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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1620Z Jul 10, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1220 PM EDT THU JUL 10 2014

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

LAST NO AMENDS...NEXT BULLETIN ON MONDAY JULY 14.

MODEL DISCUSSION (VALID FROM 10 JULY 00UTC): GLOBAL MODELS NOW
TRENDING TOWARDS A DEEPER MID/UPPER LEVEL TROUGH PATTERN TO
DEVELOP DURING THE MEDIUM RANGE PERIOD. THIS IS TO FOCUS A LOT OF
ENERGY AND MOISTURE ACROSS CHILE WHERE IT IS TO TRIGGER ORGANIZED
CONVECTION. LATER ON DAY 05...AS IT SPILLS ACROSS THE ANDES...IT
WILL SUSTAIN POTENTIALLY SEVERE CONVECTION ACROSS THE BUENOS AIRES
PROVINCE IN ARGENTINA.

A BROAD/MID UPPER LEVEL TROUGH DOMINATES FLOW OVER THE WESTERN
SOUTH ATLANTIC. THROUGH 24 HRS TROUGH IS TO MOVE ACROSS
30W...NEARING 10W BY 48 HRS. BUT AS IT PULLS AWAY ANOTHER TROUGH
IS TO DEEPEN TO THE WEST...WITH AXIS TO AMPLIFY ACROSS THE SOUTH
GEORGIA ISLANDS THROUGH 48 HRS...AND BY 72-96 HRS IT IS TO EVOLVE
INTO A DEEP TROUGH BETWEEN 40W-10W AND TO THE SOUTH OF 25S. AT LOW
LEVELS THIS SI TO SUSTAIN AN ELONGATED FRONT ACROSS THE SOUTH
ATLANTIC TO RIO DE JANEIRO/SAO PAULO IN BRASIL. THIS FRONT...AND A
BROAD RIDGE TO THE SOUTH...WILL ENHANCE MOISTURE CONVERGENCE ALONG
THE COAST OF BRASIL. EARLY IN THE CYCLE MOST ACTIVE IS EXPECTED
OVER NORTHERN SAO PAULO-SOUTHERN ESPIRITO SANTO WITH ACCUMULATION
OF 15-20MM...WHILE OVER RIO GRANDE DO SUL-PARANA EXPECTING
ACCUMULATION OF 05-10MM. THROUGH 72-84 HRS CONVECTION OVER
SOUTHERN BRASIL IS TO WEAKEN.

OVER THE EASTERN PACIFIC...A SHORT WAVE TROUGH ON THE NORTHERN
STREAM REMAINS OFF THE COAST OF CHILE. THE TROUGH IS TO REMAIN
NEARLY STATIONARY THROUGH 18-24 HRS...THEN STARTS TO MIGRATE EAST
AS THE NEXT MID LEVEL PERTURBATION APPROACHES FROM THE WEST. AS IT
PULLS AWAY...THE ASSOCIATED CLOSED LOW IS TO WEAKEN TO AN OPEN
TROUGH BY 36-42 HRS. THE TROUGH IS FORECAST TO ENTER
SOUTHERN-CENTRAL CHILE BY 48-54 HRS...AND ACROSS LA PAMPA/CENTRAL
ARGENTINA BY 72 HRS. THIS SUSTAINS A SURFACE TROUGH/FRONT OVER THE
EASTERN PACIFIC THAT IS TO SLOWLY MOVE INTO SOUTHERN CHILE THROUGH
24-36 HRS...AND PATAGONIA IN ARGENTINA BY 48 HRS. THROUGH 72-84
HRS THE FRONT MEANDERS ACROSS LA PAMPA/CENTRAL PROVINCES IN
ARGENTINA. ACROSS SOUTHERN CHILE...TIGHTENING PRESSURE GRADIENT
WILL RESULT IN STRONG WINDS ON DAYS 01-02...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 72-84 HRS. AS IT
SPREADS TO SOUTHERN BRASIL THIS WILL DECREASE TO 10-15MM.

THE GLOBAL MODELS THEN FORECAST A HIGH AMPLITUDE MID/UPPER LEVEL
TROUGH TO DEVELOP ACROSS THE EASTERN PACIFIC BETWEEN 110W-70W TO
20S THROUGH 72 HRS. AS THE TROUGH AMPLIFIES...IT IS TO FOCUS ITS
SHORT WAVE ENERGY ACROSS SOUTHERN-CENTRAL CHILE TO
ARGENTINA...WHERE IT IS TO FAVOR HEIGHT FALLS OF 75-125GPM. THIS
QUICKLY EXPANDS ACROSS LA PAMPA TO THE BUENOS AIRES PROVINCE
THROUGH 120-132 HRS. THE HIGH AMPLITUDE LONG WAVE TROUGH IS TO
SUSTAIN A STRONG BAROCLINIC BOUNDARY ACROSS SOUTHERN CHILE LATER
ON DAY 03...MOVING EAST ACROSS PATAGONIA-LA PAMPA IN ARGENTINA TO
CENTRAL CHILE ON DAY 04. THROUGH DAY 06 IT WILL MOVE ACROSS RIO DE
LA PLATA BASIN/URUGUAY TO SOUTHERN BRASIL-NORTHERN PROVINCES IN
ARGENTINA. AS IT MOVES TOWARDS THE CONTINENT...THE DEEP TROUGH 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 03-04...WHILE OVER CENTRAL CHILE THIS
IS TO INCREASE TO 25-50MM ON DAY 04. UNDER FAVORABLE JET DYNAMICS
HIGHER RAINFALL AMOUNTS ARE HIGHLY LIKELY. OVER ARGENTINA...A
STRONG NORTHERLY LOW LEVEL JET IS TO ESTABLISH LATER ON DAY 03.
THIS IS TO SUSTAIN A WARM/MOIST ADVECTIVE PATTERN...RESULTING IN
PRECIPITABLE WATER CONTENT OF 40-50MM AND LOW LEVEL DEW POINT
TEMPERATURES OF 18-20C ACROSS CENTRAL-NORTHERN ARGENTINA. THIS
WILL COMBINE WITH INFLOW OF MID LEVEL ENERGY TO TRIGGER MODERATE
TO HEAVY CONVECTION...WITH MAXIMA OF 25-50MM IN POTENTIALLY SEVERE
CONVECTION.

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
PERSISTS. 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 01 AND AGAIN ON DAY 04. TRADE WIND CONVERGENCE ACROSS ESPIRITO
SANTO AND BAHIA IS TO FAVOR SCATTERED COASTAL CONVECTION WITH
ACCUMULATION OF 05-10MM/DAY.

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