Prognostic Meteorological Discussion
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FXUS02 KWBC 091508
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1008 AM EST FRI DEC 09 2016

VALID 12Z MON DEC 12 2016 - 12Z FRI DEC 16 2016

...PATTERN OVERVIEW...

IT REMAINS THE CASE THAT A DEEP UPR LOW FCST TO BE JUST W OF
HUDSON BAY AS OF EARLY MON SHOULD TRACK SEWD INTO MIDWEEK AND
CONTINUE EWD INTO ERN CANADA THOUGH WITH INCREASING TIMING
UNCERTAINTY. UPSTREAM THE MEAN RIDGING OVER THE NERN PAC/ALASKA
SHOULD ENCOURAGE SOME DEGREE OF ERN PACIFIC TROUGHING WHOSE AXIS
MAY REACH THE WEST TOWARD LATE NEXT WEEK. EXPECT THE LOWER 48 TO
REMAIN UNDER FAST AND LOW AMPLITUDE FLOW. PSBL INTERACTIONS AMONG
NRN STREAM FLOW AND INCOMING PAC IMPULSE/S WILL ADD TO THE
UNCERTAINTIES THAT ARE ALREADY TYPICALLY GREATER THAN AVG DUE TO
THE PROGRESSIVE NATURE OF THE FLOW. THE LARGE SCALE PATTERN WILL
LIKELY MAINTAIN VERY COLD TEMPS DOWN FROM THE NRN TIER STATES
WHILE ANOTHER COLD SURGE WILL REACH THE S-CENTRAL/SERN STATES BY
THE LATTER HALF OF THE WEEK. HEAVIEST PRECIP SHOULD FOCUS BE ALONG
CENTRAL LATITUDES OF THE WEST.

...GUIDANCE EVALUATION/PREFERENCES...

THE WPC PRODUCT SUITE FCST WAS PRIMARILY DERIVED FROM THE
GEFS/ECMWF MEAN BLEND AS OPERATIONAL SOLNS SHOW FURTHER DIVERGENCE
AND REMAINING TIMING DIFFS ARE WITHIN TYPICAL ERROR RANGE FOR THE
VALID TIME. TELECONNECTIONS RELATIVE TO NERN PAC/ALASKA RIDGING
RECOMMEND GOING AT LEAST 2/3 TOWARD THE GEFS MEAN VS THE ECMWF
MEAN AND THAT ALLOWS FOR BETTER CONTINUITY.

WRN CANADIAN AND NWRN US GUIDANCE TROUGH/HEIGHT FALLS DEVELOPMENTS
STILL OFFER SOME TIMING ISSUES BUT HAVE BECOME BETTER CLUSTERED
INTO EARLY NEXT WEEK AND ALLOW FOR A WINTERY COLD PUSH ACROSS THE
REGION UNDERNEATH. DOWNSTREAM...UNCERTAINTY ACROSS THE
EAST-CENTRAL US ACCOMPANIES A POTENT ARCTIC SURGE FRONT REACHING
THE EAST COAST PAST MIDWEEK...WITH SOME SOLNS SHOWING POTENTIAL
FOR SFC DEVELOPMENT WITHIN AN AREA COVERING FROM OFF THE MID ATLC
COAST THROUGH NEW ENGLAND INTO THE CANADIAN MARITIMES. VERY WIDE
SPREAD AMONG INDIVIDUAL MODEL RUNS/ENSEMBLE MEMBERS FAVORS A
CONSERVATIVE APPROACH CLOSER TO THE MEANS AT THIS TIME THAT OFFERS
DECENT WPC CONTINUITY.

