215  
FXUS02 KWBC 060651  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
150 AM EST TUE FEB 06 2018  
 
VALID 12Z FRI FEB 09 2018 - 12Z TUE FEB 13 2018  
   
..OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE INTRIGUE CONTINUES FOR FORECAST DETAILS WITHIN MORE BROADLY  
AGREEABLE NORTH AMERICAN MEAN TROUGHING BETWEEN PERSISTENT RIDGES  
ANCHORED OVER THE EAST PACIFIC AND OVER/EAST OF THE BAHAMAS.  
GIVEN THE CONTINUED WIDE SPREAD OF GUIDANCE THAT BEGINS TO DEVELOP  
FAIRLY EARLY IN THE PERIOD AND MIXED TRENDS AMONG SOME SOLUTIONS,  
PREFERENCES REMAIN NEAR THE MIDDLE OF THE ENVELOPE AMONG  
OPERATIONAL SOLUTIONS EARLY WITH A TREND TOWARD AN ENSEMBLE MEAN  
AVERAGE LATER IN THE PERIOD TO PROVIDE STABILITY AS INDIVIDUAL  
MODEL RUNS FURTHER DIVERGE. WHILE THE DETAILS REMAIN IN QUESTION,  
TELECONNECTIONS RELATIVE TO THE MEAN PATTERN SHOW THE STRONGEST  
SIGNALS FOR ONE OR MORE EPISODES OF SIGNIFICANT PRECIP FROM THE  
GULF COAST REGION NORTHEASTWARD AND BELOW NORMAL TEMPS OVER THE  
CENTRAL U.S.  
 
MODELS/ENSEMBLES CONTINUE TO HAVE DIFFICULTY IN RESOLVING THE  
EVOLUTION OF SHORTWAVE ENERGY DROPPING INTO THE NORTHWEST STATES  
AS WELL AS UPSTREAM ENERGY HEADING INTO THE EAST PACIFIC RIDGE.  
THROUGH THE 12Z/18Z CYCLE, THE UKMET/ECMWF HAD THE LEAST  
AMPLIFIED/MOST PROGRESSIVE DEPICTION OF THE LEADING ENERGY DUE TO  
FAST PROGRESSION OF UPSTREAM NORTH PACIFIC ENERGY. ON THE OTHER  
HAND RECENT GFS RUNS HAVE BEEN SHOWING A MUCH DEEPER WESTERN  
TROUGH WITH AN EMBEDDED CLOSED LOW. THE FULL ENSEMBLE SPREAD  
ENCOMPASSES BOTH EXTREMES. THE GFS SCENARIO IS NOT FAR FROM DEEP  
CLOSED LOW SOLUTIONS OFFERED BY SOME CMC RUNS/ENSEMBLES 2-3 DAYS  
AGO. THE 12Z CMC WAS CLOSER TO THE MIDDLE OF THE SPREAD. ALSO OF  
NOTE, MANY MORE ECMWF ENSEMBLE MEMBERS HAD A FAIRLY DEEP WESTERN  
TROUGH TWO DAYS AGO ONLY TO HAVE BARELY TEN PERCENT OF SUCH  
MEMBERS REMAINING AS OF THE 12Z/05 CYCLE. TELECONNECTIONS HAVE  
BEEN FAVORING MODERATE TROUGHING EXTENDING INTO THE SOUTHWEST  
U.S., WHICH AT LEAST RECOMMENDS GREATER TROUGH AMPLITUDE THAN THE  
ECMWF/ECMWF MEAN. OTHERWISE VARIOUS INDIVIDUAL EVOLUTIONS COULD  
FIT WITHIN THE FAVORED PATTERN ON A MULTI-DAY MEAN BASIS. LOOKING  
AT THE NEW 00Z GFS/GEFS/UKMET/CMC RUNS, THE GFS HAS STRAYED EVEN  
FARTHER WEST WITH ITS CLOSED LOW VERSUS THE 18Z RUN WHILE THE  
CMC/UKMET HAVE ADJUSTED CLOSE TO THE 18Z GFS THROUGH SUN. THE  
GEFS MEAN BECOMES SLOWER THAN THAT CLUSTER.  
 
BEHIND THIS FIRST FEATURE, THERE IS SOME PERSISTENCE IN THE  
FORECAST OF ANOTHER SHORTWAVE REACHING THE NORTHWEST AROUND  
SUN-MON BUT LIKE ITS PREDECESSOR THERE IS A LOT OF SPREAD WITH  
RESPECT TO HOW MUCH AMPLIFIES THROUGH THE WEST VERSUS PROGRESSING  
ACROSS THE NORTHERN TIER. THE FACT THAT THE EAST PACIFIC RIDGE  
SHOULD BE FARTHER WEST LATE IN THE PERIOD SUGGESTS A POTENTIAL FOR  
DEEPER AND/OR FARTHER WEST DOWNSTREAM TROUGHING BY EARLY NEXT WEEK  
VERSUS LATE THIS WEEK/WEEKEND. INTERESTINGLY, MODEL/ENSEMBLE  
GUIDANCE APPEARS TO SHOW BETTER AGREEMENT IN PRINCIPLE AROUND  
EARLY DAY 7 TUE THAN WHAT EXISTS DAYS 4-5 SAT-SUN.  
 
