Prognostic Meteorological Discussion
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FXSA20 KWBC 061550
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1150 AM EDT WED MAY 06 2015

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

MODEL DISCUSSION (VALID FROM MAY 06 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH THROUGH 84-96 HRS...WITH THE DETERMINISTIC
AND GLOBAL ENSEMBLE MEMBERS FOLLOWING A SIMILAR EVOLUTION ACROSS
THE DOMAIN.

BROAD MID/UPPER LEVEL TROUGH DOMINATES THE FLOW ACROSS THE WESTERN
ATLANTIC. THROUGH 96-120 HRS THE TROUGH IS TO SLOWLY PULL TO THE
EAST-SOUTHEAST ACROSS THE SOUTH ATLANTIC. AT LOW LEVELS THIS IS TO
SUSTAIN AN ELONGATED FRONT ACROSS RIO DE JANEIRO/NORTHERN SAO
PAULO IN BRASIL TO MATO GROSSO DO SUL IN BRASIL-PARAGUAY. THE
MEANDERING FRONT IS TO ENHANCE MOISTURE CONVERGENCE ACROSS RIO DE
JANEIRO/ NORTHERN SAO PAULO...TO FAVOR SCATTERED CONVECTION WITH
MAXIMA OF 20-30MM THROUGH 36-42 HRS. THIS THEN DECREASES TO
05-10MM/DAY BY 48-72 HRS.

MID LEVEL PERTURBATIONS ARE TO THEN INTERACT WITH THE MEANDERING
FRONT. ONE IS TO PULL ACROSS NORTHERN CHILE/NORTHWEST ARGENTINA BY
48 HRS...TO QUICKLY TRACK ACROSS SOUTHEAST BRASIL BY 60-66 HRS. AS
IT INTERACTS WITH THE SURFACE FRONT THIS IS TO SUSTAIN SCATTERED
DEEP CONVECTION WITH ACCUMULATION OF 15-20MM THAT IS TO FOCUS
ACROSS CENTRAL PARAGUAY-MATO GROSSO DO SUL IN BRASIL. A STRONGER
PERTURBATION IS TO FOLLOW...SPILLING ACROSS THE NORTHERN ANDES OF
CHILE INTO NORTHWEST ARGENTINA BY 96 HRS...AND ACROSS PARAGUAY TO
SOUTHERN BRASIL BY 120 HRS. AS IT INTERACT WITH THE SURFACE FRONT
THE LATTER IS TO SUSTAIN CYCLOGENESIS OVER PARAGUAY BY 96 HRS.
THIS LOW IS TO THEN DEEPEN THROUGH 132-144 HRS AS IT MOVES ACROSS
SOUTHERN BRASIL TO THE WESTERN ATLANTIC. THIS IS TO ALSO FAVOR
SCATTERED DEEP CONVECTION WITH RAINFALL AMOUNTS OF 20-40MM.

A MID/UPPER LEVEL RIDGE DOMINATES THE FLOW ACROSS THE SOUTHERN
CONE-DRAKE PASSAGE/ANTARCTIC PENINSULA. THE RIDGE PATTERN IS TO
HOLD IT GROUND THROUGH 48-60 HRS...THEN RELOCATES TO THE EAST TO
ALIGN ALONG 50W AS A BROAD TROUGH PRESSES ACROSS THE EASTERN
PACIFIC. THE TROUGH IS TO NEAR SOUTHERN CHILE BY 60 HRS...AND
THROUGH 72 HRS IT MOVES EAST INTO PATAGONIA IN ARGENTINA. THE
TROUGH IS TO THEN WEAKEN AS SHORT WAVE ENERGY SHEARS SOUTH AROUND
THE MID LEVEL RIDGE. AT LOW LEVELS THIS IS TO SUSTAIN A BROAD
TROUGH ACROSS THE FAR EASTERN PACIFIC BY 36-96 HRS...WITH A SERIES
OF POLAR FRONTS FORECAST TO REVOLVE AROUND THIS AXIS. ACROSS
SOUTHERN CHILE THIS IS TO SUSTAIN A TIGHT GRADIENT AND STRONG LOW
LEVEL WINDS THAT ARE TO PEAK AT 35-45KT. THIS IS TO ALSO FAVOR
ORGANIZED CONVECTION BY 60-84 HRS...WITH RAINFALL MAXIMA TO PEAK
AT 20-30MM.

BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES CONTINENTAL AREA TO
THE NORTH OF 20S. AS SHORT WAVE PERTURBATIONS STREAM ACROSS MID
SECTIONS OF SOUTH AMERICA THE MODELS FORECAST GRADUAL EROSION OF
UPPER RIDGE PATTERN AS THE CYCLE PROGRESSES. MEANWHILE...RIDGE
ALOF TIS TO VENT DEEP CONVECTION ACROSS NORTHERN PARA-SOUTHERN
COLOMBIA AND NORTHERN JUNGLE OF PERU...WITH RAINFALL MAXIMA OF
20-40MM/DAY EXPECTED THROUGH 84 HRS. ACROSS NORTH COAST OF BRASIL
TO NORTHERN PARA EXPECTING MAXIMA OF 15-30MM EARLY IN THE CYCLE.
THROUGH 84-96 HRS THIS DECREASES TO 15-20MM. SCATTERED CONVECTION
IS TO ALSO CLUSTER BETWEEN ACRE/SOUTHERN AMAZONAS IN WESTERN
BRASIL AND MINAS GERAIS. IN THIS AREA MAXIMA IS TO PEAK AT 20-30MM
THROUGH 36-48 HRS. BUT AS THE RIDGE ALOFT WEAKENS THIS WILL
DECREASE TO 15-20MM IN SCATTERED CONVECTION.

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





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