016
FXSA20 KWBC 251658
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1258 PM EDT MON AUG 25 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
NOTE: STRONG TRANSITION PATTERN OVER ARGENTINA-URUGUAY-SOUTHERN
BRASIL ON DAYS 02-04 ARE LIKELY TO FAVOR SEVERE THUNDERSTORMS.
MODEL COMPARISON (VALID FROM 00Z AUG 25). THE GLOBAL MODELS SHOW
GOOD AGREEMENT ON THE UPSTREAM AND CONTINENTAL PATTERN DURING THE
CYCLE...WITH DIFFERENCES CONFINING TO THE DOWNSTREAM PATTERN OVER
THE WESTERN ATLANTIC ON DAY 05. IN THIS REGION THE GFS IS
FORECASTING A METEOROLOGICAL BOMB...SHOWING A LOW THAT DEEPENS
OVER 30 HPA IN 24 HRS. THE ECMWF/UKMET GUIDANCE FAVOR A
SUBSTANTIALLY WEAKER SURFACE FEATURE...SO FOR NOW WE ARE GOING TO
DOWNPLAY THE GFS SOLUTION.
AT MID LEVELS...A BROAD TROUGH IS INITIALIZED OVER THE EASTERN
PACIFIC...WITH AXIS TO SLOWLY SPILL ACROSS THE SOUTHERN CONE
DURING THE NEXT THREE DAYS. INITIALLY THE TROUGH WILL FOCUS ITS
SHORT WAVE ENERGY ACROSS CENTRAL/SOUTHERN CHILE...BUT STARTING
AROUND 36 HRS EXPECT A STRONG INCURSION ACROSS THE CENTRAL
PROVINCES OF ARGENTINA...WHERE IT WILL FAVOR HEIGHT FALLS OF 75-
150 GPM. ON DAY 03 THIS WILL INCREASE TO 200 GPM HEIGHT FALLS
OVER RIO DE LA PLATA BASIN-CORDOBA. THE MEAN AXIS WILL GRADUALLY
MOVE ACROSS 55W/60W BY 96 HRS...AND IT WILL EJECT ACROSS 40W
LATER IN THE PERIOD. AS IT MEANDERS OVER THE EASTERN PACIFIC...
THE TROUGH WILL ESTABLISH A SUBTROPICAL CONNECTION...ADVECTING
MOISTURE INTO CENTRAL/SOUTHERN CHILE. THIS...IN-TURN...WILL TAKE
ADVANTAGE OF FAVORABLE JET DYNAMICS TO SUSTAIN ORGANIZED
CONVECTION WITH ACCUMULATION OF 30-60MM/DAY THROUGH 36 HRS.
AFTERWARDS...DAILY MAXIMA WILL DECREASE TO 15-30MM/DAY THROUGH
72-84 HRS. AT LOW LEVELS...A STRONG NORTHERLY JET WILL ESTABLISH
ACROSS EASTERN BOLIVIA/PARAGUAY BY 30-36 HRS...TO SUSTAIN
ADVECTION OF WARM/MOIST AIR INTO THE CENTRAL PROVINCES OF
ARGENTINA. A POLAR FRONT PUSHES ACROSS LA PAMPA ON DAY 02...WHERE
IT WILL TRIGGER A PREFRONTAL SQUALL LINE AND SEVERE CONVECTION.
THROUGH 72 HRS THE FRONT WILL MOVE ACROSS BUENOS AIRES PROVINCE-
CORDOBA IN ARGENTINA...WITH THE SEVERE CONVECTION PERSISTING
ALONG AND AHEAD OF THIS FRONT.TSC AT 96 HRS THE FRONT PUSHES
NORTH INTO SOUTHERN BRASIL-PARAGUAY TO CENTRAL/NORTHERN
BOLIVIA...DISPLACED BY A SOUTHERLY JET. BY 120 HRS IT WILL
MEANDER ACROSS SAO PAULO-MATO GROSSO DO SUL IN BRASIL TO NORTHERN
BOLIVIA. IN ADDITION TO THE HEAVY RAINFALL OVER CHILE...THIS WILL
SCATTERED CONVECTION ACROSS LA PAMPA AND BUENOS AIRES
PROVINCE...WITH MAXIMA OF 15-30MM ON DAY 02...FORECAST TO
INCREASE TO 30-60MM/DAY ON DAY 03 AS IT SPREADS NORTH INTO
URUGUAY-MESOPOTAMIA VALLEY TO SOUTHERN BRASIL. BY 96 HRS MAXIMA
WILL DECREASE TO 10-20MM/DAY AS THE FRONT ENTERS SOUTHERN BRASIL-
SOUTHEAST PARAGUAY...WHILE OVER CENTRAL/NORTHERN BOLIVIA TO THE
SOUTHERN JUNGLE OF PERU MAXIMA WILL PEAK AT 15-30MM IN SCATTERED
CONVECTION.
AT UPPER LEVELS...UNDER THE INFLUENCE OF THE LONG WAVE TROUGH
ENTERING THE SOUTHERN CONE...THE SUBTROPICAL RIDGE OVER NORTHERN
SOUTH AMERICA IS TO WEAKEN/NEARLY COLLAPSE...WITH A CELL
RELOCATING TO THE EASTERN PACIFIC NEAR 15S 90W. AS THE UPPER
PATTERN EVOLVES...CONVECTION OVER NORTHERN PARA-AMAZONAS IN
BRASIL IS EXPECTED TO SLOWLY SHIFT NORTHWARD AS THE CYCLE
PROGRESSES...WITH MOST INTENSE EXPECTED DURING THE NEXT TWO DAYS
WITH MAXIMA OF 20-40MM. AFTER 60 HRS EXPECT A SHARP DECREASE WITH
MAXIMA OF 10-20MM. OVER RIO GRANDE DO NORTE IN BRASIL...ALSO
EXPECT SCATTERED CONVECTION TO ASSOCIATE WITH TRADE WIND
CONVERGENCE. BUT IN THIS AREA DAILY MAXIMA WILL PEAK AT 10-15MM.
GUZMAN...SENAMHI (BOLIVIA)
URRA...DMC (CHILE)
DAVISON...HPC (USA)
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