465
FXUS02 KWBC 211853
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
153 PM EST SUN JAN 21 2024
VALID 12Z WED JAN 24 2024 - 12Z SUN JAN 28 2024
...MULTI-DAY EXCESSIVE RAINFALL/FLOODING THREAT FROM SOUTHEAST
TEXAS TO THE LOWER MISSISSIPPI/TENNESSEE VALLEYS AND GULF COAST
STATES THIS WEEK...
..OVERVIEW
GUIDANCE STILL OVERALL AGREES THAT THE LARGE SCALE PATTERN ALOFT
THIS WEEK WILL SHIFT NOTABLY FROM THE ONGOING FRIGID PATTERN, AS A
RIDGE SHIFTS FROM THE CENTRAL U.S. INTO THE EAST COAST AND
TROUGHING BECOMES ESTABLISHED IN THE WESTERN/CENTRAL U.S.. THIS
WILL CHANNEL MOISTURE RETURN FROM THE GULF OF MEXICO, WITH WARMING
TEMPERATURES IN THE EASTERN HALF OF THE COUNTRY. A SERIES OF
DEEPENED PACIFIC SYSTEMS WILL PERIODICALLY FOCUS LEAD
FLOW/PRECIPITATION INLAND INTO THE PACIFIC NORTHWEST BEFORE
DIGGING INTO A MEAN WESTERN U.S. TROUGH IN UNSETTLED/COOLED FLOW.
MEANWHILE DOWNSTREAM, A SIGNIFICANT RAINFALL EVENT REMAINS LOOMING
AS MULTIPLE DAYS OF HEAVY RAIN AND RUNOFF THREATS ARE EXPECTED
AMID THE STALLING UPPER FLOW MEAN PATTERN, WITH PRIMARY FOCUS FROM
SOUTHEAST TEXAS THROUGH THE LOWER MISSISSIPPI/TENNESSEE VALLEYS
AND GULF COAST STATES. FAVORABLE UPPER JET/FRONTAL WAVES SUPPORT
WILL ACT TO INCREASE AND FOCUS MOISTURE AND INSTABILITY RETURN AS
EJECTING IMPULSES RIDE/LIFT ON THE WESTERN PERIPHERY OF A SLOW TO
DISLODGE EASTERN U.S. RIDGE. EXPECT WIDESPREAD ACTIVITY TO ALSO
SPREAD TO THE MIDWEST/GREAT LAKES AND THE SOUTHEAST/EAST THROUGH
LATER WEEK, WITH SNOW/ICE POTENTIAL ON THE NORTH SIDE OF THE
PRECIPITATION SHIELD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE CONTINUES TO SHOW VERY GOOD AGREEMENT WITH RESPECT TO THE
OVERALL SYNOPTIC PATTERN FEATURING CENTRAL/WESTERN U.S. LONGWAVE
TROUGH DIGGING INTO NORTHERN MEXICO AT THE START OF THE PERIOD MID
WORK-WEEK (WEDNESDAY JAN 24). THERE HAS BEEN A TREND IN BOTH SOME
OF THE LATEST GFS/ECMWF RUNS FOR SHORTWAVE ENERGY EMBEDDED WITHIN
THE LONGWAVE TROUGH TO LIFT NORTHWARD OVER THE MIDWEST THURSDAY
(JAN 25) AS THE AXIS OF THE MEAN LONGWAVE TROUGH BEGINS TO SHIFT
SLIGHTLY MORE TOWARDS THE CENTRAL U.S. AND THE PATTERN BECOMES A
BIT LESS AMPLIFIED. THE 00Z CMC SOLUTION IS A BIT SLOWER AND MORE
AGGRESSIVE WITH THIS EMBEDDED ENERGY, LINGERING INTO FRIDAY (JAN
26). A TREND NOTED IN THE PRIOR FORECAST FOR UPSTREAM ENERGY OVER
THE NORTHEASTERN PACIFIC TO TRANSLATE QUICKLY SOUTHWARD AND DIG
INTO THE SOUTHWEST TO HELP REINFORCE THE MEAN TROUGH POSITION BACK
TOWARDS THE WESTERN U.S. BY FRIDAY REMAINS IN THE LATEST 00Z
ECMWF/CMC RUNS, WITH THE CMC ON THE MORE AGGRESSIVE SIDE, AND THE
00Z/06Z GFS REMAINING A BIT LESS AGGRESSIVE. THE CORRESPONDING
ENSEMBLE MEAN GUIDANCE FOLLOWS A SIMILAR EVOLUTION FAVORING THE
TRENDS OF THEIR DETERMINISTIC COUNTER-PARTS, WITH THE 00Z ECENS
MEAN RESIDING GENERALLY IN THE MIDDLE OF THE ENVELOPE OF
SOLUTIONS.
A NOTABLE TREND DIFFERENCE COMPARED TO THE PRIOR FORECAST ARISES
DURING THE MID- TO LATE PERIOD, AS THE MORE AGGRESSIVE UPSTREAM
ENERGY DIGGING INTO THE SOUTHWEST IN PRIOR RUNS OF THE ECMWF AND
CMC CONTINUED TO HOLD THE POSITION OF THE LONGWAVE TROUGH TO THE
WEST WHILE THE GFS SHOWED A MORE PROGRESSIVE, FASTER EVOLUTION
EASTWARD INTO THE CENTRAL U.S. INTO THE WEEKEND (SATURDAY JAN 27).
