271  
FXUS02 KWBC 261854  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
153 PM EST FRI JAN 26 2024  
 
VALID 12Z MON JAN 29 2024 - 12Z FRI FEB 2 2024  
 
19Z UPDATE: THE 12Z MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT  
WITH THE AMPLIFYING TROUGH FROM THE GREAT LAKES TO THE EAST COAST  
FOR THE MIDDLE OF NEXT WEEK, ALTHOUGH THE GFS REMAINS A SLIGHTLY  
SLOWER SOLUTION. IT APPEARS THAT ENSUING COASTAL LOW CYCLOGENESIS  
SHOULD BE FAR ENOUGH AWAY FROM THE COAST TO KEEP PRECIPITATION  
AMOUNTS LIGHT AS THE FORECAST STANDS RIGHT NOW. THERE IS BETTER  
THAN AVERAGE MODEL AGREEMENT WITH THE LARGE SCALE TROUGH SETTING  
UP ALONG THE WEST COAST BY MID-LATE WEEK, WITH THE GREATEST MODEL  
DIFFERENCES RESIDING ACROSS SOUTHEAST CANADA WITH TIMING  
DIFFERENCES IN NORTHERN STREAM FLOW. BY FRIDAY, THE GFS IS  
STRONGER WITH A SHORTWAVE/UPPER LOW OVER THE GREAT LAKES REGION,  
BUT IT IS COMPATIBLE WITH THE MODEL CONSENSUS ELSEWHERE. A  
MULTI-DETERMINISTIC MODEL BLEND SUFFICED AS A STARTING POINT IN  
THE FORECAST PROCESS FOR THE MONDAY-WEDNESDAY TIME PERIOD, AND  
THEN GRADUALLY INCREASING PERCENTAGE OF THE ENSEMBLE MEANS FOR  
LATER IN THE WEEK TO IRON OUT THE DIFFERENCES ACROSS THE EASTERN  
U.S. AND SOUTHEAST CANADA. THE PREVIOUS FORECAST DISCUSSION IS  
APPENDED BELOW FOR REFERENCE. /HAMRICK  
--------------------  
   
..OVERVIEW
 
 
MOST GUIDANCE AGREES ON A LARGE SCALE UPPER PATTERN FEATURING AN  
AMPLIFIED PACIFIC TROUGH ARRIVING INTO THE WEST LATE IN THE WEEK,  
A DOWNSTREAM RIDGE DRIFTING FROM THE INTERMOUNTAIN WEST INTO THE  
PLAINS/MISSISSIPPI VALLEY, AND AN EAST COAST MEAN TROUGH THAT  
SHOULD TREND MORE SHALLOW BY THE END OF THE WEEK. STRONG AND  
MOIST SOUTHERLY FLOW AHEAD OF THE PACIFIC TROUGH WILL SUPPORT AN  
ATMOSPHERIC RIVER EVENT WHOSE FOCUS SHOULD PROGRESS SOUTHWARD  
ALONG THE WEST COAST OVER THE COURSE OF THE WEEK, WITH SOME  
MOISTURE LIKELY EXTENDING FARTHER INLAND OVER THE WEST AFTER  
WEDNESDAY. THE FORECAST PATTERN WILL PRODUCE DRIER CONDITIONS  
FARTHER EAST, WITH THE PRIMARY AREAS OF PRECIPITATION BEING THE  
POTENTIAL FOR LINGERING SNOW OVER SOUTHERN NEW ENGLAND ON MONDAY  
WITH A DEPARTING STORM SYSTEM AND MOSTLY LIGHT RAIN/SNOW WITH A  
TRAILING SYSTEM CROSSING THE EAST EARLY-MID WEEK.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
OVER THE WEST, THE PATTERN SEEMS TO EXHIBIT BETTER THAN AVERAGE  
PREDICTABILITY AS AN OVERWHELMING MAJORITY OF DYNAMICAL  
MODELS/ENSEMBLE MEANS AND 12Z ECMWF-INITIALIZED MACHINE LEARNING  
MODELS BRING THE AMPLIFIED PACIFIC UPPER TROUGH TO OR JUST INLAND  
FROM THE WEST COAST AS OF EARLY NEXT FRIDAY. GFS RUNS HAVE  
EXHIBITED SOME VARIABILITY AT THAT FRIDAY VALID TIME, WITH THE 12Z  
RUN STRAYING A BIT FAST BUT THE 18Z AND NEW 00Z RUNS SLOWER THAN  
CONSENSUS. AS FOR OTHER EMBEDDED DETAILS, THE GFS EVENTUALLY  
STRAYS NORTHWARD WITH THE FAIRLY DEEP LOW PRESSURE OFFSHORE THE  
PACIFIC NORTHWEST, WITH THE MAJORITY OF GUIDANCE HOLDING ONTO A  
DEFINED SURFACE LOW (ALBEIT WEAKENING) THAT DRIFTS TOWARD THE  
COAST LATE IN THE WEEK. THERE ARE ALSO DIFFERENCES IN EXACTLY HOW  
QUICKLY LEADING HEIGHT FALLS REACH THE WEST COAST, WITH A GUIDANCE  
AVERAGE PROVIDING A REASONABLE STARTING POINT IN LIGHT OF NO CLEAR  
CLUSTERING AT THIS TIME.  
 
