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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1732Z Apr 27, 2022)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
132 PM EDT WED APR 27 2022

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

FORECAST DISCUSSION FROM APR 27/18 UTC: THE GLOBAL MODELS
INITIALIZE A HIGH AMPLITUDE LONG WAVE TROUGH WITH AXIS TO THE
NORTH/NORTHWEST FROM THE WEDDELL SEA/ANTARCTIC PENINSULA TO MID
SECTIONS OF SOUTH AMERICA. A SUBTROPICAL AND A NORTHERN POLAR JET
MAXIMA ROUNDING THE BASE OF THE TROUGH COUPLED OVER THE WESTERN
ATLANTIC...SUSTAINING A BROAD AREA OF DIVERGENCE OFF THE COAST OF
ARGENTINA. THIS IS INDUCING THE RAPID INTENSIFICATION OF A SURFACE
LOW AS IT STREAMS TOWARDS THE SOUTH GEORGIA ISLANDS...WITH CLOSED
CIRCULATION EXPLOSIVELY INTENSIFYING FROM A 985 HPA LOW EARLY THIS
MORNING TO A 952 HPA LOW LATER THIS EVENING. EARLY ON THURSDAY
MORNING THE LOW REACHES PEAK INTENSITY...WITH CENTRAL PRESSURE
FORECAST TO DROP TO 936 HPA. THE INTENSE RATE OF INTENSIFICATION
WILL LEAD TO HURRICANE INTENSITY WINDS NORTH AND EAST OF THE
SURFACE LOW...WHILE INTENSE UPWARD VERTICAL MOTION IS LIKELY TO
RESULT IN EXTREME TURBULENCE.

THE BROAD SURFACE TROUGH AND THE DEEPENING LOW/METEOROLOGICAL BOMB
SUSTAINS A SURFACE FRONT OVER THE CONTINENT THAT MOVES NORTH
ACROSS URUGUAY TO SOUTHERN BRASIL/NORTHERN ARGENTINA LATER THIS
EVENING. ON THURSDAY...DRIVEN BY A POLAR RIDGE BUILDING ACROSS THE
SOUTHERN CONE...THE FRONT SURGES ACROSS PARAGUAY TO CENTRAL
BOLIVIA...WHERE IT IS EXPECTED TO STALL THROUGH THE END OF THE
WEEK. MEANWHILE...ACROSS URUGUAY TO RIO GRANDE DO SUL IN
BRASIL/CORRIENTES IN ARGENTINA THIS WILL SUSTAIN ORGANIZED DEEP
CONVECTION...WITH MAXIMA OF 75-150MM IN HIGHLY LIKELY SEVERE
THUNDERSTORMS. ON THURSDAY-FRIDAY EXPECTING MODERATE RAINFALL
AMOUNTS TO PERSIST ACROSS SOUTHERN BRASIL TO SOUTHEAST
PARAGUAY...WITH MAXIMA OF 20-35MM/DAY...WHILE OVER CENTRAL BOLIVIA
IT SURGES TO 30-60MM AS ENHANCED BY A SOUTHERLY LOW LEVEL JET
ACROSS PARAGUAY. OTHER PRECIPITATION IS EXPECTED ACROSS THE
SOUTHERN TO CENTRAL ANDES OF CHILE...WHERE THE BROAD TROUGH WILL
SUSTAIN HEAVY SNOWFALL AMOUNTS...WITH ACCUMULATION OF 15-30CM.

THROUGH THE WEEKEND...A MID/UPPER LEVEL SHORT WAVE TROUGH LIFTS
ACROSS THE SOUTHERN CONE. THROUGH SUNDAY MODELS FORECAST THIS
VORTEX TO DEEPEN AS IT LIFTS ALONG THE EASTERN FRINGES OF A BROAD
RIDGE TO THE WEST. THE MID/UPPER LEVEL TROUGH WILL THEN INTERACT
WITH THE AFOREMENTIONED FRONT AS IT MEANDERS ACROSS SOUTHERN
BRASIL-PARAGUAY. THIS WILL STRENGTHEN THE BAROCLINIC BOUNDARY AND
WOULD LIKELY TRIGGER ANOTHER ROUND OF ORGANIZED DEEP CONVECTION
ACROSS SOUTHERN BRASIL-MISIONES IN ARGENTINA AND SOUTHEAST
PARAGUAY. DURING THIS PERIOD THE CONSENSUS AMONG THE DETERMINISTIC
AND ENSEMBLE GUIDANCE IS HIGH...LEADING TO A HIGHER THAN NORMAL
CONFIDENCE IN THE FORECAST AS WE ENTER THE LONG RANGE PERIOD.

DAVISON...WPC (USA)