Prognostic Meteorological Discussion
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000
FXSA20 KWBC 251739
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
138 PM EDT THU AUG 25 2016

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

MODEL DISCUSSION (VALID FROM AUG 25 AT 0000 UTC): FORECAST
CONFIDENCE CONTINUES HIGH THROUGH THE CYCLE. SIGNIFICANT
DISCREPANCIES START TO APPEAR AFTER 120 HRS OVER THE SOUTHEASTERN
PACIFIC/SOUTHERN CONE.

STATIONARY FRONT WEAKENING OVER THE COAST OF BAHIA-BRASIL WILL
CONTINUE TO BE A FOCUS OF MOISTURE CONVERGENCE. THIS WILL SUSTAIN
MAXIMA OF 15-30MM/DAY THROUGH EARLY FRIDAY. AMOUNTS WILL INCREASE
TO MAXIMA OF 20-35MM/DAY ON FRIDAY-SATURDAY...AS A POCKET OF
INSTABILITY IN THE TRADES ARRIVES INTO THE CONTINENT. EXPECTING A
DECREASING TREND AFTERWARDS.

ALSO IN NORTHERN SOUTH AMERICA...THE SOUTHERN TAIL OF A TROPICAL
WAVE IS PROPAGATING WESTWARD FROM 64-65WW ON TUESDAY...TO 70-72W
BY FRIDAY...TO THEN LOSE DEFINITION. CONVECTION IS ENHANCED ALONG
THIS TROUGH...AND WILL BE FURTHER ENHANCED BY VENTILATION IN THE
BASE OF A SOUTHERN HEMISPHERE UPPER TROUGH THAT WILL RELOCATE FROM
THE AMAZON DELTA/PARA IN BRASIL ON TUESDAY...TO AMAZONAS-BRASIL ON
FRIDAY. EXPECTING MAXIMA OF 15-35MM/DAY IN THE THUNDERSTORMS THAT
DEVELOP ALONG THIS TROUGH AS THEY PROPAGATE WESTWARD ACROSS THE
NORTHERN AMAZON BASIN. A DECREASING TREND IN ACCUMULATIONS AND
COVERAGE IS EXPECTED THROUGH THE CYCLE.

IN THE SOUTHERN CONE...AN OCCLUDED LOW WILL CROSS THE CONTINENT ON
FRIDAY...AS A SHORT WAVE TROUGH CROSSES THE SOUTHERN ANDES. MODELS
ARE SHOWING MOISTURE AND INSTABILITY UP TO 700 HPA. THIS WILL
SUSTAIN HEAVY SHOWERS AND ISOLATED THUNDERSTORMS IN THE AYSEN
REGION WITH MAXIMA OF 15-30MM/DAY. SOME OF THIS ACTIVITY WILL
CROSS INTO PATAGONIA WHERE EXPECTING MAXIMA OF 10-15MM/DAY.

THE NORTHERN TIER OF THE UPPER TROUGH OVER THE EASTERN PACIFIC
WILL APPROACH CENTRAL AND NORTHERN CHILE DURING SATURDAY. MOISTURE
IS LIMITED...YET UPPER DYNAMICS WILL BE SUFFICIENT TO TRIGGER SNOW
SHOWERS IN THE ANDES OF COQUIMBO AND ATACAMA. ON SATURDAY AND
SUNDAY. MODELS CONTINUE CONFIDENT ON A SHORT WAVE TROUGH
DEVELOPING AND CROSSING THE ANDES OF NORTHERN CHILE ON SATURDAY
EVENING. THIS TROUGH WILL HAVE AN IMPACT ON ACTIVITY ACROSS THE
RIO DE LA PLATA BASIN (SEE BELOW). AFTER THIS TROUGH
CROSSES...MODELS CONTINUE CONFIDENT ABOUT A SOUTHERLY UPPER JET
OFF THE COAST OF CHILE AMPLIFYING THE UPPER TROUGH. THIS WILL LEAD
TO THE DEVELOPMENT OF A SECONDARY VORTEX THAT WILL CROSS THE ANDES
ON SUNDAY-MONDAY. THE STRONGEST WINDS AND CYCLONIC VORTICITY
ADVECTION ARE EXPECTED IN THE ATACAMA/ANTOFAGASTA REGIONS IN
NORTHERN CHILE. ALTHOUGH MOISTURE IS LIMITED...INSTABILITY AND
UPPER DYNAMICS WILL BE SUFFICIENT TO TRIGGER SCATTERED SNOW
SHOWERS ACROSS THE TRIPLE FRONTIER OF BOLIVIA-ARGENTINA-CHILE.
NOTE THAT BOUNDARY-LAYER WINDS WILL BE STRONG AS WELL...WITH GUST
EASILY EXCEEDING 25-30KT. THE IMPACT OF THIS TROUGH WILL BE MORE
SIGNIFICANT ONCE IT CROSSES THE ANDES AND INTERACTS WITH A SURFACE
COLD FRONT PROPAGATING ACROSS CENTRAL SOUTH AMERICA.

