730
FXUS02 KWBC 131911
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
210 PM EST SAT JAN 13 2024
VALID 12Z TUE JAN 16 2024 - 12Z SAT JAN 20 2024
...HAZARDOUS AND RECORD-BREAKING COLD FROM AN ARCTIC AIRMASS WILL
SPREAD ACROSS THE NORTHWEST INTO THE CENTRAL AND EAST-CENTRAL U.S.
NEXT WEEK...
...POTENTIAL FOR AN IMPACTFUL STORM SYSTEM NEAR THE EAST COAST
NEXT TUESDAY BUT STILL WITH LOW CONFIDENCE...
..OVERVIEW
LATEST GUIDANCE MAINTAINS A DEEP AND BROAD MEAN TROUGH ALOFT OVER
MUCH OF THE LOWER 48 THROUGH MUCH OF THE WEEK, AHEAD OF THE
UPSTREAM MEAN RIDGE OVER THE EASTERN PACIFIC TRACKING INTO THE
WESTERN U.S. LATE WEEK INTO THE WEEKEND. THIS UPPER PATTERN AND
ARCTIC HIGH PRESSURE FILTERING IN AT THE SURFACE WILL SUPPORT VERY
COLD TEMPERATURES OVER AREAS FROM THE NORTHWEST THROUGH MUCH OF
THE PLAINS/MISSISSIPPI VALLEY INTO TUESDAY, WITH NUMEROUS DAILY
RECORDS FOR COLD LOWS/DAYTIME HIGHS. BY WEDNESDAY-THURSDAY THERE
SHOULD BE SOME MODERATION AND EASTWARD SHIFT OF THE COLD
TEMPERATURES BEFORE ANOTHER SURGE OF COLD AIR PUSHES INTO THE
CENTRAL U.S. AND EVENTUALLY THE EAST LATE WEEK INTO SATURDAY. AT
MOST LOCATIONS THIS SECOND ROUND OF COLD TEMPERATURES SHOULD BE
LESS EXTREME THAN THE THE FIRST. PRECIPITATION-WISE, MEANINGFUL
SNOW IS STILL POSSIBLE IN PARTS OF THE MID-ATLANTIC/NORTHEAST ON
TUESDAY, THOUGH WITH CONTINUED UNCERTAINTY IN AMOUNTS. THE EAST
MAY SEE ANOTHER EPISODE OF PRECIPITATION LATE IN THE WEEK BUT
AGAIN WITH CONSIDERABLE UNCERTAINTY FOR DETAILS. MEANWHILE THE
NORTHERN HALF OR SO OF THE WEST SHOULD SEE INCREASING
PRECIPITATION CHANCES TUESDAY AND BEYOND, FIRST WITH A SYSTEM
AFFECTING THE PACIFIC NORTHWEST AND THEN FROM MOISTURE ON THE
LEADING SIDE OF AN APPROACHING UPPER TROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS/MEANS AGREE WELL ON THE LARGE SCALE EVOLUTION DURING
THE PERIOD. DURING TUESDAY-WEDNESDAY EXPECT A LEADING DEEP TROUGH
CROSSING THE EAST DURING TUESDAY-WEDNESDAY, SUPPORTING LOW
PRESSURE THAT RAPIDLY TRACKS NORTHEASTWARD FROM NEAR THE SOUTHEAST
COAST, WHILE A GRADUALLY IMPROVING CONSENSUS SHOWS A COMPLEX
UPSTREAM INTERACTION OF ELONGATING WESTERN CANADA INTO PACIFIC
SHORTWAVE ENERGY TO THE NORTH OF A PIECE OF MID-LATITUDE ENERGY
THAT BREAKS OFF FROM THE EAST SIDE OF A MID-LATITUDE PACIFIC UPPER
LOW--BRINGING SURFACE LOW PRESSURE INTO VANCOUVER ISLAND OR A
LITTLE SOUTH. AFTER WEDNESDAY, GUIDANCE HAS BEEN VERY CONSISTENT
WITH THE COMBINATION OF THIS ENERGY AND SOUTHERN CANADA ENERGY
AMPLIFYING INTO THE EAST AS THE WEST COAST RIDGE REBUILDS AND
DRIFTS INLAND WHILE AN EASTERN PACIFIC TROUGH APPROACHES THE WEST
COAST. TYPICAL DIFFERENCES IN UPPER TROUGH DETAILS OVER THE EAST
LATE IN THE WEEK LEAD TO MEANINGFUL SPREAD FOR SURFACE LOW/FRONTAL
DETAILS AND ASSOCIATED PRECIPITATION.
