143  
FXUS02 KWBC 270717  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
216 AM EST WED FEB 27 2019  
 
VALID 12Z SAT MAR 02 2019 - 12Z WED MAR 06 2019  
   
..PATTERN OVERVIEW
 
 
BROADLY CYCLONIC MEAN FLOW ACROSS THE LOWER 48 AT THE START OF THE  
WEEKEND SHOULD TRANSITION TOWARD INCREASINGLY AMPLIFIED TROUGHING  
OVER THE EAST BY THE MIDDLE OF NEXT WEEK AS AN UPPER RIDGE REACHES  
THE ROCKIES AND A TRAILING TROUGH APPROACHES THE WEST COAST. MEAN  
RIDGING ALOFT OVER NORTHWESTERN NORTH AMERICA (SPECIFICALLY AN  
INITIAL UPPER HIGH DROPPING SOUTH OVER WESTERN CANADA FOLLOWED BY  
ANOTHER RIDGE BUILDING OVER EASTERN ALASKA AND THE YUKON) WILL  
SUPPORT A CORE OF EXTREMELY LOW TEMPERATURES OVER THE CENTRAL U.S.  
WITH ANOMALIES UP TO 30-45F BELOW NORMAL DURING SAT-MON AND LIKELY  
WIDESPREAD NEW DAILY RECORDS. SOME OF THIS COLD AIR WILL EXTEND  
INTO NORTHERN PARTS OF THE WEST AND THROUGH MUCH OF THE EAST. TWO  
SOUTHERN STREAM PACIFIC SYSTEMS WILL BRING MORE SIGNIFICANT  
PRECIPITATION TO PARTS OF THE WEST WITH HEAVIEST FOCUS OVER  
CALIFORNIA, WHILE THERE IS STILL A SIGNAL FOR HEAVY RAINFALL  
POTENTIAL OVER PARTS OF THE SOUTHEAST. FARTHER NORTH OVER THE  
EASTERN STATES THERE WILL BE ONE OR MORE POSSIBILITIES FOR SNOW  
BUT WITH A FAIR DEGREE OF UNCERTAINTY OVER THE SPECIFICS.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
EARLY IN THE PERIOD A BLEND OF OPERATIONAL MODEL GUIDANCE THROUGH  
THE 12-18Z CYCLES PROVIDED A GOOD STARTING POINT FOR YIELDING THE  
DESIRED SOLUTION FOR SYSTEMS OF INTEREST. THERE HAVE BEEN  
CONTINUED DIFFERENCES FOR THE OVERALL AREA OF LOW PRESSURE  
EXPECTED OVER THE NORTHEASTERN U.S./SOUTHEASTERN CANADA AND OFF  
THE NEW ENGLAND COAST DURING THE WEEKEND. IN THE 12-18Z ARRAY OF  
GUIDANCE THERE WERE ESSENTIALLY TWO CLUSTERS, THE GFS/CMC AND  
THEIR MEANS THAT WERE BETTER DEFINED ALONG/INLAND FROM THE NEW  
ENGLAND COAST AND THE ECMWF/ECMWF MEAN/UKMET THAT PLACED MORE  
EMPHASIS ON OFFSHORE LOW PRESSURE. DEPENDENCE ON LOW  
PREDICTABILITY SMALL SCALE FEATURES (ORIGINATING IN PART FROM THE  
UPPER LOW NOW NEAR THE PACIFIC NORTHWEST) FAVORED A BLENDED  
APPROACH THAT KEPT THE FORECAST CLOSE TO CONTINUITY. THERE HAVE  
BEEN SOME TRENDS TOWARD A MORE FRAGMENTED EJECTION OF THAT UPPER  
LOW ENERGY SO THE WEAKER ADJUSTMENT IN THE 00Z GFS IS PLAUSIBLE.  
MEANWHILE TRAILING WAVINESS AFFECTING THE SOUTHEAST/MID-ATLANTIC  
WILL BE INFLUENCED BY ENERGY FROM THE SYSTEM INITIALLY NEARING  
CALIFORNIA (CONSENSUS MEAN STILL LOOKING GOOD FOR THIS SYSTEM) AND  
POSSIBLY INTERACTION WITH NORTHERN STREAM FLOW. THE MULTI-MODEL  
BLEND YIELDED A FORECAST CLOSE TO THE 12Z ECMWF MEAN, A REASONABLE  
INTERMEDIATE SOLUTION BETWEEN THE WEAKER GFS/GEFS MEAN RUNS AND  
STRONGER/NORTHWARD 12Z ECMWF/UKMET/CMC. A MAJORITY OF NEW 00Z  
RUNS (MINUS THE GFS) MAINTAIN SUPPORT FOR SIGNIFICANT WAVINESS.  
 
