543  
FXUS02 KWBC 100657  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
157 AM EST FRI JAN 10 2025  
 
VALID 12Z MON JAN 13 2025 - 12Z FRI JAN 17 2025  
   
.. ARCTIC AIRMASS TO REINFORCE EAST OF THE ROCKIES NEXT WEEK  
 
   
..OVERVIEW  
 
THE START OF THE PERIOD EARLY MONDAY SHOULD FEATURE A SOUTHERN  
CANADA/UPPER MIDWEST INTO WESTERN U.S. UPPER TROUGH. GUIDANCE SHOWS  
THIS TROUGH QUICKLY SPLITTING, DEPOSITING AN UPPER LOW OFFSHORE  
SOUTHERN CALIFORNIA AS A RIDGE BUILDS INTO THE NORTHWEST AND  
ROCKIES WHILE THE REST OF THE TROUGH, WITH SOME REINFORCEMENT FROM  
UPSTREAM ENERGY, DRIFTS ACROSS THE EAST. THIS PATTERN EVOLUTION  
WILL LEAD TO COLD TEMPERATURES OVER THE CENTRAL U.S. ON MONDAY AND  
SETTLING INTO THE EAST THEREAFTER, ALONG WITH MULTIPLE DAYS OF LAKE  
EFFECT SNOW PLUS A COUPLE POTENTIAL EPISODES OF SYNOPTIC-SCALE SNOW  
OVER/NEAR THE GREAT LAKES IN ASSOCIATION SURFACE LOWS/FRONTAL  
SYSTEMS. TOWARD THE END OF THE WEEK SOME PACIFIC SHORTWAVE ENERGY  
ROUNDING THE RIDGE SHOULD BEGIN TO AMPLIFY INTO THE NORTHWEST  
AND/OR NORTHERN PLAINS WHILE THE OFFSHORE UPPER LOW OPENS UP AND  
EJECTS INLAND.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT  
 
DURING MONDAY-WEDNESDAY THERE IS FAIRLY GOOD AGREEMENT IN MOST  
GUIDANCE FOR SPECIFICS OF THE FORECAST. THE PRIMARY EXCEPTION IS  
THE CMC, WHOSE 12Z RUN WAS A SLOW EXTREME WITH THE UPPER LOW  
EXPECTED TO TRACK ACROSS THE UPPER GREAT LAKES AND NEW ENGLAND WITH  
BOTH 12Z AND 00Z RUNS WHICH ARE MORE RELUCTANT TO CLOSE OFF AN  
UPPER LOW OFFSHORE CALIFORNIA. REMAINING DYNAMICAL MODELS DO SHOW A  
MODERATE/TYPICAL AMOUNT OF SPREAD FOR UPPER LOW POSITION BY EARLY  
WEDNESDAY, WITH THE MACHINE LEARNING (ML) MODELS SHOWING A FAIR  
AMOUNT OF SPREAD MOSTLY IN EAST-WEST FASHION NEAR 30N LATITUDE.  
MEANWHILE TO VARYING DEGREES THE DYNAMICAL AND ML MODELS ARE NOW  
HINTING AT A MIDWEST TO SOUTHERN MID-ATLANTIC/SOUTHEAST SURFACE WAVE  
AROUND TUESDAY-WEDNESDAY IN RESPONSE TO SHORTWAVE ENERGY WHOSE  
SPECIFICS MAY CONTINUE TO ADJUST IN FUTURE RUNS. OVERALL THE 18Z  
GFS/12Z ECMWF WITH MINORITY INPUT FROM THE 12Z UKMET REPRESENTED  
THE BEST IDEAS OF GUIDANCE FOR THIS PART OF THE FORECAST.  
 
