Prognostic Meteorological Discussion
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000
FXSA20 KWBC 281634
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1233 PM EDT THU JUL 28 2016

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

MODEL DISCUSSION (VALID FROM JULY 28 AT 0000 UTC): OVER THE
EASTERN PACIFIC...ON THE SOUTHERN STREAM...A MID/UPPER LEVEL RIDGE
IS TO BUILD SOUTH OF 50S INTO THE DRAKE PASSAGE/ANTARCTIC
PENINSULA DURING THE NEXT FEW DAYS. NORTH OF THIS RIDGE...IN A
SPLIT FLOW PATTERN...A TROUGH LIES OFF THE SOUTHERN/CENTRAL COAST
OF CHILE...WHERE IT IS FORECAST TO REMAIN NEARLY STATIONARY
THROUGH THE MEDIUM RANGE PERIOD. AS IT MEANDERS OVER THE EASTERN
PACIFIC THIS WILL FAVOR A MOIST ADVECTIVE PATTERN...WITH DEEP
SUBTROPICAL MOISTURE CONVERGING ON THE SOUTHERN ANDES. AT LOW
LEVELS THIS WILL SUSTAIN A BROAD TROUGH...WITH POLAR FRONTS TO
STREAM ACROSS SOUTHERN CHILE INTO PATAGONIA WHILE REVOLVING AROUND
THE SURFACE TROUGH. THIS IS TO ALSO SUSTAIN A STRONG NORTHWESTERLY
FLOW INTO SOUTHERN REGIONS OF CHILE...WITH MECHANICAL/ADIABATIC
LIFTING EXPECTED DURING THE NEXT FEW DAYS. THIS WILL RESULT IN
AREAS OF MODERATE TO HEAVY CONVECTION...WITH MAXIMA OF 25-50MM
EXPECTED BETWEEN TEMUCO-ISLA DE CHILOE ON DAY 01. MODERATE
CONVECTION WILL THEN PERSIST THROUGH DAY 03...TO RESULT IN STORM
TOTAL AMOUNTS OF NEARLY 100MM.

AS THE MID LEVEL TROUGH REMAINS OVER THE EASTERN PACIFIC...IT IS
TO SHEAR SHORT WAVE ENERGY ACROSS THE CENTRAL/NORTHERN ANDES OF
CHILE INTO ARGENTINA. IN THIS PATTERN A FAIRLY STRONG VORTEX IS TO
STREAM ACROSS THE ANDES INTO MENDOZA ARGENTINA BY 72-84
HRS...CROSSING RIO DE LA PLATA BASIN BY 96 HRS. AT LOW LEVELS THIS
IS TO SUSTAIN A FRONTAL LOW OVER ENTRE RIOS IN ARGENTINA/URUGUAY
BY 84-96 HRS...TO SLOWLY PULL TO THE EAST SOUTHEAST ACROSS URUGUAY
WHILE THE ASSOCIATED FRONT MEANDERS NORTH INTO SOUTHERN
BRASIL-NORTHERN ARGENTINA. UNDER FAVORABLE JET DYNAMICS THIS WILL
TRIGGER MODERATE CONVECTION WITH ACCUMULATION OF 15-20MM BY 84
HRS...INCREASING TO 20-30MM BY 84-108 HRS. ON THE CENTRAL ANDES OF
CHILE THIS IS TO ALSO TRIGGER MODERATE SNOWFALL AMOUNTS...WITH
ACCUMULATION OF 15-20CM.

OVER THE ATLANTIC...MEANWHILE...BROAD TROUGH DOMINATES THE FLOW
BETWEEN 50W-10W AND TO THE SOUTH OF 20S. THE TROUGH IS TO SLOWLY
PULL TO THE EAST-SOUTHEAST OVER THE NEXT THREE DAYS. AT LOW LEVELS
THIS SUSTAINS A BROAD TROUGH...WITH POLAR FRONT TRAILING ACROSS
RIO DE JANEIRO/NORTHERN SOA PAULO TO BOLIVIA. THROUGH 48 HRS THE
FRONT MEANDERS NORTH INTO ESPIRITO SANTO WHILE TRAILING END
WEAKENS AS IT RETROGRESSES ACROSS PARAGUAY TO NORTHERN ARGENTINA.
BUILDING RIDGE DISPLACES THIS BOUNDARY FARTHER NORTH INTO BAHIA
BRASIL LATER IN THE CYCLE. THE BUILDING RIDGE WILL SUSTAIN A TRADE
WINDS SURGE ACROSS NORTHEAST BRASIL...AND IT IS TO ALSO FAVOR
GENERATION OF A PREFRONTAL SHEAR LINE. THE SHEAR LINE IS TO SLOWLY
MOVE NORTH ACROSS ESPIRITO SANTO-BAHIA TO RIO GRANDE DO NORTE
THROUGH 72-84 HRS. MEANWHILE...THIS IS TO ENHANCE LOW LEVEL
MOISTURE CONVERGENCE...FAVORING SCATTERED COASTAL CONVECTION WITH
ACCUMULATION OF 10-15MM/DAY. MOST INTENSE IS EXPECTED AFTER 48-60
HRS...TO PERSIST THROUGH AT LEAST 108 HRS.

NORTH OVER THE CONTINENT...AT 200 HPA...A NEAR ZONAL WESTERLY FLOW
PREVAILS PERU TO BRASIL. THROUGH 48-72 HRS PATTERN WILL GROW MORE
AMPLIFIED...WITH A RIDGE BUILDING ACROSS PERU/AMAZONAS IN BRASIL
AND A TROUGH DIGGING ACROSS PARA TO THE EAST. THE AMPLIFYING
TROUGH IS TO THEN ENHANCE CONVECTION ALONG THE NORTH COAST OF
BRASIL...TO RESULT IN AREAS OF MODERATE CONVECTION. MAXIMA IN THIS
AREA IS TO PEAK AT 15-25MM/DAY. OTHER DIURNAL CONVECTION TO THE
WEST IS TO BUILD ACROSS NORTHERN PERU-ECUADOR TO COLOMBIA-NORTHERN
AMAZONAS IN BRASIL. IN THIS AREA THE DAILY MAXIMA IS TO PEAK AT
05-10MM...INCREASING TO 10-15MM/DAY LATER IN THE CYCLE.

AYALA...DINAC (PARAGUAY)
OSORIO...DMC (CHILE)
DAVISON...WPC (USA)
$$




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