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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1614Z Jul 18, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 PM EDT FRI JUL 18 2014

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

MODEL DISCUSSION (VALID FROM 18 JULY 00UTC): HIGH CONFIDENCE IN
THE FORECAST THROUGH DAY 06...AS MODELS CONTINUE TO CONVERGE ON A
SIMILAR SOLUTION. MINOR PATTERN DIFFERENCES...HOWEVER...DEVELOP
LATER ON DAY 06. DURING THAT PERIOD MODELS ARE DIVERGING ON THE
INTENSITY AND TRAJECTORY OF A CLIPPER LOW NEARING THE SOUTHERN
CONE...WITH THE UKMET FAVORING A DEEPER/STRONGER PERTURBATION TO
ENTER SOUTHERN CHILE/PATAGONIA IN ARGENTINA. IF THE UKMET
VERIFIES...THIS HAS THE POTENTIAL OF BEING A HEAVY SNOWFALL
PRODUCER.

MID/UPPER LEVEL RIDGE EXTENDS SOUTH ALONG THE COAST OF CHILE. AS
THE RIDGE HOLDS TO THE WEST...IT IS INDUCING THE NORTHWARD
AMPLIFICATION OF A TROUGH OVER THE WESTERN ATLANTIC/SOUTHERN
STATES OF BRASIL. INFLOW OF COLD POLAR AIR WILL HELP SUSTAIN A
RAPID RATE OF INTENSIFICATION...WITH TROUGH FORECAST TO RAPIDLY
DEEPEN DURING THE NEXT 36-48 HRS. EARLY IN THE CYCLE THE TROUGH IS
TO EXTEND NORTH ALONG 45W TO SOUTHEAST BRASIL. THROUGH 48 HRS IT
WILL MOVE ACROSS 35W...SLOWLY PULLING ACROSS 20W BY 78-84 HRS. AT
LOW LEVELS THIS SUSTAINS AN OCCLUDING LOW OVER THE WESTERN
ATLANTIC. UNDER FAVORABLE JET DYNAMICS...THE SURFACE LOW IS TO
RAPIDLY DEEPEN...REACHING MAXIMUM INTENSITY BY 48-60 HRS...WHEN IT
IS TO PEAK AT 970 HPA. THE DEEPENING MID LATITUDE CYCLONE...AS IT
BOMBS TO THE NORTH OF THE SOUTH GEORGIA ISLANDS...WILL SUSTAIN THE
NORTHWARD MIGRATION OF THE ASSOCIATED SURFACE FRONT ACROSS THE
CONTINENT. THROUGH 24-36 HRS THE FRONT IS TO MOVE NORTH ACROSS SAO
PAULO TO RIO DE JANEIRO...TRAILING ACROSS MATO GROSSO TO BOLIVIA.
FRONT IS TO THEN STALL OVER MID SECTIONS OF SOUTH AMERICA...WITH
TRAILING END OVER THE CONTINENT EXPECTED TO FRONTOLIZE LATER ON
DAY 03. AS THE FRONT MOVES NORTH ACROSS SAO PAULO/RIO DE
JANEIRO-MATO GROSSO IT WILL SUSTAIN SCATTERED RAINFALL WITH
ACCUMULATION OF 05-10MM. ACROSS BOLIVIA TO SOUTHERN PERU EXPECTING
HIGHER AMOUNTS...WITH ACCUMULATION OF 20-40MM.

