857
FXSA20 KWBC 181647
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1247 PM EDT THU SEP 18 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z SEP 18). THE GLOBAL MODELS ARE
SLOWLY REACHING AN AGREEMENT ON THE EVOLUTION OF A MID LEVEL
TROUGH THAT ENTERS THE CONTINENT EARLY THIS PERIOD. THE ECMWF
CONTINUES TO FAVOR A DEEPER AND SLOWER PERTURBATION THAN THE
GFS/UKMET REFLECT...PROJECTING A DEEP OCCLUDED LOW OVER URUGUAY/
RIO GRANDE DO SUL BRASIL BETWEEN 60-84 HRS...WHILE THE GFS/UKMET
FORECAST THE LOW TO CENTER OFFSHORE DURING THE SAME PERIOD. THE
ENSEMBLES DIVIDE IN TWO CAPS...WITH THE NCEP/CANADIAN ENSEMBLES
SUPPORTING THE GFS/UKMET SOLUTION AND THE EUROPEAN ENSEMBLES
SUPPORTING THE ECMWF. SO SOME UNCERTAINTY PERSISTS WITH RESPECT
TO THIS SYSTEM...BUT WE EXPECT A CLEARER PICTURE ON HOW THINGS
ARE TO EVOLVE IN THE NEXT COUPLE OF RUNS.
AS EVIDENT ON THE SATELLITE IMAGERY...OVER THE EASTERN PACIFIC...
A MID LEVEL TROUGH/LOW OFF THE COAST OF CHILE IS STARTING TO PUSH
INLAND ACROSS THE ANDES...MEANWHILE TRIGGERING MODERATE TO HEAVY
SNOWFALL ON THE HIGHER ELEVATIONS. THROUGH 24-36 HRS THE
TROUGH MOVES ACROSS 66W/67W...WITH SHORT WAVE ENERGY FOCUSING
ACROSS NORTHERN PROVINCES OF ARGENTINA TO URUGUAY/RIO DE LA
PLATA. THROUGH 48 HRS THE TROUGH MOVES ACROSS 60W...AND BY 60-72
HRS A LOW WILL FORM OFF THE COAST OF URUGUAY. THROUGH 120-132 HRS
IT WILL MOVE ACROSS 30S 40W. AT LOW LEVELS...A FRONT EXTENDS
ACROSS LA PAMPA-CENTRAL CHILE TO THE EASTERN PACIFIC. THROUGH 24
HRS A WAVE/LOW WILL FORM ALONG THIS FRONT OVER LA PAMPA/SOUTHERN
BUENOS AIRES PROVINCE...WHICH IN-TURN FORCES THE FRONT NORTHWARD
ACROSS BUENOS AIRES-CORDOBA-MENDOZA IN ARGENTINA BY 48 HRS. AT
60-72 HRS IT WILL THEN MERGE WITH AN OLD FRONT TO THE NORTH. AS
THE LOW/WAVE FORMS ALONG THE FRONT OVER ARGENTINA...IT WILL
SUSTAIN TWO AREAS OF RAINFALL...WITH STRATIFORM PRECIPITATION
OVER NORTHERN PATAGONIA/LA PAMPA-CUYO AND CONVECTIVE
PRECIPITATION OVER CORDOBA/CORRIENTES-LOWER MESOPOTAMIA-BUENOS
AIRES PROVINCE...WITH RAINFALL MAXIMA OF 15-25MM.
A MEANDERING MID/UPPER LEVEL TROUGH IS INITIALIZED OVER THE
WESTERN ATLANTIC...WITH AXIS AT 500 HPA ENVELOPING AREA BETWEEN
50W-20W AND 40S-18S. BY 24-48 HRS THE TROUGH WILL DRIFT EAST OF
45W/50W AS IT GRADUALLY MERGES WITH A BROAD TROUGH ON THE
SOUTHERN STREAM FLOW. AT LOW LEVELS AN ELONGATED FRONT EXTENDS
ACROSS THE SOUTH ATLANTIC-RIO DE JANEIRO/SOUTHERN MINAS GERAIS-
MATO GROSSO DO SUL TO NORTHERN BOLIVIA/SOUTHERN JUNGLE OF PERU.
