967  
FXUS02 KWBC 100654  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
153 AM EST SUN FEB 10 2019  
 
VALID 12Z WED FEB 13 2019 - 12Z SUN FEB 17 2019  
   
..OVERVIEW
 
 
MODELS/ENSEMBLES CONTINUE TO SHOW BROAD AGREEMENT ON ANOMALOUS  
UPPER RIDGING PERSISTING FROM THE NORTH PACIFIC ACROSS ALASKA  
DURING THE MEDIUM RANGE, WITH A PERSISTENT DOWNSTREAM MEAN TROUGH  
AXIS JUST OFF THE PACIFIC NORTHWEST, AND A SUBTROPICAL RIDGE  
ATTEMPTING TO BUILD INTO THE SOUTH CENTRAL AND SOUTHEASTERN U.S.  
PACIFIC SHORTWAVE ENERGY WILL ROUND THE RIDGE AXIS NEAR ALASKA AND  
THEN DIVE SOUTHWARD TOWARD THE U.S. WEST COAST THROUGHOUT THE  
PERIOD, BEFORE MOVING EAST ACROSS THE ROCKIES AND CENTRAL U.S. A  
SHARP THERMAL GRADIENT ACROSS THE CENTRAL U.S. BETWEEN THE LARGE  
SCALE TROUGH/RIDGE WILL SUPPORT RAPID CYCLOGENESIS AS THESE  
FEATURES ARRIVE, WITH THE LOW PRESSURE SYSTEMS MOVING  
NORTHEASTWARD TOWARD THE GREAT LAKES/NEW ENGLAND. DESPITE BROAD  
AGREEMENT ON THIS GENERAL PATTERN, FORECAST CONFIDENCE BECOMES  
QUITE LOW DURING THE MID TO LATTER PORTION OF THE MEDIUM RANGE AS  
GUIDANCE STRUGGLES TO DEAL WITH THE DEGREE OF SEPARATION/PHASING  
BETWEEN NORTHERN/SOUTHERN STREAM ENERGY ACROSS THE CENTRAL U.S. BY  
THU-FRI. ADDITIONAL MAJOR DIFFERENCES EMERGE IN THE WAKE OF THIS  
SYSTEM AND AHEAD OF THE NEXT PACIFIC SHORTWAVE, WHEN MODELS CANNOT  
EVEN AGREE ON WHETHER BROAD CYCLONIC OR ANTICYCLONIC FLOW WILL  
PREVAIL, WITH MAJOR IMPLICATIONS FOR THE NEXT INCOMING SHORTWAVE  
BY LATE IN THE WEEK, AND ITS EVOLUTION AS IT MOVES INLAND.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT AND PREFERENCES
 
 
MODELS WERE INITIALLY REASONABLY WELL-CLUSTERED WITH THE LOW  
PRESSURE SYSTEM CROSSING THE GREAT LAKES ON WED, AND THE TRIPLE  
POINT LOW DEVELOPING ALONG THE NEW ENGLAND COAST. SOME TIMING  
DIFFERENCES EMERGE AS THIS LOW PULLS NORTHEAST AWAY FROM NEW  
ENGLAND ON THU, BUT NO CLEAR OUTLIER SOLUTIONS WERE EVIDENT.  
FARTHER WEST, A COMPLEX LOW PRESSURE SYSTEM IN THE EASTERN PACIFIC  
SHOULD MOVE ONSHORE ON WED AND INTO THE FOUR CORNERS/ROCKIES ON  
THU AHEAD OF AN AMPLIFYING SHORTWAVE. MODEL SOLUTIONS SHOWED SOME  
TIMING AND SLIGHT STRUCTURAL DIFFERENCES WITH THIS FEATURE, BUT A  
CONSENSUS SOLUTION IS LIKELY BEST. THUS, THE FORECAST DURING DAYS  
3-4 WAS BASED ON A MULTI-MODEL CONSENSUS BLEND, INCLUDING THE  
ECMWF/CMC/GFS/FV3.  
 
FROM DAY 5 (FRI) ONWARD IS WHEN BIG PROBLEMS EMERGE IN THE  
FORECAST SUCH THAT IT WAS A STRUGGLE TO FIND MUCH IN THE WAY  
CONSENSUS. BY THE TIME THE AMPLIFIED PACIFIC SHORTWAVE REACHES THE  
CENTRAL U.S. FRI, SOLUTIONS DIFFER SUBSTANTIALLY AS TO HOW DEEP  
THIS FEATURE WILL BE (CLOSED VS. OPEN WAVE) AND WHETHER IT WILL  
INTERACT/PHASE WITH NORTHERN STREAM ENERGY. THIS RESULTS IN A  
RANGE OF POTENTIAL TRACKS FOR THE SURFACE CYCLONE ANYWHERE FROM A  
MIDWEST/GREAT LAKES TRACK (GFS/FV3/CMC) TO A SOUTHERN PLAINS/OHIO  
VALLEY TRACK (ECMWF/UKMET). ENSEMBLE SCATTER PLOTS REVEAL A  
BIMODAL DISTRIBUTION OF SOLUTIONS FOR THE SURFACE LOW FRI-SAT THAT  
BREAKS DOWN ALONG THE DESCRIBED SCENARIOS. A SLIGHT TREND WAS  
NOTED AMONG RECENT MODEL RUNS TOWARD KEEPING THE TWO STREAMS LESS  
PHASED FOR LONGER, SO THE RAPIDLY DEEPENING SOLUTIONS SHOWN BY  
SOME PREVIOUS GFS/FV3 RUNS SEEM LESS LIKELY, BUT IT IS ALSO  
UNCLEAR WHETHER KEEPING THE STREAMS SEPARATE AS LONG AS THE  
UKMET/ECMWF IS LIKELY. THUS, A MIDDLE GROUND SOLUTION WAS  
PREFERRED (RELATIVELY CLOSE TO THE 00Z GFS). AS THIS SYSTEM  
REACHES THE EASTERN U.S. BY SAT, DIFFERENCES IN TIMING/AMPLITUDE  
PERSIST - LIKELY STEMMING FROM THE DISPARATE SOLUTIONS ON FRI.  
THESE DIFFERENCES CONTINUE ALL THE WAY INTO DAY 7 (SUN) WITH SOME  
SOLUTIONS KEEPING A DEEP LOW ACROSS EASTERN CANADA WHILE OTHERS  
QUICKLY EJECT THE SYSTEM INTO THE NORTH ATLANTIC.  
 
