052
FXUS02 KWBC 100830
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
330 AM 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. WITH
SNOW/RAIN/WIND THREATS FOLLOWED BY AN ARCTIC BLAST THROUGH MUCH OF
THE CENTRAL U.S....
..OVERVIEW
AN UPPER LOW, RESPONSIBLE FOR THE EASTERN U.S. STORM, WILL
NEGATIVELY TILT ON SATURDAY THEN GET WOUND UP OVER SOUTHEASTERN
CANADA THROUGH THE MIDDLE OF NEXT WEEK. A CONVEYOR BELT OF
SHORTWAVE ENERGY WILL PIVOT ACROSS THE SOUTHERN PERIPHERY OF THE
NEWLY FORMED PARENT LOW, PROPAGATING THROUGH THE MIDWEST AND EAST
COAST. AN EAST PACIFIC SHORTWAVE TROUGH WILL LIKELY SWING THROUGH
THE WEST BY WAY OF THE PAC NW, FOLLOWED BY AN AMPLIFYING UPPER
RIDGE OVER THE WEST IN RESPONSE TO THE DEEPENING UPPER LOW IN
CANADA. SUCH A SETUP WILL FACILITATE THE DESCENT OF ARCTIC HIGH
PRESSURE OVER THE CENTRAL AND EASTERN U.S. THROUGH NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE NON 12Z UKMET GUIDANCE WERE IN REASONABLE AGREEMENT REGARDING
THE OVERALL EVOLUTION OF THE SYNOPTIC PATTERN OVER THE LOWER 48.
THE MODELS ARE IN GENERAL AGREEMENT THAT A TROUGH WILL AMPLIFY
OVER SOUTHEAST CANADA, AN UPPER RIDGE OVER THE WEST WILL DEEPEN IN
RESPONSE TO THAT LOW AND THAT A SHORTWAVE TROUGH WILL ENTER THE
WEST ON DAY 3. FIRST ON DAY 3, THE 12Z AND 18Z GFS DIVERGED A BIT
FROM THE CLOSED LOW OVER THE GREAT LAKES THAT PREVIOUS RUNS AS
WELL AS THE CMC AND EC HAVE CONSISTENTLY IDENTIFIED. THAT BEING
SAID, REASONABLE CLUSTERING WITH RESPECT TO THE EAST PAC SHORTWAVE
BETWEEN THE THREE OPERATIONAL MODELS' LATEST RUNS SUPPORTED A
GENERAL MODEL BLEND OF THEM ON DAY 3. THE 18Z GEFS WAS INTRODUCED
INTO THE BLEND A BIT EARLIER THAN USUAL TO ACCOUNT FOR VARIANCE IN
THE HANDLING OF AN EMERGING EAST PAC RIDGE AND A DISTURBANCE
WITHIN THE SOUTHERN PERIPHERY OF THE AFOREMENTIONED UPPER LOW IN
CANADA. THE 12Z CMC WAS DROPPED FROM THE DAY 5 BLEND FOR THE 12Z
ECE TO ACCOUNT FOR DISPLACEMENT OF THE UPPER LOW FARTHER SOUTH IN
THE 12Z CMC COMPARED TO THE THE EC AND GFS SUITES. THE EUROPEAN
AND GFS DETERMINISTIC AND ENSEMBLE MEANS CLUSTER WELL ON DAY 6 SO
THE DAY 5 BLEND IS CONTINUED. THE 12Z EC IS REPLACED WITH THE 12Z
CMC ON DAY 7 DUE TO OVER AMPLIFICATION OF THE WESTERN RIDGE
COMPARED TO THE OTHER GUIDANCE.
..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 SUB 980MB SURFACE LOW
CENTERED OVER THE UPPER MIDWEST 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 DEPARTS INTO THE
CANADIAN MARITIME. LINGERING SNOW SHOWERS ARE ALSO POSSIBLE OVER
UPSLOPE AREAS OF THE CENTRAL APPALACHIANS ON SATURDAY. SUSTAINED
WINDS OF 20-30MPH AND GUSTS OF OVER 40MPH ARE POSSIBLE FROM THE
MIDWEST TO THE NORTHEAST ON SATURDAY. WINDS CALM DOWN CONSIDERABLY
ON SUNDAY ACROSS THE EAST. HEAVY RAINFALL IS EXPECTED TO CONTINUE
ACROSS THE NEW ENGLAND COAST SATURDAY MORNING INTO AFTERNOON WITH
A LOW-END MARGINAL EXCESSIVE RAINFALL RISK OVER THE MAINE COAST.
IN THE WEST, SHORTWAVE ENERGY WILL SPREAD TROPICAL MOISTURE OVER
THE NORTHWEST ON SATURDAY. HEAVY RAINFALL IS POSSIBLE FOR PORTIONS
OF THE CENTRAL OREGON COAST DOWN INTO NORTHERN CALIFORNIA WHERE A
MARGINAL RISK OF EXCESSIVE RAINFALL IS IN EFFECT. HEAVY SNOW IS
LIKELY OVER THE CASCADES OF OREGON, SOUTHERN WASHINGTON, THE
KLAMATH MOUNTAINS AND THE SHASTA SISKIYOUS. THE INTERMOUNTAIN WEST
AND NORTHERN/CENTRAL ROCKIES WILL ALSO EXPERIENCE HEAVY SNOW
SATURDAY NIGHT INTO SUNDAY MORNING.
THE DEEPENING UPPER TROUGH OVER EASTERN CANADA WILL ACT TO
STRENGTHEN THE UPSTREAM RIDGE OVER THE WEST EARLY NEXT WEEK WHICH
WILL ALLOW ARCTIC HIGH PRESSURE TO SPILL OUT INTO THE GREAT PLAINS
AND MIDWEST/EAST LATER IN THE WEEK. EXTREMELY COLD OVERNIGHT
TEMPERATURES ARE LIKELY FROM THE NORTHERN ROCKIES INTO THE CENTRAL
PLAINS WITH MANY NIGHT TIME LOWS STRUGGLING TO GET OUT OF THE
NEGATIVE DIGITS THROUGH TUESDAY AT THE EARLIEST. LOW TEMPERATURES
IN THE -20S AND -30S WILL REPRESENT 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.
MODELS HAVE BEGUN SUGGESTING A POSSIBLE MISSISSIPPI VALLEY TO EAST
COAST STORM NEXT TUESDAY INTO WEDNESDAY WITH RAIN IMPACTS FOR THE
GULF COAST AND SOUTHEAST AS WELL AS SNOW POTENTIAL FOR THE MIDWEST
AND NORTHEAST/MID-ATLANTIC. THERE REMAINS PLENTY OF MODEL
UNCERTAINTY, ESPECIALLY WITH RESPECT TO THE TIMING OF THE EMBEDDED
SHORTWAVE PROPAGATING THROUGH THE CENTRAL U.S.. THIS DETAIL WILL
NEED TO BE RESOLVED BEFORE A MORE CONFIDENT FORECAST CAN BE ISSUED.
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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