201
FXUS02 KWBC 091901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST TUE JAN 09 2024
VALID 12Z FRI JAN 12 2024 - 12Z TUE JAN 16 2024
...ANOTHER MAJOR STORM TO IMPACT THE EAST-CENTRAL TO EASTERN U.S.
WITH SNOW/RAIN/WIND THREATS FOLLOWED BY AN ARCTIC BLAST THROUGH
MUCH OF THE CENTRAL U.S....
..OVERVIEW
MOST GUIDANCE SHOWS UPPER TROUGHING ALOFT IN THE MEAN CENTERED
OVER THE LOWER 48, HELPING TO ESTABLISH A COLD PATTERN OVER THE
CENTRAL U.S. AND A GRADUAL EASTWARD EXPANSION OF BELOW NORMAL
TEMPERATURES TOWARD THE EASTERN STATES NEXT WEEK. WITHIN THIS
PATTERN, A VIGOROUS PLAINS SHORTWAVE AS OF EARLY FRIDAY SHOULD
CLOSE OFF INTO A GREAT LAKES UPPER LOW BY SATURDAY. THIS EVOLUTION
WILL SUPPORT A RAPIDLY INTENSIFYING MISSISSIPPI VALLEY THROUGH
GREAT LAKES SURFACE LOW WHOSE ARRAY OF WEATHER HAZARDS WILL HAVE
SOME SIMILARITIES TO THE STRONG SYSTEM CURRENTLY AFFECTING THE
EAST. MEANWHILE, A SYSTEM PASSING THROUGH THE EAST PACIFIC MEAN
UPPER RIDGE SHOULD BRING AREAS OF HEAVY RAIN AND SNOW TO THE
NORTHWEST THIS WEEKEND. ARCTIC HIGH PRESSURE BUILDING IN ACROSS
THE CENTRAL U.S. WILL BRING A BROADENING AREA OF TEMPERATURES 20F
OR MORE BELOW NORMAL. THERE IS A POTENTIAL FOR A COMBINATION OF
NORTHERN STREAM AND/OR PACIFIC-WESTERN U.S. ENERGY TO PRODUCE SOME
DEGREE OF SURFACE LOW PRESSURE THAT MAY REACH NEAR THE EAST COAST
BY NEXT TUESDAY. COLDER TEMPERATURES MAY LEAD TO A FARTHER
SOUTHEAST RAIN-SNOW LINE VERSUS PREVIOUS EVENTS FOR ANY ASSOCIATED
PRECIPITATION BUT OTHERWISE THE DETAILS ARE VERY UNCERTAIN AT THIS
TIME.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MOST AGREEABLE FEATURES DURING THE FORECAST PERIOD ARE THE
INTENSIFYING STORM TRACKING FROM THE MISSISSIPPI VALLEY THROUGH
GREAT LAKES INTO EASTERN CANADA, AND TO A REASONABLE DEGREE THE
LONGER TERM MEAN PATTERN INVOLVING A BROAD TROUGH OVER MUCH OF THE
LOWER 48 AND EASTERN PACIFIC MEAN RIDGE THAT EVENTUALLY DRIFTS TO
THE WEST COAT. THE PACIFIC SYSTEM REACHING THE WEST DURING THE
WEEKEND HAS CONSIDERABLY MORE SPREAD, WITH COMBINED UNCERTAINTIES
OF THIS ENERGY AND NORTHERN STREAM FLOW LEADING TO WELL BELOW
AVERAGE CONFIDENCE FOR POTENTIAL LOW PRESSURE/FRONTAL SYSTEM THAT
CONSENSUS SUGGESTS WILL BE NEAR THE EAST COAST BY NEXT TUESDAY.
REGARDING THE INTENSIFYING FRIDAY INTO WEEKEND STORM AFFECTING THE
EASTERN HALF OF THE COUNTRY, A MODEL COMPOSITE SEEMS TO PROVIDE A
REASONABLE STARTING POINT FOR THE DEPTH AND TRACK. TAKEN AS A
WHOLE, THE OPERATIONAL MODEL FORECASTS VALID EARLY SATURDAY
INDICATE THIS STORM SHOULD BE SIMILAR TO OR POSSIBLY EVEN A LITTLE
DEEPER THAN THE CURRENT STORM AFFECTING THE EAST THROUGH THIS
WEDNESDAY. AMONG THE 00Z/06Z SOLUTIONS, THE ECMWF IS ON THE DEEP
SIDE OF THE SPREAD AND THE CMC WEAKEST. INTERESTINGLY THE 00Z
ECMWF-INITIALIZED MACHINE LEARNING MODELS ARE GENERALLY A FEW MB
WEAKER WITH THE SATURDAY STORM THAN EXTENDED RANGE RUNS WERE FOR
THE CURRENT STORM VALID WEDNESDAY.
