MODEL COMPARISON (VALID FROM 00Z AUG 09)...GLOBAL MODELS ARE
IN GENERALLY GOOD AGREEMENT THROUGH THE PD. THEY AGREE THAT
THE PATTERN WILL BE PROGRESSIVE WITH THE LONGWAVE TROUGH IN
THE ATLANTIC MOVING EAST THROUGH THE CYCLE. SOME ENERGY IN THE
NORTHERN END OF THE TROUGH IS FORECAST TO BE LEFT BEHIND JUST
EAST OF BRAZIL. A PIECE OF SHORTWAVE ENERGY...CURRENTLY OVER
TIERRA DEL FUEGO...IS FORECAST TO MOVE NORTHEAST AND REINFORCE
TROUGHING OFF THE COAST OF SOUTHEAST BRAZIL. THIS WEAKNESS IS
FORECAST TO REMAIN IN PLACE THROUGH THE REMAINDER OF THE CYCLE
AS IT BECOMES CUT OFF FROM THE FASTER SOUTHERN FLOW. 

THE LONGWAVE TROUGH IN THE PACIFIC WHICH IS CURRENTLY WEST OF
120W IS ALSO FORECAST TO BE PROGRESSIVE MIGRATING TO NEAR 100W
BY 48 HRS. THIS WILL BE THE KICKER TO THE CLOSED LOW CURRENTLY
OFF THE COAST OF NORTHERN CHILE. THIS SYSTEM IS FORECAST TO
BEGIN MOVING SOUTHEAST CROSSING OVER NORTHERN CHILE DURING THE
48-60 HOUR TIME PERIOD. ALSO BY 60 HRS...THE PACIFIC LONGWAVE
TROUGH BEGINS TO TILT SSE/NNW FROM THE CLOSED LOW AT 65S 90W
NNW TO NEAR 30S 110W. DOWNSTREAM...THE MODELS ARE FORECASTING
A HIGHLY AMPLIFIED RIDGE TO DEVELOP ALONG 55W/60W IN THE
ATLANTIC. BY 72-84 HRS...THE CLOSED LOW MOVING INTO NORTHERN
CHILE ACCELERATES SOUTHEAST AND WEAKENS INTO AN OPEN WAVE
THROUGH THE NORTHWEST PROVINCE OF ARGENTINA...THEN INTO BUENOS
AIRES. THE RIDGE AXIS SHIFTS EAST TO 45W/50W WHILE THE CLOSED
LOW IN THE SOUTH PACIFIC MOVES TO NEAR 65S 75W. THE TROUGH
AXIS IS FCST TO EXTEND NORTHWEST TO NEAR 30S 100W. BY 96 HRS
...FALLING 500 HPA HEIGHTS ARE FORECAST TO SPREAD NORTHEAST
ACROSS SOUTHERN ARGENTINA AS THE RIDGE AXIS CONTINUES TO SHIFT
EAST INTO THE ATLANTIC AND THE OPEN WAVE MOVES WELL OUT TO SEA
IN THE WESTERN ATLANTIC. BY 120 HRS...THE CLOSED LOW IN THE
SOUTHERN STREAM IS FORECAST TO BECOME AN OPEN WAVE AND SHIFT
WELL EAST INTO THE DEEP SOUTHERN ATLANTIC. THE LONGWAVE TROUGH
AXIS REMAINS GENERALLY INTACT AS MORE SHORTWAVE ENERGY IS
FORECAST TO REPLENISH THE WESTERN END OF THE TROUGH IN THE
SOUTH POLAR STREAM. 

THE GFS 06Z MODEL RUN FORECAST BELOW ZERO 850 HPA TEMPERATURES
TO SPREAD ACROSS THE SOUTHERN PORTION OF THE CONTINENT TO NEAR
42S BY 114 HRS OR 00Z SAT. 

AT THE SURFACE...THE FRONTAL SYSTEM ACROSS THE NORTHERN
LATITUDES IS FORECAST TO EXTEND FROM THE ATLANTIC ACROSS NRN
ESPIRITO SANTOS...NORTHERN MINAS GERAIS...GOIAS AND SOUTHERN
MATO GROSSO BY THIS EVENING. ONLY SCATTERED RAINFALL IS
EXPECTED WITH THIS SYSTEM WITH AMOUNTS OF 5-15 MM ALONG THE
COASTAL AREAS OF NORTHEAST BRAZIL. ANOTHER FRONT IS EXPECTED
TO EXTEND FROM THE EXTREME SOUTHWEST ATLANTIC NORTH...THEN
NORTHWEST INTO NORTHERN PATAGONIA...THEN WEST DISSIPATING IN
THE ANDES. ANOTHER FRONT IS EXPECTED TO APPROACH EXTREME
SOUTHERN CHILE...WITH YET MORE FRONTAL SYSTEMS 10...20 AND 30
DEGREES TO THE WEST. ONLY VERY LIGHT SCATTERED ACTIVITY IS
EXPECTED ACROSS SOUTHERN CHILE. FURTHER NORTH...EXPECTED
SCATTERED PRECIPITATION/SNOW SHOWERS ACROSS THE HIGHER
ELEVATIONS OF THE ANDES IN THE PERU/CHILE/BOLIVIA BORDER
REGION AS SHORT WAVE ENERGY ROTATES IN AROUND THE CLOSED LOW
TO THE WEST. 

