Prognostic Meteorological Discussion
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FXSA20 KWBC 201605
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1205 PM EDT THU JUL 20 2017

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

MODEL DISCUSSION (VALID FROM JUL 20 AT 0000 UTC): GLOBAL MODELS
FINALLY REACHED A CONSENSUS ON HOW PATTERN DURING THE MEDIUM RANGE
PERIOD IS GOING TO EVOLVE...WITH THE UKMET AND ECMWF BOTH
CORRECTING IN FAVOR OF A DEEPER TROUGH TO ENTER THE EASTERN
PACIFIC LATER IN THE CYCLE. THIS IS VERY SIMILAR TO WHAT THE GFS
HAS BEEN FORECASTING OVER THE LAST FEW DAY. THE CHANGES ARE WELL
SUPPORTED BY THE MEAN OF THE GLOBAL ENSEMBLE MEMBERS...LEADING TO
A HIGHER CONFIDENCE IN THE FORECAST.

ON THE NORTHERN STREAM FLOW...OVER THE CONTINENT...A MID LEVEL
TROUGH IS TO EXTEND NORTH ACROSS SAO PAULO-MINAS GERAIS TO
TOCANTINS/GOIAS IN BRASIL DURING THE NEXT COUPLE OF DAYS. TROUGH
AXIS IS TO MEANDER EAST OFF THE COAST OF BRASIL INTO THE WESTERN
SOUTH ATLANTIC LATER ON SATURDAY. MEANWHILE...AT LOW LEVELS...THIS
WILL SUSTAIN AN ELONGATED FRONT ACROSS ESPIRITO SANTO/MINAS GERAIS
TO AMAZONAS IN WESTERN BRASIL. AS THE UPPER TROUGH STARTS TO
WEAKEN THE FRONT IS TO THEN RETROGRESS TO MATO GROSSO EARLY ON
FRIDAY MORNING. BUT AS IT RETROGRESSES AND LOSES ITS UPPER LEVEL
SUPPORT THE FRONT IS TO FRONTOLIZE EARLY ON SATURDAY. AS IT
MEANDERS ACROSS NORTHERN RIO DE JANEIRO-ESPIRITO SANTOS THIS IS TO
SUSTAIN ISOLATED TO SCATTERED COASTAL CONVECTION...WITH
ACCUMULATION OF 00-05MM/DAY.

CONSISTENT WITH PREVIOUS FORECASTS...DEEP MID LEVEL TROUGH IS TO
STREAM ACROSS THE EASTERN PACIFIC TO THE SOUTHERN CONE OF SOUTH
AMERICA LATER ON FRIDAY/EARLY SATURDAY MORNING. THE TROUGH IS TO
FOCUS SHORT WAVE ENERGY OVER THE CONTINENT TO THE SOUTH OF
35S...MEANWHILE FAVORING HEIGHT FALLS OF 150-200GPM. A TONGUE OF
SUBTROPICAL MOISTURE IS TO ACCOMPANY THIS TROUGH AS IT MAKES
LANDFALL OVER SOUTHERN CHILE...TO FEED ORGANIZED CONVECTION OVER
THE NEXT COUPLE OF DAYS. AT LOW LEVELS...THIS WILL SUSTAIN A
PROGRESSIVE TROUGH AND ASSOCIATED POLAR FRONT THAT REACHES
SOUTHERN CHILE LATER THIS EVENING. THE FRONT CONTINUES ACROSS
PATAGONIA IN ARGENTINA ON FRIDAY...WHERE IT IS TO MEANDER THROUGH
SUNDAY. THE FRONT IS TO THEN MEANDER NORTH ACROSS RIO DE LA PLATA
BASIN ON SUNDAY TO MONDAY. AS IT ENTERS THE SOUTHERN CONE EARLY ON
FRIDAY MORNING THIS IS TO SUSTAIN SCATTERED CONVECTION ACROSS
SOUTHERN REGIONS OF CHIE...WITH ACCUMULATION OF 15-20MM. ON FRIDAY
THIS INCREASES TO 20-30MM. ACROSS TIERRA DEL FUEGO MOST INTENSE IS
EXPECTED ON FRIDAY WHEN IT IS TO SUSTAIN RAINFALL AMOUNTS OF
05-10MM. AS THE MID/UPPER LEVEL TROUGH PULLS ACROSS CENTRAL CHILE
ON SATURDAY-SUNDAY IT IS TO THEN SUSTAIN SCATTERED CONVECTION
ACROSS THE CENTRAL ANDES...WITH CONDITIONS FAVORABLE FOR LIGHT TO
MODERATE SNOWFALL AMOUNTS TO SUSTAIN ACCUMULATION OF 05-10CM. OVER
RIO DE LA PLATA BASIN THIS IS TO FAVOR SCATTERED CONVECTION WITH
ACCUMULATION OF 05-10MM.

DEEPENING TROUGH ON THE SOUTHERN STREAM IS TO LIFT ACROSS 58S 105W
LATER ON SATURDAY. THROUGH SUNDAY EVENING THIS IS TO THEN LIFT
ACROSS 50S 90W...MEANWHILE FOCUSING ITS SHORT WAVE ENERGY ACROSS
SOUTHERN CHILE. A SECONDARY VORTEX IS TO CLOSELY FOLLOW...REACHING
SOUTHERN CHILE LATER ON TUESDAY. AT LOW LEVELS THIS WILL SUSTAIN A
DEEP OCCLUDE TROUGH OVER THE FAR EASTERN PACIFIC ON
SUNDAY-MONDAY...TO CENTER ON A 964 HPA LOW OFF THE SOUTH COAST OF
CHILE ON MONDAY EVENING. POLAR FRONTS ARE TO REVOLVE AROUND THIS
AXIS....FOCUSING OVER SOUTHERN CHILE AND PATAGONIA IN ARGENTINA.
THIS IS TO FAVOR SCATTERED CONVECTION WITH ACCUMULATION OF
10-15MM/DAY.


NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE
CONTINUES TO WEAKEN UNDER PRESSURE FROM AMPLIFYING TROUGH TO THE
SOUTH. EARLY IN THE CYCLE IT WILL SPLIT IN TWO CELLS...WITH ONE
OVER THE EASTERN TROPICAL PACIFIC AND THE OTHER OVER THE TROPICAL
ATLANTIC/NORTHEAST STATES OF BRASIL. THIS PATTERN IS TO REMAIN
NEARLY UNCHANGED OVER THE NEXT THREE TO FOUR DAYS. SEA BREEZE
CONVERGENCE BETWEEN ILHA DE MARAJO AND PERNAMBUCO/RIO GRANDE DO
NORTE IS TO SUSTAIN RAINFALL AMOUNTS OF 05-10MM/DAY. THROUGH
SATURDAY THIS INCREASES TO 15-20MM. OVER RORAIMA-SOUTHERN GUIANAS
INITIALLY EXPECTING RAINFALL AMOUNTS OF 15-25MM/DAY. THROUGH
SATURDAY/SUNDAY THIS DECREASES TO 10-15MM/DAY.

ESPINOLA...DNM (PARAGUAY)
GONZALEZ...DMC (CHILE)
DAVISON...WPC (USA)
$$





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