365  
FXUS02 KWBC 231547  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1046 AM EST WED JAN 23 2019  
 
VALID 12Z SAT JAN 26 2019 - 12Z WED JAN 30 2019  
 
1530 UTC UPDATE...  
 
MODELS SHOWED RELATIVELY GOOD CONSENSUS DURING THE EARLY PORTION  
OF THE MEDIUM RANGE, WITH A SIGNIFICANT DECREASE IN PREDICTABILITY  
AT SMALLER SCALES AFTER MON. A MULTI-MODEL BLEND OF DETERMINISTIC  
GUIDANCE (ECMWF/GFS/UKMET) SERVED AS A FORECAST STARTING POINT  
DURING DAYS 3-5 (SAT-MON). THIS BLEND SHOULD RESOLVE A LOW  
PRESSURE SYSTEM CROSSING THE GREAT LAKES/NORTHEAST DURING THIS  
PERIOD, AND A NEW SURFACE LOW DEVELOPING ACROSS THE CENTRAL U.S.  
IN RESPONSE TO ANOTHER SHORTWAVE DIGGING ACROSS THE  
ROCKIES/NORTHERN PLAINS. AFTER MON, WHILE BROAD CONSENSUS EXISTS  
THAT RIDGING WILL PERSIST OFF THE WEST COAST, WITH TROUGHING FROM  
EASTERN CANADA INTO THE EASTERN U.S., MODELS HAVE SHOWN A HIGH  
DEGREE OF VARIABILITY WITH RESPECT TO INDIVIDUAL SHORTWAVES  
TRAVERSING THE EASTERN TROUGH. THE SAME HOLDS TRUE WITH THE  
POSITION OF THE UPPER VORTEX (NEAR HUDSON BAY OR FARTHER SOUTH  
ACROSS THE GREAT LAKES), WITH SIGNIFICANT IMPLICATIONS ON THE  
WEATHER IMPACTS ACROSS THE EASTERN HALF OF THE CONUS. THEREFORE,  
MADE MUCH HEAVIER USE OF ECENS/GEFS MEANS DURING DAYS 6-7  
(TUE-WED) DUE TO SIGNIFICANTLY INCREASED SPREAD AT MEDIUM/SMALLER  
SCALES.  
 
RYAN  
 
PREVIOUS DISCUSSION (ISSUED AT 07 UTC)...  
 
   
..OVERVIEW
 
 
AMPLIFIED AND EXPANSIVE MEAN TROUGHING ALOFT SHOULD PERSIST OVER  
THE EASTERN HALF OF THE CONTINENT, BETWEEN A WEST COAST/EASTERN  
PACIFIC MEAN RIDGE AND A CENTER OF STRONG POSITIVE HEIGHT  
ANOMALIES OVER THE NORTH ATLANTIC. THIS PATTERN WILL FAVOR  
PERIODIC SURGES OF COLD AIR PUSHING SOUTH FROM CANADA ACROSS THE  
CENTRAL/EASTERN U.S. THE ROCKIES MAY SEE SOME OF THIS COLD AIR AT  
TIMES AS WELL. GUIDANCE CONTINUES TO SHOW SOME RETROGRESSION OF  
THE OVERALL MEAN RIDGE WHICH TELECONNECTIONS SUGGEST COULD  
EVENTUALLY LEAD TO SOME POSITIVELY TILTED TROUGHING OVER THE WEST.  
EXACTLY HOW THIS OCCURS REMAINS QUITE UNCERTAIN. ALSO UNCERTAIN  
IS HOW ENERGY IN SEPARATE STREAMS MAY PRODUCE ONE OR MORE LOW  
PRESSURE SYSTEMS ACROSS THE GULF OF MEXICO/WESTERN ATLANTIC WITH  
POTENTIAL EFFECTS ALONG ADJACENT COASTS. A SYSTEM TRACKING ACROSS  
THE MIDWEST/GREAT LAKES/NORTHEAST DURING THE FIRST HALF OF NEXT  
WEEK MAY PRODUCE MEANINGFUL PRECIPITATION AND EXERT SOME INFLUENCE  
ON ANY ATLANTIC FEATURES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE OVERALL MEAN PATTERN HAS GOOD CONSISTENCY/CONTINUITY BUT THERE  
ARE A NUMBER OF EMBEDDED FEATURES THAT COMPLICATE THE FORECAST  
WITH MODELS AND ENSEMBLES EXHIBITING VARIOUS IDEAS AND DAY-TO-DAY  
ADJUSTMENTS. AS IS TYPICALLY THE CASE THE SOLUTION ENVELOPE  
WIDENS WITH TIME, FAVORING A CONSENSUS APPROACH EARLY IN THE  
PERIOD FOLLOWED BY INCREASING EMPHASIS ON THE ENSEMBLE MEANS.  
 
