Prognostic Meteorological Discussion
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FXSA20 KWBC 291547
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1146 AM EDT TUE JUL 29 2014

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

MODEL DISCUSSION (VALID FROM 29 JULY 00UTC): MODELS REMAIN IN
EXCELLENT AGREEMENT ON HOW THE NORTHERN STREAM IS TO EVOLVE DURING
THE NEXT FIVE TO SEVEN DAYS. THIS FORECAST HAS THE SUPPORT OF THE
GLOBAL ENSEMBLES...AND AS A RESULT...OUR CONFIDENCE IS HIGH.

OVER THE EASTERN PACIFIC...MODELS CONTINUE TO FAVOR A SLOW TO
EVOLVE PATTERN DURING THE NEXT FEW DAYS...WITH A BROAD TROUGH ON
THE SOUTHERN STREAM TO DOMINATE AREA BETWEEN 100W-70W WHILE
ANCHORING ON A CLOSED LOW THAT IS TO MEANDER NEAR 60S 90W. SHORT
WAVE PERTURBATIONS ON THE NORTHERN STREAM ARE TO REVOLVE AROUND
THIS AXIS. THE SHORT WAVE PERTURBATIONS ARE TO ENTER
CENTRAL/SOUTHERN CHILE AT AN INTERVAL OF 18-24 HRS...AND THEY ARE
TO AVERAGE AROUND ONE PERTURBATION PER DAY. DEEP SUBTROPICAL
MOISTURE IS TO ACCOMPANY THESE PERTURBATIONS AS THEY STREAM ACROSS
THE EASTERN PACIFIC... ENHANCING MOISTURE TRANSPORT AND
CONVERGENCE OVER CHILE. AT UPPER LEVELS...THE TROUGH WILL FOCUS
THE JET STREAM ACROSS CENTRAL CHILE...WITH DIVERGENCE ON ITS RIGHT
EXIT REGION TO ENVELOP AREA SOUTH OF CONCEPCION. AT LOW
LEVELS...IT WILL SUSTAIN A BROAD TROUGH ACROSS THE BELLINGSHAUSEN
SEA/SOUTHEAST PACIFIC...WITH SUCCESSIVE POLAR FRONTS FORECAST TO
REVOLVE AROUND THIS AXIS. THESE ARE TO THEN RAPIDLY STREAM ACROSS
THE SOUTHERN CONE OVER THE NEXT FEW DAYS...ENHANCING LOW LEVEL
CONVERGENCE WHILE SUSTAINING BOUNDARY LAYER WINDS OF 25-40KT.
INFLOW OF SUBTROPICAL MOISTURE AND STRONG TOPOGRAPHICAL FORCING IS
TO THEN FAVOR ORGANIZED CONVECTION. OVER THE NEXT FEW DAYS
EXPECTING MAXIMA BETWEEN CONCEPCION-ISLA DE CHILOE TO PEAK AT
30-60MM/DAY. THROUGH 72-84 HRS THIS IS TO INCREASE TO
50-100MM...WITH LOCALLY HIGHER AMOUNTS POSSIBLE DUE TO STRONG
TOPOGRAPHICAL FORCING. OTHER ACTIVITY TO THE NORTH IS EXPECTED
BETWEEN TALCA AND VALPARAISO IN CENTRAL CHILE...WITH RAINFALL
MAXIMA IN THIS AREA TO PEAK AT 20-30MM...WITH POTENTIAL FOR
ORGANIZED SNOWFALL AMOUNTS ACROSS THE CENTRAL ANDES OF CHILE ON
DAY 03.

