EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
154 PM EST THU JAN 15 2009
 
VALID 12Z SUN JAN 18 2009 - 12Z THU JAN 22 2009
 

MODELS REMAIN IN GOOD AGREEMENT AT LEAST THRU DAY 5 TUES WITH A
HIGHLY AMPLIFIED + PNA PATTERN WITH STRONG WRN CONUS RIDGING AND A
VERY DEEP MEAN TROF. ALL GUIDANCE SHIFTS THE MEAN WRN RIDGE EWD AS
AN EPAC MID LEVEL TROF DRIVES EWD TOWARDS THE WEST COAST. THE DEEP
ERN TROF LIFTS OUT EWD BY THE MIDDLE OF NEXT WEEK. A VERY LARGE
DEAL OF UNCERTAINTY IN THE EPAC PATTERN EVOLUTION AS ECMWF KEEPS
ITS IDEA OF A STRONG CLOSED MID LEVEL LOW APPROACHING THE WEST
COAST WHILE THE GFS SERIES KEEPS ITS NRN STREAM FEATURE THE
DOMINENT FEATURE. A 50/50 BLEND OF THE 00Z RUNS OF ECMWF AND GFS
WOULD YIELD A MEAN SOLUTION ESPECIALLY FOR THE EPAC/WRN CONUS
DIFFICULTIES AND WAS USED BY HPC.

12Z GFS HAS GONE CONSIDERABLY TOWARDS THE ECMWF SOLUTION IN THE
EPAC AND WEST COAST DAYS 6 AND 7 WITH NOW A SINGLE CLOSED OFF MID
LEVEL LOW DRIFTING ASHORE AND INTO THE GREAT BASIN
BY THURSDAY. THIS ALLOWS THE NRN STREAM FLOW TO DELIVER A BROAD
SHORTWAVE TROF WITH MID LEVEL NW FLOW AND A STRONGER SFC FRONT
CLOSER TO THE EARLIER 00Z ECMWF AND GFS ENS MEAN. THIS IS CLOSE
ENOUGH TO THE EARLIER HPC SOLUTION BLEND TO HAVE NO CHANGES WITH
SFC PROGS BUT H500 BLEND WILL REFLECT THE CHANGE OF THE 12Z GFS
FOR AFTN FINALS.

ERN CONUS...
CONTINUED QUITE COLD SUN THRU WED WITH RELIEF IN THE PATTERN AND
COLD BY THURSDAY AND FRIDAY. TEMPS REMAINING WELL BELOW NORMAL
THRU WED WITH CONSIDERABLE WARMING BY THURS. SHORTWAVE TIMING AND
INTENSITY. MODELS SEEM TO HAVE SETTLED DOWN WITH THE TRACK OF THE
FIRST SHORTWAVE AND SFC LOW COMING ACROSS THE OH VALLEY SUN
REFORMING OFF THE MID ATLC COAST AND MOVING NWD TO NOVA SCOTIA SUN
NIGHT-MONDAY. NEXT SHORTWAVE DROPPING SEWD INTO THE MEAN TROF
BETTER DEFINED BY GFS RUNS LATER TUES-WED AND MORE UNCERTAIN WITH
LIMITED 00Z ECMWF SFC REFLECTION RETURNING AGAIN WITH 12Z RUN.
MODEL CONSENSUS WITH THE SECOND SHORTWAVE WOULD BRING MTN SNOWS TO
THE CENTRAL AND SRN APPLCHNS. BELOW FREEZING TEMPS AND FROST
THREAT REMAINS IN NRN AND CENTRAL FLORIDA INTO SUNDAY. SEE LOCAL
NWS ADVISORIES.  

CENTRAL...
PLAINS BEGIN TO WARM THIS PERIOD AS TEH MID LEVEL RIDGE SHIFTS EWD
WHILE WEAKENING BUT NOT UNTIL WED-THURS SHOULD MUCH WARMING OCCUR
UNTIL WINDS SHIFT MORE W-SW. NEXT COLD SURGE OCCURS LATE WED-THURS
AS ANOTHER STRONG COLD FRONT DRIVES SWD THRU THE NRN AAND CENTRAL
PLAINS. TIMING BASED ON A 50/50 BLEND OF 00Z GFS AN ECMWF WHILE
CONCURRING WITH GFS ENS MEAN AND 06Z GFS TIMING. 

WEST...
STRONG RIDGING CONTS THRU DAYS 3 AND 4 WITH HIGH PRESSURE SETTLED
IN OVER THE GREAT BASIN AND ROCKIES PROVIDING A MILD OFFSHORE
EVENT ALONG CA COASTAL REGIONS. MID LEVEL TROF/POSSIBLE CLOSED LOW
APPROACH FROM THE EPAC BEGINS TO SHOW UP DAY 5 TUES AND FORECAST
DIFFICULTIES CONT THRU THURS. CMC IS TOO PROGRESSIVE WITH ITS TROF
ENDING UP WELL INLAND INTO THE PLAINS BY DAY 7 WHILE ECMWF AND GFS
ARE WELL INLAND LATER THURS IN THE GREAT BASIN. HPC HAS BLENDED
THE SOLUTIONS OF 00Z ECMWF AND 12Z GFS TO COME UP WITH MID LEVEL
AND SFC BLEND. INCREASING CONFIDENCE WITH TEH 12Z GFS AND 00Z
ECMWF SOLUTIONS. UNSETTLED CONDS WILL DEVELOP ACROSS CA AND THE
PAC NORTHWEST WED AND THURS AND INLAND INTO THE ROCKIES. 00Z GFS
PCPN  OVER DONE ACROSS BAJA/NWRN MEXICO INTO AZ AND NM LATE DAYS 6
INTO 7 AS IT BRINGS NWD TROPICAL MOISTURE. 06Z/12Z GFS HAS
SUPRESSED THIS CONSIDERABLY AS DOES ECMWF.
ROSENSTEIN