133  
FXUS02 KWBC 261558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1057 AM EST MON FEB 26 2018  
 
VALID 12Z THU MAR 01 2018 - 12Z MON MAR 05 2018  
 
...WIDESPREAD SNOWFALL EXPECTED FOR THE WESTERN U.S. LATE THIS  
WEEK AND INTO THE WEEKEND, WITH LOCATIONS ALONG THE SIERRA NEVADA  
EXPECTED TO MEASURE THE GREATEST TOTALS...  
 
...HIGH-IMPACT COASTAL STORM WILL BRING STRONG WINDS, HEAVY RAIN,  
FLOODING, AND ACCUMULATING SNOW TO PORTIONS OF THE NORTHEAST  
THURSDAY NIGHT INTO FRIDAY...  
 
15Z UPDATE...  
 
MODEL GUIDANCE REMAINED IN GOOD AGREEMENT WITH THE LARGE SCALE  
EVOLUTION OF AN UPPER LOW CLOSING OFF OVER THE PACIFIC NORTHWEST  
LATE THIS WEEK AND A SECOND CLOSED LOW PROGRESSING FROM THE OHIO  
VALLEY TO THE NORTHERN MID-ATLANTIC COAST THURSDAY INTO FRIDAY.  
THERE IS STILL SOME UNCERTAINTY IN THE FORECAST BY THE LATER HALF  
OF THE WEEKEND AS FLOW POSSIBLY FLATTENS OVER THE LOWER 48 EARLY  
NEXT WEEK, BUT THE GEFS/ECWMF ENSEMBLE MEANS STAYED IN RELATIVELY  
GOOD AGREEMENT WITH THE LONGWAVE PATTERN.  
 
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
IT REMAINS THE CASE THAT 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.  
 
MEANWHILE DOWNSTREAM...AN EJECTING AND DYNAMIC MID-UPPER LEVEL  
TROUGH SHOULD EVOLVE INTO A CLOSED LOW OVER OR JUST EAST OF THE MS  
VALLEY WITH A TRACK OVER THE LOWER GREAT LAKES/OHIO VALLEY/NRN MID  
ATLANTIC INTO THE WRN ATLANTIC. THIS SYSTEM WILL FEED INTO A  
DEVELOPING ANOMALOUSLY STRONG/BLOCKY PATTERN CONSISTING OF AN  
UPPER RIDGE THAT RETROGRADES WEST OF SRN GREENLAND AND  
TELECONNECTION-FAVORED TROUGH OVER THE WRN ATLANTIC.  
 
THE WPC MEDIUM RANGE PRODUCT SUITE TOOK ADVANTAGE OF BETTER THAN  
NORMAL CLUSTERING THU-SAT TO UTILIZE A COMPOSITE  
GFS/ECMWF/UKMET/CANADIAN BLEND. SWITCHED TO A BLEND OF QUITE  
COMPATIBLE GEFS/ECMWF ENSEMBLE MEANS LATER SAT-MON WHEN MODEL  
VARIANCE SLOWLY INCREASES.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
A MID-LATE WEEK UPPER TROUGH WILL SETTLE ALONG THE WEST COAST WITH  
AN EMBEDDED CLOSED LOW NEARING THE PACIFIC NW. A LIKELY INLAND  
PROGRESSION OF THE TROUGH/HEIGHT FALLS NEXT WEEKEND WILL BRING A  
CONSIDERABLE AREA OF ACTIVE WEATHER TO THE WRN STATES. BEST  
POTENTIAL FOR PERIODS OF HEAVY RAIN/HIGHER ELEVATION SNOW SHOULD  
EXTEND FROM COASTAL/CASCADE AREAS OF THE PACIFIC NW INTO NWRN CA  
AND THE SIERRA NEVADA RANGE... WITH HIGHEST 5-DAY PRECIP TOTALS  
OVER SW OR/NW CA AND THE SIERRA NEVADA RANGE. ENHANCED PRECIP  
ALBEIT WITH LESSER TOTALS WILL BE POSSIBLE ALONG THE REST OF THE  
CA COAST AND INLAND TO THE NRN/CENTRAL ROCKIES. ARRIVAL AND  
EVENTUAL PROGRESSION OF UPPER TROUGHING WILL LEAD TO A DECREASE IN  
SNOW LEVELS. MODEST PRECIP DEVELOPS OVER THE CENTRAL TO  
EAST-CENTRAL US AHEAD OF THE UPPER TROUGH DAYS 6/7 WITH SYSTEM  
GENESIS/SLOW MOISTURE RETURN.  
 
A WIDESPREAD SWATH OF PRECIPITATION WILL PROGRESS OVER THE ERN  
U.S. THU AS A DEEP MIDWEST LOW AND LEAD FRONTAL SYSTEM PROGRESSES  
EASTWARD TO EMERGE AS A COASTAL STORM OFF THE NERN U.S. FRI.  
ENHANCED WRAPBACK PRECIP SHOULD FOCUS FROM THE MIDWEST/GREAT LAKES  
TO THE NRN MID-ATLANTIC AND SRN NEW ENGLAND...WITH AN INCREASING  
SNOW/ICE THREAT WITH COOLING AS THE LOW INTENSIFIES. THIS SYSTEM  
MAY BRING STRONG WINDS TO SOME AREAS...WITH STRONG ONSHORE FLOW  
NORTH OF THE SURFACE LOW TRACK LEADING TO COASTAL NEW ENGLAND  
FLOODING CONCERNS.  
 
SCHICHTEL  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page