OVERALL THERE IS A LOT MORE SPREAD AND VARIABILITY WITH DETAILS  
OVER THE EAST. RECENT GFS RUNS HAVE BEEN ON THE SLOW SIDE OF THE  
SPREAD FOR THE AMPLIFYING SHORTWAVE CROSSING THE REGION. THIS IS  
STILL THE CASE WHEN ADDING IN THE NEW 00Z RUNS BUT SLOWER TRENDS  
IN THE UKMET/ECMWF MAKE THE GFS LOOK A LITTLE LESS EXTREME AND  
THUS THE FULL GUIDANCE AVERAGE IS NOW A LITTLE SLOWER WITH THE  
ASSOCIATED SURFACE REFLECTION THAN WHAT WAS SUPPORTED BY THE  
NON-GFS MAJORITY AMONG THE 12Z/18Z DYNAMICAL MODELS/ENSEMBLE MEANS  
AND MACHINE LEARNING MODELS. EASTERN CANADA INTO NEW ENGLAND FLOW  
BY MID-LATE WEEK HAS ALSO BEEN AN ISSUE, WITH THE 12Z ECMWF  
SHOWING A PARTICULARLY DEEP AND SLOW UPPER LOW IN CONTRAST TO  
REMAINING SOLUTIONS THAT DEPICT EITHER A MORE MODEST TROUGH OR  
FASTER PROGRESSION (AS REFLECTED IN THE NEW 00Z ECMWF). ANOTHER  
SHORTWAVE MAY DROP INTO THE EAST COAST MEAN TROUGH BY FRIDAY, WITH  
LATEST GFS RUNS BEING ON THE SLOW SIDE. THE GEFS/ECENS MEANS  
PROVIDE THE BEST STARTING POINT LATE IN THE PERIOD GIVEN THE  
SPREAD AND RUN-TO-RUN INCONSISTENCY IN THE GUIDANCE.  
 
