128
FXUS02 KWBC 111901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST THU JAN 11 2024
VALID 12Z SUN JAN 14 2024 - 12Z THU JAN 18 2024
...AN ARCTIC AIRMASS BLANKETS MUCH OF THE NORTHERN AND CENTRAL
U.S. THROUGH EARLY NEXT WEEK...
...MONITORING POTENTIAL FOR AN IMPACTFUL STORM SYSTEM NEAR THE
EAST COAST NEXT TUESDAY-WEDNESDAY...
..OVERVIEW
GUIDANCE IS PERSISTENT WITH A DEEP AND BROAD MEAN TROUGH ALOFT
OVER MUCH OF THE LOWER 48 WHILE THE UPSTREAM MEAN RIDGE OVER THE
EASTERN PACIFIC DRIFTS TOWARD THE WEST COAST. THIS PATTERN WILL
SUPPORT VERY COLD TEMPERATURES OVER AREAS FROM THE NORTHWEST
THROUGH MUCH OF THE PLAINS/MISSISSIPPI VALLEY INTO EARLY NEXT WEEK
WITH NUMEROUS DAILY RECORDS FOR COLD LOWS/DAYTIME HIGHS. IN
MODIFIED FORM, COLDEST ANOMALIES SHOULD FOCUS OVER THE EASTERN
HALF OF THE COUNTRY BY MIDWEEK WHILE THE WEST TRENDS WARMER. SOME
REINFORCING COLD MAY REACH THE NORTHERN PLAINS BY NEXT THURSDAY
BUT IT SHOULD BE LESS EXTREME THAN WHAT IS FORECAST EARLIER IN THE
PERIOD. THERE ARE TWO PROMINENT UNCERTAINTIES IN THE FORECAST,
BOTH DURING TUESDAY-WEDNESDAY: DETAILS OF A POTENTIALLY IMPACTFUL
STORM SYSTEM NEAR THE EAST COAST AND NORTHEASTERN PACIFIC/WESTERN
CANADA EVOLUTION ALOFT WHICH WILL AFFECT PRECIPITATION SPECIFICS
OVER THE WEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
COMPARED TO PREVIOUS DAYS, LATEST GUIDANCE HAS DISPLAYED
SIGNIFICANTLY IMPROVED CLUSTERING REGARDING THE DETAILS OF INITIAL
NORTHERN TIER SHORTWAVE ENERGY AND ITS EVENTUAL EASTWARD
PROGRESSION THAT SHOULD LEAD TO STRENGTHENING SURFACE LOW PRESSURE
NEAR THE EAST COAST TUESDAY INTO WEDNESDAY. LATEST TRENDS HAVE
BEEN TILTING TOWARD THE SLOWER SIDE OF THE PRIOR BROAD SPREAD WITH
THE UPPER SHORTWAVE, NOW TENDING TO FAVOR DEVELOPING LOW PRESSURE
NEAR THE SOUTHEAST COAST BY EARLY TUESDAY AND A FAIRLY STRONG
SYSTEM REACHING NEW ENGLAND OR THE CANADIAN MARITIMES BY EARLY
WEDNESDAY (WHICH IS CLOSEST TO SOME PRIOR ECMWF RUNS AND
ECMWF-INITIALIZED MACHINE LEARNING MODEL RUNS). 00Z
ECMWF-INITIALIZED MACHINE LEARNING MODELS FIT THIS THEME AS WELL.
RELATIVE TO THIS MAJORITY SCENARIO, THE 00Z CMCENS APPEARS A
LITTLE FAST ON TUESDAY WHILE THE PAST COUPLE UKMET RUNS HAVE BEEN
A BIT ON THE WESTERN SIDE OF THE ENVELOPE (BUT TO A LESSER DEGREE
IN THE NEW 12Z RUN). RECENT GEFS MEANS HAVE BEEN A BIT FARTHER
OFFSHORE AROUND TUESDAY. THE NEW 12Z GFS FITS WELL BETWEEN ITS
SLIGHTLY WESTWARD 06Z RUN AND EASTWARD 00Z RUN.
