Prognostic Meteorological Discussion
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FXSA20 KWBC 271658
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 AM EST TUE JAN 27 2015

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

MODEL DISCUSSION (VALID FROM JANUARY 27 AT 00UTC): MINOR
CORRECTIONS TO THE PREVIOUS FORECAST...WITH THE MODELS FOLLOWING A
SIMILAR PATTERN EVOLUTION THROUGH 132 HRS. CLUSTERING AMONG THE
GLOBAL ENSEMBLE MEMBERS IS HIGH.

AT 500 HPA...DEEP SHORT WAVE TROUGH MOVES ACROSS SOUTHERN
CHILE-PATAGONIA IN ARGENTINA TO THE WESTERN SOUTH ATLANTIC EARLY
IN THE CYCLE. MODELS THEN FORECAST A RAPID RATE OF INTENSIFICATION
THROUGH 60-72 HRS...WHEN IT IS TO EVOLVE INTO A BROAD TROUGH
BETWEEN 60W-20W TO 28S. LATER IN THE CYCLE THE DEEP/BROAD TROUGH
IS TO MEANDER EAST. AT LOW LEVELS THIS SUSTAINS A DEEPENING
SURFACE LOW TO THE NORTH OF THE MALVINAS/FALKLAND ISLANDS AND A
PROGRESSIVE FRONT. THROUGH 24 HRS THE FRONT MOVES NORTH ACROSS LA
PAMPA TO THE BUENOS AIRES PROVINCE/CENTRAL ARGENTINA. THE FRONT IS
TO THEN MOVE NORTH ACROSS URUGUAY/RIO GRANDE DO SUL IN
BRASIL-CORDOBA TO MENDOZA IN ARGENTINA BY 48 HRS...WITH BOUNDARY
TO STALL OVER SOUTHERN BRASIL-NORTHERN PROVINCES IN ARGENTINA
LATER IN THE CYCLE. UNDER FAVORABLE JET DYNAMICS...ENVIRONMENTAL
CONDITIONS APPEAR FAVORABLE FOR AN MCS TO DEVELOP ACROSS THE
BUENOS AIRES PROVINCE/RIO DE LA PLATA BASIN EARLY ON WEDNESDAY
MORNING...WITH RAINFALL MAXIMA TO RANGE BETWEEN 50-100MM IN
POTENTIALLY SEVERE CONVECTION. ACROSS URUGUAY-SOUTHERN
BRASIL-MESOPOTAMIA IN ARGENTINA THIS IS TO THEN FAVOR RAINFALL
MAXIMA OF 30-60MM. THROUGH 96-108 HRS THIS DECREASES TO 20-45MM
WHILE BUILDING NORTH ACROSS SAO PAULO TO MATO GROSSO DO SUL IN
BRASIL.

CONSISTENT WITH PREVIOUS FORECAST...MODELS THEN FORECAST A LONG
WAVE TROUGH TO ENTER THE EASTERN PACIFIC BY 48-60 HRS...WITH AXIS
TO ENVELOP AREA BETWEEN 120W-65W AND TO THE SOUTH OF 50S. THROUGH
108-120 HRS THE TROUGH IS TO MOVE ACROSS THE DRAKE PASSAGE TO THE
SOUTHERN CONE. AS IT APPROACHES THE CONTINENT...THE DEEP TROUGH IS
TO FOCUS SHORT WAVE ENERGY ACROSS SOUTHERN PORTIONS OF CHILE TO
PATAGONIA IN ARGENTINA. AN INDUCED RIDGE IS TO BUILD TO THE
EAST...WITH AXIS TO EXTEND SOUTH FROM THE SOUTHERN CONE TO THE
DRAKE PASSAGE/ANTARCTIC PENINSULA. AT LOW LEVELS...THE TROUGH
ALOFT IS TO SUSTAIN A BROAD TROUGH ACROSS THE SOUTHEAST
PACIFIC-ANTARCTIC PENINSULA LATER ON DAY 02...WHERE IT IS TO
GENERALLY PERSIST THROUGH DAY 05. POLAR FRONTS ARE TO REVOLVE
AROUND THIS AXIS...TO STREAM ACROSS SOUTHERN CHILE TO THE
ANTARCTIC PENINSULA. THESE ARE TO GENERALLY FAVOR LIGHT RAINFALL
AMOUNTS AS THEY STRIKE THE SOUTHERN CONE OF SOUTH AMERICA...WITH
RAINFALL AMOUNTS OF 00-05MM/DAY.

AT 200 HPA...A WEAK CELL OF THE SUBTROPICAL RIDGE IS INITIALIZED
OVER PERU-BOLIVIA-MATO GROSSO IN BRASIL. THROUGH 48-72 HRS THE
HIGH/RIDGE BECOMES BETTER ORGANIZED...AS IT IS TO ANCHOR ON A
CLOSED HIGH OVER NORTHERN CHILE WHILE EXPANDING ACROSS
PERU-WESTERN BRASIL TO NORTHERN ARGENTINA/CHILE AND PARAGUAY.
LATER IN THE CYCLE...AN ANTICYCLONICALLY CURVED SUBTROPICAL JET
MAXIMA IS TO BOUND THE SOUTHERN PERIPHERY OF THE RIDGE. AS THE
RIDGE BUILDS OVER THE CONTINENT...A LOW/TROUGH OVER THE TROPICAL
ATLANTIC IS TO RETROGRESS TO NORTHEAST BRASIL...TO ENTER NORTHEAST
BRASIL LATER ON DAY 02 WHILE THE TROUGH EXPANDS INLAND ACROSS
EQUATORIAL SOUTH AMERICA. AS THE UPPER PATTERN EVOLVES...A
CONVERGENT/SUBSIDENT PATTERN IS TO ESTABLISH ACROSS BRASIL TO THE
EAST OF 60W AND NORTH OF 20S. EARLY IN THE CYCLE EXPECTING
SCATTERED CONVECTION IN THIS AREA TO RESULT IN RAINFALL AMOUNTS OF
15-25MM/DAY. ON THE CENTRAL/SOUTHERN JUNGLE OF PERU-NORTHERN
BOLIVIA AND ACRE IN BRASIL...EXPECTING SCATTERED DEEP CONVECTION
TO SUSTAIN RAINFALL AMOUNTS OF 20-35MM/DAY. THROUGH 96-108 HRS
THIS IS TO INCREASE TO 30-60MM AS THE SUBTROPICAL RIDGE PATTERN
OVER THE CONTINENT STRENGTHENS.

ARREAGA...INAMHI (ECUADOR)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)

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