558  
FXUS02 KWBC 131939  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
338 PM EDT WED MAR 13 2019  
 
VALID 12Z SAT MAR 16 2019 - 12Z WED MAR 20 2019  
   
..OVERVIEW
 
 
GUIDANCE CONTINUES TO SHOW A STRONG RIDGE ALOFT THAT WILL BUILD  
INTO WESTERN CANADA AND DRIFT SLOWLY EASTWARD WITH TIME.  
CORRESPONDING TO THIS RIDGE THE MULTI-DAY MEANS AT D+8 ARE  
REMARKABLY SIMILAR IN SHOWING A STRONG POSITIVE HEIGHT ANOMALY  
CENTER OVER THE NORTHEAST CORNER OF ALBERTA. TELECONNECTIONS ON  
THIS CENTER SUPPORT THE CONSENSUS IDEA OF A BROAD EASTERN NORTH  
AMERICA TROUGH. THE WESTERN U.S. WILL LIKELY SEE SOME DEGREE OF  
MEAN RIDGING ALOFT BUT MIXED WITH ONE OR MORE SMALLER SCALE  
SHORTWAVES. MEANWHILE SOME GUIDANCE IS HINTING THAT A TROUGH  
ALOFT APPROACHING THE WEST COAST NEXT WEEK MAY TRY TO SEPARATE AND  
LEAD TO AN UPPER LOW REACHING NEAR CALIFORNIA. SOUTHERN STREAM  
FLOW WILL CARRY ALONG ONE OR MORE SHORTWAVES THROUGH THE SOUTHWEST  
U.S./NORTHERN MEXICO AND LOCATIONS TO THE EAST.  
 
   
..GUIDANCE ASSESSMENT/PREFERENCES
 
 
WHILE THE FORECAST LARGE-SCALE PATTERN EVOLUTION IS AGREEABLE,  
THERE ARE STILL MEANINGFUL UNCERTAINTIES WITH EMBEDDED SHORTWAVES.  
ONE SHORTWAVE POSSIBLY REACHING THE MISSISSIPPI VALLEY REGION  
AROUND DAY 4 SUN MAY REFLECT AT THE SURFACE AS A LEADING  
WAVE/FRONTAL SYSTEM THAT CROSSES THE EASTERN HALF OF THE COUNTRY.  
CMC/UKMET RUNS HAVE GENERALLY BEEN ON THE STRONG SIDE OF GUIDANCE  
WITH THIS SHORTWAVE WHILE LATEST ECMWF RUNS ARE ON THE  
FASTER/WEAKER SIDE OF THE ENVELOPE. FAIRLY LOW PREDICTABILITY  
GIVEN THE FEATURE'S SCALE FAVORS MAINTAINING AN INTERMEDIATE  
SOLUTION.  
 
ANOTHER ONGOING QUESTION MARK INVOLVES THE WEAK PACIFIC ENERGY  
HEADING INTO/AROUND THE MEAN RIDGE DURING THE WEEKEND--ALONG WITH  
THE EXACT CHARACTER OF THE RIDGE. OVER THE PAST DAY THE GUIDANCE  
HAS BECOME MORE COMMITTED TO THE IDEA THAT THE RIDGE WILL BRIEFLY  
CLOSE OFF A HIGH OVER SOUTHWESTERN CANADA EARLY NEXT WEEK. THIS  
WOULD ALLOW FOR SOME SOUTHWESTWARD ELONGATION OF SHORTWAVE ENERGY  
AFTER IT PASSES BY THE RIDGE AXIS, AS SUGGESTED BY SOME EARLIER  
GFS/GEFS RUNS. HOWEVER IT REMAINS TO BE SEEN WHETHER AS MUCH  
ENERGY GETS PULLED BACK AS DEPICTED IN 00Z GFS/06Z FV3 GFS RUNS.  
DIFFERENCES IN SPECIFICS EARLY IN THE WEEK LEAD TO SPREAD FOR  
TROUGH DETAILS FROM THE EASTERN PLAINS EASTWARD BY DAY 7 WED. THE  
BEST CLUSTERING OF GUIDANCE SUGGESTS THAT SHORTWAVE ENERGY  
REACHING THE NORTHERN PLAINS BY TUE SHOULD AMPLIFY AND REACH NEAR  
THE MISSISSIPPI VALLEY BY WED, SUPPORTING ANOTHER WAVE/FRONT AT  
THE SURFACE. THE 00Z ECMWF AMPLIFIES ITS TROUGH IN THE WESTERN  
PART OF THE ENVELOPE WHILE THE 00Z GFS IS ONE OF THE MOST  
PROGRESSIVE (DUE TO DEPOSITING MORE ENERGY OVER THE WEST). THE  
06Z GFS/00Z CMC ARE CLOSEST TO THE ENSEMBLE MEANS BUT RECENT  
TRENDS ALLOW FOR SOME CONSIDERATION OF THE 00Z ECMWF. THESE  
SHORTWAVE DIFFERENCES WILL PLAY A GREATER ROLE IN THE EASTERN U.S.  
FORECAST JUST AFTER THE END OF THE CURRENT EXTENDED PERIOD.  
 
