118  
FXSA20 KWBC 241659  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1259 PM EDT TUE OCT 24 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM OCT 24 AT 0000 UTC): THE GLOBAL  
MODELS REMAIN IN GOOD AGREEMENT THROUGH THE MEDIUM RANGE  
PERIOD...WITH ENSEMBLE MODEL GUIDANCE PROVIDING GOOD SUPPORT TO  
THE DETERMINISTIC SOLUTION. OUR CONFIDENCE IN THE FORECAST IS HIGH  
THROUGH 108-120 HRS.  
 
SOUTH OVER THE DOMAIN...A DEEP MID LEVEL LOW OVER THE ANTARCTIC  
PENINSULA EXTENDS A SHORT WAVE TROUGH NORTH ACROSS THE DRAKE  
PASSAGE TO THE SOUTHERN CONE. AXIS IS TO SLOWLY PULL ACROSS  
PATAGONIA IN ARGENTINA EARLY ON WEDNESDAY...WHILE THE LOW DRIFTS  
TO THE WEDDELL SEA. THE TROUGH IS TO THEN MEANDER TO THE  
EAST-SOUTHEAST ACROSS THE SOUTH ATLANTIC WHILE GENERALLY REMAINING  
TO THE SOUTH OF 50S. AT LOW LEVELS THE TROUGH ALOFT SUSTAINS A  
BROAD TROUGH ACROSS THE ANTARCTIC PENINSULA TO THE SOUTHERN CONE.  
THE TROUGH IS TO MOVE ACROSS THE SOUTHWEST ATLANTIC TO THE SOUTH  
GEORGIA ISLANDS LATER ON THURSDAY. AS IT MEANDERS ACROSS THE  
SOUTHERN CONE POLAR FRONTS ARE TO REVOLVE AROUND THIS AXIS...WITH  
ONE TO EXTEND NORTH ACROSS LA PAMPA IN ARGENTINA TO CENTRAL CHILE  
EARLY IN THE CYCLE. ON WEDNESDAY EXPECTING SCATTERED CONVECTION TO  
BUILD OVER CENTRAL ARGENTINA...WITH CONVECTION BECOMING BETTER  
ORGANIZED LATER ON THURSDAY. IN THIS AREA EXPECTING MAXIMA OF  
15-20MM ON THURSDAY TO FRIDAY.  
 
A DEEPENING SHORT WAVE TROUGH ON THE SOUTHERN STREAM IS TO  
FOLLOW...WITH MID LEVEL AXIS TO MOVE ACROSS 90W TO 35S LATER ON  
THURSDAY. ON FRIDAY...AS IT NEARS THE SOUTH COAST OF CHILE...THE  
MID LEVEL PERTURBATION IS TO INTENSIFY. THROUGH SATURDAY THIS  
EVOLVES INTO A BROAD TROUGH ACROSS THE SOUTHERN CONE. AT LOW  
LEVELS THIS WILL SUSTAIN A DEEP OCCLUDED TROUGH OVER SOUTHERN  
CHILE LATER ON FRIDAY...WITH THE OCCLUDED LOW TO MOVE TO SOUTHERN  
PATAGONIA IN ARGENTINA ON SATURDAY. THE ASSOCIATED FRONT ENTERS  
SOUTHERN CHILE EARLY ON FRIDAY...AND LATER IN THE DAY RACES ACROSS  
PATAGONIA IN ARGENTINA. ON SATURDAY...AIDED BY A PAMPERO LOW LEVEL  
JET...THE FRONT MOVES NORTH ACROSS THE BUENOS AIRES  
PROVINCE-MENDOZA IN ARGENTINA-SANTIAGO DE CHILE TO THE EASTERN  
PACIFIC. OVER SOUTHERN CHILE THIS WILL SUSTAIN SCATTERED  
CONVECTION WITH ACCUMULATION OF 15-20MM. HIGHER AMOUNTS ARE  
EXPECTED OVER THE BUENOS AIRES PROVINCE-MENDOZA IN  
ARGENTINA...WHERE THIS IS TO TRIGGER MAXIMA OF 20-35MM. THE DEEP  
OCCLUDED LOW IS TO ALSO TRIGGER HEAVY RAINFALL AMOUNTS ACROSS  
SOUTHERN PATAGONIA IN ARGENTINA...WITH MAXIMA OF 20-35MM.  
 
