022  
FXUS02 KWBC 020646  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 AM EST FRI FEB 02 2018  
 
VALID 12Z MON FEB 05 2018 - 12Z FRI FEB 09 2018  
   
..OVERVIEW
 
 
LATEST GUIDANCE SHOWS A CONTINUATION OF THE SHORT RANGE PATTERN,  
FEATURING A STRONG EASTERN PACIFIC RIDGE ALOFT AND FAIRLY  
AMPLIFIED CYCLONIC FLOW OVER MUCH OF THE LOWER 48 STATES/CANADA  
WITH PERIODIC EAST PACIFIC SHORTWAVES GENERATING SURFACE SYSTEMS  
AS THEY CONTINUE INLAND. FLOW WITHIN THE CANADIAN STREAM MAY ALSO  
HAVE SOME INFLUENCE ON SYSTEM EVOLUTION. THE FIRST FEATURE IN THE  
SERIES WILL BE DEPARTING FROM NEW ENGLAND ON DAY 3 MON. THE NEXT  
SYSTEM SHOULD CROSS THE WESTERN-CENTRAL U.S. MON-TUE AND THEN  
TRACK NORTHEASTWARD OVER THE EASTERN STATES BY DAY 5 WED. THERE  
IS LESS CONSENSUS THUS FAR FOR A TRAILING SYSTEM THAT MAY EXIST  
DURING THE LATTER HALF OF THE WEEK.  
 
   
..MODEL GUIDANCE/UNCERTAINTY ASSESSMENT/PREFERENCES
 
 
IN MOST RESPECTS A BLEND OF OPERATIONAL GUIDANCE REPRESENTED  
CONSENSUS IDEAS WITH MINIMAL ADJUSTMENT TO CONTINUITY FOR THE  
EARLY TO MIDDLE PART OF THE FORECAST. FOR THE LEADING SYSTEM  
EXITING THE NORTHEAST BY AROUND THE START OF THE PERIOD EARLY MON,  
THERE HAVE BEEN SOME SIGNIFICANT TRENDS FOR IMPORTANT ASPECTS OF  
DEVELOPMENT OVER THE PAST COUPLE DAYS BUT LATEST SOLUTIONS ARE  
SIMILAR ASIDE FROM MINOR DETAILS THAT CAN STILL TAKE A PORTION OF  
THE SHORT RANGE TIME FRAME TO BE RESOLVED. GUIDANCE SPREAD FOR  
THE MON-TUE ROCKIES/PLAINS SYSTEM REACHING THE EAST BY  
WED--SUPPORTED BY A SHORTWAVE REACHING THE NORTHWEST AS OF EARLY  
MON--HAS NARROWED CONSIDERABLY OVER THE PAST 24 HOURS. HOWEVER  
THE BEHAVIOR OF THE PRECEDING SYSTEM AS WELL AS A FAIR AMOUNT OF  
LINGERING MODEL AND ENSEMBLE SPREAD FOR EXACT TIMING/ORIENTATION  
OF SHORTWAVE ENERGY BY WED SUGGEST THERE IS STILL THE RISK THAT  
MEANINGFUL CONTINUITY CHANGES MAY OCCUR IN FUTURE RUNS. AS  
DIFFERENCES BECOME NOTICEABLE OVER THE EAST, PREFER AN  
INTERMEDIATE SOLUTION AS YESTERDAY'S 00Z/12Z ECMWF RUNS ARE ON THE  
STRONG/WESTERN SIDE OF THE SPREAD (AND WEST OF THE ECMWF MEAN)  
WHILE THE NEW 00Z GFS IS ON THE EASTERN SIDE OF THE ENVELOPE. THE  
12Z/18Z GFS WERE A LITTLE CLOSER TO THE MIDDLE OF THE SPREAD.  
UKMET/CMC RUNS OFFER THE POSSIBILITY FOR SLIGHTLY SLOWER TIMING  
OVER THE EAST BUT WITH INTERMEDIATE TRACK.  
 
