Prognostic Meteorological Discussion
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FXUS02 KWBC 250612
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
112 AM EST THU DEC 25 2014

VALID 12Z SUN DEC 28 2014 - 12Z THU JAN 01 2015

...GUIDANCE/UNCERTAINTY ASSESSMENT...

MEDIUM-RANGE FLOW OVER NOAM SHOWS AMPLIFIED NRN AND SRN STREAMS
THAT INCREASINGLY PHASE WHILE BECOMING NRN STREAM DOMINANT AND
COLD OVER TIME FOR MUCH OF THE NATION.
A HIGHLY AMPLIFIED MID-UPPER LEVEL RIDGE BUILT FROM THE ERN PAC
INTO AK/NW CANADA FAVORS DOWNSTREAM DIGGING OF IMPULSES ALOFT AND
LOWER ATMOSPHERIC COLD AIR INTO A BROAD YET AMPLIFIED MID-UPPER
LEVEL LOWER 48 MEAN TROUGH. DECENT SYSTEM CLUSTERING ALLOWS
INCLUSION OF SOME 12 UTC ECMWF/18 UTC GFS PARALLEL ALONG WITH
ENSEMBLE MEANS IN THE WPC BLEND SUN/MON...BUT RECENT RUN-RUN
CONTINUITY FROM DETERMINISTIC MODELS REMAINS LESS THAN
STELLAR...ESPECIALLY BEYOND DAY 3/4. THIS LENDS AN ENSEMBLE MEANS
APPROACH FEATURING THE COMPATABLE 12 UTC NAEFS/ECMWF ENSEMBLE
MEANS. THE FLOW PATTERN OFFERS LINGERING FORECAST SPREAD AND
UNCERTAINTY AT SMALL-MID SCALES EVEN WITH LATEST MODELS/ENSEMBLES
OVERALL TRENDING MORE SIMILAR ALOFT.

...PATTERN/SENSIBLE WEATHER THREATS HIGHLIGHTS...

AN INITIALLY SEPARATED SRN STREAM AMPLIFIED MID-UPPER LEVEL TROUGH
ALOFT OVER THE SWRN US SAT SHEARS NEWD OVER THE S-CENTRAL THEN ERN
US SUN/MON BETWEEN A SERN US MEAN RIDGE AND EMERGING NRN STREAM
TROUGH DOWN TO THE W-CENTRAL US. THIS FAVORS A LEAD LOW/FRONTAL
SYSTEM AND PCPN SWATH. THE TRACK OF THE LOW REMAINS QUITE VARIED
IN GUIDANCE RANGING BY 12 UTC MON FROM A DEEPENED GREAT LAKES LOW
TO A MUCH MORE SHEARED VERSION OVER THE SERN US. WPC PROGS
MAINTAIN DECENT CONTINUITY WITH A LOW FROM THE CENTRAL GULF COAST
STATES TO THE MID-ATLANTIC SUN/MON. TEMPS SEEM COLD ENOUGH FOR A
BAND OF SNOW ON THE NW PERIPHERY OF THE PCPN SHIELD FROM THE OH
VALLEY TO THE NRN MID-ATLANTIC/NORTHEAST. LOW/FRONTAL POOLED AND
WARM SECTOR MOISTURE MEANWHILE SEEM DEEP ENOUGH TO FUEL HEAVIER
CONVECTIVE RAINS UNDERNEATH FROM THE CENTRAL GULF COAST NEWD TO
THE S-CENTRAL APPALACHIANS/SERN US AND MID-ATLANTIC SUN/MON.
OVERRUNNING RAINS MAY LINGER ACROSS THE US SRN TIER INTO MIDWEEK
AS UNCERTAIN RIPPLES WITH THE UPPER JET WORK OVERTOP COOLED LOWER
LEVELS. DEEPER COOLING AND DRYING SHOULD OCCUR FROM THIS WEEKEND
INTO THE NEW YEAR AS A BLAST OF HIGH LATITUDE AIR IS SLATED TO DIG
DOWN OVER MUCH OF THE LOWER 48. IN THIS FLOW STILL EXPECT THAT
DIGGING EMBEDDED SHORTWAVES SHOULD FAVOR PERIODIC DYNAMICALLY
ENHANCED SNOWS PRIMARILY OVER FAVORED TERRAIN FROM THE NWRN US
SEWD TO THE ROCKIES.

MERRY CHRISTMAS/MIKE SCHICHTEL

$$




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