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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1614Z Sep 09, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 PM EDT TUE SEP 09 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 09 AT 00UTC): EXCEPT FOR
MINOR CORRECTIONS TO SHORT RANGE PERTURBATIONS ENTERING THE SOUTH
AMERICAN DOMAIN...THE GLOBAL MODELS MAINTAIN CONTINUITY WITH
PREVIOUS RUN. OUR CONFIDENCE IN THE FORECAST IS HIGH.

AT MID LEVELS...A BROAD TROUGH ENTERED THE SOUTHERN CONE. THIS IS
FORECAST TO QUICKLY PULL ACROSS ARGENTINA TO THE WESTERN ATLANTIC
EARLY IN THE CYCLE. AS IT MIGRATES ACROSS ARGENTINA...THIS IS TO
TRIGGER HEIGHTS FALLS OF 75-125GPM ACROSS CENTRAL ARGENTINA/RIO DE
LA PLATA BASIN. AS IT EMERGES TO THE EAST...A DEEP CLOSED LOW IS
TO FORM TO THE EAST-NORTHEAST OF THE MALVINAS/FALKLAND ISLANDS.
THIS IS TO THEN EVOLVE INTO A BROAD TROUGH OVER THE WESTERN
ATLANTIC...TO DOMINATE AREA BETWEEN 65W-25W AND TO THE SOUTH OF
25S BY 48-60 HRS. THIS TROUGH IS TO SLOWLY WEAKEN AS IT PULLS TO
THE EAST-SOUTHEAST LATER IN THE CYCLE. AT LOW LEVELS...THE
ASSOCIATED FRONT EXTENDS ACROSS RIO DE LA PLATA BASIN-CUYO IN
ARGENTINA. A BUILDING POLAR RIDGE TO THE SOUTH IS TO SUSTAIN A
PAMPERO JET THAT DISPLACES THE FRONT NORTH ACROSS URUGUAY TO
NORTHERN ARGENTINA BY 24 HRS. AS THE FRONT SURGES NORTH...IT IS TO
SUSTAIN A PREFRONTAL SQUALL LINE OVER URUGUAY-ENTRE
RIOS/CORRIENTES IN ARGENTINA. BY 48 HRS THE FRONT IS TO THEN STALL
OVER RIO GRANDE DO SUL IN BRASIL-NORTHERN PROVINCES IN
ARGENTINA/PARAGUAY...WHERE IT IS TO REMAIN NEARLY STATIONARY
THROUGH 96-108 HRS. AS THE FRONT SURGES ACROSS ARGENTINA IT IS TO
TRIGGER ORGANIZED CONVECTION...WITH GLOBAL AND ENSEMBLE MODELS
AGREEING ON A HIGH RISK OF HEAVY RAINS AND POTENTIAL FOR SEVERE
CONVECTION OVER URUGUAY-ENTRE RIOS/CORRIENTES IN ARGENTINA. UNDER
FAVORABLE JET DYNAMICS EXPECTING RAINFALL MAXIMA TO PEAK AT
75-125MM BY 36 HRS...WITH FORECASTED HELICITY VALUES OF 300-350
SUGGESTING POSSIBLE SUPER CELL DEVELOPMENT. THROUGH 36-60 HRS THE
MAXIMA DECREASES TO 20-30MM...AND BY 60-96 HRS EXPECTING DAILY
MAXIMA OF 10-15MM OVER SOUTHERN BRASIL/MISIONES-CORRIENTES IN
ARGENTINA.

MODELS THEN FORECAST A SHORT WAVE TROUGH ON THE NORTHERN STREAM TO
LIFT ACROSS 45S 90W EARLY THIS CYCLE. A BUILDING RIDGE TO THE WEST
DISPLACES THIS CENTER NORTH TO 34S 89W BY 48 HRS...NEARING 28S 80W
BY 120 HRS. THE FORECAST TRACK IS A FEW DEGREES TO THE RIGHT
(EAST) OF PREVIOUS PROJECTION...WITH GFS SHOWING THE LOW MAKING
LANDFALL A DAY SOONER THAN PREVIOUSLY INDICATED. INFLOW OF SHORT
WAVE ENERGY IS TO THEN TRIGGER SCATTERED SHOWERS ACROSS CENTRAL
PORTIONS OF CHILE...WITH MOST ACTIVE CONVECTION EXPECTED ACROSS
THE ANDES...WHERE WE EXPECT SNOWFALL AMOUNTS OF 05-10CM. THE MID
LEVEL TROUGH IS TO THEN MOVE ACROSS THE CENTRAL ANDES OF CHILE
INTO ARGENTINA BY 120-132 HRS...MEANWHILE TRIGGERING HEIGHT FALLS
OF 75-100GPM. THIS IS TO THEN FAVOR CYCLOGENESIS OVER RIO DE LA
PLATA BASIN...WITH SURFACE LOW TO RAPIDLY DEEPEN AS IT MOVES OFF
THE COAST BY 132-144 HRS. UNDER FAVORABLE JET
DYNAMICS...ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE AND CONDUCIVE
TO SEVERE CONVECTION...WITH RAINFALL MAXIMA OF 40-80MM.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE
CONTINUES TO EVOLVE...WITH CLOSED ANTICYCLONIC CIRCULATION
DEVELOPING TO THE SOUTH-SOUTHEAST OF THE GALAPAGOS ISLANDS EARLY
IN THE CYCLE. RIDGE PATTERN IS TO THEN WEAKEN OVER THE CONTINENT.
A TROUGH TO THE EAST IS TO ALSO WEAKEN...WITH AXIS TO MEANDER
INLAND ACROSS PARA-AMAZONAS-RORAIMA EARLY IN THE CYCLE. THIS IS TO
EVOLVE INTO AN EAST-TO-WEST UPPER TROUGH ACROSS BRASIL ALONG
12S/13S BY 72 HRS...AND A WEAK SHEAR AXIS LATER IN THE CYCLE.

IN THIS PATTERN...DIURNAL CONVECTION IS TO CLUSTER OVER NORTHWEST
BRASIL-SOUTHERN COLOMBIA-NORTHERN PERU...WITH MAXIMA IN THIS AREA
TO PEAK AT 15-20MM/DAY. AN INCREASE IN ACTIVITY IS EXPECTED BY MID
CYCLE AS A NORTHERN HEMISPHERE TROPICAL WAVE PULLS ACROSS
VENEZUELA TO COLOMBIA...WITH MAXIMA FORECAST TO INCREASE TO
15-30MM. OTHER ACTIVITY IS EXPECTED ACROSS ILHA DE MARAJO-AMAPA IN
BRASIL...WHERE UNDER INFLUENCE OF THE UPPER TROUGH SEA BREEZE
CONVERGENCE IS TO RESULT IN RAINFALL AMOUNTS OF 05-10MM.
FURTHERMORE...TRADE WIND CONVERGENCE ACROSS NORTHEAST BRASIL IS TO
SUSTAIN SCATTERED SHOWERS BETWEEN EASTERN BAHIA AND RIO GRANDE DO
NORTE...WITH ACCUMULATION OF 05-10MM/DAY.

JALFIN...SMN (ARGENTINA)
CAROCA...DMC (CHILE)
DAVISON...WPC (USA)