226  
FXUS02 KWBC 121559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT TUE MAR 12 2019  
 
VALID 12Z FRI MAR 15 2019 - 12Z TUE MAR 19 2019  
   
..OVERVIEW AND GUIDANCE ASSESSMENT/PREFERENCES
 
 
EXPECT BROAD TROUGHING ALOFT TO PREVAIL OVER EASTERN NORTH AMERICA  
DOWNSTREAM FROM A RIDGE THAT BUILDS OVER THE CANADIAN ROCKIES AND  
INTERIOR WEST. OVER THE EASTERN PACIFIC A LEADING WEAK SHORTWAVE  
WILL LIKELY PASS INTO/AROUND THE BUILDING RIDGE WHILE A TRAILING  
TROUGH SHOULD AMPLIFY AND SHARPEN AS IT APPROACHES THE WEST COAST.  
 
THERE ARE ESSENTIALLY TWO LARGER-SCALE GUIDANCE DISAGREEMENTS.  
THE FIRST INVOLVES ENERGY INITIALLY MOVING INTO THE SOUTHWEST AND  
EVENTUAL POSSIBLE INTERACTION WITH NORTHERN STREAM SHORTWAVE  
ENERGY AMPLIFYING INTO THE EAST. EVEN COMPARED TO ITS ENSEMBLES  
THE 00Z CMC IS RATHER EXTREME WITH ITS COMBINED STRENGTH AND FAST  
PROGRESSION OF THE SOUTHWEST SHORTWAVE. THEN A FAIRLY STRONG  
DEPICTION OF AN AMPLIFYING MIDWEST SHORTWAVE BY SUN-MON IN THE CMC  
(SIMILAR TO THE 00Z UKMET THROUGH THE END OF ITS RUN LATE SUN)  
ALLOWS FOR A PHASED TROUGH WHICH BY EARLY MON LEADS TO A SURFACE  
LOW TRACKING CLOSER TO THE EAST COAST THAN MOST OTHER GUIDANCE.  
RELATIVE TO THE FULL ARRAY OF ENSEMBLE MEMBERS THE 00Z CMC IS ON  
THE FRINGE OF THE ENVELOPE BUT NOT EXTREME ENOUGH TO BE CONSIDERED  
AN OUTLIER. THE CMC SCENARIO HAS SUFFICIENTLY LOW PROBABILITY NOT  
TO INCLUDE IN A MOST-LIKELY SINGLE DETERMINISTIC FORECAST.  
HOWEVER THE POTENTIAL FOR EVOLUTION TO CHANGE FROM THE CURRENT  
CONSENSUS REPRESENTED BY THE ECMWF/GFS AND ITS ENSEMBLE MEANS WILL  
HAVE TO BE MONITORED.  
 
THE SECOND ISSUE INVOLVES THE WEAKENING PACIFIC SHORTWAVE ENERGY  
THAT REACHES WESTERN NORTH AMERICA BY AROUND SUN. IN VARYING WAYS  
THE LATEST GFS/GEFS RUNS (AND FV3 GFS) ARE MORE ENTHUSIASTIC ABOUT  
THE SHORTWAVE'S STRENGTH PASSING THROUGH/AROUND THE MEAN RIDGE AND  
THEN WESTWARD/SOUTHWESTWARD ELONGATION OF THIS ENERGY INTO THE  
FIRST HALF OF NEXT WEEK. BY THEN THIS EVOLUTION LEADS TO A  
FLATTER UPPER TROUGH OVER THE EAST VERSUS MOST OTHER GUIDANCE.  
THE 06Z GFS/GEFS MEAN ARE MORE PRONOUNCED WITH THE  
WESTWARD/SOUTHWESTWARD ELONGATION THAN THEIR 00Z COUNTERPARTS.  
TELECONNECTIONS RELATIVE THE STRONG CORE OF POSITIVE HEIGHT  
ANOMALIES OVER THE WESTERN HALF OF CANADA SEEN IN THE D+8  
MULTI-DAY MEANS SUGGEST AN EASTERN U.S. TROUGH THAT IS ROUNDED  
ENOUGH TO ALLOW FOR SOME 00Z GFS/GEFS INPUT ALONG WITH THE MORE  
AMPLIFIED ECMWF/ECMWF MEAN SOLUTION. ON THE OTHER HAND THE  
TELECONS SUPPORT LOWER HEIGHTS OVER THE EAST THAN DEPICTED IN THE  
06Z GFS/GEFS MEAN AND LAST COUPLE FV3 GFS RUNS.  
 
