600
FXSA20 KWBC 301642
PMDSA
SOUTH AMERICA SYNOPTIC DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1242 PM EDT WED JUL 30 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z JULY 30). THE GLOBAL MODELS
MAINTAIN CONTINUITY WITH THE PREVIOUS RUNS...AS THEY SHOW A
STRONG POLAR INCURSION INTO MID SECTIONS OF SOUTH AMERICA BY THE
END OF THE CYCLE. THIS FORECAST IS WELL SUPPORTED BY THE GLOBAL
ENSEMBLES...SO CONFIDENCE IN THE FORECAST REMAINS HIGH.
AT 500 HPA...A SHORT WAVE TROUGH OFF THE NORTHERN COAST OF CHILE
IS TO SLOWLY SPILL ACROSS THE NORTHERN ANDES TO THE NORTHERN
PROVINCES OF ARGENTINA EARLY THIS PERIOD...AND THROUGH 48-60 HRS
IT WILL MOVE OFF THE SOUTHERN COAST OF BRASIL. THIS TROUGH IS
INTERACTING WITH A FRONT OVER SOUTHERN BRASIL-NORTHERN ARGENTINA/
PARAGUAY...FAVORING FORMATION OF LOWS/WAVES ALONG THE
QUASISTATIONARY BOUNDARY. THESE ARE TO ALSO TRIGGER SCATTERED
DEEP CONVECTION...WITH MOST INTENSE TO CONCENTRATE OVER SOUTHERN
BRASIL-NORTHERN URUGUAY/MESOPOTAMIA TO SOUTHERN PARAGUAY. DAILY
MAXIMA WILL PEAK AT 25-50MM THROUGH 24-36 HRS...WITH A GRADUAL
DECREASE IN ACTIVITY THROUGH 48-60 HRS...WITH MAXIMA TO DECREASE
TO 10-15MM/DAY.
ON THE SOUTHERN STREAM...A BROAD MID LEVEL TROUGH EXTENDS ACROSS
THE DRAKE PASSAGE TO THE SOUTHERN CONE. THE TROUGH IS TO SLOWLY
MOVE ACROSS 55W/60W BY 24-36 HRS...AND BY 48-72 HRS IT IS TO
BOUND BETWEEN 70W/30W. THE TROUGH WILL THEN REMAIN NEARLY
STATIONARY WHILE AMPLIFYING TO THE NORTH-NORTHWEST ACROSS RIO DE
LA PLATA BASIN TO NORTHWEST ARGENTINA/PARAGUAY BY 72-96 HRS. BY
120 HRS THE TROUGH WILL START TO PULL EAST ACROSS SOUTHERN BRASIL
TO THE WESTERN ATLANTIC...TO MOVE OFF THE COAST BY 132-144 HRS.
UPSTREAM FROM THIS TROUGH...OVER THE EASTERN PACIFIC...THE MODELS
CONTINUE TO FORECAST A HIGH AMPLITUDE/LONG WAVE RIDGE TO
ESTABLISH ACROSS THE SOUTHERN CONE/DRAKE PASSAGE TO THE ANTARCTIC
PENINSULA. THIS...IN-TURN...WILL FEED COLD/POLAR ENERGY INTO THE
BACKSIDE OF THE AMPLIFYING TROUGH...TO RESULT IN THE
AFOREMENTIONED HIGH AMPLITUDE LONG WAVE PATTERN. AT LOW
LEVELS...THE MID/UPPER TROUGH IS TO ALSO FAVOR A BROAD TROUGH
PATTERN ACROSS THE ANTARCTIC PENINSULA TO THE SOUTHERN CONE...
