144  
FXUS02 KWBC 282056  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION...AMENDED  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
355 PM EST SUN JAN 28 2024  
 
VALID 12Z WED JAN 31 2024 - 12Z SUN FEB 4 2024  
 
...LARGE SCALE SYSTEM LIKELY TO SPREAD PRECIPITATION ACROSS MUCH  
OF THE WEST THIS WEEK AND THEN REACHING THE GULF COAST BY NEXT  
SUNDAY...  
 
19Z UPDATE: THERE IS GOOD OVERALL SYNOPTIC AGREEMENT AMONG THE  
GFS/ECMWF/UKMET MODELS THROUGH THE END OF THE WEEK WITH ONLY MINOR  
MESOSCALE DIFFERENCES NOTED, SO A GENERAL BLEND OF THOSE MODELS  
SUFFICES AS A GOOD STARTING POINT IN THE FORECAST PROCESS. THE  
CMC WAS SLIGHTLY OUT OF PHASE WITH THAT OVERALL FLOW PATTERN  
ACROSS THE EASTERN U.S. AND STRAYED FROM THE MODEL CONSENSUS AS  
EARLY AS THURSDAY AND WAS SLOWER WITH THE ARRIVAL OF THE NEXT  
SHORTWAVE TROUGH ACROSS THE GREAT LAKES, SO THE 00Z RUN WAS NOT  
USED FOR THIS FORECAST. MORE NOTEWORTHY DIFFERENCES ARE EVIDENT  
BY NEXT SUNDAY AS THE LOW PRESSURE SYSTEM NEAR THE GULF COAST  
TRACKS SOUTH OF A CLOSED HIGH CENTERED OVER THE NORTH-CENTRAL  
STATES. IN PARTICULAR, THE GFS WAS SOUTH OF THE MODEL CONSENSUS  
WITH THE LOW AND MORE SUPPRESSED WITH THE UPPER HIGH ACROSS THE  
CENTRAL PLAINS, WHEREAS THE CMC IS TO THE NORTH OF THE CONSENSUS.  
THEREFORE, THE ENSEMBLE MEANS WERE INCREASED TO ABOUT 40 PERCENT  
ALONG WITH SOME PREVIOUS WPC CONTINUITY FOR NEXT WEEKEND. NO  
MAJOR CHANGES WERE NEEDED FOR THE UPDATED DAY 4 AND 5 EXCESSIVE  
RAINFALL OUTLOOKS. THE PREVIOUS DISCUSSION FROM LAST NIGHT IS  
APPENDED BELOW FOR REFERENCE. /HAMRICK  
----------------------  
   
..OVERVIEW  
 
GUIDANCE CONTINUES TO SHOW THE LARGE SCALE PATTERN BECOMING MORE  
BLOCKY BY LATER THIS WEEK AND NEXT WEEKEND. EXPECT UPPER RIDGING  
TO SETTLE OVER THE CENTRAL U.S. WHILE EXTENDING NORTH INTO CANADA,  
AS A PACIFIC UPPER TROUGH REACHING THE WEST BECOMES NEGATIVELY  
TILTED BY FRIDAY. THE SOUTHERN PART OF THE TROUGH WILL LIKELY  
CONTINUE ELONGATING EASTWARD AND BREAK OFF AN UPPER LOW THAT  
UNDERCUTS THE CENTRAL U.S. RIDGE NEXT WEEKEND. SOME LINGERING  
UPPER TROUGHING/POSSIBLE EMBEDDED LOW SHOULD LINGERING NEAR THE  
NORTHERN-CENTRAL WEST COAST THROUGH THE WEEKEND. MEANWHILE EAST  
COAST MEAN TROUGHING WILL COMPRISE ONE SHORTWAVE PASSING THROUGH  
AROUND MIDWEEK AND THEN REINFORCING ENERGY ARRIVING FARTHER NORTH  
TOWARD THE END OF THE WEEK AND LIKELY PERSISTING THROUGH THE  
WEEKEND. STRONG AND MOIST SOUTHERLY FLOW AHEAD OF THE PACIFIC  
TROUGH WILL SUPPORT AN ATMOSPHERIC RIVER EVENT WHOSE FOCUS SHOULD  
BE MOST PRONOUNCED OVER NORTHERN CALIFORNIA ON WEDNESDAY AND  
FARTHER SOUTH BY THURSDAY. A BROAD AREA OF RAIN/SNOW WILL LIKELY  
EXTEND FARTHER INLAND OVER THE WEST AFTER WEDNESDAY AND RAIN  
SHOULD DEVELOP OVER PARTS OF THE PLAINS BY FRIDAY OR SATURDAY.  
THIS MOISTURE SHOULD THEN STREAM INTO THE SOUTHEAST. AN AREA OF  
MOSTLY LIGHT PRECIPITATION SHOULD ACCOMPANY A MODEST MIDWEEK EAST  
COAST SYSTEM WHILE THE NORTHEAST MAY SEE SOME PRECIPITATION MOSTLY  
IN THE FORM OF SNOW LATE IN THE WEEK AND NEXT WEEKEND AS  
REINFORCING ENERGY ALOFT SETTLES INTO THE MEAN TROUGH POSITION.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT  
 
