151
FXUS02 KWBC 050658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 AM EST FRI JAN 5 2024
VALID 12Z MON JAN 8 2024 - 12Z FRI JAN 12 2024
...INTENSE LOW PRESSURE SYSTEM TRACKING FROM THE SOUTHERN PLAINS
TO THE GREAT LAKES EXPECTED TO BRING WIDESPREAD RAIN, SNOW, WIND,
AND SEVERE THUNDERSTORMS FOR EARLY IN THE WEEK...
..GENERAL OVERVIEW
A MAJOR UPPER TROUGH WILL BE DIGGING ACROSS AN UNSETTLED WESTERN
U.S. THIS WEEKEND, FOCUSING WINTRY THREATS FOR TERRAIN/MOUNTAIN
SNOWS AND WINDS. DEEP SURFACE CYCLOGENESIS IS EXPECTED ACROSS THE
SOUTH-CENTRAL PLAINS BY MONDAY, WITH IMPRESSIVE MOISTURE AND
INSTABILITY RETURNING TO FUEL WIDESPREAD HEAVY RAINFALL/CONVECTION
AND RUNOFF ISSUES ACROSS THE SOUTH-CENTRAL TO EASTERN U.S. THROUGH
THE MIDDLE OF NEXT WEEK. TO THE NORTH OF THE DEEP LOW'S TRACK,
THERE IS ALSO A SIGNIFICANT SNOW/ICE THREAT FROM THE CENTRAL
PLAINS TO THE MIDWEST/GREAT LAKES AND NORTHEAST MONDAY-WEDNESDAY,
ALONG WITH STRONG AND GUSTY WINDS. ADDITIONAL DYNAMIC SYSTEMS IN
THE SERIES LOOK TO MOVE INTO THE PACIFIC NORTHWEST EARLY NEXT WEEK
BEFORE DIGGING ACROSS THE WEST INTO MID-LATE NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE HAS A GOOD OVERALL DEPICTION OF THE
SYNOPTIC SCALE WEATHER PATTERN FOR THE FIRST HALF OF THE WEEK AND
THE EVOLUTION OF THE MAJOR LOW PRESSURE SYSTEM OVER THE PLAINS AND
GREAT LAKES. THE 12Z CMC THAT WAS AVAILABLE AT THE TIME OF
FRONTS/PRESSURES COMPOSITION WAS NOTED TO BE WELL SOUTH OF THE
EXISTING MODEL CONSENSUS ACROSS THE SOUTHERN U.S., AND ALSO SOUTH
OF THE PRIOR CMC RUNS, SO THE 00Z THURSDAY RUN OF THE CMC WAS
SUBSTITUTED FOR THE 12Z RUN SINCE IT BETTER MATCHED THE CONSENSUS.
TAKING THAT INTO ACCOUNT, A MULTI-DETERMINISTIC MODEL BLEND WAS
USED FOR THE MONDAY-TUESDAY TIME PERIOD WITH GREATER WEIGHTING
TOWARDS THE GFS/ECMWF. GOING INTO THE LATTER HALF OF THE WEEK,
INCREASING MODEL DIFFERENCES IN THE WAKE OF THE STRONG LOW
NECESSITATED THE USE OF MORE ENSEMBLE MEANS, UP TO ABOUT 40-50% BY
FRIDAY.
