110  
FXUS02 KWBC 142009  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
408 PM EDT THU MAR 14 2019  
 
VALID 12Z SUN MAR 17 2019 - 12Z THU MAR 21 2019  
   
..OVERVIEW
 
 
MODEL AND ENSEMBLE GUIDANCE MAINTAINS GOOD AGREEMENT/CONTINUITY IN  
SHOWING THE MEAN RIDGE-TROUGH PATTERN OVER NORTH AMERICA DRIFTING  
SLOWLY EASTWARD WITH TIME. AS HAS BEEN THE CASE IN RECENT DAYS,  
THERE IS STILL SOME QUESTION AS TO THE SPECIFICS OF SMALLER SCALE  
SHORTWAVES WITHIN/AROUND THE WESTERN MEAN RIDGE AND EXACT  
CHARACTER OF THE EASTERN TROUGH. MEANWHILE THERE IS STEADILY  
INCREASING POTENTIAL THAT AN UPPER TROUGH APPROACHING THE WEST  
COAST DURING THE FIRST HALF OF NEXT WEEK WILL CLOSE OFF AN UPPER  
LOW THAT REACHES CALIFORNIA AROUND LATE WED-THU. THE OVERALL  
PATTERN WILL BE FAIRLY DRY ACROSS THE LOWER 48 ASIDE FROM THE  
POSSIBILITY OF HEAVY RAINFALL OVER THE FLORIDA PENINSULA NEXT WEEK  
DUE TO A WAVY FRONT NEAR THE KEYS/SOUTHERN STREAM SHORTWAVE  
ENERGY, AND MOISTURE MOVING INTO THE WEST WITH THE UPPER LOW.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
AN OPERATIONAL MODEL BLEND (06Z GFS/00Z ECMWF AND SOME ASPECTS OF  
THE 00Z UKMET/CMC) PROVIDES A REASONABLE STARTING EARLY IN THE  
PERIOD. THEN INCREASING 06Z GEFS/00Z ECMWF ENSEMBLE MEAN WEIGHT  
TOWARD HALF ALONG WITH THE GFS/ECMWF (AND CMC NEAR THE WEST COAST)  
HELPS TO SMOOTH OUT THE INCREASINGLY UNCERTAIN SHORTWAVE DETAILS  
AND YIELDS A FORECAST CLOSE TO CONTINUITY.  
 
MODEL DIFFERENCES AND RUN TO RUN VARIABILITY PERSIST FOR THE  
EVOLUTION OF ENERGY INITIALLY COMING THROUGH/AROUND THE WESTERN  
NORTH AMERICA RIDGE AND THEN FEEDING INTO THE EASTERN MEAN TROUGH.  
THUS FAR WHICHEVER SOLUTIONS HAVE DEPOSITED THE MOST ENERGY  
OVER/NEAR THE NORTHERN ROCKIES/INTERIOR WEST BY EARLY NEXT WEEK  
HAVE NOT HELD UP IN SUCCESSIVE RUNS, WHICH IN THIS CYCLE FAVORS  
LEANING AWAY FROM THE 00Z GFS/06Z FV3 GFS. THEN BEYOND THIS ISSUE  
THERE IS STILL A FAIR DEGREE OF SPREAD FOR THE SHORTWAVE ENERGY  
OVER THE CENTRAL/EASTERN STATES. THE 00Z UKMET/CMC ARE IN THE  
WESTERN PART OF THE MODEL/ENSEMBLE ENVELOPE, WITH SOME SIMILARITY  
TO A COUPLE EARLIER ECMWF RUNS. ON THE OTHER HAND THE 00Z ECMWF  
EVENTUALLY STRAYS TO THE FASTER SIDE OF THE SPREAD. AT THE MOMENT  
GFS RUNS ARE CLOSEST TO THE ENSEMBLE MEANS. THE  
SPREAD/VARIABILITY FAVOR MAINTAINING AN INTERMEDIATE SOLUTION FOR  
THE DETERMINISTIC MANUAL FORECAST, BUT WITH THE UNDERSTANDING THAT  
THE POTENTIAL STILL EXISTS FOR A SLIGHTLY FARTHER WESTWARD TROUGH  
AND MORE SENSIBLE WEATHER EFFECTS OVER THE EAST. FARTHER SOUTH  
THERE IS A REASONABLE SIGNAL THAT SOUTHERN STREAM ENERGY HELP  
GENERATE A FRONTAL WAVE NEAR THE FLORIDA KEYS WITH A TRACK  
CONTINUING NORTHEASTWARD BUT GUIDANCE IS STILL ATTEMPTING TO  
RESOLVE PRECISE PATH AND TIMING. A COMPROMISE APPEARS BEST FOR  
THIS FEATURE AS WELL.  
 
