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000
FXSA20 KWBC 221607
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1206 PM EDT WED MAY 22 2013

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

MODEL COMPARISON (VALID FROM 00 UTC MAY 22): MODELS ARE IN
EXCELLENT AGREEMENT IN FORECAST EVOLUTION THROUGH THE CYCLE. A FEW
DISCREPANCIES START DEVELOPING AFTER 108-120 HRS IN THE SOUTHERN
STREAM.

LONG WAVE TROUGH IS SLOWLY EVOLVING OVER THE BELLINGSHAUSEN
SEA/ANTARCTIC PENINSULA WHILE MOVING INTO THE WEDDELL SEA. THIS
TROUGH HAS SEVERAL SHORT WAVE VORTICES REVOLVING RAPIDLY AROUND
MAIN AXIS...LEADING TO SEVERAL ROUNDS WITH SHOWERS AND MODERATE
WINDS IN SOUTHERN CHILE/SOUTHERN PATAGONIA. MOISTURE WILL BE
LIMITED SO EXPECTING MOSTLY LIGHT ACCUMULATIONS WITH THE SYSTEMS.
OROGRAPHICAL CONVERGENCE WILL ENHANCE ACCUMULATIONS FURTHER NORTH.
EXPECTING ISOLATED MAXIMA PEAKING AT 10-15MM/DAY NEAR ISLA CHILOE
ON DAY 01...AND BETWEEN TEMUCO AND PUERTO MONTT ON DAY 02.

MODELS CONTINUE FORECASTING LONG WAVE RIDGE BUILDING OVER THE
EASTERN PACIFIC THROUGH MID CYCLE. THIS WILL HELP AMPLIFY LONG
WAVE TROUGH TO THE EAST. AT LOW LEVELS...THIS WILL SUSTAIN A DEEP
POLAR TROUGH OVER THE WESTERN ATLANTIC WITH ASSOCIATED FRONT TO
RACE ACROSS RIO DE LA PLATA TO URUGUAY-CORDOBA IN ARGENTINA BY 72
HRS. THROUGH 96 HRS THE FRONT WILL MOVE FARTHER NORTH ACROSS THE
SOUTHERN STATES OF BRASIL TO SAO PAULO-PARAGUAY. AS THE FRONT
SURGES NORTH...A POLAR RIDGE IS TO THEN BUILD ACROSS ARGENTINA
WHILE CENTERING ON A 1025 HPA HIGH. THIS IS TO SUSTAIN A COLD
ADVECTIVE PATTERN INTO MID SECTIONS OF SOUTH AMERICA.
ACCUMULATIONS WITH THIS SYSTEM WILL BE GENERALLY LIGHT...AS HIGH
PRECIPITABLE WATER WILL REMAIN BLOCKED TO THE NORTH OF 10/15S.

A SUBTROPICAL UPPER JET WILL DOMINATE MID SECTIONS OF THE
CONTINENT. A FEW WEAK PERTURBATIONS WILL PROPAGATE EASTWARD IN THE
REGION ENHANCING ACCUMULATIONS LOCALLY. AT LOW-LEVELS...A
STATIONARY FRONT IS TO PERSIST FROM SOUTHEASTERN BRASIL INTO
CENTRAL BOLIVIA. MOST ACTIVE CONVECTION WILL CLUSTER ALONG
SOUTHEASTERN BRASIL...WHERE HIGHER MOISTURE AND BETTER
DYNAMIC/OROGRAPHICAL FORCING WILL ENHANCE ACCUMULATIONS THROUGH
MID-CYCLE. THROUGH 36 HRS...EXPECTING HEAVIEST ALONG
PARANA/NORTHERN SANTA CATARINA INTO EASTERN SAO PAULO WITH
ACCUMULATIONS OF 15-20MM/DAY. ON DAY 02...HEAVIEST WILL
CONCENTRATE ALONG EASTERN RIO DO JANEIRO WITH ISOLATED
ACCUMULATIONS OF 15-20MM/DAY. LIGHTER AMOUNTS ARE EXPECTED FURTHER
INLAND/NORTHWEST INTO SOUTHEASTERN MATO GROSSO DO SUL/NORTHEASTERN
PARAGUAY. NEAR THE TAIL OF THE STATIONARY FRONT...LIGHT CONVECTION
INITIALLY WILL INCREASE IN STRENGTH THROUGH MID-CYCLE AS LOW-LEVEL
MOISTURE CONVERGENCE IMPROVES...AND AN UPPER TROUGH ARRIVES IN
FROM THE WEST. EXPECTING ACCUMULATIONS TO PEAK AT 15-20MM/DAY IN
THE BOLIVIAN YUNGAS/CEJA DE SELVA OF SOUTHERN PERU ON DAY 03.
OTHERWISE EXPECT ISOLATED SHOWERS AND ISOLATED DIURNAL
THUNDERSTORMS ALONG THE EASTERN SLOPES.

AT 200 HPA...A WEAK CELL OF THE SUBTROPICAL RIDGE IS FORECAST TO
CONCENTRATE ON A CLOSED HIGH FORMING OVER AMAZONAS IN
BRASIL-NORTHERN JUNGLE OF PERU BY 48-72 HRS...WITH AXIS TO THEN
BUILD WHILE GRADUALLY MIGRATING EAST ACROSS NORTHERN STATES OF
BRASIL LATER IN THE CYCLE. THE AFOREMENTIONED UPPER TROUGH WILL
MOVE IN FROM THE EASTERN PACIFIC ON DAY 03 AND AMPLIFY WHILE
MOVING EASTWARD. BY 120 HRS THE TROUGH WILL EXTEND ACROSS BAHIA
INTO AMAPA IN BRASIL. THE EFFECT OF THE TROUGH IN ACCUMULATIONS
WILL BE MARGINAL...ENHANCING CONVECTION ACROSS THE NORDESTE
SLIGHTLY BY LATE CYCLE. BEST VENTILATION WILL PERSIST IN NORTHERN
PERIPHERY OF UPPER HIGH...LEADING TO SEASONAL CONVECTION ACROSS
NORTHERN PERU/ECUADOR/COLOMBIA INTO NORTHERN BRASIL. EXPECTING
ACCUMULATIONS IN THE ORDER OF 15-35MM/DAY DECREASING TOWARDS LATE
CYCLE.

MAQUEDA...DINAC (PARAGUAY)
SILVA DE SOUZA...INMET (BRASIL)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)
$$