MEANWHILE THE QUESTION MARK FARTHER WEST INVOLVES THE DEGREE TO
WHICH A TROUGH CROSSING OVER/SOUTH OF ALASKA (AND POSSIBLY ENERGY
TO THE SOUTH) ULTIMATELY DENTS THE EAST PACIFIC/WEST COAST UPPER
RIDGE AROUND TUESDAY-WEDNESDAY, BEFORE CONSENSUS RETURNS TO A MORE
AGREEABLE UPPER RIDGE NEAR THE WEST COAST BY NEXT THURSDAY. OVER
THE PAST COUPLE DAYS GUIDANCE HAS FORMED TWO PRONOUNCED CLUSTERS
IN PRINCIPLE, WITH THE GFS/GEFS HOLDING ONTO A PERSISTENT RIDGE
VERSUS REMAINING GUIDANCE SHOWING VARYING DEGREES OF HEIGHT FALLS.
THIS MAKES FOR A SIGNIFICANT DIFFERENCE IN HOW STRONG OF A
SURFACE SYSTEM MAY REACH THE PACIFIC NORTHWEST AND FOR
PRECIPITATION AND COVERAGE AMOUNTS OVER THE WEST, WITH THE
GFS/GEFS SCENARIO MUCH LIGHTER AND CONFINED WITH WHAT
PRECIPITATION OCCURS. THE 00Z CMC SEEMED TO OFFER THE LEAST
CONFIDENT EXTREME AMONG THE ECMWF CLUSTER, WITH MORE EXAGGERATED
AMPLITUDE OF UPPER TROUGHING AND SOUTHWARD PATH OF A SEPARATE
FEATURE TO THE SOUTH (LEADING TO VERY FAR SOUTHWARD MOISTURE
COVERAGE OVER THE WEST). 00Z ECMWF-INITIALIZED MACHINE LEARNING
MODELS DO NOT HELP IN DETERMINING THE RELATIVE POTENTIAL OF EITHER
SCENARIO, BEING ONLY 3-2 IN FAVOR OF THE ECMWF SCENARIO.
THE UPDATED FORECAST STARTED THE FIRST PART OF THE PERIOD WITH A
BLEND EMPHASIZING THE 00Z/06Z GFS AND 00Z PLUS 12Z/10 ECMWF RUNS
WITH LESS WEIGHT ON THE 00Z CMC/UKMET, FOLLOWED BY SOME
INCORPORATION OF 06Z GEFS/00Z ECENS MEANS AND REMOVAL OF THE CMC.
DURING THE LESS CONFIDENT TUESDAY-WEDNESDAY PERIOD, THIS APPROACH
PROVIDED A REASONABLE INTERMEDIATE SOLUTION ALONG THE EAST COAST
AND A COMPROMISE ALONG THE WEST COAST WITH MODEST DENTING OF THE
UPPER RIDGE AND ASSOCIATED WEAK LOW PRESSURE.
..WEATHER/HAZARDS HIGHLIGHTS
A WEATHER HIGHLIGHT DURING THE PERIOD WILL BE THE ARCTIC BLAST
LIKELY TO IMPACT THE NORTHERN ROCKIES, NORTHERN GREAT BASIN, GREAT
PLAINS, MISSISSIPPI VALLEY AND MIDWEST. THE SYNOPTIC SETUP
FEATURING A STRENGTHENING UPPER RIDGE IN THE EASTERN PACIFIC AND
AMPLIFIED DOWNSTREAM TROUGH WILL SUPPORT THE DESCENT OF SURFACE
HIGH PRESSURE THROUGH THE CENTRAL U.S. THIS WEEKEND THROUGH EARLY
NEXT WEEK. THE COLDEST PART OF THIS AIRMASS WILL BE OVER PORTIONS
OF NORTHERN MONTANA WHERE LOW TEMPERATURES COULD BOTTOM OUT AROUND
40 DEGREES BELOW ZERO SUNDAY MORNING. PORTIONS OF THE NORTHERN
ROCKIES DOWN THROUGH THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI
VALLEY MAY DROP TO BELOW ZERO DEGREES SATURDAY, SUNDAY, AND MONDAY
NIGHTS. THIS WILL MAKE FOR VERY DANGEROUS OUTDOOR CONDITIONS.
MINIMUM TEMPERATURE ANOMALIES WILL LIKELY BE BETWEEN 20-40 DEGREES
BELOW AVERAGE FOR THESE AREAS. FREEZING TEMPERATURES WILL ALSO
MAKE THEIR WAY TO THE GULF COAST MONDAY AND TUESDAY NIGHT.
