Prognostic Meteorological Discussion
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FXSA20 KWBC 161743
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 PM EST TUE JAN 16 2018

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

MODEL DISCUSSION (VALID FROM JAN 16 AT 0000 UTC): MODELS ARE IN
AGREEMENT ON PATTERN EVOLUTION ACROSS THE SOUTH AMERICAN DOMAIN
THROUGH 72-84 HRS. THEREAFTER THEY THEN DEVELOP AMPLITUDE/SPEED
DIFFERENCES. ON THE SOUTHERN STREAM FLOW THE GFS FAVORS A FASTER
PROGRESSION THAN WHAT THE EUROPEAN MODELS SUGGEST...WHILE ON THE
NORTHERN STREAM FLOW THE UKMET AND ECMWF BOTH FAVOR A DEEPER
TROUGH ON THE NORTHERN STREAM TO MEANDER OVER NORTHERN ARGENTINA
BY 96-144 HRS.

ON THE SOUTHERN STREAM FLOW...EXPECTING A PROGRESSIVE MID LEVEL
TROUGH TO QUICKLY MOVE ACROSS THE DRAKE PASSAGE/SOUTHERN CONE OF
SOUTH AMERICA LATER TODAY. ON WEDNESDAY...BUILDING RIDGE TO THE
WEST IS TO THEN INDUCE THE NORTHWARD AMPLIFICATION OF THIS TROUGH
ALONG 50W TO 40S...TO MEANDER ACROSS 35W/40W LATER ON THURSDAY. AT
LOW LEVELS...THIS SUSTAINS AN ELONGATED FRONT THAT IS TO MEANDER
OVER PATAGONIA IN ARGENTINA-SOUTHERN CHILE DURING THE NEXT FEW
DAYS. AS IT MEANDERS ACROSS SOUTHERN CHILE THIS WILL SUSTAIN A
SUBTROPICAL CONNECTION...WITH DEEP MOISTURE CONVERGING OVER THE
CONTINENT TO THE SOUTH OF 40S. IN THIS AREA INITIALLY EXPECTING
RAINFALL AMOUNTS OF 15-20MM...INCREASING TO 15-30MM ON WEDNESDAY.
ON THURSDAY THE MAXIMA DECREASES TO 10-15MM IN SCATTERED
CONVECTION.

AS THE SOUTHERN STREAM TROUGH PULLS ACROSS THE SOUTHERN CONE IT IS
TO DRAW A SHORT WAVE TROUGH TO THE NORTH. THE MID LEVEL
PERTURBATION ENTERS CENTRAL-NORTHERN CHILE LATER TODAY...CROSSING
CENTRAL PROVINCES IN ARGENTINA-RIO DE LA PLATA BASIN ON WEDNESDAY.
AT LOW LEVELS THIS WILL INTERACT WITH A SURFACE FRONT OVER BUENOS
AIRES PROVINCE/LA PAMPA-CENTRAL CUYO IN ARGENTINA TO SUSTAIN
MODERATE TO HEAVY RAINFALL AMOUNTS. THROUGH WEDNESDAY MORNING
EXPECTING ACCUMULATION OF 25-50MM IN POTENTIALLY SEVERE
CONVECTION....WHILE ON WEDNESDAY EXPECTING MAXIMA OF 20-35MM TO
CLUSTER OVER URUGUAY-ENTRE RIOS IN ARGENTINA.

