Prognostic Meteorological Discussion
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000
FXUS02 KWBC 191612
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1111 AM EST SUN FEB 19 2017

VALID 12Z WED FEB 22 2017 - 12Z SUN FEB 26 2017

16Z UPDATE...

NO MAJOR CHANGES WERE MADE TO THE PREVIOUS WPC DAY 3-7 FORECAST.
THE LATEST AVAILABLE 00Z AND 06Z GUIDANCE REMAINED IN AGREEMENT
WITH THE LARGE SCALE FLOW PATTERN DURING THE SECOND HALF OF THIS
WEEK AND INTO NEXT WEEKEND...WHICH WILL FEATURE UPPER RIDGING
BUILDING IN OVER THE NORTHEAST PACIFIC/ALASKA WHILE A DOWNSTREAM
TROUGH CARVES OUT OVER THE WESTERN AND EVENTUALLY CENTRAL U.S..
GENERALLY FLATTER FLOW WITH ABOVE NORMAL HEIGHTS IS EXPECTED OVER
THE EASTERN U.S..

THE LATEST MODELS ALSO CONTINUED TO SHOW A STRONG SIGNAL FOR A
POTENTIAL HIGH-IMPACT STORM SYSTEM TRACKING FROM THE CENTRAL
PLAINS TO THE UPPER GREAT LAKES LATE THIS WEEK...WHICH WOULD BRING
HIGH WINDS AND HEAVY SNOW TO LOCATIONS NORTHWEST OF THE ASSOCIATED
SURFACE CYCLONE AND POSSIBLY STRONG TO SEVERE THUNDERSTORMS WITH
THE ASSOCIATED COLD FRONT PRESSING THROUGH THE OHIO VALLEY.
DESPITE THE STRONG SIGNAL FOR A HIGH-IMPACT STORM SYSTEM...THERE
REMAINS A LARGE AMOUNT OF SPREAD AMONG DETERMINISTIC
GUIDANCE/ENSEMBLE MEMBERS WITH THE EXACT TIMING/TRACK OF THE
SURFACE CYCLONE...WITH THE 06Z GFS TAKING THE LOW ALL THE WAY INTO
NORTHERN MICHIGAN BY 00Z SATURDAY WHILE AT THE SAME TIME...THE 00Z
UKMET HAS THE LOW OVER EASTERN KANSAS.

UNCERTAINTY ALSO CONTINUES TO PLAGUE THE FORECAST OVER THE WESTERN
U.S. LATE THIS WEEK AND INTO NEXT WEEKEND...WHERE ENSEMBLE SPREAD
REMAINS UNUSUALLY HIGH WITH THE EXACT EVOLUTION OF MULTIPLE
SHORTWAVES DROPPING SOUTHWARD ALONG THE WEST COAST.  THE MAJORITY
OF GUIDANCE SUGGESTS THE WEST COAST SHOULD SEE A BREAK IN THE
HEAVY RAINFALL THREAT BY THE LATER HALF OF THIS WEEK.
HOWEVER...THE 06Z GFS REMAINED CONSISTENT WITH ITS PREVIOUS RUNS
IN ADVERTISING THE POTENTIAL FOR A PERIOD OF FOCUSED RAINFALL OVER
NORTHERN CALIFORNIA BY NEXT WEEKEND.

GERHARDT


...OVERVIEW...

GUIDANCE SO FAR IS CONSISTENT IN ESTABLISHING A STRONG NERN
PAC/ALASKA MEAN RIDGE THAT SHOULD BECOME A PRIMARY INFLUENCE ON
NORTH AMERICAN FLOW ALOFT.  TELECONNECTIONS RELATIVE TO THE ASSOC
CORE OF POSITIVE HGT ANOMALIES SUGGEST THAT THE DOWNSTREAM PATTERN
SHOULD ULTIMATELY EVOLVE TOWARD A MEAN TROUGH EXTENDING FROM
NRN/NERN CANADA THROUGH THE WRN U.S. AND ABOVE NORMAL HGTS WITH
WSWLY FLOW OVER THE EAST.  IN THE PROCESS GUIDANCE CONTINUES TO
SHOW CONSIDERABLE SPREAD WITH ERN PAC/WRN U.S. DETAILS ESPECIALLY
BY DAYS 5-7 FRI-SUN WITH SOME EFFECTS OF THIS UNCERTAINTY
EXTENDING TO THE SIGNIFICANT STORM SYSTEM FCST TO CROSS THE WEST
WED-THU AND THEN TRACK NEWD FROM THE CNTRL PLAINS.