THE MID LEVEL RIDGE PATTERN OVER THE EASTERN PACIFIC IS EXPECTED
TO REMAIN OFF THE COAST OF CHILE THROUGH 24-36 HRS. IT IS TO THEN
RELOCATE ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC BY 72-84
HRS...WHILE GRADUALLY YIELDING TO THE NEXT POLAR TROUGH. THE POLAR
TROUGH IS FORECAST TO MOVE ACROSS 100W BY 48 HRS...AND MOVES
ACROSS 85W BY 72 HRS. IT IS TO ENTER CHILE BY 96 HRS. THROUGH
108-120 HRS IT IS TO MOVE ACROSS THE SOUTHERN CONE WHILE TRAILING
TO THE NORTHWEST TO AN ILL ORGANIZED LOW JUST WEST OF LA SERENA
CHILE. THE HIGH AMPLITUDE LONG WAVE TROUGH...AS IT MOVES ACROSS
THE SOUTH PACIFIC TOWARDS THE CONTINENT IT IS TO SUSTAIN A
SUBTROPICAL CONNECTION. AT LOW LEVELS THE ASSOCIATED FRONT SLIDES
UNDER THE RIDGE TO THE EAST...MEANDERING ACROSS SOUTHERN CHILE TO
PATAGONIA IN ARGENTINA EARLY IN THE CYCLE. THE FRONT REMAINS
NEARLY STATIONARY THROUGH 60-72 HRS. MEANWHILE...THE INFLOW OF
SUBTROPICAL MOISTURE WILL COMBINE WITH STRONG BOUNDARY LAYER WINDS
TO SUSTAIN MODERATE TO HEAVY CONVECTION ACROSS SOUTHERN CHILE. IN
THIS AREA EXPECTING MAXIMA OF 20-40MM/DAY THROUGH 36 HRS...AND
15-25MM/DAY AT 36-60 HRS. SCATTERED CONVECTION IS TO THEN PERSIST
THROUGH DAY 04. LATER IN THE CYCLE THE FRONT IS TO RACE TO
NORTHERN ARGENTINA AS A POLAR RIDGE BUILDS TO THE WEST...REACHING
NORTHERN PROVINCES LATER ON DAY 05. AS IT SURGES ACROSS ARGENTINA
THE FRONT IS TO TRIGGER ORGANIZED/ POTENTIALLY SEVERE CONVECTION
ACROSS RIO DE LA PLATA BASIN-MESOPOTAMIA VALLEY IN
ARGENTINA...WITH RAINFALL MAXIMA OF 25-50MM.

BROAD TROUGH IS TO THEN REMAIN ACROSS THE ANTARCTIC PENINSULA TO
THE BELLINGSHAUSEN SEA. PROGRESSIVE CLIPPER LOW IS TO THEN LIFT
ALONG THE WESTERN PERIPHERY OF THIS TROUGH...REACHING TIERRA DEL
FUEGO/EXTREME SOUTHERN PORTIONS OF CHILE BY 120 HRS. AS PREVIOUSLY
INDICATED...GLOBAL MODEL GUIDANCE THEN DIVERGE ON HOW THIS IS
GOING TO EVOLVE...WITH SOME SHOWING POTENTIAL FOR FURTHER
INTENSIFICATION AS THE ANTARCTIC SYSTEM ENTERS THE CONTINENT.
DEPENDING ON TRAJECTORY AND RATE OF INTENSIFICATION THIS COULD
PRODUCE HEAVY SNOWFALL OVER THE SOUTHERN CONE WHILE SUSTAINING
ADVECTION OF BELOW FREEZING TEMPERATURES INTO MID SECTIONS OF
ARGENTINA LATER ON DAY 07.

NORTH OVER TROPICAL SOUTH AMERICA...A NEAR ZONAL WESTERLY FLOW IS
TO DOMINATE OVER THE NEXT FEW DAYS...WITH ILL ORGANIZED CELL OF
THE SUBEQUATORIAL RIDGE TO CONFINE TO CONTINENTAL AREA TO THE
NORTH OF 03S. ISOLATED DIURNAL CONVECTION IS TO LIMIT TO NORTHERN
PORTIONS OF PARA-AMAZONAS IN BRASIL...WITH RAINFALL AMOUNTS OF
05-10MM. HIGHER AMOUNTS...HOWEVER...ARE POSSIBLE ACROSS NORTHERN
PERU/SOUTHERN COLOMBIA AS A NORTHERN HEMISPHERE TROPICAL WAVE
PULLS ACROSS THE CONTINENT. THIS IS LIKELY TO TRIGGER SCATTERED
CONVECTION WITH ACCUMULATION OF 20-30MM. OVER NORTHEAST
BRASIL...MEANWHILE...TRADE WIND CONVERGENCE WILL SUSTAIN SCATTERED
COASTAL CONVECTION. THIS IS TO PEAK AT 20-35MM EARLY IN THE
CYCLE...BUT THROUGH 36-60 HRS IT DECREASES TO 05-10MM. IT IS TO
THEN SURGE ONCE AGAIN LATER IN THE CYCLE...WHEN IT IS TO PEAK AT
15-25MM.

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