Prognostic Meteorological Discussion
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1229 PM EDT FRI SEP 30 2016

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 30 AT 0000 UTC): CONFIDENCE
IN THE FORECAST REMAINS HIGH...WITH MODELS STILL AGREEING QUITE
WELL ON SYNOPTIC PATTERN EVOLUTION DURING THE NEXT FIVE DAYS.
DURING MEDIUM RANGE PERIOD THE ENVIRONMENTAL CONDITIONS ACROSS MID
SECTIONS OF SOUTH AMERICA WILL BECOME FAVORABLE FOR THE GENERATION
OF MESO SCALE CONVECTIVE SYSTEMS. THIS WILL RESULT IN HEAVY RAINS
AND SEVERE WEATHER.

SOUTH OVER THE CONTINENT...AT 500 HPA...SHORT WAVE TROUGH IS TO
MEANDER ACROSS PATAGONIA/LA PAMPA IN ARGENTINA EARLY IN THE
CYCLE...WHILE ANOTHER IS TO PULL ACROSS SOUTHERN/CENTRAL CHILE
LATER ON SATURDAY. AT LOW LEVELS THESE ARE TO FAVOR A BROAD TROUGH
ACROSS THE SOUTHERN CONE...WITH SUCCESSIVE POLAR FRONTS TO REVOLVE
AROUND THIS AXIS DURING THE NEXT TWO DAYS. AS THEY MAKE LANDFALL
OVER SOUTHERN CHILE THIS WILL RESULT IN MOSTLY LIGHT RAINFALL
AMOUNTS...WITH ACCUMULATION OF 00-05MM/DAY. OVER LA PAMPA/BUENOS
AIRES IN ARGENTINA EXPECTING HIGHER AMOUNTS...WITH ACCUMULATION OF
10-15MM THROUGH SATURDAY MORNING...AND 05-10MM ON SATURDAY TO
SUNDAY.

BROAD MID/UPPER LEVEL TROUGH IS TO DOMINATE THE FLOW ACROSS THE
WESTERN SOUTH ATLANTIC DURING THE NEXT FEW DAYS. AT LOW LEVELS
BROAD RIDGE IS TO LIE OFF THE COAST OF ARGENTINA...WHILE TO THE
EAST A TROUGH IS TO DOMINATE THE CENTRAL/EASTERN SOUTH ATLANTIC.
EMBEDDED IN THIS AXIS A POLAR FRONT IS TO EXTEND TO THE NORTHWEST
ACROSS RIO DE JANEIRO/SAO PAULO IN BRASIL TO PARAGUAY/NORTHERN
ARGENTINA. THE MEANDERING FRONT WILL BE THE FOCUS OF MOISTURE
CONVERGENCE ACROSS MID SECTIONS OF SOUTH AMERICA. BROAD CELL OF
THE SUBTROPICAL RIDGE TO THE NORTH IS TO FOCUS THE SUBTROPICAL JET
ACROSS NORTHERN ARGENTINA-PARAGUAY-SOUTHERN BRASIL. AS JET STREAM
MAXIMA STREAK ACROSS MID SECTIONS OF SOUTH AMERICA THIS IS TO
FAVOR PERIODS OF UPPER DIVERGENCE. THIS WILL COMBINE WITH INFLOW
OF MID LEVEL ENERGY TO GRADUALLY FAVOR CYCLOGENESIS ALONG THE
MEANDERING FRONT OVER PARAGUAY. THROUGH SUNDAY EVENING A FRONTAL
WAVE/LOW IS TO DEVELOP OVER SOUTHEAST PARAGUAY. THROUGH MONDAY
AFTERNOON THIS IS TO THEN LIFT ACROSS THE SOUTHERN TO SOUTHEAST
BRASIL. THIS WILL THEN DRAW THE FRONT NORTH TO EXTEND ACROSS
ESPIRITO SANTO/MINAS GERAIS TO MATO GROSSO IN BRASIL. STARTING ON
SUNDAY THIS IS TO THEN RESULT IN HEAVY RAINS WITH EMBEDDED SEVERE
CONVECTION...WITH MAXIMA OF 30-60MM ACROSS NORTHERN PROVINCES IN
ARGENTINA AND PARAGUAY. THROUGH MONDAY EVENING ACTIVITY SPREADS
EAST AND NORTH...WITH MAXIMA OF 50-100MM ACROSS NORTHERN SAO
PAULO-RIO DE JANEIRO/SOUTHERN MINAS GERAIS...WHILE OVER MATO
GROSSO/MATO GROSSO DO SUL AND PORTIONS OF PARAGUAY THE DAILY
MAXIMA WILL PEAK AT 20-45MM.

UPSTREAM OVER THE PACIFIC A LONG WAVE TROUGH IS TO THEN PULL
ACROSS 90W TO 25S LATER ON SUNDAY. THROUGH MONDAY THE TROUGH IS TO
MOVE ACROSS 80W...MEANWHILE FOCUSING SHORT WAVE ENERGY ACROSS
CENTRAL/ SOUTHERN PORTIONS OF CHILE. AS IT ENTERS THE CONTINENT
THE TROUGH WILL INDUCE HEIGHT FALLS IN EXCESS OF 150GPM. ON
TUESDAY THE FOCUS OF THE SHORT WAVE ENERGY WILL SHIFT TO THE
CENTRAL PROVINCES IN ARGENTINA. AT LOW LEVELS THIS WILL SUSTAIN A
POLAR FRONT ACROSS SOUTHERN CHILE EARLY ON MONDAY MORNING...THAT
MOVES EAST TO PATAGONIA-LA PAMPA LATER IN THE DAY. ACROSS LA
PAMPA/NORTHERN PATAGONIA THIS WILL TRIGGER A SQUALL LINE...WITH
MAXIMA OF 25-50MM IN SEVERE CONVECTION. THROUGH TUESDAY...AS THE
FRONT ACCELERATES ACROSS ARGENTINA MAXIMA IS TO INCREASE TO
50-100MM.

NORTH OVER THE CONTINENT...AT 200 HPA...A LOW AMPLITUDE RIDGE IS
TO EXTEND ACROSS EQUATORIAL SOUTH AMERICA AND THE NORTHERN STATES
OF BRASIL. THROUGH SUNDAY EVENING THE RIDGE IS TO GRADUALLY BUILD
IN RESPONSE TO SURGING CONVECTION TO THE NORTHWEST. EARLY IN THE
PERIOD DIURNAL CONVECTION OVER NORTHERN SOUTH AMERICA IS TO PEAK
AT 15-30MM. THROUGH SATURDAY EVENING CONVECTION ACROSS NORTHERN
PERU-COLOMBIA AND EASTERN ECUADOR WILL INCREASE TO
40-80MM/DAY...TO PERSIST THROUGH MONDAY MORNING AS ENHANCED BY A
TROPICAL CYCLONE OVER THE CARIBBEAN. LATER ON MONDAY...IN
SCATTERED CONVECTION...MAXIMA ACROSS NORTHWEST SOUTH AMERICA IS TO
PEAK AT 20-35MM/DAY.

OSORIO...DMC (CHILE)
ALVA...SENAMHI (PERU)
DAVISON/GALVEZ...WPC (USA)
$$





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