ON THE NORTHERN STREAM FLOW...A 500 HPA LOW NEAR 40S 32W ANCHORS A  
SHORT WAVE TROUGH OFF THE SOUTH COAST OF BRASIL. LATER ON  
WEDNESDAY THE TROUGH MEANDERS ACROSS 25W...NEARING 15W ON  
THURSDAY. THE TROUGH ALOFT SUSTAINS A POLAR FRONT ACROSS RIO DE  
JANEIRO/NORTHERN SAO PAULO IN BRASIL TO SOUTHEAST  
PARAGUAY/CORRIENTES IN ARGENTINA. THE BOUNDARY IS TO REMAIN NEARLY  
STATIONARY OVER THE NEXT COUPLE OF DAYS...TO FAVOR SCATTERED  
CONVECTION ACROSS MID SECTIONS OF SOUTH AMERICA...WITH MAXIMA IN  
THIS AREA TO PEAK AT 15-25MM.  
 
SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO THEN PULL ACROSS  
CENTRAL/NORTHERN CHILE LATER ON TUESDAY...CROSSING NORTHERN  
ARGENTINA/SOUTHERN BRASIL ON WEDNESDAY. THIS WILL BE ACCOMPANIED  
BY A SUBTROPICAL JET MAXIMA...WITH DIVERGENCE ON ITS RIGHT EXIT  
REGION TO ENVELOP THE MESOPOTAMIA VALLEY IN ARGENTINA-SOUTHEAST  
PARAGUAY ON WEDNESDAY. AS THE MID LEVEL TROUGH MOVES ACROSS  
SOUTHERN BRASIL TO THE WESTERN ATLANTIC ON THURSDAY IT IS FORECAST  
TO INTENSIFY. AS IT MEANDERS ACROSS MID SECTIONS OF SOUTH AMERICA  
THE MID LEVEL TROUGH WILL THEN INTERACT WITH THE MEANDERING  
SURFACE FRONT OVER SOUTHERN BRASIL-NORTHERN ARGENTINA...FAVORING  
CYCLOGENESIS ALONG THE FRONTAL BOUNDARY. THIS IS TO FAVOR SEVERE  
CONVECTION AS IT STREAMS ACROSS NORTHERN  
ARGENTINA-PARAGUAY...TRIGGERING HEAVY CONVECTION WITH ACCUMULATION  
OF 50-100MM. STRONG DYNAMICAL FORCING WILL LIKELY RESULT IN LARGE  
HAIL STONES. ON THURSDAY THE FOCUS OF THE HEAVY CONVECTION SHIFTS  
TO SOUTHERN BRASIL-PARAGUAY...WHERE IT IS TO TRIGGER MAXIMA OF  
35-70MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A BROAD RIDGE ENVELOPS  
CONTINENTAL AREA TO THE NORTH OF 20S. THIS PATTERN IS TO GRADUALLY  
INTENSIFY THROUGH FRIDAY EVENING...WHEN MODELS CONTINUE TO AGREE  
ON A HIGH CLOSING OVER AMAZONAS IN WESTERN BRASIL. THE BROAD UPPER  
LEVEL RIDGE PATTERN IS TO VENT DEEP CONVECTION ACROSS NORTHWEST  
SOUTH AMERICA. OVER AMAZONAS IN BRASIL-AMAZONIA IN SOUTHERN  
COLOMBIA AND THE NORTHERN JUNGLE OF PERU THIS IS TO FAVOR MAXIMA  
OF 20-40MM. THROUGH WEDNESDAY THE DAILY MAXIMA DECREASES TO  
20-35MM...SURGING AGAIN LATER ON SATURDAY WHEN THE MAXIMA IS TO  
PEAK AT 20-45MM. OVER MATO GROSSO-SOUTHERN PARA AND RORAIMA IN  
BRASIL EXPECTING SCATTERED CONVECTION TO BUILD IN A DIURNAL  
PATTERN...WITH ACCUMULATION OF 15-25MM/DAY. ON THE  
CENTRAL-SOUTHERN JUNGLE OF PERU THE DAILY MAXIMA IS TO PEAK AT  
15-20MM.  
 
OVIEDO...SHIN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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