AS HAS BEEN THE CASE RECENTLY, MOST ASPECTS OF THE WESTERN U.S.  
PATTERN (AT LEAST THROUGH FRIDAY) ARE MORE STABLE AND AGREEABLE  
THAN FOR DETAILS OVER THE EAST. LEADING HEIGHT FALLS WITH THE  
UPPER TROUGH ARRIVING INTO THE WEST STILL BECOME A LITTLE FASTER  
IN THE CMC BUT OTHERWISE A CONSENSUS APPROACH LOOKS GOOD THROUGH  
FRIDAY. THEN GUIDANCE FAIRLY RAPIDLY DIVERGES REGARDING THE PATH  
OF A POTENTIAL UPPER LOW EXPECTED TO BREAK OFF FROM THE SOUTHERN  
PART OF THE WESTERN TROUGH. LATEST CMC RUNS REPRESENT THE  
NORTHERN EXTREME OVER THE CENTRAL PLAINS WHILE THE NEW 00Z GFS HAS  
BECOME A SOUTHERN EXTREME JUST OFFSHORE THE WESTERN GULF COAST AS  
OF EARLY NEXT SUNDAY, AND THE 12Z ECMWF STRAYS TO THE FAST SIDE  
NEAR THE GULF COAST (ADJUSTED BACK TO SLOWER TIMING IN THE NEW 00Z  
RUN). A COMPOSITE OF THE 12Z/18Z GFS, 00Z/27 ECMWF, AND 18Z  
GEFS/12Z ECENS MEANS SEEM TO PROVIDE THE BEST INTERMEDIATE  
STARTING POINT AT THIS TIME. WORTH MONITORING IS A POTENTIAL  
SOUTHWARD TREND AS THE 12Z ECMWF-INITIALIZED MACHINE LEARNING  
MODELS LEANED ALONG OR JUST NORTH OF THE GULF COAST FOR THE UPPER  
LOW TRACK.  
 
OVER THE EAST, THE LEADING SYSTEM ON WEDNESDAY IS GRADUALLY COMING  
INTO BETTER AGREEMENT WITH MOST SOLUTIONS DEPICTING RAPID  
PROGRESSION INTO THE ATLANTIC AFTER EARLY WEDNESDAY. CMC RUNS ARE  
A NOTABLE SLOW EXTREME COMPARED TO THIS EMERGING MAJORITY. BEHIND  
THIS SYSTEM, INDIVIDUAL MODEL RUNS CONTINUE TO BE QUITE DIVERSE  
AND ERRATIC REGARDING HOW UPSTREAM SOUTHERN CANADA ENERGY MAY  
AMPLIFY INTO THE NORTHEASTERN U.S. WITH THE ECMWF-INITIALIZED  
MACHINE LEARNING MODELS BECOMING MORE EMPHATIC ABOUT AN UPPER LOW  
REACHING OVER OR NEAR NEW ENGLAND BY NEXT WEEKEND, LATEST GFS RUNS  
AND 00Z/27 ECMWF MATCH THAT IDEA THE BEST OVERALL WITHIN A  
FAVORABLY COMPARABLE GEFS/ECENS MEAN TROUGH. THE 12Z/27 ECMWF WAS  
A SOUTHWEST EXTREME WITH THE UPPER LOW WHILE THE CMC/CMCENS HAVE  
BEEN SHIFTING THE OVERALL TROUGH AXIS FARTHER EAST. THE NEW 00Z  
ECMWF HAS DIFFERENT DETAILS THAN SOME OTHER SOLUTIONS BUT DOES  
ULTIMATELY ACHIEVE A NEW ENGLAND UPPER LOW BY NEXT SUNDAY.  
 
