####018005720#### FXSA20 KWBC 131733 PMDSA SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 1232 PM EST FRI FEB 13 2009 GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/ COR NOTE: LAST NO AMENDS...NEXT BULLETIN TO BE ISSUED O/A FEB 17. MODEL COMPARISON (VALID FROM 00Z FEBRUARY 13). THE GFS ONCE AGAIN MAKES AMPLITUDE/TIMING CORRECTIONS TO SHORT WAVE PERTURBATIONS STREAMING ACROSS THE EASTERN PACIFIC TO THE SOUTHERN CONE. LATEST RUN(S) FAVORS SLIGHTLY SLOWER AND AMPLER PERTURBATIONS...WITH MOST SIGNIFICANT CHANGE NOTED ON DAY 05 WHEN IT SHOWS A HIGH AMPLITUDE TROUGH ACROSS ARGENTINA...WITH A LOW CUTTING OFF NEAR CORDOBA. NON OF THE OTHER MODELS OFFER THIS SOLUTION...WITH BOTH EUROPEAN MODELS AND LARGE MAJORITY OF THE GLOBAL ENSEMBLES SUSTAINING THE PREVIOUS TREND. THE SURFACE ANALYSIS SHOWS AN ELONGATED FRONT OVER THE SOUTH ATLANTIC TO SAO PAULO IN SOUTHEAST BRASIL. THE FRONT WILL REMAIN NEARLY STATIONARY THROUGH 72 HRS...THEN RAPIDLY WEAKENS. THIS BOUNDARY LINKS WITH THE SOUTH ATLANTIC CONVERGENCE ZONE OVER BRASIL AS IT EXTENDS ACROSS SAO PAULO-MATO GROSSO/RONDONIA TO NORTHERN BOLIVIA. BUT THE BOUNDARY IS BECOMING ILL ORGANIZED... AND THROUGH 36-48 HRS IT WILL WEAKEN TO A TROUGH...THAT GRADUALLY WEAKENS THROUGH 72-84 HRS. ALTHOUGH INITIALLY MAXIMA ACROSS SOUTHEAST BRASIL IS TO PEAK AT 25-50MM/DAY...AFTER 36 HRS IT WILL DECREASE TO 15-30MM/DAY. OVER BOLIVIA TO SOUTHERN PERU...THE MAXIMA WILL PEAK AT 10-20MM/DAY THROUGH 36 HRS...THEN SURGE TO 25-50MM/DAY ON DAY 02 AS A MID/UPPER LEVEL TROUGH INTERACTS WITH THE REMNANTS OF THE SURFACE TROUGH. OVER THE EASTERN PACIFIC...IN A TIGHT BELT OF MID LATITUDE WESTERLIES...A PROGRESSIVE SHORT WAVE TROUGH ENTERED THE SOUTHERN CONE. THE 500 HPA TROUGH MOVES TO THE WESTERN ATLANTIC ALONG 50W/55W BY 24 HRS...AND CONTINUES ACROSS 30W BY 48 HRS. THE ASSOCIATED FRONT EXTENDS ACROSS PATAGONIA/SOUTHERN CHILE TO THE EASTERN PACIFIC...AND THROUGH 24 HRS IT WILL MOVE TO THE BUENOS AIRES PROVINCE/RIO DE LA PLATA...WHERE IT WILL WEAKEN/DISSIPATE THROUGH 36-48 HRS. CONVECTION WITH THIS BOUNDARY WILL LIMIT TO SOUTHERN CHILE...WHERE MAXIMA WILL PEAK AT 10-20MM/DAY IN DEEP CONVECTION. STRONG BOUNDARY LAYER WINDS ARE TO PERSIST OVER SOUTHERN CHILE THROUGH 48 HRS. ANOTHER MID LEVEL PERTURBATION FOLLOWS...FORECAST ACROSS 90W/95W BY 48 HRS. THIS TROUGH WILL CONTINUE ACROSS 75W BY 72 HRS...WITH SHORT WAVE ENERGY FOCUSING OVER CONTINENTAL AREA SOUTH OF 30S. IT THEN MOVES ACROSS 60W TO 30S BY 96 HRS...AND THEN QUICKLY PULLS EASTWARD ACROSS 35W BY 120 HRS. MODELS CONTINUE TO MAKE ADJUSTMENTS TO THE AMPLITUDE/SPEED OF THIS TROUGH...SO UNCERTAINTY REMAINS HIGH. THE ASSOCIATED FRONT IS TO ENTER SOUTHERN CHILE BY 24-36 HRS...THEN MOVE NORTH ACROSS