Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXSA20 KWBC 231548
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1148 AM EDT MON APR 23 2018

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

MODEL DISCUSSION (VALID FROM APR 23 AT 0000 UTC): ON THE NORTHERN
STREAM THE GLOBAL MODELS ARE IN VERY GOOD AGREEMENT THROUGH
132-144 HRS. ON THE SOUTHERN STREAM THEY FOLLOW A SIMILAR
EVOLUTION THROUGH 84-96 HRS...THEN START TO DIVERGE ON HOW MID
LEVEL SYSTEMS ENTERING THE EASTERN PACIFIC  EVOLVE LATER IN THE
PERIOD. THESE DIFFERENCE BECOME MORE PRONOUNCED THROUGH 132-144
HRS.

THERE IS A HIGHER CONFIDENCE IN THE FORECAST DURING THE SHORT
RANGE PERIOD...WITH DEEPENING MID LEVEL TROUGH TO SLOWLY MOVE OFF
THE SOUTHERN REGIONS OF CHILE ON TUESDAY-WEDNESDAY. LATER IN THE
DAY THIS EVOLVES INTO A DEEP CLOSED LOW CENTERING NEAR 50S 80W.
THE DEEPENING TROUGH IS TO FOCUS SUBTROPICAL MOISTURE AND SHORT
WAVE ENERGY ON THE CONTINENT TO THE SOUTH OF 38S...WHILE INDUCING
HEIGHT FALLS OF 75-150GPM. THE DEEP MID LEVEL TROUGH IS TO THEN
SLOWLY PULL ACROSS SOUTHERN CHILE/PATAGONIA IN ARGENTINA TO THE
WESTERN ATLANTIC LATER ON THURSDAY. AT LOW LEVELS THIS WILL
SUSTAIN EXPLOSIVE CYCLOGENESIS...WITH ASSOCIATED SURFACE LOW
DEEPENING FROM A 998/1000 HPA LOW LATER ON TUESDAY TO A 974 HPA
LOW AS IT NEARS SOUTHERN CHILE ON WEDNESDAY EVENING. NOTE THAT
THIS RAPID RATE OF INTENSIFICATION IS CONSISTENT WITH A
METEOROLOGICAL BOMB. THE ASSOCIATED FRONT IS TO ENTER SOUTHERN
CHILE EARLY ON WEDNESDAY MORNING. THIS WILL BE ACCOMPANIED BY
STRONG BOUNDARY LAYER WINDS...EXPECTED TO PEAK AT 30-50KT. THE
SURFACE FRONT WILL CONTINUE ACROSS PATAGONIA TO LA PAMPA IN
ARGENTINA ON THURSDAY...AND ON FRIDAY IT WILL RACE ACROSS RIO DE
LA PLATA BASIN-CENTRAL PROVINCES IN ARGENTINA. OVER SOUTHERN CHILE
THIS IS TO FAVOR MODERATE TO HEAVY RAINFALL AMOUNTS...WITH MAXIMA
OF 20-45MM ON WEDNESDAY-THURSDAY. OVER TIERRA DEL FUEGO/EXTREME
SOUTHERN CHILE THIS IS TO ALSO TRIGGER LIGHT TO MODERATE RAINFALL
AMOUNTS...WITH MAXIMA OF 10-15MM IN MIXED (RAIN/SNOW SHOWERS)
PRECIPITATION. AS IT SURGES ACROSS CENTRAL ARGENTINA ON THURSDAY
THIS IS TO SUSTAIN MODERATE RAINFALL AMOUNTS WITH MAXIMA OF
20-35MM IN POTENTIALLY SEVERE CONVECTION. ON FRIDAY THIS IS TO
ALSO FAVOR SIMILAR RAINFALL AMOUNTS ACROSS ENTRE RIOS-CORRIENTES
IN ARGENTINA.

DOWNSTREAM FROM THIS AXIS...OVER THE WESTERN ATLANTIC...A MID
LEVEL TROUGH EXTENDS FROM THE WEDDELL SEA TO CENTRAL ARGENTINA.
THROUGH TUESDAY EVENING THE TROUGH IS TO SLOWLY PULL TO THE
EAST-SOUTHEAST AS IT NEARS 10W/20W. AT LOW LEVELS THIS SUSTAINS A
SURFACE FRONT THAT STRETCHES ACROSS URUGUAY TO NORTHERN ARGENTINA.
THE BOUNDARY IS TO REMAIN NEARLY STATIONARY DURING THE NEXT THREE
DAYS...THEN RETROGRESS ACROSS CENTRAL ARGENTINA LATER IN THE WEEK.
MEANWHILE...THIS IS TO ENHANCE MOISTURE CONVERGENCE ACROSS
URUGUAY-SOUTHERN BRASIL TO NORTHERN ARGENTINA. EARLY IN THE CYCLE
THIS IS TO FAVOR MAXIMA OF 25-50MM. ON TUESDAY IT INCREASES TO
30-60MM WITH MOST INTENSE CLUSTERING ACROSS URUGUAY-ENTRE RIOS TO
CORDOBA IN ARGENTINA. ON WEDNESDAY...AS THE FRONT LOSES ITS UPPER
LEVEL SUPPORT...THE MAXIMA WILL DECREASE TO 10-15MM/DAY.

NORTH OVER THE CONTINENT...AT 200 HPA...A SHORT WAVE TROUGH IS TO
LIFT ACROSS THE SOUTHEAST STATES OF BRASIL EARLY IN THE PERIOD. AS
A RIDGE BUILDS OVER CENTRAL BRASIL...THIS IS TO THEN AMPLIFY TO
THE NORTH-NORTHWEST ACROSS TOCANTINS/GOIAS TO NORTHEAST BRASIL ON
WEDNESDAY-THURSDAY. THE DEEPENING TROUGH WILL INTERACT WITH SEA
BREEZE RELATED CONVERGENCE ALONG THE NORTH/NORTHEAST COAST OF
BRASIL. IN THIS AREA INITIALLY EXPECTING MAXIMA OF 15-20MM. ON
THURSDAY THIS INCREASES TO 20-30MM...WITH MODERATE TO HEAVY
CONVECTION TO THEN PERSIST THROUGH THE END OF THE WEEK. ACROSS
NORTHERN PARA/AMAZONAS-RORAIMA IN BRASIL...NEAR EQUATORIAL TROUGH
RELATED CONVERGENCE IS TO TRIGGER RAINFALL AMOUNTS OF 20-45MM/DAY.
UNDER INFLUENCE OF THE DEEPENING UPPER LEVEL TROUGH THIS INCREASES
TO 30-60MM/DAY LATER ON FRIDAY. LESSER AMOUNTS ARE EXPECTED ON THE
PERUVIAN JUNGLE/EASTERN ECUADOR...WITH DIURNAL CONVECTION
TRIGGERING DAILY MAXIMA OF 10-15MM.

BALBINO...INMET (BRASIL)
DIAZ...INUMET (URUGUAY)
DAVISON...WPC (USA)
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.