Prognostic Meteorological Discussion
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000
FXSA20 KWBC 291706
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 PM EST THU JAN 29 2015

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

MODEL DISCUSSION (VALID FROM JANUARY 29 AT 00UTC): THE 00 UTC GFS
OVERCORRECTED ACROSS THE WESTERN SOUTH ATLANTIC ON DAYS 04-06...
DEVELOPING A DEEPER/STRONGER TROUGH THAN WHAT THE OTHER MODELS
SUGGEST. MEAN OF THE GLOBAL ENSEMBLES FAVOR A WEAKER PERTURBATION
TO DEVELOP...A SOLUTION THE 06 GFS SUPPORTS. ALTHOUGH UNCERTAINTY
IS HIGH...OUR FORECAST CHARTS ARE HEAVILY BIASED TOWARDS THE
LATTER RUN OF THE MODEL.

BROAD MID/UPPER LEVEL TROUGH DOMINATES FLOW ACROSS THE WESTERN
SOUTH ATLANTIC EARLY IN THE CYCLE. THE TROUGH IS TO GRADUALLY PULL
TO THE EAST-SOUTHEAST AS THE CYCLE PROGRESSES...DAMPENING LATER IN
THE CYCLE AS SHORT WAVE ENERGY RAPIDLY SHEARS TO THE
EAST-SOUTHEAST. AT LOW LEVELS...BROAD RIDGE IS TO DOMINATE MOST OF
ARGENTINA/WESTERN ATLANTIC...WITH POLAR HIGH TO CENTER TO THE
EAST-SOUTHEAST OF THE BUENOS AIRES PROVINCE. AN ELONGATED FRONT
FLANKS THIS RIDGE...WITH AXIS TO THE NORTHWEST ACROSS SAO PAULO IN
BRASIL TO CORRIENTES IN ARGENTINA. THROUGH 36-48 HRS THE FRONT
LOSES UPPER LEVEL SUPPORT...WEAKENING TO A TROUGH OVER THE
SOUTHERN STATES OF BRASIL. EARLY IN THE CYCLE THIS IS TO FAVOR
ORGANIZED CONVECTION ACROSS SOUTHERN STATES OF BRASIL AND PORTIONS
OF SAO PAULO...WITH RAINFALL MAXIMA OF 30-60MM. THROUGH 48-60 HRS
THIS DECREASES TO 20-35MM...AND BY 96-108 HRS IT IS EXPECTED TO
PEAK AT 10-15MM.

PROGRESSIVE MID/UPPER LEVEL TROUGH IS TO FOLLOW...TO ENTER THE
EASTERN PACIFIC EARLY IN THE CYCLE. THIS IS TO THEN PRESS AGAINST
A RIDGE TO THE EAST...AS THE LATTER EXTENDS FROM NORTH-TO-SOUTH
ACROSS THE WESTERN ATLANTIC TO THE WEDDELL SEA. UNDER PRESSURE
FROM THE TROUGH TO THE WEST...THE RIDGE RELOCATES ALONG 30W/40W
LATER ON DAY 03...ALLOWING THE TROUGH TO MOVE INLAND ACROSS CHILE
TO ARGENTINA. THE TROUGH IS TO THEN PULL TO THE EAST-SOUTHEAST
WHILE GRADUALLY SHEARING SHORT WAVE ENERGY. AT LOW LEVELS...THIS
IS TO SUSTAIN A BROAD TROUGH ACROSS THE SOUTHEAST PACIFIC EARLY IN
THE CYCLE. SUCCESSIVE FRONTS ARE TO REVOLVE AROUND THIS AXIS...TO
THEN STREAM ACROSS TIERRA DEL FUEGO/EXTREME SOUTHERN PORTIONS OF
CHILE. THIS PATTERN IS TO PERSIST THROUGH 42-54 HRS...MEANWHILE
FAVORING LIGHT CONVECTION ACROSS TIERRA DEL FUEGO WHERE THE MAXIMA
IS TO PEAK AT 05-10MM ON DAY 02. BY 72-84 HRS THE FRONT IS TO
FINALLY MOVE NORTH ACROSS PATAGONIA IN ARGENTINA TO LA
PAMPA...WHERE IT IS TO STALL THROUGH 96-108 HRS. AS IT MOVES NORTH
ACROSS NORTHERN PATAGONIA TO LA PAMPA/BUENOS AIRES PROVINCE THIS
IS TO THEN TRIGGER SCATTERED CONVECTION WITH ACCUMULATION OF
10-15MM.

AT 200 HPA...BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES
NORTHERN CHILE/ARGENTINA-BOLIVIA-PERU AND SOUTHWEST BRASIL...WHILE
CENTERING ON A CLOSED HIGH OVER SOUTHERN BOLIVIA/NORTHERN CHILE.
RIDGE PATTERN IS FORECAST TO STRENGTHEN THROUGH 96-120 HRS...WITH
AXIS EXPECTED TO BUILD EAST ACROSS BRASIL. A TUTT TO THE
EAST...MEANWHILE...IS TO ORIGINATE ON A CLOSED LOW NEAR 12S
40W...WITH A TROUGH EXTENDING TO THE NORTHWEST ACROSS NORTHEAST
BRASIL TO THE GUIANAS. TUTT LOW IS TO RETROGRESS TO NORTHEAST
BRASIL THROUGH 48-60 HRS...BUT LATER IN THE CYCLE IT IS TO FILL TO
AN OPEN TROUGH AS THE RIDGE TO THE SOUTH STRENGTHENS/BUILDS.
BETWEEN THE RIDGE TO THE WEST AND THE TUTT TO THE EAST...AN UPPER
CONVERGENT PATTERN IS TO DOMINATE THE EASTERN STATES OF BRASIL
DURING THE NEXT 48-60 HRS. BUT AS THE TROUGH BEGINS TO
WEAKEN...AND THE RIDGE BUILDS...CONVECTION ACROSS NORTHEAST BRASIL
IS TO INTENSIFY. THROUGH 72-96 HRS ACTIVITY INCREASES TO SUSTAIN
MAXIMA OF 15-25MM. FARTHER WEST...THE BUILDING RIDGE IS TO
INITIALLY FOCUS MOISTURE ACROSS NORTHERN BOLIVIA TO SOUTHERN
PERU...WHERE WE EXPECT MAXIMA OF 30-60MM. THROUGH 48-60 HRS FOCUS
OF THE ORGANIZED CONVECTION SHIFTS TO AMAZONAS/ACRE IN
BRASIL-JUNGLE OF PERU TO SOUTHERN COLOMBIA. THIS IS TO THEN
PERSIST THROUGH 72-84 HRS. LATER IN THE CYCLE MOST ACTIVE
CONVECTION IS EXPECTED ALONG THE NEAR EQUATORIAL TROUGH TO THE
NORTH...WITH MAXIMA OF 20-35MM...WHILE OVER CENTRAL/SOUTHERN
PERU-ACRE-PARA IN BRASIL THE MAXIMA PEAKS AT 15-25MM.

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

$$




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