BY DAY 2...THE FRONT IN THE NORTHERN LATITUDES IS FORECAST TO
DISSIPATE...EXCEPT FOR A SHEAR LINE ALONG THE COAST OF
NORTHEAST BRAZIL NEAR 10S. RAINFALL AMOUNTS OF 10-20 MM ARE
POSSIBLE. THE FRONT WHICH WAS JUST WEST OF SOUTHERN CHILE ON
DAY 1 IS FORECAST TO QUICKLY MOVE SOUTHEAST ACROSS THE DRAKE
PASSAGE WHILE THE NEXT FRONT IS JUST WEST OF THE SOUTHERN
CHILE COAST. MOISTURE IS FORECAST TO INCREASE AHEAD OF THIS
FRONT AS WELL AS THE LOW LEVEL WIND FIELD...HENCE INCREASED
CONVERGENCE AND OROGRAPHIC LIFT. THIS SYSTEM COULD SUPPORT
20-30 MM OF PRECIPITATION ON DAY 2. FURTHER NORTH...
PRECIPITATION IS EXPECTED TO CONTINUE ACROSS THE ANDES BORDER
REGION OF PERU/ BOLIVIA/CHILE. AMOUNTS OF 10-20 MM ARE
FORECAST...BUT LOCALLY HEAVIER AMOUNTS OF SNOW ARE POSSIBLE
DUE TO THE STRONG DYNAMICS ASSOCIATED WITH THE MID-LEVEL
SYSTEM. 

BY DAY 3...DYNAMICS AND MOISTURE WILL BEGIN TO DECREASE ACROSS
THE TRI-BORDER ANDES REGION...HENCE A DECREASE IN
PRECIPITATION IS EXPECTED. THE FRONT WHICH WAS MOVING INTO
SOUTHERN CHILE IS FORECAST TO MOVE EAST AND BE ALONG THE COAST
OF PATAGONIA. ANOTHER FRONT IS FORECAST TO BE ALONG THE
EXTREME SOUTHERN CHILE COAST AND EXTEND NORTHWEST INTO THE
PACIFIC. EXPECT LIGHT PRECIPITATION FROM 37S SOUTHWARD WITH
ONE AREA OF ENHANCED ACTIVITY NEAR 40S AND ANOTHER MORE
IMPRESSIVE AREA SOUTH OF 47S WHERE 30-40 MM IS POSSIBLE. 

ON DAY 4...THE TRI-BORDER ANDES REGION SOUTHEASTWARD THROUGH
THE BOLIVIAN ANDES COULD CONTINUE TO EXPERIENCE LIGHT-MODERATE
PRECIPITATION IN THE FORM OF SNOW IN THE HIGHER ELEVATIONS.
FURTHER SOUTH...THE FRONT NEAR THE COAST OF PATAGONIA IS
FORECAST TO SHIFT QUICKLY EAST. THE TRUE COLD FRONT IS
FORECAST TO ADVANCE EAST AND EXTEND FROM THE SOUTHEAST
ATLANTIC NORTHWEST THROUGH CENTRAL PATAGONIA...EXITING CHILE
NEAR 40S AND INTO THE PACIFIC. PRECIPITATION AMOUNTS OF 10-30
MM ARE POSSIBLE FROM 40S SOUTHWARD...WITH RAIN CHANGING TO
SNOW IN THE HIGHER ELEVATIONS AS THE COLD AIR PUSHES NORTHEAST
BEHIND THE FRONT. 

ON DAY 5...THE FRONT ADVANCES SLOWLY NORTHEAST APPROACHING
BUENOS AIRES PROVINCE AND INTO SOUTH-CENTRAL ARGENTINA. EXPECT
PLEASANT CONDITIONS AHEAD OF THE FRONT WITH STRONG NORTHERLY
FLOW ADVECTING WARM AIR THROUGHOUT MUCH OF NORTHERN ARGENTINA
AND URUGUAY.

IN THE TROPICS...THE CROSS EQUATORIAL RIDGE CENTER IS FORECAST
TO MIGRATE SOUTHWEST INTO ECUADOR LATER IN THE CYCLE. A
LONGWAVE TROUGH IS FORECAST TO DEVELOP ACROSS MUCH OF BRAZIL
ON DAYS 4 AND 5. THE TREND WILL BE FOR PRECIPITATION TO STAY
NORTH OF 05S THROUGH DAY 3...THEN THE FORECAST CALLS FOR SOME
RAINFALL TO MIGRATE SOUTHWEST WITH THE RIDGE INTO ECUADOR AND
NORTHERN PERU.

BARROLA...SHIN (ARGENTINA)
NUSA......DNM  (URUGUAY)
CARR......NCEP (HPC)