AS EXPECTED THESE DIFFERENCES ALOFT ARISING OVER THE WEST  
ULTIMATELY LEAD TO UNCERTAINTY FOR SPECIFICS OF SURFACE EVOLUTION  
EAST OF THE ROCKIES. THE MOST COMMON THEME IN GUIDANCE IS FOR A  
WAVY GREAT LAKES TO SOUTH-CENTRAL PLAINS FRONT TO PUSH SOUTHEAST  
AND THEN DECELERATE AS ENERGY ALOFT APPROACHES, WITH A DEFINED  
THOUGH MODEST EASTERN WAVE DEVELOPING BY SUN. PROGRESSION OF THIS  
WAVE PROVIDES ANOTHER SOUTHEASTWARD PUSH OF THE FRONT, WHICH MAY  
EVENTUALLY STALL AGAIN AS IT BECOMES PARALLEL TO FLOW ALOFT. LATE  
PERIOD DETAILS ARE VERY UNCERTAIN PENDING THE ULTIMATE EVOLUTION  
OF WESTERN TROUGH ENERGY.  
 
TO ACHIEVE THE PREFERRED INTERMEDIATE APPROACH BASED ON GUIDANCE  
AVAILABLE THROUGH THE 18Z CYCLE, THE FORECAST STARTED WITH AN  
OPERATIONAL MODEL BLEND (18Z GFS AND 12Z ECMWF/UKMET/CMC) DAYS 4-5  
FRI-SAT FOLLOWED BY RAPIDLY INCREASING 18Z GEFS/12Z ECMWF MEAN  
INPUT DAY 5 SUN ON THE WAY TO AN EXCLUSIVELY ENSEMBLE MEAN BLEND  
FOR DAYS 6-7 MON-TUE.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
GUIDANCE IS STILL SHOWING THE MOST AGREEABLE SIGNALS FOR LOCALLY  
HEAVY RAINFALL POTENTIAL FROM THE GULF COAST REGION INTO THE TN  
VALLEY/SOUTHERN APPALACHIANS/SOUTHERN MID ATLANTIC. CURRENTLY  
EXPECT THE MOST FAVORED PERIOD OF FOCUSED ACTIVITY TO BE FROM FRI  
NIGHT-SAT THROUGH SUN BUT SOME MOISTURE MAY LINGER INTO NEXT WEEK.  
GULF INFLOW OF AT LEAST MODERATE STRENGTH, SHORTWAVE IMPULSES  
WITHIN SOUTHWESTERLY FLOW ALOFT, AND AT TIMES SLOW MOVEMENT OF THE  
FOCUSING FRONTAL BOUNDARY WILL BE AMONG THE INGREDIENTS THAT MAY  
SERVE TO ENHANCE RAINFALL. MEANWHILE THE NORTHERN INTO CENTRAL  
ROCKIES WILL SEE A PERIOD OF SNOW WITH ONE OR MORE AREAS OF SNOW  
EXTENDING ACROSS PARTS OF THE NORTHERN U.S. INTO NEW ENGLAND.  
UNCERTAINTY IN THE SPECIFICS OF FLOW AT THE SURFACE AND ALOFT LEAD  
TO FAIRLY LOW CONFIDENCE IN DETERMINING HOW MUCH INTERACTION WILL  
OCCUR BETWEEN THE NORTHERN PERIPHERY OF THE GULF TO MID ATLANTIC  
MOISTURE SHIELD AND SUFFICIENTLY COLD TEMPS THAT WOULD SUPPORT  
WINTRY PRECIP TYPES. ALSO UNCERTAIN IS THE PRECIP COVERAGE AND  
INTENSITY WEST OF THE ROCKIES, WITH UT/AZ MOST LIKELY TO SEE SOME  
PRECIP IN THE EVENT OF A MODERATELY DEEP UPPER TROUGH. UPSTREAM  
ENERGY MAY BRING AN EPISODE OF MOSTLY LIGHT PRECIP TO THE  
NORTHWEST DURING THE LATTER HALF OF THE PERIOD.  
 
THE WEST WILL LIKELY SEE A COOLING TREND AFTER DECENT COVERAGE OF  
PLUS 10-20F ANOMALIES LATE THIS WEEK. THE EXTENT OF THIS COOLING  
TREND WILL DEPEND ON DETAILS ALOFT BUT ANOMALIES SHOULD DECLINE AT  
LEAST TO SINGLE-DIGIT POSITIVE VALUES. MUCH OF THE PLAINS SHOULD  
SEE BELOW NORMAL TEMPS DURING THE PERIOD ALBEIT WITH A MODERATING  
TREND FOR MON-TUE. SOME AREAS OVER THE NORTHERN-CENTRAL PLAINS  
MAY SEE TEMPS AS MUCH AS 20-30F BELOW NORMAL ON FRI-SAT. FINALLY,  
WITH THE INCREASED FLOW OF MOISTURE FROM THE GULF COAST  
NORTHEASTWARD ANTICIPATE A PERIOD OF VERY WARM MIN TEMPS OVER THE  
SOUTHEAST THIRD OF THE U.S. WITH SOME PLUS 10-20F ANOMALIES.  
 
RAUSCH  
 

 
 
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