896  
FXUS02 KWBC 070548  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
147 AM EDT SUN APR 07 2019  
 
VALID 12Z WED APR 10 2019 - 12Z SUN APR 14 2019  
 
...HEAVY RAIN AND SNOW, AND HIGH WINDS ARE EXPECTED WITH A STORM  
ACROSS THE CENTRAL TO THE NORTHERN PLAINS AND UPPER MS VALLEY MID  
TO LATE NEXT WEEK...  
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
AN UPPER LEVEL TROUGH AMPLIFIES AS IT CROSSES FROM THE ROCKIES ON  
TO THE PLAINS WED, WHICH RESULTS IN A MAJOR CYCLONE ACROSS THE  
CENTRAL U.S. WED-FRI.  
MODELS STILL HAVE SIGNIFICANT DIFFERENCES TO RESOLVE, WITH THE 18Z  
GFS NORTHWEST OF THE 12Z ECMWF CYCLONE POSITIONS, IN TURN  
IMPACTING THE AXIS/ORIENTATION OF THE BANDS OF PRECIPITATION,  
INCLUDING SNOW. THE 181Z GEFS MEAN TRACK IS SOUTHEAST OF THE 18Z  
GFS AND OVERLAPS THE 12Z ECMWF ENSEMBLE MEAN WELL, SO THIS TANDEM  
IS AGAIN GIVEN MORE WEIGHT THAT EITHER OPERATIONAL MODEL. THE 12Z  
CANADIAN GLOBAL AND 00Z GFS WED-THU AGREE WITH THE MEAN TRACK AS  
WELL, WITH THE 12Z UKMET WITHIN THE DOMINANT CLUSTER OF SOLUTIONS  
AS WELL.  
 
SPREAD INCREASES DURING FRI-SAT, FOLLOWING INTERACTION WITH THE  
NORTHERN STREAM AS IT MOVES INTO CANADA. GIVEN SIGNIFICANT  
CONTINUED RUN-TO-RUN VARIABILITY FROM FRI ONWARD, OPTED TO LEAN  
MUCH MORE HEAVILY ON ECENS/GEFS ENSEMBLE MEANS DURING THAT TIME  
FRAME.  
 
THIS PREFERENCE HOLDS ALONG THE WEST COAST AS WELL, WHERE MODELS  
HAVE STRUGGLED TO DEAL WITH THE SPECIFICS OF A SERIES OF  
SHORTWAVES DROPPING SOUTHWARD ACROSS THE PACIFIC NORTHWEST THU  
SOUTHEAST ACROSS THE GREAT BASIN FRI AND SOUTHWEST TO SOUTHERN  
HIGH PLAINS SAT. THE SYSTEM MOVES EAST ON SUN.  
 
ON SUN 14 APR, AS THE TROUGH MOVES OUT OF THE SOUTHWEST ONTO THE  
SOUTHERN PLAINS, LOW PRESSURE DEVELOPS IN THE LOWER MS VALLEY TO  
SOUTHEAST, AND MOVES NORTHEAST TOWARDS THE TN VALLEY OR SOUTHERN  
APPALACHIANS. THE MODELS AND ENSEMBLES HAVE TIMING DIFFERENCES  
WITH GREATER WEIGHTING TO THE SLOWER 18Z GEFS/12Z ECMWF MEANS  
APPLIED AS THE HIGH AMPLITUDE FL RIDGE HAS PROVEN TO BE A  
PERSISTENT FEATURE MOST OF THE WINTER AND SHOULD ACT TO SHUNT THE  
SYSTEM A BIT FURTHER NORTHWEST. THE 00Z GFS AND CANADIAN GLOBAL  
NOW CLUSTERS WELL WITH THIS GROUP.  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE UPPER-LEVEL SHORTWAVE WILL INITIALLY BRING POTENTIALLY HEAVY  
MOUNTAIN SNOWS TO MUCH OF THE ROCKIES OF ID/WESTERN MT/WY TUE INTO  
WED. AFTER THE SYSTEM EMERGES INTO THE PLAINS, MODELS SHOW A  
LARGE AREA OF PRECIPITATION IS LIKELY TO THE NORTH OF THE LOW  
TRACK, FROM PORTIONS OF EASTERN WYOMING AND ACROSS MOST OF  
NEBRASKA AND THE DAKOTAS EAST TO THE UPPER MIDWEST. A VARIETY OF  
PRECIPITATION TYPES ARE LIKELY, BUT SUFFICIENT COLD AIR SHOULD BE  
IN PLACE TO SUPPORT A BAND OF MODERATE TO HEAVY SNOW.  
ECMWF AND GEFS PLUME DIAGRAMS SHOW POTENTIAL FOR A FOOT OF SNOW AT  
MULTIPLE LOCATIONS IN SD AND MN, IN ADDITION TO THOSE AT HIGHER  
ELEVATIONS IN WY.  
 
