Prognostic Meteorological Discussion
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FXSA20 KWBC 181810
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
110 PM EST THU JAN 18 2018

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

MODEL DISCUSSION (VALID FROM JAN 18 AT 0000 UTC): NORTHERN
ARGENTINA-SOUTHERN BRASIL IS THE AREA OF CONCERN...WHERE
ENVIRONMENTAL CONDITIONS ARE LIKELY TO BECOME FAVORABLE FOR THE
GENERATION OF MESO SCALE CONVECTIVE SYSTEMS DURING THE NEXT
SEVERAL DAYS. THE GFS IS SLOWLY TRENDING TOWARDS A MORE
ACTIVE/BETTER ORGANIZED SYSTEM...FOLLOWING THE TREND OF THE
EUROPEAN AND CANADIAN MODELS.

AN AMPLIFYING MID LEVEL TROUGH IS TO DOMINATE THE FLOW OVER THE
WESTERN ATLANTIC DURING THE NEXT COUPLE OF DAYS...WITH MID LEVEL
TROUGH TO SLOWLY PULL ACROSS THE CENTRAL SOUTH ATLANTIC LATER ON
SATURDAY. A SHORT WAVE TROUGH ON THE NORTHERN STREAM CLOSELY
FOLLOWS...NEARING CENTRAL CHILE LATER TODAY. THIS IS TO MEANDER
OFF THE COAST OF CHILE THROUGH FRIDAY EVENING...MEANWHILE SHEARING
SHORT WAVE ENERGY ACROSS THE CENTRAL ANDES INTO CENTRAL
ARGENTINA-RIO DE LA PLATA BASIN. ON SATURDAY THE SHORT WAVE TROUGH
SPILLS ACROSS THE ANDES AND MOVES TO CENTRAL/NORTHERN
ARGENTINA-RIO DE LA PLATA BASIN/SOUTHERN STATES OF BRASIL...WHERE
IT IS TO REMAIN THROUGH SUNDAY EVENING. AS IT SPILLS ACROSS THE
ANDES...AT 250 HPA A SUBTROPICAL JET MAXIMA IS TO ACCOMPANY THIS
FEATURE. THE JET ALOFT IS TO FAVOR AN UPPER DIVERGENT PATTERN
ACROSS NORTHERN ARGENTINA STARTING DURING THE EARLY MORNING HOURS
ON SATURDAY...TO PERSIST THROUGH SUNDAY EVENING/MONDAY MORNING. AT
LOW LEVELS...A POLAR FRONT SURGES ACROSS THE BUENOS AIRES PROVINCE
TO RIO DE LA PLATA/MENDOZA IN ARGENTINA LATER TODAY. ON FRIDAY IT
PUSHES FARTHER NORTH...MERGING WITH AN OLD BOUNDARY TO THE NORTH.
THE LATTER EXTENDS ACROSS THE SOUTH ATLANTIC TO SOUTHERN
BRASIL-NORTHERN ARGENTINA/PARAGUAY. THE MID LEVEL TROUGH IS TO
INDUCE CYCLOGENESIS ALONG THIS BOUNDARY...WITH THE
CANADIAN/EUROPEAN MODELS FAVORING A DEEPER/STRONGER CYCLONE THAN
WHAT THE GFS. THIS IS TO TRACK TO THE SOUTH-SOUTHEAST ACROSS
URUGUAY LATER ON SUNDAY...DEEPENING AS IT MOVES OFF THE COAST
EARLY ON MONDAY. AS IT MEANDERS OVER THE CONTINENT...THIS BOUNDARY
IS THE FOCUS OF LOW LEVEL MOISTURE CONVERGENCE ACROSS MID SECTIONS
OF SOUTH AMERICA...WITH PRECIPITABLE WATER CONTENT EXPECTED TO
PEAK AROUND 50-60MM DURING THE NEXT SEVERAL DAYS. HIGH MOISTURE
CONTENT WILL COMBINE WITH FAVORABLE MID/UPPER DYNAMICS TO LIKELY
FAVOR GENERATION OF HEAVY RAINFALL PRODUCING MESO SCALE CONVECTIVE
SYSTEMS. STARTING TODAY EXPECTING MAXIMA OF 25-50MM OVER CHACO
ARGENTINO-CORRIENTES-PARAGUAY. ON FRIDAY TO SATURDAY THIS
INCREASES TO 35-70MM WHILE BUILDING EAST ACROSS MISIONES IN
ARGENTINA TO SOUTHERN BRASIL. PEAK IN CONVECTION IS EXPECTED ON
SATURDAY TO SUNDAY...AS THE LOW LEVEL CYCLONE FORMS ALONG THE
MEANDERING FRONT...WITH MAXIMA OF 50-100MM. DURING THIS PERIOD
LOCALLY HIGHER AMOUNTS HIGHLY PROBABLE...WITH SOME OF THE MODELS
SHOWING MAXIMA OF 150-200MM. OVER THE NEXT FEW DAYS STRONG
MESO-SYNOPTIC FORCING IS ALSO LIKELY TO RESULT IN SEVERE
CONVECTION.

