131  
FXUS02 KWBC 161551  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1050 AM EST FRI FEB 16 2018  
 
VALID 12Z MON FEB 19 2018 - 12Z FRI FEB 23 2018  
   
..COOLED/UNSETTLED WEATHER FOR THE WEST
 
   
..FRIGID CONDITIONS FOR THE NORTH-CENTRAL ROCKIES/PLAINS
 
   
..RECORD WARMTH FROM THE SOUTH-CENTRAL TO EASTERN US
 
   
..HEAVY RAINFALL THREAT FROM THE ARKLATEX TO THE TN/OH VALLEYS
 
 
   
..PATTERN OVERVIEW
 
 
IT REMAINS THE CASE THAT A RATHER STAGNANT SYNOPTIC-SCALE PATTERN  
IS FAVORED NEXT WEEK AS A SUBTROPICAL RIDGE HOLDS STRONG FROM THE  
CENTRAL/EASTERN CARIBBEAN UP TOWARD BERMUDA. WELL ABOVE AVERAGE  
MID-LEVEL HEIGHTS ARE EXPECTED ACROSS THE EASTERN U.S. AS VALUES  
IN THE 582-588 DM RANGE ARE SUGGESTED BY MOST GUIDANCE. RELATIVE  
TO CLIMATOLOGY...THESE COULD EASILY REACH THE 2 TO 2.5 STANDARD  
DEVIATION RANGE. MEANWHILE...ACROSS THE WESTERN/CENTRAL U.S...A  
MEAN UPPER TROUGH WILL SITUATE ITSELF OVER THE REGION WITH A  
TENDENCY FOR UPPER TROUGHS TO PEEL BACK OVER THE SOUTHWESTERN U.S.  
AND INTO THE OFFSHORE PACIFIC WATERS. AN EVENTUAL SPLIT IN THE  
FLOW IS ANTICIPATED AS NORTHERN STREAM AMPLIFICATION TAKES SHAPE  
ACROSS THE MIDDLE OF THE COUNTRY BY DAY 6/7...FEBRUARY 22/23.  
 
   
..GUIDANCE AND UNCERTAINTY ASSESSMENT
 
 
A STRONG GUIDANCE SIGNAL CONTINUES TO POINT TO AN INCREASINGLY  
AMPLIFIED PATTERN NEXT WEEK WITH A DEEP AND POSITIVELY-TILTED  
WESTERN US TROUGH WITH SOME FLOW SEPARATION POTENTIAL HELD IN  
PLACE BY PERSISTENT/SIGNIFICANT MID-LEVEL POSITIVE HEIGHT  
ANOMALIES SOUTH OF ALASKA AND OVER THE MID-ATLANTIC/SERN US.  
 