AT THE START OF THE PERIOD EARLY SAT THE BLEND EXCLUDED THE 12Z  
CMC DUE TO BEING A FAST/WEAK EXTREME WITH THE WEAK WAVE FORECAST  
TO BE OVER THE OHIO VALLEY AT THAT TIME. THEN FROM SUN ONWARD THE  
18Z GFS TRACED A WIDER ARC WITH AN UPPER LOW WHICH OTHER GUIDANCE  
KEPT OVER CANADA INSTEAD OF BRUSHING NEW ENGLAND BY MON--FAVORING  
THE 12Z CYCLE FOR THE FORECAST BLEND'S GFS COMPONENT. THE NEW 00Z  
GFS IS NOT AS EXTREME AS THE 18Z VERSION THOUGH BY MON IT STILL  
SHOWS MORE EASTWARD ELONGATION ALOFT VERSUS MOST OTHER SOLUTIONS.  
THIS UPPER LOW SHOULD SUPPORT A SYSTEM TRACKING FROM LAKE SUPERIOR  
INTO QUEBEC.  
 
GULF OF ALASKA SHORTWAVE ENERGY ROUNDING THE MEAN RIDGE AND  
REACHING WESTERN CANADA BY EARLY SUN. AS IT DROPS SOUTH/SOUTHEAST  
IT WILL SERVE TO FLATTEN EASTERN U.S. FLOW TEMPORARILY. OVER  
RECENT DAYS THERE HAS BEEN SIGNIFICANT UNCERTAINTY OVER HOW  
EASTERN U.S. TROUGHING AND NORTHERN MEXICO/GULF SHORTWAVE ENERGY  
MAY IN SOME FASHION SUPPORT GULF/WESTERN ATLANTIC LOW  
PRESSURE--MAINLY IN THE SUN-TUE TIME FRAME. YESTERDAY'S GFS/ECMWF  
RUNS BEGAN SUGGESTING MID-LATITUDE CONUS FLOW WOULD BE  
SUFFICIENTLY PROGRESSIVE TO DEFLECT ANY DEVELOPING LOW PRESSURE  
WELL AWAY FROM THE COAST. THE 12Z UKMET AND WEAKER/EASTWARD CMC  
HELD ONTO THE IDEA FROM EARLIER GEFS/ECMWF MEAN RUNS BUT 12Z/18Z  
MEANS HAVE REFLECTED THE GFS/ECMWF TREND. INSTEAD THERE IS NOW  
SOMEWHAT OF A DELAY WITH POSSIBLE ATLANTIC DEVELOPMENT. THE 12Z  
ECMWF SCENARIO OF ATLANTIC AND MIDWEST SYSTEMS MERGING OVER NEW  
ENGLAND HAS LOW CONFIDENCE BUT THE ECMWF MEAN HINTS AT IT AND FOR  
THE PURPOSES OF THE MANUAL FORECAST REPRESENTS THE ONGOING  
POTENTIAL FOR AN ATLANTIC SYSTEM. AS FOR THE NORTHERN PLAINS INTO  
NORTHEAST SYSTEM LATE WEEKEND INTO NEXT WEEK, THE 12Z GFS WAS  
CLOSER TO THE MAJORITY CLUSTER VERSUS THE FARTHER SOUTH 18Z GFS.  
NEW GUIDANCE STILL SHOWS A MODERATE AMOUNT OF NORTH-SOUTH SPREAD.  
 
