435  
FXSA20 KWBC 311707  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1207 PM EST WED JAN 31 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 31 AT 0000 UTC): MODELS SLOWLY  
REACHING A CONSENSUS ON HOW PATTERN IS GOING TO EVOLVE DURING THE  
NEXT FEW DAYS...WITH MODELS AGREEING ON MID/UPPER LEVEL RIDGE TO  
BUILD ACROSS THE SOUTHERN CONE/DRAKE PASSAGE. ALTHOUGH THEY  
GENERALLY AGREE ON HOW SYNOPTIC PATTERN IS GOING TO EVOLVE...THEY  
CONTINUE TO DISAGREE ON THE INTENSITY AND SPEED OF MESO SCALE  
PERTURBATIONS REVOLVING AROUND THE LONG WAVE AXIS.  
 
DEEPENING MID LEVEL TROUGH OVER THE SOUTHWEST ATLANTIC REACHES  
MAXIMUM AMPLITUDE LATER TODAY...WITH DEEP LOW NEAR THE SOUTH  
GEORGIA ISLANDS TO ANCHOR A HIGH AMPLITUDE TROUGH BETWEEN 60W-30W  
AND TO THE SOUTH OF 35S. BROAD MID LEVEL TROUGH IS TO REMAIN  
NEARLY STATIONARY THROUGH THURSDAY EVENING. ON FRIDAY AND ONWARD  
IT IS TO THEN MEANDER TO THE EAST-SOUTHEAST. AT LOW LEVELS THIS  
SUSTAINS A BROAD TROUGH OVER THE SOUTHWEST ATLANTIC THAT IS TO  
CENTER ON A VERY INTENSE LOW NEAR THE SOUTH GEORGIA  
ISLANDS...WHILE EXTENDING A FRONT TO THE NORTHWEST ACROSS RIO DE  
LA PLATA BASIN TO CENTRAL ARGENTINA. BROAD SURFACE TROUGH IS TO  
ALSO PERSIST DURING THE NEXT COUPLE OF DAYS WHILE ASSOCIATED FRONT  
MEANDERS OVER CENTRAL ARGENTINA. EARLY IN THE CYCLE THIS IS TO  
FAVOR SCATTERED CONVECTION ACROSS CORDOBA-MENDOZA IN ARGENTINA  
WITH MAXIMA OF 15-20MM. ON THURSDAY IT IS TO ONLY FAVOR WIDELY  
ISOLATED CONVECTION.  
 
DEEPENING MID LEVEL TROUGH IS TO FOLLOW...WITH AXIS TO MOVE ACROSS  
120W/130W LATER TODAY. DOWNSTREAM FROM THIS FEATURE A RIDGE IS TO  
BUILD SOUTH ACROSS CHILE/ARGENTINA TO THE DRAKE PASSAGE LATER ON  
THURSDAY. AS THE TROUGH TO THE WEST PRESSES AGAINST THIS AXIS...IT  
IS TO SHEAR SHORT WAVE PERTURBATIONS THAT ARE TO THEN PROPAGATE  
ACROSS EXTREME SOUTHERN CHILE-TIERRA DEL FUEGO. AT LOW LEVELS THIS  
WILL FAVOR A BROAD TROUGH OVER THE SOUTHEAST  
PACIFIC/BELLINGSHAUSEN SEA...WITH POLAR FRONTS REVOLVING AROUND  
THIS AXIS TO STREAM ACROSS SOUTHERN CHILE/PATAGONIA IN ARGENTINA.  
OVER TIERRA DEL FUEGO THIS IS TO ONLY FAVOR LIGHT CONVECTION WITH  
ACCUMULATION OF 05-10MM/DAY...WHILE OVER SOUTHERN CHILE EXPECTING  
A MAXIMA OF 15-20MM EARLY IN THE CYCLE.  
 
OTHER SHORT WAVE PERTURBATIONS ARE TO STREAM ACROSS SOUTHERN CHILE  
TO PATAGONIA/LA PAMPA IN ARGENTINA...WITH A MID LEVEL PERTURBATION  
CROSSING THE SOUTHERN CONE ON FRIDAY. THIS WILL BE FOLLOWED BY A  
STRONGER SHORT WAVE TROUGH ON SUNDAY. AS THE MOVE ACROSS NORTHERN  
PATAGONIA-LA PAMPA THESE ARE TO TRIGGER SCATTERED  
CONVECTION...WITH THE ONE ON FRIDAY TO TRIGGER MAXIMA OF 05-10MM.  
HIGHER AMOUNTS ARE EXPECTED ON SUNDAY WITH MAXIMA OF 15-25MM IN  
POTENTIALLY SEVERE CONVECTION.  
 
