835  
FXSA20 KWBC 041843  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
242 PM EDT THU JUN 04 2020  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
COR DTG  
 
FORECAST DISCUSSION FROM JUNE 04/18UTC: A DEEPENING MID/UPPER  
LEVEL TROUGH IS TO RAPIDLY BECOME THE DOMINANT SYNOPTIC SCALE  
FEATURE OVER THE EASTERN PACIFIC LATER THIS EVENING...WITH AXIS TO  
SPAN BETWEEN 70W-106W AND TO THE SOUTH OF 25S BY DAYBREAK ON  
FRIDAY. UNDER THE INFLUENCE OF A RIDGE TO THE WEST...THE HIGHLY  
AMPLIFIED TROUGH IS TO PERSIST THROUGH THE WEEKEND TO EARLY NEXT  
WEEK. MEANWHILE...THE MID LEVEL TROUGH IS TO FOCUS SHORT WAVE  
PERTURBATIONS AND DEEP SUBTROPICAL MOISTURE ACROSS THE SOUTHERN  
REGIONS OF CHILE. AT LOW LEVELS THIS WILL SUSTAIN A BROAD TROUGH  
THAT IS TO EXTEND BETWEEN THE BELLINGSHAUSEN-WEDDELL SEAS TO THE  
THE SOUTHERN CONE OF SOUTH AMERICA...FAVORING A TIGHT PRESSURE  
GRADIENT AND STRONG BOUNDARY LAYER WINDS ACROSS SOUTHERN CHILE AND  
PATAGONIA IN ARGENTINA. IN THIS AREA THE WINDS ARE FORECAST TO  
PEAK AT 35-50KT DURING THE NEXT SEVERAL DAYS. THIS WILL ENHANCE  
LOW LEVEL MOISTURE TRANSPORT AND CONVERGENCE ON THE SOUTHERN  
REGIONS OF CHILE...WHILE ADIABATICALLY LIFTING ACROSS THE SOUTHERN  
ANDES. THE MOST ACTIVE CONVECTION WITH THIS FEATURE IS EXPECTED  
BETWEEN PUERTO MONTT AND ISLA DE CHILOE IN SOUTHERN CHILE...WITH  
MAXIMA OF 20-45MM/DAY EXPECTED OVER THE NEXT TWO DAYS AND  
20-30MM/DAY DURING THE WEEKEND TO EARLY NEXT WEEK. DUE TO STRONG  
TOPOGRAPHICAL FORCING AND ABOVE NORMAL MOISTURE CONTENT...LOCALLY  
HIGHER AMOUNTS ARE HIGHLY LIKELY. FURTHERMORE...THE INFLOW OF COLD  
AIR ALOFT WOULD LIKELY FAVOR ISOLATED THUNDERSTORMS OVER SOUTHERN  
CHILE DURING THE DAY ON SUNDAY THROUGH MONDAY MORNING.  
 