ADDITIONALLY, THE STRONG INTENSITY OF THE LOW (CENTRAL PRESSURES  
LIKELY IN THE MID 980-MB RANGE), WILL LIKELY RESULT IN THE  
POTENTIAL FOR STRONG AND GUSTY WINDS ACROSS A LARGE AREA OF THE  
CENTRAL U.S. FARTHER SOUTH, LIMITED MOISTURE RETURN AND POTENTIAL  
FOR A CAPPING INVERSION WILL LIMIT PRECIPITATION COVERAGE AHEAD OF  
THE SYSTEM FROM THE SOUTHERN PLAINS TO THE LOWER MISSISSIPPI  
VALLEY, BUT SCATTERED CONVECTION COULD BE STRONG.  
 
AS THE LOW MOVES INTO CANADA BY FRI-SAT AND THE COLD FRONT SWEEPS  
INTO THE EASTERN U.S., SHOWERS ARE LIKELY FROM THE OHIO VALLEY TO  
THE MID-ATLANTIC AND NORTHEAST. FARTHER WEST, THE SERIES OF  
SHORTWAVES DIVING SOUTH ALONG THE WEST COAST WED-SAT WILL SUPPORT  
CONTINUED SCATTERED AND PERIODIC ROUNDS OF VALLEY RAIN AND  
MOUNTAIN SNOW SHOWERS ALONG THE PATH OF FALLING HEIGHTS.  
 
ONCE THE TROUGH MOVES EAST ON TO THE HIGH PLAINS, RETURN LOW LEVEL  
SOUTHERLY FLOW AND MOISTURE LEADS TO RAINFALL AMOUNTS PICKING UP  
IN THE SOUTHERN PLAINS TO LOWER MS VALLEY NEXT WEEKEND, WITH  
LOCALLY HEAVY RAIN SUN 14 APR.  
 
WARM TEMPERATURES ARE EXPECTED AHEAD OF THE DEEP LOW PRESSURE  
SYSTEM WED FROM THE SOUTH CENTRAL TO SOUTHERN PLAINS TO THE  
LOWER/MID-MISSISSIPPI VALLEY, WHERE HIGH TEMPERATURES OF 5 TO 15  
DEG F ABOVE AVERAGE ARE LIKELY. IN THE WAKE OF THIS LOW PRESSURE  
SYSTEM, A COLDER POLAR AIR MASS WILL OVERSPREAD AREAS FROM THE  
GREAT BASIN TO THE CENTRAL ROCKIES AND THEN TO THE UPPER MIDWEST,  
WITH HIGH TEMPERATURES AS COLD AS 15 TO 25 DEG BELOW AVERAGE  
EXPECTED ON THU IN THE CENTRAL HIGH PLAINS. A BROAD AREA OF COOL  
TEMPERATURES IS EXPECTED ACROSS THE WESTERN AND CENTRAL U.S. NEXT  
WEEKEND, GRADUALLY MODIFYING WITH TIME.  
 
PETERSEN  
 
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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