Preliminary Forecasts
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
000
FXUS02 KWNH 210646
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 AM EST TUE FEB 21 2017

VALID 12Z FRI FEB 24 2017 - 12Z TUE FEB 28 2017

...OVERVIEW...

THE ERN PAC/WRN U.S. CONTINUES TO BE AN AREA OF HIGH FCST
SENSITIVITY FOR SPECIFIC DETAILS WITHIN AN OVERALL MEAN TROUGH
ALOFT DOWNSTREAM FROM A STRONG NERN PAC RIDGE.  ISSUES WITHIN THIS
REGION WILL THEN HAVE AN IMPACT ON THE REMAINDER OF THE LOWER 48
WHERE MEAN FLOW SHOULD EVOLVE TOWARD A SWLY ORIENTATION.
MEANWHILE THERE ARE STILL DETAIL UNCERTAINTIES FOR A STRONG SYSTEM
TRACKING NEWD FROM THE MIDWEST FRI ONWARD.

...MODEL EVALUATION/PREFERENCES...

AFTER GUIDANCE HAD APPEARED TO START THE PROCESS OF CONVERGING
TOWARD A COMMON SOLN FOR THE EVOLUTION OF ERN PAC/WEST COAST
ENERGY ALOFT BY THE WEEKEND... 12Z/18Z MODEL RUNS ADJUSTED TOWARD
TAKING NWRN NOAM ENERGY AND WRAPPING UP A FAIRLY DEEP SYSTEM JUST
OFF THE WEST COAST.  MANY OF THESE MODELS ALSO INCORPORATED ENERGY
FROM A CLOSED LOW FARTHER OFFSHORE.  GIVEN THE DIFFICULTY THAT
GUIDANCE HAS IN RESOLVING DETAILS OF FLOW IN THIS KIND OF PATTERN
IT WOULD NOT BE SURPRISING FOR FURTHER CHANGES TO OCCUR IN THE
FCST.  ALSO THERE IS STILL WIDE SPREAD IN ENSEMBLE MEMBERS BY DAY
5 SUN.  SOME MEMBERS LOOKED MORE SIMILAR TO THE LATEST OPERATIONAL
CLUSTER WHILE OTHERS REPRESENTED THE QUICKER EJECTING SOLNS THAT
WERE THE MAJORITY 24-36 HRS AGO.  THIS DIVERGENCE LED TO A 12Z SUN
FCST THAT HAD ENSEMBLES RANGING ANYWHERE FROM RIDGE TO TROUGH OVER
THE INTERIOR WEST/ROCKIES.  OVER SOME AREAS SPREAD ACTUALLY
DAMPENED OUT A LITTLE BY DAYS 6-7 MON-TUE AS AGREEMENT IMPROVED
TOWARD A POSITIVELY TILTED MEAN TROUGH SETTING UP OVER THE WEST
WITH SOME EJECTING ENERGY SUPPORTING A WAVE THAT REACHES THE
MIDWEST/UPR MS VLY BY NEXT TUE.  CONFIDENCE IS NOT VERY HIGH THAT
CURRENT CONSENSUS WILL VERIFY BUT THESE MODEL RUNS PROVIDED ENOUGH
OF A COMMON SIGNAL TO INCORPORATE A PORTION OF THE OPERATIONAL
MODEL EVOLUTION WITH THE WEAKER ENSEMBLE MEANS AS THE BEST OPTION
FOR THE DETERMINISTIC FCST UPDATE.  THE 00Z GFS/UKMET/CMC AT LEAST
MAINTAIN A REASONABLE DEGREE OF CONTINUITY.

FOR THE SYSTEM TRACKING NEWD FROM THE MIDWEST AN AVG AMONG THE 18Z
GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN PROVIDED THE MOST STABLE
SOLN FOR TRACK AND TIMING.  IN VARYING WAYS UKMET/CMC RUNS HAVE
TENDED TO DEVIATE MORE FROM THE MAJORITY CLUSTER THOUGH THEY
ILLUSTRATE SOME OF THE LINGERING DETAIL UNCERTAINTIES WITH THE
SUPPORTING ENERGY ALOFT.  AS THE TRAILING COLD FRONT HEADS
TOWARD/INTO NEW ENGLAND... ONE TREND OF NOTE FROM YDAY IS TOWARD
SOMEWHAT MORE POTENTIAL THAT FLOW COULD TAP SOME OF THE MSTR ASSOC
WITH A FEATURE TRACKING FROM THE GULF OF MEXICO ACROSS THE FL
PENINSULA AND INTO THE ATLC DURING THE SHORT RANGE TIME FRAME.

