Prognostic Meteorological Discussion
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000
FXSA20 KWBC 201543
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1142 AM EDT MON APR 20 2015

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

NOTE: STRONG HURRICANE INTENSITY WINDS ARE TO AFFECT SOUTHERN
CHILE/TIERRA DEL FUEGO AND PATAGONIA IN ARGENTINA THROUGH TUESDAY
EVENING. WINDS ARE TO PEAK AT 65KT EARLY ON TUESDAY MORNING...WITH
GUSTS TO 80-90KT LIKELY ACROSS THE MOUNTAIN PASSES TO THE SOUTH.

MODEL DISCUSSION (VALID FROM APRIL 20 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH THROUGH 96-108 HRS...WITH GLOBAL MODELS
FOLLOWING SIMILAR EVOLUTION THROUGH THE SHORT RANGE PERIOD. LATER
IN THE CYCLE THEY START TO DIVERGE AS SHORT WAVE PERTURBATIONS
POPULATE THE DOMAIN.

A BROAD MID/UPPER LEVEL TROUGH IS TO MOVE INTO THE WESTERN
ATLANTIC EARLY IN THE CYCLE...WITH AXIS TO ENVELOP AREA BETWEEN
60W-20W AND TO THE SOUTH OF 30S. THROUGH 72 HRS THE TROUGH IS TO
SLOWLY PULL ACROSS 20W...THEN RAPIDLY WEAKEN AS IT MEANDERS EAST
ACROSS THE SOUTH ATLANTIC. SHORT WAVE PERTURBATIONS ARE TO
FOLLOW...TO STREAM ACROSS NORTHERN CHILE INTO NORTHERN ARGENTINA.
STRONG MID LEVEL PERTURBATIONS ARE EXPECTED THROUGH 72-84 HRS AND
AGAIN BY 108-120 HRS. AT 250 HPA A SUBTROPICAL JET MAXIMA IS TO
EXTEND ACROSS NORTHERN CHILE-ARGENTINA...WITH DIVERGENCE ON ITS
LEFT ENTRANCE REGION TO ENVELOP MID SECTIONS OF SOUTH AMERICA OVER
THE NEXT SEVERAL DAYS. AT LOW LEVELS BUILDING POLAR RIDGE OVER
ARGENTINA IS TO DRIVE A SURFACE FRONT NORTH ACROSS URUGUAY-CORDOBA
IN ARGENTINA EARLY IN THE CYCLE. THIS IS TO THEN MERGE WITH A
FRONT TO THE NORTH...AS THE LATTER MEANDERS OVER RIO GRANDE DO
SUL-NORTHERN PROVINCES IN ARGENTINA. BOUNDARY IS TO THEN STALL
OVER SOUTHERN BRASIL-PARAGUAY THROUGH 120-132 HRS WHEN IT IS TO
FRONTOLIZE. DEEP MOISTURE IS TO CONVERGE ALONG THIS
BOUNDARY...WITH PRECIPITABLE WATER CONTENT OF 50-60MM OVER THE
NEXT FEW DAYS. THIS IS TO FEED ORGANIZED DEEP CONVECTION ALONG THE
FRONT...WITH RISK OF MCS FORMATION ACROSS SOUTHERN BRASIL-ENTRE
RIOS/MISIONES IN ARGENTINA-SOUTHEAST PARAGUAY OVER THE NEXT 48-60
HRS TO RESULT IN DAILY MAXIMA OF 20-45MM. BY 60-108 HRS THE FOCUS
OF THE CONVECTION WILL SHIFT TO PARANA-SANTA CATARINA AND SOUTHERN
SAO PAULO WHERE THE MAXIMA IS TO PEAK AT 15-20MM.