UNCERTAINTY INCREASES TO A GREATER EXTENT BEHIND THIS SYSTEM AS  
THERE IS A FAIRLY WIDE SPREAD WITH RESPECT TO TIMING AND OTHER  
DETAILS OF THE NEXT SHORTWAVE PROGRESSING AROUND THE EAST PACIFIC  
RIDGE AROUND MIDWEEK. BASED ON GUIDANCE THROUGH THE 12Z/18Z  
CYCLES, THE 12Z/18Z GFS AND 00Z/01 ECMWF RUNS WERE CLOSEST IN  
PRINCIPLE TO THE 12Z/18Z GEFS AND 12Z ECMWF MEANS WITH A SYSTEM  
REACHING THE NORTHERN TIER BY LATE IN THE WEEK--WITHIN THE GENERAL  
AREA OF LOWER PRESSURES SUGGESTED IN THE MEANS BY FRI. THE 12Z  
ECMWF IS FASTER DUE IN PART TO A BRIEF FLATTENING OF THE UPSTREAM  
RIDGE NOT INDICATED BY MOST OTHER MODELS/MEANS. ON THE OTHER SIDE  
OF THE SPECTRUM SOME INDIVIDUAL ENSEMBLES (MORE FROM THE CMC THAN  
GEFS/ECMWF) AS WELL AS THE NEW 00Z GFS SHOW POTENTIAL FOR GREATER  
AMPLIFICATION OF INCOMING SHORTWAVE ENERGY OVER THE WEST, WHICH  
WOULD LEAD TO DIFFERING SURFACE EVOLUTION. THUS CONFIDENCE IN  
FORECAST SPECIFICS DECREASES CONSIDERABLY BY NEXT THU-FRI IN SPITE  
OF THE MUCH BETTER CONFIDENCE IN THE OVERALL MEAN PATTERN. WITH  
THE ABOVE CONSIDERATIONS IN MIND, THE DAYS 6-7 THU-FRI FORECAST  
BROUGHT TOTAL ENSEMBLE MEAN WEIGHT TO 60 PERCENT WITH REMAINING  
INPUT FROM THE 12Z/18Z GFS AND 00Z/01 ECMWF.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
ACROSS THE WEST EXPECT MOST PRECIP DURING THE PERIOD TO BE  
CONFINED TO SNOW AND LOW ELEVATION RAIN OVER THE PACIFIC NORTHWEST  
AND NORTHERN-CENTRAL ROCKIES, WITH HIGHEST TOTALS OVER FAVORED  
WINDWARD TERRAIN. ACTIVITY SHOULD TEND TO BECOME LIGHTER/MORE  
SCATTERED TOWARD WED-THU BUT LATE WEEK DETAILS BECOME MORE  
UNCERTAIN GIVEN FORECAST SPREAD FOR INCOMING SHORTWAVE ENERGY.  
EAST OF THE ROCKIES A BAND OF MOSTLY LIGHT SNOW MAY CROSS THE  
NORTH-CENTRAL STATES EARLY IN THE WEEK. THEN LOW PRESSURE  
EMERGING OVER THE PLAINS BY TUE AND TRACKING THROUGH THE EAST  
AROUND WED WILL GENERATE A BROAD AREA OF VARIOUS PRECIP TYPES OVER  
THE EASTERN HALF OF THE U.S. EXPECT A BAND OF MEANINGFUL SNOW TO  
THE NORTH/WEST OF THE SURFACE LOW CENTER, WITH A MOST LIKELY AXIS  
FROM THE LOWER GREAT LAKES AND/OR UPPER OH VALLEY INTO NEW  
ENGLAND/SOUTHEASTERN CANADA. SOME OF THE SNOW MAY EXTEND BACK  
INTO THE CENTRAL PLAINS. MEANWHILE THERE IS POTENTIAL FOR OVER  
THE LOWER MS VALLEY INTO THE TN VALLEY. SOME OF THIS MOISTURE  
SHOULD EXTEND TO THE EAST/NORTHEAST.  
 
THE MEAN PATTERN ALOFT WILL KEEP TEMPS QUITE WARM OVER THE WEST  
THROUGH THE PERIOD WITH SOME AREAS SEEING PLUS 10-20F ANOMALIES ON  
MULTIPLE DAYS. POTENTIAL FOR DAILY RECORD MAX/WARM MIN VALUES AT  
SOME LOCATIONS SHOULD BE BEST DURING THE LATTER HALF OF THE WEEK.  
TO THE EAST OF THE ROCKIES EXPECT THE COLDEST TEMPS TO BE ANCHORED  
OVER THE NORTHERN PLAINS MON-WED WITH SOME READINGS 10-20F BELOW  
NORMAL. THE PLAINS INTO EASTERN U.S. SYSTEM WILL BRING A BRIEF  
EPISODE OF WARMER TEMPS TO THE SOUTH AND EAST AROUND MIDWEEK  
BEFORE BRINGING COLDER TEMPS INTO THE EAST FOR THU-FRI. BY THAT  
TIME THE CORE OF COLDEST READINGS WILL BE SENSITIVE TO EXACT  
LOCATION OF NEW SNOW COVER. MEANWHILE THE PLAINS SHOULD SEE A  
WARMING TREND BY THU-FRI.  
 
RAUSCH  
 

 
 
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