Prognostic Meteorological Discussion
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FXSA20 KWBC 261448
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
948 AM EST WED NOV 26 2014

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

NOTE: FORECAST PRODUCTS WILL NOT BE AVAILABLE ON NOVEMBER 27-28.

MODEL DISCUSSION (VALID FROM NOVEMBER 26 AT 00UTC): GLOBAL AND
ENSEMBLE GLOBAL MEMBERS CONTINUE TO AGREE ON PATTERN EVOLUTION
THROUGH 96-108 HRS. THEY DO STILL DIVERGE...HOWEVER...ON HOW MID
LEVEL TROUGH ENTERS THE SOUTHERN CONE BY MID-CYCLE. SOME
UNCERTAINTY LIES ON THE EXACT EVOLUTION OF THIS TROUGH...AND ON
HOW FAR NORTH THIS IS GOING TO EVOLVE.

AT MID LEVELS...LONGER WAVE PATTERN IS ESTABLISHING. NEXT TROUGH
OF INTEREST IS FORECAST TO AMPLIFY AND ORGANIZE AS IT APPROACHES
FROM THE EASTERN PACIFIC TO CROSS THE ANDES ON FRIDAY INTO
SATURDAY. INITIALLY...WEAK SHORT WAVE TROUGH WILL PRECEDE AND WILL
LEAD TO HEIGHT FALLS OF 25-75GPM IN NORTHERN PATAGONIA DURING
THURSDAY. THIS WILL TRIGGER SOME CONVECTION...YET MOISTURE WILL BE
THE LIMITATION. EXPECTING ACCUMULATIONS OF 05-10MM/DAY DURING
THURSDAY INTO EARLY SATURDAY. MAIN TROUGH HOWEVER WILL PUSH IN
FROM THE WEST DURING FRIDAY INTO SATURDAY. AS MAIN TROUGH
APPROACHES CHILE...IT WILL ENHANCE ACCUMULATIONS SOUTH OF PUERTO
MONTT TO PRODUCE MAXIMA OF 10-15MM/DAY DURING THURSDAY. AMOUNTS
WILL DECREASE AFTERWARDS. ACROSS ARGENTINA HOWEVER...TROPICAL
MOISTURE WILL HAVE RETURNED BY LATE FRIDAY-SATURDAY. ALTHOUGH
EXACT PROGRESSION OF SYSTEM IS STILL BECOMING MORE CLEAR AS NEW
RUNS APPEAR...THE SYNOPTIC SETUP IS LOOKING IDEAL FOR A SEVERE
WEATHER EVENT THAT WILL LIKELY INCLUDE A PRE-FRONTAL SQUALL LINE
AND HEAVY RAINFALL. BY SATURDAY EVENING COLD FRONT IS EXPECTED TO
RACE INTO THE RIO DE LA PLATA REGION-SANTA FE-SOUTHERN SANTIAGO
DEL ESTERO PRECEDED BY A PRE-FRONTAL SQUALL LINE. STRONG
THUNDERSTORMS ARE TO PRODUCE ACCUMULATIONS OF 50-10MM/DAY IN
SEVERE CONVECTION. BY SUNDAY...FRONT WILL START TO STALL ACROSS
RIO GRANDE DO SUL INTO EXTREME SOUTHERN PARAGUAY-CHACO IN
ARGENTINA. PRE-FRONTAL SQUALL LINE IS EXPECTED TO THE NORTH ACROSS
SANTA CATARINA INTO MISIONES-SOUTHEASTERN PARAGUAY. THIS WILL LEAD
TO ACCUMULATIONS OF 40-80MM/DAY IN STRONG THUNDERSTORMS...STILL
WITH A RISK FOR SEVERE WEATHER.

NORTH ACROSS THE CONTINENT...SUBTROPICAL HIGH IS ESTABLISHED OVER
SOUTHERN MATO GROSSO RIDGING TO THE NORTHEAST INTO NORTHERN PERU.
A RATHER STRONG UPPER LOW IS FORECAST TO RETROGRESS INTO THE
CENTRAL AMAZON ARRIVING INTO THE DELTA ON FRIDAY AND MOVING JUST
EAST OF RORAIMA INTO SUNDAY. PRECIPITATION WILL HOWEVER BE LIMITED
BY STRONG SUBSIDENCE INVERSION. AS THIS SYSTEM PUSHES
IN...EXPECTING THE SUBTROPICAL RIDGE TO GRADUALLY BECOME NARROW
AND ELONGATED FROM PERU INTO PARTS OF SOUTHEASTERN BRASIL THROUGH
THE CYCLE. THIS WILL VENTILATE CONVECTION IN THESE REGIONS...IN
ASSOCIATION WITH FEATURES AT THE LOW-LEVELS AND PLENTIFUL
CONVECTIVE INSTABILITY. INITIALLY...FOCUS FOR CONVECTION WILL BE
THE NORTHERN TIER OF TROUGH THAT EXTENDS FROM MATO GROSSO DO SUL
INTO SOUTHERN PERU/NORTHERN BOLIVIA. THIS WILL LEAD TO
ACCUMULATIONS OF 30-60MM/DAY THROUGH SATURDAY. DIURNAL CONVECTION
ACROSS SOUTHEASTERN BRASIL INTO SAO PAULO/PARANA IS TO PRODUCE
MAXIMA OF 20-45MM/DAY THROUGH EARLY THURSDAY. BY THURSDAY INTO
EARLY FRIDAY...EXPECTING AN INCREASE IN ACCUMULATIONS TO MAXIMA OF
30-60MM/DAY. AMOUNTS ARE TO START DECREASING AFTERWARDS...TO
PRODUCE SCATTERED MAXIMA OF 20-40MM/DAY IN DIURNAL CONVECTION FOR
THE REST OF THE CYCLE. TO THE WEST ACROSS THE PERUVIAN/ECUADORIAN
AMAZON...AMOUNTS WILL GRADUALLY DECREASE FROM MAXIMA OF
20-40MM/DAY BY FRIDAY INTO EARLY SATURDAY...TO MAXIMA OF
10-15MM/DAY INTO EARLY MONDAY. A RETURN OF MOIST MID-UPPER
EASTERLIES ACROSS THE CENTRAL ANDES WILL LEAD TO A REACTIVATION OF
THE DIURNAL CONVECTION TO PRODUCE SCATTERED MAXIMA OF 05-10MM/DAY
STARTING SATURDAY AND CONTINUING MONDAY.

CAROCA...DMC (CHILE)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)
$$




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