000 FXSA20 KWBC 061651 PMDSA SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 1151 AM EST FRI NOV 06 2009 GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/ MODEL COMPARISON (VALID FROM 00Z NOV 06). THE GFS AND UKMET GLOBAL MODELS CONTINUE TO AGREE ON THE EVOLUTION ACROSS THE DOMAIN THROUGH DAY 05-06. THE ECMWF REMAINS THE ODD MODEL...AS IT IS THE ONLY ONE THAT DOES NOT FORECAST THE EASTERN PACIFIC LONG WAVE RIDGE TO CRUMBLE LATER IN THE CYCLE. THE GLOBAL ENSEMBLES...INCLUDING THE EUROPEAN MEMBERS...GENERALLY SUPPORT THE DETERMINISTIC GFS/UKMET SOLUTIONS OVER THIS REGION. THE EASTERN PACIFIC LONG WAVE RIDGE...AT 500 HPA...EXTENDS SOUTH BETWEEN 90W-120W TO 65S/70S. THE STRONG RIDGE PATTERN WILL PERSIST THROUGH 84-96 HRS...THEN BEGIN TO WEAKEN BETWEEN 120-132 HRS AS A NORTHER STREAM SHORT WAVE TROUGH PIERCES THIS AXIS. BY 144 HRS IT IS TO NEARLY FLATTEN/COLLAPSE AS SUCCESSIVE IMPULSES STREAK ACROSS THE EASTERN PACIFIC. THIS WILL SIGNAL THE END OF THE LONG WAVE BLOCKAGE AND A CHANGE IN THE SYNOPTIC SCALE PATTERN ACROSS THE DOMAIN. EAST OF THIS AXIS...A MID LEVEL TROUGH OVER THE CONTINENT IS FORECAST TO GRADUALLY PULL EAST DURING THE NEXT 36-48 HRS. IN THIS PROCESS IT WILL SHEAR A SHORT WAVE TROUGH ON THE NORTHERN STREAM FLOW...FORECAST TO MEANDER OFF THE CENTRAL COAST OF CHILE EARLY IN THE FORECAST CYCLE. BUT BY 30-36 HRS...THE SHORT WAVE TROUGH WILL SPILL ACROSS THE CENTRAL ANDES/CUYO IN ARGENTINA... AND OFF THE COAST OF BUENOS AIRES/URUGUAY BY 48 HRS...TO THEN RAPIDLY ACCELERATE INTO THE SOUTH ATLANTIC. AS THE SHORT WAVE TROUGH SPILLS ACROSS THE ANDES...IT WILL INTERACT WITH AN ELONGATED FRONT THAT STRETCHES ACROSS SOUTHERN BRASIL TO NORTHWEST ARGENTINA. BY 30-36 HRS...AS A WAVE/LOW FORMS ALONG THIS FRONT...THE MODELS THEN SHOW THE FRONTAL BOUNDARY SLIDING NORTH ACROSS SANTA CATARINA IN SOUTHERN BRASIL TO PARAGUAY... WHERE IT WILL MEANDER THROUGH 48-72 HRS. BY 96 HRS A WEAK FRONT WILL MOVE NORTH ACROSS SAO PAULO...TO REACH RIO DE JANEIRO LATER IN THE CYCLE. THE TAIL END OF THE FRONT OVER THE CONTINENT WILL WEAKEN TO A NARROW LOW LEVEL TROUGH. AN 850 HPA NORTHERLY JET ACROSS PARAGUAY WILL SUSTAIN A MOIST/WARM TRANSPORT THAT IS TO CONVERGE ALONG THE QUASISTATIONARY FRONT...WHILE ALSO SUSTAINING A HIGH SHEAR ENVIRONMENT. ALOFT...THE SUBTROPICAL/ POLAR JETS WILL ENTER THE CONTINENT AT A PERPENDICULAR ANGLE... WHILE WILL CONTINUE FAVORING GENERATION OF LEE SIDE PERTURBATIONS. AS THE FRONT BEGINS TO UNDULATE NORTH INTO PARAGUAY-SOUTHERN BRASIL...THE MAXIMA WILL INCREASE TO 35- 70MM/DAY...WITH A SLIGHT DECREASE ON DAY 02 WHEN THE MAXIMA IS TO PEAK AT 30-60MM/DAY. THE RISK OF SEVERE CONVECTION PERSISTS AS MESO SCALE CONVECTIVE SYSTEMS DEVELOP ALONG THE