Prognostic Meteorological Discussion
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FXSA20 KWBC 171730
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1229 PM EST FRI NOV 17 2017

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM NOV 17 AT 0000 UTC): THE GLOBAL
MODELS GENERALLY AGREE ON OVERALL SYNOPTIC PATTERN EVOLUTION
DURING THE NEXT SIX DAYS. THEY...HOWEVER...CONTINUE TO DIVERGE ON
THE SPEED AND AMPLITUDE OF SHORT WAVE PERTURBATIONS REVOLVING
AROUND THE LONG WAVE AXIS. THESE DIFFERENCE GRADUALLY BECOME MORE
PRONOUNCED BY 84-96 HRS...GRADUALLY BUILDING FROM WEST TO EAST.
RESULTING IN LOWER CONFIDENCE IN THE FORECAST LATER IN THE CYCLE.

BUILDING MID/UPPER LEVEL RIDGE OVER THE EASTERN PACIFIC WILL
INDUCE THE NORTHWARD AMPLIFICATION OF A TROUGH ACROSS ARGENTINA TO
PARAGUAY LATER TODAY. AS IT DEEPENS...THE TROUGH WILL SUSTAIN
HEIGHT FALLS OF 150-200GPM ACROSS RIO DE LA PLATA BASIN...WHILE
OVER NORTHERN ARGENTINA HEIGHT FALLS WILL RANGE BETWEEN 35-70GPM.
ON SATURDAY-SUNDAY THE TROUGH WILL THEN PULL TO THE EAST-SOUTHEAST
INTO THE WESTERN SOUTH ATLANTIC. AT LOW LEVELS...THIS SUSTAINS A
POLAR FRONT ACROSS RIO DE LA PLATA BASIN TO MENDOZA IN ARGENTINA
LATER TODAY. EARLY ON SATURDAY THE FRONT RACES ACROSS URUGUAY TO
NORTHERN ARGENTINA...DRIVEN BY A 35-40KT PAMPERO LOW LEVEL JET.
THIS IS TO THEN MERGE WITH A MEANDERING FRONT OVER SOUTHERN
BRASIL-PARAGUAY...DISPLACING THE FRONT NORTH ACROSS PARANA/SANTA
CATARINA IN SOUTHERN BRASIL TO NORTHERN PARAGUAY/SANTA CRUZ IN
EASTERN BOLIVIA LATER ON SATURDAY/SUNDAY MORNING. FRONT IS TO THEN
REMAIN STATIONARY. ACROSS PARAGUAY-SOUTHERN BRASIL ENVIRONMENTAL
CONDITIONS REMAIN FAVORABLE FOR AN MCS TO FORM EARLY ON SATURDAY
MORNING...TO TRIGGER MAXIMA OF 75-150MM. LOCALLY HIGHER AMOUNTS
ARE HIGHLY PROBABLE...WITH SOME OF THE ENSEMBLE MEMBERS SHOWING
MAXIMA OF 200MM. ON SATURDAY AFTERNOON THE CONVECTION IS TO SPREAD
ACROSS SOUTHERN TO SOUTHEAST BRASIL WHERE IT IS TO TRIGGER
RAINFALL AMOUNTS OF 25-50MM. ON SUNDAY IT MOVES TO NORTHERN SAO
PAULO/SOUTHERN MINAS GERAIS-RIO DE JANEIRO...WITH MAXIMA OF
35-70MM. OTHER CONVECTION TO THE WEST IS TO BUILD ALONG THE
TRAILING END OF THE SURFACE FRONT OVER BOLIVIA...WITH MAXIMA OF
75-125MM ON SATURDAY TO SUNDAY...WHILE ON SUNDAY-MONDAY THE MAXIMA
DECREASES TO 20-35MM. OVER SOUTHERN/ CENTRAL PERU TO ACRE IN
BRASIL MAXIMA WILL PEAK AT 30-60MM ON SATURDAY...WITH AN
ADDITIONAL RAINFALL AMOUNTS OF 25-50MM ON SUNDAY. ON MONDAY FOCUS
OF THE CONVECTION SHIFTS TO NORTHERN PERU-EASTERN ECUADOR WITH
MAXIMA DECREASING TO 20-40MM.

ANOTHER SHORT WAVE TROUGH ON THE SOUTHERN STREAM IS TO THEN LIFT
ACROSS THE BELLINGSHAUSEN SEA-DRAKE PASSAGE TO TIERRA DEL FUEGO
LATER TODAY...AND ACROSS PATAGONIA IN ARGENTINA TO THE WESTERN
ATLANTIC ON SATURDAY. ASSOCIATED SURFACE FRONT REACHES SOUTHERN
CHILE LATER THIS EVENING...AND ON SATURDAY IT IS TO QUICKLY MOVE
ACROSS PATAGONIA TO LA PAMPA...REACHING RIO DE LA PLATA BASIN ON
SUNDAY. OVER SOUTHERN CHILE THIS IS TO FAVOR A COLD ADVECTIVE
PATTERN...WITH ENVIRONMENTAL CONDITIONS FAVORING SOLID
PRECIPITATION ACROSS THE SOUTHERN ANDES AND MIXED PRECIPITATION
ALONG THE COAST TO PUNTA ARENAS CHILE. IN THIS AREA EXPECTING
ACCUMULATION OF 05-10MM ON BOTH FRIDAY AND SATURDAY.

NORTH OVER THE CONTINENT...AT 200 HPA...A HIGH OVER ACRE/NORTHERN
BOLIVIA IS TO ANCHOR A SHORT WAVE RIDGE ACROSS NORTHWEST SOUTH
AMERICA. A TROUGH TO THE EAST...MEANWHILE...EXTEND OVER THE
NORTHEAST STATES OF BRASIL. THE LATTER EVOLVES INTO A CLOSED LOW
NEAR THE CITY OF RECIFE LATER ON SUNDAY. THE RIDGE-TROUGH PATTERN
ALOFT IS TO VENT CONVECTION ACROSS CENTRAL BRASIL...TO FAVOR
RAINFALL AMOUNTS OF 20-35MM/DAY. THROUGH MONDAY THIS DECREASES TO
15-20MM. OTHER CONVECTION IS TO CLUSTER ACROSS SOUTHERN
COLOMBIA-NORTHERN PERU TO EASTERN ECUADOR...WITH ACCUMULATION OF
15-20MM. THIS INCREASES TO 20-40MM LATER ON SUNDAY-MONDAY.

OVIEDO...SHN (ARGENTINA)
VANNUCCI...SMN (ARGENTINA)
RIVAS...SENAMHI (PERU)
DAVISON...WPC (USA)
$$





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