140  
FXUS02 KWBC 080536  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1235 AM EST FRI FEB 08 2019  
 
VALID 12Z MON FEB 11 2019 - 12Z FRI FEB 15 2019  
   
..OVERVIEW
 
 
THE LARGE SCALE PATTERN ACROSS NORTH AMERICA WILL REMAIN LARGELY  
UNCHANGED THROUGH THE MEDIUM RANGE. A PERSISTENT UPPER-LEVEL RIDGE  
FROM THE NORTH PACIFIC TO ALASKA WILL BE THE MOST DOMINANT  
FEATURE, GOVERNING WHAT HAPPENS DOWNSTREAM ACROSS THE CONUS. THE  
EVOLUTION OF SHORTWAVE ENERGY TRAVERSING THIS RIDGE, EITHER BY  
CRESTING THE RIDGE OR BY UNDERCUTTING IT AND THEN DIVING  
SOUTHEASTWARD TOWARD THE WESTERN U.S. CONTINUES TO BE ONE OF THE  
MORE UNCERTAIN, AND MOST IMPACTFUL ASPECTS ON THE MEDIUM RANGE  
FORECAST. DOWNSTREAM OF THE RIDGE, A POSITIVELY-TILTED MEAN TROUGH  
AXIS APPEARS LIKELY TO PERSIST OFF THE U.S. WEST COAST, KEEPING A  
VERY STORMY PATTERN IN PLACE. FARTHER EAST, THE SUBTROPICAL RIDGE  
WILL ATTEMPT TO EXERT ITSELF ACROSS THE SOUTH CENTRAL AND  
SOUTHEAST U.S. A RELATIVELY INTENSE THERMAL GRADIENT WILL CONTINUE  
THROUGH THE PERIOD ACROSS THE CENTRAL U.S., BETWEEN THESE TWO  
LARGE SCALE FEATURES, RESULTING IN THE CONTINUED POTENTIAL FOR AN  
ACTIVE CYCLONE TRACK FROM THE CENTRAL PLAINS TO THE MIDWEST AND  
GREAT LAKES.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
A SIGNIFICANT DEGREE OF UNCERTAINTY AND RUN-TO-RUN VARIABILITY  
CONTINUES IN THE MODEL GUIDANCE WITH RESPECT TO THE AFOREMENTIONED  
SHORTWAVE ENERGY ORIGINATING IN THE NORTH PACIFIC AND EVENTUALLY  
NEARING THE WESTERN U.S. AND EVENTUALLY CROSSING THE ROCKIES. ONE  
SUCH SHORTWAVE SHOULD MOVE FROM THE FOUR CORNERS REGION INTO THE  
PLAINS ON DAY 3 (MON), WITH EXPECTED DEVELOPMENT OF ANOTHER  
POTENTIALLY SIGNIFICANT LOW PRESSURE SYSTEM TRACKING NORTHEAST  
INTO THE GREAT LAKES/NORTHEAST TUE-WED (PERHAPS DEPENDENT ON  
INTERACTIONS WITH ADDITIONAL NORTHERN STREAM SHORTWAVE ENERGY).  
MODEL SOLUTIONS SHOW MORE VARIABILITY WITH THE AMPLITUDE OF THIS  
SHORTWAVE RATHER THAN THE TIMING, MAKING A BLEND IDEAL. MEANWHILE,  
ANOTHER SHORTWAVE REACHES THE PACIFIC NORTHWEST ON MON WHILE YET  
ANOTHER DIVES SOUTHWARD ALONG THE COAST TUE-WED. THE FIRST OF  
THESE SHOWS RELATIVELY GOOD CONSENSUS AMONG THE GUIDANCE, WHILE  
THE SECOND BEGINS TO SHOW MUCH MORE SPREAD BY THU. WHETHER THIS  
SECOND SHORTWAVE PRESSES INLAND BY THU OR REMAINS OFFSHORE  
REINFORCING THE MEAN TROUGH IS A SIGNIFICANT QUESTION. THE ECMWF  
WAS THE MOST AGGRESSIVE TO MOVE THIS FEATURE INLAND, WHILE THE CMC  
KEEPS ALL THE ENERGY CONFINED OFFSHORE. THE ECENS SEEMS TO SUPPORT  
SOMETHING MORE ALONG THE LINES OF THE CMC, WHILE THE GFS/GEFS ARE  
IN BETWEEN. THERE IS SOME BROAD CONSENSUS AMONG THE GUIDANCE THAT  
THE ARRIVAL OF ADDITIONAL SHORTWAVE ENERGY BY THU WILL CONTINUE TO  
REINFORCE THE POSITIVELY-TILTED MEAN TROUGH OFFSHORE.  
 