BASED ON GUIDANCE COMPARISONS OVER THE COURSE OF THE PERIOD, DAY 3  
WEDNESDAY STARTED WITH A MODEL COMPOSITE INCLUDING A SPLIT OF  
OLDER 00Z/12Z ECMWF RUNS AND 12Z/18Z GFS RUNS WITH SOME 12Z UKMET  
AND MINIMAL 12Z CMC INCLUSION. THEREAFTER, THE BLEND FIRST  
EXCLUDED THE CMC AND THEN EVENTUALLY PHASED OUT 12Z ECMWF INPUT  
WHILE INCORPORATING ONLY 30 PERCENT WEIGHT OF 18Z GEFS/12Z ECENS  
MEANS AS THE 12Z ECMWF AND TWO GFS RUNS TOGETHER ALREADY COMPARED  
FAIRLY WELL TO THE MEANS.  
   
..WEATHER/HAZARDS HIGHLIGHTS  
 
THE UPPER TROUGH AND LEADING FRONTAL SYSTEM APPROACHING THE WEST  
COAST AROUND MIDWEEK WILL SUPPORT A STRONG SOUTHERLY FLOW OF  
ENHANCED MOISTURE AND LIKELY BRING A PERIOD OF SIGNIFICANT  
RAINFALL AND HIGH ELEVATION SNOW TO THE WEST COAST STATES. DURING  
THE PERIOD COVERED BY THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS  
(EARLY WEDNESDAY THROUGH THURSDAY NIGHT), GUIDANCE HAS BEEN  
CONSISTENT IN BRINGING THE HEAVIEST RAINFALL TO NORTHERN  
CALIFORNIA AROUND WEDNESDAY WHEN A SLIGHT RISK AREA REMAINS AS  
CARRIED OVER FROM THE PRIOR DAY 5 OUTLOOK. THIS OUTLOOK STILL  
CORRESPONDS TO THE BEST OVERLAP OF GUIDANCE SIGNALS WITHIN  
PERSISTENT TIMING SPREAD, THOUGH NOW WITH A LITTLE CLOSER  
AGREEMENT AMONG THE GFS/ECMWF/UKMET AND THE GEFS/ECENS VERSUS THE  
CMC/CMCENS THAT ARE STILL A LITTLE FASTER. THE SURROUNDING  
MARGINAL RISK AREA REFLECTS AN INTERMEDIATE TIMING OF SIGNIFICANT  
BUT LESS EXTREME RAINFALL POTENTIAL. THERE IS ALSO A MARGINAL  
RISK AREA OVER THE OLYMPIC PENINSULA IN WESTERN WASHINGTON IN THE  
DAY 4 OUTLOOK WITH GUIDANCE STILL SHOWING SOME RELATIVE QPF MAXIMA  
WITH WET FROM PRIOR DAYS' RAINFALL. NO CHANGES WERE NEEDED FOR  
THE UPDATED ERO FOR DAY 4 ACROSS THE WEST COAST REGION.  
 
BY DAY 5/THURSDAY, EXPECT THE BEST PRECIPITATION FOCUS TO SHIFT  
FARTHER SOUTH OVER CALIFORNIA AS THE UPPER TROUGH AXIS NEARS THE  
COAST. A MAJORITY OF HEAVY QPF OVER THE SIERRA NEVADA SHOULD BE  
IN THE FORM OF SNOW, LEAVING AREAS NEAR THE SOUTHERN CALIFORNIA  
COAST AS THE REGION OF INTEREST FOR EXCESSIVE RAINFALL POTENTIAL.  
A MARGINAL RISK AREA REMAINS VALID OVER AND SOUTH OF THE  
TRANSVERSE RANGES, WITH SOME ACCELERATION OF THE MOISTURE BAND  
RELATIVE TO DAY 4 HELPING TO TEMPER AMOUNTS SOMEWHAT. HOWEVER THE  
GFS/ECMWF SUGGEST THERE MAY BE SOME INSTABILITY WITH THIS  
ACTIVITY, SO THERE COULD BE POTENTIAL FOR FAIRLY INTENSE RAIN  
RATES OVER FAVORED SOUTHWARD-FACING TERRAIN. A NARROWING OF  
EXISTING TIMING SPREAD AND BETTER RESOLUTION IN THE SHORT-TERM  
MODELS OVER THE COMING DAYS COULD EVENTUALLY HELP TO DEFINE ANY  
POTENTIAL EMBEDDED SLIGHT RISK AREA. FOR THE 12Z UPDATE, THE  
EXISTING MARGINAL RISK AREA FOR DAY 5 WAS EXTENDED SLIGHTER  
FARTHER TO THE NORTH ALONG THE CENTRAL CALIFORNIA COAST TO ACCOUNT  
FOR SOME POTENTIALLY LINGERING HEAVIER SHOWERS THROUGH LATE  
THURSDAY MORNING. FARTHER INLAND, EXPECT A BROAD AREA OF MOISTURE  
TO SPREAD ACROSS THE WEST FROM THURSDAY INTO THE WEEKEND AND  
PRODUCE RAIN/HIGHER ELEVATION SNOW. SOUTHWARD-FACING TERRAIN  
SHOULD SEE THE HIGHEST TOTALS OVER THE WEST, WHILE PORTIONS OF THE  
CENTRAL AND/OR SOUTHERN ROCKIES INTO HIGH PLAINS COULD EVENTUALLY  
SEE EASTERLY ENHANCEMENT AS ELONGATING UPPER TROUGH ENERGY FORMS A  
CLOSED LOW OVER OR JUST BEYOND THE FOUR CORNERS REGION. THEN A  
FAIRLY STRONG SYSTEM MOST LIKELY CONTINUING EASTWARD ACROSS THE  
SOUTHERN TIER SHOULD EXTEND RAINFALL FROM THE CENTRAL-SOUTHERN  
PLAINS THROUGH THE SOUTHEAST, WITH SOME OF THIS RAIN POTENTIALLY  
HEAVY.  
 
