Prognostic Meteorological Discussion
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000
FXSA20 KWBC 041612
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1211 PM EDT MON MAY 04 2015

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

MODEL DISCUSSION (VALID FROM MAY 04 AT 0000 UTC): MODELS ARE IN
GOOD AGREEMENT THROUGH 96-108 HRS...WITH SHORT WAVE PATTERN
DIFFERENCES LATER IN THE CYCLE. THE HIGH VARIABILITY AMONG THE
DETERMINISTIC MODELS IS ALSO EVIDENT ON THE ENSEMBLE
MEMBERS...WITH LARGE DIVERGENCE ON PATTERN EVOLUTION DURING THE
LATER PART OF THE FORECAST.

A MID/UPPER LEVEL TROUGH IS INITIALIZED OVER THE WESTERN ATLANTIC.
THE HIGH AMPLITUDE/LONG WAVE PATTERN IS TO PERSIST THROUGH 96-108
HRS. AT LOW LEVELS THIS IS TO SUSTAIN AN ELONGATED FRONT ACROSS
THE SOUTH ATLANTIC INTO THE SOUTHEAST STATES OF BRASIL...THEN
NORTHWEST ACROSS MATO GROSSO DO SUL-BOLIVIA. THROUGH 48-72 HRS THE
FRONT UNDULATES NORTH ACROSS SAO PAULO TO RIO DE JANEIRO/ESPIRITO
SANTO...WHILE TRAILING END MEANDERS OVER MATO GROSSO DO SUL TO
PARAGUAY. MOST ACTIVE CONVECTION IS EXPECTED ALONG THIS FRONT OVER
THE NEXT 24 HRS...WITH RAINFALL MAXIMA OF 20-40MM. THROUGH 36-60
HRS THE FOCUS OF THE MODERATE TO HEAVY CONVECTION SHIFTS TO SAO
PAULO/MINAS GERAIS...WHERE THE MAXIMA IS TO PEAK AT 20-35MM.
MODERATE CONVECTION IS TO THEN CLUSTER ACROSS ESPIRITO SANTO.

SOUTH OVER THE CONTINENT...DEEP LAYER RIDGE IS TO ESTABLISH ACROSS
CHILE/ARGENTINA EARLY IN THE CYCLE. THIS IS TO HOLD THROUGH 72-84
HRS. BUT LATER IN THE CYCLE IT IS TO RELOCATE TO THE WESTERN
ATLANTIC AS A DEEP TROUGH MOVES ACROSS THE SOUTHERN PACIFIC TO THE
SOUTHERN CONE. THE TROUGH IS TO FOCUS SHORT WAVE ENERGY AND
SUBTROPICAL MOISTURE ACROSS CHILE SOUTH OF CONCEPCION. AT LOW
LEVELS THIS IS TO SUSTAIN A BROAD TROUGH OFF THE COAST OF CHILE BY
72-84 HRS. AS IT MEANDERS OVER THE SOUTHEAST PACIFIC POLAR FRONTS
ARE TO REVOLVE AROUND THIS AXIS...TO THEN STREAM ACROSS SOUTHERN
CHILE/PATAGONIA IN ARGENTINA TO THE WESTERN SOUTH ATLANTIC. THESE
ARE TO FAVOR SCATTERED CONVECTION ACROSS SOUTHERN CHILE LATER ON
DAY 04...WITH RAINFALL MAXIMA OF 15-20MM. THROUGH DAY 05 THIS
INCREASES TO 20-30MM.

AT 200 HPA...WEAK CELL OF THE SUBTROPICAL RIDGE DOMINATES
NORTHWEST SOUTH AMERICA. A TROUGH TO THE
EAST...MEANWHILE...EXTENDS ACROSS THE NORTHEAST STATES OF BRASIL.
THROUGH 60-72 HRS THE RIDGE BUILDS EAST ACROSS NORTHERN SOUTH
AMERICA...DISPLACING THE TROUGH EAST INTO THE TROPICAL ATLANTIC.
AS IT MEANDERS OVER NORTHEAST BRASIL...THE TROUGH ALOFT IS TO
ENHANCE DIURNAL CONVECTION ALONG THE NORTH COAST OF BRASIL TO
FAVOR MAXIMA OF 20-40MM. THROUGH 36-60 HRS FOCUS OF THE MODERATE
TO HEAVY CONVECTION SHIFTS WEST TO EQUATORIAL SOUTH AMERICA...TO
AFFECT NORTHERN BRASIL-SOUTHERN COLOMBIA/NORTHERN PERU AND EASTERN
ECUADOR. ALONG THE NORTH COAST OF BRASIL... MEANWHILE...THE DAILY
MAXIMA IS TO PEAK AT 15-20MM.

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




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