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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1759Z May 02, 2022)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EDT MON MAY 02 2022

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

FORECAST DISCUSSION FROM MAY 02/18 UTC: STEERED BY A MID/UPPER
LEVEL RIDGE TO THE WEST...A SHORT WAVE TROUGH LIFTS ACROSS
CENTRAL/NORTHERN ARGENTINA TO MID SECTIONS OF SOUTH AMERICA LATER
TODAY. THROUGH TUESDAY THIS WILL STRENGTHEN INTO A CLOSED LOW OVER
CORRIENTES/MISIONES IN NORTHERN ARGENTINA WHILE THE SHORT WAVE
TROUGH AMPLIFIES ACROSS PARAGUAY TO SOUTHEAST BOLIVIA. AT 250 HPA
A SUBTROPICAL JET MAXIMA ROUNDING THE BASE OF THE UPPER TROUGH
WILL THEN INTERACT WITH A NORTHERN POLAR JET IN SUPPORT OF A BROAD
AREA OF UPPER DIVERGENCE ON THE SOUTHERN STATES OF BRASIL. THROUGH
THURSDAY MORNING THE SLOW TO EVOLVE MID/UPPER LEVEL LOW WILL
MEANDER EAST ACROSS SOUTHERN BRASIL TO THE WESTERN ATLANTIC.
THROUGH FRIDAY AFTERNOON THE LOW WILL START TO WEAKEN TO AN OPEN
TROUGH WHILE MEANDERING EAST ACROSS 40W.

AT LOW LEVELS...THE UPPER LEVEL LOW WILL THEN INTERACT WITH A
MEANDERING FRONT EXTENDING ACROSS SOUTHERN BRASIL-PARAGUAY TO
CENTRAL BOLIVIA. UNDER THE CYCLOGENIC INFLUENCE OF THE MID LEVEL
VORTEX AND FAVORABLE UPPER LEVEL JET DYNAMICS A FRONTAL LOW
DEVELOPS ALONG THIS BOUNDARY BETWEEN SOUTHEAST PARAGUAY/MISIONES
IN ARGENTINA LATER TODAY/EARLY ON TUESDAY. THE LOW IS TO GRADUALLY
OCCLUDE WHILE DRIFTING TO THE EAST-NORTHEAST ACROSS THE SOUTHERN
STATES OF BRASIL. AS IT DEEPENS...THIS WILL FAVOR A MOIST ONSHORE
FLOW ACROSS RIO GRANDE DO SUL IN SOUTHERN BRASIL...WHILE OVER THE
CONTINENT IT WILL SUSTAIN A SOUTHERLY FLOW. THIS DRIVES THE FRONT
FARTHER NORTH ACROSS CENTRAL TO NORTHWEST BRASIL...WITH TRAILING
END WEAKENING TO A FRONTAL SHEAR LINE AS IT PUSHES NORTH ACROSS
AMAZONAS IN BRASIL TO SOUTHERN COLOMBIA/NORTHERN PERU LATER ON
WEDNESDAY EVENING. OVER SOUTHERN BRASIL THIS WILL SUSTAIN THREE
DAYS OF HEAVY RAINFALL...WITH THE DEEPENING LOW LIKELY TO RESULT
IN A TOPOGRAPHICALLY ENHANCED ECHO TRAINING PATTERN. STARTING
EARLY ON TUESDAY AND PERSISTING THROUGH THURSDAY...EXPECTING
RAINFALL AMOUNTS OF 20-40MM/DAY AND MAXIMA OF 75-150MM/DAY. IN
THIS AREA...STORM TOTAL AMOUNTS OF 350-450 MM ARE HIGHLY LIKELY.
FURTHERMORE...AS THE FRONT SURGES ACROSS BOLIVIA TO ACRE/RONDONIA
IN BRASIL-SOUTHERN PERU ON TUESDAY THROUGH WEDNESDAY EXPECTING
MAXIMA OF 25-50MM IN SCATTERED DEEP CONVECTION. LATER IN THE
WEEK...ACTIVITY CLUSTERING ALONG THE FRONTAL SHEAR LINE OVER
NORTHWEST BRASIL WILL SPREAD ACROSS NORTHERN PERU INTO SOUTHERN
COLOMBIA/EASTERN ECUADOR. MOST INTENSE...HOWEVER...IS EXPECTED ON
THE LEE OF THE ANDES BETWEEN SOUTHWEST COLOMBIA AND EASTERN
ECUADOR...WITH DAILY MAXIMA OF 75-150MM/DAY ON WEDNESDAY THROUGH
FRIDAY MORNING. IN THIS AREA CONDITIONS APPEAR FAVORABLE FOR AN
MCS TO FORM.

ON THE SOUTHERN STREAM FLOW...IN A TIGHT BELT OF MID LATITUDE
WESTERLIES...PROGRESSIVE MID LEVEL PERTURBATIONS ARE TO STREAM
ACROSS THE DRAKE PASSAGE/SOUTHERN REGIONS OF CHILE TO PATAGONIA IN
ARGENTINA FROM TIME-TO-TIME. TRACKING OVER WARMER THAN NORMAL
WATERS OVER THE SOUTH PACIFIC...THESE PERTURBATIONS WILL ENHANCE
MOISTURE TRANSPORT. AT LOW LEVELS PROGRESSIVE FRONTAL LOWS ARE TO
ACCOMPANY THE MID/UPPER LEVEL PERTURBATIONS AS THEY STREAM ACROSS
THE SOUTHERN CONE...SUSTAINING A TIGHT GRADIENT AND STRONG
BOUNDARY LAYER WINDS. ON THE SOUTHERN ANDES OF CHILE AND TIERRA
DEL FUEGO THESE WILL ENHANCE TOPOGRAPHICAL ASCENT TO HELP SUSTAIN
HEAVY RAINFALL AMOUNTS. NOTE THAT THERE IS A STRONG CONSENSUS
AMONG THE DETERMINISTIC AND ENSEMBLE GUIDANCE THROUGH OUT THE
FORECAST CYCLE...LEADING TO HIGHER THAN NORMAL CONFIDENCE IN THE
FORECAST THROUGH THE MEDIUM RANGE PERIOD.

DAVISON...WPC (USA)