THE SYSTEM CROSSING THE EAST INTO WEDNESDAY WILL PRODUCE AN AREA  
OF MOSTLY LIGHT PRECIPITATION WHICH MAY BE SNOW OVER THE CENTRAL  
APPALACHIANS/NORTHERN MID-ATLANTIC AND RAIN FARTHER SOUTH. THERE  
IS STILL SOME UNCERTAINTY OVER THE EXACT MOISTURE COVERAGE. THEN  
UPPER TROUGHING AND POTENTIAL SURFACE DEVELOPMENT MAY PRODUCE SOME  
PRECIPITATION OVER THE NORTHEAST FROM LATE WEEK THROUGH THE  
WEEKEND. MOST OF THIS PRECIPITATION SHOULD BE SNOW, BUT SOME RAIN  
COULD BE POSSIBLE DEPENDING ON DETAILS WHICH REMAIN FAIRLY  
UNCERTAIN.  
 
THE NORTHERN-CENTRAL PLAINS INTO THE MIDWEST AND GREAT LAKES  
SHOULD SEE THE MOST CONSISTENTLY ABOVE NORMAL TEMPERATURES DURING  
THE PERIOD, WITH NORTHERN AREAS SEEING THE BEST POTENTIAL FOR  
MULTIPLE DAYS OF MORNING LOWS UP TO 20-30F ABOVE NORMAL AND HIGHS  
UP TO 15-25F ABOVE NORMAL. SOME DAILY RECORDS WILL BE POSSIBLE,  
PRIMARILY FOR WARM LOWS. THE WEST WILL BE WARM INTO MIDWEEK WITH  
LESS EXTREME ANOMALIES, GENERALLY UP TO PLUS 10-20F AND ESPECIALLY  
FOR MORNING LOWS WHICH COULD HOLD ABOVE SOME DAILY RECORDS. THE  
UPPER TROUGH MOVING IN WILL BRING A COOLING TREND FOR THE LATTER  
HALF OF THE WEEK THROUGH NEXT WEEKEND WITH HIGHS OVER PORTIONS OF  
CALIFORNIA AND SOUTHWEST U.S. UP TO 10-15F BELOW NORMAL  
FRIDAY-SUNDAY. THE ABOVE NORMAL MIN TEMPERATURES WILL TAKE AN  
EXTRA DAY OR SO TO TREND TOWARD NORMAL. OVER THE EAST, THE  
SOUTHERN PART OF THE FLORIDA PENINSULA MAY SEE TEMPERATURES UP TO  
A FEW DEGREES BELOW NORMAL MID-LATE WEEK BUT OTHERWISE EXPECT NEAR  
TO ABOVE NORMAL TEMPERATURES. THERE IS CONTINUED UNCERTAINTY FOR  
HIGHS OVER THE NORTHEAST BY NEXT WEEKEND, DEPENDING ON THE DEPTH  
AND LOCATION OF UPPER TROUGHING AND A POSSIBLE EMBEDDED CLOSED  
LOW. THERE IS BETTER CONFIDENCE IN ABOVE NORMAL MORNING LOWS OVER  
THIS REGION.  
 
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  
 
 
 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.
The Nexlab HPC Page
Main Text Page