...MODEL EVALUATION/PREFERENCES...

REGARDING ERN PAC/WRN U.S. DETAILS... THERE IS DECENT AGREEMENT
INTO THU THAT INITIAL NRN PAC/SRN ALASKA ENERGY WILL ELONGATE WWD
OFF THE PAC NW COAST.  THE MUCH BIGGER QUESTION MARK COMES WITH
TRAILING ENERGY FROM FARTHER N OVER ALASKA.  OVER THE PAST DAY OR
SO GFS/CMC RUNS HAVE TENDED TO BE ON THE STRONG/WRN SIDE OF THE
GUIDANCE SPREAD WITH A POTENTIAL UPR LOW NEAR/OFFSHORE THE WEST
COAST.  INDIVIDUAL GEFS/ECMWF/CMC ENSEMBLE MEMBERS VARY GREATLY
WITH AT LEAST SOME MEMBERS FROM EACH MODEL SYSTEM SHOWING A FAIRLY
DEEP/WWD ELONGATED TROUGH.  HOWEVER THERE IS ENOUGH SPREAD TO
YIELD ENSEMBLE MEANS THAT MAINTAIN AN OPEN TROUGH THAT IS NOT AS
DEEP AS THE GFS/CMC RUNS.  TELECONNECTION-FAVORED FLOW RECOMMENDS
LEANING AWAY FROM THE DEEPEST/MOST WWD SOLNS BUT PERHAPS A LITTLE
DEEPER TROUGHING THAN ECMWF/ECMWF MEAN RUNS.  THIS FAVORS
INCORPORATION OF SOME GEFS/NAEFS MEAN GUIDANCE ALONG WITH THE
ECMWF-BASED SOLNS FOR THE FCST BLEND.

THERE IS STILL GOOD AGREEMENT IN PRINCIPLE THAT INITIAL WEST COAST
UPR TROUGH ENERGY WILL SUPPORT A SYSTEM CROSSING THE WEST EARLY IN
THE PERIOD AND A FAIRLY STRONG LATE WEEK/WEEKEND SYSTEM TRACKING
NEWD FROM THE CNTRL PLAINS.  MODEL/ENSEMBLE CLUSTERING HAS
ADJUSTED A BIT WITH SFC LOW TRACK OVER THE PAST DAY... SOMEWHAT
SWD AS OF EARLY FRI AND MORE EWD BY EARLY SAT.  THIS TREND
CORRESPONDS TO A SOMEWHAT DELAYED CLOSURE AND/OR WEAKENING OF THE
UPR LOW THAT HAS BEEN FCST TO FORM WITHIN THE TROUGH.  OVER THE
CNTRL-ERN STATES EVOLUTION OF THIS SYSTEM MAY BE INFLUENCED BY THE
UNCERTAIN FLOW UPSTREAM AS WELL AS ENERGY OVER SRN CANADA THAT
SHOWS SOME SPREAD AS WELL.  IN SPITE OF THE TRENDS... HISTORICAL
BIAS GENERALLY FAVORED LEANING AWAY FROM THE 12Z/18Z GFS RUNS FROM
EARLY FRI ONWARD AS THEY OUTPACED MOST OTHER SOLNS INCLUDING THE
GEFS MEAN.  THE 00Z GFS HAS PULLED BACK A BIT BY LATE FRI SO WILL
SEE IF THIS TREND CONTINUES.

