885  
FXSA20 KWBC 071943  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
243 PM EST TUE NOV 07 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 07 AT 0000 UTC): THE UKMET MADE  
PATTERN CORRECTIONS AND IT IS NOW IN BETTER AGREEMENT WITH THE  
FAVORED GFS/ECMWF SOLUTION. ON THE NORTHERN STREAM FLOW THE MODELS  
ARE IN EXCELLENT AGREEMENT THROUGH 168 HRS...WHILE ON THE SOUTHERN  
STREAM THEY START TO DISAGREE BY 96-108 HRS. THESE DIFFERENCES ARE  
MORE PRONOUNCED ACROSS THE DRAKE PASSAGES. BUT THESE WILL BE  
INCONSEQUENTIAL TO THE OVERALL MEDIUM-LONG RANGE FORECAST.  
 
AS PREVIOUSLY NOTED...A MID/UPPER LEVEL RIDGE EXTENDS SOUTH FROM  
CENTRAL ARGENTINA TO THE ANTARCTIC PENINSULA/WEDDELL SEA. A BROAD  
POLAR TROUGH TO THE WEST CONTINUES TO PRESS AGAINST THIS RIDGE. AS  
THE RIDGE HOLDS...THE TROUGH IS TO GRADUALLY WEAKEN WHILE SHEARING  
SHORT WAVE ENERGY TO THE SOUTH-SOUTHEAST ACROSS THE ANTARCTIC  
PENINSULA TO THE WEDDELL SEA. THE TROUGH IS TO GRADUALLY WEAKEN  
WHILE THE RIDGE IS EXPECTED TO FLATTEN. REMNANTS OF THE MID LEVEL  
TROUGH REACHES SOUTHERN CHILE LATER ON THURSDAY...TO SLOWLY TRACK  
ACROSS SOUTHERN PATAGONIA TO THE FALKLAND ISLANDS/MALVINAS ON  
FRIDAY. AT LOW LEVELS THIS WILL SUSTAIN AN ELONGATED FRONT ACROSS  
EXTREME SOUTHERN PORTIONS OF CHILE/SOUTHERN PATAGONIA LATER IN THE  
WEEK...WHERE IT IS TO TRIGGER LIGHT RAINFALL AMOUNTS.  
 
ALSO AT MID LEVELS...SHORT WAVE PERTURBATIONS POPULATE THE  
NORTHERN STREAM FLOW...WITH ONE TO MIGRATE ACROSS RIO DE LA PLATA  
BASIN/URUGUAY LATER THIS AFTERNOON AS ANOTHER SHORT WAVE TROUGH  
REACHES SOUTHERN/CENTRAL CHILE. THE LATTER MOVES ACROSS PATAGONIA  
LA PAMPA TO THE WESTERN ATLANTIC ON WEDNESDAY. AS A SHORT WAVE  
RIDGE BUILDS TO THE WEST THIS IS TO THEN INDUCE THE NORTHWARD  
AMPLIFICATION OF THE TROUGH OVER THE WESTERN ATLANTIC. ON FRIDAY  
THIS IS TO THEN AMPLIFY BETWEEN 60W-40W TO THE SOUTHERN STATES OF  
BRASIL. AT LOW LEVELS THIS SUSTAINS A MEANDERING FRONT OVER  
CENTRAL ARGENTINA. THIS IS TO SLOWLY INTENSIFY WHILE MEANDERING  
EAST AND NORTH ACROSS URUGUAY-CORDOBA/MENDOZA IN ARGENTINA LATER  
ON WEDNESDAY. ON THURSDAY-FRIDAY THE SURFACE LOW IS TO INTENSIFY  
WHILE OCCLUDING OFF THE COAST OF ARGENTINA. THIS WILL THEN DRIVE  
THE ASSOCIATED FRONT NORTH ACROSS THE SOUTHERN STATES OF BRASIL TO  
CHACO PARAGUAYO ON FRIDAY. OVER CENTRAL ARGENTINA THIS IS TO  
INITIALLY TRIGGER SCATTERED DEEP CONVECTION WITH MAXIMA OF  
15-25MM. AS THE FRONT ADVANCES NORTH ON WEDNESDAY-THURSDAY  
PREFRONTAL CONVECTION ON THE NORTHWEST PROVINCES IN ARGENTINA IS  
TO FAVOR MAXIMA OF 20-35MM...WITH SIMILAR AMOUNTS ACROSS  
SOUTHERN/SOUTHEASTERN STATES OF BRASIL-PARAGUAY ON  
THURSDAY-FRIDAY. PREFRONTAL CONVECTION OVER NORTHERN  
BOLIVIA-RONDONIA IN BRASIL WILL RESULT IN MAXIMA OF 20-40MM ON  
FRIDAY-SATURDAY.  
 
