531  
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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