ALSO OVER THE EASTERN PACIFIC...A MID/UPPER LEVEL LOW ON THE  
NORTHERN STREAM MEANDERS OFF THE NORTH COAST OF CHILE. AS THE  
AFOREMENTIONED TROUGH AMPLIFIES...IT IS TO DISPLACE THE NORTHERN  
STREAM VORTEX EAST ACROSS THE ANDES OF CHILE TO THE NORTHWEST  
PROVINCES IN ARGENTINA LATER THIS EVENING/EARLY FRIDAY MORNING.  
UNDER FAVORABLE JET DYNAMICS...THE CLOSED LOW IS TO GRADUALLY  
INTENSIFY/DEEPEN AS IT THEN TRACK TO THE EAST-SOUTHEAST ACROSS  
NORTHERN ARGENTINA TO SOUTHERN BRASIL/URUGUAY LATER ON FRIDAY. AS  
A SHORT WAVE RIDGE BUILDS TO THE EAST...THE CLOSED LOW IS TO  
BRIEFLY STALL OVER URUGUAY/RIO GRANDE DO SUL THROUGH MIDAFTERNOON  
ON SUNDAY...THEN WEAKEN AS IT MEANDERS EAST INTO THE WESTERN  
ATLANTIC ON SUNDAY-MONDAY. AT 250 HPA...A POLAR JET MAXIMA...IN  
ADDITION TO FAVOR THE RAPID INTENSIFICATION OF THE MID LEVEL LOW  
ON FRIDAY...IT IS TO ALSO FAVOR AN UPPER DIVERGENT PATTERN ACROSS  
URUGUAY-CORRIENTES/MISIONES IN NORTHERN ARGENTINA TO SOUTHERN  
BRASIL-PARAGUAY...VENTING ORGANIZED/POTENTIALLY SEVERE CONVECTION.  
AT LOW LEVELS...THE MID LEVEL VORTEX WILL SUSTAIN CYCLOGENESIS  
ALONG A MEANDERING FRONT OVER CENTRAL SOUTH AMERICA...WITH CLOSED  
LOW FORMING OVER CORRIENTES ARGENTINA/SOUTHEAST PARAGUAY EARLY IN  
THE CYCLE. THE FRONTAL LOW IS THEN FORECAST TO DEEPEN AS IT  
GRADUALLY OCCLUDES ACROSS URUGUAY TO ENTRE RIOS/CORRIENTES IN  
ARGENTINA. THE DEEPENING LOW WILL THEN DRIVE THE FRONT NORTH  
ACROSS SOUTHEASTERN BRASIL-MATO GROSSO TO CENTRAL BOLIVIA ON  
SATURDAY-SUNDAY. OVER PARAGUAY-MISIONES IN ARGENTINA-SOUTHERN  
BRASIL THIS WILL TRIGGER ORGANIZED/POTENTIALLY SEVERE CONVECTION  
EARLY IN THE CYCLE...WITH MAXIMA OF 40-80MM. ON FRIDAY...AS THE  
CONVECTION BUILDS EAST ACROSS PARANA/SANTA CATARINA IN BRASIL TO  
SAO PAULO-MATO GROSSO DO SUL THE MAXIMA DECREASES TO  
20-40MM...WHILE OVER URUGUAY-ENTRE RIOS IN ARGENTINA IT WILL SURGE  
TO 30-60MM AS MOISTURE WRAPS AROUND THE OCCLUDING LOW IN SUPPORT  
OF AN ECHO TRAINING PATTERN. ACROSS CENTRAL BOLIVIA...AS THE FRONT  
SURGES ACROSS MID SECTIONS OF SOUTH AMERICA...IT WILL SUSTAIN  
MODERATE TO HEAVY RAINFALL AMOUNTS DURING THE NEXT TWO DAYS...WITH  
MAXIMA OF 20-40MM/DAY.  
 
AT 200 HPA...A CLOSED HIGH OVER NORTHEAST BRASIL ANCHORS A RIDGE  
OVER NORTHERN SOUTH AMERICA...WITH AXIS DOMINATING THE UPPER FLOW  
TO THE NORTH OF 20S. CONSISTENT WITH PREVIOUS FORECASTS...THE HIGH  
IS TO MEANDER TO THE WEST-SOUTHWEST DURING THE NEXT FEW  
DAYS...REACHING ACRE IN WESTERN BRASIL/NORTHERN BOLIVIA LATER  
DURING THE WEEKEND. AS THE RIDGE HOLDS TO THE NORTH...A  
SUBTROPICAL JET IS TO BOUND THE SOUTHERN FRINGES OF THIS RIDGE  
DURING THE NEXT COUPLE OF DAYS...MEANWHILE FAVORING A DIVERGENT  
PATTERN ALOFT THAT IS TO VENT THE AFOREMENTIONED CONVECTION OVER  
PARAGUAY-SOUTHERN BRASIL. THE RIDGE ALOFT IS TO ALSO VENT  
CONVECTION ACROSS EQUATORIAL SOUTH AMERICA...WITH MOST INTENSE AS  
TROPICAL WAVE STREAMING TO THE NORTH INTERACT WITH THE NEAR  
EQUATORIAL TROUGH. ACROSS AMAZONAS IN BRASIL-SOUTHERN  
COLOMBIA/NORTHERN PERU-EASTERN ECUADOR THIS IS TO FAVOR SEVERAL  
DAYS OF SCATTERED DEEP CONVECTION WITH MAXIMA IN THIS AREA PEAKING  
AROUND 30-60MM EARLY IN THE CYCLE. SCATTERED CONVECTION IS TO THEN  
PERSIST THROUGH THE WEEKEND...WITH DAILY MAXIMA SETTLING AROUND  
20-40MM/DAY. OTHER CONVECTION IS TO CLUSTER ACROSS AMAPA IN  
BRASIL/NORTHERN PARA TO THE SOUTHERN GUIANAS...WITH MAXIMA OF  
15-30MM EXPECTED OVER THE NEXT FEW DAYS.  
 
DAVISON...WPC (USA)  
GALVEZ...WPC (USA)  

 
 
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