HOWEVER, THE LAST FEW RUNS OF THE ECMWF CULMINATING IN THE MOST
RECENT 00Z RUN HAVE BEGUN TO PROGRESS THE TROUGH EASTWARD FASTER.
ON THE OTHER HAND, BY THE END OF THE FORECAST PERIOD SUNDAY (JAN
28), THE MOST RECENT 06Z RUN OF THE GFS SHOWS A DRAMATIC SHIFT
TOWARDS A MORE ENHANCED POSITIVELY TILTED ORIENTATION OF THE
TROUGH WITH LOWER HEIGHTS REMAINING FURTHER TO THE SOUTHWEST OF
THE 00Z ECMWF RUN, WHICH CONTINUES AN EASTWARD PROGRESSION OF THE
TROUGH AS UPSTREAM RIDGE AMPLIFICATION OVER THE WESTERN U.S. IS
STRONGER. THE COMBINED MOST RECENT GFS/ECMWF RUNS ARE THUS IN MUCH
BETTER AGREEMENT WITH THE OVERALL PHASING OF THE TROUGH, EVEN IF
THEIR POSITIONS HAVE SHIFTED PAST EACH OTHER. THE GEFS MEAN
CONTINUES TO FOLLOW THE PRIOR TREND SEEN IN THE GFS FOR THE TROUGH
TO PROGRESS DOWNSTREAM FASTER THAN ANY OF THE OTHER SOLUTIONS,
WHILE THE ECENS IS GENERALLY SIMILAR TO THE ECMWF WITH RESPECT TO
THE POSITION/PHASING OF THE TROUGH AND WESTERN RIDGE. THE CMC HAS
BECOME MORE OF AN OUTLIER TO THE OTHER SOLUTIONS WITH EMBEDDED
ENERGY DIGGING WELL SOUTHWEST OF THE OTHER GUIDANCE INTO NORTHERN
MEXICO. ONE FINAL NOTABLE TREND COMPARED TO THE PRIOR FORECAST IS
FOR STRONGER EMBEDDED SHORTWAVE ENERGY LIFTING NORTHEASTWARD FROM
THE PLAINS THROUGH THE MIDWEST AT THE END OF THE PERIOD IN BOTH
THE 06Z GFS AND 00Z ECMWF, WHICH LOOKS TO INCREASE PRECIPITATION
CHANCES IN THE PLAINS, AS WELL AS A SLOWER PROGRESSION OF A
FRONTAL SYSTEM THROUGH THE SOUTHEAST NEXT WEEKEND.
THE UPDATED WPC MEDIUM RANGE FORECAST BEGINS WITH A COMPOSITE
BLEND OF THE DETERMINISTIC GUIDANCE, WITH AN EDGE TOWARDS THE 06Z
GFS AND 00Z ECMWF AND A CONTRIBUTION FROM THE ECENS MEANS WHICH
FALLS THE CLOSEST TO THE MIDDLE GROUND OF THE SOLUTIONS.
CONTRIBUTIONS FROM THE CMC AND UKMET ARE REDUCED BY MID-PERIOD DUE
TO THE NOTED DIFFERENCES BETWEEN THE CMC AND OTHER
DETERMINISTIC/ENSEMBLE MEAN GUIDANCE WITH RESPECT TO THE INITIAL
SHORTWAVE LIFTING THROUGH THE MIDWEST AND MORE AGGRESSIVE ENERGIES
DIGGING SOUTHWEST INTO NORTHERN MEXICO LATE IN THE PERIOD. A
GREATER RELIANCE ON THE ECENS MEAN TOWARDS THE END OF THE PERIOD
HELPS ACCOUNT FOR INCREASING DIFFERENCES WITH EMBEDDED SHORTWAVE
ENERGIES, SPECIFICALLY WITH EMBEDDED ENERGY IN THE WESTERN RIDGE
APPROACHING CALIFORNIA IN THE GFS, AN OUTLIER COMPARED TO THE
OTHER GUIDANCE. THE GEFS MEAN IS NOT INCLUDED AS THE SOLUTION
REMAINS SIMILAR TO PRIOR RUNS OF THE DETERMINISTIC GFS WITH
RESPECT TO A MORE PROGRESSIVE DOWNSTREAM EVOLUTION OF THE
CENTRAL/WESTERN U.S. LONGWAVE TROUGH LATE IN THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE PACIFIC NORTHWEST/NORTHERN CALIFORNIA WILL SEE PERIODS OF
MODERATE RAINS INTO MID-LATER WEEK WITH MULTIPLE PACIFIC SYSTEM
APPROACHES. DIGGING ENERGIES INTO A MEAN UPPER TROUGH OVER THE
WEST IN THIS PERIOD SHOULD ALLOW FOR PRECIPITATION TO WORK INLAND
TO THE NORTH-CENTRAL INTERMOUNTAIN WEST/ROCKIES TO INCLUDE SOME
ENHANCED TERRAIN/MOUNTAIN SNOWS. UPPER RIDGE BUILDING UP/INLAND
THROUGH THE WEST COAST HEADING INTO THE WEEKEND SHOULD
INCREASINGLY LIMIT ACTIVITY WITH A MORE NORTHWARD TO OFFSHORE
FOCUS.
