146
FXUS02 KWBC 141858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EST SUN JAN 14 2024
VALID 12Z WED JAN 17 2024 - 12Z SUN JAN 21 2024
...RECORD-BREAKING COLD COULD LINGER IN THE SOUTH-CENTRAL U.S.
MIDWEEK, WITH ANOTHER ARCTIC AIRMASS COMING INTO THE CENTRAL U.S.
LATE WEEK...
..OVERVIEW
A DEEP AND BROAD MEAN TROUGH ALOFT WILL STAY ATOP MUCH OF THE
LOWER 48 THROUGH LATE WEEK, AHEAD OF AN UPPER RIDGE THAT TRACKS
FROM THE EASTERN PACIFIC INTO THE WESTERN-CENTRAL U.S. LATE WEEK
INTO THE WEEKEND. PROGRESSION OF THE UPPER RIDGE SHOULD DISPLACE
THE TROUGH TO THE EAST COAST/WESTERN ATLANTIC BY NEXT SUNDAY. THIS
PATTERN WILL ALLOW FOR A COUPLE OF ARCTIC HIGH PRESSURE CENTERS AT
THE SURFACE TO SUPPORT VERY COLD TEMPERATURES WITH THE FIRST
LINGERING IN THE EASTERN TWO-THIRDS OF THE COUNTRY FOR MIDWEEK,
AHEAD OF ANOTHER SURGE OF COLD AIR THAT PUSHES INTO THE CENTRAL
U.S. AND EVENTUALLY THE EAST LATE WEEK INTO THE WEEKEND. AT MOST
LOCATIONS THIS SECOND ROUND OF COLD TEMPERATURES SHOULD BE LESS
EXTREME THAN THE THE FIRST. SNOW AND SOME LOWER ELEVATION RAIN ARE
FORECAST ACROSS THE NORTHERN HALF OR SO OF THE WEST ESPECIALLY ON
WEDNESDAY AND LINGERING INTO THURSDAY, WITH A PRECIPITATION FOCUS
MORE ALONG THE WEST COAST BY FRIDAY INTO THE WEEKEND FROM MOISTURE
ON THE LEADING SIDE OF AN APPROACHING UPPER TROUGH. IN THE EAST,
POSSIBLE LOW DEVELOPMENT ALONG A SURFACE FRONTAL SYSTEM REACHING
THE AREA COULD PRODUCE SOME WINTER WEATHER DURING
THURSDAY-SATURDAY, BUT WITH CONTINUED SIGNIFICANT UNCERTAINTY FOR
DETAILS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS AND MEANS CONTINUE TO AGREE WELL FOR THE LARGE SCALE
EVOLUTION THROUGH THE PERIOD. A LEADING UPPER TROUGH WILL DEPART
FROM THE EAST WHILE TWO SMALLER SCALE SHORTWAVES AS OF EARLY
WEDNESDAY (ONE REACHING THE NORTHWEST AND THE OTHER EXTENDING FROM
BRITISH COLUMBIA INTO THE PACIFIC) SHEAR INLAND UNDERNEATH AN
ELONGATED SOUTHERN CANADA TROUGH. THIS COMBINATION OF ENERGY WILL
ROTATE THROUGH THE EASTERN HALF OF THE LOWER 48 AS A DEEP UPPER
TROUGH LATE IN THE WEEK (WITH AN UPPER LOW NEAR NEW ENGLAND BY
SATURDAY) AS A REBUILDING WEST COAST UPPER RIDGE MOVES INLAND.
AHEAD OF THE TROUGH, SURFACE DETAILS ALONG THE EAST COAST AS OF
EARLY FRIDAY ARE STILL UNCERTAIN BUT CONSENSUS IS STEADILY
IMPROVING UPON THE IDEA OF LOW PRESSURE CONSOLIDATING OVER THE
WESTERN ATLANTIC BY LATER IN THE DAY AND CONTINUING EAST/NORTHEAST
THEREAFTER. NEXT WEEKEND THE GUIDANCE SHOWS THE UPPER RIDGE
BROADENING AS IT REACHES THE CENTRAL U.S., PUSHING THE EASTERN
TROUGH TO AND BEYOND THE EAST COAST, WHILE MEAN TROUGHING SETS UP
ALONG THE WEST COAST AND SUPPORTS THE ARRIVAL OF A COUPLE FRONTAL
SYSTEMS.
THE PRIMARY GUIDANCE DIFFERENCES EARLY IN THE PERIOD INVOLVE THE
LOW PRESSURE SYSTEM NEARING THE PACIFIC NORTHWEST AS OF EARLY
WEDNESDAY. OVER THE PAST COUPLE DAYS THERE HAS BEEN STEADY
IMPROVEMENT FOR THE TRACK FORECAST, WITH CONSENSUS NARROWING ON
SOUTHERN VANCOUVER ISLAND OR NORTHWESTERN WASHINGTON. DURING THE
DAY WEDNESDAY THE GFS/GEFS BECOME WEAKER THAN MOST OTHER GUIDANCE
DUE TO THE GFS CLUSTER INCORPORATING LESS BRITISH COLUMBIA-PACIFIC
SHORTWAVE ENERGY. AN INTERMEDIATE SOLUTION TILTED SOMEWHAT AWAY
FROM THE GFS CONTINUES TO BE REASONABLE FOR THIS SYSTEM.