UPSTREAM OVER THE EASTERN SOUTH PACIFIC...A MID LEVEL TROUGH IS TO
EXTEND NORTH BETWEEN 120W-100W TO 34S LATER TODAY. THE TROUGH IS
TO PRESS AGAINST A RIDGE TO THE EAST...WITH THE LATTER TO EXTEND
SOUTH ALONG 80W TO 60S. ON FRIDAY THE RIDGE RELOCATES TO THE
WESTERN ATLANTIC AS THE TROUGH MOVES TO THE SOUTHEAST
PACIFIC/SOUTHERN CONE OF SOUTH AMERICA. ON SATURDAY TO SUNDAY THE
TROUGH IS TO RAPIDLY WEAKEN WHILE ITS SHORT WAVE ENERGY SHEARS
UNDER THE RIDGE TO THE EAST. AT LOW LEVELS THIS SUSTAINS A BROAD
TROUGH OVER THE SOUTHEAST PACIFIC...FORECAST TO SLOWLY MOVE ACROSS
THE ANTARCTIC PENINSULA-DRAKE PASSAGE LATER TODAY/EARLY FRIDAY
MORNING. POLAR FRONTS ARE TO REVOLVE AROUND THIS AXIS...WITH ONE
TO MEANDER EAST ACROSS SOUTHERN CHILE-PATAGONIA IN ARGENTINA
THROUGH SUNDAY. OVER SOUTHERN CHILE THIS IS TO GENERALLY FAVOR
LIGHT TO MODERATE CONVECTION WITH ACCUMULATION OF 05-10MM/DAY AND
MAXIMA OF 15MM. OVER TIERRA DEL FUEGO EXPECTING LESSER
AMOUNTS...WITH ACCUMULATION OF 00-05MM/DAY OVER THE NEXT FEW DAYS.

NORTH OVER THE CONTINENT...AT 200 HPA...AN EAST-TO-WEST RIDGE
EXTENDS ACROSS SOUTHERN BRASIL-PARAGUAY-BOLIVIA TO THE EASTERN
PACIFIC....WITH AXIS ANCHORING ON CLOSED HIGHS OVER BOLIVIA AND
PARAGUAY/MATO GROSSO DO SUL IN BRASIL. LATER ON FRIDAY THESE ARE
TO COMBINE INTO A SINGLE HIGH THAT IS TO MEANDER BETWEEN THE
ALTIPLANO OF BOLIVIA AND NORTHERN CHILE/SOUTHERN SIERRA OF PERU.
AS THE RIDGE MEANDERS OVER MID SECTIONS OF SOUTH AMERICA IT IS TO
STEER AN UPPER LEVEL LOW/SHORT WAVE TROUGH ACROSS NORTHEAST BRASIL
TO PARA LATER ON FRIDAY. AS IT MEANDERS WEST...THIS WILL INTERACT
WITH THE NEAR EQUATORIAL TROUGH OVER NORTHERN BRASIL TO FAVOR
ORGANIZED DEEP CONVECTION. ALONG THE CONVERGENCE ZONE OVER
NORTHERN AMAZONAS-PARA/RORAIMA EXPECTING RAINFALL AMOUNTS OF
25-50MM/DAY...WITH LOCALIZED MAXIMA OF 80MM. THROUGH SUNDAY THIS
DECREASES TO 10-15MM/DAY AND MAXIMA OF 20-35MM...WHILE OVER
NORTHEAST BRASIL THE MAXIMA IS TO PEAK AT 25-50MM. MODERATE TO
HEAVY RAINS ARE ALSO EXPECTED ACROSS ECUADOR ON
FRIDAY-SATURDAY...WITH MAXIMA OF 20-35MM/DAY. OVER THE
ALTIPLANO-SOUTHERN SIERRA OF PERU THE DAILY MAXIMA WILL RANGE
BETWEEN 10-15MM/DAY THROUGH SATURDAY...INCREASING TO 15-20MM ON
SUNDAY.

OVIEDO...SHN (ARGENTINA)
POMIER...SENAMHI (BOLIVIA)
DAVISON...WPC (USA)
$$





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