572
FXSA20 KWBC 261644
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1244 PM EDT TUE AUG 26 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
NOTE: STRONG/RAPID TRANSITION PATTERN OVER ARGENTINA-URUGUAY-
SOUTHERN BRASIL DURING THE NEXT 60 HRS WILL PRESENT A RISK OF
SEVERE THUNDERSTORMS...TO AFFECT AREA BETWEEN BAHIA BLANCA-
CORDOBA-RESISTENCIA-PELOTAS.
MODEL COMPARISON (VALID FROM 00Z AUG 26). CONSISTENT WITH THE
PREVIOUS ANALYSES AND FORECASTS...THE GLOBAL MODELS REMAIN IN
GENERAL AGREEMENT ON THEIR FORECAST OVER THE EASTERN PACIFIC AND
THE SOUTH AMERICAN CONTINENT. SIGNIFICANT DIFFERENCES/PATTERN
CORRECTIONS CONFINE TO THE DOWNSTREAM PATTERN OVER THE WESTERN
ATLANTIC ON DAYS 04-05...WHERE THE GFS CONTINUES TO FORECAST A
SIGNIFICANTLY DEEPER LOW THAN WHAT THE EUROPEAN MODELS PROJECT.
WE MADE CORRECTIONS TO THE MODEL FORECAST IN FAVOR OF A SLIGHTLY
WEAKER SYSTEM...AND THIS IS REFLECTED IN OUR SURFACE CHARTS.
AT MID LEVELS...A BROAD TROUGH CONTINUES TO DOMINATE THE FLOW
OVER THE FAR EASTERN PACIFIC/SOUTHERN CONE. SHORT WAVE ENERGY IS
TO SLOWLY SPILL ACROSS THE SOUTHERN ANDES INTO ARGENTINA DURING
THE NEXT TWO DAYS....MEANWHILE INDUCING HEIGHT FALLS OF 75-150
GPM...WITH MOST INTENSE TO CONCENTRATE OVER RIO DE LA PLATA
BASIN-CORDOBA ARGENTINA ON DAY 02. THE MEAN AXIS WILL GRADUALLY
MOVE ACROSS 55W BY 72 HRS...AND IT WILL EJECT ACROSS 40W BY 96
HRS. THIS TROUGH ESTABLISHED A SUBTROPICAL CONNECTION...ADVECTING
MOISTURE INTO CENTRAL/SOUTHERN CHILE...WHICH CURRENTLY FAVORS
ORGANIZED RAINFALL OVER SOUTHERN CHILE AS PROGRESSIVE POLAR
FRONTS STREAM ACROSS THIS AREA. MODERATE TO HEAVY RAINFALL IS TO
PERSIST THROUGH 72-84 HRS...WITH DAILY MAXIMA OF 15-30MM/DAY.
ALSO AT LOW LEVELS...A STRONG NORTHERLY JET ESTABLISHED ACROSS
EASTERN BOLIVIA/PARAGUAY...WHICH SUSTAINS THE ADVECTION OF
WARM/MOIST AIR INTO THE NORTHERN/CENTRAL PROVINCES OF ARGENTINA.
IN THIS AREA DEW POINT TEMPERATURES WILL RAPIDLY INCREASE TO 15-
18C. SIMULTANEOUSLY...A POLAR FRONT WILL PUSH ACROSS LA PAMPA-
CENTRAL CHILE ON DAY 01...WHERE IT WILL TRIGGER A PREFRONTAL
SQUALL LINE AND SEVERE CONVECTION. THROUGH 48 HRS THE FRONT WILL
MOVE ACROSS BUENOS AIRES PROVINCE-CORDOBA IN ARGENTINA...WITH THE
SEVERE CONVECTION PERSISTING ALONG AND AHEAD OF THIS FRONT. AT 72
HRS THE FRONT PUSHES NORTH INTO SOUTHERN BRASIL-PARAGUAY TO
CENTRAL/NORTHERN BOLIVIA...DISPLACED BY A BUILDING POLAR RIDGE
AND A SOUTHERLY JET. BY 96 HRS IT WILL MEANDER ACROSS SAO PAULO-
MATO GROSSO DO SUL IN BRASIL TO NORTHERN BOLIVIA...WHERE IT
REMAINS THROUGH 120 HRS. IN ADDITION TO THE HEAVY RAINFALL OVER
CHILE...THIS WILL FAVOR SCATTERED CONVECTION ACROSS LA PAMPA AND
BUENOS AIRES PROVINCE...WITH MAXIMA OF 20-40MM ON DAY 01. ON DAY
02 WE EXPECT A SHARP INCREASE IN ACTIVITY ACROSS URUGUAY-CORDOBA-
CORRIENTES-MESOPOTAMIA VALLEY-URUGUAY TO RIO GRANDE DO SUL
BRASIL. BY 72-84 HRS MAXIMA WILL DECREASE TO 10-20MM/DAY AS THE
FRONT ENTERS SOUTHERN BRASIL-SOUTHEAST PARAGUAY...WHILE OVER
CENTRAL/NORTHERN BOLIVIA TO THE SOUTHERN/CENTRAL JUNGLE OF PERU
MAXIMA WILL PEAK AT 15-30MM IN SCATTERED CONVECTION.
A BROAD MID/UPPER TROUGH WILL THEN SLOWLY FOLLOW...WITH SYSTEM TO
GRADUALLY EXPAND NORTH TO LOWER LATITUDES BY MID CYCLE. AT 96 HRS
THE BROAD TROUGH IS TO EXTEND BETWEEN 120W-80W AND SOUTH OF
20S...TO THEN FOCUS ITS SHORT WAVE ENERGY ACROSS CHILE SOUTH OF
TEMUCO. THE ASSOCIATED FRONT ENTERS SOUTHERN CHILE BY 84-96
HRS...AND THROUGH 120 HRS MOVES ACROSS PATAGONIA. THIS WILL FAVOR
SCATTERED CONVECTION ACROSS SOUTHERN CHILE...WITH MAXIMA OF 10-
20MM/DAY.
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 36 HRS
WITH MAXIMA OF 20-40MM. AFTER 36 HRS EXPECT A SHARP DECREASE WITH
MAXIMA OF 15-30MM. 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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