219  
FXUS02 KWBC 071600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT SUN APR 07 2019  
 
VALID 12Z WED APR 10 2019 - 12Z SUN APR 14 2019  
 
...MAJOR WINTER STORM LIKELY FROM THE NORTHERN HIGH PLAINS TO THE  
UPPER MIDWEST BY MID TO LATE THIS WEEK...  
 
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
A VIGOROUS UPPER-LEVEL TROUGH MOVING FROM THE ROCKIES TO THE  
CENTRAL U.S. ON WED IS EXPECTED TO QUICKLY DEEPEN AND SPIN UP A  
SIGNIFICANT LOW PRESSURE SYSTEM. THE SURFACE LOW IS EXPECTED TO  
MOVE FROM THE CENTRAL HIGH PLAINS WED MORNING TO THE MIDWEST ON  
THU AND THE GREAT LAKES BY FRI, BEFORE QUICKLY MOVING NORTHEAST  
INTO QUEBEC BY FRI NIGHT/SAT. CONFIDENCE IN THE FORECAST FOR THIS  
SYSTEM HAS IMPROVED SIGNIFICANTLY OVER THE PAST 24-48 HOURS.  
DETERMINISTIC MODEL SOLUTIONS AND ENSEMBLE MEMBERS ARE NOW VERY  
WELL-CLUSTERED WITH RESPECT TO THE SURFACE LOW TRACK WED-FRI, WITH  
THE ECMWF AND UKMET THE TWO SOLUTIONS MOST WELL-CENTERED WITHIN  
THE BROAD CONSENSUS. THE UKMET HAS PERFORMED PARTICULARLY WELL  
WITH THIS SYSTEM OVER THE PAST FEW DAYS, SHOWING A HIGHLY  
CONSISTENT STRUCTURE AND TRACK FOR THE SYSTEM FOR AT LEAST THE  
PAST 4-5 RUNS. FARTHER WEST, ADDITIONAL SHORTWAVE ENERGY IS  
EXPECTED TO DIVE SOUTH ACROSS THE WESTERN U.S. BEFORE AMPLIFYING  
AND PERHAPS CLOSING OFF ACROSS THE GREAT BASIN THU-FRI. MODELS  
CONSENSUS HAS IMPROVED SIGNIFICANTLY ON THIS SYSTEM AS WELL, WITH  
A LARGE REDUCTION IN SPREAD NOTED OVER THE PAST 12-24 HOURS. GIVEN  
THESE CONSIDERATIONS, THE WPC FORECAST DURING DAYS 3-5 (WED-FRI)  
WAS BASED ON A MULTI-MODEL BLEND OF DETERMINISTIC SOLUTIONS  
INCLUDING THE 00Z ECMWF/UKMET/CMC AND 06Z FV3 (WHICH WAS CLOSER TO  
CONSENSUS THAN THE GFS WITH THE CENTRAL U.S. SYSTEM). PARTICULAR  
WEIGHT WAS PLACED TOWARD THE HIGHLY CONSISTENT ECMWF/UKMET  
SOLUTIONS.  
 
