SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
106 PM EDT TUE MAY 03 2022

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

FORECAST DISCUSSION FROM MAY 03/18 UTC: UNDER THE INFLUENCE OF A
SHORT WAVE RIDGE TO THE WEST...A MID/UPPER LEVEL SHORT WAVE TROUGH
ON THE NORTHERN STREAM FLOW LIFTS ACROSS NORTHERN ARGENTINA/RIO DE
LA PLATA BASIN TO SOUTHERN BRASIL-PARAGUAY LATER THIS
AFTERNOON...WHERE IT ORGANIZES INTO A MID LEVEL LOW. AT 250
HPA...A SUBTROPICAL JET MAXIMA ROUNDING THE BASE OF THE UPPER
LEVEL TROUGH WILL COUPLE ON ITS DIVERGENT RIGHT EXIT REGION WITH A
NORTHERN POLAR JET OFF THE SOUTH COAST OF BRASIL. THIS WILL RESULT
IN A BROAD AREA OF UPPER DIVERGENCE AND ENVIRONMENTAL CONDITIONS
FAVORABLE FOR THE INSTENSIFICATION OF A FRONTAL LOW. THROUGH LATE
WEDNESDAY EVENING/EARLY ON THURSDAY THE SLOW TO EVOLVE MID/UPPER
LEVEL LOW WILL MEANDER EAST ACROSS SOUTHERN BRASIL TO THE WESTERN
ATLANTIC. BUT WHILE REMAINING CUT OFF FROM THE FLOW...IT WILL THEN
WEAKEN TO AN OPEN TROUGH EARLY ON FRIDAY.

AT LOW LEVELS...THE MID/UPPER LEVEL LOW IS INTERACTING WITH A
MEANDERING FRONT OVER NORTHERN SOUTH AMERICA...TRIGGERING
CYCLOGENESIS OVER SOUTHERN BRASIL. UNDER THE FAVORABLE INFLUENCE
OF THE UPPER LEVEL JETS...THE SURFACE LOW IS EXPECTED TO RAPIDLY
OCCLUDE THROUGH THIS EVENING. THIS...IN-TURN...WILL ALSO FAVOR A
SOUTHERLY JET ACROSS BOLIVIA TO PERU. THIS WILL DRIVE THE FRONT
NORTH ACROSS SAO PAULO-MATO GROSSO TO RONDONIA/NORTHERN BOLIVIA
LATER TODAY. ON WEDNESDAY THE FRONT ADVANCES ACROSS RIO DE
JANEIRO/MINAS GERAIS TO SOUTHERN AMAZONAS...WEAKENING TO A FRONTAL
SHEAR LINE ACROSS CENTRAL AMAZONAS TO NORTHERN JUNGLE OF
PERU/SOUTHERN COLOMBIA. THIS WILL PERSIST THROUGH THURSDAY...THEN
RAPIDLY WEAKEN OVER THE CONTINENT ON FRIDAY. THE REMAINING
PORTION...MEANWHILE...WHILE PERSIST OVER THE ATLANTIC INTO
NORTHERN RIO DE JANEIRO/ESPIRITO SANTO-MINAS GERAIS THROUGH THE
END OF THE WEEK. AS THE FRONTAL LOW OCCLUDES OVER SOUTHERN
BRASIL...IT WILL SUSTAIN A MOIST ONSHORE FLOW. IN THIS AREA THIS
WILL FAVOR HEAVY RAINFALL AMOUNTS DURING THE NEXT 48-60 HRS...WITH
ACCUMULATION OF 30-60MM/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 EXPECTING ADDITIONAL RAINFALL AMOUNTS OF
25-50MM THROUGH WEDNESDAY MORNING. ON WEDNESDAY TO THURSDAY THE
FOCUS OF THE ORGANIZED CONVECTION SHIFTS ALONG THE SHEAR LINE TO
THE NORTHERN JUNGLE OF PERU/EASTERN ECUADOR TO SOUTHERN
COLOMBIA...WITH MAXIMA OF 75-150MM. ON THURSDAY TO FIRDAY IT
WEAKENS TO MAXIMA OF 25-50MM

IN A TIGHT BELT OF MID LATITUDE WESTERLIES...PROGRESSIVE SHORT
WAVE PERTURBATIONS WILL POPULATE THE SOUTHERN STREAM FLOW. THESE
ARE TO PROPAGATE ACROSS THE DRAKE PASSAGE/SOUTHERN REGIONS OF
CHILE TO PATAGONIA IN ARGENTINA FROM TIME-TO-TIME. AS THESE TRACK
OVER WARMER THAN NORMAL WATERS OVER THE SOUTHEAST PACIFIC...THESE
PERTURBATIONS WILL ENHANCE MOISTURE TRANSPORT WHILE PROVIDING THE
DYNAMICAL SUPPORT. 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. OVER THE NEXT TWO DAYS
MAXIMA TO THE SOUTH OF TEMUCO/PUERTO MONTT WILL PEAK AT
30-60MM/DAY. ON FRIDAY...UNDER THE INFLUENCE OF A DEEPER/HIGHER
AMPLITUDE TROUGH...THIS INCREASES TO MAXIMA OF 50-100MM...WITH AN
ADDITIONAL 20-45MM/DAY DURING THE WEEKEND.

DAVISON...WPC (USA)