Prognostic Meteorological Discussion
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FXSA20 KWBC 221618
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1218 PM EDT TUE AUG 22 2017

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

MODEL DISCUSSION (VALID FROM AUG 22 AT 0000 UTC): SHORT WAVE
TROUGH ON THE NORTHERN STREAM MEANDERS OVER THE SOUTH ATLANTIC
NEAR 39S 25W. THROUGH FRIDAY EVENING THE LOW IS TO MEANDER TO 19S
17W. MEANWHILE...AT LOW LEVELS...THIS SUSTAINS AN OCCLUDING LOW
OVER THE CENTRAL SOUTH ATLANTIC...WITH ASSOCIATED FRONT TRAILING
ACROSS RIO DE JANEIRO-SAO PAULO-MATO GROSSO TO RONDONIA IN BRASIL.
THROUGH WEDNESDAY EVENING THE FRONT IS FORECAST TO FRONTOLIZE OVER
THE CONTINENT...WHILE TRAILING END PERSIST OVER ESPIRITO
SANTO/MINAS GERAIS IN BRASIL. EARLY IN THE CYCLE THIS WILL SUSTAIN
SCATTERED CONVECTION ACROSS MATO GROSSO IN BRASIL WITH
ACCUMULATION OF 05-10MM. AS THE FRONT WEAKENS OVER THE
CONTINENT...THIS IS TO THEN ENHANCE COASTAL CONVECTION ACROSS
NORTHEAST BRASIL TO RESULT IN RAINFALL AMOUNTS OF 05-10MM/DAY.
THROUGH THURSDAY THIS INCREASES TO 15-20MM...WITH MOST INTENSE
OVER PERNAMBUCO/RIO GRANDE DO NORTE.

FARTHER UPSTREAM...A HIGH AMPLITUDE LONG WAVE RIDGE IS BUILDING
OVER THE SOUTH PACIFIC BETWEEN 125W-105W.
THIS...IN-TURN...SUSTAINS THE NORTHWARD AMPLIFICATION OF A TROUGH
ACROSS SOUTHERN/CENTRAL CHILE TO ARGENTINA. THE TROUGH IS FOCUSING
SHORT WAVE ENERGY ACROSS CENTRAL CHILE INTO CUYO/CENTRAL
ARGENTINA...WHERE IT SUSTAINS HEIGHT FALLS OF 75-150GPM. THE LONG
WAVE AXIS IS FORECAST TO PERSIST DURING THE NEXT 72-84 HRS. AS IT
HOLDS...IT IS TO FOCUS A STRONG SUBTROPICAL/ POLAR JET PAIR ACROSS
CENTRAL REGIONS OF CHILE TO CENTRAL PROVINCES IN ARGENTINA. THE
JET ALOFT IS TO INITIALLY FAVOR A DIVERGENT PATTERN ACROSS CENTRAL
CHILE. ON WEDNESDAY TO THURSDAY THIS IS TO SPREAD TO RIO DE LA
PLATA BASIN/ENTRE RIOS IN ARGENTINA. AT LOW LEVELS THIS SUSTAINS A
DEEP OCCLUDED LOW OVER THE DRAKE PASSAGE/ SOUTHERN CONE OF SOUTH
AMERICA EARLY IN THE CYCLE. THE ASSOCIATED FRONT WILL EXTEND
ACROSS NORTHERN PATAGONIA-CENTRAL REGIONS OF CHILE LATER TODAY. ON
WEDNESDAY IT PUSHES NORTH ACROSS RIO DE LA PLATA-MENDOZA IN
ARGENTINA...WHERE IT IS TO THEN REMAIN NEARLY STATIONARY THROUGH
THE END OF THE WEEK. EARLY IN THE CYCLE THE HIGH AMPLITUDE TROUGH
IS TO SUSTAIN A MOIST ADVECTIVE PATTERN ACROSS CENTRAL REGIONS OF
CHILE...WHERE IT IS TO SUSTAIN MODERATE TO HEAVY CONVECTION. ALONG
THE CENTRAL COAST THIS WILL RESULT IN RAINFALL AMOUNTS OF
15-20MM...WHILE OVER THE ANDES IT IS TO TRIGGER SNOWFALL AMOUNTS
OF 25-50CM. FARTHER EAST...A NORTHERLY LOW LEVEL JET ACROSS
BOLIVIA/PARAGUAY TO CENTRAL ARGENTINA IS TO SUSTAIN A MOIST
ADVECTIVE PATTERN AHEAD OF THIS BOUNDARY. THIS WILL FEED
CONVECTIVE DEVELOPMENT OVER THE RIO DE LA PLATA BASIN-ENTRE RIOS
IN ARGENTINA ON WEDNESDAY AND ONWARD. THE SLOW TO EVOLVE PATTERN
WILL RESULT IN SEVERAL DAYS OF HEAVY RAINFALL AMOUNTS...WITH
ENVIRONMENTAL CONDITIONS TO FAVOR THE FORMATION OF MESO SCALE
CONVECTIVE SYSTEMS ON THURSDAY AND FRIDAY. ON WEDNESDAY EXPECTING
RAINFALL AMOUNTS OF 20-35MM. ON THURSDAY THIS INCREASES TO 35-70MM
IN POTENTIALLY SEVERE CONVECTION...WHILE ON FRIDAY THE MAXIMA WILL
RANGE BETWEEN 40-80MM.

