Prognostic Meteorological Discussion
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FXSA20 KWBC 301602
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1102 AM EST FRI JAN 30 2015

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

MODEL DISCUSSION (VALID FROM JANUARY 30 AT 00UTC): THE GLOBAL
MODELS ARE IN CLOSER AGREEMENT THAN ON PREVIOUS CYCLES...WITH THE
EUROPEAN ENSEMBLE MEMBERS PROVIDING GOOD SUPPORT TO THE
DETERMINISTIC SOLUTION. THE CANADIAN AND NCEP
ENSEMBLES...HOWEVER...START TO DIVERGE AFTER 72/84 HRS...AND
DIFFERENCES AMONG THE MEMBERS GROW PROGRESSIVELY LARGE THROUGH
132-144 HRS. AS A RESULT...CONFIDENCE IN THE FORECAST BEYOND 84
HRS IS LOW.

MID/UPPER LEVEL TROUGH OVER THE WESTERN SOUTH ATLANTIC CONTINUES
ITS EASTWARD MIGRATION...AND THROUGH 48 HRS IT IS TO PULL ACROSS
30W/40W. THE TROUGH IS TO THEN MOVE ACROSS 00W THROUGH 60-72 HRS.
AT LOW LEVELS...A BROAD RIDGE MEANDERS OFF THE COAST OF ARGENTINA/
URUGUAY-SOUTHERN BRASIL. THE RIDGE IS TO MEANDER EAST ACROSS THE
SOUTH ATLANTIC THROUGH THE END OF THE CYCLE. AS THE RIDGE
RELOCATES...IT IS TO DISPLACE A POLAR TROUGH TO THE EAST. EARLY IN
THE CYCLE THE TROUGH IS TO LIE OVER THE CENTRAL ATLANTIC...AND
THROUGH 60-72 HRS IT REACHES THE EASTERN ATLANTIC. ASSOCIATED
FRONT IS TO TRAIL ACROSS THE SOUTH ATLANTIC TO SAO PAULO/SANTA
CATARINA IN BRASIL DURING THE NEXT FEW DAYS. MEANWHILE...THIS IS
TO ENHANCE CONVECTIVE DEVELOPMENT ACROSS SAO PAULO-MATO GROSSO DO
SUL...WITH MAXIMA OF 20-35MM EXPECTED THROUGH 36-48 HRS. THIS THEN
DECREASES TO 15-25MM/DAY LATER ON DAY 03.

