199  
FXUS02 KWBC 160659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 AM EST THU JAN 16 2025  
 
VALID 12Z SUN JAN 19 2025 - 12Z THU JAN 23 2025  
 
...STRONG ARCTIC SURGE WILL PUSH INTO THE CENTRAL U.S. THIS  
WEEKEND AND REACH THE EAST BY EARLY NEXT WEEK...  
   
..OVERVIEW  
 
MODELS AND ENSEMBLES CONTINUE TO SHOW A VERY AMPLIFIED MEAN PATTERN  
CONSISTING OF A DEEP TROUGH FROM NORTHEASTERN CANADA THROUGH THE  
LOWER 48 AND AN EASTERN PACIFIC RIDGE EXTENDING WELL NORTHWARD.  
THUS CONFIDENCE REMAINS HIGH IN THE FORECAST OF ARCTIC AIR DROPPING  
SOUTHWARD OVER THE CENTRAL U.S. THIS WEEKEND AND EXPANDING TO  
INCLUDE MUCH OF THE EAST BY EARLY NEXT WEEK. BY MIDWEEK MOST OF THE  
PLAINS SHOULD SEE MODERATING TEMPERATURES WHILE THE COLD WILL  
LIKELY LINGER OVER THE SOUTH AND EAST. IN CONTRAST, GUIDANCE IS  
HAVING A LOT OF DIFFICULTY IN RESOLVING IMPORTANT EMBEDDED  
SHORTWAVES THAT WILL PLAY AN IMPORTANT ROLE IN DETERMINING THE  
COVERAGE AND AMOUNTS OF POTENTIAL WINTRY PRECIPITATION ACROSS THE  
SOUTH NEXT WEEK, WITH SOME LINGERING ISSUES ALSO CONTINUING FOR A  
PROGRESSIVE WAVE TRACKING OFF THE EAST COAST ON SUNDAY.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT  
 
VERY EARLY IN THE FORECAST, SPREAD PERSISTS FOR THE DETAILS OF A  
SHORTWAVE REACHING THE EASTERN HALF OF THE COUNTRY BY SUNDAY ALONG  
WITH ITS ACCOMPANYING WAVE THAT SHOULD TRACK OFF THE EAST COAST AND  
MOST LIKELY REACH A POSITION JUST SOUTH OR EAST OF NOVA SCOTIA BY  
EARLY MONDAY. THE RELATIVE MAJORITY OF GUIDANCE (ALSO ACCOUNTING  
FOR THE 12Z MACHINE LEARNING MODELS) CLUSTERS WITHIN THE REALM OF  
THE ECMWF/UKMET/ICON FOR TRACK AND TIMING. IN CONTRAST TO RECENT  
GFS TENDENCIES TO BE ON THE FASTER SIDE FOR THE SHORTWAVE AND  
SURFACE FEATURE, LATEST RUNS HAVE ADJUSTED SLOWER THAN OTHER  
GUIDANCE. MEANWHILE THE LATEST CMC RUNS ARE A DEEP AND WESTERN  
EXTREME WITH THE SURFACE LOW (LEADING TO HEAVIER NORTHEAST  
PRECIPITATION THAN OTHER GUIDANCE), THOUGH THEIR UPPER DYNAMICS  
FINALLY LOOK A LOT BETTER VERSUS CONSENSUS THAN IN RECENT DAYS WHEN  
THEY WERE EXCESSIVELY SLOW/AMPLIFIED WITH THE ORIGINATING ENERGY  
OVER THE WEST.  
 
