188
FXUS02 KWBC 101908
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
207 PM EST WED JAN 10 2024
VALID 12Z SAT JAN 13 2024 - 12Z WED JAN 17 2024
...ANOTHER MAJOR STORM TO IMPACT THE EASTERN U.S. INTO SATURDAY
WITH SNOW/RAIN/WIND THREATS FOLLOWED BY AN ARCTIC BLAST THROUGH
MUCH OF THE CENTRAL U.S....
..OVERVIEW
A DEEP UPPER LOW CLOSING OFF OVER THE GREAT LAKES BY EARLY
SATURDAY, SUPPORTING A STRONG STORM AFFECTING THE EAST AT THE
START OF THE FORECAST PERIOD, WILL LIKELY SETTLE NEAR HUDSON BAY
AND BECOME THE NEW ANCHOR OF A LARGE SCALE MEAN TROUGH COVERING
MUCH OF THE LOWER 48 THROUGH THE PERIOD. AT THE SAME AN EASTERN
PACIFIC MEAN RIDGE COULD GET CLOSE TO THE WEST COAST FOR A TIME. A
LEADING SYSTEM PASSING THROUGH THE RIDGE WILL AFFECT PARTS OF THE
WEST THIS WEEKEND WITH ANOTHER ONE POSSIBLY ARRIVING AROUND THE
MIDDLE OF NEXT WEEK. THE FORECAST LARGE SCALE PATTERN WILL PROMOTE
VERY COLD TEMPERATURES OVER THE CENTRAL U.S. FROM THE WEEKEND INTO
NEXT WEEK WITH SOME LOCATIONS POTENTIALLY BREAKING DAILY RECORDS.
BY NEXT WEEK THE EASTERN STATES WILL SEE A MODIFIED FORM OF THIS
COLD AIR WHILE SOME WINTRY PRECIPITATION MAY SPREAD FROM THE
SOUTH-CENTRAL PLAINS/MISSISSIPPI VALLEY AND INTO PARTS OF THE
EAST. HOWEVER THE PRECIPITATION/SURFACE SYSTEM DETAILS AFFECTING
THE EAST DURING THE FIRST HALF OF NEXT WEEK REMAIN VERY UNCLEAR AT
THIS TIME.
..GUIDANCE/PREDICTABILITY ASSESSMENT
EARLY IN THE PERIOD, CONSENSUS LOOKS QUITE GOOD FOR THE DEEP STORM
TRACKING FROM THE GREAT LAKES INTO EASTERN CANADA DURING THE
WEEKEND. THE AVERAGE OF RECENT GUIDANCE HAS HELD UP WELL FOR
DEPICTING THE STORM'S DEPTH WHICH MAY BE SIMILAR TO THE PRECEDING
STORM CURRENTLY TAKING A SIMILAR TRACK. MEANWHILE THE GUIDANCE
SPREAD IS GRADUALLY NARROWING FOR THE SYSTEM ARRIVING INTO THE
PACIFIC NORTHWEST/CENTRAL WEST COAST. THE GFS HAS CONSISTENTLY
BEEN ON THE NORTHERN SIDE OF THE SPREAD (BUT WITH A SUBTLE
SOUTHWARD TREND OVER THE PAST DAY) WHILE THE FARTHER SOUTH UKMET
HAS ADJUSTED NORTHWARD SOMEWHAT. THE AVERAGE OF 00Z
ECMWF-INITIALIZED MACHINE LEARNING MODELS SUPPORTS AN INTERMEDIATE
SURFACE LOW TRACK INTO OREGON.
HEADING INTO EARLY NEXT WEEK, THE SHORTWAVE ENERGY MOVING
INTO/THROUGH THE WEST SHOULD SHEAR OUT/ACCELERATE UNDERNEATH MORE
PRONOUNCED NORTHERN TIER U.S. ENERGY. DYNAMICAL MODELS AND
ENSEMBLES PLUS MACHINE LEARNING MODELS CONTINUE TO DIVERGE
CONSIDERABLY FOR THE DETAILS OF HOW THIS NORTHERN TIER ENERGY MAY
EVOLVE AS IT REACHES THE EASTERN U.S. THIS LEADS TO A REMARKABLY
BROAD SPREAD FOR THE STRENGTH AND TRACK OF ANY LOW PRESSURE
SYSTEM(S) FROM THE EASTERN U.S. INTO THE WESTERN ATLANTIC/CANADIAN
MARITIMES. FOR EXAMPLE, FORECASTS VALID EARLY NEXT TUESDAY SHOW
THE POTENTIAL FOR BEST-DEFINED LOW PRESSURE TO BE ANYWHERE FROM
THE SOUTHEAST U.S. (12Z/09 ECMWF AND A COUPLE MACHINE LEARNING
MODELS) TO THE CANADIAN MARITIMES (06Z GEFS/00Z CMCENS MEANS).
