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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1706Z Jan 22, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1206 PM EST THU JAN 22 2015

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

MODEL DISCUSSION (VALID FROM JANUARY 22 AT 00UTC): ONCE AGAIN
MODELS AGREE QUITE WELL ON PATTERN EVOLUTION THROUGH DAY 04...THEN
DEVELOP SOUTHERN STREAM PATTERN DIFFERENCES DURING THE LATTER PART
OF THE FORECAST. AS A RESULT...OUR CONFIDENCE IN THE FORECAST
BEYOND 96-108 HRS IS LOW.

A MID LEVEL RIDGE IS TO ANCHOR OVER THE EASTERN PACIFIC...WITH
AXIS EAST ACROSS NORTHERN CHILE-ARGENTINA TO PARAGUAY/SOUTHERN
STATES OF BRASIL. THIS RIDGE IS TO GENERALLY HOLD OVER THE NEXT
FEW DAYS. BUT AS SUCCESSIVE PERTURBATIONS STREAM TO THE
SOUTH...SOME WEAKENING IS POSSIBLE DURING THE LATTER PART OF THE
FORECAST. MEANWHILE...THIS IS TO STEER SHORT WAVE VORTICES
EASTWARD ACROSS THE SOUTHERN CONE... WITH ONE TO PULL ACROSS LA
PAMPA-CENTRAL PROVINCES IN ARGENTINA THROUGH 24 HRS...THEN DRIFT
OFF THE COAST INTO THE WESTERN ATLANTIC BY 42-48 HRS. AS IT PULLS
ACROSS CENTRAL ARGENTINA THIS IS TO SUSTAIN HEIGHT FALLS OF
35-60GPM. THE INFLOW OF COLD AIR ALOFT IS TO COMBINE WITH A
WARM/MOIST ADVECTIVE LOW LEVEL PATTERN TO FAVOR GENERATION OF
SCATTERED CONVECTION ACROSS LA PAMPA-NORTHERN PATAGONIA IN
ARGENTINA. MOST INTENSE IS EXPECTED THROUGH 24-30 HRS...WHERE IN
POTENTIALLY SEVERE CONVECTION WE NOW EXPECT MAXIMA OF 25-50MM.

OTHER PERTURBATIONS ON THE SOUTHERN STREAM FLOW ARE TO
FOLLOW...WITH ONE TO QUICKLY MOVE ACROSS THE DRAKE
PASSAGE/PATAGONIA IN ARGENTINA BY 24 HRS. BUT AS IT PRESSES
AGAINST THE RIDGE TO THE NORTH...THE TROUGH IS FORECAST TO WEAKEN
TO A SHORT WAVE TROUGH OVER THE SOUTHWEST ATLANTIC BY 48 HRS. THE
ASSOCIATED SURFACE FRONT IS TO MOVE EXTEND ACROSS PATAGONIA IN
ARGENTINA/SOUTHERN CHILE EARLY IN THE CYCLE. IT IS TO THEN STALL
ACROSS LA PAMPA/SOUTHERN BUENOS AIRES PROVINCE-CENTRAL CHILE
THROUGH 72-84 HRS. MOST ACTIVE CONVECTION WITH THIS FEATURE IS
EXPECTED OVER SOUTHERN CHILE THROUGH 36 HRS... WHEN IT IS TO
SUSTAIN RAINFALL MAXIMA OF 15-20MM. ACROSS CENTRAL ARGENTINA THIS
DECREASES TO 00-05MM IN SCATTERED CONVECTION.

ANOTHER MID LEVEL PERTURBATION RACES ACROSS THE SOUTHEAST PACIFIC
TO SOUTHERN CHILE BY 54-60 HRS. THIS IS TO RAPIDLY PULL ACROSS THE
SOUTHERN CONE TO THE WESTERN ATLANTIC BY 72 HRS...AND ACROSS 40W
BY 96 HRS. THE ASSOCIATED SURFACE FRONT MOVES EAST ACROSS TIERRA
DEL FUEGO CHILE BY 48-54 HRS...INTO PATAGONIA BY 72 HRS. THROUGH
84-96 HRS IT IS TO REINFORCE/MERGE WITH THE OLD FRONT TO THE
NORTH. AS IT ENTERS SOUTHERN CHILE THIS IS TO ONLY TRIGGER LIGHT
CONVECTION... LIKEWISE OVER CENTRAL ARGENTINA...WITH MOST ACTIVE
ACROSS RIO DE LA PLATA BASIN LATER ON DAY 04.

NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE
SUBTROPICAL RIDGE EXTEND ACROSS SOUTHERN BRASIL-PARAGUAY-BOLIVIA
TO PERU...CENTERING ON A HIGH OVER SOUTHWESTERN BOLIVIA. THROUGH
24-48 HRS THE HIGH MOVES WEST TO THE EASTERN PACIFIC...TO THEN
REMAIN OFF THE NORTH COAST OF CHILE/SOUTH COAST OF PERU THROUGH
72-96 HRS.  ASSOCIATED RIDGE...MEANWHILE...IS FORECAST TO
GRADUALLY WANE THROUGH 96 HRS. MEANWHILE...THIS IS TO VENT DEEP
CONVECTION ACROSS SOUTHERN PERU TO THE ALTIPLANO IN BOLIVIA. EARLY
ON EXPECTING MAXIMA OF 05-10MM. THROUGH 48 HRS THIS INCREASES TO
10-15MM/DAY.

ALSO AT UPPER LEVELS...A 200 HPA LOW OVER ESPIRITO SANTO IN BRASIL
 ANCHORS A TROUGH ACROSS NORTHEAST-CENTRAL BRASIL. THROUGH 48
HRS...AS THE RIDGE PATTERN TO THE WEST EVOLVES...THE TROUGH IS TO
ALIGN ACROSS BAHIA IN BRASIL TO PARA. BUT AS THE RIDGE TO THE WEST
WEAKENS...THROUGH ALOFT IS TO ALSO WEAKEN. MEANWHILE...THIS IS TO
ENHANCE CONVECTIVE DEVELOPMENT ALONG THE NEAR EQUATORIAL TROUGH
OVER NORTHWEST BRASIL-SOUTHERN COLOMBIA-NORTHERN PERU...WHERE WE
EXPECT MAXIMA OF 20-45MM. THROUGH 48-72 HRS CONVECTION BUILD EAST
ACROSS NORTHERN PARA...WITH MAXIMA OF 20-45MM. ACROSS MATO
GROSSO-TOCANTINS/GOIAS EXPECTING RAINFALL AMOUNTS OF 15-20MM/DAY
IN DIURNAL CONVECTION.

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