THE FRONT WILL DRIFT SOUTH INTO PARAGUAY EARLY THIS PERIOD...WITH
A WAVE/LOW TO FORM ALONG THIS BOUNDARY OVER CENTRAL PARAGUAY BY
24-36 HRS...WHEN THE AFOREMENTIONED MID LEVEL TROUGH OVER
ARGENTINA IS TO INTERACT WITH THIS BOUNDARY. THE SURFACE LOW
DEEPENS AS IT MOVES TO SOUTHEAST PARAGUAY THROUGH 48 HRS...AND
BETWEEN 48-72 HRS IT WILL OCCLUDE/DEEPEN OVER URUGUAY/RIO GRANDE
DO SUL BRASIL. THIS...IN-TURN...WILL FORCE THE FRONT TO ONCE
AGAIN MIGRATE NORTH INTO SOUTHERN BRASIL-MATO GROSSO DO SUL-
NORTHERN JUNGLE OF BOLIVIA BY 60-72 HRS. BY 84-96 HRS THE LOW
WILL OCCLUDE OFF THE COAST OF URUGUAY/RIO GRANDE DO SUL
BRASIL...WHILE THE FRONT MEANDERS ACROSS SAO PAULO-MATO GROSSO DO
SUL TO NORTHERN BOLIVIA. CONVECTION IS EXPECTED OVER NORTHERN SAO
PAULO-RIO DE JANEIRO-ESPIRITO SANTO...WITH DAILY MAXIMA OF 10-
20MM/DAY THROUGH 48-60 HRS. AS THE WAVE/LOW FORMS ALONG THE
SURFACE FRONT BY 24-36 HRS...EXPECT A SURGE IN ACTIVITY ACROSS
CENTRAL-SOUTHEAST PARAGUAY-CHACO ARGENTINO/CORRIENTES-MESOPOTAMIA
VALLEY...WHERE WE EXPECT MAXIMA OF 25-50MM/DAY BY 36-60 HRS...TO
AFFECT SOUTHERN BRASIL-MATO GROSSO DO SUL AND EASTERN/NORTHERN
BOLIVIA BY 60-84 HRS. AT 96-108 HRS CONVECTION ALONG THE FRONT
WILL DECREASE TO 10-20MM/DAY AS IT MOVES TO NORTHERN SAO PAULO/
GOIAS-MINAS GERAIS.
THE MODELS THEN FORECAST ANOTHER TROUGH TO MOVE ACROSS THE
EASTERN PACIFIC ALONG 100W/110W TO 20S BY 48 HRS. THROUGH 96 HRS
IT WILL MOVE ACROSS 85W...THEN SLOW DOWN AS IT PUSHES AGAINST A
BLOCKING RIDGE OVER THE SOUTHERN CONE/WESTERN ATLANTIC. THE
ASSOCIATED FRONT WILL ENTER SOUTHERN CHILE BY 84 HRS...INTO
PATAGONIA THROUGH 96-108 HRS. AS IT ENTERS SOUTHERN CHILE/TIERRA
DEL FUEGO IT WILL FAVOR SCATTERED CONVECTION WITH ACCUMULATION OF
05-10MM.
AT 200 HPA...AN ILL ORGANIZED SUBTROPICAL FLOW PATTERN IS
INITIALIZED ACROSS NORTHERN SOUTH AMERICA. THIS IS TO GRADUALLY
CHANGE THROUGH 48-60 HRS...WHEN A HIGH IS TO CLOSE OVER THE
EASTERN PACIFIC NEAR 13S 90W. THIS HIGH WILL BUILD A RIDGE SOUTH
INTO THE EASTERN PACIFIC...MEANWHILE INDUCING/FAVORING THE
NORTHWARD AMPLIFICATION OF TROUGH INTO SOUTHERN PERU/BOLIVIA.
THIS WILL ENHANCE CONVECTION OVER THE BOLIVIAN JUNGLE/SOUTHERN
PERU BY 48-84 HRS...WITH MAXIMA OF 10-20MM/DAY. MOST
INTENSE...HOWEVER...IS EXPECTED OVER PARA-AMAZONAS TO NORTHERN
PERU/SOUTHERN COLOMBIA...WHERE DAILY MAXIMA WILL PEAK AT 15-
30MM/DAY. LESSER AMOUNTS ARE EXPECTED ACROSS ECUADOR.
GUZMAN...SENAMHI (BOLIVIA)
URRA...DMC (CHILE)
DAVISON...HPC (USA)
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