213  
FXUS02 KWBC 230653  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
152 AM EST SUN DEC 23 2018  
 
VALID 12Z WED DEC 26 2018 - 12Z SUN DEC 30 2018  
   
..SIGNIFICANT PLAINS/MIDWEST WINTER STORM WED-FRI
 
 
   
..OVERVIEW
 
 
A ROBUST AND IMPACTFUL WINTER STORM WILL LIFT THROUGH THE CENTRAL  
PLAINS TO THE MIDWEST WED-THU BRINGING WIND-DRIVEN SNOW TO PARTS  
OF NEBRASKA/SOUTH DAKOTA/MINNESOTA AND LOCALLY HEAVY RAIN TO  
PORTIONS OF THE GULF COAST. THE SYSTEM WILL MOVE INTO THE GREAT  
LAKES ON FRIDAY AND THEN OFF THE NORTHEAST/MID-ATLANTIC COAST  
SATURDAY AS THE FRONT SETTLES INTO THE GULF. ANOTHER STORM IS  
FORECAST TO MOVE THROUGH THE WEST/SOUTHWEST JUST BEHIND THE FIRST  
STORM WHICH WILL SPREAD PRECIPITATION THROUGH THE GREAT BASIN/FOUR  
CORNERS REGION.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
A MAJORITY DETERMINISTIC MODEL BLEND WAS USED FOR THE FIRST FEW  
DAYS OF THE FORECAST AS THE MODELS REMAIN IN GOOD SYNOPTIC  
AGREEMENT. THIS BLEND INCLUDED THE 12Z  
ECMWF/GFS/FV3/CANADIAN/UKMET FOR WED-FRI WHICH WAS A BIT SLOWER  
THAN THE ENSEMBLE MEANS GIVEN THE TREND BUT NOT AS SLOW AS THE  
ECMWF/UKMET GIVEN THE ENSEMBLE SPREAD (ONLY A FEW MEMBERS SLOWER  
THAN THEM).  
 
BY NEXT SAT/SUN, THE ENSEMBLES DIVERGE IN THE WEST (AND EASTERN  
PACIFIC) AS THE PATTERN BECOMES MUCH LESS PREDICTABLE EVEN AT THE  
SYNOPTIC SCALE. AGREEMENT IS BEST OVER THE BAHAMAS/CUBA WHERE THE  
ENSEMBLES SHOW UPPER RIDGING BUILDING WESTWARD FROM NORTH OF  
PUERTO RICO LATE THIS WEEK. IN THE PACIFIC, QUESTION IS HOW MUCH  
SEPARATION IN THE FLOW WILL OCCUR AROUND 150-160W LATER THIS WEEK  
WHICH WILL DETERMINE THE SHAPE/STRENGTH OF RIDGING JUST OFF  
CALIFORNIA. TELECONNECTIONS TO A DEEP NEGATIVE HEIGHT ANOMALY  
AROUND 38N/163E (SOUTH OF KAMCHATKA) POINT TO A POSITIVELY TILTED  
TROUGH FROM NW MEXICO TO THE GREAT LAKES WITH RIDGING INTO  
CALIFORNIA, WHICH IS MORE IN LINE WITH THE ECMWF/CANADIAN  
ENSEMBLES RATHER THAN THE GEFS. TRENDED TOWARD A MAJORITY  
ECMWF/ECMWF ENSEMBLE MEAN BLEND BY NEXT SAT/SUN BUT DID NOT RULE  
OUT THE GEFS SOLUTION OF A FARTHER WEST TROUGH AXIS GIVEN THE  
UPSTREAM UNCERTAINTY.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
FOCUS WILL BE ON THE MAJOR SYSTEM IN THE CENTRAL PLAINS WEDNESDAY  
AS IT LIFTS NORTHEASTWARD THROUGH KANSAS. PRECIPITATION WILL  
EXPAND AROUND AND AHEAD OF THE DEEPENING LOW AND COLD FRONT WITH  
THE FLOW OUT OF THE GULF. TO THE NORTHWEST OF THE SURFACE LOW,  
SNOW WILL COME DOWN HEAVY AT TIMES WITH INCREASING WIND AND  
POSSIBLE BLIZZARD CONDITIONS (BLOWING AND DRIFTING SNOW WITH  
LIMITED VISIBILITY) OVER PARTS OF KANSAS AND NEBRASKA THURSDAY.  
THIS WILL MAKE TRAVEL DIFFICULT IF NOT IMPOSSIBLE. SEVERAL INCHES  
OF SNOW ARE LIKELY OVER A LARGE AREA WITH OVER A FOOT QUITE  
POSSIBLE FOR SOME AREAS, ESPECIALLY FROM NW KANSAS/NE COLORADO  
NORTHEASTWARD TO MINNESOTA/WISCONSIN AS THE SURFACE LOW TRACKS  
TOWARD LAKE MICHIGAN. PLEASE CONSULT THE LATEST WINTER WEATHER  
PROBABILITIES FOR A DAILY GRAPHICAL DEPICTION OF THE BEST CHANCE  
OF SNOW. IN THE WARM SECTOR, RAINFALL COULD BECOME LOCALLY HEAVY  
NEAR THE GULF COAST AS THE SYSTEM INFUSES GULF MOISTURE NORTHWARD  
UP AND OVER THE WARM FRONT. SEVERAL INCHES OF RAIN ARE POSSIBLE IN  
SOME AREAS WITH A MORE WIDESPREAD 1-2" LIKELY BETWEEN I-10 AND  
I-20. THE SYSTEM WILL EXIT THROUGH SOUTHERN ONTARIO AND NORTHERN  
NEW ENGLAND WHERE SOME ONSET FROZEN PRECIPITATION (PERHAPS  
APPRECIABLE FREEZING RAIN AS WARM AIR ADVANCES OVER IN SITU LOWER  
LEVEL COLD AIR) IS LIKELY. NEXT SYSTEM IN THE WEST WILL BRING MORE  
SNOW AND SOME LOWER ELEVATION RAIN TO THE FOUR CORNERS REGION BUT  
WILL BE DEPENDENT ON THE TROUGH STRENGTH.  
 
TEMPERATURES WILL BE COOLER THAN AVERAGE IN THE WEST BEHIND THE  
FRONT BUT WILL BE WELL ABOVE AVERAGE OVER THE MISSISSIPPI VALLEY  
EASTWARD (10-30 DEG F ANOMALIES ESPECIALLY OVERNIGHT). WITH  
REINFORCING TROUGHING INTO THE WEST LATER IN THE WEEK,  
TEMPERATURES WILL STAY BELOW AVERAGE FROM THE GREAT BASIN/ROCKIES  
INTO THE PLAINS, ESPECIALLY OVER NEWLY SNOW-COVERED AREAS. COOLER  
AIR WILL FILTER INTO THE EAST NEXT WEEKEND AS THE FRONT SINKS INTO  
THE GULF AND NORTHERN FLORIDA.  
 
FRACASSO  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES 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  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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