Prognostic Meteorological Discussion
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1105 AM EST FRI DEC 19 2014

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

MODEL DISCUSSION (VALID FROM DECEMBER 19 AT 00UTC): STRONG
AGREEMENT AMONG GLOBAL MODEL GUIDANCE...AS THEY CONTINUE TO
FORECAST A HIGH AMPLITUDE/LONG WAVE RIDGE TO ESTABLISH OVER THE
EASTERN SOUTH PACIFIC. THE MID LEVEL RIDGE IS TO EXTEND SOUTH
BETWEEN 120W-90W TO 70S. THE RIDGE REACHES MAXIMUM AMPLITUDE
THROUGH 24-36 HRS. IT IS TO THEN HOLD THROUGH 72-84 HRS. AT LOW
LEVELS IT IS TO SUSTAIN A BROAD RIDGE OVER THE EASTERN SOUTH
PACIFIC...FORECAST TO ANCHOR ON A 1031-1033 HPA HIGH.

AS THE RIDGE BUILDS TO THE WEST...IT IS TO SUSTAIN THE NORTHWARD
AMPLIFICATION OF A TROUGH ACROSS THE DRAKE PASSAGE TO THE SOUTHERN
CONE OF SOUTH AMERICA. THROUGH 24 HRS THE TROUGH AMPLIFIES ACROSS
CHILE/ARGENTINA TO 30S...MEANWHILE FOCUSING SHORT WAVE ENERGY
ACROSS THE CENTRAL PROVINCES. BY 48 HRS THE TROUGH WILL MOVE TO
25S...AND THROUGH 72 HRS IT REACHES 20S. THIS IS TO THEN SLOWLY
PULL TO THE EAST-SOUTHEAST...WITH CLOSED LOW TO FORM ALONG THIS
AXIS OVER RIO DE LA PLATA/URUGUAY BY 96-108 HRS. AS THE MID/UPPER
LEVEL TROUGH DEEPENS ACROSS ARGENTINA...IT IS TO DRIVE A SURFACE
FRONT NORTH ACROSS THE CONTINENT. THROUGH 24 HRS THE FRONT MOVES
NORTH ACROSS PATAGONIA/CENTRAL PORTIONS OF CHILE...TRIGGERING
SCATTERED DEEP CONVECTION WITH ACCUMULATION OF 15-30MM. BUILDING
POLAR RIDGE OVER ARGENTINA IS TO THEN SUSTAIN A PAMPERO
JET...SUSTAINING THE NORTHWARD ACCELERATION OF THE FRONT ACROSS
RIO DE LA PLATA BASIN/MENDOZA IN ARGENTINA. AS IT
ACCELERATES...THIS IS TO TRIGGER A PREFRONTAL SQUALL LINE THAT IS
TO AFFECT URUGUAY-NORTHERN PROVINCES IN ARGENTINA-SOUTHEAST
PARAGUAY. UNDER FAVORABLE JET DYNAMICS EXPECTING SEVERE
THUNDERSTORMS AND HEAVY RAINFALL AMOUNTS WITH MAXIMA OF 75-150MM.
STRONG MESO-SYNOPTIC FORCING IS LIKELY TO RESULT IN LOCALIZED
MAXIMA IN EXCESS OF 200MM. THROUGH 72-84 HRS THE FRONT MOVES NORTH
ACROSS PARANA IN BRASIL-PARAGUAY...AND BY 96 HRS IT IS TO EXTEND
ACROSS SAO PAULO-PARAGUAY. ACROSS SOUTHEAST BRASIL EXPECTING
STRONG CONVECTION TO PERSIST ON DAYS 04-05...WITH MAXIMA OF 35-70
HRS. HIGHER AMOUNTS ARE EXPECTED TO THE WEST...AS THE STRONG
PAMPERO JET EXPANDS ACROSS PARAGUAY/EASTERN BOLIVIA TO
RONDONIA/ACRE IN BRASIL. THIS IS TO ENHANCE MOISTURE CONVERGENCE
TO ACROSS NORTHERN BOLIVIA TO SOUTHERN PERU...WHERE WE EXPECT
MAXIMA OF 75-125MM. THROUGH 120-132 HRS ACTIVITY THEN BUILDS
ACROSS ACRE-AMAZONAS IN BRASIL TO CENTRAL/NORTHERN JUNGLE OF PERU
WITH MAXIMA IN THIS AREA TO PEAK AT 30-60MM LATER IN THE CYCLE.

AT 200 HPA...A RIDGE DOMINATES CONTINENTAL AREA TO THE NORTH OF
30S. THIS PATTERN IS TO PERSIST NEARLY UNCHANGED DURING THE NEXT
48-60 HRS. MEANWHILE...IT IS TO CENTER ON A CLOSED HIGH THAT
MEANDERS BETWEEN BOLIVIA AND MATO GROSSO IN BRASIL. AS DEEP POLAR
TROUGH ENTERS THE CONTINENT...AND COLD/DRY AIR ADVECTS ACROSS MID
SECTIONS OF SOUTH AMERICA...RIDGE TO THE NORTH IS TO WEAKEN AND
THE CLOSED HIGH REPOSITIONS TO SOUTHEAST BRASIL LATER ON DAY 03.
ALSO AT UPPER LEVELS...A TROUGH LIES TO THE EAST OF THIS
RIDGE...WITH AXIS NORTH ALONG THE NORTHEAST COAST OF BRASIL TO THE
TROPICAL ATLANTIC. AS RIDGE TO THE SOUTH WEAKENS...THE LOW/TROUGH
IS TO RETROGRESS TO NORTHEAST BRASIL. A BROAD AREA OF DIVERGENCE
ALOFT IS TO DEVELOP BETWEEN THIS TROUGH AND THE RIDGE TO THE WEST.
THIS IS TO VENT DEEP CONVECTION ACROSS NORTHEAST AND CENTRAL
STATES OF BRASIL...TO SUSTAIN SCATTERED CONVECTION WITH DAILY
MAXIMA OF 20-40MM. LOCALLY HIGHER AMOUNTS ARE HIGHLY LIKELY OVER
MOUNTAINOUS TERRAIN. BUT AS CONVECTION OVER MID SECTIONS OF SOUTH
AMERICA INTENSIFIES...THIS WILL DECREASE TO 15-30MM/DAY.

ARREAGA...INAMHI (ECUADOR)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)

$$




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