SURFACE LOW DEPTH FROM TUESDAY INTO WEDNESDAY IS JUST AS DIVERSE,
WITH ENSEMBLE MEMBER SPREAD LEADING TO A WEAK DEPICTION IN THE
MEANS, WHILE OTHER SOLUTIONS RANGE FROM MODERATE TO VERY STRONG
SURFACE DEVELOPMENT. THE COMBINED HIGH UNCERTAINTY OF SURFACE LOW
TRACK AND STRENGTH AT ANY PARTICULAR VALID TIME CONTINUES TO FAVOR
A CONSERVATIVE APPROACH FOR THE DETERMINISTIC FORECAST (A
NORTH-SOUTH MEAN FRONTAL ZONE WITH EMBEDDED WAVES) UNTIL BETTER
CLUSTERING ARISES.
BY LATE IN THE PERIOD SOME OPERATIONAL GUIDANCE AND MACHINE
LEARNING MODELS SUGGEST ANOTHER WEAK FEATURE MAY PASS THROUGH THE
EASTERN PACIFIC MEAN RIDGE ALOFT, BUT WITH TYPICAL UNCERTAINTY FOR
THE SPECIFICS. RECENT ECMWF RUNS HAVE BEEN OSCILLATING FOR THE
RELATIVE STRENGTH OF MEAN RIDGING VERSUS SOUTHWESTERN CANADA
SHORTWAVE ELONGATION (00Z RUNS FAVORING THE LATTER AND WITHOUT
GREAT SUPPORT FROM OTHER GUIDANCE). ALSO OF NOTE, ALREADY BY
MONDAY THE NEW 12Z UKMET BECOMES AN AMPLIFIED/WESTERN EXTREME WITH
THE PACIFIC RIDGE, THROWING ITS DOWNSTREAM TROUGH OUT OF SYNC WITH
THE MODEL/MEAN CONSENSUS.
FORECAST CONSIDERATIONS BASED ON 00Z/06Z GUIDANCE LED TO STARTING
WITH A COMPOSITE OF 00Z/06Z OPERATIONAL MODELS FOR THE FIRST HALF
OF THE PERIOD, FOLLOWED BY A TRANSITION TO A MODEL/MEAN BLEND
ALONG WITH SPLITTING THE ECMWF INPUT BETWEEN THE 00Z AND 12Z/09
RUNS.
..WEATHER/HAZARDS HIGHLIGHTS
THE MISSISSIPPI VALLEY TO EAST COAST STORM WILL BE WELL UNDERWAY
BY SATURDAY WITH SNOW, RAIN AND WIND THREATS LIKELY FROM THE
MIDWEST TO THE EAST COAST. AN OCCLUDED GREAT LAKES SURFACE LOW IN
THE 970S MB AS OF EARLY SATURDAY WILL PRODUCE HEAVY SNOW AND
STRONG WINDS OVER THE MIDWEST AND GREAT LAKES WITH NORTHWESTERLY
FLOW OVER LAKES HURON, SUPERIOR AND MICHIGAN EARLY ON IN THE DAY
FOLLOWED BY LAKE EFFECT SNOW DOWNWIND OF LAKES ERIE AND ONTARIO IN
THE AFTERNOON THROUGH SUNDAY AS THE SYSTEM LIFTS NORTHWARD INTO
EASTERN CANADA. LINGERING SNOW SHOWERS ARE ALSO POSSIBLE OVER
UPSLOPE AREAS OF THE CENTRAL APPALACHIANS ON SATURDAY. SUSTAINED
WINDS OF 20-30 MPH AND GUSTS OF OVER 40 MPH ARE POSSIBLE FROM THE
MIDWEST TO THE NORTHEAST ON SATURDAY. WINDS CALM DOWN CONSIDERABLY
ON SUNDAY ACROSS THE EAST. AHEAD OF THE STORM'S FRONTAL SYSTEM,
EXPECT HEAVY RAINFALL TO CONTINUE NORTHEASTWARD ACROSS THE NEW
ENGLAND COAST SATURDAY MORNING INTO AFTERNOON WITH THE DAY 4
EXCESSIVE RAINFALL OUTLOOK DEPICTING A MARGINAL RISK AREA.
IN THE WEST, SHORTWAVE ENERGY AND ASSOCIATED LOW PRESSURE WILL
FOCUS MOISTURE OVER THE NORTHWEST/CENTRAL WEST COAST ON SATURDAY.
