Prognostic Meteorological Discussion
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FXSA20 KWBC 221621
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1220 PM EDT MON SEP 22 2014

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM SEPTEMBER 22 AT 00UTC): GLOBAL MODEL
GUIDANCE FOLLOW SIMILAR EVOLUTION THROUGH 120-132 HRS...LEADING TO
A HIGH CONFIDENCE FORECAST INTO THE MEDIUM RANGE PERIOD. IN THIS
PATTERN...MID LEVEL PERTURBATIONS ARE TO STREAM ACROSS NORTHERN
CHILE/ARGENTINA. AS THEY STREAM ACROSS MID SECTIONS OF SOUTH
AMERICA...THESE ARE TO PROVIDE DYNAMICAL SUPPORT TO CONVECTIVE
COMPLEXES THAT ARE TO FORM OVER NORTHERN
ARGENTINA-PARAGUAY-SOUTHERN BRASIL ON DAYS 02 AND 05.

DURING THE NEXT FEW DAYS...THE GLOBAL MODELS AGREE ON A VERY
ACTIVE PATTERN...WITH A STRONG PERTURBATION ON THE SOUTHERN STREAM
TO ENTER SOUTHERN CHILE BY 30-36 HRS. A STRONGER PERTURBATION
FOLLOWS...TO ENTER SOUTHERN CHILE/DRAKE PASSAGE BY 48-54 HRS.
THROUGH 72 HRS THESE ARE TO COMBINE INTO A BROAD TROUGH THAT IS TO
ENVELOP THE SOUTHERN CONE OF SOUTH AMERICA/WESTERN ATLANTIC.
ACROSS SOUTHERN CHILE AND PATAGONIA IN ARGENTINA THESE ARE TO
FAVOR PROGRESSIVE FRONTS...WITH ONE TO ENTER SOUTHERN CHILE
BETWEEN TEMUCO-ISLA DE CHILOE EARLY IN THE CYCLE...AS ANOTHER
FRONT APPROACHING FROM THE SOUTH ENTER SOUTH OF ISLA DE CHILOE BY
42-48 HRS. THESE ARE TO SUSTAIN A TIGHT PRESSURE GRADIENT ACROSS
THE SOUTHERN CONE DURING THE NEXT THREE DAYS...WITH BOUNDARY LAYER
WINDS OF 35-45KT EXPECTED THROUGHOUT THE SHORT RANGE PERIOD.
STRONG TOPOGRAPHICAL FORCING WILL LIKELY RESULT IN MODERATE TO
HEAVY RAINFALL AMOUNTS...WITH ACCUMULATION OF 15-30MM...WITH
MODELS SHOWING POTENTIAL FOR SCATTERED SNOW SHOWERS ACROSS THE
SOUTHERN ANDES. THROUGH 72-96 HRS THE DAILY MAXIMA DECREASES TO
05-10MM AS THE GRADIENT STARTS TO SLACKEN AND POLAR TROUGH MOVES
FARTHER EAST INTO THE SOUTH ATLANTIC.

A PROGRESSIVE TROUGH ON THE NORTHERN STREAM PULLS ACROSS ARGENTINA
EARLY IN THE CYCLE. THIS IS TO SUSTAIN A SURFACE FRONT ACROSS RIO
DE LA PLATA BASIN-CORDOBA IN ARGENTINA EARLY IN THE CYCLE.
BUILDING POLAR RIDGE IS TO THEN DRIVE THIS BOUNDARY NORTH ACROSS
URUGUAY-SOUTHERN BRASIL TO NORTHERN PROVINCES IN ARGENTINA BY
54-60 HRS. AS THE FRONT ACCELERATES...IT IS TO TRIGGER A
PREFRONTAL SQUALL LINE. HEAVY CONVECTION IS TO AFFECT THE
PROVINCES OF CHACO-CORRIENTES-MISIONES IN ARGENTINA...RIO GRANDE
DO SUL IN BRASIL AND CENTRAL/ SOUTHEAST PORTIONS OF PARAGUAY. IN
POTENTIALLY SEVERE CONVECTION... AND UNDER FAVORABLE JET
DYNAMICS...EXPECTING MAXIMA OF 35-70MM BY 48-72 HRS. THROUGH 84
HRS THIS DECREASES TO 30-60MM. SURFACE FRONT IS TO THEN STALL OVER
SOUTHERN BRASIL-PARAGUAY...WHERE IT IS TO REMAIN THROUGH 120-132
HRS. IN A MOIST NORTHERLY FLOW...SCATTERED CONVECTION IS TO
DEVELOP ALONG THIS BOUNDARY WITH DAILY MAXIMA OF 20-40MM EXPECTED
THROUGH 96-108 HRS.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO THEN ENTER
CENTRAL/NORTHERN CHILE BY 96-108 HRS. THIS IS TO QUICKLY SPILL
ACROSS THE ANDES INTO THE NORTHERN PROVINCES IN ARGENTINA. THE
SHORT WAVE TROUGH WILL THEN INTERACT WITH AFOREMENTIONED FRONT
OVER SOUTHERN BRASIL-NORTHERN ARGENTINA...TO TRIGGER ANOTHER ROUND
OF POTENTIALLY SEVERE CONVECTION LATER IN THE CYCLE MOST ACTIVE IS
EXPECTED ACROSS PARAGUAY TO SOUTHERN BRASIL...WITH MAXIMA OF
35-70MM.

AT 200 HPA...SUBTROPICAL RIDGE PATTERN IS FORECAST TO STRENGTHEN
AS THE CYCLE PROGRESSES. EARLY IN THE CYCLE THE RIDGE IS TO
CONFINE TO CONTINENTAL AREA NORTH OF 25S AND WEST OF 50W. THROUGH
72-84 HRS RIDGE IS TO BUILD EAST ACROSS BRASIL...AND BY 96 HRS IT
IS FORECAST TO ENVELOP CONTINENTAL AREA TO THE NORTH OF 30S. AS
THE RIDGE BUILDS...A MID/UPPER CONVERGENT PATTERN IS TO ESTABLISH
THROUGH 108-120 HRS ACROSS CENTRAL-EASTERN PORTIONS OF BRASIL.
THIS...IN-TURN...WILL SUSTAIN EROSION OF AVAILABLE MOISTURE. MOST
ACTIVE CONVECTION IS EXPECTED ACROSS WESTERN BRASIL-NORTHERN
PERU/ECUADOR...WHERE MAXIMA IS TO PEAK AT 20-35MM EARLY IN THE
CYCLE. THROUGH 72-96 HRS THIS DECREASES TO 05-10MM. OTHER ACTIVITY
IS TO DOT THE SOUTHERN SIERRA OF PERU AND THE ALTIPLANO OF
BOLIVIA...WITH MAXIMA OF 05-10MM OVER THE NEXT COUPLE OF
DAY...INCREASING TO 15-20MM LATER ON DAY 04.

JALFIN...SMN (ARGENTINA)
CAROCA...DMC (CHILE)
DAVISON...WPC (USA)
$$




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