591  
FXUS02 KWBC 140650  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
250 AM EDT TUE MAY 14 2019  
 
VALID 12Z FRI MAY 17 2019 - 12Z TUE MAY 21 2019  
 
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
MEAN TROUGHING ALOFT WILL BRING A WET PERIOD TO A LARGE PORTION OF  
THE WESTERN U.S. AND PLAINS STATES DURING THE WEEKEND TO EARLY  
NEXT WEEK. MUCH OF THE WESTERN US TO THE NORTHERN HIGH PLAINS  
WILL TURN COLDER, WITH MUCH OF THE LOWER MS VALLEY AND TN VALLEY  
TO THE SOUTHEAST TURNING WARM TO HOT.  
 
GUIDANCE IS STEADILY TRENDING TOWARD RESOLVING THE LEADING STRONG  
TROUGH PROGRESSING FROM THE NORTHERN ROCKIES ONTO THE PLAINS BY  
DAY 3 FRI AND PROGRESSING ACROSS THE NORTHERN PLAINS THEREAFTER.  
BY DAY 4 SAT THE OPERATIONAL GFS RUNS BECOME FASTER THAN THE OTHER  
MODELS IN MOVING THE CLOSED LOW SFC/ALOFT OUT OF THE PLAINS ACROSS  
THE UPPER MS VALLEY AND UPPER GREAT LAKES. THE 12Z ECMWF/00Z  
UKMET/12Z CANADIAN SUGGEST THAT SOUTHERN TROUGH ENERGY COULD FORM  
ANOTHER UPPER LOW THAT REACHES THE PLAINS LATE SAT-SUN, WHICH  
LEADS TO SLIGHTLY SLOWER FORWARD MOTION, WHICH IS PREFERRED.  
 
THERE IS GOOD AGREEMENT THAT UPSTREAM FLOW WILL BRING ANOTHER  
ROUND OF STRONG HEIGHT FALLS TO THE WESTERN STATES THIS WEEKEND,  
CONTINUING INLAND EARLY WEEK ACROSS THE GREAT BASIN TO THE  
NORTHERN HIGH PLAINS. THE 12Z ECMWF AND 12-18Z GFS INDICATE A  
DEEPER LOW IN THE EASTERN PACIFIC EARLY NEXT WEEK, WHICH HAS  
POTENTIAL TO REACH CA TUE 21 MAY.  
 
MODELS/ENSEMBLES INCREASINGLY DIVERGE FOR NORTHEASTERN/MID  
ATLANTIC U.S. FLOW, HIGHLIGHTED BY A DEEP NEW ENGLAND/MID-ATLANTIC  
TROUGH ALOFT IN THE 00Z UKMET VERSUS A STRONG RIDGE IN RECENT GFS  
RUNS. THE 12Z ECMWF/12Z CANADIAN HAD LOWER HEIGHTS THAN THE GFS,  
WHICH WERE GIVEN A LITTLE MORE WEIGHT. TELECONNECTIONS RELATIVE TO  
THE NEGATIVE HEIGHT ANOMALY CENTER ASSOCIATED WITH THE WEST COAST  
MEAN TROUGH FAVOR MODEST CYCLONIC FLOW ALOFT, THUS THE GFS WAS  
GIVEN LESS WEIGHT. MORE WEIGHTING WAS GIVEN TO THE 12Z ECMWF  
MEAN/18Z GEFS MEAN TO AVOID COMMITTING TO ANY PARTICULAR MODEL  
SOLUTION GIVEN CONTINUING SPREAD.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
OVER THE WEST ENHANCED PRECIPITATION IS EXPECTED WITH THE MID  
LEVEL CLOSED LOW OVER THE NORTHERN ROCKIES AND HIGH PLAINS  
FRI-SAT. THE NEXT SIGNIFICANT PRECIP EVENT IS EXPECTED SAT-SUN  
EXTENDING FROM FAVORED TERRAIN IN NORTHERN-CENTRAL CALIFORNIA INTO  
THE NORTHERN ROCKIES AND THEN THE NORTHERN GREAT BASIN TO THE THE  
HIGH PLAINS MON 20 MAY-TUE 21 MAY. THIS PERIOD IS EXPECTED TO BE  
UNUSUALLY WET FOR SO LATE IN THE WET SEASON FROM CA TO THE  
NORTHERN ROCKIES. THE GREATEST POTENTIAL FOR HIGH ELEVATION SNOW  
SHOULD BE IN THE NORTHERN SIERRA NEVADA.  
 
PROGRESSION OF THE INITIAL WESTERN STORM WILL GENERATE AREAS OF  
HEAVY RAIN/THUNDERSTORMS OVER THE CENTRAL TO SOUTHERN PLAINS OVER  
THE WEEKEND, WITH THE STORM PREDICTION CENTER ALSO INDICATING  
SEVERE WEATHER POTENTIAL FOR FRI-SAT.  
WIDESPREAD RAIN IS EXPECTED OVER THE NORTHERN PLAINS TO UPPER MS  
VALLEY THIS WEEKEND.  
 
WELL BELOW NORMAL HIGHS (CLUSTERS OF MINUS 10-20F ANOMALIES) OVER  
CALIFORNIA/ NEVADA/UTAH ON DAY 3 FRI WILL SPREAD NORTHEAST OVER  
THE WEEKEND INTO THE NORTHERN PLAINS AND REMAIN IN PLACE THROUGH  
EARLY NEXT WEEK. CLOUDS AND PRECIP SHOULD KEEP MORNING LOWS MOSTLY  
A FEW DEGREES BELOW NORMAL WITH ONLY ISOLATED LOCATIONS TEN OR  
MORE DEGREES BELOW NORMAL THIS WEEKEND INTO EARLY NEXT WEEK.  
 
WELL ABOVE NORMAL HIGHS WILL PROGRESS FROM THE PLAINS FRI AND  
GRADUALLY RELOCATE INTO THE MS VALLEY AND OH VALLEY OVER THE  
WEEKEND AND THE SOUTHERN MID ATLANTIC INTO THE SOUTHEAST EARLY  
NEXT WEEK, WITH TEMPS COMMONLY 10-15 DEGREES ABOVE NORMAL IN THE  
CORE OF THE WARMEST AIR. FROM SAT-MON TEMPERATURES OVER THE MID  
ATLANTIC STATES ARE VERY UNCERTAIN GIVEN A WIDE RANGE OF  
POSSIBILITIES FOR FRONTAL POSITION WITHIN A REGION OF STRONG  
TEMPERATURE CONTRAST.  
 
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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