999  
FXUS02 KWBC 081550  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1049 AM EST THU FEB 08 2018  
 
VALID 12Z SUN FEB 11 2018 - 12Z THU FEB 15 2018  
   
..OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE LATEST GUIDANCE MAINTAINS SIMILAR THEMES FROM RECENT DAYS WITH  
RESPECT TO THE OVERALL PATTERN AND UNCERTAINTIES. MODELS AND  
MEANS AGREE UPON A PERSISTENT EASTERN PACIFIC RIDGE AND A  
POSITIVELY TILTED MEAN TROUGH COVERING A MAJORITY OF NORTH  
AMERICA. TO THE SOUTHEAST OF THE MEAN TROUGH, CONSENSUS STILL  
SHOWS AN INITIAL WESTERN ATLANTIC RIDGE RETROGRADING FROM EAST OF  
THE BAHAMAS TOWARD THE GULF OF MEXICO. FORECAST UNCERTAINTIES  
INVOLVE THE EVOLUTION OF INDIVIDUAL SHORTWAVES PROGRESSING AROUND  
THE EAST PACIFIC RIDGE AND FEEDING INTO THE MEAN TROUGH, AS WELL  
AS DETAILS OF CANADIAN/NORTHERN TIER U.S. FLOW AROUND THE  
PERIPHERY OF A BROAD UPPER LOW ANCHORED OVER NORTHEASTERN CANADA.  
 
THE UPDATED WPC FORECAST MAINTAINED FAIRLY GOOD CONTINUITY BY WAY  
OF A 60/40 MODEL/ENSEMBLE MEAN BLEND (00 UTC GFS/ECMWF AND 00 UTC  
GEFS/ECMWF ENSEMBLE MEANS) EARLY IN THE PERIOD FOLLOWED BY A SLOW  
TRANSITION TO ALMOST EXCLUSIVELY ENSEMBLE MEANS BY DAY 7/THU.  
MODEL AND ENSEMBLE FORECAST CLUSERTING REMAINS AVERAGE AT BEST,  
BUT THESE GUIDANCE PIECES SEEMED COMPATABLE ENOUGH FOR BLENDING,  
ALBEIT WITH A GRADUALLY DECREASING MODEL COMPONENT.  
 
AS WESTERN TROUGH ENERGY SETTLES OVER/NEAR THE SOUTHWEST, RECENT  
TRENDS SHOWN BY MODELS AND HINTED AT BY THE ENSEMBLE MEANS HAVE  
BEEN TOWARD GREATER POTENTIAL FOR AN EMBEDDED LOW TO CLOSE OFF BY  
NEXT TUE-THU. WPC PRODUCTS HAVE MODESTLY TRENDED IN THIS DIRECTION  
AS WELL. REMAINING FLOW UNCERTAINTIES TEND TO BE BLENDED OUT AS  
CONSISTENT WITH PREDICTABILLITY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
SHORTWAVE ENERGY MOVING INTO AND EVOLVING OVER THE WEST WILL  
SUPPORT AREAS OF MOSTLY LIGHT-MODERATE PRECIP, FIRST OVER THE  
PACIFIC NORTHWEST AND NORTHERN ROCKIES THEN PUSHING SOUTHWARD WITH  
TIME. INCREASING GUIDANCE SPREAD FOR SPECIFICS OF FLOW ALOFT  
LEADS TO DECLINING CONFIDENCE IN PRECISE COVERAGE/INTENSITY OF  
PRECIP ESPECIALLY OVER THE CENTRAL/SOUTHERN PARTS OF THE WEST.  
EXPECT RAIN OVER COASTAL/LOW ELEVATION AREAS AND SNOW AT HIGHER  
ELEVATIONS. ANOTHER AREA OF LIGHT PRECIP MAY BRUSH NORTHERN AREAS  
AROUND MIDWEEK. SLIGHTLY BELOW TO MODERATELY ABOVE NORMAL TEMPS  
WILL LIKELY TREND WARMER BY WED-THU AS HEIGHTS ALOFT RISE.  
 
GUIDANCE HAS BEEN CONSISTENT IN SUGGESTING THAT THE MEAN PATTERN  
WILL SUPPORT A RELATIVELY WET PERIOD OVER THE SOUTH AND EAST WITH  
AREAS FROM THE SOUTHEASTERN PLAINS THROUGH SOUTHEAST/MID ATLANTIC  
HAVING THE HIGHEST POTENTIAL FOR ONE OR MORE PERIODS OF MODERATE  
TO HEAVY RAINFALL. ONE AREA OF ORGANIZED RAIN WITH A WAVY FRONT  
SHOULD TAPER OFF AFTER SUN. FURTHER ACTIVITY IS LIKELY TO DEVELOP  
BY TUE-THU WITH THE INITIAL FRONT LINGERING NEAR GULF/SOUTHEAST  
COASTS AND THE NEXT FRONT APPROACHING FROM THE PLAINS. EXPECT  
MOST SNOW THAT OCCURS OVER THE EAST TO BE CONFINED TO PORTIONS OF  
THE GREAT LAKES AND NEW ENGLAND. THE SOUTHEAST WILL SEE THE MOST  
PERSISTENT WARMTH DURING THE PERIOD WITH CLOUDS/MOISTURE ENHANCING  
ANOMALIES FOR MORNING LOWS IN PARTICULAR. THIS INCLUDES SOME  
READINGS 20-30F ABOVE NORMAL ON SUN. THE PLAINS AND MID-UPPER MS  
VALLEY WILL START THE PERIOD ON THE COLD SIDE WITH TEMPS 10-20F  
BELOW NORMAL. THE COLD SHOULD PERSIST OVER THE NORTHERN PLAINS  
INTO WED WITH MOST OF THE CENTRAL U.S. WITHIN A FEW DEGREES ON  
EITHER SIDE OF NORMAL BY THU.  
 
SCHICHTEL  
 

 
 
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