009  
FXUS02 KWBC 240601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
200 AM EDT WED APR 24 2019  
 
VALID 12Z SAT APR 27 2019 - 12Z WED MAY 01 2019  
   
..OVERVIEW AND GUIDANCE PREFERENCES
 
 
MODELS SUGGEST THE POTENTIAL FOR AT LEAST SOME DEGREE OF PATTERN  
CHANGE ACROSS THE CONUS DURING THE MEDIUM RANGE. INITIALLY  
SEPARATE STREAMS WITH A PROGRESSIVE NORTHERN STREAM AND LESS  
PROGRESSIVE SOUTHERN STREAM APPEAR SET TO CONSOLIDATE BY THE  
MIDDLE OF NEXT WEEK. THIS IS EXPECTED TO OCCUR AS THE NORTHERN  
STREAM UNDERGOES AMPLIFICATION IN RESPONSE TO A PERSISTENT  
UPSTREAM REX BLOCK EXTENDING FROM ALASKA TO HAWAII. AMPLIFICATION  
OF AN UPPER TROUGH ACROSS THE WESTERN U.S. BY THE MIDDLE OF NEXT  
WEEK IS EXPECTED ALONG WITH AN EXPANSION OF THE SUBTROPICAL RIDGE  
NORTHWARD INTO THE SOUTHEAST AND SOUTHERN MID-ATLANTIC.  
 
A NEGATIVELY TILTED UPPER TROUGH IS EXPECTED TO BE IN PLACE ON DAY  
3 (SAT) ACROSS THE NORTHEAST, WITH A PHASED SURFACE LOW PRESSURE  
SYSTEM EXPECTED TO BE DEEPENING AS IT PULLS AWAY FROM NEW ENGLAND.  
FARTHER WEST, THE NORTHERN STREAM REMAINS ACTIVE WITH ONE COMPACT  
BUT ENERGETIC SHORTWAVE CROSSING THE MIDWEST/GREAT LAKES SAT-SUN  
AND YET ANOTHER DIVING INTO THE PACIFIC NORTHWEST/NORTHERN  
ROCKIES. MEANWHILE, A CUTOFF UPPER-LEVEL LOW SHOULD APPROACH  
CALIFORNIA BY SUN NIGHT/MON BEFORE MOVING INLAND AND INTERACTING  
IN SOME FASHION WITH THE BROADER UPPER TROUGH AMPLIFICATION ACROSS  
THE WEST BY EARLY-MID NEXT WEEK.  
 
