199
FXSA20 KWBC 121557
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1156 AM EDT TUE JUN 12 2012
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
NOTE: HEAVY RAINS ARE TO CONTINUE OVER CENTRAL CHILE DURING
THE NEXT 36 HRS. DURING THAT PERIOD EXPECTING MAXIMA OF 75-100MM.
ALSO EXPECTING HEAVY SNOWFALL AMOUNTS ACROSS TIERRA DEL FUEGO AND
THE OFFSHORE ISLANDS.
MODEL COMPARISON (VALID FROM 00 UTC JUN 12): MODELS AGREE QUITE
WELL INTO THE SHORT RANGE PERIOD...THEN DEVELOP PATTERN
DIFFERENCES DURING THE MEDIUM RANGE AS THEY FAIL TO AGREE ON
INTENSITY/AMPLITUDE OF SHORT WAVE PERTURBATIONS ENTERING THE
SOUTH AMERICAN DOMAIN.
OVER THE EASTERN PACIFIC...A MID/UPPER LEVEL LONG WAVE RIDGE
EXTENDS SOUTH ALONG 120W TO THE POLAR ICE CAP. THE STRONG
MID/UPPER LEVEL RIDGE WILL PERSIST OVER THE NEXT 72-84 HRS...THEN
RAPIDLY CRUMBLE LATER IN THE CYCLE AS PROGRESSIVE PERTURBATIONS
STREAM UNDER THIS AXIS. MEANWHILE...THIS RIDGE WILL DRIVE A
SERIES OF SHORT WAVE PERTURBATIONS NORTHWARD ACROSS THE
BELLINGSHAUSEN SEA/DRAKE PASSAGE TO THE SOUTHERN CONE. THE MOST
INTENSE ARE EXPECTED OVER THE NEXT TWO DAYS. AT LOW LEVELS THESE
WILL SUSTAIN PROGRESSIVE CLIPPER LOWS THAT ARE TO AFFECT EXTREME
SOUTHERN CHILE-PATAGONIA IN ARGENTINA. THE INFLOW OF COLD AIR
WILL RESULT IN SCATTERED CONVECTION...WITH SNOW/SNOW SHOWERS
LIKELY TO DEVELOP. IN THIS AREA EXPECTING LIQUID WATER EQUIVALENT
OF 10-15MM/DAY THROUGH 48-54 HRS. THIS IS LIKELY TO RESULT IN
MODERATE TO HEAVY SNOWFALL AMOUNTS...WITH MOST INTENSE ON THE
OFFSHORE ISLANDS AND THE SOUTHERN ANDES OF CHILE.
THESE PERTURBATIONS...AS THEY LIFT NORTH...THEY WILL FEED INTO A
NORTHERN STREAM TROUGH OFF THE CENTRAL/NORTHERN COAST OF CHILE.
THIS WILL HELP SUSTAIN THIS TROUGH OVER THE NEXT 48-60 HRS...WITH
BROAD TROUGH FORECAST TO MEANDER BETWEEN 100W-70W AND TO THE
NORTH OF 40S. THE DEEP TROUGH PATTERN WILL SUSTAIN A SUBTROPICAL
CONNECTION...ENHANCING MOISTURE CONVERGENCE ACROSS CENTRAL
PORTIONS OF CHILE...WHILE ALSO FAVORING A JET MAXIMA OF 140-160KT
ACROSS THE CENTRAL ANDES INTO MID SECTIONS OF ARGENTINA. THIS
WILL PERSIST THROUGH 36-48 HRS. AT LOW LEVELS IT SUSTAINS A BROAD
TROUGH OVER THE FAR EASTERN PACIFIC...AND A SURFACE FRONT ACROSS
CENTRAL CHILE/PORTIONS OF PATAGONIA IN ARGENTINA. THROUGH 24 HRS
THE FRONT WILL SLOWLY MOVE NORTH ALONG THE COAST OF CHILE WHILE
EXPANDING EASTWARD ACROSS NORTHERN PATAGONIA/LA PAMPA IN
ARGENTINA. THE INFLOW OF SUBTROPICAL MOISTURE AND FAVORABLE JET
DYNAMICS WILL FAVOR ORGANIZED CONVECTION WITH RAINFALL MAXIMA OF
75-100MM. THE MOST INTENSE IS EXPECTED BETWEEN SANTIAGO AND
CONCEPCION. ACROSS SANTIAGO THE MAXIMA WILL PEAK AT 25-50MM
DURING THIS PERIOD. HEAVY SNOWFALL AMOUNTS ARE EXPECTED ACROSS
THE CENTRAL ANDES. AS THE FRONT UNDULATES EAST ACROSS NORTHERN
ARGENTINA...IT IS TO THEN TRIGGER SCATTERED CONVECTION ACROSS
URUGUAY-MESOPOTAMIA VALLEY IN ARGENTINA...WITH RAINFALL MAXIMA OF
20-35MM/DAY IN POTENTIALLY SEVERE CONVECTION BY 42-48 HRS. AS THE
FRONT STALL OVER SOUTHERN BRASIL-PARAGUAY...IT IS TO THEN FAVOR
SCATTERED CONVECTION WITH RAINFALL AMOUNTS OF 15-30MM/DAY.