HEAVY RAINFALL IS POSSIBLE FOR PORTIONS OF THE OREGON COAST DOWN
INTO NORTHERN CALIFORNIA WHERE A MARGINAL RISK OF EXCESSIVE
RAINFALL IS IN EFFECT. THERE IS STILL SOME NORTH-SOUTH UNCERTAINTY
FOR THE AXIS OF HEAVIEST PRECIPITATION BUT THIS RISK AREA DEPICTS
THE BEST OVERLAP OF GUIDANCE AND PRIOR EXTREMES HAVE BEEN
GRADUALLY TRENDING CLOSER. HEAVY SNOW IS LIKELY OVER THE CASCADES
OF OREGON, SOUTHERN WASHINGTON, THE KLAMATH MOUNTAINS AND THE
SHASTA SISKIYOUS. COLD AIR IN PLACE OVER PARTS OF THE NORTHWEST
COULD ALSO SUPPORT SIGNIFICANT SNOWFALL AT LOW ELEVATIONS. THIS
SYSTEM SHOULD ALSO BRING HEAVY SNOW INTO THE INTERMOUNTAIN WEST
AND NORTHERN/CENTRAL ROCKIES SATURDAY NIGHT INTO SUNDAY MORNING.
BY NEXT TUESDAY-WEDNESDAY, PARTS OF THE NORTHWEST MAY SEE ANOTHER
EPISODE OF PRECIPITATION WITH A PERIOD OF SNOW POSSIBLE IN THE
NORTHERN ROCKIES/HIGH PLAINS.
ARCTIC HIGH PRESSURE SPILLING INTO THE GREAT PLAINS DURING THE
WEEKEND WILL BUILD INTO THE MIDWEST/EAST LATER IN THE WEEK.
EXTREMELY COLD OVERNIGHT TEMPERATURES ARE LIKELY FROM THE NORTHERN
ROCKIES INTO THE CENTRAL PLAINS WITH MANY NIGHTTIME LOWS
STRUGGLING TO GET OUT OF THE NEGATIVE DIGITS THROUGH TUESDAY AT
THE EARLIEST. LOW TEMPERATURES IN THE -20S AND -30S WILL REPRESENT
NEGATIVE 30-50 DEGREE TEMPERATURE ANOMALIES OVER PARTS OF NORTHERN
IDAHO, MONTANA AND WYOMING THIS WEEKEND INTO EARLY NEXT WEEK. HIGH
TEMPERATURES IN THE NEGATIVE TO SINGLE DIGITS WILL REPRESENT
SIMILAR ANOMALIES DOWN INTO THE SOUTHERN PLAINS EARLY NEXT WEEK.
THE COLD BLAST EXPANDS THROUGH THE MISSISSIPPI VALLEY AND INTO THE
GULF COAST ON MONDAY AND TUESDAY WHEN LOW TEMPERATURES MAY DROP
BELOW FREEZING IN MANY PLACES. TUESDAY MORNING LOWS MAY BOTTOM OUT
INTO THE 20S FOR SOUTH TEXAS AND THE CENTRAL GULF COAST MONDAY
NIGHT. THESE ANOMALOUS FREEZING TEMPERATURES WILL BE DANGEROUS,
PARTICULARLY FOR THOSE WITHOUT ADEQUATE HEATING OR SHELTER. WITHIN
THE CORE OF COLDEST ANOMALIES FROM THE NORTHERN HIGH PLAINS INTO
THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY, DAILY RECORDS FOR
COLD MORNING LOWS/DAYTIME HIGHS WILL BE POSSIBLE.
GUIDANCE IS GRADUALLY INCREASING THE SIGNAL FOR SOME WINTRY
WEATHER FROM THE SOUTH-CENTRAL PLAINS INTO LOWER OHIO
VALLEY/TENNESSEE VALLEY DURING SUNDAY-SUNDAY NIGHT WITH THE
COMBINATION OF SHORTWAVE ENERGY AND SOUTHERN TIER SURFACE
WAVINESS. LATEST WPC PROBABILITIES OF AT LEAST 0.25 INCH LIQUID IN
THE FORM OF SNOW REACH AT LEAST 30 PERCENT ALONG AN AXIS FROM
SOUTHERN MISSOURI/NORTHERN ARKANSAS INTO THE LOWER OHIO VALLEY
DURING THAT TIME FRAME. THEREAFTER, EXPECT SOME RAIN TO ACROSS
PORTIONS OF THE GULF COAST/SOUTHEAST BUT THE COVERAGE AND
ACCUMULATIONS OF WINTER WEATHER (AND ANY OTHER EFFECTS SUCH AS
WIND) FARTHER NORTH OVER THE EAST REMAIN VERY UNCERTAIN. AT THE
VERY LEAST, THE COLDER PATTERN SHOULD LEAD TO A RAIN-SNOW LINE
FARTHER SOUTHEAST THAN WITH PREVIOUS SYSTEMS.
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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