473
FXSA20 KWBC 021618
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1217 PM EDT THU OCT 02 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
THERE WILL BE NO AMENDMENTS TO THIS PRODUCT UNTIL 06 OCT 2008.
MODEL COMPARISON (VALID FROM 00Z OCTOBER 02) THE GLOBAL MODELS
ARE IN VERY GOOD AGREEMENT WITH THE MAJOR FEATURES THROUGH DAY 3.
THE TROUGH OVER THE SOUTHERN CONE WILL MOVE INTO THE ATLANTIC
EARLY IN THE PERIOD AND FILL WITH THE NORTHERN END COMING INTO
PHASE WITH SOME NORTHERN STREAM ENERGY CROSSING THE CENTRAL PART
OF THE CONTINENT. BEYOND THIS TIME MODEL DIFFERENCES DEVELOP
UPSTREAM IN THE HANDLING OF THE BUILDING RIDGE MOVING FROM THE
EASTERN PACIFIC ACROSS THE SOUTHERN CONE. HOWEVER THESE
DIFFERENCES ARE MOSTLY WITH HANDLING OF SOUTHERN STREAM ENERGY
SOUTH OF THE CONTINENT AND THEREFORE WILL HAVE LITTLE IMPACT ON
THE DAILY FORECASTS OVER THE SOUTHERN CONE DAYS 4-5.
AS WAS THE CASE YESTERDAY A MAIN FOCUS FOR PRECIPITATION OVER THE
CONTINENT WILL BE A WAVY FRONTAL ZONE THAT RUNS FROM PERU THROUGH
CENTRAL BOLIVIA INTO PARAGUAY AND ACROSS SOUTHEASTERN BRASIL.
SHORT WAVES MOVING THROUGH THE NORTHERN STREAM WESTERLIES WILL
COMBINE WITH FAVORABLE UPPER DYNAMICS AND DEEP MOISTURE POOLED
ALONG THE FRONT TO SUPPORT DAILY PERIODS OF ORGANIZED CONVECTION.
AT THIS TIME IT APPEARS THE MOST SIGNIFICANT PRECIPITATION WILL
BE IN THE DAY 2-3 TIME FRAME AS A POTENT SHORT WAVE MOVES ACROSS
THE CONTINENT AND INDUCES DEVELOPMENT OF A SURFACE LOW ALONG THE
FRONT. THIS LOW IS EXPECTED TO TRACK SOUTHEASTWARD FROM CENTRAL
BOLIVIA AT 48 HOURS THROUGH PARANA AT 72 HOURS. ENHANCED
CONVERGENCE ALONG THE FRONT ALONG WITH A STRONG LOW-LEVEL FLOW OF
TROPICAL MOISTURE WILL SUPPORT WIDESPREAD MODERATE TO HEAVY
RAINFALL ACROSS PARAGUAY MATO GROSSO DO SUL PARANA AND SANTA
CATARINA. MAXIMUM AMOUNTS OF UP TO 40-60MM ARE POSSIBLE BOTH
DAYS 2 AND 3. FARTHER WEST HIGH PRESSURE BUILDING INTO NORTHERN
ARGENTINA DAYS 3-4 WILL ENHANCE MOISTURE CONVERGENCE ALONG THE
FRONT TO THE NORTH AND WITH LIFT PROVIDED BY AN UPPER SHEAR
AXIS BRING A GOOD CHANCE FOR HEAVY RAINS INTO CENTRAL BOLIVIA AND
SOUTHERN PERU. MAXIMUM AMOUNTS MAY APPROACH 50MM EACH DAY.
FINALLY BY DAY 5 THIS FRONT WILL GRADUALLY BECOME LESS ACTIVE AS
UPPER RIDGING BUILDS IN.