TO DEAL WITH THE VARYING SOLUTIONS, A MULTI-MODEL/ENSEMBLE BLEND  
WAS USED AS A BASIS FOR THE FORECAST. THIS INCLUDED THE  
ECMWF/UKMET/CMC/GFS AS WELL AS THE ECENS/NAEFS ENSEMBLE MEANS.  
MAJORITY WEIGHT WAS PLACED ON DETERMINISTIC SOLUTIONS DURING DAYS  
3-5 WITH MAJORITY WEIGHT PLACED ON ENSEMBLE MEANS DURING DAYS 6-7.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
ANOTHER ROUND OF POTENTIALLY HEAVY PRECIPITATION WILL SPREAD INTO  
THE LOWER TO MID-MISSISSIPPI AND TENNESSEE VALLEYS EARLY NEXT WEEK  
AS MOISTURE SURGES NORTHWARD ATOP A WARM FRONT ALONG THE GULF  
COAST. AS THE LOW PRESSURE SYSTEM STRENGTHENS IN THE MIDWEST ON  
TUESDAY, PRECIPITATION IS EXPECTED TO PUSH THROUGH THE OHIO VALLEY  
AND INTO THE MID-ATLANTIC/NORTHEAST. WINTRY PRECIPITATION WILL BE  
POSSIBLE ON THE NORTHWEST/NORTH SIDE OF THE LOW AND WELL AHEAD OF  
THE WARM FRONT. IN THE WEST WHERE PERSISTENT TROUGHING WILL REMAIN  
WITH FREQUENT SHORTWAVES/FRONTAL SYSTEMS, MODERATE PRECIPITATION  
(VALLEY RAIN AND MOUNTAIN SNOW) IS EXPECTED ACROSS THE PACIFIC  
NORTHWEST AT DAYS 4-5, SHIFTING SOUTHWARD AND BECOMING HEAVIER ON  
DAY 6-7 ACROSS MUCH OF CALIFORNIA.  
 
MUCH BELOW AVERAGE TEMPERATURES WILL PERSIST NORTH OF AN ARCTIC  
FRONT FROM THE PACIFIC NORTHWEST TO THE NORTHERN ROCKIES AND  
NORTHERN HIGH PLAINS THROUGHOUT THE PERIOD. THE COLDEST  
TEMPERATURES WILL OCCUR MON-TUE, WHEN TEMPERATURES MAY REACH 30-40  
DEG F ACROSS THE NORTHERN HIGH PLAINS AND 15 TO 25 DEG BELOW  
AVERAGE BELOW AVERAGE IN THE PACIFIC NORTHWEST. SOME RECORD COLD  
TEMPERATURES ARE POSSIBLE FOR PORTIONS OF WA/OR SUN/MON. SLIGHTLY  
BELOW AVERAGE TEMPERATURES WILL SPREAD INTO THE UPPER MIDWEST AND  
THEN GREAT LAKES BEHIND THE MIDWEEK SYSTEM. A SURGE OF ABOVE  
AVERAGE TEMPERATURES WILL PRECEDE THE COLD FRONT MON-TUE ACROSS  
THE LOWER MISSISSIPPI VALLEY AND THE SOUTHEAST.  
 
RYAN  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION AND WINTER WEATHER OUTLOOK  
PROBABILITIES ARE FOUND AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page