443
FXUS02 KWBC 171933
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
320 PM EDT SAT OCT 17 2009
VALID 12Z TUE OCT 20 2009 - 12Z SAT OCT 24 2009
MEAN 500 MILLIBAR PATTERN SHOWS PACIFIC ENERGY FLATTENING A WRN
CONUS RIDGE IN THE SHORT RANGE...WITH A FLAT RIDGE REMAINING OVER
WRN CANADA. RATHER ZONAL MEAN FLOW AT THE BEGINNING OF THE MEDIUM
RANGE PERIOD SHOWS SIGNS OF RE-AMPLIFYING DURING THE LATTER HALF
OF THE PERIOD WITH A MEAN NEGATIVE HEIGHT ANOMALY DEVELOPING OVER
THE CENTRAL/SRN PLAINS IN RESPONSE TO RIDGING OFF THE CA COAST AND
A DEEP NEGATIVE HEIGHT ANOMALY OVER THE E CENTRAL PAPCIFIC.
FINAL PROGS MADE NO SIGNIFICANT CHANGES TO THE UPDATED PRELIM
PRODUCT. THE DAY 3-7 FCST WAS BASED ON THE 12Z/16 AND 00Z/17
DETERMINISTIC ECMWF AND 00Z/17 GEFS/ECMWF ENSEMBLE GUIDANCE IN
LIGHT OF THEIR BETTER OVERALL CONSENSUS. EVEN THOUGH THERE IS
BETTER AGREEMENT TODAY AMONG THE DETERMINISTIC GFS AND ECMWF
MODELS ON SHORTWAVES AFFECTING THE LOWER 48...MODEL ENSEMBLE
MEANS...ESPECIALLY THOSE OF THE CANADIAN AND ECMWF...SUGGEST AN
AREA OF HIGH UNCERTAINTY DEVELOPING OVER THE MID AND UPPER MS VLY
THU DAY 5. THIS AREA SPREADS NE THEREAFTER ACROSS THE GREAT LAKES
INTO THE ST LAWRENCE SEAWAY...ON THE NRN EDGE OF THE DEVELOPING
NEGATIVE HEIGHT ANOMALY.
CONSENSUS OF 12Z/17 MODELS SUPPORTS OUR UPDATED PRELIM GRAPHICS.
WE ARE STILL SEEING A FAIR AMOUNT OF SPREAD IN THE LATEST 12Z/17
DETERMINISTIC MODELS ESPECIALLY FOR THE LATTER PORTION OF NEXT
WEEK. THE 12Z/17 GFS HAS GREAT CONTINUITY WITH ITS PREVIOUS 00Z
RUN THRU DAY 5. IT THEN DEPARTS FROM CONTINUITY DAYS
6-7...WEAKENING A SHORTWAVE CROSSING THE ROCKIES DAY 7 WHILE
STRENGTHENING AND SL0WING DOWN THE SRN END OF THE DOWNSTREAM TROF
APPROACHING THE APPALACHIANS. THE 12Z/17 ECMWF...HOWEVER...ALSO
HAS GREAT CONTINUITY THRU DAY 6 BUT AGREES WITH ITS GFS
COUNTERPART IN SHARPENING THE SRN END OF THE TROF BY SAT DAY 7. IT
IS A HALF FARTHER W WITH THIS SHARPENING THAN THE GFS. THE 12Z
UKMET CONTINUES UNIQUE IN PUTTING SO MUCH ENERGY IN THE NRN
PORTION OF THE TROF CROSSING THE ERN PORTION OF THE CONUS DAYS
5-6...AT THE EXPENSE OF ENERGY IN THE SRN PORTION OF THE TROF
WHICH IT DEPICTS AS TOO SEPARATED/FAR S/WEAK. IT AND THE CANADIAN
ALSO APPEAR TO STRING OUT TOO MUCH ENERGY ACROSS THE SWRN STATES
DAY 6. IN GENERAL..THE 12Z/17 GFS/ECMWF SOLUTIONS LOOK REASONABLE.
THE PRECIP FORECAST TODAY NOT QUITE AS UNCERTAIN AS YESTERDAY. IN
LINE WITH OUR PREFERRED CONSOLIDATED GFS/ECMWF SOLUTION ALOFT...WE
EXPECT AN ORGANIZED AREA OF PCPN TO DEVELOP IN THE DEFORMATION
ZONE OF THE UPPER TROF/CLOSING OFF LOW WED DAY 4...AS CONVECTIVE
PRECIP BREAKS OUT ON THE TRAILING SRN END OF THE COLD FRONT. BY
THU DAY 5...WE EXPECT A MATURE AREA OF CONVECTIVE PRECIP TO BE IN
FORCE ALONG THE TRAILING PORTION OF THE LOWER MS VLY COLD FRONT.
WE EMPHASIZED THE QPF IN THIS CONVECTIVE REGION DAYS 5 AND BEYOND
AS IT SHIFTS EWD WHILE DOWNPLAYING THE STILL SIGNIFICANT
DEFORMATION ZONE PRECIP FARTHER N.
CONSULT THE LATEST DISCUSSION/ADVISORY FOR FURTHER INFO REGARDING
HURCN RICK WHICH IS FCST TO TRACK OVER THE ERN TROPICAL PAC AND
APPROACH SRN BAJA CALIF BY MID-PERIOD. THE UPDATED PRELIM FCST
REPRESENTS EXTRAPOLATION FROM THE 17/1200Z TPC ADVISORY. MAIN
CONCERN HERE WOULD BE WHETHER SOME OF RICKS MID AND HIGH LEVEL
MOISTURE WOULD EVENTUALLY AFFECT TX LATE IN THE PERIOD. THE
12Z/17 CANADIAN/UKMET WOULD DRAW THIS HIGH LEVEL MOISTURE INTO TX
PREMATURELY.
FLOOD
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page