EAST OF THE ANDES...A SURFACE COLD FRONT WILL ORGANIZE LATE ON
THURSDAY AND MOVE NORTHWARD INTO THE RIO DE LA PLATA REGION BY
FRIDAY. A LOW-LEVEL JET FROM BOLIVIA IS BUILDING A MOISTURE POOL
THAT WILL REACH 40MM OF PRECIPITABLE WATER BY FRIDAY AND SATURDAY.
MODELS ARE ALL AGREEING ON A STRONG UPPER DIVERGENT PATTERN
SETTING UP ON SATURDAY AS THE DIVERGENT ENTRANCE OF AN UPPER JET
SETS OVER THE REGION. ALTHOUGH INSTABILITY WILL BE LIMITED...THE
CONFIGURATION WILL BE CONDUCIVE FOR LOCALLY HEAVY RAINS BETWEEN
ENTRE RIOS AND URUGUAY ON SATURDAY. IN ENTRE RIOS...EXPECTING
MAXIMA OF 20-40MM/DAY. LONGER-LASTING PRECIPITATION IN URUGUAY
WILL LEAD TO MAXIMA OF 40-80MM/DAY PEAKING ON SATURDAY
EVENING/SUNDAY MORNING. A NEW AREA OF CONVECTION WILL DEVELOP OVER
CORRIENTES/CHACO-ARGENTINA ON LATE SATURDAY...TO SUSTAIN MAXIMA OF
20-40MM/DAY THROUGH EARLY SUNDAY. THIS CONVECTION WILL LEAD TO
MAXIMA OF 35-70MM/DAY ON SUNDAY-MONDAY ACROSS SOUTHEASTERN
PARAGUAY AND RIO GRANDE DO SUL. NORTHWEST...ALSO ON SUNDAY-EARLY
MONDAY...EXPECTING MAXIMA OF 20-45MM/DAY FROM SOUTHERN BOLIVIA
INTO THE CHACO PARAGUAYO.  COLD FRONT IS FORECAST TO PROGRESS INTO
NORTHERN BOLIVIA BY MONDAY-EARLY TUESDAY. UNDER THE PRESENCE OF A
SOUTHERLY JET OVER BOLIVIA...THIS WILL PRODUCE SCATTERED
THUNDERSTORMS DEVELOPMENT IN SOUTHERN PERU/NORTHERN BOLIVIA WITH
ACCUMULATIONS IN THE ORDER OF 25-50MM. EXPECTING SIMILAR AMOUNTS
DOWNSTREAM FROM SURFACE LOW ACROSS MATO GROSSO DO SUL/PARANA INTO
SOUTHERN SAO PAULO...TO DECREASE AFTER. IN MATO GROSSO/MATO GROSSO
DO SUL EXPECTING ACCUMULATIONS OF 15-30MM.

OSORIO...DMC (CHILE)
CASTILLO...UCR (COSTA RICA)
ALVA...SENAMHI (PERU)
GALVEZ...WPC (USA)
$$




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