GUIDANCE AS A WHOLE STILL DISPLAYS A SLOWER AND MORE SEPARATED  
TREND WITH THE UPPER TROUGH NEARING THE WEST COAST NEXT WEEK. A  
COMBINATION OF OPERATIONAL MODELS AND ENSEMBLE MEANS WOULD PROVIDE  
A REASONABLE STARTING POINT TO BALANCE RECENT TRENDS TOWARD MORE  
SEPARATION (I.E. POSSIBLE CLOSED UPPER LOW APPROACHING CALIFORNIA  
PER GFS/ECMWF RUNS) ALONG WITH TYPICALLY INCREASING UNCERTAINTY  
THAT EXISTS 6-7 DAYS OUT IN TIME.  
 
BASED ON THE PREFERENCE FOR A CONSENSUS/INTERMEDIATE FORECAST, THE  
UPDATED BLEND STARTED WITH THE 06Z GFS/00Z ECMWF AND LESSER WEIGHT  
OF THE CMC/UKMET DURING THE FIRST HALF OF THE PERIOD AND THEN  
TRENDED TOWARD A MODEL/MEAN BLEND INVOLVING THE 06Z GFS/00Z  
ECMWF/00Z CMC AND 06Z GEFS/00Z ECMWF MEANS.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
THE FORECAST PATTERN SHOULD LEAD TO FAIRLY LOW COVERAGE OF  
SIGNIFICANT PRECIPITATION DURING THE SAT-WED PERIOD. THE FLORIDA  
PENINSULA WILL BE THE PRIMARY FOCUS FOR HIGHEST RAINFALL TOTALS AS  
A WAVY FRONT SETTLES OVER OR JUST SOUTH OF THE KEYS AND ONE OR  
MORE SHORTWAVES PROGRESS WITHIN SOUTHERN STREAM FLOW ALOFT. MOST  
GUIDANCE SUGGESTS THERE WILL BE HIGHER POTENTIAL FOR A PERIOD OF  
ENHANCED RAINFALL DURING THE FIRST HALF OF NEXT WEEK VERSUS THE  
WEEKEND. THE SOUTHERN STREAM ENERGY MAY ALSO GENERATE SOME RAIN  
OVER SOUTHERN TEXAS BUT WITH LOWER TOTALS. ONE OR TWO SURFACE  
WAVES/FRONTAL SYSTEMS MAY BRING SCATTERED AREAS OF PRECIPITATION  
TO PARTS OF THE CENTRAL/EASTERN STATES. CONFIDENCE IN SPECIFICS  
IS STILL FAIRLY LOW BUT OVERALL EXPECT MOST RAIN/SNOW TO BE IN THE  
LIGHTER HALF OF THE SPECTRUM. LAKE EFFECT SNOW DOWNWIND FROM OPEN  
WATERS WILL TAPER OFF DURING THE COURSE OF THE WEEKEND. SLOWER  
TREND WITH THE SYSTEM APPROACHING CALIFORNIA WILL DELAY THE  
ARRIVAL OF ASSOCIATED MOISTURE INTO AT LEAST TUE-WED. THERE IS A  
FAIR DEGREE OF SPREAD IN CURRENT GUIDANCE, RANGING BETWEEN LIGHT  
RAIN REACHING THE COAST BY TUE AND DRY WEATHER CONTINUING THROUGH  
WED.  
 
THE NORTH-CENTRAL AND SOUTHERN PLAINS SHOULD SEE THE MOST  
PERSISTENT COLD ANOMALIES WITH SOME LOCATIONS 10-20F BELOW NORMAL  
FOR HIGHS THROUGH THE WEEKEND. THE MOST EXTREME ANOMALIES SHOULD  
BE OVER SOUTHERN AREAS. THE WARMING TREND OVER/NEAR THE WEST  
COAST STATES SHOULD BRING READINGS 5-10F OR SO ABOVE NORMAL BY  
SUN-MON WITH ABOVE NORMAL READINGS EXTENDING INTO THE INTERIOR  
WEST BY TUE-WED. THE EAST WILL GENERALLY SEE COOLER THAN NORMAL  
TEMPERATURES THROUGH THE PERIOD UNDER MEAN TROUGHING ALOFT.  
   
..BULLET POINTS FROM MEDIUM RANGE HAZARDS
 
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, TUE-WED, MAR 19-MAR  
20.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE PLAINS, MISSISSIPPI  
VALLEY, THE TENNESSEE VALLEY, AND THE GREAT LAKES.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST,  
THE MIDDLE/LOWER MISSISSIPPI VALLEY, AND THE OHIO/TENNESSEE  
VALLEYS.  
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN/CENTRAL PLAINS,  
AND THE UPPER/MIDDLE MISSISSIPPI VALLEY.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHERN  
ROCKIES, THE SOUTHERN PLAINS, AND THE SOUTHWEST, SAT-SUN, MAR  
16-MAR 17.  
 
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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