273
FXSA20 KWBC 091630
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1229 PM EDT THU OCT 09 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z OCTOBER 09). NORTH OF 50S...THE
MODELS ARE IN EXCELLENT AGREEMENT THROUGH 132 HRS...WITH ENSEMBLE
MODELS SHOWING LITTLE VARIABILITY AMONG THE ENSEMBLE MEMBERS.
SOUTH OF 50S THE OPPOSITE IS TRUE...WITH MODELS DEVELOPING
PATTERN DIFFERENCES AS EARLY AS 60/72 HRS. THE DIFFERENCES AMONG
THE GLOBAL MODELS BECOME MORE PRONOUNCED THROUGH 120 HRS...AS
THEY FAIL TO AGREE ON THE SPEED OF PROPAGATION AND THE AMPLITUDE
OF PROGRESSIVE VORTICES.
A 500 HPA RIDGE IS INITIALIZED OVER THE WESTERN ATLANTIC...
ENVELOPING AREA BETWEEN 65W-40W. THE RIDGE WILL PERSIST THROUGH
60 HRS...THEN RAPIDLY WEAKEN/COLLAPSE THROUGH 84-96 HRS AS STRONG
MID LEVEL PERTURBATIONS EJECT ACROSS THE SOUTHERN CONE TO THE
WESTERN ATLANTIC. AT LOW LEVELS IT WILL SUSTAIN A BROAD SURFACE
RIDGE... WITH MODELS SHOWING A MASSIVE 1033-1035 HPA HIGH CLOSING
OVER THE WESTERN ATLANTIC EARLY IN THE PERIOD. THE STRONG RIDGE
PATTERN WILL PERSIST THROUGH AT LEAST 72 HRS. UNDER INFLUENCE OF
THIS RIDGE...A WARM/MOIST NORTHERLY FLOW IS TO ESTABLISH ACROSS
PARAGUAY TO NORTHERN/CENTRAL ARGENTINA BY 48-60 HRS.
CONSISTENT WITH PREVIOUS RUNS...A SHORT WAVE TROUGH IS FORECAST
AT 500 HPA TO MOVE ACROSS NORTHERN CHILE TO THE NORTHWEST
PROVINCES OF ARGENTINA BY 24-30 HRS. THE TROUGH QUICKLY EJECTS
ACROSS PARAGUAY/SOUTHERN BRASIL BY 48-54 HRS...AND THROUGH 72 HRS
IT IS TO MOVE ACROSS SAO PAULO/RIO DE JANEIRO. IT WILL THEN MERGE
INTO A BROAD TROUGH PATTERN OVER THE WESTERN ATLANTIC. THIS
PERTURBATION IS TO TRIGGER SCATTERED DEEP CONVECTION OVER
PARAGUAY-EL PANTANAL AND SANTA CATARINA IN BRASIL...WITH RAINFALL
MAXIMA OF 20-40MM/DAY. AS IT MOVES ACROSS SOUTHEAST BRASIL ON DAY
03...IT WILL INTERACT WITH THE TAIL END OF AN OLD FRONT TO
SUSTAIN RAINFALL AMOUNTS OF 20-35MM/DAY...WITH MOST INTENSE OVER
EASTERN MINAS GERAIS/ESPIRITO SANTO AND PORTIONS OF BAHIA.
FURTHERMORE...THE MODELS REMAIN IN EXCELLENT AGREEMENT ON THEIR
FORECAST OF A LONG WAVE TROUGH ALONG 90W TO 30S BY 24 HRS. THE
TROUGH WILL CONTINUE EAST ACROSS 80W BY 42 HRS... WITH A LOW
FORMING/CLOSING NEAR 42S 78W BY 48 HRS. THIS LOW WILL EJECT
ACROSS PATAGONIA TO THE WESTERN ATLANTIC BY 72-84 HRS. A
SECONDARY VORTEX IS TO FOLLOW...WITH MODELS FORECASTING A LOW TO
MOVE NEAR 40S 85W BY 72 HRS. THE MODELS NOW AGREE QUITE WELL ON
THE INTENSITY/MOVEMENT OF THIS VORTEX. THE PERTURBATION IS TO
CONTINUE EAST INTO CENTRAL CHILE THROUGH 108-120 HRS. THESE
PERTURBATIONS WILL COMBINE IN SUPPORT OF A BROAD TROUGH PATTERN
ACROSS THE SOUTHERN CONE AND THE EASTERN PACIFIC ON DAYS 03-05.