AS THE FRONTS STREAM ACROSS CHILE TO ARGENTINA...THEY ARE TO
GRADUALLY MEANDER NORTH ACROSS RIO DE LA PLATA-CORDOBA IN
ARGENTINA TO URUGUAY/RIO GRANDE DO SUL BRASIL TO ENTRE RIOS
ARGENTINA. THIS WILL SUSTAIN A LOW LEVEL CONVERGENT PATTERN ACROSS
MESOPOTAMIA VALLEY IN ARGENTINA-URUGUAY AND RIO GRANDE DO SUL IN
BRASIL. FURTHERMORE...BROAD RIDGE OVER THE WESTERN ATLANTIC IS TO
SUSTAIN A NORTHERLY JET ACROSS BOLIVIA-PARAGUAY TO CENTRAL
PROVINCES IN ARGENTINA. THIS WILL ADVECT WARM MOIST AIR
SOUTH...HELPING SUSTAIN A HIGH MOISTURE CONTENT VALUE AHEAD OF THE
SURFACE FRONT TO THE SOUTH. THROUGH 36-48 HRS THE INFLOW OF MOIST
AIR IS FORECAST TO INTENSIFY. THESE...IN INTERACTION WITH
AFOREMENTIONED SHORT WAVE PERTURBATIONS WILL SUSTAIN SCATTERED
CONVECTION...RESULTING IN ACCUMULATION OF 15-25MM/DAY. THIS IS TO
START ON DAY 01 AND PERSIST THROUGH DAY 05. NOTE THAT ON DAY 04-05
MODELS SUGGEST POSSIBILITY OF SEVERE CONVECTION DEVELOPING IN THIS
AREA AS DEEP MID LEVEL SHORT WAVE TROUGH CROSSES THE CONTINENT.
ALTHOUGH MODELS FORESEE A VERY UNSTABLE AIR MASS...JET DYNAMICS
APPEAR MARGINAL AT BEST...REDUCING POTENTIAL FOR SEVERE CONVECTION
TO LOW.

ANOTHER MESO-SYNOPTIC FEATURE OF INTEREST IS AN ELONGATED FRONT
WITH AXIS WEST-NORTHWEST ACROSS THE SOUTH ATLANTIC TO ESPIRITO
SANTO/EASTERN BAHIA. ALSO...UNDER INFLUENCE OF THE SOUTH ATLANTIC
RIDGE...THE MODELS FORECAST A STRONG SOUTHEASTERLY FLOW OF 25-30KT
ACROSS ESPIRITO SANTO/BAHIA. AS MOISTURE CONVERGES ALONG THE
SURFACE FRONT THE STRONG EASTERLIES WILL ENHANCE CONVECTIVE
DEVELOPMENT. THROUGH 36-48 HRS THIS WILL INCREASE TO
20-40MM...WITH LOCALLY HIGHER AMOUNTS HIGHLY LIKELY. THROUGH
96-108 HRS THIS DECREASES TO 10-15MM/DAY.

NORTH OVER THE CONTINENT...AT 200 HPA...A HIGH SOUTH OF THE
GALAPAGOS ISLANDS IS TO ANCHOR A RIDGE OVER THE EASTERN TROPICAL
PACIFIC. THIS WILL PERSIST OVER THE NEXT 48-72 HRS. A SHORT WAVE
TROUGH LIES TO THE EAST...WITH AXIS NORTHWEST ACROSS MATO GROSSO
IN BRASIL TO AMAZONAS/SOUTHERN COLOMBIA. THROUGH 72-96 HRS THE
TROUGH IS TO DAMPEN AS THE RIDGE TO THE WEST WEAKENS.
MEANWHILE...THE SHORT WAVE TROUGH IS TO ENHANCE CONVECTIVE
INSTABILITY ACROSS NORTHWEST BRASIL-NORTHERN JUNGLE OF
PERU/EASTERN ECUADOR...WITH DIURNAL CONVECTION IN THIS AREA TO
INITIALLY PEAK AT 10-15MM. THROUGH 72 HRS THIS DECREASES TO
05-10MM AS PATTERN TO THE WEST STARTS TO EVOLVE AND SHORT WAVE
TROUGH WEAKENS. A TROPICAL DISTURBANCE ALONG THE ATLANTIC ITCZ IS
TO ALSO ENHANCE CONVECTIVE DEVELOPMENT ALONG THE NORTH COAST OF
BRASIL...TO RESULT IN RAINFALL AMOUNTS OF 10-15MM/DAY. THROUGH
72-96 HRS THIS IS TO SPREAD WEST ACROSS AMAPA IN BRASIL TO THE
GUIANAS.

FERNANDES...INMET (BRASIL)
JALFIN...SMN (ARGENTINA)
DAVISON...WPC (USA)
$$




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