Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXSA20 KWBC 271601
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1200 PM EDT THU JUL 27 2017

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

MODEL DISCUSSION (VALID FROM JUL 27 AT 0000 UTC): ON THE NORTHERN
STREAM FLOW...THE GLOBAL MODELS MAINTAIN GOOD CONTINUITY WITH
PREVIOUS FORECASTS...AND THEY REMAIN IN GENERAL AGREEMENT THROUGH
132-144 HRS. ON THE SOUTHERN STREAM...THERE IS GOOD CONTINUITY
THROUGH 72/84 HRS...WITH MODELS THEN DISAGREEING ON THE
AMPLITUDE/SPEED OF SHORT WAVE PERTURBATIONS STREAMING ACROSS THE
DRAKE PASSAGE/ANTARCTIC PENINSULA. THE HIGH VARIABILITY AMONG THE
DETERMINISTIC MODELS IS ALSO EVIDENT AMONG THE ENSEMBLE
MEMBERS...LEADING TO A LOWER CONFIDENCE IN THE FORECAST.

EARLY IN THE CYCLE THE DOMINANT FEATURE WILL BE A MID/UPPER LEVEL
LONG WAVE TROUGH THAT IS TO EXTEND FROM THE ANTARCTIC
PENINSULA-TIERRA DEL FUEGO INTO THE EASTERN PACIFIC ALONG 33S
90W...AND 30S 110W. AS IT MEANDERS OVER THE SOUTHERN CONE...THE
DEEP MID LEVEL TROUGH IS TO FOCUS SHORT WAVE ENERGY ACROSS THE
SOUTHERN REGIONS OF CHILE AND PATAGONIA IN ARGENTINA...WHERE IT IS
TO SUSTAIN HEIGHT FALLS OF 150-200GPM THROUGH FRIDAY MORNING.
LATER IN THE DAY...MODELS FORECAST THE SOUTHERN HALF OF THIS
TROUGH TO ACCELERATE ACROSS THE WEDDELL SEA/SOUTHWEST
ATLANTIC...WHILE THE TRAILING END OVER THE PACIFIC IS TO SLOWLY
PULL ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA LATER ON
FRIDAY. EARLY ON SATURDAY...THE REMAINING SHORT WAVE TROUGH/ENERGY
WILL THEN PULL ACROSS PATAGONIA TO THE WESTERN ATLANTIC WHERE IT
WILL THEN MERGE WITH A SHORT WAVE TROUGH TO THE SOUTH. AT LOW
LEVELS...THIS REFLECTS AS A POSITIVELY TILTED TROUGH THAT EXTENDS
TO THE NORTHWEST FROM THE WEDDELL SEA/ANTARCTIC PENINSULA...ALONG
THE SOUTH COAST OF CHILE TO THE EASTERN PACIFIC. THE ASSOCIATED
FRONT MOVES NORTH ACROSS PATAGONIA/LA PAMPA IN ARGENTINA-TEMUCO
CHILE-EASTERN PACIFIC EARLY IN THE PERIOD...MEANDERING NORTH
ACROSS THE BUENOS AIRES PROVINCE-MENDOZA ARGENTINA-LA SERENA CHILE
ON FRIDAY. ON SATURDAY...AS A POLAR RIDGE BUILDS TO THE
SOUTH...THE FRONT WILL MEANDER NORTH ACROSS RIO DE LA
PLATA/SOUTHERN URUGUAY-ENTRE RIOS IN ARGENTINA TO THE NORTHWEST
PROVINCES. OVER SOUTHERN CHILE THE FRONT WILL SUSTAIN SCATTERED
CONVECTION WITH RAINFALL AMOUNTS OF 15-25MM THROUGH FRIDAY
MORNING...AND 10-15MM ON FRIDAY TO SATURDAY. OVER ARGENTINA...
UNDER THE INFLUENCE OF THE BUILDING POLAR RIDGE...POST FRONTAL
CONVECTION IS TO BUILD BETWEEN THE BUENOS AIRES PROVINCE-MENDOZA
IN ARGENTINA...WITH ACCUMULATION OF 05-10MM/DAY AND ISOLATED
MAXIMA OF 15MM ON FRIDAY AND SATURDAY. ON SATURDAY TO SUNDAY
ACTIVITY WILL THEN BUILD ACROSS URUGUAY WHERE IT IS TO FAVOR
RAINFALL AMOUNTS OF 05-10MM.

