Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXUS02 KWBC 251618
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1117 AM EST SAT FEB 25 2017

VALID 12Z TUE FEB 28 2017 - 12Z SAT MAR 04 2017

...OVERVIEW AND GUIDANCE PREFERENCES...

A LONGWAVE TROUGH INITIALLY ALIGNED OVER THE WESTERN U.S. ON
TUESDAY WILL STEADILY PRESS EASTWARD THROUGH THE CENTRAL AND
EASTERN U.S. WEDNESDAY AND THURSDAY, BEFORE RELATIVELY ZONAL FLOW
SETS UP OVER THE NORTHERN TIER OF NATION BY THE END OF WEEK.
MEANWHILE, SLOW-MOVING SOUTHERN STREAM ENERGY IS EXPECTED TO DIG
FROM THE SOUTHWEST TO NORTHERN MEXICO DURING THE LATER HALF OF THE
WEEK.

DESPITE REASONABLE AGREEMENT WITH THE LARGE SCALE FLOW PATTERN,
THERE IS STILL A CONSIDERABLE AMOUNT OF SPREAD AMONG MODEL
GUIDANCE WITH THE SMALLER SCALE FEATURES IMPACTING THE LOWER 48
NEXT WEEK.  DETERMINISTIC GUIDANCE CONTINUES TO TREND SLOWER WITH
THE TIMING OF THE COLD FRONT PUSHING THROUGH THE EASTERN HALF OF
THE COUNTRY WEDNESDAY INTO THURSDAY, WHERE THE GFS WAS ONCE A FAST
OUTLIER AND IS NOW ON THE SLOWER SIDE OF MODEL SPREAD.  ALSO,
MODELS CONTINUE TO MAKE RUN-TO-RUN CHANGES WITH THE EVOLUTION OF
SURFACE LOW/LOWS POSSIBLY STRENGTHENING ALONG THE BOUNDARY.  THE
LATEST ENSEMBLE MEAN GUIDANCE SHOWS THE POTENTIAL FOR A SURFACE
LOW ALONG THE FRONT TO RAPIDLY DEEPEN WHILE LIFTING FROM THE LOWER
GREAT LAKES TO SOUTHERN QUEBEC WEDNESDAY INTO THURSDAY.

ELSEWHERE, THE GFS STILL APPEARS TO BE A STRONG OUTLIER WITH
SHORTWAVE ENERGY AND POSSIBLE SURFACE WAVE DROPPING INTO THE NORTH
CENTRAL U.S. THURSDAY, AND ENSEMBLE MEMBERS, ESPECIALLY ECMWF
ENSEMBLE MEMBERS, ARE SHOWING AN ALARMINGLY LARGE AMOUNT OF SPREAD
WITH FLOW SETTING UP OVER THE NORTHEAST PACIFIC/NORTHWESTERN U.S.
LATE NEXT WEEK.

THE WPC DAY 3-7 FORECAST STARTED WITH A BLEND BETWEEN THE 06Z GEFS
MEAN, 00Z ECMWF ENSEMBLE MEAN, AND 00Z ECMWF, WHICH SEEMED TO BEST
ACCOUNT FOR SOME OF THE UNCERTAINTY AND REPRESENT THE MIDDLE OF
MODEL SPREAD WITH SOME OF THE SMALLER SCALE FEATURES.


...WEATHER HIGHLIGHTS/THREATS...

SHOWERS WITH EMBEDDED HEAVY RAIN AND CONVECTION WILL BE POSSIBLE
WITH THE COLD FRONT PUSHING THROUGH THE EASTERN HALF OF THE NATION
TUESDAY-THURSDAY, AND THE STORM PREDICTION CENTER IS HIGHLIGHTING
A RISK OF SEVERE WEATHER OVER PORTIONS OF THE LOWER MISSISSIPPI
AND TENNESSEE VALLEYS.  SNOW AND STRONG WINDS WILL BE POSSIBLE TO
THE NORTHWEST OF A SURFACE LOW POTENTIALLY DEEPENING ALONG THE
BOUNDARY, WHICH IS CURRENTLY EXPECTED TO TRACK FROM THE LOWER
GREAT LAKES TO SOUTHERN QUEBEC WEDNESDAY INTO THURSDAY.  BEHIND
THIS SYSTEM, PRECIPITATION COVERAGE SHOULD DECREASE ACROSS THE
CONUS LATER IN THE WEEK, WITH THE EXCEPTION OF THE NORTHWEST,
WHERE MODERATE TO HEAVY RAIN AND HIGHER ELEVATION SNOW WILL BE
POSSIBLE WITH STRONG ONSHORE FLOW.

TEMPERATURES SHOULD TREND BACK TOWARD MORE TYPICAL LEVELS IN THE
EAST AFTER THE FRONT CLEARS THE COAST, WHILE TEMPERATURES SHOULD
RISE BACK ABOVE AVERAGE IN THE WEST AND THEN THE PLAINS BY NEXT
FRIDAY AND SATURDAY.


GERHARDT


$$





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