418  
FXUS02 KWBC 040654  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
153 AM EST MON MAR 4 2019  
 
VALID 12Z THU MAR 7 2019 - 12Z MON MAR 11 2019  
 
WEATHER PATTERN OVERVIEW  
~~~~~~~~~~~~~~~~~~~~~~~~  
 
THE AMPLIFIED FLOW PATTERN THAT EXISTS DURING THE SHORT RANGE  
FORECAST PERIOD IS EXPECTED TO TRANSITION TO A MORE QUASI-ZONAL  
PATTERN ACROSS THE CONTINENTAL U.S. BY THE BEGINNING OF THE MEDIUM  
RANGE PERIOD ON THURSDAY. THE ANOMALOUS UPPER LEVEL RIDGE OVER  
THE EASTERN U.S. LIFTS OUT WHILE AN UPPER LEVEL TROUGH BUILDS IN  
ACROSS THE WEST COAST REGION BY FRIDAY, AND IT WILL BE THIS TROUGH  
AXIS THAT INDUCES SURFACE LOW CYCLOGENESIS ACROSS THE PLAINS BY  
THIS WEEKEND. A SECOND AND WEAKER DISTURBANCE IS LIKELY TO AFFECT  
THE WEST COAST REGION BY THE END OF THE FORECAST PERIOD NEXT  
MONDAY WITH A MORE AMPLIFIED PATTERN IN PLACE.  
 
MODEL GUIDANCE EVALUATION AND PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
THE MODELS AND ENSEMBLE MEANS INDICATE REASONABLE AGREEMENT ON THE  
SYNOPTIC SCALE FOR THE END OF THE WEEK, BUT NOT QUITE AS GOOD AS  
PREVIOUS DAYS WHEN CONFIDENCE WAS ABOVE AVERAGE. ONE OF THE MAIN  
DIFFERENCES ON THURSDAY WAS THE CMC HAVING A FLATTER 500MB HEIGHT  
CONFIGURATION OVER THE WEST COAST REGION COMPARED TO MORE  
TROUGHING EVIDENT IN ALL OF THE OTHER GUIDANCE. BOTH THE 18Z AND  
00Z GFS INDICATE A MORE DEVELOPED LEAD SURFACE LOW CROSSING THE  
OHIO VALLEY REGION ON FRIDAY, WHEREAS THE MODEL CONSENSUS AND FV3  
SUPPORT MORE OF AN ELONGATED SURFACE TROUGH.  
 
THE STRONG SURFACE LOW THAT IS FORECAST TO DEVELOP ACROSS THE  
PLAINS AND THEN TRACK NORTHEASTWARD IS INDICATING VERY GOOD  
AGREEMENT ON SATURDAY MORNING ACROSS EASTERN COLORADO AS LEE  
CYCLOGENESIS GETS UNDERWAY. MODEL DIFFERENCES GROW SIGNIFICANTLY  
BY SUNDAY REGARDING THE TRACK OF THE SURFACE LOW ACROSS THE  
MIDWEST STATES AND THEN THE GREAT LAKES REGION. IN TERMS OF  
TRENDS, BOTH THE EC MEAN AND GEFS MEAN HAVE TRENDED STRONGER WITH  
THIS STORM SYSTEM, AND THE CANADIAN MEAN MORE SUPPRESSED TO THE  
SOUTH AND NOT AS STRONG. THE FV3 IS FASTER THAN THE MODEL  
CONSENSUS AND IS NOT PREFERRED BEYOND SATURDAY. THERE IS BETTER  
AGREEMENT AMONG THE EC AND GEFS ENSEMBLE MEMBERS COMPARED TO THE  
CMC MEMBERS, AND THE EC MEAN PROVIDED A REASONABLE IDEA ON LOW  
PLACEMENT. TAKING ALL OF THESE FACTORS INTO ACCOUNT, THE FORECAST  
WAS PRIMARILY DERIVED FROM THE 12Z ECMWF/18Z FV3/12Z UKMET FOR THE  
FIRST HALF OF THE FORECAST PERIOD, AND THEN SOME OF THE ECMWF AND  
EC/NAEFS MEAN FOR THE LAST TWO DAYS.  
 
SENSIBLE WEATHER AND POTENTIAL HAZARDS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
HEAVY SNOW WILL LIKELY BE ONGOING ACROSS THE HIGHER ELEVATIONS OF  
THE SIERRA NEVADA AND MUCH OF THE INTERMOUNTAIN WEST AND ROCKIES  
THROUGH FRIDAY AS THE STRONG PACIFIC DISTURBANCE CROSSES THE  
REGION. SNOWFALL AMOUNTS ON THE ORDER OF 1 TO 2 FEET ARE LIKELY  
ACROSS PARTS OF THE CENTRAL AND NORTHERN ROCKIES, MAINLY ON  
FRIDAY. TEMPERATURES ARE EXPECTED TO SLOWLY MODERATE ACROSS THE  
NORTH-CENTRAL U.S. COMPARED TO EARLY THIS WEEK WHILE STILL  
REMAINING BELOW AVERAGE.  
 
WITH A LARGE STORM SYSTEM LIKELY DEVELOPING ACROSS THE CENTRAL  
U.S. NEXT WEEKEND, WIDESPREAD RAIN IS EXPECTED TO DEVELOP FROM THE  
GULF COAST TO THE OHIO VALLEY AND SOUTHERN APPALACHIANS AS A RICH  
SUPPLY OF GULF MOISTURE SURGES NORTHWARD AHEAD OF A STRONG COLD  
FRONT. THE HEAVIEST RAINFALL IS LIKELY ACROSS THE DEEP SOUTH AND  
TENNESSEE RIVER VALLEY, WHERE A GENERAL 1 TO 3 INCHES OF RAIN IS  
LIKELY THAT MAY LEAD TO SOME FLOODING ISSUES BASED ON THE CURRENT  
FORECAST. DEPENDING ON WHERE THE SURFACE LOW DEVELOPS, A CORRIDOR  
OF BLIZZARD CONDITIONS WILL BE POSSIBLE ACROSS PARTS OF THE  
NORTHERN PLAINS, UPPER MIDWEST, AND WESTERN GREAT LAKES REGION.  
IT IS STILL TOO EARLY TO MENTION PRECISE LOCATIONS GIVEN CURRENT  
MODEL DIFFERENCES. ANOTHER FACET TO THIS LOW PRESSURE SYSTEM WILL  
BE THE POTENTIAL FOR STRONG TO SEVERE THUNDERSTORMS TO DEVELOP IN  
THE WARM SECTOR, AND THIS IS SOMETHING THAT THE STORM PREDICTION  
CENTER IS CURRENTLY MONITORING.  
 
D. HAMRICK  
 
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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