NEAR THE EAST COAST ON TUESDAY, THE PAST 24 HOURS OF GFS RUNS AND
GEFS/ECENS/CMCENS MEANS HAVE GRAVITATED MORE OFFSHORE TOWARD THE
ECMWF THAT HAD FIRST SIGNALED THE POSSIBILITY. THE 00Z
ECMWF-INITIALIZED MACHINE LEARNING MODELS ALSO FALL IN LINE WITH
THE GFS/ECMWF/ENSEMBLE MEAN CLUSTER AND YESTERDAY'S MACHINE
LEARNING RUNS SEEMED TO PROVIDE AN EARLY LEAD ON THE FASTER TRENDS
SEEN IN LATEST GUIDANCE. WHILE TRENDS WOULD SUGGEST THIS CLUSTER
AS THE MOST PROBABLE AT THE MOMENT, THERE ARE STILL LINGERING
FARTHER WEST TRACKS. THIS INCLUDES THE CMC (NOW CLOSER TO
CONSENSUS FROM 24-36 HOURS AGO) AND THE UKMET THAT HAS
CONSISTENTLY BEEN A WESTERN EXTREME. FROM THE SHORT-RANGE REALM,
THE CANADIAN REGGEM AND NAM ALSO HAVE A FAIRLY WESTERN TRACK.
FINALLY THERE IS THE OCCASIONAL HISTORICAL TENDENCY FOR GUIDANCE
SOMETIMES TO BACK OFF FROM AN EAST COAST SYSTEM IN THE
EARLY-MIDDLE PART OF THE MEDIUM RANGE PERIOD BEFORE RETURNING
WESTWARD IN THE SHORTER TERM. PREFERENCE IS TO STAY CLOSE TO
CONTINUITY NEAR THE GFS/ECMWF/ENSEMBLE MEAN CLUSTER BUT WITH
MODEST CONFIDENCE.
GUIDANCE IS STEADILY IMPROVING ITS AGREEMENT FOR THE EVOLUTION
AFFECTING THE PACIFIC NORTHWEST INTO MIDWEEK. AFTER THE 12Z/12 GFS
FINALLY LATCHED ONTO THE MAJORITY EVOLUTION ALOFT, SOLUTIONS SINCE
THEN HAVE STILL VARIED WITH THE NORTH-SOUTH TRACK OF LOW PRESSURE
WITH THE 00Z MACHINE LEARNING MODELS ALSO SHOWING THIS SPREAD.
HOWEVER THE NEW 12Z RUNS HAVE NARROWED THE SPREAD, DEPICTING A
FAIRLY COMPACT BUT VIGOROUS SYSTEM REACHING VANCOUVER ISLAND OR
NORTHERN WASHINGTON. THE 00Z CMC REPRESENTED A SOUTHERN EXTREME
AND THE 00Z ECMWF WAS ON THE DEEP EDGE OF THE ENVELOPE. A 00Z/06Z
MODEL COMPOSITE REFLECTED A GOOD INTERMEDIATE SOLUTION FOR THIS
PART OF THE FORECAST.
WITH GOOD LARGE SCALE AGREEMENT FOR THE REBUILDING UPPER RIDGE
THAT MOVES INTO THE WEST AS WELL AS THE TROUGH NEARING THE WEST
COAST (ASIDE FROM LOW-PREDICTABILITY DETAILS), PRIMARY FOCUS FOR
UNCERTAINTY AFTER MIDWEEK IS ON HOW INCOMING WESTERN ENERGY AND
SOUTHERN CANADA DYNAMICS EVOLVE AS THE AMPLIFY INTO THE EAST ALONG
WITH THE RESULTING SURFACE EVOLUTION. THE 00Z CMC WAS SLOWEST WITH
THE UPPER TROUGH ESPECIALLY AROUND THURSDAY-FRIDAY AND THUS WAS
PHASED OUT OF THE FORECAST BLEND. THE NEW 12Z CMC COMPARES BETTER
TO CONSENSUS. OTHERWISE CONFIDENCE IS LOW FOR SPECIFICS. DYNAMICAL
MODELS/ENSEMBLES AND MACHINE LEARNING MODELS SUGGEST POTENTIAL FOR
DEFINED LOW PRESSURE TO BE ANYWHERE FROM THE SOUTHEAST INTO UPPER
OHIO VALLEY OR FARTHER EAST OVER THE WESTERN ATLANTIC AS OF EARLY
FRIDAY. BY SATURDAY THE ENSEMBLE MEANS AND MACHINE LEARNING MODELS
GENERALLY SHOW FASTER PROGRESSION OF LOW PRESSURE THAN SEEN IN
LATEST GFS/ECMWF RUNS. THUS PREFERRED TO TILT THE UPDATED FORECAST
SOMEWHAT MORE TOWARD THE GEFS/ECENS/CMCENS MEANS (WITH SOME
LINGERING GFS/ECMWF INPUT FOR DEFINITION) BY NEXT SATURDAY.
