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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1647Z Dec 09, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1147 AM EST TUE DEC 09 2014

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

MODEL DISCUSSION (VALID FROM DECEMBER 09 AT 00UTC): CONFIDENCE IN
THE FORECAST IS HIGH...WITH MODELS IN EXCELLENT AGREEMENT THROUGH
DAY 07.

A 500 HPA SHORT WAVE TROUGH ON THE SOUTHERN STREAM PULLS ACROSS
SOUTHERN CHILE/PATAGONIA IN ARGENTINA THROUGH 24-39 HRS...CROSSING
40W BY 48 HRS. THROUGH 96 HRS IT IS TO THEN ACCELERATE ACROSS 00W.
THIS SUSTAINS A SURFACE FRONT THAT SURGES ACROSS PATAGONIA TO LA
PAMPA IN ARGENTINA EARLY IN THE CYCLE...AND NORTH ACROSS URUGUAY
TO RIO GRANDE DO SUL/NORTHERN PROVINCES IN ARGENTINA BY 48 HRS.
THE FRONT IS TO THEN REMAIN NEARLY STATIONARY THROUGH 96-108 HRS.
AS IT SURGES ACROSS THE CENTRAL-NORTHERN PROVINCES IN ARGENTINA
THIS IS TO TRIGGER SCATTERED/POTENTIALLY SEVERE CONVECTION
STARTING LATER THIS EVENING/EARLY ON WEDNESDAY MORNING...WITH
RAINFALL MAXIMA OF 20-45MM. THROUGHOUT THE DAY INTO EARLY MORNING
ON THURSDAY ACTIVITY IS TO BUILD NORTH INTO THE NORTHWEST
PROVINCES IN ARGENTINA...WHERE UNDER FAVORABLE JET DYNAMICS
ORGANIZED CONVECTION IS TO PERSIST OVER THE NEXT FEW DAYS.
SUCCESSIVE MID LEVEL VORTICES ARE TO THEN STREAM ACROSS THE
CENTRAL/NORTHERN ANDES OF CHILE...TRIGGERING ADDITIONAL CONVECTION
IN THIS AREA.

AS THE FRONT MEANDERS TO THE SOUTH...A SURFACE LOW IS TO THEN FORM
OFF THE COAST OF SAO PAULO EARLY ON DAY 04. THIS IS TO PERSIST
THROUGH THE END OF THE CYCLE WHILE SLOWLY MEANDERING TO THE
EAST-SOUTHEAST. THIS IS TO ENHANCE MOISTURE CONVERGENCE BETWEEN
SANTA CATARINA AND NORTHERN SAO PAULO...FAVORING ORGANIZED
CONVECTION ALONG THE SERRA DO MAR. IN THIS AREA EXPECTING MODERATE
TO HEAVY RAINS ON DAY 04 TO SUSTAIN MAXIMA OF 30-60MM.

A MID/UPPER LEVEL RIDGE IS TO THEN BUILD ACROSS THE EASTERN
PACIFIC. THROUGH 72 HRS THE RIDGE WILL BUILD SOUTH ALONG 80W/90W
TO 70S. IT THEN SETTLES ALONG 80W LATER IN THE CYCLE. AS THE RIDGE
BUILDS TO THE WEST...THIS IS TO THEN SUSTAIN THE NORTHWARD
AMPLIFICATION OF A TROUGH. THE TROUGH IS TO EXTEND BETWEEN 75W-30W
WHILE ANCHORING ON A CLOSED LOW TO THE WEST OF THE SOUTH GEORGIA
ISLANDS. SHORT WAVE VORTICES ARE TO THEN ROUND THIS AXIS...TO
STREAM ACROSS THE DRAKE PASSAGE/TIERRA DEL FUEGO. AT LOW LEVELS A
BROAD RIDGE IS TO THEN ESTABLISH OVER THE EASTERN PACIFIC WHILE A
BROAD TROUGH IS TO EXTEND NORTH ACROSS THE WEDDELL SEA TO THE
SOUTHWEST ATLANTIC. POLAR FRONTS ARE TO REVOLVE AROUND THIS
TROUGH...AND THEY ARE TO CONFINE TO EXTREME SOUTHERN PORTIONS OF
CHILE. IN THIS AREA EXPECTING LIGHT RAINFALL OVER THE NEXT FEW
DAYS WITH ACCUMULATION OF 00-05MM/DAY.

PATTERN TO THE NORTH IS TO GRADUALLY EVOLVE THROUGH 96-120 HRS. AT
200 HPA THE SUBTROPICAL RIDGE IS TO ORIGINATES ON A CLOSED HIGH TO
THE SOUTH OF THE GALAPAGOS ISLANDS...AND IT IS TO EXTEND TO THE
EAST-SOUTHEAST ACROSS SOUTHERN PERU/NORTHERN
CHILE-BOLIVIA-SOUTHERN STATES OF BRASIL TO THE WESTERN ATLANTIC.
ALTHOUGH RIDGE PATTERN IS TO GENERALLY HOLD...HIGH ALOFT IS TO
RELOCATE ALONG THIS AXIS. THROUGH 48 HRS THE HIGH MOVES TOWARDS
NORTHERN COAST OF CHILE/SOUTHERN PERU...AND BY 96 HRS IT IS TO
MOVE INLAND ACROSS LAKE TITICACA. BY 120 HRS IT IS TO MOVE FARTHER
TO THE EAST...TO CENTER BETWEEN SANTA CRUZ IN EASTERN BOLIVIA/MATO
GROSSO DO SUL IN BRASIL. EARLY IN THE CYCLE THIS IS TO FAVOR A
SOUTH-SOUTHEASTERLY FLOW ACROSS AMAZONAS IN BRASIL/JUNGLE OF
PERU...FORCING CONVECTIVE CELLS TO SPREAD NORTHWARD ALONG THE FOOT
OF THE ANDES. BUT AS THE HIGH RELOCATES...WINDS WILL GRADUALLY
SHIFT TO THE EAST ACROSS PERU. EARLY IN THE CYCLE THIS IS TO
ENHANCE VERTICAL WIND SHEAR TO FAVOR MCS DEVELOPMENT ACROSS
EASTERN PERU-ACRE IN BRASIL-NORTHERN BOLIVIA. EARLY IN THE CYCLE
EXPECTING RAINFALL AMOUNTS OF 20-45MM/DAY...BUT THIS DECREASES TO
15-30MM BY MID CYCLE. ALSO...AS THE RIDGE BUILDS
INLAND...ORGANIZED CONVECTION IS TO BUILD ACROSS PARA TO
TOCANTINS/GOIAS-BAHIA/MINAS GERAIS IN BRASIL...WITH MAXIMA IN THIS
AREA TO PEAK AT 20-40MM/DAY. THIS STARTS TO FLARE UP EARLY ON DAY
02 AND PERSIST THROUGH DAY 04.

ARREAGA...INAMHI (ECUADOR)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)