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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