593  
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)  

 
 
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