ALONG THE EAST COAST ON FRIDAY, THE PAST DAY'S TRENDS HAVE YIELDED
SOME LOOSE CLUSTERING TOWARD A BROAD AREA OF ONE OR MORE SURFACE
LOWS OVER OR A LITTLE SOUTH OF THE CENTRAL
APPALACHIANS/MID-ATLANTIC EASTWARD INTO THE WESTERN ATLANTIC EARLY
IN THE DAY AND THEN RAPID CONSOLIDATION OFFSHORE THE MID-ATLANTIC
BY LATER IN THE DAY. GUIDANCE STILL DIVERGES FOR EXACT TRACK WITH
MEANINGFUL DIFFERENCES AS FAR AS EAST COAST EFFECTS. GFS RUNS
CONTINUE WAFFLING WITH THE NEW 12Z RUN WEST OF 00Z/06Z RUNS, AND
THE NEW 12Z ECMWF IS CLOSE TO IT BY EARLY SATURDAY. CMC RUNS
REMAIN FASTER/EASTWARD. THE ENSEMBLE MEANS BECOME FAIRLY
EAST/PROGRESSIVE AS WELL. AS WAS THE CASE YESTERDAY, 00Z
ECMWF-INITIALIZED MACHINE LEARNING MODELS ARE EMPHATIC WITH FASTER
PROGRESSION THAN THE ENSEMBLE MEANS. THE FULL ARRAY OF GUIDANCE
FAVORS STAYING CLOSEST TO THE ENSEMBLE MEANS WITH ONLY SOME
OPERATIONAL INPUT FOR DETAIL ENHANCEMENT.
OVER THE WEST NEXT WEEKEND, GUIDANCE AGREES WITH THE GENERAL THEME
OF ONE SHORTWAVE REACHING THE WEST COAST BY SATURDAY AND ANOTHER
FOLLOWING ABOUT A DAY BEHIND, SUPPORTING TWO SEPARATE SURFACE
FRONTAL SYSTEMS. DIFFERENCES IN TIMING AND AMPLITUDE HAVE LOW
PREDICTABILITY 6-7 DAYS OUT IN TIME SO A MODEL/MEAN BLEND IS A
GOOD STARTING POINT TO REPRESENT THE LARGER SCALE CONSENSUS AT THE
SURFACE AND ALOFT.
THE UPDATED FORECAST UTILIZED THE 00Z-06Z GFS AND 00Z
ECMWF/UKMET/CMC FOR THE FIRST HALF OF THE PERIOD AND THEN TRENDED
TOWARD A BLEND OF ABOUT HALF MODELS/HALF ENSEMBLE MEANS. THIS
APPROACH PROVIDED REASONABLE CONTINUITY FOR SIGNIFICANT FEATURES.
..WEATHER/HAZARDS HIGHLIGHTS
THOUGH THE COLDEST AIR NOW PHASES INTO THE SHORT RANGE PERIOD
EARLY THIS WEEK, CHILLY TEMPERATURES REMAIN ACROSS THE PLAINS TO
EAST COAST WEDNESDAY, AROUND 10-25F BELOW AVERAGE. LOW
TEMPERATURES WEDNESDAY MORNING COULD SET RECORDS IN THE SOUTHERN
PLAINS/LOWER MISSISSIPPI VALLEY. THESE AREAS WILL WARM CLOSER TO
NORMAL THURSDAY, BUT ANOTHER REINFORCING SURGE OF COLD AIR IS
FORECAST TO PUSH INTO THE NORTH-CENTRAL U.S. THURSDAY, WELL INTO
THE PLAINS/MISSISSIPPI VALLEY FRIDAY, AND INTO THE EAST-CENTRAL
U.S. SATURDAY. BELOW NORMAL TEMPERATURES BY 15-30 DEGREES SHOULD
BE WIDESPREAD, AND THIS COLD EPISODE WILL STILL BE NOTABLE EVEN IF
NOT QUITE AS EXTREME AS THE CURRENT/SHORT RANGE COLD EVENT OVER
MOST AREAS. LOCATIONS NEAR THE EAST COAST COULD SEE THE COLDEST
DAYTIME HIGHS OF THE WEEK ON SATURDAY THOUGH. MEANWHILE WEST OF
THE ROCKIES, RIDGING ALOFT WILL PROMOTE ABOVE NORMAL TEMPERATURES
INCREASING IN MAGNITUDE AND COVERAGE LATE WEEK INTO THE WEEKEND.
