Prognostic Meteorological Discussion
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000
FXSA20 KWBC 251638
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1238 PM EDT MON JUL 25 2016

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

MODEL DISCUSSION (VALID FROM JULY 25 AT 0000 UTC): A MID LEVEL
SHORT WAVE TROUGH IN THE NORTHERN STREAM IS THE SYSTEM OF
CONCERN...WITH SYSTEM FORECAST TO TRIGGER HEIGHTS FALLS OF
100-150GPM AS IT PULLS ACROSS RIO DE LA PLATA BASIN/MESOPOTAMIA
VALLEY IN ARGENTINA EARLY IN THE CYCLE. UNDER COUPLED JETS...THE
TROUGH IS FORECAST TO RAPIDLY INTENSIFY THROUGH 48 HRS WHILE
MEANDERING EAST INTO THE WESTERN ATLANTIC. THROUGH 120 HRS IT IS
TO THEN SLOWLY PULL TO THE EAST-SOUTHEAST ACROSS THE CENTRAL SOUTH
ATLANTIC. AT LOW LEVELS THE MID LEVEL PERTURBATION IS INTERACTING
WITH A SURFACE FRONT OVER CENTRAL ARGENTINA...TRIGGERING
CYCLOGENESIS OVER ENTRE RIOS ARGENTINA/ URUGUAY. THROUGH 24-36 HRS
THIS LOW IS TO RAPIDLY DEEPEN... INTENSIFYING FROM A 1010 HPA LOW
LATER TODAY TO A 998 HPA LOW EARLY ON TUESDAY MORNING. RAPID
INTENSIFICATION IS TO PERSIST THROUGH WEDNESDAY EVENING...WHEN THE
LOW IS TO REACH MAXIMUM INTENSITY. THE DEEPENING LOW WILL DRIVE A
FRONT NORTH ACROSS URUGUAY/SOUTHERN BRASIL TO PARAGUAY LATER
TODAY. AS IT SURGES NORTH THIS IS LIKELY TO TRIGGER SEVERE
CONVECTION ACROSS NORTHERN URUGUAY/RIO GRANDE DO SUL-MISIONES IN
ARGENTINA...WITH MAXIMA IN THIS AREA TO PEAK AT 25-50MM. HIGHER
AMOUNTS...HOWEVER... ARE TO CLUSTER ACROSS SOUTHERN URUGUAY-ENTRE
RIOS IN ARGENTINA WHERE THE OCCLUDING LOW IS TO SUSTAIN BOUNDARY
LAYER WINDS OF 35-45KT AND A MOIST ONSHORE FLOW. IN THIS AREA
MAXIMA IS TO PEAK AT 75-125MM. STRONG COASTAL WINDS AND HEAVY
RAINS ARE TO GRADUALLY WANE DURING THE DAY ON TUESDAY.

FARTHER UPSTREAM...BROAD TROUGH IS TO PULL ACROSS THE SOUTHEAST
PACIFIC. AS IT PRESSES AGAINST A MID LEVEL RIDGE TO THE EAST THE
TROUGH IS TO SLOW TO A CRAWL. THROUGH 72-84 HRS THE RIDGE WEAKENS
ENOUGH TO ALLOW THE TROUGH TO FINALLY MOVE INLAND INTO THE
SOUTHERN REGIONS OF CHILE...AND BY 108-120 HRS IT IS TO MOVE INTO
PATAGONIA IN ARGENTINA. AT LOW LEVELS THIS WILL SUSTAIN A DEEP
OCCLUDED LOW AND STRONG BOUNDARY LAYER WINDS BY 66-84 HRS. BEST
MOISTURE CONVERGENCE...HOWEVER...IS EXPECTED BY 96-108 HRS WHEN
ONSHORE FLOW AND TOPOGRAPHICALLY INDUCED CONVECTION INTENSIFIES.
MOST INTENSE IS EXPECTED BETWEEN TEMUCO AND ISLA DE CHILOE...WHERE
THE MAXIMA PEAKS AT 25-50MM. BETWEEN TEMUCO AND CONCEPCION THE
MAXIMA IS TO ONLY PEAK AT 10-15MM.

NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE
SUBTROPICAL RIDGE DOMINATES AREA TO THE NORTH OF 30S. AS THE
AFOREMENTIONED MID/UPPER LEVEL PERTURBATION MOVES EAST...AND THE
ASSOCIATED FRONT ADVANCES NORTH ACROSS MID SECTIONS OF SOUTH
AMERICA...THE UPPER LEVEL RIDGE PATTERN IS FORECAST TO WEAKEN.
THROUGH 36-48 HRS THE RIDGE IS TO NEARLY COLLAPSE...WITH A NEAR
ZONAL WESTERLY FLOW TO THEN ESTABLISH ACROSS TROPICAL AND
SUBTROPICAL SOUTH AMERICA. IN THIS PATTERN MOST ACTIVE CONVECTION
IS EXPECTED NORTH OF THE EQUATOR ALONG THE NEAR EQUATORIAL TROUGH.
OTHER DIURNAL CONVECTION IS TO BUILD ACROSS AMAZONIA IN SOUTHERN
COLOMBIA TO NORTHERN JUNGLE OF PERU/EASTERN ECUADOR...WHERE THE
MAXIMA IS TO PEAK AT 15-25MM OVER THE NEXT FEW DAYS.

AYALA...DINAC (PARAGUAY)
OSORIO...DMC (CHILE)
DAVISON...WPC (USA)
$$




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