142  
FXUS02 KWBC 040621  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
120 AM EST FRI JAN 04 2019  
 
VALID 12Z MON JAN 07 2019 - 12Z FRI JAN 11 2019  
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
A MODERATELY PROGRESSIVE FLOW PATTERN WILL BE IN PLACE ACROSS THE  
CONUS DURING THE EXTENDED FORECAST PERIOD, WITH FAIRLY AMPLIFIED  
UPPER WAVES TRAVERSING THE COUNTRY EVERY FEW DAYS. NO SIGNALS FOR  
ANY SIGNIFICANT INCURSIONS OF ARCTIC AIR ARE SEEN IN THE GUIDANCE.  
A LOOK AT HEMISPHERIC D+8 500 HPA ANOMALIES REVEALS STRONGLY  
POSITIVE HEIGHT ANOMALIES CENTERED BETWEEN GREENLAND AND WESTERN  
EUROPE, HELPING TO DISPLACE COLD AIR FROM HIGH LATITUDES INTO  
EURASIA AND AWAY FROM NORTH AMERICA. TELECONNECTIONS ASSOCIATED  
WITH THIS AND OTHER HEMISPHERIC ANOMALY CENTERS SUGGEST THAT WE  
SHOULD SEE A TENDENCY FOR UPPER RIDGING TO REBUILD ACROSS WESTERN  
NORTH AMERICA, BUT WITH CONTINUED PROGRESSIVE FLOW ACROSS THE  
NORTH PACIFIC THE RIDGE WILL LIKELY BE SOMEWHAT TRANSIENT.  
 
MODEL GUIDANCE HAS STRUGGLED RECENTLY WITH THE PROGRESSIVE FLOW  
ACROSS THE NORTH PACIFIC AND WITH THE TIMING AND AMPLIFICATION OF  
THESE WAVES AS THEY CROSS THE CONUS, AND MODELS STILL APPEAR TO BE  
STRUGGLING WITH THIS TO SOME DEGREE. ENSEMBLE SPAGHETTI PLOTS SHOW  
A RATHER SIGNIFICANT REDUCTION IN SPREAD OVER THE PAST COUPLE  
ENSEMBLE CYCLES IN THE DAY 3-4 TIME PERIOD (MON-TUE), WITH THE  
ECMWF SEEMING TO BE AMONG THE MORE STABLE AND WELL-CENTERED OF THE  
DETERMINISTIC SOLUTIONS WITHIN THE SPREAD WITH RESPECT TO THE  
SHORTWAVE CROSSING THE CENTRAL/EASTERN STATES DURING THAT TIME  
FRAME. GIVEN THESE CONSIDERATIONS, THE FORECAST DURING DAYS 3-5  
WAS BASED ON A MULTI-MODEL DETERMINISTIC BLEND, BUT WEIGHTED A BIT  
MORE HEAVILY TOWARD THE ECMWF.  
 
GUIDANCE SHOWS GOOD AGREEMENT THAT ANOTHER AMPLIFIED UPPER TROUGH  
SHOULD APPROACH THE WEST COAST AND MOVE INLAND FROM DAY 5 (WED)  
ONWARD. MODEL VARIABILITY IS A BIT HIGHER AS TO THE SPECIFIC  
DETAILS OF THIS SYSTEM, SUCH AS WHETHER IT WILL HAVE A CLOSED  
MID/UPPER-LEVEL CIRCULATION OR WILL BE MORE OF AN OPEN WAVE. IN  
GENERAL, THE TREND HAS BEEN TOWARD A MORE OPEN AND SOMEWHAT MORE  
PROGRESSIVE WAVE, WITH THE ECMWF LEADING THIS TREND AND THE GFS  
LAGGING. THUS, CONTINUED TO EMPHASIZE THE ECMWF MORE HEAVILY  
RELATIVE TO THE GFS DURING THE DAY 6-7 (THU-FRI) TIME FRAME, WITH  
MAJORITY WEIGHT SHIFTED TOWARD THE ENSEMBLE MEANS (ESPECIALLY THE  
ECENS).  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE LOW PRESSURE SYSTEM CROSSING THE CENTRAL/EASTERN U.S. MON-WED  
WILL BE ACCOMPANIED BY THE POTENTIAL FOR SNOWFALL, PERHAPS HEAVY  
FOR SOME AREAS, ALONG/NORTH OF THE LOW TRACK, FROM THE NORTHERN  
GREAT LAKES TO NEW ENGLAND. ADDITIONAL HEAVY SNOWS WILL BE  
POSSIBLE ACROSS THE HIGHER ELEVATIONS OF THE WEST COAST STATES,  
SUCH AS THE CASCADES AND THE SIERRA, WITH HEAVY RAIN AT THE LOWER  
ELEVATIONS, AS THE NEXT PACIFIC TROUGH/FRONTAL SYSTEM MOVES ASHORE  
TUE-WED. LOCALLY HEAVY RAIN MAY REACH COASTAL AREAS OF SOUTHERN  
CALIFORNIA BY WED/WED NIGHT. AS MENTIONED ABOVE, THE LARGE SCALE  
FLOW PATTERN WILL BE SETUP SUCH THAT NO SIGNIFICANT OUTBREAKS OF  
ARCTIC AIR ARE EXPECTED ACROSS THE CONUS DURING THE FORECAST  
PERIOD. HIGH TEMPERATURES ARE EXPECTED TO BE WELL ABOVE AVERAGE  
THROUGH MOST OF THE PERIOD ACROSS MUCH OF THE CENTRAL/EASTERN  
STATES, WITH THE GREATEST ANOMALIES (+15 TO 20 DEG F) CENTERED  
ACROSS PORTIONS OF THE CENTRAL PLAINS AND MIDWEST.  
 
RYAN  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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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