OVER THE PAST DAY THE ENSEMBLE MEANS HAVE TRENDED DEEPER AND MORE  
CLOSED WITH THE UPPER TROUGH ENERGY HEADING TOWARD CALIFORNIA BY  
THE MIDDLE OF NEXT WEEK. THIS REPRESENTS A TREND TOWARD RECENT  
GFS/ECMWF RUNS WHICH WERE EARLIER TO DEPICT A CLOSED SYSTEM. A  
NORTHWARD ADJUSTMENT IN THE ECMWF OVER THE PAST 1-2 DAYS COULD BE  
A TAD OVERDONE BY LATE DAY 7 THU BUT OTHERWISE BRINGS IT INTO  
REASONABLE AGREEMENT WITH THE MAJORITY CLUSTER. THE 06Z FV3 GFS  
BECOMES FASTER THAN CONSENSUS LATE IN THE PERIOD. GEFS MEANS  
BECOME SLOWEST LATE IN THE PERIOD--PLAUSIBLE IN LIGHT OF MULTI-DAY  
TRENDS BUT POSSIBLY A LITTLE SLOW BASED ON OVERALL PROGRESSION OF  
SOUTHERN STREAM FLOW.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
THE FLORIDA PENINSULA--MORE LIKELY THE SOUTHERN HALF--WILL HAVE  
THE BEST POTENTIAL TO SEE THE HIGHEST RAINFALL TOTALS DURING THE  
PERIOD. A WAVY FRONT STALLED NEAR/SOUTH OF THE KEYS AND SOUTHERN  
STREAM ENERGY ALOFT WILL PROMOTE A PERIOD OF UNSETTLED WEATHER  
FROM THE WEEKEND INTO NEXT WEEK, WITH THE BEST RAINFALL  
ENHANCEMENT OCCURRING AS A MORE DEFINED FRONTAL WAVE DEVELOPS  
AFTER MON. MOISTURE EXTENDING TO THE NORTHEAST FROM FLORIDA  
SHOULD REMAIN OFFSHORE BUT IT WILL BE CLOSE ENOUGH TO THE  
SOUTHEASTERN COAST THAT ONLY A SLIGHT CHANGE IN GUIDANCE WOULD  
LEAD TO MORE RAINFALL OVER THAT REGION. OVER THE REST OF THE U.S.  
EAST OF THE ROCKIES THERE MAY BE ONE OR MORE AREAS OF  
PRECIPITATION WITH SHORTWAVE ENERGY ALOFT AND ASSOCIATED SURFACE  
REFLECTIONS. ANY SUCH PRECIP IS MOST LIKELY TO BE LIGHT/SCATTERED  
AND CONFIDENCE REMAINS LOW IN SPECIFICS. MEANWHILE THE SYSTEM  
DRIFTING TOWARD CALIFORNIA SHOULD START TO BRING MOISTURE INTO THE  
STATE TUE NIGHT-WED WITH PRECIPITATION SPREADING FARTHER INTO THE  
WEST THROUGH THU. THERE MAY BE LOCALIZED AREAS OF FOCUSED  
ACTIVITY BUT LOCATION OF HIGHEST PRECIP TOTALS WILL BE SENSITIVE  
TO EXACT TRACK/EVOLUTION OF THE SYSTEM.  
 
THE LARGE SCALE PATTERN EVOLUTION WILL TEND TO FAVOR AN EXPANDING  
AREA OF PLUS 5-15F TEMPERATURE ANOMALIES OVER THE WEST DURING THE  
PERIOD, THOUGH MAX TEMPS SHOULD COOL DOWN OVER/NEAR CALIFORNIA  
WITH ARRIVAL OF THE WED-THU SYSTEM. UPPER TROUGHING OVER THE EAST  
WILL KEEP THAT PART OF THE COUNTRY BELOW NORMAL BY UP TO 5-10F.  
EXPECT CHILLY READINGS UP TO 10-20F BELOW NORMAL OVER PARTS OF  
TEXAS AND THE EXTREME SOUTHERN ROCKIES SUN-MON WITH GRADUAL  
MODERATION TOWARD NORMAL THEREAFTER. THE NORTHERN PLAINS SHOULD  
ALSO SEE A WARMING TREND DURING THE PERIOD.  
 
RAUSCH  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, TUE-WED, MAR 19-MAR  
20.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS, THE  
NORTHERN PLAINS, THE TENNESSEE VALLEY, THE GREAT LAKES, THE MIDDLE  
MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI VALLEY, THE SOUTHERN  
PLAINS, AND THE OHIO VALLEY.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE CENTRAL  
PLAINS, THE MIDDLE MISSISSIPPI VALLEY, THE LOWER MISSISSIPPI  
VALLEY, THE OHIO VALLEY, AND THE TENNESSEE VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL PLAINS, THE  
MIDDLE MISSISSIPPI VALLEY, THE GREAT LAKES, THE UPPER MISSISSIPPI  
VALLEY, AND THE NORTHERN PLAINS.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHERN  
PLAINS, SUN-MON, MAR 17-MAR 18.  
 
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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