AS IS TYPICALLY THE CASE FOR SMALLER SCALE FEATURES PASSING
THROUGH A MEAN RIDGE, GUIDANCE VARIES CONSIDERABLY FOR EXACTLY HOW
ELONGATED NORTH PACIFIC SHORTWAVE ENERGY AS OF EARLY FRI EVOLVES
AS IT PROGRESSES THROUGH THE RIDGE. ECMWF/GFS RUNS AND 00Z
UKMET/CMC AGREED ON AT LEAST BRIEF CLOSURE OF AN UPPER LOW BUT
WITH SOME LATITUDE DIFFERENCES (GFS FARTHEST NORTH) WHILE THE NEW
12Z UKMET ACTUALLY SHEARS THE ENERGY TO YIELD A VERY WEAK AND
SUPPRESSED SURFACE WAVE. ENSEMBLE MEANS ARE MORE OPEN ALOFT AS
EXPECTED, BUT FAVOR A SURFACE LOW TRACK INTO THE PACIFIC
NORTHWEST. 00Z ECMWF-INITIALIZED MACHINE LEARNING MODELS VARY BUT
WITH A SLIGHT MAJORITY CLOSEST TO THE 00Z ECMWF/ECENS TRACK. THUS
PREFER AN INTERMEDIATE SCENARIO AT THIS TIME.
BY THE LATTER HALF OF THE PERIOD THERE HAS BEEN A LOT OF
MODEL/ENSEMBLE SPREAD AND RUN-TO-RUN VARIABILITY FOR DETAILS OF
THE INCOMING WESTERN ENERGY AS WELL AS NORTHERN STREAM ENERGY,
PLUS HOW FLOW MAY EVOLVE OVER SOUTHWESTERN CANADA (00Z ECMWF
SHOWING MORE WESTWARD ELONGATION OF SHORTWAVE ENERGY THAN MOST
OTHER GUIDANCE). THIS LEADS TO WELL BELOW AVERAGE CONFIDENCE FOR
DETAILS OF POTENTIAL SURFACE LOW PRESSURE/FRONTAL SYSTEM EXPECT TO
BE NEAR THE EAST COAST BY NEXT TUESDAY--RANGING BETWEEN STRONG
DEVELOPMENT PER THE PAST COUPLE ECMWF RUNS AND MODEST WAVINESS PER
THE GFS/CMC/ENSEMBLE MEANS. THE UNCERTAINTY FAVORS MAINTAINING A
CONSERVATIVE APPROACH CLOSER TO THE MEANS BY NEXT TUESDAY.
..WEATHER/HAZARDS HIGHLIGHTS
ANOTHER INTENSE MISSISSIPPI VALLEY THROUGH GREAT LAKES STORM
SYSTEM LATE THIS WEEK INTO THE WEEKEND WILL PRODUCE A SWATH OF
HEAVY SNOW AND STRONG WINDS FROM MISSOURI THROUGH THE GREAT LAKES
ON FRIDAY, AND INTO NEW ENGLAND ON FRIDAY NIGHT WITH LAKE EFFECT
SNOW LIKELY OCCURRING BEHIND THE ARCTIC COLD FRONT (LIKELY
HEAVIEST DOWNWIND FROM LAKES ERIE AND ONTARIO ON SATURDAY). SOME
LIGHT TO MODERATE SNOW MAY OCCUR DOWN THROUGH THE CENTRAL
APPALACHIANS ON FRIDAY NIGHT AND SATURDAY AS WELL. THE THREAT FOR
HIGH WINDS ACROSS MUCH OF THE NORTHEASTERN QUADRANT OF THE EAST ON
SATURDAY WILL ADD TO THE HAZARDOUS CONDITIONS OVER AREAS WHERE
SNOW IS FALLING. MEANWHILE SHOWERS AND SCATTERED THUNDERSTORMS ARE
LIKELY FROM THE MIDWEST TO THE MID-ATLANTIC AND SOUTHEAST/GULF
COAST WITHIN THE WARM SECTOR OF THE STORM ON FRIDAY. THE STORM
PREDICTION CENTER HIGHLIGHTS A 15% PROBABILITY OF SEVERE
THUNDERSTORMS FROM FAR EASTERN LOUISIANA ACROSS THE SOUTHEAST,
