Prognostic Meteorological Discussion
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FXSA20 KWBC 051733
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1232 PM EST MON DEC 05 2016

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

MODEL DISCUSSION (VALID FROM DECEMBER 05 AT 0000 UTC): CONFIDENCE
IN THE FORECAST IS HIGH THROUGH 96-108 HRS...WITH MODELS DIVERGING
ON THE INTENSITY/AMPLITUDE OF A MID LEVEL TROUGH ENTERING THE
NORTHERN REGIONS OF CHILE/NORTHWESTER ARGENTINA LATER IN THE
PERIOD. THIS IS ADDING TO THE UNCERTAINTY AND LOWER CONFIDENCE IN
THE FORECAST.

A MID LEVEL SHORT WAVE TROUGH ON THE NORTHERN STREAM FLOW PULLS
ACROSS CENTRAL PROVINCES IN ARGENTINA EARLY IN THE PERIOD...TO
MEANDER EAST ACROSS 50W LATER ON TUESDAY. AS IT MEANDERS OVER THE
SOUTH ATLANTIC...THIS IS TO THEN MERGE WITH A SOUTHERN STREAM
PERTURBATION. THROUGH THURSDAY THEY ARE TO GRADUALLY EVOLVE INTO A
BROAD/LOW AMPLITUDE TROUGH BETWEEN 50W-20W AND TO THE SOUTH OF
30S. AT LOW LEVELS THIS SUSTAIN AN OCCLUDING LOW OFF THE COAST OF
PATAGONIA...WHILE THE ASSOCIATED FRONT MEANDERS NORTH ACROSS RIO
DE LA PLATA BASIN/MENDOZA IN ARGENTINA LATER TODAY. ON TUESDAY
AFTERNOON IT WILL MOVE NORTH TO RIO GRANDE DO SUL BRASIL-NORTHERN
PROVINCES IN ARGENTINA WHERE IT IS FORECAST TO FRONTOLIZE EARLY ON
WEDNESDAY. MEANWHILE...THIS WILL TRIGGER SCATTERED CONVECTION ON
THE RIO DE LA PLATA BASIN WITH ACCUMULATION OF 10-15MM...WHILE
ACROSS MENDOZA AND CORDOBA MAXIMA PEAK AT 20-35MM. ON TUESDAY THIS
WILL DECREASE TO MAXIMA OF 10-15MM.

A SHORT WAVE TROUGH WILL FOLLOW...WITH MID LEVEL AXIS REACHING
SOUTHERN/CENTRAL CHILE LATER ON TUESDAY. THROUGH THURSDAY MORNING
THE TROUGH WILL DEEPEN WHILE DRIFTING NORTH ALONG THE CENTRAL
COAST. LATER ON THURSDAY IT IS TO THEN CENTER ON A CLOSED LOW JUST
WEST OF LA SERENA CHILE. AS IT MEANDERS OFF THE CENTRAL COAST OF
CHILE THIS IS TO SHEAR SHORT WAVE ENERGY WESTWARD ACROSS THE
NORTHERN ANDES INTO THE NORTHERN PROVINCES IN
ARGENTINA-PARAGUAY-SOUTHERN STATES OF BRASIL. IN A MOIST NORTHERLY
LOW LEVEL JET ENVIRONMENTAL CONDITIONS WILL THEN BECOME FAVORABLE
AND HIGHLY CONDUCIVE TO GENERATION OF MESO SCALE CONVECTIVE
SYSTEMS AND POTENTIALLY SEVERE CONVECTION. IN THIS AREA EXPECTING
RAINFALL AMOUNTS OF 35-70MM ON WEDNESDAY EVENING/THURSDAY MORNING
AND AGAIN LATER ON THURSDAY/EARLY FRIDAY MORNING.

LATER IN THE PERIOD A PROGRESSIVE MID LEVEL PERTURBATION IS TO
PULL ACROSS SOUTHERN CHILE TO PATAGONIA ARGENTINA...THEN EAST
ACROSS THE SOUTHERN CONE TO THE WESTERN ATLANTIC LATER ON FRIDAY.
AT LOW LEVELS THIS WILL SUSTAIN A DEEP OCCLUDED LOW OVER THE
BELLINGSHAUSEN SEA LATER ON WEDNESDAY...THAT PULLS INTO THE DRAKE
PASSAGE/SOUTHERN CHILE LATER ON THURSDAY. THIS WILL FAVOR LIGHT
CONVECTION AND STRONG BOUNDARY LAYER WINDS OF 20-35KT.

NORTH OVER THE CONTINENT...AT 200 HPA...THE BOLIVIAN HIGH WILL
DOMINATE THE FLOW ACROSS NORTHWEST SOUTH AMERICA...WHILE A CLOSED
LOW DOMINATES THE FLOW OVER NORTHEASTERN BRASIL. THROUGH THURSDAY
THE RIDGE WILL BUILD EAST AND NORTH TO ENVELOP MOST OF BRASIL. AS
IT BUILDS...IT WILL DISPLACE THE TROUGH NORTH AND EAST INTO
EQUATORIAL SOUTH AMERICA/TROPICAL ATLANTIC. THE RIDGE ALOFT WILL
VENT SCATTERED CONVECTION ACROSS PARA-AMAZONAS TO THE SOUTHEAST
STATES OF BRASIL...WITH RAINFALL AMOUNTS OF 15-20MM IN SCATTERED
DEEP CONVECTION. THROUGH THURSDAY MORNING...AS THE RIDGE
BUILDS...ACTIVITY ACROSS BAHIA-MINAS GERAIS WILL INTENSIFY...WITH
DAILY MAXIMA TO PEAK AT 20-30MM. ACROSS ECUADOR EXPECTING MAXIMA
OF 05-10MM/DAY...WITH AN INCREASE POSSIBLE ON TUESDAY WHEN THE
MAXIMA IS TO PEAK AT 15-20MM. OVER SOUTHERN PERU-CENTRAL BOLIVIA
THE DAILY MAXIMA IS TO PEAK AT 15-20MM OVER THE NEXT FEW DAYS.

ALVA...SENAMHI (PERU)
DURAN...SMN (ARGENTINA)
DAVISON/GALVEZ...WPC (USA)
$$





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