FOR THE UPDATED FORECAST BASED ON 12Z/18Z GUIDANCE, AN OPERATIONAL  
MODEL COMPOSITE PROVIDED A REASONABLE STARTING POINT EARLY IN THE  
PERIOD. DECREASINGLY FAVORABLE COMPARISONS FOR THE GFS OVER THE  
EAST FROM MIDWEEK ONWARD AND TO SOME DEGREE OVER THE WEST BY  
FRIDAY, AS WELL AS LOW CONFIDENCE IN THE 12Z ECMWF OVER THE EAST  
AFTER MIDWEEK, LED TO PHASING OUT THE GFS AND QUICKLY INCREASING  
TOTAL 18Z GEFS/12Z ECENS WEIGHT TO 70 PERCENT BY DAYS 6-7  
THURSDAY-FRIDAY. MINORITY LINGERING INPUT FROM 12Z CMC/ECMWF  
PROVIDED A LITTLE OPERATIONAL DETAIL OVER THE WEST WITHOUT  
ADVERSELY IMPACTING THE PATTERN OVER THE EAST.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE UPPER TROUGH APPROACHING THE WEST COAST MONDAY-WEDNESDAY AND  
THEN ARRIVING INTO THE WEST BY LATE WEEK WILL PROMOTE A STRONG  
SOUTHERLY FLOW OF ENHANCED MOISTURE AND LIKELY BRING A PERIOD OF  
SIGNIFICANT RAINFALL AND HIGH ELEVATION SNOW TO THE WEST COAST  
STATES, EVENTUALLY REACHING FARTHER INLAND WITH TIME. DURING THE  
PERIOD COVERED BY THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS (EARLY  
MONDAY THROUGH TUESDAY NIGHT), THE MARGINAL RISK AREA THAT WAS  
OVER THE OLYMPIC PENINSULA IN WESTERN WASHINGTON ON DAY 4 HAS BEEN  
DROPPED, WITH THE LATEST OVERALL QPF MODEL SIGNAL OF LESS THAN 1  
INCH AND HOURLY RAINFALL RATES LIKELY TO BE UNDER A QUARTER INCH,  
BUT THE MARGINAL RISK REMAINS HERE FOR THE DAY 5 PERIOD AS  
MOISTURE FLUX INCREASES. MEANWHILE, THE SEPARATE MARGINAL RISK  
AREA ALONG COASTAL AREAS OF SOUTHERN OREGON/NORTHERN CALIFORNIA ON  
DAY 5 REMAINS IN PLACE, AND THIS REFLECTS THE CONSENSUS TIMING FOR  
THE ARRIVAL OF MODERATE TO LOCALLY HEAVY RAINFALL WITH THE  
ATMOSPHERIC EVENT EXPECTED ON WEDNESDAY. AGAIN WITH SOME  
UNCERTAINTY ON EXACT TIMING, HEAVIEST TOTALS CURRENTLY APPEAR TO  
BE MOST LIKELY OVER NORTHERN-CENTRAL CALIFORNIA ON WEDNESDAY AND  
THEN SHIFTING INTO CENTRAL-SOUTHERN CALIFORNIA BY THURSDAY. ALSO  
BY THURSDAY EXPECT ORGANIZED PRECIPITATION TO EXTEND INTO THE  
INTERMOUNTAIN WEST/SOUTHWEST. THE SOUTHERN ROCKIES/PLAINS COULD  
SEE SOME PRECIPITATION BY FRIDAY.  
 
THE SYSTEM TRACKING AWAY FROM THE EAST COAST ON MONDAY MAY PRODUCE  
SOME LINGERING SNOW OVER SOUTHERN NEW ENGLAND ALONG WITH BRISK TO  
STRONG WINDS OVER THE WESTERN ATLANTIC. A SYSTEM PASSING THROUGH  
THE EAST EARLY-MID WEEK MAY SPREAD AN AREA OF MOSTLY LIGHT  
PRECIPITATION (SNOW NORTH, RAIN SOUTH) ACROSS THE REGION.  
 
THE NORTHERN-CENTRAL PLAINS WILL SEE ANOMALOUSLY WARM TEMPERATURES  
THROUGH THE PERIOD, WITH NORTHERN AREAS TENDING TO SEE THE BEST  
CHANCE FOR MULTIPLE DAYS OF MIN/MAX TEMPERATURES AT LEAST 20F  
ABOVE NORMAL. SOME MORNING LOWS COULD BE UP TO 25-30F ABOVE  
NORMAL AND A FEW DAILY RECORDS WILL BE POSSIBLE. THE WEST WILL BE  
WARM AS WELL EARLY IN THE WEEK WITH SOMEWHAT LESS EXTREME  
ANOMALIES (GENERALLY UP TO PLUS 10-20F), BUT THAT MAY STILL BE  
ENOUGH TO PRODUCE SOME DAILY RECORDS. THE UPPER TROUGH MOVING IN  
SHOULD BRING A COOLING TREND FOR THE LATTER HALF OF THE WEEK WITH  
HIGHS OVER CALIFORNIA AND AN EXPANDING PORTION OF THE SOUTHWESTERN  
U.S. TRENDING BELOW NORMAL THURSDAY-FRIDAY. BELOW NORMAL READINGS  
OVER THE EAST WILL TEND TO BE CONFINED TO FLORIDA EARLY IN THE  
WEEK. THE REMAINDER OF THE EAST WILL LIKELY SEE MORNING LOWS THAT  
ARE WARMER THAN AVERAGE AND DAYTIME HIGHS NEAR TO SLIGHTLY ABOVE  
NORMAL, WITH A COUPLE FRONTAL PASSAGES PROVIDING SOME DAY-TO-DAY  
VARIABILITY.  
 
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, 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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