THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


SOUTH AMERICAN MODEL DISCUSSION




SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1138 AM EDT THU APR 17 2014

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

LAST NO AMENDS. NEXT BULLETIN ON APRIL 21.

MODEL DISCUSSION (VALID FROM 17 APRIL 00UTC): THE DETERMINISTIC
GLOBAL MODELS AND MEMBERS OF THE GLOBAL ENSEMBLE ARE IN EXCELLENT
AGREEMENT THROUGH 96-120 HRS...SHOWING PATTERN EVOLVING FROM SHORT
WAVE RIDGE/TROUGH EARLY IN THE CYCLE TO ONE WHERE HIGHER AMPLITUDE
LONG WAVE PERTURBATIONS DOMINATE. CONFIDENCE IN THE FORECAST IS
HIGH.

BROAD MID/UPPER LEVEL TROUGH DOMINATES FLOW ACROSS THE DRAKE
PASSAGE TO THE SOUTHERN CONE OF SOUTH AMERICA. BUILDING RIDGE TO
THE WEST...AS IT MEANDERS OFF THE COAST OF CHILE...IS TO THEN
INDUCE THE NORTHWARD AMPLIFICATION OF THIS TROUGH ALONG 60W TO RIO
DE LA PLATA BASIN BY 48-60 HRS. THROUGH 84-96 HRS THIS IS TO THEN
EVOLVE INTO A BROAD TROUGH WITH AXIS ENVELOPING AREA BETWEEN
60W-20W AND TO THE SOUTH OF 25S...WHILE CENTERING ON A CLOSED LOW
NEAR 50S 45W. THE AMPLIFYING/DEEPENING TROUGH SUSTAINS A SURFACE
TROUGH AND FRONT INTO PATAGONIA/SOUTHERN CHILE EARLY IN THE CYCLE.
THIS THEN SURGES NORTH ACROSS THE BUENOS AIRES PROVINCE TO RIO DE
LA PLATA BASIN THROUGH 60-72 HRS. AS IT PUSHES NORTH...THIS IS TO
THEN REINFORCE AN OLD BOUNDARY TO THE NORTH. THE LATTER IS TO
INITIALLY EXTEND ACROSS SOUTHERN BRASIL-NORTHERN PROVINCES IN
ARGENTINA. THROUGH 60-72 HRS...AS THE BOUNDARIES COMBINE...THIS IS
TO THEN MEANDER NORTH INTO SOUTHERN BRASIL-PARAGUAY. LATER IN THE
CYCLE THE FRONT UNDULATES ACROSS SAO PAULO-MATO GROSSO DO SUL
WHILE TRAILING TO PARAGUAY. THE BEST MOISTURE CONVERGENCE IS
EXPECTED ALONG THE OLD FRONT TO THE NORTH...WHERE UNDER FAVORABLE
JET DYNAMICS EXPECTING MODERATE TO HEAVY CONVECTION ACROSS
PARAGUAY-MISIONES IN ARGENTINA...WITH RAINFALL AMOUNTS OF 25-50MM
THROUGH 36-48 HRS. THROUGH 48-72 HRS THIS WILL DECREASE TO
20-30MM/DAY AS THE FRONT MEANDERS NORTH TO SOUTHEAST BRASIL. OTHER
ACTIVITY TO THE SOUTH IS EXPECTED WITH SURFACE FRONT ENTERING
SOUTHERN CHILE EARLY IN THE CYCLE. THIS BOUNDARY WILL MAINTAIN A
SUBTROPICAL CONNECTION AS IT RACES ACROSS THE EASTERN
PACIFIC...TRIGGERING MODERATE CONVECTION WITH ACCUMULATION OF
15-20MM.

MID/UPPER LEVEL RIDGE PATTERN IS TO HOLD OVER THE EASTERN PACIFIC
THROUGH 108-120 HRS. A HIGH AMPLITUDE POLAR TROUGH IS TO PRESS
AGAINST THIS AXIS. STARTING AT 48 HRS THE TROUGH WILL MOVE BETWEEN
150W-100W AND TO THE SOUTH OF 30S. BY 96 HRS IT IS TO SLOWLY
MIGRATE TO EXTEND BETWEEN 130W-80W...AND LATER IN THE CYCLE SHORT
WAVE ENERGY WILL BEGIN TO SPILL UNDER THE WANING RINDGE INTO THE
DRAKE PASSAGE/TIERRA DEL FUEGO. AT LOW LEVELS THIS WILL SUSTAIN A
BROAD POLAR TROUGH OVER THE SOUTH PACIFIC. THROUGH 120-132 HRS THE
TROUGH MOVES TO THE BELLINGSHAUSEN SEA...WITH AXIS ENTERING TIERRA
DEL FUEGO IN SOUTHERN CHILE LATER ON DAY 06. ASSOCIATED SURFACE
FRONT IS TO ENTER SOUTHERN CHILE LATER IN THE CYCLE TO TRIGGER
SCATTERED CONVECTION WITH ACCUMULATION OF 05-10MM.

NORTH OVER THE CONTINENT MOST ACTIVE CONVECTION NOW CONCENTRATES
ALONG AND NORTH OF THE EQUATOR...AFFECTING CONTINENTAL AREA TO THE
NORTH OF 05S...WITH RAINFALL AMOUNTS OF 20-35MM FROM NORTHERN
PERU/ECUADOR TO THE NORTHEAST STATES OF BRASIL. EVOLVING MJO
CONDITIONS ACROSS THE EASTERN TROPICAL PACIFIC AND ARRIVAL OF
OCEANIC KELVIN WAVE WILL SUSTAIN AN INCREASE IN CONVECTION ACROSS
NORTHWEST PORTIONS OF SOUTH AMERICA...WITH RAINFALL AMOUNTS
FORECAST TO INCREASE TO 25-50MM/DAY THROUGH DAY 04. MODERATE
CONVECTION IS TO THEN PERSIST ACROSS NORTHEAST BRASIL...WITH
ACCUMULATION OF 15-20MM/DAY.

ITA...SENAMHI (PERU)
FERNANDES...INMET (BRASIL)
GALVEZ...WPC (USA)




Last Updated: 1138 AM EDT THU APR 17 2014