CONSIDERATIONS OVER AREAS OF INTEREST LED TO STARTING WITH A BLEND
OF THE 18Z GFS/12Z ECMWF AND THEIR MEANS FOR DAYS 3-5 FRI-SUN WITH
A TRANSITION MOSTLY TO THE MEANS THEREAFTER AS OPERATIONAL RUNS
DIVERGED MORE GREATLY WITH SOME DETAILS.


...WEATHER HIGHLIGHTS/THREATS...

THERE ARE PERSISTENT UNCERTAINTIES WITH SPECIFICS BUT IN PRINCIPLE
THE FCST IS STILL ON TRACK FOR THE STORM TRACKING NEWD FROM THE
MIDWEST FRI INTO THE WEEKEND.  YDAYS SPC OUTLOOK MAINTAINED A
FOCUS ON AN AREA OVER AND AROUND INDIANA AS BEST POTENTIAL FOR
SEVERE CONVECTION IN THE FRI-FRI NIGHT PERIOD.  CONSULT LATEST SPC
PRODUCTS FOR UPDATED INFO.  SNOW TO THE NW OF THE SFC LOW TRACK
MAY BE HVY AT TIMES WHILE THERE MAY ALSO BE AREAS OF MDT-HVY RAIN
AHEAD OF THE COLD FRONT CROSSING THE EAST.  HOW MUCH ATLC MSTR MAY
REACH NEW ENGLAND BY SAT-SAT NIGHT WILL HAVE TO BE MONITORED.
SOME LOCATIONS MAY SEE STRONG WINDS.  ALONG THE WEST COAST THE
LATEST EVOLUTION SFC/ALOFT SHOWN IN MOST GUIDANCE HAS INCREASED
THE POTENTIAL FOR A PERIOD OF HEAVIER RAIN/HIGHER ELEV SNOW
FOCUSED OVER CALIFORNIA... MOST LIKELY DURING THE WEEKEND... WITH
A PERIOD OF STRONG WINDS ALSO A PSBL THREAT.  SOME MSTR WILL
EXTEND INTO FAVORED TERRAIN OF THE INTERIOR WEST/ROCKIES.  THEN
BEYOND THE ROCKIES ONE OR MORE AREAS OF PCPN MAY DEVELOP WITH THE
AID OF IMPULSES EMBEDDED WITHIN FLOW ALOFT THAT SHOULD BE TURNING
SWLY AS WELL AS A WAVY FRONT GRADUALLY LIFTING NWD OVER THE
CNTRL-ERN STATES.  NRN AREAS MAY SEE SOME WINTRY PCPN TYPES WITH
RAIN FARTHER S.

ON FRI MUCH OF THE ERN U.S. SHOULD SEE TEMPS 15-30F ABOVE NORMAL
WITH WARMTH HANGING ON INTO SAT ALONG THE EAST COAST.  EXPECT SOME
LOCATIONS TO SEE RECORD WARM VALUES FOR MAX/MIN READINGS.  IN
SPITE OF A SIGNIFICANT COOLING TREND... TEMPS SHOULD ONLY DROP TO
NEAR OR SLIGHTLY BELOW NORMAL LEVELS BRIEFLY BEFORE REBOUNDING
ABOVE NORMAL AGAIN EARLY NEXT WEEK.  THE WARMING TREND SHOULD
START ON SUN OVER THE SRN PLAINS.  MUCH OF THE WEST AND INTO THE
N-CNTRL PLAINS WILL LIKELY SEE BELOW NORMAL TEMPS WITH SOME
LOCATIONS SEEING MINUS 10-15F OR SO ANOMALIES ONE OR MORE DAYS.

RAUSCH

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.