..WEATHER/HAZARDS HIGHLIGHTS
VERY COLD AIR ORIGINALLY STEMMING FROM THE ARCTIC WILL BE ATOP THE
NORTHERN GREAT BASIN AND ROCKIES AND SOUTHEASTWARD THROUGH THE
CENTRAL U.S. ON TUESDAY, THOUGH STARTING TO MODERATE A BIT FROM
THE SHORT RANGE PERIOD. STILL, WIDESPREAD TEMPERATURES OF 20 TO 40
DEGREES BELOW NORMAL ARE FORECAST, WITH LOW TEMPERATURES IN THE
-10 TO -20 RANGE ACROSS THE NORTHERN HALF OF THE PLAINS AND INTO
THE UPPER MIDWEST, AND LOCALLY EVEN COLDER IN HIGHER ELEVATIONS OF
THE ROCKIES. HIGH TEMPERATURES AT LEAST LOOK TO BE ABOVE 0F IN
MOST AREAS BY TUESDAY. ANY WIND CHILLS WOULD BE EVEN COLDER AND
THUS MORE DANGEROUS. THE COLD AIR DIVING FARTHER SOUTH INTO THE
SOUTHERN HALF OF THE PLAINS AND MISSISSIPPI VALLEY WILL NOT BE AS
COLD IN TERMS OF ABSOLUTE TEMPERATURES, BUT TEMPERATURE ANOMALIES
OF 20 TO 40 DEGREES BELOW AVERAGE ARE LIKELY TO SET WIDESPREAD
RECORDS ACROSS THE SOUTH INTO TUESDAY. BY WEDNESDAY TEMPERATURES
FINALLY LOOK TO MODERATE IN THE ROCKIES TO HIGH PLAINS, THOUGH
CHILLY TEMPERATURES (ALBEIT IN MODERATED FORM) WILL SHIFT INTO THE
EASTERN HALF OF THE COUNTRY BEFORE WARMING CLOSER TO NORMAL ON
THURSDAY. LOCATIONS OVER THE LOWER MISSISSIPPI VALLEY AND WESTERN
GULF COAST MAY SEE RECORD LOWS WEDNESDAY MORNING. REINFORCING COLD
AIR SHOULD REACH THE NORTHERN PLAINS BY THURSDAY AND EXPAND TO
INCLUDE MOST AREAS BETWEEN THE ROCKIES AND APPALACHIANS FRIDAY AND
FARTHER EAST BY SATURDAY. EXPECT LESS EXTREME TEMPERATURE
ANOMALIES THAN THOSE FORECAST EARLIER IN THE PERIOD, BUT FRIDAY
AND SATURDAY MAY STILL SEE TEMPERATURES 10-25F OR SO BELOW NORMAL.
A LOW PRESSURE SYSTEM DEVELOPING ALONG A FRONT IN THE WESTERN
ATLANTIC WILL TRACK QUICKLY NORTHWARD TUESDAY INTO WEDNESDAY. SNOW
COULD SPREAD ACROSS THE MID-ATLANTIC AND NORTHEAST TO THE WEST OF
THE LOW TRACK, BUT SNOW AMOUNTS AND PLACEMENT/COVERAGE WILL BE
VERY SENSITIVE TO THIS STORM TRACK AND STRENGTH. THE GENERAL MODEL
TREND OVER RECENT CYCLES HAS BEEN FOR A FARTHER EAST/MORE OFFSHORE
LOW TRACK, PLUS WITH A FASTER SPEED THAT WOULD ALSO LESSEN TOTALS.
