THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


EXTENDED FORECAST DISCUSSION




EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1200 PM EDT TUE APR 15 2014

VALID 12Z FRI APR 18 2014 - 12Z TUE APR 22 2014

...MODEL/PATTERN OVERVIEW...

MUCH OF THE MEDIUM RANGE PERIOD WILL BE DOMINATED BY A SPLIT FLOW
REGIME WITH GRADUAL DEAMPLIFICATION EXPECTED AS THE TRAJECTORIES
TURN A BIT MORE ZONAL BY THE WEEKEND. ON DAY 3...FRIDAY...THE
MODELS ARE IN REASONABLE AGREEMENT WITH THE PATTERN FEATURING A
PAIR OF NORTHERN STREAM TROFS AFFECTING THE PACIFIC
NORTHWEST/GREAT LAKES REGION...RESPECTIVELY. MEANWHILE...THE
SOUTHERN BRANCH OF THE JET WILL ALSO BE QUITE ACTIVE WITH A COUPLE
OF SYSTEMS IMPACTING NORTHERN BAJA CA AND THE SOUTHEASTERN U.S.
THE LATTER IS OF INTEREST AS THE GUIDANCE REMAIN AT ODDS WITH HOW
MUCH SURFACE DEVELOPMENT WILL INDEED TAKE PLACE ACROSS THE
NORTHERN GULF OF MEXICO AND EVENTUALLY THE SOUTHEASTERN U.S.
COAST. THE SPLIT IN CAMPS CONTINUE TO BE THE 06Z GFS/00Z CMC AND
THEIR RESPECTIVE ENSEMBLE MEANS VS THE 00Z UKMET/ECMWF/ECMWF
ENSEMBLE MEAN. THE LATTER GROUPING ALLOW FOR MORE SHORTWAVE ENERGY
TO TRACK ACROSS THE FL PANHANDLE THROUGH SATURDAY WHICH INDUCES A
STRONG AREA OF LOW PRESSURE IN THE NORTHERN GULF WATERS. THE
AVAILABLE SPAGHETTI PLOTS CONTINUE TO SHOW A LITTLE MORE SUPPORT
TOWARD THE AGGRESSIVE SOLUTIONS WHICH FAVORS THE 00Z
UKMET/ECMWF/ECMWF ENSEMBLE MEAN. INTERESTINGLY THE PAST FOUR RUNS
OF THE GFS/ECMWF SHOW EACH INDIVIDUAL MODEL HAVE NOT BUDGED ON
THEIR SOLUTIONS WITH THE GFS KEEPING MORE EMPHASIS ON THE NORTHERN
STREAM WAVE. GIVEN THIS FACT...THE GFS SUITE HAS BEEN SLOWER IN
CARRYING THE SYSTEM OFFSHORE OF THE NORTHEASTERN CONUS AS IT
CLOSES OFF AN UPPER LOW IN THE VICINITY OF UPPER NEW ENGLAND BY
EARLY SUNDAY. FURTHER UPSTREAM...THE UPPER PATTERN RELAXES AHEAD
OF A STRONG AXIS OF HEIGHT FALLS TRACKING THROUGH THE NORTHEAST
PACIFIC ON SUNDAY MORNING. MODELS QUICKLY DIVERGE ON THE
TIMING/INTENSITY OF THIS SYSTEM WITH THE PAST SEVERAL RUNS OF THE
GFS ALONG WITH THE 06Z GEFS MEAN BEING MUCH MORE PROGRESSIVE. AT
21/1200Z...THE 00Z CMC/ECMWF/ECMWF ENSEMBLE MEAN DEPICT NEARLY
ZONAL FLOW ACROSS THE PACIFIC NORTHWEST WHILE THE 06Z GFS/GEFS
MEAN HAVE ALREADY SHAPED A WELL-DEFINED TROF JUST WEST OF WA/OR.
SUCH DIFFERING SOLUTIONS PREVAIL THROUGH APRIL 22 WITH THESE
UNCERTAINTIES STRONGLY NOTED IN THE ENSEMBLE SPAGHETTI PLOTS.

...WPC PREFERENCES...

GIVEN THE REASONABLE AGREEMENT VISIBLE IN THE GUIDANCE ON DAY
3...WPC WENT WITH A COMBINATION OF THE 06Z GFS AND 00Z ECMWF/UKMET
WITH A BIT MORE EMPHASIS ON THE GFS/ECMWF. BEYOND THIS
PERIOD...REMOVED THE 06Z GFS GIVEN THE MANUAL PROG FAVORED MORE
AMPLIFICATION IN THE SOUTHERN STREAM WHICH WENT ALONG THE LINES OF
THE 00Z ECMWF/UKMET. FOR DAYS 4/5...SATURDAY/SUNDAY...UTILIZED A
BLEND OF THE 00Z ECMWF/UKMET WITH GROWING EMPHASIS ON THE ECMWF AS
THE UKMET BECAME SLOWER IN TIME EJECTING THE COASTAL WAVE OFFSHORE
OF THE SOUTHEASTERN U.S. BY DAYS 6/7...MONDAY/TUESDAY...CHOSE NOT
TO INCLUDE ANY OF THE 06Z GEFS MEAN GIVEN THE AFOREMENTIONED
FAST/MORE AMPLIFIED SOLUTION AFFECTING THE WEST COAST. THIS
DIFFERENCE IN TIMING APPEARS DUE TO COMPLEXITIES IN THE UPSTREAM
PATTERN EVOLVING ACROSS THE ALEUTIANS. GIVEN THE GROWING
UNCERTAINTY IN THE FORECAST...WENT ALL IN ON THE 00Z ECMWF
ENSEMBLE MEAN FOR NEXT WEEK.

...SENSIBLE WEATHER HIGHLIGHTS...

AS THE UPPER FLOW CONTINUES TO DEAMPLIFY...THE NEGATIVE
TEMPERATURE ANOMALIES WILL DIMINISH AS THE PATTERN TURNS A BIT
MORE ZONAL. THIS WILL LEAD TO A MAJORITY OF THE COUNTRY BEING
INFLUENCED BY ABOVE 540-DM 1000-500 MB THICKNESSES. GIVEN MODEST
RIDGING AHEAD OF THE APPROACHING PACIFIC STORM EARLY NEXT
WEEK...ABOVE NORMAL TEMPERATURES WITH ANOMALIES IN THE 5 TO 10
DEGREES F RANGE ARE EXPECTED OVER THE WESTERN/CENTRAL U.S. FROM
SUNDAY THROUGH TUESDAY. MEANWHILE...ACROSS THE NORTHEASTERN
U.S...TEMPERATURES WILL BE BELOW NORMAL THROUGH THE WEEKEND AS THE
PASSAGE OF THE NORTHERN STREAM TROF USHERS IN COOL CANADIAN AIR
INTO THE REGION. IN TERMS OF PRECIPITATION...IT SHOULD BE QUITE A
WET PERIOD THROUGH SUNDAY FOR THE CENTRAL/EASTERN GULF COAST AND
ACROSS THE SOUTHEASTERN U.S. THIS IS PARTICULARLY THE CASE IF THE
00Z UKMET/ECMWF/ECMWF ENSEMBLE MEAN SOLUTIONS VERIFY. THESE MODELS
SHOW AREAS OF 2 TO 4 INCHES OF RAINFALL IN 24 HOURS WITH LOCALLY
HEAVIER AMOUNTS POSSIBLE.


RUBIN-OSTER





Last Updated: 1200 PM EDT TUE APR 15 2014