THEY WILL ALSO DRAW THE SUBTROPICAL JET INLAND ACROSS NORTHERN
CHILE INTO THE CENTRAL/NORTHERN PROVINCES OF ARGENTINA. AT LOW
LEVELS EXPECT A PROGRESSIVE FRONT TO ENTER SOUTHERN CHILE EARLY
IN THE PERIOD...AND THROUGH 36-48 HRS IT WILL EJECT ACROSS
PATAGONIA TO LA PAMPA/CENTRAL CHILE BY 48 HRS. AT 72 HRS IT WILL
MOVE NORTH ACROSS BUENOS AIRES PROVINCE/CORDOBA...AND INTO
URUGUAY/RIO GRANDE DO SUL-NORTHWEST ARGENTINA BY 96 HRS...WHERE
IT WILL BECOME NEARLY STATIONARY. AS IT ENTERS SOUTHERN CHILE WE
EXPECT RAINFALL AMOUNTS OF 15-25MM/DAY...WITH MOST INTENSE
BETWEEN TEMUCO/ISLA DE CHILOE. OVER LA PAMPA/NORTHERN PATAGONIA
MAXIMA WILL PEAK AT 10-20MM BY 48 HRS. BUT AS IT MOVES NORTH
ACROSS CENTRAL ARGENTINA...SCATTERED DEEP CONVECTION WILL
PRECEDE/ACCOMPANY THIS FRONT...WITH MAXIMA OF 20-35MM ON DAY 03
AND 30-60MM/DAY ON DAY 04. THIS WILL INCREASE TO 35-70MM/DAY ON
DAY 05. ALTHOUGH STABILITY INDICES DO NOT SUGGEST POSSIBILITY OF
SEVERE CONVECTION...IN A STRONG SHEARED ENVIRONMENT...CONSIDER
POSSIBILITY OF A SQUALL LINE AND SEVERE THUNDERSTORMS FORMING
AHEAD OF THIS FRONT.
AT 200 HPA...A BROAD SUBTROPICAL RIDGE DOMINATES CONTINENTAL AREA
NORTH OF 15S. BUT...THIS WILL BE SHORT LIVED...WITH THE HIGH TO
COLLAPSE TO AN OPEN RIDGE EARLY IN THE PERIOD. IT THEN BECOMES
NARROW AND ELONGATED...AND BY THE END OF THE CYCLE IT WILL YIELD
TO AN AMPLIFYING UPPER LEVEL TROUGH OVER BRASIL. MEANWHILE...THE
AREAS OF MOST ACTIVE CONVECTION ARE EXPECTED ACROSS PARA-AMAZONAS
IN NORTHERN BRASIL...WITH DAILY MAXIMA OF 20-35MM. AFTER 48-60
HRS EXPECT A GRADUAL INCREASE IN CONVECTION ACROSS THE
PERUVIAN JUNGLE AND NORTHERN PORTIONS OF BOLIVIA...WITH
MAXIMA OF 10-20MM. OTHER CONVECTION WILL FALL OVER ESPIRITO
SANTO/MINAS GERAIS...WHERE A MEANDERING SURFACE FRONT IS TO
CONTINUE FAVORING SCATTERED DEEP CONVECTION. IN THIS AREA DAILY
MAXIMA WILL PEAK AT 25-50MM THROUGH 36-48 HRS...AS A STRONG LOW
LEVEL JET ENTERS THIS REGION. THIS WILL THEN DECREASE TO 10-
20MM/DAY BY MID CYCLE...TO PERSIST THROUGH DAY 04-05.
URRA...DMC (CHILE)
MOREYRA...SENAMHI PERU
DAVISON...HPC (USA)
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page