Prognostic Meteorological Discussion
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FXSA20 KWBC 091558
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EDT THU APR 09 2020

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

FORECAST DISCUSSION FROM APR 09/15UTC: GLOBAL MODELS MAINTAIN GOOD
CYCLE-TO-CYCLE CONTINUITY THROUGH 96-108 HRS...THEN MAKE PATTERN
CORRECTIONS TO SHORT WAVE PERTURBATIONS PROPAGATING ACROSS THE
EASTERN SOUTH PACIFIC. THESE DIFFERENCES AMONG THE MODELS BECOME
MORE PRONOUNCED THROUGH 132-144 HRS. OVERALL CONFIDENCE IN THE
FORECAST IS HIGH THROUGH DAY 4.

MID LEVEL LOW ON THE NORTHERN STREAM EXTENDS A SHORT WAVE TROUGH
TO THE SOUTHERN/SOUTHEASTERN STATES OF BRASIL. DURING THE WEEKEND
THE LOW IS TO GRADUALLY FILL AND THE TROUGH WILL START TO PULL TO
THE EAST SOUTHEAST. AT LOW LEVELS...THE TROUGH ALOFT SUSTAINS AN
ELONGATED FRONT THAT STRETCHES TO THE WEST-NORTHWEST ACROSS THE
SOUTH ATLANTIC TO ESPIRITO SANTO/MINAS GERAIS IN BRASIL...TRAILING
ACROSS MATO GROSSO DO SUL TO CHACO PARAGUAYO. AS IT LOSES ITS
UPPER LEVEL SUPPORT THE PORTION OVER THE CONTINENT FRONTOLIZES ON
SUNDAY MORNING...WHILE REMNANTS OVER THE ATLANTIC DISSIPATE EARLY
NEXT WEEK. EARLY IN THE CYCLE THIS IS TO SUSTAIN SCATTERED DEEP
CONVECTION ACROSS ESPIRITO SANTO-MINAS GERAIS-BAHIA IN
BRASIL...WITH MAXIMA OF 35-70MM. ON FRIDAY EXPECTING ADDITIONAL
RAINFALL AMOUNTS OF 20-40MM...WHILE ON SATURDAY MAXIMA PEAKS AT
15-25MM. POTENTIALLY HIGHER AMOUNTS ARE EXPECTED ON SUNDAY...WHEN
MAXIMA IN THIS AREA INCREASES TO 20-40MM AS THE MID LEVEL TROUGH
STARTS TO PULL TO THE EAST-SOUTHEAST. OTHER CONVECTION IS EXPECTED
ACROSS RIO GRANDE DO SUL IN BRASIL...AS ENHANCED BY THE MID/UPPER
LEVEL TROUGH. IN THIS AREA EXPECTING MAXIMA OF 05-10MM IN
POTENTIALLY SEVERE CONVECTION THIS AFTERNOON THROUGH FRIDAY
MORNING.

OVER THE EASTERN PACIFIC...MEANWHILE...A TROUGH ON THE SOUTHERN
STREAM MOVES ACROSS THE BELLINGSHAUSEN SEA TO THE SOUTHERN CONE
EARLY IN THE FORECAST CYCLE. AS IT PRESSES AGAINST A RIDGE TO THE
NORTH AND EAST...THE MID LEVEL TROUGH IS TO INITIALLY FOCUS ITS
SHORT WAVE ENERGY ACROSS THE SOUTHERN REGIONS OF CHILE/TIERRA DEL
FUEGO. ON FRIDAY THE RIDGE WEAKENS ENOUGH TO ALLOW THE MID LEVEL
TROUGH TO MOVE FARTHER INLAND ACROSS SOUTHERN CHILE TO PATAGONIA
IN ARGENTINA. ON ITS WAKE...A SHORT WAVE TROUGH ON THE NORTHERN
STREAM IS TO THEN LIFT ACROSS THE EASTERN PACIFIC TO THE CENTRAL
REGIONS OF CHILE EARLY LATER ON SATURDAY EVENING. THIS IS TO
SLOWLY SPILL ACROSS THE CENTRAL ANDES OF CHILE TO CENTRAL
ARGENTINA ON SUNDAY...MEANWHILE SHEARING SHORT WAVE VORTICES. AT
250 HPA...THE SUBTROPICAL AND POLAR JETS ARE TO ACCOMPANY THE
SHORT WAVE TROUGH AS IT PROPAGATES ACROSS CENTRAL ARGENTINA ON
SUNDAY...WITH THE JETS FORECAST TO COUPLE ON THEIR DIVERGENT
ENTRANCE/EXIT REGIONS. AT LOW LEVELS...THIS WILL SUSTAIN AN
OCCLUDED LOW OFF THE SOUTH COAST OF CHILE EARLY IN THE
PERIOD...WITH FRONT STREAMING ACROSS PATAGONIA IN
ARGENTINA-SOUTHERN CHILE. THE FRONT IS TO SLOWLY MOVE NORTH ACROSS
PATAGONIA TO LA PAMPA IN ARGENTINA ON FRIDAY-SATURDAY...MOVING
NORTH ACROSS CENTRAL CUYO LATER IN THE DAY. MID LEVEL TROUGH WILL
THEN INDUCE A FRONTAL WAVE/LOW ON SUNDAY THAT PROPELS THE FRONT
NORTH ACROSS RIO DE LA PLATA BASIN TO MENDOZA...WITH FRONT
TRIGGERING A PREFRONTAL SQUALL LINE AS IT SURGES ACROSS SOUTHERN
BRASIL-NORTHERN ARGENTINA ON MONDAY. ACROSS SOUTHERN CHILE
EXPECTING SCATTERED CONVECTION OVER THE NEXT TWO DAYS...TO RESULT
IN MAXIMA OF 10-15MM/DAY. AS THE FRONT PUSHES NORTH ACROSS CENTRAL
ARGENTINA ON SATURDAY IT IS TO SUSTAIN LIGHT TO MODERATE
CONVECTION WITH MAXIMA OF 05-10MM. ON SUNDAY THIS INCREASES TO
20-40MM WHILE BUILDING NORTH ACROSS THE BUENOS AIRES
PROVINCE...WHERE IT IS PROBABLE TO FAVOR SEVERE THUNDERSTORMS.
MOST INTENSE CONVECTION...HOWEVER...IS EXPECTED IN ASSOCIATION
WITH THE PREFRONTAL SQUALL LINE ON MONDAY...WITH MAXIMA OF 25-50MM
ACROSS PARAGUAY-MATO GROSSO DO SUL. OVER CENTRAL BOLIVIA...AS
ENHANCED BY A SOUTHERLY LOW LEVEL JET...THIS INCREASES TO 40-80MM.
ALSO ON SUNDAY...AS THE MID LEVEL TROUGH SPILLS ACROSS THE CENTRAL
ANDES OF CHILE...IT WILL SUSTAIN SCATTERED SNOW SHOWERS...WITH
ACCUMULATION OF 04-08CM.