..WEATHER/HAZARDS HIGHLIGHTS
WITH THE NORTHEAST U.S. STORM SYSTEM MOVING WELL OUT TO SEA BY
MONDAY MORNING, ATTENTION THEN TURNS TO THE DEVELOPING MAJOR LOW
PRESSURE SYSTEM ACROSS THE SOUTH-CENTRAL U.S. THAT HAS BEEN ON THE
WEATHER HORIZON FOR THE PAST SEVERAL DAYS. CONFIDENCE CONTINUES
TO INCREASE FOR A HIGHLY IMPACTFUL EVENT SPANNING FROM TEXAS TO
THE GREAT LAKES AND NORTHEAST U.S. THROUGH THE MIDDLE OF THE WEEK
AS THE SURFACE LOW BECOMES ANOMALOUSLY STRONG OVER ARKANSAS AND
THEN LIFTS NORTHEAST TOWARDS THE EASTERN GREAT LAKES BY WEDNESDAY
MORNING. HEAVY RAINFALL WILL INDEED BE ONE OF THE THINGS MAKING
WEATHER HEADLINES AS A VERY STRONG LOW LEVEL JET ADVECTS DEEP GULF
OF MEXICO MOISTURE NORTHWARD ACROSS THE CENTRAL GULF COAST REGION
ON MONDAY, AND WITH THE POTENTIAL FOR 2 TO 4 INCHES OF RAINFALL
FROM MULTIPLE ROUNDS OF CONVECTION, A SLIGHT RISK REMAINS
WARRANTED FOR THE NEW DAY 4 ERO ON MONDAY FROM SOUTHERN LOUISIANA
TO THE FLORIDA PENINSULA, WHERE HOURLY RAINFALL RATES COULD EASILY
EXCEED ONE INCH PER HOUR.
THE HEAVY RAINFALL THREAT CONTINUES GOING INTO DAY 5 ON TUESDAY
WITH WIDESPREAD 2-3 INCH RAINFALL TOTALS LIKELY FROM THE SOUTHERN
APPALACHIANS TO SOUTHERN NEW ENGLAND. A SLIGHT RISK AREA IS
PLANNED FROM EXTREME NORTHEAST GEORGIA TO WESTERN VIRGINIA WHERE A
STRONG SOUTHEASTERLY LOW LEVEL JET WILL ADVECT HIGHLY ANOMALOUS
MOISTURE TOWARDS THE TERRAIN AND RESULT IN ENHANCED RAINFALL
TOTALS AND RATES FOR THESE AREAS, INCREASING THE THREAT OF
FLOODING PROBLEMS. A SECOND SLIGHT RISK AREA IS PLANNED FOR
EASTERN PA TO WESTERN MA AND MOST OF CT AND RI, WHERE THERE IS A
STRONG DETERMINISTIC MODEL SIGNAL FOR 2 TO 4 INCH RAINFALL TOTALS
DURING THIS TIME WITH IMPRESSIVE IVT VALUES EXPECTED. A BROADER
MARGINAL RISK AREA INCLUDES ALL AREAS FROM SOUTHERN GEORGIA TO
SOUTHERN NEW HAMPSHIRE.
IN ADDITION TO THE HEAVY RAINFALL WILL BE THE INCREASING THREAT OF
STRONG TO SEVERE THUNDERSTORMS IN THE WARM SECTOR OF THE LOW WHERE
THE BEST COMBINATION OF KINEMATICS AND INSTABILITY WILL EXIST, AND
THIS IS EXPECTED FROM THE CENTRAL GULF COAST TO THE COASTAL
PORTION OF THE CAROLINAS ON MONDAY AND INTO TUESDAY. ON THE
NORTHWEST SIDE OF THE LOW WILL BE THE INCREASING PROSPECTS FOR AN
IMPACTFUL WINTER STORM FROM KANSAS TO THE WESTERN GREAT LAKES, AND
GIVEN THE STRONG PRESSURE GRADIENT EXPECTED, SOME BLIZZARD
CONDITIONS ARE EXPECTED. WIDESPREAD WINDY CONDITIONS ARE EXPECTED
ACROSS MUCH OF THE EASTERN HALF OF THE NATION TUESDAY AND GOING
INTO WEDNESDAY AS THE SURFACE LOW LIKELY DROPS BELOW 980 MB. IN
TERMS OF TEMPERATURES, AN ARCTIC BLAST IS FORECAST FOR THE
NORTHERN PLAINS TO CLOSE OUT THE WEEK WITH WIDESPREAD SUBZERO LOWS
FOR THE DAKOTAS AND INTO MONTANA, AND HIGHS ONLY IN THE 0S AND 10S
FOR MANY OF THOSE SAME AREAS.
HAMRICK
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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