TEMPERATURES WILL BEGIN TO REBOUND OVER THE NORTHERN PLAINS
TUESDAY-TUESDAY NIGHT AND ELSEWHERE OVER THE PLAINS BY WEDNESDAY
AS A DISTURBANCE ENTERS THE NORTHERN PLAINS/UPPER MIDWEST AND
SHIFTS SURFACE WINDS OUT OF THE SOUTH OR WEST. ANOTHER PUSH OF
COLD AIR MAY REACH THE NORTHERN TIER BY NEXT THURSDAY BUT WITH
LESS EXTREME 10-15 DEGREE BELOW NORMAL ANOMALIES.
PARTS OF THE INTERMOUNTAIN WEST INTO SOUTH-CENTRAL ROCKIES SHOULD
SEE HEAVY SNOW ON SUNDAY, A CONTINUATION OF THE MOIST SYSTEM
AFFECTING LOCATIONS TO THE WEST BEFORE THE START OF THE FORECAST
PERIOD. SNOW PROBABILITIES REMAIN HIGH FOR THE WASATCH, UINTA,
COLORADO ROCKIES, SAN JUAN AND SANGRE DE CRISTO MOUNTAINS. A BAND
OF SNOW MAY ALSO SPREAD ACROSS THE SOUTH-CENTRAL PLAINS INTO THE
LOWER OHIO VALLEY/TENNESSEE VALLEY SUNDAY INTO MONDAY. WITH A
SLIGHT SOUTHWARD ADJUSTMENT OVER THE PAST 24 HOURS, THE LATEST
PROBABILITIES FOR 0.25 INCH LIQUID IN THE FORM OF SNOW HIGHLIGHT
AN AXIS OF 30 PERCENT OR GREATER VALUES ALIGNED FROM EASTERN
OKLAHOMA TO THE MISSISSIPPI RIVER. THEN WITH THE DEVELOPMENT OF
NORTHERN GULF TO EAST COAST/WESTERN ATLANTIC LOW PRESSURE, PARTS
OF THE SOUTHEAST MAY SEE SHOWERS AND THUNDERSTORMS EARLY NEXT
WEEK. WITH A LEADING STALLED FRONT AS A FOCUS AND GUIDANCE SHOWING
INCREASING DEEP MOISTURE WITH POTENTIAL FOR A BAND OF HEAVY
RAINFALL, THE DAY 5 EXCESSIVE RAINFALL OUTLOOK COVERING
MONDAY-MONDAY NIGHT HAS INTRODUCED A MARGINAL RISK AREA COVERING
PARTS OF NORTHERN FLORIDA AND FAR SOUTHEASTERN GEORGIA. MEANWHILE
LOCATIONS WEST OF THE SURFACE LOW TRACK WILL SEE THE POTENTIAL FOR
MEANINGFUL SNOWFALL. LATEST SNOW PROBABILITIES DEPICT A BAND OF 30
PERCENT OR GREATER POTENTIAL FOR 0.25 INCH LIQUID IN THE FORM OF
SNOW FROM NEAR THE NORTHERN MID-ATLANTIC COAST THROUGH NEW
ENGLAND. SNOW COVERAGE/AMOUNTS WILL BE VERY SENSITIVE TO STORM
TRACK AND STRENGTH SO ADDITIONAL CHANGES IN THE "MOST LIKELY
SCENARIO" ARE LIKELY. FARTHER NORTH, EXPECT CONTINUED PERIODS OF
LAKE EFFECT SNOW WITH PERSISTENCE OF COLD AIR AND BREEZY
CONDITIONS.
MOISTURE SHOULD INCREASE OVER THE NORTHWEST AROUND
TUESDAY-WEDNESDAY, BUT WITH LOW CONFIDENCE IN SPECIFICS OF
PRECIPITATION TOTALS AND SOUTHWARD EXTENT. THIS EVENT WILL LIKELY
SEE SNOW CONFINED TO HIGHER ELEVATIONS THAN IN THE SHORTER TERM,
BUT AREAS WHERE EARLIER COLD AIR PERSISTS LONGER THAN FORECAST
COULD STILL PRESENT SOME LOWER ELEVATION WINTER WEATHER ISSUES.
RAUSCH/KEBEDE
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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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