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FXUS02 KWBC 180700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST WED JAN 18 2023
VALID 12Z SAT JAN 21 2023 - 12Z WED JAN 25 2023
..OVERVIEW
LATEST MODELS AND ENSEMBLES STILL MAINTAIN THE THEME OF A
POSITIVELY TILTED MEAN TROUGH OVER THE LOWER 48 WHILE A STRONG
RIDGE PERSISTS OVER THE EASTERN PACIFIC AND ANOTHER RIDGE PREVAILS
SOUTHEAST OF FLORIDA. EXPECT THIS PATTERN TO PRODUCE HIGHEST
PRECIPITATION TOTALS OVER THE SOUTHEAST AND VICINITY, BUT WITH
MEANINGFUL TOTALS OF RAIN OR SNOW ALSO POSSIBLY EXTENDING FARTHER
WEST AND NORTH FROM THE PLAINS INTO THE NORTHEAST WITH INDIVIDUAL
EMBEDDED SYSTEMS. LOCATIONS FROM THE NORTHWEST U.S.
EAST/SOUTHEAST INTO THE ROCKIES SHOULD SEE PERIODS OF RAIN AND
MOUNTAIN SNOW WHILE MUCH OF THE WEST REMAINS BELOW NORMAL FOR
TEMPERATURES. THERE HAS BEEN CONSIDERABLE GUIDANCE SPREAD AND
VARIABILITY FOR THE SYSTEMS OF INTEREST BUT LATEST RUNS ARE
STARTING TO SHOW BETTER CLUSTERING IN SOME RESPECTS, PROVIDING
HOPE FOR IMPROVED CONFIDENCE SOMETIME SOON FOR SENSIBLE WEATHER
DETAILS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT FORECAST UNCERTAINTY HAS REVOLVED AROUND TWO PRIMARY
FEATURES, A LEADING UPPER LOW EMERGING FROM THE SOUTHERN ROCKIES
EARLY SATURDAY (WITH QUESTIONS OVER INTERACTION WITH SOUTHERN
CANADA/NORTHERN PLAINS ENERGY TO THE NORTH) AND TRAILING SHORTWAVE
ENERGY DROPPING INTO THE WEST DURING THE WEEKEND INTO EARLY NEXT
WEEK. THROUGH THE 00Z/17 CYCLE, GFS RUNS WERE GENERALLY ON THEIR
OWN IN DEPICTING PRONOUNCED PHASING OVER THE CENTRAL U.S. VERSUS
HAVING THE NORTHERN STREAM SHORTWAVE BYPASS THE UPPER LOW.
HOWEVER THE 12Z MODELS UNANIMOUSLY SWITCHED TO THE PHASED GFS
SCENARIO AND THE LATEST 00Z RUNS ARE MAINTAINING CONTINUITY WITH
THAT IDEA. THE END RESULT IS A TREND TOWARD AT LEAST SOME DEGREE
OF LOW PRESSURE TRACKING WEST OF THE APPALACHIANS BY AROUND SUNDAY
(THOUGH NOT AS STRONG AS SOME EARLIER GFS RUNS) AND THEN FAIRLY
STRONG LOW PRESSURE OVER OR NEAR NEW ENGLAND BY EARLY MONDAY. THE
ECMWF/GFS AND THEIR MEANS ARE FAIRLY CLOSE WHILE LATEST CMC RUNS
HAVE TENDED TO BE SLOW/SOUTH. THE NEW 00Z UKMET IS THE MOST
EXTREME WITH ITS FARTHER SOUTHEAST TRACK OFF THE COAST. EVEN WITH
ALL OF THE MODEL AND ENSEMBLE MEMBER SPREAD AND INCONSISTENCY
BEFORE THIS RECENT CONVERGENCE OF SOLUTIONS, ENSEMBLE MEANS HAD
BEEN HINTING AT SOME DEGREE OF LOW PRESSURE REACHING THE NEW
ENGLAND AREA FOR MULTIPLE DAYS.
