698  
FXUS02 KWBC 251557  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1056 AM EST SUN FEB 25 2018  
 
VALID 12Z WED FEB 28 2018 - 12Z SUN MAR 04 2018  
   
..STORMY PATTERN FOR BOTH THE WESTERN AND EASTERN U.S
 
 
...MORE MID-LOWER MS VALLEY/MID-SOUTH HEAVY RAINS AND AN ONGOING  
FLOODING CONCERN...  
 
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
REASONABLE CLUSTERING IN PRINCIPLE AMONG THE CURRENT CYCLE OF  
MODEL/ENSEMBLE GUIDANCE MAINTAINS A DECENT LEVEL OF FORECAST  
CONFIDENCE IN THE LARGE SCALE. HOWEVER SOME RESERVATIONS PERSIST  
FOR IMPORTANT DETAILS OF SEPARATE ANOMALOUS/AMPLIFIED SYSTEMS  
BRINGING SOME SIGNIFICANT WEATHER IMPACTS/THREATS TO THE WESTERN  
AND EASTERN STATES WITHIN A TRANSITIONAL FLOW PATTERN.  
 
THE ESTABLISHED CONSENSUS SCENARIO SHOWS AN AMPLIFYING/SHARPENING  
EAST-CENTRAL PACIFIC RIDGE EXTENDING INTO AND BEYOND ALASKA, WHICH  
SUPPORTS DOWNSTREAM DIGGING OF ENERGY INTO A DEEP WEST COAST  
TROUGH THAT WILL MOST LIKELY FEATURE AN EMBEDDED CLOSED LOW JUST  
OFF THE PACIFIC NORTHWEST COAST BY DAYS 4-5 THU-FRI. IN VARYING  
WAYS GUIDANCE HAS BEEN SIGNALING THAT UPSTREAM ENERGY WILL PUSH  
INTO/THROUGH THE UPSTREAM RIDGE BY NEXT WEEKEND THUS LEADING TO A  
FLATTER WEST COAST MEAN PATTERN AND SPECIFICALLY INLAND  
PROGRESSION OF THE WEST COAST TROUGH AND EVENTUAL DEVELOPMENT OF  
PLAINS LOW PRESSURE. AHEAD OF THESE HEIGHT FALLS A RIDGE WILL  
BUILD INTO/SETTLE OVER THE EAST-CENTRAL U.S..  
 
DOWNSTREAM AN EJECTING SOUTHERN ROCKIES/HIGH PLAINS MID-UPPER  
LEVEL TROUGH AND INITIALLY MORE DIFFUSE NORTHERN STREAM ENERGY  
SHOULD IN SOME FASHION EVOLVE INTO A CLOSED LOW OVER OR JUST EAST  
OF THE MS VALLEY WITH A TRACK OVER THE LOWER GREAT LAKES/OHIO  
VALLEY/NORTHERN MID ATLANTIC INTO THE WESTERN ATLANTIC. THIS  
SYSTEM WILL FEED INTO A DEVELOPING ANOMALOUSLY STRONG/BLOCKY  
PATTERN CONSISTING OF AN UPPER RIDGE THAT RETROGRADES TO A  
POSITION JUST WEST OF SOUTHERN GREENLAND AND  
TELECONNECTION-FAVORED TROUGH OVER THE WESTERN ATLANTIC.  
 
THE UPDATED FORECAST BLEND INCORPORATED VARIOUS ASPECTS OF THE 00Z  
AND 12Z/24 ECMWF, 06Z GFS, AND 00Z CMC/UKMET FROM DAY 3 WED INTO  
DAY 5 FRI TO YIELD A GOOD BALANCE OF CONTINUITY/DETAIL/ACCOUNT FOR  
ONGOING DETAIL UNCERTAINTIES. ALONG THE WEST COAST THERE IS STILL  
A MODERATE DEGREE OF MODEL/ENSEMBLE SPREAD AND RUN TO RUN  
VARIABILITY FOR THE EXACT TRACK OF LOW PRESSURE MOST LIKELY TO  
WRAP UP NEAR VANCOUVER ISLAND WED-THU AND THEN BEGIN WEAKENING AS  
IT DRIFTS SOUTHWARD OFF THE PACIFIC NORTHWEST COAST. WITH NO WELL  
DEFINED TRENDS ESTABLISHED SO FAR, PREFER KEEPING THE TRACK NEAR  
THE CENTER OF MODEL/ENSEMBLE GUIDANCE. FARTHER INLAND THE 00Z GFS  
BECOMES MORE PROGRESSIVE THAN OTHER GUIDANCE WITH LEADING HEIGHT  
FALLS ALOFT BY LATE WEEK. OVER THE EAST THE RESULTING BLEND  
NAVIGATES BETWEEN THE 00Z ECMWF THAT MAY BE A LITTLE SLOW TO  
DEVELOP DUE TO ITS EVOLUTION ALOFT EARLY IN THE PERIOD VERSUS THE  
POTENTIALLY OVER-DEVELOPED/NORTHWARD 12Z/24 ECMWF. THE 06Z GFS  
MAY ALSO TRACK TOO FAR NORTHWARD GIVEN THE UPPER RIDGE BEGINNING  
TO BUILD INTO EASTERN CANADA.  
 
