755  
FXUS02 KWBC 160651  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
150 AM EST FRI FEB 16 2018  
 
VALID 12Z MON FEB 19 2018 - 12Z FRI FEB 23 2018  
 
...EXTREMELY COLD TEMPERATURES EXPECTED OVER THE NORTHERN ROCKIES  
WHILE RECORD WARMTH STRETCHES FROM THE SOUTHERN PLAINS TO NEW  
ENGLAND...  
 
...HEAVY RAINFALL THREAT LOOMS FROM THE ARKLATEX INTO THE TN/OH  
RIVER VALLEYS...  
 
   
..PATTERN OVERVIEW
 
 
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 ALL OF THE 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 EVALUATION/FORECAST TRENDS/PREFERENCES
 
 
THE LATEST GUIDANCE REMAINS IN DECENT LARGE-SCALE AGREEMENT WITH  
THE HIGH AMPLITUDE PATTERN IN PLACE. A DEEP UPPER TROUGH WILL  
INITIALLY SITUATE ITSELF OVER THE DESERT SOUTHWEST WITH GRADUAL  
EASTWARD PROGRESSION INTO THE FOUR CORNERS BY THE FOLLOWING DAY.  
SHORTWAVE ENERGY ASSOCIATED WITH THIS FEATURE SHOULD BECOME MORE  
STRETCHED OUT AS IT TRAVERSES INTO A HIGHLY CONFLUENT FLOW ACROSS  
THE MIDDLE OF THE COUNTRY. WEAK WAVES OF LOW PRESSURE ARE EXPECTED  
TO MOVE ALONG THE ADVANCING BOUNDARY WITH THE BAROCLINIC ZONE  
LIKELY REACHING THE I-95 CORRIDOR BY WEDNESDAY AFTERNOON/EVENING.  
WHILE 500-MB HEIGHTS REMAIN RATHER HIGH INTO THE MIDDLE OF NEXT  
WEEK...SURFACE TEMPERATURES SHOULD DROP CONSIDERABLY AS A STRONG  
ARCTIC RIDGE SETS UP ALONG THE EASTERN SEABOARD BY THURSDAY. THIS  
ANTICYCLONE IS FORECAST TO WEAKEN AND MOVE OFFSHORE ALLOWING FOR  
RETURN FLOW TO ENSUE IN EARNEST. OVERALL...TIMING/PLACEMENT  
DIFFERENCES ARE EVIDENT FROM MID-WEEK ONWARD AS THE 00Z/12Z CMC  
LAG THE CONSENSUS WITH THE EVOLUTION OF THE MENTIONED COLD FRONT.  
ADDITIONALLY...THE ENSEMBLE MEANS DISPLAY SOME UNCERTAINTY WITH  
THE POSITION OF THE ARCTIC HIGH AS THE QUICKER 12Z GEFS/NAEFS  
ENSEMBLE MEANS SITS DOWNSTREAM OF THE 12Z ECMWF ENSEMBLE MEAN.  
 
BACK TO THE WESTERN U.S...THE RE-LOADING OF THE UPPER TROUGH  
APPEARS TO BE ANOTHER REGION OF CONTENTION IN THE GUIDANCE. RECENT  
RUNS OF THE GFS/ECMWF FAVOR A SEPARATION OF THE STREAMS AS A SLUG  
OF SHORTWAVE ENERGY SINKS SOUTHWARD ALONG THE EASTERN  
PACIFIC...GENERALLY SETTLING OFFSHORE OF CA BY WEDNESDAY/THURSDAY.  
ON THE CONTRARY...THE 00Z/12Z CMC FAVOR KEEPING MORE OF A LONGWAVE  
TROUGH PATTERN. ENSEMBLE SPAGHETTI PLOTS DO SHOW PLENTY OF MEMBERS  
WITH THIS MORE SEPARATED SOLUTION. MANY OF THE OPERATIONAL MODELS  
DEPICT THIS SLOWER SCENARIO UNFOLDING BUT THERE IS PLENTY OF NOISE  
AMONGST THEIR FORECASTS. ENSEMBLE MEANS CLUSTER WELL WITH THE 12Z  
ECMWF ENSEMBLE MEAN A HAIR AHEAD OF THE OTHER ENSEMBLE SOLUTIONS  
WHILE EVEN HIGHER CONFIDENCE EXISTS WITH NORTHERN STREAM  
AMPLIFICATION OVER THE DAKOTAS/UPPER MIDWEST.  
 
GIVEN SOLID OPERATIONAL MODEL AGREEMENT BETWEEN THE 12Z  
GFS/ECMWF/UKMET...FAVORED A THREE-WAY BLEND OF THESE FORECASTS  
THROUGH DAY 4/TUESDAY BEFORE REMOVING THE 12Z UKMET. GRADUALLY  
INCORPORATED EQUAL CONTRIBUTIONS OF THE 12Z GEFS/ECMWF ENSEMBLE  
MEANS WHILE HOLDING ONTO A SMALLER FRACTION OF THE 12Z GFS/ECMWF  
THROUGH THE REMAINDER OF THE PERIOD. WHILE DIFFERENCES IN THE  
DETAILS EXIST...THE LARGE-SCALE PATTERN APPEARS TO BE RESOLVED  
WELL ENOUGH TO ADD SOME CONFIDENCE IN THE FORECAST.  
 
   
..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 INCLUDING SEATTLE WA AND PORTLAND OR.  
MEANWHILE...IN THE EXPANSIVE WARM SECTOR...PERSISTENT MID-LEVEL  
SOUTHWESTERLY FLOW COUPLED WITH WELL ABOVE AVERAGE HEIGHTS WILL  
KEEP TEMPERATURES AROUND 20 TO 30 DEGREES ABOVE AVERAGE. THIS WILL  
ULTIMATELY SUPPORT A MULTI-DAY PERIOD OF BROKEN DAILY TEMPERATURE  
RECORDS...PARTICULARLY EAST OF THE MS RIVER. ON TUESDAY...READINGS  
IN THE 70S CAN BE FOUND AS FAR NORTH AS SOUTHERN OH INTO THE  
CENTRAL MID-ATLANTIC STATES WHILE LOWS HOLD IN THE 50S UP TO THE  
LOWER GREAT LAKES. 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.  
 
RUBIN-OSTER  
 

 
 
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