PATAGONIA BY 48 HRS...INTO LA PAMPA/CENTRAL CHILE BY 72 HRS. AT A SLOWER PACE THAN PREVIOUSLY INDICATED...IT IS TO NOW MOVE ACROSS THE BUENOS AIRES PROVINCE-CENTRAL CUYO BY 96 HRS. AS IT ENTERS SOUTHERN CHILE...THE GFS SHOWS HIGH MOISTURE CONTENT WITH THIS BOUNDARY...WITH MIXING RATIO VALUES OF 12-13G/KG...WHICH IS QUITE HIGH FOR THIS AREA. THIS WILL BE CONDUCIVE TO ORGANIZED CONVECTION...HEAVY AT TIMES...WITH RAINFALL MAXIMA OF 15- 35MM/DAY. THE MOST INTENSE AT 48-72 HRS...WITH LOCALLY HIGHER AMOUNTS IN EXCESS OF 50MM QUITE POSSIBLE. STRONG BOUNDARY LAYER WINDS ARE ALSO EXPECTED OVER CHILE/PATAGONIA SOUTH OF 40S. OTHER CONVECTION IS EXPECTED OVER CENTRAL ARGENTINA ON DAYS 03-04... WITH MAXIMA OF 10-15MM/DAY. OTHER CONVECTION IS POSSIBLE ON THE LEE OF THE ANDES ACROSS NORTHWEST ARGENTINA...WITH MAXIMA OF 10- 20MM/DAY EXPECTED ON DAYS 01 AND 03. WATER VAPOR IMAGERY NOW SHOWS THE SUBTROPICAL HIGH CENTERING OVER THE EASTERN PACIFIC NEAR 20S 80W. AT 200 HPA THE HIGH IS FORECAST TO MEANDER WEST TO 20S 95W BY 72 HRS. SIMULTANEOUSLY...ANOTHER HIGH WILL FORM OVER THE CONTINENT NEAR 15S 50W...WITH THE LATTER TO SLOWLY BUILD A RIDGE TO THE NORTHWEST ACROSS BRASIL TO PERU. THE INHERENT WEAKNESS BETWEEN THE TWO HIGHS/RIDGES... WILL ALLOW FOR NORTHWARD AMPLIFICATION OF SHORT WAVE TROUGHS ACROSS NORTHWEST ARGENTINA TO SOUTHERN BOLIVIA...WITH A STRONG PERTURBATION TO MOVE ACROSS NORTHERN CHILE TO NORTHWEST ARGENTINA/SOUTHERN BOLIVIA BY 36-42 HRS...WHERE IT WILL REMAIN THROUGH 60-72 HRS. AS THE TROUGH ENTERS THE CONTINENT...IT WILL FAVOR A SURGE IN CONVECTION ACROSS CENTRAL/NORTHERN BOLIVIA- RONDONIA IN BRASIL...WHERE RAINFALL MAXIMA WILL PEAK AT 25- 50MM/DAY BY 36-60 HRS...WITH MODERATE CONVECTION TO THEN PERSIST THROUGH 48-72 HRS. OTHER CONVECTION IS EXPECTED FARTHER NORTH ACROSS NORTHWEST BRASIL TO SOUTHERN COLOMBIA-NORTHERN PERU TO ECUADOR...WITH MAXIMA OF 20-40MM/DAY ON DAY 01...TO THEN SETTLE AT 15-30MM/DAY ON DAYS 02-04. FURTHERMORE...AS THE SUBTROPICAL RIDGE ESTABLISHES OVER THE CONTINENT...A TROUGH WILL AMPLIFY OVER THE ATLANTIC ALONG 30W. BY 72 HRS THE TROUGH MOVES ALONG 35W...WITH A CLOSED LOW FORMING NEAR 05S 35W. THIS LOW MOVES INLAND ACROSS BAHIA BY 72 HRS...AND CONTINUE WEST TO 10S 55W BY 120 HRS. THIS IS CONSISTENT WITH PREVIOUS FORECASTS. AS THE PATTERN ESTABLISHES...IT WILL SUSTAIN A SURGE IN CONVECTION ACROSS TOCANTINS/GOIAS-MINAS GERAIS/EASTERN BAHIA...WITH MAXIMA OF 35-50MM/DAY EXPECTED BY 36-72 HRS. THROUGH 72-84 HRS THIS SPREADS WEST TO THE AMAZON RIVER DELTA...AND INTO AMAPA/RORAIMA-GUIANAS BY THE END OF THE CYCLE. IN THIS AREA STRONG TOPOGRAPHICAL FORCING WILL LIKELY FAVOR RAINFALL MAXIMA IN EXCESS OF FORECAST GUIDANCE. PEREZ...SENAMHI (BOLIVIA) DAVISON...HPC (USA)$$