROSS THE
CONTINENT/SOUTH ATLANTIC THE GLOBAL MODELS CONTINUE TO AGREE ON
PATTERN EVOLUTION THROUGH DAY 06. OVER THE EASTERN PACIFIC...
MEANWHILE...THEY AGREE THROUGH 96-108 HRS...BUT THEN START TO
DIVERGE ON HOW AN AMPLIFYING TROUGH IS TO EVOLVE AS IT ENTERS THE
SOUTHERN CONE LATER IN THE CYCLE. ALTHOUGH MODELS TRENDING TOWARDS
A DEEPER/HIGHER AMPLITUDE TROUGH TO DEVELOP...THEY DIVERGE ON
PLACEMENT OF A CLOSED LOW ALONG THIS AXIS. THE HIGH VARIABILITY IS
ALSO EVIDENT AMONG THE GLOBAL ENSEMBLE MEMBERS...SO EXPECTING
FURTHER CORRECTIONS IN FUTURE RUNS.

OVER THE SOUTH ATLANTIC...A BROAD TROUGH IS TO EXTEND BETWEEN
55W-20W TO THE SOUTH OF 20S EARLY IN THE CYCLE. THROUGH 72 HRS THE
MID LEVEL TROUGH WILL PULL ACROSS 15W/20W AS ANOTHER AMPLIFIES TO
THE WEST ACROSS THE MALVINAS/SOUTH GEORGIA ISLANDS. THE LATTER IS
TO THEN AMPLIFY BETWEEN 40W-10W THROUGH 96-108 HRS...WITH HIGH
AMPLITUDE TROUGH PATTERN TO THEN PERSIST THROUGH 120 HRS. AT LOW
LEVELS THIS SUSTAINS A SURFACE FRONT ACROSS THE SOUTH ATLANTIC TO
SOUTHEAST BRASIL-MATO GROSSO DO SUL/NORTHERN BOLIVIA. UNDER
INFLUENCE OF A RIDGE TO THE SOUTH...FRONT WILL MEANDER NORTH
ACROSS SAO PAULO-RIO DE JANEIRO TO SOUTHERN ESPIRITO SANTO/MINAS
GERAIS BY 36-42 HRS...WHILE THE TRAILING END OVER BRASIL IS TO
GRADUALLY WEAKEN/DISSIPATE. EARLY IN THE CYCLE THIS IS TO FAVOR
SCATTERED CONVECTION ACROSS MATO GROSSO-SOUTHEAST BRASIL...WITH
ACCUMULATION OF 15-25MM IN SCATTERED CONVECTION. BY 36-72 HRS THE
MOST ACTIVE CONVECTION IS THEN EXPECTED ALONG THE COAST BETWEEN
ESPIRITO SANTO AND SAO PAULO...WITH ACCUMULATION OF 15-20MM IN
SCATTERED CONVECTION. THROUGH 72-84 HRS THIS SI TO DECREASE TO
05-10MM/DAY.

