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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1642Z Sep 24, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 PM EDT WED SEP 24 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 24 AT 00UTC): THE MODELS
AGREE ON GENERAL SYNOPTIC SCALE PATTERN EVOLUTION THROUGH 84-96
HRS. THEY THEN DEVELOP PATTERN DIFFERENCES AS SHORT WAVE
PERTURBATIONS MOVING ACROSS THE EASTERN PACIFIC ENTER THE
CONTINENT. ALTHOUGH DIFFERENCES ARE NOT AS PRONOUNCED AS THEY WERE
ON PREVIOUS RUNS...THEY ARE SIGNIFICANT ENOUGH TO SUGGEST
LIKELIHOOD OF ADDITIONAL CORRECTIONS IN FUTURE RUNS.

SOUTH OVER THE CONTINENT...AT 500 HPA...A TROUGH EXTENDS FROM THE
ANTARCTIC PENINSULA TO SOUTHERN CHILE/ARGENTINA. THROUGH 48 HRS
THE TROUGH IS TO PULL ACROSS THE SOUTHERN CONE TO THE WEDDELL SEA/
SOUTHWEST ATLANTIC. THIS IS TO THEN EVOLVE INTO A BROAD/HIGH
AMPLITUDE TROUGH WHILE GRADUALLY EXPANDING EAST TO ENVELOP THE
ATLANTIC BASIN TO THE SOUTH OF 30S BY 108-120 HRS. SIMILAR PATTERN
IS EXPECTED AT LOW LEVELS OF THE ATMOSPHERE. UNDER INFLUENCE OF A
RIDGE TO THE WEST...PROGRESSIVE FRONTS AND ASSOCIATED FRONTAL LOWS
ARE TO LIFT NORTH ACROSS THE BELLINGSHAUSEN SEA TO TIERRA DEL
FUEGO/SOUTHERN CHILE. THIS IS TO PERSIST OVER THE NEXT THREE TO
FOUR DAYS. INFLOW OF COLD ANTARCTIC AIR ACROSS THE DRAKE PASSAGE
IS LIKELY TO TRIGGER SNOW SHOWERS ACROSS THE SOUTHERN ANDES OF
CHILE AND PORTIONS OF TIERRA DEL FUEGO. IN THIS AREA LIQUID WATER
EQUIVALENT IS TO PEAK AT 05-10MM/DAY.

FURTHERMORE...AS A BROAD MID LEVEL TROUGH MEANDERS TO THE
SOUTH...IT IS TO FOCUS SHORT WAVE VORTICES ACROSS CENTRAL CHILE-LA
PAMPA/ CENTRAL ARGENTINA. A STRONG ONE IS EXPECTED EARLY THIS
PERIOD...WITH A SOMEWHAT WEAKER ONE TO MAKE LANDFALL BY 72-84 HRS.
EARLY IN THE CYCLE THIS IS TO FAVOR SCATTERED CONVECTION BETWEEN
CONCEPCION AND TEMUCO IN SOUTHERN CHILE...WITH MAXIMA TO PEAK AT
20-35MM. THROUGH 72-96 HRS THIS DECREASES TO 05-10MM.

A BROAD CELL OF THE SUBTROPICAL RIDGE IS TO EXTEND ACROSS CENTRAL
BRASIL TO NORTHERN BOLIVIA. POLAR TROUGH TO THE SOUTH OVER
CHILE/ARGENTINA IS TO PRESS AGAINST THIS RIDGE. A SUBTROPICAL JET
IS TO SEPARATE THE TROUGH FROM THE RIDGE...WITH ANTICYCLONICALLY
CURVED JET TO EXTEND ACROSS NORTHERN CHILE/ARGENTINA-SOUTHERN
STATES OF BRASIL TO THE SOUTH ATLANTIC. AS THE FLOW IS TO REMAIN
AT A PERPENDICULAR ANGLE TO THE CENTRAL ANDES...THIS IS TO FAVOR
GENERATION OF LEESIDE PERTURBATIONS ACROSS ARGENTINA. AT LOW
LEVELS...A FRONT IS TO MEANDER WEST ACROSS THE SOUTH ATLANTIC TO
SOUTHERN BRASIL-PARAGUAY. THE BAROCLINIC BOUNDARY IS TO PERSIST
OVER THE NEXT FEW DAY...BLOCKING MOISTURE TRANSPORT ACROSS MID
SECTIONS OF SOUTH AMERICA. IN A PERSISTENT NORTHERLY FLOW ACROSS
BOLIVIA-MATO GROSSO IN BRASIL...PRECIPITABLE WATER CONTENT VALUES
ALONG THE MEANDERING FRONT ARE TO PEAK AT 40-50MM OVER THE NEXT
FEW DAYS. THIS WILL COMBINE WITH FAVORABLE UPPER DYNAMICS AND
INFLOW OF MID LEVEL SHORT WAVE VORTICES TO SUSTAIN GENERATION OF
MESO SCALE CONVECTIVE SYSTEMS ACROSS PARAGUAY-SOUTHERN BRASIL OVER
THE NEXT FEW DAYS. IN THIS AREA THE DAILY MAXIMA IF TO GENERALLY
PEAK AT 25-50MM...EXCEPT FOR DAY 02 WHEN INFLOW OF MID LEVEL
VORTEX IS TO TRIGGER STRONGER CONVECTION. DURING THAT PERIOD THE
MAXIMA WILL INCREASE TO 30-60MM.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS
TO ENVELOP CONTINENTAL AREA TO THE NORTH OF 30S...WHILE CENTERING
ON A CLOSED HIGH AT 10S 60W. AS THE RIDGE HOLDS TO THE NORTH...IT
IS TO STEER A SHORT WAVE TROUGH ACROSS EQUATORIAL SOUTH AMERICA.
UPPER VORTEX ENTERS THE GUIANAS BY 48-60 HRS...AND THROUGH 96-108
HRS IT MOVES TO RORAIMA IN NORTHERN BRASIL. THIS IS TO THEN
ENHANCE DIURNAL CONVECTION ACROSS NORTHERN PARA-ILHA DE MARAJO
LATER IN THE CYCLE...TO FAVOR RAINFALL AMOUNTS OF 10-15MM IN
SCATTERED CONVECTION. DIURNAL CONVECTION TO THE WEST IS TO CLUSTER
ALONG THE SIERRA/JUNGLE OF PERU AND EASTERN ECUADOR...WITH
ACCUMULATION OF 05-10MM/DAY IN SCATTERED CONVECTION. THROUGH 48-72
HRS THIS IS TO INCREASE TO 10-15MM/DAY.

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