FORECAST SPREAD/UNCERTAINTY SEEMS MOST ASSOCIATED WITH THE  
EVOLUTION OF THE EMBEDDED SHORTWAVES IN THE WESTERN US TROUGH AND  
THE PROGRESSION OF THE COLD FRONT IN THE PLAINS AND EASTERN US  
LATER NEXT WEEK. UPSTREAM SPREAD IN THE NORTH PACIFIC SHOULD  
CONTINUE TO LEAD TO RUN-RUN AND MODEL-MODEL VARIANCE WITH TROUGH  
SPECIFICS IN THE WEST AND OUT ACROSS THE REMAINDER OF THE CONUS.  
LEAD WAVY FRONTAL TIMING/PROGRESSION REMAINS UNCERTAIN...BUT  
RECENT GFS/GEFS RUNS HAVE BEEN POSITIONED ON THE WARMER SIDE OF  
THE GUIDANCE ENVELOPE POST-FRONTAL ACROSS THE WRN AND CENTRAL  
STATES. THE PATTERN/TELECONNECTIONS SEEMS COLDER WITH SEVERAL  
SURFACE HIGH PRESSURE SURGES...SO WPC MEDIUM RANGE GUIDANCE WAS  
PRIMARILY DERIVED FROM THE COMPATABLE/WELL CLUSTERED GUIDANCE OF  
THE 00 UTC NAEFS/ECMWF ENSEMBLE MEANS VERSUS THE 06 UTC GEFS MEAN  
OR WITH INCLUSION OF MORE VARIED INDIVIDUAL MODEL RUNS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
AS IS COMMON WITH PERSISTENT HIGH-AMPLITUDE PATTERNS...THERE WILL  
BE IMPRESSIVE TEMPERATURE ANOMALIES COUPLED WITH HEAVY  
PRECIPITATION THREATS. STARTING WITH THE TEMPERATURE  
FORECAST...RATHER EXTREME DEPARTURES FROM CLIMATOLOGY EXIST ON  
MONDAY/TUESDAY ACROSS THE NORTHERN ROCKIES INTO THE ADJACENT HIGH  
PLAINS. OVERALL TEMPERATURES MAY RANGE FROM 35 TO 40 DEGREES BELOW  
AVERAGE WHICH SUPPORTS HIGHS HOVERING AROUND 0 DEGREES WHILE  
OVERNIGHT LOWS PLUNGE INTO THE NEGATIVE TEENS/POSSIBLY LOWER -20S.  
IN SPITE OF THESE EXTREME READINGS...WIDESPREAD DAILY TEMPERATURE  
RECORDS WILL LIKELY NOT BE BROKEN. UNLIKE PREVIOUS ARCTIC  
SURGES...COLDER WEATHER WILL SPILL WEST OF THE CONTINENTAL DIVIDE  
INTO THE PACIFIC NORTHWEST. MEANWHILE...PERSISTENT MID-LEVEL  
SOUTHWESTERLY FLOW COUPLED WITH WELL ABOVE AVERAGE HEIGHTS WILL  
KEEP TEMPERATURES WELL ABOVE AVERAGE IN THE EXPANSIVE WARM SECTOR.  
THIS WILL ULTIMATELY SUPPORT A MULTI-DAY PERIOD OF BROKEN DAILY  
TEMPERATURE RECORDS...PARTICULARLY OVER THE EASTERN US. WHILE  
TEMPERATURES SHOULD COOL AS A FRONTAL ZONE STALLS OVER THE  
CAROLINAS BACK TOWARD THE MID-SOUTH...READINGS SHOULD STILL STAY  
SOMEWHAT ABOVE CLIMATOLOGY.  
 
THE HIGHLY CONFLUENT MID-LEVEL FLOW OVER THE CENTRAL U.S. WILL BE  
THE SITE OF A FAIRLY EXTENSIVE PERIOD OF HEAVY RAINFALL.  
INITIALLY...THE UPPER LOW BARRELING OUT OF THE SOUTHWESTERN U.S.  
WILL BE THE FOCUS FOR PRECIPITATION EXITING THE FOUR CORNERS WITH  
SNOW LINGERING OVER THE CENTRAL ROCKIES. EVENTUALLY THE DOWNSTREAM  
FRONTAL ZONE SHOULD LIGHT UP WITH MODERATE TO HEAVY RAINFALL  
ANYWHERE FROM THE ARKLATEX THROUGH THE OZARKS AND INTO THE TN/OH  
VALLEYS. THE PERIOD OF INTEREST GENERALLY SPANS FROM TUESDAY  
THROUGH THURSDAY ALTHOUGH THE TIMING IS VARIABLE BASED ON  
GUIDANCE. SOME WINTRY PRECIPITATION THREAT WOULD BE LIKELY ALONG  
THE NORTHERN EXTENT WHICH WOULD INCLUDE THE UPPER MIDWEST INTO THE  
GREAT LAKES. EVENTUALLY THE ACTIVITY WILL SLIDE EASTWARD AND  
WEAKEN IN INTENSITY WHILE UNSETTLED CONDITIONS RETURN TO THE  
PACIFIC NORTHWEST.  
 
SCHICHTEL/RUBIN-OSTER  
 

 
 
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