A SECONDARY FRONT WILL FOLLOW...ENTERING SOUTHERN CHILE LATER
TODAY...AND ACROSS PATAGONIA TO THE WESTERN ATLANTIC EARLY ON
FRIDAY MORNING. AS IT PROPAGATES ACROSS THE SOUTHEAST PACIFIC ITS
COLD CONTINENTAL AIR MASS IS TO GRADUALLY MODIFY. MEANWHILE...THIS
IS TO TRIGGER SCATTERED SNOW SHOWERS ACROSS SOUTHERN ANDES OF
CHILE-TIERRA DEL FUEGO. OVER TIERRA DEL FUEGO IT WILL RESULT IN
SNOWFALL AMOUNTS OF 03-05CM...WHILE OVER THE SOUTHERN ANDES IT
WILL PEAK AT 10-15CM.

A SECONDARY SHORT WAVE TROUGH IS TO THEN LIFT ACROSS 50S 105W
LATER TODAY. UNDER THE INFLUENCE OF A MID LEVEL RIDGE TO THE
WEST...THE SHORT WAVE TROUGH WILL THEN LIFT TO THE NORTH-NORTHWEST
TO 40S 100W ON FRIDAY. ON SATURDAY-SUNDAY THIS IS TO THEN EVOLVE
INTO A CLOSED LOW TO THE WEST-SOUTHWEST OF THE ARCHIPELAGO DE JUAN
FERNANDEZ...AND LATER DURING THE WEEKEND IT WILL MOVE TO CENTRAL
CHILE. SHORT WAVE ENERGY IS TO THEN SPILL ACROSS THE CENTRAL ANDES
TO ARGENTINA. THE INFLOW OF SHORT WAVE ENERGY WILL REINFORCE THE
AFOREMENTIONED FRONT AS IT MEANDERS ACROSS NORTHERN ARGENTINA-RIO
DE LA PLATA BASIN...WHILE ALSO PROVIDING DYNAMICAL SUPPORT TO
CONVECTIVE DEVELOPMENT.

FARTHER NORTH...AT 200 HPA...A BUILDING CELL OF THE SUBEQUATORIAL
RIDGE IS TO QUICKLY BECOME THE DOMINANT FEATURE ACROSS THE EASTERN
TROPICAL PACIFIC LATER ON FRIDAY. THE UPPER LEVEL RIDGE IS TO THEN
BUILD TO THE SOUTHEAST ALONG THE COAST OF PERU TO THE NORTHERN
REGIONS OF CHILE/NORTHWEST ARGENTINA LATER ON SATURDAY/SUNDAY
MORNING. AS THE RIDGE BUILDS...IT WILL INDUCE A SHORT WAVE TROUGH
THAT MOVES ACROSS BOLIVIA-PERUVIAN JUNGLE TO EASTERN ECUADOR. THE
EVOLVING PATTERN ALOFT WILL VENT CONVECTION ACROSS EQUATORIAL
SOUTH AMERICA...TO FAVOR RAINFALL AMOUNTS OF 15-25MM. THIS IS TO
GRADUALLY BUILD SOUTH ACROSS NORTHERN AMAZONAS IN BRASIL-SOUTHERN
COLOMBIA TO EASTERN ECUADOR/NORTHERN PERU. OTHER CONVECTION IS TO
CLUSTER ON THE NORTHEAST COAST OF BRASIL...BETWEEN PERNAMBUCO AND
ESPIRITO SANTO...AS ENHANCED BY BRISK EASTERLY TRADES. IN THIS
AREA EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY...WITH ISOLATED
MAXIMA OF 20-25MM.

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





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.