BY NEXT WEEKEND, THE PRIMARY FORECAST CONCERN BECOMES HOW QUICKLY  
THE ENERGY ACROSS THE SOUTHWEST THU-FRI EJECTS EASTWARD INTO THE  
CENTRAL U.S. MODELS SEEM TO BE DEMONSTRATING THEIR USUAL BIASES  
WITH THIS SYSTEM, WITH THE 06Z GFS RACING THE SHORTWAVE EASTWARD  
FASTER THAN MOST OTHER SOLUTIONS, AND THE ECMWF ON THE SLOW SIDE  
OF THE SPREAD. THE GFS HAS SHOWN RUN-TO-RUN INCONSISTENCY,  
FLIPPING BETWEEN A FAST SOLUTION (06Z RUN) AND A SLOWER MORE  
ECMWF-LIKE IDEA (00Z RUN). IN MOST CASES SUCH AS THIS, THE ACTUAL  
VERIFICATION OFTEN ENDS UP IN BETWEEN THE TWO CAMPS, PERHAPS A BIT  
MORE TOWARD THE SLOWER SOLUTIONS. ENSEMBLES PROVIDE STRONG SUPPORT  
FOR THE SLOWER SOLUTIONS (INCLUDING EVEN THE GEFS MEAN), DESPITE A  
VERY SLIGHT FASTER TREND OVER THE PAST COUPLE RUNS. THUS, LEANED  
HEAVILY TOWARD THE ECENS/NAEFS ENSEMBLE MEANS AND THE 00Z ECMWF  
DURING DAYS 6-7 (SAT-SUN). MOST SOLUTIONS, REGARDLESS OF THEIR  
TIMING, SPIN UP A LOW PRESSURE SYSTEM ACROSS THE CENTRAL GULF  
COAST/LOWER MISSISSIPPI VALLEY BY NEXT SUN AHEAD OF THE UPPER  
TROUGH.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE LOW PRESSURE SYSTEM CROSSING THE CENTRAL U.S. WED-FRI IS  
EXPECTED TO BRING SIGNIFICANT WINTER WEATHER IMPACTS FROM PORTIONS  
OF THE CENTRAL/NORTHERN ROCKIES AND ADJACENT HIGH PLAINS TO THE  
UPPER MIDWEST/GREAT LAKES. MODELS SHOW STRONG SIGNAL FOR A BAND OF  
DYNAMICALLY FORCED MODERATE TO HEAVY SNOW NORTH OF THE SURFACE LOW  
TRACK. STRONG AND GUSTY WINDS DUE TO THE DEEP NATURE OF THE LOW  
PRESSURE SYSTEM WILL LIKELY RESULT IN BLOWING SNOW AND PERHAPS  
BLIZZARD CONDITIONS FOR SOME AREAS. FARTHER SOUTH, A STRONG  
CAPPING INVERSION WILL INITIALLY PREVENT MUCH IN THE WAY OF  
CONVECTION IN THE WARM SECTOR ACROSS THE SOUTHERN PLAINS ON WED.  
BY THU-FRI, INCREASING MOISTURE RETURN AS THE SYSTEM ENTERS THE  
MISSISSIPPI VALLEY SHOULD LEAD TO SCATTERED TO NUMEROUS SHOWERS  
AND THUNDERSTORMS, SOME OF WHICH COULD BE STRONG TO SEVERE. THE  
SYSTEM ACROSS THE WESTERN U.S. WED-FRI SHOULD PRODUCE SCATTERED  
AREAS OF RAIN AND MOUNTAIN SNOW FROM THE WEST COAST TO THE GREAT  
BASIN AND ROCKIES. AS THE SYSTEM ENTERS THE CENTRAL U.S. BY NEXT  
WEEKEND, A DEVELOPING FRONTAL WAVE ALONG THE GULF COAST/LOWER  
MISSISSIPPI VALLEY SHOULD PROMOTE STRONG MOISTURE RETURN AND  
WIDESPREAD RAIN AND THUNDERSTORMS FROM THE LOWER MISSISSIPPI  
VALLEY TO THE TENNESSEE/OHIO VALLEYS AND THE SOUTHEAST, WITH AREAS  
OF HEAVY RAINFALL POSSIBLE.  
 
ABOVE AVERAGE TEMPERATURES ARE EXPECTED IN THE WARM SECTOR AHEAD  
OF THE DEEP LOW PRESSURE SYSTEM. HIGH TEMPERATURES ARE FORECAST TO  
BE 10 TO 20 DEG F ABOVE AVERAGE ACROSS SOUTHERN/CENTRAL PLAINS AND  
LOWER/MID MISSISSIPPI VALLEY ON WED, AND 10-15 DEG ABOVE AVERAGE  
ACROSS PORTIONS OF THE SOUTHEAST AND TENNESSEE/OHIO VALLEYS ON  
THU. IN THE WAKE OF THE LOW PRESSURE SYSTEM, MUCH COLDER AIR IS  
EXPECTED TO SPREAD INTO THE ROCKIES AND THE CENTRAL U.S., WITH  
HIGH TEMPERATURES 15-25 DEG BELOW AVERAGE POSSIBLE THROUGH LATE IN  
THE WEEK.  
 
RYAN  
 
ADDITIONAL 3-7 DAY HAZARDS INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE 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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