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)