SPAGHETTI PLOTS AND OPERATIONAL MODEL COMPARISONS BECOME  
INCREASINGLY DIVERSE OVER THE EASTERN PACIFIC/WESTERN U.S. TOWARD  
MIDWEEK WITH A VARIETY OF POSSIBLE OUTCOMES FOR THE NEXT BUNDLE OF  
ENERGY HEADING INTO/AROUND THE MEAN RIDGE. THIS IS IN ADDITION TO  
THE 18Z GFS THAT IS IN THE MINORITY FOR HOW MUCH WESTWARD  
ELONGATION OCCURS WITH THE PRECEDING SHORTWAVE.  
TELECONNECTION-FAVORED FLOW SUGGESTS SOME POTENTIAL FOR SHORTWAVE  
ENERGY TO REACH THE WEST BUT CONFIDENCE IN HOW THIS OCCURS IS LOW.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE NORTHERN PLAINS THROUGH THE NORTHEAST WILL SEE ONE OR MORE  
PERIODS OF SNOW DURING THE PERIOD. TWO SYSTEMS WILL PROVIDE  
SYNOPTIC FOCUS. THE FIRST SHOULD DEVELOP OVER LAKE SUPERIOR BY  
SUN AND THEN TRACK INTO EASTERN CANADA, WHILE THE SECOND WILL  
LIKELY ENTER THE NORTHERN PLAINS BY LATE IN THE WEEKEND AND THEN  
PROGRESS ACROSS THE OHIO VALLEY OR LOWER GREAT LAKES INTO NEW  
ENGLAND. THERE MAY BE A BAND OF SIGNIFICANT SNOWFALL JUST NORTH  
OF THE LOW TRACK BUT THERE IS STILL A DECENT AMOUNT OF SPREAD  
AMONG MODEL/ENSEMBLE GUIDANCE FOR EXACTLY HOW MUCH LIQUID THIS  
SYSTEM WILL PRODUCE. TRAILING COLD CYCLONIC FLOW SHOULD PROMOTE  
AREAS OF LAKE EFFECT SNOW. SOUTHERN STREAM ENERGY WILL PRODUCE A  
BRIEF PERIOD OF ENHANCED RAINFALL PRIMARILY OVER SOUTHERN TEXAS.  
THEN WAVINESS PROGRESSING ACROSS THE SOUTHERN HALF OF THE GULF MAY  
PRODUCE A PERIOD OF LOCALLY HEAVY RAINFALL OVER PARTS OF THE  
FLORIDA PENINSULA. TRENDS HAVE LOWERED THE POTENTIAL FOR  
MEANINGFUL PRECIPITATION ALONG SOUTHEAST/MID-ATLANTIC COAST  
COMPARED TO PREVIOUS DAYS BUT SOME COMBINATION OF ATLANTIC LOW  
PRESSURE AND THE EARLY WEEK MIDWEST SYSTEM MAY STILL BRING SNOW  
INTO THE NORTHEAST. FARTHER WEST EXPECT AN AREA OF SNOW TO DROP  
SOUTHWARD THROUGH THE ROCKIES, PRIMARILY IN THE SUN-MON TIME FRAME.  
 
THE MIDWEST/UPPER MISSISSIPPI VALLEY INTO WESTERN GREAT LAKES  
REGION CONTINUES TO BE THE MOST LIKELY AREA FOR COLDEST  
TEMPERATURE ANOMALIES WITH READINGS 15-25F BELOW NORMAL MOST  
LIKELY ON SAT AND THEN OVER A LARGER AREA EXTENDING  
SOUTH/SOUTHEAST WITH ANOTHER COLD SURGE TUE-WED. THE HIGH PLAINS  
SHOULD SEE A BRIEF PERIOD OF WELL ABOVE NORMAL TEMPERATURES (BY  
10-25F) ESPECIALLY ON SUN BEFORE COLDER AIR DROPS SOUTHWARD AND  
BRINGS TEMPERATURES TO 5-15F BELOW NORMAL OVER THE ROCKIES/HIGH  
PLAINS. THE WEST COAST STATES WILL REMAIN ON THE WARM SIDE WITH  
BEST POTENTIAL FOR PLUS 10F OR GREATER ANOMALIES DURING THE FIRST  
HALF OF THE FORECAST PERIOD.  
 
RAUSCH  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION AND WINTER WEATHER OUTLOOK  
PROBABILITIES 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  
 

 
 
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