Prognostic Meteorological Discussion
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000
FXSA20 KWBC 051627
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1226 PM EDT TUE MAY 05 2015

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

MODEL DISCUSSION (VALID FROM MAY 05 AT 0000 UTC): GLOBAL MODELS
CONTINUE TO AGREE ON PATTERN EVOLUTION DURING THE MEDIUM RANGE
PERIOD. THEY THEN START TO DIVERGE ON TIMING AND AMPLITUDE OF
SHORT WAVE PERTURBATIONS REVOLVING AROUND A BROAD TROUGH OVER THE
EASTERN PACIFIC.

OVER THE WESTERN ATLANTIC...A MID/UPPER LEVEL TROUGH DOMINATES THE
FLOW...WITH AXIS NORTH BETWEEN 60W 30W TO 20S. THE HIGH AMPLITUDE/
LONG WAVE PATTERN IS TO PERSIST THROUGH 72/84 HRS...THEN RAPIDLY
WEAKEN WHILE SHEARING TO THE EAST-SOUTHEAST. AT LOW LEVELS THIS
SUSTAINS A BROAD TROUGH AND AN ELONGATED FRONT THAT EXTENDS ACROSS
RIO DE JANEIRO/SOUTHERN MINAS GERAIS TO MATO GROSSO DO
SUL/SOUTHEAST BOLIVIA. THE FRONT IS TO REMAIN NEARLY STATIONARY
OVER THE NEXT FEW DAYS...WITH A SUBTROPICAL JET ALOFT TO MAINTAIN
BAROCLINIC BOUNDARY OVER THE NEXT FEW DAYS. OVER RIO DE
JANEIRO-NORTHERN SAO PAULO THIS IS TO FAVOR SCATTERED CONVECTION
WITH ACCUMULATION OF 20-35MM. THROUGH 72-84 HRS IT DECREASES TO
05-10MM...WITH A SURGE IN CONVECTION EXPECTED BY 96-108 HRS. OTHER
CONVECTION IS EXPECTED BETWEEN RONDONIA/SOUTHERN AMAZONAS-NORTHERN
PARA TO MINAS GERAIS...WITH DAILY MAXIMA OF 15-20MM.

SOUTH OVER THE CONTINENT...A TROPOSPHERIC RIDGE DOMINATES THE FLOW
ACROSS THE SOUTHERN CONE/DRAKE PASSAGE. THIS RIDGE IS FORECAST TO
HOLD THROUGH 48-60 HRS. THROUGH 72-96 HRS THE RIDGE RELOCATES TO
THE WESTERN ATLANTIC AS A DEEP TROUGH MOVES TO THE EASTERN SOUTH
PACIFIC. BY 84-96 HRS THE TROUGH IS TO IMPINGE THE SOUTHERN
PORTIONS OF CHILE/PATAGONIA IN ARGENTINA...BUT IT IS TO THEN
RAPIDLY SHEAR SOUTH ALONG THE WESTERN FRINGES OF THE RIDGE. AS IT
APPROACHES THE CONTINENT...THE DEEP 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 48-60 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 03...WITH RAINFALL MAXIMA OF 15-20MM. THROUGH
DAY 04 THIS INCREASES TO 20-30MM.

NORTH OVER THE CONTINENT...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 36-48 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 15-20MM. MOST INTENSE CONVECTION IS EXPECTED
BETWEEN NORTHERN PARA/AMAZONAS IN BRASIL TO NORTHERN PERU/SOUTHERN
COLOMBIA...WITH MAXIMA OF 20-45MM EXPECTED THROUGH 36 HRS...AND
20-35MM/DAY AT 36-84 HRS. AN INCREASE IN ACTIVITY IS POSSIBLE
LATER IN THE CYCLE.

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




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