OVER THE EASTERN PACIFIC...A SHORT WAVE TROUGH ON THE NORTHERN
STREAM MEANDERS OFF THE COAST OF CHILE WHILE ANCHORING AT 500 HPA
ON A CLOSED LOW NEAR 43S 95W. THE TROUGH IS TO REMAIN NEARLY
STATIONARY THROUGH 36-42 HRS...THEN STARTS TO MIGRATE EAST AS THE
NEXT MID LEVEL PERTURBATION APPROACHES FROM THE WEST. THROUGH
54-60 HRS THE CLOSED LOW WEAKENS TO AN OPEN TROUGH...FORECAST TO
ENTER SOUTHERN-CENTRAL CHILE BY 72-78 HRS...AND ACROSS LA
PAMPA/CENTRAL ARGENTINA BY 96 HRS. THIS SUSTAINS A SURFACE
TROUGH/FRONT OVER THE EASTERN PACIFIC THAT IS TO SLOWLY MOVE INTO
SOUTHERN CHILE THROUGH 42-48 HRS...AND PATAGONIA IN ARGENTINA BY
72 HRS. THROUGH 96-108 HRS THE FRONT MEANDERS ACROSS LA
PAMPA/CENTRAL PROVINCES IN ARGENTINA. ACROSS SOUTHERN
CHILE...TIGHTENING PRESSURE GRADIENT WILL RESULT IN STRONG WINDS
ON DAYS 02-03...AND SCATTERED RAIN SHOWERS WITH ACCUMULATION OF
05-10MM. ACROSS ARGENTINA IT IS TO TRIGGER PREFRONTAL CONVECTION
ACROSS THE BUENOS AIRES PROVINCE-ENTRE RIOS THAT QUICKLY BUILD
EAST ACROSS URUGUAY...WHERE IT WILL SUSTAIN RAINFALL AMOUNTS OF
20-40MM BY 96-108 HRS.

MODELS THEN FORECAST A HIGH AMPLITUDE MID/UPPER LEVEL TROUGH TO
DEVELOP ACROSS THE EASTERN PACIFIC BETWEEN 110W-70W TO 20S.
AMPLIFYING TROUGH IS TO FOCUS ITS SHORT WAVE ENERGY ACROSS
SOUTHERN-CENTRAL CHILE TO ARGENTINA...WHERE IT IS TO FAVOR HEIGHT
FALLS OF 75-125GPM. THE HIGH AMPLITUDE LONG WAVE TROUGH IS TO
SUSTAIN A STRONG BAROCLINIC BOUNDARY ACROSS SOUTHERN CHILE LATER
ON DAY 04...MOVING EAST ACROSS PATAGONIA-LA PAMPA IN ARGENTINA TO
CENTRAL CHILE ON DAY 05. AS IT MOVES TOWARDS THE CONTINENT THIS IS
TO SUSTAIN A SUBTROPICAL CONNECTION...AND IT IS LIKELY TO TRIGGER
ORGANIZED CONVECTION. ACROSS SOUTHERN CHILE WE EXPECT RAINFALL
AMOUNTS OF 10-15MM ON DAYS 04-05...WHILE OVER CENTRAL CHILE THIS
IS TO INCREASE TO 20-40MM ON DAY 05. UNDER FAVORABLE JET DYNAMICS
HIGHER RAINFALL AMOUNTS ARE HIGHLY LIKELY.

NORTH OVER THE CONTINENT...AT 200 HPA...ILL ORGANIZED CELL OF THE
SUBEQUATORIAL RIDGE WILL CONFINE TO CONTINENTAL AREA TO THE NORTH
OF 00N. SOUTH OF THE EQUATOR...A NEAR ZONAL WESTERLY FLOW IS TO
DOMINATE FLOW ACROSS TROPICAL SOUTH AMERICA. IN THIS
PATTERN...DIURNAL CONVECTION IS TO GENERALLY LIMIT TO EQUATORIAL
SOUTH AMERICA WITH RAINFALL AMOUNTS OF 10-15MM/DAY. HIGHER
AMOUNTS...HOWEVER...ARE EXPECTED ACROSS AMAPA/AMAZON RIVER DELTA
REGION AS ENHANCE BY SEA BREEZE CONVERGENCE...WITH RAINFALL MAXIMA
OF 15-20MM. OTHER ACTIVITY IS TO CONVERGE ON THE NORTHEAST STATES
OF BRASIL DUE TO TRADE WIND EASTERLY CONVERGENCE AND THE
OCCASIONAL TROPICAL WAVE. IN THIS AREA MAXIMA IS TO PEAK AT
20-35MM...WITH MOST ACTIVE EXPECTED ON DAY 02 AND AGAIN ON DAY 05.

FERNANDES...INMET (BRASIL)
JALFIN...SMN (ARGENTINA)
DAVISON...WPC (USA)