AS THE MID/UPPER LEVEL RIDGE BUILDS TO THE WEST...THIS WILL STEER
A PROGRESSIVE SHORT WAVE TROUGH ON THE SOUTHERN STREAM FLOW ACROSS
THE SOUTHEAST PACIFIC TO SOUTHERN PORTIONS OF CHILE LATER ON
WEDNESDAY. STRONG LOW LEVEL WINDS OF 35-50KT ARE TO ACCOMPANY THIS
SYSTEM AS IT MAKES LANDFALL OVER SOUTHERN CHILE/PATAGONIA IN
ARGENTINA ON WEDNESDAY EVENING. THIS WILL SUSTAIN A COLD ADVECTIVE
PATTERN THAT IS LIKELY TO TRIGGER THUNDERSTORMS AS IT MAKES
LANDFALL BETWEEN TEMUCO AND ISLA DE CHILOE...TO RESULT IN RAINFALL
AMOUNTS OF 20-40MM ON WEDNESDAY. SOUTH OF CHILOE THE MAXIMA WILL
PEAK AT 10-15MM IN MIXED PRECIPITATION (RAIN AND SNOW). ON
THURSDAY THE AIR MASS WILL COOL ENOUGH TO SUSTAIN SCATTERED SNOW
SHOWERS ACROSS THE SOUTHERN ANDES/TIERRA DEL FUEGO...WHERE WE
EXPECT SNOWFALL AMOUNTS OF 05-10CM.

A DEEPER TROUGH IN THE SOUTHERN STREAM IS TO FOLLOW...WITH MID
LEVEL VORTEX NEARING SOUTHERN CHILE LATER ON FRIDAY. THIS IS THEN
TO STALL OFF THE SOUTH COAST ON FRIDAY-SATURDAY...MEANWHILE
FOCUSING SHORT WAVE ENERGY BETWEEN CONCEPCION AND PUERTO MONTT IN
SOUTHERN CHILE. THIS IS TO ALSO FAVOR STRONG LOW LEVEL WINDS AND
MODERATE RAINFALL AMOUNTS...WITH MAXIMA OF 20-35MM EXPECTED
BETWEEN TEMUCO-PUERTO MONTT...AND 15-20MM BETWEEN PUERTO MONTT AND
ISLA DE CHILOE.

NORTH OVER THE CONTINENT...A 200 HPA RIDGE IS TO EXTEND WEST
ACROSS THE TROPICAL ATLANTIC TO NORTHERN BRASIL. THE RIDGE IS TO
CONFINE TO AREA NORTH OF 10S DURING THE NEXT THREE DAYS...WITH A
SECONDARY HIGH/RIDGE TO DEVELOP OVER AMAZONAS IN BRASIL-NORTHERN
PERU/ECUADOR LATER DURING THE WEEKEND. THE RIDGE ALOFT IS TO VENT
CONVECTION ACROSS SOUTHERN COLOMBIA-NORTHERN AMAZONAS IN
BRASIL-NORTHERN JUNGLE OF PERU AND EASTERN ECUADOR. IN THIS AREA
EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY WITH MAXIMA OF 15-25MM
IN SCATTERED DEEP CONVECTION. OVER THE AMAZON RIVER DELTA REGION
AND AMAPA TO THE NORTH EXPECTING RAINFALL AMOUNTS OF
05-10MM/DAY...WITH LOCALIZED MAXIMA OF 15MM.

GONZALEZ...DMC (CHILE)
VANNUCCI...SMN (ARGENTINA)
GALVEZ...WPC (USA)
$$





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