BEST POTENTIAL FOR PLUS 10F OR GREATER ANOMALIES WILL BE FOR
MORNING LOWS NEXT WEEKEND. MODESTLY ABOVE NORMAL TEMPERATURES MAY
EXTEND INTO THE NORTHERN PLAINS BY NEXT SUNDAY.
A SURFACE LOW PRESSURE SYSTEM AND A SHORTWAVE ALOFT COMING INTO
THE NORTHWEST BY WEDNESDAY WILL HELP CAUSE WIDESPREAD
PRECIPITATION ACROSS THE NORTHERN HALF OF CALIFORNIA INTO THE
PACIFIC NORTHWEST AND EAST TO THE ROCKIES. 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, INCLUDING POTENTIAL
FOR FREEZING RAIN IN THE NORTHERN GREAT BASIN. SNOW AMOUNTS COULD
BE HEAVY IN HIGHER ELEVATION AREAS INCLUDING THE CASCADES TO
NORTHERN/CENTRAL ROCKIES. MEANWHILE COASTAL AREAS OF THE PACIFIC
MAY SEE OCCASIONAL ENHANCED RAINFALL AMOUNTS FOR PERHAPS A NONZERO
POTENTIAL FOR FLOODING CONCERNS. ON WEDNESDAY COASTAL OREGON COULD
BE A FOCUS FOR HEAVY RAIN WHILE ON THURSDAY COASTAL WASHINGTON
SEEMS MORE LIKELY AS MOISTURE INCREASES AHEAD OF A PACIFIC WARM
FRONT LIFTING NORTHWARD. HOWEVER, A LACK OF INSTABILITY, GUIDANCE
NOT SHOWING ANY FOCUSED ATMOSPHERIC RIVER TAKING AIM AT THE
REGION, AND CONTINUED MODEL DIFFERENCES FOR AMOUNTS/PLACEMENT OF
HEAVIEST RAIN, STILL SUGGEST THAT FLASH FLOOD POTENTIAL REMAINS
BELOW THE MARGINAL RISK THRESHOLD OF 5 PERCENT FOR THE DAYS
4-5/WEDNESDAY-THURSDAY EXCESSIVE RAINFALL OUTLOOKS. ADDITIONAL
ROUNDS OF PRECIPITATION FOR THE WEST COAST STATES ARE POSSIBLE
LATE WEEK THROUGH THE WEEKEND AS UPPER TROUGHING SETTLES OVER THE
REGION. SOME LOCALLY MODERATE/HEAVY TOTALS ARE POSSIBLE OVER
FAVORED TERRAIN, DEPENDING ON UPPER LEVEL AND SURFACE DETAILS THAT
WILL BE BETTER RESOLVED IN COMING DAYS, AND PRECIPITATION COVERAGE
SHOULD EXTEND FARTHER SOUTHEASTWARD WITH TIME OVER THE WEEKEND.
FARTHER EAST, EXPECT CONTINUED PERIODS OF LAKE EFFECT SNOW WITH
PERSISTENCE OF COLD AIR AND BREEZY CONDITIONS INTO SATURDAY. LAKE
EFFECT SNOW WILL LIKELY TAPER OFF BY SUNDAY AS SURFACE HIGH
PRESSURE BUILDS INTO THE EAST. A FRONTAL SYSTEM WITH EMBEDDED LOW
PRESSURE REACHING THE EAST DURING THE LATTER PART OF THE WEEK MAY
PRODUCE SOME PRECIPITATION. THIS SYSTEM COULD INITIALLY SPREAD
SOME LIGHT SNOW ACROSS THE NORTHERN-CENTRAL PLAINS BY THURSDAY
WHILE SOME LIMITED GULF MOISTURE COMES INTO THE EAST-CENTRAL U.S.,
SHIFTING TO THE EAST COAST FRIDAY. THE PRECIPITATION TYPE IN THE
SOUTHEAST SHOULD STAY RAIN WHILE GENERALLY FROM THE OHIO VALLEY
INTO THE APPALACHIANS AND THE NORTHERN MID-ATLANTIC TO NORTHEAST
SHOULD HAVE SNOW. AREAS IN BETWEEN ARE MORE UNCERTAIN WITH
PRECIPITATION TYPE WHILE UNCERTAINTY ALSO REMAINS WITH THE
COVERAGE AND AMOUNTS OF PRECIPITATION, WHICH WILL CONTINUE TO BE
REFINED IN FUTURE FORECASTS. CURRENTLY THE MAJORITY OF GUIDANCE
SUGGESTS THAT SNOWFALL SHOULD BE FAIRLY LIGHT THE LATEST
PROBABILITIES FOR 0.25 INCH LIQUID IN THE FORM OF SNOW ARE NO MORE
THAN 10-30 PERCENT OR SO DURING THE FRIDAY-FRIDAY NIGHT TIME FRAME.
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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