850
FXSA20 KWBC 191610
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1210 PM EDT TUE JUN 19 2012
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
NOTE: MEANDERING FRONT AND FAVORABLE UPPER DYNAMICS WILL FAVOR
ORGANIZED CONVECTION ACROSS SOUTHEAST BRASIL DURING THE NEXT
THREE. DURING THIS PERIOD...STRONG TOPOGRAPHICAL FORCING ALONG
THE SERRA DO MAR AND SERRA PARANAPIACABA WILL LIKELY RESULT IN
LOCALIZED MAXIMA IN EXCESS OF 125MM. THIS WILL BE CONDUCIVE TO
FLASH FLOODING/MUD SLIDES.
MODEL COMPARISON (VALID FROM 00 UTC JUN 19): THE MODELS CONTINUE
TO DIVERGE ON THE SOUTHERN STREAM EVOLUTION DURING THE MEDIUM
RANGE PERIOD...AS THEY FAIL TO REACH A CONSENSUS ON
AMPLITUDE/SPEED OF SHORT WAVE PERTURBATIONS ENTERING THE SOUTH
AMERICAN DOMAIN. THE HIGH VARIABILITY AMONG THE DETERMINISTIC
SOLUTIONS IS ALSO OBSERVED AMONG THE ENSEMBLE MEMBERS...LEADING
TO A LOW CONFIDENCE FORECAST.
MODELS FORECAST PROGRESSIVE SOUTHERN STREAM PERTURBATIONS TO
STREAM ACROSS THE SOUTH PACIFIC INTO THE SOUTHERN CONE DURING
THE NEXT FEW DAYS. THE MID LEVEL PERTURBATIONS WILL FOCUS THEIR
SHORT WAVE ENERGY ON CONTINENTAL AREA TO THE SOUTH OF 40S.
PROGRESSIVE FRONTS AND STRONG BOUNDARY LAYER WINDS ARE TO
ACCOMPANY THESE WAVES...TO ALSO LIMIT TO AREA SOUTH OF 40S. THE
POLAR/MARITIME AIR MASSES WILL SUSTAIN A WET WEATHER PATTERN
ACROSS SOUTHERN PORTIONS OF CHILE-TIERRA DEL FUEGO...AND ARE TO
CONTINUE TRIGGERING SCATTERED CONVECTION. SNOW/SNOW SHOWERS WILL
CONCENTRATE ON AREA SOUTH OF ISLA DE CHILOE...WHILE TO THE NORTH
EXPECTING MOSTLY LIQUID PRECIPITATION. DAILY MAXIMA WILL PEAK AT
10-15MM/DAY. NOTE THAT THIS IS CONSIDERABLY LESS THAN WHAT
GUIDANCE SUGGESTS FOR THE REGION.
ON THE NORTHERN STREAM...THE GLOBAL MODELS CONVERGE ON PATTERN
EVOLUTION THROUGH DAY 05. EARLY ON...A TROUGH WILL MOVE EAST
ACROSS ARGENTINA TO THE WESTERN ATLANTIC...WITH AXIS TO THEN
GRADUALLY PULL TO THE EAST-SOUTHEAST. A SECONDARY VORTEX IS TO
CLOSELY FOLLOW...MOVING ACROSS PATAGONIA BY 30-36 HRS...INTO
CENTRAL PROVINCES IN ARGENTINA BY 48 HRS. BY 72 HRS IT IS TO
STREAM ACROSS SOUTHERN BRASIL...MEANWHILE FOCUSING ITS SHORT WAVE
ENERGY ACROSS URUGUAY/RIO GRANDE DO SUL IN BRASIL. AT 250 HPA A
SUBTROPICAL JET MAXIMA WILL BOUND THE NORTHERN FRINGES OF THIS
TROUGH...AS IT IS TO STRETCH ACROSS NORTHERN CHILE/SOUTHERN
BOLIVIA-SOUTHERN BRASIL TO THE ATLANTIC. BY 96-108 HRS...AS THE
TROUGH PULLS INTO THE ATLANTIC...THE MAXIMA IS TO QUICKLY WEAKEN
OVER THE CONTINENT. BUT AS THE JET MEANDERS OVER THE
CONTINENT...IT WILL SUSTAIN AREAS OF DIVERGENCE ALOFT ACROSS
BOLIVIA-MATO GROSSO/MATO GROSSO DO SUL IN BRASIL TO SOUTHEAST
BRASIL. THIS WILL PROVIDE THE VENTILATION ALOFT IN SUPPORT OF
ORGANIZED DEEP CONVECTION. AT LOW LEVELS...AN ELONGATED FRONT
WILL STRETCH TO THE WEST-NORTHWEST ACROSS SAO PAULO-MATO
GROSSO DO SUL/RONDONIA IN BRASIL TO NORTHERN BOLIVIA/SOUTHERN
PERU. THIS BOUNDARY IS GOING TO BE THE FOCUS OF MOISTURE
CONVERGENCE...WITH FORECASTED PRECIPITABLE WATER CONTENT VALUES
TO GENERALLY RANGE BETWEEN 40-60MM ALONG AND NORTH OF THIS
BOUNDARY. THE HIGH MOISTURE CONTENT VALUE AND FAVORABLE UPPER
DYNAMICS WILL BE CONDUCIVE TO SEVERAL DAYS OF ORGANIZED
CONVECTION. OVER SOUTHEAST BRASIL EXPECTING RAINFALL AMOUNTS OF
35-70MM/DAY THROUGH 48 HRS...AND 40-80MM/DAY AT 48-72 HRS AS
ENHANCED BY MID LEVEL TROUGH STREAMING ACROSS MID SECTIONS OF
SOUTH AMERICA. STRONG TOPOGRAPHICAL FORCING ALONG THE SERRA DO
MAR AND SERRA PARANAPIACABA WILL LIKELY RESULT IN LOCALIZED
MAXIMA IN EXCESS OF 125MM...AND THIS WILL BE CONDUCIVE TO FLASH
FLOODING/MUD SLIDES. OTHER ACTIVITY ALONG THE TAIL END OF THIS
BOUNDARY WILL AFFECT CENTRAL/NORTHERN BOLIVIA TO SOUTHERN JUNGLE
IN PERU. SCATTERED CONVECTION IS TO BUILD OVER THE NEXT FEW
DAYS...WITH MAXIMA EXPECTED TO PEAK AT 15-20MM.
NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE IS
TO INITIALLY DOMINATE CONTINENTAL AREA TO THE NORTH OF 25S. THIS
PATTERN WILL PERSIST OVER THE NEXT 36-48 HRS...THEN RAPIDLY
CRUMBLE AS POLAR TROUGH PATTERN TO THE SOUTH EVOLVES. INITIALLY
IT IS TO FAVOR SCATTERED CONVECTION ACROSS EQUATORIAL SOUTH
AMERICA...BUT AS THE RIDGE PATTERN WEAKENS...MODELS SHOWING
ACTIVITY SLOWLY BUILDING SOUTH AND WEST ACROSS AMAZONAS IN BRASIL
INTO THE JUNGLE OF PERU. OTHER ACTIVITY IS TO BUILD ALONG THE
NORTHEAST COAST OF BRASIL...WITH MODELS TRENDING TOWARDS MORE
ACTIVE/BETTER ORGANIZED CONVECTION ON DAYS 03-04...WHEN MAXIMA
PEAKS AT 15-30MM/DAY.
PARRENO...INAMHI (ECUADOR)
SANTAYANA...DNM (URUGUAY)
SOLORZANO...SMN(HONDURAS)
DAVISON...HPC (USA)
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