NORTH OVER THE CONTINENT...AT 250 HPA...AN ILL ORGANIZED CELL OF
THE SUBTROPICAL RIDGE WILL CONFINE TO CONTINENTAL AREA NORTH OF
20S. THE RIDGE ALOFT SUSTAINS AN UPPER DIVERGENT PATTERN ACROSS
NORTHERN BRASIL TO EQUATORIAL SOUTH AMERICA...WITH DEEP
MOISTURE/CONVECTION CLUSTERING ALONG THE NEAR EQUATORIAL TROUGH TO
THE NORTH. ACROSS AMAPA TO PARA IN BRASIL...THIS WILL HELP SUSTAIN
ORGANIZED DEEP CONVECTION...WITH MAXIMA OF 35-70MM EARLY IN THE
CYCLE INCREASING TO 40-80MM ON SATURDAY-SUNDAY. OVER AMAZONAS TO
THE WEST...MEANWHILE...INITIALLY EXPECTING ACCUMULATION OF
35-70MM...TO ALSO INCREASE TO 40-80MM WHILE BUILDING WEST ACROSS
AMAZONIA IN SOUTHERN COLOMBIA TO NORTHERN PERU. THIS IS TO THEN
GRADUALLY DECREASE TO 20-35MM/DAY LATER DURING THE WEEKEND/EARLY
NEXT WEEK. OVER THE EASTERN PACIFIC EXPECTING BOTH BRANCHES OF THE
ITCZ TO BECOME VERY ACTIVE EARLY IN THE CYCLE AS ENHANCED BY
DIVERGENT PHASE OF THE MADDEN-JULIAN OSCILLATION. PER THE CLIMATIC
FORECAST SYSTEM THIS IS TO ALSO COINCIDE WITH AN ATMOSPHERIC
KELVIN WAVE PROPAGATING ACROSS THE BASIN. AT LOW LEVELS THIS WILL
CONTRIBUTE TO THE INTENSIFICATION OF THE PANAMANIAN LOW/TROUGH.
THIS...IN-TURN...IS TO THEN FAVOR A LONG FETCH WESTERLY FLOW THAT
IS TO ENHANCE MOISTURE CONVERGENCE ACROSS ECUADOR. THROUGH FRIDAY
CONVECTION WILL SURGE...WITH MAXIMA INCREASING TO 40-80MM ON
FRIDAY-SATURDAY...WITH SIMILAR AMOUNTS ON SUNDAY-MONDAY. IN
BETWEEN...THE DAILY MAXIMA DECREASES TO 20-40MM/DAY. THE RIDGE
ALOFT IS TO ALSO VENT DIURNAL CONVECTION ALONG THE SIERRA OF PERU.
IN THIS AREA INITIALLY EXPECTING ACCUMULATION OF 10-15MM. ON
FRIDAY-SATURDAY AS A DEEPER PLUME OF MOISTURE ADVECTS FROM THE
EAST THIS INCREASES TO 20-30MM...THEN WEAKENS TO 05-10MM/DAY ON
SATURDAY-SUNDAY.

DAVISON...WPC (USA)
GALVEZ...WPC (USA)
$$




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