FARTHER NORTH...SHORT WAVE TROUGH ON THE NORTHERN STREAM MEANDERS  
OFF THE SOUTHEAST COAST OF BRASIL. DEEPENING MID LEVEL TROUGH TO  
THE SOUTH IS TO INTERACT WITH THIS FEATURE EARLY IN THE  
PERIOD...TO SUSTAIN GRADUAL INTENSIFICATION OF MID LEVEL VORTEX TO  
THE NORTH THROUGH FRIDAY EVENING. THE GLOBAL  
MODELS...HOWEVER...DIVERGE ON THE INTENSITY OF THIS FEATURE...WITH  
BOTH THE UKMET AND THE ECMWF FAVORING A DEEPER PERTURBATION THAN  
WHAT THE GFS SUGGESTS. AT LOW LEVELS THIS IS INTERACTING WITH A  
SURFACE FRONT IN SUPPORT OF A FRONTAL WAVE OFF THE SOUTHEAST COAST  
OF BRASIL. THIS IS DRAWING THE FRONT ACROSS SAO PAULO-SANTA  
CATARINA TO MISIONES IN ARGENTINA/SOUTHEAST PARAGUAY...WHERE IT IS  
TO MEANDER DURING THE NEXT FEW DAYS. THIS COINCIDES WITH A PEAK IN  
MJO ACTIVITY ACROSS THE CONTINENT TO SUSTAIN FORMATION OF THE  
SOUTH AMERICAN CONVERGENCE ZONE (SACZ) ACROSS BRASIL. THE SACZ IS  
TO MEANDER ACROSS NORTHERN SAO PAULO/SOUTHERN MINAS GERAIS TO MATO  
GROSSO/SANTA CRUZ IN EASTERN BOLIVIA. OVER MINAS GERAIS-BAHIA AND  
TOCANTINS/GOIAS THE ENVIRONMENTAL CONDITIONS ARE TO FAVOR  
GENERATION OF MESO SCALE CONVECTIVE SYSTEMS...WITH RAINFALL MAXIMA  
OF 75-150MM. MOST ACTIVE IS EXPECTED TODAY AND ON FRIDAY-MONDAY.  
THIS IS TO ALSO FAVOR ORGANIZED DEEP CONVECTION ACROSS MATO  
GROSSO-SOUTHERN PARA/AMAZONAS-RONDONIA IN BRASIL...WITH DAILY  
MAXIMA IN THIS AREA TO PEAK AT 35-70MM. LOCALLY HIGHER AMOUNTS ARE  
HIGHLY PROBABLE.  
 
AT 200 HPA...THE BOLIVIAN HIGH IS INITIALIZED OVER MATO GROSSO DO  
SUL IN BRASIL...ANCHORING A BROAD RIDGE OVER THE CONTINENT TO THE  
NORTH OF 40S. THROUGH FRIDAY AFTERNOON THE HIGH WILL DRIFT WEST  
ACROSS SOUTHERN BOLIVIA/NORTHWEST ARGENTINA...TO SETTLE OVER  
NORTHERN CHILE. AS THE RIDGE PULLS AWAY THE AFOREMENTIONED TROUGH  
OVER SOUTHEAST BRASIL IS TO DEEPEN/ AMPLIFY ACROSS NORTHEAST SOUTH  
AMERICA...INTERACTING WITH THE SACZ IN SUPPORT OF ORGANIZED DEEP  
CONVECTION. THE RIDGE ALOFT...MEANWHILE...IS TO VENT ORGANIZED  
DEEP CONVECTION ACROSS SOUTHEASTERN BOLIVIA-CHACO PARAGUAYO AND  
NORTHWEST ARGENTINA...TO SUSTAIN MAXIMA OF 40-80MM/DAY DURING THE  
NEXT 48-60 HRS. BUT AS THE UPPER RIDGE PATTERN EVOLVES...ACTIVITY  
IS TO WEAKEN. OTHER CONVECTION IS TO BUILD ACROSS THE ALTIPLANO OF  
BOLIVIA TO SOUTHERN PERU...WITH MAXIMA TO PEAK AT 20-30MM OVER THE  
NEXT 48-72 HRS...DECREASING TO 15-20MM LATER IN THE CYCLE. ON THE  
SIERRA OF PERU EXPECTING ACCUMULATION OF 05-10MM/DAY. OVER  
ECUADOR...UNDER THE INFLUENCE OF THE PANAMANIAN TROUGH...A MOIST  
NORTHWESTERLY FLOW IS TO PERSIST DURING THE NEXT FIVE DAYS TO  
GENERALLY FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY. LOCALLY HIGHER  
AMOUNTS ARE HIGHLY PROBABLE.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page