Prognostic Meteorological Discussion
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FXUS02 KWBC 221601
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EST MON JAN 22 2018

VALID 12Z THU JAN 25 2018 - 12Z MON JAN 29 2018

...PATTERN OVERVIEW...

A WAVY MID-LATITUDE PATTERN IS IN STORE FOR THE PERIOD WITH THE
PRIMARY LONGWAVE TROUGH INITIALLY OVER THE WEST COAST ON THURSDAY
MORNING. THIS PATTERN WILL SHIFT EASTWARD IN TIME WHILE ABSORBING
A SOUTHERN STREAM FEATURE IN THE VICINITY OF THE ARKLATEX ON
THURSDAY NIGHT. A DEEP SURFACE CYCLONE SHOULD ACCOMPANY THIS
AMPLIFIED FLOW WITH THE PARENT WAVE LIFTING INTO FAR WESTERN
ONTARIO BY 27/1200Z. THE ATTENDANT SURFACE FRONT IS EXPECTED TO
CROSS THE I-95 CORRIDOR BY SUNDAY AFTERNOON WHILE AN ADDITIONAL
CLIPPER-LIKE SYSTEM SWEEPS ACROSS THE NORTHEASTERN U.S. BY EARLY
NEXT WEEK. ACROSS THE EASTERN PACIFIC AND ADJACENT WEST
COAST...QUASI-ZONAL FLOW WILL BE ESTABLISHED EARLY IN THE WEEKEND
WITH A POWERFUL SURFACE CYCLONE CRASHING INTO COASTAL BRITISH
COLUMBIA BY SATURDAY MORNING. IN ITS WAKE...MID-LEVEL HEIGHTS
BUILD FOR THE REMAINDER OF THE WEEKEND WHILE A STRONG UPPER TROUGH
LOOMS OFFSHORE BY DAY 7/JANUARY 29.


...MODEL GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES...

THROUGH DAY 4/JANUARY 26...OPERATIONAL/ENSEMBLE GUIDANCE APPEAR TO
BE IN SOLID AGREEMENT WITH THE EVOLVING SYNOPTIC-SCALE PATTERN.
TOWARD THE END OF THE WORK WEEK...THE BIGGEST SHIFT IN THE
GUIDANCE IS TO BE QUICKER WITH THE NORTH-CENTRAL SURFACE LOW PER
MULTI-DAY ENSEMBLE LOW COMPARISONS. MARKED DIFFERENCES APPEAR OVER
THE WEEKEND AS THE GUIDANCE STRUGGLE WITH THE DEGREE OF
AMPLIFICATION ACROSS THE EASTERN U.S. CONSIDERING MODELS FROM THE
OVERNIGHT SHIFT...RELEVANT OPERATIONAL SOLUTIONS AS WELL AS
ENSEMBLE SPAGHETTI PLOTS SHOWED AN UPPER TROUGH DIGGING THROUGH
THE OZARKS ON 28/1200Z. HOWEVER...THE 00Z SUITE OF MODELS HAS MADE
A SIGNIFICANT EASTWARD/FLATTER ADJUSTMENT WITH THE LONGWAVE
PATTERN. IT IS WORTH NOTING THERE ARE A SIGNIFICANT NUMBER OF 00Z
ECMWF/CMC ENSEMBLE MEMBERS WHICH FAVOR THE SLOWER/DEEPER SOLUTION
SO NOT COMPLETELY SOLD ON THIS LATEST FORECAST TREND. REGARDLESS
OF MODEL CHOICE...LOWER HEIGHTS DO APPEAR TO BE FAVORED INTO EARLY
NEXT WEEK ACROSS THE EAST COAST CHARACTERIZED BY VARIOUS LEVELS OF
AMPLIFICATION.

ACROSS THE WESTERN U.S...AS THE INITIAL SYSTEM TRACKS TOWARD THE
GREAT PLAINS ON FRIDAY...A POWERFUL UPPER LOW WILL SWING SOUTHWARD
FROM AK RESULTING IN GENERAL ZONAL FLOW INTO THE PACIFIC
NORTHWEST. AN EMBEDDED WAVE WITHIN THIS FLOW REGIME WILL CONSIST
OF A RATHER POTENT/COMPACT SURFACE CYCLONE TAKING AIM ON THE
BRITISH COLUMBIA COAST. MODELS SHOW AN ATMOSPHERIC RIVER SETUP
WITH THE 00Z GFS SHOWING INTEGRATED VAPOR TRANSPORT VALUES NEARING
1000 KG/M/SEC ON FRIDAY EVENING/NIGHT OVER THE OR COAST. DURING
THE WEEKEND...THE GUIDANCE AGREE ON BUILDING HEIGHTS OVER THE
WESTERN U.S. AS THE MENTIONED UPPER LOW EMANATING FROM AK
APPROACHES THE COAST BY EARLY NEXT WEEK.