DETAIL CONFIDENCE DROPS PRECIPITOUSLY BEHIND THIS FEATURE, AS  
MODELS SHOW WIDE VARIATIONS AMONG EACH OTHER AND FROM RUN TO RUN  
FOR IMPORTANT SHORTWAVES. THE FIRST ONE SHOULD DIG INTO THE WEST BY  
NEXT MONDAY, WITH ITS EVENTUAL EVOLUTION AFFECTING HOW MUCH WINTRY  
PRECIPITATION MAY SPREAD ACROSS THE SOUTHERN TIER EARLY-MID WEEK.  
THROUGH THE 12Z/18Z MODEL RUNS, THERE WAS A PROMINENT CLUSTERING  
TOWARD GREATER SOUTHWESTWARD ELONGATION OF THIS SHORTWAVE VERSUS  
THE GFS. THIS WAS DUE TO THE MAJORITY NOT DAMPENING THE NORTHERN  
SIDE OF THE UPSTREAM RIDGE AS MUCH AS GFS RUNS. GEFS MEANS HAVE A  
GFS FLAVOR BUT SHOW SOME NUDGE TOWARD A LITTLE MORE TROUGH  
AMPLITUDE. MEANWHILE THE 12Z ML MODELS ALSO SHOW MORE ELONGATION  
THAN THE GFS BUT WITH FASTER TIMING THAN MOST OF THE DYNAMICAL  
MODELS. THE PAST COUPLE UKMET RUNS APPEARED CLOSEST TO THE ML MODEL  
IDEAS. THE NEW 00Z ECMWF HAS INTRODUCED A COMPLICATION IN THAT IT  
NOW LOOKS MORE LIKE A SLIGHTLY SLOWER VERSION OF THE GFS. AS FOR  
EVENTUAL EFFECTS ACROSS THE SOUTH, THE OVERALL ARRAY OF GUIDANCE  
HAS SUPPORTED A MOISTURE SHIELD SOMEWHERE IN THE REALM OF THE PRIOR  
TWO ECMWF RUNS (12Z AND 00Z/15) AND THE GEFS/ECENS MEANS--BETWEEN  
THE EXTREMES OF THE RELATIVELY DRY GFS AND HEAVY/NORTHWARD CMC.  
WHILE SOME ASPECTS OF GUIDANCE ACTUALLY TRENDS A LITTLE CLOSER  
TOGETHER AS THE NEXT BUNDLE OF SHORTWAVE ENERGY DROPS INTO THE MEAN  
TROUGH BY WEDNESDAY-THURSDAY, SIGNIFICANT DIFFERENCES DEVELOP  
REGARDING WHETHER/HOW MUCH FLOW SPLITS OVER THE EAST-CENTRAL  
PACIFIC. THIS DOES NOT BODE WELL FOR THE FORECAST IMMEDIATELY  
AFTER EARLY THURSDAY.  
 
BASED ON THE ABOVE CONSIDERATIONS, THE EARLY PART OF THE UPDATED  
FORECAST STARTED WITH THE 12Z ECMWF/12Z UKMET/12Z GFS IN ORDER FROM  
MORE TO LESS WEIGHT. THE 12Z GFS WAS LITTLE MORE PALATABLE THAN THE  
18Z RUN WHERE DIFFERENCES EXISTED. THE BLEND STARTED TO INTRODUCE  
THE 18Z GEFS/12Z ECENS MEANS BY DAY 5 TUESDAY AND REACHED 60  
PERCENT TOTAL MEAN WEIGHT BY THE END OF THE PERIOD, WITH 30/10  
LINGERING PERCENTAGES OF THE 12Z ECMWF/GFS RESPECTIVELY. THIS  
APPROACH HELPED TO PROVIDE THE BEST CONTINUITY POSSIBLE UNDER THE  
CIRCUMSTANCES WHILE WAITING FOR BETTER EVENTUAL AGREEMENT FOR  
DETAILS.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS  
 
BY SUNDAY A BROAD AREA OF HAZARDOUSLY COLD ARCTIC AIR WILL ALREADY  
COVER THE CENTRAL U.S. AND SHOULD EXPAND TO COVER MUCH OF THE EAST  
BY MONDAY. EXPECT MANY AREAS TO SEE HIGHS AT LEAST 20F BELOW  
NORMAL, WITH THE COLDEST ANOMALIES LIKELY TO BE OVER THE HIGH  
PLAINS AND VICINITY WHERE HIGHS COULD BE 30-40F BELOW NORMAL.  
COLDEST TEMPERATURES ON AN ABSOLUTE BASIS SHOULD BE OVER NORTHERN  
PLAINS AND UPPER MIDWEST WHERE SUBZERO HIGHS AND LOWS IN THE -20S  
ARE LIKELY. WIND CHILLS SHOULD BE EVEN COLDER AND MORE DANGEROUS.  
WPC IS POSTING KEY MESSAGES REGARDING THIS COLD OUTBREAK. THE  
NORTHERN-CENTRAL ROCKIES/PLAINS SHOULD MODERATE CONSIDERABLY BY  
TUESDAY-WEDNESDAY (THOUGH WITH A POTENTIAL FOR HIGH WINDS) WHILE  
COLD WEATHER MAY PERSIST INTO WEDNESDAY AND POSSIBLY TO SOME EXTENT  
THURSDAY ACROSS THE SOUTH AND EAST. THE WEST WILL SEE A PERIOD OF  
COOL BUT NOT EXTREME TEMPERATURES FROM THE WEEKEND INTO THE START  
OF NEXT WEEK, WITH NEAR NORMAL AND THEN SLIGHTLY ABOVE NORMAL  
READINGS SLOWLY BEGINNING TO PUSH EASTWARD FROM THE WEST COAST.  
 