AFTER MIDWEEK MOST GUIDANCE SHOWS NORTH PACIFIC SHORTWAVE ENERGY  
PUSHING INTO/AROUND INITIAL WESTERN U.S.-CANADA RIDGE AND  
BEGINNING TO AMPLIFY INTO THE NORTHWEST AND/OR NORTHERN PLAINS AS A  
NEW RIDGE BUILDS OVER THE EASTERN PACIFIC. MEANWHILE THE UPPER LOW  
OFFSHORE CALIFORNIA SHOULD OPEN UP AND EJECT INLAND WHILE EASTERN  
TROUGHING SHOULD REACH NEAR THE EAST COAST BY EARLY FRIDAY. THE  
PRIMARY THEME FROM AT LEAST SOME OF THE ML MODELS IS THE POTENTIAL  
FOR NORTHWESTERN HEIGHT FALLS TO BE QUICKER/MORE PRONOUNCED THAN  
MOST DYNAMICAL GUIDANCE, AND LEADING TO SURFACE LOW PRESSURE  
REACHING THE PLAINS BY NEXT FRIDAY. THIS AT LEAST FAVORS LEANING  
MORE TO RECENT ECMWF/ECENS/CMCENS MEANS RATHER THAN THE 12Z/18Z  
GFS RUNS THAT WERE SLOW WITH THE INCOMING PACIFIC SHORTWAVE AND  
ACTUALLY STILL HAD HIGH PRESSURE OVER THE CENTRAL U.S. ON FRIDAY.  
THE NEW 00Z GFS HAS ADJUSTED FAVORABLY TOWARD THE OTHER GUIDANCE.  
THE 18Z GEFS MEAN WAS AT LEAST CLOSER TO THE ECMWF CLUSTER THAN THE  
OPERATIONAL RUN. FARTHER EAST, ML MODELS GENERALLY FAVORED A  
COMPROMISE BETWEEN THE AMPLIFIED ECMWF/FLATTER GFS WITH THE UPPER  
TROUGH NEARING THE EAST COAST.  
   
..WEATHER/HAZARDS HIGHLIGHTS  
 
THE FORECAST PATTERN WILL SUPPORT ANOTHER SURGE OF ARCTIC AIR THAT  
SHOULD PROGRESS FROM THE CENTRAL U.S. EARLY IN THE WEEK TO THE  
EAST/SOUTHEAST BY TUESDAY-THURSDAY. OF PARTICULAR NOTE, EXPECT  
AREAS OF HAZARDOUS COLD OVER THE FAR NORTHERN PLAINS MONDAY-TUESDAY  
AND THEN MOST OF THE SOUTHERN HALF OR SO OF THE EAST BY TUESDAY-  
THURSDAY. WITHIN THESE AREAS TEMPERATURES SHOULD BE 10-20F BELOW  
NORMAL WITH EVEN COLDER WIND CHILLS. A FEW LOCATIONS AROUND THE  
UPPER OHIO VALLEY/CENTRAL APPALACHIANS COULD CHALLENGE DAILY  
RECORDS FOR COLD HIGHS ON TUESDAY. COLD CYCLONIC FLOW WILL PROMOTE  
PERIODS OF LAKE EFFECT SNOW, SOME OF IT HEAVY, WHILE SEPARATE LOW  
PRESSURE/FRONTAL SYSTEMS ON MONDAY AND THEN AFTER MIDWEEK MAY  
PRODUCE BROADER COVERAGE OF AT LEAST LIGHT SNOW OVER THE GREAT  
LAKES AND VICINITY.  
 
ELSEWHERE, A WAVY FRONT CROSSING THE GULF OF MEXICO ON MONDAY MAY  
PRODUCE RAIN OF VARYING INTENSITY OVER FLORIDA, WHILE SOME MOSTLY  
LIGHT RAIN MAY EXTEND INTO SOUTHERN TEXAS FOR A TIME. UPPER RIDGING  
THAT BUILDS OVER THE WEST THROUGH THURSDAY SHOULD KEEP MOST OF THE  
REGION DRY. SOME LIGHT PRECIPITATION MAY REACH THE NORTHEAST BY  
LATE WEEK WITH THE ARRIVAL OF A FRONT. AN UPPER LOW CLOSING OFF TO  
THE WEST/SOUTHWEST OF SOUTHERN CALIFORNIA MAY PRODUCE SCATTERED  
LIGHT PRECIPITATION OVER THE SOUTHWEST/FOUR CORNERS BY LATE WEEK AS  
IT OPENS UP AND EJECTS INLAND, THOUGH LATEST TRENDS HAVE BEEN  
LIGHTER AND SLOWER TO DEVELOP THIS ACTIVITY. MOSTLY BELOW NORMAL  
TEMPERATURES OVER THE WEST WILL GRADUALLY MODERATE TO NEAR/SLIGHTLY  
ABOVE NORMAL INTO THURSDAY, FOLLOWED BY A COOLER TREND IN THE  
NORTHWEST ON FRIDAY. WARMEST TEMPERATURE ANOMALIES NEXT WEEK SHOULD  
BE OVER THE NORTHERN PLAINS/UPPER MIDWEST DURING WEDNESDAY-FRIDAY  
WITH SOME LOCATIONS 10-20F OR SO ABOVE NORMAL.  
 
RAUSCH  
 
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 (QPF), EXCESSIVE RAINFALL  
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT  
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:  
 
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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