ELSEWHERE... WITHIN NRN TIER/NERN U.S. FLOW AHEAD OF THIS STORM
GFS RUNS CONTINUE TO BE FASTER THAN MOST OTHER GUIDANCE WITH A
WAVE EXPECTED TO TRACK FROM THE NRN PLAINS ACROSS/NEAR NRN NEW
ENGLAND WED-THU.  THE NEW 00Z UKMET/CMC MAINTAIN CLOSER AGREEMENT
WITH THE 12Z ECMWF/ECMWF MEAN TIMING.  MEANWHILE THERE IS ONGOING
SPREAD/TRENDING WITH THE INITIAL GULF OF MEXICO UPR LOW.
MULTI-DAY TRENDS HAVE BEEN WEAKER/MORE SUPPRESSED.  THIS COULD
SUGGEST THAT ECMWF-BASED GUIDANCE MAY BE A LITTLE STRONG GIVEN THE
ARRAY OF OTHER SOLNS... BUT WOULD AT LEAST PROVIDE A MORE MEASURED
ADJUSTMENT FROM CONTINUITY.  THE 00Z UKMET HAS COME IN WITH A MUCH
STRONGER FEATURE THAN ITS PREVIOUS RUN SO A MAJORITY ECMWF/ECMWF
MEAN BLEND MAY STILL BE PLAUSIBLE.

BASED ON ABOVE PREFS BY SYSTEM/AREA THE EARLY PART OF THE FCST WAS
WEIGHTED MORE TOWARD THE 12Z ECMWF/ECMWF MEAN VS THE 18Z GFS/GEFS
MEAN.  AFTER THU THE 18Z GFS WAS FULLY EXCLUDED WHILE SOME 00Z/18
ECMWF WAS INCLUDED WITH THE 12Z RUN TO SMOOTH OUT DETAIL DIFFS.
SOME 12Z NAEFS MEAN WAS ADDED BY SAT-SUN.


...WEATHER HIGHLIGHTS/THREATS...

STORM SYSTEM TRACKING THROUGH THE WEST AND THEN NEWD FROM THE
CNTRL PLAINS WILL SPREAD MOSTLY SNOW ACROSS THE NRN-CNTRL INTERIOR
WEST AND THEN A BAND OF POTENTIALLY HVY SNOW FROM THE N-CNTRL
ROCKIES INTO THE UPR GRTLKS... NW OF THE SFC LOW TRACK... WITH
SOME AREAS OF MDT-HVY RNFL PSBL IN THE WARM SECTOR E OF THE MS
RIVER.  SOME AREAS MAY SEE STRONG WINDS WITH THIS SYSTEM.  SPC IS
MONITORING POTENTIAL FOR STRONG CONVECTION.  CONSULT FUTURE SPC
OUTLOOKS/DISCUSSIONS AS DETAILS BEGIN TO TAKE SHAPE.  THE FL
PENINSULA MAY SEE PERIODS OF RNFL WITH LOW LVL FLOW FROM THE ATLC
THOUGH GENERAL TRENDS OVER THE PAST COUPLE DAYS HAVE BEEN TOWARD
LIGHTER AMTS DUE TO A WEAKER/MORE SUPPRESSED DEPICTION OF THE GULF
OF MEXICO UPR LOW.  THE WEST COAST MAY SEE A BREAK FROM HVY RNFL.
HOWEVER WITH CONSIDERABLE SPREAD IN DETAILS ALOFT BY FRI-SUN THERE
IS LOW CONFIDENCE REGARDING COVERAGE/INTENSITY OF RAIN AND HIGHER
ELEV SNOW.  SOME LOWER PROBABILITY SOLNS LIKE GFS RUNS DO SHOW
POTENTIAL FOR A PERIOD OF HEAVIER FOCUSED ACTIVITY OVER THE PAC
NW/AND OR CA.

EXPECT VERY WARM TEMPS AHEAD OF THE EMERGING WRN U.S./PLAINS
SYSTEM WITH A BROAD AREA OF PLUS 15-30F ANOMALIES AND PSBL DAILY
RECORDS FOR HIGHS AND WARM LOWS WED-FRI.  COLD FRONT PROGRESSING
EWD WILL PUSH THE WARMTH OFF THE EAST COAST BY NEXT WEEKEND.  THE
LARGE SCALE PATTERN WILL FAVOR PERSISTENCE OF BELOW NORMAL TEMPS
OVER THE WEST AND EXTENDING AT TIMES INTO THE PLAINS.  SOME
LOCATIONS MAY SEE ONE OR MORE DAYS WITH HIGHS 10-15F BELOW NORMAL.
 EVEN WITH A SIGNIFICANT COOLING TREND OVER THE EAST BY NEXT
WEEKEND TEMPS MAY STILL HOLD AT NEAR TO ABOVE NORMAL VALUES.

RAUSCH

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