MEANDERING FRONT...WITH HIGHEST RISK OVER CENTRAL/SOUTHERN MESOPOTAMIA- URUGUAY AND SOUTHERN BRASIL. AFTER 72-84 HRS...THE MAXIMA WILL DECREASE TO 15-35MM/DAY WHILE CONCENTRATING ACROSS SOUTHERN/ SOUTHEAST BRASIL-PARAGUAY AND SOUTHEAST BOLIVIA. ALONG THE COAST...ACROSS NORTHERN SAO PAULO/RIO DE JANEIRO...THE MAXIMA WILL PEAK AT 20-45MM/DAY THROUGH 72-96 HRS AS A STRONG ONSHORE FLOW ESTABLISHES BEHIND THE BAROCLINIC BOUNDARY. UNDER INFLUENCE OF THE EASTERN PACIFIC RIDGE...A SURGE IN THE SOUTHERN STREAM IS FORECAST EARLY THIS CYCLE...WHEN A TROUGH ACROSS THE ANTARCTIC PENINSULA/BELLINGSHAUSEN SEA IS FORECAST TO AMPLIFY NORTH. THE MID/UPPER LEVEL TROUGH WILL RAPIDLY AMPLIFY AS IT MOVES NORTH INTO SOUTHERN CHILE/PATAGONIA THROUGH 48-72 HRS...WITH A BROAD TROUGH PATTERN TO ESTABLISH OVER THE SOUTHERN CONE/WESTERN ATLANTIC BY 72-96 HRS. SECONDARY SHORT WAVE VORTICES WILL ENTER THE BACKSIDE OF THIS TROUGH AND MOVE NORTH INTO SOUTHERN CHILE/PATAGONIA. AT LOW LEVELS A PROGRESSIVE FRONT WILL MOVE ACROSS TIERRA DEL FUEGO INTO PATAGONIA THROUGH 36 HRS...WITH ADDITIONAL FRONTAL BOUNDARIES TO STREAM ACROSS THE SOUTHERN CONE AS A DEEP TROUGH ESTABLISHES OVER THE SOUTHERN CONE/WESTERN ATLANTIC. IN ADDITION TO SUSTAINING STRONG BOUNDARY LAYER WINDS...THIS WILL FAVOR SCATTERED PRECIPITATION OVER SOUTHERN CHILE WITH ORGANIZED SNOWFALL ON THE SOUTHERN ANDES...WITH ACCUMULATION OF 05-10MM/DAY. AT 200 HPA...THE SUBTROPICAL RIDGE EXTENDS FROM THE GALAPAGOS ISLANDS-SOUTHEASTWARD ACROSS PERU/BOLIVIA-PARAGUAY TO THE WESTERN ATLANTIC. ALTHOUGH IT IS TO INITIALLY CENTER ON TWO CLOSED HIGHS...BY 24 HRS A SINGLE HIGH WILL REMAIN...TO CENTER OVER BRASIL/BOLIVIA NEAR 15S 60W. THIS HIGH WILL THEN MEANDER BETWEEN RONDONIA IN BRASIL AND SANTA CRUZ IN BOLIVIA THROUGH 96-108 HRS...THEN RELOCATES TO WESTERN MINAS GERAIS BY 120 HRS. ALSO...A TROUGH DEVELOPED TO THE EAST OF THIS RIDGE...EXTENDING TO THE NORTH OF 23S AND BETWEEN 50W-30W. A CLOSED LOW OVER EASTERN BAHIA WILL ANCHOR THIS TROUGH DURING THE NEXT THREE DAYS...BUT BY 96- 120 HRS THE LOW WILL FILL AND THE TROUGH IS TO WEAKEN. MEANWHILE...IT WILL SUSTAIN A CONVERGENT/SUBSIDENT PATTERN ALOFT THAT IS TO INHIBIT ORGANIZED DEEP CONVECTION TO THE EAST OF 45W. MOST ACTIVE CONVECTION DURING THE CYCLE IS EXPECTED TO THE WEST...TO CONCENTRATE ON THE PERUVIAN/BOLIVIAN JUNGLE-AMAZONAS IN WESTERN BRASIL WITH DAILY MAXIMA OF 20-45MM. THIS WILL DECREASE TO 15-30MM/DAY BY MID CYCLE. OTHER CONVECTION IS EXPECTED ACROSS WESTERN BAHIA-TOCANTINS/GOIAS AS A DIVERGENT PATTERN ALOFT ESTABLISHES BETWEEN THE CONTINENTAL RIDGE AND THE TROUGH...WITH DAILY MAXIMA OF 15-30MM THROUGH 36-48 HRS. FERNANDES...CHM (BRASIL) GARCIA...SENAMHI (PERU) DAVISON...HPC (USA)$$