OVER THE EASTERN PACIFIC...AT 500 HPA...A NORTH TO SOUTH RIDGE IS
TO EXTEND ALONG 80W/90W TO 50S. BROAD TROUGH ON THE SOUTHERN
STREAM IS TO EXTEND NORTH ACROSS THE BELLINGSHAUSEN SEA TO THE
DRAKE PASSAGE...WITH AXIS TO PRESS AGAINST RIDGE TO THE NORTH.
THIS...IN-TURN...WILL SUSTAIN A TIGHT GRADIENT ACROSS SOUTHERN
PORTIONS OF CHILE TO PATAGONIA IN ARGENTINA. SIMILAR PATTERN IS
EXPECTED AT LOW LEVELS...WITH BROAD RIDGE ON THE NORTHERN STREAM
WHILE A BROAD/LOW AMPLITUDE TROUGH DOMINATES THE SOUTHERN STREAM.
AN ELONGATED FRONT IS TO SEPARATE THESE FEATURES...WITH AXIS
EAST-TO-WEST ACROSS SOUTHERN PATAGONIA/SOUTHERN CHILE TO THE
EASTERN PACIFIC. ALTHOUGH A TIGHT GRADIENT IS EXPECTED TO 66-72
HRS...THE STRONGEST WINDS ARE TO DEVELOP LATER THIS EVENING
THROUGH MIDDAY ON TUESDAY...WITH SUSTAINED WINDS OF 65KT AND GUSTS
TO 80-90KT HIGHLY LIKELY.

FARTHER UPSTREAM...A BROAD TROUGH IS TO DEVELOP ACROSS THE EASTERN
PACIFIC BY 72-96 HRS...WITH MID LEVEL AXIS TO SLOWLY MOVE EAST
INTO THE SOUTHERN CONE LATER IN THE CYCLE. AS IT NEARS SOUTHERN
CHILE...THE BROAD TROUGH IS TO ESTABLISH A SUBTROPICAL
CONNECTION...WITH DEEP MOISTURE TO CONVERGE ACROSS SOUTHERN
PORTIONS OF CHILE. AT LOW LEVELS THIS IS TO SUSTAIN A BROAD TROUGH
OVER THE FAR EASTERN PACIFIC LATER IN THE CYCLE...WITH ASSOCIATED
FRONTAL LOW TO ENTER SOUTHERN CHILE BY 96-108 HRS. DEEP
SUBTROPICAL MOISTURE IS TO FEED ORGANIZED CONVECTION IN THIS
AREA...TO RESULT IN RAINFALL MAXIMA OF 15-30MM.

NORTH OVER THE CONTINENT...BROAD CELL OF THE SUBTROPICAL RIDGE IS
TO DOMINATE AREA TO THE NORTH OF 30S...WHILE ANCHORING ON A CLOSED
HIGH OVER WESTERN MINAS GERAIS IN BRASIL. THE SUBEQUATORIAL RIDGE
TO THE NORTH...MEANWHILE...IS TO EXTEND WEST ACROSS THE TROPICAL
ATLANTIC ALONG 05N TO THE GUIANAS-VENEZUELA. DIFFLUENCE BETWEEN
THE RIDGE TO THE SOUTH AND THE ONE TO THE NORTH IS TO VENT DEEP
CONVECTION ACROSS EQUATORIAL PORTIONS OF SOUTH AMERICA...WITH
DAILY MAXIMA TO PEAK AT 20-35MM. ALONG THE NORTH COAST OF BRASIL
THIS IS TO ALSO VENT DIURNAL CONVECTION WITH RAINFALL AMOUNTS OF
15-20MM IN SCATTERED CONVECTION. ACROSS PERU MOST ACTIVE IS
EXPECTED OVER THE SOUTHERN JUNGLE...WHERE MAXIMA ON DAY 02 IS TO
PEAK AT 15-30MM. OTHERWISE...MAXIMA IN THIS AREA IS TO PEAK AT
10-15MM/DAY.

SCHNEIDER...INMET (BRASIL)
CALLE...UNALM (PERU)
CHARPENTIER...DMC (CHILE)
DAVISON/GALVEZ...WPC (USA)
$$





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