THEREFORE THE LATEST PROBABILISTIC GUIDANCE FOR 0.25 INCH LIQUID
IN THE FORM OF SNOW HAS DECLINED TO ONLY 10-30 PERCENT ALONG THE
NORTHERN MID-ATLANTIC/NEW ENGLAND COAST. HOWEVER THERE IS STILL A
LINGERING MINORITY SCENARIO MAINTAINING A FAR ENOUGH WEST TRACK TO
PRODUCE GREATER SNOWFALL THAN THE CURRENTLY PREFERRED SOLUTION SO
CONTINUE TO MONITOR FORECASTS FOR ANY ADDITIONAL CHANGES. FARTHER
SOUTH, MOISTURE MAY FOCUS ALONG AND AHEAD OF THE FRONT THAT MOVES
ACROSS FLORIDA ON TUESDAY. THERE IS PERHAPS A NONZERO CHANCE OF
HEAVY RAINFALL, BUT DOES NOT LOOK IMPACTFUL ENOUGH FOR AN AREA IN
THE EXCESSIVE RAINFALL OUTLOOK TUESDAY. BACK TO THE NORTH, EXPECT
CONTINUED PERIODS OF LAKE EFFECT SNOW WITH PERSISTENCE OF COLD AIR
AND BREEZY CONDITIONS. THEN A FRONT AND POSSIBLE LOW PRESSURE
SYSTEM REACHING THE EAST LATE IN THE WEEK MAY PRODUCE SOME
PRECIPITATION. THIS SYSTEM COULD INITIALLY SPREAD SOME LIGHT SNOW
ACROSS THE NORTHERN-CENTRAL PLAINS BY THURSDAY, WITH INCREASING
UNCERTAINTY FOR COVERAGE AND AMOUNTS OF PRECIPITATION OVER THE
EAST LATE IN THE WEEK. CURRENTLY EXPECT MOST OF THIS ACTIVITY TO
BE SNOW OVER AND NORTH OF THE OHIO VALLEY/NORTHERN MID-ATLANTIC
WITH PERHAPS SOME RAIN OVER THE SOUTHEAST.
EXPECT MOISTURE TO INCREASE OVER THE NORTHWEST AROUND TUESDAY,
WITH STEADILY INCREASING CONFIDENCE THAT FAIRLY VIGOROUS LOW
PRESSURE TRACKING TOWARD OR NEAR VANCOUVER ISLAND BY WEDNESDAY
WILL HELP TO ENHANCE AMOUNTS. THIS EVENT WILL LIKELY SEE SNOW
CONFINED TO HIGHER ELEVATIONS THAN IN THE SHORTER TERM, BUT INLAND
AREAS WHERE COLD AIR PERSISTS LONGER COULD STILL SEE SOME LOWER
ELEVATION WINTER WEATHER ISSUES. EXPECT THIS SYSTEM TO SPREAD SOME
ENHANCED SNOW INTO THE NORTHERN-CENTRAL ROCKIES AS WELL.
PRECIPITATION IS LIKELY FOR THE NORTHERN HALF OR SO OF THE WEST
INTO WEDNESDAY-THURSDAY, WHILE COASTAL AREAS SHOULD GENERALLY SEE
THE BETTER PRECIPITATION FOCUS LATE WEEK INTO THE WEEKEND AS A
PACIFIC UPPER TROUGH APPROACHES. IN TERMS OF THE DAYS 4-5
(TUESDAY-WEDNESDAY) EXCESSIVE RAINFALL OUTLOOKS, BOTH DAYS
MAINTAIN NO RISK AREAS FOR THE TIME BEING BUT THERE MAY EVENTUALLY
BE ENOUGH OF A SIGNAL TO MERIT A MARGINAL RISK AREA SOMEWHERE OVER
THE PACIFIC NORTHWEST. OVERALL THE COMBINED MAGNITUDE/DURATION OF
MOISTURE ANOMALIES FROM MOST GUIDANCE TEMPERS CONFIDENCE IN THE
HIGHEST END OF THE QPF SPREAD, BUT IMPROVING CONSENSUS FOR
SUPPORTING LOW PRESSURE DOES RAISE THE POTENTIAL FOR A BRIEF
PERIOD OF ENHANCED FOCUS WHICH MAY BE SPLIT BETWEEN THE DAY 4 AND
DAY 5 PERIODS. EMERGING THEMES FROM LATEST MODEL RUNS SEEM TO
SUGGEST A GREATER RAINFALL POTENTIAL FOR WESTERN WASHINGTON SOUTH
INTO PARTS OF OREGON FOR DAY 5/WEDNESDAY VERSUS BROADER
NORTH-SOUTH COVERAGE WITH LESSER TOTALS ON DAY 4.
RAUSCH/TATE
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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