THROUGH DAY 4/JANUARY 26...UTILIZED A MULTI-MODEL CONSENSUS OF THE
06Z/00Z GFS AND 00Z ECMWF/CMC/UKMET GIVEN REASONABLE AGREEMENT.
ALSO...THE GLOBAL ENSEMBLE MEANS SEEM TO WASH OUT THE DEEP SURFACE
LOW APPROACHING BRITISH COLUMBIA ON FRIDAY EVENING. THUS...THEIR
CONTRIBUTIONS ARE MINIMIZED AT LEAST INITIALLY. BY THE
WEEKEND...AS THE UPPER PATTERN BEGINS TO BREAK DOWN ACROSS THE
EASTERN U.S...STARTED TO LEAN MORE ON THE SLOWER GUIDANCE WHICH
REQUIRED USE OF QUITE A BIT OF OVERNIGHT CONTINUITY COUPLED WITH
THE 00Z ECMWF ENSEMBLE MEAN. THIS PARTICULAR SOLUTION WILL HOLD
THE PATTERN BACK A BIT IN CASE THE RECENT QUICKER TREND REVERTS
BACK.


...SENSIBLE WEATHER HIGHLIGHTS/THREATS...

MULTIPLE ROUNDS OF PRECIPITATION ARE LIKELY OVER THE PACIFIC
NORTHWEST/CENTRAL BASIN/UPPER INTERMOUNTAIN WEST EXTENDING DOWN
INTO NORTHERN CA. AS MENTIONED EARLIER...THE HEAVIEST ACTIVITY IS
EXPECTED ON FRIDAY/SATURDAY GIVEN THE ATMOSPHERIC RIVER SET UP.
24-HOUR QPF MAY APPROACH THE 3 TO 4 INCH RANGE IN SOME LOCATIONS
BASED ON SOME OF THE LATEST GUIDANCE. SOME WINTRY PRECIPITATION
COULD LEAK INTO THE LOWER ELEVATIONS EARLY IN THE FORECAST GIVEN
RATHER LOW 1000-500 MB THICKNESSES. LOOKING ACROSS THE
CENTRAL/EASTERN U.S...THE ADVANCING FRONTAL ZONE WILL EVENTUALLY
LIGHT UP FROM THE ARKLATEX UP INTO THE MO VALLEY ON FRIDAY AS
APPRECIABLE MOISTURE LIFTS POLEWARD. THERE IS A HEAVY RAINFALL
SIGNAL NOTED ACROSS THE NORTHERN GULF OF MX WHICH COULD EASILY
PUSH INTO THE CENTRAL/EASTERN GULF COAST STATES. OTHERWISE...A
BROAD SHIELD OF LIGHT/MODERATE RAINFALL WILL SPREAD ALONG THE
FRONTAL ZONE WITH THE POTENTIAL FOR SOME SNOW IN ITS WAKE AS
ADDITIONAL UPPER TROUGHING SWEEPS OVERHEAD.

A VAST MAJORITY OF THE COUNTRY CAN EXPECT ABOVE AVERAGE
TEMPERATURES GIVEN THE HEAVY INFLUENCE OF PACIFIC AIR MASSES ON
THE DOMINANT WEATHER PATTERN. ANOMALIES ON THE ORDER OF 10 TO 20
DEGREES ABOVE CLIMATOLOGY ARE POSSIBLE IN ADVANCE OF THE COLD
FRONT WITH THE POTENTIAL FOR SOME RECORD OVERNIGHT WARMTH ON
SUNDAY MORNING ACROSS THE NORTHEASTERN STATES. PROJECTS LOWS MAY
RANGE FROM THE MID 30S TO LOWER 40S OVER THIS REGION WHICH COULD
SET SOME DAILY RECORDS. ACROSS THE WESTERN U.S...THE DEEP UPPER
TROUGH AND ACCOMPANIED PRECIPITATION THREATS SHOULD KEEP
TEMPERATURES BELOW CLIMATOLOGY THROUGH SATURDAY.
HOWEVER...DEPARTURES ARE ONLY EXPECTED TO BE IN THE 5 TO 10 DEGREE
RANGE. ELSEWHERE...CONDITIONS COULD BE ON THE COOLER SIDE ALONG
THE GULF COAST GIVEN HEAVY RAINFALL AND ABUNDANT CLOUD COVER
EXPECTED.



RUBIN-OSTER

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