Preliminary Forecasts
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000
FXUS02 KWNH 160650
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
149 AM EST MON JAN 16 2017

VALID 12Z THU JAN 19 2017 - 12Z MON JAN 23 2017

...GUIDANCE EVALUATION/PREFERENCES...

GUIDANCE CONTINUES TO ADVERTISE A SERIES OF ENERGETIC SYSTEMS
PROGRESSING FROM THE PACIFIC INTO THE LOWER 48 WITH LEADING HGT
FALLS EVENTUALLY PUSHING INTO EAST COAST/ERN CANADA MEAN RIDGING.
MULTI-DAY MEANS STILL AGREE ON A VERY STRONG CORE OF POSITIVE HGT
ANOMALIES CENTERED NEAR THE ERN SHORE OF HUDSON BAY BY LATE IN THE
PERIOD.  TELECONNECTIONS RELATIVE TO THIS FEATURE SUGGEST THERE
SHOULD BE A TENDENCY TOWARD A CORE OF NEGATIVE HGT ANOMALIES ALONG
THE WEST COAST WITH WEAKER NEG HGT ANOMALIES ACROSS THE REST OF
THE WRN/SRN U.S..

THROUGH THE 12Z/18Z CYCLES THE MODEL/ENSEMBLE MEAN RUNS AGREE
MODERATELY WELL IN PRINCIPLE FOR INDIVIDUAL PACIFIC SYSTEMS.
BASED ON THE BEST SOLN CLUSTER THE FIRST UPR TROUGH SHOULD BE NEAR
THE WEST COAST AS OF EARLY DAY 3 THU AND THEN LIFT NWD OVER THE
PLAINS BY FRI-SAT WITH A COMPACT LOW AS A SFC REFLECTION.  THERE
IS SOME SPREAD REGARDING HOW LONG THE PLAINS FEATURE MAINTAINS ITS
IDENTITY AFTER EARLY SAT.  THE SECOND SYSTEM WILL APPROACH THE
WEST COAST THU NIGHT-FRI WITH A STRONG SFC LOW THAT IS MOST LIKELY
TO TRACK SOMEWHAT OFFSHORE THE PAC NW COAST.  ENERGY FROM THIS
SYSTEM IS FCST TO REACH THE PLAINS IN THE FORM OF AN AMPLIFIED
TROUGH WITH PSBL EMBEDDED CLOSED LOW BY SUN AND THEN CONTINUE INTO
THE ERN STATES.  THEN ANOTHER STRONG UPR TROUGH SUPPORTING ONE OR
MORE SFC LOWS SHOULD REACH THE WEST COAST DAYS 6-7 SUN-MON.

THERE IS MODERATE CLUSTERING FOR THE FRI-SAT LOW PRES OFF THE PAC
NW COAST WITH AN AVG AMONG GFS/ECMWF RUNS AND THEIR ENSEMBLE MEANS
PROVIDING FAIRLY GOOD CONTINUITY.  THE 12Z CMC FALLS INTO THIS
GROUP AS WELL.  FROM THE PLAINS EWD SUN-MON IS WHERE GUIDANCE
DIVERGES MORE NOTICEABLY AS GFS/CMC RUNS AND THEIR MEANS SHOW A
SLOWER AND/OR FARTHER SWD TRACK THAN RECENT ECMWF/ECMWF MEAN RUNS.
 PREFER A COMPROMISE TRACK AS ENSEMBLE SPREAD BY DAY 7 MON RANGES
FROM THE GRTLKS TO THE SRN STATES.  SOME ECMWF/CMC RUNS BACK IN
THE DAYS 8-10 TIME FRAME HAD DEPICTED A VERY SRN TRACK... WHILE IT
ALSO APPEARS PSBL THAT A SYSTEM COULD REACH AS FAR NWD AS THE OH
VLY/LWR GRTLKS EVEN WITH THE STRONG POSITIVE HGT ANOMALIES OVER
ERN CANADA.  INTERESTINGLY THE NEW 00Z GFS HAS ADJUSTED CLOSE TO
THE ECMWF/ECMWF MEAN SCENARIO.  FOR THE LATE PERIOD UPR TROUGH
NEARING/REACHING THE WEST COAST THERE IS A DECENT SIGNAL IN THE
GUIDANCE TOWARD TWO SFC LOWS... ONE NEAR THE PAC NW COAST AND
ANOTHER TO THE S THAT MAY TRACK INTO CA.  THE 12Z GFS/CMC AND NEW
00Z GFS ARE A LITTLE FASTER THAN OTHER MODELS AND THE ENSEMBLE
MEANS.

