571
FXUS02 KWBC 241752
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
152 PM EDT THU SEP 24 2009
VALID 12Z SUN SEP 27 2009 - 12Z THU OCT 01 2009
OP MODELS AND ENSEMBLES ARE IN VERY GOOD AGREEMENT FOR THE SECOND
DAY IN ROW FROM THE EPAC TO THE WRN ATLC. CLOSED TO CUTOFF LOW
OVER THE CENTRAL PLAINS WILL EJECT OFF THE NE COAST DAY 3 SUN
WHILE A SHORTWAVE CURENTLY COMING INTO THE GLFAK DIVES SEWD ALONG
THE SRN CANADIAN PLAINS AND CLOSES OFF OVER THE GREAT LAKES REGION
FORMING AN INTENSE EARLY FALL STORM. THIS STORM MOVES EWD TO THE
CANADIAN MARITIMES MID TO LATE WEEK. NEXT STRONG EPAC SHORTWAVE
COMES INTO B.C AND THE PAC NORTHWEST MONDAY AMPLIFYING SWD THRU
THE GREAT BASIN AND WORKING EWD INTO THE PLAINS FRIDAY. THE ECMWF
IS FASTEST WITH THIS TROF ON ITS APPROACH TO THE COAST WITH
GFS/CMC/UKMET ABOUT 6 HRS SLOWER AND THE ECMWF ENS MEAN ALSO
FASTER.
LATE PERIOD..DAYS 7-8 THE CMC/GFS AND ECMWF DIFFER WITH THE AMOUNT
OF ENERGY LEFT AT TEH BASE OF THE PROGRESSIVE TROF COMING ACROSS
THE WEST AS ECMWF AND CMC LEAVE MORE BASE ENERGY AND SEPERATION
WHICH WOULD ALLOW FOR DIFFERENT SFC REFLECTION CYCLOGENSIS IN THE
PLAINS WHILE GFS WOULD SIMPLY PUSH A FRONT EWD TO THE MS VALLEY.
USING A BLEND OF OPERATIONAL 00Z GFS/ECMWF WOULD COMPENSATE THE
TIMING DIFFERENCE OF THE APPROACHING EPAC TROF. UPDATED HPC PROGS
USE A 50/50 GFS/ECMWF BLEND DAYS 3-5 FOLLOWED BY A 50/50 BLEND OF
GFS AND ECMWF ENSEMBLES FOR DAYS 6 AND 7. HIGH CONFIDENCE FORECAST
THROUGH THE PERIOD.
12Z GFS DAY 3 SHORTWAVE AND SFC LOW COMING INTO THE MID ATLC
REGION SEEMS TOO FAST AS PER HPC MODEL DIAG. SLOWING PROGRESSION
TOWARDS THE NAM FOR DAYS 3 AND 4 SUN/MON. ELSW LATE PERIOD THE 12Z
GFS HAS MORE AMPLITUDE IN THE BASE OF ITS WRN CONUS TROF BY DAYS 6
INTO 8 CLOSER TO THE SOLUTIONS OFFERED BY EMWF AND 12Z CMC.
UPDATED FINAL PROGS SLOW AND DEEPEN THIS SYSTEM CLOSER TOWARDS 00Z
ECMWF AS THE FRONT AND LOW COME INTO THE SRN AND CENTRAL PLAINS
THURS AND FRI.
A MODERATE TO LOCALLY HVY RAIN EVENT SUNDAY FROM THE MID ATLC
REGION NEWD INTO NEW ENG WITH THE FIRST EXITING SHORTWAVE. A HVY
RAIN EVENT OVER SRN ONT WITH MDT GREAT LAKES RAINFALL SUNDAY AND
MON. HIGH WIND EVENT OVER THE NRN PLAINS SUNDAY SHIFTING EWD OVER
THE UPPER MS VALLEY WITH GALES ACROSS LAKES SUPERIOR AND MI SUNDAY
NIGHT INTO TUES WORKING EWD TUES. HIGH CONFIDENCE EVENT. NEXT
PLAINS LOW AND FRONT FORMS IN RESPONSE TO THE NEXT WRN TROF COMING
EWD ACROSS THE ROCKIES TO THE PLAINS DAY TUES-THURS. INCREASED
MOISTURE ADVECTION AHEAD OF THIS SYSTEM WILL INCREASE RAIN CHANCES
AND AMOUNTS THRU THE PLAINS DAYS 7-8 THU-FRI WITH A NEG TILTED
CLOSED OFF MID LEVEL POTENTIAL SYSTEM.
ROSENSTEIN
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