ADDITIONALLY, AS ALLUDED TO IN THE OVERVIEW, MODELS STRUGGLE WITH  
THE NATURE OF THE UPPER-LEVEL FLOW ACROSS THE WESTERN/CENTRAL U.S.  
IN THE WAKE OF THE LOW PRESSURE SYSTEM. THE GFS AND CMC BUILD AN  
UPPER RIDGE AXIS WITH BROAD ANTICYCLONIC FLOW, WHILE THE ECMWF  
KEEPS A STREAM OF STRONG PACIFIC INTO THE WESTERN U.S., WHICH IS  
ABLE TO QUICKLY AMPLIFY ACROSS THE CENTRAL U.S. IN A BROAD REGION  
OF ZONAL TO EVEN SLIGHTLY CYCLONIC UPPER FLOW. ENSEMBLES SHOW  
LITTLE REDUCTION IN SPREAD (AND PERHAPS EVEN A SLIGHT INCREASE)  
ACROSS RECENT CYCLES BY DAYS 6-7 ON THESE ASPECTS OF THE LARGE  
SCALE FLOW. GIVEN THE PERSISTENT MEAN TROUGH AXIS NEAR/OFF THE  
PACIFIC NORTHWEST, WAS A BIT SKEPTICAL TO ALLOW STRONG HEIGHT  
FALLS PUSHING WELL INLAND AS SHOWN BY THE 12Z ECMWF. THE GFS HAS  
PERHAPS SHOWN A BIT MORE CONSISTENCY FOR AT LEAST A FEW RUNS BUT A  
LOOK BACK SEVERAL RUNS DOES REVEAL A MORE ECMWF LIKE SCENARIO.  
THUS, OPTED TO LEAN HEAVILY ON ENSEMBLE MEANS BY DAYS 6-7, AND  
FORECAST CONFIDENCE IS QUITE LOW.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE LOW PRESSURE SYSTEM AFFECTING NEW ENGLAND ON WED IS EXPECTED  
TO PRODUCE WINTRY PRECIPITATION ACROSS MUCH OF NEW ENGLAND, WITH  
HEAVY SNOW POSSIBLE ON WED FOR PORTIONS OF NORTHERN MAINE. THE  
NEXT DEEPENING LOW PRESSURE SYSTEM MOVING FROM THE CENTRAL U.S.  
TOWARD THE GREAT LAKES FRI-SAT COULD PRODUCE AN AREA OF WINTRY  
WEATHER NORTH OF THE LOW TRACK, ACROSS PORTIONS OF THE  
MIDWEST/GREAT LAKES ON THU AND PERHAPS PORTIONS OF NEW ENGLAND ON  
FRI-SAT. AS MENTIONED ABOVE, CONFIDENCE IN THE TRACK OF THIS  
SECOND SYSTEM IS LOW, AS ARE ANY POTENTIAL WINTER WEATHER IMPACTS.  
FARTHER SOUTH, THIS SECOND SYSTEM IS EXPECTED TO PRODUCE  
WIDESPREAD SHOWERS AND THUNDERSTORMS AS GULF OF MEXICO MOISTURE  
STREAMS NORTHWARD INTO THE DEEPENING SURFACE LOW. LOCALLY HEAVY  
RAINS WILL BE POSSIBLE FROM PORTIONS OF THE SOUTHEAST/TENNESSEE  
VALLEY REGIONS TO THE MID-ATLANTIC. MEANWHILE, THE WEST COAST WILL  
ALSO REMAIN ACTIVE WITH THE MEAN UPPER TROUGH OFFSHORE  
CONTINUOUSLY EJECTING SHORTWAVE ENERGY TOWARD THE COAST. HEAVY  
RAIN AND MOUNTAIN SNOWS ARE EXPECTED TO CONTINUE THROUGH THE  
EXTENDED FORECAST PERIOD, WITH AREAS FROM CALIFORNIA NORTH TO  
OREGON LIKELY SEEING THE MOST WIDESPREAD HEAVY PRECIPITATION.  
 
THE PATTERN WILL CONTINUE TO FAVOR VERY COLD TEMPERATURES FROM THE  
PACIFIC NORTHWEST TO THE NORTHERN ROCKIES AND NORTHERN PLAINS  
THROUGH THE WEEK. HIGH TEMPERATURES ARE FORECAST TO BE 15 TO 30  
DEG F BELOW AVERAGE ACROSS MANY OF THESE AREAS THROUGH THE  
FORECAST PERIOD. MEANWHILE, AREAS FROM THE SOUTHERN/CENTRAL PLAINS  
TO THE EASTERN SEABOARD WILL SEE NEAR TO ABOVE AVERAGE  
TEMPERATURES VARYING BY DAY WITH THE WARMEST TEMPERATURES AHEAD OF  
THE LATE WEEK LOW PRESSURE SYSTEM, WHEN HIGHS MAY REACH 10 TO 15  
DEG ABOVE AVERAGE FOR SOME AREAS.  
 
RYAN  
 
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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