AS MID/UPPER LEVEL SHORT WAVE ENERGY SHEARS EASTWARD A SECONDARY
LOW WILL THEN FORM OVER THE EASTERN PACIFIC THROUGH 60-72 HRS...
WHERE IT IS TO MEANDER THROUGH 120-132 HRS. MEANWHILE...THIS IS
TO SHEAR SHORT WAVE ENERGY EASTWARD ACROSS THE CENTRAL ANDES TO
THE CENTRAL PROVINCES IN ARGENTINA. THE INFLOW OF SHORT WAVE
ENERGY IS TO ENHANCE CONVECTION ACROSS CENTRAL CHILE...WITH
RAINFALL AMOUNTS OF 15-30MM/DAY EXPECTED ON DAY 04...AND 10-
15MM/DAY ON DAY 05. IT IS TO ALSO INTERACT WITH THE MEANDERING
FRONT OVER SOUTHERN BRASIL-PARAGUAY...TO CONTINUE FAVORING
SCATTERED DEEP CONVECTION OVER THE NEXT FEW DAYS.
NORTH OVER THE CONTINENT...AT 200 HPA...A NEAR ZONAL WESTERLY
FLOW IS TO INITIALLY DOMINATE THE FLOW. BUT AS DEEP POLAR TROUGH
ESTABLISHES OVER THE EASTERN PACIFIC/SOUTHERN CONE THIS WILL
FAVOR GRADUAL AMPLIFICATION OF A CELL OF THE SUBTROPICAL RIDGE
ACROSS WESTERN BRASIL/PERU BY 24-36 HRS...WHERE IT IS TO THEN
PERSIST THROUGH 132 HRS. THE RIDGE IS TO INITIALLY ANCHOR ON A
CLOSED HIGH OVER AMAZONAS/ACRE IN WESTERN BRASIL. THROUGH 96 HRS
THE HIGH WILL START TO DRIFT TO THE SOUTHWEST ACROSS CENTRAL
PERU...TO SETTLE OFF THE COAST OVER THE EASTERN PACIFIC LATER IN
THE CYCLE. THE BUILDING RIDGE...IN-TURN...WILL SUSTAIN THE
NORTHWARD AMPLIFICATION OF A TROUGH ACROSS NORTHEAST BRASIL.
ALTHOUGH UPPER FLOW PATTERN EVOLVES...EXPECTING MOST ACTIVE
CONVECTION TO CONFINE TO PARA-AMAZONAS IN BRASIL TO ECUADOR...
WHERE WE EXPECT RAINFALL MAXIMA TO PEAK AT 10-15MM/DAY. OTHER
ACTIVITY ACROSS ECUADOR IS TO PEAK AT 10-15MM/DAY...WITH MOST
ACTIVE BETWEEN THE COAST AND THE ANDES MOUNTAINS.
PARRENO...INAMHI (ECUADOR)
SANTAYANA...DNM (URUGUAY)
SOLORZANO...SMN(HONDURAS)
DAVISON...HPC (USA)
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