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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1643Z Jul 17, 2018)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1243 PM EDT TUE JUL 17 2018

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

MODEL DISCUSSION (VALID FROM JUL 17 AT 0000 UTC): CONSISTENT WITH
PREVIOUS FORECAST...A MID/UPPER LEVEL TROUGH IS TO AMPLIFY ALONG
THE COAST OF CHILE EARLY IN THE CYCLE...WITH AXIS REACHING MAXIMUM
AMPLITUDE ON WEDNESDAY...WHEN THE BASE OF THE TROUGH BOTTOMS OUT
AROUND 15S AND A LOW CLOSES JUST WEST OF CONCEPCION IN CENTRAL
CHILE. THE DEEP TROUGH IS TO THEN FOCUS ITS SHORT WAVE ENERGY
ACROSS CENTRAL/NORTHERN CHILE TO ARGENTINA. ON THURSDAY TO FRIDAY
THE TROUGH WILL GRADUALLY SPILL ACROSS THE CENTRAL
ANDES...MEANWHILE FAVORING HEIGHT FALLS OF 125-150GPM ACROSS
CENTRAL ARGENTINA AND THE RIO DE LA PLATA BASIN. THE TROUGH WILL
THEN MEANDER EAST ACROSS MESOPOTAMIA VALLEY IN ARGENTINA/BUENOS
AIRES PROVINCE LATER ON FRIDAY.

AT LOW LEVELS...THE TROUGH ALOFT IS TO INTERACT WITH A SURFACE
FRONT MEANDERING ACROSS THE SOUTH ATLANTIC TO MID SECTIONS OF
SOUTH AMERICA... TRIGGERING CYCLOGENESIS OVER ENTRE RIOS/URUGUAY
LATER TODAY. THIS LOW IS TO RAPIDLY DEEPEN WHILE OCCLUDING ACROSS
CENTRAL ARGENTINA. AS THE LOW DEEPENS...THE ASSOCIATED SURFACE
FRONT WILL SURGE ACROSS URUGUAY TO NORTHERN ARGENTINA ON
WEDNESDAY. ON THURSDAY-FRIDAY A SOUTHERLY LOW LEVEL JET WILL DRIVE
THIS FRONT NORTH ACROSS PARAGUAY TO SOUTHERN BRASIL-MATO GROSSO DO
SUL-CENTRAL BOLIVIA. THIS IS TO THEN SUSTAIN A PREFRONTAL SHEAR
LINE ACROSS CENTRAL-NORTHWEST BRASIL/SOUTHERN COLOMBIA LATER IN
THE CYCLE. A BUILDING POLAR RIDGE TO THE SOUTH IS TO BRIEFLY
DOMINATE THE FLOW ACROSS SOUTHERN PATAGONIA/CHILE. THIS WILL BE
ACCOMPANIED BY BELOW FREEZING TEMPERATURES. UNDER INFLUENCE OF
THIS RIDGE...AND DEEPENING LOW TO THE NORTH...MOIST AIR WILL THEN
ADVECT ACROSS PATAGONIA/LA PAMPA IN ARGENTINA. THIS WILL RESULT IN
SCATTERED SNOW SHOWERS OVER NORTHERN PATAGONIA AND THE CENTRAL
ANDES OF CHILE. OVER THE ANDES THE MAXIMA IS TO PEAK AT 20-40CM
EARLY IN THE CYCLE...WHILE OVER PATAGONIA EXPECTING SNOWFALL
AMOUNTS OF 05-10CM. OVER MID SECTIONS OF SOUTH AMERICA...AS
ENHANCED BY A NORTHERLY LOW LEVEL JET...MOISTURE IS TO CONVERGE
ACROSS SOUTHERN BRASIL-CORRIENTES/MISIONES IN ARGENTINA...TO
SUSTAIN RAINFALL AMOUNTS OF 20-45MM/DAY. THROUGH THURSDAY THIS IS
TO BECOME BETTER ORGANIZED WHILE BUILDING NORTH ACROSS
CORRIENTES/CHACO IN ARGENTINA TO URUGUAY...WITH MAXIMA OF 35-70MM.
ON FRIDAY THIS DECREASES TO 15-25MM. PREFRONTAL CONVECTION ACROSS
SOUTHERN PERU TO CENTRAL BOLIVIA IS TO INITIALLY FAVOR
ACCUMULATION OF 15-20MM ON THURSDAY. THROUGH FRIDAY THIS INCREASES
TO 20-40MM.

NEXT MID LEVEL TROUGH MOVES ACROSS THE SOUTHEAST PACIFIC TO
SOUTHERN PORTIONS OF CHILE ON THURSDAY-FRIDAY. THIS IS TO THEN
SPLIT IN TWO...WITH SOUTHERN HALF TO ACCELERATE ACROSS THE DRAKE
PASSAGE/ANTARCTIC PENINSULA WHILE THE NORTHERN HALF LAGS OFF THE
SOUTHERN/CENTRAL COAST OF CHILE. AT LOW LEVELS THIS WILL SUSTAIN A
PROGRESSIVE FRONT ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA
LATER ON FRIDAY. AS IT MOVES ACROSS SOUTHERN CHILE THIS WILL
SUSTAIN SCATTERED CONVECTION WITH ACCUMULATION OF 10-15MM.

NORTH OVER THE CONTINENT...AT 200 HPA...A RIDGE WILL EXTEND TO THE
SOUTH-SOUTHEAST FROM AMAZONAS IN WESTERN BRASIL TO
PARAGUAY/SOUTHERN BRASIL. THIS...IN-TURN...WILL SUSTAIN THE
NORTHWARD AMPLIFICATION OF A TROUGH ACROSS THE NORTHEAST STATES OF
BRASIL TO PARA. THE TROUGH WILL ENHANCE DIURNAL CONVECTION ACROSS
NORTHERN PARA-AMAPA/AMAZON RIVER DELTA REGION...WITH DAILY MAXIMA
IN THIS AREA PEAKING AT 15-20MM. THROUGH FRIDAY THIS WILL
WEAKEN...DECREASING TO 05-10MM/DAY. HIGHER AMOUNTS ARE EXPECTED
ACROSS SOUTHERN COLOMBIA/NORTHERN AMAZONAS-NORTHERN JUNGLE OF PERU
TO EASTERN ECUADOR...WHERE THE MAXIMA IS TO INITIALLY PEAK AT
20-30MM...DECREASING TO 15-20MM/DAY ON WEDNESDAY TO THURSDAY.
SURGE IN ACTIVITY ON FRIDAY WILL THEN LEAD TO ACCUMULATION OF
20-40MM.

DIAZ...INUMET (URUGUAY)
SANCHEZ...SMN (ARGENTINA)
DAVISON...WPC (USA)