AHEAD OF THE PACIFIC SYSTEMS THERE IS STILL A FAIR AMOUNT OF
UNCERTAINTY WITH THE DETAILS OF EJECTING PLAINS/NRN MEXICO ENERGY
DURING THE FIRST HALF OF THE PERIOD.  THIS ENERGY WILL BE HEADING
INTO AN AREA OF MEAN RIDGING WHICH USUALLY LEADS TO LOW
PREDICTABILITY... SO CONFIDENCE IS LOW IN ANY PARTICULAR SOLN.
MEANWHILE SOME TROUGHING IS STILL FCST OVER THE NORTHEAST FOR A
TIME WITH BEST CONSENSUS STILL LEANING AWAY FROM THE DEEPER/SLOWER
SIDE OF THE SPREAD SUCH AS 18Z GFS.

THE 18Z GEFS/12Z ECMWF MEANS PROVIDED A GOOD FOUNDATION FOR THE
FCST TO YIELD ONLY MODERATE ADJUSTMENTS TO CONTINUITY.  A SMALL
WEIGHT OF THE 18Z GFS/12Z ECMWF RUNS HELPED TO ADD A LITTLE MORE
DEFINITION TO THE MOST SIGNIFICANT FEATURES WITHOUT ADVERSELY
AFFECTING THE FCST WHERE LOCALLY QUESTIONABLE DETAILS EXISTED.


...WEATHER HIGHLIGHTS/THREATS...

THE FCST SERIES OF PACIFIC SYSTEMS WILL LIKELY BRING PERIODS OF
HVY COASTAL RAIN AND HIGH ELEV SNOW ALONG WITH STRONG WINDS TO THE
WEST COAST STATES.  EXPECT HEAVIEST 5-DAY PRECIP ACCUMULATIONS
ALONG COASTAL LOCATIONS FROM THE SWRN CORNER OF OREGON SWD THROUGH
CALIFORNIA AS WELL AS ALONG THE SIERRA NEVADA RANGE... WITH SOME
5-10 INCH TOTALS STILL PSBL OVER THESE AREAS.  THE BEST SURGE OF
MSTR ACROSS SRN CA AND INTO FAVORED TERRAIN OF AZ APPEARS MOST
LIKELY AROUND FRI-FRI NIGHT.  MUCH OF THE REMAINDER OF THE WEST
SHOULD SEE SOME RAIN AND INLAND/HIGHER ELEV SNOW BUT WITH LESSER
INTENSITY.  THE UNSETTLED WEATHER WILL KEEP HIGHS BELOW NORMAL
MOST AREAS BUT MIN TEMPS NEAR TO ABOVE NORMAL.

ACROSS THE ERN HALF OF THE COUNTRY... EJECTING PLAINS/MEXICO
ENERGY WILL GENERATE ONE AREA OF POTENTIALLY HVY RNFL FROM THE
W-CNTRL GULF COAST INTO PARTS OF THE SOUTHEAST AND TN VLY/SRN
APLCHNS EARLY IN THE PERIOD.  LIGHTER ACTIVITY WILL COVER A LARGER
AREA BUT TO WHAT EXTENT IS UNCERTAIN GIVEN SPREAD IN DETAILS
ALOFT.  LINGERING SFC FRONT ALONG THE GULF COAST MAY FOCUS
ADDITIONAL RNFL DURING THE WEEKEND.  THEN THE LARGE SCALE
PLAINS-ERN U.S. SYSTEM SUN-MON WILL BE ACCOMPANIED BY A BROAD PCPN
SHIELD.  WITH EACH EPISODE THERE MAY BE POTENTIAL FOR SOME
CONVECTION TO BE ON THE STRONG SIDE OVER SRN AREAS.  DEPENDING ON
EXACT DETAILS OF EVOLUTION THERE MAY BE A PERIOD OF STRONG ATLC
INFLOW THAT COULD ENHANCE RNFL ALONG PORTIONS OF THE EAST
COAST/ERN SLOPES OF THE APLCHNS.  GIVEN THE RELATIVE LACK OF COLD
AIR TO WORK WITH... THIS LATE PERIOD STORM MAY GENERATE AN
UNUSUALLY SMALL COVERAGE OF SNOW FOR SUCH A MASSIVE SYSTEM IN THE
LATTER HALF OF JANUARY.  WHAT SNOW THERE IS MAY BE CONFINED TO
NEAR THE UPR LOW... IF DEEP ENOUGH... AND OVER THE NRN PLAINS.
FCSTS CONTINUE TO SHOW MUCH ABOVE NORMAL TEMPS OVER MOST AREAS E
OF THE ROCKIES WITH SOME PLUS 30F AND GREATER ANOMALIES AND PSBL
DAILY RECORD WARM LOW READINGS CENTERED OVER/NEAR THE UPR MS VLY.

RAUSCH

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