THE WAVE FORECAST TO TRACK QUICKLY OFF THE EAST COAST ON SUNDAY MAY  
PRODUCE A BAND OF MOSTLY LIGHT PRECIPITATION BEFORE ITS DEPARTURE.  
SOME WINTRY WEATHER IS POSSIBLE OVER PARTS OF THE MID-ATLANTIC AND  
SOUTHERN NEW ENGLAND. ALTHOUGH THERE IS AN INTERMEDIATE MAJORITY  
CLUSTER FOR THIS SYSTEM IN THE GUIDANCE, THERE ARE STILL A COUPLE  
SOLUTIONS ON THE EXTREME ENDS OF THE ENVELOPE SO CONTINUE TO  
MONITOR FORECASTS.  
 
FARTHER WEST, A SHORTWAVE DIGGING INTO THE WEST EARLY NEXT WEEK MAY  
PRODUCE SOME SCATTERED SNOW DEPENDING ON ITS EVOLUTION. WHAT THIS  
SHORTWAVE DOES AFTER MONDAY WILL DETERMINE HOW MUCH PRECIPITATION  
EMERGES OVER THE SOUTHERN TIER FROM TEXAS EASTWARD ON THE SOUTHERN  
PERIPHERY OF THE OVERALL UPPER TROUGH AND SURFACE HIGH PRESSURE.  
THE SOUTHERN EXTENT OF THE COLD AIR AT THE SURFACE MEANS THAT A  
MAJORITY OF PRECIPITATION COULD BE OF A WINTRY VARIETY, PERHAPS  
ALL THE WAY TO THE GULF COAST. FREEZING RAIN/ICE IS ALSO AN  
INCREASING CONCERN FOR PARTS OF THE SOUTH GIVEN THE POSSIBILITY OF  
A WARM NOSE ATOP ARCTIC COLD AIR. SOUTHERN TIER SNOW POTENTIAL  
CONTINUES TO SHOW UP IN THE WINTER WEATHER PROBABILITIES FOR 0.25  
INCH LIQUID IN THE FORM OF SNOW, NOW 10-20 PERCENT OVER AN AREA  
JUST NORTH OF THE WESTERN GULF COAST FOR THE EARLY MONDAY-EARLY  
TUESDAY PERIOD AND 10-40 PERCENT ACROSS A MUCH BROADER SWATH OF  
THE SOUTH INTO SOUTHERN MID-ATLANTIC EARLY TUESDAY INTO EARLY  
WEDNESDAY. SOME PRECIPITATION POTENTIAL LINGERS THEREAFTER, BUT  
THROUGH THIS WHOLE PERIOD CONFIDENCE IN DETAILS IS BELOW AVERAGE  
DUE TO CONSIDERABLE MODEL DIFFERENCES AND VARIABILITY.  
 
UNCERTAINTIES IN DETAILS ALOFT OVER THE SOUTHWEST INTO NEXT WEEK  
MAKE THE SURFACE PATTERN UNCERTAIN AS WELL. HOWEVER, THERE IS SOME  
POTENTIAL FOR A PERIOD OF RELATIVELY STRONGER WINDS OVER PARTS OF  
CALIFORNIA AND VICINITY AROUND MONDAY-TUESDAY. CONTINUE TO MONITOR  
STORM PREDICTION CENTER FIRE WEATHER FORECASTS FOR FURTHER  
INFORMATION.  
 
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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