THE FORECAST DURING DAYS 3-5 (SAT-MON) WAS BASED ON A MULTI-MODEL  
DETERMINISTIC BLEND INCLUDING THE 12Z ECMWF/UKMET AND 18Z FV3-GFS.  
MODEL SOLUTIONS DIFFERED ON THE EVOLUTION OF THE NEGATIVELY TILTED  
UPPER TROUGH AND DEEPENING SURFACE LOW AS THEY PULL AWAY FROM THE  
NORTHEAST SAT-SUN, BUT A BLENDED APPROACH APPEARED BEST AT THIS  
TIME. PREFERRED THE GFS/FV3/UKMET IDEA OF A MORE AMPLIFIED  
SHORTWAVE CROSSING THE GREAT LAKES/OHIO VALLEY SAT-SUN OVER THE  
WEAKER/MORE SUPPRESSED ECMWF SOLUTION. FARTHER WEST, CONSENSUS HAS  
IMPROVED WITH RESPECT TO AMPLIFIED SHORTWAVE ENERGY REACHING THE  
NORTHWEST/NORTHERN ROCKIES SAT/SUN, BUT SOME TIMING DIFFERENCES  
REMAIN, AND MODELS ALSO DIFFER AS TO WHETHER THE WAVE QUICKLY  
MOVES EAST INTO THE NORTHERN PLAINS BY LATE SUN OR SHEARS OUT WITH  
MORE ENERGY REMAINING ACROSS THE INTERIOR NORTHWEST. THE 12Z UKMET  
SUGGESTED THAT A COMPROMISE BETWEEN THESE IDEAS WAS FEASIBLE AND  
THUS THIS WAS THE PREFERENCE. ENSEMBLES DO PROVIDE A FAIR DEGREE  
OF SUPPORT FOR THE IDEA OF KEEPING A SIGNIFICANT PORTION OF THE  
SHORTWAVE ENERGY BACK ACROSS THE INTERIOR WEST INTO EARLY/MID NEXT  
WEEK, WITH THE ARRIVAL OF ADDITIONAL ENERGY HELPING TO LOWER  
HEIGHTS AND AMPLIFY A BROADER UPPER-LEVEL TROUGH. THE EVOLUTION OF  
THE UPPER TROUGH WILL ALSO IMPACT WHAT HAPPENS FARTHER SOUTH AS  
THE INITIALLY CUTOFF PACIFIC ENERGY MOVES INLAND ACROSS THE FOUR  
CORNERS REGION, WITH THE EVENTUAL FORWARD SPEED OF THIS SYSTEM AS  
IT BEGINS TO BECOME ABSORBED TIED TO THE DEGREE OF NORTHERN STREAM  
AMPLIFICATION. WHILE MODELS DIFFER AS TO EXACTLY HOW THIS OCCURS,  
ENSEMBLE MEANS AGREE IN PRINCIPLE, THIS LEANED HEAVILY TOWARD  
ECENS AND GEFS MEANS BY DAYS 6-7 (TUE-WED).  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WIDESPREAD RAIN IS EXPECTED ACROSS NEW ENGLAND ON SAT AS THE  
DEEPENING LOW PRESSURE SYSTEM MOVES AWAY FROM THE REGION. LOW  
PRESSURE MOVING FROM THE CENTRAL/NORTHERN PLAINS TO THE  
MIDWEST/GREAT LAKES/NORTHEAST SAT/SUN SHOULD BE ACCOMPANIED BY  
SHOWERS AND THUNDERSTORMS, WITH THE POTENTIAL FOR LOCALLY HEAVY  
RAINFALL. A FEW AREAS ON THE NORTHERN FRINGE OF THIS PRECIPITATION  
AREA MAY SEE THE POTENTIAL FOR SNOW OR A RAIN/SNOW MIX,  
PARTICULARLY PORTIONS OF NORTHERN WISCONSIN AND MICHIGAN ON SAT.  
THROUGH THE REMINDER OF THE FORECAST PERIOD, INTO THE MIDDLE OF  
NEXT WEEK, THE FOCUS FOR SCATTERED TO NUMEROUS SHOWERS AND  
THUNDERSTORMS WILL SHIFT BACK TO THE CENTRAL U.S., WHERE A  
STATIONARY SURFACE FRONT ALONG WITH ARRIVAL OF ADDITIONAL  
UPPER-LEVEL SHORTWAVES WILL FOCUS MULTIPLE ROUNDS OF SHOWERS AND  
THUNDERSTORMS. MODELS CURRENTLY SHOW THE GREATEST POTENTIAL FOR  
HEAVY RAINFALL ACROSS AREAS FROM THE CENTRAL PLAINS TO THE UPPER  
MIDWEST MON-TUE. THE CENTRAL/NORTHERN ROCKIES WILL ALSO SEE AN  
INCREASE IN PRECIPITATION (RAIN AND MOUNTAIN SNOW) BY EARLY TO MID  
NEXT WEEK AS THE UPPER TROUGH AMPLIFIED ACROSS THE WEST AND  
ADDITIONAL SOUTHERN STREAM PACIFIC ENERGY ARRIVES.  
 
BELOW AVERAGE TEMPERATURES ARE EXPECTED THROUGH MUCH OF THE  
FORECAST PERIOD FROM THE NORTHERN ROCKIES TO THE UPPER MIDWEST AND  
GREAT LAKES, WHERE HIGH TEMPERATURES OF 5 TO 15 DEG F BELOW  
AVERAGE MAY BE COMMON. ABOVE AVERAGE TEMPERATURES INITIALLY IN  
PLACE FROM CALIFORNIA TO THE SOUTHERN ROCKIES AND ADJACENT PLAINS  
SHOULD SHIFT EAST TO THE SOUTHEAST AND SOUTHERN MID-ATLANTIC  
REGIONS BY EARLY TO MID NEXT WEEK AS THE WESTERN TROUGH AMPLIFIES  
AND RIDGING BUILDS INTO THE SOUTHEAST.  
 
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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