A HIGHER AMPLITUDE TROUGH IS TO FOLLOW...TO EXTEND NORTH BETWEEN
120W-90W TO SOUTH OF 45S LATER ON THURSDAY. THE DEEPENING TROUGH
IS TO THEN INDUCE A NORTH-TO-SOUTH RIDGE ALONG THE COAST OF CHILE
TO THE BELLINGSHAUSEN SEA/ANTARCTIC PENINSULA. AS THE TROUGH
PUSHES EAST IT IS TO SLOWLY DISPLACE THE RIDGE ACROSS THE SOUTHERN
CONE TO THE WESTERN ATLANTIC LATER ON FRIDAY. AS IT YIELDS...THE
POLAR TROUGH IS TO THEN FOCUS ITS SHORT WAVE ENERGY ACROSS
SOUTHERN REGIONS OF CHILE AND PATAGONIA IN ARGENTINA LATER IN THE
CYCLE. AT LOW LEVELS THIS IS TO SUSTAIN A BROAD TROUGH ACROSS THE
SOUTHEAST PACIFIC LATER ON WEDNESDAY...THAT SLOWLY MOVES ACROSS
THE ANTARCTIC PENINSULA-DRAKE PASSAGE LATER ON THURSDAY/EARLY
FRIDAY MORNING. ASSOCIATED FRONT IS TO MEANDER EAST ACROSS
SOUTHERN CHILE-PATAGONIA IN ARGENTINA ON
THURSDAY-SATURDAY...MEANWHILE FAVORING SCATTERED CONVECTION WITH
MAXIMA OF 05-10MM/DAY.

SIMULTANEOUSLY...A SHORT WAVE TROUGH ON THE NORTHERN STREAM FLOW
IS TO REACH CENTRAL CHILE LATER ON FRIDAY...TO MEANDER EAST ACROSS
CUYO TO CENTRAL ARGENTINA LATER ON SATURDAY. AS PREVIOUSLY
INDICATED...BOTH EUROPEAN MODELS FORESEE A DEEPER TROUGH THAN WHAT
THE GFS SUGGESTS. AT LOW LEVELS AN ELONGATED FRONT EXTENDS ACROSS
THE SOUTH ATLANTIC TO SOUTHERN BRASIL-PARAGUAY/NORTHERN ARGENTINA.
THIS BOUNDARY IS THE FOCUS OF THE LOW LEVEL MOISTURE....WITH HEAVY
RAINS TO AFFECT SOUTHERN BRASIL-SOUTHEAST PARAGUAY EARLY IN THE
CYCLE...WITH RAINFALL MAXIMA OF 40-80MM. ON WEDNESDAY-THURSDAY
THIS DECREASES TO 15-25MM. ON FRIDAY-TO-SATURDAY...AS THE MID
LEVEL TROUGH SPILLS ACROSS THE CENTRAL ANDES...ENVIRONMENTAL
CONDITIONS OVER CENTRAL SOUTH AMERICA ARE TO BECOME FAVORABLE FOR
GENERATION OF A MESO SCALE CONVECTIVE SYSTEM. IN THIS AREA
EXPECTING MAXIMA OF 35-70MM.

AT 200 HPA...A RIDGE EXTENDS EAST-TO-WEST ACROSS SOUTHERN
BRASIL-PARAGUAY-BOLIVIA TO THE EASTERN PACIFIC. AS IT HOLDS...THE
RIDGE IS TO STEER A SHORT WAVE TROUGH TO THE NORTH. EARLY IN THE
CYCLE THE TROUGH WILL EXTEND OVER NORTHEAST BRASIL WHILE CENTERING
ON A CLOSED LOW AT 10S 40W. THIS MEANDERS WEST TO PARA LATER ON
WEDNESDAY/THURSDAY MORNING. BUT AS IT MOVES FARTHER WEST TO
AMAZONAS ON FRIDAY-SATURDAY THE LOW/TROUGH IS TO RAPIDLY WEAKEN.
EARLY IN THE CYCLE THIS IS TO ENHANCE CONVECTION ACROSS NORTHERN
PARA-NORTHEAST COAST OF BRASIL TO SUSTAIN MAXIMA OF 15-25MM/DAY.
HIGHER AMOUNTS ARE EXPECTED TO THE WEST ACROSS
AMAZONAS-RONDONIA-ACRE IN BRASIL...WITH MAXIMA OF 40-80MM. ON
WEDNESDAY AND THURSDAY THE MAXIMA IS TO PEAK AROUND 25-50MM/DAY.
HIGHER AMOUNTS ARE EXPECTED ON FRIDAY...WHEN CONVECTION ALONG THE
NEAR EQUATORIAL TROUGH (NET) OVER NORTHERN PARA-AMAZONAS-RORAIMA
IS TO PEAK AT 30-60MM.

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





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