CAROLINAS AND INTO FAR SOUTHERN VIRGINIA. SOME HEAVY RAINFALL IS
POSSIBLE OVER PARTS OF THE CENTRAL MIDWEST FRIDAY AFTERNOON WHERE
SOME INSTABILITY MAY CREEP IN, LEADING TO THE THREAT OF EXCESSIVE
RAINFALL. THIS THREAT MERITS A MARGINAL RISK (AT LEAST 5%) IN THE
DAY 4 EXCESSIVE RAINFALL OUTLOOK. THERE WILL ALSO BE A FOCUS FOR
HEAVY RAINFALL POTENTIAL FROM THE EASTERN SLOPES OF THE
APPALACHIANS INTO SOUTHERN NEW ENGLAND FRIDAY-FRIDAY NIGHT,
DENOTED BY A SEPARATE MARGINAL RISK AREA, ALONG WITH AN EMBEDDED
SLIGHT RISK (AT LEAST 15%) FOR THE AREA ENCOMPASSING THE I-95
CORRIDOR BETWEEN BALTIMORE AND WESTERN RHODE ISLAND WHERE
FAVORABLE JET DYNAMICS AND MOISTURE FLUX WILL BE PRESENT. WET
CONDITIONS FROM MELTING OF AT LEAST A PORTION OF THE EXISTING
SNOWPACK IN NORTHEASTERN PENNSYLVANIA INTO NORTHERN NEW JERSEY,
SOUTHERN NEW YORK AND SOUTHERN NEW ENGLAND PLUS THE HEAVY RAIN
FROM THE CURRENT STORM MAY ALSO CONTRIBUTE TO THE FLASH FLOODING
THREAT.
THE SYSTEM EXPECTED TO REACH THE PACIFIC NORTHWEST DURING THE
WEEKEND SHOULD ALSO PRODUCE A PERIOD OF HEAVY RAIN AND MOUNTAIN
SNOW, BUT WITH TEMPERED CONFIDENCE FOR SPECIFICS DUE TO GUIDANCE
SPREAD FOR THE SYSTEM'S EVOLUTION AND TRACK. THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS CURRENTLY DEPICT MARGINAL RISK AREAS,
WITH THE DAY 4 PERIOD HAVING THE GREATER POTENTIAL FOR A POSSIBLE
EMBEDDED SLIGHT RISK AT SOME POINT IF GUIDANCE ALIGNS BETTER FOR
HIGHEST TOTALS. THE COMBINATION OF THIS ENERGY AND NORTHERN STREAM
FLOW MAY PROMOTE SOME WAVINESS OVER THE FAR SOUTHERN PLAINS/GULF
COAST TO EAST COAST DURING THE FIRST PART OF NEXT WEEK, WITH SNOW
POSSIBLY SPREADING FROM THE CENTRAL/SOUTH-CENTRAL PLAINS INTO
PARTS OF THE EAST WITH RAIN FARTHER SOUTHEAST. PRECIPITATION AND
SURFACE EVOLUTION DETAILS ARE STILL VERY UNCERTAIN AT THIS TIME.
THE MOST EXTREME ANOMALIES FOR THE UPCOMING COLD PATTERN OVER THE
CENTRAL U.S. SHOULD BE OVER THE NORTHERN HIGH PLAINS/MONTANA WITH
SOME TEMPERATURES AT LEAST 40F BELOW NORMAL. EXPECT A MUCH BROADER
AREA OF TEMPERATURES AT LEAST 20F BELOW NORMAL TO BECOME MORE
ESTABLISHED BETWEEN THE ROCKIES AND APPALACHIANS WITH TIME,
LEAVING THE IMMEDIATE EAST COAST AND CALIFORNIA AS THE ONLY PLACES
WITH NEAR NORMAL HIGHS BY NEXT TUESDAY. THE EAST WILL SEE A BRIEF
PERIOD OF WARMTH AHEAD OF THE LATE WEEK STORM SYSTEM.
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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