814
FXSA20 KWBC 011649
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1249 PM EDT WED OCT 01 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z OCTOBER 01) THE GLOBAL MODELS
AGREE THAT THERE WILL BE SIGNIFICANT CHANGES TO THE PATTERN BY
THE END OF THIS 5-DAY PERIOD. TROUGHING IN THE EASTERN PACIFIC
WILL GIVE WAY TO A BUILDING FULL LATITUDE RIDGE WHILE A
BROAD DEEP TROUGH CARVES OUT IN THE WESTERN ATLANTIC.
OVERALL THERE IS GOOD AGREEMENT WITH THE DETAILS OF THIS PATTERN
CHANGE THROUGH DAY 3 HOWEVER BEYOND THAT TIME THE ECMWF/UKMET
TREND TOWARD A MORE AMPLIFIED EASTERN PACIFIC RIDGE THAN SHOWN IN
THE GFS. ENSEMBLE GUIDANCE SUPPORTS THE LESS AMPLIFIED
SOLUTION AND THE GFS IS SHOWING FAIRLY GOOD RUN-TO-RUN CONTINUITY
FOR THE LAST FEW CYCLES. AT THIS TIME WILL LEAN TOWARD THE GFS
THROUGH THIS FORECAST PERIOD.
OVER THE NEXT SEVERAL DAYS THE FOCUS FOR THE MOST SIGNIFICANT
PRECIPITATION WILL BE A MEANDERING FRONT STRETCHING ACROSS
SOUTHERN/SOUTHEASTERN BRASIL PARAGUAY AND BOLIVIA. ENERGY
ASSOCIATED WITH A NORTHERN STREAM SHORT WAVE CROSSING THE
CONTINENT WILL COMBINE WITH LIFT FROM AN UPPER JET COUPLET AND
DEEP MOISTURE TO BRING WIDESPREAD RAINFALL FROM NORTHERN
PARAGUAY/MATO GROSSO DO SUL EASTWARD THROUGH SECTIONS OF
PARANA SAO PAULO AND SANTA CATARINA DAY 1. RAINFALL AMOUNTS
COULD APPROACH 40-60MM. AS THE SHORT WAVE PASSES THE FRONT WILL
TEMPORARILY PUSH NORTHWARD AND SHIFT PRECIPITATION ON DAY 2 INTO
MATO GROSSO SAO PAULO AND RIO DE JANEIRO. THEN ON DAYS 3-4 A
DEVELOPING SURFACE WAVE OVER BOLIVIA ASSOCIATED WITH UPSTREAM
HEIGHT FALLS WILL TRACK ACROSS PARAGUAY AND PARANA. STRONG
LOW-LEVEL CONVERGENCE ALONG WITH VERY FAVORABLE MID-UPPER
DYNAMICS WILL SPAWN HEAVY ORGANIZED CONVECTION IN MUCH THE SAME
REGION THAT WILL RECEIVE PRECIPITATION DAY 1. RAINFALL AMOUNTS
WILL AGAIN APPROACH 40-60MM EACH DAY. IN ADDITION AS THE FRONT
DROPS NORTHWARD THROUGH BOLIVIA STRONG UPSLOPE FLOW AND DEEP
TROPICAL MOISTURE ALREADY IN PLACE WILL LIKELY ALLOW THE
WIDESPREAD CONVECTION TO BUILD WESTWARD THROUGH CENTRAL BOLIVIA
ON DAY 4.