BROAD MID/UPPER LEVEL TROUGH MOVES TO THE EASTERN PACIFIC/SOUTHERN
CONE OF SOUTH AMERICA EARLY IN THE CYCLE. AS IT NEARS THE SOUTHERN
CONE...THE TROUGH IS TO PRESS AGAINST A RIDGE TO THE EAST.
INITIALLY THE RIDGE IS TO EXTEND SOUTH FROM CENTRAL ARGENTINA TO
THE WEDDELL SEA. BUT AS THE TROUGH PUSHES EAST...AND SHORT WAVE
ENERGY SHEARS UNDER THIS AXIS...THE RIDGE IS TO FLATTEN AND THE
TROUGH IS EXPECTED TO WEAKEN TO A SHORT WAVE TROUGH BY 60-72 HRS.
THIS IS TO THEN SHEAR A VORTEX ON THE NORTHERN STREAM OVER
NORTHERN PATAGONIA...THAT IS TO MEANDER EAST-NORTHEAST TO LA
PAMPA/SOUTHERN BUENOS AIRES PROVINCE. AT LOW LEVELS...THE TROUGH
ALOFT SUSTAINS A BROAD TROUGH ACROSS THE SOUTHEAST
PACIFIC/BELLINGSHAUSEN SEA EARLY IN THE CYCLE. THROUGH 48-54 HRS
IT IS TO THEN MIGRATE ACROSS THE ANTARCTIC PENINSULA/DRAKE PASSAGE
TO THE SOUTH ATLANTIC. AS IT MEANDERS OVER THE SOUTHERN
CONE...SUCCESSIVE FRONTS ARE TO REVOLVE AROUND THIS AXIS. THESE
ARE TO STREAM ACROSS TIERRA DEL FUEGO/EXTREME SOUTHERN PORTIONS OF
CHILE. THIS PATTERN IS TO PERSIST THROUGH 30-36 HRS...MEANWHILE
FAVORING LIGHT CONVECTION ACROSS TIERRA DEL FUEGO WHERE THE MAXIMA
IS TO PEAK AT 05-10MM ON DAY 01. BY 48-60 HRS THE FRONT MOVES
NORTH ACROSS PATAGONIA IN ARGENTINA TO LA PAMPA. IN INTERACTION
WITH MID LEVEL TROUGH OVER PATAGONIA...A FRONTAL LOW IS TO DEVELOP
ALONG THIS BOUNDARY ACROSS LA PAMPA/BUENOS AIRES PROVINCE. THE
MODELS DIVERGE ON THE INTENSITY OF THIS LOW...WITH ECMWF FAVORING
A DEEPER PERTURBATION THAN WHAT THE GFS AND UKMET SUGGEST. IN THIS
AREA THERE IS HIGH VARIABILITY AMONG THE GLOBAL ENSEMBLE
MEMBERS...SO FURTHER CORRECTIONS ARE EXPECTED. MEANWHILE...OVER
CENTRAL ARGENTINA EXPECTING RAINFALL AMOUNTS OF 10-15MM BY 72-96
HRS. THROUGH 108-120 HRS THIS INCREASES TO 20-35MM...WITH THE MOST
INTENSE EXPECTED OVER THE BUENOS AIRES PROVINCE-URUGUAY-ENTRE RIOS
ARGENTINA.

AT 200 HPA...A BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES
NORTHERN CHILE/ARGENTINA-BOLIVIA-PERU AND SOUTHWEST BRASIL...WHILE
CENTERING ON A CLOSED HIGH THAT MEANDERS BETWEEN SOUTHERN
BOLIVIA-NORTHERN CHILE-NORTHWEST ARGENTINA. THE RIDGE PATTERN IS
FORECAST TO STRENGTHEN THROUGH 48-72 HRS...WITH AXIS EXPECTED TO
BUILD EAST ACROSS BRASIL AND SOUTH INTO CENTRAL ARGENTINA. A TUTT
TO THE EAST...MEANWHILE...IS TO ORIGINATE ON A CLOSED LOW NEAR 10S
45W...WITH A TROUGH THAT EXTENDS TO THE NORTHWEST ACROSS NORTHEAST
BRASIL TO THE GUIANAS. TUTT LOW IS TO RETROGRESS TO NORTHEAST
BRASIL THROUGH 24-36 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 36-48 HRS...WHILE OVER NORTHWEST SOUTH AMERICA A
DIVERGENT PATTERN ALOFT IS EXPECTED THROUGH 60-72 HRS. BUT AS THE
TROUGH BEGINS TO WEAKEN...AND THE RIDGE BUILDS...THE MID/UPPER
CONVERGENCE IS TO WEAKEN. AS A RESULT...CONVECTION ACROSS
NORTHEAST BRASIL IS TO INTENSIFY THROUGH 72 HRS...WITH RAINFALL
MAXIMA OF 15-25MM IN SCATTERED DEEP CONVECTION. FARTHER WEST...THE
BUILDING RIDGE IS TO ENHANCE CONVECTIVE DEVELOPMENT ACROSS THE
PERUVIAN JUNGLE-EASTERN ECUADOR-AMAZONIA IN COLOMBIA TO
AMAZONAS/ACRE IN BRASIL. IN THIS AREA CONVECTION IS TO PEAK OVER
THE NEXT COUPLE OF DAYS WITH MAXIMA OF 30-60MM/DAY. THIS IS TO
GRADUALLY DECREASE TO 15-20MM/DAY BY 96-108 HRS.

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

$$




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