DURING THE LATTER HALF OF THE PERIOD, MODEL/ENSEMBLE CLUSTERING  
HAS SHOWN A PRONOUNCED DEEPER TREND WITH THE UPPER TROUGH AXIS  
THAT CROSSES THE MIDWEST/GREAT LAKES AND VICINITY. HOWEVER LATEST  
OPERATIONAL RUNS HAVE SHOWN LESS EVIDENCE OF A CLOSED LOW THAN 24  
HOURS AGO. RECENT GFS RUNS STRAYED A LITTLE FASTER THAN CONSENSUS  
WITH THIS TROUGH OVER THE EAST BY TUE-WED. MEANWHILE BY DAY 7 WED  
THE NEXT SYSTEM TO AFFECT THE WEST COAST SHOWS EXPECTED  
TRACK/TIMING DIFFERENCES BUT IN GENERAL THE CLUSTERING IS NOT BAD  
FOR THAT TIME FRAME AND AN INTERMEDIATE SOLUTION APPEARS  
REASONABLE AT THIS TIME. ONE COMPLEXITY THAT WILL HAVE TO BE  
MONITORED IS POTENTIAL FOR ELONGATING SOUTHWESTERN CANADA ENERGY  
TO CLOSE OFF AN UPPER LOW OFF VANCOUVER ISLAND AND HAVE SOME  
INFLUENCE ON THE INCOMING SYSTEM. OVERALL BOTH THE MODELS AND  
MEANS APPEARED TO PROVIDE SOME USEFUL INFORMATION TO CONTRIBUTE TO  
THE DAYS 6-7 FORECAST SO THE BLEND FOLLOWED AN EVEN WEIGHT BETWEEN  
THE 18Z GEFS/12Z ECMWF MEANS AND 12Z ECMWF-CMC/12-18Z GFS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
ACROSS THE WEST THE PRIMARY AXIS FOR HEAVIEST RAIN AND HIGHER  
ELEVATION SNOW WILL EXTEND FROM CALIFORNIA EASTWARD THROUGH THE  
CENTRAL/SOUTH-CENTRAL ROCKIES WITH THE SIERRA NEVADA LIKELY SEEING  
THE HIGHEST 5-DAY TOTALS. TWO SYSTEMS WILL AFFECT THE REGION  
DURING THE PERIOD, ONE ARRIVING EARLY IN THE WEEKEND AND SPREADING  
MOISTURE RAPIDLY EASTWARD THEN FOLLOWED BY A SECOND ARRIVING  
TUE-WED. AS MOISTURE FROM THE SECOND SYSTEM SPREADS NORTHWARD  
THERE MAY BE POTENTIAL FOR WINTRY PRECIPITATION AT LOW ELEVATIONS  
OVER INTERIOR PORTIONS OF THE NORTHWEST GIVEN THE COLD AIR LIKELY  
TO BE IN PLACE.  
 
THE SYSTEM AFFECTING THE NORTHEAST DURING THE WEEKEND SHOULD BRING  
SOME SNOWFALL TO THE REGION BUT WEAKENING AND POSSIBLY OFFSHORE  
TRENDS FOR LOW PRESSURE AS WELL AS FAST PROGRESSION MAY LIMIT  
ACCUMULATIONS. SOUTHERN STREAM ENERGY INTERACTING WITH THE  
TRAILING FRONT MAY PRODUCE A PERIOD OF HEAVY RAINFALL OVER PARTS  
OF THE SOUTHEAST WITH THE WEEKEND INTO EARLY MON TIME FRAME THE  
MOST LIKELY PERIOD FOR THIS ACTIVITY. GUIDANCE HAS NOT YET FULLY  
CONVERGED FOR DETAILS SO CONFIDENCE IS ONLY MODERATE THUS FAR.  
SNOW WILL BE POSSIBLE IN THE NORTHERN PART OF THE MOISTURE  
SHIELD--FROM THE SOUTH-CENTRAL MISSISSIPPI VALLEY INTO THE  
MID-ATLANTIC. LIGHTER RAINFALL COULD LINGER OVER PARTS OF THE  
EXTREME SOUTHEAST/FLORIDA INTO NEXT WEEK.  
 
WITHIN THE WIDESPREAD AREA OF EXTREMELY COLD AIR OVER THE CENTRAL  
U.S., EXPECT THE MOST EXTREME ANOMALIES TO BE OVER THE  
NORTHERN-CENTRAL PLAINS DURING SAT-MON WITH ANOMALIES OF 30-45F  
BELOW NORMAL. ESPECIALLY ON SUN-MON MANY PLACES OVER THE PLAINS  
AND MIDWEST SHOULD CHALLENGE OR EXCEED DAILY RECORD  
VALUES--ESPECIALLY FOR COLD HIGHS BUT ALSO FOR MORNING LOWS AT  
SOME LOCATIONS. LESS EXTENSIVE COVERAGE OF DAILY RECORDS MAY  
CONTINUE INTO TUE. THE EASTERN U.S. WILL SEE A MODIFIED FORM OF  
THIS COLD AIR BY THE FIRST HALF OF NEXT WEEK WITH READINGS "ONLY"  
10-20F BELOW NORMAL. LOCALIZED PARTS OF THE INTERIOR NORTHWEST  
MAY SEE TEMPERATURES 10-30F BELOW NORMAL. RELATIVE WARMTH WILL BE  
CONFINED TO THE SOUTHERN HALF OF THE WEST AND MORE SO FOR MORNING  
LOWS THAN AFTERNOON HIGHS.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page