A HIGH AMPLITUDE MID/UPPER LEVEL TROUGH DOMINATES THE FLOW OVER  
THE SOUTH ATLANTIC...AS IT EXTENDS BETWEEN 50W-10W AND TO THE  
SOUTH OF 20S. THIS IS A SLOW TO EVOLVE SYSTEM...TO REMAIN NEARLY  
UNCHANGED THROUGH MIDDAY ON WEDNESDAY. LATER IN THE DAY/EARLY  
THURSDAY THE TROUGH BEGINS TO WEAKEN WHILE PULLING TO THE  
EAST-SOUTHEAST. AT LOW LEVELS THE TROUGH ALOFT SUSTAINS AN  
ELONGATED FRONT THAT EXTENDS TO THE NORTHWEST ACROSS THE SOUTH  
ATLANTIC TO RIO DE JANEIRO/ESPIRITO SANTO...THEN TO THE SOUTHWEST  
TO PARAGUAY. THIS BOUNDARY IS TO PERSIST DURING THE NEXT THREE  
DAYS...DISSIPATING LATER ON FRIDAY. MEANWHILE...MOISTURE IS TO  
CONVERGE ALONG THIS BOUNDARY. ACROSS PARAGUAY THIS IS TO INITIALLY  
SUSTAIN MODERATE CONVECTION WITH MAXIMA OF 20-45MM...DECREASING TO  
20-35MM ON WEDNESDAY-THURSDAY.  
 
FEW DAYS. ACROSS ESPIRITO SANTO/RIO DE JANEIRO THIS IS TO FAVOR  
LIGHT TO MODERATE CONVECTION WITH MAXIMA OF 15-30MM/DAY. ON  
WEDNESDAY-THURSDAY THIS DECREASES TO 15-20MM/DAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A NARROW CELL OF THE  
SUBTROPICAL RIDGE EXTENDS WEST-TO-EAST BETWEEN PERU AND THE  
SOUTHEAST STATES OF BRASIL...CENTERING ON A CLOSED HIGH OVER  
NORTHERN BOLIVIA/ACRE IN BRASIL. NORTH OF THIS RIDGE...A SHORT  
WAVE TROUGH EXTENDS OVER THE NORTHEAST STATES OF BRASIL...WITH  
AXIS CENTERING ON A CLOSED LOW THAT MEANDERS BETWEEN NORTHERN  
PARA-AMAPA IN BRASIL. THE RIDGE ALOFT IS VENTING CONVECTIVE  
DEVELOPMENT ACROSS CENTRAL AND EASTERN STATES OF BRASIL. OVER THE  
NEXT FEW DAYS...CONVECTION ON THE STATES OF TOCANTINS-GOIAS-BAHIA  
IS TO BECOME BETTER ORGANIZED. IN THIS AREA INITIALLY EXPECTING  
RAINFALL MAXIMA OF 35-70MM. THROUGH WEDNESDAY THIS BECOMES BETTER  
ORGANIZED...WITH MAXIMA OF 40-80MM IN ASSOCIATION WITH A BROAD  
MESO SCALE CONVECTIVE SYSTEM. NOTE THAT LOCALLY HIGHER AMOUNTS IN  
EXCESS OF 125MM ARE HIGHLY PROBABLE. ON THURSDAY-FRIDAY THE DAILY  
MAXIMA DECREASES TO 25-50MM. OTHER CONVECTION IS EXPECTED ACROSS  
NORTHERN AMAZONAS IN BRASIL TO SOUTHERN COLOMBIA...WITH MAXIMA TO  
PEAK AT 20-35MM. THIS SPREADS WEST ACROSS NORTHERN PERU TO EASTERN  
ECUADOR ON THURSDAY-SATURDAY TO SUSTAIN MAXIMA OF 20-30MM/DAY.  
OTHER CONVECTION TO THE SOUTH IS EXPECTED ON THE SOUTHERN SIERRA  
OF PERU...WHERE UPPER LEVEL TROUGH IS TO FAVOR A DIVERGENT PATTERN  
ALOFT. ON FRIDAY THIS WILL TRIGGER RAINFALL MAXIMA OF  
15-20MM...DECREASING TO 05-10MM ON SATURDAY.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page