Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6
000
FXUS02 KWBC 041613
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1111 AM EST SUN DEC 04 2016

VALID 12Z WED DEC 07 2016 - 12Z SUN DEC 11 2016

...OVERVIEW...

THE MEDIUM-RANGE PERIOD WILL BEGIN WITH A DEVELOPING LOW PRESSURE
CENTER MOVING OFF THE MID-ATLANTIC COAST ON WEDNESDAY AS THE FIRST
SURGE OF ARCTIC AIR THIS SEASON IS WELL UNDER WAY ACROSS THE
WESTERN AND CENTRAL U.S. MODELS STILL SHOW NOTICEABLE DIFFERENCES
IN THE SPEED OF PROGRESSION OF THE ARCTIC AIR MASS THROUGH DAY 4
THURSDAY IN THE EASTERN U.S.  MEANWHILE...PRECIPITATION FROM THE
NEXT PACIFIC CYCLONE SHOULD HAVE MOVED ONSHORE AND HAVE PENETRATED
WELL INTO THE MOUNTAINOUS TERRAIN IN THE NORTHERN ROCKIES.  A
PIECE OF THE ASSOCIATED ENERGY SHOULD MOVE OFF INTO THE PLAINS
WHERE RETURN FLOW FROM THE ARCTIC HIGH SHOULD SPREAD MOISTURE
NORTHWARD AHEAD OF A FRONT AND A LEAD LOW PRESSURE SYSTEM FROM THE
GULF TOWARDS THE GREAT LAKES BY THE WEEKEND.


...MODEL EVALUATION/PREFERENCES...

MODELS CONTINUE TO DISAGREE ON HOW FAST THE FIRST ARCTIC OUTBREAK
OF THE SEASON SPREADING ACROSS THE COUNTRY ON DAY 3 AND 4 WED/THU.
 THE ECMWF...WITH CYCLOGENESIS SHOWN ALONG THE ARCTIC FRONT IN DAY
4 OVER THE OHIO VALLEY...CONTINUES TO OFFER A RELATIVELY SLOW
SOLUTION BUT HAS SHOWN A TENDENCY TO SPEED UP IN THE PAST FEW
RUNS.  ON THE OTHER HAND...THE GFS OFFERS THE FASTEST SOLUTION AND
THE ASSOCIATED UPPER-LEVEL ENERGY HAS PROGRESSIVELY SLOWED
DOWN...WITH LITTLE INDICATIONS OF CYCLOGENESIS ON THE ARCTIC
FRONT.  THEREFORE...IT APPEARS THAT A BLEND OF THE TWO SOLUTIONS
SHOULD YIELD A GOOD STARTING POINT FOR THE DAY 3 AND 4 SEA-LEVEL
PRESSURE FIELD IN THE U.S.  IT WAS NOTED THAT THE 00Z UKMET
SOLUTION IS A GOOD MIDDLE GROUND BETWEEN THE ECMWF AND GFS AND
THUS...WAS INCORPORATED INTO THE BLEND THROUGH DAY 5 FRI.
AFTERWARD...BOTH THE GFS AND ECMWF ENSEMBLE MEANS AGREE REASONABLY
WELL...ALTHOUGH THEY DISAGREE WITH THE SPEED OF ADVANCEMENT OF A
COLD FRONT THROUGH THE WEST ON DAY 6. THEREFORE...A 50-50 BLEND OF
THE 00Z EC MEAN AND THE 06Z GEFS WAS USED AS A COMPROMISE THROUGH
DAY 7.

...WEATHER HIGHLIGHTS/THREATS...

VERY COLD TEMPS OVER THE WRN-CNTRL STATES AS OF WED WILL PUSH EWD
WITH TIME.  DURING WED-THU SOME LOCATIONS FROM THE ERN SLOPES OF
THE ROCKIES INTO THE NRN-CNTRL PLAINS SHOULD SEE HIGHS 20-30F
BELOW NORMAL.  COLD AIR REACHING THE EAST LATE IN THE WEEK SHOULD
BRING A COUPLE DAYS OF MINUS 10-20F ANOMALIES.  A WARMING TREND
WILL COMMENCE BEHIND THE CORE OF COLDEST AIR BUT CNTRL-ERN U.S.
TEMPS SHOULD TEND TO REMAIN SOMEWHAT BELOW NORMAL THROUGH NEXT
WEEKEND WITH THE NRN PLAINS LIKELY TO SEE THE MOST PERSISTENT COLD
ANOMALIES.  THERE MAY BE A BAND OF PCPN ACCOMPANYING THE LEADING
COLD FRONT... FOLLOWED BY MEANINGFUL LAKE EFFECT SNOW IN STRONG
CYCLONIC FLOW DURING THE LATTER HALF OF THE WEEK.  POTENTIAL
SYSTEM NEXT WEEKEND MAY SPREAD A SHIELD OF PCPN FROM THE PLAINS
INTO THE EAST WITH SNOW N/RAIN S.

AFTER WED EXPECT A MULTI-DAY PERIOD OF PCPN FOCUSED OVER WINDWARD
TERRAIN FROM THE NRN-CNTRL WEST COAST INTO THE ROCKIES.  HIGHEST
TOTALS WILL LIKELY BE FROM THE PAC NW COAST AND CASCADES INTO THE
NRN SIERRA NEVADA RANGE.  TEMPS OVER THE WEST WILL MODERATE FROM A
CHILLY START TO THE PERIOD WED BUT SHOULD REMAIN COOL ENOUGH TO
KEEP SNOW LEVELS FAIRLY LOW.  DEPENDING ON OFFSHORE SFC LOW
TRACK/STRENGTH THE PAC NW MAY SEE A PERIOD OF ENHANCED WINDS
MID-LATE WEEK.

KONG/RAUSCH

$$





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