OVER THE WEST THE PRIMARY QUESTION MARKS INVOLVE ONE OR MORE WAVES
THAT MAY COME IN FROM THE PAC CORRESPONDING TO SHRTWV ENERGY
WITHIN COMPLEX MEAN TROUGHING. THE ELONGATED NATURE OF ENERGY
INITIALLY OFF THE PAC NW COAST LEADS TO REDUCED PREDICTABILITY FOR
HOW IT EVOLVES WITH TIME. THEN GUIDANCE SUGGESTS POTENTIAL FOR
THIS ENERGY TO INTERACT WITH AN UPR TROUGH THAT WILL BE PASSING
ACROSS/N OF HAWAII EARLY IN THE WEEK. BY MID-LATE WEEK GUIDANCE
REALLY BEGINS TO DIVERGE ON THE AMPLITUDE/POSN OF TROUGHING NEAR
THE WEST COAST. RECENT GFS RUNS APPEAR TO BE ON THE DEEPER SIDE.
HOWEVER TELECONNECTIONS RELATIVE TO NERN PAC/ALASKA RIDGING
SUPPORT A MORE WWD AND MODERATELY AMPLIFIED TROUGH AS PER RECENT
GEFS MEANS VS THE QUITE DIFFERENT FLATTER/EWD RECENT ECMWF MEANS.
PRECISE DETAILS OF THIS OVERALL EVOLUTION WILL BE CRITICAL FOR
DETERMINING HOW MUCH LOW LATITUDE MSTR MAY GET DRAWN NEWD TOWARD
THE WEST COAST AND WHERE THIS MSTR IS ORIENTED WITH THE 00 UTC
GEFS/ECMWF ENSEMBLES OFFER A SEEMINGLY REASONABLE PCPN AREAL
COVERAGE/FOCUS BETWEEN THE NWRN US WET TROUGH APPROACH SOLUTION OF
AN OUTLIER AND RECENTLY ERRATIC DETERMINISTIC ECMWF AND SOUTHWARD
SUPPRESSED QPF FOCUS FROM RECENT GFS RUNS. LOOKING AHEAD...THESE
MODEL/ENSEMBLE DIFFERENCES LEAD TO SIGNIFICANT RETURN FLOW TIMING
AND SYSTEM DEVELOPMENT UNCERTAINTIES DOWNSTREAM ACROSS THE US SRN
TIER DAYS 7/8 TO BE DETERMINED.

...WEATHER HIGHLIGHTS/THREATS...

ACROSS THE WEST...EXPECT BEST POTENTIAL FOR ONE OR MORE EPISODES
OF ENHANCED COASTAL RAIN AND INLAND/HIGHER ELEV SNOW FROM
NRN-CNTRL CA INTO THE CNTRL ROCKIES. COMPLEXITY OF ERN PAC
EVOLUTION LOWERS CONFIDENCE IN SPECIFICS BUT THERE WILL BE
POTENTIAL FOR SIGNIFICANT LOCALIZED TOTALS OVER PARTS OF NRN-CNTRL
CA DEPENDING ON HOW MUCH TROPICAL MSTR MAY GET INCORPORATED INTO
THE FLOW. ARCTIC BNDRY DUG/DRAPED THROUGH THE NORTHWEST AND
N-CENTRAL ROCKIES/HIGH PLAINS MAY PROVIDE ANOTHER FOCUS FOR PCPN
WITH SNOWS ENHANCED BY POST-FRONTAL UPSLOPE FLOW. EXPECT TEMPS TO
RANGE TO 20-30F BELOW NORMAL FOR COLDER POST-FRONTAL AREAS.

OVER THE ERN 2/3 OF THE COUNTRY...THE NRN PLAINS SHOULD BE MOST
CONSISTENTLY VERY COLD WITH HIGHS LIKELY TO AVG 20-30F BELOW
NORMAL FOR THE 5-DAY PERIOD. IN MODIFIED FORM SOME OF THIS COLD
AIR WILL PUSH SEWD FROM THE NRN PLAINS MON ONWARD...BRINGING SOME
MINUS 10-20F OR SO ANOMALIES TO THE NRN-CNTRL PARTS OF THE CENTRAL
US THEN EAST FOR THE LATTER HALF OF THE WEEK. DAILY RECORDS ARE
QUITE EXTREME BY THIS POINT IN THE SEASON SO CURRENT FCSTS MAY
ONLY YIELD ISOLATED RECORD VALUES. GRTLKS/NERN SYSTEM MON WILL
BRING A WIDESPREAD AREA OF SNOW TO LOCATIONS WITH LOW CIRCULATION
AND RAIN FARTHER SWD. PASSAGE OF THIS SYSTEM AND UPSTREAM ARCTIC
FRONT SHOULD PROMOTE A MULTI-DAY PERIOD OF LAKE EFFECT SNOW.
TOWARD THE LATTER HALF OF THE WEEK THERE MAY BE ONE OR MORE AREAS
OF MOSTLY LGT PCPN OVER PARTS OF THE CNTRL-ERN STATES BUT WITH LOW
CONFIDENCE ON LOCATION/TIMING DUE TO UNCERTAINTIES WITH SHRTWV
DETAILS ALOFT. THE SOUTHWARD EXTENT OF WINTER AIR AND WAVY
TRAILING FRONT POTENTIAL MAY OFFER SOME OVER-RUNNING SNOW/ICE
THREAT POTENTIAL.

SCHICHTEL

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