WITH SUCCESSIVE FRONTS TO REVOLVE AROUND THIS AXIS DURING THE
NEXT 24-36 HRS. DURING THIS PERIOD...THE FRONTS ARE TO GENERALLY
FOCUS OVER CHILE/PATAGONIA SOUTH OF 40S...WITH QUITE A FEW
REACHING AS FAR NORTH AS 34S. BUT MOST ACTIVE CONVECTION IS TO
CONCENTRATE BETWEEN CONCEPCION AND ISLA DE CHILOE...WITH DAILY
MAXIMA TO PEAK AT 10-15MM. AT 36-60 HRS EXPECT A FRONT TO PUSH
ACROSS RIO DE LA PLATA BASIN-CORDOBA IN ARGENTINA. BY 72-84
HRS...A 1025-1027 HPA POLAR HIGH IS TO BUILD ACROSS THE SOUTHERN
CONE...WHICH WILL SUPPORT THE NORTHWARD MIGRATION OF THE SURFACE
FRONT ACROSS URUGUAY-SOUTHERN BRASIL TO THE NORTHERN PROVINCES OF
ARGENTINA. BY 84-108 HRS THE NEW FRONT WILL MERGE WITH/REINFORCE
THE OLD BOUNDARY OVER NORTHERN ARGENTINA/PARAGUAY...WITH THE
POLAR RIDGE TO THE SOUTH DISPLACING THIS FRONT FARTHER NORTH
ACROSS SOUTHERN BRASIL-PARAGUAY TO EASTERN BOLIVIA. AT 120 HRS
THE FRONT WILL MOVE FARTHER NORTH ACROSS SOUTHEAST BRASIL-MATO
GROSSO TO RONDONIA/CENTRAL PERU. UNDER THE INFLUENCE OF THE
BUILDING POLAR RIDGE TO THE SOUTH...A SOUTHERLY JET WILL
ESTABLISH ACROSS PARAGUAY/EASTERN BOLIVIA BY 108-114 HRS...TO
PERSIST THROUGH 120-132 HRS WHILE MIGRATING ACROSS NORTHERN
BOLIVIA TO SOUTHERN PERU. THIS WILL LEAD TO A RAPID CHANGE IN AIR
MASS. AS THE FRONT PUSHES NORTH ACROSS ARGENTINA...IT WILL
SUPPORT MOSTLY LIGHT RAINFALL. BEST CHANCE FOR ORGANIZED RAINFALL
WILL BE AT 108-120 HRS...WHEN THE FRONT IS TO MOVE NORTH INTO THE
BOLIVIAN JUNGLE AND TRIGGER MAXIMA OF 30-60MM. CONVECTION WILL
RAPIDLY BUILD WEST ACROSS SOUTHERN PERU...WITH SIMILAR AMOUNTS.
ACROSS NORTHERN BOLIVIA TO SOUTHERN/CENTRAL PERU THE GFS MODEL
SHOWS RISK OF SEVERE CONVECTION. NEAR FREEZING TEMPERATURES ARE
EXPECTED ACROSS THE RIO DE LA PLATA BASIN TO SOUTHERN BRASIL BY
120-132 HRS.
AT 200 HPA...THE SUBTROPICAL RIDGE EXTENDS FROM A HIGH OVER PARA
IN CENTRAL BRASIL TO THE EASTERN TROPICAL PACIFIC. THE RIDGE
PATTERN WILL START TO EVOLVE EARLY THIS PERIOD...WITH THE HIGH
TO MOVE EAST TO 10S 50W BY 24 HRS. THROUGH 60-72 HRS THE HIGH
WILL MOVE OFF THE COAST OF BAHIA IN NORTHEAST BRASIL...WHILE THE
RIDGE OVER THE CONTINENT STARTS TO WEAKEN UNDER INFLUENCE
OF POLAR TROUGH TO THE SOUTH (SEE ABOVE). LOW LEVEL TRADE WIND
EASTERLY CONVERGENCE WILL SUSTAIN COASTAL RAINFALL OVER NORTHEAST
BRASIL...WITH MOST INTENSE ACROSS NORTHERN ESPIRITO SANTO AND
BAHIA WITH MAXIMA OF 10-20MM/DAY THROUGH 24-36 HRS...AND 05-
10MM/DAY THEREAFTER. OTHER CONVECTION WILL CONCENTRATE ACROSS THE
NORTHERN COAST OF BRASIL...WITH SIMILAR AMOUNTS. OVER
AMAPA/GUIANAS AND ALONG THE NEAR EQUATORIAL TROUGH TO THE NORTH
THE DAILY MAXIMA WILL PEAK AT 15-25MM...WHILE OVER WESTERN
ECUADOR AND CAUCA VALLEY IN SOUTHWEST COLOMBIA THE DAILY MAXIMA
WILL PEAK AT 10-15MM. ACTIVITY IS TO ALSO DOT THE PERUVIAN JUNGLE
OVER THE NEXT THREE DAYS...WITH DAILY MAXIMA OF 10-15MM THROUGH
48 HRS...AND 20-35MM/DAY BY MID CYCLE. A SURGE IN ACTIVITY IS
EXPECTED LATER IN THE CYCLE AS THE POLAR FRONT MOVES NORTH ACROSS
MID SECTIONS OF SOUTH AMERICA.
COLMAN...DMH (PARAGUAY)
GUZMAN...SENAMHI (BOLIVIA)
DAVISON...HPC (USA)
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