BASED ON MAJORITY CLUSTERING THE FORECAST INCORPORATED THE 00Z  
GFS/ECMWF AND LESSER WEIGHT OF THE UKMET FROM EARLY DAY 3 FRI INTO  
DAY 5 SUN. THE FORECAST STARTED TO INCLUDE 00Z GEFS/ECMWF MEANS  
LATE SUN AND INCREASED THEIR TOTAL INFLUENCE TO 60 PERCENT TOTAL  
BY DAY 7 TUE, WITH LINGERING OPERATIONAL INPUT FROM THE 00Z  
GFS/ECMWF.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
THE COLD FRONT CROSSING MUCH OF THE EAST COAST LATE THIS WEEK WILL  
LIKELY SETTLE NEAR THE FLORIDA KEYS AS A WAVY STATIONARY FRONT.  
THE COMBINATION OF THIS FRONT AND ONE OR MORE SOUTHERN STREAM  
SHORTWAVES ALOFT MAY PRODUCE PERIODS OF LOCALLY MODERATE OR HEAVY  
RAINFALL OVER THE FLORIDA PENINSULA. EXTREME SOUTHERN TEXAS MAY  
SEE SOME ENHANCED RAINFALL WITH THE ENERGETIC FLOW ALOFT AS WELL.  
THE REST OF THE EAST WILL SEE A DRIER TREND AS FRONTAL RAINFALL  
PASSES OFF THE EAST COAST AFTER FRI. COOL CYCLONIC FLOW WILL  
PRODUCE SOME AREAS OF LAKE EFFECT SNOW PRIMARILY TO THE LEE OF  
OPEN WATERS (MOSTLY LAKE MICHIGAN AND LAKE ONTARIO). DURING THE  
WEEKEND LIGHT PRECIPITATION COULD BRUSH PARTS OF THE PACIFIC  
NORTHWEST AND SOME LIGHT/SCATTERED ACTIVITY MAY OCCUR OVER THE  
SOUTHERN ROCKIES. OTHERWISE THE WEST SHOULD BE MOSTLY DRY UNTIL  
MOISTURE REACHES THE WEST COAST NEXT TUE. THERE MAY BE ONE OR  
MORE AREAS OF PRECIPITATION BETWEEN THE NORTHERN HALF OF THE  
PLAINS AND GREAT LAKES DURING THE PERIOD, IN ASSOCIATION WITH  
FEATURES PROGRESSING INTO THE LOWER 48 FROM CANADA, BUT WITH LOW  
CONFIDENCE IN TIMING AND COVERAGE.  
 
EXPECT BELOW NORMAL TEMPERATURES INITIALLY OVER THE WEST TO  
MODERATE WITH TIME WHILE COOL AIR MOVING INTO THE EAST BEHIND  
FRIDAY'S COLD FRONT SHOULD REBOUND CLOSER TO NORMAL AFTER SAT.  
THE NORTH-CENTRAL AND SOUTHERN ROCKIES/HIGH PLAINS MAY SEE THE  
MOST PERSISTENT COLD ANOMALIES WITH SOME LOCATIONS AT LEAST 15-20F  
BELOW NORMAL FOR HIGHS THROUGH THE WEEKEND. THE WARMING TREND  
OVER/NEAR THE WEST COAST STATES SHOULD BRING READINGS 5-10F ABOVE  
NORMAL BY SUN-TUE.  
 
RAUSCH  
 
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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