FOR THE NEXT SYSTEM DROPPING INTO THE WEST, THE BEST RECENT SIGNAL
HAS BEEN FOR AN OPEN WAVE TO CLOSE OFF AN UPPER LOW NEAR THE FOUR
CORNERS (A LITTLE LATER/SOUTH VERSUS A NUMBER OF GFS RUNS) THOUGH
THE LATEST CMC/UKMET ACTUALLY SHOW AN UPPER LOW TRACK FARTHER
SOUTHWEST. THE MOST EXTREME SIDE OF THE SPREAD IS STILL A
QUESTION MARK SINCE TELECONNECTIONS RELATIVE TO THE UPSTREAM RIDGE
DO NOT SEEM TO FAVOR STRONGLY NEGATIVE HEIGHT ANOMALIES OVER THE
SOUTHWEST, THOUGH PERHAPS SUFFICIENT PROGRESSION TO TEMPER THE
MULTI-DAY MEAN COULD STILL LEAVE THE DOOR OPEN TO THAT
POSSIBILITY. MEANWHILE THE 12Z ECMWF STRAYED TO THE FAST SIDE OF
THE ENVELOPE WITH THE ECMWF MEAN PARTWAY BETWEEN THE ECMWF AND
SLOWER GFS/GEFS MEAN/CMC CLUSTER. THE NEW 00Z ECMWF IS STILL ON
THE EAST SIDE OF THE SPREAD, JUST WITH A SOMEWHAT DEEPER TREND AS
ITS SHORTWAVE DROPS SOUTHWARD OVER THE ROCKIES. BY EARLY NEXT
WEDNESDAY THE LOOSE CLUSTERING OF GFS/GEFS MEAN/CMC/ECENS WOULD
HAVE A LOW PRESSURE SYSTEM REACHING SOMEWHERE BETWEEN THE
MISSISSIPPI VALLEY AND THE APPALACHIANS/MID ATLANTIC/GREAT LAKES,
VERSUS THE SOUTHEAST COAST IN THE 12Z ECMWF. EVEN WITH ITS
DIFFERENT DETAILS THE NEW 00Z ECMWF ENDS UP WITH ITS SURFACE LOW
NEAR THE 12Z ECMWF MEAN.
BASED ON LATEST TRENDS AND CLUSTERING, THE EARLY PART OF THE
UPDATED FORECAST FOLLOWED AN OPERATIONAL MODEL COMPOSITE EARLY AND
THEN TRANSITIONED TOWARD A COMBINATION OF THE 18Z GFS/12Z CMC AND
THE 18Z GEFS/12Z ECMWF MEANS TO REFLECT THE MODERATE MAJORITY
SCENARIO BY LATE IN THE PERIOD.
..WEATHER/HAZARD HIGHLIGHTS
WHILE THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY IN FORECAST
SPECIFICS, THERE HAS BEEN SOME IMPROVEMENT IN THE BROAD THEME OF
TWO PRIMARY SYSTEMS AND THEIR GENERAL TIMING. THE FIRST SHOULD
TRACK FROM THE PLAINS THROUGH THE CENTRAL/NORTHERN EAST COAST
SATURDAY-MONDAY, BRINGING THE POTENTIAL FOR WINTRY WEATHER FROM
THE CENTRAL PLAINS INTO THE NORTHEAST AND RAIN TO THE SOUTH.
EXPECT THE HEAVIEST RAIN OVER THE SOUTHEAST WHERE GULF MOISTURE
MAY INTERACT WITH A LEADING WARM FRONT. MOST GUIDANCE HAS BEEN
TRENDING DEEPER FOR THIS STORM NEAR NEW ENGLAND BY MONDAY, SO
BRISK TO STRONG WINDS COULD BE POSSIBLE. THERE IS STILL POTENTIAL
FOR A MEANINGFUL CHANGE IN THE MOST LIKELY TRACK SO CONTINUE TO
MONITOR FORECASTS FOR THIS SYSTEM. THE NEXT SYSTEM MAY AFFECT THE
CENTRAL-EASTERN U.S. BY TUESDAY-WEDNESDAY WITH A PRECIPITATION
DISTRIBUTION THAT COULD HAVE SOME SIMILARITIES TO THE FIRST
SYSTEM. HOWEVER THERE ARE SIGNALS THAT THIS LATTER SYSTEM COULD
BE DEEPER WHILE STILL WEST OF THE APPALACHIANS. ACROSS THE WEST,
RAIN AND MOUNTAIN SNOW OF MOSTLY MODERATE AMOUNTS SHOULD EXTEND
FROM THE NORTHWEST/NORTHERN ROCKIES TO THE SOUTH/SOUTHEAST.
SOUTHWESTWARD EXTENT OF THE PRECIPITATION WILL DEPEND ON EXACT
TRACK/AMPLITUDE OF THE WEEKEND FEATURE WHOSE DETAILS REMAIN
UNRESOLVED.
MOST ASPECTS OF THE TEMPERATURE FORECAST HAVE CHANGED LITTLE OVER
THE PAST DAY. THE NORTHERN THREE-FOURTHS OF THE WEST AND INTO
PARTS OF THE HIGH PLAINS STILL LOOK CHILLY THROUGH THE PERIOD WITH
HIGHS 5-20F BELOW NORMAL. AN ISOLATED LOCATION OR TWO COULD SEE A
RECORD COLD HIGH. LOCATIONS ACROSS THE EASTERN U.S. AND NORTHERN
PLAINS SHOULD SEE NEAR TO ABOVE NORMAL HIGHS WITH GENERALLY WARMER
ANOMALIES (UP TO PLUS 10-20F OVER SOME AREAS) FOR LOWS.
RAUSCH
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, 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/#PAGE=ERO
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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