951
FXUS02 KWBC 191902
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
302 PM EDT SAT SEP 19 2009
VALID 12Z TUE SEP 22 2009 - 12Z SAT SEP 26 2009
THE MEDIUM RANGE FORECAST TODAY WILL BE CHARACTERIZED BY TWO
FEATURES DUELING FOR CONTROL OF THE PATTERN OVER ERN NOAM THE
LATTER PART OF NEXT WEEK. INITIALLY A CLOSED LOW IS FORECAST BY
CONSENSUS OF MODELS (EXCEPT FOR THE DETERMINISTIC GFS) TO FORM IN
THE W CENTRAL PLAINS EARLY IN THE PERIOD.
THE NEW 12Z DETERMINISTIC GFS PERSISTS IN TURNING ITS UPPER LOW
FORMING NEAR THE DAKOTAS/WY BORDER MON SWWD INTO THE CENTRAL GREAT
BASIN BY THU....CONTINUING ON THE FAR WRN EDGE OF MODEL AND
ENSEMBLE SOLUTIONS. THE NEW 12Z/19 CANADIAN AND UKMET ARE STILL
STAYING WITH THEIR EARLIER CONTINUITY OF CLOSING OFF A LOW VCNTY
OF KS BY TUE DAY 3. THE NEW 12Z/19 ECMWF IS IN BETWEEN THE GFS AND
CANADIAN/UKMET SOLTIONS HERE. BY NEXT FRI THE CANADIAN/UKKMET ARE
IN FAIRLY GOOD AGREEMENT NEAR THE KS/MO/IL INTERSECTION. THE NEW
ECMWF DAY 5 IS OVER THE OK PANHANDLE. THE NEW 12Z/19 GEFS ENSEMBLE
MEAN HAS TRENDED W FROM ITS 00Z/19 CONTINUITY AND PLACES A WEAK
CLOSED LOW OVER THE SRN ROCKIES.. HOWEVER WE FEEL CONSTRAINED BY
CONTINUITY TO STAY A TAD W OF THE LATEST 12Z/19 CANADIAN AND UKMET
UPPER LOW SOLUTIONS.
FINAL PROGS GENERALLY STAYED WITH A ECMWF/CANADIAN BLEND THRU THIS
MEDIUM RANGE PERIOD.
ENSEMBLE SPAGHETTI PLOTS LEFT LITTLE DOUBT TODAY AS TO WHO THE
OUTLIER SOLUTIONS WERE...THE LAST THREE DETERMINISTIC 00Z/06Z/12Z
RUNS OF THE GFS. THESE GFS RUNS ARE ON THE WRN EDGE OF THE
ENVELOPE OF SOLUTIONS WITH THE CENTRAL CONUS UPPER LOW NEXT WEEK.
THE VAST MAJORITY OF OTHER ENSEMBLES FROM 00Z/19 RETAIN CONTINUITY
OF A WOBBLING CLOSED LOW IN THE S CENTRAL PLAINS WED-FRI. THE
12Z/18 AND 99Z/19 UKMET RUNS WERE ON THE E SIDE OF THE SOLUTION
ENVELOPE...SHOWING SLOW EWD PROGRESSION OF THE UPPER LOW. NEEDLESS
TO SAY...CONTINUITY WAS OUR FAVORED SOLUTION TODAY.
ANOTHER FORECAST PROBLEM IS THE FATE OF THE POLAR BRANCH OF THE
WESTERLIES ACROSS CANADA AND THE SWD EXTENT OF THESE WESTERLIES
INTO THE NE QUADRANT OF THE CONUS DAYS 5-7. MODELS SHOW A TENDENCY
IN THE POLAR BRANCH OF THE WESTERLIES FOR RIDGING OVER WRN CANADA
AND TROFFING OVER FAR ERN CANADA. IF THE SOLUTIONS SHOWING A
VIGOROUS CLOSED LOW IN THE HIGH PLAINS PREVAIL...THERE SHOULD BE A
DOWNSTREAM RIDGE OVER THE S ATLANTIC STATES THAT WILL BLUNT THE
SWD EXTENT OF ANY CANADIAN TROFFING INTO NEW ENG THE LATTER HALF
OF NEXT WEEK. IF THE SOLUTIONS IN WHICH THE CANADIAN NRN STREAM IS
DOMINANT WERE TO PREVAIL...THE TROFFING COULD EXTEND FARTHER S BY
THU INTO THE NERN CONUS.
THE ECMWF AND GFS ENSEMBLE MEANS ARE QUITE DIFFERENT HERE...WITH
THE 00Z/19 ECMWF ENSEMBLE MEMBERS AND THE UKMET MAINTAINING AN
UPPER RIDGE ACROSS THE MID ATLANTIC/SERN STATES WHILE THE GFS AND
ITS ENSEMBLE MEMBERS CRASH HEIGHTS OVER THE NE/MID ATLANTIC BY
DAYS 5-6. TELECONNECTIONS ON THE STRONG POSITIVE HEIGHT ANOMALY
OVER THE PACIFIC NW DO NOT SUPPORT DEEP TROFFING INTO NEW ENG THE
LATTER PORTION OF THIS MEDIUM RANGE PERIOD....FAVORING INSTEAD A
TROF OVER THE GREAT LAKES.
THE WEATHER HIGHLIGHTS OF THE MEDIUM RANGE WILL BE LARGELY
DETERMINED BY THE FATE OF THE PLAINS CLOSED LOW. WITH SUCH A WIDE
RANGE OF SOLUTIONS OUR CONFIDENCE IN THE DETAILS IS BELOW
AVERAGE. WE EXPECT AN AREA OF HEAVY PRECIP IN THE COMMA HEAD
PORTION N-NW OF THE UPPER LOW...WHILE A AREA OF CONVECTION SHOULD
OCCUR E OF THE UPPER LOW EXTENDING S TO THE GULF COAST. STILL
FATHER E...A BROAD AREA OF DISORGANIZED SHOWERS SHOULD OCCUR IN
THE HUMID AIRMASS THAT WILL BE LIMITED ONLY BY THE POSSIBLE
PENETRATION OF DRIER AIR INTO THE NE STATES. SOME UNUSUALLY COOL
TEMPS CAN BE EXPECTED VICINITY OF THE UPPER LOW IN THE HIGH
PLAINS.
FLOOD
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