DAYS 6-7 SAT-SUN INTRODUCED AN INCREASING WEIGHT OF THE 06Z  
GEFS/00Z ECMWF MEANS WHILE SCALING BACK OPERATIONAL MODEL INPUT.  
CONTINUING FROM THU-FRI, THE 06Z GFS COMPARES MUCH BETTER TO OTHER  
GUIDANCE VERSUS THE MORE PROGRESSIVE 00Z RUN FOR THE WESTERN U.S.  
TROUGH WHOSE LEADING HEIGHT FALLS EXTEND INTO THE PLAINS. THIS  
TROUGH LOOKS TO BE STUCK BETWEEN AN EVOLVING PACIFIC PATTERN THAT  
FAVORS FLATTER MEAN FLOW ALONG/INLAND FROM THE WEST COAST  
(SUGGESTING THE 00Z CMC MAY BECOME TOO SLOW) AND AN INCREASINGLY  
BLOCKY EASTERN NORTH AMERICAN/WESTERN ATLANTIC PATTERN THAT WOULD  
ARGUE AGAINST ANY RELATIVELY FAST SOLUTIONS FOR PLAINS HEIGHT  
FALLS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
MID-LATE WEEK UPPER TROUGH SETTLING ALONG THE WEST COAST AND  
POSSIBLE EMBEDDED CLOSED LOW NEARING THE PACIFIC NORTHWEST, THEN  
LIKELY INLAND PROGRESSION OF THE TROUGH NEXT WEEKEND, WILL BRING A  
CONSIDERABLE AREA OF ACTIVE WEATHER TO THE WESTERN STATES DURING  
THE PERIOD. BEST POTENTIAL FOR PERIODS OF HEAVY RAIN/HIGHER  
ELEVATION SNOW SHOULD EXTEND FROM COASTAL/CASCADE AREAS OF THE  
PACIFIC NORTHWEST INTO NORTHERN CA AND THE SIERRA NEVADA RANGE,  
WITH HIGHEST 5-DAY PRECIP TOTALS OVER SOUTHWEST OR/NORTHWEST CA  
AND SIERRA NEVADA RANGE. ENHANCED PRECIP ALBEIT WITH LESSER  
TOTALS WILL BE POSSIBLE ALONG THE REST OF THE CA COAST AND INLAND  
TO THE NORTHERN/CENTRAL ROCKIES. ARRIVAL AND EVENTUAL PROGRESSION  
OF UPPER TROUGHING WILL LEAD TO A DECREASE IN SNOW LEVELS. LATE  
IN THE PERIOD SOME PRECIP MAY EXTEND INTO THE PLAINS AHEAD OF THE  
UPPER TROUGH. SOUTHERN ROCKIES SNOW/LOW ELEVATION RAIN ON WED  
SHOULD TAPER OFF WITH THE DEPARTURE OF A LEADING STRONG SHORTWAVE  
ALOFT.  
 
WIDESPREAD CONVECTION AND POTENTIALLY HEAVY RAINS WILL ONCE AGAIN  
POSE A THREAT ACROSS PORTIONS OF THE MID-LOWER MS VALLEY AND  
MID-SOUTH WITHIN THE POTENTIAL FOR A WIDESPREAD SWATH OF  
PRECIPITATION ACROSS MUCH OF THE EASTERN HALF OF THE LOWER 48 AS  
DEVELOPING PLAINS LOW PRESSURE PROGRESSES EASTWARD. THIS THREAT  
WOULD BE FUELED FROM LATE TUE THROUGH THU NIGHT AS MOIST LOW-LEVEL  
SOUTHERLY FLOW WITHIN THE CYCLONE'S WARM CONVEYOR BELT SPREADS  
AMPLE MOISTURE NORTHWARD. IN ADDITION TO THE MID-SOUTH HEAVY  
RAINFALL THREAT, SPC OUTLOOKS INDICATE POTENTIAL FOR SOME STRONG  
TO SEVERE CONVECTION FROM NORTHEAST TX EAST-NORTHEASTWARD.  
ENHANCED PRECIP WILL ALSO BE POSSIBLE FROM THE MIDWEST INTO  
SOUTHERN NEW ENGLAND, WITH SOME BEING OF THE WINTRY VARIETY TO THE  
NORTH OF THE PLAINS/MIDWEST/GREAT LAKES/NORTHERN MID ATLANTIC  
SURFACE LOW TRACK. THIS SYSTEM MAY BRING STRONG WINDS TO SOME  
AREAS, WITH STRONG ONSHORE FLOW TO THE NORTH OF THE SURFACE LOW  
LEADING TO COASTAL FLOODING CONCERNS OVER NEW ENGLAND.  
 
EXPECT BELOW TO WELL BELOW NORMAL TEMPS TO PERSIST OVER MUCH OF  
THE WEST INTO THE NORTHERN PLAINS. THE AXIS OF COLDEST ANOMALIES  
SHOULD EXTEND FROM OR/NORTHERN CA INTO THE HIGH PLAINS WITH HIGHS  
10-20F BELOW NORMAL ON MULTIPLE DAYS. A FEW DAILY RECORDS FOR  
COLD MAX/MIN VALUES ARE POSSIBLE AS WELL. THE WARM SECTOR OF THE  
DEVELOPING PLAINS STORM WILL BRING MUCH ABOVE MIN TEMPS IN  
PARTICULAR TO THE EASTERN HALF OF THE LOWER 48 WED-THU WITH PLUS  
10-25F ANOMALIES AND DAILY RECORDS AT SOME LOCATIONS.  
DURING/AFTER SYSTEM PASSAGE, CLOUDS/WIND MAY KEEP MINS NEAR TO  
ABOVE NORMAL OVER THE EAST BUT SOME LOCATIONS MAY SEE BELOW NORMAL  
HIGHS.  
 
RAUSCH/SCHICHTEL  
 

 
 
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