DOWNSTREAM, INCREASING MOISTURE AHEAD OF THE WESTERN U.S. UPPER
TROUGHING WILL INCREASINGLY SPREAD RAIN INTO THE SOUTH-CENTRAL
U.S. EARLY WEEK. HEAVIEST RAIN TOTALS REMAIN FORECAST TO SLOWLY
SPREAD THROUGH TEXAS TO THE LOWER MISSISSIPPI/TENNESSEE VALLEYS
AND GULF COAST STATES AND SOUTHEAST INTO MID/LATER WEEK, AND THESE
WILL FUEL GROWING FLOODING CONCERNS GIVEN SIGNIFICANT
REPEAT/TRAINING POTENTIAL AND A SIGNAL IN THE GUIDANCE FOR LOCALLY
VERY HEAVY DAILY TOTALS OF 3-4"+. WPC DAY 4/WEDNESDAY AND DAY
5/THURSDAY EXCESSIVE RAINFALL OUTLOOKS HAVE SLIGHT RISK AND
SURROUNDING MARGINAL RISK AREAS FROM SOUTHEAST TEXAS TO THE LOWER
MISSISSIPPI/TENNESSEE VALLEYS, GULF COAST STATES, AND SOUTHERN
APPALACHIANS GIVEN SLOW PATTERN TRANSLATION WITH FAVORABLE UPPER
SUPPORT, DEEP MOISTURE RETURN, AND REPEAT ACTIVITY SIGNATURE.
THERE REMAINS QUITE A BIT OF SPREAD IN THE EXACT AXIS OF HEAVIER
QPF AMONG BOTH THE DETERMINISTIC AND ENSEMBLE GUIDANCE,
PARTICULARLY ON DAY 4/WEDNESDAY, WITH THE GFS/GEFS MEAN FAVORING
AREAS FURTHER NORTH AND THE ECMWF/ECENS MEAN FAVORING AREAS ALONG
THE GULF COAST. HOWEVER, AS CONFIDENCE INCREASES IN BOTH THE AXIS
OF HEAVIEST RAINFALL AS WELL AS POTENTIAL OVERLAP WITH RAINFALL ON
DAY 3/TUESDAY LEADING TO WETTER ANTECEDENT CONDITIONS, A HIGHER
RISK THRESHOLD MAY BE NEEDED.
PRECIPITATION WILL ALSO START SPREADING MORE EARNESTLY ACROSS THE
MIDWEST/GREAT LAKES AND THE EAST INTO MID-LATER WEEK AFTER A DRY
PERIOD, AND GIVEN MUCH WARMER TEMPERATURES AND SNOWMELT, AREAL AND
STREAM FLOODING MAY BECOME A CONCERN. THERE IS ALSO QUITE A BIT OF
UNCERTAINTY WITH LATER WEEK INDIVIDUAL LIFTING FRONTAL WAVES
WITHIN THE LARGER SCALE FLOW AND THE EXTENT AND FOCUS OF POTENTIAL
COASTAL WAVES NEXT WEEKEND TO MONITOR. MEANWHILE, THERE REMAINS
SOME PROBABILITIES FOR FREEZING RAIN ACROSS PARTS OF THE
MIDWEST/GREAT LAKES INTO MID-LATER WEEK. WINTRY PRECIP SHOULD
TRANSITION TO RAIN AS WARM AIR SPREADS FARTHER NORTH. LINGERING
COOLED AIR FROM THE GREAT LAKES/APPALACHIANS TO THE NORTHERN
NORTHEAST SEEM MOST LIKELY TO LEAD TO WINTRY WEATHER LATER WEEK
AND INTO THE NEXT WEEKEND BUT AGAIN, STILL UNCERTAIN NORTHERN
PROGRESSION OF WARMER AIR MAY LIMIT THE DURATION/IMPACT.
RIDGING OVER THE EAST WITH TROUGHING OVER THE WESTERN/CENTRAL U.S.
WILL CONTINUE TO BRING ABOVE AVERAGE TEMPERATURES TO MUCH OF THE
EASTERN U.S. THROUGH NEXT WEEKEND, WITH THE GREATEST WARM
ANOMALIES OF 15-25 DEGREES CENTERED OVER PORTIONS OF THE OHIO
VALLEY/MID-ATLANTIC/CAROLINAS LATER THIS WEEK. INCREASING RIDGE
AMPLIFICATION OVER THE WESTERN U.S, AND STRETCHING INTO THE
NORTH-CENTRAL U.S., WILL BRING A WARMING TREND WITH HIGH
TEMPERATURES RISING ABOVE AVERAGE OVER THE REGION NEXT WEEKEND.
PUTNAM/SCHICHTEL
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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