OVER THE SOUTHERN CONE UNDER THE COLD UPPER TROUGH DAY 1 WILL
FEATURE INSTABILITY SHOWERS OVER TIERRA DEL FUEGO SOUTHERN
PATAGONIA AND CHILE SOUTH OF 40S. MAXIMUM RAINFALL AMOUNTS WILL
BE AROUND 10MM. ON DAY 2 A POTENT SOUTHERN STREAM SHORT WAVE AND
ASSOCIATED SURFACE FRONT IS EXPECTED TO BRING WIDESPREAD RAINFALL
INTO EXTREME SOUTHERN CHILE MAINLY SOUTH OF 50S WHERE UP TO
10-15MM MAY FALL. A VERY STRONG POST-FRONTAL ONSHORE FLOW OF
MOIST AIR WILL MAINTAIN A CHANCE FOR SHOWERS OVER THIS AREA DAY
3 BUT THE MAIN FOCUS WILL SHIFT NORTHWARD TOWARD THE ARCHIPIELAGO
DE LOS CHONOS. THE MODELS EJECT A PIECE OF ENERGY TOWARD THE
COAST FROM THE CLOSED LOW WELL OUT IN THE CENTRAL PACIFIC AND
THIS SYSTEM IS ABLE TO TAP INTO SOME DEEPER PACIFIC MOISTURE.
MAXIMUM RAINFALL AMOUNTS MAY APPROACH 20MM WITH THIS FEATURE.
BEYOND DAY 3 THERE WILL BE A GRADUAL DRYING TREND AS UPPER
RIDGING BUILDS OVER THE REGION.
FARTHER NORTH ENERGY ON THE TAIL END OF THE SOUTHERN STREAM
TROUGH WILL INTERACT WITH A WEAK FRONT TO SPAWN SOME CONVECTION
OVER CENTRAL ARGENTINA ON DAY 1. MOISTURE IS FAIRLY LIMITED SO
MAXIMUM AMOUNTS OF ONLY 10-15MM ARE POSSIBLE. AS THIS SHORT WAVE
MOVES INTO THE ATLANTIC IT WILL DRAG THE COLD FRONT NORTHWARD AND
ANOTHER FAST MOVING IMPULSE WILL BRING THE CHANCE FOR ADDITIONAL
CONVECTION OVER NORTHERN ARGENTINA AND BUENOS AIRES PROVINCE DAY
2.
FARTHER NORTH IN THE CONTINENT THE UPPER HIGH OVER SOUTHERN PERU
WILL SPLIT EARLY IN THE PERIOD AS A TROUGH IN THE EASTERN PACIFIC
PROGRESSES EASTWARD AND AMPLIFIES. ONE CENTER WILL FORM AND
REMAIN IN THE EASTERN ATLANTIC WHILE A SECOND DEVELOPS OVER MATO
GROSSO BY DAY 1 AND QUICKLY ADVANCES ACROSS SOUTHEASTERN BRASIL
DAYS 2-3. MEANWHILE A DEEP TROUGH WILL GRADUALLY CARVE OUT OVER
NORTHERN CHILE AND SOUTHERN PERU. ELSEWHERE AN UPPER LOW WILL
SPIN UP OVER THE AMAZON RIVER DELTA AROUND 72 HOURS AND
RETROGRADE THROUGH AMAZONIA ALMOST PHASING WITH THE TROUGH TO ITS
SOUTHWEST BEFORE EVENTUALLY MOVING INTO MATO GROSSO BY 120 HOURS.
CONVECTION THROUGH DAY 2 SHOULD BE MOST ORGANIZED OVER NORTHERN
AND EASTERN AMAZONIA THROUGH TOCANTINS WITH DAILY MAXIMA OF
15-30MM POSSIBLE. FOR DAYS 3-5 THE HEAVIEST ACTIVITY IS FORECAST
TO SHIFT MOSTLY WEST OF 60W IN THE DIFFLUENT REGION NORTH OF THE
UPPER TROUGH IN NORTHERN CHILE/SOUTHERN PERU. AGAIN EXPECT
RAINFALL IN ANY CONVECTION TO BE AROUND 15-30MM THOUGH LOCALLY
HIGHER AMOUNTS ARE LIKELY.
URRA...DMC (CHILE)
MOREYRA...SENAMHI PERU
KLEIN...HPC (USA)
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