FARTHER SOUTH THE STRONG TROUGH IN THE SOUTHEASTERN PACIFIC WILL
PROGRESS ACROSS THE CONTINENT DURING THE NEXT 60-72 HOURS. A
SERIES OF IMPULSES ROTATING THROUGH THIS TROUGH WILL BRING
UNSETTLED WEATHER AND COOLER CONDITIONS TO THE SOUTHERN CONE. ON
DAY 1 STRONG MID-UPPER DYNAMICS WILL SUPPORT WIDESPREAD RAINFALL
OVER SOUTHERN CHILE MAINLY SOUTH OF 40S AND NORTH OF 55S WHERE UP
TO 10-20MM COULD FALL. FOR DAY 2 POST-FRONTAL ONSHORE FLOW AND
INSTABILITY UNDER THE COLD POOL ALOFT WILL CONTINUE THE THREAT
FOR AT LEAST SCATTERED PRECIPITATION WITH THE POTENTIAL FOR SOME
LIGHT SNOW ACCUMULATIONS IN THE HIGHER ELEVATIONS IN THE SOUTHERN
ANDES. MORE WIDESPREAD PRECPITATION WILL RETURN ON DAY 3 AS
FAST-MOVING SHORT WAVES IN THE SOUTHERN STREAM FOCUS LIGHT
OVERRUNNING PRECIPITATION OVER EXTREME SOUTHERN CHILE AND TIERRA
DEL WITH MAXIMUM AMOUNTS AROUND 10-15MM. THERE ARE SIGNS THAT A
PIECE OF ENERGY FROM A NORTHERN STREAM CLOSED LOW IN THE CENTRAL
PACIFIC WILL EJECT INTO THE WESTERLIES AND BRING A RENEWED CHANCE
FOR RAINFALL ACROSS SOUTHERN AND SOUTH-CENTRAL CHILE DURING DAY
4.
THE NORTHERN STREAM UPPER TROUGH INITIALLY OFF THE COAST OF
NORTHERN/CENTRAL CHILE WILL PUSH QUICKLY EASTWARD AND HELP
TRIGGER ORGANIZED CONVECTION ALONG A WEAK FRONTAL ZONE OVER
BUENOS AIRES PROVINCE AND NORTH-CENTRAL ARGENTINA ON DAY 1.
AMOUNTS WILL RANGE UPWARDS OF 10-20MM. BY DAY 2 TRAILING SHORT
WAVE ENERGY ASSOCIATED WITH THE SOUTHERN STREAM TROUGH (DISCUSSED
ABOVE) WILL SUPPORT MORE RAINFALL OVER CENTRAL ARGENTINA WITH
THIS ACTIVITY SHIFTING INTO NORTHERN ARGENTINA BUENOS AIRES
PROVINCE AND SOUTHERN URUGUAY BY DAY 3. AMOUNTS WILL RANGE UP TO
10-20MM BOTH DAYS.
FARTHER NORTH IN THE CONTINENT THE UPPER HIGH JUST OFF THE
PERUVIAN COAST WILL MEANDER BETWEEN THE COAST AND 95W GENERALLY
BETWEEN 10-15S FOR THE NEXT SEVERAL DAYS. THE RIDGING TO ITS
EAST IS EXPECTED TO NARROW AS THE NORTHERN PORTION BETWEEN THE
EQUATOR AND 10S ERODES HOWEVER IT WILL BUILD EASTWARD ACROSS THE
CONTINENT. BY DAY 5 IT APPEARS A SECOND HIGH CENTER WILL SET UP
OVER SOUTHEASTERN BRASIL. MEANWHILE THE MODELS SUGGEST AN UPPER
LOW WILL FORM OVER EASTERN AMAZONIA ON DAY 3 THEN RETROGRADE INTO
CENTRAL AMAZONIA BY DAY 5. MOST OF THE ORGANIZED CONVECTION WILL
REMAIN IN PERU/WESTERN AMAZONIA AND SOUTHERN COLOMBIA DURING DAY
1. THEN THE ECMWF AND GFS SUGGEST THIS ACTIVITY WILL SHIFT INTO
CENTRAL AMAZONIA FOR DAYS 2-4 AND PERHAPS BACK TO THE WEST AGAIN
FOR DAY 5. MAXIMUM RAINFALL WILL AVERAGE 15-20MM DAILY WITH
ISOLATED HIGHER AMOUNTS IN HEAVIER CELLS. FINALLY DAILY
CONVECTION WILL CONTINUE OVER THE HIGHER TERRAIN IN
CENTRAL/SOUTHERN PERU AND WESTERN BOLIVIA THROUGH PERIOD PERHAPS
ENHANCING ON DAYS 4-5 WITH INCREASING UPSLOPE FLOW.
URRA...DMC (CHILE)
MOREYRA...SENAMHI PERU
KLEIN...HPC (USA)
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